US2437703A

US2437703A - Process and apparatus for the extrusion of fused artificial materials

Info

Publication number: US2437703A
Application number: US519613A
Authority: US
Inventors: Moncrieff Robert Wighton
Original assignee: Celanese Corp
Current assignee: Celanese Corp
Priority date: 1943-01-04
Filing date: 1944-01-25
Publication date: 1948-03-16
Anticipated expiration: 1965-03-16
Also published as: GB565981A

Description

March 16, 1948. R. w. MONCRIEFF 2,437,703

PROCESS AND APPARATUS FOR THE EXTRUSION 0F FUSED ARTIFICIAL MATERIALS Filed Jari. 25, 1944 ?0 FIG. I

ff 4 1 ii I iii; I

1 B R-w-MoNcmEFF 50 6 TATES' PATENT OFFICE PROCESSv AND APPARATUS FOR THE EX- 1 TRUSSiON OF FUSE!) ARTIFICIAL MATE- Robert Wighton Moncrieff, Spondon, near Derby, England, assiznor, by mcsnc assignments, to Celanese Corporation of America, a corporation oi Delaware Application January 25, 1944, Serial No. 519,613 lin Great Britain January 4, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires January 4, 1963 This invention relates to the production of artificial materials and particularly to the spinning I from the fact that the composition, whether solid or molten, is a poor conductor of heat. The first of these facts limits the time during which it is permissible for the composition to be exposed to the temperature necessary to melt it while the second makes it diflicult to melt the composition in the limited time available and to avoid locally heating the composition to a temperature above "that at which the composition decomposes. It is an object of the present invention to provide a method and means for carrying out this operation in which, these difficulties are overcome or substantially reduced.

According to the present invention a process for the spinning or otherwise shaping by extrusion of a molten organic filament-forming composition comprises feeding the composition be low the surface of a body of liquid that is inert to and of greater density than the composition and is maintained at a temperature sumciently high to melt the composition as it passes upwards through said inert liquid, and withdrawing the molten composition from the surface of said inert liquid and extruding the molten composition. By immersing the solid composition in a hot liquid, heat is applied to the whole surface of the solid composition so as to achieve rapid and complete melting of the composition, and at the same time the liquid character of the heating medium enables the temperature applied to the solid composition to be substantially uniform by reason of convection and heat conduction through the body of the medium, and avoids local overheating.

Preferably, the liquid employed is a molten metal of a specific gravity several times that of the filament-forming composition employed. Use of a molten metal not only enables a very substantial difference between the specific gravities of the heating fluidand the composition being heated to be obtained, but also has the advantage of high thermal conductivity,

For the purpose or feeding the solid composition below the surface of the molten metal, the main body of the metal may be enclosed in a vessel communicating at the bottom with a chamber or passage to the bottom of which the solid composition can be forced by suitable mechanical means. Means may be provided to maintain the quantity of molten composition available in the melting vessel by employing the level of the molten com osition within the chamber as a control.

Thus, the rise and fall of the level of the molten composition may make and break an electrical contact by means of which the feeding means may be intermittently driven and stopped. Alternatively, the making or breaking of an electrical contact in this manner may serve to give a visual indication of the amount of molten composition available, the further supply of solid composition being controlled manually in accordance with such visual indication.

In order to prevent solid composition from reaching the surface of the molten metal, a grid or sieve is provided a short distance below said surface in order to strain the composition and retain any pieces of solid composition until they are melted. On reaching the surface of the molten metal, the melted composition constitutes a reservoir or pool from which material is drawn for the purpose of spinningorextrusion. Thus, the

molten composition may be extruded by means of I a constant-delivery pump supplied through a tube which rises up through the body of molten metal and terminates at its upper end in a funnel over the edges of which the molten composition flows. Alternatively, the molten composition may flow over a sill or weir into the supply pipe of the spinning pump, or again, the pump may be disposed above the pool of molten composition so as to draw the composition directly upwards from said pool. Difilculties in initiating the flow of molten composition through the pump, arising from a high viscosity in the molten composition, can be reduced or overcome, if necessary, by priming the pump with a material that is more readily fusible than the composition, or that has a lower viscosity at the temperature at which the comheat-insulated unit.

tus along with the composition a substance that forms with the composition a. freely flowing solution, which solution primes the pump and enables the spinning of the molten composition itself to proceed.

