This invention relates to spinnerette assemblies for forming hollow fibers. It particularly relates to an improved spinnerette for more efficient and precise production of hollow fibers.
It is well known to use various hollow fibers for various applications. For example, hollow fibers are used in carpets, as fill materials for pillows, as insulation materials for blankets and garments, and as membranes for gas separation, blood dialysis, purification of water, and other filtering applications. For membrane applications, the hollow fibers can be bundled together and disposed in a tubular housing to provide a separation device known as a permeator. Ordinarily, the hollow fibers are relatively small, having a diameter on the order of 30 to 1000 micrometers. Accordingly, the apparatus and method for manufacturing hollow fibers must be very precise to be able to control the diameter of the fiber, and the concentricity of the core around the bore.
Numerous spinning assemblies have been devised for the production of hollow fibers. Particularly, devices have been proposed for ensuring uniform supply of the fiber-forming fluid or fluids to the orifices of a spinnerette with the object of producing hollow fibers identical in diameter, composition, and concentricity. These spinnerettes use a means for supplying the bore fluid positioned in the spinning orifice for forming the bore or “hollow” of the hollow fiber. Usually, a tube or needle is used for this purpose and a gaseous or liquid fluid is injected from the tube, thus forming the bore of the fiber as it is being extruded from the spinnerette orifice. For melt spinning, the nascent fiber can be solidified by cooling in a gaseous or liquid cooling fluid. For solution spinning, the nascent fiber can be solidified by evaporation of the solvent or by contacting the fiber with a solvent-extracting liquid that results in coagulation of the polymer solution(s) to form the fiber wall.
In order to maintain the concentricity of fiber diameter and the bore diameter, other spinnerettes have been provided with members for centering the tube and the bore of the spinnerette plate. For example, U.S. Pat. No. 4,493,629 describes a modular spinnerette assembly fitted with multiple screws threaded through the spinnerette plate to center the tube and orifice of the spinnerette. However, these adjusting screws are unreliable and are prone to error when the spinnerette is disassembled, cleaned and then reassembled.
Typically, spinnerettes of this type are made largely by hand, one at a time. As a result, parts made for one spinnerette will not always fit another spinnerette. When parts are not interchangeable, any damage to one part of the spinnerette assembly may render the entire assembly useless. In assembling or cleaning conventional hollow-fiber spinnerettes, it is very easy to slightly bend the fluid-injection tube or needle, such that it is off center of the spinning orifice. When this happens, the spinnerette cannot be used until repaired.
Yet another problem with existing spinnerette designs is the ability to deliver the polymer fluid uniformly around the tube or needle within the spinnerette. U.S. Pat. No. 5,320,512 discloses a spinneret that has a plurality of discrete material passages formed around the needle to deliver the polymer fluid around the needle. This design enables the uniform delivery of the polymer fluid around the tube or needle within the spinnerette. However, in order to attain concentricity and uniformity in the manufacturing process, the polymer fluid from these individual passages must converge and meld together to form a singular annular flow around the tube or needle as the polymer fluid traverses through the main polymer fluid passage. If complete convergence and melding are not attained, seams may develop down the length of the spun fiber at the interfaces where the individual flows did not fully converge and meld together completely.
Thus, there still remains a need to overcome this problem of interface convergence and melding of the fluid polymer in order to be able to produce a concentric spun hollow fiber with minimal seaming potential.
The present invention provides an improved spinnerette for the production of hollow fibers.
It is an object of the invention to overcome the limitations of conventional spinnerettes.
It is another object of the invention to reduce imperfections in hollow fibers.
It is another object of the invention to extend hollow-fiber production run times.
It is another object of the invention to reduce the time for spinnerette maintenance.
It is another object of the invention to simplify spinnerette fabrication.
