steady state mechanics of the false twist yarn

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ISTEADY STATE MECHANICS OF THE FALSE

TWIST YARN TEXTURING PROCESS

by

RAYMOND Z. NAAR

Ing. A.I.V., Ecole Superieure des Textiles de Verviers(1955)

S.M., Massachusetts Institute of Technology(1958)

SUBMITTED IN PARTIAL FULFILLMENTOF THE REQUIREMENTS FOR THE

DEGREE OF

DOCTOR OF SCIENCE

at the

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

FEBRUARY 1975

Signature of Author_

Department of Mechanica4 Engineering,

Certified by

December 5, 1974

- - -- -Nw, V

ThesiA Supervisor

Accepted by

Chairman, Department Committee on Graduate Students

AfAR 3 1975LOR 1ctS _

II

STEADY STATE MECHANICS OF THE FALSE

TWIST YARN TEXTURING PROCESS

by

RAYMOND Z. NAAR

Submitted to the Department of Mechanical Engineeringon December 5, 1974 in partial fulfillment of the requirements

for the Degree of Doctor of Science

ABSTRACT

In the false twist texturing process a moving threadlineis subjected to temporary twist while heat is applied to partof the twist zone. The purpose of the process is to heat setthe twist deformation so that after cooling and twist removal,the filaments will seek to return to their set helicallycrimped paths. This crimping action leads to bulk and/orstretch development such as is encountered in double knitsuitings and/or stretch hosiery.

During processing, the entire twisted threadline is underconstant tension and torque, but is not at constant temperature,since part of it is intentionally heated to effect the settingprocess. The threadline is thus divided into three contiguouszones, all under the same stress field but each with differentmechanical properties. The threadline tension is a result offilament strain which arises from the difference between thedenier of the exiting yarn (imposed by the feed and exit rollvelocities) and the equilibrium denier for the unrestrainedyarn at the heater temperature, while the torque is due to thetwist imparted by the spindle. In the portion of the thread-line before the heater, the torque is supported by componentsof the bending and torsional moments acting on the individualfilaments, as well as the moment due to the tension of thefilaments. At the heater, the bending and torsional momentsbecome insignificant, and the torque is supported by tensioncomponents only; the twist, therefore, increases to maintaintorque equilibrium. This uptwisting is assumed to occur with-out filament migration. As the properties of the filamentchange along the threadline due to temperature changes, so doesthe mechanism by which the yarn is deformed.

The pertinent filament properties and yarn twistingmechanism have been analyzed. Values of tension and torquehave been calculated for a wide range of temperatures and over-feeds and are in agreement with experiment.

Thesis Supervisor: Professor Stanley BackerTitle: Professor of Mechanical Engineering

3

ACKNOWLEDGEMENTS

The author is indebted to the Phillips Petroleum Company

and to the WESTVACO Corporation for their fellowship support

in the early stages of his graduate program. Thanks are due

also to Burlington Industries, Inc. and to the E. I. du Pont

de Nemours & Company for fellowship and research assistantship

support during the latter part of his doctoral research. With-

out this generous industrial backing and encouragement the

completion of this program would not have been realized.

The author wishes to thank Professor S. Backer, Professor

M. B. Bever, Professor E. Orowan and Professor I. V. Yannas who

served on his Doctoral Committee. He greatly profited by con-

tact and discussions with them on scientific and other topics.

He also profited by discussions and collaboration with a number

of classmates and office mates, among them A. Crugnola,

D. Brookstein, A. Tayebi, S. Arghyros, B.Y. Lee, C. Brogna.

He also greatly profited from contact, discussions and

friendship with Drs. S. Batra and W. L. Yang, staff members of

the Fibers and Polymers Laboratories. The support of

Professor Yannas, who was always ready to help, listen and make

suggestions is most gratefully acknowledged. Professor

J. J. Thwaites was most helpful and gave unstintingly of his

time. The writer greatly profited from discussions with a

person of such critical and creative wit and is sincerely

grateful to him.

The author wishes to acknowledge the moral support he

received from his colleagues in the Department of Chemical

Engineering at Tufts University, Professors van Wormer, Botsaris

and Sussman. He is also grateful to Professor Gyftopoulos who

never ceased to encourage him towards completion.

