brinelling

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Punk_shore
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brinelling

Postby Punk_shore » 5 Feb 2019, 2:08pm

The front wheel, when turning, has a flywheel effect. Similarly, so does the back wheel.

Each wheel "wobbles" relative to the other. This is known as gyroscopic precession.

Front/ rear axle(s) could thus move about the steering head. Would this contribute towards brinelling (pitting) of the steering head bearing(s)? :idea:
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Brucey
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Re: brinelling

Postby Brucey » 5 Feb 2019, 2:55pm

excess preload is the primary cause of headset damage.

cheers
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Airsporter1st
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Re: brinelling

Postby Airsporter1st » 5 Feb 2019, 3:19pm

Brinelling, of the sort you are concerned about, usually affects stationary (rotationally speaking) bearings which are subjected to vibration for lengthy periods. This used to affect our cargo pumps on long ocean voyages, when the pumps would not be used for as much as 2 months.

Whether your relatively stationary headset bearings are subjected to sufficient vibration from the source you describe, for sufficient time, is doubtful IMHO.

I could see the cause of pitting being crevice and/or fretting corrosion, however.
Last edited by Airsporter1st on 5 Feb 2019, 6:14pm, edited 1 time in total.

Brucey
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Re: brinelling

Postby Brucey » 5 Feb 2019, 3:27pm

sounds like false brinelling to me.

cheers
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Vorpal
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Re: brinelling

Postby Vorpal » 5 Feb 2019, 3:58pm

Punk_shore wrote:The front wheel, when turning, has a flywheel effect. Similarly, so does the back wheel.

Each wheel "wobbles" relative to the other. This is known as gyroscopic precession.

Front/ rear axle(s) could thus move about the steering head. Would this contribute towards brinelling (pitting) of the steering head bearing(s)? :idea:

As above, if you observe 'brinell' shapes in the races, it is 'false brinelling', as Brucey says.

I think that the potential for the gyroscopic precession to affect bearing wear is quite small, especially compared to the other things that cause wear or failure, such as, contamination (e.g. water, dirt, etc.) or grease deterioration.
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rogerzilla
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Re: brinelling

Postby rogerzilla » 8 Feb 2019, 9:54pm

I'm with Jobst Brandt on this one (I know this isn't universally accepted, so forgive me, Brucey).

The dents in the races, mainly the lower race, are always worst at the front and back of the races. With traditional caged ball headsets, road bikes suffer badly from it, MTBs not so much (even if they have 1" headsets). The dents are caused by fork flex, which the bearing races can't properly accommodate. Road bikes are ridden mostly with the steering in the straight ahead position and the grease is displaced from under the balls, MTBs get thrown around a lot more, which keeps the grease distributed. The flexing action causes fretting between the balls and the races once the grease has been displaced, and this makes pits in the races.

Headsets with loose races, like the Stronglight A9, or cartridge bearing headsets with angled interfaces, can accommodate fork flex in the 45 degree interface between race and cup (or cartridge and cup), so the balls don't have to try and do it. I've never had a cartridge bearing headset "brinell", even at ten times the mileage of a conventional headset.

1 1/8" forks help reduce indexed steering a bit because the steerer is stiffer and there are more/bigger bearings, but that is a less significant factor.

Samuel D
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Re: brinelling

Postby Samuel D » 11 Feb 2019, 10:21am

rogerzilla wrote:I'm with Jobst Brandt on this one (I know this isn't universally accepted, so forgive me, Brucey).

Oh, another point of disagreement between Brandt and Brucey!

rogerzilla wrote:The dents are caused by fork flex, which the bearing races can't properly accommodate.

It’s not clear to me how fork flex causes dents in this hypothesis. By not ‘accommodate’, you mean the balls are minutely displaced axially (one side up and the other down) as the steerer tube bends?

I wrecked a roller head bearing in one winter as reported here. I think lack of adequate lubrication and a corrosive sludge from salt water breaching the seals was the main problem there. The wear pits caused by the rollers, by whatever mechanism, were worst on the front quarter of the crown race.

rogerzilla wrote:The flexing action causes fretting between the balls and the races once the grease has been displaced, and this makes pits in the races.

