L-shaped cartridge heaters are commonly used for side-heating hot runner nozzles, but a frequent error is bending the tube into a sharp 90° angle. This deforms the internal resistance wire and creates voids in the MgO powder, leading to localized overheating or open circuits. The correct solution is the copper-sleeved L-type heater, where the pre-formed copper sleeve (bend radius ≥15mm) acts as a thermal conductor (398 W/m·K) and mechanical buffer. The copper sleeve is cold-pressed onto the stainless tube-no welds-to prevent cracking under thermal cycling. During installation, ensure the copper sleeve fully contacts the mold bore, leaving a 5–8mm expansion gap. Never strike the tube with tools. For non-sleeved L-types, a guiding sleeve must be pre-installed in the mold to prevent bending. In hot runner systems, copper-sleeved heaters reduce thermal response time by 70% and extend service life by over 3x compared to standard L-types.
