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european middle sized rock crushers

portable rock crushers

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.

rock crushing

rock crushing

An objective of the present contract is to provide a concept for the design of a portable underground hard rock crusher in order to insure that future development will lead to maximum utilization by industry. The preceding section has concluded that the industry can indeed use such a machine and that, within desired performance and dimensional parameters defined by this study, no standard crushers are suitable for handling hard rock.

As indicated in Section 3, and stated in standard references such as (5),and (6), hard rock of large feed dimensions is best handled by jaw and gyratory crushers. This conclusion is of little value for present purposes unless we can determine fundamentally why these machines, and only these machines, are satisfactory. Using this knowledge, then, we stand a much better chance of devising satisfactory new concepts.

The following section describes three new crusher concepts, one of which, though earlier thought to be an attractive new concept, can be discarded (for hard rock) because it clearly does not have the third fundamental characteristic mentioned above.

In view of the strong, and perhaps obvious, conclusion that portable crushers will accentuate the need for breaking occasional oversize feed fragments, some thoughts on handling this problem are also presented.

Each of the following subsections presents a new crusher concept for hard-rock, portable, underground applications. The first, which will be rejected, is discussed in part to illustrate the importance of the previously noted fundamental characteristics of successful hard rock crusher concepts. The third, on the other hand, indicates that, while valid for reasonably conventional concepts, it would be inappropriate and restrictive to apply such conventional design criteria to unconventional concepts.

Based on the successful development of the RAPIDEX conical reamer, a skewed rolling element crusher was conceived using the same principles. The conical reamer is a roller cutter device which s self-advancing by virtue of its wedge-like shape and skewed rollers. A crusher using the principles would be essentially inside out, and it would self-feed rock fragments between the rollers.

Figure 13 is a sketch of basic concept, which consists of opposed rollers arranged in a row of V shaped pairs. The rollers are powered (i.e., rotated) and skewed (tilted forward) such that a rock fragment placed within the V will be simultaneously propelled forward and drawn downward until it is crushed. Product size is determined by the (adjustable) axial space between rollers. Downward and outward flow of product would provide quick clearing of smaller material, thus allowing effective crushing of larger material carried forward between the rollers.

While all of these features would be desirable, it was noted that a large fragment could simply fall downward between two V sections rather than feed downward gradually as intended. From this position a fragment would then be driven forward and crushed substantially in a single, large compaction, in violation of the third listed desirable characteristic of a hard rock crusher. Large downward motion between rollers could be avoided, or at least reduced, by placing baffles between rollers, but this would also stop the free discharge of undersize materialone of the major claimed virtues of the concept.

In conclusion, the V roller crusher is judged to be unsuitable for hard rock crushing. It would be suitable, and would provide a good, free flowing design, for coarse crushing of softer of friable materials that can now be handled by conventional roll crushers.

The jaw crusher, either Blake or overhead eccentric as appropriate. is the conventional machine most nearly satisfactory for the subject hard rock portable application. It is entirely satisfactory in terms of crushing performance feed size, hard rock capability, reduction ratio, product characteristics, throughput, and economy. However, it cannot meet the necessary installed dimension requirements, particularly with regard to headroom. Although basic crusher dimensions (i.e., the jaws themselves) are not too bad, the conventional top feed arrangement requires much too much headroom, particular if slabby material (which would have to be vertically oriented) is to be handled.

It is appropriate, then, to search for a horizontal feed jaw-crusher concept. One obvious approach, tipping a basically conventional jaw crusher on its edge, (i.e. with the eccentric shaft vertical has been attempted in this country, and several such units are said to be in use in an iron mine hematite) in Europe. All use a horizontal chain conveyor travelling just beneath the lower edge of the jaws to move material through the machine. Although this configuration obviously does work, it must do so at some sacrifice in performance. It seems clear that a feed mechanism working only at one edge of the jaws must be at a disadvantage relative to the uniform (gravity) feed of the standard upright configuration. In fact, gravity acting transverse to the horizontal throughflow causes a downward migration of finer material, thus encouraging early choking in the vicinity of the chain conveyor.

