A screening machine is a vibrating screening device that uses the relative motion between bulk material and the screen surface to allow some particles to pass through the screen holes, separating sand, gravel, crushed stone, and other materials into different particle size grades. Based on the screen surface design, screening machines can be classified into several types.
1. Fixed Screen
The fixed screen is the simplest and oldest type of screening machine. The screen surface consists of many parallel screen bars, which are generally aligned with the direction of material flow on the screen. The screen surface is installed at an incline and remains stationary during operation. Material slides downward along the screen surface under its own weight and is screened in the process. The inclination angle can be between 35° and 45°. Depending on the size of the screen gaps, the screen surface can be made of round steel, square steel, rails, or T-shaped steel.
The advantages of the fixed screen include simple structure, no power consumption, no moving parts, and low equipment and operating costs. Its disadvantages are low processing capacity per unit area, low screening efficiency, and a large drop height during installation. Therefore, this type of screen is generally used only for screening materials with a particle size of 100 mm or larger. For fixed screen bars and support frames, Hansheng Automation provides custom machining according to customer drawings.
2. Roller Screen
The roller screen surface consists of multiple rollers arranged perpendicular to the material flow on the screen frame. Each roller is driven by a motor through chain or gear transmission to rotate in the same direction. Star wheels installed on the rollers strike and convey the material. Its production capacity and screening efficiency are higher than those of the fixed screen. To enhance material conveying, the screen surface is installed at an inclination of 12° to 15°. The roller screen has a sturdy structure, reliable operation, and stable running, but it is complex and heavy, and its production capacity and screening efficiency are relatively low. When the feed particle size is large, the roller screen is suitable for pre-screening raw coal.
3. Rotary Screen or Trommel Screen
The screen surface of a rotary screen is a cylindrical or conical screen drum, with a rotating shaft installed along the symmetrical axis of the drum. When the transmission device drives the shaft to rotate, the screen drum rotates as well. A conical screen drum is installed horizontally. Material is fed from the small end of the drum and is carried upward as the drum rotates. When it reaches a certain height, it falls back down under gravity, allowing fine particles to pass through the screen while coarse particles are gradually conveyed to the large end of the drum and discharged. For a cylindrical drum screen, the rotating shaft must be installed at an inclination of 3° to 5° to allow axial movement of material inside the drum.
The rotary screen operates smoothly and reliably, but it has low production capacity, easily clogged screen holes, and low screening efficiency. It is mainly used for screening coarse and medium-sized materials.
