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2012
Loom Speed and Tension to Reduce
Warp and Weft Breaks in Air Jet Weaving
Nkiwane, Londiwe C.
Scientific & Academic
Nkiwane, L and Marashe S. 2012. Loom Speed and Tension to Reduce Warp and Weft Breaks
in Air Jet Weaving, pp. 1-8
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Loom Speed and Tension to Reduce Warp and
Weft Breaks in Air Jet Weaving
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Nkiwane, L and Marashe S. 2012. Loom Speed and
Tension to Reduce Warp and Weft Breaks in Air Jet
Weaving, pp. 1-8
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Loom Speed and Tension to Reduce Warp and Weft
Breaks in Air Jet Weaving
Londiwe Nkiwane*, Shepherd Marashe
Department of Textile Technology, National University of Science and Technology, P.O. Box AC 939, Ascot, Bulawayo, Zimbabwe
Abstract The study sought to identify correct values of loom speed and warp tension suitable for weaving 100% cotton
yarn on Dornier double beam Air Jet Looms, AWSE2/E type. The causes of warp breaks are, poor quality yarn, uncontrolled
temperature and humidity, uncontrolled weaving tension and loom speed. The experiments were conducted to determine
warp and weft breaks at i) varying warp tension (50cN to 85cN) and constant speed (560 rpm,), ii) at constant warp
tension(80cN) and different loom speed (520 to 560 rpm). The company where the study was conducted is referred to as
‘Company A’. Temperature and relative humidity and were kept constant at 27℃ and 75% respectively. The yarn quality
was good (11cN/tex), according to the Ulster Statistics standard levels which was the exact tenacity of the 30 tex yarn used at
‘Company A’. The results showed that warp and weft breaks occur even if the maximum warp tension during weaving is
lower than the breaking strength of the yarn. A combination of high loom speed (560 rpm ) and high tension (80cN) lead to
increased breaks, but breaks become reduced with the reduction in tension to 70cNeven if the machine speed was maintained
at 560 rpm . Above that tension, warp breaks start to increase. The number of warp breaks was also found to increase with the
loom speed. Weft breaks also occurred due to entanglement at low warp tension (50cN). Adjustment of warp tension and
loom speed can help to determine the optimum values of warp tension and loom speed to be used in order to reduce the
number of warp breaks for individual Air Jet Looms. An equation to determine the number of warp breaks which can occur at
a given warp tension was modelled. This equation[eq 4] can be used to provide very good estimations for initial setting of
warp tension. Another modelled equation[eq5] can be used to estimate the number of weft breaks at a given warp tension.
Keywords Warp Breaks, Weft Breaks, Warp Tension, Loom Speed
1. Introduction
In weaving, unwanted loom stoppages always occur
leading to low production rates. Loom stoppages during
the weaving process usually occur as a result of warp breaks,
weft breaks, mechanical breakdown, electrical faults, beam
gaiting, shortage of spare parts, power cuts, beam changing,
cleaning, oiling and lubricating. Amongst these warp and
weft breaks, and beam gaiting occur more frequently than the
rest[1].
In Air Jet Looms, warp and weft breaks causing loom
stoppages during weaving, are more frequent when using
100% cotton yarn. Wrongly adjusted machine parameters
and weaving conditions lead to yarn breaks during weaving.
For instance, warp breaks can be a result of uncontrolled
room temperature and relative humidity, poor quality yarn,
excessive loom speed, uncontrolled warp tension[1]. Other
causes can be due to knots on warp yarn, poor size pick-up,
loose ends, fly stuck onto threads and abrasive effect of the
* Corresponding author:
[email protected] (Londiwe Nkiwane)
Published online at http://journal.sapub.org/textile
Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved
drop wires and the heddles. Warp breaks cause longer
stoppages as compared to weft breaks since they require
more time for repair particularly when using 100% cotton
yarn[1].
1.1. Machine Parameters
At two textile companies (‘Company A’ and ‘Company B’)
using Air Jet Looms in Zimbabwe, it was observed that
more than 45 warp breaks occurred within a period of8hours,
against an acceptable number of breaks which should be less
than 0.4 per 1000 warp threads and 100 000 picks in 3hours,
which gives 8.2 acceptable warp breaks for 8 hours[2] [eqs 1
and 2].
