Patent Publication Number: US-7708219-B2

Title: Mineral breaker

Description:
The present invention relates to a mineral breaker having a plurality of side-by-side breaker drum assemblies. 
   The kind of mineral breaker with which the present invention is particularly concerned functions to break down mineral lumps by a snapping action; see for example the mineral breaker described in our European patent no. 0 167 178 and our PCT patent application no. PCT/GB2004/004665. 
   This type of mineral breaker includes a pair of breaker drum assemblies, each of which includes a plurality of axially spaced annuli having on them circumferentially spaced breaker teeth. The annuli on one of the breaker drum assemblies are axially off-set from the annuli on the other of the breaker drum assemblies such that the breaker teeth of one annulus on one of the breaker drum assemblies pass in-between breaker teeth on a pair of neighbouring annuli on the other of the breaker drum assemblies. 
   With this type of mineral breaker, the breaker teeth interact to restrict the passageway in-between the breaker drum assemblies such that oversized lumps of mineral are prevented from passing therethrough. 
   Typically infill material being deposited onto the mineral breaker will contain a high proportion of fines and undersized lumps of mineral. Passage of this undersized mineral between the breaker drum assemblies affects the handling capacity of the mineral breaker (i.e. rate per hour of deposit of material into/through the mineral breaker). 
   Ideally, the lateral spacing between the adjacent breaker drum assemblies should be sufficiently narrow to restrict the passage of oversized lumps, but to facilitate rapid passage of undersized mineral therebetween. 
   In addition, the presence of oversized lumps is undesirable as they also act to restrict rapid passage of the undersized mineral through the mineral breaker. 
   A general object of the present invention is to provide a mineral breaker of the type described above, which has a high throughput capacity. 
   According to an aspect of the invention, there is provided a mineral breaker including a row of side-by-side breaker drum assemblies having radially projecting breaker teeth, the row including at least four breaker drum assemblies arranged to define an inner pair of adjacent breaker drum assemblies located in-between a pair of outer breaker drum assemblies, said inner pair of breaker drum assemblies defining therebetween a mineral deposit region for receiving mineral in-flow, the breaker drum assemblies of said inner pair of breaker drum assemblies being rotated in opposite directions such that, in use, breaker teeth on each of said inner breaker drum assemblies act upon mineral being deposited in said deposit region to cause agitation of the deposited mineral in-flow in order to encourage undersized mineral to pass therebetween whilst preventing oversized mineral passing therebetween, and each breaker drum assembly of said inner pair of breaker drum assemblies acting upon oversized mineral in the material in-flow to cause the oversized mineral to be moved outwardly towards a respective one of said outer breaker drum assemblies. 

   
     Embodiments of the present invention are hereinafter described, by way of non-limiting example, with reference to the accompanying drawings in which: 
       FIG. 1  is a plan view of a mineral breaker according to a first embodiment of the present invention; 
       FIG. 2  is a side view of the mineral breaker shown in  FIG. 1 ; 
       FIG. 3  is an end view of the mineral breaker shown in  FIG. 1 ; 
       FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 2 ; 
       FIG. 5  is a part cross-sectional view taken along the line II-II in  FIG. 1 ; 
       FIG. 6  is a sectional view along the line II-II shown in perspective; 
       FIG. 7  is a perspective view from above of a breaker bar assembly; 
       FIG. 8  is a view similar to  FIG. 7  showing the breaker teeth removed; 
       FIG. 9  is a schematic end view illustrating the relative rotational positions of a pair of opposed toothed annuli; 
       FIG. 10  is a part plan view of a breaker unit of the mineral breaker shown in  FIG. 1 ; 
       FIG. 11  is an axial section through a pair of adjacent toothed annuli mounted on a shaft; 
       FIG. 12  is a perspective view of a toothed annulus of the breaker unit shown in  FIG. 10 ; 
       FIG. 13  is a plan view of a breaker drum assembly assembled from toothed annuli according to a further embodiment of the present invention; 
       FIG. 14  is an axial section through the breaker drum assembly of  FIG. 13 ; and 
       FIG. 15  is a cross-sectional view similar to  FIG. 4  of a mineral breaker according to a yet further embodiment of the present invention. 
