WO1996026009A1

WO1996026009A1 - Method and apparatus for the grinding of elastomeric material, especially elastomeric scrap material

Info

Publication number: WO1996026009A1
Application number: PCT/SE1996/000244
Authority: WO
Inventors: Nils Erik Gustav Klyft; Bo Anders Nilsson; Sture Bertil Mattsson
Original assignee: Svedala-Arbrå Ab
Priority date: 1995-02-24
Filing date: 1996-02-22
Publication date: 1996-08-29
Also published as: SE9501014D0; SE9501014L; AU4853396A

Abstract

Elastomeric material, especially elastomeric scrap material, is subjected in a ring grinder to simultaneous grinding and peeling for separating reinforcing material and elastomeric material. The ring grinder has its inlet (12) arranged to supply grinding material substantially horizontally towards the rotor (20) of the ring grinder, and supplied elastomeric scrap material is caused to pass the major part of the grinding chamber before reaching the grinding material outlet (15) of the ring grinder.

Description

METHOD AND APPARATUS FOR THE GRINDING OF ELASTOMERIC MATERIAL, ESPECIALLY ELASTOMERIC SCRAP MATERIAL

The present invention relates to the recovery of elastomeric material, especially rubber scrap material in the form of e.g. worn-out car tyres or other reinforced rubber or elastomeric materials. For many years, efforts have been made to work up elastomeric material either to be regenerated for reuti- lisation or to be used as fillers or the like when manu¬ facturing quite different products. Such a field of uti¬ lisation is the use as admixture for asphaltic concrete mixtures. A further field of utilisation is the use as fuel in e.g. powder-fired furnaces in power and heating plants.

One problem in the previous refining of the elasto¬ meric material, especially the elastomeric scrap mate- rial, to make it usable for reutilisation or combustion is the question how the reinforcing material should be separable from the elastomers as such. In respect of heavy metallic reinforcing materials such as embedded metal sections or sheets, the problems have in fact not been insurmountable, since in any case the magnetic metal materials have been possible to separate to a relatively large extent from the material ground or crushed to powder or pieces. It has instead been difficult to remove a substantial part of or preferably all the fibrous rein- forcing material made of metal, for instance steel cord or layers of steel cord fabric. The probable reason why such a material is more difficult to remove than the heavy metallic materials is that in most cases the cord material has at least partially been impregnated with the elastomeric material in the forming and vulcanisation thereof. The forces to which the reinforced elastomeric material is subjected during the crushing procedure are both shear forces and peel forces. The shear force causes cutting-off or shearing-off of the elastomeric material and its reinforcement along the shear plane, i.e. the elastomeric material and the embedded reinforcement are "cut" off. Such a force does not cause the elastomeric material and the reinforcing material to be separated from each other to any considerable extent. The peel force, i.e. the force striving to peel or rip off the elastomeric material from the reinforcing material, is very efficient when separating elastomeric material and heavy metallic reinforcing material from each other, since it is a matter of overcoming the often fairly small adhesive force between the elastomeric material and the heavy metal reinforcing material. Steel cord or steel cord fabric is usually much more strongly fixed to the elastomeric material as compared with heavy metallic reinforcing material. This probably depends on the above- mentioned complete or partial penetration of elastomeric material into this type of reinforcing material during the vulcanisation of the elastomeric material. The methods that have been used up till now for grinding elastomeric material, especially elastomeric scrap material, have not been good enough to accomplish an extensive separation of especially metal cord rein¬ forcing material from elastomeric material. The prior-art grinding methods include grinding in different types of hammer mills, sometimes under cryogenic conditions to make the elastomeric material hard and brittle. Although such grinding under cryogenic conditions produces ground material containing fine grains, the grains are not sub- stantially free from metal cord reinforcing material.

This also applies if grinding takes place under ordinary room temperature conditions and also under conditions with elevated temperatures. Besides, this applies to the use of other known grinding methods, for instance by crushing machines which operate with cutting or tearing tools. Since apparatus and crushing methods known so far have not been able to produce extensive separation of all types of reinforcing material from elastomeric material, especially rubber scrap material, there is a great demand for such apparatus and methods. This demand is emphasised by the amounts of scrap material becoming larger and larger and more and more difficult to handle in a manner that is acceptable from the environmental point of view.

An object of the present invention therefore is to provide an apparatus and a method for producing a reco¬ vered elastomeric material that is substantially free from reinforcing material, by improved separation of elastomeric material and reinforcing material.

This object is achieved by a method and an apparatus as defined in claims 1 and 6, respectively. The subclaims define particularly preferred embodiments.

