The 2-cavity mold adopts a balanced symmetrical layout. The center distance between the two cavities is precisely calculated based on the preform’s external dimensions and the tie-bar space of the injection molding machine, typically ranging from 300 to 350 mm. The runner system employs a full hot runner design with independent zonal temperature control, where each cavity corresponds to an individual hot runner branch. The main runner features an open structure with a diameter of Φ8–10 mm, while the sub-runners utilize a circular cross-section with a diameter of Φ6–8 mm. The gate design incorporates a needle valve control mechanism, with a gate diameter of Φ3–4 mm, enabling sequential opening and closing to ensure uniform filling of both cavities. The runner system requires melt flow balance analysis to ensure the filling time difference between the two cavities does not exceed 0.1 seconds.
The cooling system employs a multi-layer water channel layout. The core section incorporates spiral water channels, while the cavity section utilizes a series-connected water channel design. The water channel diameter is Φ10–12 mm, arranged equidistantly at 15–20 mm from the cavity surface. For thick-walled areas such as the neck, mouth, and base, independent cooling circuits are added, utilizing fountain-type cooling structures. Temperature control is divided into no fewer than six zones, with temperature variations within each zone controlled within ±2°C. The cooling water flow rate should reach 20–25 L/min at a pressure of 0.3–0.5 MPa to ensure heat exchange efficiency. The target temperature difference between the inlet and outlet water is 3–5°C, with a cooling time of 25–35 seconds.
The ejection system adopts a hydraulic-mechanical hybrid design, incorporating 12–16 ejector pins with diameters of Φ8–10 mm. These pins are distributed in areas of higher structural strength, such as the bottom flange and neck reinforcement ribs of the preform. The ejection stroke ranges from 100 to 120 mm, with adjustable ejection speeds in segments. The venting system includes continuous venting slots on the parting surface, with slot widths of 8–10 mm and depths of 0.02–0.03 mm. Auxiliary venting inserts are added in the last-to-fill areas of the melt, with venting clearances of 0.01–0.015 mm. The fit clearance between the ejector pins and holes is controlled at 0.02–0.03 mm, also serving a venting function.
The core and cavity are made from 1.2344 (H13) electroslag remelted steel with a hardness of 48–52 HRC. The hot runner system utilizes high-temperature alloy steel capable of withstanding continuous operating temperatures of 400°C. The mold base is made from P20 pre-hardened steel with a hardness of 30–33 HRC. Guide pillars and bushings are made from GCr15 bearing steel with a hardness of 58–62 HRC. Ejector pins are made from SKD61 material and undergo surface nitriding treatment.
H13 steel undergoes vacuum high-pressure gas quenching, with quenching temperatures of 1020–1050°C and tempering temperatures of 580–620°C. Triple tempering ensures structural stability. After heat treatment, deep cryogenic treatment is applied at temperatures below -80°C for 4–6 hours to eliminate retained austenite. Finally, surface polishing is performed, achieving a cavity surface roughness of Ra 0.025–0.1 μm and a draft angle of 1.5°–2.5°.
Cavity dimensional tolerances are ±0.02 mm, with parting surface flatness of 0.02 mm/300 mm. The fit clearance between guide pillars and bushings is 0.01–0.015 mm. The coaxiality of the hot runner system is Φ0.02 mm. Cooling water channels undergo a seal pressure test at 0.8 MPa for 30 minutes without leakage. After final assembly, the mold clamping clearance does not exceed 0.03 mm.
A coordinate measuring machine (CMM) is used to inspect cavity profile accuracy with a precision of 0.003 mm. A white light interferometer measures surface roughness. An infrared thermal imager monitors temperature distribution uniformity. Pressure sensors measure in-mold pressure curves. During trial molding, process parameters such as injection pressure, holding pressure, and cooling time are recorded to establish a standard process window.
Melt temperature: 270–285°C; mold temperature: 95–110°C. Injection speed is controlled in multiple stages: slow initial breakthrough, fast filling in the middle stage, and reduced speed for packing at the end. Injection pressure: 80–120 MPa; holding pressure: 40–60 MPa; holding time: 8–12 seconds. Cooling time: 25–35 seconds; mold opening and closing time: 8–12 seconds; total cycle time: 60–80 seconds.
