Gear oil pump often chooses mechanical seal to prevent leakage when conveying high temperature and high pressure oil, and mechanical accident caused by leakage accounts for about 50% of the total maintenance of vertical roller mill oil pump. It can be seen that the reliability of mechanical seal is efficient for oil pump operation. And the extension of service life is of vital importance.
Mechanical seals are generally composed of auxiliary components such as a rotating ring, a stationary ring, a seal ring or a gasket, and an elastic compensating element. The working principle is that a pair of end faces perpendicular to the rotation axis are fitted to each other and relatively rotated, and a very thin liquid film is maintained between the end faces. Under the cooperation of the auxiliary seal, the end faces are subjected to the medium fluid pressure and compensate the mechanical elastic force. The role of maintaining a close fit to achieve the purpose of sealing.
Reasonable design is the basis for the mechanical seal to achieve its function, but the overall design optimization of the oil pump, the selection of equipment accessories, and the choice of material of each component directly affect the sealing performance of the vertical roller mill oil pump.
Taking the magnetic separator in the oil pump as an example, the component not only has the disadvantages of being unable to separate and filter non-metallic particles, is bulky, and is difficult to be repaired, but may also cause the rotation of these and non-metallic materials due to the metallic substances in the magnetic adsorption oil. The moving ring or the stationary ring generates friction, which causes the wear of the component. The non-metallic substance produced by the wear and tear enters the system due to the inability to be adsorbed and filtered to increase the wear, and the long-term operation inevitably leads to a decrease in the sealing performance.
Improper construction of the installation can also cause seal damage. If the hexagon socket screw that is axially positioned in the mechanical seal is not tightly installed, the seal will axially move. When the amount of turbulence is too large, the compression spring cannot make the stationary ring close to the rotating ring. Causing leakage; the shaft end face of the ring seal and the sealing gland end face of the static ring seal ring are not clean enough, which may damage the swivel ring and the stationary ring during installation; and the spring compression of the mechanical seal is also the focus of the installation. The error is less than ±2mm, which may increase the end face specific pressure and friction heat due to the excessive compression. The wear and thermal deformation of the end face are intensified, or the specific pressure of the end face of the stationary ring is insufficient due to the small amount of compression, which affects the sealing effect.
1) Installation is too tight
Observe the static and dynamic ring plane of the mechanical seal. If there is severe scorching, the plane will be black and deep, and the sealing rubber will become hard or lose elasticity. This is caused by the installation being too tight.
Treatment method: adjust the installation height. After the impeller is installed, pull the spring with a screwdriver. The spring has a strong tension. After the release, it is reset, and there is a moving distance of 2-4mm.
2) Installed too loose
Observing machine seals, static ring plane, its surface has a thin layer of grease (can be wiped off), and the surface is basically no wear, which is caused by the loss of elasticity and assembly of the spring, or caused by the axial movement of the motor. .
For example, the pump cover is caused by a static ring chamber. The static ring indoor hole has large dimensional error and rough surface. The phenomenon of performance is that the oil is injected from the axial direction, there is a gap between the static ring and the inner hole, or the inner hole is rough, the static ring is rotated, and the rubber is worn.
1) Pressure causes leakage.
When the pressure in the sealed chamber is less than 3 MPa during use, the end face may be overpressured, the liquid film is difficult to form, the sealing end face is seriously worn, and the heat generation is increased, resulting in thermal deformation of the sealing surface. In the process of starting and stopping the pump, due to the blockage of the pump inlet and the gas contained in the pumping medium, negative pressure may occur in the sealing chamber, which may cause dry friction of the sealing end face, and the internal mechanical seal may cause oil leakage.
2) Media problems.
First of all, because the auxiliary components such as the sealing ring often use organic materials that are not resistant to acid and alkali and high temperature, when the medium contains weak acid and weak alkali, the long-term use will make it lose its elasticity or even rot; when solid particles and other substances appear in the medium. It will also scratch the end face and cause wear, and grease, oil and the like may also accumulate on the shaft surface. In addition, excessive oil temperature is also the main cause of the decline in mechanical seal performance, so when the cooling capacity of the heat exchanger is insufficient, the service life of the seal is often greatly shortened.
3) Fatigue damage to the rotating ring and the stationary ring.
Inconsistent oil pump axis or improper adjustment of bearing clearance will cause vibration of the oil pump, and vibration will cause friction in the static and dynamic parts of the mechanical seal assembly, even if the oil film on the contact surface is damaged, causing it to lose oil film lubrication and damage.
4) Lack of production management.
The unit is not working according to the operating procedures. Improper opening and closing or human error causes the power supply to fluctuate and the oil pump may reverse.
5) Dry grinding damage caused by lack of oil operation.
This phenomenon is more common in the negative pressure at the inlet of the bottom valve type installation. There is air in the inlet pipe. There is air in the pump cavity. After the pump is turned on, the friction of the machine seal is high during high-speed operation, and cooling cannot be obtained. Check the machine seal and spring tension. Normal, the friction surface is burnt black, and the rubber hardens and cracks.
Treatment: Discharge the air in the channel and the pump chamber or replace the mechanical seal.
6) There is gas, which is mainly generated by the hot oil pump.
Since the medium is hot oil, the oil temperature is too high to generate steam, and the vapor in the pipeline enters a high place in the pump chamber, and this part of the vapor can not be eliminated, thereby causing oil shortage operation, and the machine seal dry grinding fails.
7) Mechanical sealant failure.
The main reason is the aging and deformation of the old rubber parts of the rubber parts, mainly the deformation and deformation in the hot oil pump. The phenomenon of failure of mechanical sealant is that the oil temperature is too high and the medium dissolves the rubber. From the appearance, the surface of the rubber member is loose, rough, and loses elasticity, thereby causing the rubber to fail.