Various thermocouple types are used in hot runners, with differences in temperature range, accuracy, stability, cost, and applicability. Understanding these differences helps users select cost-effective thermocouples that match their specific material, temperature, precision, and environmental requirements.
K-Type Thermocouples. K-type thermocouples are the most common choice in hot runner applications. Composed of nickel-chromium and nickel-aluminum alloys, they have a wide working range from -200°C to 1200°C. They feature good linearity, strong oxidation resistance, low cost, and easy matching with controllers. Suitable for most plastics such as PP, PE, ABS, PC, and PA, they are widely used in general and medium-to-high-end molds.
J-Type Thermocouples. J-type thermocouples use iron-constantan alloys, with a range of -40°C to 750°C. They have higher output voltage and sensitivity at medium temperatures, making them responsive. However, they oxidize quickly at high temperatures and have poor humidity resistance. Suitable for low-to-medium temperature molds and general-purpose applications.
T-Type Thermocouples. T-type thermocouples use copper-constantan, with good low-temperature stability but limited high-temperature performance. They are rarely used in hot runners except for specialized clean, low-temperature medical applications.
E-Type Thermocouples. E-type has high sensitivity but limited high-temperature durability, mainly used for special low-temperature scenarios.
R-Type and S-Type Thermocouples. R-type and S-type thermocouples are noble-metal types, using platinum-rhodium alloys. They have extremely high accuracy and stability up to 1600°C, but high cost. Used in high-temperature engineering plastics such as PEEK, PPS, and PEI, or ultra-precision molds requiring long-term stability.
Mineral-Insulated vs. Plastic-Insulated. In terms of structure, mineral-insulated thermocouples have metal sheaths and compressed magnesium oxide insulation, offering flexibility, pressure resistance, fast response, and long life-ideal for embedded hot runner installation. They are far more resistant to thermal shock than plastic-insulated or fabricated thermocouples.
Sheath Material Differences. Sheath materials differ: 304 stainless steel for general use, 316L for corrosion resistance, and high-temperature alloys for extreme conditions. Lead wires include high-temperature silicone, fiberglass, and Teflon, selected based on environmental temperature.
Installation Structure Types. Installation structures include threaded, bayonet, patch, and needle types. Threaded types are stable for manifolds; needle types fit compact nozzles.
Response Speed Considerations. Response speed varies by probe diameter: thinner probes respond faster but have lower strength. Hot runner thermocouples usually balance speed and durability. Anti-interference designs such as shielded cables improve stability in complex workshop environments.
