Ginning


Once Valledupar's main economic produce; Cotton

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Gin equipment is designed to remove foreign matter, moisture, and cottonseed from raw seed cotton. Two types of gins are in common use—the saw gin and the roller gin. Saw gins are normally used for Upland cottons, whereas roller gins are used for the ELS (Pima) cottons. In a saw gin, the cotton enters the saw gin stand through a huller front and the saws grasp the seed cotton and draw it through widely spaced ribs. The ginning action is caused by a set of saws rotating  between a second set of narrowly spaced ginning ribs. The saw teeth pass between the ribs pulling the fiber through at the ginning point. The space is too narrow for the seed to pass and so the fiber is pulled from the seed. A roller gin consists of a ginning roll (covered with a compound cotton and rubber material), a stationary knife held against the roll, and a rotary knife. The rotating roll pulls the fiber under the stationary knife. The seeds cannot pass under the stationary knife and is separated from the fiber. The rotary knife then pushes the ginned seed away from the ginning point allowing room for more seed cotton to be ginned.

image

Fig. 1. A modern gin stand that separates fiber from cottonseed.

Typical types of gin equipment are cylinder cleaners, stick machines, and lint cleaners for cleaning; hot air driers for removing moisture; gin stands for separating the fiber from the cottonseed; and the bale press for packaging the lint . The gin stand (Fig. 1) is actually the only item of equipment required to gin cotton, the other equipment is for trash removal and drying. About 636 kg of seed cotton is required to produce a bale (∼227 kg; 500 lb) of lint cotton from spindle-harvested cotton. The remainder consists of about 354-kg seed and 55-kg trash and moisture. Typical gins contain one to four individual gin stands, each rated at 6–15 bales/h. However, a few gins contain as many as eight gin stands and produce up to 100 bales/h. The greatest number [30,498] of gins existed in the United States in 1902. The majority were on plantations, and they processed 10.6 million bales (2.3 × 109 kg) of cotton (43). Since then the number of gins has declined, and the average number of bales processed per gin has increased. In 2000, a total of ∼1018 active gins handled a crop of 16,742,000 bales (∼3.65 × 109 kg) for an average of 16,446 bales (3.58 × 106 kg) per gin plant. The number of bales produced in the United States varies substantially from year to year, which places a severe financial burden on the ginning industry.

Mechanical harvesting systems were made possible by the invention of saw type lint-cleaning systems in the early 1950s. Lint cleaners enabled gins to remove from the cotton the additional trash that resulted from mechanical harvesting. The mechanical systems reduced the harvesting period from 4–5 months to ∼6–8 weeks of intensive operation. Severe congestion problems at the gin were eased with the storage of seed cotton in 8- to 15-bale, freestanding modules. Modules avoided the massive need for wheeled trailers during the compressed harvest season. Storage of seed cotton in modules increased rapidly from the 1970s onward, accounting for >90% of the crop in 2000. At present, the average U.S. cotton ginning capacity is ∼30 bales/h. A few gins process in excess of 100 bales/h.

Most of the U.S. gins are now operated as cooperatives or as corporations serving many cotton producers. Automatic devices do the work faster, more efficiently,and more economically than hand labor. High volume bulk seed cotton handling systems and hydraulic suction systems to remove cotton from modules, high volume trailers to get cotton into the gin, larger trailers and modules, increased processing rates for gin equipment, automatic controls, automated bale packaging and handling devices, and improved management have all increased efficiency.

After ginning, baled cotton is sampled so that grade and quality parameters can be determined (classification). The fiber quality/physical attributes affect the textile manufacturing efficiency and the quality of the finished product. Cotton bales are normally stored in warehouses in the form of highly compressed bales.The International Organization for  Standardization (ISO) specifies that bale dimensions should be of length 140 cm (55 in.), width 53.3 cm (21 in.), height 70–90 cm (27.6–35.4 in.), and density of 360–450 kg/m 3 (22.4–28 lb/ft 3) . Bales of cotton produced in the United States meet these dimensional standards. Bales of cotton packaged in accordance with these dimensions (ISO 8115) are not considered a flammable solid by the International Maritime Organization and the U.S. Department of Transportation for transportation purposes for vessel and other types of shipment  and are considered to present no measurable pest risk to the importing country. Baled cotton fiber is merchandized and shipped by the merchant to the textile
mill for manufacturing into products for the consumer. The seed is shipped directly for feeding to dairy cattle or to a cottonseed oil mill for crushing.

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Cotton Fibers 2


Once Valledupar's main economic produce; Cotton
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WHAT IS COTTON?:

COTTON is defined as white fibrous substance covering seeds harvested from Cotton Plant.

SEED COTTON (called Kapas in India – Paruthi in Tamil)harvested from Cotton Plant.

LINT COTTON (RUIA in Hindi, PANJU in Tamil) is obtained by removing the seeds in a ginning machine.

LINT COTTON is spun into Yarn, which is woven or knitted into a Fabric. Researchers have found that cotton was grown more than 9000 years ago. However large scale cultivation commenced during middle of 17th Century AD.

Many varieties of Cotton are cultivated mainly from 3 important genetic species of Gossipium.

G. HIRSUTUM – 87% Grown in America, Africa, Asia, Australia Plant grows to a height of 2 Meters.

G. BARBADENSE– 8% Grown in America, Africa & Asia. Plant grows to a height of 2.5 Meters with yellow flowers, long fibers with good quality, fibers with long staple and fineness

G. Arboreum – 5% Perennial plant grows up to 2 meters with red flowers, poor quality fibers in East Africa and South East Asia.

There are four other species grown in very negligible quantities. Cotton harvested from the Plant by hand – picking or machine picking is ginned to remove seeds and the lint is pressed into Bales for delivery to Spinning Mills. Cotton is Roller Ginned (RG) or Saw Ginned (SG) depending varieties and ginning practices.

Cotton is cultivated in 75 Countries with an area of 32 Million Hectares. Cultivation period varies from 175 days to 225 days depending on variety. Cotton is harvested in two seasons, summer and winter seasons.

