Troubleshooting Methods for Abnormal Hot Runner Temperature Control
2026-05-11 10:31:12
Injection Mold
In injection molding production, common faults of hot runner temperature control include unstable temperature, sudden temperature fluctuation, failure to heat up, over-temperature alarm and intermittent heating tripping. These anomalies directly lead to runner carbon deposition, yellowing and wire drawing, material shortage and shrinkage as well as degradation and scrapping of rubber materials, seriously affecting mass production stability. Mastering systematic and progressive troubleshooting steps can quickly locate the root cause of abnormal temperature control and restore normal production rhythm without blind replacement of accessories.
Identify Fault Phenomena to Determine Fault Types Rapidly
The first step of troubleshooting is to distinguish fault phenomena and lock the general direction. Common abnormalities are classified into several categories: single zone fails to heat up completely, temperature cannot reach the set value, severe random temperature fluctuation, actual temperature far exceeding the set value with over-temperature alarm, tripping after short-time heating, and lagging temperature of hot runner zone despite normal mold temperature. Record whether the fault occurs in a single zone or all zones simultaneously. Abnormalities in all zones are mostly caused by main power supply, main contactor and zero line loop problems, while single zone faults are basically limited to thermocouples, heating coils, wiring and temperature control cards. Clarifying the scope first can greatly reduce ineffective maintenance time.
Basic Inspection of Power Supply and Circuit
Unstable power supply is a high-frequency inducement for abnormal temperature control. First check the input voltage of the hot runner temperature control box to confirm three-phase voltage balance, no phase loss and no sudden voltage fluctuation. Large voltage fluctuation in the workshop easily causes temperature zone drift. Check whether the air switch, leakage protector and AC contactor contacts are burnt, blackened or poorly contacted. Oxidized contacts lead to intermittent power supply, discontinuous heating and temperature drift.
Inspect terminal blocks one by one for looseness, oxidation, virtual connection and burning blackening. Loose wire pressing generates contact resistance, resulting in inaccurate temperature and intermittent heating. Circuit inspection also includes checking whether wiring is squeezed and worn with damaged outer skin and electric leakage, avoiding short circuit caused by wire grounding and over-temperature tripping. Retighten all wiring terminals, polish and clean oxidized terminals or replace them directly to eliminate hidden dangers of basic circuits.
Special Inspection of ThermocouplesThermocouples are the core of temperature measurement. Ninety percent of temperature drift, random fluctuation and inaccurate temperature measurement stem from this part. First confirm the matching of thermocouple models; K-type and J-type cannot be mixed, and mismatching leads to large temperature difference and serious distorted display temperature. Check whether the positive and negative poles of thermocouples are reversely connected, which causes continuous temperature drop and failure of normal temperature control.
Verify whether the thermocouple probe fits the temperature measuring position of hot nozzle and manifold. Loose, suspended and poorly contacted probes result in temperature measurement lag and random fluctuation. Aging probes, internal disconnection and damaged shielding layer interference also cause numerical disorder. The replacement method can be adopted for troubleshooting: directly replace with a new thermocouple of the same specification for comparison. If the temperature returns to stability after replacement, the old thermocouple is confirmed invalid. Meanwhile, compress and fix the probe to ensure close fitting with the temperature measuring surface.
Inspection of Heating Coil and Heating LoopInsufficient temperature rise and slow heating focus on checking heating coils. Power off and measure the resistance of heating coils with a multimeter. Infinite resistance indicates open circuit, and low resistance indicates local short circuit, both requiring direct replacement. Check whether heating coils are aging, burnt, cracked or partially carbonized and blackened. Aging leads to power attenuation, failing to reach the set temperature.
Verify the fitting degree between heating coils and hot nozzles as well as manifold. Excessive gap and loose wrapping cause rapid heat dissipation, slow temperature rise and temperature control drift. During installation, ensure heating coils closely fit the mold body with complete thermal insulation cotton to reduce heat loss. Meanwhile, check heating wires for disconnection and internal copper wire breakage. Complete appearance with internal disconnection also causes intermittent heating and abnormal temperature control.
Inspection of Temperature Control Card and Parameter Setting
If hardware and circuits are normal, focus on troubleshooting temperature control cards of the temperature control box. Random temperature fluctuation, disordered temperature control logic and failed PID adjustment are mostly caused by aging temperature control cards, breakdown of silicon controlled rectifiers and module damage. The cross exchange method is adopted: swap the temperature control card of the abnormal zone to the normal zone. If the fault follows the card, replace the faulty temperature control card directly.
Meanwhile, verify basic temperature control parameters. Wrong temperature control mode, unreasonable PID parameter ratio and improper heating slope setting all cause over-temperature, oscillation and unstable temperature maintenance. Restore factory default parameters and rematch them. Adjust heating rate according to runner size and rubber melting point to avoid artificial abnormal temperature control caused by improper parameters.
Inspection of Mold Environment and Production Working ConditionsExternal working conditions also interfere with the stability of hot runner temperature control. Mold cooling water too close to the hot runner or excessive water flow continuously takes away heat, resulting in low temperature that cannot reach the set value. Direct cold wind from the workshop blowing to the hot runner area also causes excessive heat dissipation and difficult temperature control.
Carbon deposition of degraded rubber materials attached to the inner wall of the runner leads to poor local thermal conductivity, causing partial abnormal temperature and unstable glue output. Long-term production without cleaning runner carbon deposition forms thermal insulation and affects temperature measurement and heat conduction, requiring regular mold disassembly and carbon cleaning maintenance. Frequent start-stop and shutdown without turning off the hot runner during short downtime also cause disordered temperature gradient. Standardize the start-stop temperature control process to reduce abnormal temperature control induced by working conditions.
SummaryTroubleshooting of abnormal hot runner temperature control follows the sequence of observing phenomena first, then checking power supply, circuit, thermocouple, heating coil, temperature control card and finally working conditions, eliminating faults from outside to inside and from simplicity to complexity. Prioritize rapid fault location by observing phenomena, measuring voltage, checking wiring and replacing accessories without blind mold disassembly. Regularly fasten wiring, inspect thermocouples and heating coils, standardize parameter setting and mold heat dissipation management in daily maintenance. It can not only quickly handle existing abnormal temperature control faults but also reduce repeated abnormal shutdown in the later stage, ensuring long-term stable mass production of hot runner molds.
