Title:
APPARATUS FOR CONTROLLED QUENCHING OF MELT EXTRUDED FILAMENTS
United States Patent 3855453
Abstract:
An improved apparatus for critically controlling the rate of cooling melt extruded filaments which comprises a sleeve constructed from a material having an electrical resistivity. The sleeve is equipped with an electrical power supply input means for heating the sleeve to provide a heated environment within the sleeve.
US Patent References:
Electric fluid heater
Evans - April 1933 - 1906145
Electric water heater
Evans - August 1933 - 1920685
Electrically heated hose
Marick - March 1942 - 2274839
Heated wiper
Marick - September 1947 - 2427502
Metal foil heating device
Cox - June 1952 - 2600485
Electric fluid heater
Evans - April 1933 - 1906145
Electric water heater
Evans - August 1933 - 1920685
Electrically heated hose
Marick - March 1942 - 2274839
Heated wiper
Marick - September 1947 - 2427502
Metal foil heating device
Cox - June 1952 - 2600485
Inventors:
Manning, Don P. (Colonial Heights, VA)
Flower, Thomas A. (Colonial Heights, VA)
Flower, Thomas A. (Colonial Heights, VA)
Application Number:
05/171717
Publication Date:
12/17/1974
Filing Date:
08/13/1971
View Patent Images:
Export Citation:
Assignee:
Allied Chemical Corporation (New York, NY)
Primary Class:
Other Classes:
219/385, 219/549, 392/459, 219/535
International Classes:
H05B3/00; H05B3/12; H05B3/10
Field of Search:
219/304,311,385,535,549,552,553 338/208,210,211,212 264/210,176
US Patent References:
| 2740035 | Heating device | March 1956 | Young, Jr. | |
| 2809223 | Terminal for heating furnaces | October 1957 | Stevenson | |
| 2896004 | Electric heating furnace and method of heating | July 1959 | Duffy et al. | |
| 3053611 | Process for spinning of synthetic fibers | September 1962 | Griehl | |
| 3057936 | Electrical heating device | October 1962 | Hill | |
| 3296415 | Electrically heated dispensable container | January 1967 | Eisler |
Primary Examiner:
Mayewsky, Volodymyr Y.
Attorney, Agent or Firm:
Anderson, Richard A.
Parent Case Data:
This is a division of application Ser. No. 836,553, filed June 25, 1969 now abandoned.
Claims:
It is claimed
1. An improved apparatus for critically controlling the rate of cooling melt extruded filaments which comprises a sleeve constructed from a material having an electrical resistivity of 60 to 675 ohms per circular mil-foot, axial length of the sleeve being about 1 to 12 inches, diameter of the sleeve being about 3 to 20 inches, and thickness of the material from which the sleeve is constructed being about 0.001 to 0.125 inch, said sleeve being equipped with an electrical power supply input means for heating said sleeve to provide a heated environment within said sleeve, whereby the temperature of said sleeve is maintained at about 200° to 525°C. thereby creating said heated environment within said sleeve at about 175° to 450°C.
2. The apparatus of claim 1 wherein said sleeve is constructed from stainless steel.
3. The apparatus of claim 1 wherein the thickness of the material from which the sleeve is constructed varies thereby producing different temperatures within said sleeve.
4. The apparatus of claim 1 wherein the heated environment within said sleeve is air.
5. The apparatus of claim 1 wherein the cross-sectional shape of the sleeve, perpendicular to the axis of the sleeve is circular.
6. An improved apparatus for critically controlling the rate of cooling of melt extruded filaments which comprises a sleeve axially positioned concentrically around said melt extruded filaments, said sleeve constructed from a material having an electrical resistivity of from about 10 to about 870 ohms per circular mil-foot, said sleeve being equipped with an electrical power supply input means for heating said sleeve to provide a heated environment within the sleeve of about 175° to about 450°C. by maintaining the temperature of said sleeve at about 200° to about 525°C., axial length of said sleeve being about 1 to 12 inches, diameter of said sleeve being about 3 to 20 inches, thickness of said sleeve being about 0.001 to about 0.0125 inch, the power input requirement of said sleeve being from about 200 to about 5,000 amps, and the voltage supply to the sleeve being from about 1 to about 12.
1. An improved apparatus for critically controlling the rate of cooling melt extruded filaments which comprises a sleeve constructed from a material having an electrical resistivity of 60 to 675 ohms per circular mil-foot, axial length of the sleeve being about 1 to 12 inches, diameter of the sleeve being about 3 to 20 inches, and thickness of the material from which the sleeve is constructed being about 0.001 to 0.125 inch, said sleeve being equipped with an electrical power supply input means for heating said sleeve to provide a heated environment within said sleeve, whereby the temperature of said sleeve is maintained at about 200° to 525°C. thereby creating said heated environment within said sleeve at about 175° to 450°C.
2. The apparatus of claim 1 wherein said sleeve is constructed from stainless steel.
3. The apparatus of claim 1 wherein the thickness of the material from which the sleeve is constructed varies thereby producing different temperatures within said sleeve.
4. The apparatus of claim 1 wherein the heated environment within said sleeve is air.
5. The apparatus of claim 1 wherein the cross-sectional shape of the sleeve, perpendicular to the axis of the sleeve is circular.
