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The role of welding
Mar 21, 2018

First, improve the stability of the arc burning. Non-coated skin electrodes are not prone to ignition arcs. Even if it ignites, it cannot stably burn. In the electrode coating, it generally contains substances with low ionization potentials such as potassium, sodium, and calcium, which can improve the stability of the arc and ensure that the welding process continues.

Second, protect the welding pool. During the welding process, oxygen, nitrogen, and water vapor in the air are immersed in the weld, which can adversely affect the weld seam. Not only the formation of air holes, but also reduce the mechanical properties of the weld, and even lead to cracks. When the electrode coating melts, a large amount of gas is generated which covers the arc and the molten pool, which reduces the interaction between the molten metal and the air. As the weld seam cools, the molten coating forms a layer of molten slag covering the surface of the weld, protecting the weld metal and allowing it to cool slowly, reducing the possibility of pinholes.

Third, to ensure deoxidation of welds, desulfur phosphorus impurities. Although the welding process is protected, it is inevitable that a small amount of oxygen will enter the bath, causing oxidation of metal and alloy elements, burning of alloying elements, and reducing weld quality. Therefore, it is necessary to add a reducing agent (such as manganese, silicon, titanium, aluminum, etc.) to the coating of the electrode to reduce the oxide that has entered the bath.

Fourth, for the weld to add alloy elements. Due to the high temperature of the arc, the alloying elements of the weld metal will be vaporized and burned and the mechanical properties of the weld will be reduced. Therefore, it is necessary to add appropriate alloying elements to the weld seam through the coating to compensate for the burning of alloying elements and to ensure or improve the mechanical properties of the weld. For the welding of some alloy steels, it is also necessary to infiltrate the alloy into the weld through the skin, so that the weld metal can be close to the base metal and the mechanical properties can even exceed the base metal.

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