CA1060614A

CA1060614A - Method for treading tyres

Info

Publication number: CA1060614A
Application number: CA208,176A
Authority: CA
Inventors: Peter J. Kent; John E. Phillips; Jan H. Farquharson Kent
Original assignee: Kentredder Ltd
Current assignee: Kentredder Ltd
Priority date: 1973-09-07
Filing date: 1974-08-30
Publication date: 1979-08-21
Also published as: DE2442401A1; SE416185B; AT340789B; CH595209A5; AR202660A1; DE2442401C3; JPS5072977A; NL164800B; NL164800C; FR2243073A1; ATA717174A; MY7800031A; SU648068A3; BR7407453D0; DK467774A; OA04774A; FR2243073B1; IT1019212B; JPS5423956B2; GB1460297A

Abstract

ABSTRACT OF THE DISCLOSURE

A method of treading or re-treading tyres involves compression of the wearing surface of the tread. A tread strip, which may be an annular band, is compressed in a direction paral-lel to its longitudinal axis and is bonded to a tyre carcass, while being maintained under compression. This may be done by compressing a tread band into an undersized mould by using a mould in which a series of transversely extending rods spaced around the periphery of the mould bold the tread strip away from the mould. Removal of the rod allows the band to fit snugly against the mould. Alternatively, the tread strip may be of finite length, for example to form a lug, in which case the strip is formed with a radius of curvature less that of the surface to which it is to be applied, so that the convex (wearing) surface of the strip is compressed upon application to the carcass.

Description

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This invention relates to applying a tread to a tyre, for example a pneumatic tyre, either for retreading used tyres or for applying the treads of new tyres.
The terms tread and tyre are used generically herein to mean the wearing surface and the body or carcass of a natural or synthetic rubber tyre assembly, respectively.
It is known to make or retread a tyre assembly by 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 unvulcanized rubber, may be interposed between the carcass and the tread band, and pressure and/or heat may be applied to set the 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 with the tyre carcass and may be inflated to press the carcass outwardly against the tread ~and while the latter is held in a mould. It is also known ~20~ to sandwich the tyre carcass and tread band assembly between two air bags in a relatively large mould and then inflate -these bags to press the tread band and tyre carcass against each other (this method is particularly applicable to radial ply tyres). British Patent specifications 1379253 and 1389421 both in the name of Kentredder Ltd. and sealed on April 30, 1975 and July 30, 1975 respectively, describe such prior methods.

-According to the present invention there is provided amethod of applying a tread to a tyre carcass by compressing at least the wearing surface of a precured tread in strip form in a direction parallel to the longitudinal axis of the strip and bonding the tread to a carcass whilst maintaining the compres-sion of the tread whereby the wearing surface of the final assembly remains under compression.
The compression is preferably such that the periphery of the wearing surface is shortened by at least 0.5~, and prefer-ably by 1~ to 10%, more preferably by l~ to 6~.
The tread band may be formed of any conventional materialused for making t~res, such as natural or synethetic rubber ;~ (including plastics material such as polyurethane~ When it is of rubber, it is desirable that it should be vulcanized before ~-being applied to the carcass, as this provides the optimum im-provements in the wearing properties of the products of the present invention.
The tread strip may for example be prepared as an annular band made in a mould whose radius is such that the annular band is slightly too big for the carcass. In accordance with the present invention, the annular band is then compressed and is bonded onto the carcass while being maintained in its compress-ed state. In one preferred embodiment, the annular band is coated on its inner surface with a solution of bonding agent , (for example an uncured rubber) and a thin layer of cushion rub~er is interposed between it and the carcass to which has been applied an appropriate bonding agent; pressure is then ap-plied to force the annular band against the carcass while reducing the radius of the annular band, resulting in compres-sion of the tread band.

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~0~ 614 A form of fluid pressure may be used to appl~ the tread band to the carcass; for example the assembled tread and carcass may be surrounded by an inflatable vessel (such as an air bag) itself surrounded by a rigid frame, so that the pressure applied to the assembly may be controlled by controlling the degree of inflation. Alternatively, a clip of the "Jubilee" type may be used to compress the tread band onto the carcass.
It is also possible for the tread band, along with the cushion rubber strip if desired, to be bonded (while under compression~ to an inextensible breaker strip so that the tread is maintained in compression; the combined tread/breaker ~-strip is then applied to the carcass.
In another preferred method, where a preformed annular tread band is used, it may be formed in the usual manner in a mould, and it may then be compressed into another mould having a smaller diameter than the first mould, being held in the other mould while the carcass is applied to it and while bonding is effected. This method is for example particularly suitable for retreading radial ply or bias-belted tyres, as it does not require extension of the tyre carcass, which extension is difficult or impossible to effect with such tyres. Again, it is possible to use an adjustable mould whose radius may be decreased, for example by mechanical means.
In an alternative method, a strip of tread band material may be used instead of a preformed annular band.
The strip is moulded as a curved strip having a radius of curvature less than that of the carcass. As a result, when the strip is fitted onto the carcass, its outer or ~4~

