Patent Publication Number: US-10307793-B2

Title: Reusable material handling disc for recovery and separation of recyclable materials

Description:
STATEMENT OF RELATED MATTERS 
     This application claims priority to U.S. Provisional Application No. 62/326,637, filed on Apr. 22, 2016 and entitled Reusable Material Handling Disc for Recovery and Separation of Recyclable Materials; the contents of which are incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     Material sorting discs and material sorting screen. 
     BACKGROUND 
     Disc screens may be used in the materials handling industry for processing large flows of materials and removing certain items of desired dimensions and or shapes. In particular, disc screens may be configured to classify, sort, separate or otherwise distinguish between what may be considered debris or residual materials versus recoverable commodities. Different industries have multitudes of uses for these materials; and what is considered recoverable can vary according to geographical location and the particular application for the screen. The separable materials may consist of soil, aggregate, asphalt, concrete, wood, biomass, ferrous and nonferrous metal, plastic, ceramic, paper, cardboard, or other products or materials which may be recognized as having a relatively lower recoverable value throughout consumer, commercial and/or industrial markets. 
     The industry standards for known disc screens have primarily been directed to three major areas of design related to the equipment used in the material sorting systems. These include the frame and drive system, the shaft design, and the disc design. 
     Additionally, known disc screens may be configured to classify material in two distinct ways. A first method of classifying materials may be based on relative size. For example, the disc screen may be configured to separate undersized materials, which may range between one-fourth inches to twelve inches, from oversized materials. 
     A second method of classifying materials may be based on physical characteristic. For example, known disc screens may be configured to separate two-dimensional objects, such as Old Corrugated Cardboard (OCC), newsprint, office paper, and other fiber materials, from three-dimensional objects, such as plastic jugs, metal containers, and other objects. Material sorting systems may combine multiple methods of classifying material at various stages of processing the material flow. 
     In known material separation systems, the discs are either welded to the shaft or fastened using bolts or compression fittings. If the discs are fastened on, replacement can be expensive and time consuming; however, the shaft can be reused for a longer period of time. If the discs are welded on, then the entire shaft may require periodic replacement. 
     Reconfiguring a material processing system to alter the method(s) of separating materials, and/or replacing one or more parts of the equipment due to component failure or wear, may affect the efficiency of operation and add increased costs while the system is not operating. Additionally, worn-out equipment may need to be disposed of or otherwise stored after its useful life is over. 
     This application addresses these and other problems associated with the prior art. 
     SUMMARY OF THE INVENTION 
     A disc assembly is disclosed herein as comprising a substantially rigid disc core including a first section removably attached to a second section and mounted to a disc screen shaft. The disc core may comprise a textured transport surface extending between a left side of the disc core and a right side of the disc core. A replaceable coating of wear material may be deposited along an outer perimeter of the disc core and penetrate into the textured transport surface. 
     Another example disc assembly is disclosed herein as comprising a substantially rigid disc core including a first section removably attached to a second section and mounted to a disc screen shaft. The disc core includes a transport surface extending between a left side of the disc core and a right side of the disc core, and a replaceable coating of textured wear material may be deposited along the transport surface. 
     Additionally, a disc assembly is disclosed herein, as comprising a first disc including a first transport surface located along an outer perimeter of the first disc and associated with a first diameter, and a second disc having a second diameter and including a transport surface extending between a left side of the second disc and a right side of the second disc. The second diameter may be larger than the first diameter. A replaceable coating of textured wear material may be deposited on the transport surface. 
     A method is also disclosed herein. The method may comprise attaching a first portion of a disc assembly to a second portion of a disc assembly in order to mount the disc assembly to a shaft. The disc assembly may comprise a coating of wear material applied to the disc assembly. The method may further comprise separating materials transported over the disc assembly, and detaching the disc assembly from the shaft in response to a thickness of the wear material being decreased during material separation. The coating of wear material may be reapplied on the disc assembly in order to reuse the disc assembly. Additionally, the wear material may be textured. 
     In some examples, the disc assembly may comprise a disc core and a textured transport surface extending between a left side of the disc core and a right side of the disc core. Reapplying the coating may comprise depositing the wear material along an outer perimeter of the disc core. The wear material may penetrate into the textured transport surface. Additionally, the coating of wear material may comprise a substantially non-rigid wear material that penetrates into the textured surface of a substantially rigid disc core of the disc assembly. 
     The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a side sectional view of an example material separation system. 
         FIG. 2  illustrates a more detailed top view of example multi-diameter disc assemblies. 
         FIG. 3  illustrates an isolation view of an example shaft. 
         FIG. 4  illustrates the example shaft of  FIG. 3  with spacer discs. 
         FIG. 5  illustrates the example spacer discs of  FIG. 4  in more detail. 
         FIG. 6A  illustrates the example spacer discs of  FIG. 4  attached to the shaft and compound discs shown in an exploded view. 
         FIG. 6B  illustrates a partially exploded view of an example apparatus configured for sorting paper products such as newspaper. 
         FIGS. 7A-7C  illustrate example compound discs. 
         FIG. 8A  illustrates an example disc assembly comprising a channel. 
         FIG. 8B  illustrates cross-sectional view of the example disc assembly of  FIG. 8A , including a wear material. 
         FIG. 9  illustrates an example disc assembly in which substantially the entire outer surface may be coated with a wear material. 
         FIG. 10  illustrates an example disc assembly in which need only the outer material transport surface may be coated with a wear material. 
         FIG. 11  illustrates an example multi-disc and shaft assembly that may be coated with a wear material. 
         FIG. 12  illustrates an example disc assembly comprising a dis-shaped hub. 
         FIG. 13  illustrates an example disc assembly comprising a round-shaped hub. 
         FIG. 14  illustrates an enlarged partial view of a disc assembly that includes an attachment design comprising a through hole. 
         FIG. 15  illustrates an enlarged partial view of a disc assembly that includes an attachment design comprising an overlapping tab. 
         FIG. 16  illustrates an enlarged partial view of a disc assembly that includes a side plate. 
         FIG. 17  illustrates an example disc assembly comprising a textured wear surface. 
         FIG. 18  illustrates an example process of applying a coating of wear material to a reusable disc assembly. 
         FIG. 19  illustrates an exploded view of an example disc assembly. 
         FIG. 20  illustrates the disc assembly of  FIG. 19  as assembled. 
