Method for Manufacture of Rubber Granulate From Old Tires

The invention relates to a method for the manufacture of rubber granulate from old tires, in which the tire is pre-disintegrated into pieces in two subsequent steps, the pieces are torn by stretching and the carcass fabric, steel or textile cord is rejected.

The invention also relates to a device for carrying out the method.

Such a method is known from German Pat. No. 2,427,070, which in itself is a modification of a method described in U.S. Pat. No. 2,471,043.

In view of the continuous development of tires from a rubber tire with a textile ply to tires which are presently predominently available on the market and have a bead with a steel wire insert and the carcass of which is partly or fully composed of steel cord, it was necessary to adapt also the method of disintegration of old tires to obtain suitable rubber pieces, free of other material, for further use of old rubber.

The task of the present invention is therefore to devise a method which is suitable for the treatment both of tires with textile and old tires having a steel bead, steel fabric ply and a steel belt while avoiding the expenses on machinery, considered presently as necessary, to produce rubber granulates without fabric portions, i.e. without textile and without steel particles.

This is according to the invention achieved in that

(1) the tire is in a first cutting operation cut into a plurality of strips extending along its perimeter that

(2) the bead strips which contain steel elements are rejected, that

(3) at least the strips which extend substantially in the direction of the tyre perimeter and contain textile fibres are in a second cutting operation cut through in a direction which is oblique to the first cutting, that

(4) in all cut-up tires pieces rubber is separated from the fabric in a crushing mill, and finally

(5) the pieces are sorted according to the size in a sieving operation, while, if necessary, the steps (4) and (5) are repeated in a cycle until the desired size of the pieces is obtained.

The method according to the invention takes into consideration primarily the construction of radial tires having steel bracing belts, which today dominate the market. It is based on the principle that by suitable guiding of the cutting operations first only pieces should be made from the old tires the length of which corresponds to that of the steel components embedded in the rubber, and remains below a desired length. In view of the aimed at guiding of the cut according to the invention, namely approximately along and transversely to the direction of the steel fabric plies in the tire and the steel bracing belts, this desired maximum cutting length is ensured so that pieces of old rubber of approximately uniform size are brought to the crushing mill. In comparison with disintegration by means of chopping and tearing tools in which the tires are disintegrated into old rubber pieces of arbitrary size, there is the further advantage of energy saving because chopping and tearing machines need much more energy than cutting machines. Due to the inventive guiding of the cut the bead is rejected in the form of a continuous marginal strip before further treatment, without requiring magnetic separation in a separate and parallel working operation. Because the method according to the invention ensures unity of composition of the pieces of old tires there is little danger of damage to the crushing mill. Moreover the mill may be selected according to the now defined properties of the disintegrated material. In view of the tearing and sorting operation which may be, if necessary, made in cycle, expensive intermediate selection stages, used in known methods, may be avoided. The size of the granulate may be determined according to the mesh aperture size of the sieve in the cycle of the crushing mill. The textile fabric and steel fabric parts are separated on passing through the crushing mill as loose free fibres and threads from the rubber granulate. These textile and steel fibres and threads may be rejected after sieving and this is achieved preferably mechanically, pneumatically and/or magnetically.

According to a further advantageous variant of the method according to the invention also the first cutting operation in the circumferential direction of the tire is subdivided into two subsequent cutting steps. In the first cutting step are from the old tire, the sidewall parts of which are preferably pressed on to each other, made approximately uniformly wide strips of a length corresponding to the circumference of the tire. In view of the guiding of the cut the fabric fibres in the strips cut from the tire sidewall approximately perpendicularly to the cutting edges and their length consequently is approximately the same as the width of these cut strips. The tread part of the carcass is usually built up from a plurality of approximately mutually diagonally extending cord plies from textile material or steel and has between the tread and the described structure belts the threads (wire or textile) of which are approximately parallel to each other in the circumferential direction. In view of the cut guiding according to the invention in the second cutting step rubber strips with fabric threads are therefore obtained the length of which, due to the diagonal positioning of the fabric threads, is only slightly greater than the width of the cut strips and fabric threads which lie in the longitudinal direction of the strips and may have a length which corresponds at the most approximately to the circumference of the tire. These steel wires are in the second cutting operation cut also into pieces of uniform length. The second cutting operation may preferably be so performed that it is harmonized with the width of the strips obtained in the first cutting operation, and the length of the strip pieces obtained in the second cutting operation corresponds to the width of the strips obtained in the first cutting operation.

The apparatus, to which the invention also relates, for carrying out a method according to the invention has a cutting device for cutting old tires into pieces, a crushing mill for tearing the cut pieces and a sieving and sorting device, all the devices being interconnected by conveyor means. The apparatus according to the invention is characterized in that the cutting device comprises a longitudinally cutting device with cutting edges extending in the direction of conveying of the tire and, downstream thereof in the direction of conveying is situated a transversely cutting device having cutting edges extending at right angles to the direction of conveying.

The invention will now be described in detail with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram showing operational steps of a method according to the invention,

FIG. 2 is a side view of a cutting device,

FIG. 3 is a section along line 2--2 in FIG. 2, and

FIG. 4 is a further embodiment of a knife head used in the second cutting operation.

