Electrode coating is coated on the surface of the core layer of paint. During the welding process, the medicinal leather decomposes and melts to form gas and slag, which plays the role of mechanical protection, metallurgical treatment and improvement of process performance. The composition of the medicinal skin includes: minerals (such as marble, fluorite, etc.), ferroalloy and metal powder (such as ferromanganese and ferrotitanium), organic substances (such as wood flour and starch), chemical products White powder, water glass, etc.). Electrode coating is to determine the quality of the weld an important factor in the welding process has the following aspects:
First, improve the stability of the arc burning. Caked electrode is not easy to ignite the arc. Even if ignited can not be stable combustion. In the electrode coating, usually containing potassium, sodium, calcium ionization potential low material, which can improve the stability of the arc, to ensure the welding process continued.
Second, to protect the welding pool. Welding process, the air of oxygen, nitrogen and water vapor into the weld, will have a negative impact on the weld. Not only the formation of pores, but also reduce the mechanical properties of the weld, and even lead to cracks. The melted electrode coating, the large amount of gas generated arc and molten pool, will reduce the molten metal and air interaction. When the weld cools, the melted skin forms a layer of slag that covers the surface of the weld to protect the weld metal and allow it to cool slowly, reducing the chances of porosity.
Third, to ensure that the weld deoxidation, desulphur impurities. Although the welding process has been carried out to protect, but still inevitably have a small amount of oxygen into the pool, the metal and alloy elements oxidation, burning alloying elements, reducing weld quality. Therefore, it is necessary to add a reducing agent (such as manganese, silicon, titanium, aluminum, etc.) to the electrode coating to reduce the oxides that have entered the weld pool.
Fourth, for the weld alloying elements. Due to the high temperature of the arc, alloying elements of the weld metal will be burned by evaporation, reducing the mechanical properties of the weld. Therefore, we must add appropriate alloy elements to the weld through the coating to make up for the loss of alloying elements, to ensure or improve the mechanical properties of the weld. Some of the alloy steel welding, but also need to penetrate the weld alloy into the alloy, the weld metal can be close to the parent metal composition, mechanical properties to catch up with or even exceed the base metal.
Fifth, improve welding productivity, reduce splashing. Electrode coating with droplets to increase the role of reducing the splash. The melting point of the electrode coating is slightly lower than the solder joint of the welding core. However, because the welding core is in the center of the arc, the welding temperature is high, so the welding core first melts and the coating melts at a later time. In this way, the end of the electrode to form a short section of the drug casing, coupled with the role of the arc blowing force, the drop diameter straight shot to the pool, so that it is conducive to Yang welding and vertical welding. In addition, the coating coated with drug skin, the arc heat more concentrated. At the same time, welding productivity is improved by reducing the metal loss caused by spatter and increasing the cladding coefficient. In addition, the amount of dust in the welding process will be reduced.
Sixth, the skin plays an extremely important role in the welding process. In the welding process, the oxygen and nitrogen in the air will invade the molten metal in a large amount, and the metal iron and beneficial elements such as carbon, silicon and manganese will be oxidized and nitrided to form various oxides and Nitride, and remain in the weld, resulting in weld slag or cracks. The melting of molten gas into the weld pool may produce a large number of pores, these factors can make the weld mechanical properties (strength, impact value, etc.) greatly reduced, while making the weld brittle. In addition, the use of light welding electrode, the arc is very unstable, serious splash, weld formation is poor. People in the process of practice found that if coated with a layer of light from the skin and other minerals composed of medicine can make the arc burning stable, improve the quality of the weld, the welding rod called the electrode. With the continuous development of industrial technology, people have created a wide range of high-quality thick-skinned electrode.
Seven, electrode coating type and main features. According to the main components of the coating can determine the electrode type of coating. Due to the composition of different prescription drugs, resulting in a variety of drug-type electrode slag properties, welding performance and weld metal mechanical properties are very different. Even the same type of coating, but different grades of welding rod because of the composition and the ratio of different ingredients, welding rod and other performance characteristics will be significantly different.