Overview
EN ISO 787-18:1995 (ISO 787-18:1983) specifies a mechanical flushing procedure to determine the residue on a sieve for pigments and extenders dispersed in water. The method measures the coarse fraction (residue) retained on a specified test sieve after dispersion and flushing with rotating water jets. Results are expressed as a percentage of the test portion and are used for quality control and specification compliance of powders and granules that are insoluble in water. The procedure is not applicable to hydrophobic or pelletized materials.
Key topics and requirements
- Scope: Applies to pigments, extenders and other powders/granules insoluble in water; excludes hydrophobic and pelletized materials.
- Principle: Material is dispersed in water and subjected to centrifugal motion via rotating water jets; fines pass through the sieve while coarse particles remain and are weighed after drying.
- Apparatus essentials:
- Mechanical flushing unit with rotating jets/nozzles (nozzle diameter typically 1 ± 0.2 mm).
- Water pressure maintained at 300 ± 20 kPa (approx. 5 L/min flow with given nozzle sizes).
- Test sieves per ISO 565 (select nominal mesh aperture; 45 µm often used).
- Oven at 105 ± 2 °C, balance accurate to 0.1 mg, desiccator.
- Sample & preparation:
- Typical test portion: 5–50 g (up to 300 g for very low residue materials).
- Use wetting agents (e.g., 95% ethanol or sulphonates) when samples are difficult to wet; wetting agent must be recorded.
- Procedure notes:
- Carry out duplicate determinations; repeat if duplicates differ by more than 0.1% absolute.
- Flush until fine particles have passed (audible change), then continue flushing for a further 10 minutes unless validated shorter time is agreed and recorded.
- Dry residue and sieve, cool in desiccator, weigh and calculate residue:
- R (%) = ((m2 − m1) / m) × 100, where m = test portion, m2 = sieve + residue, m1 = empty sieve.
- Reporting: Include product ID, reference to ISO 787-18, nominal mesh aperture, wetting agent, test portion mass, any deviations, and mean of duplicates (or all values if disagreement persists).
Applications and users
- Used for quality control, batch acceptance, and specification testing in:
- Paints, coatings and varnish manufacturers
- Pigment and extender producers
- Independent testing and accreditation laboratories
- R&D and formulation labs assessing dispersion and particle-size-related performance
- Practical benefits: consistent measurement of coarse fractions, detection of agglomerates or extraneous matter, reproducible basis for supplier specifications and product acceptance.
Related standards
- ISO 787-7: Determination of residue on sieve - water method (manual procedure)
- ISO 565: Test sieves - woven wire cloth and perforated plate
- ISO 842: Sampling of raw materials for paints and varnishes
Keywords: EN ISO 787-18:1995, ISO 787-18, residue on sieve, mechanical flushing procedure, pigments and extenders, sieve analysis, test method, paint raw materials.
