Method and apparatus for sorting recycled material

Abstract: A compound disc is used to eliminate a secondary slot normally formed between adjacent shafts of a material separation screen. The compound disc comprises a primary disc (172) joined to an associated secondary disc (176). The primary disc and the secondary disc each have the same shape but the secondary disc has a smaller outside perimeter (178) and is wider. The primary disc and associated secondary disc are formed from a unitary piece of rubber. The compound discs are interleaved with oppositely aligned compound discs on adjacent shafts. In other words, the large disc is positioned on a shaft to align with a smaller disc on an adjacent shaft. The oppositely aligned and alternating arrangement between the large discs and small discs reduce problems that exist in screens that use in-line multi-sided discs.

Description: This invention relates to an apparatus and method for separating various materials, and in particular, to improvements in a disc screen. Disc or roll screens, are frequently used as part of a multi-stage materials separating system. Disc screens are used in the materials handling industry for screening large flows of materials to remove certain items of desired dimensions. In particular, disc screens are particularly suitable for classifying what is normally considered debris or residual materials. This debris may consist of various constituents, such as soil, aggregate, asphalt, concrete, wood, biomass, ferrous and nonferrous metal, plastic, ceramic, paper, cardboard, or other products or materials recognized as debris throughout consumer, commercial and industrial markets. The function of the disc screen is to separate the materials fed into it by size. The size classification may be adjusted to meet virtually any specific application. Disc screens generally having a screening bed having a series of rotating spaced parallel shafts each of which has a longitudinal series of concentric screen discs separated by spacers which interdigitate with the screen discs of the adjacent shafts. The relationship of the discs and spacers on one shaft to the discs and spacers on each adjacent shaft form an opening generally known in the industry as the interfacial opening or "IFO". The IFOs permit only material of acceptable size to pass downwardly through the rotating disc bed. The acceptable sized material which drops through the IFO is commonly referred to in the industry as Accepts or Unders. The discs are all driven to rotate in a common direction from the infeed end of the screen bed to the outfeed or discharge end of the bed. Thus, materials which are larger than the IFO, referred to in the industry as Overs, will be advanced on the bed to the outfeed end of the bed and rejected. A major problem with such disc screens is jamming. When the discs are not in line, material tends to jam between the disc and the adjacent shaft, physically forcing the screen to stop. Although the jamming phenomenon may not cause the roll screen to stop completely, it may cause momentary stoppages. Such stoppages may not cause the drive mechanism of the roll screen to turn off but may cause substantial mechanical shock. This mechanical shock eventually results in the premature failure of the roll screen's roll assemblies and drive mechanism. Another problem with disc screens is effectively separating debris having similar shapes. It is difficult to separate office sized waste paper (OWP) and old newspapers (ONP) since much of the OWP and ONP has the same long thin shape. For example, it is difficult to effectively separate notebook paper and ONP from old corrugated cardboard (OCC) since each is long and relatively flat. A secondary slot is formed between the discs on adjacent shafts. OWP and/or OCC is difficult to work effectively because most categories of OWP and some OCC can slip through the secondary slot. Further, OWP has a tendency to slip off a bottom end of the disc screen, while being transported up the screen at an incline. Thus, a need remains for a system that can classify materials more effectively and is also more resistant to jamming. WO 9,535,168 on which the precharacterising portion of claim 1 is based, discloses a disc screen apparatus and disc screens as illustrated in Figures 1-13 of the attached drawings. It illustrates the use of discs having 3, 4 or 5 arcuate sides in inclined multi section disc screen. In the disc screen sections the discs on adjacent shafts may be arranged in some places to interdigitate, and in other places to be in line with each other. DE 9,309,872 U discloses a disc screen using interdigitated discs. DE 657 918 C discloses a disc screen using interdigitated discs. DE 657,918 C and DE 607,459 C illustrate the use of different diameter discs. According to the present invention there is provide a material separation screen, comprising: a frame; a first shaft and a second shaft mounted adjacent to and substantially parallel with one another on the frame, said first and second shafts capable of rotating in a common direction; and a first set of discs mounted on and spaced apart from each other on the first shaft and a second set of discs mounted on and spaced apart from each other on the second shaft, characterised in that said discs are compound discs comprising a primary