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August 2017


Mr. Akshay H. Bohara

Bohara Impex (Airjet Weaving Division), Ichalkaranji, INDIA

ABSTRACT

As it is well known, power consumption due to compressed air is the main disadvantage of Air jet loom when compared to rapier and projectile looms. This is making air jet less preferable where energy cost is the problem, despite their high production speeds. Studies which have been taken to reduce them, included manufacturing of different parts i.e. Researches have been taken place on the manufacturing levels. But, we decided to reduce the consumption of air which may be due to some wrong settings, ignorance, etc. Without any investment which can give profits to the mill by reducing the consumption of air. A decrease of air consumption by 18% was accomplished in a weaving mill by just changing the process parameters consisting mainly the blowing time of nozzles. By improving work practices i.e. by implementing KAIZEN we could save the compressed air. 

1. Introduction to Air Jet Weaving

For the weft insertion mechanisms of air jet looms, the profile reeds with sub-nozzle systems are the most advantageous in terms of improving high speed weaving and wider cloth width. Not only the airflow from the main nozzle and sub-nozzles but also the airflow in the weft passage is closely related to the flying state of the yarn at the time of weft insertion in this system. In order to manufacture high quality textiles with air jet looms, it is necessary to establish optimum weaving conditions. These conditions include the supply air pressure and air injection timing for the main nozzle and sub-nozzles according to the kind of well yarn. Energy saving is the most important of the technical subjects related to air jet looms today. 

Research about the improvement in performance of main nozzles and sub-nozzles, which plays an important role for weft insertion, has been performed by various researchers. Although some effort has been made to improve the efficiency of compressed air usage, the effort has not been uniform. There is still a critical need to understand the energy loss or consumption in filtration, distribution and machine usage in the textile industry. Due to technical barriers, reducing energy consumption by compressed air systems has been viewed as a complicated task. 

Optimization of Air Consumption of AirJet Weaving Machine
Optimization of Air Consumption of AirJet Weaving Machine
Intensive efforts have been made by researchers and air –jet loom makers to overcome this problem and achieve a dramatic reduction in air consumption without any decrease in loom performance and fabric quality, but due to faulty mill practices and ignored settings, air consumed by looms is on higher side. So, our project aims to reduce the air consumption significantly, by optimizing some loom parameters. These parameters, includes mainly the relay nozzles because they consume 80% of the compressed air produced.

2. Terms Related to Air Jet Weaving Technology

2.1 Air Index value

A term designated to quantify the velocity of yarn in air as well as the deviation in velocity when tested on a diagnostic testing machine known as the Air Index Tester. 

2.2 Arrival Time

The amount of time required for the pick to travel the width of the fabric being manufactured during weaving, expressed either in terms of degrees of shed rotation or units of time.

2.3 Count

A numerical designation of yarn size indicating the relationship of length to weight, defined as the amount of 840 -yard skeins required to weigh one pound.

2.4 Filling Stop

A temporary shutdown of a weaving machine due to an error in filling yarn insertion.

2.5 Pick

The length of yarn required to be woven into a particular width of fabric.

2.6 Spun Yarn

A cotton-based yarn consisting of staple fibres usually bound together by twist.

2.7 Yarn Hairiness

A quantitative method of describing the surface roughness of cotton based spun yarn by counting the amount of broken fibres that protrude from the surface of the yarn, giving it a fuzzy appearance.

2.8 Yarn Package

A large spool of yarn.

3. Brief Description of Air Jet Weaving Process

The air jet loom feeds the filling as in Figure 1. The filling length is measured according to the width of the fabric by 1 rotation of the loom. It is accelerated by the main nozzle at a specific timing, and is inserted into the air guide o the reed. Groups of sub-nozzles are located across the whole width. Each group jets compressed air in a specific order to feed the filling tip to the right end of the fabric. The compressed air is supplied from the compressor, its pressure is adjusted by the regulators for the main nozzle and the sub-nozzles, and it is stored in the proper tank. The control system of the loom opens and closes the electro-magnetic valve, and sends the compressed air to the nozzles.

Filling feeding system
Filling feeding system

Comparative power consumption figures for different types of shuttle less looms and the shuttle loom (for 190 cm width looms) are worked out (i.e. estimated) and are given in Table below. 
Table
Figures in Table are only for loom drive and do not include power requirement for humidification, lighting, etc.