6. An improved apparatus for critically controlling the rate of cooling of melt extruded filaments which comprises a sleeve axially positioned concentrically around said melt extruded filaments, said sleeve constructed from a material having an electrical resistivity of from about 10 to about 870 ohms per circular mil-foot, said sleeve being equipped with an electrical power supply input means for heating said sleeve to provide a heated environment within the sleeve of about 175° to about 450°C. by maintaining the temperature of said sleeve at about 200° to about 525°C., axial length of said sleeve being about 1 to 12 inches, diameter of said sleeve being about 3 to 20 inches, thickness of said sleeve being about 0.001 to about 0.0125 inch, the power input requirement of said sleeve being from about 200 to about 5,000 amps, and the voltage supply to the sleeve being from about 1 to about 12.
Description:
BACKGROUND OF THE INVENTION
This invention relates to an improvement in the apparatus used in melt extruding filaments and is more particularly related to an improved apparatus for critically controlling the rate of cooling melt extruded filaments after the filaments have left the spinnerette in order to produce greater cross-sectional uniformity in the undrawn filaments and improved physical properties in the drawn yarn.
It is known in the art that the melt extrusion of filaments is greatly improved by controlling the cooling of the filaments as they extrude from the spinnerette under critical temperature conditions. Suitable temperature control can be accomplished by surrounding the filaments, as they extrude from the spinnerette, with a heater provided with means for regulating the amount of heat supplied at various distances from the spinnerette. Such a heater is commonly known in the art as a heated sleeve.
The prior art discloses that such a heater or heated sleeve can be constructed by imbedding insulated wires having a high electrical resistance inside a metal cylinder which surrounds the melt extruded filaments as they leave the spinnerette. Such a heater construction has the disadvantage of producing areas of uneven temperature or hot spots, as they are commonly called, at the points where the insulated wires are imbedded inside the metal cylinder. These hot spots tend to produce non-uniformity in the cross-sections of the melt extruded filaments. Furthermore, such a heater is difficult and expensive to construct since wires having a high electrical resistance have to be first insulated and then imbedded inside the metal heater. Finally, such a heater has a high rate of oxidation which limits its useful life to below practical limits.
The prior art also discloses that a heater or heated sleeve can be constructed by inserting heating rods or coils around the inner surface of a non-conductive cylinder, usually a ceramic material, which surrounds the melt extruded filaments as they leave the spinnerette. This type of heater construction also has the disadvantage of producing areas of uneven temperature or hot spots in the area near the heating rods or coils which produce nonuniformity in the cross-sections of the melt extruded filaments. Such a heater is also difficult and expensive to construct. Furthermore, ceramic materials are brittle and do not stand up to normal industrial abuse.
The prior art heaters or heated sleeves described above have the further disadvantages in that they require high voltages for proper operation and these high voltages present a very serious shock hazard. As a result, relatively expenive safety measures are required in order to safeguard personnel operating equipment whereon these heaters or heated sleeves are used.
It has now been discovered that a heater or heated sleeve for controlling the temperature around the filaments, as they extrude from the spinnerette, can be constructed from a material having an electrical resistivity wherein the material used as the heated sleeve functions both as the heated sleeve and the heating element thereby greatly simplifying the design and construction of the heated sleeve and eliminating the problem of hot spots in prior art heated sleeves which produced non-uniformity in the cross-sections of the melt extruded filaments.
Furthermore, the novel heater or heated sleeve of the present invention requires only low voltages for proper operation and these low voltages eliminate the shock hazard present in the prior art heaters or heated sleeves. Thus, the expensive safety measures which were required in order to safeguard personnel operating equipment whereon the prior art heaters or heated sleeves were used are now no longer necessary.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an improved apparatus for critically controlling the rate of cooling a melt extruded filament which comprises a sleeve constructed from a material having an electrical resistivity. The sleeve is equipped with an electrical power supply input means for heating the sleeve to provide a heated environment within the sleeve.
The dimensions of a typical heated sleeve of the present invention which is cylindrical in shape can be determined from the following formula:
TL(D -1 ) = 2.05 PR(E -2 )(10 -7 )
wherein:
T is the average sleeve thickness, inches.
L is the sleeve axial length, inches.
D is the sleeve diameter, inches.
P is the power input requirement of the sleeve, watts.
E is the voltage supplied to the sleeve, volts.
R is the electrical resistivity of the material the sleeve is constructed from, ohms per circular mil.-foot.
In accordance with the above formula, the thickness, T, of the sleeve can range from about 0.001 to 0.125, preferably about 0.016 to 0.025, inch and the thickness can vary from the top of the sleeve to the bottom thereby producing different temperatures profiles within the sleeve. The axial length, L, of the sleeve can range from about 1 to 12, preferably about 3 to 6 inches and the diameter, D, of the sleeve can range from about 3 to 20, preferably about 6 to 10, inches. The power input requirement, P, of the sleeve can range from about 200 to 5,000, preferably about 700 to 1,200 watts and the voltage, E, supplied to the sleeve can range from about 1 to 12, preferably about 2 to 6, volts. The voltage, E, can be A.C. or D.C. but preferably is A.C. The electrical resistivity, R, of the material from which the sleeve is constructed can range from about 10 to 870, preferably about 60 to 675, ohms per circular mil-foot. The amperage of the current passing around the sleeve can range from about 100 to 3,000, preferably about 200 to 600 amps.
The temperature of the sleeve can range from about 200 to 525, preferably about 275 to 375, °C thereby creating a heated environment within the sleeve which can range from about 175 to 450, preferably about 250 to 350, °C.
