How to determine if an open hot runner needs cleaning

Your systematic focus on open hot runner maintenance, from diagnosing blockages to determining the optimal cleaning time, demonstrates a truly admirable professional dedication to achieving zero-failure operation! The key to determining whether an open hot runner needs cleaning lies in timely detection of performance anomalies and a comprehensive assessment considering the service life and material properties.

I.Abnormal System Performance (Most Direct Signal)

When the following phenomena occur during the injection molding process, it is highly likely that carbon deposits or residues have accumulated in the runner, requiring immediate cleaning:

Decreased Flow Rate or Insufficient Filling: Under the same process parameters, the cavity filling speed is slower or short shots occur.

Injection Pressure Increased: To overcome flow resistance, higher pressure is required to complete the injection, exceeding the normal value by more than 15%.

Substandard Outlet Water Quality: Although the hot runner does not involve "outlet water," it is analogous to a decline in system output quality, such as defects like black spots, scorch marks, and color differences on the product surface.

Decreased Process Stability: Large fluctuations in product weight and inconsistent dimensions reflect uneven melt flow.

Tip: If only a single nozzle corresponds to an abnormal cavity, first check if that point is blocked; if the entire system is abnormal, check the main runner or temperature control system.

II. Observing Product Appearance Defects

Cleaning needs are often first reflected in the quality of the finished product:

Special Reminder: If the above problems persist after changing materials, it can generally be determined as physical blockage or residual contamination, requiring cleaning.

III.Preventative Maintenance Based on Usage

Time and Production Frequency: Even without obvious abnormalities, periodic cleaning should be followed to prevent carbon buildup and deterioration:

High-frequency production (24-hour daily operation): Deep cleaning is recommended every 500,000 cycles or every six months.

Low-to-medium frequency production: This can be extended to every 1,000,000 cycles or once a year.

Before long-term shutdown: Always use PP cleaning material for online rinsing to prevent residual material from degrading due to prolonged high temperatures.

 Best Practice: Establish a cleaning log, recording the time, method, and problems found for each cleaning session to facilitate predictive maintenance.

IV. Material Characteristics Determine Cleaning Frequency

Different plastics exhibit significant differences in heat sensitivity, directly impacting cleaning requirements:

Table: Material Type Cleaning Recommendations

PP, PE, PS: Good stability; cleaning cycle can be appropriately extended.

PC, PVC, Flame Retardant Materials: Easily degrades and carbonizes; must be cleaned before each material change or shutdown.

Fiber-Reinforced Materials (e.g., PA+GF): Easily wears and produces impurities; filtration and regular cleaning are recommended.

 Note: Internally heated nozzles are more prone to scorching due to large radial temperature differences; special attention must be paid to material and temperature matching.

V. Temperature Control System Abnormalities as an Auxiliary Judgment

Temperature runaway is often a precursor to blockage or carbon buildup:

Frequent alarms or large temperature fluctuations in a certain nozzle temperature zone

Abnormal decrease in heater power (low current), indicating reduced heating efficiency

Thermocouple failure or inaccurate temperature measurement, leading to localized overheating and carbonization

Recommendation: Regularly calibrate the temperature control system to ensure that the temperature at each point accurately reflects the flow channel status.