Abstract:
A disc screen apparatus is disclosed for separating mixed recyclable materials of varying sizes and shapes. The disc screen apparatus has an enclosure or frame with an input, a container discharge location and a paper discharge location. A first plurality of shafts and second plurality of shafts are rotatably supported by the frame. The first plurality of shafts form a first disc screen disposed in a first plane and the second plurality of shafts form a second disc screen at least a portion of which is disposed in a second plane. The second plane is disposed beneath and angled with respect to the first plane such that the planes at least partially overlap. One or more motors rotate the first and second plurality of shafts. Each shaft has a plurality of discs positioned along it. The discs are offset between adjacent shafts such that discs on each shaft interleave with discs on an adjacent shaft but do not touch the adjacent shaft. The discs are substantially square in shape with radiused corners. The radiused corners have a texture, such as ridges. The arrangement of the discs on the shafts creates a screening pattern capable of screening a portion of the mixed recyclable materials. Each disc is assembled about a shaft from two identical portions. The portions are clamped together, about the shaft to form the disc. If the disc is damaged or worn, it may be removed from the shaft for repair or replacement without disassembly of the shaft from the apparatus or removal of other discs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention is in the field of machines for processing recyclable material, and particularly concerns machines that separate paper, bulk containers, broken glass and other materials.  
           [0002]    More specifically, the invention relates to a disc screen apparatus for classifying material in a stream of heterogeneous materials. More specifically still, the invention concerns a disc screen apparatus with discs that may be mounted to and removed from the apparatus without disassembly of the apparatus.  
           [0003]    Material recycling has become an important industry in recent years due to decreasing landfill capacity, environmental concerns and the dwindling of natural resources. Many industries and communities have adopted voluntary and mandatory recycling programs for reusable materials. Solid waste and trash that is collected from homes, apartments or companies often combine the recyclable materials into one container, usually labeled “RECYCLABLE MATERIAL”. Recyclable materials include newspaper, magazines, aluminum cans, glass bottles and other materials that may be recycled. When brought to a processing center, the recyclable materials are frequently mixed together in a heterogenous mass of material. Ideally, the mixed materials should be separated into common recyclable materials (i.e., papers, cans, etc.).  
           [0004]    Disc screens are increasingly used to separate heterogeneous streams of recyclable material into respective streams or collections of similar materials. This process is referred to as “classifying”, and the results are called “classification”.  
           [0005]    A disc screen apparatus typically includes a frame in which a plurality of rotatable shafts are mounted in parallel. A plurality of discs are mounted on each shaft and means are provided to rotate the shafts commonly in the same direction. The discs on one shaft interleave with the discs on an adjacent shaft to form screen openings between the peripheral edges of the discs and structures on the adjacent shaft. The sizes of the openings determine the size (and thus the type) of material that will fall through the screen. Rotation of the discs carries the larger articles along or across the screen in a general flow direction from an input where a stream of material pours onto the disc screen to an output where those articles pour off of the disc screen.  
           [0006]    In disc screen apparatuses that are used for classification of recyclable materials I have found that the heavy continuous flow of recyclable material tends to result in quick wear and a significant degree of damage to the discs, requiring a high level of maintenance and repair. My observation is that the discs are typically slidably engaged to their shafts, fixed in their positions by spacers, and retained in the shafts by clamping applied to the ends of the shafts. Therefore; to replace a damaged disc, the shaft on which the disc is mounted must be disassembled from the screen, the disc slid off the shaft and replaced, and the shaft reassembled to the screen. Much time is consumed in this process.  
         SUMMARY OF THE INVENTION  
         [0007]    The invention is based upon the critical realization that a disc for a disc screen apparatus can be provided in two (or more) matching pieces having opposing surfaces that are clamped together around a shaft. When damaged, the matching pieces are separated, removed from the shaft and replaced by the pieces of another, undamaged disc.  
           [0008]    One of the principal objects of this invention is therefore to provide a disc screen apparatus for use in a heavy duty processing operation in which screen repair time must be minimized.  
           [0009]    In connection with this objective, the invention is directed toward provision of a disc that can be attached to and removed from the shaft of a disc screen apparatus without disassembling the shaft from the screen apparatus.  
