GB2109750A

GB2109750A - Applying tread to tyres

Info

Publication number: GB2109750A
Application number: GB08130991A
Authority: GB
Inventors: Jan Herbert Farquharson Kent
Original assignee: Kentredder Ltd
Current assignee: Kentredder Ltd
Priority date: 1981-10-14
Filing date: 1981-10-14
Publication date: 1983-06-08
Also published as: IT8223602A0; IT8223602A1; ZA827095B; IT1152682B; AU8878882A; FR2514292A1

Abstract

Apparatus for applying tread lugs or segments to a tyre carcass (1) comprises a matrix (4) provided with a cavity or cavities (5) for receiving new tread material which may be unvulcanised, or vulcanised and provided with a voiding agent. The matrix is mounted on a harness (6) attached to an arm (7) which is pivotable by a ram (9) to maintain the matrix and thus the new tread material against a portion of the tyre carcass (1). Means are provided for applying pressure locally to the inside of the tyre carcass opposite the matrix (6) such that the carcass is forced against the new tread material in the matrix. These pressure means may comprise an inflatable bag (10) fixed to an arcuate backing plate (11), or an inextensible fluid filled bag forced against the carcass by a hydraulic ram. The pressure means may be rotatable within the tyre carcass for positioning adjacent the matrix (4). Heat is applied to the new tread material, e.g. by electric heating elements or hot fluid pipes in the matrix. The tyre carcass may be rotatably mounted in the apparatus, e.g. by rollers (2), (3), and the mounting means may be adjustable to accommodate different diameter carcasses. <IMAGE>

Description

SPECIFICATION Apparatus and procesS for applying tread to tyres This invention relates to an apparatus and a process for applying tread to tyres.

In particular, it relates to an apparatus and a process for treading (especially re-treading) large tyres such as are commonly referred to as "offthe-road" tyres. These tyres are used on farm tractors and other agricultural implements, and also on heavy machinery used on mining or construction sites. In all these applications, a tyre must be of great strength and in most applications must also possess a tread with a very pronounced pattern to afford the tyre a firm purchase on the soft and often slippery terrain over which machines fitted with such tyres are required to operate. The tread of large tyres commonly comprises a series of raised ribs (known as lugs) arranged around and substantially transverse to the circumference of the tyre which forms the tread-carrying surface.

In certain cases it is now becoming a practice to apply a "slick" tread to large tyres for use in quarries and other environments where a harsh, rocky surface itself provides sufficient friction to prevent wheel slip. Whichever type of tread is used it will be worn away until insufficient exists to provide either reasonable traction or sufficient strength. New replacement tyres of this size are expensive and retreading offers an economic and therefore attractive alternative.

Conventional retreading equipment uses a mould into which is placed the tyre carcass to be retreaded. This mould must be of substantially the same dimensions as the tyre. In order to effect a strong bond between new tread material and a tyre carcass it is necessary to provide both high pressure and heat. When retreading a large tyre it is difficult to supply sufficient pressure, firstly to overcome the great strength of the tyre casing, thereby forcing the tyre into the contours of the mould, and secondly to obtain the requisite flow or movement of tread material within the mould. A further problem is the supply of heat to the surface of the tyre where bonding is to occur.

In the case of large tyres, these problems have, in the past, been mitigated by the use of a large autoclave. The surface of a tyre carcass is first cleaned to remove pieces of vestigial tread. This process is commonly referred to as buffing and comprises removing the remaining tread with rotary abrasive and cutting tools. New lugs of unvulcanised material are then individually built onto the tyre. The tyre is next placed within the autclave and rotated. Compressed air and then steam are admitted to the autoclave to build up a contact pressure between the lug material and the buffed surface of the tyre carcass and to raise the temperature of the tyre carcass and lugs in order simultaneously to vulcanise the lug material and to bond it to the buffed surface. The above procedure avoids the need to provide an expensive mould which accurately fits the dimensions of the tyre.It is, however, highly labour-intensive. Each lug must be formed individually and placed on the prepared tyre The operator of such aprocess must be both skilled and careful if reliable and neat tyres are to result. A further disadvantage of the system is the capital cost of the equipment. To provide the requisite pressure and steam heating, the autoclave must be of massive construction. As a result, the plants now able to retread large tyres by the above process are expensive and relatively rare.