The rotary jaw crusher, to be described, employe a curved flow path in an attempt to both decrease the vertical dimension of the jaws themselves and provide for horizontal feed without the above problems, it achieves uniform feed distribution across the jaws, with at least a portion of this being gravitational, while avoiding transverse migration of material within the jaws. It uses no conveyor within the crushing zone (although for low headroom applications a conveyor may be used to feed the crusher.)

Figure 14a illustrates a typical jaw crusher profile in simplest schematic form neglecting curved non-choking jaw features, all of which can be provided later as necessary. After Me Grew let us assume that the included angle between jaw faces is 200, that is. a small value for hard rock. Then, for vertical jaws having a 30 inch inlet and a 6 discharge, the bare jaw height must be 69 inches. (Recall the striking uniformity of conventional machine heights noted in Section 3.)

Figure 14b illustrates a schematic of an equivalent jaw crusher in which inlet and discharge dimensions and mean path length (hence convergence angle) are preserved while wrapping the mean path around a 180 curve. For these dimensions, the curved path results in a decrease of 7 inches in height (assuming for the moment a circular mean path). While this is not an enormous saving in itself, the configuration does provide horizontal feed, and this is a substantial improvement. Other advantages will become evident as the concept is further described.

Crushing motion of the curved jaw machine may be provided by several means, the most obvious of which would be oscillation of the external jaw (the right-hand element in Figure 14b) against a stationary internal member. Jaw motion may be maximum at the discharge, in a Blake-type action, or near the inlet, in an overhead eccentric type action, depending upon the choice of the designer. However, it is believed that neither of these will provide the best design.

Figure 15 illustrates what we shall call a rotary jaw crusher having the preferred inner element crushing motion. A cylindrical inner element is driven in an orbiting motion by a central eccentric shaft, essentially identical to that of an overhead eccentric crusher. It is expected that this orbiting motion will require less force than would oscillation of the outer elements, and less force than is required by conventional jaw designs. The latter must subject their entire rock charge to crushing forces simultaneously as the jaws converge everywhere at the same time. Furthermore, with conventional gravity feed of reasonably graded material, it is virtually certain that rock fragments will in fact be tightly lodged throughout the converging crushing zone as the crushing stroke commences. In contrast, the orbiting cylinder of the rotary jaw crusher produces only a local zone of maximum convergence which travels through the rock charge. Hence, although crushing the enclosed rock charge in approximately 180 of eccentric motion (like conventional designs), it does not crush the entire charge simultaneously. The rotary jaw eccentric bearing should thus see a force that is reasonably uniformly spread through 180, rather than the conventional force which rises to a peak at the end of 180.

Orbiting motion of the inner element provides one more major advantage if the motion is in the forward direction illustrated in Figure 15. In this case, the crushing action moves through the rock charge in the flow direction providing a peristaltic pumping action to assist throughput.

With regard to throughput, disruption of the simple straight through gravity flow of conventional designs is clearly the major drawback of the rotary design. Refering to the limiting 180 design of Figure 15, gravity feed will be effective only in the middle half of the passage. Feed can no doubt be enhanced in the inlet quarter of the passage by stuffing this region with a forcing conveyor feed, but no such assistance is available in the discharge region.

With the peristaltic action described above, it is quite possible that no throughput problems will be encountered particularly if the discharge region is cut back as discussed below. However, if difficulties are encountered, it is expected that rotation of the cylindrical inner element about its own axis will be very effective in urging material through the crusher. If simple feed enhancement

is all that is desired, rotary drive via a torque source that acts when large crushing forces are absent would suffice. On the other hand, perhaps considerably more rotary torque would benefit crushing action as well, via shearing forces on the rock (like those of an overhead eccentric design). In fact, one might consider a family of designs which distribute orbiting and rotating power differently for different rocks: ranging from pure orbiting on one extreme to pure rotary (i.e., a single sledging roll crusher) on the other.

Rotation of the inner element (either freely or driven) also provides for balanced wear between the two jaw surfaces, since the full circumference of the inner element is about equal to the total length of the outer jaw. Obviously, both jaws would be provided with replaceable wear surfaces. It may also be beneficial to use different surfaces (for example ribbed or smooth), depending on the proportions of crushing and shearing desired.

