Dave Biering
We are often asked about what can be expected when you use a Rulon bearing or any PTFE in high temperatures. Many things can occur, and it varies from material to material based on the use of different fillers. Let’s review:
PTFE is an odd material in that it is a thermoplastic material, but dressed in thermoset clothes. Once molded, the material can’t be remolded like other thermoplastics, so it acts like a thermoset. The other interesting feature of PTFE is that while it has an operating temperature range of -400 to +550°F, it actual starts to transition at around 78°F. This means that the material is “moving” with thermal changes, which is known as cold flow. The big feature of Rulon materials is that the additives used in the hundreds of different Rulon materials help to stabilize the PTFE components to resist cold flow.
So, what happens when these materials are taken to higher temperatures?
It again depends on the nature of the fillers used. As an example, virgin PTFE has a tensile strength of 4075 psi at room temperature, but at 500°F the tensile drops to just over 1000 psi.
As a comparison, a carbon graphite filled material has a tensile at room temperature of 3300 psi but 990 psi at 500°F. Elongation numbers will also be impacted. Virgin PTFE has an elongation of approximately 330% at room temperature but only 210% at 500°F. The carbon graphite is 240% at room temperature and 180% at 500°F.
Why is this information important?
It’s important in the design of seals, bearings and even structural components used at high temperatures. Add to this the thermal conductivity and thermal expansion of these different materials, and it’s clear how important it is to get the right information at the beginning of your design.
For assistance in making heads or tails of the world of PTFE components contact TriStar Engineering.
