Grease is the word; a complicated word...

General cycling advice ( NOT technical ! )
Canuk
Posts: 1105
Joined: 4 Oct 2016, 11:43pm

Re: Grease is the word; a complicated word...

Postby Canuk » 20 Nov 2018, 5:14am

The utility cyclist wrote:
Canuk wrote:I put copper base gear on everything, even my carbon frames. It's probably overkill but I've yet to experience a problem with anything seizing or getting stuck.

Why would you put copper grease in a carbon frame with a carbon seatpost and/or handlebars, that's actually detrimental and absolutely no need ever to do that. metal on metal, sure, carbon, no way, you could use some carbon paste on the bars if you really want to but that's a different thing altogether. I've been riding dry mounted carbon posts and bars for over a decade on several bikes.


Carbon to carbon bonding is even more likely than aluminium to steel. I got this tip from my lbs who has had the gruesome task of sawing off dozens of carbon posts and delicately reaming out the frame. He says his success rate is only about 20%. The microstructure of carbon fibre is very rough. If you look at it under a microscope you'll see just how rough it really is. Dry carbon into carbon can over time create a fine dirty paste which when it bonds is near impossible to dislodge.

I've been there myself with a Look KG 555. A smear of copper grease would have saved me £1100 on a new frame. In the aerospace industry you'll never find a dry carbon to carbon contact area. For precisely the same reasons. I suppose its like any other mechanical disaster : you never think twice about it till it happens to you!

boris
Posts: 433
Joined: 5 Nov 2010, 1:58pm

Re: Grease is the word; a complicated word...

Postby boris » 26 Nov 2018, 8:13pm

Super essay on grease.

So do I carry on using vaseline or not? The mysterious tube of Lithium grease in my toolbox : does this have unpleasant reactive tendencies as I have always suspected ? I see copper is also being discussed.

I do not understand why metal powder or ions between two other metal surfaces is a good idea.

I had to scrap my 40year old peugeot a few weeks ago so had a good look in the headset , which had never been adjusted or regreased and functioned perfectly. The ball bearings and surfaces were perfect .It was well packed with a transparent brown grease or thick oil which must have magical properties; if only we knew what it was.

Brucey
Posts: 42193
Joined: 4 Jan 2012, 6:25pm

Re: Grease is the word; a complicated word...

Postby Brucey » 26 Nov 2018, 9:14pm

a 40-year old Peugeot could well have had a stronglight headset in it of a type that is basically styled like the old Campag NR headset. There is little to choose in terms of durability between them either. The only black mark against this model of stronglight headset is that it is notoriously difficult to build it up with loose (rather than clipped) ball bearings.

A lot of what happens in a headset or other bearing is simple chemistry; if the conditions (say) tip the pH of the environment very slightly one way, this can favour corrosion of the metal (thus further accelerating the pH change), and in addition degrade the thickener in the grease so that the grease cannot possibly work any more. Depending on the chemistry of the grease one drop of slightly salty water might be enough to set off a chain of events that will result in destruction of the bearing.

I don't understand what you mean by your comment about 'metal particles'. Various EP additives and solid lubricants all work in highly specific fashions and in the main they prevent wear that would otherwise occur e.g. via micro-welding between asperities on the surfaces. None of them might be described as 'metal particles'. Metal particles are used in anti-seize compounds but that is a whole different subject.

Vaseline has its uses for sure but in a rolling element bearing there is always something better you could be using.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

boris
Posts: 433
Joined: 5 Nov 2010, 1:58pm

Re: Grease is the word; a complicated word...

Postby boris » 26 Nov 2018, 9:43pm

Thankyou. I meant in particular copper grease , which looks as though it literally has finely ground copper in it, and is it the same for zinc, aluminium, and molybdenum grease. I suspect that , unlike the truly magical potion added to the peugeot headset, those are sold on a promise that they will somehow reduce reactions that fuse joints and tubes but perhaps they actually increase fusing reactions.

P S yes I have always thought it was a stronglight 1inch headset, but not marked as such. It was of a hardness and overall quality of metal and make that we may never see again. Some old raleigh bikes have similarly tough components.

Brucey
Posts: 42193
Joined: 4 Jan 2012, 6:25pm

Re: Grease is the word; a complicated word...

Postby Brucey » 26 Nov 2018, 10:31pm

you are really talking about anti-seize compounds then. They are not really 'lubricants' per se, not in a bicycle context anyway. They work as anti seize compounds on static parts by inhibiting the reactions that cause seizure, even if it promotes other reactions which you mightn't think are 'harmless' when taken in isolation.

