Acid Dipping
Thread Starter
Team Owner
Joined: Jul 2004
Posts: 40,408
Likes: 792
From: Redondo Beach, California
Acid Dipping
After reading the other thread about using vinegar to loosen up those rusty seat tracks, I thought I'd relate some experiences with using acid to derust.
Vinegar is a good derusting agent. It etches away the rust, but it acts slowly so you can remove your part before etching starts to cause damage. It's also nice because you can put your hands in it and move your parts around. I used it on my rear spindle housings because it's slow action meant that it wouldn't damage the accurately machined surfaces where the bearing races are press fitted.
A little faster is phosphoric acid. Also, you can put your fingers in it. It's a little more aggressive. For hardened steel parts, forgings, pressed steel, etc it works fine, but if you put a low quality steel part in it, the phosphoric acid can start acting unexpectedly fast. I left a rusty bicycle chain (made in China) in a tray of it overnight, and the next morning it was history. The phosphoric acid leaves a plate like coating on the steel that is a good primer for paint.
For more aggressive derusting, I use diluted muratic (hydrocloric acid). It's the stuff sold in hardware stores for pool owners. I dilute it about 10:1. This is for stuff that is really rusty, like removeable crossmembers. Also, forged iron castings are good. You can do a part overnight. It also is good to remove old cad plating and chrome plating. It won't remove nickel plating. Takes the cad plating off in a few minutes. I put my bare hands in it, but within a few minutes I start to get a burning sensation. So you need to wash your hands with water pretty soon. It also does a pretty good job removing paint.
Where to I get the trays to hold my acid solutions? I can't find plastic trays big enough. I get cardboard boxes and tape the sections together to make a tray the size I need. Then I line the tray with epoxy resin and fiberglass. Basically I end up with a homemade fiberglass tray. It can be surprisingly expensive. A gallon of resin and hardener is about $30. So... one big tray I built probably cost close to $100.
Vinegar is a good derusting agent. It etches away the rust, but it acts slowly so you can remove your part before etching starts to cause damage. It's also nice because you can put your hands in it and move your parts around. I used it on my rear spindle housings because it's slow action meant that it wouldn't damage the accurately machined surfaces where the bearing races are press fitted.
A little faster is phosphoric acid. Also, you can put your fingers in it. It's a little more aggressive. For hardened steel parts, forgings, pressed steel, etc it works fine, but if you put a low quality steel part in it, the phosphoric acid can start acting unexpectedly fast. I left a rusty bicycle chain (made in China) in a tray of it overnight, and the next morning it was history. The phosphoric acid leaves a plate like coating on the steel that is a good primer for paint.
For more aggressive derusting, I use diluted muratic (hydrocloric acid). It's the stuff sold in hardware stores for pool owners. I dilute it about 10:1. This is for stuff that is really rusty, like removeable crossmembers. Also, forged iron castings are good. You can do a part overnight. It also is good to remove old cad plating and chrome plating. It won't remove nickel plating. Takes the cad plating off in a few minutes. I put my bare hands in it, but within a few minutes I start to get a burning sensation. So you need to wash your hands with water pretty soon. It also does a pretty good job removing paint.
Where to I get the trays to hold my acid solutions? I can't find plastic trays big enough. I get cardboard boxes and tape the sections together to make a tray the size I need. Then I line the tray with epoxy resin and fiberglass. Basically I end up with a homemade fiberglass tray. It can be surprisingly expensive. A gallon of resin and hardener is about $30. So... one big tray I built probably cost close to $100.
Le Mans Master
Joined: Apr 2005
Posts: 6,357
Likes: 427
From: Seattle Area WA
I'd be careful using acids on any fastener hardware for cleaning because it can cause Hydrogen Embrittlement. Same goes for using any replated fasteners that have not been heat treated.
Thread Starter
Team Owner
Joined: Jul 2004
Posts: 40,408
Likes: 792
From: Redondo Beach, California
I haven't deplated any cad fasteners, just other stuff. Since getting part cad plated is such a problem - it's hard to find cad platers now plus when you do they want a volume of parts to be plated. As a substitute for cad, I'm deplated some cad parts and then having them copper/nickel plated. Nickel plating is not as expensive as chrome and it looks almost as nice.
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Joined: Sep 2001
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From: Wellington, FL
St. Jude Donor '11 thru '25
