[How do I?] Mill Scale Removal

Metal and glass don't mix very well. Add acid (full strength) and it could be a catastrophe. Beakers are not the strongest glass either. Not to be a nay-sayer, just something to consider.
Dave
 
Well I did an experiment yesterday evening. I had some paint mixing plastic cups..... I put some Limeaway in one cup and some muriatic acid in the other. I put one of the plates that I am wanting to work with in the limeaway and a piece of A36 roundbar in the acid. Small amounts of each. Since the mureatic acid requires more ventilation, it was placed outside where the temps were falling below zero for my test and the limeaway was inside the garage and covered.

I left both pieces to soak for 3 hours and then rinsed and scrubbed with a nylon/plastic parts brush. The Limeaway piece was completely stripped of the mill scale and the slag left over from the laser cut. The acid piece was spotty and will require more time or the use of an abrasive. I rinsed both pieces and sprayed them down with some Windex w/ ammonia, dried and coated with some of the WD-40 Dry Lube.

My conclusion is that the Limeaway does an excellent job when used at somewhat of a room temperature, and the acid is less effective when used outside in cold temperatures. I am assuming that warmer temps would probably help with the acid. Since I have quite a few pieces that I will be wanting to strip in the near future, neither of these processes will do what I need done. I wasn't able to try the vinegar because mamma didn't have enough in the kitchen for me to try.

So for occasional need for removing the scale, I recommend the Limeaway, based on the fact that it is easier/safer to work with and will remove any trace of mill scale and rust in just a short time..... depending on the size of work piece and is easily disposed of.

For my needs and the fact that I will likely be needing a repeat process on a bigger scale, I guess I am going to have to look more closely at the electrolysis method and spend some $$ to get set up.

Many thanks for the advice and information. You've been a big help.

Jim
 
Thanks for reporting on your test of Limeaway.

Since time usually isn't a concern for me, it'll most likely come down to what's cheaper or cheapest.
 
I soaked the piece in the Limeaway for like 3-4 hours and could see that it was still coated with what I thought was the original mill scale. Once I took the part out and dipped in my rinse bucket, the smut started rubbing off. The brush removed all traces of the dark coating. My point is that it may not be necessary to leave in the Limeaway for 3-4 hours. I plan to try this in a larger tupperware pan that I have and try different time periods to see if the process will work faster..... the larger pan will allow me to do several pieces at the same time. I am fairly new to metal working so everything I try has a learning curve.
 
Not trying to be a jackazz. Your original post said you tried to sand the scale off in the lathe. Couldn't you just turn a couple thousands off and save all the chemicals? I might be missing something
Martin W
Sorry I didn't read it properly and didn't realize they were so thin
 
Just as a reference, this is what an overnight soak in vinegar does. These are 2 pieces from the same piece of flat stock that I have had laying around in my garage for ages.

rust-scale.jpg
 
Not trying to be a jackazz. Your original post said you tried to sand the scale off in the lathe. Couldn't you just turn a couple thousands off and save all the chemicals? I might be missing something
Martin W
Sorry I didn't read it properly and didn't realize they were so thin

no problem. As I said earlier I am relatively new to metal working and trying to figure out a process for making some specialty tools to sell. When I got the plates from the laser cutter there was a hard mill type crust around the outside edge of the plates. That is what I was using the sandpaper on.... then a few thousands off with the lathe to true it up.

The mill scale is tough on carbide cutters. The two faces of the plate had the mill scale and rust spots, but I had already drilled and pressed in four pins in each plate and welded the back side of the pins. Now I am faced with trying to clean up the mill scale as well as grinding down most of the weld beads so I can face off the back side with the lathe. I have made a whole lot of extra work for myself getting things figured out on how I wanted to make these tools. What I have discovered on some of the welds, is that I didn't get a good penetration on a few of the welds, because of the mill scale and now have to do a little touch up on those few spots. This has been a huge learning process, but now I know what NOT to do.

My next batch of tool plates will be a lot easier to do now since I have a better idea of what is needed and an order for doing different steps.
 
I remember shot blasting cutting edges to remove mill scale for loader buckets to get better penetration on the welds when I worked at John Deere. This helped with tracking of the seam for the robot also.
Cheers
Martin
 
I have also just used vinegar to remove scale. That stuff is very hard,and very difficult to remove by mechanical means,like sanding,etc..

HOWEVER I would really caution you about keeping ANY container of muriatic acid in your shop. HCL gets through plastic containers,and can even get past glass bottles with bakelite lids and a gasket inside.

I would strongly advise that no container of HCL be kept in a shop. I had an unopened container in the garage back in the 50's. The chrome plated wrenches kept starting to rust. Finally,I realized that the HCL was getting vapors through the UNOPENED(You'd have to SNIP off a corner to open the plastic container). I took the plastic container and emptied it away from the shop. The rusting ceased. Lesson learned!
 
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