portable rock crushers
As it relates to portable crushers, the basic portability concept under investigation here might better be described by the phrase decentralized crushing to allow automated ore haulage. Clearly this means more and smaller crushers exhibiting some degree of mobility, and automated ore haulage usually means belt conveyors. The trade-off is a necessarily more costly crushing system against a more efficient and productive ore handling system. From the crusher manufacturers point of view the challenge is to achieve small size and portability without sacrificing too much in the important areas of feed opening, throughput, system availability, and capital and operation costs.
Portable in Portable Rock Crushers simply means that the crusher is moved periodically in order to be close to production, thus minimizing costly haulage of run of mine material. Within this simplified definition however, portability has quite different meanings in mines of widely varying ore bodies and mining plans. We shall further assume that a portable crusher is one that can be moved through standard mine passageways with minimal dismantling, and can be set up with little or no site excavation.
Underground is obvious, and when taken with portable brings to mind such terms as low, narrow, horizontal, light, serviceable, and mobile. This study may define a machine that is also applicable to some above ground installations but no attempt will be made to enhance such applicability at the expense of underground performance.
Hard-rock is sometimes taken to mean non-coal, but this broad definition would include many weaker mineral mines not in need of the fundamentally new equipment that is the subject of this study. Many of these non-coal mines have, however, developed highly efficient and mechanized coal-like mining methods that would be applicable to hard-rock mines if suitable equipment (crushers) were available. We have therefore gained valuable information by studying these mines, but the intended beneficiary of this investigation is the underground hard-rock industry, defined as those mines that cannot economically make use of presently available portable underground crushers.
To begin, let us attempt to define approximate requirements in order to establish a background for further specification of performance parameters, and to form the basis for a critical examination of existing crusher designs. In fact, it seems clear that no single optimum set of parameters can ever be sharply defined. However, with adequate documentation and an appreciation of likely individual case variations, such an approximate set of parameters can serve as the basis for new concept generation and further development work.
Before defining what a portable rock crusher is, we need to know how it will be used. Fortunately for the purposes of this study, portable underground crusher applications may be divided into two rather distinct categories, and one of these, though worthy of further thoughts and development, does not require fundamentally new hardware development. The distinction, perhaps predictably, is primarily one of physical machine size, although, to a lesser degree, distinctions can also be made in the desired degree of portability within a given size category.
The first category, which we shall dismiss for the moment, is one in which machine size, per se, is not limiting. Applications in this category are high head-room room and pillar mines, such as large limestone mines having 35 foot backs , and, in the future, oil shale mines having even higher backs. While significant portability improvements can be made in assembly methods and general layout, as discussed in Section 9, this category of applications ran in general be satisfied by existing manufacturers through modification of essentially standard machine components.
The second category is that in which machine size is very much a limiting factorso much so that todays standard hard rock primaries are simply not applicable. The two general mine types falling in this category include, obviously, low head room room and pillar mines and, perhaps not so obviously, most mines with vertically oriented ore bodies. The latter include caving mines, whatever the caving mechanism (block caving, sub-level caving, etc.), and other generally vertical mine plans such as open stope, shrinkage stoping, cut and fill, etc. . For purposes of this study, these mines are collectively characterized by gravity delivery of ore to a stationary or nearly stationary, draw point or chute from which the ore is handled (and often rehandled) by a variety of means in both the horizontal and vertical directions. Even though massive ore bodies may be involved, typical drift dimensions in such mines are not large, on the order of 8 to 12 feet high by not much greater widths.
Both mine types in this category of small applications suggest maximum installed crusher sizes of 7 to 9 feet high, 8-10 feet wide, and any reasonable length (the latter determined by transport conditions rather than installed dimensions. It is important to note that this height includes whatever overhead feed components (and dump space) may be required by vertical feed crushersthus standard top fed jaw crushers, which would normally be selected for hard rock, are much too tall.
