The basic form of injection molded straight-through water channel
Injection molding straight-through water channels are one of the most commonly used structures in mold cooling systems. By machining straight holes in the mold template to serve as cooling channels, coolant flows in a straight line, cooling the cavity or core. Compared to complex, irregularly shaped channels, straight-through water channels offer advantages such as simple processing, low cost, and easy maintenance. They are widely used in molds for plastic parts with regular shapes and uniform wall thicknesses. Their basic forms can be categorized based on the water channel layout, connection method, and cooling range. Different types of straight-through water channels are suitable for different mold structures and cooling requirements. Choosing the right water channel configuration can significantly improve cooling efficiency, shorten molding cycles, and ensure consistent product quality.
The single, straight-through water channel is the most basic type. It consists of a straight hole running through the mold template, with a water inlet and outlet connected at each end. Coolant flows in through the hole and out through the other end, directly removing heat from the cavity or core. This type of water channel is suitable for molds for simple, flat or block-shaped parts, such as plastic covers and trays. The cooling area is limited to the area surrounding the water channel, so the water channel must be placed at a uniform distance from the cavity surface (typically 15-25mm) and parallel to the cavity surface. For example, in a mold for a 30mm-thick flat part, a single, straight-through water channel with a diameter of 10mm can be installed 18mm below the cavity. The channel length should match the width of the part, ensuring a roughly uniform cooling rate across the part. The advantage of a single, straight-through water channel is its ease of fabrication, requiring only deep-hole drilling and low cost. However, its disadvantage is its limited cooling area, making uneven cooling more likely with larger parts.
Parallel, straight-through water channels consist of multiple parallel, straight holes connected by manifolds (collection blocks) to achieve parallel coolant flow. This design is suitable for molds with large, elongated plastic parts, such as plastic door panels and decorative panels. The synergistic effect of multiple water channels expands the cooling range and improves cooling uniformity. Parallel water channels should be spaced evenly (generally 30-50mm) and positioned at a consistent distance from the mold cavity surface to ensure that each channel provides essentially the same cooling effect. For example, in an 800mm long mold, five straight-through water channels with a diameter of 12mm can be arranged along the length, spaced 160mm apart. Manifolds connect the channels at both ends, allowing coolant to enter each channel simultaneously and then converge at the other end. To avoid uneven flow among the channels, the inlet manifolds should be symmetrical to ensure consistent inlet pressure across the channels. The advantages of parallel straight-through water channels are large cooling area and good uniformity; the disadvantage is that additional water collection blocks are required for connection, which increases the complexity of the mold and processing costs.
A series-connected, straight-through water channel system consists of multiple straight holes connected in series by pipes to form a series loop. Coolant flows from the first channel, through the connecting pipe, into the second channel, and then flows through all channels before exiting the outlet. This system is suitable for molds with complex shapes and multiple independent cooling zones, such as shell-type parts with multiple bosses. The series-connected system allows for flexible water channel arrangement and targeted cooling of different areas. The diameter of each section of the series-connected, straight-through water channel system can be adjusted according to cooling requirements. Larger diameters ( 12-14mm) are used in heat-concentrated areas (such as thick-walled bosses), while smaller diameters (8-10mm) are used in thinner-walled areas to match the heat dissipation requirements of different areas. For example, in a mold with three thick-walled bosses, three series water channels can be installed, one for each boss location. The first and third sections have a diameter of 10mm, while the second section (corresponding to the largest boss) has a diameter of 12mm. This naturally distributes the flow to enhance cooling in key areas. Its advantages are flexible layout and targeted cooling; its disadvantages are that the coolant temperature gradually increases along the flow direction, which may lead to large differences in the cooling effects of each section of the water channel. Therefore, the number of water channels in series should not be too many, generally not more than 5 sections.
A stepped straight-through waterway is a special type of straight-through waterway. Its diameter varies in a stepped pattern along the flow direction, typically decreasing from the inlet to the outlet to maintain a stable coolant flow rate. This type of waterway is suitable for molds with long cooling paths, addressing the problem of decreased flow rate caused by increased waterway length and ensuring consistent cooling efficiency throughout the entire waterway. For example, in a mold 1000mm long, the straight-through waterway can be divided into three sections: an inlet section with a diameter of 14mm, a middle section with a diameter of 12mm, and an outlet section with a diameter of 10mm. By reducing the waterway diameter to compensate for pressure losses along the way, the coolant flow rate in each section remains roughly constant at a turbulent state of 1.5-2m/s, enhancing heat transfer. Stepped straight-through waterways can also be adapted to different inlet and outlet locations. For example, if the inlet is located in the middle of the mold, the waterway tapers in a stepped pattern toward each end, diverting the coolant flow to both sides and further improving cooling uniformity. Its advantage is that it can maintain stable cooling efficiency during long-distance cooling; its disadvantage is that it is difficult to process and requires accurate calculation of the change ratio of the diameter of each section to avoid water flow turbulence caused by sudden changes in local pressure.
