GB2032858A

GB2032858A - The Retreading or Repairing of Pneumatic Tyres for Vehicle Wheels

Info

Publication number: GB2032858A
Application number: GB7934298A
Authority: GB
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1978-10-04
Filing date: 1979-10-03
Publication date: 1980-05-14
Also published as: FR2437928B1; ES484699A1; IT7953596V0; DE2940314A1; AU5140479A; IT7968862A0; JPS5549241A; SE7908192L; NL7907363A; DE7928274U1; FR2437928A1; BE878959A; LU81746A1

Abstract

A device for applying a flexible casing in a pressure-tight manner against the bead of a pneumatic tyre which is to be retreaded or repaired, consists of an elastic ring (1) which is manually deformable in the radial and axial directions and has an outer periphery which forms a cylindrical or frusto-conical shaped bearing surface (11) terminating in at least one circumferential rim forming an axial abutment (12). There can be two rims if required and the inner rim can, if provided, have an interruption in its circumferential direction to assist in the eventual removal of the device from a tyre bead. Also, the ring can have reinforcement, e.g. in the form of a ply or plies of cords. For the ring may have an annular inflation cavity with a metal collar on the radially inner side of the ring. <IMAGE>

Description

SPECIFICATION The Retreading or Repairing of Pneumatic Tyres for Vehicle Wheels This invention relates to the retreading or repairing of pneumatic tyres for vehicle wheels and more particularly to repairing or retreading which, when carried out, uses a flexible casing into which the type which is to be repaired or retreaded is introduced.

The flexible casing usually consists of two sheets of elastic material each in the form of a crown. These two sheets, which have the same dimensions, are superimposed and joined to each other by welding along their great circle. Their small circles are free, i.e. not fixed in any way. One of the two sheets comprises a tube and is intended to be connected to a pressure reducing means.

When the tyre which is to be repaired or retreaded has been suitably prepared and is to be subjected to heating under pressure, it is first placed in the flexible casing described above so that the great circle of this casing is located substantially in the mid-circumferential plane of the tyre and its two small circles are located if the region of the circles formed by the bases of the beads of the tyre. In order to be able to create underpressure between the outer wall of the tyre and the inner wall of the flexible casing so that the latter abuts firmly on the outer wall, the zone of the casing located in the region of the beads must first be applied against the beads in order to ensure a fluid-tight seal between the beads and that zone of the casing.

Various devices have been designed for providing this leak-tight contact. Such devices may consist of metal rings, in one or more parts, which are fixed radially inside the beads of the type, whilst the part of the casing adjacent to its small circle is held clamped between the base of the beads of the tyre and the metal rings. These rings have disadvantages; they are heavy, difficuit to manipulate, expensive, and not infrequently they damage the flexible casing. The casing then has to be taken out of service for the time it takes to repair it or it may not be repairable.

It has also been proposed to fix the casing along each of the tyre beads by means of flexible clamps, as described in United States Patent Specification No. 3 730 801. The grip provided by the clamps shown in Figure 3 of that patent Specification is an axial grip, i.e. it is exerted solely along the inner and outer walls of each of the tyre beads. However, this type of grip is often defective since the outer walls of the beads of some tyres have radial channels, grooves or ribs, with the result that the flexible casing applied against this wall never completely seals off these channels or grooves, thus preventing, or at least retarding, the establishment of underpressure between the flexible casing and the tyre.

It is therefore an object of this invention to provide a device, for repairing or retreading pneumatic tyres, which does not have the disadvantages listed above and which ensures the leaktight seal of the flexible casing placed round the tyre.

According to the invention, there is provided a device for applying a flexible casing in pressuretight manner against the bead of a tyre during the repairing or retreading, the device consisting of an elastic ring, e.g. made of rubber or a similar material which is deformable in the radial and axial directions, the outer periphery or "bearing surface" of which is cylindrical or frusto-conical shaped, preferably only slightly frusto-conical shaped, and which is provided with at least one circumferential rim forming an axial abutment.

Also according to the invention, there is provided a method of applying a flexible casing in a pressure-tight manner against the bead of a tyre during its repairing or retreading in which an elastic ring is fitted in the circular opening of the tyre and traps the flexible casing between itself and the bead of the tyre, the elastic ring being manually deformable in the radial and axial directions, and its outer periphery forming a cylindrical or frusto-conical shaped bearing surface terminating in at least one circumferential rim which forms an axial abutment.

