Your triceps make up two-thirds of your upper arm, and are involved in overhead presses, bench pressing, and other pushing exercises. If you want to build an impressive pair of arms while improving your upper-body strength,then you cannot neglect your tris.
The skull crusher is one of the best exercises for improving your triceps. Anyone from seasoned powerlifters, who want to improve their bench, to bodybuilders looking for more size, to general gym-goers who want a solid pump its a triceps exercise for the people! Below, we dig deep into the skull crusher to give form tips, outline benefits and provide alternatives and variations to best suit your training needs.
Start by lying down, back first, on a sturdy workout bench. The barbell should be locked out at the top position, with your hands set about shoulder-width apart. The width of your grip can vary based on flexibility and comfortability. The key is that the lifter should feel that they can flex the upper back muscles and squeeze their shoulder blades together. This will be essential for the next steps.
Now, begin to lower the barbell towards the forehead (hence the name, skull crusher). Its important to keep the elbows actively tucked in. If the elbows flare out a little, thats ok and even natural, but too much flare will deactivate the triceps.
After youve held the bottom position of the lift for a beat, drive the bar back up, reversing the path you took to lower the bar. You should keep your elbows tucked throughout the lifting (or concentric) phase.
Strong triceps are key for all pressing movements and overhead stability. Powerlifters must have strong triceps to assist in locking out of the bench press. Weightlifters must perform triceps work as they are necessary for elbow extension in the receiving phases of the snatch and jerk. And strongmen who hoist logs that weigh over 300 pounds overhead need triceps strength to finish the lift. The stronger you get, the more you lift, and the more you lift, the more your triceps become a factor.
The triceps are responsible for elbow extension, which is a key factor in finishing the end of the range of motion of the bench press, snatch,clean & jerk, and overhead press. Most power and strength athletes will see improvements in lockout performance with added triceps strength and hypertrophy work (assuming they are perfecting any technical faults resulting in press outs).
Healthy joints often come from proper training volume, technique, and increasing muscle hypertrophy and force production so that volumes and loading can be absorbed by the muscles themselves rather than on the tendons, ligaments, and joints. Stronger triceps (along with using proper form) is key toincreasing pressing performance and minimizing overuse injury to the joints and connective tissues.
For some strength and power athletes, bigger, leaner arms are an added goal. The triceps are roughly two-thirds of the arm, so more dedicated tricep work could help you achieve a superior set of pipes.
The skull crusher is a single-joint exercise that specially targets the triceps. Unlike other triceps movements, like close-grip bench press and dips, which recruit multiple muscles, the skull crusher primarily hits the triceps. That said, theres another important and often overlooked muscle group that benefits.
The triceps are responsible for elbow extension, which is a factor in most pressing movements (bench press, overhead presses, push-ups, dips, overhead stability, etc.). The skull crusher isolates the triceps by having the lifter perform deep elbow flexion while stabilizing the shoulder and wrist joints (see below).
While the shoulder muscles themselves are not as engaged, the scapular stabilizers and rear deltoids are working diligently to stabilize the shoulder socket to allow the lifter to remain in a fixed position. By not allowing shoulder movement, the lifter can force the elbows to flex to acquire necessary ranges of motion, increasing the demands on the triceps to extend the elbow joint fully. Simply put: Your shoulder stability will improve.
The skull crusher is an accessory movement to increase triceps strength and hypertrophy. This can also help increase injury resistance for the elbow joint and improve overall elbow extension abilities necessary for sports performance.
The triceps are responsible for overhead stability and elbow extension in the snatch and the jerk portions of the competitive lifts. By increasing triceps training by implementing single-joint exercises like skull crushers, you can help a lifter build more raw strength and muscle mass necessary to lock out lifts (assuming there is no technical fault).
The skull crusher, while not as functional as other pressing movements like push-ups and dips, can be a good option for lifters looking to increase triceps training volume without the added wear and tear on the shoulders and chest (such as if they were to do more push-ups, bench press, etc.) They also are vital for proper elbow extension and upper body strength.
Whether you want to get bigger, stronger, or increase your triceps work capacity, your sets and reps and rest time will be the determining factor. Heres how many you need to do based on a different training goal.
Lifting heavier weight with longer rest time is the key here. Youll overload your triceps but also engage your central nervous system, essentially priming your body to lift heavier loads in the future. Do four to six sets of four to eight repetitions, resting two to three minutes between sets.
Be like Goldilocks here and find a set and rep scheme in the middle of light and heavy. Typically, you want to lift a weight that allows you to do around ten reps. Youll accumulate more mechanical tension or stress, which is what your muscle needs to breakdown and then bounce back stronger. Do four to six sets of eight to 12 repetitions, and rest one to two minutes between sets.
