ELASTO-PLASTIC BENDING OF A FLUOROPLASTIC TAPE AT BENDING IN A RING

A technological process of production of sealing fluoroplastic rings from a band workpiece is considered and the possibility of their production by a method of cold coiling of the tape on a cylindrical mandrel is investigated; the helix is cut in rings without subsequent heating operation and thermal fixing of sizes. The basis for adoption of such a technology is the analysis of mechanical properties and deformation behavior of fluoroplastic-4 in the conditions of power influence. Researches show that high plasticity of material and tendency of fluoroplastic-4 to cold flow contribute to emergence of irreversible deformations at low temperatures and low loadings and make possible obtaining fluoroplastic products by method of cold formation just as it occurs in metals, but taking into account particularities of polymer properties. Since the process of reorganization of structure and achievement of the equilibrium state has relaxation character, a necessary stage of cold forming is the endurance of a product under loading during the time required for preservation of given sizes by a detail. At the same time the accuracy of sizes of obtained rings is substantially defined by the tool accuracy (cylindrical caliber) on which is produced by winding of the tape. Considering this scheme of deformation as a pure bending at which there are areas of stretching and compression in a billet, and accepting for a fluoroplastic a model of a solid deformable body with possibility of elastic and residual deformations, it is for the first time proved by authors that fluoroplastic-4 behaves at compression as a rigid and plastic material, and at stretching the model of its behavior corresponds to elastic-plastic material. It means that zone of compression is completely captured by irreversible deformation and its sizes after unloading aren’t restored, and stretching zone even at considerable irreversible changes keeps some share of elastic deformations. After unloading, even after completion of relaxation processes, it leads to springing and, as a result, to partial restoration of its form and changes of its design size that should be considered during the development of technological process and designing of the tool. Authors have developed the method of calculation of the calibration tool taking into account effect of elastic after-effect in a product allowing obtaining fluoroplastic rings of required sizes and forms. The obtained results are reliable and are confirmed experimentally.

fluoroplastic, structure, mechanical properties, material model, deformation behavior at power loading, elastic and residual deformations, recrystallization, cold forming of preparation, bending of a tape, behavior model at stretching and compression, springing, calculation of the tool

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