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system description of stone crushing system

stone crusher | cone & jaw crushers machine manufacturer - jxsc

stone crusher | cone & jaw crushers machine manufacturer - jxsc

According to the crushing force mode, the crusher machine divides into stone crushers and grinding machine.Whats the difference between stone crusher and grinding mill?General speaking, the former one is used to reduce the larger slab into a smaller size, various models of crusher are designed to maximize productivity at the lowest cost. The configuration of the suited crush machine is varied with different crushing stages in the complete crushing circuit, coarse crushing, medium-sized crushing, and fine crushing. The latter one of grinding mill machines are preferred to process fine and extremely fine material, grinding mediums include steel ball, steel rod, gravel, and metal lump so on. Some equipment is capable of crushing and grinding, such as self mill.Discrimination of the working principle1 Jaw Crusher. The movable jaw plate continually presses against the fixed die at a set time and force to squeeze the rock material caught in it.2 Cone Crusher. The inner movable cone rotates eccentricity and bumps the outer fixed cone, thus exerting strong crushing force on the ore material.3 Roll Crusher. The ore material is subjected to continuous crushing and impacting force between the two rollers.4 Impact Crusher. The ore lump crushed by the impact force of rapidly rotating moving parts.5 Ore Grinding Machine. The ore slab is crushed by the impact and grinding force of the grinding medium (steel ball, bar, gravel or lump) in the rotating cylinder. Rod mill, pan mill, ball mill, vibration mill, centrifugal mill, etc.Each kind of crusher has various models to suit different applications. Jaw crusher has the features of large crushing ratio, uniform product size, simple structure, reliable work, easy maintenance and economical operation cost. PF-I series impact crusher can crush materials with length less than 100 ~ 500 mm and its compressive strength can reach up to 350 MPA, which has the advantages of large crushing ratio. It is suitable for crushing medium hard materials, such as limestone in cement plant.

1 Adjustable fine crusherThe adjustable fine crusher mainly consists of a rotary part, guard plate, crushing chamber. The latest fine crusher equipped with a hydraulic device can be very convenient to maintain, save time cost.2 Jaw crushing typeJaw crusher, is the first choice for primary crushing equipment, with large crushing ratio, uniform product size, simple structure, the relatively small volume can be installed in the tiny space, etc. Therefore, it is widely used in mines, metallurgy, construction material, water conservancy and chemical industries.Compared with cone crusher, jaw type crusher has less investment, less finished flake and lower production cost. Compared with hammer crusher, the wear resistant parts have longer service time, high production efficiency and fewer maintain fees.The common jaw crusher has single toggle type and double toggle type, the former one also called as simple swing crusher, the latter one is called as complex swing crusher.3. Gyratory crusherThe gyratory crusher is a large scale crushing machine which uses the gyratory movement of the crushing cone in the crushing cavity to extrude, squeeze and bend the materials. When the shaft sleeve rotates, the crushing cone is moving in eccentric around the center line of the machine continuously. The productivity of gyratory crusher is higher than that of jaw crusher.There are two types of discharging material and overload insurance, one is mechanical type, by adjusting the nuts on the top of the main shaft to lift up or down the crushing cone, thus change the discharge outlet width, and by cutting the safety pin on the driving pulley to stop overload. Another way is hydraulic gyratory crusher type, by changing the plunger under the hydraulic oil volume can adjust the crushing cone position, thus changing the size of the discharge port.4 Cone crusherCone crusher widely used in the metal and mon-metal mines, cement, sand & gravel, aggregate, quarry, metallurgy and other industries. it is suited for fine crushing all kinds of ores and rocks with hardness 5 ~ 16, such as iron ore, Non-ferrous metal ore, granite, limestone, quartzite, sandstone, cobblestone, etc.The working principle of cone crusher is the same as that of gyratory crusher, but it is only suitable for medium-sized crushing or fine crushing. The requirements of uniformity of particle size distribution in medium and fine crushing operations are generally higher than that in the coarse crushing operation. Therefore, a section of the parallel zone should be set at the lower part of the crushing cavity. In addition, the rotating speed of the crushing cone should be accelerated so that the material can be squeezed more than once in the parallel zone.The crushing of fine crushing operation is larger than that of coarse crushing operation, so the loose volume after crushing increases greatly. In order to prevent the crushing chamber from blocking, the total discharging cross section must be increased by increasing the diameter of the lower part of the crushing cone without increasing the discharging opening to ensure the required discharging granularity.When the Simon Spring Safety cone crusher overloads, the cone-shaped Shell forces the spring to compress and raise itself in order to enlarge the discharge port and discharge the non-broken material. The adjustment of the discharge opening is carried out by the adjusting cover, and the adjusting cover fixed with the shell can be rotated to drive the shell up or down by the thread on the outer circle, so as to change the size of the discharge opening. The safety and adjustment mode of hydraulic cone crusher is the same as that of hydraulic gyratory crusher.Maintenance of cone crusher1, Ensure full load production, avoid too coarse product granularity.2, Optimize the cone crusher productivity by setting reasonable crushing ratio.3, It is necessary that equipped with an iron removal device.4, The spring cannot be too heavy pressured, the large pressure may occur shaft broke, light pressure may cause spring vibrating, influence the crushing efficiency.

Right way. First of all, you need to know the crusher materials, the maximum feeding size, finished particle size, handling capacity, crushing environment. With detailed information, JXSC will provide the stone crusher suitable for your production needs.

The humidity and hardness of different materials are different. The higher the hardness, the higher the degree of difficulty. For example, granite hardness, the jaw crusher, cone crusher, impact crusher will better. River pebble texture hard wear-resistant, roller crusher crushing effect is better. Brittle materials are more suitable for heavy hammer crushers, such as calcite.

2. Sorting machineWe can design the crushing plant flow chart when knowing the crushing demand and determine the primary, secondary and tertiary crusher use of which type. crusher. The next step is to choose the type of device. In order to improve efficiency, the general primary crusher processing capacity will be larger than the secondary.

1. Control material sizeThe crusher has a maximum feed size. When the feed particle size is too large to the equipment caused serious damage. Whether soft or medium-hard material, both cause different damage. If some of the materials are larger than the maximum feeding size of the crusher, the crusher is easy to appear stuck cavity, blocking phenomenon, affecting the aggregate production efficiency. 2. Correct feeding materialMany enterprises in order to increase the production capacity and blindly carry out the transformation of the bunker. It resulted in excessive feeding. And that feed too much, it will cause the material too late to break, and the broken material can not be discharged in time, resulting in blocking. Therefore, material cut-off and excessive feeding will affect the capacity of the crusher. 3. Maintenance and repairsThe daily maintenance and repair of the stone crusher is the key to the effective operation of the equipment. Check the machine regularly and replace the wear-out parts in time.

Jiangxi Shicheng stone crusher manufacturer is a new and high-tech factory specialized in R&D and manufacturing crushing lines, beneficial equipment,sand-making machinery and grinding plants. Read More

rockbreaker boom system

rockbreaker boom system

The stationary rockbreaker boom system consists of the rotating upper part of the frame or a swivel console, lift boom, arm with a hydraulic hammer attached to it. The lower part of the frame is firmly fixed to a base. Power is supplied by a hydraulic unit. The rockbreaker boom system is used to break up and crush stone, ore, slag, concrete and other materials.

When excavating and processing rock, the primary stone crusher becomes blocked by larger pieces of boulders and it is precisely the rock breaker boom system which solves the dangerous and laborious problem of clearing these boulders in the crusher. It is also used during primary crushing on frames. The relevant parameters are chosen for the rock breaker boom system depending on the given use: size and method, reaches, lifting capacity, the size of the hydraulic hammer and the output of the hydraulic unit.

Lighter types of rock breaker boom systems are used for primary jaw crushers or impact crushers, with smaller hydraulic hammers capable of breaking extremely hard and abrasive large rocks. The rock breaker boom system is used to break up oversized pieces in the crusher or to free up the transport routes to the crusher.

Large and powerful rock breaker boom systems with large hammers constructed for continuous and heavy operation are intended for primary gyratory crushers. They are used to break up oversized pieces of crushed material or to free up caving (vaults) in the crusher.

For this type of crushing a rock breaker boom system with a suitably massive structure and a powerful and strong hammer which crushes the rock on a horizontal grid with defined opening sizes is used. This is primary crushing under continuous operation.

The hydraulic unit is the source of power for hydraulic hammers from all major manufacturers. It is designed for maximum performance, reliability, and simple and efficient maintenance.

The boom system is designed to provide a high level of safety even during a power failure. The construction is carefully designed, optimized, and checked using the finite element method (fem).

The sophisticated control system meets safety and reliability requirements and at the same time is user-friendly. It communicates in profibus, profinet, modbus and other networks.

The GSM router allows you to monitor work conditions, failures, etc., in real time and thus prevent unplanned downtimes caused by neglecting regular maintenance.

The remote control provides operators with simple and well-arranged controls, as well as comfortable work throughout the shift and in all conditions. It meets the requirements of current and future trends.

p&q university lesson 7- crushing & secondary breaking : pit & quarry

p&q university lesson 7- crushing & secondary breaking : pit & quarry

In the quarry, crushing is handled in four potential stages: primary, secondary, tertiary and quaternary. The reduction of aggregate is spread over these stages to better control the product size and quality, while minimizing waste.

The primary stage was once viewed merely as a means to further reduce stone following the blast or excavation prior to secondary crushing. Today, primary crushing is viewed as more important within the balance of production and proper sizing needs. The size and type of the primary crusher should be coordinated with the type of stone, drilling and blasting patterns, and the size of the loading machine. Most operations will use a gyratory, jaw or impact crusher for primary crushing.

In the secondary and subsequent stages, the stone is further reduced and refined for proper size and shape, mostly based on specifications to produce concrete and asphalt. Between stages, screens with two or three decks separate the material that already is the proper size. Most secondary crushers are cone crushers or horizontal-shaft impact crushers. Tertiary and quaternary crushers are usually cone crushers, although some applications can call for vertical-shaft impact crushers in these stages.