Why doesn’t flex instead replenish the grease? Taken to extremes, a loose head bearing (zero preload) should move enough to replenish grease.

rogerzilla wrote:1 1/8" forks help reduce indexed steering a bit because the steerer is stiffer and there are more/bigger bearings, but that is a less significant factor.

But the smaller the steerer tube, the greater will be the conformity between the radii of the balls and the cups and therefore the greater the contact area. On the other hand, the crown race will conform less to the balls.

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Re: brinelling

Postby Vorpal » 11 Feb 2019, 2:32pm

When I was younger, I got lots of 'junk' bikes, found, gifted to me, etc., and with a little TLC, they were rideable bikes, sometimes sold on or given away, sometimes kept and used to commute to university until they 'disappeared'.

All of the headsets I diassembled, if the races were damaged, it was one of three things:
-'grooves' worn from repeated steering with old, contaminated grease and/or the races moving against bearings that no longer rolled
-rust
-damage directly from contaminants

I have seen a sort of brinelling effect sometimes when the bearings were held in place by old, stiff grease, and obviously used that way for some length of time. It was, IIRC, always on the lower races. The upper races would move relative to the bearings, instead of the bearings moving, when they got into that state. It was less unusual than you might think.
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Brucey
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Re: brinelling

Postby Brucey » 11 Feb 2019, 2:41pm

actually I think most of what rogerzilla has said is what I've said, not what Brandt has said. Its been a while since I have read what Brandt said in detail but IIRC he maintained that it couldn't possibly be real brinelling because the loads would be too low for that to happen and he couldn't see any displaced material in the damaged races. Thus he maintained that such headset damage had to be false brinelling.

My argument has always been that

a) because it is spread over a much wider area the raised material around the indent associated with true brinelling may not be easily visible when the indents are very shallow. (Also NB the way a piece with a hardened surface deforms may not give a classic 'crater shape' either.)

b) Brandt made no allowance for the fact that he had the world's longest (and flexiest) 1" steerer (until he changed in latter years to a 1-1/8" setup) which meant that the loading per ball was much higher than you might expect; enough to cause true brinelling.

c) in a badly adjusted headset, such damage can be seen in just a few tens or a few hundred miles; far too few cycles for it to be 'false brinelling'.

So I'm not saying that false brinelling can't possibly happen in a bicycle headset, more that in many (most) cases it can't be that and must be something else. Far from the loads being too small for true brinelling to occur they are concentrated on just a few balls as soon as the steerer flexes appreciably.

Re steerers; very short steerers see much higher loads and this can cause trouble in its own right. Very long steerers (esp in 1") are just very flexible and this (plus riding over rough ground and using the brakes hard) is bound to cause higher than normal loads on the balls in a headset with fixed races. For the rest of us (with medium length steerers) the loads are moderate and the flex is acceptably small, so headsets have a fairly easy time of it.
It is argued that in headsets with races that are not fixed (i.e. the bearings are on tapered seats) his gives some articulation and this reduces the additional loads when the steerer flexes. This is true but it still isn't a perfect arrangement; for a start the tapered seating in many headsets is at too shallow an angle (so I have yet to see a roller bearing headset of a common pattern where the elements weren't routinely displaced by the lateral loads) and second such articulation cannot occur without the bearing also deforming into an oval shape. This again concentrates the load, but not as much as with fixed races, probably.

BTW as soon as there is water in the bearings all bets are off; you are liable to get rates of erosion that are x10 or x100 faster than normal, because material is removed by a kind of corrosion-assisted fretting process. In a regularly-used bike the wearing surfaces may not look badly corroded because they are constantly being polished, and the wear debris disappears in the grease. Once the corrosion inhibitors in the grease have been overwhelmed (which doesn't take much water/road salt with a lot of greases) the conditions at the contact can become highly acidic and this allows much higher wear/erosion rates.

