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Multi-layer coating protects chain against corrosion

15 November, 2007

Tsubaki has developed a RoHS-compliant carbon steel roller chain with a specialised coating that allows it to be used in wet conditions without corroding. The multi-layer coating process is modified for different parts of the NEP chain, balancing corrosion protection against wear resistance. It is claimed to outperform alternative technologies.

Waterproof drive chain is not suitable for most "wet" applications because it is usually produced using a combination of stainless steel or engineered plastics, which are not as strong as carbon steel chain and need to be oversized for high-load applications. A corrosion-resistant chain based on carbon steel chain is therefore more attractive because it can operate with standard power transmission components and sizing calculations.

Various coating methods have been used in the past to protect carbon steel chain against corrosion but some of these – such as chromium – are extremely hard and have tended to peel off because of surface pressure exerted by drive sprockets. Another approach, galvanisation, is softer but wears away quickly as the chains articulate, leaving critical components open to corrosion.

Tsubaki NEP chain

Tsubaki’s NEP chain (above) uses a combination of three layers of surface coating, with a resistant base layer bonding a harder, wear-resistant, coating onto the chain bushes where they come into contact with sprocket teeth. A tough external coating covers and seals all the other component surfaces.

Tsubaki claims that in a saltwater immersion test, the new chain survived more than 300 hours of immersion without any sign of corrosion. Under similar circumstances, a standard carbon steel chain would corrode to the point of being useless within 24 hours.

Samples of the NEP chain have been tested for up 1,500 hours, and have shown only slight surface discolouration.

In practical applications, where it is more common for chain to be exposed to far lower concentrations of potentially corrosive water-based solutions, the new chain is expected to have extremely long service life. In most applications, it will also be far less expensive than oversized stainless steel chains.

The drive chain is compatible with standard sprocket dimensions and is available in various sizes and configurations. A specialised, self-lubricating lambda version is planned.

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