Patent Publication Number: US-2022226863-A1

Title: Disc, spacer and transportation assembly

Description:
TECHNICAL FIELD 
     The present disclosure relates to a disc, a spacer, and a transportation assembly arranged to cooperate for transporting materials on a roller screen and in particular, although not exclusively to a disc and a spacer having wear resistant areas to contact the materials for transportation. 
     BACKGROUND 
     A roller screen is a type of heavy machinery equipment for screening/sorting feed materials, e.g., coal. The transportation system of the roller screen is highly exposed to the feed materials, as the transportation system comes into contact with the feed materials and transports the materials in a rotating way. Such sorting screens are known from US20140202933 and WO9420227A1. In U.S. Patent Publication US20140202933, a sorting screen comprising a row of rotatable, driven shafts mutually spaced in a conveying direction is described. Each of the shaft carries a row of radially extending rotor bodies for intermittently urging material on the sorting screen upward and in a conveying direction. The rotor bodies of each of the rows are mutually spaced in a longitudinal direction of the respective shaft by spacers, and each spacer is a tubular spacer and each rotor body is provided with a number of projections retaining a respective end face of a respective tubular spacer. In the International Patent Publication WO9420227A1, a roller screen with a plurality of parallel shafts, each having a plurality of circular discs that are separated by spacers is described. The discs are eccentrically mounted on the respective shafts, and the discs on each shaft have an eccentricity that is circumferentially offset from disc to disc. The spacers are made of rubber and are concentric with respective shafts. 
     Since discs and the spacers are wear parts, after having been used for a certain period of time, worn out discs or spacers need to be replaced with a new one. 
     SUMMARY 
     It is an objective of the present invention to provide a disc and a spacer that cooperate for transporting materials on a roller screen. The disc and the spacer should be wear resistant against the feed materials and preferably have increased wear resistant properties at the high wear zone. It is a further specific objective to provide a disc and a spacer that are optimised to be integrated respectively, to particularly increase the service lifetime of the disc and the spacer. 
     The objectives are achieved by providing a disc having a circular main body and a wear resistant portion arranged around the main body. The wear resistant portion comprises a first material, and the main body comprises a second material that has a different wear resistant property from the first material. Such a configuration is cost efficient, while the wear resistance of the disc is increased. In particular, a plurality of protuberances is arranged circumferentially along the periphery of the wear resistant portion to contact the feed materials, to optimise the wear resistance and the transfer of feed materials. The objectives are further achieved by providing a spacer having a cylindrical main body and at least one ridge, wherein the ridge comprises a third material, and the main body comprises the third material or a fourth material having a different wear resistant property than the third material. Such a configuration is cost efficient and increases the wear resistance of the spacer. In particular, the spacer and the disc are arranged to cooperate to transport the feed materials on a roller screen. to be specific, a plurality of discs and a plurality of spacers are installed one by one on each of a plurality of shafts in parallel on the roller screen, the discs and spacers are further rotated together with the shafts being driven by the roller screen, so as to roll the feed materials and further transport the material in a desired way. 
     According to a first aspect of the present invention there is provided a disc arranged for cooperating with a spacer for transporting materials on a roller screen, the disc comprising: 
     a circular main body having a centrally arranged opening, through which opening a centrally arranged axis extends; and a wear resistant portion arranged around the circular main body, the wear resistant portion comprises a plurality of teeth which are circumferentially arranged along the periphery of the wear resistant portion and project radially outward from the main body; characterised by: the wear resistant portion comprises a first material, the main body comprises a second material, and the first and second materials have different wear resistant properties. 
     Optionally, the wear resistance of the first material is higher than that of the second material. Such a configuration is cost efficient, as the wear resistant portion includes a high wear resistant zone as compared to the circular main body of the disc. 
     Optionally, the first material is bonded with the second material so that the wear resistant portion and the main body are integrated. Such a configuration further improves the wear resistance of the disc as an integrated piece has higher wear resistance and a longer life of service. 
     Optionally, the second material comprises a matrix material, and the first material comprises cemented carbides metallurgically bonded to the matrix material. 
     Advantageously, the disc is an integrated piece given that the wear resistant portion and the main body are metallurgical bonded. In another embodiment, the first material further comprises the matrix material, such that the cemented carbides and the matrix materials in the wear resistant portion are metallurgically bonded, and the wear resistant portion is further integrated with the main body. 
     Optionally, the cemented carbides in the wear resistant portion can be in a form of a plurality of segments arranged on the radially outermost region of the teeth. In this configuration, the teeth are made of the matrix material and the segments are made of the cemented carbides that are metallurgically bonded to the teeth. 
     Optionally, the cemented carbides in the wear resistant portion can be in at least one of the forms: granules, balls, and/or cubes, metallurgically bonding to the matrix material in the wear resistant portion. 
