World’s largest mechanical clock marks time with lightweight composite hands

News From: CompositesWorld,

Posted on: 5/17/2010

Fabricator epm:technology has produced 12 carbon fiber/epoxy hands for a huge clock destined for the top of the Harmony Tower in Ganzhou, China.


Fabricator epm:technology (Draycott, Derby, U.K.) has produced 12 carbon fiber/epoxy hands for a huge clock destined for the top of the Harmony Tower in Ganzhou, China. The company, a specialist in Formula 1 racing components, was contracted by the designer and maker of the clockworks, Smith of Derby (Derby, U.K.). Reportedly the world’s largest, the mechanical clock will have four faces (12.8m/41.6 ft in diameter) that are two-and-a-half times the size of the face on London’s Big Ben clock tower. Each minute hand measures 7.8m/25.4-ft long, and the hour hands are 6.2m/20.2-ft long. Each dial also has a third 4.4m/14.3-ft hand, which will be painted red for luck and will point to a series of animals to indicate the Chinese lunar month.

A venerable veteran of thousands of public clock projects, Smith of Derby placed the winning bid in a competitive selection process. The company decided to use carbon fiber/epoxy composites for the hands because of their high strength-to-weight ratio. The minute hands weigh just 60 kg/132 lb each, compared to 1 metric tonne/2,204 lb each if cast in steel. Besides ease of installation, the hands reportedly will not require maintenance during the 100-year service period planned between major overhauls.

The hands are sandwich constructions made by hand layup of carbon/epoxy prepreg skins and aluminum honeycomb core and are cured in an autoclave. Prepreg was supplied by Amber Composites (Langley Mill, Nottingham, U.K.). Tooling and bonding jigs for the project were designed and CNC-manufactured inhouse. The hour hands were made in one piece, and the minute hands were made in two parts that were subsequently bonded together. All four hand sets have been painted and shipped to China. The clock installation will be complete by the end of this month.

“It has been a fascinating project,” says Graham Mulholland, managing director of epm:technology. “The minute hands are, by far, the biggest structural components we have ever produced at epm:technology, and we have enjoyed the challenge of working out how best to manufacture them and then putting it into practice.”

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