Indian Journal of Textile Research
Vol. 13, March 1988,pp.I-6
Coefficient of Friction betweenYams and Contact Surfaces
A R KALYANARAMAN
South India Textile Research Association, Coimbatore 641014, India
./
Received4 June 1987; revised and accepted27 July 1987
The nature of the coefficient of friction between yarns and contact surfaces is discussed.The SITRA friction measuring instrument was used for the measurements.The results indicate that the hypothesis by Hansen and Tabor [Text ResJ,
27 (1957) 300] that the friction between the yarn and the guide surface is equivalent to the frictional behaviour oflubricated journal bearing is true. There is a count-wise variation as well as TPI-based variation of friction. The open-end
yarns have lower friction whereas acrylic and wool fibres have higher friction coefficients. A procedure to measure the
lateral pressure extended by the moving yarn on a stationary surface is suggested.Thus, the lateral pressure excerted by
yarn on knitting and sewing needles could be studied.
--
Keywords: Coefflcient of friction, Contact surfaces, Traveller, Yarn guide
1 Introduction
scribed
Differential
motion
between
the two
moving
boundaries
involves friction.
Thus, in all technologies engaged in the movement
of masses, friction is
an inevitable force to be reckoned with. The process
of textile manufacturing
needs the movement of yam
the present
1.1 Instrument
The principle
of the instrument,
described
in detail earlier3, is based on the principle
of inclined
over and
plane. The material
through
a number
of guide .surfaces
like
travellers,
knitting
needles, ceramic
and metallic
rollers
and surfaces in spinning,
winding,
weaving
and stitching operations.
Production
of an even product warrents
uniform
friction
and lower friction
saves energy and helps towards
faster production.
Thus, any new instrument
designed to measure friction is a desirable
addition and a useful tool in the
progress of technology.
Much work has been done on the measurement
of
friction and all the earlier instruments
are based on
the measurement
of tension in the yam before and
after its contact with the corresponding
metallic surface made in the form of a cylinder. The friction is
evaluated by using the capstan equation:
72/n
by KaIyanaraman
and Prakasam
was used in
study and is shown in Fig. 1.
the friction
of which with respect
to yam is to be estimated is mounted on the yam and
the yam on its mount is tilted by a suitable mechanism. As the tilting proceeds the material starts slipping on its own at a particular angle of tilt and the tangent of the angle of tilt of the yam with respect to
horizontal
gives the coefficient
of friction.
The instrument in this form could be utilized to measure
dynamic friction also and in such a situation the yam
is allowed to move at a constant speed. Tne only limitation of this method is that the material must not
be very heavy so as to cause yam to slacken under
the weight of the material
between the two fixed
mounts. Under certain situations, it may be desirable
= ef!B,
where nand
72 are the tensions before and after
the contact; e, the angle of lap; and 1-1.,
the coefficient
of friction.
Howell and Mazur
described a sliding fibre apparatus for the measurement
of fibre friction.
Based on Howell and Mazur's principle2,
Kalyanaraman and Prakasam3 developed
a simple friction
measuring
device for measuring
the 1'tatic and dynamic friction
of guide materials
with respect to
yams. This paper presents the results obtained with
Kalyanaraman
and Prakasam's
instrument3.-1
and
compares the same with the results obtained by earlier workers. A commercial
model of the set up de-
"
Fig. I-SlTRA
.
friction measuring instrunient
1
INDIAN J. TEXT. RES.,VOL 13,MARCH 1988
to supply a certain amount of tension to the yam so
as to avoid the sagbetween the mounts.
2 Experimental Procedure
The instrument was first levelled with the help of
levelling screws. The yam was stretched under a
constant tension of 25 g between the mounts. The
traveller was mounted on the yam and with the help
of a screw mechanism the yam was tilted till the traveller slid down the yam. The angle of tilt corresponding to the onset of sliding was noted. The experiment was repeated severaltimes and the average
of 20 readings was taken. The tangent of the average
angle of tilt directly gave the coefficient of friction.
