Repair service gears up for big job

Renold Gears' gearbox repair service was put to the test just recently when it won the contract from steel maker Corus to refurbish the massive dog-bar gearboxes at its Teesside Beam Mill.

The gearboxes are among the biggest Renold has ever repaired, standing over 1.5m high and weighing in at around 10t each. They are over 40 years old and now require re-engineering to a very high standard.

Renold's ability to repair old gearboxes and improve on the original specification was one of the key factors that helped the company win the prestigious contract.

Corus' Beam Mill manufactures a range of steel sections for the construction industry at its large plant on Teesside, measuring around 1km.

The sections are produced from 10 tonne steel blooms or larger slabs weighing up to 30 tonnes, following which they are cut to length and then stacked in cooling banks where they are allowed to cool to ambient temperature prior to despatch.

It is here, in pits beneath the floor of the cooling banks that the dog-bar gearboxes are found.

Cam arms attached to the output shafts of the gearboxes rise up when rotated and transfer the hot sections over to the cooling banks.

The gearboxes were originally manufactured in 1964 by Crofts Engineers, of Bradford, a company that was acquired by Renold just three years later in 1967.

The original blueprints were found in the company's archives and so components for the gearboxes could be manufactured to their original specifications, but modified for enhanced performance.

The gearboxes are being refurbished one at a time and the first of four was returned to its Teesside home in May 2006.

Renold's repair team improved the original specification in several ways so that the repaired unit was better than when it was new.

The team redesigned and upgraded the material of the output shaft and fitted an internal pumping system to feed lubrication directly to the gears and bearings.

The case was also ultrasonically tested for leaks prior to reassembly with the new gears, shafts, bearings and the new pumping system.

The second gearbox is due to be installed during the plant's shutdown when the next gearbox will be taken away for repair.