In the world of advanced materials, PEI plastics have emerged as a game – changer. Polyetherimide (PEI), a high – performance thermoplastic, offers a unique combination of properties that make it suitable for a wide range of applications.
What is PEI Plastics?
PEI plastic, short for Polyetherimide, is a high – performance thermoplastic.
It has a high glass transition temperature (around 217°C), endowing it with excellent high – temperature resistance. This means it can maintain its shape and integrity under intense heat. In terms of mechanical properties, it has high tensile strength (resisting being pulled apart) and good flexural strength (able to bend without breaking easily).
PEI also shows strong chemical resistance, being able to endure exposure to fuels, oils, and many common solvents. Additionally, it is flame – resistant, with a low flammability rating and the ability to self – extinguish. These properties make it suitable for diverse applications across aerospace, automotive, electronics, and medical industries.
Properties Of PEI Plastics
High Temperature Resistance:
PEI plastics can withstand extremely high temperatures. They have a high glass transition temperature (Tg), typically around 217°C. This makes them ideal for applications where materials need to maintain their structural integrity under intense heat, such as in aerospace components, where parts are exposed to high – temperature environments during flight.
Mechanical Strength:
PEI exhibits excellent mechanical properties. It has high tensile strength, which means it can resist being pulled apart, and good flexural strength, allowing it to bend without breaking easily. This makes it suitable for applications where parts need to endure mechanical stress, like in automotive engine components.
Chemical Resistance:
PEI is highly resistant to a variety of chemicals. It can withstand exposure to fuels, oils, and many common solvents. This property makes it useful in industries such as chemical processing, where equipment needs to come into contact with different chemicals without degrading.
Flame Resistance:
PEI plastics are inherently flame – resistant. They have a low flammability rating and can self – extinguish when the source of ignition is removed. This makes them a popular choice in applications where fire safety is crucial, such as in the construction of electrical enclosures and aircraft interiors.
Advantages Of PEI Polymer
Lightweight:
Compared to metals, PEI plastics are much lighter. This not only reduces the weight of the final product but also leads to energy savings in transportation – related applications. For example, in aerospace, lighter components mean less fuel consumption.
Cost - Effective:
Although PEI is a high – performance material, in the long run, it can be cost – effective. Its durability and resistance to various environmental factors reduce the need for frequent replacements, lowering maintenance costs.
Design Flexibility:
PEI can be easily molded into complex shapes using injection molding and other manufacturing processes. This allows designers to create innovative and efficient product designs that may not be possible with traditional materials.
Common processing methods for PEI plastics include injection molding, extrusion molding, and blow molding. The following are the precautions for these processes.
PEI Injection Molding
Raw Material Preparation
PEI has strong hygroscopicity and must be dried before injection molding. It is usually placed in a drying oven at 150-180 ° C to dry for 3-5 hours, so that the moisture content is controlled below 0.02%-0.05%. This is because the presence of water may cause the material to hydrolyze during injection molding, affecting product quality, such as bubbles and surface defects.
To ensure that the raw material is in line with the high temperature requirements of the PEI grade, check the quality index and certification of the raw material. If you need to add other additives (such as reinforcement fibers, lubricants, etc.) to improve performance or processing performance, it should be mixed in accordance with the proportion after drying, and to ensure uniform mixing, you can use a high-speed mixer for full mixing.
Injection Molding Parameter Setting
- Temperature control: the cylinder temperature generally needs to be set between 340-400 ℃, and the nozzle temperature is slightly lower, about 320-360 ℃. Due to the high processing temperature of high temperature resistant PEI, only in this temperature range can the material be fully melted and have good fluidity to successfully fill the mold cavity.
- Pressure regulation: The injection pressure is usually between 70-150MPa. This is because the PEI material itself has a higher viscosity and requires a higher injection pressure to overcome the resistance, so that the material is evenly filled into the complex shape of the mold. The holding pressure is generally 50%-70% of the injection pressure, and the holding time is about 5-15 seconds, which can ensure the density and dimensional accuracy of the product.
- Speed adjustment: The injection speed is generally 20-50mm /s. For thin-walled products or products with complex shapes, appropriately accelerating the injection speed can prevent excessive cooling and insufficient filling, but too fast injection speed may lead to greater internal stress within the material, affecting product quality, such as warping, cracking and other phenomena.