The invention is based on the surprising discovery that a special grinding method and a special grinder pro¬ duce the desired result. According to the invention, elastomeric material, especially elastomeric scrap mate¬ rial, thus is subjected, in a ring grinder, to simulta¬ neous grinding and peeling actions for the separation of reinforcing material and elastomeric material. The inlet of the ring grinder preferably is positioned for supply- ing grinding material in a substantially horizontal direction towards the rotor of the ring grinder, and sup¬ plied elastomeric scrap material is caused to pass the major part of the grinding chamber before reaching the grinding material outlet of the ring grinder, thereby eddying the material to be subjected to still more power¬ ful peel forces.

Summing up, the invention thus resides in the elas¬ tomeric material being processed and ground in a so-call¬ ed ring grinder, i.e. a grinder having a grinding cham- ber, which has a grinding material outlet in its circum¬ ferential surface and contains a rotor which is rotatable about an axis and in whose circumferential surface a num- ber of rings are mounted such that they project partially outside the circumferential surface and are independently rotatable relative to the rotor and can, to a limited extent, move towards and away from the axis of the rotor. In fact, it has surprisingly been found that precisely this type of grinder subjects the grinding material to such a combination of shear and peel forces that the aimed-at separation of reinforcement and elastomeric material is obtained and such that the ground elastomeric material has, to a very great extent, been separated from all types of reinforcing material after the grinding material has been discharged through the grinding mate¬ rial outlet. The ground material is then subjected to ordinary separating procedures, for instance wind screen- ing in a wind sifter, separating magnetic material in a magnetic separator and other known separating techniques.

The great advantage of the invention thus is that elastomeric material and reinforcing material are phy¬ sically separated from each other by breaking the exist- ing adhesive force in the very comminuting in the ring grinder.

Experiments have shown that an optimum result is obtained if the grinding material is caused to stay in the grinding chamber for a maximum time by causing the grinding material to move through a large part of the chamber before reaching a grinding material outlet in the circumferential surface of the ring grinder. The optimum results so far have been achieved if known ring grinders are modified in such a manner that feeding takes place laterally through the circumferential surface of the grinder instead of from above, and if the grinder is ope¬ rated such that the grinding material when entering is given an upward motion and moves up over the rotor of the grinder, before reaching the grinding material outlet of the grinder. Such a feeding and grinding process further makes it possible in a simpler manner to hold the grind¬ ing chamber of the ring grinder almost completely closed during the grinding procedure, such that the aimed-at peeling and mechanical crushing or comminution can, by a combination of separating and grinding, be carried out continuously and while affecting the environment as little as possible in the room or in the position where the ring grinder is placed.

In a particularly preferred embodiment of the ring grinder, the inlet opening has been arranged on approxi¬ mately the same level as the rotor shaft and has been formed with a slotted opening in the circumferential sur¬ face of the grinding chamber. Into this opening projects a feeder, especially a conveyor belt or a slat conveyor, which supplies the elastomeric material intended to be ground and separated. At the upper edge of the opening there is a pivotable cover or, preferably, a pivotable arm, at whose outer end a roller is mounted to roll on the upper side of the bed of material on the feeder. By subjecting the roller to a suitable load towards the con¬ veyor, for instance, by yieldably pressing the roller against the feeder and the material conveyed thereon, by spring action or the like or by gravity, the opening area can be kept at a minimum. Thus, the grinding procedure can be carried out under the most favourable conditions and the influence on the outer environment can be kept at a minimum. Moreover, the aimed-at effect, i.e. producing a peel force for the separation of metallic reinforcing material and elastomeric material, will be more easily achieved by feeding the ring grinder in this manner. When testing the invention, it has besides been found advantageous if the rotor is arranged in the annu¬ lar casing eccentrically relative to the centre line of the grinding chamber, such that the shortest distance between the rotor and the circumferential surface of the grinding chamber is to be found in the lower parts of the grinding chamber, where the grinding material outlet is arranged. As a result, the grinding material, which when passing through the gap between the grinding material outlet with its grating and the rotor with its grinding rings, has not passed through the grinding material out¬ let, will be thrown upwards and away from the rotor and mixed with newly supplied material and, together with this, eddy in the upper parts of the grinding chamber, before again being passed down to the grinding material outlet. Such eddying probably has a great effect on the grinding result and the achieving of the desired combina¬ tion of shear and peel forces for separating elastomeric material and reinforcing material, especially steel-cord- based reinforcing material. Although such eddying occurs independently of whether the rotor of the grinder is driven such that the new grinding material, which is fed through the inlet opening of the grinder, is initially passed down between the rotor and the grating or initial¬ ly moves upwards and over the rotor before being moved down between the rotor and the grating, the optimum result is obtained if the grinder is operated according to the last-mentioned alternative. Ring grinders as such are disclosed in e.g. US-A- 1,862,889. This US publication discloses a ring grinder of a special type for pulverising and crushing of mate¬ rial, the grinder operating according to the principle of separating uncrushable material from crushable by using the inertia and kinetic energy of the heavy particles to throw them out into special collecting pockets. This publication says nothing about separating metallic mate¬ rial from reinforced elastomeric scrap material.

