103

CHAPTER 6 SEAM SLIPPAGE AND THREAD SLIPPAGE

6.1 INTRODUCTION This

chapter is concerned with seam

slippage

and

thread slippage in the fabrics. In

the past ten years or so, an increasing

amount

of work has been reported on the study of factors involved in the seaming of thread in high speed industrial sewing machines. Studies have also been made of the properties

of

the thread in the seams after sewing and these include seam slippage. recent

Thread slippage tests have been carried out

years principally to have an idea about the

in

fabric

softness. 6.2 LITERATURE REVIEW 6.2.1 Seam slippage Seam of

the

slippage in sewn fabrics is the

fabric yarns parallel and adjacent to

displacement the

stitch

line. It is described as the amount or degree, a fabric pulls away at the seam. Unsatisfactory seams may be due to yarn slippage or yarn breakage. Yarn slippage is associated with fabrics such as satins. It occurs in fabrics in which warp and weft interlacings are relatively few in number, particularly, when such materials are woven lustrous and slippery yarns [81].

from

highly

104

Seam

slippage property is associated

with

thread

slippage which is very important in man made fabrics

[82].

Thread slippage, is defined as the pulling force needed

to

produce movement of one thread over the cross threads. slippage properties mainly depend upon weave and sett.

The The

thread

the

slippage

quantitative

property

difference

is useful

in

determining

between the washed

and

unwashed

fabrics. Galuszynski some

under

[83] has stated that when the seam

transverse

strain,

then

displacement

slippage) of stitch relative to one or more of the can

occur.

The

displacement other,

stitch

displacement

(seam fabrics

produces

of one yarn system in the fabric against

which

causes some opening in the

fabric

is

to

some the take

place. This phenomenon is an adverse feature of some woven fabrics, decreasing the range of their possible end uses and causing some problems in the clothing industry. Seam

slippage may occur in a garment or

household

item, because of a lower number of warp or filling yarn an

inch,

too

construction latitudinally

shallow

fabric

seam

slipping

allowance, either

improper

longitudinally

whilst being sewn, by the use

of

to seam or

incorrect

threads and too large an eye in the needle plate. The size of the seam opening is used to measure resistance to slippage [84]. When two pieces of fabric joined together with a row of stitching in a plain seam (type SSa-1), are strained to a point below the breaking point of the seam, at right angles to the seam, one observations may be made:

or

both

of

the

following

105

(a)

The seam itself may open and produce a gap between the two places of fabric.

This is termed seam grin and is

controlled by stitching tension and stitch density. (b)

The fabric at both sides of the stitching may threads

and seam.

within the fabric slide

away

This is seam slippage and arises,

distort from

the

principally,

from the construction of fabric [85]. The factors which lead to seam slippage are: 1)

Weave with

- A lower weft

number of interlacings (warp

threads)

per unit area

permits

threads the

easy

sliding movement of threads when a seam is subjected to a load. 2)

Fabric density - A relatively open fabric

construction

allows the threads easy freedom of movement 3)

Type

of fibre/yarn - A smooth yarn moves readily

other are

yarns.

very

Continuous filament yarns in

slippery and can produce fabrics

over

particular which

are

highly susceptible to seam slippage. 4)

A lower number of ends and picks per inch with coarse yarns - Seam slippage and seam failure are likely if narrow seam allowances are used.

5)

Crimp ratio - If warp and weft threads are crimp free, for any reason, then seam sewn at right angles to this direction may be susceptible to seam slippage.

6)

A lubricant or softener applied to the fabric may allow yarns within the fabric to move more freely.

