GB772281A - Improvements in or relating to the manufacture of artificial filamentary materials - Google Patents

Abstract

Filaments formed by extrusion of a spinning solution into a coagulating liquid are drawn from the liquid at a constant speed under tension sufficient to stretch them and the coagulating or swelling properties of the liquid are so controlled that the tension in the filaments at any given point between that at which they leave the liquid and that at which the drawing force is applied is maintained substantially constant. Preferably the properties of the liquid are automatically controlled by means operated by the tension in the filaments. Control may be exercized over the composition <PICT:0772281/IV(a)/1> or the temperature of the liquid. For carrying out the process there may be used apparatus comprising a container for the liquid, means for applying a drawing force to the filaments whereby they are drawn at a constant speed from the liquid, a sensing device adapted to measure the tension in the filaments at a point between that at which they leave the liquid and that at which the drawing force is applied and means operated by the sensing device acting in response to deviations in the tension from a given control value for varying the characteristics of the liquid in such a way that the tension is restored to the control value. The sensing device may operate a control valve or other device through the intermediary of a fluid under a pressure which is caused to vary in accordance with variations in the tension of the filaments. Such apparatus may be used generally for the drawing, e.g. stretching, of filaments through and out of a body of liquid having a swelling action. A plurality of exactly similar spinning cells may be supplied with a coagulating liquid from a common source, and spinning solution from a common source may be extruded into each of the cells. An automatic control system of the kind claimed in Specification 772,282, [Group XXIX], may be provided. The filaments from each cell may be drawn under tension and a sensing device in one of the cells may contact the filaments and measure the tension. A second similar sensing device may be provided in another of the cells, and under normal operting conditions it may have an output in balance with that of the first device. Means operatively connected to both sensing devices may so act that when the outputs of these devices become out of balance the operative connection between the first sensing device and the means for altering the composition or temperature of the coagulating liquid is broken and the alterations may be made under manual control. As shown in Figs. 1 and 2, spinning solution, e.g. a solution of cellulose acetate in acetone is supplied through pipe 12 to a wet-spinning cell 11 and extruded into a coagulating liquid comprising a mixture of solvent and non-solvent, e.g. acetone and water. The coagulating liquid is supplied from container 15 through pipes 16 and 17. Pipes 161, 171 supply coagulating liquid to a similar spinning cell. The filaments 13 come together as a yarn, pass through a wiping zone 24 and then pass over roller 28 and godet 29. Filaments from a similar cell pass over roller 281 and godet 291. The free-running roller 28 forms part of a sensing device or tensiometer 31 which is connected to a source of compressed air 33 and a compressed air conduit 34, the pressure in which is a function or measure of the tension in the yarn. Conduit 34 is connected to a pressure controller 36. This is connected to a primary air transmission line 37 supplied through the controller from a source 39 of compressed air. Line 37 leads through chamber 41 and pipe 42 to a control valve 43 which controls the rate of flow of acetone into a line 44 leading to a mixer 45, kept at a constant temperature. Water is led into the mixer through line 46. Chamber 41 forms part of an auto-manual relay 47. It communicates near one end with a by-pass 48 leading from the compressed air source 39 through a manually-controlled pressure reducing valve 49. A movable piston 51 keeps air from line 37 separate from that from line 48 and its movement is limited so that when it is against the stop 52, pipe 42 is connected through chamber 41 to line 37, but when it is against stop 53, the pipe 42 is connected to the by-pass 48. Piston 51 is mounted on rod 54 which passes through a wall 55 to a chamber 56 where it carries another piston 57. A compressed air pipe 58 leads into the free end of chamber 56, the air in which acts in opposition to the spring 59. The compressed air is supplied from a source 61a through a valve 61b. This is operated by compressed air from a pipe 61c which has a flared end 63 facing a nozzle 62 (Fig. 2). Between nozzle 62 and the flared end 63 is a slot 64 in a vane 66 mounted at one end of a lever 67, the other end of which is linked with air bellows 73, 74. A visual or aural alarm 79 is connected to pipe 58. An increase in the tension of the yarn causes the pressures in pipes 34, 37 and 42 to be altered and the valve 43 to be operated so that a greater proportion of acetone is admitted to the mixing chamber 45. This results in the emergence of a more plastic yarn and the restoration of the tension to the desired value. If a mechanical defect arises, causing a difference to develop between the outputs of the sensing devices 31, 77, the bellows 73, 74, will operate lever 67, and move the vane 66 so that the slot 64 is not in register with the nozzle 62. This causes a drop in the pressure in pipe 58 and this operates the alarm 79 and allows pistons 51, 57, to move under the action of spring 59 to cut the connection between the controller 36 and the valve 43. This valve is then amenable to manual control by means of the valve 49. Instead of using a pneumatic system in which all communication between controlling elements and controlled elements is carried out by the use of compressed air, one or all of the pneumatic components of the system may be replaced by electrical or hydraulic components. Specifications 728,778, 737,629, [Group XXIX], and 744,319 also are referred to.