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Today we’re going to talk about PTFE rotary seals.
PTFE is more commonly known in the industry as Teflon, but today we’re going to refer to it as PTFE because Teflon is the DuPont trade name. Reasons we would choose to use PTFE over your normal rubber elastomer style seal would be that we’ve exceeded the capabilities. Whether it be speed, pressure, temperature, and maybe the chemicals that it meets. PTFE is a very low friction material – so it’s able to operate at very high speeds.
It’s got a very broad temperature range. Virgin PTFE can handle ranges from -425 Fahrenheit up to 450 Fahrenheit and we can even shift that range a little higher depending on the fillers that we add to it. So, it can handle a wide range of temperatures and basically any fluid or chemical that you throw at it.
For this one, we’ve got very lightly loaded and very flexible lips that are machined. They’re very lightly engaged, so we need a shaft that runs very true – no runout because PTFE is not a very resilient material. It needs some form of energizer in order to make sure that it remains in contact with the shaft.
So with this profile here, we’re going to be limited to about 50 psi, but we can run up to about 5,000 surface feet per minute for speeds. We have an excluder and then the main lip to retain the fluid.
We can change that a little bit – we could do away with that lip and possibly add a redundant lip for fluid retention.
If we had additional pressure, we could reinforce this a little bit with a metal band – increasing the rigidity of it. We could increase the pressure rating of up to 150 psi.
If we did have a little bit of runout that we needed to handle we could modify this lip a little bit and include what we call an “elf toe”. And then we could add a small spring to help the lip maintain contact with the shaft. But still, the runout must be minimal. We’re talking about maybe 20 thousandths depending on the speed.
If we shift gears and go over to this other style, we’re looking at high pressure but relatively low speed.
The pressure rating on this profile would be about 3,000 PSI and your surface speed is going to be limited to about 1,000 surface feet per minute.
We’ve got quite a few different options as far as lip styles:
Several different spring options:
– Another option would be a canted coil if we wanted to reduce the lip loading a little bit.
And we’ve got several different options for the bore:
So, we’ve got a wide range of possibilities with PTFE and we can tailor the fillers depending on the application conditions and the performance criteria needed. There’s a wide range of additives that we can put in the PTFE to tailor to the needs.
Wide range of applications that these seals can be used in:
Another benefit of PTFE versus a rubber elastomer seal is that there’s no tooling required for these. These get machined out of a sleeve or billet of material. So prototyping and initial samples are very fast and inexpensive.
And that’s it for PTFE seals.