Some lifters may want to train greater muscle endurance (for sport), in which higher repetition ranges and/or shorter rest periods are recommended. To achieve this, simply up the reps youre doing, but be sure to lighten the weight on the bar. Perform two to three sets of 15 to 20 reps, resting for a minute to a minute and a half between sets.
Dumbbell skull crushers are done similarly to the barbell or EZ-bar variation; however, you can attack the triceps unilaterally by using dumbbells. This can be beneficial for lifters who may have muscle imbalances or coordination issues. Additionally, this may allow for a deeper elbow flexion angle, which may improve muscle development.
The incline bench skull crusher variation can be done with any loading (barbell, dumbbell, kettlebell, etc.) and is set up with the bench at a slight incline. By adding the incline, you can slightly increase the stretch on the triceps and hit the muscle from slightly different angles.
Negatives, also called eccentrics, are highly effective at creating muscle damage and hypertrophy. To do this, an athlete should have a spotter spot them as they slowly lower the supra heavy load down under control. The spotter should keep control and make sure the load doesnt come crashing down on them. When it is time to lift the load, the spotter can lift the weight to the top position, repeating for reps.
The close-grip bench press is a bench press variation that targets the triceps and chest by narrowing the grip width on the barbell. In doing so, the lifter must tuck their elbows into their sides. This variation can be easily swapped for regular bench press when athletes have issues locking out bench press reps or limiting shoulder involvement in the press.
Dips are a great mass building exercise for the triceps, chest, and front shoulders. You can do them with your own bodyweight or strap on a dipping belt to add weight and overload the target muscles even more.
The overhead triceps extension can be done with a dumbbell, a barbell, an EZ-bar, ora cable machine. This exercise targets the similar segments of the triceps that the skull crusher does and may be less painful on joints if a lifter has elbow issues. Note: pain should not be dismissed and properly reviewed by a medical professional.
Do skull crushers early in your arms training. The reason being that the skull crusher can be loaded up with more weight, and so you dont to rob yourself of the potential to lift heavier by pre-fatiguing your muscles with other exercises.
Probably not skull crushers. First, if youre experiencing any pain, you should consult with a doctor. However, a good rule of thumb is: if it hurts (and not in a typical workout way), you should steer clear. Try some cable variations, like pushdowns. These are generally a little easier on the elbow and shoulder joints.
Not necessarily. The aim of this exercise, like all exercises, is to tax the target muscle as effectively as possible. If you can feel your muscle working, then it is. And if you cant, then you need to try something else. Which exercise works best is different for everyone. If you dont feel your tris engage while using a barbell, then try attaching a triceps handle to a cable. Or use a pair of dumbbells. Even kettlebells work. Play with it.
BarBend is an independent website. The views expressed on this site may come from individual contributors and do not necessarily reflect the view of BarBend or any other organization. BarBend is the Official Media Partner of USA Weightlifting.
With a three-decade heritage of providing expert equipment solutions, technical support and expert advice, Pilot Crushtec International (Pty) Ltd is southern Africas leading supplier of quarrying and mining equipment. We are proud to offer a range of industry-leading OEM and in-house quarrying, mining, recycling and materials-handling solutions, including:
Mobile and semi-mobile crushing Screening Modular plants Recycling Stockpiling Materials-handling Spare and wear parts Mobile lighting Dust fighters Impactors Sand washing Technical support Repair services
Our team of experts and specialists is backed by 30 years of experience in the field, in the harshest environments and toughest applications. Thats why we only offer the best OEM product ranges which include jaw crushers, cone crushers, vertical shaft impactors (VSI), screens, skid frames, feeders, hoppers and conveyors.
With a three-decade heritage of providing expert equipment solutions, technical support and expert advice Pilot Crushtec International (Pty) Ltd is southern Africas leading supplier of quarrying and mining equipment. We are proud to offer a range of industry-leading OEM and in-house quarrying, mining, recycling and materials-handling solutions including:
Mobile and semi-mobile crushing Screening Modular plants Recycling Stockpiling Materials-handling Spare and Wear parts Mobile lighting Dust fighters Impactors Sand washing Technical support Repair services
Our team of experts and specialists is backed by 30 years of experience in the field, in the harshest environments and toughest applications. Thats why we only offer the best OEM product ranges which include jaw crushers, cone crushers, vertical shaft impactors (VSI), screens, skid frames, feeders, hoppers and conveyors.
Pilot Crushtec International (Pty) Ltd is South Africas leading supplier of mobile and semi-mobile crushing, screening, recycling, sand washing, stockpiling, compacting and material handling solutions. Our product range includes jaw crushers, cone crushers, vertical shaft impact (VSI) crushers, impact crushers, screens and conveyors.
The 1 X 2 911MPEJAC12Small Rock Crusheris designed to finely crush rock and stone like aggregates or your favourite ore type (gold, silver, copper, etc.) from 3/4 (20mm) feed size down to a D50 50% passing 50 Mesh (300um).
