FIELD OF THE INVENTION

The present invention relates generally to a tip holder assembly for use in a mineral crushing mill and relates particularly, though not exclusively, to a tip holder assembly for use in a centrifugal mineral crushing mill having a rotor to which the tip holder assembly is coupled.

BACKGROUND TO THE INVENTION

A known centrifugal mineral crushing mill such as that described in Australian Patent No. 557168 comprises a rotor axially mounted within a housing, the housing defining a series of rock boxes and a crushing chamber. Mineral fed axially to the rotor is accelerated and flung from the rotor so as to impact upon itself and with mineral cascading through the rock boxes and crushing chamber of the crushing mill. Thus, the crushing of mineral iε largely effected by collisions between minerals rather than minerals colliding with components of the crushing mill.

This produces both a relatively fine mineral product of good shape, and significantly reduces wear on the crushing mill.

In the various known mills there are from between two (2) to six (6) main tip holders each equally spaced circumferentially about the rotor and coupled to the rotor via a backup tip holder. Typically, both the main and backup tip holders include a recess with a tungsten carbide wear tip seated therein. A stream of mineral exiting the rotor flows across the wear tip which serves to maximise the life of the tip holder. However, after extended periods of use the main and/or backup tip holders must be replaced. Under particularly aggressive and severe operating conditions one or more of the tip holders may require frequent replacement.

There are currently two (2) tip holder designs, namely a "bolt-in" and a "drop-in" design. With the "bolt-in" design, the backup tip holder is welded to the rotor and sandwiched between the main tip holder and a tip carrier wear plate. This "bolt-in" design has at least the following problems:

(i) the tip carrier plate and/or backup tip holder can break free from the rotor resulting in significant downtime; (ii) in operation mineral "streams" are created along top and bottom edges of the main tip holder adjacent top and bottom rotor plates, respectively, leading to premature rotor failure; and (iii) for replacement of the main tip holder, the rotor must be substantially cleared of mineral and the bolts connecting the tip holder to the rotor accessed from inside the crushing chamber which is particularly cumbersome and time consuming.

With a view to alleviating the above problems the "drop-in" design is configured to locate in a socket formed in the top and bottom rotor plates. A releasable ring is then used to secure the main tip holders to the rotor so that they do not dislodge from the sockets. The main tip holders are thus said to "drop-in" to the rotor through the top rotor plate. Top and bottom wear plates fixed to the top and bottom rotor plates, respectively, "wrap around" each end of the main tip holders. This "drop-in" design does not include tip carrier wear plates and the onset of

"streaming" is eliminated because of the top and bottom wear plates.

However, a large number of crushing mills only provide access to the rotor from the side of the mill and for this type of mill the "drop-in" design is not appropriate. Furthermore both tip holder designs are relatively time consuming to replace taking from anywhere between 20

minutes to k hour to replace a set of three (3) tip holders . Various tip holders, such as that described in Australian patent application no. 52770/93 have been designed with a view to extending the life of the tip holders. Australian patent application no. 52770/93 describes a tip holder design including two (2) or more tungsten carbide tips, namely a main tungsten tip and backup tungsten tips. Having more than one (1) tungsten carbide tip is intended to extend the operating life of the tip holder. However, with this design the entire tip holder must be replaced when only the main tungsten tip may have worn, even though the backup tungsten tip(s) show little wear. In this respect this tip holder design is unnecessarily expensive, tungsten carbide tips being relatively expensive.

SUMMARY OF THE INVENTION

An intention of the present invention is to provide a tip holder assembly, for use in a mineral crushing mill, which in use is relatively effective and inexpensive to maintain.

