US2777160A - Control system, wet spinning process and apparatus - Google Patents

Description

Jan. 15, 1957 R, N. RULISON ETAL 2,777,160

CONTROL SYSTEM, WET SPINNING PRocEs AND APPARATUS Filed Dec. 15, 1952 FIGJ.

INVENTORS. RICHARD N.RULISON EDWARD T. JONES,JR. RUSSELL O. DENYES V WM ATTORNEYS.

United States Patent CONTROL SYSTEM, WET SPINNING PROCESS AND APPARATUS Application December 13, 1952, Serial No. 325,798

20 Claims. (Cl. 18-8) This invention relates to the production of artificial filaments and more particularly relates to a process and apparatus for producing wet-spun artificial filaments of uniform quality.

In the production of artificial filaments by the wet-spinning process, a spinning solution, i. e. a solution of the filament-forming material in a suitable solvent, is forced through a spinning jet having one or more orifices into a liquid coagulating medium, or spin bath, which causes the filament-forming material to set and which extracts at least a part of the solvent therefrom. The filaments thus produced pass through the spin bath and are then drawn from the bath, usually at a constant linear speed, by a godet roller. If it is desired to produce filaments of higher tenacity the filaments are stretched to a considerable degree during their passage through the spin bath and while they are still in a relatively plastic state. in all of these wet-spinning processes, and especially in the wet-spinning processes involving a substantial stretching of the still plastic filament, it has been difiicult to produce filaments whose characteristics are uniform throughout the length of the filament.

Non-uniformity of wet-spun filaments is often caused by variation in the coagulating characteristics of the spin bath during the spinning process. Such variations may result, for example, from changes in the temperature of the spin bath due to drafts. Conventional control devices, such as temperature controllers or specific gravity controllers, while useful, are generally inadequate to maintain the coagulating characteristics of the spin bath at a precise constant value throughout the process.

Another important cause of non-uniformity of wetspun filaments is the fact that the properties of the filament-forming material, which is usually a high polymer, may vary during the spinning process. For example, in the spinning of cellulose acetate solutions, the cellulose acetate being spun may vary, in the distribution of its molecular weight or in the distribution of its acetyl groups, during the spinning process. That is, two samples of cellulose acetate supplied to the spinning jets at different times during the process may have the same average molecular weights, but the distribution of the molecular weights in the samples may be different, with one sample having I more molecules of molecular weight above and below the average and fewer molecules of nearly average molecular weight. Similarly, two samples of cellulose acetate may have the same average degree of acetylation but one sample may have more molecules of both higher and lower acetyl content than the average and fewer molecules of nearly average acetyl content. Again, the molecules may have substantially the same acetyl content but the acetyl groups may be located in different parts of the long chain cellulose molecules. When the properties of the filament-forming material vary during the spinning process, it has been practically impossible to obtain filaments of uniform properties even if the coagulating characteristics of the spin bath are maintained substantially constant throughout the process.

It is, therefore, an object of this invention to provide an easily controlled process and apparatus for the wetspinning of artificial filaments of uniform characteristics throughout their lengths.

An additional object of this invention is the provision of a novel process and apparatus for the wet-spinning of filaments of uniform high tenacity and elongation.

further object of this invention is to provide a novel automatic control system particularly suitable for use in the wet-spinning of artificial filaments.

Still another object of this invention is the provision of a novel automatic control system which will automatically shift from automatic to manual control when there is a failure in the control system.

Other objects of this invention will appear from the following detailed description and accompanying drawing.

We have found that the properties of a wet-spun synthetic filament may be maintained substantially uniform along its length by varying the coagulated characteristics of the spin bath during the spinning process in such a manner as to maintain a substantially uniform tension on the filament at any chosen point in its path. In carrying out our invention, we measure the tension of the filamerit continuously at any chosen point and vary the coagulating characteristics of the spin bath in response to deviations in such tension. In other words, when the tension deviates from .a predetermined value, i. e. a control value, We change the coagulating characteristics of the spin bath in such a manner as to bring the value of the tension back to that predetermined control value. More particularly, when the tension on the filaments rises above the control value we increase the swelling power of the spin bath thereby decreasing the tension. Conversely, when the tension falls below the control value We decrease the swelling power of the spin bath, so that the tension is maintained substantially constant throughout the process.