The apparatus is preferably arranged so that the quantity of molten composition available for extrusion at any time is reduced to a minimum consistent with the maintenance of a constant supply. In this way, the period during which the composition is exposed to the temperature necessary to melt it is further reduced. For reasons of lightness and economy, it is also desirable that the mass of molten metal employed should be as small as possible having regard to its function as a reservoir of heat from which heat is drawn to melt the composition employed. If desired, the apparatus may be arranged so that two or more pumps may be fed from a single pool or reservoir of molten composition.

The heating of the molten metal may be effected by any convenient means according to the temperature to be maintained and other relevant considerations. Thus. the vessel in which the composition is melted may be enclosed in a Jacket containing a heating fluid or it may be surrounded with electrical windings. Or again, the molten metal may be heated in a separate vessel and circulated through the vessel in which the composition is melted, or through several such vessels. The whole apparatus is preferably externally lagged so as to prevent loss of heat and discomfort to the operatives. Whatever means are employed for the application or heat to the apparatus, a steady temperature should be maintained in every part of the apparatus containing the molten metal or the molten composition. Thus, it is convenient for the vessel containing the main body of molten metal and the chamber through which the solid composition is led, and also the pump by means of which the molten composition is extruded, to be enclosed together as a single The heat capacity of the unit may be augmented by including in its structure large bodies of metal. Thus, for example, the spinning or extruding pump may be surrounded by a heavy block of metal or by a mass of metal turnings or filings so as to provide a reservoir of heat to prevent undesirable fluctuations in temperature.

Control of the heat supplied to the apparatus can be effected by suitable temperature-regulating means in accordance with the temperature existing within the apparatus. While it is desirable to supply heat to all parts of the apparatus containing molten metal or molten composition, separate sources oi heat under separate temperature controls may be employed for the diflerent parts, e. g. one control for the main compartment, another for the supply compartment, and another for the pump and the passage by which the molten composition is fed to it. Or again, the supply of heat to the main and supply compartments may each be effected by circulation oi! molten metal separately heated. and controlled by controlling the circulation, while the heating of the pump and the control of that heating may be effected electrically.

The invention is applicable generally to the spinning or extrusion of organic filament-forming compositions that may be spun in the molten state and is particularly advantageous where, as is commonly the case with such compositions, the compositions are liable to decompose or be otherwise injuriously affected at temperatures not much exceeding those necessary to melt them. Examples 0! such materials are the synthetic linear superpolyamides, e. g. those obtainable by the condensation of diamines with dicarboxylic acids. Or the composition may have a basis of a polyvinyl compound, e. g. polyvinylidene chloride or a copolymer of vinyl chloride and vinyl acetate. Or again, the invention may be applied to compositions having a basis of a cellulose derivative such as an organic ester or mixed ester of cellulose, e. g. cellulose acetate, cellulose propionate or celullose butyrate, cellulose acetatebutyrate, cellulose acetate-propionate and cellulose acetate-stearate or cellulose ethers such as ethyl and benzyl cellulose.

The method and apparatus described above may be modified in various ways. Thus, instead of a molten metal, an organic substance that is 'of greater density than the composition and is liquid at the appropriate temperatures may be used.

By way of example, apparatus embodying the present invention will now be described in greater detail with reference to the accompanying drawings in which Figure 1 is a sectional side elevation of the complete apparatus,

Figure 2 shows a detail of Figure 1, and

Figures 3 and 4 show two alternative forms of feed device which may be used instead oi that shown in Figure 1.

