Specific Features of Fluoroplastic Band Bending with Due Account of Various Modularity of Material

Abstract

The paper considers a technological process for production of sealing rings by winding a band work-piece on a cylindrical caliber mandrel with subsequent endurance under load and further cutting of a spiral in rings and also studies the possibility to obtain products while using a method for cold forming of a work-piece which excludes thermal stabilization operation. Taking into account the fact that fluorine plastic is a high-plastic material even at very low temperatures such technology looks quite real. Therefore winding of a band on a mandrel, endurance of a spiral work-piece without heating but under conditions of force action within the time which is necessary for completion of relaxation processes, and the subsequent cutting in rings will allow to obtain finished ring products of the required size. However fluoroplastic has specific mechanical properties and a number of specific features which are revealed during deformation process. Its deformation behavior considerably differs from behavior of low-molecular materials and therefore it requires a solid approach while using the existing theoretical base and developing calculation methodologies. While taking into consideration the fact that fluorine plastic is high density material and has structure with high degree of crystallinity, the mechanism of deformation behavior in it under conditions of a force field is mainly similar to metal behavior that allows to use methods and approaches for calculation of fluoroplastic products which are accepted in mechanics of solid bodies. However the applied calculating formulae require a certain correction and adaptation to specific features of mechanical fluoroplastic properties, one of which is its various rigidity at stretching and compression that is revealed in case of winding band work-piece on a mandrel. Fluorine plastic is a material with various modularity and its rigidity is higher during compression than under stretching and consequently in the case of band bending a neutral axis of section is displaced from the center of gravity to the area of compressed fibers, and the area of stretching is increasing. High elasticity at stretching and increase of this area lead to large accumulation of elastic deformations causing springing after unloading and changes in size of a finished product. These facts must be taken into account while calculating and designing a mandrel tool, it is also necessary to keep in mind various modularity of a material and possibility that a section being led to an uniform rigidity may take some other shape due to this. Calculation methodologies have been developed by the authors for both versions of section that take into consideration directly or indirectly a material with various modularity and which do not contradict each other and which are rather precisely proved by experimental data.