A screening machine is specialized process equipment designed to classify dried wood flakes into distinct size fractions: fine surface flakes, coarse core flakes, oversized rejects, and wood dust. It serves as an indispensable unit operation in the particleboard (PB) manufacturing process to ensure board density uniformity, surface smoothness, and structural integrity.
Industrial separation relies on two primary physical principles: mechanical sieving and pneumatic (air) classification. In high-capacity particleboard lines, mechanical screeners and air classifiers are routinely deployed in tandem to achieve optimal fraction purity and dust extraction.
1. Mechanical Screening Machines
Mechanical screeners are classified by their motion kinematics into gyratory (oscillating) screens, vibrating screens, and tumbler screens. Despite differences in drive dynamics, their core architecture consists of four primary assemblies: the screen housing, drive transmission, suspension and damping buffers, and the base support frame.
Gyratory Oscillating Screens
The screen housing incorporates multi-tiered wire mesh decks, dust-tight enclosures, an upper infeed chute, and discharge outlets. Material enters through the top inlet, where planar oscillating motion induces particle stratification:
The upper coarse mesh retains oversized wood chips and directs them to an oversize discharge chute for re-chipping.
Qualified flakes pass through the upper deck onto the secondary mesh deck, which retains core and surface particles and routes them to their respective process lines.
Wood dust and micro-fines pass through the lowest screen deck into the bottom collection pan for boiler fuel or exhaust extraction. Additional screening decks with varying mesh counts can be added to classify flakes into multiple discrete grades.
Suspension dampers and buffer linkages absorb harmonic vibration and constrain excessive horizontal displacement to protect the base structure.
Tumbler Screening Machines (e.g., BF Type)
Tumbler screens represent an advanced mechanical separation design widely adopted in continuous particleboard operations. Driven by a specialized eccentric counterweight shaft, the screen body executes a three-dimensional motion combining planar gyratory swinging with vertical tumbling. This compound motion keeps flakes rolling across the screen surface rather than bouncing excessively, preventing mesh blinding, enhancing particle stratification, and significantly improving fine-particle screening efficiency.
Hansheng Automation precision-machines custom eccentric drive shafts, heavy-duty bearing housings, and reinforced screen deck frames according to customer drawings, ensuring high fatigue strength and dimensional stability under continuous cyclic loads.
2. Pneumatic Air Classification Systems
Air classifiers utilize aerodynamic drag and buoyant forces to separate particles based on differences in their terminal settling velocities. Because thin, light surface flakes exhibit lower settling velocities than thick, dense core chips, controlled air currents selectively convey specific particle fractions. Air classification systems are generally categorized into suspension classifiers, throw-type classifiers, and vertical wind-sifters.
In a representative multi-stage air classification chamber:
- Dried flakes enter the upper sorting chamber through an airtight rotary valve or feed hopper.
- An upward crossflow air stream carries lightweight, fine surface flakes into a primary pneumatic collector (cyclone separator).
- Heavier fractions settle against the air stream and are guided along an inclined chute into the lower secondary classification zone.
- A secondary high-velocity air current strips out qualified core flakes into a dedicated collector, while heavy, thick, and knotty chips drop into the bottom rejection hopper for return to the flaker or hammer mill for re-refining.
We also manufacture custom wear-resistant guide vanes, adjustable damper plates, and precision mechanical drive couplings to support the maintenance and operational overhaul of industrial classification equipment.
