The main machine overload of the extrusion blow molding machine is a common and hazardous fault during the operation process. It refers to the situation where the load torque of the main motor exceeds the rated torque, triggering the overload protection mechanism of the equipment (such as frequency converter overload alarm, circuit breaker tripping). This fault not only causes the extrusion blow molding machine to stop production abruptly but also may cause permanent damage to key components such as the main motor, gearbox, and screw if not handled in a timely manner. Based on on-site production practice, this document summarizes the typical phenomena of main machine overload, comprehensively analyzes the potential causes involving mechanical transmission, process parameters, raw material quality, and electrical systems, and proposes targeted troubleshooting solutions and systematic preventive maintenance measures to ensure the safe and stable operation of the extrusion blow molding machine.

1. Fault Phenomena

The typical manifestations of main machine overload of extrusion blow molding machines include the following aspects: First, the control panel of the extrusion blow molding machine displays an “overload alarm” (such as “Motor Overload” or “Drive Overload”), and the main machine automatically shuts down to protect the system; second, the current of the main motor of the extrusion blow molding machine is significantly higher than the rated current (exceeding 110% of the rated value), and the current curve fluctuates violently; third, the rotation speed of the screw of the extrusion blow molding machine decreases sharply or even stalls, the extrusion output drops significantly, and the parison formation is abnormal; fourth, abnormal noises (such as heavy friction sound, gear impact sound) are emitted from the main motor, gearbox or barrel during operation, and the surface temperature of the motor or gearbox rises rapidly; fifth, the frequency converter of the extrusion blow molding machine enters the protection state, and the output frequency and voltage are automatically reduced.

2. Fault Causes

The main machine overload of the extrusion blow molding machine is usually caused by the comprehensive effect of mechanical resistance increase, unreasonable process settings, poor raw material quality and electrical system faults. The specific causes are analyzed in detail as follows:

(1) Faults of the Mechanical Transmission System

• Increased resistance of the screw and barrel: The screw and barrel of the extrusion blow molding machine are partially stuck due to material carbonization (local overheating of the barrel leads to melt degradation and carbonization), residual material solidification (improper shutdown without purging) or foreign objects (such as metal debris, hard plastic particles) entering; the wear gap between the screw and barrel is too small due to long-term use, resulting in excessive friction resistance during screw rotation.
• Gearbox failure: The gearbox of the extrusion blow molding machine lacks lubricating oil or uses unqualified lubricating oil, leading to increased friction between gears; the gears in the gearbox are worn, pitted or broken, resulting in unsmooth power transmission and increased load; the bearing of the gearbox is severely worn or stuck, restricting the rotation of the transmission shaft.
• Transmission component failure: The transmission belt of the extrusion blow molding machine is too tight or stuck, increasing the load of the main motor; the coupling between the main motor and the gearbox is misaligned or stuck, resulting in additional resistance during torque transmission; the thrust bearing of the screw is worn or damaged, leading to axial movement of the screw and increased rotation resistance.

(2) Unreasonable Process Parameter Settings

• Improper temperature setting: The temperature of the barrel (especially the feeding section and compression section) of the extrusion blow molding machine is too low, resulting in insufficient plasticization of the raw materials, high viscosity of the melt, and increased extrusion resistance; the temperature of the die head is too low, leading to poor melt flow and increased back pressure, which is transmitted to the screw and causes overload.
• Excessive screw speed or extrusion amount: The screw speed of the extrusion blow molding machine is set too high, exceeding the load-bearing capacity of the main motor; the extrusion amount is adjusted too large, and the material processing amount exceeds the design capacity of the extrusion system, leading to excessive load on the main motor.
• Improper die head gap setting: The die head gap of the extrusion blow molding machine is too small, resulting in excessive flow resistance of the melt, sharp rise in die head pressure, and increased load on the screw and main motor.

(3) Poor Raw Material Quality

• Unqualified raw material performance: The melt flow index (MFI) of the raw material is too low, resulting in poor fluidity of the melt and increased extrusion resistance; the raw material contains a large amount of hard impurities (such as sand, metal particles) or unplasticized aggregates, which cause additional friction and blocking during the conveying and plasticizing process of the screw.
• Improper raw material processing: The raw material is damp and agglomerated, and the moisture evaporates into water vapor during the heating process, which increases the internal pressure of the barrel and the load of the screw; different batches of raw materials are mixed unevenly, resulting in unstable melt viscosity and sudden increase in load.

(4) Faults of the Electrical System

• Main motor failure: The main motor of the extrusion blow molding machine has insulation damage or winding short circuit, resulting in increased motor current and overload; the motor bearing is severely worn, leading to increased rotation resistance and load.
• Frequency converter fault: The parameter setting of the frequency converter of the extrusion blow molding machine is unreasonable (such as too small acceleration time, too high torque limit), leading to excessive current during the startup or operation of the main motor; the frequency converter’s internal circuit board is damaged or the cooling system fails, resulting in incorrect output and triggering overload protection.
• Unstable power supply: The input power supply voltage of the extrusion blow molding machine is too low or fluctuates sharply, leading to increased current of the main motor to maintain the rated power, thus causing overload.