Although complete rotary jaw crusher design is beyond the scope of this study. Figure 16 illustrates schematically a more complete concept. Refering back to Figure 15, clearly the greatest throughput problems will occur near the discharge, where neither gravity nor force feed are effective, and where choking would be most likely to occur in a straight (i.e., continuously converging) design in any case. Proven methods, described by McGrew, can be used to design non-choking discharge regions to ease this problem, but it may also be necessary to simply move the crusher discharge point up as shown in Figure 16 to completely eliminate the problem. Furthermore, since the complete crusher must incorporate a discharge conveyor, the higher discharge point (and correspondingly higher inlet) may not result in an overall taller machine if it allows the elevated conveyor placement illustrated in Figure 16.

The rotary jaw crusher concept has been described in schematic form and certain of its important advantages have been cited. Other advantages are also derived from the curved mean path geometry. In summary, the following features are expected to be of special advantage in portable, low head room, hard rock crushing applications:

Section 9.2 discusses the use of impact hammers, probably hydraulically actuated, to break occasional abnormally large material feeding the portable crusher. If suitable means are developed for impact breaking occasional large pieces, then it would be a logical extension of that development to attempt automated breakage of all unbeltable material particularly when the latter constitutes a reasonably small fraction of total production. Such development should follow that of the occasional oversize breaking system (particularly its automated actuation) and, although no overall concept is presented here, the idea is suggested as a goal of impact breakage systems. It would seem to promise extreme portability together with the ability to handle widely varying feed dimensions.

Obviously, an impact breaker has to be strong, but meaningful strength parameters for an impacting machine are quite different from those of a conventional machine which uses essentially static forces and brute strength. For example, an impact bit cannot be blunt, at least in the same sense as a crusher jaw, but other design features, like assuring proper orientation, can compensate for this.

In contrast to conventional machines, an impact breaker definitely should not have a limited motion, since the rock to be broken cannot be well restrained at the time of impact. Thus, the second conventional characteristic actually is not correct for this particular unconventional approach. Finally, since an impact breaker would be intended to produce major fracture in a single blow, the third conventional characteristic is also simply not appropriate in this case.

In summary, fundamental characteristics of successful conventional hard rock crushers have been noted. It is believed that these are very useful in judging the suitability of new concepts utilizing the same basic crushing means, but they are not appropriate, and should not be restrictively used, in judging concepts utilizing different crushing or breaking principles.

As concluded in Section 8, breaking of oversize feed material will be increasingly important as crusher dimensions are reduced to enhance portability. Indeed, the importance of feed size in crusher design suggests that the handling of oversize should be considered an integral part of the hard rock portable crusher development program. Hence, although impact breaker design and application in general are beyond the scope of this study, it is appropriate to discuss breaker problems and features insofar as they relate to portable crusher development. Although oversize feed may be handled at a variety of locations, that most directly related to crusher development would be immediately upstream of the crusher, and it is primarily this location that will be considered.

Ideally, the device should run without an operator, breaking all oversize material without interrupting throughput. The following are, very briefly, the major problems that can be expected in the development of such a system.

The first problem will be to identify those fragments which are oversize. Once located, each oversize fragment must be properly positioned relative to the hammer, by moving either the rock, or the hammer, or perhaps both. Preferably, if slabby material is being handled, proper positioning will also include advantageous orientation of the rock. When properly positioned, the hammer should strike the rock with enough energy to fracture the piece in a single blow. If the rock does not fracture, or if fragments are still oversize, this must be quickly determined and another blow struck. Proper support of the oversize rock at impact is important, both to promote effective energy transfer from the impacting device, and to insure that impact does not damage the supporting machinery. In view of the variability of rock size and shape, and the possibility of its motion upon impact, the impacting memeber must be capable of sustaining glancing, or even entirely missed, blows without damage.