It can be easily seen from the block diagram in FIG. 1 of the method that the method according to the invention is much simpler than methods which have been used. Intermediate sorting operations and the return of a separately treated material component into the working process before the tearing means are completely absent. The process flow in the method according to the invention is apparent from the subsequent steps explained below, which are in FIG. 1 indicated by corresponding references. Old tires are fed at 110 into a disintegrator while the mutually opposite sidewall parts of the tire are pressed against each other. In a first cutting stage 120 the marginal strip which contains the steel packet of the tire bead is so cut off in the circumferential direction that its rubber component is as small as possible. From the tire sidewall part may be simultaneously cut about 5 cm wide strips which may be directly supplied to a crushing mill 170. The bead strip is rejected via a conveyor path 130, 140 and discarded. The tangentially cut tire proceeds to station 150. On this occasion the sidewall parts may be approximately in the plane of the carcass spread and cut together with it into strips of equal width extending parallel to the circumferential direction. The strips from the sidewall of the tire may be fed from here directly to the crushing mill 170. In the station 160 are cut in a second cutting operation preferably the strips of the tread part transversely to the longitudinal axis. To the crushing mill 170 are then supplied the old rubber pieces with textile and steel fabric plies the width and length of which depend on the spacing of the knives in the stations 120 and 150 and their length depends on the speed of conveying of the strips and on the speed of cutting in the station 160.

The rubber parts are disintegrated in the crushing mill 170 by stretching up to the breaking limit in a manner known per se, the rubber components are separated from the fabric ply and both are together fed to the sieving device 180. Parts of the desired size fall through the sieve 180 into a container 190, while larger parts travel on the conveyor 200 back to the crushing mill 170. This process may be repeated as required until all parts are smaller than the mesh aperture size of the sieve 180. The fabric component is then rejected along the conveyor 210, e.g. by means of a magnetic drum and a cord separator at 220.

In FIG. 2, which is a side elevation of an apparatus for carrying out the cutting operation, are shown devices for the steps taking place at 110, 120, 150 and 160.

An old tire 1 is at 2 positioned on to a holder 3 having a stationary roller 12 and two displaceable rollers 13 and is lifted by means of a lifting device, here in the form of a swingable arm 5 on a pivot 4, and is delivered to a pressing tool 6. This pressing tool 6 consists of two rollers 7, 8 rotatable in opposite direction, which press the mutually opposite sidewall parts of the old tire 1 flatly against each other so that they form an approximately annular double surface before they are delivered to the first cutter 10. This cutter 10 consists in the illustrated embodiment of a circular knife 15 on a shaft 11 which is at an angle to horizontal and, when the arm 5 is lifted, is at a predetermined distance from the stationary roller 12. The cutting edge of the circular knife 15 presses the flatly compressed sidewall ring against a transport roller 14 which rotates in opposite direction. The circular knife 15 cuts the tire 1 first of all tangentially. The circular knife 15 is so adjusted that its cutting curve runs in close proximity to the bead, to cut off from the tire 1 a narrow marginal strip including the bead. The bead can then be rejected without any significant loss of rubber material.

The tire 1 has at 16 a still slightly curved surface and runs on to a shoulder 17 which is slightly curved in the upward direction, where it is caught by a transport roller 18 which conveys it to a second cutter 20a which is composed of spaced-apart circular knives 19 arranged on a shaft 20, the cutting edges lie between and below transport rollers 21. The flat tire 1 is pressed, by a pressing roller 22 rotating in opposite direction, against transport roller 21 and against the cutting edges of the circular knives 19. The tire is here cut into strips of a width which corresponds to the spacing of the circular knives 19 on the shaft 20. The individual plies of the carcass formed by fabric threads extending diagonally to the circumferential direction, are cut through along a cutting curve which is at an angle to the extension of the carcass, so that the length of the obtained fabric threads is somewhat greater than the width of the cut strips. The bracing belts which form one or more layers extending parallel to the circumferential direction and are situated between the tread and the carcass are cut along cutting curves extending into circumferential direction into more or less long threads. The maximum length of these threads could theoretically correspond to the circumferential size.

The cut strips arrive at a guiding channel 35 and are conveyed by a conveyor roller 36 to the cutting device 23 situated downstream of the strip cutters 10 and 20. The purpose of this cutting device is to cut the strips into pieces by a knife 25 which has four cutting edges 26 and is mounted on a shaft 24 extending transversely to the direction of conveying of the tire strips. When the shaft 24 is driven by the motor 27 and transmission 28 each cutting edge 26 cuts in a scissor-like manner all the strips fed to the cutting device 23 by means of a cooperating cutting edge 29, transversely to the direction of conveying, into individual pieces. The length of these pieces is determined by the selection of the speed of rotation of the knives and may be varied. The wires of the steel belt, which lie in the supplied rubber strips in longitudinal direction, are now by means of the cutting device 23 cut into preferably about 5 cm long pieces so that the crushing mill (not shown) situated downstream thereof is supplied with pieces of rubber in which all the textile and steel fabric components have an identical length of about 5 cm.

FIG. 4 shows a further embodiment 23a of the cutting device 23 in the form of a circular knife 30. This circular knife 30 is carried by a shaft 31. Its cutting edge lies in a rotatable groove on the surface of a shaft 32. The shaft 31 revolves in a circular path about the strips 37 arriving from the cutting device 20a on to the shaft 32, so that the circular knife 30 performs the desired cuts extending transversely to the length of the strips. The approximately square-shaped pieces of rubber formed thereby are finally fed to a crushing mill (not shown), designed in a manner known per se, in which they are made into granulate.