Portable crushers will receive run of mine material from the face regardless of the mining method or the primary haulage system used, and then crush this ore and feed it into a more continuous and efficient ore haulage system. Within these applications it appears that for a decentralised crusher arrangement a throughput of 100 to 800 tons per hour will suffice. Although there is no clear-cut limit, this throughput is obviously a function of the size of the mining unit it services, and the ability, within the stated drift dimensions, of the primary haulage system to deliver material to the crusher. Thus it is not surprising that a limited range of throughputs will serve a wide variety of mining operations.
Just like the very large central crusher located (probably) at the shaft, the proposed decentralised portable crusher system must handle ROM (run of mine) ore. This fact, when taken with the low headroom restrictions, will continually challenge the would be portable crusher designer.
A study by the U. S. Bureau of Mines in five underground mines, utilising five different mining methods, in extremely different types of rocks, showed a striking similarity of over-size ore, not only in mean size but in shape as well. Table I presents these results. The indicated size uniformity is considered misleading, particularly in view of the fact that the study did not attempt to
determine the percentage of ore exceeding the stated oversize. The shape trend of this data (3:2:1) is more interesting, indicating a condition somewhere between block and slabby. Larger variations in size of oversize are supported by another study which was concerned with block caving mines. Results of this study, also presented in Table I, characterize the block cave mine of the preceding study as having fine ore. There is clearly no single optimum crusher feed opening for these, let alone all, block caving mines, although it is probably safe to say that block caving permits the least control of fragment size and can thus be expected to present highly variable conditions.
Mining plans relying on drilling and blasting for fragmentation control will, no doubt, show greater uniformity in size of oversize, but great variations are to be expected in the size distribution of ROM ore from mine to mine. Assuming a successful crusher can avoid direct attack of the three-to-five font major fragment dimension indicated in Table I, and assuming some form of control over occasional abnormal oversize, it is likely that minimum or critical feed openings in the 30-36 inch range will satisfy a very large percentage of mines.
To establish approximate product size, let us assume that the product is to be belt conveyed. In most cases this will be true, and it is expected that maximum economic benefit will occur in this combination. The feeder-breaker, so successfully used on coal mine section belts, is generally set to produce nine inch maximum lumps for 36 inch belts. For first-cost and other reasons, this belt width appears to be very common for section and feeder applications, and for the denser-than-coal ores found in the hard rock industry, a maximum product size in the range of 6-8 inches is appropriate, it is interesting to note that even for very large oil shale installations (very wide belts) a six inch product is recommended.
It appears that there is relatively little need to simultaneously develop a range of machinery between these small units and the large central primaries now being used. Ultimately a range of intermediate sizes will be desirable, of course, but this can easily be developed from low head room equipment meeting the above specifications.
As will be illustrated in the following section, these requirements cannot be met by existing hard rock crushing equipment. In fact, noting that the desired dimensions include whatever overhead clearance is needed to load the crusher proper, and space underneath to deliver its product (assuming a typical vertical jaw or gyratory design), it is obvious that standard machines are far from satisfactory. It follows, then, that satisfactory new concepts cannot be found among minor variations of standard concepts: the sought after design will differ substantially from present designs. At the same time, it would be comforting if a new concept did not depart substantially from the basic comminution means of proven designs. Economical crushing of hard rock, day in and day out, through many millions of tons, is, after all, a rather difficult task, even without severe space limitations, and proven means should not be so quickly discarded.
The inventors task is not quite so formidable as the proceeding may suggest. In comparison to a typical aggregate production application for example, some aspects of the portable application actually ease the design problems: The crusher is needed only for oversize (unbeltable) material. Thus, while the crusher should avoid fines, it has no rigid product size requirement other than maximum size, and essentially no product shape requirement (a requirement that justifies some rather subtle variations of crusher geometry in many conventional applications). Furthermore, if the crusher is designed to pass undersize material freely, or if its feed mechanism provides scalping to bypass smaller material, much of the throughput will be free, a provision which will also reduce the production of fines, and, more importantly, dust.