This elastic ring is intended to be fitted in the circular opening of the tyre, circumscribed by the base of each of its two beads, the zone of the small circle of the flexible casing being interposed and gripped between the ring and the base of the bead of the tyre. This mounting is easily carried out, thanks to the flexibility of the deformable ring.

To ensure that the zone of the flexible casing adjacent to the bases of the tyre beads is well clamped between the base and the bearing surface of the elastic ring, it is advantageous for the diameter of this bearing surface to be such as to ensure adequate clamping; in practice, therefore, the bearing surface of the elastic ring will have a diameter at least equal to that of the base of the tyre bead.

The circumferential rim of the bearing surface of the ring comes to abut on the axially outer wall of the tyre bead, via the zone of the flexible casing adjacent to the bases of the tyre beads. The outer rim is not needed to ensure a tight seal, which is essentially provided along the bearing surface of the ring and the base of the tyre bead, but it is needed to prevent the ring from penetrating too far into the tyre and ensures that the ring is satisfactorily positioned, in the axial direction, relative to the base of the bead of the tyre.

It is also possible to provide a second circumferential rim at the other axial end of the bearing surface. This second rim is particularly useful when the base of the tyre bead forms a relatively large angle, for example 1 5O, with the rotation axis of the tyre. In fact, in this case, an elastic ring not equipped with the second rim might have a tendency to be pushed axially outwards under the effect of the axial component of the gripping stresses exerted between the base of the bead and the bearing surface of the flexible ring, resulting in a loss of grip which would jeopardise the establishment and/or maintenance of the underpressure. Thanks to this second rim which is located in front of the tip of the tyre bead when the elastic ring is put into position, this risk of slackening is eliminated.

In one advantageous embodiment of the invention, the axially inner rim of the elastic ring comprises, along its periphery and over its entire height, an interruption which extends over an angular distance of from about 300 to about 450.

The advantage of this interruption is to facilitate the removal of the elastic ring, by axially pulling the ring, starting with the sector of the ring where this interruption is situated.

At least one reinforcement of cords, e.g. wires, cables or fibres may be embedded in the ring in order to increase the resistance of the ring to mechanical and/or thermal stresses.

When the elastic ring according to the invention has been used a number of times, it may be that the outer diameter of its bearing surface has decreased and is no longer adequate to ensure a leak-tight seal between the flexible casing and the base of the bead of the tyre. The original diameter of the bearing surface can then easily be restored by winding a strip of elastic material of the required thickness around the bearing surface.

The invention will now be described, by way of example, with reference to the drawings, in which: Figures 1 to 5 are radial sections through various embodiments of elastic rings according to the invention; Figure 6 is a side elevation of the ring shown in Figure 5 as viewed in the direction of the arrow A of Figure 5; and Figure 7 is a radial section of another embodiment of elastic ring according to the invention.

The flexible ring 1 shown in Figure 1 is made of elastic material, for example rubber. This ring has a cylindrical bearing surface 11 and a continuous circumferential rim 12. When a tyre is to be repaired, a flexible casing (not shown) is interposed between this ring and the bead of the tyre (not shown) which is to be repaired or retreaded, along the bearing surface 11 and the surface 12' of the rim 12.

The ring 2 shown in Figure 2 differs from that shown in Figure 1 in that it has a reinforcement consisting of two plies of cords 25 and 25'. The cords in each ply 25 and 25' are parallel to one another but the cords of ply 25 are at an angle to those of ply 25'. This ring has a bearing surface 21 and an outer rim 22. Another reinforcement could be provided just below the bearing surface 21.

Figure 3 shows another embodiment of a flexible ring 3 according to the invention. It differs from the preceding ones in that it has two circumferential rims 32 and 33 of different diameters between which is a bearing surface 31.