Many of these problems are already handled to some degree by present feeder units. For example, the typical feeder that utilizes a chain flite conveyor to pull material from the bottom of a surge bin generally extracts small material first. In slabby material the larger fragments are usually well oriented, with the maximum dimension parallel to the conveyor motion, and the minimum dimension normal to the conveyor surface. Combined with suitable gates, sensing devices, and hammers, it is not unreasonable to expect that such a feeder can be equipped to automatically reduce all feed material to a size which can be handled by a portable crusher. It can also be expected that considerable development effort and operating experience will be required before untended operation of such a system becomes routine.

Handling oversize material is a very important mine problem in general, and worthy of considerable attention. The preceding example, though selected because it relates directly to portable crusher design, illustrates many of the problems that might be expected in the development of any automated impact type breaker system, whether it be applied at a draw point, over a grizzly or on a feeder conveyor, and many of the comments in the following subsection are thus of general interest.

In a complete study of handling oversize material it would not be appropriate to assume that hydraulically actuated impact devices represent the best or only breaking means. For the purpose of this crusher study, we shall limit this discussion to such devices simply because they are the most nearly suitable of todays readily available means. That is not to say, however, that a typical off the shelf hydraulic demolition tool is ideally suited to this task.

For the hard rock, portable crushers contemplated in this study, fragments having minimum dimensions of the order of 30 inches would be considered oversize. It is desireable to break such a fragment in a single blow if possible, both to minimize positioning and holding problems and to avoid throughput interruptions, and because it is more efficient. One manufacturer suggests that this requires 1000 to 3000 foot pounds per blow, obviously depending on rock properties. This same manufacturer has found that repeated blows of too little energy tend to drill holes in large fragments without causing fracture.

In view of the generally poor confinement of target fragments and likely positioning errors at the time of impact, an efficient impactor should be capable of delivering an effective blow throughout a rather long stroke perhaps as long as 12 inches. In this sense, the typical demolition hammer, although certainly the most suitable off the shelf item, is not ideal.

Depending upon overall system design, rapid automatic blow capability may not be required. Thus the rapid cyclic action of a conventional hammer may be economically omitted in favor of a simpler design that triggers discrete blows after proper hammer position is established.

These two features, very long stroke and discrete blows, suggest that it may be appropriate to reexamine the hurled bit or projectile bit (after reference 8) concept. As the name indicates, this device uses a one-piece bit-piston which is (hydraulically) hurled directly against the rock without the internal metal-to-metal impact of conventional struck bit designs. The major virtue of the hurled bit concept is the substantial reduction of peak stress within the steel for a given rock stress),which in turn, for a given blow energy, permits the use of a lighter machine at higher impact velocities. Many of the admitted design difficulties of the concept have to do with rapid sequencing, a feature that may not be required in this application. Furthermore, with proper actuator design, the hurled bit breaker is compatible with very long effective strokes.

Single blow breaking, although fast and efficient, does have one obvious drawback: the required high blow energy may cause damage to the supporting structure. Figure 17 illustrates a novel concept in which the oversize fragment is struck from below, with reaction coming solely from the inertia of the fragment itself, rather than the surrounding machinery. This figure also illustrates a simple gating arrangement which might be used to trigger the impact. Such a design might well use multiple fixed impactors triggered by multiple gates (for example, spread across the width of the feed conveyor) to avoid the complexities of moveable components. The assembly would also require means to contain fragments.

There is a need, often cited by others, for a better method of controlling oversize, independent of the existance or use of portable crushers. One grizzly-drift block cave mine is experimenting with a low profile crawler mounted impactor, capable of servicing several drifts and many drawpoints, and results to date are promising. The Maysville Operation at Dravo Lime is also using an impactor, mounted on a tractor, to service their portable jaw crushers and all the working faces.

Non room and pillar mines using mechanized (non-slusher) face haulage have a common characteristic; namely, the ability to load quite large muck and haul it to a few (relative to production sites) dump points. Grizzlies at the dump pocket represent one method of filtering out problem-causing muck, but the oversize remains, to be handled by costly secondary means. These mines may not be able to convert existing rail systems to belts and (if they existed) crusher, but they can consider automatic, untended devices at the pockets to break oversize.

