Blacking and rust proofing Steel parts

[Roger]

So far I haven't found a reliable way to Black Steel parts and also make them rust proof. There are two particular situations that come to mind...

1) Steel bolts that need to be Black and have to be removed on occasion. These can't really be painted Black because the paint would chip.

2) Bare Steel parts such as connecting rods.

I've used the Blacking treatment Metalblak for quite some time and it certainly gives a good result, however it doesn't provide any protection from rust.

From discussion on my main thread, there are clearly other treatments you can apply to kill rust, so the question I have is this. What methods are there for Blacking and then protecting against rust, and what is the best treatment for those parts that have to remain bare?

I've got Fertan to kill rust, and it does appear to Black if it's left on. Whether that prevents further rusting is open to question.

I also have a product called MetalGuard from Shield Technology that is an Anti-Rust coating which they claim forms a soft, clear 2micron film which will not yellow with age and is easily wiped clean and has excellent water displacing characteristics.



So my thoughts are as follows...

1) For Blacked parts, use MetalBlak to give the colour, and then instead of drying in the De-watering oil, use either Fertan or Phosphoric acid solution to wash it off and then let it dry. Once dry, apply the MetalGuard.

2) Use Phosphoric acid or wipe with Fertan (not so much as to make it Black!) and then apply MetalGuard to protect against further rust.

I'd be interested to hear any views on this idea or any other that gives a good rust resistant finish on either surface.

[timb]

I have used gun blue with some good results but by far the most reliable I have used is to 'oil black'. This means heating up the part until it starts to glow - not bright, just a hint of colour - then drop in some mineral motor oil (NOT synthetic). This gives the metal a mottled black finish which is quite resistant to rust. I am not talking about leaving it in sea water for long periods but certainly will withstand a period in a damp shed. I have some toolmakers clamps that have been treated this way and look as good as when they were done some 20 years ago, granted they have a lot of hadling but they are also left out on the bench in a damp garage for extended periods.

Tim

[Doug]

Have been using gun blue myself too and also metalguard from shield which does work. My Locos are covered in oil on bare surfaces anyway so they are unlikely to rust and have kept stored in fairly good conditions for 6 years. So far no issues with surface rust.

[Deleted]

Hi Roger

I used the blacking kit from Frost Restoration, a well known classic car restorer company. Their kit includes an oiling solution to stop rust, it worked well on my tender brake components which were done some years ago now. You may find other products of theirs of use for ME uses, I have recently bought some paint for when redoing my smokebox, it's enamel and it sprays very nicely from an aerosol. It is rated for 150c which I'm going to test in the oven to higher temps, the good thing about it for me is it's an 80% gloss finish which is probably just what I need/want. I was introduced to this paint by my son when visiting him at his garage, he was spraying a rad and intercooler with special paint from the same manufacturer, it had an excellent finish in satin black, I plan to test it on my gunmetal cylinders, it doesn't need a primer.

Pete

[ettingtonliam]

I used the blacking kit from Polly Models, it worked well, and the finishing treatment was a dewatering oil, in which, it was suggested, 10 minutes immersion would give about 6 months protection from rust, after which, presumably, the parts would need re oiling. As I've been using it on items such as cloc k hands which will live in the house, hopefully warm and dry, I'm not expecting a problem. I'm intending to use it on Locomotion's tender ironwork too, this might be a different case.

[abby]

I have found the most durable finish is to heat to an even dull red then dump into a container of old oil , I use old cooking oil.
I use this method for such items as T-bolts , toolposts etc where the item is not hardened and tempered.
I have found the jet black finish is more durable and even than home chemical treatments and it resists rusting admirably.
Dan.

[andyhigham]

The place where I served my time used a process called "blackodising" It involved dipping the pieces in warm baths of ??

[92220]

A tip for anyone who uses any kind of system that requires a final rinse in water: The water rinse will obviously cause rust so there is often a 'de-watering' oil bath. Definitely NOT good if the parts are going to be either painted or lacquered! De-watering oil can obviously be removed with solvents, but if the final wash is in water, it is almost impossible to dry the water from the surface without risking flash-rusting. To get over this dilemma, buy a 5 litre can of isopropyl alcohol (I.P.A.) and dunk the wet parts in the IPA (No. Not the beer! Too much of a waste!!) The IPA will absorb all the water droplets and the surface will dry as the IPA evaporates.

High Andy.

The product you are referring to is basically caustic soda solution. We used to use the same system at one of the companies I worked at. We called it Black Oxidising Salts. In the early days of Precision Paints, I used to sell small quantities of it. The problem was that it is a hot process with a critical temperature, I seem to remember, between 240C and 260C. The difficulty for DIY was the temperature really was critical. 5 degrees either side and the process wouldn't work. When it did though the blacking was superb. As far as I am aware, though, there is no steel blacking process that protects against rust. It will delay the onset but not for long.

Bob.

[Roger]

Mar 18, 2019 17:40:55 GMT 92220 said:

A tip for anyone who uses any kind of system that requires a final rinse in water: The water rinse will obviously cause rust so there is often a 'de-watering' oil bath. Definitely NOT good if the parts are going to be either painted or lacquered! De-watering oil can obviously be removed with solvents, but if the final wash is in water, it is almost impossible to dry the water from the surface without risking flash-rusting. To get over this dilemma, buy a 5 litre can of isopropyl alcohol (I.P.A.) and dunk the wet parts in the IPA (No. Not the beer! Too much of a waste!!) The IPA will absorb all the water droplets and the surface will dry as the IPA evaporates.

