Basic principle of grinding valve sealing surface

Grinding is a commonly used finishing method for the sealing surface of valves during the manufacturing process. Grinding can achieve high dimensional accuracy, geometric roughness, and surface roughness of the valve sealing surface, but it cannot improve the mutual positional accuracy between the surfaces of the sealing surface. The size accuracy of the valve sealing surface after grinding is usually 0.001~0.003mm; Geometric 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 sealing ring surface are well fitted together, and the grinding tool performs complex grinding movements along the bonding surface. There is a grinding agent placed between the grinding tool and the sealing ring surface. When the grinding 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 grinding tool and the sealing ring surface, cutting off a thin layer of metal on the sealing ring surface. 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 metal by abrasives, 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 grinding tool and the sealing ring surface move relative to each other, 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 motion should constantly change. The continuous change in the direction of movement prevents each abrasive particle from repeating its own trajectory on the surface of the sealing ring, thus avoiding obvious wear marks and increasing the roughness of the sealing ring surface. In addition, the direction of movement cannot make the abrasive evenly distributed, thus cutting off the metal on the surface of the sealing ring more evenly.

Although the grinding motion is complex and the direction of motion varies greatly, it always occurs along the contact surface between 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 motion.

3 Grinding speed

The faster the grinding motion, the higher the grinding efficiency. The grinding speed is fast, and more abrasive particles pass through the surface of the workpiece per unit time, resulting in more metal being cut off.

The grinding speed is usually 10~240m/min. For workpieces with high grinding accuracy requirements, 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 copper and cast iron sealing surfaces is 10-45m/min; The sealing surface of quenched steel and hard alloy 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 high, generally ranging from 0.01 to 0.4 MPa.

When grinding the sealing surface of cast iron, copper, and austenitic stainless steel materials, the grinding pressure is 0.1~0.3 MPa; The sealing surface of quenched steel and hard alloy is 0.15~0.4MPa. Take the larger value for rough grinding and the smaller value for fine grinding.

5 Grinding allowance

The sealing surface should generally undergo precision grinding before grinding. The sealing surface after precision grinding can be directly polished, with a minimum grinding allowance of 0.008-0.020mm for diameter allowance; The plane allowance is 0.006-0.015mm. When manually grinding or material hardness is high, take the smaller value; when mechanically grinding or material hardness is low, take the larger value.

The sealing surface of the valve body is inconvenient for grinding and processing, and can be precision machined. The sealing surface after finishing must be roughly ground before finishing, with a flat allowance of 0.012-0.050mm.