disc and a secondary disc abutted against a lateral side of the primary disc and having a perimeter smaller than the perimeter of the primary disc, and in that the compound discs are spaced apart from adjacent compound discs on the same respective shafts and a compound disc of the first set of compound discs on the first shaft is aligned to overlap the periphery of a compound disc in the second set of compound discs on the second shaft to define a stair-shaped gap between them. The secondary disc may be wider than the primary disc. The primary disc and associated secondary disc may be formed from a unitary piece of rubber, or from two pieces of steel. The rubber discs provide additional gripping for flat materials such as paper while inducing oversized materials, such as plastic bottles, to roll off a bottom end of the screen. The use of the compound disc separates materials more effectively than current disc screens while also reducing jamming. The invention will be further described by way of example with reference to the accompanying drawings, wherein figures 4, 6 and 7 do not constitute embodiments of the invention FIG. 1 is an enlarged fragmental top plan view of a conventional screening bed; FIGS. 2a-2c show a front view, side view and perspective view, respectively, of a compound disc according to the invention; FIG. 3 is a top plan view of a disc screen section using the compound disc in FIGS. 2a-2c; FIG. 4 is a top plan view of a disc screen section; FIG. 5 is a side elevation view of a two stage screen system using the compound disc shown in FIGS. 2a-2c; FIG. 6 is a side elevation of another two stage screen system using compound discs; and FIG. 7 is an enlarged plan of a portion of the system of FIG. 6. Referring to FIG. 1, with conventional screens, in addition to the IFO a secondary slot D sp extends laterally across the screen. The slot D sp is formed by the space that exists between discs 18 on adjacent shafts. The secondary slot D sp allows unintentional accepts for some types of large thin material, such as cardboard. The large materials pass through the screen along with smaller material. The large materials must then be separated by hand from the rest of the accepts that fall into the hopper. Thus, the secondary slot D sp reduces screening efficiency in disc based screening systems. Referring to FIGS. 2a-2c, with the present invention a compound disc 170 is used to eliminate the secondary slot D sp that extends between discs on adjacent shafts. The compound disc 170 includes a primary disc 172 having three arched sides 174 that form an outside perimeter. A secondary disc 176 extends from a side face of the primary disc 172. The secondary disc 176 has three arched sides 178 that form an outside perimeter substantially the same shape as disc 172. However, the outside perimeter of the secondary disc 176 is smaller than the outside perimeter of the primary disc 172 and is approximately twice as wide as the width of the primary disc 172. During rotation, the arched shape of the primary disc 172 and the secondary disc 176 maintain a substantially constant spacing with similarly shaped discs on adjacent shafts. However, the different relative size between the primary disc 172 and the secondary disc 176 eliminate the secondary slot D sp that normally exists between adjacent shafts. The compound disk 170 is made from a unitary piece of rubber or can be made from two pieces of steel, one taking the shape of the primary disc and one taking the shape of the secondary disc. The rubber material grips onto certain types and shapes of materials providing a more effective screening process as described below. Referring to FIG. 3 a portion of a screen 180 includes a first shaft 182 and a second shaft 184 mounted to a frame (not shown) in a substantially parallel relationship. A first set of primary discs 172 and associated secondary discs 176 are mounted on the first shaft 182 and separated by spacers 30. A second set of primary discs 172 are mounted on the second shaft 184 and are aligned laterally on shaft 184 with secondary discs 176 on the first shaft 182. A second set of secondary discs 176 are mounted on the second shaft 184 and align laterally with primary discs 172 on the first shaft 182. The primary discs 172 on the first shaft 182 and the secondary discs 176 on the second shaft 184 maintain a substantially constant spacing during rotation. The secondary discs 176 on the first shaft 182 and the primary discs 172 on the second shaft 184 also maintain a substantially constant perimeter spacing during rotation. Thus, jamming that typically occurs with toothed discs is substantially reduced. The alternating alignment of the primary discs 172 with the secondary discs 176 both laterally across each shaft and longitudinally between adjacent shafts eliminate the rectangularly shaped secondary slots D sp that normally extends laterally across the entire width of the screen 180. Since large thin materials, such as cardboard, can no longer unintentionally pass through the disc screen via the secondary slot D sp , oversized materials are more accurately separated and deposited in the correct location with other oversized materials. The compound disc 170 is shown as having a triangular profile with three arched sides. However, the compound discs can have any