This small jaw crusher and its miniature opening gape of25 mm X 50 mm, can easily adjust by hand. The CSS, known as the closed-side-setting, can be choked down to effectively pulverize the rocks you feed in. With a short throw at fast 500 RPM, this small rock breaker acts as a quasi-sample pulverizer without the dust of your typical cheap hammermill, chain beating, impact crusher amateur prospectoroften fall for and purchase online.
The 911MPEJAC12 with a crushing capacity of 10pounds (5 kg) per hours, ultra-portable (20 lbs.), and Small Rock Crusheris a Blake type crusher with a high-speed eccentric overhead. The product from this crusher is generally liberated enough and ready to pan or table for gravity gold separation. When you buy this Small Rock Crusher, you also get: An operating manual, the pulley, pre-installed AR450 jaw plates. Without the 1 HPmotor or mounting frame. This crusher canoperate with gas/diesel engine as well as electric motor. Be sure to ration your speed/sheaves to have 500 RPM on the jaw and you are set to crush-those-rocks.
Roll crushers are generally not used as primary crushers for hard ores. Even for softer ores, such as chalcocite and chalcopyrite, they have been used as secondary crushers. Choke feeding is not advisable as it tends to produce particles of irregular size. Both open and closed circuit crushing is employed. For close circuit the product is screened with a mesh size much less than the set.
Figure6.4 is a typical set-up where ores crushed in primary and secondary crushers are further reduced in size by a rough roll crusher in an open circuit followed by finer size reduction in a closed circuit by a roll crusher. Such circuits are chosen as the feed size to standard roll crushers normally does not exceed 50mm.
A distinct class of roll crushers is referred to as sizers. These are more heavily constructed units with slower rotation, and direct drive of the rolls rather than belt drives. They have a lower profile, allowing material to be easily fed by loaders, and are a good choice for portable crushers at the mine that reduce the coal in size for conveying to the preparation plant. An example of these units is shown in Fig.9.4.
9.4. (a) Primary sizer with attached feeder. The large motors and gearboxes drive the relatively low-speed toothed rolls that break the coal. (b) Haulage truck dumping coal directly into the feed hopper for a primary sizer, which discharges onto a product belt. (c) Tertiary sizer for crushing coal to the desired size for a preparation plant.
Their lower speeds are claimed to reduce fines generation, while lending themselves to high throughput applications. Sizers can either have the rolls rotate towards each other to carry feed between the rolls to be broken, or can be constructed as tertiary sizers with the rolls rotating away from each other. With tertiary sizers, feed coal is added between the rolls, and much of the fine material falls through. The coarser material is then carried to the outside to be broken against fixed sizing combs. This design increases the capacity by producing two main product streams instead of one, and also minimizes overcrushing by removing a large fraction of the fines. Tertiary sizer capacities range from 440 tons/h (400 metric tons/h) for 2448 inch (61122cm) rolls producing a 2-inch (5cm) product, up to 3968 tons/h (3600 metric tons/h) for 2096 inch (51244cm) rolls producing a 10-inch (25cm) product (Alderman and Edmiston, 2010).
A typical coal handling package using sizers would comprise a dump pocket discharging to a primary sizer discharging to a product belt, as shown in Fig.9.4b. This product belt would then feed a secondary or tertiary sizer, such as is shown in Fig.9.4c, which may include intermediate screening to remove product prior to subsequent stages of breakage. Typical size ranges would start with run-of-mine coal feeding to the primary sizer at 2000mm, and reducing to 350mm. The secondary sizer would receive this coal and discharge at a nominal 125mm, followed by a tertiary sizer/screen combination to generate a 50mm topsize preparation plant feed (FLSmidth, 2011).
The intermediate crushing in the cut roll crusher is mainly used for the crushing of brittle materials like concrete and clay sintered bricks, along with the compression of rough materials like wood and fabric (to avoid being too small in size) after the coarse (primary) crushing. The selective crushing in this process is good for the separation of impurities. Impact crushers are commonly applied in intermediate crushing. However, when used in crushing of mixed C&D waste, the wood and fabric materials will be broken and mixed in recycled aggregate materials by the high-speed operating rotors and are difficult to be separated.
Although not widely used in the minerals industry, roll crushers can be effective in handling friable, sticky, frozen, and less abrasive feeds, such as limestone, coal, chalk, gypsum, phosphate, and soft iron ores.
Roll crusher operation is fairly straightforward: the standard spring rolls consist of two horizontal cylinders that revolve toward each other (Figure 6.14(a)). The gap (closest distance between the rolls) is determined by shims which cause the spring-loaded roll to be held back from the fixed roll. Unlike jaw and gyratory crushers, where reduction is progressive by repeated nipping action as the material passes down to the discharge, the crushing process in rolls is one of single pressure.