3. Solutions

Aiming at the above fault causes, the following step-by-step troubleshooting and solution measures are proposed to quickly resolve the main machine overload problem of the extrusion blow molding machine:

(1) Overhaul the Mechanical Transmission System

• Eliminate screw and barrel resistance: Immediately shut down the extrusion blow molding machine and cool down appropriately; if there is material carbonization or solidification, heat the barrel to the process temperature and keep it warm for a period of time, then manually rotate the screw to loosen the blocked material; if there are foreign objects, disassemble the barrel and screw to remove the foreign objects; check the wear gap between the screw and barrel, and repair or replace the screw and barrel if the gap is abnormal.
• Maintain the gearbox: Drain the old lubricating oil in the gearbox of the extrusion blow molding machine, clean the gearbox interior, and add lubricating oil that meets the specifications; check the gears and bearings, and replace the worn or damaged gears and bearings; calibrate the gearbox to ensure smooth power transmission.
• Repair transmission components: Adjust the tightness of the transmission belt of the extrusion blow molding machine to the appropriate range, and replace the worn or stuck belt; correct the misalignment of the coupling, and replace the damaged coupling; check the thrust bearing of the screw, and replace the worn or damaged bearing.

(2) Optimize Process Parameters

• Adjust temperature parameters: Increase the temperature of the feeding section and compression section of the extrusion blow molding machine’s barrel appropriately to ensure sufficient plasticization of the raw materials; increase the die head temperature to reduce melt flow resistance and stabilize die head pressure.
• Adjust screw speed and extrusion amount: Reduce the screw speed of the extrusion blow molding machine to within the load-bearing range of the main motor; adjust the extrusion amount reasonably to match the design capacity of the extrusion system; extend the acceleration time of the frequency converter to avoid sudden load increase during startup.
• Optimize die head gap: Appropriately increase the die head gap of the extrusion blow molding machine to reduce melt flow resistance and lower die head back pressure; ensure that the die head gap is uniform to avoid local excessive resistance.

(3) Improve Raw Material Quality

• Strictly control raw material quality: Screen the raw materials to remove hard impurities; test the melt flow index of the raw materials, and select raw materials that meet the process requirements; avoid mixing raw materials of different batches randomly, and homogenize them before use if necessary.
• Preprocess raw materials: Dry the damp raw materials thoroughly to reduce moisture content; crush the agglomerated raw materials to ensure uniform feeding; remove unplasticized aggregates in the raw materials to avoid blocking the screw and barrel.

(4) Troubleshoot the Electrical System

• Inspect the main motor: Use a multimeter to detect the motor winding of the extrusion blow molding machine, and repair or replace the motor if there is insulation damage or short circuit; check the motor bearing, add lubricating oil or replace the bearing if necessary; measure the motor current during operation to ensure it is within the rated range.
• Maintain the frequency converter: Reset the parameters of the frequency converter of the extrusion blow molding machine (such as acceleration time, torque limit) to standard values; clean the frequency converter’s cooling fan and heat sink to ensure good heat dissipation; replace the faulty frequency converter if there is internal circuit damage.
• Stabilize the power supply: Install a voltage stabilizer to ensure that the input power supply voltage of the extrusion blow molding machine is within the rated range (380V±10% for three-phase power); check the power line and terminals, and re-tighten the loose connections to avoid voltage loss.

4. Preventive Maintenance Suggestions

To fundamentally reduce the occurrence of main machine overload of the extrusion blow molding machine, it is necessary to establish a comprehensive preventive maintenance mechanism:

• Regular mechanical system inspection: Conduct daily inspections on the screw, barrel, gearbox, transmission belt, and coupling of the extrusion blow molding machine; add lubricating oil to the gearbox and motor bearing according to the specified cycle; check the wear status of key components regularly, and replace aging and worn parts in advance.
• Standardized process parameter management: Establish a process parameter database for the extrusion blow molding machine, and set reasonable temperature, speed, and extrusion amount parameters according to different raw materials and products; avoid arbitrary adjustment of process parameters, and record parameter changes and their effects.
• Strict raw material management: Establish a raw material inspection and acceptance mechanism, and reject unqualified raw materials; formulate a raw material preprocessing process, ensure that the raw materials are dry, clean, and homogenized before entering the machine; record the batch information of raw materials to facilitate traceability.
• Regular electrical system maintenance: Inspect the main motor, frequency converter, power line, and terminals of the extrusion blow molding machine daily; clean the electrical cabinet regularly to ensure heat dissipation; calibrate the frequency converter and current sensor every 3-6 months to ensure accurate detection and control.
• Strengthen operator training: Train operators of the extrusion blow molding machine to master the correct operation procedures and fault judgment methods; guide operators to monitor key parameters (current, temperature, pressure) in real time during operation, and stop the machine in time when abnormal signs appear; avoid forced operation when the machine is overloaded.