A successful pocket breaker must be funded (i.e., justified) by savings derived from increased productivity (fewer disruptions), reduced secondary breakage costs, reduced ore pass and chute maintenance, reduced spillage and wear in main haulage, and, perhaps, reduced ore pass costs (size). While these effects are far

reaching, no single item predominates, none are easily estimated, and it is clear that the pocket breaker must be very simple and inexpensive. Impact breakers represent only one potential solution, and since they may not be the most satisfactory or economical, we should consider other means.

Muck at the pocket may have major dimensions exceeding six feet and minor dimensions approaching three feet. Discharge from the pocket breaker should be in the minus 20 to minus 26 inch range in order to eliminate downstream problems (and to enhance eventual conversion to low profile crushers). The tonnage requiring breakage, and the reduction ratio, are therefore quite small, indicating that the pocket breaker need not run all the time. A simple jaw, or a vise, perhaps actuated by cylinders, driven by a source of high peak (but low average! power, might be sufficiently simple. Shafts and bearings could be eliminated in favor of less expensive pivots. Servicing should be simple, and the pocket should be useable even if the breaker is not functioning, perhaps by automatically (passively) shunting aside the very large oversize.

Obviously the portable crusher must include some sort of hopper or surge bin to accommodate this highly unsteady delivery, and the hopper design must be compatible with the low head room restrictions and the dumping geometry of the load-haul-dump (or other) haul equipment within those restrictions. Present machines, both the coal feeder-breaker type in use and the horizontal jaw crushers that have been tested, are one-piece machines that feed from the hopper via a chain type conveyor. The feed conveyor also travels through, and is an integral part of, the crushing mechanism.

In soft materials like coal, potash, and trona, feeder-breakers are often self-propelled, offering the ultimate in portability. Applications in harder materials have not enjoyed this degree of portability, although size alone has not been the major problem. Rather, portability has been substantially restricted because of costly and time consuming site preparations deemed necessary in the heavy duty applications. For example, rather extensive foundation structures, requiring subgrade excavation, have been used to avoid damage caused by impact from discharging haul vehicles, and to accomodate the discharge belt. Furthermore, in a wet application any sub-grade excavation must allow additional room to accomodate drainage and clean out functions. Complications such as these make it abundantly clear that the desired hard rock portable crusher should require essentially no site preparation, or at least no site excavation.

After some thought it becomes clear from the foregoing that the desired portable crusher might better consist of a least two independent pieces: a hopper-feeder unit, and a crusher-discharge unit. The former can be virtually identical to the simple, proven hopper end of present machines. The latter, being independent of the present integral feed conveyor, cannot be identical to the present machines. Several significant advantages may be derived from this multiple piece approach:

The hopper envisioned in this discussion is a very simple device, similar to the present crushing equipment except that the feed conveyor would be inclined to accept input at the necessary low level while discharging into the top of the crusher. With gravity feed into the crusher, and either a large inlet for the latter or a simple chute arrangement between the two, the hopper feeder need not be fastened to, or even precisely located, relative to the crusher. This would permit easy set-up and it may provide for much simpler protection against impacts from haul vehicles. For example. Figure 18 illustrates schematically a set-up having the following features:

Actual layout of the equipment is, of course, dependent upon a variety of mining conditions. The sketch is intended to suggest one possiblity, and to illustrate the flexibility inherent in a two-piece design.

Modular assemblies, which offer interesting advantages in this simple two-piece concept, are virtually a necessity if additional crusher features are to be provided. For example, if oversize feed is to be broken on the feed conveyor, as discussed in

a preceding section, it is unlikely that a one piece hopper-feeder-breaker-crusher design will be either portable or maintainable. Furthermore, it has been suggested that feed scalping be employed to avoid additional crushing of already beltable material. Suitable equipment for this feature is well within the present state of the art, and development of a one-piece integrated unit is not only not necessary: it may well be undesirable.

In view of the conclusions reached in this Applications Study, presented in Section 8, and reviews of present equipment together with new concepts presented in Section 9, three recommendations are made for further design, development, and testing of a portable hard rock crusher.

