Causes and Solutions for Hot Runner Blockage in Injection Molds
2026-04-09 10:47:39
Injection Molds
Hot runner systems are widely used in modern injection molds for their high efficiency, energy saving and stable molding quality. However, blockage frequently occurs during long-term production, leading to short shots, burns, black spots, color streaks and even complete production shutdown. This article summarizes the main causes of hot runner blockage in injection molds and provides practical on-site treatment and long-term prevention methods.
Main Causes of Hot Runner BlockageHot runner blockage usually results from material, temperature, structure and maintenance issues.
First, raw material problems are the most common cause. Materials with high viscosity, excessive regrind, high moisture content or mixed impurities easily decompose, carbonize or accumulate in the runner. Insufficient drying leads to hydrolysis and thermal degradation, forming carbon deposits that stick to the runner wall and nozzle.
Second, abnormal temperature control causes severe blockage. Overheating leads to material degradation and carbonization; low temperature increases melt viscosity and causes solidification. Damaged heating coils or faulty thermocouples result in uneven heating, creating local blocked areas.
Third, unreasonable mold and hot runner design increases blockage risk. Sharp corners, dead zones, rough inner surfaces and poor matching between nozzle and gate cause material retention. Over time, retained material ages and hardens, blocking flow channels.
Fourth, inadequate daily maintenance accelerates blockage. Lack of regular cleaning, incomplete color change or material change, and delayed replacement of worn parts allow residual material to accumulate. Dust, metal debris and mold wear particles also enter the system and cause blockage.
On-Site Treatment Methods for Hot Runner BlockageWhen blockage occurs, proper treatment can quickly restore production without damaging the mold.
For mild blockage, increase the hot runner temperature appropriately to melt the blocked material. Use high-pressure nitrogen or compressed air to purge the system from the feeding end. Repeat several times until smooth flow is restored.
For moderate blockage, remove the nozzle and heat it separately. Clean carbon deposits using soft brushes and non-abrasive tools. Avoid hard tools that may scratch the inner surface. Clean the runner plate with professional cleaning agents if necessary.
For severe blockage, disassemble the entire hot runner system including manifolds, nozzles and inserts. Use ultrasonic cleaning or high-temperature soaking to remove stubborn carbon deposits. Polish worn areas and replace damaged components before reassembly.
After cleaning, use special purging materials to flush the system before formal production to ensure complete removal of residual contaminants.
Long-Term Prevention MeasuresEffective prevention can greatly reduce the frequency of hot runner blockage.
Strictly control raw material quality and drying process. Use clean, well-dried materials and control the ratio of regrind. Perform complete purging during material or color changes.
Optimize temperature settings and monitor heating systems regularly. Calibrate thermocouples and replace faulty heating elements in time to avoid local overheating or insufficient heating.
Improve hot runner design with streamlined runners, rounded corners and highly polished inner surfaces. Ensure precise alignment between nozzles and gates to prevent leakage and cold slug formation.
Establish a regular maintenance system. Clean the hot runner system after long production runs, inspect wearing parts and perform preventive maintenance. Proper mold storage also prevents dust and rust.
In conclusion, hot runner blockage in injection molds is avoidable through scientific operation and maintenance. By addressing the root causes, implementing correct cleaning methods and establishing preventive mechanisms, manufacturers can achieve continuous and stable production, reduce downtime and improve overall efficiency.
