The self-extinguishing time of a silicone glass fiber self-extinguishing tube is a core indicator of its flame-retardant performance, influenced by multiple factors including material formulation, fiber structure, coating process, environmental conditions, combustion testing standards, tube thickness, and external combustion aids. These factors directly determine its self-extinguishing performance by altering the heat release rate, flame propagation path, and heat transfer efficiency during combustion.
Material formulation is the fundamental factor affecting self-extinguishing time. Silicone glass fiber self-extinguishing tubes use alkali-free glass fiber as the base material, coated with silicone resin or silicone rubber. The high bond energy of silicon-oxygen bonds in the molecular structure of silicone resin allows the silica ceramic layer formed during combustion to effectively isolate oxygen and inhibit flame spread. Adding inorganic flame retardants (such as aluminum hydroxide or magnesium hydroxide) to the formulation can lower the material surface temperature due to their endothermic decomposition effect, further shortening the self-extinguishing time. Conversely, if the proportion of organic components in the coating is too high, flammable gases are easily generated during combustion, thus prolonging the self-extinguishing time.
The fiber structure affects self-extinguishing time through weaving density and fiber arrangement. High-density woven fiberglass tubes form a denser physical barrier, limiting the contact between oxygen and combustibles, thus accelerating flame extinguishing. The fiber orientation is also crucial; longitudinally aligned fibers easily form a continuous carbonized layer during combustion, while transversely interwoven fibers shorten self-extinguishing time by blocking the flame propagation path. Furthermore, fiber fineness (diameter) also affects the burning area; finer fibers have a smaller surface area in contact with oxygen per unit volume, resulting in superior self-extinguishing performance.
The uniformity and thickness of the coating process directly determine the stability of the flame-retardant effect. A coating that is too thin may lead to insufficient local coverage, creating weak points during combustion and prolonging self-extinguishing time; a coating that is too thick may crack due to internal stress, reducing thermal insulation performance. In the dip-coating process, the adhesion between the coating and the fiberglass is critical. If adhesion is weak, the coating is prone to detachment during combustion, exposing the underlying fibers and significantly increasing self-extinguishing time. Therefore, the coating process needs to optimize dip-coating time, temperature, and curing conditions to ensure a uniform, dense coating that bonds firmly to the substrate.
Environmental conditions have a significant impact on self-extinguishing time. High temperatures accelerate material thermal decomposition, reducing self-extinguishing performance; high humidity environments can cause moisture penetration, leading to coating hygroscopicity and affecting its flame-retardant effect. Oxygen concentration is another key factor; in oxygen-rich environments, flames burn more intensely, prolonging self-extinguishing time; while in oxygen-deficient environments, flames easily extinguish due to lack of oxygen. Furthermore, external wind speed alters the flame propagation direction; strong winds may cause the flame to deviate from the tube, indirectly affecting self-extinguishing time.
Combustion testing standards play a normative role in assessing self-extinguishing time. Different standards (such as UL VW-1 and GB/T 5169.11) specify different flame application times, angles, and observation conditions, directly limiting the comparability of test results. For example, the UL VW-1 standard requires five flame applications, each lasting 15 seconds, while the GB standard may use different application methods. This difference can cause the self-extinguishing time of the same product to vary in different tests. Therefore, it is necessary to clarify the testing standards to accurately assess self-extinguishing performance.
Tube thickness is a direct factor affecting self-extinguishing time. Thicker tubes require more heat to penetrate during combustion, thus extending self-extinguishing time. However, increased thickness also raises material costs and weight, necessitating a balance between performance and cost-effectiveness. In practical applications, the appropriate thickness of the silicone glass fiber self-extinguishing tube should be selected based on the specific scenario (e.g., high-temperature cable sheathing, motor insulation) to ensure cost optimization while meeting self-extinguishing requirements.
The presence of external accelerants can significantly alter self-extinguishing time. If the tube surface is covered with grease, dust, or other flammable materials, a continuous combustion source can easily form during combustion, prolonging self-extinguishing time. Furthermore, if the tube is installed near other flammable materials (e.g., plastics, wood), the risk of flame spread increases, potentially affecting self-extinguishing performance. Therefore, the tube surface must be cleaned before use, and close contact with flammable materials should be avoided to ensure the stability of self-extinguishing performance.
