Åtdragning

Åtdragning is the process of applying a specific torque to a fastener, such as a bolt or screw, to achieve a defined clamping force in a joint. The objective is to attain sufficient preload, ensure even load distribution, and control joint stiffness while avoiding over- or under-tightening. The exact torque depends on fastener size, material, lubrication, thread condition, joint design, and operating temperature.

Common methods include manual torque with a calibrated torque wrench, automatic or digital torque wrenches, hydraulic or pneumatic torque wrenches, and torque-angle methods. The torque-angle method adds a rotation after the initial torque to achieve the intended preload, especially for gasketed or high-pressure joints.

Before torquing, joints are prepared: surfaces are clean and free of debris, fasteners are inspected, and lubrication is applied according to specifications. Thread lubrication can significantly alter the friction coefficient and thus the resulting preload. In many applications, a lubricant is specified; in others, bolts are left dry. When tightening multiple bolts, a tightening sequence ensures even clamping.

Standards and quality control require torque tools to be calibrated regularly and used within their rated range. Bolts designed for yield or torque-to-yield operation may be tightened to a specified angle or elongation to achieve the required preload.

Risks of improper åtdragning include bolt fatigue, thread stripping, joint leakage, or catastrophic failure. Proper procedure, appropriate tools, and adherence to specifications are essential.