Material Blockage in Plastic Extrusion Production Line: A Solution Manual for 3 Common Blockage Scenarios

In plastic extrusion production line, material blockage is a frequent fault that causes equipment downtime, reduced productivity, and even component damage. The feed inlet, screw compression section, and die head are the three core areas most prone to blockage. Many operators, due to improper handling methods, not only prolong downtime but also may cause secondary damage to the equipment. This article details emergency handling steps and long-term prevention plans for these three scenarios to help enterprises quickly resume production and reduce losses.

I. Feed Inlet Blockage: Emergency Resolution for Material "Bridging" and "Caking"

Feed inlet blockage often occurs during initial startup or when processing wet materials/powders, manifesting as material accumulation under the hopper that fails to enter the screw normally. The equipment exhibits symptoms such as "idling noise" and "no melt output".

1. Core Causes

• Excessive material moisture content, leading to caking when heated at high temperatures and blocking the feed channel;

• Overly high temperature below the hopper, causing premature melting and "wall sticking" of the material;

• Large impurities mixed in the material or excessive powder, forming a "bridging" structure.

2. Emergency Handling Steps (Shutdown Operation, Wear High-Temperature Gloves Throughout)

• Step 1: Safe Shutdown

Immediately press the equipment's "emergency stop" button, turn off the feeding motor and main motor, and cut off the barrel heating power (to prevent material degradation due to continuous heating in the blocked area).

• Step 2: Clean the Hopper and Feed Inlet

Remove the hopper and clean the accumulated caked material with a wooden or plastic shovel (metal tools are prohibited to avoid scratching the barrel inner wall). For bridging blockage, gently tap the outside of the hopper with a rubber hammer to break the material support structure and pour out residual materials.

• Step 3: Unclog the Feed Channel

Insert a dedicated rod into the feed inlet slowly and rotate it to unclog the wall-sticking material inside. For hard blockages, spray a small amount of release agent (e.g., silicone oil) into the feed inlet, let it stand for 5 minutes, then unclog.

• Step 4: Inspection Before Restart

Manually rotate the screw coupling to confirm no jamming. Reassemble the hopper, add a small amount of dry-cleaning material, start the feeding motor to test material delivery, and resume normal production only if there is no abnormality.

3. Prevention Measures

• Materials must be strictly dried before processing. Equip with an online moisture detector to monitor moisture content in real-time;

• The feeding section temperature must be set below the material's glass transition temperature. If necessary, install a cooling water jacket outside the hopper;

• Install a "double-layer filtration device" at the feed inlet: upper screen to filter large impurities, lower magnetic separator to adsorb metal particles. For powder processing, add an agitator in the hopper to prevent bridging.

II. Screw Compression Section Blockage: Solutions for "Uneven Melting" and "Insufficient Shear"

The screw compression section is the core area where materials transform from solid to molten state. Blockage is often characterized by "sudden rise in melt pressure" and "excessive screw torque", which in severe cases can cause screw jamming and motor overload tripping.

1. Core Causes

• Unreasonable temperature settings (compression section temperature below the material's melting point leading to insufficient melting; or excessive temperature difference between feeding and compression sections causing unbalanced melting speed);

• Mismatch between screw compression ratio and material (e.g., using a low compression ratio screw for high-filled materials, resulting in insufficient compaction and blocked melting);

• Sudden excessive feeding speed exceeding the screw's conveying capacity, causing material accumulation and compaction in the compression section.

2. Emergency Handling Steps (Professional Operation Required to Avoid Screw Damage)

• Step 1: Emergency Pressure Relief and Shutdown

Open the melt pressure relief valve (if equipped) to release die head pressure slowly. Immediately turn off the main motor, feeding motor, and heating system. Cut off the main power after the equipment comes to a complete stop.

• Step 2: Disassemble the Barrel and Clean

Remove the die head, flange, and other components, loosen the barrel fixing bolts, and translate the barrel axially. Clean the molten blockage in the barrel inner wall with a brass brush. Use 80-mesh sandpaper to gently polish the sticky material on the screw surface (avoid damaging the screw flight).