BTW 'Molybdenum' greases usually contain Molybdenum Disulphide; this is a very effective solid lubricant.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

alexnharvey
Posts: 1441
Joined: 10 Jan 2014, 8:39am

Re: Grease is the word; a complicated word...

Postby alexnharvey » 1 Dec 2018, 10:16pm

Is Mobil shc460 a good choice for hubs, headsets and possibly BBs? It seems to meet a lot of the requirements. EP, anti corrosion, slow rotation under heavy load. Not too thick overall (nlgi 1.5) and with high viscosity synthetic base.

I think others in the shc range (100, 220, 1500) have been suggested before.

alexnharvey
Posts: 1441
Joined: 10 Jan 2014, 8:39am

Re: Grease is the word; a complicated word...

Postby alexnharvey » 9 Dec 2018, 5:49pm

https://ac.els-cdn.com/S0301679X1500461 ... b75777ba06

The LiPAO grease in this study uses a low viscosity synthetic base oil (18cst) yet maintained a good film thickness in their testing. Is there an argument for using such a grease rather than the high viscosity bases we generally discuss here?

Something like skf lgbb2 is the closest I've found at 68cst. Designed for low speed high load applications.

Brucey
Posts: 42193
Joined: 4 Jan 2012, 6:25pm

Re: Grease is the word; a complicated word...

Postby Brucey » 9 Dec 2018, 10:48pm

I would ask 'where is the benefit?' in that at very high speeds there might be a benefit in friction losses but at low speeds they are arguably so small that they are not really worth worrying about in the same way. Possibly there is more lost in the seals (if they are properly wetted with lube) than in the bearings anyway. Also in reality a lot depends on how stable the thickener is, if you are reliant upon that for the low speed film thickness. Plenty of greases start to degrade by the thickener changing first of all. Unfortunately bicycle parts see some pretty horrible conditions and they don't always have perfectly smooth surfaces in the bearings either.

So a grease that works great in a lab test might not work so well in the real world. Ideally you would want to have

- super anti-corrosion additives (clue; the grease is recommended for 'open' bearings and/or gears in mucky conditions)
- grease fluid enough that it keeps seal lips wetted (so the seals can work as intended) but not so fluid that the lube just runs out of the hub (*)
- grease that shears in a particular way so that it doesn't 'ball up' in seals (*)
- EP additives and/or solid lubricants to inhibit wear at the very lowest speeds (they don't even measure at bearing speeds that correspond to climbing in bottom gear)
- a thickener system that isn't destabilised by water, road salt, small amounts of rust, or typical soil chemistries, even under long term exposure.
- a thickener system that works differently under different conditions (**)

(*) the NLGI consistency is rather a blunt tool in relation to what you really need in a bike part. The NLGI test basically measures how easily the grease shears at a certain speed under a drop weight test, i.e. the distance the grease is penetrated is measured. The grease sample is 'freshly worked'; you would get a completely different result if the grease is left for different lengths of time. Nearly all commercial greases 'shear thin' so a small change in viscosity at high speeds affects the test score greatly whereas a large change in the low speed viscosity has a relatively small effect on the test score, even if it profoundly influences the way the grease will work in a bike part.

I've concocted lubes which when sheared, are little more draggy than plain oil is, yet stop flowing under their own weight within fifteen seconds of not being actively worked; to my mind this makes for a pretty good bike hub lube to use in sealed hubs because the lube will keep the seals wetted and coat all the parts inside a hub nicely, but won't allow excessive amounts of leakage to occur when the bike is not in use. In an unsealed hub you would want something thicker than that.

(**) in an unsealed hub especially, how the grease is pushed around by the ball bearings is important. Some greases use additives that tackify the grease and/or make it 'stringy'. In low speed bearings this can help to keep parts coated under conditions that would just push other greases aside.

So the bottom line is that you usually can't just choose a grease meant for another application entirely on the basis of test scores meant for that application; basically you need to do some tests to show that it isn't going to fail (usually in some terribly prosaic fashion) when you start using it on bike parts.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

zeluzel
Posts: 22
Joined: 27 Jan 2020, 11:38am
Location: Wrocław, PL

Re: Grease is the word; a complicated word...

Postby zeluzel » 10 Dec 2020, 5:50pm

I have yet another question to you, Brucey :P. It's concerning the right grease for IGH. In one thread you said that
Brucey wrote:Bicycle IGHs are characterised by very low speeds, low temperatures, extremely high loadings.[

Could you elaborate on that high loadings part? I mean why are they higher than the ones in car's gearbox let's say?

