Selection of Sample - Textile testing and quality control.pptx

This PDF explains the principles and methods of sample selection in textile testing, ensuring accurate and reliable results. It highlights why correct sampling is essential, as test results depend heavily on how well the sample represents the bulk material.

Key topics include:

Definition and importance of sampling

Types of samples (laboratory sample, test specimen, bulk sample)

Factors influencing proper sample selection

Standard procedures and guidelines for sampling

Role of sampling in ensuring quality control and reproducibility of results

This document serves as a practical guide for textile students and professionals to understand the importance of representative sampling in achieving trustworthy test results.

1. 1 Sample: It is a relatively small fraction selected from a population; the sample is supposed to be a true representative of the population.

2. Sampling For research purposes, individual textile can be selected for examination or testing. It is not possible or desirable to test all the raw material or all the final output from a production process because of time and cost constraints. Because of this, representative samples of the material are tested. The amount of material that is actually tested can represent a very small proportion of the total output. It is therefore important that this small sample should be truly representative of the whole of the material. 2

3. Types of sample I. Biased Sample: - Where a selection of an individual is influenced by factors other than chance. - The sample does not truly represent the bulk and the result is biased sample result. - Bias may be caused by physical properties (e.g. chance of higher length of fiber in the sample), position of the sample (e.g. yarn of outer layer from bobbin), position of the person as well as subconsciously. - The effect of bias on the test result may be negligible or not. II. Random Sample: - In this type of sample every individual in the population has an equal chance of being included in it. - The number of the sample must be sufficiently large to include all the variations of the individuals in the population. 3

4. Fiber sampling Serial Sampling technique Scop e 1. Squiring Where the material is composed of parallel order e.g. sliver, roving, yarn . (Numerical sampling gives a random sample ) 2. Cut Squiring (modified squiring) 3. Zonning Raw cotton or wool (Random sample) 4. Dye Sampling From sliver and webs in which the fibers are entangled (wool). (Random sample) 5. Tong Sampling For wool (extent biased sample) 6. Core Sampling From wool bale (for assessing the impurities) 7. Random Draw method Sliver, tops (numerical sample) 4

5. Squaring Technique for Fiber Squaring is a method that is applicable to slivers, rovings or yarns in which the fibers are in a reasonably ordered state and give a numerical sample. A length of the yarn/sliver being tested is cut off and the end untwisted by hand. The end is laid on a small black velvet board and covered with a glass plate. The untwisted end of the yarn is then cut about 5mm from the edge of the plate as shown in figure . All the fibers that project in front of the glass plate are removed one by one with a pair of forceps and discarded. By doing this all the cut fibers are removed, leaving only fibers with their natural length. The glass plate is then moved back a few millimeters, exposing more fiber ends. These are then removed one by one and measured. 5

6. When these have all been measured the plate is moved back again until a total of 50 fibers have been measured. In each case once the plate has been moved all projecting fiber ends must be removed and measured. The repeat is essential because the fringe formed at the broken edge of any fibrous strand naturally contains a predominance of longer fibers, and this initial bias can be eliminated only in the manner described. 6 6 Yarn Velvet board Glass plate Approx. 5mm

7. Zonning Technique 7

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9. Yarn Sampling Sampling for determination of Yarn Count Take sixteen packages (cops / roving bobbins / any other primary packages). The skeins should be wound from the top portion eight packages and from about half-way from remaining eight. For the large packages such as cone/cheese, take eight packages and wrap two skeins from each, where one skein from outer portion and one skein from inner portion. 9

10. Sampling for determination of Yarn Twist Take the test specimens in equal numbers from ten packages. No specimen being taken from within 1 yard length of the end of the package. Allow a minimum distance of 1 yd between consecutive specimens Sampling for determination of Lea strength Take 20 packages from each of which a complete lea may be withdrawn. If 20 packages are not available a smaller multiple of four packages may be used. For e.g. eight packages, three leas from each of four and two leas from each of other four packages. 10