Definition
A laboratory sieve is an instrument used to separate and grade particle or powder samples by particle size. It mechanically sieves samples through a series of standard screens with different pore sizes, resulting in quantitative data on sample size distribution. This equipment plays an important role in quality control, R&D and production process monitoring, and its operation must comply with relevant international or national standards such as ISO 3310 and ASTM E11.
Principle
The basic working principle of laboratory screening is based on geometric screening. The instrument typically consists of a set of screens stacked from top to bottom by aperture diameter, with the receiving tray at the bottom and the cover plate at the top. When the sample is placed on the top screen, the sieve pile is vibrated, slapped or moved in a horizontal circular motion through a mechanical drive. In this process, particles smaller than the size of the screen hole fall through the screen into the next layer, while particles larger than the size of the screen hole are trapped on the current screen surface. After a period of screening for a specified period of time, the mass of residual material on each screen is weighed separately, according to which the particle size distribution of the sample expressed as mass fraction is calculated.
Measurement method
Laboratory screening is usually performed using dry or wet methods. Dry screening is suitable for dry, fluid and non-agglomerative particles. During operation, put the weighed sample into the top sieve, start the instrument operation set time, and weigh the weight of each sieve layer by layer. Wet screening is often used for fine particles or samples prone to electrostatic agglomeration with the help of water flow, through which the particles are driven through the screen, and finally the residue on the screen is dried and weighed. Both methods require a screening endpoint, where the mass of material passing through the screen per minute is less than a specific percentage (e.g., 0.1%) of the total mass of the sample. The screening results can be expressed as cumulative distribution or differential distribution, and its basic calculation formula is:
Mass percentage of a particle size interval = (Mass of sieve material / Total mass of sample) × 100%
Influencing factors
The accuracy and repeatability of screening results are influenced by several factors. In terms of sample characteristics, physical properties such as particle shape, density, agglomeration tendency, and surface electrostatic will significantly affect the pass rate. In the instrument parameters, the setting of screening time, vibration mode, amplitude and frequency should match the characteristics of the sample. Environmental conditions such as air humidity may cause fine powder adhesion. In addition, the manufacturing tolerances, wear degrees, and load of the screen surface of the screen itself also need to be checked and controlled regularly to ensure the consistency of the measurement.
Applications
Laboratory screening instruments have a wide range of applications. In the building materials industry, it is used to analyze the particle size gradation of sand and gravel and cement; In the food industry, it is used to monitor the fineness of flour and powdered sugar; In the chemical field, it is used to control the particle size of pigments and fillers; In metallurgical mining, it is used to determine the particle size composition of ores or metal powders; In environmental monitoring, it can be used for soil texture analysis. This technology provides basic data support for product performance evaluation, process optimization, and quality standard compliance verification in these industries.
Selection considerations
When choosing the right laboratory screener, there are many aspects to consider. First, it is necessary to clarify the characteristics of the sample, such as the approximate range of particle size, fluidity, brittleness, etc., to decide whether to choose a dry or wet model, and whether ultrasonic assistance or vacuum assistance is required. Secondly, according to daily flux and accuracy requirements, consider the degree of automation of the instrument, such as automatic weighing and result calculation functions to improve efficiency. The standard system for screens (e.g. ISO or ASTM) needs to be consistent with the common standards of the industry or region. The instrument's operational stability, noise level, ease of maintenance, and the supplier's technical support capabilities are also key considerations for long-term use. It is recommended to perform sample measurements before making a decision to verify the suitability of the instrument for a specific sample.