FALL 2023

14 THE DISTRIBUTOR’S

14 THE DISTRIBUTOR’S LINK Guy Avellon Guy Avellon has been in MRO and Fastener Distribution for over 30 years, in such positions Sales Engineer, Chief Engineer, Manager of Product Marketing, Product Engineering & Quality and Director of Quality & Engineering. He founded GT Technical Consultants where he performs failure analysis, lectures on fastener safety, works for law firms and designs/audits Quality systems. He is a member of SAE, is Vice Chairman of the ASTM F16 Fastener Committee, Chairman of the F16.01 Test Methods Committee and received the ASTM Award of Merit in 2005. Guy can be contacted at 847- 477-5057, Email: ExpertBoltGuy@gmail.com or visit www.BoltFailure.com. WHAT DISTRIBUTORS NEED TO KNOW ABOUT STRUCTURAL BOLTING Structures do not have to be only buildings and bridges; they are anything larger than a PC board that is assembled outside of a mass assembly line. This would include cranes, lift trucks, wind turbines, storage tanks, amusement rides, etc. Each structure has special assembly needs to assure safety and performance of the finished product. The only accurate method of producing a predictable amount of clamp load is by measuring the actual stretch of the fastener. This may be achieved by several different means and products that produce a low amount of error. Those methods include load cells, load washers, load indicating cap screws, ultrasonic transducers and even the turn-of-the-nut method. Load cells are used on site to ‘qualify’ the projected performance of job-site bolts and nuts. This, of course, is used in conjunction with a digital or click-type torque wrench. This method, like others, does not guarantee installation performance due to some external variables. However, the per-cent of errors are low. Load indicating washers, or Direct Tension Indicators (DTI) are quite simple to use, are a bit expensive but very useful on critical assemblies. Their accuracy is only as consistent as the operator. Ultrasonic transducers are also an extremely accurate means of measuring the stretch of the fastener. This method is very expensive and is not a permanent fixture as is a load washer. The transducer head can CONTRIBUTOR ARTICLE be moved from one fastener to the next, but the only drawback is that the head and point end of the cap screw must be smooth and flat to accept the transducer head. This would mean grinding off the grade markings and manufacturer’s identification marks: removing all traceability of the fastener. Torque multipliers are very useful and accurate for large diameter bolts requiring high torque values. As torque values increase, so does the lever requirement of the wrench. Torque is measured in the amount of force (pounds for example) times the distance of the lever (foot for example). Therefore, we have a pound-foot. Some torque wrenches are up to three feet long to provide the leverage needed to tighten the nut or bolt. Beyond this, a torque multiplier is used. Torque multipliers are extremely useful when mounting wind generator platforms or rotating crane structures. Some units are manually operated while others are either electric or pneumatically actuated. Another great tool used in structures is by not using torque at all, but by turning the nut a certain degree of rotation. This method works with coarse threaded fasteners only and on solid metal-to-metal joints whose joint compression has been removed by pre-tightening with a short handled wrench. This will not directly translate to Metric bolts, as the same thread pitch is used on other metric bolt diameters. Actual experimentation is needed for a particular size, thread pitch and joint thickness. CONTINUED ON PAGE 120