FAQ in cotton spinning-5

FAQ in Cotton Spinning-5

Question: What is the function of calender rollers.
Answer: The function of calender rollers primarily is:
a. To draw the web away from the doffer at a uniform rate as fast as it is stripped.
b. It exerts sufficient pressure on the sliver in order to reduce the bulkiness of this sliver.

Question: How diameter of trumpet hole varies with the thickness of the sliver.
Answer:

Diameter of hole in inches= constant x sqrt (grains/yard of sliver)

constant= 0.022

Question : How does the setting to the following pair of card points affect the quality of sliver produced.
Answer:
Taker in to cylinder: wider settings: creates neps and licker-in gets covered with fibres.
Back Plate to cylinder: wider setting causes fly to blow between flats.
Flats to cylinder: Closer settings gives better quality.
Front Plate to cylinder: closer setting-> reduces the weight of flat strip. wider setting-> results in heavier flat strips.
Doffer to cylinder: wider settings-> creates more neps as fibres go round the cylinder unnecessarily more times.
Feed plate to Licker in : wider settings-> lap is plucked without sufficient opening. So web quality is reduced.

Question: What are different types of carding wastes and their constituents
Answer: Licker- in waste-> short fibres, trash.
Flat Strips-> cotton fibres (short)
Stripping waste ( on cylinder and doffer wire)-> short fibres and trash

Question: Why flexible wire clothing is preferred over metallic wire clothing for running long fibres.
Answer: It is observed that flexible fillet has a more gentle carding action and gives lesser damage to good fibres.

Question: Why draw frame is needed
Answer: The fibres in a card web lie haphazardly criss cross to the web. Besides, fibres have either one or both end bent into the form of hooks. These haphazard fibres are required to be straightened and parallelised to the possible extent, also evenness and regularity of sliver is improved.

Process Control in Cotton Mixing- Part 1

How Cotton Mills Select Bales: Cotton Mix Profile, Population Profile and Bale Picking Explained with a Simple Example

Cotton mixing is one of the most important decisions in spinning. Many people think that a mill buys cotton, opens the bales, mixes them, and starts spinning yarn. In reality, good spinning mills do not mix cotton casually. They create a cotton mix profile, study the population profile of available bales, and then use a bale picking scheme to ensure consistency in yarn quality and processing performance.

The central message is simple: cotton should not be selected only on the basis of price. It should be selected on the basis of fibre properties, yarn requirements, processing performance, variability, and cost together. A cheaper cotton bale may look attractive at the purchase stage, but it may create higher hidden costs during spinning, winding, weaving, knitting, or finishing.

Table of Contents

• 1. Why Cotton Mixing Matters
• 2. What Is a Cotton Mix Profile?
• 3. Fibre-to-Yarn Thinking
• 4. Denim Yarn and Knit Yarn Need Different Cotton
• 5. What Is Population Profile Analysis?
• 6. Why Random Bale Picking Can Be Risky
• 7. Grouping and Categorization of Cotton Bales
• 8. A Simple Hypothetical Example
• 9. Method 1: Random Picking
• 10. Method 2: Proportional Weight Category Picking
• 11. Method 3: Optimum Category Picking
• 12. Adding Cost to the Problem
• 13. Final Comparison of Picking Methods
• 14. Practical Meaning for a Spinning Mill
• 15. Related Reading
• 16. Conclusion
• 17. General Disclaimer

1. Why Cotton Mixing Matters

Cotton is a natural fibre. No two bales are exactly the same. One bale may have higher fibre strength, another may have more short fibres, a third may have higher micronaire, and another may have more neps or trash. These differences directly affect yarn quality and processing behaviour.

A poor cotton mix can lead to lower yarn strength, more end breakages, higher hairiness, more imperfections, more fly generation, poor weaving or knitting performance, higher waste, and higher hidden manufacturing cost. This is why the lowest-priced cotton is not always the cheapest cotton in real terms.

