Field of the Invention

[0001] This invention relates to crushing apparatus for frangible or friable material.

Background Art

[0002] Australian Patent No. 618545 relates to a suspended shaft gyratory crusher comprising a bowl having a chamber for receiving material to be crushed with the bowl having a central discharge opening at its base. A crushing head, with a gyratory axis, is disposed generally centrally within the discharge opening having a crushing space spaced from the wall of a throat to define an annular nip. The crushing head is driven by a drive assembly to permit rotational and oscillatory motion of the crushing head about a pivot point to crush material to a finer particle size.

[0003] Crushers of gyratory type have until recently proved successful, for example, in iron ore mining operations. However, market conditions in extractive industries such as iron ore are dynamic and customer demand for ores of various types can change. Iron ore, for example, is available in fine and lump ore sizes. As indicated by the terminology, these iron ore types vary in both particle size and, sometimes, iron oxide content.

[0004] As customers have sought lump ore, of a greater particle size, the previously described gyratory crusher has met operational challenges with failures becoming more frequent and material throughput falling. Indeed, the challenges have risen to the point that customer preference for the previously described crusher is falling and focus on possible substitutes has increased with concern that the gyratory crusher, for example as described in Australian Patent No. 618545 amongst others is fundamentally unsuitable for the application. This discussion is not intended to indicate limitation of potential problems to the iron ore sector, the problems would also occur for other ore types, for example in the base metal sector. Analogous problems could also be expected in other mineral resource sectors. [0005] Solution to the excessive crusher failure problem must engage with various issues. For example, whatever the ore size, the crusher must have a limited footprint/packaging volume to integrate with existing structural engineering constraints, particularly where used for sampling purposes and must also integrate with other related equipment to allow in-situ sampling performance (i.e. whilst the bulk material is being conveyed) to occur. As capital cost is always a significant constraint in resource operations, it is an inadequate solution to propose an alternative in which a material requires secondary/further crushing, than currently available, before being directed to a gyratory crusher for use in sampling; or an alternative crusher design solution that has a mass increase and that requires substantial support infrastructure.

Summary of the Invention

[0006] It is an object of the present invention to address the maintenance problems with existing gyratory crushers as encountered by customers caused by inadequate crusher performance specifications and capability, especially when seeking to handle larger dimensional ore sizes.

[0007] With this object in view, the present invention provides a crushing apparatus for frangible or friable material comprising: a bowl having a chamber for receiving said material and a discharge opening disposed at the base thereof, said discharge opening defining a throat having a circumferential wall and the bowl having a central axis; a crushing head disposed within said discharge opening having a crushing face in spaced relation to said circumferential wall of said throat defining a nip between said circumferential wall and the crushing face of said crushing head, said crushing head having a gyratory axis extending at an angle to the central axis; and a drive assembly including a transmission and a rotatable eccentric shaft for driving said crushing head within said bowl and about said gyratory axis in a nutating motion wherein said bowl comprises feed and discharge sections, each defined by a wall and spaced by a mid-section of said bowl also defined by a wall, wherein thickness of said wall defining at least the mid-section of said bowl is greater than thickness of the wall of the discharge section. [0008] The wall of the feed section of the bowl may have approximately the same thickness as the wall of the discharge section of the bowl. Outer and inner surfaces of each of the respective feed wall and discharge wall, are conveniently both circular (resulting in cylindrical feed and discharge sections) and, conveniently, concentric. A convenient bowl cavity configuration comprises two intersecting frusto-conical portions, defined by the mid section wall, the first frusto-conical portion forming the upper portion of the bowl and tapering in a downward direction, desirably at an angle of between 30 and 35 degrees from the central axis. The second frusto-conical portion, forming the lower portion of the bowl, tapers in a downward direction. The thickest section of the walls of the bowl, being the wall of the mid-section, conveniently aligns with a plane at which the first and second frusto- conical portions intersect, desirably about the mid depth of the bowl. In such case, the bowl cavity cross sectional area is least on this plane. The plane also conveniently extends along the transverse central axis of the bowl. The outer surface of the bowl is desirably generally smooth and not provided with a webbed configuration to avoid compromising bending strength. The wall of the mid-section preferably comprises solid material with a wedge shaped or triangular section with an apex of this section located about the middle of the depth of the bowl. The wedge section preferably has a scalene or obtuse triangle shape, with one side corresponding with an inner wall of the upper portion of the bowl and another side corresponding with an inner wall of the lower portion of the bowl, this latter side having lesser length. The increased bending strength is associated with an increase in crushing efficiency.