US-A-1,892, 697 discloses a hammer-type crusher, whose hammer is, at the outer end, provided with rotat- able grinding rings to increase the impact effect. This publication says nothing about the problems which the present invention intends to solve, i.e. to provide a high degree of separation of metallic material from elas- tomeric material during grinding, thereby obtaining a final product which is substantially free from metallic material. DE-C-27 49 162 discloses a hammer crusher, whose grinding material chamber has two openable, perforated walls. The publication does not disclose a ring grinder of the type used in the present invention, and nothing is said about the problems which are intended to be solved by the present invention.

Derwent's Abstract, No. 93-233799/29, week 9329, Abstract of SU, 1,748,860, discloses a ring grinder whose rings have on their inner circumference a permanent-mag- netic inner shell for keeping the rings engaged with the stub shaft of the rings. The grinder is said to be suit¬ able for crushing of material in the building industry and other industries. However, nothing is said about the problems which are intended to be solved by the present invention.

Derwent's Abstract, No. C8141 D/13, week 8113, Abstract of SU, 749,424, discloses a hammer mill for mechanical processing and grinding of hard materials. Derwent's Abstract, No. D3597 K/10, week 8310, Abstract of SU, 923,598, discloses a ring crusher, whose crushing elements have a corrugated surface and roll along the crushing material moving along arcuate abutment plates which are settable towards or away from the crushing elements to determine the width of the crushing gap and, thus, the particle size of the crushed material. Nothing is said about a ring grinder of the type used according to the present invention, let alone anything about the problems which are intended to be solved by the present invention. The invention will now be further described by means of the accompanying drawings illustrating a particularly preferred embodiment.

Fig. 1 is a cross-sectional view of a ring grinder according to the present invention. Fig. 2 is a sectional view along line II-II in Fig. 1. The ring grinder shown in the drawings is the embo¬ diment of the invention, which at present is preferred owing to the design of the inlet and outlet of the grinder. The ring grinder has a casing 10 which defines a grinding chamber 11. At the lower end of the grinding chamber, the casing is formed substantially as a circular arc in cross-section. A grinding material outlet 12 is formed within this part of the casing. In the embodiment illustrated, the outlet 12 is formed as a grating 13, which can be made of a number of juxtaposed grating ele¬ ments, which are arcuate and have grating rods 13A and transverse grating members 13B. In this respect, the inventive ring grinder does not differ from prior-art ring grinders.

The grinding chamber has, in the remaining parts of the casing, been provided with a wear lining 14 of an abrasion-resistant material, e.g. manganese steel. In Fig. 1, the right side of the casing has a feed opening 15. A belt conveyor 16 serving as feeder projects into this opening. A cover formed as a roller 17 is arranged in the upper part of the opening 15 above the belt con¬ veyor 16. By the roller 17 being mounted on arms 18 and these in turn being mounted on a stub shaft 19 in the casing at a distance from the opening 15, the cover or roller 17 can move towards and away from the belt con¬ veyor 16 in order to abut against the material fed by the belt conveyor and move upwards and downwards according to the thickness and appearance of the bed of material. The roller can be idle but preferably is driven by a motor 17A. If desired, the roller 17 can besides be yieldably pressed in the direction of the conveyor belt 16, for instance by means of a piston-and-cylinder assembly 17C. A rotor 20 is rotatably mounted in the grinding chamber 11. The rotor is connected to a driving motor 21 at least at one end of the grinder. The rotor 20 has a straight-through shaft 22, on which a number of rotor discs 23 are arranged and attached, such that they are entrained in the rotation of the shaft 22 and such that they are interconnected. On one side of the rotor discs, two radially opposite recesses 24 are to be found in the embodiment illustrated to provide space for hammer rings 25 arranged in the recesses.

Succeeding rotor discs 23 are rotated through 90° relative to each other, such that the recesses 24 of one disc are offset 90° relative to the recesses of the sub- sequent disc.