number of arched sides such as four or five. In one embodiment of the invention, the primary disc 172 and the associated secondary disc 176 are formed from the same piece of rubber. However, the primary discs and associated secondary discs can also be formed from separate pieces of rubber. If a rubber material is not required for screening materials, the primary and secondary discs may be formed from either a unitary piece of metal of from two separate pieces of metal. In FIG. 4 the primary discs 172 and secondary discs 176 are separate pieces formed from either rubber or from a metal material. The primary discs 172 are mounted laterally across the shaft 182 between secondary discs 176 and separated by spacers 30. The primary discs 172 are mounted laterally across shaft 184 in alignment with secondary discs on shaft 182. In turn, the secondary discs on shaft 184 are aligned with primary discs 172 on shaft 182. The different sizes and alignment of the discs on the adjacent shafts 182 and 184 create a stair-step shaped spacing between the discs on the two adjacent shafts. Different spacing between the primary discs 172 and secondary discs 176, as well as the size and shapes of the primary and secondary discs can be varied according to the types of materials being separated. For example, for separation of larger sized materials, the configuration in FIG. 3 is used. For separation of smaller sized material, the configuration in FIG. 4 is used. FIG. 5 shows a two stage screen 182 that uses the compound disk 170 shown in FIGS. 2a-2c. A first frame section 184 is angled at an upward incline from a bottom end 186 to a top end 188. A second frame section 190 is angled at an upward incline adjacent to the first frame section 184 and includes a bottom end 192 and a top end 194. Multiple shafts 16 are attached on both the first frame section 184 and the second frame section 190. Multiple primary discs 172 and associated smaller secondary discs 176 are aligned in rows on each one of the shafts 16 as previously shown in either FIG. 3 or FIG. 4 Each one of the primary discs 172 on the shafts 16 are aligned longitudinally on screen 182 with a secondary disc 176 on adjacent shafts 16. Materials 195 are categorized as either oversized (large) items or sized (small) items. The unsorted materials 195 are dropped onto the bottom end of screen section 184. Due to gravity, some of the oversized materials drop or roll off the bottom end of screen section 184 onto a conveyer or bin 208, as shown by arrow 196. For example, certain large round items, such as jugs and cartons are more likely to roll off the bottom end 186 of screen section 184 than smaller flat materials. The rubber compound discs 170 grip the smaller sized materials preventing them from sliding off the bottom end of screen section 184. While in rotation, the rubber compound discs 170 help transport the smaller size materials up the screen while inducing additional oversized materials to roll back off the bottom end 186 of screen section 184. The remaining materials 195 are agitated up and down by the arched shape discs while being transported up the angled screen section 184. The vibration, in conjunction with the spacing between the discs (FIGS. 3 and 4) shifts the smaller sized materials through the screen, as shown by arrow 198, onto a conveyer or bin. The stair-step spacing, created by the large primary discs 172 and small secondary discs 176, prevent oversize materials from falling through the screen section 184. The materials 195 reaching the top end 188 of screen section 184 are dropped onto the bottom end 192 of the second screen section 190, as represented by arrow 200. Some of the oversized materials roll off the bottom end 192 of screen section 190 into the collection conveyer 208 as represented by arrow 202. The remaining material 195 is vibrated up and down by the compound discs 170 while being transported up screen section 190. Remaining smaller sized materials are sifted through the screen section 190 as represented by arrow 204. The remaining oversized material is transported over the top end 194 of screen section 190 and dropped into an oversized material bin or conveyer 208. The rubber compound discs 170 in one embodiment allows only paper material to be conveyed up the surface of the screen 182 at a specific angle of incline. The angle of the screen is set between 25° and 45° from horizontal to achieve the proper separation of newspaper from containers. The system described above allows less than 1% of containers or glass fragments to remain commingled with paper products, such as newspaper, after reaching the top end 194 of screen section 190. Thus, the rubber compound discs in combination with the dual-stage screen assembly provide more effective material separation than current disc screen systems and single stage material separation systems. FIGS. 6 and 7 show a two stage screen 220 utilizing the primary and secondary disc arrangement shown in FIG. 4. A first frame section 222 is angled at an upward incline from a bottom end 224 to a top end 226. A second frame section 228 is angled at an upward incline and positioned beneath the first frame section 222. Second frame section 228 includes a bottom end 230 and a top end 232. Multiple shafts 16 are attached on both the first frame section 222 and