IE43980B1

IE43980B1 - Method of re-treading tyres

Info

Publication number: IE43980B1
Application number: IE2224/76A
Authority: IE
Inventors: Wilhelm Schelkmann
Original assignee: Vakuum Vulk Holdings Ltd
Priority date: 1975-10-10
Filing date: 1976-10-08
Publication date: 1981-07-15
Also published as: NL7611239A; JPS6139185B2; EG12502A; PT65692B; DK156382C; DK453176A; IL50635A0; JPS5278284A; YU248176A; HU175749B; SE7611061L; IL50635A; BR7606805A; SE428778B; CA1113211A; PL111002B1; SE444913B; DK156382B; LU75962A1; IE43980L

Abstract

METHOD OF RENEWAL OF THE TREAD ON A WORN PNEUMATIC OF SOLID RUBBER TYRE The invention is concerned with a method of renewal of the tread of a worn pneumatic or solid rubber tyre. A layer of bonding rubber is applied to the prepared body of the tyre and a prefabricated rubber tread ring is applied. Gaseous inclusions between the applied layers are avoided or led away and the resulting blank is heated in an autoclave for vulcanizing the bonding rubber. The tread rins, which on its underside exhibits a rough face of projections and recesses forming a net work of passages, produced in a press mould simultaneously with the production of the tread and kept fit for bonding, is applied to the body coated with the layer of bonding rubber and any gaseous inclusions are led away out of the layers by application of reduced pressure, where upon the lateral outlet openings from the super imposed layers are sealed off, and/or by squeezing out by means of the exertion of mechanical pressure on the tread.

Description

The invention refers to a method of re-treading pneumatic or solid rubber tyres, in which a layer of bonding rubber is provided between the prepared body Of the tyre and a vulcanised rubber tread section;any gaseou inclusions between the applied layers are led away, and the blank prepared in this way is heated in an autoclave for vulcanizing the layer of bonding rubber. In the case of heavy-cleated large tyres, the tread-section may be in the form of one of separate segments and/ or tread rings to be connected together, although it will usually be a single tread ring.

In known methods the blank is enclosed in a rubber jacket onto which pressure is then brought into action so that the gas inclusions present in the layered structure of the blank escape. Furthermore the layered structure of the blank is fixed by the jacket, especially for the critical state which appears when under the influence of the heat of vulcanization the bonding rubber becomes plastic and finally shortly before vulcanization even liquid. Jackets are costly to produce, they are easily damaged and are then leaky. Their life is limited, depending upon the material, vulcanization temperature and kind of treatment.

Other known methods no longer indeed require rubber jackets, but they are suited only to certain types of tyre and require additional measures which increase the cost of the renewal considerably. - 3 43980 The practice is also fundamentally known of producing in the press mould a rough face on the underside of the tread section, necessary to the fastening of the tread section to the body, at the same time as the profile of the tread. For this purpose a die with the negative profile of the desired rough face is forced onto or into the raw rubber in the press mould and kept there during the vulcanising. The die may be formed as a loose part such, e.g., as a layer of fabriczor else directly on the inside of one of the halves of the press mould or fitted there. In any case the die is re10 leased from the rough face at the end of the pressing process. The surface of a rough face produced in that way has, however, after longish storage proved to have lost its good bonding capacity as a result of aging and oxidation.

The object of the invention consists in providing a tyre-retreading method utilising a tread section, which can be stored without significant deterioration in its bonded capacity prior to being bounded to a tyre body.

In accordance with the invention, a method of retreading a rubber tyre comprises the steps of: a) producing a tread section having an internal rough surface consisting of projections and recesses for bonding and forming a network of passages to assist in evacuating gaseous inclusions between the internal surface of the tread section and a layer of bonding rubber during subsequent bonding, and an outer tyre tread surface; b) coating the internal rough surface.,having unsaturated vulcanized rubber molecules just after producing the rough surface.,with a solution of a bonding rubber to tie the unsaturated molecules and thus to prevent deterioration of the bonding capacity of the internal rough surface during storage and thereby enhance its bonding capacity during subsequent vulcanization without needing a subsequent mechanical roughening of the internal tread surface; c) applying the tread section to the rubber tyre with a layer of vulcanizable bonding rubber between the prepared body of the tyre and the internal rough surface of the tread section; and, d) after evacuation through the network of passages of gaseous inclusions occurring between the coated internal rough surface and the layer of bonding rubber and after evacuation of any gaseous inclusions between the layer of bonding rubber and the tyre body, subjecting the tyre and tread section to heat and pressure in an autoclave to vulcanize the bonding rubber and unite the tread section to the rubber tyre.

