Abstract:
The present invention concerns an adjustable shroud useful with any melt spinable polymers during their production. The adjustable shroud can be produced from different embodiments such as hinged wall sections, bellows, or collapsible or nesting walls. The adjustable shroud may be controlled by means of hydraulics, pneumatics, mechanical worm screws powered by an electrical motor or manually, or any other suitable means obvious to those skilled in the art. The length of the adjustable shroud functions such that it extends toward or away from the spinneret depending on the desired length of the shroud.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1) Field of the Invention  
           [0002]    The present invention relates to an adjustable shroud for controlling the thermal environment around synthetic yarn, as the yarn exits the spinneret. The cooling rate of yarn affects a number of physical and mechanical properties of the yarn. The adjustable shroud controls the cooling rate, thereby controlling the physical and mechanical properties of the yarns. The present invention is particularly useful when switching from one yarn type to another that requires a different length shroud. The adjustability of the shroud may be accomplished by pneumatic means, hydraulic means, electric motors, or done manually. Preferably pneumatic or hydraulic means are employed that are controlled by computer.  
           [0003]    2) Prior Art  
           [0004]    Fibers are broadly used in industrial applications such as automobile tires, v-belts, conveyor belts, and the like. Fibers are also used in textile applications such as sewing thread, woven and nonwoven fabric, and knitted fabric. The manufactured fibers of the present invention are conventionally spun from a melt through a plurality of orifices in a spinneret. Many physical and mechanical properties of the fibers depend on the polymer, the temperature of the polymer, the rate at which the fiber is spun and the quenching of the yarn, all of which effect the cooling rate. Thus when the yarn denier or number of filaments change, the shroud length needs to be optimized for these changes.  
           [0005]    In a conventional system, polymer is extruded through a spinneret to form fibers and cooled at a rate in part determined by the shroud length and the quench characteristics, if any. The shroud functions primarily to delay the cooling and to increase the draw down prior to quenching. Depending upon the fiber use, the length of the shroud may be from about 50 mm to about 500 mm. The cross section of the shroud preferably conforms approximately to the dimensions of the spinneret. Typically the spinneret is rectangular or round. However a round or oval shroud can be used with a rectangular pack, and a rectangular shroud with a round pack. In order to effect any necessary changes in the aforementioned properties, generally the length of the shroud must be changed. Often, a set of shrouds of varying lengths is designed. The product changeover requires that production be halted, the existing shroud removed from each spinneret, and a new shroud installed that is compatible with the new product specifications. In so doing, up to 8 hours of production may be lost for every changeover.  
           [0006]    U.S. Pat. No. 4,690,866 to Kumakawa et al. discloses a set of shrouds of different lengths. In Table 1, reference is made to the length (in mm) of the heating zone below the spinneret. The shroud length varies between 100 to 300 mm.  
           [0007]    The key object of the present invention is to provide an adjustable shroud for synthetic yarn production such that changeover from one yarn product to another may be accomplished with minimal disruption to yarn production.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention consists of an adjustable shroud employed in a synthetic yarn production system. The length of the shroud may be adjusted without disruption in production whereby the changeover time is reduced from about 8 hours to a fraction of an hour. The shroud having adjustable length is positioned adjacent the spinnerets such that the molten polymer exits from the spinneret, passes through the shroud, and continues to other known equipment and processes.  
           [0009]    In the broadest sense, the present invention relates to a shroud having means to adjust the length of the shroud. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawing in which:  
         [0011]    [0011]FIG. 1 is a cross section of a conventional fixed length shroud positioned beneath the spinneret.  
         [0012]    [0012]FIG. 2 is a cross section of a first embodiment of an adjustable shroud positioned beneath the spinneret according to the present invention.  
         [0013]    [0013]FIG. 3 is a cross section of a second embodiment of an adjustable shroud according to the present invention.  
         [0014]    [0014]FIG. 4 is a cross section of a third embodiment of an adjustable shroud according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    The present invention relates to an adjustable shroud for controlling the thermal environment around synthetic yarn, as the yarn exits the spinneret. The cooling rate of yarn affects a number of physical and mechanical properties of the yarn. The adjustable shroud controls the cooling rate, thereby controlling the physical and mechanical properties of the yarns. The present invention is particularly useful when switching from one yarn type to another that requires a different length shroud.  
         [0016]    Because yarn properties are a strong function of the shroud length, the mechanism to position and reposition the shroud should be precise—within 1 to 2 mm. The adjustability of the shroud may be accomplished by pneumatic means, hydraulic means, electric motors, or done manually. Preferably pneumatic or hydraulic means are employed that are controlled by computer. The details of computer control and its relationship to pneumatic, hydraulic or electrical motors means to position the shroud are not a part of the present invention.  
         [0017]    The present invention is useful with any melt spinnable polymers such as polyesters, polyamides, or polyolefins or a combination of these. Suitable polyesters are polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene bibenzoate, or copolyesters such as polyethylene terephthalate-isophthalate or polyethylene naphthalate-bibenzoate, or mixture of two or more of these. Suitable polyamides are nylon 6 or nylon 6,6, or a mixture thereof. Suitable polyolefins are polyethylene, polypropylene, polybutylene, or a mixture of two or more of these.  
