Research on Service Life Difference of Thermocouples Under Different Working Shifts

Depending on order volume and production schedule, production modes in contemporary injection molding plants are separated into three categories: single-shift, double-shift alternating, and three-shift uninterrupted continuous. The actual running time, rest interval, and cold-hot alternation frequency of hot runner thermocouples are all directly determined by different working shift types. Additionally, there are clear variations in aging speed, performance attenuation degree, and overall stable service life. A thorough understanding of the law of service life change under various shift systems can assist businesses in creating scientific replacement plans, scheduling equipment maintenance tasks sensibly, and preventing unexpected shutdown losses brought on by accessory failure during periods of high production.

Thermocouples have enough rest and natural cooling time each day for single-shift production workplaces that only operate during the day and shut down at nite. The internal alloy wire core and insulating materials can completely release the thermal tension built up during operation after daily production is over, allowing the entire hot runner system to gradually drop from working temperature to room temperature. Internal structural components experience a sluggish rate of fatigue loss and a low frequency of cold and hot alternation. Standard approved hot runner thermocouples may sustain stable precision and good sensing performance for an extended period of time under such moderate operating conditions, and the actual service life can approach the upper limit of the design cycle. Probe surface carbon deposition and internal performance drift are significantly slowed down, and the daily temperature rise and fall process is mild with no significant temperature influence. Businesses can set up routine maintenance and precise calibration in accordance with the traditional cycle, and the low replacement frequency can effectively limit accessory usage costs.

The most popular production method in the majority of medium-sized injection molding businesses is double-shift alternating manufacturing. The equipment only takes a little break in between shifts, and the manufacturing time is lengthy every day. The hot runner cannot be fully cooled and frequently maintains a steady temperature in order to preserve heat. The internal components of thermocouples are always in a high-temperature stress environment with insufficient relaxation period, and they are in a long-term high-temperature standby and repeated heating operating condition. The aging of insulating fillers and the deterioration of thermoelectric conversion performance will be accelerated by long-term continuous high-temperature operation, and the temperature drift value will rise more quickly than in single-shift production. Subtle structural fatigue inside the wire core will progressively accumulate as a result of frequent start-up heating and shutdown heat preservation, which will increase the amount of small-range temperature variations. When compared to single-shift operation, the total service life of thermocouples operating under double-shift conditions will be cut by over one-third. To avoid performance failure beforehand, the daily inspection cycle must be suitably shortened, and the scheduled replacement time must be advanced.

The majority of large-scale mass production companies with adequate orders use three-shift uninterrupted full-load continuous manufacturing. The thermocouples are in a long-term high-temperature stable functioning state for a considerable amount of time, and the hot runner system operates continuously throughout the year, nearly without any cooling or rest periods. The long-term, continuous high-temperature baking will result in irreversible changes in the metal grain structure of the internal alloy wire core, the sensing sensitivity will continue to decrease, and the precision loss speed is the fastest, even though there is no frequent cold and hot alternating impact in this working mode. Additionally, compared to other production modes, the probe surface accumulates carbon deposits and corrosive attachments more quickly due to the continuous, long-term flow of melt, and the degree of wear and erosion is significantly higher. The effective stable service life of thermocouples will be cut in half during full-load three-shift manufacturing compared to the standard design life. To guaranty that all temperature measurement components are constantly in qualifying operating condition, maintenance staff must rigidly execute frequent batch replacement systems and improve the frequency of probe cleaning and accuracy calibration.

Businesses must specifically modify their management techniques in order to address the variations in service life brought about by various shift manufacturing modalities. Create distinct use cycles and maintenance requirements based on each production line's real daily operating hours. Prioritize choosing high-temperature resistant, low-drift, high-grade thermocouples for long-term continuous manufacturing lines. Use high-performance accessories to compensate for the service life loss brought on by high-load operation. Organize equipment centralized maintenance time in a reasonable manner, take advantage of monthly and quarterly shutdown chances to do thorough disassembly inspection and thermocouple performance testing, and promptly remove any probable aging problems. It is possible to maximize thermocouple use efficiency, balance use effect and service life, and guaranty reliable temperature management for production lines with varying operation intensities by scientifically matching accessory grades and maintenance cycles according to production shifts.333