Selection Guide – PTFE & Filled Grades

Key factors influencing PTFE selection

Operating conditions:
-Consider the temperature, pressure, speed, load, and media the PTFE product will encounter.
-PTFE offers a wide operating temperature range, typically from -200°C to +260°C (-328°F to +500°F). However, specific grades may have different temperature limitations, especially when subjected to high pressure or dynamic loading.

Desired properties:
-Identify the crucial properties needed for your application. These could include:

Chemical resistance:
-PTFE is highly resistant to most chemicals, but some fillers may affect compatibility with specific media.

Mechanical strength:
-Virgin PTFE is relatively soft and prone to cold flow (creep). Fillers such as glass fiber, carbon, or bronze can enhance its mechanical strength, hardness, and wear resistance.

Wear resistance:
-Filled PTFE grades are often preferred in dynamic sealing or bearing applications where improved wear resistance is crucial.

Frictional properties:
-PTFE's exceptionally low coefficient of friction is a key advantage for non-stick applications or where reduced friction is desired.

Electrical properties:
-PTFE boasts excellent electrical insulation properties, including high dielectric strength and a low dielectric constant.

Dimensional stability:
-The choice of PTFE grade and manufacturing process can significantly impact dimensional stability, particularly under varying temperatures and loads.

Biocompatibility:
-Virgin and ePTFE are non-toxic and biocompatible, making them suitable for use in food, pharmaceutical, and medical applications.

Common PTFE grades and their applications

Virgin PTFE:
-Offers excellent chemical resistance, outstanding electrical properties, and good flexibility.
-It is suitable for general applications, including gaskets and bellows, especially in food and medical contact situations.

Chemically Modified PTFE:
-Provides less creep, improved permeation resistance, smoother surfaces, and better high voltage insulation compared to virgin PTFE.
-It is suitable for pumps, diaphragms, ball valve seats, and vessel linings.

Glass Filled PTFE:
-Increases compressive strength, enhances wear resistance under load, and reduces permanent deformation.
-Applications include ball valve components and Bridge Bearing Pads.

Carbon/Coke Filled PTFE:
-Offers high compressive strength, improved wear resistance, and better thermal/electrical conductivity.
-It is ideal for rider and piston rings of air compressors.

Graphite Filled PTFE:
-Provides high compressive strength, improved wear resistance and frictional properties, and good chemical resistance.
-It is commonly used for shaft bearings and in high-speed chemical pumps.

Bronze Filled PTFE:
-Exhibits excellent wear resistance, high compressive strength, very low cold flow, and good thermal/electrical conductivity.
-It finds applications in wear strips, machine tool liners, and hydraulic seals.

Expanded PTFE (ePTFE):
-Possesses a unique microstructure that provides multi-directional strength, high porosity, and exceptional conformability, making it ideal for sealing irregular or fragile flanges, even with low bolt loads.
-It is also highly creep and cold flow resistant and retains the universal chemical resistance of virgin PTFE.

Manufacturing processes and considerations

-PTFE is processed using methods like compression molding, ram extrusion, isostatic molding, skiving, and machining due to its high melt viscosity.
-The chosen manufacturing method impacts the final product's properties, dimensional accuracy, and suitability for specific applications. For example, compression molding allows for a wide range of shapes, while ram extrusion is well-suited for producing long lengths of rods and tubes.