US 3303530 A
Description (OCR text may contain errors)
Feb. 14, 1967 J, 5, 055, JR 3,303,530
SPINNERETTE Filed Jan. 13, 1965 ,substantially.
United States Patent 3,303,530 SPINNERETTE James Stanley Cobb, Jr., Martinsville, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Jan. 13, 1965, Ser. No. 425,219 4 Claims. (Cl. 18-8) This invention rel-ates to spinnerettes and, more particularly, to arrangements for improved material flow in the spinnerette nozzle which feeds a discharge orifice.
Spinnerettes are used for the extrusion of plastics or polymers, e.g., nylon or polyesters, into filaments. As the polymer is forced through extrusion nozzles in the spinnerette plate, its rate of flow or velocity increases In available spinnerettes, particularly those used to produce filaments of odd cross section, there are dead spots and/ or excessively high shear sections in each nozzle which have an adverse effect on quality and uniformity of the :spun filaments. In the extrusion of round filaments, it is relatively easy to achieve a smooth flow through the spinnerette plate by machining steps which give a gradual reduction of the nozzle diameter from the intake to the discharge orifice. An example of such a construction, having an intermediate nozzle section in the shape of a truncated cone, was disclosed by Jones in US. 2,341,555. In addition to the difiiculties involved in producing an odd-shaped capillary in a truncated cone, the resulting vertical walls vary in depth, which means that more polymer will flow through the center of the discharge orifice and less at the extreme ends. This gives poor filament cross sections.
Odd-shaped capillaries have been machined through a fiat-bottom counterbore, as disclosed by Lehmicke in US. 2,945,739 and by Cobb in US. 3,017,789. However, this leaves dead spots which permit time-sensitive polymers to degrade. Furthermore, different flow patterns develop as the polymer is forced to change direction abruptly. Both of these factors have an adverse effect on the final filament product.
It is a general objective of this invention to provide for the smooth fiow of a viscous material to and through capillaries from which filaments having nonround cross sections are extruded.
Specifically, the object of my invention is to provide a nozzle configuration which not only insures a substantial increase in the velocity of material flowing through the nozzle, with a minimum of dead spots and a minimum of excessively high shear sections, but also preforms the material in advance of a terminal, odd-shaped capillary.
With these and other objects in view, one or more nozzles are fabricated in a spinneret plate. Each nozzle extends through the plate to an orifice in the form of symmetrically disposed, interconnected slots. It originates in a cylindrical entrance hole and terminates in a capillary section defined by planar walls which are substantially normal to the discharge face and of equal and constant height. From the capillary section, the nozzle extends toward the entrance hole in first and second divergent sections, the latter having an angle of divergence greater than that of the first section.
Additional objectives and advantages will be apparent from the following specification wherein reference is made to the accompanying drawing in which:
FIGURE 1 is a fragmentary top view of a spinnerette plate, showing one of the nozzles of thep resent inventions;
FIG. 2 is a transverse sectional view taken on irregular line IIII in FIG. 1;
FIG. 3 is a transverse sectional view taken on irregular line IIIIII in FIG. 1;
FIG. 4 is a fragmentary bottom view of the spinnerette plate showing the discharge orifice configuration; and
FIGS. 5-10 illustrate other discharge orifice configurations.
In FIGS. 14, one embodiment of the nozzle is shown at 10 in a spinnerette plate 12 which has a pressure face 14 and a discharge face 16. Plate 12 has one or more nozzles 10 and is dimensioned to withstand high extrusion pressures. Since it would be difficult to form minute capillaries extending from face 14 to face 16 and since the pressure drop across such a capillary would be too high, an entrance hole 18 is provided. Nozzle 10 extends through plate 12 to a discharge orifice 20 in the form of three, interconnected, symmetrically disposed slots 22 (FIG. 4) which interrupt the continuity of face 16. With three slots 22, there are six side walls 23 and three end walls 24 in the terminal or capillary section of nozzle 10 (FIGS. 2 and 3). Side and end walls 23, 24 are perpendicular to the discharge face 16 and of equal and constant height through the periphery of orifice 20, i.e., are uninterrupted. This assures an equal and uniform flow of polymer through each slot 22. If the height varied or if there were interruptions in the side or end walls, polymer flow would be disturbed in such a manner as to affect uniformity of the filaments being formed.
