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.