4. Optimization of Compressed Air 

Compressed air cost can be minimized broadly in two ways: 
  • Firstly, by minimizing wasteful compressed air consumed i.e. by preventing compressed air leakages and, 
  • Secondly by improving the efficiency of compressors. Ways and means for both these aspects are discussed.

5. Preventing Air Leakages

Leakages usually occur in small openings; but the cumulative effect is great. Some tips for preventing the air leakage are given herewith.
  1. Standardise on good hose clamps.
  2. Inspect steam packing of valves in the system periodically, repack when necessary.
  3. Replace/repair leaky shut-off valves.
  4. Install condensate separators with automatic traps to eliminate the need for operators, opening the manual valve to clear water, thereby wasting air.
  5. Use good quality air hoses to avoid breaks and leaks.

[update title="Leaks may cost you significant amounts of money and CFM each year." icon="info-circle"]
  • A 1/16” leak may cost $523, 6.49 CFM
  • A 1/8” leak may cost $2,095, 26 CFM
  • A 1/4” leak may cost $8,382, 104 CFM
[/update]

6. Improving Volumetric Efficiency of Air Compressors

Volumetric efficiency of an air compressor has a significant bearing on the operational cost of air compressors. Low volumetric efficiency results in higher per unit cost of compressed air. The main contributing factors for low efficiency are:
  • Clogged air inlet filters.
  • Obstruction at the inlet valve.
  • Piston ring leakage.
  • Hot inlet air.
  • Inter cooler working inefficiently.
  • Increase in impeller-diffuser clearance in case of centrifugal compressors.
It is therefore, necessary to check the volumetric efficiency periodically and if it falls below stipulated value the compressor should be checked and attended.

7. Cost Reduction Opportunities

Cost reduction opportunities that were explored include re-use of plant air, compressor motor selection, optimizing compressor control schemes, recovering the heat of compression, ensuring that the distribution lines are properly configured and free of leaks, and determining the minimum pressure and flow requirements at the end use.

7.1 Air Intake

Typically, the air being compressed is taken from outside the plant, from air at ambient temperature and relative humidity. This creates wide varieties of conditions that the compressor has to be adjusted to meet. During the summer months, the compressor is under the greatest load. The volumetric flow rate of the inlet must be higher (around 10%) to provide the same SCFM (standard cubic feet per minute) during the summer months as in the winter. After air is used at its point of operation, it is added to the air already in the plant. This additional volume of air must leave the plant somehow, i.e. open doors, cracks in door and window frames, etc. This air that is being leaked from the plant would have much lower moisture content than the outside air. The air inside the plant will also have a higher density in the summer months due to a lower temperature. 

The implementation of a system that recovers the conditioned plant air may prove to be useful in reducing air compression costs. The potential energy savings from reusing this already dry air could be significant when the conditions outside the plant are extremely hot and humid. Certain geographic locations would benefit more than others from this reuse which has extremely hot and humid summer months. The installation cost of such a system can be very high for an existing plant, but this option should be considered when a new plant is designed.

7.2 Compressor Motor Efficiency

Improvements in motor design have led to increased energy efficiency in motor operation. New motors that are suitable for textile manufacturing plants operate at an efficiency of 95%, comparing to motors designed 15 years ago at 90% or less. Over time, the efficiency of the motors may be reduced. 

It is not uncommon for the efficiency to drop several percentage points after 10 years of operation. High efficiency new motors should be considered when a replacement or major maintenance is needed on the motors.

7.2.1 Compressor Controls

Centrifugal compressors typically use inlet guide vanes to control the airflow through the compressor. This throttling is beneficial in that the efficiency is not reduced significantly with this method of control. The typical throttle range is down to around 80% of maximum airflow capacity. 
The highest efficiency is reached when the compressor is operating at 100% capacity. 
If air is not being used on the demand side as fast as it is being produced, the pressure will rise in the air receiver. A compressor (or multiple compressors) must be throttled to prevent this. All of the compressors should be operating at full capacity except for the one(s) being throttled. If the total compressor output is still greater than the demand after the compressor(s) has been throttled to their limit, air must be exhausted from the system through the blow -off valve. 

An appropriate control scheme can reduce or eliminate this wasteful blow-off. A precise compressor control scheme with little pressure variation is desired. The compressor does not need to produce air at a higher pressure than the minimum pressure required for proper plant operation. The typical pressure output by a compressor tends to fluctuate somewhat throughout the day. A good control scheme would minimize these fluctuations.

