In Fig. 4, we give values of X at 60 = 2.4.10 -2 cm and D = 1.9-10- 5. If one analyzes relationship (4), one can say that

the greater the diffusion coefficient, i.e., the higher the washing temperature of the PAN tow, the smaller the path of the PAN

tow in wash-out, the thinner the tow and also the smaller its path in the wash-out bath. It is also possible to estimate the time

of diffusion of NaSCN from the fibre from the relationship t = rb02/4D, whencc it also follows that the thinner the tow and the

higher the diffusion coefficient, the more rapidly wash-out takes place.

CONCLUSIONS

-- A procedure has been developed for determining the diffusion coefficient of sodium thiocyanate in freshly formed

PAN tow during wash-out which is based on refractometry.

-- The temperature dependence of the diffusion coefficient of NaSCN has been investigated using a thermostattable

cuvette.

- - The distribution of NaSCN concentrations in PAN tow during the process of wash-out has been given.

LITERATURE CITED

1.

2.

.

News in the Region of Viscose Fibre Manufacture [in Russian]. Collection of Scientific Works, A. T. Serkov (ed.),

Mytishchi (1986), p. 4.

Control of Man-Made Manufacture [in Russian], A. B. Pakshver and A. A. Konkina (eds.), Khimiya, Moscow (1967), p.

418.

A. I. Pekhovich and V. M. Zhidkikh, Calculations of the Heat Regime of Solids [in Russian], l~nergiya, Leningrad

(1976).

U S E O F A N A I R - J E T T O C O O L Y A R N S W H I C H A R E B E I N G S P U N

F R O M A P O L Y M E R M E L T

I. D. P u p y s h e v and I. A. Zarubin UDC 677.494.021.125.56

In spinning yarns from a polymer melt, the intensity of cooling is one of the basic parameters which determine yarn

quality and the output of the spinning machines. Active yarn cooling is carried out in two zones: with a transverse air stream in

the air-cooling tower and with water cooled to 6-8°C in the spinning tower [1]. The scheme for a process of spinning polycapro-

amide yarn having a linear density of 187 tex is shown in Fig. 1. It is evident (16) that the yarn is cooled to an extent of 85% in

the air-cooling tower and 15% in the spinning tower [2]. The maximum nonuniformity in the temperature field 17 over the cross

section of the bundle of yarn reaches 33°C [3]. Nonuniformity of the yarn temperature field over the cross section of the bundle

is the main reason for nonuniformity in elementary filament properties, and this causes utilization of the strength of the

elementary filaments in forming the strength of the complex yarn to be in quantity from 50-90% [4].

One of the basic reasons for a decrease in yarn cooling intensity is the presence of a boundary layer of air on the surface

of the yarn being spun. The thickness of the boundary air layer around an elementary filament for a laminar 3 t and turbulent 3 t

motion regimes is described by the formulas of [5]

61=5.2LRe- I~,~; 6~0,37LRe -°.2,

where L is the yarn path; Re = vyLpa]/~ a is the Reynold's number; Pa a n d / q are the density and viscosity of the air; Vy is the rate of yarn movement.

Translated from Khimicheskie Volokna, No. 6, pp. 26-29, November-December, 1990.

0015-0541/90/2206-0387$12.50 ©1991 Plenum Publishing Corporation 387

5

Z"

1

18

19

3-

4.

0 0,5 1 Pu 0 100 ZOO ~00 "~,*C

J i / i ,y 50 oc 17

5.

L,M

1 0 . ~ ) _ 9

o Vs max

-1 0 I V, m / s e e

L, b¢

Fig. 1. Scheme of yarn spinning process: 1) spinning block; 2) spinneret; 3) air-cooling tower;

4) yarn; 5) spinning tower; 6) lubricating roll; 7) press roll; 8) spinning roll; 9) take-up pack;

10) friction roll; 11) source of excess air pressure; 12) air pressure regulator; 13) jet-forming

device; 14) manometer; 15) coefficient of resistance of yarn (Pu) to change in its linear density

from the action of pulsations in the cooling air; 16) temperature field of yarn over its length;

17) temperature field of yarn over its cross section; 18) horizontal component of air velocity

over the length of the yarn at a distance of 5 cm from it; 19) change in rate of structure forma-

tion (vs) over yarn length.

The boundary air layer will move along with the yarn, forming a companion air stream which retards the intensity of

yarn cooling. This is one of the reasons for a decrease in spinning speed, i.e., a decrease in productivity of the spinning machines.

Studies of tire cord yarns prepared from polymer melts have shown that if one directs transfers to the yarn being spun

toward the sweeping stream of a fine jet of air then the companion air stream which has been formed is carried away from the

bundle of elementary filaments. This will lead to an increase in yarn cooling intensity and to an equalization of the temperature

field in the bundle cross section.

