The system of the present invention is particularly suited for use with a gyratory crusher of the type disclosed in Australian patent specification 618545 (AU-B-19935/88). However, while the system will be described in large part with reference to a crusher of that type, it is to be understood that the system also has application to other types of gyratory crushers.

Australian patent specification 618545 teaches in relation to its gyratory crusher that, in the absence of any resistive force being applied to the head of the crusher during revolution of the same about the central axis, the head may rotate relative to the bowl and to a shaft by which gyratory motion is imparted to the head. It is further stated that when frangible or friable material is deposited into the crushing chamber defined by the bowl, and is received within the confines of the annular nip between the bowl and head, the material will tend to resist rotation of the head relative to the bowl.

When there is no frangible or friable material present in the crushing chamber, the heads of most gyratory crushers rotate relative to the bowl if they are not restrained. The heads of crushers which are mounted on and supported by commercial ball and roller bearings often rotate at virtually the same speed as the drive shaft gyrates. Such rotation is undesirable, since: (1) The head rotating needlessly is an avoidable danger to operators.

(2) The closest proximity of the crushing head to the bowl during operation of the crusher is called the closed side setting (CSS) and this determines the size of the resultant product (crushed material). The CSS is adjusted whenever necessary to maintain the size of the product within the desired limits. It is usual for the CSS to be audited by measurement periodically and in many crusher installations this is most conveniently done by lowering a soft deformable material such as lead, on a suspension wire, into the crushing chamber whilst the crusher is operating without feed. After it is crushed, the deformable material is withdrawn, by raising the suspension wire, and its thickness measured to determine the CSS. In other installations the deformable material can be dropped into the crushing chamber and recovered, for

measurement, from below the crusher. However, when the head is rotating at approximately the speed of gyration such auditing procedures are impossible. It is far too dangerous to lower a suspended item into the chamber and in any case the rotation distorts the deformable material making accurate CSS measurement impossible.

(3) If the head is rotating at approximately gyratory speed in an empty crushing chamber, the entry of new feed material is impeded and chamber wear is excessive. Firstly the new material is ejected by the centrifugal force transferred from the head. Secondly the head and bowl suffer premature gouging wear by the new material as the rotation inertia (energy) of the head is absorbed.

For these reasons the natural tendency of the head to rotate when the crusher is running with the crushing chamber empty is not acceptable to the industry. A head anti-rotation device is required.

Specific to its type of gyratory crusher, but also of relevance to others, Australian patent 618545 further teaches that, when a gyratory crusher is crushing frangible or friable material, there is often a slight circular inching of a point on the lower periphery of the head with respect to an adjacent point on the circumferential wall of the discharge opening in a clockwise or anti-clockwise direction during nutation (gyration) of the head. The circular inching (rotation) of the head cannot be resisted except by the application of a high restraining force, and it is not appropriate to restrain it because: a) the force is high and an adequate restraining device must be large and expensive, b) restraint will cause unnecessary gouging wear of the crushing head and bowl by the friable and frangible material, and c) normal wear of the crushing head and bowl is likely to be uneven, causing wear channels in the bowl and head which allow oversize product to pass through the crusher and mix with correctly crushed product, such that close control of crushed product grade is impossible.

It follows that a desirable crushing head anti-rotation device is required to apply adequate but minimal restraint to keep the head stationary, without rotation, when gyrating with the crushing chamber empty, and to permit slight rotation of the head relative to the bowl when crushing.

