Abstract:
A mineral breaker including a pair of breaker drum assemblies rotatably housed in a housing with their axes parallel, each drum assembly including circumferentially extending groups of teeth, the groups being spaced axially along the drum assembly to define a circumferentially extending channel between adjacent circumferential groups of teeth, the drum assemblies being arranged such that each circumferential group of teeth on one drum assembly is located to enter a circumferentially extending channel between a pair of neighboring circumferential groups of teeth on the other drum assembly, the cross-sectional shape and size of each tooth and channel being complementary such that the sides and tip of a tooth when entering a channel are closely spaced from the sides and bottom of the channel, and an elongate breaker bar extending longitudinally in a direction parallel to the axes of the drum assemblies, the breaker bar being located with its longitudinal axis positioned inbetween and beneath the axes of rotation of the drum assemblies, the breaker bar including a plurality of breaker teeth spaced along its length, each breaker tooth of the breaker bar projecting upwardly into a channel defined between a pair of circumferential groups of teeth on one of the drum assemblies, each breaker tooth being of a size and shape complementary to the channel into which it projects so as to be closely spaced from the sides and bottom of the channel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of prior PCT Application PCT/GB2004/004665, filed 5 Nov. 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a mineral breaker, in particular but not exclusively to a mineral breaker capable of a high sizing reduction ratio and also to a drum construction for a mineral breaker. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention there is provided a mineral breaker including a pair of breaker drum assemblies rotatably housed in a housing with their axes parallel, each drum assembly including circumferentially extending groups of teeth, the groups being spaced axially along the drum assembly to define a circumferentially extending channel between adjacent circumferential groups of teeth, the drum assemblies being arranged such that each circumferential group of teeth on one drum assembly is located to enter a circumferentially extending channel between a pair of neighbouring circumferential groups of teeth on the other drum assembly, the cross-sectional shape and size of each tooth and channel being complementary such that the sides and tip of a tooth when entering a channel are closely spaced from the sides and bottom of the channel, and an elongate breaker bar extending longitudinally in a direction parallel to the axes of the drum assemblies, the breaker bar being located with its longitudinal axis positioned inbetween and beneath the axes of rotation of the drum assemblies, the breaker bar including a plurality of breaker teeth spaced along its length, each breaker tooth of the breaker bar projecting upwardly into a channel defined between a pair of circumferential groups of teeth on one of the drum assemblies, each breaker tooth being of a size and shape complementary to the channel into which it projects so as to be closely spaced from the sides and bottom of the channel. 
     In accordance with another aspect of the present invention there is provided a drum construction for a mineral breaker, the drum construction including a drive shaft and a plurality of toothed annuli mounted on the drive shaft, adjacent annuli being axially spaced along the shaft, each annulus being fixedly connected to the shaft by welding at least a portion of the annulus to at least a part of an adjacent exposed circumferential portion of the shaft. 
     Preferably adjacent annuli are axially spaced apart along the shaft to expose a circumferential portion of the shaft therebetween. 
     In a particular embodiment, each annulus is axially spaced from its neighbouring annulus so as to define an open topped annular channel in which the bottom of the channel is defined by the exposed circumferential portion of the shaft and opposed sides of the channel are defined by opposed axial end faces of the neighbouring toothed annuli, the channel being filled with weld to weldingly secure the annuli to said shaft. 
     Preferably each toothed annulus includes an annular boss and a row of teeth spaced circumferentially about the boss, each tooth extending generally radially from the boss. The number of teeth in the row is preferably in the range of 3 to 8. 
     Each toothed annulus may be a unitary metal casting or forging or profile cast from metal plate wherein the teeth are integrally joined with the annular boss. Each tooth may define a breaker tooth per se. Alternatively each tooth may define an inner core or horn of a breaker tooth wherein the outer shape of the breaker tooth is defined by a tooth sheath or wear plates secured to the horn. 
