CA1102291A

CA1102291A - Comminuting rubbery material

Info

Publication number: CA1102291A
Application number: CA252,324A
Authority: CA
Inventors: Herbert Ruf
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-05-14
Filing date: 1976-05-12
Publication date: 1981-06-02
Also published as: DE2521486C2; DE2521486A1

Abstract

ABSTRACT OF THE DISCLOSURE
A method for producing moulded parts from flakes of toughly resilient material especially rubber, reduced to the form of granules and to moulded parts made according to the method. Upon replacement of worn-out automobile tires or upon retreading such tires, scrap rubber is obtained which is normally of no use, and is frequently dumped or burned. This is particularly undesirable today in view of the emphasis being placed on environmental protection, as well as the in-creasing costs of raw material. Attempts to utilize such scrap rubber have encountered problems, particularly when attempting to reduce the scrap rubber to a size which will make it possible to obtain a homogeneous mixture for further processing. The present invention proposes a simple and relatively inexpensive method, and an apparatus for carrying out the method, by which flakes of rubber, especially scrap rubber, are comminuted to a readily usable size. The device comprises a housing having a feed aperture, and having a drive shaft mounted therein. A feed disc is rotatably mounted on the shaft at a location spaced from the feed aperture, the feed disc adapted to feed the flakes to a first of at least one cutting disc rotatably mounted on the shaft. Apertures are provided in the cutting disc to permit passage of material there-through, edges of the apertures also providing cutting edges. The cutting edges of the cutting disc cooperate with a respective perforated disc mounted in the housing adjacent to the cutting disc to comminute the material. The housing is provided with means for supplying pressurized fluid to the housing so as to pre-vent clogging of the material therein, and discharge means are secured to the housing downstream of the last perforated disc to permit removal of pressurized fluid from the housing.
The perforated discs have openings therein to permit passage of the comminuted material therethrough.

Description

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This invention relates to a method for producing moulded parts from flakes of toughly resilient material, especially rubber, reduced to the form of granules, and to moulded parts made according to the method, as well as to a device for carrying out the said method.
Scrap rubber occurs in many forms, for instance, upon replacement of worn-out automobile tires, or upon retreading such tires,at which time the worn tread is cut away. Since this rub-ber is normally of no use, it is usually dumped or burned. This is particularly undesirable today, considering the emphasis being placed on protecting our environment, as well as the costs of raw materials. At-tempts have frequently been made to convert this scrap rubber into a new ~orm, but the problem has always been to reduce the scrap rubber, ~or example, rubber flakes produced dur-ing retreading worn tires, to a size which will make it possible to obtain a homogeneous mixture for further processing.
The present invention proposes to provide a simple and relative inexpensive method and an apparatus of the type mentioned above, by means of which rubber, especially scrap rub-ber, can be reused.
The method according to the present invention isachieved by feeding flakes of toughly resilient material under positive pressure of a pressure fluid and by means of a rotating feed disc to a rotating cutting disc provided with cutting aper-tures through which the flakes fall into holes in a non-rotating perforated disc, the holes being of a diameter smaller than that of the said flakes, the flakes being held in the non~rotating perforated disc and being reduced in size by the cuttiny edyes of the said rotatating cutting disc, resulting granular material falling downwardly through the said holes, and being introduced into a mould of a configuration corresponding to that of the moulded part to be produced,-the gra~ular material being compressed at a temperature of up to 140C.

