Why are such high requirements placed on the roughness of the sealed end surface?
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The smoother the sealed end face, the greater its load-bearing capacity; this is especially important for seals with high end-face specific pressures. Due to the different roughnesses of the sealed end faces, the bearing areas vary significantly. Some people simply grind the sealed end face and then install it for use. As can be seen from Table 1, only 40% of the bearing area is available in this case, and obviously the end-face specific pressure increases by 1.5 times. If the end-face specific pressure is 0.4 MPa, it will actually reach 1.0 MPa. In friction pairs consisting of tungsten carbide rings and graphite rings, due to differences in hardness and elasticity, excessive local pressure at the higher points on the surface of the tungsten carbide rings can cause heating or even cracking; meanwhile, fine circular grooves will form on the surface of the graphite rings. Vibration of the pump and misalignment of the rotating and stationary rings can exacerbate this wear. The worn graphite exists between the sealing surfaces, causing abrasive wear which intensifies the wear process; the leaked fluid contains graphite particles and thus appears black. This phenomenon occurs when the pump is started after many seals have been installed, and the reason for this is that the sealing surfaces are not smooth or even.
The roughness requirement for the sealed end face is very high because it is directly related to the quality of the sealing performance and the service life. Here are the main reasons: 1. Reducing leakage: When the roughness of the sealed surface is lower, that is, when the surface is smoother, a better fit can be achieved, which effectively reduces the leakage of the medium. When the pump is in operation and the medium leaks through the tiny gap between the sealed end faces, the leakage will be reduced if the end faces are smooth. 2. Improve load-bearing capacity: A smooth sealing surface can provide a larger effective load-bearing area. As you described, if the end face has only 40% of the bearing area, the actual end face specific pressure will increase due to the reduction in the effective area. This increased specific pressure makes the friction pair more prone to damage. 3. Prevent wear: Rough end faces generate significant friction between the stationary and moving parts of the seal ring, leading to accelerated wear. Particles generated by wear further exacerbate wear, creating a vicious cycle. 4. Avoid damage: In pairings of materials with different hardnesses, such as tungsten carbide rings and graphite rings, highly rough end surfaces can cause excessive local pressure at the contact points, leading to overheating and cracks, and even material failure. 5. Reduce vibration: Mechanical vibration can be transmitted more effectively through smooth sealing surfaces, thereby preventing excessive wear. When the stator and rotor rings are not aligned, a lower roughness also helps to reduce additional damage caused by vibration or misalignment. Therefore, when designing and maintaining sealing systems, it is crucial to ensure that the sealing surfaces have a high level of smoothness. This not only helps improve the sealing performance but also extends the service life of the seals, reduces the frequency of repairs and replacements, and thus lowers costs and maintenance efforts. .