Saw ginned cotton is more uniform and cleaner than Roller Ginned Cotton. But fibers quality is retained better quality in Roller Ginning than Saw Ginning which has high productivity.

Cotton Fiber is having a tubular structure in twisted form. Now. researchers have developed coloured cotton also. As on date, percentage of Cotton fiber use is more than synthetic fibers. But, its share is gradually reducing. Cotton is preferred for under garments due its comfort to body skin. Synthetics have more versatile uses and advantage for Industrial purposes.

PROPERTIES OF COTTON

No other material is quite like cotton. It is the most important of all natural fibres, accounting for half of all the fibres used by the world’s textile industry.
Cotton has many qualities that make it the best choice for countless uses:
Cotton fibres have a natural twist that makes them so suitable for spinning into a very strong yarn.
The ability of water to penetrate right to the core of the fibre makes it easy to remove dirt from the cotton garments, and creases are easily removed by ironing.
Cotton fabric is soft and comfortable to wear close to skin because of its good moisture absorption qualities.
Charges of static electricity do not build up readily on the clothes.

HISTORY OF COTTON

Nobody seems to know exactly when people first began to use cotton, but there is evidence that it was cultivated in India and Pakistan and in Mexico and Peru 5000 years ago. In these two widely separated parts of the world, cotton must have grown wild. Then people learned to cultivate cotton plants in their fields.
In Europe, wool was the only fiber used to make clothing. Then from the Far East came tales of plants that grew “wool”. Traders claimed that cotton was the wool of tiny animals called Scythian lambs, that grew on the stalks of a plant. The stalks, each with a lamb as its flower, were said to bend over so the small sheep could graze on the grass around the plant. These fantastic stories were shown to be untrue when Arabs brought the cotton plant to Spain in Middle Ages.

In the fourteenth century cotton was grown in Mediterranean countries and shipped from there to mills in the Netherlands in western Europe for spinning and weaving. Until the mid eighteenth century, cotton was not manufactured in England, because the wool manufacturers there did not want it to compete with their own product. They had managed to pass a law in 1720 making the manufacture or sale of cotton cloth illegal. When the law was finally repealed in 1736, cotton mills grew in number. In the United States though, cotton mills could not be established, as the English would not allow any of the machinery to leave the country because they feared the colonies would compete with them. But a man named Samuel Slater, who had worked in a mill in England, was able to build an American cotton mill from memory in 1790.

GROWING THE COTTON

Cotton plant’s leaves resemble maple leaves and flowers look very much like pink mallow flowers that grow in swampy areas. They are relatives and belong in the same plant family.

Cotton is grown in about 80 countries, in a band that stretches around the world between latitudes 45 North to 30 South. For a good crop of cotton a long, sunny growing season with at least 160 frost-free days and ample water are required. Well drained, crumbly soils that can keep moisture well are the best. In most regions extra water must be supplied by irrigation. Because of it’s long growing season it is best to plant early but not before the sun has warmed the soil enough.

Seedlings appear about 5 days after planting the seeds. Weeds have to be removed because they compete with seedlings for water, light and minerals and also encourage pests and diseases. The first flower buds appear after 5-6 weeks, and in another 3-5 weeks these buds become flowers.
Each flower falls after only 3 days leaving behind a small seed pot, known as the boll. Children in cotton-growing areas in the South sometimes sing this song about the flowers:
First day white, next day red,
third day from my birth – I’m dead.
Each boll contains about 30 seeds, and up to 500 000 fibres of cotton. Each fibre grows its full length in 3 weeks and for the following 4-7 weeks each fiber gets thicker as layers of cellulose build up the cell walls. While this is happening the boll matures and in about 10 weeks after flowering it splits open. The raw cotton fibres burst out to dry in the sun. As they lose water and die, each fibre collapses into what looks like a twisted ribbon. Now is time for harvesting. Most cotton is hand-picked. This is the best method of obtaining fully grown cotton because unwanted material, called “trash”, like leaves and the remains of the boll are left behind. Also the cotton that is too young to harvest is left for a second and third picking. A crop can be picked over a period of two months as the bolls ripen. Countries that are wealthy and where the land is flat enough usually pick cotton with machines – cotton harvesters.

