Patent GB-763489-A (GB)
Title: Improvements in the melt-spinning of filamentary materials
IPC: D01D1/06
Filed: 1954-03-25
Abstract: <FORM:0763489/IV(a)/1> <FORM:0763489/IV(a)/2> <FORM:0763489/IV(a)/3> Apparatus for the prodduction of filamentary products from comminuted fusible filament-forming materials comprises a vessel for receiving particles of fusible filament-forming material, a spinning jet adapted to be heated and having at least one spinning orifice leading from the vessel, a plurality of rams each having a working face disposed within the vessel and adapted to act against the jet, and means for reciprocating the rams to exert pressure in turn on the particles of material adjacent to the jet.  The rams may be reciprocated in different directions along intersecting paths and the areas of the spinning jet acted against by the different rams may overlap or coincide.  As shown in Fig. 1, comminuted thermoplastic filament-forming material, in flake or powder form, passes down by gravity from the hopper 17 through the channel 22 and over the tapered upper surfaces of a central divider bar 24, and is then forced by tampers or rams 26, 26a, having working faces 27, 27a, through an aperture 28 formed in a strip cover 29, and through spinning orifices located along the length of an electrically heated jet plate 31, which is in the form of a strip mounted between the strip cover 29 and a strip support 32.  In order to cause the material to flow smoothly and evenly through the channel 22, a long vibrating comb 33 having teeth 34 is oscillated longitudinally by means of a vibrator 36 mounted on one side wall 12 (Fig. 2).  The comb 33, divider bar 34, rams 26, 26a, aperture 28, strip cover 29 and strip support 32 extend substantially the entire width of the hopper 17, the divider bar being secured to the side walls 12 of the vessel, the strip cover 29 being mounted in a long slot 37 in the bottom 11 of the vessel, and the strip support 32 being fixed to the bottom 11. The jet plate 31 is adapted to be heated by the passage of an electric current along it, the current being regulated so that the plate is maintained at a controlled temperature sufficient to melt the thermoplastic material forced against the plate by the action of the rams 26, 26a.  The strip cover 29 is made of an electrically insulating material and the strip support 32 is faced at 38 with such insulating material to prevent short circuits through the cover and support.  The rams 26, 26a are arranged in V-form and are adapted to be reciprocated in sliding contact with, and guided by, the smooth back surfaces 39 of the lower plates 19 and the smooth outer surfaces of the ram guides 42, each of which extends substantially the entire width of the hopper 17, being secured to the side walls 12, and is notched at each end to receive side guides 43 adapted to engage the side edges of the rams 26, 26a.  The lower sides 44 of the divider bar 24 are suitably tapered so that the rams 26, 26a fit against these sides during their oscillation.  The sides of the passageway 28 in the strip cover 29 are also tapered in alignment with the outer surfaces 41 of the ram guides 42, the bottom of the passageway 28 providing an exposed area of the jet plate 31 of such size that, when the areas of the working faces 27, 27a of the rams 26, 26a are projected on the jet plate along the lines of downward movement of the rams, the projected areas are substantially congruent and equal to the exposed area of the jet plate.  The rams 26, 26a are secured by means of blocks 46, 46a to reciprocating rods 47, 47a (Figs. 1 and 2) moving in sleeve guides 48, 48a and attached to yokes 49, 49a joined to piston rods 51, 51a at the ends of which are pistons 52, 52a mounted in cylinders 53, 53a.  Each of these is provided with ports 54, 54a and 56, 56a for admitting compressed air to operate the pistons.  The supply of compressed air to these ports is controlled by the movement of the pistons 52, 52a through a four-way air valve 57 (Fig. 3) of a known type having a double solenoid, operating on momentary electrical impulses, for controlling the position of a valve rod (not shown).  In this type of valve, the valve rod remains in its last operating position after the solenoid is de-energized. The four ports with which the valve 57 is provided are port 58, communicating with the pipe 59 leading to a source of compressed air, port 61, open to the atmosphere, and ports 62, 63 communicating with pipes 64, 66 respectively.  The valve 57 is so constructed that, when its rod is in one position, the port 62 is connected with the port 58, and therefore with the source of compressed air, and the port 63 is connected with the port 61, and therefore with the atmosphere, while when the rod is in its other position these connections are reversed.  The pipe 64 is connected by means of branches 67, 68 to the lower port 56a of the right cylinder 53a, and to the upper port 54 of the left cylinder 53, while the pipe 66 is connected, by means of branches 69, 71 to the upper port 54a of the cylinder 53a and to the lower port 56 of the cylinder 53.  