The

fabric resistance to seam slippage depends

on

the yarn to yarn friction, the contact angles between the threads (fabric geometry), the number of threads in fabric being

pierced during sewing, the stitch density,

and

the

yarn flexural rigidity, that is an increase in the value of the above factors causes an increase in the fabric resistance to seam slippage. There are other factors, such as,

sewing-thread

thread

diameter,

effects. The resistance to

tension, that

have

needle

diameter

increasing

and

and

sewing

decreasing

seam allowance does not affect the fabric seam slippage but affects only the seam

failure due to slippage [83]. Seam varying the

slippage

strength can also be

increased

finish. The term cover factor is used

to

relationship that exists between the number

by

signify of

yarns

per inch necessary to give enough compactness to keep yarns from slipping the seam objectionably [77],

the

The cover factor or compactness of weave cannot be considered a constant value correlated only to yarn weight. The

coefficient

compactness change author's

of

of friction of the yarn surface the yarn diameter are factors

and

which

the cover factor for a given yarn weight. (Jacob

Solinger)

[77]

experience,

In the

the will the seam

slippage strength of a certain fabric was made satisfactory for a given seam specification by raising the pick count from 42 to 44. However, this same fabric was made with a 41 pick count and satisfactory seam slippage strength by using one of two alternatives, one is by changing the finish and the other is by changing the yarn structure although such as wholly

the yarn size remained intact. Other situations this were found to be true for fabrics - made from

natural

fibres as well as

those

made

from

107

synthetics or blends. same.

The basic principle involved was the

The greater the weave compactness and/or coefficient

of friction of the yarn surface, the greater the slippage strength. These factors also control

seam yarn

severance and fabric distortion. 6.2.2 Thread slippage Seam

slippage property is associated

with

thread

slippage which is very important in man made fabrics

[82].

It is related to abrasion resistance and a high degree of correlation exists between resistance to thread slippage and

abrasion.

It

is

possible

to

evaluate

abrasion

resistance from the values of total force of warp and thread

of

the

modern fabrics are so loosely constructed that they do

not

posses

slippage. Kendal [88] has stated that some

weft

the

requisite cohesion of warp and weft and

consequence, There

are very susceptible to slipping or

as

a

fraying.

have been many attempts made by previous workers

to

determine the accurate method to measure the resistance

to

slip. In 1935, the ASTM published a proposed method of test for slippage of silk and rayon woven Broad Goods, and at that time, they appealed for suggestions as to how this property of resistance to slippage could be measured

[89].

It appears that upto 1942, no further suggestions or improvements, had been accepted and therefore, they proposed a standard test for the measurement of resistance to slippage by means of seam testing. While seam had many good points, the information obtained

testing can be

acceptable and reliable only if the work is conducted by one person. Standardization of this type of testing may therefore,

be

very difficult, because, in

practice,

the

work has to be done in many laboratories with the employment of entirely different apparatus and personnel. The preparation of the sample in a uniform or standard manner is not easy. Even slight variations in the preparation of seams unquestionably may have a very marked influence

on

the

result.

There

are

many

technical

difficulties which could have a most serious effect on

the

test results, even though the tests may superficially appear to have been carried out strictly in accordance with the prescribed method. For e.g., needle damage gripping or binding properties of the stitching

and the material

used may vary enormously, although these variations are not apparent on normal visible examination. Moreover, the complaints in the industry regarding slippage or fraying are by no means confined to the slippage at the seams only, and further, the seams concerned are not those made parallel to either warp or weft, but those made on the bias and with insufficient overlap. These conditions put an entirely different complexion on the material serviceability, and also on the relative value of the seam tests carried out as in the American Standards

Designation

D434/42. Therefore, complications

it

was

necessary

to

eliminate

associated with the stitching seams

and

the to

develop a simpler and more easily controlled method of ascertaining the resistance to slippage of fabric. Kendal [88] suggested a method of measuring thread slippage force in fabrics and was supported and commented by Lomex [86]. Cowles [87] followed a method of measuring force of thread slippage of, warp over weft or weft over warp in nylon and rayon

apparel

fabrics

on

tensile

strength

testing

instrument

fitted

with a stress-strain

recorder

without

introducing the factor of seam opening. Rao and Sukumar [88] studied the subject of thread slippage by method of seam opening. Aswani [82] developed a new method which is free from seam slippage. This method is

based

on measuring resistance to

slippage

of

single

thread by pulling it through the fabric. 6.3

SUMMARY It

carried

is evident that a number of studies

out

on

the seam slippage

and

have

thread

been

slippage.

There is less emphasis on the relationship of seam slippage and thread slippage on apparel, commercial fabrics; this aspect

has been considered in the present study.

