SPRING 2024

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94 THE DISTRIBUTOR’S LINK GUY AVELLON WHAT DISTRIBUTORS NEED TO KNOW ABOUT HOW FASTENERS ARE TIGHTENED IN MAINTENANCE ASSEMBLIES from page 26 This would mean that at the same torque, the cadmium plated lock nuts would produce more tensile load on the fastener, with the potential of stretching the fastener into yield, than the zinc plated lock nut. The connection would be compromised. Some maintenance shops and those performing field repair work will use a micrometer adjustable torque wrench. This is also referred to as a ‘click-type’, where the torque value is numerically adjusted on the handle. The wrench will produce an audible ‘click’, which can also be felt, when the set torque value is reached. At this point, the operator stops turning the wrench. However, there is no provision for preventing the operator to continue turning the wrench and applying more torque to the fastener which will increase the load on the fastener joint. There are special adjustable torque wrenches available that have a cam in the head that will prevent over tightening. Realistically, most of the maintenance performed on fasteners is done without using a torque wrench but with the ‘calibrated elbow’. And, many times using either the torque wrench or elbow, the tightening procedure is incorrect. Torque charts have been printed as guides to achieving the proper tension on the bolt but it may not be as perfect for the connection or overall joint. We can achieve adequate tension on one bolt, but what about multiple fasteners in the joint? What about environmental FIGURE 1 conditions? Is it a rigid joint or compressible joint? A common practice in the maintenance industry is to calculate the torque to produce a clamp load that was 75% below proof load. Proof load being approximately 9% below yield gave the operator a good margin of safety to avoid stretching the fastener into yield. However, there are many variables to consider which can affect the clamp load by over ±50%. In Figure 1 we have the ideal clamp load with 25% safety factor. Figure 2 represents an example of where a small installation torque error will result in a wide clamp load variance. This wide range of a variance is not good for a multiple bolting assembly. FIGURE 2 So, the man with the wrench must be consistent. But the joint will never be consistent with material hardnesses, flatness, smooth surfaces, burrs, rust, etc. Then, after tightening, all clamping forces will decrease as soon as the wrench stops turning and the joint relaxes from the compression. Typically, a joint relaxes anywhere between 5-15%, depending on whether the head of the bolt or nut is turned. As the joint enters service, the joint may relax even more which is why critical joints are retightened shortly after the initial installation, then again after experiencing service loads. CONTINUED ON PAGE 95
THE DISTRIBUTOR’S LINK 95 GUY AVELLON WHAT DISTRIBUTORS NEED TO KNOW ABOUT HOW FASTENERS ARE TIGHTENED IN MAINTENANCE ASSEMBLIES from page 94 The joint will also lose clamp load due to material creep. That is, under a sustained load, the length of the bolt will continue to elongate without any change in the external loads especially when experiencing elevated temperatures. Even the thickness of the metal joint can change the clamp load with decreasing or increasing temperatures. Most repairs are of the type where the mechanic must get in and go quickly, sometimes in hostile environments. For example, with replacing a single bolt in a multiple bolted joint, the ideal situation would be to loosen all of the bolts, then tighten all of them together in a criss-cross pattern. This technique hardly ever happens. Gasketed joints are even more complicated because the joint interfaces are designed to compress a material between them for the purpose of sealing any leaks from a flanged joint. Sealing becomes complicated because if the mechanic begins to tighten one bolt in an attempt to stop a leak, he may be compressing the gasket material even further, damaging the flange or stretching the bolt into yield after repeated tightening efforts. There are many different types of gasket materials with their own elastic or compressive properties. There is no non-compressible gasket because all materials are compressible. It does make a difference to have the correct bolt torque and proper tightening sequence so the gasket is not crushed beyond its sealing capabilities and to avoid fracturing the flange material. As with any multiple bolted connection, if one bolt needs to be replaced it is incumbent upon the maintenance personnel to determine the cause. By replacing just the failed bolt may exacerbate the problem and the adjacent bolts will be subject to failure as well. It is always best to replace the adjacent bolts as well. GUY AVELLON
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In the Spring 2024 issue of 6 DISTR
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6 THE DISTRIBUTOR’S LINK E&T Fast
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10 THE DISTRIBUTOR’S LINK Eric Du
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14 THE DISTRIBUTOR’S LINK Rob LaP
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28 THE DISTRIBUTOR’S LINK Bruno M
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32 THE DISTRIBUTOR’S LINK Jo Morr
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36 THE DISTRIBUTOR’S LINK INDUSTR
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40 THE DISTRIBUTOR’S LINK Larry B
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Page 118 and 119: MWFA PUTT SHACK EVENT OAKBROOK, IL
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Page 136 and 137: fastenerlinks THE DEFINITIVE WEB DI
Page 138 and 139: fastenerlinks BRINGING YOU THE FAST
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PAC-WEST HOLIDAY PARTY & TOYS FOR T
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THE DISTRIBUTOR’S LINK 145 CHRIS
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148 THE DISTRIBUTOR’S LINK ROBERT
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150 THE DISTRIBUTOR’S LINK NELSON
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THE DISTRIBUTOR’S LINK 153 SPIROL
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THE DISTRIBUTOR’S LINK 155 METROP
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160 THE DISTRIBUTOR’S LINK BRUNO
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AFC Industries has acquired West Ch
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THE DISTRIBUTOR’S LINK 165 BRUNO
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168 THE DISTRIBUTOR’S LINK Joe Sh
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advertisers index E E & T FASTENERS
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SPRING 2024

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