A suitable device for this purpose is provided by the system incorporated in the gyratory crusher disclosed in International patent application PCT/AU95/00489 (W096/04993), corresponding inter alia to Australian patent 684382 and U. S. patent 5,775,607 to Bayliss et al. In its broadest form, PCT/AU95/00489 discloses a gyratory crusher which includes a bowl defining a chamber for receiving material to be crushed, and further defining a discharge opening at the base thereof through which crushed material is able to discharge. The crusher also includes a crushing head mounted in the bowl at an offset position with respect to a central axis of the bowl, and a drive assembly for driving the crushing head within the bowl for imparting gyratory motion to the head about a gyratory axis inclined with respect to and intersecting the central axis. The arrangement is such that frangible or friable material received into the chamber is subjected to crushing between an inner peripheral surface of the bowl and an outer peripheral surface of the head by the gyratory motion of the head. The crusher further includes a system for restraining rotation of the head relative to the bowl and the gyratory axis, the system including : (i) an annular resilient member disposed between an annular lower peripheral region of the head and an annular surface, of a fixed structure of the crusher, which is spaced from and substantially co-axial with said region; (ii) securing means for securing a first edge of the resilient member to one of the annular region of the head and the annular surface of the fixed structure; (iii) an annular band of friction material provided around a second edge of the resilient member; and (iv) biasing means for urging the friction band into friction contact with the other one of the annular region of the head and the annular surface of the fixed structure.

In the system of that crusher, the biasing means is operable to provide a sufficient said friction contact to restrain the head from rotating relative to the bowl and gyratory axis while the head is gyrating in the absence in the chamber of material to be crushed, while allowing the head to rotate relative to the bowl and gyratory axis, during a crushing operation, by slippage between the friction material and the other one of the annular region of the head and the annular surface of the fixed structure.

It has been demonstrated that the benefits set out in PCT/A95/00489 are able to be achieved, and the gyratory crusher providing these has considerable commercial potential. Thus, the system of the crusher provides an effective restraint to undesirable crushing head rotation. Furthermore, the system provides an effective seal between the gyratory and stationary parts. That is, the system acts to seal lubricant required by the mechanism inside the crusher, while it also prevents the ingress of crushed product and other undesirable foreign contaminants from outside the crusher into the mechanism.

Figures 1 and 2 of PCT/AU95/00489 illustrate the embodiment considered to offer the greatest commercial potential. The reasons for this are that: (a) The arcuate clamps which combine to form clamping assembles 76 and 77 are independent of seal 70 so that seal 70 may be replaced as an individual item if worn or damaged. Clamping parts 74,90,92 and 93 are able to be reused to clamp the new (replacement) seal 70, reducing replacement part costs.

(b) Springs 97 are able to be set with the deflection and force required to restrain undesired head rotation and are static in this condition during the operation of the crusher. In this respect they are protected from metal fatigue which applies to springs that sustain variable deflection in service.

They are able to have a long and indefinite life. In this respect they are superior to those illustrated in Figure 3, item 178, of PCT/AU95/00489.

(c) It has been found that clamp part 93 can be manufactured from a material which provides the necessary clamping of seal 70 and also the appropriate friction between 93 and lower body part 18a. Thus the assembly can be made less costly by eliminating friction lining material 95 for some applications.

However, notwithstanding these reasons, there are problems with the system of PCT/AU95/00489 including the embodiment of its Figures 1 and 2. A first of these problems arises from the need for seal 70 to be made from a flexible material which will permit it to accept relative movement between the upper part and base part of the crusher without failure or distress. It is possible for suitable metals to be used, although the cost of such metal parts is a significant disadvantage. More economical suitable material has properties

most commonly found in oil resistant rubber and plastics such as PVC and polyurethane. For this reason rubber and plastic materials are preferred.

These materials accept distortion from clamping and are effectively fixed and retained by clamping. Clamping also creates a seal between the clamping and clamped parts. However, the extent of the clamping must be closely controlled to avoid overstressing the rubber or plastic and causing it to extrude from between the clamping surfaces. For this reason the clamp parts 74,90,92 and 93 must be arranged to come metal to metal or surface to surface contact in pairs to prevent further clamping or squeezing of the rubber or plastic. They need to be clamped in a way which provides the exact degree of clamping required whilst at the same time positively preventing excessive clamping.

They must be manufactured to close tolerance to achieve this result which makes them costly.