Experiments were conducted, using Donier Air Jet
Loom sat ‘Company A”. When weaving for a period of
8hours at a loom speed of 560 revolutions per minute (560
rpm),using a reed width of 3.2 m, and producing a fabric with
24 ends per centimetre (24 ends/cm), the acceptable number
of warp breaks for 100% cotton yarn was calculated as
follows:
Total number of ends in a 3.2m fabric width
= 24 ends/cm × 320 cm
= 7680 ends.
An acceptable number of warp breaks in 7680ends and
100 000 picks inserted
=(7680 ends÷1000 ends) × 0.4
= 3.072 breaks
[eq 1]
The time taken by a loom running at 560 rpm to insert 100
000 picks is given by;
(100 000picks÷560picks-min)
= 178.6mins
= 3.0hours
That is, for looms used for the study, the acceptable
warp breaks in 3.0hours is 3.072, which means that in 8
hours , warp breaks should not be more than;
(8 hours ÷3 hours ) × 3.072 breaks
= 8.2 breaks
[eq 2]
Breaks did not occur due to weakness in yarn strength
because the cotton yarn used at the textile company
conformed to the Ulster Statistics standard levels. The Ulster
Statistics recommend yarn to have a tenacity of 11cN/tex,
which was the exact tenacity of the 30 tex yarn used at
‘Company A’. The twist level was 900turns per metre whilst
elongation of sized yarn ranges between 4-5%. Conditions in
the weaving room at the time of the study were 27℃ for the
temperature and 75% for relative humidity. The drop wires
for 100% cotton yarn of 30texhad a weight of 3grams per
piece, thickness of 0.3mm, width of 0.5mm. The number of
drop wires per centimetre per row is five, as recommended
by the International Standard Organisation (ISO 1150 and
441). The drop wires operated efficiently and did not abrade
the warp yarn to cause warp breaks. The weaver’s beams
prepared had no loose ends, the recommended minimum
number of warp breaks is 0.5 per one million metre length of
yarn and the knots on joined ends should have tails of the
correct size of not more than 3 mm[3].
Despite all efforts in making sure that all the weaving
conditions and yarn parameters are within the well-known
Ulster Statistics standard levels, warp breaks continued to
occur. The loom speeds used ranged between 500-660
revolutions per minute (rpm) for Dornier Air Jet Looms
whilst the warp tension used for yarn of 30tex was
80cN/thread. At these speeds and warp tension values, warp
breaks occurred. High loom speeds usually cause warp
breaks, but reducing the speed does not necessarily mean that
the warp breaks will not occur since the loom speed and the
warp tension have an effect on one another. If the loom speed
is high (560 rpm) and the warp tension is also high
(80cN/thread), warp breaks will occur. If the loom speed is
low (500rpm) and the warp tension is high(80cN/thread),
warp breaks will still occur. On the other hand, when warp
tension is low, and the loom speed is high or low, warp
breaks will occur as a result of warp entanglement. The
arising question therefore is:
What is the most appropriate combination of loom speed,
warp tension and weaving conditions, which can be used in
Air Jet Looms to further reduce the number of warp breaks?
1.2. Weaving Conditions
In textile production processes, there are more stringent
requirements of temperature, and humidity levels required
for cotton weaving. For any process, temperature cannot be
less than 20 ℃ and not more than 31 ℃ , and relative
humidity should not vary excessively, thus the only
acceptable variation can only be ± 5%, based on the Zig Bee
802.15.4 protocol technology[4]. Weaving conditions
for100% cotton fabric are designed to maintain high relative
humidity (RH) of 80% to 85% at the warp sheet level i.e. at
'loom sphere' as high humidity helps to increase the abrasion
resistance of the warp. Whereas it would suffice to maintain
general humidity condition in the room at around 65%
R.H[5]. However, warp sized with ELVANOL (polyvinyl
alcohol), do not require high weave room humidity
necessary for handling starch sized yarn. Relative humidity
may be reduced to 65% or even lower if desired to provide
more comfortable working conditions and reduce
maintenance costs on loom parts that are sensitive to
humidity[6]. Warner[7] states that the strength of cotton yarn
increases as it is exposed to moisture e.g. 75% relative
humidity. A further increase in relative humidity will not
increase the strength of the fibres.