The hammer rings 25 have an axially through hole 26. This hole has a greater diameter than a shaft 27 extend¬ ing through the rotor discs 23 and the recesses 24 there¬ in, such that the hammer rings are freely rotatable about their shafts 27 and, besides, are free to move away from and towards the rotor shaft 22.

The outer circumference of the hammer rings 25 can be smooth, but preferably is profiled to increase the peeling effect. The preferred embodiment of the outer circumferential surface of the hammer rings 25 is illu¬ strated in the drawings. The circumferentially outer part of the rings has been recessed on one ring side and the other alternately, such that the circumferential surface is formed of a series, of lugs 28 and intermediate recesses 29, the lugs and the recesses along each side of the outer circumference of the hammer ring being off¬ set a pitch in the circumferential direction relative to the corresponding recesses and lugs on the other side. The lugs on one side of the hammer ring thus are posi- tioned just in front of a recess on the other side of the hammer ring so as to form a zigzag pattern. Other embodi¬ ments of the circumferential surface of the hammer rings, also a smooth design, are however within the scope of the invention. To hold the rotor discs 23 together in the axial direction of the rotor, there are a number of connecting rods 30, in the example shown four connecting rods, which also have a stabilising and reinforcing effect on the rotor 20.

In the grinding of elastomeric material, especially elastomeric scrap material, in the above-described ring grinder, the elastomeric material is fed on the conveyor 16 in the form of a layer of material (not shown). As a rule, the elastomeric material can be supplied without any preceding primary crushing. For instance, it is pos¬ sible to feed to the grinder complete car tyres and lorry tyres, while off-the-road tyres and other large tyres can advantageously be pretreated by being cut to pieces of suitable sizes.

When the bed of elastomeric material reaches the cover or roller 17, this will be raised against the action of gravity (possibly also against the action of an optional spring device which yieldably loads the cover or roller for pivoting downwards towards the conveyor 16). In this manner, the free opening at the grinder inlet can be kept at a minimum. If the roller 17, as is preferred, is driven by the motor 17A, the roller can be used to control the supply to the grinding chamber 11 and to retain supplied material in the opening 15, such that this is already subjected to comminuting and peeling apart to smaller pieces when entering. This can be advan- tageous if the elastomeric material is in the form of elongate pieces which are longitudinally supplied by the conveyor belt 16 and therefore cannot be supplied as an integrated piece directly to the grinding chamber 11. By adapting the speed of rotation of the roller 17 to the speed of the conveyor belt 16 and by controlling the pressure exerted by the roller on the conveyor belt 16, it is thus possible to achieve improvements in the ope¬ ration of the grinder and the supplying of material. In the grinding chamber 11, the rotor 20 rotates under the action of the driving motor 21. Although rota¬ tion can take place clockwise or counterclockwise in respect of Fig. 1, an optimum result is obtained if rota¬ tion takes place counterclockwise, as pointed out above.

If rotation takes place clockwise in respect of Fig. 1, the entering material will be pulled down in the gap between the rotor 20 and the grating 13 and at the same time be strongly affected by the hammer rings 25 and also the grating 13. If rotation takes place counter¬ clockwise in respect of Fig. 1, the entering material will, however, be moved up over the rotor together with the material which has already passed through the gap between the rotor and the grating 13 and which will then be mixed with the supplied new material and be agitated in the space above the rotor, before all the material is pulled down into the gap between rotor and grating. In the latter case, the individual pieces of the grinding material will be affected not only by the hammer rings 25 and the casing but also by each other, which all in all has been found to yield a more efficient peeling effect and, thus, separating effect. The hammer rings 25 have a crushing and peeling effect on the grinding material by being rotatable about the shafts 27 and movable radially relative thereto and relative to the shaft 22 of the rotor. The hammer rings 25 will therefore roll along the grinding material and be pressed firmly against this when the material passes through said gap. When the hammer rings pass over the individual piece of grinding material in the batch, they will first roll onto this piece of grinding material and then squeeze this against the grating 13, when the grind- ing material has reached this. When the surface pressure becomes high, the rolling function will be rendered dif¬ ficult by high friction arising between the wall surface in the through holes 26 of the hammer rings and the shaft 27. As a result, the friction against the piece of elas- tomeric material increases, such that it is subjected to increased peel forces by the piece of elastomeric mate¬ rial also abutting firmly against the grating 13. The working will therefore be a combination of peeling, shearing and crushing, such that the aimed-at separation also of metal cord material from the elastomeric material is achieved. In a particularly preferred embodiment of the inven¬ tion, the rotor and its rotor rings can have a radius of about 50 cm, and the hammer rings can have a radius of about 20 cm. The hole of the hammer rings can have a radius of about 6 cm, while the shafts 27 can have a radius of about 4 cm. This means that the hammer rings can move about 4 cm in the radial direction relative to the shaft 22 of the rotor. The surface of the grating facing the rotor can be arcuately curved by a radius of curvature of about 66 cm, such that the gap between the rotor rings of the rotor and the grating is about 16 cm. The gap width of the grating in the circumferential direction of the casing can be, for instance, about 3 cm, while the length of the gaps of the grating in the axial direction of the grinder can be e.g. about 10 cm. In a thus designed ring grinder, grinding can advantageously be carried out at a circumferential speed of about 50 m/s at the circumference of the rotor rings, which corre¬ sponds to a speed of about 700 r/m. Of course, other dimensions of the various components can be used within the scope of the invention.

