Mastering PSU Injection Molding

Mastering PSU Injection Molding: A Comprehensive Processing Guide

Polysulfone (PSU, also known as PSF) is a high-temperature, high-strength thermoplastic engineering plastic. It is renowned for its high mechanical strength, excellent electrical insulation, high heat deflection temperature, and good chemical resistance. Notably, it exhibits superior thermal aging resistance, creep resistance, and dimensional stability.

Typical Applications

PSU is widely used across various sectors including electronics, food & daily commodities, automotive, aerospace, medical, and general industry.

Electronics: Contactors, connectors, transformer insulation parts, SCR caps, insulating bushings, coil bobbins, terminals, PCBs, bushings, covers, TV system parts, capacitor films, brush holders, and alkaline battery boxes.
Aerospace & Automotive: Protective cover assemblies, electric gears, battery covers, aircraft interior/exterior parts, and spacecraft protective shields.
Consumer Goods: Camera baffles, lighting components, and sensors.
Food & Medical: Replacing glass and stainless steel for steam trays, coffee servers, microwave cookers, milk containers, milking machine parts, and beverage dispensers. In the medical field, it is used for surgical trays, atomizers, humidifiers, dental instruments, flow controllers, and laboratory equipment.
Chemical Industry: Pump covers, tower protective layers, acid-resistant nozzles, pipes, and valve containers.

Injection Molding Process Characteristics

Understanding the rheological properties of PSU[^1] is crucial for successful molding.

Amorphous Polymer: PSU has no distinct melting point. The Glass Transition Temperature ($T_g$) is approximately 190°C. Molding temperatures generally exceed 280°C. The finished products are transparent.
Viscosity Sensitivity: Similar to Polycarbonate (PC), PSU melt behaves like a Newtonian fluid. The viscosity is highly sensitive to temperature. When the melt temperature exceeds 330°C, viscosity drops by 50% for every 30°C increase.
Flow & Stress: Despite temperature sensitivity, the viscosity remains high, resulting in poor flow. The melt cools rapidly, and due to the rigid molecular chains, internal stress is difficult to eliminate.
Moisture Sensitivity: Although PSU has no hydrophilic groups and low equilibrium moisture absorption (0.6%), trace moisture during molding can cause melt degradation due to high heat and shear. Drying is mandatory.
Shear Sensitivity: Excessive injection rates can cause melt fracture, limiting the filling rate and making mold filling difficult.

Machine & Equipment Requirements

To process PSU effectively, specific machine configurations are recommended to handle its high viscosity and temperature requirements.

Screw and Barrel Specifications:

Component	Requirement	세부 정보
Screw Type	Single flight, Full thread	Constant pitch, Low compression ratio.
L/D Ratio	14:1 to 20:1	Ensures proper melting and homogeneity.
Speed Control	Variable Speed Drive	Required to reduce screw load. Speed: 15–45 rpm (stepless speed regulation).
Temperature Control	High Precision	Must be stable up to 400°C.
노즐	Extension Type	Must have independent heating control. Aperture > 5mm (no drooling due to high viscosity).

Product & Mold Design

Designing for PSU requires accounting for its flow limitations and thermal properties.

Wall Thickness & Geometry

Minimum Thickness: Due to poor flow (Flow Length/Thickness ratio $approx$ 80), wall thickness should not be less than 1.5mm (ideally > 2mm).
Corners: PSU is sensitive to notches. Use fillets (arc transitions) for all right or sharp angles to prevent stress concentration.
Shrinkage: Stable at 0.4% – 0.8%. Shrinkage is consistent in both flow and transverse directions.
Draft Angle: Recommended at 1:50.

Mold Layout

표면 마감: Cavity surface roughness should be Ra 0.4 or better for a glossy finish.
Runners: Main sprue should be short and thick (diameter $ge$ 1/2 of part thickness) with a 3°–5° taper. Sub-runners should be circular or trapezoidal; avoid bends.
Gates: Size should be as large as possible. The land length (straight part) should be short (0.5–1.0mm). Locate gates at thick wall sections.
Cold Slug Well: Essential at the end of the sprue.
하소연: Critical for thin-walled parts requiring high injection speed. Vent depth should be controlled below 0.08mm.
금형 온도[^2]: High mold temperature is necessary to improve flow. Ideally > 140°C (minimum 120°C).

Processing Parameters

Optimizing these parameters is key to preventing defects like degradation or melt fracture.

Drying Process

Hot Air Circulation: 120–140°C for 4–6 hours. Bed thickness: 20mm.
Vacuum/Desiccant Drying: 130°C for 0.5–1.0 hours.

Temperature Settings

배럴 온도:
- **Thin Wall ( 300°C (up to 320°C or 350°C for specific grades).
- Thick Wall (> 5mm): 280–300°C.
- ️ Warning: Decomposition begins visibly above 360°C. Do not exceed 400°C.

Pressure & Speed

사출 압력[^3]: High pressure is required due to poor flow. Generally > 100 MPa, sometimes up to 140 MPa. This increases density and reduces shrinkage.
Injection Speed: Generally Low to Medium. High speeds cause melt fracture. Exception: Thin walls (~2mm) may require higher speeds to fill before freezing.
Screw Speed: Low speed recommended (15–45 rpm) due to high melt viscosity.

Cycle & Post-Processing

Mold Temp:
- Wall 2–5mm: 100–120°C.
- Wall > 5mm or 320°C should be avoided to prevent degradation.

[^1]: Understanding rheological properties is crucial for optimizing PSU processing and product quality. [^2]: Explore the significance of mold temperature in achieving optimal flow and product quality. [^3]: Discover how injection pressure influences the quality and characteristics of molded thermoplastic products.

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.