Worm gear helps astronomers with Big Bang theory

Rochdale-based machine tool and precision gear specialist Holroyd is playing a major role in helping astronomers investigate the 'Big Bang' theory for the global evolution of the universe. Dean Palmer reports

Rochdale-based machine tool and precision gear specialist Holroyd is playing a major role in helping astronomers investigate the 'Big Bang' theory for the global evolution of the universe.

The company, now part of Renold Precision Technologies Group, is supplying a dual lead adjustable backlash worm gear to provide precise orientation on a new radio telescope being built by the Instrumentation Group at Cardiff University to measure levels of 'cosmic background radiation' in the universe.

Perhaps the most conclusive piece of evidence supporting the 'Big Bang' theory is the existence of an anisotropic (meaning not the same in all directions) radiation bath that permeates the entire universe.

Known as the 'cosmic microwave background' or CMB, scientists and astronomers have concluded that the CMB is the relic thermal radiation from the creation of the universe, released about 300,000 years after the 'Big Bang'.

The Cardiff Instrumentation Group plans to study the anisotropy of the CMB (fluctuations in its temperature) in order to determine how the Universe behaved at the dawn of time (around 15 billion years ago). The means by which the Group plans to undertake its study is a new 2.6 metre diameter radio telescope. Many of the University's experiments are mounted upon the University roof at Cardiff, but this one is different.

Its location is to be one of the driest places in the world, the Atacama desert plateau in Chile at an elevation of 5,000 metres. Final completion and commissioning of the radio telescope in Chile is planned for the middle of 2004. Meanwhile, building of the telescope is at an intermediate stage, with delivery of the worm gear (which inclines the radio dish) imminent.

Designed with a dual lead, 405mm centre distance and a reduction ratio of 130:1, the worm gear is being manufactured at Holroyd's specialist gear manufacturing facility in Rochdale, which currently holds the world record for worm gearing efficiency (recorded at 98%).

"The advantage of our precision, dual lead specification worm gears is that they provide the facility for backlash adjustment, to offset wear," said Steve Whitehead, Holroyd sales director for the Worm Gears division. "We've supplied similar worm gears to other observatories, the last one being Geneva, so we are fully aware of the levels of precision required in astronomical observations. In this application, the pointing accuracy of the telescope is 0.5 minute of arc, and the maximum level of angular backlash from our worm gear is 10 to 11 arc seconds."

The Cardiff worm gear was manufactured using Holroyd's new 'worm gear contact analysis program'. This reduces both the margin for error in the manufacture of precision, made-to-order gear sets and also lead times. It also ensures greater manufacturing consistency and longer gear life by providing benefits such as improved controllable contact spread, smoother unscraped finish, enhanced lubrication and the ability to cut wormgears off-load to offset distortion due to loading during use. "The wormgear analysis program functions as an integral part of our wormgear design process," added Whitehead.

"It removes our reliance on traditional – and declining – skills-based manufacturing, enabling us to eliminate trial and error from the design and production process using contact prediction graphics and revised calculations.
The result is that we are able to manufacture accurate and efficient gear sets right first time."

From its state-of-the-art manufacturing facility in Rochdale, UK, Holroyd supplies large wormgears, with centre distances up to 1041.4mm, for a wide range of demanding applications throughout the world, including steel mill screw-downs, coal pulverizers, process mixing and elevator drives. DP

Author
Dean Palmer

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