I: Concept of magnetic pump
Magnetic drive pump is also known as magnetic pump, its significant characteristic is that the pump has no shaft seal parts, that is, there is no dynamic seal leakage point. The magnetic drive pump consists of a pump, a magnetic drive, a magnetic drive pump and a motor. The key parts of the magnetic drive are composed of an external magnetic rotor, an internal magnetic rotor and a non-magnetic isolation sleeve.
II: Transmission principle
According to the magnetic field can penetrate air gap and the principle of magnetic medium, when the motor drives the outer magnetic rotor rotation, through the lines of magnetic force coupling is combined with the impeller of the inner magnetic rotor synchronous rotation, realize the non-contact transmission torque, adding a shaft from the conventional pump shaft sealing parts to set up two axis of sleeve structure, the dynamic seal into static seal, By pump body, pump shaft, the magnetic rotor of sleeve completely closed, so as to thoroughly solve the problem of the leakage of the medium, also solved the problem of "run, run, drip, leak", eliminates the oil refining chemical industry flammable, explosive, toxic and harmful medium through the pump seal leakage of potential safety problems, effectively guarantee the staff's physical and mental health and safety in production.
III: Magnetic pump working conditions
Magnetic pump conveying medium density is not more than 1300kg/m3, viscosity is not more than 30×10-6m3/S does not contain ferromagnetic and fiber liquid. The rated temperature of conventional magnetic pump for the pump body is metal material or F46 lining, the highest working temperature is 80℃, the rated pressure is 1.6mpa; High temperature magnetic pump temperature ≤350℃; For non-metallic pump body, the maximum temperature shall not exceed 60℃, and the rated pressure shall be 0.6mpa.
For conveying medium density more than 1600kg/m3 liquid, magnetic coupling needs to be designed separately. The bearing of magnetic pump is lubricated and cooled by the medium to be transported. The drum magnetic pump is generally prohibited from no-load operation.
1.The permanent magnet
The permanent magnet made of rare earth permanent magnet material has a wide operating temperature range (-45-400℃), high coercivity, good anisotropy of magnetic field direction, and no demagnetization when the same pole is close to each other, so it is a good magnetic field source.
2.Sleeve
In the use of metal isolation sleeve, the isolation sleeve is in a sinusoidal alternating magnetic field, in the direction perpendicular to the magnetic field lines of the section induced eddy current and converted into heat. The vortex is expressed as:. Pe-vortex; K - constant; N -- rated speed of the pump; T-magnetic drive torque; F- Pressure in the liner; D- inner diameter of sleeve; The resistivity of a material; -- Tensile strength of the material. When the pump is designed, n and T are given working conditions, and the eddy current can only be reduced from F, D, and other aspects. Non-metallic materials with high resistivity and high strength are selected to make isolation sleeve, which has obvious effect in reducing eddy current.
3.Control the flow of cooling lubricant
When the pump is running, a small amount of liquid must be used to wash and cool the annulus between the inner magnetic rotor and the isolation sleeve and the friction pair of the sliding bearing. Coolant flow is usually 2%-3% of the pump design flow, and the annulus region between the inner magnetic rotor and the isolation sleeve generates high heat due to eddy currents. When the cooling lubricant is not enough 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, so that the inner magnetic rotor gradually loses magnetism and the magnetic drive fails. When the medium is water or water-based liquid, the temperature rise in the annulus region can be maintained at 3-5℃. When the medium is hydrocarbon or oil, the temperature rise in the annulus region can be maintained at 5-8℃.
4.Plain bearings
Magnetic pump sliding bearing materials are impregnated graphite, filled ptfe, engineering ceramics and so on. Because engineering ceramics have good heat resistance, corrosion resistance and friction resistance, the sliding bearings of magnetic pumps are made of engineering ceramics. Because the engineering ceramics are very brittle and the coefficient of expansion is small, the bearing clearance shall not be too small to avoid the occurrence of shaft holding accidents.
Because the sliding bearing of magnetic pump is lubricated by the conveying medium, it should be made of different materials according to different media and working conditions.
5.Protective measures
When the driven parts of the magnetic drive run under overload or the rotor stuck, the main and driven parts of the magnetic drive will automatically slip to protect the pump. Under the action of the alternating magnetic field of the active rotor, the permanent magnet on the magnetic drive will produce vortex loss and magnetic loss, resulting in the rise of the temperature of the permanent magnet and the slip of the magnetic drive.