IE41951B1 - Radial tyres - Google Patents

Abstract

1471547 Moulding tyres P J KENT and J E PHILLIPS 28 Nov 1975 [28 Nov 1974] 51585/74 Heading B5A In a process for making a radial ply tyre, a tread band 2 of precured elastomeric material is placed in the ring mould 1 and plies 11 are circumferentially located on the band; an uncured tyre carcass 4 is then positioned within the band and forced into contact with it whereby the assembly is bonded together and cured. Side wall plates 6 are clamped to the ring mould and are associated with bead plates 5. Gas, e.g. superheated steam is fed under pressure into a bag 7 via an inlet 8.

Description

This invention relates to a method and apparatus for making radial ply pneumatic tyres.

In the manufacture of such tyres, it has been found essential to follow complex procedures and to use large and expensive apparatus in order to produce a satisfactory tyre, free of dangerous or unsightly blemishes, such as a departure from perfect circularity, an unbalancing displacement of the plies or other faults resulting from the slightest imperfection in the conformation and structure of the tyre.

The procedures and apparatus must haye closely controlled tolerances throughout the sequence of manufacture of the tyre, to give a reasonable chance of the final product having the correct structure, conformation and therefore balance.

In conventional methods, a cylindrical first stage carcase assembly is formed on a drum with, the radial plies ! . i 41851 extending parallel to its axis; bead assemblies are then looated over the radial plies on the first stage carcase assembly at appropriate distances from its edges. The outer edges of the radial ply or plies, that is the part of the radial ply or plies between the bead assemblies and the outer edges are then folded over and suitably fixed. The first stage carcase assembly can then extend off the drum so that the central portion obtains a predetermined diameter while the outer portions form the side walls. If this method is not used on the first stage carcase assembly, it can be carried out on a separate apparatus, designed to ensure conformation of the carcase assembly to a specific overall crown diameter. The aforementioned carcase assembly must conform to exact dimensions so that subsequent building operations yield a tyre carcase of precise and accurate configuration. Varying angular crown plies are applied successively circumferentially, one above the other, to form a bracing structure or crown block to the crown area of the carcass assembly, each being appropriately stitched or laid in place, in such a way that the build up of the varying angular crown plies has a precise configuration. Suitable outer layers of unvulcanized elastomers are added thereon and the complete unvulcanized tyre assembly is placed in a mould. This usually comprises 6 or 8 crown Segments, 2 sidewall plates and 2 bead plates, to form the tread pattern, sidewalls and bead mouldings respectively and in which the unvulcanized tyre assembly is formed and vulcanized by the application of heat and pressure. It is usually important to use a mould consisting of several segments, each of which is retractable away from the axis of the tyre, to ensure an even pressure over the complete surface of the tyre, because the complex arrangement of plies would not allow the tyre to be fitted into a conventional tyre mould without serious deformation. The unvulcanized tyre must be of such dimensions that upon the application of heat and pressure it fits the closed-mould precisely.

If the unvulcanized tyre is either too large or too small for the mould, the resulting finished tyre must be discarded .

The present invention provides a prates $ and apparatus which greatly facilitate the production of substantially faultless radial ply tyres without the necessity for lengthy, complex and expensive procedures.

According to the invention, a process for making a radial ply tyre comprises the successive steps of: a) precisely locating'a tread band of precured elastomeric material in a ring mould so that the band is retained therein; b) circumferentially locating a breaker assembly on the inner surface of the tread band while the band is retained in the mould; • c) accurately positioning an uncured tyre carcass relative to the combination of tread band aHd breaker assembly, and d) bringing the tyre carcass into contact with the combination, the resulting assembly of tread band, breaker assembly and carcass being bonded together and cured to form a finished tyre.

The breaker assembly may be formed by successively building up breaker plies on the inner surface of the - 4 41951 tread band, or by preforming a combination of the plies before locating them on the inner surface of the tread band. The breaker assembly in process step (b) is advantageously unvulcanized.

The holding of a tread band in the mould while the final stages of building the tyre are performed within the tread band is a crucial feature in ensuring that the structure and dimensions of the finished tyre conform to the required plan.

A further feature of the invention lies in curing the tread band before the building up of the remainder of the tyre. This has been found to be essential in ensuring that the required dimensions are maintained through the building up process and thereafter.

A further desirable feature is that the precured tread band should be under longitudinal compression when placed in the mould, so that compressive forces are exerted along the direction of the circumference of the tread band, generally enough to shorten the tread band circumference by over 2%, preferably over 6%, as compared with what would otherwise be the final circumference. This feature, while desirable as a part of the overall process, is not per se the invention of the present application. The feature is, however, desirable in providing a single co-ordinated process which achieves the best product in the technically easiest fashion.

By virtue of using a preoured tread band, which already has a tread pattern formed thereon it is not necessary to apply heat to the tread band and consequently not necessary to heat the mould provided use is made of some other method of heating the inner layers of the tyre which require to be cured and bonded to the tread band. The invention facilitates this by providing the further feature that heat may be fed from the inside of the tyre to the area to be heated. In particular, fluid, especially pneumatic, pressure may be applied within the tyre to force the inner layers against the tread band, for example by using a pressure bag, and in this case any necessary heat can be provided by inflating the bag with a hot gas such as steam, for example super-heated steam.

In carrying out the process of the invention, one may make use of a conventional first stage carcase building machine to produce a carcase assembly which is located within the mould and pressed speedily and accurately, for example by pneumatic pressure, against the pre-located layers and tread band in the mould. However, a significant advantage of the invention in this case is that the first stage carcase assembly need not have been formed with suoh exceedingly fine tolerances as in conventional processes for making radial tyres, because the rigid mould which . holds the tread band assembly while the first stage carcase assembly is located and then bonded therein, forces it to conform to the required configuration.

