The Fiber Length Difference
Glass fiber reinforcement is the single most effective way to boost nylon’s strength, stiffness, and heat resistance. But not all glass fiber nylon is created equal. The critical variable is fiber length—and the difference between short glass fiber (SGF) and long glass fiber (LGF) reinforced nylon translates directly into real-world performance gaps that can determine whether a part succeeds or fails.
Short glass fiber nylon starts with chopped strands 3–4 mm long, but after compounding and injection molding—where the fibers are subjected to intense shear in the screw, barrel, and gate—the final fiber length in the molded part averages just 200–400 microns (0.2–0.4 mm).
Long glass fiber nylon is produced using a pultrusion process that encapsulates continuous fiber bundles in the nylon matrix, creating pellets typically 10–12 mm long with fibers running the full pellet length. After molding, the retained fiber length is 1–3 mm—roughly 5–10 times longer than SGF. This length retention is the source of all performance advantages.
Property Comparison: SGF vs LGF
| 속성 | PA6-SGF30 | PA6-LGF30 | Difference |
|---|---|---|---|
| 인장 강도(MPa) | 160–180 | 190–210 | +10–15% |
| 인장 계수(GPa) | 9–10 | 10–12 | +10–20% |
| 노치 이조드(kJ/m²) | 10–15 | 20–35 | +100–130% |
| Unnotched Izod (kJ/m²) | 55–70 | 80–100 | +40–50% |
| HDT @ 1.82MPa(°C) | 195–205 | 210–215 | +5–10°C |
| Creep Resistance | Good | 우수 | 2–3× improvement |
The most dramatic difference is in impact resistance: LGF nylon can absorb more than double the impact energy of SGF nylon. This is because long fibers bridge across crack fronts, requiring significantly more energy to propagate a fracture. Under sustained load, LGF also shows 2–3× better creep resistance—the long fiber network resists the time-dependent deformation that affects SGF parts under constant stress.
Processing: What You Need to Know
Processing LGF nylon requires specific attention to preserve fiber length:
- Screw design: Low-shear screws with deep flights and gentle compression ratios (1.8:1 to 2.2:1) are essential. High-shear general-purpose screws will destroy the fiber length advantage.
- Gate size: Gates should be at least 50% larger than for SGF to avoid excessive fiber breakage at the gate. Edge gates and fan gates are preferred over pin gates.
- 용융 온도: Run at the upper end of the recommended range to reduce melt viscosity and shear on fibers.
- Back pressure: Keep minimal—excessive back pressure grinds fibers in the compression zone.
- Tool wear: Both SGF and LGF are abrasive. Use hardened tool steel (54+ HRC) for production volumes over 50,000 parts.
When to Choose LGF Over SGF
Choose LGF when:
- Impact resistance is the primary failure mode (power tools, automotive crash components)
- Part experiences sustained static loads where creep is a concern (structural brackets, support frames)
- Metal replacement is the goal—LGF nylon more closely mimics the stiffness and creep behavior of die-cast aluminum and magnesium
- Fatigue life under cyclic loading is critical
- Part length-to-thickness ratio is high (long fibers provide better directional reinforcement)
Stick with SGF when:
- Part has thin walls (<1.5 mm) where long fibers cannot orient properly
- Complex geometry with multiple flow fronts—LGF’s longer fibers can create anisotropic shrinkage patterns
- Surface appearance matters—SGF provides a more uniform surface finish
- Cost is the primary driver—SGF is typically 10–20% less expensive per kilogram
엔지니어링 플라스틱에 나일론 플라스틱을 선택해야 하는 이유는?
- ✅ 300대 이상의 사출 성형기 50T에서 2000T까지
- ✅ 하루 10,000개 이상의 부품 생산 능력
- ✅ ±0.02mm 정밀도 모든 재료에 대한 허용 오차
- ✅ MOQ 단 1개 프로토타이핑용, 수백만 개로 확장 가능
- ✅ 24시간 견적, 리드 타임 3~15일
- ✅ ISO 9001 인증 품질 관리 시스템
관련 기사
- 유리 충전 나일론과 비충진 나일론 비교: 완벽한 성능 비교
- Carbon Fiber Reinforced Nylon: Properties, Processing, and Applications
- 충격 개질 나일론: 강화 폴리아미드 등급에 대한 완벽한 가이드
자주 묻는 질문
Can I use my existing SGF mold for LGF material?
Often yes, but gate and runner modifications are usually recommended. Pin gates should be enlarged, and runner diameters increased by 20–30% to minimize fiber breakage. Shrinkage may also differ slightly, so dimensional validation on first shots is essential.
Is LGF nylon more expensive than SGF?
On a per-kilogram basis, LGF is typically 10–25% more expensive. However, the ability to down-gauge wall thickness while maintaining or improving performance often results in lower cost per part. A complete cost-benefit analysis should consider part weight reduction, not just material price per kilogram.
Can LGF nylon be reground and reused?
Yes, but the fiber length will degrade with each regrind cycle, approaching SGF properties after 2–3 recycles. For premium applications, limit regrind to <15% and qualify performance with physical property testing on molded specimens.
What fiber percentage do I need?
LGF is most commonly offered at 30%, 40%, and 50% fiber weight fractions. 30% LGF provides a good balance of processability and performance. 50% LGF maximizes stiffness and HDT but requires careful processing and is limited to thicker-walled parts (>2.5 mm).