A gyratory crusher uses a mantle that gyrates, or rotates, within a concave bowl. As the mantle makes contact with the bowl during gyration, it creates compressive force, which fractures the rock. The gyratory crusher is mainly used in rock that is abrasive and/or has high compressive strength. Gyratory crushers often are built into a cavity in the ground to aid in the loading process, as large haul trucks can access the hopper directly.

Jaw crushers are also compression crushers that allow stone into an opening at the top of the crusher, between two jaws. One jaw is stationary while the other is moveable. The gap between the jaws becomes narrower farther down into the crusher. As the moveable jaw pushes against the stone in the chamber, the stone is fractured and reduced, moving down the chamber to the opening at the bottom.

The reduction ratio for a jaw crusher is typically 6-to-1, although it can be as high as 8-to-1. Jaw crushers can process shot rock and gravel. They can work with a range of stone from softer rock, such as limestone, to harder granite or basalt.

As the name implies, the horizontal-shaft impact (HSI) crusher has a shaft that runs horizontally through the crushing chamber, with a rotor that turns hammers or blow bars. It uses the high-speed impacting force of the turning blow bars hitting and throwing the stone to break the rock. It also uses the secondary force of the stone hitting the aprons (liners) in the chamber, as well as stone hitting stone.

With impact crushing, the stone breaks along its natural cleavage lines, resulting in a more cubical product, which is desirable for many of todays specifications. HSI crushers can be primary or secondary crushers. In the primary stage, HSIs are better suited for softer rock, such as limestone, and less abrasive stone. In the secondary stage, the HSI can process more abrasive and harder stone.

Cone crushers are similar to gyratory crushers in that they have a mantle that rotates within a bowl, but the chamber is not as steep. They are compression crushers that generally provide reduction ratios of 6-to-1 to 4-to-1. Cone crushers are used in secondary, tertiary and quaternary stages.

With proper choke-feed, cone-speed and reduction-ratio settings, cone crushers will efficiently produce material that is high quality and cubical in nature. In secondary stages, a standard-head cone is usually specified. A short-head cone is typically used in tertiary and quaternary stages. Cone crushers can crush stone of medium to very hard compressive strength as well as abrasive stone.

The vertical shaft impact crusher (or VSI) has a rotating shaft that runs vertically through the crushing chamber. In a standard configuration, the VSIs shaft is outfitted with wear-resistant shoes that catch and throw the feed stone against anvils that line the outside of the crushing chamber. The force of the impact, from the stone striking the shoes and anvils, fractures it along its natural fault lines.

VSIs also can be configured to use the rotor as a means of throwing the rock against other rock lining the outside of the chamber through centrifugal force. Known as autogenous crushing, the action of stone striking stone fractures the material. In shoe-and-anvil configurations, VSIs are suitable for medium to very hard stone that is not very abrasive. Autogenous VSIs are suitable for stone of any hardness and abrasion factor.

Roll crushers are a compression-type reduction crusher with a long history of success in a broad range of applications. The crushing chamber is formed by massive drums, revolving toward one another. The gap between the drums is adjustable, and the outer surface of the drum is composed of heavy manganese steel castings known as roll shells that are available with either a smooth or corrugated crushing surface.

Double roll crushers offer up to a 3-to-1 reduction ratio in some applications depending on the characteristics of the material. Triple roll crushers offer up to a 6-to-1 reduction. As a compressive crusher, the roll crusher is well suited for extremely hard and abrasive materials. Automatic welders are available to maintain the roll shell surface and minimize labor expense and wear costs.

These are rugged, dependable crushers, but not as productive as cone crushers with respect to volume. However, roll crushers provide very close product distribution and are excellent for chip stone, particularly when avoiding fines.

Hammermills are similar to impact crushers in the upper chamber where the hammer impacts the in-feed of material. The difference is that the rotor of a hammermill carries a number of swing type or pivoting hammers. Hammermills also incorporate a grate circle in the lower chamber of the crusher. Grates are available in a variety of configurations. The product must pass through the grate circle as it exits the machine, insuring controlled product sizing.

Hammermills crush or pulverize materials that have low abrasion. The rotor speed, hammer type and grate configuration can be converted for different applications. They can be used in a variety of applications, including primary and secondary reduction of aggregates, as well as numerous industrial applications.

Virgin or natural stone processing uses a multi-stage crushing and screening process for producing defined aggregate sizes from large lumps of rock. Such classified final fractions are used as aggregates for concrete, asphalt base, binder and surface course layers in road construction, as well as in building construction. The rock is quarried by means of drilling and blasting. There are then two options for processing the bulk material after it has been reduced to feeding size of the crushing plant: mobile or stationary plants.

When stone is processed in mobile primary crushing plants, excavators or wheel loaders feed the rock into the crusher that is set up at the quarry face, gravel pit or in a recycling yard or demolition site. The crushed material is then either sent to the secondary/tertiary processing stage via stacking conveyors or transported by trucks. Some mobile crushers have an independent secondary screen mounted on the unit, effectively replacing a standalone screen.

The higher the compressive strength of rock, the higher also is its quality, which plays an important role particularly in road construction. A materials compressive strength is delineated into hard, medium-hard or soft rock, which also determines the crushing techniques used for processing to obtain the desired particle sizes.

The materials quality is influenced significantly by particle shape. The more cubic-shaped the individual aggregate particles are, the better the resulting particle interlock. Final grains of pronounced cubic shape are achieved by using several crushing stages. A cubicity showing an edge ratio of better than 1-to-3 is typical of high-quality final aggregate.

As the earths natural resources are becoming ever more scarce, recycling is becoming ever more important. In the building industry, recycling and reuse of demolition concrete or reclaimed asphalt pavement help to reduce the requirements for primary raw materials. Mobile impact and jaw plants are uniquely positioned to produce high-quality reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) for reuse in pavements, road bases, fill and foundations.

Use of RAP and RCA is growing dramatically as road agencies accept them more and more in their specs. But because RAP and RCA come from a variety of sources, to be specified for use by most departments of transportation they must be processed or fractionated and characterized into an engineered, value-added product. RCA or RAP are very commonly crushed and screened to usable sizes often by impact crushers and stored in blended stockpiles that can be characterized by lab testing for use in engineered applications.

Impact crushers are increasingly used for crushing recycling material. Impact crushers are capable of producing mineral aggregate mixes in one single crushing stage in a closed-cycle operation, making them particularly cost-effective. Different crusher units can alternatively be combined to process recycling material. A highly efficient method of processing recycling material combines crushing, screening and separation of metals. To produce an end product of even higher quality, the additional steps of washing to remove light materials such as plastics or paper by air classification and via electromagnetic metal separator are incorporated into the recycling process.

Mobile impact crushers with integrated secondary screens or without integrated screen used in conjunction with an independent mobile screen are ideal for producing large volumes of processed, fractionated RAP or RCA on a relatively small footprint in the plant. Mobile impactors are especially suited for RAP because they break up chunks of asphalt pavement or agglomerations of RAP, rather than downsize the aggregate gradation. Compression-type crushers such as jaws and cones can clog due to packing (caking) of RAP when the RAP is warm or wet.

Contaminants such as soil are part of processing demolition concrete. Mobile impact and jaw crushers when possessing integrated, independent prescreens removing dirt and fines before they ever enter the crushing circuit reduce equipment wear, save fuel, and with some customers, create a salable fill byproduct. A lined, heavy-duty vibrating feeder below the crusher can eliminate belt wear from rebar or dowel or tie bar damage. If present beneath the crusher, this deflector plate can keep tramp metal from degrading the conveyor belt. That way, the feeder below the crusher not the belt absorbs impact of rebar dropping through the crusher.

These mobile jaw and impact crushers may feature a diesel and electric-drive option. In this configuration, the crusher is directly diesel-driven, with the conveyor troughs, belts and prescreen electric-driven via power from the diesel generator. This concept not only reduces diesel fuel consumption, but also results in significantly reduced exhaust emissions and noise levels. This permits extremely efficient operation with low fuel consumption, allowing optimal loading of the crusher.

Jaw crushers operate according to the principle of pressure crushing. The raw feed is crushed in the wedge-shaped pit created between the fixed crusher jaw, and the crusher jaw articulated on an eccentric shaft. The feed material is crushed by the elliptic course of movement and transported downwards. This occurs until the material is smaller than the set crushing size.

Jaw crushers can be used in a wide range of applications. In the weight class up to 77 tons (70 metric tons), they can be used for both virgin stone and recycled concrete and asphalt aggregates processing as a classic primary crusher for natural stone with an active double-deck grizzly, or as a recycling crusher with vibrating discharge chute and the crusher outlet and magnetic separator.

Output for mobile jaw crushers ranges from 100 to 1,500 tph depending on the model size and consistency of the feed material. While larger mobile crushers produce more aggregate faster, transport weights and dimensions may limit how easily the crusher can be shipped long distances. Mobile jaw crushers can have either a vibratory feeder with integrated grizzly, or a vibrating feeder with an independent, double-deck, heavy-duty prescreen. Either way, wear in the system is reduced because medium and smaller gradations bypass the crusher, with an increase in end-product quality because a side-discharge conveyor removes fines. A bypass flap may provide easy diversion of the material flow, eliminating the need for a blind deck.

Jaw crusher units with extra-long, articulated crusher jaws prevent coarse material from blocking while moving all mounting elements of the crusher jaw from the wear area. A more even material flow may be affected if the transfer from the prescreen or the feeder trough is designed so material simply tilts into the crushing jaw.

Mobile jaw and impact crushers alike can be controlled by one operator using a handheld remote. The remote also can be used to move or relocate the crusher within a plant. In other words, the crusher can be run by one worker in the cab of an excavator or loader as he feeds material into the crusher. If he sees something deleterious going into the hopper, he can stop the crusher.