Masudur[1] measured and analysed how temperature and
relative humidity affect the efficiency of looms for cotton
weaving. He concluded that, the highest efficiency was
obtained at 65% relative humidity and 27℃ temperature,
which are in agreement with the international standards for
cotton weaving in European countries. However in hot
climates, such as those found in Zimbabwe, the
recommended relative humidity in a weaving room ranges
between 70-85%[8]. For the study the experiments were
conducted at 27℃ temperature and 75% relative humidity.
2. Aim and Objectives
2.1. Aim
To determine the loom parameters and weaving
conditions for 100% cotton yarn, suitable for increasing
loom efficiency by reducing the number of warp and weft
breaks in Dornier Air Jet Looms.
2.2. Objectives
The objectives of the study were to:
i) vary loom speed and determine the number of warp
breaks and weft breaks which will occur,
ii) vary the warp tension and determine the number of
warp breaks and the number of weft breaks which will occur,
iii) compile the extent to which warp and weft breaks
contribute to low loom efficiencies,
iv) determine the time taken to repair a warp breaks, and
the time taken to repair a weft breaks, and
v) make suggestions to weaving companies on how the
number of warp breaks in Air Jet Looms can be reducedso as
to maximise loom efficiency.
3. Experimental Design
3.3. Experimental Methods
Experiments were conducted at controlled weaving
conditions of 270±20 Cand 75±2% RH. These conditions
concur with Masudur[1],Roy[5] and Warner[7] who
recommend that general humidity conditions should be
between 65% and 85% R.H. The temperature cannot be less
than 20℃ and not more than 31℃[4].For all experiments,
five weavers operating two or three looms were observed
and their looms used for the study. The study was conducted
in February 2012.
Experiments were carried out on looms with the
specifications given in section 3.1 and the looms were set to
produce plain woven fabrics.
3.1. Loom Specifications
A Donier Air Jet Loom with specifications as shown in
Table 1 were used
Table 1 Loom Parameters
Type of parameter
Loom Parameter
AWSE 2/E Dornier Air jet
Loom type
Loom speed
500-660rpm
Weft insertion type
Air
Nominal width
380 cm
Reed width
330 cm
Warp detection
Positive Dobby
shedding (Staubli)
6 bar electrical drop wire
Let-off system
mechanism
Electronic
Shed formation
Electronic
Take-up system
3.2. Yarn Specifications
Table 2 Yarn and
Its Properties
Yarn characteristic
Yarn Property
Yarn type
100% cotton, open-end spun
Size take-up(%)
10, for warp only (weft yarn
was unsized)
Yarn fineness
30 tex, for both warp and
weft
Yarn tenacity
11 cN/tex
Using loom and yarn specifications, a 1/1 plain weave
fabric with a warp density of 24 ends/cm, a weft density 24
picks/cm and a fabric width of 320 cm was woven.
3.3.1. Experiment 1 (constant loom speed and constant warp
tension)
The aim of this experiment was to determine the number
of warp and weft breaks which occurred when the loom ran
at a loom speed (560 revolutions per minute) and warp
tension of 80cN/thread for a 30tex yarn. These were the
maximum speed and tension values used at the company. For
this experiments, the speed and tension were maintained as
they were used in the company
Procedure was as follows:
a) Warp tension and the loom speed were maintained for a
chosen loom,
b) The picks counter was reset and the loom ran for a
period of two hours whilst noting down the number of warp
breaks and the number of weft breaks,
c) The total number of picks inserted was also recorded,
d) Loom efficiency was calculated as follows:
Loom efficiency =
Reed space (m)x no. of picks inserted x 100%
Reed space (m)x loom speed (rpm)x 2hrs x60mins
[eq 3]
Where:
Reed space X no of picks inserted: represents the actual
length of yarn inserted and;
Reed space X loom speed X 4hours x60mins: represents
the theoretical length of weft inserted.
3.3.2. Experiment 2 (variation in warp tension and constant
loom speed)
In this experiment, warp tension was varied and the loom
speed kept constant and the number of warp and weft breaks
that occurred recorded.