The combination of the aforesaid measures leads to a simple and cheap method.

The producing step may comprise moulding and vulcanizing a body of vulcanizable material in a press mould to form the tread section.

The press mould may be filled with a body of vulcanizable material for the production of the tread section by an injection moulding technique.

There may be applied to an area of the press mould which creates the 5 internal rough surface,or directly to a face of the body of vulcanizable material inserted in the press mould opposite to that area thereof,a material, such as a silicon solution, which delays the vulcanization reactions of the internal rough surface.

An essential part is played by the employment of a tread section with an internal rough face, preferably produced simultaneously with the tread section.

Roughening of the tread section by means of a roughening machine directly before the tread section is applied is dispensed with as well as the thereby ensuing loss of rubber material as well as the considerable consumption of time for the work itself of roughening.

Furthermore mechanical roughening cannot be performed when mixtures of rubber of high wear-resistance are used with heavy-cleated tread rings or tread segments, unless an additional special reinforcement is used under the rubber and a rubber mixture is applied. This causes an undesirable increase in the outlay of material and in the operating temperature of the tyre retreaded in this way, without any gain in additional depth of tread profile.

An advantage of moulding the tread section is that, in the case of mechanical roughening of the tread section only fine roughening can be achieved, so thatclogging.of a possible network of passages within the rough profile may occur with the danger of undesirable inclusions of gaseous and liquid components when the tread is applied to a tyre. This leads to rejects because of the formation of bubbles and hollows in the vulcanized layer of bonding rubber. The rough face forms on the contrary a highly effective network pfipassages for leading away possible inclusions because of the appreciable separation between its projections and recesses as well as because of the height of the projections and recesses being equally open to choice. i The bonding rubber can now flow very easily into the deeper parts of the rough face, whilst the roughening applied hitherto on the underside of t trend-secLion was merely slashed, so that the bonding rubber in running in had to remain on the surface. A transition layer from the tread section to the layer of bonding rubber is created, the two of them exhibiting different physical values. The deeper the transition layer, that is, the layer which exists from overlapping of the two materials, the more intimate and robust is not only the bond finally attainable by the vulcanization but also already the force of adhesion with which the tread section is secured by the unvulcanised layer of bonding rubber. The layer structure of the blank thus obtains adequate fixing because of the essentially intensive sticking together of the layers through the rough face. The considerably enlarged and therefore considerably more effective rough face thereby takes over the retaining function of the rubber jacket employed hitherto. - 7 43880 It is of course very important that the rough face maintain its bonding capacity, i.e., that the surface of the rough face even after a time in storage can always enter into an intimate bond with the bonding rubber by vulcanization. The rough face of the tread is for this purpose after withdrawal of the die when one is employed, coated shortly after removal of the tread from the press mould with a known solution of an unvulcanized mixture of bonding rubber dissolved in a solvent such as petrol or benzene. In that case the solution ties the unsaturated molecules in the surface of the rough face, the structure of which, that is to say, is opened up by breaking the rough face out of the metallically clean face of the press mould, and thus a physiochenrical association takes place, that is, an ion exchange between the H bonds of the sulphhydryl groups. The surface of the solvent coating thus remains activated by a film of unvulcanized rubber molecules and may,where necessary directly before applying the tread to the body7 be made tacky to increase the activity by spreading on more solution.

After applying the coating of solution to the rough face of the tread section a protective foil is advantageously stuck to the rough face, which foil is removed before the tread can be applied to the body.

In producing the layered structure the layer of bonding rubber in the plastic state is preferably brought into contact with the rough surface.

For plasticity imparts to the layer of bondinq rubber the degree of flowability necessary to flowing into the rough surface.

The plastic state is achieved either by the employment of fresh bonding rubber or by heating the bonding rubber or by appropriate additions to the bonding rubber. By the flowing of the bonding rubber into the rough surface an intimate connection between tyre body, bonding rubber and tread section is already brought about before vulcanization, and this is an important prerequiste for auxiliary means such as a rubber jacket or the like being able to be dispensed with in vulcanization. The process of flow of the bonding rubber is completed by the usual heat and pressure treatment in an autoclave.

The tread section whenever possible is applied in ring form to the body coated with the layer of bonding rubber, preferably under prestress. For the preparation of the blank for the heat treatment there are a number of advantageous methods: The tread section may be rolled free of inclusions of air onto the body coated with bonding rubber, that is, starting from the centre and proceeding steadily towards the sides so that the inclusions can flow along to lateral openings and there escape. This discharge is promoted if the tread section is applied under prestress. Afterwards the openings can be closed in order on the one hand to avoid fresh penetration of inclusions into the layered structure and on the other hand to achieve additional fixing of the layered structure.

