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-   -   prep work for powder coating (http://www.hotrodders.com/forum/prep-work-powder-coating-1410.html)

mike bryan 05-15-2003 11:28 AM

prep work for powder coating
 
Hey there- I am in the process of getting my project car together and have a question. I have the rearend narrowed and ready to throw underneath this thing. My plan is to powdercoat the housing, but there are some unsightly dings and scratched on it. I don't really want to grind and sand them out because I am concerned about loosing strentgh in the housing. Is there a filler product out there that I can use and will bond well and hold up to the heat of powdercoat baking? It would need to be able to withstand 400 degrees. Any suggestions would be of much help. Thanks. Mike

willys36@aol.com 05-15-2003 11:38 AM

Best bet would be to braze them then sand to shape.

scott011422 05-15-2003 11:47 AM

Willys, I totally agree. The company I work for does CNC machining and powdercoating. What ever you use has to be electrically conductive for the powerpaint to stick. Metallic body filler stays, But the paint doesn’t stick too well. Brazing sounds like a great idea.

willys36@aol.com 05-15-2003 12:36 PM

I do the same thing for stuff I have chrome plated. Brazing is a great metallic 'bondo'.

scott011422 05-15-2003 12:45 PM

So Is lead if it isn't going to get too hot.

willys36@aol.com 05-15-2003 01:16 PM

True, solder is great if there isn't any stress on the repair. I like brazing 'cause it is more the same hardness of the steel substrate and is much stronger than lead. I have had better luck smoothing brazing than lead. I always seem to end up with a shadow outline with lead 'cause of the softness. I guess I am not real carful in finishing! I had a '41 Willys inside windshield frame (rarer than a '90s White House teenage inturn not molested by Bill Clinton) that was totally swiss cheesed by rust in the bottom corners. Brazed the whole thing, covering holes and pitted metal and it chromed like new.

scott011422 05-15-2003 01:25 PM

What kind of acid do you use as a flux??

mike bryan 05-15-2003 01:26 PM

Thanks guys- I had not thought about brazing. I have the equipment in the garage. Does anyone have any suggestions regarding the best material to use for brazing? Thanks again. Mike

willys36@aol.com 05-15-2003 02:02 PM

I use the standard brass rod from my welding supplier. I get the smallest rod they carry (3/32"?) 'cause it is easier to work with. I get bare rod and a can of flux but you can get prefluxed rod too. Whatever spins your prop. If you go with bare rod, get a can of their standard brass brazing flux. It will last through your grandchildren's lifetime.

If you aren't used to brazing, practice a little on a scrap piece of steel. Set your torch like you would for welding steel except add a little more acetylene (slight blue tail off the tip of the inner blue-white flame). Important to have the flame reducing (gas rich) rather than oxidizing (oxygen rich). Heat the rod and stick it into the flux so some sticks to the rod. Heat the steel to just below red-hot and start to feed in the brazing rod. If you get the steel too hot, the rod will sizzle and burn into the steel which gives a brittle steel/brass alloy that isn't good. Very weak, porous, and ugly. If the metal is too cold, the brass will stand up like a wart and not adhere very well or simply melt and roll off the steel. When the conditions are just right, the brass will flow out over the steel like ranch dressing on a salad. You can then smooth it out by playing with the flame. Done right, there is very little finishing needed.

You can tell you have too much acetylene in the flame if the brass puddle bubbles like boiling water. Too much oxygen 'burns' the brass and it acts like over-cooked bacon in a frying pan.

If you are comfortable welding steel with oxy-acetylene, you can learn brazing in a few minutes. Same torch techniques, just different gas settings and heating/puddle control techniques.

Forgot to mention that the steel needs to be bright white clean but that is no different from the spec for any type of welding.

[ May 15, 2003: Message edited by: willys36@aol.com ]</p>

mike bryan 05-15-2003 02:25 PM

Thanks loads Willys36. I'll play around in the garage tonight and get the process down. Your advice is very much appreciated. I have a couple of spots on the frame that I'll use the same treatment for before shooting it. Thanks again. Mike

62slantsix 05-15-2003 03:11 PM

Could you use a LPG torch to braze??

willys36@aol.com 05-15-2003 04:17 PM

Probably. Just need to get the steel to just at red hot.


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