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Accurate selection and application of mechanical seals for solid-liquid two-phase flow pumps
by：Lepu Seal
2022-09-21
Accurate selection and application of mechanical seals for solid-liquid two-phase flow pumps
Accurate selection and application of mechanical seals for solid-liquid two-phase flow pumps?
Because of the existence of abrasive particle medium in the solid-liquid two-phase flow, the usual mechanical seals for mechanical seals for kettles often cause the following five kinds of damage: 1. Increased wear of the sealing end face. Between the sealing surfaces, the particles leak into the end surface, which plays an abrasive effect and accelerates the wear of the sealing surface. ②The particles on the medium side are blocked. Because of the accumulation of particles, the bridging prevents the movement of the spring, pin and auxiliary seal ring, and then causes the followability and floatability of the compensation ring to decrease. ③ Atmospheric particle blockage. Due to the conventionally designed mechanical seal, the gap between the inner diameter of the sealing surface and the shaft (or shaft sleeve) is small, and the leaking solid particles cannot be discharged in time, which is easy to accumulate and block, which prevents the movement of the auxiliary seal ring, and then causes the seal to fail. ④Abrasion. Refers to the partial bite and tear of the mechanical seal of the kettle due to the effect of abrasive particles on the surface of the sealing element. It usually occurs when using softer steel or graphite materials due to the impact of flushing water or sealing fluid. In the presence of particulate media, it will be more severe; ⑤ Wear of transmission elements. Because these elements of the drive pin are in the particle medium, the wear of the elements itself is aggravated by the grinding effect of the particles during movement. When selecting models, the mechanical seal products should be made to prevent the effect of particles as much as possible, so that these five kinds of failures will not occur. There are two major paths for the mechanical seal to deal with the effect of particle media: one is to set some additional internal structures for the mechanical seal or adopt auxiliary Methods (such as screw seal, lip seal, sealing liquid, flushing water, water tank or fuel tank to establish a liquid barrier to prevent particle accumulation, etc.), or external equipment (such as cyclone solid-liquid separator, magnetic filter, etc.), try to avoid the above five kinds of failures Present and maintain the excellent working condition of the mechanical seal. This approach is important for situations where contrast is important and important equipment can be used. However, because of space constraints, or because the auxiliary equipment cost is too high, and because in some cases, the material does not allow sealing liquid or flushing water to enter the product, a new type of mechanical seal structure should be selected and designed, which can It is directly used in granular media to meet the sealing requirements of the production process. In order to make the mechanical seal achieve the purpose of reliable sealing, long service life, simple structure, convenient assembly and disassembly, easy adjustment and low cost, the specific methods are as follows: use a combination of tension spring and auxiliary sealing ring. The main advantage is: high elasticity, and the spring does not touch the medium, preventing the problem of being easily blocked by particles. In order to ensure that the abrasive pair has the purpose of wear resistance and abrasion resistance in the granular medium, the hardness of the abrasive pair material must be higher than that of the abrasive particles. Usually hard-to-hard pairing can be selected, and the raw material can be tungsten carbide or silicon carbide. Compared with tungsten carbide, silicon carbide has higher hardness, better thermal conductivity, better chemical stability, and self-smoothing, but higher cost. According to the conclusion drawn by A.I.GoLubiev (the former Soviet Union) and others on the wear mechanism of high-hardness conflict pair in abrasive granular media, the width of the conflict pair should be wider than that of the usual mechanical seal in order to obtain a higher service life. The width of the dynamic and static rings is equal, which is beneficial to prevent the wear of the sealing end face by the particles, and at the same time, there is enough area to prevent large mismatch. Thus, much larger radial and axial runout than usual mechanical seal faces can be used. The mechanical seal of the mixed-flow pump should be designed as an internal flow, and the particle medium is outside the seal ring. The effect of centrifugal force and inertial force makes the particles and impurities move outward and throw away from the sealing surface. Different from the usual mechanical seals, the gap between the shaft sleeve and the seal ring should be large. When there is material leakage, it can be discharged in time to prevent the accumulation and blockage of particles. The design of the sealed cavity must have an appropriate space, so that the materials in the sealed cavity can move, not accumulate sediment, and be easy to cool and seal smoothly. In order to reduce the influence of the medium pressure in the pump on the specific pressure of the seal face, a balanced mechanical seal structure is selected. The specific pressure of the end face is one of the most important factors affecting the sealing function and service life. In order to prevent the particulate medium from entering the seal end face, the leakage increases, the end face wear is aggravated, and the seal fails, the end face specific pressure should be larger than usual. However, if the specific pressure of the end face is too large, the heating and wear of the conflicting surface will increase, and the power consumption will increase. When planning, the specific pressure of the end face is about 0.3MPa. When using a single-end mechanical seal, in order to prevent the damage of particles and impurities, it is necessary to adopt methods such as washing, filtration, separation, isolation, insulation, heat preservation and heating according to different conditions. The reliability and quality of the flushing fluid is the key to the success of sealing. If the cleaning and flushing fluid is written from the outside, the sealed working environment can be improved, but the flushing fluid must be lost, and the prerequisite is that the fluid delivered is allowed to be slightly diluted by the flushing fluid. When a double-end mechanical seal is used, the sealing liquid is required to establish pressure in the sealing cavity for sealing, smoothing and cooling cycles. The double-end seal has high reliability,But the manufacturing cost and installation cost are higher. The selection of materials for most double seal groups is standardized. In practical application, the collision pair at the dielectric end uses a cemented carbide pair or a silicon carbide pair; the carbon graphite and nickel-chromium steel pair at the atmospheric end are used.