6.4 EXPERIMENTAL MATERIALS AND METHODS 6.4.1 Materials The 5.3.3

and

materials described in sections 5.3.1, 5.3.4 were used for seam

slippage

and

5.3.2, thread

slippage. 6.4.2 Methods 6.4.2.1 Determination of seam slippage The method was based on British Standard [89].

3320:1970

This method describes the method of determining

the

ability to slippage of woven fabric at stitched seams. samples were prepared in the standard atmosphere

The but

110

stitched

in

the

ready

made

garment

factory

at

room

temperature. 6.4.2.1.1 Preparation of the fabric sample The samples were cut to a length of 180 mm width of 100 mm. Five specimens parallel to the warp five specimens parallel to weft which did not contain

and and the

same warp or weft threads were selected. The thread, stitch type, stitch density and speed were used as mentioned folding

in section 5.3.4. The samples were stitched, them

together

in

half, matching

the

two

shorter

and seam parallel to and at a distance of 12

by

edges mm.

from the fold. After the seam was completed, the ends of the threads were tied and the fold of each specimen was cut. 6.4.2.1.2 Testing for seam slippage After conditioning the samples, they were tested on Instron model 4301 with the load cell of 5 KN and the speed of 10 mm. per minute. Grab-test was adopted. The clamps were aligned parallel and set at a distance of 75 mm apart. The

specimens

midway

between

were mounted in the clamps

with

and parallel to the edges of

the

the

seam

clamps.

The load was increased to 8Kg for shirting materials and 12 Kg. for suiting materials. After two minutes, the width of the seam opening was measured at its widest place i.e. at right

angles to the seam from the edge of the

undistorted

fabric on one side of the seam, to the edge of the undistorted fabric on the other. Then, the load was reduced to 0.25 Kg on the specimen for two minutes. The seam was remeasured at its widest place. readings was taken.

The mean of

five

111

6.4.2.2 Determination of thread slippage force The method developed by Aswani [82] was

adopted

for the study. 6.4.2.2.1 Preparation of the sample As

illustrated

in

Fig.

specimen was 7.5 cm x 3.75 cm.

6.1,

the

size

of

the

After unraveling, this

was

reduced to 2.5 cm x 2.5cm. The thread which was to be tested was marked in the longitudinal direction. The warp and weft samples were prepared. 6.4.2.2.2 Testing for thread pulling force The test was carried out on Instron model 4301 with the

load

lower

cell of 1 Kg. The specimen was clamped

in

the

jaw of Instron with all the threads, except the

one

which was marked and in the upper jaw, fibre clamp was used to clamp the marked thread. The cross head was allowed to move up, at a speed of 500 mm. per minute. The marked thread was pulled out and the force of slippage recorded on the chart, as illustrated in Fig 6.2.

was The

force

weft

way

An average of ten

readings

was

gives the values of seam

slippage

and

It is clear that, in general,

the

in

direction

grams,

was obtained in warp way

of the fabric.

and

taken. 6.5 RESULTS AND DISCUSSION 6.5.1 Effect of Weave Table thread plain

6.1

slippage force. weave

fabrics

show

greater

resistance

to

seam

112

f

vpei*

jaw

►o

Fj^F^T”

town jflw

----- r 1*5=-----

Fig.6.1

Preparation of the sample

Fig.6.2

Thread slippage force curve

4 3 4

3 2

2 2

HI H2 H3 K

60 90

3 75 4 00

2 2

80 50 10 70 00 65 85 90

3 25 3 80 3 22

10 60 95 20 50 10 55

40

15 55 40 60 10 20

MAX.

Q 1 R Group III

N2 01 02 PI P2

Ml M2 M3 N1

Group II

B1 B2 C D E FI F2 G 11 12 J L

A1 A2

Group

FABRIC CODE

15 50 10 80

65 85 38 15 95 25 20 45 55 00 50

75 20 50 65 00 40 25 45 95 00 45 75

60 95

MIN.