A second problem with the system of PCT/AU95/00489 arises from the need for the seals to be moulded to shape and provided with beads 72 and 73 for clamping. For this, the seals are formed in moulds and then cured by chemical or heat setting or vulcanising. The curing process causes shrinkage of the beads and the shrinkage is not completely uniform from one seal to another. Non-uniformity sometimes creates a problem when a seal cannot be adequately clamped or is excessively clamped by standard clamp parts.

The present invention seeks to provide a gyratory crusher which has an improved anti-rotation and sealing system that, at least in preferred forms, obviates or reduces the risk of these problems encountered with the system of PCT/AU95/00489. Also, at least in preferred forms, the system of a crusher according to the invention can enable a reduction in production costs and increased longevity in service.

According to the present invention, there is provided a gyratory crusher which includes a bowl defining a chamber for receiving material to be crushed, and further defining a discharge opening at the base thereof through which crushed material is able to discharge. The crusher also includes a crushing head mounted in the bowl at an offset position with respect to a central axis of the bowl, and a drive assembly for driving the crushing head within the bowl for imparting gyratory motion to the head about a gyratory axis inclined with respect to and intersecting the central axis. The arrangement is such that frangible or

friable material received into the chamber is subjected to crushing between an inner peripheral surface of the bowl and an outer peripheral surface of the head by the gyratory motion of the head. The crusher further includes a system for restraining rotation of the head relative to the bowl and the gyratory axis, the system including: (i) an annular resilient member disposed between an annular lower peripheral region of the head and an annular surface, of a fixed structure of the crusher, which is spaced from and substantially co-axial with said region; (ii) first clamping means encircling a first portion of the resilient member and clamping the first portion against a radially outwardly facing peripheral surface of the lower peripheral region of the head; (iii) second clamping means encircling a second portion of the resilient member and clamping the second portion against a radially outwardly facing peripheral surface of an annular plate mounted co-axially on the fixed structure of the crusher; and (iv) biasing means acting on the annular plate to bias it towards the fixed structure and thereby maintain friction contact between friction surfaces sufficient to restrain the head from rotating relative to the bowl and gyratory axis while the head is gyrating in the absence in the chamber of material to be crushed, while allowing the head to rotate relative to the bowl and the gyratory axis, during the crushing of material in the bowl to be crushed, by slippage between the friction surfaces.

One of the first portion of the resilient member and the radially outwardly facing peripheral surface of the head may define a circumferential bead, with the other one of the first portion and the surface defining a groove which is substantially complementary in radial cross-section to the radial cross-section of the bead. In each case, the first clamping means acts to clamp the first portion against the peripheral surface of the head to securely and sealingly clamp the bead in the groove. Most preferably the groove and the surface of the bead clamped against the surface of the groove are of substantially semi-circular form in radial cross-section. Preferably the first portion of the resilient member defines a radially inwardly facing bead and the radially outwardly facing peripheral surface of the head defines a radially outwardly opening groove.

One of the second portion of the resilient member and the radially outwardly facing peripheral surface of the plate may define a circumferential bead, with the other one of the second portion and the surface defining a groove which is substantially complementary in radial cross-section to the radial cross-section of the bead. In each case, the second clamping means acts to clamp the first portion against the peripheral surface of the plate to securely and sealingly clamp the bead in the groove. Most preferably the groove and the surface of the bead clamped against the surface of the groove are of substantially semi-circular form in radial cross-section. Preferably the second portion of the resilient member defines a radially inwardly facing bead and the radially outwardly facing peripheral surface of the plate defines a radially outwardly opening groove.

The first portion of the resilient member most preferably is at or adjacent to the upper peripheral edge of the member. The second portion of the resilient member may be at or adjacent to the lower edge of the member. However, it is preferred that the second portion is intermediate the upper and lower edges. In the latter case, the resilient member preferably defines a peripheral skirt between the second portion and the lower edge. Most preferably the skirt extends across the circumferential interface between the friction surfaces, with the skirt resiliently engaging the annular plate and the fixed structure, adjacent to that interface, to thereby provide a seal.