It is recommended that a program be initiated to develop a hard rock, low head room, portable crusher of the rotary jaw crusher type. It is believed that this concept is the simplest available based on proven hard rock crushing principles, and therefore, it is the best concept for full development.

Although the machine should ultimately be designed within those parameters cited in Section 8, early experimental work can profitably be done on a smaller prototype of perhaps 20-inch critical inlet dimension. The purpose of this experimental phase of the development would be to establish (above ground) proper jaw shape, eccentric motion, and rotary motion to assure proper feed. Once this is assured, full scale underground prototype development could be undertaken with confidence.

It has been concluded that feed scalping to avoid unnecessary crushing of beltable material would enhance the performance and capacity of any portable crusher. It is not believed that provision of this feature will require an elaborate development program: therefore, initiation of such a program at this time is not recommended, However, when a full scale prototype crusher design is undertaken, it is recommended that feed requirements be defined in suitable terms to permit procurement of a suitable feed system for use in early field tests.

It is recommended that a program be undertaken, in parallel with crusher development, for the development of suitable means for breaking oversize feed material. This program can be divided into three major subprograms and, in view of the widespread occurance of the problem (it has been cited by others), and the variety of possible applications, it is recommended that all three sub-programs be undertaken simultaneously. They are:

diamond exploitation and diamond mine crushing equipment in russia

diamond exploitation and diamond mine crushing equipment in russia

Diamond, also means mineralogy diamond,it is formed by geological processes.The primary ore mainly are kimberlite and lamproite. Modern science and technology provide new ideas and methodsfor diamond exploitation and diamond formation. As we all know, diamond is the hardest gem in the world, it has thesimplest ingredients, which is composed of carbon, and a natural cubic crystal structure. Its composition is same ascoal, pencil and sugars that are closely related to us. Under the pressure (high temperatures), carbon will crystallize to form graphite (black), while under high pressures and high temperature, carbon will crystallize to form precious diamonds (white). So diamonds are very precious, and so it has very high value, and lots of people want to own them in Russia, so diamond exploitation is very important for the investors who want to gain many profits from diamond industry.

Diamond is a natural mineral that is rough diamonds. It is understood that the diamond native deposits, mostly adopt the method of combination between the open-pit mining and underground mining. On the part of earths surface, directly along the rock excavate the pit barrel, and stepped down mining drill, each step will spiral downward which is easy for truck to transport the ore out. On the other hand, when deep underground (300 meters), the first thing is to dig a well next the mineral deposit, then dig a lateral tunnel leading to the deposit, then through technical means to make internal ore be crushed, and then through a series of horizontal and vertical roadway to transport the ore out.

As for the diamond sand deposits, which can be divided into two categories: one is the ancient beach, the ancient river diamond deposits exposed above the water, it can removethe overlying sediment, then using the method of open pit mining, then sent the gravel to the concentrator, while the other deposit is located at the bottom of the modern river, known as the "wet deposit", you need to first drain the water or diverse the river, and then adopt the method of open-pit mining.

It is reported that the ore after mined first should use jaw crusher and cone crusher for crushing, sometimes also put the ore in open pit mine, and then natural weathering crushing. After the ore were crushed to 3 to 6cm,and then will remove the clay with roller washing machine.Then you can use the bouncing beneficiation method to separate coarse gravel after washing, as to the separated coarse gravel, you can have second crushing and panning separation. Or use gravity beneficiation methods, because diamond ore density is larger than other ores, so the ore contains diamonds will be discharged from the bottom of the funnel-shaped container.

After above these coarse dressing, if diamonds still cannot be completely separated, then should have further selection. In fact we can use the diamond lipophilic water-repellent properties, the ore which containing diamonds will be scattered evenly on the tapewith grease and kept turning, so make the surface of grease tostick the diamond.Then, the oil will be collected in a container which is made of fine metal sieve cloth, then put in the hot water pool, let the oil melting and then drift away. After roughing and fine selection, then manually recycle diamondby the professional technical personnel.

SBM is professional in producing crushing equipment, grinding equipment and beneficiation equipment, so we can provide you high efficiency and low cost Russia diamond crushing equipment. We believe that our machine will make a big difference in your diamond business.

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