Roller screen is a type of equipment that consists of multiple circular rollers with sieve discs laid out side by side. Materials enter from the feed inlet and fall onto the sieve discs. The rotation of the discs drives the materials forward. The materials are classified based on the gap sizes between different rollers. Roller screens are commonly used in industries such as coal, mining, cement, sand and gravel aggregates, and waste recycling. They can handle materials with a maximum size of up to 2.4 meters and typically classify materials ranging from 10 to 100 millimeters, with a processing capacity ranging from 150 to 1800 tons per hour.

Problems encountered during the operation of roller screens:
As an efficient material screening device, roller screens have been widely applied in industries such as mining, metallurgy, chemical engineering, and building materials. The working principle is that multiple parallel rotating rollers drive the materials to roll along the axial direction and simultaneously complete the screening process, thereby achieving precise classification of solid particles. However, during actual operation, problems such as material retention, accumulation, and sieve hole blockage frequently occur, which have become the key technical bottlenecks restricting the continuous and stable operation of the equipment. These issues not only significantly reduce the screening efficiency and processing capacity but also accelerate the wear of critical components, thereby affecting the service life of the equipment and increasing the overall operation and maintenance costs. Components of roller screens:
Roller screens are mechanical grading devices with clear structures and definite functions. Their overall configuration is based on a modular design concept and mainly consists of four systems: the roller assembly, the drive system, the support frame, and auxiliary functional components. The roller assembly is the core execution unit of the entire machine, including multiple parallel arranged roller bodies, sieve discs (or sieve plates) installed on them, high-precision rolling bearings, cast iron or ductile iron bearing housings, elastic pin couplings or membrane couplings, etc.

The rollers are typically made of Q345B or 42CrMo alloy steel, which are subjected to quenching and tempering treatment and surface hardening to ensure good bending strength and wear resistance. The sieve discs can be made of perforated steel plates, cast manganese steel comb plates, rubber composite elastic sieve plates, or ceramic inlaid wear-resistant discs, depending on the characteristics of the materials. This not only ensures the screening efficiency but also takes into account the service life and ease of replacement.

The center distance between adjacent rollers is generally controlled between 120 and 300 millimeters. Through precise assembly, the gap between the rollers is ensured to be uniform and stable. This gap forms the dynamic sieve holes, whose effective opening size depends not only on the roller spacing but also on the outer diameter of the sieve discs, the height of the protruding ribs, and the movement posture of the materials. The actual screening particle size range usually covers 15 to 200 millimeters, making it suitable for the pre-screening and grading of medium and coarse-grained materials.

The drive system provides stable and controllable power input to the rollers. It mainly includes three-phase asynchronous motors, hard-toothed surface parallel shaft reducers, safety couplings, and the corresponding electrical control cabinets. The motor power is selected based on the processing capacity (typically 150 to 1800 tons per hour) and the bulk density of the materials. The output end of the reducer drives the first roller through chain transmission or direct connection, and the remaining rollers are rigidly linked through synchronous gear sets or double-row sleeve roller chains to ensure that all rollers rotate at the same speed and are in phase, avoiding material segregation or local blockage caused by asynchrony.

The sieve frame and support frame together form the load-bearing skeleton of the equipment. The sieve frame is a rectangular welded frame for carrying the roller assembly, with adjustable sliding grooves inside for fine-tuning the position of the rollers. The support frame is an overall floor-standing support structure, welded from thickened steel sections, with adjustable foot bolts and vibration damping pads at the bottom to adapt to uneven foundations and suppress operational vibrations.

The protective cover is a fully enclosed side plate and top cover structure, usually made of Q235 steel plates or stainless steel, providing dust-proof, noise-reducing, and personnel protection functions. The comb plate, as a crucial auxiliary component, is installed above or on both sides of the feeding end of the screen shaft, arranged at an incline. It is used to initially break up agglomerated materials, guide the material flow to be evenly distributed at the starting section of each screen shaft, and effectively prevent large foreign objects or flexible impurities from entangling the screen shaft, significantly enhancing the stability of the feed and the continuous operation of the equipment. All components of the entire machine are designed and matched in accordance with the ISO 286 tolerance standard. Key connection points use high-strength bolts and apply specified preload to ensure structural integrity and functional reliability during long-term operation.

Reasons for material accumulation on the screen surface:
The primary cause of material accumulation is the blockage in the screen surface and the area around the screen shaft. When the screen shaft is jammed by large foreign objects or when the screen surface accumulates adherent substances such as coal powder, mud, and oil, the screening capacity and classification accuracy will be significantly weakened, which will then lead to local or even overall blockage, creating a vicious cycle. Existing technical literature generally points out that the easy clogging of screen holes is a typical technical challenge faced by roller screens in practical applications and is also the most direct structure-process coupling factor causing material accumulation.
The formation mechanism of screen hole blockage can be summarized into three typical patterns: the first is particle jamming blockage, which occurs when the feed contains particles with a diameter close to the equivalent diameter of the screen hole (usually 0.8 to 1.2 times the screen hole size). Under the rotation of the screen shaft and the disturbance of the material, these particles are prone to instantaneous jamming and are difficult to dislodge by their own weight or inertial force. The second is adhesion blockage, which is common in handling materials with high humidity, high viscosity, or containing fine mud. Fine particles adhere to the edge of the screen holes and the surface of the screen plate under the action of moisture or surface tension, and accumulate continuously to form a dense adherent layer, gradually reducing the effective area of the screen holes. The third is debris blockage, which results from non-target impurities such as metal parts, wood chips, fragments of woven bags, and rubber blocks mixed in the raw material. These debris can entangle between adjacent screen shafts, hook onto the comb plate, or jam in the gaps of the screen plate, not only directly blocking the material flow path but also providing physical anchor points for the other two types of blockage. In engineering practice, the above three types of blockage mechanisms often present a composite and superimposed feature: the adhesion layer can increase the probability of particle jamming and reduce the kinetic energy for their dislodgement; while the local obstacles formed by debris significantly alter the flow field distribution, intensifying adhesion deposition and particle retention, thereby accelerating the blockage process. This multi-factor coupling mechanism further increases the complexity of the blockage problem, posing systematic requirements for equipment structure optimization, operation parameter control, and pretreatment process configuration.