The resilient member most preferably is imperforate. It may, for example, be made of neoprene or similar material, and preferably is reinforced with woven or non-woven fabric. Where the resilient member is imperforate, it provides the benefit of effecting a circumferential seal between the head and the fixed structure. However, simply for the purpose of achieving necessary strength, the resilient member can be formed of a perforate material, with a seal being provided by other means such as a film or coating provided over the perforate material.

The biasing means preferably comprises a plurality of compression springs disposed in an angularly or circumferentially spaced array. Each spring may be mounted on a respective bolt which passes down through a pressure plate and is tightened into the fixed structure. The pressure plate overlies the inner periphery of the annular plate against which the second portion of the

resilient member is clamped. The springs are compressed by their bolts to apply pressure to the pressure plate, whereby the pressure plate biases the annular plate towards the fixed structure.

The friction surfaces in the crusher of the invention preferably comprise a lower surface of the annular plate and an opposed upwardly facing surface of the fixed structure. The annular plate may, for example, be of spheroidal cast iron. The graphite content of the plate preferably is able to act as a lubricant enabling the annular plate to be drawn by the resilient member so as to rotate with rotation of the head when the head is gyrating and crushing material in the chamber defined by the bowl.

In order that the invention may more readily be understood, reference now is directed to the accompanying drawings, in which: Figure 1 is a sectional view of a gyratory crusher having an anti-rotation system according to the prior art comprising the first embodiment shown in Figure 1 of PCT/AU95/00489; Figure 2 is similar to Figure 1, but shows on an enlarged scale, the prior art arrangement of the first illustrated embodiment of PCT/AU95/00489; Figure 3 is similar to Figure 1, but shows a gyratory crusher having an anti-rotation and sealing system according to the present invention; and Figure 4 is similar to Figure 3, but shows on an enlarged scale the anti- rotation and sealing system according to the present invention.

In the prior art arrangement of Figures 1 and 2, there is shown a gyratory crusher 10 which has an anti-rotation system 12. Much of the construction and operation of the crusher 10 readily will be understood. Accordingly only broad detail is provided in relation to features which are not directly concerned with the system 12.

The crusher 10 has a bowl 14 and a head 16. The bowl 14 is mounted on a fixed, bowl support frame 18. The bowl 14 is of circular transverse cross- section, and converges frusto-conically from its open upper end to a constriction at 20, and thereafter diverges frusto-conically to its open lower end. The head 16 also is circular in transverse section and comprises an inner bearing housing 22 on which a head liner 24 is secured, and a head cap 26. The liner 24 diverges slightly from its upper end to a region below the constriction 20, and thereafter flares downwardly and outwardly to provide a skirt portion 24a.

The crusher 10 includes an eccentric shaft 28 on which head 16 is rotatably mounted. The shaft 28 has a lower portion 28a which has an axis of rotation substantially co-incident with the axis of bowl 14, and which is rotatable in upper and lower bearing assemblies 30 and 30a. Each of the assemblies 30 and 30a is located in lower support frame 18a which can form part of the frame 18. The shaft 28 also has an upper portion 28b which has an axis which is inclined with respect to the axis of the shaft portion 28a, with the respective axes of the shaft portions 28a and 28b intersecting at a fixed point P which is on or closely adjacent to a basal plane of the head 16. That is, point P is so located relative to a plane containing the lower peripheral extremity of the skirt portion 24a. Mounting of the head 16 on shaft 28 is by means of an upper bearing assembly 32 and a lower bearing assembly 32a, with each of the assemblies being concentric with and provided between the upper shaft portion 28b and the housing 22 of the head 16.

Below the head cap 26, the interior of the head 16 is protected by a top seal 34 and a retaining plate 36. At the base of head 16, the interior of the head 16 and of sub-frame 18a is protected by a resilient annular seal provided by anti-rotation system 12.