In our earlier British Patent (No. 1471535), we describe a method and an apparatus for retreading a tyre. The apparatus is capable of exerting a high bond pressure between new lug material and a buffed tyre surface. This high bond pressure is achieved by maintaining a matrix (i.e. a mould) which contains, within its relief pattern, prevulcanised or unvulcanised material against a portion of prepared tread-carrying surface on a tyre. The material is bonded to the tyre by applying gas pressure to force the material in the matrix out of the relief pattern and against the tyre. Heat is applied simultaneously to bond the new tread to the tyre. This process may be carried out sequentially on segments of the tyre, thus obviating the need for a large mould. In addition, the degree of skill necessary to operate such apparatus is greatly reduced in comparison with previous techniques.These factors combine to reduce both the capital and running costs of a retreading plant using the method described.

The method, the subject of British Patent No.

1471535 does, however, itself have certain disadvantages. In order to apply a force to the material in the matrix, to load it against the buffed tread-carrying surface of the tyre, it is necessary to provide a point against which the force generated can react. In 1471535 this reaction is provided by a plate braced diametrically opposite the matrix, and abutting the outer circumference of the tyre. The tyre is mounted on the apparatus, inflated and on its normal wheel hub. Under the pressure involved, deformation and failure of the tyre are possible. In this way, a limitation is placed upon the maximum pressure which can be exerted upon the lug material as it is forced against the tyre surface. This limitation is particularly acute when the tyre to be retreaded is designed for a relatively low inflation pressure.Examples of such tyres include "off-the-road" tyres such as those used on farm tractors and other agricultural machines.

The present invention seeks to avoid this limitation and also provides embodiments capable of increasing the operating speed of the retreading process and reducing the amount of manual labour and skill required of an operator of the process.

According to the present invention, we provide an apparatus for applying lugs or segments of tread to a tyre carcass, the apparatus comprising; a matrix provided with at least one cavity for receiving new tread material, means for holding the new tread material in the cavity adjacent a portion of tread-carrying surface of the tyre carcass, means for applying heat to the new tread material in the cavity, and means for applying pressure locally to the inside surface of the tyre carcass opposite the matrix cavity, whereby the said portion of tread carrying surface of the tyre carcass may be forced against the new tread material whilst heat is applied to bond the new tread material to the tread carrying surface of the tyre carcass.

Preferably, the new tread material is unvulcanised material or is pre-vulcanised material bearing a suitable bonding material whereby the new tread material may be bonded to the tread carrying surface.

Preferably, the matrix is attached to means allowing the matrix to be moved away from the tread carrying surface of the tyre.

Preferably, the apparatus includes means to adjust the height of the matrix.

In one aspect of the present invention the means for applying pressure comprises an inflatable, inextensible fluid filled bag located adjacent the inside surface of the portion of tyre carcass opposite the matrix cavity or cavities and supported by an arcuate backing plate, the backing plate providing a surface against which the fluid bag may bear upon inflation, thereby forcing the tread carrying surface of the tyre against the new tread material held within the matrix.

The said fluid is normally a gas, preferably air.

Preferably, the backing plate is attached to pivot means such that the backing plate may be moved through an arc concentric with the circumference of the tyre carcass.

Preferably, the movement of the backing plate is actuated by means of a fluid ram.

Preferably, the backing plate is demountable from the apparatus in two or more components.

In another aspect of the invention, the means for applying pressure comprises an inextensible fluid filled bag located adjacent the inside surface of the portion of tyre carcass opposite the matrix cavity or cavities and supported by an arcuate backing plate, the backing plate being connected to a radially extensible fluid ram such that the backing plate may be forced against the inextensible fluid filled bag thereby exerting a pressure on the inside surface of the tyre carcass, forcing the said portion of tread carrying surface against the new tread material held within the matrix.

Preferably, the back plate and fluid ram are attached to pivot means such that the backing plate may be moved through an arc concentric with the circumference of the tyre carcass.

Preferably, the movement of the back plate is actuated by means of a fluid ram.

The apparatus may include means for mounting the tyre carcass in the apparatus, such that the tyre carcass may be rotated in the apparatus.

Preferably, the mounting means allow an adjustment of the level of the centre of rotation of the tyre carcass.

Preferably, the mounting means include powered means for rotating the tyre carcass.

Preferably, the apparatus includes a buffing head, suitably the buffing head being adjustable in height.

