METHOD
United States Patent 3834251
This invention is a method for making punches for punching complicated hollow filament spinning capillaries in one step. An inverse first punch is machined and then used to punch complicated inner recesses in the end of punch stock for the ultimate second punch. The second punch is further finished by machining. In addition, the complete method requires punching a complete female die using the second punch and then punching capillaries in spinneret webs located between the aligned die and second punch.
US Patent References:
Method of stamping printing type with aligning marks
Guttel - August 1937 - 2091097
Spinneret production
Cobb - January 1962 - 3017789
Method for forming spinning orifices in spinneret plate structures
Burke, Jr. et al. - July 1964 - 3141358
METHOD FOR PRODUCING A PUNCH
Hawkins - October 1973 - 3768343
Method of stamping printing type with aligning marks
Guttel - August 1937 - 2091097
Spinneret production
Cobb - January 1962 - 3017789
Method for forming spinning orifices in spinneret plate structures
Burke, Jr. et al. - July 1964 - 3141358
METHOD FOR PRODUCING A PUNCH
Hawkins - October 1973 - 3768343
Application Number:
05/336196
Publication Date:
09/10/1974
Filing Date:
02/27/1973
View Patent Images:
Export Citation:
Assignee:
E. I. du Pont de Nemours and Company (Wilmington, DE)
Primary Class:
Other Classes:
264/166, 264/177.150
International Classes:
B23P15/16; D01D5/24; D01D5/00; B21K5/20
Field of Search:
70/17A,107,17S,17C
Primary Examiner:
Juhasz, Andrew R.
Assistant Examiner:
Briggs W. R.
Claims:
What is claimed is
1. A method for forming a punch and die for punching complex shaped spinneret capillaries extending from an entrance to an exit face of a spinneret plate and having plural slot like openings separated end-to-end by thin webs, the walls of each opening intersecting the exit face of the spinneret perpendicularly and tapering from a larger spacing at the entrance face to a minimum spacing at a point between the entrance and exit faces and the openings generally surrounding minute profiled inner areas said method comprising:
1. A method for forming a punch and die for punching complex shaped spinneret capillaries extending from an entrance to an exit face of a spinneret plate and having plural slot like openings separated end-to-end by thin webs, the walls of each opening intersecting the exit face of the spinneret perpendicularly and tapering from a larger spacing at the entrance face to a minimum spacing at a point between the entrance and exit faces and the openings generally surrounding minute profiled inner areas said method comprising:
Description:
BACKGROUND OF THE INVENTION
This invention relates to a new method for forming complex spinneret capillaries and more especially to the formation of slot type capillaries for the extrusion of filaments which have one or more continuous longitudinal hollows.
Spinneret capillaries comprising plural slot type openings to form hollow filaments by post extrusion coalescence are known. Each slot of the spinneret capillary converges from a greater width at the entrance face to a minimum intermediate width which remains constant through to the exit face; i.e., it has a tapered counterbore leading to a narrow straight portion. Such complex spinneret capillaries are usually formed by punching with male punches through the uniformly thick residuum at the bottom of a larger cylindrical counterbore in a spinneret plate. Each spinneret plate usually has from several to a multiplicity of such complex capillaries, and it has heretofore been substantially impossible to fabricate the capillaries so that all are identical both in each spinneret plate and from plate-to-plate. Customary machining yields male punches with the most accurate and reproducible dimensions, but it is almost impossible to machine the inner minute profiled areas bounded by extending arc like segments. Some relatively less complicated inner profiled areas can be provided by broaching the inner portion of a punch, but this approach has very limited application. It is also possible to use multiple punches, each performing part of the shaping required for the final spinneret capillaries; e.g., one punch to form the individual counterbore and another punch for forming the straight sided slots. For this purpose, a soft metal backing under the spinneret blank is used. Not only does multiple punching permit some nonuniformity among the punched capillaries because perfect alignment is difficult to achieve, but also this punching technique deforms the thin portion of the plate where punching occurs. The latter requires flattening of these portions after punching. In still another variation, tapered holes are formed in the distorted portions, their walls becoming parallel upon flattening the distortions.
SUMMARY OF THE INVENTION
The method of this invention provides for punching of complex slot type spinneret capillaries in one punching step to simultaneously form the straight walled portions and their corresponding tapered portions. It also provides for such punching without any distortion of those portions of the spinneret plate in which the capillaries are formed.