The traveller was then changed and the experiment
was repeated. For measuring the kinetic friction, the
yam was advanced at a constant speed.To start with
the metal, e.g.traveller, yam guide or sewingneedle,
was mounted on the yam and the yam was moved.
The mount with the yam was then tilted. At a certain
angle of tilt the metal piece just started sliding down.
The moving yam pulled it up and the gravity pulled
it down. The angle at which the movement was more
or less arrested was noted. For eachcase,20 observations were made. The tangent of the angle gave the
kinetic friction coefficient of the metal piece with respect to yam. The experiment was repeated for all
the counts and travellers. In the case of yam guides
since the weight of the yam guide was found to be
..I
high a part of the yam guIde was cut and only the
guide loop with its appropriate contact surface was
used. The yam tension was also increased from 25
to 45 g to avoid the sagging of the moving yam. In
the case of sewing needle the commercial sewing
thread (3/60 s) and the needle number 16 were used
in the experiment. In all the cases 20 observations
were made and the average was taken.
advanced the concept that the frictional behaviour
of a thread line passing over a cylindrical guide is analogous to the frictional pattern exhibited by a journal bearing. Thus, according to them a hydrodynamic lubrication exists between a lubricated yam and
the metallic surface. They further observed that the
unlubricated yam also shows a variation iri dynamic
friction that qualitatively follows the variation seen
in the case of a lubricated yam. All workers observed that friction increases at higher speeds.Lyne5
reported that at high speeds the fibres soften due to
the generated heat and thus give increased area of
contact. Such an observation may be true for a synthetic filament but for cotton yam perhaps such an
argument may not be fully appropriate. However,
the observations made here using the SITRA instrument more or less agree with the observations by
other workers5 -Mand the Hansen and Tabor's similarity of the lubrication of journal bearing (Fig. 2)
seems to be the general pattern observed in all the
casesinvestigated.
The coefficients of friction for unwaxed and
waxed yam of 40s count and for polyester yam are
given in Table 1. The coefficient of variation and the
standard deviation are also given. All the values are
the average of 20 readings as recorded with the instrument. The values are reproducible and thus sug-
r
BOUNDARY
REGION
YA'RN-SPE-EO
alb h .
f.
lbe
.I
e aVlour0 Journa anng
"
Table I-Coefficient of Friction betweenYam and Traveller
[Travellerwt, 0.1315g]
Waxedyarn
'/1"",
Polyesteryarn
speed
cm/min
0
120
240
360
480
600
2
,
Coeff. of
friction
0.423
0.171
0.166
0.153
0.150
0.144
CV'/o
5.6
4.2
4.5
2.4
3.0
2.7
-c'/""".
Std.
deviation
0.024
0.007
0.007
0.004
0.005
0.004
;"i'
Coeff. of
friction
0.269
0.138
0.147
0.137
0.133
0.136
~
u
F. 2 F ..
Ig. -fiction
Nonnal yarn
~
SEMI- HYDRODYNAMIC
REGION
<.> BOUNDARY
~~~.
~~~~~~
r;
,.."'~""
~
,,"
~
,"
~
u
~
~
3 Results and Discussion
The effect of filament friction on metallic surfaces
have been
tions
by the
studied
earlierinworkers.
detail under
Hansen
different
and Tabor
condi-I
Yarn
)
CV'/o
4.2
3.8
4.6
2.8
2.4.
3.0
Std.
deviation
0.011
0.005
0.007
0.004
0.003
0.004
Coeff. of
friction
0.244
0.064
0.079
0.122
0.211
0.225
,
CV'/o
3.1
4.1
2.6
3.3
2.3
22
Std.
deviation
0.007
0.003
0.002
0.004
0.005
0.005
KALYA~ARAMAN: COEFFICIENTOF FRICTIONBElWEENYARNSAND CONTACfSURFACES
..
gest the usefulness of this instrument for the measurement of friction.