The use of a pressure -~luid ensures frictionless passa~e of the flakes o~ rubber beiny reduced in size. The flakes are fed by the feed disc to the cutting disc and ~all into the holes in the perforated disc~ Due to their size, the ~lakes are held in the holes and are sheared o~f b~ the rotating cutting disc. This reduction in size may be repeated until granules of the desired size are obtained. The granular rubber thus obtained is "sintered" in the mould, under the action of heat, into a homogeneous, tough, flexible moulded article~
In vlew o~ its pourable configuration, this granular material may be used as a base ~or several products, for example, for mats, buffers, insula~ing material, road and floor coverings, grinding discs, etc.O
The device according to the present invention com-prises a housing provided with a feed aperture for the fla~es, the housing having a drive shaft mounted therein. ~ feed disc is rotatably mounted on the shaft at a location spaced from the ; feed aperture, the feed disc adapted to feed the flakes received from the feed aperture to a first of at least one cutting discs rotatably mounted on the drive shaft. Each o~ the at least one cutting discs has apertures therein, the apertures adapted to permit passage of material through the cut~ing disc. A-t least lower edges of the apertures are provided with cutting edges.
Means urge a lower surface of each of the at least one cutting discs against a respective perforated disc mounted in the housing adjacent to the respective cutting disc. Connector means are connected to the housing upskream o~ the feed disç, the connec-tor means adapted to be connected to a supply of pressurized fluid, whereby pressurized ~luid is fed into the housing~
Discharge means are secured to the housing downstream of a last per~orated disc, the discharge means adapted to permit removal of pressurized ~luid from the housing. Each perforated disc has means adapted to cooperate with the adjacent cutting disc to

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permit reduction in size of the ~lakes of material, the perfor-ated disc having openings therein to permit passage therethrough of material which has been reduced in size. The pressurized fluid is adapted to urge the ma-terial through the discs to pre-vent clogging in the housing.
The device according to the invention is reliable in operation. The driven discs are secured to the drive shaft, whereas the perforated discs are secured to the housing. The means for urging the cutting discs against the perforated discs ensures that the feed and cutting discs are correctly pressed against the perforated discs in order to ensure that, on the one hand, the flakes of rubber are reduced in size and, on the other hand, that the device is not damaged by any foreign body which cannot be cut up~
According to a preferred embodiment of the invention, the holes in the perforated discs are arranged along at least one cutting groove running radially outwards from the centre of the disc. The said cutting grooves trap and retain the flakes which come to rest in them so securely that the apertures in the cutting disc passing thereabove can easily cut through the flakes. The cutting grooves greatly lncrease'he cutting ability of the device according to the inventionO
One moulded part produced according to the invention is characterized by a granular material made of flakes of rubber reduced in size, baked together, and moulded into the form of a strip~ A moulding of this kind may be used, more particularly, as a covering for sports arenas or for rubber mats. A second moulded part produced according to the invention is characterized in that grains of a grinding material are embedded into a ~ranu-lar material made of fla~es of rubber, reduced in size and baked together. This moulding may be used with advantage as a flexible grinding element and may be moulded into the form of a grinding disco

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In drawings which illustrate embodiments of the present inven~ion:
Figure 1 is a longitudinal section through a device according to the present invention;
Figure 2 is a plan view of a perforated disc, Figure 3 shows a plan view of a cutting disc, and : -Figure 4 is a plan view of a grinding disc produced by the method according to -the invéntion~
In Figure 1 of the drawings,the device for producing granular material out o~ toughly resilient rubber flakes 2 is indicated generally by re-ference numeral 1~ Rubber flakes are shown in the vicinity of a feed aperture 3, the latter being obliquely fitted to a housin~ ~ and being in the form of a funnel4 The housing ~ is in the form of an upright cylinder, with a drive shaft 5 mounted at its vertical axis. The upper end of the shaft 5 is driven by a motor, not shown~ The drive shaft 5 is cylindrical throughout its length, except fortwo flats 6 arranged symmetrically opposite each other at its lower end. As will be explained, these flats are used to hold discs mounted on the said shaft from rotating on it.
Secured to the upper part of the shaft 5, is a retain-ing plate 7. One end of a spiral spring 8 bears against this plate, the other end bearing against a bushing 9 mounted on drive~shaft 5 and secured to a circular feed disc 10~having feed va~es 10a attached to the bushing 9~ The ~anes 10a are arranged obliquely and ha~e the Eunctlons of unlforml~ distri-buting the flakes dellvered from the feed aperture 3, and forcing the flakes into the cutt.ing disc 11 arranged under the vanes 10aO The feed disc 10 is thus driven by frictional enga~ement with the drive shaft 5.
The cutting disc ll,shown in plan view in Fig. 3,is located below the feed disc 10. The disc 11 is secured t~ the drive shaft 5 by the two flats 6 engaging an appropriately shaped , ~;2æ~

