IL48815A

IL48815A - Process for reconditioning a worn tyre by direct application of a premoulded tread to the carcass of the tyre

Info

Publication number: IL48815A
Application number: IL48815A
Authority: IL
Original assignee: Ital Rubber Srl
Priority date: 1975-01-21
Filing date: 1976-01-09
Publication date: 1977-11-30
Also published as: FR2298429B1; NL7515035A; GB1503027A; BR7508773A; DE2553975A1; FR2298429A1; AT349918B; SE428279B; SU938734A3; CA1078120A; AR206369A1; SE7513550L; IT1028591B; ES443860A1; CH591947A5; ATA939875A; JPS5193982A; AU1009776A; IL48815A0

Description

38899 AN IMPROVED PROCESS FOR RECONDITIONING A WORN TYRE BY DIRECT APPLICATION OF A PREMDULDED TREAD TO THE CARCASS OF THE TYRE.

This invention relates to an improved process for reconditioning a worn tyre by direct application of a premoulded tread to the carcass of the tyre.

The processes employed to date for^conditioning worn tyres can essentially be divided into two groups: a) High temperature or so called "Hot" processes b) Low temperature processes With the former, the yet unvulcanised tread is applied to the previouely rasped carcass; the ensemble constituted by the carcass and the unvulcanized tread is placed inside special mould and then, with heat provided in the form of steams gas or hot air, vulcanization is brought abou t hgh temperatures* Simultaneously with the above step, the profile of the tread is formed too and this naturally depends on the way the mould is shaped, and the pattern thereo This process presents various problems> principally; - the early ageing of the finished product because of the high temperature used; - high plant costs due to the large number of moulds needed to have sufficient production elasticity.! In other hot processes, although the technology described above continues to be used, the application of a prevulcanized tread is envisaged.^ This modi ication makes it possible to do away, at least in part, with the problem of the great number of moulds but it introduces another big difficulty, namely double vulcanisation which notably impairs the mechanical characteristics of the tyre.* The low temperature processes currently known envisage the application of the tread to the carcass of the tyre to be reconditioned, using an intermediate strip of adhesive material.' The.sold strip, having a natural rubbe base and containing, amongst other substances* an accelerator and a vulcanizing agent, is ¾i-ei. kept at a low temperature, protected by a special casing in order to prevent undeeired prevulcanisation and only at the time it is to be used is the said strip applied to the tread*: Other low temperature processes envisage, instead of one single strip of adhesive material* tvo separate strips, again vith a rubber base, one of which contains the accelerator and the other, the vulcanising agent.i ■■. ·■ _■ ' · ·. ■.. . , These particular strips also have to be kept carefully isolated from one another until the time they are used so as to prevent undeeired reactions** During the vulcanization phase the complete ensemble is enclosed in a protective casing which is made suitably, taut so, that it is tightly up against the surface of the tread and the sidewaHs of the tyre*! The said casing is provided with a valve to externally relieve the air trapped in between it an the tyr at the time of the fitting of the casing.

The purpose of this Is to prevent oxidation from occurring during the vulcanization phase or alterations from taking place in the chemical-physical characteristics of the material to be vulcanized, which is Subsequently vuleenlzed** , .

The application of the strips of adhesive material and of the tread to the carcass of the tyre is carried out through tollin operations performed in such a way as to enhance and furthe the lateral expulsion of ai trapped between the carcass, the strips of adhesive material and the tread during the application phase.- To be xac * the normal procedure 4s to perform the rolling operation with a reciprocatin motion in a direction diagonal to the surface of the tread while atr du»'S*»e; tine the tyre is being rotated*; The latter process, which is widely used, present*, however* various other problems: ., _ - the strips of adhesive materiel pre likel to elide outside the area in vUch the tread has to be applied; - It is difficult to get the final thickness of the stripe of adhesive material to be uniform because, due to the tendency to slide mentioned above* in some places the material accumulates, whilst in others it is in short supply and might even be present to an insufficient degree only»; On account of the aforementioned dif iculties* the bond between the tread end the carcass becomes irregular and areas are created which become unstuck and tliese shorten considerably the life span of the reconditioned tyre.) A. further problem* which is by no means of minor importance* is that of air pockets which, durin vulcanisation become, encapsulated between the protective casing and the treed since* despite every care with which the protective casing is put into position and technical expedients used* it is not possible to fully eliminate the presence of air inside the said casing end thus a certain quantity of air, though of minimal volume* is always trapped in the interstices of the surface of the tread.* Shis consistutes a actor which notably reduces the global heat transmission coefficient, thereby impeding proper vulcanisation.