The shaft 28 is driven by drive assembly 40, so as to rotate on the axis of its lower shaft portion 28a, utilising a drive motor (not shown). The assembly 40 has a drive shaft 42 mounted in support frame 18a by inner and outer bearing assemblies 44 and 44a. A pinion 46 is mounted on the inner end of the shaft 42, and meshes with a crown wheel 48 secured around portion 28a of the shaft 28. A pulley 50 on the outer end of the drive shaft 42 enables the shaft 42 to be rotated by operation of the motor, via drive belts (not shown), for rotation of the shaft 28.

In operation of the crusher 10, the drive assembly 40 rotates the shaft 28 on the axis of its lower portion 28a. As the axis of the upper shaft portion 28b is inclined to the axis of lower shaft portion 28a, and as head 16 is co-axially mounted on portion 28b, rotation of the shaft 28 on the axis of its lower portion 23a 28a causes head 16 to gyrate about the fixed point P. Moreover, as the lower end of head 16 is located proximate to, or coincident with point P, the gyratory motion of head 16 is such that movement of its upper end is

predominantly transverse to the axis of bowl 14 and such that movement of the lower end of head 16 is substantially parallel to the axis of bowl 14.

Material to be crushed is fed into the upper end of bowl 14 to a crushing chamber 60 defined within the bowl 14 around the head 16. The movement of the head 16, during rotation of the shaft 28, provides a crushing action in which, where the gap between the crushing surface 62 of bowl 14 and head 16 is a minimum at the upper end of the chamber 60, as shown for a representation of a particle of material to be crushed at location"A", the gap is: -a maximum at the diametrically opposed side of the upper end of chamber 60, -a maximum at the lower end of chamber 60 at the same side, i. e. directly below location A, and -a minimum at the lower end of chamber 60 at the diametrically opposed side, i. e. at the location"B".

Furthermore, as shaft 28 rotates, the gyratory motion of head 16 causes the location of the upper maximum and minimum gap openings, and of the lower minimum and maximum gap openings to be in successive diametrical planes of bowl 14. Thus, after rotation of shaft 28 through 180° from the position shown in Figure 1, there will be a maximum gap at each of locations A and B.

With further reference of the prior art of Figures 1 and 2, it will be noted that system 12 of the crusher 10 has an annular resilient seal 70, which has upper and lower peripheral beads 72 and 73. An upper clamping assembly 76 secures seal 70 in relation to surface 74 of the head 16, and a lower clamping assembly 77 secures seal 70 in relation to support frame 18a.

Assembly 76 simply comprises an annular clamp plate 90 which is retained on head 16 by bolts 91. The upper surface of plate 90 is grooved (as also is surface 74 of the head 16 if required) for locating bead 72 securely and sealingly against surface 74. Thus, with rotation of head 16 seal 70 is drawn by its bead 72 to rotate with head 16.

Clamping assembly 77 has upper and lower annular clamping plates 92 and 93 each grooved to locate bead 73. The plates 92 and 93 are secured together, to securely and sealingly hold bead 73, by bolts 94. Plate 92 has a larger internal diameter than plate 93 such that an inner margin of the top surface of plate 93 is thereby exposed. Also, bonded to the lower surface of

plate 93 there is an annular friction lining 95 which engages surface 75 of support frame 18a.

System 12 has an annular biasing plate 96 which has a stepped lower surface to define a lip 96a. Plate 96 fits radially within clamping assembly 77 but with lip 96a resting on the exposed top surface of plate 93. Additionally, a plurality of circumferentially spaced springs 97 are provided to apply pressure to biasing plate 96. As shown each spring 97 is secured in position and compressed by a respective bolt 98 which passes through a respective aperture in plate 96 and is threaded into support frame 18a.

Working of system 12 generally will be understood in the context of the preceding description. As will be appreciated, friction lining 95 is positioned for friction engagement with surface 75 of frame 18a such that, with any rotation of head 16 seal 70, each of assemblies 76 and 77 and hence lining 95 rotate with head 16. The springs 97 are arranged so that they compress lining 95 against surface 75, but without the need for the springs 97 to expand and compress as the head gyrates.