Impact crushing is totally different from pressure crushing. In impact crushing, feed material is picked up by a fast moving rotor, greatly accelerated and smashed against an impact plate (impact toggle). From there, it falls back within range of the rotor. The crushed material is broken again and again until it can pass through the gap between the rotor and impact toggle.

A correctly configured mobile jaw or impact crusher will enhance material flow through the plant and optimize productivity. New-design mobile jaw and impact crushers incorporate a highly efficient flow concept, which eliminates all restriction to the flow of the material throughout the entire plant. With this continuous-feed system, each step the material goes through in the plant is wider than the width of the one before it, eliminating choke or wear points.

For example, a grizzly feeder can be wider than the hopper, and the crusher inlet wider than the feeder. The discharge chute under the crusher is 4 inches wider than the inner width of the crusher, and the subsequent discharge belt is another 4 inches wider than the discharge chute. This configuration permits rapid flow of crushed material through the crusher. Also, performance can be significantly increased if the conveying frequencies of the feeder trough and the prescreen are adapted independently to the level of the crusher, permitting a more equal loading of the crushing area. This flow concept keeps a choke feed to the crusher, eliminating stops/starts of the feed system, which improves production, material shape and wear.

Users are focused on cost, the environment, availability, versatility and, above all, the quality of the end product. Simple crushing is a relatively easy process. But crushing material so that the particle size, distribution and cleanliness meet the high standards for concrete and asphalt requires effective primary screening, intelligent control for optimal loading, an adjustable crusher with high drive output, and a screening unit with oversize return feed.

This starts with continuous flow of material to the crusher through a variable-speed control feeder. Having hopper walls that hydraulically fold integrated into the chassis makes for quick erection of hopper sides on mobile units. If available, a fully independent prescreen for either jaw or impact models offers the ability to effectively prescreen material prior to crushing this allows for product to be sized prior to crushing, as opposed to using a conventional vibrating grizzly. This has the added value of increasing production, reducing wear costs and decreasing fuel consumption.

This independent double-deck vibrating screen affects primary screening of fines and contaminated material via a top-deck interchangeable punched sheet or grizzly, bottom-deck wire mesh or rubber blank. Discharged material might be conveyed either to the left or to the right for ease of positioning. The independent double-deck vibrating prescreen improves flow of material to the crusher, reducing blockages and feed surges.

Modern electrical systems will include effective guards against dust and moisture through double-protective housings, vibration isolation and an overpressure system in which higher air pressure in the electrical box keeps dust out. Simple and logical control of all functions via touch panel, simple error diagnostics by text indicator and remote maintenance system all are things to look for. For crushing demolition concrete, look for a high-performance electro- or permanent magnet with maximum discharge capacity, and hydraulic lifting and lowering function by means of radio remote control.

For impact crushers, a fully hydraulic crusher gap setting with automatic zero-point calculation can speed daily set-up. Featured only on certain mobile impact crushers, a fully hydraulic adjustment capability of the crushing gap permits greater plant uptime, while improving quality of end product.

Not only can the crushing gap be completely adjusted via the touch panel electronic control unit, but the zero point can be calculated while the rotor is running. This ability to accurately set the crusher aprons from the control panel with automatic detection of zero-point and target-value setting saves time, and improves the overall efficiency and handling of the crusher. On these mobile impact crushers, the zero point is the distance between the ledges of the rotor and the impact plates of the lower impact toggle, plus a defined safety distance. The desired crushing gap is approached from this zero point.

While the upper impact toggle is adjusted via simple hydraulic cylinders, the lower impact toggle has a hydraulic crushing gap adjustment device, which is secured electronically and mechanically against collision with the rotor. The crushing gap is set via the touch screen and approached hydraulically. Prior to setting of the crushing gap, the zero point is determined automatically.

For automatic zero-point determination with the rotor running, the impact toggle moves slowly onto the rotor ledges until it makes contact, which is detected by a sensor. The impact toggle then retracts to the defined safe distance. During this procedure, a stop ring slides on the piston rod. When the zero point is reached, the locking chamber is locked hydraulically and the stop ring is thus fixed in position. The stop ring now serves as a mechanical detent for the piston rod. During the stop ring check, which is carried out for every crusher restart, the saved zero point is compared to the actual value via the electronic limit switch. If the value deviates, a zero-point determination is carried out once again.

These impact crushers may feature a new inlet geometry that allows even better penetration of the material into the range of the rotor. Also, the wear behavior of the new C-form impact ledges has been improved to such an extent that the edges remain sharper longer, leading to improved material shape.

The machines come equipped with an efficient direct drive that improves performance. A latest-generation diesel engine transmits its power almost loss-free directly to the crushers flywheel, via a fluid coupling and V-belts. This drive concept enables versatility, as the rotor speed can be adjusted in four stages to suit different processing applications.

Secondary impact crushers and cone crushers are used to further process primary-crushed aggregate, and can be operated with or without attached screening units. These crushers can be used as either secondary or tertiary crushers depending on the application. When interlinked to other mobile units such as a primary or screen, complicated technical processing can be achieved.

Mobile cone crushers have been on the market for many years. These machines can be specially designed for secondary and tertiary crushing in hard-stone applications. They are extraordinarily efficient, diverse in application and very economical to use. To meet the diverse requirements in processing technology, mobile cone crushing plants are available in different sizes and configurations. Whether its a solo cone crusher, one used in addition to a triple-deck screen for closed-loop operation, or various-size cone crushers with a double-deck screen and oversize return conveyor, a suitable plant will be available for almost every task.

Mobile cone crushers may be available with or without integrated screen units. With the latter, an extremely efficient triple-deck screen unit may be used, which allows for closed-loop operation and produces three final products. Here the screen areas must be large so material quantities can be screened efficiently and ensure that the cone crusher always has the correct fill level, which is particularly important for the quality of the end product.

Mobile, tracked crushers and screen plants are advancing into output ranges that were recently only possible using stationary plants. Previously, only stationary plants were used for complicated aggregate processing applications. But thanks to the advancements made in machine technology, it is becoming increasingly possible to employ mobile technology for traditional stationary applications.

Mobile crushers are used in quarries, in mining, on jobsites, and in the recycling industry. These plants are mounted on crawler tracks and can process rock and recycling material, producing mineral aggregate and recycled building materials respectively for the construction industry. A major advantage of mobile crushers is their flexibility to move from one location to the next. They are suitable for transport, but can also cover short distances within the boundaries of their operating site, whether in a quarry or on the jobsite. When operating in quarries, they usually follow the quarry face, processing the stone directly on site.

For transport over long distances to a new location or different quarry, mobile crushers are loaded on low trailers. No more than 20 minutes to an hour is needed for setting the plant up for operation. Their flexibility enables the mobile crushers to process even small quantities of material with economic efficiency.

Mobile plants allow the combination of prescreening that prepares the rock for the crushing process and grading, which precisely separates defined aggregate particle sizes into different end products to be integrated with the crushing unit into one single machine. In the first stage, the material is screened using an active prescreen. After prescreening, it is transferred to the crusher, from where it is either stockpiled via a discharge conveyor or forwarded to a final screen or a secondary crushing stage. Depending on the specified end product, particles are then either graded by screening units or transported to additional crushing stages by secondary or tertiary impact crushers or cone crushers. Further downstream screening units are used for grading the final aggregate fractions.

The process of prescreening, crushing and grading is a common operation in mobile materials processing and can be varied in a number of ways. Mobile crushers with up to three crushing stages are increasingly used in modern quarries. Different mobile crushing and screening plants can be combined for managing more complex crushing and screening jobs that would previously have required a stationary crushing and screening plant.

Interlinked mobile plants incorporate crushers and screens that work in conjunction with each other, and are coordinated in terms of performance and function. Mining permits are under time constraints and mobile plants provide faster setup times. They provide better resale value and reusability, as mobile plants can also be used individually. They also reduce operating costs in terms of fewer haul trucks and less personnel.

With a so-equipped mobile crusher, the feed operator can shut the machine down or change the size of the material, all using the remote control, or use it to walk the crusher from one part of the site to the other, or onto a flat bed trailer for relocation to a different quarry or recycling yard. This reduces personnel and hauling costs compared to a stationary plant. With the mobile jaw or impact primary crusher, the only additional personnel needed would be a skid-steer operator to remove scrap steel, and someone to move the stockpiles.

Thanks to better technology, mobile plants can achieve final aggregate fractions, which previously only were possible with stationary plants. Production availability is on par with stationary plants. Theyre applicable in all quarries, but can be used for small deposits if the owner has several quarries or various operation sites. For example, an operator of several stone quarries can use the plants in changing market situations at different excavation sites. In addition, they also can be used as individual machines. A further factor is that mobile plants, in general, require simpler and shorter licensing procedures.

The high cost of labor keeps going up. A stationary crusher might be able to produce multiple times the amount of product, but also would require about seven or eight workers. Aggregate producers can benefit when producing material with the minimized crew used for mobile jaw and impact crushers.

Using correct maintenance practices, mobile crushers will remain dependable throughout their working life. Crushing and processing material can result in excessive wear on certain components, excessive vibration throughout the plant, and excessive dust in the working environment. Some applications are more aggressive than others. A hard rock application is going to require more maintenance on top of standard maintenance, as there will be more vibration, more dust and more wear than from a softer aggregate.

Due to the nature of its purpose, from the moment a mobile crusher starts, the machine is wearing itself out and breaking itself down. Without routine, regular maintenance and repair, a mobile crusher will not be reliable nor provide the material customers demand.

The first area of wear on any machine is the feed system. Whether its a feeder with an integrated grizzly, or a feeder with an independent prescreen, how the machine is fed contributes to wear. When setting up and maintaining a machine, the machine must be level. A machine that is unlevel left to right will experience increased wear on all components, including the feeder, the screens, the crushing chambers and the conveyor belts. In addition, it reduces production and screening efficiency, as the whole area of the machine is not being effectively used. Also, having the machine sit high at the discharge end will have the effect of feeding the material uphill in the feeder and reducing its efficiency, thus reducing production.

