Hexagonal Head Bolt

The Hexagonal Head Bolt is an absolutely critical fastener within large-scale power equipment, including turbines, generators, and boilers. By ensuring the rock-solid connection of various components, these bolts guarantee the equipment's operational safety and stability under extreme conditions.

Core Functions and Challenge Mitigation

These bolts are meticulously designed to handle the unique stresses faced by heavy-duty power generation machinery:

• Secure Fastening Connections: Through the precise cooperation of nuts and threads, hexagonal head bolts rigidly connect components, actively preventing dangerous loosening caused by high temperatures or severe vibration.
• Withstanding Extreme Environments: Since generator sets often operate under high heat and pressure, the bolts must possess superior high-temperature resistance and creep resistance to maintain a stable, specified clamping force.
• Excellent Anti-Vibration Performance: To counter the constant vibration generated during equipment operation, these bolts require robust vibration resistance to prevent fatigue and unexpected loosening.

Materials, Performance, and Stringent Requirements

To meet the unforgiving demands of the power industry, hexagonal head bolts adhere to strict standards for material selection and performance grading:

Critical Material Selection

Bolts are typically manufactured from high-strength alloy steels such as 15CrMoA, 35CrMoA, 12Cr1MoV, and 25Cr2MoVA, chosen for their optimal mechanical strength and heat endurance. For applications requiring better corrosion resistance, stainless steels like 0Cr18Ni9 or 0Cr17Ni2Mo2 may be employed.

Performance Grades and Temperature Range

• Performance Grades: Grades like 5.6, 8.8, A2-70, and A4-70 are used to guarantee the bolt's minimum tensile and yield strength.
• Temperature Requirements: The general service temperature is typically -20°C to +300°C. Critical high-temperature components, such as turbine stud bolts, must be capable of operating reliably from -100°C up to +525°C to handle the severe thermal cycling in power plants.

Precision Installation and Maintenance Protocols

Correct installation and rigorous maintenance are paramount for maximizing a bolt's functional lifespan:

Installation Essentials: Cold and Hot Tightening

• Cold-tightening: Initial manual tightening to eliminate gaps and check contact surfaces, preparing the joint for the final high-stress phase.
• Hot-tightening: The critical process of heating the bolt to a calculated temperature and tightening to a specific elongation. This compensates for thermal expansion, ensuring the bolt maintains a constant, predictable clamping force under high-temperature operation.

Disassembly and Inspection

• Position Marking: Every bolt and nut must be numbered and marked before removal to ensure it is reinstalled in its exact original position, preventing component failure caused by incorrect seating.
• Even Removal: Bolts must be loosened gradually in a symmetrical, step-by-step sequence to prevent localized stress buildup that could damage equipment flanges.
• Inspection and Storage: Removed bolts must be thoroughly cleaned, inspected for any damage, and then properly stored in a dry environment with protective oil applied to ensure long-term reliability.