Expanded PTFE Tape and Cord are high-performance sealing materials derived from Polytetrafluoroethylene (PTFE). Through a unique expansion process, the base PTFE is stretched, creating a microporous structure that enhances its properties. This results in a material that is highly flexible, compressible, and exceptionally resistant to a wide range of chemicals and extreme temperatures. Unlike solid PTFE, expanded PTFE offers superior sealing capabilities for irregular surfaces and is widely used in industries such as chemical processing, pharmaceuticals, food and beverage, and energy for creating reliable gaskets and thread seals.
Understanding the technical specifications of Expanded PTFE Tape and Cord is crucial for selecting the right product for your application. Below are the detailed parameters presented in both a list and a table for clarity.
| Parameter | Expanded PTFE Tape | Expanded PTFE Cord | Test Method / Notes |
|---|---|---|---|
| Standard Width | 1/4", 1/2", 1", 2", 3" (Custom widths available) | 1/8", 3/16", 1/4", 3/8", 1/2" (Custom diameters available) | - |
| Standard Thickness/Diameter | 1/64", 1/32", 1/16" | Refer to "Standard Width" column for diameters | - |
| Specific Gravity (Density) | 0.4 - 0.7 g/cm³ | 0.5 - 1.0 g/cm³ | ASTM D792 |
| Tensile Strength | 500 - 1500 psi | 1000 - 3000 psi | ASTM D638 |
| Elongation at Break | 50% - 200% | 100% - 400% | ASTM D638 |
| Compression Set (22 hrs @ 25°C) | 5% - 15% | 5% - 15% | ASTM D395, Method B |
| Maximum Service Temperature | 600°F (315°C) | 600°F (315°C) | Short-term exposure up to 650°F (343°C) possible |
| Minimum Service Temperature | -450°F (-268°C) | -450°F (-268°C) | Remains flexible |
| Thermal Conductivity | 0.15 - 0.25 W/m·K | 0.15 - 0.25 W/m·K | ASTM C177 |
The unique properties of Expanded PTFE make it suitable for a vast array of demanding applications. Its primary function is to create a tight, reliable seal in environments where other materials would fail.
What is the main difference between expanded PTFE and standard (skived) PTFE tape?
Standard PTFE tape is typically skived, or shaved, from a solid billet of PTFE, resulting in a solid, non-porous film. Expanded PTFE is created by stretching PTFE, which forms a microporous, fibrillated structure. This makes expanded PTFE much softer, more flexible, and more compressible than skived tape. It can conform to surface imperfections much better, creating a superior seal, especially on flanges. Skived tape is often used as a liner or for non-sealing applications, while expanded PTFE is specifically engineered for high-performance sealing.
Can expanded PTFE cord be used as a replacement for pump packing?
Yes, expanded PTFE cord is an excellent material for pump and valve packing. Its braided or plaited forms provide the necessary resilience and self-lubricating properties to create a durable seal around rotating or reciprocating shafts. It resists the harsh chemicals and high temperatures often encountered in pump applications and is easy to install and adjust.
Is expanded PTFE tape suitable for oxygen service and other strong oxidizers?
Yes, but with a critical caveat. Pure PTFE itself is highly resistant to oxidizers. However, for oxygen service, it is imperative to use a grade of expanded PTFE that is certified clean for oxygen. This means it has been manufactured, handled, and packaged in a controlled environment to be free of contaminants like oils, greases, and particulates that could ignite in a high-pressure oxygen environment. Always verify the manufacturer's certification for oxygen service before use.
How do I select the correct density for my gasket application?
Density is a key indicator of compressibility and recovery. Lower density grades (e.g., 0.4-0.6 g/cm³) are softer and more compressible, making them ideal for sealing uneven or damaged flanges with low bolt torque. Medium density grades (e.g., 0.6-0.8 g/cm³) offer a good balance of conformability and strength for standard flanges. Higher density grades (e.g., 0.8-1.2 g/cm³) are less compressible but offer higher tensile strength and resistance to blow-out, suitable for high-pressure applications. Consult with your supplier for the best grade for your specific pressure, temperature, and flange condition.
Does expanded PTFE have a shelf life? How should it be stored?
Expanded PTFE is an extremely stable polymer and does not technically have a shelf life; it will not degrade or perish over time under proper storage conditions. It should be stored in a cool, dry place away from direct sunlight and sources of heat. Keep it in its original packaging until use to prevent contamination from dust, dirt, or other chemicals. Proper storage ensures the material's performance characteristics remain unchanged for years.
Can I use expanded PTFE tape on tapered pipe threads (NPT)?
Absolutely. Expanded PTFE tape is one of the most common and effective sealants for NPT (National Pipe Tapered) threads. Its flexibility allows it to fill the minor imperfections in the threads, creating a pressure-tight seal. When applying, wrap the tape in the direction of the thread (usually clockwise) for 2-3 wraps, ensuring not to cover the first thread to prevent tape fragments from entering the system.
Is this material FDA approved for direct food contact?
Many grades of virgin, unpigmented expanded PTFE are compliant with FDA regulation 21 CFR 177.1550, which covers fluoropolymer articles intended for repeated use in contact with food. Furthermore, many are also certified to USP Class VI for pharmaceutical applications. It is essential to request and verify the manufacturer's Certificate of Compliance (CoC) for the specific grade you are purchasing to ensure it meets the regulatory requirements for your application.
What are the limitations of expanded PTFE?
While highly versatile, expanded PTFE has a few limitations. It is not recommended for use with molten alkali metals and certain fluorine compounds at high temperatures and pressures, as these can cause degradation. Its mechanical strength, while sufficient for sealing, is lower than that of metals, so it is not a structural material. In thread sealing, if over-tightened, the tape can be sheared. Understanding the specific chemical and physical demands of your application is key to successful implementation.