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wearing surface is compressed relative to the inner or bonding surface. In this case, it is desirable to form the strip so that it includes an inextensible reinforcing strip along or near its inner surface so that, when the strip is fitted onto the carcass, the bonding surface of the strip is not under tension.
This method may also be used when a tyre, e.g. an agricultural tyre is treaded with lugs. In this case, a lug to be applied to a particular part of a tyre carcass surface is formed with a radius o~ curvature less than that of the surface to which it is to be applied. Again, it is desirable to incorporate a reinforcing strip adjacent the bonding surface of the lug.
When an annular tread band is to be fitted to a tyre carcass in accordance with the present invention, the tread band can be inserted into an annular mould of smaller radius ~ -(as mentioned above) and the tyre carcass is then inserted within the tread band. ~his can be done by spreading apart the beads of the tyre carcass so that its circumference is reduc-ed. However, it has been found in practice, especially with rad-ial tyres, that the spreading apart of the beads has a tendency to cause the formation of a single large inward fold or crinkle in the carcass, and this is difficult to remove once the tyre is in the mould and it may lead to a defective final product if allowed to persist throughout the curing operation.
A similar problem can occur, although to a lesser extent, when the tread band is compressed into the mould of smaller diameter; in this case, if an inward crinkle or fold occurs, then it is difficult to achieve an even compression.

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10ti06~4 The present invention provides an apparatus which avoids this tendency to ~orm an inward deformation and which can be adapted to give even compression of a tread band in a mould.
According also to the present invention there is provided apparatus comprising a tyre mould having an inner annular surface for holding a tread band, in which means are provided at spaced intervals around the circumference of the mould for preventing a tyre carcass or a tread band inserted into the mould from touching the said inner surface at the places where such means are located, the said means being removable after the tyre carcass or tread band has been placed in the mould so that the tyre carcass or tread band can then accurately bear against the whole of the inner annular surface of the mould.
The said means may comprise a series of pairs (for exam-ple, six pairs) of holes at equal intervals through the side walls of the mould and corresponding rods slidable through each pair of holes so that the rods are spaced from the inner annular surface of the mould. With the rods in place in the corresponding pairs of holes, the tread band is placed in the mould and is induced to form small inward crinkels ~for example, six) rather than a single large crinkle; the rods are then withdrawn and the small crinkles are readily accommodated by even compression of the tread band.
More important, after the tread band has thus ~een placed in the mould, the rods may again be inserted through the corresponding pairs of holes and the tyre carcass may then be introduced into the mould where it also forms a corresponding number (for example six) of small inward crinkles, which, after withdrawal of the rods, are readily accommodated. By this, a complete contact of the ~onding surfaces of the tread band and the tyre carcass may be achieved.

