The heating and temperature control system is a critical auxiliary unit of extrusion blow molding machines, which is responsible for heating the barrel, die head, and other key components of the extrusion blow molding machine to the temperature required for plastic melting and plasticization, and maintaining stable temperature during the production process of the extrusion blow molding machine. The stability and accuracy of temperature control directly affect the melt fluidity, plasticization quality, and product forming effect of the extrusion blow molding machine. Due to long-term high-temperature operation, frequent temperature switching, aging of electrical components, and improper maintenance, the heating and temperature control system of extrusion blow molding machines is prone to various faults. This document focuses on common faults of the heating and temperature control system in extrusion blow molding machines, analyzes the causes in depth based on fault phenomena, and proposes corresponding solutions and preventive maintenance measures for extrusion blow molding machines.

1. Temperature Out of Control (Excessively High or Too Low)

(1) Fault Phenomena

Temperature excessively high: The actual temperature of the barrel or die head of the extrusion blow molding machine is significantly higher than the set value; the melt is degraded, resulting in product defects such as yellowing, blackening, and bubbles of the extrusion blow molding machine; the heating power cannot be automatically reduced, and the temperature of the extrusion blow molding machine’s heating zone continues to rise. Temperature too low: The actual temperature of the extrusion blow molding machine’s key heating components cannot reach the set value for a long time; the melt plasticization is insufficient, the product surface of the extrusion blow molding machine is rough with granular feeling, and the mechanical properties are reduced; the extrusion resistance of the extrusion blow molding machine increases, and the extrusion output is unstable.

(2) Fault Causes

• Malfunction of heating elements: The heating coil (or heating tube) is short-circuited or aged, leading to excessive heating power (for excessive temperature) or insufficient heating power (for too low temperature); the heating coil is loosely connected or in poor contact, resulting in intermittent heating and unstable temperature.
• Failure of temperature detection components: The thermocouple (temperature sensor) is damaged, corroded, or loosely installed, leading to inaccurate temperature detection or no signal transmission; the thermocouple compensation wire is short-circuited, open-circuited, or mismatched, resulting in large errors in temperature measurement.
• Abnormality of temperature control instrument: The temperature controller (PLC or intelligent temperature control meter) is faulty, and the output signal is abnormal, which cannot effectively control the on-off of the heating element; the parameter setting of the temperature controller is incorrect (such as excessive proportional band, improper integral time), leading to loss of control of temperature regulation.
• Failure of cooling system: The cooling fan or cooling water circuit of the heating zone is blocked or faulty, resulting in poor heat dissipation; the temperature of the heating element cannot be reduced in time when the temperature is too high, leading to continuous temperature rise.
• Other factors: The power supply voltage for the extrusion blow molding machine is unstable, causing abnormal operation of the heating element; the thermal insulation layer of the barrel or die head of the extrusion blow molding machine is damaged, resulting in excessive heat loss and difficulty in reaching the set temperature.

(3) Solutions

• Check and replace heating elements: Use a multimeter to detect the resistance of the heating coil; replace the short-circuited, aged, or damaged heating coil; re-tighten the connecting terminals of the heating coil to ensure good contact.
• Maintain and replace temperature detection components: Check the thermocouple for damage and corrosion, and replace the faulty thermocouple; re-install the loose thermocouple to ensure close contact with the heated component; check the compensation wire, replace the short-circuited or open-circuited compensation wire, and ensure that the model of the compensation wire matches the thermocouple.
• Calibrate and maintain the temperature control instrument: Calibrate the temperature controller with a standard thermometer; reset the parameters of the temperature controller according to the process requirements; replace the faulty temperature controller if necessary.
• Overhaul the cooling system: Clean the cooling fan and cooling water circuit to remove dust and scale, ensuring smooth heat dissipation; check the operation of the cooling pump and fan, and replace the faulty cooling components.
• Stabilize power supply and repair thermal insulation layer: Install a voltage stabilizer to ensure stable power supply for the extrusion blow molding machine; repair or replace the damaged thermal insulation layer of the barrel and die head of the extrusion blow molding machine to reduce heat loss.

