Using Muriatic Acid to remove scale from Hot Rolled Steel! MFG@Home
Vložit
- čas přidán 20. 08. 2024
- Skip to 10:45 for the acid bath
I've been cutting a lot of parts on the Torchmate plasma lately which need to be either polished or engraved. The scale on the hot rolled steel had been problematic. Many folks have discussed using muriatic acid (a.k.a.hydrocholric acid) to remove the scale - a similar process done by industrial mills in a process called pickling - but it's easy to do at home!
This video discusses the process and some of the safety tips and tricks.
see more at www.nyccnc.com and / nyccnc 5 Reasons to Use a Fixture Plate on Your CNC Machine: bit.ly/3sNA4uH
I would also have a bath of water and baking soda on hand to passivate the metal.
Meaning, pull parts from the acid, straight into baking soda and water solution....just have to wait for the reaction to stop (wait for the bubbles to stop). Then if you don't plan on painting the part, lightly oil for rust protection.
I really feel stupid. I've been working with steel for over 30 yrs and never realized I could use muriatic to remove scale like that. Cool vid will subscribe.
I did know the scale is harder that the steel.
This is a video that will help me to no end. I have been thinking about a project and will be using some hot roll steel for some of the parts. I even tried using my blast cabinet with glass beads. Didn't work. You did this video at the perfect time! Oh I also love having my shop tools. I will be trying this out.
I used to work in a Fab shop, and we started using pickled and oiled sheet steel as it would clean up/prep easier for painting. I don't remember the cost difference (minimal), but it was lightly oiled, and had thin layer of Mylar that would keep the oil on the surface of the steel.
Couple of other things when working with aromatic acids:
1. Always work outside.
2. Create an upwind situation by placing a fan behind you...it will blow the harmful fumes away from you.
3. Decent pair of rubber gloves.
4. Keep lots of Baking Soda (sodium bicarbonate) on had for spills, and it will neutralize the bath when you are done pickling.
Just my 2 cents.
I recently made this switch and it's been great! I'm using the same setup and after a month the acid is still pretty strong. I've noticed it's heat sensitive too - much more effective when it's warm versus cold.
I haven't done any timing checks but that might make for a good test. Also, I let mine soak a bit to soften the edges of my artwork.
What I have observed is much more rapid activity as the temp goes up. A couple of hours typically removes all of the dross as well as mill scale.
Definitely watch those fumes! I do mine all outside...
NYC CNC Most chemical reactions have standardized rate data at 20 C = 68 F, or at 25 C = 77 F
If you want to speed things up, you can work at the temperature of a *warm* cup of coffee - *HOT* coffee is at 140 F = 60 C when made to European safety standards - stay down around 122 F = 50 C, and you won't have any worries about thermal issues...
The chlorine vapors will be stronger at warmer temperatures however - for the same reason that the reactions will go faster, as the chemical activity of the ions in the solution goes up with temperature - work out doors, or with a fan blowing fresh air past you towards the work.
Keep baking soda handy when using this acid.
Not only will it help keep things from getting destroyed due to spills, you can also use it as a "stop bath" (I call it that because it reminds me of the photography method), which should help prevent the surface rust issues you and some other comments are seeing.
Rinsing in water doesn't seem to be quite enough for me to prevent future rusting over time.
I've used this technique for a few years....then I switched to having everything cut in HRPO(Hot Rolled Pickled & Oiled) which does not have mill scale.
The mill scale is extremely hard. For grinding, I've had the best luck with Strip-it-all type discs. I think I saw that in a Ron Covell vid.
You might try the full strength version. It's more like 15-20 min instead of 2hrs. If I left a part in for 2 hrs, it would come out looking like Damascus....you can see all grain of the steel and the surface will be rippled.
Like you were saying about the vapors.....extremely bad for you lungs, or anything else in the vicinity.....especially steel. Even with my bucket closed, all my steel items within about a 6' radius turned orange with rust.
Loved the first way of removing dross.....I've never seen that. I'll definitely use that next time I fire up my plasma.
Great vid!!!! Thanks!!
Great video! I like this method but have never tried it myself. The safety is very important so it's great you went into detail about how to do it safely and even showed it's info on line where we all can get it.. Kicken video..
Dennis
This is excellent info and very well presented too. I've not considered removing mill scale using acid before. BTW, I'm most envious of your CNC plasma cutter there. My method is manual, create cad drawing, offset lines to accommodate cutting head diameter, print on paper, glue to cardboard, cut out card templates, glue to steel sheet and hand cut around template edges with plasma torch. Works OK, but your CNC setup would be 100X faster. Many thanks for posting your work!