Another area for consideration is the equipment used to feed the machine. The operator using a loader to feed the crusher will have no control over the feed size, as he cannot see whats in the bucket. Whereas with an excavator, the operator can see whats inside and has more control over the feed into the hopper. That is, the operator is not feeding so much material all at once and is controlling the size of the feed. This reduces wear in the feed hoppers impact zones and eliminates material blockages due to feed size being too large to enter the chamber.

Dust is a problem in its own right, especially for the power plant of the mobile crusher. In a very dusty application, it is easy to plug the radiator and have engine-overheating problems. High dust levels cause increased maintenance intervals on air filters, and if not controlled properly, can enter the diesel tank and cause problems with the fuel system. Also, dust that gets inside the crusher increases wear. But if systems are put in place to remove the dust, it should keep it from going into the machine in the first place.

Dust also is a hazard on walkways and a problem for conveyors. If maintained, side-skirting and sealing the conveyors keeps dust from spilling out, building up underneath the conveyor, or building up in rollers, pulleys, bearings, and causing wear on shafts. Its important to maintain the sealing rubbers on the conveyor belts to avoid those issues. Routine maintenance calls for removing accumulated dust from inside and under the machine.

Dust also is a problem for circuit boards and programmable controllers. Dust causes electrical switches to malfunction because it stops the contacts from correctly seating. Electrical systems under positive air pressure dont permit dust to penetrate the control system. In control panels with a correctly maintained positive pressure system, filters remove dust from air that is being pumped into the cabinets. If the filters are plugged, the system will not pull as much air through, allowing dust, moisture and heat to build in the cabinet.

There are also impact aprons against which the rock is thrown, which also see high wear. There are side plates or wear sheets on the sides of the machine. The highest wear area is around the impact crusher itself, around the circumference of the rotor. If not maintained, the wear items will wear through and compromise the structure of the crusher box.

Conduct a daily visual check of the machine. The jaw is simple; just stand up on the walkway and take a look down inside. A crushers jaw plate can be flipped so there are two sides of wear on them. Once half the jaw is worn out, flip it; once that side is worn, change it.

The impact crusher will have an inspection hatch to see inside. Check to see how much material is left on the blow bars and how much is left on the wear sheets on the side of the crusher box. If half the bar is worn out after one week, change the blow bars in another week.The frequency of changes depends entirely on the application and the rock that is being crushed.

They have to be user serviceable, user friendly, and able to be changed in a short time. The best way to change these parts is a service truck with a crane; some use excavators but thats not recommended by any means.

After initial blasting, breakers are used to break down aggregate that typically is not only too large to be hauled in dump trucks, but also too large for crushers that size rock to meet asphalt, drainage system, concrete and landscaping specifications. Breakers can be mounted to a mobile carrier, such as an excavator, or to stationary boom systems that can be attached to a crusher. The total number of hydraulic breakers can vary from site to site depending on production levels, the type of aggregate materials and the entire scope of the operation.

Without hydraulic breakers, workers rely on alternative practices that can quickly affect production rates. For instance, blasting mandates shutting down operations and moving workers to a safe location. And when you consider how many times oversize aggregate might need to be reduced, this can lead to a significant amount of downtime and substantially lower production rates.

Aggregate operations can use hydraulic breakers to attack oversize without having to clear the quarry. But with an ever-growing variety of manufacturers, sizes and models to choose from, narrowing the decision to one hydraulic breaker can be overwhelming with all of the stats and speculation. Thats why its important to know what factors to consider before investing in a new hydraulic breaker.

In most cases, heavy equipment dealers are very knowledgeable about quarry equipment, including breakers, so they are a good resource for finding the best model for a carrier, usually an excavator or stationary boom system. More than likely, they will have specifications and information about various breaker sizes to help gauge what model is best. But being familiar with what to look for in a breaker can streamline the selection process.

The best places to look for breaker information are in the manufacturers brochure, website, owners manual or catalogue. First, carefully review the carrier weight ranges. A breaker that is too big for the carrier can create unsafe working conditions and cause excessive wear to the carrier. An oversized breaker also transmits energy in two directions, toward the aggregate and through the equipment. This produces wasted energy and can damage the carrier. But using a breaker thats too small puts excessive force on the tool steel, which transmits percussive energy from the breaker to the material. Using breakers that are too small also can damage mounting adapters and internal components, which considerably decreases their life.

Once you find a breaker that meets the carriers capacity, check its output power, which is typically measured in foot-pounds. Foot-pound classes are generalizations and are not based on any physical test. Often the breakers output will be documented in one of two ways: as the manufacturers calculated foot-pound class or as an Association of Equipment Manufacturers measured foot-pound rating. Foot-pound class ratings can be deceiving since they are loosely based on the breakers service weight and not the result of any physical test. The AEM rating, on the other hand, measures the force a breaker exerts in a single blow through repeatable and certified testing methods. The AEM rating, which was developed by the Mounted Breaker Manufacturers Bureau, makes it easier to compare breaker models by reviewing true figures collected during an actual test procedure.

For instance, three breaker manufacturers might claim their breakers belong in a 1,000-lb. breaker class. But AEM testing standards could reveal all three actually have less foot-pound impact. You can tell if a breaker has been AEM tested if a manufacturer provides a disclosure statement or if the breaker is labeled with an AEM Tool Energy seal. If you cannot find this information, contact the manufacturer. In addition to output energy specifications, manufacturers often supply estimates for production rates on different types of aggregate material. Make sure to get the right measurements to make the best decision.

In addition to weight and output power, look at the breakers mounting package. Two things are crucial for mounting a breaker to a carrier: a hydraulic installation kit and mounting components. Breakers need hydraulic plumbing with unidirectional flow to move oil from the carrier to the breaker and back again. A one-way flow hydraulic kit is sufficient to power the breaker as long as the components are sized to properly handle the required flows and pressures. But, consider a bidirectional flow hydraulic kit if you plan to use the same carrier with other attachments that require two-way flow. Check with the dealer or breaker manufacturer to determine which hydraulic package best fits current and future needs.

Hydraulic flow and pressure specifications also need to be considered when pairing a breaker to a hydraulic system. If the carrier cannot provide enough flow at the right pressure, the breaker wont perform with maximum output, which lowers productivity and can damage the breaker. Additionally, a breaker receiving too much flow can wear quickly, which reduces its service life. For the best results, follow the hydraulic breaker specifications found in owners manuals, catalogs and brochures. Youll find out if a breaker has additional systems that might require additional servicing. For instance, some breakers feature nitrogen gas-assist systems that work with the hydraulic oil to accelerate the breakers piston. The nitrogen systems specifications need to be followed for consistent breaker power output.

Brackets or pin and bushing kits are commonly required to attach the breaker to the carrier. Typically they are bolted to the top of a breaker and are configured to match a specific carrier. Some manufacturers make universal mounting brackets that can accommodate two or three different sizes of carriers. With the adjustable pins, bushings or other components inside these universal brackets, the breaker can fit a range of carriers. However, varying distances between pin centers can complicate hookups to quick coupling systems. In addition, loose components, such as spacers, can become lost when the breaker is not in use and detached from the carrier.

Some carriers are equipped with quick-coupling systems, which require a breakers mounting interface to be configured like the carriers original attachment. Some manufacturers produce top-mount brackets that pair extremely well with couplers. This allows an operator to use the original bucket pins from the carrier to attach the breaker, and eliminates the need for new pins. This pairing also ensures a fast pickup with the quick coupler.

Its also a good idea to check which breaker tools are available through the dealer and manufacturer. The most common for aggregate mining are chisels and blunts. There are two kinds of chisels commonly used in aggregate mines: crosscut and inline. Both chisels resemble a flat head screwdriver, but the crosscut chisels are used when carrier operators want to direct force in a left-to-right concentration; whereas, inline chisels direct force fore and aft. With chisel tools, operators can concentrate a breakers energy to develop cracks, break open seams or define scribe lines.

If a chisel cant access or develop a crack or seam, a blunt can be used. Blunts have a flattened head that spreads the energy equally in all directions. This creates a shattering effect that promotes cracks and seam separation. Ask your dealer if the tools you are considering are suited for the application. Using non-original equipment manufacturer tool steel can damage the percussive piston in the breaker, seize into the wear bushings, or cause excessive wear.

Regular breaker maintenance is necessary, yet its one of the biggest challenges for aggregate operations. It not only extends the life of the breaker, but also can keep minor inconveniences from turning into expensive problems. Some manufacturers recommend operators inspect breakers daily to check grease levels and make sure there are no worn or damaged parts or hydraulic leaks.

Breakers need to be lubricated with adequate amounts of grease to keep the tool bushing area clear and reduce friction, but follow the manufacturers recommendations. For example, adding grease before properly positioning the breaker can lead to seal damage or even catastrophic failure. And too little grease could cause the bushings to overheat, seize and damage tools. Also, manufacturers advise using high-moly grease that withstands working temperatures greater than 500 degrees. Some breakers have automatic lube systems that manage grease levels, but those systems still need inspections to ensure there is adequate grease in their vessels. Shiny marks on the tool are a good indication the breaker is not properly lubricated.

Little has changed in basic crusher design over past decades, other than that of improvements in speed and chamber design. Rebuilding and keeping the same crusher in operation year after year has long been the typical approach. However, recent developments have brought about the advent of new hydraulic systems in modern crusher designs innovations stimulated by the need for greater productivity as well as a safer working environment. Importantly, the hydraulic systems in modern crusher designs are engineered to deliver greater plant uptime and eliminate the safety risks associated with manual intervention.

Indeed the crushing arena is a hazardous environment. Large material and debris can jam inside the crusher, damaging components and causing costly downtime. Importantly, manually digging out the crusher before repairs or restarts puts workers in extremely dangerous positions.

