Mastering PC Injection Molding

Introduction: Understanding Polycarbonate (PC)

폴리카보네이트(PC)[^1] is renowned for its exceptional performance, offering high transparency, excellent impact toughness, creep resistance, and a wide operating temperature range. However, processing this engineering plastic requires precision.

Key Material Characteristics:

Viscosity Sensitivity: PC melt viscosity is highly sensitive to temperature but less sensitive to shear rate.
No Clear Melting Point: It softens over a range.
High Melt Viscosity: Requires higher processing temperatures.
Hydrolysis Risk: The resin is prone to hydrolysis at high temperatures if moisture is present, leading to part degradation.

> 전문가 팁: To improve melt flow, do not rely solely on increasing injection pressure. Instead, raise the injection temperature. However, strict moisture control is non-negotiable.

?️ Critical Pre-Processing: Drying & Mold Design

Before the injection process begins, specific steps must be taken to ensure quality.

Drying is Mandatory[^2]: PC must be dried thoroughly to reduce moisture content to below 0.02%.
Moisture Protection: Keep the resin insulated during processing to prevent re-absorption of moisture from the air.
Mold Design: Runners and gates should be short and thick to minimize pressure loss.
Stress Reduction: High mold temperatures and post-processing annealing are recommended to eliminate internal stress and prevent cracking.

⚙️ The 7 Key Parameters of PC Injection Molding

Here is a detailed breakdown of the processing window for PC.

1. Injection Temperature[^3] Temperature selection depends on part geometry, mold structure, and requirements.

Standard Range: 270°C – 320°C.
경고: Exceeding 340°C can cause decomposition. Signs include darkened color, silver streaks, dark spots, and bubbles. Mechanical properties will significantly degrade.

2. 사출 압력[^4] Pressure affects physical properties, internal stress, and shrinkage.

Standard Range: 80 – 120 MPa.
High Pressure (120 – 145 MPa): Required for thin-walled, long-flow, or complex parts with small gates to overcome flow resistance.

3. Holding Pressure & Time Crucial for preventing vacuum voids and sink marks.

Strategy: Low holding pressure with high melt temperature is often the best approach to reduce internal stress.
Timing: Thin parts need short holding times; thick parts require longer times. This is often determined by the gate freeze-off time.

4. Injection Speed While speed has less impact on PC properties, flow control is key.

Recommendation: Use medium to slow speeds.
Technique: Multi-stage injection (Slow-Fast-Slow) is preferred to ensure smooth filling without trapping air.

5. 금형 온도[^5]

Standard: 80°C – 100°C.
Complex/Thin Parts: Can be increased to 100°C – 120°C (ensure this is below the mold steel's tempering temperature).

6. Screw Speed & Back Pressure[^6] Due to high viscosity, excessive speed can damage the machine or the material.

Screw Speed: 30 – 60 r/min.
Back Pressure: 10% – 15% of injection pressure.

7. Material Usage

Release Agents: Use strictly controlled amounts.
Recycled Material: Limit re-grind usage to max 20% and no more than 3 cycles.

Quick Reference: PC Processing Parameters

For easy reference, here is a summary of the optimal settings.

매개변수	Recommended Setting	Notes
Drying Temp/Time	120°C / 4+ Hours	Moisture < 0.02%
용융 온도	270°C - 320°C	Do not exceed 340°C
사출 압력	80 - 145 MPa	Higher for thin walls
금형 온도	80°C - 120°C	Higher temp reduces stress
Screw Speed	30 - 60 r/min	Prevents shear heating
배압	10% - 15%	Ensures melt density

Screw Selection & Machine Requirements

Choosing the right hardware is as important as setting the parameters.

Machine Requirements:

Shot Size: The maximum part weight (including runners) should not exceed 70-80% of the machine's nominal injection capacity.

Screw Specifications:

Type: Single-flight, constant pitch, gradual compression screw with a non-return valve (check ring).
L/D Ratio (Length/Diameter): 15:1 to 20:1.
Compression Ratio: 2:1 to 3:1.

결론

Mastering PC injection molding requires a balance of thermal control and pressure management. By strictly controlling moisture and adhering to the temperature and screw speed guidelines above, you can produce high-clarity, impact-resistant parts with minimal internal stress.

[^1]: Explore the advantages of Polycarbonate (PC) to understand its applications and benefits in various industries. [^2]: Understand the importance of drying Polycarbonate to ensure optimal processing and part quality. [^3]: Find out the best injection temperature settings for Polycarbonate to ensure quality and performance. [^4]: Explore how injection pressure affects the molding process and the final properties of Polycarbonate parts. [^5]: Explore the relationship between mold temperature and the quality of Polycarbonate parts in injection molding. [^6]: Learn how screw speed and back pressure influence the injection molding process and material quality.

저자 소개

Alex Yu

아이디얼 프로 매뉴팩처링

알렉스는 Ideal Pro의 공동 창립자이지만, 주요 프로젝트를 총괄하거나 기술 팀을 이끌지 않을 때는 장거리 자전거 타기를 즐기거나, 동네에서 가장 맛있는 커피를 찾아다니거나, 다음 여행 계획을 세우는 모습을 볼 수 있습니다. 국제 무역 영업과 프로젝트 관리 분야에서 20년 이상의 경력을 쌓아온 그는 촉박한 마감 기한부터 까다로운 엔지니어링 문제까지, 그 사이의 모든 상황을 다 겪어보았습니다. 그는 훌륭한 성과는 충분한 휴식을 취한 마음과 맛있는 커피에서 나온다고 믿으며, 맡은 모든 프로젝트에 그와 같은 호기심과 세심한 주의를 기울입니다. 사무실에 있지 않을 때는 대개 야외 어딘가에서 새로운 장소를 탐험하며, 나중에 나눌 이야기를 수집하곤 합니다.