Referring to Figure 1, the apparatus comprises generally a supply chamber l, a melt chamber 2, a pump chamber 3 and a filter and spinning jet assembly 4, all assembled as a unit and enclosed in a block 5 of insulating material that is built up round the assembly. A communicating passage 8 slopes obliquely upwards from the bottom of the supply chamber I, to the bottom of the melt chamber 2. The supply chamber I and melt chamber 2 are almost filled with a molten alloy comprising approximately equal parts by weight of tin and lead and melting at about C., the main body I of the molten metal being contained in the melt chamber 2.

The supply chamber l contains a supply wheel 8, the chamber I being shaped to conform to the periphery of the wheel 8 and to leave a clearance. Round the periphery of the wheel 8 are recesses 9 adapted to receive short cylindrical rods ID of the composition to be spun or extruded, the rods l0 being fed to the wheel 8 by way of a chute l I. The wheel is mounted on and driven by a shaft I2 extending through the side of the supply chamber I. Heat is supplied to the chamber by means of a flat heating element [3 held in contact with the wall of the chamber by a cover plate ll. In this way the metal in the chamber is kept at a temperature a little over its melting point. At the bottom of the supply chamber 1 is a shoe or ram l5 lying outside the periphery of the wheel 8 in the clearance between the wheel and wall of the chamber I. the shoe l5 being adapted to engage the rods of composition In as the recesses 9 containing them reach the bottom of the chamber, and to push them sideways out of the recesses so that they float upwards through the oblique passage 6 into the melt chamber 2.

In the melt chamber 2 the pieces of solid composition fioat upwards until they encounter a perforated sheet l8 extending completely across the chamber 2 and constituting a grid to allow molten composition to pass through. While' solid, however, the composition remains on the underside of the sheet 16 as indicated at IT.

Heat is supplied'to the melt chamber 2 by means of a heavy electrical winding I8, by means of which the molten metal I is maintained at a temperature sumcient to melt the pieces of composition I l by surface contact. The temperature of the molten metal in the chamber 2 is higher than that in the chamber I, the latter bein maintained only slightly above the melting point of the metal in order that premature melting of the sticks of composition Ill may not take place.

The melted composition passing through the perforations in the sheet I rises to the surface of the body of molten metal I and forms a pool or reservoir 19 from which the molten composition is drawn for spinning or extrusion. An atmosphere of nitrogen is maintained over the surface of the molten composition 19 by means of a supply pipe 28 the nitrogen escaping by way of a relief pipe 2| which may be provided with a relief value so as to maintain a slight but constant pressure in the top of the melt chamber. Fioating on the surface of the molten composition I9 is a float 22 carrying contact rod 23 adapted to make and break contact with a further contact rod 26 carried by and insulated from the top of the melt chamber 2. These are shown diagrammatically in Figure l and in greater detail in Figure 2. The rod 23 passes through a guide plug screwed into a. sleeve 28 which is let into the top of the chamber 2 and extends through the insulating material I. The rod 24 is held in the sleeve 28 by means of insulating packing 21 compressed into position by means of a screw 28 through which the rod 24 passes without making n By these means an electrical circuit between the rod 24 on the one hand and the molten composition H9 or the wall of the vessel 2 on the other may be made or broken as the level of the molten composition in the chamber 2 rises and falls. The circuit may be adapted to give a. visual indication so that the wheel 8 may be driven by hand for the feeding of fresh composition, or the wheel may be driven by a motor acting on the electrical circuit between

rods

22 and 24. An indicator lamp 1 may be arranged in electrical cir- I cult d. The upper section 30 of the melt chamber 2 converges towards the top so as to be of relatively small. cross section at the part containing the pool of molten composition IS. The molten composition flows over a sill 3! into a funnel 32 communicating with the spinning pump 33 contained in the pump chamber 3. The pump chamber 3 is.

formed of sheet metal and is tightly packed with copper turnings as so as to provide a high heat capacity. The pump 33 is driven by means of a pump shaft 35 and forces the molten compositlon through a pipe 38 and filter 37 to a spinning jet 38. ,Light electrical windings 38 may be provided round the communicating passage 8, the funnel 32, the pump chamber 8 and the filter and jet assembly d so as to compensate for slight heat losses by radiation.

