Injection molding circular cooling water channel
Injection molding circular cooling channels are a highly efficient cooling structure designed for circular or annular plastic parts. By arranging a circular water channel around the mold cavity or core, the coolant flows evenly along the circumference, achieving rapid and uniform cooling of the part. Compared to traditional linear or branched cooling channels, circular cooling channels significantly reduce temperature differences across the part. They are particularly suitable for circular products such as bottle caps, gears, and seals. They effectively control shrinkage and deformation of the part, improving dimensional accuracy. The rationality of this cooling structure’s design directly impacts cooling efficiency and product quality, requiring precise calculation and layout based on the part’s wall thickness, material properties, and molding cycle requirements.
The basic structural design of a circular cooling channel must meet the requirements of uniform water distribution and efficient heat exchange. Key parameters include the channel diameter, the ring diameter, and the location of the inlet and outlet. The channel diameter is typically determined based on the size of the plastic part and the cooling requirements, generally ranging from 8-12mm. A diameter that is too small will result in excessive water flow and increased pressure loss; a diameter that is too large will occupy excessive mold space and affect mold strength. The ring diameter should be slightly larger than the outer diameter of the plastic part (for cavity cooling) or slightly smaller than the inner diameter of the plastic part (for core cooling). The distance between the channel and the plastic part surface should be maintained at 15-25mm. This distance ensures sufficient heat exchange area while avoiding local mold strength deficiencies caused by close proximity. The inlet and outlet should be symmetrically arranged on both sides of the ring, allowing the coolant to enter from one side and flow bidirectionally along the circumference, converging and exiting on the other side. This ensures uniform water flow and temperature distribution across the ring and avoids cooling dead spots.
Controlling the coolant flow rate and velocity is crucial to maximizing the effectiveness of circular cooling channels. Hydraulic calculations are required to ensure turbulent flow in the cooling system. Turbulence enhances convective heat transfer between the coolant and the channel walls. A Reynolds number greater than 4000 is typically required. For a 10mm diameter channel, the water velocity must reach 1.5-2m/s to achieve turbulent flow. Flow rate calculation is based on the heat dissipation of the plastic part using the formula Q = cmΔt, where Q is the heat dissipation, c is the specific heat capacity of the coolant, m is the mass flow rate, and Δt is the inlet and outlet water temperature difference. Generally, the inlet and outlet water temperature difference should be controlled within 5-10°C. Excessive temperature differences indicate insufficient cooling capacity, resulting in uneven cooling of the plastic part; too small a temperature difference increases the cooling system’s energy consumption. In practical applications, flow control valves and pressure gauges can be installed to monitor the flow rate and pressure of each channel section in real time to ensure stable operation of the cooling system.
The design of annular cooling channels that are compatible with the shape of the plastic part is particularly important, and the structure needs to be optimized according to the complexity of the plastic part. For simple circular plastic parts with uniform wall thickness, such as plastic bottle caps, a single annular cooling channel can be used. The water channel surrounds the cavity to ensure consistent cooling speed in all parts. For annular plastic parts with uneven wall thickness or with bosses or ribs, it is necessary to set up denser annular branches in the thick-walled area or locally expand the water channel diameter. For example, at the corresponding position of the plastic part’s reinforcement ribs, the water channel diameter can be increased from 10mm to 12mm, and the distance between the water channel and the plastic part surface can be shortened to 10-15mm to enhance the local cooling effect and reduce the uneven shrinkage caused by wall thickness differences. For double-layer annular plastic parts that need to be cooled on both the inner and outer surfaces, a concentric double-annular cooling structure can be used. The inner ring cools the core, and the outer ring cools the cavity. By controlling the coolant flow of the inner and outer rings separately, synchronous cooling of the inner and outer surfaces of the plastic part can be achieved.
The machining and maintenance of circular cooling channels directly impact the stability of cooling performance. Ensure accurate machining and cleanliness. Channels are typically processed using deep-hole drilling or electrospark machining. For large circular channels, segmented processing followed by welding is acceptable. However, welds must be smooth and burr-free to avoid obstructing water flow or creating localized vortices. The surface roughness of the channel inner wall should be controlled below Ra1.6μm. Excessive roughness increases flow resistance, reduces flow velocity, and promotes scale formation. During maintenance, the channels should be regularly cleaned of scale and impurities. Chemical cleaning or high-pressure water flushing can be used, typically every three to six months, with the frequency determined by the coolant quality and duration of use. Additionally, check the tightness of the channels, especially at joints and welds, to prevent coolant leakage that could affect cooling efficiency and mold life. For molds that have been out of service for extended periods, drain any accumulated water from the channels to prevent rust and blockage. Through scientific processing and maintenance, the annular cooling water channel can maintain efficient cooling performance for a long time, providing a guarantee for the stable quality of injection molded products.
