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
Poor Below 30 Unusable
M= 50% SL
UHM SL - Average value of length of Longest of 50% of Fibers
UI Uniformity Index
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, 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,
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
Micronaire Value of 3.8 is higher than 3.2 of low maturity cotton. Another American Cotton was tested and results are as follows
Hence, it is essential to know what Micronaire value is good for each variety of Cotton.
|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 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
|4||STRICT LOW MIDDLING||SLM||41|
|6||STRICT GOOD ORDINARY||SGO||61|
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
Go to Top of Page