According to the present invention there is provided a tip holder assembly for use in a mineral crushing mill including a rotor, said assembly comprising: a central tip holder designed to couple to the rotor in a relatively high-wear zone of the rotor, the central tip holder having a first recess adapted to fixedly receive a first abrasion resistant insert which is contactable by mineral to be crushed; and a pair of end tip holders configured to couple to the rotor, each located adjacent opposite sides of the central tip holder in a side-to-side relationship, said pair of end tip holders located in a relatively low-wear zone of the rotor, and each of said pair of end tip holders including a second recess adapted to fixedly receive a second abrasion resistant insert which is also contactable by said mineral so that, in use, when the central tip

holder or first insert is excessively worn following repeated collisions with minerals, said central tip holder together with its first abrasion resistant insert can be replaced independent of the pair of end tip holders together with their second abrasion resistant inserts.

Typically, the central tip holder is substantially trapezium-shaped and coupled to the rotor so that, in use, opposing non-parallel sides of the central tip holder diverge in the general direction of rotation of the rotor wherein the centrifugal force created by rotation of the rotor forces and locks the central tip holder into location between the pair of end tip holders. Preferably, each of the pair of end tip holders includes an engaging side being shaped substantially complementary to and, in use, abutting one of the non-parallel sides of the central tip holder.

Preferably, the non-parallel sides of the central tip holder are defined by a pair of first raked surfaces which diverge in a direction toward a connecting surface of the rotor to which said central tip holder couples wherein each of the first raked surfaces is at least partly lapped by and locked-in behind the engaging side of each end tip holder, respectively.

Typically, each of the pair of end tip holders is also substantially trapezium-shaped so that with the central tip holder located between the pair of end tip holders, parallel sides of both the central tip holder and the pair of end tip holders are substantially aligned.

Typically, the first and second recesses each comprise an elongate channel formed in the central and end tip holders, respectively. Preferably, the first and second recesses are formed between a mineral retaining surface and a mineral contacting surface of the respective holders, a flow of mineral exiting the rotor across the mineral

contacting surface and thereafter impacting upon itself and with mineral cascading through the crushing mill thereby breaking or fracturing said minerals. Preferably, the first and second recesses are substantially aligned when the central tip holder is coupled to the rotor between the pair of end tip holders.

Advantageously, the central tip holder and pair of end tip holders abut thereby defining a join line which is at an acute angle relative to the general direction of the flow of mineral exiting the rotor thereby minimising the likelihood of mineral streaming within the mill.

Typically, the central tip holder and pair of end tip holders are coupled to the rotor via a backup tip holder, said backup tip holder fixed to the connecting surface of the rotor. Preferably, the backup tip holder includes a third recess capable of fixedly receiving a third abrasion resistant insert designed to be contactable by mineral should the central or end tip holders wear excessively. Typically, the third recess is an elongate channel formed in the backup tip holder so as to extend substantially parallel to the first and second recesses formed in the central and end tip holders, respectively.

Typically, the pair of end tip holders are each coupled to the backup tip holder by one or more bolts, screws, or pins. In this example, the backup tip holder is either welded or bolted to the rotor. Alternatively, the pair of end tip holders seat in sockets formed in a rotor top and bottom plate, respectively.

Typically, the central tip holder includes a threaded hole designed to receive a bolt or screw which when tightened forces the pair of first raked surfaces of the central tip holder against the engaging side of each of said end tip holders. Alternatively, the central tip holder is held in

location between said end tip holders solely by the centrifugal force imparted on the central tip holder by rotation of the rotor. Typically, the engaging side of each of the end tip holders is defined by a second raked surface shaped and profiled substantially complementary to the first raked surfaces. In one example the first and second raked surfaces are constructed of a hardened material wherein wear between said surfaces is substantially minimised.