WARP

10 75 75 05

90

4 35 7 10

2 40 2 75

11 50 1 95

2 95 2 95

2

2 85 2 15

4 00 4 63 3 20

247 122 1260 28

00 05 65 5 80

2 2 3

1

10

2

2 2

1

2

2

3

2

733 380 386 453 397 679 495 214 217 124 795

126 201 88 151 126 280 437 170 171 175 281 140 88 30

69 24 60 10

80 60 23 84 40 25 18 26 43 40 80

89 50 33 90 15 70 00 17 80 30 60 10

30 00

40 40 00

88 44

74 72 64 50

37 18 46 44

28 00 80 76

56 48 13 44 116 58 46 03

73 70 20 32 34 30 23 16

50 40 84 88 64 20 36 00 17 96 16 39 19 12

18 26 20 45 30 20 20 14 37 41 29

310 68 106 58

518 227 246 418 269 393 201 1127 701 178 684

97 101 120 144 122 176 157 165 290 190 209 143 180 155

)

52 65

90 31

00 50

55

00

59 60 20

40 00 71 65

68 38 40 31 00 00 70 05 95 33

89 00 30 40

04 44 08 82 60 24 82

78 22 52 20

22 16 16 40 20 28 70

96

30 30 94 00 12 00

45.20

77 79 32 00 33 28

54 60 17 19 17 30 13 40 31 62 48

17 25 22 28 33 24 21 26 26 48 29 30 36 32

THREAD SLIPPAGE FORCE (Gms. WARP WEFT LOAD EXT% LOAD EXT%

60 85 33 45 30 70 30 33 35 70 60

90

10 60 75 17 20

20 40

55 65

15 10 75

90 45 85

90 00 55 00

2

MIN.

45 75 05 50

MAX.

WEFT

3 15

(mm)

SEAM SLIPPAGE

TABLE 6.1 SEAM SLIPPAGE VERSUS THREAD SLIPPAGE FORCE

113

slippage

as

fabrics,

H3p

slippery

and smooth compared to other

Also

the values are low.

Among

the

shows greater seam slippage

plain

weave

because

polyester

due to low friction, it is prone for

it

is

fabrics.

slippage.

The

fabric L, which has dobby weave, shows higher value, due to its

fibre content.

It is a blend of polyester /

viscose.

The

seam slippage is greater also in case of satin

weave.

The matt weave fabric R, has resistance to seam slippage as the yarn is coarser. 6.5.2 Effect of Ends and Picks Seam

slippage in weft was higher than that in

warp direction. material itself,

The fabric Q,

of

satin

where

as

subjected

(Fig.6.3) which is a suiting

weave, gave way with all the other

the

suiting

seam

slippage,

load

4

materials

to 12 Kg as per British Standard,

fabric has the lowest number of picks. minimum

the

because,

Kg were the

The fabric D showed

as the ends and

picks

are

more

comparatively. 6.5.3 Tightness factor and fabric density Neither product between

of

a

correlation between seam

tightness factor and mass of

seam

slippage

and

density has

the

slippage

and

fabric

nor

been

observed

(Tables 3.1, 5.2, 6.1). 6.5.4 Effect of washing, mercerization and heat setting

fabric

In the case of the shirting materials, the exhibits slightly more seam slippage, where

washed as in

case of suiting material, the opposite is the case, but it is not very significant. After mercerization and heat

setting, in

there is a slight increase in the slippage,

the warp and weft direction. Washing and

make the fabric soft,smooth and, slippage of seams.

slippery

both

mercerization enabling

the

6.5.5. Thread slippage Figure 6.2 shows the thread slippage curve recorded by Instron. in grams. then

This is the value of force of thread

slippage

The force of slippage is maximum initially,

drops

gradually

till

the

thread

gets

and

removed

completely from the specimen. The curve has several peaks and the fluctuations in the force of thread slippage are assumed

to

be the result of static

friction,

stick-slip

friction and thread displacement. The portion AB of the curve corresponds to static friction and high peak value before the slipping movement of

the thread commences.

Then the force of

the

slippage

reduces as shown at BC of the curve and here the thread

is

under kinetic friction.

by gets

The slipping thread during the test is obstructed the friction of threads over which it crosses and it stick-slip friction.

