How to Use Thermocouples to Detect Gas Trapping in the Hot Runner Manifold?

Gas trapping is a common issue in hot runner systems, causing defects such as burns, voids, and hesitation marks on the part. Thermocouples can indirectly detect gas trapping. The first sign of gas trapping is a localized hot spot. The trapped gas is compressed during injection, generating heat (like a diesel engine). The heat causes a temperature spike, which the thermocouple can detect. The second sign is an unstable temperature. The gas may be trapped intermittently, causing the temperature to fluctuate. The third sign is a change in the required heater power. If gas is trapped, it can act as an insulator, reducing heat transfer. The thermocouple will read a lower temperature, causing the controller to apply more power. A sudden increase in power may indicate gas trapping. The fourth step is to use a thermal image. A thermal imager can show a hot spot at the gas trapping location. The thermocouple data can prompt this inspection. The fifth step is to correlate the thermocouple data with the part defects. If parts show burns or voids, check the thermocouple data for a temperature spike at the time of injection. The sixth step is to use a flow simulation. If gas trapping is suspected, a flow simulation of the manifold can be used to identify the areas where gas is likely to be trapped. The thermocouple data can be used to validate the simulation. The seventh step is to take corrective action. If gas trapping is confirmed, it may be necessary to add a vent to the manifold or to modify the manifold geometry to allow the gas to escape. The eighth step is to monitor the temperature after the corrective action. Use the thermocouple data to verify that the hot spot has been eliminated. By using thermocouple data to detect gas trapping, molders can identify and correct this issue, improving part quality and reducing scrap.