     The metallurgical bonding within the wear resistant portion increases the wear resistance thereof. And the configuration of using the cemented carbide granules, balls, and/or cubes, further increases the contact area between the cemented carbides and the matrix material in the wear resistant portion, which increases the metallurgical bonding. Advantageously, such configuration largely increases the wear resistance of the wear resistant portion. 
     Optionally, the matrix material comprises iron. And more preferably, the iron is spheroidal cast iron or high-chromium iron. The metallurgical bonding between the cemented carbides and spheroidal cast iron (or high-chromium iron) are known to be rather strong, and thus advantageously, the wear resistance of the disc is enhanced. 
     According to a second aspect of the present invention there is provided a spacer arranged to cooperate with the disc for transporting materials on a roller screen, the spacer comprising: a cylindrical main body having an outer surface and a centrally arranged passage, through which passage a centrally arranged imaginary axis extends; and at least one ridge extending axially and/or radially on the outer surface of the main body, characterised by: the ridge comprises a third material, the main body comprises the third material or a fourth material, the third and fourth materials have different wear resistant properties. 
     Optionally, the wear resistance of the third material is higher than that of the fourth material, and more preferably, the third material is bonded with the fourth material so that the main body and the ridge are integrated. Such configuration improves the wear resistance of the spacer as an integrated piece. 
     Optionally, the fourth material comprises a matrix material, and the third material comprises cemented carbides that are metallurgically bonded to the matrix material. The matrix material comprises iron, and in one embodiment, the iron is spheroidal cast iron or high-chromium iron. Such configuration creates strong metallurgical bonding between the ridge and the main body, and further creates a strong metallurgical bonding within the main body. Thus, the wear resistance of the spacer is increased, and the service life of the spacer is thus prolonged. 
     Optionally, the main body comprises at least two elements that are made of the third material. The elements are located on top of one another so as to form the main body in a cylindrical shape. More preferably, one of the elements comprises a protrusion projecting axially to sit on the next one of the elements, to allow for the two adjacent elements to be spaced apart so as to let the fourth material to fit in between. With the fourth material fit in between the elements to contact with the top/bottom surfaces of the two elements, metallurgical bonding is created between the two elements. Such a configuration of having multiple elements set on top of each other increases the area of contact of the third and fourth material, and thus increases the metallurgical bonding in-between. 
     Optionally, each of the elements comprises a side protrusion protruding radially outward of the outer surface, wherein the side protrusion forms at least partial the ridge on the outer surface of the main body. The ridge is configured for contacting with the feed materials on the roller screen. Such a configuration of having the side protrusions of the elements forming the ridge enables the ridge to be further integrated with the main body. The ridge is made of the third material, and it is further formed by the side protrusions metallurgically bonding with the fourth material, such that the third and fourth materials in the ridge are metallurgically bonded to be more wear resistant. 
     Optionally, the spacer further comprises an extending portion extending axially from a first axial end or a second axial end of the main body, the extending portion being generally cylindrical and made of the fourth material. Such a configuration enables the spacer to be used in various applications. In one application scenario, where a relatively longer spacer is needed, the spacer includes the extending portion extended axially from the main body. 
     The extending portion can be made of the fourth material. In another application scenario, end spacers on the shaft of the roller screen may have the extending portion axially longer than the main body of the end spacers, since the end spacers do not contact the feed material as frequently as the intermediate spacers. Advantageously, it is cost efficient to include a high wear resistant part—the main body and include a less wear resistant part—the extending portion, to form the spacer of preferred length. 
     Optionally, the ridge is further extended axially and/or radially on the extending portion. In this embodiment, the ridge is further increased in length, thus enabling the spacer to be more wear resistant on the extending portion. 
     Moreover, an axial length of the main body is in a range 25%-100% of the axial length of the spacer. Since the main body is the high wear part of the spacer, by having the main body in the above range of the spacer, it guaranteed a high wear resistance of the spacer and is also cost efficient. 
     According to a third aspect of the present invention there is provided a roller screen for processing materials comprising: a shaft having a rotational axis; a plurality of the discs, the discs are installed on the shaft through the openings of the discs; and a plurality of the spacers, the spacers are installed on the shaft through the passages of the spacers, each two adjacent discs are separated by one of the spacers. 