Procedure was as follows:
a) Warp tension was set at 50 cN/thread and the loom
speed at 560 rpm, the maximum possible value (560 rpm ). It
was assumed that loom speed higher than that may strain and
damage the loom.
b) The picks counter was reset and the loom made to run
for 2hours, whilst recording the number of warp and weft
breaks which occur.
c) The total number of picks inserted, number of warp
breaks and number of weft breaks that occur were recorded.
d) warp tension was increased by 10 units whilst
maintaining a constant loom speed and picks counter reset.
e) The Loom was made to run for 2hoursand warp and
weft breaks, and the total number of picks recorded.
The warp tension was continually increased by 10 units,
maintaining the constant loom speed and breaks record
g) Loom efficiency was calculated using equation 3[eq
3]for each value of warp tension and recorded.
3.3.3. Experiment 3 (variation of loom speed and constant
warp tension)
The experiment was carried out to determine the number
of warp and weft breaks which occur on varying loom speed
at constant warp tension.
Procedure was as follows:
a) The warp tension was set at its maximum possible as
used by the company (80 cN/thread). This maximum value
of warp tension should not be more than the mean tensile
strength of the warp yarn. The yarn used had an average
breaking strength of 11 cN/tex (330 cN), and the acceptable
range was 8-12 cN/tex (240-360 cN).
b) The Loom was set at a speed 5 units less than the speed
value used in experiment 2 and the picks counter were reset.
c) The Loom ran for 2hours whilst warp and weft breaks,
and the total number of picks were recorded.
d) The speed was then reduced further by 5 units whilst
maintaining a constant warp tension, and number reset the
picks counter.
e) Steps 3 and 4 were repeated two more times resulting in
the reduction of the loom speed by 15 units.
f) Loom efficiency for each value of loom speed is
calculated [eq 3].
the warp (Figure 1). This was in agreement with Weinsdorfer
in Severine[9] who proved that the number of end breaks was
directly related to warp tension. Figure 1 shows that the
number of warp breaks recorded at a tension of 50 cN is 17
which is higher than the acceptable of warp breaks of not
more than 3.02[9]. This was because at low tension, the warp
yarn was slack, and a clinging effect that subsequently led to
more breaks was created. Literature shows that low yarn
tension creates a clinging effect, resulting in yarn breaks[9].
As a result, the number of picks inserted was very low due to
more loom stoppages which lead to the reduction in loom
efficiency. As the warp tension was increased, the number of
warp breaks began to decrease until the tension of 70 cN was
reached, beyond which any further increase in tension
showed an increase in the number of warp breaks. From
Figure 1, the optimum range of warp tension ranges between
65 cNand 70 cN, with 70 cN registering the lowest number of
warp breaks. At 70 cN, the tension in the warp was high
enough to prevent yarn entanglement and at the same time
not excessive to impose more stress on the yarn and cause
lots of breaks. Further increase in tension above 70 cN
resulted in more warp breaks as the warp yarn was being
subjected to more tensional force.
3.3.4. Experiment 4
The experiment was conducted to determine the average
time taken by a weaver to repair a warp break, as well as the
average time taken to repair a weft break. Five weavers were
observed at different times.
Procedure
a) The weaver was observed whilst he/she operated the
loom. When a warp or a weft yarn broke it was recorded and
a stop watch was used to determine the time taken to repair
the broken yam.
b) The number of looms each weaver operated was noted
because the time taken to repair a warp or weft break was
affected by the number of looms the weaver operated.
c) Step 1and 2were repeated for each of the 5 weavers.
d) For each weaver, the average time needed to repair the
breaks was calculated
4. Results and Discussion
The results were analysed so as to find the most
appropriate warp tension and loom speed values that could
be used for initial machine settings, and contribute to
minimising breaks in Air Jet Looms. These results can be
used as a guide for weavers working under similar working
environments
4.1. Effect of variation of warp tension and constant loom
speed on warp breaks
The results obtained on varying warp tension at constant
loom speed show that the number of warp breaks which
occurred during weaving were proportional to the tension of
Figure 1. Warp breaks against warp tension curves, for experimental data
and a theoretical model
Figure 1 shows a curve plotted from experimental data
that is defined by the following quadratic equation
Nw = 0.025T2w - 3.469Tw +127.8
[eq 4]
Where; Nw= number of warp breaks and;
Tw = tension in the warp
The number of warp breaks which can occur at any given
warp tension when producing plain woven structure, in Air
Jet Looms can be predicted using the modelled equation[eq
4]. Theoretical values of tension were substituted into the
modelled equation to obtain a theoretical model curve. The
theoretical curve for warp breaks is very similar to the
experimental curve, which means that the theoretical model
is in good agreement with the experimental results. This
implies that the modelled equation can be used to predict the
number of warp breaks which can occur at a given warp
tension. However, the modelled equation does not guarantee
the exact predictions of the warp tension values that can
register the lowest number of warp breaks at a first attempt,
but can provide very good estimations for initial setting of
warp tension.