The invention is a method for punching spinneret capillaries having plural slot like openings separated end-to-end by thin webs, the walls of each opening intersecting the exit face of the spinneret perpendicularly and tapering from a larger spacing at the entrance face to a minimum spacing at a point intermediate of the entrance and exit faces, and the openings generally surrounding minute profiled inner areas. The method comprises:
Forming on one end of a length of tool punch stock a replica of the minute profiled inner areas to form a first punch;
hardening said first punch;
forming a second punch by punching on one end of a length of soft tool punch stock with said first punch, said punching step forming minute inner profiled female areas recessed in one end of the second punch;
machining the outside shape of the capillary and the slot like openings into said one end of the second punch;
hardening said second punch;
punching with said second punch a soft die stock material to form a die;
hardening the die;
aligning said punch with said die;
placing the spinneret plate between said second punch and said die;
punching said plate to extrude a portion of said plate into said die; and
removing said portion of said plate, thereby forming a spinneret capillary of the desired shape and size.
At the conclusion of the above process, the spinneret capillaries are complete except for usual polishing. It is clear that the first punch can be used repeatedly to form additional identical second punches. Ordinarily, the spinneret plate is hardened after all the capillaries required have been formed in it.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a portion of the exit face of a spinneret plate having one spinneret capillary typical of those formed by the process of this invention.
FIG. 2 is a cross-sectional view of the spinneret plate taken along 2--2 of FIG. 1.
FIG. 3 is an end view of the machined first punch.
FIG. 4 is a cross section of the first punch taken along 4--4 of FIG. 3.
FIG. 5 is an end view of the second punch after formation by the first punch and after subsequent outside machining. FIG. 6 is a cross section of the second punch taken along 6--6 of FIG. 5.
FIG. 7 is an outside view of the second punch taken along 7--7 of FIG. 5.
FIG. 8 shows the upper surface of the die stock after punching with the second punch.
FIG. 9 shows the arrangement of second punch, spinneret plate and die just prior to punching.
FIGS. 10-15 show additional complex spinneret capillaries which may be formed following the teachings of this invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
While the method of this invention can produce any of a great number of complex slot type spinneret capillaries, it is described hereinafter with reference to one particular form. It is to be understood, however, that the method is in no way limited to the particular form of capillary illustrated.
FIG. 1 is the plan view of the portion of the exit face of a spinneret plate 10 having one complex slot type spinneret capillary 12. Ordinarily, finished spinneret plates have from several to a multiplicity of capillaries identical to the one shown. As is apparent, "spinneret capillary" as herein defined is a complex arrangement of slot type openings together providing for the extrusion of one filament. The capillary 12 comprises four peripheral slot type openings 14 generally surrounding an inner minute area. Extending radially inward short of a common intersection are four straight slot type openings 18 each joining the peripheral openings 14 at their centers. Air vents 16, coextensive with the surrounding spinneret plate 10, separate peripheral openings 14. Preferably, the peripheral width of air vents 16 is less than the radial width of each opening 14.
During extrusion of, e.g., a molten polymer through capillary 12, four T-shaped streams are formed at and immediately downstream of the exit face of spinneret plate 10. Adjacent ends of the T-shaped streams then coalesce to form a continuous integral filament having four uniform voids extending continuously therealong. Air vents 16 allow entrance of air into the voids before coalescence, thus, preventing the collapse of the filament due to the internal vacuum which otherwise would result.
By way of providing scale to desirable spinneret capillaries, one preferred capillary 12 formable by single step punching according to this invention has air vents 16 of 0.003 inch (0.076 mm.) peripheral width and openings 14 of 0.0035 inch (0.089 mm.) radial width. Openings 18 are preferably equal in width to openings 14. It is immediately apparent that a punch capable of punching in one step both the openings shown in FIG. 1 and also their corresponding tapered upstream counterbores has very complicated minute recessed inner areas generally surrounded by raised arcs corresponding to openings 14. While customary machining techniques are necessary for accurately forming such shapes, machining of such minute recessed profiles is virtually impossible. This is best appreciated by considering the cross section (FIG. 2) of spinneret capillary 12.
In FIG. 2, peripheral openings 14 are shown at exit face 28 leading to their simultaneously punched tapered counterbores 22. Likewise shown are radial openings 18 with counterbores 26 separated by unpunched area 24. Spinneret plate 10 is ordinarily much thicker than the punched thickness between entrance face 30 and exit face 28. Before punching, larger counterbore 20 with flat entrance face 30 is machined into plate 10 at each location where a spinneret capillary is to be punched.
