What should the temperature of plastic injection molds be?

The importance of mold temperature
Mold temperature is a key variable in the injection molding process, which determines the cooling rate, crystallinity, and physical properties of the plastic melt inside the mold. Excessive or insufficient mold temperature can have adverse effects on the product. For example, if the mold temperature is too low, it can cause the plastic melt to cool too quickly, resulting in significant internal stress and reducing the dimensional stability and impact strength of the product; If the mold temperature is too high, it may cause the plastic to overheat and decompose, resulting in defects such as bubbles and discoloration. At the same time, it can also increase cooling time and reduce production efficiency.
The specific range of mold temperature
The suitable temperature range for injection molds varies depending on various factors such as the type of plastic, product structure, and mold design. The following are some common mold temperature ranges for plastics:
PP (polypropylene): The mold temperature is generally set at 40-80 ℃. The melting temperature of polypropylene materials is relatively low, and the requirements for mold temperature are relatively low. However, an appropriate mold temperature can help improve the surface glossiness and dimensional stability of the product.
PPS (polyphenylene sulfide): The mold temperature range is between 120 and 180 ℃. PPS is a high-performance thermoplastic with high heat resistance and chemical corrosion resistance, therefore requiring a higher mold temperature to ensure sufficient flow and crystallization of plastic melt.
POM (Polyoxymethylene): The mold temperature is generally 80-105 ℃. For products with larger surface areas, a higher mold temperature may be required to ensure uniform cooling of the plastic melt.
PE-HD (high-density polyethylene): The mold temperature is usually between 50-95 ℃. The melting temperature of high-density polyethylene is relatively low, but an appropriate mold temperature can help reduce the shrinkage rate and internal stress of the product.
PC (polycarbonate): It is recommended to set the mold temperature between 70-120 ℃. Polycarbonate has a high glass transition temperature and good mechanical properties, but excessive mold temperature may cause product deformation or stress cracking.
PBT (polybutylene terephthalate): The mold temperature for unreinforced materials is generally between 40-60 ℃. For reinforced materials, the mold temperature may need to be appropriately increased to ensure sufficient flow and crystallization of plastic melt.
PA6 (polyamide 6 or nylon 6): For thin-walled and long process plastic parts, the recommended mold temperature is 80-90 ℃; When the wall thickness is greater than 3mm, it is recommended to use a low-temperature mold at 20-40 ℃ to reduce internal stress and warping deformation. For glass reinforcement materials, the mold temperature should be greater than 80 ℃.
ABS (acrylonitrile butadiene styrene copolymer): The mold temperature range is wide, generally between 25-70 ℃. The temperature of the mold will directly affect the smoothness and dimensional stability of the product.
PA12 (polyamide or nylon 12): The mold temperature for unreinforced materials is 30-40 ℃; For thin-walled or large-area components, the mold temperature can be increased to 80-90 ℃; For reinforced materials, the mold temperature should reach 90-100 ℃. Increasing the mold temperature will increase the crystallinity of the material, thereby improving the physical properties of the product.
PA66 (Nylon 66): The mold temperature for unreinforced materials is 60-90 ℃; The recommended mold temperature for reinforced materials (with fiber addition of over 30%) is 80-120 ℃.
Influencing factors and control methods
The temperature of the mold is influenced by various factors, including the nozzle and barrel temperature of the injection molding machine, the type and quality of plastic materials, the material and structure of the mold, the pressure and flow rate of the injection molding machine, environmental temperature and humidity, etc. In order to maintain the stability of mold temperature, injection molding machines are usually equipped with mold temperature control equipment. The mold temperature machine can accurately control the temperature of the mold, heating it to the working temperature and maintaining it constant, thereby improving the quality and production efficiency of injection molded parts.
In actual production, selecting the appropriate mold temperature and maintaining stability is the key to ensuring product quality. In addition, it is necessary to adjust the injection molding process parameters based on the product structure and material characteristics, such as injection speed, injection pressure, holding time, etc., to achieve the best molding effect.