III. Component processing
3.1 Edge machining: for webs, flange plates, stiffened plates, bearing support surfaces, and technically cut welding groove, cutting or gas cutting steel plate edges need to be processed. There are four kinds of edge machining methods: shovel edge, planing edge, milling edge and carbon arc edge planing.
3.2 bending molding
（1） Steel plate crimp: steel plate crimp is formed by continuous three-point bending of sheet metal by rotating roller shaft. Steel plate crimping consists of three processes: prebending, counterwinding and crimping.
①Pre-bending: when the steel plate is curled on the reeling machine, the edges at both ends always have parts that cannot be rolled, that is, the remaining straight edges. Eliminate the remaining straight edges by prebending.Pre-bending: when the steel plate is curled on the reeling machine, the edges at both ends always have parts that cannot be rolled, that is, the remaining straight edges. Eliminate the remaining straight edges by prebending.
②alignment: in order to prevent the bending of steel plate in the bending machine, the steel plate should be aligned so that the longitudinal center line of the steel plate and the roller axis are kept strictly parallel.
③crimping: after adjusting the position of the roller, the steel plate is bent initially, and then rolled back and forth and crimped
(2) profile bending
①Section steel bending: section bending section will be distorted, the smaller the bending radius, the greater the distortion. The minimum bending radius of the section should be controlled. Because the curvature radius of the component is larger, the cold bending should be adopted, and the curvature radius of the component is smaller, so the thermal bending is suitable.
② bending of steel tube: when bending in free state, the section will deform, the outer wall will be thinned, and the inner wall will be thickened. Bending method: insert filler (sand) into the tube or bend through the mandrel; or bend outside the tube with rollers and chute. Radius of bending: 3.5 times (hot bending) to 4 times (cold bending) of pipe diameter
(3) flanging: the process of bending the edge of a member into an obliquity or a certain shape is called an edge folding. Folding can improve the strength and stiffness of the construction. The bending edge is carried out by the edge folding machine.
(4)Hole making: including rivet hole and bolt hole, which can be drilled and punched. Drilling with drilling machine, can be used for steel plate, section steel hole processing; punching machine for punching, generally only in the thin steel plate, rigid punching, and the diameter of the general steel thickness. The hole control in the construction site can be processed by electric drill, air drill, etc.
3.3 component correction
Steel in the storage, transportation, lifting and processing of the process of deformation, must not meet the technical standards of steel, components for correction. The correction of steel structure is to force the steel into reverse deformation by external force or heating, so that the steel or component can meet the requirements of the technical standard of straight or geometric shape. Methods of correction include: thermal correction, mechanical correction, cold correction
(1) Thermal correction: local heating of steel by flame, compression plastic deformation of heated metal due to expansion, shortening of long metal fiber after cooling. The factors that affect the effect of thermal correction include: the position of flame heating, the form of heating, and the temperature of heating. Thermally corrected temperature: 600-800 degrees for low carbon steel and common alloy steel
(2) Mechanical correction: it is to produce excessive plastic deformation under the action of external force of the steel which is bent by the right to use the special corrector, in order to achieve the purpose of straightening. Drawing machine correction: used in thin plate distortion, profile steel distortion, steel pipe, strip, wire, etc. Press correction: used for plate, steel pipe and profile correction. Multi-roll straightening machine: used for the correction of profile, plate, etc.
(3) Cold correction: by hammering method, the operation is simple and flexible. Cold correction is used in steel with smaller size because of its small correction force, high labor intensity and low efficiency. Or when mechanical correction equipment is not easy to use.
Rust removal, anticorrosion and finishing
The anticorrosion and finishing of steel structure includes common coating and fire resistant coating. The steel surface should be rusted before painting.
4.1 Rust removal of steel: the methods used just now include sandblasting, shot blasting, pickling and manual rust removal with steel wire brushes, grinding wheel on site, etc. Shot blasting is the best way to remove rust.
4.2 anticorrosion and finishing: the methods of painting include brushing method (coating of oily base material) and spraying method (coating of fast drying and high volatility). The number of times of coating and the thickness of coating layer shall conform to the design requirements, and the surface of steel should not be misapplied or missed. The coating should be uniform, without obvious wrinkle, drop, needle eye, bubble grade molting and back embroidery, etc. Coating thickness of fire resistant coatings shall meet the requirements of fire resistance limit