Definition
A scraper fineness meter is a physical inspection instrument used to evaluate the degree of dispersion of solid particles in a liquid system. It characterizes the fineness or size distribution of particles by measuring the depth of particle appearance in the trench of a sample under specific conditions. The instrument has a wide range of applications in the quality control process of many industries such as coatings, inks, and chemical raw materials.
Principle
The core component of a scraper fineness gauge is a finished single- or double-slot plate with a groove depth that decreases evenly to zero along the length. To measure, place an appropriate amount of sample at the end of the groove with a large depth and use a scraper to scrape along the groove towards the shallow end at a constant speed and pressure. Particles in the sample larger than the depth of the slot form visible marks on the slot walls during scraping. Observe where these traces first appear steadily, and the groove depth value corresponding to this location is the fineness reading of the sample, usually expressed in microns.
The principle is based on geometry, and the relationship between reading H and particle size d can be approximated as:
d ≈ k · H
where k is the coefficient related to particle shape and instrument calibration. This measurement reflects the upper limit of the size of the larger particles in the sample.
Measurement method
Standard measurement processes typically follow relevant industry norms. First, ensure that the temperature of the instrument and the sample is stable, stir the sample thoroughly and drop it into the starting end of the trench, paying attention to avoid bubbles. The scraper is then held perpendicular to the plate surface and scrapes the sample across the trench in 1 to 2 seconds at a uniform speed. Immediately after scraping, under standard lighting conditions, observe the location of particle aggregation or scratches in the trench for the first time consecutively, and read the depth value corresponding to the scale line next to the location. The same sample often requires multiple parallel measurements to improve the reliability of the results.
Influencing factors
The accuracy of the measurement results is influenced by multiple factors. The characteristics of the sample itself, such as rheological properties, particle concentration, and dispersion stability, will directly affect the distribution of the particles after scraping. Operating conditions are critical, including the speed of scraping, the pressure applied, and the angle between the scraper and the plate, and any deviation can lead to uneven film thickness. Environmental conditions such as temperature and humidity can change the viscosity and volatilization rate of the sample. The condition of the instrument is the foundation, and the wear of the groove, the flatness of the scraper and the clarity of the scale need to be checked regularly. In addition, the observer's visual condition and interpretation experience are also human factors that need to be considered.
Applications
This instrument is mainly used in industrial fields where rapid quality control of particle fineness is required. In the coatings industry, it is used to detect the dispersion quality of pigments and fillers in paints, which is related to the gloss and durability of coatings. In the ink industry, fineness affects the color uniformity and clarity of printed products. This method is also often used in the R&D and production process of ceramic glazes, cosmetic slurries, magnetic material slurries, and some nanomaterial primary dispersions for process monitoring and product acceptance.
Selection considerations
The selection of scraper fineness meter should be judged comprehensively according to the specific application needs. The measurement range is the primary parameter that covers the expected fineness of the sample to be tested, with common ranges of 0-25 microns, 0-50 microns, 0-100 microns, and wider ranges. Groove type, single or double slot, double slot design for easy parallel contrast. The resolution and accuracy of the scale must meet the requirements of industry standards. The material of the instrument, usually hardened stainless steel or tool steel, determines its hardness and wear resistance. At the same time, consider whether it is equipped with a standard lighting source to uniformize the observation conditions and whether the manufacturer provides a traceable calibration certificate. Compliance with relevant international or national standards is a prerequisite for ensuring the comparability and credibility of measurement results.