Release time：2020-01-16 18:44 Browse：
### 1. **Material Composition & Strength Grade** - **Base Material**: High-strength carbon steel (e.g., 45# steel, 40Cr, or 35CrMo), selected for its excellent machinability and ability to withstand heat treatment. - **Strength Rating**: Classified as high-strength, typically meeting Grade 8.8 or higher (tensile strength ≥800MPa, yield strength ≥640MPa for Grade 8.8; higher grades like 10.9 offer tensile strength ≥1000MPa). This ensures suitability for heavy-load applications such as structural bracing or machinery anchoring. - **Alloy Additives**: May include chromium, molybdenum, or manganese to enhance hardenability during heat treatment, improving wear resistance and tensile performance. ### 2. **Surface Treatment: Galvanization** - **Galvanizing Process**: Hot-dip galvanization (most common for high-strength variants) or electro-galvanization, creating a zinc coating (8–15μm thickness) to form a sacrificial barrier against corrosion. - **Benefits**: - Resists rust and oxidation in humid, outdoor, or industrial environments (salt spray test survival ≥72–120 hours, depending on coating thickness). - Zinc layer bonds tightly to steel, with minimal risk of flaking during installation or vibration. - Compatible with plain finish on threaded sections (see below) for balanced functionality. ### 3. **Design & Thread Specifications** #### - **Hexagon Head** - Standard hexagonal (hex) profile with flat bearing surface, compatible with metric hex wrenches, sockets, or automated torque tools for secure tightening. - Head dimensions (width across flats, height) conform to ISO 4762 or DIN 931 standards, ensuring interchangeability with nuts and washers. - Chamfered edges reduce stress concentration at the head-shank junction, preventing cracking under high torque. #### - **Partial Threading** - Threads extend only partway up the shank (e.g., 1/2 to 2/3 of total length), with the remaining section unthreaded (smooth shank). - Purpose: - Allows deeper insertion into thick or blind holes without thread binding. - Smooth shank improves alignment in misaligned assemblies, reducing lateral stress on threads. - Enhances clamping force by concentrating tension in the threaded portion (where engagement with nuts occurs). #### - **Plain Finish Details** - "Plain finish" refers to the uncoated state of the threaded section (post-galvanization), ensuring precise mating with nuts (coated threads can cause galling or poor fit). - The unthreaded shank retains the galvanized coating for corrosion protection, balancing functionality (thread engagement) and durability (rust resistance). ### 4. **Manufacturing Processes** - **Cold Heading**: Shank and head formed via cold forging to maintain grain structure, enhancing strength compared to machined parts. - **Heat Treatment**: Quenching and tempering to achieve high tensile strength and toughness (e.g., 850°C quenching in oil, 550°C tempering for Grade 8.8). - **Thread Rolling**: Threads formed via rolling (not cutting) to work-harden the surface, improving fatigue resistance by 20–30% versus cut threads. - **Galvanization**: Post-threading zinc coating application, followed by passivation (optional) to enhance coating adhesion. ### 5. **Performance & Durability** - **Load-Bearing Capacity**: Designed to withstand static and dynamic loads in heavy machinery, construction steel, or automotive chassis—clamping force exceeds 10kN for M12 sizes (Grade 8.8). - **Corrosion Resistance**: Galvanized coating protects against moisture, chemicals, and outdoor elements; suitable for agricultural equipment, marine docks, or outdoor structures. - **Anti-Loosening**: Partial threading minimizes thread-to-hole friction, reducing the risk of loosening under vibration compared to fully threaded screws. ### 6. **Applications** - **Industrial Machinery**: Securing gearboxes, hydraulic cylinders, or conveyor frames where high strength and precise alignment are critical. - **Construction**: Fastening steel beams, brackets, or concrete formwork in bridges, buildings, or infrastructure projects. - **Automotive & Transportation**: Heavy-duty truck suspensions, trailer hitch assemblies, or railway components requiring resistance to road salt and vibration. - **Energy Sector**: Wind turbine towers, solar panel mounts, or power plant equipment (withstanding extreme temperature fluctuations). ### 7. **Quality Control & Compliance** - **Testing Protocols**: Each batch undergoes tensile testing, hardness measurement (Rockwell C scale), and thread gauging (6g tolerance for external threads). - **Coating Checks**: Zinc thickness verified via magnetic induction; adhesion tested per ASTM B571 (tape test) to ensure no flaking. - **Standards Compliance**: Manufactured to ISO 4762 (hex head cap screws), DIN 931 (partially threaded), and ASTM A307 (for general carbon steel) or ASTM A354 (for high-strength) standards. ### 8. **Handling & Storage** - **Installation**: Use lubricated nuts (or anti-seize compound) for galvanized threads to prevent galling during tightening. - **Storage**: Keep in dry, sealed containers to avoid white rust (zinc oxidation); avoid contact with sharp objects that may scratch the galvanized layer.