To address preform weight variations, adjust hot runner temperature balance, controlling the temperature difference between cavities to within ±1°C. To resolve weld lines, optimize gate locations and adjust injection speeds. To prevent mouth deformation, optimize cooling water distribution and adjust ejection timing. To avoid stress whitening, reduce holding pressure and increase mold temperature.
The mold design life exceeds 1 million cycles, with a normal production rate of 12–15 cycles per hour. Mold changeover time is controlled within 2 hours, including hoisting, positioning, and debugging. Routine maintenance is performed every 50,000 cycles, including water channel cleaning, wear inspection, and replacement of wear-prone parts.
Preform weight tolerance: ±1.5%; wall thickness deviation: ≤8%; mouth dimension accuracy: ±0.1 mm. Crystallinity: 30–35%; acetaldehyde content: ≤4 μg/L. Burst pressure: ≥1.8 MPa; drop test passing height: 1.5 m. Visual inspection confirms no defects such as bubbles, impurities, or scratches.
Primarily used for producing 5-gallon and 6-gallon water bottle preforms, also suitable for large-capacity packaging containers in chemical, food and beverage, and industrial liquid applications. Compatible with various materials such as PET, PE, and PP, meeting different liquid packaging requirements.
A single mold investment ranges from approximately 250,000 to 400,000 RMB, with an annual output of 300,000–400,000 preforms. Compared to single-cavity molds, production efficiency increases by 80–100%. Annual mold maintenance costs account for 5–8% of the initial investment, with overall operating costs 30–40% lower than imported molds. The typical investment payback period is 12–18 months.
Daily checks of hot runner thermocouples and heating rings. Weekly cleaning of filters and inspection of water channel通畅性. Biweekly lubrication of guide pillars and ejection mechanisms. Monthly inspection of parting surface sealing and tightening of connection bolts. Regular cleaning of venting slots to prevent clogging.
Inspect cavity surface condition every 30,000 cycles, polishing as needed. Check cooling water channels for scaling every 50,000 cycles, performing chemical cleaning. Inspect the hot runner system every 100,000 cycles, replacing aging seals. Maintain a mold maintenance log to record all maintenance activities and part replacements.
High-speed machining reduces mold manufacturing time by 30%, while five-axis machining improves the precision of complex surfaces. Electrical discharge machining (EDM) accuracy reaches ±0.003 mm, enhancing surface quality. Laser cladding technology enables local mold repair, extending service life.
Multi-layer composite cooling channels improve cooling efficiency by over 20%. Quick mold change systems reduce changeover time to under 1 hour. Standardized mold bases reduce machining requirements and costs. Lightweight designs lower mold weight for easier handling.
Determine the number of cavities based on production needs, ensuring compatibility with the injection molding machine’s clamping force and shot volume. Consider factory ceiling height and crane lifting capacity. Select experienced mold manufacturers and evaluate their machining equipment and technical teams. Request detailed design proposals and mold flow analysis reports.
Workshop temperature: 20–28°C; humidity: 40–60%. Injection machine hydraulic system cleanliness: NAS Class 8 or higher. Cooling water temperature: 10–15°C; hardness: ≤8°dH. Stable power supply with voltage fluctuations within ±5%. Equip with specialized hoisting tools and standardize operational procedures.
The technical level of 2-cavity 6-gallon preform molds directly impacts the production quality and economic efficiency of large plastic packaging containers. By optimizing design, ensuring precision manufacturing, and implementing scientific maintenance, mold performance can be fully utilized to improve production efficiency and reduce costs. In the future, advancements in materials science and manufacturing technology will drive these molds toward higher efficiency, longer service life, and easier maintenance, providing the packaging industry with superior technical equipment. Users should select appropriate mold configurations based on their production needs, establish comprehensive usage and maintenance systems, ensure stable mold operation, and maximize economic benefits.