The first stage carcase assembly may be maintained on a drum· of the usual type which may be brought within the mould and then the first stage carcase assembly may be forced by pneumatic pressure to move out radially to contact the tread band. At the. same time, sidewall forming disclike members, parallel to the plane of the mould, may be brought up from either side to press the side walls of the tyre into the right configuration. Advantageously, pneumatic pressure is applied from within so that the side walls are held firmly against these disc-like members.

The tyre may be finally cured and finished in this position.

The precuring of the tread band has various advantages. Not only does it permit one to dispose with heating of the mould, as mentioned above, but also it makes the tread band relatively rigid so that the plies subsequently applied thereto remain firmly in position and do not tend to move out of position during the continuation of the process of making the tyre. Such movement can destroy the value of a radial tyre, and such movement often occurs in prior methods of making these tyres, starting from a first stage carcase assembly and building outwardly.

By means of the present invention, the production of radial tyres can be accomplished with numerous advantages over existing methods. For example, it is possible by using the present invention to achieve a method of producing radial tyres which: (a) Ensures consistent accuracy of construction. (b) Reduces defects inherent in many other methods of construction. (c) Substantially reduces the complexity and cost of equipment normally required. (d) Enables mass flow line production with a minimum of human skill and effort. (e) Substantially reduces the need for large areas of factory floor space. (f) Produces unparalleled tread life, when a precured and compressed tread is used. (g) Enables the potential use of cheaper materials than are normally used in conventional radial tyre treads, whilst offering comparable tread life.

The invention is illustrated by the accompanying drawings in which Figure 1 is a cross section of a ring mould holding a pre-cured tread band; Figure 2 is a similar cross section showing a first stage carcase on a drum within the ring mould; Figure 2a is an enlarged section of part of the ring mould showing the breaker plies in position; and Figure 3 is a partial cross section of a ring mould containing a formed tyre in process of curing.

As shown in the drawings, the ring mould 1 has precisely located therein a pre-cured elastomeric tread band 2. The vertical line 10, shown in Figures 1 and 2 bisecting the mould 1, represents a datum centre line showing the central positioning of tread band 2 within the mould .1, A building drum 3 is placed along the axis of the ring mould, and carries a first stage carcase 4, which is expanded (for example by pneumatic pressure) so as to fit into the tread band 2. Before the carcase 4 is brought into contact with the tread band 2, appropriate angular crown plies 11 are successively placed on the inner surface of the tread band 2. The resulting assembly of plies 11 (see Figure 2a) constitutes a bracing block 12 which serves to brace the tread band 2 above it and the carcase 4 inside it. The various plies are appropriately stitched or otherwise held in place to produce the necessary precise configuration, before the carcase 4 is brought up against them. Alternatively a single combination of plies in the form of a preformed bracing block (which may be pre-vulcanized) is placed on the inner surface of the tread band 2 and the carcase 4 is brought up against it.

The drum 3 is then withdrawn and appropriate 10 bead plates 5 of appropriate shape and dimension to hold the beads 13 of the carcase 4 in place are placed in position and side wall plates 6 are clamped on either side of the ring mould 1, the plates 6 being constructed of heat conductive metal and shaped to fit the carcase wall. Within the assembly is located a pressure membrane or bag 7 into which a gas can be pumped through inlet 8.

By pumping super-heated steam into the bag 7, the carcase 4 is forced to conform to the tread band 2 which is itself maintained immovable by the ring mould 1. At 2 the same time, the super-heated steam applies the necessary heat and pressure to cure the tyre assembly.

Claims (14)

1. Claims:1. A process for making a radial ply tyre comprising the successive steps of: a) precisely locating a tread band of precured 5 elastomeric material in a ring mould so that the band is retained therein; b) circumferentially locating a breaker assembly on the inner surface of the tread band while the band is retained in the mould; c) accurately positioning an uncured tyre carcass relative to the combination of tread band and breaker assembly and; d) bringing the tyre carcass into contact with the combination, the resulting assembly of tread 15 band, breaker assembly and carcass being bonded together and cured to form a finished tyre.

2. A process according to claim 1 wherein the breaker assembly comprises a plurality of breaker plies.

3. A process according to claim 1 or 2 wherein the bonding and curing is effected by heat and pressure.

4. A process according to claim 3 wherein heat is fed to the bonding region from inside the tyre carcass.

5. A process according to any one of claims 1 to 4 wherein the precured tread band is placed in the mould so that the wearing surface of the band is compressed longitudinally, compressive forces thereby being exerted along the direction of the circumference of the tread band, the longitudinal compression causing the tread band circumference to be shortened as compared with the uncompressed tread band, and wherein, in said resulting- assembly, a compressive stress is maintained in the wearing surface of the tread band.

6. A process according to claim 5 wherein the tread band circumference is shortened by over 2% as compared with the uncompressed tread band.

7. A process according to claim 5 wherein the tread band circumference is shortened by over 6% as compared with the uncompressed tread band.

8. A process according to any one of claims 1 to 7 wherein the breaker assembly is formed by successively building up a plurality of breaker plies on the inner surface of the tread band.

9. A process according to any one of claims 1 to 7 wherein the breaker assembly is preformed before being located on the inner surface of the tread band.

10. A process according to any one of claims 1 to 9 wherein, in process step (b), the breaker assembly is uncured.

11. A process for making a radial ply tyre substantially as hereinbefore described with reference to the accompanying drawings. 11 41951

12. A radial ply tyre whenever made by a process according to any one of claims 1 to 11.

13. An apparatus for carrying out the process according to any one of claims 1 to 11 substantially as hereinbefore described.

14. An apparatus according to claim 13 substantially as hereinbefore described with reference to the accompanying drawings.