Bolt-ball trusses are a common spatial grid structure widely used in large-span buildings such as stadiums, exhibition halls, and airport terminals. The production process primarily includes spatial structure design, raw material procurement, fabrication, quality inspection, and on-site installation. The detailed production process is as follows:
Space Frame Design and Layout
1. Space Frame Design
Perform load calculations and force analysis based on building requirements to determine the truss form (e.g., square pyramid, triangular pyramid, etc.).
Use professional software (such as MST, 3D3S, SAP2000, etc.) to perform modeling and joint force analysis.
Determine parameters such as bolt-ball node location, member length, and sleeve angle.
2. Fabrication Drawings
Draw the bolt-ball fabrication drawings (including sphere diameter, number of screw holes, angle, and thread specifications).
Draw the rod fabrication drawings (including steel pipe length, end cone or cover plate dimensions, and high-strength bolt specifications).
Provide a materials list (bolt-balls, members, sleeves, high-strength bolts, etc.).
Raw Material Procurement and Inspection
1. Material Procurement
Bolt balls: Generally, 45-gauge steel is forged into blanks, or finished forgings can be purchased directly.
Rods: Seamless or welded steel pipes (Q235B or Q355B) are used, with tapers or end plates welded on both ends.
High-strength bolts: Grade 8.8 or 10.9 are commonly used and must comply with GB/T 16939.
Sleeves and fasteners: Match the bolts and be made of No. 45 steel or alloy steel.
2. Material Inspection
Inspect the steel’s material certification and mechanical property report.
Bolt ball blanks must undergo ultrasonic testing (UT) to detect internal defects.
Rod steel pipes must be inspected for wall thickness, straightness, and weld quality.
Bolt Ball Machining
1. Turning
The sphere’s outer shape is machined on a CNC lathe, maintaining a diameter tolerance (typically ±0.5mm).
A center reference hole is drilled to serve as a positioning reference for subsequent machining.
2. Screw Hole Machining
Use a five-axis CNC drilling machine or indexing head fixture to machine the screw holes to the designed angle.
The screw holes must be tapped (thread accuracy 6H), ensuring that the axis of each hole intersects the center of the sphere (deviation ≤ 0.1mm).
Rod Fabrication
1. Cutting
Steel pipes are cut to the designed length (allowing for welding shrinkage). The verticality deviation of the cut should be ≤1°.
2. Cone/Sealing Plate Riveting Assembly
Weld the cone or sealing plate to both ends of the steel pipe using CO₂ gas shielded welding or argon arc welding.
The weld must meet Class I or Class II weld standards (as specified in the design documents).
3. Weld Quality Inspection
After the rods are welded, the welds are first inspected visually. This inspection primarily assesses the weld’s appearance, checking for cracks, pores, undercuts, and incomplete welds. Next, the weld quality is assessed, primarily through ultrasonic testing, magnetic particle testing, and X-ray testing. If necessary, a tensile test may be performed on the welds, with the tensile test value used to determine weld compliance.
4. Anti-corrosion Treatment
Rust removal (sandblasting or shot blasting) to Sa2.5 is recommended. Hot dip zinc coating with a thickness of 80µm or greater is also available. Alternatively, spray painting is an alternative. Typically, two coats of epoxy zinc-rich primer (60µm or greater), two coats of epoxy micaceous iron sealer (60µm or greater), and two coats of aliphatic polyurethane topcoat (60µm or greater) are used. Topcoat colors can be customized to meet customer needs.
Component Numbering, Inspection, Packaging, and Transportation
1. Each rod is individually numbered, and the bolt balls also have their own code. The significance of component numbering is that upon arrival at the construction site, installers can quickly locate and use them for installation.
Trial assembly: Select a portion of the bolt balls and rods for partial assembly to check the joint fit accuracy. Measure grid size deviation (≤±1mm) and screw hole alignment. Bolt balls: ball diameter, screw hole angle, and thread go/no-go gauge. Rods: length tolerance (±1mm), weld quality, and bolt hole alignment. Paint layer: adhesion and thickness inspection.
On-site Installation
Lineout and Positioning: Mark the positions of the bearings and reference spheres according to the drawings.
Unit Assembly: Install the units layer by layer using the “high-altitude bulk assembly method” or “block-by-block lifting” method.
Bolt Tightening: Tighten the high-strength bolts using a torque wrench (torque values meet design requirements).
Inspection: Check joint clearances, overall deflection, and bolt tightening rate (100% inspection).
Key Quality Control Points
Bolt ball screw hole angle accuracy (±0.2°).
Rod length tolerance (±1mm).
High-strength bolt final tightening torque (tolerance ≤±5%).
Anti-corrosion coating uniformity with no missing coatings.