That's an interesting method. I've always just ended up using a steel wire wheel on the bench grinder to get the scale off. It leaves a quite nice, albeit quite different than from hydrochloric acid, finish as well.
Thanks for the tip!
/Daniel
NYC CNC For sure, if you're doing one or a few parts that's no big deal, in the hundreds I'd be looking for a method you could just set up and walk away from as well.
You can always neutralise the acid with bicarbonate of soda. Just remember that it's going to bubble and foam, so don't stick your face next to it.
The people making printed circuit boards agitate the acid they're using to get more consistent results. It's probably not an issue for the stuff you're doing though.
Thanks for the vid. :)
These videos are very well done! I love how you even show where to buy the equipment and supplies, the safety concerns with using them and your own take on how they can be used. Thank you so much for making these. I'm just starting out and I'm learning so much! Many thanks NYC CNC!
I haven't watched all of your videos yet, by may I make a request if you haven't done this? Can you do a walk-through of your shop and show us some of the tools you have and offer a brief explaination of what you use them for and what tools you would like to add in the future?
I have also used the liquid CLR (calcium lime rust) product on a bunch of old drills and end mills given to me that were coated with surface rust. I let them soak over night and rinsed them off with water. It removed the rust and left a nice even black finish on the tools. I coated them with light oil after treatment and hsve put them to good use. As John states SAFETY is a must, good ventilation, rubber gloves, and splash face shield are a minimum.
CLR is a diluted solution of a couple of acids as near as I can puzzle out from their MSDS.
It works great for cleaning limescale and rust stains off of plumbing fixtures without damaging the enamel finish.
It does however release a gaseous byproduct that smells a lot like sulfur dioxide = SO2 and can trigger coughing fits and asthma attacks, so good ventilation is even more critical than you might think...
Great video! Thanks for all the detail in the videos and the time you put into them to share with us. I just started making a few video on my channel and now I know how much time you spend making videos to share with people.
Keep it up!
Wow there are so many interesting videos on your channel. Glad I stumbled upon this. And this video was quite useful as well.
Great video, Wish I would have seen it before I opened my acid in the shop. It rusted a lot of the exposed metal in the shop. Kind of a unique finish actually that I like
Tip: Use a sawdust/acid combo to "pack" the material in. no splash and seems safer.
Looks like you need to increase your pierce delay. Your torch is moving before the pierce is complete.
Add me to the list of never thought of using Muriatic acid for this. I have read and know people who use this to accelerate rust formation on steel.
I use it frequently when welding hardware to strip the coating off (Zinc or Cadmium). It works way better than physical abrasion methods (blasting or wire wheel) IMHO.
NYC CNC TIG /stick / MIG
NYC CNC
I've used mainly Lincoln and Miller machines. I know someone who bought a longevity machine and they seem pleased with it.
Bill De La Vega
The gloves you used looked like cloth that will absorb the acid like a sponge and did not cover up some of the skin on your forearm. Leather gloves are only slightly better, but for safety you should use thick chemical resistant gloves that extend up your forearm. A respirator is probably not required but goggles (not glasses or a face shield) is critical when handling this stuff. You only need about 15 minutes for concentrated muriatic acid to work in the summer. 30 minutes in the winter. But since you used diluted muriatic acid it might take longer. After the acid bath you should neutralize the acid with baking soda. Other wise your metal will rust very quickly, but you also need to rinse off the baking soda really well or it too will rust your metal. A less toxic acid is acetic acid, but it takes 24 hours instead of 15 minutes.
Hi John, you didn't mention how to prevent the part from rusting. Do I just rinse it with water and give it a decent oiling? Or is there some other voodoo to end the process. Great video. I've been struggling with removing scale for my swage press build. Thanks
Oh yeah I know what you mean by you "love having that equipment" ... I would love that too =) Have a nice day John =)
Does muriatic acid need to be mix with water for this metal process, or let's just muriatic acid alone?
I used this stuff to clean steel but i didn't dilute it.. Is that bad for the steel? I noticed some rust quickly accumilated so i stopped using it and cleaned the rust up with steel wool and oil. Other than the rust is this stuff bad for steel as in weakens it?
heat up white vinegar and it should be gone in 10 minutes or so , is much safer abd fast.
Did you use full strength muriatic acid? Looks like it. The black/grey tint may be copper and other alloy components.
From what I have seen on CZcams, your vid is the best (especially about the safety). Congrats!
