# Coating For Mild Steel



## cncastle (Sep 22, 2016)

I'm new to all this.  One of my first projects is going to be making some spacers on my mill. They'll be about a half inch thick with a couple holes drilled through.  In the end they'll be on a table in my garage and will see whatever humidity is there.  I'd like to get them coated with some sort of coating that will protect from corrosion, add negligible thickness, and whatever thickness it does add should be uniform. I don't mind sending them off for the coating. Any suggestions?


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## Tony Wells (Sep 22, 2016)

Material?


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## cncastle (Sep 22, 2016)

I haven't selected the exact material yet but probably something like 1018


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## 4GSR (Sep 22, 2016)

Down here in oilfield country, we use and have many different coatings available to us for corrosion protection. 
If you have access to stainless steel supply, select a 300 series stainless steel and make the spacers from this material.
I went back are reread what you are doing, It might be good enough to make the spacers out of steel and have them phosphate coated till they are black in color.  As long as they stay oiled you shouldn't have any issues with corrosion.  You are going to have a bigger problem keeping things on your mill from turning into a rust bucket than a couple of spacers. Ken


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## Tony Wells (Sep 22, 2016)

Kind of depends on how much trouble and expense you want to go to. You can get some black oxide type coatings from many of the gun suppliers, like Brownelle's, or even a cold blue. I'd agree heartily with Ken though, if you can get some 303 or something like it, you'd never have to worry about them. And 303 machines about as easy as anything.


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## chips&more (Sep 22, 2016)

Sorry, not enough info. I’m guessing a bench mill size? I think plastic, like Delrin, would even work...Dave


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## John Hasler (Sep 22, 2016)

4gsr said:


> It might be good enough to make the spacers out of steel and them phosphate coated till they are black in color. As long as they stay oiled you shouldn't have any issues with corrosion


Phosphate them, oil them with linseed oil, and then bake them at 200F or so until it isn't sticky.


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## Tony Wells (Sep 23, 2016)

Phosphate is a good solution, and one that can be done in the home shop easily and cheaply. It's a good coating, and a great surface prep for painting, as long as you don't oil it.


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## Martin W (Sep 23, 2016)

Wool wax will keep it from corroding. Fluid Film is made from wool wax.

Martin W


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## Smithdoor (Sep 23, 2016)

For tooling I some times use gun bluing just use the cold type can be purchase for you local gun shops even Amazon and Walmart has this low costs
https://www.amazon.com/dp/B00SOUKFLW?psc=1
https://www.walmart.com/ip/Perma-Blue-Liquid-Gun-Blue/17163515
The other way is put in a oven at 450 and let set for few hours

Dave


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## FLguy (Sep 23, 2016)

John Hasler said:


> Phosphate them, oil them with linseed oil, and then bake them at 200F or so until it isn't sticky.


Yup, it works very well. If pc. is too big to bake it just use Ospho by Skyco. Must clean part very well, think acetone.


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## TOOLMASTER (Sep 23, 2016)

on steel i find that a nice rust finish lasts forever.


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## John Hasler (Sep 23, 2016)

FLguy said:


> If pc. is too big to bake it just use Ospho by Skyco.


Or hang it out in the sun for a couple of days.  Too late in the season for that here, though.


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## FLguy (Sep 23, 2016)

John Hasler said:


> Or hang it out in the sun for a couple of days.  Too late in the season for that here, though.


Do I see snow flacks in the air???


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## John Hasler (Sep 23, 2016)

FLguy said:


> Do I see snow flacks in the air???


Not quite yet.


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## TOOLMASTER (Sep 23, 2016)

just rain....again....hope it stops by winter


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## Wreck™Wreck (Sep 24, 2016)

Iron oxide is a common surface finish for low carbon steels.

If you are serious however have the parts hard chromed at 2-3 tenths a side.


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## 4GSR (Sep 25, 2016)

Before I would do hard chrome, have them electroless nickel plated.


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## Tony Wells (Sep 25, 2016)

I'd go back to ss before I did that lol, but ENP is easier and cheaper than chrome.


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## Ed ke6bnl (Oct 23, 2016)

FLguy said:


> Yup, it works very well. If pc. is too big to bake it just use Ospho by Skyco. Must clean part very well, think acetone.


How exactly do you phosphate coat let say a .5 bolt by 4 in. verses just oil and bake


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## John Hasler (Oct 23, 2016)

Ed ke6bnl said:


> How exactly do you phosphate coat let say a .5 bolt by 4 in. verses just oil and bake


I dilute some of the phosphoric acid I buy at the farm store about 5:1 and just soak the bolt in it overnight.  If you heat the solution to near boiling it takes about 15 minutes.


