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PostPosted: February 23, 2021, 7:56 pm 
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Location: Carlsbad, California, USA
Removing mill scale is a time consuming, laborious process. Usually, I use an abrasive process like a wire wheel, flap disk, or a 3M plastic stripper disk on my 4-1/2" angle grinder. However, as a person who shares back issues with a number of other builders on LocostUSA, I decided it was time to work smart, and save what's left of my back if I can.

I'd seen videos on YouTube about ways to remove mill scale, and decided to give some of the chemical methods a go. I planned the experiment last week, but spent most of yesterday helping a neighbor clear a common drain, and boy do I need it to work this time. I'm really hurting today, and pain killers aren't touching the back pain. So, I'm taking a break and posting this.

I bought two chemicals to try: muriatic acid; and an industrial grade vinegar cleaner. That last one sounds weird, but white vinegar is one recommended method on YouTube. I couldn't find a gallon of white vinegar, but could find the ZEP industrial product at Home Depot and decided to try it instead.
Attachment:
File comment: Industrial Vinegar - biodegradable and has no vinegar smell to it.
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DSC05639.JPG [ 159.46 KiB | Viewed 1266 times ]

Attachment:
File comment: Been around forever, but is somewhat dangerous (fumes, mostly) and harder to handle due to safety concerns.
DSC05640.JPG
DSC05640.JPG [ 153.45 KiB | Viewed 1266 times ]


Sunday night, I put some 2"x3"x0.120" mild steel pieces into a cheap plastic container,a and covered the parts with the ZEP vinegar.
Attachment:
File comment: Mild steel with mill scale in vinegar bath.
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DSC05641.JPG [ 143.58 KiB | Viewed 1266 times ]


I'd planned to work on them Monday morning, but due to the drain issue, put it off until today, Tuesday. So, I guess they've been in solution for around 36 hours. Here's what was achieved in that time.
Attachment:
File comment: The mill scale comes off if you rub it with your finger. Rust is a little tougher, but not much.
DSC05642.JPG
DSC05642.JPG [ 138.44 KiB | Viewed 1266 times ]


I washed the off with a stream of water while brushing them with a small stainless steel brush. They really cleaned up well. All the rust, mill scale and paint came off with moderate effort. They need a little wire wheel time, but not much.
Attachment:
File comment: After brushing and running water over the metal pieces.
DSC05643.JPG
DSC05643.JPG [ 141.32 KiB | Viewed 1266 times ]


In the photo above, the last one brushed (foreground) is bright and shiny. The big one lying down has a slight orange cast to it. The first one done on the left has a discernible orange cast to it. I'm not sure why this is so. There wasn't enough time for oxidation to form. We're talking 15 minutes time between the 1st and 3rd piece.

I assumed it was some kind of chemical process caused by the vinegar. I thought I'd try neutralizing the vinegar (acid) with some baking soda (base) in solution and see if that stopped it.
Attachment:
File comment: Baking soda (base) put into a water solution to try neutralizing the chemical process.
DSC05645.JPG
DSC05645.JPG [ 134.86 KiB | Viewed 1266 times ]

After I post this and have some coffee, I'll go out and wire brush the neutralized pieces. If they spend overnight in the garage, and don't turn orange, I'll consider the case closed. I'll post again when I have those results.

There is one more thing. The two big pieces had to lie flat on their longest side to fit in the container and stay covered with vinegar. The sides lying down against the plastic container did not turn out well. So, I've placed them in solution again with the mill scale side up. I guess the not enough chemical got to the bottom side to react with it.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: February 23, 2021, 8:22 pm 
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Very interesting experiment. I'll be watching this one with interest!!! :thmbsup:

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PostPosted: February 23, 2021, 10:01 pm 
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Location: Under the weather. (Seattle)
Lonnie-S wrote:
There wasn't enough time for oxidation to form.[
Flash rust.

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PostPosted: February 24, 2021, 10:33 am 
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Location: Carlsbad, California, USA
Driven5 wrote:
Lonnie-S wrote:
There wasn't enough time for oxidation to form.[
Flash rust.

Flash rust? Seriously? Wuz dat?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: February 24, 2021, 10:48 am 
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Location: Carlsbad, California, USA
Here's the overnight results.
Attachment:
File comment: Wire wheeled, emoreyed and wiped piece on right. Untouched after baking soda soak on left.
DSC05646.JPG
DSC05646.JPG [ 144.28 KiB | Viewed 1229 times ]


The shiny piece I did on my usual way. I wire wheeled it with a electric drill, went over it quickly with emery cloth, and wiped it down with alcohol. In my world, it's ready to weld or be marked up using using machinists die and a scratch awl.

I consider the experiment a success. The piece on the left looks nasty, but it all came of in seconds very easily. I don't think I put more that 4 minutes into cleaning it up from wire wheel to alcohol wipe down. It sat overnight in the garage, and no new orange stuff appeared, so I think the baking soda soak stopped whatever was going on. The initial soak in vinegar takes overnight, but if you don't need something right away, it saves you a lot of effort over mechanical removal of the mill scale.