     Preferably, the axis of the discs, the axis of the spacers, and the rotational axis of the shaft are generally coincided, so that the discs and the spacers are located concentrically on the shaft. Such a configuration allows high efficiency for transporting the feed materials as required on the roller screen. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: 
         FIG. 1A  is a perspective view of a disc of a roller screen according to a specific implementation of the present invention; 
         FIG. 1B  is a planar view of the disc of  FIG. 1A ; 
         FIG. 2  is a planar view of the disc of a roller screen according to another specific implementation of the present invention; 
         FIG. 3  is a perspective view of a spacer of a roller screen according to a specific implementation of the present invention; 
         FIG. 4A  is a perspective view of a ring of the spacer of  FIG. 3  according to a specific implementation of the present invention; 
         FIG. 4B  is another perspective view of the ring of  FIG. 4A ; 
         FIG. 4C  is a side view of two overlaid rings of  FIGS. 4A and 4B ; 
         FIG. 4D  is an enlarged view on protrusions of the two overlaid rings of  FIG. 4C ; 
         FIG. 5A  is a perspective view of a ring of the spacer of  FIG. 3  according to another specific implementation of the present invention; 
         FIG. 5B  is another perspective view of the ring of  FIG. 5A ; 
         FIG. 5C  is a side view of two overlaid rings of  FIGS. 5A and 5B ; 
         FIG. 5D  is an enlarged view on the side protrusions of the two overlaid rings of  FIG. 5C ; 
         FIG. 6  is a perspective view of the spacer of a roller screen according to another specific implementation of the present invention; 
         FIG. 7  is a perspective view of the spacer of a roller screen according to another specific implementation of the present invention; 
         FIG. 8  is a perspective view of an assembly of the discs of  FIG. 1  and the spacers of  FIG. 3  in cooperation on a shaft of a roller screen; 
         FIG. 9  is a perspective view of an assembly of the discs of  FIG. 1  and the spacers of  FIG. 6  in cooperation on a shaft of a roller screen. 
     
    
    
     DETAILED DESCRIPTION 
     In the present application, a disc, a spacer, and a roller screen of which a plurality of the discs and spacers are installed on a shaft, are introduced for the purpose of material transportation of the roller screen. Details of the disc, the spacer, and the cooperation between the disc and the spacer are introduced in the following paragraphs. 
       FIG. 1A  is a perspective view of a disc  100  of a roller screen (not shown) according to a specific implementation of the present invention.  FIG. 1B  is a planar view of the disc  100 . The disc  100  is adapted for cooperation with a spacer ( FIG. 3 ) on the roller screen, the spacer will be later described in more details. The disc  100  includes a circular main body  104  and a wear resistant portion  102 , wherein the wear resistant portion  102  includes a first material, and the main body  104  includes a second material that has a different wear resistant property from the first material. 
     The main body  104  has a centrally arranged opening  106  through which a centrally arranged axis  101  extends, and as shown in  FIG. 1A , the main body  104  is generally thicker than the wear resistant portion  102  such that a shoulder  103  is formed between the main body  104  and the wear resistant portion  102 . In one embodiment of the present invention, the main body  104  includes at least one projection  110  that projects from the main body  104  and extends axially inside the opening  106 . The wear resistant portion  102  is arranged around the main body  104  and comprises a plurality of protuberances  108  which are circumferentially arranged along the periphery of the wear resistant portion  102 . The protuberances  108  project radially outward from the main body  104 . For example, the protuberances  108  can be similar to the shapes of flower petals, the petals  108  can have a parabolic shape without any angle, as seen in the figures, or the protuberances  108  can be similar to the shapes of teeth, the teeth  108  can be of trapezoidal or other shapes having angles. Thus, it should be appreciated that the term protuberance, petal or teeth shall not be given a strict literal meaning. For instance, the tips of the protuberance  108  which are a radially furthest end of each pedal may form an imaginary circle around the axis  101 , and the pits of the protuberance  108  which is radially innermost end of each pedal may form another imaginary circle with a smaller diameter, while the peripheral edge of the protuberance  108 , varies back and forth in-between the two imaginary circles in the parabolic shape. 
     In one embodiment, the disc  100  is installed onto a shaft  802  ( FIG. 8 ) of the roller screen. The shaft is elongate and passes through the opening  106  of the disc  100  based on the cooperation of the projection  110  of the disc  100  and a recess on the shaft which receives the projection  110 . The projection  110  further helps to rotate the disc  100  along with the rotation of the shaft. In one embodiment, a plurality of discs  100  are installed onto the shaft with the protuberances  108  of each disc  100  arranged to be in contact with feed materials for transportation. More details will be described further herein in relation to  FIGS. 8-9 . 
     According to a specific implementation, the wear resistance of the first material is higher than that of the second material, in such a way that the wear resistant portion  102  is more wear resistant than the main body  104 . During operation in the specific implementation, the plurality of protuberances  108  projecting axially outward the wear resistant portion  102  are in close contact with the materials, and the main body  104  is more distant from the feed materials than the wear resistant portion  102 . Alternatively, in one embodiment, at least part of the main body  104  is covered by adjacent spacers that cooperate with the discs  100 , as will be described further in relation to  FIGS. 8-9 . 
