Material blockage: the most common failures of screw conveyors
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Material blockage is one of the most common failures of screw conveyors. If not dealt with in time, it can lead to more serious problems such as motor overload and burnout or deformation of the screw shaft. The following are actionable solutions from three aspects: “Locating the Cause of Blockage,” “Emergency Handling Steps,” and “Long-term Preventive Measures.”
Ⅰ Quickly Locate the Cause of Blockage
Before dealing with the blockage, it is necessary to identify the cause to avoid blind operation. The common causes mainly fall into four categories:
• Imbalanced Feeding Rate: The actual feeding rate far exceeds the designed conveying capacity of the equipment(for example, increasing the feeding rate forcibly to pursue efficiency), resulting in material accumulation in the trough, beyond the pushing capacity of the screw blade.
• Material Characteristics Issues: The conveyed material has high humidity and strong adhesion(such as sludge, wet flour), or is prone to lumping(such as damp cement powder), which adheres to the screw blade and the inner wall of the trough, gradually forming a “material arch” that hinders the forward movement of the material.
• Outlet End Blockage: The manual gate valve or pneumatic valve at the outlet is not fully open, or there are foreign objects jammed inside the valve, preventing the material from being discharged smoothly and causing it to accumulate back in the trough.
• Component Wear and Failure: The screw blade, after long-term use, is severely worn (such as the edge becoming thin or having notches), reducing the effective area for pushing the material, and failing to convey the material to the outlet in time, resulting in material retention and blockage.
II. Emergency Handling Steps(Safety First)
• Immediate Shutdown and Power Off: Upon discovering the blockage, the first step is to shut down the feeding equipment (such as the feeder), press the emergency stop button on the control cabinet, cut off the power supply of the screw conveyor, and hang a “Do Not Close the Switch” sign at the power switch to prevent accidental startup and safety accidents.
• Clear Residual Material: Open the inspection cover on the top of the trough (if it is a sealed trough, loosen the cover bolts first), and use special tools(such as long-handled scrapers, air guns) to clean up the accumulated material. When cleaning, note that if the material is highly adhesive, you can first mix it with a small amount of dry material (such as quartz sand, dry sawdust, which must be compatible with the conveyed material) to reduce its adhesion before cleaning; avoid inserting hands directly into the trough to prevent cuts from residual material or components.
• Check Key Components: After cleaning, focus on checking whether the outlet valve is unobstructed (manually rotate the valve handle to ensure there is no jamming), and replace the valve if it is damaged; at the same time, check the screw blade for deformation or wear. If the blade wear exceeds 40%of its original thickness or there are obvious notches, replace the blade before restarting the equipment.
• Test Run and Adjustment: After restoring the equipment to its original state, first run it unloaded for 5 minutes to ensure the screw shaft rotates smoothly and without noise; then slowly start the feeding equipment, adjust the feeding rate to 70%–80%of the designed value, and observe whether the flow at the outlet is continuous and uniform. Gradually adjust to the normal conveying rate to avoid overloading again.
III. Long-term Preventive Measures(Reducing Blockage Frequency)
• Control Feeding Rate: Install a flow control valve or vibrating feeder at the inlet to feed material steadily according to the designed conveying capacity of the equipment (e.g.,25t/h), avoiding excessive instantaneous feeding rates; if using an automatic feeding system, set up a current warning in the control cabinet (e.g., automatically reduce the feeding rate when the current exceeds 110%of the rated value).
• Optimize Material Pre-treatment: For high-humidity, lump-prone materials, dry them in advance (e.g., reduce moisture to below 15% using a dryer), or install a crushing device (such as a jaw crusher) before feeding to crush lumps; for sticky materials, line the inner wall of the trough with polyethylene wear-resistant lining to reduce material adhesion.
• Regular Component Maintenance: Check the wear of the screw blade monthly, clean residual material inside the trough every quarter (especially after conveying corrosive or sticky materials); regularly check the outlet valve to ensure it operates smoothly and avoid blockages caused by valve jamming.
• Install Blockage Warning Devices: Install blockage sensors (such as ultrasonic sensors, rotary level switches) in the middle of the trough and near the outlet. When the material accumulates to the warning position, the sensor triggers an alarm and automatically shuts down the machine to avoid serious blockage in advance.
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