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Seawater-cooled clutches and brakes

27 June 2011

A composite water jacket has been developed that enables seawater to be used directly to cool clutches and tensioning brakes deployed in offshore duties, without fear of corrosion damage

A new design of composite water jacket from Wichita Clutch enables seawater to be used to cool tensioning brakes, improving the operational reliability of marine-duty water cooled clutches and brakes used for tensioning on offshore oil and gas platforms and in other heavy-duty applications. The new composite water jacket enables Wichita’s AquaMaKKs clutches and brakes to be cooled either with salt water, or water with low pH levels.

Hitherto, the industry standard approach was to use cast iron water jackets, alternating with copper wear plates, to dissipate the heat generated in heavy-duty tensioning applications. In marine environments, however, salt corrosion has proved a problem for cast iron jackets, which were subject to frequent repair or replacement.

The composite material used in the new water jackets was jointly developed by Wichita and a partner firm. Several polymer combinations were tested before the design team settled for a blend that satisfied one essential design requirement - it had to be as strong as the original iron part and be capable of coping with the stresses placed upon it.

In the event, structural testing proved that the AquaMaKKs 36-inch diameter composite water jacket could cope, even when the part was submitted to more than four times its maximum design load. Further testing, to determine the longevity of the composite jackets has been ongoing for two years at Wichita's engineering test laboratory, and this has shown that the composite water jackets are at least as long-lived as the cast iron jackets, while also providing superior corrosion resistance in offshore applications.

Material selection aside, the second most difficult technical challenge facing the AquaMaKKs design team was how to achieve satisfactory connections for water entering and leaving water jacket. Initially, because composite materials can be moulded into threads, it was thought the water porting could be built into the base material; however, this configuration failed to meet the level of robustness demanded by the industry. The appropriate connection method was finally achieved by including metal threads (both male and female) within the composite material moulding.

Since the composite material also acts as an efficient thermal insulator, the cooling water moving through the water jacket conducts more of the frictional heat compared with that of a cast iron water jacket. The surrounding parts in a unit are subsequently maintained at a cooler temperature, which contributes to longer life.

As well as their anti-corrosion benefits, composite water jackets offer an additional benefit of weight reduction, with some units weighing considerably less than half that of cast iron jackets. For example, the 36-inch AquaMaKKs cast iron water jacket weighs 375 pounds, whereas the composite version weighs just 90-96 pounds. This becomes significant for the multi-plate (friction disc) design where each of the copper friction discs requires two water jackets, one on each side of the disc. Depending on the braking/holding requirement of the application, some units may have up to four discs and eight water jackets.

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