Solid-liquid two-phase flow pump the correct selection of mechanical seal use (a)

Due to the presence of abrasive particulate media in a solid-liquid two-phase flow, the use of a general mechanical seal often constitutes the following five hazards: (1) increased wear of the sealing face. Between the sealing surface due to particle leakage into the end, plays the role of abrasive, accelerated sealing surface wear. ② media-side particle blockage. Due to the accumulation of particles, bridging hinders the movement of the spring, the pin and the auxiliary sealing ring, resulting in a reduction of followability and floating of the compensating ring. ③ air-side particle blockage. Due to the conventional design of the mechanical seal, the gap between the inner diameter of the sealing surface and the shaft (or sleeve) is small, and the leaking solid particles can not be discharged in a timely manner, which can easily accumulate and block the movement of the auxiliary sealing ring, thereby causing the sealing failure. ④ abrasion. Refers to the sealing element surface due to the role of abrasive particles generated by local bite, tear. It usually occurs when using softer steel or graphite materials due to the impact of flushing water or sealant. In the case of granular media, occurred even worse; ⑤ transmission wear. Since these components of the drive pin are in a granular medium, the abrasion of the component itself is exacerbated by the grinding action of the particles during the movement. In the selection, should make the mechanical seal products try to avoid the role of particles, will not produce these five kinds of failure, the mechanical seal to solve the problem of the role of particulate media has two ways: First, the mechanical seal set some additional internal structure or take the auxiliary Measures such as spiral seals, lip seals, sealing fluids, flushing water, tank or tank build up liquid slugs to prevent particle build-up, etc., or external devices such as swirling solids-liquid separators, magnetic filters, Appear, maintain a good working condition mechanical seal. This approach for more important occasions, important equipment can be used. However, due to space constraints or due to excessive consumption of auxiliary equipment, and because of some occasions, the material is not allowed to seal fluid or flush water into the product, you should choose to design a new type of mechanical seal structure, can be directly Used in granular media to meet the sealing requirements of the production process. In order to seal the reliable mechanical seal, long life, simple structure, easy assembly and disassembly, easy adjustment, low cost, the specific methods are as follows: The use of a combination of spring and auxiliary seal. The main advantages are: high elasticity, and the spring is not in contact with the medium, to avoid the problem of particle blockage. In order to ensure that the friction pair has the purpose of abrasion resistance and abrasion resistance in the granular medium, the hardness of the friction material must be higher than the hardness of the abrasive particles. Usually hard and hard pairs can be used, the material can be tungsten carbide or silicon carbide. Compared with tungsten carbide, silicon carbide has higher hardness, better thermal conductivity, good chemical stability, as well as self-lubricating, but the cost is higher. According to the conclusion of AIGoLubiev (former Soviet Union) et al. On the wear mechanism of high hardness friction pair in abrasive granular media, the width of the friction pair should be wider than the average mechanical seal to obtain a higher service life. Dynamic and static ring width equal to help prevent the particles on the sealing end wear and tear, at the same time, there is sufficient area to avoid large mismatch. Therefore, much larger radial and axial runout than conventional mechanical seal faces can be accommodated. Francis pump mechanical seal should be designed for inflow, particulate media outside the seal ring, the centrifugal force and inertia force of the particles, impurities outward movement, throw away from the sealing surface.