Roll crushers are also manufactured with only one rotating cylinder (Figure 6.14(b)), which revolves toward a fixed plate. Other roll crushers use three, four, or six cylinders, although machines with more than two rolls are rare today. In some crushers the diameters and speeds of the rolls may differ. The rolls may be gear driven, but this limits the distance adjustment between the rolls. Modern rolls are driven by V-belts from separate motors.
The disadvantage of roll crushers is that, in order for reasonable reduction ratios to be achieved, very large rolls are required in relation to the size of the feed particles. They therefore have the highest capital cost of all crushers for a given throughput and reduction ratio.
The action of a roll crusher, compared to the other crushers, is amenable to a level of analysis. Consider a spherical particle of radius r, being crushed by a pair of rolls of radius R, the gap between the rolls being 2a (Figure 6.15). If is the coefficient of friction between the rolls and the particle, is the angle formed by the tangents to the roll surfaces at their points of contact with the particle (the angle of nip), and C is the compressive force exerted by the rolls acting from the roll centers through the particle center, then for a particle to be just gripped by the rolls, equating vertically, we derive:
The coefficient of friction between steel and most ore particles is in the range 0.20.3, so that the value of the angle of nip should never exceed about 30, or the particle will slip. It should also be noted that the value of the coefficient of friction decreases with speed, so that the speed of the rolls depends on the angle of nip, and the type of material being crushed. The larger the angle of nip (i.e., the coarser the feed), the slower the peripheral speed needs to be to allow the particle to be nipped. For smaller angles of nip (finer feeds), the roll speed can be increased, thereby increasing the capacity. Peripheral speeds vary between about 1ms1 for small rolls, up to about 15ms1 for the largest sizes of 1,800mm diameter upwards.
Equation 6.6 can be used to determine the maximum size of rock gripped in relation to roll diameter and the reduction ratio (r/a) required. Table 6.1 gives example values for 1,000mm roll diameter where the angle of nip should be less than 20 in order for the particles to be gripped (in most practical cases the angle of nip should not exceed about 25).
Unless very large diameter rolls are used, the angle of nip limits the reduction ratio of the crusher, and since reduction ratios greater than 4:1 are rare, a flowsheet may require coarse crushing rolls to be followed by fine rolls.
Smooth-surfaced rolls are usually used for fine crushing, whereas coarse crushing is often performed in rolls having corrugated surfaces, or with stub teeth arranged to present a chequered surface pattern. Sledging or slugger rolls have a series of intermeshing teeth, or slugs, protruding from the roll surfaces. These dig into the rock so that the action is a combination of compression and ripping, and large pieces in relation to the roll diameter can be handled. Toothed crushing rolls (Figure 6.16) are typically used for coarse crushing of soft or sticky iron ores, friable limestone or coal, where rolls of ca. 1m diameter are used to crush material of top size of ca. 400mm.
Wear on the roll surfaces is high and they often have a manganese steel tire, which can be replaced when worn. The feed must be spread uniformly over the whole width of the rolls in order to give even wear. One simple method is to use a flat feed belt of the same width as the rolls.
Since there is no provision for the swelling of broken ore in the crushing chamber, roll crushers must be starvation fed if they are to be prevented from choking. Although the floating roll should only yield to an uncrushable body, choked crushing causes so much pressure that the springs are continually activated during crushing, and some oversize escapes. Rolls should therefore be used in closed circuit with screens. Choked crushing also causes inter-particle comminution, which leads to the production of material finer than the gap of the crusher.
The objective of sample preparation is to prepare test samples from a parent sample or individual primary increments, Fig.5.19 for analysis. Sample preparation includes all procedures that a sample is subjected to in order to produce a reduced mass of sample (analysis sample) that is representative of the parent sample and from which subsamples of relatively small mass can be used directly for analysis. Samples for general analysis (proximate, ultimate, calorific value, total sulphur, etc.) are typically milled samples with 95% passing 0.212mm. Standard AS4264.1 stipulates that the minimum mass required for general analysis is 30g.
However, some laboratory analyses will require larger sample masses. Some examples from AS 4264.1 include Hardgrove grindability index (AS 1038.20) which requires 1kg at 4.75mm top size, and total moisture (AS 1038.1 Method A and B) 300g at 4mm. However, the principles of preparing a representative analysis sample from the original coal sample are the same.
Taking the ash determination as an example: 1g of coal is used in a single ash determination, and that 1g has to be representative of the coal sample. At a top size of 0.212mm the sampling constant, Ks, for most coals will be very small and this constant combined with a 1g mass of coal enables the variance contribution from the IH of the analysis sample to be almost insignificant and therefore a high level of precision can be expected.