The multiple peaks seen

at

portion of the curve are the result of displacement of

BC the

threads which are being crossed by the slipping thread and thereby recording low value. The displaced threads get jammed and offer more resistance to the slipping thread thereby increasing the force.

116

Fie : 6 3

6.5.5.1 Effect of weave The

plain

weave fabrics resist

both in the warp and weft directions. the

groups shows

the

weave

float.

slippage,

Satin weave in

the least slippage force.

This

With the increase in weave

thread slippage force reduces. the

thread

thread.

due

float,

to the

It is also observed that in

satin weave, the thread slippage force is low

warp direction, direction. The

both

in

the

because the weave float is in the warp satin weave enables easy slippage of

In the respect of the matt weave, in both the warp

and

weft directions, the thread slippage is higher,

which

may

be due to the higher linear density.

weave

in

group

II,

shows a higher value,

The twill

because

of

greater

thread density. Similarly, in the weft rib fabrics the slippage force is higher in the weft direction. In this case, interlacement is greater in the weft direction. In the warp direction, even though 4 yarns are physically laid parallel,

the

interlacement

of

yarns

is

much

less.

Therefore, the value is low. 6.5.5.2 Washing treatment and finishing process Thread washed

slippage force is considerably reduced in samples. Since the fabric becomes smooth and more

slippery, the thread can be pulled with lesser force, both in the warp and weft directions.

amount of Similarly,

compared to grey unfinished sample (M^), the bleached fabrics (M2) and (P2 in the weft direction only) require significantly less force to pull the thread. This is attributed

to

drop in the interfibre friction

and

inter

yarn force following swelling of the threads; also the weft yarn used in the fabric is coarser than that of the warp and hence the force required to withdraw the yarn is less.

118

The

force is reduced even in heat set fabric

setting

treatment

leads to a reduction in

forces.

A

of

number

literature

evidences

are

(M3) . the

available

to demonstrate the effect of heat

Heat

interyarn in

the

setting

and

finishing treatment on the interyarn forces. 6.5.6

CORRELATION

BETWEEN

BEAM

SLIPPAGE

AND

THREAD

SLIPPAGE It is seen from figures 6.3a to 6.4c, that there is negative

correlation between seam slippage measurement

mm and thread slippage force in gms.

As the seam

in

slippage

decreases in mm., the thread slippage force increases.

The

plain weave fabrics offer more resistance to seam slippage, which

require additional load, to pull the thread,

where

as in slack weave fabrics like satin, the seam slippage greater and requires less load to pull the thread. 6.6

is

CONCLUSION The

seam

plain

and thread pulling force.

resistance

to

Therefore,

the

seam slippage is minimum and the load required to pull

the

thread

slippage

weave fabrics show more

is greater.

The satin weave exhibits greater

opening and requires less load to pull the thread. made

fabrics,

being more slippery due to

less

seam

The man friction,

show a higher seam opening. The

washing

and

finishing

treatments

such

as

mercerization and heat setting affect the seam slippage and thread slippage force significantly. Both these treatments have led to a significant drop in the thread slippage and seam slippage.

O O

T—

30Vddl1S QV3dHI

o

2.75

□

3.5 SEAM SLIPPAGE

□

IN

mm.

4.25

y

- 0 .7

F ig .6 * 3 a Seam s lip p a g e v s th r e a d s l i p p a g e (G ro u p I w a rp )

a

□

500

o

□

□

o o CN

□D

O O fO

□ □

□

o o ■'4(•sluq)

T-

m

CO

-r~ o

D

n

r-

m o CM

(•sujo) 30Vddl1S QV3dHX

o

3.375 SEAM SLIPPAGE

IN

mm.

4.1875

6 .3 b Seam s lip p a g e vs th re a d s lip p a g e (G roup

2.5625

□

□

820

□

□

□

•H

O'

fn

II

w arp)

r - 0 .7 5

0



125

The prove

that

seam

slippage test and thread

they are interrelated.

correlation between these properties.

There

slippage is

a

test

negative

As the seam slippage

decreases, the force required to pull the thread also shows an increase.