any metologist's on the forum?

[sneaky beaky]

bit different i know... but very gun related

i remember an old chefing trick to proof a pan (to make non-stick) was to take it up to a high temp... pour oil on and leave for a day or two... repeat a couple of time's ect.

the question is... what would be the safe temp to bring a piece of aluminium alloy up to, without damaging the structure... to bathe in "oil".

metal expand's when hot... and absorb's when cooling if im right?

how many time's could you repeat this process safely... 3-4-5? and would the alloy abrorb the "oil" over a long soak??

grateful for some "different" advice sneaky

[Scooby]

Proofing a pan really only works well on a carbon steel pan/wok.

I'm not sure this would work on a piece of Aluminium but either way no oil is absorbed into the surface of the metal, it is only a surface treatment.

[snock]

I thought this thread was going to be a weather related one.

[itsa344]

OK, this might be total bull but here are my thoughts;

The reason Ali doesn't 'rust' or corrode like steel is because its oxide forms a protective layer on its skin. In other words, steel oxidizes (i.e. rusts) as forms a crust that allows water / damp air through to the steel , trapping it and actually promoting further oxidization or rust. Ali, on the other hand, oxidizes just the same, but its 'oxide' layer is cannot be permeated by water / air, and is thus protected from further oxidization.

Thus heating / cooling alu would cause the alu oxide layer to form and 'set' for want of a better word, and thus no oil would ingress or soak in and the desired effect wouldn't occur.

But then again, this might be total rollocks ~

[CarpeDiem]

OK, this might be total bull but here are my thoughts;

The reason Ali doesn't 'rust' or corrode like steel is because its oxide forms a protective layer on its skin. In other words, steel oxidizes (i.e. rusts) as forms a crust that allows water / damp air through to the steel , trapping it and actually promoting further oxidization or rust. Ali, on the other hand, oxidizes just the same, but its 'oxide' layer is cannot be permeated by water / air, and is thus protected from further oxidization.

Thus heating / cooling alu would cause the alu oxide layer to form and 'set' for want of a better word, and thus no oil would ingress or soak in and the desired effect wouldn't occur.

But then again, this might be total rollocks ~

I am not a metallurgist but many years ago I worked in a lab where we experimented in our lunch break with anodising aluminium. As I recall, this works by electrolytic action building up a much thicker than usual layer of oxide on the surface and this layer is, in fact, porous. To colour the layer you simply immerse the workpiece with thick oxide layer in a bath of the appropriate dye and it is absorbed into the oxide layer. The layer is then sealed by boiling the workpiece in water.

I also seem to recall that simply heating aluminium will not increase the thickness of the oxide layer because once it forms it prevents oxygen from coming into contact with the aluminium any further. That's why it's a very thin layer and the only way to increase its thickness is by electolytic action.

It's possible that oil may be absorbed into the surface of freshly anodised aluminium but I can't see the point as Al and its oxide are fairly soft and would abrade fairly rapidly.

There was a firearm lubrication product marketed some time ago that claimed to be absorbed into the surface structure of metals, including rifle bores, but I cannot recall the name. Same company made a variety of other firearms products such as a surfactant cleaner for cartridge cases.

G

[Frogfoot]

Al and its oxide are fairly soft and would abrade fairly rapidly.

I agree with most of what you say in your post, however Aluminium Oxide (Alumina) is actualy very hard and used in some grinding wheels. The coating produced by the hard anodising process is chemically akin to many gemstones and shares their property of extreme hardness and resistance to abrasion. Hardness of anodised coatings is specified in British Standards using the Vickers Micro Hardness Test in which the hardness is measured on a section through the film giving micro hardness values of 250 to 600; depending on the aluminium alloy, the process and the sealing.

[CarpeDiem]

I agree with most of what you say in your post, however Aluminium Oxide (Alumina) is actualy very hard and used in some grinding wheels. The coating produced by the hard anodising process is chemically akin to many gemstones and shares their property of extreme hardness and resistance to abrasion. Hardness of anodised coatings is specified in British Standards using the Vickers Micro Hardness Test in which the hardness is measured on a section through the film giving micro hardness values of 250 to 600; depending on the aluminium alloy, the process and the sealing.

Fair point, but the anodised films we produced in the lab weren't very durable. I see from Google search that there is a specific process of hard anodising, which will produce good hardness and abrasion resistance. A quote from the page I found - The reason why anodic oxide coatings produced under hard anodising conditions have high hardness values and very good abrasion resistance, is due to the low anodising temperature the low electrolyte concentration, and the high current density compared to normal sulphuric acid anodising.

To keep the temperature on the low level good cooling and agitation are of great importance. At these temperatures water cooling is not possible, and some type of refrigerant must be used. Air agitation is sometimes not sufficient, but agitation can be provided by pumping the electrolyte through an external heat exchanger which thus combines cooling with agitation.

One of the main developments in hard anodising has been the use of more complex power supplies with biased, pulsed or interrupted current used to reduce burning problems and make highly alloyed materials easier to process. Much of the work has used AC superimposed on DC.

I strongly suspect that these requirements are not easily achievable in a home workshop environment, but I'm aware that there are folk out there who would simply regard that as a challenge!

G

[Evoman]

If you want something really durable best go for hard coat anodising. I used to have it done on yacht stuff and in addition moving parts were PTFE impregnated. Really hard and very, very slippery. Nothing else we tried lasted as well and the finish was really good. Not a DIY job though, and I recall it used to be about £40 per batch minimum cost 8 years ago. A batch was loads.

[hareng]

Evoman that is hard anodising what Carpdiem describes.
It is very durable and can be impregnated with ptfe, had a few batches done over the years.
A bit hit and miss at the moment doing it myself, harder than 01 or D5 tool steel for sure.

[sneaky beaky]

wow! thanks for the reply's

so therefore... heating and then soaking a piece of alloy in some ptfe based oil would be un-effective...

hard anodising, then PTFE impregnated (thanks evo) would be the way to go...

ta for the reply's

[M ROBSON]

I get a lot of machine parts anodised for my work at a local engineering workshop. It improves the finnish and makes it a lot harder wearing.

It's fairly cheap and most engineering workshops will do it for you.

Mark.

[Thunderbolt A10]

Hi,

This may be a little out of the thread but there is alot of different hard coatings on the market for use on alu. and especially steel. But these coatings should be chosen with great care to get the optimum performance out of each coatings.

For example for steels coatings can be PVD, Boron Carbide, Tungsten Carbide, Titanium Carbide or you can give a gas nitriding to the surface of steels. There are many others surface treatment too but info about each coating is needed to get the optimum performance. By this I mean that some coatings do not bond as well to the surface than other coatings of certain steels or if the steel subject is bend the coating may break free from the surface of the steel.