Fibre Chemistry, Vol. 27, No. 2, 1995

PRODUCTION CONTROL

MONITORING AND CONTROL OF FABRICATION OF FIBRES

FROM A POLYMER MELT BASED ON THE FIBER

TEMPERATURE (REVIEW)

I. D. Pupyshev and A. Yu. Dvilis UDC 677.494.021.125.27:66.012.1

The literature on use of the "fibre temperature "parameter for monitoring and control of fabrication of fibres from a polymer melt, in particular, cooling of the spun fibre and thermoplasticization drawing, was reviewed. A thin jet of air passed through the bundle of spun fibres has effective characteristics which can be used to

monitor and control the fibre cooling conditions, to increase the intensity of cooling of the fibre, and to improve the fibre quality indexes. The efficiency of controlling fibre drawing with the Amur system increases if the temperature of the fibre at the outlet of the thermoplasticizer is measured instead of the thermoplasticizer temperature. A direct regulator using a bimetallic plate can be used instead of the Amur system," this allows

increasing the stability of the fibre temperature during drawing by 3-5 times. The characteristic sections of deviation of the fibre temperature during spinning and the increase in its temperature during coM drawing bear information on the process and fibre parameters, but require additional studies to determine the important parameters and their correlations. The informativeness of the "fibre temperature" parameter increases if it is examined in association with the other properties of the fibre and the operating parameters of the process. A realization algorithm is possible in terms of the sign of the deviation of the properties of the fibres and the parameters of the process. Most technical solutions can be implemented with standard thermistors and thermocouples. The proposed information can be used by specialists in chemical fibres for automatic monitoring and control, optimization of the process, and improvement of the equipment.

According to patent-information materials, a relatively large number of new indirect nondestructive methods of

monitoring and controlling fabrication of chemical fibres (based on the tension, temperature, electrostatic charge, and others

[1]) has been developed. However, the use of these methods in chemical fibre enterprises is not defined by standard documents,

and their use is therefore very limited.

The possibility of using the fibre temperature for monitoring and controlling fibre fabrication from a polymer melt is

examined here on the example of polycaproamide (PCA) fibre with a linear density of 187 tex.

The basic stages of fibre formation which primarily determine the fibre quality indexes are spinning and orientational

strengthening (drawing) [2]. Diagrams of spinning and drawing of PCA fibre for the individual method of fabrication and the

fibre temperature diagrams corresponding to these stages are shown in Figs. 1 and 2. During spinning, the fibre temperature changes from the temperature of the polymer melt to the temperature of the

ambient air in the spinning shop (Fig. 1B).

The fibre is cooled in a blowing shaft by an air current directed across the fibre and in a spinning shaft with water cooled to +6-8°C circulating in its wall in most spinning machine designs [2, 3].

To ensure the required fibre quality indexes, the intensity Of cooling the fibre in each zone must be defined [2, 4]. As

a consequence, the temperature of the spun fibre must be monitored by shaft zones and maintained within the established limits.

However, the fibre in the shafts moves at a speed of more than 10 m/sec, making it impossible to measure the temperature by the contact method, and contactless, low-inertia, highly sensitive, temperature gauges convenient to use on multiposition

spinning equipment in the region of 20-300°C are not manufactured by domestic industry. On this basis, a number of indirect methods of monitoring the fibre cooling conditions has been proposed in information-patent materials.

Barnaul'sk OKB Avtomatiki Corp. Translated from Khimicheskie Volokna, No. 2, pp. 50-54, March-April, 1995.

0015-0541/95/2702-0125512.50 ©1995 Plenum Publishing Corporation 125

, 4

<

ter 6

Fig. 1

: - h Z o o

I s

2 5 7 L

Fig. 2

I , ' c

100 200

?

Fig. 1. A: Diagram of fibre spinning: 1) spinning unit; 2) spinneret; 3) blowing shaft; 5) gate;

6) spinning shaft; 7) fibre; 8) oiling disk; 9) pack. B: Fibre surface temperature diagram.

Fig. 2. A: Diagram of orientational strengthening of a fibre on a twisting-drawing machine:

1) pack; 2) pressure roller; 3) drive shaft; 4) brake rod; 5) thermoplasticizer; 6) drawing unit;

7) fibre; 8) chuck; 9) box; 10) drive. B: Fibre surface temperature diagram.

