SOME PROBLEMS IN IMPROVING APPARATUS DESIGN FOR PROCESSES OF SPINNING MAN-MADE FIBRES FROM POLYMER MELTS V. I. Stupa

UDC 677.494.021

In devising equipment for spinning man-made yarns and flbres, the development of constructional answers which are aimed at reducing cost and improving product quality is urgent. In developing assemblies for spinning textile-trade yarns, this involves further increase in the rate of spinning several yarns from a common operation site to spin yarns of a high llnear density, improvement in apparatus design for the spinning process, and combination of this with subsequent operations. Thereupon, special attention is given to problems in mechanizing and automating the technological process, and also to improving the sanitary-hygienic conditions of worker labor. In spinning man-made fibres from polymer melts, as before, extruder design is promising and guarantees obtaining a high-quality yarn and maneuverability of the technological process. In connection with the fact that the extruder output is sensitive to change in melt viscosity, to fluctuations in pressure caused by a change in take-up, clogging of the filter, or nonuniformity of the material being extruded, it is recommended to install a gear pump after the extruder [i]. Gear pumps which have been specially devised for this purpose have, in the housing around the rotors, a wedge-shaped compression chamber, which leaves the gears open for an additional time on the intake side and thereby increases the efficiency of pump operation [2, 3]. The advantages of these pumps are their comparatively small size, evolution of only a small amount of heat under the action of the shear stress which arises in the melt [4], and also the ability to discharge a melt which is present under vacuum. The use of an extruder-pump system makes it possible to create the necessary head in front of the preliminary clean-up filter; to optimize the extruder as a melting and mixing device in which the polymer melt will not be subjected to uncontrolled friction or thermal loading; to reduce wear on the worm and bushings; and to extrude hEat-sensitive materials, for example polymers which have been dyed in bulk with dyes having a low heat-resistance, and thereby to enlarge the use of a very economical method of dyeing -- in bulk -- in the manufacture of large lots of yarn having a common color [5]. The homogeneity and cleanness of the melt are important conditions, not only for improving yarn quality, but also for increasing the productivity of equipment designed for yarn preparation. Preliminary filters are widely used for the filtration of melts. Having a large filtration surface and fine pores and cells (from i0 to 40 ~), they make it possible to separate not only foreign inclusions, but also melt particles having an increased molecular weight, which cause bumps on the yarn surface. To make the residence time of the melt in the filter as small as possible and constant, filters with a small housing volume are used. At present, such filters are used both after the polymerization apparatus in the lines for production of polycaproamide granules, and also in the make-up of the spinning machines. Thereupon, the service life of the spinneret assemblies is increased by a factor of 3 to 5 [6], with a simultaneous decrease in breakage and increase in quality of the spun yarns. Melt homogeneity in the spinning stage also depends on the efficiency of operation of the dynamic mixers, which are most often a component part of the extrude, although they are sometimes used as individual units. In use in machines for spinning man-made fibres in high-productivlty group melting devices, static mixers are finding increasingly wide application [7-9]. Installed ahead of the spinning devices, they make it possible to reduce the radial temperature gradient in the melt, and thereby improve the physicomechanical properties of the spun yarn. Static mixers are also used in mixing melts or solutions of polymers containing dyes, fillers, or stabilizers. In the manufacture of textile yarns, multi-line metering gear metering pumps of the i planetary or combined types have received steadily increasing circulation. Planetary pumps Translated from Khimicheskie Volokna, No. 4, pp. 25-27, July-August, 1984.

