The extrusion system is the core power unit of an extrusion blow molding machine, responsible for the key tasks of melting and plasticizing plastic raw materials and continuously and stably transporting them to the die head. Its operating status directly determines product quality, production efficiency, and enterprise production costs. Due to factors such as long-term high-intensity operation of the equipment, complex operating environment, and variable raw material characteristics, the extrusion system is prone to various faults. This document will focus on common faults of the extrusion system, start with fault phenomena, conduct in-depth analysis of the causes, and propose corresponding solutions and maintenance points.

1. Unstable Extrusion Output

(1) Fault Phenomena

The size of the bubble changes frequently, and the longitudinal thickness deviation of the film exceeds the allowable range; the pressure at the front end of the die head fluctuates greatly, and the motor current has instantaneous large fluctuations; the weight or length of the final products (such as films, preforms) fluctuates significantly, and in severe cases, it may cause blow-up rupture and interrupt the production cycle.

(2) Fault Causes

• Raw material factors: Uneven particle size of raw materials, or mixed with damp and agglomerated materials, leading to changes in feeding resistance; differences in melt flow index (MFI) between different batches of raw materials, which are mixed without sufficient homogenization, causing plasticization fluctuations; the raw materials contain powdery impurities, resulting in large differences in melting rate, which are easy to adhere to the screw and affect transportation stability.
• Screw and barrel wear: After long-term use, the matching gap between the screw and the barrel increases, especially in the feeding section and compression section, which significantly reduces transportation efficiency and plasticization uniformity; the screw surface is damaged or adheres to materials, increasing the friction coefficient and causing intermittent stagnation of material transportation.
• Abnormal heating system: A certain section of the heating coil is damaged and ineffective, or the temperature control instrument and thermocouple are malfunctioning, leading to local overheating or underheating and causing unstable melt viscosity; the cooling circuit of the heating system is blocked or has poor heat dissipation, affecting the accuracy of temperature regulation.
• Feeding system faults: Unstable speed of the feeding motor, or loose and slipping transmission belt; the feeding screw adheres to materials, and the hopper has a “bridging” (material blocking the feeding port) phenomenon, which cannot ensure a constant feeding amount; poor cooling of the hopper causes the raw materials to melt and agglomerate in advance at the feeding port.
• Other factors: Wear of gears in the gearbox, breakage or slipping of the drive belt, leading to fluctuations in screw speed; clogging of the filter screen causes increased back pressure, prolonged melt residence time, and indirectly affects the stability of extrusion output.

(3) Solutions

• Raw material control: Fully dry the raw materials to avoid damp agglomeration; thoroughly stir and homogenize different batches of raw materials before mixing to ensure consistent melt flow index; install a raw material screening device to remove impurities and powdery materials; regularly clean the hopper and check the smoothness of the suction system.
• Screw and barrel maintenance: Regularly measure the matching gap between the screw and the barrel, and repair or replace them in time when exceeding the specified value; keep the screw surface smooth, and perform polishing and electroplating treatment if necessary to reduce the friction coefficient; avoid idling the extrusion blow molding machine to prevent metal foreign objects from entering the barrel and causing damage.
• Calibration and maintenance of the heating system: Regularly use an infrared thermometer to detect the actual temperature of each heating section and compare and calibrate it with the display value of the instrument; replace damaged heating coils, temperature control components and thermocouples; check the cooling circuit, clean blocked pipelines, and ensure normal heat dissipation.
• Optimization of the feeding system: Adjust the tightness of the transmission belt of the feeding motor and check the stability of the motor speed; clean the material adhering to the feeding screw, and install a stirring or bridge-breaking device in the hopper to solve the problem of unsmooth feeding; check the cooling water circuit of the hopper to ensure that the temperature of the feeding port meets the process requirements.
• Inspection of the transmission and filtration system: Overhaul the gearbox and replace worn gears; check the status of the drive belt and replace broken or slipping belts in time; regularly replace the filter screen, and use a multi-station continuous screen changing device if necessary to avoid affecting production continuity due to shutdown for screen changing.

2. Main Machine Failed to Start or Overload

(1) Fault Phenomena

The main extrusion blow molding machine has no response and cannot start after startup; or an overload alarm occurs immediately after startup, and the motor stops; in some cases, accompanied by abnormal mechanical friction noise.

