Definition
A scraper fineness meter, also known as a fineness scraper or fineness meter, is a physical inspection instrument used to determine the degree of dispersion of pigments or solid particles in fluid materials such as coatings, inks, and slurries. It cooperates with a scraper with a specific structure of scrape groove to scrape the sample into a film with decreasing thickness, and evaluates the fineness or maximum particle size of the particles by observing the film morphology, so as to judge whether the grinding process and dispersion quality meet the requirements.
Principle
The core working principle of scraper fineness meter is based on the geometric relationship of the wedge gap and visual alignment. The instrument body typically contains a finished rectangular metal plate with one or two wedge-shaped grooves engraved from deep to shallow. The depth of the groove decreases uniformly along the length, e.g. from a certain depth value to zero. When the operator places an appropriate amount of sample at the deep end of the groove and scrapes it along the groove at a constant speed and pressure using the matching scraper, the sample is scraped into a film with a continuously decreasing thickness. Where the film is thinner, larger particles can bulge or create scratches. The observer uses the naked eye or auxiliary light source to find the critical position where the particles appear, and the groove depth scale value corresponding to this position represents the maximum particle size or fineness value of the particles in the sample that significantly affect the surface.
The relationship between depth and position can be expressed as: H = H0 - (H0/L) × X。 where H is the groove depth at the current position, H0is the maximum depth at the beginning of the groove, L is the effective scraping length of the groove, and X is the distance from the start to the observation point. This linear relationship ensures a direct correspondence of the scale readings.
Measurement method
The measurement process needs to follow relevant standard methods, such as GB/T 1724, ASTM D1210, ISO 1524, etc. First, make sure that the instrument and sample temperature are close to the standard test temperature, usually 23±2°C. Clean the scraper and scraper with a suitable solvent and dry thoroughly. Take a sufficient amount of sample and drop it in front of the deepest end of the groove. Holding the scraper in both hands and aligning it perpendicular to the surface of the scraper and at a 90-degree angle, smoothly and evenly pull the scraper through the entire groove length within 1 to 2 seconds to form a flat film of the sample. Immediately after scraping, observe at an angle of 15 to 30 degrees from the plane of the scraper under standard lighting conditions to look for the demarcation line where particles accumulate or scratches begin to appear in large numbers. The scale value corresponding to this dividing line is the fineness reading, usually in microns. Multiple parallel assays are recommended to improve the reliability of the results.
Influencing factors
The accuracy of the measurement results is influenced by several factors. The rheological properties of the sample itself, such as viscosity and thixotropy, affect the uniformity of the film after scraping and the rate at which the particles settle. Environmental conditions, especially temperature, can alter sample viscosity and thus affect scraping behavior. Operating techniques are key human factors, including uniformity of scraping speed, stability of applied pressure, and maintenance of scraper angle. The instrument's own condition, such as the wear and cleanliness of the scraper groove and blade edge, as well as the ambient lighting conditions and viewing angle, will have a direct impact on the interpretation of the demarcation line. Therefore, standardized operating procedures and regular calibration of instruments are essential.
Applications
Scraper fineness meters are widely used in industrial fields where quality control of particle dispersion fineness is required. In the coating industry, it is used to detect the grinding fineness of pigments and fillers in products such as color paints, varnishes, and primers, which directly affects the gloss, color uniformity and protective performance of the coating. In ink manufacturing, it is used to control the fineness of printing ink to ensure the clarity and color performance of printed products. In addition, the instrument is often used for quality inspection and process monitoring in the R&D and production process of electronic paste, ceramic glaze, dye, cosmetic paste, magnetic materials, and certain greases and paste products in the petrochemical field.
Selection considerations
The selection of scraper fineness time should be considered based on the main testing needs and the standards to be followed. The primary parameters are the range and scale, and the common range is 0-25μm, 0-50μm, 0-100μm, 0-150μm, etc., which need to cover the expected fineness range of the sample to be tested. The second is the scale index value, which should be selected according to the required accuracy, such as single scale or double scale. The material of the instrument is usually hardened stainless steel, and its wear resistance and corrosion resistance directly affect the service life and measurement stability. The standards met are also an important basis, and it should be confirmed whether the instrument design and scale meet the provisions of the target country or industry standards. In addition, the material and size of the matching scraper must match the scraper, and some applications may require explosion-proof or special material requirements. Ergonomics of operation, such as the weight of the instrument, the feel of the hold, and the availability of standard illumination sources or observation plates as accessories, also contribute to ease of use and consistency of results.