7.3 Distribution Lines

The distribution system represents a great source for energy savings. There are pressure drops associated with the flow through all equipment in the line, even in the piping itself. The pressure drop from the point of use and from the output of the compressor should be as low as possible. Equipment should be properly sized to give a minimum pressure drop. 

End use equipment should be evaluated so that it is using the lowest possible pressure and flow. The ultrasonic detector is able to focus the sensor at a specific point, making it suitable for detecting leaks while machinery is in operation. 

Escaping air produces the highest noise levels at a frequency around 40 kHz, well beyond the human audible frequency range. The device measures the loudness level at this frequency. Estimates of the amount of air can be obtained from the dB reading.

7.4 Physical Properties and Characteristics of Yarn

Several physical properties and characteristics of yarn are thought to have an effect on yarn velocity in air jet weaving applications. The yarn characteristic thought to have the most effect on yarn velocity (and therefore, Air Index value) is the yarn hairiness, which is a quantitative means of describing the surface roughness of a cotton-based spun yarn. Yarn hairiness is a means of counting the broken fibres that protrude from the surface of a spun yarn, giving the yarn a fuzzy appearance. It is hypothesized that yarns with higher hairiness values will result in higher Air Index values, due to an increase in surface area of the yarn for the air to “push” on; i.e., an increased aerodynamic drag. 

Other physical characteristics of yarn will be investigated in this report to determine whether or not they have an influence on Air Index value, especially yarn count. The count of a spun yarn is a numerical designation of yarn size that relates the length of the yarn to its weight, as well as describing its diameter. The higher the yarn count, the smaller the diameter and density of the yarn is, so it is thought that higher yarn counts will result in higher Air index values. This is due to the increased surface area-to-mass ratio as yarn count is increased.

7.5 Opening & closing timing of nozzle

Correction made delayed opening loss pressure through valve enhance the efficiency of machine. Early opening will reduce the air consumption. Improper opening & closing timing of valves lead to undue stress on yarn thereby leading to break. After proper adjustment the no. of end breaks can be reduced. The air consumption can be reduced up to 5 to 6%.

7.6 Pressure on the nozzle

Pressure on nozzle has more impact on the m/c performance. Improper pressure adjustment will causes the weft stop during working so quality & productivity can be minimized. To avoid the problem, proper setting of pressure can be required. These can be adjusted according to count, rpm, width of m/c. Proper combination between main & relay nozzle will reduce the air consumption.

7.6.1 Setting of nozzle

Setting of Nozzle
Setting of Nozzle
  1. Distance between two nozzles: Improper setting between to relay nozzle will cause to variation in air pressure and will cause m/c performance to be in decreasing the air consumption will be unnecessary increases.
  2. Nozzle height: Proper height setting of relay nozzle will causes reduction in air pressure during weft insertion & air consumption can be reduced. Proper setting of the nozzle height will provide the uniform displacement of yarn during insertion.
  3. Nozzle angle: For uniform weft insertion of yarn during insertion proper nozzle angle will reduce air consumption. Pressure required for insertion can be reduced.

7.6.2 Multi hole versus single hole

The multi hole relay nozzles guarantee a very stable blowing angle at different pressure levels. This is recommended for style changes that require different relay nozzle pressure settings. The single-hole nozzles need to be adjusted by hand whereas multi-hole nozzles keep their blowing angle stable and do not need any adjustment or fine tuning. Due to the pre-given horizontal and vertical jetting angles, the multi-hole nozzle requires less space between the warp yarns, which prevents nozzle marks in your fabric. The multi hole pattern allows also a more efficient air stream, thus delivering a better performance over single hole nozzles, giving up to 15% higher yarn speed for the same air consumption. Single-hole nozzles are recommended in case of a dusty environment or low air quality.

Multi-hole Nozzle Vs. Single-hole Nozzle
Multi-hole Nozzle Vs. Single-hole Nozzle

7.6.3 Different Hole patterns

The D-type nozzle is available with different hole patterns (1 – 7 – 16 – 19 holes) to suit your specific need. The highest performance is given by the 16 hole nozzle, offering you specific benefits.
Types of Relay Nozzles
Types of Relay Nozzles 1.C Type 2.S Type 3.D type 4.B type.

