Silicone rubber cables, due to their excellent flexibility and temperature resistance, are widely used in industrial equipment, robots, mobile devices, and other applications requiring frequent bending. However, prolonged bending can have multi-dimensional effects on their internal structure, affecting key components such as the conductor, insulation layer, shielding layer, and sheath. A comprehensive analysis from the perspectives of material properties, stress distribution, and environmental interaction is necessary.
The conductor, as the core of current transmission, directly impacts cable performance due to its structural stability. Silicone rubber cable conductors are typically made of multiple strands of fine copper wire. While this design improves flexibility, during prolonged bending, the outer copper wires can experience metal fatigue due to repeated stretching, leading to microcrack propagation and even wire breakage. If the bending radius is too small, the stress on the conductor will exceed the yield strength of copper, accelerating the wire breakage process. Furthermore, the "pitch balance" of the conductor stranding structure can be disrupted by excessive bending, creating gaps at the strands, increasing conductor resistance, and exacerbating heat generation during operation, creating a vicious cycle of "overheating-increased resistance," further threatening conductor integrity.
The insulation layer is a crucial barrier ensuring electrical safety, and its performance is significantly affected by bending. Silicone rubber insulation relies on the elastic deformation of its molecular chains to withstand bending stress. However, when the bending radius is less than a critical value, excessive stretching of the outer insulation layer can cause molecular chain breakage, forming microcracks invisible to the naked eye. These cracks become a breeding ground for partial discharge. Under the influence of an alternating electric field, the high temperature, ozone, and reactive particles generated by air ionization within the cracks corrode the silicone rubber, forming electrical dendrite-like channels, leading to a gradual decline in insulation performance. In the long term, the insulation dielectric loss may increase significantly, the breakdown voltage may decrease significantly, and ultimately lead to leakage or short-circuit faults.
The shielding layer plays a crucial role in electromagnetic interference protection, and its integrity directly affects signal transmission quality. For braided shielding layers, prolonged bending can cause the outer copper wires to break, significantly reducing shielding effectiveness and failing to effectively block electromagnetic interference. This may cause control signal disturbances, such as equipment malfunctions or program errors. For aluminum-plastic composite film shielding layers, excessive compression or stretching during bending may cause wrinkling or cracking, resulting in poor contact between the shielding layer and the conductor, further weakening the anti-interference capability.
As the outermost protective layer of a cable, the sheath's performance directly affects the cable's mechanical lifespan. Prolonged bending can cause whitening and wrinkling on the sheath surface, a direct indication of excessive material stretching. If the bending radius remains below the material's limits, the sheath may crack, especially at low temperatures where silicone rubber hardens and becomes brittle, increasing the risk of cracking. Once the sheath cracks, moisture and chemical media can penetrate the cable, accelerating conductor oxidation and insulation aging, creating a chain reaction of "sheath damage - internal corrosion - performance degradation."
Environmental factors can synergistically exacerbate cable aging in conjunction with bending stress. For example, at high temperatures, silicone rubber softens, reducing bending resistance, but prolonged high temperatures accelerate thermo-oxidative aging, increasing the risk of molecular chain breakage. Conversely, at low temperatures, the material hardens and becomes brittle, making it more prone to cracking during bending. Furthermore, acids, alkalis, and oils corrode silicone rubber, weakening its mechanical strength and making the sheath more susceptible to breakage under bending stress.
To address the challenges posed by prolonged bending, measures must be taken in three areas: material optimization, structural design, and usage specifications. In terms of materials, the anti-aging properties of silicone rubber can be improved by adding antioxidants and light stabilizers, or a high-flexibility formula can be used to reduce the stress required for bending. In terms of structural design, a layered composite structure can be adopted, such as using highly flexible silicone rubber as the insulation layer and slightly harder silicone rubber as the sheath, balancing bending performance and structural stability. The conductor structure can also be optimized, such as using stranding technology or fine copper wire conductors, to reduce stress concentration during bending. Regarding usage specifications, the minimum bending radius standard must be strictly followed to avoid excessive bending; bending radius limiters should be installed at frequently bent locations to force the cable to bend along the specified path; the cable condition should be checked regularly to promptly detect and address potential problems such as sheath cracking and conductor breakage.