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## Ed ke6bnl (Oct 23, 2016)

John Hasler said:


> I dilute some of the phosphoric acid I buy at the farm store about 5:1 and just soak the bolt in it overnight.  If you heat the solution to near boiling it takes about 15 minutes.


Thanks, I will be trying that, I believe big box stores have phosphoric solutions


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## kingmt01 (Oct 24, 2016)

John Hasler said:


> I dilute some of the phosphoric acid I buy at the farm store about 5:1 and just soak the bolt in it overnight.  If you heat the solution to near boiling it takes about 15 minutes.


Very interesting subject. What is the brand name of what you use? Any detailed procedure that you use?


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## John Hasler (Oct 24, 2016)

kingmt01 said:


> Very interesting subject. What is the brand name of what you use? Any detailed procedure that you use?


I buy whatever brand of phosphoric acid-based pipeline cleaner the farm store stocks.  The procedure as described: I'm just after a protective coating, not a firearm-quality finish.  You do need to remove all oil. If the parts are rusty it helps to scrub them a couple of times during the soak with a stiff plastic brush.  After the acid treatment I rinse with tap water and air dry.  I often then apply boiled linseed or or tung oil to tools and then bake them for an hour at 250F.


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## kingmt01 (Oct 24, 2016)

Thanks. I've never used phosphoric acid. The name brand is so I know what I'm looking for. It seems I've heard of this before. I'm not sure of the word but here is a shot at it. Is Parkanising or something similar to that word the correct term for it?


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## John Hasler (Oct 24, 2016)

kingmt01 said:


> Thanks. I've never used phosphoric acid. The name brand is so I know what I'm looking for. It seems I've heard of this before. I'm not sure of the word but here is a shot at it. Is Parkanising or something similar to that word the correct term for it?


Parkerizing uses phosphoric acid, but there's a bit more to it if you want the full effect.  

I just emptied a jug of "Sterosol Milkstone Remover and Acid Rinse".


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## kingmt01 (Oct 24, 2016)

I thought it sounded like something I'd read before. I couldn't remember exactly what it was tho. Good information that I may have to research again.

Where I live you can actually watch the rust grow. I've just come to accept it as another coating in itself. I've pulled parts out of acid to paint & before I can get the water wiped off to spray them they are already rusting again.


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## John Hasler (Oct 24, 2016)

kingmt01 said:


> I thought it sounded like something I'd read before. I couldn't remember exactly what it was tho. Good information that I may have to research again.
> 
> Where I live you can actually watch the rust grow. I've just come to accept it as another coating in itself. I've pulled parts out of acid to paint & before I can get the water wiped off to spray them they are already rusting again.


Nothing encourages rust like HCl (muriatic acid).  Phosphoric provides a pretty good base for paint and discourages rust.


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## Tony Wells (Oct 24, 2016)

I add manganese dioxide to my phosphoric acid. Therefore I get something akin to KemPlate from the old days. Big Red spec'd it, as did most of the oilfield service companies.


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## Dan_S (Oct 24, 2016)

Unless it's a surface that's going to see a lot of impacts I'd just hit it with a good industrial enamel.

I use this a lot and it holds up really well to all manner of shop chemical s and oils. It can be sprayed or brushed.
http://www.valsparpaint.com/en/find...y-paint-1/anti-rust-armor-enamel.html#/colors


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## 4GSR (Oct 24, 2016)

Here's what I use.

http://www.brownells.com/gunsmith-t...-chemicals/oxpho-blue--prod1072.aspx?psize=96

This is also sold by Birchwood Technologies under the name "Presto- Black". Used to be called "Tool Black" and may still be called that when bought at certain tool houses that would carry the stuff.

https://www.birchwoodtechnologies.com/store/Room-Temperature-Blackening-for-Iron-and-Steel.html

A couple of things to remember,  degrease the parts.  I go borrow a little Dawn dish washing soap from the kitchen.  Use hot water to wash and rinse the parts off with.  Do this wearing HF disposable gloves so you don't get finger prints on the parts from your oily hands.  While the part is still fairly warm, head for the garage and start to applying the blackening solution using shotgun bore wipes or cotton balls.  It should turn black instantly.  After about 20 minutes, wipe off parts with paper towels and oil.  DO USE WD-40!  Steels with a high Chrome content may not coat evenly or coat at all.  I've had this to happen, too.  High hardness with high Chrome content like in some of the 4140-4145, 4340 materials may not coat very good.  Heat in the parts does help, say 180-220 degrees F.  Just a few pointers I've experienced in the past using this stuff.

Until about six months ago, I had a local source that did manganese phosphate coating which we use extensively for down oilfield equipment.  What little stuff I needed done, they would do it for me.  In exchange, I usually ground up special cutting tools for them in trade.

Ken


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## John Hasler (Oct 24, 2016)

Tony Wells said:


> I add manganese dioxide to my phosphoric acid


So do I.  It's the black stuff in alkaline batteries.