(2) Fault Causes

• Temperature not up to standard: Each temperature zone (especially the key sections of the die head, mold head and barrel) has not reached the set temperature, or the heat preservation time is insufficient, the materials are not melted, and the screw rotation torque is too large.
• Mechanical jamming: Residual hard objects (such as metal foreign objects, solidified materials) in the screw are stuck; the screw and barrel are not concentric, the barrel center line is bent, or the screw is twisted and deformed, causing mutual friction and jamming during operation; the thrust bearing of the gearbox is worn and damaged, affecting power transmission.
• Electrical faults: Unstable power supply voltage or phase loss; faults of the motor itself; abnormal signals of the control system, which cannot normally output startup commands.

(3) Solutions

• Strictly implement the heating process: After each temperature zone reaches the set temperature, maintain sufficient heat preservation time (usually 30-60 minutes) to ensure full melting of materials and stable torque before starting the main extrusion blow molding machine slowly.
• Eliminate mechanical jamming: After shutting down and cooling, disassemble relevant components to clean residual hard objects and solidified materials in the screw; check the concentricity of the barrel and screw and the straightness of the barrel center line, and adjust and calibrate deviations; check whether the screw is deformed, and replace the twisted or severely worn screw; overhaul the gearbox and replace the damaged thrust bearing.
• Troubleshoot the electrical system: Detect the power supply voltage and phase to ensure stable power supply; check the motor windings and terminal blocks to eliminate motor faults; overhaul the control system, confirm that the signal transmission is normal, and restart the control system or replace faulty components if necessary.

3. Excessively High Pressure at the Extrusion Die Head

(1) Fault Phenomena

The displayed pressure at the die head continues to rise, exceeding the normal process range; the extrusion output decreases significantly; the melt flow speed is uneven, and the products are prone to defects such as scorch marks and cracks.

(2) Fault Causes

• Clogging of the filtration system: The filter screen has not been replaced for a long time, and impurities and degradation products in the raw materials accumulate, hindering melt flow and causing increased back pressure.
• Improper temperature setting: The temperature of the die head or mold head is too low, the material viscosity is too high, and the flow resistance increases; some heating elements are damaged, leading to low local temperature, uneven melt plasticization, and formation of flow obstacles.
• Abnormal die head structure: The die lip gap is too small, hindering the outflow of melt; carbonized materials accumulate in the die head, blocking the flow channel; the mandrel is offset or deformed, affecting the uniform flow of melt.
• Changes in raw material characteristics: The melt flow index of the raw material is too low, or high-viscosity impurities are mixed, leading to a decrease in melt flow performance.

(3) Solutions

• Clean or replace the filtration system: Immediately shut down the extrusion blow molding machine to replace the clogged filter screen; if the production continuity requirement is high, a multi-station continuous screen changing device can be used; regularly check the filtration system and formulate a reasonable replacement cycle according to the cleanliness of the raw materials.
• Optimize temperature setting: Appropriately increase the temperature of the die head and mold head to ensure that the melt viscosity meets the flow requirements; check each heating section component and replace the damaged heating coil to ensure uniform temperature distribution.
• Overhaul the die head: Disassemble the die head and clean the internal carbonized materials; adjust the die lip gap to the process requirement range; calibrate the mandrel position and replace the deformed mandrel components.
• Control raw material quality: Replace raw materials that meet the process requirements to ensure stable melt flow index; preprocess the raw materials to remove impurities.

4. Abnormal Wear and Jamming of Screw and Barrel

(1) Fault Phenomena

Obvious barrel scraping noise and metal friction noise are emitted during the operation of the equipment; the extrusion output gradually decreases, and the product size deviation increases; in severe cases, the screw cannot rotate, jamming occurs, and the main extrusion blow molding machine shuts down due to overload.

(2) Fault Causes

• Foreign object mixing: The raw materials contain metal impurities (such as screws, nuts, metal debris), or hard objects are mixed during the recycling and crushing process, which enter the gap between the screw and the barrel with the materials, causing severe wear or even jamming.
• Material and heat treatment problems: The material of the screw and barrel is poor, or the heat treatment hardness does not meet the standard, which cannot bear long-term friction and impact; the proportion of fillers in the raw material formula is too high, which aggravates wear.
• Installation and precision problems: The barrel and screw are not concentric, or the geometric tolerance of related parts is too large; the barrel center line is bent, leading to mutual friction during operation.
• Improper operation: The extrusion blow molding machine idles for too long, causing dry friction between the screw and the barrel; forced startup of the main machine when the temperature is not up to standard, the materials are not melted, resulting in excessive torque and aggravated wear.

