Magnetic drive pump, abbreviated as magnetic pump. Like shielded pumps, there is only a static seal in the structure without a dynamic seal. So there can be no leakage when transporting liquids. Used in the transportation of flammable, explosive, volatile, toxic, corrosive, and valuable liquids in petrochemical systems.
The main structure of this pump is still a centrifugal pump. But the drive adopts the principle of magnetic transmission. The electric motor is connected to the external magnetic steel through a coupling. The impeller is connected to the inner magnetic steel. There is a fully sealed isolation sleeve between the inner and outer magnetic steels, which completely separates the inner and outer magnetic steels and keeps them in the medium.
The shaft of the electric motor directly drives the impeller to rotate synchronously through the attraction of the magnetic poles between the magnetic steels. The main components of a magnetic pump are the pump body, impeller, inner magnetic steel, outer magnetic steel, isolation sleeve, pump inner shaft, pump outer shaft, as well as sliding bearings, rolling bearings, couplings, etc. The key component is the magnetic coupling.
It is composed of inner magnetic steel, (including guide ring and sleeve), outer magnetic steel (including guide ring), and isolation sleeve. The material selection of internal and external magnetic steels has a significant impact on the efficiency and reliability of magnetic pumps.
At present, the commonly used materials are as follows: rare earth cobalt, which is a new type of permanent magnetic steel. Such as samarium cobalt, aluminum nickel cobalt, praseodymium cobalt, mixed rare earth cobalt, and rare cobalt copper. Its magnetic energy product can reach 80-240kl/m, with high magnetic transmission efficiency and strong anti demagnetization ability. Its coercivity HCT is 360~1200kA/m. The operating temperature can reach 300cc. Neodymium iron boron is also a rare earth permanent magnet. The basic performance is similar to samarium cobalt, but the magnetic energy product is higher than samarium cobalt. The disadvantage is that the operating temperature is only 120. C. And the magnetic stability is relatively poor.
In the early days, ferrite was chosen as the material for magnetic pumps, but due to the magnetic energy product being only 10-30kj/m3, the operating temperature being only 85 ℃, and the large magnetic transmission loss, it is now less commonly used. Metal isolation sleeves, due to the presence of eddy current losses inside the sleeve, usually use high resistance materials such as Hastelloy C to reduce eddy current losses and improve transmission efficiency. At this time, eddy current losses account for about 5% to 25% of the total transmission efficiency. The non-metallic isolation sleeve can improve transmission efficiency due to the absence of eddy current losses inside the sleeve, but has low temperature resistance, generally only 100-120 ℃. Magnetic pumps have similar performance to centrifugal pumps, but with low efficiency.
Once the operating temperature of the magnetic pump exceeds the allowable temperature of the magnetic steel during operation, demagnetization will occur. Domestic magnetic pumps are generally used at a temperature of IOO ℃. The medium conveyed by the magnetic pump should not contain impurities or hard impurities containing iron or ferromagnetism. In order to prevent overheating or burning of bearings and isolation sleeves, it is necessary to avoid idling and not allow operation below 30% of the rated flow rate. Due to the fact that the magnetic pump fundamentally eliminates shaft seal leakage and has an automatic overload protection function in power transmission. In industries such as petrochemicals and pharmaceuticals, applications are gradually expanding when the driving power is not high.
At present, the performance of stainless steel magnetic pumps is generally as follows: flow rate is 0.2-200 Ⅱ i3/h, head<125m, motor power ≤ 75kW, temperature is -20~OO ℃.