mechanics of fiber entanglement

Mechanics of Fiber Entanglement

Part 1: Fiber Entanglement by Mason-type Machine

By Megumu Suzuki*,t Setsuko Kobayashi*, Kenichi Emoto*

and Tsuneo Tsukada**, Members, TMSJ

*Faculty of Textiles, Shinshu University, Ueda, Nagano Pref.,

*Production Engineering Division, Yanagisawa Seiki Co., Sakaki

Based on the Journal of the Textile Machinery Society of Japan, (Part 1) Vol. 17, No. 12, 867-872 (Part 2) Vol. 18, No, 2, 117-122

(Part 3) Vol. 18, No. 4, 274-287 (Part 4) Vol. 18, No. 10, T607-614 (Part 5) Vol. 18, No. 11, T642-648 (Part 6) Vol. 18, No. 12, T678-684

Abstract We devised a Mason-type machine, a kind of Couette-type viscometer, and studied the buckling of fibers in the shearing field, a matter related to fiber entanglement problems, such as hooks, nep formation and pilling. We concluded that bent fibers increased in number with an increase in the viscosity of liquid.

We studied what bearing the roughness degree of the cylinder surface had on fiber entanglement. With the cylinders finished at degree W, slivers disordered and buckled fibers increased in number.

We were able to see the process of slivers buckling and forming fiber assemblies when emery paper was stuck on the cylinder surface. We found that two fiber balls in a row merged easily into a larger ball.

We attached ordinary cloth wires or metallic wires to the cylinders and thought of it as a service carding machine because of its dynamic similarity. We observed nep formation by varying the sliver density and the number of cylinder revolutions. More neps formed with an increase in the sliver density. The larger the number of cylinder revolutions, the smaller the rate of nep formation per revolution.

The mechanism of nep formation, in our opinion, consists of the buckling of slivers and the tightening of buckled slivers. The larger the number of fibers sinking among wires, the larger the number of neps forming. We were able to explain nep formation and disappearance by the rate process theory.

1. Introduction

Fiber entanglements in fairly parallel slivers or in

fiber assemblies influence their mechanical properties,

e.g., tensile, bending and shearing. They were also influenced with textile manufacturing processes, e.g.,

opening, carding and drafting.

Formation of hooks and neps by fiber entanglee ment is a hurdle to the spinning process and reduces

the strength and elongation of the yarn. Pillings small fiber balls made by fiber entan-

tPresent address : Faculty of Textiles, Kyoto University of Industrial Arts and Textile Fibers

glements spoil the looks of fabrics and knit goods made of synthetic fibers. Fiber entanglement is caused, in most cases, by the bending of fibers. With this in mind, we made experiments and observations and phenomenally studied the bending of fibers and fiber entanglement.

We began by dipping a tracer fiber in a viscous liquid -a uniform shearing field and looking at its bending by the force of the liquid.

In the second stage, we placed a sliver between two cylinders (we did not dip it in the viscous liquid), thus replacing a uniform shearing field with a friction force field, and watched the bending of the tracer fiber.

In the third stage, we built a test carding machine by attaching wires to the cylinder surfaces, thought of this test machine as a service carding machine and,

Vol. 12, No. 3 (1966) 107

with its aid,

of the fiber

inquired

and fiber

phenomenally into

entanglement.

the bending

2. Experimental Apparatus

Observations were made with the test machine of the Couette type on which two concentric cylinders ran

independently at varying speeds and rotated in opposite

directions or in the same direction. This Couette-type machine is generally used to measure viscosity, but

we called it a Mason-type machine in honor of Prof.

Mason[1] who used it to observe the proneness of fibers to bend in the viscous liquid.

Figs. 1 and 2 show a

machine. The theory of in what follows. [2]

schematic diagram of this

this apparatus is illustrated

The flow between the two cylinders in Fig. 3 is a laminar and Newtonian flow. The pattern of its velocity distribution is expressible by these equations :

-`~ (wl+CO2) (.y2-R12)R22 (~ ~~) WY (:1 (R 2_R2y2 2 1 )

and dcoy ((orr(o2) R12R22

y_ y dy (R22-R12) y2

where coy=the angular velocity of the clockwise direction of

the flow at radius y, (ol =the angular velocity of the counterclockwise direc-

tion of the inner cylinder at radius R, (02 =the angular velocity of the clockwise direction of

the outer cylinder at radius R, Gy=shearing rate at y.