Apart from exploration samples, most samples received by laboratories are from mechanical sampling systems at coal handling facilities at mine sites, ports or power stations. In some areas where coal is being sold across land boarders such as the MongolianChinese border, most samples will be extracted directly from haulage trucks. Many samples, such as ship loading samples and some coal preparation plant samples, are produced by multistage mechanical sampling systems. Other samples may be produced from single-stage samplers. As a result, laboratories can receive samples in a wide range of conditions, most importantly sample mass, moisture content and particle size distributions. Sample preparation procedures have to be tailored to suit the samples and the proposed testing and analyses procedures that the sample has been collected for.
In some instances the particle size reduction may be omitted before sample subdivision, for example at the first stage after collection of the primary increment. However, generally before subdivision (subsampling) the particle size should be reduced.
In each case at every stage, the process recognises the relationships between the number of increments, sample mass and particle size to sampling variance, as each stage is a standalone sampling exercise.
Hammers mills comprise a set of swinging hammers attached to a rotating shaft (Fig.5.22). Typically, they are fed a 4mm top size coal to produce analysis samples with >95% passing 0.212mm. They have a device for feeding the coal into the mill. This is often a screw-type feeder. They also usually have a screen on the outlet to ensure that the entire sample achieves a specific top size. Hammer mills tend to generate excessive fines and should not be used in some instances, such as preparation of samples for petrographic analysis and Hardgrove grindability index determination.
Ring mills comprise a cylindrical canister and lid, a steel ring, and a smaller steel cylinder that fits inside the canister (Fig.5.23). The coal is placed in the canister with the ring and the cylinder, and the lid is attached. This is then placed in a jig that moves the canister in a circular motion. The movement of the various metal components within the canister crushes the coal. There is some concern that these mills can become heated and that this may affect the coal quality, particularly CSN values. This type of mill is particularly useful for crushing low mass samples as sample loss is kept to a minimum. Automated ring mills have been in use in laboratories handling large sample volumes to ensure consistent milling and improved productivity.
Roll crushers are comprised of two steel cylinders (Fig.5.24). The coal is crushed as it passes between the cylinders. This type of crusher is useful when preparing samples with a minimum of fines generation.
Incremental division is a manual method of subdivision that can provide precise subsamples. This method requires that the coal is well mixed prior to division. The coal is spread onto a flat surface in the form of a rectangle in a thickness approximately three times the nominal top size of the sample. A grid pattern is marked out on the sample (usually composed of at least 20 rectangles in a 54 grid) and a single increment is obtained from each square. The increment is removed from the sample using a suitable scoop and bump plate to prevent the increment from falling out of the scoop. Incremental division is used almost exclusively in obtaining the final (0.212mm) laboratory sample after the hammer mill operation, because of excessive dust losses by other methods.
Rotary sample division (rsd) is the most common method for subdivision of large samples in coal laboratories. The rotary sample divider (Fig.5.25) comprises a feed hopper, a device for feeding the coal at a constant rate (usually a vibratory feeder) and a number of sector-shaped canisters formed into a cylinder on a rotating platform. The uniform coal stream produces a falling stream of coal that is collected in the rotating canisters, dividing the sample into representative parts.
As the coal particles move through the feed hopper there is a high potential that some segregation and grouping will occur. To counter the effect that this may having on sample preparation variance it is advisable to ensure that each canister cuts the falling stream at least 20 times, i.e. there are at least twenty rotations of the turntable as the coal flows into the canisters. Additionally, it is a good practice to combine material collected in two or more canisters to form the divided increment or subsample. When doing so, canisters that are opposite each other in the rotary sample divider should be selected for recombination. The machine pictured in Fig.5.25 is set to divide a sample into eight divisions. If the requirement was to extract a quarter of the sample for analysis, two of the 1/8th divisions would be recombined.
Riffles (Fig.5.26) are less regularly used in laboratories. Riffles divide the coal into halves by allowing the coal to fall through a set of parallel slots of uniform width. Adjacent slots feed opposite containers. The width of the slots should be at least three times the nominal top size of the coal. There should be at least eight slots for each half of the riffle.
Fractional shovelling may be used for subsampling when a large rotary sample divider is not available. In this process, the coal is formed into a conical heap. Successive shovels of coal are removed from the base of the heap and are placed into daughter heaps. The shovels of coal should be allocated consecutively and systematically to each daughter heap.
Shredding rubber waste reduces the volume of used tires. Generally, the cost of shredding increases with the need to obtain pieces as small as possible. For grinding, rubber wastes are initially processed through mechanical cutters, roll crushers and screw shredders. To obtain finer particles, shear crushers and granulators are used. The final processing of rubber wastes is with high-temperature shredding equipment, such as rotary shredders, where degradation occurs during compression simultaneously with shear and wear (Mikulionok, 2015). In the initial phase, shredding rubber wastes results in dimensions of approximately 7.6210.16cm. These pieces are then placed in cutters that reduce the size to 0.630.63cm (Rafique, 2012).
