I started brazing my first frame yesterday -- lugged, silver brazed. Paterek suggests a mild acid based toilet bowl cleaner for the final prep -- to remove any oxidation -- prior to brazing. The mildest acid product I've been able to find is muriatic acid which is 20% hydrochloric acid, 80% water, but I believe it is still far stronger than the toilet bowl cleaner, and Paterek warns against using anything too strong.
So yesterday, I made sure my joints were freshly sanded just before brazing, and I skipped the acid wash. (I had previously cleaned with min. spirits and lacquer thinner). I think I made strong joints, so I'm wondering how important or necessary the acid wash is, and if so then how much I should dilute the muriatic product.
Also, Paterek recommends lacquer thinner after the min. spirits, so that's what I used, but I'm wondering if I can substitute denatured alcohol since it's a little less toxic.
there was a recent thread on frameforum.org about this. Most clean with sandpaper. Doesn't hurt to use something like acetone to get rid of the oil. This is all I have ever done, never even thought about using acid. A few use an acid, particularly for small parts. When I was at trek, they used a very mild acid, dunno which acid. It was just strong enough to cut a hole in your pants, but you had to wash them before the hole would show up. One day an electrician fell in the acid bath, and the worst part was convincing him that nothing bad was going to happen. They also used the same bath to remove flux. The tank was heated. When I first started working there, they were using a sandblaster for both operations.
One day an electrician fell in the acid bath, and the worst part was convincing him that nothing bad was going to happen.
I'd probably need some convincing too !
It seems hard to get rid of all the rust on little intricate parts like the fork crown, BB shell, etc., especially after soaking them in water to remove the flux from a previously brazed joint. I'd like to try diluting some of this muriatic acid. Any suggestions on what the final ratio of hydrochloric acid to water should be?
Forget the HCL- wait till you have the whole thing done and give it a good cleaning with an etching solution (usually 1 part phosphoric acid to 3 parts water) before painting. The solution will clean the rust off inside and out and it preps the metal for better primer adhesion.
It's unnecessary to burn the invisible oxide off with acid since that's what the flux does. Alcohol is a better choice than acetone because acetone often leaves an oily residue from petroleum residues that are contaminants in the acetone.
I had no problem finding the kind of acid Paternek used at a home depot, it was another brand but it served the same purpose, though unecesarry.
I generally gave up on the toilet bowl cleaner as you get flash rust so quickly after use that you end up having to sand anyway. I give everything an initial soak in mineral spirits, and then when I'm ready to use the part it gets a quick rubdown with sandpaper, wipe off the loose dust with fresh rag, flux, and braze.
I've played around with the acid but found it unnecessary. Sand the completed joining area and then degrease with something like acetone or lacquer thinner. Denatured alcohol should work fine as well. The only time I use mineral spirits is on raw tubes; there is often a lot of gunk on the inside.
Becareful buying/selling bike parts on-line. I learned the hard way. :(