Assuming R to be the distance from the Couette axis to the fiber, then WR = 0, which, in the light of eq. (1), develops into : 1/R2=(R12w1+R22w2)/R12R22(col (02) .........(3) Shearing rate G at this point is :

G=2(R12w1+R22w2)/(R22-R12) .........(4) Assume that this apparatus has R1=7.0 cm, R2= 9.5 cm ; that the inner cylinder rotates in a clockwise direction with revolutions n1 per minute ; that the outer cylinder makes revolutions n2 per minute ; and that n1 and n2 are 20 and 1 rpm, respectively. The shearing rate, then, is :

2(-R12.2,rn1 +R22.2,zn2) G = (R22 -R12) -4.5 (sec 1) ...(5)

Fig. 1 Principle of double Couette apparatus

Fig. 2 Schematic diagram of Mason-type machine

Fig. 3 Detailed diagram of cylinder part

108 Journal of The Textile Machinery Society of Japan

The route of transmition of power for the outer cylinder is 1--> 2-~ 3, as shown in Fig. 1. The route of transmition of power for the inner cylinder is 7-+6 -~5--4-~3' . The inner cylinder is varied in speed by speed changer 4. The outer cylinder is fixed at 1 rpm by the speed reduction device.

The details of the cylinder part are shown in Fig. 2. The two concentric cylinders are driven by two motors. The inner cylinder Al (7.0 cm in outer diameter) transmits power from C1 of the same shaft and rotates with the same number of revolutions per minute as Cl. Cl is varied in speed from 20 to 200 rpm by the speed changer shown in Fig. 1. A1, too, rotates with the same number of revolutions per minute. The outer cylinder A2 (diameter 9.5 cm in inner diameter) transmits power from C2 of the same shaft. A2 rotates with the same number of revolutions. C2 is driven at 1 rpm, because its motor revolutions are reduced to 1/200. We used a transparent plastic plate for the bottom of A2 so as to observe, from above the cylinders, buckling or entanglement of fibers illuminat-ed by light from lower point E.

3, Method of Experiment

We began by dipping nylon fibers, one each of different lengths-such as 1.0, 1.5, 2.0 and 2.5 cm all about 3.7 in denier, in the liquid between the two cylinders. As the two cylinders rotated and the liquid moved with them, we saw that the fibers in the liquid flowed with the rotations of the cylinders.

The behavior of each fiber during the rotations is shown in Fig. 4 and is classified into one of three types of orbits :

Type A, in which a fiber rotates like a rod without flexing or bending. Type B, in which a fiber bends or buckles during cylinder rotations, the bending occurring simultaneously along its length or at one or two points of weakness. The motions of the two ends are usually not independent of each another.

Type C, in which a fiber being flexible, bends. The region of the maximum curvature moves along the fiber as cylinder rotations progress. The ends of the fiber move independently of each another.

We then used water (0.01 poise) and polyvinyl alcohol of two different degrees of viscosity to measure fiber behavior during flow at a nearly constant tem-

perature and humidity. The two kinds of polyvinyl alcohol were 20 and 500 poises, respectively, in viscosity

by the ball-dropping type method. [3) Dry fibers were 0.0240 mm in diameter and wet fibers 0.0258 mm. In Young's modulus, dry fibers were 4.7 x 104 kg/cm2 and wet fibers 2.7 x 104 kg/cm2.[4] The behaviors of 50 fibers of the same length at one viscosity degree were observed, classified into orbits A, B and C and shown in percentages.

In the second stage, we placed a sliver between the two cylinders, changed their surface roughness and studied how the fiber assembly behaved with the sur. face roughness of the cylinders changed. Then we obtained the distance between the inner cylinder (5.5 in. in outer diameter) and the outer cylinder of the Mason-type machine as follows :

Assume Reynolds number Re, dynamic viscosity coefficient v of air, surface velocity v of the cylinders, distance d between the two cylinders, cylinder diameter D, and revolutions per minute (rpm) n. Then :

Re=vd/v .........(6)

and v=,rDn .........(7)

Therefore, Re=,rDnd/v .........(8)

We used the dimensions of a Saco-Lowell flat card, D=40 in., n=165 rpm, v=15.61x10 .6 ft2 sec-1, d=10/ 1000 in., to determine distance d between the cylinders and the number of revolutions of the test machine. We may use its dynamic similarity[5] if we think of the test machine as a service carding machine. Then Saco-Lowell flat card and the Mason-type machine (the inner cylinder D=5.5 in. in diameter) are equal in Reynolds number :

40x65x10/1000=5.5xnxd=154 (9) If n is 120 rpm, d is 1/10 in. in the light of eq.

