GB573325A - Improvements relating to the extrusion of fused filament-forming compositions - Google Patents

Abstract

<PICT:0573325/IV/1> Artificial filaments, foils, films and like materials are obtained by the continuous meltspinning of thermoplastic compositions, solid composition being fed, preferably automatically, to the fusion vessel upon detection of the temperature change occurring whenever a boundary between two fluid phases within the vessel falls below a fixed level. The solid composition may be melted in the fusion chamber by an inert heating liquid in which the composition is immersed and above which exists an inert gaseous atmosphere as described in Specifications 565,489 and 565,981. By observing the temperature at a fixed point within the vessel, the temperature difference between adjacent fluid phases is indicated as a boundary between the phases moves past the fixed point. The temperature difference between the inert gaseous phase and that of the heating liquid is preferably employed. The temperature change at the fixed point may be indicated visually by a thermometer, or mechanically by a large bulb of mercury communicating with mercury-filled bellows, or the movement of the free mercury surface in the stem of the bulb may be adapted to make and break an electrical contact. Alternatively, a thermocouple having one junction at the fixed point and the other at a point that is constantly in one of the fluid phases may be employed. A resistance bridge may be similarly employed. Solid material may be fed to the melt chamber through a lock chamber as described in Specifications 573,324 and 573,327, the operation of the lock chamber also being controlled automatically, if desired, by the temperature change at the fixed point. The melt chamber may be heated externally, and means may be provided to control the heat supplied to the apparatus. Suitable thermoplastic compositions are synthetic linear superpolyamides, polyvinyl compounds, and esters, mixed esters and ethers of cellulose. The composition is melted by heating liquid 4 and forms a pool 3 in the base of melt vessel 2, from which it is withdrawn by pump 6 and forced through filter 8 and extrusion jet 9. The molten composition can be displaced, for cleaning purposes, from the pump, filter and jet by means of main valve 13 and auxiliary valve 16, the device also serving to prime the pump with heating liquid. Solid composition is deflected towards the vessel walls by baffle 21 of the kind described in Specification 573,326, and the vessel is surrounded by heating jacket 24. The level-indicating device comprises a conical bulb 28 containing mercury and connected with capillary 29 and mercury-filled bellows 31. The material is fed into chamber 2 through conical plug valve 34 and passage 32. The conical plug 35 and cylinder 36 are adapted to turn through 90 degrees so that the cylinder 36 aligns with passage 32. Sticks of composition are fed to cylinder 36 through bore 38, and ejected therefrom into passage 32 by plunger 40. Contraction of bellows 31, due to the temperature difference indicated when the level of heating liquid 4 drops below the base of bulb 28, actuates eccentric 52, which, in turn, rotates plug 35 to the charging position. Sprocket 59 is then engaged and effects the inward stroke of plunger 40, thereby feeding a stick of composition to chamber 2. Further rotation of eccentric 52 and sprocket 59 returns the plunger 40 and plug 35 to their initial positions.