jaw crusher working principle

jaw crusher working principle

A sectional view of the single-toggle type of jaw crusher is shown below.In one respect, the working principle and application of this machine are similar to all types of rock crushers, the movable jaw has its maximum movement at the top of the crushing chamber, and minimum movement at the discharge point. The motion is, however, a more complex one than the Dodge motion, being the resultant of the circular motion of the eccentric shaft at the top of the swing jaw. combined with the rocking action of the inclined toggle plate at the bottom of this jaw. The motion at the receiving opening is elliptical; at the discharge opening, it is a thin crescent, whose chord is inclined upwardly toward the stationary jaw. Thus, at all points in the crushing chamber, the motion has both, vertical and horizontal, components.

It will be noted that the motion is a rocking one. When the swing jaw is rising, it is opening, at the top, during the first half of the stroke, and closing during the second half, whereas the bottom of the jaw is closing during the entire up-stroke. A reversal of this motion occurs during the downstroke of the eccentric.

The horizontal component of motion (throw) at the discharge point of the single-toggle jaw crusher is greater than the throw of the Dodge crusher at that point; in fact, it is about three-fourths that of Blake machines of similar short-side receiving-opening dimensions. The combination of favorable crushing angle, and nonchoking jaw plates, used in this machine, promotes a much freer action through the choke zone than that in the Dodge crusher. Capacities compare very favorably with comparable sizes of the Blake machine with non-choking plates, and permissible discharge settings are finer. A table of ratings is given.

The single-toggle type jaw crusher has been developed extensively. Because of its simplicity, lightweight, moderate cost, and good capacity, it has found quite a wide field of application in portable crushing rigs. It also fits into the small, single-stage mining operation much better than the slower Dodge type. Some years since this type was developed with very wide openings for reduction crushing applications, but it was not able to seriously challenge the gyratory in this field, especially when the high-speed modern versions of the latter type were introduced.

Due to the pronounced vertical components of motion in the single-toggle machine, it is obvious that a wiping action takes place during the closing strokes; either, the swing jaw must slip on the material, or the material must slip along the stationary jaw. It is inevitable that such action should result in accelerated wear of the jaw plates; consequently, the single-toggle crusher is not an economical machine for reducing highly abrasive, or very hard, tough rock. Moreover, the large motion at the receiving opening greatly accentuates shocks incidental to handling the latter class of material, and the full impact of these shocks must be absorbed by the bearings in the top of the swing jaw.

The single-toggle machine, like the Dodge type, is capable of making a high ratio-of-reduction, a faculty which enables it to perform a single-stage reduction of hand-loaded, mine run ore to a suitable ball mill, or rod mill, feed.

Within the limits of its capacity, and size of receiving openings, it is admirably suited for such operations. Small gravel plant operations are also suited to this type of crusher, although it should not be used where the gravel deposit contains extremely hard boulders. The crusher is easy to adjust, and, in common with most machines of the jaw type, is a simple crusher to maintain.

As rock particles are compressed between the inclined faces of the mantle and concaves there is a tendency for them to slip upward. Slippage occurs in all crushers, even in ideal conditions. Only the particles weight and the friction between it and the crusher surfaces counteract this tendency. In particular, very hard rock tends to slip upward rather than break. Choke feeding this kind of material can overload the motor, leaving no option but to regulate the feed. Smaller particles, which weigh less, and harder particles, which are more resistant to breakage, will tend to slip more. Anything that reduces friction, such as spray water or feed moisture, will promote slippage.

Leading is a technique for measuring the gap between fixed and moveable jaws. The procedure is performed while the crusher is running empty. A lead plug is lowered on a lanyard to the choke point, then removed and measured to find out how much thickness remains after the crusher has compressed it. This measures the closed side setting. The open side setting is equal to this measurement plus the throw of the mantle. The minimum safe closed side setting depends on:

Blake (Double Toggle) Originally the standard jaw crusher used for primary and secondary crushing of hard, tough abrasive rocks. Also for sticky feeds. Relatively coarse slabby product, with minimum fines.

Overhead Pivot (Double Toggle) Similar applications to Blake. Overhead pivot; reduces rubbing on crusher faces, reduces choking, allows higher speeds and therefore higher capacities. Energy efficiency higher because jaw and charge not lifted during cycle.

