Definition
Vibrating screen is a screening equipment that uses the principle of mechanical vibration to classify particle size, solid-liquid separation, or impurity removal of granular, powdery, or slurry materials. It makes the screen surface periodically vibrate through the driving device, so that the material is thrown on the screen surface and moves forward, and the particles smaller than the size of the screen hole are separated through the screen hole, and the particles larger than the size of the screen hole are discharged along the direction of the screen surface. In the field of laboratory and industrial testing, vibrating screens are commonly used for sample preparation, particle size distribution analysis, and quality control.
Principle
The core working principle of the vibrating screen is based on directional mechanical vibration and screening motion. The drive motor drives the eccentric block or vibrator to rotate, generating periodic excitation forces that cause the screen box and the screen installed on it to vibrate in a specific direction (e.g. vertical, horizontal or elliptical trajectory). The material is affected by the vibration acceleration on the screen surface to produce a throwing motion, and the fine particles have the opportunity to pass through the screen orifice under the action of gravity and vibration, while the coarse particles move along the screen surface to the outlet. Its screening efficiency is closely related to the motion state of the material, and the throwing index D is commonly used to describe the vibration intensity, and the formula is:
D = (2πn)2a sinβ / (g cosα)
where n is the vibration frequency, a is the amplitude, β is the vibration direction angle, α is the inclination angle of the screen surface, and g is the gravitational acceleration. When the D value is within a certain range, the material can achieve effective layering and screening.
Measurement and operation methods
In laboratory testing, the operation of vibrating screens follows standard procedures to ensure reliable results. First, according to the characteristics of the sample and the target particle size range, the standard screen with the corresponding pore size is selected and stacked in order (usually decreasing pore size from top to bottom). Weigh an appropriate amount of dry samples and place them on the top screen, cover them and fix them on the vibrating screen host. Set vibration parameters such as time and amplitude to start the device. After the screening is completed, the materials on each screen are collected layer by layer and weighed to calculate the particle size distribution. During operation, attention should be paid to sample representativeness, environmental humidity control and screen cleaning to avoid clogging and cross-contamination. For difficult-to-screen materials, manual assistance or wet screening can be supplemented.
Influencing factors
The screening effect of the vibrating screen is affected by multiple factors. The material characteristics include particle shape, density, water content and electrostatic properties, among which too high moisture can easily lead to agglomeration and network blockage. In terms of equipment parameters, the vibration frequency, amplitude and inclination angle of the screen surface determine the motion state of the material; The screen aperture accuracy, weaving method and effective screening area directly affect the grading accuracy. Operating conditions such as screening time, feeding volume and uniformity also need to be reasonably controlled, and excessive feeding can easily reduce screening efficiency. Environmental factors such as temperature and humidity can alter material flow, and testing is required under standard conditions to ensure comparable results.
Applications
Vibrating screen is widely used in the field of testing and quality control. In the building materials industry, it is used for particle size analysis of sand and gravel and cement; The chemical field is used for powder coating, resin particle classification; Food and pharmaceutical industry to detect raw material powder particle size and impurities; processing soil and sediment samples in environmental monitoring; Mining laboratories are used for ore size composition determination. In addition, during the research and development process, the vibrating screen can be used to evaluate the characteristics of new material powders and optimize the process.
Selection considerations
When choosing a laboratory shaker, consider your testing needs and sample characteristics. The screening accuracy requirements determine the screen material and pore size standards, and common standards include ISO, ASTM or GB. The sample throughput affects the size and power configuration of the screen. For samples that are easy to agglomerate, consider slapping or ultrasonic net clearing. The equipment should have parameter adjustable functions to adapt to the vibration needs of different materials. In terms of safety, it needs to have good sealing to prevent dust from escaping, and the electrical system meets laboratory safety standards. Ease of maintenance, such as the ease of screen replacement and the clean design of the equipment, should also be evaluated.