The present invention relates to a mineral sizer. According to the present invention there is provided a tooth construction for a mineral breaker having at least one breaker drum, the tooth construction including a cover portion for extending over a portion of the drum surface, a spigot for releasable retention in a complimentary pocket formed in the drum, and at least one breaker tooth protruding from said cover portion.

Reference is now made to the accompanying drawings, in which:-

Figure 1 is a schematic perspective view of a mineral sizer according to the present invention;

Figure 2 is a schematic axial section through a breaker drum according to the present invention; Figure 3 is a more detailed axial section through a pair of tooth support rings;

Figure 4 is a side view of a tooth support ring showing several teeth in position;

Figure 5 is a front view, partly in section, of one of the teeth shown in Figure 4;

Figure 6 is a side view of an alternative construction of tooth;

Figure 7 is a section along line VII-VII in Figure 6. Figure 8 is a view similar to Figure 4 showing a further embodiment according to the present invention;

Figures 9 and 10 are respective side views of different tooth shapes.

Referring initially to Figure 1 there is shown a mineral sizer 10 having a pair of breaker drums 14 which are in driving connection with one another for rotation in opposite directions. In the illustrated embodiment the drums are intended for rotation so" that the upper surfaces move away from one another so that material deposited on the drums is moved towards the sides of the mineral sizer. It will be

appreciated that, if desired, the drums 14 may rotate in the opposite fashion so that their upper surfaces move toward one another so that material is fed between the drums.

Each drum 14 is provided with a plurality of teeth 16

5 which are arranged in longitudinally extending rows 17, preferably each row extending along the drum to define a discrete helical formation (for example passing through 90 along the length of the drum). The rows 17 may, if desired, extend linearly along the drum and be substantially parallel

_] _0 to the axis of rotation.

The teeth 16 each include a cover portion 16a which together with the cover portions l6a_ of other teeth serve to totally cover the outer surface of each breaker drum 14 and thereby provide a wear resistant shroud.

3_5 The teeth 16 are releasably mounted in each drum 14 so that in the event of breakage, broken teeth can be easily replaced.

The releasable mounting of teeth 16 can be clearly seen in Figures 2, 3 and 4. Each tooth 16 is provided with a

20 spigot 18 which, in use, seats in a pocket 19 formed in a breaker drum 14. There are close tolerances in the dimensions of the spigot 18 and pocket 19 so that the spigot 18 is a close fit within the pocket 19. The length of the spigot 18 and depth of the pocket 19 are chosen so that the

25 length of abutting faces 20 is sufficient to accommodate the working loadings. Additionally, the longitudinal axis of each pocket is offset but parallel to a radius so that the trailing face 20a_ of each pocket forms an acute angles with the periphery of the drum. Such an arrangement helps the

30 teeth to accommodate working loadings and resist withdrawal of the spigot during use by said working loadings.

In order to provide resistance to withdrawal of the spigot 18 of a tooth from a pocket, the spigot is provided with a resiliently deformable projection 25 which extends 5 into a groove 26 when the spigot 18 is fully inserted into the pocket. Conveniently the projection 25 is made of a resilient plastics material such as polyurethane. The

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projection 25 is preferably made hollow a shown so as to facilitate inward deformation of the projection when the spigot 18 is forced into the pocket 19. To facilitate insertion without damage to the projection the mouth of the pocket is provided with a chamfered edge 27.

As shown in Figure 4 the leading face l6b_ of each tooth is provided with a rebate 16£ which receives the rearward marginal portion I6d_ of the cover portion l6a_ of the preceding tooth (in the direction of rotation of the drum). Accordingly when all teeth in a circumferential group of teeth are inserted into the drum, the overlapping nature of the teeth serves to restrain withdrawal of teeth from the drum, particularly if the drum is rotated in the opposite direction to which it normally runs for sizing, as for instance when attempting to clear a blockage.

In order to enable removal of teeth within a circumferential group, at least one tooth (not shown) is provided which has a cover portion 16a which does not enter the rebate of the succeeding tooth 16, for instance the cover portion 16a. may be provided with a recess. This tooth is withdrawn first and then successive teeth (in the direction of normal rotation of the drum) may then be removed.

An alternative construction for interlocking neighbouring teeth is illustrated in Figure 8 wherein the rebate 16 is replaced by a projecting lug l6f_ which has a curved face I6g. The lug l6_f extends over the width of the tooth. The rearmost edge of the neighbouring tooth cover portion is provided with a complimentary recess l6h_ which , in use, overlaps the lug I6f_. In use, when a tooth engages mineral to be broken, a turning force is created which tends to urge the rearmost edge of each cover portion toward the periphery of the drum. Accordingly, during use, recess I6h_ is urged into contact with the lug l6f and thereby discourages ingress of dirt particles. This is advantageous since ingress of dirt particles could encourage a given tooth to lift away from the drum and thereby run the danger of the tooth pulling out of the pocket 19 during use.