The Mine Safety and Health Administration has reported numerous injuries and fatalities incurred when climbing in or under the jaw to manually clear, repair or adjust the typical older-style jaw crusher. Consider that fatalities and injuries can occur even when the machine is locked out and tagged out. Recent examples include a foreman injured while attempting to dislodge a piece of steel caught in the primary jaw crusher. Another incident involved a fatality when a maintenance man was removing the toggle plate seat from the pitman on a jaw crusher. The worker was standing on a temporary platform when the bolts holding the toggle seat were removed, causing the pitman to move and strike him.

The hydraulic systems on modern crusher designs eliminate the need for workers to place themselves in or under the crusher. An overview of hydraulic system technology points to these three key elements:

A hydraulic chamber-clearing system that automatically opens the crusher to a safe position, allowing materials to pass. A hydraulic overload relief that protects parts and components against overload damage. A hydraulic adjustment that eliminates the maintenance downtime associated with manual crusher adjustments, and maintains safe, consistent crusher output without the need for worker intervention.

Whether a crusher is jammed by large material, tramp iron or uncrushable debris; or is stalled by a power failure the chamber must be cleared before restarting. Manual clearing is a lengthy and risky task, especially since material can be wedged inside the crusher with tremendous pressure, and dislodging poses much danger to workers placed in harms way inside the crusher.

Unlike that of the older-style jaw, the modern jaw will clear itself automatically with hydraulics that open the crusher to a safe position, and allow materials to pass again, without the need for manual intervention. If a feeder or deflector plate is installed under the crusher, uncrushable material will transfer smoothly onto the conveyor without slicing the belt.

To prevent crusher damage, downtime and difficult maintenance procedures, the hydraulic overload relief system opens the crusher when internal forces become too high, protecting the unit against costly component failure. After relief, the system automatically returns the crusher to the previous setting for continued crushing.

The modern crusher is engineered with oversized hydraulic cylinders and a traveling toggle beam to achieve reliable overload protection and simple crusher adjustment. All closed-side setting adjustments are made with push-button controls, with no shims being needed at any time (to shim is the act of inserting a timber or other materials under equipment). This is a key development as many accidents and injuries have occurred during shim adjustment, a process which has no less than 15 steps as described in the primary crusher shim adjustment training program offered by MSHA.

crushing&screening system for mineral processing | prominer (shanghai) mining technology co.,ltd

crushing&screening system for mineral processing | prominer (shanghai) mining technology co.,ltd

For mineral processing project, after blasting, crushing and screening system is always the first stage to reduce the big raw ore lumps to proper small particle size for following mill grinding system. Normally to reduce the big ore lumps to small particles, two to three stages crushing is required.

Prominer has the ability to supply complete crushing and screening system, including various crusher, screen, belt conveyor, iron remover, etc. For minerals with different properties and hardness, we can recommend suitable crusher accordingly, including jaw crusher and cone crusher for hard material, impact crusher and roller crusher for relatively soft material. In addition, for some mineral projects, the mining sites are in different locations, which is far from processing plant, and Prominer can also supply portable crushing station to make the crushing and screening from one mining site to another to make it convenient.

Prominer has been devoted to mineral processing industry for decades and specializes in mineral upgrading and deep processing. With expertise in the fields of mineral project development, mining, test study, engineering, technological processing.

a simple system dynamics model for the global production rate of sand, gravel, crushed rock and stone, market prices and long-term supply embedded into the world6 model | springerlink

a simple system dynamics model for the global production rate of sand, gravel, crushed rock and stone, market prices and long-term supply embedded into the world6 model | springerlink

A model for global supply of sand, gravel and cut stone for construction based on a system dynamics model was developed for inclusion in the WORLD6 model. The Sand-Gravel-Stone model simulates production and market supply, demand and price for natural sand and gravel, sand and gravel from crushed rock and cut stone. The model uses market mechanisms where the demand is depending on population size, maintenance and price. For the period 20002050, the WORLD6 model outputs correlate with the GINFORS model outputs (r 2=0.98), but they may take different pathways after 2050. The resources of sand and gravel are estimated at 12 trillion ton each, another 125 trillion tons of rock is suitable for crushing to sand and gravel and at least 42 trillion ton of quality stone is available for production of cut stone. The simulation, under assumed business-as-usual conditions, shows that cut stone production will reach a maximum level by about 20202030 and stabilize after that. The cause for this is that demand exceeds extraction as well as slow exhaustion of the known reserves of high-quality stone. Sand and gravel show plateau behaviour and reach their maximum production rate in 20602070. The reason for the slight peak towards a plateau behaviour is partly driven by an expected population decline and increasing prices for sand and gravel, limiting demand. Assuming business-as-usual conditions rates remain at that level for centuries.

A conventional view is that there is, for practical purposes, endless resources of sand, gravel and stone on the earth for human use. Given that we are in the midst of the great acceleration in resource extraction and use (Steffen et al. 2015), this view needs to be critically examined. Construction materials, such as sand, gravel, stone aggregates and rock are fundamental for human development and wellbeing. Materials play a central role in the economy, and stony aggregates are one of the largest material flows humans move around in terms of weight. Sand and gravel occur naturally either as naturally sorted aggregates or as mixed aggregates. Some measure of crushing is also frequently employed. USGS (2015) and UNEP GEAS (2014) estimate that sand, gravel and stone materials use in construction amounts to about 4759billion tons per year, the range shows the uncertainty in the estimate. Sand and gravel, account for both the largest share (from 65 to 85%). The worlds use of aggregates for concrete can be estimated at 2630billion ton a year for 2012 (BMI 2014; Chilamkurthy et al. 2016; Giljum et al. 2008; 2011). Another large driver in North America for sand demand was the activity of fracking for shale gas (BMI 2014). China, India, Brazil, USA and Turkey are currently the worlds biggest concrete producers, with China and India accounting for two-thirds of total global production. In the past 20 years, cement demand in China has increased fourfold compared to a growth of about 58% in the rest of the world (Giljum et al. 2008, 2011; UNEP 2014). There are significant concerns about the sustainability of the present global material extraction rates, including the issue of sand, gravel and stone extraction rates (Aquaknow 2014; Bardi 2013; Giljum et al. 2000, 2008, 2011; Heinberg 2001, 2011; Horwath 2004; Krausmann et al. 2009; Meadows et al. 1972, 1974, 2005; Morrigan 2010; Nickless et al. 2014; Peduzzi 2014; Sverdrup and Ragnarsdottir 2014).

Until recently, most construction sand was mined from riverbanks and local pits. With the dramatic increase in demand, industrial scale marine and beach sand mining are increasingly common, along with sand and gravel made from industrially crushed stone (BMI Research 2014; Langer 2002, 2014; Merwede 2014; OSPAR 2003; Radzeviius et al. 2010; Robinson and Brown 2002; Velegrakis et al. 2010; Sutphin et al. 2002; Morrow 2011; Krause et al. 2010; Ravishankar 2015; Anthoni 2000; Ashraf et al. 2011).

While many of the worlds deserts are rich in sand, much of the material is often too well sorted, have the wrong shape (the grains may be round and polished) or too fine grained for use in construction materials. Crushed sand and gravel are characterized by the fact that the particles are sharp edged thereby binding well with cement owing to their shape. The more polished and rounded the particles of deserts and certain beaches are, the less suitable they are for construction and, in particular, as fillers in cement. Thus, a large part of natural sand and gravel deposits found will be unsuitable for construction and building because of wrong physical properties.

Sand mining, irrespective of where it occurs, usually has major environmental impacts. Earlier modelling approaches have been attempted, however, the methods used have some significant shortcomings. Econometric input/output table generated time series work as a short-term extrapolation tool, but lacks stocks and thus cannot handle delays. Only a limited amount of feedbacks is possible in such models, and the inclusion of market dynamics mechanisms is not possible. Material flow analysis can deal with stocks, but only step forward in a spread-sheet manner. Thus, no market dynamics or systemic feedbacks can be included (Graedel and Allenby 2003; Moll et al. 2002; Nakamura et al. 2007; Hirschnitz-Garber et al. 2015; Sverdrup and Ragnarsdottir 2014; Pauliuk et al. 2015). In the WORLD6 model being developed by the authors, most major resources (metals, rock materials, fossil energy, renewable energy, phosphorus, agricultural land, population) are modelled together with their causal connections through energy consumption, infrastructures and mass balances. The WORLD6 model generates resource supply to global markets and generates global supply and global market prices endogenously.

The objective is to make and test a first global assessment of long-term use and availability of sand, gravel, stone and rock for human use through an integrated global model for the extraction and market supply of sand, gravel (glacial, fluvial and marine) and cut quality stone from rock for construction needs. The model will be tested on independent observed dataproduction and market priceto ensure that the model developed has satisfactory performance. The purpose is to make a simplified model that will still perform satisfactorily well when compared to the available data. A secondary objective is to link such a model within the WORLD6 model being developed by the authors. The test here will be module performance inside the WORLD6 model to be assessed by comparing observed data and consistency with the outputs of the GINFORS model. Finally, global production rates, prices and supply of sand, gravel, crushed rock and stone will be assessed using the model. The standard for evaluating the performance of the model will be by comparison to observed data on sand, gravel and cut stone extraction rates, rates of sand and gravel from crushing of stone and recorded market price for sand, gravel and cut stone.

It is outside the scope here to make a sensitivity analysis of the Sand-Gravel-Stone (SGS) sub-model in WORLD6 and explore its sensitivity. We will analyse the model qualitatively using the available causal loop diagrams, but the rest will be the subject of a future study. It is also outside the scope of this study to investigate different policy interpretations or future policy options. That will be the subject of a future study. The model is run for the time interval from 1900 to 2400AD, or 500 years; 115 years of known history to evaluate the model and validate its performance and for 385 years under assumed business-as-usual conditions. We have adopted the long time-span because of the long delays in the system (residential time in use of 100 years) and that a proper run should normally cover at least three system delay times to evolve through all the inherent dynamics of the system. An approach of using business-as-usual was adopted. Alternative pathways are thinkable, but this will be the subject of later studies.