We have found that a relatively slight variation in the coagulating characteristics of the spin bath causes a relatively marked variation in the tension on the filament, all other factors being constant. Thus, when the supply of filament-forming material available has substantially constant properties throughout the spinning operation, our invention makes it possible to control the coagulating characteristics of the spin bath at a substantially constant value much more precisely than the processes of the prior art wherein temperature controllers or specific gravity controllers are used, with the result that the filaments are much more uniform.

In addition, we have found that even when the properties of the filament-forming material available varies somewhat during the spinning process in the manner set out above, our invention causesan automatic adjustment of the coagulating characteristics of the spin bath to take care of these variations in properties, so that the filaments being spun still have uniform properties, e. g. uniform tenacity or elongation at break. In fact, we have found that our invention produces filaments of uniform properties even where there are significant variations in the average molecular weight or average chemical composition of the filamentary material being spun. For example, cellulose acetate filaments of uniform properties have been obtained when the average acetyl content varies about 0.2% during spinning, whereas in the spinning processes of the prior art such a variation in acetyl content would producea distinct change in the properties of the filament. Thus, when the filament-forming material is a blend of two or more different cellulose acetates, filaments of uniform properties are obtained despite variations in the composition of the blend and errors in the analysis of the blend and the components thereof.

The process of this invention may be used with a wide variety of spinning solutions and spin baths. For example, it may be used for spinning a solution of cellulose acetate in acetone intoa mixture of acetone and water; for spinning a viscose solution into a spin bath containing sulfuric acid; or for spinning a protein dispersion into an acid salt spin bath.

The coagulating characteristics of the spin bath may be varied in any desired manner, such as by changing the composition or the temperature of the bath. For example, when a solution of cellulose acetate in acetone is extruded into a spin bath comprising water and acetone the swelling power of the bath may be increased by raising the proportion of acetone in the bath or by raising the temperature of the bath. Conversely, the swelling power of the bath may be decreased by lowering the acetone concentration or the temperature. However, we prefer to vary the composition of the bath, e. g. the acetone/water ratio, rather than its temperature, since the composition can be varied muchmore rapidly in an accurate manner.

The apparatus of this invention includes a primary sensing or measuring device for measuring the tension on the filaments and means, operatively connected to this sensing device, for varying the coagulating characteristics of the spin bath. For example, a suitable sensing device includes a roller over which the filament passes, an inlet for receiving air under pressure and an outlet connected to an air pipe, the sensing device being so constructed that it causes the pressure of the air in the air pipe to vary in accordance with the variations in the tension on the filament passing over the roller. That is, the pressure of the air in the air pipe, which pressure may be termed the output of the sensing device, is a measure of, or a precalibrated function of, the tension on the filament. It is to be understood that we may use other sensing devices in which the output is delivered in a ditferent form e. g. sensing devices delivering electrical or hydraulic outputs. The output of the primary sensing device is transmitted to the means for varying the coagulating characteristics of the bath, which means comprises an ultimate control element, such as a valve or other device for changing the composition of the spin bath or a temperature regulator for varying the temperature of the bath.

Usually the spinning apparatus includes a plurality of spinning cabinets adapted to spin filaments under identical conditions, each cabinet receiving spinning solution from a common source. The individual spin baths employed with the said spinning cabinets are furnished from a main spin bath supply, and the coagulating characteristics of that main spin bath are varied by an ultimate control element which is operatively connected to the primary sensing device located on one of the spinning cabinets. However, we have found it advantageous to guard against failure in the mechanical elements of the control system by providing at least one additional secondary sensing device to measure the tension of the filaments being spun in another one of the cabinets of the spinning apparatus and by providing means, responsive to a substantial difference in the outputs of these two sensing devices, for disconnecting the entire system from automatic control. Since the primary and secondary sensing devices are identical and are located at corresponding points of the two cabinets, and since the spinning conditions in these two cabinets are identical, .the outputs of both sensing devices should be substantially equal except when there is a failure in the control system. Such a failure, which may result, for example, from extraneous matter in one of the sensing devices, from faulty lubrication or from a' break in a filament, will cause the outputs of the two sensing devices to drtfer substantially. When this happens, the means responsive to a substantial difference in the two outputs automatically removes the entire spinning arrangement from automatic tension control and places it under manual control. At the same time a visual or audible signal is turned on the warn the operating personnel that there is a defect which requires correction.

