Views: 0 Author: Site Editor Publish Time: 2025-07-08 Origin: Site
The heart of cap production lies in the mold. Key design considerations include:
Thread Formation
Rotating cores or collapsible segments create the spiral grooves.
Multi-start threads (2-4 leads) allow faster twisting.
Draft angles (0.5°–2°) ensure easy ejection.
Ejection Mechanism
Unscrewing molds: Motorized cores rotate to release the cap.
Split cavities: The mold opens sideways for complex threads.
Stripper plates: Push the cap off without distortion.
Cooling Channels
Strategically placed to solidify the threads first, reducing warpage.
The molding process requires tight control over:
| Parameter | Typical Setting | Why It Matters |
|---|---|---|
| Melt Temp | 180–280°C | Prevents material degradation |
| Injection Pressure | 60–120 MPa | Ensures thread detail fills completely |
| Cooling Time | 8–15 sec | Minimizes cycle time while preventing defects |
| Mold Temp | 40–80°C | Affects surface finish & shrinkage |
Material Choices:
Polypropylene (PP): Most common (flexible, chemical-resistant).
Polyethylene (PE): For squeezable caps.
PET/PETG: Clarity & stiffness (e.g., premium cosmetics).
After molding, caps undergo:
A. Finishing
Ultrasonic trimming: Removes microscopic flash from parting lines.
Vision inspection: Cameras detect defects like short shots or burrs.
B. Functional Enhancements
Liner insertion: Foam or foil seals for airtightness.
Tamper-evident bands: Added via secondary molding or welding.
Decoration: Hot stamping, silk screening, or UV printing.
C. Rigorous Testing
Torque testing: Measures opening/closing force (0.4–2.5 N·m ideal).
Leak tests: Pressurized air or water checks seal integrity.
Drop tests: Ensures durability (e.g., 1.2m drops onto concrete).
Stripped threads: Increase core cooling or adjust ejection speed.
Sink marks: Boost packing pressure or extend cooling time.
Jamming during use: Fine-tune thread pitch tolerance (±0.02 mm).
Next time you twist open a bottle, remember the engineering marvel in your hand! From mold design to material science, every detail ensures that tiny threads perform flawlessly—proof that great packaging blends innovation with precision.
