How does a Welding Machine Work?
The electric welding machine makes full use of the high-temperature arc generated when the positive and negative poles are short-circuited instantaneously to melt the solder on the welding rod and the material to be welded, so that the contacted objects are combined. Electric welding machines are generally divided into two types according to the type of output power, one is AC power and the other is DC. The welding machine uses the principle of inductance. The inductance will produce huge voltage changes when it is switched on and off. The welding machine makes full use of the high-pressure arc generated when the positive and negative poles are short-circuited instantaneously to melt the solder on the welding rod and the material to be welded, so as to realize atom integration.
The welding machine is a special transformer. The difference between it and the voltage transformer is that the voltage drop is small when the transformer is connected to the load, and the voltage drop is large when the welding machine is connected to the load. This is mainly achieved by adjusting the inductance of the magnetic flux and series inductance. Although the circuit is closed, it is precisely because of this that the current is equal everywhere in the entire closed circuit. However, the resistance is different everywhere, especially the resistance at the unfixed contact is the largest, which is called contact resistance in physics. According to the law of thermal effect of electric current (also called Joule law), it can be known that if the electric current is equal, the part with the larger resistance will generate more heat. If the contact resistance of the contact of the electrode and the metal body to be connected is the largest during electric welding, the electric heat generated in this part will naturally be the most. The welding rod is an alloy with a lower melting point, which is naturally easy to melt. The melted alloy electrode core is bonded to the object to be welded, and after cooling, the welding object is bonded together. At this time, due to the extremely small instantaneous gap when the electrode is lifted, the voltage between the electrode and the weldment is higher (60-70V), and preheating makes the end of the electrode and the welded part easy to emit electrons, the air in the gap is penetrated to conduct electricity, and at the same time a dazzling spark is generated. This is the arc discharge phenomenon. The temperature at the arc discharge can reach more than 2000K, so the welding rod and the weldment are melted, thus realizing welding. After the arc discharge starts, the voltage of the electrode end and the weldment (referred to as the arc voltage) is reduced by about 30V. The load formed by the arc is a resistive load.
It is worth mentioning that the coating on the outer layer of the welding rod plays a very important role. The welding rod used in manual arc welding consists of two parts: the coating and the core. When welding, as an electrode, the welding rod plays a role of conducting current and igniting the arc, so that a continuous and stable arc is generated between the welding rod and the base metal to provide the necessary heat for fusion welding. On the other hand, the welding rod is added to the weld as a filler metal, thus becoming the main component of the weld metal. Therefore, the composition of the welding rod and the quality of the welding rod will directly affect the chemical composition, mechanical properties and physical properties of the weld metal. In addition, the welding rod has a great influence on the stability of the welding process, the quality of the appearance of the weld, and the welding productivity.
Welding core refers to the metal core of the welding rod. In order to ensure the quality of the weld, there are strict regulations on the content of various metal elements in the welding core, especially for harmful impurities, such as sulfur and phosphorus. The quality of the core metal should be better than the base metal.
The polished rod electrode without the coating cannot be used for arc welding, because in this case, the arc stability is very poor, the spatter is large, and the weld seam is not well formed. After long-term practice, it has gradually been discovered that certain mineral materials (ie, electrode coating) can be coated on the outside of the welding core, which greatly improves the performance of the welding electrode.