     
    
    
     DETAILED DESCRIPTION 
     Solid Waste recovery pertains to the ability to separate for recycling or re-use a multitude of materials and products once they have reached the end of their life cycle. Solid Waste can include typical recyclable material including but not limited to Municipal Solid Waste (MSW), Refuse Derived Fuel (RDF), Construction and Demolition (C&amp;D) or Residential Single Stream. These different kinds of Recoverable Solid Waste can include but is not limited to, fiber material such as newspaper, mixed paper, Old Corrugated Cardboard (OCC), other cardboard and office paper product; light plastic containers and film plastic, aluminum containers, tin containers and other containers or materials with two or three dimensional shapes; as well as wood and aggregate. 
     Some of the MSW can be used for making new products that may use the same material as the recycled items. For example, the paper and cardboard fiber material can be re-pulped to make new paper, cardboard or other fiber products. The recyclable MSW, such as plastic containers, can be shredded and melted into new containers and other types of plastic products that may not be related to the original recovered product. For example, PET bottles can be used as fiber fill for winter jackets or as fill for mattresses. 
     Most of the material stream, whether two-dimensional or three-dimensional objects, may be recovered and used for making new products or used as an energy source. The ability of a disc screen to efficiently separate by size and physical characteristic may significantly limit the amount of contaminant found in the final recovered commodity. 
     Equipment used in material sorting systems may include fairly heavy duty components with an associated cost per ton of material used. The ability to reduce the cost per ton can similarly reduce the cost of manufacturing and/or reduce the cost of maintenance associated with the system. Despite being made out of steel or other types of metal, material sorting discs in particular may be subject to considerable wear and require relatively frequent replacement over the life of the material separation system. 
       FIG. 1  illustrates an example separation system  100  configured to separate recyclable two-dimensional fiber materials from other three dimension materials such as recyclable plastic and metal containers. The separation system  100  includes a frame  103  that supports a disc screen  102 . The disc screen  102  includes shafts  182  that attach to the frame  103  and multi-diameter disc assemblies  110  that attach to the shafts  182 . The shafts  182  and disc assemblies  110  may be rotated in unison by a motor. The disc screen  102  may be orientated at an upwardly inclined angle from an in-feed end  106  to an out-feed end  104 . A portion of the disc screen  102  is shown in more detail below in  FIG. 2 . 
     The disc screen  102  may be configured to sort recyclable items from a comingled MSW stream  200 . Smaller objects and residue  204  typically falls through InterFacial Openings (IFOs)  108  formed between the disc assemblies  110 . The objects and residue  204  drop through the disc screen  102  and into a central chute  122 . Other flatter and larger fiber material  206 , such as paper and OCC, may be transported by the disc assemblies  110  over the top out-feed end  104  of disc screen  102  and dropped into a chute  124 . Containers and other more three dimensional shaped objects  202 , such as plastic and metal bottles, cans, jugs, other containers, etc. either fall through the IFOs  108  in the disc screen  102  and into chute  122  or tumble backwards off the back in-feed end  106  of the disc screen  102  into a chute  120 . 
       FIG. 2  illustrates a section of the example disc screen  102  of  FIG. 1 . Referring to both  FIGS. 1 and 2 , the disc screen  102  includes shafts  182  mounted to the sidewalls of frame  103  in a substantially parallel relationship. Each multi-diameter disc assembly  110  may comprise a small diameter spacer disc  130 , an intermediate diameter disc  170 , and a larger diameter large disc  150 . The large diameter disc  150  and an associated intermediate diameter disc  170  in the same disc assembly  110  may alternatively be referred to as a compound disc  140  and in some examples, may be formed from a same unitary piece of rubber. In other examples, the compound discs  140  may be made from some material other than rubber, such as steel or a relatively hard resin. Additionally, compound discs  140  may be formed from a different type of material than the spacer discs  130  and may be mounted to the shafts  182  separately from the spacer discs  130 . 
     The multi-diameter disc assemblies  110  may be aligned laterally on the shafts  182  so that the discs assemblies on adjacent shafts  182  overlap in a stair step manner as shown in  FIG. 2 . For example, the large diameter disc  150 A is aligned laterally on the shaft  182 A with the small diameter spacer disc  130 B on shaft  182 B. The intermediate discs  170 A and  170 B are aligned with each other on adjacent shafts  182 A and  182 B, respectively. The small diameter spacer disc  130 A on shaft  182 A is aligned with the large diameter disc  150 B on adjacent shaft  182 B. 
     During rotation, the disc assemblies  110  on adjacent shafts  182  may be configured to maintain a substantially constant spacing. The space between adjacent intermediate diameter discs  170 A and  170 B form one of the inter-facial openings (IFOs)  108  that remain substantially constant during disc rotation. The IFOs  108  allow smaller sized objects  204  to drop through the disc screen  102  while some of the material  206  is transported up the disc screen  102 . The spaces between the large diameter discs  150  and small diameter spacer discs  130  on adjacent shafts  182  form secondary slots  112 . The secondary slots  112  may be configured to remain at a substantially constant size during disc rotation. 
     The alternating alignment of the smaller spacer discs  130 , large discs  150 , intermediate discs  170  both laterally across each shaft  182  and longitudinally along the disc screen  102  between adjacent shafts  182  may be configured to eliminate long secondary slots that would normally extend laterally across the entire width of the disc screen  102  between discs on adjacent shafts  182 . Large thin materials  206 , such as paper and cardboard, cannot easily pass through the secondary slots  112  or IFOs  108 . This allows the materials  206  to be carried up the disc screen  102  and deposited in chute  124  with other recyclable MSW fiber materials. 
     In some examples, openings  108  are around 2 inches by 2 inches but different dimensions cam be used for different material separation applications. For example, the size of IFO openings  108  can vary according to the market for the fines material  204  which can differ according to region. In other types of news sorter screens, the openings  108  may be larger, such as 3.25, 4.25, or 5.25 inches by 5 inches. 
     Referring still to  FIGS. 1 and 2 , the different discs  130 ,  150 , and  170  may be configured to function differently during the separation of material stream  200  and therefore exhibit different wear patterns. For example, the large diameter discs  150  extend out above the intermediate and small diameter discs  170  and  130 , respectively. Accordingly, the large diameter discs  150  may be configured to take on much of the task of transporting material  200  up disc screen  102 . 
     The large diameter discs  150  also may be configured to absorb much of the initial contact of the materials that are dropped and then fall back off the back end  106  of disc screen  102 . For example, the three-dimensional containers  202  in material stream  200  are dropped onto the counter-clockwise rotating large discs  150  in  FIG. 1  and tumble back over the back end  106  of disc screen  102  into chute  120 . 