FIGS. 3-8 illustrate the tooling techniques by which the one step punching of complex spinneret capillaries is made possible. In general, this involves machining a first punch, using the first punch to generate the inner profiled area of a second punch, performing outside machining of the second punch, and using the second punch to generate a matching female die.
FIG. 3 is a plan view of the machined end of first punch 32 and FIG. 4 is its cross section. Soft cylindrical punch stock 34 has a diameter selected to just fit within counterbore 20 (FIG. 2). Punch stock 34 is first reduced in diameter to diameter D corresponding to the inside diameter of openings 14 (FIG. 1), the depth of the diameter reduction being slightly greater than the punching depth d required in the next punching step. Next, passing through the center end at right angles to one another, are machined two grooves 36 having the combined inverse shape of counterbore 26 and openings 18 (FIGS. 1 and 2). Finally, circular taper 38 is machined around the resulting protrusions, taper 38 corresponding to the inside tapers of counterbore 22 (FIG. 2). If desired, notches 40 can be marked for later location of air vents 16 (FIG. 1). This first punch 32 is then hardened in known fashion, depending on the type of hardenable tool stock employed.
A second piece of soft tool stock of the same diameter as the first punch 32 (FIG. 4) is punched on one end to the designed punched depth d (FIG. 4) using first punch 32. Except that second punch 50 (FIGS. 6 and 7) is an inverse of the first punch 32, an end view at this stage is exactly as shown in FIG. 3. The outside machining of second punch 50 is now performed to yield a punch as shown in FIGS. 5-7.
The outside is machined down at its end to a straight cylindrical portion 44 corresponding to the outside walls of openings 14 of FIGS. 1 and 2 and then a taper 46 is machined corresponding to the outside wall of counterbore 22 of FIG. 2. Using the guide notches introduced at FIG. 3, radial air vent slots 48 are machined as indicated in FIGS. 5 and 7, and then center portion 52 is machined out to the same depth as the air vent slots 48. After appropriate hardening, second punch 50 is complete. The four upstanding male portions producing openings 14 and 18 (FIG. 1) in spinneret plate 10 are readily apparent, each comprising peripheral arc like segment 54 and radial segment 56.
A soft die blank 60 (FIG. 8) is mounted in a punch press and punched with second punch 50 (FIGS. 5-7). Punching into die 60 is to the same depth of penetration as the thickness of the spinneret-plate portion ultimately to be punched, i.e., thickness between entrance face 30 and exit face 28 of FIG. 2. FIG. 8 shows a plan view of punched die blank 60 containing the inverse replica of the second punch. Portions 62 corresponding to ultimate air vents, void areas 64 and center portion 66 are undeformed. Downwardly tapered portions 68 lead to the most deeply punched slots 70 and 72 corresponding to the ultimate peripheral openings 14 and radial openings 18 of the spinneret capillary 12 of FIG. 1. The punched die 60 is then hardened in customary fashion.
Finally, in FIG. 9, is illustrated the arrangement by which multiple spinneret capillaries can be obtained using the second punch 50 and the die 60 as described above. A spinneret plate 10 with preformed large counterbore 20 is placed over die 60 in a punch press and located such that mounted punch 50 can be lowered into counterbore 20. The punch 50 and die 60 are previously aligned in the press. Shapes of die and punch details shown are intended only to show the punching operation and are not necessarily accurate. When punch 50 is forced down, metal is extruded into die 60 corresponding precisely to the metal to be removed from web 74 in plate 10 to form the desired capillary. Following punching, the extruded metal extending from the exit face of plate 10 is removed by lapping and the edges finished off by broaching leaving a perfectly formed capillary 12 (FIG. 1).
In one punching operation, a capillary with complex inner profiled areas is produced without distorting the planarity of web 74. Except for final polishing, no more machining is required.
Other spinneret capillaries for forming hollow filaments by post extrusion coalescence are shown in FIGS. 10-15, all analagously to FIG. 1. Using the techniques of this invention, all can be prepared in a single punching step providing both tapered inlet portions (not shown) and the final straight walled portions. The capillaries of FIGS. 10-12 produce four void filaments, while those of FIGS. 13-15 provide six, 12 and 16 voids. It is apparent that the latter are almost impossible to fabricate by customary machining of a single punch blank. Fabrication of more complicated punches corresponding to the capillaries of FIGS. 14 and 15, wherein one ring of orifice elements 80 is surrounded by a second ring of orifice elements 90, can be accomplished in either of two ways.
