While rubber or elastomeric compounds are the most typical materials for o ring manufacturers, specific hardware designs and operating circumstances call for the usage of PTFE instead.
PTFE is superior than elastomers in several ways. These benefits include, among others, a nearly limitless shelf life, good electrical characteristics, and corrosion resistance across a wide temperature range.
But before switching to a PTFE O-Ring, there are a few things to keep in mind.
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Out of our whole selection of PTFE blends, Eclipse provides completely customizable PTFE O-Ring sizes that may improve the performance and durability of your seals. For the finest sealing performance, however, an Eclipse Spring Energized seal may be the best option in specific circumstances.
Here's how to decide whether seal is ideal for your application: a PTFE O-Ring or a Spring Energized seal.
The Benefits Of PTFE O-Rings
When defining an O-Ring material, one of the first things to be evaluated is often chemical compatibility.
The ideal material to use may be PTFE in situations where caustic or corrosive chemicals, or normal rubber compounds, are incompatible.
One of the most corrosion-resistant materials accessible across all sectors is PTFE since it is resistant to practically all industrial solvents. Additionally, PTFE could work if a chemical assault threatens the integrity of rubber composites.
Extended Shelf Life
The usage of PTFE may also be beneficial for applications needing long lifespans or prolonged service intervals in harsh conditions.
While certain elastomers may survive for a brief period of time or under intermittent exposure, long-term deterioration might lead to issues, while PTFE's resistant qualities would continue permanently.
Wide Range Of Temperature Tolerance
The temperature range that PTFE can withstand, from -325°F to +500°F, is also far wider than that of the majority of elastomers.
Again, PTFE is the optimum material for applications involving cryogenics or high temperatures, such as those found in ovens or combustion processes, which may rule out the use of any elastomer compound.
Most rubber compositions will harden to the point that any elastomeric qualities are no longer present at very low temperatures. This, together with material contraction, may cause it to lose its ability to operate as a seal.
On the other hand, even at cryogenic temperatures, PTFE maintains its flexural and pliability qualities.
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Advantages of PTFE O-Rings
PTFE also provides certain extra benefits over rubber-based compounds:
- PTFE has an unlimited shelf life since it does not deteriorate with time and is not affected by UV radiation. It also does not expand when exposed to moisture and is not vulnerable to explosive decompression.
- Virgin PTFE meets FDA requirements.
- PTFE offers superior electrical characteristics, including electrical resistance and dielectric strength.
The Problems With PTFE O-Rings
There are several drawbacks to the material that could have an impact on your project, even though chemical assault or high temperatures can leave you with no other option.
A typical Nitrile O-Ring has a hardness of 70 Shore A, which is on a softer scale than virgin PTFE, which has a hardness of 55 Shore D.
Higher hardness has a negative impact on salability since it makes it more difficult for the material to conform to mating hardware surfaces.
Rate Of Leakage
While PTFE may need post-process surface quality modifications to minimize leakage to acceptable levels, rubber O-Rings may conform to "as machined" surfaces.
A PTFE O-Ring will typically have a greater leakage rate than any other elastomeric material under normal operating circumstances.
Applications that don't call for very high temperatures or harsh chemical conditions shouldn't utilize PTFE O-Rings.
Because PTFE is an inelastic substance by nature, it cannot be reused or installed more than once.
Contrary to rubber composites, once bent during installation and usage, PTFE will not revert to its original shape and cross-section. PTFE O-Rings are therefore normally only advised for flange configurations or static face seals that are not continuously engaged and disengaged.
A PTFE O-Ring, for instance, would not be suggested for a chamber door seal that must be opened and closed regularly since the O-Ring would probably need to be changed after each usage.
A rubber O-Ring with severe compression set may resemble a reused PTFE O-Ring in appearance and functionality. Contrary to rubber, this compression set only happens after one usage.
In flange gasket applications, where the seal will stay static and undisturbed until the next service period, PTFE O-Rings are more often seen.
When to Use an Energized Eclipse Spring Seal
The advantages of a spring-energized seal should also be taken into account when determining whether to employ a PTFE O-Ring in your application.
All the advantages of employing PTFE as a sealing material will still apply to spring-energized seals, but they won't be affected by the drawbacks of PTFE on its own.
The PTFE can be kept energized at all times if a seal jacket has a metallic spring.
With the spring of a spring-energized seal, which guarantees the sealing surfaces' excellent contact in all circumstances, PTFE's rigidity and cold flow tendencies are no longer a concern. This makes it feasible to use a spring-energized seal at high cycle rates and for many installations.
In comparison to an O-Ring made of PTFE, spring activated seals provide better salability and friction performance.
A spring-energized seal can be a superior option in situations where PTFE O-Rings need to be changed often.
PTFE O-Ring Sizes and Materials Made to Order from Eclipse
PTFE O-Rings are widely used in the seal industry and are often available off-the-shelf. However, options are often limited to Virgin PTFE due to the material's conformance to AS568B standards and its sizes.
Custom O-Ring cross-sections and diameters may be produced on demand, free of tooling costs, thanks to Eclipse's in-house machining skills and knowledge.
Customers that are upgrading outdated gear or buying equipment from abroad that may not employ common O-Ring sizes often contact Eclipse.
The right size for an O-Ring is particularly important when using PTFE since it won't stretch or adapt as readily as a rubber compound would.
It is often easy to stretch the smaller size elastomer O-Ring into a groove when a normal dash size falls between two diameters. With a PTFE O-Ring, however, this may not be feasible, hence in this case a custom machined size may be required.
Custom size cross-sections are another feature of made-to-order machining that may be used to modify the O-compression Ring's or squeezing.
Depending On The Pressure, High Or Low
A thicker than usual cross-section may enhance sealing effectiveness in high-pressure conditions when high clamping force may be generated by increasing the squeezing and, therefore, the contact area and force.
On the other hand, a smaller than usual O-Ring cross-section might assist fulfil application requirements or enable appropriate assembly of the hardware in an application where clamping stresses are minimal or friction is an issue.
Several Different PTFE Mixes
Customers may choose O-Ring materials from Eclipse's complete selection of PTFE mixes and Polymer seal materials when they use bespoke machining from the company.
The mechanical characteristics, stability, and wear resistance of virgin PTFE may all be significantly enhanced by the use of fillers. Mechanical characteristics and wear life may be considerably improved by adding glass fibres or graphite fillers.
A filled PTFE may significantly improve performance and increase seal durability in situations where high pressure extrusion is a problem.
In dynamic applications, other fillers, such the solid lubricant molybdenum disulfide, may significantly decrease friction.
The presence of an internal lubricant will lower the temperatures at the contact surface, improving durability and extending seal life.
If the application calls for one of Eclipse's non-PTFE based polymers, such as UHMW and Thermoplastic Elastomer, such materials are also easily accessible.