Furthermore* in all low temperature processes, the strips of adhesive material between the tread and the carcass* whether consisting of one or more layers* have to be kept awy rom the tread and also separate from one another under special ambient conditions, duly protected by a special easing in order to prevent the danger of pre-vulcanisation which would greatly reduce their adhesive properties·< Only at the time of their actual use can the said strips be applied to the tread or to the carcass of the tyre and this rendere the task The main object of the present invention is to overcome the problems to which reference, has been made , by means of a process for reconditioning a worn tyre which envisages the direct application to the carcass, of the tyre of a single assembly constituted by the premoulded tread and the strip or shee of adhesive material* in which process: . - a sheet of adhesive material can be prepared and be applied to the tread at the time when it is handled* without any danger of a prevulcanizatlon reaction - the application of the said sheet to the tread takes place without any dange of displacemen occurring and wi h the maximum certainty of no air pocket being present between the tread and ,the sheet; _t r there is definitely no air at all between the protective casing and; the tyre during, the vulcanization phase.' These and other objects , which will be seen in due course have been achieved with the process forming the subject of the present invention which is mainly characterised by the fact that i comprises the following phases: ... γ , . . _ i . . ; i ... · ■■ . . t . , t ., .- , ·-., . .. : . , - the preparation of a sheet of adhesive material with which to firmly connect the tread to the carcass of the tyre with the use of reagents comprising, in addition to at least one non vulcanized bonding material* at least one vulcanisation accelerator end at least one vulcanising agent, a high percentage by weight of ,, covulcanizing resins* plus an agent for the prevention of scorching, adapted to vulcanize the said non vulcanised bonding material at a temperature of about WJO°G and to rende stable th .reagents and thus prevent a commencement of the vuteanization reaction, up to temperatures of between 35 *C and 40°C inclusive; , , - the bondin of the said sheet of adhesive material to the inner ^ · · ·· sur ace of the trea through a rolling operation and the simultaneous perforation of the said sheet in order to expel the air trapped between the tread and the sheet of adhesive material* via the perforations made in the aaid sheet of adhesive material*1 Further characteristics and advantages of the process forming the subject of the invention will become more apparent from the following description of a preferred form of embodiment referred to tbe accompanying drawings in which: - Fig* 1 shows in block diagram form the operational phases in the process; - Fig* 2 shows in a schematic view how the assembly constituted by the premoulded tread and the sheet f adhesive material is achieved; - Fig*) 3 shews in a schematic cutaway view the assembly constituted by the tread> the sheet of adhesive material* the carcase of the tyre and the protective casing mounted on a supporting rim; - Fig.I 4 shows schematically the assembly of Fig.i 3 placed in a vulcanizing oven** A phase which is not within the scope of the process according to the invention^ consists in producing the tread 1 i accordance vith known techniques, preferably giving it a particular profile* see Fig.i 3 and, to be more precise* providing it with an inne surface la destined* as will be seen below* to match the rollin surface of the carcass 2 o the tyre* suitably arcuate and having a bending radius such that it be possible to bond the single assembly constituted by the tread and the sheet of adhesive material perfectly to the pre-reated rolling surface of the carca s 2 of the tyre* The preparation of the rolling surface of the carcass 2 of the tyre involves rasping operations whereby all reaidual parts of the tread to be reconditioned are removed from the carcass. The rasping operation is tyre and once the said operations have been concluded* the rolling surface 2a is arcuate* virtually as shown in Fig»i 3 with a bendin , . ·% radius l»i The said bending radius R has to be borne in mind when preparing the tread 1 in order that the inne surface la of the latter be arcuate with a bending radius identical to the radius R* so that the sur aces la of the tread 1 and 2a of the carcass ore on the same planes and that they match each other*' Ibis preferred operating phase makes it possible to solve a considerable problem which is experienced when preparing the tread and the carcass o the tyre on the basis of certain techniques known today* whereby the tread is provided with a perfectly lat inner surface and the adhesive material is built up in the areas close to the sidewal s of the carcass of the tyre* the purpose of this being to bring the rolling surace into the right condition to receive the tread.' As previously stated* the proceed according to the invention envisages the preparation of a sheet of adhesive material 3 to be applied to the tread at the time when it is built up, so that the single assembly constituted b the tread and the sheet of adhesive material can subsequently be made and stored without the risk of any kind of reaction occurring*) These characteristics are obtained* with the process according to the Invention, by dosing reagents to permit the sheet of adhesive material to be produced so as to have a high percentage of covulcanisslng resins and by having* furthermore* a suitable percentage off.) an anti scorching agent which is given the task of preventing the previously mentioned undeslred reactions from taking place.'< The reagents with which it is possible to produce the sheet of adhesive material can vary bot qualitatively and quantitatively depending upon the composition of the tread*) ' By way of an example) the composition in weight is shown below of the reagents with which it is possible to produce a standard sheet of adhesive material suitable for most of the tyres currently on the marked: COMPONENTS Natural rubber or polyisoprene Zinc oxide Stearic acid Anti-oxidant (Poly 2-3-4 trimethyl dihydroquinaldine) Anti-ozonant (in-phenyl - M - cyclohexyl para phenylendiamine) Pine tar Covulcanizing resins (Polyhalethyl phenol) Adhesive agents (liquid coumarone/indene resin) Buna weld (polymer 780) Insoluble sulphur Accelerators (diphenyl guanadin and merea to benzothiazole) High structure carbon black Anti-schorching agent (Santocard PVI) The high percentage of covilcanizing resins used makes it possible to obtain a stabilized product which retains its adhesive properties indefinitely* The addition of a suitable percentage of an agent for the prevention of scorching prevents there being any danger of undesired prevulcanization reactions and makes it possible for the sheet of adhesive material 3 to be applied to the tread 1 while yet maintaining unchanged the properties of the assembly of tread and sheet of adhesive material during a long time* The sheet 3 produced in accordance with the formula given above and subjected to "Monsanto" rheometric tests* using a sample vulcanized at 100°C, gave the following physical characteristics as a function of time: 2h 3h 4h Modulus at 300% 63 64 85 Tensile strees 238 237 235 Ultimate elongation 640 610 560 Shore Test A 46 49 53 The operational phases for producing the sheet of adhesive material comprise: - precomminuting and mixing of the mixture of the rubber by the combined action of mechanical and temperature treatment and the use of peptization means until a degree of viscosity is obtained such that in the subsequent mixing phase with reinforcing* charging and vulcanising substances* these can be suitably broken up in the mixture; - first non operative phase for a period of approximately 12 hours; - dosing and mixing of the components that make up the mixture (excluding the vulcanizing agents and the accelerators) in open mixers at low temperature; - second non operative phase for approximately 12 hours in order to allow the perfect diffusion of the reagents and the inert bodies that make up the mixture; - mixing in the mixture of the accelerators and of the vulcanizing agents in an open mixer at low temperature (30 - 40C)i - calendering into sheets of a small thickness; - cutting of the sheets to a size corresponding to the dimensions of the tread on which they will be applied* Once the sheet 3 has been prepared in accordance with the method described above, it is applied to the smoothed surface la of the premoulded tread 1, over the contact surface of which is spread a special rubber base bonding solution.