In a first method, the first punch is machined with continuous, unbroken, intersecting circular and radial grooves corresponding to the elements shown. Each groove has deeper straight walled portions and shallower tapered portions. The hardened first punch is then used to form a second punch having continuous, unbroken, intersecting circular and radial protrusions. Before the second punch is hardened, it is further machined to form the indicated discontinuities shown in FIGS. 14 and 15.
By an alternative method for forming the more complicated punches, first and second punches are fabricated corresponding to each of the inner and outer portions, the second punch for the outer portion being hollow to fit over and be continuous with the second punch of the inner portion. The final punch is then completed by fitting one portion onto the other as taught by Hawkins in U.S. Pat. No. 3,525,282.
The spinneret capillaries shown in the Figures are exemplary, but by no means exhaustive, of the variety of complicated ones which can be formed according to this invention; i.e., more specifically, by machining an inverse punch which is used to form the recessed inner portions of a second final punch which is itself completed by further outside machining.
This invention relates to a new method for forming complex spinneret capillaries and more especially to the formation of slot type capillaries for the extrusion of filaments which have one or more continuous longitudinal hollows.
Spinneret capillaries comprising plural slot type openings to form hollow filaments by post extrusion coalescence are known. Each slot of the spinneret capillary converges from a greater width at the entrance face to a minimum intermediate width which remains constant through to the exit face; i.e., it has a tapered counterbore leading to a narrow straight portion. Such complex spinneret capillaries are usually formed by punching with male punches through the uniformly thick residuum at the bottom of a larger cylindrical counterbore in a spinneret plate. Each spinneret plate usually has from several to a multiplicity of such complex capillaries, and it has heretofore been substantially impossible to fabricate the capillaries so that all are identical both in each spinneret plate and from plate-to-plate. Customary machining yields male punches with the most accurate and reproducible dimensions, but it is almost impossible to machine the inner minute profiled areas bounded by extending arc like segments. Some relatively less complicated inner profiled areas can be provided by broaching the inner portion of a punch, but this approach has very limited application. It is also possible to use multiple punches, each performing part of the shaping required for the final spinneret capillaries; e.g., one punch to form the individual counterbore and another punch for forming the straight sided slots. For this purpose, a soft metal backing under the spinneret blank is used. Not only does multiple punching permit some nonuniformity among the punched capillaries because perfect alignment is difficult to achieve, but also this punching technique deforms the thin portion of the plate where punching occurs. The latter requires flattening of these portions after punching. In still another variation, tapered holes are formed in the distorted portions, their walls becoming parallel upon flattening the distortions.
SUMMARY OF THE INVENTION
The method of this invention provides for punching of complex slot type spinneret capillaries in one punching step to simultaneously form the straight walled portions and their corresponding tapered portions. It also provides for such punching without any distortion of those portions of the spinneret plate in which the capillaries are formed.
The invention is a method for punching spinneret capillaries having plural slot like openings separated end-to-end by thin webs, the walls of each opening intersecting the exit face of the spinneret perpendicularly and tapering from a larger spacing at the entrance face to a minimum spacing at a point intermediate of the entrance and exit faces, and the openings generally surrounding minute profiled inner areas. The method comprises:
Forming on one end of a length of tool punch stock a replica of the minute profiled inner areas to form a first punch;
hardening said first punch;
forming a second punch by punching on one end of a length of soft tool punch stock with said first punch, said punching step forming minute inner profiled female areas recessed in one end of the second punch;
machining the outside shape of the capillary and the slot like openings into said one end of the second punch;
hardening said second punch;
punching with said second punch a soft die stock material to form a die;
hardening the die;
aligning said punch with said die;
placing the spinneret plate between said second punch and said die;
punching said plate to extrude a portion of said plate into said die; and
removing said portion of said plate, thereby forming a spinneret capillary of the desired shape and size.
At the conclusion of the above process, the spinneret capillaries are complete except for usual polishing. It is clear that the first punch can be used repeatedly to form additional identical second punches. Ordinarily, the spinneret plate is hardened after all the capillaries required have been formed in it.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a portion of the exit face of a spinneret plate having one spinneret capillary typical of those formed by the process of this invention.