The sleeve can be constructed from any material having an electrical resistivity within the above defined ranges and having sufficient structural strength and oxidation resistance to provide a dimensionally stable sleeve thereby conforming to the above defined thickness, axial length, and diameter ranges. Certain metals are particularly advantageous for use in forming the heated sleeve of the present invention. Suitable metals include Chromel A (1) (Ni 80%-Cr 20%), Chromel C (1) (Ni 60%-Cr 16%-Fe 24%), Chromel D (1) (Ni 35%-Cr 20%-Fe 45%), Chromax (2) (Ni 35%-Cr 20%-Fe 45%), Kanthal (3) (Cr-Al-F), Lohm (2) (Cu 94%-Ni 6%), Grade "A" nickel (Ni 99%), Nichrome (2) (Ni 60%-Cr 16%-Fe 24%), Nirex (2) (Cr 13%-Fe 8%-Ni 79%), stainless steel, preferably types 304, 310, 316 and 410 stainless steel, and the like and suitable sintered, porous, perforated, expanded, or felt metals of those metals described above. The preferred metals are those metals which will form a black oxide coating when heated. A high emissivity of 0.6 to 0.98 to a black surface of the same temperature can be obtained with such metals by the principle of black-body radiation heating. Also suitable are semiconductive materials such as titania, graphite and the like.
The electrical power supply means for heating the sleeve to provide a heated environment within the sleeve can be controlled by either a manual means or an automatic means. A typical manually controlled power supply means can comprise a high voltage power source connected to a step-down transformer or auto-transformer. The power input to the heated sleeve can be controlled by a variable rheostat which is connected in series with the primary side of the step-down transformer. The temperature of the heated sleeve or the heated environment within the heated sleeve can be determined by suitable temperature sensing means such as a thermister, thermocouple, or optical pyrometer and the variable rheostat can accordingly be manually adjusted to provide the desired temperature in the heated sleeve and in the heated environment within the heated sleeve.
Accordingly, a typical automatic power supply means can comprise a high voltage power source connected to a step-down transformer. The power input to the heated sleeve can be controlled by an automatic electrical temperature controller which contains a temperature sensor and a power control. The temperature sensor of the automatic controller is connected to or is adjacent to the heated sleeve and the power control of the automatic controller is connected in series with the primary side of the transformer. The temperature of the heated sleeve or the heated environment within the sleeve is determined by the temperature sensor, which can be any suitable temperature sensing means such as a thermister, thermocouple, or optical pyrometer. The temperature sensor relays a temperature control signal to the automatic temperature controller which in turn regulates the power supplied to the sleeve by the step-down transformer. Thus, the desired temperature is maintained in the heated sleeve and in the heated environment within the heated sleeve.
For purposes of definition in this application, the terms low voltage, high voltage, low amperage, and high amperage are generally defined as follows:
Low Voltage -- 24 volts or less
High Voltage -- 110 volts or more
Low Amperage -- 30 amps or less
High Amperage -- 50 amps or more
The heated environment within the sleeve can be an inert gas, for example, carbon dioxide, nitrogen and the like. The heated environment can also be continuously purged with an inert gas in order to exclude oxygen from the space between the face of the spinnerette and the point of solidification of the melt extruded filaments.
The cross-section of the sleeve of the present invention, perpendicular to the axis of the sleeve, can be any desired shape, for example, circular, elliptical, polygonal, that is, triangular, square, rectangular, pentagonal, hexagonal, octagonal and the like; starshaped, S-shaped and the like. The above defined parameters of T, L, P, E and R as defined above also apply to these cross-sectional sleeve shapes.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a typical heater or heated sleeve of the present invention wherein the material used as the heated sleeve functions both as the heated sleeve and the heating elment.
FIG. 2 is a cross-sectional view showing a typical heater or heated sleeve of the present invention, wherein the material used as the heated sleeve functions both as the heated sleeve and the heating element, positioned in a filament melt extrusion apparatus.
FIG. 3 is a top-sectional view showing a typical heater or heated sleeve of the present invention positioned in the filament melt extrusion apparatus below the spinnerette assembly.
Referring now to FIG. 1, the heated sleeve 11 can be formed into a cylindrical configuration from flat sheet stock material having the required electrical resistivity. Ends 12 of the flat sheet stock are folded towards the outer surface of the heated sleeve 11 to form channels 13 wherein electrical bus bar conductors 14 are positioned on the heated sleeve 11. Electrical conductors 14 which are positioned in channels 13 are secured to the ends 12 of the heated sleeve 11 by mechanical fastening means 15 which can be bolts, rivets or the like. A good electrical contact can be formed between electrical conductors 14 and the heated sleeve 11 by silver soldering or brazing the joints. Insulation means 16 is inserted between folded ends 17 of heated sleeve 11 to prevent folded ends 17 from contacting each other and thereby short circuiting the heated sleeve 11. Insulation means 16 can be any conventional insulating means such as porcelain, glass, asbestos, mica, or a resin such as phenolic. Insulation means 16 can be held in place by riveting or bolting through folded ends 17.
Referring now to FIG. 2, the heated sleeve 11 is positioned in filament melt extrusion apparatus 18 as shown in FIG. 2. Filament melt extrusion apparatus 18 comprises spinnerette assembly 19, cylindrical wall 21, filament quenching and cooling chamber 22 and a filament take-up means (not shown). Cylindrical wall 21 surrounds and encloses filaments 26 extruding from spinnerette 19. Quenching and cooling chamber 22 is connected to the lower portion of cylindrical wall 21. Filaments 26 extruding from spinnerette 19 are quenched and then cooled in chamber 22.