[0009] In a preferred embodiment, the crusher head includes a head liner or mantle - of wear resistant material - and, advantageously, the head liner comprises two parallel vertically extending side walls (conveniently of a cylindrical portion of the head liner and so providing the head liner with a substantially cylindrical shape) joined at the top by a crown portion. The parallel vertically extending side walls of the head liner may also be formed integral with a lower frusto-conical crushing face. The parallel geometry assists in reducing or avoiding problems of material ejection from the crusher bowl, a problem associated with reduced crushing efficiency. The wall of the crown portion preferably has greatest thickness of the above defined portions of the head liner; in particular, in the portion where the crown portion transitions to the parallel side walls of the head liner. This wall thickness may taper downward along the parallel side walls and crushing face of the head liner or mantle as a consequence of reduced stress profile in these portions compared to the crown portion. The crown portion may promote some fragmentation of material fed to the crusher. [0010] Conveniently, part of an adjusting means for adjusting height of the bowl may be located in the mid-section wall in a manner not achieved with the prior art crusher. A convenient adjusting means includes a plurality of boss holes spaced around the perimeter of the mid-section and located within spaced apertures arranged circumferentially about, and partly through, the mid-section. Bolts co-operate with a clamp or like means that can be worked to rotate the bowl and adjust its height, desirably in co-operation with the threaded portion of the bowl as described below.

[0011] The crusher conveniently includes a housing, known as a base spider, for supporting the crusher and accommodating the drive assembly and a lubrication system. The bowl, which is conveniently a replaceable component which may be supplied separately, is connected to the base spider by suitable means which may include a combination of fasteners, such as bolts, sufficient to maintain a secure connection during operation of the crusher. Conveniently, an outer wall of the discharge section of the bowl may be threaded enabling a threaded connection to be made with a threaded aperture of the spider. Such threaded connection may have a plurality of threads selected to allow height adjustment for the bowl in combination with use of the bolts of the adjusting means described above. The spider may be connected to a frame or other surface through a flange or plate.

[0012] The crusher conveniently includes a discrete feed portion through which material is preferably gravity fed to the bowl. The feed portion could form part of the bowl but a separate feed chute is conveniently disposed above the bowl and connected to the bowl by suitable fastening means. The feed portion, whether provided as a chute or not, conveniently includes an elevated vertical section with walls preferably slightly angled to the longitudinal central axis to direct feed material in desired direction towards the crusher nip. Advantageously, the head liner or mantle is confined within the bowl and feed chute with the crown portion extending a short distance into the feed chute. This feature assists in reducing or avoiding the problem of material, especially lump, ejection. [0013] The drive assembly prime mover may include an electric motor or engine for providing power to the rotatable eccentric shaft through a drive assembly or powertrain including a transmission system conveniently located at a base of the crusher. The rotatable eccentric shaft is connected to an output shaft of the transmission system, the input shaft of the transmission system being rotated by a suitable drive such as a belt drive linking an output shaft of the prime mover and the input shaft of the transmission system through a pulley or gear arrangement. Rotation of the head liner is prevented, conveniently by bearing arrangement(s) between the eccentric shaft and head liner, from causing rotation of the head liner. Rather, the crusher head liner is caused to move in a gyratory or nutating motion about the gyratory axis without the head liner itself rotating about the eccentric shaft.

[0014] Components of the crusher are conveniently available, in further embodiments of the invention, as separate replaceable components. So, for example, the feed chute and bowl - as described above - may both be replaced as part of routine or breakdown maintenance.

[0015] Where a feed chute is provided as a separate replaceable component, The feed chute - as described above - conveniently includes an elevated vertical section with walls preferably slightly angled to the longitudinal central axis, as above described, to direct choke feed material in desired direction towards the crusher nip and improve material charge area.

[0016] Other components of the crusher are likewise replaceable during maintenance which is preferably provided on a regular, scheduled basis to minimise risk of failure during service.