According to the present invention, we further provide a process for applying a tread to a portion of a tyre carcass comprising the steps of: maintaining new tread material adjacent the portion of the tread carrying surface of the tyre, applying pressure locally to the inside surface of the tyre carcass opposite the new tread material, and applying heat to the new tread material, such that the portion of tread carrying surface of the tyre carcass is forced against the new tread material whilst heat is applied, thereby bonding the new tread material to the tread carrying surface of the tyre carcass.

Preferably, the portion of tread carrying surface is buffed.

Preferably, the process is repeated until the entire circumference of the tread carrying surface of the tyre carcass has been treated or lugs have been applied at appropriate intervals over the surface.

The apparatus and process of the invention are described by the following embodiments. These are illustrated in the accompanying drawings, in which: Figure 1 is a front elevation of one embodiment of the complete apparatus showing additionally the position of a tyre in the apparatus; Figure 2 is a cross-section along the line 1-1 of Figure 1: Figure 3 is a front elevation of a backing plate; Figure 4 is a side elevation of the backing plate shown in Figure 3; Figure 5 is a front elevation, partially sectioned, of an embodiment of the means for applying pressure; Figure 6 is a front elevation of a drive mechanism for tyres of various sizes, and Figure 7 is a plan view of the drive mechanism of Figure 5.

in one embodiment of the invention (see Figure 1), a tyre carcass, shown generally at 1, is rotatably mounted in an upright position on two rollers 2 and 3. A matrix 4, provided with cavities 5 for receiving new tread material, is supported by a harness 6. The harness is attached to a first arm 7 pivotable about a first axle 8. The first axle is attached to a fixed member of the apparatus (not shown). In this way, the matrix may be moved through an arc. The motion is powered by a first pneumatic ram 9. The cooperation of the components supporting the matrix allows the matrix to be placed adjacent a portion of the tread carrying surface of the tyre (the position depicted in Figure 1) and allows movement of the matrix to a position well clear of the tyre carcass to facilitate the loading of the cavities with new tread material.

An inflatable, inextensible air bag 10 is placed in the base of the channel section formed by the two walls and the tread carrying material of the tyre carcass (see Figures 1 and 2). An arcuate backing plate 11 abuts the air bag. The backing plate is releasably attached to a rotatable member 12 keyed to a second axle 13. The second axle is rotatable in a bearing mounted on a fixed member of the apparatus (not shown). The tyre carcass is arranged in the apparatus such that the second axle is coincident with the axis of rotation of the tyre carcass. A second arm is keyed to the second axle such that torque may be applied to the second axle by a second pneumatic ram 1 5. The cooperation of the components supporting the backing plate allows the backing plate to be rotated within the tyre carcass.A flange member 1 6 extends from the harness 6 radially towards the second axle 13 and is provided with an aperture 1 7. The backing plate 11 is also provided with an aperture 1 8. In the process of bonding new tread material to the tyre carcass the matrix 4 is positioned adjacent the portion of tread carrying surface to be treaded and the air bag 10 and the back plate 11 are rotated to a postion adjacent the inside of the tyre carcass opposite to the matrix, such that the material of the tyre carcass lies between the matrix 4 and the air bag 10.In this position the apertures 1 7 and 1 8 are co-axial and a pin 1 9 may be inserted through them, thereby mechanically bracing the matrix and the backing plate together. In this way, when the air bag is inflated, the tread carrying surface of the tyre carcass is forced against the new tread material contained in the cavities of the matrix.

The matrix 4 may include means for heating the cavity region.

We now describe some of the components of the apparatus in more detail and describe the process of applying tread to a tyre carcass.

The tyre carcass, shown generally at 1, is placed upon rollers 2 and 3. The rollers may be adjustable such that the axis of rotation of the tyre carcass is coincident with second axle 1 3. In this way, the apparatus may be readily adjusted to conform with tyres of differing diameter. The adjustment may, for example, be achieved by altering the horizontal separation of the rollers or by altering the vertical level of the rollers. One or both of the rollers may be driven (for example by a small electric motor and a suitable gear chain). In this way the tyre carcass may readily be rotated within the apparatus. Vestigial tread on the tyre may be removed using a conventional buffing machine (e.g. a double disc machine with cutters).

The facility for rotating the tyre carcass in the apparatus assists this operation, although it would, of course, be possible to buff the tyre carcass prior to placing it in the apparatus.

