Calculation of volume flow rate of injection molding cooling medium
Calculating the volume flow rate of injection molding coolant is a key step in mold cooling system design, directly impacting cooling efficiency and part quality. Insufficient flow of the coolant (usually water or oil) results in slow cooling and uneven cooling of the part, leading to defects such as warping and excessive shrinkage. Excessive flow wastes energy and increases equipment load. Therefore, precise flow rate calculation using scientific formulas is essential, tailored to mold structure, part size, and cooling requirements.
The basic formula for calculating the volume flow of the cooling medium is: Q = P/(c×ρ×ΔT) , where Q is the volume flow ( m³/h ), P is the heat released during the molding process ( W ), c is the specific heat capacity of the cooling medium ( J/kg・℃), and ρ Where ΔT is the cooling medium’s density ( kg/m³ ), and ΔT is the cooling medium’s inlet and outlet temperature difference (°C). For example, if the heat released during plastic part molding is 5000W and water is used as the cooling medium ( c=4200J/kg・°C, ρ =1000kg/m³ ), and the inlet and outlet temperature difference is controlled at 5 °C, substituting this into the formula yields Q = 5000/(4200×1000×5)×3600, which is approximately 0.86m³/h . In actual calculations, the heat quantity P must be accurately calculated based on parameters such as the molding temperature of the plastic part material and the molding cycle to ensure reliable results.
In practical applications, the impact of the layout and diameter of the cooling water channels on flow rate must also be considered. According to fluid mechanics, the flow rate of the cooling medium in the pipes must be controlled within a reasonable range. A typical flow rate for water is 1.5-3 m/s. A flow rate that is too low will cause precipitation and scaling in the pipes, affecting heat transfer efficiency. A flow rate that is too high will increase pressure loss and require a more powerful pump. Therefore, when calculating flow rate, the water channel diameter must be considered: Q = 3600 × v × A, where v is the flow rate (m/s) and A is the cross-sectional area (m²). For example, for a 10mm diameter water channel (A = 7.85 × 10^-5 m²), at a flow rate of 2 m/s, Q is calculated to be 3600 × 2 × 7.85 × 10^-5 ≈ 0.565 m³/h. If the flow rate calculated based on heat is 0.86 m³/h, the water channel diameter must be increased or the number of channels must be increased to meet the flow rate requirement.
Different plastic part shapes and mold structures have different requirements for cooling flow, and targeted calculations are required. For large flat plastic parts, due to the large heat dissipation area, multiple sets of parallel water channels are required. The flow rate of each set of water channels should be distributed according to the heat distribution in the area. Usually, the flow rate in the edge area needs to be higher than that in the center area to balance the cooling speed. For molds with complex cavities, such as plastic parts with deep cavities or thin walls, conformal water channels are required. At this time, the flow calculation needs to consider the impact of the curvature and length of the water channel on pressure loss. The flow formula can be corrected by the local resistance coefficient to ensure that the actual flow rate of each section of the water channel meets the design requirements. In addition, for multi-cavity molds, it is necessary to ensure that the cooling flow rate of each cavity is uniform to avoid inconsistent plastic part sizes due to flow rate differences.
The calculation of the cooling medium’s volume flow rate must be adjusted based on actual production conditions. In summer, due to higher ambient temperatures, the cooling medium’s inlet temperature rises. To ensure effective cooling, the flow rate needs to be increased to maximize heat dissipation. In winter, the flow rate can be reduced to conserve energy. The purity of the cooling medium must also be considered. Impurities in the water can increase pipe roughness and pressure loss, potentially leading to lower actual flow rates than calculated. Therefore, regular cleaning of the waterways and a 10%-15% flow margin should be included in the calculation. Dynamic adjustment of flow calculation parameters ensures the cooling system maintains efficient operation under varying operating conditions, reliably guaranteeing the quality of plastic parts.
