In the field of injection molding, the “cold-runner three-plate mold” has been the mainstream for decades. However, its inherent shortcomings—requiring the removal of the entire sprue solidified material after each injection—have given rise to three major issues: cycle times are constrained by cooling periods, raw material utilization is low, and gate marks are conspicuous. The advent of hot-runner systems, which continuously heat the melt within the mold, fundamentally addresses these pain points. The operational logic of a hot-runner system can be summarized as “four points in one line”: 1. Heat Source—Heating rods, heating coils, or thick-film heaters are closely attached to the distributor plate and nozzle, and a PID temperature controller ensures that the melt temperature fluctuation remains within ±0.5℃; 2. Runner System—The internal melt channels are polished to a surface roughness below Ra0.4, with no dead corners or stagnant zones, guaranteeing color-change times of less than 5 minutes; 3. Nozzle—Nozzles are categorized according to gating requirements into open-type, needle-valve type, spiral type, edge-type, and others, paired with independent temperature-compensation structures to prevent “dripping” and “stringing”; 4. Valve Control—The needle-valve system, controlled by a sequential controller, achieves millisecond-level opening and closing, eliminating weld lines, reducing internal stresses, and delivering a high-gloss, seamless surface finish.
Take Husky’s Ultra Helix needle valve hot runner nozzle as an example: its valve needle is made of nitrided H13 material with a DLC coating on its surface, achieving a hardness of 2300 HV. After 5 million cycles, the wear amount is less than 0.01 mm. Paired with the UltraSync-E electronically controlled needle valve actuator, this nozzle can achieve complete closure in just 0.08 seconds at a melt pressure of 0.1 MPa, with a minimum gate diameter of 0.3 mm, making it ideal for manufacturing optical lens rings for mobile phones with wall thicknesses as low as 0.2 mm. From an economic perspective, although the initial investment in hot runner molds is relatively high—approximately RMB 80,000 to 120,000 per set of an 8-cavity valve system—in projects with annual production volumes exceeding 500,000 units, the savings in raw materials, labor, and energy consumption can recoup the initial cost within 6 to 9 months. More importantly, the “zero-waste” production model enabled by hot runners aligns closely with the principles of green manufacturing and has become a mandatory requirement for Tier-1 suppliers from major OEMs in Europe and the U.S.