Causes of roller screen blockage:
Due to its unique mechanical configuration and dynamic screening mechanism, roller screens exhibit several representative blockage forms during actual operation. The causes and evolution paths of these blockages are closely related to the structural parameters and material characteristics.
Screen shaft winding blockage: This type of blockage often occurs in the processing of materials containing flexible impurities. Due to the spiral, fan-shaped or comb-shaped distribution of screen plates or screen discs on the surface of the screen shaft, the geometric profile provides winding support points for fibrous materials (such as hemp, straw fibers), strips (such as plastic strapping bands, rubber strips) and slender foreign objects (such as wood chips, bamboo sticks). During the rotation of the screen shaft, these impurities are gradually wound in and layered, causing the distance between adjacent screen shafts to continuously narrow, ultimately blocking the axial material conveying channel and possibly triggering an overload of the transmission system.
Screen gap jamming blockage: The annular or rectangular gaps formed by the edges of adjacent screen plates or discs constitute the physical aperture for actual screening. When the feed contains particles with a size close to the equivalent width of the gap (typically 0.9 to 1.1 times the gap size), they are prone to instantaneous embedding under the combined action of centrifugal force, friction, and local vortices. Due to the lack of high-frequency vibration or reverse screening mechanism in roller screens, the embedded particles are difficult to dislodge during subsequent rotation cycles. Instead, they are further wedged under continuous rolling and squeezing, resulting in irreversible reduction of the effective flow area of the screen gap.
Adhesive thickening type blockage: For materials with high water content, high specific surface area or rich in colloidal components (such as wet coal slime, fermentation residue, bentonite, etc.), fine particles are prone to form an initial thin layer adsorption on the body of the screen shaft and the working surface of the screen plate. As the operation time increases, this adsorption layer continuously thickens. On the one hand, it effectively increases the equivalent outer diameter of the screen shaft, indirectly compressing the clearance between the shafts. On the other hand, it reduces the surface smoothness and hydrophobicity, further enhancing the adhesion tendency of subsequent particles. The resulting "adhesion - thickening - re-adhesion" positive feedback process eventually leads to a significant deterioration or complete failure of the screening function.

Solution to material accumulation and blockage of roller screen:
The comb plate developed by our company can be installed under each screen shaft, effectively reducing the blockage problem caused by easily entangled materials. It can effectively clean the material adhering to the screen plate and screen shaft, reducing the occurrence of blockage and material accumulation.

On the other hand, due to its unique mechanical configuration and dynamic screening mechanism, roller screen presents several representative blockage forms during actual operation. The causes and evolution paths of these blockages are closely related to its structural parameters and material properties.
Screen shaft winding blockage: This type of blockage often occurs in the processing of materials containing flexible impurities. Due to the spiral, fan-shaped or comb-shaped distribution of screen plates or screen discs on the surface of the screen shaft, the geometric profile provides winding support points for fibrous materials (such as hemp, straw fibers), band-shaped objects (such as plastic strapping bands, rubber strips) and slender foreign objects (such as wood chips, bamboo sticks). During the rotation of the screen shaft, these impurities are gradually wound in and layered, causing the distance between adjacent screen shafts to continuously narrow, ultimately blocking the axial material conveying channel and possibly triggering an overload in the transmission system.
Screen gap jamming type blockage:
The annular or rectangular gaps formed by the edges of adjacent screen plates or discs constitute the physical aperture for actual screening. When the feed contains particles with a size close to the equivalent width of the gap (typically 0.9 to 1.1 times the gap size), they are prone to instantaneous embedding under the combined action of centrifugal force, friction, and local vortices. Due to the lack of high-frequency vibration or reverse screening mechanisms in roller screens, the embedded particles are difficult to dislodge during subsequent rotation cycles and instead become further wedged under continuous rolling and squeezing, resulting in irreversible reduction of the effective flow area of the screen gap.

Adhesive thickening type blockage: For materials with high moisture content, high specific surface area, or rich in colloidal components (such as wet coal slime, fermentation residue, bentonite, etc.), fine particles tend to form an initial thin layer of adsorption on the screen shaft body and the working surface of the screen plates. As the operation time extends, this adsorption layer continuously thickens. On one hand, it effectively increases the outer diameter of the screen shaft, indirectly compressing the clearance between shafts; on the other hand, it reduces the surface smoothness and hydrophobicity, further enhancing the adhesion tendency of subsequent particles. The resulting "adhesion-thickening-re-adhesion" positive feedback process ultimately leads to significant deterioration or complete failure of the screening function.