Different types of injection molding plastics have different melting points, thermal stability and molding temperature ranges, and targeted selection of matched hot runner thermocouples is an important means to improve molding quality. For conventional general-purpose plastics such as PP, PE, ABS and PS, the molding temperature is concentrated between 180℃ and 260℃, with good fluidity and strong thermal stability, and will not decompose and deteriorate easily at medium and low temperature. When matching hot runner thermocouples, users can select ordinary K-type straight rod universal thermocouples with high cost performance. This type of thermocouple has stable performance within conventional temperature range, low price, convenient replacement, fully meets the daily constant temperature demand of open hot runners, and is suitable for mass production of daily necessities and ordinary packaging products.
For medium-grade engineering plastics such as PA66, PBT, POM and PC, the molding temperature needs to be controlled at 260℃ to 310℃. Such plastics have high melt viscosity, are easy to produce internal stress, and are sensitive to temperature changes. It is necessary to select high-sensitivity fast-response hot runner thermocouples, preferably embedded deep insertion models. By improving the temperature sensing accuracy, the subtle temperature changes inside the hot runner can be captured in time, avoiding uneven melt viscosity caused by temperature fluctuation, effectively reducing product welding lines, shrinkage marks and deformation defects, and matching valve gate hot runners to achieve high-quality molding of engineering plastic parts.
For filled modified plastics such as glass fiber reinforced PA and flame-retardant modified PPS, besides high molding temperature, the raw materials will produce certain corrosive volatile gas in the melting state. It is required to select hot runner thermocouples with anti-corrosion coating treatment on the probe surface, which can resist gas corrosion, delay aging speed and prolong service life. For high-performance special engineering plastics such as PEEK, PEI and PPSU, the molding temperature is above 320℃, which belongs to ultra-high temperature molding field. Conventional K-type thermocouples cannot bear long-term ultra-high temperature operation, and must be matched with R-type or S-type platinum-rhodium high-grade high-temperature resistant thermocouples. Such thermocouples have ultra-high temperature resistance, stable signal transmission and extremely low temperature drift rate, which can ensure the long-term stable operation of ultra-high temperature hot runner systems.
For medical-grade plastics and food-contact safe plastics, in addition to meeting the temperature demand, the matched hot runner thermocouples must adopt non-toxic and pollution-free raw material standards, without heavy metal precipitation and high-temperature harmful substance volatilization, to ensure that the plastic melt is not polluted and the produced products meet food and medical safety certification standards. Reasonable matching of thermocouples according to plastic characteristics can maximize the performance advantages of hot runner systems.
