Characteristics Types and Applications of Plastic Screws
Plastic screws, also known as (sùjiāo luósī) in Chinese, are threaded fasteners made from plastic materials through processes such as hot-melt injection molding. Compared to traditional metal screws, they offer numerous unique advantages.
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Excellent Insulation Performance: A standout feature, as plastics are poor conductors of electricity. This makes plastic screws invaluable in electrical equipment, electronic instruments, and other fields requiring insulation, effectively reducing risks like short circuits or electric shocks caused by current conduction. For example, in securing circuit boards, plastic screws ensure insulation between components, guaranteeing stable operation of electronic devices.
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Strong Corrosion Resistance: Unlike ordinary metal screws, which easily rust or corrode in acidic, alkaline, or corrosive environments, plastic screws resist erosion by various chemicals. In highly corrosive scenarios such as chemical production equipment or coastal outdoor facilities, their corrosion resistance extends equipment lifespan and lowers maintenance costs. In the electroplating industry, for instance, where strong acids and alkalis dominate, PVDF plastic screws are widely used due to their durability.
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Additional Advantages: Plastic screws are also lightweight, non-magnetic, cost-effective, and aesthetically pleasing. Their lightweight nature is critical in industries with strict weight requirements, such as aerospace and shipbuilding, as it reduces overall weight and energy consumption. Non-magnetic properties make them suitable for magnetically sensitive equipment like medical MRI machines and precision electronic instruments, avoiding magnetic interference.
However, plastic screws have limitations: Their mechanical strength is generally lower than metal screws, making them prone to stripping or breaking under high tensile or torsional forces—unsuitable for heavy-load connections requiring extreme strength. Additionally, due to shrinkage during plastic molding (influenced by temperature, humidity, and molding cycles), controlling dimensional accuracy is challenging, resulting in larger size tolerances compared to metal screws.
Common Types of Plastic Screws
Classified by Material
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Nylon (PA) Screws: Most commonly made from nylon 66. They offer high mechanical strength, good toughness (withstanding moderate impacts), excellent fatigue resistance (retaining performance after repeated bending), and high heat resistance (glass fiber-reinforced nylon 66 has a heat distortion temperature above 250°C). They feature a smooth surface with low friction and wear resistance, along with acid/alkali resistance, self-extinguishing properties, non-toxicity, and excellent electrical insulation. Widely used in medical devices, wind power, aerospace, office equipment, petrochemicals, electronics, and communications.
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PP (Polypropylene) Screws: Boast good acid/alkali resistance and chemical stability, low density (lightweight), and excellent fatigue resistance under bending. They retain strength at relatively high temperatures and are commonly used in chemical equipment, food packaging machinery, and daily plastic product assemblies.
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PVC (Polyvinyl Chloride) Screws: Offer basic corrosion resistance and insulation at a low cost but have lower heat resistance and mechanical strength compared to PA or PP screws. Used in general industrial and civilian products with low performance requirements and mild corrosion environments, such as plastic furniture and toy assembly.
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PVDF (Polyvinylidene Fluoride) Screws: Excel in acid/alkali resistance among plastic screws, withstanding strong corrosive substances. They have good chemical stability, weather resistance, UV resistance, high mechanical strength, and insulation. Ideal for harsh corrosive environments in chemical engineering, marine engineering, and solar photovoltaics.
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PE (Polyethylene) Screws: Include high-density polyethylene (HDPE) and low-density polyethylene (LDPE). PE screws offer corrosion resistance, flexibility, and insulation. LDPE screws are soft, used for buffering or sealing (e.g., bottle cap connections), while HDPE screws have higher mechanical strength, suitable for outdoor plastics and simple structural fixes.
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PTFE (Polytetrafluoroethylene) Screws: Known as the "king of plastics," they have an extremely low friction coefficient (excellent self-lubrication), exceptional chemical stability (resisting almost all substances), and wide temperature resistance (-200°C to 260°C for long-term use), along with superior insulation. Used in special equipment requiring low friction, extreme temperatures, or strong corrosion, such as chemical pipelines and high-end electronics.
Classified by Head Shape
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Pan Head Plastic Screws: Have a disc-shaped head with a large contact area, distributing pressure to prevent damage to connected surfaces. Used in applications needing high bearing area and aesthetics, such as electronic device housings or plastic panels.
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Countersunk Head Plastic Screws: Feature a (conical) head that sits flush with the surface after installation, ensuring a smooth appearance without protruding parts. Suitable for furniture manufacturing or precision instrument enclosures requiring surface flatness.