Granulators are used in the second step of the recycling process, where pieces of waste tyres are grinded in the large-sized granulators to produce a large quantity of granules. The use of pulverises can reduce the rubber granulated material into fine powder. The rubber particles size can range from a few micrometres up to centimetres.
Rotary Breakers (Fig. 1). The rotary breaker serves two functionsnamely, reduction in top size of ROM and rejection of oversize rock. It is an autogenous size-reduction device in which the feed material acts as crushing media.
Roll Crusher. For a given reduction ratio, single-roll crushers are capable of reducing ROM material to a product with a top size in the range of 20018mm in a single pass, depending upon the top size of the feed coal. Double-roll crushers consist of two rolls that rotate in opposite directions. Normally, one roll is fixed while the other roll is movable against spring pressure. This permits the passage of tramp material without damage to the unit. The drive units are normally equipped with shear pins for overload protection.
Process is designed to reduce the size of large pieces with minimum production of dust. Two main types of breakers are used in Great Britain, viz. (a) Pick Breaker and (b) Bradford Breaker. Other crushers commonly used are jaw crushers, roll crushers, disc crushers, cone crushers and hammer crushers.
Pick breakerdesigned to imitate the action of miners' picks. Strong pick blades are mounted rigidly on a solid steel frame moving slowly up and down. Coal passes under the picks on a slowly moving horizontal plate conveyor belt. The amount of breakage is roughly controlled by the height to which picks are raisedupper limit is 0.5 m Typical performances: 450 ton/hr with a 2-m-wide machine. Size reduction from 500 mm to 300 mm. Several machines may be placed in series, with screens in between to remove fines. Main advantageminimum production of fines can be achieved. Fines production is controlled by the diameter and spacing of picks. Reduction in diameter and increase in spacing, decrease the proportion of fines.
Bradford breakerScreens break and removes large pieces of accidental material, e.g. pit props, chains or tramp iron, in one operation. Consists essentially of a massive cylindrical screen or Trommel, with fins fitted longitudinally inside the screen. These raise the lumps of coal as the cylinder rotates, until they fall, break, and are screened. Unbroken material passes out of the end of the cylinder. Production of fines is also small. Capacity of machine: up to 600 ton/hr.
Blake jaw crusher. Consists of a heavy corrugated crushing plate, mounted vertically in a hollow rectangular frame. A similar moving plate (moving jaw) is attached at a suitable angle to a swinging lever, arranged so that the reciprocating movement opens and closes the gap between the plates, the greater movement being at the top. The machine is available with top opening up to 2 2.7 m. Usual capacity up to 300 ton/hr. Horsepower required: up to 150.
Corrugated and toothed roll crushers. Two heavily toothed, or corrugated, cylindrical rollers (Fig. 10.1) are mounted horizontally and revolve in opposite directions. (Towards each other at the top side or nip, one being spring loaded.) Alternatively, a single roll may revolve against a breaker plate. Capacity of a 1.5 m-long machine with a 300 mm opening and roll speed 40 r.p.m. is about 350 ton/hr, with a power consumption of about 200 h.p. Best results are obtained by the use of several rolls in series, with screens between.
Run-of-mine coal produced by mechanized mining operations contains particles as small as fine powder and as large as several hundred millimeters. Particles too large to pass into the plant are crushed to an appropriate upper size or rejected where insufficient recoverable coal is present in the coarse size fractions. Rotary breakers, jaw crushers, roll crushers, or sizers are used to achieve particle size reduction. Crushing may also improve the cleanability of the coal by liberating impurities locked within composite particles (called middlings) containing both organic and inorganic matter. The crushed material is then segregated into groups having well-defined maximum and minimum sizes. The sizing is achieved using various types of equipment including screens, sieves, and classifying cyclones. Screens are typically employed for sizing coarser particles, while various combinations of fine coal sieves and classifying cyclones are used for sizing finer particles. Figure 2 shows the typical sizes of particles that can be produced by common types of industrial sizing equipment.
The sponge masses as produced by vacuum distillation have to be prepared before melting. The nine ton mass of sponge has to be crushed to about 12mm size pieces. The sponge in contact with retort wall and the push plates have a high likelihood of contamination with iron and nickel since these metals are soluble in titanium. The top of the mass may also have some contamination of iron and nickel from reaction with the radiation shield and substoichiometeric chlorides. To remove this contamination the outer skin of the sponge mass is removed by use of powered chisels. This material is downgraded from aerospace use and used in less critical applications. The sponge mass then is sliced radially to one to 5cm sections with a large guillotine or similar blade. The bottom section of the mass is removed first as this likely has the most amount of iron incorporated into the sponge. The sponge mass is removed from the working table, so this material can be segregated from the balance of the mass. At this point the mass is placed back on the table, sliced and then sent to a crushing circuit. Titanium sponge is malleable material, thus traditional mineral processing equipment such as roll or jaw crushers are not as effective as high shear shredding machines such as rotary shears or single rotor/anvil shears in preparing sponge with limited very fine particle generation.