     Additionally, according to a specific implementation, the first material is adjoined with the second material so that the wear resistant portion  102  and the main body  104  are integrated. Additionally, the second material includes a matrix material, and the first material includes cemented carbide metallurgically bonded to the matrix material. More specifically, the main body  104  including the matrix material is bonded to the wear resistant portion  102  on the outermost surface (not shown) of the main body  104 . 
     In one embodiment, the peripheral outermost surface of the main body  104 , which is generally circular around the axis  101 , is the contact surface of the main body  104  and the wear resistant portion  102 , and thus provides an area where the cemented carbide and the matrix material are metallurgically bonded. As is well known in the art, the metallurgical bonding between the main body  104  and the wear resistant portion  102  enables the disc  100  to be an integrated part. And advantageously, the integrated disc  100  has improved wear resistance, and thus has a prolonged service life. 
     In one embodiment of the present invention, the matrix material comprises iron. Additionally, the iron is spheroidal cast iron or high-chromium iron. The metallurgical bonding between iron and cemented carbide are extremely strong as it is well known by the technical person skilled in the art, details of the metallurgical bonding will not be illustrated in detail in this application. 
     Additionally, according to a specific implementation, the wear resistant portion  102  also includes the matrix material, and additionally, the cemented carbide included in the wear resistant portion  102  is in at least one of the forms of granules, balls, and/or cubes. By way of example, the wear resistant portion  102  includes cemented carbide granules, metallurgically bonded to the matrix material in the wear resistant portion  102 . Preferably, the granule size is in a range of 1-15 mm, which provides maximized contact area between the cemented carbide granules with the matrix material, the maximized contact area enables maximized metallurgical bonding in the wear resistant portion  102 . The metallurgical bonding in the wear resistant portion  102  allows the disc  100  to be highly wear resistant when encountered with the feed materials on the roller screen, and thus prolongs the service lifespan of the disc  100 , which reduces the frequency of replacements and overall cost. 
     In one embodiment, the wear resistant portion  102  includes iron, and preferably spheroidal cast iron or high-chromium iron. As it is well known by the technical person skilled in the art, the metallurgical bonding between spheroidal cast iron or high-chromium iron, and cemented carbides is extremely strong, and details and properties of the strong bonding will not be further described. 
       FIG. 2  is a planar view of the disc  200  of a roller screen according to another specific implementation of the present invention. The disc  200  is similar with the disc  100  as shown in the  FIGS. 1A and 1B , thus similar numerals represent similar components having similar functions. The disc  200  includes a circular main body  204  and a wear resistant portion  202 . The main body  204  is generally thicker than the wear resistant portion  202  such that a shoulder  203  is formed between the main body  204  and the wear resistant portion  202 . The wear resistant portion  202  includes a first material, and the main body  204  includes a second material that has a different wear resistant property than the first material. The main body  204  has a centrally arranged opening  206 , and further has at least one projection  210  extending axially inside the opening  206 . The wear resistant portion  202  is arranged around the main body  204  and comprises a plurality of protuberances  208  which are circumferentially arranged along the periphery of the wear resistant portion  202 . The protuberances  208  project radially outward from the main body  204 . 
     Furthermore, in the embodiment of  FIG. 2 , the wear resistant portion includes multiple segments  214  arranged on the radially outermost region of the protuberances  208 , so to contact with the materials when assembled on the shaft of the roller screen for the transportation of the materials. In this embodiment, the segments  214  generally have the same thickness with the protuberances  208  of the wear resistant portion  202 , so that there is no ridge, or protrusion, or shoulder formed between the segments  214  and the protuberances  208 . Furthermore, in the embodiment, each segment  214  can correspond to each protuberance  208 , however, such is not required. 
     In another embodiment, more than one segment may correspond to one protuberance  208 , or vice versa, i.e., one segment may cover the outermost region of more than one protuberance  208 , as long as the segments  214  in combination form a complete protection of the radially outermost region of the protuberances  208 . 
     In the present invention, the segments  214  are made of cemented carbides, the protuberances  208  are made of matrix material, such that the segments  214  are metallurgically bonded to the protuberances  208 . For example, the main body  204  and the protuberances  208  of the wear resistant portion  202  are of an integrated piece made of matrix materials. By configuring the segments  214  to be metallurgically bonded to the protuberances  208 , the segments  214  are further integrated with the wear resistant portion  202  and the main body  204 , so that the disc  200  forms an integrated piece. 
     In one embodiment, the matrix materials in the main body  204  and the protuberances  208  includes iron, and preferably spheroidal cast iron or high-chromium iron. As is well known by the technical person skilled in the art, the metallurgical bonding between spheroidal cast iron or high-chromium iron, and cemented carbides is extremely strong. 