     The large diameter discs also may be configured to provide much of the up and down agitation of the MSW material  206  carried up the screen  102 . Because of the large amount of contact with material  200 , the larger discs  150  tend to have their cross sectional area reduced at a faster rate than the other smaller diameter discs  170  and  130 . 
     As explained above, the intermediate discs may be configured to form the IFOs  108  between adjacent shafts  182 . However, in other example systems, such as a news sorter or a Debris Roll Screen (DRS), the IFO may be primarily created by the shaft and not the shape of the disc. In still other examples, the IFO may be created by a combination of shaft, spacer, and/or disc configurations. Sorting systems comprising a variable IFO are described in U.S. Pat. No. 8,991,616 entitled Material Sorting Disc with Variable Interfacial Opening, the contents of which are herein incorporated by reference in their entirety. 
     As shown in  FIG. 1 , the smaller diameter materials  202  fall through the IFOs  108  while being carried up screen  102 . Although to a lesser extent than the large discs  150 , the intermediate discs  170  also may be configured to transport some of the materials  206  up the screen  102  and contact, rotate, and cause some of materials  202  to fall off the back end  106  of screen  102 . The intermediate diameter disc  170  may be configured to contact less of the material stream  200  than the large diameter discs  150  and therefore their cross sectional area may be reduced at a slower rate than the large discs  150 . 
     The spacer discs  130  may have a smaller outside diameter than both the large discs  150  and the intermediate discs  170 . Accordingly the spacer discs  130  may be configured to come in much less contact with material stream  200  and transport relatively little of the material  206  up the screen  102 . Rather, in some examples, the primary function of the spacer discs  130  may be to form the thin secondary slots  112  with the large discs  150  on adjacent shafts that are offset from the laterally adjacent IFOs  108 . As explained above, the secondary slots  112  may be configured to prevent relatively flat materials  206 , such as paper and OCC, from dropping through the screen  102 . 
     In some examples, the large discs  150  and intermediate discs  170  may be made out of a softer rubber material to better grip, transport, and separate out different parts of MSW material stream  200 . Rubber discs often grip MSW materials  206  better than a hard steel disc and therefore may be more effective at separating the MSW material  200 . 
       FIGS. 3-5  illustrate in more detail how the spacer discs  130  may be separately interlocked together and attached to the shaft  182 . In some examples, the shaft  182  may be made from a round elongated steel pipe. However, other triangular or square shapes shafts can also be used. The shaft  182  may be connected to the opposite walls of the screen frame  103  ( FIG. 1 ) via guides  188 , end plates  190  and cap plates  192 . 
     Holes  186  ( FIG. 3 ) may be drilled through one side of the shaft  182  along substantially the entire shaft length. The holes  186  are positioned at the desired lateral positions on shaft  182  for locating the spacer discs  130 . Key pins or spring pins  184  insert and compressibly attach into holes  186 . Alternatively, dowel pins can be force fit or welded into the holes  186  or pins can be welded onto the outside surface of shaft  182 . 
     Referring to  FIG. 5 , the spacer disc  130  may comprise two sections  132 A and  132 B that are the exact same shape and therefore can both be made from the same mold. One of the sections  132 A or  132 B may be turned upside down and attaches and interlocks with a corresponding end of the other section  132 . The two sections  132 A and  132 B when attached together around shaft  182  form a symmetrical half of a triangular profile perimeter with three arched sides and three lobes  146 A,  146 B, and  146 C. 
     The two sections  132 A and  132 B each have an inside wall  135 A and  135 B, respectively, that are each sized and shaped to snugly press against and around half of the outside circumference of the shaft  182 . Where the shaft  182  has a circular outside cross-sectional shape, the inside walls  135 A and  135 B each form a semi-circular shape that extends around half of the outside surface of the shaft  182 . 
     The two sections  132 A and  132 B may each include an interlocking end  133  and a coupling end  143 . The interlocking ends  133  include notches  138 A and  138 B that extend perpendicular into a first side of the sections  132 A and  132 B, respectively. Locking members  136 A and  136 B may extend perpendicularly from a second side of the sections  132 A and  132 B above the notches  138 A and  138 B, respectively. 
     Additionally, one or both of sections  132 A and/or  132 B may have a hole  134 A and/or  134 B formed in the inside wall  135 A and/or  135 B, respectively. The hole  134 A and/or  134 B may be sized to slidingly receive one of the pins  184  that extend out of the shaft  182  as shown in  FIG. 3 . One of the two sections  132 A or  132 B is attached to the shaft  182  such that the pin  184  slidingly inserts into hole  134 A or  134 B. The pin  184  may be configured to prevent any rotational movement of the spacer disc  130  against the shaft  182  during operation as well as guaranteeing the location of the spacer disc  130  during maintenance replacement. 
     The section  132 A or  132 B that is not attached to pin  184  may be rigidly interlocked with the other section  132  currently attached to shaft  182 . In some examples, section  132 B has already been attached to the shaft  182 , one of the pins  184  inserts into hole  134 B, and the inside wall  135 B presses and extends against half of the outside circumference of the shaft  182 . 
     Section  134 A is flipped around 180 degrees from the position shown in  FIG. 5 . The section  132 A is then pressed against the opposite half of the outside circumference of the shaft  182  but in a lateral position on shaft  182  adjacent to spacer section  134 B. Spacer section  134 A is then slid over the same lateral portion of shaft  182  where section  134 B is located. While sliding over section  134 B, the locking member  136 A in section  132 A  134 A inserts into the notch  138  B formed in spacer section  132 B. At the same time the locking member  136 B in spacer section  132 B slides into notch  138 A formed in spacer section  132 A. This interlocks the two sections  132 A and  132 B together at the interlocking end  133 . 
     When the two sections  134 A and  134 B are interlocked together, the coupling ends  143  of spacer sections  132 A and  132 B are positioned against each other face to face. Holes  140 A and  140 B are aligned with each other and form one continuously hole through lobe  146 A. A bolt (not shown) is inserted into one of the cavities  142  formed in one of the spacer sections  132 A or  132 B, and through the two holes  140 A and  140 B. A threaded nut (not shown) is inserted into a similar shaped cavity  142  formed in the opposite section  132 A or  132 B and screwed onto the end of the bolt locking the two spacer sections  132 A and  132 B together as shown in  FIG. 6A  below. 
