Thermocouple failures are among the most frequent issues in hot runner systems, leading to temperature errors, production downtime, and defective parts. The most common problem is open circuit, caused by broken internal alloy wires due to thermal expansion, vibration, or improper installation. Frequent heating and cooling cycles accelerate metal fatigue, especially in low-quality thermocouples.
Short circuit occurs when the insulation layer is damaged, causing signal interference and unstable readings. Plastic melt, high humidity, or chemical corrosion can erode the magnesium oxide insulation inside the sheath. Another common issue is temperature drift, where the thermocouple provides inaccurate readings over time, leading to overheating or underheating. Poor alloy purity and low-grade construction are the main causes.
Mechanical damage such as bending, crushing, or pulling during mold assembly often breaks the thermocouple probe. Loose connectors also result in intermittent signal loss and temperature fluctuations. In addition, incorrect grounding and electrical interference from heaters or motors can distort thermocouple signals. Many failures can be avoided by using high-quality mineral-insulated thermocouples, proper installation, and regular inspection. Understanding these common failures helps maintenance teams diagnose problems quickly and reduce unplanned downtime.