Owing to data constraints several approaches to quantification of reserves and resources have been taken. The reserve estimates are based on classical Geological Survey estimates, and the allocation of extractable amounts according to ore quality, stratified after extraction costs (Singer 1993, 1995, 2007; Singer and Menzie 2010; Sutphin et al. 2002; Stockwell 1999; US Environmental Protection Agency 1994; USGS 2009, 2013; US department of the interior 1980; Sverdrup et al. 2015a, b, c, d). However, an extensive compilation of regional reserve and resource assessments have not yet been done, making our reserve and resource estimates difficult to do with accuracy. For sand, gravel and stone the data availability is less straightforward in the sense that while there is a wealth of information at small local scales, but few regional summaries and compilations there is almost none at the global scale. Our resource estimates for sand, gravel and stone are very approximate, and are of a back-of-the-envelope type of approximation that may need to be revised dramatically in the near future (Singer 1993; Kostka 2011; Kogel et al. 2006).

This implies that persistent price increases are an indicator of soft scarcity, and this may occur long before any physical scarcity is visible. Soft scarcity is frequently occurring in society, it is reflected in changes in price. Society is well adapted to handle soft scarcity. Hard scarcity has more severe effects, and for general large-scale commodities, hard scarcity may be disruptive. Hard scarcity occurs already for some commodities, and is reflected by very high and strongly fluctuating prices. Examples where this occur are metals like, platinum, rhodium or rhenium. The results of our simulations will be evaluated with respect to this definition of scarcity.

Standard methods of system analysis and system dynamics have been used (Sterman 2000; Senge 1990; Sverdrup and Svensson 2002, 2004; Haraldsson and Sverdrup 2004; Sverdrup et al. 2014a, b; 2015a, b). Material flow pathways and the causal chains and feedbacks loops in the system are mapped using a causal loop diagram (CLD) methodology. The resulting coupled differential equations are transferred to computer codes for numerical solutions using the STELLA system dynamics software (Fig.4). For validation, to assess performance and robustness of the model, it is used to reconstruct the past (19002015). When performance is satisfactory, the model is used to simulate the future (20152300) under business-as-usual (BAU) conditions. In this context, it is important to stress that we do not aim to prognosticate or describe the likely future at this future timescale but rather to illustrate implications on resource use and availability under assumed BAU conditions. The iterations were used to set the parameterization to such values that the mining history, observed ore grades and price picture could be reproduced. This allows us to see where the intervention points in the system are, and to propose policy interventions (Haraldsson and Sverdrup 2004; Bardi and Lavachi 2009; Sverdrup and Ragnarsdottir 2014).

We have earlier successfully employed these methods and quantification approaches for assessments of Rare Earths (Kifle et al. 2012), natural resources in general (Sverdrup et al. 2012b, 2013, 2017b); copper (Sverdrup et al. 2014a); silver (Sverdrup et al. 2014b), aluminium (Sverdrup et al. 2015a), Gold (Sverdrup et al. 2012a), platinum (Sverdrup et al. 2017a); lithium (Sverdrup 2016) and further papers being prepared for iron (Sverdrup et al. 2015b), stainless steel, nickel, manganese, chromium (Sverdrup 2016), copper, lead, zinc, indium (Sverdrup et al. 2015c; Sverdrup and Ragnarsdottir 2016), molybdenum and rhenium (Sverdrup 2016) and cobalt (Sverdrup et al. 2015c). There are other simpler modelling methods available, but we have avoided these as they lack market dynamics and they lack most of the feedbacks known to be present in the real global mining and metal trading systems (Bardi and Lavacchi 2009). The model also profited from the earlier efforts by Meadows et al. (1974) in preparation of the Limits to growth study (Meadows et al. 1972). The SGS model was initially developed as a stand-alone model, driven by several exogenous variables. Then it was incorporated into the WORLD6 model, and operated from within that structure.

The flowchart for the sand-gravel-stone (SGS) model. Maintenance flow is assumed to be the replacement for lost material and thus do not add to stock-in-use. Known corresponds to known reserves. All known plus all hidden corresponds to total resources

This makes a model with 16 linked material stocks, resulting in a system of 16 linked differential equations to be solved. The mining activity is price driven, the price is the market price. Figure2 shows the flowchart used for the SGS model. Figure3 shows the price-extraction driving mechanism used in the SGS model. In the model, the market price is set twice every week throughout the simulation. The extraction is in the real world driven by operations profit. This implies that the main driver is the difference between the income from material sales (market price times shipped amount) and the extraction cost. The cost is estimated as extracted amount times the total cost, where the total cost is made up of three components; labour cost, capital expenses costs and energy costs. We have tried this out (Fig. S2 in the supplementary material), as well as a simpler model where we use the price as a proxy for the profit (Fig.3). Both approaches work well. The extraction for sand, gravel and cut stone also competes with recycling for sand, gravel and cut stone, mostly on a cost basis (Fig.3).

In the model, crushed stone is processed to sand and gravel. The simple flowchart for aggregates processing from mixed substrate to sand fractions and gravel products in a typical industrial operation is shown

The basic causal loop diagram applied for the simplified SGS model. The causal loop diagrams for sand, gravel, stone for crushing and cut stone were linked as shown in the flow chart of Fig.1. The actual model consists of four such coupled causal loop diagrams for sand, gravel, crushed stone and cut stone as Fig.1 will demand (Fig. S3 in the supplementary material). The bold arrows show the reinforcing. The reinforcing loops (R) keep the system running. The balancing loops (B) act as brakes in the system. The system is driven by demand from general consumption, demolition and maintenance (R1R2) and income through price and pushed by demand (R3R4)

Figure S1 in the appendix shows the WORLD6 model in outline, and Fig.4 shows the STELLA model diagram for the SGS model. The SGS model uses a 4-step RungeKutta integration method, with a 1/100-year time-step (3.6 days).

In the model, we have assumed that sand and gravel stay 100 years in the infrastructure before the structure is destroyed, based on an evaluation of research literature (Hsu 2009; Korre and Durucan 2007). For cut stone we have assumed that the residence time in society is 100 years. The average lifetime on a concrete infrastructure unit is set to 60 years, based on data from United States, Germany and China.

The SGS model was embedded into the WORLD6 model (see supplementary material, Fig. S1 and S2). In the model, the profit is generated by sales to the market, but reduced with extraction costs and prospecting costs. There are three reinforcing loops in the system. The reinforcing loop marked as R1 in Fig. S2 is driven by the profits-extraction-supply loop. The reinforcing loop R3 is driven by the supply-market, taken from market-society-demolish-recycle loop. The most important balancing loops; B in Fig.3 are two, the first when the known reserves become depleted, the other when the hidden resources become exhausted and the known reserves can no longer be supplemented with new material. The final loop is when the waste has been exhausted and the last resource runs out. Price is calculated internally in the model as a result of the feedbacks illustrated in Fig. S4 and S5 in the supplementary material. Three parameters intervene to create price dynamics: the effect of market volume on price, and the effect of price on supply, demand and recycling. In the model used, a simplified version of the model shown in S2 in the supplementary materials was used, this is shown in Fig.3. The characteristic curves for how this is expressed are shown in Fig. S4 and S5 in the supplementary material. The material mining rate was estimated with the following equation:

where r is the rate of mining, k is the rate coefficient and m is the mass of the ore body, and n is the mining order. The mining order depends on the difficulty of access, and the access or the technological capacity is the main limiting factor. When extraction capacity is the limiting factor for extraction it becomes zeroth order, when the resource availability limits, depending on the geometry n will be in the range 071. f(price) is a feedback function of price, increasing mining at higher extraction profits and lowering it at lower metal prices (see the causal loop diagram in Fig.3). g(T) is a technology factor accounting for the invention of technologies used in efficient mining, refining and extraction of metal. We have chosen to set the mining order at n=1 as most materials are extracted in open pit mining. The rate coefficient is modified with ore extraction cost and ore grade. There are many different definitions of recycling available (Graedel and Allenby 2003; UNEP 2011). For the purpose of clarity, the recycling fraction displayed in the Results section was calculated as follows in this study:

The cost of the mining and extraction operation is mainly determined by two important factors beside cost of investments, the energy price and the ore grade. The size of the extractable ore body is determined by the rate of extractions (r mining) and the rate of prospecting (r discovery):

The resource discovery is a function of how much prospecting we do and how much there is left to find. The amount hidden reserve (m hidden) decreases with the rate of discovery. The rate is first order as prospecting is three-dimensional by drilling. The driving mechanism of mining comes from profits and availability of a mineable resource used in the model. The rate of discovery is dependent on the amount sand, gravel or stone hidden (m H) and the prospecting coefficient k prospecting. The prospecting coefficient depends on the amount of effort spent and the technical method used for prospecting.

where \({x_{{\text{recycling}}}}\) is the fraction of the flow out of stock-in-use that is recycled. g(price) is a feedback function, increasing recycling when the commodity market price increases, improving recycling profits (see Sverdrup et al. 2014a). A simple flowchart for crushed stone to general aggregates processing to sand fractions and gravel products is shown in Fig.5. The diagram shows the process in far more detail than actually pictured in this flow chart. The parameterization of the significant feedbacks used in the SGS model, has been shown in the supplementary material. Table1 shows the base parameter settings of the model. These parameters define the equation coefficients in the equations given above. The parameters have been set using generic extraction rate coefficients for the different processing rates (Lewis and Clark 1964; Pohl 2011; Darling et al. 2011). Other coefficients were taken from Graedel and Allenby (2003). Table2 shows the typical composition of concrete. The use of concrete is an important driver of sand, gravel and stone demand. Gravel use for concrete is 4.6 times the weight of the cement and sand use for concrete is about three times the weight of the cement used.