GLOBAL COTTON – VATIETIES – PLANTING AND HARVESTING PERIODS

SNo Country Planting Period Harvesting Staple-mm Mike Variety
1 AFGHANISTAN APRIL-MAY OCT-DEC 26-28 4.0 ACALA
2 ARGENTINA SEPT-OCT FEB-JUNE 24-28 3.9-4.1 TOBA
3 AUSTRALIA SEPT-NOV MAR-JUNE 24-29 3.2-4.9 DPL
4 BRAZIL OCT-NOV MAR-JUNE 26-28 3.2-4.0 IAC
BRAZIL PERENNIAL 32-35 3.2-4.8 MOCO
5 BURKIN JUNE-JULY NOV-DEC 25-28 3.6-4.8 ALLEN
6 CAMERRON JUNE NOV-DEC 25-28 3.8-4.3 ALLEN
7 CENTRAL AFRICA JUN-JULY NOV-DEC 25-28 3.8-4.2 ALLEN
8 CHAD JUNE NOV-DEC 25-28 3.8-4.4 ALLEN
9 CHINA APRIL-JUNE SEP-OCT 22-28 3.5-4.7 SHANDONG
XINJIANG
MNH-93
10 COTED IVORIE JUN-AUG OCT-JAN 24-28 2.6-4.6 ALLEN
11 EGYPT MARCH SEP-OCT 31-40 3.24.6 GIZA
12 GREECE APRIL SEPT-OCT 26-28 3.8-4.2 4S
13 INDIA APRIL-NOV SEP-NOV 16-38 2.8-7.9 SEPARATE LIST
INDIA SEPT-NOV FEB-APR
14 IRAN MAR-APR SEP-NOV 26-28 3.9-4.5 COKER
15 ISRAEL APRIL SEP-OCT 26-37 3.5-4.3 ACALA
PIMA
16 KAZAKSTAN APR-MAY SEP-NOV
17 MALI JUN-JUL OCT-NOV 26-27 3.7-4.5 BJA
18 MEXICO MAR-JUNE AUG-DEC 26-29 3.5-4.5 DELTAPINE
19 MOZAMBIQUE NOV-DEC APR-MAY 25-29 3.6-4.2 A637
20 NIGARIA JUL-AUG DEC-FEB 24-26 2.5-4.0 SAMARU
21 PAKISTAN APR-JUN SEP-DEC 12-33 3.5-6.0
22 PARAGUAY OCT-DEC MAR-APR 26-28 3.3-4.2 EMPIRE
23 PERU JUL-NOV FEB-AUG 29-.8 3.3-4.2 TANGUIS
PIMA
24 SPAIN APR-MAY SEP-NOV 25-28 3.3-4.9 CAROLINA
25 SUDAN AUG JUN-APR 27-E0 3.8-4.2 BARAKAT
ACALA
26 SYRIA APR-MAY SEP-NOV 25-29 3.8-4.8 ALEPPO
27 TAZIKSTAN APR-MAY SEP-NOV
28 TOGO JUN-JUL NOV-DEC 28-29 4.3-5.5 ALLEN
29 TURKMENISTAN APR-MAY SEP-NOV 24-29 3.5-5.5 DELTAPINE
COKER
30 TURKEY APR-MAY SEP-NOV 24-28 3.5-5.5 DELTAPINE
31 UGANDA APR-JUN NOV-FEB 26-28 3.3-4.8 BAP-SATU
32 UZBEKISTAN APR-MAY SEP-NOV 24-41 3.5-4.7
33 USA APR-MAY SEP-DEC 26-40 3.8-4.5 VARIETIES
28-30 3.0-4.0 ACALA 151T
28-29 3.8-4.6 DELTAPINENC
25-28 3.2-4.6 PAYMASTER 280
27-28 3.7-4.7 STONOVILLE ST
35-40 3.5-4.5 PIMA S7
34 YEMEN AUG-SEP JUN-APR 36-40 3.5-4.9 K4

COTTON AND YARN QUALITY CO-RELATION:

Instead of buying any cotton available at lowest price, spinning it to produce yarn of highest count possible and selling Yam at any market in random, it is advisable to locate a good market where Yarn can be sold at highest price and select a Cotton which has characteristics to spin Yarn of desired specifications for that market.

ESSENTIAL CHARACTERISTICS of cotton quality and characteristics of Yarn quality of Yarn are given from detailed experimental investigations. Some of the important conclusions which help to find co-relation between Yarn quality and Cotton quality are given below

  • STAPLE LENGTH: If the length of fiber is longer, it can be spun into finer counts of Yarn which can fetch higher prices. It also gives stronger Yarn.
  • STRENGTH : Stronger fibers give stronger Yarns. Further, processing speeds can be higher so that higher productivity can be achieved with less end-breakages.
  • FIBER FINENESS: Finer Fibers produce finer count of Yarn and it also helps to produce stronger Yarns.
  • FIBER MATURITY : Mature fibers give better evenness of Yarn. There will be less end – breakages . Better dyes’ absorbency is additional benefit.
  • UNIFORMITY RATIO: If the ratio is higher. Yam is more even and there is reduced end-breakages.
  • ELONGATION :A better value of elongation will help to reduce end-breakages in spinning and hence higher productivity with low wastage of raw material.
  • NON-LINT CONTENT: Low percentage of Trash will reduce the process waste in Blow Room and cards. There will be less chances of Yarn defects.
  • SUGAR CONTENT: Higher Sugar Content will .create stickiness of fiber and create processing problem of licking in the machines.
  • MOISTURE CONTENT : If Moisture Content is more than standard value of 8.5%, there will be more invisable loss. If moisture is less than 8.5%, then there will be tendency for brittleness of fiber resulting in frequent Yarn breakages.
  • FEEL : If the feel of the Cotton is smooth, it will be produce more smooth yarn which has potential for weaving better fabric.
  • CLASS : Cotton having better grade in classing will produce less process waste and Yarn will have better appearance.
  • GREY VALUE: Rd. of calorimeter is higher it means it can reflect light better and Yam will give better appearance.
  • YELLOWNESS : When value of yellowness is more, the grade becomes lower and lower grades produce weaker & inferior yarns.
  • NEPPINESS : Neppiness may be due to entanglement of fibers in ginning process or immature fibers. Entangled fibers can be sorted out by careful processing But, Neps due to immature fiber will stay on in the end product and cause the level of Yarndefects to go higher.

An analysis can be made of Yarn properties which can be directly attributed to cotton quality.

1. YARN COUNT: Higher Count of Yarn .can be produced by longer, finer and stronger fibers.

2. C.V. of COUNT: Higher Fiber Uniformity and lower level of short fiber percentage will be beneficial to keep C.V.(Co-efficient of Variation) at lowest.

3. TENSILE STRENGTH : This is directly related to fiber strength. Longer Length of fiber will also help to produce stronger yarns.

4. C.V. OF STRENGTH : is directly related CV of fiber strength.

5. ELONGATION : Yam elongation will be beneficial for weaving efficiently. Fiber with better elongation have positive co-relation with Yarn elongation.

