Processing Methods of Fluid Dynamic Pressure Groove on End Face of Mechanical Seal Ring

The dynamic pressure groove of the seal ring is used more and more in the non-contact mechanical seal. However, the shape of the dynamic pressure groove is complex, the structure is fine, the precision is high, and the roughness requirements are also strict. In particular, most of the seal rings for processing dynamic pressure grooves are made of hard materials, so the processing of dynamic pressure grooves is very difficult, and conventional machining methods are almost powerless. Therefore, people have explored a variety of methods, mainly including the following:

Ⅰ. Photolithography of mechanical seal ring

The photosensitive film is first applied to the grooved workpiece, and then the prepared negative is placed on it. The required dynamic pressure groove can be obtained after exposure, development, coating of the protective layer, and then etching in the etching solution. This method is acceptable for carving grooves on bronze, but when carving grooves on cemented carbide, the quality of the carved grooves is not high because the adhesive film cannot withstand the long-term corrosion of the etching solution at higher temperatures.

Ⅱ. EDM machining of mechanical seal ring

In this method, the material to be removed in the dynamic pressure groove is etched away by the discharge method of two electrodes. The key to this method is to make a discharge head. The end face structure of the discharge head is the same as that of the dynamic pressure groove on the end face of the sealing ring, but the pattern is prominent. The sealing ring and the discharge head are respectively energized as two electrodes. When the two end faces are in contact, a discharge is generated, and the material in the dynamic pressure groove on the end face of the seal ring is etched away. However, this method requires better dielectric performance, and the end face of the discharge head and the end face of the sealing ring should be parallel to achieve the effect of uniform discharge, otherwise the groove depth of each groove will be difficult to guarantee. The disadvantage of this method is that it is difficult to process the discharge head. The efficiency of electro-etching is too low so that the loss of the discharge head is large and the processing cost is high, thus the effect is not good. At the same time, microcracks caused by surface stress generated by electrical machining will reduce the strength of the material.

Ⅲ. Electroplating method of mechanical seal ring

This method is to coat the parts other than the dynamic pressure groove on the end face of the mechanical seal ring with a layer of hard material to make the pattern of the dynamic pressure groove. The conditions for using this method are: firstly, the groove should be shallow; secondly, the plated end surface must be a material that can be plated, and the plating layer should be dense and the bonding strength of the plated surface should be high enough. At the same time, the plated parts should be hung correctly during the electroplating process, otherwise the thickness error of the coating at different parts will increase, resulting in uneven groove depth, which also destroys the extremely high parallelism of the two end faces of the sealing ring.

Ⅳ. Sandblasting method of mechanical seal ring

First, a sandblasting mask must be manufactured, and the pattern of openings on the mask is the same as that of the dynamic pressure groove structure. When the mask is placed on the end face of the seal, the parts other than the dynamic pressure groove on the end face are covered, and the exposed material is removed by high-energy sandblasting to form a dynamic pressure groove with a certain depth. The technical key of this method lies in the selection of the mask material, the manufacture of the mask, the lamination of the mask, the end face of the seal ring, the mastery of the sandblasting process and so on. The problems of the sandblasting method are low manufacturing accuracy, uneven edges of the processed dynamic pressure groove, serious distortion of fine parts such as sharp corners, poor cross-sectional groove shape, and rough sandblasting surface. These will affect the hydrodynamic effect and sealing characteristics of the groove line.

Ⅴ. Laser processing method of mechanical seal ring

Laser processing is a method of industrial thermal processing that utilizes the high energy of a laser. This method is used for practical processing of material removal, including cutting, punching, dynamic balancing, marking, etc. Any material can be vaporized, melted and removed in a very short time. The process of machining the dynamic pressure groove of the mechanical seal ring with a laser is actually laser marking, which is a relatively new work.