IE45099B1 - Method for treading tyres - Google Patents

Abstract

A method of applying a pre-vulcanised tread band to a tyre carcass comprises placing the tread band in an annular mould, the dimensions of the mould and tread band being chosen such that the radius of curvature of the inner face of the tread band is greater than that of the outer periphery of the tyre carcass and bonding the carcass to the tread band. When the assembly of tread band and carcass is inflated on a wheel the ground engaging surface of the assembly is compressed longitudinally.

Description

This invention relates to applying a tread band,to a. tyre carcass, for example a pneumatic tyre, either for . retreading.used, tyres or for applying the treads of new tyres.

It is known to make or retread a tyre assembly by 5 preparing- a tread band In a. mould to give the desired tread' , pattern and then to apply the tread band onto a prepared (e.g* buffed and trued) tyre carcass. The tread band may be vulcanised before being applied to the carcass. A bonding material, such as unvulcanised rubber, may be interposed - 10 between the carcass and the tread band before the tread band is placed on the carcass, and pressure and/or heat may be applied to set ths bonding material and unite the tread band -. with the tyre carcass. The pressure may be applied in various ways; for example, an air bag may be placed within the tyre . . ' carcass and may be inflated to press the carcass outwardly against the tread band while the latter is held in a mould.

It has recently been found that improved wearing performance in a tyre can be obtained by compressing a pre? vulcanised tread band onto a tyre carcass and bonding the 20 tread band to the carcass while the tread band remains under compression, resulting'in a compressive stress being ι retained in the road engaging surface of the finished assembly of tread band and tyre carcass. This method of treading tyres is disclosed in British Patent Specification , No. 1460297.

By means of the present invention, it is also possible to produce a tyre assembly comprising a tread band bonded ' to a tyre carcass so that the wearing surface of the assembly has maintained therein a compressive stress, but instead of - 2 compressing the tread band onto an uncompressed tyre carcass, the carcass is distorted from its normal shape and is placed in contact with the tread band in the mould. The tread band is then bonded to the tyre carcass in the usual way.

C The term ’’tyre carcass is used herein to wear the assemblage of the tyre components other than the tread band.

According to the invention, there is provided a method of applying a tread band to a tyre carcass comprising the steps of: (a) placing a pre-vulcanised tread band in an ίΟ annular mould having a diameter such that the circumferential radius of curvature of the inner face of the tread band, when said band is located in the mould, is greater than that of the outer periphery of the tyre carcass when said carcass is in its related, unstressed condition, (d) locating the tyre carcass ; s within the mould so that the tread band overlies the outer periphery cf the carcass, (c) simultaneously displacing the median portions of the sidewalls of the carcass towards each other and forcing the outer periphery of the carcass radially outwardly and into contact with the tread band, and (d) bondband ing the tread/to the tyre carcass, wherein the above steps are such that, when the assembly of tread band and carcass has been removed from the mould and inflated on a wheel, the median portions of the sidewsils will have moved away from each other and the ground engaging surface of the assembly radially inwardly so as tr to compress the said surface circumferentially, and preferably transversely as well.

The tyre carcass can generally be any tyre carcass, except of course for such carcasses as may be of unalterable length, e.g., those which incorporate inextensible breaker strips or circumferential reinforcement.

Preferably, the tyre carcass is a cross-ply carcass whose circumferential length can readily be varied through - .3 /1¾0 9° relative movement of the tyre carcass beads and sidewalls.

The longitudinal compression of the ground engaging surface of the assembly is preferably such that the outer periphery of the tread band is shortened by at least 0.25% and preferably g by 0.5% bo 10$, more preferably by 1$ to 6$.

The tread band may be formed of any conventional .material used for malting tyres, such as natural or synthetic rubber (including plastics material such as polyurethane).

The tread band is preferably preferred as an annular band whose outer periphery exactly matches that of the inner annular surface of the mould, so that when the band is positioned in the mould it is in an unstressed condition. It is, of course, also possible to compress circumferentially the tread band, in accordance with the method of British Patent Specific-. ΐς ation No. 1400297, in which case the method of the present invention imposes an additional compressive stress on the tread band. In one preferred embodiment, the annular tread hand is coated on its inner surface with a solution of bonding agent (for example uncured rubber) and a layer of cushion rubber is applied to the carcass, an appropriate bonding agent being used to bond the cushion rubber to the carcass; pressure is then applied to force the carcass against the tread band.

A form of fluid pressure may be used to press the tread band and the carcass together after they have been brought into contact as described above; for example the tread band may be surrounded by an air bag and the carcass may contain a further air bag, each air bag reacting on a rigid frame,, so that the pressure applied to the assembly may be controlled by controlling the degree of inflation of the air bags. - 4 A single curved strip may be used, either in the form of an endless ring or with two ends which are brought together to complete the tread band; a number of separate strips may be located end to end in the mould so that together they form a complete tread. The bonding process can then be carried out as described above.

A preferred embodiment of the invention is now described with reference to the accompanying schematic drawings, wherein Figure 1 is a section of a mould with a pre-vulcanised 19 tread band in position, showing part of an unstressed tyre carcass prior to being forced into contact with the tread band Figure 2. is a section of the tyre made by the assembly of the tyre carcass and tread band of Figure 1 showing, in chain lines, the configuration of the assembly when the carcass ' is being forced into contact v/ith the tread band, and, in full lines, the configuration -A. the assembly after inflation as described belov'.

