GB2375742A

GB2375742A - Tyre repair patch

Info

Publication number: GB2375742A
Application number: GB0112625A
Authority: GB
Inventors: Stuart Robertson Lawrence
Original assignee: MONARCH VULCANISING SYSTEMS LT
Current assignee: MONARCH VULCANISING SYSTEMS LT
Priority date: 2001-05-23
Filing date: 2001-05-23
Publication date: 2002-11-27
Also published as: GB0112625D0; WO2002094541A1

Abstract

The patch 10 has a layer of soft uncured material 11 and a heating element layer 14. The heating element is encapsulated along with a thermocouple wire 25 in further layers 15 and 17. The heating element is in a planar form and when connected to an energy source activates the base layer 11 to enable it to bond with the surface of a tyre to be repaired. The ends of the heating element (28 and 29, figure 2) protrude from the patch to allow attachment to an energy source such as an electrical power supply. The thermocouple may be connected to a heating element controller to provide a temperature feedback from the patch. The heating element is a continuous strand of wire shaped to provide a tortuous route through the patch. Further layers 20 and 21 of material are provided above the heating element that successively reduce in length and width to produce a dome-shaped section to the patch. An additional compressive pressure may be applied to the patch during or after heating to assist in the bonding.

Description

Tyre Repair The present invention concerns the field of tyre repair, and particularly relates to the repair of heavy duty pneumatic vehicle off the road (OTR) tyres of the type used in earth moving, mining and quarrying vehicles, amongst others.

Very large tyres, of the type used in OTR vehicles such as earth movers and quarrying vehicles, are prone to damage in their normal harsh working environment.

Because of their size, these tyres are extremely expensive to replace. Hence it is usual practice to repair, insofar as is possible, damage in order to extend the life of the tyres.

Repairs of heavy duty tyres are typically carried out by use of a reinforced patch. The patches are multilaminate, of rubber layers and reinforcement layers which aligned according to the repair. For example the reinforcement layer may be unidirectional for a radial tyre or bi-directional for a cross-ply tyre. The re-

enforcement itself may comprise one or more of fabric, fibres and filler.

The laminate patches are formed by heat curing, although an unvulcanised (uncured) surface is provided to be placed over the area to be repaired-typically an interior surface of the tyre. The patch is held in place by vulcanising solution and cured by application two heat pads, one on a outside surface of the tyre over-laying the damaged area, and a second over-laying the patch and surrounding inside surface of the tyre.

The damaged area, such as rupture or gouge, may be plugged by a soft uncured rubber plug.

The heat pads provide heating to activate the curing process which bonds the patch to the tyre inside surface. Air bags are provided exert pressure onto the heat pads, in order to squeeze the patch and associated repair site, so as to promote an homogeneous and strong bond. Once the curing process is complete, the heat pads and pressure bags are removed, and the tyre prepared for re-use on a vehicle.

This method works effectively to repair tyres, but is not without its problems. One problem is that the heat transfer process between the heat pad and the patch involves conduction of heat through the entire thickness of the patch, down to the active face at which curing takes place. This takes time, and significant heat energy input. The heat can damage the patch causing a reduction in life span or effectiveness of the repair. The heat may also cause bulging in the tyre at the region of the repair. It is also difficult to achieve uniform heating across the width of the tyre, and therefore a uniform curing of -he rubber at the active face. Hence generally, the size of the patch, both in area and thickness, and the composition of the patch, is limited by its heat transfer response.

There is a need therefore for a more versatile and effective repair method, which does not suffer from the foregoing disadvantages.

According to one aspect of the present invention there is provided: a tyre repair patch formed with an active surface comprising a material which is capable of forming a bond with a rubber tyre in response to heat activation, and a heating element integrated into the patch for heating the bonding material when in use.

In a preferred embodiment, the patch has a laminate construction and the heating element comprises a planar component. Preferably, the heating element comprises a wire structure of substantially planar configuration.

In order to promote even heat distribution, the heating element may be formed with a plurality of bends to provide a tortuous route through the patch.

The heating element may have a generally planar configuration and is configured to provide a structure which is compliant in bending along one coplanar direction and relatively stiff in bending along an orthogonal coplanar direction. This allows the

structural re-enforcement imparted by the patch to be tailored according to the desired orientation.

Typically, the heating element is an electrically responsive element, although elements heated by conduction or induction heating are not excluded.

According to another aspect of the invention the patch may be formed with an integral heat sensor, such as a thermocouple. Preferably the sensor is located at a site which is indicative of the temperature of the heat-responsive bonding layer.

The heating element may be beneficially situated adjacent the active surface, for direct heating thereof in use.

According to another aspect of the invention, there is provided a method of repairing a damaged tyre, comprising: providing a patch as hereinbefore described; locating the patch on an inside surface wall portion of the tyre overlaying the damage site; connecting the heating element to a source of heating

energy; and allowing a bond to form between the active surface of the patch and a juxtaposed wall surface of the tyre.

Preferably the method includes the application of compressive pressure to the patch during and/or after heating of the contact surface.

Following is a description, by way of example only and with reference to the drawings, of methods of putting the present invention into effect.

In the drawings :Figure 1 is a cross-sectional view through a patch according to one embodiment of the present invention.

Figure 2 is a sectional plan view through the patch of figure 1, sectioned in the direction AA'indicated in figure 1.

Figure 3 is a cross-sectional view of the patch of figure 1 when placed over a damaged section of a tyre.

Figure 4 is a sectional plan view of a patch according to a second embodiment of the invention.

