First, surfacing welding process
Surfacing welding process is a kind of process in which materials with certain mechanical ability are piled on the welded surface of the base material by welding method. The purpose is not to directly weld the weldment with the base material, but to obtain the weldment surface with special properties such as wear resistance, heat resistance and corrosion resistance, and also to restore or increase the size of the weldment. Surfacing welding method has been widely used in manufacturing and repair.
Second, the selection of surfacing metal requirements
The surfacing metal should first meet the use conditions of the welding base metal, and then consider the welding mechanical ability of the surfacing metal, and then choose the most appropriate method in the appropriate way.
In the common welding methods, the total argon surfacing welding process has a small heat input and a small deformation. The advantages of small expansion coefficient after welding, beautiful weld formation, good interlayer fusion ability, etc., are widely used in surfacing welding, this method of welding temperature requirements and pressure layer are very strict. Today, I will introduce the requirements of the surfacing welding process.
Three, carbon steel and stainless steel surfacing welding
Welding example: pressure vessel flange waterline sealing disc. In order to ensure the corrosion resistance requirements of large manhole flanges, the carbon steel layer cannot be directly contacted with chemical raw materials. Choose to weld a layer of stainless steel on top of carbon steel metal as a contact surface, and process after welding.
Four, welding material selection
ER309MO carbon steel Q345R is surfacing welded metal S31603. Surfacing thickness 6mm height.
Austenite plus carbon steel these two types of metals in welding, although 309L welding wire can be used directly. However, due to the application in Class 2 containers containing high temperature, corrosive media, to choose a higher MO component.
Five, welding current
Welding current first time, 135A; The second layer 160A; Last floor 150A. The amount of heat input is related to the deformation ability of the welded base material. Strict control of the size of the current is an important factor in welding.
Six, the first layer welding
When welding the first layer, it is required to move quickly after melting the metal as deep as possible. The welding thickness of the first layer is controlled below 3 mm. The swing width should be small, and the second circle of welding should be performed after the completion of one circle of welding. When the first layer of surfacing is finished. Let the temperature drop and then proceed to the second layer welding. The weld should be pressed between each strand at half the position of the first strand. The pressure channel control can not be too small, too small is easy to cause too low between layers. Too large will cause too much tension crack defects.
Seventh, the second layer welding
When welding the second layer, the current is slightly amplified, so that the metal of the second layer and the first layer are well fused. Welding swing amplitude can be properly amplified. The number of passes between the second layer can be reduced.
Eight, the final layer of welding
When welding the last layer, it is necessary to grasp the height of welding. The height of 6 mm allows stacking up to more than 8 mm. Higher metal can be processed through the remaining amount. The height is less than 6 mm and cannot be machined by the turning tool. In order to avoid the processing caused by the welding pattern is too large, the last layer can be used to pull the method, so that the middle layer of the weld is closely integrated.
Nine, the gas flow rate is 12L
Gas flow using 12L. Argon flow control can not be too small, which will cause too much oxidation, welding molten iron can not be spread. Too much argon flow will cause the gas deviation of the weld and produce a bailing arc. Argon purity is recommended to choose high purity argon, tungsten electrode extension length is controlled below 6mm.
Ten, weld from the outside in
When welding, weld from the outside in, so that the contraction force is directly placed in the circle. When there is a vertical fillet weld position, direct melt welding without wire should be used first. Melt the weld at the Angle once before adding wire welding.