Copper grease - or not?
Discussion
Mave said:
witko999 said:
You're talking about the hub face of the wheel slipping against the hub. Fair enough and I now understand your point, but unless you've carried out some testing on whether the hub face is slipping, dry vs. lubed, I remain dubious.
Have a look at the charts in this link - you can see how the load transfers from hub face to bolt as the clamp load reduces, which is directly analogous to what happens if the friction coefficient reduces. https://link.springer.com/article/10.1007/s11668-0...
Edited by Mave on Friday 24th September 12:07
Re the link above, it's a good paper, obviously USA biased, and whilst also concentrating on the engineering science, one thing that it fails to mention specifically, though it sort of covers it by distant implication, is incorrect maintenance through fitting of non standard parts, which may explain why increased use of alloy wheels has seen an increase of incidents on light vehicles with fitting of after market parts. I've certainly seen failures, mostly on large vehicles admittedly, where people have substituted incorrect spec components. This includes wrong spec studs, right size, right thread, incorrect heat treatment spec and hence strength, incorrect nuts/bolts with a mismatch on taper, even incorrect spigot size.Some mechanics have fitted wheels where they'd ground out the spigot hole to make them fit, which results, in the case of non conical mating faces results in a discrepancy between wheel and fixing centres, resultant vibration, significant bending moments applied to fixings leading to failure.
On the issue of overtightened fixings an anecdote from a failure on an 8 wheel tipper driven by a real old timer. He did a proper check on his vehicle every morning, including as he put it, "a daily cracking of my nuts." Quiet at the back there! Essentially he put a brace on the wheel nuts, a ruddy great pipe on the brace and bounced up and down on the end till he heard the crack. Eventually so much preload that on one journey some plastically yielded, loss of clamping force, downward slope from there.
FiF said:
seems a fair number of people are thinking of excessive quantities of substance
The problem with lubricant on the friction mounting face is loss of friction. You're implying that trace amounts of anti-seize can be applied with compromising the friction. That seems unlikely to me and I'd be interested to know whether you have anything to support that theory.GreenV8S said:
FiF said:
seems a fair number of people are thinking of excessive quantities of substance
The problem with lubricant on the friction mounting face is loss of friction. You're implying that trace amounts of anti-seize can be applied with compromising the friction. That seems unlikely to me and I'd be interested to know whether you have anything to support that theory.I'd then say you're still thinking in terms of there being sufficient material remaining to potentially create a hydrodynamic lubricant situation, and that's just not the case. Not even mixed lubrication but what is often termed boundary lubrication. Note I used the term which you edited out, namely wipe on wipe off, the aim being to remove as much of any carrier as possible only leaving a trace of the anti seize components. Only so little that all the load is born by the interaction of the surface asperities, remembering that there is a high load on the joint, and there is insufficient lubricant to form any load bearing layer. All the load is born by the component surface interaction. In this case the molecules of the anti seize compound interact with the molecules of the components and do their job. There's also an argument that if the area reaches quite low temperatures, say 200C/ 400F, then any remaining carrier traces would be 'burnt off" leaving just the anti seize component, which is not a lubricant.
I would apply a caveat to all that, to say it does depend on the materials and the surface states, for example two smooth machined maybe polished surfaces then application of such a compound, even in the lightest of applications would imo not be advisable, nor perhaps if just one of them is quite smooth, but for example a cast wheel being attached to a cast hub /drum, there really isn't an issue. Though it must be noted even polished surfaces have some asperities at a microscopic level.
Though application to the area of the spigot / wheel centre bore is much less critical as the clearance there is not exactly a mating surface is it?
FiF said:
Though application to the area of the spigot / wheel centre bore is much less critical as the clearance there is not exactly a mating surface is it?
I'd agree, I don't think theres any problem using it in the spigot / Centre bore area as that doesn't take any load once the wheel is fastened. FiF said:
I'm assuming you meant to say without compromising the friction.
