1. Structural characteristics
Lightweight steel structures usually use Q345 and Q235 steel, and most of them are Q345 steel. Q345 steel is the most commonly used and mature low-alloy high-strength structural steel with excellent performance and good weldability. Except for some column base plates, the thickness of the web and wing plates is basically 4-20mm medium thin plates, which is the most favorable thickness range for the welding process. Light steel structures generally do not use box-shaped and cross-shaped structures, and most of the members are H-shaped cross-sections. Due to the characteristics of economy, stress, and structure, rolled H-shaped steel is generally not used, and most of them are welded H-shaped steel.
For H-shaped solid web beam-column structure, it is easy to realize the automation of welding and assembly. However, except that the sandwich beam, part of the side columns, and the middle column have the same cross section, most of the members are of variable cross section, which also puts forward higher requirements for the automation of welding.
2. Cutting method
Gate-type multi-head flame cutting is the main cutting method of wing opening strips. Propylene, propane, LPG-type new gas has gradually replaced acetylene.
Because the web thickness is thin, and most of them are wedge-shaped, CNC plasma cutting method is usually used. Plasma cutting method using oxygen, the cutting speed is fast, the cutting quality is good, but the requirements for the consumption electrode are higher.
The cutting quality of web has a great influence on the assembly and welding quality of components. Due to the thin plate thickness, the deformation or residual stress after cutting will cause the wave-shaped deformation of the web. The quality of the cutting edge will directly affect the welding and quality of the fillet weld between the web and the wing.
3. Welding method
The welding process and production process depend on the assembly of the H-beam, the welding of the main weld between the web and the wing, which varies depending on the assembly method, welding method and welding position. Such as the movement of the head or the movement of the workpiece; the horizontal position or the position of the ship; the single head or the double head; the single wire or the double wire, etc.
For dry sheet structure, gas shielded welding is undoubtedly the most ideal welding method. Therefore, in addition to the submerged arc automatic welding, most of the board assembly welding uses gas shielded welding. In particular, argon-rich mixed gas shielded welding is more suitable for light steel structures due to its good forming and low spatter.
In order to prevent rusting during stacking, transportation and installation, and to lay the foundation for further coating, pre-treatment and spraying of primer are required after welding of components.
The surface quality of the surface treatment and rust removal of the component is required to be above Sa2.0～Sa2.5. According to the different environmental media of the component, choose anti-rust primer. The light steel structure primer is mainly alkyd type, but also epoxy zinc-rich type. At the installation site, apply topcoat or fire retardant paint as needed.
Light steel structure is mainly H-shaped solid web beam column structure, so the surface treatment and coating process is relatively simple, and it is also easy to realize mechanized flow operation. The surface treatment adopts the shot blasting technology, the raceway type or the hanging type feeding method. Paint spraying is generally manual operation, combined with hanging shot blasting, or semi-mechanized assembly line operation.
The surface treatment before painting is critical to the anticorrosive effect of the component primer, and the thickness and uniformity of the paint film will directly affect the anticorrosive performance of the component.
5. Main process issues
Since light steel structure and heavy steel structure are very different in steel type, plate thickness and structural form, the main difficulties and problems in welding production are also very different.
If the heavy steel structure is due to the thickness of the steel plate, high material grade, and poor welding conditions, the manufacturing problems are mainly reflected in the welding operability of the structure, the weldability of the steel, and the prevention of joint welding defects. The light steel structure is mainly Prevent and reduce the deformation and correction of welding, and improve the problem of welding productivity.