Claims

1. A method of producing a recovered elastomeric material which is substantially free from reinforcing material, by grinding elastomeric material, especially elastomeric scrap material, in which elastomeric material is supplied to a grinder and in said grinder is given a smaller particle size and subsequently is discharged from the grinder, c h a r a c t e r i s e d in that the grind¬ ing operation for effecting a simultaneous reduction of the particle size and separation of elastomeric material and reinforcing material included therein is carried out in a ring grinder with a grinding chamber (11) and, arranged therein, a rotor (20) having movable hammer rings (25).

2. The method as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the grinder is operated such that the rotor thereof carries the entering elastomeric mate- rial through the major part of the grinding chamber of the grinder, before the elastomeric material reaches the grinding material outlet of the grinder.

3. The method as claimed in claim 1 or 2, c h a r ¬ a c t e r i s e d in that the elastomeric material is supplied approximately horizontally to the ring grinder.

4. The method as claimed in claim 3, c h a r a c ¬ t e r i s e d in that the rotor (20) of the grinder is rotated in such a direction that the material, when being fed to the grinder, is caused to move upwards over the rotor, before being pulled down under the rotor (20) and into a gap between this and a grating (13) forming the grinding material outlet (12) of the ring grinder.

5. The method as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the ring grinder is ope- rated to produce an upwardly directed cascade of insuf¬ ficiently crushed and separated grinding material in the grinding chamber (11) of the grinder above the rotor (20).

6. A grinder for grinding elastomeric material, especially elastomeric scrap material, said grinder hav- ing a grinding chamber (11) and, arranged therein, a rotor (20) rotatable about an axis (22 ) and having grind¬ ing elements (25), said grinder further having a grinding material discharge opening (12) with a grating (13) for retaining insufficiently crushed grinding material in the grinding chamber, c h a r a c t e r i s e d in that it is formed as a ring grinder, in which the grinding elements (25) arranged on the rotor (20) consist of hammer rings (25) which are arranged on the rotor (20) and project partially from the circumferential surface of the rotor and are rotatable relative to the rotor and, besides, movable towards and away from the shaft (22) of the rotor.

7. The grinder as claimed in claim 6, c h a r a c ¬ t e r i s e d in that the feed opening (15) and the dis- charge opening (12) of the grinder are arranged relative to each other such that supplied elastomeric material is carried through the major part of the grinding chamber of the grinder before reaching the discharge opening (12).

8. The grinder as claimed in claim 6 or 7, c h a r a c t e r i s e d in that it has its feed opening (15) positioned to supply grinding material substantially horizontally towards the rotor (20).

9. The grinder as claimed in claim 6, 7 or 8, c h a r a c t e r i s e d in that the rotor (20) is posi- tioned eccentrically in the grinding chamber ( 11 ) for forming a cascade- and mixing-space above the rotor.

10. The grinder as claimed in any one of claims 6-9, c h a r a c t e r i s e d in that the grating ( 13 ) extends arcuately below the rotor (20) .

11. The grinder as claimed in any one of claims 7-10, c h a r a c t e r i s e d in that adjacent the feed opening (15) of the grinder there is a pivotable cover means (17) for controlling the supply of material to the grinder and for retaining supplied material in the grinding chamber of the grinder.

12. The grinder as claimed in claim 11, c h a r - a c t e r i s e d in that the cover means (17) at its free outer end comprises a roller (17) which is adapted to abut against and roll on a bed of supplied material on a feeder (16) .

13. The grinder as claimed in claim 12, c h a r - a c t e r i s e d in that the roller ( 17 ) is connected to a driving motor (17A).