6. C.V. OF ELONGATION: C.V. of Yarn Elongation can be low when C.V. of fiber elongation is also low.

7. MARS VARIATION : This property directly related to fiber maturity and fiber uniformity.

8. HAIRINESS : is due to faster processing speeds and high level of very short fibers,

9. DYEING QUALITY : will defend on Evenness of Yarn and marketing of cotton fibers.

10. BRIGHTNESS : Yarn will give brighter appearance if cotton grade is higher.

COTTON QUALITY SPECIFICATIONS:

The most important fiber quality is Fiber Length

Length

Staple
classification
Length mm Length inches Spinning Count
Short Less than 24 15/16 -1 Coarse Below 20
Medium 24- 28 1.1/132-1.3/32 Medium Count 20s-34s
Long 28 -34 1.3/32 -1.3/8 Fine Count 34s – 60s
Extra Long 34- 40 1.3/8 -1.9/16 Superfine Count 80s – 140s

Notes:

  • Spinning Count does not depend on staple length only. It also depends on fineness and processing machinery.
  • Length is measured by hand stapling or Fibrograph for 2.5% Span Length
  • 2.5%SL (Spun Length) means at least 2.5% of total fibers have length exceeding this value.
  • 50% SL means at least 50% of total fibers have length exceeding this value.

LENGTH UNIFORMITY

Length Uniformity is Calculated by 50SL x 100 / 2.5 SL

Significance of UR (Uniformity Radio) is given below:

UR% Classification 50-55
Very Good 45-50 Good 40-45
Satisfactory 35-40
Poor Below 30 Unusable
M= 50% SL
UHM SL – Average value of length of Longest of 50% of Fibers
UI Uniformity Index
UI M/UHM

Interpretation of Uniformity Index

U.INDEX CLASSIFICATION UHM CLASSIFICATION
Below 77 Very low Below 0.99 Short
77-99 Low 0.99-1.10 Medium
80-82 Average 1.11-1.26 Long
83-85 High Above 1.26 Extra Long
Above 85 Very High

Now Uniformity is measured by HVI

Fiber Strength

Fiber Strength, next important quality is tested using Pressley instrument and the value is given in Thousands of Pounds per Square inch. (1000 psi) For better accuracy, Stelometer is used and results are given in grams / Tex.

Lately, strength is measured in HVI (High Value Instrument) and result is given in terms of grams/tex.

Interpretation of Strength value is given below

G/tex Classification
Below 23 Weak
24-25 Medium
26-28 Average
29-30 Strong
Above 31 Very Strong

Strength is essential for stronger yarns and higher processing speeds.

  • Fiber Fineness Fiber Fineness and maturity are tested in a conjunction using Micronaire Instrument.
  • Finer Fibers give stronger yarns but amenable for more neppiness of Yarn due to lower maturity.
  • Micronaire values vary from 2.6 to 7.5 in various varieties.

FINENESS AND MATURITY

Usually Micronaire value is referred to evaluate fineness of Cotton and its suitability for spinning particular count of Yarn. As the value is a combined result of fineness and maturity of Cotton fiber, it cannot be interpreted, property for ascertaining its spinning Value. This value should be taken in conjunction with standard value of Calibrated Cotton value.

The following table will explain that micronaire value goes up along with maturity but declines with thickness of fiber. An Egyptian variety of Cotton, three samples of High maturity. Low maturity and Medium maturity were taken and tested. Test results are given below,

Maturity Micronaire Perimeter Maturity Maturity Ratio
High 4.3 52.9 85.1 1.02
Medium 4.0 54.4 80.1 0.96
Low 3.9 54.7 79.3 0.95

Here, Micronaire Value of 4.3 is higher than 3.9 of low maturity cotton Another Greek Cotton was tested and results are give below

High 3.8 57.0 75.1 0.88
Medium 3.5 54.9 70.7 0.84
Low 3.2 55.2 65.8 0.80

Micronaire Value of 3.8 is higher than 3.2 of low maturity cotton. Another American Cotton was tested and results are as follows

High 4.1 64.4 75.9 0.87
Medium 3.4 62.1 68.0 0.80
Low 2.7 59.8 56.1 0.67

Hence, it is essential to know what Micronaire value is good for each variety of Cotton.

Maturity Ratio Classification
1.00 and above Very Mature
0.95 – 1.0 Above Average
0.85 – 0.95 Mature
0.80 – 0.85 Below Average
Less than 0.80 immature

COTTON GRADE

Cotton grade is determined by evaluating colour, leaf and ginning preparation. Higher grade cottons provide better yarn appearance and reduced process waste.

Colour is determined by using Nickerson-Hunter Calorimeter. This gives values Rd (Light or Dark) and +b (Yellowness).

AMERICAN UPLAND COTTONS ARE CLASSIFIED
ACCORDING TO GRADES AS GIVEN BELOW

WHITE COLOUR

S.NO GRADE SYMBOL CODE
1 GOOD MIDDLING GM 11
2 STRICT MIDDLING SM 21
3 MIDDLING M 31
4 STRICT LOW MIDDLING SLM 41
5 LOW MIDDLING LM 51
6 STRICT GOOD ORDINARY SGO 61
7 GOOD ORDINARY GO 71
8 BELOW GRADE

Similar grading is done for Light Spotted, Spotted, Tinged and Yellow Stained Cottons. PIMA cottons are graded I to 9

HOW TO BUY COTTON?

COTTON BUYING is the most important function that will contribute to optimum profit of a Spinning Mill.

EVALUATION of cotton quality is generally based more on experience rather than scientific testing of characteristics only.

TIMING of purchase depends on comprehensive knowledge about various factors which affect the prices.

CHOOSING the supplier for reliability of delivery schedules and ability to supply cotton within the prescribed range of various parameters which define the quality of Cotton.

BARGINING for lowest price depends on the buyer’s reputation for prompt payment and accept delivery without dispute irrespective of price fluctuations.

ORGANISING the logistics for transportation of goods and payment for value of goods will improve the benefits arising out of the transaction.

PROFIT depends on producting high quality Yarn to fetch high prices. Influence of quality of raw material is very important in producing quality Yarn. But, quality of yam is a compound effect of quality of raw material, skills of work-force, performance of machines,- process know-how of Technicians and management expertise.

A good spinner is one who produces reasonably priced yarn of acceptable quality from reasonably priced fiber. Buying a high quality, high priced cotton does not necessarily result in high quality Yarn or high profits.

GUIDELINES FOR COTTON CONTRACTS:

Buyer and seller should clearly reach correct understanding on the following factors.

