Lecture – Tribology in Horology

[gerry maddenParticipant @gerrymadden53711]

Just seen that the IMechE is doing a lecture (webinar?) in the above on 19th Nov 12pm.

It’s a subject that is occasionally aired, but often covered in very superficial way based on traditional theoretically-based teachings regurgitated for the umpteenth time. I’ll be keep my fingers crossed that they explore some new ideas :).

Even if not, I’m sure some of us on here might find it interesting presentation.

I think it’s a ‘zoom’ call so you may need to download the software to join in.

Gerry.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Gerry

… unfortunately I have failed to find any reference to it, aside from your post

🙁

MichaelG.

[gerry maddenParticipant @gerrymadden53711]

Michael, that’s not a good sign! I usually work on the basis that if YOU can’t find something on the internet it doesn’t exist!  So I wonder if I’ve viewed an ancient page or misread something.

I will investigate and report. 🙂

[Michael GilliganParticipant @michaelgilligan61133]

Thanks Gerry … only event I could find on 19-Nov was a Dinner in the evening

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Your Google fu has deserted you Michael. Here’s the link. No need to be a member

Tribology in mechanical watches

[Michael GilliganParticipant @michaelgilligan61133]

Mea Culpa !

Thanks for that, Duncan

MichaelG.

.

Duly registered, and on my Calendar

[gerry maddenParticipant @gerrymadden53711]

Thanks Duncan.

Yes, on second searching it seems one has to delve into the ‘speciality areas’ to find it. That might be good for keeping IMechE’s calendars uncluttered, but for those of us with wide-ranging interests we could easily miss something useful.

Gerry

[duncan webster 1Participant @duncanwebster1]

I just found the list of webinars and scrolled down, easy enough

[Peter Cook 6Participant @petercook6]

Should be fun! Questions about clock and watch oil tend to generate strong (religious) opinions on the  NAWCC forum.

[Richard SimpsonParticipant @richardsimpson88330]

That takes me back.  We did Tribology at college for my Second Class Certificate in 1983 and my First Class Certificate in 1987, both at Liverpool University.  The lecturer was an ex mechanical designer who used to work at Ford Halewood.  I remember he started off both courses with exactly the same question, “What does ‘popping’ your fingers by pulling them have in common with erosion of marine propellers?”

I’m sure you will all be impressed with the fact that I worked out the one word answer, although I can’t claim much for the 1987 course as I simply remembered it from 1983!

[Richard Simpson]

On Richard Simpson Said:

…  “What does ‘popping’ your fingers by pulling them have in common with erosion of marine propellers?”

I’m sure you will all be impressed with the fact that I worked out the one word answer,…

Cavitation?  Hope there’s a prize!

Much we were taught in our yoof is wrong, and in this example Richard was misled on two occasions.   Unlike propellers, finger joints don’t cavitate!  Widely believed in the past, not confirmed by post-mortem examination.

Dave

[SillyOldDuffer]

On SillyOldDuffer Said:

On Richard Simpson Said:

…  “What does ‘popping’ your fingers by pulling them have in common with erosion of marine propellers?”

I’m sure you will all be impressed with the fact that I worked out the one word answer,…

Cavitation?  Hope there’s a prize!

Much we were taught in our yoof is wrong, and in this example Richard was misled on two occasions.   Unlike propellers, finger joints don’t cavitate!  Widely believed in the past, not confirmed by post-mortem examination.

Dave

My osteopath told me that it’s crepitation of the synovial fluid in finger joints.  I can’t answer for propellors.

George

[Richard SimpsonParticipant @richardsimpson88330]

Just put:

” Is finger popping cavitation?”

into Google and read some of the results, many from well established medical sources, and all appear to confirm that the popping of fingers is indeed cavitation of dissolved gasses such as nitrogen and carbon dioxide in the synovial fluid in the joint.

Maybe I wasn’t misled on this occasion.

[Richard Simpson]

On Richard Simpson Said:

Just put:

” Is finger popping cavitation?”

into Google and read some of the results, many from well established medical sources, and all appear to confirm that the popping of fingers is indeed cavitation of dissolved gasses such as nitrogen and carbon dioxide in the synovial fluid in the joint.

Maybe I wasn’t misled on this occasion.

Depends how you define ‘cavitation’.

The vacuum created by rotating propellers damages them by creating cavities.  Metal is ripped from the blades causing holes that reduce efficiency.  And the holes cause progressively more damage by increasing the vacuum.   The force comes from the engines, and it becomes significant.

On a small powerboat no-one cares much, but cavitation reduces warship speed and range, and makes them easy to detect and kill.  Also important to cargo carriers: as I’m sure you know, these operate on tiny margins.  Not keeping the hull and propeller clean, shiny and dent free makes the ship unprofitable.

Finger joints don’t cavitate in that sense.  The force that creates the pop is low and infrequent, and, though it might damage cells, there are no cavities.  Whilst finger popping is a useful training analogy, it’s not correct engineering.  Never take analogies too literally.

