Roughness of paper is defined as the volume of air that, forced a specified pressure difference escapes in unit time by passing between the surface of the paper and a flat metal ring resting on the paper and exerting a definite pressure on int.
This method applies to all kinds of paper and paper-board and describes the testing of conditioned specimens
A measuring head with an air inlet tube on one side: on the bottom is a flat ring made of acid-proof steel: it has a mean thickness of 0.150 mm ± 0.002 mm and an inner diameter of 31.5 mm ± 0.2 mm. The range of the thickness readings should not exceed 0.004 mm. The mass of the measuring head should be 267.0 g ± 0.5 g .
An air flow meter, consisting of three rotameter tubes :
First tube - 10 to 150 ml/min
Second tube - 50 to 500 ml/min.
Third tube 300 to 3000ml/min
The rotameter tubes should allow these air flows to be determined with an error of less than 2 ml/min and 5 ml/min, respectively.