Overhead Eccentric (Single Toggle) Originally restricted to sampler sizes by structural limitations. Now in the same size of Blake which it has tended to supersede, because overhead eccentric encourages feed and discharge, allowing higher speeds and capacity, but with higher wear and more attrition breakage and slightly lower energy efficiency. In addition as compared to an equivalent double toggle, they are cheaper and take up less floor space.

Since the jaw crusher was pioneered by Eli Whitney Blake in the 2nd quarter of the 1800s, many have twisted the Patent and come up with other types of jaw crushers in hopes of crushing rocks and stones more effectively. Those other types of jaw crusher inventors having given birth to 3 groups:

Heavy-duty crushing applications of hard-to-break, high Work Index rocks do prefer double-toggle jaw crushers as they are heavier in fabrication. A double-toggle jaw crusher outweighs the single-toggle by a factor of 2X and well as costs more in capital for the same duty. To perform its trade-off evaluation, the engineering and design firm will analyze technical factors such as:

1. Proper selection of the jaws. 2. Proper feed gradation. 3. Controlled feed rate. 4. Sufficient feeder capacity and width. 5. Adequate crusher discharge area. 6. Discharge conveyor sized to convey maximum crusher capacity.

Although the image below is of a single-toggle, it illustrates the shims used to make minor setting changes are made to the crusher by adding or removing them in the small space between the crushers mainframe and the rea toggle block.

The jaw crusher discharge opening is the distance from the valley between corrugations on one jaw to the top of the mating corrugation on the other jaw. The crusher discharge opening governs the size of finished material produced by the crusher.

Crusher must be adjusted when empty and stopped. Never close crusher discharge opening to less than minimum opening. Closing crusher opening to less than recommended will reduce the capacity of crusher and cause premature failure of shaft and bearing assembly.

To compensate for wear on toggle plate, toggle seat, pitman toggle seat, and jaws additional shims must be inserted to maintain the same crusher opening. The setting adjustment system is designed to compensate for jaw plate wear and to change the CSS (closed side setting) of the jaw crusher. The setting adjustment system is built into the back frame end.

Here also the toggle is kept in place by a compression spring. Large CSS adjustments are made to the jaw crusher by modifying the length of the toggle. Again, shims allow for minor gap adjustments as they are inserted between the mainframe and the toggle block.

is done considering the maximum rock-lump or large stone expected to be crushed and also includes the TPH tonnage rate needing to be crushed. In sizing, we not that jaw crushers will only have around 75% availability and extra sizing should permit this downtime.

As a rule, the maximum stone-lump dimension need not exceed 80% of the jaw crushers gape. For intense, a 59 x 79 machine should not see rocks larger than 80 x 59/100 = 47 or 1.2 meters across. Miners being miners, it is a certainty during day-to-day operation, the crusher will see oversized ore but is should be fine and pass-thru if no bridging takes place.

It will be seen that the pitman (226) is suspended from an eccentric on the flywheel shaft and consequently moves up and down as the latter revolves, forcing the toggle plates outwards at each revolution. The seating (234) of the rear toggle plate (239) is fixed to the crusher frame; the bottom of the swing jaw (214) is therefore pushed forward each time the pitman rises, a tension rod (245) fitted with a spring (247) being used to bring it back as the pitman falls. Thus at each revolution of the flywheel the movable jaw crushes any lump of ore once against the stationary jaw (212) allowing it to fall as it swings back on the return half-stroke until eventually the pieces have been broken small enough to drop out. It follows that the size to which the ore is crushed.

The jaw crusher is not so efficient a machine as the gyratory crusher described in the next paragraph, the chief reason for this being that its crushing action is confined to the forward stroke of the jaw only, whereas the gyratory crusher does useful work during the whole of its revolution. In addition, the jaw crusher cannot be choke-fed, as can the other machine, with the result that it is difficult to keep it working at its full capacity that is, at maximum efficiency.

Tables 5 and 6 give particulars of different sizes of jaw crushers. The capacity figures are based on ore weighing 100 lb. per cubic foot; for a heavier ore, the figures should be increased in direct proportion to its weight in pounds per cubic foot.