     The length of the shaft  182  and alignment of the multi-diameter disc assembly  110  may include single end discs  152  attached on the lateral ends of shafts  182 . The end discs  152  may have the same shape as a single intermediate disc  170  or a single large diameter disc  150 . The end discs  152  may have two different sections  152 A and  152 B that attach together around the shaft  182  in a manner similar to the compound discs  140  as described in more detail below in  FIGS. 6A and 7A-7C . Further example interlocking disc assemblies are described in U.S. Pat. No. 8,424,684 entitled Multi-Diameter Disc Assembly for Material Processing Screen, the contents of which are herein incorporated by reference in their entirety. 
     As explained above, in some examples the smaller diameter spacer discs  130  do not transport much of materials  206  up the disc screen  102  ( FIG. 1 ). Therefore, the spacer discs  130  may be made out of a harder less gripping material than the compound discs  140 . For example, the spacer discs  130  may be made from a relatively hard fiberglass, polymer, nylon, or metal material, while the compound discs  140  may be made out of a substantially softer rubber material. In some examples, the spacer discs  130  may be made from a polyphthalamide (aka. PPA, High Performance Polyamide) which is a thermoplastic synthetic resin of the polyamide (nylon) family. In still other examples, the spacer discs  130  may be made from polyurethane. 
     The spacer discs  130  can not only be made from a harder material than the rubber compound discs  140  but can also be separately attached to the shaft  182 . Thus, the compound discs  140  can be replaced without also having the replace the spacer discs  130 . In other tri-disc designs, all three discs may be formed from the same piece of rubber material. Thus, whenever the large and/or intermediate discs wear out, smaller discs may also be replaced. 
     Using a harder material for the smallest diameter spacer discs  130  may allow for the use of larger diameters shafts  182  that reduce the overall amount of material needed for the multi-diameter disc assembly  110 . Referring to  FIG. 5 , the spacer discs  130  have the smallest outside diameter of the three discs  130 ,  150  and  170 . Therefore, the spacer discs  130  may be configured with the smallest material thickness between the outside surface of the shaft  182  and the smallest outside perimeter of the spacer disc  130  at locations  145 . 
     A minimum material thickness is provided at locations  145  to keep the spacer disc  130  from tearing apart. Using materials that are harder and more wear resistant than rubber allow the spacer discs  130  at locations  145  to be thinner. This allows the use of larger diameter shafts  182 , resulting in larger center holes  172  ( FIG. 7C ) in the multi-diameter disc assemblies  110 , and the use of less material in the multi-diameter disc assemblies  110 . Thus, the costs of manufacturing and shipping the multi-diameter discs  110  may be reduced. 
       FIG. 6A  illustrates an isolated view of one row of the example disc screen  102  of  FIG. 1  with the spacer discs  130  attached to the shaft  182  and the compound discs  140  shown in an exploded view. In some examples, the example disc screen  102  illustrated in  FIG. 6A  may be configured as a polishing screen. 
       FIG. 6B  illustrates a partially exploded view of an example sorting apparatus  1900  configured for sorting paper products such as newspaper. The sorting apparatus  1900  may comprise a partially exposed shaft  1910  with a plurality of hubs  1920  for attaching one or more sorting discs, such as disc  1950 . In some examples, the hubs  1920  may be welded or bolted to the shaft  1910 , such that some or all of the discs may be removed from the shaft  1910  without removing the hubs  1920 . 
     One or more of the discs may comprise a first disc portion  1930  and a second disc portion  1940  which may removably attached to the shaft  1910 . The first disc portion  1930  may be configured to mount to an opposite side of the shaft  1910  as the second disc portion  1940 . Additionally, the first disc portion  1930  may be configured to mount to the second disc portion  1940 , such as with an interlocking attachment, one or more bolts, or other attachment means. 
     In order to separate larger fiber materials, sorting apparatus  900  may be configured as part of a screen, comprising a plurality of shafts, having openings that allow smaller fiber and containers to pass through the screen. An IFO may be formed between two discs, such as a first disc  1950  and a second disc  1960 , such that the distance  1975  between discs may determine a length of the IFO. Additionally, the shaft surfaces of two parallel spaced apart shafts may further bound a width of the IFO. By creating the IFO along the shaft  1920  and between discs  1950 ,  1960 , the IFO may be formed with a constant length  1975 , and also a constant width between shafts, to accurately sort material according to its size, while selectively transporting fiber material, such as newspaper, up the screen. 
     Additionally, some or all of the discs may be coated with a wear material to further facilitate sorting and/or transport of select materials up the screen. Different types of material may be sorted by varying the spacing of the discs, the number of the discs, the diameter of the discs, the outer profile of the discs, the type of wear material used to coat the discs, an inclination angle of the screen, or any combination thereof. 
       FIGS. 7A-7C  illustrate examples of the compound discs  140  in more detail. As described above, the compound discs  140  may be formed from a separate piece of material than the spacer discs  130 . Forming the spacer discs  130  and compound discs  140  out of separate pieces of material may allow the compound discs  140  to be separately replaced while the spacer discs  130  remain attached to the shafts  182 . 
     Each of the separate discs can have any variety of different shapes, sizes, and number of sides. Discs with different combinations of shapes, sizes, and number of sides can also be combined together. For example, a three sided triangular disc may be combined with a four sided square shaped disc in the same compound disc. 
     The compound discs  140  may be configured to include an upper section  140 A and a lower section  140 B that connect together around the shaft  182 . The lower compound disc section  140 B includes a lower large disc portion  150 B that that may be integrally formed with a lower intermediate disc portion  170 B from a same piece of material. Holes  164  extend through opposite ends of the lower intermediate disc portion  170 B. An inside wall  169  of the lower compound disc section  140 B has a semi-circular shape that snugly presses around half of the outside circumference of the shaft  182 . 
     The upper compound disc section  140 A includes a large disc portion  150 A and intermediate disc portion  170 A that may both be integrally formed together from the same piece of material. A U-bolt  160  may be molded into the intermediate disc portion  170 A with opposite ends  161  that extend out from opposite ends  168 A of the compound disc section  140 A. A locating pin  162  is located at the center of the U-bolt  160  and extends out from an internal wall  167 . The inside wall  167  of the upper compound disc section  140 A also has a semi-circular shape that snugly attached around a second half of the circumference of the shaft  182 . 
     The locating pin  162  is inserted into one of the holes  198  in shaft  182  shown in  FIG. 4  and prevents the compound disc  140  from sliding against the shaft  182 . The inside surface  167  is pressed down against the upper half of the shaft  182  so that the opposite ends  161  of the U-bolt  160  extend on opposite sides of the shaft  182 . 
