Precautions for using extruder screws

The extruder screw is the core component in plastic processing, which directly affects extrusion efficiency, product quality, and equipment life. Its use must strictly follow the operating specifications to avoid screw wear, material degradation, or equipment failure caused by misoperation. From the followingOperating standards, material adaptation, maintenance, and exception handlingFour aspects, systematically summarize key considerations.

1、 Operating standards

1. Start and Stop
   • Warm-up phase：
     • Before starting, it is necessary to preheat the screw and barrel according to the process requirements (temperature deviation ≤ ± 5 ℃) to avoid adhesion or wear between the screw and barrel caused by cold start.
     • exampleA certain factory started up without preheating, resulting in scratches on the surface of the screw and an increase of 20000 yuan in maintenance costs.
   • Shutdown sequence：
     • Stop feeding first and wait for the material inside the screw to be emptied before stopping to prevent residual material from solidifying and jamming the screw.
     • During emergency shutdown, it is necessary to immediately clean the material inside the screw (such as blowing with high-pressure gas).
2. speed control
   • Avoid speeding：
     • The screw speed should be set according to the material characteristics and extrusion volume. Overspeed may cause excessive shear heat, leading to material degradation.
     • reference value：
       • PVC: ≤ 40r/min (easily decomposed by high cutting)
       • PE/PP: ≤ 100r/min (adjusted according to screw diameter)
   • Stable speed regulation：
     • Avoid frequent start stop or rapid acceleration/deceleration to prevent torque impact from causing screw breakage.
3. pressure monitoring
   • Back pressure setting：
     • Excessive back pressure (>20MPa) will increase the screw load, leading to wear or motor overload; Low back pressure (<5MPa) may lead to uneven plasticization of materials.
   • Melt pressure monitoring：
     • Install a melt pressure sensor to monitor pressure fluctuations in real-time and promptly shut down for inspection in case of abnormalities.

2、 Material adaptation

1. Material selection
   • Match screw type：
     • Different screws (such as single screw, twin screw, barrier screw) are suitable for different materials and should be used according to their design purposes.
     • exampleBarrier type screws are suitable for high filling materials (such as calcium carbonate filled PE), while ordinary screws are prone to clogging.
   • Avoid mixing：
     • It is prohibited to mix PVC with PE/PP on the same screw, as the corrosiveness of PVC will accelerate the wear of the screw.
2. Preprocessing requirements
   • Drying treatment：
     • Materials with high moisture content (such as PA and PC) need to be dried to ≤ 0.02%, otherwise water vaporization will cause pressure fluctuations inside the screw.
   • Impurity removal filtration：
     • Impurities such as metal and sand mixed in the material can scratch the screw, and a magnetic separator and filter screen need to be installed.
3. Effects of additives
   • Corrosive additive：
     • Materials containing halogens (such as PVC stabilizers) and glass fibers can accelerate screw corrosion, and corrosion-resistant materials (such as bimetallic screws) should be selected.
   • Lubricant dosage：
     • Excessive lubricants (such as PE wax) can reduce the friction between the material and the screw, leading to slipping or poor plasticization.

3、 Maintenance and upkeep

1. regular cleanup
   • Shutdown cleaning：
     • After each shutdown, use screw cleaning materials (such as PE wax, specialized cleaning agents) to clean residual materials and prevent carbonization.
     • methodRun the cleaning material at low speed (10~20r/min) until the discharge is uniform.
   • Dismantling and cleaning：
     • Disassemble the screw every 3-6 months, clean the residue on the inner wall of the machine barrel with a copper brush or wood chip, and prohibit using a steel brush to damage the surface.
2. Wear and tear inspection
   • inspection cycle：
     • Measure the diameter and rib height of the screw every quarter. If the diameter decreases by ≥ 2mm or the rib wear is ≥ 1mm, it needs to be repaired or replaced.
   • Repair method：
     • Spray wear-resistant alloy (such as tungsten carbide) on the surface, or replace the screw as a whole.
3. Lubrication and cooling
   • Bearing lubrication：
     • Regularly add lubricating grease (such as lithium based grease) to the screw drive bearings and check every 500 hours of operation.
   • cooling system：
     • Ensure that the cooling water in the barrel is unobstructed. Excessive temperature (>60 ℃) can cause the screw to expand and get stuck.

4、 Exception handling

1. Common faults and countermeasures

   Fault phenomenon	Possible reasons	Solution
   Unstable extrusion volume	Screw wear and insufficient back pressure	Repair the screw and adjust the back pressure
   Material degradation (discoloration)	Excessive shear heat and prolonged residence time	Reduce the speed and shorten the length of the barrel
   Screw stuck	Foreign objects entering, material carbonization	Shutdown cleaning and installation of filter screen

2. Emergency shutdown process

   • When abnormalities are detected (such as abnormal noise or smoke), immediately press the emergency stop button to cut off the power.
   • Do not forcefully rotate the screw. Check the cause of the malfunction after the equipment has cooled down.

3. Maintenance safety

   • Before disassembling the screw, ensure that the temperature of the barrel drops below 50 ℃ and wear protective gloves to prevent burns.
   • Use specialized tools (such as hydraulic puller) to disassemble the screw, and prohibit violent tapping.

5、 Screw selection and upgrade suggestions

1. Based on material selection
   • High filling materialChoose barrier type screws or double stage screws to improve mixing efficiency.
   • Thermally sensitive materialsChoose low shear screws (such as large aspect ratio and shallow groove screws) to reduce degradation.
2. Material Upgrade
   • corrosion-resistantBimetallic screw (base made of alloy steel, surface coated with tungsten carbide).
   • wear-resistantNitrided screw (surface hardness HV ≥ 900, life extended by 2-3 times).
3. intelligent transformation
   • Install an online monitoring system to monitor screw temperature, torque, and melt pressure in real-time, and provide early warning of faults.

summary

The use of extruder screws must be strictly followedMatch materials, standardize operations, and conduct regular maintenanceThe principle is to extend the life of the screw and improve product quality through the following measures:

1. Operating SpecificationsPreheating, speed control, pressure control to avoid overload operation.
2. Material adaptationSelect materials according to screw type and perform pre-treatment, impurity removal, and dehumidification.
3. maintenanceRegularly clean, inspect for wear, lubricate and cool.
4. exception handlingQuick response to faults, safe disassembly and maintenance.

Recommended Practice：

• Establish a 'Screw Usage Ledger' to record data such as rotational speed, temperature, output, and maintenance records.
• Conduct professional inspections (such as non-destructive testing) on the screws every six months to evaluate their remaining lifespan.

Through scientific use and maintenance, the lifespan of the screw can be extended to 3-5 years, production efficiency can be increased by more than 15%, and the failure rate can be reduced by more than 40%.