ZONING TECHNIQUE: A SAMPLING METHOD FOR COTTON FIBERS

ZONING TECHNIQUE: A SAMPLING METHOD FOR COTTON FIBERS

SCOPE: 

This practice covers procedures for taking a lot sample, at the source, of cotton fibers and reducing this sample through a series of steps to provide a relatively small test specimen of loose cotton fibers, representative of the source material and suitable for the determination of a single property, or a series of fiber properties, according to established procedures.

SUMMARY: 

Sampling procedures for obtaining samples from the lot sample and for the reduction of the lot samples to the size required for fiber test specimens are presented. Steps are outlined to secure reduction of the amount of cotton fibers to be handled at various stages, so that the reduced sample continues to be representative of the lot. Provision is made for the omission of intermediate steps in the reduction of the lot sample in cases where this is desirable or necessary.

EQUIPMENT/MACHINE

Manual skill required

DISCUSSION/THEORY

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. Also many tests are destructive so that there would not be any material left after it had been tested. 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. For instance if the test for cotton fiber length is considered, this requires a 20 mg sample which may have been taken from a bale weighing 250 kg. The sample represents only about on eleven millionth of the bulk but the quality of the whole bale is judged on the results from it. The aim of sampling is to produce an unbiased sample in which the proportions of, for instance, the different fiber lengths in the sample are the same as those in the bulk or to put it another way, each fiber in the bale should have an equal chance of being chosen for the sample. Zoning is a method that is used for selecting samples from raw cotton or wool or other loose fiber where the properties may vary considerably from place to place.

TERMS USED IN SAMPLING

Several of the terms used in sampling have different meanings depending on whether wool or Cotton, yarn or fiber is being sampled. This is due to the different representative organizations which have historically grown around each industry. The appropriate standard should always be consulted:

Consignment: 

This is the quantity of material delivered at the same time. Each consignment may consist of one or several lots.

Test Lot or Batch: 

This consists of all the containers of a textile material of one defined type and quality, delivered to one customer according to one dispatch note. The material is presumed to be uniform so that this is the whole of the material whose properties are to be characterized by one set of tests. It can be considered to be equivalent to the statistical population.

Laboratory Sample: 

This is the material that will be used as a basis for carrying out the Measurement in the laboratory. This is derived by appropriate random sampling methods from the test lot.

Test Specimen: 

This is the one that is actually used for the individual measurement and is derived from the laboratory sample. Normally, measurements are made from several test specimens.

Package: 

Elementary units (which can be unwound) within each container in the consignment.

They might be bump top, hanks, skeins, bobbins, cones or other support on to which have been Wound tow, top, sliver, roving or yarn.

Container or Case: 

A shipping unit identified on the dispatch note, usually carton, box, bale or other container which may or may not contain packages.

PROCEDURE

1.      Collect a handful of fibers randomly from each of at least 40 widely spaced places (zones) throughout the bulk of the consignment.
2.      Each handful is divided into two parts a done half of it is discarded at random.
3.      Divide the retained half into two and half of that discarded.
4.      Repeat the above process until about 5 grams of fibers remain in handful.
5.      Treat each handful in a similar manner and the fibers that remain are placed together to Give a correctly sized test sample containing about 5 grams of  fibers.
6.      Test the whole of the final sample.