The vent of the injection mold is an essential part for mold operation. It makes it possible for the incoming gas during filling to be ventilated out of mold preventing molding defects such as burn mark or short shot. Many additives such as flame retardants, UV stabilizer or lubricants are compounded to resins to enhance products quality and processing capability. The resins are likely to produce a large amount of gas during processing. The gas includes organic substances that can easily condense and be accumulated on the surface of the vent, which reduces the vent to make it difficult for the gas to be ventilated easily. The mold with the clogged vent should be cleaned regularly. If the cleaning time could be predicted by monitoring, it can make mold operators to set up the working schedule with proper preparation ahead. In this work, how to measure the temperature and pressure changes of the gas in the cavity during filling is examined to make the vent clogging to be monitored efficiently. The gas in the cavity during filling is compressed adiabatically in a moment due to the fast filling speed. As the vent gets clogged, the adiabatic compression would become severe. When the adiabatic compression occurs, the temperature and pressure of the gas in the cavity will increase sharply. We developed temperature and pressure sensors to detect the adiabatic compression in the cavity. A sensitivity of the sensors was tested in a compression chamber. We developed and tested methods to measure the temperature and pressure changes in the chamber in this work. We discussed the problems to affect the sensitivity and the long-term reliability of the sensors.
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