Fig. 4 Schematic representation of rotational orbits

Vol. 12, No. 3 (1966) 109

(9). We used these figures as the standard condition for our experiment and experimented with cotton card slivers 40/s and nylon card slivers (1.5 d X 3.8 cm). We made these slivers as long as the length of the circum-ference of the inner cylinder and inserted them uni-formly between the cylinders. To observe fiber configuration with the cylinder surfaces finished at degree p j, we varied the revolutions of the inner cylinder in number from 90 to 120 and 150 rpm, and fixed the number of revolutions of the outer cylinder at 1 rpm. The nylon and cotton slivers inserted between the cylinders were 0.05, 0.10 and 0.15 g in weight. Fifty tracer fibers, dyed red, 1.0, 1.5, 2.0 and 2.5 cm long, were placed in a sliver parallel to the inner cylinder surface. The tracer fibers were de-formed by rotations of the cylinder for one minute. The degree of deformation of configuration depended upon the quantity of fibers between the cylinders and the rotation speed. The deformed fibers were removed from between the cylinders and classified as in Table 1.

To observe fiber configuration with emery paper

(Grid No. 380c) stuck on the cylinder surfaces, we kept the outer cylinder stationary and rotated the inner cylinder at 20 and 70 rpm, the two cylinders being spaced 1/10 inch. Slivers weighing 0.03, 0.05 and 0.07

gram were inserted between the cylinders. After ro-tating the inner cylinder one minute, we classified the fiber configuration, and measure the length, diameter and weight of the fiber assembly. Rotating radius re of the fiber assembly was given by the ratio of length l to apparent diameter d of the fiber assembly

re=l/d .........(10)

The outer cylinder being kept stationary, shearing rate G was calculated by eq. (5) as follows :

G=56.65 sec-1 on n1=20 rpm

G=198.28 sec-1 on n1=70 rpm

In the third stage, we attached metallic wires to

the inner cylinder and cloth wires to the inside of the

outer cylinder of the Mason type machine to experi-

ment with nylon. The card wires used are listed in

Table 2.

We kept the outer cylinder stationary and varied

the revolutions of the inner cylinder in number from

90 to 120 and 150 rpm. We inserted nylon slivers

between the cylinders, counted the number of neps

forming after one minute's revolutions of the inner

cylinder and classified them as in Table 3. The quan-

tity of nylon slivers was varied from 0.2 to 0.4 and

0.6 gram. The true number of neps formed was

obtained by deducting the number of pre-rotation neps

from the number of post-rotation neps.

4. Results Discussed

4-1 Fiber Orbits Deformed by the Viscous Liquid among the Cylinders

(1) Liquid viscosity and critical modulus of buckl-ing of fiber. Fig. 5 shows the types of fiber orbits for various viscosity degrees and various fiber lengths. It points to two features : i) With a low viscosity degree, the number of orbits declines in order of types A>B>C ; ii) With a high viscosity degree, the order is reversed : types C>B>A.

It is, therefore, difficult for a fiber to bend or buckle with a low viscosity degree-but easy for a

Table 1 Fiber Orbits Classified

Table 2 Card Wires Used

Table 3 Neps Classified


fiber to do so with a high viscosity degree. The smallness of the number of orbits of type B shows that a nylon fiber, being limited in the number of defects, does not bend easily at one or two points in its whole length. Generally, the longer a fiber, the more clearly it exhibits features 1 and 2 and the more flexible it is. The reason seems to be that a fiber rotating in a uni-form circle receives compressive force and tension in some part of the shearing field.

