Prevention of seizure in aluminium threads

Had a wee set back the day before yesterday when machining an internal thread in aluminium. A piece with a male thread (obviously!) fits into the internal thread. Was just about there, tried the male thread and it was screwing in OK if a little stiffly when suddenly it seized. My fault, forgot about the chance of that happening, perhaps pushed on for too long instead of pulling out, and hadn't used any anti-seizure lubricant on it even though I have Copaslip right by the lathe.

Managed to cut - machine - the male piece out and should be able to save the piece with the internal thread, but.......

But it made me wonder if Copaslip was the best to use, or is there a better ant-seize product available for aluminium?

Any thoughts anyone?

Chris

Chris,

The copper compounds seem to work fine ... But we [aerospace & defence] also used a yellow compound [a chromate of some sort, I think] which is excellent on Aluminium threads and on dissimilar metals. ... It was more of a sealant than a lubricant though.

I will rack the brain & see if I can remember more !

MichaelG.

Duralac. Stocked at decent chandlers (stainless and aluminium is a common mix on marine work). May also be available from bearing stockists as well, but it isn't the sort of thing I buy very often - one tube will last almost a lifetime (or at least until you accidentally tread on it.....)

I think it is either zinc chromate or barium chromate. Coppaslip is frowned on because copper and aluminium in the presence of sea water is not good, and Duralac is more of an isolator between the components.

Edited By Steve Pavey on 17/10/2015 13:33:16

Edited By Steve Pavey on 17/10/2015 13:34:13

Cheers, Steve

You just beat me to it

**LINK**

MichaelG.

Yes, but did't we use a process called ALACROM to put a passive coating onto the Aluminium (alloy) first. It was a brown acid which when washed off left a nice gold coloured surface.

**LINK**

Then we used the Duralac - all good toolboxes had a good glob of it spread all over tools !!
BobH

Duralac! You have kick started the little grey cells! I remember now way back when I had a boat using that or something like it when pop riveting stainless steel fittings to the aluminium mast, otherwise in all probability the two would 'fuse' (for want of a better word) together permanently. I had a tube of it once but I let it go with the boat I think.

I also remember that copaslip was frowned upon (on boats when used between aluminium and stainless) but couldn't remember why, but it should be good on my engine as if sea water gets anywhere near it there will be far more serious issues arising, like my house flooding 20 miles inland! So probably copaslip will be quite OK.

Chris

Duralac is new to me but seems to be promoted as a jointing compound which is not what the OP was looking for.

Another product that might be more appropriate is Tef-Gel. I use it on SS and aluminium components that are exposed to salt water as it inhibits corrosion, again its not exactly what the OP was looking for but its non setting and would prevent aluminium threads galling.

One thing that might be with bearing in mind is that some sellers of both of the above products show a pretty picture of the container but rarely tell you the quantity it contains! The price (of Tef-Gel anyway) seems quite high for the quantity purchased (like some Loctite products) so its worth doing some research before spending £25 and then getting only a few grams.

Ian P

I use graphite grease on aluminium.

I was having a discussion about corrosion in Aluminium brake calipers with a bloke in the the technical department of a large automotive part manufacturer and he said ' that he wished Coppaslip had never been invented as the copper element of it actually made electrolytic corrosion in aluminium worse'. We discussed how it is really a high temperature clay based lubricant to stop exhaust manifold nuts etc seizing, not as a day to day thread seizure lubricant.

Edited By stevetee on 17/10/2015 23:28:13

Touched a raw nerve there Chris, regularly have the problem even feeling for the pickup it catches me out fairly often.

Have made parts been in use two months then stripped down and washed. Partially re threaded on and seized solid no warning - scrap 3 days work down the pan. Even had three of same assembly all pickup that week so 9 days lost replacing and been in use. Normally more of a problem on finer threads with decent tolerances, at times I hate threading up them M30X0.75.
Many a time just feels like a touch of grit suddenly felt, if cant back out rock the thread, work it either side don't force it too much of where its picked up. Lube, may take 15 mins unless really bad.
If forcefully back out the stud it will strip the thread.

Any form of a lubricant would do, if use an oil screwing it will leave a black deposit in the thread. Have heard of fat used but often just test fit with coolant or if in good mood oil suitable for hand tapping.

Seem to get good results with cutting/tapping aluminium by using WD40 as a lubricant

Auto parts stores (Halfords etc to you I'd guess) sell a non-metallic anti-sieze compound designed for dissimilar metals, such as spark plugs and temperature sensors screwed into aluminium heads etc.