     Preferably for each toothed annulus wherein each tooth defines a breaker tooth per se, the ratio of the radial height of the tooth tip relative to the maximum axial width of the tooth is approximately 2:1 and the ratio of the height of the tooth tip relative to the radius of the toothed annulus is approximately 1:2. Preferably the ratio of the shaft diameter relative to the diameter of the annulus is 1:2 or more, more preferably about 1:2.2 and the ratio of the radial height of the tooth tip (as measured from the peripheral surface of the shaft) relative to the diameter of the shaft is 1:about 1.7 or less, more preferably 1:about 1.6. 
     According to another aspect of the invention there is provided a mineral breaker including a breaker drum construction as defined above. 
     According to another aspect of the present invention there is provided a mineral breaker including a pair of breaker drum constructions as defined above rotatably housed in a housing with their axes parallel, the drum constructions being arranged such that each toothed annulus on one drum is located inbetween a pair of neighbouring annuli on the other drum. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present invention are hereinafter described by way of example with reference to the accompanying drawings, in which:— 
         FIG. 1  is a perspective view from above of a mineral breaker according to an embodiment of the present invention; 
         FIG. 2  is a part cross-sectional view taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a sectional view along line II-II shown in perspective; 
         FIG. 4  is a perspective view from above of the breaker bar assembly; 
         FIG. 5  is a similar view to  FIG. 4  showing the breaker teeth removed; 
         FIG. 6  is a schematic end view illustrating the relative rotational positions of a pair of opposed toothed annuli; 
         FIG. 7  is a part detail plan view of the mineral breaker shown in  FIG. 1 ; 
         FIG. 8  is an axial section through a pair of adjacent toothed annuli mounted on a shaft; 
         FIG. 9  is a perspective view of a toothed annulus of the mineral breaker shown in  FIG. 1 ; 
         FIG. 10  is a plan view of part of a breaker drum assembled from toothed annuli according to a further embodiment of the present invention; 
         FIG. 11  is an axial section through the breaker drum of  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A mineral breaker according to an embodiment of the present invention is shown generally at  10  in  FIG. 1 . 
     The breaker  10  includes a box-like housing  12  having opposed side walls  14 ,  16  and opposed end wall assemblies  18 ,  20 . 
     A pair of breaker drum assemblies  30  are rotatably mounted in the housing  12  so as to extend longitudinally from one end wall assembly  18  to the other end wall assembly  20 . 
     Each breaker drum assembly  30  includes a shaft  31  which is rotatably mounted at opposite ends in respective end wall assemblies  18 ,  20  via bearings. The shaft  31  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  40  of disc-like form. As shown in  FIG. 9 , each toothed annulus  40  includes an annular boss  41  from which a plurality of teeth  43  radially project; the teeth  43  per se defining breaker teeth. Preferably the annular boss  41  and breaker teeth  43  are formed in one-piece such that the toothed annulus  40  is of a unitary construction with the teeth  43  being integrally connected with the boss  41 . Each tooth  43  has a leading face  43 F which extends upwardly from the outer circumferential periphery of the boss  41  to a tooth tip T and a trailing face  43 T which extends downwards from the tooth tip T to merge with the leading face  43 F of the succeeding tooth  43 . There is thereby defined a series of material accommodating pockets P ( FIG. 9 ) on each annulus  40 , each pocket P being defined between the leading face  43 F of one tooth  43  and the trailing face  43 T of the preceding tooth  43 . 
     Preferably each toothed annulus  40  is located on a shaft  31  ( FIG. 2 ) and is fixedly secured thereto by welding as will be described below. 
     One advantage of fixedly securing the annuli  40  to the shaft  31  by welding is the avoidance of keyways both in the annuli and shaft. This avoids localised stress weakness in both the annuli and shaft created by the provision of keyways and also enables the difference in diameter size between the annulus boss  41  and shaft diameter to be relatively small; in other words a relatively large diameter shaft  31  can be accommodated in a given diameter size of tooth annulus  40 . This has the significant advantage of enabling a relatively large diameter shaft to be used which thereby enables a relative large amount of torque or load to be transmitted to the breaker teeth  43 . 
     As shown, by way of illustration in  FIG. 2 , the ratio of the diameter D S  of the shaft relative to the diameter D A  of the annulus  40  is about 1:2.2 and the ratio of the radial height H T  of the tooth tip T of tooth  43  (as measured from the periphery of the shaft  31 ) to the diameter D S  of the shaft is about 1:1.6. In other words the tooth height H T  is greater than the radius of the shaft  31 . 
