To improve individual, especially mechanical properties, fillers (compounds) are added to pure PTFE. Individual components have a specific effect on particular quality characteristics, which depends on the quantity (per cent) of the additional filler. The added filler improves or changes the characteristics of the material according to the properties and the quantity of the filler:
significant enhancement of resilience against wear and tear
reduced deformation under pressure
reduced thermal expansion
some fillers increase the thermal and electrical conductivity
Most commonly used fillers: glass fibre, carbon, bronze or powdered graphite, strengthened mixed with PTFE; other fillers are: molybdenum disulphide, metal powder, ceramic, PEEK, metal oxides and a mixture of two or several additives.
Properties of PTFE with fillers
glass fibre: PTFE is strengthened with glass fibre by 5 to 40% Added glass fibres improve the properties of abrasion resistance, as well as deformation in case of strain. The chemical and electric properties are not changed. Glass has poor alkali and hydrofluoric acid resistance. The friction coefficient is slightly increased and thus graphite is sometimes added to eliminate this effect.
carbon: PTFE has 10 to 35% of added carbon with a small percentage of graphite. Similar to glass fibre, carbon improves the abrasion resistance and strengthens the PTFE, while the chemical resistance remains the same and the electrical properties are changed.
bronze: PTFE has 40 to 60% of added bronze. This filler most effectively improves the abrasion resistance, the resistance against deformations and thermal conductivity, while it affects the electrical properties and chemical resistance.
graphite: 5 to 15% is added. Graphite reduces the friction coefficient and is often added to other fillers. It improves resistance against deformation, strength and partly also wear and tear.
other fillers: molybdenum disulphide reduces the friction coefficient and is sometimes used instead of graphite. Some metal particles (stainless steel, nickel, titanium) are sometimes added as fillers, if we consider their resistance against chemical influences. They are used to improve abrasion resistance, although their resistance to abrasion is lower in comparison with bronze.
Most frequent versions:
TEFLON + 15% GRAPHITE Very good resistance against abrasion and thermal conductivity with satisfactory elasticity. It is used for the bearings and gaskets of rotating axles – oil sealing rings. Volume mass:2.16 +/– 0.04g/cm3
TEFLON + 15% GLASS FIBRE Due to the improved mechanical properties, it is used mostly for parts with high tensile stress. Most often, these are flat gaskets, piston rings, bearings, chemically resistant valve seats, O-rings, cuff seals etc. Volume mass:2.21 +/-0.04g/cm3
TEFLON + 25% CARBON For areas with larger mechanical stress, increased wear, chemical influence and thermal stress. They are most often used for piston rings, guide rings, bearings, cuff seals, valve seats etc. Volume mass:2.09 +/-0.04g/cm3
TEFLON + 60% BRONZE Material with high tensile strength and resistance against wear. Products are usually in the form of bearings, piston rings, machine guide bushes, hydraulic cylinders etc. Volume mass:3.85 +/-0.15g/cm3