It is common knowledge that compressive force and tension have a maximum value when they are in the direction shown by the small arrows in Fig. 4. Since a flexible f lber buckles under comporessive stress, it follows that a flexible fiber buckles if maximum com-

pressive force Fmax satisfies the following condition : Finax 4EbI/12 .........11

where Eb is the bending modulus, I is the moment of inertia of the fiber around its axis and l is the fiber length. Evaluation of Fmax and I leads to this approximate equation : [6]

(G71)critical=Ei(log 2re - 1.75)/2re4 .........(12)

where G=rate of shear, sec-1

re=axis ratio, l/d, (length/diameter)

~=liquid viscosity, poises If the critical value of (G,~) exceeds the critical

value given by eq. (12) is just exceeded, a fiber buckles and then rotates in a type-B orbit. If shearing forces far exceed the critical limit, the buckling force become severer and a more complex rotational orbit, type C, develops.

Eb for uniform cylindrical rods should be identical with Ebo=Fl3/48I~ measured by putting a load in the middle of a beam and supporting its ends, where load F

produces maximum deflection on a beam of length 1. Ebo and Eb are compared in Table 4. The differences between Eb and Ebo are large.

Fig. 5-1 Orbit

Fiber

distribution as

length 10mm

a function of liquid viscosity.

Fig. 5-2 Orbit

Fiber

distribution as

length 15mm


Table 4 Critical Bending Modulus, Eb, with young's modulus of wet 104kg/cm2

for

fiber,

comparison

Ebo = 2.7 x

Fig. 5-3 Orbit distribution as a

Fiber length 20mm

function of liquid viscosity.

Fig. 5-4 Orbit

Fiber

distribution as

length 25mm


Vol. 12, No. 3 (1966) 111

We see from Table 4 that the modulus of the bending of a fiber must exceed the critical bending modulus if a fiber is not to buckle in viscous liquid. We find many orbits of type A at 0.01 poise. At 500

poises we find only a few type-A orbits and an in-crease in the number of type-C orbits.

(2) Reproducibility Table 5 gives the results of experiments with 50 fibers 1.5cm long in water (0.01 poise). The exper-iments were made by two men, identified here as S

and K. Experiment Nos. 1 and 2 were made at the same temperature and humidity ; Nos. 3, 4, and 5 at a lower temperature. The experiments suggested good reproducibility.

(3) Preparing test fibers. We used filaments in these experiments. We cut

them in a desired fiber length and left them in a liquid

for one day, because dry and wet fibers differ in

Young's modulus. The filaments were removed from

the water with a pair of tweezers. Bent fibers were

discarded. Straight fibers were compressed lightly and

dipped one by one in the liquid. Table 5 shows that

Table 5 Reproducibility of Experiment

Table 6 Nylon Fiber Orbits

112 Journal o f The Textile Machinery Society of Japan

variations in the viscosity of the liquid with varying temperatures is larger than the influence mentioned earlier.

(4) Sources of errors. Some fibers did not rotate in a horizontal plane

and their observed orbits were incomparable with those of more ideally orientated fibers. This was true of rigid fibers or permanently deformed fibers. They were excluded from the data. Some skill being requir-ed to classify the orbits of fibers, classification was made by a specially chosen person. It is clear from the data in Table 5 that errors having to do with the classifier's skill are only slight and that the measured data are reproducible.

(5) Factors contributing to buckling of fibers Fibers do not get entangled without buckling.

Whether fibers buckle depends on the following factors: i) the cross-sectional form of a fiber and the fiber length ; ii) the inner structure of the fiber ; iii) the

presence or absence of points of weakness along the fiber length ; and iv) permanent deformation of the fiber.

4.2 Fiber Configuration Depending on Roughness of Cylinder Surface.

The observed values of fiber configuration with the cylinder surface finished at degree qp are given in Tables 6 (for nylon) and 7 (for cotton). The follow. ing conclusions are deducible from the experimental values :

(1) Orbits B are larger in number than orbits A, C. D and E.

(2) Orbits B decreases in number with an increase

Table 7 Cotton Fiber Orbit

Vol. 12, No. 3 (1966) 113

in fiber length. This relation is clear so long as cylinder revolutions are 90 rpm, but ceases to

be clear if revolutions increase beyond this figure.

(3) Where the number of revolutions and the fiber length are the same, orbits B decrease in number

and orbits C increase with an increase in the

quantity of fibers. The number of orbits (B+C) is unrelated to the number of revolutions and is

constant.