The Heated sleeve 11 is positioned within cylindrical wall 21 below the face of spinnerette 19 and is held in position by non-conductive ceramic support rods 23 which protrude inward from their location in cylindrical wall 21 and by electrical conductors 14 which protrude through cylindrical wall 21. Electrical conductors 14 are supported in and insulated from cylindrical wall 21 by insulators 24. Insulators 24 can be any conventional insulating means such as porcelain, glass, asbestos, mica or a resin such as phenolic. Low voltage electric power is supplied to electrical bus bar conductors 14 by power supply means 20 thereby heating sleeve 11.
In one embodiment of the present invention, there is small space or gap 25 between the top of heated sleeve 11 and the face of spinnerette 19 which can range from about 1/8 to 4 inches, preferably from about 1/4 to 3/4 inch. This embodiment of the present invention is called on "open-end" heated sleeve.
In another embodiment of the present invention, gap 25 is filled by a suitable insulation material (not shown) which can be porcelain, glass, asbestos, mica or fiberglass thereby closing gap 25 and sealing heated sleeve 11 around filaments 26. This embodiment of the present invention is called a "closed-end" heated sleeve.
The "open-end" heated sleeve as described above stresses simplicity in design and produces streamline gas flow within the heated sleeve. This streamline gas flow within the heated sleeve is believed to produce better cross-sectional uniformity in the filaments than eddying gas flow which is characteristic within a "closed-end" heated sleeve. Eddying gas flow within a "closed-end" heated sleeve can cause filament movement which may produce poor cross-sectional uniformity in the filaments. The "open-end" heated sleeve can be converted to a "closed-end" heated sleeve with the addition of an insulating ring conforming to the dimension of the space or gap between the face of the spinnerette and the heated sleeve.
The streamline gas flow within the "open-end" heated sleeve is cocurrent with the filament line. A predictable gas flow can be obtained by measuring the thermal differences adjacent to the filaments and the aerodynamic drag on the filaments. The streamline gas flow within the "open-en" heated sleeve is believed to produce better performance than the "closed-end" heated sleeve with respect to convection heat transfer and filament movement. This results in the gas temperature surrounding the spinnerette being very close to the sleeve temperature.
A black matte sleeve surface will produce radiation heating of the gas molecules and will add to the overall heat transfer coefficient of the heated sleeve.
The test data indicate that, because of the streamline gas flow and the uniform cooling rate produced by the "open-end" heated sleeve, better cross-sectional uniformity in the undrawn filaments and better denier uniformity, higher ultimate tensile strength and elongation in the drawn yarn can be obtained using the "open-end" heated sleeve of this embodiment of the present invention than can be obtained without the use of a heated sleeve.
The "closed-end" heated sleeve as described above operates on the principle that the stagnant gas temperature within the heated sleeve is the predominant factor in controlling the rate of solidifying or quenching of the filaments. The gas temperature within the heated sleeve is varied by the surface temperature of the heated sleeve which is controlled by the power input to the sleeve and by gas convections which are uncontrolled because of thermal currents within the heated sleeve and aerodynamic drag on the filaments.
A change in the "closed-end" heated sleeve surface temperature, assuming air convection to be within normal limits, will result in a smaller change in gas temperature. A change in gas temperature, however, will result in an even smaller change in the temperature of the filaments at the lower end of the heated sleeve.
As with the "open-end" heated sleeve, a black matte sleeve surface will produce radiation heating of the gas molecules and will add to the overall heat transfer coefficient of the heated sleeve.
Referring now to FIG. 3, the above described components of FIG. 2 are shown in a top-sectional view from spinnerette 19.
In operation, synthetic filaments 26 are melt extruded through spinnerette 19 and are passed through the heated environment within heated sleeve 11. Heated sleeve 11 is heated by a low voltage, high amperage electrical power supplied by power supply means 20. The electrical power supplied to heated sleeve 11 can range from about 200 to 5,000, preferably about 700 to 1,200, watts at a voltage of about 1 to 12, preferably about 2 to 6, volts. The temperature of sleeve 11 can range from about 200 to 525, preferably about 275 to 375, °C thereby creating a heated environment within sleeve 11 which can range from about 175 to 450, preferably about 250 to 350, °C. The rate of solidifying or quenching of filaments 26 is thereby controlled by the heated environment within heated sleeve 11. Filaments 26 are then passed through chamber 22 where they are quenched and cooled and are then wound on a suitable takeup means (not shown).
PREFERRED EMBODIMENTS
The following example illustrates the practice and principles of this invention and a mode of carrying out the invention.
EXAMPLE
In the operation of the heated sleeve of FIG. 1 positioned in the apparatus as shown in FIG. 2, polycaproamide was melt extruded at a temperature of 260°C, under a pressure of 3,500 psig through 204-orifice spinnerette assembly 19, each of the orifices having a diameter of 0.022 inch, to produce a 6,000 denier undrawn fiber comprised of filaments 26. The polycaproamide was melt extruded through spinnerette 19 at a rate of 45 pounds per hour.