The JAW crusher and the GYRATORY crusher have similarities that put them into the same class of crusher. They both have the same crushing speed, 100 to 200 R.P.M. They both break the ore by compression force. And lastly, they both are able to crush the same size of ore.

In spite of their similarities, each crusher design has its own limitations and advantages that differ from the other one. A Gyratory crusher can be fed from two sides and is able to handle ore that tends to slab. Its design allows a higher-speed motor with a higher reduction ratio between the motor and the crushing surface. This means a dollar saving in energy costs.

A Jaw crusher on the other hand requires an Ely wheel to store energy. The box frame construction of this type of crusher also allows it to handle tougher ore. This design restricts the feeding of the crusher to one side only.

The ore enters from the top and the swing jaw squeezes it against the stationary jaw until it breaks. The broken ore then falls through the crusher to be taken away by a conveyor that is under the crusher.Although the jaws do the work, the real heart of this crusher is the TOGGLE PLATES, the PITMAN, and the PLY WHEEL.

These jaw crushers are ideal forsmall properties and they are of the high capacity forced feed design.On this first Forced Feed Jaw Crusher, the mainframe and bumper are cast of special alloy iron and the initial cost is low. The frame is ribbed both vertically and horizontally to give maximum strength with minimum weight. The bumper is ruggedly constructed to withstand tremendous shock loads. Steel bumper can be furnished if desired. The side bearings are bronze; the bumper bearings are of the antifriction type.

This bearing arrangement adds both strength and ease of movement. The jaw plates and cheek plates are reversible and are of the best-grade manganese steel. The jaw opening is controlled by the position of an adjustable wedge block. The crusher is usually driven by a V-to-V belt drive, but it can be arranged for either V-to-flat or fiat belt drive. The 8x10 size utilizes a split frame and maybe packed for muleback transportation. Cast steel frames can be furnished to obtain maximum durability.

This second type of forced feed rock crusher is similar in design to the Type H listed above except for having a frame and bumper made of cast steel. This steel construction makes the unit lighter per unit of size and adds considerable strength. The bearings are all of the special design; they are bronze and will stand continuous service without any danger of failure. The jaw and cheek plates are manganese steel; and are completely reversible, thus adding to their wearing life. The jaw opening is controlled by the position of an adjustable wedge block. The crushers are usually driven by V-to-V but can be arranged for V-to-flat and belt drive. The 5x6 size and the 8x10 size can be made with sectionalized frame for muleback transportation. This crusher is ideal for strenuous conditions. Consider a multi jaw crusher.

Some jaw crushers are on-floor, some aboveground, and others underground. This in many countries, and crushing many kinds of ore. The Traylor Bulldog Jaw crusher has enjoyed world wide esteem as a hard-working, profit-producing, full-proof, and trouble-free breaker since the day of its introduction, nearly twenty years ago. To be modern and get the most out of your crushing dollars, youll need the Building breaker. Wed value the privilege of telling you why by letter, through our bulletins, or in person. Write us now today -for a Blake crusher with curved jaw plates that crush finer and step up production.

When a machine has such a reputation for excellence that buyers have confidence in its ability to justify its purchase, IT MUST BE GOOD! Take the Type G Traylor Jaw Crusher, for instance. The engineers and operators of many great mining companies know from satisfying experience that this machine delivers a full measure of service and yields extra profits. So they specify it in full confidence and the purchase is made without the usual reluctance to lay out good money for a new machine.

The success of the Type G Traylor Jaw Crusheris due to several characteristics. It is (1) STRONG almost to superfluity, being built of steel throughout; it is (2) FOOL-PROOF, being provided with our patented Safety Device which prevents breakage due to tramp iron or other causes of jamming; it is (3) ECONOMICAL to operate and maintain, being fitted with our well-known patented Bulldog Pitman and Toggle System, which saves power and wear by minimizing frictionpower that is employed to deliver increased production; it is (4) CONVENIENT to transport and erect in crowded or not easily accessible locations because it is sectionalized to meet highly restrictive conditions.

Whenever mining men need a crusher that is thoroughly reliable and big producer (which is of all time) they almost invariably think first of a Traylor Type G Jaw Crusher. By experience, they know that this machine has built into it the four essentials to satisfaction and profit- strength, foolproofness, economy, and convenience.

