Influence of Vicat Softening Temperature on Extrusion Stability of LSZH Materials and Its Optimization Strategy

To clarify the influence mechanism of Vicat softening temperature (VST) of low smoke zero halogen (LSZH) flame-retardant materials on the extrusion process, and to solve the extrusion quality anomalies of LSZH-1 material on the HT-12 production line, an actual production case was taken as the research object. Comparative tests were designed to identify the root causes from three dimensions: material, process and equipment; targeted optimization strategies were proposed and verified in production. It is found that the VST of LSZH-1 material is only 84.4 °C due to its formulation system. Combined with the excessively high temperature in the feeding section and the weak pressure-building capacity of the low-pressure screw of the HT-12 line, this induces plastic bridging in the barrel, resulting in reduced outer diameter of the product and large fluctuations in barrel pressure and main motor current. By replacing with a high-pressure flame-retardant screw and optimizing the drying and feeding section temperatures, the fluctuation of extrusion pressure is controlled within ±0.3 MPa, current fluctuation within ±1.5 A, and outer diameter deviation within ±0.3 mm, achieving continuous and stable production. This paper reveals the correlation between VST and extrusion stability of LSZH materials: the lower the VST, the easier premature softening and bridging occur, requiring temperature adjustment and stable barrel pressure; materials with higher VST exhibit better process adaptability and stronger extrusion stability.