Talking Torque

Torque Talk

Earlier this year, Boeing uncovered issues with improperly torqued bolts on the landing gears and wing ribs of their new 737 Max jets. This discovery echoed a similar quality concern flagged by the Federal Aviation Administration (FAA).

Although these were not identified as reasons behind the fatal crashes of the jet in 2018 and 2019, they were discovered during ongoing quality control processes. These issues illustrate the vital and often undervalued role of torque in the integrity and strength of joints in any assembly.

Torque Fundamentals

Defined as the rotational force applied to tighten a fastener, an incorrect torque application can lead to failures of a structure and can compromise safety.

Torque goes beyond just tightening. It directly determines how well a fastener sits in place. Over-torquing or under-torquing can be equally dangerous. In this way, the amount of torque impacts the quality of the finished product. But it’s only part of the story.

As mentioned, torque is the rotational force applied to tighten a fastener. It’s measured in units like Newton-meters or foot-pounds. Keep in mind, however, there’s a difference between torque and tension.

Simply put, while torque is the force used to rotate the faster in place, tension is the stretch or load resulting from this force. They’re both important for achieving optimal performance of the fastener.

Non-negotiable Torque Specs

Adhering to manufacturer torque specifications is non-negotiable for best results. Over-tightening doesn’t make a structure more secure. Quite the opposite. Excessive torque can result in the fastener breaking when subjected to even slight external loads.

In some cases, torque specs are not enough. In specialized applications that require high precision (e.g.: automotive assemblies or scientific equipment) the concept of “torque plus angle” comes into play. This refers to applying specific torque followed by additional rotational degrees. This gives a more precise clamping force. Be sure to also align with the design specs of the material being used. Achieving the desired force between the materials being joined doesn't necessarily mean fully tightening the screws.

High-Stake Tightening

In situations requiring high accuracy, standard torque wrenches may fall short. In such cases, advanced methods such as ultrasonic sensing of bolt length or using strain gauges may be necessary in these high-stake cases.

Best Practices

Following industry standards is not optional. It’s crucial to comply with these standards to ensure quality, safety and even legal protections.

Be sure to

• Calibrate torque tools regularly
• Stay updated with design specifications and industry standards
• Cross-check torque readings, paying special attention to critical joints

Mastering the science of torque is a calculated process not to be taken lightly. It requires adhering to guidelines, understanding the physics involved and knowing when to use advanced methods for finer adjustments in highly detailed assemblies.

Keeping these guidelines in mind is critical for getting the most value from your fasteners. In addition, they ensure your manufactured products meet any quality regulations.

For more information on torque, check out these posts:

• Fastener Tightening Specifications You Need to Understand
  https://www.melfast.com/blog/2015/08/3-fastener-tightening-specifications-you-need-to-understand
• Is the Torque You Use Important When Fastening Bolts?
  https://www.melfast.com/blog/2014/05/is-the-torque-you-use-important-when-fastening-bolts
• How Tight Should You Tighten a Screw?
  https://www.melfast.com/blog/2015/10/how-tight-should-you-tighten-a-screw

Photo by Nina Mercado on Unsplash