Stem Summary:
The valve stem is an important part of the valve, which is used for transmission, connecting the actuator or handle, and directly driving the valve core to move or rotate below to realize the valve switch or regulation.
Stem characteristics:
The valve stem is not only a moving part and a stress part, but also a sealing part in the opening and closing process of the valve. At the same time, it is impacted and corroded by the medium, and it also rubs against the filler. Therefore, when choosing stem material, it is necessary to ensure that it has sufficient strength, good impact toughness, abrasion resistance and corrosion resistance at the specified temperature. The valve stem is a fragile part, and the mechanical and heat treatment properties of the material should be paid attention to when selecting the valve stem.
Commonly used materials for stem:
1. Copper alloys
Generally, QA19-2 and HPb59-1-1 are selected. Suitable for low pressure valves with nominal pressure less than or equal to 1.6 MPa and temperature less than or equal to 200 degrees.
2. Carbon steel
Generally, A5 and 35 steels are selected and nitrided. They are suitable for ammonia valves with nominal pressure less than or equal to 2.5 MPa, low and medium pressure valves with water, steam and other media. A5 steel is suitable for valves whose temperature does not exceed 300 degrees; 35 steel is suitable for valves whose temperature does not exceed 450 degrees. (Note: The actual route proves that the use of carbon steel nitriding for valve stem can not solve the problem of corrosion resistance, and should be avoided.)
3. Alloy steel
Generally, 40Cr, 38CrMoA1A, 20CrMo1V1A and other materials are selected. After chromium plating treatment, 40Cr is suitable for water, steam, oil and other media whose nominal pressure is less than or equal to 32 MPa and temperature is less than or equal to 450 degrees. 38CrMoA1A is nitrided and can withstand 10 MPa pressure at 540 degrees. It is commonly used in power station valves. 20CrMo1V1A can withstand 14MPa pressure at 570 degrees, which is often used in power station valves.
4. Stainless steel
Generally, 2Cr13, 3Cr13, 1Cr17Ni2, 1Cr18Ni12Mo2Ti and other materials are selected. 2Cr13 and 3Cr13 stainless steels are suitable for water, steam and weak corrosive media with nominal pressure less than or equal to 32MPa and temperature less than or equal to 450 degrees. They can be strengthened by chromium plating and high frequency quenching. 1Cr17Ni2 stainless steel valve, low temperature valve, corrosion resistant medium. 1Cr18Ni9Ti and 1Cr18Ni12Mo2Ti stainless steel are used in high temperature valves with nominal pressure less than 6.4MPa and temperature less than 600 degrees, stainless steel valves with temperature less than - 100 degrees and low temperature valves. 1Cr18Ni9Ti can resist corrosive media such as nitric acid and 1Cr18Ni12Mo2Ti can resist corrosive media such as acetic acid. When 1Cr18Ni9Ti and 1Cr18Ni12Mo2Ti are used in high temperature valves, nitriding treatment can be used to improve the scratch resistance.
5. Bearing chromium steel
GCr15 is suitable for ultra-high pressure valves with nominal pressure less than or equal to 300 MPa and temperature less than or equal to 300 degrees.
There are many materials for making valve stem, such as 4Cr10Si2Mo martensitic heat-resistant steel, 4Cr14Ni14W2Mo austenitic heat-resistant steel, etc.
Stem nut and stem are matched by threads, directly bearing the axial force of the stem, and the friction between the plate and the bracket and other valves. Therefore, in addition to the strength of the stem nut, it also requires the performance of small friction coefficient, stainless steel, and not biting with the stem.