     The lower compound disc section  140 B is pressed underneath a bottom end of the shaft  182  so that the ends  161  of U-bolt  160  insert into holes  164 . The inside surface  169  of lower section  140 B is pressed against the lower outside surface of the shaft  182  while the opposite ends  168 A and  168 B of the upper and lower compound disc sections  140 A and  140 B, respectively press against each other. 
     The opposite ends  168 A of the upper section  140 A have a flat surface  174 A ( FIG. 7B ) and an inclined surface  175 A. The opposite ends  168 B of the lower section  140 B also have a flat surface  174 B and an upwardly inclined surface  175 B oppositely opposed with surfaces  174 A and  175 A, respectively. The surfaces  174 A and  174 BA and surfaces  175 A and  175 B press against each other when the two sections  140 A and  140 B are pressed against the shaft  182 . 
     When the two sections  140 A and  140 B are fully attached together, the ends  161  of U-bolt  160  extend through holes  164  and into the openings  166  formed in intermediate disc portion  170 B. Nuts (not shown) are inserted into openings  166  and screwed onto the ends  161  of U-bolt  160  holding the two sections  140 A and  140 B of the compound disc  140 ) tightly together and tightly against the shaft  182 . The compound discs  140  when fully assembled as shown in  FIG. 7C  having a triangular profile with three arched sides and a circular center hole  172 . 
       FIG. 8A  illustrates an example compound disc  230 , including a side view and front view, similar to the compound disc  140  described above that includes an intermediate disc  234 , a large disc  232 , and upper and lower compound disc sections  230 A and  230 B that attach around the shaft  182  of the disc screen  102  shown in  FIG. 1 . A channel  236  is formed into an outside perimeter surface of the large diameter disc  232 . The channel  236  effectively forms a tread of two parallel ribs  238  that extend above and around opposite sides of the entire outside perimeter of the large diameter disc  232 . This tread design can more effectively grip and transport certain types of material up disc screen  102  ( FIG. 1 ) for more efficient material separation. 
       FIG. 8B  illustrates a cross-sectional view of the example compound disc  230  of  FIG. 8A  with a wear material  280  provided around the perimeter of the disc  232 . Wear material  280  may be formed at the exterior contact surface, or transport surface, of the disc  232 . In some examples, wear material  280  may be formed, molded, sprayed on, or otherwise deposited into channel  236  and onto ribs  238 . Channel  236  may provide additional surface area to which wear material  280  may adhere and therefore be configured to resist separation of the wear material  280  from the disc  232  during operation. 
     Disc assembly  230  may comprise a substantially rigid disc core  232  including a first section  230 A removably attached to a second section  230 B and configured to be mounted to a disc screen shaft. The disc core  232  may comprise a textured transport surface extending between a left side of the disc core  232  and a right side of the disc core  232 . Wear material  280  may comprise a replaceable coating of substantially non-rigid wear material that is deposited along an outer perimeter of the disc core  232  and penetrates into the textured transport surface. 
     The textured transport surface may comprise a grooved recess, such as channel  236 , located in the outer perimeter of the disc core  232 , and at least a portion of the wear material may be deposited into the grooved recess along the outer perimeter of the disc core  232 . Additionally, the wear material may be deposited on the two parallel ribs  238  of the textured transport surface. 
     In some examples, the replaceable coating may be bounded by the textured transport surface without the wear material  238  being deposited on the left side and the right side of the disc core  232 . In other examples, at least a portion of the wear material may be additionally deposited on the left side and the right side of the disc core  232 . 
     Wear material  280  may radially extend from the channel  236  and/or exterior surface of the ribs  236  and increase the effective diameter of the disc  32 . The diameter of the disc  232  may vary according to the amount or thickness of wear material  280  that is attached to the channel  236  and/or ribs  238 . In some examples, the thickness of wear material  280  that extends outside of the ribs  238  may be approximately 0.125 inches. 
       FIG. 9  illustrates an example disc assembly  900  including as a front view and a side view, in which substantially the entire outer surface may be coated with a wear material. For example, the disc assembly  900  may comprise a substantially rigid structure which may be dipped into, sprayed, or otherwise coated with, wear material, such that not only a transport surface  950  but also side surfaces  960  of the disc assembly  900  may be coated with wear material. 
     Disc assembly  900  may comprise one or more discs, such as a small disc  910  and a large disc  920 , which may be attached to shaft. In some examples, disc assembly  900  may comprise a clamping device  930  which may be being used to attach the discs  910 ,  920  to the shaft. The discs  910 ,  920  may also be attached using fasteners or weldments, for example. 
     Small disc  910  and large disc  920  may be manufactured and/or attached to the shaft as an integral assembly. In other examples, small disc  910  and large disc  920  may be separately manufactured and/or attached to the shaft. Disc assembly  900  may comprise a two-part assembly which attach about either side of the shaft. In other examples, disc assembly  900  may comprise a multitude of parts that assemble together. 
       FIG. 10  illustrates an example disc assembly  1000 , including as a front view and a side view, in which only the outer material transport surface  1050  may be coated with a wear material  1080 . Selectively applying wear material to transport surface  1050  may reduce the amount of raw material used to create the assembly  1000  and similarly reduce the overall cost and weight. 
     Similar to the disc assembly  900  illustrated in  FIG. 9 , disc assembly  1000  may comprise a small disc  1010 , a large disc  1020 , and a clamping device  1030 ; however, other examples may include fasteners, weldments, and discs comprising individual, two-part, or a multitude of parts, assemble and/or arranged in any number of ways. 
     A first disc, such as small disc  1010  may comprise a first transport surface located along an outer perimeter of the first disc  1010 . First disc  1010  may be associated with a first diameter. Similarly, a second disc such as larger disc  1020  may be associated with a second diameter. The second diameter may be larger than the first diameter. 
     Second disc  1020  may include a textured transport surface  1050  extending between a left side  1022  of the second disc  1020  and a right side  1024  of the second disc  1020 . A replaceable coating of substantially non-rigid wear material  1080  may be deposited along an outer perimeter of the second disc  020  and penetrates into the textured transport surface  1050 . 
     In some examples, second disc  1020  may be separately attachable to a shaft from the first disc  1010 . The first disc  1010  may abut up against a side of the second disc  1020 , such as right side  1024 , after the disc assembly  1000  is attached to the shaft. Additionally, a replaceable coating of wear material  1080  may be bounded by the textured transport surface  1050  without the wear material being deposited on the side(s) of the second disc  1020 . In some examples, the wear material  1080  may be deposited on both the first disc  1010  and the second disc  1020  after the disc assembly  1000  is attached to the shaft, and may be deposited on one or more sides of second disc  1020 . 
