Cooling circuit for common cores
The cooling circuit of an ordinary core is a core component of the injection mold cooling system, directly affecting the cooling rate, molding cycle, and dimensional stability of plastic products. As a key component on the inner surface of the molded product, the core continuously absorbs heat from the melt during the injection molding process. If the heat cannot be dissipated in time, the product will cool slowly, shrink unevenly, and even have defects such as warping and sink marks. The cooling circuit sets a circulating water channel inside or around the core, using cooling water to remove heat and quickly shape the product. A reasonable design of the cooling circuit must take into account cooling efficiency, uniformity, and core structural strength to avoid a decrease in core strength or cooling dead corners due to improper water channel layout.
The layout of the cooling circuit must be specifically designed based on the core’s shape and size to ensure uniform cooling. For cylindrical cores, the most commonly used design is an axial, straight-through cooling channel. This involves drilling a hole along the core’s axis from the bottom, with inlets and outlets located on the side. This allows cooling water to flow along the core’s center, directly removing heat. While this design is simple and easy to manufacture, it offers a limited cooling range and is suitable for cores with relatively low heights. For rectangular or irregularly shaped cores, a wraparound cooling channel design can be employed. This involves creating spiral or serpentine channels along the core’s contour, allowing cooling water to flow around the core and expand the cooling surface. For example, spiral cooling channels around automotive instrument panel cores ensure uniform cooling of complex curved surfaces and minimize deformation caused by temperature differences. For cores with deep cavities or bosses, a layered cooling channel design is required, with independent cooling circuits at different heights to avoid sink marks caused by insufficient cooling at the bottom of the deep cavity. The distance between the cooling channel and the core surface should be kept within 15-25mm. Too close weakens the core’s strength, while too far reduces cooling efficiency.
The dimensional parameters of the cooling water channels must be determined based on the core volume and heat load to ensure adequate cooling capacity. The channel diameter is a critical parameter. A too small channel diameter results in slow water flow and insufficient heat dissipation, while a too large channel diameter occupies excessive core space, compromising structural strength. Generally, channels with a diameter of 8-12 mm are used for small and medium-sized cores, while channels with a diameter of 12-16 mm are suitable for large cores. This ensures a water flow velocity of 1-3 m/s, creating turbulent flow and improving heat transfer efficiency. The inlet and outlet temperature difference of the channel should be controlled within 5°C. Excessive temperature differences can lead to uneven temperatures across the core, necessitating flow control valves to regulate the water flow in each circuit. For example, in multi-cavity molds, each core cooling circuit requires a separate flow valve to adjust the water supply based on the filling order and heat distribution of each cavity. Furthermore, channel bends should be rounded to avoid increased flow resistance and localized vortices caused by right-angle elbows, ensuring smooth water circulation.
The cooling circuit’s water inlet and outlet design should adhere to the principle of “bottom-in, top-out, low-in, high-out” to maximize cooling efficiency. The water inlet should be located at the bottom of the core, and the outlet at the top, allowing cooling water to flow from the low-temperature area to the high-temperature area, effectively absorbing heat. For multi-layer water channels, they should be connected in series or parallel. The series arrangement is suitable for small cores, as water flows sequentially through each layer of channels, ensuring efficient heat exchange but with significant pressure loss. The parallel arrangement is suitable for large cores, as each layer of channels has its own independent water supply, minimizing pressure loss but requiring precise flow balance between each branch. Sealing devices (such as O-rings) should be installed at the connection between the inlet and outlet and the main water channel to prevent cooling water leakage from affecting other mold components. For example, a sealing groove can be created at the interface between the core and the mold plate, and a heat-resistant rubber seal can be installed to ensure leak-free operation at a water pressure of 0.5-1.5 MPa. Furthermore, a filter should be installed at the water inlet to prevent impurities from clogging the channel. Especially when using groundwater or tap water, the filter should be cleaned regularly to prevent clogging and cooling failure.
The design and maintenance of cooling circuits are crucial for ensuring long-term cooling effectiveness. For cores with complex shapes that are difficult to machine with water channels, a modular design can be used. This design divides the core into multiple sections, processes the water channels separately, and then reassembles them. This facilitates machining and improves cooling uniformity. For example, cores with deep holes can employ a modular design with prefabricated cooling water pipes embedded within them, effectively cooling the deep cavity. Vents should be installed at the ends of the water channels to remove air trapped in the water and prevent air blockage that could affect heat transfer efficiency. These vents should be located at the highest point in the circuit, with automatic vent valves continuously discharging air. During routine maintenance, the water channels should be regularly cleaned of scale and impurities. A citric acid solution can be used for circulating flushing at least annually to ensure the inner walls of the channels are clean. Additionally, monitor the pressure and flow of the cooling system. Any sudden drop in pressure or decrease in flow may indicate a leak or blockage in the channels, requiring prompt repair. For molds that have been out of service for extended periods, drain any accumulated water from the channels to prevent rust or freezing that could damage the core.
