Due to their characteristics, pharmaceutical powders (especially traditional Chinese medicine powders) are prone to screen clogging during the sieving process, leading to reduced production efficiency, loss of screening accuracy, and even cross-contamination. Resolving clogging issues is key to ensuring drug quality and improving production capacity. Coreal Machinery has compiled some information for your reference.
I,Analysis of Drug Powder Characteristics and Causes of Blockage
Drug Powder Characteristics
- Hygroscopicity: Medicinal herbs with high sugar content, such as Rehmannia root and Ophiopogon japonicus, are prone to moisture absorption and agglomeration.
- Electrostatic adsorption: In dry winter conditions, particles tend to adhere to the equipment walls.
- Particle size variation: Fine powdered herbs tend to accumulate in pipes.
Main Causes of Blockage
- Uneven particle size; excessive fines lead to accumulation on the screen surface.
- High material humidity or viscosity easily forms lumps that clog the pores.
- Improper screen mesh selection, mismatched with material particle size.
- Excessive screening speed exceeds the equipment's processing capacity.
- Inadequate screen cleaning leads to hardened residual material and blockage.
II,Design and Selection Solutions
Optimization of Screen Structure and Materials
- Bouncing Ball Cleaning System: The most classic and effective anti-blocking design. A ball support plate is installed below the screen, housing silicone or pharmaceutical-grade polyurethane bouncing balls. During operation, the bouncing balls continuously impact the bottom of the screen, effectively breaking up and ejecting particles stuck in the mesh.
- Ultrasonic cleaning system: Bouncing balls may be limited in effectiveness for extremely fine, highly viscous, and highly static pharmaceutical powders. The ultrasonic system transmits vibrations at a frequency that prevents particles from adsorbing and becoming lodged in the mesh.
Advantages: Excellent anti-clogging effect, particularly suitable for fine screening; improves screening efficiency and throughput; and extends screen life.
- Screen Material:
Stainless steel woven mesh: The most commonly used, but pay attention to the wire diameter and surface finish. Choose a smooth, polished surface to reduce adsorption.
Electroformed screen: Produced through an electroplating process, it features precise hole shapes, smooth, burr-free walls, and a high open area ratio, fundamentally reducing the risk of clogging. While costly, it is an ideal choice for high-value, difficult-to-screen pharmaceutical powders.
Screen Frame Design and Sealing
- Main-and-Sub-Screen Design: Utilizes a two-layer screen structure. The bouncing balls bounce between the two layers, enhancing cleaning effectiveness while protecting the working screen from deformation caused by ball impact.
- Quick tensioning and disassembly mechanisms：such as airbag tensioning screen frames, ensure uniform surface tension on the screen, eliminating slack areas. This ensures even material movement and reduces accumulation in depressions. The quick-release design allows for quick disassembly and cleaning, minimizing downtime.
III,Process and Operating Parameters
Feed Control
- Uniform Feeding: Use a screw feeder or vibrating feeder to ensure that the material is spread evenly across the screen surface. Avoid dumping large amounts of material, as excessively thick layers can lead to blockage and reduced efficiency.
- Pre-cleaning and Pretreatment: Pharmaceutical powders containing noticeable lumps or fiber nodules should be pre-treated by a coarse screen (such as a rotary vibrating screen or crusher) to reduce the burden on the linear vibrating screen.
Screening Parameter Adjustment
- Vibration Motor Angle:
The combined angle of the two vibrating motors in a linear vibrating screen directly affects the speed and dispersion of material on the screen surface. Appropriately adjusting the angle can optimize material conveying and screening efficiency.
- Amplitude and Frequency:
Large amplitude: The material is thrown with great force and conveyed quickly, which facilitates impurity removal, but may affect screening accuracy and screen life.
Small amplitude: The material is more easily dispersed, and fine powders are more likely to pass through the screen. However, slow conveying may result in an excessively thick material layer.
Recommendation: For materials prone to clogging, a "high frequency, low amplitude" mode can be used to maintain material flow while providing sufficient screening force.
IV,Cleaning and Maintenance
- In-line Cleaning System: High-end Linear Vibrating Screens can be equipped with a CIP system. After a batch, cleaning nozzles on the screen box automatically spray water for injection or detergent to clean the screen and interior, followed by air drying. This significantly reduces the intensity of manual cleaning and the risk of cross-contamination.
- Thorough Manual Cleaning:
- A standard operating procedure must be established to specify a thorough cleaning process after each batch or daily production.
- Disassemble all material-contacting components (screen, bouncing balls, seals, etc.).
- Use an appropriate cleaning agent (such as alcohol) for soaking, scrubbing, and rinsing. Allow to dry completely or blow dry with filtered compressed air before reassembly. Moisture is the primary cause of clogging and microbial growth, so complete drying is essential.
- This systematic solution significantly reduces clogging issues with linear vibrating screens in pharmaceutical powder screening, ensuring production continuity, product quality, and regulatory compliance.
Coreal Machinery is committed to providing you with high-quality screening equipment and industry solutions.