Preferably, the first, second, and/or third abrasion resistant inserts are constructed from a tungsten carbide alloy. Typically, the central, end, and/or backup tip holders are constructed from a ferrous material, such as a quenched and tempered steel or equivalent cast material.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a tip holder assembly will now be described in some detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a rear view of a tip holder assembly together with a backup tip holder;

Figure 2 is a front, rear and side view of the central tip holder shown in Figure 1; Figure 3 is a top, front and rear view of the pair of end tip holders shown in Figure 1;

Figure 4 is a top, front and side view of the backup tip holder shown in Figure 1; and

Figure 5 is a perspective view of the end tip holders and backup tip holder shown in Figure 1 detached from each other.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As shown in Figure 1 there is tip holder assembly shown generally as 10 comprising a central tip holder 12 and a

pair of end tip holders 14A, 14B respectively. The central tip holder 12 is shown removed from the pair of end tip holders 14A, 14B which are located on a backup tip holder 16. The tip holder assembly 10 together with the backup tip holder 16 is designed to couple to a rotor of a mineral crushing mill (not illustrated) .

As best illustrated in Figure 2 the central tip holder 12 is substantially trapezium-shaped having a connecting portion 18 and a head portion 20 formed integral therewith. The central tip holder 12 also includes a first recess 22 formed in the head portion 20, said recess 22 designed to fixedly receive a complementary-shaped first abrasion resistant insert 24. The first recess 22 is an elongate channel being shaped rectangular in cross-section.

Opposing non-parallel sides of the central tip holder are defined by a pair of first raked surfaces 26A, 26B. The connecting portion 24, being in the form of a plate, has a front connecting surface 28 and a rear surface 30. The head portion 20 includes a step 32 defined by first and second mineral retaining surfaces 34, 36, respectively, located adjacent and at an obtuse angle relative to each other. The first recess 22 is substantially parallel to the first mineral retaining surface 34. The head portion 20 further includes a first and second mineral contacting surface 38, 40, respectively, also located adjacent and at an obtuse angle relative to each other. The first mineral contacting surfaces 38, 40 extend from the first recess 22 and the rear surface 30 of the connecting portion 24, respectively. Finally, the connecting portion 24 includes a threaded and countersunk hole 42 formed therein.

With reference to Figure 3 the pair of end tip holders 14A, 14B are also substantially trapezium-shaped. One of the non-parallel sides of each end tip holder 14A, 14B is defined by a second raked surface 46A, 46B respectively.

In this embodiment, the first and second raked surfaces 26, 46, respectively, are shaped substantially complementary to each other (see Figure 1) . Each of the end tip holders 14A, 14B has a second recess 48A, 48B formed as a longitudinal channel of rectangular cross-section in the end tip holder 14A, 14B. A second abrasion resistant insert 50A, 50B is fixedly received within each of the second recesses 48A, 48B.

Each of the end tip holders 14A, 14B has a mounting portion 52A, 52B, being in the form of a plate, formed integral with a head portion 54A, 54B. Each mounting portion 52A, 52B has a pair of countersunk holes 55A, 55B for connecting the end tip holders 14A, 14B to the backup tip holder 16. The mounting portion 52A, 52B of each end tip holder 14A, 14B has a front mounting surface 56A, 56B and a back surface 58A, 58B. The head portion 54A, 54B of each end tip holder 14A, 14B in cross-section is shaped substantially identical to the head portion 20 of the central tip holder 12. Thus, the head portion 54A, 54B of the end tip holders 14A, 14B each include a pair of both mineral retaining and mineral contacting surfaces.

Figure 4 illustrates the backup tip holder 16 to which the tip holder assembly 10 is connected. The backup tip holder 16 is generally rectangular shaped with a rebate 60 formed along a longitudinal side thereof. A third recess 62 is machined in the backup tip 16 adjacent the rebate 60. A third abrasion resistant tip 64 is fixedly received in the third recess 62 being square in cross-section. The backup tip holder 16 has a mineral retaining surface 66 and a mineral contacting surface 68 extending from opposite sides, respectively, of the third recess 62. A longitudinal side of the backup tip holder 16 has a rectangular-shaped cut-out portion 69 positioned for ease of removal of the central tip holder 12. Four (4) locating holes 70A, 70B, 70C, 70D are machined in the backup tip

holder 16, these holes 70 positioned so as to align with the corresponding countersunk holes 55A, 55B of the end tip holders 14A, 14B (refer to Figure 5) .

