PEI Injection Molding

Comparison of PEI with Other High Temperature Injection Molding Materials

Polyetherimide (PEI) is often compared to other materials with good-performance like Polyamide 46 (PA46), Liquid Crystal Polymer (LCP), Polyphenylsulfone (PPSU), Polyimide (PI), Polyphthalamide (PPA), and Polyetheretherketone (PEEK). Here’s a detailed comparison of these materials to help you figure out which one is best for your specific application needs.

PEI resists a wide range of chemicals, making it perfect for use in demanding environments.

Its ability to withstand sterilization processes makes PEI a top choice for medical applications.

PEI delivers exceptional tensile strength, impact resistance, and modulus for reliable mechanical performance.

With a glass transition temperature of approximately 217°C (423°F), PEI excels in high-temperature applications.

PEI’s flame-retardant properties meet UL94 V-0, V-2, and 5VA standards, offering inherent fire safety.

What are the basic conditions for PEI Injection Molding?

PEI is a fantastic plastic known for its ability to handle high temperatures, corrosion, and fatigue. To make high-quality PEI parts, you’ll need to follow these guidelines:

① Mold Temperature: 150-200°C (302-392°F)
Maintain this mold temperature range for optimal part filling and easy ejection.

② Injection Temperature: 350-400°C (662-752°F)
Ensure the injection temperature stays within this range to melt and flow the PEI material correctly.

③ Injection Pressure: 100-200 bar (1450-2900 psi)
Set the injection pressure within this range for proper mold cavity filling and packing.

④ Injection Speed: 50-100 mm/s (2-4 in/s)
Keep the injection speed in this range to fill and eject the part effectively.

⑤ Cool Time: 10-30 Seconds
Allow the part to cool for the right amount of time to solidify and ensure it maintains its shape and durability.

⑥ Ejection Temperature: 100-150°C (212-302°F)
Ensure the ejection temperature is within this range to allow the part to exit the mold correctly.

⑦ Mold Material: Steel or Aluminum
Select the mold material based on the specific needs of your part and PEI material.

⑧ Cooling System: Proper Cooling Design
Design an efficient cooling system to cool and cure the part effectively, ensuring stability and precision.

⑨ Mold Design: Tailored for Specific Needs
PEI injection molding can create complex shapes, but the mold design should be customized for the part and material.

⑩ Ventilation: Proper Airflow for Ejection
Good ventilation is essential for proper filling and ejection. Ensure vents allow air and gases to escape during injection.

⑪ Gate Location: Strategic Placement
Position the gate strategically to ensure smooth filling and efficient mold release.

⑫ Material Selection: Tailored to Requirements
Choose PEI material based on the part’s temperature tolerance, chemical exposure, and strength requirements.

How to Perform PEI Injection Molding: A Step-by-Step Guide​

The Polyetherimide, or PEI injection molding process involves several crucial steps to ensure the production of high-quality parts capable of withstanding extreme conditions:

1. Mold Design:
Create and design the mold, ensuring it includes the appropriate cavities, gates, and runner systems for optimal part production.

2. Material Selection:
Choose the right PEI material based on the specific needs of your application, considering factors such as temperature resistance, chemical exposure, and required strength.

3. Material Preparation:
Since PEI is hygroscopic (it absorbs moisture), it must be thoroughly dried before processing to prevent performance degradation. Non-filled grades should be dried at 150°C for about 4 hours, while filled grades may require up to 6 hours.

4. Machine Setup:
a. Temperature Settings: The injection molding machine should be set to high temperatures. The typical melt temperature range for PEI is 350°C to 410°C, while the mold temperature should be between 150°C and 180°C.
b. Injection Pressure: Injection pressures typically range from 100 to 200 MPa (700 to 1500 bar), depending on the part design and processing conditions.

5. Injection Process:
a. Injection Speed: To fill the mold quickly, injection speed should be fast. The runner system should be filled in 0.5 to 1.5 seconds, followed by cavity filling in 1 to 5 seconds.
b. Holding and Packing: After filling the mold, maintain pressure on the material to ensure complete packing. Hold time will depend on gate size; larger gates require longer hold times.

