Torque vs. Tension: What’s the Difference?

Torque vs. Tension What's the Difference

When tightening a bolt, you want to ensure it is secure. This is done by applying torque or tension. But what’s the difference? And which one should you be using? 

In this article, we will discuss the difference between torque and tension and show you how to apply them correctly!

 

Tightened Bolt Behavior

Before we compare torque with tension, it’s important to know and understand how a tightened bolt behaves. Bolts that are tightened correctly make use of their elastic properties. 

To create an airtight joint, bolts need to behave like springs. So when a torque wrench or tensioner applies a load, the bolt will stretch and return to its original length. 

The amount of tension produced by the load will trigger a clamping force, which works with the friction happening on the bolts threads to produce a secure joint. When a torque wrench or tensioner applies a load, the bolt starts to stretch and slowly returns to its normal, original length. 

 

Different Between Torque and Tension

Now that we know how a tightened bolt behaves, let’s compare torque with tension and see how they differ from each other:

Torque

Torque is the force that produces rotation. The force measurement causes something to move in a rotational motion. For example, when you use a torque wrench to tighten a bolt, you are measuring the amount of force required to turn the bolt. 

The unit of measurement for torque is Newton-meter (Nm).

Tension

Tension, on the other hand, is the force that produces linear motion. It is the measurement of the stretch or elongation of a bolt that provides the joint’s clamping force. When you use a tensioner to tighten a bolt, you measure the force required to pull the bolt. 

The unit of measurement for tension is Newton (N).

 

Torquing and Hydraulic Torque Wrenches

A torque wrench functions by applying the principle of Newton’s law. This law states that every force applied produces an equal and opposite reactive force.

This principle allows torque wrenches to apply a specific torque to a bolt. The amount of torque applied to the bolt is determined by the length of the torque wrench and the amount of force applied to it. 

This practice means that as a nut is turned, the bolt stretches. This motion creates tension, acting as the clamping force over the effective thread length. As a result, the clamping force pulls the two bolted components together and retains a load (tension) within the bolt.

 

Torquing and Friction

Friction plays an integral role in torquing a bolt. The amount of torque that is required to turn a bolt is affected by the coefficient of friction between the nut and the bolt. 

In fact, the initial torque only covers an estimated 10 to 15% of the stretched bolt. The remaining 85 to 90% of input torque is used to overcome the friction between the threads and nut and bolt head.

The friction coefficient measures how much force is required to move one object over another. The lower the coefficient of friction, the less force that is required to move an object. 

If you need to change a car wheel or dismantle an engine, a manual or digital handheld torque wrench is more than enough to get the job done. However, more powerful tools and equipment are needed for industrial applications such as tightening pipe flanges in the gas and oil industry.

The higher torque output required and the greater number of bolts make hydraulically powered torque wrenches an excellent option for these applications.

 

How Hydraulic Tensioning Works

A hydraulic tensioner is a device that uses fluid pressure to generate the force required to stretch a bolt. The tensioner consists of two cylinders: a high-pressure cylinder and a low-pressure cylinder. 

The high-pressure cylinder contains a piston that is connected to the bolt. The low-pressure cylinder contains a piston connected to the hydraulic fluid pump. 

When the piston in the high-pressure cylinder is forced down, the piston in the low-pressure cylinder is also forced down. This action causes hydraulic fluid to flow from the low-pressure side of the pump to the high-pressure side. 

The fluid pressure on the high-pressure side of the pump is increased, which in turn increases the force on the piston in the high-pressure cylinder. 

This increased force is transferred to the bolt, stretching it and creating tension.

 

General Tensioning Procedure

A general tensioning procedure follows the steps outlined below:

  1. The tensioner is fitted over the bolt stud.
  2. Hydraulic pressure is applied to the tensioner, stretching the stud in the process.
  3. The tensioner starts to wound down the stud nut against the joint face.
  4. Pressure is released, and the tensioning tool is removed.

 

Once the tensioner is removed, the bolt will remain stretched, creating tension in the joint. This tension is what prevents the joint from coming apart under load. 

It is important to note that the amount of tension in a joint can be affected by many factors, such as the bolt type, the number of bolts, the amount of torque applied to the bolt, and friction between the threads. 

In general, the more bolts that are used in a joint, the less tension each bolt needs to create. This is because the bolts are sharing the load, and each bolt only needs to create enough tension to hold its share of the load. 

 

Why Use DATAMYTE?

So, torque is completely different from tension. But they have one thing in common: both values need to be monitored and recorded to ensure a secure, well-functioning joint.

This is where DATAMYTE comes in handy. DATAMYTE is a quality management platform that lets you create an entire workflow dedicated to torque and tension monitoring. 

The DataMyte Digital Clipboard is a tool that you can use to customize your workflow to your specific needs. It will guide your operators through every process step, from setting up the equipment to recording the results. 

Plus, all data collected with DATAMYTE is stored in a secure cloud database. This lets you track, trend, and analyze your data to improve your process. You can even create reports and share them with your team.

Schedule a demo today to learn more about how DATAMYTE can help you improve your process.

 

Conclusion

It pays to know the difference between torque and tension in manufacturing or any other industry. But while they are completely different, both values are important in ensuring that a joint is secure and will function properly.

 

 

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