           [0010]    Other objects and advantages of the invention will become apparent when the following detailed description is read with reference to the below-described drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]    [0011]FIG. 1 is a side view of a disc screen machine that embodies the invention;  
         [0012]    FIGS.  2 A- 2 C are top views of rotatable shafts and discs showing different screen configurations;  
         [0013]    [0013]FIG. 3A is a side elevation view of a disc, with a portion cut away, showing certain elements with hidden lines;  
         [0014]    [0014]FIG. 3B is an elevation view of an edge of the disc of FIG. 3A;  
         [0015]    [0015]FIG. 3C is a top plan view of an edge of the disc of FIG. 3A;  
         [0016]    [0016]FIG. 4A is a side elevation view, with a portion cut away, of one of two pieces of the disc of FIG. 3A;  
         [0017]    [0017]FIG. 4B is an end elevation view of the one piece of FIG. 4A;  
         [0018]    [0018]FIG. 4C is sectional view of the one piece, taken along C-C of FIG. 4A;  
         [0019]    [0019]FIG. 5A is a side elevation view of a rigid frame or an embedment in the one piece of FIG. 4A;  
         [0020]    [0020]FIG. 5B is a front elevation view of the embedment of FIG. 5A;  
         [0021]    [0021]FIG. 5C is a sectional view of the embedment of FIG. 5A, taken along C-C of FIG. 5A;  
         [0022]    [0022]FIG. 6 is a top view taken along  6 - 6  in FIG. 1 showing the relationship of the motor, rotatable shafts, pulleys and drive mechanism;  
         [0023]    [0023]FIGS. 7A, 7B and  7 C are views of a shaft assembly; and  
         [0024]    [0024]FIGS. 8A and 8B show some details of the shaft assembly in FIG. 7.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    My invention is a disc screen apparatus (“hereinafter “apparatus”) that separates mixed recyclable materials, of various sizes and shapes, including paper, magazines, plastic or aluminum containers and the like. The apparatus, indicated generally by  100 , includes a frame (or housing)  102 , having a first plurality of rotatable shafts  108  (“first rotatable shafts”) and a second plurality of rotatable shafts  112  (“second rotatable shafts”) rotatably supported in the frame  102 . A first motor  118  mounted on the frame  102  is coupled to a drive chain  119  that imparts a rotational force to the first rotatable shafts  108 , while a second motor  130 , also mounted on the frame  102 , is coupled to a drive chain  131  that imparts a rotational force to the second rotatable shafts  112 .  
         [0026]    Preferably, the frame  102  is constructed using durable, heavy duty materials, such as steel. The precise shape of the frame  102 , and its structure and layout, are subject to the design considerations and operational constraints of any particular application. However, in this example the frame  102  is a generally closed structure with an mixed material input area  104 , container discharge area  114  and a paper discharge area  116 .  
         [0027]    Although the frame  102  forms an enclosure, this is not absolutely necessary to the invention, but it may be required for safety reasons. The mixed material input area  104  is generally located near a first end  105  of the frame  102 , where a heterogenous material stream  106  of recyclable materials enters the apparatus. As can be seen in FIG. 1, the material stream  106  travels through the mixed material input area  104 , and falls onto the first rotatable shafts  108 . The first rotatable shafts  108  rotate in such a direction that the material stream  106  travels from the first end  105  of the apparatus toward a second end  107  of the apparatus in a general flow direction. Mounted on the first rotatable shafts  108  are a plurality of discs  110  that both agitate and propel the material stream  106 . The discs  110  may be spaced on the shafts in a variety of patterns. Depending on the patterns of the discs  110 , the material stream  106  starts to separate in one way or another. In this manner, the first rotatable shafts  108  with discs  110  act as a first disc screen. (Hereinafter, these terms are interchangeable.) In the preferred embodiment, the discs  110  are positioned in the first disc screen so that the material stream  106  is initially screened, with small materials  120  passing through the openings and larger materials continuing along the first rotatable shafts  108 , all the while being agitated by the discs  110 . At the end of the plane of first rotatable shafts  108 , the larger materials fall onto the second rotatable shafts  112  (the direction shown as arrow  124 ). Mounted on the second rotatable shafts  112  are a plurality of discs  110 . Thus, the second rotatable shafts with discs  110  act as a second disc screen, and these terms are interchangeable hereinafter. The discs  110  may be mounted on the second rotatable shafts in a variety of patterns. The second rotatable shafts  112  are generally positioned in an inclined plane  160  that has an angle  162 . This inclined arrangement of the second rotatable shafts  112  allows heavier objects  122 , such as bottles and cans, to bounce on the discs  110  and tumble backward and downward toward the container discharge area  114 , finally falling out of the container discharge area  114  into a container or plenum  150 . Lighter material such as cardboard and paper falling on the second disc screen does not bounce and is carried toward and upwardly to the paper discharge area  116 . To assist in propelling the paper  126  toward the paper discharge area  116 , one or more fans  128  may be mounted near the first end  105  of the frame to blow air  130  at the second rotatable shafts  112 .  
