BS ISO 8791-5:2020 Paper and board – Determination of roughness/smoothness (air leak methods) Part 5: Oken method.
5 Apparatus
5.1 Oken Smoothness apparatus (two types)
Use either the water column type described in 52 or the electronic sensor type described in 5.3.
5.2 Water column type
5.2.1 The water column type, see Figure 1. consists of an air compressor, filter, pressure regulator, water column regulator, capillary, water column manometer, measuring head, and scale plate. The measuring head, see Figure2., consists of a loading weight, rubber plate, and sensing head. The loading weight and rubber plate, the loading weight has a circular even surface of not less than 48 mm in diameter and a mass that clamps the test piece at a pressure of (98,1 ± 1,0) kPa. The rubber plate has a diameter of not less than 48 mm, a thickness of (4 ± 0,2) mm, a hardness of (50 ± 5) IRHD in accordance with Iso 48, and a rebound resilience of not less than 62 % in accordance with ISO 4662. The sensing head, has 10 concentric measuring lands and nine grooves. The outermost measuring land has a width of (0,5 ± 0,03) mm, and an outside diameter of (46 ± 0,03) mm. The width of the other nine measuring lands is (1 ± 0,03) mm. The inside diameter of innermost measuring land is (9 ± 0,03) mm. All grooves have a width of (1 ± 0,03) mm, and a depth of 0,5 mm to 1,2 mm. Five grooves have air outlet holes and four grooves have air inlet holes arranged alternately. A tube connects the sensing head to the pressure measuring chamber. The air compressor and regulator, supply compressed and filtered air. The air is controlled to approximately 10 kPa by the air regulator. The water column regulator and capillary, provide a constant pressure. The water column regulator consists of a water tank with an internal diameter of approximately 100 mm and a height of approximately 700 mm, and a constant pressure chamber with a side tube. The open end of the side tube is (500 ± 0,5) mm below the water surface.
The air at approximately 10 kPa introduced into the constant pressure chamber is controlled to (4,90 ± 0,01) kPa (500 ± 1 mmH2O) and transferred to the pressure measuring chamber through the capillary.
The capillary consists of a narrow tube made of stainless material with an inner diameter of approximately 0,3 mm and a length of approximately 50 mm. The capillary length shall be strictly adjusted so that constant K in Formula (1). see is 100.BS ISO 8791-5 pdf download.