| Abstrakt: |
1.The mechanism of warping based on uneven residual deformation permits the yield strength to be considered as the main factor in the disruption of the balance of moments and warping.2.In the ideal process relaxation does not induce disruption of the balance of moments and warping. In the actual process relaxation may become a factor in warping, but its role in warping decreases as the process approaches the ideal; in this case the percentage of relaxed stresses increases and thus the percentage of stresses limited by the yield strength decreases, i.e., relaxation becomes a sizing factor in the ideal and the actual processes.3.Relaxation cannot exclude warping during heating if the stresses from preliminary forming operations are close to the yield strength at room temperature. Warping can be avoided in this case only with prolonged heating, which limits the possibilities of practical use of relaxation for sizing machine parts in the free condition.4.With holding during heating the process approaches the ideal, and thus relaxation can be utilized as a factor retaining the geometry obtained at the end of heating.5.With complete removal of stresses in the process of holding, the stresses that occur during cooling may be relaxed at a high rate, and therefore the optimal cooling rate in the actual process becomes the most significant factor. For most large and medium-size shells it matches the cooling rate in air.6.The conditions in which relaxation plays a sizing role in the actual process of annealing shells on mandrels with high coefficients of thermal expansion are complete removal of internal stresses during holding and the optimal cooling rate. |
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