Grinding is a commonly used finishing method for the sealing surface of the valve in the manufacturing process of the valve. Grinding can make the valve sealing surface obtain high dimensional accuracy, geometric shape roughness and surface roughness, but it cannot improve the mutual position accuracy between the surfaces of the sealing surface. The dimensional accuracy of the ground valve sealing surface 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 principles of sealing surface grinding include five aspects: grinding process, grinding motion, grinding speed, grinding pressure and grinding allowance.
1 Grinding process
The grinding tool and the surface of the sealing ring fit together well, and the grinding tool performs complex grinding motions along the contact surface. There is an abrasive 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 grinding agent slide or roll between the grinding tool and the surface of the sealing ring, and the surface of the sealing ring is very thin after cutting. a layer of metal. The peaks on the surface of the sealing ring are first ground off, and then gradually achieve the required geometry.
Grinding is not only the mechanical process of the metal by the abrasive, but also the chemical action. The grease in the abrasive can form an oxide film on the machined surface, thereby accelerating the grinding process.
2 grinding movement
When the grinding tool and the sealing ring surface move relatively, the relative sliding path 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 changed. The constant change of the movement direction keeps each abrasive particle from repeating its own trajectory on the surface of the sealing ring, so as to avoid obvious wear marks and increase the roughness of the surface of the sealing ring. In addition, the continuous change of the movement direction cannot make the abrasive distribution more uniform, so as to cut off the metal on the surface of the sealing ring more uniformly.
Although the grinding movement is complicated and the movement direction changes greatly, the grinding movement is always carried out along the contact surface of the grinding tool and the surface of the sealing ring. Whether it is manual grinding or mechanical grinding, the geometric shape accuracy of the sealing ring surface is mainly affected by the geometric shape accuracy of the grinding tool and the grinding motion.
3 Grinding speed
The faster the grinding motion, the more efficient the grinding. The grinding speed is fast, more abrasive particles pass on the surface of the workpiece per unit time, and more metal is cut.
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 sealing surface of the valve 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 10~25m/min.
4 Grinding pressure
The grinding efficiency increases with the increase of the 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, the grinding pressure is 0.1~0.3MPa; the sealing surface of hardened steel and cemented carbide is 0.15~0.4MPa. Take the larger value for rough grinding, and take the smaller value for fine grinding.
5 Grinding allowance
Since grinding is a finishing process, the cutting amount is very small. The size of the grinding allowance depends on the machining accuracy and surface roughness of the previous process. Under the premise of ensuring the removal of machining marks in the previous process and the correction of the geometrical 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 ground, and the minimum grinding allowance is: the diameter allowance is 0.008~0.020mm; the plane allowance is 0.006~0.015mm. Take the small value for manual grinding or high material hardness, and take the large value for mechanical grinding or low material hardness.
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 ground before fine grinding, and the plane allowance is 0.012~0.050mm.
