Operation Guidelines for Using Thermocouples in Ultra-low Temperature Injection Environment

Injection molding must be finished in a long-term ultra-low temperature workshop environment in specialized industries such the production of cryogenic industrial accessories, low-temperature food packaging materials, and cold-resistant plastic parts. Conventional hot runner thermocouples' material properties, structural stability, and temperature measurement accuracy will all be negatively impacted by the ongoing low temperature. Additionally, standard thermocouples are vulnerable to wire body embrittlement, signal distortion, and measurement failure in such challenging conditions. To guaranty the stable operation of temperature sensing job, specific low-temperature resistant models must be chosen, and standardized usage operation rules must be followed.

The internal connecting wires of standard thermocouples are prone to become hard and brittle, which is the main issue in extremely low temperature environments. Long-term low temperatures cause the plastic insulating layer of compensating wires to lose its original flexibility, become rigid and inelastic, and break easily when slightly twisted or tugged. This can lead to internal wire core exposure, open circuit, and signal disruption. At very low temperatures, the traditional alloy wire core will also result in a drop in material toughness and a significant reduction in fatigue resistance. Internal fracture damage is quite likely to result from frequent mold opening and shutting vibration. Thus, configuring low-temperature flexible thermocouples specifically is the initial selection concept. These products effectively prevent brittle fracture failure of lines and internal components by using cold-resistant elastic insulating materials and low-temperature resistant special alloy wire cores that can maintain good soft bending performance and structural toughness in ultra-low temperature states.

The extremely low ambient temperature will significantly interfere with the thermocouples' cold junction reference value in terms of temperature measurement accuracy control, leading to a significant departure of the automatic cold junction compensation data. The temperature value that the thermocouple feeds back is much higher than the actual temperature within the hot runner, which causes the temperature controller to prematurely halt heating, insufficient melt temperature, and numerous molding errors. In order to ensure that the displayed temperature is consistent with the actual melt temperature, it is necessary to manually optimize and adjust the temperature controller's cold junction compensation parameters in accordance with the workshop's real-time low-temperature environment value, increase the low-temperature compensation value in a targeted manner, and routinely use high-precision infrared temperature measuring instruments for data comparison and calibration to correct systematic temperature errors in time.

More uniform safety precautions must be used during the wiring construction and installation processes. Avoid tension and torsion extrusion of the wires in the low-temperature hardening stage, reserve enough wire body allowance for the moving elements of the mold, and try to minimize the repetitive bending times of the thermocouple connecting wires in the ultra-low temperature area. To stabilize the cold junction's reference temperature and lessen the range of ambient temperature fluctuations, all wiring terminals and cold junction connection locations should be kept away from direct low-temperature air supply ports. Additionally, any necessary thermal insulation and wind shielding protection measures should be added. In order to prevent further slowing down the temperature detecting speed due to low-temperature heat conduction attenuation, the installation gap of the measuring probe should be minimized to ensure close heat conduction contact.

Create specific maintenance guidelines appropriate for low-temperature environments for daily maintenance and production start-stop management. To preserve the internal structure of the thermocouple and postpone material aging, use the step-by-step slow preheating mode before beginning the formal heating production each time. Gradually raise the temperature from low temperature to the production set temperature, and avoid rapid heating from ultra-low temperature state to produce severe cold and hot alternating impact. To avoid damp short circuits and poor contact issues, regularly inspect the surface insulation integrity of all connected wires, promptly replace the wires with cracked and hardened skin, and clear the frost and condensed water that has accumulated at the wiring terminals.

Additionally, in an ultra-low temperature environment, minimize long-term standby shutdown and fairly arrange the production rhythm. Reduce the irreversible deterioration of material performance, prevent the thermocouple from being in an extremely low-temperature static state for an extended period of time, and maintain the hot runner in a slight heat preservation condition while production is momentarily halted. The stable temperature measurement performance of low-temperature special thermocouples can be effectively exerted by strictly adhering to the use guidelines for ultra-low temperature environments. This will also eliminate various hidden dangers caused by low temperature and guaranty the smooth progress of low-temperature injection molding production work.