I've been thinking about how to stop the tools and machinery in my shed from rusting. Every now and then I come across a tip but have no idea if it's a good solution or not.
To protect my lathe, I simply make sure it's well oiled and I cover it in an oil soaked sheet.
To find out for myself what rust protection treatments work and to satisfy myself that I am protecting my lathe, I decided to do a simplistic experiment.
I cleaned up and cut up a bar of steel. It was initially covered in surface rust, so I knew it was the right type of steel.
I've coated them in different things that I had to hand. They are a bit of a random selection and not all are suitable for the same applications.
The mineral oil based products probably don't need any explanation. That's ISO 68 oil (2), white marine grease (7) and multipurpose lithium based grease (8). Those sorts of things are common in most workshops and, I assume, most people are familiar with coating things in oil or grease to keep rust at bay. Their disadvantage is that they wear off easily.
The caustic soda (9) probably needs the most explanation. This is sodium hydroxide, chemical symbol NaOH. Usually used as a drain cleaner. According to what I have read, rust needs a moist or acidic atmosphere. NaOH is alkaline. The residue on the surface of the metal forms an alkaline solution when it gets moist. This should, to some degree, protect the steel against rust but will need a top up wash whenever the surface is disturbed.
It's big advantage is that the film on the surface is not sticky. This makes it useful for things like woodworking machines where oil would hold sawdust and contaminate the finished product.
I use silicone oil (6) over finished painted surfaces to keep them clean. It's disadvantage is that once used, it can be very difficult to ever get anything to stick to the surface again! As an anti-rust treatment that longevity on the surface should work to our advantage. So I've read.
It's non-toxic and environmentally harmless, so it sounds perfect.
It's one of the reasons I decided to give this experiment a go. When you see the results, you can see why I was glad I tried this for myself.
Water displacement formula, 40th attempt, or so the rumours go. WD-40 (4) is probably well known to most of us. I've used it for years, for lots of things, mainly as a cleaner, for getting stuck things moving again and to try to stop things rusting. It wears off or perhaps evaporates over time, so needs regular re-treatment.
ACF-50 (5) is an anti-corrosion product with the addition that it is also a lubricant. I originally bought it because there was a claim that it stops car locks freezing stuck in cold weather. I'm not entirely convinced about that claim, at least it's not reliable for that purpose on my cars. However, as a surface treatment and lubricant, it has it's uses.
Owatrol oil (3) is completely different to the other products. It's easiest thought of as a varnish for steel. It's of no use for machine surfaces but might be OK on extension handles and shanks that don't get any wear. It's sticky when applied and usually takes several days before it can be handled. Commonly used on steel ornamental objects that are going to live outside. I had some, and wanted to see how it stood up.
I have put all my test strips outside but, unusually for the UK, at the moment the weather is not conducive to rust. It's been very dry so I've had to spray them with water, from time to time, to help things along.
I started this in early May and it's now early June.
Results after 7 days
Just a week is too soon to draw significant conclusions, but some of the treatments were already showing signs of rust.
1. Control - no treatment - clearly starting to rust.
6. Silicone oil - dots of rust forming.
This is not what I had expected from what I had seen elsewhere online. It does slow down the formation of rust but it's not perfect and its properties offer nothing significant above the mineral oil based methods. It's disappointing, but silicone oil, as a rust treatment, is unlikely to be useful for me.
9. Caustic soda - weak solution of drain cleaner wiped over the surface - dots of rust forming.
It clearly reduces the formation of rust and I can see that a non-sticky finish could be useful for a number of applications, but it does not completely prevent rust.
I have two other bits of steel, slightly outside my main experiment.
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| Nickel Electroplate |
The bar I recently electroplated with nickel has started to rust, but only in some places.
The other bit (A) is cut from the same bar as the rest of the test strips. It's an untreated piece that I have left inside the workshop, in the dry. That is showing no signs of rust.
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| Kept inside |
I also have some parts that I
cold blued some time ago. They have been stored randomly in the old and now the new workshop and none of them have started to rust.
Results after 30 days
Based on the results, this is sufficient to draw some conclusions, with the caveat, that this is only one test.
1. Control - no treatment - clearly rusting, as expected.
2. Slideway oil (ISO 68) - significant rust.
This started out well, but as with other methods, the rain soon washed this away and started to rust. It's good when it's on there but is not tacky enough to stay.
3. Owatrol oil - no sign of rust.
I think this confirms that it does what it is designed to do.
Nickel electro plate - as it's shown in the above photo I'll mention it here. Clearly not a useful rust protection method.
4. WD-40 - has minimal sign of rust.
It leaves a yellowish colour film on the surface. This is still likely to be my first choice to quicky give some protection to tools. The rain just sat on the surface in drops and eventually evaporated. It has not washed off the treatment, nor has the moisture penetrated. Rust is just starting to edge in from the sides after a month.
5. ACF-50 - significant rusting.
This started out well but after the first week, the rain wore away the treatment and it then rusted quickly after that. In a static environment, this is going to do well, but not if it can be washed off.
6. Silicone oil - significant rusting round the edges.
As mentioned above, this is disappointing. It's not a good rust prevention treatment.
7. White marine grease - no sign of rust.
It's a bit messy. As expected, I've confirmed that it works to inhibit rust. Where I need to apply that type of grease it's also going to protect against rust, but I'm not going out of my way to use it elsewhere.
8. Multipurpose lithium based grease - no sign of rust.
It inhibits rust and lubricates. Like the white grease, it's useful where it's needed as a lubricant, but there is no real advantage trying to use it elsewhere.
9. Caustic soda - weak solution of drain cleaner wiped over the surface - very rusty.
Once the rust caught hold, it spread rapidly. No use for rust protection in a wet atmosphere.
Conclusions
Any mineral oil based coating will protect from rust until it wears off. The stickier it is the longer it will protect. However, the tried and tested WD-40 worked the best in my trial. It is a lot more resistant to being washed off than I had expected..
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| Temperature (C) and humidity (%) |
As a consequence of the dry weather, I have an additional observation that would be useful for the workshop. That is, if the relative humidity can be kept below about 50%, then the steel won't rust.
These one-off results are not to be taken as definitive. I would need to repeat them a few more times, to check them, however that is likely to be a less formal experiment.
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