ISO 8791-4:2021 pdf download – Paper and board – Determinationof roughness/smoothness (air leakmethods)— Part 4: Print-surf method
ISO 8791-4:2021 pdf download – Paper and board – Determinationof roughness/smoothness (air leakmethods)— Part 4: Print-surf method.
Note that the spring loading In the protective collar (iZ.3) and the weight of the backing and its holder need to be taken into account. The rate of clamping shall be such that the pressure reaches 90 % of its linal value in about 0.4 s. and 99% of its final value in about 0,8 s.
NOTE 2 A third pressure of 490 kPa (5 kgf/cmZ) is available on most Instruments, but Is not acceptable (or use with thia part document because of a tendency for air to leak under the guard lands.
Variable.area fluwmeter mcasurenient 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 L3.
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 Ilowmeter Instruments shall be fitted with flowmeters which arc 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 he calibrated by the procedures outlined in AnnenC
5.3.3 Impedance instruments measure air leakage by means of iluidic impedance, a pressure transducer and a function generator They display or print the roughness, in micrornetres to [1w nearest 0,1 pm. based on automatic measurement of pressure difference, over the range 0,6 pm to 6,0 pm. The value displayed shall be the value calculated after 3 s to 5 s.
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 olihe sample received.
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 z 100 mm. and their surfaces shall be identitied 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.
9.1 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. Before use on any particular day, check the system for leakage as specified in B.1.
9.S For a tester of the variable-area flowmeter type, select the lowest-range flowmeter which will give a reading greater than 20% of the scale range.
Always start with the highest-range Ilowmeter and turn the flow range selector switch successively to a tlowmeter of lower range, in order to avoid subjecting the low-range flowmeters to a high air flow.
9.6 Test the first test piece by the following procedure.
9.6.1 Variable-area flowmeter type
Set the sensing-head differential pressure to 6.2 kPa ± 0,1 kPa by adjusting the pressure from the low side.
NOTE I lithe pressure gauge Indicates differential pressure in metres of water gauge, 0.63 m is equivalent to 6,18 kPa.
NOTE 2 The pressure gauge on some instruments has been found to be sensitive to jolts and. if the adjustment Is made downwards from a higher pressure, the resulting pressure for a given scale reading will be higher than If the adjustment is made upwards from a lower pressure.
Clamp the first test piece under the sensing head, with the side to be tested uppermost. This operation can cause the reading on the sensing-head pressure gauge to change, but such a change may be ignored. Record the reading on the flowmeter to the nearest 0,05 pm, 3 s to 5 s after application of clamping pressure. Readings shall he taken level with the top of the flowmeter float. Select the lowest-range flowmeter which gives results greater than 20% of the scale range.
If the reading obtained is less than 20 % of the range of the lowest-range Ilowmeter, increase the sensing-head pressure to 19,6 kPa ± 0.5 kPa (2,0 m water gauge), All readings taken at this pressure shall be multiplied by 0,667 (for the background of this factor. see Annex A. frnnilajAJj) to give the roughness, in micrometres, unless the flowmeters are calibrated for this pressure.
9.6.2 Impedance type
Place a test piece under the head with the side to be tested uppermost. Clamp the test piece either automatically or manually. Record the reading, 3 s to S s after application of clamping pressure.
9.1 Repeat step 9.6 for the other test pieces and calculate the arithmetic mean and standard deviation or coefficient of variation for the side tested. For variable-area flowmeter-type Instruments, do not repeat the procedure for selection of the appropriate flowineter and sensing-head pressure.