Many manufacturers were contacted in an extensive effort to include all available equipment and manufacturing capability in this study. Appendix A is a list containing the names and (if available) addresses of those manufacturers who were contacted. Although not all were responsive, many were quite helpful and the majority expresses the opinion that they would need the results of this study if the industry or any single manufacturer were to consider the development of portable, underground, hardrock crushers.
This study was neither intended, nor will it attempt, to instruct the reader in the complete art of primary rock crushing. There are many good references in this area; notable among these is McGrew. Our goal is to define the optimum parameters for the design of a portable, underground, hard rock crusher in order to insure that future development will lead to maximum utilization by the industry.
In summary then, we want to study present crusher types with an eye toward moving them around in hard-rock mines. Though small, these units will handle essentially as mined or ROM material, and should rightfully be called primary crushers.
This class of crusher historically has been used on the strongest ores. Crushing is accomplished by relatively slow moving members exerting very high force levels. Understandably, these crushers are typically very big, very strong, and heavy.
Figure 1 shows a simplified section of a typical gravity fed gyratory crusher. Clearly the typical portable underground crusher requirements presented in Section 2 cannot be met by a standard gyratory. However, because the crushing action of the gyratory works well on hard rock, the portable crusher designer should be aware of the favorable features exhibited by this important member of the primary field:
Single and double toggle jaw crushers differ in the motion characteristics of the moving jaw, which results in somewhat different operating characteristics. Jaw action in the Blake (double toggle) type is a simple pivoting motion about a stationary bearing near the receiving opening. Displacement is thus a maximum at the discharge, tapering to zero at the pivot.
Because of its simplicity, the overhead eccentric (single toggle type) exhibits lighter weight, much lower cost, and a greater potential for portability, although it is not significantly shorter thanthe Blake (double toggle type). Due to the pronounced vertical components of motion from the overhead eccentric, it elliptical wiping motion provides good feeding action, and hence capacity. The price for this action is, of course, accelerated wear of the jaw plates in addition to increased shock loading on the eccentric and shaft bearings caused by the large jaw motion relative to Blake type machines at the receiving opening. Consequently, Blake types, with their low scrubbing motion and great leverage on larger feed, tend to be favoured for highly abrasive or very hard, tough rock.
The basic overhead eccentric jaw motion has been built in a vertical double-eccentric version (both jaws moving in unison), with the intention of providing more capacity for a given feed opening and longer jaw life due to reduced scrubbing provided by lower relative jaw velocity. The Eimco Division of Knvirotech, and the Westfalia Company of Germany, have tipped this arrangement on edge (eccentrics vertical), thereby changing the feed direction from vertical to horizontal and greatly reducing machine height.
Little is known about the German machines, as none are in use in North America and none are believed to be handling predominately hard rock. Eimco, on the other hand, has built two prototypes which have been tested in medium and hard rock in low headroom conditions. The Eimco crusher, shown in Figure 4, utilizes a feeder-breaker style chain flite conveyor which pulls material from the bottom of the surge pile and stuffs it into the jaw region. Discharge occurs immediately after the choke region of the jaws, onto a customer supplied conveying means. The chain conveyor obviously must pass beneath the active region between the jaws, severely diminishing or eliminating its feeding ability, particularly during the crushing stroke. To achieve better feeding in the crushing zone, Eimco has modified the common overhead eccentric toggle geometry so that both jaws close every where at the same time, with the crushing stroke strongly oriented in the feed direction. These measures enable a second generation machine to achieve throughputs approaching (perhaps 80%) the capacity of a vertical, single overhead eccentric crusher of comparable inlet dimensions. The Eimco inlet is approximately 40 x 40 inches.