The temperature of the depleted cooling air current is correlated with the temperature of the spun fibre, and at the outlet

of the spinning shaft, the air temperature in the fibre bundle is 0.98 of the surface temperature of the filaments [5]. Indirect

methods of monitoring the intensity of cooling of the spun fibre and several of its parameters are therefore based on

measurement of the temperature of the air currents in the spilming machine shafts.

Let us briefly analyze the existing methods of monitoring.

For different spinning machine designs and different fibre varieties, the cooling zone of the jets of polymer melt coming

out of the spinneret openings by the blowing air current is 0.3-1 m [3]. For this reason, it is recommended that the intensity

of cooling of the fibre be monitored with the temperature of the exhaust air or the difference in the temperatures of the exhaust

and blowing air currents [6, 7].

The fibre stream from the lower boundary of the fibre blowing zone to its emergence from the shaft is not blown with

the blowing air stream, but the co-current air stream moves together with the fibre [3]. The accuracy of measuring the intensity

of cooling of the fibre in this segment of its path with the temperature of the co-current air stream is thus determined to a

significant degree by the position of the temperature sensor relative to the spun fibre bundle. In this segment of the path, the

filament bundle has transverse vibrational motions. It is very difficult to stabilize the position of the temperature sensor relative

to the fibre bundle. It is recommended that a thin (100 gin) jet of air be passed across the spun fibre at the rate of 3-8 m/sec

(as a function of the variety of fibre) to eliminate the effect of this factor on the accuracy of monitoring and the intensity of

cooling of the fibre be monitored with the temperature of the exhaust (passed through the fibre bundle) air jet [8]. A thin air

jet is formed by a slit nozzle with an adjustable slit height within the limits of 0.005-0.5 mm and a slit width greater than the

diameter of the spun fibre bundle. Consumption of air for formation of one jet with a different fibre bundle shape is 0.2-1

m3/h. The air jet is thin and easily passes through the fibre bundle, virtually not altering the form of its movement. The advantage of this method of monitoring is that the co-current air stream is carried away from the filament bundle by the jet,

increasing the intensity of cooling the spun fibre to 35 % and stabilizing the properties of the filaments in the section of the

complex fibre [8].

The integral fibre temperature index by monitoring its temperature in the takeup pack after winding is of practical

interest [9]. The measured temperature range for a fibre with a linear density of 187 tex is 24-36°C. Technical realization of the monitoring method is by needle thermistor or thermocouple.

The fibre temperature also bears information on other parameters of the spun fibre. For example, the region of its phase

transition from the liquid to the solid state is monitored with the minimum temperature gradient of the spun fibre [10]; the

126

difference in he fibre temperatures before and after the devices for application of the oiling agent provides an estimation of

the amount of oiling agent applied on the fibre [11].

The intensity of cooling the fibre is determined for monitoring production with the temperature of the exhaust air in

many chemical fibre enterprises. The temperature sensor is placed on the interface of the blowing and spinning shafts [12].

A region of increased air pressure is formed in this zone and directed to the temperature sensor with a specially designed short

tube. The region of high air pressure at the joint of the two shafts is created as a result of the interaction of the co-current air

stream in the complex fibre bundle with the air stream reflected from the valves of the connector in the lower part of the

spinning shaft. A TSM thermistor is used as the temperature sensor, and an A701-03 installation is used as the measuring

system [ 12]. The "fibre temperature" parameter can be used for automatic control of cooling of the spun fibre: feed of blowing

air into the shaft can be regulated based on the difference in the temperatures of the exhaust and blowing air streams [7]. If

the temperature of the exhaust air jet is measured at the outlet of the spinning shaft, the temperature of the water fed into the

jacket of the spinning shaft can be regulated with it.

Three characteristic segments of deviations are observed in the spun fibre surface temperature diagram (Fig. 1B). The

temperature is almost constant in segment 1. This is due to solidification of the polymer melt jets [13]. On segment 2, the

increase in the fibre surface temperature gradient is due to application of oiling agent on the fibre. In segment 3, the

temperature of the fibre increases. This is due to equalization of the temperatures of the filaments in their section, since the

temperature is 30-40°C higher in the center of the spun filament than on its surface [9].

