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Learning how to build Lotus Seven replicas...together!
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PostPosted: March 3, 2021, 12:03 pm 
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@rx7locost

That's interesting, Chuck. I've never looked for phosporic acid. I don't even know where you'd find it.

I haven't used the muriatic acid yet. Subsequent to my post I learned a disquieting fact about using it and leaving it inside your garage/shop when it's outgassing. I guess the fumes will cause everything steel thing within a few feet of the solution to rust up and/or discolor. So, it's imperative you use it outside in an open area. Also, the fumes can damage human lung tissue pretty easily. It's recommended you wear a respirator at all times when using it.

I'm kind of sorry I bought it. One of my neighbors tells me a gallon of white vinegar at Walmart is super cheap, like $2.50-$3.00 or so. I think that's a better way for me to go.

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 10, 2021, 6:55 pm 
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Just as an added little bonus, I tried using Naval Jelly.

Having a very limited window to work yesterday, and needing to cut and finish new suspension brackets by afternoon, I decided to try some Naval Jelly that I had on hand, and give it 30 minutes to work. Here are the results.
Attachment:
File comment: Two 2" x 3" x 0.120", hot rolled RHS after 30 minutes of Naval Jelly applied. Some scale came off, but not all of it.
DSC05664.JPG
DSC05664.JPG [ 143.56 KiB | Viewed 640 times ]

Probably 60% of the mill scale was removed. It looked pretty ugly. However, when I used a wire wheel on the pieces attached to my electric hand drill, they cleaned up relatively well.

You could rub the remaining mill scale off with your fingers using the vinegar cleaner. Not so here, but they did clean up pretty well in about 4 minutes additional work on each piece.
Attachment:
File comment: Finished pieces.
DSC05666.JPG
DSC05666.JPG [ 139.79 KiB | Viewed 640 times ]


I'd guess they came out something like 90% as well as the ones I did with the vinegar cleaner, which the metal sat in for about 30 hours. That's a pretty good trade off, IMHO, especially if you're in a rush.

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 11, 2021, 12:43 am 
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You'll have to excuse my ignorance here, but what are the applications where removing all the mill scale is imperative? I'm not an experienced fabricator and I'm quite curious. Usually I've just been hitting the area I want to weld with a flapper wheel or the like. Does mill scale have to be removed prior to applying primer/paint?

Don't get me wrong, the results do look really good, so I love that you're doing the experiments.


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PostPosted: March 11, 2021, 11:40 am 
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Lonnie, update on vinegar. My wife buys it at Aldi or Lidl for 69 cents per gallon

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PostPosted: March 11, 2021, 12:03 pm 
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Posthumane wrote:
You'll have to excuse my ignorance here, but what are the applications where removing all the mill scale is imperative? I'm not an experienced fabricator and I'm quite curious. Usually I've just been hitting the area I want to weld with a flapper wheel or the like. Does mill scale have to be removed prior to applying primer/paint?

Don't get me wrong, the results do look really good, so I love that you're doing the experiments.

You've raised a good question. I don't have a for-sure answer. The stuff seems to stick like crazy. On the other hand, I've cleaned it with acetone once, and then came back and did it some time later, and lots of junk still comes off. It's basically oils, debris and impurities all cooked up together by heat on the surface of the steel.

My understanding is that paint does not stick well long term. If someone knows of other reasons, please chime in.

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 11, 2021, 12:08 pm 
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TooBusy wrote:
Lonnie, update on vinegar. My wife buys it at Aldi or Lidl for 69 cents per gallon


I'd never heard of either of those stores. However, I did a Google search, and we have an Aldi's in the next town south of me. I'll be darned. Thanks for the tip. My best price previously was the local Walmart at $1.69 per gallon.

Cheers,

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

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PostPosted: March 11, 2021, 2:21 pm 
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That's interesting, Chuck. I've never looked for phosporic acid. I don't even know where you'd find it.

I haven't used the muriatic acid yet. Subsequent to my post I learned a disquieting fact about using it and leaving it inside your garage/shop when it's outgassing. I guess the fumes will cause everything steel thing within a few feet of the solution to rust up and/or discolor. So, it's imperative you use it outside in an open area. Also, the fumes can damage human lung tissue pretty easily. It's recommended you wear a respirator at all times when using it.

I'm kind of sorry I bought it. One of my neighbors tells me a gallon of white vinegar at Walmart is super cheap, like $2.50-$3.00 or so. I think that's a better way for me to go.


Muriatic acid is basically Hydrochloric acid, so yes, pretty nasty stuff. Depends on the concentration, but it can do bad things to you. Great for etching concrete and removing lime deposits (if the substrate can handle it).

Phosphoric acid is the active ingredient in Naval Jelly and most "met-l-prep" type solutions. It burns through the rust and leaves a phosphate based film on the parts, works quite well and leaves a great tooth on the surface for paint adhesion. It generally prevents flash rust as well. You will also find it in Coke, hence why Coke removes rust (and just being on the acidic side of neutral too).