Both prototypes were tested at White Pine Copper in White Pine, Michigan. Problems were encountered and changes were made, as with most prototypes, but large blocks of 20-28,000 psi sandstone were successfully handled on a regular basis. Since Dial time, mining
at White Pine has been concentrated in medium strength shale, where the horizontal jaw is not sufficiently perfected to be competitive with heavy duty feeder-breakers, about which more is presented in subsequent sections. Very strong ores have not been tried on a significant scale in the horizontal jaw.
Though low in profile, this crusher design utilizes a feed means that tends to orient slabby material horizontally, hence the wide, square jaw opening. Slabs that do get fed on edge can be passed untouched through the jaws, a common problem with vertically fed jaw crushers as well. Dimensionally, horizontal jaw crushers are quite acceptable, though they could use elevating discharge means to reduce site excavation requirements, and with more development in hard rock applications, this concept may become an economical alternative candidate for the subject application.
True impact crushers for primary crushing are limited to hammer types. They are included here only because there may be a specialized situation justifying their unique characteristics. Figure 5 shows a section of a typical hammermill; Figure 6 shows an Impactor.
Impact type crushers are high reduction machines (up to 40:1 vs. 8:1 for a jaw). In part because of this, they produce a considerably finer product than is necessary to achieve mechanized underground haulage. Very large feed, as is common with ROM material, is not easily handled by the hammer mill because of its impact principle of operation. Crushing is accomplished by the high velocity impact (5000 fpm) between the hammers (and liners) and individual pieces of rock in the feed, with the only means of support of rock fragments being the inertia of the rock itself. Under these conditions the rock fragments should not only be less massive than the hammer, but also quite friable. Abrasive feeds cannot be economically handled by hammermills or by impactors.
Impactors, as Figure 6 indicates, are better suited to large feeds than is the hammermill. This type uses fewer and stouter hammers, but, like the hammermill, relies on the inertia of the feed to hold the rock while it is chipped away. Primary crushing, even of non-abrasive and friable material, and particularly underground, is better handled by other machines unless very special conditions exist. An admittedly unlikely example of a situation in which an impact type crusher could be successfully employed as a portable underground primary crusher might be described by thefollowing conditions:
(a) abnormally small ROM material suitable for impactor feed but too big to be conveyed. (b) very friable, non-abrasive feed, material. (c) fine product allows less expensive form of mechanized haulage and eliminates the need for secondary crushing equipment.
Roll crushers is a term sometimes used to describe the combination (impact & pressure) class of crushers. Sledging roll crushers is a more suitable name, since it is distinguishing from the impact and pressure terminology and, in fact, the rotor in a roll crusher is frequently called a sledging roll. Sledging roll crushers are characterized by a medium velocity impact (500 fpm or less) between a rotor protrusion and the feed material while the feed is supported in the crusher, hence the term sledging.
The term roll is used in a wide variety of non-sledging equipment types and needs clarification here. Crushing rolls, two-roll feed-pinching machines, are really a high speed continuous pressure class of crusher used for secondary and tertiary crushing. Sometimes they are confusingly called two-roll crushers, or double roll crushers, or four-roll crushers. The roll surfaces are usually smooth or nearly so and impact or even sledging does not play a significant part in the comminution process. Roll crusher may also be used to describe a high speed machine in which the feed is neither supported by the crusher nor nipped by the roll protrusions. As described in the previous section, this is a high reduction pure impact class crusher sometimes used to avoid secondary crushing.
Sledging roll crushers may be of the single- or double-roll type, the latter being distinguishable from smooth pressure class crushing rolls by the characteristic protrusions (sledges) which work on the feed material. Double-roll sledging crushers usually employ more impact and less sledging by virtue of higher tip speeds, and are principally used for secondary crushing. Figure 7 shows a typical single-roll sledging crusher. There are several features of this type of crusher worthy of mention.
The feeder-breaker is an adaptation of the single roll-sledging crusher developed specifically for portability and use in low headroom coal mines. Since it has found successful use in a number of non-coal mines it is therefore worthy of mention. Figure 8 shows a typical feeder breaker.