Fig. 3 shows the friction for the different counts of
yarn and a traveller (weight, 0.2972 g). For all the
counts the general pattern of theyariation of friction
with speed is the same. As the count increases the
coefficient of friction decreases.This may be owing
to the decrease in the area of contact with the increase in count. Such an observation that the decrease in area of contact decreasesthe friction coefficient has also been reported by Olsen6,Schick7.8and
Kleber9. The hydrodynamic nature of the friction
with speed is also seen(Fig. 2). Figs 4a and 4b show
the variation in yarn-to-metal friction by changing
yarns were made of the same type of cotton and.hall
the sameTPI, the difference in the observed property may be owing to the structural difference in the
yarns. Also, the stick-slip observed for ring yarns between speeds 350 cm/min and 550 cm/min is not
seen for the open-end yarn. Thus, from the point of
view of lower friction the open-end yarn is preferable.
fig. 6b shows the variation in friction with speed
for 16s count ring-spun yarn with two different TPIs.
'
0-300
0-280
the traveller for the same yarn. It is observed that as
the traveller weight increases the metal-to-yarn friction decreases.This is of interest to spinners and it
suggests one possibility of reducing end breaks
caused by traveller although the effect of travellers
on yarn tension involves several other forces. ,8
Figs 5aand5bshowthevanationmfrictionfor
34s
and 100s count yarns with respect to plated yam
guide and porcelain yam guide .respectively. AIthough the porcelain guide offers a slight edge at
lower speeds, at higher speeds.the plated yarn guide
has been found to be better. The plated yam guide
al
" I f t. I
t
Th d t
so oIlers ess nc lona reSlSance. e a van age
of waxing disappears at higher speeds (Fig. 5c). Fig.
6a.shows the frictional pattern of yarn-to-metal friction for ring-spun and open-end yams. It is observed
that the open-end yarn has lower friction. As the
.
0'26
Trav.".r
I (wl,005859
J
~ 0-2"
~
~ 0.220
wl,0-13159)
0200
~
~ 0180
...
"I.r 22(wt,
029729
)
0-16
0-1"0
.
200
"00
600
800
1000
LINEAR
YARN
SPEED,cml
mi.
Fig. 4a-Coefficientoffrictionvslinearyamspeed
[Yamcount,100s]
0.2
Traveller
1(wt,O0585gJ
0-32
0
0-3
Travellerwt-,0-29729
0'210
0-250
0.28
0131~)
0.2
~0.260
.:z
~o~
UJ
-Z
U
0.-
~ 0,240
't:0'
UJ
:::
S 0,220
~ 0'
u.
-
z
0
u
z
~
U 0.20
~
LL
t20-2
«
...0.1
..0.18
0.1
0.1
0,1
0-1
001
00
LINEAR
YARN SPEED,
cm/min
Fig. 3-Coefficientof frictionv.\"
linearyarnspeed
400
600
800
1000
LINEAR
YARN
5PEED
,cm/min
F ' 4b C ff .'
ff
'
Ig. -oe IClent0 nCtlonvsI mear
yamspee
d
[Yamcount,34s}
"
3
INDIAN J. TEXT. RES.,VOL 13,MARCH 1988
Although the higher TPI yarn shows a higher friction
as it should be for speeds between 200 crr)imili and'
500 cm!miIi, it follows the pattern of the lower TPI
yarn. Also, the stick-slip observed for lower TPI
a
019
YarnGuide(Plated)3's
017
r
yarns between speeds 500 ~wlmiIi and 700 cm!min
is not seen for the higher TPI yarn.
0.15
r013
Fig. 7 shows yarn-to-metal friction for the sewing
needle. The experiment was done with the commercial sewing thread (3/60s cotton yarn). The stick-slip
is seen very well. Also, it is clear that at certain
speeds the yarn flow is smooth through the needle.