the second frame section 228. Multiple primary discs 172 and secondary discs 176 are alternately mounted on each of multiple shafts 16 as shown in FIG. 7. Multiple primary discs 172 and secondary discs 176 are aligned in rows on each one of the shafts 16. Each one of the primary discs 172 is aligned longitudinally on first screen 222 with a secondary disc 176 on an adjacent shaft 16. Likewise, each one of the primary discs 172 are aligned longitudinally on second screen section 228 with a secondary disc 176 on an adjacent shaft 16. The two stage screen 220 shown in FIG. 6 operates particularly well for separating wood or pulp products when used in conjunction with five-sided discs. In the wood or pulp products industry, the average size of the wood or pulp chips found in a lot determines the lot's commercial value. Likewise, the size variation of the chips also affect the lot's commercial value. Thus, accuracy and repeatability in sizing chips is very important. Referring to FIG. 6, the first inclined screen section 222 receives the wood or pulp material to be separated at bottom end 224. The upward movement of screen section 222 and the vibration of the screen bed as shafts 16 are rotated at an appropriate speed promotes the separation of oversized wood chips from proper sized and very small chips. The proper and very small wood chips pass through about the first two thirds of first screen section 222 and are delivered to bottom end 230 of second screen section 228 through chute 234. By the time the material moves up to about the upper third of second screen section 222, the very small wood chips have been separated from the oversized and proper sized chips through the vibration action of shafts 16 in combination with the upward movement of first screen section 222 and delivered to second screen section 228. The material sifted through the upper third or so of first screen section 222 comprises primarily oversized chips and proper sized ships. Thus, the upper third or so of first screen section 222 further separates the proper sized chips only from oversized chips, passes the proper sized chips through the first screen section 222, and delivers the proper sized chips to chute 236 which, in turn, delivers the proper sized chips directly to conveyor belt 238 for further processing. The second screen section 228 receives the separated chips from first screen section 222 through chute 234 as shown in FIG. 6. Second screen section 228 separates the proper sized chips from the very small chips. The very small chips are delivered to a container (now shown) through chute 240. The proper sized chips are delivered to conveyor belt 238. By funnelling the wood chips from the upper third of screen 222 directly onto conveyor 238, the number of proper sized wood chips separated is increased. This is because there are few undersized wood chips in the upper third portion of screen 222. Thus, there is no need for screening the wood chips a second time. By not re-screening the wood chips that sift through the upper third portion of first screen 222, no proper sized wood chips will be lost through second screen 228. The above screen can be modified by eliminating chute 236 thereby delivering all of the separated material from first screen section 222 to second screen section 228. The speed at which the shafts 16 are rotated varies depending on a variety of factors including environmental conditions, the type and quality of the infeed chip material, and type and quality of the desired outfeed chip material. If shafts 16 are rotated at a faster speed, more rejects or unders are produced. Conversely, if the shafts 16 are rotated at a slower speed, less rejects or unders are produced. Referring specifically to FIG. 7, the primary discs 172 and secondary discs 176 (FIG. 3) are of substantially equal width. Also, each of primary discs 172 have a larger outer diameter than each of secondary discs 176. The relative diameter and width of primary discs 172 and secondary discs 176 and length and width of spacers 30 vary depending on the size of the material sifted through the screen. In order to produce chips having the preferred dimensions, an IFO spacing 250 is created by varying the outside diameter and width of spacers 30. The area of secondary slots 252 are varied by varying the outside diameter and thickness of both the primary discs 172 and secondary discs 176. For screen 228, the IFO's 250 are made smaller by increasing the diameter and reducing the width of spacers 30. Alternatively, the IFO's are reduced by reducing the diameter of the primary and secondary discs and then moving the shafts 16 closer together. The two stage screen 220 in one embodiment uses five sided discs. The five sided discs have several advantages when used in combination with the primary and secondary disc configuration shown in FIG. 7. First, using a five sided disc is very beneficial for separating fragile wood or pulp chips from oversized and very small chips without damaging the proper sized wood chips. Higher amplitudes of the sifting action are more likely to damage delicate or fragile materials like wood or pulp chips. As the number of sides increases, from 3 to 5, for example, the amplitude of rotation decreases. Thus, five sided discs tend to minimize damage to wood or pulp chips as they pass