Magnetic chucks are gradually replacing mechanical hooks and become the main trend for lifting and moving steels. Magnetic chucks can be divided into three types: permanent magnetic chuck, electromagnetic chuck and electric permanent magnetic chuck. The permanent magnet chuck is mainly used to fix the workpiece during machining, it generally is not used for the lifting of heavy steels. The suction force of the electromagnetic chuck is maintained by energization, it has a greater safety hazard in the process of use. Once the power is accidentally cut off, the steel would fall down and may hurt people. At the main time, the electromagnetic chuck generates a lot of heat in long-term energization thus it cannot work for a long time. Compared with other magnetic chucks, the electric permanent magnetic chuck has better reliability moving steels. When lifting the steel, the magnetic chuck is positively energized to excite the magnetic field so that the permanent magnet material maintains the magnetic force. When unloading, reverse power on to eliminate the magnetic force of the magnetic chuck and unload the steel. The whole process is only energized once when lifting and when unloading. In the movement of steel, since the permanent magnets attract the steel without power, it not only reduces the risk of steel movement, but also saves electricity.
The electric permanent magnet chuck is mainly composed of a main magnet, a secondary magnet, an excitation coil and a control module. The main magnet is generally using high-coercivity neodymium magnet, even in a strong magnetic field, the magnetism of the neodymium magnet would not be changed. The secondary magnet generally selects low-coercivity AlNiCo magnet. Under the magnetic field excited by the pulse current, the magnetism and the magnetization direction of the AlNiCo magnet are relatively easy to be changed, thereby changing the magnetism of the entire chuck. The excitation coil is mainly used to generate a pulsed magnetic field when lifting and unloading the steel, and to change the magnetism and magnetization direction of the AlNiCo magnet.
Referring to Figures A and B, the magnetic polarity of the main magnet 2 remains unchanged all the time. When the secondary magnet 5 is positively magnetized by the excitation coil 4, the direction of the magnetic polarity of the main magnet 2 and the secondary magnet 5 stay the same, the suction force of the magnetic chuck is the largest at this time. The magnetic field lines pass through the external magnetic pole 1 and the internal magnetic pole 3 to penetrate the steel plate 6, presenting magnetic adsorption. When the secondary magnet 5 is reversely magnetized by the excitation coil 4, the magnetic polarities of the main magnet 2 and the secondary magnet 5 are opposite, causing the external magnetic lines of force cancel out, so no magnetic force lines penetrate the steel plate. The magnetic chuck is not magnetic to the steel plate and cannot be adsorbed to the steel plate in this case.