First embodiment A section through a multi-laminate patch according to the present invention is shown in figure 1 as 10. The patch has a lower layer 11 of soft uncured rubber material, known in the trade as cushion gum. The next layer 12 is a layer of reinforcing nylon web material.

Above layer 12 is a further layer of cured rubber material 13. Above layer 13 is a heating element layer 14.

The heating element layer consists of a nickel/ chromium heating element 16 sandwiched between a base layer 15 of butyl rubber and an upper layer 17 of butyl rubber. A thermocouple wire 25 is also disposed between the butyl rubber layers, and centrally located. A layer of vulcanising solution is coated at the interface of the base and upper layers. The sandwich is then heat cured to provide a solid encapsulation of the heating element and thermocouple.

The butyl rubber has good heat resistance and relatively low gas permeability.

Above the heating element layer are several further layers of alternately reinforcement layer 20 and rubber layer 21, each of which is gradually reduced in width and length with respect to its underlying neighbour to produce a dome-shaped section in the patch. An overlaying layer of cushion gum provides an outside protective and constraining layer which helps prevent damage and de-lamination of the patch.

Other than the heating element layer described in the foregoing, the construction of the patch is carried out according to conventional methods in the repair industry, basically involving pressing of layer upon layer to form a complete patch, followed by vulcanising by heat curing in a press (not shown).

In figure 2, a plan section through the heating element layer is shown. The base layer 14 is a rectilinear elongate sheet. The heating element 16 is laid out as a continuous strand of wire configured in

two crenelated mirror image portions 18,19. The wire is configured by bending to form short longitudinally oriented portions 26 and long laterally oriented portion 27. This provides strong resistance to lateral bending of the patch, and relatively weak resistance to longitudinal bending of the patch. This structural anisotropy permits longitudinal bending of the patch to adopt a curve corresponding to a tyre inside circumference, but provides significant lateral bending reinforcement which helps strengthen the tyre in the region of the damage being repaired. Each end 28,29 of the wire protrudes from the patch at one side thereof in order to permit attachment of the element to an electrical power supply and controller (not shown) which manages the heating of the element.

The thermocouple 25 is disposed along a longitudinal line in between the two crenelated portions 18,19 of the heating element. A free end of the thermocouple is connected to the heating element controller (not shown) so as to provide a temperature feedback which allows accurate control of heating of the patch.

Figure 3 shows a patch 10 according to the present invention placed on an inside wall 30 of an OTR tyre over a damaged portion thereof. The rupture in the tyre wall is shown as 31. A foil layer (not shown) is overlaid the patch in order to promote heat transfer to the edges of the patch. Pressure is applied (by conventional air bags, not shown) as indicated by arrows A and A'. The heating element is activated by a power controller, such as a Eurotherm (trade name) device. The thermocouple is connected to the controller to provide temperature feedback. In this way temperature may be gradually ramped to the optimum vulcanising temperature, and maintained there so long as is necessary to provide the optimum bond (along dotted line 36) between patch and tyre inner wall.

Once the curing is complete the controller is disconnected and the pressure A, A'released.

The heating element and thermocouple are left in situ and serve to provide useful reenforcement of the repair.

Second embodiment

Figure 4 shows a self explanatory second embodiment of the present invention of a patch configured as a cross, with identical features to those shown in figure 2 correspondingly numbered.

The present invention provides a patch and repair method which directs curing heat direct to the site of the interface between the patch and the tyre to be repaired. Thus it is no longer necessary to apply curing heat by means of external heating plates or pads, which operate by conduction of heat through the entire thickness of the patch. The present invention therefore allows for a reduction in heat energy supplied, as well as helping to prevent heat damage to outer layers of the patch which may be caused by contact with conventional external heating pads or plates or other heat sources. The heating element integrated into the patch also serves to allow structural re-enforcement which may be tailored

in orientation by appropriate configuration of the element wire within the patch.

Claims

Claims 1. A tyre repair patch formed with an active surface comprising a material which is capable of forming a bond with a rubber tyre in response to heat activation, and a heating element integrated into the patch for heating the bonding material when in use.
2. A patch as claimed in claim 1 wherein the patch has a laminate construction and the heating element comprises a planar laminate component.
3. A patch as claimed in any preceding claim wherein the heating element comprises a wire structure of substantially planar configuration.
4. A patch as claimed in any preceding claim wherein the heating element is formed with a

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plurality of bends to provide a tortuous route through the patch.
5. A patch as claimed in any preceding claim wherein the heating element has a generally planar configuration and is configured to provide a structure which is compliant in bending along one co-planar direction and relatively stiff in bending along an orthogonal co-planar direction.
6. A patch as claimed in any preceding claim wherein the heating element is an electrically responsive element.
7. A patch as claimed in any preceding claim wherein the patch is formed with an integral heat sensor.
8. A patch as claimed in claim 7 wherein the heat sensor is a thermocouple.

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9. A patch as claimed in any preceding claim wherein the heating element is situated adjacent the active surface, for heating thereof in use.
10. A method of repairing a damaged tyre, comprising: providing a patch according to any preceding claim; locating the patch on an inside surface wall portion of the tyre overlaying the damage site ; connecting the heating element to a source of heating energy, and allowing a bond to form between the active surface of the patch and a juxtaposed wall surface of the tyre.
11. A method as claimed in claim 10 wherein compressive pressure is applied to the patch during and/or after heating of the contact surface.

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12. A method substantially as hereinbefore described with reference to the figures of the drawings.