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Mechanical Seal Analysis. Nicholas McDermott Friction, wear and lubrication of materials final project. Background/What I Did. A mechanical seal is used to prevent fluid from leaking in between the rotating shaft and the stationary housing.
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Mechanical Seal Analysis Nicholas McDermott Friction, wear and lubrication of materials final project
Background/What I Did • A mechanical seal is used to prevent fluid from leaking in between the rotating shaft and the stationary housing. • The seal is ideally two opposing plane perpendicular to the shaft’s axis of rotation, forced together by a spring. • For the project four design variables were examined to see their effect on the leakage rate and the operational envelope of the seal. • The operational envelope is the area of pressure and fluid temperature combinations that the seal is safe to operate without causing the fluid to vaporize. If the fluid vaporizes the seal face will be subject to cavitation corrosion. • The four variables considered are the pressure distribution factor, the spring force/pressure, operating pressure, and the shaft speed.
Pressure Distribution Factor • Is the ratio of the average pressure between the seal faces and the pressure drop across the face. • Based off of the results of the COMSOL models it was assumed that analyzing the seal varying the P.D. From .5 to .9 was reasonable.
Spring Pressure • The spring force affects the seal performance and the operational envelope. The correct spring force is a balance between the wear of the spring and the leakage rate. • As the spring pressure increases the temperature rise increases and the leakage rate decreases.
Operating Pressure • The environment the mechanical seal needs to operate in effects the seal performance. Although it may not be possible to choose the environmental pressure the effects of the pressure should be fully understood in order to properly design the seal.
Shaft Speed • In many pumps and propulsion trains the speed of the shaft is varying depending on the work it is expected accomplish. As a result it should be fully understood the effects of varying the shaft speed. Although shaft speeds can vary from a few rotations per minute (RPM) to a few thousand RPMs the calculations in this paper were concerned with the range of 10 to 100 RPM.
Conclusion • Shaft speed has the greatest effect on the operational envelope of the seal, with Pressure Distribution Factor having the least effect on the seal • The outer pressure has the greatest effect on the leakage rate of the seal.