304/316 K2-K6 high salt spray plastic special fast thread self-tapping screw is a fastener designed for use in high corrosion environments, such as coastal, chemical and plastic substrate design fields. The following is a customized solution for 304/316 high salt spray plastic special fast thread self-tapping screws. It combines the core requirements of salt spray protection, thread design, material adaptation, etc., to systematically design fasteners, combining specific stainless steel materials, salt spray protection processes, and fast thread structures.
1. Material selection and salt spray protection
304 vs 316 stainless steel
304 stainless steel: basic corrosion-resistant material, conventional salt spray test up to 96 hours, high-quality process can be increased to 2000 hours.
316 stainless steel: adding the molybdenum element, chemical corrosion resistance is significantly better than 304, suitable for marine, chemical, and other scenes.
Surface treatment technology: passivation plus sealant: neutralize and seal micropores through passivation liquid, and the salt spray time is increased from 96 hours to more than 360 hours.
Black zinc/Dacromet coating: The black coating is both beautiful and highly protective, with a salt spray test of 240–1000 hours and an outdoor life of 3–5 years.
2. Thread design (K2–K6) and plastic compatibility
K2/K3 are fine-toothed and shallow-pitch, suitable for hard engineering plastics such as PC and POM, and play a role in preventing cracking of high-hardness materials.
K4/K5 are standard self-tapping threads, suitable for nylon, PP, and glass fiber reinforced plastics, and play a universal role in balancing strength and anti-slip.
K6 is wide-toothed and large-lead, suitable for soft materials such as PE and foamed plastics to reduce material stress cracking.
Design points
Tail optimization: The drill tail design improves the efficiency of plastic cutting and reduces the installation torque by 30%.
Thread lubrication: Nylon material has its own lubricity, which reduces the resistance to screwing in, and is especially suitable for K6 threads.
3. Key technologies for performance enhancement
Hardness and toughness balance
Surface hardness: 550–750 HV to ensure self-tapping capability.
Core hardness: 350–450 HV (anti-fracture, bending > 15%).
It should be noted that 410 stainless steel can achieve this performance through heat treatment, but its corrosion resistance is lower than 304/316, and coating compensation is required.
Temperature and chemical compatibility: long-term use ≤100℃ (strength decays by 5% per 100℃ after overheating).
Solvent resistance: avoid nylon from contacting strong acids (such as sulfuric acid), PP/PE has good oil resistance.
316 stainless steel has better acid and alkali resistance than 304, and is suitable for plastic equipment in a chemical environment.
Customized application scenarios
Electronic appliances: K2 fine teeth + 304 black zinc screws, which can insulate and prevent short circuits, salt spray 240 hours) 5.
Outdoor structure: K5 thread + 316 Dacromet, can withstand 1000 hours of salt spray, and has a service life of 1.5-2 years at the seaside.
Lightweighting of automobiles: K6 wide thread + glass fiber reinforced nylon screws, which can reduce weight by 30% and resist vibration.
