Uster Technologies AG, Uster, Switzerland

 

Introduction

 

The raw material costs are mostly more than 50% of the total manufacturing costs of a spinning mill. Therefore, the spinning mills always had a considerable interest to know the quality characteristics of fibers to reduce costs and to optimize the spinning process.

 

The disadvantage of the conventional manual fiber length measuring systems was the time and the skill needed for a single test.

 

The conventional nep counting system was atime-consuming visual test with limited reproducibility.

 

In 1968 the United States Department of Agriculture started to push highly automated electronic fiber testing systems for a quick determination of the most important fiber characteristics of bales, the HVI System.The measuring principle is based on a fiber bundle test. The USTER HVI System can now be considered as the most important instrument to measure the quality characteristics of cotton in bales.

 

However, some of the cotton fiber parameters such as the number and size of neps cannot be measured with a fiber bundle testing system. Therefore, the single fiber testing system USTER AFIS was introduced in the market in 1990. This system has proved to be the most reliable fiber testing system for single fibers and serves particularly for monitoring of the entire spinning process.

 

Measurement of neps in cotton fibers

 

Neps deteriorate the appearance of fabrics considerably.Therefore, it is the intention of spinning mills to keep the nep content ofcotton fibers and the formation of neps under control.

 

Neps do not exist in cotton bolls. Neps are produced by ginning, opening and cleaning of cotton. We distinguish 2 types of neps:

The fiber neps which are defined as an entanglement of fibers. They are formed under mechanical treatment as mentioned above (Fig. 2).

 

The seed coat neps are fragments of cotton seeds with remaining fibers. They are mainly produced in ginning when the fibers are separated from the cotton seeds (Fig. 3).

 

 

For this single fiber measuring system there are various benchmarks available, the USTER STATISTICS. Fig. 4 shows the USTERSTATISTICS for neps measured with a single fiber measuring system.

 

In Fig. 4, the horizontal scale represents the fiber length; the vertical scale represents the number of neps. These statistics can be interpreted as follows:

 

The evaluation of thousands of samples worldwide has shown that the average number of neps (50%-line) is equal to 300 neps per gram for a fiber length of 28 mm (1 1/8). The best cotton samples, however, had only about 120 neps per gram, the cotton samples with the highest figures had 450 neps per gram. In long staple cotton less neps were measured because a considerable amount of this cotton is roller-ginned.

A = Bale, B = Card mat, C = Card sliver, D = Ribbon lab, E = Comber sliver, F = Finisher sliver, G = Roving

 

Fig. 5 is also part of the USTER STATISTICS and shows the formation and elimination of cotton during the entire spinning process. The opening/cleaning line produces additional neps. It must be expected that the opening/cleaning line doubles the amount of neps. The card is able to eliminate 70 to 90% of the neps, depending on the card maintenance. The comber also can reduce the remaining number of neps in the sliver by 50 to 60%.

 

Fig. 6 shows the nep counts in the card slivers of 30 cards in a spinning mill.

 

It is obvious when analyzing Fig. 6 that the cards have a different status of maintenance, because the same raw material was processed by all the cards. The lowermost value was reached by card no. 17 with 45 neps per gram, the highest value by card no. 26 with 88 neps gram.

 

In this spinning mill the maintenance status of the cards is controlled by the number of neps in the card sliver.

 

Measurement of the fiber length of cotton

 

Since the single fiber measuring system is able to measure each individual fiber, it is possible after the test to mathematically arrange the fibers as an end-aligned staple diagram. Such a staple diagram is shown in Fig. 7, which shows the fiber length definitions.

L5%(n) represents the fiber length which is only exceeded by 5% of all fibers.

 

UQL(w) represents the Upper Quartile Length. This is the most important length definition. This value is equivalent to the classers staple.

 

L(n,w) is the mean length by number or by weight

 

L is the length (12,7mm) which defines the amount of short fibers. Fibers below this length are counted as short fibers.

 

Measurement of trash and dust in cotton fibers

 

Trash and dust particles are foreign particles which are mostly part of the cotton plant (leaf or stem fragments, etc.). These particles need to be extracted during the ginning and spinning process.

 

A = Bale, B = Card mat, C = Card sliver, D = Ribbon lab, E = Comber sliver, F = Finisher sliver, G = Roving, H = Yarn

 

Fig. 8 shows a few trash particles. Fig. 9 represents the Uster Process Statistics for trash particles. The most efficient machines to eliminate trash particles are again the card and the comber. If we follow the 50%-line of the USTER STATISTICS we notice that the opening/cleaning line can reduce the amount of trash by about 30%, the card by about 85% and the combing machine by about 80%.

