The cone crusher, was designed primarily with a view to achieving top performance in the field of fine-reduction crushing. It has also been adapted to what is designated simply as “fine-crushing,” which extends into a range below that ordinarily defined by the term “fine-reduction.”
Although the eccentric speeds of the various sizes of this type are not quite so high as the speeds used for the Newhouse crusher, the Hydro-cone crusher definitely rates as a high-speed machine, its product comparing quite closely to that of the former type, for equal close-side settings. Probably the outstanding feature of the. Hydrocone crusher is the hydraulic support, from which its name is derived and which is clearly shown in the sectional view. This device makes it possible to adjust the crusher to any desired setting within its range in a matter of seconds; adjustments may be made while the crusher is running, although the feed must be shut off before operating the adjusting pump. An accumulator in the hydraulic system provides protection against tramp iron or packing.
Cone crushers are used in AG and SAG grinding circuits to increase tonnage by effectively dealing with any pebble (critical size) build-up problem. Normally, heavy duty short-head crushers are employed to crush pebbles. Power and crusher cavity level are the key variables for monitoring and controlling the crusher operation. Crusher product size is adjusted by changing the closed side setting.
On the left is a diagram of the Hydro-cone crushing chamber. A comparison of this chamber with those previously discussed is interesting. It will be noted that the choke-point has been raised far above the discharge level, in fact, to a point not far below the nip- point for the recommended maximum one-way feed dimension. By virtue of the decided flare of the head, and the corresponding flare of the top shell bore, the line-of-mean-diameters slopes sharply away from the crusher centerline. For some, distance above the discharge point the angle between head and concave is very acute; in fact, at the open-side position of the head this zone is almost parallel.
For recommended operating conditions, i.e., for safe combinations of throw and setting, and with screened feed, this type of crushing chamber does not approach anything like a choke or near-choke condition. For the combination shown in the diagram the ratio of volume reduction is almost 1:1 from zone 0-1 to zone 2-3 at the choke-point; consequently, if the crusher is given a screened feed (as all fine-reduction crushers should be) the reduction in voids by the time the choke-point is reached cannot very well reach serious proportions. The diagram shows the standard chamber. With screened feed these crushers will operate at close-side discharge settings equal to the throw of the head at the discharge point (usually spoken of as “eccentric-throw.”)
The level in the crusher feed pocket is an important variable, since it can indicate whether the feed is building up. A build-up could lead to a plug in the feed chute, a spill through the skirting on the crusher feed, or a crusher plug. None of these are desirable.
In a normal feed situation the level in the crusher cavity is kept fairly low, just enough to ensure that there is sufficient feed to keep the crusher working, but if the feed has to be suspended suddenly because of impending plugging, the crush-out won’t take too long (10 seconds or less). Normal feed is usually used in standard crushers where the feed particle size is quite large, say greater than 65 mm.
Choke feed is when the crusher cavity is kept full, without spilling out through the skirting. Choke feeding is usually used in short-head crushers where the feed particle is smaller than that for a standard crusher.
Medium and Fine Crushing Chamber
This crusher is a modification of the standard machine, developed for fine-crushing duty. Mechanically, the machine is the same in every respect as the standard crusher of the same type, but for each developed size of machine a special top shell and concave ring has been designed, with reduced receiving opening, reduced angularity between head and concave, and, consequently, superior characteristics at the finer settings. Medium crushing chambers may be operated at close-side settings of one-half the eccentric-throw, on screened feed; hence capacities at the finer settings are better than those of the standard type. Fine crushing chambers operate at one-fourth the eccentric throw. Inasmuch as the maximum feed-size is smaller in the case of the fine chamber, the ratios of reduction are approximately the same for both machines.
There are two main types of cone crushers: standard and shorthead. They differ by the shape of the cavity. The standard crusher cavity is wider to accommodate larger feed size material. The short head crusher is designed to crush finer material and to produce a finer product.
The closest approach between the mantle and the bowl liner is called the closed side setting. This is usually specified by the metallurgist to give the desired crusher product discharge size. It can be checked by running the crusher empty, hanging a lead plug into the crusher bowl, and then removing it to measure the “gap”. The gap is adjusted by rotating the bowl. Some crushers are equipped with an hydraulic jack mechanism on the crushing head assembly instead of having a bowl adjustment ring. The head can be raised or lowered to meet the operator’s needs. It can be very helpful in operation and process control.