I'd then say you're still thinking in terms of there being sufficient material remaining to potentially create a hydrodynamic lubricant situation, and that's just not the case.
You're right, I did mean to write 'without'.I'd then say you're still thinking in terms of there being sufficient material remaining to potentially create a hydrodynamic lubricant situation, and that's just not the case.
But I was not assuming any sort of hydrodynamic lubrication and it's obvious that won't occur in a stationary clamped bearing. The presence of a lubricant between two stationary surfaces can reduce the friction considerably. Just think of tightening an oiled bolt versus a dry one. The thickness of the oil film between the thread contact points is approximately zero and there definitely isn't any hydrodynamic effect but it reduces friction considerably.
Do you have any evidence or corroborating sources to support your suggestion that anti-seize does not reduce friction? It seems unlikely to me.
GreenV8S said:
Do you have any evidence or corroborating sources to support your suggestion that anti-seize does not reduce friction?.
Problem is, haven't actually made that suggestion. It's something completely of your own invention and misunderstanding..To be clear, there are some circumstances where imo anti-seize shouldn't be applied, and I certainly wouldn't, eg heavy vehicles / lorry / bus wheels. As stated before the window to get the correct clamping pressure is small enough as it is, without introducing something that would reduce that window. Although, as stated before, spigot / wheel bore is less critical. If you don't agree with that then pointless to continue.
For light vehicles, it depends, and certainly, again as previously stated, excessive applications can reduce interface friction to result in failure or severely compromise security even though it's not a sliding interface.
However the assembly design on light vehicles is often so over engineered, coupled with the increasing tendency for garages to not remove wheels when servicing normally, that when any extremely limited use is as described, i.e. h film thickness ~0 and significantly <<<<< surface roughness, then is any reduction significant probably the more relevant question. Experiment and experience suggests not. Also see Stribeck curve by way of illustration. YMMV.
Hammer67 said:
Found this whilst searching for something else for my Jagdeo.
Jag seem to think it`s ok to lightly grease between wheels and hubs.
This is the advice to follow.Jag seem to think it`s ok to lightly grease between wheels and hubs.
There should be NO attempt to lubricate the threads, the purpose of the grease is to help put a moisture barrier between the two different metals of the wheel and hub, this reduces the likely oxidisation and sticking of the components. Never lubricate non-moving parts.
kambites said:
RizzoTheRat said:
donkmeister said:
I'm one for a small amount of copper slip on the mating surfaces though, I have needed to whack wheels to unstick them in the past.
That's a whole other debate. Lots of people seem to do it with no problem, but the bolts provide the clamping force to get the friction on the mating surface between the hub and the wheel. Greasing that surface is in theory a bad idea.
In practice I think there's so much margin for error that it does no harm, but it does sound like a thoroughly daft idea!Thinking about an analogous situation, dielectric grease in exposed electrical connection is an accepted approach as the grease squeezes out where there is metal-metal contact but remains in the microscopic voids to ensure water doesn't get in.
Hubs and wheels have, at best, a clean machined finish. I don't know what mechanical engineers call the different levels of surface roughness, but these are not gauge block levels of flatness, but more akin to a single pass of a flycutter. So when you clamp the mating surfaces of the wheel and hub together, would the mating friction not be from the areas where there is actual contact? Hence antiseize would just sit in the troughs and the actual friction would be provided by the points where there is contact?
Or is this why it's debated?
donkmeister said:
kambites said:
RizzoTheRat said:
donkmeister said:
I'm one for a small amount of copper slip on the mating surfaces though, I have needed to whack wheels to unstick them in the past.
That's a whole other debate. Lots of people seem to do it with no problem, but the bolts provide the clamping force to get the friction on the mating surface between the hub and the wheel. Greasing that surface is in theory a bad idea. In practice I think there's so much margin for error that it does no harm, but it does sound like a thoroughly daft idea!Thinking about an analogous situation, dielectric grease in exposed electrical connection is an accepted approach as the grease squeezes out where there is metal-metal contact but remains in the microscopic voids to ensure water doesn't get in.