Dust generation in the crushing process is a very important aspect of operation. Control of the dust by collection and washing of equipment on a periodic basis is very important to reduce the risks of fire in the processing of sponge. Care has to be taken to avoid working on equipment when dust present as titanium metal fires are difficult to extinguish; a class D extinguisher or rock salt are used to suppress the first. The high temperature of the fire and the low melting point of iron-titanium eutectic can result in melting of equipment, supports or piping in these plants if a fire does occur.
The core of the sponge mass has the lowest level of metal contamination. To harvest the material for applications that need low iron and low nickel levels, it is necessary to core the mass. This is done in several ways; the mass can be upended and the guillotine blade can be used to remove thick layers of outer skin, or chisels can be used to remove the outer layers. Control of the lot by separation during the crushing campaign is used to separate the high-purity products from the normal grades of sponge. Control of the nickel level in the magnesium used in the reduction is also important. Removal of as much stainless steel in piping, retorts and metal reservoirs is also important, as nickel in the magnesium will be incorporated into the sponge. Small concentrations of nickel in magnesium can take a long time to be purged from the process. Control of the quality of magnesium used for make up in the VDP process is as important, as some magnesium can be contaminated with nickel during production. Iron is not as significant an issue as its solubility in magnesium is low.
Roll Crushers are designed to handle the primary, secondary and tertiary stage crushing of friable materials such as coal, salt, clay, bauxite, limestone and other minerals of similar characteristics in the mining, power generation and numerous other industries. Roll Crushers are one of the most widely used crushers in the mining industry and have numerous advantages, such as high capacity, low headroom, low horsepower, the ability to handle wet, sticky feeds and the generation of minimum fines while producing a cubical product.
The simplified design gives these units excellent reliability and requires very little maintenance. Roll Crushers are designed with built-in tramp relief that allows for the passing of uncrushable materials while continuing operation and returning to the initial product setting.
Since patenting the first Single Roll Crusher in 1894, McLanahan has become an expert and leader in the industry in the design and manufacture of single and two stage Roll Crushers. The selection process for each application is based on extensive equipment knowledge and a wealth of test data developed in our research lab or through on-site testing.
McLanahan offers belt-driven Roll Crushers in four designs: Single Roll, Double Roll, Triple Roll and Quad Roll Crushers, which provide a substantial return on investment by operating at low cost and maximizing yield by generating minimal fines. The rugged design, which incorporates a fabricated steel base frame lined with replaceable abrasion-resistant steel liners, stands up to the toughest mineral processing applications while providing safe and simple operation, including an automatic tramp relief system to allow uncrushable objects to pass while the crusher remains in operation. These crushers are also versatile, allowing for adjustments in roll speeds and gap settings to meet most any application requirement.
Whether the application requires a single-stage or two-stage crusher, the forces necessary to perform the crushing remain the same: a combination of impact, shear and compression. The impact force occurs as the material enters the crusher and is impacted by the rotating roll. Shear and compression forces occur as the feed material is pulled between the crushing plate and/or crushing rolls.
Depending on the feed size, material is fed into the crushing chamber and encounters a single or a pair of rotating rolls. If a two-stage reduction is required, either a Triple or Quad Roll configuration can be used. In this scenario, the top stage of the crusher performs the primary reduction either by crushing the material between the roll and crushing plate or between a pair of rolls. The material is then fed directly between the two bottom-stage rolls for additional processing.
If a single-stage reduction is required, then depending on the feed-to-product-size ratio of reduction, either a Single or Double Roll Crusher can be selected. Regardless of the crusher type selected, Roll Crushers allow for the material to fracture along naturally occurring cleavage lines, which helps with minimizing fines generation.
Yes, it will. When a wet, sticky feed is fed to a two-stage crusher, you run the risk of plugging the crusher between the top and bottom stages. If a wet, sticky feed is anticipated and the ratio of reduction requires two stages of crushing, it is recommended that two separate single stages be used.
A good rule of thumb is: Single Roll Crushers have a 6:1 ratio of reduction, Double Roll Crushers have a 4:1, Triple Roll Crushers have a 6:1 on the top stage and a 4:1 on the bottom stage, and Quad Roll Crushers have a 4:1 on both the top and bottom stage.
Single Roll Crushers are typically used as primary crushers that provide a crushing ratio of up to 6:1. They crush materials such as ROM coal, mine refuse, shale, slate, gypsum, bauxite, salt, soft shale, etc., while producing minimal fines. Designed with intermeshing roll teeth and a curved crushing plate, they are extremely effective in reducing slabby feeds.
