Trouble welding trans oil pan / galvanizing

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I'm trying to weld up an oil pan - the junkyards around here poke holes in them to drain, so I'm trying to see if I can fix this one up instead of getting another from the dealer.First question - on my first attempt at tig welding, a thick white cob-web like substance formed on/around the weld. It's extremely light, I can easily blow it off. Is this the galvanizing that I didn't grind deep enough, or am I dealing with some funky alloy?Wonder if sandblasting will work better then a flap disc, especially since the surface isn't flat.I was able to tig in the patch but there was a small tiny crack. Thinking it would leak, I figured I would braze over it. Brazed both sides. The braze on the outside cracked as well. End result, is it did leak when I tested it with water.At this point I'm thinking I may cut the area out and fit a bigger patch once I know that I just need to spend more time cleaning. Attached ImagesLast edited by pierre71; 12-10-2008 at 03:55 AM.
Reply:Is the cob web substance white with a blue-ish tint? If so it is galvanized and that is the zinc burning off due to the heat. Just take better care in cleaning the work area before welding.
Reply:Sandpaper ?  David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:Personally i wouldn't sand blast something like a sump, especially if it incorporates a windage tray- gotta get all the sand out after. I usually use a 'clean 'n strip' disc in a grinder- you can go nuts with 'em without fear of thinning of the actual sump. You can see the colour change as the coating comes off- you see a change very quickly as the majority is removed leaving a slick surface but you have to go a bit further to get back to clean steel which looks a bit yellower (or less blue). Hope that makes senseThere's several different coatings used, sounds and looks like yours was galvanised or made from zintec. Last one i was asked to modify was cadmium plated- really want to make sure that stuffs properly removed!
Reply:The cob web stuff is a pure white, snow I woud say, no tint. It looked pretty dense, I thought I would be scraping it forever, was surprised when it just blew away.It's a plain pan with a few curves for bracing, like that X pattern you see. No hidden areas or windage tray. I thought I was aggressive enough with the flap discs, but apparently not. If a 40grit flap didn't do it, I don't think a strip & clean disc will. Those do nice on hot roll scale though. I think its down to sandblasting or using muriatic acid, always wanted to try that.Why on earth did Ford do this to a pan? What happend to the days of plain steel pans with a simple paint on the outside? At this point I may end up getting a new one just for time concerns, but dang I want to get this one solved just to know I haven't been defeated!
Reply:Pure white 'dust' was probably zinc oxide.Try the localized application of muriatic acid (hydrochloric acid).  That should dissolve the zinc coating and turn it into zinc chloride, which you then neutralize the acid with some plain baking soda and then rinse-rinse-rinse well.  And then you scuff it down to bare clean steel with a flap-disc or 'scotchbrite'-type pad or gentle sand-blasting.  And then you TIG it.  Because TIG really-really needs/wants CLEAN metal to work with.  Oh, and you have to make sure the oil is cleaned off/out first too.  The braze 'cracked' probably from too much hot metal that then shrank and tore the base steel.  Cause usually brazing filler is soft enough to not crack itself.  BTDT.  Go easy on the filler amount.Quick test with the acid to see if the zinc was all removed or if you left some on:  Put a drop (CAREFULLY!) of acid on the area in question.  If it bubbles and fizzes, then was some zinc (or other crud) there.  If it pretty much just sits there, you are down to clean steel.Oh, and I don't -know- if the pan is just plain low-carbin steel with a galvanized coating.  If the pan is for some reason some -other- kind of steel, like leaded or resulphurized or some other alloy for machining/stamping ease, then all bets are off on welding or brazing a repair.  The best laid schemes ... Gang oft agley ...
Reply:I had a similar problem with an oil pan that I was modifying only there was plating under a coat of paint that I had to remove from the pan. I used an aluminum Oxide Discs and had good results. Attached Images
Reply:Perhaps if its Zink or galv, you could heat it red with a torch to burn it off, then wire brush it.  Simple like me.David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:I know WeldingWeb has skinned this cat a few times, but I guess today was my turn.I just touched the torch to the pan for a test, when Alfred yelled: Hold it! Remember what happened to Pierre71?Attachment 26486I guess you know the rest of the story. Last edited by denrep; 10-19-2010 at 11:37 PM.