Welding rods are used as welding materials for arc welding. Welding rods play an important role in welding quality, production efficiency and economic benefits. Welding rods are widely used and consume a lot. Therefore, it is necessary to master the composition, function, classification and performance of welding rods, understand the influence of welding rods on welding quality, as well as the inspection, storage and selection of welding rod quality.
The welding rod is a welding melting electrode composed of a welding core (metal core) and a coating (coating). Its shape and structure are shown in Figure welding rod and Figure Schematic diagram of electrode structure. One end of the electrode is the arc starting end, and the flounder skin at the arc starting end is generally ground to a certain angle so that the welding core is exposed for easy arc starting. For better arc ignition, low-hydrogen electrodes are often coated with arc ignition agent at the arc ignition end, or drill a small hole or open a slot on the end face of the welding core at the arc ignition end to increase the current density, as shown in Figure Schematic diagram of electrode structure—b Show. The other end of the electrode is the clamping end, and the clamping end is a section of exposed welding core with a length of 15-25 mm, which is clamped on the welding tongs during welding. The brand name of the welding rod is printed on the coating near the clamping end.
The end face shape of common electrode is shown in Figure End shape of welding rod-a, and Figure End shape of welding rod-b is a double-coated electrode, which is mainly to improve the process performance of low-hydrogen electrodes. The core is a hollow tube, the outer skin is covered with drug skin, and the center of the tube is filled with alloy agent or paint. This electrode is used in wear-resistant surfacing electrodes containing a large amount of alloy powder. Commonly used welding rod diameters are
φ2.5 mm, φ3.2 mm, φ4.0 mm three types.
In the process of electrode arc welding, the electrode plays the role of conducting current and igniting the arc on the one hand; on the other hand, it acts as a filler metal to form a weld with the molten base metal.
The metal covered by the coating in the electrode is the welding core, which is both the electrode and the molten filler metal. The composition of the welding core directly affects the composition and properties of the deposited metal. During electrode arc welding, the core metal accounts for about 50% to 70% of the entire weld.
The active ingredient coated on the surface of the welding core is the coating, 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 configured in a certain proportion. The main functions of the drug skin are as follows:
(1) Guarantee the concentration and stability of the arc, so that the molten metal is easy to transfer, as shown in Figure The drug skin makes the arc burn stable.
(2) Create a reducing or neutral atmosphere around the arc to prevent oxygen and nitrogen in the air from entering the deposited metal, as shown in Figure Solder coating prevents air from entering.
(3) The generated slag evenly covers the surface of the weld metal, slows down the cooling rate of the weld metal, and obtains a good weld shape, as shown in Figure The coating makes the weld well formed.
(4) Ensure that the slag has a suitable melting point, viscosity, density, etc., so that the electrode can be used for all-position welding or easy to perform special operations, such as downward vertical welding.
(5) Under the action of high temperature of the arc, the coating undergoes a series of metallurgical chemical reactions to remove harmful impurities such as oxides and S, P, and can also add appropriate alloying elements to ensure that the deposited metal has the required mechanical properties or Other special properties, such as corrosion resistance, high heat resistance, wear resistance, etc.
In addition, adding a certain amount of iron powder to the electrode coating can improve the performance of the welding process or increase the deposition efficiency.
There are many kinds of welding rods, there are about 300 kinds.
Electrodes can be divided into acid electrodes and basic electrodes according to the properties of slag after melting the coating. Generally, acid electrodes are mainly used for welding of metal materials. The acid electrode is easy to start the arc, the arc is stable, suitable for AC and DC power supply welding, good slag removal, insensitive to rust, oil, moisture, etc., less spatter and less smoke during welding, but the metal mechanical properties of the weld- Generally, it is mainly suitable for the welding of low-carbon steel plates that do not require high weld joints. The stability of the basic electrode arc is poor, and only DC welding power can be used for welding. The slag removal is poor, and the spatter and dust are more during welding . But the plasticity, impact toughness and crack resistance of weld metal are better. Generally, it is mostly used for metal materials that require high welding quality. See Table Acid electrode and basic electrode operation performance for the comparison of the operating performance of acidi c electrodes and basic electrodes.
Electrodes can be divided into: carbon steel electrodes, low alloy steel electrodes, molybdenum and chromium molybdenum heat-resistant steel electrodes, stainless steel electrodes, surfacing electrodes, low temperature steel electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes , Aluminum and aluminum alloy electrodes, electrodes for special purposes, etc.