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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.

BARGAINING 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

 

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