1. Country of Origin, Area of Growth, Variety, Crop year

2. Quality – Based on sample or

Description of grade as per ASTM standard or sample
For grade only and specifying range of staple length,
Range of Micronaire, range of Pressley value, uniformity,
Percentage of short fiber, percentage of non-lint content,
Tolerable level of stickiness

3. Percentage of Sampling at destination

4. Procedure for settling disputes on quality or fulfillment of contract obligations.

5. Responsibility regarding contamination or stickiness.

6. Price in terms of currency, Weight and place of delivery.

7. Shipment periods

8. Certified shipment weights or landing Weights

9. Tolerances for Weights and Specifications

10. Port of Shipment and port of destination, partial shipments allowed or not, transshipment allowed or not, shipments in containers or Break-bulk carriers

11. Specifications regarding age of vessels used for shipment, freight payment in advance or on delivery

12. Responsibility regarding Import & Export duties

13. Terms of Insurance cover

14. Accurate details of Seller, Buyer and Broker

15. Terms of Letter of. Credit regarding bank .negotiation, reimbursement and special conditions, if any

Choose Correct Supplier or Agent:

Apart from ensuring correct terms of Contract, Buyer should ensure that purchase is made from Reliable Supplier or through a Reliable Agent. Some suppliers evade supplies under some pretext if the market goes up. Otherwise, they supply inferior quality Either way buyer suffers.

By establishing long term relationship will reliable Suppliers, Buyers can have satisfaction of getting correct quality, timely deliveries and fair prices.

CHOOSING SUPPLIER:

It is good to establish long term relationship with a few Agents who represent reputed Trading Companies in various Cotton Exporting Countries. They usually give reliable market information on quality, prices and market trends so that buyer can take intelligent decision. As cotton is not a manufactured Commodity, it is good to buy from dependable suppliers, who will ensure supply of correct quality with a variation within acceptable limits at correct price and also deliver on due date.

CHOOSING QUALITY:

In a market with varying market demand situation. Buyers should decide which counts of Yarn to spin. Buyer can call for samples suitable for spinning Yarn counts programmed for production. Many spinners plan to do under-spinning. For Example, cotton suitable for 44s is used for spinning 40s. Some spinners do over-spinning. They buy cotton suitable for 40s and spin 44s count. But, is advisable to spin optimum count to ensure quality and also keep cost of raw material at minimum level as for as possible. Some spinners also buy 2 or more varieties and blend them for optimum spinning. For’ this purpose, a good knowledge to evaluate cotton quality and co-relate with yarn properties of required specifications. Cotton buyer should develop expertise in assessing cotton quality. Machine tests must be done only to confirm manual evaluation.

TAKING RIGHT OPTION:

It is not advisable just to look at price quoted by supplier. Correct costing should be done to work out actual cost when the cotton arrives at Mills. Further lowest price does not always mean highest profit for buying. Profitability may be affected by anyone or more of the following factors.

  • If the trash is higher, more waste will be produced reducing the Yarn out- turn and hence profit.
  • If the uniformity is less, end – breakages will be more reducing productivity and profitability.
  • If grade is poor or more immature fibers are found in cotton, the yarn appearance will be affected and Yarn will fetch lesser price in the market.
  • If the transit period for transport of cotton is longer, then also profitability will be reduced due blocking of funds for a longer period and increased cost of Interest.
  • Rate of Sales Tax varies from State to State. This must be taken in to account.
  • Hence, thorough costing should be worked out before deciding on the quoted pnce onlv

The margin of profit in spinning cotton should be calculated before deciding on The various options available depending on market conditions should be studied.

The factors to be considered for taking options are as follows.

  • Count for which demand is good in market
  • Prices for various counts for which demand exists.
  • Cost of manufacturing various counts.
  • Adequacy of machinery for the selected count.
  • Various varieties of cotton available for spinning the selected count.
  • Profit margin for each count using different varieties.
  • Price quoted by different Agents for same variety of selected cotton.
  • Reliability of supplier for quality and timely delivery.

Cost Consideration:

Apart from the price quoted by the seller, other incidental costs must be taken into consideration before buying.

a) Duration for goods to reach Buyer’s godown from the seller’s Warehouse. If the duration is longer, buyer will incur higher interest charges.

b) Cost of Transportation and taxes.

Resolution of differences

If any discrepancy arises in the quality, weight and delivery periods, sellers should be willing to resolve the differences amicably and quickly. In case the matter is referred to Arbitrator, the award of the Arbitrator must be immediately enforced.

Bench Marks for Easy Reference

It is better if quality bench marks are established for different varieties so that buying decisions are easy for buyers Following standards have been found to be appropriate for Strict Middling Grade Cotton of staple 1.3/32″.

  1. Staple Length ( 2.5% Spun Length) – Minimum 1.08″ or 27.4 mm
  2. Micronaire : Minimum 3.8, Maximum-4.6 Variation within bulk sample should not be more than _ 0.1
  3. Colour : Rd not less than 75 not more than 10
  4. Nep Content: Less than 150 per gram
  5. Strength : More than 30 grams/tex
  6. Length Uniformity Ratio: Not less than 85%
  7. Elongation : More than 8%
  8. Short Fiber Content: Less than 5%
  9. Seed Count Fragments : Less than 15 per grams
    1. Commercial Bench marks can be given as follows:
      1. Price Competitiveness
      2. Price Stability
      3. Easy Availability throughout year
      4. Uniform Classing and Grading system
      5. Even- running Cotton in all Characteristics
      6. Reliable deliveries òr Respect for sanctity of contract.

QUALITY EVALUATION:

The need for quality evaluation is for following purposes

a) To get optimum quality at lowest price.
b) To decide whether cotton bought will can be processed to spin Yarn of desired specifications.
c) To check the quality of sample cotton with quality of delivered cotton.
d) To decide about correct machine settings and speeds for processing the cotton
e) To estimate profitability of purchase decisions.