I have 2 questions...
First question is: I'm using Muriatic to clean some stainless steel tubing (inside and out). I don't know the diff between reg steel and stn steel but I am presuming that I don't leave it in the bath for as long as you do for the scale removal? I'm concerned about etching. Just wanting to remove rust.
Second... the M acid I'm using is at a 30% concentrate (M acid is sold in different degrees of concentration from 20 to 35%). Do I need to dilute it for the stainless steel?
Thanks!
What do you use to wipe off (clean) the acid from the piece after you pull it from the bath? I thought about using water but I don't want my piece to rust and I wasn't sure if water would completely remove the acid anyway.
Does the muriatic acid process stop working when you remove the metal from the acid? Or do you have to rinse?
Good information. Thanks!
did you just wash it of with water after taking it out of the acid?
just to add a little trivia, gun bluing is done with acid
You should neutralize any acid on the part with a baking soda-water solution. Metals are porous so some of the acid will work it's way in. You will get instant rust on the clean metal. To prevent that either coat with a light oil such as WD40, or use phosphoric acid to create an iron phosphate coating which also prevents rust.
do you have a spring type switch for Z touch off? or Ohmic sensor?
Doing this after finding out how well and fast it eats lime scale from a poor flushing toilet. Shit’s a miracle lol. My question is once you have this set up fir a project, have you reused the acid. Meaning will it last a week in the plastic bin where you can reuse it a few times or is the acid pretty much dead or useless after one session? Lastly, once you removed the parts did you just rinse them off with water and is there any special procedure for disposal of the acid / metal mix.
What about tumbling in media to get the mills scale off?
NYC CNC Those surface dings are work hardened by the tumbling - if you can get access to some data, you will find that they have a Rockwell C hardness much greater than mill-run stock...
If this is done inside a garage everything in the garage will later rust. Ask me how I know!
Chrome was fine and the farther away from it things were the better they came out. I put old tools in a tub with acid and set it by the overhead door and left it for a day with the door up a foot or so. All my shovels and garden tools were closest and took it the worst. If the door was down I don't know how bad it could have been. It took months to show on some things. Blood red rust.
Good video but you should be warned that pickling steel with muriatic/HCL will causes the steel to absorb hydrogen from the acid and pool up in voids or bond with carbon to form methane inside the metal.
Heat treating the metal is required to restore its strength back to normal.
NYC CNC It can cause structural failure, specifically - fracturing. The technical term is Hydrogen Embrittlement.
Some commercial "all purpose" cleaners(not meant for metal, obviously) have induced failures on aircraft landing gear due to hydrogen embrittlement. Basically anything that provides a source of hydrogen will cause it, and HCL(muriatic acid) is essentially a solution of hydrogen ions.
My understanding is that it is not a material change but simply due to the nature of hydrogen being able to fill the microscopic pores of metal but it completely reversible by heat treatment(bake it in your oven).
Wikipidia has more info, but I found this far more informative: www.heat-treat-doctor.com/documents/hydrogen%20embrittlement.pdf
Hydrogen embrittlement is a problem that can happen in steel exposed to hydrogen gas under pressure - such as in a hydro-treater in an oil refinery - not so much when it's an aqueous solution of a mineral acid... the hydrogen ions are actually hydronium ions - H3O+ - where the H+ shares the electrons with the water molecule... this is an aqueous (water based) solution...
Forms methane from reacting with carbon??? We do this in refineries and steel mills at *very* high temperatures with gaseous hydrogen, sometimes liberated from water vapor - not possible in a ionized water bath with acidity. Graphite is actually a reasonably inert material to acids.
Hydrogen embrittlement involves the formation of iron hydride - not going to happen without some serious pressure and some heat...
What is a problem with chlorides and stainless steel is stress-corrosion cracking, where chloride ions from seawater get into cracks in the stainless part, and the localized high pressures make chromium chloride, ripping the chromium out of the crystal structure.
A problem in the metalworking community is that there are many folks out there who don't know as much chemistry as they think that they do - and all too often not all that much metallurgy either - and they come up with half-baked theories which sound good to someone who may or may not have had high school chemistry..
Then those old-wives tales get repeated as gospel truth by folks who don't know why they aren't possible as stated - and repeated again & again...
If pickling reduced the strength of the steel, none of the steel makers (US Steel, Arcelor-Mittal, NUCOR, et al) would be using it to clean the coiled steel used for making galvanized sheet metal, which often gets stamped into the final form to make a product...
My piece is turning yellow as soon as it dries? Why?
