Study On Strength Of Spiral Ring Dry Gas Seal Ring

Nowadays the spiral groove dry gas is more and more used in high pressure, high speed and big dimension of size conditions. The materials of rotary ring are made of silicon carbide, tungsten carbide or other hard brittle materials. Although these materials have high hardness, they belong to plastic materials, and may crack or break under the action of high force or high pressure, which may lead to seal failure, even harm to the main machine. Thus the strength and vibration of rotary ring in spiral groove dry gas seal has been studied in this paper.By analyzing the forces which act on rotary ring of inward pumping spiral groove gas seal, considering that when the rotary ring of spiral groove dry gas seal operated under the action of the centrifugal force, the stress of rotary ring is the maximum of all. Based on elastic mechanics theory and numerical simulation, the stress distribution of rotary ring under the centrifugal force has been investigated, and some specific cases were given in this paper. The results showed that the stresses made by the numerical analysis methods and the elastic mechanics theory were very close, and the radial stress of rotating ring increased at first then decreases with the radius increasing. The maximum tangential stress was at inner diameter, and the tangential stress decreased with radius increasing. Both the radial stress and the tangential stress increase rapidly with the increasing of angular velocity. The tangential stress was far greater than the radial stress, so the tangential stress was mainly checked when checking the operation security of rotary ring. When the maximum tangential stress equaled its allowable strength, rotary ring could crack or break, leading to the seal failure.Approximate analytical methods of the gas film pressure in the inward pumping and outward pumping spiral groove gas seals were presented, according to the narrow groove theory by Muijderman, and the opening forces of the gas film were obtained too. With the finite element software ANSYS-Mechanical, the distribution state of stress and strain under the action of the centrifugal force, the gas film pressure and the media pressure of moving ring was obtained. In addition, the security operation of moving ring was checked as well. Then find out the main factors which influence the strength of sealing ring. The results showed that:In inward pumping spiral groove gas seals, the strain and the stress under the action of the centrifugal force, the media pressure and the gas film pressure combined were minimum. The stress of moving ring was far smaller than the allowable stress. In outward pumping spiral groove gas seals, the strain and the stress under the action of the centrifugal force, the media pressure combined were maximum. The strain and the stress under the action of the centrifugal force alone were minimum. The stress of moving ring under the centrifugal force, the media pressure and the gas film pressure was bigger than the allowable stress, the moving ring may crack or break under this operating condition so it is necessary to optimization the structural and the operation parameters. The rotational speed, the media pressure, the thickness of gas film and the dimension of size were indicated a significant influence of rotary ring’s strength.The finite element software ANSYS-Modal was used for the free and under constraint modal analysis of the spiral groove dry gas seal rotary ring model. The inherent frequency and mode of vibration were obtained. Compared the inherent frequencies of rotary ring under the centrifugal force, media pressure or gas film pressure. Then the calculation results of inherent frequency in free state were compared with the vibration test. The results showed that under free mode, the vibration deformation of the sealing ring was small enough, exhibited an axial-radial alternative pattern. Under the constraints modal, at the low mode part, the main vibration deformation was in the axial; the radial deformation occured in the high mode part, the inherent frequencies were too high to appear resonance. So that under normal operating conditions the impact of vibration on sealing performance do not need to be considered.