A magnetic pump consists of three parts: a pump, an electric motor, and a magnetic drive. The key component of the magnetic drive is composed of an external magnetic rotor, an internal magnetic rotor, and a non magnetic isolation sleeve. When the electric motor drives the outer magnetic rotor to rotate, the magnetic field can penetrate the air gap and non magnetic substances, driving the inner magnetic rotor connected to the impeller to rotate synchronously, achieving contactless transmission of power and converting the dynamic seal into a static seal. Due to the complete closure of the pump shaft and internal magnetic rotor by the pump body and isolation sleeve, the problem of "leakage, leakage, dripping, and leakage" has been completely solved, eliminating the hidden danger of flammable, explosive, toxic, and harmful media leaking through the pump seal in the refining and chemical industry, effectively ensuring the health and production safety of employees. According to the magnetic pump, n pairs of magnets (n being even numbers) are arranged and assembled in a regular manner on the inner and outer magnetic rotors of the magnetic drive, so that the magnet parts form a complete coupled magnetic system with each other. When the inner and outer magnetic poles are opposite each other, that is, the displacement angle between the two magnetic poles Φ= At this point, the magnetic energy of the magnetic system is the lowest; When the magnetic poles rotate to the same pole relative to each other, that is, the displacement angle between the two magnetic poles Φ= At 2 π/n, the magnetic energy of the magnetic system is at its maximum. After removing the external force, due to the mutual repulsion of the magnetic poles of the magnetic system, the magnetic force will restore the magnet to its lowest state of magnetic energy. So the magnet generates motion, driving the principle of magnetic rotor rotation. Permanent magnets made of rare earth permanent magnet materials have a wide operating temperature range (-45-400 ℃), high coercivity, good anisotropy in the direction of the magnetic field, and do not undergo demagnetization when the same pole is close, making them a good magnetic field source. When using a metal isolation sleeve, the isolation sleeve is in a sinusoidal alternating magnetic field, inducing eddy current on a cross-section perpendicular to the magnetic field line and converting it into heat. The expression for eddy current is:. Among them, Pe eddy current; K - constant; N - rated speed of the pump; T-magnetic transmission torque; F - pressure inside the spacer; D-inner diameter of the spacer sleeve; The electrical resistivity of a material; - The tensile strength of the material. After the pump is designed, n and T are given by the operating conditions, and reducing eddy currents can only be considered from aspects such as F, D, and so on. Selecting non-metallic materials with high resistivity and strength to make isolation sleeves has a significant effect in reducing eddy currents. When the pump is running, a small amount of liquid must be used to flush and cool the annular gap area between the inner magnetic rotor and the isolation sleeve, as well as the friction pair of the sliding bearing. The flow rate of coolant is usually 2% -3% of the pump design flow rate, and the annular gap area between the inner magnetic rotor and the isolation sleeve generates high heat due to eddy currents. When the cooling lubricant is insufficient or the flushing hole is not smooth or blocked, it will cause the medium temperature to be higher than the working temperature of the permanent magnet, gradually losing the magnetism of the inner magnetic rotor, and causing the magnetic drive to fail. When the medium is water or water-based liquid, the temperature rise in the annular gap area can be maintained at 3-5 ℃; When the medium is hydrocarbon or oil, the temperature rise in the annular gap area can be maintained at 5-8 ℃. The materials used for magnetic pump sliding bearings include impregnated graphite, filled PTFE, engineering ceramics, etc. Due to the excellent heat resistance, corrosion resistance, and friction resistance of engineering ceramics, the sliding bearings of magnetic pumps are mostly made of engineering ceramics. Due to the brittleness and low expansion coefficient of engineering ceramics, the bearing clearance should not be too small to avoid shaft holding accidents. Due to the fact that the sliding bearings of the magnetic pump are lubricated with the medium conveyed, different materials should be selected to make bearings based on different media and operating conditions. When the driven components of the magnetic drive operate under overload or the rotor gets stuck, the main and driven components of the magnetic drive will automatically slip off to protect the pump. At this point, the permanent magnet on the magnetic actuator will generate vortex loss and magnetic loss under the action of the alternating magnetic field of the active rotor, causing the temperature of the permanent magnet to rise and the magnetic actuator to slip and fail. Compared with centrifugal pumps that use mechanical seals or packing seals, magnetic pumps have the following advantages. 1. The pump shaft has changed from a dynamic seal to a closed static seal, completely avoiding medium leakage. 2. No need for independent lubrication and cooling water, reducing energy consumption. 3. Transforming from coupling transmission to synchronous driving, without contact or friction. Low power consumption, high efficiency, and damping effect, reducing the impact of motor vibration on the pump and the impact of pump cavitation vibration on the motor. When overloaded, the inner and outer magnetic rotors slip relatively, providing protection for the motor and pump. Precautions for operation: 1. Prevent particles from entering (1) No ferromagnetic impurities or particles are allowed to enter the magnetic drive and bearing friction pairs. (2) After transporting media that is prone to crystallization or sedimentation, it is necessary to wash it in a timely manner (after stopping the pump, pour clean water into the pump cavity, and discharge it clean after running for 1 minute) to ensure the service life of the sliding bearing. (3) When conveying media containing solid particles, it should be filtered at the inlet of the pump flow pipe. 2. Prevent demagnetization (1) The magnetic torque cannot be designed too small; (2) It should be operated under the specified temperature conditions, and it is strictly prohibited to exceed the medium temperature. 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 annular gap area, so as to alarm or shut down when the temperature exceeds the limit. 3. Prevent dry friction (1) It is strictly prohibited to empty the medium; (2) Do not idle; (3) When the outlet valve is closed, the continuous operation time of the pump should not exceed 1 to 3 minutes to prevent the magnetic drive from overheating and failure.
Do you know the working principle of magnetic pumps, which have many advantages?
started by
yibomine
11 Apr 2023 - 07:12 AM
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