It's probably flash rusting. You have to neutralize immediately and wipe with oil.
Where do you buy your steel?
I tried this method after watching your video and it did remove the mill scale as suggested, but now what I'm seeing is accelerated rust. I did rinse and dry the metal after the acid bath. Is it possible I didn't dilute the acid enough? As it stands now I'm trading mill scale for rust...
+NYC CNC I watched some other videos and it seems you need to flush the metal with water into a waste bucket, then apply a baking soda mix to the metal to neutralize the acid, and then flush again with water before drying thoroughly.
+zachmanx Maybe it's more porous after the acid treatment, providing more surface to oxidize.
+zachmanx the mill scale actually protects the steel from oxygen in the atmosphere. with a super clean part exposure to air will cause the steel to react with the oxygen forming iron oxide (rust) you could oil it if you dont need it to be clean or paint it or electroplate it!
+zachmanx Don't know if you had any progress with this but if you make a baking soda solution that should neutralize the muriatic acid. Also like the guy above me said, a light oiling will help protect the steel as well.
pmc.ucsc.edu/~apaytan/pdfs/Acid%20Neutralization.pdf
+Plazmattack Yeah, I tried the baking soda solution with mixed results. I think just that much moisture on bare steel is just going to lead to some rusting unless you're just very quick and thorough about protecting it. I ultimately found it to be unnecessary where MIG welding and sand blasting are involved. At the time I was just trying to get clean metal for TIG. Thanks for the tip though.
Btw what I was getting at with that rant is this. Dont store the acid in your shop! Whether the container has been opened or not. Way away from any machinery.
I had some muriatic acid around from doing some brass instrument cleaning. Silly me, I thought the bottle would be sealed if I closed the top. Put the bottle near my motorcycle. The copper plating under the chrome plating on my motorcycle muffler corroded, giving a nice green bloom coming through the porosity of the chrome. I've got a lot of expensive rechroming to do now. Yes, store this stuff outside away from anything else.
Please don't be like this idiot and put rusty metal into a closed container with the acid. I just had my container explode because of the pressure created with the reaction between the rust/metal and the HCl acid. It will expand the container. It got all over my back patio and on the new grill. Thank god I wasn't standing near it. The lid was 6 feet away.
His steel wasn't rusty, but thanks for mentioning the pressure buildup!
Desir Leather Mill scale basically is rust (iron oxide...)
The container he is using is a snap lid container it is NOT an airtight container and he will have no problems with that I think you will find that it is you who is the idiot
you could just soak it in vinegar
I heard it works its an hour for per inch of metal
works great but takes 24-47 hours
Are you using two layers of gloves? It's looking like you're using gardening gloves...
NYC CNC one thing that might be better is to use a mesh basket rather than dropping them in with pliers. My first thought was those sonic cleaning baskets, but you could probably find something cheaper like dishwasher silverware baskets or fryer baskets.
NYC CNC Cloth gloves are worse than working bare handed with strong acids and caustics - we didn't need to wear gloves in the chem labs until after 1984 when I was in college. The risks we took in Organic chem with the solvents would cause a safety person to have conniptions today.
For what you are doing with essentially pool acid - somewhat diluted HCl - good old fashioned dishwashing gloves - the heavier duty latex gloves - should be the best bang for your buck - we wore them when washing laboratory glassware, and cleaning it with concentrated HCL, HNO3, or H2SO4 in the labs where I used to work - when working with small amounts, and not all day...
The butyl rubber gauntlets - up to the elbows! - and PVC aprons were used by the folks who worked with larger quantities of the liquids - they also did a good job of keeping hot soapy water off of people...
Work outdoors, or in a *WELL* ventilated room, with a fan blowing fresh air past you and out an open door or window at at least 100 ft/min...
As others have pointed out, the chlorine vapors will attack any iron objects - if you must work indoors, you want a room set up like a laundry or janitorial slop sink, with plastics or enamels for the hardware.
Eye safety is crucial - wear at the least some Z87 rated goggles specified as being splash protection.
A face shield is nice to have, but is less important for HCl than for many other acids and caustics... so long as you have:
Baking soda and a good supply of *LOTS* of fresh water.
But, remember, pool service people work with Muriatic Acid (HCl) safely, and battery shop people work with battery acid - concentrated H2SO4 - with reasonable precautions for their own safety.
When in doubt, read the label on the bottle of the chemical, and you can go online and get a Material Safety Data Sheet (MSDS) for free for any chemical which you intend to use...
babble? babble babble... babble?