Verification of Fundamental Materials and Structure
Verify that the sheath is made of 304 or 316L stainless steel, which is appropriate for hot runner systems' high temperatures of 200–600°C. Avoid using materials that aren't resistant to high temperatures, like regular carbon steel.
Using an ultrasonic thickness gauge, measure the armoured layer's thickness at six uniformly spaced places around the diameter. To guarantee mechanical protection criteria are satisfied, the armour coverage must be at least 90% and the minimum value must be at least 90% of the stated level.
Key Dimensions and Bending Performance Verification
To ensure a gap-free fit and effective heat transmission after installation, make sure the sheath's outer diameter precisely matches the temperature-sensing bore of the hot runner.
Conduct five cycles of repeated bending tests with a bending radius equal to five times the outer diameter of the sheath; the internal insulation must not be damaged and the armoured layer must not exhibit any signs of fracture or loosening, confirming the flexibility needed for the small installation spaces of hot runner systems.
Confirmation of Fundamental Operational Effectiveness
Make sure there is no chance of electrical leakage by confirming that internal insulation resistance is ≥100 MΩ at ambient temperature and that resistance stays ≥100 MΩ following exposure to a 400°C environment.
Test the sheath's suitability for the frequent temperature swings typical of hot runner operations by subjecting it to five thermal shock cycles between room temperature and 600°C. The sheath must exhibit no cracking or deformation, and insulation performance must not noticeably deteriorate.
Operational Testing on-site
Install the sheath in a hot runner system and run it continuously for eight hours while keeping an eye on the temperature signal from the thermocouple. If there is no signal drift or irregular jumps and the temperature fluctuates within ±1°C, the sheath fully satisfies the requirements of real hot runner production conditions.
