Selection and use of magnetic coupling

Selection and use of magnetic coupling

Generally speaking, coaxial transmission includes the following parts: outer rotor, inner rotor, spacer sleeve, and bearing system. The isolation sleeve and bearing system are mainly used in the structure of magnetic drive seal. The outer circumference of the inner rotor and the inner circumference of the outer rotor are respectively equipped with magnets. The magnets are an even number ji, arranged circumferentially in a NS cross pattern. Align the magnet working surfaces of the inner and outer rotors, i.e., automatic coupling. There is an air gap between the inner and outer rotors to isolate the active and driven components. The size of air gap is mostly between 2mm and 8mm. The smaller the air gap is, the higher the effective utilization of the magnet is, and the more difficult the isolation is; The larger the air gap is, the easier it is to isolate, but the less effective the magnetic field of the magnet is.

Common metal materials include austenitic stainless steel, titanium alloy, Hastelloy, etc. Take stainless steel as an example, under the operating condition of centrifugal pump at 1900rpm, the eddy current loss is as high as 15% - 20%. Hastelloy alloy has high resistivity and strength, which can effectively reduce eddy current loss. But the material cost is too high, which 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. The isolation sleeve is made of ceramic materials abroad, with zero eddy current loss. However, ceramic materials are fragile, with poor mechanical and thermal shock resistance, complex processing, high price and difficult assembly, so they are not widely used.

A Neodymium iron boron magnetic steel is selected. When the working condition temperature is ≤ 80 ℃, the rotating speed is ≤ 1000rpm, and the pressure is ≤ 0.5MPa, or samarium cobalt magnetic steel is selected. When the working condition temperature is ≤ 200 ℃, and the rotating speed is ≤ 1000rpm, the large turning radius R is adopted as far as possible to reduce the length of the outer rotor cantilever and save the magnetic steel materials; On the contrary, the radius of gyration R should be kept as small as possible to ensure the design magnetic torque value by increasing the axial length of the rotor, that is, increasing the volume of the magnetic steel.

B If the working conditions are high temperature, medium high pressure and high speed, such as 300 ℃, 3000 rpm and 5 MPa, it is necessary to consider what cooling measures should be taken during design, and then optimize the structural design to achieve a good length diameter ratio of zui on the premise of ensuring the design magnetic torque.

C. Generally, forced air cooling and water circulation cooling with double-layer isolation hood are adopted. Among them, forced air cooling is generally used under medium and high pressure working conditions, when eddy current heat is not large but cannot be ignored and double isolation hood cannot be used; It is characterized by that no additional magnetic steel consumption is required. For the structure designed with large magnetic moment, it is generally a slender structure. There are many auxiliary parts and components for the cooling device, which requires good ventilation conditions around the equipment.

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