To achieve low profile, this specialized machine passes material horizontally under the roll, or breaker shaft as it is usually called. The anvil (or bed in this configuration) is flat, and feed is accomplished by a chain-flite conveyor which pulls feed from under the pile of material in the attached surge hopper, and, after passing through the breaking zone, continues on to feed at a relatively controlled rate over the conveyor head pulley, hence the name feeder-breaker. Another characteristic of this single-roll sledging crusher is the shape of the breaker teeth, or picks, as they are generally called. They are relatively few in number (particularly for weak material), replaceable, and pointed, generally being carbide tipped.
Feeder breakers have greatly advanced the practice of conveyorized haulage in coal mines, and during recent years beefed-up versions, pioneered by the W. R. Stamler Corporation, have been successfully employed in a variety of non-coal mines. Among these are underground salt, potash, trona, iron, copper mines, and some open pit mines. These mines use a wide variety of primary short haulage means, but they all make use of low labor, high capacity conveyor systems made possible by the feeder-breaker.
When applied to stronger and/or more abrasive ores, feeder breaker crushing costs naturally escalate to levels well above those of conventional hard rock (i. e., jaw) crushers. In fact it appears that feeder-breakers are used, in some applications, solely because of their low headroom characteristics, and despite crushing costs from 3 to 5 times what could be expected of a jaw crusher in the same material. However, sufficient savings are achieved elsewhere in the haulage system, so that feeder-breakers are the economic choice in one copper mine where the ore is routinely between 12-20,000 psi compressive strength, and also abrasive. That mine also uses feeder-breakers in sandstone sections where ore strength runs to 28,000 psi. Maintenance and rebuild costs are higher in such areas, and this is considered by many to be about the hard rock limit of feeder breakers as a class of crusher.
A narrow version of the feeder-breaker has been developed by a German company for use on longwall systems. Various sledge configurations (not sharp picks) are used, and the unit is generally incorporated in a chain-flite bridge conveyor between the longwall system and a headgate conveyor. Two such units are in use on longwalls in U.S. trona mines (7000 psi max.), which accounts in part for their mention here. The concept (sizing of longwall discharge) is worth noting, in view of U.S. research efforts to apply new technology and longwall methods to hard rock mines.
There are many other comminution processes that one could bring to mind. Among these would be all the primary and secondary breakage methods, grinding and milling methods, thermomechanical, and even ballistic and nuclear concepts. These are not considered here because there are no presently available machines using these processes. Other comminution methods in general will be considered in the concepts section (Section 9) after the problem statement has been fully developed and conclusions drawn.
Having discussed the various classes and types of hard rock primary crushers, we can examine their potential for meeting the general requirements previewed in Section 2. Those requirements call for a crusher of low height, large feed opening, and modest throughput. Since multiple small crushers will be less efficient to operate and more costly to purchase than one central crusher, we must also consider cost as a factor in suitability.
The one mining parameter that is least controllable in a given mine and has the greatest influence on crusher selection is size of feed. Although drift dimensions obviously cannot be specified by the crusher designer, machine height, to some extent, is in his hands. Accordingly, machine height, throughput, and cost will be examined with respect to the common parameter, feed opening. Since feed opening implies a two dimensional passageway for material, the smaller or Critical Input Dimension (CID) will be used where appropriate. The implication is that most any crusher can (and should) be fed so as to avoid direct attack of the largest dimension of the feed material. Also implied, but perhaps less obvious, is the desire and intention to feed material so as to attack the smallest dimension of the feed, not the middle dimension.
Figure 9 presents representative manufacturers throughput data as a function of CID for 3 classes of crushers totalling six different types. Capacities have been normalized on medium limestone and minus 6 inch product in most cases. Gyratories are clearly high capacity machines at any feed size, and they tend to he applied to very large material. The Blake type jaw crushers are considerably lower in capacity, reflecting to some extent their application to very hard and abrasive feeds. Also noticeable is the range of capacities available for a given CID, a favorable feature afforded by variable jaw or rotor width. The tremendous forces encountered in crushing very large feed tend to leave the stronger Blake as the only jaw type in this region.
