Basic Principles of Cooling Channel Design
1. Uniform Cooling Principle
Cooling channels should ensure uniform temperature distribution throughout the mold, avoiding localized overheating or undercooling. Uneven cooling can lead to uneven internal stress distribution in the product, causing warping, deformation, or decreased transparency. The design should consider the differences in wall thickness across different parts of the preform, achieving balanced cooling by adjusting the density and position of the cooling channels.
2. High-Efficiency Heat Exchange Principle
Cooling channels should be as close as possible to the cavity surface to improve heat exchange efficiency. Studies show that the distance between the cooling channel and the cavity surface is generally controlled within the range of 1.5-2 times the channel diameter. Simultaneously, the turbulent flow state of the cooling medium within the channel (Reynolds number Re>4000) should be maintained to enhance heat exchange.
3. Pressure Balance Principle
The flow resistance of each branch of the cooling system should be balanced to ensure uniform distribution of the cooling medium to each channel. The design should avoid structures that cause pressure loss, such as sharp bends or abrupt changes in cross-section; parallel loop designs can be used when necessary.
Cooling Channel Structure Optimization Methods
1. Conformal Cooling Channel Design
Traditional straight-line drilled cooling channels are difficult to adapt to complex preform shapes. Conformal cooling technology can be used. Through 3D printing or special processing techniques, cooling channels are distributed along the cavity contour, significantly shortening the heat conduction path. Conformal cooling can improve cooling efficiency by more than 30% and reduce cooling time by 20%-40%.
2. Layered Cooling System
Layered cooling design is implemented for areas with different wall thicknesses. The mold is divided into multiple temperature control zones, each with an independent cooling loop. Precise temperature control is achieved by adjusting the flow rate of each loop. For example, the bottle neck area is usually thicker and requires stronger cooling capacity.
3. Spiral Cooling Channel
Using a spiral cooling channel design in the core mold area can enhance the turbulence effect of the cooling medium and improve the heat transfer coefficient. The spiral angle is generally controlled between 15° and 30°, and the pitch is 1.5-2 times the channel diameter. This design is particularly suitable for cooling preform core molds with large length-to-diameter ratios.
4. Jet-type Cooling Structure
A jet-type cooling structure is installed in key heat-concentrated areas (such as the bottom of the preform), directly impacting the high-temperature area by spraying cooling medium at high speed. The jet orifice diameter is typically 2-3 mm, and the spray velocity is controlled at 5-8 m/s, which can significantly reduce the local temperature.