     In the embodiment of  FIGS. 1 to 9 , each toothed annulus  40  is a casting or forging formed from a suitable metal which is capable of being welded to the shaft  31 . 
     As shown in  FIG. 9 , all the teeth  43  are arranged in a single row which extends circumferentially around the boss  41 . The teeth  43  are equally spaced about the circumference of boss  41 . In the illustrated embodiment, there are five teeth  43  in the row, it is to be appreciated that the number of teeth  43  in the row may be in the range of 3 to 8 teeth. 
     To enable the toothed annulus  40  to be received on shaft  31 , the boss  41  is provided with a through bore  45 . The diameter of bore  45  is the same as the external diameter of shaft  31 . To enable the toothed annulus  40  to positively seat upon the shaft  31  without rocking (caused by slight differences of size due to tolerances of manufacture) the inner wall  46  of the boss  41  which defines the bore  45  is preferably provided with an annular recess  47  to thereby define two axially spaced apart raised annular seats  48  of relatively shortly axial extent. Accordingly, the toothed annulus  40  seats upon the shaft  31  only via the axially spaced annular seats  48 . 
     As illustrated more clearly in  FIG. 8 , to fixedly secure the toothed annuli  40  to the shaft  31 , adjacent annuli  40  are spaced apart long the shaft  31  such that opposed axial end faces  49 ,  50  of neighbouring annuli  40  define a gap therebetween with a circumferential portion of the shaft  31  being exposed by the gap. In other words, adjacent annuli  40  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  49 ,  50  and the bottom of the channel is defined by the exposed circumferential portion of the shaft  31 . The channel defines a welding receptor and enables each end face  49 ,  50  to be welded to the exposed portion of the shaft  31 ; in practice this means that the channel is filled with weld  51  which is preferably machined to define a smooth solid top face  52  for the channel. 
     As indicated above, the annuli  40  are of disc-like form (i.e. the axial dimension of each annulus relative to its diameter is small, and the row of teeth on each annulus have substantially planar side faces which collectively define substantially planar axial side faces of a disc). 
     Accordingly, by arranging the annuli  40  side by side on shaft  31  a series of annular channels R along the breaker drum are formed, the sides RS 1 , RS 2  of each channel R being defined by facing axial side faces of each pair or neighbouring annuli  40  and the bottom R B  of the channel R being defined collectively by the outer circumferential face of the bosses  41  and weld face  52 . The effective working height h of each tooth  43  is the height of its tip above the bottom R B  of the neighbouring channel R (hereinafter the effective working height h of each tooth  43  is referred to as the ‘drum height’ h of the tooth. The drum height h of each tooth  43  is necessarily less than the height H T  due to the intermediate provision of the boss  41  which is required for securing the teeth  43  to the shaft  31  (as well as providing a protective covering for the shaft  31 ). Accordingly the smaller the radial thickness of boss  41 , the greater the possible drum height h of the teeth  43 . As indicated above, welding of the boss  41  directly to the shaft  31  enables the radial thickness of the boss  41  to be kept to a minimum and so this capability can be utilised to maximise the drum height h of the teeth  43 . This is advantageous as it enables relatively tall teeth  43  to be provided and so provides the breaker with the capability of gripping large mineral lumps contained in the in-feed of material. 
     Preferably, the rotary position of a given toothed annulus  40  relative to its neighbour is off-set by a predetermined increment such that the teeth on the annuli  40  on a given shaft extend along a predetermined helical path in order to define a series of discrete scrolls of teeth as disclosed in our European patent 0167178. 
     In the illustrated machine, the increment by which adjacent annuli  40  are off-set is such that the starting point of each discrete scroll at one end of the drum assembly is off-set from the finishing point of the scroll at the other end of the drum assembly by an angular distance equivalent to two teeth pitch spacings between teeth  43 . In the illustrated embodiment, the angular off-set increment between adjacent annuli  40  is 6°. 
