Rusty Bolt Cleaning

[Patrick H.]

Hi,

I'm trying to clean some rusty bolts, and for whatever reason they are being much more stubborn than the dozens of bolts I've done previously.

Examination before I started showed original zinc plating. There was a moderate amount of corrosion which had for the most part hardened into VERY hard black "chips" adhering to the bolts, especially the sides of the head and inside the recess of the head.

After running the bolts for a LONG time through my tumbler, they did not clean up as easily as I had expected. I've tried a wire wheel, which helped a little and also then some phosphoric acid. This seemed to do the best job, but a couple of the black dots of corrosion (i.e. hardened rust) remain. I'm not enthused about bead blasting as it REALLY changes the surface appearance. I"ve tried tediously using a pick, but the black dots of corrosion still remain.

Before I leave the bolts in the phosphoric acid for too long, is there a limit as to how long they can be left in there? I only did it for a few minutes previously. My end goal is to clean them enough to have them zinc plated, and I've never had bolts require this much work.

Thanks for any tips you might have.

FYI, they are not load-bearing bolts, so cosmetics is the "most" important factor.

Patrick

[Dick W.]

Re: Rusty Bolt Cleaning

Patrick you know that you have left them in too long when they are no longer visible in the container. Seriously it is trial and error to determine how long to leave the bolts in. Some will clean in just an hour or so and some will take over 24 hours. If the flakes are in the threads, why not run a thread chasing die over them and clean them up. Most of the bolts that I do are thread chased before they are replated. Makes assembly a lot easier.

[Randy R.]

Re: Rusty Bolt Cleaning

The zinc plating itself will alter the surface appearance. I clean mine by dunking them in a 30% muratic acid solution, then rinsing with water, drying, bead blasting, then plating. They look good when complete.

[Patrick H.]

Re: Rusty Bolt Cleaning

Dick,

I always run a thread chaser over them too. I've done that already; in fact, that was one of the first steps.

The flakes are adhered to the sides of the head and inside the head's recess. The threads look great since they were never exposed to the elements. Even the underside of the bolt head looks great.

Patrick

[Mike McKown]

Randy's got the right idea

You're using the wrong acid, Patrick.

[Tracy C.]

Re: Randy's got the right idea

Agree, But you should dunk the parts in baking soda water to neutralize the acid before the final rinse. A heaping tablespoon of soda in a quart of water is all you need.

This really knocks down the propensity to "rerust" after treatment.

tc

[Patrick H.]

Re: Randy's got the right idea

I assume the muriatic is stronger than the phosphoric?
I should know this, but it's been 15 years since I had to calculate this stuff in Chemistry class.

Patrick

[Chuck S.]

Re: Randy's got the right idea

Patrick, I don't know how to calculate acid "strength" scientifically (What is a molal anyway?), but for rust removal, muriatic acid is definately
"stronger". I have only used phosphoric acid as a pre-phosphate rinse of fasteners cleaned with muriatic acid and/or bead-blasted, and found it to be a poor metal cleaner by comparison.

I have used 3 parts water to 1 part muriatic acid, which is a STRONG solution. It sounds like you have "pitting corrosion"; beneath the "scale" is a depression well below the surface. You might try using small tools like dental picks to dig the scale off the surface, then do the acid bath. Removing the scale mechanically will substantially reduce the residence time in the acid. If the scale is in the threads, use Dickie's suggestion above, but the picks may still be helpful.

[Tracy C.]

Re: Randy's got the right idea

Much stronger and cheaper too. You can get a gallon at your local Tractor & Supply, or Hardware store or where they sell Concrete supplies for less than $5

I use this stuff all the time. Just do your mixing and dunking outside with plenty of fresh air as the fumes are pretty caustic and will promote rust all by themselves.

If you get any on you, wipe off quickly with a rag dunked in the soda water.

tc

[Tracy C.]

And always add acid to water.. never water to acid *NM*

[Rob A.]

Re: Rusty Bolt Cleaning

Blue Lightning Rust Remover (they also make paint remover) works great. 1 800 501 1562. They'll deliver right to your door...

[Patrick H.]

Re: Randy's got the right idea

Tracy,

I already have a gallon of it that I've used for realy rusty parts that aren't quite so "delicate" in their appearance, i.e. no tiny headmarks to worry about.

Believe it or not I was a Chemistry major in college, but haven't used it on a daily basis to calculate anything in many years. Medical school sends one in a different direction, and what you don't use, you lose.

Patrick

[Chas Kingston]

[David Bodily]

Re: Rusty Bolt Cleaning

Patrick,
Go here http://www.stovebolt.com/techtips/ru..._derusting.htm
This is a description of electrolitic de-rusting. I have used this method and it works. It is slow but absolutly works without any erosion of the base metal. It also leaves an oxide that protects from immediate re-rusting so you have time to re-plate, paint etc. Hope this helps. David Bodily

[GL Anderson]

Re: Rusty Bolt Cleaning

I have also used this method for years. It works great even with a small home battery charger. To remember which way to hook up the positive and the negative I use the phrase "negative rust" It means the negative cable hooks up to the rusted part. I usually use a plastic bucket and clamp the anode to the side of the bucket with the positive side of the battery charger. Make sure the part and the anode don't touch! You won't believe how the rust just melts off the part. I have used everything for a charger from a 2 amp to a 250 amp arc welder with this process. Just my experience. GL