Analysis of the Influence of Plastic Volatile Gas on Thermocouple Service Cycle

Many different kinds of volatile gasses will break down and be emitted during the high-temperature melting and flow of diverse plastic raw materials, which are influenced by the molding temperature, material formula, and raw material purity. These volatile gasses include a variety of chemical impurity components, greasy, sticky materials, and acidic, caustic compounds. One of the main invisible factors that shortens the actual service cycle of temperature measuring parts is long-term erosion and infiltration, which will cause all-around damage to the external structure and internal precision components of hot runner thermocouples. This type of damage is frequently slow and cumulative, making it difficult to detect in the early stages of use.

The outside metal protective sleeve is the first line of defense against volatile gas erosion for typical unprotected thermocouple products. Strong acidic volatile gasses produced by engineering plastics and modified plastics will gradually erode the protective sleeve's metal surface over an extended period of time, eroding the surface anti-oxidation coating, creating rust spots and corrosion pits on the probe surface, and steadily reducing the protective sleeve's wall thickness. The internal alloy wire core and high-temperature insulating filler of the thermocouple will be directly eroded by the invasion of external gas as the corrosion degree deepens and even local perforation damage occurs as the service period is extended.

The oily, sticky components of the volatile gas will stick to the internal wire core's surface once it enters the thermocouple, creating a sticky isolation layer that raises the internal signal transmission resistance and causes unstable thermoelectric conversion efficiency. The welding points of the measuring head and the wire core connection parts will sustain oxidation and corrosion damage from the acidic chemical components. This will make it easier to create hidden cracks and virtual connection faults at the welding position, progressively increase the temperature measurement drift error, and continuously lower the thermocouple's temperature sensing sensitivity and measurement accuracy.

Furthermore, the volatile gas will seriously contaminate and adhere to the thermocouple probe's surface. The oily volatile materials will combine with plastic carbonized leftovers after cooling and condensing to create hard composite filth, which is more challenging to clear than typical single carbon deposits. This type of filth will create a thick layer of heat insulation on the detecting head's surface, severely impeding heat conduction, causing continuous temperature measurement lag and data divergence, and raising the frequency of equipment maintenance and cleaning.

Targeted protection measures must be implemented in actual manufacturing to effectively decrease the erosion damage caused by plastic volatile gasses and extend the service life of thermocouples. Choose fully sealed anti-corrosion thermocouples with premium metal casings and surface anti-corrosion treatment for manufacturing materials that are prone to creating corrosive volatile gasses. Reduce the amount of volatile gas decomposition from the source, control the molding temperature and material residence time inside the flow channel, and optimize the injection molding process parameters. Check the protective sleeve's level of corrosion damage on a regular basis, disassemble and clean the dirt and corrosive attachments on the probe's surface, and promptly replace any seriously corroded aging products. The erosion damage caused by volatile gasses can be successfully minimized and the long-term stable operating state of hot runner thermocouples can be preserved through scientific material matching, process optimization, and routine maintenance.