(3) Solutions

• Source control of foreign objects: Install a strong magnetic iron device or a metal automatic separation device at the feeding port of the hopper to intercept metal impurities; strengthen raw material control to avoid pollution; strictly screen recycled materials to remove hard objects.
• Optimize material and formula: Replace the screw and barrel with good material and qualified heat treatment; adjust the raw material formula, reduce the proportion of fillers, and reduce wear.
• Calibrate installation precision: Check the concentricity of the barrel and screw and the straightness of the barrel center line, adjust the position of related parts to eliminate precision errors; replace the twisted screw or the barrel with excessive wear.
• Standardize the operation process: Prohibit long-term idling of the extrusion blow molding machine ; strictly implement the heating and heat preservation process, and start the main machine after the temperature and torque are stable; regularly check the wear of the screw and barrel, record wear data, and formulate a reasonable replacement cycle.

5. Abnormal Melt Temperature (Too High or Too Low)

(1) Fault Phenomena

Excessively high melt temperature: The products are prone to scorch marks, discoloration, and degradation bubbles; the cooling load increases, affecting product shaping. Excessively low melt temperature: Insufficient plasticization of materials, rough product surface with granular feeling, and decreased mechanical properties; increased extrusion resistance and unstable extrusion output.

(2) Fault Causes

• Improper temperature setting: Incorrect parameter setting of the temperature control instrument, or incorrect adjustment of the temperature curve by the operator; unreasonable temperature matching of each temperature zone, leading to heat accumulation or insufficient supply.
• Faults of the heating and cooling system: Local damage or insufficient power of the heating coil, leading to low temperature; malfunction of the temperature control instrument and thermocouple, which cannot accurately detect and control the temperature, may cause excessive or low temperature; blockage of the cooling circuit and failure of the cooling fan, leading to failure to dissipate heat in time and uncontrolled temperature rise.
• Matching problems between equipment and process: Unreasonable screw design, which cannot adapt to the characteristics of raw materials, leading to excessive or insufficient shear heat; too high screw speed, large accumulation of shear heat, increasing the melt temperature; excessive back pressure at the die head (such as clogged filter screen), prolonged melt residence time, absorbing too much heat.
• Raw material factors: Large fluctuations in the melt flow index of raw materials; mixing of different batches of raw materials without sufficient homogenization, leading to changes in heat demand during the plasticization process.

(3) Solutions

• Calibrate the temperature control system: Recheck and set the process temperature of each temperature zone to ensure reasonable temperature matching; use an infrared thermometer to detect the actual temperature, calibrate the temperature control instrument and thermocouple, and replace malfunctioning components.
• Overhaul the heating and cooling system: Replace the damaged heating coil to ensure sufficient power of each heating section; clean the blocked pipeline of the cooling circuit, overhaul the cooling fan, and ensure the normal operation of the cooling system.
• Optimize equipment and process parameters: Replace the screw matching the characteristics of raw materials (such as a separate screw to solve the problem of uneven plasticization); adjust the screw speed to balance the generation of shear heat; regularly replace the filter screen, reduce the back pressure at the die head, and shorten the melt residence time.
• Stabilize raw material quality: Select raw materials with stable melt flow index, and thoroughly homogenize different batches of raw materials before mixing; preprocess the raw materials to remove moisture and impurities, ensuring stable plasticization process.

6. Preventive Maintenance Suggestions

1. Regular inspection: Establish a three-level inspection system of daily, weekly and monthly, focusing on checking the heating system, feeding system, transmission system and the wear of the screw and barrel, and timely discover potential faults.

2. Standardized operation: Operators must be professionally trained before taking up their posts, strictly implement the heating, startup and shutdown processes, and avoid equipment damage caused by incorrect operation.

3. Raw material control: Establish a raw material warehousing inspection mechanism to ensure stable raw material quality; pre-dry moisture-absorbing raw materials to avoid damp agglomeration.

4. Data recording: Regularly record equipment operating parameters (such as temperature, pressure, speed, extrusion output), grasp the equipment operating status through data analysis, and predict fault trends in advance.