Methods of Tightening

Ensuring secure and reliable bolted joints is crucial in various industrial applications. But did you know there's more than one way to tighten a bolt? Here's a quick breakdown of some common industrial bolting methods:

The Tried-and-True: Direct Torque Method: This method utilizes a torque wrench to apply a specific rotational force (torque) measured in ft-lbs (foot-pounds) to the bolt. It's simple and widely used, but torque can be affected by factors like friction, making tension (the actual stretching force in the bolt) less predictable.

In torque-controlled connections, torque is often taken as the reference value for accuracy. However, the key factor in all connections is the accuracy of the bolt load. Therefore, by means of mechanical optimization a large gain can usually be achieved in terms of accuracy and stability of the bolt load. Some examples of mechanical optimization are:

• Bolts and nuts with high degree of finish: correct surface roughness, correct tolerances, flattened nuts for so that the hole and mirror face are right-angled.
• Coatings for friction optimization.
• Through hardened washers to guarantee the correct surface over which the nut or bolt head rotates.
• Axial support of the torque tool so that (de)assembly is free of bending forces / side load.

(source: HYTORC NL)

Reaching the Yield Point: Yield Point Method: This method takes things a step further. It involves tightening the bolt until it reaches a specific yield point, where the bolt undergoes a slight permanent stretch. This ensures a more consistent clamping force, but requires specialized equipment and expertise.

Yield point controlled bolting is a very well established method which has been used in the automotive industry for several decades. With yield point controlled tightening of bolted connections, bolts are tightened to the yield strength-/elasticity limit of a unique connection during the tightening process. The yield point is used as a control parameter for determining the bolt load. The objective here is to make maximum use of the strength potential of each unique bolt, as this differs for each bolt. A material strength class says something about the minimum tensile strength of the material, but manufacturers apply a safety margin and the bolt therefore has latent reserves. (source: HYTORC NL)

Precise Tensioning: Hydraulic Tensioning: This method uses a hydraulic pump and tensioner to directly stretch the bolt to a predetermined length or load. This ensures the most accurate and reliable tension, making it ideal for critical applications like wind turbine towers or pressure vessels.

Seeing the Stretch: Ultrasonic Method: This innovative method uses ultrasonic waves to measure the actual stretch of the bolt as it's tightened. This provides real-time feedback on the tension being achieved and eliminates reliance on estimated torque values.

Choosing the Right Method:

The best method for your application depends on factors like:

• Criticality of the joint: How important is absolute precision and reliability?
• Accessibility: Can you easily access the joint for direct torque measurement?
• Material properties: How do the materials being joined react to stretching?

By understanding these methods and your specific needs, you can select the most effective and safe bolting technique for your industrial projects.

To know more about our bolting tools, click here: https://hytorctexas.com/

Article source: https://www.hytorc.nl/en/tightening-methods/#:~:text=Yield%20point%2Dcontrolled%20tightening%20method&text=With%20yield%20point%20controlled%20tightening,for%20determining%20the%20bolt%20load.