     An alternative toothed annulus  140  for use in the mineral breaker of the present invention is illustrated in  FIGS. 10 and 11 . Parts similar to those in  FIGS. 1 to 9  have been designated by the same reference numerals. 
     The toothed annulus  140 , instead of being a metal forging or casting, is formed from a suitable metal plate preferably by profile cutting. Forming the toothed annulus  140  from metal plate has several advantages including ease and consistency of manufacture and improved breaking performance of the teeth derived from absence of forging/casting faults within the metal grain structure. 
     The toothed annulus  140  includes a through bore  145  to enable it to be slid onto shaft  31 . Adjacent annuli  140  are spaced apart, preferably by an intermediate spacing ring  146 . The intermediate spacing ring  146  is axially spaced from the annuli  140  between which it is located in order to define an open topped annular channel therebetween which acts as a welding receptor for weld  51 . Accordingly, annuli  140  are weldingly secured to shaft  31  in a similar manner to annuli  40 . In the embodiment of  FIGS. 10 ,  11  the outer circumferential face of spacer rings  146  and outer face  52  of welding  51  collectively define the channel bottom R B . 
     One aim of a mineral breaker according to the illustrated embodiment of the invention is to provide a mineral breaker which is capable of breaking down relatively large lumps of mineral to a relative small size of lump. For example, a machine  10  having a distance of 625 mm between the axes of the drum assemblies  30  is expected to be capable of breaking down lumps of about 0.6 meter cubed down to a lump size having a maximum dimension of about 150 mm. 
     In order for the machine to be capable of gripping relative large lumps of mineral, it is necessary for the drum height h of the teeth relative to the outer diameter of the annulus to be relatively large. This is illustrated diagrammatically in  FIG. 6  wherein the mineral breaker includes 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 tooth having a drum height h of about 175 mm as measured from the outer diameter of the boss  41  (which defines the recess bottom R B ) and the tip T of the tooth  43 . 
     With such an arrangement the gap  60  defined between the tips of two opposed teeth  43  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 tooth above the bottom of the gap  60  as defined by the trailing faces  43 T of the preceding tooth  43 ). In other words, gap  60  enables relatively large lumps of mineral to be grippingly received between opposed teeth  43  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 0167178. 
     In the above example, the ratio of the drum height h relative to the radius of the tooth annulus  40  is approximately 1:2.2. 
     It is envisaged however that the ratio of the drum height h of a tooth  43  relative to the radius of the annulus  40  may be varied in order to achieve different sizes of gap  60 . 
     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 mineral breaker, it is necessary for the axial dimension of channel R between adjacent annuli  40  to be relatively small which also requires the width w t  of the teeth  43  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 mineral breaker  10  illustrated in  FIG. 6 , the maximum width w t  of each tooth  43  at its base is chosen to be about 85 mm. With the tooth 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 annuli  140  are cut is about 70 mm. 
     With such an arrangement each tooth  43  on one drum assembly acts to break lumps down by a snapping action by forcing mineral lumps downwardly through the channel R defined between two adjacent teeth  43  on the opposed drum assembly. 
     As seen in  FIG. 7 , the dimensions of each channel R in the longitudinal direction of the drum assemblies, will determine the maximum size dimension of the broken lump in the longitudinal direction of the mineral breaker. 
     Preferably the relative cross-sectional size and shape of each tooth  43  and the channel R through which it sweeps during rotation of the drum assemblies are such that the tooth  43  at least the front and trailing faces  43 F,  43 T (and preferably the sides of each tooth) are closely spaced with the sides of the channel R. This helps to ensure that material passing between the breaker drums predominantly has to be passed through the pockets P inbetween adjacent teeth on a given annulus  40 ,  140  rather than being allowed to pass through gaps between an 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 teeth  43  on the same annulus  40  may have a dimension in excess of the desired maximum lump dimension in the direction of rotation of the annulus  40  after a tooth  43  has forced the lump through the channel R on the opposed drum assembly. 
     In order to ensure that such a lump is broken down further, the mineral breaker preferably includes a breaker bar assembly  70  located beneath the drum assemblies  30 . The provision of breaker bar assembly  70  also ensures that long thin lumps of mineral extending longitudinally of the drum assemblies cannot pass through without being broken down. 
