Too Loose or Too Tight? Determining a Suitable Tightening Torque
In both manufacturing and assembly, it's important to focus on production efficiency. If you are to avoid disasters and ensure economical, reliable and safe products, you must appreciate the importance of torque control when it comes to fasteners. Here are a few simple steps to help you calculate and determine a suitable tightening torque.
The Importance of Torque
To be sure that the bolt will function as expected, it is important to focus on proper torquing. When a bolt is appropriately tightened, its material is slightly stretched but not in a way that exceeds its elastic limit.
If the bolt is over-torqued, it will be stretched beyond its elastic limit. This could weaken it significantly and affect its load capacity.
On the other hand, a bolt that is under-torqued will create a gap between the workpieces, ultimately leading to joint failure.
Determine Torque Requirements
It is important for engineers to establish the correct torque specifications before using fasteners on certain materials. When doing this, the engineer has to keep in mind the expected maximum load to be placed on the fastener, whether it is a soft or hard joint as well as the strength of the material to be joined. This can be done by using a calibrated torque control tool to perform a destructive test. The first step would be to tighten the fastener to the point of failure. This process is done a number of times to establish the consistency of the point of failure.
Use a Torque Calculator
Today, it is possible to use a torque calculator to help you determine the rough tightening torque. While the calculator may not be exact, it is a great way to verify some of the results you got when determining torque requirements.
However, you will have to input relevant information such as bolt strength, bolt diameter and the coefficient of friction for the calculator to give you the tightening torque.
Test Your Torque
Once you have the torque specifications, you will want to verify the accuracy of the torque values by testing them. This will involve the use of a calibrated hand torque wrench. Accurate torque values will go far in helping you have a reliable, safe and quality project. Here are three ways to test your torque.
- The First Movement Test – Once you have tightened the fastener, you will need to apply force on the torque wrench. This should be done up to that point where you note the first movement of the fastener.
- The Loosening Test – This test is done in much the same way as the first movement test. The only difference is that force is applied in the opposite direction to loosen the fastener. Immediately, the fastener breaks loose, the corresponding torque reading is noted.
- Marking Test – This test involves marking the fastener and continuously marking the surface to be clamped. You will have to keep loosening and tightening until the marks match up.
After assembly, checking torque will help you to establish whether the fastener has adequate torque. You will also be in a better position to detect joint relaxation and missed or loose fasteners.
Use the Right Tools
When looking to determine a suitable tightening torque, it's important to use the right tools. Some of the tools you need to measure and control the torque applied to fasteners include electric screwdrivers, pneumatic screwdrivers, torque testers, torque wrenches, torque multipliers and torque sensors.
Generally, the type of materials being joined and the fasteners to be used will determine the specific materials you need to use.
Employee Training
As much as you may provide a safe working environment and invest in high-quality tools, you will also need to organize personnel training sessions. This will give employees knowledge on the types of tools available, how to operate the tools, basic torque theory, preventative maintenance and safety.
At Aztec Bolting, we make use of the latest technology to provide hydraulic tooling products and services for controlled bolt tightening. For all your critical bolting needs, contact us for solutions.
