To improve hardness, thermal conductivity and wear resistance of PTFE, and reduce load deformation and thermal expansion, various fillers capable of withstanding the PTFE processing temperature (360°С) are used.

PTFE-based filled compounds are mainly used as antifriction materials for fabrication of parts of bearings; piston rings used in air compressors; gaskets and seals for heavy-duty applications; valve seats and membranes; sealing rings and other items used in engineering, chemical and other industries.

The use of fillers generally improves PTFE characteristics such as tensile strength, elongation at break, impact resistance, modulus of elasticity (especially glass fiber with molybdenum disulfide and bronze) and compression strength.

Wear resistance of filled compounds is greatly dependent on the type of filler used, e.g. bronze increases wear resistance by 450 times, nickel by 260 times, and copper by 22 times, while aluminium powder decreases wear resistance.

The best wear resistance parameters are achieved in PTFE compounds filled with coke, artificial graphite, molybdenum disulfide, boron nitride and bronze. Selection and quantity of the above fillers depend on the intended use of a finished item.

Most common are coke-filled and power bronze-filled compounds with improved thermal conductivity and mechanical properties of PTFE. 15-25%-filled PTFE-based compounds have 1.5-1.8 times better hardness, while a higher filler content decreases compounds' hardness.
PTFE-based compounds can be used as a material for making bearings, rings, gaskets, parts, valves and other items in industries where high thermal and chemical resistance plays a key role.

We currently use the following inorganic fillers:

• crushed glass fiber;
• ground coke;
• graphite;
• disulfuric molybdenum;
• boron nitride or cobalt blue;
• anhydrous alumina (Аl);
• copper, bronze, nickel, etc. powders

Our company fabricates various filled PTFE-based blanks for antifriction applications such as:

• F4К20 (TU 6-05-1413-76, 20% coke);
• F4К15М5 (TU 6-05-1413-76, 15% coke and 5% molybdenum disulfide);
• F4С15 (TU 6-05-1413-76, 15% glass fiber);
• F4С15М5 (TU 6-05-1413-76, 15% glass fiber and 5% molybdenum disulfide);
• F4К15UV5 (TU 6-05-041-781-84, 15% coke and 5% carbon fiber);
• F4КС2 (TU 6-05-041-913, 2% cobalt blue);
• F4М5 (TU 301-05-109-91, 5% molybdenum disulfide).

As compared to PTFE,F4К20 has 600 times greater wear resistance and 30% higher stress at 10% compression within the temperature range of -60 to +250оС. F4К20 is the best all-purpose compound. Recommended applications include fabrication of seals for moving joints (e.g. piston rings) and antifriction items. F4К20 piston rings for air compressors enable lubricant-free operation of cylinders which eliminates polluting of industrial gases with oil. The use of the F4К20 compound for fabrication of cups is limited due to its relatively low elasticity. The F4К20 compound can be used in fine vacuum environments in media such as hydrocarbon gases, dry air, liquid hydrocarbon and solvents. Graphite and carbon-filled compounds have good abrasive resistance. These compounds are suitable for use in dry-friction bearings operated under low temperatures.

The F4С15 is easily processable and resistant to any aggressive media, and has good performance in aggressive dry-gas media. Addition of crushed glass to PTFE significantly reduces its flowability (creep). As compared to F4К20, glass-filled PTFE has better elasticity. This compound is used for fabrication of various bearings and other items for applications where chemical resistance is critical. Another remarkable feature of this material can be utilised: good static properties of the compound make it suitable for use as a conductor (electrode) for storing charge of the material (liquid) flowing through the conductor.

Addition of 5% molybdenum disulfide to the F4К20 and F4С15 compounds increases their wear resistance by 1.6 times and decreases the coefficient of friction by 1.2 times. These compounds (F4С15М5 and F4К15М5) are recommended for use in humid gas environments, including those condensate-containing media.

The low-filled F4КС2 and F4С5 compounds differ very little from unfilled PTFE in terms of their mechanical and chemical properties. Addition of alloy fillers such as cobalt blue and molybdenum disulfide significantly increase wear resistance. The F4КС2 and F4М5 compounds are suitable for fabrication of moving antifriction parts operated under low loads in conjunction with resins, aluminium alloys and bronze. These materials have a high elasticity and improved break-in and electric properties. These characteristics coupled with high chemical resistance make this material suitable for a wide range of applications in chemical industry.

The F4АО10 material contains fine alumina powder which makes this compound resistant to an electric arc induced by a corona discharge. Parts made of this PTFE-based compound are used as insulators in switching devices.