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mobile crushers - metso outotec

mobile crushers - metso outotec

Mobile crushers are often referred to as mobile crushing plants. They are track-mounted crushing machines which, thanks to their mobility, can maximise productivity and reduce operating costs while increasing safety and reducing environmental impact.

The concept of mobile and semi-mobile crushers has been around for a long time, but for years many machines were very heavy and moving them required thoughtful planning. As result, the crushers that were supposed to be mobile were seldom relocated and tended stay put in permanent facilities.

Nowadays, the weight of mobile crushers has decreased considerably, and crushing as well as mobility properties improved notably. Mobility is not substitute for effective crushing anymore, and tracked mobile crushers meet the same basic criteria as stationary plants.

Mobile cone crushers are traditionally used as secondary, tertiary, and quaternary crushers. However, if the grain size of the processed material is small enough by nature, then they can also operate at the first stage of the crushing process.

Mobile HSI crushers have a horizontal impact crushing unit and they are used as primary, secondary, or tertiary crushers. Mobile VSI crushers, in turn, are equipped with vertical shaft impact crushing unit, and they are extremely efficient in the last stage of the crushing process, producing precisely shaped cubical end products.

Metso Outotecs mobile crushing equipment consists of two different product families, Lokotrack mobile crushers and Nordtrack mobile crushers. Both families can be utilized in aggregates production in quarries and construction sites, recycling applications, as well as in mining operations.

Nordtrack, on the other hand, is ideal if you work in short-term contracting jobs or are just starting your own operations. The family consists of two mobile jaw crusher models and one mobile impact crusher.

8 top rock crusher brands

8 top rock crusher brands

Were proud to sell and service a range of industry-leading rock crushers. From jaw crushers to cone crushers and from stationary plants to mobile crushers, we offer a selection of models and parts that can suit any rock crushing need so we have a wide-ranging familiarity with the industrys leading brands.

Pegson was well-known for dependable lines of jaw crushers and cone crushers. The company was headquartered in the UK, but American distributors have helped to facilitate the provision of Pegson machines on this side of the Atlantic for decades.

Cedarapids is also owned by Terex, but this brand is still on the market. Cedarapids crushers are designed specifically to be modular machines, allowing them to be flexible in application and making setup efficient.

Home to the number one portable crusher in the world, Eagle Crusher supports the industry with it's extensive catalog of equipment options. Eagle produces an extensive catalog of heavy-duty impact crushers, portable crushing and screening plants, jaw crushers, and conveyors.

They offer mining jaw crushers, cone crushers, impact crushers, roll crushers and primary gyratory crushers for mining, quarrying and aggregate production, and boast expertise in a broad range of applications from greenfield mining projects to site expansions.

Allis Chalmers is another long-respected company that, today, has been dissolved into several different entities (none of which continue to provide rock crushers). However, as with Pegson rock crushers, there are still many Allis Chalmers rock crushers and parts available for resale.

Its widely held that the Symons brothers designed the first spring cone crusher in the late 1940s. Today, Symons isnt a brand as much as it is a type of crusher; the word is still used to denote machines that use this cone crusher technique. However, since it was the original brand, it merits an inclusion on this list.

Extec is another rock crushing brand thats still widely available for resale. Extec was based in the UK with a network of global distributors and was known for its leading design and manufacturing of mobile crushing machines.

If youd like more insight into any of these brands, get in touch with us. At Mellott Company, we have experience in servicing a broad range of rock crusher brands, including all of those listed here. Were experts at navigating all of the different components of rock crusher selection, setup, and maintenance.

types of rock crushers | quarry crushing equipment | kemper

types of rock crushers | quarry crushing equipment | kemper

Do you need to process sand, gravel, minerals, rock, or other aggregate products and have not yet purchased or leased crushing equipment? Theres no questionyou need to work with a capable and professional material handling equipment design and engineering company dedicated to selling, renting, and installing the best new crushers for your needs.

However, if youre new to the aggregate processing industry, you probably have a lot of questions about rock crushers. As foundational material handling equipment in all plants, crushers need to coordinate seamlessly with screens, conveyor systems, and washing equipment.

It is common to use multiple crusher types within a project and set them up as stations in a circuit format to perform the necessary material reduction work. In many cases, primary, secondary, and tertiary, and quaternary stations are installed to reduce the rock to the desired size, shape, and consistency.

For instance, if the final size of your product only needs to be between 4 inches and 6 inches, a primary jaw or impact crusher can accomplish your goals. However, you will likely require a much finer product, and that means incorporating up to threeor even fourstations with a variety of crusher types.

As the first stage in a crushing circuit following extraction from a mine site, (or in the case of recycled asphalt production, delivery to the RAP processing plant via truck transport), primary crushing reduces material to a size and shape that can be handled by the secondary crusher.

Typically, the minimum setting on most primary crushers will be about 4 to 6 inches, as noted above. Compression-style jaw, cone, impact crushers, and gyratory crushers are most often appropriate as primary crushing equipment types, though there can be overlap between primary and secondary crushers as far as suitable types.

In secondary crushing, reduction ratios become an essential consideration. Knowing just how fine you need your final output to be, along with the feed requirements of your tertiary or final reduction crushing station, will help you determine how much reduction needs to take place within this stage.

Cone crushers are often placed within the secondary crushing station because they are versatile in terms of feed, closed side setting, speed, and throw. With cone crushers, though, it is essential to operate them at consistent choked settings to keep productivity up.

The goal of the tertiary (third), quaternary (fourth) or final reduction stage of the crushing process is to size and shape rock or other material into a marketable product. Again, there may be overlap between stages in terms of which crusher styles work best.

Sandstone, limestone, gravel, and granite are arguably the most common aggregates used in the construction industry today, but these rocks have very different hardness and abrasiveness characteristics.

The answer might be three to four if youre talking about setting up stations in a complete rock crushing plant. Those are the primary, secondary, and tertiary/quaternary/final reduction rock crushers, which we covered above.

