"Weeping" metal

[drussell2337]

This is my first post to this forum - not sure if this is the right forum, but I have an interesting problem regarding metal that I'm hoping someone can educate me on.  Recently, I decided that I would like to make my own plow disc grill.  I've had one that I purchased from a company  that specializes in making these for cooking, and I wanted a second one.  I had read that people used to get used plow discs (also called harrow discs) from farms, plug weld the center hole, then grind all the rust and paint off, then season the disc like you would a cast iron pan, then they would cook off of them.  I though I'd give it a try - seemed easy.  I found a source for used plow discs and got one.  I'm attaching pix below to show what I'll describe.  I brushed and ground all the rust and scale off the disc, and polished it to a shiny finish.  When I put it over a propane burner to start seasoning it, I just happened to wipe the cooking surface with a paper towel and I noticed a orangish yellow reside on the paper towel.  I thought I had left a layer of simple green or dish soap on the surface so I filled up the disc with water and boiled it, thinking I'd get the reside off.  When I did that, the metal started "weeping" a dark gray residue that would partially wipe off the surface, but discolored the metal on the surface.  Also, the side of the metal facing the burner developed a fine sheen of rust after being exposed to the propane flame.  I reground the disc with 120 grit fiber disc and shined it up again, removing the discoloration, and repeated the process.  The same thing happened, but there was substantially less residue.  I then tried boiling vinegar and water in the pan, and that took the discoloration off the surface, but when I boiled it again with just water the reside reappeared.  I'm wondering what is happening with this metal.  I'm attaching pix of the marks on the back side of the disc.  This appears to be a Case IH Earth Metal harrow disc - the website says it's a boron/steel alloy.  Obviously, I'm not going to eat off of this thing, but I'm wondering that is happening here, and if it is even possible to get it completely clean so it no longer "weeps."

 

[BIGGUNDOCTOR]

Looks like rust to me. I have pressure washed parts at work, and by the time I walked back to the shop they were rusting like that.

That is also how the older firearms were "blued" they would expose them to a high humidity environment with a blueing solution to make them rust. As the rust started to form like what thou have, they would brush the orange off, and repeat the process until the proper deep black was achieved. Blueing is nothing more than controlled rusting.

Metal is porous, and when you heat it up you can see the moisture coming out.

[Jackdawg]

I also think it is just residual rust coming out. Just keep seasoning it and wiping away, it shouldn't take to much for it to stop.

[Eli Taylor]

 

On 3/25/2017 at 2:52 PM, BIGGUNDOCTOR said:

Metal is porous, and when you heat it up you can see the moisture coming out.

 

On 3/25/2017 at 4:35 PM, Jackdawg said:

I also think it is just residual rust coming out.

On this note I recently restored a rusty post vice (wire-cup and oiling). I was told to hit it with a torch to "force out the remaining water".

I was hesitant because I don't want to alter any potential hardening, however it made sense.

Short of heat, anyway to force it out?

[SLAG]

Mr. Taylor,

Alcohol will form a solution with water. That solution has a much lower vaporization temperature than water. It also has less cohesion than water has. For moist wood, wipe the wood with the solution and wait until it has all evaporated. You may with to do it several times. Warming the treated wood will speed up the process.

An alcohol wipe will remove the moisture from metals too. Do it thoroughly and apply a rust resistant coating after that.

SLAG.

[Frosty]

When you sand or sandblast steel your are leaving a surface that's down right shaggy and it WILL rust almost immediately and a propane burner will do it much faster because of the water vapor in the exhaust. Also the hotter a chemical reaction like oxidization (rusting) the faster it happens. 

Next time you brush it oil it immediately or better yet, wire brush, wipe it down, fry some bacon on it and Reward yourself with a bacon sandwich! Wipe the bacon grease around and off while the disc harrow is still hot and it'll be seasoned. Store it where the dog can't help keep it clean, once cool a plastic trash bag is good.

How about checking with a restaurant supplier for their grill care products? You have to keep your flat top seasoned you know.

Frosty The Lucky.

[BeaverNZ]

I think you will find metal is not porous, the water that appears on the surface is water condensing on the cold metal from the chemical reaction of the hyrogen in the  fuel combining with oxygen and making water. This can also be a problem in the workshop if you have a unventilated fuel burner for heating LPG is quite bad for this as it has more hydrogen in its makeup than say diesel so makes more water when burnt. I have this happening in my workshop over winter and have found that a wipe with LPS2 works well on unpainted steel Cheers Beaver PS the surface getting a slight rust when heating may also be caused by carbolic acid from the CO2 combining with the water formed as well

[Frosty]

Yes. I forgot to address that question.

Frosty The Lucky.

[SLAG]

Gaseous carbon dioxide plus water yields the weak acid carbonic acid. (CO2 + H2O yields H2CO3)

Carbolic acid is the old name for phenol, an aromatic compound (which is a benzene compound with one hydrogen substituted by a OH (organic alcohol moiety)).

I suppose this entry will make me look like a pedant to many.

Regards,

SLAG.