The diameter d of the rim 33 which is intended to be located inside the tyre is slightly larger than that of the bearing surface 31 but is smaller than the diameter D of the rim 32 which is intended to be applied against the axially outer wall of the bead of the tyre via the flexible casing. The fact that the diameter d is slightly larger than the diameter of the bearing surface makes it easier to position the ring with the flexible casing interposed. The axial distance 36 between the rims 32 and 33 is substantially equal to the width of the base of a bead (not shown) of the tyre which is to be repaired or retreaded.

The flexible ring 4 shown in Figure 4 differs from the one shown in Figure 3 in that the rims 42 and 43 have the same diameter D. Between these arms 42 and 43 is a bearing surface 41.

The flexible ring 5 shown in Figures 5 and 6 has a bearing surface 51 which is conical and is positioned between rims 52 and 53. The inner rim 53 has an interruption 54 in the circumferential direction, extending over an angular distance of about 300.

In the embodiments shown in Figures 3 to 6, the flexible ring may have a reinforcement of the type shown in Figure 2; similarly, the inner rims 31 and 41 of the rings shown in Figures 3 and 4 may have an interruption similar to the interruption 54 shown in Figures 5 and 6.

The ring 7 shown in Figure 7 has an annular inflation cavity 70. A lateral extending valve 72 enables this cavity to be inflated and thus increase the diameter of the bearing surface 71 in order to apply the flexible casing satisfactorily against the base of the bead of a tyre (not shown).

Radially inside the cavity 70 there is provided a collar 73, made of metal strip, for example, which prevents the ring 7 from being deformed in the direction of its axis 74 under the effect of inflation pressure of the cavity 70. In order to ensure that the pressure prevailing in the heating enclosure in which the tyre mounted on this ring is placed is uniformly distributed all round the section of the ring, including the radially inner wall 75 thereof, apertures 76 are provided on or in the metal collar 73. Instead of these apertures, elements in relief (not shown) on the radially outer wall of the collar 73 can be provided.

It is found that, during the heating of the tyre under pressure to repair it, generally carried out in an autoclave, the diameter of the rings according to the invention increases slightly, thus promoting a leaktight seal between the tyre and the flexible casing. This is the case, for example, with a ring made from a mixture based on 60% by weight of natural rubber, 30% by weight of carbon black, 3% by weight of zinc oxide and 1% by weight of stearic acid, the remainder being sulphur, a thiuram, a thiazole and an antioxidant.

Claims

1. A method of applying a flexible casing in a pressure-tight manner against the bead of a tyre during its repairing or retreading in which an elastic ring is fitted in the circular opening of the tyre and traps the flexible casing between itself and the bead of the tyre, the elastic ring being manually deformable in the radial and axial directions, and its outer periphery forming a cylindrical or frusto-conical shaped bearing surface terminating in at least one circumferential rim which forms an axial abutment.

2. A method of applying a flexible casing in a pressure-tight manner against the bead of a tyre during its repairing or retreading, substantially as herein described with reference to any of Figures 1 to 4, Figures 5 and 6, or Figure 7, of the accompanying drawings.

3. A device for applying a flexible casing in pressure-tight manner against the bead of a tyre during its repairing or retreading, the device consisting of an elastic ring which is manually deformable in the radial and axial directions, the outer periphery of which forms a cylindrical or frusto-conical shaped bearing surface terminating in at least one circumferential rim forming an axial abutment.

4. A device as claimed in Claim 3 which has a second circumferential rim.

5. A device as claimed in Claim 4, in which the second rim has an interruption in the circumferential direction.

6. A device as claimed in Claim 4 or Claim 5, in which the second rim has a smaller diameter than the diameter of the said one rim.

7. A device as claimed in any of claims 3 to 6, in which the elastic ring contains a reinforcement composed of filiform elements.

8. A device as claimed in any one of claims 3 to 7, in which the elastic ring has an annular inflation cavity, an inflation valve and a flexible annular reinforcement arranged radially inside the inflation cavity.

9. A device as claimed in Claim 8, in which the flexible annular reinforcement comprises means enabling the radially inner wall of the ring to be directly exposed to contact with a fluid under pressure.

10. A device as claimed in Claim 9, in which these means consist of apertures.

11. A device for applying a flexible casing in pressure-tight against the bead of a tyre during its repairing or retreading, substantially as herein described with reference to any of Figures 1 to 4r Figures 5 and 6, or Figure 7 of the accompanying drawings.