Multiple pass welds

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I have a question for welding beveled pieces with multiple passes .Is it ok to let the piece cool for just about 10 minutes beforebrushing and making another pass?? Doesnt seem like you would have to wait till it cools completely .. But I dont know .. I'm practicing on a 3/8" thick piece , and put a shallow bevelon it .. I only have a 120 AMP FCAW / MIG and am FCAW 'nthe joint ..Randy
Reply:Originally Posted by Lanmanb4I have a question for welding beveled pieces with multiple passes .Is it ok to let the piece cool for just about 10 minutes beforebrushing and making another pass?? Doesnt seem like you would have to wait till it cools completely .. But I dont know .. I'm practicing on a 3/8" thick piece , and put a shallow bevelon it .. I only have a 120 AMP FCAW / MIG and am FCAW 'nthe joint ..Randy
Reply:very good ... but the question is ... how long? Or does it depend on the metal thicknessand sensitivity to warping?
Reply:The thinner the metal the longer between run's. Also if you have much trouble with destoration try putting some preset into your plates, ie: a slight vee away from the side your going to weld. Don't let the weld cool completely between run's as that can cause cracking.Stephen
Reply:Actually complete heat cycling of a weld joint will increase shrinkage forces.  That is why a thicker joint would be more prone to cracking.  Keep the heat up and just go for it.  In some cases once the weldment really warms up the heat can be turned down a bit.You reduce weldng distortion by putting down the largest possible amount of weld in the minumum time.  In extreme cases this of course is not a good thing.3/8 inch material is not very thick by industrial standards.  Presetting  your joint the opposite way is an excellent suggestion.
Reply:Spot on lotechman, but I didn't think he'd be into any heavy section.One job I did was to weld adapter's onto a cutting edge of a bigger bucket, the day shift preheated for the whole day. They had burners underneath and heating torches on top for 10 or 11 hour's. Then us on night-shift came in and welded the adapter's on, 11 hour's or so to weld one adapter on. When we had smoko we had to put a bit more heat in when we got back then rapped the top up with the heaters on underneath for a post heat at the end of the night.   One guy crapped out it was that hot, the heat just beat him. Can't remember what the preheat was but it would have been around 200 degrees celcuis if not more.Stephen
Reply:Sounds like a nice Winter job Wirenut.  I will try to post some pics of you electric heting pad system.  I never used one before this shop.    The only situation I can think of when cooling off between welds is if it is some sort of stainless or very thin material.
Reply:lotech sounds right on track with what Ive been taught.  However, for most of my work, except some hardfacing on the farm, preheat was never needed.  When I do multipass I've always been taught the quicker you can knock out the weld the better off you are.  after your first pass or two it keeps your part preheated and your fill and cap run a little better.Good luckCHRIS
Reply:Remember Randy is using fairly light steel and theres every chance he's only using small pieces which will heat up very quick then give trouble with undercut etc, how many runs are you putting in Randy?Lotechman, It was summer in Western Australia, which get's a wee bit warm at the best of times!Stephen
Reply:wirehunt:  You poor soul.  At least we can put it off to cooler days or wish for winter.  If the picture comes through it is of the heating pads we use to heat stuff.  This way we get a nice even heat that is all the way through the metal rather than just in one locality.  The ceramic mats contain nichrome wire and are fed DC current through a power supply. Attached ImagesLast edited by lotechman; 07-11-2005 at 10:29 PM.
Reply:awesome pics lotech, see something new everyday chris
Reply:great pic's lotech.  Look like the same setup as what the post heating crew was using on my last job. Heated to well above 500 degrees celcius then held there for four or five hours. Chart recorded the whole process as part of the incpection package.Stephen