aperture 12 in the cutting disc. The cutting disc 12 has ~our large, circular cuttiny apertures 13l between whi'ch four smaller cutting apertures 14 are arranged~ The section shown in Figure 1 o~ the cutting disc 11 passes through the large cut-ting apertures. From this section, it may be seen tha-t the interior of each cutting aperture has a concave surface, so that cutting edges 15, between:the edges o~ t'he apertures and the ends of the cutting disc,taper towards each other. The flats 6 prevenk the cutting disc from rotating relative to the drive shaft 5, but allow it to move axially thereon. The concave configuration of the apertures is shown in dotted lines in Fig~ 3. The smal'ler cutting apertures 1~ are similar in configuration and li~ewise have cutting edges.
; Arranged below cutting disc 11, and secured by means of a pin 17 in a vertical groove 16 in the housing 4~is a per-forated disc 18. The disc 18 has a central bore 19 from which cutting grooves 20 extend radially outwardly on the u,~per surface o~ the disc, AS best seen in Figure 2, vertical holes 21 extend through the disc, the holes 21 being arranged in such a manner that one edge of -the cuttLng grooves is tangential to one side of the radially aligned holes, whereas the other edge of each groove 20 passes transversely through the holes~
In the structure shown as an exa~ple, each cutting groove 20 has six holes 21, each hole 21 being between 2 and 3 mm in dia-meter~ The pin 17 locks the disc 18 against rotation, but allows it to move axially, so t'hat the per~orated disc 18, l.ike the cutting disc 11 located above it, is acked upon by the -force of the spring 8, through the feed disc 10 and the bushing 9 attached to it~
Located under the disc 18, and secured to the sha~t 5 by flats 6, is another cutting disc 22, designed and arranged substantially the same as cutting disc 11.
Arranged below the cutting disc 22 is a further per-: ~ 5 -.. . :

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~orated disc 23~ The disc 23 di~ers ~ro~ the disc 18 in tha' it has seven holes, instead o~ six, along cutting grooves 20. The diameter of ~hese holes is about 0.9 mm. The disc 23 i.s also secured against rotation by means of a pin 24 which slidably engages groove 16 in the housing 4. The disc 23 is otherwise of the same design as the disc 18, however, while the perforated disc..18 can move vertically, the lower surface of disc 23 bears against the flanged edge of a suction tube 25, the tube 25 being secured to the bottom o~ the housing 4 b~ means o~ a ring 26. Within the suction tube 25, the lower end of the drive sha~t 5 runs in a bearing 27 secured to the tube by arms 280 The suction tube 25 leads to means for the removal of pressure fluid. The housin~ ~ is fitted with a connection 29 through which pressure fluid enters the said housing. The housing 4 is also fitted with a window 30 through which the interior of the said housing may be observed, A method according to the in~ention proceeds as follows:
Rùbber flakes 2 are fed into the feed aperture 3~ The drive shaft 5 runs at a speed of about 100 r.p,m. The cutting discs 11 and 22, secured to drive shaft 5, rotate at its speed.
The feed disc 10, driven merely by the friction between bushing 9 and the spring 8 and between the vanes and the underl~ing cut-ting disc, runs at a slightly lower rotational speed~ ~ub~er fla~es 2 are distributed uniformly over cutting disc 11 by the feed vanes lOa, and are forced into the vertlcal apertures in the cutting disc~ The fla~es 2 then fall into the holes 21 and the cutting grooves 20 in the stationary perforated disc 18, in which they are caught and are sheared by cutting edges 15 passing over themO The particles of rubber, thus reduced in size, pass through the holes 21 into the apertures in the cutting disc 22, where they are further reduced in size in the same manner as in ~he holes of the disc 18.
Figure 1 shows that both the upper and the lower ;22Yi~