The demand per person follows a typical pattern with rise, peak and decline to a maintenance level. Most industrialized countries are in the decline to maintenance phase, whereas developing countries are on the rise or close to the peak, depending on what stage they are in their development

The demand was modelled based on a number of parameters and their values drawn from a number of references (Bolen 2011; Distelkamp et al. 2010; Korre and Durucan 2007; Kostka 2011; Krausmann et al. 2009; Merwede 2014, Oijens 2014; Robinson and Brown 2002; Gutowski et al. 2013; Chilamkurthy et al. 2016). The following parameters were evaluated for setting the demand:

World cement production, which correlates straight to world construction activity and infrastructure maintenance. Cement demand per person and year follows a pattern with increasing demand during the transition to industrial society with a peak and a decline down to a maintenance level. This is paralleled by the demand development for iron and steel (Cullen et al. 2012; Giurco et al. 2013; Hu et al. 2010; Moynihan and Allwood 2012; Pauliuk et al. 2012; 2013; Stanway 2014; OSS 2014). The cement demand per capita has peaked and declined in most of the industrial countries, China and India are in their major transitional stages now, and Africa is about to start. Cement demand is taken from another part of the WORLD6 structure.

World fracking activity for oil and natural gas extraction, dominated by use in North America. Fracking is a way to extract oil and gas from deposits where these are not otherwise extractable. The ground is hydraulically fracked, expanded and the cracks propped open using sand. In the United States of America, fracking takes 5060% of the domestic sand demand. Fracking activity is generated inside the energy module in WORLD6 as a part of oil and natural gas production.

where D is the demand, r C is the rate of cement production, r R the rate of gravel use for roads and railroads, r FF the rate of fossil fuel production using sand, r M is the rate of sand, gravel or cut stone use for the maintenance of stony material infrastructures, k 1, k 2, k 3, k 4, k 5 are stony material use coefficients calibrated to the year 2000 for the specific commodity or activity, E A is economic affluency and N is the global population in number of persons. The numbers to calibrate this relationship came from a number of sources, exemplified by Gutowski et al. (2013), Chilamkurthy et al. (2016) and CemNet (2014) as well as commercial market analysis such as those referred to by NewsChannel110 (2014). The maintenance demand for material is calculated as follows:

where k M is the decay rate of the infrastructure and M i is the amount of sand, gravel or cut stone in the infrastructure. An inherent assumption is that the decay of the stock-in-use is compensated for by maintenance. When the lifetime of an infrastructure is passed, it is demolished. The average lifetime is set at 100 years for sand and gravel in infrastructures and at 200 years for cut stone. We have also looked at the retention times for iron and steel in buildings, giving indications for concrete and stony materials (Cullen et al. 2012; Giurco et al. 2013; Hu et al. 2010; Moynihan and Allwood 2012; Pauliuk et al. 2012, 2013; Stanway 2014). The resulting demand is shown in Fig. S3 for sand and gravel combined and for cut stone.

The input data in terms of resource size, mining rates and other key parameters were quite difficult. Large parts of the sand, gravel and stone production are outside the official economy or in a grey zone, and only partially represented in the public statistics and UN or USGS databases. There is not much data available, and what is available is very uncertain. No good global synthesis is available. We have pulled together what we could find in the scientific literature, in corporate brochures and branch organization websites, and made a synthesis of that to our best estimate. Tables1, 2, 3 and 4 show what we could find.

There are no published reserve and resource estimates of sand, gravel and quality stone for construction at the global scale, thus we can give no proper reference for it. However, estimates were made anyhow, based on the available information (Singer 1993, 1995, 2007, 2010, 2011, 2013; Harben and Kuzwart 1996; Chen et al. 2006; Kogel et al. 2006; Korre and Durucan 2007; Bolen 2011; Velegrakis et al. 2010; Kostka 2011; Maps of the World 2012; Moll et al. 2002; Krausmann et al. 2009; Langer 2011; Bliss et al. 2012; Merwerde 2014). The resources are hypothetically huge, but a large portion are economically and geographically unavailable because of lack of transport infrastructure or being located unavailable by occurring in built-up areas, with other types of major infrastructure, or conflicting with agricultural use. Further significant amounts of sand and gravel are located in protected areas and natural reserves and are physically, technically or logistically challenging to extract. Thus, a significant amount of the resources is currently out of reach because of difficulties of extraction, remoteness, conflicting land-use and significant parts are socially unavailable. The available resources have thus been estimated based on the available information. If we assume that the materials are exploited at a rate of 23% of known reserves, this suggests reserves of about 1.62.5 trillion ton. Resources are at about five times known reserves for many other resources, and adopting this ratio for sand, gravel and rock materials suggests an extractable resource of about 812.5 trillion ton. Table2 shows an overview of primary and secondary mining of resources. Table3 shows the typical composition of concrete. We have assumed that 1km3 of calcite limestone is 2.7billion ton of stone. Yield is the % weight of the content that ends up as final product. Table4 shows the Ultimately Recoverable Resource (URR) estimates for the SGS model. The resources include both known reserves and different types of resources we have reasons to assume are there, but where the exact location and quality has not yet been identified. Only industrial quality for sand and gravel has been considered. For stone, only stone prime quality that can be manufactured to quality building stone has been assessed. For limestone, we have done a very preliminary resource estimate (Bliss et al. 2012). The reserve and resource estimates are shown in Tables1, 3 and 4. The resources were estimated looking at area underlain by limestone rock.

The model outputs for mining, from crushing and as by-product from sand, gravel, stone or concrete, supply, recycling, for a sand, b gravel, c stone and d concrete. The amounts shown are in billion ton of stony material, flows are in billion ton of material per year

The model outputs market demand and degree of supply sufficiency a sand, b gravel, c stone for construction and d all stony materials aggregated. In diagram (d), line 5 represents the observed data that should be ignored after 2015. The amounts shown are in billion ton of material, the flows are in billion ton of material per year

The model outputs for materials (sand, gravel, stone) as a known reserves and stocks-in-use in society. The flows are in billion ton of material per year. In concrete, the weight of the concrete itself is also included. b Shows the hidden resources declining slowly with time

Figure6 shows the model outputs for extraction, supply, recycling for (a) sand, (b) gravel, (c) stone and (d) all stony materials aggregated. The fit for the stone production data to the simulation is r 2=0.52. Records for validation are available from the USGS database available on the web (USGS 2015). The amounts shown are in billion ton of material, the flows are in billion ton of material per year.

Figure7 shows the model outputs, market demand and modified demand for (a) sand, (b) gravel, (c) stone for construction and (d) all stony materials aggregated. The circles represent the observed data. The observed data in this case are very uncertain estimates, and the available numbers are not properly published and substantiated; thus the validation is only qualitative. The simulations seem to behave correctly; the simulation fits the observations on global total stony materials produced quite well, if we can assume the available data are valid. The simulation of total stony materials extraction seems, likewise, to fit the observations quite well, the correlation coefficient is r 2=0.73. From the diagram, we can see that whereas we will not run out of physical supply of sand, gravel and stone (hard scarcity), we will encounter increased prices and a peak production followed by a near constant production, suggesting future soft scarcity.

Figure8 shows the model outputs for the maintenance of the infrastructures built with stony materials. Figure9 shows the materials (sand, gravel, stone) in use in society (a), known reserves (b) and hidden extractable resources (c). The stock-in-use is important for the maintenance flow. It can be seen that we will not run out of sand, gravel or stone in a very long time. But that if the demand stays on a high level, it will eventually be a finite resource that can be depleted.

Figure10 shows the model outputs for price in the market, the simulated and observed price for stone, gravel and sand. The comparison with observed data for price shows a satisfactory fit. The results show that the world is not running out of stone, but that we may run out of sand, gravel and cut stone of the right quality for many purposes. The model suggests future increases in price for sand, gravel, crushed aggregates and cut stone. The world market price reconstruction for sand and cut stone is quite successful, for crushed stone to sand and gravel less so, even if the order of magnitude is correct. This is done under the assumption that there is a functioning global market for sand, gravel and cut stone. There is such a global market, but the prices show huge variations locally, depending on transportation costs and local cost conditions. Considering the inherent inaccuracies one would think was in this approach, it is amazing how well the produced amounts and global prices are simultaneously modelled. The prices are expressed as 1998 inflation-adjusted dollars.

The curves have a behaviour consisting of a period of strong growth, an end of growth and stabilization at a stable level. The reason for this is the way demand is driven by population and the typical demand per person and year curve as shown in Fig.5. Figure11 shows the material supply expressed as ton per person per year, and as stock-in-use per person. It can be seen that the use per person cannot grow indefinitely. For cut stone, growth will peak about 2020, and sand and gravel around 2055. The following parameters affected the shape of the curve the most:

The shape of the demand per person and year curve, and the approach to infrastructural saturation. The shape of this curve was taken from the scientific literature and UNEP reports from the International Resource Panel.

The prospecting activity level, determining how fast hidden is transferred to known. As long as prospecting and finding matches the extraction, production can be kept up or grow, if not known will decline and extraction with it.

It also shows that 2020 supply level can be kept for a significant long time. Sand, gravel and cut stone run into soft scarcity because of rising prices as the response to increased demand. Cut stone approaches physical scarcity for short periods after 2100. The world will not run out of sand, gravel or cut stone, but high prices will limit demand through feedbacks. The amount of these materials extracted annually are very large, and as the price increases, it will be foreseeable that resources unavailable under present social conditions or restrictions to extraction. These conditions and restrictions may be challenged and brought under pressure to be released for exploitation as the price increases. In the model a technology development curve is used, this was adapted after results like those presented by Gutowski et al. (2013).