In order to lock the teeth in a given annulus to one another, in the embodiment of Figure 8 one of the teeth is omitted and replaced by a locking member 60. The locking member 60 includes a cover portion I6a_ and spigot 18 and also includes a plate 61 which overlaps a neighbouring cover portion I6a_. The plate 61 includes a recessed bore 63 through which passes a bolt 64 which is threadedly received in a threaded bore formed in the cover portion of the preceding tooth. Accordingly, the locking member 60 is positively locked in position to one tooth construction and interlocks with the other one so that it has to be removed before any of the teeth forming the annulus can be removed. In the embodiment in Figure 8, the shape of pocket 19 and spigot 18 is changed from having a circular terminal end to having a flattened shape. The resilient projection 25 is also positioned further away from the terminal end. The change in shape is advantageous in that it provides a greater thickness and thereby strength of material between the terminal end of the pocket and the internal periphery of the drum. The change in position of the projection 25 is advantageous as it enables a greater length of the spigot to be inserted into the pocket before the projection 25 enters. This stabilises the tooth construction during insertion and thereby facilitates its insertion. The teeth shown in Figures 4 and 5 are conveniently made in one piece from a suitable material bearing in mind the type of material to be sized.

An alternative construction of tooth is illustrated in Figures 6 and 7 which is basically a tooth constructed from two components viz. a spigot 40 and a tooth portion 41.

Such a construction enables different materials to be adopted for the spigot 40 and tooth portion 41. In this respect the tooth can be designed to cope with a wide variety of materials which are to be sized e.g. the spigot 40 can be made from a material which can withstand high shear loadings whilst the material of the tooth portion 41 may be chosen so as to have good wear characteristics.

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In the tooth construction illustrated in Figures 6 and 7 the upper portion of spigot 40 is received in a pocket 42 formed within the tooth portion 41. Preferably the upper portion of spigot 40 is a tight fit within the pocket 42, for instance the tooth portion 41 is heat expanded and then contracted onto the spigot.

The tooth portion 41 and spigot are formed so as to define pockets 43 which are filled with a suitable weld. Additionally, apertures 44 may be provided which also provide sites for welding the tooth portion 41 to the spigot 40.

The pockets 19 in each drum 14 are preferably provided by assembling each drum from a series of tooth support rings 30 which have a series of recesses or slots formed in one face and an annular groove 26 formed in the opposite face. Accordingly, when rings 30 are in abutment, pockets 19 are formed. The rings 30 are keyed onto a shaft 35 and the angular position of the key ways on different rings is indexed in relation to the slots so as to provide the desired degree of offsetting between adjacent teeth in a longitudinal group of teeth to provide the longitudinal group with the desired helix.

Preferably, one face of each ring is provided with a shallow chamfer 38 so as to enable a wedge to be forced between adjacent rings for facilitating separation of rings. In the illustrated embodiment, the rings are prevented from axial displacement by being held in abutment between a shoulder 39 formed on the shaft 35 and a removable collar 37.

It is envisaged that the tooth portion of teeth 16 may be shaped as desired to cope with different requirements in sizing. For instance, the tooth portion may be divided to provide two or more separate teeth for each spigot.

By way of illustration, a tooth construction is illustrated in Figure 9 wherein two teeth 16£ of different heights are provided on a cover portion l6t. The difference in heights of the teeth is desirable in certain circumstances in order to create agitation of the mineral being broken. In Figure 10, a plurality of teeth 16k are provided on the cover

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portion. These teeth may be arranged in one or more circumferentially extending rows on each cover portion. Such a construction enables a high density of teeth to be provided on the surface of the drum. Each cover portion is provided with a protrusion 16m which enters a recess l6n of a succeeding tooth when in use.

It has been found that the mode of mounting a tooth in a breaker drum as described above is particularly suitable for sizing of material to below 2 inches, although obviously larger sizing may be achieved if desired.

In the tooth construction illustrated in Figures 4, 6, 9 and 10 the cover 16a extends rearwardly from its associated tooth portion toward the succeeding tooth construction in order to cover the portion of the drum lying therebetween. It is envisaged that the cover portion could terminate adjacent to the rearward end of the tooth portion and project forwardly therefrom toward the preceding tooth construction.

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