As upper bead 72 of seal 70 is clamped directly to surface 74 of the head 16, seal 70 is carried with head 16 in the event of slight circular inching of the latter.

The combined effect of all springs 97 is adequate to provide sufficient friction between lining 95 and the support frame 18a to prevent rotation of the head 16 when the head is gyrating with the crushing chamber 60 empty.

However the friction does not prevent the head 16 creeping around as frangible and friable materials are crushed.

The seal 70 excludes dirt, water and chemical and retains the lubricants.

It also prevents free rotation of the crushing head 16 by transferring the resistance generated at the friction surfaces of lining 95 and surface 75 to the crushing head 16.

In Figures 3 and 4, there is shown a gyratory crusher 110 which has an anti-rotation system 202 according to the present invention. For ease of reference, those parts of the crusher 110 of Figures 3 and 4 which are substantially the same as parts of crusher 10 of Figures 1 and 2 are designated by the same reference numeral, plus 100. A brief comparison of Figures 1 and 2 with Figures 3 and 4 will establish that the form and functioning of parts so

designated readily can be understood from the description of Figures 1 and 2.

Further description therefore principally is limited to features of the system 202.

System 202 of Figures 3 and 4 has an annular resilient seal 204 which has an upper peripheral bead 206 and a lower peripheral bead 207. The seal 204 is clamped, at its upper bead 206, in relation to the lower peripheral extent of head 116; while the seal 204 is clamped, at its lower bead 207, in relation to the peripheral extent of support frame 118a. In these broad, general terms, rather than as illustrated, seal 204 is similar to seal 70 of the prior art crusher of Figures 1 and 2 of PCT/AU95/00489. However, beyond this, there are important differences in seal 204, and also the manner of its securement at its respective beads 206 and 207.

Each bead 206 and 207 is somewhat, preferably substantially, semi- circular in cross-sections taken radially of the annular form of seal 204. The disposition of each of seals 206 and 207 is similar, to give rise to a respective convex inner peripheral surface 206a and 207a and a somewhat cylindrical outer surface.

To accommodate seal 204, a radially outwardly facing peripheral surface 116a, of the lower extent of head 116, is provided with a radially outwardly open groove 208. As seen most clearly in Figure 4, groove 208 has a cross-section complementary to that of bead 206, such that surface 206a of bead 206 is able to sealingly bear against the concave surface of groove 208. The respective peripheral extent of bead 206 and groove 208 preferably is such that a good surface to surface contact therebetween is able to be achieved around the periphery of head 116 due to the resilience of the material from which seal 204 is made. However, to retain seal 204 in relation to head 116, to provide necessary sealing therebetween and to enable torque transfer between parts of the crusher, bead 206 is clamped onto head 116. For this, an upper annular clamping element or ligament 210 is provided around the cylindrical outer surface of bead 206, and tightened so as to radially inwardly clamp bead 206 securely in groove 208.

System 202 includes an annular plate 212 which is secured to support frame 118a. It is at a radially outwardly facing peripheral surface 212a of plate 212 that seal 204 is clamped in relation to the peripheral extent of support frame 118a. The arrangement of clamping is similar to that provided for head 116.

Thus, the outer peripheral surface 212a of plate 212 is provided with a groove 209 which has a cross-section complementary to that of bead 207, such that surface 207a of bead 207 is able to sealingly bear against the concave surface of groove 209. The respective peripheral extent of bead 207 and groove 209 is such that, again, a good surface to surface contact is achieved therebetween, around plate 212, due to the resilience of the seal 204.

However, for the same reasons indicated for the provision of clamping element 210 around bead 206, a further clamping element 211 is provided around the cylindrical outer surface of bead 207 and tightened so as to radially inwardly clamp bead 207 securely in groove 209.