The diagram of measurement of the fibre temperature in different segments of its path in drawing on a twisting-drawing

machine is shown in Fig. 2. Our experimental studies show that the fibre temperature in the segment of its path from points

t 1 to t 2 for a drawing ratio of 2.5 for different positions in the twisting-drawing machine are within the limits of 25-65°C. The

fibre temperature increases as a result of release of internal heat during orientational shear of the polymer macromolecules

during drawing of the fibre. In the hot drawing zone, the fibre temperature increases primarily due to transfer of heat from

thermoplasticizer 5. The fibre is cooled in the other segments of its path by transfer of heat to the ambient air.

The fibre temperature in the cold drawing zone in chemical fibre plants is not currently monitored and regulated,

although the temperature difference attains 40°C. This difference in temperatures is caused by the uneven application of oiling

agent on the spun fibre and the nonuniformity of the fibre structure, namely, the concentration of low-molecular-weight

compounds and viscosity of the polymer melt.

Orientational strengthening of the fibre in the hot drawing zone is controlled in chemical fibre plants by automatic

regulation of the temperature of the working surface of the thermoplasticizer within the limits of tnorn+At, where tno m is the

nominal temperature and At is the deviation from the nominal temperature during regulation.

However, this method of control does not ensure a stable fibre temperature in the hot drawing zone. Measurements

of the fibre temperature at the outlet of the thermoplasticizer with the work places of the spinning-drawing machine show that

the constant component of the fibre surface temperature is within the limits of 120-160°C for a thermoplasticizer temperature

of 170+3°C. Nonuniformity of the fibre temperature is caused by the nonuniform application of oiling agent on the spurt fibre,

the form of spreading of the filaments on the working surface of the thermoplasticizer, cleanness of its working surface, and

changes in the properties of the freshly spun fibre.

Based on these drawbacks, it was suggested that the fibre temperature be measured after the thermoplasticizer for

stabilization of the properties of the fibre and strengthening (drawing) of the fibre be controlled with the value of the deviation

of the measured fibre temperature from the defined temperature by altering the arc of contact of the fibre from the working

surface of the thermoplasticizer [14]. It is suggested that a direct regulator, a bimetallic plate installed after the

thermoplasticizer, be used to implement this method of stabilization of the fibre temperature. The plate is in contact with the

fibre [15]. If the fibre temperature deviates to either side of the nominal temperature, the curvature of the bimetallic plate is

changed, so that the length of the arc of contact of the working surface of the thermoplasticizer with the fibre changes. The

fibre temperature is thus maintained within the established limits.

The degree of contamination of its working surface can be monitored with the difference in the fibre temperatures

before and after the thermoplasticizer [16]. The more soiled the working surface of the thermoplasticizer, the less heat is transmitted from the thermoplasticizer to the fibre and consequently the smaller the difference in the measured temperatures.

In chemical fibre plants, the degree of soiling of the working surface of the thermoplasticizer is assessed visually, while the working surface of the thermoplasticizer is cleaned after a certain period of operation, for example, once a shift.

KVSh-250-KA twisting-drawing machines are primarily used in plants manufacturing PCA fibre with a linear density

of 187 tex. For automatic definition and maintenance of the fibre temperature within the required limits, Amur systems are

127

TABLE 1. Signs of Deviation of Basic Fibre Properties

and Operating Parameters of Fabrication

Basic fibre properties Process and fibre parameters

combination [signor deviation vp[ ,p[ 's I ' s l °~1 ~dl Xdl 'dl td

P + L + + + - - +

P - L - - - + + -

PL P - L + + - - -

P + L - - + + +

P + Q+ + -- + -- -- + p - Q - - + - _ - +

PQ P + Q - + + + p - Q + - _ _

LQ

L + Q + • + + -

L - Q - - - + + + + - + L - Q +

L + Q - +

used in the hot drawing zone. This system automatically stabilizes the thermoplasticizer temperature, but not the fibre

temperature. The temperature sensor (thermocouple or thermistor) is installed in the body of the thermoplasticizer [17].

Measurement of the fibre temperature immediately after the heating element is of practical interest for stabilization of the

fibretemperature in the hot drawing zone [14]. In this case, the fibre temperature can be stabilized within the defined limits

with respect to the work positions of the system by regulation of the thermoplasticizer temperature with Amur systems.