Visual 1: Cotton bale selection map connecting fibre properties with yarn quality and processing performance.

2. What Is a Cotton Mix Profile?

A cotton mix profile is the desired fibre-property profile required for a particular yarn. Before deciding the cotton mix, the mill must first ask what yarn is being made. The required cotton will depend on the spinning system, yarn preparation, yarn count, twist level, yarn quality requirement, end product, cotton price, and yarn selling price.

For example, cotton required for coarse denim yarn will not be the same as cotton required for fine knitwear yarn. Denim yarn may demand strength and weaving performance, while knit yarn may demand softness, flexibility, low hairiness, low fly generation, and good dimensional stability.

An optimum cotton mix is therefore not merely a cheap mix. It is a bale laydown that provides the desired yarn characteristics, good processing performance, and lowest possible total cost.

3. Fibre-to-Yarn Thinking

This leads to the idea of fibre-to-yarn modelling. This means understanding how fibre properties influence yarn properties. It is a practical way of connecting raw material decisions with final yarn behaviour.

Forward Projection

Forward projection asks: if I use cotton with these fibre properties, what yarn quality will I get? For example, micronaire, fibre length, fibre strength, and short fibre content may influence yarn strength, hairiness, imperfections, and processing performance.

This relationship may be represented as:

\[ \text{Fibre Properties} \rightarrow \text{Yarn Quality and Processing Performance} \]

Backward Projection

Backward projection asks: if I want this yarn quality, what fibre properties should I choose? For example, if the mill wants a soft, low-hairiness knit yarn, it must select fibre properties that help achieve that goal.

This can be represented as:

\[ \text{Required Yarn Quality} \rightarrow \text{Required Fibre Properties} \]

This is very close to modern predictive modelling. Today, we may use regression, machine learning, optimization, or simulation, but the basic textile logic remains the same.

4. Denim Yarn and Knit Yarn Need Different Cotton

Denim Yarn

For denim yarn, the important factors are yarn strength, spinning ends-down, rope beaming efficiency, and weaving performance. The important fibre properties include micronaire, fibre strength, short fibre content, variability in fibre strength, and variability in micronaire.

In denim production, rope beaming is especially important. If the yarn has high hairiness, weak places, or excessive splices, rope beaming efficiency may suffer badly. So for denim, the cotton mix must support strength, weaving performance, and processing efficiency.

Knit Yarn

For knit yarn, the priorities are different. Important parameters include yarn strength, twist, hairiness, imperfections, fly generation, softness, flexibility, and dimensional stability.

Knit yarn should usually be soft. So twist cannot be too high. But if twist is too low, the yarn may lose strength and integrity. Therefore, knit yarn requires a balance between enough twist for strength and low enough twist for softness.

This balance may be expressed as:

\[ \text{Optimum Twist} = \text{Sufficient Strength} + \text{Required Softness} \]

Longer, stronger, and finer fibres help achieve this balance. Short fibre content and neps are especially damaging in fine knit yarns because they increase imperfections and fly generation.

5. What Is Population Profile Analysis?

After deciding the desired cotton mix profile, the next question is whether the bales available in the warehouse match this requirement. This is called population profile analysis.

The bale population is studied using three main parameters: population size, average value of fibre attributes, and variability of fibre attributes. For example, suppose a warehouse has 2,000 cotton bales. Their micronaire values may have a mean of 4.0 and a standard deviation of 0.8.

The selected cotton laydown should be representative of the population, unless there is a deliberate reason to modify it. Ideally, the cotton mix should match the population in terms of mean value, within-mix variance, and controlled between-mix variation.

In simple language, this means every laydown should be consistent. One laydown should not be very different from another laydown, because that difference will later appear as variation in yarn and fabric performance.

Visual 2: Population profile of cotton bales showing mean, variation and selected laydown.

