V-belts for high temperatures

Paul Boughton

Wolfgang Körfer explains how V-belts are driving forward progress across a range of applications

V-belts are used for easy drive design, especially for greater axial shaft distances, quiet operation, simple installation and also a low overall cost in comparison with other drive systems. They were originally introduced to improve drive performance, replacing flat belts made from leather and then rubber.  V-belts transfer torque from one pulley to another by means of friction. The wedge effect from a V-belt in a grooved pulley allows guidance and transmission of a higher torque in a smaller installation space with a smaller preload.

Industrial V-belts made from ethylene propylene diene monomer (EPDM) rubber were first introduced by Gates in 2009, as single Quad-Power III belts. Since then the company has also introduced EPDM multi-belts, which are suitable for drives with fluctuating loads thanks to their increased power density and low vibration.

EPDM, a synthetic rubber, has been used in recent years in a wide variety of products ranging from tyres and roofing materials to gaskets, and increasingly also in the manufacturing of V-belts.

Using EPDM belts at high temperatures

The main advantages of EPDM belts lie in the long maintenance-free period, resistance to severe operating conditions and the operation at temperatures up to 130°C. The very precise ground sides of the belt in combination with narrow and consistent tolerances are advantageous when using the belts in sets or as multi-belts. Conventional V-belts are usable at temperatures of up to 90°C, however, at 60°C there is accelerated ageing of rubber.  If we want to achieve the same durability and performance of the drive, we must considerably oversize the drive at higher temperatures.  For every 10° above 60°C the belt life will be shortened by 50%. This means that at a working temperature of around 90°C, we would need 3.375 times more belts. EPDM belts, on the other hand, produce a stable performance between -40°C and 110°C and can operate above 130°C. For any drive designs over 110°C and below -40°C it is advised to contact an EPDM belt manufacturer.

Belt drives in cars, buses and trucks are generally exposed to higher temperatures, and therefore V- or Micro-V belts made from EPDM rubber are often used in these cases. In industry, its use is also commonplace, both in the production of original equipment and in the optimisation of existing drives.

V-belts and vibrations

Vibrations are an issue that should always be addressed when designing machines with variable speeds. The belts transfer not only the torque, but partly also dampen system vibrations on the way from one shaft to another. This applies, unless the speed is in the resonance band, where vibration is amplified by V-belts. It is necessary to avoid such bands or change the drive design i.e. the drive ratio and shift the resonance band. As has already been mentioned, V-belt drives are characterised by quiet operation, but this is not entirely so. V-belts produce noise by oscillations that occur as the tension force pushes the belt into the pulley wedge on entry and then pulls it out upon exit. When rotating, the belt transfers the energy (torque) by means of friction to the other shaft. This oscillation causes considerable noise, but fortunately the frequency of the noise is low and inaudible to the human ear. However, this oscillation can cause problems with sensitive measuring devices or precision machine tools, etc.

Good results and the smallest vibrations are achieved by bandless cut belts, which are, with few exceptions, produced as notched belts.  For notched belts we have a choice of ground belts and belts with a reinforced tensile layer, usually made of polyester fibres. This reinforcement (cord support) increases the transverse rigidity of the belt and improves the performance and accuracy of the belt profile during operation. It is this group of belts that has been manufactured from EPDM rubber in recent years. They are among the most powerful wedge belts in the market and are available in lengths up to 5m. The length is constrained by the manufacturing technology, i.e. vulcanisation in moulds whose maximum length is only up to 5m at present. The designation of notched belts is defined by the profile XPZ, XPA, XPB, XPC, followed by the reference length in mm. The letter X represents a notched belt, while Z to C are the profile of the belt, which specifies the appropriate pulley profiles from SPZ to SPC.

Elastic belts

Another category of EPDM belts are those designed for drives with fixed axial distances between the shafts and without any means of tensioning or belts in a very confined space. These drives make use of grooved belts with Micro-V PJ or PK profile that can be used for large drive ratios (1:20), high speeds and on small pulleys. These are called elastic belts and are usually custom designed and manufactured. They are tailored to the geometry and dynamic load of a specific machine drive. Because of the custom-tailored manufacturing requirements, they are used in serially produced machines, with volumes ranging from several hundreds to hundreds of thousands of belts.

Thanks to the unique properties of EPDM rubber belts, more and more European manufacturers offer these belts as premium products. It is always a technically advanced product, and one of the outcomes of this is the increasing pressure on the price of the belt, mainly from competition by Asian manufacturers. Unfortunately, increasing numbers of relatively well-known brands outsource the production of belts to low quality Asian suppliers and, as the brand can command a high price, sell substandard products, as they cannot control production and quality. This practice leaves customers disappointed. As regards the belts designed to transfer the power, it is always advisable to request a drive calculation, containing the lifetime and all the technical parameters  -  then the decision is much easier.

For more information, visit www.engineerlive/ede

Wolfgang Körfer is business unit director PT at Gates Europe Industrial

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