ENERPAC - Bolting Tools Strana 122
Nabídka komerčních zákazníků **Nejlépe prodávané z ENERPAC
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Bolting Theory Function of Bolts and Nuts Threaded fasteners are used across industry to assemble products ranging from pipelines to heavy-duty earth movers and from cranes to bridges and many more. Their principle function is to create a clamping force across the joint which is able to sustain the operating conditions without loosening. Hooke’s Law of Physics Elastic Range Plastic Range Behavior of Bolts and Nuts Bolt Failure UltimateTensile Point Tensile Point Stress Proof Load Over tight 4 5 1 6 2 3 1. Bolt loosens due to cycle loads of vibration. 2. Sealing face surface damage. 3. No compression. 4. Cracking. 5. Flange rotation. 6. Yielding of bolts. 7. Over compression of gasket. In the plastic deformation a part of the elongation will remain after the load is removed. The point where this permanent elongation occurs is called the yield strength. The further application of load takes the bolt to a point where it begins to fail this is termed its ultimate tensile strength (UTS). At this UTS-point, if additional force is applied to the bolt it will continue to elongate until it finally breaks. The point at which the bolt breaks is called the tensile point. Careful attention must be paid to the grade of bolt being used as bolt grades differ in the elastic range. Preload Uniform preload (residual load) 120 Elasticity is defined in Hooke’s Law of physics: The stress in a bolt is directly proportional to its strain. The stressstrain of a bolt has an elastic range and a plastic range. In the elastic range Hooke’s Law is true. All of the elongation applied within the elastic range is relieved when the load is removed. The amount of elongation increases when more load is applied. When a bolt is stressed beyond its proof load (maximum load under which a bolt will behave in an elastic manner), the elastic elongation changes to plastic deformation and the strain will no longer be proportional to the stress. Strain Under tight Correctly tightened bolts make use of their elastic properties, to work well they must behave like springs. When load is applied, the bolt stretches and tries to return to its original length. This creates compressive force across the joint members. 7 The main purpose of a bolt and nut is to clamp parts together with the correct force to prevent loosening in operation. The term preload refers to the loading in a bolt immediately after it has been tightened. The amount of preload (residual load) is critical as the joint can fail if the load in the bolt is too high, too low or not uniform in every bolt. Uneven Bolt Loads can Result in: • Some bolts being loose while others are overloaded. • Crushing of the gasket on one side, leakage on the other side. Preload is normally dictated by the joint design, (see Enerpac Bolted Joint Integrity) for information on common joint types or contact your local representative. www.enerpac.com
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