7.6.4 Insertion time

With the revolutionary 16-hole pattern, the air stream is now perfectly parallel to the warp yarns, thus making maximum use of the insertion time. As a result, higher weaving speed for increased productivity or a gentler yarn passage for better fabric quality is guaranteed.

7.6.5 Higher performance

The D-type 16 hole nozzle can offer you significant cost savings. This nozzle can generate the same yarn speed with less air consumption in some cases up to 15 – 20 % depending on the weaving condition. Either, with the same air consumption, you are able to increase the yarn speed.

Air Consumption Vs. Yarn Speed
Air Consumption Vs. Yarn Speed

7.6.6 DLC Coating

The D-type nozzles are exclusively coated with Diamond -Like carbon coating which is superior to any other coating. It increases life time up to 5 times and avoids wear and yarn cuts. DLC coating is therefore specially recommended for abrasive warp yarns.

7.6.7 Control of sub-nozzles

Control of sub-nozzles by increased groups conventionally, as in Fig. sub-nozzles are arranged in groups of 4 nozzles. An electro-magnetic valve is attached to each group and the sub-nozzles of the same group jet simultaneously.
 
Sub-Nozzles
Sub-Nozzles
Tsudakoma’s new arrangement, as in Figure, has an electro-magnetic valve with a smaller inner volume so that it matches to 2 sub-nozzles. The control of valve is improved, and extra jetting time is reduced.

8. Effect of costing

Saving the compressed air required for the air jet weaving which is a major cost element in the fabric costing. And by saving this compressed air we can make the profits of our company by saving power units required. Because of this, fabric conversion cost is also reduced.
  • 1 kwh = 5.5 Cfm 
  • 1kwh = Rs. 2.98
  • 11 Cfm = Rs. 5.96/hr/loom
=Rs. 51494/year/loom
= Rs. 2574720/year/50 loom shed.

Thus a huge amount of capital can be saved just by proper setting of various machine parts without having any additional cost incurred.

Conclusion

  • This shows that the weaving mills could obtain considerable saving in energy cost by just improving the work practices and by avoiding ignorance in settings. 
  • Reduction of air consumption by about Rs. 2574720/year/50 loom shed by achieving shortest possible blowing time of various nozzles, and optimizing this setting by trial and error method without affecting the performance of loom and quality of fabric can be achieved. 
  • Hence considerable saving in Energy cost can be achieved and Miracles can be created thus Investors can be boosted to move to Airjet technology resulting into new scale of measure of woven fabric production.

Refrences

  1. Adanur, S., and Mohamed, M. H., Analysis of Air Flow in Air-Jet Filling Insertion, Text. Res. J., 61(5), 253-258 (1991).
  2. Adanur, S., and Bakhtiyarov, S., Analysis of Air Flow in Single Nozzle Air-Jet Filling Insertion: Corrugated Channel Model, Text. Res. J., 66(6), 401-406 (1996).
  3. Adanur, S., and Turel, T., Effects of Air and Yarn Characteristics in Air-Jet Filling Insertion Part II: Yarn Velocity Measurements with a Profiled Reed, Text. Res. J., 74(8), 657-661 (2004).
  4. Mohamed, M. H., and Salama, M., Mechanics of a Single Nozzle Air-Jet Filling Insertion System Part I: Nozzle Design and Performance, Text. Res. J., 56(11), 683-690 (1986).
  5. Ishida, T, "Air-Jet Loom, Present and Future, Part 5: Technical Problems Caused by Air-Jet", JTN, November, 1982.
  6. Tarabadkar, S. A., Sharma, H. M., and Yadav, D. H., "Assessment of Compressed Air Requirement for Spinning and Weaving Machines", Vol. XXXI, No. 3, The Bombay Textile Research Association, September, 2001.

Mr. Akash S. Bansode

D.K.T.E. Society’s Textile and Engineering Institute, Ichalkaranji - 416115.

ABSTRACT

A 1% reduction in yarn realization has almost the same economic impact on the mill’s profit as an increase on 1% in the mixing cost. This is because the resale value of wastes is much less than the price of the cotton or the yarn. The control of yarn realization is thus as important to a mill as the control of cotton and mixing cost. And yet in most mills, the approach to the control of yarn realization is half-hearted, and depends on records of dubious accuracy.