Getting down into the throughputs of most concern (400 tph and less), both Blake and overhead eccentric types appear, with the edge in capacity going to the overhead eccentrics. Also appearing are the horizontal jaw crushers and the sledging class, both single roll and feeder-breaker types. Maximum feed size for a given CID will be somewhat less in the case of horizontal jaws because the feed mechanism for this type tends to cause attack of the middle, rather than the smallest dimension of the feed material.
Figure 10 is a plot of bare machine height as a function of CIB for the same six types of crushers. Keeping in mind that bare height is exclusive of any foundations if required) or feeding and discharge means, all conventional gyratory and vertical jaw types are clearly beyond our need for 7-9 foot installed height at 30-36 inch CID. Nor can these standard machines be significantly shortened, as an examination of earlier figures will reveal.
We are left, at present, with horizontal jaws and the sledging class of crusher. But sledging roll crushers and to a lesser extent, feeder breakers, reach their economic limit at medium strength ore, characterized by (among other things) compressive strengths
in the 12-20,000 psi range and, even then, only under specialized conditions. The horizontal jaw crusher would appear to be the lone contestant, but it is relatively new and little can be learned about its economic performance at this time. Westfalia, a German manufacturer of longwall and other mining equipment, developed the concept, and, although machines are in use in Europe, no information is available regarding hard or very strong ore applications, and none are in service in North America. Eimco Division of Envirotech is the U.S. pioneer of horizontal jaw crushers, having built two generations of machines. These machines were technically successful in crushing a regular diet of stronger ore (20-28,000 psi) but could not compete economically in the medium strength range against the then highly developed heavy duty feeder-breakers, a statement which most certainly would apply to weaker ores as well. Dimensionally, the horizontal jaw is virtually identical to the successful feeder-breaker (Eimco data is plotted) and with further experience this basic concept may prove to he one answer to low profile hard-rock crushing.
Figure 11 shows the bare cost (no drives, hoppers, feeders, etc. ) of the various crushers under discussion. Some of the data are approximations, but the plot is useful in several respects. It shows, for instance, that something must be sacrificed to get low profile. In the case of horizontal jaws, increased initial cost is the penalty. Feeder-breakers, the low profile member of the sledging class, cannot economically handle the stronger ores. To work on the very hard or abrasive ores, machine height aside, requires that one choose the more expensive Blake type vertical jaw instead of the lighter overhead eccentric. Gyratories having the required CID again are inherently much too much machine for this application.
Using the larger Blake type or gyratories as an example (they dominate as centralized crushers in hard-rock mines) we can get an idea of the capital investment against which a multiplicity of portable crushers must inevitably be judged. Suppose a 7000 tpd mine would need a 4860 Blake type jaw crushing 500 tph of minus 6 inch product. Such a crusher would cost perhaps $350,000 including significant installation costs. An equivalent portable crusher system might involve five machines, four of which would be in service, with each capable of 250 tph. The greater total crushing capacity of the portable system is necessitated by its need to keep moving up, and by its vulnerability to downstream haulage interruptions. If these five portables cost in the vicinity of $200,000
each (a reasonable assumption for hard rock), the capital investment for portables becomes one million dollars versus $350,000 for a fixed installation. In addition, since the operating and maintenance costs of the two crusher systems are likely to be in about the same ratio, it is clear that the portable system must achieve great savings in other categories. These would likely include primary and secondary haulage costs (capital and labor) find productivity.
The primary use of a portable crusher, i.e., a crusher mounted on crawlers or tires, in the rock and mining industries is to reduce costs by permitting the substitution of conveyor belt haulage for truck or track haulage. The usual sequence of operations in surface mining is drilling, blasting, loading, haulage, and crushing. Haulage is normally accomplished by truck or track-mounted cars, the latter method being used for the longer distances.
