The core factors influencing the removal of impurities from beans using an air-screen cleaner can be categorized into four main groups: airflow parameters, screen structure, material characteristics, and operational parameters. These factors must be optimized in concert to strike a balance between the “impurity content rate” and the “loss rate.”
I. Airflow Parameters (The Core of Air Separation)
Air Velocity and Volume: If the air velocity is too low, light impurities (such as straw, husks, and dust) will not be effectively blown away; conversely, if the velocity is too high, sound kernels are prone to being carried away by the airflow, resulting in an increased loss rate. The air volume must be matched to the specific size of the beans and the type of impurities present; this can be adjusted by altering the fan speed.
Airflow Direction and Distribution: The airflow must cover the entire screen surface uniformly to prevent localized variations in air velocity. The airflow’s directional angle influences the trajectory along which impurities are expelled; typically, a diagonal or lateral airflow arrangement facilitates the more efficient discharge of light impurities.
II. Screen Structure (The Key to Screening)
Screen Aperture Specifications and Layout: The apertures on the upper screen should be slightly larger than the beans to screen out large impurities (such as stones, clods of earth, and straw). The apertures on the lower screen should be slightly smaller to retain the beans while screening out small impurities (such as broken kernels and sand).
Screen Layers and Types: Multi-layer screens (typically 2 to 4 layers) allow for finer-grained classification. Common screen types include louvered screens (fish-scale screens), perforated screens, and woven-wire screens; louvered screens are well-suited for removing elongated impurities, perforated screens offer high efficiency, and woven-wire screens minimize kernel breakage.
Screen Inclination Angle: If the inclination angle is too steep, the beans will flow too rapidly, resulting in insufficient screening. Conversely, if the angle is too shallow, the material will accumulate and clog the screen apertures. For bean processing, an inclination angle of 3° to 6° is recommended, though this should be adjusted based on the specific size of the beans being processed.
Vibration Parameters: The amplitude and frequency of vibration determine the looseness of the bean mass and the probability of kernels passing through the screen apertures. To prevent kernel breakage—a critical concern when processing beans—the vibration amplitude should ideally be set between 3 mm and 6 mm, with a frequency of 50 Hz to 65 Hz, thereby balancing the need for effective impurity removal with the imperative to protect the integrity of the kernels.
III. Material Characteristics (The Fundamental Premise)
Bean Attributes: Factors such as size uniformity, density, and moisture content significantly influence the effectiveness of the separation process. Beans with high moisture content are prone to clumping and clogging the screen apertures; therefore, a preliminary drying treatment may be required. **Types of Impurities:** Light impurities (straw, hulls) are removed via air separation; heavy impurities (stones, soil clumps) are cleared by the sieve surfaces. When the proportion of mixed impurities is high, the synergistic operation of the air and sieve systems must be optimized.
Feed Rate: An excessive feed rate per unit of time leads to material accumulation and overloading of the sieve surfaces, resulting in an increased impurity content. Conversely, a feed rate that is too low results in low efficiency; the rate must be matched to the equipment’s rated processing capacity.
IV. Operational and Equipment Status
Feeding Uniformity:An excessively thick material layer can obstruct sieve perforations and disrupt airflow; therefore, it is essential to ensure uniform feeding and control the thickness of the material layer.
Equipment Maintenance: Clogged sieves, dust accumulation in the blower, and worn bearings can all reduce efficiency; regular cleaning of sieve perforations and maintenance of transmission components are required.
Optimization Recommendations
Determine Sieve Sizes First: The aperture size of the upper sieve should be slightly larger than the maximum dimension of the beans, while the aperture size of the lower sieve should be slightly smaller than the minimum dimension of the beans, thereby matching the size distribution of the impurities.
Adjust Air-Sieve Synergy: Gradually increase the airflow velocity until light impurities are completely blown away without any beans being blown out; simultaneously, adjust the sieve inclination angle and vibration parameters to strike a balance between minimizing impurity content and minimizing material loss.
Control Feed Rate: Feed material in accordance with the equipment’s rated processing capacity to ensure the material layer remains thin and uniform, thereby preventing accumulation.
Pre-treat Materials: If the moisture content of the beans is excessively high, dry them beforehand to reduce clumping and prevent clogging.
Perform Regular Maintenance: Clean the sieve perforations and inspect the blower and transmission components during every shift to ensure the stable and reliable operation of the equipment.
Post time: Mar-16-2026