     The breaker bar assembly  70  as illustrated in  FIGS. 4 and 5  is elongate and extends longitudinally in a direction parallel to, and centrally located between, the axes of rotation of the drum assemblies  30 . 
     The breaker bar assembly  70  includes a main elongate support body  71  which is secured at each end to a respective end wall assembly  18 ,  20  of housing  12 . The body  71  is of generally ‘T’ shaped cross-section having a horizontal part  71   a  and a vertical part  71   b . Preferably a strengthening bar  72  extends along the upper edge of the vertical part  71   b.    
     The body  71  has mounted thereon a plurality of breaker teeth  72 . 
     The breaker teeth  72  are each of blade like form and project upwardly into the annular recess R defined between adjacent toothed annuli  40 ,  140  on one drum. 
     The cross-sectional shape and size of each tooth  72  is similar to that of channel R so that each tooth  72 , in cross-section substantially fills channel R. This has the effect of enabling the leading face  72 F of teeth  72  to act as scrapers to clear material adhering between adjacent annuli  40 ; this is particularly useful when handling sticky materials such as clays or tar sand. 
     In addition since each tooth  72  substantially fills each channel R, the teeth  72  on the breaker bar act to choke flow of material emerging from between the drum assemblies  30 . This has the effect of agitating material emerging from between the drum assemblies  30  and so assist in dislodging any oversized lumps located inbetween adjacent teeth  41  on the same annulus  40 . These oversized lumps are then broken down further by interaction between breaker teeth  41  and adjust teeth  72  between which it passes. 
     As seen in  FIGS. 4 and 5 , the teeth  72  are arranged in two longitudinally extending rows  74 ,  75  wherein the teeth  72  in one row co-operate with one drum assembly  30  and the teeth  72  in the other row co-operate with the other drum assembly  30 . 
     Teeth  72  in a given row are spaced apart in the longitudinal direction of support  71  to define a groove or recess  78  through which the teeth  41  on an associated tooth annulus  40  pass during rotation of the drum assembly  30 . The groove  78  has sides defined by opposed sides of adjacent teeth  72  on one row and a bottom  79  defined by a side edge of an intermediate tooth  72  from the other row. The bottom  79  at the mouth entrance to groove  78  is preferably closely spaced from the tip T of teeth  41  passing into groove  78  so as to reduce the available pocket size in which an oversize lump may be accommodated between the leading face of one tooth  41  and the trailing face of an adjacent tooth  41  on the same annulus  40 . 
     Preferably the teeth  72  are formed in blocks of teeth  80  which straddle the vertical part  71   b  of the elongate support  71  and are secured thereto by through bolts (not shown) passing through bores  73  formed in the vertical part  71   b  and bores  83  formed in blocks  80 . Preferably the blocks  80  are each cast from a suitable metal and each comprise a number of teeth  72  for forming one row  74  and a number of teeth  72  for forming the other row  75 . Conveniently the number of teeth  72  in each block  80  is five with three teeth  72  on one side and two teeth  72  on the other side. Thus by mounting adjacent blocks  80  on the vertical part  71   b  with alternate blocks  80  having three teeth  72  on one side of part  71   b  and two teeth  72  on the other side of part  71   b  it is possible to create the two rows of teeth  74 ,  75 . 
     The elongate body  71  is preferably provided with mounting flanges  90  at each end via which the breaker bar assembly  70  may be mounted on the opposed end walls  18 ,  20  of the breaker housing. 
     It is envisaged that the height of the breaker bar assembly  70  relative to the drum assemblies  30  may be adjusted by the placement of shims beneath flanges  90 . This enables the terminal edges  72   a  of teeth  71  to be closely spaced relative to the bottom of recess R and also enables bottom  79  at the mouth entrance to grooves  78  to be closely spaced relative to tips T of teeth  41 . 
     In the examples described in  FIGS. 1 to 11 , the teeth  43  per se of each annulus  40  define a breaker tooth. It is envisaged that the teeth  43  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 EP patent 0167178.