Brucey
Posts: 42193
Joined: 4 Jan 2012, 6:25pm

Re: Grease is the word; a complicated word...

Postby Brucey » 10 Dec 2020, 6:49pm

anytime the gear ratio is a long way from unity it is likely that the internal gear loadings are much higher than in more moderate gear ratios (although this will vary with the design of the hub of course). When you are 'tapping along' (pedalling in steady state, sat in the saddle), the load on the pedals is unlikely to exceed low tens of kg. However when you are standing on the pedals, or starting off, loadings can be about x10 as high. These efforts result in some pretty brutal loadings inside the hub. As mentioned, the speeds are low enough that the lubricant film is almost certain to fail at high loads and it will then only be a matter of how the additives in the lubricant manage to mitigate the wear that occurs.

Note also that even if the gears are operating under low stress when 'tapping along' such that they have a virtually infinite fatigue life, they certainly won't be suffering no fatigue damage under the higher service loads.

Torque overload at low speeds is a real gearbox killer; to simulate these loadings in a car gearbox you would probably have to drop the clutch from a standstill; repeats of this will soon wreck the clutch so are not normally seen. On a bike the only limit to the repetition of torque overloads is the rider. Peak engine torque in most cars occurs at reasonably high engine speeds and this means that normally, the gear teeth are moving faster and the lubricant film is less likely to be breached. Electronic engine management can be used to limit the torque at low engine speeds in low gears; this is often done (at least in part) to spare the gearbox.

If you want to estimate the loadings in an IGH, reckon that the peak chain tension might be of the order of 300-400kg and the diameter of the sprocket is comparable to that of the ring gear inside the hub. If there are three planet gears then (momentarily) each will be bearing that load one tooth at a time, meaning that peak tooth loadings in a bicycle IGH are likely to be around 100-130kgf per tooth. The contact area of each tooth might be 5mm x 0.2 to 0.4mm so about 1 to 2mm^2, undergoing a load of 1000 to 1300 N. You don't need to be a genius to see that this is comparable to yield even in quite hard steels; put it this way if you put an usually strong rider on an IGH you might expect the hardest efforts to start shearing teeth off inside the hub; in most cases there is little leeway for making the pinions smaller etc, and it is only the fact that most folk don't have enough energy to be leaping on the pedals ad infinitum which spares them.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

zeluzel
Posts: 22
Joined: 27 Jan 2020, 11:38am
Location: Wrocław, PL

Re: Grease is the word; a complicated word...

Postby zeluzel » 10 Dec 2020, 7:59pm

Okay, so, from what I understood, the reason for those high loadings, in comparison with cars, are:
  • riders not using "clutch", that is gears, the right way (whereas in car, given the rotation speed differences and torque, it'd soon destroy the gearbox. Am I right, looking at it like that?)
  • small rotation speeds, resulting in improper lubrication
  • small components taking up big loads
From those 3, I understand, that the 1st and 3rd are what makes the main difference between car's and bicycle's gearbox, right? Are they likely to be destroyed, ex. when riding with low cadence, or off road? I read people use some of them in MTBs, but, from what you wrote, it looks like it, they're by design meant to fail in such application.
I'm not very good at cars and mechanics, so may be asking the super stupid questions, but why is it, that torque is the highest on low gears? Or is it just about, as you wrote in the beginning, the distance from unity ratio? I remember reading about Sturmey Archer's hub generating very big torque, because it gears up, starting at unity.
I'm now going through some college physics articles and videos on YouTube :P, but, if you'd be kind enough, I'd be very happy, to understand how it applies to IGH.

Brucey
Posts: 42193
Joined: 4 Jan 2012, 6:25pm

Re: Grease is the word; a complicated word...

Postby Brucey » 10 Dec 2020, 10:41pm

you asked about the loading so I wrote about the loading, as best I could. But that also varies with the design of the gear; in some IGHs the gear ratios close to unity are created by using the difference between two gear trains, each of which is highly loaded. The effects of loading are at their worst at low speeds, and there are only ever low speeds on a bike. I didn't mention temperature; the cool bicycle gearbox benefits the integrity of the lubricant film (provided the lube is still mobile with in the gearbox) but the chemistry of EP additives may work better at higher temperatures.

In a typical SA 3s hub, there is no load on any of the gears in gear 2. Same for the middle gear in most SA 5s, 7s hubs, SRAM 3s,5s,7s hubs, shimano 3s hubs. In shimano IGHs with 7 or more gears, only Nexus/Alfine 8s hubs have a direct drive ratio, being gear 5. If you otherwise use measured efficiency as a proxy for loading, in comparing IGHs with the same construction (roller bearings on the pinions or not) then you won't go so very far wrong.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

zeluzel
Posts: 22
Joined: 27 Jan 2020, 11:38am
Location: Wrocław, PL

Re: Grease is the word; a complicated word...

