Brazing Rust Pinholes

[Dat73z]

I've been preparing my windshield frame for a new seal and have a couple of minor rust pinholes. I have a tig welder and was contemplating tacking over these areas with er70s since that is what I had.

 

However, I saw some 1/16" silicon bronze filler at the store and thought maybe that would work better since brazing wouldn't require melting the base metal which looks to be quite thin so I picked up some rods. 

 

Has anyone brazed over rust pinholes and how did that work out for you? I was thinking of keeping it simple tig brazing, grind down, then epoxy seal and filler over that. Since I would be using the tig I figured I could run maybe 20 amps and prevent distortion, blowing holes, bubbling paont, etc. Just enough heat to open the pores of the base metal and braze in the pinholes. Any holes (no pun intended) in my strategy? 

 

Picture attached for the worst of it. 

[grannyknot]

I haven't used the brazing rods for tig welding but have used the silicon/bronze mig wire with 100% Argon gas, excellent product, low temp welding, easy to grind.

I would think silicon/bronze with tig or mig would work well for your job.

[Ironhead]

I don't know what your skill level is at TIG welding, but if you can do what you propose, it would be a good repair.

 

I can tell you that using TIG on the thin Datsun sheet metal....particularly when it is even thinner from corrosion, is very difficult.  Even at 20 amps, burn through will happen extremely quickly.  If you can pull it off, you are way more skilled than I am.

 

I found the best way to remove pinholes was to cut out all the corroded metal and weld in a patch.  But that's just me....

Edited August 30, 2021 by Ironhead

[fusion]

I like to use a low power setting on my MIG and make a couple of small tacks next to, but not on, the hole.  This acts as a heat sink.  Then I do small tacks butting up to the heatsink and move subsequent tacks across the hole until it's filled in.  If this method blows through the metal then it needs to be cut out anyways.

[Ironhead]

I know what you are saying for sure....the inclination is to cut out as little metal as possible.  But where there are pinholes, there will be pits, so the surrounding metal that is not pin-holed will be massively thinned and weakened from the corrosion....

 

Working on my shell, I found myself making larger and larger patches.  It just seemed to work better than trying to fill pinholes or using a large number of smaller patches.

 

 

[Dat73z]

Thanks for the replies guys good insights. I've been busy with other projects but am planning to get to this later in the week and will update. 

 

With the tig I've welded thin sheetmetal and done repairs before, but never brazing. I'm not planning to melt the base metal so hopefully blowthrough won't be an issue but we will see. Maybe I'll just preheat the area and lay the rod right over the hole then give it a quick jab of the pedal. 

[AydinZ71]

7 hours ago, fusion said:

I like to use a low power setting on my MIG and make a couple of small tacks next to, but not on, the hole.  This acts as a heat sink.  Then I do small tacks butting up to the heatsink and move subsequent tacks across the hole until it's filled in.  If this method blows through the metal then it needs to be cut out anyways.

^this

 

I do the same. Use high-heat setting and do very very quick taps. Low heat settings will have poor fusion and leave holes when you grind flush. As always, be very cautious adding too much heat at once. If you get more than a 1/8” blob glowing red, you are adding too much heat. The metal 2” away should be hot to the touch but not enough to burn you. Go sloooooow….. this is an exercise in patience. 

[Dat73z]

So I finally got around to this. Welding was ok but my grinding skills could definitely use improvement. 

 

I really like the way the silicon bronze filler rod flows. At the right temp it's it melts and flows out like butter. With more practice I could probably get the heat affected zone really small. Anyways, after some quick practice tacks and dabs what I found that worked:

 

Focus the torch on the rod not the base material. I laid the rod over the pinholed areas and quick jabs of the foot pedal to build up some tacks (maybe 15-20amps). This was not quite enough heat to flow the rod so after building up the area I focused the torch on the top of the filler and hit it with probably 20-30 amps until the material just started to flow. Some pics below.

 

Now for paint and the next project. 

[mutantZ]

I came across this solution I may try for the holes in my car

 

[AydinZ71]

I put a sheet of thick copper flush on the opposite side of the hole, then go to town with my mig. I can fill in a 1/4” hole in just a few minutes then grind flush with an angle grinder and flap wheel. Works for me, but takes some practice. The cooler helps pull the heat from the molten steel and “dams” it so it doesn’t flow through to the other side. Here are the inner fenders with all holes and OEM rack welded nuts removed. 

Edited November 13, 2021 by AydinZ71