Precautions for PES Plastic Injection Molding
PES (Polyethersulfone) is a high-performance special engineering plastic with excellent high-temperature resistance, mechanical strength, dimensional stability, and electrical insulation properties. It is widely used in electronics, automotive, medical, precision instruments, and other industries. However, PES has strong hygroscopicity, high melting temperature, and a narrow processing window, requiring strict requirements for processes, equipment, and molds. Improper processing can easily lead to defects such as bubbles, silver streaks, yellowing, brittleness, and excessive internal stress. To achieve stable mass production, refined control must be implemented in raw material handling, process control, equipment and molds, production operations, and post-processing.
Raw Material Drying Treatment
PES is highly hygroscopic. Trace moisture at high temperatures can cause hydrolytic degradation, leading to reduced product performance and appearance defects. Drying is the primary key step in processing.
A dehumidifying dryer must be used; ordinary hot air drying cannot meet the low moisture content requirement.
Drying temperature is controlled at 150–160℃, and drying time is 4–6 hours. For glass fiber-reinforced grades, it can be extended to 6–8 hours.
After drying, keep warm at 120–140℃ in the hopper to prevent reabsorption of moisture. The raw material should not be exposed to air for more than 15 minutes.
Before production, check by empty injection. If there are no bubbles, silver streaks, or foaming, it can be determined that the drying is qualified.
Temperature Parameter Control
PES is extremely sensitive to temperature. Too low temperature leads to difficult filling and high internal stress, while too high temperature easily causes decomposition, discoloration, and brittleness.
Barrel temperature in sections: 320–330℃ at the rear section, 330–340℃ at the middle section, and 340–355℃ at the front section and nozzle.
The nozzle is independently temperature-controlled to reduce drooling. The actual melt temperature is controlled at 340–355℃, and must not exceed 365℃.
The mold temperature is maintained at 140–160℃, controlled by a high-temperature oil temperature machine. Insufficient mold temperature can easily lead to stress cracking and difficult demolding.
Injection Molding Process Settings
Reasonable process parameters can ensure uniform filling and reduce shear overheating and material degradation.
Injection speed adopts medium-high speed. For thin-walled and complex parts, the speed can be appropriately increased to avoid local overheating and decomposition.
Injection pressure is 100–140MPa, and holding pressure is 50%–60% of the injection pressure, balancing density and mold load.
Back pressure is 5–10MPa to improve melt uniformity, and screw speed is 50–80rpm to reduce shear heat.
The residence time of the melt in the barrel should not exceed 5–8 minutes, and the injection volume should be controlled at 30%–60% of the barrel capacity.
Cooling time is set according to the wall thickness, generally 20–60 seconds. The product can only be ejected after full solidification to prevent deformation and cracking.
Equipment and Mold Requirements
Equipment and molds must be adapted to the high-temperature and high-fluidity characteristics of PES to ensure long-term stable operation.
The rated temperature of the injection molding machine is not less than 400℃, the screw length-diameter ratio is 20–25, and components such as the check ring are wear-resistant and high-temperature resistant.
Mold steel is selected from S136, H13, NAK80, etc., treated by quenching and nitriding, with a hardness of HRC48–52.
Set exhaust grooves at the weld line and the end of the material flow, with a groove depth of 0.015–0.02mm and a groove width of 5–10mm to improve air trap and scorching problems.
Runners and gates preferably adopt circular runners and large-size gates to reduce pressure loss. The hot runner system has no dead ends and is easy to clean.
The ejection mechanism is evenly arranged, with ejection delay to reduce cracking caused by stress concentration.
Post-Processing and Production Maintenance
Proper post-processing can eliminate internal stress, and standardized maintenance can improve production continuity and mold life.
Annealing treatment is recommended for thick-walled and precision parts: keep warm at 160℃ for 2–4 hours and then cool with the furnace to eliminate internal stress.
Clean the mold parting surface, cavity, and runner before and after production, and regularly add lubricating oil to moving parts.
When shutting down, the machine must be thoroughly cleaned with PP or PE material at high temperature to ensure no residual PES in the barrel and hot runner.
Stabilize parameters during production, reduce random adjustments, keep records, and handle abnormalities in a timely manner.
By fully controlling all links including drying, temperature, process, equipment, mold, and maintenance, PES injection molding defects can be greatly reduced, product qualification rate and stability can be improved, and the high-performance advantages of the material can be fully exerted to meet the production needs of high-end products.
