Re-Treading of Truck Tyres

Tyres for cars and trucks has become a very advanced construction, consisting of many layers of different materials. The outer layer is the tread which is made from rubber. The tread can be exchanged, when it is worn, or if it gets damaged. Earlier, a tyre was discarded, when the tread was worn out, but the expensive tyre constructions and the wish for re-cycling of materials means that a retreading of the tyres does pay.

Retreading of tyres is made by first removing the old tread and afterwards applying a new one. Naturally, it is important that only the old tread is removed and that the layers below are not damaged. It is also important that the tyre is round after the planing off, so that it will also be round, when the new tread is applied. To make the tread fit the pattern at the junction, the cir­cumference of the tyre must fit very accurately to the tread.

The used and worn tyre is mounted in a holder, and the tyre is inflated by compressed air. The tyre is rotated, while an ODS 200 sensor measures the profile of the tread, not only on the run­ning surface but also up the sides. A computer calculates how much is to be planed off to obtain the optimal result. After the planing, the tyres is measured once more. This is done to secure that the re­sult was as expected and to make possible for the computer to allow for wear in the planing tool. Even though the new tread can be stretched or pressed a little bit, the accuracy of the tyre cir­­cumference must be within a few millimetres. The process of measuring and planing a tyre takes app. 3 – 5 minutes. Out of consideration for the safety of the operator, the laser in the ODS 200 is switched off, when no tyre is mounted in the machine. This is done by means of the sensor’s ‛La­ser inter­lock’ output.

Black rubber is the type of material which is most difficult to measure optically, since the dull black surface absorbs the light almost 100 %. ODS 200 is equipped with an almost intelligent optical system, controlling the amount of laser light emitted to the object as a function of the amount that is reflected to a built-in light meter. Thus, an optimal light intensity is obtained on the CCD camera in sensor, for almost any object – including black rubber.

Another problem of the retreading machine is that the sensor is exposed to a very severe shak­ing during the planing off of the tread. The sensor is built to withstand this shaking, but as a precaution it is mounted in vibration damping material.