Heated sleeve 11 was fabricated from type 304 stainless steel into a cylindrical configuration as shown in FIG. 1 and had an outside diameter of 7.5 inches, a length of 4 inches and a metal thickness of 0.020 inch. Heated sleeve 11 was of the "open-end" type as described in the Description of the Drawings and was positioned below spinnerette 19 thereby creating space or gap 25 between the face of spinnerette 19 and the top of heated sleeve 11 which had the dimension of one-fourth inch.
As filaments 26 were extruded from spinnerette 19, they were passed through heated sleeve 11 and were then passed through quenching and cooling chamber 22 and taken up on a suitable take-up means (not shown). The heated environment within heated sleeve 11 was air. The undrawn fiber thus produced was then drawn into yarn. The results of several runs using different power inputs to heated sleeve 11 and a control run using no heated sleeve are contained in Table I below.
As can be seen from the data contained in Table I, the heated sleeve of the present invention produced a significant improvement in yarn physical properties as compared to the physical properties of yarn produced using no heated sleeve. The heated sleeve of the present invention produced best results when it was operated with an optimum or near optimum power input of 300 to 500 watts which created a desirable heated environment within the heated sleeve surrounding the extruding filaments.
It is interesting to also note that the heated sleeve of the present invention produced improved yarn physical properties as compared to the physical properties of yarn produced using no heated sleeve even when no power was supplied to heat the sleeve. This improvement in yarn physical properties can be attributed to the fact that the sleeve retained, around the extruding filaments, some of the heat given off by the extruding filaments which otherwise would have been dissipated. This illustrates a further advantage of the heated sleeve of the present invention wherein the diameter of the heated sleeve of the present invention can be much smaller than prior art heated sleeves because of its simplicity in design. Because of this simplicity in design, the spin packs are not removed through the sleeve during a pack change. This smaller diameter of the heated sleeve of the present invention therefore permits more heat to be retained around the extruding filaments thereby decreasing power requirements and producing yarns having improved physical properties.
TABLE I ____________________________________________________________ ______________ AIR CROSS- ULTIMATE POWER SURFACE TEMPERA- SECTION TENSILE TOUGH- INPUT TEMPERA- TURE SPREAD OF ULTIMATE STRENGTH NESS TO HEATED TURE OF WITHIN UNDRAWN MAXIMUM ELONGA- OF YARN INDEX OF RUN SLEEVE 11, HEATED HEATED FILA- YARN TION OF (UTS), YARN NUM- WATTS SLEEVE 11, SLEEVE MENTS, DRAW YARN (UE), GRAMS PER (UTS) BER (A.C.) °C 11, °C* MICRONS RATIO** PERCENT DENIER (UE)1/2) ____________________________________________________________ ______________ A 0 174 184 18 5.1 14.6 8.8 33.6 B 300 242 232 16 5.1 15.4 9.3 36.5 C 1,100 360 338 15 4.9 15.4 9.1 35.7 D NO HEATED SLEEVE USED 20 4.8 19.7 8.3 36.8 ____________________________________________________________ ______________ *Measured at 1.5 inches below the face of spinnerette 19 and 1 inch from the filament bundle with a special radiation shielded thermocouple. **To meet acceptable commercial plant standards in yield and quality of yarn.
This invention relates to an improvement in the apparatus used in melt extruding filaments and is more particularly related to an improved apparatus for critically controlling the rate of cooling melt extruded filaments after the filaments have left the spinnerette in order to produce greater cross-sectional uniformity in the undrawn filaments and improved physical properties in the drawn yarn.
It is known in the art that the melt extrusion of filaments is greatly improved by controlling the cooling of the filaments as they extrude from the spinnerette under critical temperature conditions. Suitable temperature control can be accomplished by surrounding the filaments, as they extrude from the spinnerette, with a heater provided with means for regulating the amount of heat supplied at various distances from the spinnerette. Such a heater is commonly known in the art as a heated sleeve.
The prior art discloses that such a heater or heated sleeve can be constructed by imbedding insulated wires having a high electrical resistance inside a metal cylinder which surrounds the melt extruded filaments as they leave the spinnerette. Such a heater construction has the disadvantage of producing areas of uneven temperature or hot spots, as they are commonly called, at the points where the insulated wires are imbedded inside the metal cylinder. These hot spots tend to produce non-uniformity in the cross-sections of the melt extruded filaments. Furthermore, such a heater is difficult and expensive to construct since wires having a high electrical resistance have to be first insulated and then imbedded inside the metal heater. Finally, such a heater has a high rate of oxidation which limits its useful life to below practical limits.
The prior art also discloses that a heater or heated sleeve can be constructed by inserting heating rods or coils around the inner surface of a non-conductive cylinder, usually a ceramic material, which surrounds the melt extruded filaments as they leave the spinnerette. This type of heater construction also has the disadvantage of producing areas of uneven temperature or hot spots in the area near the heating rods or coils which produce nonuniformity in the cross-sections of the melt extruded filaments. Such a heater is also difficult and expensive to construct. Furthermore, ceramic materials are brittle and do not stand up to normal industrial abuse.
The prior art heaters or heated sleeves described above have the further disadvantages in that they require high voltages for proper operation and these high voltages present a very serious shock hazard. As a result, relatively expenive safety measures are required in order to safeguard personnel operating equipment whereon these heaters or heated sleeves are used.
It has now been discovered that a heater or heated sleeve for controlling the temperature around the filaments, as they extrude from the spinnerette, can be constructed from a material having an electrical resistivity wherein the material used as the heated sleeve functions both as the heated sleeve and the heating element thereby greatly simplifying the design and construction of the heated sleeve and eliminating the problem of hot spots in prior art heated sleeves which produced non-uniformity in the cross-sections of the melt extruded filaments.
