Views: 64 Author: Site Editor Publish Time: 2022-11-24 Origin: Site
Cotton fabrics are made of cotton and come in many grades. The fiber covered on the seeds of cotton plants of mallow family, also known as cotton, short for cotton. It is an important raw material in the textile industry. Cotton fiber products have good moisture absorption and air permeability, soft and warm. It is often used for short cuts because it is not as durable as silk. The inspection and testing of cotton goods is also extremely important. Then how to inspect cotton goods? This article will give you a detailed introduction to the cotton goods inspection methods and standards, I hope you have learned something successful.
I. Inspection and sampling of cotton goods
(1) Definition and purpose of sampling
Sampling of cotton goods is a process in which a certain number of representative unit products are selected from a batch of homogeneous products in the production factory or warehouse as samples for testing, analyzing and evaluating the quality of this batch of products according to the standard or protocol.
For all kinds of inspection of cotton goods, it is impossible to inspect all of them because the total number of tested objects is relatively large. In fact, only a very small part of the total materials can be taken. The extracted individuals are called samples, and all samples constitute the total sample, and the number of individuals contained in the sample is called the sample size.
In cotton fabrics, individual properties generally show great differences. The larger the sample size, that is, the more individuals contained in the sample, the closer the measured results will be to the overall experimental results. Generally, statistical methods are used to determine the sample size to ensure the reliability of experimental results. However, regardless of the size of the sample and the accuracy of the instruments used, the results can be unreliable if the sampling methods themselves are not representative. Therefore, the accuracy of measurement and experimental results depends on the integrated result of instrument error and sample error.
The purpose of sampling is to statistically infer the quality level of the whole batch of products by using the quality condition reflected by the smallest possible sample. In other words, to extract some sub-samples representing the whole population, and to minimize the sampling error, reasonable sampling methods must be adopted.
(2) Sampling method
The sampling method is the method by which samples are obtained from a batch. Sampling is the process of obtaining the samples specified in the inspection scheme from the batch. The basis of batch judgment is all from the quality characteristic values of the samples, and the randomness of the samples is the guarantee of the objectivity of the judgment batch. In order to ensure the representativeness of the sample to the whole population, it is necessary to adopt a reasonable sampling method, which not only avoids the systematic sampling error, but also reduces the random error. Therefore, random sampling method is often used in textile inspection.
1. Pure random sampling
Pure random sampling method is also known as simple random sampling, the population does not go through any grouping queue, completely by chance from the extraction. Theoretically speaking, pure random sampling conforms to the random principle of sampling, which is the basic form of sampling. However, in practice, pure random sampling has a great chance, especially when the total variation is large, the representativeness of pure random sampling is not as high as that of group resampling.
2. Equidistant sampling method
Equidistant sampling method is to first line up the population according to a certain symbol, and then extract the same distance.
Compared with pure random sampling, equidistant sampling can make the sub-samples evenly distributed in the population, and can make the sub-samples have better representativeness. However, if the product quality fluctuates regularly and coincides with equidistant sampling, systematic errors will be produced.
For example, there are 1000 bales of raw cotton to be sampled, n = 10 bales are to be selected, and equidistant sampling method is to be adopted, that is, one bales should be selected out of every 100 bales. The 1000 packets of raw cotton are numbered from 0001 to 1000. If a number is randomly determined within 100, such as 36, the last two digits of the raw cotton number are 36, which are selected as samples, namely 036, 136, 236...... No. 936, a total of 10 bales of raw cotton were taken as sub-samples.
3. Representative sampling Method
Using statistical grouping method, a batch of products are divided into representative type groups, and then in a certain way in each group to adopt the pure random sampling method to obtain samples, these samples together into samples sampling method, known as representative sampling method. How to determine the number of samples in each group, one method is to determine the degree of variation within each group, the group with large variation takes a little more, the group with small variation takes a little less, there is no uniform proportion; The other is to determine the number of each group according to the proportion of each part to the whole.
4. Phased random sampling method
Phased random sampling is to take a part of the subsample from the population, and then extract the sample from this molecular sample. The acquisition of samples from a batch of textiles can be divided into three stages, namely batch sample, laboratory sample and sample.
Batch: A certain number of packages (or cases) from the whole batch of products to be inspected is called the batch. Laboratory specimen: specimen reduced from batch to laboratory by appropriate means.
Sample: from laboratory samples, according to certain methods to obtain the physical and chemical properties of the test sample.
Taking the preparation of fiber sample as an example, batch sample, laboratory sample and sample preparation are analyzed to illustrate the randomness and representativeness reflected in the preparation process.
The number of laboratory samples extracted from each batch of lint should be determined according to the number of bags in each batch of lint. 100 packets or less take 1; Take 2 copies of 101 ~ 300 packets; 301 ~ 500 packets take 3 copies; Over 500 packets take 4.
During the sampling, at least 100 points were randomly selected from various parts of the cotton bales of the sample batch, and 2 ~ 2 cheg 5g was sampled from each point, so as to obtain 200-250g laboratory samples.
The 200-250g laboratory samples were shredded and mixed, and placed flat on the work table to form a cotton layer with uniform thickness and an area of about 0 chang 25m2. A total of 32 clusters were randomly selected from 16 parts evenly distributed on both sides to form samples of a certain quality, and the sample extensor or fiber mixer was used to make experimental cotton strips with a mass of about 2g.