In addition to potential cost savings in haulage procedures, a portable crusher would allow better utilization and performance of shovels. Loading operations would not be interrupted as often by the necessity of waiting for cars or trucks. Unfortunately, the application of belts in open pits for haulage from bench sites is generally not practical under existing conditions because a belt fed directly by a mechanical shovel can be torn, damaged, or worn out quickly by the large rock fragments falling on it during loading.
As previously noted, the use of a portable crusher would increase the performance of a loading shovel and thereby decrease the number of shovels required to maintain the same rate of production. However, there are quarries where rock must be taken from different parts of the pit and mixed together in order to get a desirable composition. This is usually done in cement quarries. For such cases, storage of material at the end of the stationary conveyor or along its route is suggested, where the desirable mixture of product could be achieved.
Quarries or open pits using track haulage often require a large number of workers to move the track after blasting as well as to operate the railroad switches. The use of a long-boom shovel would make it possible to increase the distance between the bench face and the track. It would also aid in reducing the amount of time now consumed in moving the track and the number of workers to do the job, but such a shovel is more expensive and slower.
Application of the portable crusher might encourage the use of higher benches with the commensurate less blasting that would be required. Domestic practice, however, does not favor the use of high bench faces, partly for safety reasons during loading and partly because higher benches usually require a large borehole diam, larger drill, etc. Inclined drilling might solve such blasting problems because it reduces the resistance of the rock to blasting at the toe of the bench.
in-pit crushing and conveying solutions
In-pit crushing and conveying solutions can cut truck fleets and reduce operational costs for green- and brownfield operations. Following recent acquisitions in this area, we can deliver credible and integrated solutions from primary crushing to tailings handling.
The deepest range of In-Pit Crushing and Conveying (IPCC) options in the mining industry are now available to you through one provider. The assortment of market-leading excavators and IPCC solutions provide uniquely compact, flexible, and fully mobile/relocatable options, allowing you to improve throughput and productivity and lower CAPEX, OPEX and other operating costs.
For instance, cutting truck fleets is one of the main reasons for looking at IPCC solutions, and operators are increasingly discovering how conveyors can be the most economical approach when transporting material from A to B.
Previously operators looked at shovel-to-truck. Now practically every greenfield project, every expansion project and even brownfield operations are investigating alternatives to shovel and truck. There is also growing interest from greenfield operators, even those who have not previously introduced any conveyors. We are working with them to show the potential cost-benefit and productivity gains that a conveyor system can deliver in terms of lower OPEX, more robust operations and less downtime.
In 2018 we completed the acquisition of Sandvik Mining Systems. The acquisition made us a provider of full flow sheet technology to the mining industry. Everything from primary crushing to tailings handling is covered and this combined product portfolio will benefit you wherever your location.
Together we can look at how well one piece of equipment is performing and how its performance is affecting other parts of the flowsheet downstream. For example, crusher selection is a key discipline in introducing IPCC, but we also know that crusher selection is not the end of the story. Since we also deliver downstream solutions, we are familiar with the whole process and can deliver credible and integrated solutions looking at the whole mining value chain from pit to plant.
We can now digitalize your entire supply chain to provide pro-active condition monitoring and data collection, identifying damage or wear ahead of any failure, even on mobile IPCC and stacking equipment. The data can be benchmarked with best practise and used to optimise the production. We keep investing in being on the forefront of IPCC systems and Dry Tailing Stacking technologies going forward. This will allow customers to reduce total cost of ownership and increase throughput in order to increase their productivity.
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in pit crushing and conveying systems
Belt conveyor systems, long the standard transportation technique in soft-rock open-pit applications, are encountering growing interest in the hard-rock open-pit sector as economic factors force companies to seek an alternative to costly truck haulage. A general review of mine conveyor systems is followed by detailed analysis of the mobile and semi-mobile in-pit crushing plant essential to successful use of mine conveyors.