in a preferred embodiment of our apparatus the primary sensing device is connected with the ultimate control element, i. e. the valve for controlling the composition of the spin bath or the temperature regulator for the spin bath, through an auto-manual relay. This automanual relay, which is also connected to a manual control, is operated by compressed air. When the compressed air is supplied to the auto-manual relay the relay is moved to its automatic position, in which position it connects the ultimate control element only with the primary sensing device. When this compressed air supply is shut elf the relay is moved to its manual position, in which position it connects the ultimate control element only with the manual control. The compresed air supply for operating the relay is controlled by the primary and secondary sensing devices acting through a slotted vane connected with both of these sensing devices. When the outputs of the primary and secondary sensing devices are substantially equal, the vane permits air under pressure to pass through its slot, thus maintaining the relay in its automatic position, while when the outputs of the sensing devices differ substantially the slotted vane is caused to move to a position blocking the flow of air, thus causing the relay to move to its manual position. In practice, it is preferred not to supply the air passing through the slot directly to the auto-manual relay, but rather to use this air to operate a pilot, or booster, valve, through which air from a source at high pressure flows directly to the relay. By theme of a pilot valve it is possible to obtain a higher air pressure at the relay and thus insure positive operation of said relay.

In the drawing, wherein a preferred embodiment of this invention is shown,

Fig. 1 is a diagrammatic view of the spinning apparatus and control system, with parts omitted in the interest of clarity,

Fig. 2 is a cross-sectional view of a portion of the control system taken along the line 22 of Fig. 1.

Fig. 3 is a cross-sectional view of a portion of the spinning apparatus, showing details of a wiping zone thereof.

Like reference numerals indicate like parts in both views of the drawing.

The basic spinning apparatus comprises a wet-spinning cabinet indicated generally by reference numeral 11. A spinning solution, such as a solution of cellulose acetate in acetone, is pumped at a constant rate through an inlet 12 into the bottom of the wet-spinning cabinet 11, where it is extruded in filamentary form through a number of holes in a spinnerette (not shown). The extruded filaments 13 travel upwardly through a coagulating zone, indicated generally by reference numeral 14, filled with a moving coagulatingliquid spin bath, specifically a mixture of water and acetone, which is pumped at a constant rate into the coagulating zone 14 from a header 15, through a lower inlet pipe 16 and an upper inlet pipe 17. The coagulating zone 14 is of the type shown in the copending application of W..H. Bradshaw and R. O. Denyes, Serial No. 285,238, filed April 30, 1952, now Patent No. 2,732,586, and includes a lower spin pot 18 connected with lower inlet 16, a tapered lower spin tube 19, an upper spin pot 21 connected with upper inlet 17, and an upper spin tube 23. The filaments, which at this stage are in a parallel bundle hereinafter designated as a yarn, and the coagulating liquid emerge from the upper spin tube 23 intoa wiping zone 24. A major portion of the coagulating liquid is discharged from a conduit 26 at the bottom of this wiping zone 24, which is of the type disclosed in the copending application of Edward T. Jones. Jr., Serial No. 261,439 filed December 13, 1951, now Patent No. 2,674,112 of April 6,, 1954. In the wiping zone 24 the yarn passes through'slotted wiping elements 26a, which remove a certain amount of the liquid adhering to the wet yarn, and then through one or more suckers 2611 connected witha suction pipe 27. In passing through the suckers the yarn is subjected to suction to extract liquid from the yarn with a minimum of mechanical contact. After leaving the wiping zone 24, the yarn passes over a freely rotatable roller 28 and then over a driven godet roller 29, or other suitable drawing roller. The godet roller rotates at a constant speed and supplies the force for leading the yarn through the wiping zone 24. It is to be understood that after passing over the godet roller 29 the yarn may be subjected to any desired subsequent treatment, such as washing and drying, with or without a preliminary saponification step, all in a manner well known in the art.

The spinning apparatus includes another spinning cabinet 13 which is identical in every respect with spinning cabinet 11. This latter spinning cabinet is also supplied with coagulating liquid from the header 15 through inlet pipes 16 and 17. The yarn spun in said latter spinning cabinet passes over a freely rotatable roller 28' and is taken up on a take-up device 29' in exactly the same mannor as the yarn spun in cabinet 11. Any desired number of additional spinning cabinets of the same construction may be provided and operated in the same manner.