(3) Sampling inspection scheme for cotton goods
Sampling inspection is the main form of textile inspection. A sampling test is when a certain number of samples are taken from a submitted batch and only the samples are tested to determine whether the batch is qualified. On the one hand, sampling is very important to carry out sampling inspection. On the other hand, a reasonable sampling scheme must be designed in advance so as to ensure the quality of the inspection. There are many sampling schemes, which are classified according to their characteristics as follows:
1, according to the quality characteristic value and the corresponding determination method
(1) Count sampling scheme: count sampling scheme uses the count method to test the quality of unit products in the sample, divides the product quality into qualified or unqualified products, and then counts the number of unqualified products in the sample, and compares the number of unqualified products with the judgment array to determine whether the batch products are qualified. The determination array is composed of the upper limit standard of the number of nonconforming items in the samples of the qualified batch and the lower limit standard of the number of nonconforming items in the samples of the unqualified batch. Textiles with multiple quality indexes are suitable for counting sampling scheme.
(2) Metrological sampling scheme: The metrological sampling scheme is to obtain the mean value or standard difference of samples by using the metrological method in sample inspection, and then determine whether a batch of products is qualified according to the judgment rules. The metrological sampling scheme has the advantages of small sample size, making full use of the quality information obtained from the inspection sample, but the use procedure is tedious and the calculation is complex, so it is more suitable for sampling inspection of single quality index in textile inspection.
2, according to the principle of the scheme
(1) Standard type: According to the principle of controlling the error size in sampling inspection, only the batch is qualified or not. The distinguishing feature is a definite solution that meets the quality requirements of both the producer and the user. It is suitable for situations where the product quality is unknown.
(2) Selection type: During the inspection, replace the unqualified products found in the samples with qualified ones, conduct 100% inspection on the rejected batches, and eliminate the unqualified products. Suitable for non-destructive testing.
(3) Adjusted sampling scheme: Adjusted sampling scheme is a complete system composed of normal, strict, relaxed, extra wide and other sampling schemes, which are connected with the transfer rules. When the product quality is reduced, the use of tightening program; If the quality of the product is stable and relatively high, the relaxed scheme is used. In general, the normal scheme is used. Which scheme to use is determined by the transition rules. This scheme is especially suitable for continuous batch sampling inspection.
(4) Continuous production: The continuous production of products on the conveyor belt, in the middle of the inspection, after passing the inspection of the product's average unqualified rate is controlled below a certain value (AQL). At the beginning, 100 percent inspection is carried out continuously on each product. If the result is that the number of nonconforming products is below a certain value, it is changed to sampling inspection at regular intervals. If the inspection results are found again, it will be changed to 100 percent inspection method.
3. Score according to the number of sample extraction
(1) One-time sampling scheme: The one-time sampling scheme only needs to extract 1 sample N from the total n of the inspected batch. According to the result of sample inspection, the qualified products of the batch can be determined. Primary sampling is also called single sampling or primary sampling. It is characterized by simple scheme, convenient use and wide application, but the sample is large and the workload of sampling inspection is also large.
(2) Secondary sampling scheme: In the secondary sampling scheme, the first sample n1 is taken from the total N of the inspected batch for inspection. If the quality of this batch of products can be judged based on this, the inspection will be terminated. Otherwise, take a second sample n2 and test it again, and judge whether this batch of products is qualified or not by combining the results of the two tests.
(3) Multiple sampling scheme: In the multiple sampling scheme, only after one or two samples (usually the same N, but not necessary) are extracted from the total n of the inspected batch, can the quality of the batch be qualified or not be concluded. It is the extension of the secondary sampling scheme, also known as multiple sampling. The characteristics of secondary and multiple sampling schemes are that the average inspection samples are smaller than that of primary sampling schemes, which can save inspection costs. However, the management is more complicated and requires special training of quality inspection personnel, so the management costs will increase and it is not suitable for textiles with low value.
(4) Sequential sampling scheme: only one unit of product is selected from the inspected batch for inspection each time, and then the judgment of qualified, unqualified or continued random inspection will be made until the judgment of qualified or unqualified batch can be made. The number of spot checks cannot be determined in advance and will only be known after a decision has been made.
4, according to the composition of the sample
(1) Batch by batch sampling inspection scheme: the products are divided into batches first, and then samples are extracted from a batch of products.
(2) Continuous sampling inspection scheme: the products do not need to form batches, but directly inspect the products at a certain inspection point on the continuous production line.
Ii. Types and inspection standards of cotton fabrics
Cotton, white, plain color to do not fade prevail, colorless flowers, no color difference, soft feel, good water absorption performance, no stains, no obvious damage defects. Comply with the provisions of GB/T14308-2003. Ordinary towel yarn: ground warp 21S/2, wool warp 21S/2, weft 21S; High quality towel yarn: ground warp 32S/2, wool warp 32S/2, weft 32S.
2. Bath towels
Specification is not less than 1400MM*750MM, weight is not less than 600g.
3. Face towel
Specification is not less than 700MM*350MM, weight is not less than 140g.
4. Floor towel
Specification is not less than 750MM*450MM, weight is not less than 350g.
5. Square towel
Specification is not less than 320MM*320MM, weight is not less than 55g.
6. Bathrobe made of cotton or silk
Soft and comfortable, warm.
(2) Soft cushion
Smooth, suitable elasticity, no dirt.