Overview
ISO 8791-3:2017 - "Paper and board - Determination of roughness/smoothness (air leak methods) - Part 3: Sheffield method" specifies the established Sheffield test for measuring the surface roughness of paper and board. The standard defines the test principle, apparatus, calibration, sample preparation, conditioning and the procedure for determining Sheffield roughness (expressed as air flow in ml/min). It applies to papers and boards with Sheffield roughness values between 10 ml/min and about 3 000 ml/min and notes types of papers for which the method is unsuitable (soft papers that indent, high air‑permeance papers, or sheets that will not lie flat).
Key Topics and Requirements
- Principle: Measures the rate of air flow between two concentric annular lands and the sample surface under a specified pressure; air flow correlates to surface roughness.
- Apparatus: Air supply (clean, oil/water free), pressure regulators, flow‑measuring device (variable‑area flowmeters or electronic flowmeter), test assembly with measuring head and optically flat plate. Variable‑area flowmeters operate at ~10.3 kPa; electronic devices at ~9.85 kPa.
- Measuring head specifics: Two concentric annular lands, defined land widths and diameters, and a dead weight to apply a defined contact load (details and tolerances provided in the standard).
- Range & limitations: Designed for 10–3 000 ml/min. Not suitable for soft, highly porous, or non‑flat materials.
- Calibration & maintenance: Flowmeters must be calibrated against external standards; calibration frequency and care procedures are specified (Annexes A and B). Variable‑area instruments use three columns to cover the full range.
- Sampling & conditioning: Follow ISO 186 for sampling when assessing lots and condition samples per ISO 187 before testing.
- Results & reporting: Convert instrument readings to ml/min using calibration charts (Annex C), report arithmetic mean (to three significant figures), standard deviation/coefficient of variation, instrument type/range, conditioning atmosphere and any deviations (Clause 12).
Practical Applications
- Quality control and incoming inspection at paper mills and board manufacturers.
- Surface characterization to predict printability, ink holdout, coating behavior and tactile properties.
- Specification checking in procurement and supply chains where surface roughness affects converting, laminating, or printing performance.
- R&D and process optimization for papermaking, calendaring and coating operations.
Who Would Use This Standard
- Laboratory technicians in paper testing labs and QC teams in paper and packaging manufacturers.
- Printing and converting companies concerned with substrate surface properties.
- Standards bodies, test equipment manufacturers and product developers requiring a consistent method to compare surface roughness.
Related Standards
- ISO 8791 series (other parts covering air‑leak roughness/smoothness methods)
- ISO 186 - Sampling to determine average quality
- ISO 187 - Standard atmosphere for conditioning and testing
Keywords: ISO 8791-3, Sheffield method, paper roughness, paper and board, air leak methods, Sheffield roughness, flowmeter calibration, surface roughness testing.