How often do you find loose screws at home with household items? May seem like a simple nuisance, but not too costly for you to fix. For the US Air Force and Toyota, loose screws and improper torque control have recently proven to be costly and critical key issues.
Last week, Toyota announced a recall of certain Tacoma pickup trucks, equipped with an access cab, due to fasteners within the driver and front passenger seat belt assemblies that could loosen if the access doors are repeatedly and forcefully closed over an extended period of time.
If the fasteners loosen completely, the seat belt may not properly restrain the occupant, which could increase the risk of injury in a crash or sudden stop. (Sources – Auto123.com and Toyota USA Newsroom).
After the Air Force investigated the crash of the Global Hawk aircraft drone that occurred on August 20, 2011, in Afghanistan, improper torque was one contributing factor. A loose fastener that was not properly torqued cost the US Air Force $73 million.
“Post-mishap analyses of in-service LRU-X-1 cap screws reflect a significant departure from required values of 18-22 inch-pounds above prevailing torque,” reads the report. “Improper torque, insufficient use of thread locking compound or reuse of a deformed lock washer could allow cap screws to vibrate loose during flight operations.” (Source – Flight International).
Torque control is not something that should be overlooked for many manufacturers. It’s a critical component in the assembly process. A costly issue if not properly addressed before the assembly process begins. Later a fastening error is detected during the assembly process, the more it costs to correct it. It becomes very costly when failures in a product involves lawyers and lawsuits.
What is Torque?
Torque is a “turning” or “twisting” force and differs from tension, which is created by a straight pull. However, we use torque to create a tension.
How?
As the nut and bolt are tightened, the two plates are clamped together. The thread angle in the bolt converts the force applied into tension (or stretch) in the bolt shank. The amount of the tension created in the bolt is critical.
Why?
A bolt tensioned properly works at its optimum efficiency and will resist coming undone. However, if the tension is too low, the nut could vibrate or work loose. If the tension is too high (overstretched), the bolt could break. Every bolt has a correct optimum torque/tension figure for each fastening application. It is important to have these figures available so that the end product will be safe, efficient and economical.
How do We Measure Torque?
Torque is the result of multiplying the value of Force applied by the Distance from the point of application.
The Importance of Torque Control?
The reliability of machine parts subjected to fluctuating loads and stress depends on the fatigue strength of the materials. A threaded fastener, however, relies upon an elastic interaction between the mating components. Its objective is to clamp parts together with a tension greater than any external force trying to separate them. The bolt then remains under almost constant stress and is immune to fatigue. If the initial bolt tension is too low, the fluctuating load in the shank in much greater and it will quickly fail. Reliability, therefore, depends on correct initial tension and is ensured by specifying and controlling the tightening torque.
Using a quality torque tool makes a safer world through accuracy and precision. Controlling torque is essential for companies to ensure their product’s quality, safety and reliability isn’t compromised. The failure of a three-cent fastener that isn’t properly tightened can lead to catastrophic or latent failures. Fasteners that are insufficiently fastened can vibrate loose and excessive torque can strip threaded fasteners.
Do you have a nagging torque or fastening problem that needs to be solved? Ask Mountz, our torque experts are happy to assist you. Contact us, we are happy to assist with the solving the issue.
