Runner Lock Pin Tip Comparison: Standard, Hard Lock, Edge & Cone
All Four Tip Types at a Glance
| Tip Type | Undercut Depth | Grip Force | Release Force | Runner Mark | Best For |
|---|---|---|---|---|---|
| Standard | 0.3–0.5 mm | Low–Medium | Low | Small circular indent | ABS, PP, PE, PS — general purpose |
| Hard Lock | 0.5–1.0 mm | High | High | Deep circular indent with barb mark | PA-GF, PBT-GF, POM — stiff/high-shrink resins |
| Edge | 0.1–0.3 mm | Low | Very Low | Thin line impression | Thin runners, soft resins, minimal mark required |
| Cone | 0.5–0.8 mm (conical) | Medium–High | Medium | Conical indent | Large runner sections, thick runners |
Standard Tip
The standard tip has a simple cylindrical undercut near the tip end. When resin solidifies around this undercut, the resulting mechanical interlock holds the runner in the runner plate during first-stage mold opening.
Standard tips are the industry default because they balance grip strength with ease of runner release. The shallow undercut (0.3–0.5 mm) provides sufficient grip for most commodity resins while allowing the runner to release cleanly during second-stage opening without excessive force.
- Advantages: Lowest cost, easiest runner release, works with most resins
- Limitations: Insufficient grip for high-shrinkage or glass-filled resins that shrink away from the undercut during cooling
Hard Lock Tip
Hard lock tips feature a deeper undercut with a barbed profile — a sharp edge that digs into the runner material and resists pull-out. The deeper undercut (0.5–1.0 mm) and barb geometry increase grip force by 2–3× compared to standard tips.
These tips are essential for resins that shrink significantly during cooling (high mold shrinkage resins like POM, PA, PBT) or that develop high stiffness at mold temperature (glass-filled grades). Without hard lock tips, these resins pull free from standard tips during first-stage opening, causing the runner to stick to the cavity plate and damage the parts.
- Advantages: Strongest grip, handles high-shrinkage and stiff resins
- Limitations: Higher release force may cause runner breakage with brittle resins; leaves a more visible mark
Edge Tip
Edge tips grip the runner with a thin, sharp ridge rather than a cylindrical undercut. The edge bites into the runner surface to create a friction grip with minimal penetration depth (0.1–0.3 mm).
This design is optimized for two scenarios: thin runners where there is insufficient material for a deep undercut, and applications where the runner mark must be minimized (e.g., when the runner is reground and runner marks can cause cosmetic issues in the next molding cycle).
- Advantages: Smallest runner mark, works in thin runner cross-sections
- Limitations: Lowest grip force — only suitable for soft, flexible resins with low shrinkage
Cone Tip
Cone tips have a conical undercut that provides a large grip surface area. The cone geometry distributes the holding force over a larger contact area than cylindrical undercuts, making it suitable for large-diameter runners where the runner mass generates high pull-out forces during mold opening.
- Advantages: High grip force with distributed stress, good for large runners
- Limitations: Requires more runner material around the pin, not suitable for thin runners
According to ScienceDirect's injection moulding reference, runner lock pin tip selection should match the specific resin's mold shrinkage rate — resins with shrinkage above 1.5% generally require hard lock or cone tips.
Selection Decision Matrix
| Resin Family | Mold Shrinkage | Recommended Tip | Reason |
|---|---|---|---|
| ABS, PS, PMMA | 0.3–0.7% | Standard | Low shrinkage, adequate grip |
| PP, PE | 1.0–2.5% | Standard or Hard Lock | High shrinkage may need stronger grip |
| PA6, PA66 | 0.8–1.5% (unfilled) | Hard Lock | Crystalline, shrinks away from pin |
| PA-GF, PBT-GF | 0.3–0.7% (filled) | Hard Lock | Stiff at mold temp, resists deformation |
| POM | 1.5–2.5% | Hard Lock | Very high shrinkage |
| TPE, TPU | 0.5–1.5% | Edge | Soft, flexible — deep undercuts tear |
According to ISO 20457, mold shrinkage values vary with part thickness and processing conditions. Always verify the actual shrinkage of your specific resin grade before selecting lock pin tip type.
Frequently Asked Questions
Which tip type provides the strongest runner grip?+
Which tip type leaves the smallest mark on the runner?+
Can I mix different tip types in the same mold?+
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