Thus, when the valve rod is in one position, compressed air is admitted above the piston 52 and below the piston 52a, while the opposite sides of these pistons are in communication with the atmosphere, thereby causing the piston 52 to be driven in a downward direction and the piston 52a in an upward direction.  When the valve rod is moved to its other position, the connections are reversed so that piston 52a is forced downwards and piston 52 upwards.  The double solenoid of the valve 57 has two portions 72, 73 electrically connected to power lines 74, 76 through microswitches 77, 77a respectively, mounted in flanges 78 (Fig. 2) of the lower hopper plates 19 and provided with operating plungers 79, 79a.  During the movement of the rams 26, 26a, pistons 52, 52a and yokes 49, 49a, the plungers 79, 79a are engaged and moved so as to close the microswitches 77, 77a by means of bolts 81, 81a threaded adjustably in openings 82, 82a carried at the ends of angle bars 83, 83a which are mounted on the yokes 49, 49a.  The bolts 81, 81a are so adjusted that, when a ram 26 or 26a reaches the lower desired limit of its travel, i.e. the position of the ram 26 shown in Fig. 1, the corresponding microswitch 77 or 77a will become closed, thus energizing the corresponding portion 72 or 73 of the solenoid and causing the valve rod to move to reverse the valve connections. Valves 84, 84a, 86 and 86a, located in the branches 68, 69, 71 and 67 respectively and of known construction, cause the downstrokes of the pistons to be relatively rapid while the upstrokes are slow. None of the valves impedes the flow of compressed air entering the upper and lower portions of the cylinders 53, 53a, but they throttle the air expelled from the cylinders.  The throttling action of the valves 84, 84a is sufficient to cause the pistons 52, 52a to move slowly during their upstrokes, while the valves 86, 86a are set to throttle the air expelled from the lower portions of the cylinders 53, 53a to only a slight extent, so that the downstrokes of the pistons 52, 52a take place quite rapidly though not so fast as to cause the rams 26, 26a to exert a sharp, sudden impact on the powdered material below the rams.  Assuming the parts to be initially in the position shown in Fig. 1, the closing of the left microswitch 77 causes the right ram 26a to descend rapidly into contact with the powdered filament-forming material which has flowed, from above, into the space below the ram.  As the powder at this stage is unconsolidated and therefore in a state at which the application of a small force suffices to compress it considerably, the right ram 26a travels downward rather quickly for some distance.  At the same time the left ram 26 moves upward slowly, so that it is still quite close to its initial position and prevents any of the powdered material from being forced upwards around the left side of the bottom of the separator bar 24 by the downward motion of the right ram 26a. The material below the ram 26a is now tightly packed so that further downward movement of the ram is slower and the ram exerts a constant pressure on the material below it, due to the constant pressure of the compressed air above the piston 52a.  After a substantial period, e.g. 3 minutes, the ram reaches the lower limit of its travel, with its working face 27a adjacent to the lower edge of the divider bar 24.  At this point the right microswitch 77a is actuated, causing the right ram 26a to ascend and the left ram 26 to descend.  In this manner pressure is exerted substantially constantly on the material below the rams and above the jet plate, the intervals in which no pressure is exerted on the material being a very small fraction, e.g. about 0.1 per cent, of the total time.  The material within the hopper 17 is placed under reduced pressure by means of a vacuum pump (not shown) connected to the hopper through a vacuum pipe 87.  The hopper is sealed against air leaks, particularly around the rams 26, 26a, back plates 88 having gaskets 89 being provided for this purpose.  After the comminuted material has been placed in the hopper 17 and the cover 14 has been tightly closed, vacuum is applied until the pressure in the hopper has been reduced to, for example, 20 inches of mercury, the rams 26, 26a are set in operation and the pressure in the hopper is further reduced to the desired operating value, e.g. about 1 pound per square inch absolute.  The filament-forming material used may be a fully acetylated or partially deacetylated cellulose acetate, the latter preferably having been stabilized against heat decomposition by ripening at a temperature substantially above room temperature after neutralizing part or all of the sulphuric acid used as a catalyst in the acetylation process. The deacetylated cellulose acetate is then preferably further stabilized by heating under pressure with water or very dilute acid