[0017] The crusher, as above described, can crush feed of a higher particle size (e.g +60%) than previous gyratory crushers supplied by the Applicant with minimised risk of failure and a higher degree of availability and utilisation while minimising power requirements for a given crushing pressure; these advantages being achieved within the same overall packaging size as compared to previous gyratory crushers. In this regard, the preferred substantially cylindrical geometry of the head liner with its parallel vertical sides - together with the extension of the crown portion a short distance into the feed chute - has the consequence that the head liner is confined within the bowl cavity and the feed chute effectively lowering the crush zone and essentially avoiding lump ejection and the inefficient crushing that results from that. At the same time, the crusher can be accommodated within the same ground or floor space as available for earlier crushers, making retrofit a straightforward task. Description of Preferred Embodiments

[0018] The crushing apparatus of the invention will be better understood in view of the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:

[0019] Figure 1a is a schematic side section elevation of a prior art gyratory crusher.

[0020] Figure 1b is an orthogonal view of the gyratory crusher of Figure 1a.

[0021] Figure 2 is an orthogonal view of a gyratory crusher according to one embodiment of the present invention.

[0022] Figure 3 is a detailed side section of the gyratory crusher of Figure 2.

[0023] Figure 4 is a partial orthogonal view of a crusher being a further embodiment of the crusher of the present invention.

Figure 4a is a schematic side section of an upper portion of the crusher showing bowl, feed chute, crushing head and rotating shaft in operative condition. [0024] Figure 5 is an orthogonal schematic side section of an upper portion of the crusher showing bowl, feed chute, crushing head and rotating shaft in operative condition.

[0025] Figure 6 is an orthogonal schematic side section of an upper portion of the crusher similar to Figure 5 and showing the rotating shaft in section.

[0026] Figure 7 is a top view of the bowl shown in Figures 4 to 6.

[0027] Figure 8 is a side view of the bowl shown in Figures 4 to 7.

[0028] Figure 9 is a side section view of the bowl shown in Figures 4 to 8.

[0029] Figure 10 is an orthogonal view of the feed chute shown in Figures 4a to 6.

[0030] Figure 11 is a side section view of the feed chute shown in Figures 4a to 6 and

10.

[0031] Figure 12 is a side section view of the feed chute shown in Figures 4a to 6, 10 and 11 .

[0032] Figure 13 is a side view of the crushing head shown in Figures 4 to 6.

[0033] Figure 14 is a side section view of the crushing head shown in Figures 4 to 6 and 13. [0034] Figure 15 is a side view of the rotating shaft of the crusher as shown in Figures 4a to 6.

[0035] Figure 16 is a side section view of the rotating shaft of the crusher as shown in Figures 4a to 6 and 15.

[0036] Referring to Figures 1a and 1b, there is shown a prior art gyratory crusher 1 for crushing iron ore samples having a crushing head 2 connected to a rotatable eccentric shaft 3 by a roller bearing assembly 3a disposed within the cavity of a bowl 4. Eccentric shaft 3 extends in the direction of a gyratory axis 1a disposed at an angle from a centre axis 1a of the crusher 1 which also corresponds with a centre axis (or axis of symmetry) of bowl 4.

[0037] Crushing head 2, which is symmetrical about gyratory axis 1a, comprises a bell or frusto-conically shaped wear resistant head liner or mantle 2a bolted to a hub or bearing housing 2b by circumferentially spaced bolts 2c. Head liner 2a, having a lower frusto-conical crushing face 2d of relatively substantial dimension relative to the dimensions of head liner and a smaller crown portion 2aa joining side portions 2e from each other which diverge at a small angle, is bolted to a rotating hub 2b by circumferentially spaced bolts 2c. Crown portion 2aa has a near constant thickness.

[0038] Bowl cavity 4a has a feed section 4b including an upper flange 4ba and a discharge section 4d separated by a mid-section 4c which includes circumferential wall 4k. As apparent from Figure 1 , the wall thickness throughout the sections 4b-d of bowl 4 is approximately constant. The bowl has a webbed outer wall and webs 4e, which are spaced about the perimeter of bowl 4, are shown in Figure 1b.

[0039] Bowl 4 has a threaded section 4da of the discharge section 4d connected with a housing, known as a base spider, 5 by circumferentially arranged bolts 35 extending through bolt holes 47 and into bolt holes of the spider 5. This ensures a secure connection during crushing. Spider 5 supports bowl 4 and accommodates a drive assembly 6 for transmitting power from a prime mover, such as an engine through a transmission 6a to rotate the eccentric shaft 3. Spider 5 has, as shown in Figure 1a, a base flange 9 connected by bolts, inserted through bolt holes 9a located at the corners of the base flange 9, to an iron ore processing plant floor/frame.

