I. Safety Preparation for Pre-treatment (Completed in 5 minutes)
Tools List: Copper hammer, copper rod, high-temperature penetrating loosening agent, air gun, local heating gun, special hot runner removal tool, feeler gauge, and heat-resistant gloves.
Safety Red Lines: It is imperative that the hot runner components not be struck directly with a mallet. You should never pour frigid water directly onto the hot mould core in order to prevent the mould core from suddenly cooling and cracking, which would render it unusable.
Confirmation of Pre-treatment: Disconnect the heated runner from all heating sources. To prevent burns, verify that the hot runner's present temperature is at least 100℃.
II. Initial Stage: Natural Cooling and Loosening (Prioritised to prevent secondary injury)
Activate the cooling system of the mould to facilitate the natural cooling of the entire hot runner to room temperature, which is approximately 25℃. Allow the metal to naturally contract by allowing it to stand for 15-20 minutes.
Place a copper rod against the non-sealed surface of the hot runner manifold. Gently tap the locked area 3-5 times with the copper hammer in the opposite direction of thermal expansion to induce a slight displacement.
Insert a feeler gauge into the distance between the mounting hole and the surface. Use a specialised instrument to gradually extract the hot runner component if a movable gap of ≥0.1mm is observed.
III. Second Stage: Penetration Lubrication Unlocking (For minor localised jamming)
Slowly inject a high-temperature penetrating loosening agent into the gap between the heated runner and the mounting hole to ensure that the agent completely penetrates the metal mating surface gap.
Allow the loosening agent to completely dissolve the metal oxide layer that was formed under high temperature by allowing it to remain for 2-3 hours.
Alternately tap the hot runner in a circumferential orientation using a copper rod and hammer to gradually loosen the mating interface. In order to prevent excessive localised stress, each tap should be executed with a consistent force.
Use a pulling tool to apply force outwards at a uniform speed, gently pulling the hot runner out of the mounting hole once the component can rotate slightly.
IV. Third Stage: Thermal Expansion Unlocking (For severe blockage scenarios)
Cover the heated runner body entirely with a heat insulation baffle, leaving only the template area surrounding the jammed mounting hole exposed.
Utilise a heating gun to uniformly heat the template around the mounting hole, maintaining a temperature of 120-150℃ for 5-8 minutes. This will enable the template mounting hole to expand and establish a breach.
Concurrently, employ an air gun to direct cold air onto the hot runner core, thereby maintaining the hot runner component at a comparatively low temperature. Utilise the expansion discrepancy between the two to rapidly establish a mating gap of 0.05-0.1mm.
Immediately upon the gap's appearance, employ a pull-out tool to draw the hot runner component outwards at a consistent pace, avoiding any pauses that could result in the temperature dropping and the gap disappearing.
V. Rapid Reinstallation Verification Following Repair
After the hot runner has been removed, use metallographic sandpaper to gently sand down any burrs or protrusions on the inner wall of the mounting hole, ensuring that all metal debris is removed.
Confirm that the gap value satisfies the thermal expansion allowance requirements and that there are no indications of uneven wear by re-measuring the mating gap between the mounting hole and the hot runner using a feeler gauge.
To prevent subsequent heating and seizing, apply a uniform layer of high-temperature-resistant anti-seize agent to the mating surfaces prior to installing the heated runner.
Perform a segmented heating operation after reassembly, increasing the temperature by 50°C every 30 minutes. Throughout the process, monitor the hot runner displacement to ensure that no new jamming phenomena occur.
