Application of Count Adjustment and Isometric Sampling Method in Steel Drum Inspection

I. INTRODUCTION The count adjustment type sampling plan is a kind of sampling method commonly used in the world. It is a kind of adjustment of the degree of strictness based on the actual changes in product quality, to minimize the two types of misjudgment (ie, false acceptance: the unqualified misjudgment as qualified, to receive. Misuse: the qualified miscarriage of justice , Will not receive) Probabilistic sampling programs, generally applicable to large batches of continuous production occasions, especially suitable for continuous quality control of multiple batch production occasions.
Isometric sampling program is also called mechanical sampling or system sampling. It is a kind of sampling method in which all units (or products) in the survey population are numbered and arranged in a certain order, and then samples are sampled at regular intervals to conduct surveys.
Combining these two options, it is scientific and effective to control, inspect and accept the quality of steel drums.
Second, the program proposed China's existing steel drum production plant more than 200, with an annual output of more than 30 million steel barrels, the annual output value of more than 600 million yuan. The steel drum is a kind of packaging, which is widely used in industry, agriculture, national defense, foreign trade, and grain sectors, and plays an important role in socialist construction. Steel drums are generally subjected to processes such as blanking, stamping, rolling, seam welding, ribbing, crimping, painting, and pressure testing. Steel drum production is generally an assembly line production with large batches and high mechanization. At present, due to the reasons of raw materials, equipment, and management, the quality of steel drums in China's barrel making industry is not yet stable. The quality of products of most manufacturers has not yet reached the requirements set out in the "International Maritime Dangerous Goods Transportation Regulations." Compared with the world's developed countries, there is still a big gap between the barrel factories. Therefore, how to stabilize product quality and improve the quality level of steel drums have become serious problems that must be carefully studied and solved. We believe that the reason for the instability of the quality of steel drums is that, besides raw materials, equipment, and processes, it is an important reason that the steel drum production process cannot be controlled. In recent years, according to the characteristics of steel barrel production, we have designed steel tank counting and isometric sampling inspection programs. Through the experiments in production, we have achieved good results in the supervision, inspection and control of the production process.
Third, the program features Count adjustment type sampling program has a dynamic feature. For a given product lot quality, instead of using a single solution, it uses a different set of rigorous programs (normal, tightened, and relaxed) and links them with a set of conversion rules. Under normal circumstances, the use of normal testing programs, when the test results show that the quality of the product has become significantly better, it will be converted to use the relaxation test program, when the test results show that the product quality is significantly worse or unstable production, then switch to the use of strict Inspection program. In this way, the three programs are converted according to the quality of the product, so as to achieve the supervision and control of the steel drum production process.
The equidistant sampling program has the characteristics of being easy to use and easy to use. This method, because all parts of the whole can be included in the sample to a certain extent, can ensure that the extracted sample is evenly distributed in the whole, thus improving the representativeness of the sample; moreover, as the steel drum production is generally continuous Pipeline production, sampling is carried out at a certain production interval, therefore, the work of drawing samples in the production process can also be performed by the machine, which is more convenient.
When these two schemes are combined together for the quality inspection of steel drums, the respective roles are different. The role of the adjustment-type sampling inspection program is to determine the number of samples to be tested, the number of acceptances, and the number of distances to be collected according to the production volume or stacking quantity of steel drums and the quality level of steel drums (Table 1), and convert them according to (Table 2). The rules are converted. The role of the equidistant type sampling program is to provide a method of sampling. Combining the two to form a complete inspection program is of great significance to the quality inspection of steel drums. First of all, these two kinds of schemes are based on the spot inspection characteristic curve, accord with the binomial distribution and Puhuasong distribution, the sampling error is small, the use is available, it can be used to estimate the overall quality level, and secondly, due to the adjustment type sampling inspection. The scheme includes a set of schemes that can be converted into each other. Therefore, it can be used not only for the acceptance of steel drums, but also for the dynamic control and supervision of the drum production process. Finally, the number of samples can be determined without using a complicated formula ( Directly check the table a), easy to use, easy to implement.
Therefore, the inspection and control of the quality of steel drums by the count-adjusting and isometric sampling programs is scientific and simple and easy.
For example, according to the Ministry of Commerce's Food System “200-liter Closed-barrel Steel Quality Inspection Regulations”, our factory previously conducted 18 routine inspections on finished products. Since the sampling inspection is carried out after all the products are produced, it is equivalent to the “postmortem autopsy” and cannot reach the control of the product quality in the production process. It is also extremely inconvenient to carry out manual number sampling after the products are stacked. With the "count adjustment and isometric sampling method", the product is electronically or mechanically counted (such as the counting device for the crimping machine at Shanxi Water Machinery Factory), random closure, sampling is convenient, testing is performed simultaneously with production, and product quality information The timely feedback has played a role in supervising, controlling and ensuring the product quality in the production process. At the same time, the product quality of the process is detected and controlled manually by this method, and the quality of the process product is also improved.
Fourth, the implementation of the program (a), steps:
1. First determine the quality level of the drum and the number of batches (parents). The general quality level can be based on the product's national standards, ministerial standards, corporate standards, or agreed standards with the user; the volume (maternal) quantity is given in Table 1 according to the principle of large batch size and large sample size. For example, the general quality level of steel drums in our factory is 2.5% (nonconforming product rate) and the batch size is 151-280.
2. According to the batch (maternal) number and quality level, check the table to determine the number of normal, tightened, and relaxed plans (n), the number of acceptances {Ac), and the number of rejections (Re).
3. Use an isometric sampling scheme to draw a sample (1) The stacked, flat steel drums will be numbered in order from left to right (or top to bottom, or in order). According to the number of drums produced, make the same number of tickets and number them sequentially. If the number is 97, then the first steel drum is No. 97, and one will be taken (not back). If the number is 88, the second The barrel number is number 88... and so on, numbering all steel drums. Steel drums in production may not be numbered. According to the sampling distance, sampling buckets may be randomly selected and collected.
(2) According to the formula h = N / n to calculate the sampling distance (N in the formula represents the number of mothers. n indicates the number of samples. H indicates the sampling distance), and then sampled according to the sampling distance. In the production process, qualified manufacturers can also mechanically count and mechanically sample according to the sampling distance.
4. Detect the extracted sample according to the quality inspection item of the steel drum. Determine the quality of the drums and their direction of change.
(1) First, determine whether the batch of steel drums pass or fail. If the non-conforming product is less than or equal to the number of acceptances, judge that the batch of products is qualified before accepting it. If the rejected product is greater than or equal to the rejected quantity, determine the batch of steel drums. Failed or full inspection.
(2) After several batches of steel drums are tested, they shall be converted according to the rules in Table 2 in order to control the product quality in the production process.
(II) Example: Set up a factory with N=250 steel drums per class, requiring the quality level to be AQL=2.5%, and formulate a sampling inspection plan for the batch of steel drums.
Steel barrel adjustment type sampling plan (Table 1)

