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Learn how to quickly solve molding machine nozzle clogging problems in 5 minutes

2025/11/05 By le zhan

nozzle clogging 1-1

Unplanned downtime in injection molding often stems from nozzle clogging, resulting in an average loss of hundreds of dollars per hour in production. A Michigan-based auto parts manufacturer reported losing over a dozen hours per month due to nozzle clogging, resulting in significant waste of production time. Nozzle clogging, caused by solidified molten plastic or debris blocking flow, leads to production stoppages, mold damage, and material waste. 90% of molding machine clogging issues can be resolved within 30 minutes with the right steps.

Causes of Molding Machine Nozzle Clogging

Before troubleshooting nozzle clogging, it is essential to understand its causes. Molding machines nozzle clogging is typically caused by four common problems, each with clear signs:

Material Residue Accumulation: Over time, carbonized (burnt) residue can remain in the nozzle, forming a hard, black blockage. This results in reduced flow and burnt marks on parts.

Cold Blockage: If the nozzle temperature is below the plastic’s melting point, the molten plastic can solidify at the nozzle tip, forming a “blockage” that obstructs flow. This can cause sudden pressure spikes during injection molding and incomplete part filling.

Foreign Objects: Contaminants enter the nozzle, blocking fluid flow. Symptoms: Abnormal noise during injection and uneven part quality. Incompatible Materials: Mixing resins or using additives that react at high temperatures can produce viscous deposits that clog the nozzle. This can result in plastic stringing and inconsistent injection volumes.

Causes of Molding Machine Nozzle Clogging

Steps for Quickly Clearing Molding Machine Nozzles Clogs

When clogging occurs, speed is crucial. Follow these steps to quickly and safely clear the blockage: First, stop and lock the machine, then turn off the molding machine’s power and release the hydraulic pressure. Wait 5-10 minutes to allow the nozzle to cool slightly. Then, determine the type of blockage. For soft blockages, heat the nozzle to 10-15°C above the material’s melting point. For stubborn blockages, keep the nozzle at operating temperature to avoid breakage during the clearing process. Simultaneously, clean the nozzle by loading a cleaning agent into the hopper. Perform 2-3 short-distance injections at 80% pressure; the abrasive will remove soft residue. Alternatively, manual clearing can be used; gently push the blockage away with a nozzle cleaning tool. Be careful not to use sharp tools, as they can scratch the nozzle and cause re-clogging. Finally, test with pure resin. Perform 1-2 injections with the virgin resin to ensure smooth flow. Before resuming production, check that the pressure is stable and that the parts are of good quality.

Preventive measures to avoid clogging

The best way to prevent clogging is to avoid it altogether. The following proactive measures can reduce the risk of clogging by 70%. First, optimize temperature settings by using a heat probe to verify that the nozzle temperature is within the recommended range for the resin. For sensitive materials, increase the buffer temperature by 5°C to prevent cold spots. Then, pre-treat the material. For hygroscopic resins, dry them before use using a desiccant dryer, setting the settings according to the resin’s drying specifications. For example, PC resin requires drying at 120°C for 4 hours.

In injection molding, cleaning is necessary when changing materials. When changing resins, use a neutral detergent to clean the injection molding machine nozzles to remove residual material. This is especially important when switching from PVC to other plastics. During daily production, inspect the nozzles for wear, cracks, or buildup, and replace any worn nozzles to ensure a smooth water flow.

Preventive measures to avoid clogging.

When quick fixes are insufficient to resolve the problem

If clogging persists after taking preventative measures, a thorough investigation is required. These problems often lurk behind persistent blockages:

Heating belt malfunction: A malfunctioning heating belt can create cold spots within the nozzle, leading to recurring cold sprays. Use an infrared thermometer to check for temperature consistency.

Nose alignment issues: Misalignment between the nozzle and the mold gate bushing can cause material backflow and blockages. Use a feeler gauge to check alignment; adjustments are needed if the gap is greater than 0.05 mm.

Excessive back pressure: Setting the injection molding machine‘s back pressure too high can cause plastic shearing and overheating, leading to carbonization. The back pressure should be reduced to the minimum required to ensure material uniformity.

Material contamination: If foreign matter persists, check the hopper, feed inlet, and material storage device. Install a magnetic separator in the feed line to capture metal debris.

Tools to simplify blockage troubleshooting

Having the right tools can reduce troubleshooting time for blockages by 40%. Here are some tools that should be readily available for every injection molding operation:

Nose cleaner: Select a grade that matches your resin type. For example, use a high-temperature resistant formula for PEEK and a grinding formula for carbonized residues.

Nozzle Cleaning Tools: A set of heat-resistant rods with blunted tips to prevent sharp edges from damaging the injection molding machine nozzles.

Thermal Probe/Infrared Thermometer: Used to verify nozzle temperature and identify cold spots.

Feeler Gauge: Used to check the alignment of the nozzle mold.

Magnetic Separator: Installed on the feed line to intercept metal contaminants before they reach the nozzles.

Troubleshooting Nozzle Clogging and Improving Production Efficiency

Nozzle clogging is unavoidable in injection molding, but it doesn’t necessarily kill production. By understanding the root cause, taking quick cleanup steps, and implementing preventative measures, you can resolve 90% of injection molding machine clogging issues within 30 minutes and reduce recurrence rates by 70%. The key is to act quickly, use the right tools, and conduct regular inspections and maintenance.

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