Maximum STRENGTH lies in the liberal design and the steel of which crushers parts are made-cast steel frame, Swing Jaw, Pitman Cap and Toggles, steel Shafts and Pitman rods and manganese steel Jaw Plates and Cheek Plates. FOOLPROOFNESS is provided by our patented and time-tested safety Device which prevents breakage due to packing or tramp iron. ECONOMY is assured by our well-known Bulldog Pitman and Toggle System, which saves power and wear by minimizing friction, the power that is used to deliver greater productivity. CONVENIENCE in transportation and erection in crowded or not easily accessible locations is planned for in advance by sectionalisation to meet any restrictive conditions.

Many of the worlds greatest mining companies have standardized upon the Traylor Type G Jaw Crusher. Most of them have reordered, some of them several times. What this crusher is doing for them in the way of earning extra dollars through increased production and lowered costs, it will do for you! Investigate it closely. The more closely you do, the better youll like it.

rock crushers | aggregate processing equipment | lippman-milwaukee

rock crushers | aggregate processing equipment | lippman-milwaukee

Lippmann offers a full line of Crushing, Screening, Stacking, and Specialty equipment used for the aggregate, mining, and recycling industries. Discover your perfect stationary, portable, and track equipment for your specific processing application.

crushers for sale at grinder crushers screen

crushers for sale at grinder crushers screen

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jaw crushers | mclanahan

jaw crushers | mclanahan

Jaw Crushers are used to reduce the sizeof many different types of materials in many applications. The Jaw Crusher was first introduced by Eli Whitney Blake in 1858 as a double-toggle Jaw Crusher. Introduced in 1906, McLanahans Universal Jaw Crusher was one of the first modern era overhead eccentric Jaw Crushers. On the overhead eccentric style Jaw Crusher, the moving swing jaw is suspended on the eccentric shaft with heavy-duty double roll spherical roller bearings.

The swing jaw undergoes two types of motion: one is a swing motion toward the opposite chamber side (called a stationary jaw die due to theaction of a toggle plate), and the second is a vertical movement due to the rotation of the eccentric. These combined motions compress and push the material through the crushing chamber at a predetermined size.

More than 110 years of engineering and customer service experience keep customers running to McLanahan tomeet their production goals. McLanahan Jaw Crushers are proudly made in the USA and have imperial designs. With our grass roots design coupled with listening to customer needs for product enhancement over the years, McLanahan offers traditional hydraulic-shim adjustment Jaw Crushers as well asH-Series Jaw Crushers that featurehydraulic discharge setting adjustment, adjust-on-the-fly chamber clearing in the event the site loses power (once power is restored) and hydraulic relief for overload events with auto-reset.

Whether the traditional hydraulic-shim adjustment or the H-Series Jaw Crushers, both machines have an aggressive nip angle that providesconsistent crushing throughout the entire crushing chamber, which leads to increased production and less downtime on maintenance.

A Jaw Crusher uses compressive force for breaking material. This mechanical pressure is achieved by the crusher'stwo jaws dies, one of which is stationary and the other is movable. These two vertical manganese jaw dies create a V-shaped cavity called the crushing chamber, where the top of the crushing chamber is larger than the bottom. Jaw Crushers are sized by the top opening of the crushing chamber. For example, a 32 x 54 Jaw Crusher measures 32" from jaw die to jaw dieat the top opening or gape opening and54 across the width of the two jaw dies.

The narrower bottom opening of the crushing chamber is used to size the discharge material. A toggle plate and tension rods hold the pitman tight near the bottom of the moving swing jaw. The toggle plate is designed to perform like a fuse and protect the crusher in the event that an uncrushable materialenters the crushing chamber. As a rule, Jaw Crushers have a 6:1 or 8:1 ratio for crushing material. Still using the 32 x 54 Jaw Crusher example, the top size of thefeed entering the crushing chamber has to follow the F80 rule that 80% of the top size feed material is smaller than the gape opening. Using the F80 rule with the 32 x 54 Jaw Crusher, the32 gape opening equals a26 top sized feed, and with the 6:1 ratio of reduction, the discharge setting would be around 4.