     One or more of the discs and/or disc assemblies described herein may be manufactured or otherwise configured to include a wear material having different material characteristics than the underlying rigid disc structure. The wear material may have a different adhesive characteristic, for example to provide a better grip or increased friction force on the material being sorted. In some examples, the wear material may provide for a softer contact surface, such as when handling relatively fragile materials. Additionally, the wear material may be lighter than the material of the underlying disc, and decrease the overall weight of the disc assembly. 
     Different types of wear material may be used to provide different material sorting characteristics. For example, some type of wear material may provide for increased friction and/or durability in hot or cold temperatures, in dry or humid conditions, in air that is dusty or includes particulates, other types of operating environments, or any combination thereof. Additionally, as the system may be configured to sort a wide range of materials which may interact or behave differently in the operating environment, the wear material for the discs may be selectively applied to provide a particular function or exhibit a particular behavior in a customized manner. 
     In some examples, the discs may be removed and installed as individual discs or disc assemblies. The new discs max comprise a different wear material than the discs which were removed. Discs having different wear materials may be combined in the same material sorting system, whether on the same separation screen or on two or more separation screens which may be sequentially linked to each other in the material stream. 
     The material separation screen may comprise both primary and secondary discs. In some examples, the primary discs may be relatively larger than the secondary disc. Additionally, the wear material may be preferentially applied to one or both of the primary and secondary discs according to the material separation system specifications. In some examples a relatively softer wear material may be applied to the primary or large discs. The wear material may be replaced and/or recoated on to the primary discs as needed. Accordingly, the primary discs may be refurbished at much lower cost as compared to manufacturing new discs. 
     As discussed above, the disc and shafts may be considered wear items that may be replaced or refurbished at certain intervals depending on the material characterization being processed. Providing a disc with a replaceable wear surface may substantially eliminate the costly replacement and disposal of disc materials by creating a re-useable underlying rigid disc structure or core that may be remanufactured and/or refurbished with a new wear surface and then used over and over again in a separation screen. 
     In some examples, the wear material may comprise a single part or a two part coating of urethane and/or polyuria. The coating(s) may be applied to the disc core by pouring, spraying or over-casting. The wear material may have a high tear and tensile strength while also maintaining a high coefficient of friction. The wear material&#39;s physical attributes may also be modified through chemistry and/or heat treatment to alter the properties for use in different markets, such as cold weather, compost, fuel, concrete, mining, wood products, MSW, and Construction and Demolition (C&amp;D). 
       FIG. 11  illustrates an example composite disc and shaft assembly  1100 , comprising a first portion  1110  of the multidisc assembly  1100  detached from a second portion  1120  of the multidisc assembly  1100 , which may be coated with a wear material. Both the interior and exterior of the first and second portions  1110 ,  1120  are shown for purposes of illustration. In some examples, substantially the entire outer surface of the assembly  1100  may be coated with a wear material. 
     The assembly  1100  may comprise a plurality of discs and/or spacers manufactured as an integral assembly that may be attached to a shaft of a separation screen. Assembly  1100  may comprise two halves  1110 ,  1120  configured to be clamped, secured, or otherwise attached about either side of the shaft. In some examples, a number of such assemblies may be attached or bolted directly to the shaft to create a larger final assembled component that is used in the screening system. 
     A multi-disc shaft assembly, such as the example composite disc and shaft assembly  1100 , may be configured to allow for changes in the geometry that provide a different sized IFO for use with different shafts. For example, the composite disc and shaft assembly  1100  may be configured to allow fine material to pass through the screen. Additionally, the individual disc shapes and/or outer profiles may be modified to allow a range of materials of varying size or dimensions, such as between two and twelve inches, to pass through the screen. Once the wear material has been worn through or otherwise reached an end of useful life, the composite disc and shaft assembly  1100  may be removed and recoated. 
       FIG. 12  illustrates an example disc assembly  1200  comprising a disc-shaped hub  1240 . Hub  1240  may be manufactured out of steel and expected to have a long lifespan and, in some examples, may comprise a semi-permanent bolt in core. Disc assembly  1200  may additionally comprise one or more discs, such as a small disc  1210  and a large disc  1220 , which may be attached to hub  1240 . In some examples, disc assembly  1200  may comprise a clamping device  1230  which may be being used to attach the disc assembly  1200  to a shaft. 
     Small disc  1210  and large disc  1220  may be manufactured and/or attached to the hub  1240  as an integral assembly. In other examples, small disc  1210  and large disc  1220  may be separately manufactured and/or attached to hub  1240 . Disc assembly  1200  may comprise a two-part assembly which attach about either side of the shaft. In other examples, disc assembly  1200  may comprise a multitude of parts that assemble together. 
     The disc shape of hub  1240  may comprise a generally triangle, pentagon, or star shaped profile, for example, where the distance of the exterior surface of the hub  1240  from the interior cylindrical surface may vary along the circumference. Varying the wall thicknesses of the hub  1240  may be operable to transmit additional energy from the shaft into the disc assembly  1200 . 
     In some examples, one or both of the large disc  1220  and the small disc  1210  may be manufactured out of a wear material which may be substantially softer than the material used for the core  1240 . In other examples, an outer material transport surface  1250  of the disc assembly  1220  may be coated with a wear material. Additionally, the outer transport surface  1250  may comprise the outer perimeter of the large disc  1220  and/or the outer perimeter of the small disc  1210 . In still other examples, the transport surface  1250  and one or more sides  1260  of the disc(s) may be coated with wear material. 
       FIG. 13  illustrates an example disc assembly  1300  comprising a round-shaped hub  1340 . Other than the round-shaped hub  1340 , disc assembly  1300  may be configured similarly as disc assembly  1200  of  FIG. 2 , including a small disc  1310  and a large disc  1320  attached to hub  1340 . 
       FIG. 14  illustrates an enlarged partial view of a disc assembly  1400  that includes an attachment system  1430  comprising a through-hole  1490 . In some examples, attachment system  1430  may be configured similarly as clamping device  1230  of  FIG. 2 , in which through-hole  1490  may pass through at least a portion of a small disc  1410  of disc assembly  1400 . 
       FIG. 15  illustrates an enlarged partial view of a partially disassembled disc assembly  1500  that includes an attachment system  1530  comprising one or more tabs  1580 . Tabs  1580  may be used to attach two or more portions of disc assembly  1500  to each other. In some examples, tabs  1580  may be configured as an overlapping tab arrangement comprising two spaced apart tabs. Tabs  1580  may be configured to be inserted into complimentary receiving slots  1590  of attachment system  1530 . Attachment system  1530  may be configured to attach one or more discs  1520  of disc assembly  1500  about or to a rigid hub  1540 . 
