USTER® AFIS PRO
APPLICATION REPORT
Cotton card maintenance with
a single fiber testing system
THE FIBER PROCESS CONTROL SYSTEM
Editorial team, UTUS
March 2006
SE 595
THE FIBER PROCESS CONTROL SYSTEM
Copyright 2007 by Uster Technologies AG
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, translated or transmitted in any form or by any means, electronically, mechanically, photocopying, recording or otherwise, without the prior permission in writing of the copyright owner.
veronesi\TT\Schulung_Dokumente\Off-line\AFIS\SE-595_Cotton card maintenance\SE_595.doc
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Table of contents
1
Introduction ................................................................................ 5
2
Carding department analysis .................................................... 6
2.1
Historical scheduling of maintenance........................................... 6
2.2
Nep variation in card sliver ........................................................... 6
3
Application of USTER® AFIS nep data ..................................... 7
3.1
Process control chart ................................................................... 7
3.2
Setting control limits ..................................................................... 8
3.3
Nep removal efficiency................................................................. 8
4
Reducing maintenance costs ................................................... 9
4.1
Historical card rebuilding and grinding ......................................... 9
4.2
Maintenance based on AFIS control chart nep levels ................ 10
5
Conclusions.............................................................................. 10
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1
Introduction
The carding department in a spinning mill is the most critical area for maintaining proper control. The cotton card is the last opportunity to remove
neps and trash in sliver before the spinning process. However, additional
removal of neps and trash can be accomplished in the combing process.
Neps in card sliver produce imperfections in carded yarn as measured by
USTER® TESTER. The number of imperfections in terms of neps and thick
places can be directly associated with the neps and seed coat fragments in
cards sliver. Neps in card and draw frame sliver cannot be detected by only
controlling sliver weight and evenness. This is the reason that sliver with
acceptable evenness and count variation values may produce unacceptable spinning efficiencies and poor quality yarn. The application information
presented in this paper will focus on cotton neps in the carding process.
New high speed cards have a very high production rate compared to the
cards produced just a few years ago. Normal production rate for a new card
is approximately 100 pounds (44 kg) to 120 pounds (53 kg)/hour. This
means a card can produce 2,400 pounds (1065 kg) of sliver in 24 hours.
Visual inspection of the card web by the technician has been used to judge
the performance of the carding elements such as cylinder wire, flat settings,
and licker-in cylinder. These visual determinations can be very subjective
and lead to unnecessary maintenance and rebuilding. Visual counting of
neps also is complicated by trash and seed coat fragments in the card web,
new design, etc. New designs of cotton cards have moved the doffer cylinder very close to the main cylinder. This new design has eliminated access
to the card web that has traditionally been inspected by the quality control
technician.
The USTER® AFIS (neps) instrument allows the spinning mill to quickly test
each card sliver to determine the quality level of the sliver being produced.
The repeatability and consistency of the USTER® AFIS measurement gives
valuable information to the card room technician. This information can be
used to establish a detailed maintenance schedule for the carding department. The information provided by the USTER® AFIS instrument can improve yarn quality by reducing the number of imperfections in the yarn such
as neps and thick places. Intelligent scheduling of card maintenance can
substantially reduce the amount of money and time spent on card rebuilding.
This paper only deals with one quality parameter which can be measured
with USTER® AFIS: neps in raw material and slivers.
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2
Carding department analysis
2.1
Historical scheduling of maintenance
A line or group of cotton cards do not operate or wear the same throughout
the Carding department. Because of the mechanical nature of the card design, the components of each card wear differently from one another. This
has led to establishing general maintenance and rebuilding schedules
based on experience. Typical schedules are as follows:
Operation
Schedule
Grinding
cylinder wire and flats
6 months or 500’000 Ibs (225’000 kg)
Rebuilding
replace cylinder wire and flats
1 year or 1 million Ibs (450’000 kg)
Licker-in Cylinder
replace
6 months or 500’000 Ibs (225’000 kg)
Table 1
Recommended procedure
The use of AFIS can produce a more realistic and practical schedule.
2.2
Nep variation in card sliver
The variation of neps in sliver from card to card results in maintenance being done on cards that are producing a good quality sliver. This also means
that some cards that are producing off quality sliver are not scheduled for
maintenance at the optimum time. Regularly scheduled testing of card
sliver on the USTER® AFIS instrument can provide the necessary information for determining which cards are in need of maintenance. The graph
below shows the typical variation in a single line of cotton cards.
180
160
Neps/gram in sliver
140
120
100
80
60
40
20
0
1
6 (12)
2
3
4
Card number
5
6
7
Fig. 1
Significant differences
across card line
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THE FIBER PROCESS CONTROL SYSTEM
This graph clearly shows that some of the cards have a low nep count and
some of the cards have a higher than acceptable nep count. This example
is very typical of the variation of neps in sliver in a normal carding department. The cotton used in this carding process was a saw ginned American
upland variety.
3
Application of USTER® AFIS nep data
3.1
Process control chart
The best way to make sure the cards are operating as efficiently as possible is to begin by setting up a process control chart for each card. This
chart should be kept in the file that records maintenance for each individual
card. A typical chart for a high speed cotton card is shown below:
120
Upper limit
Neps/gram: Card no. 12
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
Week number
Fig. 2
Process control chart
Neps in card sliver will increase with time as the card wire and other components deteriorate. This type chart applies to any make of card, slow or
high speed as well as single or tandem. Cards operating at slower speeds
will generally take a longer time to reach the upper limit.
