304/316 K2-K6 high salt spray plastic special fast thread self-tapping screw is a fastener designed for use in highly corrosive environments, such as coastal, chemical and plastic substrate design fields. The following is a surface treatment solution for 304/316 high salt spray plastic special fast thread self-tapping screws, combining corrosion resistance, assembly performance and cost-effectiveness to optimize the design:
Core surface treatment solution
1. Closed passivation treatment (preferred)
Process principle:
A dense oxide film is formed on the surface of the screw through chromate or chromium-free passivation liquid to close the metal micropores on the surface of the stainless steel.
Salt spray performance: 304 stainless steel: ≥500 hours (neutral salt spray test, no red rust)
316 stainless steel: ≥1000 hours (meets C5 level anti-corrosion requirements)
Advantages of closed passivation treatment: It can maintain the original dimensional accuracy of the screw (coating thickness ≤0.5μm), does not change the thread cutting performance, ensures rapid penetration into the plastic,
Environmentally friendly and with no heavy metals, the cost is reduced by more than 30% compared with electroplating.
2. Nano-composite coating (alternative for extreme environments)
Technical combination: SILANE silane treatment + nano-ceramic coating
Salt spray performance:
304 stainless steel: ≥800 hours
316 stainless steel: ≥1500 hours
Features:
Ultra-thin coating (1-2μm) does not affect thread bite force, reduces friction coefficient by 15%, increases plastic penetration speed, and is resistant to acid, alkali, and UV aging.
Selection suggestions:
In coastal industrial areas (C4), it is recommended to use 304 stainless steel after closed passivation treatment, and it can be used for 5-8 years of safe life.
For offshore platforms (C5-M), it is recommended to use 316 stainless steel with nano-coating for more than 10 years.
Precautions
Assembly compatibility:
Preferably use a triangular tooth type or a double lead thread design, suitable for engineering plastics such as PA66 and PC.
Pre-drilling suggestion: hard plastic) needs to pre-drill the bottom hole (diameter = screw core diameter × 85%).
Failure warning: Regularly check the corrosion depth of the screw head slot, and replace it immediately when it is greater than 0.1mm.
Technical summary: Closed passivation is the most cost-effective solution, and nano-coating is suitable for extreme environments without maintenance; avoid any electroplating process that may thicken or embrittle, and ensure that the self-tapping efficiency and anti-corrosion performance of the fast-thread screws coexist.
