Recently, Nippon Closures’ technology is helping customers in the civil engineering and construction industries.
Since the Kasago Tunnel collapse accident in 2012, safety awareness has increased at construction sites, and we are checking to see that nuts are tightened to the proper torque.However, this reduced work efficiency and there were cases of forgetting to tighten the bolts due to human error.
Therefore, we were asked if we could develop an attachment that would break when tightened to the proper torque and disengage from the nut.The development of the attachment was started based on the concept that if the attachment was removed, it would prove that the proper torque had been applied and prevent forgetfulness.

Torque management and prevention of forgetting to tighten with a single cap.

It was a completely new industry, and development was also a process of exploration.First of all, the product was to be used outdoors, and the material used for standard caps is fundamentally insufficient in terms of durability and strength.More than 10 different materials were tested to find the best fit, and dozens of product shapes were tested.
Through this process of gradually accumulating know-how, the decision was finally made to commercialize a product that fulfilled the required functions.However, the decision to commercialize the product was short-lived, and a glitch occurred.After about a week of setting the nuts, about 1% of the time, the nuts were damaged without the proper torque.The cause was too strong of a mating* with the nut.We urgently and radically re-looked the mating methods, and at the same time, we constructed a severe test in which the frequency of defect occurrence was more than 90%.After optimizing the mating until zero breakage was achieved in a severe test, the product was successfully productization.

*Mating: A relationship in which various parts of a machine fit together, as in the case of a shaft and bearing. Also, its condition.