Stepped disc screens of unequal inclination angles for conveying and grading recycling materials

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.

BACKGROUND OF THE INVENTION
 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.
 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.
 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.).
 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".
 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.
 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
 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.
 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.
 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.
 The present invention provides a disc screen apparatus for separating mixed
 materials for recycling. The disc screen apparatus includes a frame with a
 mixed material input area in the frame near a first end of the frame, a
 paper discharge area in the frame near a second end of the frame, and a
 container discharge area in the frame. First and second pluralities of
 shafts, each having a plurality of discs attached thereto, are rotatably
 mounted in the frame to define first and second planes that extend at
 first and second angles, respectively. The second plane is angled upwardly
 from the first end of the frame to the second end of the frame so that the
 second angle is greater than the first angle. A lower portion of the
 second plane is disposed underneath a portion of the first plane in an
 overlapping relationship. Separate drive mechanisms are coupled to the
 first and second pluralities of shafts.
 Other objects and advantages of the invention will become apparent when the
 following detailed description is read with reference to the
 below-described drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 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.
 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.
 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 shaft 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.
 FIGS. 2A, 2B and 2C 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.
 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 112a, 112b, and 112c
 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 from 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 ajack 134 at
 the second point 133. This rotation of the frame up or down may also be
 used to vary the angles of the shafts.
 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.
 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. 2A-2C; 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. 2A-2C.
 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 108a 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 151 on the sides 136 and 138 to
 allow access or viewing of the interior of the machine.
 The first motor 118 turns the drive chain 119 and drive sprocket 142,
 thereby rotating the first rotatable shaft 108a 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
 3HP, with a 90 degree worm drive.
 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.
 FIGS. 3A-3C 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
 302a and disc portion 302b. Screws 304 clamp the disc halves 302a and 302b
 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 302a and 302b 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.
 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.) 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.
 With reference to FIGS. 3A, 4A, 4B, 5A and 5B, 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 302a and 302b.
 As best seen in FIGS. 4A-4C, a disc portion 302 (representing both of
 portions 302a and 302b) 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 302a, with its top and bottom ends rotated
 180.degree. ). 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 302a and 302b 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 302a and 302b
 together about the shaft such that the through hole 320 in the portion
 302a faces the threaded portion 322 in the portion 302b, and the through
 hole 320 in the portion 302b faces the threaded portion 322 in the disc
 portion 302a. The two portions 302a and 302b 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.
 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 302a and 302b 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 310a 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 302a and 302b and
 replacing either or both.
 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 302a and 302b 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 comers
 314, filaments, such as strings or threads are less likely to snag in the
 seams than if they were located at the comers of the disc 110.
 The rigid frame 318, shown in FIG. 5A-5C, 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.
 FIGS. 7A-7C and 8A-8B 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 arc 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.
 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.