Ripening of viscose compositions

摘要

Viscose is ripened by causing it to flow in a continuous stream through a system in which it is freed from dispersed gases, filtered and then ripened. As shown in Fig. 1, viscose is pumped continuously by means of a pump 26 from a first storage tank 21 equipped with electrically driven paddle stirrers 23 through conduits 25, 27 and a restricted orifice into a first de-aerator 29 which is maintained at sub-atmospheric pressure by withdrawing gases and vapours from it through a vacuum line 30. Excess of the viscose from the conduit 27 is by-passed back to the conduit 25 through a conduit 31 provided with a valve 32 operated by a controller 33 which maintains a constant level of the viscose in the de-aerator 29. The viscose is pumped continuously by means of a pump 62 from the de-aerator 29 through conduits 61, 63, manifold 64, valves 69, filter presses 65, valves 71, manifold 66 and conduit 67 into a second storage tank 68. The valves 69 and 71 permit the filter presses to be cut out and re-dressed individually without interrupting the continuity of operation and also permit the pressures on both the input and output sides to be kept constant. Excess of the viscose from the conduit 63 is by-passed back to the conduit 61 through a conduit 72 provided with a valve 73 operated by a controller 74 which maintains a constant level of the viscose in the second storage tank 68, which is equipped with a motor-driven stirrer 75. From the tank 68 the viscose is pumped continuously by a pump 78 through conduits 77, 79 to a viscose heater 81, in which it is heated to the required ripening temperature, and from which it flows through a conduit 82 into a tank 83, in which it is held at this temperature. From the tank 83 the viscose flows through a conduit 84 and a flow obstruction orifice 85 into a second de-aerator 86, from which gases and vapours are withdrawn through a vacuum line 87A to maintain a sub-atmospheric pressure therein. The level of the viscose in the second de-aerator 86 is maintained constant by the same automatically controlled means as are provided for the first de-aerator 29. The viscose is pumped continuously by means of a pump 163 from the second de-aerator 86 through conduits 162, 164 into a spin tank 165 provided with motor-driven paddle stirrers 166. Thereafter, the viscose is pumped continuously from the base of the spin tank 165 through a conduit 168 by means of a pump 169 which recirculates it back to the top of the spin tank through the conduit 164. The viscose is also pumped continuously by the pump 171 from the spin tank 165 through conduits 168, 172, manifold 173, valves 177, filter presses 174, valves 178, manifold 175 and conduit 176 to a shaping device (not shown). Excess viscose from the conduit 172 is by-passed back to the conduit 168 through a conduit 179 provided with a valve 180 operated by a controller 181 which maintains a constant pressure in the conduit 176 and a constant delivery of viscose through the shaping device. The viscose flows in a thin film down the walls of the de-aerators 29 and 86 and is subjected to a pressure sufficiently below atmospheric to cause it to boil and become freed from dissolved and displaced gases and to be cooled. The boiling of the viscose in the first de-aerator 29 causes a drop in its temperature, which is employed to control the degree of vacuum in the de-aerator and thus the amount of boiling which takes place. The temperature of the viscose flowing through the conduit 27 into the de-aerator 29 actuates a thermo element 53 and the temperature of the viscose flowing down the walls of the de-aerator 29 and just before reaching a pool of viscose collected at the bottom thereof actuates a thermo element 54. Both thermo elements are connected to a controller 57 which, when the viscose cools too much when flowing down the de-aerator, opens a valve 58 to permit steam to flow from a conduit 59 into the vacuum line 30 so as to lower the vacuum in the de-aerator. A similar arrangement is used to control the degree of vacuum in the second de-aerator 86. A hot-water heating system for raising the temperature of the viscose to the ripening temperature as it passes through the heater 81 and the hot tank 83 comprises a surge tank 91 which is filled with water and to which make up is added through a conduit 92. Water is pumped from the surge tank 91 by the pump 93 through a steam-heated water heater 94 and through the jacket of the viscose heater 81, and a portion of it returns to the surge tank 91; the remainder flows through a tempering unit 97 in which it is cooled by means of a stream of cold water to the temperature at which the viscose leaves the viscose heater, and then flows through the jacket of the hot tank 83 to maintain the temperature of the viscose constant during the ripening period. The water then returns to the surge tank 91. The viscose heater 81 comprises a a narrow heating zone of which at least one bounding surface is heated, and scrapers by means of which the viscose in contact with the heated surface may be removed therefrom and replaced by viscose from the interior of the heating zone. The de-aerators, ripening tank and viscose heater are described in Specifications 722,888, 722,889 and 722,890 respectively.