Development and testing of conical tantalum spinnerets

Abstract

677.4.051.261 The spinning stability and thread defectiveness are not only a function of the degree of purity of the industrial solutions, correspondence of the parameters of the viscose and spinning bath, but also the conditions of flow of the viscose through, the spinneret openings and formation of a threadlike jet.Since precipitation of the polymer and structure formation take place in the immediate vicinity of the spinneret (0.02-0.2 ram) -in the zone where the thread is subject to high tension from contact with the spinrfing bath (SB), it is necessary to create conditions which will decrease the length of this "liquid" section. It is also necessary for the elementary jet of viscose coming out of the spinneret to be uniform, for its surface to have no defects, and for the shape to be close to cylindrical. These conditions can be created not only with the material but also with the use of spinnerets of special design.As published sources indicate, the characteristics of the spinnerets which affect the spinning stability and thread defectiveness are the following: the shape of the spinneret, the angle of the input cone, the ratio of the channel length to the diameter//d, and the density of the openings on the bottom. The currently used cup-shaped spinnerets have a significant drawback -stagnant zones appear inside them along the generator of the bottom. Contaminants and air bubbles can accumulate and the viscose can coagulate in stagnant zones.In going from a cylindrical to a conical spinneret, where the openings are positioned over the entire surface of the bottom, stagnant zones are almost totally eliminated. In addition, the normal constituent (directed perpendicular to movement of the thread) of the force of the hydrodynamic resistance of the SB decreases, deforming the jet, and causing formation of splices and breaks. Due to these advantages, conical spinnerets have long been used by many foreign manufacturers of viscose textile thread.The uniformity of flow of the viscose in the channel of the spinneret opening greatly affects the stability of the spinning process. In going into the channel of the opening, the shear stress increases sharply and the input energy increases [1]. If it exceeds a certain critical value, the continuity of the jet is perturbed and it breaks. Spinnerets with conical expansion of the opening at the inlet are used to reduce the shear stress.For uniform flow of the viscose, this angle must be no less than 20* [2]. In our opinion, the angle of the input cone should be within the limits of 20-30 ~ In the platinum-palladium spinnerets manufactured by Mostochlegmash Co., the angle of the input cone, calculated with the standard channel dimensions (USSR Technical Standard TU 3-17A.4-88) is 18"; this could be a possible cause of the appearance of unstable flow of the viscose in the channel.Expansion of the viscose jet in coming out of the opening channel is an unfavorable factor in spinning. Many factors affect expansion of the jet: the viscose flow rate, density of the SB, spinneret ...

Investigation on microstructure and high strain rate behaviour of pure tantalum prepared by hot press and subsequent annealing treatment

“…Among refractory metals, tantalum has proper properties such as high density, high melting point, good heat conductivity, good fracture toughness, and excellent corrosion resistance; hence, this metal has gained a proper stability in industrial applications including the manufacture of equipment for chemical processing plants, devices for electronic, aerospace, and high strain rate applications [1][2][3][4][5][6]. Besides, tantalum has better cold fabricability and a lower ductile-to-brittle transition temperature than some other bcc metals such as molybdenum, alpha iron (α-Fe), and their alloys, [7][8][9].…”