MD type wear-resistant centrifugal pumps for coal mines are widely used in mining, petroleum, chemical and other industries, and play a very important role. A slight failure of wear-resistant centrifugal pump parts may cause major mechanical and electrical accidents.
The structure and principle of MD type wear-resistant centrifugal pump for coal mine
The pump body of MD type wear-resistant centrifugal pump for coal mine is mainly composed of suction section, middle section, discharge section, balance device, sealing device and cooling device. When the motor drives the water pump to rotate at high speed, the impeller throws the fluid medium at high speed to the periphery of the blades, and transfers the high speed fluid medium to the lower impeller through the guide vanes. After gradual acceleration, a higher head can be obtained, and in general, it can meet the requirements of drainage. .
Failure analysis and treatment of parts and components of MD wear-resistant centrifugal pump used in coal mine
Impeller and mouth ring:
Most of the blades of water pump impellers are damaged due to cavitation or inhalation of solid objects and metal impurities. The wear of the mouth ring (also known as the sealing ring) is generally caused by improper wear during the installation process, or the back cap of the impeller may loosen and cause the wear of the mouth ring. If the mouth ring is severely worn, the impeller should be replaced; if the mouth ring is lightly worn, it can be repaired.
Balance device:
If the balance disc and the balance ring are worn too much (usually more than 2mm) or unevenness, first repair welding or grinding the groove on the pump casing, and add a 3mm thick tetrafluoroethylene gasket at the joint surface of the balance ring and the pump casing . In this way, the unevenness of the flat plate caused by manual grinding after repair welding is eliminated, and the gasket material is moderately soft and hard. Replace the balance ring and balance plate with a new one when there is too much wear
Machinery Seal:
The mechanical seal has a pair of end faces perpendicular to the axis of rotation. The end faces rely on the cooperation of the auxiliary seal under the action of fluid pressure and compensating the mechanical external elastic force to keep close to the other end and slide relatively to prevent fluid leakage. The proportion of mechanical seal leakage accounts for more than 50% of all maintenance pump leakage. The operation of mechanical seal directly affects the normal operation of the pump. The leakage of the mechanical seal will cause the axial movement of the pump rotor to increase, and the interference between the auxiliary seal and the shaft will increase, and the moving ring cannot move flexibly on the shaft. When the pump is turned over, the displacement of the dynamic and static rings cannot be compensated after they are worn out. When the assembly machinery is sealed, the axial window momentum of the shaft should be less than 0.1mm, and the interference between the auxiliary seal and the shaft should be moderate. While ensuring the radial seal, it is also necessary to ensure that the movable ring can move flexibly on the shaft after assembly. The movable ring can spring back freely when pressed against the spring).
Pump shaft:
The pump shaft is the core part of the rotor. It is equipped with an impeller and a shaft sleeve and rotates at a high speed in the pump body. The concentricity deviation of the pump shaft bending bearing seat and the pump shaft will cause wear of the impeller, guide vane, pump casing, seal ring and shaft sleeve, which will increase the vibration of the pump body and increase the axial thrust. The balance disc and the balance seat There is friction. As long as the pump shaft does not produce cracks and serious surface wear or bending, it can be repaired and used. The bending amount of the shaft cannot exceed 0.06mm, and it should be straightened when it is greater than this value.It is best to use a screw press to straighten it without heating.
Bearing temperature:
The factors that cause the bearing temperature rise to be too high and eventually burn the bearing are: ①The balance drum has a poor effect of balancing the axial force, and the residual axial force is too large to cause excessive bearing load. ②The lubricating oil is unqualified, the amount of oil is insufficient, or impurities such as iron filings in the oil cavity enter the bearing. ③ Excessive angle error of pump bearing will increase bearing load. ④ Insufficient bearing clearance or cross positioning of the inner and outer rings of the bearing causes the inner and outer rings to be misaligned, which increases the load.
Axial movement of rotor:
After the pump is assembled, the overall displacement of the rotor should be measured. Do not install the balance plate first, install a shaft sleeve where the balance plate is installed and use a lock nut to lock it together with the rotors of all levels into a rigid body. First push the rotor in the suction direction so that the seal rings of the impeller and the pump body are close. Use the depth gauge to measure the distance a from the shaft shoulder to a certain plane of the pump body. Then pull the rotor to the discharge side so that the back cover of the impeller is close to the guide vane. The distance measured at this time is b, and a-b is the total displacement of the pump. After measuring the total channeling volume, compare it with the channeling volume value given in the pump manual. If the measured value is greater than the given value 1mm, the worn impeller should be replaced. If the amount of axial movement is large, it is allowed to add an adjustment pad with a smooth surface and uniform thickness between the balance plate and the balance ring.
Coupling clearance:
During the operation of the wear-resistant centrifugal pump used in coal mines, the rotor will continue to move to the suction side as the balance plate wears out. Therefore, the clearance of the coupling should be adjusted appropriately during maintenance. Taking into account the influence of thermal expansion of the pump shaft, according to the relevant maintenance standards, the gap of the coupling should be 2-3mm larger than its specified value.