In this paper, we will first consider the quantities for which records have to be maintained for estimating waste losses and yarn realization, and then give specific recommendations on how to collect data, and use them for computing accurately the mixing wise yarn realization. A simple but effective method of crosschecking the accuracy of the entire recording system will also be outlined. Norms for waste losses and yarn realization will be given mixing wise, and an appropriate procedure will be suggested for utilizing the norms for evaluating the performance of a mill.

Keywords

Yarn Realization, Process Waste, Product Waste, Invisible Loss, Assessment of Yarn Realization, Doff Weight method, Hank Meter Reading.

1. INTRODUCTION

Yarn Realization denotes the percentage of yarn produced from a given weight of bale material. The rest is the waste which has much less worth compared to fresh fibers or yarn. In the last decade or so, the Indian mills have become acutely aware of this aspect and have introduced effective control and monitoring mechanism. The wastes are distinctly of two types:
  1. The Process waste taken out in the blow room, cards and combers which accounts for nearly 80% of the total wastes losses in cotton spinning and 50% in manmade and blends spinning. The process waste is decided by arriving at optimum levels required to achieve the desired yarn quality.
  2. The product wastes which are incurred at each stage of processing, the control over product wastes has to be exercised through effective floor supervision.
The levels should also be guided by the standards arrived at by the research associations. A 1% reduction in yarn realization has almost same economic impact on mill’s profit as increase of 1%. The records required to be maintained for waste losses and yarn realization are outlined here. Norms for waste losses and yarn realization are also given.

To have a good control on the process wastes it is important to assess the wastes in blow room, carding, comber and ring frame at regular intervals. It should be noted here that the control on wastes has to be concomitant with achieving the desired level of cleaning.
YARN REALIZATION AND CONTROL OF WASTE IN SPINNING
YARN REALIZATION AND CONTROL OF WASTE IN SPINNING



2. YARN REALIZATION

Establishment of norms for wastes is a pre-requisite for a successful waste control in a mill. Yarn realization (YR) is largely governed by the level of trash in cotton, expected yarn quality and type of machinery. Yarn Realization is governs to improve Yarn Quality, Productivity & waste reduction in process. From the SITRA paper publication achievable yarn realization can be obtained using the following formulae:

A. For mills reusing the entire usable wastes in the same mixing 

  • YR (%) = 97.5 – t – Wk – Wh for carded yarn
  • YR (%) = (100 – t – Wk) {1-(Wc/100)} – Wh – 2.5 for combed yarn

B. For mills not reusing the usable wastes in the same mixing
  • YR (%) = 97.5 – t – Wk – Wh – Wu for carded yarn 
  • YR (%) = (100 – t – Wk) {1-(Wc/100)} – Wh – Wu – 2.5 for combed yarn

Where,
t = trash in mixing (%) 
Wk = card waste (%)
Wc = comber noil (%) 
Wh = yarn waste (%)
Wu = usable waste (%)

2.1 Yarn Realization is affect by following cotton characteristics


A. Trash % in cotton purchased
Higher the trash% content in bale, higher will be need remove waste in Blow Room & lower is the Yarn Realization. Material handling storing of material in ginning process is more responsible for trash% in cotton.
B. Moisture content in cotton
As amount of moisture in cotton goes up, the yarn realization goes down.
C. Short Fiber content in material

Higher the short fiber content, higher is the removing efficiency of short fiber at comber stage because of that yarn realization become lower.
D. Departments for Yarn Realization
  • For Carded Yarn: Blow Room, Carding & Ring Frame
  • For Combed Yarn: Blow Room, Carding, Comber & Ring Frame
The control over the Yarn Realization can be done by Owner of Organization, Manager of Organization, H. O. D. of each department, Supervisors, Workers these peoples.

3. How Yarn Realization will improve?

Yarn Realization associated mainly with Cotton Feed, Yarn Produce & Waste generation. To improve yarn realization % we have to concentrate on reduction in waste generation. Better way to control over the yarn realization by means of better practical way to control over the waste generation. 

The percentage yarn realization depends primarily on process waste taken out at blow room, card & comber. Waste taken out in bow room depends on trash content of the mixing. The waste in Cards depends on type of card& also to some extent, on trash in lap. The waste in comber, depends on nature if fiber length distribution in feed.


Record to Account for Yarn Realization

Record to Account for Yarn Realization

3.1 Cotton Consumed

3.1.1 Cotton issued

In Bale form of 160 to 165 kg. 