Furthermore, the novel heater or heated sleeve of the present invention requires only low voltages for proper operation and these low voltages eliminate the shock hazard present in the prior art heaters or heated sleeves. Thus, the expensive safety measures which were required in order to safeguard personnel operating equipment whereon the prior art heaters or heated sleeves were used are now no longer necessary.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an improved apparatus for critically controlling the rate of cooling a melt extruded filament which comprises a sleeve constructed from a material having an electrical resistivity. The sleeve is equipped with an electrical power supply input means for heating the sleeve to provide a heated environment within the sleeve.
The dimensions of a typical heated sleeve of the present invention which is cylindrical in shape can be determined from the following formula:
TL(D -1 ) = 2.05 PR(E -2 )(10 -7 )
wherein:
T is the average sleeve thickness, inches.
L is the sleeve axial length, inches.
D is the sleeve diameter, inches.
P is the power input requirement of the sleeve, watts.
E is the voltage supplied to the sleeve, volts.
R is the electrical resistivity of the material the sleeve is constructed from, ohms per circular mil.-foot.
In accordance with the above formula, the thickness, T, of the sleeve can range from about 0.001 to 0.125, preferably about 0.016 to 0.025, inch and the thickness can vary from the top of the sleeve to the bottom thereby producing different temperatures profiles within the sleeve. The axial length, L, of the sleeve can range from about 1 to 12, preferably about 3 to 6 inches and the diameter, D, of the sleeve can range from about 3 to 20, preferably about 6 to 10, inches. The power input requirement, P, of the sleeve can range from about 200 to 5,000, preferably about 700 to 1,200 watts and the voltage, E, supplied to the sleeve can range from about 1 to 12, preferably about 2 to 6, volts. The voltage, E, can be A.C. or D.C. but preferably is A.C. The electrical resistivity, R, of the material from which the sleeve is constructed can range from about 10 to 870, preferably about 60 to 675, ohms per circular mil-foot. The amperage of the current passing around the sleeve can range from about 100 to 3,000, preferably about 200 to 600 amps.
The temperature of the sleeve can range from about 200 to 525, preferably about 275 to 375, °C thereby creating a heated environment within the sleeve which can range from about 175 to 450, preferably about 250 to 350, °C.
The sleeve can be constructed from any material having an electrical resistivity within the above defined ranges and having sufficient structural strength and oxidation resistance to provide a dimensionally stable sleeve thereby conforming to the above defined thickness, axial length, and diameter ranges. Certain metals are particularly advantageous for use in forming the heated sleeve of the present invention. Suitable metals include Chromel A (1) (Ni 80%-Cr 20%), Chromel C (1) (Ni 60%-Cr 16%-Fe 24%), Chromel D (1) (Ni 35%-Cr 20%-Fe 45%), Chromax (2) (Ni 35%-Cr 20%-Fe 45%), Kanthal (3) (Cr-Al-F), Lohm (2) (Cu 94%-Ni 6%), Grade "A" nickel (Ni 99%), Nichrome (2) (Ni 60%-Cr 16%-Fe 24%), Nirex (2) (Cr 13%-Fe 8%-Ni 79%), stainless steel, preferably types 304, 310, 316 and 410 stainless steel, and the like and suitable sintered, porous, perforated, expanded, or felt metals of those metals described above. The preferred metals are those metals which will form a black oxide coating when heated. A high emissivity of 0.6 to 0.98 to a black surface of the same temperature can be obtained with such metals by the principle of black-body radiation heating. Also suitable are semiconductive materials such as titania, graphite and the like.
The electrical power supply means for heating the sleeve to provide a heated environment within the sleeve can be controlled by either a manual means or an automatic means. A typical manually controlled power supply means can comprise a high voltage power source connected to a step-down transformer or auto-transformer. The power input to the heated sleeve can be controlled by a variable rheostat which is connected in series with the primary side of the step-down transformer. The temperature of the heated sleeve or the heated environment within the heated sleeve can be determined by suitable temperature sensing means such as a thermister, thermocouple, or optical pyrometer and the variable rheostat can accordingly be manually adjusted to provide the desired temperature in the heated sleeve and in the heated environment within the heated sleeve.
Accordingly, a typical automatic power supply means can comprise a high voltage power source connected to a step-down transformer. The power input to the heated sleeve can be controlled by an automatic electrical temperature controller which contains a temperature sensor and a power control. The temperature sensor of the automatic controller is connected to or is adjacent to the heated sleeve and the power control of the automatic controller is connected in series with the primary side of the transformer. The temperature of the heated sleeve or the heated environment within the sleeve is determined by the temperature sensor, which can be any suitable temperature sensing means such as a thermister, thermocouple, or optical pyrometer. The temperature sensor relays a temperature control signal to the automatic temperature controller which in turn regulates the power supplied to the sleeve by the step-down transformer. Thus, the desired temperature is maintained in the heated sleeve and in the heated environment within the heated sleeve.
For purposes of definition in this application, the terms low voltage, high voltage, low amperage, and high amperage are generally defined as follows:
Low Voltage -- 24 volts or less
High Voltage -- 110 volts or more
Low Amperage -- 30 amps or less
High Amperage -- 50 amps or more
The heated environment within the sleeve can be an inert gas, for example, carbon dioxide, nitrogen and the like. The heated environment can also be continuously purged with an inert gas in order to exclude oxygen from the space between the face of the spinnerette and the point of solidification of the melt extruded filaments.
