This non-standard cold-forged carbon steel zinc-nickel alloy hexagonal self-tapping screw with a black oversized ferrule washer is a high-performance fastener. Below is a detailed explanation of its custom requirements, balancing technical details with practicality.
I. Basic Parameter Requirements
Material
Carbon steel grade: SCM435.
Surface treatment: Zinc-nickel alloy electroplating (thickness 8-12μm) + black passivation (meets 72-hour neutral salt spray test).
Structural Design
Screw head: External hexagonal (across-flat dimensions as per customer drawing; a 10% oversize is recommended for increased torque).
Integrated washer: Oversized ferrule washer (outer diameter 1.5 times the screw head, thickness 1.2-1.5mm, chamfer required for scratch protection).
Thread: Self-tapping (ST4.2-ST6.3 recommended, thread profile according to GB/T 5280).
Dimensional Tolerances
Total length ±0.1mm, head height ±0.05mm, washer flatness ≤0.03mm.
II. Key Points in the Cold Forging Process
Mold Design: Use a tungsten steel mold, with 3-4 forming stages: preforming → head extrusion → washer forming → thread rolling.
Mold drawings are required for confirmation to avoid cracking at the joint between the washer and the head.
Processing Control
Cold Forging Speed: 150-200 pieces/minute, annealed material hardness HRB 75-85.
Go/no-go gauge inspection required after thread rolling.
Mold drawings are required for confirmation to avoid cracking at the joint between the washer and the head.
Processing Control
Cold Forging Speed: 150-200 pieces/minute, annealed material hardness HRB 75-85.
Go/no-go gauge inspection required after thread rolling.
III. Surface Treatment and Performance
Zinc-Nickel Alloy Electroplating
Composition: Zn-Ni 12-15%.
Black Passivation Process: Chromium-free passivation, color difference ΔE ≤1.5.
Performance Testing
Torque Test: No fracture at 80% of the standard value.
Hydrogen Embrittlement Risk: Bake at 200°C for 4 hours after electroplating to remove hydrogen.
IV. Packaging and Delivery
Packaging Method
Inner Packaging: Anti-rust paper + blister tray (100 pieces per tray); Outer Packaging: Waterproof carton (10 trays per box).
Document Requirements
Submit material report (SGS), salt spray test report, and full-size inspection report (CPK ≥ 1.33).
V. Notes
Customization Lead Time: Mold development: 15 days + production: 10 days (first batch); mass production lead time negotiable.
Minimum Order Quantity: 5,000 pieces (negotiable).
Special Requirements: Requirement for ROHS/REACH certification must be specified in advance.
The above solution balances technical details with production feasibility. Parameters can be adjusted based on actual needs. We recommend providing sample drawings or application scenarios for further design optimization.