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In the method of the invention (whether or n~t the special apparatus just described is used), the bonding of a tyre tread to a wheel or carcass may be effected with the application of heat. The pressure assembly, including the tread and the carcass, may be placed in a heated chamber.
If a metal mould is being used, heat may be applied directly to it so as to be conducted to the bonding surface.
Generally in the present invention, the periphery of the tread band is reduced by at least 0.5~, preferably 1 - 10~, by the compression applied to it in accordance with the invention.
The important thing in the present invention is for the wearing surface~of the tread band to be under compression.
This is usually most easily achieved by placing the whole thickness of the tread band under compression, but this is not essential, especially if the tread band is of substantial thickness. It is the wearing surface ~the surface which meets the road surface) which must be under the specified compression.
The invention will now be described with reference to the accompanying schematic drawings, in which Figuxe 1 is a section of a mould with a compressed, pre-vulcanised tread band in position, :
Figure 2 is a section of a mould with a tread band and a breaker strip in place ready to receive a tyre carcass: -Figure 3 is a section of a conventional mould -containing a tread band and a radial-ply tyre, Figure 4 i9 a cross-section of a mould provided with means for facilitating the insertion of a radial ply tyre, .
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Figures S and 6 are sections of the mould of Figure 4 showing a radial-ply tyre being inserted, Figure 7 is a part cross~section of a tyre carcass suitable for a tyre of an agricultural vehicle, Figure 8 is a cross-section of a lug for application to the carcass of Figure 7, and Figure 9 is an ele~ation o~ a tyre having tread applied in segments. - -Referring to Figure 1, a tyre carcass which is to be treaded is buffed down to the correct size for a plain ring mould 1. A pre~vulcanised tread band 2 is then prepared whose periphery is about 2~ longer than the periphery of the mould 1.
The pre-vulcanised tread band 2 is then placed in the mould as seen in Figure 1 so that it is in e~en compression throughout.
The oversize tread band 2 may be more easily compressed into the mould 1 if a silicone rubber lubricant is spread around the surface of the mould 1.
In the remainder of the procedure (not illustrated) a layer of bonding material, with or without cement, is applied to the buffed surface of the carcass or to the inside of the tread band 2 (preferably the former) and the beads of the tyre are - -spread apart in order to reduce its diameter and allow its -insertion into the mould inside the tread band 2. On release of the beads, the prepared bonding surfaces are brought into contact and heat and pressure are applied to secure the bond. This method is applicable to cross ply, radial or bias-belted tyres. ~ -: .
A very similar method may be employed when it is desired to incorporate a breaker strip. Referring to Figure 2, the tread band 2 is similarly compressed into a mould 1, and then an in-extensible breaker strip 3 is bonded to the tread band. The breaker strip 3 will ensure that the tread band 2 will be '~
~8 10~i0~i14 maintained ~nder compression. A layer of bonding material 4 is then applied to the breaker strip 3, and a tyre carcass is then inserted into the mould 1. In this case, the buffed tyre carcass has the same diameter as the breaker strip 3.
If this method used with a cross-ply tyre, the tyre is converted into a bias-belted tyre.
In the methods of both Figuxes 1 and 2, pressure may for example be applied to assist bonding by means of an air-bag inflated within the tyre carcass in the mould, and heat may be applied by placing the entire mould in an oven or by using a mould having internal heating elements.
When superimposing the prepared tyre on to the compressed tread band, there may be a risk of trapping air between the two. This can be guarded against by providing blow holes through the thinner parts of the vulcanised tread through -which air can escape.
Referring to ~igure 4, an annular mould 21 is channel-shaped to recei~e a tread band 22. The side walls of the mould project beyond the tread band 22 and include a series of pairs of holes 7, 7' spaced around the circumference. A ~ -rod 8 is received in each pair of holes 7, 7' and extends through the mould at a spaced distance from the inner (tread-receiving) wall of the mould.
Referring to Figure 3, the mould 21 carrying a tread band 22, but nct having the rods 8 in place, has received a radial-ply tyre carcass 5. A large inward crinkle 6 has formed in the tyre carcass 5; this crink~e is very difficult to remove, and will cause an area of weakness in the f;nished tyre.
Referring to ~igures 5 and 6, a generally similar mould ;
21 carries a tread band 22 but with six rods 8 in place!The ~' :

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iOf~)614 tyre carcass 5, which has been placed in the mould 21 with the rods 8 in place, has been induced to form six small --crinkles 9 instead of a single large crinkle. When the rods 8 are removed (Figure 6) the small crinkles are easily accommodated in the mould and disappear, and a good seal of tread band 22 to carcass 5 is now possible.
Referring now to Figure 7, there is shown a section of a tyre carcass 10 suitable for an agricultural vehicle. The radius of curvature of the outer surface of this section of carcass is r. Figure 8 shown a lug 12 to be fitted to this section of tyre. The lug comprises a pre-vulcanised rubber strip having a radius of curvature rl, where rl is less than r.
The wearing surface of the lug is indicated at 11 and adjacent the other surface 13 there is provided reinforcement 14 le.g. -a wire mesh) in the rubber which makes the lug inextensible at that point.
The lug 12 is fitted over the tyre section 10 and as its radius of curvature is increased, the wearing surface of the lug is brought under compression.
Figure 9 shows a tyre carcass 5 being treaded in a seg-mental fashion, for example as described in British Patent spec-ification 1471535 in the name of Kentredder sealed on April 29, 1977~ A number of strips, for example four, are prepared for ., .
; appllcation to the crown of the carcass so that together they form a complete tread which may, for certain purposes have a smooth wearing surface. A strip 23 (Figure 9) is moulded with : :
a radius of cuxvature less than that of the tyre so that the strip, strip 24 in the Figure, has a compressed wearing surface. ~ -It has subsequently been found that by means of the pre-sent invention the life of a tyre is made much greater than , .

if the treading were carried out in the convention~.l way.
Thus, pneumatic tyres retreaded in accordance with the present invention have given much longer services than tyres similarly retreaded without compression of the tread surface and have even given longer service than new tyres made in the conventional way.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of applying a tread to a tyre carcass by compressing at least the wearing surface of a precured tread in strip form in a direction parallel to the longitudinal axis of the strip and bonding the tread to a carcass whilst maintaining the compression of the tread whereby the wearing surface of the final assembly remains under compression.

