Mechanical seal repair

Mechanical seal repair

The mechanical seal is a sealing device composed of two sealing elements (static ring and moving ring) perpendicular to the shaft, and the smooth and flat surfaces are mutually abutted and rotated relative to each other. It generates a proper pressing force on the contact surface (end surface) of the rotating moving ring and the static ring by the pressure of the sealing medium, so that the two end faces are tightly combined, and a very thin liquid film is maintained between the end faces to achieve sealing. Purpose. This liquid film has hydrodynamic pressure and static pressure, and plays a role in lubricating balance.

1. Cleaning and inspection of mechanical seals

1) The working principle of the mechanical seal requires no impurities inside the mechanical seal. Thoroughly clean the moving ring, static ring, bushing and other components before assembling the mechanical seal.

2) Check the surface of the static and dynamic ring for defects such as scratches and cracks. These defects may cause serious leakage of the mechanical seal. Conditional can use special tools to check whether the sealing surface is flat, the sealing surface is not flat, the pressure water will enter the dynamic and static ring sealing surface of the mechanical seal after assembly, the static and dynamic rings will be separated, and the mechanical seal will be invalid. If necessary, the tooling can be used to test the hydraulic pressure before assembly.

3) Check if the static and dynamic ring seat has defects that affect the seal. For example, if there is a defect in the surface of the dynamic ring seat and the static and dynamic ring seal ring.

4) Check whether the mechanical seal compensation spring is damaged or deformed, and whether the reluctance coefficient changes.

5) Check the seal bushing for defects such as burrs and groove marks.

6) Clean and inspect all seal rubber rings for defects such as cracks and blowholes, and measure whether the diameter of the rubber ring is within the tolerance range.

7) The mechanical seal with the pumping mechanism should also check whether the spiral of the screw pump has defects such as cracks and broken wires.

2. Mechanical seal assembly technology size check

1) Measure the size of the static and dynamic ring sealing surface. The data is used to verify the radial width of the static and dynamic ring. When different friction materials are used, the radial width of the friction surface of the hard material should be 1~3mm larger than the soft one. Otherwise, the edge of the hard material end surface is embedded in the end surface of the soft material. Go up.

2) Check the gap between the static and dynamic ring and the shaft or bushing. The inner diameter of the static ring is generally 1~2mm larger than the shaft diameter. For the moving ring, to ensure the floating, the inner diameter is 0.5~1mm larger than the shaft diameter to compensate the vibration of the shaft. And skew, but the gap can not be too large, otherwise the moving ring seal will be stuck and cause mechanical seal function damage.

3) Check the mechanical seal tightness. The mechanical sealing force we usually talk about is the end face specific pressure, the end face specific pressure should be suitable, too large, will make the mechanical seal friction surface heat, accelerate the end face wear, increase the friction power; too small, easy to leak. The end face specific pressure is determined during the mechanical seal design. We can only determine the mechanical seal tightness when assembling. The usual measurement method is to measure the vertical distance from the installed static ring end face to the end face of the gland, and then measure the vertical distance from the end face of the moving ring to the end face of the gland. The difference between the two is the tightness of the mechanical seal.

4) Measure whether the length of the compensation spring changes. Changes in spring performance will directly affect the specific pressure of the mechanical seal face. Under normal circumstances, the length of the spring will be shortened after a long time of operation, and the mechanical seal of the compensation spring on the moving ring will also be deformed due to centrifugal force.

5) Measure the length of the static ring anti-rotation pin and the depth of the pin hole to prevent the pin from being too long to be assembled in place. This condition can damage the mechanical seal.

3. Grinding of moving ring and static ring end face

1) After the moving ring is removed, after grinding, the rough grinding is carried out first, followed by the fine grinding, and the condition can be polished.

2) When rough grinding, use abrasives with a particle size of 80 to 160 #, and first remove the processing marks. Fine grinding can then be carried out with more than 160# abrasives to achieve the design requirements. After the cemented carbide or ceramic moving ring is refined, it needs to be polished with a polishing machine. The strength of the polishing machine can be selected from boron carbide of M28 to M5. After polishing, it reaches the mirror surface. The ceramic ring can be polished with chrome oxide after fine grinding with M5 agate powder.

3) The static ring of graphite filled polytetrafluoroethylene, due to the soft material, can be refined with kerosene, gasoline or water, without adding abrasive. In the process of running and running, you can also self-develop, so the finish requirements are not too high.

4) Grinding method, the grinder can be ground on the grinder, and the grind-free method can be used on the flat glass by a figure-shaped manual grinding method.

4. Bushing inspection

1) Check the rust and wear after inspection and removal of the bushing. If the rust or wear is relatively slight, use fine sandpaper to illuminate the light. If the rust or wear is serious, use the post-processing electroplating method or replace the bushing. .

5. Sealing ring

1) After a period of use, the seal ring loses its elasticity or aging in most cases. In general, it needs to be replaced with a new one.

6. Spring

1) If the spring is not rusted, it can maintain its original elasticity and can not be replaced. If the rust is severe or the elasticity is much reduced, a new spring needs to be replaced.

2) For mechanical seals with assembled boxes, clean the box and check for worn or deformed grooves for corrective repair, re-grooving or replacement.

3) After the mechanical seal is repaired, reassemble it, and after the assembly, the pressure test is also performed, and then put into normal operation. (Source: Sealed Net)

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Hebei Innovation Sealing Material Co., Ltd.

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'Overhaul of mechanical seals

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