BS ISO 8791-4 pdf free download
BS ISO 8791-4-2021 pdf free download.Paper and board – Determination of roughness/smoothness (air leak methods) Part 4: Print-surf method.
5.2.5 Two resilient backings, of different types, which can be held in the recessed holders by means of double-sided adhesive tape:
5.2.5.1 Soft backing, resilient, consisting of an offset printing blanket composed of a layer of synthetic
rubber, at least 600 pm thick, bonded to a fabric backing giving an overall thickness of 2 000 pm ± 200 pm.
The apparent hardness of the complete backing shall be 83 IRIID ± 6 IRHD (international Rubber
Hardness Degrees).
5.2.5.2 Hard backing, resilient, usually made from a polyester film bonded at its periphery to cork, offset blanket or similar material. A small exhaust hole shall be provided to prevent air being trapped between the film and the backing. The apparent hardness of the assembly shall be 95 IRHD ± 2 IRHD.
5.2.6 Clamping mechanism, allowing clamping of the resilient backing at pressures of either
980 kPa ± 30 kPa or 1960 kPa ± 30 kPa, the pressure being calculated from the total area of the measuring and guard lands.
NOTE I On some earlier instruments, these values can be displayed on the gauge as 10 kgf/cm2 and 20 kgf/cm2.
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 instruments, but is not acceptable for use with this part document because of 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 he 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 ‘l’he air-tlow 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 Aowmeter 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 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 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 S 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. Before use on any particular day, check the system for leakage as specified in Bi.
9.3 Select and fit the backing disc appropriate for the material being tested. In general, the hard backing should be used for papers that are to be printed by letterpress presses fitted with paper backings. Papers to be printed by other processes, and boards however printed, should be tested with the soft backing.
9.4 Select and adjust the clamping pressure, using the following as a guide:
— Hard backing letterpress 1 960 kPa ± 30 kPa.BS ISO 8791-4 pdf download.
