Наука и техника (Feb 2019)
Influence of Elastic Core on Size of Ring Product under Bending of Fluoroplastic Band
Abstract
The paper is devoted to study of a possibility to manufacture fluoroplastic products while using method of cold deformation of pressed blanks and research of peculiar features in mechanical behavior of fluoroplastic which are revealed during deformation that affects quality and accuracy of the manufactured parts. Manufacturing technique of fluoroplastic sealing rings which are obtained while using method of coiling a band blank on a cylindrical mandrel with further endurance in a wound state and subsequent cutting of a spiral on rings has been considered in the paper. An important stage in the development of the technological process is a calculation and a design of a tool (mandrel caliber) that ensure obtaining of ring products with the required size and shape. Deformation behavior of fluoroplastic under conditions of force action is significantly different from the behavior of the known classical materials and it has a number of specific features and manifestations. Therefore the problem for creation of a calculation methodology for tool development looks as a complicated one and it requires a justified approach while selecting a mechanical model of polymer. Considering the fact that fluoroplastic has a structure with a high degree of crystallinity, a mechanism and sequence of deformations in it due to load are largely similar to the behavior of metals and other low-molecular materials. It allows to use methods and approaches adopted in the mechanics of solids for a calculation of fluoroplastic products however it is necessary to take into account the fact that deformation processes in polymers proceed in time and have a different nature of elastic and residual deformations. When bending the fluoroplastic band in case of winding it on the mandrel residual deformations which provide the required size and shape play the most significant role. However elastic deformations which cause springing and change of size in a finished product after removal of loading are also important. It has been proved that an elastic zone of finite width which has a certain influence on accuracy of manufactured products with due account of all accumulated elastic deformations will be present in the field of a neutral layer even at high degrees of deformation. In this case, fluoroplastic is a multi-modulus material having elasticity which at stretching is significantly higher than in compression, and therefore elastic recovery is more associated with the area of stretched fibers. The authors have developed a methodology for calculation of the tool for obtaining rings of the required size on the basis of the analysis pertaining to deformation behavior of the fluoroplastic while taking into account specificity of its mechanical properties. The proposed methodology with a sufficient degree of accuracy is consistent with the results of experimental studies.
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