An overview of the principle of electromagnet

Electromagnets use electromagnetic suction to operate mechanical equipment to complete the expected action, or for holding and fixing steel parts, lifting and transferring ferromagnetic materials, etc. It is a low-voltage electrical appliance that converts electrical energy into mechanical energy. The electromagnet is mainly composed of an iron core, an armature, a coil and a working structure. According to the type of current passing through the coil, the electromagnet can be divided into a communication electromagnet and a DC electromagnet.

Communication electromagnet, when the working voltage of the coil is constant, the magnetic flux value in the iron core does not change at all, so the electromagnetic attraction between the iron core and the armature also does not change at all. However, the current in the core mainly depends on the inductive reactance of the coil. In the process of the electromagnet pulling in, with the reduction of the air gap, the magnetic resistance decreases, the inductive reactance of the coil zeng is large, and the current decreases. The current of the communication electromagnet is the largest when it starts to pull in, which is generally several times to ten times the working current after the pull-in. Therefore, when the armature of the communication electromagnet is stuck and cannot be pulled in, the coil will burn out quickly due to overheating. At the same time, the communication electromagnet is not allowed to operate too frequently to avoid the coil being burned out due to the continuous impact of the starting current. And the uniform suction is independent of the armature stroke.

In order to reduce the eddy current hysteresis loss, the iron core and armature of the communication electromagnet are laminated with silicon steel sheets, and a short-circuit ring is installed on the end face of the iron core. There are many varieties of communication electromagnets, which are divided into single-phase, two-phase and three-phase according to the number of current phases; 220V and 380V according to the coil voltage; according to their functions, they are divided into traction electromagnets, braking electromagnets and lifting electromagnets. Brake electromagnets can be divided into short strokes and long strokes according to the armature stroke.

DC electromagnet, the coil resistance of the DC electromagnet is constant. Under the condition of constant operating voltage, the current of the coil is also constant. It will not change with the change of the air gap during the pull-in process, so the operating frequency is allowed to be high. Before it is pulled in, the air gap is larger, the magnetic resistance of the magnetic circuit is larger, and the magnetic flux is smaller, so the attraction force is smaller. After the suction, the air gap is very small, the magnetic resistance is also small, the magnetic flux is the largest, and the electromagnetic attraction force is the largest. The test proves that the electromagnetic attraction force of the DC electromagnet is inversely proportional to the square of the air gap size. The electromagnetic suction force of the iron core and the armature gradually increases during the suction process. The DC long-stroke braking electromagnet is mainly used for the shoe brake, and its working principle is the same as that of the AC braking electromagnet.