My first attempt at removing dross with muriatic acid_ Good Results......but

[tinspark]

I have always kept a gallon of muriatic acid around here in my shop area, and out back away from tools. But have only used it for a soldering flux for galvanized steel. At work We don’t wear any special equipment besides safety glasses gloves, which is always required.. And read the postbelow about buying all sorts of gear for this stuff. I have never really used muriatic acid to take dross off until the other day I finally burned out an Eiffel Tower pattern that I spent many hours resizing and fixing notches etc. to cut it out of 12 gauge black iron which turned out good once I fit it up after cutting.It should be about 4’ tall when actually assembled and welded out. Now I want to find some sort of LED lights to put inside of it after completion and will likely put it in a flower bed out back and may just let it rust up in the weather, or throw a solution on it to speed up the patina process. My results with the acid were good but varied.
I initially left a few parts in the bath for a couple of hours 50-50 mix and it did a great job stripping the mill scale off, which was really cool. but not so much the dross from the plasma cut, which was my goal. The patterns have over 2,500 Pierce points for a little bit less than a 4 x 4 sheet of metal 12 gauge Hot Roll (see pic, and schedule from DE software). I knew it would be a pain in the rear to grind all the slag/dross from the backside of so many opening and all of the start and stops. so I decided to finally try the acid method. I threw everything in my tub for a 24 hour soak and the results were what I was hoping for. For this application, it worked great, and I would use it again with this many start and stops/ pierrce points. But definitel not for the run of the mill stuff that I normally do. Most of the dross was completely gone. And I was able to use a 2" paint scraper to get the rest off without much effort. But for me, I would not spend this much time to play with this stuff unless I had a big dross issue, like I was expecting with over 2500 cut paths in such a small footprint. But it is a good tool in the arsenal from here on out! And it worked to almost perfection for me in this application.
Also, as a side note, I changed out my consumables before I started cutting these parts out. And I was able to complete the entire job with 2,542 start and stops without replacing consumables, and do not know how much more consumable life is actually left in my nozzle and electrode. (fine cut) which I thought was pretty good and maybe some sort of record. Well at least for me. . and the cuts turned out pretty good from start to finish with no issues, skipped cut paths, or misfires with my Hypertherm 45XP non-sync.and genuine hypertherm consumables.
I think what really extended my consumable life was the fact that I paused the cut at approximately every few hundred pierce points and used my stainless toothbruch to scrub the nozzle to clear any stuck slag on the face of the nozzle which may have thrown off the THC or create a misfire from crud sticking where it aught not. Thought I would share my acid bath results. Overall I was pleased with the results, but for the normal brackets and parts that I do around here at my home shop, I will not be using the stuff. or keeping open acid in a bath covered up out back

[adbuch]

Doug - thanks for the report! It looks like it turned out great for you. I have tried the acid bath approach in the past - I was not happy with the surface finish it left plus it was pretty sticky and took me some time to clean off. I was planning to leave the part in bare metal with only a clear coat.

I recently cut some small parts from 16 ga. steel for Christmas gifts and the slag on the back was a real problem. Hypertherm says that 16 ga. steel with FineCuts is not a dross free cut. I believe it. Anyway, I spent lots of time grinding the slag off and then painted the parts. They turned out fine, but would have benefited from the acid bath treatment if I had extra time to burn on that particular project.

David

[Joe Jones]

I am not sure why I should go through the process of removing mill scale, when I can buy cold roll steel that doesn't HAVE mill scale on the surfaces. Cut the pieces, run them through a belt sander, and coat them with clear coat or something to prevent rust. What am I missing?

Joe

[Scratch]

I am not sure why I should go through the process of removing mill scale, when I can buy cold roll steel that doesn't HAVE mill scale on the surfaces. Cut the pieces, run them through a belt sander, and coat them with clear coat or something to prevent rust. What am I missing?

Joe

I think In this case, the OP is using the acid to remove dross, not mill scale.

[abmetal]

I used muriatic acid for years for intricate parts, mainly signs. It always worked great leaving parts in the acid for a couple hours max. But I always used it full strength. Yeah, I know, that's bad stuff. But I ALWAYS used it outside away from everything and stored it in sealed containers. The back of the cut parts always came out slick as a whistle.

Allen

[tinspark]

I am not sure why I should go through the process of removing mill scale, when I can buy cold roll steel that doesn't HAVE mill scale on the surfaces. Cut the pieces, run them through a belt sander, and coat them with clear coat or something to prevent rust. What am I missing?