Postby zeluzel » 11 Dec 2020, 2:00pm

Okay, thanks for reply. To anyone interested, after looking at this video:
https://www.youtube.com/watch?v=H9_Llzcz2cY
how I understand it is that, when we assume that input's rotation speed (our cadence) and torque (we're tapping along) is constant, then ratio is in inverse proportion to torque on the output, so
  • on the underdrive: the smaller the ratio, the bigger the torque on the output
  • on the overdrive: the bigger the the ratio, the smaller the torque on the output
However, talking about gearbox, every time it has to convert rotational speeds of input and output, it's under torque (except for the 1:1 in single planetary gearhubs, like 3-speeds), but, judging from the above, the torque is bigger on underdrive. Given the small size and great proportional differences of input torque (when we stand on pedals or start on high gear), IGHs' gears are subject to greater torque, than properly used car's transmission.

Back to the topic xD - that justifies using EP additives in grease for IGH (apart from what Brucey wrote about great differences in rotational speed of bicycle bearings compared to what greases are normally engineered for).

Another question - what would you say about greases for (coaster and roller) brakes? It's written everywhere that you should use high-temperature grease for coaster brake hubs, but I never understood, if it means the whole hub, especially the left side bearings, or just the brake shoe... Also how high temperatures should it withstand? Bearing greases' labelled "high temperature" normally go up to 150 celsius, which is not much higher, than standard bearing greases I checked. In my city, there was old bicycle mechanic, one of few, who would deal with IGHs, and he told me, he uses standard, cheap graphite grease just on the brake shoe.

My tactics with coaster brake hubs is to use normal, NLGI 2 grease for bearings (more of it on the left side), semi-fluid one for gears, and high temperature, super thick MoS2 paste (meant for brake pistons and backside of brake shoes to prevent squealing). My intuition tells me, that:
  • bigger amount of grease on the left side bearing will compensate for its melting under high temperature.
  • MoS2 paste will prevent it from seizing, while, being thick, stay on the brake shoe and not migrate to other parts of the hub.

To be honest though, in 99% cases you could probably use anything, as coaster brake hubs are mostly used for super leasure cycling and won't see that much of this heat :P.

When it comes to rollerbrake, MoS2 paste is so thick, it definitely induces drag. Since Shimano grease is so expensive, but also out of curiosity and experience with their white Nexus grease (which turns out to be inferior to widely available competitors), I was trying to find an alternative. What rollerbrake grease seems to be, is MoS2/grafite (it's black), low viscosity (NLGI 0?) grease. Similar things I managed to find, were meant for 150 celsius, or were, at least, NLGI 2 thickness. However, a copper grease seems to match the criteria - it's both supper high temperature (actually used around brakes in automotive) and I managed to find low viscosity versions of it. Do you think it's a good candidate? Or maybe it's wiser to try to dilute one of those ceramic/moly grease (if yes, than with what? gear oil?).

Cheers ;)

Brucey
Posts: 42193
Joined: 4 Jan 2012, 6:25pm

Re: Grease is the word; a complicated word...

Postby Brucey » 11 Dec 2020, 7:07pm

I wouldn't use copper grease in a coaster brake; whatever you use in the brake itself ends up getting mixed with the grease in the LH bearing. I have seen a wheel bearing which someone had packed with copper ease and then used; it wasn't pretty!

In the old days greases were often thickened with various fats which would simply melt when they got hot. Better brakes and higher speeds meant more heat into wheel bearings on cars etc, hence 'high melting point grease', even though the melting points don't seem that high. IME it doesn't matter what grease you use in a coaster brake; if you get the brake properly hot the grease will no longer be in the right places inside the hub afterwards.

I at first thought shimano roller brake grease must have MoS2 and/or graphite in it, but I've since noted that it doesn't smell like any other greases which do have these ingredients, so I'm not 100% sure.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

zeluzel
Posts: 22
Joined: 27 Jan 2020, 11:38am
Location: Wrocław, PL

Re: Grease is the word; a complicated word...

Postby zeluzel » 11 Dec 2020, 7:29pm

I was talking about using it in ROLLER brake. I also tend to think, that it doesn't t really matter that much, but my perfectionism doesn't let me leave it (even though the only rollerbrake I ever serviced was fine with standard Nexus Grease :p). Maybe next time I'll get to service one, I'll buy that damn grease for all the money earned :p.