Product category:
Gears, brakes, couplings and engines
News Release from: Eriks UK | Subject: Gearbox repairs
Edited by the Engineeringtalk Editorial
Team on 19 November 2004
Speedy gearbox repair minimises
treatment downtime
The Transline Division of Wyko Industrial Services has recently carried out a skilled repair to a speed increaser gearbox used at a large sewerage treatment plant in North London.
The Transline Division of Wyko Industrial Services has recently carried out a skilled repair to a speed increaser gearbox used at a large sewerage treatment plant in North London Condition monitoring reports showed that the white metal lined bearings in the unit were failing and needed to be replaced against the clock to avoid unplanned downtime
With an output of up to 6000rev/min, the complete set of specialist bearings had to be fitted to both the input and output shafts of the 3.486:1 unit, a process that involved altering the bores to within very tight tolerances.
On a routine condition monitoring survey, conducted by Engenica at the Thames Water purification plant in Edmonton, North London, a speed increaser gearbox showed unusually high thermographic readings.
The unit drives a fan blower, which supplies air to the underground purification tanks where it is passed through the dirty water, feeding the "friendly" bacteria essential to the cleansing process.
Although there was a back up unit on site, at that point an unexpected failure could stop the plant completely.
Leadtimes for a new unit are typically 14-16 weeks and the cost in excess of GBP 20,000, hence a repair was the most viable option.
Engenica contacted their local Wyko Dartford branch who for arranged repair at the Transline division of Wyko.
A team of engineers were immediately organised to arrive at the plant, remove the 1.25t unit and transport it to Wyko Transline in Dudley for further examination.
Mahesh Patel, Technical Manager at the site explains: "Most drive systems require gearboxes to reduce the speed from a motor and increase the torque, but in some applications such as the blower systems at Thames Water, there is a need to significantly increase output speed".
"In this case the ratio of the speed increaser gearbox was 3.486:1, taking input from an 800hp AC motor from 1480rev/min to an output speed of over 5600rev/min".
Due to the high speeds and forces generated, these gearboxes feature a robust double helical gearwheel design with input and output shafts held by white metal lined bearings, which turned out to be the source of the errant condition monitoring readings.
After a successful overhaul proposal in terms of time and cost, Wyko were commissioned to carry out the repairs on the basis of a 3-4 week turnaround.
However, to replace the full set of bearings was no simple task, as the white metal lined designs needed to be machined and seats hand scraped (a skilled art) to produce the special bores.
Wyko is one of the few engineering companies who can provide this service and their engineers achieved the correct running clearances of between 0.004 and 0.006in.
Once the bearings were fitted, all rotating elements of the gearbox were then dynamically balanced and Wyko was able to reduce the residual imbalance to lower than even the original design calculations.
Following the rebuild, the unit underwent an 8 hour test run at full operating speed, while oil flow, temperature and power absorption were closely monitored.
The in-house testing rig is comprised of an inverter driven input drive and a purpose built force lubrication system that hydrodynamically feeds the white metal bearings, enabling the engineers to accurately mirror the set up at the Thames Water site.
The overhauled unit was delivered to the site less than four weeks after the faults had been discovered and cost a fraction of the total replacement value.
Wyko Industrial Services offers a complete repair or replace service for helical and worm gearboxes of any size, ie fractional kilowatt sizes up to 25t+.
Collection from site and a condition report is provided free of charge.
As a supplier of new replacement gearboxes Wyko also offers a choice of units from many of the world's leading manufacturers and keeps comprehensive stocks of standard sizes for next or same day delivery. Request a free brochure from Eriks UK ...
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