A device for forming the air jet has been developed, fabricated, and tested on polyamide and polyester yarns to deter-

mine the optimum jet action [6]. The air jet is formed by a nozzle having a regulatable slot height from 0.05 to 0.5 mm and a

slot width which exceeds the cross-sectional diameter of the bundle of filaments being spun by no more than 40 mm [2]. The

distribution of air velocity over the width of the slot may be uniform, but it is preferable that the velocity be proportional to the

distribution of the temperature field over the cross section of the bundle [3]. The range of air pressure in the distributing

chamber of the jet-forming device is set within the range of 0.01-0.1 Pa by use of an air-pressure regulator 12. The air jet must

be delivered onto the yarn being spun always below the section after which the coefficient of yarn resistance (Pu) to change in

its linear density from the action of pulsations in the cooling air 15 approaches zero. In this case, impairment in yarn properties

is eliminated. This is confirmed still again by the fact that the points of solidification of the elementary, filaments being spun are

approximately 0.5 m closer to the spinneret relative to the section of yarn having a Pu coefficient which is close to zero [6].

Tests of the jet-forming device have shown that by the use of a fine jet of air it is possible to solve a number of practical

problems on improving the construction of spinning machines and also on optimization, monitoring, and control of the yarn-

spinning process from a polymer melt.

388

1. In winding freshly spun yarn on a package, it is necessary to maintain a n optimum figure for yarn tension; more

tension increases the number of breaks in the complex yarn and underwinding of the elementary filaments during the process of

orientation strengthening of the complex yarn on the twisting--stretching machine; a small tension causes slippage of the layers

of wound yarn from the take-up package, which also hinders yarn processing [6]. It is well known that 60% of the drawing force

on exit of the filaments from the tower is consumed in overcoming the inertial force of the companion air stream [7]. When a

fiat thin jet is delivered, the bundle of filaments being spun is freed from the companion air stream, and thus the yarn tension is

reduced. Studies have shown that a change in air pressure in the distributing chamber of the jet-forming device 13 from 0.01 to

0.1 Pa changes the yarn tension from 5 to 35%. It is recommended to make use of this phenomenon to regulate the tension on

the freshly spun yarn in winding onto take-up packages 17]. 2. Monitoring the temperature of the spent (which has passed through the bundle of filaments) jet of air makes it

possible to estimate with high accuracy the intensity of cooling of the spun yarn in the air-cooling tower. To solve this problem,

a standard thermal resistance of type TSM is placed in the spent jet of air, and its output is connected to the input of a measur-

ing or recording device, for example, type KSP-4 or a system of centralized control, of type A701-03. This method has been

tested and introduced into plants which produce polycaproamidc yarn having a linear density of 187 tex [8].

3. It is well known that the supermolecular structure of yarn spun from a polymer melt is formed between the point

where it hardens and the glass point. Thereupon, there is a section having a maximum rate of supermolecular structure forma-

tion on the yarn [9]. To find this section of the yarn, the point of action of the air-jet is moved along the length of the yarn and

one measures thereupon the mean dcviation in elongation at break of the elementary filaments in a section of the freshly spun

complex yarn. A minimum value of the mean deviation in elongation at break determines the position of the section of yarn

having a maximum rate of supermolecular structure formation [10]. In the opinion of the authors, the yarn section examined will

determine the point of action of the air-jet on the yarn being spun [2, 10].

The point on the spun yarn after which the mean deviation in elongation at break for the elementary filaments in a

section of complex yarn due to the action at the air-jet remains constant indicates the position of the glass point for the yarn

being spun [11].

4. The yarn becomes electrified on movement through the air medium. The strength of the electrostatic charge on the

yarn on exit from the spinning tower is 0.5-3 kV [12]. The presence of the electrostatic charges and pulsations in the cooling air

lead to the situation that some elementary filaments become separated from the bundle and come in contact with the wall of the

spinning tower. Observation of spinning machines in the manufacture of polycaproamidc tire cord yarns has shown that up to

30% of the spinning sites display contact of the elementary filaments with the internal walls of the spinning tower. Contact of

the fibres with the walls of the tower causes defects in the yarn and breaks in it, especially on drawing in the twisting and

drawing machine. It is known that the use of a closed air-jet makes it possible to stabilize the position of the elementary

filaments in the spinning machine tower [13]. Therefore, the presence of a jet collector consisting of four jet-forming devices, for

example, located around the perimeter of the cross section of the complex yarn at intervals of 90 ° and displaced in height by

10-20 cm, fixes the position of the elementary filaments in the bundle and eliminates contact of these with the wall of the tower.