The cross-section of the sleeve of the present invention, perpendicular to the axis of the sleeve, can be any desired shape, for example, circular, elliptical, polygonal, that is, triangular, square, rectangular, pentagonal, hexagonal, octagonal and the like; starshaped, S-shaped and the like. The above defined parameters of T, L, P, E and R as defined above also apply to these cross-sectional sleeve shapes.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a typical heater or heated sleeve of the present invention wherein the material used as the heated sleeve functions both as the heated sleeve and the heating elment.
FIG. 2 is a cross-sectional view showing a typical heater or heated sleeve of the present invention, wherein the material used as the heated sleeve functions both as the heated sleeve and the heating element, positioned in a filament melt extrusion apparatus.
FIG. 3 is a top-sectional view showing a typical heater or heated sleeve of the present invention positioned in the filament melt extrusion apparatus below the spinnerette assembly.
Referring now to FIG. 1, the heated sleeve 11 can be formed into a cylindrical configuration from flat sheet stock material having the required electrical resistivity. Ends 12 of the flat sheet stock are folded towards the outer surface of the heated sleeve 11 to form channels 13 wherein electrical bus bar conductors 14 are positioned on the heated sleeve 11. Electrical conductors 14 which are positioned in channels 13 are secured to the ends 12 of the heated sleeve 11 by mechanical fastening means 15 which can be bolts, rivets or the like. A good electrical contact can be formed between electrical conductors 14 and the heated sleeve 11 by silver soldering or brazing the joints. Insulation means 16 is inserted between folded ends 17 of heated sleeve 11 to prevent folded ends 17 from contacting each other and thereby short circuiting the heated sleeve 11. Insulation means 16 can be any conventional insulating means such as porcelain, glass, asbestos, mica, or a resin such as phenolic. Insulation means 16 can be held in place by riveting or bolting through folded ends 17.
Referring now to FIG. 2, the heated sleeve 11 is positioned in filament melt extrusion apparatus 18 as shown in FIG. 2. Filament melt extrusion apparatus 18 comprises spinnerette assembly 19, cylindrical wall 21, filament quenching and cooling chamber 22 and a filament take-up means (not shown). Cylindrical wall 21 surrounds and encloses filaments 26 extruding from spinnerette 19. Quenching and cooling chamber 22 is connected to the lower portion of cylindrical wall 21. Filaments 26 extruding from spinnerette 19 are quenched and then cooled in chamber 22.
The Heated sleeve 11 is positioned within cylindrical wall 21 below the face of spinnerette 19 and is held in position by non-conductive ceramic support rods 23 which protrude inward from their location in cylindrical wall 21 and by electrical conductors 14 which protrude through cylindrical wall 21. Electrical conductors 14 are supported in and insulated from cylindrical wall 21 by insulators 24. Insulators 24 can be any conventional insulating means such as porcelain, glass, asbestos, mica or a resin such as phenolic. Low voltage electric power is supplied to electrical bus bar conductors 14 by power supply means 20 thereby heating sleeve 11.
In one embodiment of the present invention, there is small space or gap 25 between the top of heated sleeve 11 and the face of spinnerette 19 which can range from about 1/8 to 4 inches, preferably from about 1/4 to 3/4 inch. This embodiment of the present invention is called on "open-end" heated sleeve.
In another embodiment of the present invention, gap 25 is filled by a suitable insulation material (not shown) which can be porcelain, glass, asbestos, mica or fiberglass thereby closing gap 25 and sealing heated sleeve 11 around filaments 26. This embodiment of the present invention is called a "closed-end" heated sleeve.
The "open-end" heated sleeve as described above stresses simplicity in design and produces streamline gas flow within the heated sleeve. This streamline gas flow within the heated sleeve is believed to produce better cross-sectional uniformity in the filaments than eddying gas flow which is characteristic within a "closed-end" heated sleeve. Eddying gas flow within a "closed-end" heated sleeve can cause filament movement which may produce poor cross-sectional uniformity in the filaments. The "open-end" heated sleeve can be converted to a "closed-end" heated sleeve with the addition of an insulating ring conforming to the dimension of the space or gap between the face of the spinnerette and the heated sleeve.
The streamline gas flow within the "open-end" heated sleeve is cocurrent with the filament line. A predictable gas flow can be obtained by measuring the thermal differences adjacent to the filaments and the aerodynamic drag on the filaments. The streamline gas flow within the "open-en" heated sleeve is believed to produce better performance than the "closed-end" heated sleeve with respect to convection heat transfer and filament movement. This results in the gas temperature surrounding the spinnerette being very close to the sleeve temperature.
A black matte sleeve surface will produce radiation heating of the gas molecules and will add to the overall heat transfer coefficient of the heated sleeve.
The test data indicate that, because of the streamline gas flow and the uniform cooling rate produced by the "open-end" heated sleeve, better cross-sectional uniformity in the undrawn filaments and better denier uniformity, higher ultimate tensile strength and elongation in the drawn yarn can be obtained using the "open-end" heated sleeve of this embodiment of the present invention than can be obtained without the use of a heated sleeve.
