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This article deals with mechanical seal failure forms——fracture and deformation and how to choose carbon graphite as friction pair material to avoid such occasions .
1.Fracture
Graphite cracks are caused by the vibration of the transmission parts, the expansion of the sealing ring of the mechanical seal, and the stress concentration at the sharp corners of the graphite ring itself.When the carbon graphite ring is used in a high viscosity fluid, especially as a floating non-compensation ring of mechanical seal, due to viscous resistance of the fluid, the carbon graphite seal ring will be bumped back and forth and broken.Therefore, carbon graphite sealing ring should use fluid whose viscosity is below 30Pa.s；for high viscosity fluid, copper alloy ring can be used instead of carbon graphite ring in the mechanical seal.
2.Deformation
Floating carbon graphite non-compensation ring is prone to deformation under high pressure, so contact installation is recommended for mechanical seals under high pressure conditions.
For non-compensation rings with large shaft diameters, more attention should be paid to the design of their shape and dimensions, and the radial and axial dimensions should be increased to prevent deformation of the mechanical seal.
For the carbon graphite ring with clamping structure, when the shaft diameter is more than 100mm, it is clamped with a PTFE O-ring, which is easy to cause deformation of the carbon graphite ring. Therefore, it is recommended to use a rubber O-ring.
1.Fracture
Graphite cracks are caused by the vibration of the transmission parts, the expansion of the sealing ring of the mechanical seal, and the stress concentration at the sharp corners of the graphite ring itself.When the carbon graphite ring is used in a high viscosity fluid, especially as a floating non-compensation ring of mechanical seal, due to viscous resistance of the fluid, the carbon graphite seal ring will be bumped back and forth and broken.Therefore, carbon graphite sealing ring should use fluid whose viscosity is below 30Pa.s；for high viscosity fluid, copper alloy ring can be used instead of carbon graphite ring in the mechanical seal.
2.Deformation
Floating carbon graphite non-compensation ring is prone to deformation under high pressure, so contact installation is recommended for mechanical seals under high pressure conditions.
For non-compensation rings with large shaft diameters, more attention should be paid to the design of their shape and dimensions, and the radial and axial dimensions should be increased to prevent deformation of the mechanical seal.
For the carbon graphite ring with clamping structure, when the shaft diameter is more than 100mm, it is clamped with a PTFE O-ring, which is easy to cause deformation of the carbon graphite ring. Therefore, it is recommended to use a rubber O-ring.
