A method for piecing in the production of melt-spun polymeric threads

摘要

PICT:0913615/IV(a)/1 PICT:0913615/IV(a)/2 In the melt-spinning of synthetic polymer filaments, air is expelled from within the pack of the melt-spinning unit immediately prior to the commencement of spinning therethrough and the pack is maintained substantially free of air or its constituent gases until a sole filament, or all of a plurality of filaments, has or have emerged from an orifice, or orifices, in the spinneret contained in the pack. The pack is defined as a unit containing a filter and a spinneret. Air may be expelled from the pack by diffusing, or sucking steam therethrough, but preferably the expulsion of air and maintenance of the pack free of air or its constituent gases are achieved by evacuation. Steam may be passed through the pack after it has been evacuated. Vacuum may be applied to the pack through the spinneret orifice or orifices, at or before the time that molten polymer is pumped to the pack and maintained until the filament, or all the filaments, has or have fully emerged from the spinneret. The filaments may be of polyhexamethylene adipamide, or synthetic linear polyamides in general, polyesters, polyethylene or polypropylene. A funnel, adapted to be connected to a source of vacuum and having a lip diameter sufficient to encompass all the orifices of the spinneret through which evacuation is to take place, may be applied to the spinneret prior to commencing spinning to evacuate the pack. A glass funnel may be used, having its edge ground to provide a good seal with the spinneret face and greased with a silicone grease, or a metal funnel, having a window, suitably of "Perspex" (Registered Trade Mark) through which the filaments may be viewed after they have emerged, and fitted with a heat-resistant rubber sleeve secured at the lip of the funnel and extending a short way proud thereof, may act as the vacuum seal between the funnel and the spinneret. As shown (Fig. 2), a funnel 19 has a hollow handle 21, connected to the source of vacuum and separated from the body of the funnel by a wire mesh screen to prevent filaments which have emerged from the spinneret orifices from being sucked down the handle. The window 25 is made a vacuum tight fit by means of the screw collar 27 and neoprene gasket 29. The upper end portion of the funnel is frustoconical in shape and is fitted with a silicone rubber sleeve 31, extending just proud of the funnel, and clamped in position by tightening the threaded ring 33, an upper flange of which bears down on a flange of a clamping ring 35. As shown in Fig. 3 the funnel is pushed upwardly into contact with the spinneret plate at the lower end of the pack body 7, the silicone rubber sleeve 31 making a vacuum tight seal with the plate, once the vacuum is applied to the funnel. Vacuum is applied until all the filaments 15 are at least in view through window 25 and normally until all the filaments have reached screen 23. The process of the invention minimises "spitting" and filament breakages on starting spinning, and enables larger diameter packs and spinnerets to be used.