Of course, there are also different styles of rock crushers. Compression-style jaw and cone crushers, for example, fit into the various stations in a crushing circuit (depending on factors like the sizes, varieties, and hardness of the rock you need to crush, as well as the necessary output).

The number of crusher types in terms of style and configuration can be more challenging to quantify, as there are lots of ways to customize rock crushers. However, youll find four basic designscone, jaw, gyratory, and impact crushersoperating within many crushing plants.

Jaw crushers are also known as rock breakers and are used to break up larger, harder materials into more manageable pieces. They tend to do well with many different types of materials and dont display as much wear and tear as impact-style rock crushers. They also produce minimal fine materials and dust, though the finished product with this type of rock crusher almost always requires secondary crushing.

To learn more about jaw crushers, youll want to catch our previous blog post all about these tough pieces of material handling equipment and the most common questions operators have about jaw crushers.

Cone crushers can accept medium-hard to very hard and abrasive feeds that might be dry or wet, though not sticky (whereas gyratory crushers are better at handling softer, dryer feeds). Their output will be a relatively cubical product, with a reduction ratio of about 6-to-1 through 4-to-1.

Impact-style crushers include VSIs, as well as horizontal shaft impactors (HSIs), and are best used with less abrasive rock types, like limestone. These types of machines break apart material by the impacting forces of certain wear parts known as blow bars and impact plates or toggles.

Some operations also use impact-style crushers after they have already used a different type of rock crusher that produces a more elongated stone. This helps further shape the crushed material into a finer consistency with a more cubical nature.

Impact crushers tend to be less expensive than compression crushers (aka cone and jaw crushers, which we already covered) and have a higher reduction ratio. They can also break sedimentary deposit-type rockslimestone and similaralong natural lines, which rounds off sharp angles and weak edges. This can produce a result that is more sand-like in nature.

Drawbacks of impact crushers include their tendency to produce an excess of fine materials if used with softer rocks. Impact rock crushers can also require frequent part changes and can create a large amount of dust that can be an issue on some worksites.

Stationary plants have long been preferred because they feature a higher capacity and efficiency and lower production costs with easier maintenance. They also have historically featured a lower energy cost if you have on-site electricity, and no additional equipment is needed to move them from place to place.

Its true that portable material handling equipment already offers unmatched production flexibility. For instance, if you need to move your crushing plant more than once a year to multiple job sites, you are likely better off investing in portable equipment.

These self-contained plants are better suited to smaller projects and can be moved from project to project as necessary. They are often still not quite as efficient and have less capacity than stationary plants, but they can be more cost-effective in the long run if you have multiple projects in different areas.

Here at Kemper Equipment, we offer the best performing crushing equipment that will work hard to make any finished products you plan to produceincluding sand, gravel, fertilizer, specialty mineral products, recycled asphalt, salt, coal, and slagefficiently and affordably. Contact us today to discover how we can provide a custom-designed crushing circuit or retrofit a new rock crusher into your existing operation.

aggregate & rock crushing equipment | stedman machine company

aggregate & rock crushing equipment | stedman machine company

Many different industries have a solid foundation rooted in aggregates. Recognizing the extensive use of these aggregates motivates us to continuously create and improve our rock crushing equipment to help you increase production, decrease maintenance and improve the overall efficiency of your operation. When it comes to quality and efficiency, our rock crushers are perfect for the job.

Primary crushers are first in a typical size reduction operation. Primaries like our Mega-Slam horizontal shaft impactor are commonly used in the aggregates industry to handle large feed sizes.The Grand-Slam HSI is well suited as secondary crusher for aggregate production for a wide range of materials including limestone, frac sand, gravel, stone, and more. Tertiary crushers are commonly used in the aggregates industry for final particle shaping to increase cubicity, and to produce a product size beyond what is capable from a primary or secondary. This stage of crushing is typically accomplished using a vertical shaft impactor or cage mill.

Specialty uses of limestone include the manufacturing of pharmaceuticals, toothpaste, paint, paper, caulking, and glass. Flooring materials, carpet, and plastics all contain finely ground recycled limestone. Common antacids are virtually 100% finely ground limestone. Farmers can reuse limestone to neutralize acidity in their soils, saving money by reducing fertilizer use while improving crop yields.

The 4-Row Cage Mill allows Aglime producers to meet most state Aglime specifications in open circuit. It will economically produce Aglime to any specification for both large and small producers. The 4-Row Cage Mill feed does not have to be dry. Clogging, jamming and plugging are eliminated. Available with capacities as low as 5 TPH up to 100 TPH, the 4-Row Cage Mill produces consistent product quality.

Stedman Machine and Innovative Processing Solutions, an affiliate of Stedman, worked with Duff Quarry Inc. to incorporate two large industrial crushers to handle the size of limestone crushed annually. Their previous machines required a great amount of maintenance, but with Stedman machines, Duff Quarry Inc. spends less time fixing and more time crushing. With the installed plant and crushers, the quarry can produce up to 1.5 million tons of limestone a year running at full capacity.

Theres no reason to guess what method will meet your needs.The Stedman Testing and Toll Processing Facility is the place to test your material in our full size equipment. If it can be crushed, ground, pulverized or mixed, chances are weve done it. We have more than 10,000 test reports to help get you to the best solution quickly.

Test Before You Buy! Why Test? Stedman's testing facilities provide real-world conditions to view your materials being processed. Test out a range of different size reduction methods, saving you both time and money when selecting the proper size reduction method. Learn More

Stedman's testing facilities provide real-world conditions to view your materials being processed. Test out a range of different size reduction methods, saving you both time and money when selecting the proper size reduction method.

