optimum surface finish for dodgey baked oil coating? - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 05:35:04 am
content: In the interest of keeping my costs down, I am thinking about finishing mild steel with a baked oil coat.Since its not a frying pan, and my goal is corrosion resistance, what do you think a good surface finish is for this job? Should it be as smooth as possible, or do you want a coarse grit (it does not really matter) so the polymer can build up in grooves?I was thinking maybe using like 40 grit sand paper on it, bluing it with a torch, then putting a coat of oil (motor oil and canola are options) then baking it in a oven for 1 hour @ 400F and repeating it a few times. Or might sand blasting be superior? Maybe you can cross hatch the work some how(for oil retention)? (right angles of attack with 40 and 60 grit maybe?)It's a large frame object, I can't do a hot dunk into an oil pool. It needs to be a bake coat. Lots and lots of surface area with tons of stamped metal. Will barely fit into oven I think.I am only interested in solutions relating to using oil as a coat, I know you can powder coat spray paint etc.

author: KL27x
author_rank: Super Contributor
timestamp: February 25, 2019, 08:12:49 am
content: Age old traditional solution. Linseed oil. You bake/torch the part, first, then apply it to the hot steel. This turns the steel jet black. Unlike motor and canola oil, linseed oil is a polymerizing oil. Other oils might work, but maybe this polymerizing thing makes a difference. It's the traditional oil for this, anyhow, and I can't be sure why. I expect it's because it contains oxidizers that help to form an oxide layer on the steel. I doubt any polymerized oil sticks around for long, and if you applied a thick layer of it, it would be sticky and gross. The surface finish doesn't really matter, AFAIK. Smoother the better, if you want protection against rust. Dunno what you're doing, but this would be a good, quick and dirty finish for a cheap wheel barrow that was recently cleaned of dried cement.But definitely not as good as paint; I don't know of any "oil finish" for steel that will protect an outdoor tool from rust without regular maintenance. Military arms are traditionally stored coated in a heavy grease like cosmoline and wrapped in paper. But for a working tool, this is not a solution.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 12:16:45 pm
content: won't the oil hang around better in grooves of some kind?

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 12:18:35 pm
content: and what about people saying online that motor oil is good for this job because it 'has a high carbon content'? They call this process 'blackening'. They say used is better?Maybe the metal fragments in it act as some kind of binder?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2019, 02:01:48 pm
content: Yes, linseed oil, or the food-grade equivalent, flaxseed oil. You want high polyunsaturated content. These polymerize into a varnish.Or you can use regular oil based varnish, which dries much faster and is generally better formulated. The chemical reactions are similar -- this is just optimized for faster drying, better finish and a flexible result.Motor oil I think only works when it's literally burned on. That's the only time the carbon content would matter. More a blacksmithing thing as far as I know, and even then not very good? May also date to the days when vegetable oils were commonly used for lubrication, and so, varnish formation would follow the usual process.Surface prep: I'd put on whatever finish looks and feels good. 220 grit belt sander would give a nice satiny brushed look, or an orbital sander for a more nondirectional pattern. Clean with soapy water and/or solvent wash.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 02:49:39 pm
content: Lol i think i renembered the location of an old can of aluminum paint.Ill put it this way this peice od shit i am restoring is built so bad i had to jury rig a sand blaster to get into its geometry. If i was ant man i might try a orbital sander xdI hope that can of paint is still wedged into the wall where i renember lolAs for the blacksmithing technique, if i got tge steel hot and sprayed it with oil from a spray thing would it work? Then that coating can be polished down a bit and covered with a polymerized oil coating?If you can do a motor oil spray section by section at a high temp, clean it up a bit and then do a bake seed oil at low temperature it might be pretty robust and sleeek even?Do you know if motor oil carburizes it or something?Or cleaner then spray, can you just get it to whatever temperature and press a rockwool or fiberglass used motor oil soaked rag on it to dab coat it?

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 02:54:49 pm
content: It actually has really good geometry for absorbing heat and strenght is not really a issue. Its a sawhorse.If someone knows whats going on with the hot oil blacksmith process i can get sections to whatever temp with blowtorch. It will eat heat in the folds it has.If you got just regular paint btw, is the polymerized oil a good primer?

author: KL27x
author_rank: Super Contributor
timestamp: February 25, 2019, 05:58:03 pm
content: No. You can apply oil paint over oiled wood. You should probably card scrape, first, if it's practical. But on steel, if you're going to paint it? Flap wheel, sand blast, or acid etch, IMO. If you've already oiled it, then maybe just a good wipe with solvent is sufficient. But I wouldn't go out of my way to oil first, then paint.I suggested smooth because the polymerized oil is at first gummy, then brittle. On wood, you use this stuff because it soaks into the wood; you don't want to necessarily build a surface layer. After several applications, it will sort of plasticize the top 1/4 mm of wood; and then you will still have to reapply, regularly. On metal, if you want dodgey, this is it. The oxide layer, plus regular application of (any) oil, is perhaps going to be more useful than the varnish property. Metal paint is about a hundred times more durable.