Since the crushing of the material is not performed in one stroke of the eccentric shaft, massive weighted flywheels are attached to the eccentric shaft andpowered by a motor. The flywheels transfer the inertia required to crush thematerial until it passes the discharge opening.

While Jaw Crushers are mostly used as the first stage of material reduction in systems that may use several crushers to complete the circuit, the Jaw Crusher has also been used as a second-stage crushing unit. Depending on the application requirements, Jaw Crushers can be used in stationary, wheeled portable and track-mounted locations. The Jaw Crusher is well suited for a variety of applications, including rock quarries, sand and gravel, mining, construction and demolitionrecycling, construction aggregates, road and railway construction, metallurgy, water conservancy and chemical industry.

F100 is the maximum gape opening on a Jaw Crusher. F80 is the feed size to the Jaw Crusher, calculated by taking 80 times the gape opening divided by 100. P80 is the percent passing the closed side setting in tph.

A best practice, if possible, is to blend the material arriving from the source. This will ensure a constant and well-graded feed to the crushing chamber. In turn, this will produce a steady rate of tph andpromote inter-particle crushing that helps break any flat or elongated material. It also aids in equal work hardening the manganese jaw dies and prolonging the life of the jaw dies.

Usually a Jaw Crusher is in an open circuit, but it can be used in a close circuit if the return load is not greater than 20% of the total feed and the raw feed is free of fines smaller than the closed side setting.

Efficiency can be defined by the ratio of the work done by a machine to the energy supplied to it. To apply what this means to your crusher, in your reduction process you are producing exactly the sizes your market is demanding. In the past, quarries produced a range of single-size aggregate products up to 40 mm in size. However, the trend for highly specified aggregate has meant that products have become increasingly finer. Currently, many quarries do not produce significant quantities of aggregate coarser than 20 mm; it is not unusual for material coarser than 10 mm to be stockpiled for further crushing.

used portable jaw crushers for sale. white lai equipment & more | machinio

used portable jaw crushers for sale. white lai equipment & more | machinio

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used jaw crushers for sale. metso equipment & more | machinio

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1.We are factory and be able to give you the lowest price than market one; 2.Our products have been exported to over 80 countries and widely used in global mining and construction industry; 3.we have a prof...

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portable rock crusher / aggregate crushing plant for sale - new & used crushers | at

portable rock crusher / aggregate crushing plant for sale - new & used crushers | at

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jaw crushers for sale

jaw crushers for sale

The jaw crushers we offer for sale include Superior, Type B Blake, Fine-Reduction, and Dodge sizes, 4 by 6 to 84 by 66 inches. A reciprocating machine, the crushes material in a straight line between jaws without grinding or rubbing surfaces.

As you compare this jaw crusher feature for feature with other makes youll see how this modern crusher lowers principal costspower consumption; lubrication; jaw plate, toggle plate, and bearing wear youll understand why we say the crusher promises you a new low cost per ton of material crushed!

Firstthose who have rock or ore tougher and more abrasive than most material. Secondthe operators whove had difficulty with other designs of crushers. And finallythe operators who naturally buy the bestexpecting their added investment to be written off in comparatively short time through lower operating and maintenance costs!

Compare the dimensions with those of conventional jaw crushers. It measures up to 20% longer; has up to 35% deeper crushing chamber! And while you naturally expect to pay more for this bigger,deluxe crusher, it follows that you get more too! For example:

You get a crushing chamber with a full-width receiving opening increased capacity! You get an acute crushing chamber that minimizes slippage very important with hard, tough materials. You cut down crushing power required through longer pitman and front toggle. You reduce packing, get closer setting through the longer jaw, non-choking plates. You lower maintenance cost, get longer jaw plate, toggle, and bearing life through lower structural stresses, simplified design.

Frames of these crushers are built for maximum rigidity designed to prevent distortion during operation. Side members are heavy steel plate, reinforced by steel ribbing. End members are cast steel, of box section design, to provide maximum strength.

The side frames are deep-welded and then stress-relieved in thehuge annealing furnaces to eliminate possible failure adjacent to welds. The result is a uniformly strong frame that will remain true during the long service life of the crusher.