Turning now to the control system of our invention, the roller 2% forms part of a primary sensing device 31, which is a collecting transmitter of the type shown in the copending application of E. N. Schwenninger and James H. Hoii'man, Serial No. 310,226, filed September 18, 1952. lrimary sensing device 31 is connected with a compressed air source 33 and a compressed air conduit 34, and serves to control the pressure in conduit 34 in accordance with the yarn tension. in other words, through the action of primary sensing device 31 the pressure of the air in conduit 34' is adjusted to a value which is measure of, or a function of, the tension on the yarn in contact with roller 28. The pressure of the air in conduit 34 may be termed the output of primary sensing device 31. Compressed air conduit 3 transmits this output to a pressure controller 36, which is a conventional recording proportional controller having automatic reset response. Controller 36 is also connected with a primary air transmission line 37 supplied through controller 36 from an air supply line 33, which is in turn connected to a source of compressed air Variations in the pressure in air conduit 34 act on the controller 36 to vary the pressure in air transmission line 37 in a manner well known in the art. Air transmission line 3"! is connected, through a chamber 41 and a valve control pipe 42, with an air-controlled valve 43. Valve $3 is preferably of the air-opening type, in which an increase in the pressure in valve control pipe 42 causes the valve to open further. This valve 43 controls the rate of flow of acetone through an acetone pipe 44 to an acetone-water mixer 45, maintained at a controlled temperature, which supplies the spin bath to the spinning cabinet 11 through header 15. Water is fed to the mixer 45 at a constant rate through water pipe 46. In this way, a variation in tension in the yarn, which causes a change in the pressure in air pipe 34, acts on the controller 36 so as to change the pressure of the air in transmission line 37 and valve control pipe 42 and thus change the setting of valve 43. The controller 36 is adjusted to maintain the flow of acetone through valve 43 constant when the tension of the yarn, as indicated by the pressure in conduit 3-4, is at the desired predetermined control value and to increase and decrease this how of acetone when the ension on the yarn deviates above and below the control value.

The apparatus which disconnects the automatic controls when there is a failure in the tension control system includes a cylindrical auto-manual relay 47 of'which the cylindrical chamber 41 is a part. Chamber 41 is connected at one of its ends with the primary air transmission line 37, at its center with the valve control pipe 42, and at its other end with a by-pass air transmission line 42"; leading from the compressed air source 39 through a manually controlled pressure reducing valve 49. Chamher 41 is divided into two portions by a movablepiston 51, which serves to keep the air from the primarytransmission line 37 separate from the air from by-pass line 48.

As shown in Fig. l of the drawing, when this piston 51 is at the right hand side of the chamber 41 and abutting against a stop 52 the valve control pipe 42 is connected through the chamber 41 only with the primary air transmission line 37. When the piston 51 moves to the left and abuts against another stop 53, the control pipe 42 is connected through the chamber 41 only with the by-pass line 48. Piston 51 is mounted at one end of a piston rod 54, which passes througha cross Wall 55 and into a second cylindrical chamber 56 of the auto-manual relay 47. A second piston 57 is mounted at the other end of the piston rod 54 in the second chamber 56. Compressed air, supplied to the second chamber 56 from a pipe 58, pushes against the second piston 57 and forces the whole assembly of second piston 57, piston rod 54 and piston 51 to the right against the force of a compression spring 59. The compression spring 59 is located between piston 51 and the right end wall 61 of the chamber 41 and serves to move the piston 51 to the left when the supply of compressed air from pipe 58 to second chamber 56 is shut 05. The compressed air in pipe 58 is supplied from a source 61:: through a pilot valve 61b which is operated by compressed air from a pipe 610. The source of the compressed air in pipe die is a nozzle 62 ,(Fig. 2) which directs a stream of compressed air into the flared end 63 of pipe 610. On its way from nozzle 62 to the flared end 63 this stream of air passes through a slot 64 in a vane 66 mounted at one end of a lever 6.7 which pivots on a shaft 63. At its other end 69 the lever 67 is linked, through links 71 and 72, with air bellows 73 and 74 connected with compressed air conduits 34 and 76, respectively. Air conduit 76 is connected with a secondary sensing device 77, which is supplied with compressed air from a source 78. This secondary sensing device 77, which carries the roller 2%, is identical with the primary sensing device 31, and serves to measure the tension on the yarn passing over the roller 28' in exactly the same manner as the primary sensing device 31 measures the tension of the yarn passing over its roller 28. The pres: sure in air conduit '76 may be considered to be the output of secondary sensing device 77 just as the pressure in air conduit 34 may be considered to be the output of primary sensing device 31. When these two pressures are equal the bellows 73 and 74, acting through links 71 and 72 maintain the lever 67 in the position shown in the drawing, permitting a stream of air to flow from noz- 21c 62 through slot 64 into pipe 61c. However, when these-two pressures are unequal the bellows 73 and 74 will act to tilt the lever 67 sufficiently to move the slot 64 out of alignment with nozzle 62 and flared end 63, thus causing the vane 66 to obstruct the flow of air from nozzle 62 into pipe 610. Pipe 53 leading from the pilot valve 61]) is also connected with an alarm 79, of conventional construction, which provides a visual or audible indication or both, when air in pipe 58 is no longer under pressure.