Knowing the cotton properties is only half the battle for profits. It needs expertise to know how to get best of its value.

Currently popular instrument called HVI gives ready information on various parameters to make correct purchase decisions.

If may not be possible to get all the desired qualities in one variety or one lot of Cotton. In such case, an intelligent decision to select best combination of different varieties or lots to get desired Yam quality is necessary to get optimum yarn quality at optimum cost.

If correct evaluation is made, profits are large. Hence, evaluation of quality is essential for optimum profit making and also make the customers happy with supply of correct quality of Yarn.

Expert classers can manage to achieve reasonable level of correct evaluation. Now, with availability of better instruments, it is better to check qualities to make sure that desired quality of cotton is procured.  These details should give cotton buyer reasonable guidance to make correct evaluation of cotton quality and ensure its suitability for producing required quality of yarn.

QUALITY EVALUATION        CHARACTERISTICS CO-RELATION TO YARN
1. Staple Length Spinning Potential
2. Fiber Strength Yarn strength, less Breakages
3. Fineness   Finer Spinning Potential
4. Maturity Yarn Strength and even ness, better dyeing
5. Non-Lint.content (Trash) Reduced Waste
6, Uniformity Ratio Better productivity and Evenness
7. Elongation Less end Breakages
8, Friction Cohesiveness
9. Class Yarn Appearance
10.Stickiness Spinning problem by lapping & Dyeing quality
11. Grey Value Yarn lustre
12. Yellowness Yarn Appearance
13.Neppiness Yarn neppiness
14. Moisture Content 8.5% moisture content optimum for spinning at 65%

QUALITY TESTING INSTRUMENTS:

Instrument Measurements
Fibrogaph   Length
Pressley Apparatres Fiber Bundle Strength
HV I Instrument Length, Strength, Uniformity, Elongation, Micronaire, Color and Trash
Stelometer Instrument Strength, Elongation
Micronaire Combined test of fineness & maturity
Shirley Trash Analyser Trash Content
Manual Test Class & staple length
Moisture Meter Moisture
Colorimeter Grey value & yellow ness. Brightness
Polarised light Microscope or
Casricaire test
Maturity
Photographic film   Neppiness

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PROCESS PARAMETER IN BLOW ROOM


With all harvesting methods, however, the cotton seed, together with the fibres, always gets into the ginning plant where it is broken up into trash and seed-coat fragments. This means that ginned cotton is always contaminated with trash and dust particles and that an intensive cleaning is only possible in the spinning mill.

Nep content increases drastically with mechanical harvesting, ginning and subsequent cleaning process. The reduction of the trash content which is necessary for improving cotton grade and apperance unfortunately results in a higher nep content level.

The basic purpose of  Blow room is to supply

  • small fibre tufts
  • clean fibre tufts
  • homogeneously blended tufts if more than one variety of fibre is used

to carding machine  without increasing  fibre rupture, fibre neps , broken seed particles and without removing more  good fibres.

The above is achieved by the following processes in the blowroom

  1. Pre opening
  2. pre cleaning
  3. mixing or blending
  4. fine opening
  5. dedusting

CLEANING EFFICIENCY:

Cleaning efficiency of the machine is the ratio of the trash removed  by the machine to that of  total trash fed to the machine, expressed as percentage

Cleaning efficiency % =(( trash in feed % – trash in del %) x 100) / (trash in feed%)

Following are the basic parameters  to be considered in Blowroom process.

  • no of opening machines
  • type of beater
  • type of beating
  • Beater speed
  • setting between feed roller and beater
  • production rate of individual machine
  • production rate of the entire line
  • thickness of the feed web
  • density of the feed web
  • fibre micronaire
  • size of the flocks in the feed
  • type of clothing  of the beater
  • point density of clothing
  • type of grid and grid settings
  • air flow through the grid
  • position of the machine in the sequence
  • amount of trash in the material
  • type of trash in the material
  • temp and relative humidity in the blow room department

PREOPENING:

Effective preopening results in smaller tuft sizes, thus creating a large surface area for easy  and efficient removal of trash particles by the fine openers.

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Fig:-BO-c bale opener

If MBO (Rieter) or  BO-c ( Trutzschler) type of machine is used as a first machine

  • the tuft size in the mixing should be as small as possible. Normally it should be less than 10 grams
  • since this machine does not take care of long term blending, mixing should be done properly to maintain the homogenous blending
  • the inclined lattice speed and the setting between inclined lattice and clearer roller decides the production of the machine
  • the setting between inclined lattice and clearer roller decides the quality of the tuft
  • if  the setting is too close, the tuft size will be small, but the neps in the cotton will be increased due to  repeated action of the  inclined lattice pins on cotton.
  • the clearance should be decided  first to confirm the quality, then inclined lattice speed can be decided according to the   production required
  • the setting of inclined lattice depends upon the fibre density, fibre micronaire and the tuft size fed. If smaller tuft is fed to the feeding conveyor, the fibre tufts will not be recycled many times, hence the neps will be less.
  • if the machine is with beater, it is advisable to use only disc type beater. Saw tooth and Pinned beaters should not be used in this machine, because the fibre  damage at this stage will be very high and heavier trash particles will be broken in to small pieces.
  • the beater  speed  should be around 500 to 800 rpm depending upon the rawmaterial. Coarser the fibre,  higher the speed
  • the setting between feed roller to beater should be around 4 to 7 mm
  • this machine is not meant to remove trash ,  hence the fibre loss should also be less
  • trash removal in this machine will result in breaking the seeds, which is very difficult to remove
  • It is easier to remove the bigger trash than the smaller trash, therefore enough care should be taken to avoid breaking the trash particles
  • this machine is  just to open the tufts into small sizes so that cleaning becomes easier in the next machines.
  • the fibre tuft size from this  machine should be  preferably around 100 to 200 milligrams.
  • If tuft size is  small, removing trash particles becomes easier , because of large surface area