A buffing machine may be mounted on the apparatus and allowance can be made for variations in the diameters of the tyres to be treated by providing means to adjust the height of the buffing head within the apparatus.

When the tyre carcass has been suitably prepared, the air bag, 10, in a deflated state, is placed between the beads of the tyre carcass such that it rests about the lowest point of the inside of the tyre carcass (the position shown in Figure 1).

Next the backing plate 11 is inserted between the beads of the tyre. The backing plate has an arcuate surface which abuts the air bag 10. In order that an even pressure is exerted on the inside of the tyre, the backing plate must be of a width similar to that of the inside of the tyre carcass and a radius slightly less than that of the inside of the tyre carcass. During the process of applying the new tread material to the tyre carcass, the backing plate necessarily bears a force of several tons. As a result, the backing plate must be strongly built and therefore may be heavy, and this could create a potential handling problem for the operator of the present apparatus. This problem is solved in two ways in the present embodiment. Firstly, the backing plate is inserted in a vertical or hanging position.This considerably eases the handling problem of a heavy and awkwardly-shaped backing plate. Secondly the backing plate is formed from two components which may be separately inserted between the beads of the tyre carcass. In the embodiment presently being described, the backing plate comprises two members 21 and 22 (see Figure 2).

Each member consists of a flat plate of segmental cross-section in the plane of the plate with a web extending perpendicular to the arcuate edge of the plate. The web provides the surface against which the air bag abuts. Each member has, therefore a substantially "L"-shaped radial cross-section. The two members are bolted to the rotatable member 12 such that the flat plates lie parallel with their respective webs extending in opposite directions, the two plates being separated by the thickness of the rotatable member 1 2. Two apertures 18, one in each of the "L"-shaped members, are positioned such that they can receive the pin 1 9 when the backing plate and the matrix are in position for bonding new tread material. The gap between the two component members of the backing plate may receive a valve for inflation of the air bag.

Once the backing plate 11 is assembled and bolted to the rotatable member 12 it may be rotated within the apparatus. The rotatable member is, in this embodiment, provided with a square aperture adapted to receive a portion of the second axle 1 3 which is of square cross-section.

The second arm 14 is arranged to apply torque to the axle by means of the second pneumatic ram 15. The ram may act directly on the backing plate.

Activating the second pneumatic ram rotates the backing plate and the air bag through an arc such that it assumes a position on the inside of the tyre carcass opposite the first segment of tyre to be treated. To ensure that the air bag remains in the appropriate position adjacent the backing plate during this operation means are provided to attach the air bag to the backing plate.

The matrix 4 is of arcuate longitudinal crosssection and is provided with one or more cavities 5, on its concave surface for receiving new tread material. The radius of the concave surface is substantially the same as the radius of the tread carrying surface of the type to be retreaded. The matrix is mounted on the harness 6 which is arranged to move in an arc about the first axle 8.

By means of the first pneumatic ram 9 the matrix is moved away from the tyre carcass and the cavities are loaded with new tread material. This material may be unvulcanised material or it may be pre-vulcanised material with an unvulcanised bonding agent arranged to be sandwiched between this pre-vulcanised material and the carcass surface.

Where the segment to be treated is to receive a 'slick' tread a precured segment of new tread material may be formed on a smaller radius than the tyre carcass to which it is to be bonded. The bonding process produces a compressive stress on outer surface of the tread, conferring upon it a resistance to cutting.

Once the cavities are loaded, the matrix is moved by means of the first pneumatic ram 9 to a position adjacent the portion of tread carrying surface of the tyre carcass to be treated. In this position the apertures 1 8 in the backing plate 11 and the aperture 1 7 in the harness flange 16 are co-axial. The pin 1 9 may be inserted mechanically to brace the matrix and the backing plate. The air bag 10 is inflated, for example to a pressure of about 100 p.s.i.g., thereby forcing the tread carrying surface of the tyre against the new material contained in the matrix. Heat is applied simultaneously in the region 20.The heat may be applied by means of electric heating elements in the matrix, or by passing a hot fluid through piping in the matrix or by means of electric heat elements built into the new tread material.

After an appropriate length of time, the air bag is deflated, the pin 19 is removed and the matrix is moved away from the tyre carcass. The tyre carcass is rotated with the apparatus to present the next segment of tread carrying surface to be processed. The matrix is reloaded with new tread material, moved into position against the tyre carcass and the process of bonding is repeated.