0015-0541/84/1604-0241508.50

© 1985 Plenum Publishing Corporation

241

have the advantage that an identical residence time of the melt in individual pump sections is assured, as well as uniform heating of these [I0]. Work is being carried out on devising 2-, 3-, 4-, 6-, 8-, and 24-stream metering gear pumps of the planetary type, which are characterized by a high economy of operation [ii]. An increase in the constructional rigidity of metering pumps has been caused by the tendency to increase the working pressure in spinning both textile and technical yarns which has been noted in recent times. Correctly chosen end and radial clearances exert a large effect on the quality of operation of metering gear pumps. Small clearances, especially in metering highly-viscous polymers, cause high shear stresses and, as a consequence, a significant (several degrees) heating of the polymer, due to energy dissipation. Such an uncontrolled change in polymer temperature between the spinning blocks can exert asignificant effect on the quality of the spun yarn, for example on the degree of dye absorption. In spinning technical purpose yarns, as a rule, a significantly more viscous polymer is used; and incorrectly chosen clearances and pump operation regime can lead to thermal degradation of the polymer. Therefore, in spinning high-strength yarns from highly viscous polymers, it has been proposed to use metering pumps with large delivery per revolution, and a correspondingly low frequency of rotation [12]. Together with improvement in the technical characteristics of metering pumps, work is being carried out continuously on devising and selecting wear-resistant and corrosion-resistant materials for making them. The apparatus design of the yarn cooling process in spinning is being improved in two ways. The first way is in improving the tower construction for yarn cooling by continuous sweeping with air, with the objective of eliminating pulsations and turbulence of the air stream, and of ensuring a good quality of the spun yarns at a high productivity of the spinning process. Thus, it is considered to be quite attainable to reach a spinning rate of 20 kg/h of yarns per i00 mm of tower width [13]. In high-speed spinning (up to i00 m/sec), a tendency to cool the spun yarn with the aid of a lubricant directly in the sweeping tower [14] has been noted, which makes it possible tointensify the process of yarn cooling in the section between the spinneret and the winding mechanism, and also to considerably reduce the height of the machine. Bringing the elementary filaments into a bundle with the aid of a lubricating device makes it possible to reduce the air resistance in the sweeping tower, and thereby to reduce the yarn tension to an optimum value (200 N), and also to eliminate the involvement of significant masses of hot air from the spinning tower in the winding zone. By using the lubricating device as an intermedlate movable support, one can vary the number of inherent vibrations in the spun yarn and thereby increase its uniformity in linear density. Along with this, the above-indicated spinning method has both purely technical defects, associated with the inconvenience of servicing such machines and also technological defects, which are displayed in nonuniform application of lubricant and varying tension of low linear density elementary filaments, which leads to the formation of loops. The system of spinning in a tube permits one to eliminate these defects [15]. In this system, a bundle of elementary filaments passes from the end of the sweeping tower to a windingmachine through an individual tube. At the entry to each tube there is an ejector, in which, for a short time at the moment of servicing, air passes for transporting the bundle of elementary filaments, and then the compressed air is shut off and the nozzle serves as a fibre guide. Holding the complex yarn at the end of the sweeping tower ensures a quiet state, which reduces its nonuniformity in linear density to 0.6-0.7%. A second trend in improving the sweeping tower, which has been developed for the process of spinning high linear density yarns, primarily technical yarns, is the development of socalled closed sweeping towers, in which the spent sweeping air is drawn off together with the low-molecular-weight compounds (LMC) at the outlet from the sweeping chamber. The VNIIMSV has developed two tower constructions of this type: with transverse radial and transverse one-sided sweeping. The closed tower, with transverse radial sweeping (cylindrical in form) which is used in combination with a spinneret of increased diameter, ensures stability of the position of the spun filaments in the sweeping tower, and, as a consequence, uniformity in its linear density. 242