Stedman Machine Company is involved in professional organizations to better understand the knowledge and skills needed to serve our customers in the Aggregates Industry. These memberships give us better insight into the standards of the industry, updates to new and more efficient technologies and to the wants and needs of our customers. With the information obtained from our memberships, we can safely maintain the highest level of performance. Aggregate Industry associations include:

rock crushing & sand making machine for sale - eastman rock crusher

rock crushing & sand making machine for sale - eastman rock crusher

In the past 30 years, we have focused on the research, development and manufacture of mining crushing equipment, sand making equipment, industrial milling equipment, and keep improving them to build more environmentally friendly equipment.

Ganzhou Eastman Technology Co., Ltd. has for the target market in selling mineral processing equipment for rock crushing/grinding and sand making/washing operations. We provide those machines directly from our owned manufacturing workshop located in Shangyou factory or Shicheng factory based in Ganzhou, Jiangxi, China. So, as a customer you can properly get the most reasonable price equipment, also with promised good quality.Except saling our rock crushing & sand making equipment, we have Mining & Mineral Processing Engineer helping you make the right choice in crushing process and sand making processing. Also, our experienced exports are willing to help you design the perfect product line for your aggregate plant or sand making plant.

You can buy from us almost every material crushing processing equipment starting from crushing, grinding, sand washing & making, classification. And there are many customers cases you can find in our site.

Sand making production line consists of vibrating feeder, Jaw Crusher, Cone Crusher, Impact Crusher (sand-maker), Vibrating Screen, Sand Washer (sand classifier), Belt Conveyor, water treatment system and centralized electronic control system.

rock stone crushing machine impact crusher 30tph line - best stone crusher plant solution from henan dewo

rock stone crushing machine impact crusher 30tph line - best stone crusher plant solution from henan dewo

Dewo machinery can provides complete set of crushing and screening line, including Hydraulic Cone Crusher, Jaw Crusher, Impact Crusher, Vertical Shaft Impact Crusher (Sand Making Machine), fixed and movable rock crushing line, but also provides turnkey project for cement production line, ore beneficiation production line and drying production line. Dewo Machinery can provide high quality products, as well as customized optimized technical proposal and one station after- sales service.

China Stone Impact Crusher manufacturers - Select 2021 high quality Stone Impact Crusher products in best price from certified Chinese Impact Crusher manufacturers, Mining Equipment suppliers, wholesalers and factory on Made-in-China.com

Stationary Crusher. made by LGD Heavy Industry are well received in the market, such as C6X jaw crusher, CI5X impact crusher, HPT hydraulic cone crusher, etc. products. These machines take advantages of large capacity and high efficiency, and some of them even got international awards.

China Impact Stone Crusher manufacturers - Select 2021 high quality Impact Stone Crusher products in best price from certified Chinese Crushing Machine manufacturers, China Crusher suppliers, wholesalers and factory on Made-in-China.com

Impact Crusher,Stone Crusher Machine Price In India,Small Used Rock . crushing screening plant manufacturer supply specifications and small stone . price PE 400 x 600 small stone jaw crusher harga machine for 30tph gold processing.

rock crusher - eastman rock crusher

rock crusher - eastman rock crusher

Granite is not easy to crush to sand, main equipment has PE-7501060 jaw crusher (coarse crusher), HP300 cone crusher (fine crusher), bin, 490110 vibrating feeder, B1000x22 conveyor belt, B1000x30m conveyor belt, B800x31 conveyor belt, 4YK2460 vibrating screen, etc. contact us!

In this case, we recommend the use of a PCZ1308 heavy hammer crusher with a feed size of 930x650mm, the feed particle size is less than 600mm, the motor power is 4P 132Kw, and the processing capacity of the equipment is 100-180t/h.

Eastman is a typical direct selling enterprise with green and standardized production plants. All the delivery of the equipment will be completed within the delivery period signed by the contract to ensure the smooth commissioning of the equipment.

Rock crushers have a wide range of suitable material to choose from, whether its soft or hard, or even very hard, rock crushers can reduce those large rocks into smaller rocks, gravel, or even rock dust.Here are some typical materials that break or compress by industry crushers, such as Granite, quartz stone, river pebble, limestone, calcite, concrete, dolomite, iron ore, silicon ore, basalt and other mines, rocks and slag.

Understanding the stages of crushing process and the types of crushers that best fit each stage can simplifies your equipment selection. Each type of crusher is different and used to achieve a certain end result.

Similarly, a certain output is expected at the end of each crushing stage for the next phase of the process. Aggregate producers who pair the correct crusher to the correct stage will be the most efficient and, in turn, the most profitable.

A jaw crusher is a compression type of crusher. Material is reduced by squeezing the feed material between a moving piece of steel and a stationary piece. The discharge size is controlled by the setting or the space between those two pieces of steel. The tighter the setting, the smaller the output size and the lower the throughput capacity.

As a compression crusher, jaw crushers generally produce the coarsest material because they break the rock by the natural inherent lines of weakness. Jaw crushers are an excellent primary crusher when used to prepare rock for subsequent processing stages.

Although the chamber is round in shape, the moving piece of steel is not meant to rotate. Instead, a wedge is driven around to create compression on one side of the chamber and discharge opening on the opposite side. Cone crushers are used in secondary and tertiary roles as an alternative to impact crushers when shape is an important requirement, but the proportion of fines produced needs to be minimized.

An impact crusher uses mass and velocity to break down feed material. First, the feed material is reduced as it enters the crusher with the rotating blow bars or hammers in the rotor. The secondary breakage occurs as the material is accelerated into the stationary aprons or breaker plates.

Impact crushers tend to be used where shape is a critical requirement and the feed material is not very abrasive. The crushing action of an impact crusher breaks a rock along natural cleavage planes, giving rise to better product quality in terms of shape.

Most aggregate producers are well acquainted with the selection of crushing equipment and know it is possible to select a piece of equipment based solely on spec sheets and gradation calculations. Still, theoretical conclusions must always be weighed against practical experience regarding the material at hand and of the operational, maintenance and economical aspects of different solutions.

The duty of the primary crusher is, above all, to make it possible to transport material on a conveyor belt. In most aggregate crushing plants, primary crushing is carried out in a jaw crusher, although a gyratory primary crusher may be used. If material is easily crushed and not excessively abrasive, an impact breaker could also be the best choice.