• Step 3: Inspect Core Components

Focus on checking if the screw flight in the compression section is worn and if the barrel inner wall is scratched. If blockage is accompanied by screw jamming, inspect for bearing and gearbox damage.

• Step 4: Reassembly and Commissioning

Reassemble the barrel and screw in their original positions, ensuring all gaskets are intact. Use "gradient heating" during startup. Start the main motor for 2 minutes of no-load operation, then slowly increase feeding speed to the normal range.

3. Prevention Measures

• Optimize the temperature curve based on material properties: for high-viscosity materials, set the compression section temperature 5-10℃ lower than the homogenization section; for low-viscosity materials, set it 5℃ higher;

• Select a screw with a matching compression ratio;

• Equip a "feeding-torque linkage control system" that automatically reduces feeding speed when the screw torque exceeds 80% of the rated value to avoid excessive material accumulation.

III. Die Head Blockage: Quick Solutions for "Impurity Clogging" and "Low Temperature"

The die head is the final link of melt molding. Blockage often manifests as "uneven product discharge" and "charred material at the die orifice", commonly caused by filter clogging and die lip material accumulation.

1. Core Causes

• Long-term failure to replace the filter, leading to impurity accumulation and blocked melt flow;

• Die head temperature set too low, causing melt solidification at the die orifice;

• Infrequent die lip cleaning, leading to long-term high-temperature carbonization of residual material and formation of charred material that blocks the flow channel.

2. Emergency Handling Steps (High Die Head Temperature, Wear Heat-Resistant Protection)

• Step 1: Pressure Reduction and Material Cutoff

Reduce the screw speed to the minimum, turn off the feeding motor, and after the die head pressure drops below 0.5MPa, turn off the main motor and die head heating power.

• Step 2: Disassemble the Die Head for Cleaning

Loosen the die head fixing bolts in a diagonal sequence with a wrench, remove the die head, and clean the blocked material and charred material in the die cavity with a heated dedicated scraper. For filter clogging, directly replace with a new filter.

• Step 3: Unclog Flow Channels and Die Lip

Use a rod matching the flow channel shape to clean solidified material in the flow channel. Insert a thin copper sheet into the die lip gap to scrape off residual material; sharp tools are prohibited to avoid scratching the die lip surface.

• Step 4: Restart and Test Run

Reassemble the die head, heat the die head to 10℃ higher than the normal production temperature, start the main motor for low-speed material delivery, and adjust to normal temperature and speed after uniform melt flows out of the die orifice.

3. Prevention Measures

• Equip a "twin-station automatic screen changer" that allows filter replacement without shutdown when melt pressure rises by 10%. Replace filters every 8 hours;

• Set the die head temperature 5-10℃ higher than the homogenization section. Install an insulation cover outside the die head to reduce heat loss;

• Flush the flow channel with cleaning material before each shutdown. Stop the machine only after clean melt flows out of the die orifice. Purge the die lip with compressed air before startup to remove residual material.

IV. General Principles and Safety Specifications for Blockage Handling

1. Safety First: Before handling any blockage, confirm the equipment is powered off, pressure is released, and temperature drops to a safe range (<50℃).  Never touch the blocked area while the equipment is running;

2. Prohibit Forced Prying: Use wooden, plastic, or brass tools for cleaning to avoid damaging high-precision components such as screws, barrels, and die heads;

3. Record and Analyze: After each blockage, record "material properties, temperature parameters, blockage location, and handling process" in a log. Regularly analyze frequent blockage causes;

4. Personnel Training: Conduct "blockage emergency drills" for operators to ensure proficiency in handling steps for different scenarios and avoid fault escalation due to misoperation.

Material blockage essentially stems from a broken balance in the "material conveying, melting, and molding" process. Emergency handling requires speed and accuracy, while long-term prevention can fundamentally reduce fault frequency. By optimizing material pretreatment, matching equipment parameters, and strengthening daily maintenance, blockage downtime can be reduced by over 70%, significantly improving the stability and economic efficiency of extrusion production lines.