GB2209814A - Fatigue-resistant V-belts - Google Patents

Abstract

A method for manufacturing a toothed V-belt comprising assembling and moulding the belt with the teeth set on the outer curvature at the same angular displacement as would usually be provided on the inner curvature of the belt prepared by current processes. The belt is then reversed before use to provide the teeth on the inner curvature. The method may comprise laying up a rubber and fabric composite on a plain metal roll and compressing same between the two halves of a mould whose inner surface is provided with the required toothed configuration. Heat is then applied for vulcanisation, and the resultant band is cut into strips.

Description

Manufacture of V-Belts Having Reduced Fatigue Susceptibility This invention relates to rubber toothed V-belts having intrinsic resistance to failure from fatigue and to a method of manufacturing the same.

Belts of this kind have been manufactured in the past by moulding processes. The most common method has been to lay up successive plies of rubber and fabric, according to the specification desired, on a drum into the surface of which the required configuration of teeth has been cut. The drum is finally wrapped and then introduced into an autoclave to be vulcanised. Once this has been accomplished and the belt removed from the autoclave the laid-up band produced is cut into strips of the width required and these are removed from the drum.

Such products may also be made by building up individual belts on a drum using tyre building technique.

When a V-belt is made in this way it is 'neutral' in terms of stresses until it is bent over a pulley system when the inner layers are compressed as the belt passes over the pulleys, but are in tension when passing between the pulleys. The outer layers are in tension over the pulleys and also, to a lesser extent, between pulleys. Between the outer and inner layers is a zone which is neutral.

It will be understood that the inner layers of the belt pass continually from regions of compression to regions of tension and there is therefore a high probability of rapid fatigue failure. Additionally, in the regions of tension there is an increased likelihood of ozone attack or other oxidative failure. Again, in instances when metal inserts are incorporated into the teeth of the belt the passage from compression to tension will promote failure of the bond between the rubber and the metal.

The present invention describes a toothed V-belt which is substantially free from fatigue in operation.

Also according to the present invention a method of manufacture is described in which belts are made in such a way as to eliminate areas of tension within the inner layers of the belt, thereby rendering them substantially resistant to failure through fatigue.

The method by which this is accomplished is to assemble and mould the belt with the teeth set on the outer curvature at the same angular displacement as would normally be provided on the inside curve of belts made by the current processes.

This may be done by laying up the rubber and fabric composite on a plain metal roll and finally compressing the whole between two halves of a mould in which the teeth have already been cut to the required configuration, then bringing the whole to the vulcanisation temperature required. Heat may be applied by inserting the whole into an autoclave or by direct heating of the mould by steam or other means. The band is then cut into strips and removed as individual belts, in the manner already indicated.

Before use, a belt made according to our method has to be reversed so that the teeth then lie on the inside curvature, when the whole inside surface passes into a state of compression. This state of compression is retained even when the belt passes through straight regions of the cycle, for the compression is not reduced to zero unless the curvature is reversed to that used in the original moulding operation. Therefore in service the fatigue life of the belt is enhanced and ozone and oxidative attack minimised, so giving an advantage over belts made by the current normal process.

In a belt made by this process, the inside surface goes into tension when it is reversed, so becoming the outside. This tension remains even when the belt enters the straight portions of the cycle. The fatigue cycle does not pass through zero and therefore even this situation represents an improvement on that encountered with belts made by the conventional process.

If there are metal inserts in the base teeth these prevent any expansion of the rubber at the base of the said teeth.

When the belts as conventionally moulded enter a region of tension the whole of the tension is transmitted to the area between the teeth and the extension in these areas is approximately twice that found in a flat belt of similar dimensions.

Because the fabric is asymmetrically placed, the improvement is better than might at first be expected. On reversing the belt the change in tension or compression is proportional to the displacement from the neutral axis. The thin cover, which when in use becomes the outside of the belt, is much closer to the neutral axis than the drive portion. on the inside curvature. Thus the increase in tension outside is small compared with the the increase in compression on the inside. However, ozone attack on the outside of the belt is now a danger. A cover compound with low modulus has the effect of reducing the tension force in the outside layer thus helping to minimise such attack.

A further aspect of this invention is therefore to provide a cover compound of rubber of low modulus which will act in this way. One method by which this may be done is to use a cover compound especially formulated for resistance to ozone, as well as oil, and having a modulus slightly lower than that normally found in a conventional belt.

Another method of reducing tension in the thin outer layer of the belt is to make use of a delayed cure system in the cover compound. Once the tooth portion is fully cured the belt is reversed and subjected to a post-cure in order to vulcanise what is then'the outside layer. Since this layer is not fully vulcanised when reversed, the tension in it diminishes during the early part of the post-curing cycle.

Whilst the invention has been described in relation to rubber toothed V-belts, it is to be understood that the invention will also have applicability to V-belts in general as sell as to the production of other endless belts particularly those built up from layers of rubber and fabric.

Claims (7)

1. A method for manufacturing a toothed V-belt comprising assembling and moulding the belt with the teeth set on the outer curvature at the same angular displacement as would usually be provided on the inner curvature of the belt prepared by current processes.

2. A method as claimed in claim 1, comprising laying up a rubber and fabric composite on a plain metal roll, compressing same between the two halves of a mould which the teeth have already been cut to the required configuration, bringing same to the vulcanisation temperature required, subsequently opening the mould, cutting the resultant band into strips and removing same as individual belts.

3. A method as claimed in claim 2, in which heat is applied by inserting the device into an autoclave or by direct heating of the mould by steam or other means.

4. A method as claimed in any preceding claim, in which metal inserts are provided in the base region of each tooth.

5. A method as claimed in any preceding claim in which the cover layer of the belt is formed from a rubber compound of low mudulus.

6. A method as claimed in any preceding claim, substantially as hereinbefore described.

7. A V-belt whenever prepared by a method as claimed in any preceding claim.