ISO 8791-4 pdf download – Paper and board-Determinationof roughness/smoothness (air leakmethods)一 Part 4: Print-surf method

ISO 8791-4 pdf download – Paper and board-Determinationof roughness/smoothness (air leakmethods)一 Part 4: Print-surf method.
Note that the spring loading in the protective collar (5.2.3) 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 final 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/cm2) Is available on most Insruments, but Is not acceptable for use with this part document because or a tendency for air to leak under the guard lands
Variable-area flowmeter measurement systems shall have a pressure gauge fitted to the instrument to indicate the clamping pressure, which shall be ad)ustable. 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 8.3.
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 AnnexA). The tlowmeters 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 sm, based on automatic measurement of pressure difference, over the range 0.6 urn to 6,0 tm. The value displayed shall be the value calcubted 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 x 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. Hefore use on any particular day, check the system for leakage as specified in 8.1.
8.1.3 Damage to the sensing head is detected as follows:
a) Carefully wipe the face of the sensing head with a lint- and oil-free, soft clean material.
b) Clamp a smooth scratch-free piece of 125 pm thick film, such as cellulose acetate, between the
sensing head and the hard hacking. Measure the air flow.
c) This test is very sensitive to dust, due to static charges and even to fingerprints. If a muasurble flow is found, carefully wipe the surface of the Film and repeat the test.
d) It Is recommended that a suitable film be obtained from the Instrument manufacturer/supplier.
e) If it is impossible to obtain a zero reading on the lowest range flowmeter, confirm damage by Inspecting the measuring surface at a magnification of about 50 with a stereoscopic microscope. On impedance instruments, a reading greater than 0,8 pm indicates the possibility of damage.
1) II pits or scratches arc apparent, replace the sensing head
B.2 Sensing head
At frequent intervals, inspect the head, preferably with a stereoscopic microscope, to ensure that the gaps between the measuring land and guard lands are free from debris. If necessary, clean as advised by the instrument manufacturer.
B.3 Pressure gauges
Whenever the instrument is used, check that both gauges register zero when the air supply is disconnected.
At least once a year. check the accuracy of pressure gauges and transducers by connecting in parallel a manometer or transducer, the latter having been calibrated against dead weights. Operate the instrument normally and record the actual static pressures achieved.