[0040] As to operation of crusher 1 , the eccentric shaft 3 is connected to a crown gear 6b driven by an output gear 6c connected to the output shaft 6d of the transmission 6. Output shaft 6d is connected to a pulley 6e driven by a belt (not shown). The bottom end of eccentric shaft 3 is journalled in a bottom bearing arrangement 7 connected with a lubricant system including an oil pump 8. When crown gear or eccentric 6b rotates, the eccentric shaft 3 rotates and, through connection of the eccentric shaft 3 to the bearing housing or hub 2b of crusher head 2 and head liner 2a through suitable bearing arrangements as known in the art, the crushing head 2 to which it is connected is caused to gyrate or nutate within bowl cavity 4a. The gyration causes the head liner 2a to progressively approach, and recede from, circumferential wall 4k on a cyclical basis, each cycle representing an oscillation of crusher head 2. As the head liner 2a approaches the circumferential wall 4k, material of higher dimension than the nip size between the two is progressively crushed, through both action of the crusher head 2 and autogenous action between particles of material, and directed downward into discharge chamber 5a of spider 5.

[0041] Crusher 1 performs well for smaller iron ore sizes, with size below about 40- 50mm. However, failure has occurred frequently and at unacceptably short intervals as iron ore sizes increase beyond the 40-50mm level. As a result, users of crusher 1 have been forced to look for other sample crusher options. Failure occurs predominantly in the crown 2aa of head liner 2a along the horizontal plane at the top of bowl 4 with bogging of the crusher 1 also being a potential issue at higher lump ore particle sizes. Another problem, correlated with the divergent sides 2e of head liner 2a, is ejection of lumps from crusher 1 which reduces efficiency whilst still causing wear on the head liner 2a.

[0042] Referring to Figures 2 and 3, there is shown a crusher 10 again for crushing lump iron ore (though crusher 10 may be applied to other crushing of ores and other friable materials). Crusher 10 may be used for sample crushing applications though this is not intended to be limiting on potential applications as it will be understood that gyratory crushers can have high throughput and can be used in production applications.

[0043] Crusher 10 has an upper portion 10A comprising a bowl 104 having a chamber 104a for receiving a lump iron ore feed and a discharge opening 104j disposed at its base. Discharge opening 104j defines a throat having a circumferential wall 104k. Bowl 104 may be provided as shown in Figures 2 and 3 with a substantially smooth cylindrical outer surface at its mid-section wall 104c or, as shown in Figures 4 to 9, with circumferentially arranged dimples 104g with boss holes 104h useful to engage with a tool for adjusting the height of the bowl 104 relative to the base spider 105, and nip dimension, as described below.

[0044] Bowl 104 comprises feed and discharge walls 104b and 104d, spaced by a mid section wall 104c, wherein thickness of the mid-section wall 104c is greater than thickness of the feed and discharge walls 104b and 104d respectively. Surprisingly, the thickness of the wall of the feed and mid-sections - and corresponding bending strength - needs to be greater than in the discharge section of the bowl 104 despite significant cyclic impacts during crushing. The wall of the mid-section 104c is a solid wedge or triangular shaped section, more specifically having the shape of a scalene triangle.

[0045] Referring further to the configuration of the bowl cavity 104a, this comprises two intersecting frusto-conical portions, each defined by mid-section wall 104c, the first portion forming a feed chamber 104m of the bowl 104a and tapering, from a greater dimension and at a greater acute angle (32 degrees cf. 21 degrees to the central axis) than for bowl cavity 4a of crusher 1 , in a downward direction. The second portion, forming a crushing chamber 104n of the bowl, tapers in a downward direction. The thickest section of the wall of the bowl 104a aligns with a plane A, along a transverse central axis of the bowl 104a, at which the first and second portions, or the feed and crushing chambers 104m, 104n, intersect. Bowl cavity 104a cross sectional area is least on this plane.

[0046] The feed wall 104b of the bowl 104 has approximately the same thickness as a lower portion 104da of the discharge section 104d of the bowl 104. The outer surfaces of the wall at both the feed section 104a and at lower discharge portion 104da are substantially cylindrical and symmetric or co-centric about central axis 101a. The outside of the bowl 104 is smooth and not, unlike crusher 1 shown in Figures 1 and 2, provided with a webbed configuration to avoid compromising bending strength. Despite the greater bending strength, failure will still occur after a certain number of crushing oscillations or cycles. To this end, bowl 104 is a replaceable component which may be supplied separately for installation as part of a repair or preventative maintenance programme.

