PTFE (Teflon) bearings

[21121956]

Hello everybody:

Ever since the 1970's, the use of PTFE faced pads in large vertical axis hydro-generators was pioneered in Russia and China, prompted by a series of failures of conventional Babbitt-faced bearings.

At present, I have heard very little about the application of this material, Teflon, mainly in thrust bearing pads in hydro generators.

I would like to know the development or state of the art today on the use of Teflon or, was it not possible to win the race against the Babbitt?

Thanks in advance for your opinions.

El que no puede andar, se sienta.

 

[dik]

I have some samples of early ones used, and I think repair/replacement, they still are. It's hardwood called lignum vitae. They used to use it on the rudder bearings of 'tall ships' in the good old days... I sanded down my first little sample, about a 1" cube using my belt sander and 80 grit. By the time it was smoothed, there was no grit left and the sample was smooth. It's really a hard and heavy wood product, and used to be an 'endangered species' I understand. I don't know what the current status of it is.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

Lignum vitae was never used as a thrust bearing, radial only. Rubber is the most common replacement today.

I don't kow why anybody would want to run anything but a hydrodynamic bearing in such an application. Hydrodynamic bearings are not subject to fatigue failure and don't experience wear of the surfaces under good operating conditions. There would be no benefit to using PTFE in a hydrodynamic bearing.

 

[dik]

They could be, but at the site I was at, I'm pretty sure they were use in bearing also. Pie shaped segments that were at the bottom of the spindle.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

Maybe they do exist in smaller flavors.

https://lignumvitaesolutions.com/products/hydro-bearings/thrust-bearings/

 

[Windward]

Sorry I can't help the OP, but I want to respond to some comments.

For a long time, lignum vitae was the only material we had for shaft bearings in ships. It might have been used for rudder bearings also.

These bearings were on the part of the shaft that met the water, where it penetrated the hull. If the ship had a strut on the outside of the hull to stabilize the shaft , the strut bearings were also lignum vitae. Inside the ship, in the engine room, oil-lubricated spring bearings did the job.

The lignum vitae was lubricated by the water. For the hull penetration, the engine room watch made sure to allow a little water to leak into the engine room through the stuffing box, to keep the lignum vitae lubricated.

Lignum vitae is an excellent bearing material, but probably too hard to get now. Nitrile rubber has taken over the job in smaller vessels. These are called cutless bearings, but I don't know the reason for that name. They are also lubricated by the water. I suppose they are not as slippery as lignum vitae.

I have worked on ships that had oil-lubricated bearings for the hull penetration. They eliminate the need for a little lubricating water to leak into the bilge, and there is no stuffing box to maintain. I suppose they also reduce friction to a minimum.

Tall ships, having no engine or propeller shaft, were in no need of lignum vitae for that purpose. They might have used it elsewhere, say in deck machinery.

 

[Gr8blu]

One of the benefits to a PTFE (Teflon) pad facing compared to a traditional babbitt surface is that the PTFE material can be considered "sacrificial" and much easier to replace. The intent was to still have a slippery surface in the event of a lubrication failure: the babbitt provided this also, at least for a short period. However, the whole bearing assembly would need to be removed to re-babbitt the surface. The PTFE "pads" could be just glued or bolted on without all the added hassle.

The other reason to use PTFE material was to try and keep the rotor from grounding out (e.g., insulated bearing approach) and damaging the radial bearings. Didn't always work as intended, but was better than a metal-on-metal contact.

Converting energy to motion for more than half a century

 

[21121956]

Hello everybody:

I am very grateful for the comments from all of you.

El que no puede andar, se sienta.

 

[Windward]

Just found another use for lignum vitae. Clocks. The wood is both hard and oily, so it is a fine material for clockworks. No need to lubricate it. Most lubricants start to gum up as they age, which slows the clock down.

In the early 1700's, John Harrison used lignum vitae to make clocks that were accurate to one second a month. Then, using what he learned about clocks, he solved the navigation problem. You can get the whole story at

https://www.youtube.com/watch?v=T-g27KS0yiY

"The Clock That Changed the World (BBC History of the World)"

 

[dik]

Thanks Windward... I was told that it was used for the rudder bearing... don't know when I encountered it the first time, I didn't know it was used for bearings... I have half a dozen small pieces and it's harder than a ... cannot even shave it with my pocket knife... blade just slides.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[zeusfaber]

@Windward: "Cutlass" is simply a brand name.

The large-ship equivalent is fibre-reinforced thermoset materials like Orkot. Generally run water-lubricated like lignum vitae does, but also contain a bit of laminated-in dry lubricant (as an analogue to the natural oils in the lignum vitae) so they've got some dry-running capability too.

A.

 

[Pud]

Lignum Vitae (aka "Ironwood") was used not so long ago to make formers for producing holloware such as teapots, kettles etc. by spinning. The cores were assembled from parts interlocking like a Chinese Puzzle kid's toy and released by pulling put one locking piece.

As told to me by my long dead father in law who worked at such a company in Birmingham (UK) as an electrician.

And PTFE suffers from creep. Badly. Was the once upon a time wonder material for hip and knee joints. I think PEEK is used now.


Politicians like to panic, they need activity. It is their substitute for achievement.

 

[Windward]

Zeusfaber, thanks for mentioning Orkot. I didn't know about it, might have a use for it.

I found a good article on how the cutless bearing got its name: "...The rubber bearing had, in fact, 'cut less' into the shaft surface than the hardwood bearings..."

https://www.seattleyachts.com/news/...hydrodynamic standard rubber sleeve bearing.”

Wikipedia has a good article on lignum vitae: "...The aft main shaft strut bearings for USS Nautilus (SSN-571), the world's first nuclear-powered submarine, were composed of this wood..."