   

   A mineral breaker  10  according to a first embodiment of the present invention is illustrated in  FIGS. 1 to 14 . 
   The mineral breaker  10  includes a pair of breaker units BU, which are located side by side on a support frame  12 . The support frame  12  is preferably constructed from a pair of opposed front and rear beams  14  (the front beam not being visible) and a pair of opposed side beams  16 ,  18 . 
   The beams are secured end to end to define a generally rectangular support frame  12 . The bottom surface  20  of the support frame  12  would, in use, be seated on the infrastructure of a conveyor unit (not shown). Preferably each beam is fabricated from steel plate. 
   Each breaker unit BU includes a drum casing  22  having a pair of end walls  24 ,  26  and a side wall  28 . 
   Preferably, each breaker unit BU includes a pair of side-by-side contra-rotating breaker drum assemblies  30  rotatably mounted in the drum casing  22  so as to extend longitudinally from one end wall  24  to the other end wall  26 . Each breaker drum assembly  30  is preferably driven independent by an individual motor  92  via a gear box  94 . Preferably, each motor  92  is an electric motor. However, it will be appreciated that other forms of motor, such as a fluid motor, may be used. 
   Each breaker drum assembly  30  includes a shaft  32 , which is rotatably mounted at opposite ends in the respective end walls  24 ,  26  via bearings. The shaft  32  is preferably of solid section, and is preferably formed from a suitable steel. 
   Each breaker drum assembly  30  further includes a plurality of toothed annuli  34  of disc-like form. As shown in  FIG. 12 , each toothed annulus  34  includes an annular boss  36  from which a plurality of teeth  38  radially project; the teeth  38  per se defining breaker teeth. 
   Preferably, the annular boss  36  and breaker teeth  38  are formed in one-piece such that the toothed annulus  34  is of a unitary construction with the breaker teeth  38  being integrally connected with the annular boss  36 . 
   Each breaker tooth  38  has a leading face  38   F , which extends upwards from the outer circumferential periphery of the annular boss  36  to a tooth tip T, and a trailing face  38   T  which extends downwards from the tooth tip T to merge with the leading face  38   F  of the succeeding breaker tooth  38 . There is thereby defined a series of material accommodating pockets P on each toothed annulus  34 , each pocket P being defined between the leading face  38   F  of one breaker tooth  38  and the trailing face  38   T  of the preceding breaker tooth  38 . 
   Preferably, each toothed annulus  34  is located on the shaft  32 , and is fixedly secured thereto by welding, as will be described below. 
   One advantage of fixedly securing the toothed annuli  34  to the shaft  32  by welding is the avoidance of keyways both in the toothed annuli  34  and the shaft  32 . This avoids localised stress weakness in both the toothed annuli  34  and the shaft  32  that would otherwise be created by the provision of keyways, and also enables the difference in the diameter size of the annular boss  36  and the shaft  32  to be relatively small; in other words, a relatively large diameter shaft  32  can be accommodated in a given diameter size of toothed annulus  34 . This has the significant advantage of enabling a relatively large diameter shaft  32  to be used, which thereby enables a relatively large amount of torque or load to be transmitted to the breaker teeth  38 . 
   As shown, by way of illustration in  FIG. 5 , the ratio of the diameter D S  of the shaft  32  relative to the diameter D A  of the toothed annulus  34  is about 1:2.2, and the ratio of the radial height H T  of the tooth tip T of one of the breaker teeth  38  (as measured from the periphery of the shaft  32 ) to the diameter D S  of the shaft  32  is about 1:1.6. 
   In other words, the tooth height H T  is greater than the radius of the shaft  32 . 
   In the breaker unit shown in  FIGS. 5 to 12 , each toothed annulus  34  is a casting or a forging formed from a metal capable of being welded to the shaft  32 . 
