Rollers are one of the main components of a belt conveyor, accounting for a significant portion of the overall cost. Rollers are considered wear parts, and the quality of rollers directly affects the stability of the belt conveyor's operation. Damaged rollers can even scratch the conveyor belt, leading to greater economic losses. Therefore, it's essential to analyze the causes of roller wear, address them in the design and usage processes, and improve the efficiency and cost-effectiveness of belt conveyor operations.
1.Types of Belt Conveyor Rollers
Belt conveyor rollers come in various types, including:
-
Upper idler rollers, installed on the upper branch of the conveyor to support the conveyor belt and materials.
-
Lower idler rollers, installed on the lower branch to support the conveyor belt.
-
Impact idler rollers, installed on the loading section to absorb the impact forces of materials on the conveyor.
-
Transition idler rollers and alignment idler rollers, which are derived from these primary structures.
-
Common troughed upper idler rollers have a trough angle typically not exceeding 35° and are used for belt conveyors with an incline of less than 16°. Deep trough idler rollers, with trough angles of 45° and 60°, are used for conveyors with inclines greater than 16°. V-shaped idler rollers have a trough angle of approximately 10°. Forward-inclined idler rollers have a forward inclination angle usually less than or equal to 1.5° and serve to align the belt. A greater forward inclination angle enhances alignment but increases friction and resistance between the roller and the conveyor belt.
2.Main Forms and Analysis of Damage to Conveyor Rollers
(1) Common Forms of Damage to Conveyor Rollers
-
a. Roller Shell Wear: Typically, wear occurs in the middle of the roller shell, leading to eventual fracture. Some rollers can also experience wear at the points where they come into contact with the conveyor belt's edges.
-
b. Bearing Damage: This includes situations where the roller's bearings become less flexible, resulting in worn bearing points. Severe rust can also prevent the roller from rotating.
-
c. Roller Deformation: This damage form is more complex and may include significant bending and deviation angles that lead to increased friction between the shaft and the bearing seat, potentially causing seal damage.
Other damage forms may involve the roller shell detaching from the bearing seat, cracking, or bearings coming loose.
(2) Analysis of the Main Causes of Roller Damage
-
For the first form of roller damage: Complex factors can contribute to this type of damage. Common causes include high resistance to roller rotation, high friction between the roller and the conveyor belt, and misalignment between the roller's rotation direction and the conveyor belt's travel direction, leading to deviation friction. Adverse operating conditions for the roller, such as direct contact or friction with coal, rocks, or other materials, can also contribute to wear.
-
For the second form involving bearing damage: Common reasons include inadequate roller selection, leading to bearing damage due to exceeded bearing lifespan; poor sealing of roller bearings causing lubricating grease contamination, which in turn leads to poor lubrication and damage; insufficient or poor-quality lubricating grease during roller assembly, causing lubrication failure and damage; and inadequate overall design of the rollers, leading to resonance and accelerated bearing damage.
-
For the third form, where rollers deform and damage: Inadequate roller selection for the belt conveyor may lead to insufficient strength and rigidity to withstand the applied loads. Poor design of the belt conveyor, leading to localized areas of high roller stress, can cause overloading and deformation damage.
-
For other forms of roller damage: Poor manufacturing quality, inadequate bearing positioning, thin or poorly-welded roller shell, inadequate bearing installation, and other factors can contribute to these various types of damage.
3.Analysis of the Main Measures to Avoid Roller Damage
(1) Measures Taken in Design
The overall design and roller layout of belt conveyors should be rational to prevent localized overloading of rollers. The layout of troughing idlers in convex arc sections should have reduced spacing, increase the number of rollers, and decrease the load on individual rollers. The layout spacing of troughing idlers in convex arc sections is typically half the normal spacing. When subjected to higher loads, the spacing can be reduced further, and larger-sized rollers may be selected if necessary.
The selection of design parameters, such as belt speed, roller type, conveyor belt selection, and roller spacing, should be rational. It is crucial to avoid roller resonance and implement anti-resonance design in areas prone to resonance.
Roller selection should be based on the belt speed and the loads to choose suitable roller specifications (including roller diameter and shaft diameter). This ensures that roller design life, load-bearing capacity, and rotational speed requirements are met. Roller rotational speed is generally below 500 r/min but not exceeding 600 r/min. The national standard GB10595-1989 specifies that rollers should have a design life of 20,000 hours with a damage rate not exceeding 12% under normal operating conditions, but specific selection should meet user and design requirements for a design life of typically 30,000 hours.
Roller structure design should incorporate advanced sealing methods to ensure both effective and long-lasting sealing, while keeping rotational resistance to generally not exceed the values specified in standard MT821-1999.
Roller lubrication should be long-lasting, using high-quality lubricating grease, typically lithium-based, with a fill quantity generally set at two-thirds of the bearing clearance.
(2) Measures Taken in Roller Manufacturing
Roller shell processing should use dedicated fixtures to minimize pipe deformation during cutting and ensure compliance with roller rotational eccentricity requirements (meeting the values specified in standard MT821-1999). Dedicated bore machine tools should be used, allowing simultaneous machining of roller pipes at both ends where bearings are mounted, ensuring high concentricity.
During the welding of roller shell to bearing seat, the coaxiality at both ends of the bearing should be ensured to reduce additional resistance, enhancing bearing life.
Roller shaft processing should use dedicated machine tools for cutting material, end-facing, and center hole drilling, followed by precise center hole positioning at all locations to maintain concentricity. Special welding machines should be used during the welding of roller shell to the bearing seat, ensuring proper welding quality without voids or detachment and producing even welds. When assembling rollers, strict adherence to the installation process is essential to achieve accurate bearing fit, avoiding extra friction between inner and outer rings.
(3) Measures to Be Taken in Installation, Usage, and Maintenance
Enhance ventilation within the conveyor corridor, maintain reasonable temperature and humidity, and minimize dust to improve the working environment.
Install rollers flexibly, ensuring a clear space around them to prevent individual rollers from being buried in coal, ore, or other materials or from making contact and friction with other objects.
Install rollers with proper alignment to avoid poor contact with the conveyor belt and ensure that the direction of roller rotation matches the direction of the conveyor belt.
In normal circumstances, the top surfaces of rollers (except for self-aligning and transition rollers) should be in the same plane (horizontal or inclined) or on a common radius arc (concave or convex arc section of the conveyor). The height difference between adjacent sets of three rollers should not exceed 2 mm for fixed conveyors and 3 mm for extendable and suspended conveyors.
During conveyor belt operation, conduct regular inspections of rollers and replace damaged or less flexible rollers promptly to ensure the conveyor's reliable operation. In case of belt misalignment, correct it promptly to maintain proper conveyor operation. Rigorous on-site management and strict implementation of maintenance and inspection protocols are essential. These actions ensure the longest possible service life and highest performance of conveyor rollers, considering not only the quality of design and manufacturing but also maintenance and proper usage.