author: langwadt
author_rank: Super Contributor
timestamp: February 25, 2019, 06:36:08 pm
content: Quote from: coppercone2 on February 25, 2019, 02:54:49 pmhttps://youtu.be/hS2MMlDiQLo

author: KL27x
author_rank: Super Contributor
timestamp: February 25, 2019, 06:54:42 pm
content: ^Yeah that's a different sort of finish. He's torching it just to melt the wax. If you want to oil-patina fresh steel, you get it way hotter than that. Maybe over 400F.IME, wax might work pretty well for a sculpture, but on a working steel surface it is pretty close to useless.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 07:58:14 pm
content: its actually kind of appealing because it is sooooo easy to redo if it gets stained. Like for a painting table or something. I wonder if wax would work well over some kind of oxide process like gun blue.If you put phosphoric acid on a rusty object, let it react, then put more phosphoric acid (say navel jelly) on it and then cook it, do you get a in-situ parkerization going on (with the iron phosphate that is formed by the phosphoric acid)?

author: KL27x
author_rank: Super Contributor
timestamp: February 25, 2019, 08:15:45 pm
content: Yeah, you can reapply phosphoric acid. Wipe with acetone, apply the acid (naval jelly or cover a flat surface with sawdust before applying liquid acid). Any red rust will very quickly dissolve and leave black patina. Then wipe with oil. But eventually, the surface will have areas of deeper pits.This isn't parkerization, though. To parkerize you dissolve some zinc or manganese into the phosphoric acid. This builds a layer of zinc/manganese (phosphate/oxide?) that is very (relatively) thick and porous. Parkerizing a part usually increases the dimensions by a thou or 2.Colors vary. Zinc park is usually some sort of grey or grey blue. Manganese is usually black or almost black.You'd still have to apply oil, regularly, even if you did a proper park finish.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 08:21:32 pm
content: if you have a iron oxide coating, then react it with phosphoric acid,it should form iron phosphate, which can then be baked with a coat of phosphoric acid (this time the acid has no oxide to reduce, since the surface oxide was consumed) and parkerize if baked?I thought you can do iron phosphate parkerization.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2019, 08:23:23 pm
content: a horribly technical forum post on finishing.com says to add one shot of phosphoric acid to 1 shot of manganese dioxide to 1 steel wool pad to 1 gallon water to make some kind of coating solution.Might try it if I clean up some battery mangenese oxide with the remains of my navel jelly to make a quart of this... i wonder..Does the reaction need to be liquid phase or can you cook the phosphoric acid in a oven?

author: KL27x
author_rank: Super Contributor
timestamp: February 25, 2019, 08:27:29 pm
content: I dunno. I thought parkerization was initially a trademark or patent of the zinc process. I think the guy's name was Parker or something. But maybe it's all called parkerization, now.I have done a zinc parkerized finish on a couple of hand gun slides and on a cast iron band saw table. Didn't get too technical, and I didn't get very close to actually following any directions. Didn't have a sand blaster. I just hand sanded the gun parts and the cast iron table was simply cleaned with acetone. They all came out pretty good, if you were to ask me.Try it. Naval jelly plus heat gun/torch leaves a black finish. I suppose it's iron phosphate. It's not as thick or durable without the Zn/Mn, and it will wear through showing scratches and whatnot over time. But as you say, it is very easy to reapply when it gets worn. This is also a good finish for adhering to paint, if you omit the oiling.

author: eKretz
author_rank: Frequent Contributor
timestamp: February 26, 2019, 04:29:03 am
content: Linseed oil. It will not be sticky when finished if you get it to the right temperature. It needs to be hot. Heat your part then dab a little oil. If it doesn't blacken get it hotter and try again. Repeat until it blackens then keep it hot and apply the oil with an oil-wetted rag images in next post. You don't want it so wet that it's runny, just wet enough to apply a film of oil. I use this method now and then for certain projects. Here's a door knocker I refinished to match my new door lock hardware. It started as weathered brass, so I cleaned it, polished it, copper plated it, then applied the oil finish and weathered it to match the new hardware. Turned out pretty decent. Further images in next post

author: eKretz
author_rank: Frequent Contributor
timestamp: February 26, 2019, 04:30:37 am
content: Couple more.