To achieve these objects, a first aspect of the invention is a spinnerette assembly for forming a composite hollow fiber comprising:
A second aspect of the invention is a method of forming a composite hollow fiber comprising the steps of:
The invention is described through a preferred embodiment and the attached drawings in which:
In the first preferred embodiment of the invention for the extrusion of multiple hollow fibers, as illustrated in
Bore forming fluid passage 112 is formed in spinnerette body 110 and extends through spinnerette body 110 to a respective needle mounting hole 111 to be in communication with the passage formed through needle 130. Each bore forming fluid passage 112 includes a bore forming fluid inlet port 113 at the surface of spinnerette body 110. This structure permits a bore forming fluid to be introduced into an extruded fiber to maintain the hollow structure of the extruded fiber in the manner described below.
Fiber-forming material passages 150 are formed in spinnerette body 110 through which a fiber-forming material, such as a polymer material, is delivered to the extrusion orifices 155. Each fiber-forming material passage 150 includes an inlet port 151 that is a hole extending in a direction that is substantially parallel to needle 130. Each fiber-forming material passage 150 also includes a transverse passage 152 that extends from fiber-forming inlet port 151 to a top portion of annular passage 153 that defines the upper portion of extrusion orifice 155. Transverse passage 152 is defined by a backcut portion formed in spinnerette body 110 by a tool inserted through fiber-forming material port 151. Transverse passage 152 extends entirely around needle 130 to permit fiber-forming material to be evenly distributed around needle 130 and evenly introduced into annular passages 153 and 154.
In operation, spinnerette assembly 100 is mounted to a spinning machine through mounting holes 115 using an appropriate fastening mechanism such as bolts or the like. A bore forming fluid supply and a fiber-forming material supply of the machine are coupled respectively to the bore forming fluid inlet port 113 and the fiber-forming material inlet port 151. Note that there is one bore forming material inlet port 113 and one fiber-forming material inlet port 151 for each extrusion orifice 155. These ports can be arranged in any way and can be of any number as is appropriate to deliver the materials to the proper passages. For the spinning of hollow fibers, a fiber-forming material and a bore forming fluid are simultaneously delivered into spinneret 100 at know pressures and flow rates to extrude (i.e., spin) hollow fibers. Typically, the fiber-forming material is injected at about 300-500 psig and the bore forming fluid is injected at about 4-5 psig.
Fiber-forming material travels through fiber-forming material inlet port 151, through the fiber-forming material passage 150, into transverse passage 152, and into upper annular passage 153. Simultaneous with the delivery of the fiber-forming material, a bore forming fluid is injected into the bore forming fluid inlet port 113, through bore forming fluid passage 112, and into needle 130. The bore fluid emerges from the distal end of needle 130 at a position within or just downstream of extrusion orifice 155. Since the fiber-forming material is being extruded through the lower annular passage 154 and out of the extrusion orifice 155 concentrically around needle 130 and the emerging bore forming fluid therefrom, the resultant extrudate is a fiber comprised of a bore forming fluid at the center, concentrically surrounded by a fiber-forming material.
As best illustrated in
Spinnerette assembly 100 of the preferred embodiment has fewer parts and is more easily manufactured as compared to conventional spinnerettes.
A second preferred embodiment in accordance with the invention is illustrated in
The various ports, channels, and passages in the spinnerette assemblies described above can be formed in any manner and can be of any number to produce hollow fibers. For example, the fiber-forming material passage can be of any shape or configuration and can comprise plural channels or a single channel. The spinnerette assemblies can be machined using any known techniques such as drilling, electronic discharge machining (EDM), or any other suitable process or processes. There can be any number of extrusion orifices. The invention can be used to make hollow fibers of any type and of any material amenable to extrusion. The various angles and dimensions can be varied to suit the particular application. The spinnerette assemblies can be manufactured of any suitable material such as steel, monel, titanium, aluminum, or alloys thereof. The fiber-forming material can be of any type amenable to extrusion such as polymer melts or solutions, ceramic pastes, and the like. The bore forming fluid can be an inert gas or liquid for example.
The invention has been described through preferred embodiments. However, various modifications can be made without departing from the scope of the invention as defined in the appended claims.
Number | Date | Country | |
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Parent | 09733304 | Dec 2000 | US |
Child | 10940073 | Sep 2004 | US |