The closed tower with transverse one-slded sweeping which is used in combination with a rectangular spinneret ensures, in addition to a high quality of the spun yarn due to the use of this spinneret, additionally better sanitary-hygienlc conditions of worker labor, due to the fact that the removal of the spent air and low-molecular-weight compounds is not interrupted even during servicing of the spinneret assembly [16]. Thus, the use of closed-type towers under conditions of a continuous increase in unit capacity of spinning machines and in linear density of the technical and filament yarn makes it possible to significantly improve the sanitary-hygienic conditions of worker labor. In connection with the increase in requirements for environmental protection, much attention is being paid to the development of highly effective systems which permit one to trap out low-molecular-weight compounds, both evolved from freshly-spun yarns in the zone of the sub-spinneret space and also contained in the spent air which is drawn off from closed-type sweeping towers. As spinning speeds, and further yarn processing speeds (texturizing), are increased, demands on the lubricant and the quality of its application are increased. The very widely circulated disk lubricating systems do not apply lubricant sufficiently uniformly onto the yarn, but this defect does not play an important role in the application of large amounts of lubricant. At present, these systems are being used successfully in spinning carpet yarn and technical yarns [17]. As technology for high-speed spinning becomes more widespread, the method of yarn lubrication in a fibre guide with a hole for metered delivery of lubricant by a gear pump is receiving increasingly wide use. Here it is important to correctly select the length of yarn contact with the fibre guide which ensures uniform distribution of lubricant on the elementary filaments at a low frictional force along the fibre guide. As was indicated above, a large frictional force causes a larger yarn tension, which shows up adversely on the quality of yarn winding. There have been attempts to combine the advantages of the disk application of a preparation with metered delivery of it using metering pumps and porous lubricating disks. A high quality of yarn lubrication is ensured on application of lubricant by the spraying method [18], Improvement in winding mechanisms, together with further increase in the rate of yarn take-up, is proceeding along the path of complete automation of all operations associated with the preparation of finished packages, and of maximum utilization of the entire width of the winding mechanism by the produced package. Thereupon, as before, the tendency is to increase the number of yarns which are taken up on one bobbin-holder. Contemporary winding machines, which are used in spinning completely or partially oriented polyester yarns, or, particularly, polyamide yarns, are provided with elongated bobbinholders mounted on a horizontally movable carriage. The latter, in turn, is installed on a vertically movable carriage which is held in an assigned position by use of a hydraulic cylinder and descends as the bobbin is finished. This makes it possible to use practically the entire width of the winding mechanism, and, at an interval Of 400 mm, to produce packages of up to 360 mm diameter [19]. Winding mechanisms with a turbine start-up and an axial drive of the bobbin-holder, which make it possible to develop a rate of yarn take-up up to 100 m/sec, are increasingly being introduced. In spinning carpet and technical yarns, winding mechanisms are used which have a reserve bobbin-holder and which are able to take up one to two, or sometimes even four yarns. Winding mechanisms of the revolver type are promising, especially in machines for combined spinning, stretching, and texturizingyarns of the carpet type, with a large linear density. Due to the fast production of a package, these machines (depending on the linear density of the yarn, the spinning speed, and the mass of the package produced, the time for production of a package may be less than i0 min) should be equipped in compulso=y order with a system for automatic waste-free yarn reservicing, holder replacement, and removal and transportation of finished packages. A further increase in spinning speed or increase in number of yarns spun at a single working site [20] requires complete automation of the process of preparing carpet tow yarn, including control and packaging of the finished bobbins.

243

Since hlgh-speed spinnin 8 has a number of advantages over classical spinning, it will undoubtedly be extended to the manufacture of staple fibres. Combining the operations of spinning, stretching, and applying twist will open up new opportunitles in the field of devising staple units [21]. Along with the trend toward increasing productivity, a tendency toward developing compact assemblies is observed, due to locating the extruder after the sweeping towers below the spinning devices, and reducing the distance from the spinneret to the winding machine b y using a shortened sweeping tower. At present, such units are being produced by foreign companies [4, 21]. Further combination of the technological operations in yarn preparation is dictated by economics. However, it is not always advisable or economically suitable to select an integrated process in devicing new manufacturing operations, since, as was shown above, traditional processes are always being continuously improved. At present, the decisive and almost only factor which speaks in favor of using combined processes is the reduction in the service by servicing personnel [22]. Equipment which permits one to combine several technological operations on a single unit is characterized by much complexity, and also by a wide use of microelectronics and microprocessor techniques; therefore work on increasing its reliability is acquiring special urgence. From this, the main trends in developing aggregates for the manufacture of man-made fibres are the following: improving classical methods of spinning, with the objective of raising the physicochemical properties of the spun yarns; further increase in spinning speed in the manufacture of technical assortment yarns; combination of other technological operations with the spinning process (dyeing, stretching, texturizing, pneumatic combination, etc.) in the manufacture of yarns of large linear density; increasing the number of yarns spun at a single operational site, in assemblies for highspeed and combined spinning; increasing the unit capacity of the spinning assemblies; improving the sanitary-hygienic labor conditions of workers and simultaneous performance of measures to protect the environment. LITERATURE CITED i. 2. 3. 4.

5. 6. 7. 8. 9. i0. ii. 12. 13. • 14. 15. 16.

