Described a high pressure valve seals in different types of axial force to identify and to demonstrate calculation and analysis of the high pressure valve sealing mechanism and the sealing surface precision valve axial force on impact and sealing materials use.
1 Overview
High pressure valve sealing materials are usually metal on metal, in order to tightly seal off valve must be sealed to improve the machining accuracy and surface roughness level, and imposed on the sealing surface of a very large axial sealing force. However, the axial sealing force is not always better. In one view, high pressure valve (≥ 300MPa) should be sealed plastic method, and the mostly linear with cone seal. The so-called plasticity seal, the seal is the sealing surface pressure is equal to Sealing than the soft material yield limit, so that joint surface in close contact, use the plastic deformation of soft materials, blockage hardware uneven surface, and forms similar to the ideal plane, and generated equal to the soft material yield limit of the reaction and remain sealed.
2, axial force of
Stem sealing surface of the axial force depends on the total force, the valve sealing surface design to determine the key parameter is the total force than the pressure seal. But in the high pressure valve of the cone, sealing case, the axial force Q in the absence of medium pressure generated by sealing off more than it can be larger than pressure q Sealing of soft material yield limit δs, medium pressure in a closed q than the pressure when the seal is necessarily equal to δs, this paper will discuss the appropriate value of q.
3, the sealing surface roughness effects on the axial force
According to the surface only when the seal gap between the molecular diameter less than the media in order to ensure the media are not the views of leakage can be considered to prevent fluid leakage clearance value must be as small as 0.003μm. However, even after lapping, metal surface on the convex peak height is still more than 0.05μm, to achieve the ideal plane, we must exert a certain force contact surface, the force size and Sealing of soft material and the sealing surface of the rough σs degrees about.
When the sealing surface of the specific pressure q <40MPa, the sealing surface quality plays a decisive role. For example, when q = 65MPa, with the increasing roughness level, infiltration capacity decreases rapidly, which means that q <40MPa when a leakage in the same grade, roughness, the more the higher the required q small, the smaller the axial force.
But σs> 900MPa sealing materials are used in the 300MPa grade high pressure valve, in addition to linear elastic fracture mechanics from the point of view, [σ] from the intensity asked to consider, Ra0.05μm above, but also from the sealing mechanism to consider. Therefore, σs the high pressure valve for the 900MPa with seals, the sealing surface roughness must Ra0.05μm above. As for the WC hard alloy by HIP treatment Sealing, because of its more brittle nature, to increase the sealing surface pressure to compress the sealing surface than the peak, so that the axial force will increase considerably, and will make the valve to crack, (in the Fisher valve in the use of the company, there is a result of the axial force caused by improper seat adjustment faults example), and therefore its sealed surface roughness must be higher than Ra0105μm. Only in this context, in order to use equation (13) of the axial force calculations.
4 Conclusion
High pressure valve seal mechanism of the narrow sub-surface plastic seal and the sealing of two types. As the seat (or valve flaps) after sealing the surface of dough deformation of cold hardening, so the increase of axial force and the valve seat sealing surface is not proportional to the increase in width. Diameter 1/2in. (15mm) or more high pressure valve sealing materials to use HIP treatment is appropriate WC carbide, sealing surface roughness must be very high level, while the formula for calculating the axial force the use of certain .