The amounts of sand, gravel and stone on the Earth are truly enormous, but what part of this exists in extractable form is dependent on materials having the desired mechanical or chemical properties. Major uncertainties in the output from the model are associated with the lack of reliable global sand, gravel and stone resource estimates. Furthermore, and this need to be emphasized, the very long time-perspective of the model runs as such, is a complicating factor. Very long-term demographic, economic and technological development are obviously hard to foresee on century scales. Likewise, what is extractable resources from a social perspective will be highly dependent on social and environmental development. We do not attempt to prognosticate future resource use or availabilitywe attempt to provide a scenario assessment, based on a business-as-usual run, of potential future resource scarcity horizons. We attempt to do this with a simplified model to obtain a sense of orders of magnitude and relevant times involved. The model was not intended to capture all details, and it seems to work well at the global level.

The only performance measures available for validation are the ability to predict the past mining trajectory, and the market price (Fig.10) for these commodities. When considering the difficulties in the input data, and the challenge of getting the market response curves correct, the model performs surprisingly well (Figs.4, 13).

While we can securely assume mass balance principles to be valid at all times which is adding robustness to mass balance-based models like the SGS model, other factors are less straightforward. It appears more than likely that values with regard to landscape, nature conservation, recreation and perceived resource needs and balance and trade-offs between different needs, societal actors and sectors will be significantly different from today in the long perspective and time-frame covered by our calculations. We are not attempting to model such societal change. Technological change (substitution, increased resource efficiency, etc.) will have impact, but probably less so than changes in values, on resource availability as sand, gravel and rock resources to a large degree are used as bulk materials. The apparent model output should be seen as a representation of an illustrative future under assumed business-as-usual conditions rather than a projection of a likely future as such. Nevertheless, seen as a scenario, the results allow a better informed discussion about the magnitudes of future resources, their long-term use and sustainability than the alternative of no attempt at assessment.

The success when testing the model suggests that the SGS model already has about an adequate level of complexity and that the key parameters seem to have been set at appropriate value. Figures11 and 12 show the result of the SGS model integrated into the WORLD6 model and tested against observed data on production of sand, gravel and rock materials as reported by the US Geological Survey Minerals database for 2015. The forecasts made with the GINFORS model were also tested (Meyer and Lutz 2007; Meyer et al. 2012). The test shows that the SGS model performs very well within the WORLD6 model, and that the outputs are consistent with the GINFORS outputs. Figure13 shows a plot of modelled production of rock materials versus observed total rock materials extraction amounts using the SGS model as a stand-alone model. The plot shows that the model is sufficiently accurate for assessing global production rates. Figure13 shows the outputs from the SGS model when it is integrated into the WORLD model and tested against data. The correlation between the WORLD6 simulation and the USGS data is r 2=0.76, which is better than the performance of the SGS model when it is run as a stand-alone model (r 2=0.72). The consistency between the GINFORS forecast and the WORLD6 is r 2=0.98 (Fig.13). The test of the SGS incorporated in WORLD6 against the GINFORS model outputs and the USGS data pooled together has the correlation coefficient r 2=0.86.

The SGS model was integrated into the WORLD6 model and tested against observed data on supply to the market as reported by the US Geological Survey Minerals database for 2015. The plot shows that the model is able to reconstruct the right orders of magnitude for the production when compared to data

A simple plot of modelled versus observed total stony material extraction amounts using the SGS model as a stand-alone model is shown in diagram (left). Diagram (right) shows the outputs from the SGS model when it is integrated into the WORLD6 model and tested against data

A successful test of an integrated complex model like the SGS model inside the WORLD6 model on field data, makes the discussion over what could be wrong from a theoretical point of view less relevant, giving more emphasis on simulation performance with respect to testing recorded extraction data. A next step, but outside the scope of this paper, will be to run the model through a number of sensitivity runs in order to assess the robustness and variability of the outputs. At this stage, it is obvious to the user that the results are quite sensitive to the demand created by aggregated per capita consumption as well as by maintenance of built infrastructures. It would be of priority to analyse the effect of different resource magnitudes (varying those shown in Tables2, 3, 4) and extraction rates (varying those shown in Table1).

The used volumes of sand, gravel, crushed rock and stone are truly huge. Extracting, moving, crushing, shaping these materials at the present volumes require large amounts of energy. When energy eventually becomes expensive and/or transport distances, i.e. transport costs, increase significantly, the price of these products will go up. The curves in Fig.6 exhibit a rapid growth, stagnation and almost flat development for sand, gravel and stone with time. But from Fig.9, it appears that even its known reserves may decrease, hidden reserves are far from being exhausted. In fact, they seem to be able to last for several centuries. Hence, on a global scale stone for crushing stone to sand and gravel fractions appears not deplete significantly for the next centuries.

While there is no imminent prospect of stony building materials becoming globally scarce this is unlikely to be the case at other scales. Natural sand and gravel are indeed limited finite resources, and they may be excavated to depletion, in particular at a regional scale around populated centres. Locally, sand and gravel scarcity is already an observable fact (UNEP GEAS 2014; Ashraf et al. 2011; Ooijens 2014; Morrow 2011; OSPAR 2003; Ravishankar 2015), putting demand pressure for long-distance supply into the global markets, and potentially causing environmental impacts where it is extracted.

The primary substitute for natural sand and natural gravel is industrially produced sand and gravel from crushed stone and rock. This is nearly inexhaustible from a point of view of having enough raw material, while not necessarily in the longer run as the long-term supply of sand and gravel from crush is likely to be limited by the future energy supply, availability of long range transport, ability to pay, availability of resources from a social context and not only rock quality. Sand, gravel and crushed rock long-distance transportability, between extraction site and final use, is for economical and energy reasons limited50billion ton of stony material cannot be moved without significant use of energy and not without impacts of roads, noise and pollution. As the price increases, the feedback from price tends to reduce demand, thus implying soft scarcity. In the continuation, the prices may rise even more owing to competition with other land-use, prices for mining rights and further increases in energy pricing, leading to unaffordability; a transition to economic scarcity, rather than physical scarcity. In a distant future, the primary extractable resource may in practical terms end up being exhausted. Recycling rates remain low in the sand, gravel and stone use systems, much because of the low commodity cost. Currently, the drive to recycle for economic reasons is not particularly strong; however, this will change when resource prices increase.

Given the long time-perspective of this study and the substantial uncertainties with regard to important data general policy recommendations would be premature. Still, we may speculate based on common sense, generic knowledge and evaluations based on our outputs.

We need to consider that management of the resources in question for practical and economic reasons operates at a regional as well as at a global scale. Scarcity increases efforts of globalization, shifting to other sources of supply and to increased efficiency, minimizing transient stocks. Nevertheless, there is an apparent agreement in the available publications that we are moving towards a possible risk of more widespread sand and gravel soft scarcity, at least regionally.

We think that increasing prices will drive the market towards more globalization, a process already in progress. The conditions and restrictions imposed on and limiting extraction are often rooted in the local communities and regions. The policy challenges will involve how these different scales interact, and their relative strengths.

We would suggest that there is a need to put some effort into getting better regional overviews of available reserves and resources. Such assessments need to include informal or illegal extraction which currently is omitted from official estimates. Similarly, better data on recycling and re-use of bulk materials are needed.

Further, we would suggest that there is a need to assess the large difference between what is actually present and what may be technically and socially viable to extract, as well as how this relates to the available future energy. The amounts extracted, processed and transported run in the size of 30billion ton per year, and the amount of energy used in such task is significant.

The developed model performs well and, given input data constraints and uncertainty, successfully reproduces production and global market price when compared with independently observed data. The modelling of sand, gravel and stone resources have reached a level of complexity with this model where few further improvements can be made until better data become available in open scientific sources. At present, this is very limited, making assumptions necessary. The simplifications done to the model from the full concept still retain a good level of performance and show the same dynamics as the full model, but with better stability. For this reason, the simplified version is the best practical modelling option.

The simulation, under assumed business-as-usual conditions, shows that cut stone production will reach a maximum level about 20202030 and may slowly decline after that. The cause for this is that demand exceeds extraction as well as slow exhaustion of the known reserves of high-quality stone. Sand and gravel also show peak behaviour and reach their maximum production rate in 20602070. The reason for the peak behaviour is partly driven by an expected population maximum in 2065 and later slow decline combined with increasing prices for sand and gravel, limiting the demand.

The developed SGS model appears to perform well enough when compared to observations to justify for it to be included in the WORLD6 model. The outputs from the SGS model when embedded in WORLD6 show a slightly better performance against observed data. The outputs appear to be consistent with the GINFORS forecasts in the interval from 200 to 2050.

While in a global perspective, supply may seem to be inexhaustible and availability is already a growing problem at a local to regional scale, signalling that global trade with sand, gravel and stone will continue to increase. We need better data on production rates, use and recycling to better assess risks of regional scarcity, as well as a model of this kind divided into different regions. The state of the research is at present not at a stage where this is possible without substantial research funding to support it. The SGS model, given better data, could be used for this as it could be down-scaled to regions.

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This study was done as a part of the SIMRESS project (Models, potential and long-term scenarios for resource efficiency), funded by the German Federal Ministry for Environment and the German Environmental Protection Agency (FKZ 3712 93 102). Other partners to the SIMRESS project are Ecologic Institute, Berlin, Germany (Martin Hischnitz-Garber and Susanne Langsdorf); the Institute of Economic Structures Research, GWS, Osnabrck, Germany (Mark Meyer and Martin Distelkamp); European School of Governance, EUSG, Berlin, Germany. Dr. Ullrich Lorenz is the Project Officer at the German Environmental Protection Agency (UBA). The GINFORS simulations and output tables were done by Martin Distelkamp and Mark Meyer at the GWS.

Sverdrup, H.U., Koca, D. & Schlyter, P. A Simple System Dynamics Model for the Global Production Rate of Sand, Gravel, Crushed Rock and Stone, Market Prices and Long-Term Supply Embedded into the WORLD6 Model. Biophys Econ Resour Qual 2, 8 (2017). https://doi.org/10.1007/s41247-017-0023-2

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