The sealing function of graphite packing is achieved through a three-stage dynamic process: contact-deformation-maintenance:
1. Initial Seal Establishment
When the packing is installed in the seal cavity and an axial preload is applied (e.g., via gland bolts), the packing rings are compressed and expand radially, forming close contact with the rotating shaft or reciprocating rod surface. The key to this stage is to ensure the effectiveness of the initial contact pressure by overcoming the effects of medium pressure and axial vibration through the preload force.
2. Maintaining the Seal Under Dynamic Conditions
During equipment operation, the movement of the rotating shaft or reciprocating rod causes relative displacement between the sealing surfaces (e.g., from rotating friction on the shaft or reciprocating sliding on the piston). The self-lubricating properties of graphite packing significantly reduce frictional resistance, minimizing the risk of seal failure due to adhesive wear or heat buildup. Furthermore, the packing's flexibility enables it to adapt to even small shaft deflections or vibrations, maintaining the continuity of the contact interface through local deformation.
3. Wear Compensation and Long-Term Stability
Over extended operation, friction inevitably wears the sealing surfaces, causing a decrease in initial contact pressure. At this point, the packing's residual compressive elasticity and the medium pressure work together to push the packing toward the worn area, creating a "self-compensating" effect. Furthermore, under certain operating conditions, an external lubrication system (such as water, oil, or inert gas injection) can further reduce frictional heat and extend service life.