cut-ting edges of cutting discs 11 and 22 reduce the size of the rubber fla~es. The cutting action is influenced by the force o~ spring 8, since it applies pressure, through bushing 9, upon all of the discs below, so 'ihat these vertically mobile discs are forced into close contact with each other. The reduc-tion in size effected between cutting disc 22 and perforated disc 23 comminutes the rubber flakes into fine granules. This granular material then falls into suction tube 25. A negative pressure may be provided in the suction tube 25 to assist in removing granular material from the device. Further, a pres-sure di~ference of greater ~han 0~5 atmospheres may exist between the feed side of the first feed disc and the disc~arge side of the last perforated disc.
In the device illustrated, the reduction in the size of the flakes is carried out using air as the pressure fluid. The air is pumped into thehousing 4 through connection 29 at a pressure of about`1.5 atmospheres, and is drawn out through the suction tube 25. The ~eed aperture 3 is adequately sealed by rubber ~la~es 2 drawn into it. The flow of compressed air throuyh the device ensures that the rubber flakes, after bein~ reduced in size, pass through stationary discs 18 and 23 without backing up. In certain cases, for example, if a synthetic material is reduced in size in -the device instead of rubber, water, for exarn-ple, may be used as the pressure fluid instead of a gas.
After the rubber has been reduced to the desired particle size, it may be introduced into a mould, and shaped in accordal~ce with the moulded part to be produced. Pressure is applied for a period of up to 40 minutes at a temperature of about 140C. As a result, the granular material is either 'highly compacted or sintered, depending upon pressure and tirne, with the particles being ~used toget~er to form a compact mass.
Figure 4 shows a grinding disc 31 made from the granular material according to the invention~ The clisc 3] has 2~

a retaining zone 32 and a grindiny zone 33. Particles of abras-ive material, for e~ample, corundum, are embedded into the grinding zone, ~Ihereas the said retaining area is free from such gxains. A grinding disc 31 according to the invention has the great advantage that it is flexible so as the disc wears, -the more or less sintered granular material, with the abrasive em-bedded particles, does not allow the disc to smear, since the par-ticles of rubber leave the disc separately as wear proceeds.
The particles of abrasive material are added to the yranular rubber material before the latter is moulded.
The granular material according to the invention may also be used to make other products, floor coverings for sports arenas, roads, sheets for buffering purposes, and the likeO

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method for producing moulded parts from toughly resilient rubber flakes reduced in size to the form granules, the method including the following steps: feeding the flakes under positive pressure of a pressure fluid and by means of a rotating feed disc to a rotating cutting disc provided with cutting apertures through which the flakes fall into holes in a non-rotating perforated disc, the holes being of a diameter small-er than that of the flakes, the flakes being held in the non-rotating perforated disc and being reduced in size by the cutting edges of the said rotating cutting disc, resulting granular material falling downwardly through the holes, introducing the resulting granular material into a mould of a configuration corresponding to that of a moulded part to be produced; and moulding the granular material at temperatures of up to 140°C.

2. A method according to claim 1, including the step of feeding the granular material passing from the holes in the non-rotating perforated disc into a second rotating cutting disc and second non-rotating perforated disc, whereby the granular material is more finely divided before introducing same into the mould.

3. A method according to claims 1 or 2, including the step of providing a negative pressure in the pressure fluid on the discharged side of the last perforated disc through which the flakes pass, to assist in removal of granular material from the device.

4. A method according to claims 1 or 2, wherein a pressure differential between a feed side of the first feed disc and a discharge side of the last perforated disc is maintained at greater than 0.5 atmospheres.

5. A method according to claims 1 or 2, wherein air is used as the pressure fluid.

6. A method according to claims 1 or 2, wherein water is used as the pressure fluid.

7. A method according to claims 1 or 2, including the step of maintaining the granular material introduced into the mould for up to 40 minutes.