The lowest observed friction for this yarn needle
combination was at 200 cm!miIi. Thus, if the speed
is maintained around 200 cm!min the end breakages of the sewing thread will be minimum. However, since the minimum is sharp, if there is a small
change in speed the pull on the yarn would be more
and the stitch uniformity will be lost. If stitch uniformity is the primary criterion it is desirable to use
yarn speeds between 250 cm!min and 400 cm!min.
Thus, this instrument could be effectively used to select advantageous speeds for improving the performance of sewing and thus there appears to be a
sufficient reason why the estimation of friction be-
1005
I
0.11
0.0
b
0.230
0.220
0.210
~
~ 0.200
~
-.1
0
0
u
z
tween sewing thread and the needle would be useful
9
:tw
0
technologically.
0.180
~
Traveller
~
~ 0.170
0.270(a)
lL
0.26
wt,0.2972g
RINGYARN
I-
a:
0'16
0.25
0.1
0.2'
0.1'
<. 0.23
I-
0-16
~ 0.220
-,..
~
L1.
0'15
~
0210
0
u
z 031
0-1'
~
19
I-
u
cr:
0290
L1.
0.13
0.27
0.12
16.
YARN
GUIDE(PAINTED)
0.11
0.25
~
COUNT,'Os
0-23
2
0
::.
0.21
LINEAR YARN SPEED,
cml min
260
4~0
6~0
8bO
~O~O
LINEAR
YARN
SPEED.
cm/mln
Fig. 5-Coefficient
4
of friction vslinear yarn speed
Fig. 6-Coefficient
of friction vslinear yarn speed
KALYANARAMAN: COEFFICIENT OF FRICDON BETWEEN YARNS AND CONTACf SURFACES
Figs 8 and 9 show the friction for the acrylic yam, would lead to greater wear and tear in the drafting
wool yam and cotton yam of the samediameter. It is arrangement. The wool yam also shows a similar
observed that the acrylic yam has .a comparatively trend; however, it does not have the coefficient of
high coefficient of friction. This is an important find- friction as high as in the case of acrylic yam. Wool
ing since the acrylic yam when spun in cotton system yam also exhibits a stick-slip between speeds 300
cm/min and above 700 cm/rnin.
0440
From the above study it appears that the acrylic
processing and wool processing need rollers which
0-42
should have more smooth finishes and hardened
surfaces so that the wear out is minimum. Perhaps
-0
the higher friction exhibited by these fibres may set a
040
limit to the speed of processing these fibres.
0-380
~
t-""
!f! 0.360
Thus, the necessity to check the frictional behav.
f fib
b f
th
f
..
lour 0
res e ore
e onset 0 processmg IS
brought out clearly. This would help in bringing
about changes in the process and the process ma-
t:
~ 0-34
~
g 0-320
~
u.0.3CJ
chinery used for these fibres.
It is concluded here that the yam-to-met.al friction
generally follows the metal lubrication with boundary, semi-boundary and hydrodynamic conditions.
This division is based on the sharp transitions observed in the friction vs yam speed plots. As the
0.280
0-260
2
0
LINEAR
YARNSPEED,
cm/mi~OOO
Fig. 7-Coefficient
of friction \ISlinear yam speed [Sewing yam
and sewing needle]
speed increases initially the friction decreases.This
may perhaps be due to the fact that the protruding
hairs of yam reduce the area of contact of the metal
to the yam. At initial speeds, the object perhaps
leap-frogs from hair to hair and thus the area of contact being small the friction decreases.As the speed
increases the hairs might bent down and the surface
Wool yarn
0.25
1
,
0-2
Acrylicyarn
0.2
0-24!
,
,,
~- ---,*,'
0-23
~
Z
Q 0.220
.:
.: Travellerwt_,03570g
~:
Q:
.
~
0.2
~~
z
Q
I-
Travellerwt_,O-3570g
I
u;
0-25
/
/
0-210
u.
u
0
a:
I-
Iz
--u.
u. 0-24
~
.
I
'
I
~ 0-200""
j
u
". "
w 0100
-w
~
u.