High Andy.

The product you are referring to is basically caustic soda solution. We used to use the same system at one of the companies I worked at. We called it Black Oxidising Salts. In the early days of Precision Paints, I used to sell small quantities of it. The problem was that it is a hot process with a critical temperature, I seem to remember, between 240C and 260C. The difficulty for DIY was the temperature really was critical. 5 degrees either side and the process wouldn't work. When it did though the blacking was superb. As far as I am aware, though, there is no steel blacking process that protects against rust. It will delay the onset but not for long.

Bob.

Hi Bob,
Out of interest, the dewatering oil smells suspiciously like that MetalGuard product I mentioned, so I wonder if they use the same formulation?

[92220]

Hi Roger.

You may be right. I have never used the de-watering oil when I've blackened parts because, having been in the paint business, I just automatically steer clear of anything associated with 'oil' if paint has to possibly be applied. I have often wondered if the de-watering oil is the same sort of oil that is used for the suds oil in cutting fluid, because that absorbs water.

Bob.

[steamer5]

Hi Roger,
Cheers for starting this thread! Makes it easier to find this sort of information in the future.

Not sure if I've commented on this forum & posted this before, if you can find clean zinc metal add this to your phosphoric acid, it should dissolve pretty quick in neat acid, we use to keep adding it until it didn't dissolve any more, then when you put your steel part in it to remove rust you will get it zinc plated at the same time! It will only be an extremely thin layer but still works great!

Cheers Kerrin

[Roger]

Mar 19, 2019 9:20:18 GMT 92220 said:

Hi Roger.

You may be right. I have never used the de-watering oil when I've blackened parts because, having been in the paint business, I just automatically steer clear of anything associated with 'oil' if paint has to possibly be applied. I have often wondered if the de-watering oil is the same sort of oil that is used for the suds oil in cutting fluid, because that absorbs water.

Bob.

Hi Bob,
I don't think the soluble oil used in Suds is the same, it smells different to the de-watering oil.

I've realised an anomaly in what I said earlier in the fact I've noticed that de-watering oil smells like MetalGuard. I assume the de-watering oil absorbs water and the other repels it, so they can't be the same?

The problem with paint is that it's not really any good on nuts and bolts. There's also a problem where there's a bearing surface in the painted part, such as in brake hangers. If you paint Steel brake hangers, how do you protect the place where the paint has to be removed or wears away of its own accord? This is why I Blacked the brake hangers, but I still need to coat them with something really. That's why I was wondering if a protective film would be a better option.

As an aside, the inside of body panels on cars used to be protected by Waxoyl which I see is still available. Is there any value in having a really thin coating of hard wax on the Blacked or unpainted rods for example? I see there's another product called LPS3 which you can find if you google it.

[44767]

I have been looking into this very thing. I would normally use the commercial black oxiding process as it is reliable but unfortunately it's expensive for small quantities due to a minimum charge and indeed for larger quantities as it depends on raising the temperature of the parts in the solution and therefore is charged per kg. The oxide layer is ferric oxide (as opposed to normal rust which is ferrous oxide) It is very thin and does not add any dimension to the part (as opposed to plating). The surface is modified somewhat like anodising aluminium and it becomes porous and takes on the black ferric oxide colour. It is the porous surface which holds oil and this is the actual protective layer. I have black oxiding done over thirty-five years ago which is still rust free and very black.

Anyway, I wanted to have a quick process which did not involve heat at all and added almost no thickness which I would use on nuts and bolts as parts were assembled. To cut a long story short, I dip the cleaned parts into phosphoric acid for a couple of minutes, they are then rinsed and dried. I then dip them in a meths based wood die and the drips blotted dry with a kitchen towel. When the parts are dry they are smeared with a light oil.

Here are some bolts done this way

[44767]

For parts which are to be left bright, the best way to stop rusting is to polish them. There is less surface area then to absorb moisture and so they are unlikely to rust. Of course, a light smear of oil will help this even more.

[Gary L]

Mar 18, 2019 16:19:34 GMT abby said:

I have found the most durable finish is to heat to an even dull red then dump into a container of old oil , I use old cooking oil.
I use this method for such items as T-bolts , toolposts etc where the item is not hardened and tempered.
I have found the jet black finish is more durable and even than home chemical treatments and it resists rusting admirably.
Dan.

Yes, I do that too; simple, quick and ultra-cheap.

For parts that are too big to get to uniform red heat, or for sensitive small items, I have taken to heating the steel only to blue-tempering temperature. I suspect the subsequent oil dunk doesn't add a lot, but the colour is acceptable (not a dead black by any means) and still a lot more resistant to rubbing off than chemical blackening is on brass.

I'm not convinced that any blackening process makes a significant rustproof layer in itself; the protection seems to largely come from the subsequent oil dunk that they all seem to have in common.

The old boatbuilders used to do what they called 'Chinese Galvanising'. It involved heating to cherry red then quenching in Coal Tar or bitumen. It was reputed to work well, but not exactly the ideal Model Engineering finish.

-Gary