(4) Orbits D and E are smaller in number than orbits A,BandC.

(5) Orbits D and E of cotton are larger in number than orbits D and E of nylon. Orbit D is in-

fluenced by the shape of the cross section of the fiber ; orbit E, by the breaking strength.

(6) Cotton being shorter in fiber length, its orbits (B+C) increase with an increase in the quantity

of fibers. Furthermore, these orbits decrease in number and orbits (D+E) increase with an increase

in the number of revolutions. This tendency is not as clear in nylon as in cotton.

We took the mean values of 12 experiments with nylon and 20 experiments with cotton, with emery

paper stuck on the cylinder surfaces during the experi-ments. The results on fiber configurations are given in Table 8. The weight of the configurated fibers is

given in Figs. 6 (for nylon) and 7 (for cotton). From these data we conclude :

(1) That a fiber assembly increases in weight with an increase in the quantity of slivers placed bet-

ween the cylinders. A nylon fiber assembly is heavier in weight than a cotton fiber assembly.

Nylon being 1.14 in specific weight and cotton 1.54, the fibers in a nylon fiber assembly exceeds in number the fibers in a cotton fiber assembly.

Obviously, then, nylon buckles more easily than cotton.

(2) Assemblies of both nylon and cotton fibers contacts with both cylinders while rotating, the radius of

rotation being about equal for both fiber assemblies.

(3) Fig. 8 contains photographic observations of the process of slivers buckling and forming a fiber assembly. Fig. 9 is a model of this process.

Fig. 9 (1) shows fibers being caught on the cylinders and beginning to buckle by their axial force. As the inner cylinder rotated in the direction of the arrow, the buckling of fibers progressed as in Figs. 9 (2) and (3), fibers being bent by the rotations of the inner cylinder.

Fig. 6 Relation between weight

and sliver weight

of configurated nylon fibers

Fig. 7

Table

Relation between weight of configurated cotton fibers

and sliver weight

g configurated Nylon and Cotton Fibers with Emery

Papers Stuck on Cylinder Surfaces

114 Journal of The Textile Machinery Society o f Japan

Fig. S Process of nylon fibers forming assembly

Vol. 12, No. 3 (1966) 115

Fig. 10 Process of two nylon fibers balls merging into one


Part a of the bent fibers in Fig. 9 (4) was detached from the inner cylinder by its rotations, as shown in Fig.9 (5). Furthermore Part a of the bent fibers was caught

in the upper part of the fiber assembly and formed the nucleus of a fiber assembly as in Fig. 9 (7).

(4) Fig. 10 is a photographic illustration of two fiber assemblies in a row merging into one by reason of rotations. Fig. 11 is a model of the process shown in Fig. 10

Fiber assemblies b and c are connected in a row by fibers, as shown in Fig. 11 (1), and, therefore, rotate by slipping.

b is pulled by, and close to, c as in Fig. 11 (2) ; they merge into one and rotate as in Fig. 11 (3). They keep rotating together and form a perfect fiber assembly, as in Figs. 11 (4) and (5).

4-3 Nep Formation When Mason-type Machine is Used in Place of Service Carding Machine.

The number of neps forming in the experiment under review in this section is given in Tables 9 (for nylon) and lOa (for cotton). These tables are the mean values of five experiments on nep formation conducted by varying the quantity of slivers and the number of revolutions. The number of nylon neps before revolutions started was zero. The number of cotton neps at this time was as given in Table 11. The true number of neps resulting from carding is obtaina-ble by deducting the number of the neps in Table 11

from the number

unmber is given

of neps

in Table

in

10b.

Table 10a. The trueFig. 9 The process model of Fig. 8

Fig. 11 Process model of Fig. 10

Table 10a Number of Cotton Neps

(Mean value of five experiments)

Table 10b Number of Cotton Carding Action

(neps determined

Neps

from

Formed by

Tables 9, bOa)

Vol. 12, No. 3 (1966) 117

Fig. 12 Process of cotton fibers sinking and increasing among card wires. Arrow shows direction of the cylinder revolutions. (8) Fibers removed from among card wires

118 Journal o f The Textile Machinery Society of Japan

Fig. 13 Process of cotton nep formation

Vol. 12, No. 3 (1966) 119

The number of pre-experiment neps was the number of neps in slivers of a uniform weight and was the mean value of five experiments each with nylon and cotton. Nep formation was subject to variation, the coefficients of variation being 0.2' 0.4 for nylon and O.1-O.2 for cotton. With an increase in the number of revolutions of the cylinders, neps increased in num-ber on the outer cylinder.