Joe

I think In this case, the OP is using the acid to remove dross, not mill scale.

Yup, the OP was indeed trying to get a dross free part. I can be sure of that 100%.
Worked as hoped for

[tinspark]

I used muriatic acid for years for intricate parts, mainly signs. It always worked great leaving parts in the acid for a couple hours max. But I always used it full strength. Yeah, I know, that's bad stuff. But I ALWAYS used it outside away from everything and stored it in sealed containers. The back of the cut parts always came out slick as a whistle.

Allen

I am not sure of the strength of the muriatic acid even at full strength. I picked up a gallon at Home Depot for this project in mind and figured I would mess around with it. I went out at about 2 hours after I read someone’s prior post about 2 hours being enough without knowing what strength to go with, but it is etched in my brain now in case I just want to remove mill scale, which is not usually something that I normally concern myself with. But will store the knowledge away in the memory archives.
So much easier than grinding in this application. It did slightly flash rust after I dried it all off with my shop air after a few hours, but I threw each piece on my magnetic table and lightly sanded each piece with almost zero effort and it has been shiny ever since without any further oxidation.
Nice option for this application. I will try to remember this option too, and could use it when the Mrs. Has me do her artsy fartsy kinda stuff. But most of my parts come out virtually slag free, and what may be there it is normally light work tapping the edge slightly with the side of a thinners hammer or a swipe of a 2” paint scraper does the trick. Hanks for all of the responses. I love learning and experimenting with new stuff. Even if it is a fail I figure it is worth the effort and will aleways be a learning experience, no matter (my) current experience or knowledge level. This was not a fail however

[tinspark]

I am not sure why I should go through the process of removing mill scale, when I can buy cold roll steel that doesn't HAVE mill scale on the surfaces. Cut the pieces, run them through a belt sander, and coat them with clear coat or something to prevent rust. What am I missing?

Joe

The goal wasn’t to remove mill scale, but dross removal. There are many ways to skin a cat, and the acid method is a lazy mans way of removing it. But the mill scale will be removed like it or not with this process before the dross is eaten away.
And no, I do not have a timesaver to run my pieces of metal through to clean everything up, which would work too
JIC you were thinking of another way to remove it. lol! Trying new stuff some good, some not so good . livin’ and learning”…

[Dirtmotor]

I like the acid bath method , I use a 250 gallon tote bottom with a corragated plastic pitched lid , its about 30 % acid the rest water . I leave parts in over night , blow it off with air , then dry it some more with a torch , almost all dross is gone and what little is left I
scrape off with a 5 and one .

[acourtjester]

I use 50-50 overnight soak cleans both mill and dross, I rinse and scrub with borax and water and s stiff brush, then clear water, blow dry. these parts dross was heavier the normal 3/8".

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[tinspark]

I use 50-50 overnight soak cleans both mill and dross, I rinse and scrub with borax and water and s stiff brush, then clear water, blow dry. these parts dross was heavier the normal 3/8".
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Those turned out looking great Tom!

[adbuch]

Doug - this was my first attempt and using an acid bath for dross removal. I used Tom's advise with a 50/50 mix or muriatic acid and water. This was Home Depot swimming pool acid in the gallon jugs. I think next time I would use it full strength and perhaps forgo the wash soda rinse. For these particular parts, I wanted them in bare metal with a clear coat finish. The acid bath certainly removed the dross - but left a sticky coating that was hard to clean off.

I suppose it this was for parts to be painted (or powder coated as Tom does) then they would have been fine "as is". The parts I was making are circle templates to use for layout work. I marked them with the sizes before spraying on the satin clear finish.

David

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[tinspark]

David, I vaguely remember seeing those parts a while back. I didn’t get any stickiness with my parts. But those would be a good candidate for an acid ath. I like the bucket storage idea. I did go with bill Wardens (Steel FX) recommendation and used a little dawn dish washing detergent in the rinse. But mainly because I had it on hand from the kitchen and took the easy route. But did get a slight rust flash which sanded off very easily with a dull 80 grit sanding disc. Which was almost a wipe with the sander. I might try full strength next time also. Can always dilute it if its a fail, but I doubt it will be

[adbuch]

Tim - these were the finished parts. The one on the left was sanded, the one on the right was from the acid bath.

David

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[PlasmaDon]

I am not sure why I should go through the process of removing mill scale, when I can buy cold roll steel that doesn't HAVE mill scale on the surfaces.

You can get HR P&O which is cheaper than Cold rolled.

The supplier "pickles" in acid, and then "oils" the steel before you get it.