         [0028]    [0028]FIGS. 2A, 2B and  2 C show examples of the discs  110  mounted on the first and second rotatable shafts  108  and  112 , with varied spacing, creating a variety of screen patterns. FIGS. 2A and 2B show examples of two screen patterns  202  and  204  of the discs  110  mounted on the first rotatable shafts  108 . FIG. 2A shows the discs  110  mounted on the shaft in a fine screen pattern, with small spaces between the edges of the discs  110  and adjacent shafts. One such space is indicated by  204 . This fine screen pattern  202  is used in the apparatus where small materials are screened. In FIG. 2B, the discs  110  are mounted in a gross screen pattern  206  with large openings such as  208  such that larger, heavier materials are able to fall through the openings  208  between the discs  110 . In some cases, it may be desirable to have a combination of spacings between the discs (i.e., have both small openings  204  and large openings  208 ). In this way, as the material stream travels along a plurality of rotating shafts, the mixed material is separated and screened in successive stages on one disc screen. One example combination pattern formed by varying the screen patterns is shown in FIG. 2C. In fact, this pattern describes the layout of the first disc screen. In this regard, as the material stream pours onto the disc screen apparatus in the inlet are  104  on the fine screen pattern  202 , the material stream is agitated and moved by rotation of the discs with the shafts toward and over the gross screen pattern  206 . Over the fine screen pattern  202 , relatively fine grit, glass shards, and other small materials are screened out. Over the gross screen pattern  206 , larger objects such as cans, bottles, and envelopes pour through the larger openings onto the lower end of the second rotatable shafts  112 . In the preferred embodiment, the entire second disc screen has the gross screen pattern  206  of FIG. 2B.  
         [0029]    In the apparatus  100 , the first and second rotatable shafts  108  and  112  extend through and are supported between sides  136  (near side shown in FIG. 1) and  138  (far side) of the frame  102 . The first rotatable shafts  108  are located in a first plane and the second rotatable shafts  112  are located below and partially underneath the first rotatable shafts  108  in an overlapping manner, with the first three shafts  112   a,    112   b,  and  112   c  defining a plane that is parallel to that of the first rotatable shafts  108 , and the remaining twelve defining a second plane. In the preferred embodiment, the first plane is generally disposed at a slight incline from horizontal to assist in the initial separation of the material stream  106 . The first plane angle may vary form 0 to 45 degrees, with the preferred embodiment angle being 20 degrees. The second plane is generally disposed at an inclined angle such that the larger objects  122  do not readily go up the incline. The angle may vary from 25 to 60 degrees with the preferred embodiment angle being 35 to 45 degrees. In one embodiment, the frame  102  is mounted at a fixed first point  132  and a rotatable second point  133 . The frame  102  may be rotated up or down, with the first point  132  as the pivot point, to alter an incline angle of the frame  102  using a jack  134  at the second point  133 . This rotation of the frame up or down may also me used to vary the angles of the shafts.  
         [0030]    The number of shafts is dependent on the size of the machine  100  and on intershaft spacing. In the embodiment shown in FIG. 1, the number of shafts in the first plurality of rotatable shafts  108  is less than the number of shafts in the second plurality of rotatable shafts  112 . In the FIG. 1, there are eight first rotatable shafts  108  and fifteen second rotatable shafts  112 . The first shafts  108  and second shafts  112  are supported by bushings or bearings  140  positioned along sides  136  and  138 .  
         [0031]    The plurality of discs  110 , made from a hard durable material with a high coefficient of friction, such as rubber, are mounted on the first rotatable shafts  108  and the second rotatable shafts  112  to form the screen patterns shown in FIGS.  2 A- 2 C; however, the discs  110  may be mounted along the first rotatable shafts  108  and the second rotatable shafts  112  in a variety of spacing patterns. The discs  110  on adjacent shafts are offset on their respective shafts such that the discs  110  on one shaft fit between (interleave with) the discs on the other shaft without touching the other shaft. This is best seen in FIGS.  2 A- 2 C.  
