The Continuous High-Temperature Ageing Test
Sheath samples should be placed in a high-temperature test chamber that is set to the highest working temperatures that are common for hot runner systems, such as 400°C or 600°C. The samples should be taken out and allowed to cool to room temperature after 72 hours of continuous exposure at the designated temperature. Examine the look; if there is no chalking, cracking, or noticeable distortion, the sheath passes.
Measure the mechanical property retention rate as well; a strength retention rate of at least 80% shows that structural stability satisfies requirements at high temperatures.
High-Temperature Insulation Performance Verification Use an insulation resistance tester to assess the sheath's insulation resistance after placing it in the appropriate high-temperature environment. To prevent temperature measurement signal drift due to insulation leakage at high temperatures, an approved hot runner sheath must maintain an insulation resistance of ≥100 MΩ at 400°C.
Test for Thermal Shock Cycling
Hold the sheath at 150°C for an hour, then quickly move it to a -15°C environment for another hour in compliance with IEC 60811-509 and GB/T 2951.31 standards. This high-low temperature shock cycle should be repeated five times. The sheath surface must be free of obvious fractures once it has returned to room temperature. This indicates that it satisfies the criteria for thermal shock resistance and is appropriate for the repeated heating and cooling cycles of hot runner operations.
Verification of Simulated Field Operations
Ten consecutive manufacturing cycles of heating from ambient temperature to 600°C and then cooling must be completed after installing the sheath in a real hot runner system. Throughout the procedure, keep an eye on the sheath's state; steady temperature measurement signals and the lack of deformation or insulation deterioration verify that the sheath's high-temperature performance completely satisfies the criteria for real hot runner applications.
