Fundamentals Of Valve Sealing Surface Grinding
2016-10-22
Grinding, one kind of finishing machining methods to valve sealing surface in process of valve manufacturing.Grinding can make the valve sealing surface to obtain high dimensional accuracy, geometric roughness and surface roughness but can not improve mutual position accuracy of different surfaces on sealing surface.After grinding, the valve sealing surface usually can reach dimensional accuracy of 0.001 ~ 0.003mm; geometrical precision of 0.001mm; surface roughness of 0.1 to 0.008.mm
Fundamentals of valve vealing surface grinding are made of 5 parts:grinding process,grinding movement,grinding speed,grinding pressure and grind allowance.
- The grinding process
The grinding machine faying sealing surface closely and do complex grinding movement along with faying surface, between the machine and sealing ring surface,there are some abrasive. When the grinding wheel moves relative to the sealing ring surface, the grains in the abrasive are slid or rolled between the grinding machine and the sealing ring surface to remove a thin layer of metal on the sealing ring surface.The rasied portion will be rubbed off first and then gradually reach to the desired geometry.
Grinding is not only a mechanical process of abrasive to metal, but also a chemical action. The grease in the abrasive can form an oxide film on the surface being machined, thus accelerating the grinding process.
- Grinding movement
When grinding machine do relative movement to sealing surface, every relative sliding path of each point on the sealing surface relative to the machine should be the same. Also, the direction of relative movement should be changed continually.
The changing direction of movement makes each abrasive grain not repeat motion trail on the surface, so as not to cause significant wear and increase the surface roughness of the seal. In addition, the successive change in the direction of movement can not make the distribution of abrasive more uniform, so more evenly to cut off the metal on sealing surface.
Although the grinding movement is complex and the movement direction varies greatly, the grinding movement is always carried out along the faying surface between the grinding machine and the sealing ring surface. Whether hand grinding or mechanical grinding, the geometric accuracy of the sealing surface is mainly affected by the accuracy of the geometry of grinding machine and grinding movement.
- Grinding speed
The faster the grinding movement, the higher the grinding efficiency. Faster grinding speed can make more grains go through surface of workpiece in the unit time and cut off more metal.
Generally, the grinding rate is usually 10 to 240 m / min. For the high-precision required workpiece, the grinding speed is generally not more than 30m / min. The grinding speed of the sealing surface is related to the material of the sealing surface, the grinding speed of copper and cast iron sealing surface is 10 ~ 45m / min, quenched steel and hard alloy is 25 ~ 80m / min, t austenitic stainless steel is 10 to 25 m / min.
- Grinding pressure
Grinding efficiency improved with the increase of grinding pressure, grinding pressure cannot be too large, usually 0.01 ~ 0.4MPa.For cast iron, copper and austenitic stainless steel sealing surface, the grinding pressure is 0.1 ~ 0.3MPa; quenched steel and hard alloy sealing surface ,0.15 ~ 0.4MPa. Rough grinding take the bigger value, while precision grinding , take a smaller value.
- Grinding allowance
As the grinding is the finishing process, so the amount of cutting is very small. The amount of the grinding allowance depends on the machining accuracy and the surface roughness of the grinding process. Under the premise of ensuring the removal of the processing traces on the working procedure and the correction of geometrical shape error of the sealing ring, the grinding margin should be as small as possible.
Sealing surface grinding generally have fine wearing before precision grinding. The minimum grinding allowance: diameter margin of 0.008 ~ 0.020mm; plane margin of 0.006 ~ 0.015mm. For manual grinding or high-hardness material, take a small value; mechanical grinding or low-hardness material, take a large value.
Valve body sealing surface is not good to grinding machining, but can adopt precision lathing. After lathing ,rough grinding goes before precision grinding, and the allowance is 0.012 ~ 0.050mm.