   As shown in  FIG. 12 , all of the breaker teeth  38  are arranged in a single row, which extends circumferentially around the annular boss  36 , and are equally spaced about the circumference of the annular boss  36 . In the illustrated embodiment, there are five breaker teeth  38  in the row. It is to be appreciated however that the number of breaker teeth  38  in the row may be in the range of 3 to 8 breaker teeth. 
   To enable the toothed annulus  34  to be received on the shaft  32 , the annular boss  36  is provided with a through bore  40 . The diameter of the bore  40  is the same as the external diameter of the shaft  32 . To enable the toothed annulus  34  to positively seat upon the shaft  32 , without rocking (caused by slight differences of size due to tolerances of manufacture), the inner wall  42  of the annular boss  36 , which defines the bore  40 , is preferably provided with an annular recess  44  to thereby define two axially spaced apart raised annular seats  46  of relatively short axial extent. Accordingly, the toothed annulus  34  seats upon the shaft  32  only via the axially spaced annular seats  46 . 
   As illustrated more clearly in  FIG. 12 , to fixedly secure the toothed annuli  34  to the shaft  32 , adjacent toothed annuli  34  are spaced apart along the length of the shaft  32  such that opposed axial end faces  48 ,  50  of neighbouring toothed annuli  34  define a gap therebetween with a circumferential portion of the shaft  32  being exposed by the gap. In other words, adjacent toothed annuli  34  are spaced axially apart such that an open topped annular channel is formed therebetween in which the opposed sides of the channel are defined by opposed axial end faces  48 ,  50 , and the bottom of the channel is defined by the exposed circumferential portion of the shaft  32 . The channel defines a welding receptor and enables each end face  48 ,  50  to be welded to the exposed portion of the shaft  32 ; in practice this means that the channel is filled with weld  52 , which is preferably machined to define a smooth solid top face  54  for the channel. 
   As indicated above, the toothed annuli  34  are of disc-like form (i.e. the axial dimension of each toothed annulus relative to its diameter is small, and the row of breaker teeth on each toothed annulus have substantially planar side faces, which collectively define substantially planar axial side faces of a disc). Accordingly, by arranging the toothed annuli  34  side by side on the shaft  32 , a series of annular channels R along the breaker drum assembly  30  are formed, the sides R S1 , R S2  of each channel R being defined by facing axial side faces of each pair of neighbouring toothed annuli  34 , and the bottom R B  of the channel R being defined collectively by the outer circumferential face of the annular bosses  36  and top faces  54 . 
   The effective working height h of each breaker tooth  38  is the height of its tip T above the bottom R B  of the neighbouring channel R, and hereinafter the effective working height h of each breaker tooth  38  will be referred to as the “drum height” of the breaker tooth  38 . 
   The drum height h of each breaker tooth  38  is necessarily less than the height H T  due to the intermediate provision of the annular boss  36 , which is required for securing the breaker teeth  38  to the shaft  32  (as well as providing a protective covering for the shaft  32 ). Accordingly, the smaller the radial thickness of the annular boss  36 , the greater the possible drum height h of the breaker teeth  38 . 
   As indicated above, welding of the annular boss  36  directed to the shaft  32  enables the radial thickness of the annular boss  36  to be kept to a minimum, and so this capability can be utilized to maximize the drum height h of the breaker teeth  38 . 
   This is advantageous as it enables relatively tall breaker teeth  38  to be provided and so provides the mineral breaker with the capability of gripping large mineral lumps contained in the in-flow mineral. 
   Preferably, the rotary position of a given toothed annulus  34  relative to its neighbour is off-set by a predetermined increment such that the breaker teeth  38  on the toothed annuli  34  on a given shaft  32  extend along a predetermined helical path in order to define a series of discrete scrolls of breaker teeth, as described in our European patent no. 0 167 178. 