Figure 3 shows an alternative form of feeding device which may be used in place of the wheel 8. The oblique r described with reference to Figure 1 communicates at its lower? end with a vertical tube 40 having an internal groove 4| on the side adjacent to melt chamber 2, and containing a screw 42 fitting closely inside.it. The shaft 43 of the screw passes through the cover 44 of the tube 40 and is driven by means of a wheel 45 and worm 46. Short cylinders of composition l0, similar to those described with reference toFigure 1 are fed along horizontal guideway 41 to the top of the tube 58, the radius of which is slightly enlarged on one side so as to be equal to the radius of the bottom of the groove 4|. The pieces of composition l9 enter the top of the tube tangentially and pass horizontally round it under the influence of the screw. resting on the ledge 48 formed by the enlargement of the top of the tube 40. When they reach the groove 4!, however, the screw forces them down the tube as indicated at 49. At the bottom of the tube 40, the shaft 63 is enlarged to a conical form at 50 so as to tilt the pieces of composition outwards and to allow them to float up the communicating passage 6. Preferably, the screw $2 is constantly driven, the cylinders of composition It being fedto it when fresh composition is required in the melt chamber 2 as indicated by the state of the circuit including the contacts 23. 24.

Figure 4 showsa simple form of feeding device constituted by a mere oblique tube 6! containing a plunger 52 having a disc 53 on the inner if end thereof, and a handle 54 at the outer end.

By these means pieces of composition may be dropped into the open end of the tube El and forced down by means of the plunger 52 so as to be able to float upwards through the communieating passage 6.

Having described my invention, what I desire to secure by Letters Patent is:

1.Process for the extrusion of a fusible organic filament-forming composition comprising feeding the composition upwards through a liquid that is inert to and of greater density than the composition, maintaining said inert liquid at a temperature sufficiently high to melt the composition during its passage through said inert liquid, withdrawing the molten composition from the surface of said inert liquid and extruding said molten composition.

2. Process according to claim 1, wherein the inert liquid is a molten metal having a specific gravity several times that of the composition.

3. Process according to claim 1, wherein the inert liquid is a molten metal that is an alloy of equal parts by weight of tin and lead.

4. Process for the extrusion of a fusible organic filament-forming composition comprising feeding the composition upwards through a liduid that is inert to and of greater density than the composition, maintaining said inert liquid at a temperature sufllciently high to melt the composition during its passage through said inert liquid, straining the composition while it is in said inert liquid so as to prevent solid composition from reaching the surface of said inert liquid, withdrawing the molten composition from the surface of said inert liquid and extruding said molten composition.

5. Process for the extrusion of a fusible organic filament-fanning com-position comprising feeding the composition upwards through a molten alloy of equal parts by weight of tin and lead, maintaining said alloy at a temperature suf-" position while it is in said alloy so as to prevent,

solid composition from reaching the surface of 6. Apparatus for the production of artificial materials by the extrusion of fusible organic filament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel, a charge of a metal of low melting point in said vessel, means for melting said metal and heating it to a temperature sufilcient to melt said composition, means for feeding solid composition into the molten metal below the surface thereof and means for withdrawing molten composition exclusively from above the surface of said molten metal for extrusion by said extrusion means.

7. Apparatus for the production of artificial materials by the extrusion of fusible organic filament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel, a charge of an alloy of equal parts by weight of tin and lead within said vessel, means for melting said alloy and heating it to a temperature sumcient to melt said composition, means for feeding solid .oomposition'below the surfaceof. the molten alloy and means for withdrawing molten compo sition exclusively from above the surface of said molten alloy for extrusion by said extrusion means.