Unifloc11

Fig:- Unifloc11

If Uniflco11(Rieter) or Blendomat BDT 019(Trutzschler) is used as a first machine

  • It helps to maintain the homogeneity of the long term blending
  • cotton is opened gently without recyling as it is done in manual bale openers
  • with the latest automatic bale opening machines,  the tuft size can be as small as 50 to 100 grams without  rupturing the fibres
  • the opening roller speed should be around 1500 to 1800 rpm.
  • the depth of penetration of the opening  should be as minimum as possible for better quality
  • It is better to use this machine with one mixing or maximum two mixing at  the same.
  • If the production per feeding machine is less than 150 kgs, then four mixings can be recommended
  • production rate of this machine depends upon the no of mixings working at the same time
  • production rate depends  upon opening roller depth, traverse speed and the fibre tuft density
  • in general , the machine parameters should be set in such a way that  maximum number of take-off points are available  per unit time.
  • with the latest machines (Rieter -Unifloc A11), around 60% of take-off points are more compared to earlier machines

PRECLEANING:

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Fig: Uniclean B12

Precleaning should be gentle. Since removing finer trash particles is difficult , seeds and bigger trash particles should not be broken. Finer trash particles require severe treatment in Fine openers. This will lead to fibre damage and more nep generation. Therefore, precleaning should be as gentle as possible and no compromise on this. If preopening and precleaning are done  properly,  consistency in trash removal by fine openers is assured. Dust removal should be started in this machine. Enough care should be taken remove dust  in this process.

Rieter’s Uniclean B11 and Trutzschler’s Axiflow or Maxiflow  are the machines which does this work

  • the fibre treatment in this machine is very gentle because  the fibres are not gripped by the feed roller during beating.  Fibre tufts treated by the pin beater when it is carried by air medium
  • all heavy trash particles fall down before it is broken
  • cleaning efficiency of this machine is very high in the blow room line
  • Mostly all heavy seeds( full seeds) fall in this machine without any problem
  • around 50 pascal suction pressure should be maintained in the waste chamber for better cleaning efficiency
  • beater speed, air velocity through the machine, grid bar setting and gap between grid bars will affect the cleaning efficiency
  • higher the cleaning efficiency,  higher the good fibre loss, higher the nep generaion and higher the fibre rupture
  • the optimum cleaning means maximum cleaning performance, minimum loss of good fibres, a high degree of fibre preservation and minimum nep generation
  • Rieter has a unique concept called “VARIOSET”. With this machine, selective trash removal is possible. Waste  amount can be changed in a range of 1:10.

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fig: from Rieter which shows , degree of cleaning, fibre loss, neps, fibre damage.

  • with normal machines like Monocylinder or axiflow, a lot of trials to be conducted to arrive at optimum beater speed, air velocity(fan speed), grid bar setting and grid bar gap.
  • in general the beater speed is around 750 and  minimum 50 Pascal suction pressure to be maintained in the suction chamber

BLENDING:

  • Barre or streakiness is due to uneven mixing of different cottons. Hence mixing technology is a decisive factor in spinning mill technology
  • bigger the differences of cotton parameters like fineness, color and staple length, the greater the importance of mixing
  • if the cotton has honeydew, the intensive mixing of the rawmaterial is a precondition  for an acceptable running behaviour  of the complete spinning mill

following  fig is given by trutzschler for different  mixing requirements

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standard               standar- plus              high                   high-end

  • Trutzschler’s tandem mixing concept is an  ultimate solution, if the mixing requirement is very high. This principle guarantees a maximum homogeneous of the mix

FIG.Tandem mixing concept from TRUTZSCHLER:

FINE CLEANING:

Fine cleaning is done with different types of machines. Some fine cleaners are with single opening rollers  and some are with multiple opening rollers.

  • If single roller cleaning  machines are used, depending upon the  amount and type of trash in the cotton, the number of fine cleaning points can be either one or two.
  • If the production  rate is lower than 250 kgs and the micronaire is less than 4.0, it is advisable to use single roller cleaning machines instead of multiple roller cleaning machine.
  • Saw tooth beaters can be used, if trash particles are more and the machine is not using suction and deflector blades. i.e beater and regular grid bar arrangements
  • Normal beater speeds with saw tooth beater depends upon the production rate,  fibre micronaire and trash content
TYPE OF COTTON COTTON MICRONAIRE PROUDCTION RATE kgs/hr BEATER SPEED rpm
more trash 3.5 to 4.0 200 to 300 kgs /hr 600 to 750
less trash 3.5 to 4.0 200 to 300 kgs/hr 600 to 750
more trash 4.0 to 4.5 200 to 300 kgs 700 to 850
less trash 4.0 to 4.5 350 to 500 kgs 1000 and above
  • the number of wire points depends on the production rate and trash.
  • setting between feed roller and beater depends on the production rate and micronaire.  The setting should be around 2 to 3 mm.  Wider setting always result  in higher rawmaterial faults, if carding does not take care.
  • closer the setting between beater and mote knives, higher the waste collected. It is advisable to keep around 3 mm.
  • If it is a Trutzschler blowroom line, it is better to use  CVT1 ( single opening roller machine) if  roller ginned cotton  is used.
  • CVT3  or CVT4 machines with 3 or 4 opening rollers can be used for saw ginned cotton.
  • The cleaning points in CVT1, CVT3, CVT4 etc consists of opening roller, deflector blades, mote knives and suction hood. Trash particles released due to centrifugal forces are  separated at the mote knives and continuously taken away by the  suction. This gives better cleaning

FIG: trash removal concept in CVT cleaners:

  • suction plays a major role in these machines. If suction  is not consistent , the performance will be affected badly.  Very high suction will result in more white fibre loss and less suction will result in low cleaning efficiency.
  • The minimum recommended pressure in the waste chamber (P2) is 700 Pascal’s. It can be upto 1000 Pascal’s.
  • material suction (P1) should be around 500 Pascal’s
  • Whenever the suction pressure is changed, the deflector blade settings should be  checked
  • Deflector blade setting can not be same for all the three rollers or four rollers. The setting for deflector blades in the panel looks like this 3, 12, 30 for 1st, 2nd and 3rd deflector blades.
  • The deflector blade setting should be done in such a way that  the setting should be opened till the fibres start slipping on the deflector blade.
  • wider the deflector blade setting, higher the waste. If the setting is too wide, white fibre loss will be very high.
  • for saw ginned cottons, the above concepts helps a lot because of constant suction concentrated directly at the moteknives, ensures much removal of dust from the cotton.

