Diameter and position design of straight-through cooling water channel for injection molding
Through-the-channel cooling channels are the most common design in injection molding mold cooling systems. By creating straight holes through the mold plate, circulating cooling water removes heat from the melt, enabling rapid cooling and finalization of the molded part. The diameter and placement of through-the-channel cooling channels directly impact cooling efficiency and uniformity, which in turn influences the molding cycle, dimensional accuracy, and surface quality of the part. A proper design can shorten cooling time by 20%-30% and limit part shrinkage variation to less than 0.5%. Improper design can lead to uneven cooling, resulting in defects such as warping and sink marks. For example, in PC lens molds, improper cooling channel design can extend lens cooling time by 5-10 seconds, increase internal stress, and cause deformation later in the mold. Therefore, in-depth research on the design principles of through-the-channel cooling channel diameter and placement is crucial for improving injection molding efficiency and product quality.
The diameter of cooling channels should be determined based on a comprehensive consideration of cooling efficiency, water flow velocity, and mold strength. A diameter that is too small (less than 6 mm) results in slow water flow (less than 0.5 m/s), low cooling efficiency, and increased clogging due to scale. A diameter that is too large (greater than 16 mm) weakens mold strength, especially when opening around the cavity, potentially causing mold plate deformation. A commonly used diameter range is 8-12 mm, and the specific choice depends on the size of the part and mold: small molds (mold plates less than 300 mm × 300 mm) use a diameter of 8-10 mm; large molds (mold plates greater than 500 mm × 500 mm) use a diameter of 10-12 mm. The water flow velocity should be controlled between 1-2 m/s for optimal turbulence and heat exchange efficiency. This can be calculated using the formula: Q = v × A × 3600 , where Q is the flow rate ( L/h ), v is the flow velocity ( m/s ), and A is the cross-sectional area of the channel ( m² ). For example, for a 10mm diameter water channel ( A = 7.85 × 10⁻⁵ m² ) with a flow rate of 1.5m/s , the required flow rate Q = 1.5 × 7.85 × 10⁻⁵ × 3600 ≈ 4.24L/h . Furthermore, the diameter must match the cooling system’s water pump power to ensure sufficient flow and pressure.
The location of cooling channels should be designed according to the “equidistant cooling” principle to ensure consistent cooling rates across the cavity. The distance from the center of the channel to the cavity surface (referred to as “channel distance”) is a key parameter and is typically 1.5-2.5 times the channel diameter. For example, a 10mm diameter channel should be 15-25mm from the cavity surface. For parts with uniform wall thickness, the channels should be evenly distributed around the cavity, with the distance between each channel and the cavity varying by no more than 2mm to ensure uniform cooling. For example, molds for circular parts should utilize circular channels, with each channel equidistant from the center of the circle. Rectangular parts should utilize parallel channels with spacing of 30-50mm. For parts with uneven wall thickness, the principle of “closer channels in thicker walls, farther channels in thinner walls” should be employed. The channel distance in thicker areas can be reduced to 1-1.5 times the diameter to accelerate cooling; in thinner areas, maintain a distance of 1.5-2.5 times the diameter to avoid stress concentration caused by overcooling. For example, if the wall thickness of a certain part of a plastic part is 5mm (2mm in other parts), the water channel distance in that part can be shortened from 20mm to 10-15mm to match the cooling speed with the thin-walled part.
The layout of the water channels needs to be flexibly designed based on the part shape and mold structure. Common layouts include parallel, wraparound, and stepped. Parallel water channels are suitable for long, strip-shaped parts. The channels are arranged parallel to the length of the part, with inlets and outlets located at either end to ensure consistent water flow. For example, when producing a 300mm long plastic strip, using three to four parallel water channels, spaced 40-50mm apart, can keep the temperature difference within ±2°C across all parts of the part. Wraparound water channels are suitable for round or irregularly shaped parts. The channels are arranged in a circular pattern around the mold cavity, with inlets and outlets symmetrically positioned to ensure uniform cooling. For example, a round bottle cap mold uses a double-layer wraparound water channel, with the inner layer 15mm away from the cavity and the outer layer 30mm away. This improves cooling efficiency by 40% compared to a single layer. Stepped water channels are suitable for taller parts (such as buckets and cups). The channels are arranged in layers along the height, with the distance and diameter of each layer adjusted according to the wall thickness of the part. For example, a plastic cup mold with a height of 100mm has three layers of water channels set along the height direction, with a spacing of 30-40mm between each layer. A 12mm diameter water channel is used at the thick wall at the bottom, and a 10mm diameter water channel is used at the thin wall at the top.
The design of the cooling water channel’s inlet and outlet, along with supporting measures, is crucial for ensuring effective cooling. The inlet and outlet should be arranged diagonally to avoid short-circuiting and ensure sufficient flow in all channels. For example, for a rectangular mold, the inlet should be located in the lower left corner, and the outlet in the upper right corner, ensuring that water flows through all channels before exiting. Channel bends should be rounded (with a radius of at least 5mm) to reduce flow resistance and pressure loss. For complex cavities where straight-through channels are impractical, a modular design can be employed, with channels created within inserts and then connected to the main channel. Channels should be treated with rust-proof treatment (such as chrome plating), with a surface roughness of Ra ≤ 1.6μm to reduce scale accumulation. Furthermore, filters (80-100 mesh) and thermostats should be installed in the cooling system. The filters prevent impurities from clogging the channels, while the thermostats maintain the water temperature within ±1°C of the set value (e.g., 80±1°C for PC molds and 40±1°C for PE molds). Through these measures, the heat exchange efficiency of the straight-through cooling water channel can be increased by more than 25%, significantly shortening the molding cycle and improving the quality of plastic parts.
