Injection molding spiral cooling water channel
Spiral cooling channels in injection molding, thanks to their uniform distance from the mold cavity surface, excel in cooling complex curved parts (such as automotive headlights and mobile phone cases). They effectively reduce temperature differences across the part. For example, in a car bumper mold, the use of spiral channels reduced surface temperature differences from ±8°C to ±3°C, and warpage was reduced by 60%. Spiral channel design parameters include pitch, diameter, number of turns, and distance from the mold cavity. The pitch is typically 2-3 times the channel diameter (e.g., a 10mm diameter channel has a 25mm pitch) to ensure adequate heat transfer from the cooling medium. The distance from the mold cavity surface is controlled at 1.5-2 times the diameter (15-20mm). Using these parameters, a mobile phone case mold reduced cooling time from 35 seconds to 22 seconds. The spiral direction (left-hand/right-hand) must be aligned with the mold structure to avoid interference with components such as ejector pins and inclined guide pins. In one mold, a conflicting spiral direction caused the water channel to detour, resulting in a 20% decrease in cooling efficiency. Adjusting the direction restored the desired effect.
The diameter of spiral cooling channels should be determined based on the part’s volume and heat distribution. Small parts (<100g) are suitable for 8-10mm diameters, while large parts (>500g) require 12-16mm diameters to ensure adequate flow. A 50g PC lens mold uses an 8mm spiral channel, achieving a flow rate of 2.5m³/h. A 1000g PP bumper mold requires a 16mm channel and a flow rate of 4m³/h to keep the cooling time under 60 seconds. The matching of channel diameter and pitch must be verified through heat transfer calculations. A spiral channel with a 10mm diameter and a 20mm pitch increases the heat transfer area by 40% compared to a straight channel of the same length. One test showed that, at the same flow rate, spiral channels have a 35% higher cooling efficiency. For plastic parts with uneven wall thickness, variable diameter spiral water channels can be used. The diameter of the thick-walled area is 12mm, and the diameter of the thin-walled area is 8mm. A washing machine drum mold uses this design to reduce the cooling time difference between different areas from 5 seconds to 1 second.
The inlet and outlet layout of spiral water channels affects the flow uniformity of the cooling medium. Proper inlet and outlet positioning can avoid localized high-temperature zones. A counterflow layout with water inlet at the bottom and outlet at the top allows for more efficient heat exchange between the cooling medium and the mold cavity. This layout reduced the temperature difference at the water channel outlet from 5°C to 2°C in a cosmetic bottle cap mold. Using the same-side inlet and outlet can easily lead to local short-circuits, with a temperature difference of up to 8°C in one case, requiring the addition of guide plates to improve flow. The inlet and outlet diameters should be 1-2mm larger than the water channel diameter (e.g., a 10mm water channel with a 12mm inlet and outlet) to reduce local resistance. In one mold, the pressure loss reached 0.3MPa due to the same inlet and outlet diameter (10mm). This pressure loss decreased to 0.1MPa after increasing the diameter to 12mm. For multiple spiral water channels, parallel rather than series connection is recommended. In an automotive instrument panel mold, four sets of spiral water channels connected in parallel achieved flow rate deviation within each set of less than 5%, compared to 15% when connected in series, significantly improving cooling uniformity.
3D printing technology makes it possible to manufacture complex spiral water channels, particularly suitable for conformal spiral structures that are difficult to achieve using traditional machining. In a 3D-printed turbine mold, the spiral water channel perfectly conforms to the blade curve, reducing cooling time from 45 seconds to 25 seconds and blade deformation from 0.5mm to 0.1mm. The surface roughness of the 3D-printed water channel can reach Ra1.6μm, smoother than the Ra3.2μm achieved with traditional drilling, reducing flow resistance by 20%. Tests have shown that the flow rate of 3D-printed water channels is 15% higher than that of traditional channels at the same flow rate. Regarding material selection, 316L stainless steel-printed water channels offer superior corrosion resistance to traditional mold steel. Using 3D-printed water channels in a PVC mold reduced corrosion by 80% and extended its service life to over 100,000 mold cycles. While 3D printing costs 30% more than traditional machining, the improved cooling efficiency and shortened cycle time mean the cost can be recovered within three months.
Optimizing the operating parameters of spiral cooling channels requires integrating actual production data to ensure efficient heat transfer under turbulent flow conditions. The flow rate should be controlled between 1.5 and 3 m/s (Reynolds number > 4000 ). A 10 mm spiral channel achieved a heat transfer coefficient of 5000 W/(m²・K) at a flow rate of 2 m /s , four times higher than laminar flow ( 0.5 m/s ) . The cooling medium temperature should be set 5-10 °C lower than the mold temperature. For a PC mold (with a mold temperature of 80 °C), using 70 °C cooling water achieved 15% energy savings compared to 60 °C water while maintaining comparable cooling performance. Regular cleaning of the channels (every three months) is crucial to prevent scale accumulation. On one production line, cooling efficiency decreased by 30% due to scale as thick as 0.5 mm . Chemical cleaning restored performance. By installing flow meters and temperature sensors for real-time monitoring, the spiral water channel system of a smart factory can automatically adjust the flow rate and water temperature, so that the cooling time fluctuation is controlled within ±1 second, and the CPK value of the dimensional stability of plastic parts is improved from 1.2 to 1.8.