However, use of a direct regulator with a bimetallic plate is naturally of the greatest interest [15]. In this case, the need for

Amur systems for regulating the fibre temperature in the hot drawing zone becomes superfluous. Monitoring and control of fabrication of PCA fibre with a linear density of 187 tex consisting of 280 filaments were

examined. This also applies to complex fibres with a larger number of filaments, for example, staple fibres, and for thinner

fibres with less than 100 filaments. Textile fibres containing from 1 to 24 filaments produce a weak temperature field during spinning, and they are primarily cooled by transfer of heat to the ambient air. As a result of this, the spinning machine has

no spinning shaft, and the function of the blowing air feed system is reduced to drawing the convection air flow from the

spinning zone off of the fibre [3]. For this reason, the technical solutions for monitoring the temperature fields during spinning

of textile fibres are practically difficult to implement. The technical solutions concerning monitoring of the fibre temperature in cold drawing can also be applied to textile

fibres. Hot drawing with a separate method of fabrication of textile fibres is not used in chemical fibre plants.

Production of fibres from a polymer melt is extended in time and space. It is therefore frequently very difficult to

determine the cause of a decrease in the fibre quality indexes. Solving this problem is simplified if the monitored fibre

temperature is used together with other monitorable parameters of the fibre and process. It is recommended that an analysis

of the signs of the deviation in certain combinations of basic properties of the fibre and parameters of the process and fibre

be used for this purpose [18]. Variants of the signs of deviation of the basic properties of the fibre: strength P, elongation at

break L, and processability of the fibre Q, are reported in Table 1 as a function of the operating parameters of the process and

other parameters of the fibre: viscosity Up and temperature tp of the polymer; temperature t s, tensionfs, and velocity v s of the

fibre during spinning; velocity v d, drawing ratio K d, temperature t 0, and tension fd of the fibre in the hot drawing zone [18]. The proposed method of monitoring with the signs of the deviations is recommended for use as an "advisor" in

searching for the causes of a decrease in the fibre quality indexes. The method is simple to implement with the computers in

chemical fibre plants. The monitoring and control algorithms for the computer do not require large outlays. The methods of monitoring and controlling fabrication of fibres examined here not only apply to polycaproamide fibre

but also to other types of fibres from polymer melts - - polyester, polypropylene, and others.

REFERENCES

1. I .D. Pupyshev, Khim. Volokna, No. 1, 53-56 (1990).

128

2. A.B. Pakshver, Physicochemical Principles of Production of Artificial and Synthetic Fibres [in Russian], Khimiya, Moscow (1972).

3. I .D. Pupyshev and M. P. Zverev, Khim. Volokna, No. 4, 26-30 (1990). 4. K.E. Fishman and A. N. Khruzin, Production of Caprone Fibre [in Russian], Khimiya, Moscow (1966). 5. N.F. Klochko and A. M. Pankeev, Creation and Study of Equipment for Production of Synthetic Fibres [in Russian],

No. 4, Naukova Dumka, Kiev (1974), pp. 60-66. 6. USSR Inventor's Certificate No. 477,118 (1975), GO3B 37/00. 7. USSR Inventor's Certificate No. 494,448 (1981), DOID 5/04. 8. I .D. Pupyshev and I. A. Zarubin, Khim. Volokna, No. 6, 26-29 (1990). 9. USSR Inventor's Certificate No. 668,985 (1979), DOID 5/00.

10. USSR Inventor's Certificate No. 817,105 (1981), DOID 5/04. 11. USSR Inventor's Certificate No. 755,904 (1980), DOIH 13/30. 12. I .D. Pupyshev, New Methods of Monitoring and Control of Fabrication of Fibres from Polymer Melts [in Russian],

"General Industrial Problems" Data Sheets, No. 1, NIITEKhim, Moscow (1985), p. 231. 13. S.P. Papkvo, Physicochemical Principles of Chemical Fibre Technology [in Russian], Khimiya, Moscow (1972), p.

432. 14. USSR Inventor's Certificate No. 735,679 (1980), D02J 1/22. 15. USSR Inventor's Certificate No. 1,057,585 (1983), DO2J 1/22. 16. USSR Inventor's Certificate No. 732,417 (1980), DOIH 5/60. 17. R.L. Rabkin, Khim. Volokna, No. 3, 18-20 (1989). 18. I .D. Pupyshev, Khim. Volokna, No. 2, 50-54 (1993).

129