GB2296335A

GB2296335A - A method of checking the structural integrity of tyres

Info

Publication number: GB2296335A
Application number: GB9425958A
Authority: GB
Inventors: Martin Howard Walters
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1994-12-22
Filing date: 1994-12-22
Publication date: 1996-06-26
Anticipated expiration: 2014-12-22
Also published as: GB2296335B; DE19547303A1; GB9425958D0

Description

1 2296335 A METHOD OF CHECKING THE STRUCTURAL INTEGRITY OF TYRES The

present invention relates to a method of checking the structural integrity of tyres and particularly but not exclusively to checking the tread region of heavy duty radial tyres for vehicles such as trucks or buses.

Tyres are complex fabrications of reinforcing fabric plies and numerous rubber components each of a specific shape and composition designed to suit a particular role in the structure. In manufacturing the tyre it is required to assemble these elements in a consolidated structure avoiding the inclusion of trapped air or moisture which might cause voids. In use of the tyre it is important that the adhesive bonds between the numerous components hold such that the structural integrity and hence the safety of the tyre is assured.

Heavy duty tyres have wide relatively flat ground contacting tread regions reinforced by a breaker assembly which is disposed adjacent to and radially outside of the main tyre carcass reinforcement and underlying the tread rubber. Such reinforcing 1 2 breaker assemblies normally comprise three or more breaker plies of- fabric each consisting of rubber coated metallic cords laid parallel to each other and inclined with respect to the equatorial direction of the tyre.

Conventionally the metallic breaker ply cords used in heavy duty tyres comprise steel wires which are surface coated with brass to promote adhesion to their rubber coating. In the cutting of the breaker plies from the fabric sheet, the metallic cords are cut at an acute angle to the cord direction resulting in cut faces of the wire which are both sharp and devoid of brass coating. The combination of the factors of high stress concentration at the breaker edge, sharp cut ends of the cords and poor adhesion due to lack of brass coating promote the cutting of the rubber and breakdown of adhesion at the breaker edge. In use of the tyre this so-called "breaker edge looseness" can propagate far beyond the breaker edge and this breakdown in the structural integrity of the tyre is a major cause of premature failure of tyres.

In the caSEt of heavy duty tyres it is common practice when the tread pattern has worn beyond 1 3 acceptable 11MitS to retread the tyre, such that two or three or even more tread lives may be obtained with the same carcass. The retreading operation involves selecting suitable worn tyres which are without visible damage and removing the remaining tread rubber which may be in the order of up to 7mm thick by buf f ing or grinding to leave only a thin layer of rubber over the outermost breaker ply. This removal of the remaining tread is a time consuming operation which has to be done carefully to avoid damaging the underlying breaker package. Only after the removal of the tread rubber does it become possible to assess the extent of any structural breakdown of the breaker resulting from breaker edge looseness or other causes. Thus it is the case that significant numbers of tyres are found unsuitable for retreading only after the expensive operation of removal of the tread has been carried out.

Accordingly it is an objective of the present invention to provide a method of checking the structural integrity of a tyre and in particular to provide a method of determining the extent of structural breakdown due to breaker edge looseness 4 in heavy duty truck tyres without the necessity of first removing the tread rubber.

According to the present invention a method of checking the structural integrity of a radial tyre comprises heating the surface of the region of the tyre to be examined by applying an external source of continuous low intensity energy having an harmonically modulated intensity, viewing the heated area with a zhermal imaging camera to detect emitted thermal infrared radiation at points across the surface, coriparing the emitted thermal radiation with the applied low intensity energy to provide a thermal picture of the tyre surface and determining discontinuit:.es in the thermal picture obtained such that voids or other defects in the structure are found.

Preferably the thermal imaging camera detects at each point on the surface emitted thermal infra-red radiation intermittently at regular intervals of time throughout the harmonic period of the applied low intensity energy source and the total emitted thermal infra-red radiation at each point is derived from the intermittently detected radiations at that point.

The comparison of the detected emitted thermal radiation and the applied low intensity energy may be carried by interference set up between the two.

The applied low intensity energy may be radiant energy such its infra-red radiation or visible light.

The thermal imaging camera may be of the raster scanning type wherein a thermal picture of the area under examination is obtained keeping the camera and tyre in a fixed relationship. Alternatively in a preferred me-hod the thermal imaging camera is of a less expensive linescan type and the tyre is rotated on its axis by a small amount such that the thermal picture of the viewed area is built up from a series of single-line scans.

Further aspects of the present invention will become apparent frcm the description, by way of example only, of cne embodiment of the invention in conjunction,,iith the following drawings in which:

Figure 1 shows a schematic diagram of a front view of an apparatus used in carrying out the present method of the invention; and 6 Figure 2 shows a schematic diagram of a side view of the apparatus of Figure 1 taken in the direction of arrow "V".