   In the breaker unit BU shown, the increment by which adjacent toothed annuli  34  are off-set is such that the starting point of each discrete scroll at one end of the breaker drum assembly  30  is off-set from the finishing point of the scroll at the other end of the breaker drum assembly  30  by an angular distance equivalent to two teeth pitch spacings between breaker teeth  38 . In the illustrated embodiment, the angular off-set increment between adjacent toothed annuli  34  is 6°. 
   An alternative toothed annulus  56  is illustrated in  FIGS. 13 and 14 . Parts similar to those described earlier with reference to  FIGS. 5 to 12  have been designated by the same reference numerals. 
   The toothed annulus  56 , instead of being a metal forging or casting, is formed from a suitable metal plate, preferably by profile cutting. Forming the toothed annulus  56  from metal plate has several advantages including ease and consistency of manufacture and improved breaking performance of the breaker teeth derived from the absence of forging/casting faults within the metal grain structure. 
   The tooth annulus  56  includes a through bore  58  to enable it to be slid onto the shaft  32 . Adjacent tooth annuli  56  are spaced apart, preferably by an intermediate spacing ring  60 . The intermediate spacing ring  60  is axially spaced from the toothed annuli  56  between which it is located in order to define an open topped annular channel therebetween, which acts as a welding receptor for weld  52 . Accordingly toothed annuli  56  are weldingly secured to the shaft  32  in a similar manner to the toothed annuli  34  described with reference to  FIGS. 5 to 12 . 
   In  FIGS. 13 and 14 , the outer circumferential face of the spacing rings  60  and the top face  54  of the weld  52  collectively define the channel bottom R B . 
   One aim of the breaker unit BU is to break down relatively large lumps of mineral to relatively small lumps of mineral. For example, a breaker unit BU having a distance of 625 mm between the axes of the breaker drum assemblies  30  is expected to be capable of breaking down lumps of about 0.6 m 3  down to lumps having a maximum dimension of about 150 mm. 
   In order for the breaker unit BU to be capable of gripping relatively large lumps of mineral, it is necessary for the drum height h of the breaker teeth relative to the outer diameter of the toothed annulus to be relatively large. This is illustrated diagrammatically in  FIG. 9  where the breaker unit includes breaker drum assemblies  30  having axes of rotation separated by a distance of about 625 mm and toothed annuli having an outer diameter of about 780 mm, each breaker tooth having a drum height h of about 175 mm as measured from the outer diameter of the annular boss  36  (which defines the recess bottom R B ) and the tip T of the breaker tooth  38 . 
   With such an arrangement, the gap  62  defined between the tips of two opposed breaker teeth  38  is shown as having a width W of about 625 mm and a depth d of about 160 mm (the depth d being defined as the height of the tip of a breaker tooth above the bottom of the gap  62 , as defined by the trailing faces  38   T  of the preceding breaker tooth  38 ). In other words, gap  62  enables relatively large lumps of mineral to be grippingly received between opposed breaker teeth  38  to permit a primary breaking action to be performed on the mineral lump, in accordance with the principles of breaking discussed in our European patent no. 0 167 178. 
   In the above example, the ratio of the drum height h of a breaker tooth  38  relative to the radius of the toothed annulus  34 ,  56  is approximately 1:2.2. 
   It is envisaged however that the ratio of the drum height h of a breaker tooth  38  relative to the radius of the toothed annulus  34 ,  56  may be varied in order to achieve different sizes of gap  62 . 
   In this respect, it is expected that this ratio will be in the range of about 1:2.5 to 1:1.5. 
   In order to achieve a relatively small size of broken lump emerging from the breaker unit BU, it is necessary for the axial dimension of channel R between adjacent tooth annuli  34 ,  56  to be relatively small, which also requires the width w t  of the breaker teeth  38  to be relatively small and preferably be of a width dimension which is less than a maximum dimension of the desired broken lumps to be achieved. 
   In the breaker unit BU illustrated in  FIG. 9 , the maximum width w t  of each breaker tooth  38  at its base is chosen to be about 85 mm, with the breaker tooth  38  tapering to its tip T, which has a width of approximately 27 mm. In the embodiment of  FIG. 10 , the plate thickness from which the toothed annuli  56  are cut is about 70 mm. 