[Aside; local conditions at small area contacts can be extreme in ways that you can't imagine. One of my pet ideas is that in ancient times folk worked hard rock to fantastically smooth finishes not with soft metal or other hard stone tools, but using those/other tools plus chemistry. For example some plants soon yield a moderately strong acid and this combined with a gentle rubbing contact (which creates some local warmth and keeps fresh reagents where they are needed) can erode material at a surprisingly high rate. In Egypt, Peru, Bolivia etc there are worked stones which cannot easily be recreated using mechanical work (and the available tools) alone and no-one has yet worked out how they did it (in a reasonable time period). This has lead some folk toward wild speculations but I think chemistry may be the key. in some of these worked stones you can see what might have been small area 'support pads' (of raised material) which could have been left if (say) a cord impregnated with organic acids was passed repeatedly between two stones so as to make a uniform clearance between them elsewhere. Modern examples of this sort of thing are not unknown; for example it is reported that there was quite recently a jail break in which a prisoner used dental floss and salsa sauce (which is slightly acidic) to cut through the steel bars of his cell; either thing by itself could have taken years but clearly didn't take as long as that in combination.]

Anyway I digress; the point is that gentle/moderate rubbing plus the right (wrong) chemistry can soon cause damage inside a bearing and the exact mechanism isn't always clear. If your grease isn't rated for some kind of horrible (e.g. exposed) application, then it can soon go bad enough at the contact points to become chemically aggressive. It can't really 'lubricate' any more, not under those conditions.

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

Samuel D
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Re: brinelling

Postby Samuel D » 12 Feb 2019, 6:33am

Brandt talks about this here, in the old Rec.Bicycles FAQ to which he contributed much. Search the page for “Indexed Steering” to find the relevant section. It appears he’s not a fan of roller bearings either.

MikeDee
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Re: brinelling

Postby MikeDee » 13 Feb 2019, 3:51pm

Brucey wrote:actually I think most of what rogerzilla has said is what I've said, not what Brandt has said. Its been a while since I have read what Brandt said in detail but IIRC he maintained that it couldn't possibly be real brinelling because the loads would be too low for that to happen and he couldn't see any displaced material in the damaged races. Thus he maintained that such headset damage had to be false brinelling.

My argument has always been that

a) because it is spread over a much wider area the raised material around the indent associated with true brinelling may not be easily visible when the indents are very shallow. (Also NB the way a piece with a hardened surface deforms may not give a classic 'crater shape' either.)

b) Brandt made no allowance for the fact that he had the world's longest (and flexiest) 1" steerer (until he changed in latter years to a 1-1/8" setup) which meant that the loading per ball was much higher than you might expect; enough to cause true brinelling.

c) in a badly adjusted headset, such damage can be seen in just a few tens or a few hundred miles; far too few cycles for it to be 'false brinelling'.

So I'm not saying that false brinelling can't possibly happen in a bicycle headset, more that in many (most) cases it can't be that and must be something else. Far from the loads being too small for true brinelling to occur they are concentrated on just a few balls as soon as the steerer flexes appreciably.

Re steerers; very short steerers see much higher loads and this can cause trouble in its own right. Very long steerers (esp in 1") are just very flexible and this (plus riding over rough ground and using the brakes hard) is bound to cause higher than normal loads on the balls in a headset with fixed races. For the rest of us (with medium length steerers) the loads are moderate and the flex is acceptably small, so headsets have a fairly easy time of it.
It is argued that in headsets with races that are not fixed (i.e. the bearings are on tapered seats) his gives some articulation and this reduces the additional loads when the steerer flexes. This is true but it still isn't a perfect arrangement; for a start the tapered seating in many headsets is at too shallow an angle (so I have yet to see a roller bearing headset of a common pattern where the elements weren't routinely displaced by the lateral loads) and second such articulation cannot occur without the bearing also deforming into an oval shape. This again concentrates the load, but not as much as with fixed races, probably.