The most important characteristics of a primary crusher are the capacity and the ability to accept raw material without blockages. A large primary crusher is more expensive to purchase than a smaller machine. For this reason, investment cost calculations for primary crushers are weighed against the costs of blasting raw material to a smaller size.

A pit-portable primary crusher can be an economically sound solution in cases where the producer is crushing at the quarry face. In modern plants, it is often advantageous to use a moveable primary crusher so it can follow the movement of the face where raw material is extracted.

The purpose of intermediate crushing is to produce various coarser fractions or to prepare material for final crushing. If the intermediate crusher is used to make railway ballast, product quality is important.

In other cases, there are normally no quality requirements, although the product must be suitable for fine crushing. In most cases, the objective is to obtain the greatest possible reduction at the lowest possible cost.

In most cases, the fine crushing and cubicization functions are combined in a single crushing stage. The selection of a crusher for tertiary crushing calls for both practical experience and theoretical know-how. This is where producers should be sure to call in an experienced applications specialist to make sure a system is properly engineered.

impact crusher - an overview | sciencedirect topics

impact crusher - an overview | sciencedirect topics

The impact crusher (typically PE series) is widely used and of high production efficiency and good safety performance. The finished product is of cube shape and the tension force and crack is avoided. Compared with hammer crusher, the impact crusher is able to fully utilize the high-speed impact energy of entire rotor. However, due to the crushing board that is easy to wear, it is also limited in the hard material crushing. The impact crusher is commonly used for the crushing of limestone, coal, calcium carbide, quartz, dolomite, iron pyrites, gypsum, and chemical raw materials of medium hardness. Effect of process conditions on the production capacity of crushed materials is listed in Table8.10.

Depending on the size of the debris, it may either be ready to enter the recycling process or need to be broken down to obtain a product with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimise the degree of contamination of the final product.

The three types of crushers most commonly used for crushing CDW materials are the jaw crusher, the impact crusher and the gyratory crusher (Figure 4.4). A jaw crusher consists of two plates, with one oscillating back and forth against the other at a fixed angle (Figure 4.4(a)) and it is the most widely used in primary crushing stages (Behera etal., 2014). The jaw crusher can withstand large and hard-to-break pieces of reinforced concrete, which would probably cause the other crushing machines to break down. Therefore, the material is initially reduced in jaw crushers before going through any other crushing operation. The particle size reduction depends on the maximum and minimum size of the gap at the plates (Hansen, 2004).

An impact crusher breaks the CDW materials by striking them with a high-speed rotating impact, which imparts a shearing force on the debris (Figure 4.4(b)). Upon reaching the rotor, the debris is caught by steel teeth or hard blades attached to the rotor. These hurl the materials against the breaker plate, smashing them into smaller particle sizes. Impact crushers provide better grain-size distribution of RA for road construction purposes, and they are less sensitive to material that cannot be crushed, such as steel reinforcement.

Generally, jaw and impact crushers exhibit a large reduction factor, defined as the ratio of the particle size of the input to that of the output material. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike and thus generates a higher amount of fine material (OMahony, 1990).

Gyratory crushers work on the same principle as cone crushers (Figure 4.4(c)). These have a gyratory motion driven by an eccentric wheel. These machines will not accept materials with a large particle size and therefore only jaw or impact crushers should be considered as primary crushers. Gyratory and cone crushers are likely to become jammed by fragments that are too large or too heavy. It is recommended that wood and steel be removed as much as possible before dumping CDW into these crushers. Gyratory and cone crushers have advantages such as relatively low energy consumption, a reasonable amount of control over the particle size of the material and production of low amounts of fine particles (Hansen, 2004).

For better control of the aggregate particle size distribution, it is recommended that the CDW should be processed in at least two crushing stages. First, the demolition methodologies used on-site should be able to reduce individual pieces of debris to a size that the primary crusher in the recycling plant can take. This size depends on the opening feed of the primary crusher, which is normally bigger for large stationary plants than for mobile plants. Therefore, the recycling of CDW materials requires careful planning and communication between all parties involved.

A large proportion of the product from the primary crusher can result in small granules with a particle size distribution that may not satisfy the requirements laid down by the customer after having gone through the other crushing stages. Therefore, it should be possible to adjust the opening feed size of the primary crusher, implying that the secondary crusher should have a relatively large capacity. This will allow maximisation of coarse RA production (e.g., the feed size of the primary crusher should be set to reduce material to the largest size that will fit the secondary crusher).

The choice of using multiple crushing stages mainly depends on the desired quality of the final product and the ratio of the amounts of coarse and fine fractions (Yanagi etal., 1998; Nagataki and Iida, 2001; Nagataki etal., 2004; Dosho etal., 1998; Gokce etal., 2011). When recycling concrete, a greater number of crushing processes produces a more spherical material with lower adhered mortar content (Pedro etal., 2015), thus providing a superior quality of material to work with (Lotfi etal., 2017). However, the use of several crushing stages has some negative consequences as well; in addition to costing more, the final product may contain a greater proportion of finer fractions, which may not always be a suitable material.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Fig. 15.9), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 15.9. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements. (A) Single-toggle jaw crusher, (B) disc or gyrosphere crusher, (C) gyratory crusher and (D) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (Section 15.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Figure 16.8), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 16.8. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements (redrawn, adapted and modified from Ref. 39). (a) Single-toggle jaw crusher, (b) disc or gyrosphere crusher, (c) gyratory crusher, and (d) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (section 16.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

The main sources of RA are either from construction and ready mixed concrete sites, demolition sites or from roads. The demolition sites produce a heterogeneous material, whereas ready mixed concrete or prefabricated concrete plants produce a more homogeneous material. RAs are mainly produced in fixed crushing plant around big cities where CDWs are available. However, for roads and to reduce transportation cost, mobile crushing installations are used.