~
,
Cottonyarn
u. 0.190
0
u
u.
~ 0-190
0.180
u
018
0.17
0-17
0-160
0-16
0-150
LINEAR
YARN
SPEED,cml
min
Fig. 8-Coefficient of friction vslinearyamspeed
2
LINEAR
YARN
SPEED
, cm/min
00
Fig. 9-Co::fficient of friction vslinearyamspeed
5
INDIANJ.TEXT.RES.,VOL 13,MARCH1988
area of the contacts increases, contributing to in~
crease in friction. The flat regions of the graph where
the friction remains constant over a small range may
be owing to the constant hair resilience. As the speed
increases further the secondary set of hairs, having
lower protruding length, may assume importance
and thus it could show a second flat region.
Thus, it appears that as the speed increases, in addition to the forward component of friction opposing the movement, there is a lateral component of
frict~on working at ri~t .an~es to the direction of
motIon and thus the fnctIon mcreases as the result~
ant of the~e two forces6...
Ac~ordmg to Olsen, an m~rease m the roughness
?f guide ~urface can be considered analbgous to an
m~rease m the pressur~ between the yam and t~e
guide. Olsen's observatIon w.aso~ ~laments and m
the present case the change m hamness or the TPI
variation. of the yam cau~esthe change in roughness.
Thus, If one could estImate.fro~ p~ots~h~later~1
pressure exert~d ~y the yam (m pnnclple It ISPOSSIble), the contnbutIon of l~t~ral pressure by the y~m
on the performance of knittmg needle or the sewmg
h
I .
needle could be understood. Suc an ana ysls wouId
help in understanding the knitting and stitching processesbetter.
All observations were made only up to 800 cm/
min speed under laboratory conditions (RH 65%
and 22.2°C) except for data presented in Table ~
4 Conclusions
4.1 The kinetic friction of unlubricated cotton
yam follows the.hydrodynamic profile qualitatively
as has been reported earlier for lubricated filaments.
The stick-slip phenomenon is observed and as the
yam count increases the coefficient of friction dec~
reases for the same reference surface. Open-end
yams have lower frictional coefficient. Plated surfaces are superior to ceramic surfaces and the advantage of waxing disappears at higher speeds.
4.2 The method could be effectively used for measuring the coefficient of friction of new synthetic
yams so as to bring out specification changes for
optimal performance in the spinning machinery. Also, this method could be used as a qlrality control
procedure to check yam guides, lappets, sewing needies, knitting needles, etc.
which were obtained at 35°C and 60% RH. The reI
Th
I
d .5
4 KalyanaramanA R, J TextInst,(accepted).
LyneDG,JTextlnst,46(1955) 112.
Acknowledgement
The author thanks Mr H. Balasubramanian of the
Instrumentation Division for the collection of data
and Mr T.V. Ratnam, Director, SITRA, for encouragemen.t
References
1 Hansen
WW andTaborD. TextResJ,27(1957)300.
2 HowellH GandMazurJ,J TextInst,44 (1953)T 59.
3 Kalyanaraman
A Rand Prakasam
R. TextResJ. 57 (1987)
307.
su ts are on cotton yam.
e s.ampe yam use m 6 OlsenJ S,TextResJ,39 (1969)31.
34s, 40s and 100s and the seWIng yam were com~ 7 SchickM J,Surfacecharacteristics
offibresand textiles,
PartI
(MarcelDekker,NewYork)1975,Chapter1,Section1.
mercial samples.The waxed yam used was the sam~
pIe yam of 40s and the open~end yams were spun 8 SchickM J, Handbookoflubrication
(CRCPress,
BocaRatfrom the same cotton samples. Th~ yam tension
on,Florida)1983,Section1,341.
used was 25 g. In the case of plated, painted and 9 KleberR,Proceedings
of theworldsurfactant
congress,
Vol.IV
.porcelain yam ~ides a tension of 45 g was used.
(1984)274.
.
6
I
J