       FIG. 3  is a perspective view of a spacer  300  of a roller screen according to a specific implementation of the present invention. The spacer  300  is arranged for cooperation with the disc  100 ,  200  as mentioned in the above embodiments. The spacer  300  and the disc  100 ,  200  are cooperating for transporting materials on the roller screen. In one embodiment, the spacer  300  and the disc  100 ,  200  are installed one by one on the shaft of the roller screen, details of the assembly will be described further in relation to  FIGS. 8-9 . 
     Referring to  FIG. 3 , the spacer  300  comprises a cylindrical main body  304  having an axial length A, and along the axial length A, the main body  304  has an outer surface  303  and a centrally arranged passage  306 , through the passage  306  which a centrally arranged axis  301  extends. The spacer  300  further includes at least one ridge  308  extending axially and/or radially on the outer surface  303  of the main body  304 . As shown, the spacer  300  includes two ridges  308  extending axially and radially on the opposite sides on the outer surface  303 . In one embodiment of the present invention, the main body  304  includes at least one projection  310  that projects from the main body  304  and extends axially inside the passage  306 . In one embodiment, the spacer  300  is installed onto the shaft of the roller screen and the projection  310  of the spacer  300  helps to rotate the spacer  300  along with the rotation of the shaft. The spacer  300  and the disc  100 ,  200  can be both installed on the shaft. The shaft is elongate and passes through the opening  106 ,  206  of the disc  100 ,  200  and the passage  306  of the spacer  300 , based on the cooperation of the projections  110 ,  210 ,  310  and a recess on the shaft that receives the projections  110 ,  210 ,  310 . The profile of the opening  106 ,  206  of the disc  100 ,  200  is similar to the profile of the passage  306  of the spacer  300 , and the projections  110 ,  210  and  310  are of similar shape, to allow the shaft to be assembled with the disc  100 ,  200  and the spacer  300 . 
     The main body  304  of the spacer  300  comprises a third material and/or a fourth material, and the ridge  308  comprises the third material, wherein the third and fourth materials have different wear resistant properties. The wear resistance of the third material can be higher than that of the fourth material, and the third material is bonded with the fourth material so that the main body  304  and the ridge  308  are integrated. 
     In one embodiment of the present invention, the third material in the main body  304  is in a form of at least two elements  312 ,  412 ,  512  and the fourth material  313 ,  413 ,  513  in the main body  304  is fit between the two elements  312 ,  412 ,  512 , details will be described in relation to  FIGS. 4A-4D  and  FIGS. 5A-5D . 
     As shown in  FIG. 3 , the elements  312  are on top of one another so that the main body  304  is cylindrical, and the elements are generally annular when viewed from a direction parallel to the axis  301 , e.g., the elements are ring shaped. In a specific embodiment, two adjacent elements  312  are further spaced apart with a certain distance within which the fourth material is fit in and adjoin with the third material of the elements. 
     In one embodiment, the fourth material comprises a matrix material, and the third material comprises cemented carbides, so that when the matrix material is fit in between the elements  312 , the cemented carbides and the matrix material can form an integrated piece by metallurgical bonding at the contact area of the two materials. The metallurgical bonding between the cemented carbides and matrix material is such that the integrated main body  304  has improved wear resistance, and thus with a prolonged service lifetime. 
     According to a specific implementation, the matrix material comprises iron. Additionally, the iron is spheroidal cast iron or high-chromium iron. The metallurgical bonding between iron and cemented carbides is also extremely strong and as it is well known, details of the bonding will not be described further. 
     The spacer  300  further includes at least one ridge  308  partially extending axially along the outer surface  303  of the main body  304 . The ridge  308  further projects radially from the outer surface  303  to contact with the feed materials on the roller screen. Further details of the ridge  308  will be described in relation to  FIGS. 4A-4D and 5A-5D . 
     The spacer  300  further includes an extending portion  314  and/or  316  extending axially from a first axial end  305  and/or a second axial end  307  of the main body  304 , the extending portions  314 ,  316  being generally cylindrical. The axial length A of the main body  304  can be in a range 25%-100% of an axial length B of the spacer  300  including the main body  304  and the extending portion  314  and/or  316 . In one embodiment of the present invention, the axial length A of the main body  304  is about 25% of the axial length B of the spacer  300 , when the spacer is arranged as an end spacer installed on the shaft of the roller screen. In another embodiment of the present invention, the axial length A of the main body  304  is more than 25%, e.g., 40%, 50%, or 60%, of the axial length B of the spacer  300 , so the spacer is arranged as intermediate spacer installed between the end spacers. 
     Referring to  FIGS. 4A-4D , elements  412  are rings having at least one protrusion  402 .  FIG. 4A  is a perspective view of a ring  412  of the spacer  300  of  FIG. 3  according to a specific implementation of the present invention.  FIG. 4B  is another perspective view of the ring  412  of  FIG. 4A .  FIG. 4C  is a side view of two overlaid rings  412 ,  412 ′ of  FIGS. 4A and 4B .  FIG. 4D  is an enlarged view on protrusions  402 ,  402 ′ of the two overlaid rings  412 ,  412 ′ of  FIG. 4C . 
