How to Perform a Temperature Uniformity Study on a Hot Runner?

A temperature uniformity study is a systematic evaluation of the thermal consistency across the hot runner manifold and nozzles. This study is important for qualifying a new mold, diagnosing problems, and validating after maintenance. The process involves using the installed thermocouples plus additional temporary sensors to create a detailed thermal map. Begin by setting the hot runner to the nominal operating temperature and allowing it to stabilize for at least 30 minutes, ensuring all zones have reached steady state. Record the reading of each zone's controller. Next, use a portable infrared thermometer or, better, a contact thermocouple with a fine tip to measure the temperature on the outer surface of the manifold at multiple points, including at the centre, near the entry, over each heater, and near each drop. Plot these readings on a schematic of the manifold. The goal is to identify any zones that are more than ±2°C from the average. If the hot runner has additional spare holes, insert a reference thermocouple into them and compare readings with the installed sensors. A deviation of more than 1°C indicates the installed sensor may be drifting. For a nozzle uniformity check, measure the temperature at the tip area of each nozzle (carefully, without touching the melt). The difference between the coldest and hottest nozzle should ideally be less than 5°C. If it is greater, investigate thermal imbalances-uneven cooling lines, variations in heater power, or clogged gates. The study should be repeated at different setpoints (e.g., low, mid, high of the material's window) to see how the thermal profile changes. During the study, also monitor the stability over time; temperature should not drift by more than ±0.5°C over a 60-minute period. Any persistent drift suggests a faulty thermocouple or controller. Document all readings and note the location of any "hot spots" (areas where temperature is higher than expected) or "cold spots." Hot spots can indicate localized heater failure (it works too hard), while cold spots may indicate a cooling water leak or a broken heater. A temperature uniformity study should be performed during the mold trial and then annually or whenever a thermocouple is replaced. The resulting thermal map becomes a baseline for future comparisons; if the profile changes significantly, it signals a developing problem, allowing proactive maintenance. This study is also required by some standards (e.g., automotive industry) to demonstrate process capability.