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Performance and causes: mechanical seal failure of reducer

fubao speed reducer

1. Mechanical seal parts failure

In the operation of rotating equipment, the sealing end face often appears wear, hot cracking, deformation, damage and so on, and the spring will relax, break and corrode after long use. The auxiliary sealing ring will also be cracked, twisted, deformed and broken.

2. Mechanical seal vibration, heating fault causes

During the rotation of the equipment, the end face of the moving and static rings will be rough, and the gap between the moving and static rings and the sealing cavity is too small, which will cause vibration due to the collision caused by vibration. Sometimes, due to the poor corrosion resistance and temperature resistance of the seal end face, or insufficient cooling or particle impurities in the end face during installation, the vibration and heat of the mechanical seal will also be caused.

3. The failure cause of mechanical sealing medium leakage

3.1— Leakage during static pressure test

When mechanical seal is installed carelessly, it often causes the seal end face to be bruised, deformed and damaged, and it is not cleaned cleanly, with granular impurities, or because the positioning screw is loose, the gland is not pressed tightly, and the precision of the machine and equipment is not enough, so that the sealing surface is not completely attached, which will cause media leakage. If the shaft sleeve leaks, the shaft sleeve sealing ring is not pressed or compressed enough or damaged during assembly.

3.2— Periodic or paroxysmal leakage

The periodic vibration and excessive axial channeling of the rotor assembly of mechanical seal will cause leakage. The sealing surface of mechanical seal should have a certain specific pressure, so as to play a sealing role, which requires that the spring of mechanical seal should have a certain amount of compression, give a thrust to the sealing end surface, and rotate to make the sealing surface produce the specific pressure required for sealing.

In order to ensure this specific pressure, the mechanical seal requires that the pump shaft should not have too much channeling, generally within 0.25 mm. However, in the actual design, due to the unreasonable design, the pump shaft often produces a large amount of channeling, which is very unfavorable to the use of mechanical seals.

3.3— Frequent leakage of mechanical seal

There are many reasons for the frequent leakage of mechanical seals of reducer.

On the one hand, frequent leakage caused by defects in the sealing end face.

The second aspect is the frequent leakage caused by the auxiliary sealing ring.

The third aspect is the leakage caused by spring defects.

Other aspects include leakage caused by rotor vibration, leakage caused by poor quality or looseness of transmission, fastening and thrust parts, leakage caused by auxiliary mechanism of mechanical seal, frequent leakage caused by medium problems, etc.

3.4— Mechanical seal vibration is too large.

The vibration of mechanical seal is too large, which eventually leads to the loss of sealing effect. However, the vibration of mechanical seal is often caused not only by the mechanical seal itself, but also by other parts of the pump, such as unreasonable design of pump shaft, processing reasons, insufficient bearing accuracy, poor parallelism of coupling, large radial force and so on.

Third, the measures taken to deal with the fault of gear reducer

If the mechanical seal parts fail, it is necessary to replace the parts or improve the machining accuracy of the parts. Improving the machining accuracy of the mechanical seal itself and other parts of the pump body is very beneficial to the effect of the mechanical seal. In order to improve the sealing effect, the smoothness and roughness of the friction surface of the dynamic and static rings are required. The width of the friction surface of the dynamic and static rings is not large, generally between 2 and 7 mm.

1. Treatment of vibration and fever of mechanical seal

If the gap between the dynamic and static rings and the sealing cavity is too small, it is necessary to increase the inner diameter of the sealing cavity or decrease the rotating outer diameter to ensure at least a gap of 0.75 mm. If the friction pair is not properly matched, it is necessary to change the material of the dynamic and static rings to make them resistant to temperature and corrosion. This will reduce the vibration and heat of the mechanical seal.

2. Handling of mechanical seal leakage

The leakage of mechanical seal is caused by many reasons, so we need to deal with the specific problems. In order to minimize the leakage, the mechanical seal must be assembled in strict accordance with the technical requirements, and the following matters should also be paid attention to.

2.1— The assembly shall be clean and bright.

Mechanical seal parts, tools, lubricating oil and wiping materials should be very clean. The sealing end face of the dynamic and static ring should be wiped with soft gauze.

2.2-Trimming chamfer and rounding

The chamfers of shaft and sealing end cover should be trimmed smoothly, and the relevant rounded corners of shaft and end cover should be sanded and polished.

2.3— When assembling the auxiliary sealing ring, the rubber auxiliary sealing ring should not be soaked and washed with gasoline or kerosene to avoid swelling and deformation and premature aging. After the assembly of dynamic and static rings, press the compensation ring by hand to check whether it is in place and flexible; Whether the elastic split ring is positioned reliably. After the moving ring is installed, it must be ensured to move flexibly in the axial direction on the shaft.

3. Treatment of large amount of pump shaft channeling

Reasonably design the balance device of axial force to eliminate axial channeling. In order to meet this requirement, for multi-stage centrifugal pump, the design scheme is: balance plate with axial thrust bearing, balance the axial force by balance plate, and axially limit the pump shaft by axial thrust bearing.

4. Add auxiliary flushing system

The sealing medium in the sealing cavity contains particles and impurities, so it must be washed. Otherwise, the spring of the mechanical seal will fail due to the precipitation of crystals and the deposition of particles and impurities. If the particles enter the friction pair, the mechanical seal will be quickly destroyed. Therefore, the auxiliary flushing system of mechanical seal is very important, which can effectively protect the sealing surface and play a role in cooling, lubricating and washing away impurities.

Link: Fubao Mechanical >> Performance and causes: mechanical seal failure of reducer

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