In general, coaxial drives consist of the following parts: external rotors, inner rotors, isolation sleeves, bearing systems. Among them, the isolation sleeve and bearing system are mainly used in the structure of magnetic drive seal. The outer circumference part of the inner rotor and the inner circumference part of the outer rotor are fitted with magnets respectively. The magnets are even-numbered poles, arranged in circumference according to NS crossover. The magnets of the inner and outer rotors are aligned, i.e. automatically coupled. There is a certain air gap between the internal and external rotors to isolate the active and driven components. 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, the larger the air gap, the more convenient the isolation, but the effective use of the magnetic field of the magnet is worse.

       Common metal materials are Australasus stainless steel, titanium alloy, Hatch alloy and so on. In stainless steel, for example, the vortex loss is as high as 15%-20% under centrifugal pump 1900rpm conditions. Hatch alloy has high resistivity and high strength, which can effectively reduce vortex loss. However, the cost of materials is too high, limiting the application. Non-metallic materials can reduce or even completely avoid eddy current loss. If the working pressure is not high, you can choose high-strength engineering plastic PEEK and so on. Foreign countries have the use of ceramic materials to manufacture isolation sets, vortex loss is zero. However, ceramic materials are fragile, resistant to mechanical impact and thermal impact performance is not good, complex processing, high price, assembly difficulties, so it has not been widely used.

       A the choice of ferrite boron magnetic steel, in the operating temperature of ≤80 degrees C, speed ≤1000rpm, pressure ≤ 0.5MPa, or the choice of cobalt magnetic steel, in the operating temperature ≤ 200 degrees C When the speed ≤ 1000rpm, try to take a large swing radius R, and strive to reduce the length of the outer rotor cantilever, save magnetic steel material;

       B If the operating conditions belong to high temperature, medium and high pressure, high speed conditions, such as 300 degrees C, 3000rpm, 5MPa, then the design must first consider what cooling measures to take, and then under the premise of ensuring the design of magnetic torque, optimize the structure design to the best long diameter ratio.

       C cooling mode is generally forced air-cooled, two-layer isolation cover water cycle cooling two ways. Among them, forced air cooling, generally in medium and high-pressure operating conditions, vortex heat is not large but can not be ignored and can not be used in the case of double-layer isolation cover, which is characterized by no additional use of magnetic steel, the design structure of large magnetic moment, generally slender structure, cooling device peripheral auxiliary components more, requiring good ventilation conditions of the surrounding environment of the equipment.