Hydrostatic extrusion method

In Ref [62], the studied object was an epoxy polymer on the basis of resin UP5-181, cured by iso-methyltetrahydrophthalic anhydride in the ratio by mass 1 0.56. Testing specimens were obtained by the hydrostatic extrusion method. The indicated method choice is due to the fact, that high hydrostatic pressure imposition in deformation process prevents the defects formation and growth, resulting to the material failure [64]. The extrusion strain was calculated according to the Eqs. (14.10) and (4.39) and makes up 0.14, 0.25, 0.36, 0.43 and 0.52. The obtained by hydrostatic extrusion specimens were annealed at maximum temperature 353 K during 15 min. 

Most of the experiments described in the literature, including the pioneering work by Pugh, were performed as hydrostatic extrusions. For materials like HOPE, PP, and POM this method is considered to be the only one which allows cxmtinuous preparation of extrudates, due to the reduced friction between billet and barrel and the decrease in strain hardening. The apparatus also used for hydrostatic extrusion is schematically depicted in Fig. 1. 

There are two major methods used to produce very highly oriented, high-modulus polymers cold drawing and hydrostatic extrusion. Although the highest moduli may be reached by way of the cold-drawing technique, hydrostatic extrusion provides better control over the final product dimensions than does drawing. 

There are two methods of solid-state extrusion one is direct solid-state extrusion, the other is hydrostatic extrusion. In direct solid-state extrusion, a pre-formed solid rod of material (a billet) is in direct contact with the plunger and the walls of the extrusion die, see Fig. 2.20. The material is extruded as the ram is pushed towards the die. 

This article gives a brief information on different SSE methods and their influence on structure and properties of polymer materials. Attention is primarily paid to the most known methods, such as plimger extrusion and hydrostatic extrusion. Two new methods of SSE implementation are analyzed in brief, which, in contrast to the conventional ones, are based on polymer simple shear, not drawing. Lately, they have been of high interest in view of the production of nanostructural metallic materials (17) and are now known as methods of severe plastic deformation (SPD). 

Extrusion Methods. There exist two approaches to SSE implementation. These are the methods of plunger and hydrostatic extrusion. The first investigations by using the plunger extrusion were made on polyethylene. Extrudates were produced by melt crystallization under pressure and by orientation in a capillary rheometer of the Instron type (1,24-26). Moreover, the crystallization of polymer took place at die entrance and in the rheometer cylinder. Such a technique made it possible to produce short transparent and strong fibers of less than 1 mm diameter or films of similar characteristics. 

Capaccio, Gibson, and Ward, and Zachariades, Mead, and Porter have reviewed these methods up to 1977 with particular emphasis upon the linear polyethylenes. Gibson and Ward have recently described the creation of a high modulus polythene (60 GPa) by drawing out of a heated conical die. The array of techniques described produce fibres of relatively small diameter and were mainly developed for the linear polythenes. Enhanced stiffnesses have been produced in quite thick rods of ca. 25 mm diameter and in more complex shapes by hydrostatic extrusion again with linear polythenes. 

Hydrostatic extrusion is a variation of solid-state extrusion in which a billet of melt-crystallized polymer is snrrounded by a film of oil that reduces die friction. Filaments with tensile moduli of up to 46 GPa have been produced by this method [58],... 

For the solid-state extrusion several tedmiques have been developed. They are either bz ed on pure ram extrusion or on hydrostatic methods. 

Methods of aerosol generation—ultrasound, electrohydrodynamics, hydrostatic pressure extrusion of liquid through small orifices—that, just ten years ago, might have been considered laboratory curiosities or perhaps only implemented as laboratory prototype generators, are now in late-stage development as handheld inhalers. In addition, precision dry-powder inhalers are in late-stage development. Chlorofluorocarbon (CFC)-free MDIs, often more... 

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