The materiel for RA manufacturing does not differ from that of producing NA in quarries. However, it should be more robust to resist wear, and it handles large blocks of up to 1m. The main difference is that RAs need the elimination of contaminants such as wood, joint sealants, plastics, and steel which should be removed with blast of air for light materials and electro-magnets for steel. The materials are first separated from other undesired materials then treated by washing and air to take out contamination. The quality and grading of aggregates depend on the choice of the crusher type.

Jaw crusher: The material is crushed between a fixed jaw and a mobile jaw. The feed is subjected to repeated pressure as it passes downwards and is progressively reduced in size until it is small enough to pass out of the crushing chamber. This crusher produces less fines but the aggregates have a more elongated form.

Hammer (impact) crusher: The feed is fragmented by kinetic energy introduced by a rotating mass (the rotor) which projects the material against a fixed surface causing it to shatter causing further particle size reduction. This crusher produces more rounded shape.

The type of crusher and number of processing stages have considerable influence on the shape and size of RA. In general, for the same size, RAs tend to be coarser, more porous and rougher than NAs, due to the adhered mortar content (Dhir etal., 1999). After the primary crushing, which is normally performed using jaw crushers (Fong etal., 2004), it is preferable to adopt a secondary crushing stage (with cone crushers or impact crushers) (CCANZ, 2011) to further reduce the size of the CDW, producing more regularly shaped particles (Barbudo etal., 2012; Ferreira etal., 2011; Fonseca etal., 2011; Pedro etal., 2014, 2015; Gonzlez-Fonteboa and Martnez-Abella, 2008; Maultzsch and Mellmann, 1998; Dhir and Paine, 2007; Chidiroglou etal., 2008).

CDW that is subjected to a jaw crushing stage tends to result only in flatter RA (Ferreira etal., 2011; Fonseca etal., 2011; Hendriks, 1998; Tsoumani etal., 2015). It is possible to produce good-quality coarse RA within the specified size range by adjusting the crusher aperture (Hansen, 1992). In addition, the number of processing stages needs to be well thought out to ensure that the yield of coarse RA is not affected and that the quantity of fine RA is kept to the minimum (Angulo etal., 2004). This is because the finer fraction typically exhibits lower quality, as it accumulates a higher amount of pulverised old mortar (Etxeberria etal., 2007b; Meller and Winkler, 1998). Fine RA resulting from impact crushers tends to exhibit greater angularity and higher fineness modulus compared with standard natural sands (Lamond etal., 2002; Hansen, 1992; Buyle-Bodin and Hadjieva-Zaharieva, 2002).

One of the commonly known issues related to the use of RCA is its ability to generate a considerable amount of fines when the material is used (Thomas etal., 2016). As the RCA particles are moved around, they impact against one another, leading to the breakage of the friable adhered mortar, which may give rise to some technical problems such as an increase in the water demand of concrete mixes when used as an NA replacement (Thomas etal., 2013a,b; Poon etal., 2007).

The coarse fraction of RMA tends to show a higher shape index owing to the shape of the original construction material (e.g., perforated ceramic bricks) (De Brito etal., 2005). This can pose a problem in future applications as RMA may not compact as efficiently as RCA or NA (Khalaf and DeVenny, 2005). Its shape index may be reduced if the material is successively broken down to a lower particle size (De Brito etal., 2005).

Impact crushers (e.g., hammer mills and impact mills) employ sharp blows applied at high speed to free-falling rocks where comminution is by impact rather than compression. The moving parts are beaters, which transfer some of their kinetic energy to the ore particles upon contact. Internal stresses created in the particles are often large enough to cause them to shatter. These forces are increased by causing the particles to impact upon an anvil or breaker plate.

There is an important difference between the states of materials crushed by pressure and by impact. There are internal stresses in material broken by pressure that can later cause cracking. Impact causes immediate fracture with no residual stresses. This stress-free condition is particularly valuable in stone used for brick-making, building, and roadmaking, in which binding agents (e.g., tar) are subsequently added. Impact crushers, therefore, have a wider use in the quarrying industry than in the metal-mining industry. They may give trouble-free crushing on ores that tend to be plastic and pack when the crushing forces are applied slowly, as is the case in jaw and gyratory crushers. These types of ore tend to be brittle when the crushing force is applied instantaneously by impact crushers (Lewis et al., 1976).

Impact crushers are also favored in the quarry industry because of the improved product shape. Cone crushers tend to produce more elongated particles because of their ability to pass through the chamber unbroken. In an impact crusher, all particles are subjected to impact and the elongated particles, having a lower strength due to their thinner cross section, would be broken (Ramos et al., 1994; Kojovic and Bearman, 1997).

Figure 6.23(a) shows the cross section of a typical hammer mill. The hammers (Figure 6.23(b)) are made from manganese steel or nodular cast iron containing chromium carbide, which is extremely abrasion resistant. The breaker plates are made of the same material.

The hammers are pivoted so as to move out of the path of oversize material (or tramp metal) entering the crushing chamber. Pivoted (swing) hammers exert less force than they would if rigidly attached, so they tend to be used on smaller impact crushers or for crushing soft material. The exit from the mill is perforated, so that material that is not broken to the required size is retained and swept up again by the rotor for further impacting. There may also be an exit chute for oversize material which is swept past the screen bars. Certain design configurations include a central discharge chute (an opening in the screen) and others exclude the screen, depending on the application.

The hammer mill is designed to give the particles velocities of the order of that of the hammers. Fracture is either due to impact with the hammers or to the subsequent impact with the casing or grid. Since the particles are given high velocities, much of the size reduction is by attrition (i.e., particle on particle breakage), and this leads to little control on product size and a much higher proportion of fines than with compressive crushers.

The hammers can weigh over 100kg and can work on feed up to 20cm. The speed of the rotor varies between 500 and 3,000rpm. Due to the high rate of wear on these machines (wear can be taken up by moving the hammers on the pins) they are limited in use to relatively non-abrasive materials. They have extensive use in limestone quarrying and in the crushing of coal. A great advantage in quarrying is the fact that they produce a relatively cubic product.

