Comprehensive analysis of runner adaptation strategy of 58 kinds of plastic materials: from classifi

Time：2025-04-16 08:18:13 / Popularity： 49 / Source：

Runner design is "lifeline" of injection molds, material properties directly determine shape and parameters of runner. Faced with hundreds of plastic materials on the market, how to accurately match runner system? This article divides 58 common materials into 15 categories, deeply analyzes key points of their runner adaptation, and attaches practical case analysis.

1. Material classification framework and core logic

Based on three dimensions of thermal performance, fluidity, and application scenarios of materials, a classification system is established:

Classification dimension	Core considerations
Thermal performance	Melting point, thermal stability, thermal expansion coefficient, cooling shrinkage rate
Fluidity	Melting index (MFR), viscosity curve, shear sensitivity
Application scenarios	Structural parts/appearance parts/functional parts, heat resistance/weather resistance/chemical resistance, transparency/conductivity and other special requirements

2. Detailed explanation of 15 major categories of materials and runner adaptation solutions

1. General plastics (7 types)

Representative materials: PP, PE (HDPE/LDPE), ABS, PS, PVC, EVA, GPPS
Features: Medium fluidity, shrinkage of 0.5-2%, low cost
Main points of runner design:
Preferably choose trapezoidal or semicircular cold runners (cross-sectional area ratio: 1:1.2)
PP/PE needs to increase runner corner radius (R≥3mm) to prevent melt fracture
PVC avoids long runners (recommended <150mm) to prevent thermal decomposition and production of HCl gas
Case:
PP trash can: Use 6mm diameter circular runner + 30° taper injection to balance flow and cooling efficiency
PVC pipe fittings: Short-distance U-shaped runner + chrome surface treatment to reduce material retention

2. Engineering plastics (12 types)

Representative materials: PC, PA6/PA66, POM, PET, PBT, PMMA, ASA, PPO, PPS, PEEK, PEI, LCP
Features: High rigidity, temperature resistance (120-260℃), large shrinkage difference (0.2-1.8%)
Main points of runner design:
PA/PET: runner length to wall thickness ratio ≤100:1 to prevent premature crystallization
PC/PMMA: polished mirror runner (Ra≤0.1μm) to eliminate flow lines
PEEK/LCP: high temperature runner (mold temperature 150-200℃) + cross-sectional area enlarged by 20%
Example:
PA66 gear: hot runner needle valve control + ring balanced layout to eliminate weld lines
PMMA optical lens: 3mm diameter circular runner + diffusion gate to avoid birefringence

3. High-temperature special plastics (8 types)

Representative materials: PI (polyimide), PBI (polybenzimidazole), PFA, PTFE, PVDF, PES, PSU, PAS
Features: Melting point > 300℃, narrow viscosity mutation range, easy to degrade
Main points of runner design:
Fully hot runner system (independent temperature control ±2℃)
Runner cross section adopts a parabolic shape to reduce shear heat
PTFE needs to pre-sinter runner (surface roughness Ra≤0.8μm) to reduce friction
Case:
PTFE sealing ring: Conical tapered runner (inlet 8mm→outlet 4mm) to alleviate creep effect

4. Elastomers and rubber (6 types)

Representative materials: TPU, TPE, SEBS, silicone (LSR), fluororubber, EPDM
Characteristics: high elasticity, mold sticking tendency, poor fluidity
Main points of runner design:
Open runner (width-to-depth ratio ≥ 2:1), inlet angle ≥ 60°
LSR requires pre-cooling runner (temperature gradient control) to prevent premature vulcanization
DLC coating on runner surface (thickness 2-5μm) reduces demolding resistance
Case:
TPU mobile phone case: fan-shaped gate + 8mm thick runner to compensate for elastomer rebound