DEDUSTING:

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Fig: Dustex

Apart from opening cleaning of rawmaterial, dedusting is the very important process in blowroom process.

  • normally dedusting  starts with precleaning
  • it is always better to have a separate machine like DUSTEX of TRUTZSCHLER  for effective dedusting
  • dedusting keeps the atmospheric air clean
  • dedusting in machines like unimix , ERM of Rieter is  good
  • stationary dedusting condensers can be used for this purpose
  • in exhausts of  unimix , condensers , ERM etc, positive pressure of 100 pascal should be maintained. Exhaust fan speed and volume should be accordingly selected
  • DUSTEX should be installed before feeding to the cards, because better the fibre  opening better the dedusting
  • fine openers like ERM, CVT cleaners also help in dedusting
  • It is always better to feed the material through condenser for a feeding machine of cards.  Because condenser continuously removes the dust from a small quantity of fibres  and the material  fed to the feeding machine is opened to some extent.
  • Since material is not opened well in Unimix, the dedusting may not be very effective, even though  dedusting concept in Unimix is very good
  • for rotor spinning dedusting is very important. It is better to use a machine like DUSTEX  after the fine opener.

OTHERS:

  • setting between feed rollers is different for different types. It should be according to the standard specified by the manufacturer.  For Unimix it should be around 1 mm.
  • it is advisable to run the fans at optimum speeds.  Higher fan speeds will increase the material velocity and will create  turbulence  in the bends.This will result in curly fibres which will lead to entanglements.
  • If the feeding to cards  is not with CONTI -FEED, the efficiency of the feeding machine should be minimum 90 % and can not be more than 95%.
  • if the cards are fed by CONTI-FEED system,  the feed roller speed variation should not be more than 10%.  If the variation is more, then the variation in tuft size also will be more. Hence the quality will not be uniform
  • If two feeding machines feed to  10 cards and the no of cards can be changed according the requirement, then frequent changes will affect the tuft size which will affect the quality, if the line is fixed with CONTI-FEED.
  • if contifeed system is tuned properly and there are no machine stoppages, continuous material flow will  result in better opening and even feeding to the cards
  • If the production rate per line is high, the reserve chamber  for  the feeding machine should be big enough to avoid long term feed variations.
  • it is advisable to reduce the number of fans  in the line.
  • fan speeds, layout of machines should be selected in such a way that material choking in the pipe line, beater jamming etc will not happen.  This will lead to quality problems
  • all blowroom machines should work with maximum efficiency. The feed roller speeds  should be selected in such a way that  it works atleast 90% of the running time of the next machine.
  • blow room stoppages will always affect the sliver quality both in terms of linear density and  tuft size. Blow room stoppages  should be nil in a mill
  • heavy particles like metal particles, stones should be removed using heavy particle removers , double magnets etc, before they damage  the opening rollers and other machine parts.
  • Number of cleaning  points are decided based on  type of ginning (whether roller ginned or saw ginned), the amount of trash, and the number of trash particles and the type of trash particles.
  • machinery selection should be based on the type of cotton and production requirement. If the production requirement of a blowroom line is less than 200 kgs,  CVT-4 cleaner can not be  recommended, instead CVT-1 can be used.
  • Since blow room requires more space and power, it is better to make use of the maximum production capacity of the machines
  • material level in the storage chambers  should be full  and it should never be less than 1/4 th level.
  • grid bars should be inspected periodically, damaged grid bars  should be replaced.
  • grid bars in  the front rows can be replaced earlier
  • if the cotton is too sticky, the deposits on the machine parts  should be cleaned atleast once in a week, before it obstruct the movement of the fibre
  • fibre rupture should be checked for each opening point.  2.5 % span length should not drop by more than 3% . If the uniformity ratio drops by more than 3%, then  it  is considered that there is fibre rupture.
  • high fan speed, which will result in high velocity of air will increase neps in cotton
  • nep is increased in the blowroom process.  The increase should not be more than 100%.
  • the nep increase in each opening machine should be checked  with different beater speeds and settings, and the optimum  parameters  should be selected. But please remember that everything should be based on  yarn quality checking.  e.g. if nep increase in blow room is  more and the beater speed or feed roller setting is changed, the tuft size will become more. This may result in bad carding quality. Sometimes if the neps are slightly more and the  fibre is well opened, the neps can be removed by cards and combers and the yarn quality may be better.  Therefore all trials should be done upto yarn stage.
  • No of neps and trash particles  after different processes is given below.(an approximate value)
  • Blow room machinery lay out should be desined in such a way that there should be minimum number of bends, and there should not be sharp bends  to avoid fibre entanglements.
  • fibre travelling  surface should be smooth and clean
  • temperature should be around 30 degrees and the humidity is around 55 to 60%.

A best blowroom can be achieved by selecting the following machines:

1.RIETER UNIFLOC- A11 ( pre opening)

2.RIETER UNICLEAN B11 (  pre cleaning)

3.TRUTZSCHLER MPM 6 + MPM6 ( two mixers for blending)

4.TRUTZSCHLER CVT-1 ( for  roller ginned cotton) CVT-3 ( for saw ginned)

5.CONTAMINATION DETECTOR from either BARCO OR JOSSI

6.TRUTZSCHLER  DUSTEX-DX ( for dedusting)

7.TRUTZSCHLER CONTI-FEED and others

But enough care should be taken to synchronise the machines for better performance  , and to run the line without any electrical system breakdowns.

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