|Swarf, Mostly!||07/03/2021 16:45:19|
|606 forum posts|
Hi there, all,
Back in the days when I was in gainful employment, I had a colleague who was a mechanical engineer. He observed that ball races were/are intended for continuous rotaion and that if they habitually only rotate less than a full turn the races would 'brinell', damaging the bearing.
This comment interested me at the time because there was an advertiser in the Amateur Radio magazines who used to sell Morse keys with their beam pivoted on ball races - he claimed this method was superior to keys with plain pivots. (A counter opinion at that time was that the best Morse key was that made for the Royal Navy which employed flexure pivots. The RAF Pattern D Morse key employed a taper pin pivot. )
Nowadays, I occasionally dismantle the odd computer hard drive or two. These usually employ two sets of ball races, one set on the platter motor, the other on the read/write head arm. The angular excursion of the latter is only about 45°. The head arm is light but moves quite quickly so its bearings might experience relatively high stress.
I've accumulated quite a few of these ball races - do members think they are fit for 'normal' bearing duty or should I scrap them?
Edited By Swarf, Mostly! on 07/03/2021 16:46:03
|John Haine||07/03/2021 16:55:35|
|4169 forum posts|
There's a chap called Dick Stephen who made quite a few clocks and I'm fairly certain he used miniature ball bearings for the pendulum in at least one of them. I'm not sure of their longevity in that application though. They are used on church bells apparently, where the load is very large, but I guess the actual operating hours are small. In a disc drive the load is very small and the consequences of failure significant so I expect they are perfectly OK though might wear out slightly earlier.
|Nicholas Wheeler 1||07/03/2021 17:18:55|
|739 forum posts|
There's nothing special about the bearings used in church bells. They're just pillow blocks, available from any industrial bearing supplier, bolted to the top of the frame. The 1500kg one I ring frequently(when not in lockdown) has been on the same bearings for the last 60years, as have the other, lighter, nine.
|Jeff Dayman||07/03/2021 17:22:14|
|2176 forum posts|
Whether or not a ball bearing exhibits Brinelling in time during use will depend on 4 things - load, lubrication, speed, and metallurgy / finish quality of the bearing. If the bearing sees low loads, low speeds and has good lubrication and was decent quality to begin with, it could last a very long time with no Brinelling.
Huge loads, high speed, someone hammering on it, lubrication loss, rough quality bearing to start with, and problems are inevitable.
Re telegraph key pivots - if designed correctly I would suggest flexures would give the longest service life with least wear, compared to ball bearings or cones / taper pivots. Depending on the operator's keying style, the bearings in a telegraph key could see high loads which could induce Brinelling.
I am not a "clock guy" but I do recall seeing both knife edge and flexure type pendulum suspension for clocks. (may be many other types, I bow to the clock experts on that)
|Michael Gilligan||07/03/2021 17:48:50|
18921 forum posts
See the second photo on this page: **LINK**
The reasons for the instruction engraved on that disc are twofold:
In case it's not obvious by now ... Brinelling is the creation of [typically very shallow] dents in the surface of the races, by pressure from the [static] balls ... Name relates to the Brinell Hardness test.
|duncan webster||07/03/2021 18:21:29|
|3504 forum posts|
My understanding of the term 'Brinelling' as applied to ball/roller bearings is a potential issue if the rotation is so small that the paths of the balls don't overlap, and so some of the track gets wear and some doesn't. If the outer race is stationary and the inner moves by +- 30 degrees, the balls in their cage will move _-15 degrees, so if there are less than 12 balls there will be gaps where the balls don't run.
Church bells rotate +- half a rev plus a little bit. The little bit is vital, get it right and you can park the bell mouth up, a fraction more and you break the stay, the rope (known as a Sally) disappears up through the hole in the ceiling. Hopefully the campanologist has let go.
I doubt it really matters unless the bearing is heavily loaded. In a similar vein, in days of old some bearings had their stationary races rotated from time to time to spread the load round. I doubt anyone bothers nowadays.
|noel shelley||07/03/2021 18:44:52|
|754 forum posts|
This fault is quite common on hardy spicer joints ! Needle rollers ! Its a catch 22 if the angle of articulation is great enough for the roller to roll round far enough to stop wearing on one spot then the velocity will not be constant. If the joint is in line the velocity will be steadt but it will groove the outer race. If the outer race moves it will destroy the yoke bore. Good quality bearings,High load,good lube, under 1000 rpm, they still fail. Noel
6036 forum posts
You probably all know but early car shipments from japan suffered early life failures of wheel bearings owing to the damage down by constant vibration in one position during the voyage. Initially cured by having the crew move the cars a few inches every few days. Not done now so they must have found a way of mitigating the stress. Since cars had before that been shipped say to Oz from the UK but in low volumes did they just put the failures down to 'crap UK products'?
Following the mention of repeated movement of morse keys - did telegraph and radio operators suffer RSI and or long term in retirement effects?
|Nicholas Wheeler 1||07/03/2021 19:12:32|
|739 forum posts|
???? Every one I've seen has gone from mouth upright, round to upright again. There are plenty of belfry videos that show this. The stay is about another 10 degrees past vertical. It shouldn't break if you just bump it, although learning not to do that is the first thing a beginner should be taught once they're ringing without help.
