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Valve Main Parts and Materials
Star: Post Date:2013/01/23 Click Count:3668 Author:Our Site Source:

Manufacture of valve parts and materials are many, including various grades of ferrous and nonferrous metals and their alloys, various non-metallic materials.

 

Manufacture of valve components of materials to choose according to the following factors:
  1, the working medium pressure, temperature and characteristics.
  2, the force components as well as the role of the valve structure.
  3, there is a better manufacturability.
  4, in the circumstances to meet the above conditions, there must be a lower cost. 
 

Material of valve body, valve cover and valve plate (flap valve) 
 

Valve body, valve cover and the gate (valve flap) is a valve, one of the major components, direct to withstand medium pressure, the materials used must conform to "valve pressure and temperature rating" requirement. Common materials for the following categories:

1, gray cast iron: gray cast iron for nominal pressure PN ≤ 1.0MPa, a temperature of -10 ℃ ~ 200 ℃ of water, steam, air, gas and oil and other media. Common grades of gray cast iron: HT200, HT250, HT300, HT350.

2. malleable iron: for nominal pressure PN ≤ 2.5MPa, a temperature of -30 ~ 300 ℃ of water, steam, air and oil medium, commonly used brands are: KTH300-06, KTH330-08, KTH350-10.

3. nodular cast iron: for PN ≤ 4.0MPa, a temperature of -30 ~ 350 ℃ of water, steam, air and oil and other media. Common brands are: QT400-15, QT450-10, QT500-7.
Given the current level of domestic technology, the plant varies, users are often difficult to test. Based on experience, the proposed PN ≤ 2.5MPa, valves, or the introduction of steel valves for safety.

4, acid-resistant high-silicon ductile iron: for nominal pressure PN ≤ 0.25MPa, temperature lower than 120 ℃ of the corrosive medium.

5, carbon steel: for nominal pressure PN ≤ 32.0MPa, a temperature of -30 ~ 425 ℃ of water, steam, air, hydrogen, ammonia, nitrogen and petroleum products and other media. Common brands are WC1, WCB, ZG25 and high-quality steel 20,25,30 and low-alloy steel 16Mn.

6, copper alloys: for PN ≤ 2.5MPa water, sea water, oxygen, air, oil and other media, as well as the temperature of -40 ~ 250 ℃ steam medium, commonly used grade for ZGnSn10Zn2 (tin bronze), H62, Hpb59-1 (brass), QAZ19-2, QA19-4 (aluminum bronze).

7, high-temperature copper: for nominal pressure PN ≤ 17.0MPA, temperature ≤ 570 ℃ steam and petroleum products. Common brands are ZGCr5Mo, 1Cr5M0. ZG20CrMoV, ZG15Gr1Mo1V, 12CrMoV, WC6, WC9 and other brands. The specific use must be in accordance with the valve pressure and temperature norms.

8, low temperature steel, suitable for nominal pressure PN ≤ 6.4Mpa, temperature ≥ -196 ℃ ethylene, propylene, liquefied natural gas, liquid nitrogen and other media, popular brands) has ZG1Cr18Ni9, 0Cr18Ni9, 1Cr18Ni9Ti, ZG0Cr18Ni9

9, stainless acid-resistant steel, for nominal pressure PN ≤ 6.4Mpa, the temperature ≤ 200 ℃ nitric acid, acetic acid and other media, popular brands are ZG0Cr18Ni9Ti, ZG0Cr18Ni10 <resistance to nitric acid>, ZG0Cr18Ni12Mo2Ti, ZG1Cr18Ni12Mo2Ti <acid and urea " 
 

Sealing surface material 
 

The valve sealing surface is the most critical level of coverage, good or bad the quality of the sealing surface related to the life of the valve, usually sealing surface material to be considered anti-corrosion, anti-abrasion, anti-erosion, anti-oxidation and other factors.

Generally two broad categories:
(A) soft materials
1, rubber (including NBR, fluorine rubber, etc.)
2, plastic (PTFE, nylon, etc.)

(B) hard sealing material
1, copper alloys (for low-pressure valve)
2, chromium stainless steel (for the general high and medium pressure valve)
3, stellite alloy (for high temperature and pressure valve and strong corrosion of the valve)
4, nickel-based alloys (for corrosive media) 
  

 Stem Material 
 

Stem in the valve opening and closing process, to withstand tension and compression and torsion forces, and direct contact with the media, and also to fill the friction between the relative movement there, so stem material must ensure that the required temperature there is sufficient The strength and impact toughness, there is a certain degree of corrosion resistance and scratch resistance, and good manufacturability.

Stem materials commonly used in the following.

1, carbon steel
For low and medium temperature does not exceed 300 ℃ of water, steam medium, the general use A5 ordinary carbon steel.
For medium pressure and medium temperature does not exceed 450 ℃ of water, steam medium is generally selected 35 high-quality carbon steel.

2, the alloy steel
For medium-pressure and high pressure, medium temperature does not exceed 450 ℃ of water, steam, oil and other media, they generally use
40Cr (chromium steel).
For the high-pressure, medium temperature does not exceed 540 ℃ of water, steam and other media, they can use 38CrMoALA infiltration
Nitrogen steel.
For the high-pressure, medium temperature does not exceed 570 ℃ steam medium, the general use 25Cr2MoVA Cr-Mo-V steel.

3. acid-resistant stainless steel
For medium-pressure and high pressure, medium temperature does not exceed 450 ℃, non-corrosive medium and weak corrosive media, optional
With 1Cr13, 2Cr13, 3Cr13 chrome stainless steel.
Used in corrosive media, it can use Cr17Ni2, 1Cr18Ni9Ti, Cr18Ni12Mo2Ti, Cr18Ni12Mo3Ti
And other acid-resistant stainless steel and PH15-7Mo precipitation hardening steel.

4, heat-resistant steel
Used for medium temperature does not exceed 600 ℃ high temperature valve, it can use 4Cr10Si2Mo martensitic-type heat-resistant steel and
4Cr14Ni14W2Mo Austenitic heat-resistant steel. 
 

stem nut material 
 

Stem nut on the valve opening and closing process, stem directly to bear axial force, it must possess the necessary strength. At the same time it is a threaded valve stem drive to require the friction coefficient is small, does not rust and to avoid the phenomenon was bitten to death.

1, copper alloy
A smaller coefficient of friction of copper alloy, stainless, is one of the commonly used materials. For Pg <1.6Mpa low-pressure valve can be used ZHMn58-2-2-cast brass. For Pg16-6.4Mpa of the medium pressure valve can be used ZQAL9-4 Wuxi bronze. For the high-pressure valve can be used ZHAL66-6-3-2-cast brass.

2, steel
When the working conditions do not allow use of copper alloy, it can use 35,40 and other high-quality carbon steel, 2Cr13, 1Cr18Ni9, Cr17Ni2 such as acid-resistant stainless steel.

 

Working conditions, not allowed to refer to the following conditions.
1, for electric valve on the stem with a melon-shaped clutch nut, the need for heat treatment to obtain a high hardness or surface hardness.
2, the working media or the surrounding environment is not suitable for use copper alloy, such as when there is corrosion of copper ammonia medium.
Use steel stem nut, we should pay special attention to the phenomenon of thread bite.

 

 

 

 

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