2. Large Temperature Fluctuations

(1) Fault Phenomena

The actual temperature of the extrusion blow molding machine’s heating zone fluctuates around the set value with a large amplitude (exceeding ±5℃); the temperature display value of the extrusion blow molding machine jumps up and down; the melt viscosity changes alternately, resulting in uneven product thickness and unstable forming quality of the extrusion blow molding machine.

(2) Fault Causes

• Poor contact of heating elements: The connecting terminals of the heating coil are loose or corroded, leading to intermittent on-off of the heating circuit; the heating coil is partially damaged, resulting in uneven heating power.
• Instability of temperature detection: The thermocouple is loosely installed or contaminated, leading to unstable detection signals; the thermocouple compensation wire is in poor contact, resulting in intermittent signal transmission.
• Improper parameter setting of temperature controller: The proportional band of the temperature controller is too small, leading to over-adjustment; the integral time is too short, resulting in frequent fluctuation of the output signal; the derivative time is improper, which cannot effectively suppress temperature fluctuations.
• Fluctuation of power supply voltage: The input voltage of the heating system fluctuates greatly, leading to unstable heating power of the heating element.
• Unstable heat loss: The ambient temperature around the extrusion blow molding machine changes greatly; the thermal insulation layer of the heated component of the extrusion blow molding machine is partially damaged, leading to uneven and unstable heat loss.

(3) Solutions

• Process heating element connections: Re-tighten the loose connecting terminals, clean the corroded terminals, and apply conductive paste if necessary to ensure good contact; replace the partially damaged heating coil.
• Stabilize temperature detection: Re-install the thermocouple to ensure it is closely attached to the heated surface, and clean the contaminated thermocouple probe; check the compensation wire and its connections, and replace the faulty parts.
• Optimize temperature controller parameters: Adjust the proportional band, integral time, and derivative time of the temperature controller according to the characteristics of the heating system to achieve stable temperature control; use the self-tuning function of the temperature controller to automatically optimize parameters if available.
• Stabilize power supply: Install a voltage stabilizer or UPS power supply to reduce the impact of power supply voltage fluctuations on the heating system.
• Improve thermal insulation effect: Repair the damaged thermal insulation layer of the extrusion blow molding machine, and take heat insulation measures for the heating zone to reduce the impact of ambient temperature changes on the extrusion blow molding machine’s heating system.

3. Heating Element Failure

(1) Fault Phenomena

The heating zone of the extrusion blow molding machine cannot be heated, and the temperature display remains unchanged; the heating power of the extrusion blow molding machine is significantly reduced, and the temperature rises slowly; the heating element of the extrusion blow molding machine makes abnormal noises (such as buzzing) during operation, and may trip the power supply of the extrusion blow molding machine in severe cases.

(2) Fault Causes

• Aging and damage of heating elements: Long-term high-temperature operation leads to oxidation and aging of the heating coil, and finally breaks; the heating coil is burned out due to excessive local temperature caused by poor heat dissipation.
• Electrical faults: The heating circuit is short-circuited or open-circuited; the contactor or relay controlling the heating element is faulty, leading to failure to supply power to the heating element.
• Improper use and maintenance: The heating element is contaminated by melt or other impurities, which affects heat dissipation and causes overheating damage; the heating element is collided or scratched during disassembly and assembly, leading to damage to the surface insulation layer.
• Unstable power supply: The power supply voltage for the extrusion blow molding machine is too high, exceeding the rated voltage of the heating element, leading to burning out; frequent power on and off of the extrusion blow molding machine causes impact on the heating element and accelerates damage.

