1- Classic tightening methods, torque tightening and torque angle do not satisfy the performance and precision criteria of tomorrow’s technical industries.
After hundreds of visits to industrial sites, TRAXX has confirmed that torque tightening can lead to a final bolt tension variance of as much as ± 50%. The accuracy of these methods is affected by parameters such as temperature, variations between the parts and bolts. These methods do not allow for these parameters. Sometimes this can result in excessive or insufficient tightening which could lead to critical situations: loosening, breakage, failure. For example: for a series of automobile engine cylinder head bolts which has been theoretically tightened homogeneously, we have used the TRAXX system to observe that certain bolts are sometimes as much as two times less tensioned than others.
2- Tension tightening is far more precise and reliable but is still underused
Other methods exist: the load-cell method or the strain gauge method, both of which have the major disadvantage of requiring modifications to the assembly process before making the measurement. These are what we call invasive methods: they are complicated to implement. They are unsuitable for on-site use, and are really only suited to laboratory experiments.
As a result, since 1998, TRAXX has been working on the development of an innovative bolt tension measurement solution suitable for daily on-site use. TRAXX has now developed and produced 3 device families (the MX32, the M1 and the M2), and has since become the world’s leading bolt tension measurement specialist.
An innovative method
The measurement principle is very simple.
It involves measuring the elongation of the screw or bolt under the effect of the tension applied during tightening. When a screw is tightened it elongates proportionally to the applied force. The measurement of the extension of the screw provides a means to establish the amount of tension present within the screw and thus the force applied into the assembly.
How can we measure this elongation? By sending ultrasound waves along the screw. Since a tightened screw is longer than an untightened one, the time taken by the ultra sound waves to propagate along the length of the screw will therefore be longer. From this variation in the time taken by the ultrasound waves to travel along the screw we can calculate the bolt tension in the screw.
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