Welding Method
Common welding methods for steel structures include arc welding, such as manual arc welding, automatic or semi-automatic arc welding, and gas shielded welding, among others.
Manual arc welding is a commonly used welding method in steel structures, characterized by its simple equipment and flexible, convenient operation. However, the working conditions are poor, the production efficiency is lower than that of automatic or semi-automatic welding, and the variability of weld quality is significant, which is to some extent dependent on the welder's technical proficiency.
Automatic welding ensures stable weld quality with fewer internal defects, good plasticity, and excellent impact toughness, making it suitable for longer straight welds. Semi-automatic welding, due to manual operation, is ideal for welding curves or irregularly shaped welds. Both automatic and semi-automatic welding should use welding wire and flux compatible with the base metal. The welding wire must comply with national standards, while the flux should be determined based on the welding process requirements.
Gas shielded welding uses inert gases (or CO2) as the protective medium for the arc, isolating molten metal from the air to maintain a stable welding process. The arc heating is concentrated, resulting in faster welding speeds, greater penetration, and thus higher weld strength compared to manual welding. Additionally, it boasts good plasticity and corrosion resistance, making it suitable for welding thick steel plates.
Section II: Weld Seam Styles
Welding joints can be categorized into four types based on the relative positions of the components being connected: butt joints, lap joints, T-joints, and corner joints. These connections utilize two basic types of welds: butt welds and fillet welds. In actual application, the choice should be made according to the stress conditions of the joints, considering the manufacturing, installation, and welding conditions.
(Weld Seam Structure)
1. Weld Seam Connection
Direct and smooth transmission of force through the butt weld without significant stress concentration, hence excellent load-bearing performance. Suitable for connections of components subjected to both static and dynamic loads. However, due to the high quality requirements for the butt weld, the welding gap between the weldments must be strictly controlled, and it is generally used more in factory-manufactured connections.
2. Angular Weld Seams
Weld Seam Forms: Weld seams can be categorized according to their lengthwise direction and the direction of external force, including lateral seam welds parallel to the force direction, frontal seam welds perpendicular to the force direction, diagonal seam welds oblique to the force direction, and encircling weld seams.
The angular weld cross-sections are further divided into standard, flat slope, and deep penetration types. In the figure, "hf" refers to the weld leg size of the angular weld. The standard cross-section has a weld leg edge ratio of 1:1, approximating an isosceles right triangle, with a more abrupt bend in the force transmission line, hence severe stress concentration. For structures directly subjected to dynamic loads, to ensure smooth force transmission, the face angular welds should be in the flat slope type with a weld angle ratio of 1:1.5 (the long side along the internal force direction), while the side angular welds should be in the deep penetration type with a ratio of 1:1.
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