GB573327A - Improvements in the extrusion of fused filament-forming compositions - Google Patents

Abstract

<PICT:0573327/IV/1> Artificial filaments, films, foils and like materials are obtained by the extrusion of fused thermoplastic compositions, solid composition being fed to the melt vessel by means of a chamber, movable between the charging and feeding positions, adapted to be charged with composition whilst open to the atmosphere and closed to the vessel, and adapted to feed composition to the vessel, whilst closed to the atmosphere and open to the vessel, whereby the vessel is sealed to the outer atmosphere during the feeding operation. A piston or like means may be employed to force the composition from the chamber to the vessel, and the composition is preferably fed to the chamber in solid pellets of the same shape and size as the chamber to prevent air from entering the vessel. The chamber may be formed as a <PICT:0573327/IV/2> <PICT:0573327/IV/3> cylindrical hole in a thick disc arranged to rotate about a spindle fixed to the melt vessel in the neighbourhood of the vessel inlet, or as a lateral bore in a tapered plug spring-pressed into a valve body, two apertures being provided in the body, one in communication with the melt vessel and the other with the atmosphere. The chamber may be operated manually on a visual indication that fresh composition is required in the vessel, or automatically in accordance with a mechanical or electrical indication as described in Specification 573,325. The melt vessel may take the form of that described in Specification 565,489, in which melting is effected by a heating liquid contained in the vessel and above which exists an atmosphere of inert gas under pressure, and melting may be facilitated by deflecting the composition towards the walls of the vessel by a baffle as described in Specification 573,326. Referring to Fig. 1, the composition is melted by heating liquid 4 and forms a pool 3 at the base of melt vessel 2, from which it is withdrawn by pump 6 and forced through filter 8 and extrusion jet 9.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 conical baffle 21 and the vessel is surrounded by heating jacket 24. A 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 vessel 2 through conical plug valve 34 and passage 32. The conical plug 35 and cylinder 36 are adapted to rotate 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. A manually-operated type of movable feed chamber adapted for use with the melt vessel of Fig. 1 is shown in Figs. 3 and 5. The movable chamber is formed as a cylindrical hole 95 through a thick disc 96 arranged to rotate about spindle 97 mounted on plate 98 which forms an eccentric flange to the inlet passage 99 of the melt vessel. A stick of composition adapted to fit chamber 95 is inserted therein. The cylinder 96 is then rotated by handle 121 against the stop 123 to bring chamber 95 in alignment with passage 99. Disc 100 is then rotated by handle 101 against stop 103 and the handle 116 is forced down so that the piston 111 forces the composition into the melt vessel. The handle 101 is then rotated away from stop 103 so as to seal passage 99, the handle 116 is lifted and the cylinder 96 rotated to the supply position. Suitable thermoplastic compositions are synthetic linear superpolyamides, polyvinyl compounds, and esters and ethers of cellulose.