Basic knowledge of welding rods
Basic knowledge of welding rods
Blog Article
The welding rod is a melting electrode coated with flux for arc welding. It consists of two parts: flux and welding core.
The metal core covered by flux in the welding rod is called welding core. The welding core is generally a steel wire with a certain length and diameter.
The welding core has two functions:
1. Conducting welding current, generating arc to convert electrical energy into heat energy.
2. The welding core itself melts as filler metal and fuses with liquid parent metal to form a weld. When welding with welding rods, the welding core metal accounts for a part of the entire weld metal. Therefore, the chemical composition of the welding core directly affects the quality of the weld. Therefore, the steel wire used as the welding rod core has its brand and composition specified separately.
If it is used as filler metal in fusion welding methods such as submerged arc automatic welding, electroslag welding, gas shielded welding, and gas welding, it is called welding wire.
The welding rod coating refers to the coating layer applied on the surface of the welding core. The coating decomposes and melts during the welding process to form gas and slag, which plays a role in mechanical protection, metallurgical treatment, and improvement of process performance.
The components of the coating include: minerals (such as marble, fluorite, etc.), ferroalloys and metal powders (such as ferromanganese, ferrotitanium, etc.), organics (such as wood powder, starch, etc.), and chemical products (such as titanium dioxide, water glass, etc.). The coating of the welding rod is an important factor in determining the quality of the weld.
It has the following functions during the welding process:
1. Improve the stability of arc burning.
It is not easy for a bare welding rod without a coating to ignite the arc. Even if it is ignited, it cannot burn stably.
2. Protect the welding pool.
During the welding process, oxygen, nitrogen and water vapor in the air penetrate into the weld, which will have an adverse effect on the weld. Not only will pores be formed, but it will also reduce the mechanical properties of the weld and even cause cracks. After the welding rod coating melts, a large amount of gas is generated to cover the arc and the molten pool, which will reduce the interaction between the molten metal and the air. When the weld is cooled, the melted coating forms a layer of slag, which covers the weld surface, protects the weld metal and allows it to cool slowly, reducing the possibility of pores.
3. Ensure the deoxidation of the weld and the removal of sulfur and phosphorus impurities.
Although protection is carried out during the welding process, it is inevitable that a small amount of oxygen enters the molten pool, oxidizing the metal and alloy elements, burning the alloy elements, and reducing the quality of the weld. 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 molten pool.
4. Supplement alloy elements for the weld.
Due to the high temperature of the arc, the alloy elements of the weld metal will be evaporated and burned, which will reduce the mechanical properties of the weld. Therefore, appropriate alloy elements must be added to the weld through the coating to compensate for the burning of the alloy elements and 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 coating so that the weld metal can be close to the composition of the parent metal and the mechanical properties can catch up with or even exceed the base metal.
5. Improve welding productivity and reduce spatter.
The electrode coating has the function of increasing molten droplets and reducing spatter. The melting point of the electrode coating is slightly lower than the welding point of the welding core.
However, because the welding core is in the center of the arc and the temperature is higher, the welding core melts first and the coating melts a little later. At the same time, since the metal loss caused by spatter is reduced and the deposition coefficient is increased, the welding productivity is also improved.