3.1.2 Stock in process

Stock in process at various stages has to be adjusted as the weight in kg. should be multiplied by a factor:          
  • Blow Room Lap= 100/ (100-B. R. Waste %)
  • Card sliver/Drawing sliver/ Roving= 100/ {100-(B. R. waste%+ Card Waste %)}
  • Combed Yarn= 100/ {100-(B. R. waste%+ Card Waste %+comber Waste %)}

3.1.3 Waste Generate

  • The Process Waste taken out in Blow room, Cards & Combers which account for nearly 80% of total waste losses in cotton spinning & 50% manmade & blend spinning.
  • The Product wastes which are required a specified treatment at each stage of processing.
  • The Invisible loss is not directly measured. The invisible loss refers to loss caused by evaporation of moisture content in cotton, dust in atmosphere, fluff. The amount of soft waste generated in order of 6% for medium & fine count and 8-12% for coarse count.

3.1.4 Yarn Produce

The amount of Yarn Produce is measured by two methods as:
  1. Doff Weight Method: In this method the amount of yarn produce is measure by governs the weight of Empty bobbin, weight of tray & weight of full doff.
  2. Hank meter Reading: In this method the yarn produced is measured on length basis as the hank meter is attaché with front roller on ring frame.

4. Assessment of Yarn Realization

The exact assessment of Yarn Realization is not possible. Because problems associated with Assessments of:
  1. Exact amount of Fiber Feed. 
  2. Determination of exact Yarn Formed.
  3. Exact amount of Waste.

4.1 Problems associated with Assessments of Exact amount of Fiber Feed

  • Weight of bale is high so that to weigh the bale more number of laboures are required
  • The quantity of Fiber feed to process is very high it’s more than 10.000 kg/ day
  • High capacity & sensitive weight balance is required to weigh the bale of high weight which is not easily available in mill.
  • TOTAL WEIGHT of BALE = Net Weight of fiber + Weight of Packing Material.

4.2 Problems associated with Assessments of Exact amount of Waste

  • Some amount of Fiber goes in atmosphere in the form of FLUFF.
  • Moisture affects on waste amount.

4.3 Problems associated with Assessments of Determination of exact Yarn Formed

4.3.1 Limitations of Doff weight Method

  • Lot of Labour required. 
  • Transportation required.
  • Handling of Material. 
  • Exact weight of Yarn produce.

4.3.2 Limitations of Hank Meter Method

  • Accuracy of Hank Meter. 
  • Twist Contraction.
  • Idle Spindle percentage. 
  • Bonda Waste

5. Norms for Wastes &Yarn Realization


The values of all wastes are expressed as % of cotton consumed

Content
Carded
Combed
MMF
Count
4-9
10-13
14-25
26-34
28-34
35-44
45-70
71-99
-
Trash%
11
10
7
5
5
4
3
2
-
B.R. Dropping
12
11
7.7
5.4
5.4
4.4
3.2
2.2
0.1
Card waste
4.2
4.2
4.4
4.5
4.5
4.3
4.3
6.4
0.1
Comber Waste
-
-
-
-
9
10.9
12
13
-
Sweeping
2
1.8
1.6
1.4
1.4
1.2
1
1
0.5
Clearer waste
0.6
0.5
0.4
0.4
0.4
0.3
0.2
0.1
0.1
Hard waste
0.6
0.5
0.3
0.3
0.3
0.3
0.3
0.3
0.4
Invisible loss
1.8
1.7
1.6
1.5
1.5
1.3
1.3
1.3
0.3
Y. R %
78.1
79.7
83.6
86.5
77.5
77.4
77.9
77.9
97.6


Standards for Yarn Realization

Category
B. R. Waste (%)
Card waste (%)
Comber Waste (%)
Ring Frame (%)
Yarn Realization (%)
Carded Cotton Count
5 – 6
5 – 6
-
3
85 – 88
Combed Cotton Count
5 – 6
5 – 6
3 – 5
3
70 – 75
Manmade Fibers
1
1
-
2
95 – 97


6. Control on waste in spinning

To have a good control on the process waste it is important to assess the waste in Blow Room, Carding, Comber & Ring Frame at regular intervals. It should be noted here that the control on waste has to be concomitant with achieving the desired level of cleaning.