(Continued in Table 1)

1. According to N=250 and AQL=2.5%, the sample size (n), the number of acceptances (Ac), and the number of rejections (Re) at various degrees of strictness can be found in the table. See (Table 3)
Drum counter adjustment and isometric sampling schedule (Table 3)
Known batch N=250, quality level AQL=2.5%

That is, from the 250 steel barrels of the class, under the normal inspection conditions, the number of samples in the inspection table is n=32, the number of acceptances is Ac=2, the number of rejections is Re=3, and the sampling interval is h=8. For steel barrels in production, one for every eight intervals. A total of 32 barrels were drawn for testing. If the test result is within 2 rejects, the batch is accepted and accepted; if the test result is more than 3 rejects, the batch is considered unqualified and not accepted, and after processing in the workshop Re-delivery inspection. Under relaxed inspection conditions, when the number of unqualified items in the sampling inspection is 2, it exceeds the acceptance number 1 and is lower than the rejection number 3. It can be determined that the batch of steel drums is qualified, but it will return to the normal inspection in the next batch, that is, For qualified conditions.
2. After testing several batches of barrels, convert them according to the rules in the table below. See Table 2.
Drum sampling conversion rules (Table 2)

V. Problems that need attention and research (1). Practical conditions of the plan:
1. The production of steel drums must be continuous line production. The larger the batch, the better the practical effect.
2. Production must be in a stable state. When trial run, trial production, and production are not in stable anger, this plan cannot be used.
3. Quality management personnel must have a certain amount of mathematical statistics and quality management quality; they must strengthen comprehensive quality management education for workers and emphasize the three-level inspection system.
4. The key items of product quality should be tested. For example, the steel drum leakage test shall be checked by the production workshop and the inspector shall make a random inspection.
(b) Dealing with defective products:
1. Disposal of unqualified batches: For unqualified batches that have been tested and judged, in principle, they will be returned to the production workshop. After picking out unqualified products, the inspector will perform sampling inspection according to the above method. If it is detected that the number of nonconforming products is less than or equal to the number of acceptances, then the batch of products is deemed to be acceptable. If the number of nonconforming items is still greater than or equal to the number of rejected products, the batch of products is deemed to be unqualified. And require the production workshop for full inspection.
2. Disposal of non-conforming product: The non-conforming product found in the inspection process shall be returned to the production workshop for repairs, exchanges, repairs, and exchanged products, and shall also be accepted after inspection.
(c) Simplification of inspection items:
The workload of steel drum quality inspection is largely determined by the number of inspections and the degree of difficulty of inspections. Therefore, strengthening process quality control and simplifying inspection items has become a problem that should be carefully studied.
1. Modification of GB325: Testing items are based on product standards. In the past few years, the GB325 has played an important guiding role in the production of barrels. However, in the implementation, many can makers have found some problems that need to be modified. For example, there are too many routine inspection items; product classification is too strict, testing workload is large; paint film thickness and paint film adhesion are not easy to detect. The formulation of product standards must first meet the principle of improving product quality and facilitating implementation. Therefore, when modifying standards, serious consideration should be given to simplifying the detection of items.
2, in the process of production of steel drums in the process of product quality testing and finished product testing, should create some special cards measuring tools and tooling. For example, test presses, tools to ensure the distance between the two holes, cutting tooling, threaded plugs, etc.
In general, the "count-adjustment and isometric sampling program" is a scientific and easy-to-use method based on total quality management. It will play a decisive role in improving the quality of steel drums and raising the scientific management level of steel drum production.