With the process according to the invention* the application of the sheet of adhesive material to the tread envisages the tread 1 and the sheet 3 being passed not only through normal drive and pressure rollers 17 but also through two rollers 4 and 5» the latter having over its full rolling surface a series of sharp tips 6 dimensioned in such a way as to perforate the sheet 3 until the surface la of the tread 1 is reached and* subsequently} inside a vacuum chamber 7» to cause both the expulsion of the air trapped between the tread 1 and the sheet of adhesive material* via the perforations made in the sheet 3 and the air to be purged from the said perforations*' j. Prior to the assembly constituted by the tread and the sheet of adhesive material leaving the chamber 7» the free surface of the sheet 3 has a protective film 3a of polythene or some other synthetic material applied to it in order to prevent air from entering the perforations made in the sheet 3 and to preserve the chemical-physical characteristics of the said sheet against extraneous factors and against dust·* At the reconditioning of a tyre* the assembly constituted by the tread and the sheet of adhesive material is thus pre-prepared ready to be applied to the rolling surface of the previously rasped* smoothed and solution treated carcass of the tyre* The said application is performed in accordance with known techniques and without there being any danger of the tread or the sheet of adhesive material becoming dislocated with respect to the carcass o the tyre* this mainly being due to the fact that the sheet 3 alread forms one single body with the tread 1* Upon completion of this phase* the tyre, as also already envisaged with known techniques, is mounted on a special rim 10 once a protective .<· casing 8 has been placed around the tyre in such a way as to enshroud the tread 1 and the sidewalls 9 of the tyre* with its edges kept tightly pressed up against the said sidewalls by the said rim 10.i The protective casing 8 is provided with a vent 11 which allows the air trapped inside the said casing at the time it is being fitted on to the tyre to be discharged.