Hubs and wheels have, at best, a clean machined finish. I don't know what mechanical engineers call the different levels of surface roughness, but these are not gauge block levels of flatness, but more akin to a single pass of a flycutter. So when you clamp the mating surfaces of the wheel and hub together, would the mating friction not be from the areas where there is actual contact? Hence antiseize would just sit in the troughs and the actual friction would be provided by the points where there is contact?
Or is this why it's debated?
E-bmw said:
donkmeister said:
kambites said:
RizzoTheRat said:
donkmeister said:
I'm one for a small amount of copper slip on the mating surfaces though, I have needed to whack wheels to unstick them in the past.
That's a whole other debate. Lots of people seem to do it with no problem, but the bolts provide the clamping force to get the friction on the mating surface between the hub and the wheel. Greasing that surface is in theory a bad idea. In practice I think there's so much margin for error that it does no harm, but it does sound like a thoroughly daft idea!Thinking about an analogous situation, dielectric grease in exposed electrical connection is an accepted approach as the grease squeezes out where there is metal-metal contact but remains in the microscopic voids to ensure water doesn't get in.
Hubs and wheels have, at best, a clean machined finish. I don't know what mechanical engineers call the different levels of surface roughness, but these are not gauge block levels of flatness, but more akin to a single pass of a flycutter. So when you clamp the mating surfaces of the wheel and hub together, would the mating friction not be from the areas where there is actual contact? Hence antiseize would just sit in the troughs and the actual friction would be provided by the points where there is contact?
Or is this why it's debated?
As a caveat I would say that in the example of the electrical contacts mentioned above, if sufficient grease is applied that it relies on the excess being squeezed out so the asperities make direct contact then that's getting towards film thickness approaching surface roughness and in this region coefficient of friction can drop rapidly, as always devil is in the detail. That's way too much grease imo for the wheel/hub application being considered by the thread, but just a different point on the same curve.
Repeat reminder, if going to apply on wheel/hub, only do so very very sparingly, even wipe on wipe off to leave only a trace, and not on heavy vehicles unless manufacturer says you can, don't know of any that do on trucks/buses but it's possible I guess.
As a real world example:-
Some while back in this thread, I think, I told of going to take off the alloy wheels from my Citroen, to find them apparently welded to the hubs. I had to get the local Citroen garage to do it for me. They delegated it to a tyre shack down the road, which did the bolts up THREE times tighter than they should, but that is a different story, of monkeys with rattle guns.
After this, I went around the wheels again to smear some copperease on the faces, discovering the overtight bolts on the way.
Yesterday, about five years later, I wanted to inspect my brake pads. I don't have a lift as used in ithe annual MoT, so I went to take off the wheels. Two were 'glued on', but yielded to a soft hammer to jolt them free, the others I was able to pull off, so I am sure that I could actually change a wheel at the road side if needed! On replacing each I again smeared copperease on the mating faces - a mere smear! - in the confidence that it is not dangerous, and is actually helpful.
John
Some while back in this thread, I think, I told of going to take off the alloy wheels from my Citroen, to find them apparently welded to the hubs. I had to get the local Citroen garage to do it for me. They delegated it to a tyre shack down the road, which did the bolts up THREE times tighter than they should, but that is a different story, of monkeys with rattle guns.
After this, I went around the wheels again to smear some copperease on the faces, discovering the overtight bolts on the way.
Yesterday, about five years later, I wanted to inspect my brake pads. I don't have a lift as used in ithe annual MoT, so I went to take off the wheels. Two were 'glued on', but yielded to a soft hammer to jolt them free, the others I was able to pull off, so I am sure that I could actually change a wheel at the road side if needed! On replacing each I again smeared copperease on the mating faces - a mere smear! - in the confidence that it is not dangerous, and is actually helpful.
John
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