         [0032]    Referring again to FIGS. 1 and 6, in the preferred embodiment, the first motor  118  and second motor  130  are positioned on the side  138  (far side) of the frame  102 . The motors  118  and  130  are shown with dashed lines. A drive chain  119  attaches between the motor  118  and a drive sprocket  142  mounted on the end of the first shaft  108   a  that is on the side of  138  (far side). A plurality of rotation sprockets  144  are mounted at the end of each first shaft  108 , that is on the side  136  (near side). A rotation chain  146  interconnects the plurality of rotation sprockets  144 , as shown in FIG. 1. A drive chain  131  attaches between the motor  130  and a drive sprocket  142  on the end of the second shaft  112  that is on the side  138  (far side). A plurality of rotation sprockets  144  are located at the end of each second shaft  112  on side  136  (near side). A rotation chain  148  interconnects the plurality of rotation sprockets  144 . Safety covers (not shown) cover the plurality of rotation sprockets and rotation chains. There may also be access doors or panels  150  on the sides  136  and  138  to allow access or viewing of the interior of the machine.  
         [0033]    The first motor  118  turns the drive chain  119  and drive sprocket  142 , thereby rotating the first rotatable shaft  108   a  in a first direction. Since all of the first rotatable shafts  108  are interconnected by rotation sprockets  144  and rotation chain  146 , all of the first rotatable shafts  108  rotate together in the first direction at the same speed. The second motor  130  turns the drive chain  131  and drive sprocket  142 , thereby rotating the second rotatable shaft  112  in a second direction. Since all of the second rotatable shafts  112  are interconnected by rotation sprockets  140  and rotation chain  148 , all the second rotatable shafts  112  rotate together in the second direction at the same speed. The rotating second direction of the second rotatable shafts  112  is in the same direction as the rotating first direction of the first rotatable shafts  108 . Each motor may rotate its plurality of shafts at a particular speed. In the illustrative embodiment, the rotation speed of the first rotatable shafts  108  is around  60 - 100  revolutions per minute (rpm) and the rotation speed of the second rotatable shafts  112  is around 200-300 rpm. Although the preferred embodiment couples the motors to the shafts by sprocket/chain drives, other couplings may be used including, but not limited to, transmission couplings, geared couplings, direct couplings, and so on. Alternatively, separate individual shafts may be powered by separate individual motors. Further, the motors may be stationed at positions other than those shown, both on and off the frame  102  as design and installation considerations dictate. The sizes of the motors are dependent on a number of factors such as the number of rollers, type of drive mechanism, and so on. For example, each may have a rating of around 3 HP, with a 90 degree worm drive.  
         [0034]    The operation of the disc screen apparatus  100  is as follows. Initially, the material stream  106  pours upon the first disc screen in the material entry area  104 . In the fine screen section  202  of the first disc screen, the material stream is agitated and small matter is screened out, falling downwardly through the apparatus  100  to be collected by conventional means. The material stream  106  is propelled upwardly by the rotation of the discs toward, over, and off of the gross screen section  206 . As it passes over the gross screen section  206 , intermediate-sized objects such as cans, twelve-ounce bottles and envelopes fall through the gross mesh onto to the lower end of the second rotatable shafts  112 . Meanwhile, the larger objects including large containers, newspapers, and cardboard sections of the material stream  106  are propelled off the upper end of the first disc screen onto the midsection of the second disc screen. Thus, the material stream  106  pours onto the second disc screen for screening already in a somewhat differentiated state, with smaller objects falling onto the lower rear portion of the second disc screen, and larger objects onto its midsection. The smaller objects are screened at the lower portion of the second disc screen, either passing through the gross screen pattern into the plenum  150  or tumbling downwardly off the lower end of the second disc screen into the plenum  150 . The larger objects that pour onto the midsection of the second disc screen separate, with the larger, heavier objects such as large bottles and plastic containers being bounced off the screen and rolling downwardly toward the lower end of the second disc screen from which they fall into the plenum  150 . Meanwhile, the larger light objects such as newspapers, magazines, and cardboard sections are carried upwardly by rotation of the second rotatable shafts  112  toward, over, and off of the upper end of the second disc screen from which they fall onto a collection conveyor  152 . A distinct advantage of this operation is that the material stream  106  is classified essentially into three sections on the first disc screen. Advantageously, the second disc screen receives a material stream that has been partially classified into smaller heavier objects that pour onto the lower portion of the second disc screen and a mixture of larger heavy and light objects that pour onto the second disc screen in its midsection. This avoids the prior art problem of a single, large, very dense stream of material pouring onto a single disc stream, creating a large eddying slurry of undifferentiated material at its impact point. As is known, such a large slurry reduces the effectiveness of a disc screen, providing less sharply differentiated collections of material than are afforded by the apparatus  100 .  