In the operation of the apparatus of this invention, the output of the primary tension sensing device 31 acts through'the controller 36 to vary the setting of acetone valve 43 and thus varies the composition of main spin bath mixture in header 15 in a manner to maintain the tension of the yarn passing over roller 28 substantially constant. By adjustment of the controller 36 any desired control value of yarn tension may be maintained. The precise control value to be chosen depends on the product desired, the number of filaments per spinnerette, the denier per filament, the position of the sensing devices, the exact relationship of the wipers to the filaments and the various other mechanical factors. In practice, the spinning apparatus and conditions are arranged in a manner known to yield approximately optimum yarn properties, such as optimum tenacity The yarn tension is, measured for that specific arrangement and, at the same time the effects 'of variations intension on the properties of the you are determined. From this "data the tensioncontrol point is chosen and the pressure controller 36 is adjusted so to maintain the tension at about that control point.

When there is a mechanical failure resulting in a sub stantial difference in the outputs of the primary and secondary sensing devices 31 and 77, the alarm 79 is actuated and the piston 51 of the auto-manual relay 47 moves to the left, thus disconnecting the acetone control valve 43 from the controller 36 and connecting this valve 43 with the air in by-pass line 48. The pressure in by-pass line 48 is pre-set, by the manually controlled pressure reducing valve 49, at a value which will maintain the air-operated acetone control valve 43 at approximately the desired setting. The alarm 79 calls the attention of the operating personnel to the fact that there is a mechanical failure which must be corrected.

The sensitivity of the system to differences in the outputs of the two sensing devices 31 and 77 may be con trolled by varying the size of slot 64. Increasing the size of the slot allows a greater movement of the lever 67 before the automatic controls are disconnected, and thus permits the system to operate under automatic controls despite a greater degree of difierence between the two outputs. If desired, any other suitable means for regulating the sensitivity of the system may be provided, e. g. an adjustable linkage between links 71 and 72 and lever 67.

As shown in the drawing, it is preferred to sense or measure the tension of the yarn after the bulk of the liquid has been removed in the wiping zone 24 in order to minimize corrosion of the sensing device and eliminate periodic small variations in tension due to cascading of liquid carried up from the spin bath. However, in the practice of ourinvention, the tension may be sensed at any other point in the travel of the filaments from the spin bathto the godet roller, for example in the wiping zone 24.

While in our preferred apparatus we use a pneumatic system in which all communication between controlling elements and controlled elements is carried out by the use of compressed air, one or all of the pneumatic components of this system may be replaced by electrical hydraulic components. However, the use of electrical components increases fire hazards.

The following example is given to illustrate the invention further.

