10.9 grade carbon steel black plated pan head cross recessed screw (GB818 standard) is a high-strength anti-loosening fastener suitable for occasions that require frequent disassembly and assembly, and need to prevent loosening. Its surface treatment must take into account corrosion resistance, aesthetics, and functionality. The specific requirements are as follows.
1. Substrate and pretreatment
Material: 10.9 grade high-strength carbon steel, must meet the mechanical properties requirements of GB/T 3098.1.
Pretreatment
Degreasing and degreasing: alkaline cleaning to remove surface oil stains.
Pickling and rust removal: a hydrochloric acid or sulfuric acid solution to remove the oxide layer.
Phosphating treatment (optional): forming a phosphate film to improve the adhesion of the coating.
2. Plating process
Electroplating zinc-nickel alloy (recommended):
The thickness is recommended to be 8-12μm, providing basic corrosion protection (salt spray test ≥500 hours).
Black passivation treatment: chromate or chromium-free passivation (environmental protection requirements) is used to form a uniform black appearance.
Alternatives: Black oxidation (blackening): beautiful but weak corrosion resistance (salt spray test ≤ 24 hours), suitable for low corrosion environment.
Dacromet coating: high corrosion resistance (salt spray test ≥ 1000 hours), but the color may be grayish black.
3. Anti-loosening treatment
Nylon glue (PA66) embedding: pre-set hot melt glue ring in the middle or tail of the thread, and produce friction to prevent loosening when screwing in.
Temperature resistance range -40℃ to +120℃, vibration test (such as GB/T 10431) must be passed.
4. Performance and testing
Corrosion resistance: neutral salt spray test (GB/T 10125) ≥ 500 hours without red rust.
Adhesion: cross-cut test (GB/T 9286), no peeling of the coating.
Torque test: ensure that the anti-loosening effect of the nylon rubber ring meets the standard.
Notes
The black coating may affect the conductivity, and the purpose (such as grounding of electronic equipment) must be stated in advance.
In high temperature environments (＞120℃), the performance of nylon glue needs to be evaluated, or a metal anti-loosening structure needs to be used instead.
This solution balances the high strength, anti-loosening requirements, and appearance requirements, and is suitable for harsh working conditions such as machinery and electronics.
Through standardized operation and regular maintenance, the high strength and anti-loosening performance of the 10.9-level captive screws can be fully utilized to ensure connection reliability.
