GB2232492A

GB2232492A - Method of measuring tyre wear

Info

Publication number: GB2232492A
Application number: GB8912840A
Authority: GB
Inventors: Martin Howard Walters
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1989-06-03
Filing date: 1989-06-03
Publication date: 1990-12-12
Anticipated expiration: 2009-06-03
Also published as: JPH0367708A; GB2232492B; GB8912840D0

Abstract

Method of measuring tyre wear comprising applying two or more layers of different coloured paints to ground engaging tread surface, bonding the paint layers to the tread surface and to one another, running a tyre on a vehicle for a short distance to wear the paint layers and assessing the rate of wear of the tread surface by the exposed colours. Preferably a rubber based paint including an ultra accelerator is used to provide the necessary bond between the layers.

Description

METHOD OF MEASURING TYRE WEAR This invent ion provides a method of measuring tyre wear and is applicable to tyres for cars, trucks and the like.

There has long been a need for an accurate method to predict the wear rate of a tyre tread and also the wear distribution across the pattern. Present techniques include determining the tread groove depth with a potentiometer probe or a laser measuring des-ice, and measuring repeatedly after periods of -running the tyre on the road. Such techniques, however, are slow as a test distance of at least 5000 Kilometers is needed before any meaningful measurement can be made and even then indications of uneven wear across the patterns are very poor.

Another test used to predict the wear rate of car tyres has been the so-called tape test in which a layer of strong self-adhesive fabric reinforced tape is stuck to the tyre surface and the wear is assessed from the damage to the tape after a short distance of running. This method however is not very discriminating and problems can arise from failure of the adhesive bond.

It is an objective of the present invention to provide a method of quantitatively assessing the wear rate of the ground-engaging surfaces of a tyre after only a very limited road mileage which allows the wear rate effects of the pattern or the tyre structure to be accurately predicted.

According to one aspect of the present invention a method of measuring tyre wear comprises applying two or more layers of different coloured paints to the ground-engaging tread surface, bonding the paint layers to the tread surface and to one another, running the tyre on a vehicle for a short distance to wear the paint layers and assessing the rate of wear of the tread surface by the exposed colours.

Several paint layers are preferably applied and five have been found to be a useful number.

The type of paint is preferably a rubber-based paint and the bonding of the paint layers to themselves and to the tread surface is obtained by using an ultra accelerator added to the paint immediately prior to applying to the tyre. The ultra accelerator causes crosslinking of the paints both to the other layers and to the surface of the tyre tread and this is preferably assisted by means of heating the tyre in an oven. Crosslinking the paint in this manner reduces the tackiness, and thus the amount of dirt picked up from the road.

Moreover, the tyre surface can readily be cleaned with solvent. The advantage of using the rubberbased paints is that they are of similar flexibility and other properties to the tread rubber and so they do not crack or flake as the tyre deflects.

A preferred method of applying the paint to give an even thickness of coating is to use a spray technique allowing between successive coats a short time for the solvent to dry but not sufficient time for the layer to begin to cure. It is preferable to use a spray gun suitable for high viscosity paints (e g Binks Bullows Model 830).

Further aspects of the present invention will become apparent from the following description by way of example only of one embodiment in which a five layer paint system was used on a car tyre.

The description is to be read in conjunction with the attached diagrammatic drawing which shows the resultant wear pattern across a tyre tread.

A new car tyre was taken from the production line and the spue pips and mould lubricant were removed by means of running the tyre on a vehicle for 10 Kilometers to give a short conditioning period and then cleaning the tyre several times with naphtha on a cleaning paper.

Five different paint layers in colours white, red, yellow, blue and green were then applied successively to the tyre using a spray gun. The paint used was of the Vitabond type made by Vita- Sal ford and had a 17% solid content in a petroleumbased solvent. The solids comprises 100 parts of natural rubber with a conventional sulphur cure system, 170 parts of white filler and the necessary colour pigment.

To produce a vulcanising system for the paint zinc dibutyl dithio carbonate was added at the rate of 6ml per 100ml of paint.

After applying each layer of paint five minutes was allowed for the layer to dry before the next layer was applied. Finally the tyre was placed in an oven at 100 degrees Centigrade for twelve hours to provide a full crosslinking of the layers of paint and to give a good bond between each of the layers and to the tread surface. The sufficiency of cure could be checked by the fact that the paint layers were not dissolved in naphtha.

Whilst it would be expected that the vulcanisation system used would give a cold cure avoiding the need to put the tyre in an oven that was not in fact the case but alternative systems to give a cold cure can be used, for example by adding zinc isobutyl xanthate to the zinc dibutwl dithio carbonate.

Immediately following curing the tyre was fitted to a vehicle and run round a test route giving a mixture of service conditions, taking care to maintain prescribed speeds, particularly on corners. After a short distance of 15-50 Kilometers the different paint layers were abraded and when it was seen that each of the layers had been abraded at least in part of the tyre tread surface the tyres were removed and cleaned of oil and dirt contamination by wiping with acetone and then washing with a water-based detergent system to ensure cleaning without further abrasion of the paint films. The tyres were then photographed in colour to provide a permanent record.

The test technique has also been proven on truck tyres where once again the layers were found to wear in a short distance.

The test method has been shown to give a good correlation to the irregular wear and general wear patterns found in several conditions and long term road testing.

sing the colours of this example which were white, blue, yellow, red and green, finishing with the green on the upper surface the photographs could be converted to a quasi-numerical measure of wear rate by ascribing values to the colours as follows: Green No. 1 Green/Red No. 2 Red No. 3 Red/Yellow No. 4 Yellow No. 5 Yellow/Blue No. 6 Blue No. 7 Blue/White No. 8 White No. 9 White/Black No.10 Black (ie tread rubber) No.ll Figure 1 shows a simplified version of a test result showing different areas where different colours were exposed. For example in area 1 the colour observed was black whereas in areas 2 it was white, showing that the wear rate in the white areas was at rate 9 whereas in the areas where it was black the rate was at rate 11. As will be realised the wear rate across the pattern is shown in great detail, including the higher wear rates at the edges of the tread blocks and the lower wear rates within solid ribs.

It is believed that the accuracy of the system is dependent on the effective bond between the layers, including the crosslinking of the paint to the tread surface by the highly active ultra accelerator. This system does not affect the tread rubber itself as long as the wear test is carried out within a few days of the application of the paint. If the tyres, having been painted, are left for a substantial period, of for example 3 or 4 weeks, then the ultra accelerator would be expected to begin to change the properties of the tread rubber of the tyre which will in turn affect the flexibility of the tread and therefore the wear results obtained.

Claims

C L ,4

1. A method of measuring tyre wear comprising applying two or more layers of different coloured paints to the ground-engaging tread surface, bonding the paint layers to the tread surface and to one another, running the tyre on a vehicle for a short distance to wear the paint layers and assessing the rate of wear of the tread surface by the exposed colours.

2. A method according to claim 1 wherein the coloured paint comprises a rubber-based paint and an ultra accelerator is added to the paint to cause bonding of the rubber paint layers to one another and to the tread surface.

3. A method according to claim 2 wherein the curing of the rubber-based paint with the ultra accelerator is assisted by heating the tyre in an oven.

4. A method according to any one of claims 1, 2 or 3 wherein the paint layers are applied to the tyre by spraying to provide a controlled even thickness of paint for each colour.