6.1 Blow Rom Waste

The cleaning at Blow Room should always be considered alongwith the following things:-
  1. The cleaning efficiency of blow room machines for, seed coats is much less than for leafy matter & sand dust taken together.
  2. The cleaning efficiency & waste increases as trash content increases.
  3. No aspect of yarn quality other than neps & foreign matter is influenced by the quality of blow room processing.
  4. An optimum level of opening is essential for cleaning of cotton.

Improving Cleaning Efficiency & Reducing waste at Blow room

To improve cleaning efficiency of beater, first examine the mechanical condition of machine, spikes on Krischner beater, blades and fingers on bladed and Porcupine openers & repair or replace as required. The inter grid bars space should be check for any chock up. The waste is affected by changes such as:
  1. Distance between the grid bars and the angle of inclination of bars.
  2. Speed of Beater.
  3. Fan speed in relation to the beater speed.
  4. Setting between feed rollers & Beaters.
  5. Setting between Beater & Grid bars.

6.2 Carding waste

The behavior of waste & cleaning at cards depends on the following considerations:
  1. The total collected waste at card does not show any close relationship with the trash in the lap feed to the card.
  2. The cleaning efficiency achieve in mills is about 80% for most mixing. However, for fine and superfine mixing for which very high flat speed and low production rates are employed, a cleaning efficiency of 85% or more is achieved. The overall effect is that the lint loss in card waste will increases with decreasing trash content in lap.
  3. There is a tendency for the card to compensate for any lack of cleaning in blow room. The overall cleaning efficiency achieve in the blow room & the card taken together remains within a narrow range of 93-95%.

Controlling the waste at Card

The following facts should be kept in mind while controlling the waste & cleaning at cards:
  1. Use of only one mote knife, placed slightly below the normal position of the top mote knife has been observed to give less waste and better cleaning in cotton mixing.
  2. Higher licker-in speed or greater wire point density on licker-in gives higher cleaning efficiency accompanied by some increase in the lint lost under the licker-in.
  3. Use of perforated undercasing helps in reducing waste.
  4. With other speeds and setting held constant, the flat strip waste varies almost proportionately with the flat speed.
  5. Wider front plate and back plate setting increase flat strip waste.
  6. For controlling cleaning of the card, almost the only place is the licker-in region.
  7. Card is excellent cleaning machine for seed coats especially the cylinder-flat region which removes 80% of the seed coats. A higher flat alongwith higher cylinder speed can be use for better removal of seed coats and also reducing neps, thick places and Classimat A & B faults. The seed coat content of 0.1% in the card sliver can be considered as satisfactory.
  8. The tandem card gives 5-7% higher cleaning efficiency and better removal of seed coats.

6.3 Comber waste

One of the main functions of combing is to remove short fibers through taking out a certain amount of comber waste. The waste thus removed also contains a large number of neps and foreign matter. Obviously, combing is not required for manmade fibers as they are free from short fibers and foreign matter. A higher % of comber waste need not always means that better removal of short fibers and neps, and therefore may not always be advantageous either for yarn quality or performance beyond a certain level.

6.3.1 Technological Consideration

For an effective removal of short fibers, retention of long fibers and removal of neps the following considerations are of up-most importance:
  1. The card trailing hooks are longer and more numerous than the leading hooks. They are removed when fed as leading hooks by keeping an even number of reversals between the cards and the comber.
  2. The waste at comber can be reduced by increasing pre-comber draft without affecting the resultant yarn quality. However, a high comber draft also result in extremely low inter fiber cohesion causing excessive lap linking, frequent sliver breaks at comber, draw frame and the can feed inter creel. Therefore, a pre-comber draft of 30-40 for counts upto 40ŝ is adequate. Pre-comber draft of above 20 is suitable only for very long staple cottons.
  3. The proper place for controlling neps is carding and no combing. It is often more economical to run cards a somewhat low production rate than to take out extra comber waste.

6.3.2 The waste at comber needs to check and controlling due to the following reasons

  1. More waste than the nominal means financial loss.
  2. Less waste than the nominal could lead to unacceptable yarn quality and performance.
  3. Comber waste variation could contribute to lea count variation.