Accurate selection and application of mechanical seals for solid-liquid two-phase flow pumps?
Because of the existence of abrasive particle medium in the solid-liquid two-phase flow, the usual mechanical seals for mechanical seals for kettles often cause the following five kinds of damage: 1. Increased wear of the sealing end face. Between the sealing surfaces, the particles leak into the end surface, which plays an abrasive effect and accelerates the wear of the sealing surface. ②The particles on the medium side are blocked. Because of the accumulation of particles, the bridging prevents the movement of the spring, pin and auxiliary seal ring, and then causes the followability and floatability of the compensation ring to decrease. ③ Atmospheric particle blockage. Due to the conventionally designed mechanical seal, the gap between the inner diameter of the sealing surface and the shaft (or shaft sleeve) is small, and the leaking solid particles cannot be discharged in time, which is easy to accumulate and block, which prevents the movement of the auxiliary seal ring, and then causes the seal to fail. ④Abrasion. Refers to the partial bite and tear of the mechanical seal of the kettle due to the effect of abrasive particles on the surface of the sealing element. It usually occurs when using softer steel or graphite materials due to the impact of flushing water or sealing fluid. In the presence of particulate media, it will be more severe; ⑤ Wear of transmission elements. Because these elements of the drive pin are in the particle medium, the wear of the elements itself is aggravated by the grinding effect of the particles during movement. When selecting models, the mechanical seal products should be made to prevent the effect of particles as much as possible, so that these five kinds of failures will not occur. There are two major paths for the mechanical seal to deal with the effect of particle media: one is to set some additional internal structures for the mechanical seal or adopt auxiliary Methods (such as screw seal, lip seal, sealing liquid, flushing water, water tank or fuel tank to establish a liquid barrier to prevent particle accumulation, etc.), or external equipment (such as cyclone solid-liquid separator, magnetic filter, etc.), try to avoid the above five kinds of failures Present and maintain the excellent working condition of the mechanical seal. This approach is important for situations where contrast is important and important equipment can be used. However, because of space constraints, or because the auxiliary equipment cost is too high, and because in some cases, the material does not allow sealing liquid or flushing water to enter the product, a new type of mechanical seal structure should be selected and designed, which can It is directly used in granular media to meet the sealing requirements of the production process. In order to make the mechanical seal achieve the purpose of reliable sealing, long service life, simple structure, convenient assembly and disassembly, easy adjustment and low cost, the specific methods are as follows: use a combination of tension spring and auxiliary sealing ring. The main advantage is: high elasticity, and the spring does not touch the medium, preventing the problem of being easily blocked by particles. In order to ensure that the abrasive pair has the purpose of wear resistance and abrasion resistance in the granular medium, the hardness of the abrasive pair material must be higher than that of the abrasive particles. Usually hard-to-hard pairing can be selected, and the raw material can be tungsten carbide or silicon carbide. Compared with tungsten carbide, silicon carbide has higher hardness, better thermal conductivity, better chemical stability, and self-smoothing, but higher cost. According to the conclusion drawn by A.I.GoLubiev (the former Soviet Union) and others on the wear mechanism of high-hardness conflict pair in abrasive granular media, the width of the conflict pair should be wider than that of the usual mechanical seal in order to obtain a higher service life. The width of the dynamic and static rings is equal, which is beneficial to prevent the wear of the sealing end face by the particles, and at the same time, there is enough area to prevent large mismatch. Thus, much larger radial and axial runout than usual mechanical seal faces can be used. The mechanical seal of the mixed-flow pump should be designed as an internal flow, and the particle medium is outside the seal ring. The effect of centrifugal force and inertial force makes the particles and impurities move outward and throw away from the sealing surface. Different from the usual mechanical seals, the gap between the shaft sleeve and the seal ring should be large. When there is material leakage, it can be discharged in time to prevent the accumulation and blockage of particles. The design of the sealed cavity must have an appropriate space, so that the materials in the sealed cavity can move, not accumulate sediment, and be easy to cool and seal smoothly. In order to reduce the influence of the medium pressure in the pump on the specific pressure of the seal face, a balanced mechanical seal structure is selected. The specific pressure of the end face is one of the most important factors affecting the sealing function and service life. In order to prevent the particulate medium from entering the seal end face, the leakage increases, the end face wear is aggravated, and the seal fails, the end face specific pressure should be larger than usual. However, if the specific pressure of the end face is too large, the heating and wear of the conflicting surface will increase, and the power consumption will increase. When planning, the specific pressure of the end face is about 0.3MPa. When using a single-end mechanical seal, in order to prevent the damage of particles and impurities, it is necessary to adopt methods such as washing, filtration, separation, isolation, insulation, heat preservation and heating according to different conditions. The reliability and quality of the flushing fluid is the key to the success of sealing. If the cleaning and flushing fluid is written from the outside, the sealed working environment can be improved, but the flushing fluid must be lost, and the prerequisite is that the fluid delivered is allowed to be slightly diluted by the flushing fluid. When a double-end mechanical seal is used, the sealing liquid is required to establish pressure in the sealing cavity for sealing, smoothing and cooling cycles. The double-end seal has high reliability,But the manufacturing cost and installation cost are higher. The selection of materials for most double seal groups is standardized. In practical application, the collision pair at the dielectric end uses a cemented carbide pair or a silicon carbide pair; the carbon graphite and nickel-chromium steel pair at the atmospheric end are used.
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