In actual injection molding production, most technicians only pay attention to the working temperature inside hot runners, but ignore the influence of external workshop ambient temperature on thermocouple detection effect. The change of ambient temperature will directly interfere with the cold junction reference value of thermocouples, resulting in systematic temperature measurement deviation, which brings hidden troubles to accurate temperature control.
When the workshop ambient temperature is too low, the cold junction of the thermocouple connected to the temperature controller is in a low-temperature state for a long time. The original cold junction temperature compensation value set by the system cannot match the actual low-temperature environment, resulting in insufficient compensation effect. At this time, the temperature value fed back by the thermocouple is lower than the actual working temperature of the hot runner. The temperature control equipment will continuously increase heating power to raise the temperature, which is easy to cause invisible overheating of melt inside the flow channel, leading to material decomposition, product yellowing and carbon deposition problems. Especially in winter low-temperature production workshops, such temperature deviation is more obvious.
On the contrary, if the ambient temperature is too high in summer or near high-temperature baking equipment, the cold junction temperature will rise sharply and exceed the standard compensation range. Excessive cold junction temperature will cause the temperature signal output by the thermocouple to be higher than the real temperature of the hot runner. The controller will prematurely cut off the heating output, resulting in insufficient actual melt temperature, poor fluidity, and easy occurrence of molding defects such as weld lines, sink marks and incomplete product filling.
In addition, unstable fluctuating ambient temperature will cause continuous changes in the cold junction reference benchmark of thermocouples. The temperature feedback data keeps floating up and down, making it impossible for the temperature control system to form a stable constant temperature adjustment logic. Each temperature zone of the hot runner cannot maintain balanced heating state, resulting in inconsistent product quality in different time periods and difficult parameter solidification of injection molding processes.
Moreover, extreme ambient temperature will also affect the performance of thermocouple compensation wires. Too high temperature will accelerate the aging and insulation damage of the wire skin, and too low temperature will make the wire body hard and brittle, increasing the risk of internal wire core fracture. To eliminate such interference effectively, enterprises should keep the workshop temperature relatively stable, avoid direct cold and hot wind blowing at the temperature control box and wiring terminals, reasonably adjust the cold junction compensation parameters of the controller according to seasonal temperature changes, and increase the frequency of temperature comparison and calibration in extreme temperature environments, so as to eliminate ambient temperature deviation and ensure that thermocouple detection data is true and accurate.