The Symons Cone Crusher has come into almost universal use during the last few years for the final stage of crushing. It is a development of the secondary gyratory crusher, which is merely a small gyratory crusher designed to break the product of the primary machine down to about 1½-in. size ; but the main shaft of a cone crusher instead of being suspended from a spider is supported on a large socket bearing situated immediately under the crushing head and protected from grit and dust by a sealing assembly, this bearing taking the whole of the crushing load.
Fig. 8 gives a sectional view of the machine. The main shaft is carried in a long gear-driven eccentric, the rotation of which causes the gyration of the head in the usual way, but the centre of gyration is at the apex of the crushing head instead of in the spider. At the top of the bowl, therefore, the lumps of ore entering the crushing zone are cracked by short powerful strokes ; but at the bottom the head has a much longer but less powerful stroke, enabling the ore in the finishing stages to be rapidly crushed and quickly discharged without any tendency to choke, a condition which reduces over crushing to a minimum. This, together with the curved shape of the bowl, accounts for the large reduction ratio possible with this type of machine and makes it superior to other secondary crushers and coarse rolls.
It will be seen that the head and the bowl are parallel at the lower part of the crushing zone. The parallel space is deep enough, in conjunction with the speed of gyration, to ensure that no piece of ore can pass through it without being struck two or three times by the head before it falls clear. It follows that, unlike the jaw and gyratory crushers, the size of the product is determined by the distance apart of the bottom edges of the head and bowl in the position when they are closest together.
Coarse buttress threads on the outer circumference of the bowl fit into corresponding threads on the inner side of the adjusting ring, which is held down to the main frame by a circle of long heavy springs, flexible enough to allow the whole assembly to rise should “ tramp ” iron or other uncrushable material enter the crushing zone. By means of a windlass and chain the bowl can be rotated in the threads that support it in the adjusting ring while the machine is running, thus enabling the bowl liner to be adjusted for wear or the size of the product to be changed without stopping. The cone crusher is usually set to give a 3/8-in. or ½-in. product when discharging to ball mills.
Table 9 gives particulars of the different sizes of crushers. The capacity figures are based on material weighing 100 lb. per cubic foot and must be increased in direct proportions for heavier ores. It will be noted that each size of machine has two ranges of capacity ; this is due to the fact that it can be fitted with a coarse or a fine crushing bowl according to the duty that is required of it. With either one the range of reduction is greater than is economically possible with any other type of dry crushing machine.
A possible disadvantage of the cone crusher is that as a rule it cannot be choke-fed, but must be given an even feed of ore if it is to do efficient work. Should circumstances call for the installation of a machine which can be run if necessary with the ore piled up over the top of the head, a secondary gyratory crusher of the suspended shaft type will be required. The Traylor Reduction Crusher Type TZ, which is constructed on the principles of an ordinary gyratory crusher, but is fitted with a curved bowl liner similar to that of the Symons Cone Crusher, is designed to meet the case. Although the suspension of the shaft restricts the movement of the head to a smaller circle of gyration than that of the cone crusher, the ratio of reduction is still large enough to enable it to crush the product of the primary breaker to ½-in. size (¾-in. for the large machines), and it fulfils the condition that it can be choke-fed. Owing to the smaller movement of the head, however, the capacity for a given range is much less than that of the equivalent size of cone crusher and the latter is therefore preferred when choke-feeding can be avoided.
Symons Cone Crusher
The Symons Shorthead Cone Crusher, which is constructed on the same general principles as the larger machine, is designed to follow the latter, taking its product at 1-in. and reducing it to about ¼-in. size. The strains imposed on the crushing members, however, would be very heavy if the machine were run with the discharge opening set to ¼-in. or less. It is usual, therefore, to crush in closed circuit with a screen, the discharge opening of the bowl being set to 5/8 or ½ in. Thus a circulating load is built up and a certain amount of choke-crushing takes place, but the method actually gives greater efficiency with a finer product than can be obtained in an open circuit, whatever the discharge setting of the bowl in the latter case.
In ordinary crushing practice the grinding section is supplied with ½-in. or 3/8-in. material direct from Symons Cone Crushers. But the demand is for a finer feed and it seems likely that the Shorthead Cone Crusher will satisfy this demand to the exclusion of fine crushing rolls.