         [0018]    [0018]FIG. 1 illustrates the prior art in which a fixed shroud generally indicated by reference  10  comprises a wall  12 . The wall  12  may be a continuous circular wall, if the shroud is circular, or the wall may be quadrilateral, for example. The shroud  10  is generally secured to a supporting structure  14  which typically is a dowbox employed to keep the polymer molten, however any structure capable of supporting the weight of the shroud is sufficient for the present invention. The shroud is secured to the supporting structure  14  by means of bolts  16  (two are illustrated but the actual number is whatever is necessary to support the shroud in a secure manner). The supporting structure  14  surrounds the pack  18  which contains molten polymer. At the bottom of the pack  18  is a typical spinneret  20 . The use of spinnerets is well known to those skilled in the art and the spinneret shown in FIG. 1 only serves to illustrate the position of the shroud relative to the pack. The shroud  10 , may optionally have one or more heaters  22  which may be in the form of electrical elements, or tubing for a heated fluid (such as liquid or steam). Typically the shroud  10  has electric elements  22  in its sidewall.  
         [0019]    In operation, the prior art system shown in FIG. 1 contains molten polymer in the pack  18  under pressure such that it is extruded through the small holes (not specifically shown) in the spinneret  20  forming a plurality of filaments  24  that can be combined to make a yarn.  
         [0020]    FIGS.  2 - 4  demonstrate the embodiments of the present invention. Where reference numerals are the same as those in FIG. 1, the elements described are the same.  
         [0021]    [0021]FIG. 2 illustrates a quadrilateral adjustable shroud generally indicated by reference numeral  30 . The adjustable shroud  30  is secured to the supporting structure  14  by bolts  16  in similar fashion described relative to FIG. 1. The adjustable shroud  30  comprises an upper section  32  which is secured to the supporting structure  14 . The adjustable shroud also comprises folding walls  34  and  36 . Wall  34  is secured to the upper section  32  by means of a hinge  38 . Additionally, the wall  34  is secured to wall  36  by a hinge  40 . Lastly, the lower portion of the adjustable shroud  30  includes a lower wall segment  42  which is likewise hinged to the folding wall  36  by means of a hinge  44 . Typically, the lower wall segment  42  may optionally contain a heating element  46  similar to those disclosed in the FIG. 1 prior art device. In addition to the folding wall sides  34 ,  36  the adjustable shroud  30  has two fixed walls in sliding contact with the folding walls, only one of which is shown and is indicated by reference numeral  52 . The function of the fixed walls is to seal the adjustable shroud  30 . Preferably the edges of the folding walls  34  and  36  are covered with an insulating fabric to insure sealing. The fixed walls are attached to the supporting structure  14  by bolts  54  and they are in close proximity to the upper section  32  and the lower segment  42 . An optional control mechanism  48  may be linked with the adjustable shroud  30  via link  50  which functions to move the lower wall segment  42  up or down (toward the spinneret  20 , or away from it). To adjust the shroud length it is not necessary that there is a control  48 , since the device could be manually positioned, for example. However, it is also contemplated that the adjustable shroud  30  can be moved by a control  48  through its link line  50  by electric powered mechanical worm screw pneumatic or hydraulic systems (where link line  50  would be an air line or hydraulic line respectively) well known to those skilled in the art. The mechanism to position and reposition the adjustable shroud  30  should be precise—within 1 to 2 mm.  
         [0022]    [0022]FIG. 3 is a second embodiment of the present invention, which can be round, oval or quadrilateral. In this embodiment the adjustable shroud  30  is also secured to the supporting structure  14  by means of bolts  16 . Additionally, the adjustable shroud  30  has the upper section  32  and the lower wall segment  42  which may optionally contain the heater  46 . Between the upper section  32  and the lower wall segment  42  are bellows  60  which may be circular, oval or quadrilateral in shape. The bellows  60  may be constructed in part mineral fibers such as mica wool, asbestos, glass wool fibers, and other materials that can withstand the temperature. The movement toward and away from the spinneret may optionally be controlled by control  48  through line link  50  as was previously discussed, or the entire adjustable shroud may be adjusted manually.  
         [0023]    With reference to FIG. 4 which shows a third embodiment of the present invention, which can be round, oval or quadrilateral, again similar reference numerals indicate identical apparatus. However, instead of using bellows as shown in FIG. 3, a series of collapsible wall sections (nesting walls) are employed. In FIG. 4, the adjustable shroud  30  is shown extended to its maximum length. Any material that can withstand the temperature would be suitable for the collapsible wall sections  66 , such as metal, certain plastics, glass, fiberglass, composite materials, etc. The collapsible wall sections  66  may be circular, oval or quadrilateral in shape. Optionally a control  48  with a link line  50  may be employed to move the adjustable shroud toward and away from the spinneret  20 . Otherwise, the adjustment of the adjustable shroud  30  may be done manually.  
         [0024]    Thus, it is apparent that there has been provided, in accordance with the invention, an adjustable shroud that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. According, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the invention.