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Automatic variable diameter roll welding machine
Welding machine refers to an electrical appliance that provides a certain power supply for welding. Welding is widely used in various industrial fields, such as aerospace, ships, automobiles, containers, etc., due to its advantages of flexibility, simplicity, convenience, firmness and reliability, and even the same strength as the base metal after welding.
An electric welding machine is actually a transformer with reduced external characteristics, which converts 220V and 380V AC into low-voltage DC. Generally, electric welding machines can be divided into two types according to the type of output power supply, one is AC power supply; It is direct current. The DC electric welding machine can also be said to be a high-power rectifier, which is divided into positive and negative poles. When the AC power is input, it is transformed by the transformer, then rectified by the rectifier, and then outputs a power supply with reduced external characteristics. The output terminal is switched on and off. A huge voltage change will be generated when the two poles are short-circuited in an instant, and the arc will be used to melt the welding rod and welding material, and then the purpose of combining them will be achieved after cooling. The welding transformer has its own characteristics, the external characteristic is the characteristic that the voltage drops sharply after the welding rod is ignited.
The main part of the electric welding machine is a step-down transformer. The two ends of the secondary coil are the workpiece to be welded and the electrode. When working, the arc is ignited, and the electrode is fused to the gap of the workpiece in the high temperature of the arc. Because the iron core of the welding transformer has its own characteristics, it has the characteristics of a sharp drop in voltage, that is, the voltage drops after the welding rod is ignited; when the welding rod is stuck and short-circuited, the voltage drops sharply. During the welding operation, although the current in the circuit is equal everywhere, because the resistance of each place is different, the resistance at the unfixed contact is the largest (this resistance is called contact resistance), according to the law of thermal effect of current (also called Joule's law) , that is, Q=IRt. It can be seen that when the current is equal, the part with greater resistance will generate more heat. Therefore, during welding, the contact resistance of the contact of the electrode, that is, the contact of the metal body to be connected, is the largest. The electric heat generated is naturally the most, and the welding rod is an alloy with a low melting point, so it is easy to melt. The molten alloy electrode core sticks to the object to be welded, and after cooling, the welded object is bonded together. Generally, the panel of the DC inverter welding machine is equipped with an output DC current adjustment knob. The inverter DC welding machine first performs bridge rectification and filtering on single-phase AC 220V voltage or three-phase AC 380V voltage, and then supplies power switching devices for inverter processing. A small number of inverter welding machines first use pulse generating circuits such as 555 time base circuits to generate rectangular pulse waves, then use transistors to amplify current, and then use a pair of complementary field effect transistors to amplify voltage to generate high-frequency signals, and finally use boost The transformer boosts the voltage and induces alternating current on the secondary winding. The size of its power depends on the amplification capability of the amplifier circuit. The inverter welding machine mostly adopts a single-ended forward inverter circuit composed of IGBT tubes, and its control system mostly uses a pulse width modulation chip SG3525, whose inverter frequency is 20kHz, and can perform constant current external characteristic control. When the system is no-load, due to the voltage feedback control, the PWM modulator outputs pulses intermittently. Because the frequency of intermittent oscillation is low and the pulse width is narrow, not only the no-load loss is small, but the transformer is not easy to saturate. Because this type of welding machine adopts the control technology with pulse width modulation PWM as the core, it can obtain better constant current characteristics and excellent welding process effects.
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