 

Measurement of the maturity of cotton fibers

 

The fiber maturity is an important quality parameter of cotton. Since immature fibers can only absorb a reduced amount of dyestuff, shade variations must be expected in woven or knitted fabrics, particularly if immature fibers are not evenly distributed.

 

Fig. 10 is a scanning electron microscope photography of a fiber nep consisting of mature and immature fibers.

 


The sensor of the single fiber testing system produces two light beams to measure the wall thickness of the fibers, because the wall thickness is a measure of the maturity.

 

In order to calculate the amount of immature fibers the cross-section of the fibers has to be compared with a fiber of the same perimeter, but with a circular cross-section.

 

The Immature Fiber Content IFC is the percentage of all fibers within a cotton sample which have a cross-section covering less than 25% of fibers with the same perimeter having a circular cross-section.

 

As reference figures the

Table 1 can be used for short and medium staple cotton. The

Table 1 has to be considered as a general rule for raw cotton.

 

Maturity

Description

Immature Fiber Content %

Description/Maturity

< 0.75

Very immature

> 15

Very Low

0.76 0.85

Immature

12 14

Low

0.86 0.90

Mature

9 11

Medium

0.91 0.95

Mature

6 8

High

> 0.96

Very mature

< 6

Very High

 

Table 1: Ranges of Maturity and Immature Fiber Content in Raw Cotton (short/medium staple)

 

 

Fiber information on the screen and as a print-out

 

Table 2 represents a print-out of the USTER AFIS. The figures are the quality characteristics of 10 repetitions determined from the same bale.

 

Table 2 Print-out of USTER AFIS PRO with 20 selected result column

 

Description

 

 

 

 

A

Number of test repetitions

M

Short fiber content by number in percent

 

B

Number of neps per gram

N

Length of the longest fibers / 5% of the sample

 

C

Neps diameter in micrometer

O

Fiber fineness in mtex

 

D

Number of seed coat neps

P

Immature fiber content in percent

 

E

Diameter of seed coat neps in micrometer

Q

Maturity ratio

 

F

Mean length by weight in mm

R

Total of all dust and trash particles per gram

 

G

Coefficient of variation of mean length by weight in percent

S

Mean size of the particle in micrometer

 

H

Short fiber content by weight in percent

T

Dust particles per gram

 

J

Upper Quartile Length by weight in mm

U

Trash particles per gram

 

K

Mean length by number in mm

V

Visible foreign matter in percent

 

L

Coefficient of variation of mean length by number in percent

 

 

 

Mean

Mean of the test repetitions

S.D.

Standard deviation of the test repetitions

%CV

Coefficient of variation of the test repetitions

 

 

The comparison of the values in Table 2 to the USTER STATISTICS is shown in Table 3.

 

Quality characteristics

Value

USTER STATISTICS 2007

Number of neps (1/g)

194

50%

Upper Quartile length (mm)

31,7

50%

Short fiber content SFC(n) (%)

20,4

50%

Fineness (mtex)

183

>95%

Dust (-)

137

65%

Trash (-)

26

5%

Maturity(-)

0,92

45%

Table 3 Comparison to the USTER STATISTICS

 

 

Comment to Table 3:

The values for this type of raw cotton are in the middle of the world production for most of the quality characteristics. The only 2 values which deviate considerably from the 50% line are the fineness of the fibers and the trash. For a fiber length UQL of 31,7 mm the fibers are coarse, and the amount of trash is rather low.

 

Summary

 

As has been mentioned above, the raw material costs represent more than 50% of the entire manufacturing costs in most of the spinning mills. Therefore, it was always the intention of mill owners and managers to have an excellent knowledge of the raw material, because the right selection of the raw material determines in many cases whether the mill generates a sufficient margin. In order to obtain this knowledge the mill has to determine the basic quality characteristics of cotton.

 

For a long period of the textile history the determination of fiber quality characteristics was difficult and time-consuming.

 

The textile electronics industry has developed two fiber measuring systems to overcome these restrictions:

The USTER HVI, a bundle fiber measuring system for a fast measurement of cotton bales and for a bale lay-down.

The USTER AFIS, a single fiber measuring system as a process control tool. This instrument is able to measure fiber samples from the bale, from the opening/cleaning line, from slivers and rovings.

 

This paper contributes to the options of a spinning mill when using the USTER AFIS PRO in the textile laboratory. The large number of quality characteristics as shown in Table 2 are an enormous help for managers in spinning mills to optimize the selection of cotton, to establish a spinning process of consistent quality and to build up a continuous improvement process in the mill.

 

 

 

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