[SEL] heating large castings for welding

[John Hall]

Did something a couple of weeks ago some of you may find helpful. If you 
have ever tried welding or brazing castings you know and understand the 
necessity of preheating and slow cooling. If its small use a torch for 
heating and bury it in a sand pile to let it cool slowly. I've heard of 
doing mid-sized parts by initially heating on a barbecue grill as well as 
putting them back on for controlled cooling.

I got hold of one to big for either a couple of weeks ago. I had to weld up 
a transmission housing that measuered roughly 1 x 2 x 3 feet. First off it 
was very greasy so I sent it to an automotive machine shop to be cleaned. To 
initially preheat it I used one of those torpedo shaped kerosene heaters 
like you see used on construction sites. I heated the part for about an hour 
until you couldn't touch it by hand. Then we used the rosebud to finish 
preheating the area to be welded. After welding I put it back in front of 
the heater for another hour to equalize the temp. Nothing went CRACK!!! so I 
assume all worked well.

John Hall