     Advantageously, cemented carbides in ring shape is more cost efficient than e.g., cemented carbides in a solid cylinder shape, and multiple rings on top of one another provide maximized contact area for the metallurgical bonding than e.g., a solid cylinder, to substantially provide the same wear resistant area. 
     In the embodiment of  FIGS. 4A and 4B , the ring  412  has two protrusions  402  protruding axially at different axial positions on the ring  412 . The protrusions  402  can be clearly observed from the enlarged view in  FIGS. 4A and 4B . Referring to  FIGS. 4C and 4D , two rings  412  and  412 ′ are overlaid and axially spaced apart by a certain distance due to the protrusions  402 . As shown in the enlarged section as shown in  FIG. 4D , one of the protrusions  402  projects axially from the bottom annular surface  410  of the ring  412  and in a direction away from the top annular surface  406  of the ring  412 . The bottom surface  408  of the protrusion  402  is arranged on the top annular surface  406 ′ of the next ring  412 ′ to provide the required distance between the rings  412  and  412 ′ to allow the fourth material (e.g., matrix material), indicated by numeral  413  to fit in between the rings  412 ,  412 ′. The matrix material fit of  413  contacts the bottom annular surface  410  of the ring  412 , and the top annular surface  406 ′ of the ring  412 ′, and thus metallurgical bonding can be created at the contact area. 
     In a more specific embodiment, the spacer  300  includes a plurality of rings  412  on top of one another, thus the fourth material fit in each two adjacent rings  412 , this may provide a maximized metallurgical bonding inside the main body  304  of the spacer  300  as a maximized surface area is created for the two materials to bond, and advantageously, the spacer  300  has improved wear resistance, especially on the main body  304  of the spacer  300  where the feed materials are more frequently contacted. 
     Referring to  FIGS. 5A-5D , the rings  512  and  512 ′ are similar to the rings  412  and  412 ′ as shown in  FIGS. 4A-4D , except that in the embodiment of  FIGS. 5A-5D , the rings  512  and/or  512 ′ include at least one protrusion  502  and at least one side protrusion  504 , wherein the side protrusions  504  on a plurality of rings  512 / 512 ′ are arranged on top of one another to form the at least one ridge  308  ( FIG. 3 ). Each of the ridges  308  extend radially and/or axially on the outer surface  303  in a way that the ridges  308  are arranged circumferentially along the outer surface  303 . By way of example, two ridges  308  can be arranged oppositely on the outer surface  303  of the main body  304 . 
       FIG. 5A  is a perspective view of a ring  512  of the spacer  300  of  FIG. 3  according to another specific implementation of the present invention.  FIG. 5B  is another perspective view of the ring  512  of  FIG. 5A .  FIG. 5C  is a side view of two overlaid rings  512 ,  512 ′ of  FIGS. 5A and 5B .  FIG. 5D  is an enlarged view on side protrusions  504 ,  504 ′ and protrusions  502 ,  502 ′ of the two overlaid rings  512 ,  512 ′ of  FIG. 5C . 
     In the embodiment of  FIGS. 5A and 5B , the ring  512  has two protrusions  502  protruding axially at different axial positions on the ring  512 . In one embodiment, the protrusions  502  may be of the same shape as the protrusions  402  as shown in  FIGS. 4A-4D , while in another embodiment, the protrusions  502  may be different from the protrusions  402 . As shown in the embodiment of  FIGS. 5A-5D , the protrusions  502  are thinner in the radial direction when compared to the protrusions  402  and protrude from the ring  512  in the axial direction so as to create a gap  513  in-between the ring  512  and the next ring  512 ′. 
     Referring to  FIGS. 5A and 5B  again, the ring  512  further includes two side protrusions  504  protruding radially outward of the outer surface  303  of the main body  304  ( FIG. 3 ) at different radial positions. The side protrusions  504  can generally be of a curved shape with the middle part wider and the two ends pointed. In the other embodiments, the side protrusion  504  can be generally cuboid shaped as long as it protrudes from the outer surface  303  of the main body  304  to form at least one ridge, e.g., the ridge  308  extending axially and/or radially on the outer surface  303  of the main body  304 . Both protrusions  502  and side protrusions  504  are made of the third material, so that the protrusions  502 , the side protrusions  504 , and the ring  512  form an integrated part. 
     In the embodiment of  FIGS. 5A-5D , the side protrusions  504  protrude at the same radial position with a corresponding protrusion  502 , however, it should be appreciated that the side protrusions  504  protrude at a different radial position from any of the protrusions  502 , without deviating from the scope of the present invention. The protrusions  502  and the side protrusions  504  can be clearly observed from the enlarged view in  FIGS. 5A and 5B . 