   With such an arrangement, each breaker tooth  38  on one breaker drum assembly  30  acts to break lumps down by a snapping action by forcing mineral lumps downwardly through the channel R defined between two adjacent breaker teeth  38  on the opposed breaker drum assembly  30 . 
   As seen in  FIG. 10 , the dimensions of each channel R in the longitudinal direction of the breaker drum assemblies  30  will determine the maximum size dimension of the broken lump in the longitudinal direction of the breaker unit BU. 
   Preferably, the relative cross-sectional size and shape of each breaker tooth  38  and the channel R through which it sweeps during rotation of the breaker drum assemblies  30  are such that at least the leading and trailing faces  38   F ,  38   T  (and preferably the side faces of each breaker tooth  38 ) are closely spaced with the side of the channel R. This helps to ensure that material passing between the breaker drum assemblies  30  predominantly has to be passed through the pockets P in-between adjacent breaker teeth  38  on a given toothed annulus  34 ,  56  rather than being allowed to pass through gaps between a toothed annulus and the sides/bottom of a channel R in which it is located. 
   With the above arrangement, it will be appreciated that a mineral lump seated in the pocket P between two adjacent breaker teeth  38  on the same toothed annulus  34 ,  56  may have a dimension in excess of the desired maximum lump dimension in the direction of rotation of the toothed annulus  34 ,  56  after a breaker tooth  38  has forced the lump through the channel R on the opposed breaker drum assembly  30 . 
   In order to ensure that such a lump is broken down further, the breaker unit BU preferably includes a breaker bar assembly  64  located beneath the breaker drum assemblies  30 . The provision of the breaker bar assembly  64  also ensures that long thin lumps of mineral, extending longitudinally of the breaker drum assemblies  30 , cannot pass through without being broken down. 
   The breaker bar assembly  64  illustrated in  FIGS. 7 and 8  is elongate and extends longitudinally in a direction parallel to, and centrally located between the axes of rotation of the drum assemblies. 
   The breaker bar assembly  64  includes a main elongate support body  66 , which is secured at each end to a respective end wall  24 ,  26  of the drum casing  22 . The breaker bar assembly  64  thereby preferably serves as a strengthening beam extending in-between, and connecting, the opposed end walls  24 ,  26 . 
   The support body  66  is of generally “T” shaped cross-section, having a horizontal part  66   a  and a vertical part  66   b . Preferably, a strengthening bar  68  extends along the upper edge of the vertical part  66   b.    
   The support body  66  has mounted thereon a plurality of breaker teeth  70 . 
   The breaker teeth  70  are each of blade-like form, and project upwardly into the annular recess R defined between adjacent toothed annuli  34 ,  56  on one breaker drum assembly  30 . 
   The cross-sectional shape and size of each breaker tooth  70  is similar to that of channel R so that each breaker tooth  70 , in cross-section, substantially fills channel R. This has the effect of enabling the leading face  70 F of breaker teeth  70  to act as scrapers to clear material adhering between adjacent toothed annuli  34 ,  56 ; this is particularly useful when handling sticky materials such as clays or tar sand. 
   In addition, since each breaker tooth  70  substantially fills each channel R, the breaker teeth  70  on the breaker bar assembly  64  act to choke the flow of mineral emerging from between the breaker drum assemblies  30 . This has the effect of agitating mineral emerging from between the breaker drum assemblies  30 , and so assist in dislodging any oversized lumps located in-between adjacent breaker teeth  38  on the same toothed annulus  34 ,  56 . These oversized lumps are then broken down further by interaction between the breaker teeth  38  and the adjacent breaker teeth  70  between which it passes. 
   As seen in  FIGS. 7 and 8 , the breaker teeth  70  are arranged in two longitudinally extending rows  72 , 74  wherein the breaker teeth  70  in one row  72  co-operate with one breaker drum assembly  30  and the breaker teeth  70  in the other row  74  cooperate with the other breaker drum assembly  30 . 
