PEI Injection Molding Drying, Temperature Settings

1. Introduction PEI Injection Molding

Polyetherimide (PEI), sold under brand names like SABIC Ultem™ and Valiant PEI, is a high-performance amorphous engineering plastic. It offers exceptional thermal stability (Tg 217°C), inherent flame retardancy (UL94 V0), and excellent mechanical properties up to 170°C. However, these benefits come at a cost: PEI demands precise injection molding conditions.

Unlike commodity plastics like polypropylene or ABS, PEI is hygroscopic and sensitive to moisture, requires high melt and mold temperatures, and can exhibit defects if parameters are not carefully controlled. Whether you are molding a thin‑wall electrical connector or a structural aerospace bracket, understanding the correct processing window is essential for producing consistent, high‑quality parts.

In this guide, we will walk through every critical step: drying, machine settings, troubleshooting common defects, post‑molding operations, and how CISKO NEW MATERIAL can support your processing success.

2. Pre‑Molding: The Critical Drying Step

2.1 Why PEI is Hygroscopic

PEI absorbs moisture from ambient air. In fact, Ultem 1000 can absorb up to 0.25% water by weight in just 24 hours at 50% relative humidity. This moisture becomes trapped within the polymer matrix and, when exposed to the high melt temperatures (350–410°C), turns into steam. The result is cosmetic and structural defects.

Moisture Content	Consequence
< 0.02% (dry)	Optimal molding, clear surface, good mechanicals
0.02–0.05%	Minor splay, reduced tensile strength
> 0.05%	Severe splay, silver streaks, voids, hydrolytic degradation

2.2 Recommended Drying Parameters

To achieve moisture levels below 0.02%, follow these drying guidelines:

Temperature: 150°C (302°F) – do not exceed 160°C to avoid oxidation.
Time: 4–6 hours (up to 24 hours cumulative if left in dryer).
Dew point: −40°C or lower. Only dehumidifying or desiccant dryers work; hot air dryers are insufficient.
Airflow: Ensure sufficient circulation around pellets (typically 0.5–1.0 m³/min per kg).

Practical tip: Use a hopper dryer attached to the injection molding machine. Never dry PEI in an open oven unless it has forced air and a dew point monitor – most ovens recirculate humid air.

2.3 Consequences of Insufficient Drying

If you skip drying or do it improperly, you will likely encounter:

Splay / silver streaks: Water vapor expands explosively as it exits the nozzle, creating gas bubbles that stretch into streaks on the part surface.
Voids (internal bubbles): Trapped moisture vapor that cannot escape solidifies into spherical voids, weakening the part.
Hydrolytic degradation: At 350–410°C, water reacts with the polymer chains, causing chain scission. This reduces molecular weight, leading to lower tensile strength, elongation, and impact resistance. The material becomes brittle and may yellow excessively.

Our recommendation: Invest in a moisture analyzer to verify pellet moisture before molding. Target 0.02% or less. If you see splay, stop and dry for another 2–4 hours.

3. Machine & Mold Settings

Once the resin is properly dried, the next step is setting up the injection molding machine and mold for PEI.

3.1 Melt Temperature (Barrel Zones)

PEI requires a high melt temperature to achieve adequate flow and fusion. The glass‑filled grades (e.g., Ultem 2200, 2300) need slightly higher temperatures than unfilled grades.

Zone	Ultem 1000 / 1010 (unfilled)	Ultem 2100–2400 (glass filled)
Rear (feed)	330–350°C	340–360°C
Middle	340–370°C	350–380°C
Front (metering)	350–390°C	360–400°C
Nozzle	345–400°C	355–410°C

Important: Do not exceed 410°C for extended periods, as thermal degradation can occur, causing black specks and loss of properties.

3.2 Mold Temperature

Unlike semi‑crystalline plastics that use cold molds, PEI (amorphous) benefits from hot molds. A hot mold:

Improves surface finish (glossy, defect‑free)
Reduces internal stresses (less warpage)
Allows better replication of fine details

Parameter	Typical Range
Mold temperature	135–180°C (oil or cartridge heater controlled)
For thin walls (<1.5 mm)	Use higher end (160–180°C)
For thick walls (>4 mm)	Use lower end (135–150°C) to reduce cooling time

Tip: If your mold cannot reach 135°C, you will struggle to produce acceptable parts. Consider an external oil temperature control unit.

3.3 Back Pressure & Screw Speed

Back pressure: 0.3–0.7 MPa (3–7 bar). Higher back pressure helps melt homogeneity but may increase residence time. Keep moderate.
Screw speed: 40–70 rpm (circumferential speed 0.2–0.3 m/s). Too fast can cause shear heating and degradation.

3.4 Injection Speed

Thin‑wall parts (<2 mm): Medium to fast injection speed to fill cavity before the melt freezes.
Thick‑wall parts (>4 mm): Slower injection speed to avoid excessive shear and reduce risk of burn marks.
General rule: Start at 50–80% of machine maximum, then adjust based on visual inspection.

3.5 Venting

Proper venting is essential for PEI to allow air and small amounts of volatiles to escape. Recommended vent depth: 0.025–0.076 mm (0.001–0.003 inches). Deeper vents may cause flash.

4. Troubleshooting Common Defects

Even with proper drying and machine settings, defects can occur. Below are the most frequent issues with PEI, their root causes, and solutions.

4.1 Splay / Silver Streaks

Appearance: White or silvery streaks on the part surface, usually near the gate.

Root cause: Moisture in the resin (or, less commonly, trapped air or contamination).

Solutions:

Re‑dry the resin – 150°C for another 2–4 hours. Verify moisture content.
Check dryer dew point – should be ≤ -40°C.
Ensure the hopper is closed and resin not exposed to ambient air for long.
Reduce back pressure slightly (if moisture is not the issue, but moisture is the primary cause).

