| Description |
[ix], 156 leaves : illustrations ; 28 cm |
| Summary |
"Stresses, in bolts, caused by initial tightening have long been a problem to machine designers. To take care of these unknown stresses, produced by initial tightening, designers have used empirical formulas. These formulas originally used for National Coarse Threads, have been carried over into the field of National Fine Threaded bolts. No known tests have been conducted to determine whether or not these formulas hold in the initial tightening of Fine Threaded bolts. Initial tightening stresses may be caused by one of two ways. First, consider two flat ground plates to be held together by bolts to form a steam tight joint. If the bolts do all the deforming and plates do not deform any in the process of initial tightening then the maximum load on the bolts is the amount of the initial tightening, because any additional deformation of the bolt would cause the joint to leak. This condition is not attainable in practice. Second, consider two flat plates separated by a perfectly elastic gasket. When initial tightening takes place the bolts cause the gasket material to deform. When an additional load is placed on the bolts the joint will not leak because as the two plates move apart the gasket expands and prevents the leak. In this condition the total load on the bolts is then equal to the sum of the initial tightening and the external load. This condition of a perfectly elastic gasket is impossible to attain. Initial tightening as the designer knows it, must lie somewhere between the value for initial tightening stress alone and must be less than the sum of initial tightening and the external load. It is this third consideration that we must deal with in design work"--Introduction, leaves 1-2. |
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