What is Torque?

Torque, in the most basic terms, is a twisting force that tends to cause rotation. Imagine using a wrench to tighten a bolt. The force you apply to the wrench creates a twisting action on the bolt, and that's what we call torque. It's a measure of how much force is needed to rotate an object around an axis.

Why is Torque Important?

In the world of fasteners, torque is crucial because it directly relates to the clamping force or tension created in the bolt. This clamping force is what holds two or more components together securely. Applying the correct torque ensures that the joint is strong enough to withstand external forces without coming loose or failing.

How is Torque Applied to Screw/Bolt Fastening?

When you tighten a screw or bolt, you're essentially applying torque to it. This torque creates tension in the bolt, which in turn generates a clamping force between the parts being joined. The amount of torque required depends on several factors, including the size and type of fastener, the materials being joined, and the desired clamping force.

The Torque-Tension Relationship

It's important to understand that torque is not the same as tension, although they are related. Torque is the rotational force applied to the fastener, while tension is the internal force generated within the fastener as a result of that torque. The relationship between torque and tension is influenced by friction. A significant portion of the applied torque is used to overcome friction between the threads of the fastener and the mating threads in the joint, as well as friction under the bolt head or nut.

Controlling Torque

To achieve accurate and consistent clamping force, it's essential to control the torque applied to fasteners. This is where torque tools come into play. Torquve wrenches, for example, are designed to limit the amount of torque applied to a fastener, preventing overtightening and potential damage to the joint. Other tools, such as Torque Wrenches, Hand Torque Screwdrivers , Electric Torque Screwdrivers , Air Torque Screwdrivers , Cordless Torque Screwdrivers , Pulse tools, and Programmable DC electric tools, offer varying levels of torque control and accuracy.

Factors Affecting Torque

Several factors can affect the torque required to achieve a desired clamping force. These include:

• Friction: As mentioned earlier, friction plays a significant role in the torque-tension relationship. Factors that influence friction include the type of materials being joined, the surface finish of the threads, and the presence of lubricants.
• Lubrication: Applying lubricant to the threads can reduce friction, allowing for greater clamping force with the same amount of torque.
• Fastener Type: Different types of fasteners have different thread profiles and materials, which can affect the torque-tension relationship.
• Joint Material: The materials being joined also influence the torque required. For example, softer materials may require lower torque to avoid stripping the threads.

1. Clamping Torque (Clamp Load)

• Definition: This is the most common type of torque, and it refers to the rotational force applied to a fastener to achieve a specific clamping force between the joined parts.
• Importance: Clamping torque is crucial because the clamping force it generates holds the components together, preventing loosening or separation under various loads and vibrations.
• Measurement: Torque wrenches are commonly used to measure and control clamping torque, ensuring accurate and consistent tightening.

2. Running Torque (Prevailing Torque)

• Definition: This is the torque encountered during the tightening process before the fastener starts to clamp the joint. It's essentially the resistance the tool must overcome to rotate the fastener.
• Causes: Running torque can be caused by friction between the threads, the bearing surface under the head, and any interference from paint, debris, or misalignment.
• Types:
• Intentional Prevailing Torque: This is designed into certain fasteners, like thread-forming or lock nuts, to increase resistance to loosening.
• Unintentional Prevailing Torque: This can arise from manufacturing variations, debris in threads, or bent parts, and can lead to inconsistent tightening.

3. Dynamic Torque

• Definition: Dynamic torque is measured while the fastener is being rotated and tightened.
• Accuracy: It provides a more accurate representation of the actual torque applied to the fastener during the tightening process.
• Measurement: Dynamic torque is typically measured using a rotary transducer, a device that senses the torque in real-time as the fastener is turned.

4. Static Torque

• Definition: Static torque is measured after the fastener has been tightened and is at rest.
• Purpose: It helps verify that a minimum torque has been applied to the joint.
• Measurement: Static torque can be measured using a torque wrench to check the "breakaway" torque required to loosen the fastener.

5. Breakaway Torque

• Definition: This is the torque required to loosen a fastener that's already been tightened.
• Relationship to other Torques: Breakaway torque is typically higher than the applied tightening torque due to factors like embedding of the fastener, joint relaxation, and the setting of adhesives (if used).
• Measurement: A torque wrench is used to measure breakaway torque.

Understanding these different types of torque is essential for selecting the right tools, establishing proper tightening procedures, and ensuring the integrity and reliability of fastened joints.

Conclusion

Torque is a fundamental concept in screw and bolt fastening. Understanding the role of torque and its relationship to clamping force is essential for achieving reliable and secure joints. By carefully controlling torque and considering the factors that influence it, you can ensure that your assemblies are strong, durable, and perform as intended.