Webinar: Torque Theory

Date: Tuesday, October 27th, 2020: 2:00 - 2:30 PM EST

Welcome to the ‘Torque Theory’ webinar. 

Leading the session is Hans Mandahl, a Product Specialist here at Atlas Copco. In this webinar, we’re exploring the science behind torque theory, an important theory to Atlas Copco and our customers. The webinar begins with a brief review of the definition of torque, which is the measurement of the rotational moment of force into a fastener. Common torque measurement units include newton meters, foot-pound force, inch-pounds, and more. Twisting force, as Hans explains, is the product of force and the wrench length applied to a nut or a bolt. Following these definitions, Hans goes into the reasons why bolted joints are used in tightening. To clamp components together, bolted joints are used because they are serviceable, cost-efficient, easy to assemble and use, and they provide traceability. We then move into discussing clamping force. 

Clamping force is the target of all tightening, and it holds the joint together. Hans poses a rhetorical question to his viewers: if clamping force is the goal of tightening, why do we measure torque? The answer is that clamping force is achieved through the application of torque. Following this, Hans moves into the four phases of tightening. The order of these phases goes rundown, draw-down, elastic, and plastic. In the rundown phase, there is no contact between the fastener head and the part. Draw-down is the next phase, and there is contact. The joint is seated. The third phase is elastic, and this phase includes elastic deformation of the bolt. In this phase, clamping force is built up. Finally, the last phase of tightening is plastic. The plastic phase refers to the plastic deformation of the bolt. Hans then moves into discussing where the torque goes during tightening. About 90% of torque is used to overcome friction, and the goal is to make friction constant. Decreased friction results in an increased clamping force. Increased friction results in decreased clamping force. 

In the final part of the webinar, Hans goes into the subject of prevailing torque. The two types of prevailing torque are intentional and unintentional. Prevailing torque can cause a handful of effects during tightening. Reduced rundown and increased torque reaction force are just two of the possible effects if prevailing torque is not properly accounted for. Joint relaxation is another phenomenon that happens after tightening, resulting in the loss of torque and clamping force in the joint. This can be avoided by using two-stage tightenings, advanced tightening strategies, and impulse tightening strategies. Following this, Hans goes through the tool types used in torque applications. We have direct-drive nutrunners, DC electric tools, and Low Reaction Tools, and more. The accuracy of the tools listed above depends on the type of tool being used during tightening. The accuracy of tools refers to the repeatability of a tool or fastening process. If you’re interested in learning about everything Hans covered during this webinar, be sure to watch it in full.