Optimizing silicone rubber cable formulations to balance flexibility and mechanical strength requires comprehensive control across five aspects: base material selection, reinforcement system, additive synergy, process adaptation, and structural design. The core performance of silicone rubber cable is determined by its molecular structure, and base material selection must consider both the intended use case and performance requirements. Methyl vinyl silicone rubber, due to the incorporation of vinyl groups into its molecular chains, forms a three-dimensional network structure upon crosslinking. This improves tensile and tear strength while maintaining flexibility, making it suitable for general industrial applications. For higher temperature resistance, phenyl silicone rubber can be used. Its phenyl groups enhance high-temperature oxidation resistance while reducing low-temperature brittleness. However, caution should be exercised that excessive phenyl content may increase hardness, requiring adjustment of the vinyl content to balance flexibility.
The reinforcement system is key to improving the mechanical strength of silicone rubber cable. Fumed silica, due to its high surface area and nanoparticle size, is the most commonly used reinforcing agent. Its surface silanol groups physically adsorb or chemically bond with silicone rubber molecular chains, significantly enhancing strength. However, excessive addition can lead to a surge in compound viscosity, deteriorate processing properties, and even induce stress concentration due to agglomeration. Therefore, fumed silica and precipitated silica are often used together. The former provides primary reinforcement, while the latter improves processability. Surface treatment also reduces silica's polarity, reducing interchain friction and balancing flexibility and strength.
The synergistic effects of additives can further optimize performance. The choice of curing agent directly influences crosslink density and network structure. Peroxide-cured systems form C-C crosslinks with high thermal stability, making them suitable for high-temperature environments, but the dosage must be controlled to avoid excessive crosslinking and increased hardness. Addition-cured systems offer high crosslinking efficiency and lack of byproducts, making them more suitable for applications requiring high flexibility. Plasticizers, such as silicone oil, can reduce interchain forces and enhance flexibility, but excessive addition can weaken mechanical strength, so the optimal ratio must be determined through experimentation. Furthermore, antioxidants can inhibit high-temperature oxidative chain scission reactions, extending service life. Flame retardants must be compatible with silicone rubber to avoid affecting electrical properties.
Process adaptation is crucial for achieving formulation optimization. Temperature and time must be strictly controlled during the mixing process to prevent premature agglomeration of silica or premature decomposition of the curing agent. For example, a staged mixing method is used: silica is first mixed in at low temperature to ensure uniform dispersion; the curing agent is then added at elevated temperatures to avoid premature vulcanization. During the extrusion process, screw speed and temperature must be adjusted according to the formulation to prevent overheating and decomposition of the rubber compound. Mold design must also be optimized to reduce stress concentration. The vulcanization process requires a balanced time and temperature to ensure sufficient cross-linking without excessive hardening.
Structural design can create a synergistic effect with material optimization. For example, a layered design is employed: the insulation layer uses highly flexible silicone rubber to ensure bending performance, while the sheath uses slightly harder silicone rubber to enhance lateral pressure resistance, making the cable both flexible and resilient. The conductor utilizes a bundled twisted structure, with multiple fine copper wires being more flexible than a single thick conductor, resulting in less stress concentration during bending. A gradient insulation thickness design, with a thick outer layer and thin inner layer, places greater tensile stress on the outer layer during bending. The thicker outer layer enhances tensile resistance without compromising overall softness. These comprehensive measures effectively balance the flexibility and mechanical strength of silicone rubber cables to meet the needs of diverse application scenarios.