       FIG. 16  illustrates an enlarged partial view of a disc assembly  1600  comprising a side plate  1670 . Certain types of coating applications may be physically affected by sharp edges and cavities, which may decrease the life expectancy of usability of the coating material. The side plate  1670  may comprise a plastic molded part configured to snap into a cavity of the disc assembly  1600  prior to applying the surface coating or wear material  1680 . In some examples, wear material  1680  may be applied both to a contact surface of an outer disc  1620  and the side plate  1670 . 
     Side plate  1670  may be attached to a side surface of disc assembly  1600  via an attachment mechanism  1675 , such as one or more press-fit tabs, snap-in pins, and/or bosses. The attachment mechanism  1675  may be configured to attach side plate  1670  to one or more discs of disc assembly  1600 . In some examples, attachment mechanism  1675  may be configured to attach side plate  1670  to a core  1640  of disc assembly  1600 . 
       FIG. 17  illustrates an example disc assembly  1700  comprising a textured wear surface  252 . Disc assembly  250  may comprise a small disc  256 , a large disc  254 , and in some examples may comprise upper and lower sections  250 A and  250 B that attach together around a shaft. The textured wear surface  252  may comprise slits, grooves, bumps, dimples, peening, other textured surfaces, or any combination thereof. In some examples, textured wear surface  252  may comprise siped surfaces including thin slit that are cut in diagonal directions with respect to the outside surface of large disc  254 . 
     The textured wear surface  252  may comprise features which extend some distance from the outside surface toward the center of disc  254 . In some examples, textured wear surface  252  may comprise slits or sipping that extend anywhere from around 0.1 inches to 0.5 inches into the exterior contact surface of disc  254 . In some examples, the slits may incline in a direction of disc rotation which may provide a serrated rough outside perimeter surface that improves the ability of the disc  254  to grip and carry materials. 
     In some examples, textured wear surface  252  may be configured to provide an adhering surface for a wear material to be applied to. The surface features may increase the surface area of textured wear surface  252  as compared to a smoot exterior surface, and therefore provide better adhesive characteristics for the wear material. 
     The textured transport surface  252  may comprise a plurality of grooves arranged in a siped pattern along the outer perimeter of a disc core, and at least a portion of the wear material may be deposited into the plurality of grooves. 
     The first section  250 A of disc assembly  1700  may comprise a first interlocking end and a first coupling end, and the second section  250 B may comprise a second interlocking end that interlocks with the first interlocking end and a second coupling end that couples to the first coupling end. 
     In some examples, wear material may be separately deposited onto the first section  250 A and the second section  250 B prior to mounting the disc assembly  1700  to the shaft. In other examples, wear material may be deposited onto the disc assembly  1700  after mounting the disc assembly  1700  to the shaft. 
     In addition to filling in any slits, grooves, or other features of textured wear surface  252 , the applied wear material may extend away from the outer contact surface of the disc  254 , effectively increasing the outer diameter of the disc assembly  1700 . In some examples, the thickness of the wear material which extends out and away from the outer contact surface may be approximately 0.01 inches to 0.5 inches, or more. 
     In some examples, the outer surface of the disc  254  may be substantially smooth prior to applying the wear material. Instead, the wear material itself may provide the textured wear surface  252 . For example, the wear material may be coated onto the contact surface of the disc  254  with a texture and/or spackled finished. The spackled finish of the texture wear material  252  may be achieved by include the texture in a mold or by spraying on the wear material in an uneven or distributed manner. 
     The textured wear surface  252  may be configured to provide additional friction in certain environmental conditions to move the material through the screen and achieve proper separation. In some examples, the textured spackle may be added to the wear material during an application process by using the same material as the wear material, but applied from a longer distance. For example, the texturing may be completed by holding an application spray device and shooting a light mist so the material settles onto the disc assembly after it has partially dried in the air; creating a textured surface. The textured surface may provide for an approximately 20-30% increase in the coefficient of friction, allowing the screen to be run at higher angles and/or with wet slick materials. 
       FIG. 18  illustrates an example process  1800  of applying a coating of wear material to a reusable disc assembly. At operation  1810 , a coating of wear material may be applied to a disc assembly. In some examples, the disc assembly may comprise first and second portions removably attachable to one another about a shaft. 
     At operation  1820 , the first portion and the second portion may be placed on opposite sides of the shaft. In some examples, the first portion and the second portion may comprise identical halves of the disc assembly. 
     At operation  1830 , the first portion of the disc assembly may be attached to the second portion of a disc assembly in order to mount the disc assembly to the shaft. The disc assembly may comprise a coating of wear material applied to the disc assembly. 
     At operation  1840 , the disc assembly may be operated to separate materials transported over the disc assembly. 
     At operation  1850 , the coating of wear material may be worn away due to contact and friction with the materials being separated at operation  1840 . 
     At operation  1860 , the disc assembly may be detached from the shaft in response to a thickness of the wear material being decreased during the material separation operation. 
     At operation  1870 , the coating of wear material may be reapplied on the disc assembly in order to reuse the disc assembly. The disc assembly may comprise a disc core and a textured transport surface extending between a left side of the disc core and a right side of the disc core. In some examples, reapplying the coating may comprise depositing the wear material along an outer perimeter of the disc core, such that the wear material penetrates into the textured transport surface of the disc core. 
     Additionally, the coating of wear material may comprise a substantially non-rigid wear material that penetrates into the textured surface of a substantially rigid disc core of the disc assembly. 
     At operation  1880 , the refurbished disc assembly may be replace on the shaft, or a different shaft, as described at operations  1820  and  1830 . 
     At operation  1890 , the refurbished disc assembly may again be used to separate materials. In other examples, the disc assemblies may be refurbished without removing or otherwise detaching the cores from the shaft. For example, some or all of a sorting screen and/or assembled shaft may be coated with wear material. 
       FIG. 19  illustrates an exploded view of an example disc assembly  2000 , comprising a hub  2020 , a first disc portion  2030 , and a second disc portion  2040 . One or both of first disc portion  2030  and second disc portion  2040  may comprise an attachment mechanism  2045 . Attachment mechanism  2045  may be configured to interlock or otherwise attach first disc portion  2030  to second disc portion  2040 . For example, attachment mechanism  2045  may be configured to be inserted into a receiving slot or groove of first disc portion  2030 . Additionally, one or more bolts may be used to removably attach first disc portion  2030  to second disc portion  2040 . 