Extending upwardly from the capillary section, there is a first divergent section 26 which has six side walls 28 and three end walls 30, i.e., the same number of fiat, planar walls as the capillary section. Both the side walls 28 and the end walls 30 diverge from the vertical planes of the adjoining side and end walls 23, 24. Angle x (FIG. 3) is the angle of divergence between each end wall 24 and the adjoining end wall 30 of first divergent section 26. Angle y (FIG. 2) is the divergence angle between each side wall 23 and the adjoining side wall 28 of first divergent section 26. It should be noted that, in any plane parallel to discharge face 16 and cutting exclusively through section 26, nozzle 10 has an outline corresponding to that of discharge orifice 20 when angle x equals angle y. When angle x is different from angle y, the first divergent section 26 is not geometrically identical but is sufliciently similar to preform the polymer so that it will accelerate readily and flow equally through slots 22 of orifice 20.
Directly above the first divergent section 25 and intersecting with it, there is a second divergent section 32 which is a portion of a truncated cone. Angle z is the divergence angle between the conical side wall of section 32 and a line perpendicular to discharge face 16. In all cases, angle 2 is greater than angles x and y. Connecting the second divergent section 32 with the entrance hole 18, there is a third section 34 which has the angle of divergence indicated at w and is also a portion of a truncated cone. Entrance hole 18 is circular.
Where nozzle 10 is referred to herein as convergent, that term is meant to be descriptive of the constant or decreasing diameter in the direction of flow and the absence of fiat-bottom counterbores corresponding to those disclosed by Lehmicke and Cobb. In this connection, the cross-sectional area of entrance hole 18 is considerably larger than that of discharge orifice 20. Thus, entrance hole 18 causes relatively little pressure drop. There is some pressure drop in sections 34, 32, 26 but the principal resistance to flow is in the terminal, capillary section defined by vertical walls 23, 24.
Fabrication of nozzle 10 is started by drilling entrance hole 18 to the desired depth in a blank of stainless steel or other suitable material. As indicated above, there may be one or more nozzles in each spinnerette plate 12.
Normally, the drill which is used to remove most of the material from entrance hole 18 does not have the proper tip angle to form the third divergent section 34. That effect is achieved by removing a small amount of material with a shaped drill. Alternately, the third divergent section 34 can be formed with a punch. Next, another drilling or punching step is used to form the second divergent section 32. A punching step follows, using a shaped punch, which forms the first divergent section 26. This deforms sufficient metal to form a protuberance on the discharge face 16 which is removed by rubbing on abrasive paper or by any other suitable technique. The next step is to form the capillary section of nozzle with a shaped punch. This punching step forms another protuberance. The punch may or may not break through the protuberance. Again, the protuberance is removed by rubbing or a similar technique. The rubbing may leave burrs at the discharge orifice 20 which can be removed by a repetitive process of cleaning out the capillary section with the shaped punch which was used to form it and then rubbing again. By doing this a suflicient number of times, the burr is removed. The face of the spinnerette is then given a high polish to decrease the likelihood of corrosion during spinning.
An alternate method for removing burrs from orifice 20 is to place the discharge face 16 on a lapping wheel which has a long nap cloth. The long nap apparently reaches into the capillary and pulls out the burrs. Depending upon the time of lapping, a rounded edge may be formed between walls 23, 24 and discharge face 16. For good spinnability, it is essential that there be a sharp edge at this point so that a light, final lapping step is required. The abrasive used to resharpen the edge produces a finish which is not highly polished. Therefore, a final polishing step is required.
