Articles 

Understanding When to Use Torque Equations

2011-02-23

I was recently invited to act as a consultant on an issue involving a gasketed joint. The joint was composed of doubled ended studs torqued into aluminum and then secured a steel cover. The information I was given was that the gasket deteriorated and that the clamp-load was lost in the joint. The problem was that the manufacturer of the joint did not know what came first. I thought I would pass on the information I learned from this meeting as well as some general guidelines on using torque/clamp-load relationships found in many specifications. Of course, some test data will be discussed. I promise not to be academic. We all have been scheduled for the “death by meeting” day. A meeting lasting 8 hours with 60 of your closest colleagues all eating pastries and drinking coffee just to stay awake. During the afternoon session of Day 1, I am looking ahead in the presentation material and found an interesting bit of information. All morning, briefers had indicated that joint always loosed at the 90deg position (the other two studs were 120deg apart). The interesting information was that the effective length of the 90deg position was 40% smaller than the other two positions. The first thing I thought of was the relationship between applied torque and developed clamp-load, Equation 1. This equation is used everywhere in one form or another. But the remarkable thing is that nowhere in the equation is effective length, or stiffness used.