Basic details of the Sampling method
(Part-1 Introduction of textile testing)
(Part-2 Sampling method.)
(Part-2 Sampling method.)
- Testing of any materials in the lab is only possible by the sample of that particular material.
- The textile industry has a large amount of production.
- Checking each and every product by all parameters is practically not possible.
- Therefore from all products, some of them are selected by various methods for testing and those selected amounts of materials are known as 'Sample' for lab testing.
- Technically producing all products are known as population and a very small portion of that population is selected for testing as the sample.
- The sample should equally represent the whole population.
- If it is mixed with lab samples, then they should be equally mixed with each other.
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| Sampling method diagram |
Basic details of various sampling methods
Random sample
- The sample which is randomly picked from the population is known as a random sample.
- In this type of sample, every individual in the population has an equal chance of being included in it.
- It is free from bias, therefore truly representative of the population.
Numerical sample
- The numerical sample is a sample that has percentages of all kinds of parameters that are equal to the percentage of parameters of bulk materials.
- In other words ratio of bulk quality to sample, quality is almost 1:1. which means the sample truly represents the whole quality of bulk.
Biased sample
- A biased sample is sample whose selection is influenced by factors other than chance is known as a biased sample.
- A biased sample will probably never represents the whole population.
- Biased samples have certain types of Bias due to physical characteristics or relative position.
- In Physical characteristics type of bias physical properties or nature of fibres will influence the sampling process.
- i.e. - Long fibres have a greater chance of being selected.
- In the Relative position type of bias position of materials and the person’s nature will influence the sampling process.
- This type of bias is generally faced when the sampling person has taken the sample from only one particular location like surface, edges, etc.
- I.e. - Fibre collected from the top layer of the bale.
- Subconscious bias - If the person collects the samples which are free from ridges without thinking about it will lead to subconscious bias.
Core sampling
- Core sampling is the method generally used o evaluate the amount of grease, and vegetable matter present in the sample taken from unopened bales of raw wool.
- The core sample is basically a sampling of bales from halfway or from the centre.
- In this sampling, the technique was first developed as core boring in which the tube was rotated by a portable electric drill.
- The method was then developed further to enable the cores to be cut by pressing the tube into the bale manually.
- In modern core sampling, the instrument tube enters in the bale compression direction. (Generally perpendicular to the bale’s outer surface.)
- This tube structure is such a way that, Cutting tip diameter is sharp and lesser than the coring tube so it easily slides and penetrates the materials.
- The difference in diameter also helps retain the cores in the tube as it is withdrawn.
- The required number of samples is withdrawn and then combined with each other.
- In Core sampling, various sizes of tubes are used 14, 15, and 18mm diameter and 600 mm length of the tube to withdraw materials.
- After removal cores are kept in an airtight container immediately.
- A hydraulic coring machine is used for a large number of samples.
- The method has been further developed to allow hydraulic coring by machine in warehouses where large numbers of bales are dealt with.
- Such machines compress the bale to 60% of its original length to allow the use of a tube that is long enough to core the full length of the bale.
Planned sampling
- The planned sample is used in specific cases when a particular test needs to take place.
- The planned sample is useful to cover up a complete assembly line or provide production in machines in any time frame.
- i.e. checking of USTER & imperfections in the case of the ring frame.
- A sampling plan is a detailed outline of which measurements will be taken at what times, on which material, in what manner, and by whom.
- The planned sample should be designed in such a way that the data of the final output will contain representative sample parameters of interest and allow for all questions, as per the requirements.
Zoning method
- The zoning method is used for sampling from one or more than one batches or a lot of materials that are used as testing materials.
- It is used in ginning bale samples, yarn bobbin samples, cone samples, and sometimes in fabric samples.
- Zoning is basically, the selection of a sample that comes from large bulk.
- The zoning sample is prepared by a special technique.
- The zoning method basically creates a small sample from various batches or groups of materials.
- In the zoning method, any two or four handful samples are carried out from a batch or group of materials.
- All collecting samples are divided into two equal parts and one part from each sample is discarded and other random parts remain.
- Then again divide these remaining parts into two parts with doubling and drawing and discarded one of them and the remaining others.
- By doing this, samples are getting smaller and smaller.
- Repeat this process until it reaches its size with the required sampling size.
- The final prepared sample of the zoning method truly represents the whole lot's quality.
- (It is important to keep in mind that, the discarded half portion is done until the required size of the sample is not achieved. In the final sample, Less material is not able to be properly tested or extra materials go to waste, therefore the appropriate size of the zoning sample is important.)
- (More details of zoning method and zoning technique.)
Questions -
- What is sampling in textiles?
- What are the different ways of sampling?
- What is random sampling?
- What is the numerical sample?
- What is the biased sample?
- What is core sampling?
- What is planned sampling?
- What is the zoning method?
References
Cenote, M. (2015). Google Books. In The SAGE Guide to Key Issues in Mass Media Ethics and Law (pp. 847–858). SAGE Publications, Inc.
Fundamental textile testing: Mechanical and Physical Tests. (n.d.). Fundamental Textile Testing: Mechanical and Physical Tests. from https://www.eurofins.com/textile-leather/articles/fundamental-textile-testing-mechanical-and-physical-tests/
Handbook of textile testing and quality control - Google search. (n.d.). G.Co. from https://g.co/kgs/RvVMgm
NPTEL IIT. (n.d.). Nptel.Ac.In. from https://nptel.ac.in/courses/116102029
Reading further
Writer - DSPAT Team