6. Why Random Bale Picking Can Be Risky

In random bale picking, bales are selected randomly from the warehouse. This may sound fair, but it can create inconsistency. One laydown may accidentally get more high-micronaire bales, while another may get more low-micronaire bales.

Random bale picking works better when the total bale population is already very uniform and the number of bales in each laydown is large. But if the warehouse has high variability, random selection can create unstable results.

7. Grouping and Categorization of Cotton Bales

Grouping

Grouping means dividing cotton bales into broad groups. For example, the mill may create separate groups for denim yarn, knit yarn, low-quality cotton, high-quality cotton, cotton from different regions, or cotton for different spinning systems.

If a mill produces both denim yarn and knit yarn, it should not blindly pick cotton from one common pool. Each yarn style needs its own cotton population.

Categorization

Categorization means dividing bales within a group based on fibre-property ranges. Bales may be categorized by micronaire, fibre length, fibre strength, short fibre content, or other important fibre attributes.

Suppose we use two fibre properties: micronaire and fibre length. If each property is divided into three categories, then total combinations are:

\[ 3^2 = 9 \]

If three properties are used, such as micronaire, fibre length, and fibre strength, then:

\[ 3^3 = 27 \]

So the number of combinations increases rapidly. This is why modern cotton mixing requires systematic data handling.

8. A Simple Hypothetical Example

Let us take a small example. A spinning mill has 100 cotton bales in the warehouse. The mill wants to prepare a 20-bale laydown. We will use only one fibre property: micronaire.

Category	Micronaire Range	Number of Bales	Average Micronaire
A	Low Mic	30	3.5
B	Medium Mic	50	4.0
C	High Mic	20	4.5

The warehouse average micronaire is:

\[ \frac{(30 \times 3.5) + (50 \times 4.0) + (20 \times 4.5)}{100} \]

\[ = \frac{105 + 200 + 90}{100} \]

\[ = 3.95 \]

So the target population average is 3.95. The mill wants every 20-bale laydown to remain close to this value.

9. Method 1: Random Picking

Suppose the mill randomly picks 20 bales. One random laydown may contain 5 bales from category A, 8 bales from category B, and 7 bales from category C.

Category	Bales Selected
A	5
B	8
C	7

Average micronaire:

\[ \frac{(5 \times 3.5) + (8 \times 4.0) + (7 \times 4.5)}{20} = \frac{17.5 + 32 + 31.5}{20} = 4.05 \]

This laydown has average micronaire of 4.05, which is higher than the target of 3.95. Another random laydown may contain 9 bales from A, 9 bales from B, and 2 bales from C.

\[ \frac{(9 \times 3.5) + (9 \times 4.0) + (2 \times 4.5)}{20} = \frac{31.5 + 36 + 9}{20} = 3.825 \]

Now the average is lower than the target. So random picking may create different laydowns with different fibre profiles.

Laydown	A Bales	B Bales	C Bales	Average Micronaire
Random Laydown 1	5	8	7	4.05
Random Laydown 2	9	9	2	3.825

This variation may later appear as variation in yarn quality.

10. Method 2: Proportional Weight Category Picking

Now let us use Proportional Weight Category Picking, also called PWC. In this method, bales are selected from each category in proportion to their presence in the warehouse.

Category	Number of Bales	Percentage
A	30	30%
B	50	50%
C	20	20%

The laydown size is 20 bales. So we select:

\[ A = 30\% \times 20 = 6 \]

\[ B = 50\% \times 20 = 10 \]

\[ C = 20\% \times 20 = 4 \]

Category	Bales Selected
A	6
B	10
C	4

Average micronaire:

\[ \frac{(6 \times 3.5) + (10 \times 4.0) + (4 \times 4.5)}{20} = \frac{21 + 40 + 18}{20} = 3.95 \]

This exactly matches the warehouse average. So PWC gives a much more stable laydown than random picking.

11. Method 3: Optimum Category Picking

Now suppose the mill wants to reduce variation even further. Let us assume the categories have different internal variation.