A jaw crusher frames are of sectionalized construction to facilitate handling. This design minimizes heavy lifts makes the crusher suitable for installations where parts must be passed down a shaft or through a tunnel. End members are attached between side members with vertical tongue and groove joints and held together with fitted bolts. Long-bearing surfaces prevent angular distortion.

Important differences in design show up visually when a cross-section of the crushing chamber of a conventional crusher is superimposed over that of the crusher. Now you can see the advantages of the 1 /3 deeper chamber using non-choking jaw plates. Its more acute crushing angle is carried to the very top of the chamberpermits nipping the largest material that can enter the receiving opening!

Lower plates on the swing and stationary jaws are suspended from projections on jaws. These plates also support the upper plates. This exclusive feature permits the free expansion of manganese steel jaw plates greatly minimizes the possibility of buckling or warping prevents costly shutdowns!

SWING AND STATIONARY JAWS on the jaw crusher are annealed cast steel box section construction designed for maximum rigidity. The jaw swings on a sturdy shaft that is clamped to the crusher frame. This shaft also serves as a reinforcing tie across the top of the frame. The entire design facilitates lubrication and replacement of shaft bearings.

Jaw plates are constructed of manganese steel and have corrugated crushing surfaces which reduce the power required for fracturing material. The jaw plates are built into two pieces to jaw. Those on the swing jaw are interchangeable. Plates on the stationary jaw are the non-choking type, not interchangeable. Lower plates on both jaws are suspended from jaw projections and support upper plates. The main advantage of this construction (see above) is to permit the free flow of manganese steel. All four plates are held in place by large through-bolts equipped with springs to prevent bolt breakage.

Heres still another feature youll find on the jaw crusher! Renewable wearing plates between the cast manganese steel jaw plates and swing and stationary jaws provide a firm backing for the jaw plates. If, for any reason, looseness develops in the jaw plates, these wearing plates, not the jaws, take the wear! By protecting expensive jaw castings, these wearing plates increase crusher life simplify maintenance minimize causes for shutdowns.

The heavy, two-piece corrugated manganese steel jaw plate is designed to fracture the toughest kinds of rock or ore with a minimum of power. The unobstructed clearances above, between, and below the plate sections permit free flow of manganese steel.

This construction eliminates the need for extra holding pieces, greatly minimizes the shearing of bolts. The amply designed shaft not only supports the swing jaw but reinforces the frame, serving as a tie between sides.

Notice the extra length of this jaw as compared to conventional types. Designed up to one-third longer, it exerts greater pressures in the upper portion of the crushing chamber, distributes crushing action more evenly. The result is a gradual reduction of ore to the choking point, and increased capacity!

Another, southern iron ore mining company, chose this 48 by 42-inch crusher to replace a conventional design that had failed. They explained, In our process, weve got to have a ruggedly designed crusher capable of continuous operation!

CRUSHERSin sizes from 36 by 25 to 60 by 48 inchesare giving these and other operators more for their money more capacity; more crusher life; more satisfaction! It can pay you too, to know more about this great crusher! Why not call in your use today!

All sizes of crushers feature a three-piece toggle plate construction. Worn ends may be replaced no need to discard the entire toggle. Bronze toggle ends fit into replaceable hardened steel toggle seats in swing jaw. Properly lubricated, this assembly materially reduces maintenance.

Toggle plates for these jaw crushers are of three-piece construction, consisting of an iron center section (2) to which are bolted two replaceable bronze ends (1 and 3). Toggle seats are carefully machined and equipped with protecting shields that deflect dust and dirt.

A toggle block, arranged for both vertical and horizontal adjustment, is provided at the rear of the frame. By inserting shims above the toggle block, the crushing stroke can be adjusted. Insertion of shims behind the toggle block adjusts the size of the discharge opening. Parallel alignment is assured and unnecessary strain in the crushing machine is avoided.

The pitman in any jaw crusher is essentially a tension member. However, because it also has a vertical reciprocating movement, it is desirable to keep its weight as low as possible, consistent with maintaining the required strength.

In the crusher this is accomplished by designing the pitman as a skeleton member, first to provide the necessary strength for tension and with stiffness against overturning thrust provided for by deep integral webs.

