According to industry data from Plastics Today and Grand View Research, global demand for plastic injection molded parts is projected to grow at an annual rate of 4.8% through 2030, driven primarily by industries such as automotive, medical devices, and electronics. The injection molding machine screw is central to material preparation during this process—melting, mixing, and injecting molten plastic into the mold. However, when the injection molding machine screw becomes stuck, production efficiency plummets. Downtime can result in thousands of dollars in lost production, material waste, and equipment damage. Addressing this issue requires not only technical expertise but also a deep understanding of mechanics, material properties, and thermal management.
Injection Molding Machine Screw Seizures Due to Overheating and Resin Degradation
One of the most common causes of screw seizures in a plastic injection molding machine is barrel overheating. When the temperature distribution across the barrel is uneven, the plastic resin degrades and carbonizes, forming hard deposits around the screw flights.
This problem is widespread when operators are processing high-temperature engineering plastics such as PEEK, PC, or PPS without proper cleaning or temperature control. When degraded material hardens around the screw, it increases friction and restricts rotation, ultimately leading to screw sticking.
Solution: Balance barrel temperatures and regularly calibrate heaters and thermocouples to maintain a gradual temperature increase from the feed to the nozzle. Also, perform a purge cycle, using a high-temperature purge agent after each production run, especially when changing materials. Monitor residence time to prevent resin from idling in the barrel for extended periods. Proactive thermal control methods extend screw life, reduce maintenance frequency, and ensure consistent injection quality between batches.
Injection Molding Machine Screw Stuck by Contaminated or Moist Material
Another major cause of injection molding machine screw sticking is material contamination or moisture absorption. Many thermoplastics, especially hygroscopic materials like nylon, ABS, and PET, readily absorb moisture from the air. During melting, this moisture converts to vapor, forming microbubbles that lead to inconsistent melt viscosity and corrosion of the screw and barrel surfaces.
Foreign matter, such as metal fragments, paper labels, or improperly mixed masterbatch, can also become lodged between the screw flights and the barrel wall, causing physical sticking. Properly dry raw materials and use dehumidifying or vacuum dryers with precise temperature and time control. Install magnetic traps and filter packs in the hopper to capture contaminants. Also, clean the barrel regularly: perform preventive maintenance cleaning every 500-1,000 hours of machine operation. Finally, by maintaining a clean feed system and monitoring the quality of incoming raw materials, manufacturers can avoid costly downtime caused by screw jams and material buildup.
Improper Startup or Shutdown Procedures Lead to Screw Jams
A common cause of screw jams in plastic injection molding machines is improper startup or shutdown sequence. If the screw doesn’t start rotating after the barrel is heated, localized overheating can occur. Conversely, if the machine is shut down without purging the material, residual melt will remain in the barrel, harden upon cooling, and lock the screw.
Solution: Follow standardized startup procedures. Once the melt temperature reaches the recommended level, immediately start screw rotation to ensure uniform material flow. Additionally, practice proper shutdown and purging: purge the barrel with a compatible resin or commercial purge agent before shutting off the heater. Never attempt to rotate the screw until the barrel reaches operating temperature. These strict operating procedures are part of a best-practice methodology that every injection molding machine manufacturer should train its operators to follow. According to our internal maintenance data, proper operating procedures can extend the life of critical components and reduce downtime by up to 40%.
Screw Sticking Due to Mechanical Wear and Barrel Deformation
Over time, high-volume production puts significant mechanical stress on the screw and barrel assembly. When wear accumulates beyond tolerance limits, it can lead to misalignment, metal-to-metal contact, and sticking.
Abrasive fillers commonly used in reinforced plastics can accelerate wear. Once the clearance between the screw flights and the barrel wall exceeds the specified value, molten resin can leak backward (called backflow), creating uneven pressure zones and ultimately causing the screw to lock. We can regularly inspect wear by measuring the screw and barrel diameters at predetermined intervals. For high-wear materials, upgrade to a bimetallic barrel or nitrided screw. Additionally, keep the gearbox, thrust bearings, and motor coupling in optimal condition to reduce mechanical drag.
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Screw sticking due to incorrect back pressure or screw speed settings
Improper machine parameter settings can also cause screw sticking. Excessive back pressure increases melt density and screw load, while excessive screw speed leads to overheating and frictional wear. Both of these conditions can cause material solidification or overload the screw drive, making it difficult for the screw to rotate smoothly. Optimize back pressure to maintain the minimum level required for uniform mixing—typically 5-15 bar, depending on the resin type—also, control screw speed according to manufacturer recommendations and material supplier datasheets. Modern injection molding machines equipped with servo drive systems automatically adjust screw speed and torque to prevent overload. Continuously monitoring process parameters not only ensures smoother operation but also higher-quality molded parts with better dimensional stability and a smoother surface finish.
Build long-term reliability into every injection molding machine
Solving screw sticking in plastic injection molding machine requires a comprehensive understanding of the material, mechanical, and thermal systems. Whether it’s overheating, contamination, mechanical wear, or improper settings, each factor can disrupt production and affect part quality. Our engineering team has found that over 70% of screw jamming incidents can be prevented through ongoing maintenance, proper cleaning, and operator training. As a professional injection molding machine manufacturer, we are committed to helping our customers not only solve existing problems but also build a comprehensive prevention system.