BTW as soon as there is water in the bearings all bets are off; you are liable to get rates of erosion that are x10 or x100 faster than normal, because material is removed by a kind of corrosion-assisted fretting process. In a regularly-used bike the wearing surfaces may not look badly corroded because they are constantly being polished, and the wear debris disappears in the grease. Once the corrosion inhibitors in the grease have been overwhelmed (which doesn't take much water/road salt with a lot of greases) the conditions at the contact can become highly acidic and this allows much higher wear/erosion rates.

[Aside; local conditions at small area contacts can be extreme in ways that you can't imagine. One of my pet ideas is that in ancient times folk worked hard rock to fantastically smooth finishes not with soft metal or other hard stone tools, but using those/other tools plus chemistry. For example some plants soon yield a moderately strong acid and this combined with a gentle rubbing contact (which creates some local warmth and keeps fresh reagents where they are needed) can erode material at a surprisingly high rate. In Egypt, Peru, Bolivia etc there are worked stones which cannot easily be recreated using mechanical work (and the available tools) alone and no-one has yet worked out how they did it (in a reasonable time period). This has lead some folk toward wild speculations but I think chemistry may be the key. in some of these worked stones you can see what might have been small area 'support pads' (of raised material) which could have been left if (say) a cord impregnated with organic acids was passed repeatedly between two stones so as to make a uniform clearance between them elsewhere. Modern examples of this sort of thing are not unknown; for example it is reported that there was quite recently a jail break in which a prisoner used dental floss and salsa sauce (which is slightly acidic) to cut through the steel bars of his cell; either thing by itself could have taken years but clearly didn't take as long as that in combination.]

Anyway I digress; the point is that gentle/moderate rubbing plus the right (wrong) chemistry can soon cause damage inside a bearing and the exact mechanism isn't always clear. If your grease isn't rated for some kind of horrible (e.g. exposed) application, then it can soon go bad enough at the contact points to become chemically aggressive. It can't really 'lubricate' any more, not under those conditions.

cheers


How do you explain that when Brandt switched to cartridge bearing headsets, he had no more headset pitting problems? He also pounded on a loose ball headset bearing and race with a hammer and observed no brinelling. I admit a cheap headset with unhardened bearing races can brinnell, but that's not what we're talking about here. I've got a 20 year old bike with a 1" threaded cartridge bearing Shimano headset, and it's not pitted.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: brinelling

Postby Brucey » 13 Feb 2019, 4:22pm

MikeDee wrote:
How do you explain that when Brandt switched to cartridge bearing headsets, he had no more headset pitting problems?


he originally had a long and ridiculously flexible 1" steerer. His change to a cartridge bearing headset may well have coincided with the change to a much stiffer 1-1/8" steerer too. In any event the articulation between a cartridge bearing and the crown race may have saved it.

He also pounded on a loose ball headset bearing and race with a hammer and observed no brinelling.


this is a very poor test if the intention is to simulate the operational loads in a headset. In his test the loads are shared well between balls (for several reasons), but in a real headset they are not.

I admit a cheap headset with unhardened bearing races can brinnell, but that's not what we're talking about here. I've got a 20 year old bike with a 1" threaded cartridge bearing Shimano headset, and it's not pitted.


Those cartridges (unlike many) have about as many ball in as a loose ball headset. They also have different seating angles from many modern headsets. It would be a mistake to assume that they are like all cartridges. I am presuming that you don't have a thin-walled steerer that is about a foot long either, which is a far more important consideration. Brandt destroyed many high quality headsets in his bike, of a type that (with correct adjustment, lubrication, and a much shorter, less flexy steerer) I have used for many years/many tens of thousands of miles with zero problems. [I have several such headsets that make yours look like a youngster.]

Brandt's problematically long steerer was IMHO the main cause of his troubles and he simply didn't realise that. Many people have read what he wrote and have assumed that they must be having similar problems. I think this is incredibly unlikely; most loose ball headsets die because they are badly fitted and/or badly adjusted. I have proven this to doubters (who have a damaged headset) on many occasions; checking/correcting the race alignment, turning the crown race slightly, rebuilding the headset with loose balls and adjusting it correctly normally provides complete and permanent solution.

cheers
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