Working principle of magnetic pump
The magnetic pump is composed of three parts: a pump, a magnetic drive, and a motor. The key component of the magnetic drive consists of an outer magnetic rotor, an inner magnetic rotor and a non-magnetic isolation sleeve. When the motor drives the outer magnetic rotor to rotate, the magnetic field can penetrate the air gap and non-magnetic materials, and drive the inner magnetic rotor connected to the impeller to rotate synchronously, realize the contactless transmission of power, and convert the dynamic seal into a static seal. Because the pump shaft and inner magnetic rotor are completely enclosed by the pump body and the isolation sleeve, the problem of "running, emitting, dripping, and leakage" is completely solved, and the leakage of flammable, explosive, toxic and harmful media in the refining and chemical industry through the pump seal is eliminated. The potential safety hazards effectively ensure the physical and mental health and safe production of employees.
1. Working principle of magnetic pump
N pairs of magnets (n is an even number) are assembled on the inner and outer magnetic rotors of the magnetic actuator in a regular arrangement, so that the magnet parts form a complete coupled magnetic system with each other. When the inner and outer magnetic poles are opposite to each other, that is, the displacement angle between the two magnetic poles Φ=0, the magnetic energy of the magnetic system is the lowest at this time; when the magnetic poles rotate to the same pole, the displacement angle between the two magnetic poles Φ=2π /n, the magnetic energy of the magnetic system is maximum at this time. After removing the external force, since the magnetic poles of the magnetic system repel each other, the magnetic force will restore the magnet to the lowest magnetic energy state. Then the magnets move, driving the magnetic rotor to rotate.
2. Structural features
1. Permanent magnet
Permanent magnets made of rare earth permanent magnetic materials have a wide operating temperature range (-45-400°C), high coercivity, and good anisotropy in the direction of the magnetic field. Demagnetization will not occur when the same poles are close. It is a good source of magnetic field.
2. Isolation sleeve
When the metal isolating sleeve is used, the isolating sleeve is in a sinusoidal alternating magnetic field, and eddy current is induced in the cross section perpendicular to the direction of the magnetic force line and converted into heat. The expression of eddy current is: where Pe-eddy current; K-constant; n-rated speed of the pump; T-magnetic transmission torque; F-pressure in the spacer; D-inner diameter of the spacer; resistivity of a material;-material The tensile strength. When the pump is designed, n and T are given by the working conditions. To reduce the eddy current can only be considered from the aspects of F, D, and so on. The isolation sleeve is made of non-metallic materials with high resistivity and high strength, which is very effective in reducing eddy current.
3. Control of cooling lubricant flow
When the magnetic pump is running, a small amount of liquid must be used to wash and cool the annular gap area between the inner magnetic rotor and the isolating sleeve and the friction pair of the sliding bearing. The flow rate of the coolant is usually 2%-3% of the design flow rate of the pump. The annulus area between the inner magnetic rotor and the isolating sleeve generates high heat due to eddy currents. When the cooling lubricant is insufficient or the flushing hole is not smooth or blocked, the temperature of the medium will be higher than the working temperature of the permanent magnet, and the inner magnetic rotor will gradually lose its magnetism and the magnetic drive will fail. When the medium is water or water-based liquid, the temperature rise in the annulus area can be maintained at 3-5°C; when the medium is hydrocarbon or oil, the temperature rise in the annulus area can be maintained at 5-8°C.
4. Sliding bearing
The materials of the sliding bearings of magnetic pumps are impregnated graphite, filled with polytetrafluoroethylene, engineering ceramics and so on. Because engineering ceramics have good heat resistance, corrosion resistance, and friction resistance, the sliding bearings of magnetic pumps are mostly made of engineering ceramics. Because engineering ceramics are very brittle and have a small expansion coefficient, the bearing clearance must not be too small to avoid shaft hung accidents.
Since the sliding bearing of the magnetic pump is lubricated by the conveyed medium, different materials should be used to make the bearings according to different media and operating conditions.
5. Protective measures
When the driven part of the magnetic drive is running under overload or the rotor is stuck, the main and driven parts of the magnetic drive will automatically slip off to protect the pump. At this time, the permanent magnet on the magnetic actuator will produce eddy loss and magnetic loss under the action of the alternating magnetic field of the active rotor, which will cause the temperature of the permanent magnet to rise and the magnetic actuator to slip and fail.
Three, the advantages of magnetic pump
Compared with centrifugal pumps that use mechanical seals or packing seals, magnetic pumps have the following advantages.
1. The pump shaft changes from a dynamic seal to a closed static seal, completely avoiding medium leakage.
2. There is no need for independent lubrication and cooling water, which reduces energy consumption.
3. From coupling transmission to synchronous drag, there is no contact and friction. It has low power consumption, high efficiency, and has a damping and vibration reduction effect, which reduces the impact of motor vibration on the magnetic pump and the impact on the motor when the pump occurs cavitation vibration.
4. When overloaded, the inner and outer magnetic rotors slip relatively, which protects the motor and pump.
Four, operation precautions
1. Prevent particles from entering
(1) Ferromagnetic impurities and particles are not allowed to enter the magnetic pump drive and bearing friction pairs.
(2) After transporting the medium that is easy to crystallize or precipitate, flush it in time (pour clean water into the pump cavity after stopping the pump, and drain it after 1 min of operation) to ensure the service life of the sliding bearing.
(3) When transporting the medium containing solid particles, it should be filtered at the inlet of the pump flow pipe.
2. Prevent demagnetization
(1) The magnetic pump torque cannot be designed too small.
(2) It should be operated under the specified temperature conditions, and the medium temperature is strictly prohibited from exceeding the standard. A platinum resistance temperature sensor can be installed on the outer surface of the magnetic pump isolation sleeve to detect the temperature rise in the annulus area, so that it can alarm or shut down when the temperature exceeds the limit.
3. Prevent dry friction
(1) Idling is strictly prohibited.
(2) It is strictly forbidden to evacuate the medium.
(3) With the outlet valve closed, the pump should not run continuously for more than 2 minutes to prevent the magnetic actuator from overheating and failing.