In special cases, e.g., in the application of heavy- cleated tread materials, especially in the form of separate rings or segments, it is advantageous to lay a so called building-jacket (not to be confused with the hitherto usual high grade rubber jacket) loosely round the blank and seal it at the sides to the tyre, to put it under vacuum and roll on the loosely laid tread material. - 9 43860 With this procedure air-inclusion-free rolling of the tread material onto the body can be enabled also in the case of a very thin underlayer of rubber. Discharge of the inclusions is effected through a network of passages kept free at the side of the tyre. The jacket is taken off again and the openings from the layers are sealed off.

For leading away the inclusions of air and for holding the tread firmly onto the body the tread section laid on the body may be enclosed by means of an elastic rubber or plastics pressure-band which is provided with many perforations,or by means of an elastic net. The cross10 section of the pressure-band may be arranged so that the pressure decreases from the centre to the sides, whereby a pressure gradient results for automatic leading away of inclusions to the sides, this being further enhanced by the curvature of the tyre body.

Leading away the gaseous inclusions out of the layers of the blank may be further facilitated if the inclusions are additionally led via channels leading directly to the sides of the tread, which channels may be produced in the rough face of the tread section at the same time as the rough face is produced in the press mould.

During building and vulcanizing the body of a pneumatic tyre should be put on a rim and under air pressure. This is particularly to be recommended in the case of those bodies which tend to shrink.

As heating medium in the autoclave, besides water, hot air is also suitable, especially moist air, and steam.

If the body to be retreaded has a damaged ply a tread section may be employed which consists of a top part and a bottom part, of which the bottom part has reinforcing inserts of steel mesh, plastics mesh or the like. In order to tierform this method economically and reliably the bottom part and the top part of the tread section are advantageously respectively produced in a press mould as independent parts already having rough faces at the bonding sides and applied to the body one after the other with a further bonding layer interposed.

Since the bottom part because of the inserts cannot be stretched, in covering the body with the annular bottom part the circumference of the body must be reduced, for example, by kinking the body during the covering at a number of points along the body circumference.

The method in accordance with the invention is explained in greater detail below with the aid of the drawings. In the drawings there is shown in: Figure 1 - a perspective of a tread ring with a rough face produced in the press mould; Figure 2 - a perspective of a tread ring with a rough face produced in the press mould on the underside and on the edges; Figure 3-a cross-section through a tread with a rough face formed in the press mould; - Π 43980 Figures 4 to 7 - a number of portions cut from a rough face produced in a press mould, but with different patterns of rough face; Figure 8 - a cross-section through a blank which is covered by a tread section consisting of a bottom part and a top part; Figure 9 - a cross-section through a built-up tyre or blank, in which for the tyre in the lefthand half of the illustration the tapering edges of the tread are being put under tension and in which the righthand part shows a tyre covered by a building-jacket; and Figure 10 - a diagrammatic illustration of a body during pulling on of a bottom part of a tread.

The tread ring 1 shown in Figure 1 exhibits on its inside a rough face 3 and on its outer face a profiling 2, the two of them having been formed at the same time by the production of the 'tread section Ί, in the press mould. As explained, immediately after removal from the press mould the rough face 3 is coated with a solution of a bonding rubber in a solvent, such as petrol. The tread segment 4 illustrated in figure 2 and provided with heavy profiling 2 also exhibits an inner rough face 3 as well as rough edge-faces 5, 6, at the points where likewise a bond is to be carried out by means of bonding rubber. Depending upon the type and form of the die, rough faces 3 of any chosen structure as well as of size to be determined and of definable separation between the projections 14 and the recesses 15 lying between them are possible (Figure 4-7). Even undercut projections 15 may be produced as shown in Figure 6. Figure 7 illustrates, for example, a structure of an irregular rough face 3 which can be produced by mere working of irregular recesses into the top half or cover of the press mould. - 12 It is clear that a rough face 3 of that kind forms an excellent network of passages for leading away gaseous and liquid components out of the layered structure of a built-up tyre.

In Figure 8 the layered structure of a built-up tyre has been illustrated, the body 8 of which is covered by means of a tread section or tread ring 1 whic consists of a top part la and a bottom part lb which is provided with inserts 11. The bottom part lb serves for reinforcement of the body 8 the belts of which were damaged and have been totally or partially ground off in connection with preparing the body 8 for retreading. The bottom ) part lb exhibits on all sides rough faces produced in the press mould.