Norms for cleaning coefficients in Blow Room


Number of Machines
Cleaning coefficients for
Seeds & Seed coats
Leafy matter & sand dust
1
0.42
0.72
2
0.50
0.80
3
0.56
0.84
4
0.60
0.87
5
0.64
0.89
6
0.66
0.90


Norms for Collected Waste & Cleaning efficiency of Card

Mixing
Trash in lap (%)
Type of card
Category of waste
Cleaning Efficiency (%)
Flat Strips
Licker-in
Others
Total
Superfine & Fine
Less than 2
SHP
2.9
1.6
0.5
4.5
88
HP
1.9
1.6
0.5
4.0
Medium & Coarse
2.0 to 2.5
SHP
2.0
2.0
0.8
4.8
83
HP
1.5
2.0
0.8
4.3
Range
1.5-2.5
1.5-2.0
0.5-1.0
4-6
85-90


Norms for Comber Waste

Warp Count Group
Level of Comber Waste (%)
28-34
7-9
35-44
11-13
46-60
12-14
61-90
13-15
91-120
14-16

6.4 Ring Frame Waste

At many stages of spinning process waste is removed to clear the cotton or to separate the short fibers but at the stage of Ring spinning there is no need to remove waste. This step is exclusively for drafting twisting and packing the yarn in the shape of bobbin. Whatsoever material is wasted here is because of our inability to control the machine, process or processing condition. Thus control the waste we have to control all factors.

At the ring frame stage a scope for saving 1.5 to 2 % on these wastes. Waste at ring frame means wastage of raw material & wastage of conversion cost upto yarn stage. If a mill spinning 20ś count, having 25000 spindles and production 205 grams/spindle at 96% spindle utilization saves 1% waste in ring frame it can save about Rs. 12 lacs per year.

6.4.1 Factors Responsible for waste generates in Ring Frame

  1. Yarn Breakage rate. 
  2. Time taken in attending to the yarn breakage.
  3. Working practice & culture. 
  4. Housekeeping & material handling.
  5. Mechanical breakdown & failures. 
  6. Methods of attending to the break downs.

6.4.2 Waste Control in Ring frame

This is done in the following steps:-
  1. Analysis and segregation of the waste of different types
  2. Weigh that waste and recording that section wise, person wise, shift wise.
  3. Comparison with the standards.
  4. Feed backs and action to improve waste generation.

7. For check & control all types waste

The following questions are helps to check and control all types of wastes:
Q. Whether a scheduled maintenance program is followed effectively?
Q. Is there cleaning of the floor can do properly?
Q. Is the material handling minimum & adequate?
Q. Whether the stocking place for cotton & yarn is good & sufficient? 
Q. Is the average yarn content per bobbin optimum?
Q. Is the proper humidity & temperature being maintained in departments?

If the above questions are put, the solution are worked out effectively implemented with the basic principles of collection of data, analysis and feed backs are followed consistently, not only that waste would be controlled also The productivity, working environment and culture all would simultaneously improve and I feel that if firmly determined every one of us is capable of controlling it.


Conclusion

In many mills, there is good scope for improving yarn realization and reducing wastes. Because in the spinning mill waste are generates in more amount & it can controllable & reducible at some extent. Improvement in yarn realization results in Rs. 3 to 10 lakhs savings per year.

The following 6 steps would be helpful to improve yarn realization:-

  1. Calculate actual yarn realization and different categories of wastes
  2. Using the formulae given in this presentation, estimate the expected yarn realization for the existing working conditions.
  3. Compare the actual yarn realization with the expected value and actual wastes with norms.
  4. Analyse the causes for deviation and initiate corrective action. 
  5. Create awareness among the workers and technical staff about the importance of waste control. 
  6. Good supervision and proper maintenance of machinery would help to reduce the waste.


References

  1. Process Control in Spinning by Gadre & Subhramanyam: ATIRA publication, page No.(45 to 107).
  2. Process Control in Spinning by Rattnam, page No. (11 to 30)
  3. Paper published by D.Shanmuganandam (Assistant Director) SITRA.
  4. Waste Control at Ring Frame by S. K. Srivastav: NITRA publication, page No. (1.1 to 1.9)
  5. Waste Investigation & Control for a Spinning Mill article in The Indian Textile Journal, September 1984 , published by, Mr. A. R. Nityanand page no.(79 to 86)
  6. A study on carding waste collection system in mill article in The Indian Textile Journal, April 2012, published by, M Muthuvelan, H Balasubramanian and A Sivaramakrishnan
  7. www.fibre2fashion.com 
  8. www.sitra.org.in

Ashish Hulle

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