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Distributor's Link Magazine Summer 2021 / Vol 44 No 3


110 THE DISTRIBUTOR’S LINK GUY AVELLON WHAT FASTENER DISTRIBUTORS NEED TO KNOW: THE LONG AND SHORT OF BOLT FAILURES from page 110 FIGURE 2 FIGURE 3 Figure 2 illustrates a correct assembly. There are about two threads sticking out beyond the end of the nut allowing the maximum number of unengaged threads inside the grip of the connection. This provides shock absorbers to absorb any shock or vibration loads or heavy impacting during installation. A fastener’s threads are very important. They stretch significantly more than the rest of the fastener and therefore have a much higher level of stress. During axial tensile testing, the ASTM Test Method Standards of F606 and F606M require a minimum of six complete threads between the test grips for a standard fastener, and a minimum of four complete threads for the shorter thread length of a structural fastener, such as an A325 (F3125/F3125M) cap screw. If the nut or test mandrel is too close to the thread run-out, the tensile readings will not reflect the actual properties of the fastener. The stresses will be much greater on the few remaining threads. Structural fasteners (A325 and A490 for example) have a shorter thread length than standard SAE Grade 5 and 8 and their respective ASTM counterparts ASTM A449 and A354. This is to ensure that the full diameter of the fastener’s shank is completely within the shear plane of a structural joint. This now leads into assembly variables because the most critical time of a fastener’s life is when it is being tightened. Figure 3 depicts a pure axial tensile load of only one force: tension. However, when tension is combined with another force, as with torsion during tightening, the combination of forces acting on the fastener drastically reduces the amount of force required to cause it to fail. The illustration of Figure 4 shows what happens when tension and torsion are combined when installing a fastener. Once the torsional forces stop, that load dissipates and only pure tension remains on the fastener. During assembly, any quick, sharp or jerking motions while tightening the nut or bolt head can also become very detrimental. This is why the use of power assembly tools or impact wrenches can cause fasteners to fail prematurely if these power tools are not properly regulated. A fastener cannot achieve clamp loads much beyond its minimum yield strength. Any further tightening may cause the fastener to fail. However, the load by direct tension, as depicted above in Figure 3 and compared in Figure 4 with the tension by turning the nut, illustrates the ductility of the fastener and its capacity to sustain further loads. Service loads would include shear and direct tension. Torsion will not occur again. Note the reserve strength of the fastener above the minimum tension in Figure 4 as well as the increased elongation potential. The unengaged threads are critical during installation. A fastener must be able to absorb a certain amount of torsion during assembly. CONTINUED ON PAGE 166

Birmingham Fastener and Supply Inc. is excited to announce the acquisition of Steel City Bolt and Screw. With over 100 years of combined fastener production, the acquisition strengthens Birmingham Fastener’s product offering, equipment depth, and most importantly it allows us to add teammates to our world class staff. Brad Tinney, owner of Birmingham Fastener says, “With this acquisition we continue to double down on domestic manufacturing and provide our customers with a domestic solution on any fastener requirement they have. This equipment will assist in our expansion into the Carolinas and continue to expand our east coast footprint. Our customer base is second to none and we will ensure their needs are meet and expectations are exceeded.” Operations of Steel City Bolt and Screw will be consolidated into the production facility at our corporate headquarters in Birmingham Alabama. In doing this, the level of service we can offer our valued customers will be increased. Customer service remains paramount at Birmingham Fastener; in-turn, all Steel City Bolt and Screw customers will become valued partners of Birmingham Fastener and be serviced as a top priority. Birmingham Fastener continues to invest in the future and make strategic moves and acquisitions that will yield long term benefits for our customers. Our plan is to take this 100 years of customer service and turn it into 200 years of outrageous service for our entire family of customers. We can’t wait to build and strengthen new partnerships with the customers of Steel City Bolt and Screw. Founded in 1980, Birmingham Fastener is a leading domestic manufacturer and distributor of fasteners for structural steel fabrication, metal building manufacturers, water works, OEM, and MRO. The Birmingham Fastener family of companies consists of multiple locations across the nation. In 2018, Birmingham Fastener received the Alabama Manufacturer of the Year award. For further information contact Birmingham Fastener Inc. at 931 Avenue W, Birmingham, AL 35214. Call Toll-Free: 1-800- 695-3511, Local: 205- 595-3511, Fax: 205-591-7107 or visit their website at THE DISTRIBUTOR’S LINK 111

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