Cooling circuit for injection molding cavity
The cooling circuit of the injection molding cavity is a core component of the mold cooling system, and its design rationality directly affects the molding cycle, dimensional accuracy, and surface quality of the plastic part. During the injection molding process, the melt releases a large amount of heat after entering the mold cavity. This heat must be quickly removed by the cooling circuit to quickly cool and solidify the plastic part. Insufficient or uneven cooling will extend the cooling time of the plastic part, reducing production efficiency and potentially causing defects such as warping, sink marks, and excessive internal stress. Therefore, the design of the cooling circuit must take into account factors such as the shape, wall thickness, and material properties of the plastic part to ensure uniform and efficient cooling, thereby guaranteeing the high-quality molding of the plastic part.
The layout of the cooling circuit should be designed based on the structural characteristics of the plastic part. Common layouts include straight-through, wraparound, branched, and spiral. A straight-through cooling circuit, consisting of inlet and outlet pipes and linear cooling holes, offers a simple structure and ease of fabrication. It’s suitable for flat and simple-shaped parts, but offers poor cooling uniformity and can only meet basic cooling requirements. A wraparound cooling circuit, arranged in a circular pattern along the contour of the part, maintains a uniform distance from the surface and is suitable for symmetrical parts with circular or ring-shaped structures, such as cup lids and discs, offering improved cooling uniformity. A branched cooling circuit, with multiple branch pipes branching from a main pipe, can penetrate deeper into complex areas of the part. It’s suitable for parts with ribs, bosses, and other structures, providing targeted cooling enhancements. A spiral cooling circuit, consisting of spiral-shaped cooling holes, offers a large contact area and high cooling efficiency. It’s suitable for large, deep-cavity parts, such as barrels and boxes, but is more difficult to fabricate and more expensive.
The design of key parameters of the cooling circuit directly affects the cooling effect, mainly including the cooling hole diameter, spacing, depth and inlet and outlet water temperature difference. The cooling hole diameter is usually determined according to the mold size and cooling water volume, generally 8-12mm. A diameter that is too small can easily lead to slow water flow and low cooling efficiency, while a diameter that is too large will weaken the mold strength. The distance between the cooling hole and the cavity surface should be uniform, usually 1-2 times the cooling hole diameter. Too far a distance will reduce the cooling efficiency, and too close may cause uneven temperature on the cavity surface. The spacing between the cooling holes needs to be adjusted according to the wall thickness of the plastic part. The spacing of parts with thicker walls should be reduced to enhance cooling; the spacing of parts with thinner walls can be appropriately increased. The inlet and outlet water temperature difference should be controlled within 5°C. Too large a temperature difference can easily lead to uneven cooling and affect the quality of the plastic part. The temperature difference can be controlled by adjusting the water flow to ensure stable operation of the cooling system.
The selection and flow state of the cooling medium also have an important impact on the cooling effect. Commonly used cooling media include cooling water and cooling oil. Cooling water is the most commonly used cooling medium due to its low cost and wide source. It is suitable for molding cooling of most plastics. Cooling oil has a low thermal conductivity, but high viscosity and poor fluidity. It is suitable for occasions where the cooling speed is not required or the mold temperature is high. The flow state of the cooling medium should remain turbulent, and the Reynolds number must be greater than 4000. The heat exchange efficiency in a turbulent state is much higher than that in a laminar flow, which can significantly increase the cooling speed. In order to ensure a turbulent state, the cross-sectional area and flow rate of the cooling circuit need to be reasonably designed. Generally, the cooling water flow rate should be controlled at 1.5-5m/s. The flow rate of each branch can be adjusted by installing a flow control valve to ensure the stability of the medium flow state in each cooling circuit.
The design of the cooling circuit also needs to consider coordination with other mold structures to avoid interference with parts such as push rods, guide pins, and inserts. When laying out cooling holes, avoid the installation locations of these parts. If this is not possible, special-shaped cooling holes or locally deepened cooling holes can be used to ensure effective cooling without affecting the functions of other parts. For complex-shaped plastic parts, 3D printing technology can be used to create conformal cooling circuits, allowing the cooling holes to perfectly fit the contours of the plastic part for uniform and efficient cooling. Furthermore, the cooling circuit needs to be equipped with an exhaust device to exhaust air from the circuit to prevent air blockage from affecting the flow of the cooling medium and heat exchange. During mold maintenance, the cooling circuit needs to be cleaned regularly to remove scale and impurities, ensure the smooth flow of the cooling medium, and maintain the efficient operation of the cooling system. Through scientific design and proper maintenance, the cooling circuit can effectively shorten the molding cycle, improve the quality of plastic parts, and provide strong support for injection molding production.