5. Studies performed in the preparation of polyamide and polyester tire cord yarns have shown that the action of an air-

jet under optimum conditions makes it possible to stabilize yarn properties: to reduce the mean deviation in strength of

elementary filaments in a section of a complex yarn down to 40% and also the mean deviation in elongation at break of the

elementary filaments in a section of complex yarn down to 30%, and to reduce the number of underwindings of elementary

filaments in orientation strengthening on the twisting--stretching machine down to 20% of the existing values of these figures [2,

14]. It is well known that an absolute reduction in the coefficient of variation in elongation at break by 1% will lead to an

increase in tire cord strength of 2.3% [14, 15]. Calculations according to the data given show that the use of an air-jet in

spinning yarn of linear density 187 tex will make it possible to increase yarn strength up to 5 N.

6. Drawing off the companion air stream from the zone of the yarn bundle and the additional cooling under the action

of a single jet of air intensifies the process of cooling the spun yarn as much as 35%, which makes it possible to increase

spinning speed as much as 15%. The use of several air-jets displaced from one another along the length of the tower will make

it possible additionally to intensify ` the process of yarn cooling. This, in turn, offers the possibility of reducing the distance from

the spinneret to the lubricating roll (reduce the height of the spinning machine) and removing the bulky, inefficient spinning

tower involving preparation and a circulating system for cooling water [2].

389

7. It is recommended to place the jet-forming collector in a box which constructively ensures removal of the spent air.

This will reduce contamination of the air in the spinning works with vapors of low-molecular compounds (LMC) and will reduce

entrainment of these from the spinning division of the fibre-forming works into the winding division by approximately an order

of magnitude. It must be noted that on the surface of the elementary filaments there are LMC which are deposited in the

spinning zone from the surrounding air and which come off the inner layers of fibres during jet-stretch. Jets of air directed onto

the bundle of filaments and which are moving at a rate of 3-5 m/sec blow off part of the LMC from the surface of the elemen-

tary filaments. This in turn makes it possible to reduce contamination of the yarn guides and is one of the basic factors in

increasing the ability of the yarn to be processed in subsequent technological operations by up to 20% (see item number 5).

Isolation of the LMC from the spent air-jets and subsequent regeneration of caprolactam from these will lead to a reduction in

specific norms for consumption of caprolactam.

8. The construction of the jet-forming devices is simple; they can be developed and fabricated in any man-made fibre

plant. One can use serially produced air-pressure stabilizers, for example, those of type SDV-25 has air-pressure regulators.

There is a source of excess air pressure in the spinning works. The additional air consumption in forming a single jet for yarns

of various assortments is 0.5-2 m3/h. Equipping an 18-position spinning machine with jet-forming devices to the extent of four

devices for each working position requires an air consumption of no more than 150 m3/h. For comparison, we indicate that the

consumption of sweeping air per single working position of a machine in spinning yarn of 187 tex linear density is about

200 m3/h.

9. The distribution of the transverse component of air velocity 18 over the length of the yarn (v, m/sec) shows that the

bundle of spun filaments is swept by air for a distance of about 1 m. This distance also determines the necessary length of the

sweeping tower 16. Thereupon, the use of an air-jet to intensify the yarn cooling regime and optimize the spinning process does

not show up in solving questions of improving the construction of the sweeping tower.

Solution of the technical problems which are performed using an air-jet relates to spinning yarns with a large content of

elementary filaments (more than 100), located in the bundle in several rows. In spinning textile yarns, usually with 6-24 elemen-

tary filaments, and with a dispositioti of these in a single row, cooling takes place predominantly by heat transfer to the sur-

rounding air on movement of the yarn in the tower. The basic function of the sweeping air is to reduce the adverse action of the

convective stream of air in the upper part of the tower on the spun yarn [6]. As applicable to textile yarns, the use of an air-jet

is of little advantage for most of the problems examined but regulation of yarn tension in winding the yarn on a package and

removal of part of the LMC from the surface of the spun yarn by use of the air-jet presents practical interest even for textile

yarns.

The material presented in this article may be used in man-made fibre plants to improve the construction of spinning

machines, and also for optimization, monitoring, and control of the process of spinning yarn from a polymer melt.

CONCLUSIONS

- - It is possible to increase the intensity of cooling a complex yarn by the use of an air-jet having an initial thickness of

no more than 0.1 ram, delivered transverse to the yarn being spun.

- - The jet of air makes it possible to stabilize the properties of the elementary filaments in a section of complex yarn.

- - The use of the air-jet makes it possible to eliminate the spinning tower involving the preparation and the circulation

system for cooling water.