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3.2
Setting control limits
The control chart showing the card number, Fig. 1, has the AFIS nep count
per gram on the vertical axis. The weekly test results of card no. 12 are
shown in Fig. 2 on the vertikal axis. Card sliver should be tested weekly if
possible, and the results posted at the card for that particular week. When
the nep levels go above the upper control limit, the card is then scheduled
for maintenance.
The upper control limit is established using the following information:
Question
Answer
Carding Department average nep count/gram?
Check all cards for 6-8 weeks to determine card
room average.
Spinning system, ring or rotor?
Ring spinning nep counts should be lower than
those of rotor spinning for coarse and medium
count yarns. This is due to the way yarns is
formed in the two spinning systems. In fine count
yarns, the nep levels for ring and rotor systems
should be kept to a minimum.
End product, knitting or
weaving yarn?
Neps are more visually critical in finished knit fabric than in finished woven fabric. This is due to
basic fabric construction and finishing techniques.
USTER® TESTER nep
count?
Compare the counts of the yarn neps from the
Uster Evenness Tester to the quality charts in the
USTER® STATISTICS. To improve the yarn nep
count and reach a desired level, such as below
the 5% curve, the nep count in sliver must be reduced to meet this higher quality level.
3.3
Table 2
Recommended procedure
Nep removal efficiency
As the card nep removal efficiency improves, the upper limit on the control
chart should be slowly lowered. Experience has shown that the upper limit
should level off in 4 to 6 months after a maintenance program is started
using the AFIS nep data to schedule card maintenance.
There are two ways to monitor neps in card sliver. One is to use the actual
nep count per gram. Another is to use card nep removal efficiency. Removal efficiency is calculated using the following formula:
% Removal efficiency =
Neps in card mat – Neps in card sliver
x 100
Neps in card mat
Neps in card mat are the neps in samples taken from cotton going into the
back of the card either in lap or mat form.
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Neps in card sliver are the neps in samples of cotton sliver taken from the
sliver can at the front of the card.
Calculating the nep removal efficiency is a good way to analyze an individual card. The efficiency calculation is also very useful in comparing carding
elements such as different card wire, card flats, or licker-in cylinders.
This efficiency calculation is ideal for evaluating a new design of card cylinder wire. Two cards can be rebuilt, one using new wire of the old design
and one using wire of the new design. These two cards can be compared
for a 30 day period to determine which wire is best for the mill's own quality
requirements. This same procedure can be used to evaluate card flat wire,
licker-in cylinders, as well as main cylinder and flat speeds.
4
Reducing maintenance costs
Using the information from the USTER® AFIS instrument to establish a nep
control chart and limits for scheduling carding maintenance, these can reduce the overall costs for the carding department. Mill studies have shown
that it is possible for some cotton cards to process over 2 million pounds
(900’000 kg) before exceeding the upper limits for nep counts in sliver.
Typically, costs for card wire and replacement parts such as flats and
licker-in cylinders are the largest expense items in the spinning mill's machinery maintenance budget. Reducing or eliminating the grinding of cylinder wire can also be accomplished using this nep control chart for scheduling maintenance.
The following example shows a comparison between historical maintenance scheduling and the USTER® AFIS control chart for establishing a
schedule. This example is based on a single card processing 100% American upland type cottons. The cards are high speed cards producing 100
Ibs/hr (44 kg) that have been operating for 4 years. Prices for rebuilding
and grinding are typical USA costs. This same chart can be used for other
economic regions by inserting typical costs for that particular area.
4.1
Historical card rebuilding and grinding
Cards
30
Rebuild/yr
Regrind/yr
30
30
Rebuild ($) Regrind ($)
2’500
60
75’000
250
Total maintenance
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Total ($)
15’000
90’000
Table 3
Cost for maintenance
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4.2
Maintenance based on AFIS control chart nep levels
Cards
30
Rebuild/yr
Regrind/yr
18
30
Rebuild ($) Regrind ($)
2’500
21
Total ($)
45’000
250
Total maintenance
5’250
50’250
Table 4
Cost for maintenance, AFIS
based
Total savings using USTER® AFIS is $ 39’250
Savings shown are based on the following guidelines:
• Rebuild only cards that exceed established nep levels
• All cotton cards do not wear at the same rate
• Additional savings can be accomplished by reducing the replacement of
additional carding elements such as card flats and licker-in cylinder
5
Conclusions
The USTER® AFIS instrument gives modern spinning mill management the
information necessary to monitor and improve nep levels in card sliver. Reducing neps in sliver reduces the neps and imperfections in yarn and improves fabric appearance. Replacing historical card maintenance schedules with a control chart using AFIS nep information can substantially reduce the repair and replacement costs in the carding department.
The following guidelines will ensure the best process control in the carding
department:
• Weekly testing of card sliver with the USTER® AFIS
• Establishing a process control chart for each individual cotton card
• Establishing upper control limits for nep levels
• Designing maintenance schedules based only for those cards above the
upper limit of the nep control chart
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Uster Technologies AG
Wilstrasse 11
CH-8610 Uster / Switzerland
Phone +41 43 366 36 36
Fax
+41 43 366 36 37
www.uster.com
[email protected]
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