2. The method of claim 1 in which the compression is such that the wearing surface of the tread is shortened before the bonding step by at least 0.5%.

3. The method of claim 2 in which the wearing surface is shortened by from 1% to 10%.

4. The method of claim 3 in which the surface is shortened by 1% to 6%.

5. The method of claim 1 in which the precured tread strip is in the form of an annular band.

6. The method of claim 5 including the additional steps of coating the inner surface of the annular band and the outer surface of the carcass with a bonding material, interposing a layer of cushion rubber between the annular band and the carcass, and applying pressure to the wearing surface of the tread to force the annular band against the carcass while reducing the radius of the annular band resulting in compression of the tread band.

7. The method of claim 6 in which the compression is such that the wearing surface of the tread is shortened before the bonding step by from 1% to 10%.

8. The method of claim 7 in which the surface is shor-tened by from 1% to 6%.

9. The method of claim 5 comprising coating the inner surface of the annular band with a bonding material and bonding the annular band, while under compression, to an inextensible breaker strip, the combined tread and breaker strip then being bonded to the carcass.

10. The method of claim 9 in which the compression is such that the wearing surface of the tread is shortened before the bonding step by from 1% to 10%.

11. The method of claim 5, 8 or 9, in which the annular band is formed in a mould of a certain diameter and is then com-pressed into another mould of a smaller diameter than the first mould, said annular band being held in the other mould while said bonding of the tread to the carcass is effected.

12. The method of claim 1, 6 or 9, in which the tread strip is vulcanised prior to placement on the carcass.

13. A method of applying a tread to a tyre carcass comprising the steps of providing a preformed tread including an outer wearing surface and an inner concave surface, said pre-formed tread being in the form of a curved strip having a radius of curvature less than the like radius of curvature of the carcass surface to which the preformed tread is to be applied, reshaping the curvature of the preformed tread to increase the radius of curvature of said inner surface and thereby shortening the outer wearing surface in the direction of curvature with there being a compressive stress introduced in the outer wearing surface and then bonding the inner concave surface of the reshaped prevulcan-ised tread to the carcass while maintaining the compressive stress in the outer wearing surface with the compressive stress remaining in the tread after it is bonded to the carcass so that the wearing surface of the final assembly remains under compressive stress.

14. The method of claim 13 in which the compression is such that the wearing surface of the tread is shortened before the bonding step by from 1% to 10%.

15. The method of claim 14 in which the preformed tread is formed so as to include an inextensible reinforcing strip along or adjacent its concave surface so that, when the preformed tread is fitted on to the carcass, the bonding surface of the pre-formed tread is not under tension.

16. The method of claim 14 in which the curvature of said preformed tread is in a direction parallel to the circumfer-ence of the carcass.

17. The method of claim 16 in which a plurality of preformed treads are applied around the tyre carcass circumfer-entially adjacent one to another to form a complete tread.

18. The method of claim 14 in which the curvature of said preformed tread is in a direction transverse to the mid-circumferential axis of the carcass.

19. The method of claim 17 in which each preformed tread has a smooth wearing surface.

20. The method of claim 13, 15 or 17, including the step of vulcanising the tread prior to reshaping the curvature thereof.

21. The method of claim 1 wherein the tread is applied to a tyre carcass in a tyre mould having an inner annular surface for holding the tread, prior to the insertion of the carcass into the mould providing at spaced intervals around the circumfer-ence of the mould means preventing the carcass inserted into the mould from touching the inner annular surface of the tread at the places where such means are located, inserting the carcass in the mould, and then removing the means so that the carcass can accurately bear against the whole of the inner annular surface of the tread.

22. The method of claim 21 wherein providing of the means includes forming a series of pairs of holes at spaced in-tervals through the side walls of the mould and sliding a rod through each pair of holes with the rods being spaced from the inner annular surface of the mould.

23. The method of claim 1 or claim 13, wherein the tread in its compressed state has a predetermined inner diameter, and the carcass is prepared to have an outer diameter of the correct size for the tread.

24. Apparatus for use in carrying out the method of claim 1 comprising a tyre mould having an inner annular surface for holding a tread band, in which means are provided at spaced intervals around the circumference of the mould for preventing d tyre carcass or a tread band inserted into the mould from touching the said inner surface at the places where such means are located, the said means being removable after the tyre carcass or tread band has been placed in the mould so that the tyre carcass or tread band can then accurately bear against the whole of the inner annular surface of the mould.

25. Apparatus as claimed in claim 24 in which the said means comprise a series of pairs of holes at spaced intervals through the side walls of the mould and corresponding rods slid-able through each pair of holes so that the rods are spaced from the inner annular surface of the mould.