Category	Average Micronaire	Standard Deviation
A	3.5	0.20
B	4.0	0.10
C	4.5	0.20

Category B is more uniform because its standard deviation is lower. An optimum category picking method may select slightly more bales from B while still keeping the average micronaire close to the target.

Category	Bales Selected
A	5
B	12
C	3

Average micronaire:

\[ \frac{(5 \times 3.5) + (12 \times 4.0) + (3 \times 4.5)}{20} = \frac{17.5 + 48 + 13.5}{20} = 3.95 \]

This also gives the same target average of 3.95, but it uses more bales from the most uniform category. So both PWC and OPC may hit the target mean, but OPC can reduce laydown variation further.

Method	A Bales	B Bales	C Bales	Average Micronaire
PWC	6	10	4	3.95
OPC	5	12	3	3.95

Visual 3: Comparison of random picking, proportional category picking and optimum category picking.

12. Adding Cost to the Problem

Now let us add cotton cost. This makes the problem more realistic because mills must balance both quality and cost.

Category	Average Micronaire	Cost per Bale
A	3.5	₹45,000
B	4.0	₹48,000
C	4.5	₹44,000

Category C is the cheapest. A purchase manager may be tempted to use more C bales. Suppose a cost-biased laydown uses 6 bales from A, 7 bales from B, and 7 bales from C.

Average micronaire:

\[ \frac{(6 \times 3.5) + (7 \times 4.0) + (7 \times 4.5)}{20} = \frac{21 + 28 + 31.5}{20} = 4.025 \]

The average micronaire shifts upward from 3.95 to 4.025. Now compare the cost.

PWC Cost

\[ (6 \times 45000) + (10 \times 48000) + (4 \times 44000) \]

\[= 270000 + 480000 + 176000 = \text{Rs. } 926000\]

Cost-Biased Mix Cost

\[ (6 \times 45000) + (7 \times 48000) + (7 \times 44000) \]

\[ = 270000 + 336000 + 308000 = \text{Rs.} 9,14,000 \]

The saving is:

\[ 9,26,000 - 9,14,000 = 12,000 \]

At first glance, this looks attractive. But if the higher micronaire causes harsher yarn, more fly, more hairiness, more processing breaks, or poorer fabric quality, then this saving may disappear. This is the key lesson: the cheapest cotton mix is not necessarily the most economical cotton mix.

13. Final Comparison of Picking Methods

Method	Logic	Average Micronaire	Cost Control	Quality Risk
Random Picking	Pick any 20 bales randomly	May vary	Uncontrolled	High
PWC	Pick according to population proportion	Stable	Moderate	Low
OPC	Pick to reduce variation	Stable	Can be optimized	Lowest
Cost-Biased Picking	Pick more cheaper bales	May shift	High short-term saving	Possible hidden risk

It can be showed that random picking gives much higher between-laydown variation than proportional or optimum category picking. In the comparison shown there, random picking had the highest between-laydown variance, while PWC and OPC reduced this variation substantially.

14. Practical Meaning for a Spinning Mill

A spinning mill should not simply ask which cotton is cheapest. It should ask which combination of bales gives the required fibre profile with minimum variation and acceptable cost.

This question combines textile science, statistics, and cost optimization. A good bale selection system should ensure that the average fibre values are close to target, variation within the laydown is controlled, variation between laydowns is minimized, the cotton mix suits the yarn and fabric end use, and the cost is optimized without damaging process performance.

15. Related Reading

Related Reading on Cotton, Yarn Quality and Spinning Decisions

• Understanding Cotton Fibre Properties and Their Effect on Yarn Quality
• Micronaire in Cotton: Meaning, Importance and Practical Interpretation
• Yarn Count, Twist and Fibre Selection in Spinning
• How Short Fibre Content Affects Spinning Performance
• Building a Python Model for Cotton Mixing Decisions

16. Conclusion

Cotton mixing is a scientific decision. It begins with understanding the yarn requirement, continues with defining the cotton mix profile, then studying the bale population, and finally selecting bales through a suitable picking scheme.