Symons Cone Crushers have been used extensively for secondary crushing in metallic, non-metallic, rock products and industrial operations. The Symons Cone was developed to give large capacity, fine crushing. The combination of high speed and wide travel of the cone results in a series of rapid, hammer-like blows on the material as it passes through the crushing cavity and permits free flow of material through the cavity.
Reduction in size of any particle, with each impact of the head, is regulated by the opening between the head and bowl at that point. A threaded arrangement of the bowl affords a quick and easy method for changing the size of product or to compensate for wear. This adjustment can be made while crusher is operating. A parallel zone between the lower portion of the crushing members assures uniform sizing.
Frame, adjustment ring and cone are made of cast steel; gears are made of special treated steel and have cut teeth; all bearings are bronze; mantle and bowl liners are manganese steel. The head and shaft can be removed as a unit, and other parts such as the eccentric and thrust bearings can easily be lifted out after the head is removed. The countershaft assembly can also be removed as a complete unit.
The circle of heavy coil springs, which holds the bowl and adjustment ring down firmly onto the frame, provides automatic protection against damage due to tramp iron. These springs compress, allowing the bowl to rise the full movement of the head until non-crushable material passes through. The springs then automatically return to their normal position.
Symons Cone Crushers are made in Standard and Short Head types. They are of the same general construction but differ in shape of the crushing cavity. The Standard cone is used for intermediate crushing. The Short Head cone is used for finer crushing. It has a steeper angle of the head, a shorter crushing cavity and greater movement of the head at the top of the crushing cavity.
Standard Cone Crusher Capacity
Short Head Cone Crusher Capacity
Cone Crusher Components and Operating Principle
The main components of cone crushers are:
- BOWL LINER
- PINION and CROWN GEAR
- ECCENTRIC INNER and OUTER BEARING
- THRUST BEARING
- MAIN FRAME
- TRAMP STEEL RELEASE
- DISTRIBUTOR PLATE
- MAIN SHAFT
- OIL SYSTEM
- DUST SEAL
The description of the Operating Principle of cone crushers and how this machine works should begin with the drive line and how the crushing action is generated.
If you observe the illustrations you will notice that the centre line of the main shaft is on an angle to the centre line of the crusher. The centre of the main shaft bisects the centre line of the crusher at the opening of the crushing chamber. As the MANTLE revolves that point is the pivot point of the mantle. This means that both the top and the bottom of the crusher mantle have a circular gyrating motion.
TRAMP IRON & CONE CRUSHERS
Tramp iron had long been a source of worry to those engaged in fine crushing. Here is what one operator had to say. “Shutdowns were frequent, costs were uncertain because of enforced delays due to excessive breakage. Plugged machines had to be freed continually with a torch to cut out frozen and wedged-in tramp iron. The cone crusher overcame these troubles, helped reduce and stabilize costs.” The best evidence of this statement is the universal acceptance of the cone as the outstanding crusher in its field.
While tramp iron is not recommended as regular diet for a Cone Crusher, its construction is such that damage will not result should any ordinary non crushable material get into the crushing cavity. The band of heavy coil springs encircling the frame allows the bowl to lift from its seat with each movement of the head until Such non-crushable object pass off into the discharge. The tramp iron shown in the accompanying illustration passed the protective devices installed for its removal and would have resulted in expensive repairs and long shutdown periods for any crusher except the Symons Cone.
Cone Crusher Short Head VS Standard Head
Cone crushers can have two types of ‘heads’, standard and short head types. The principle difference between the two is in the shape (size and volume) of the crushing cavities and feed plate arrangements. Standard head cone crushers have cavities that are designed to take a primary crushed feed ranging up to 300mm generating product sizes around 20mm to 40mm. For finer products short head cone crushers are normally used. They have a steeper angle of the head and a more parallel crushing cavity than the standard machines. Due to the more compact chamber volume and shorter working crushing length, the much needed higher crushing forces/power can be imparted to the smaller sized material being fed to the crusher. Cavities for the short head machine are designed to produce a crushed product ranging from 5mm to 20mm in closed circuit.
At the discharge end of the cone crusher is a parallel crushing section, where all material passing through must receive at least one impact. This ensures that all particles, which pass through the cone crusher, will have a maximum size, in at least one dimension, no larger than the ‘set’ of the crusher. For this reason, the set of a cone crusher can be specified as the minimum discharge opening, being commonly known as the “closed side setting” (CSS).