Classification and selection of welding materials

When the selection of welding materials is specified in the design, it shall be selected in accordance with the requirements of the design documents. In the absence of design provisions, on the premise of ensuring structural safety and reliable use, the selection shall adhere to the principles of improving operating conditions and enhancing technical and economic benefits, with comprehensive consideration of the following factors: chemical composition and mechanical properties of metal materials, properties of weld metal, characteristics of metal structure (plate thickness, joint form) and stress state, process technology, welding position and operating conditions (indoor, outdoor, space size, etc.), and welding workload (weld length, weld equivalent).

 Principle of matching the mechanical properties and the chemical composition of the weld metal

 Principle of meeting the characteristics and stress conditions of the welded structure

 Principle of meeting the characteristics and stress conditions of the welded structure

 Principle of welding process operability

 Principle of improving productivity and reducing costs

 Pure Tungsten Electrodes: Require the welding machine to have a high no-load voltage. Pure tungsten electrodes are extremely prone to burnout and have gradually been replaced by thorium-tungsten electrodes.

 Thorium-Tungsten Electrodes: They have high thermionic emission capacity and melting resistance, with the performance of easy arc ignition and low required no-load voltage. The allowable current can be increased by 1/3 compared with pure tungsten electrodes of the same diameter, and they are not easy to burn out, with a long service life. However, the dust of thorium-tungsten electrodes is slightly radioactive, so it is necessary to strengthen labor protection measures when grinding the electrodes.

 Cerium-Tungsten Electrodes: They have more advantages than thorium-tungsten electrodes, such as easy arc ignition, stable electric arc, slender arc beam with concentrated heat, 5%~8% increase in maximum allowable current density, low burnout rate, and long service life. Since cerium-tungsten electrodes have almost no radioactive hazards, they are currently the most widely used electrode material.