Internal blockage is one of the most common operational problems when running an impact crusher. It not only interrupts production but can also lead to serious damage if not addressed promptly. Understanding why blockages occur and how to resolve them is essential for any aggregate or mining operation.
What Does “Internal Blockage” Mean?
In an impact crusher, blockage refers to material accumulating inside the crushing chamber to the point where the rotor cannot rotate freely, or the discharge opening becomes completely clogged. This often results in the crusher stalling, excessive current draw, or even belt burning and rotor seizure.
Main Causes of Internal Blockage
1. Excessive Material Moisture or Stickiness
When the feed material has high moisture content (e.g., clay-rich ores, wet river gravel, or moist limestone), the fine particles tend to stick to the impact plates, blow bars, and the inner walls of the crushing cavity. As more material enters, these sticky layers build up, eventually narrowing or closing the discharge path.
2. Uneven or Over Feeding
If the crusher receives material at a rate exceeding its designed capacity – especially during startup or when the discharge conveyor is slow – material will accumulate faster than it can be ejected. A sudden surge of feed (like dumping a full loader bucket at once) can easily overwhelm the rotor and cause an instant blockage.
3. High Fines Content in the Feed
Feed material that already contains a large proportion of fine particles (smaller than the crusher’s closed side setting) tends to compact under the rotor’s impact. These fines do not exit quickly enough and form a dense plug at the bottom of the crushing chamber.
4. Over-sized or Extremely Hard Material
When feed particles are larger than the maximum allowable size (often specified in the crusher manual), they can get wedged between the rotor and the impact plates. Similarly, extremely hard materials (e.g., granite with high compressive strength) may not break on the first impact, causing multiple pieces to stack up and block the rotor path.
5. Worn Blow Bars or Impact Plates
As blow bars and impact plates wear down, the gap between the rotor and the impact racks increases. This reduces the crushing efficiency and creates “dead zones” where material tumbles without being properly fractured. Eventually, these unbroken pieces accumulate and cause a blockage.
6. Too Low Rotor Speed
Operating the rotor below its recommended speed reduces the kinetic energy imparted to the material. Heavier or larger pieces then fail to be thrown forcefully against the impact plates, leading to poor fragmentation and a higher risk of material building up in the lower part of the chamber.
How to Solve and Prevent Internal Blockage
Once a blockage occurs, the first priority is to safely clear it – and then implement measures to stop it from happening again.
⚙️ Stop feeding immediately – continuing to add material will only worsen the jam.
⚙️ Shut down the crusher and lock out the power source. Never attempt to clear a blockage while the rotor is still moving.
⚙️ Open the inspection doors or hydraulically open the upper frame (if equipped).
⚙️ Remove the accumulated material using tools like pry bars, shovels, or a front-end loader bucket, depending on the size of the crusher. In severe cases, a high pressure water jet or air lance can help break up sticky clumps.
⚙️ Inspect for any damage – check if blow bars, impact plates, or the rotor body have been cracked or bent by the jam.
Internal blockage in an impact crusher is rarely caused by a single factor. By controlling feed characteristics, maintaining a steady feed rate, and keeping blow bars and impact plates in good condition, operators can virtually eliminate unexpected blockages.
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