8. Apparatus for the production of artificial materials by the extrusion of fusible organic fllament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel adapted to contain a liquid that is inert to and of greater density than the composition to be spun, means for heating said liquid to a temperature sufficient to melt said composition, a float within said vessel, a contact carried by said float and adapted to engage a stationary contact, an electric circuit adapted to be closed by the engagement of said contacts, automatic means under the control of said circuit for feeding solid composition below the surface of said liquid on opening of said circuit so as to maintain the level of said float substantially constant and means for withdrawing molten composition exclusively from above the surface of said liquid for extrusion by said extrusion means.

9. Apparatus for the production of artificial materials by the extrusion of fusible organic filament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel adapted to contain a liquid that is inert to and of greater density than the composition to be spun, means for heating said liquid to a temperature sufficient to melt said composition, a wheel for feeding solid composition below the surface of said liquid, said wheel dipping below the surface of said liquid and having recesses in the edge thereof for receiving and carrying downwards pieces of solid composition and means for withdrawing molten composition exclusively from above the surface of said liquid for extrusion by said extrusion means.

10. Apparatus for the production of artificial materials by the extrusion of fusible organic filament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel adapted to contain a liquid that is inert to and of greater density than the composition to be spun, means for heating said liquid to a temperature suflicient to melt said composition, a screw and casing for feeding solid composition below the surface of said liquid, said casing communicating with the bottom of said vessel and having a longitudinal groove to guide pieces of composition forced down it by said screw, and means 101 withdrawing molten composition exclusively from above the surface of said liquid for extrusion by 'said extrusion means.

11. Apparatus for the production of artificial materials by the extrusion of fusible organic iiiament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel adapted to contain a liquid that is inert to and of greater density than the composition to be spun, means for heating said liquid to a temperature suflicient to melt said composition, a float within said vessel,a contact carried by said float and adapted to engage a stationary contact, an electric circuit adapted to-be closed by the engagement of said contacts, a wheel for feeding solid composition below the surface of said liquid, said wheel dipping below the surface of said liquid and having recesses in the edge thereof for receiving and carrying downwards pieces of "solidmomposition driving means for said wheel under the control of said circuit and adapted to act on opening of said circuit so as to maintain the level of said float substantially constant and means for withdrawing molten composition exclusively from above the surface of said liquid for extrusion by said extrusion means.

12. Apparatus for the production of artificial materials by the extrusion of fusible organic filament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel, a charge of an alloy of equal parts by weight of tin and lead within said vessel, means for melting said alloy and heating it to a temperature sufficient to melt said composition, a float within said vessel adapted to float on the surface of the molten composition, a contact carried by said float and adapted to engage a stationary contact, an electric circuit adapted to be closed by the engagement of said contacts, automatic means under the control of said circuit for feeding solid composition below the surface of the molten alloy on opening of said circuit so as to maintain the level of said float substantially constant, a perforated grid extending across said vessel below the surface of said molten alloy and above the point at which the solid composition is fed thereto and means for withdrawing molten composition exclusively from above the surface of said molten alloy for extrusion by said extrusion means.

13. Apparatus for the production of artificial materials by the extrusion of fusible organic filament-forming compositions said apparatus comprising, in combination with extrusion means for extruding fused composition, a melting vessel, a charge of an alloy of equal parts by weight of tin and lead within said vessel, heating means for melting said alloy and heating it to a. temperature sufficient to melt said composition, a float within said vessel, a contact carried by said float and adapted to engage a stationary contact, an electric circuit adapted to be closed by the engagement of said contacts, a wheel for feeding solid composition below the surface of the molten alloy, said wheel dipping below the surface of said alloy and having recesses in the edge thereof for receiving and carrying downwards pieces, of solid composition, driving means for said wheel under the control of said circuit and adapted to act when said circuit is opened so as to maintain the level of said float substantially 5 constant, a perforated grid extending across said vessel below the' surface of said alloy and above the level to which the solid composition is carrled downwards by said wheel and means for withdrawing molten composition from the surface of said molten alloy for extrusion by said extrusion means. ROBERT WIGHTON MONCRIEFE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Hanson June 2, 1942