[0047] A crushing head 102, as shown in Figures 2 to 6, is disposed within the discharge opening 104j of bowl cavity 104a. A gyratory axis 101a extends along the eccentric shaft 103 at an angle (about 2 degrees) to the central axis 101b. As with crushing head 2, crushing head 102, which is symmetrical about gyratory axis 1a, comprises a wear resistant head liner or mantle 102a bolted to a hub 102b by circumferentially spaced bolts 102c inserted through bolt holes 102ca as shown in Figures 13 and 14.

[0048] Head liner 102a has a lower frusto-conical crushing face 102d integrally formed with a cylindrical portion 102e having a crown 102aa, these portions of the head liner 102a defining a hollow bore 102f for accommodating crusher head bearing housing 102. The wall of the crown 102aa is thickest (e.g. 5-6mm) at the portions 102ab where crown 102aa transitions to cylindrical portion 102e, this thickness tapering down towards the bottom of the head liner 102a as a consequence of reduced stress profile in cylindrical portion 102e and crushing face 102d compared to the crown portion 102aa. The crown portion 102aa therefore has a structure that assists fragmentation of material. It will be seen that, unlike the divergent walls 2e of head liner 2a, the vertically extending side walls of cylindrical portion 102e are substantially parallel along their length providing a substantially cylindrical shape for the head liner 102a. This results in a slight but, as will be described below important increase, in the working volume of bowl cavity 104a and crusher 10.

[0049] Crushing face 102d is disposed in spaced relation to circumferential wall 104k to define an annular nip of cyclically variant dimension typical of gyratory crushers. The arrangement is such that iron ore, or other frangible or friable material, fed into the bowl cavity 104a is subjected to crushing by the motion of the crushing head 102 relative to circumferential wall 104k, with opposite sides of the crushing head 102 co operating with a lower face of the circumferential wall 104k of the throat to maintain the gap of the nip during an entire oscillation of the crushing head 102.

[0050] Rotatable eccentric shaft 103 is journalled within a roller bearing assembly 103d, disposed within the bore of crusher head bearing housing 102b as shown in Figure 3. Eccentric shaft 103, shown in detail in Figures 3 to 6, 15 and 16, comprises three integrally formed portions of 4140 steel with tensile strength of about 925 MPa: mid portion 103a, upper portion 103b and lower portion 103c. This has substantially higher (e.g 46%) tensile stress than the eccentric shaft 3 of crusher 1. The mid-portion 103a is cylindrical and has greatest diameter of the three portions. Upper portion 103a comprises a frusto-conical section and a cylindrical section, both extending away at an angle from a longitudinal central axis of the eccentric shaft (which aligns with the longitudinal central axis 101a of crusher 10) along the gyratory axis 101 b. The drawings exaggerate this angle, which is about 2 degrees. Both upper portion 103b and lower portion 103c have cylindrical portions which are journalled into respective roller bearing assemblies 103d and 107. These require lubrication by oil pumped from oil pump 108, including through oil duct 103e extending through eccentric shaft 103. Roller bearing assemblies 103d, together with the seal 103f allow the eccentric shaft 103 to rotate without causing rotation of the crusher head 102. Rather, the crusher head 102 including head liner 102a is caused to nutate or gyrate about the gyratory axis 101a during operation of crusher 10 with progressive crushing resulting.

[0051] Bowl discharge section 104d has a threaded section 104da threadably connected with a complementary threaded bore of a housing, known as a base spider,

105. Connection also involves circumferentially arranged bolts 45 extending through bolt holes 47 of a flange 104ba engaged with the bowl 104 and into bolt holes of the spider 105. This ensures a secure connection during crushing. Base spider 105 supports bowl 104 and accommodates a drive assembly 106 of a powertrain for transmitting power from a prime mover, such as an engine through a transmission 106a to rotate the eccentric shaft 103, the bottom end of which, as with the top end, is journalled in a bottom roller bearing arrangement 107. Spider 105 also accommodates the oil pump of a lubrication system 108 which is connected to roller bearing arrangement 107. [0052] Base spider 105 has, as shown in Figures 2 and 4, a base flange 109 connected by bolts (not shown), inserted through bolt holes 109a (as shown in Figure 2) located at the corners of the base flange 109, to an iron ore processing plant frame/floor. It will be observed that the area of base flange 109 is the same as base flange 9 for crusher 1 . This illustrates both a design constraint and an advantage of crusher 10 in that, in replacing crusher 1 with benefits as described above and further below, no further floor space is required and retrofitting is straightforward.

