GSAW weld temperatures

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I have an application where 1/4" steel brackets are being fillet welded onto the top of a 1/4" low-carbon steel plate.1) Would burn-through be a concern when the welding is performed by a professional welder or is the plate sufficiently thick to prevent it?2) Under normal welding practice (standard feed rate, current, throat depth), approximately how hot will the underside of the 1/4" plate? Either a qualitative answer (could it be touched with a)a bare hand b)a gloved hand c)or would it be glowing hot) or a quantitative answer (i.e. 200F, 500F, 1000F) would be helpful.Any feedback would be greatly appreciated!
Reply:Immediately after welding, if the brackets are small, like car engine mounts , the under side could easily be 500-1000degrees for a very short time. remember that steel melts at OVER 2000 degrees , and the molten metal in the arc is as high as 10,000 degrees .( F ) I would not touch the underside , even with gloves untill the brackets cool a bunch[SIZE="5"Yardbird"
Reply:There should be no problems with burn through if the parts are welded by a skilled professional.  Exactly how hot the weld gets depends on lots of variables. The back side of the weld joint could very well be glowing red hot(1200-1500°F).The underside of the plate will certainly be very hot during, and immediately following, welding.  In still air, the metal should be cool enough to handle with gloves in ~30 minutes.  You can speed this up by waiting 5-10 minutes and then quickly cool the part by immersing it in water.You might get away with touching the back of the weld during or immediately following welding with a gloved hand; but only for a few seconds before the glove begins to burn(and the hand inside too).  Is there some reason to handle the part during or immediately following welding?  If you're considering holding the part while someone else welds it.  Don't.Supply some more information and the folks here can provide suggestions.
Reply:Thanks for the responses!To clarify on why this information is pertinent, burn-through is of concern because there is a limited amount of combustible material located 1 foot beneath the location of welding which can not be cleared prior to welding.Secondly, the underside is painted with a lead-based paint. Again, due to the location and installation, it is not possible to clear the underside of the paint. I am trying to determine the area that will be heated sufficiently to vaporize the lead in the paint to calculate if it will exceed the allowable lead exposure level for the compartment.Does anyone have any further information/experience with:-heat damage to paint on the underside of welds -welding in the vicinity of lead paint-approximate temperatures on the underside of a 1/4" plateThanks
Reply:It sounds to me like you need to place positive ventilation in the area you are going to weld ,either a blower to supply fresh air or a sucker , or better yet, one of each . If.....this is a dangerous situation , then you have absolutely no choice ,but to do it right .[SIZE="5"Yardbird"
Reply:Define 'Combustible material'... Gasoline?  Paper/Wood?  Plastic?Unless your combustibles are volatile, like gasoline, you should be ok with covering the area under the weld with a fire blanket.  Again, a pro should not have problems with burn through when welding 1/4" plate.  But you might want/need to protect that combustible material from weld spatter and slag.  Both are hot enough to easily melt plastic or scorch paper/wood.Breathing the fumes from burning paint is never good; whether it contains lead or not.  It's sure to scorch and peel off from the welding.  Best course of action would be to remove the paint before welding, and dispose of the waste created in accordance with your local regulations.  Since you mentioned this is impossible... ventilation is the only alternative.It's really difficult to estimate how much material will be heated to temps between 620°F(Pb MP) and 3200°F(Pb BP).  Certainly the whole area behind the weld, and the entire Heat Affected Zone(HAZ) will exceed Pb's melting point.  Nothing on the back side of the weld will exceed steel's melting temp of ~2800°F.  But since....grrr it's too late, and this is too complicated a problem to guestimate a solution with the available facts.  (How large are the welds to be laid down?  How thick is the paint?  What is the likely form of the Pb in the paint?  PbO(White)  or Pb(Cr2O3)2 (Yellow)?, etc....I recommend erring on the side of caution.  Ventilate the area and get your welder the appropriate respirator to wear under his/her hood.  Barring this, your best bet is to paint a piece of steel with the same paint, put it in a glove box, and let your welder lay a bead on the back side.  You measure the Pb content of the air in the box.  Then scale your results accordingly.