A model of the swing hammer mill has been developed for coal applications (Shi et al., 2003). The model is able to predict the product size distribution and power draw for given hammer mill configurations (breaker gap, under-screen orientation, screen aperture) and operating conditions (feed rate, feed size distribution, and breakage characteristics).

For coarser crushing, the fixed hammer impact mill is often used (Figure 6.24). In these machines the material falls tangentially onto a rotor, running at 250500rpm, receiving a glancing impulse, which sends it spinning toward the impact plates. The velocity imparted is deliberately restricted to a fraction of the velocity of the rotor to avoid high stress and probable failure of the rotor bearings.

The fractured pieces that can pass between the clearances of the rotor and breaker plate enter a second chamber created by another breaker plate, where the clearance is smaller, and then into a third smaller chamber. The grinding path is designed to reduce flakiness and to produce cubic particles. The impact plates are reversible to even out wear, and can easily be removed and replaced.

The impact mill gives better control of product size than does the hammer mill, since there is less attrition. The product shape is more easily controlled and energy is saved by the removal of particles once they have reached the size required.

Large impact crushers will reduce 1.5m top size ROM ore to 20cm, at capacities of around 1500th1, although units with capacities of 3000th1 have been manufactured. Since they depend on high velocities for crushing, wear is greater than for jaw or gyratory crushers. Hence impact crushers are not recommended for use on ores containing over 15% silica (Lewis et al., 1976). However, they are a good choice for primary crushing when high reduction ratios are required (the ratio can be as high as 40:1) and the ore is relatively non-abrasive.

Developed in New Zealand in the late 1960s, over the years it has been marketed by several companies (Tidco, Svedala, Allis Engineering, and now Metso) under various names (e.g., duopactor). The crusher is finding application in the concrete industry (Rodriguez, 1990). The mill combines impact crushing, high-intensity grinding, and multi-particle pulverizing, and as such, is best suited in the tertiary crushing or primary grinding stage, producing products in the 0.0612mm size range. It can handle feeds of up to 650th1 at a top size of over 50mm. Figure 6.22 shows a Barmac in a circuit; Figure 6.25 is a cross-section and illustration of the crushing action.

The basic comminution principle employed involves acceleration of particles within a special ore-lined rotor revolving at high speed. A portion of the feed enters the rotor, while the remainder cascades to the crushing chamber. Breakage commences when rock enters the rotor, and is thrown centrifugally, achieving exit velocities up to 90ms1. The rotor continuously discharges into a highly turbulent particle cloud contained within the crushing chamber, where reduction occurs primarily by rock-on-rock impact, attrition, and abrasion.

This crusher developed by Jaques (now Terex Mineral Processing Solutions) has several internal chamber configurations available depending on the abrasiveness of the ore. Examples include the Rock on Rock, Rock on Anvil and Shoe and Anvil configurations (Figure 6.26). These units typically operate with 5 to 6 steel impellers or hammers, with a ring of thin anvils. Rock is hit or accelerated to impact on the anvils, after which the broken fragments freefall into the discharge chute and onto a product conveyor belt. This impact size reduction process was modeled by Kojovic (1996) and Djordjevic et al. (2003) using rotor dimensions and speed, and rock breakage characteristics measured in the laboratory. The model was also extended to the Barmac crushers (Napier-Munn et al., 1996).

Figure 9.1 shows common aluminum oxide-based grains. Also called corundum, alumina ore was mined as early as 2000 BC in the Greek island of Naxos. Its structure is based on -Al2O3 and various admixtures. Traces of chromium give alumina a red hue, iron makes it black, and titanium makes it blue. Its triagonal system reduces susceptibility to cleavage. Precious grades of Al2O3 are used as gemstones, and include sapphire, ruby, topaz, amethyst, and emerald.

Charles Jacobs (1900), a principal developer, fused bauxite at 2200C (4000F) before the turn of the 20th century. The resulting dense mass was crushed into abrasive particles. Presently, alumina is obtained by smelting aluminum alloys containing Al2O3 in electric furnaces at around 1260C (2300F), a temperature at which impurities separate from the solution and aluminum oxide crystallizes out. Depending upon the particular process and chemical composition there are a variety of forms of aluminum oxide. The poor thermal conductivity of alumina (33.5W/mK) is a significant factor that affects grinding performance. Alumina is available in a large range of grades because it allows substitution of other oxides in solid solution, and defect content can be readily controlled.

For grinding, lapping, and polishing bearing balls, roller races, and optical glasses, the main abrasive employed is alumina. Its abrasive characteristics are established during the furnacing and crushing operations, so very little of what is accomplished later significantly affects the features of the grains.

Aluminum oxide is tougher than SiC. There are four types of gradations for toughness. The toughest grain is not always the longest wearing. A grain that is simply too tough for an application will become dull and will rub the workpiece, increasing the friction, creating heat and vibrations. On the other hand, a grain that is too friable will wear away rapidly, shortening the life of the abrasive tool. Friability is a term used to describe the tendency for grain fractures to occur under load. There is a range of grain toughness suitable for each application. The white friable aluminum oxide is almost always bonded by vitrification. It is the main abrasive used in tool rooms because of its versatility for a wide range of materials. In general, the larger the crystals, the more friable the grain. The slower the cooling process, the larger are the crystals. To obtain very fine crystals, the charge is cooled as quickly as possible, and the abrasive grain is fused in small pigs of up to 2ton. Coarse crystalline abrasive grains are obtained from 5 to 6ton pigs allowed to cool in the furnace shell.

