How to Ensure Complete Repair of Hot Runner Thermal Shock Cracks

Based on our prior experience with hot runner thermal shock crack repair, stress relief verification and penetrant testing, proper hot runner thermal shock crack repair requires whole process control from pre-weld treatment through final operational verification:

Basic I. Pre-welding Treatment

Full crack removal. Grind the crack out completely to expose the sound metal foundation. Penetrant testing should be performed to ensure no residual crack tips are left to avoid potential complications.

Matching welding wire: Choose welding wire with the same composition as the hot runner substrate, so that the thermal expansion coefficient of the welding region can be consistent with the substrate, which is conducive to decreasing the stress difference later.

II. In-Weld Process Control

Preheating and Temperature Controlled Welding » Before welding, preheat the entire hot runner to 200-300℃. In welding, low-current multi-layer multi-pass TIG welding is used to lower the instantaneous thermal stress.

Interpass Hammering tension Relief: Gently tap the weld surface with a pneumatic hammer after each weld pass to release some of the collected residual welding tension in real time. III. Stress Relief Treatment after Welding

Annealing Stress Relief: The workpiece shall be placed in a heat treatment furnace within 12 hours after the weld repair and held at 600-650℃ for 2-3 hours. Then, the workpiece shall be cooled slowly with the furnace to remove over 90% of the residual stress.

Stress Value Compliance Verification: Use an X-ray residual stress meter to randomly check important regions and verify that the stress has been reduced to a safe range within 10% of the material yield strength.

IV. Final Full Dimensional Check

Penetration Testing Re-inspection: Conduct dye penetrant testing per specification; the weld repair region and the area surrounding it shall be free of microcracks.

Pressure Leakage Test: Medium at 1.5 times working pressure is introduced and held for 30 minutes, no leakage or pressure drop noted.

Cold and Hot Cycling Test: One full cycle of simulated temperature rise and fall, no new cracks or dimensional deformation should be visible upon re-inspection.

Installation and test confirmation: After 4 hours of continuous operation, if no leakage is found in the injection molding, and the temperature and injection pressure are stable, the repair is regarded fully qualified.