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Hot Dip Galvanising of fabricated sheet metal assembly

April 22, 2010

Hello,

We remanufacture obsolete and discontinued spare parts for Land-Rovers.

We have a requirement to HDG a 5' x 3' x 1' fabricated sheetmetal assembly (a Land-Rover firewall, dash or bulkhead). Assembly is mostly 1 mm sheetmetal with folds, ribbing, flanged edges, etc. Some 1.2 mm thick reinforcement and some 3mm thick bracketry. Item is mostly spot-welded with about a total of about 500mm of fillet weld per assembly.

Our competitors seem to have success in having repaired versions HDG'd with little or no apparent distortion, but our fabricators and galvanisers we have spoken to seem to think this item will suffer severe distortion including 'popping' of the spot welds.

Are we missing a trick? What can we do to ensure successful, mostly distortion free HDG? We accept there will be some distortion and that we will need to re-tap any clogged threaded holes.

Regards,

Paul Halley
Parts remanufacturer - Dorking, Surrey, United Kingdom

I would try a stress relieve oven cycle before the galvanization. Welding produces huge stresses in iron parts.

James Watts
- Navarre, Florida
April 26, 2010

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April 28, 2010

These parts are frequently galvanized without distortion. Chassis are perhaps more common (we do perhaps 20-30 a year refurbished chassis), but often people send a box of other bits with the chassis, including the firewall, window frames and lots of small bits.
I don't remember a firewall distorting.

This is quite thin sheetmetal in very folded and welded condition. If it were a flat single sheet, expect distortion. Or if you use a G cramp, sashcramp or similar to "pull" the thing into shape then weld it, you've introduced a lot of potential distortion, but for a standard firewall, blasted clean and perhaps rusty holes welded up, should not be a problem.

Distortion is more often added by the fabricator, but revealed by the galvanizer.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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While HDG of thin walled sheet metal jobs, keep Zinc Bath Temperature 440 degree C and most important DO NOT QUENCH THE WORK IN WATER. Air cooling is advised.
Please try this and hopefully you will get rid of the problem

Umesh Dalela
- Bhuj, Gujrat, India
May 19, 2010