   Breaker teeth  70  in a given row are spaced apart in the longitudinal direction of the support body  66  to define a groove or recess  76  through which the breaker teeth  38  on an associated toothed annulus  34 ,  56  pass during rotation of the breaker drum assembly  30 . 
   The groove  76  has sides defined by a side edge of an intermediate breaker tooth  70  on one row and a bottom  78  defined by a side edge of an intermediate breaker tooth  70  from the other row. 
   The bottom  78  at the mouth entrance to groove  76  is preferably closely spaced from the tip T of breaker teeth  38  passing into groove  76  so as to reduce the available pocket size in which an oversized lump may be accommodated between the leading face  38   F  of one breaker tooth  38  and the trailing face  38   T  of an adjacent breaker tooth  38  on the same toothed annulus  34 ,  56 . 
   Preferably the breaker teeth  70  are formed in blocks of teeth  80 , which straddle the vertical part  66   b  of the support body  66 , and are secured thereto by through bolts (not shown) passing through bores  82  formed in the vertical part  66   b  and bores  84  formed in blocks  80 . Preferably, the blocks  80  are each cast from a suitable metal and each comprise a number of breaker teeth  70  for forming one row  72  and a number of breaker teeth  70  for forming the other row  74 . Conveniently, the number of breaker teeth  70  in each block  80  is five with three breaker teeth  70  on one side and two breaker teeth  70  on the other side. Thus, by mounting adjacent blocks  80  on the vertical part  66   b  with alternate blocks  80  having three breaker teeth  70  on one side of the vertical part  66   b  and two breaker teeth  70  on the other side of vertical part  66   b , it is possible to create the two rows  72 ,  74  of breaker teeth  70 . 
   The support body  66  is preferably provided with mounting flanges  86  at each end via which the breaker bar assembly  64  may be mounted on the opposed end walls  24 ,  26  of the drum casing  22 . 
   It is envisaged that the height of the breaker bar assembly  64  relative to the breaker drum assemblies  30  may be adjusted by the placement of shims beneath flanges  86 . This enables the terminal edges  70   a  of the breaker teeth  70  to be closely spaced relative to the bottom of the recess R, and also enables the bottom  78  at the mouth entrance to grooves  76  to be closed spaced relative to the tips T of the breaker teeth  38 . 
   In other embodiments, the breaker bar assembly may be of the construction described in our PCT patent application no. PCT/GB2004/001652. 
   In the breaker unit BU described with reference to  FIGS. 2 to 14 , the teeth  38  per se of each toothed annulus  34 ,  56  define a breaker tooth. It is envisaged that the teeth  38  may instead define the core or horn to which a tooth cap or wear plate may be attached to define the breaker tooth. Examples of breaker teeth having a core or horn, and a covering cap, are described in our European patent no. 0 167 178. 
   As shown in  FIG. 4 , the contra-rotating break drum assemblies  30  of each breaker unit BU rotate so as to direct mineral inwardly of the breaker unit BU, that is towards the opposing breaker drum assembly  30 . This means that oversized mineral is gripped between the opposing breaker drum assemblies  30  and broken down; the broken down mineral being forced by the rotating breaker drum assemblies  30  downwardly in-between the breaker drum assemblies  30  for further breakage, if required, with the associated breaker bar assembly  64 . 
   The breaker units BU are located side-by-side on the support frame  12  such that the open side of their respective casings  22  (i.e. the open side opposite to side wall  28 ) are located adjacent to one another. 
   This arrangement of the breaker units BU results in the breaker drum assemblies  30   a  of each breaker unit BU being located side-by-side, adjacent to one another, to form an inner pair DB of contra-rotating breaker drum assemblies  30 . 
   As seen more clearly in  FIG. 4 , the contra-rotating breaker drum assemblies  30   a  of the inner pair DB rotate such that mineral located in-between the drum assemblies  30   a  is directed outwardly toward the other breaker drum assembly  30  of each breaker unit BU. 
