1. Fabrication Procedure of Welded H-Section Steel

2.Manufacturing Technology of Welded H-Section Steel

Step 1: Steel Plate Pretreatment

The pretreatment of steel plates can eliminate local concentration of internal stress generated during steel plate production, so as to reduce stress deformation of components in the fabrication process.

Step 2: Steel Plate Straightening

All steel plates shall be inspected 100% at the factory. Any plates whose flatness exceeds specification requirements shall be straightened to guarantee the dimensional accuracy of cut parts and components.

Step 3: Cutting of Flange Plates and Web Plates

To ensure the straightness of cutting edges for all parts and components, a multi-head straight cutting machine is adopted to cut both sides of flange plates and web plates simultaneously.

Step 4: Secondary Straightening of Flange and Web Plates

Local deformation will occur on H-beam flange and web plates due to heat generated during cutting. To ensure assembly accuracy of structural members, secondary straightening shall be performed on cut parts as required.

Step 5: T-section Assembling

An automatic H-beam assembling machine is used to assemble flange plates and web plates into T-sections first, followed by tack welding with CO₂ shielded welding.

Step 6: H-section Assembling

The automatic H-beam assembling machine is utilized to assemble the T-shaped components with another flange plate into an H-section, and tack welding is performed by CO₂ shielded welding.

Step 7: Welding of H-section Steel

Automatic submerged arc welding machines are adopted for the main welds of H-beams. Run-on and run-off tabs shall be fitted at both ends before welding.

Step 8: Straightening of H-Section Steel

Special H-beam straightening machines are used to correct the angular deformation of H-beam flanges caused by welding.

Step 9: Assemble Connection Plates

Mark the positioning lines of parts in accordance with the component fabrication drawings. Fit and assemble all components along the marked lines. Carry out welding only after all dimensions are verified correct.

Step 11: End Milling

For H-section steel components that pass inspection, machine the ends flat and cut locking notches using a special tenoning machine.

Step 12: End Drilling

The connecting holes on the ends of the H-beam shall be precisely drilled with a CNC 3D drilling machine to ensure the dimensional accuracy of all hole positions.

Step 13: Stud Welding

Studs shall be welded with a stud welding machine. Mark the stud positions and bake the ferrite rings before welding.

Step 14: Sandblasting & Rust Removal

The surface of H-beams shall be derusted by a high-power shot blasting machine. Proper abrasive material shall be selected to meet the requirements for surface rust removal grade and friction coefficient of the components.

Section III Key Points for Fabrication of Welded H-Beams

(1) Cutting & Blanking

Before blanking, carefully verify the material grade, specification and dimension of steel plates. Cutting can only proceed after confirmation. Meanwhile, inspect the flatness of steel plates. Any plate exceeding the flatness limits specified in the table below shall be straightened first. Cutting shall be carried out only after straightening passes inspection.

Remove rust, oil stains and other contaminants from the steel plate surface before cutting to guarantee cutting quality.After cutting, clean off scale and dross on the cutting surface before transferring to the next process.

Cutting tolerances and quality shall comply with the requirements specified in the table below.

(2) H-beam Assembling

Before assembling welded H-beams, mark the centerline of flange plates and positioning lines of the web. Check the number, material grade, dimension and quantity of flange plates and webs. Assembly can only start after passing inspection

When assembling on the automatic H-beam assembling machine, first perform T-shaped assembly of flange plates and web plate, followed by tack welding.

When assembling H-beams on the jig frame, the assembly platform and jig shall meet the precision requirements for component fitting and possess sufficient strength and rigidity. The facilities can only be put into use after being inspected and accepted by designated personnel.

During the assembly of welded H-beams, tack welds shall be free from cracks and blowholes. Tack welding shall only be performed by certified welders with valid qualifications, using the same welding consumables as for the official welding.

The leg size of tack welds shall not exceed two-thirds of the designed weld leg height and shall not be less than one-half of the designed value.Each tack weld shall be approximately 50 mm long with spacing less than 300 mm.The tack welds shall be more than 50 mm away from the ends of the H-beam.If preheating is required for tack welding, the preheating temperature shall be higher than that for formal welding. Illegal operations are prohibited.

The assembly precision of H-beams shall meet the requirements in the table below.

(3) H-Beam Welding

After the H-beam assembly passes inspection, hoist it onto the gantry automatic submerged arc welding machine for welding. Prior to welding, remove rust, burrs, oxides, oil contamination and other impurities within the weld zone.

Before welding, install run-on plates and run-off plates made of the same material as the component at both ends. The extended length of the weld shall not be less than 50 mm.

Before welding, use ceramic electric heaters to preheat the area within 100 mm on both sides of the weld seam. The preheating temperature shall be 80~120℃. An infrared thermometer shall be used during heating to avoid overheating. Welding can start once the specified temperature is reached.

Automatic gantry submerged arc welding shall be adopted. Welding shall follow the sequence shown in the drawing: Weld 1 → Weld 4 → Weld 2 → Weld 3.

If the plate thickness is less than 40 mm, complete each weld in one pass before turning the member over.If the web thickness is 40 mm or thicker, do not finish each weld in a single pass. Turn and rotate the component several times to minimize welding distortion.

During submerged arc welding, the weld leg size shall conform to the drawing requirements. Monitor the wire position continuously and make timely adjustments to prevent wire deviation.

If arc breakage occurs during welding, the joint shall be ground into a transition slope of no less than 1:4 before resuming welding.

After welding is completed, remove welding slag on the weld surface and spatter on both sides. Cut off the run-on and run-off plates by gas cutting and grind the cutting surface smooth. It is strictly forbidden to knock them off with a hammer.

For materials below Q390 grade, non-destructive testing (NDT) of welds shall be carried out 24 hours after welding. Straightening can only be conducted after the NDT passes inspection.

(4) Straightening of Welded H-beams

Welded H-beams shall be straightened after welding. Two methods are available: mechanical straightening and flame straightening. Angular welding deformation shall be corrected by flame heating or with an H-beam flange straightening machine. The steel surface after straightening shall be free of obvious scratches and damages, and the scratch depth shall not exceed 0.5 mm.Bending and torsional deformation shall be rectified by flame straightening. The heating temperature shall be controlled between 800℃ and 900℃, and overheating is not allowed.