Dear Sirs, We have a problem and were wondering whether you could help us in sorting this out ? We are welding the backplate of a automobile brake assembly using a grease balanced multispot fixture. The thinner sheet is 0.8 mm. The spots, six in number, are equi-spaced on a PCD of 350 mm. We attempted to weld this on a 500 KVA Projection welding machine. The weld strength is adequate, however, spot depressions vary from 0.5 mm on the side of the platen near the transformer end to less that 0.1 mm on the side away from the transformer. This is not acceptable to the buyer of this component. This machine runs on the older system of a 3 phase frequency converter principle. The operating frequency is 1/3rd of 50 Hz i.e. 16.67 Hz. As a result of this introduction of inductances into individual current paths had negligible effect. Do you think a current equalising transformers like the ones from Roman can correct this problem ? What is my other option ? Do you think having a multiple secondary transformer will help ? Or would a Single Phase 50 Hz transformer with the weld equalising transformers be adequate to sort out the problem. We have a number of other Projection Welders for trying out all options. Would you be kind enough to help us out ? Regards Prithvish Chakravarti

-- Prithvish Chakravarti (welding@technologist.com), February 14, 2000

Answers

Most brake shoe welders in the USA are special seam welders. The seam weld head is brought down under pressure after the web has been clamped into a head and tail stock arrangement. The part is rotated and projection welded. The units are mostly 300 KVA and larger single phase units and three phase low frequency converter type are used where primary power is limited.

New machine price range is $225,000 to $275,000.00 US and delivery is approximate 24 to 30 weeks ARO.

If we may be of any further service, please feel to contact us direct. Good luck on your project.

Bob Balla T. J. Snow Company, Inc. 6207 Provence Street Chattanooga, TN 37421

Phone: 423-894-6234 423-308-3161 (direct line) Fax: 423-892-3889 e-mail: bobballa@tjsnow.com

-- Bob Balla (bobballa@tjsnow.com), April 24, 2001.