   The breaker drum assemblies  30   a  of the inner pair DB are laterally spaced from one another such that the toothed annuli  34 ,  56  of one breaker drum assembly  30   a  are axially off-set with the toothed annuli  34 ,  56  of the other breaker drum assembly  30   a , with the breaker teeth  38  on each toothed annuli  34 ,  56  of one breaker drum assembly  30   a  passing into the axial gap in-between a pair of adjacent toothed annuli  34 ,  56  of the other breaker drum assembly  30   a . As indicated schematically by arrow DM in  FIG. 4 , this region in-between the breaker drum assemblies  30   a  of the inner pair DB is the area into which mineral to be processed is deposited; this area being defined by the inter-leafing of the toothed annuli  34 ,  56  of the breaker drum assemblies  30   a.    
   The inter-leafing of the toothed annuli  34 ,  56  in region DM acts to prevent oversized lumps to pass therebetween. As viewed in  FIG. 4 , it will be seen that the inter-leafing also appears to substantially close off the passageway in-between the breaker drum assemblies  30   a  of the inner pair DB, and so potentially restrict passage of undersized lumps and fines therethrough. 
   However, since the breaker teeth  38  on the contra-rotating breaker drum assemblies  30   a  of the inner pair DB, in the region in-between the breaker drum assemblies  30   a , are moving in an upwards direction, in opposition to the direction of flow of the mineral being deposited into region DM, the teeth  38  act to agitate and, in effect, fluff up the deposited mineral. Accordingly, this action encourages undersized mineral to fall downwardly through the space between the breaker drum assemblies  30   a  of the inner pair DB. 
   This action also acts to remove a high proportion of the undersized mineral such that the proportion of undersized mineral being carried over with the oversized mineral, for passage between the pair of breaker drum assemblies  30  of each breaker unit BU is reduced. Accordingly, since the undersized mineral can form a large proportion of the volume of the inflow mineral being deposited in region DM, it means that the mineral breaker  10  can handle a relatively large throughput of mineral. 
   Preferably, the distance between the breaker drum assemblies  30   a  of the inner pair DB is adjustable such that the size of the effective passageway therebetween for the flow of undersized mineral can be varied. 
   Preferably, this adjustment of the distance between the breaker drum assemblies  30   a  of the inner pair DB is achieved by fixedly mounting one breaker unit BU on the support frame  12 , slidably mounting the other breaker unit BU on the support frame  12  and providing motive means  88 , such as a pair of hydraulic rams  89  for causing relative movement between the breaker units BU. 
   As schematically illustrated in  FIG. 15 , the mineral breaker  10  described with reference to  FIGS. 1-14  may be modified by the inclusion of additional breaker drum assemblies  90  to define a row of breaker drum assemblies exceeding four breaker drum assemblies  90 . 
   In the embodiment of  FIG. 15 , the breaker drum assemblies  90   b , immediately adjacent to the inner pair of breaker drum assemblies  90   a , are arranged to rotate in the same direction as its neighbouring inner breaker drum assembly  90   a.    
   Accordingly, a given inner breaker drum assembly  90   a  acts to feed oversized mineral to its adjacent breaker drum assembly  90   b , which in turn feeds the oversized mineral to the outer breaker drum assembly  90   c.    
   The outer breaker drum assembly  90   c  is arranged to rotate in the opposite direction as its neighbouring breaker drum assembly  90   b  and the breaker teeth  38  on the breaker drum assemblies  90   b ,  90   c  co-operate to break down some of the oversized mineral. The broken down undersized mineral is able to fall in-between the breaker drum assemblies  90   b ,  90   c.    
   In addition, the space between each of the inner breaker drum assemblies  90   a  and its neighbouring breaker drum assembly  90   b  provides a further opportunity for any undersized mineral fed by the inner breaker drum assembly  90   a  from region DM to fall away before reaching the outer breaker drum assembly  90   c.