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External Hex Head Plastic Screws: Hexagonal heads allow tightening/removal with wrenches, providing high torque and strong fastening. Used in open spaces needing high clamping force, such as machinery plastic parts or outdoor plastic facilities.
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Internal Hex Head Plastic Screws: Require hex keys for operation. They offer tight wrench engagement, high torque capacity, and a recessed head resistant to damage, with a neat appearance. Ideal for precision equipment or electronics with limited space and high aesthetic/fastening demands.
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Plastic Set Screws: Secure shaft-mounted parts to prevent axial movement. Tightening the screw creates friction between its tip and the part surface. Common in motors, reducers, and connections between shafts and gears/pulleys.
Classified by Drive Type
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Phillips Drive Plastic Screws: Have a cross-shaped slot, compatible with Phillips screwdrivers. They offer high (fit accuracy), resist slipping during tightening, and are efficient for mass assembly. Widely used in electronics and small machinery.
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Slotted (Flat) Drive Plastic Screws: Feature a straight slot for flat screwdrivers. Simple in structure but prone to slippage, suitable for low-torque applications like plastic toys or basic (plastic products).
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Hex Socket Drive Plastic Screws: Require dedicated hex wrenches, high torque, and ensure secure connections. Used in industrial equipment or building structures needing strong fastening and precision.
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Pozidriv Drive Plastic Screws: (rice-shaped) slots combine advantages of Phillips and hex drives, offering good fit accuracy, torque capacity, and a unique appearance. Used in high-end electronics or precision instruments with special aesthetic and fastening needs.
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Torx Drive Plastic Screws: (plum-blossom-shaped) slots require dedicated Torx screwdrivers, providing anti-tamper performance. Ideal for security equipment or electronics needing protection against unauthorized disassembly.
Classified by Thread Specification
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Metric Threads: Common sizes include M2, M2.5, M3, M4, M5, M6, M8, M10, M12, etc. Widely used domestically and internationally with standardized dimensions for interchangeability. Small sizes (M2, M2.5) suit electronics/precision instruments; larger sizes (M6, M8) are for machinery or furniture.
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Unified (Imperial) Threads: Common (specifications) include 2-56, 4-40, 6-32, 8-32, 10-32, etc. Primarily used in the U.S. and regions adopting U.S. standards. Found in imported equipment or foreign-brand electronics, with distinct sizing and thread profiles from metric threads.
Application Fields of Plastic Screws
Medical Device Industry
Insulation, non-magnetism, environmental friendliness, and anti-interference properties are critical here. For example, metal screws disrupt MRI machine magnetic fields, while non-magnetic plastic screws ensure accurate imaging. In home medical devices like blood pressure monitors or glucose meters, plastic screws prevent short circuits and meet strict material safety standards.
Wind Power Industry
Wind power equipment requires insulation for PCB boards in control cabinets. Plastic screws secure PCBs to avoid electrical interference, ensuring stable operation. Their lightweight nature reduces weight in wind turbine blades and cabin structures, lowering energy consumption and improving efficiency.
Aerospace Industry
Aerospace demands extreme material performance. Plastic screws’ lightweight, insulation, and anti-interference properties make them useful in aircraft electronics bays (reducing weight and avoiding electromagnetic interference) and satellites (ensuring stability in harsh space environments).
Office Equipment Industry
Office devices prioritize aesthetics, durability, and low maintenance. Plastic screws’ rust-free (properties) maintain equipment appearance long-term. In printers and copiers, they enable easy assembly, meet strength requirements, and reduce costs.
Petrochemical Industry
Harsh environments (high temperature, pressure, and corrosive media) require resistant materials. PVDF and PP plastic screws withstand these conditions, securing chemical pipelines, reactors, and storage tanks to extend lifespan and reduce safety risks.
Electronics Industry
As electronics trend toward miniaturization and high performance, plastic screws’ insulation, anti-interference, and lightweight properties make them ideal. They secure circuit boards and housings in smartphones, tablets, and laptops, preventing short circuits and enhancing portability.
Communications Industry
Stable signal transmission and anti-interference are vital for 通讯设备 (communication equipment). Non-metallic plastic screws avoid eddy current interference under electrical signals, ensuring reliable signal transmission in base stations, fiber optic devices, and signal boosters.
Marine Industry
Ships face seawater corrosion and humidity. Plastic screws’ acid/alkali resistance make them suitable for interior plastic panel fixing, electrical equipment installation, and pipeline connections, preventing corrosion-related damage and reducing maintenance costs.