BS ISO 8791-4:2021 pdf download – Paper and board — Determination of roughness/smoothness (air leak methods) Part 4: Print-surf method Variable-area flowmeter measurement systems shall have a pressure gauge fitted to the instrument to indicate the clamping pressure, which shall be adjustable. Impedance measurement systems shall have integrated pneumatic and electronic circuitry which automatically controls the clamping pressure. In each case, the actual pressure achieved shall be verified as specified in B.3. 5.3 Measuring system 5.3.1 The air-flow rate shall be measured with either a set of variable-area flowmeters or by measuring the pressure drop across an impedance. 5.3.2 Variable-area flowmeter instruments shall be fitted with flowmeters which are graduated to show the “cube root mean cube gap” between the paper and the measuring land surface, in micrometres (see Annex A). The flowmeters shall be calibrated by the procedures outlined in Annex C. 5.3.3 Impedance instruments measure air leakage by means of fluidic impedance, a pressure transducer and a function generator. They display or print the roughness, in micrometres to the nearest 0,1 µm, based on automatic measurement of pressure difference, over the range 0,6 µm to 6,0 µm. The value displayed shall be the value calculated after 3 s to 5 s. 6 Sampling If the tests are being made to evaluate a lot, the sample should be selected in accordance with ISO 186. If the tests are made on another type of sample, make sure that the test pieces taken are representative of the sample received. 7 Condition The sample shall be conditioned in accordance with ISO 187. 8 Preparation of test pieces Prepare the test pieces in the same atmospheric conditions as those used to condition the sample. Cut at least 10 test pieces for each side to be tested. The size of each test piece shall be 100 mm × 100 mm, and their surfaces shall be identified in some convenient way (for example, side one or side two). The test area shall be free of all folds, wrinkles, holes or other defects, and should not include watermarks. Do not handle that part of the test piece which will become part of the test area. 9 Procedure 9.1 Carry out the test in the same atmospheric conditions as those used to condition the sample (see Clause 7). 9.2 Ensure that the instrument is on a rigid horizontal surface free from vibration and that it is level....
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