The plate 212 of system 202 is of a simple annular form with groove 209 formed in its outer surface. It is firmly biased downwardly towards an upwardly facing surface of support frame 118a by a plurality of circumferentially spaced springs 197 mounted on a stepped, annular pressure plate 196. An outer rim 196a of plate bears on the annular plate 212 to enable springs 197 to bias plate 212 into strong friction engagement with the upper surface of frame 118a. For this, a respective bolt 198 passes through each of a circumferential array of springs 197 and a hole through plate 196, inwardly of plate 212, and is threaded into support frame 118a so as to compress its spring 197 and thereby provide a biasing force acting on plate 212 through plate 196.

The plate 212 corresponds to the clamping assembly 77 of the prior art arrangement of Figures 1 and 2. In contrast to the simple form of plate 212, the assembly 77 comprises a top plate 92 and a wider bottom plate 93, with each plate configured to conform to bead 73 of seal 70 and the plates 92,93 secured together to clamp bead 73 by a plurality of bolts 94. Also, the assembly 77 necessitates an additional pressure plate 96 by which plates 92 and 93 are biased towards support frame 18a. Thus, system 202 is relatively simple, and enables substantial cost reductions in these regards relative to the prior art arrangement.

To a degree, system 202 achieves further cost savings by the manner of securement of bead 206 to head 116. Thus, in the case of the arrangement of the prior art of Figures 1 and 2, an annular clamping plate 90 is secured to head 16 by bolts 91, with opposed surfaces of head 16 and plate 90 configured to conform to bead 72 of seal 70 to enable bead 72 to be secured therebetween.

In contrast, the arrangement of the system 202 simply necessitates formation of radially outwardly opening groove 208 around head 116.

Manufacturing tolerances for bead 206 and groove 208, and for bead 207 and groove 209, can be considerably more liberal than for the components of the prior art arrangement.

The clamping elements 210 and 211 preferably comprise clamps of the type which is commonly referred to as a"worm drive hose clip". That is, it is comprised of a band of relatively inextensible material which is formed into a loop able to be varied in size by a worm drive acting between overlapping portions of the band. Such elements are able to be manufactured in a wide variety of sizes and materials. However other metallic and non-metallic bands, such as those sold under the trade mark"Bandit", also are able to be used. For example clamp garter springs can be used, as can a variety of circumferential wire and non-metallic bindings.

The system 202 of the invention further includes, as an integral part of seal 204, a circumferentially continuous skirt 214. The junction between plate 212 and support frame 118a is bridged by skirt 214, thereby providing a seal between their contacting surfaces. As will be appreciated, skirt 214 is able to be retained in sealing engagement by the resilience of the material of which seal 204 is made. Thus, skirt 214 provides an effective flashing and seal against fine solids and fluids which can otherwise intrude into the sealing space underneath plate 212. The intrusion of such foreign material would accelerate wear on plate 212 and support frame 118a. The foreign matter also would contaminates lubricant inside the crushing mechanism, reducing the life of parts of the crusher. Thus, skirt 214 enables the life of the crusher to be prolonge.

In the arrangement illustrated in Figures 3 and 4, there is direct metal-to- metal contact between the lower surface of plate 212 and the opposed, upper surface of support frame 118a. With appropriate compression of springs 197, appropriate friction engagement can be achieved between those surfaces.

Thus the friction engagement can be such as to restrain rotation of plate 212, and thereby restrain rotation of head 116 due to the action of resilient member 204 therebetween, when head 116 is gyrating with no feed material supplie chamber 160 defined within bowl 114. However, the friction engagement can

be such that plate 212 can be drawn by member 204, so as to rotate with head 116, when head 116 is gyrating for crushing of material present in chamber 160.

Graphitic cast iron has been found to be a suitable material for plate 212, with support frame 118a made of non-spheroidal or spheroidal cast iron or other suitable ferrous material. However, if required, a layer of material with a relatively high co-efficient of friction can be provided on one or each of the opposed surfaces of plate 212 and support frame 118a.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.