Key Points of Injection Mold Design
- Gate design: Pin point gate, latent gate, etc., are more suitable for high temperature PEI injection gate forms. Gate size should be determined according to the size of the product and wall thickness, the general gate diameter is between 0.8-2mm, to ensure that the material can flow evenly into the mold cavity, reduce the generation of weld marks, and improve the appearance quality and strength of the product.
- Cooling system optimization: The cooling system of the mold is crucial for the injection molding of high temperature resistant PEI. Due to its relatively low heat conductivity, it is necessary to reasonably design the layout and size of the cooling channel so that the product can be uniformly cooled. Proper cooling can make the product release faster, improve production efficiency, and reduce the internal stress of the product to prevent deformation or cracking during use.
PEI Extrusion Molding
Raw Material Pretreatment
Similar to injection molding, the high temperature resistant PEI raw materials also need to be fully dried before extrusion, the drying temperature can be set at 150-180 ° C, the drying time is about 4-6 hours, the moisture content in the raw material is reduced to the appropriate range, to avoid quality problems in the extrusion process, such as material decomposition, surface roughness and so on.
Depending on the specific needs of the product, it may be necessary to add some lubricants (such as calcium stearate, etc.) to improve the extrusion performance of the material. The amount of lubricant added is generally between 0.1% and 0.5%, which can reduce the friction between the material and the screw and the barrel, making the extrusion process smoother.
Extrusion Parameter Regulation
- Temperature setting: The body temperature is generally between 330-380 ° C, and the temperature gradually rises from the feeding section to the die. For example, the temperature of the feeding section can be set at about 330 ° C, and the temperature of the die can reach about 380 ° C. This temperature gradient allows the material to gradually soften and uniformly extrude during the extrusion process, while avoiding material decomposition due to excessive temperature.
- Screw speed control: Screw speed is generally controlled between 15-40rpm. Excessive speed may lead to overheating of the material, degradation and other problems, affecting the quality and performance of the product; Too low a speed will affect production efficiency. The appropriate screw speed can ensure the stable extrusion of the material and make the surface quality of the extrude good.
Extrusion Mold design considerations
Dimensional accuracy adjustment: Design the appropriate die according to the shape and size of the product. For extruded products such as pipes and bars, the extrusion expansion rate of materials should be taken into account. The extrusion expansion rate of high temperature resistant PEI is generally between 1.1-1.3, and the size of the die should be adjusted accordingly to ensure the dimensional accuracy of the extrusion product. At the same time, the surface finish of the mouth die will also affect the appearance quality of the product, so it is necessary to carry out fine processing of the mouth die.
Blow molding
Extrusion billet temperature:
In the preparation stage of blow molding billet, the high-temperature resistant PEI raw material is heated and melted in the extruder and extruded into tubular billet. The extrusion temperature is similar to the temperature range of the above extrusion molding, between 330-380 ° C. In the extrusion process, the wall thickness uniformity of the billet should be strictly controlled, which is crucial for the quality of subsequent blow molding products.
Blow molding process essentials
Blow pressure and mold temperature: Put the billet into the blow mold, and then blow compressed air (generally between 0.6-1.2MPa) to expand the billet and fit the mold cavity to form the final product. The mold temperature in the blow molding process is generally maintained at 50-80 ° C, which can make the high temperature resistant PEI material better formed during the blow molding process and reduce the cooling time of the product.
At the same time, attention should be paid to controlling the blowing ratio, which is generally between 2-3 to ensure the uniform wall thickness and quality of the product.
Applications of Molding PEI Plastic
Aerospace Industry:
In aerospace, PEI is used for manufacturing various components. It is employed in aircraft engine parts, like compressor blades and shrouds, due to its high – temperature resistance and mechanical strength. Additionally, it is used in interior components such as luggage bins and seat parts, where flame resistance and lightweight properties are essential.
Automotive Industry:
The automotive industry benefits from PEI’s properties as well. It is used in engine components like intake manifolds, where its heat resistance and chemical resistance are crucial. PEI can also be found in lighting systems, replacing traditional materials with its lightweight and durable characteristics.
Electronics Industry:
In electronics, PEI is used for making connectors, sockets, and insulators. Its high – temperature resistance is valuable for electronic components that generate heat during operation. Moreover, its electrical insulation properties make it an ideal choice for protecting sensitive electronic circuits.
Medical Industry:
In the medical field, PEI is used in some medical devices. Its biocompatibility, along with its strength and sterilization resistance, makes it suitable for applications such as surgical instruments and implantable devices.