FIG. 2 is a cross-sectional view of the spinneret plate taken along 2--2 of FIG. 1.
FIG. 3 is an end view of the machined first punch.
FIG. 4 is a cross section of the first punch taken along 4--4 of FIG. 3.
FIG. 5 is an end view of the second punch after formation by the first punch and after subsequent outside machining. FIG. 6 is a cross section of the second punch taken along 6--6 of FIG. 5.
FIG. 7 is an outside view of the second punch taken along 7--7 of FIG. 5.
FIG. 8 shows the upper surface of the die stock after punching with the second punch.
FIG. 9 shows the arrangement of second punch, spinneret plate and die just prior to punching.
FIGS. 10-15 show additional complex spinneret capillaries which may be formed following the teachings of this invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
While the method of this invention can produce any of a great number of complex slot type spinneret capillaries, it is described hereinafter with reference to one particular form. It is to be understood, however, that the method is in no way limited to the particular form of capillary illustrated.
FIG. 1 is the plan view of the portion of the exit face of a spinneret plate 10 having one complex slot type spinneret capillary 12. Ordinarily, finished spinneret plates have from several to a multiplicity of capillaries identical to the one shown. As is apparent, "spinneret capillary" as herein defined is a complex arrangement of slot type openings together providing for the extrusion of one filament. The capillary 12 comprises four peripheral slot type openings 14 generally surrounding an inner minute area. Extending radially inward short of a common intersection are four straight slot type openings 18 each joining the peripheral openings 14 at their centers. Air vents 16, coextensive with the surrounding spinneret plate 10, separate peripheral openings 14. Preferably, the peripheral width of air vents 16 is less than the radial width of each opening 14.
During extrusion of, e.g., a molten polymer through capillary 12, four T-shaped streams are formed at and immediately downstream of the exit face of spinneret plate 10. Adjacent ends of the T-shaped streams then coalesce to form a continuous integral filament having four uniform voids extending continuously therealong. Air vents 16 allow entrance of air into the voids before coalescence, thus, preventing the collapse of the filament due to the internal vacuum which otherwise would result.
By way of providing scale to desirable spinneret capillaries, one preferred capillary 12 formable by single step punching according to this invention has air vents 16 of 0.003 inch (0.076 mm.) peripheral width and openings 14 of 0.0035 inch (0.089 mm.) radial width. Openings 18 are preferably equal in width to openings 14. It is immediately apparent that a punch capable of punching in one step both the openings shown in FIG. 1 and also their corresponding tapered upstream counterbores has very complicated minute recessed inner areas generally surrounded by raised arcs corresponding to openings 14. While customary machining techniques are necessary for accurately forming such shapes, machining of such minute recessed profiles is virtually impossible. This is best appreciated by considering the cross section (FIG. 2) of spinneret capillary 12.
In FIG. 2, peripheral openings 14 are shown at exit face 28 leading to their simultaneously punched tapered counterbores 22. Likewise shown are radial openings 18 with counterbores 26 separated by unpunched area 24. Spinneret plate 10 is ordinarily much thicker than the punched thickness between entrance face 30 and exit face 28. Before punching, larger counterbore 20 with flat entrance face 30 is machined into plate 10 at each location where a spinneret capillary is to be punched.
FIGS. 3-8 illustrate the tooling techniques by which the one step punching of complex spinneret capillaries is made possible. In general, this involves machining a first punch, using the first punch to generate the inner profiled area of a second punch, performing outside machining of the second punch, and using the second punch to generate a matching female die.
FIG. 3 is a plan view of the machined end of first punch 32 and FIG. 4 is its cross section. Soft cylindrical punch stock 34 has a diameter selected to just fit within counterbore 20 (FIG. 2). Punch stock 34 is first reduced in diameter to diameter D corresponding to the inside diameter of openings 14 (FIG. 1), the depth of the diameter reduction being slightly greater than the punching depth d required in the next punching step. Next, passing through the center end at right angles to one another, are machined two grooves 36 having the combined inverse shape of counterbore 26 and openings 18 (FIGS. 1 and 2). Finally, circular taper 38 is machined around the resulting protrusions, taper 38 corresponding to the inside tapers of counterbore 22 (FIG. 2). If desired, notches 40 can be marked for later location of air vents 16 (FIG. 1). This first punch 32 is then hardened in known fashion, depending on the type of hardenable tool stock employed.
