Power Transmission
Material success for timing belts
The driving force for innovations in timing belts has been the automotive industry, with the increasing demands on service life, noise characteristics, temperature resistance and reliability. David Clark reports.
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n recent years, the development of timing belts has been heavily focused, on the one hand, on the optimisation of timing belt geometry to increase the power density and to improve noise characteristics and, on the other hand, on the
development of new, more powerful and more resistant materials. As a result of new engine technologies and improved
sealing of engines, the ambient temperatures and dynamic forces have increased significantly, while there have also been significantly higher service life expectations. The dynamic loads on some engine types, eg direct-injection diesel engines, have almost tripled in the past 20 years, with ambient temperatures rising above 130°C. The result of this was that traditional timing belt materials could no longer be used. With new, constantly improving materials,
it has been possible to fulfil these requirements without ignoring the compactness of the drives. In addition to the traditional automotive application, the camshaft drive, the new material developments are increasingly finding their way into industrial applications. The fabrics are still based on nylon, but
today they are designed using special coatings, so that the wear behaviour has been improved by a factor of three. In addition to the traditional chloroprene
material, temperature-resistant rubber compounds such as HNBR have become much more prevalent and are used as standard in the automotive industry. They are permanently resistant up to 135°C and at the top end of the scale up to 150°C. In order to increase the tooth strength, ie to prevent
teeth shearing off during transmission of high torques, increasingly high-strength rubber materials are being used, and these materials are further reinforced by the inclusion of fibres within them. This means that 30-50 per cent higher power values are possible, depending on the timing belt technologies. Glass fibre is still primarily used as a traction mechanism. Due to its favourable bending properties, this
Fig. 1. Because of new engine technologies and improved sealing of engines, traditional timing belt materials could no longer be used.
The high-strength glass-fibre tensile members were selected for the latest Gates innovation. These afford the PowerGrip GTX high-performance synchronous belt, one of the strongest rubber synchronous belts on the market, increased strength and lower strain, low-noise operation and an extremely high resistance against shock load. It is suitable for the widest range of applications, for which long service life and thorough operational reliability are mandatory, and serves the heaviest drives in the most diverse industries and markets.
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material is an excellent choice as a traction mechanism for dynamic drives, especially in conjunction with small pulley diameters. Here too, there are further developments with regard to flexibility and traction characteristics. High-strength glass-fibre tensile members demonstrate 30-40 per cent higher tensile strength and tensile members made from aramid, an equally high-strength and high-modulus material, are available as an alternative.
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