When designing for low temperature sealing, the first step is to define the temperature range that the seal will be operating in.
Typically, cryogenic as seals are those that are operating below -65 Fahrenheit. Gallagher’s partner, Eclipse, chooses this benchmark because they currently have elastomers that have a usable TR10 value at this temperature.
When designing at this level — with high temperatures around 300 Fahrenheit — an understanding of what level of leakage control is required on the low temp end. Seals that operate in aircrafts must function within this range.
However, there may be an allowable leakage rate which allows for reduced drag. When requiring zero leak, the drag in the system is often increased to support some elastomeric contact with a dynamic surface. In the case of static seals, elastomers span this range although increased squeeze may be necessary.
Eclipse Engineering routinely designs in the range indicated above.
While -65 Fahrenheit is extreme cold, it’s not considered cryogenic. Liquid nitrogen at -320° Fahrenheit (-195°Celsius) requires special hardware and seal material consideration.
To begin, many projects and applications don’t utilize lubricant in dynamic applications. To improve sealability, a better-than-average surface finish is required.
Surface finish often holds lubricity. But without this, a smooth finish reduces friction, improves life, lowers drag, and improves sealability.
Static seals are often required to have leak rates approaching zero; meaning hardware considerations and surface can be even more important. This may mean polishing the groove, which in some applications can be very challenging.
Cryogenic Seal Materials
The next criteria are the seal materials. Elastomeric materials lose their flexibility at these extreme temperatures, so Eclipse relies on polymer-type materials to bridge the gap. When we experience temperatures below -180° Fahrenheit ( -195° Celsius), that’s when it becomes wise to move away from basic PTFE to modified fluoropolymers such as PCTFE, known for operating down to -460 Fahrenheit. Continue reading Designing Cryogenic Seals for High and Low Temperature Sealing