PTFE OR POLYTETRAFLUOROETHYLENE O-RINGS
PTFE or PolyTetraFluoroEthylene is a form of a synthetic fluoropolymer derived from tetrafluoroethylene. PTFE has some extremely distinct characteristic which makes it a very popular choice in industrial applications. One such application is for the manufacture of O-rings.
O-rings are a mechanical gasket in the shape of torus. It is a loop of elastomer with a round cross section, designed to be seated in a groove and compressed during assembly between two or more parts creating a seal at the interphase. PTFE is an excellent elastomer for the job because it provides one of the most versatile chemical compatibility as they are made with inert material.
The PTFE o-rings are white in color and the material is extremely chemically inert, tough and abrasive resistant.
TYPES AND SIZES OF PTFE BUSHES
The PTFE or Teflon bushes are primarily produced in six varied types with multiple dimensions in each type. These types are:
Shore Hardness (Shore, D)
Tensile Strength (MPa)
Elongation at Break (%)
|Specific Gravity (g/cm3)
|Coefficient of Friction
0 – 0.01%
|Operating Temperature Range (°C)
|-150 to +250
|Melting Point (°C)
CHEMICAL RESISTANCE PROPERTIES
The chemical properties of PTFE are:
• It shows excellent resistance towards almost all the chemicals.
• It has a near infinite shelf/storage life as it does not exhibit any signs of aging.
• Due to excellent chemical inertness it can be used in food, chemical and medical industries.
• It has low elasticity memory hence, making it unsuitable for dynamic applications unless it is treated and energized by suitable materials such as I.E. Rubber.
• It has a low coefficient of friction.
ADVANTAGES OF PTFE O-RINGS
The main advantages of PTFE are:
• The PTFE O-rings are compatible with most universal chemical compounds
• PTFE O-rings are the best possible solution for low pressure systems
• It can operate under wide range of temperature from -320 °F to +500 °F
• It is appropriate as a back-up ring for vacuum to high pressure sealing
• The PTFE O-ring comes in multiple sizing. However, special ring sizes could be designed on demand from the customer.
PTFE IS RECOMMENDED FOR…
The advantages of PTFE make it a suitable choice under the following environments:
• Chemical environments
• Use in the acidic or basic environment
• Sealing for moving or sliding surfaces
PTFE IS NOT RECOMMENDED FOR….
• However, the PTFE O-rings are not recommended under certain conditions such as:
• Low compression vacuum sealing
• High vacuum seals
• Exposure to high temperature steam.
The temperature range suitable for PTFE O-rings is:
• Up to 260 °C (intermittent)
• Down to -150 °C
INSTALLATION TIPS FOR PTFE O-RINGS
• During installation ensure that the O-ring is not nicked or gouged during assembly as it might cause breaks in the seal.
• During installation do not exceed the stretch of the o-ring and maintain it to a maximum of 10%.
• PTFE, like most of the thermoplastics, has a tendency to creep.
• The PTFE experiences a cold flow.
• The cold flow can be reduced by the use of special PTFE compounds that can be used to fill the empty space.
• It has an extremely long seal life.