Shielded electric pumps are widely used in chemical industry, nuclear industry and other important occasions to solve the problems that many general pumps cannot solve. However, with the rapid development of science and technology, many new topics have been proposed for shielded electric pumps.
The biggest feature of the shielded electric pump is that the motor part and the pump part are integrated, that is, share a single motor shaft, thereby eliminating the intermediate connection part, thereby solving the leakage problem that is very difficult to solve in the dynamic seal. However, the leakage mentioned here is only relative to the external environment. In fact, this part of the leakage still exists for the pump, but this part of the leakage does not leak to the external environment, but directly “leaks†into the shield motor. In the case where solid particles are contained in the transport medium, what kind of consequences will occur if the transport medium containing solid particles “leaks†into the interior of the shield motor, how will this problem be solved, and 2 the medium containing the solid particles is transported? The impact of shielded electric pump As the shielded electric pump generally uses graphite bearing and surfacing (or spray welding) cemented carbide bearing sleeve constitute the friction, "leakage" to the shield motor internal solids containing medium must flow through the graphite bearing Under normal circumstances, this part of the transmission medium can play the role of lubricating the bearings, and at the same time take away the heat generated by the shielded motor losses, and play the role of cooling. However, when the transmission medium contains solid particles, the solid particles are When passing through the gap between the graphite bearing and the bearing sleeve, friction occurs with the graphite bearing and the bearing sleeve. Accelerated wear graphite sleeve bearings and bearing friction pay once badly worn, or in the process of wear and tear, will not provide normal pump flow and pressure head, or even result in downtime or burning motor.
3 Theoretical analysis In order to solve the above problems, we may wish to do a test to fix a rolling bearing on the top of an inverted container. For example, when we put them together vertically into the liquid, we consider the air as the ideal gas, according to The Boyle-Maotte law can be obtained: the difference between the volume of the inner cavity of the container and the volume of the rolling bearing); V, the volume of the air in the container after the liquid level rises; P0 - atmospheric pressure; P/ - The pressure of the air in the container after the liquid level has risen.
The theoretical analysis of the test schematic increases and the liquid level rises. When the pressure of the air in the container rises to a certain value, this value is the same as the pressure outside the container, ie the pressure inside and outside the container rises above the liquid level in the container. When equilibrium is reached, the liquid level no longer rises.
Therefore, as long as the liquid pressure P2 and the net volume of the rolling bearing are removed from the container at this time, the final volume occupied by the air in the container can be pushed back using the Boyle-Martin specific law, so that the liquid level can be obtained under the pressure of P2. How much is raised, the position of the liquid surface must be able to ensure that the rolling bearings used are not in contact with the liquid surface. Taking into account fluctuations in the liquid level in the vessel and changes in pressure P2, the above calculated values ​​should be given sufficient margin.
4 Practical Applications Using the conclusions from the above tests, we developed a vertical shielded electric pump with a gas-tight bearing structure. The electric pump sets an upside down, inner hollow, and an upper end of the shield motor's rotor lower bearing stage into a closed cylindrical body welded to the shaft. The cylinder is welded to the rotor and rotates with the rotor. Cylindrical cylinders and rotors must be airtightly tested after welding to ensure that the sealed bearing cavities formed by the cylinders and rotors do not leak (eg).
Through careful design of the structure, the rolling bearing is positioned in the axial direction. The upper bearing is simpler in structure than the lower bearing and directly increases the axial length of the upper bearing room. At this time, the central axis of the rotor is also correspondingly lengthened, ie the same is used. The conclusion drawn from the test is that the upper bearing is mounted on the upper part of the upper bearing chamber, and the lower part is left with a liquid surface rising distance so that the upper bearing does not come into contact with the conveying medium (for example).
At this time, the circulation path of the transmission medium “leaked†to the shield motor also changes. Since the “leakage†to the shielded motor inside the transmission medium does not need to lubricate the rolling bearing, it is mainly from the shield motor upper stator and rotor. The backflow to the pump portion serves to cool the shield motor, which can reduce this portion of the "leakage" flow, ie, reduce the volume loss. Due to the change of the circulation route, the resistance at the time of circulation of the transmission medium “leaked†into the shield motor is reduced, thereby reducing the energy required to circulate this part of the transfer medium.
The vertical shielded electric pump has no problem in the actual use process, solves the problem of containing solid particles in the conveying medium, and satisfies the user's use requirements.
5 Concluding remarks The gas-shielded bearing structure of this type of vertical shielded electric pump utilizes the principle that the pressure of the gas-specific law gas changes with the change of volume. The use of rolling bearings instead of graphite bearings solves the problem of graphite bearings and stacks. Welding sleeves made of welded (or spray-welded) cemented carbide have the disadvantages of high cost and short cycle time. The heaviest (up from page 9) can be changed without loss of power and without stopping. Switch. Since the high speed pole is started with S = 0.5, the starting current is smaller. Similarly, the same is true for low speed poles and medium pole speed poles. Therefore, the use of independent windings for each pole can reduce the electrical losses during the pole-changing process.
When the pole-changing speed-regulating motor is switched from high-speed pole to medium-speed pole or medium-speed pole to low-speed pole-change pole, the motor is in regenerative braking state, so that the inrush current and torque are greater than when the electric state is started, resulting in great electric Loss and impact. If independent windings are used for each pole number, when the pole-changing is switched, the two kinds of pole numbers will be run in series and then switched to the desired number of poles. Since the equivalent impedance of the two windings in series is greater than the equivalent impedance of the individual windings, this method can effectively reduce the inrush current and torque during regenerative braking, and reduce losses and shocks. For example, a 4/8/32-pole 22/22/5kW variable-pole speed-regulating motor adopts this method, and the inrush current from 4-pole to 8-pole is reduced from 280A to 46A when the direct pole is changed, so the electrical loss Will be greatly reduced.
4 Conclusion In summary, to design an energy-saving tower crane dedicated pole-changing is to solve the problem that the general shielded electric pump can only transport medium without solid particles.
However, this type of vertical shielded electric pump also has its place to be developed, for example, it is required for the solid particles in the transmission medium, and has a certain range. Solid particles can not be too large, and can not be too hard, because although it solves the solid particles do not affect the bearing, but there are great wear on the impeller front and rear mouth ring and stator and rotor shields, especially when the solid particles are very When large, it can even block the normal circulation route of the conveying medium inside the shield motor, so that the shielded electric pump can not work normally.
What is more worth mentioning is that this type of vertical shielded electric pump adopts the rolling bearing structure, which makes the structure of the vertical shielded electric pump relatively complex compared with the general shielded electric pump using the graphite bearing, and the vertical type The shielded electric pump must be vertically mounted vertically.
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