through first screen section 222 and second screen section 228. Second, a continuous secondary slot D SP is eliminated by aligning a primary disc 172 mounted on shaft 182 with a secondary disc 176 mounted on an adjacent shaft 184. Eliminating the continuous secondary slot D SP results in fewer screen jams since an oversized wood chip cannot wedge itself between discs. Most importantly, by using alternately mounted primary discs 172 with secondary discs 176 the percentage of IFO area in a given screen increases dramatically over compound discs 170 shown in FIG. 3. This is because compound disc 170 comprises a secondary disc 176 extending outwardly from a face of primary disc 172, the secondary disc 176 being wider than the associated primary disc 172. Since secondary disc 176 is wider than primary disc 172 in compound disc 170, the amount of open space available from an IFO is reduced for a given length of shaft. For example, for 30cm (1ft) long shaft 16, 2.5cm (1") long spacer 30, 9.5mm (3/8") wide primary discs 172, and 1.6cm (5/8") wide secondary discs 176 for use in the disc arrangement of screen 180 (FIG. 3), the number of IFOs equals 6. For a 30cm (1ft) long section of shaft 16, 2.5cm (1") long spacer 30, 9.5mm (3/8") wide primary discs 172, and 9.5mm (3/8") wide secondary discs 176 for use in the disc arrangement of FIG. 7, the number of IFOs increases to between 8 and 9. Thus, a smaller screen can process the same tonnage of wood or pulp material using the screen arrangement shown in FIGS. 6 and 7 consequently decreasing processing costs. Even if both the primary and secondary discs 172 and 176 used to form compound disc 170 are of the same width, the number of IFOs would still be less than the compound disc arrangement of FIG. 7.

Claims: A material separation screen, comprising: a frame (12); a first shaft (16) and a second shaft (16) mounted adjacent to and substantially parallel with one another on the frame (12), said first and second shafts (16) capable of rotating in a common direction; and a first set of discs (170) mounted on and spaced apart from each other on the first shaft (16) and a second set of discs (170) mounted on and spaced apart from each other on the second shaft (16), characterised in that said discs (170) are compound discs comprising a primary disc (172) and a secondary disc (176) abutted against a lateral side of the primary disc and having a perimeter (178) smaller than the perimeter (174) of the primary disc (172), and in that the compound discs are spaced apart from adjacent compound discs on the same respective shafts and a compound disc (170) of the first set of compound discs on the first shaft (16) is aligned to overlap the periphery of a compound disc (170) in the second set of compound discs on the second shaft (16) to define a stair-shaped gap between them. A material separation screen according to claim 1 wherein the secondary discs (176) of each compound disc (170) are attached to and extend from a lateral side of the primary discs (172). A material separation screen according to claim 1 or 2, wherein at least one primary disc (172) has an outside perimeter (174) extending at least partially beyond a half-way point between the first shaft (16) and the second shaft (16) during rotation, and wherein an outside perimeter (178) of the secondary disc (176) does not extend beyond the half-way point between the first and second shafts (16) during rotation. A material separation screen according to claim 1, 2 or 3 wherein each of the primary discs (172) on the first shaft (16) is attached to the first shaft (16) between two secondary discs (176). A material separation screen according to any one of the preceding claims wherein a non-linear spacing (D SP ) between compound discs (170) on the adjacent shafts (16) remains substantially constant during rotation of the shafts (16). A material separation screen according to any one of the preceding claims wherein the stair-shaped gap is formed between the primary and secondary discs (172, 176), of the compound disc (170) in the first set of compound discs (170) and the primary and secondary discs (172, 176) of the compound disc (170) in the second set of compound discs (170). A material separation screen according to claim 6 wherein the primary disc (172) of the compound disc (170) in the first set is aligned with the secondary disc (176) of the compound disc (170) in the second set. A material separation screen according to any one of the preceding claims wherein each compound disc (170) is formed from two pieces of steel, a first piece of steel forming the primary disc (172) and a second separate piece of steel forming the secondary disc (176). A material separation screen according to any one of the preceding claims 1 to 7 wherein each compound disc (170) is formed from a unitary piece of rubber. A material separation screen according to any one of the preceding claims further comprising spacer elements (30) positioned along the first and second shafts (16) between compound discs (170) thereon to maintain the compound discs (170) spaced apart.

Inventors: AUSTIN FRED M, CLARK BRIAN J, MILLER ROY R, AUSTIN, FRED M., CLARK, BRIAN J., MILLER, ROY R.
Applicants: BULK HANDLING SYSTEMS INC, BULK HANDLING SYSTEMS, INC.
Application year: 1997
Main classification: B07B1
IPC codes: B07B1