The pitman is designed with only four large-cap bolts, and the pitman cap is ribbed for proper distribution of the load to these bolts. The pitman is swung on the eccentric shaft which is supported by removable, water-cooled bearings on the frame.

The pitman is a two-piece annealed cast steel construction, with a cap designed for water cooling. Bearing surfaces on both pitman and cap are babbitted and are joined together by four large forged steel bolts. The elimination of excess bolts inherently found in conventional design results in a more uniform distribution of load.

The pitman (eccentric) shaft is heat-treated, forged steel constructionof ample diameter so that stress, even under the shock of suddenly clogged jaws, is low. The shaft is carried in removable, water-cooled, babbitted bearings designed to permit quick removal or replacement without having to strip the crusher.

Heres a typical toggle plate for jaw crushers. It is constructed in three pieceswith the center section of iron, two ends of bronze, designed for quick bolting to the center section. This unique construction materially reduces replacement and maintenance costs makes it unnecessary to discard toggles when ends alone are worn!

A critical point in the operation of large jaw crushers is the arrangement of the swing jaw and its supporting shaft. While in most crushers the jaw is pressed on the shaft and the latter swings in frame, in the jaw crusher the opposite principle is usedshaft is clamped in frame and jaw swings on the shaft!

Another point has been lubrication. In operation, the actual movement of the swing jaw is relatively small. The result is difficulty in proper lubrication of bearing surfaces. The crusher uses a special means of lubrication and in addition is designed with the new replaceable, graphite-impregnated Scor-proof bushings which greatly reduce wear on the expensive shaftssince these bushings, and not the shaft, now take the wear!

Very careful attention is required in the lubrication of heavy mechanical units like the jaw crusher. A thorough study made of existing types of lubrication systems resulted in the selection of a pair of systems that assure positive delivery of lubricant to point of maximum pressure.

The 48 by 42-inch jaw crusher and smaller sizes are force-fed by an automatic high-pressure lubricator to the swing jaw, pitman, and main bearings as illustrated in Figure 1. A motor-driven pump forces the lubricant through pressure buildup cylinders and out to distributors which dispense a precise amount to each of the points on the bearings. No oil return is provided.

The 60 by 48-inch jaw crusher and larger sizes are lubricated by a closed circuit oiling system to the pitman and main bearings, as illustrated by the solid lines in Figure 2, and by high-pressure lubrication fittings connected to the swing jaw bearings, as illustrated by the dotted lines in Figure 2. A motor-driven gear pump forces the oil through pressure-type filters and a condenser-type cooler to a distribution manifold mounted on the crusher. The oil flows through the bearings, lubricating and cooling, and back to the reservoir for recirculation. The swing jaw bearings require servicing by portable grease equipment.

The capacity of the jaw crusher is greater than that of conventional jaw crushers. One reason is its uniform-wear crushing chamber with full-width receiving opening. Another reasonits a more acute crushing angle.

Slippage is reduced packing and choking are prevented by a more even distribution of crushing action throughout the entire length of the crushing chamber. The result is a gradual reduction of material to the choking point increased capacity!

Capacities given below are approximate and are based on standard speeds, jaw motions, and jaw plates, with a feed of quarry or mine run material weighing 100 lb per cu ft crushed. Most stone and low-grade ores are considered weighing 100 lb per cu ft crushed.

The table is based on continuous feeding. Reserve for normal interruption of feeding should be provided. A heavy-duty apron feeder is recommended for most installations, particularly where large cars or trucks are used in the quarry or mine.

When feed to crushers is scalped over grizzlies or screens the number of rejections, or material that will have to be crushed should be determined in establishing the tonnage to be handled by the crusher. The number of fines received from mine or quarry will vary widely depending on each application and should be taken into consideration in determining the overall capacity.

Whatever equipment you operate, you can be certain of careful, considerate handling of orders for repair or replacement parts. In most cases parts are shipped directly from stockyoure assured of fast delivery. The view at left shows a small portion of crushing, cement, and mining equipment parts normally carries.

Repair parts temporarily depleted or not carried in stock will be furnished in time to meet requirements whenever possible. Anticipation of future needs, placing orders in advance, will greatly aid in avoiding unforeseen delays. Genuine parts are exact duplicates or improvements of original components of your machinery, not makeshift substitutes.

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.

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