The "closed-end" heated sleeve as described above operates on the principle that the stagnant gas temperature within the heated sleeve is the predominant factor in controlling the rate of solidifying or quenching of the filaments. The gas temperature within the heated sleeve is varied by the surface temperature of the heated sleeve which is controlled by the power input to the sleeve and by gas convections which are uncontrolled because of thermal currents within the heated sleeve and aerodynamic drag on the filaments.
A change in the "closed-end" heated sleeve surface temperature, assuming air convection to be within normal limits, will result in a smaller change in gas temperature. A change in gas temperature, however, will result in an even smaller change in the temperature of the filaments at the lower end of the heated sleeve.
As with the "open-end" heated sleeve, a black matte sleeve surface will produce radiation heating of the gas molecules and will add to the overall heat transfer coefficient of the heated sleeve.
Referring now to FIG. 3, the above described components of FIG. 2 are shown in a top-sectional view from spinnerette 19.
In operation, synthetic filaments 26 are melt extruded through spinnerette 19 and are passed through the heated environment within heated sleeve 11. Heated sleeve 11 is heated by a low voltage, high amperage electrical power supplied by power supply means 20. The electrical power supplied to heated sleeve 11 can range from about 200 to 5,000, preferably about 700 to 1,200, watts at a voltage of about 1 to 12, preferably about 2 to 6, volts. The temperature of sleeve 11 can range from about 200 to 525, preferably about 275 to 375, °C thereby creating a heated environment within sleeve 11 which can range from about 175 to 450, preferably about 250 to 350, °C. The rate of solidifying or quenching of filaments 26 is thereby controlled by the heated environment within heated sleeve 11. Filaments 26 are then passed through chamber 22 where they are quenched and cooled and are then wound on a suitable takeup means (not shown).
PREFERRED EMBODIMENTS
The following example illustrates the practice and principles of this invention and a mode of carrying out the invention.
EXAMPLE
In the operation of the heated sleeve of FIG. 1 positioned in the apparatus as shown in FIG. 2, polycaproamide was melt extruded at a temperature of 260°C, under a pressure of 3,500 psig through 204-orifice spinnerette assembly 19, each of the orifices having a diameter of 0.022 inch, to produce a 6,000 denier undrawn fiber comprised of filaments 26. The polycaproamide was melt extruded through spinnerette 19 at a rate of 45 pounds per hour.
Heated sleeve 11 was fabricated from type 304 stainless steel into a cylindrical configuration as shown in FIG. 1 and had an outside diameter of 7.5 inches, a length of 4 inches and a metal thickness of 0.020 inch. Heated sleeve 11 was of the "open-end" type as described in the Description of the Drawings and was positioned below spinnerette 19 thereby creating space or gap 25 between the face of spinnerette 19 and the top of heated sleeve 11 which had the dimension of one-fourth inch.
As filaments 26 were extruded from spinnerette 19, they were passed through heated sleeve 11 and were then passed through quenching and cooling chamber 22 and taken up on a suitable take-up means (not shown). The heated environment within heated sleeve 11 was air. The undrawn fiber thus produced was then drawn into yarn. The results of several runs using different power inputs to heated sleeve 11 and a control run using no heated sleeve are contained in Table I below.
As can be seen from the data contained in Table I, the heated sleeve of the present invention produced a significant improvement in yarn physical properties as compared to the physical properties of yarn produced using no heated sleeve. The heated sleeve of the present invention produced best results when it was operated with an optimum or near optimum power input of 300 to 500 watts which created a desirable heated environment within the heated sleeve surrounding the extruding filaments.
It is interesting to also note that the heated sleeve of the present invention produced improved yarn physical properties as compared to the physical properties of yarn produced using no heated sleeve even when no power was supplied to heat the sleeve. This improvement in yarn physical properties can be attributed to the fact that the sleeve retained, around the extruding filaments, some of the heat given off by the extruding filaments which otherwise would have been dissipated. This illustrates a further advantage of the heated sleeve of the present invention wherein the diameter of the heated sleeve of the present invention can be much smaller than prior art heated sleeves because of its simplicity in design. Because of this simplicity in design, the spin packs are not removed through the sleeve during a pack change. This smaller diameter of the heated sleeve of the present invention therefore permits more heat to be retained around the extruding filaments thereby decreasing power requirements and producing yarns having improved physical properties.
TABLE I ____________________________________________________________ ______________ AIR CROSS- ULTIMATE POWER SURFACE TEMPERA- SECTION TENSILE TOUGH- INPUT TEMPERA- TURE SPREAD OF ULTIMATE STRENGTH NESS TO HEATED TURE OF WITHIN UNDRAWN MAXIMUM ELONGA- OF YARN INDEX OF RUN SLEEVE 11, HEATED HEATED FILA- YARN TION OF (UTS), YARN NUM- WATTS SLEEVE 11, SLEEVE MENTS, DRAW YARN (UE), GRAMS PER (UTS) BER (A.C.) °C 11, °C* MICRONS RATIO** PERCENT DENIER (UE)1/2) ____________________________________________________________ ______________ A 0 174 184 18 5.1 14.6 8.8 33.6 B 300 242 232 16 5.1 15.4 9.3 36.5 C 1,100 360 338 15 4.9 15.4 9.1 35.7 D NO HEATED SLEEVE USED 20 4.8 19.7 8.3 36.8 ____________________________________________________________ ______________ *Measured at 1.5 inches below the face of spinnerette 19 and 1 inch from the filament bundle with a special radiation shielded thermocouple. **To meet acceptable commercial plant standards in yield and quality of yarn.