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## Tony Wells (Oct 25, 2016)

I get it from pottery suppliers in bulk. Cheap. It's used in coloring ceramics. Fairly pure that way and already powdered. I have a heated stir plate and get my acid up to about 200°f and run about 10-12% by weight and cover. Sit heated for 30 mins min, then after cooling, pour off the top. What settles is excess to a saturated manganese phosphate solution. The reaction rids itself of the oxygen, if I remember my chemistry right. This I dilute about 30:1 with destilled or DI water for critical stuff, or in my bigger containers (60 gals of so) I just use tap water. It does make a difference, but on the larger parts seldom is it all that critical that it comes out perfect.


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## kingmt01 (Oct 25, 2016)

John Hasler said:


> Nothing encourages rust like HCl (muriatic acid).  Phosphoric provides a pretty good base for paint and discourages rust.


Hydrochloric is what I use before painting chrome. I also use it for mild steel at times. That fast rusting is why I think it works so well to hold paint to chrome.


Tony Wells said:


> I add manganese dioxide to my phosphoric acid. Therefore I get something akin to KemPlate from the old days. Big Red spec'd it, as did most of the oilfield service companies.





Tony Wells said:


> I get it from pottery suppliers in bulk. Cheap. It's used in coloring ceramics. Fairly pure that way and already powdered. I have a heated stir plate and get my acid up to about 200°f and run about 10-12% by weight and cover. Sit heated for 30 mins min, then after cooling, pour off the top. What settles is excess to a saturated manganese phosphate solution. The reaction rids itself of the oxygen, if I remember my chemistry right. This I dilute about 30:1 with destilled or DI water for critical stuff, or in my bigger containers (60 gals of so) I just use tap water. It does make a difference, but on the larger parts seldom is it all that critical that it comes out perfect.


Thanks Tony. 
I copied that to a word doc for future reference.


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## John Hasler (Oct 25, 2016)

Tony Wells said:


> I get [manganese dioxide] from pottery suppliers in bulk.


I'll buy some if I ever start doing a lot of phosphating.  In the meantime dead batteries are free (the stuff in dead ones is actually Mn2O3 but seems to work fine.  It's also very finely powdered).


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## 4GSR (Oct 25, 2016)

John,

I'm going to try your mix one day.  Have plenty of dead alkaline batteries daily around here.  Have plenty of muriatic acid from the swimming pool, too. 

Ken


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## John Hasler (Oct 25, 2016)

4gsr said:


> John,
> 
> I'm going to try your mix one day.  Have plenty of dead alkaline batteries daily around here.  Have plenty of muriatic acid from the swimming pool, too.
> 
> Ken


I use phosphoric acid, not muriatic acid.  Muriatic acid is good for stripping steel down to bright metal but that bright surface will rust while you are looking at it and needs some sort of paint or treatment promptly.

I also use phorphoric acid to remove rust.  It's slower than muriatic acid but less agressive.  It won't dissolve the metal and change dimensions and it leaves a rust-resistant surface.

Also note that my slapdash process does not produce a consistent firearm-quality coating. You may get blotches and variation from one part to the next even in the same bath.  It's for corrosion reduction, not appearance.  If you need a really pretty finish read up on parkerizing.


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## 4GSR (Oct 26, 2016)

Good point John, your right on the phosphoric acid. 
Thanks, Ken


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## aliva (Oct 27, 2016)

I've used this from Caswell works pretty good, it's cheap,
http://www.caswellplating.com/metal-antiquing/black-oxide-kits.html


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## f350ca (Oct 27, 2016)

I use the same product from Caswell, been pleased with the results.

Greg


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## astroracer (Oct 30, 2016)

Caswell kit here also. Works well. Posts #12 and 13 in this thread.
http://www.hobby-machinist.com/threads/a-shop-built-adjustable-angle-plate.41926/#post-363315
Mark


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## EmilioG (Dec 16, 2016)

I use Dow Corning MolyKote metal protection liquid.  It's a wax in solvent that can be thinned down and sprayed.  It's not a permanent coating but will prevent rust on all metals and easy clean up. 
Very tenacious and will prevent corrosion for a long time of stored metal and tools, etc...


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## gi_984 (Dec 21, 2016)

CN,
     I do manganese and zinc phosphating.  Running another batch over the holidays.  Send it to me and I'll do it for you no cost.  Just pay the shipping.  PM if interested.


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## cjtoombs (Dec 21, 2016)

Why coat it at all?  Lots of milling machine hardware is uncoated steel or iron (table, vise parts, vise jaws, parallels, etc).  Just keep it oiled and put away when not in use.  Otherwise, I use Van's cold bluing compound.  A word about bluing, it won't prevent rust, you still have to keep it oiled.


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