Grinding is a commonly used finishing process for the sealing surfaces in valve manufacturing. Grinding can achieve high dimensional accuracy, geometric shape accuracy and surface roughness for the valve sealing surfaces. However, it cannot improve the positional accuracy between the surfaces of the sealing surface. 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; and the surface roughness is 0.1 - 0.008. 

The basic principles of sealing surface grinding include five aspects: the grinding process, the grinding motion, the grinding speed, the grinding pressure, and the grinding allowance. 

1. Grinding process 

The tool and the sealing ring are perfectly fitted together. The tool performs a complex grinding motion along the fitting surface. A grinding agent is placed between the tool and the sealing ring surface. When the tool and the sealing ring surface move relative to each other, some of the abrasive particles in the grinding agent slide or roll between the tool and the sealing ring surface, cutting off a very thin layer of metal from the sealing ring surface. The protruding parts on the sealing ring surface are first ground off, and then gradually reach the required geometric shape. 
Grinding is not only a mechanical processing process of the abrasive on the metal, but also involves chemical reactions. The grease in the grinding agent can form an oxide film on the processed surface, thereby accelerating the grinding process. 

2. Grinding Motion 

When the abrasive tool and the sealing ring move relative to each other, the relative sliding path of each point on the sealing ring with respect to the abrasive tool should be the same. Moreover, the direction of the relative movement should constantly change. The continuous change of the movement direction ensures that each abrasive particle does not repeat its own movement trajectory on the sealing ring surface, thereby avoiding the formation of obvious scratches and increasing the roughness of the sealing ring surface. In addition, the discontinuous change of the movement direction cannot make the abrasive agent distributed relatively evenly, thus not cutting off the metal on the sealing ring surface in a relatively uniform manner. 
Although the grinding motion is complex and the direction of the motion undergoes significant changes, the grinding motion always proceeds along the surface of the fit between the grinding tool and the sealing ring. Whether it is manual grinding or mechanical grinding, the geometric shape accuracy of the sealing ring surface is mainly influenced by the geometric shape accuracy of the grinding tool and the grinding motion. 

3 Grinding speed 

The faster the grinding motion is, the higher the grinding efficiency will be. When the grinding speed is fast, more abrasive particles pass over the surface of the workpiece within a unit of time, and more metal is removed. 
The grinding speed is usually between 10 and 240 m/min. For workpieces with high grinding accuracy requirements, the grinding speed should generally not exceed 30 m/min. The grinding speed for valve sealing surfaces is related to the material of the sealing surface. For copper and cast iron sealing surfaces, the grinding speed is 10 to 45 m/min; for hardened steel and hard alloy sealing surfaces, it is 25 to 80 m/min; and for austenitic stainless steel sealing surfaces, it is 10 to 25 m/min. 

4 Grinding Pressure 

The grinding efficiency increases with the increase of grinding pressure. However, the grinding pressure should not be too high; it is generally between 0.01 and 0.4 MPa. 
When grinding the sealing surfaces of cast iron, copper and austenitic stainless steel materials, the grinding pressure is 0.1 to 0.3 MPa; for hardened steel and hard alloy sealing surfaces, it is 0.15 to 0.4 MPa. A larger value is taken during rough grinding and a smaller value during fine grinding. 

5 Grinding allowance 

Before grinding the sealing surface, it is generally necessary to undergo fine grinding. After fine grinding, the sealing surface can be directly fine-graded. The minimum grinding allowance is as follows: for the diameter, the allowance is 0.008 to 0.020 mm; for the plane, the allowance is 0.006 to 0.015 mm. When grinding by hand or when the material hardness is high, the smaller value should be taken; when grinding by machine or when the material hardness is low, the larger value should be taken. 
The sealing surface of the valve body is not suitable for grinding processing. Therefore, it can be machined by fine turning. After fine turning, the sealing surface must be rough ground before further fine grinding can be carried out. The flatness allowance is 0.012 to 0.050 mm.