(1) Experimental values discussed 1) The higher the sliver density, the larger the

number of inter-fiber contacts and the larger the force of inter-fiber friction. In our opinion, the amount of force needed to draw a fiber out of a sliver makes carding action difficult and conduces to nep formation.

2) Since our test machine was not a service card-ing machine and its revolutions were limited to one minute in time, it produced more chances of inter-fiber contact and increased the force of inter-fiber friction, thus adding to the difficulty of carding action and conducing to nep formation.

We varied the rate of the nep formation per rev-olution, with the results shown in Tables 12 (for nylon) and 13 (for cotton). The tables suggest that the rate of nep formation per revolution of the cylinder decreases with an increase in the number of cylinder

revolution and bear out Nozaki's findings.C7] 3) Figs. 12 and 13 show the process of nep for-

mation. Fig. 12 shows the state of fibers sinking among wires with time. Fig. 13 shows the process of the formation of small neps as sunken fibers increase in number among wires. Fig. 14 is a model of this

process.

Fig. 14 (1) shows the state of wires drawing fiber out of slivers soon after cleaning, arranging them ab-reast and doing sliver-carding. Fig. 14 (2) shows fibers sunk to the bottom of the

wires and floating fibers. As fibers sink among the wires, so they buckle, as they do when emery paper is stuck on the cylinder surfaces, and go to form an orbit in the shape of the capital letter S, as shown in Fig. 14 (3).

As fibers forming an orbit in the shape of the letter S strain to become a big ball, so their axial force acts toward the direction of the arrow. Then one end of the fibers become lodged at the roots of the wires, as shown in Fig. 14 (4), are pulled by the cylinders and forms the globe shown in Fig. 14 (5). Even then, they can be opened, if the heads of the wires are sufficiently out. However, when a large number of fibers sink among the wires, they very often become a large fiber assembly by a repeated

process. This process creates small fiber balls which cannot be opened even by carding. Such balls are called neps.

Table 11 Number of Cotton Neps before Carding (Mean value of five experiments)

Table 12 Rate of

(Mean

Nylon Nep

value of five

formation per

experiments)

Revolution

Table 13 Rate of (Mean

Cotton

value of

Nep

five

Formation per experiments)

Revolution

Fig. 14 Process

forming

model

peps

of entangled fibers among card wires


(2) The process of nep formation by buckled and rounded fibers.

We considered in further detail the model experi-ment-Figs. 14 (5) and (6) on the process of nep formation. To begin with, we made five polyethylene fibers, 1mm in diameter, into a ball. We thought of the small piece of wood, 2 cm high (Fig. 15), as wires.

We placed a thin plastic plate on the piece of wood. We wedged the fiber ball between the plastic

plate and the underlay We tied one end of a black tracer fiber in the fiber ball with nylon yarn and

pulled it toward the arrow and thought of the pro-cedure as carding action. Pulling out the tracer fiber changed slightly the

relative positions of the constituent fibers of the ball, but left the ball largely unchanged in size. This would

permit easy pulling out of the constituent fibers ; it would mean smooth carding action. Conceivably, the pulling out of the tracer fiber could have tightened the ball, resulting in the shrinking of the constituent fibers and in increasing the density of the ball. Large force would then have been needed to draw the fibers, and the drawn fibers would have snapped. The snapped fibers would have returned in the so-called "snap-back buckling." A tightened ball is called a nep.

The state of fibers being tightened from the side directions during drawing is shown in Fig. 16 (1). It is similar to the tightening of an elastic body while being pulled from the side directions, as illustrated in Fig. 16 (2). The constituent fibers of a ball are pulled toward the arrow by drawing force and the ball is com-

pressed and tightened further as a result. However, a fiber ball differs entirely in structure from an elastic body and is too complicated in its structure for an analysis to be easily possible. Go back to the imaginary tightened fiber ball men-tioned in the last paragraph but one. Some of the

constituent fibers, other than the broken tracer fiber, could have been drawn. Therefore, the process of nep

formation is a probability problem related to the condi-

tion of fiber entanglement and to the force and direc-tion of carding action. This relation is illustrated in

Fig. 17.