Moly slip does help to prevent seizure of aluminium components, alochrom was a low cost process for treating aluminium components to prevent corrosion yet had a negligible film thickness,it was used on hard drive components to prevent corrosion within the file.It worked well on wrought components, quite good on gravity die cast parts and a nightmare when applied to pressure die cast parts. Eventually ali cast parts were painted prior to machining,problem solved,just before hard drives got smaller and made in thousands. Hard drives and their component parts have to be ultra clean,no lubricants can be used and the internal fasteners changed from zinc plated to electropolished stainless, internal contamination was virtually eliminated but the stainless screws seized in the tapped holes unless the assemblers were were very careful,there was a lot of expensive scrap, that was 25 years ago don't know what they do nowadays in the far east.

Jon - glad I'm not the only one! As you say, seizes with no warning, just does it. And it was on a large diameter very fine thread too, where you experienced problems.

Used paraffin when cutting the aluminium as I read somewhere that was good on aluminium, seemed to help but I don't think paraffin has any lubricant within it. Tried WD40 when screwcutting, thought that might be better as it has lubricant in it - fish oil I think it is.

I also have some Tufcut metal cutting compound, which has a grease like consistency and slippy-ness. I had not really considered it at all as I had it in my mind that it was mainly for use with steel but now wonder if it would be good on aluminium - probably worth a go.

Copaslip was used on board ships for coating threads to prevent seizure especially on those bolts used on high temperature applications like flange bolts on steam pipework as it is advertised as a high-temperature anti-seize product, but I tend to use it on any nut and bolt I want to protect from seizure these days, not having any steam to deal with. Have not noticed any electrolytic action with its use within my limited applications, but have noticed when doing car brakes that often replacement parts come with a little sachet of copaslip. I think it's a great product, just not sure of it with aluminium for some reason.

Chris

Edited By ChrisH on 18/10/2015 11:28:56

Titanium 'squeaks' when nuts and bolts are assembled, so Molybdenum Disulphide is used to lubricate them. Silver is also used as a solid lubricant, but may be a little expensive...

Regards

Geoff

NASA publication:

http://file.lasersaur.com/docs-thirdparty/Fastener_Design_Manual.pdf

Geoff

Inspired by this thread!! I looked up on the web and found this, Alocrom 1200 this appears to be the stuff you referred to, it is available however its expensive 70 quid for 2 ltrs, I had a quick read and I think it could be done at home safely, its a passive coating similar to Anodising, but no electrickery involved, so I might give it a try.

Getting back to the original thing, I have had this happen loads of times over the years especially with fine threads I've noticed after anodising it rarely happens, the other thing I've noticed is when screw cutting the thread and you try the nut on for size the risk is much greater, so I now make sure its very clean first, I think what happens is it sprags, the swarf is lying in the grooves in the direction of cut so the nut will go on, but as soon as you back it of the swarf tries to rotate but cant, so it works like a sprag clutch, once this happens your more or less stuffed unless your very lucky, if a part is not going to be anodised I generally run the nut up and down the thread a couple of times with a little bit of Solvol Autosol on these this seams to help a lot........

Shaun

I too have suffered when screwcutting fine large diameter threads in aluminium and then just doing quick check of the thread fit with the mating part. Whilst its still in the chuck I don't see how Alocrom would help at that point.

Having learned my lesson I now meticulously clean the machined thread and use lots of lubricant before trying the male and female part together.

Anodising the parts is a game changer as it is no longer aluminium running on aluminium. If you think about it there are literally millions of mating aluminium threaded parts in camera lenses that never give any trouble and although most are anodised there are still quite a few lenses where they rely on lubrication only to prevent seizure.

Ian P

Castor oil and AFT(Automatic transmission fluid) will help. AFT is good if parts have just started to seize,but have not gauled. You have to be careful with castor oil, as it can allow parts that would not ordinary fit together, go together. Aluminium diesel heads, with an Aluminium contra piston, are assembled with castor oil , to prevent the 2 alloys from gauling.

Having extra clearance in the threads helps as well. On fittings that are subject to heat and vibration , I make the threads loose enough, that allow a layer of PTFE thread tape. It has worked very well for the stingers on tuned pipes so that if required, we can change them.

Neil

Involutecurve

Please do not use Alocorom, Alodine or any other Chromate conversion process at home. These products are known carcenogens and under the EU REACH programme will be outlawed in 2017 along with chromic anodising due them containing Chromium 6. It is real pain to those of us Aerospace. There are alternatives to Alocrom now that are REACH compliant which off hand I cannot remember the name but an Internet search will find them.

Regards

Dave