cooling welds,minimising distortion

[sambabug]

Have heard ov cold quenching welds with a wet towel,is there any thing that u can get to minimise distortion like sum form ov heat sink etc?.

 

[storm monkey]

Distortion is caused by large heat gradients, and adding hot metal that then cools and contracts. Pre-heating parts will help reduce distortion as well as keeping the weld as cool as possible (lower current, short bursts, intermittent welds etc). Post weld stress relief is also an option, and again usually involves heat. I think quenching a part with a wet towel is going to increase distortion and induce residual stresses, as you rapidly cool and contract parts of the welded items.

Phil

 

[English Steve]

Also, quenching the weld will harden it and make it (and the surrounding metal) more prone to cracking. Leaving it to cool naturally will normalise the weld and surrounding metal leaving it more ductile.

Steve

 

[Johnny™]

there is a type pf putty you can place adjacent to the weld that absorbs alot of the heat generated.... seems to work well, especially on car bodywork

its called cold front....
you can get it here

http://www.frost.co.uk/item_Detail....ID=33&frostCat=Welding&frostSubCat=&subCatID=

ive read impartial reviews and its does really work!

 

[MrFluffy]

Thats more to stop the weld heat going into things adjacent and ruining them (eg oil seals, pvc coated wiring etc) rather than to stave off distortion. A cold area followed by a hot area will actually promote distortion as the two pieces expand at different rates...

If Im worried about distortion on a assembly, say for instance a crankcase with all its bearing surfaces etc, Ill assemble the cases and torque them up as much as possible, and pop them in the shed wood oven before and after. During welding I stop putting fuel on the fire so it cools gently that way its all at the same temp and no sudden changes to cause problems.
You have to bear in mind this is also potentially a bad thing if theres interference fits in there too or its been tempered by heat treating or the like. I also use the same stove but with the dampers open to remove cylinder liners from blocks...

 

[sambabug]

ok stitch weld ,power settings etc can do.plumers torch to gently heat areas to be welded sounds interesting ,anymore tips?what cooldown time do ya give welds etc?whats post weld stress relief?

 

[ozzman]

little tip. if you pre-heat make sure you clean the area after you have heated it to remove any carbon deposits.

as you will be adding more carbon into the mix, so you will end up with a more brittle weld.

oh yea and when the welds cold its cooled down sufficiently , if you dont let the weld cool down of its own accord or by post heating in the correct manner the piece to be welded will not return to its original form.

 

[MrFluffy]

Another tip if the part is small enough, is to wrap it in silver foil before preheating, then it doesn't oxidise during the process and require cleaning.

 

[sambabug]

excellent !guys

 

[storm monkey]

There are many methods used for post weld stress relief. The most common is probably using heat, in which the welded part is raised to the relevant temperature for the material used (somewhere near to the first phase change temp) and held there for several hours, allowing the grain structure to modify, relieving stress. This obviously has large cost implications, and is not really suitable for larger items or field repairs.

Another method is peening, where by a spot or region close to a weld is gently hit with a ball peening hammer, (or shot blasted I think!) which also relieves stress. This is a bit of a black art, and not for the beginner. I have also heard of small holes being drilled near to welds, with similar effects, but much higher risk.
Phil