The phenomenon of entangled fibers being formed into neps by carding action is irreversible and makes

for poor reproducibility. This explains why the me-

chanism of nep formation has been studied but little. The relation between entanglement and disentangle-

ment of fibers resembles the relation between entangle-

ment and disentanglement of chain molecules[81and is presumably close to a reversible phenomenon. In

some cases, neps can be opened by carding action. Hence the dotted line in Fig. 17.

5. Conclusions

We devised a Mason-type test machine, a kind of Couette-type viscometer. We dipped a fiber of a certain length in viscous liquid. The fiber was bent by shearing force generated by the rotations of cylinders. We classified fiber orbits into three types. The sma-ller the shearing force, the larger the number of orbits of type A. The number of orbits was in order of A>B>C showing that there was little buckling of fibers. The larger the shearing force, the larger the

Fig. 15 Drawing tracer fiber from

Arrow shows direction of

model fiber

drawing

assembly.

Fig. 16 Similarity of tightening from side direction by

drawing fiber from assembly to tightening from

the side direction by

body

pulling perfect elastic

Fig. 17 Nep formation and disappearance in carding action

Vol. 12, No. 3 (1966) 121

number of type-C orbits. The order was reversed : C>B>A.

We observed fiber entanglement by the roughness of the surfaces of cylinders used for our test machine. With the cylinder surface finished at degree pp, fibers were only disarranged, there was no carding action and many fibers buckled in slivers. A few fibers were damaged ; the damage reduced the bending modulus of fibers. Presumably, therefore, the damaged fibers made the nucleus of neps during carding.

We made serial photographic observations of fiber assemblies forming when emery paper was stuck on the cylinder surfaces. Evidently, fibers buckled and made fiber balls. We found that two fibers assemblies in a row easily merged into one.

We thought of our test machine with card wires attached to its cylinders as a service carding machine and let neps form on it. This experiment showed that the higher the sliver density, the larger the number of neps. The rate of nep formation per revolution decreased with an increase in the number of cylinder revolutions. Fiber ball forming on the cylinder surfaces with card wires attached were smaller in size than fiber balls forming on the cylinder surfaces with emery paper stuck on them.

In our opinion, the mechanism of nep formation consists of the buckling of fibers and the tightening of buckled and rounded fibers by fiber-drawing from the side directions. The larger the number of fibers sinking among card wires, the larger the number of neps forming. Photographic observations showed that neps formed and disappeared in the carding process.

We thank Prof. S. Backer of the Textile Division,

Massachusetts Institute of Technology ; Mr. A. Tsubota of the Takatsuki Textiles Research Laboratory, Kureha

Spinning Co. ; and Dr. C. Nozaki of the Toyota Central Research Laboratory, for their constant and valuable

helps in this study. we express also our gratitute to

the Toyo Rayon Co., the Fuji Spinning Co., the Mitsu-bishi Rayon Co. and Yanagisawa Seiki Co. for their

cooperation in our experiments.

Literature cited

[1] A. A. Robertson, E. Meindersma and S. G. Mason ; Pulp Paper Mag. Canada, 62, No. 1, T3(1961)

[2] W. Muller ; Einf iihrung in die Theorie der Zahen Flussigkeithen, translated by H. Honma, p. 221,

Korona Press. (1942)

[3] T. Nakagawa and H. Kanbe ; Rheolog y, p. 504, Misuzushobo (1955)

[4] W. Tsuji ; "On Measuring of the Young's Modulus and Stiffness of Fibers", The Physical Research

Method of Fibers, p. 9, Boshokuzashisha (1940)

[5] K. Komodori ed ; Experimental Methods in Mecha- nical Engineering, p. 35, Nikkankogyo Press (1963)

[6] J. M. Berger ; Second Reports on Viscosity and Plas, tisity. pp. 19, 10, North Holland Publishing Co.

(1938) [7] C. Nozaki, et al.; Reports of Nagoya Kogyo Shi- ken jo, 10, 775 (1961)

[8] E. R. Eirich ed ; Rheolog y, Theory and Application 2, p. 92 (1958) Academic Press Inc Publishers. New York


mechanics of fiber entanglement

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