(3) Solutions

• Replace heating elements: Detect the heating coil with a multimeter, and replace the aged, broken, or burned heating element with a product of the same model and specification; ensure that the new heating element matches the rated power and voltage of the system.
• Troubleshoot electrical circuits: Check the contactor, relay, and other electrical components in the heating circuit, and replace the faulty components; repair the short-circuited or open-circuited circuit to ensure normal power supply.
• Standardize use and maintenance: Clean the surface of the heating element regularly to remove impurities and ensure good heat dissipation; avoid collision and scratch of the heating element during disassembly and assembly, and protect the surface insulation layer.
• Stabilize power supply: Install a voltage stabilizer to ensure that the power supply voltage is within the rated range of the heating element of the extrusion blow molding machine; reduce frequent power on and off of the extrusion blow molding machine, and follow the correct startup and shutdown procedures.

4. Temperature Display Abnormality

(1) Fault Phenomena

The temperature display value of the extrusion blow molding machine is always 0 or full scale; the display value is erratic and does not match the actual temperature of the extrusion blow molding machine; the temperature display of the extrusion blow molding machine does not change with the adjustment of the set value.

(2) Fault Causes

• Failure of temperature detection components: The thermocouple is damaged, open-circuited, or short-circuited, leading to no signal output; the thermocouple compensation wire is connected incorrectly or damaged.
• Malfunction of temperature control instrument: The temperature controller is internally faulty (such as damaged circuit board, faulty display screen), leading to abnormal display; the input type of the temperature controller does not match the thermocouple model.
• Loose or poor contact of connections: The connecting terminals of the thermocouple and compensation wire are loose, corroded, or contaminated, leading to poor signal transmission.
• Electromagnetic interference: The temperature control system of the extrusion blow molding machine is affected by electromagnetic interference from surrounding electrical equipment of the extrusion blow molding machine, leading to distorted display signals.

(3) Solutions

• Check and replace temperature detection components: Detect the thermocouple and compensation wire with a multimeter, and replace the damaged or faulty parts; ensure that the compensation wire is connected correctly (positive and negative poles are not reversed).
• Calibrate and maintain the temperature control instrument: Check the input type setting of the temperature controller, and adjust it to match the thermocouple model; calibrate the temperature controller, and replace the faulty temperature controller if the internal circuit board or display screen is damaged.
• Process connecting terminals: Re-tighten the loose terminals, clean the corroded or contaminated terminals, and ensure good contact between the terminals.
• Suppress electromagnetic interference: Install shielding sleeves for the thermocouple and compensation wire of the extrusion blow molding machine; keep the temperature control instrument of the extrusion blow molding machine away from high-voltage electrical equipment and strong electromagnetic interference sources; ground the heating and temperature control system of the extrusion blow molding machine properly.

5. Preventive Maintenance Suggestions for Heating and Temperature Control System

1. Regular inspection of heating elements: Regularly check the surface of the heating coil of the extrusion blow molding machine for damage, contamination, and loose connections; measure the resistance of the heating coil of the extrusion blow molding machine regularly, and replace the aged or damaged heating elements in advance.

2. Calibration of temperature detection and control components: Regularly calibrate the thermocouple and temperature controller of the extrusion blow molding machine with standard instruments to ensure accurate temperature detection and control; replace the thermocouple and compensation wire of the extrusion blow molding machine that have been used for a long time (generally 1-2 years) regularly.

3. Maintenance of electrical circuits: Regularly check the contactor, relay, connecting terminals, and other electrical components of the extrusion blow molding machine’s heating system; clean the dust and dirt in the electrical cabinet of the extrusion blow molding machine, and ensure good heat dissipation of the electrical components; tighten the loose terminals regularly to prevent poor contact.

4. Standardization of operation procedures: Follow the correct heating and cooling procedures of the extrusion blow molding machine, avoid rapid temperature rise and drop, and reduce the impact on heating elements and temperature control components of the extrusion blow molding machine; avoid frequent power on and off of the extrusion blow molding machine’s heating system.

5. Protection of thermal insulation layer: Regularly check the integrity of the thermal insulation layer of the barrel, die head, and other components of the extrusion blow molding machine; repair or replace the damaged thermal insulation layer of the extrusion blow molding machine in time to reduce heat loss and ensure stable temperature.