A spinning dope containing 20% of cellulose acetate dissolved in a mixture of 90 parts by volume of acetone and 10 parts by volume of water is spun, using the apparatus disclosed above, in to a coagulating medium comprising a mixture of about 27 parts by volume of acetone and 73 parts by volume of water maintained at 60 C. The spinning conditions are as set forth in the following table:

Filament speed at take-up, meters/min 75 75 Numbers of apertures in spinnerette 300 1, 400 Denier per filament 85 85 Diameter of spinnerette lace 1v 3" Internal diameterot' lower end of spin tube l. l 5" 3" Internal diameter of upper end of lower spin tube n l" 2 Ooagulating medium added to lower spin pot, ccJmin. 900 z 4, 200 Coagulatlng medium added to upper spin pot, (Be/min. l, 500 g 1, 500

1. In the process for forming filaments by extruding and drawing a spinning solution through a liquid coagulating bath, the improvement which comprises varying the coagulating characteristics of the coagulating bath in response to variations in the tension on the filaments, so as to maintain the tension substantially constant.

2. In the process for forming filaments by extruding and drawing a spinning solution through a coagulating bath which swells said filaments, the improvement which comprises varying the swelling power of said bath in response to variations in the tension on said filament in a manner to increase an decrease said swelling power upon respective increase and decrease in said tension.

3. In the process for forming filaments by extruding and drawing a spinning solution through a coagulating bath which swells said filaments, the improvement which comprises continuously measuring the tension on the filaments, and varying the swelling power of said bath in response to variations in the tension on said filaments in a manner to increase and decrease said swelling power upon respective increase and decrease in said tension.

4. In the process for forming filaments by extruding and drawing a cellulose acetate spinning solution through a coagulating bath which swells said filaments, the improvement which comprises varying the swelling power of said bath in response to variations in the tension on said filaments in a manner to increase and decrease said swelling power upon respective increase and decrease in said tension.

5. In the process for forming filaments by extruding and drawing a cellulose acetate spinning solution through a coagulating bath mixture of acetone and water which swells said filaments, the improvement which comprises continuously measuring the tension on the filaments and varying the swelling power of said bath in response to variations in the tension on said filaments in a manner to increase and decrease said swelling power upon respective increase and decrease in said tension.

6. In the process for forming filaments by extruding.

and drawing a cellulose acetate spinning solution through a coagulating bath mixture of acetone and water which swells said filaments, the improvement which comprises continuously measuring the tension on the filaments and varying the acetone concentration of said bath in response to variations in the tension on said filaments in a manner to increase and decrease said acetone concentration upon respective increase and decrease in said ten sion.

7. In the process for forming filaments by extruding and drawing a cellulose acetate pinning solution through a coagulating bath mixture of acetone and water which swells said filaments, the improvement which comprises continuously measuring the tension on the filaments and varying the temperature of said bath in response to variations in the tension on said filaments in a manner to increase and decrease said temperature upon respective increase and decrease in said tension.

8. In a continuous process in which a filament is stretched in a liquid bath having a swelling action on aid filament, the improvement which comprises contin' uously measuring the tension on the filament and varying the swelling power of said bath in response to variations in the tension on said filament in a manner to increase and decrease said swelling power upon respective increase and decrease in said tension.

9. In an apparatus for the production of filaments by the extrusion of a spinning solution into a coagulating bath, a sensing device for measuring the tension on the filaments and means operatively connected with. said sensing device for varying the coagulating power of said bath. I

10. In an apparatus for the production of filaments by the extrusion of a spinning solution into a coagulating bath, a sensing device for measuring the tension on the filaments and valve means operatively connected with said sensing device for varying the coagulating characteristics of said coagulating bath by varying the rate of flow thereto of a cons-tit-utent of said said bath.

11. In an apparatus for the production of filaments by the extrusion of a spinning solution into :a coagulating bath, a body of air under pressure, a tension sensing device operatively connected with said body of air and with said filaments forvarying the pressure of said body of air in accordance with variations in the tension on said filaments, and means responsive to said air pressure for varying the coagulating characteristics of said coagulating bath.

"12. In an apparatus for the production of filaments by the extrusion of a spinning solution into a coagulating bath, means for wiping excess liquid from said filaments after they leave said bath, a sensing device for measuring the tension on said filaments, said device including means engaged by said filaments after they have left said wiping means, and valve means operatively connected with said device for varying the coagulating characteristics of said coagulating bath by varying 'the rate of flow thereto of a constituent of said bath.

13. In a control system for a plurality of identical processes controlled by the same control agent, means having an output for measuring a controlled variable in one of said processes, control means for varying said control agent over a range of values in response to variations in the output of said measuring means, a second means having an output for measuring the same controlled variable in another of said processes, and means operatively connected to said two measuring means and responsive to the outputs thereof for disconnecting said first measuring means from said control means.