The muriatic acid is my next try (in a few days, maybe) because it only takes (they say) half an hour to work. I'm going to paint it on some raw material and then use water and baking soda to stop the process, and try knocking the scale off with a wire wheel as usual.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: February 24, 2021, 11:34 am 
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Lonnie, this is what you need!

https://www.youtube.com/watch?v=ACGSzBXKONo

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PostPosted: February 24, 2021, 2:48 pm 
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Location: Under the weather. (Seattle)
Lonnie-S wrote:
Flash rust? Seriously? Wuz dat?

It's a common occurrence after 'wet' cleaning metal. As stolen from another website: According to the SSPC Protective Coatings Glossary, flash rust is "rusting that occurs on metal within minutes to a few hours after cleaning is complete. The speed with which flash rusting occurs may be indicative of salt contamination on the surface, high humidity or both."

It's totally normal and shouldn't be difficult to remove even without any additional steps. Rust removal using electrolysis will also have a type of flash rusting, even though it uses a basic electrolyte solution.

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Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


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PostPosted: February 24, 2021, 4:46 pm 
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Location: Carlsbad, California, USA
BHRmotorsport wrote:
Lonnie, this is what you need!

https://www.youtube.com/watch?v=ACGSzBXKONo


Now, that's cool! Only $80K for the baby one, and $500K for the full deal, huh? Yeah, I might have to save up my allowance for a month or two. :rofl:

Thanks, Bill.

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: February 24, 2021, 4:47 pm 
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Location: Carlsbad, California, USA
Driven5 wrote:
Lonnie-S wrote:
Flash rust? Seriously? Wuz dat?

It's a common occurrence after 'wet' cleaning metal. As stolen from another website: According to the SSPC Protective Coatings Glossary, flash rust is "rusting that occurs on metal within minutes to a few hours after cleaning is complete. The speed with which flash rusting occurs may be indicative of salt contamination on the surface, high humidity or both."

It's totally normal and shouldn't be difficult to remove even without any additional steps. Rust removal using electrolysis will also have a type of flash rusting, even though it uses a basic electrolyte solution.

Ya learn sumthin' every day around here. Who'd thunk?

Thanks,

Justin

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: February 24, 2021, 4:56 pm 
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On little disappointment I discovered today is that the chemical effect dissipates in the vinegar solution. One YouTube video said you can keep it and reuse it. I didn't find that to be so.

The second batch I did with the two partially de-scaled faces and one new piece didn't clear up nearly as well. They cleared up about 80%, I'd say. It took a little more wire brushing to get them done. So, I'd say the vinegar is good for one batch and then you need to replace it.

I'd think the household white vinegar is likely cheaper than the industrial cleaner although I couldn't find gallon bottles at my local supermarket. I'll try harder to find it in future.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: February 24, 2021, 6:24 pm 
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BHRmotorsport wrote:
Lonnie, this is what you need!

https://www.youtube.com/watch?v=ACGSzBXKONo



I was kinda bummed when it didn't sublimate his hand. I was thinking this would be a great toy for my inner child


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PostPosted: February 24, 2021, 11:38 pm 
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I use the Vapo-Rust sold at HF and most auto parts stores.
Probably a bit more expensive but it does re-use and has an additive to stop flash rust.
For large areas I use a paper towel to retain the chemical on the surface.

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PostPosted: February 27, 2021, 5:42 pm 
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My wife buys gallons of vinegar at the local grocery. It's her go to cleaning product.

This is a big topic on the CNC plasma forums. Guys try to save $4 per 4x8 sheet of steel and buy hot rolled. Then they spend hours cleaning up stuff to be paint ready.

I buy hot rolled pickled and oiled. cut, wipe, paint, done

What you're doing with the muriatic acid or vinegar is pickling. It makes the surface very reactive, so flash rust pops up in an instant. There's a cheap rust inhibitor that is water soluble. I can't remember the name right off hand. take parts straight out of the vinegar, rinse off the crud, and dip in rust inhibitor, or give a light oiling with a rag.

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PostPosted: March 1, 2021, 1:11 pm 
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@TooBusy

Thanks for those tips.

Most steel suppliers in my area only stock hot rolled materials. I don't know why that is so. There is one supplier south of me in San Diego who has everything, but it's a 60-mile round trip too. So, if it's a small quantity I need, it's not worth the journey.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 1, 2021, 9:08 pm 
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For small parts, my go-to is phosphoric acid. I submerge the parts in it and leave it for a day or so. It is the active chemical in many commercial steel rust converters. It can be had many places. I have the remainder of a gallon that was sold as water softener cleaner/rejuvenator. It doesn't work as fast as muriatic acid but doesn't harm the steel that remains under the rust. It also leaves the surface treated with iron phosphate, a rust preventative. it stops the flash rust.

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