Mechanical seals are often categorized according to the material from which they are made. Silicone seals are made of silicone, whereas polytetrafluoroethylene (PTFE) seals are made of PTFE. While some seals are made entirely of PTFE, however, others are made with a combination of PTFE and one or more other materials. Known as filled PTFE seals, they offer some key advantages.
Overview of Filled PTFE Seals
Filled PTFE seals are mechanical seals, such as O-rings and seal jackets, that are made of PTFE with one or more filler materials. Like all mechanical seals, they are used to prevent leaks. Fluid- and gas-carrying passages can leak around mating surfaces. As pressurized fluid or gas travels through a passage, some of it may escape where two or more parts meet. A mechanical seal can prevent leaks by compressing around the mating surface to create an air-tight and fluid-tight seal.
You can find mechanical seals made of different materials. Plain PTFE seals are made of entirely of PTFE. Filled PTFE seals, on the other hand, are made of PTFE that’s been injected with one or more other materials. These injectable or filler materials enhance their properties so that the seals perform better.
Filler materials can improve the following characteristics of seals:
- Heat resistance
- Chemical resistance
- Durability
- Coefficient of friction
- Wear deformation
- Flexibility
Types of PTFE Seals
There are several types of filled PTFE seals, each of which features a different composition. One of the most common types is Molybdenum Disulphide. Also known simply as moly-filled, Molybdenum Disulphide-filled PTFE seals offer excellent extrusion resistance and heat tolerance as well as lower wear-and-tear than plain PTFE seals. They typically consist of about 5% Molybdenum Disulphide.
Another common type of filled PTFE seal is graphite. Graphite-filled PTFE seals are able to handle high temperatures — typically up to 500 degrees Fahrenheit. They can also handle moderate pressure. Graphite, though, is quite heavy, and it can become porous when exposed to high-pressure gas. Graphite-filled PTFE seals typically consist of about 15% graphite.
There are also PTFE seals filled with Molybdenum Disulphide and glass. They are designed for sealing applications involving very high pressure. The combination of Molybdenum Disulphide and glass allows them to withstand very high pressures of up to 40,000 pounds per square inch (PSI).
In Conclusion
Filled PTFE seals are exactly what they sound like: mechanical seals that have been injected or filled with one or more other materials. These additional materials enhance their properties. When compared to plain PTFE seals, filled PTFE seals often have better resistance to heat, wear and tear and deformation. Many filled PTFE seals can often handle high pressures.