white vinegar derusting disaster

[Lynrob]

Recently I bought some vintage machinist calipers on Ebay. There were some spring type toolmaker's style by Lufkin and some Yankee style by Starrett from two different sellers. Some of both lots were lightly rusted and grimey so I thought I'd try using vinegar for rust removal. I had read that it does a good job without removing base metal and I hoped that it would remove the rust without otherwise marring the finish. I soaked several of them in regular household white vinegar overnight. As advertized, the vinegar did a great job on the rust. Unfortunately, I found 4 of the spring "bows" snapped in two. One of four Starretts broke (the other three seem fine) and all 3 of the Lufkins. I have the utmost respect for these old tools and am saddened to think I (unwittingly) destroyed them by trying to return them to a usable state. I found a similar Starrett caliper in their current catalog so I am hoping that I can get a replacemet bow. I am not so hopeful for the Lufkins.

Can anyone explain to me what happened? I am completely mystified as to what would cause the bows to break whilebsoaking in a mild vinegar solution. Also, if anyone knows how I might obtain replacements for the Lufkin bows, I would be grateful.

Here's a picture of the damage:

 

[Terrywerm]

Welcome to the world of hydrogen embrittlement!

The short story is this: Acids, such as acetic acid (the acid in vinegar) contain hydrogen. When metals like steel are immersed in acid, the steel starts to absorb hydrogen molecules, which makes the steel very brittle. A little stress is all it takes to break the steel at that point, and those bows are already stressed and full of micro-cracks, so they break on their own before morning.

So, how can you avoid this problem?? Remove the bows before derusting. Use some ATF or similar and steel wool to derust the bows manually.

 

[John Hasler]

Welcome to the world of hydrogen embrittlement!

The short story is this: Acids, such as acetic acid (the acid in vinegar) contain hydrogen. When metals like steel are immersed in acid, the steel starts to absorb hydrogen molecules, which makes the steel very brittle. A little stress is all it takes to break the steel at that point, and those bows are already stressed and full of micro-cracks, so they break on their own before morning.

So, how can you avoid this problem?? Remove the bows before derusting. Use some ATF or similar and steel wool to derust the bows manually.

I think it was more likely stress corrosion cracking than hydrogen embrittlement. The springs might not have cracked had the instruments been disassembled so that they were not under stress when processed. I agree that the safe approach is to clean them by hand, though.

I do a lot of chemical derusting because I make everything out of scrap. I'll keep this experience in mind and try to remember not to derust any steel that is under stress.

 

[ScrapMetal]

You could also give Evapo-rust a try. It's not acidic and shouldn't cause embrittlement, I have had great success with it. It is a bit more expensive than vinegar though.

Just a thought,

-Ron

 

[Terrywerm]

I think it was more likely stress corrosion cracking than hydrogen embrittlement. The springs might not have cracked had the instruments been disassembled so that they were not under stress when processed. I agree that the safe approach is to clean them by hand, though.

I do a lot of chemical derusting because I make everything out of scrap. I'll keep this experience in mind and try to remember not to derust any steel that is under stress.

Stress corrosion cracking IS hydrogen embrittlement, just in more common terms.

 

[AR1911]

+1 on Evaporust. I have been meaning to try vinegar, but the Evaporust works so well I haven't bothered.

 

[Andre]

I use a mixture of vinegar, lots of salt, hydrogen peroxide, and water to de-rust parts. The bare metal on the SB carriage stop I cleaned up looks literally new. Works in 20 minutes, the parts come out looking worse than when you take them out a little brushing and scotchbrite takes the rust right off.

I soaked the ball cranks for the BP in plain diluted vinegar, it did nothing.

 

[Bill Gruby]

+2 on the Evapo-Rust. Great stuff and waste can easily discarded in the drain.. It is not hazardous. Environmentally friendly stuff.

"Billy G"

 

[darkzero]

I've been meaning to try Evaporust, heard great things about it, even saw it at HF a while back. Do parts have to be submerged to work, like can it be used as a spot remover for rust for parts that are too large to submerge? I'm assuming the reason is cause it needs plenty of time to work.

I've been using gun blue remover for parts to big to submerge. I also have a bottle naval jelly but I've never tried it yet.

Saw on TV recently they now have a bucket (2.5 gal?) that comes with a strainer to holds parts. Been thinking about getting it.

 

[silence dogood]

I've used vinegar on rust and to remove galvanized coatings with excellent results. I also rinse really well afterwards. So Wermie. let me get this straight. Do not use any kind of acid on a spring steel material. I think that I learned something. Thanks. Mark