5. Transparent materials (5 types)

Representative materials: COC, COP, SAN, MS, transparent PC
Characteristics: sensitive to light refractive index, easy to produce flow marks
Key points of runner design:
Mirror polishing of the entire runner (Ra≤0.05μm)
Adopt "slow-fast-slow" three-stage filling control
Avoid sudden changes in the runner (cross-section change rate <15%)
Case:
COC medical catheter: Spiral involute runner design to eliminate vortex flow

6. Conductive/antistatic materials (4 types)

Representative materials: Conductive PP (carbon fiber filling), antistatic ABS, conductive POM, conductive silicone
Characteristics: Filler affects fluidity and is easy to wear the mold
Key points of runner design:
Runner hardness ≥HRC60 (tungsten steel or titanium plating)
Avoid right-angle turns (changed to R≥5mm arc)
Carbon fiber materials use large-diameter runners (≥8mm) to prevent fiber breakage

7. Biodegradable materials (3 types)

Representative materials: PLA, PHA, PBAT
Characteristics: Heat sensitive (decomposition temperature <200℃), large viscosity fluctuations
Main points of runner design:
Runner length is compressed to 70% of the normal
Use low temperature mold temperature (40-60℃) + rapid cooling design
Add nitrogen purge channel to the runner wall to prevent carbonization

8. Composite materials (5 types)

Representative materials: Long glass fiber PP, carbon fiber reinforced PA, mineral filled PBT, wood plastic composite material, ceramic powder modified PE
Characteristics: Significant anisotropy, risk of filler deposition
Main points of runner design:
Static mixer is set at the runner inlet
Glass fiber material adopts stepped cross section (inlet > outlet)
Laser micro-texturing treatment of wood plastic material runner surface (groove depth 50μm)

9. Medical grade materials (4 types)

Representative materials: Medical grade PC, PEEK, TPE, silicone (in accordance with USP Class VI)
Features: Strict biocompatibility requirements, no mold release agents
Main points for runner design:
All stainless steel runner system (316L material)
Dead corner area of runner <0.1mm³
Set up online plasma cleaning interface

10. Flame retardant materials (4 types)

Representative materials: V0 grade ABS, flame retardant PC/ABS, halogen-free flame retardant PA, flame retardant PP
Features: Contains bromine/phosphorus flame retardants, easy to corrode molds
Main points for runner design:
Chemical nickel plating on the runner surface (thickness ≥ 25μm)
Avoid runner retention area (flow rate > 50mm/s)
Adopt fast color change runner structure

3. Practical design methodology

STEP 1: Reverse deduction of material properties
Query the material data sheet (TDS) and extract key parameters:
Melt density (g/cm³) → Calculate runner volume
Specific heat capacity (J/g·℃) → Determine cooling time
Thermal conductivity (W/m·K) → Design cooling water channel layout
STEP 2: CAE simulation verification
Moldflow key analysis items:
Filling pressure cloud map (target <80% injection molding machine maximum pressure)
Shear rate distribution (control <10⁴ s⁻¹ to prevent degradation)
Weld line prediction (adjust runner balance to eliminate V-level defects)
STEP 3: Economic verification
Runner cost formula:
\text{Total cost} = \left( \frac{\text{runner weight} \times \text{Material unit price}}{1 - \text{Recycled material addition rate}} \right) + \text{Processing energy cost}
Optimal solution determination: Select minimum cross-sectional area under premise of scrap rate <5%

4. Cutting-edge technological breakthroughs

AI-driven runner topology optimization: Generate three-dimensional runner shape based on GAN neural network, shortening design cycle by 70% compared with traditional design
Micro-bubble runner technology: Inject supercritical fluid (N₂/CO₂) into runner to achieve self-lubricating filling
4D printing intelligent runner: Shape memory alloy runner can automatically adjust cross-sectional shape according to temperature
Conclusion:
Adaptation of materials and runners is a dynamic game process, and it is necessary to find a balance point in "flow-cooling-contraction" triangle relationship. Only by mastering core parameters of these 58 materials and combining digital tools can we achieve leap from empirical design to scientific design.

Gud Mould Industry Co., Ltd