Research On Pressing Forming Technology Of Pumping Grooves On Mechanical Seal Rings

Based on dynamic pressure lubrication theory, the new zero leakage mechanical seal technology can improve the sealing performance by forming micro cavities or texture on its end face and thus reducing friction and wear between the end faces of the sealing medium zero(or less) leakage. Industrialization of the new mechanical seal can solve the problem of frequent failure of traditional mechanical seal and of environmental pollution caused by leakage. The research of new mechanical seal will create good economic benefit and social benefit.The laser processing is the common technique to fabricate the macro pumping grooves, micro cavities and texture. However, The thermal effect of laser pulse is serious, causing pumping groove edge hardening phenomenon. The forming efficiency is low and the laser is expensive, which is difficult to achieve the requirements of the processing industry. The punch forming technology of the macro pumping groove is effective and low cost,but it is difficult to realize mold release. This thesis employed the method of “core-pulling” punching technique to realize the rapid prototyping of the pumping grooves. The main research contents and results are as follows:Firstly, the force analysis and the effects of arch bridge as well as rebound are investigated in the powder compaction process. The stress of biscuit in the sintering process of is discussed. The phenomenon of material migration by means of flow, diffusion and liquid phase or gas phase transfer caused by surface tension is also studied, which provides a solid theoretical foundation for the subsequent sintering experiments.Secondly, the basic principle of the Si C seal rings end face with grooves fabrication via “core-pulling” punching technique is analyzed. The structure of the punching mold is designed according to this principle and the shapes of the end face grooves. To improve the uniformity of the compact, an experimental study was carried out by using the method of two-way compression. Results show that the mold structure is stable in the process of press, and the success rate of end face groove pressing is high, without shedding and cracking phenomenon. At the same time, in terms of rebound rate, the outer diameter of the compact is larger than the inner diameter, and the large diameter of the compact is larger than that of the small diameter. With increase of the pressing force, the lateral pressure increases, leading to an increase of blank rebound rate. The rebound rate of the seal ring with end pumping grooves is lower than that of the seal ring without such grooves.Thirdly, the effect of the end face grooves structure on the shrinkage rate of the sintered compact was analyzed from the point of view of surface tension.Results shows that curvature of grooves on the end face of the seal ring have a great relationship on the shrinkage rate during sintering process, because the greater the curvature of the curved grooves is, the greater the surface tension it suffers, and the greater driving force of the grooves inward contraction, thus the oval-shaped groove is the greatest shrinkage, followed by the arc-shaped groove, and spiral groove is minimal in terms of the shrinkage rate in the radial and circumferential direction. The inner and outer shrinkage of sealing ring are obvious smaller than the groove in the same direction, and the larger the groove area, the smaller the inner and outer diameter of the sealing ring. The rate of the radial direction of the groove is larger than the circumferential direction. The shrinkage rate of the sealing ring in the axial direction is larger than that in the radial direction due to the influence of gravity.Finally, pressureless sintering is employed to sinter the compact and the effects of additives(graphite, phenolic resin and boron carbide) on the density and size of the sintered samples were studied. The content of additive has a great influence on the density, weight loss rate and inside and outside diameter shrinkage rate of the sintered seal ring and the proper amount of additives can improve the volume density of the sealing ring and reduce the sintering shrinkage deformation of the sealing ring. Scanning electronic microscope(SEM) is used to observe the surface morphology of the seal ring with different particle size ratio, and the effect of the SiC particles on the density of the sintered body is studied. Results show that pure micron SiC particles can easily form closed hole, and these closed pores is not easy to be filled completely even under pressure; particle of multiple size is easy to form communicating holes in the pressing process, and fine particles can fill the gap thus forms relatively dense specimen.