The rope is called the rope; the woollen grip for the handstroke is the sally.
|John Baron||07/03/2021 20:06:09|
487 forum posts
Personally I salvage them amongst other things and find them extremely useful. I rarely buy bearings but use ones that I can salvage and test. If they are noisy and feel even slightly rough, they get binned.
|old mart||07/03/2021 20:21:56|
|3337 forum posts|
Motorcycle steering head bearings suffer form brinelling as they only move a few degrees most of the time. Replacing the loose balls in the headstocks of older bikes with taper rollers reduces the problem, as the line contact is much greater than the balls had, but cannot cure the brinelling entirely. When a bike is MOT'd, the tester feels for play and the notchy feel in the straight ahead position of the steering.
|David George 1||07/03/2021 22:01:33|
1654 forum posts
Brinell hardness is a test of hardness which uses a hardened ball pressed into a surface to check the hardness of a material. Brinelling in a bearing is caused by a large force pressing the balls or rollers onto a single point like when a motorcycle headstock is in a steadily line and hits bumps in the road etc. Or a bearing is loaded and not rotating much on a machine. Most bearings are case hardened with a very hard surface but the core is slightly softer so it is possible to dent the track with ball/ roller bearing if a shock load is given to the bearing giving a ratchet feel to the bearing.
|Clive Hartland||07/03/2021 22:12:08|
2724 forum posts
I 'kerbed' my SAAB in the snow and after that as I went round a long bend I could hear and feel a bump.
Guessing I had damaged the front wheel drive I dismantled it and found I had dented the outer bearing of the
front left drive shaft, for £10 I was able to buy a new bearing and fixed it.
5505 forum posts
Hahaha. We can disappear down the rabbit hole of some real pedantry here.
True brinelling is when the balls or rollers are stationary and too much load is applied and little round dents are made in the race by each ball or roller. Typical occurrence is when shipping large, say 50 or 100 horsepower, electric motors just sat flat on a pallet then loaded on a ship from China to UK etc. The vibration of the ships engines and movements at sea push little dimples into the races of the ball bearings due to the heavy weight of the rotor. They had big problems with this years ago when Chrysler set up a factory in Australia and shipped all the machinery over from the USA. Solution was either packing blocks or stand the motor up vertically for shipping so the load is taken on the edges of the races that is not in use under normal operating conditions.
Then there is "false Brinelling" aka fretting, which happens when ball or roller bearings move back and forth by an amount less than the pitch or diameter of a roller or ball. Lubricant gets squeezed out of that zone and not replaced so rapid wear takes place, making similar dimples in the race but elongated by the amount of repeated movement. Typical place to find this is on the taper roller bearings on rear suspension swingarm on motorbikes such as some Harleys and BMWs. The swingarm is 18" long or so and the far end moves up and and down maybe four inches. So the pivot bearings only move a few degrees back and forth, less than the diameter of a roller, and end up worn all wavy in the races. Headstock bearings might fit in this latter category as they do move but only slightly, or they might cause true brinelling when hitting bumps in the straight a head position. Maybe both?
So if your hard drive bearings have been moving through 45 degrees it seems unlikely either of these scenarios would occur. 45 degrees rotation on a tiny bearing like that would be enough to keep lubricant circulating around those tiny balls and all should be good.
But if the bearing has done enough service that it is worn out, then it is going to be worn out, regardless, just the same as a fully rotary bearing. .
Edited By Hopper on 08/03/2021 04:36:13
|Nicholas Farr||08/03/2021 08:32:54|
2984 forum posts
Hi, I guess it all depends on what you intend to use these bearings for and you may need to gather enough spares of the same type for replacements for your given project. I've used one from the head arm, in the top Nylon pulley in this drilling / tapping machine that supports the cord holding the balance weight. I made this from an old drilling machine I bought from a steam engine rally, many years ago and the motor came out of an old electric typewriter. I don't use this on any regular basis, but it does get used quite often and sometimes with small batches of holes. The balance weight, weighs about 560g and I can add extra an small weight when tapping, too help when removing the tap, the bearing is showing no sign of wearing out as yet, but it can be easily replaced with others that I have saved.
|Russell Eberhardt||08/03/2021 10:17:14|
2703 forum posts
Well, I used miniature stainless steel ball races with all the lubricant washed out on the pallet arbor of my regulator clock and it has been running for about five years with no problems. The pallets only rotate by about 20° but of course the load is very low as is the speed. They have oscillated through about 80 million cycles though.
|duncan webster||08/03/2021 11:38:25|
|3504 forum posts|
Normal parking position is mouth down, at least it was when I was involved (many moons ago), so rotation +- half a rev plus a little bit seems a reasonable description to me. I think parking mouth down was to ensure that if anyone was up in the bell chamber doing some maintenance they wouldn't nudge a bell and have it swing uncontrollably.
|Peter Cook 6||08/03/2021 12:42:47|
|164 forum posts|
That's definitely one reason. The bells in our church park mouth down so that the clock hammers can hit them when its chimes and strikes. There are wires to pull the hammers off the bells before rotating them to mouth up at the start of ringing.
|Henry Brown||08/03/2021 12:54:22|
482 forum posts
Common issue with larger rolling element bearings that are shipped around the world. The Co Iworked for installed support plates that took the load away from the bearings for transport, when the Engineer went to site to commission the gearbox they were removed before start up. Can't imagine that it would be much of a problem with bearings form a computer or printer though...
|Bill Dawes||08/03/2021 12:56:11|
|472 forum posts|
It is well known in the industrial fan industry, we recommend turning the fan by hand if left stationary for any length of time especially if situated near something like a large diesel engine or on long sea voyages, probably never done in reality. More likely on large fans though. Motor bearings can also suffer from damage due to stray currents leaking through the bearing, we are talking about motors in the order of 75 kw and above, insulated bearings are either standard or optional extra.
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