When engineers, mechanics and maintenance teams discuss fasteners, the focus often turns to torque tightening. Getting torque right is crucial for ensuring that bolts, nuts and screws hold components securely without risking damage, failure or loosening over time.
But torque doesn’t work in isolation. One of the most significant factors influencing torque tightening – and often the least understood – is lubrication. Applying (or not applying) lubricant to a threaded fastener can drastically change the clamping force achieved for the same torque value.
So what effect does lubricant really have on torque tightening and why does it matter? Here, the team of experts at Crane Electronics explores in more detail.
What is torque and clamping force?
When you tighten a bolt, you’re not just spinning metal. What you’re really doing is stretching the bolt slightly to create tension. That tension pulls the connected materials together, creating what’s known as the clamping force.
The torque you apply is essentially the input – the twisting force on the fastener. The clamping force is the output – the pressure holding the joint together.
However, not all of the torque applied goes into generating that clamping force. In fact, only around 10 to 15 per cent of the torque actually stretches the bolt. The other 85 to 90 per cent is lost to friction, which is where lubrication comes in.
What role does lubrication play in torque?
Lubrication reduces friction. When you apply oil, grease or an anti-seize compound to a threaded fastener, the torque you apply encounters less resistance.
This means:
- More of the applied torque goes into tensioning the bolt rather than overcoming friction.
- The same torque setting results in a higher clamping force compared to a dry fastener.
- Torque values need to be adjusted when lubrication is used to avoid over-tightening.
Simply put, if you don’t account for lubrication, a bolt can be stretched too much, potentially leading to long-term damage or component failure.
The difference that lubrication can make can be dramatic. In some cases, it’s believed that lubrication can reduce the amount of friction by up to 50 per cent.
What are the different types of lubrication?
Not all lubricants are the same and each type has a slightly different impact on friction and torque-tension relationships:
Light oils (e.g. machine oil):
- Reduce thread friction moderately
- This is often used in general maintenance to prevent galling and seizing.
Greases:
- Provide more consistent lubrication
- Good for long-term protection, but can significantly increase clamping force if the torque isn’t adjusted.
Anti-seize compounds:
- Designed to prevent fasteners from sticking or corroding
- Create very low friction, meaning torque adjustments are essential to avoid over-tightening.
Dry film lubricants:
- Used in aerospace and automotive industries for predictable friction coefficients
- Provide consistent results and increased efficiency in critical applications.
Each lubricant alters the torque-to-tension ratio in its own way, which is why manufacturers often specify exactly what type of lubrication should be used.
What are the benefits of lubricated torque tightening?
Lubrication can bring with it many key benefits, including:
- Consistency: lubricated fasteners tend to produce more predictable results because friction variability is reduced.
- Prevention of galling and seizing: especially important in stainless steel or high-temperature applications.
- Corrosion resistance: lubricants act as a barrier against rust and environmental damage.
- Ease of maintenance: fasteners are easier to remove later without damage.
For these reasons, many industries prefer lubricated tightening, provided adjustments are made to torque settings.
What happens if you ignore lubrication in torque?
The biggest risk is over-tightening. If a bolt is lubricated but tightened to a torque value specified for dry conditions, the clamping force may be higher than intended.
On the other hand, if a torque value is specified for lubricated conditions but applied dry, the result will be under-tightening – insufficient clamping force, leading to loosening, vibration and potential joint failure.
Best practices for torque tightening with lubrication:
- Always check manufacturer specifications, as they should state whether torque values are for dry or lubricated fasteners.
- Be consistent. Don’t mix dry and lubricated fasteners in the same assembly unless specified.
- Adjust torque values when lubricating.
- Use calibrated tools. A properly calibrated torque wrench is essential for accuracy. (Do you own or use Crane torque equipment? Book in your next calibration today or find your nearest service centre).
- Train staff and operators efficiently – awareness of how lubrication changes outcomes can prevent costly errors.
Common mistakes when torque tightening with lubrication
Let’s be honest, mistakes can happen during the assembly process. Here are some of the most frequent issues that can arise when lubrication isn’t properly considered:
Using the wrong torque values
Applying torque settings intended for dry fasteners to lubricated ones (or vice versa) is one of the biggest causes of failure. Always confirm which condition the specification is based on.
Mixing lubricants
Different lubricants have different friction coefficients. Using grease on some bolts and oil on others in the same assembly can create uneven clamping loads and compromise the joint.
Not reapplying lubrication
A fastener that’s been removed and reinstalled without fresh lubricant may not behave consistently. Always reapply for accurate results.
By properly considering and learning about lubrication when torque tightening, assembly teams will help to ensure longer-lasting, more reliable and safer results.
Precision torque tools from Crane Electronics
At Crane, we understand how critical torque control is for all types of industries across the world. Leading manufacturers and engineers trust our advanced torque measurement and tightening solutions to deliver accuracy, repeatability and peace of mind even in the most demanding applications.
From torque wrenches and transducers to torque testers and auditing systems, our products are designed to help you achieve precise tightening results, regardless of lubrication conditions or application challenges. If you want to eliminate uncertainty in your torque processes, improve safety and protect your assemblies from potentially costly errors, Crane Electronics has the expertise and tools to support you.
Contact us today to learn more about our torque solutions and how we can help improve the accuracy of your tightening processes.