I. Analysis and solution to leakage failure caused by assembly
Mechanical seals are prone to problems when installed. The mating surfaces of the moving and static ring friction pairs may have been deformed, scratched or cracked before or during installation. The end faces are contaminated with dirt or impurities, and the spring elastic force is uneven. Will cause the machine seal to fail. After the mechanical seal is installed and debugged, a static pressure test is generally performed to observe the amount of leakage. If the leakage is small, there are problems with the moving ring or static ring seal; when the leakage is large, it indicates that there are problems with the friction ring of the moving and stationary rings. On the basis of preliminary observation of the leakage amount and judging the leakage location, the vehicle can be manually observed. If there is no obvious change in the leakage amount, the static and dynamic ring seals have problems; if there is a significant change in the leakage amount during the cranking, it can be determined that it is moving. There are problems with the static ring friction pair. If the leakage medium is sprayed in the axial direction, there are many problems in the moving ring seal ring. If the leakage medium is sprayed to the periphery or leaks from the water cooling hole, the static ring seal ring is mostly invalid. In addition, the leakage channel can also exist at the same time, but there are generally primary and secondary differences. As long as the observation is meticulous and familiar with the structure, it can be judged correctly.
II. Leakage failure analysis and solution during test operation
After the static pressure test of the mechanical seal of the slurry pump, the centrifugal force generated by the high-speed rotation during operation will inhibit the leakage of the medium. Therefore, the leakage of the mechanical seal during the test run is basically caused by the failure of the friction pair of the moving and stationary rings after the failure of the seal of the shaft and the end cap is eliminated.
The main factors causing the failure of the friction pair seal are:
1. During operation, due to abnormal phenomena such as evacuation, cavitation and rolling, a large axial force is caused, and the contact surfaces of the moving and stationary rings are separated.
2. When the mechanical seal is installed, the compression amount is too large, resulting in serious wear and abrasion of the end face of the friction pair.
3. The moving ring seal ring is too tight, and the spring cannot adjust the axial floating amount of the moving ring.
4. The static ring seal ring is too loose. When the moving ring is axially floating, the static ring is separated from the static ring seat.
5. There are granular materials in the working medium, which enter the friction pair during operation, and damage the moving and static ring sealing end faces. The above phenomenon often occurs during trial operation, and can sometimes be eliminated by appropriately adjusting the static ring seat, etc., but most of them need to be reassembled and replaced.
III. Analysis and solution to the sudden leakage failure during normal operation
The slurry pump suddenly leaks during operation, and a few are due to normal wear or have reached the service life, and most of them are caused by large changes in working conditions or improper operation and maintenance. The main reasons are as follows:
1. Evacuation, cavitation or rolling for a long time, resulting in seal damage.
2. The actual output of the pump is too small, a large number of media pumps circulate, heat accumulates, causing vaporization of the medium, resulting in seal failure.
3. Sealed cooling water is interrupted.
4. For a longer period of time, there is no manual turning when restarting, and the friction pair seal tears the sealing surface due to adhesion.
5. Corrosive, polymerizable and gelatinous substances in the medium increase.
6. The ambient temperature changes drastically.
7. Frequent changes or adjustments in working conditions.
The mechanical seal of the slurry pump usually needs to be connected to the cooling water. Before using the pump, the shaft seal water must be turned on first. After the pump is stopped for five minutes, it can be turned off. Because the cooling water is interrupted, the accident of burning the machine seal often occurs. Pay special attention to it.
If the pump starts frequently or suddenly loses power, the slurry in the pipeline will be poured back. The pressure in the pump chamber will increase sharply, which will cause the machine to seal the static ring to open, thus invalidating the machine seal. For the pump to be stopped for a long time, the pump chamber and the machine seal must be cleaned with clean water before shutdown. When restarting, the machine should be manually driven to ensure that the friction pair seal is not stuck.
IV. Wear and corrosion failure analysis and solutions
Due to the presence of abrasive particulate media in the slurry pump slurry, the following effects are imposed on the mechanical seal used:
1. Intensified wear on the sealing end face. The sealing surface enters the end surface due to particle leakage, which acts as an abrasive and accelerates the wear of the sealing surface.
2. The particles on the media side are clogged. Due to the accumulation of particles, bridging hinders the movement of the spring, the pin and the auxiliary seal, resulting in a decrease in the followability and floatability of the compensating ring.
3. The particles on the atmospheric side are clogged. Due to the small gap between the inner diameter of the sealing surface and the shaft (or the bushing), the leaked solid particles cannot be discharged in time, which tends to accumulate and block, hindering the movement of the auxiliary sealing ring, resulting in failure of the sealing.
4. Abrasion. It refers to the local seizure and tearing of the surface of the sealing element due to the action of abrasive particles, which occurs more seriously in the case of particulate media.
5. Wear of the transmission components. Since the components of the drive pin are in the granular medium, the wear of the particles is exacerbated by the grinding action of the particles during the movement.