Why not "braze" reinforcements on?, info from the "Welder's Handbook" Options

[SpecialK]

I was re-reading my copy of Welder's Handbook because my practice welds on some scrap were weak as hell when trying to weld 18ga to some 12ga (rosette welds) to beef-up my seatbelt attach points that rusted out. (IMG:style_emoticons/default/headbang.gif) Needed a break (IMG:style_emoticons/default/beer.gif) to do some research and find out what I was doing wrong.

The author, Richard Finch, is big on brazing automotive sheetmetal repairs as opposed to fussion welding (MIG, Arc, etc.), particularly when it involves pre '80 cars that weren't assembled using HSS (High Strength Steel). He says that the high temps involved in fussion welding actually weakens the surrounding metal, where as the lower temps involved in brazing doesn't. You can't braze butt joints like you'd use to attach outer body panels, but the reinforcement kits like Mark's (Engman) inner long stiffener's and Brad's 10ga beasts would actually be much stronger (at the attach points). His example is taking 1" x 5" long strips of .060" mild steel, overlapping the ends by 1" and brazing them together. In a pull-test machine it takes over 3000 lbs. to pull them apart and it's always the base metal that breaks, never the brazed joint. Since lap joints are the preferred joint when brazing, and all of the weld points (holes) on the reinforcements are essentially lap joints, wouldn't it make sense to braze in the stiffeners rather than MIG weld?

Or then there's always the possibility that everyone does braze their stiffeners in, and I'm just assuming they've been MIG'd (IMG:style_emoticons/default/slap.gif)


Kevin

[SpecialK]

I've done quite a bit of "silver soldering", but that was all line-sets for air conditioners, so I was hoping that brazing would be more up my alley (plus my father-in-law has a big-ass oxyacetylene torch set sitting there collecting dust). I practiced all day Saturday with different settings to see what gave the best results for the thickness of the metals I'm going to use to do the repairs (18ga and 12ga mild steel). I had very good results (eventually) with all of the different joints "except" when trying to rosette weld the 18ga to the 12ga. The welds looked pretty, but when I gave them the BFH test the 18ga popped right off without too much effort. I ground down all surfaces to shiny metal, and clamped the pieces together for a good fit, drilled 3/16" holes in the 18ga, and concentrated the weld on the center of the hole to get the best penetration on the 12ga plate. When I cleaned off the slag, the welds looked real nice, but after the BFH test it didn't look like I was getting hardly any penetration into the thicker metal (Note: I'm using a Century 80 flux-core welder, could be part of the problem), in fact it appeared that there was a layer of slag at the surface of the 12ga plate at the point of the weld everytime (IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/headbang.gif) . I try the next higher (hotter) setting which worked great for welding 12ga to 12ga, but it was too much for the 18 ga. I wish I could throw up some pictures to show you what I'm talking about, but my camera absolutely sucks at close-ups (IMG:style_emoticons/default/mad.gif)

You guys make a good point about getting a "good fit" for brazing the repair panels, could be tricky getting them to fit just right, but would I have the same problem with mal-fitting MIG welds?

One possible solution would be to use "clecko buttons" to hold the panel tight to the structure during the weld/braze procedure. I'm actually considering taking the pieces to work and riveting the pieces I'm having problems with using monel solid steel rivets (then I'd be good for 10 G's in the corners (IMG:style_emoticons/default/wink.gif) ).

Maybe I need to find someone around here that has a Gas MIG (I know, redundant) and see if the flux-core wire is causing the problem.

Just had a thought.... (IMG:style_emoticons/default/huh.gif) Would it help if stacked the pieces when drilling the rosette weld holes, allowing the drill to slightly penetrate the 12ga metal (divot)? Then the weld would start sub-flush to the thicker metal. Or maybe I need larger holes in the 18ga (1/4", 5/16") to expose more of the 12ga.........just grasping at straws at this point.