| Fatigue properties of solid Steel Belts |
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Fatigue strength: The fatigue strength or limit of a metal is a measure of resistance to failure when subjected to cycles of repeated stress. Fatigue tests consist of testing specimens to cycles of a know range of stress of various magnitudes and recording the number of cycles required for failure or for the attainment of a specified life without failure. The fatigue strength (sometimes called endurance limit) is defined as the limiting stress below which the metal will withstand an indefinitely large number of cycles of stress without failure. Wohler diagram (S-N diagram): A Wohler diagrams (S-N diagram) plots the number of load cycles versus a stress level. The fatigue limit is defined as the stress that will not produce failure up to an arbitrary number of cycles. As long as the stress level is kept below the fatigue limit, the metal or belt should never fail. Conveyor design: In general, a conveyor is designed so that the stress level of the steel belt is well below the fatigue strength of the belt material. Therefore, the belt should not fail by fatigue. There are cases were steel belts have operated for relatively long time (10 to 15 years) with no evidence of fatigue. Belt design: Sharp edges, dents, nicks, or burrs are a common cause for early fatigue of a steel belt. For this reason, belt edges are rounded to eliminate sharp corners. It is advisable to repair any damage as soon as possible to avoid early fatigue. Bending stress: The bending of the belt around the pulley or sheaves does increase the stress level by the bending stress but if the pulley or sheave size is designed properly, the total stress level from bending and tension will be below the fatigue strength of the material. However, damage such as a dent increases the stress level and can lead to failure by fatigue in a relatively short period of time. For this reason, dents should be immediately repaired. Tensile strength: The fatigue strength of a material is closely associated with the tensile strength of the material. Steel belts are made from a relatively high tensile strength material (1/2 Hard) and therefore have a relatively high fatigue strength. An annealed stainless steel does not have sufficient fatigue strength for a belt application. |