When this phase has been completed, the tyre is then placed inside a vulcanizing oven 12.

With the process according to the invention, pior to the actual vulcanization phase being commenced, the protective casing 8 is connected up to a vacuum apparatus 14 via a pipe 13 in such a way as to fully purge from the inside of the said casing, air, even that normally trapped in the interstices of the tread 1; then, using a pipe 15, air is passed inside the carcass of the tyre or into an inner tube 16 in the said tyre, until a pressure is built up which roughly corresponds to the normal working pressure of the tyre.

After this, the oven 12 is set in operation to enable the vulcanizing to be carried out (th optimum temperature being 100°C) with a suitable heating fluid (preferably hot air or steam), the oven being pressurised at a pressure slightly below that of the tyre until the necessary conditions are reached which give rise to the vulcanization reaction, resulting in a perfect union between the tread and the carcass of the tyre, with the physical-chemical characteristics of the vulcanized material being fully retained.

The presence of the anti-scorching agent between the reagents of the sheet of adhesive material advantageously enables an initial retard to be achieved in the vulcanization reaction, in such a way as to allow the operator to intervene, even after the operation of the oven, particularly beuntl to the lacin "Monsanto" rheometric tests carried out at 1Q0*C show that unlike the sheets of adhesive material Inovn today* the sheet produced in accordance with the process in question stays perfectly stabilized at various temperatures up to 35°C - 40°C, delaying the commencement of the vulcanization reaction by approximately 20 - 30 minutes* The invention is obviously liable to undergo numerous modifications and variants* for example* the reagents stated can be replaced with others of an equivalent chemical standard, without this in any way deviating from the framework of the present invention* or from the protection afforded to the following claims.'

Claims

1. WHAT ISCLAIMED IS: 1· An improved process for reconditioning a worn tyre through the direct application to the carcass of the tyre of a premoulded tread, comprising the realization of the said tread preferably with its arcuate surface destined to be bonded to the rolling surface of the carcass of the tyre having a bending radius equal to that of the said rolling surface, as well as, after the application of the tread to the carcass of the tyre, the enshrouding of the reconstructed tyre with a protective casing which is wrapped around the tread and the side alls of the tyre in an air tight fashion, prior to the insertion of the tyre in a vulcanization oven, essential features of the process in question being that it comprises the following phases: the preparation of a sheet of adhesive material with which to affix the tread to the carcass of the tyre with the use of reagents comprising, in addition to at least one non vulcanized bonding material, at least one vulcanization accelerator and at least one vulcanizing agent, a high percentage by weight of covulcanizing resins, plus an agent for the prevention of scorching, able to vulcanize the said non vulcanized bonding material at a temperature of around 100°C and to render stable the reagents and thus prevent a commencement of the vulcanization reaction, up to temperatures of between 35°C and 40°C inclusive; the bonding of the said sheet of adhesive material to the inner surface of the tread through a roiling operation aid the simultaneous perforation of the said sheet in order to expel the air trapped between the tread and the sheet of adhesive material, via the perforations made in the said sheet of adhesive material* 2. An improved process according to Claim 1 , wherein upon completion , of the phase in which the sheet of adhesive material is affixed to the inner surface of the tread* the free surface of the said sheet has a protective film applied to it immediately after the purging of air from be ween the tread and the sheet of adhesive material* 3 , An improved process according to Cl ims 1 and 2 , wherein once the pjjaae is over in which the reconstructed tyre is enshrouded with a protective casing and the assembly is placed in a vulcanizing oven, the said protective casing is connected up to a vacuum apparatus in order to create a vacuum in the inside of the said protective casing*1 4* An improved process for reconstructing a worn tyre through the direct application to the carcass of the tyre of a premoulded tread} according to the preceding claims » substantially as described and illustrated for the purposes specified* 5. A process for reconditioning worn tyres substantially as hereinbefore described. 6. Reconditioned tyres whenever having undergone a treatment according to any of Claims 1-4. COHEN ZEDEK & SPISBACH P.p¾ BOX 33116, TEL AvlV.j ATTORNEYS FOR APPLICANT.