For the underside of the bottom part lb is connected by means of a layer 10 of bonding rubber to the upper side of the body 8, whilst a further layer 9 of bonding rubber applied all round over the bottom part lb and also advantageously as illustrated carried outwards over the bottom part lb, bonds the top part la on the one hand to the bottom part lb and also as far as the edges of the tread are concerned to the body 8. A film of material indicated by 12 is to illustrate how the lateral points of outlet 12a from the layered structure are closed before reduced pressure is applied, e.g. by inserting a hollow needle into the layered structure of the built-up tyre, for the purpose of leading away any gaseous, and possibly also some liquid, inclusions.

Figure 9 on the other hand illustrates in the lefthand part that by laying a strip 12 of bonding rubber under the tapering edges 13 of the tread section or tread ring 1 a prestress may be created at that point for the purpose of fixing the layered structure onto the body 8. - 12a43960 On the other hand the righthand part of Figure 9 illustrates how, particularly in the case of heavy-cleated profiles with a thin underlayer of rubber (not shown here),the inclusions are advantageously led away under a building-jacket 13 which is put under vacuum, whilst the tread section 1 or respectively its top part la, after it has been laid on only loosely, is rolled on, starting from the middle end proceeding towards the sides. The building-jacket 13 is advantageously sealed at the bead 16 by means of a rim and the inclusions led to the side are drawn off via a channel 15 which is formed in front of a ring 14.

Before inserting the blank in the autoclave this jacket is removed.

Figure 10 illustrates merely diagrammatically that the circumference of the wall and hence the diameter of the tyre body 8 muBt be reduced when the unstretchable bottom part lb of the tread ring 1 is being applied to the body 8, Reducing the size of the body 8 may, for example, be carried out by means of rods indicated by 18, which are pressed mechanically, advantageously in a symmetrical arrangement, into the body 8 at its periphery and thus enable pulling on of the bottom part

Claims

CLAIMS:

1. A method of retreading a rubber tyre, the method comprising the steps of: a) producing a tread section having an internal rough surface consisting of projections and recesses for bonding and forming a network 5 of passages to assist in evacuating gaseous inclusions between the internal surface of the tread section and a layer of bonding rubber during subsequent bonding, and an outer tread surface; b) coating the internal rough surface,having unsaturated vulcanized rubber molecules just after producing the rough surface^with ) a solution of a bonding rubber to tie the unsaturated molecules and thus to prevent deterioration of the bonding capacity of the internal rough surface during storage and thereby enhance its bonding capacity during subsequent vulcanization without needing a subsequent mechanical roughening of the internal tread surface; c) applying the tread section to the rubber tyre with a layer of vulcanizable bonding rubber between the prepared body of the tyre and the internal'rough surface of the tread section; and, d) after evacuation through the network of passages of gaseous inclusions occurring between the coated internal rough surface and the layer of bonding rubber and after evacuation of any gaseous inclusions between the layer of bonding rubber and the tyre body, subjecting the tyre and tread section to heat and pressure in an autoclave to vulcanize the bonding rubber and unite the tread section to the rubber tyre. - 14 43960

2. A method according to Claim 1, wherein the producing step comprises moulding and vulcanizing a body of vulcanizable material in a press mould to form the tread section.

3. A method according to claim 2, wherein the press mould is 5 filled with the body of vulcanizable material for the production of the tread section by an injection moulding technique.

4. A method according to claim 2, or claim 3, wherein the internal rough surface is produced simultaneously with the tread section.

5. A method according to claim 4, wherein there is applied to 10 an area of the press mould which creates the internal rough surface,or directly to a face of the body of vulcanizable material inserted in the press mould opposite to that area thereofja material which delays the vulcanization reaction of the internal rough surface.

6. A method according to claim 4 or claim 5, wherein the 15 producing step further comprises forming additional channels in the internal rough surface for leading gaseous inclusions directly to the sides of the tread section, the channels being produced in the internal rough surface simultaneously with the internal rough surface in the press mould. 20

7. A method according to any one of the claims 1 to 3, wherein the producing step comprises making the tread section of a radially outer and a radially inner part, of which the inner part is reinforced with inserts. - 15 4398®

8. A method according to claim 7, further comprising making the inner part and the outer part of the tread section as independent parts both having rough surfaces, at their bonding sides and the applying step comprises applying the inner and outer parts to the tyre one after the other with a further layer of bonding rubber interposed therebetween.

9. A method according to any one of the preceding claims, wherein the layer of bonding rubber is brought in the plastic state into contact with the internal rough surface.

10. A method according to claim 1, substantially as described with reference to the accompanying drawings.

11. A rubber tyre which has been retreaded by a method according to any one of the preceding claims.