The raw material is A36 carbon steel round bar and steel strip for expansion sleeve. Upon incoming delivery, we carry out strict inspection. A spectrometer is used to test chemical composition to confirm compliance with A36 carbon steel standard. Tensile strength, yield strength and elongation tests are performed to verify load-bearing capacity. Visual inspection checks for cracks, rust, folds and surface pits on steel bar and strip. We also measure diameter, thickness, straightness and flatness. Non-conforming raw materials are marked, isolated and returned to prevent mixing into production batches.
2.Cutting & Stamping Forming:
Qualified steel bars are cut to specified length by band saw for anchor bolt body. The steel strip is fed into stamping press, slitted, rolled and welded to form tubular expansion sleeve. The sleeve is stamped with anti-slip diamond knurling and expansion slots. The bottom of the sleeve is pre-shaped for expansion opening. Burrs generated in stamping and cutting are removed thoroughly to avoid sharp edges. Hex flange nuts are cold-forged separately from carbon steel wire rod.
3.Thread Rolling & Taper Head Forming:
The bolt blank is clamped on thread rolling machine to form full external threads. Thread rolling improves thread density, tensile strength and fatigue resistance compared with cutting threads. One end of the bolt is cold-forged into a conical tapered head. The taper angle is precisely controlled; this tapered section will push the sleeve open and create friction locking force when tightening the nut.
4.Pre-assembly Function Test:
Assemble the bolt, expansion sleeve and flange nut together. Rotate the nut to check thread fit, confirm no galling, jamming or loose fit. Pull test is conducted to verify that the tapered head can expand the sleeve slots smoothly. Workpieces with crack, distorted slots, incomplete knurl or unqualified thread are rejected before surface treatment.
5.Color Zinc Plating Surface Treatment:
The qualified semi-finished assemblies go through the electroplating line following the standard sequence: alkaline degreasing → water rinsing → acid pickling to remove rust and oxide → activation treatment → zinc electroplating → chromate iridescent passivation. Coating thickness and passivation time are strictly controlled to achieve uniform rainbow color, good adhesion and corrosion resistance. After plating, parts are rinsed completely and baked at low temperature to eliminate residual liquid and prevent white rust formation.
6.Final Inspection & Packaging:
Carry out finished product inspection one by one or by sampling. Check thread compatibility, expansion opening performance, coating adhesion, salt spray resistance, dimension and appearance. Reject items with plating peeling, blistering, scratches or deformation. Qualified sleeve anchors are packed into moisture-proof bags and cartons with desiccant inside. Each package is labelled with material grade A36, specification, batch number and inspection mark for storage and shipment.