A second piece of soft tool stock of the same diameter as the first punch 32 (FIG. 4) is punched on one end to the designed punched depth d (FIG. 4) using first punch 32. Except that second punch 50 (FIGS. 6 and 7) is an inverse of the first punch 32, an end view at this stage is exactly as shown in FIG. 3. The outside machining of second punch 50 is now performed to yield a punch as shown in FIGS. 5-7.
The outside is machined down at its end to a straight cylindrical portion 44 corresponding to the outside walls of openings 14 of FIGS. 1 and 2 and then a taper 46 is machined corresponding to the outside wall of counterbore 22 of FIG. 2. Using the guide notches introduced at FIG. 3, radial air vent slots 48 are machined as indicated in FIGS. 5 and 7, and then center portion 52 is machined out to the same depth as the air vent slots 48. After appropriate hardening, second punch 50 is complete. The four upstanding male portions producing openings 14 and 18 (FIG. 1) in spinneret plate 10 are readily apparent, each comprising peripheral arc like segment 54 and radial segment 56.
A soft die blank 60 (FIG. 8) is mounted in a punch press and punched with second punch 50 (FIGS. 5-7). Punching into die 60 is to the same depth of penetration as the thickness of the spinneret-plate portion ultimately to be punched, i.e., thickness between entrance face 30 and exit face 28 of FIG. 2. FIG. 8 shows a plan view of punched die blank 60 containing the inverse replica of the second punch. Portions 62 corresponding to ultimate air vents, void areas 64 and center portion 66 are undeformed. Downwardly tapered portions 68 lead to the most deeply punched slots 70 and 72 corresponding to the ultimate peripheral openings 14 and radial openings 18 of the spinneret capillary 12 of FIG. 1. The punched die 60 is then hardened in customary fashion.
Finally, in FIG. 9, is illustrated the arrangement by which multiple spinneret capillaries can be obtained using the second punch 50 and the die 60 as described above. A spinneret plate 10 with preformed large counterbore 20 is placed over die 60 in a punch press and located such that mounted punch 50 can be lowered into counterbore 20. The punch 50 and die 60 are previously aligned in the press. Shapes of die and punch details shown are intended only to show the punching operation and are not necessarily accurate. When punch 50 is forced down, metal is extruded into die 60 corresponding precisely to the metal to be removed from web 74 in plate 10 to form the desired capillary. Following punching, the extruded metal extending from the exit face of plate 10 is removed by lapping and the edges finished off by broaching leaving a perfectly formed capillary 12 (FIG. 1).
In one punching operation, a capillary with complex inner profiled areas is produced without distorting the planarity of web 74. Except for final polishing, no more machining is required.
Other spinneret capillaries for forming hollow filaments by post extrusion coalescence are shown in FIGS. 10-15, all analagously to FIG. 1. Using the techniques of this invention, all can be prepared in a single punching step providing both tapered inlet portions (not shown) and the final straight walled portions. The capillaries of FIGS. 10-12 produce four void filaments, while those of FIGS. 13-15 provide six, 12 and 16 voids. It is apparent that the latter are almost impossible to fabricate by customary machining of a single punch blank. Fabrication of more complicated punches corresponding to the capillaries of FIGS. 14 and 15, wherein one ring of orifice elements 80 is surrounded by a second ring of orifice elements 90, can be accomplished in either of two ways.
In a first method, the first punch is machined with continuous, unbroken, intersecting circular and radial grooves corresponding to the elements shown. Each groove has deeper straight walled portions and shallower tapered portions. The hardened first punch is then used to form a second punch having continuous, unbroken, intersecting circular and radial protrusions. Before the second punch is hardened, it is further machined to form the indicated discontinuities shown in FIGS. 14 and 15.
By an alternative method for forming the more complicated punches, first and second punches are fabricated corresponding to each of the inner and outer portions, the second punch for the outer portion being hollow to fit over and be continuous with the second punch of the inner portion. The final punch is then completed by fitting one portion onto the other as taught by Hawkins in U.S. Pat. No. 3,525,282.
The spinneret capillaries shown in the Figures are exemplary, but by no means exhaustive, of the variety of complicated ones which can be formed according to this invention; i.e., more specifically, by machining an inverse punch which is used to form the recessed inner portions of a second final punch which is itself completed by further outside machining.