The raw material, bauxite, containing 8590% alumina, 25% TiO2, up to 10% iron oxide (Fe2O3), silica, and basic oxides, is fused in an electric-arc furnace at 2600C (4700F). The bed of crushed and calcined bauxite, mixed with coke and iron to remove impurities, is poured into the bottom of the furnace where a carbon starter rod is laid down. A couple of large vertical carbon rods are then brought down to touch and a heavy current applied. The starter rod is rapidly consumed, by which time the heat melts the bauxite, which then becomes an electrolyte. Bauxite is added over several hours to build up the volume of melt. Current is controlled by adjusting the height of the electrodes, which are eventually consumed in the process.

After cooling, the alumina is broken up and passed through a series of hammer, beater, crush, roller, and/or ball mills to reduce it to the required grain size and shape, producing either blocky or thin splintered grains. After milling, the product is sieved to the appropriate sizes down to about 40 m (#400). The result is brown alumina containing typically 3% TiO2. Increased TiO2 content increases toughness while reducing hardness. Brown alumina has a Knoop hardness of 2090 and a medium friability.

Electrofused alumina is also made using low-soda Bayer process alumina that is more than 99% pure. The resulting alumina grain is one of the hardest, but also the most friable, of the alumina family providing a cool cutting action. This abrasive in a vitrified bond is, therefore, suitable for precision grinding.

White aluminum oxide is one of the most popular grades for micron-size abrasive. To produce micron sizes, alumina is ball-milled or vibro-milled after crushing and then traditionally separated into different sizes using an elutriation process. This consists of passing abrasive slurry and water through a series of vertical columns. The width of the columns is adjusted to produce a progressively slower vertical flow velocity from column to column. Heavier abrasive settles out in the faster flowing columns while lighter particles are carried over to the next. The process is effective down to about 5 m and is also used for micron sizing of SiC. Air classification has also been employed.

White 99% pure aluminum oxide, called mono-corundum, is obtained by sulfidation of bauxite, which outputs different sizes of isometric corundum grains without the need for crushing. The crystals are hard, sharp, and have better cleavage than other forms of aluminum oxides, which qualifies it for grinding hardened steels and other tough and ductile materials. Fine-grained aluminum oxide with a good self-sharpening effect is used for finishing hardened and high-speed steels, and for internal grinding.

Not surprisingly, since electrofusion technology has been available for the last one hundred years, many variations in the process exist both in terms of starting compositions and processing routes. For example:

Red-brown or gray regular alumina. Contains 9193% Al2O3 and has poor cleavage. This abrasive is used in resinoid and vitrified bonds and coated abrasives for rough grinding when the risk of rapid wheel wear is low.

Chrome addition. Semi-fine aloxite, pink with 0.5% chromium oxide (Cr2O3), and red with 15% Cr2O3, lies between common aloxite, having less than 95% Al2O3 and more than 2% TiO2, and fine aloxite, which has more than 95% Al2O3 and less than 2% TiO2. The pink grain is slightly harder than white alumina, while the addition of a small amount of TiO2 increases its toughness. The resultant product is a medium-sized grain available in elongated, or blocky but sharp, shapes. Ruby alumina has a higher chrome oxide content of 3% and is more friable than pink alumina. The grains are blocky, sharp edged, and cool cutting, making them popular for tool room and dry grinding of steels, e.g., ice skate sharpening. Vanadium oxide has also been used as an additive giving a distinctive green hue.

Zirconia addition. Aluminazirconia is obtained during the production process by adding 1040% ZrO2 to the alumina. There are at least three different aluminazirconia compositions used in grinding wheels: 75% Al2O3 and 25% ZrO2, 60% Al2O3 and 40% ZrO2, and finally, 65% Al2O3, 30% ZrO2, and 5% TiO2. The manufacture usually includes rapid solidification to produce a fine grain and tough structure. The resulting abrasives are fine grain, tough, highly ductile, and give excellent life in medium to heavy stock removal applications and grinding with high pressures, such as billet grinding in foundries.

Titania addition. Titaniaaloxite, containing 95% Al2O3 and approximately 3% Ti2O3, has better cutting ability and improved ductility than high-grade bauxite common alumina. It is recommended when large and variable mechanical loads are involved.

Single crystal white alumina. The grain growth is carefully controlled in a sulfide matrix and is separated by acid leaching without crushing. The grain shape is nodular which aids bond retention, avoiding the need for crushing and reducing mechanical defects from processing.

Post-fusion processing methods. This type of particle reduction method can greatly affect grain shape. Impact crushers such as hammer mills create a blocky shape while roll crushers cause splintering. It is possible, using electrostatic forces to separate sharp shapes from blocky grains, to provide grades of the same composition but with very different cutting actions.

The performance of the abrasive can also be altered by heat treatment, particularly for brown alumina. The grit is heated to 11001300 C (20152375 F), depending on the grit size, in order to anneal cracks and flaws created by the crushing process. This can enhance toughness by 2540%.

Finally, several coating processes exist to improve bonding of the grains in the grinding wheel. Red Fe2O3 is applied at high temperatures to increase the surface area for better bonding in resin cut-off wheels. Silane is applied for some resin bond wheel applications to repel coolant infiltration between the bond and abrasive grit, and thus protect the resin bond.

A limitation of electrofusion is that the resulting abrasive crystal structure is very large; an abrasive grain may consist of only one to three crystals. Consequently, when grain fracture occurs, the resulting particle loss may be a large proportion of the whole grain. This results in inefficient grit use. One way to avoid this is to dramatically reduce the crystal size.

The earliest grades of microcrystalline grits were produced as early as 1963 (Ueltz, 1963) by compacting a fine-grain bauxite slurry, granulating to the desired grit size, and sintering at 1500C (2735F). The grain shape and aspect ratio could be controlled by extruding the slurry.

One of the most significant developments since the invention of the Higgins furnace was the release in 1986, by the Norton Company, of seeded gel (SG) abrasive (Leitheiser and Sowman, 1982; Cottringer et al., 1986). This abrasive was a natural outcome of the wave of technology sweeping the ceramics industry at that time to develop high strength engineering ceramics using chemical precipitation methods. This class of abrasives is often termed ceramic. SG is produced by a chemical process. In a precursor of boehmite, MgO is first precipitated to create 50-m-sized aluminamagnesia spinel seed crystals. The resulting gel is dried, granulated to size, and sintered at 1200C (2200F). The resulting grains are composed of a single-phase -alumina structure with a crystalline size of about 0.2m. Defects from crushing are avoided; the resulting abrasive is unusually tough but self-sharpening because fracture now occurs at the micron level.