The yarn used had an average breaking strength of 11
cN/tex (330cN), and the acceptable range was 8-12 cN/tex
(240-360 cN). All the tension values which were used were
below the minimum breaking strength of the yarn that is 50
cN. The maximum breaking strength was 85 cN. Despite the
fact that the warp tension did not exceed the breaking
strength of the yarn, warp breaks still occurred, since the
adjustment of the warp tension showed a variation in the
number of warp breaks which occurred. It therefore means
that the tension values used had an effect on warp breaks.
The warp breaks at the lowest warp tension (50 cN) were due
to yarn entanglement caused by slackness in the yarn. The
breaks began to decrease as the warp tension increased, and
the slackness in the warp yarn gradually disappeared. The
least number of breaks was at 70cN when all the slackness
had disappeared. Further increase in tension (above 70 cN)
did not show any further decrease in the number of warp
breaks; instead, number of warp breaks began to increase.
Although the number of warp breaks began to increase at
the tension values above 70 cN, these tension values did not
exceed the minimum tensile strength of the warp yarn. The
number of warp breaks increased after 70 cN due to
additional stress in the warp yarn, the warp yarn was already
under alternating stress due to repeated shedding and beat-up
action of the reed and sley. According to Morton and
Hearle[10], textile materials under stress are known to “fail”
with the passage of time. So if the yarn which is already
under stress is known to fail after some time, an increase in
warp tension means more stress, implying that the time after
which the yarn will fail will decrease, the higher the stress
the shorter the corresponding time of failure[10].
The failure of sized yarns on a loom is attributed to the
cumulative damage caused by cyclic fatigue of relatively
small forces well below the breaking point applied under
static load[10,11]. This phenomenon, commonly known as
fatigue[10], is caused by the gradually diminishing
resistance of the material or loss in tensile strength, attributed
to cumulative damage. Because of this, the probability of
having more breaks as the tension increased was very high,
hence more warp breaks as the tension increased above
70cN.
Figure 2 shows the effect of warp tension on weft breaks.
The trend of weft breaks indicates that the effect of warp
tension on weft breaks can be described using a polynomial
equation of the sixth order[eq5].
= ax + bx + cx + dx + ex + fx + C
[eq 5]
15
W
14
e
f 13
t
12
b 11
r 10
e
a 9
k 8
s
y = 0.0063x6 - 0.1845x5 +
2.1763x4 - 13.071x3 +
41.841x2 - 66.387x +
49.625
Numberof
weft
breaks
50 60 70 65 75 80 85 90
Poly.
(Numberof
weft
breaks)
Warp Tension in cN
N.B. poly stands for polynomial
Figure 2. Effect of warp tension on warp breaks
From Figure 2 it can be observed that there is very good
fitting of the tredline to the experimental data. Warp tension
of 50cNhad a significant effect on weft breaks due to, the
disturbance of the smooth passage of weft yarn across the
shed because of the slack warp, causing the weft to buckle in
the shed. Low yarn tension creates a clinging effect, resulting
in yarn breaks[9] for both warp and weft. An increase of
warp tension to 60 cN resulted in sudden decrease in weft
breaks because the buckling in weft was released as it went
through a tighter warp shed. The clinging effect among the
yarns was very low at this time. With increasing warp
tension to over 70 cN weft breaks stabilised. Higher tensions
(80 cN, 85 cN and 90 cN) in the warp did not have an effect
on the weft break. This is in contrast with the warp breaks
that occur more when the tension was over 70cN. At this
tension the warp suffers longitudinal stress while the weft,
not as strained as the warp, was only in contact with the warp
at interlacing points. There was no entanglement of the warp
to cause the weft to rub against it.
