Generally, the coaxial transmission includes the following parts: outer rotor, inner rotor, spacer sleeve, and bearing system. Among them, the spacer sleeve and the bearing system are mainly used in the structure of the magnetic transmission seal.
The outer peripheral part of the inner rotor and the inner peripheral part of the outer rotor are respectively equipped with magnets. The magnets are even-numbered poles and are arranged circumferentially in an NS cross manner. Align the working surfaces of the magnets of the inner and outer rotors, that is, automatic coupling.
There is a certain air gap between the inner and outer rotors to isolate the driving and driven parts. The size of the air gap is mostly between 2mm-8mm. The smaller the air gap, the higher the effective use of the magnet, and the more difficult the isolation is; the larger the air gap, the easier the isolation, but the less effective the use of the magnetic field of the magnet.
Commonly used metal materials are austenitic stainless steel, titanium alloy, Hastelloy and so on. Taking stainless steel as an example, under the working condition of centrifugal pump 1900rpm, the eddy current loss is as high as 15%-20%.
Hastelloy alloy has high resistivity and high strength, which can effectively reduce eddy current loss. However, the high cost of materials limits the application.
Non-metallic materials can reduce or even completely avoid eddy current losses. If the working pressure is not high, high-strength engineering plastics such as PEEK can be used.
There are also spacers made of ceramic materials, and the eddy current loss is zero. However, ceramic materials are fragile, have poor mechanical shock and thermal shock resistance, complex processing, high price, and difficult assembly, so they have not been widely used.
A: Use NdFeB magnets, when the working temperature is ≤80°C, speed ≤1000rpm, pressure ≤0.5MPa, or use samarium cobalt magnets, when the working temperature is ≤200°C, speed ≤1000rpm, try to use large The radius of gyration R is to reduce the length of the cantilever of the outer rotor and save the material of the magnetic steel; on the contrary, the radius of gyration R can only be as small as possible, and the design magnetic rotation can be guaranteed by simply increasing the axial length of the rotor, that is, increasing the volume of the magnetic steel. moment value.
B: If the working condition belongs to high temperature, medium and high pressure, and high speed, such as 300°C, 3000rpm, and 5MPa, then when designing, it is necessary to consider what cooling measures to take, and then optimize the structural design on the premise of ensuring the design magnetic torque to the optimum aspect ratio.
C: The cooling method generally adopts two methods: forced air cooling and double-layer isolation cover water circulation cooling. Among them, forced air cooling is generally used in the case of medium and high pressure conditions, where the eddy current heat is not large but cannot be ignored and the double-layer isolation cover cannot be used; its characteristic is that it does not increase the amount of magnetic steel, and is designed for large magnetic moments The structure is generally a slender structure, and there are many peripheral auxiliary parts of the cooling device, which requires that the surrounding environment of the equipment is well ventilated.