What is the connection method between the squirrel cage on the motor rotor and the shaft, and why does separation occur?

This post was last edited by zhaohh3211 on 2010-6-28 07:45. There are various ways in which the slats of a squirrel-cage asynchronous motor are connected to the main shaft, but the most common method is a direct fit – the slats are placed onto the shaft based on the principle of slight expansion and contraction, so that they can bond together when the temperatures are equal, with a relatively strong connection as well. Some manufacturers use taper shapes or pins to achieve this connection; however, few manufacturers employ such methods, though it’s not impossible. To date, I’ve hardly ever seen any cases of welding being used for this purpose – anyone who does so is an amateur. It can be pulled off because of misalignment. In other words, there is now a gap between the main shaft and the squirrel cage, resulting in wear between the two.

This post was last edited by zhaohh3211 on 2010-6-28 07:48. Thank you to the friend above for their advice!

The method of connecting the cage to the shaft involves heating the steel bars of the cage and then fitting it over the shaft. Processed using the principle of thermal expansion and contraction.

This post was last edited by jjli618 on 2010-6-25 06:10. Assembly of asynchronous motor rotors: The rotor is a rotating component, and due to forces such as centrifugal force and electromagnetic force, it must possess sufficient strength and stiffness. Depending on the rotor diameter, there are different ways in which the rotor core and the shaft are combined. Rotor cores with a small diameter are generally mounted directly on the shaft, while those with a larger diameter are usually fixed to the shaft via a rotor bracket; it is also possible to weld radial ribs onto the shaft to serve as brackets, with the rotor core being placed over these radial ribs. The connection between the rotor core and the shaft or bracket must be reliable in order to transmit torque effectively; the methods of fastening include key coupling, knurling and cold pressing, as well as thermal fitting. The inner circle of the rotor core is in an interference fit with the shaft or bracket, and the degree of this interference depends mainly on the torque to be transmitted. Small asynchronous motors with a center height of 160 MM or less generally use shaft knurling cold pressing ； Small and medium-sized motors with a center height of over 180 MM usually use key connections ； For large and medium-sized motors with high rotational speeds or uneven loads, where there is a large interference fit between the rotor core and the shaft or bracket, heat fitting is used. Manufacturing process for cast aluminum cage rotors: The core laminations are first stacked on a dummy shaft or rotor holder, and aluminum is cast while under compression. After casting, the dummy shaft is removed, and the rotor is fitted onto the shaft while still hot or pressed onto it cold. Rotor cast aluminum involves melting industrial pure aluminum with a purity of not less than 99.5%, and then casting an aluminum cage composed of conductive bars and end rings into a laminated rotor core. Generally, the air blades and balance columns are also cast at the same time. The main requirements for casting aluminum for rotors are as follows: 1. There should be no cracks, significant shrinkage cavities, pores, or other defects; there should also be no signs of aluminum infiltration between the rotor core pieces. 2. The radial deviation of the inner and outer surfaces of the end rings should be minimal. 3. The gates and aluminum slag resulting from the casting process must be removed. 4. Rotors with radial ventilation grooves should not have any aluminum leakage that could block these grooves, and the core should not exhibit significant waviness. 5. The length of the rotor core and the angle of the slanted grooves must meet the specified requirements. Common methods for casting aluminum for rotors include pressure casting, centrifugal casting, and low-pressure casting. Note: To reduce the contact resistance between the aluminum bars and the core, suppress the transverse current in the rotor, and minimize stray losses, the inner surface of the core slots can be phosphated or pre-coated with a heat-resistant coating before aluminum casting is carried out. Secondly, there are also aspects related to the manufacturing process of welded cage rotors and the welding methods for such rotors; we can discuss these in more detail at a later opportunity. So why does separation occur? 1. When the tolerance fit is poor, and the combined effect of external torque, centrifugal force, and electromagnetic forces exceeds the strength and stiffness requirements of the rotor, keying phenomenon occurs. 2. If the rolling process is not proper, and thermal expansion takes place, the forces acting on the rotor exceed its capacity to withstand them, resulting in wobbling behavior that tends to worsen over time. 3. An excessive gap between the shaft and the core laminations means that after casting aluminum and pressing it onto the rotor shaft, the interference fit is small; as a result of thermal expansion and contraction, separation occurs