Structural features of magnetic pump

When a metal isolation sleeve is used, the isolation sleeve is in a sinusoidal alternating magnetic field, and eddy currents are induced on the cross section perpendicular to the direction of the magnetic field lines and converted into heat.

1.Permanent magnet

Permanent magnets made of rare earth permanent magnet materials have a wide operating temperature range (-45-400°C), high coercive force, good anisotropy in the direction of the magnetic field, and will not demagnetize when the same poles are close to each other. It is a very good magnetic field source.

2.Isolation sleeve

When a metal isolation sleeve is used, the isolation sleeve is in a sinusoidal alternating magnetic field, and eddy currents are induced on the cross section perpendicular to the direction of the magnetic field lines and converted into heat.

The expression of eddy current is: . Among them, 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 the material; —The tensile strength of the material.

After the pump is designed, n and T are given by the working conditions. To reduce the eddy current, we can only consider F, D and other aspects. The isolation sleeve is made of non-metallic materials with high resistivity and high strength, which has a very obvious effect in reducing eddy current.

3. Control of cooling lubricant flow

When the pump is running, a small amount of liquid must be used to flush and cool the annular area between the inner magnetic rotor and the isolation sleeve and the friction pair of the sliding bearing.

The flow rate of the coolant is usually 2%-3% of the pump design flow rate. The annular 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, the medium temperature will be higher than the working temperature of the permanent magnet, causing the internal magnetic rotor to gradually lose its magnetism, causing the magnetic actuator to 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 bearings

The materials of magnetic pump sliding bearings include impregnated graphite, filled polytetrafluoroethylene, engineering ceramics, etc.

Since engineering ceramics have good heat resistance, corrosion resistance, and friction resistance, the sliding bearings of magnetic pumps are mostly made of engineering ceramics. Since engineering ceramics are brittle and have a small expansion coefficient, the bearing clearance must not be too small to avoid shaft holding accidents.

5.Protective measures

When the driven part of the magnetic actuator operates under overload or the rotor is stuck, the main and driven parts of the magnetic actuator will automatically slip off to protect the pump.

At this time, the permanent magnets on the magnetic actuator will produce eddy losses and magnetic losses under the action of the alternating magnetic field of the active rotor, causing the temperature of the permanent magnets to rise and the magnetic actuator to slip and fail.