What are the commonly used non-metallic materials for valves?
Nitrile rubber Buna-N
The rated temperature range of the nitrile rubber seat is -18 ℃ ~ 100 ℃. Also commonly called NBR, NITRILE, or HYCAR. It is an excellent general purpose rubber material for water, gas, oil and grease, gasoline (except gasoline with additives), alcohol and glycol, liquefied petroleum gas, propane and butane, fuel oil and many other media . It also has good wear resistance and deformation resistance.
Food grade (FG) nitrile rubber valve seat rated temperature range is -18 ℃ ~ 82 ℃. Its composition complies with CFR Part 21 Section 177.2600. Its use range is the same as that of conventional nitrile rubber but requires FDA (US Food and Drug Administration) certification.
Ethylene propylene rubber EPDM
The rated temperature range of the ethylene-propylene rubber valve seat is -28 ℃ ~ 120 ℃. EPDM is the abbreviation of its composition, that is, a terpolymer of ethylene, propylene and diene, usually also called EPT, Nordell, EPR. Excellent ozone resistance and weather resistance, good electrical insulation performance, good resistance to polar capacitors and inorganic media. Therefore, it can be widely used in HVAC industry, water, phosphate, alcohol, ethylene glycol, etc. Ethylene-propylene rubber seats are not recommended for use with hydrocarbon organic solvents and oils, chlorinated hydrocarbons, turpentine, or other petroleum-based greases.
The rated temperature range of food grade ethylene propylene rubber valve seat is -28 ℃ ~ 120 ℃. Its composition complies with CFR Part 21 Section 177.2600. Its use range is the same as that of conventional nitrile rubber but requires FDA (US Food and Drug Administration) certification.
PTFE
The rated temperature range of the PTFE valve seat is -32℃~200℃. Excellent high temperature resistance and chemical resistance. Because PTFE has high density and excellent permeability, it can also prevent the corrosion of most chemical media.
Conductive PTFE is an improved PTFE product that allows electrical current to pass through the lining and thereby cancels the insulating properties of PTFE. Because of its conductive properties, conductive PTFE cannot be tested for quality by electric sparks.
Reinforced PTFE RTFE
RTFE is a modification of PTFE material. Although pure PTFE has a very low friction coefficient (0.02~0.04), it has a large amount of wear. Moreover, due to its easy creep, poor mechanical properties, low bearing capacity, and poor dimensional stability, it has great limitations as a friction material. Only modification can meet the special requirements of wear-resistant sealing materials from all walks of life through the method of material compounding. In improving the wear resistance of PTFE, some wear-resistant substances such as glass fiber, carbon fiber, graphite, molybdenum disulfide, Bronze powder and some organic compounds make them form network nodes in the PTFE layered structure to improve stiffness, thermal conductivity, creep resistance, and greatly improve wear resistance.
Viton
The rated temperature of the fluororubber valve seat is -18℃~150℃. Viton is a registered trademark of DuPont, and Fluorel is a registered trademark of 3M Company that is equivalent to fluororubber. This material has high temperature resistance and excellent chemical resistance. Suitable for hydrocarbon products, low and high concentrations of mineral acids, but not for steam media and water (poor water resistance).
Ultra High Molecular Weight Polyethylene UHMWPE
The rated temperature range of UHMWPE valve seat is -32℃~88℃. This material has better low temperature resistance than PTFE, but still has excellent chemical resistance. UHMWPE also has good wear resistance and corrosion resistance, and can be used in high-abrasion occasions.
Silicone copper rubber
Silicon copper rubber is a polymer with organic groups composed of silicon and oxygen atoms in the main chain. The rated temperature range is -100℃~300℃. It has good heat resistance and temperature resistance, excellent electrical insulation performance and high chemical inertness. It is suitable for organic acids and low-concentration inorganic acids, dilute alkalis and concentrated alkalis. Disadvantages: low mechanical strength. Post curing is required.
Graphite
Graphite is a crystal of carbon, a non-metallic material with silver-gray color, soft texture and metallic luster. Mohs hardness is 1~2, specific gravity is 2.2~2.3, and its bulk density is generally 1.5~1.8. It has unique physical and chemical properties such as high temperature resistance, oxidation resistance, corrosion resistance, thermal shock resistance, high strength, good toughness, high self-lubricating strength, thermal conductivity and electrical conductivity. It has special oxidation resistance, self-lubrication and plasticity at high temperature, and also has good electrical conductivity, thermal conductivity and adhesion. It can be used as a filler or performance improver for rubber, plastics and various composite materials to improve the wear resistance, compression resistance or conductivity of materials. Graphite is usually used to make valve gaskets, packings and valve seats.
The melting point of graphite is extremely high. It begins to soften and tend to melt when it reaches 3000 °C under vacuum. At 3600 °C, graphite begins to evaporate and sublime. The strength of general materials gradually decreases at high temperature, while graphite is heated to 2000 °C. On the contrary, the strength is doubled compared with that at room temperature, but the oxidation resistance of graphite is poor, and the oxidation speed gradually increases with the increase of temperature.