[0053] The crusher 10 desirably includes, as shown in Figs. 4a to 6, a feed chute 106 connected to the bowl 104 and base spider 105, through which material is gravity fed to the bowl 104, preferably as a choke feed as understood in the crushing art. Feed chute 106, as shown in detail in Figures 10 to 12, includes respective upper and lower flanges 106a and 106c formed integral an to elevated vertical section with walls 106b slightly angled to the vertical, at angle a, to direct feed material in desired direction towards the crusher nip and to improve iron ore charge area or the charge area for other crusher feed materials. Flange 106a has bolt holes 106ba which enable the same bolts 45, as used to connect the bowl 104 with the base spider 105, to secure the feed chute 106 to the bowl 104 and - indirectly - the base spider 105. It will be seen that head liner 102a is confined within the bowl 104 and feed chute 106 with the crown 102aa extending a short distance into the feed chute 106. The result is a lowered crushing zone in comparison to the crushing zone of crusher 1.

[0054] As to constructional details of the powertrain and operation of crusher 10, the eccentric shaft 103 is connected to a powertrain including a crown gear 106b driven by an output gear 106c connected to the output shaft 106d of the transmission 106. Output shaft 106d is connected to a pulley 106e driven by a belt drive (not shown). When crown gear or eccentric 106b rotates, the eccentric shaft 103 and the crusher head 102 to which it is connected by bearing arrangements as used in crusher 1 is caused to nutate or gyrate within bowl cavity 104a. The gyration causes the head liner 102a to progressively approach, and recede from, a lower face of circumferential wall 104k on a cyclical basis, each cycle representing an oscillation of crusher head 102. As the crushing face 102d of head liner or mantle 102a approaches the circumferential wall 104k, material of higher dimension than the nip size between the two is crushed and directed downward into discharge chamber 105a of base spider 105. [0055] The nip of crusher 10 can be adjusted by inserting bolts of a tool such as a G clamp or like means (not shown) into, say a pair, of boss holes 104h of dimples 104g. Torque is then applied to rotate the bowl 104 using the threaded connection as described. Adjustment of the height of bowl 104 adjusts the nip dimension.

[0056] The crusher 10, as above described, can crush feed of a higher particle size (+60%) than previous gyratory crushers supplied by the Applicant with minimised risk of failure and higher efficiency, for example 9% or higher. At the same time, the crusher 10 can be accommodated within the same space as available for earlier crushers, making retrofitting a straightforward task. Operating performance of crusher 10 in comparison to crusher 1 is tabulated below for an iron ore having 80% passing 25mm:

• 17% 25-60 mm

• 2% 60-70mm

• 1% greater than 70mm for two months of operation as respectively shown in Tables 1 and 2:

Table 1

Table 2 [0057] As to reasons for the improved performance in terms of availability, reduced downtime and more efficient utilisation including lower power consumption for given maximum crushing pressure, finite element analysis conducted for both types of crusher showed less stress penetration into the mid-section of the crusher 10 during crushing, including the mid-section of head liner 102a and bowl mid-section wall 104c due to the greater thickness and bending strength of the mid-section 104c. Tensile stress of the crown 102aa of head liner 102a was, at 300 MPa, lower than for the crown 2aa of crusher 1 with the consequence of longer service life to failure. By way of example, tensile stress was reduced at various ore sizes as follows:

• 45% reduction in head liner 102a tensile stress for 25mm ore size;

• 67% reduction in head liner 102a tensile stress for 55mm ore size; and

• 53% reduction in head liner 102a tensile stress for 70mm ore size compared to the 55mm ore size.

[0058] At the same time, the geometry of the head liner or mantle 102a with its parallel vertically extending sides in cylindrical portion 102e - together with the extension of the crown 102aa a short distance into the feed chute 106 with the consequence that the head liner 102a is confined within the bowl cavity 104a and the feed chute 106 - essentially avoids lump ejection and the inefficient crushing that results from that.

[0059] Benefits of the crusher 10, as above described include:

• < 80mm feed acceptance;

• Increased head liner thickness and strength;

• Reduced fatigue;

• Improved service life expectancy; and

• Installation compatibility with dimensionally identical installation parameters (packaging) to the prior art crusher 1 with the exception of a small (for example 25 mm height increase).

[0060] Modifications and variations to the crushing apparatus as described here may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present invention.