Traditionally, tire molds have employed a cold-runner plus cold-pool structure. However, due to the high viscosity and thermal sensitivity of rubber/TPU melts, defects such as scorching, flow marks, and bubbles tend to occur easily near the cold pool. In this study, focusing on the sidewall injection unit of a 305/30R20 high-performance run-flat tire, a three-dimensional non-isothermal viscoelastic flow model was established using Moldflow. Three hot-runner schemes were compared: Scheme A features a 4-point open-type hot nozzle; Scheme B uses a 6-point needle-valve hot nozzle with sequential control; and Scheme C employs an 8-point valve-based hot runner system with independent servo-driven needle valves. The results indicate:

1. Molding pressure: The maximum injection pressures for Schemes A, B, and C are 92 MPa, 78 MPa, and 65 MPa, respectively. The hot runner system significantly reduces the resistance at the melt front.

2. Temperature uniformity: Scheme C uses independent temperature control to keep the nozzle temperature difference within ±1.2℃, ensuring no localized overheating that could cause scorching even at the thinnest point of the tire sidewall, which measures just 1.8mm.

3. Fusion line location: Scheme B employs a timing control sequence of “first center, then两侧,” shifting the fusion line to a non-stress-bearing area and increasing the tire sidewall durability fatigue life by 18%.

4. Molding cycle: Compared to the cold-runner baseline of 180 seconds, Scheme C reduces the cycle time to 126 seconds, increasing single-shift production capacity by 28%.
   In addition, the study conducted Design of Experiments (DOE) on material selection for hot runner plates, calculation of heating power, and thermal expansion matching between nozzles and mold steel. By using Inconel 718 as the base material for the splitter plate and embedding six-zone tubular heaters (each zone with a power of 800 W), the temperature difference across the plate surface can be controlled within ±2℃ under operating conditions of 220℃. The nozzles adopt a composite structure made of Ti-6Al-4V alloy and mold steel H13. A radial clearance of 0.15 mm is designed to compensate for the thermal expansion difference of 0.08 mm at a temperature difference of 200℃, thereby preventing nozzle-pulling failures. This optimized design has been put into mass production in a 48-cavity mold at a leading tire manufacturer in China, resulting in annual savings of 120 tons of compounded rubber and generating direct economic benefits exceeding 3 million yuan.