4.2 Burn Marks (Black Specks / Discoloration)

Appearance: Dark brown or black streaks, usually at end of flow path or near vents.

Root causes: Trapped air that gets compressed and ignites (diesel effect), or thermal degradation due to excessive melt temperature or long residence time.

Solutions:

Increase venting – deepen vents (within 0.076 mm limit) or add more venting slots.
Lower melt temperature by 10–20°C.
Reduce screw speed to lower shear heating.
Minimize residence time – use a smaller barrel if cycle time is long (shot weight should be 40–60% of barrel capacity).
For glass‑filled grades, check for screw and barrel wear – degraded glass can cause black specks.

4.3 Warpage (Dimensional Distortion)

Appearance: Part bent, twisted, or out of flatness.

Root causes: Uneven cooling between core and cavity, or excessive molded‑in stress.

Solutions:

Optimize mold temperature – ensure both halves are uniformly heated (use independent controllers).
Increase mold temperature to reduce stress gradient.
Adjust cooling circuit – balance flow through all channels.
Reduce injection pressure and use a longer packing stage to allow more uniform packing.
Consider annealing post‑molding (see Section 5).

4.4 Short Shots (Incomplete Filling)

Appearance: Part not fully formed; missing features near end of flow path.

Root causes: Insufficient melt flow, low injection pressure, or cold mold.

Solutions:

Increase melt temperature (up to the grade’s limit).
Increase mold temperature (to 160°C+).
Increase injection speed (for thin walls) or pressure.
Switch to a high‑flow grade – This is often the most effective fix. Consider:
- Ultem 1010 (SABIC) – improved flow over standard 1000.
- Valiant VAT002HF (Valiant) – high‑flow PEI with melt flow rate 10–16 g/10 min (vs 6–9 for standard).
Check nozzle and sprue for obstruction or cold slug.

4.5 Flash (Excess Material at Parting Line)

Appearance: Thin plastic fins extending from the part edge.

Root causes: Excessive injection pressure or clamp force too low, or worn mold.

Solutions:

Reduce injection pressure or switch to transfer (velocity control) earlier.
Increase clamp force if mold is not fully closed.
Check mold for wear – replace or resurface parting line.

5. Post‑Molding Operations

5.1 Annealing (Stress Relief)

PEI parts, especially those with thick sections, metal inserts, or complex geometries, can benefit from annealing. Annealing reduces internal stresses that could lead to cracking or dimensional changes over time.

Recommended annealing procedure:

Heat parts in an air‑circulating oven at 150°C for 2–4 hours.
Cool slowly – at a rate of no more than 10°C per minute, ideally in the turned‑off oven for 1 hour, then to room temperature.
Do not remove parts quickly – quenching will reintroduce stress.

When to anneal:

Parts used in high‑temperature environments (above 150°C).
Parts with metal inserts (different CTE).
Parts that will be machined or bonded.

5.2 Machining

PEI can be machined using standard metalworking equipment (CNC mills, lathes, drills). Guidelines:

Use carbide tools with sharp edges.
Avoid high speeds that generate heat – use coolant or air blast.
For glass‑filled grades, tools will wear faster; diamond‑coated tools are recommended.

5.3 Bonding and Assembly

PEI can be solvent‑bonded using methylene chloride or other dichloromethane‑based solvents, but this is less common in regulated industries. Ultrasonic welding and snap‑fit designs are more reliable. For adhesive bonding, epoxy or cyanoacrylate systems designed for polyetherimide work well.

6. Processing Aids & Recommendations from CISKO

At CISKO NEW MATERIAL, we don’t just sell resins – we help you succeed in molding them.

6.1 Free Technical Documentation

Every grade we supply comes with:

TDS (Technical Data Sheet) – detailed property values.
SDS (Safety Data Sheet) – safe handling instructions.
Molding Parameter Sheet – recommended drying, temperatures, pressures for that specific grade.
COA (Certificate of Analysis) – batch‑specific traceability.

6.2 On‑Site Troubleshooting (for Qualified Customers)

For large‑volume customers, we offer on‑site support from our engineering team. We can:

Analyze defective parts and identify root causes.
Recommend parameter adjustments.
Train your operators on best practices for PEI molding.

6.3 High‑Flow Alternatives for Difficult Molds

If you struggle with short shots even after optimizing parameters, consider switching to a high‑flow PEI grade:

Grade	Melt Flow Rate (337°C/6.6kg)	Best For
Ultem 1000 (standard)	9 g/10 min	General purpose
Ultem 1010 (high flow)	10 g/10 min	Thin walls, complex parts
Valiant VAT002HF	10–16 g/10 min	Highest flow, cost‑effective

7. Conclusion

Injection molding PEI is not for the faint of heart, but with the right knowledge and discipline, it is highly repeatable and yields parts that outperform many other engineering plastics. The three pillars of successful PEI molding are:

Dry thoroughly – 150°C for 4–6 hours, dew point ≤ -40°C.
Use high temperatures – melt 350–410°C, mold 135–180°C.
Troubleshoot systematically – splay = moisture, burns = venting/temp, warpage = cooling/stress, short shots = flow/temp.

With these guidelines, you can produce high‑quality PEI parts for aerospace, medical, 5G, and industrial applications. And remember: CISKO NEW MATERIAL is here to support you with premium materials, documentation, and technical assistance.

Ready to improve your PEI molding?
📧 Email: info@pp-pei.com
📞 Call: +86 13538114678
🔧 Request technical support: Contact our engineers

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PEI Injection Molding: Drying, Temperature Settings & Troubleshooting Guide

1. Introduction PEI Injection Molding