Here’s a recent field test showing the installing of a 2”x 4.5 nut that highlights the issue.
Left: Nuts were initially tightened with an impact wrench set to 4500 ft lbs to achieve the required clamp load of 138,000 lbs.
Right: Next, the nuts were tightened with an electric reaction arm torque multiplier wrench also set to 4500 ft-lbs.
Results
An average of 30° of additional rotation was achieved when tightening with a reaction arm torque multiplier wrench versus an impact wrench. With a clamp distance of 20 inches on this assembly, this 30° translates to an additional 68,703 pounds of clamp force as shown in the downloadable calculation spreadsheet below.
* The impact torque wrench only tightened the nut to 50% of the desired clamp load
Click below to download the handy Excel spreadsheet shown above.
The result of this field test are also supported by the published laboratory tests shown in the table below.
Take Away
We’ve outlined in previous posts (listed below) why it’s important to achieve proper clamp force when tightening a bolted joint. Impact torque wrenches are commonly used due to their speed and ease of use. However, assembly planners should take into consideration the wide variance in results often achieved when using an impact torque wrench.
How much a bolt stretches
Torque explanation
How to calculate clamp force
Rotation angle explanation
Cyclical loading and why it’s important to keep a bolted joint tight
Are locknuts necessary
How does Security Locknut work
others at www.securitylocknut.com/blog
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