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The fundamental principles of valve sealing surface grinding.
Created on 2024.08.06
Grinding is a commonly used finishing method for the sealing surface of the valve in the manufacturing process. Grinding can make the valve sealing surface obtain high dimensional accuracy, geometric coarseness and surface roughness, but can not improve the mutual position accuracy between the sealing surfaces. The dimensional accuracy of the ground valve sealing surface is usually 0.001~0.003mm; Geometric accuracy (e.g. unevenness) of 0.001mm; The surface roughness is 0.1~0.008.
The basic principle of seal surface grinding includes five aspects: grinding process, grinding movement, grinding speed, grinding pressure and grinding allowance.
1 Grinding process
The grinding tool and the sealing ring surface are well bonded together, and the grinding tool makes complex grinding movements along the attached surface. When the grinding tool and the sealing ring surface move relatively, part of the abrasive particles in the abrasive slide or roll between the grinding tool and the sealing ring surface, cutting off a thin layer of metal on the surface of the sealing ring. The convex parts on the surface of the sealing ring are first ground off and then gradually reach the required geometry.
Grinding is not only the machining process of abrasives to metal, but also has a chemical effect. The grease in the abrasive accelerates the grinding process by forming an oxide film on the surface being processed.
2 Grinding movement
When the grinding tool and the sealing ring surface move relative to each other, the relative sliding path sum of each point on the sealing ring surface to the grinding tool should be the same. Also, the direction of relative motion should be constantly changing. The constant change of the direction of movement makes each abrasive grain not repeat its own movement trajectory on the surface of the sealing ring, so as not to cause obvious wear marks and increase the roughness of the sealing ring surface. In addition, the breaking change in the direction of motion does not make the abrasive more evenly distributed, so that the metal on the surface of the sealing ring can be cut more evenly.
Although the grinding movement is complex and the direction of movement changes greatly, the grinding movement is always carried out along the conforming surface of the grinding tool and the sealing ring surface. Whether it is manual grinding or mechanical grinding, the geometric accuracy of the sealing ring surface is mainly affected by the geometric accuracy of the grinding tool and the grinding movement.
3 Grinding speed
The faster the grinding movement, the more efficient the grinding will be. The grinding speed is fast, and more abrasive particles pass through the surface of the workpiece per unit time, and more metal is cut.
The grinding speed is usually 10~240m/min. For workpieces with high grinding accuracy, the grinding speed is generally not more than 30m/min. The grinding speed of the sealing surface of the valve is related to the material of the sealing surface, and the grinding speed of the sealing surface of copper and cast iron is 10~45m/min; The sealing surface of hardened steel and cemented carbide is 25~80m/min; The sealing surface of austenitic stainless steel is 10~25m/min.
4 Grinding pressure
The grinding efficiency increases with the increase of grinding pressure, and the grinding pressure should not be too large, generally 0.01~0.4MPa.
When grinding the sealing surface of cast iron, copper and austenitic stainless steel materials, the grinding pressure is 0.1~0.3MPa; The sealing surface of hardened steel and cemented carbide is 0.15~0.4MPa. The larger value is taken for rough grinding, and the smaller value is taken for fine grinding.
5 Grinding allowance
Since grinding is a finishing process, the amount of removal is very small. The size of the grinding allowance depends on the machining accuracy and surface roughness of the previous process. On the premise of ensuring the removal of the processing traces of the previous process and the correction of the geometric error of the sealing ring, the smaller the grinding allowance, the better.
The sealing surface should generally be finely ground before grinding. The sealing surface after fine grinding can be directly refined, and the minimum grinding allowance is: the diameter allowance is 0.008~0.020mm; The plane margin is 0.006~0.015mm. A small value is taken when the hardness of the material is high for manual grinding or the hardness of the material is low, and a large value is taken when the hardness of the material is low for mechanical grinding or the material.
The sealing surface of the valve body is inconvenient for grinding, and fine turning can be used. The sealing surface after finishing must be rough grinding before fine grinding, and its plane margin is 0.012~0.050mm.
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