Among others, the writer wishes to thank his wife and his

mother for their encouragement. Many thanks to

Dorothy Eastman who typed many of the progress reports connected

with the manuscript; to Joanna Larsen for typing the manuscript,

and to Guddi Wassermann for her accurate drawings.

4

Finally, it would be unfitting to conclude without stressing

the writer's deep indebtedness to Professor Stanley Backer,

the Chairman of his Doctoral Committee, who helped, advised and

encouraged the writer throughout his work. The writer considers

himself lucky to have been associated with a person of

Professor Backer's stature; he enjoyed and greatly profited

from the experience of working under a man of uncompromising

standards of quality and capability of seeing through complex

situations to the simple physical essence of a problem.

5

TABLE OF CONTENTS

Abstract

Acknowledgements

List of Tables 9

List of Figures 10

Chapter I.

Introduction 12

Chapter II.

Plan of Work 14

Chapter III. The False-Twist Process 15

(a) Description of the Process 15

(b) Twist Development in the Machine 18

(c) Controllable Machine Variables 20

(d) The False-Twisted Yarn 21

(e) Machine-Yarn Interaction 22

Chapter IV. Yarn Geometry 26

(a) Model for Yarn Geometry 26

(b) Yarn Contraction 30

Chapter V. Yarn Mechanics 31

(a) Classical Mechanics 31

1. Stress-Strain Curves of Yarns 31

2. Average Filament Strain 34

3. Yarn Torque 35

Bending Moment Contribution to Yarn Torque

Fiber Torsional Moment Contribution to Yarn

Torque

Torque due to Tension

(b) Tension and Torque for the Case of Equal

Tension on all Filaments 40

1. Tension: Stress-Strain Curve 41

2. Torque 41

(c) Overtwisting 42

1. Stress-Strain Curve 42

6

2. Torque in Overtwisted Yarn

3. Overtwisting from Zero Twist

4. Average Filament Strain on Overtwisting

5. Average Filament Strain on Overtwisting

in Various Zones of the Yarn

6. Torque on Overtwisting in Various Zones

of the Yarn

Chapter VI. Experimental Apparatus and Materials

(a) Apparatus

1. Texturing Machine

2. Torque Measuring Apparatus

3. Tensile Testing Machine

(b) Material Properties

1. Stress-Strain Curve of Feed Yarns

2. Stress-Strain Curve of Yarns Processed

through the False-Twister without Twist

3. Stress-Strain Curve of Freshly Textured

Yarns

4. Stress-Strain Curve of Yarns at Elevated

Temperatures--The Contractile Stress

Chapter VII. Experimental Results: Twist and Tension

(a) Introduction

(b) Experimental Procedure

(c) Experimental Results

1. Twist in Exit Zone

2. Twist in Entrance Zone

3. Tension

4. Denier

5. Analysis of the Data and Implications

for the Process

(d) Experimental Results: The Effect of Twist

(e) Experimental Data: The Effect of Draw Ratio

(f) Qualitative Model for the Process

Chapter VIII. Calculation of Tension

(a) False-Twister Operating, but Spindle

Stationary

1. Analysis

46

47

48

49

50

51

51

51

54

54

58

59

60

60

69

76

76

78

82

82

85

85

90

90

92

92

92

100

100

100

7

2. Experimental Verification

(b) Determination of the Tension during False-

Twisting

1. Analysis

2. Experimental Verification

3. Discussion

4. Example of Tension Calculation

Chapter IX. Measurement and Calculation of Torques

(a) Introduction

(b) Torque in the Entrance Zone

1. Torque due to Filament Bending

2. Torque due to Filament Torsion

3. Torque due to Filament Tension

4. Comparison of Calculated and Experimental

Data for the Case of the Entrance Zone

(c) Torque in the Heater Zone

1. Material Properties

2. Torque from Classical Yarn Mechanics and

from Equal Filament Tension Contributions

3. Overtwisting

4. Discussion of the Data

(d) Example of Calculation of Torque

1. Entrance Zone

(i) Torque due to Tension

(ii) Torque due to Bending

(iii)Torque due to Torsion

2. Heater Zone

(i) Torque due to Tension

(ii) Torque due to Bending

(iii)Torque due to Tension-Overtwisting

Chapte

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