Structure
The magnetic pump mainly includes motor, bracket, outer magnetic cylinder (driving rotor), inner magnetic cylinder (driven rotor), isolation cover, sliding bearing, transmission shaft, impeller and pump body, etc.
Among them, the magnetic coupling used for pump driving is composed of inner magnetic cylinder, outer magnetic cylinder, isolation cover and magnetic body, also called permanent magnetic coupling and magnetic couplings.
Inner magnetic cylinder:
The inner magnetic cylinder and the pump rotor are coaxial, and permanent magnet blocks are installed in the direction parallel to the axial direction. The magnetic blocks are isolated by stainless steel and other materials for magnetic isolation (reducing lateral magnetic flux leakage), support and protection, and to protect the inner magnetic the magnetic block on the cylinder is generally covered with a layer of protective material (such as plastic, stainless steel, etc.) on the outside of the inner magnetic cylinder.
External magnetic cylinder:
The outer magnetic cylinder is connected with the motor, and the cylindrical surface of the outer magnetic cylinder is also equipped with magnetic blocks, and the magnetic blocks are isolated and supported by magnetic isolation materials. The outer magnetic cylinder generally does not need to add a protective cover (it will not be in contact with the medium).
Isolation cover:
The isolation cover is located between the inner and outer magnetic cylinders, and is fixed with the pump body by certain measures to form a closed cavity. The main materials of the isolation cover are stainless steel, titanium alloy, plastic, carbon fiber, ceramics and other materials.
The spacer sleeve is a very important part of the magnetic pump. It is because of its combination with the pump body, inner and outer magnetic cylinders that no power seal components are needed and true zero leakage is achieved.
Bearing parts:
The pump end adopts sliding bearing structure, and the main materials are graphite, silicon carbide, polytetrafluoroethylene, etc. The driving end adopts deep groove ball bearings, angular contact ball bearings, etc.
Magnetic body:
The magnetic body is the main component for torque transmission, and its quality directly affects the life and efficiency of the magnetic pump, that is, the transmission torque. At present, ferrite, dilute thorium cobalt and neodymium iron boron are mostly used in China.
Features
The magnetic pump cancels the mechanical seal of the pump, completely eliminates the disadvantages of mechanical seal centrifugal pumps, dripping and leaking, and is the best choice for non-leakage factories. Because the flow-passing parts of the pump are made of stainless steel and engineering plastics, the purpose of corrosion resistance is achieved. The magnetic coupling of the pump is integrated with the pump body, so it has compact structure, convenient maintenance, safety and energy saving. The magnetism of the pump will inevitably run and pop, and the coupling can protect the drive motor from overload.
Working conditions
g the density of the magnetic pump conveying medium is not more than 1300kg/m3, and the viscosity is not more than 30×10-6m3/S, which does not contain ferromagnetism and fiber. The rated temperature of the conventional magnetic pump is for the pump body made of metal or F46 lining, the maximum working temperature is 80°C, and the rated pressure is 1.6MPa; the operating temperature of the high temperature magnetic pump is ≤350°C; for the pump body made of non-metallic material, the maximum temperature is not Over 60°C, the rated pressure is 0.6MPa. For liquids with a medium density greater than 1600kg/m3, the magnetic coupling needs to be designed separately. The bearing of the magnetic pump is lubricated and cooled by the conveyed medium, so the magnetic pump is generally strictly prohibited from running without load.
The similarities and differences with canned pump
Both pumps are widely used in chemical, pharmaceutical, nuclear industry, aerospace and other devices. As far as the domestic application situation is concerned, shielded pumps are still the mainstream. The main reason is that the domestic magnetic steel material technology is not yet qualified, which often leads to accidents such as degaussing and thermal overload of magnetic pumps. However, the application of magnetic pumps abroad is still very mature.
What the magnetic pump and canned pump have in common: both are leak-free pumps without any shaft seal. The difference between magnetic pump and canned pump: the structure principle is completely different.
◆The canned pump directly uses the principle of the motor, and the energy consumption of the magnetic pump motor is transmitted to the impeller through the inner and outer magnetic steel (partial energy is converted into heat of the magnetic steel), so the efficiency of the canned pump is theoretically higher than that of the magnetic pump.
◆From the structure, it can be seen that the biggest disadvantage of the canned pump is that it cannot be repaired (very difficult). Whether there is a problem with the pump body or the motor during use, the user basically cannot repair it by himself.
The repair of the magnetic pump is not much different from that of the ordinary pump. The motor bearing of the canned pump is in contact with the medium, which is difficult for daily maintenance and maintenance. The failure of the bearing cannot be detected to observe the failure phenomenon and precursor, and it is difficult to find hidden dangers in operation. Once a problem occurs, it will be fatal damage.
◆The thickness of the isolation sleeve of the magnetic pump is more than three times that of the canned pump, so the sealing and reliability are more guaranteed.
◆ The motor bearing of the canned pump is lubricated by the medium, and the motor does not have a fan. The heat dissipation of the motor is carried away by the internal circulation of the medium. This leads to a higher failure rate of this shielded motor. The magnetic pump motor is an ordinary motor, which is mature and reliable by fans for heat dissipation. But also, because the noise of this magnetic pump is bigger than that of canned pump.
◆The canned pump has a more compact structure, so it is smaller than the magnetic pump and saves space.
◆The canned pump has no coupling, and the magnetic pump and the motor are connected through a coupling, which needs to be centered.
◆Due to the problem of magnetic materials, the maximum power that the magnetic pump can achieve is lower than that of the canned pump, which leads to the limitation of the magnetic pump in some high-flow and high-pressure applications with large loads.
◆ Magnetic pumps are more suitable for strong corrosive media than canned pumps because their isolation sleeves are thicker (thicker shielded sleeves of canned pumps will affect the electromagnetic effect of stator windings and rotor windings).
◆ The magnetic pump cannot be used when the medium contains metal particles (such as iron filings), because the ferromagnetic material will be attracted by the magnetic steel, resulting in failure. Whereas canned pumps can handle it.