         [0035]    FIGS.  3 A- 3 C show details of a preferred embodiment of a disc  110 . The disc  110  is designed to be replaceable on a shaft, without disassembly of the shaft and/or removal of other discs therefrom. The disc  110  is designed to separate into two portions at a separation plane  306  into disc portion  302   a  and disc portion  302   b . Screws  304  clamp the disc halves  302   a  and  302   b  together. A central opening  308  of the disc  110  is designed to fit on the rotatable shafts  108  or  112 . The central opening  308  comprises planar sections  310 . As can be seen in the figures, the rotatable shafts  108  or  112  are eccentric (preferably square) in configuration. This provides more planar contact between the rotatable shaft and the disc. Because of the design of the disc  110 , as the disc halves  302   a  and  302   b  are clamped around the rotatable shaft  108  or  112 , the planar sections  310  make contact with the flat sides of the rotatable shafts at four clamping surfaces  312 . This allows the disc  110  to clamp or grab a shaft  108  or  112  such that it will not freely spin on the shaft. This clamping design also eliminates the need for spacers or the like to be positioned between the discs  110  to create the desired screen patterns.  
         [0036]    The disc  110  is (preferably) square in shape with an outer peripheral edge which includes four corners  314 . In the illustrated embodiment, the corners  314  are radiused to reduce the wear on the disc  110  during use. The radiused corners may also be textured with a variety of patterns. This texturing may assist in the or movement of materials with the disc  110 . In the illustrative embodiment shown, the corners  314  are textured with a plurality of ridges  316 . The outer peripheral edge of the disc  110  defines an annular impacting surface  330 . Also shown in the figures is a cylindrical shoulder  362  or boss integrally formed on and protruding from each side of the disc. The shoulder  362  allows for room between the impacting surfaces  330  of adjacent discs  110  when they are positioned in a fine mesh pattern. Further, the shoulders  362  of adjacent discs provide a lateral space within which the peripheral edge of an interleaved disc on an adjacent shaft may be received to create a small space such as the space  204  for fine material screening. (See FIG. 2A.)  
         [0037]    For the disc  110  to function well, it must have a flexible impacting surface  330  with high abrasion resistance for impacting the materials, while at the same time having a “sticky” surface with a high coefficient of friction. There are a number of materials, such as rubber, that may be used in making the disc  110 . A coating of material may also be applied to the impacting surface  330 .  
         [0038]    With reference to FIGS. 3A, 4A,  4 B,  5 A and  5 B, it should appreciated that the disc  110  comprises two identical halves, placed in opposition on a shaft and clamped thereto. Each half is referred to as a “portion”. In FIG. 3A, the disc  110  includes identical opposing portions  302   a  and  302   b . As best seen in FIGS.  4 A- 4 C, a disc portion  302  (representing both of portions  302   a  and  302   b ) has an internal rigid frame or embedment  318  to which a rubber material  326  is molded. (Note, for accuracy, that portion  302  corresponds to portion  302   a , with its top and bottom ends rotated 180°). Preferably, the rubber material is a 50-55 durometer rubber casting compression molded around the rigid frame  318 . The rigid frame  318  imparts stiffness to the disc portion  302  and improves the clamping force  312  when two disc portions  302   a  and  302   b  are clamped to a shaft. As shown in FIG. 5A and 5B, the rigid frame  318  includes a first unthreaded through hole  320  and a second, threaded hole  322 . Each of the holes  320  and  322  opens through a respective exposed clamping face  325  on a respective end of the rigid frame  318 . As best seen in FIG. 4A, a through hole  327  opens through the rubber material  326  from impacting surface  330  to the through hole  320 . Referring back to FIG. 3A, it can be seen that the disc  110  may be clamped to a shaft by bringing the two disc portions  302   a  and  302   b  together about the shaft such that the through hole  320  in the portion  302   a  faces the threaded portion  322  in the portion  302   b , and the through hole  320  in the portion  302   b  faces the threaded portion  322  in the disc portion  302   a . The two portions  302   a  and  302   b  are clamped by threaded screws  304  that are inserted through the through holes  327 ,  320 , threaded ends first, and then threaded to the respective threaded holes  322  in the opposing disc portions. This securely clamps the disc  110  to a shaft.  