Vinegar does quite nicely as was stated, and can be cheaply found (except recently it has been sold out in my local stores, probably because it is a good "natural" cleaner.

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PostPosted: March 11, 2021, 3:21 pm 
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@duratec7

Thanks for that additional info. Yes, I'm coming to the conclusion white vinegar is an excellent solution (no pun intended) to the problem if you have the time to plan for mill scale removal. Otherwise, Naval Jelly could be the solution when you're in a rush. The Naval Jelly had no real discernable smell when outgassing. I did use it outside, however.

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PostPosted: March 11, 2021, 4:11 pm 
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Lonnie, another one you you might check on is "Trader Joe's". They are connected to Aldi's at the corporate level. Just something to keep in mind.

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PostPosted: March 11, 2021, 10:59 pm 
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@ngpmike

Thanks, Mike. We have plenty of Trader Joe's around here.

Cheers,

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

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PostPosted: March 12, 2021, 6:45 am 
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Lonnie-S wrote:
@ngpmike

Thanks, Mike. We have plenty of Trader Joe's around here.

Cheers,


Yep, That's what I figgered, being a Calif ex-patriot myself! :wink:

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PostPosted: April 10, 2021, 8:03 am 
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I use vinegar for pickling hot-rolled. You can reuse it a lot, it just starts to take a little longer. I have a 3/4 full 20L bucket which now has a thick brown scum on the top after pickling probably 10m of 30x30x3 angle and is starting to slow down a bit, but will still pickle some hot-rolled completely clean in about 48 hours.

If you want rust protection and are intending to paint the metal, Penetrol is the go. It's comes in 4L cans and I transfer it to a spray bottle; you wipe it on real thin. It will protect from rust for a few months and it is designed as a paint adhesion improver. Enamel sticks to Penetrol like s**t to a blanket, though it would probably reduce the effectiveness of cold-galv primer. You can even give it a good squirt into the little crevices and gaps in your bad welds before painting and it will prevent rust-cancers forming. If you're using Penetrol under paint, let the first coat dry for at least 48 hours or (at least with the Dulux stuff we get), you risk severe frilling on the second coat.

For pickling long stock, I use a 2m length of 90mm PVC drain pipe full of vinegar. Cap at one end, screw-cap at the other. You could also use a plastic gutter or similar.


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PostPosted: April 10, 2021, 8:13 am 
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Posthumane wrote:
You'll have to excuse my ignorance here, but what are the applications where removing all the mill scale is imperative? I'm not an experienced fabricator and I'm quite curious. Usually I've just been hitting the area I want to weld with a flapper wheel or the like. Does mill scale have to be removed prior to applying primer/paint?

Don't get me wrong, the results do look really good, so I love that you're doing the experiments.


Leave mill scale on your metal stock until you use (cut and weld) it because it will prevent corrosion while on the shelf, but it is very brittle.

Once you put a metal structure into service, the slightest flexing of the metal causes the scale to crack. It doesn't matter if you've painted it, the scale will crack through the paint and expose bare metal. You get a little bit of corrosion in that tiny invisible crack, and the expanding corrosion (Fe2O3 is larger than Fe) then causes the scale on either side to lift and peel. Soon enough, you have whole chunks of painted scale lifting off and leaving the metal bare, and so it proceeds across the entire surface and your structure is quickly destroyed.

The paint manufacturers will tell you that the leading cause of steel coating failures is a failure to remove all scale before painting.


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PostPosted: April 10, 2021, 11:01 am 
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@polyglot

Thank you for the ideas (descaling) and answers (why to do it).

I'm going to have to Google Penetrol. I haven't heard of that product, but it sounds like I should know about it. I live about 1-1/2 miles from the Pacific Ocean, so I have to be very mindful of corrosion on any bare metal I expose.

If I start on a piece, and can't finish it in a day or two, I have to primer it. Either I do that, or I have to wire wheel it to knock off rust when I restart, which is time consuming. If there's something I can wipe on, and take off as easily at weld-up, maching, or drilling time, that's worth knowing about.

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: April 11, 2021, 6:28 am 
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Penetrol is also apparently popular with steel boat owners. They put a heap of it on before paint and it gets in all the crevices and fills them with wax, preventing corrosion.

It's a polymerising oil analogous to linseed as used on wood. So it goes on wet, some solvent evaporates, then the remaining oil hardens up over a few days into a waterproof membrane. You can clean it off before welding with a solvent. You can also add a small quantity (5%?) of it to enamel paint to make it stick better.

Note that the polymerisation is exothermic, same as linseed. If you leave a scrunch of oil-soaked rags in your bin, they will spontaneously combust and burn your shed down so always hang the oiled rags out to completely dry for a week or so after use.

Another product worth knowing about is Boeshield. Similar use, in that it's a wax in solvent that dries to a protective film on metals, but it's for tools not finished structures structures and it is quite expensive. You probably can't paint it but it lasts better than penetrol and does not make things dirty, so it's great for protecting things like cast iron table-saw beds, lathe ways, pliers, vise jaws, etc.


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