     Referring to  FIGS. 5C and 5D , two rings  512  and  512 ′ are overlaid and axially spaced apart by a certain distance due to the protrusions  502  and the side protrusions  504 . As shown in the enlarged section of  FIG. 5D , one of the protrusions  502  and side protrusion  504  projects axially from the ring  512  away from the top annual surface  506  of the ring  512 . The bottom end of the protrusion  502  and the bottom surface  508  of the side protrusion  504  are arranged to engage with the top surface  506 ′ of the next ring  512 ′ to provide the required distance between the rings  512  and  512 ′ to allow the channel  513  to be formed between the rings  512 ,  512 ′ to accommodate the fourth material (e.g., matrix material) therein. The embodiments of  FIGS. 5C and 5D  are similar to the embodiments of  FIGS. 4C and 4D , and similar numeral refers to similar components with similar functions and will not be illustrated in further detail herein. 
     Referring to  FIGS. 3, 5A and 5B  together, the rings  512  and  512 ′ are further extended radially at the two ends where the side protrusions  504  protrude from the outer surface  303  of the main body  304  of the spacer  300 . The side protrusions  504  form at least one ridge  308  in  FIG. 3 ., The ridge  308  extends radially from the outer surface  303  and may further extend axially on the outer surface  303  of the main body  304 . The bottom annular surface  508  of the ring  512  can be partially contacted with the top surface  506 ′ of the subsequent ring  512 ′, such that the ridge  308  is inclined and extended axially on the outer surface  303  of the main body  304  ( FIG. 3 ). 
     By way of example, the diagonal extension of the two ridges  308  ( FIG. 3 ), and the diagonal extension of the ridges  608 ,  708  ( FIGS. 6 and 7 ) are formed, as shown in  FIGS. 5C and 5D , by having the side protrusion  504  arranged on top of the consecutive side protrusion  504 ′ and further by having the side protrusion  504  displaced radially from the consecutive side protrusion  504 ′. 
     The main body  304  of the spacer  300  includes a plurality of rings  512  each having one side protrusion  504  that are overlaid one by one to form the ridge  308 , so that the ridge  308  is extended axially along the outer surface  303  and further inclined from the first axial end  305  on the top side of the main body  304  to the second axial end  307  on the bottom side of the main body  304 . In another embodiment, the main body  304  of the spacer  300  includes a plurality of rings  512  each having two or more side protrusions  504  separated by substantially the same radial distance on a corresponding ring  512 , the corresponding side protrusions  504  on the rings  512  are overlaid one by one to form two or more ridges  508 , each of the ridges  508  being extended radially and/or axially on the outer surface  503  in a way that the ridges  508  are spread circumferentially along the outer surface  503 . 
     According to a specific implementation, the ridge  508  formed by the side protrusions  504  of the overlaid rings  512  is made of cemented carbide, the ridge  508  further adjoins with the fourth material, e.g., the matrix material, to enable the ridge  508  being metallurgically bonded and thus has an improved wear resistance. 
     Referring to  FIG. 6-7 , spacers  600  and  700  according to the embodiments of the present invention are further provided.  FIG. 6  is a perspective view of the spacer  600  of a roller screen according to a specific implementation of the present invention.  FIG. 7  is a perspective view of the spacer  700  of a roller screen according to another specific implementation of the present invention. The spacers  600  and  700  are arranged for cooperation with the disc  100  on the roller screen for the transportation of feed materials. The spacers  600  and  700  are similar with the spacer  300  as shown in  FIG. 3  and described above, similar labels of the spacers  600  and  700  have similar structures and functions as in the spacer  300 . 
     In the embodiment of  FIG. 6 , the spacer  600  includes a first extending portion  614  extended axially around an axis  601  from an upper end of a main body  604 , and further includes a second extending portion  616  extended axially around the axis  601  from a lower end of the main body  604 . A centrally arranged passage  606  in the spacer  600  is generally cylindrical, so that a shaft may pass through when assembled. Preferably in this embodiment, two ridges  608  are arranged extending along the main body  604 , and one end of each ridge  608  further extends axially onto the extending portion  614  until the top annular surface  618  of the extending portion  614 . Advantageously, the elongated ridges  608  further improve the wear resistance of the spacer  600  so that the lifetime of the spacer  600  can be increased. 
     In one embodiment, the ridges  608  are formed by the side protrusions  504  arranged on top of one another, each of the protrusions  504  further staggered radially, in the same radial direction, a little bit from the adjacent side protrusion, such that the diagonal extension of the ridges  608  is formed on the outer surface  603  of the spacer  600 . In one embodiment of  FIG. 6 , the spacer  600  is arranged as an end spacer installed at the two opposite ends on the shaft of the roller screen. As end spacers are most distant away from the centre of shaft of the roller screen, the wear resistance requirement is not the highest, in  FIG. 6 , the axial length A 1  of the main body  604  is arranged at about 25% of the axial length B 1  of the spacer  600 . Advantageously, such arrangement reduces cost and simultaneously guarantees the wear resistance requirement of the end spacers. 