     First disc portion  2030  and second disc portion  2040  may be attached to each other around the hub  2020 . In some examples, first disc portion  2030  may be configured to mount to an opposite side of the hub  2020  as the second disc portion  2040 . The hub  2020  may be mounted to a shaft. Additionally, the hub  2020  may comprise two portions which are removably attached to each other about the shaft, similar to the description of the first disc portion  2030  and the second disc portion  2040 . In some examples, the hub  2020  may be secured to the shaft by an attachment device, such as by one or more bolts. 
     The hub  2020  may be attached to the shaft prior to mounting the first disc portion  2030  and the second disc portion  2040  to the hub  2020 . In other examples, one or both of the first disc portion  2030  and the second disc portion  2040  may be mounted to the hub  2020  prior to mounting the hub  2020  to the shaft. Once assembled, the first disc portion  2030  and the second disc portion  2040  may be rigidly attached to the hub  2020 , and the hub  2020  may be rigidly attached to the shaft, such that the entire disc assembly  2000  may be configured to rotate as a unitary component when the shaft rotates. 
     The hub  2020  may comprise a location device  2010  to control the spacing and/or rotational orientation of the disc assembly  2000  relative to the shaft. For example, the location device  2010  may comprise a hole configured to receive a location pin that is welded to the shaft. In other examples, the location device  2010  may comprise a location pin that is inserted into a receiving hole on the shaft. 
     The hub  2020  may be made out of steel or some other type of rigid material. In some examples, the first disc portion  2030  and the second disc portion  2040  may also be made out of steel. Additionally, one or both of the first disc portion  2030  and the second disc portion  2040  may comprise internal pockets or webbing, rather than being made out of a solid core, in order to reduce the overall weight of the disc assembly  2000  while still maintaining structural support for sorting heavy and/or abrasive materials. Additionally, the core structure may be configured to transfer or receive torque from the shaft. 
     In some examples, one or more disc covers, such as disc cover  2050 , may be attached to the sides of one or both disc portions  2030 ,  2040 , in order to protect the inner surfaces, e.g., pockets, of the core structure. Additionally, in examples in which some or all of the disc assembly  2000  may be coated with a wear material, the disc cover  2050  may comprise a flat surface that is configured to mate with a contact surface  2035  of the disc assembly  2000  to improve adhesion of the wear material to the disc assembly. The wear material may coat or encapsulate both disc portions  2030 ,  2040 , with the disc cover  2050  installed, prior to mounting the disc assembly  2000  to the shaft. 
       FIG. 20  illustrates the disc assembly  2000  of  FIG. 19  as assembled, such that the first disc portion  2030  and the second disc portion  2040  are combined to form a reusable disc core  2075 . When assembled, the disc core  2075  together with the side cover  2050  may give the appearance of a substantially solid disc, such that the internal pockets ( FIG. 19 ) may no longer be visible. 
     The use of a hinge  2025  in the hub  2020  may be configured to allow for a fastening system that creates tension through compression loading onto the shaft. As discussed above with respect to  FIG. 19 , the disc core  2075  may be fixed to the hub  2020  using an attachment mechanism such as an interlocking tab design and/or a sliding tab with axial bolt on either side of the disc core  2075 . An interlocking tab design may be configured to allow the two portions of the disc core  2075  to fasten to each and other without requiring a bolt or other fastening device associated with the disc core  2075  to penetrate into the hub  2020  itself. 
     Example Modes of Operation and Wear Materials. 
     One or more of the disc assemblies disclose herein may be configured as a removable part of a disc screen, which allows the shaft to remain on the frame while the disc assembly is being refurbished and/or recoated with new wear material. The coating or wear material selected for the disc assemblies may be configured to move material up the screen while sizing the material through the screen. Different coating materials may be selected according to their properties, such as how the material reacts to temperature and moisture content of the material being sorted. The re-useable portion of the disc assemblies may comprise an inner core of the disc assembly. These cores may be exposed as coating is worn, allowing the machine operator to identify which discs need to be removed and returned to the manufacture for re-coating. In some examples, one or more portions of discs mounted to the core may also be reusable. In addition to being reusable, one or both of the disc core and the hub may be made of recyclable and/or recycled material. 
     A multi-diameter disc assembly may comprise a two part assembly that is removable from the screen. The two parts may comprise interlocking features that are configured to attach the two parts to each other and to a shaft. The base components, such as the rigid core and/or hub, may be manufactured from a harder, wear resistant material, such as steel. The coating components or wear material, on the other hand, may be applied through pouring, molding, brushing or spraying a relatively softer material onto the base components. 
     In some examples, the attributes of the coating components may change durometer and/or toughness based on the material to be processed. The base components can be removed from the material sorting screen and recoated with new wear material when the useable life of the coating is reached. 
     Additionally, a removable and/or reusable disc assembly may be configured to be changed or use different types of core material as well as coating material, according to different applications, different sorting materials, different operating conditions, or any combination thereof. 
     For example, when sorting materials that include glass content, both a soft core and a soft coating may be used to allow the glass bottles to go over the screen without breaking. When sorting wet or frozen material, a soft coating with higher coefficient of friction may be selected for the wear material. On the other hand, when sorting large abrasive material, a harder core with a hard coating may be used to add wear life to the disc assembly. 
     When sorting fiber, a coating may be selected with properties similar to rubber. By way of further illustration, when sorting fine particle size and/or abrasive materials, a reduced core size may be configured to allow for a thicker coating to be applied which may extend the life of the disc assembly. In still other examples, the wear material may comprise a steel spray, a steel coating, a ceramic coating, a glass coating, other types of rigid materials or non-rigid materials, or any combination thereof. 
     For Construction and Demolition (C&amp;D) or Refuse Derived Fuel (RDF) applications, the disc assemblies may be coated with a wear material comprising a hard/abrasive resistant coating with a low coefficient of friction. 
     For sorting systems which include separation of glass or ceramic materials, the disc assemblies may be coated with a wear material comprising an extremely hard, low coefficient of friction material, which may be applied in a relatively thicker coating. 
     For sorting systems which include a Single Stream (SS) or MSW and which operate at ambient temperature, the disc assemblies may be coated with a relatively soft wear material have a coefficient of friction comparable to rubber. 
     SS/MSW—Cold environments—softest coating better COF than rubber coating 
     For sorting systems which include a Single Stream (SS) or MSW and which operate in cold or refrigerated temperatures, the disc assemblies may be coated with wear material having a greater coefficient of friction as compared to rubber. 
     Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention may be modified in arrangement and detail without departing from such principles.