warmstrong1955 wrote:....Yes, but one downside is that with the anti-seize applied, you can, at the same torque-wrench force, apply MORE tension to the threads.
One needs to be careful when using the term "anti-seize". That term can refer to
1.-- a particular product
2. -- a fortified grease product
3.-- A property of a particular thread treatment
For instance one would not normally think of the classic blue Loctite, (removal strength) as having an anti-seize property, but in fact it does. Seizing in threads derives from more than one source.
-- certain material in intimate contact, especially when smooth and with no other material between may actually develop a weld. An early astronaut experiment was to place two super finished blocks togehter while on a space walk. The two blocks welded.
-- With Loctite products the threads are coated with a material that adheres to them which means that the material will not be pushed out of the contact zone. When a bolt is tightened in a hole, the flank of the male thread toward the head, is intimately pressed toward the flank of the female thread away from the bolt head. If the thread locking agent cannot be expelled from between the surfaces metal to metal seizing cannot occur. But of course on the other male and female flanks there is a gap created, and foreign corrosive agents could enter and fuse the threads with corrosion products, except that the Loctite will fill that gap and seal it, blocking out the corrosive environment. The result is that even though the Loctite is put in to resist the unscrewing of the threads, it also insures that they actually will unscrew at some predictable torque.
So it would be perfectly fair to say that Loctite
-- Locks threads
-- Seals threads against leakage
-- Prevents threads from seizing
How ever if we look at the chemistry of some grades of the Never Seize brand, we find something like
-- a lithium based grease which is waterproof petroleum lubricant
-- Nickel powder which is a metalic powder with a great tendency to gall
-- Graphite, which is crystaline carbon and is both a lubricant and an abrasive
-- Aluminum Oxide which is a ceramic noted for its use in abrasives.
The product is a basically a lubricant. and accordingly
-- Because it is a lubricant with a reliable coefficient of friction it tends toward uniform tightness of bolts tightened
-- Because it contains graphite the crystal planes will slip one on another at a fairly predictable force
-- Nickel has good high temperature anti corrosion characteristics and it will adhere to the screw thread surfaces
-- The use of a ceramic aluminum oxide at any credible application temperature it will not "burn out"
I have seen a c-clamp holding parts to be welded together get hot enough for the foot on the end of the screw to require a hammer to knock it loose, but the never seize stayed in the thread and in the screw to foot joint and it unscrewed easily.So when installing exhaust manifold bolts, I rather like never seize but for most other bolts I like Loctite blue. If a fluid needs to be sealed, Loctite is also the choice. But it will melt at a few hundred degrees well below the tempering temperature of most steels.
Part of the trick however is that for any given thread treatment, the torque may be different.
If the joint is going to be subjected to forces that will try to slip the joined pieces across one another, the Loctite has another advantage, You should be aware that once surfaces start slipping the coefficient of friction reduces radically. Loctite (and its similar competitors) tend to fill all the space between the male and female thread and then harden. The space is there because of both the allowance and the tolerance of the threads. Because the space is filled with a solid or semi-solid, the screw resists moving sidewise as well as slipping along the helix that winds around the screw. Once the surfaces slip,sideways as they can in an "un-sealed" screw due to shear forces on the joint, the thread surfaces will as easily slide "downhill" on the helix as well as crosswise to the screw shank. the result is loosening of the screw as well as loss of clamp force which only makes the process more likely. This is one of the reasons that a "phonograph finish" is sometimes specified for the mating surfaces as it increases the resistance to lateral slip in the joint elements. Press fit dowels are sometimes used for the same reason.
So if temperature resistance will not be exceeded, I will likely opt for the Loctite or its similar competitors. But If the loading is not primarily a shearing one, but it is going to get hundreds of degrees hot, that weakens those products then I will favor the never-seize type of product. Of course the historic British solution for exhaust manifolds that I also like is steel studs with bronze nuts. And maybe stainless steel studs at that. Holds just fine, comes apart when you want it to without breaking things, and requires no extra goop.
On the nuclear reactors we built, we were essentially limited to neolube, a product of very fine graphite in alcohol. The alcohol evaporates and leaves the graphite behind. It was still pretty difficult because the 300 series stainless steels will gall really really easily. Other ingredients in the more common thread treatments would tend to dissolve in the reactor coolant and go through the nuclear core and transmute into rather troublesome isotopes. Or in the case of petroleum ingredients break down into smaller components and combine with radioactive iodine to produce Methyl Iodide which is gaseous and escapes when the reactor is opened for refuelling.
Just a curious side note: If a stainless screw in a stainless hole did start to gall the one penetrating lubricant that we could use to get it out was pure pharmaceutical grade Oil of Wintergreen. The other penetrating lubes were not to be allowed for various chemical and radiological reasons. It works surprisingly well. Just be aware to never get it on your skin or in your eyes because it is hyper concentrated liniment!
Smells kind of nice though
I never met anybody that I couldn't learn something from.