Development of permanent magnetic couplings
Couplings are widely used in various general machinery to connect two shafts so that they rotate together to transmit torque and motion. This paper mainly introduces the development and principle of synchronous permanent magnet couplings.
Traditional couplings must transmit torque through the interconnection of the driving shaft and the driven shaft. Its structure is complex, its manufacturing precision is high, and it is easy to cause damage to the components when overloaded. Especially when the driving shaft and the driven shaft work in two different media that need to be isolated from each other, sealing elements must be used for dynamic sealing, so there is a problem of either increasing the rotation resistance to ensure reliable sealing, or leaking due to poor sealing. In addition, with the wear and aging of sealing elements, leakage will be aggravated, especially in systems where harmful gases/liquids exist, once leakage will pollute the environment and endanger life.
Traditional couplings are all contact couplings, which can be divided into elastic couplings and rigid couplings according to whether they have elastic parts inside. The elastic coupling has elastic parts made of metal springs or rubber plastics inside, so it has the function of buffering and absorbing vibration and the ability to adapt to axis deviation. It is suitable for occasions with variable load impact, frequent starting and forward and reverse rotation, and also suitable for occasions where the two axes cannot be strictly aligned. There are no elastic parts in the rigid coupling, so there is no ability to cushion and absorb vibration.
The magnetic transmission couplings are a non-contact coupling. It is generally composed of two magnets inside and outside. The two magnets are separated by an isolation cover in the middle. The inner magnet is connected to the driven part, and the outer magnet is connected to the power part. In addition to the function of buffering and absorbing vibration of the elastic coupling, the biggest feature of the magnetic transmission couplings is that it breaks the structural form of the traditional coupling and adopts a new magnetic coupling principle to realize the non-passage between the driving shaft and the driven shaft. Direct contact can transmit force and torque, and can change dynamic seal into static seal to achieve zero leakage. Therefore, it is widely used on occasions with special requirements for leakage.
Magnetic transmission couplings mainly have two structures: planar magnetic transmission couplings and coaxial magnetic transmission couplings. The magnet is magnetized in the axial direction, and the coupled magnetic pole is arranged in the axial direction, which is called a planar magnetic transmission coupling. The magnet is magnetized in the radial direction, and the coupling magnetic pole is arranged in the radial direction, which is called a coaxial magnetic transmission coupling.
The magnetic transmission coupling consists of an outer magnet, an inner magnet and an isolation cover. Both the inner and outer magnets are composed of permanent magnets magnetized in the radial direction and magnetized in opposite directions. The permanent magnets are alternately arranged in the circumferential direction with different polarities and fixed on the low carbon steel ring to form a magnetic disconnection body. The isolation cage is made of a non-ferritic (and therefore non-magnetic) high-resistance material. In the static state, the N pole (S pole) of the outer magnet and the S pole (N pole) of the inner magnet attract each other and form a straight line, and the torque is zero at this time.
When the outer magnet rotates under the drive of the power machine, the inner magnet is still in a static state at the beginning due to the friction force and the resistance of the driven part. At this time, the outer magnet starts to deviate from a certain angle relative to the inner magnet. , the N pole (S pole) of the outer magnet has a pulling effect on the S pole (N pole) of the inner magnet, and at the same time the N pole (S pole) of the outer magnet has a push effect on the previous N pole (S pole) of the inner magnet The effect makes the inner magnet have a tendency to rotate, which is the working principle of the push-pull magnetic circuit of the magnetic coupling. When the N pole (S pole) of the outer magnet is just between the two poles (S pole and N pole) of the inner magnet, the generated push-pull force reaches the maximum, thereby driving the inner magnet to rotate. During the transmission process, the isolation cover separates the outer magnet from the inner magnet, and the magnetic field lines pass through the isolation cover to transmit the power and motion of the outer magnet to the inner magnet, thereby realizing non-contact sealed transmission.
Application field
One of the successful applications of magnetic drive couplings is its combination with pumps - magnetic pumps. In the past, it was used as a precious special product when it had to be used, but now it has a wide range of applications. Most of the liquids in petrochemical, pharmaceutical, film, electroplating, nuclear power and other industries are corrosive, flammable, explosive, toxic, and expensive. Leakage will cause waste of working liquid and environmental pollution; vacuum and semiconductor industries must prevent external gas. The intrusion of food, biology, and medicine must ensure the purity and hygiene of the medium. Magnetic drive couplings have found their uses in these fields, and it can be said that magnetic drive pumps are a big market for magnetic materials.
The permanent magnetic couplings is applied to the valve, the valve stem does not pass through the valve cover, and the stuffing box is omitted, so it is called a fully enclosed non-filling permanent magnetic transmission valve. Since the valve has no stuffing box, it can run safely and reliably for a long time; there is no frictional moment between the valve stem and the packing, and the rotation is labor-saving; negative pressure operation does not allow external gas to enter. All industrial valves such as globe valves, gate valves, ball valves, and butterfly valves can be transformed into fully enclosed valves. The reaction kettle is a kind of mixed reaction equipment widely used in chemical plants. The stirring of the liquid is often carried out under pressure. The reactants have a certain temperature, corrosiveness and volatility. Therefore, the sealing of the rotating shaft has become an important issue in the reaction kettle. The reaction equipment with agitator uses magnetic drive, in addition to achieving absolute sealing, it can also avoid the oxidation and condensation of the medium.
Development Overview
With the development of magnetic materials and the emergence of new magnetic materials, the torque transmitted by magnetic transmission couplings will become larger and smaller, and its application range will become wider and wider, except for pumps and reactors. , Valves, hydraulic cylinders and cylinders, and other occasions that need to solve the problem of dynamic seal leakage can be applied. It can be predicted that the magnetic transmission coupling will have a very broad market prospect.