Referring tc figure 1 of the drawings, a pre-vulcanised tread band 1, whose inner periphery has been suitably prepared 2G fo·· bonding to a tyre carcass, is placed into an annular mould so that it is a snug fit but is not under any compression.

The tread band 1 is thereby in a condition of neutral stress.

A cross-ply tyre carcass 3 is then located inside the mould, this step being aided by moving apart the tyre beads 4 so as 2? to contract slightly the outer periphery 7 of the carcass 3· The beads are then relaxed and the tyre carcass 3 resumes its normal, unstressed condition. The dimensions of the mould 2 εν? chosen such that, when the carcass 3 is in its unstressed condition, there Ϊ3 a small gap 5 between the outer, buffed, surface 7 of the carcass 3 4 Q 9 ® and the inner periphery of the tread band 1, The inner periphery of the tread band 1 or the buffed surface of the carcass 3 having'been coated with a layer of bonding material} the sidewalls 6 of the carcass 3 are then displaced laterally inwardly while the outer, buffed surface 7 of the carcass is forced into contact with the inner periphery of the tread band 1. This is achieved by applying pressure to’ the carcass 3, by means of, for example, an air bag {not shown) inflated within the carcass 3, so as to maintain the carcass 3 in contact with the tread band 1.

Heat is then applied to the carcass 3 and tread band 1 by placing the entire mould in an oven or by using a mould having internal heating elements or by injecting hot liquid or gas into the air bag. The heat serves to cure the bonding material) whioh is preferably un-vulcanised rubber and, after completion of the care, the pressure on the bonding surface is relaxed by removal of the pressure bag. Throughout the curing process, the sidewalls 6 of the carcass 3 are maintained in their laterally inwardly displaced condition so that, when the final assembly of carcass 3 and bonded tread band 1 is removed from the mould 2, the sidewalls 6 remain in this displaced condition.

Referring now to Figure 2, the configuration which the tyre takes up when the sidewalls 6 are laterally displaced, as described above, is shown in chain lines, ihe configuration of the tyre when the sidewalls 6 assume their final state of inflation is shown in full lines. - 6 As mentioned above, when, 'the final assembly is removed from bhe mould 2, the configuration of the carcass 3 corresponds to that shown in chain line in Figure 2 of the drawings. In order to introduce the desired compressive stress into the ground engaging surface of the final assembly the eompleted tyre Is mounted on a road rim and then inflated This causes the carcass 3 to resume its unstressed configuration as shown in. continuous lines in Figure 2 of the drawings •which in turn causes the tread area of the tyre to move radially inwardly and thereby to compress the tread area both circumferentially and transversely.

In a typical example of the method of the invention, ths carcass 3 is buffed so that its outer diameter is about 1“ less than the diameter cf the inner surface of the tread band 1 when the letter is in position in the mould 2* She carcass 3 is then bonded to the tread band 1 ia accordance with ths method of the invention and, after removal of the final assembly from the mould 2 and after inflating the assembly cn & read rim, the tread area of the assembly has a retained compression equivalent to a reduction in diameter of about I'-'. £kie as equal to a circumferential shortening cf-ίγ' x the reduction in diameter, i.e. about 3.142. In an average truck size tyre, this shortening represents a compression cf about 2.4% of the original circumferential length of the tread band.

Claims (11)

1. CLAIMSί1. A method of applying a tread band to a tyre carcasscomprising the steps of (a) placing a pre-vulcanised tread band in an annular 5 mould having a diameter such that the circumferential radius of curvature of the inner face of the tread band when said band is located in the mould is greater than that of the outer periphery of the tyre carcass when said carcass is in its relaxed, unstressed condition, 10 (b) locating the tyre carcass within the mould so that the tread band overlies the outer periphery of the carcass, (c) simultaneously displacing the median portions of the sidewalls of the c'arcass toward each other and forcing the outer periphery of the carcass radially outwardly and into 15 contact with the tread band, and (d) bonding the tread band to the tyre carcass, wherein the above steps are such that, when the assembly of tread band and carcass has been removed from the mould and inflated on a wheel, the median portions of the sidewalls will have 20 moved away from each other and the ground engaging surface of the assembly radially inwardly so as to compress said surface circumferentially.

2. A method according to claim 1 wherein th© ground engaging surface is also compressed transversely while being 25 compressed circumferentially.

3. · A method according to claim 1 or 2 wherein the tyre carcass is a cross-ply carcass.

4. A method according to any one of claims 1 to 3 wherein the circumferential compression of the ground engaging 30 surface is such that the outer periphery of the tread band is - 8 shortened by at least 0.259°.

5. A method according to claim 4 wherein the shortening is 0.5>° to 10j°.

6. A method according to any one of claims 1 to 5 wherein 5 'che tread hand is an annular band whose outer periphery matches that of the inner annular surface of the mould so that when the band is positioned in the mould it io in an unstressed condition.

7. A method according to any one of claims 1 to 5 wherein 0 the tread band is placed in the annular mould with its ground engaging surface under compression*

8. A method according to any one of claims 1 to 7 wherein fluid pressure is used to apply the carcass to the tread BSiUU * 5

9 C - A method eocording to claim-8 wherein an air bag is located within the carcass and is inflated so as to force the carcass into contact with the tread band,

10. A method of applying a tread band to a tyre carcass, substantially as hereinbefore described with reference to the 0 (accompanying tend ngs.

11. * A tyro whenever made by a method according to any one of claims 1 to 10.