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 roughness, and surface roughness, but it cannot improve the mutual position accuracy of the sealing surfaces. The dimensional accuracy of the valve sealing surface after grinding is usually 0.001~0.003mm; the geometric shape accuracy (such as unevenness) is 0.001mm; the surface roughness is 0.1~0.008.
The basic principle of sealing surface grinding includes five aspects: grinding process, grinding movement, grinding speed, grinding pressure, and grinding allowance.
1. Grinding process
The grinding tool and the surface of the sealing ring are well integrated, and the grinding tool makes complex grinding movements along the bonding surface. An abrasive is placed between the grinding tool and the surface of the sealing ring. When the grinding tool and the surface of the sealing ring move relative to each other, part of the abrasive particles in the abrasive slide or roll between the surface of the grinding tool and the sealing ring, and the surface of the sealing ring is very thin. A layer of metal. The convex peaks on the surface of the sealing ring are first ground off, and then gradually reach the required geometric shape.
Grinding is not only the mechanical processing of metals by abrasives but also chemical effects. The grease in the abrasive can form an oxide film on the processed surface, thereby speeding up the grinding process.
2. Grinding
When the grinding tool and the surface of the sealing ring move relatively, the relative sliding path of each point on the sealing ring surface to the grinding tool should be the same. And, the direction of relative movement should be constantly changed. The continuous change of the direction of movement prevents each abrasive particle from repeating its own motion track on the surface of the seal ring, so as to avoid obvious wear marks and increase the surface roughness of the seal ring. In addition, the change in the direction of movement cannot make the abrasive distribution more uniform, so that the metal on the surface of the seal ring can be cut more uniformly.
Although the grinding movement is complicated and the direction of movement changes greatly, the grinding movement is always carried out along the surface of the grinding tool and the surface of the sealing ring. 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 research tool and the grinding movement.
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3. Grinding speed
The faster the grinding movement, the higher the grinding efficiency. The grinding speed is fast, and more abrasive particles pass on the surface of the workpiece in a unit time, and more metal is cut off.
The grinding speed is usually 10~240m/min. For workpieces that require high grinding accuracy, the grinding speed generally does not exceed 30m/min. The grinding speed of the valve sealing surface is related to the material of the sealing surface. 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 It is 10~25m/min.
4. Grinding pressure
The grinding efficiency increases with the increase of the grinding pressure. The grinding pressure should not be too high, generally 0.01～0.4MPa.
When grinding the sealing surface of cast iron, copper and austenitic stainless steel, 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 used for rough grinding, and the smaller value is used for fine grinding.
5. Grinding allowance
Since grinding is a finishing process, the amount of cutting is small. The size of the grinding allowance depends on the processing 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 seal 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 finely ground. The minimum grinding allowance is: the diameter allowance is 0.008~0.020mm; the plane allowance is 0.006~0.015mm. When manual grinding or material hardness is high, take a small value, and mechanical grinding or material hardness is low, take a large value.
The sealing surface of the valve body is inconvenient for grinding, so fine-tuning can be used. The sealing surface after finishing must be rough-grinded before it can be fine-grinded, and the plane margin is 0.012~0.050mm.
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