Eliminating manual finishing improves jet fuel pump performance

Eliminating manual finishing improves jet fuel pump performance

Keywords Evans& Price, Finishing, Lead times, Pumps

A multi stage manual polishing process on the bearing journals and side faces of gear sets for jet engine fuel pumps was creating a bottleneck and extended lead times for Argo-Tech Corporation, a manufacturer of fuel pumps for the international aviation industry.

Argo produce more than 30 different sizes of pumps for Pratt & Whitney, General Electric and SNECMA. These have to pump at pressures up to 100bar at temperatures from 65 to320°F.

When the pump is in operation, the fuel also acts as the lubricant, but because of its very low viscosity, bearing journal clearances are low and exceptionally high surface finishes are specified.

Also the side faces of the gears require the same tight tolerances and finishes as the side clearances govern the pump efficiency.

The manual polishing, as well as being time-consuming, resulted in too great a variation between shafts and the requirement of a mirror finish was subject to individual operator interpretation.

To address the problems of achieving consistent quality with reduced lead times and cost, Argo-Tech engineers investigated a number of alternative solutions.

The best all-round solution proved to be a CIMTEC two-station micro finishing machine. This can handle all the sizes of gear sets produced with minimum changeover time between different jobs.

The machine, designed by CIMTEC Inc., employs a patented process called Generating Bearing Quality ­GBQ. This was developed by IMPCO of Lansing, Michigan, and is extensively used throughout the automotive industry for crankshaft and camshaft bearings.

GBQ is believed to be the only microfinishing process that not only improves surface finish, but also improves geometry by removing ­ or greatly reducing grinding lobes, chatter or taper. In the UK and Europe Tamworth-based Evans & Price, a totally-owned subsidiary of IMPCO, build both IMPCO and CIMTEC machines.

At the heart of the process is rigid formed tooling that presses an abrasive film against the part. The formed tooling is instrumental in correcting any geometry errors.

A new section of tape is automatically fed between the tooling and each part. This ensures consistent performance and plays a major role in maintaining quality.

The twin station machine installed at Argo-Tech uses one station to process the gear side faces and the other to process the two bearing journals. The CIMTEC is designed around a"centreless" process. A patented handling system passes the part over the first roll to load the machine, a similar mechanism passes the part over the second roll to unload.

This contrasts with the conventional "through-feed" for centreless machining which can only machine parallel parts. Used in conjunction with relieved rolls, parts such as the pump gears, can be processed on diameters that are smaller than the maximum.

Cycle times are said to be of the order 30 to 50 seconds per part depending on the amount of stock removal. There is a reported 50 per cent improvement in surface finish and the improved bearing geometry contributes to enhanced performance.

The original objective of eliminating a time-consuming and labour-intensive operation has been achieved.

Further details can be obtained from Evans & Price Limited. Tel: +44 (0) 1827 54472 Fax: +44 (0)1827 60906.