In the soft-rock sector, positive experience with belt conveyors was gained in lignite mine-fields in the nineteen-fifties. In Germany, for example, 103.5 km of belt conveyor line were in use by 1962, 53.3 km of which were engaged in overburden handling; roughly 50% of these belt conveyor systems had belt widths of 1200 or 2000 ram. Since the nineteen-sixties, belt conveying has continued to make great strides in soft-rock open-pit mining, becoming the most important means of transport in this sector; belt conveyor systems in current use with bucket wheel excavators achieve performances per day of up to 240000 m bank.
If the situation in hard-rock open-pit mining is compared with that outlined above, it is apparent that the belt conveyor, despite its recognized advantages as a bulk transporter, has by no means achieved the same degree of acceptance as in the soft-rock sector. However, recent cost trends call urgently for fresh consideration of all possible forms of mine transportation, including belt conveyor systems.
Many of the general features indicated above are typical of large open-pit mining operations in North America. Mines commonly handle over 100000 t of ore and waste per day, moving the material through great horizontal and vertical distances. Transportation costs constitute a very high percentage of total mining costs. According to a recent estimate, operating costs for a 108-t haul truck may represent up to 40% of the current selling price of, for example, copper. Transportation costs of this magnitude offer an obvious starting-point for cost reduction programmes.
Although truck haulage remains the most widespread method of material transportation in open-pit mining, recent advances in truck technology (e.g. larger payload capacity, electric wheels and longer drive trains) have so far failed to offset the growing economic drawbacks outlined above. Moreover, the trend towards longer hauls and greater mining depths tends to expose inherent weaknesses of the shovel/truck concept. Increased haulage distances not only result in expansion of the truck fleet to maintain previous production levels, but impose increased manpower and support equipment requirements.
There are nonetheless a number of limitations on the use of conveyor systems in the hard-rock sector, which partly explain their relatively slow acceptance in this field. Flexibility is the argument most often cited in favour of truck-based systems. Truck transport can easily be adapted to constantly changing mining faces, with less exacting demands on long-term mine-planning strategy and sore scope for tactical improvisation.
The essential task of the in-pit crusher in a belt conveyor transport system is to reduce blasted material to a conveyable size. Crushers for this purpose are almost exclusively of the low crushing ratio type (up to 1 : 10), i.e. so- called primary or pre-crushers, designed as mobile or semi-mobile units.
Further processing to end-product quality takes place centrally outside the pit. For certain applications, reduction to millable quality (crushing ratio in the range from 1 : 10 to 1 : 80) may also be carried out in-pit, dispensing with the need for further crushing.
Developments in the use of movable crushers have typically been divided into three phases: prototype operation over a number of years, followed by gradual introduction once the system philosophy has been proven, and a subsequent rapid spread to other mines.
Recent increased use of movable crushers in hard and abrasive rock applications has led to growing popularity of gyratory crushers. Roll crushers are generally used for high-throughput overburden crushing.
In 1982/83 EGAT (Electricity Generating Authority of Thailand) invited tenders for a sub-contract to remove 15 million m of overburden annually over a six-year period at its Mae Moh open-pit mine. The successful bidder was a consortium formed by Bangkok Motors and Sahakol Engineering.
Overburden is loaded on to trucks at the face and dumped into the feed bin. An apron feeder under the bin transfers the material via the feed box to the double-roll crusher. Any material passing through the apron feeder plates is caught by the spillage conveyor under the feeder and likewise led to the crusher.
In early 1983, Utah Mines Ltd. decided to modernize its copper ore mine on Vancouver Island. The costly truck fleet used for ore transport was to be replaced by a belt conveyor system combined with semi-mobile crushing plant. Cost savings in the order of 30% were anticipated for a system comprising in-pit truck haulage (truck capacity 154 t), and an in-pit semi-mobile crusher integrated with belt conveyor transport from the mine to the processing plant.