The segmental treading continues until the whole tyre carcass has been treated. It is often the case with large tyres that only a small section of the tread needs replacing (for example, just one or a few lugs may need to be applied). The apparatus of the present invention is ideal for such applications.

The matrix 4 may be changed either if it is desired to apply a different tread pattern or different lugs to a given tyre carcass 1, or if a tyre carcass 1 of different diameter is to be treated. In the latter case, it may be desirable also to change the backing plate 11, if the difference in the tyre diameters is great.

To allow for the treatment of a range of tyre carcasses the position of the matrix may be varied within the apparatus to facilitate the treatment of tyre carcasses of widely varying diameters.

Normally this adjustment will be made in the height of the matrix relative to the apparatus.

Figures 3 and 4 depict another embodiment of the backing plate. As described above, the backing plate'must be strong enough.to.bear a force Df several tons. It must also be easy to manhandle. In this embodiment the backing plate is demountable into 4 components. The general shape of the backing plate is as previously described, except that each member comprising the backing plate is further divided, along a radial line into two pieces.

The two pieces are bolted together mid-way between the arcuate edge of the members and the centre of the radius of the arc. In this embodiment the second axle may be of circular cross-section 23. The two pieces comprising each constituent member of the backing plate grip the axle between semi-circular recesses formed in each of the two pieces. A nut and bolt 14 cause the two pieces of each member to grip the second axle securely.

In another embodiment of the means of applying pressure, a radially-extendable hydraulic ram is used to apply pressure to the inside surface of the tyre carcass opposite the new tread material contained in the matrix. Figure 5 shows such an arrangement. An inextensible bag containing an incompressible fluid is used in place of the inflatable air bag of the first embodiment. A backing plate 26 is attached to an hydraulic ram 27 pivotable about an axle as previously described. The backing plate presents a surface to the fluid bag of substantially the same width as the inside of the tyre carcass and of a radius slightly less than the radius of the inside of the tyre carcass. The process for applying tread to a tyre is the same in this embodiment as was previously described.Once the matrix, the backing plate and the fluid bag are in position, hydraulic fluid is pumped to the ram, causing it to extend radially. The fluid in the extensible bag serves to distribute the load applied evenly over the inside surface of the tyre carcass. Care must be taken that the bag is sufficiently large to prevent complete collapse as the fluid distributes itself under load. Means may be provided for directly bracing the pressure-applying means of this embodiment to the matrix.

Figures 6 and 7 show a preferred means for rotatably mounting a tyre carcass on the apparatus of the present invention. Instead of the rollers 2 and 3 shown in Figure 1, the tyre carcass 1 is supported on a belt 18. The belt 18 runs on rollers 29 rotatable about axles 30. The axles 30 are provided with bearings in distance pieces 31.

Disposed between the ends of the rollers and the distance pieces the axles 30 pass through elongated apertures 32 in side plates 33. The elongated apertures are cut at such an angle that the mid-point of the belt drive lies directly below the tyre centre which may vary in position according to the diameter of the tyre being processed. In this way a constant contact point with the matrix may be maintained. A small motor 34 may be used to rotate the rollers 29.

A ram 35 is connected through a double pivot mechanism to distance pieces 31 as shown whereby the ram can force the distance pieces 31 and consequently the belt 28 towards the left in Figure 6, thus forcing the belt 28 to rise as the axles 30 move along the apertures 32.

In this embodiment, if a tyre carcass 1 is replaced by another carcass 1' of smaller diameter, the ram 35 is activated as mentioned above, whereby the carcass 1' is made to bear against the matrix 4 without there being any need to move the matrix 4 from the position it would have occupied for the treatment of carcass 1.

By means of this embodiment it is possible to accommodate a wide variety of tyre carcasses of differing sizes while using a single apparatus. If the area of the carcass to be treated is relatively small, the same matrix 4 can be used for tyres of widely differing diameters. If the area is larger, then it may be desirable to use different matrices.

If the difference in the tyre diameters is very great, different appropriately-shaped matrices can be mounted on the same harness 6 as required.

