Insulation of injection molds
Insulation of injection molds is crucial for improving injection molding efficiency and ensuring consistent part quality. Its core purpose is to reduce heat loss during the molding process, maintaining stable cavity and core temperatures, thereby reducing energy consumption and shortening the molding cycle. During mold operation, the cavity surface must maintain a certain temperature (typically 50-120°C, depending on the type of plastic). Inadequate insulation allows heat to dissipate through the mold plate into the surrounding environment, causing cavity temperature fluctuations. This not only increases the energy consumption of the heating system but can also cause defects such as warping and sink marks in the molded part due to uneven cooling. Therefore, a properly designed insulation structure is crucial for precision injection molding.
Mold insulation primarily involves installing an insulation layer on the outside of the mold plate, optimizing the mold structure to reduce heat dissipation area, and employing integrated heating and insulation designs. The insulation layer is typically made of materials with low thermal conductivity (≤ 0.1 W/m・K ), such as aluminum silicate wool, aerogel felt, or polyurethane foam. The thickness is determined by mold size and ambient temperature, typically ranging from 10-30 mm . For example, applying a 20 mm thick layer of aerogel felt to the outside of the movable and fixed mold plates of a large automotive mold can reduce mold surface temperature by 30-50 °C, reducing heat loss by over 40% . For small, precision molds, a wraparound insulation jacket can be used to completely cover the mold except for the parting surface, further minimizing heat loss. Furthermore, installing a thermal insulation board (such as a glass fiber-reinforced phenolic resin board) between the mold plate and the injection molding machine platen can effectively block heat transfer to the injection molding machine. The insulation board is typically 5-10 mm thick and has a thermal conductivity of ≤ 0.2 W/m・K.
The insulation design must take into account the efficiency of the heating system to avoid excessive mold temperature or slow heating response due to excessive insulation. When setting the insulation layer, sufficient heat dissipation space must be reserved near the heating elements (such as heating rods and heating rings) to ensure that the heat can be efficiently transferred to the cavity rather than being blocked by the insulation layer. For example, around the heating rod inside the core, the distance between the insulation material and the heating rod must be ≥5mm to prevent local overheating. For molds that use hot oil or hot water circulation heating, the insulation layer must wrap the entire piping system to reduce heat loss during transmission. At the same time, insulation joints are used at the connection between the pipeline and the mold to avoid the cold bridge effect. In addition, temperature monitoring points can be set on the outside of the insulation layer to monitor the mold surface temperature in real time. When the temperature exceeds the set value (such as ambient temperature + 20°C), active cooling is carried out through heat dissipation holes or fans to maintain a balance between insulation and heat dissipation.
Different plastic materials have different requirements for mold insulation, requiring targeted adjustments to the insulation plan. For crystalline plastics (such as PE and PP), molding requires higher mold temperatures (80-120°C) to promote crystal growth. Therefore, the insulation layer needs to have stronger thermal insulation capabilities. Thicker insulation materials (such as 30mm thick aluminum silicate wool) can be used, and auxiliary heating devices are installed around the cavity to ensure temperature stability. For amorphous plastics (such as PS and PC), the mold temperature is lower (50-80°C), and the insulation requirements are relatively low. Thin insulation materials (such as 10mm thick polyurethane foam) can be used, with a focus on preventing the impact of ambient temperature fluctuations on the cavity temperature. For heat-sensitive plastics (such as PVC), the insulation design must avoid local overheating that can cause material decomposition. Heat conduction channels can be provided in the insulation layer to dissipate excess heat, and temperature sensors can be used to achieve precise temperature control.
Maintenance and optimization of mold insulation are key to ensuring long-term insulation effects. The integrity of the insulation layer must be checked regularly during daily production. If any damage or detachment is found, it must be repaired or replaced in a timely manner to prevent rapid heat loss from the gaps. For insulation layers fixed by bonding, the bonding strength must be checked to avoid glue failure due to high temperatures. When inspecting the mold, dust and oil stains on the inside of the insulation layer must be cleaned. These impurities will increase thermal resistance and reduce heating efficiency. In addition, a thermal imager can be used to detect the temperature distribution on the mold surface, identify areas with weak insulation, and strengthen them. For example, the thickness of the insulation layer can be increased or heating elements can be added in areas where the temperature is too low. By continuously optimizing the insulation solution, the heat loss rate of the mold can be controlled within 10%, significantly improving the economy of production and the stability of plastic part quality.
