Key Points for Anti-Theft Lid Mold Design

1. Matching Precision of Anti-Theft Ring and Buckles
2. The core of an anti-theft lidlies in the connecting buckles between theanti-theft ring (pull ring) and the lid During design, strict control over the quantity, size, and angle of the buckles is required to ensure they break precisely when the lid is unscrewed while maintaining a secure connection when unopened.
3. The thickness of the buckles should be adjusted based on the lidmaterial (e.g., PP, PE). Excessive thickness will make opening difficult, while insufficient thickness may lead to accidental breakage during transportation. A general recommendation is a thickness of 3–0.5mm (to be verified based on lid diameter).
4. The anti-slip threadsinside the anti-theft ring must fit precisely with the groove on the bottle mouth to prevent slipping during screwing and ensure no mold sticking during demolding.
5. Coaxiality of Threads and Anti-Theft Ring
6. The internal threadsof the lid and the anti-theft ring must maintain high coaxiality; otherwise, it will cause misalignment during lidping, seal failure, or loss of anti-theft functionality. During mold design, concentric locating pins and guide sleeves should be used to ensure the coaxiality error between the cavity and core is ≤0.02mm.

1. Optimization of Seal Rib Design
2. The seal ribs (or gasket grooves)inside the lid are critical for leak prevention. The height, width, and quantity of the ribs must be designed to match the bottle mouth size. Typically, seal ribs adopt a trapezoidal or semicircular cross-section to avoid stress concentration during injection molding or wear during use caused by sharp corners.
3. For lids intended for special media such as carbonated beverages or chemicals, the compression rate of the seal ribs should be increased (generally 10%–15%), and seal performance should be verified through mold flow analysis.
4. Strict Control of Dimensional Tolerances
5. The outer diameter, inner diameter, and thread sizeof the anti-theft lid directly affect its compatibility with the bottle mouth. The dimensional tolerance of the mold cavity and core should be controlled within the range of ±0.01–0.03mm.
6. Considering the shrinkage rateof plastic materials (PP shrinkage rate is approximately 1.5%–2.5%, PE is about 2%–3%), shrinkage compensation based on material properties is necessary during mold design to avoid dimensional deviations in finished products.

3.Mold Structure and Demolding Efficiency Design

1. Multi-Cavity Layout and Balanced Feeding
2. Anti-theft lids are mass-produced products, so molds usually adopt a multi-cavity structure(e.g., 16-cavity, 32-cavity, 48-cavity). The cavity layout must be symmetrical and uniform to ensure consistent feeding speed across all cavities.
3. For gate design, pin-point gates or hot runner gatesare preferred. Hot runner systems can reduce sprue waste, improve production efficiency, and leave minimal gate marks that do not affect the lid's appearance or sealability. If cold runners are used, the gate position should be optimized to avoid stress concentration at the gate leading to anti-theft ring breakage.
4. Reliability of Thread Demolding Mechanism
5. Demolding the internal threads of anti-theft lids is a key challenge in mold design, requiring a rotational demolding mechanism. Two common solutions are:

• Rack-and-pinion rotational demolding: Drives the rack via the injection molding machine's mold opening force to rotate the core gear, achieving thread demolding. This structure is stable and suitable for mass production.
• Hydraulic motor rotational demolding: Offers higher precision and controllable demolding speed, suitable for high-precision lids or complex thread designs, but with higher costs.

6. During demolding, synchronization between thread rotation and axial movementmust be ensured to prevent thread scuffing or anti-theft ring deformation. Meanwhile, limit switches should be installed to avoid product dropping due to over-demolding.
7. Surface Treatment of Cavity and Core
8. The inner wall of the cavity requires polishing treatment(surface roughness Ra ≤0.2μm) to ensure a smooth lid surface and reduce demolding resistance. The core (threaded part) can undergo nitriding treatment or hard chrome plating to improve wear resistance and service life, preventing thread wear during long-term production.

4.Material Selection and Process Compatibility

1. Selection of Mold Steel
2. For the cavity and core, pre-hardened steel (e.g., P20, 718H)is preferred with a hardness of HRC 30–35, meeting the requirements of mass production. For high-transparency lids or corrosion resistance needs, stainless steel (e.g., S136) can be used.
3. For moving parts such as guide pillars and bushings, bearing steel (SUJ2)is selected to improve wear resistance and guiding precision.
4. Reserved Optimization Space for Injection Molding Processes
5. Mold design should consider the adjustability of injection parameters, such as the density of cooling channels: Independent cooling circuits should be designed for the cavity and core to ensure uniform cooling and reduce lidwarpage (especially for the anti-theft ring).
6. For lids made of different materials (e.g., PP, PE, PET), the mold should reserve temperature adjustment interfacesto adapt to the melting temperature and cooling speed of different materials.
7. Design for Production and Maintenance Convenience
8. Replaceability of Wear Parts
9. Wear-prone parts such as anti-theft ring buckles and threaded cores should be designed as detachable structuresto facilitate later maintenance and replacement, avoiding mold scrapping due to local damage.

5.Rational Layout of Venting System

1. Venting groovesshould be installed at the end of the cavity, between buckles, and other positions. The depth of the venting grooves should be ≤0.03mm (to prevent flash), and the width 5–10mm. This ensures smooth gas discharge during injection molding, avoiding defects such as bubbles, short shots, and weld lines on the lid.
2. Compliance and Standardization Considerations
3. Compatibility with Industry-Standard Bottle Mouths
4. Anti-theft lids must comply with bottle mouth standards in the target market (e.g., GB for China, ISO for international). Specific dimensional parameters of the customer's bottle mouth should be confirmed before mold design to avoid product incompatibility due to non-compliance with standards.
5. Food Safety Requirements (if used for food packaging)
6. If the mold is used to produce anti-theft lids for food or beverages, the mold steel and surface treatment must comply with food contact material safety standards(e.g., FDA, LFGB) to prevent harmful substances from mold release agents or steel from migrating to the product.

Summary

The core of anti-theft lid mold design is to balance "functional precision" and "production efficiency". Comprehensive optimization is required from four dimensions: anti-theft structure, sealability, demolding mechanism, and material technology, while considering the convenience of later maintenance and stability in mass production. It is recommended to use mold flow analysis to verify the filling, cooling, and shrinkage processes in the early design stage to avoid potential defects in advance.