T. W. Rice, Plast. Technol., Feb., 87-91 (1980). West German Patent 1941673 (1971). A. S. Idel'son, L. E. Borodulina, S. Z. Lozovskii, and I. P. Ivanov, Khim. Neft. Mashinostr., No. 8, 39-41 (1982). K. Riggert, Chemiefasern/Text. Ind., No. 9, 683-692 (1979). Chemiefasern/Text. Ind., No. 6, 419-420 (1982). F. Hensen and H. Siemetzki, Kunststoffe, No. ii, 753-758 (1980). R. Kocher, Techn. Rundschau Sulzer, No. 2, 80-82 (1977). K. Werner and A. Cybulski, Inzyneria i apparatura chemiczna, No. 6, i-7 (1978). F. Streiff, Chem. Ing. Techn., No. 6, 520-522 (1980). Chemiefasern/Text. Ind., No. 6, 417-418 (1982). Chemiefasern/Text. Ind., No. 9, 625 (1982). Int. Text. Bulletin, Spinning, No. 2, 231 (1979). F. Fourne, Chemiefasern/Test. Ind., No. 9, 604-611 (1982). F. Fourne, Chemiefasern/Text. Ind., No. i0, 838-842 (1979). R. Hoffmeister, Chemiefasern/Text. Ind., No. 12, 915-916 (1981). A. M. Kirichenko, V. M. Kholosha, Yu. A' Chernyshov et al., Khim. Volokna, No. I, 70-72

(1977). 17. 18. 19. 20. 21.

244

G. P. G. M. W.

Schubert, Mell. Textilber., No. 12, 975-979 (1980). I. Cherednichenko, V. I. Stupa, and S. A. Svirid, Khim. Volokna, No. i, 44-45 (1980). Schubert (Shubert), Text. Asia, Oct., 52-54 (1978). Mayer, Chemiefasern/Text. Ind., No. i0, 704-710 (1983). McDonald, Fiber Producer, No. 8, 38-66 (1983).

22.

L. Piehl and H. Reitger, Konventioneller oderintegrierter Synthesefaserprozess, was ist wirtschaftlisher? Vortrag auf der 21. Chemiefasertagung in Dornhirn am 22 Sept. 1982.

SUPERMOLECULAR STRUCTURE OF MODERATELY CONCENTRATED SOLUTIONS OF POLYBENZIMIDAZOLEAMIDE G. B. Kuznetsova, O. V. Kallistov, N. A. Kalinina, Z. N. Slavina, L. G. Shirokova, O. S. Karchmarchik, K. E. Perepelkin, and A. V. Sidorovich

UDC 532.77;541.64

The operational properties of polymeric materials are largely determinedby molecular characteristics, and also by the supermolecular morphology of the original concentrated systems. The structure of polymer solutions has been studied too little; therefore an evaluation of the supermolecular parameters and investigation of the structure-formation features of polybenzimidazoleamide (PABI) solutions of various thermodynamic properties presents both scientific and also practical interest. The molecular characteristics of PABI and the structure of the monomeric unit have been previously examined [i]. In the studies which are described in the present article we have investigated one of the most direct and sensitive methods of structure determination--the method of polarized light scattering in the large angle region (40-140°). The advantage of this method over others (neutron scattering or x-ray scattering) consists in the possibility of using polarized light as both the incident and also the scattered light, and in obtaining thereby additional quantitative information about the anisotropic characteristics of the scattering volume elements. The linear parts of the experimental relationships

4 Rnv from sin -~O (where Rnv and Rvv Rvv --~-

1/V'-Rtfv and 1

are the well-known Rayleigh equations for the horizontal and vertical components of scattered light on vertical polarization of the incident light, respectively; where 8 is the scattering angle); these make it possible to use the exponential form of the:correlation function of the polarizability and orientation fluctuation [2] in calculation of the following parameters: eleme

n~t' the orientation correlation radius of the optical axes of the scattering volume ; aVv ? the correlation radius of the fluctuation in polarizability; <~=>, the mean-squared value of the fluctuation in mean polarizability; I

and-~,-the mean-squared value of =he optical anisotropy of the scattering volume element. The correlation paraments, which describe the supermolecular organization of concentrated polymer solutions, are calculated from the well-known equations of [3]:

RHz, = ~

l K62 i e --r/a H° 0

sinhr J sinhr hr

R V _ + R t t v : K <~1~> ~ e --r/a Vv

r~dr

h'----7"---r'Zdr

o

where

4n

0

h:--~-o nsin-~-; K :

64n 5 ~o -; %0 is the wavelength of light in vacuum; and r is the distance

between two scattering volume elements. Translated from Khimicheskie Volokna, No. 4, pp. 28-30, July-August, 1984.

0015-0541/84/1604-0245508.50

© 1985 Plenum Publishing Corporation

245