- - The air-jet can be used for monitoring and control of a number of process parameters: intensity of yarn cooling in the

zone where it is swept, yarn tension in winding onto the takc-up package, and the position of parts involving phase changes in

the spun yarn.

- -Removal of the spent air-jets from the spinning zone reduces carry-off of low-molecular compounds from the spinning

and winding parts of the works by an order of magnitude.

LITERATURE CITED

1.

2.

3. 4.

G. Klare, Synthetic Polyamide Fibres [Russian translation], Mir, Moscow (1966).

I. D. Pupyshev, Khimich. Technol., No. 2, 23-24 (1985).

Inventor's Certificate 626129 (1979) (USSR).

M. P. Nosov, Khim. Volokna, No. 2, 48-49 (1983).

390

.

6.

7 .

8.

9.

10.

11.

12.

13.

14.

15.

16.

K. E. Perepelkin, K.him. Volokna, No. 1, 3-12 (1968)~

I. D. Pupyshev, New Methods of Monitoring and ~0~fiol of the Process of Yarn Preparation from a Polymer Melt [in

Russian], NIITI~KhlM, Moscow (1985), No. 1.

Inventor's Certificate 918343 (1983) (USSR).

I. D. Pupyshev, in: Automation of Chemical Manufacturing [in Russian], NIITt~KhlM, Moscow (1983), No. 1, pp. 18-21.

S. P. Papkov, Physico-Chemical Bases of the Manufacture of Artificial and Synthetic Fibres [in Russian], Khimiya,

Moscow (1972), pp. 170-171, 255-256.

Inventor's Certificate 726226 (1980) (USSR).

Inventor's Certificate 651056 (1979) (USSR).

I. D. Pupyshev, Tekst. Prom-st', No. 4, 66-67 (1987).

Inventor's Certificate 968113 (1982) (USSR),

I. D. Pupyshev, Monitoring Nonuniformity in Properties of Fibre-like and Film-like Materials [in Russian], NIITEKhlM,

Moscow (1986), No. 6.

M. N. Belitsin, Khim. Volokna, No. 7, 38-40 (1970).

Inventor's Certificate 489819 (1975) (USSR).

H Y D R O D Y N A M I C S O F S P I N N I N G C E L L U L O S E C A S I N G S

BY T H E T U B E M E T H O D

V. M. Irklei, O. S. Vavrinyuk, K. Ya. Reznik, and V. I. Pirogov

UDC 677.463-416.021.125.261:532.5

The tube method is widely used in viscose technology to prepare casings of various types which are in high demand in

plants of the meat industry [1]. A scheme for spinning cellulose casings is shown in Fig. 1.

The "tube" (cylinder) 1 is formed on forcing the spinning solution through annular slot 2 of the spinneret. The "outer"

precipitation bath (PB) is delivered into an annular space between the inner surface of the outer tube 3 and the outer surface of

the "tube," the "inner" one is delivered into the annular space between the inner surface of the "tube" and the outer wall of the

inner tube 4. Drawing off of the touter" bath takes place through the overflow 5, and that of the ~inner" one through the internal

tube 4,

From the point of view of hydrodynamics, spinning casings reminds one greatly of the spinning of fibres and yarns in

tubes [2-4]. However, in the tube method, the spinning conditions are made more complicated by the fact that the jet of viscose

makes contact with the PB not only on its outer but also on its inner surfacc. In such a joint movement of the jet of viscose and

the PB, hydraulic resistance may arise, which will cause additional orientation of the cellulose macromolecules along the

spinning axis and will lead to obtaining a material with a strongly expressed anisotropy in properties [5, 6]. Therefore, a determi-

nation of the conditions in spinning which assure a minimum hydraulic resistance is an important technological problem in the

search for ways to obtain materials with high service characteristics.

The following notation is used: r i is the outer radius of the inner tube, in m; r o is the radius of the tube being formed,

in m; r o is the inner radius of the outer tube, in m; / is the height of the spinning tube (half-length of the tube in the bath), in

m; w 0 is the rate of movement of the tube, in m/sec; Qo and Oi are the flow rates of the "outer" and "inner" PB, respectively, in

m3/sec; AP o and AP i are the decreases in pressure of the "outer" and "inner" PB over the length (height) of tube l, respectively,

in Pa; p is the dynamic viscosity of the precipitation bath, in Pa.sec; Wo(r ) and wi(r ) are the flow rates in the "outer" and "inner"

PB, respectively, in m/sec; and d e is the equivalent diameter of the section for passage of the PB, in m.

Translated from Khimicheskie Volokna, No. 6, pp. 29-31, November-December, 1990.

0015-0541/90/2206.0391S12.50 ©1991 Plenum Publishing Corporation 391