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The composition of the electrode
A welding electrode is a molten electrode used for welding, which is composed of a welding core (metal core) and a coating (coating). Figure Physical shape diagram of electrode and Figure Electrode structure diagram show its appearance and structure. One end of the electrode is the arc starting end. Generally, the skin of the flounder at the arc starting end is ground to a certain Angle to expose the welding core and facilitate arc starting. For better arc initiation, the low hydrogen electrode is often coated with arc initiation agent or drilled a small hole or slot on the end face of the welding core at the arc initiation end to improve the current density, as shown in Figure Electrode structure diagram-b. The other end of the electrode is the gripper end. The gripper end is a bare welding core with a length of 15~25mm and is held on the welding pliers during welding. The brand of the electrode is printed on the coating near the clamping end.
Figure Electrode end shape-a shows the end face shape of the common electrode, and Figure Electrode end shape-b shows the double coated electrode, which is mainly for improving the technological performance of the low hydrogen electrode. The ingredients of the two coated electrodes are different. In Figure Electrode end shape-c, the welding core is hollow tube, coated with coating, and the center of the tube is filled with alloying agent or coating. This electrode is used in the wear – resistant surfacing electrode containing a large amount of alloy powder. Commonly used electrode diameter φ2.5mm, φ3.2mm, φ4.0mm three kinds.
In the process of electrode arc welding, the electrode plays the role of conducting current and igniting arc on the one hand. The other side is used as a filler metal to form a weld with the molten base metal.
Welding core
The coated metal in the electrode is the weld core, which is both the electrode and the molten filler metal. The composition of weld core directly affects the composition and properties of fusible metal. In electrode arc welding, the core metal accounts for about 50%~70% of the whole weld.
Welding cover
The effective component coated on the surface of the welding core is the flux skin, which is a layer of coating on the surface of the welding core after the raw materials such as ore powder, ferroalloy powder, organic matter and chemical products are arranged in a certain proportion. The main functions of the welding cover are as follows:
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Ensure that the arc is concentrated and stable to facilitate the transition of molten metal, as shown in Figure The coating stabilizes the arc combustion.
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Create a reducing or neutral atmosphere around the arc to prevent oxygen and nitrogen in the air from entering the molten metal, as shown in Figure The skin keeps the air out.
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The generated slag uniformly covers the surface of the weld metal, slowing down the cooling rate of the weld metal and obtaining a good weld appearance, as shown in Figure The coating makes the weld well formed.
Ensure that the slag has appropriate melting point, viscosity, density, etc., so that the electrode can be welded in all positions or easy to carry out special operations, such as downward vertical welding
Under the action of high temperature arc, a series of metallurgical chemical reactions occur, to remove oxides and S, P and other harmful impurities, can also be added to the appropriate alloy cable, in order to ensure that the molten metal has the required mechanical properties or other special properties, such as corrosion resistance, high heat resistance, wear resistance.
In addition, adding a certain amount of iron powder to the electrode coating can improve the performance of welding process or increase the efficiency of welding.
Classification of welding electrodes
There are many kinds of welding rods, about 300 kinds.
According to the properties of molten slag after melting, electrode can be divided into acid electrode and alkaline electrode. The welding of general metal materials mainly uses acid electrode for welding. Acid electrode arc is easy to start, stable arc, suitable for AC and DC power welding, good slag removal, rust, oil, water and other insensitive, welding splash small, less soot, but the weld metal mechanical properties of the general, mainly suitable for welding of low carbon steel plate welding welding welding requirements are not high. Alkaline electrode arc stability is poor, can only use DC welding power source welding, slag removal is poor, welding splash larger, more smoke. But the plasticity, impact toughness and crack resistance of weld metal are better. Generally, it is used for metal materials with high welding quality requirements. The comparison of operating performance of acid electrode and alkaline electrode is shown in Table Operating performance of acid electrode and alkaline electrode.
According to the purpose of the electrode can be divided into: carbon steel electrode, low alloy steel electrode, molybdenum and chromium key heat resistant steel electrode stainless steel electrode, surfacing electrode, low temperature steel electrode, cast iron electrode, nickel and nickel alloy electrode, copper and copper alloy electrode, aluminum and aluminum alloy electrode, special purpose electrode and so on.