As depicted in Figure 1, with the end tip holders 14A, 14B connected to the backup tip holder 16, the central tip holder 12 can be wedged or forced between the end tip holders 14A, 14B. The end tip holders 14A, 14B and central tip holder 12 thus locate in a side-to-side relationship with complementary first and second raked surfaces 26, 46 abutting each other. A bolt, screw or pin arrangement may be used to either force out to the abutting surfaces 26, 46 or to secure to the backup tip holder 16.

In this configuration parallel sides of the central tip holder 12 and the end tip holders 14A, 14B are substantially in line. The first and second abrasion resistant inserts 24 and 50 of the central and end tip holders 12 and 14, respectively, also substantially align with the tip holder assembly 10 connected to the backup tip 16. Advantageously, the abrasion resistant inserts 24, 50 where they adjoin define a join line which is at an acute angle relative to the general direction of flow of mineral from the rotor. This is believed to significantly reduce the likelihood of mineral "streaming" within the crushing mill.

It is envisaged that the first and second raked surfaces 26 and 46 will be hardened using an appropriate metallurgical technique wherein wear between the surfaces 26, 46 is minimised. In this example, the central, end, and backup tip holders 12, 14, and 16 are constructed from a ferrous material, such as a quenched and tempered steel or equivalent cast material. Typically, the abrasion resistant inserts will be made from a tungsten carbide alloy. However, it will be appreciated that the invention is not limited to these materials of construction and

extend to any material which is suitable in operation within a crushing mill.

The tip holder assembly 10 is appropriate for attachment to either "bolt-on" or "drop-in" rotor designs of the known configuration. The tip holder assembly 10 is located between top and bottom rotor plates so that the central tip holder 12 is positioned in a relatively high-wear zone of the rotor. The end tip holders 14A, 14B are positioned within a relatively low-wear zone of the rotor. In operation, rotation of the rotor forces the central tip holder 12 into location between the pair of end tip holders 14A, 14B due to the centrifugal force imparted on the central tip holder 12. Thus, it may not be necessary for the central tip holder 12 to be screwed or bolted against the end tip holders 14A, 14B as described above. Rather, the central tip holder 12 may be held in location solely by the centrifugal force imparted thereon.

When the central tip holder 12 and its abrasion resistant insert 24 has excessively worn, the central tip holder 12 can be removed by releasing it from between the end tip holders 14A, 14B. This is achieved by applying pressure to or knocking the central tip holder 12 away from abutting raked surfaces 26, 46 in the direction of rotation of the rotor. This is a relatively quick procedure wherein it may only be necessary to release the screw which engages the central tip holder 12. The cut-out portion 69 formed in the backup tip holder 16 allows the central tip holder 12 to be knocked clear from the end tip holders 14A, 14B with relative ease. Because the central tip holder 12 is located in a high-wear zone of the rotor it will wear to a greater extent and thus require replacement more often than the end tip holders 14A, 14B. Removal of the central tip holder 12 in the manner described above, can be performed in-situ without necessarily having to also remove the end tip holders 14A, 14B.

Now that a preferred embodiment of the present invention has been described it will be apparent to persons skilled in the relevant arts that the tip holder assembly has at least the following advantages over the admitted prior art: (i) the central tip holder of the tip holder assembly can be changed independent of the end tip holders thereby minimising cost where previously an entire main tip holder would need to be replaced;

(ii) the central tip holder can expeditiously be removed from the rotor minimising down time; and

(iii) the tip holder assembly is designed so that "streaming" and other phenomena which lead to high wear and premature failure of rotor components are substantially eliminated.

It will be appreciated that the tip holder assembly is not limited to the embodiment described herein but rather is susceptible to numerous variations and modifications all of which are to be considered within the scope of the present invention. For example, the central and end tip holders may be shaped in a variety of ways to suit the application and preferably to maximise their life in operation. Furthermore, the invention is not restricted to the coupling arrangements described herein but may include welding or rigid fixing of various components, such as the backup and/or end tip holders. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.