14. In a control system for a plurality of identical processes controlled by the same control agent, means having an outlet for measuring a controlled variable in one of said processes, control means for varying said control agent over a range of values in response to variations in the output of said measuring means, a second means having an output for measuring the same controlled variable in another of said processes, and an alarm operatively connected to said two measuring means and constructed and arranged to give a signal when there is a substantial difference between the outputs of said two measuring means.

15. In a control system for a plurality of identical processes controlled by the same control agent, means having an output for measuring a controlled variable in one of said processes, control means for varying said control agent over a range of values in response to variations in the output of said measuring means, means including a relay selectively connecting said control means to said measuring means and to a manual control, a second means having an output for measuring the same controlled variable in another of said processes and means operatively connected to said two measuring means and responsive to the outputs thereof for operating said relay.

16. In a control system for a plurality of identical processes controlled by the same control agent, means having an output for measuring a controlled variable in one of said processes, control means for varying said control agent over a range of values in response to variations in the output of said measuring means, means including a relay selectively connecting said control means to said measuring means and to a manual control, a second means having an output for measuring the same controlled variable in another of said processes, means operatively connected to said two measuring means and responsive to the outputs thereof for operating said relay, and an alarm for giving a signal when said control means is connected to said manual control.

17. In a control system for a plurality of identical processes controlled by the same control agent, means having an output for measuring a controlled variable, control means for varying said control agent in response to deviations in said controlled variable, means including a relay operated by compressed air for selectively connecting said control means with said measuring means and with a manual control, a second means having an output for measuring the same controlled variable in another of said identical processes and means, operatively connected to said two measuring means, for shutting oil? the compressed air operating said relay, said shut-01f means including a vane having a slot through which compressed air is adapted to flow and means for moving said vane, in response to differences in the outputs of said two measuring means, to a position blocking said compressed air.

18. In a control system for a plurality of identical processes controlled by the same control agent, means having an output for measuring a controlled variable in one of said processes, control means for varying said control agent over a range of values, means including a relay selectively connecting said control means with said measuring means and with a manual control, a second means having an output for measuring the same controlled variable in another of said identical processes, means operatively connected to said two measuring means for operating said relay in response to differences in the outputs of said two measuring means, and an alarm constructed and arranged to give a signal when said control means is connected with said manual control.

19. In a control system for two identical Wet-spinning processes in which the spin bath of each process is supplied from a common source, means having an output for measuring the tension of the filament being spun in one of said processes, means for varying the coagulating power of said bath over a range of values, means including a relay selectively connecting said means for varying the coagulating power of said bath with said measuring means and with a manual control, a second means having an output for measuring the tension of the filament being spun in the second process, and means 0peratively connected to said two measuring means and responsive to the outputs thereof for operating said relay.

20. In an apparatus for the production of filaments by the extension of a spinning solution into a coagulating bath, a plurality of substantially identical spinning cabinets, each adapted to produce a yarn of said filaments, each supplied by the same coagulating bath mixture, and each having means for wiping excess liquid from said filaments after they leave said bath, means for supplying the same coagulating bath mixture to each of said cabinets, a tension-sensing device having an output for measuring the tension of the yarn being spun in one of said cabinets, said device engaging said yarn after it has left said wiping means, valve means for varying, over a range of values, the rate of flow to said supplying means of a constituent of said bath mixture, means including a relay operated by compressed air for selectively connecting said valve means with said measuring means and with a manual control, a second tension sensing device having an output located at the same point of another of said spinning cabinets, means, operatively connected with said two devices, for shutting off the compressed air operating said relay, said shut-off means including a vane having an opening through which compressed air is adapted to flow and means for moving said vane, in response to differences in the outputs of said devices, to a position blocking said compressed air, and an alarm constructed and arranged to give a signal when said compressed air is shutoff.

References Cited in the file of this patent UNITED STATES PATENTS 2,229,489 Barnard Jan. 21, 1941 2,273,127 McGoldrick et al. Feb. 17, 1942 2,383,401 Mantz Aug. 21, 1945 FOREIGN PATENTS 1,015,939 France Aug. 13, 1952

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