Random picking may be simple, but it can create unstable yarn quality. Proportional category picking gives better consistency. Optimum category picking goes one step further by considering variation and cost.

In today’s language, cotton bale selection is a classic problem of raw material optimization. It uses fibre science, yarn engineering, probability, statistical variation, cost modelling, and process knowledge.

The real objective is not merely to buy cotton cheaply. The real objective is to produce consistent yarn at the lowest total cost. That is the art and science of cotton mix profiling and bale picking.

17. General Disclaimer

This article is intended for educational and explanatory purposes. The numerical example used here is hypothetical and simplified to explain the logic of cotton mix profiling, population profile analysis, and bale picking schemes. In actual spinning mills, cotton selection should be based on reliable fibre testing data, mill-specific process conditions, yarn quality requirements, machinery constraints, commercial considerations, and expert technical judgment.

FAQ in cotton spinning-4

FAQs in Cotton Spinning
Q. Discuss about the feed rolls used in opening machine with given headings.
(i) Definition, (ii) Construction, (iii) Fundamental, and, (iv) Types of feeding
Q. Define the beater in opening machine.
Q. What are the objects of beater?
Q. Express the drafts and their calculation. What is the difference between the actual draft and mechanical draft?
Q. What are the objects of carding? How are these objects fulfilled
Q. What is meant by card clothing? With a neat sketch show the parts of a card clothing.
Q. What is meant by neps in carding?
Q. Mention and briefly explain the factors in judging the quality of carding.
Q. What are the effects of doubling
Q. Explain about the function of drawing rolls used in drawing frame.
Q. What is meant by cotton combing?
Q. What are the objects of combing? Explain briefly how these objects are fulfilled.
Q. List the various yarn characteristics improved by combing.

Please see the answers to these questions here

FAQ in cotton Spinning-3

FAQ in cotton spinning-3

Q: What are condensers, what is their role ?
Answer: These are perforated cage rollers. They supply a current of air at a high velocity, convey the cotton uniformly from stage to stage and incidently, perform a bit of cleaning by carrying away the floating dust, impurities and short fibres to a separate collection centre.

Q. What is difference between the conventional and the modern blow room lines.
Answer: Modern blowroom lines have more opening points and fewer beating points.

Q. What is the object of carding.
Answer: The objects of carding are three:
1. To open out thoroughly the tiny lumps so that every fibre becomes individualised and the cotton is no more in an entangled state.
2. To remove all impurities, neps, short fibres etc. which have escaped the blowroom action.
3. To prepare the well cleaned material into a compact sliver form and lay into containers for subsequent processes.

Q. Name the three major regions where cleaning takes place.
Answer: Taker-in and flats.

Q. What are the constituents of flat strips.
Answer: The flat strips are mostly short fibres with some of the impurities like kitty leaf bits etc.

Q. Why speed of licker-in is kept less for longer staples.
Answer: Longer fibres are held for longer time by the bite of the feed roller after the licker-in starts working on them. As a result more teeth act on the fringe of the fibres and there is every chance of fibres getting damaged.

Q. What is back plate. What is its function.
Answer: This ia a curved plate covering the cylinder just above the licker-in and its main function is to keep the fibre bunches delivered by licker-in, remain on the cylinder wire till they are taken by the flats. This also helps to prevent the development of undesirable air currents.

Q. What is front plate. What are its purposes. Why it is called percentage plate.
Answer: This is a plate similar to back plate and is fitted at the front just above the front door. This has a three fold purpose namely:
1. To keep the cylinder surface covered in order to prevent the fibres from flying off.
2. To keep all other material away from cylinder.
3. To provide the opening for stripping and grinding the cylinder.

It is known in America as 'percentage plate' as its adjustment helps to regulate the quantity of flat strips.