         [0039]    Secure clamping is provided, in this regard, by the exposed opposing clamping faces  325 , over which the rubber material  326  does not extend. Thus, where the clamping force is applied, the clamping faces  325  of the rigid frames  318  within the opposing disc portions  302   a  and  302   b  are brought together in contact to provide a stiff, nonyielding clamping interface. In addition, the planar sections  310 , which are part of the rubber material  326 , are squeezed between the metal shaft and corresponding portions  310   a  of the rigid member  318 . This compresses these planar sections  310  to such an extent that the disc  110  is firmly clamped to, and cannot slide along a shaft. Now, if the disc  110  is damaged and must be repaired or replaced, it can be dissembled from the shaft by dethreading the screws  304 , removing the portions  302   a  and  302   b  and replacing either or both.  
         [0040]    Two significant advantages of the disc configuration illustrated in FIG. 3A are evident. First, the clamping force exerted by the screws  304  is not parallel to any of the planar sections  310  of the inner opening of the disc  110  and therefore is not parallel to any of the surface portions of the shaft  108  or  112 . In other words, there is a component of a clamping force vector that is normal to the interface between each of the clamping planar sections  310  and the shaft  108  or  112 . This advantageously distributes the clamping force around the interface between the inner opening of the disc  110  and the shaft  108  or  112 . Second, the plane  306  where the disc portions  302   a  and  302   b  are brought together defines a minute seam that extends to respective opposing flat portions of the impacting surface  330 . This is best seen in FIGS. 3A and 3C. Since the impacting surface  330  tends to contact the material stream at the corners  314 , filaments, such as strings or threads are less likely to snag in the seams than if they were located at the corners of the disc  110 .  
         [0041]    The rigid frame  318 , shown in FIG. 5A- 5 C, may be made of metal, such as steel or aluminum, or a rigid plastic. In the preferred embodiment, the rigid frame is made from 356 aluminum casting that has been heat treated.  
         [0042]    FIGS.  7 A- 7 C and  8 A- 8 B show construction of details of the rotatable shafts  108 ,  112  which are represented by a shaft assembly  400 . The shaft assembly  400  consists of a central axle tube  402  and two end spindle assemblies  404 , each disposed partially in the tube  402 , near an end. In the illustrative embodiment, the axle tube  402  has a square cross-section to which the disc  110  is clamped (see FIG. 3A). The center of the axle tube  402  is generally hollow. Each spindle assembly  404  is constructed to mount within a respective end of the axle tube  402 . The spindle assembly  404  is comprises a central spindle  406  and attachment discs  408 . One end of the central spindle  406  is dimensioned to fit inside an end of the axle tube  402  while the exposed end of the spindle  406  is dimensioned to attach to a disc screen apparatus. In the present invention, the exposed spindle ends are sized to be compatible with the rotation bearings  140 , drive sprockets  142  and rotation sprockets  144  of the apparatus  100 . The attachment discs  408  are initially dimensioned to be larger than the central opening  410  of the axle tube  402 . In the configuration shown in FIG. 7 and  8 , the attachment disc  408  is circular in shape with a circular center opening that is sized to fit over the spindle  406 . One or more attachment discs  408  are welded to the spindle  406  to form the spindle assembly  404 . The spindle assembly  404  is then positioned in a fixture where the attachment discs  408  are machined to press fit into the central opening  410 . Once sized, the spindle assembly  404  is press fit into the opening  410  a set distance. The attachment discs  408  are used to center and align the spindle  406  along the axis  414  of the shaft. A plurality of holes  412  in the axle tube  402  are used to weld the attachment discs  408  in place, thus securing the spindle assembly  404  in the axle tube  402 , forming the axle assembly  400 . The axle tubes  402 , spindles  406  and attachment discs  408  are preferably made from high strength materials, such as steel.  
         [0043]    While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims. For example, the discs may have shapes other than the square one shown, and may have central openings that have eccentric shapes including curved ones such as ellipses and regular ones such as triangles, quadrilaterals, and polygons.