The apparatus shown in Figures 1 and 2 comprises a tyre 1 mounted rotatably on an axle 2 held on a stand 3. A power supply 4 is connected to a modulation unit 5 which provides a modulated power supply to an infra-red heater which is directed towards the tread surface of the tyre 1. Adjacent to the infra-red heater 6 is a thermal imaging camera 7 di..; posed to scan the region of the tyre tread surface heated by the infrared heater 6. The output from the thermal imaging camera 7 is taken via a computer 8 to a visual display unit 9.

In the method of the invention the tyre I is rotated in the direction of arrow R as shown and the tread surface is heated by continuous low energy infra-red radiation whose intensity is sinusoidally modulated with a low f requency of less than 5Hz. The heated tread region is viewed by the thermal imaging camera 7 which is arranged to make single line scans across the tread stirface from edge to edge. The output signal from the thermal imaging camera 7 is taken to an electronic computer 8 which for each point 7 axially across the tyre tread produces a signal proportioned to the emitted thermal radiation which is sent for display to the visual display unit 9.

By synchronisation of scan of the thermal imaging camera 7 with the rotation of the tyre 1 a thermal picture of the whole area of the tyre tread can be built up. Alternatively a more expensive raster scanning thEtrmal imaging camera may be employed removing the necessity for synchronising the camera scan with the tyre movement.

In a preferred method according to the invention the operation of the computer 8 is synchronised with the operation of the modulation unit 5 such that for each point across the axial width of the tyre tread the computer stores four thermal image output signals S,-S.,, each output signal being taken at a different time within the period of one modulation of the power output to the infra-read heater but separated by equal intervals of time. The computer 8 then calculates for each point a corrected thermal image output signal Sc for sending to the visual display unit 9. The corrected thermal image output signal Sc may be calculated according to either of the formulae:- 8 Sc = ARCTAN ( (S1-S3) / (S2-S4)) or Sc " 1 (-cl-S3) 2 + (S2-S4) 2 1 h Use of such a corrected thermal image output signal provides improved definition of sub-surface flaws.

The assemblE.d thermal picture of the tyre tread region is sent for display to the visual display unit 9. By arranging for different values or ranges of values cf thermal image output signal to be display by differing colours, contrast or patterns a visual thermal map of the tyre tread region may be readily presented. Since the presence of structural features or voids or flaws in the tread structure effect the emitted thermal radiation from the adjacent points on the thread surface, such features or flaws arc- immediately apparent on the displayed thermal map by their different colour, contrast or pattern from the surrounding regions Whilst the above embodiment has described a method utilising an external source of continuous infra-red energy to heat the tyre alternative sources such as modulated radiation in the visible light spectrum.

9

Claims

A method of checking the structural integrity of a radial tyre comprising heating the surface of the region of the tyre to be examined by applying an external source of continuous low intensity energy having an harmonically modulated intensity, viewing the heated i-irea with a thermal imaging camera to detect emitted thermal infra-red radiation at points across the Surface, comparing the emitted thermal radiation with the applied low intensity energy to provide a thermal picture of the tyre surface and determining discontinuities in the thermal picture obtained such that voids or other defects in the structure are found.
2. A method of checking the structural integrity of a radial tyre according to claim 1, wherein the thermal imaging camera detects at each point on the surface emitted thermal infra-red radiation intermittent',.y at regular intervals of time throughout the harmonic period of the applied low intensity energy source and the total emitted thermal infra- red radiation at each point is derived from the intermittently detected radiations at that point.
3. A method of checking the structural integrity of a radial tyre according to either of claims 1 or 2, wherein the comparison of the detected emitted thermal radiation and the applied low intensity energy is carried out by means of an interference set up between the applied energy and the emitted radiation.
4. A method of checking the structural integrity of a radial tyre according to any of claims 1 to 3, wherein the applied low intensity energy is radiant energy.
5. A method of checking the structural integrity of a radial tyre according to claim 4, wherein the applied low:-ntensity energy is infrared radiation.
6. A method according to claim 4 wherein the applied enerc.ly has a wavelength in the visible light spectrum and the interference is arranged to provide a display pattern of lighter or darker regions on that part of the tyre tread surface above or adjacent to a defect in the structure.
7. A method according to any of claims 1 to 6, wherein the thermal imaging camera scans the viewed areas in a plurality of lines in the manner of a raster scan.

S. A method according to any of claims 1 to 6, wherein the thermal imaging camera scans the heated 11 area in a single line and after each scan the tyre is rotated a small amount about its axis such that the thermal image is built up from a series of single scans.