Claims

1. An apparatus for applying lugs or segments of tread to a tyre carcass, the apparatus comprising: a matrix provided with at least one cavity for receiving new tread material, means for holding the new tread material in the cavity adjacent a portion of tread carrying surface of the tyre carcass, means for applying heat to the new tread material in the cavity, and means for applying pressure locally to the inside surface of the tyre carcass opposite the matrix cavity, whereby the said portion of tread carrying surface of the tyre carcass may be forced against the new tread material whilst heat is applied to bond the new tread material to the tread carrying surface of the tyre carcass.

2. An apparatus for applying lugs or segments or tread to a tyre carcass according to claim 1 wherein the new tread material is unvulcanised material or is a pre-vulcanised material bearing a suitable bonding material whereby the new tread material may be bonded to the tread carrying surface.

3. An apparatus for applying lugs or segments of tread to a tyre carcass according to claim 1 or 2 wherein the matrix is attached to means allowing the matrix to be moved away from the tread carrying surface of the tyre.

4. An apparatus for applying lugs or segments of tread to a tyre carcass according to any of the preceding claims wherein the apparatus includes means to adjust the height of the matrix.

5. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of the preceding claims wherein the means for applying pressure comprises an inflatable, inextensible fluid filled bag located adjacent the inside surface of the portion of tyre carcass opposite the matrix cavity or cavities and supported by an arcuate backing plate, the backing plate providing a surface against which the fluid bag may bear upon inflation, thereby forcing the tread carrying surface of the tyre against the new tread material held within the matrix.

6. An apparatus for applying lugs or segments of tread to a tyre carcass according to claim 5 wherein fluid is gas.

7. An apparatus for applying lugs or segments of tread to a tyre carcass according to claim 6 wherein the fluid is air.

8. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of claims 5 to 7 wherein the backing plate is attached to pivot means such that the backing plate may be moved through an arc concentric with the circumference of the tyre carcass.

9. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of claims 5 to 8 wherein the movement of the backing plate is actuated by means of a fluid ram.

10. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of claims 5 to 9 wherein the backing plate is demountable from the apparatus in two or more components.

11. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of claims 1 to 4 wherein the means for applying pressure comprises an inextensible fluid filled bag located adjacent the inside surface of the portion of tyre carcass opposite the matrix cavity or cavities and supported by an arcuate backing plate, the backing plate being connected to a radially extensible fluid ram such that the backing plate may be forced against the inextensible fluid filled bag thereby exerting a pressure on the inside surface of the tyre carcass, forcing the said portion of tread carrying surface against the new tread material held within the matrix.

12. An apparatus for applying lugs or segments of tread to a tyre carcass according to claim 11 wherein the backing plate and fluid ram are attached to pivot means such that the backing plate may be moved through an arc concentric with the circumference of the tyre carcass.

13. An apparatus for applying lugs or segments of tread to a tyre carcass according to claim 11 or 12 wherein the movement of the backing plate is actuated by means of a fluid ram.

14. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of the preceding claims wherein the apparatus includes means for mounting the tyre carcass in the apparatus, such that the tyre carcass may be rotated in the apparatus.

1 5. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of the preceding claims wherein the mounting means allow an adjustment of the level of the centre of rotation of the tyre carcass.

1 6. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of the preceding claims wherein the mounting means include powered means for rotating the tyre carcass.

1 7. An apparatus for applying lugs or segments of tread to a tyre carcass according to any one of the preceding claims wherein the apparatus includes a buffing head, suitably the buffing head being adjustable in height.

1 8. A process for applying a tread to a portion of a tyre carcass comprising the steps of: maintaining new tread material adjacent the portion of the tread carrying surface of the tyre, applying pressure locally to the inside surface of the tyre carcass opposite the new tread material, and applying heat to the new tread material, such that the portion of tread carrying surface of the tyre carcass is forced against the new tread material whilst heat is applied, thereby bonding the new tread material to the tread carrying surface of the tyre carcass.

19. A process of applying a tread to a portion of a tyre carcass according to claim 18 wherein the portion of tread carrying surface is buffed.

20. A process for applying a tread to a portion of a tyre carcass according to claim 18 to 1 9 wherein the process is repeated until the entire circumference of the tread carrying surface of the tyre carcass has been treated or lugs have been applied at appropriate intervals over the surface.

21. An apparatus for applying lugs or segments of tread to a tyre carcass substantially as hereinbefore described and with reference to the accompanying drawings.

22. A process for applying a tread to a tyre carcass substantially as hereinbefore described and with reference to the accompanying drawings.