An All-Pro customer was experiencing failure of a bolt assembly prior to meeting its Rotational Capacity* minimum, as detailed in testing documentation. This issue was causing cost overruns, and the construction implementation plan was being slowed.
The bolt/washer/nut assembly was being installed by a high-impact wrench on the job site. Based on testing by a Skidmore machine, the customer had come to the conclusion that the fasteners’ materials were responsible for the failure.
Problem Identified and Solved
All-Pro’s Quality team quickly reacted to the issue, sending a crew to the worksite, equipped with a portable calibrated Skidmore testing device and an electric wrench. All-Pro technicians tested the assemblies on both their portable and the customer’s Skidmore machines, using the high-impact wrenches and the electric wrenches. Through this process, it was determined that the high-impact wrench was creating too much torque and causing the assemblies to fail. When installed with the electric wrench, the assemblies met all testing requirements and never failed.
The onsite construction staff was trained on the correct installation process, using an electric torque wrench or manual hand wrench. The result…no more product issues were reported. The construction project remained on schedule, with no increase in product expense.
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* Per ASTM F3125 Annex section 2.1.1, Rotational Capacity Testing is defined as, “intended to evaluate the presence of a lubricant, the efficiency of lubricant and the compatibility of fastening assemblies.” The process of galvanizing fasteners increases the friction between the bolt and nut threads and adds variability to the torque-induced pretension. Reduced torque requirements and more consistent results are achieved when lubricated nuts are used as part of the bolt assembly. Rotational Capacity Testing must establish that the galvanized, lubricated nut may be rotated from a snug-tight condition beyond the rotation required for pre-tensioned installation…all without stripping. In order words, the test is designed to demonstrate that the nut will not gall on the bolt, and that the assembly will develop the required pretension load.