4.2. Effect of variation of loom speed at constant warp
tension on warp breaks
At a speed of 560 rpm (the maximum speed used), the
number of warp breaks recorded was 13 and this was high as
compared to an acceptable number of 3.02[eq1]. The number
of warp breaks was high because the warp yarn was under
alternating stress at high loom speeds, the rate of repeated
shedding or the number of cycles for alternating stress is
higher and this weakens the yarn, causing it to suffer cyclic
fatigue (Table 3).
Table 3. Warp breaks and weft breaks at a constant warp tension of
80cN/thread
No. of
weft
breaks
9
7
8
4
No. of picks
inserted
39600
40046
38787
40567
Loom
Efficiency
(%)
60.0
61.8
61.0
65.0
Table 3 shows that the number of warp breaks decreased
as the loom speed decreased. At lower speeds (550 rpm and
540 rpm ), the rate of repeated shedding is lower than at 560
rpm . The number of cycles for alternating stress is also low
and the yarn takes long before it weakens and finally breaks,
hence low number of warp breaks (11 and 9 respectively).
Any further reduction of speed to 530 rpm and520 rpm
showed a reduction of warp beaks to 7 at both loom speeds,
and the number of picks inserted at these speeds was low,
38787 and 40567 picks for 530 rpm and 520 rpm
respectively. Running the loom at these low speeds
however will obviously result in low productivity. It is
therefore not desirable to run the loom at low speeds. Time
might be saved repairing warp breaks and weft breaks at 560
rpm , than making a product at slow loom speeds because at
slow speeds there will still be time wasted during warp and
weft repairs as they will also occur. Variation in loom speed
did not show significant differences in weft breaks.
4.3. Time taken to repair a warp break and time taken to
repair a weft break
Five weavers were timed whilst repairing the warp breaks
and weft breaks but they were not aware of the timing. This
was done to obtain the actual time the weavers take to repair
the warp and weft breaks in a natural weaving environment.
Figure 3 shows that the weavers took almost the same
amount of time (1.7 – 2.3 min) to repair a single warp break
(1.9 mins on average) This average incorporates the time
taken by the weaver to walk to the position where the break
has occurred, the time taken to find the broken end and the
actual time taken to tie the broken yarn. The average time
recorded is twice the expected time for repairing a warp
break,(0.8 and 1.0 mins, depending on the size of the
loom)[12]. It was observed that the weavers seemed not to
worry about quickly attending to warp and weft breaks.
)
No. of
warp
breaks
11
8
7
7
(
Loom
speed
(rpm)
550
540
530
520
T
i
m t
e o
m
i r
n e
p
t a
a i
k r
e
n
2.5
2
b
1.5
r
e
a1
k
s
0.5
Warp
Weft
0
1
2
3
4
5
Weavers
Figure 3. Time taken to repair warp breaks and weft breaks
The five weavers took almost similar times to repair a weft
break. The averaged time for all the weavers was 1.3 mins.
This average incorporates the time taken to replace an empty
bobbin or the time taken to replace a faulty bobbin and the
time taken to remove the broken pick as well as the time
taken to draw the weft through the accumulator and the main
nozzle. The relaxed attitude by weavers was due to the lack
of confidence in the performance of the country’s textile
industry, and fear of losing their jobs. The African
Development Bank (AfDB) states that the textile industry,
once one of the biggest employers in Zimbabwe ,remains in a
comatose state and the introduction of the multiple currency
regime in 2009, the corporate sector was generally
characterised by a sluggish recovery mode although many
textile companies continued to close shop[13].
4.3.1. Extent to which warp breaks reduce loom efficiency
By considering a speed of 560 rpm and a tension of 80cN
which were used at the company, the number of warp breaks
which occurred was 13. The loss in loom efficiency as a
result of these warp breaks which occurred during the 2hours
for which the loom ran, was calculated as in equations 6 and
7.
Average time lost = 1.9mins x 13 breaks
= 24.7mins
[eq 6]
.
