3LIGHT WEIGHT PACKAGING SORTING PLANTS CONTROL 7. It must be verified that the materials are correctly selected, recording the result for each sampling in a characterisation sheet. The results obtained in the characterisation sheet are shown classified into requested and non-requested materials (Table 1). The requested materials are domestic light packages, and all other materials are those not requested. Quality control for selected material The objective is to analyse the quality of the various fractions of materials recovered in the sorting plants, controlling the error in the estimation of non-targeted material percentage with an error margin of 10%. Quality control can be performed on the bulk material or the material pressed in bales. The reasons for performing quality control on the materials recovered in the plants are the following: 1. Controls derived from annual scheduling (follow-up control). For material pressed into bales these controls will be limited to opening the number of bales indicated in the corresponding column of the Acceptable Quality Level in Table 2. 2. Control due to non-conformity. 3. Control due to first designation as recoverer/recycler. Bale quality control is performed using an AQL sampling system. This follows the sampling table method from MIL-STD-105D “Quality Control Manual” by J. M. Juran and Frank M. Gruyna. This control methodology is based on the following basic steps: • Obtaining the sample size according to the number of bales in the batch or in stock for each material, for a simple sampling and normal inspection level (level II). • Obtaining the number of accepted or rejected bales for the acceptable quality level selected as per Table 2. • Accepting or rejecting the batch or initial stock according to the number of rejected bales, referenced with the corresponding TSRM. If the number of rejected bales specified for the sample is reached, the batch or stock is considered to be non-conforming and identified accordingly. Selection of sample size in the quality controls. Table 2 Batch size Sample size Acceptable quality level (1) 2 to 8 2 2 9 to 15 3 2 16 to 25 5 2 26 to 50 8 3 51 to 90 13 4 91 to 150 20 6 (1) Number of bales not conforming to TSRM for rejecting the batch or stock. For sample sizes larger than those shown in the table above, the inspection level and acceptable quality must be studied.
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