The advantages and disadvantages of hydraulic seals polytetrafluoroethylene

Advantages of PTFE hydraulic seals

PTFE hydraulic seals referred to PTFE, perfluorinated polymer from the monomer tetrafluoroethylene by free radical polymerization of ethylene. Around four carbon atoms surrounded by fluorine atoms, a fluorine atom since the covalent radius (0.064nm) is greater than the radius of the hydrogen atom (0.028nm), a fluorine atom can be lined up carbon chains surrounded. Since the fluorine atoms are mutually exclusive, so that the whole chain like macromolecular chain hydrocarbon molecules, as a jagged, but the spiral structure, similar to the human DNA helix.

The helical conformation just surrounded by PTFE susceptible to chemical attack of the carbon chain backbone, the formation of a tight full "fluorinated" layer of protection, the PTFE backbone without any invasion of external agents, the PTFE has unmatched by other materials solvent resistance, chemical stability and low cohesive energy density.

Hydraulic seal is a PTFE has excellent chemical resistance and high temperature resistance of fluorocarbon chemicals, even when exposed to air, it will not go bad, long-term use in the range of -200 ~ 250 ?. Since the molecular structure containing fluorine atoms in an electron withdrawing group influence, PTFE exhibits high chemical stability, resistance to invade almost all acid and other chemicals.

PTFE hydraulic seals outstanding nonstick, abnormal lubricity and excellent electrical insulation properties, resistance to aging and radiation resistance, minimal water absorption and so called "plastic", widely used aerospace, petrochemical, machinery, electronics, electrical appliances, construction, textile and other fields. It is these characteristics, it appeared to be secretly used in military industry until the 1950s was applied to the static seal up.

The disadvantage of PTFE hydraulic seals

Despite the stable performance of PTFE, but its disadvantages are also obvious.

(1) polytetrafluoroethylene having "cold flow." When PTFE is used as a gasket for tight seal and the bolts tight, so that over a certain compression stress, the washer will have a "cold" (creep) and flattened.

(2) a high melt viscosity polytetrafluoroethylene, did not flow at high temperatures.

(3) PTFE has outstanding non-stick, limiting their industrial applications. It is an excellent release material, the surface of this performance and make it extremely difficult to bond to other objects.

Thermal conductivity (4) PTFE low, poor thermal conductivity.

Coefficient of linear expansion (5) PTFE is 10 to 20 times stronger than steel, is larger than most plastics. In the application of PTFE, if not enough attention to this aspect of performance, it is likely to cause damage.

(6) Note that the heating temperature should not exceed 400 ?, otherwise it will produce toxic gases.