×
Loss in efficiency =
= 20.6% [eq 7]
Using values in Table 3 and equations, for each warp
break that occurs, the loss in loom efficiency was 1.6%
which is equivalent to losing 1064 picks. Running the loom
for 2 hours at the warp tension of 80cNand at a speed of 560
rpm,5.76 m of fabric were lost as a result of warp breaks
alone as compared to 3.55m when the tension was at 70 cN
and a speed of 560 rpm . In 2 hours, the company could have
saved2.21m of fabric and, in 24 hours the company could
have saved 53m of fabric lost as a result of warp breaks
alone.
4.3.2. Extent to which weft breaks reduce loom efficiency
At a speed and warp tension values of 560 rpm and 80cN
respectively, the number of weft breaks which occurred was
12. The calculated loss in loom efficiency as a result of these
weft breaks which occurred during the 2hours for which the
loom was 13%[eq 9].
Average time lost = 1.3mins x 12 breaks
= 15.6mins
[eq 8]
.
×
Loss in efficiency =
= 13%
[eq 9]
For each weft break that occurs, the loss in loom
efficiency is 1.1% which was equivalent to losing 728 picks.
For a loom running for 2hours the company lost 3.64 m of
fabric as a result of weft breaks alone.
The number of weft breaks when the loom ran at a speed
of 560 rpm and a tension of 70 cN was 10, lower than the 12
when the tension was 80cN for the same speed of 560 rpm .
This difference in the number of weft breaks at a tension of
70 cN and higher, was of no great significance since
adjustment of warp tension did not have a direct effect on the
number of weft breaks except for very low warp tension
values like 50 cN (Figure 2).
Table 3, shows that a warp break requires more time for
repair than a weft break and the loss in efficiency as a result
of warp breaks was higher than that of weft breaks. Total loss
in efficiency as a result of both warp breaks and weft breaks
was 33.6%, which was too high, taking into consideration
that there were additional stoppages such as mechanical
breakdown which could occur. This makes it impossible for
the company to attain at least of 85%, efficiency hence the
need to reduce the number of warp and weft breaks.
varied helps the weaver to avoid loss of production time
when he or she tries to find the optimum warp tension or
optimum loom speed through a trial and error method. The
time taken by the weavers to repair a single warp break was
more than twice the acceptable time; the weavers therefore
need to be encouraged to improve on their time to clear
stoppages since production in a weaving business heavily
depends on the attitude of the weaver. Weavers need to be
motivated through competitive salaries and incentives
It can be concluded that warp breaks in Air Jet Looms are
caused by uncontrolled warp tension and very high loom
speeds amongst other factors like poor quality of yarn, poor
size take-up, uncontrolled room temperature and relative
humidity. The spinning industry and the preparation for
weaving processes have been successful in improving the
yarn quality but warp breaks still continue to occur. The duty
therefore remains with the weaving industry to optimise
loom efficiency in high speed looms like Air Jet Looms, by
taking a closer look at the warp tension and loom speed in
order to reduce the number of warp breaks so that higher
loom efficiency can be achieved. Adjustment of warp
tension and loom speed can help to determine the optimum
values of warp tension and loom speed to be used in order to
reduce the number of warp breaks in Air Jet Looms. A
modelled equation can be used to determine the number of
warp breaks which can occur at a given warp tension. The
time taken to repair warp breaks and weft breaks need to be
closely monitored as production in weaving depends on the
attitude of the operators.
5. Conclusions
REFERENCES
In order to reduce the number of warp breaks, warp
tension required when producing plain weaves on AWSE
2/E Dornier Air Jet Loom should be between 65 and
75cN/thread for a loom running at a speed of 560 rpm .The
modelled equation that defines the behaviour of warp breaks
on varying warp tension can help the weaving companies to
predict the number of warp breaks which can occur at any
given warp tension. This can help to determine the most
appropriate tension for initial warp tension setting.
The results show that warp breaks can still occur even if
the maximum warp tension during weaving is lower than the
breaking strength of the yarn. Care should therefore be taken
to avoid setting the warp tension closer to the breaking
strength of the yarn as this may cause the yarn to easily fail
due to cyclic fatigue experienced throughout the weaving
process. The maximum warp tension during weaving should
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When deciding on the warp tension and loom speed to use,
the number of warp breaks and loom efficiency associated
with these warp tension and loom speed should first be
established, and this can be done by conducting work studies
on the looms under consideration. Establishment of the
actual trend followed by warp breaks as the tension is being
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