With all the latest technologies, it took significant time and application knowledge to understand how to apply SG. The abrasive was so tough that it had to be blended with regular fused abrasives at levels as low as 5% to avoid excessive grinding forces. Typical blends are now five SGs (50%), three SGs (30%), and one SG (10%). These blended abrasive grades can increase wheel life by up to a factor of 10 over regular fused abrasives, although manufacturing costs are higher.

In 1981, prior to the introduction of SG, the 3M Co. introduced a solgel abrasive material called Cubitron for use in coated abrasive fiber discs (Bange and Orf, 1998). This was a submicron chemically precipitated and sintered material but, unlike SG, had a multiphase composite structure that did not use seed grains to control crystalline size. The value of the material for grinding wheel applications was not recognized until after the introduction of SG. In the manufacture of Cubitron, alumina is co-precipitated with various modifiers such as magnesia, yttria, lanthana, and neodymia to control microstructural strength and surface morphology upon subsequent sintering. For example, one of the most popular materials, Cubitron 321, has a microstructure containing submicron platelet inclusions which act as reinforcements somewhat similar to a whisker-reinforced ceramic (Bange and Orf, 1998).

Direct comparison of the performance of SG and Cubitron is difficult because the grain is merely one component of the grinding wheel. SG is harder (21GPa) than Cubitron (19GPa). Experimental evidence suggests that wheels made from SG have longer life, but Cubitron is freer cutting. Cubitron is the preferred grain in some applications from a cost/performance viewpoint. Advanced grain types are prone to challenge from a well-engineered, i.e., shape selected, fused grain that is the product of a lower cost, mature technology. However, it is important to realize that the wheel cost is often insignificant compared to other grinding process costs in the total cost per part.

The SG grain shape can be controlled by extrusion. Norton has taken this concept to an extreme and in 1999 introduced TG2 (extruded SG) grain in a product called ALTOS. The TG2 grains have the appearance of rods with very long aspect ratios. The resulting packing characteristics of these shapes in a grinding wheel create a high strength, lightweight structure with porosity levels as high as 70% or even greater. The grains touch each other at only a few points, where a bond also concentrates in the same way as a spot weld. The product offers potential for higher stock removal rates and higher wheelspeeds due to the strength and density of the resulting wheel body (Klocke and Muckli, 2000).

Recycling of concrete involves several steps to generate usable RCA. Screening and sorting of demolished concrete from C&D debris is the first step of recycling process. Demolished concrete goes through different crushing processes to acquire desirable grading of recycled aggregate. Impact crusher, jaw crusher, cone crusher or sometimes manual crushing by hammer are preferred during primary and secondary crushing stage of parent concrete to produce RA. Based on the available literature step by step flowchart for recycling of aggregate is represented in Fig. 1. Some researchers have also developed methods like autogenous cleaning process [46], pre-soaking treatment in water [47], chemical treatment, thermal treatment [48], microwave heating method [49] and mechanical grinding method for removing adhered mortar to obtain high quality of RA. Depending upon the amount of attached mortar, recycled aggregate has been classified into different categories as shown in Fig. 2.

Upon arrival at the recycling plant, CDW may either enter directly into the processing operation or need to be broken down to obtain materials with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimize the degree of contamination.

The three types of crushers most used for crushing CDW are jaw, impact, and gyratory crushers (Fig.8). A jaw crusher consists of two plates fixed at an angle (Fig.8a); one plate remains stationary while the other oscillates back and forth relative to it, crushing the material passing between them. This crusher can withstand large pieces of reinforced concrete, which would probably cause other types of crushers to break down. Therefore, the material is initially reduced in jaw crushers before going through other types. The particle size reduction depends on the maximum and minimum size of the gap at the plates. Jaw crushers were found to produce RA with the most suitable grain-size distribution for concrete production (Molin etal., 2004).

An impact crusher breaks CDW by striking them with a high speed rotating impact, which imparts a shearing force on the debris (Fig.8b). Materials fall onto the rotor and are caught by teeth or hard steel blades fastened to the rotor, which hurl them against the breaker plate, smashing them to smaller-sized particles. Impact crushers provide better grain-size distribution of RA for road construction purposes and are less sensitive to material that cannot be crushed (i.e. steel reinforcement).

Gyratory crushers, which work on the same principle as cone crushers (Fig.8c), exhibit a gyratory motion driven by an eccentric wheel and will not accept materials with large particle sizes as they are likely to become jammed. However, gyratory and cone crushers have advantages such as relatively low energy consumption, reasonable amount of control over particle size and production of low amount of fine particles.

Generally, jaw and impact crushers have a large reduction factor, defined as the relationship between the input's particle size and that of the output. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike, and thus may generate twice the amount of fines for the same maximum size of particle (O'Mahony, 1990).

In order to produce RA with predictable grading curve, it is better to process debris in two crushing stages, at least. It may be possible to consider a tertiary crushing stage and further, which would undoubtedly produce better quality coarse RA (i.e. less adhered mortar and with a rounder shape). However, concrete produced with RA subjected to a tertiary crushing stage may show only slightly better performance than that made with RA from a secondary crushing stage (Gokce etal., 2011; Nagataki etal., 2004). Furthermore, more crushing stages would yield products with decreasing particle sizes, which contradicts the mainstream use of RA (i.e. coarser RA fractions are preferred, regardless of the application). These factors should be taken into account when producing RA as, from an economical and environmental point of view, it means that relatively good quality materials can be produced with lower energy consumption and with a higher proportion of coarse aggregates, if the number of crushing stages is prudently reduced.

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