In use, spinnerette plate 12 forms part of a pack which is connected to a source of polymer and through which polymer under pressure is supplied to face 14. Because entrance hole 18 has a much larger cross-sectional area than the capillary defined by walls 23, 24, polymer moves therethrough at a relatively low velocity. However, when it comes out of the discharge orifice 20, the polymer is in the form of a relatively high velocity jet. By providing a series of sections which diverge from the capillary to the entrance hole, polymer flows through the convergent nozzle toward orifice 20 without encountering any major change in direction or velocity. This eliminates any localized high-shear spots as well as their adverse effects on the spun product. In addition, there are no dead spots where time-sensitive polymer can hold up and degrade. Since the first divergent section 26 has an outline corresponding to that of discharge orifice 20', the polymer is pre-formed and tends to accelerate uniformly as it reaches the capillary.
While a third divergent section 34 is illustrated in connection with the three-armed discharge orifice it is not always essential. For example, in situations where an imaginary circle encompassing the discharge orifice is close to the same size as the entrance hole, the third divergence is not provided. It is provided whenever the encompassing circle is considerably smaller in diameter than the entrance hole. In some situations, additional divergent sections may be required.
Preferably, divergence angles x and y range from 10 to 60 but need not be equal. Angle z ranges from 30 to 60 and angle w from 40 to 70. Angle w can be either smaller or larger than angle 2. It should be noted that these angles are all measured from lines parallel to t e zz e ax Although the above description is directed primarily to the illustrated embodiment, it is obvious that all of the objectives and advantages can be achieved with other symmetrical discharge configurations, a number of which have been illustrated in FIGS. 5-10. Similarly, the divergent sections can be comprised of other geometrical surfaces than truncated cones and fiat planes, as long as there are no dead spots and the polymer is directed to the final discharge orifice Without any abrupt change in direction. Where the spinnerette plate is intended for use in a low pressure pack, it may be thinner t0 such an extent that the nozzle has either a short entrance hole or none at all. Other modifications and adaptations of the convergent nozzle configuration disclosed herein will occur readily to those skilled in the art without departure from the invention which, accordingly, is intended to be limited only by the scope of the appended claims.
Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:
1. A spinnerette plate having at least one convergent nozzle extending therethrough to an orifice in the form of angularly disposed, interconnected slots in the discharge face, said nozzle terminating in a capillary section defined by planar walls substantially normal to the discharge face and extending from said capillary section in first and second adjoining, intersecting, divergent sections, said first divergent section having an angle of divergence less than that of said second section and being defined by uninterrupted planar surfaces each diverging from one of said walls, the latter being of equal height through the periphery of said capillary section.
2. The spinnerette plate of claim 1 wherein said second divergent section of the nozzle is a portion of a truncated cone.
3. A spinnerette plate having at least one convergent nozzle extending therethrough to an orifice in the form of angularly disposed, interconnected slots in the discharge face, said nozzle originating in a cylindrical entrance hole, terminating in a capillary section defined by planar Walls substantially normal to the discharge face, and
extending from said capillary section in first, second and third divergent sections, said first section having an angle of divergence less than that of the second section and being defined by planar surfaces each diverging from a wall, said walls being uninterrupted and equal in height.
4. The spinnerette plate of claim 3 wherein said second and third sections of the nozzle are portions of truncated cones.
References Cited by the Examiner UNITED STATES PATENTS 1,245,898 11/1917 Gates 18-12 3,001,230 9/1961 Rossi 188 3,006,026 10/ 1961 Martin et al 18-8 3,017,686 1/1962 Breen et a1. 188 3,095,607 7/1963 Cobb 18-8 3,210,451 10/1965 Manning et a1. 18-8 X FOREIGN PATENTS 25,424 5/1963 Germany.
References Cited by the Applicant UNITED STATES PATENTS 2,294,894 9/ 1942 Draemann. 2,742,667 4/1956 Clouzeau et a1.
WILLIAM J. STEPHENSON, Primary Examiner,