     In the embodiment of  FIG. 7 , the spacer  700  includes an extending portion  716  extended axially around an axis  701  from a lower end of the main body  704 . A centrally arranged passage  706  in the spacer  700  is generally cylindrical, so that a shaft (not shown) may pass through when assembled. Two ridges  708  are arranged extending along the main body  704  and reach to the top surface  718  of the main body  704 . In one embodiment, the ridges  708  are formed by the side protrusions  504  arranged on top of one another, a consecutive protrusion  504  being radially somewhat staggered or displaced, in the same radial direction, a little bit from the preceding side protrusion, such that the diagonal extension of the ridges  708  is formed on the outer surface  703  of the spacer  700 . 
     The spacer  700  can be arranged as an end spacer installed at the two opposite ends on the shaft of the roller screen, with the axial length A 2  of the main body  704  is arranged at 25-50% of the axial length B 2  of the spacer  700 . Advantageously, such arrangement reduces cost and simultaneously guaranteed the wear resistance requirement of the end spacers. 
       FIG. 8  is a perspective view of an assembly  800  of the discs  100  and the spacers  300  in cooperation on a shaft  802  of a roller screen.  FIG. 9  is a perspective view of an assembly  900  of the discs  100  and the spacers  300 ,  600  in cooperation on a shaft  802  of a roller screen. As shown in the assemblies  800  and  900 , the shaft  802  has a rotational axis  801  along which the shaft  802  extends and is installed with a plurality of the discs  100  and a plurality of the spacers  300 ,  600 . More specifically, the discs  100  and the spacers  300 ,  600  are installed on the shaft  802  through each opening  106  of the transportation elements  100 , and each passage  306 ,  606  of the spacers  300 ,  600 . The discs  100  and the spacers  300  are assembled one by one and side by side, and the spacers  600  are assembly on the two opposite ends of the shaft  802 . In one embodiment, each two adjacent discs  100  are separated by one of the spacers  300 . Referring to  FIGS. 8 and 9 , the assembly  800  in the embodiment is configured so that the axis  101  of the discs  100 , the axis  301  of the spacers  300 , the axis  601  of the spacers  600 , and the rotational axis  801  of the shaft  802  are generally coincided, so that the discs  100  and the spacers  300 ,  600  can be located concentrically around the shaft  802 . The rotation of the assembly enables the transportation of feed materials on the roller screen. 
     Moreover, in the embodiment of  FIG. 8 , on the opposite ends of the shaft  802 , one more disc  100  is installed as an end disc. It is beneficial as the end discs further helps in the transportation of feed materials at around the ends of the shaft  802 . In the embodiment of  FIG. 9 , on the opposite ends of the shaft  802 , two end spacers are respectively installed on the shaft  802 . It is beneficial to use the end spacers as it guaranteed the wear resistant requirement at the end of the shaft  802  and at the same time reduces the cost of spacers; however, it will not be used as a limitation of the present invention, in another embodiment of the present invention, the end spacers can be the same as intermediate spacers, e.g., spacer  300 , and the assembly of such will work as properly as the embodiments as shown in  FIGS. 8 and 9 . 
     As mentioned above, the wear resistant portion  102  of the disc  100  is made of cemented carbides metallurgically bonded to the matrix material, and preferably, cemented carbides metallurgically bonded to spheroidal cast iron or high-chromium iron, the wear resistance of the disc  100  is improved, and the lifetime is thus increased. Also, in the embodiments of the present invention, the axial length of the main body is in a range 25%-100% of an axial length of the spacer. Since the main body of the spacer is made of cemented carbides metallurgically bonded to the matrix material, by configuring the main body in the range 25%-100% enables the spacer with increased wear resistance, and a longer service lifespan. By way of example, for a roller screen transporting coal as feed materials, the roller screen is adapted with the disc  100  and the spacer  300 ,  600 , or  700  of the present invention, assembled on the shaft of the roller screen, under typical operating loads with coal as feed materials, the disc and the spacer as described in the present invention is expected to last around or more than 24 months, the lifetime of which is largely increased than the existing transportation and spacer in the art, which is about half the lifetime of those in the present invention. 
     Although in the embodiments of  FIGS. 8-9 , in the assemblies  800  and  900 , the spacer  300 ,  600  is assembled with the disc  800  on the shaft  802 , other embodiments of discs and spacers within the scope of protection of the present invention can also be assembled on the shaft to provide similar functions and advantages. By way of example, the spacers  700  can be configured to be installed as end spacers on the shaft  802  with the disc  100 .