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Distributor's Link Magazine Spring 2021 / Vol 44 No 2


108 THE DISTRIBUTOR’S LINK GUY AVELLON WHAT FASTENER DISTRIBUTORS NEED TO KNOW ABOUT FASTENER FAILURES from page 26 [2] Incorrect Torque ¤ This could mean that no measuring method was used and/or a lubricant was present. ¤ This could also mean that the proper torque was not applied for the conditions of the application; environmental, temperature, surface finish, lubricants, etc. [3] Lubrication ¤ All torque charts cite values for ‘as received’ product, which is mostly ‘dry’. ¤ There are numerous lubricants on the market of which some are more efficient than others. Therefore, torque values must be adjusted for each type of lubricant. ¤ Lubricants reduce the friction between the mating threads as the bolt is torsionally tightened. Therefore, torque values are generally reduced to much lower values than on torque charts. ¤ Using a ‘dry’ torque value, or no torque at all, with a lubricated fastener will generally cause the fastener to be stretched into its plastic region well past its yield point. [4] Power Wrenches ¤ Pneumatic or hydraulic power all rely on pressure. Unless regulated, there is no accurate method of applying torque. ¤ Air wrenches are much faster than hydraulic wrenches, but all seek friction to cause the wrench to stall. If a lubricant is present, there is little friction present to cause the wrench to stall. Therefore, the wrench continues to impact or turn until the fastener is beyond its yield point. ¤ As an example, an ordinary shop 1/2” unregulated impact gun has an initial impact of 425 lb-ft of torque. This will cause a 3/4”-7/8” Grade 8 lubricated bolt to yield. ¤ Impact wrench abuse can be noted by the damage to the hex corners of the nut as the socket slams repeatedly into the nut corners causing v visible deformation. [5] Speed of Applied Torque ¤ Even a matching strength grade nut will strip its threads in the presence of intentional or accidental lubricant if the applied torque is too fast. ¤ The bolt is more likely to be stretched into yield, or fractured, if the speed of assembly is high as the speed also reduces friction until contact with the surface. ¤ Speed also causes an elastic rebound effect, which in some circumstances could cause the fastener to be stretched into yield as the joint material regains its shape from compression. [6] Elevated Temperatures ¤ Joint materials expand with heat. ¤ If the fastener was tightened very tight in the connection, the joint expansion could cause the fastener to be stretched into yield. ¤ This will cause a loose bolt in the joint when it cools. Again, check the thread pitch. Underloaded If the cap screw is not tightened sufficiently to produce a clamping force greater than the load that will be applied to it, the fastener will fail from a phenomenon known as metal fatigue. Fatigue failure occurs in heat treated metals and is most frequently encountered in heavy dynamic and fluctuating load assemblies where maximum loading does not occur during installation but later, when the equipment has been placed into service and when a heavy initial load impacts the joint. In this case, a cap screw may fail even though its tensile strength is much greater than the service loads it experiences. The mechanism for this type of failure is similar to the repeated bending of a coat hanger wire. The metal becomes ‘tired’ or fatigues due to this repeated movement. CONTINUED ON PAGE 146

Martin Inc., is pleased to announce that Kelso (KG) Sims has been promoted to Vice President, Fastening Solutions. KG’s added responsibilities will include business development and fasteners market expansion throughout Martin’s territories. “Since KG joined the team, Martin Fastening has seen significant improvement in operational efficiency and profitability,” said Douglas Ruggles, CEO & President, Martin Fasteners and co-owner of Martin Inc. “I am confident that his leadership will further advance Martin’s fastening footprint and his expertise will help companies operate better.” KG joined Martin in 2018 as Director of Operations and then transitioned to Fastening General Manager in 2019. KG has over 28 years’ experience in manufacturing, engineering and operations Management and 9 years’ experience in the pneumatic and threaded component distribution industry. Martin Fastening is ISO 9001 certified and a member of Global Sourcing Alliance and National Fasteners Distributor Association. Headquartered in Florence, AL in 1934, Martin Inc. is one of the nation’s leading providers of custom-tailored solutions for maintenance, repair, operation and production supplies (MROP) to the industrial and construction markets. For more information about Martin Inc, contact them by Tel: 1-800-828-8116, Email: info@ or online at THE DISTRIBUTOR’S LINK 109


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