Double Roll Crushers provide a 4:1 reduction ratio. They are typically used as a secondary or tertiary crusher for materials such as ROM coal with refuse, limestone, gypsum, trona, shale, bauxite, oil shale, clean coal, coke, salt, quicklime, burnt lime, glass, kaolin, brick, shale and wet, sticky feeds. Each machine is custom engineered with roll elements and tooth patterns selected depending on theapplication requirements to produce a cubical product with minimal fines.
Triple Roll Crushers are ideal for producers who want to accomplish two stages of reduction in one pass. They can be used in coal, salt, coke, glass, and trona operations, among others. Triple Roll Crushers combine a Single Roll Crusher with a Double Roll Crusher to form a crusher that is capable of achieving a 6:1 reduction ratio in the primary stage and a 4:1 reduction in the secondary stage while producing a cubicle product at high capacity.
Quad Roll Crushers are ideal for producers, including those with preparation plants, who want to accomplish two stages of reduction in one pass. They can be used in coal, salt, lime, pet coke and potash operations, among others. Quad Roll Crushers are capable of achieving a 4:1 reduction ratio before feeding the crushed material to the secondary stage for an additional 4:1 reduction to make the final product.
The Single Roll Crusher, with its 6:1 ratio of reduction, is ideal for reducing large feed lumps to a medium product size while producing a considerably lower percentage of fines. The minimum product sizing of a Single Roll Crusher is generally limited to 2-3. The crushing is carried out between the full width of the extra-long curved crushing plate and the low-speed crushing roll. The curvature of the crushing plate provides an ample throat opening to capture large irregular feed lumps. The replaceable crushing plate tips or liners are slotted to intermesh with the roll teeth to produce a cubical product and effectively reduce slabbing.
Single Roll Crushers are V-belt driven and employ a large diameter flywheel with a gear and pinion set to reduce roll speed. With the assistance of the inertia generated by the flywheel, this crusher is operated with relatively low horsepower and requires lower headroom in comparison to other crushers used for primary reduction. The roll diameter and width of the crusher will ultimately be dictated by the feed size, product size and capacity.
Single Roll Crushers employ a tramp relief mechanism to allow momentary movement of the crushing plate so the uncrushable object can pass. The mechanism then allows the crusher to return to its original setting and remain in operation.
The Single Roll Crusher, which was originally patented by Samuel Calvin McLanahan in 1894, has evolved over the years to include design features to ensure many years of rugged operation. Complete with all safety guards, the Single Roll Crusher features an automatic tramp relief mechanism that allows the crushing plate to hinge open, pass non-crushable tramp material and return to the previous setting for continued operation.
Based on the application data and extensive field experience, McLanahan selects the proper duty class of Single Roll Crusher for each project. A fully-equipped application research laboratory allows for crushing tests to make sure McLanahan can provide the best possible solution.
A Single Roll Crusher is made up of a toothed roll assembly, which crushes the incoming feed material against a crushing plate. The Single Roll Crusher is designed to reduce larger feed sizes to the desired product size at a 6:1 ratio of reduction while producing a considerably lower percentage of fines. When properly fed in the direction of the roll rotation, the crushing action is carried out along the full width of the curved crushing plate, which ensures maximum throughput capacity. A properly sized roll diameter and tooth configuration grabs the incoming feed and pulls it into the crushing zone without hesitation. The crushing plate has reversible and easily replaceable crushing plate tips, which are designed to produce a cubical product while providing the producer with twice the wear life and simplified maintenance. Single Roll Crushers often require less horsepower and lower headroom in comparison to other crushers used in primary and secondary applications.
These units are designed to make crushing simpler and more effective. McLanahan Single Roll Crushers also feature hydraulic product size adjustment to perform relatively simple changes to the crusher setting if required.
When an uncrushable object, such as metal, roof bolts/timbers, etc., enters the crusher and the force necessary to crush this material is greater than the crushing forces of the crusher, the crusher allows the crushing plate to open and pass the tramp material. The crusher then returns to its previous setting and remains in operation.
Cobra Single Roll Crushers are the lightest duty in the McLanahan line of Single Roll Crushers. They are ideal for wet, sticky feeds and for processing materials such as clean coal, petroleum coke, sulfur, rosin, foundry cores, frozen agglomerates and other friable materials.
Rockmaster Single Roll Crushers are the heaviest-duty model in the McLanahan line of Single Roll Crushers. They are ideal for the most severe crushing applications and reduce extremely hard material and typical mine refuse.
Typically designed for primary crushing, McLanahan Single Roll Crushers efficiently crush material at a 6:1 crushing ratio. . They can continually withstand heavy-impact applications. Single Roll Crushers reduce large size particles in the feed to a medium size, while producing a low percentage of fines.Get in Touch with Mechanic