Wide-Mouth Preform Mould: Dimensional Consistency & Neck Crystallization Control Under Low Stretch Ratio
A wide-mouth preform mould is a critical intermediate tool in the polyester (PET/PEN) packaging chain, designed to produce preforms for jars and bottles with mouth diameters ≥48 mm and overall height ≤100 mm. Unlike standard CSD (carbonated soft drink) preform moulds, this class of tooling addresses challenges unique to low axial stretch ratiosand large cross-section injection, delivering uniform wall thickness to serve as a reliable orientation foundation for both single-stage and two-stage blow molding.
1. Process Characteristics & Design Boundaries
Wide-mouth containers are common for sauces, jams, nuts, and pet food—typically featuring PCO-1881, PCO-1810, or custom neck finishes. Their shorter height results in a low longitudinal draw ratio (LDR) of just 1.8–2.5, compared to 2.8–3.2 for soda bottles. Lower LDR means radial expansion dominates during blowing, making final jar strength highly sensitive to preform wall-thickness variation: target CT (wall thickness difference) ≤0.06 mm, with no abrupt transitions at shoulder areas to avoid bursting or stacking failure on filling lines.
2. Cavity System & Neck Ring Configuration
2.1 Rigid Neck Ring & Dual Sealing
Wider sealing surfaces experience higher filling pressures. Neck rings are machined from solid forgings with stainless steel support sleeves to resist elastic deflection. A primary seal plus auxiliary barrier edge limits clamp expansion to 0.005 mm, ensuring neck ovality ≤0.03 mm to meet high-torque metal capping requirements.
2.2 Low-Taper Cavity & Vacuum Venting
Short, broad preforms use reduced cavity draft angles (0.85°–1.2° vs. 1.5°–2° for tall preforms) to ease ejection. Annular vacuum channels below the neck flange connect to external pumps, evacuating cavity air in <0.3 s to eliminate foggy flow marks caused by fast filling, enhancing clarity.
3. Hot Runner & Filling Dynamics
3.1 Multi-Valve Sequencing & Melt Preservation
With preform weights ranging 30–70 g, moulds use 6–8 valve gates sequenced neck-first then body, directing melt downward to keep weld lines away from load-bearing seal surfaces. Manifold volume increases ~25% over standard preform moulds, with stepped bore expansion to progressively lower shear rates, limiting PET IV loss to <0.03 dl/g.
3.2 Zone Temperatures & Crystallization Management
Neck zone temperatures elevate to 125–145°C to accelerate crystallization to 22–28% for hot-fill resistance. Transition areas below the neck use independent cooling loops (95–105°C) to form a vertical thermal gradient, balancing seal integrity with visual transparency.
4. Asymmetric Cooling Intensification
Heavy neck sections slow cycle times. Moulds implement layered, staggered water channels: dual helical paths around the neck ring combined with variably spaced straight holes along the body create turbulent flow in thick regions. Separate mold-temperature control loops narrow neck-to-body ΔT to <5°C before ejection, achieving cycles of 14–18 s depending on weight.
5. Validation & Downstream Compatibility
Pre-production trials simulate blowing under specified reheat conditions: preforms must form jars without neck wrinkles or shoulder splits, and necks meet ISO-15509 sealability. Interchangeable neck inserts enable multi-format flexibility on one base mould (<4 h changeover), covering household food jars to industrial pails.