Dave

[Richard SimpsonParticipant @richardsimpson88330]

I’m sorry Dave, there is only one correct definition of cavitation, it is not open to interpretation.  Cavitation is not the damage caused by the rapidly created and collapsing bubbles of gas in a rapidly pressure reduced fluid.  That is called cavitation erosion.  Cavitation is only the process of the gas bubbles forming and collapsing quickly.  This process can occur on the trailing face of a propeller blade and, frequently inside the casing and impeller of, in particular centrifugal sea water pumps, and may or may not lead to cavitation erosion.  Cavitation can also lead to loss of propeller performance without necessarily damaging the propeller.  There also seems to be generally a blurring of two quite separate issues, that have both seem to be described as cavitation.  The second one being when a propeller is turned so quickly that the cavitation that exists to a greater or lesser degree in most marine propellers on the negative pressure face becomes so excessive that the cavitation occurring on the rear face of one blade starts to affect the positive face of the next blade.  When this happens the positive face also becomes a negative pressure area and the slip jumps to 100%.  Basically the propeller spins in its own created volume of negative pressure and produces zero thrust.

Cavitation is also what is occurring withing the synovial fluid in a finger joint when you stretch the joint, creating the low pressure liquid and hence the sudden creation of the gas bubbles, which then collapse quickly.  Again this does not necessarily lead to cavitation erosion in the joint but it is cavitation that is creating the pop.  As far as I am aware cavitation is strictly only the creation and sudden collapse of the gas bubbles within a fluid as the pressure is very quickly reduced.

[duncan webster 1Participant @duncanwebster1]

Here’s something from BHI on oils

https://bhi.co.uk/wp-content/uploads/2023/08/08-HJAugust23-AOTM.pdf

[Richard Simpson]

On Richard Simpson Said:

I’m sorry Dave, there is only one correct definition of cavitation, it is not open to interpretation. …

And Richard is straight off the rails.  No point in debating the subject unless we both accept the same definition(s), and Richard doesn’t.

Not unusual in English for the same word to have multiple definitions, even in engineering.  I’ve learned to live with it.

🙂

Dave

 

 

 

 

[cedric 1Participant @cedric]

Knuckle cracking is caused by cavitation according to every source Google throws up, from Wikipedia through to Harvard School of Medicine. I wouldn’t like to argue the point on anything medical with the good doctors at Harvard.
<p style=”text-align: left;”>Personally, the only cavitation I have dealt with was in industrial centrifugal pumps that have been overworked, usually pumping hot water etc. Never did it refer to the physical damage, known as erosion, but to the horrible loud rattle noise of all those bubbles of vapour forming and collapsing. And that included all the training manuals, college text books and manufacturers data sheets etc.</p>
Scary stuff when you are relying on that cavitating pump to keep up the water level in a steam boiler bigger than your house. At that point you don’t give a toss what some armchair expert wants to call it!

[Richard SimpsonParticipant @richardsimpson88330]

Frequently multiple definitions and confusion are created over time by those who refuse to accept that they may occasionally be wrong.

Dave, you are wrong, I have explained why, you refuse to accept it, hiding behind perceived multiple definitions doesn’t change anything, I have moved on.

[gerry maddenParticipant @gerrymadden53711]

It’s not unknown for non-engineering/physical organisations to sometimes adopt and disseminate an erroneous analogy for a phenomenon they are familiar with.

I’m just wondering if anyone here would describe the ‘click’ made by pressing or pulling off a rubber sucker onto or off a bathroom tile as ‘cavitation’ ?

 

[Michael GilliganParticipant @michaelgilligan61133]

For what little it is worth … My human biology lecturer 1968-1971 described the knuckle-cracking phenomenon thusly:

Some individuals have a tendency to develop bubbles within the synovial fluid, which are perceived as an uncomfortable pressurisation of the joint. The action of cracking the knuckle bursts these large bubbles back into solution, and relieves the discomfort.

 

Frankly, I don’t expect this [or rubber suckers] to feature in the Tribology Zoom on 19-Nov …

MichaelG.

[cedric 1Participant @cedric]

I’m just wondering if anyone here would describe the ‘click’ made by pressing or pulling off a rubber sucker onto or off a bathroom tile as ‘cavitation’ ?

 

I shouldn’t think so. Cavitation is bubbles of vapour forming and collapsing in a liquid as pressure changes. No liquid or change of state involved with your rubber sucker. It’s perhaps more akin to flatulence, involving only a gas and a flexible membrane.

 

[Charles LamontParticipant @charleslamont71117]

No, SoD, it is you that has the wrong end of the stick. Cavitation is not the damage caused. It is the formation of bubbles of vapour (cavities) in a low pressure region. As the cavity moves to a region of higher pressure the bubbles implode suddenly and violently (cavitation collapse). If this happens adjacent to a solid surface it causes ‘cavitation erosion’ of the surface.

Another common place that suffers is the delivery cone throat in boiler feed injectors.

[bernard towersParticipant @bernardtowers37738]

The tops of wet liners in diesel engines suffered with this when I was on the shop floor.

[Howard LewisParticipant @howardlewis46836]

To add some drift to this topic, waterside erosion of wet cylinder liners can be reduced by changing the location of the gudgeon pin, slightly, within the piston, to reduce piston slap. This is a combination of gas pressures and mechanical impact shaking ferrite out of the liner material.

(Liners were often made by centrifugal casting of old rail chairs).

Not really cavitation erosion as such.

The excess fuel (Shuttle pump) version of the CAV DPA never made it into production because of the cavitation erosion of the hydraulic head. This produced a “shadow” impression of the port alongside it, leading to leakage (Which at 600 bar can be very significant – enough to prevent cold starting)

A huge problem, because the material was already double nitrided, so VERY hard.

The fuel cavitated and the bursting bubbles caused the erosion.

Howard

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