6. Cooling:
Allow the PEI material to cool and harden in the mold. The cooling time depends on the wall thickness of the part, with roughly 15 to 20 seconds of cooling time for every tenth of an inch of wall thickness.

7. Ejection:
After sufficient cooling, eject the part from the mold. The ejection system must be designed carefully to avoid damaging the part.

8. Post-Processing:
Depending on the application, post-processing steps may include machining, painting, or assembly with other parts to complete the final product.

When performing injection molding with PEI (Polyetherimide), it’s important to pay close attention to several factors due to its high-performance nature. Here are key considerations to ensure a successful molding process:

PEI requires high-temperature, high-pressure injection molding machines and molds due to its elevated melting point. For molds, materials like high-speed steel or tungsten carbide are ideal for handling the demands of PEI.

Injecting too quickly or with excessive pressure can lead to issues like material breakage or poor flow, which can result in defective parts. It’s essential to adjust the injection speed and pressure according to the type of PEI used and the design of the mold to ensure accurate part formation. Maintaining consistent pressure throughout the process is key to achieving proper mold filling and packing.

Due to PEI’s high crystallization temperature and thermal conductivity, an efficient cooling system is crucial to reduce crystallinity and prevent thermal stress. Cooling methods like water, air, or gas cooling should be selected based on the specific requirements of your application.

The performance of PEI parts heavily depends on their dimensional accuracy and surface quality. Ensure precise control over these factors during production, and address any necessary adjustments to guarantee the final product performs as intended.

Different grades of PEI have varying melt index ranges, so it’s essential to select the right one based on your product’s requirements. This ensures optimal performance and appearance of the molded parts.

PEI is highly hygroscopic, meaning it absorbs moisture, which can negatively affect the molding process and material performance. To avoid defects, thoroughly dry PEI pellets in a hot air dryer for at least 4 hours to ensure there’s no moisture that could cause bubbles or weaken the final product.

PEI’s high melting point means you need to set the processing temperature correctly to melt it without degrading the material. A typical processing temperature should be above 360°C, but be cautious not to overheat it, as this can cause color changes or degradation. Maintain precise temperature control during the molding process to ensure proper flow and consistent results. The ideal mold temperature typically ranges from 120°C to 180°C, helping with shrinkage control and improving both the part’s appearance and dimensional accuracy.

Designing the mold with a good venting system is crucial to prevent the formation of bubbles or burn marks. Since PEI has high flowability, it’s also important to minimize the flow distance and sharp corners in the mold design. This reduces flow stress and prevents cracks, ensuring high-quality parts.

Proper ventilation in the mold is essential to prevent air and gases from getting trapped, which can affect the quality of the parts and cause defects.

Holding time is crucial to compensate for material shrinkage after injection. Ensure the pressure is maintained for the right duration to avoid surface defects or dimensional issues due to shrinkage.

To prevent warping or shrinkage in PEI parts, ensure your cooling system is designed to cool the parts effectively and uniformly. Proper cooling helps maintain the integrity of the part and reduces the risk of deformation during the cooling phase.

PEI parts may require post-processing steps like annealing, particularly for thicker or more complex shapes, to relieve internal stresses. Additionally, ensure the part’s surface is free from grease or contaminants before any finishing or bonding operations are carried out to ensure a high-quality result.

PEI injection molding involves high temperatures, so operator safety is crucial. Ensure the use of appropriate protective gear, such as heat-resistant gloves and goggles. Also, provide proper ventilation in the workspace to avoid exposure to potentially harmful fumes during the molding process.

What are the advantages of PEI Injection Molding?

Thanks to its high temperature resistance and excellent mechanical properties, PEI injection molding offers several advantages. Here lists several key benefits:

What are the Applications of PEI Injection Molding?

PEI injection molding is a versatile process used across various high-end industries, thanks to PEI’s exceptional properties such as temperature stability, mechanical strength, and chemical resistance. Common applications include: