On the recommendation of another forum member, I ordered some citric acid powder for mill scale removal testing.
I normally use vinegar and mix 4 gallons of grocery store vinegar with one gallon of 30% cleaning vinegar.
The vinegar usually takes about 24 hrs for full removal of the mill scale.
I mixed the citric acid powder with tap water. About 2-3 cups to 5 gallons of water.
I put a few junk parts in the solution and checked on them at 6 hrs. The scale was starting to loosen in spots, but I wasn’t able to rub off much of it.
After 24 hrs, the scale was mostly loose and would probably have come off with a wire wheel.
I added another couple of cups of citric acid powder and was not able to get the pH lower than 1 on my test strips. I’m not sure if the test strips are junk, since they were reading a pH of about 1 with the first several cups of acid.
I just threw another part in the stronger solution, so I’ll report back on that.
Overall, it seems that the citric acid is at least as good as vinegar and doesn’t smell as bad. If the current mix works well, I’ll get at least three to four batches from the 10lb bag that I bought for around $35.
So you think its cheaper ? I guess the question remains how long will it keep working.
I mix my vinegar 1 gal 45% to 8 gallons water. so a little stronger than 5%.
Do you know what your mixture of Vinegar comes out % wise? would it be 10%?
I don’t cut the vinegar with water, use straight up,2 hours of soak time mill scale rinses off with water bath. Have a tub over a year now that still removes the millscale.
I just bought a bag of the granular. Based on the “2-3 cups to 5 gallon” recommendation in the first post, it seems it would still be pretty cheap even with your 25 gallon tank. I haven’t tried yet. Still using vinegar on some stuff, but for the small signs I mostly make, I just wipe down with this and paint over it.
I checked on the part that I i threw in yesterday and the scale just wiped off after about 16hrs. It seems that about 1 cup per gallon is a more effective solution.
Pretty cool I looked yesterday I might have put 2 or 3 cups in a 5 gallon bucket. 48 hours metal had spots mill scale wiped off. About like weak vinegar.
Thanks for the share and the original idea . I will definitely try this out I sometimes use up to 20 gallons of vinegar.
I never neutralized anything. I just rinse them with the hose and dry them. I have parts that have been sitting in my shop for over a year and they don’t have any rust on them.
Ok for all you guys that were using Citric Acid what are your thoughts now?
Are you using powder or liquid?
If using powder does it mix up easy?
What Mixture?
Feel it works better than vinegar?
Average soak time to remove mill scale?
Do you think it last longer than vinegar?
Does it take much to get it off?
A lot of my tube has oil on it and I have started washing it off before I soak.
if I don’t it makes a mess of my mix
There was a Video I watched some time ago and the guys mixture was 14oz of Citric acid to a gallon of water which makes it more expenise then vinegar.
I don’t know how much I mixed. I started with someone’s recommendation and kept adding until the ph wouldn’t go any lower.
I paid $28 for the bag of powder that I have and I only used about a quarter of it in the shallow container that I use. The same volume of vinegar would have cost me about $30-35 for 4 gallons of household vinegar and 1 gallon of 30% cleaning vinegar.
The slime isn’t really an issue, except that it is disgusting. It doesn’t stick on the parts.
14oz to a gallon seems like way too much. It looks like I posted, earlier in this thread, that I used 1 cup per gallon.
100% this. If simply equating cost and taking shelf life / storage into account, citric beats acetic hands down. It does turn green in the long term, but it also doesn’t STANK up your work area.
If you really want to, you can chelate the acid.
I use a cup or two to a few gallons of water and just let it work, using a shallow cement mixing plastic tub from a certain hardware store.
Rinse the parts well in clean water afterwards and do whatever work you need to, or coat in oil, or they will flash oxidize.
Is this what hes doing by adding the sodium carbonate to the citric acid?
His mixture is considerably more expensive than just adding parts to straight citric acid.
This was the video I had found originally but never tried do the the expense.
I am going to give it a try on a small scale and see how it compares to my Vinegar mix.
