I. A car bumper injection moulding plant: Mould core cracking was caused by manifold thermal expansion locking.
Background: The manifold length of the plant's newly commissioned 1-out-of-4 hot runner bumper mould was 320mm. Thermal expansion calculations were not implemented during the design phase.
Fault Phenomenon: The heated runner manifold became directly encased in the mounting hole after the initial heating to 240℃. The mould core's localised cracking was revealed through forced prying, necessitating the cessation of production.
Root Cause: The theoretical expansion of the 316 stainless steel manifold at 240℃ is 1.27mm. The mould core compression and rigid locking were the consequences of the original design, which permitted only a 0.3mm gap, which was significantly less than the actual expansion.
Solution: The manifold mounting hole was enlarged to accommodate a new 1.8mm axial floating clearance. The floating positioning ring was replaced, and the cracked mould core was repaired through welding. The repair cost exceeded 60,000 yuan, and the total repair duration was three days. Subsequent Advantages: The mould operated continuously for two years without encountering thermal expansion lock-up failure following rectification.
II. A Unilateral Off-Center Load Causes Partial Lock-up of Mounting Holes in an Electronic Connector Injection Moulding Plant
Context: The hot runner bolts were not tightened diagonally in phases during the installation of the hot runner mould for a 16-cavity precision connector.
Fault Phenomenon: The production line was halted as a result of the hot runner becoming directly stuck in the mounting hole after the second startup and heating. It was unable to be removed without assistance.
Root Cause Identification: The hot runner plate was subjected to skewed force as a result of the bolt locking on one side in a single motion. The displacement on one side was rigorously constrained by the mounting hole during thermal expansion, which led to localised metal adhesion and locking.
Resolution: A thermal expansion release method was implemented. The hot runner core was simultaneously air-cooled to establish a gap, while the mould plate was locally heated to 130°C. The mould was reinstalled in accordance with standard procedures, the burrs in the mounting cavity were ground off, and the hot runner was successfully removed.
Consequent Advantages: The factory rigorously implemented a diagonal, step-by-step tightening procedure for all subsequent hot runner installations, which prevented the recurrence of comparable issues.
III. A Medical Consumables Injection Moulding Factory: Periodic Locking Caused by Coaxiality Deviation of Positioning Ring
Context: The coaxiality deviation of the factory's 8-cavity medical catheter hot runner mould during positioning ring processing was 0.05mm, which exceeded the standard requirements.
Fault Phenomenon: The hot runner experienced a slight locking issue approximately once per month during operation, necessitating machine shutdown and disassembly to adjust the ring each time. This had a significant impact on production efficiency.
Identification of the Root Cause: The hot runner's expansion and temperature increase were accompanied by localised asymmetrical wear due to the positioning ring's excessive coaxiality deviation. Metal debris accumulation eventually resulted in locking over the course of extended operation.
Solution: The periodic locking issue was resolved by replacing the high-precision floating positioning ring with a coaxiality of ≤0.02mm and applying a high-temperature-resistant anti-seize agent to the mating surfaces.
Subsequent Advantages: The mould operated continuously for 18 months without any additional sealing faults, which led to a 12% increase in production efficiency.
