What is the ultrasonic bolt load measurement ?
Rethinking ultrasonic bolt load measurement
1-Traditional torque and angle torque methods don’t meet future industry’s performance and precision requirements.
TRAXX found that torque tightening can cause a ±50% uncertainty in the final clamping tension on industrial sites. Factors such as temperature, friction, and material resistance during tightening influence the accuracy of these methods. However, these methods do not consider these factors.
This can result in either excessive or insufficient tightening, leading to critical situations such as loosening, breakages, and fractures. TRAXX discovered that when tightening cylinder head bolts evenly, some bolts may only be half as tight as others.
2- Although ultrasonic bolt load measurement is far more precise and rigorous, it has not gained wide adoption
Current methods, like load cell or strain gauge methods, change the assembly’s nature to measure it, which is a significant drawback. These methods are invasive, difficult to use on-site, and only suitable for experiments in a lab. So the question is : how to measure bolt stress ?
TRAXX has been developing a new method to measure bolt load since 1998. This method can be used on-site on a daily basis. TRAXX is a worldwide expert in bolt elongation measurement with ultrasonic time-of-flight measurement devices. They improved and industrialized three devices : MX32, M1, and the M2 bolt load meter.
3- Ultrasonic measurement of bolt tension is the best solution.
In essence, a bolt operates as a spring, leveraging the elastic characteristics of its materials to remain intact. Similar to an elastic band, a bolt possesses a threshold where it can be stretched while retaining its structural integrity. Design engineers strategically explore these material limits to effectively secure joints. Exceeding the optimal torque can lead a fastener to yield, while insufficient torque may result in joint failure. Joint failure because either of these scenarios can pose significant risks and incur substantial costs. Hence, understanding the tension of a fastener is crucial. Ultrasonic bolt load measurement offers a precise technique for assessing bolt tension post-preload. So, what is the ultrasonic bolt preload measurement ? The process involves sending an ultrasonic signal down one end of the fastener and measuring the time it takes to come back to the transducer. By examining the time it takes for the ultrasonic signal to travel, we can determine the elongation of the bolt using a reference measurement (unloaded fastener length). The delta, representing the change in length of the bolt before and after preload, facilitates a precise deduction of the tension within the installed bolt.
Ultrasonic bolt load measurements play a crucial role in validating torque applications and have the potential to decrease preload scatter. In contrast to deflection validation, ultrasonic measurements can be applied in scenarios featuring blind holes, as the transducer only necessitates access to one end of the fastener.
Moreover, if the unloaded length of the fasteners is known before the initial preload, ultrasonic measurements can gauge residual preloads post-loading, ensuring bolts remain within specified tolerances.
Summary of ultrasonic bolt load measurement
The principle of bolt elongation measurement using ultrasonics is simple.
It involves measuring the elongation of the bolt under the influence of the tension induced by tightening. When a bolt is tightened, it proportionally elongates due to the applied force. Measuring the elongation of the bolt allows us to determine the clamping tension present in the bolt, providing insight into the force exerted on the assembly. How is this elongation measured ? By emitting ultrasonic waves into the bolt. Since the tightened bolt is longer than the relaxed bolt, ultrasonic waves take more time to propagate through the tightened bolt. From this variation in the wave travel time, ultrasonic time of flight (TOF), we can deduce the clamping tension present in the bolt thanks to the bolt elongation measurement.
Read the complete tightening method through the article below.