8. A method according to claims 1 or 2, wherein the granular material is vulcanized in the mould.

9. A device for reducing flakes of toughly resilient materials to granular form, the device comprising a housing provided with a feed aperture for the flakes, the housing having a drive shaft mounted therein, a feed disc rotatably mounted on the shaft at a location spaced from the feed aper-ture, the feed disc adapted to feed the flakes received from the feed aperture to a first of at least one cutting discs rotatably mounted on the drive shaft, each of the at least one cutting discs having a non-circular bore whereby the disc is rotatably and slidably mounted on the drive shaft, the disc hav-ing circular openings therein, each opening having concave walls, edges of the concave walls cooperating with at least one surface of the disc to define a cutting edge, the openings being adapted to permit passage of material through the cutting disc, means urging a lower surface of each of the at least one cutting discs against a respective perforated disc mounted in the housing adjacent to the respective cutting disc, connector means connected to the housing upstream of the feed disc, the connector means adapted to be connected to a supply of pressu-rized fluid, whereby pressurized fluid is fed into the housing, and discharge means being secured to the housing downstream of a last perforated disc, the discharge means adapted to permit removal of pressurized fluid from the housing, each perforated disc having means adapted to cooperate with the adjacent cutt-ing disc to permit reduction in size of the flakes of material, the perforated disc having openings therein to permit passage therethrough of material which has been reduced in size, the pressurized fluid adapted to urge the material through the discs to prevent clogging in the housing.

10. A device according to claim 9, wherein the feed aperture is in the form of a funnel extending obliquely to the housing towards the feed disc, thereby facilitating introduc-tion of flakes of material into the feed disc.

11. A device according to claims 9 or 10, wherein the feed disc is provided with feed vanes fitted thereto, the feed vanes adapted to direct flakes of material to the aper-tures in the cutting disc.

12. A device according to claim 9, wherein the apertures in each cutting disc are circular in plan view.

13. A device according to claims 9, 10 or 12, wherein the means urging that at least one cutting disc against the adjacent perforated disc comprises a spring, one end of which bears against a retaining plate secured to the drive shaft, an opposite end of the spring bearing against the feed disc.

14. A device according to claim 9, wherein the means in the perforated disc adapted to cooperate with the cutting disc comprise at least one cutting groove in the upper surface of the disc, the at least one cutting groove extending radially outwardly from a center of a perforated disc.

15. A device according to claim 14, wherein one edge of each cutting groove is a cutting edge and extends tangentially to the holes which are radially aligned along the groove.

16. A device according to claim 9, wherein two cutting discs are rotatably mounted in the housing, each cutting disc having a respective perforated disc mounted adjacent thereto.

17. A device according to claim 16, wherein diameters of the holes in the perforated disc closer to the feed aper-ture are greater than diameters of the holes in the perfora-ted disc located closer to the discharge means.

18. A device according to claims 9, 10 or 12 wherein the apertures in each cutting disc are defined by concave walls, an edge of each aperture adjacent at least the lower surface of the cutting disc define cutting edges.

19. A device according to claims 9, 10 or 12, wherein each of the at least one cutting discs and their respective perforated discs are slidably mounted in the housing along the shaft, the cutting discs being rotatably mounted on the shaft while the perforated discs are non-rotatably mounted on the shaft cooperating means being provided between the hous-ing and perforated discs to prevent rotation thereof.

20. A device according to claims 9, 10 or 12, wherein the discharge means comprises a suction tube releasably secured to the housing, the suction tube including bearing support means thereto to rotatably support the shaft adja-cent one end thereof.

21. A device according to claims 9, 10 or 12 wherein the shaft includes flattened portions, the flattened portions adapted to cooperate with corresponding bores in each of the cutting discs, whereby the cutting discs are rotatably and slidably mounted on the shaft.

22. A cutting disc for use in a device for reducing flakes of toughly resilient, material to granular form, the cutting disc having a non-circular bore whereby the disc is rotatably and slidably mounted on a shaft, the disc having circular openings therein, each opening having concave walls, edges of the concave walls cooperating with at least one surface of the disc to define a cutting edge, the cutting edge adapted to cooperate with a perforated disc mounted in a housing to reduce material to granular form.

23. A cutting disc according to claim 22, which in-cludes four identical larger equally-spaced openings, with an identical smaller opening situated between each two of the larger openings, the smaller openings also being sym-metrically arranged in the disc.