Silicon rubber composite insulators have been widely used in high-voltage transmission, distribution lines, and some high-voltage transmission parts machinery due to their good electrical insulation, excellent antipollution characteristics, and low maintenance cost. Transmission lines often work in cold and heavily polluted conditions, and the anti-icing ability of insulators affects the safety of transmission lines. As a new anti-icing method, the superhydrophobic surface has the advantages of low energy consumption, light weight, and simple structure. It also shows a good application prospect in reducing ice-covered flashover, fouling flashover, and tower collapse accidents of high-voltage transmission lines. Many domestic and foreign researchers determined that the superhydrophobic surface has a great positive effect in reducing the adhesion strength of ice on the material surface and has a certain effect of delaying icing. The most widely used method for preparing superhydrophobic silicone rubber surfaces is the coating method due to the physical and chemical properties of silicone rubber. However, the coating in harsh environments can easily fail because of the poor mechanical stability and impact resistance of the coating. In previous studies, superhydrophobic surfaces were obtained using chemical reagents to reduce surface energy after laser processing of micro-nano structures. Herein, the silicone rubber composite insulators umbrella skirt material has the characteristics of low surface energy; thus, it requires no modification through chemical reagents. The laser engraving machine is used to process micron-scale texture to obtain a superhydrophobic surface, which has a higher processing efficiency than a nanoscale machine. Therefore, using a laser engraving machine to prepare a superhydrophobic surface to shorten the icing of the silicone rubber composite insulator has a certain application prospect.
Herein, the D80M multifunctional laser engraving machine is used to process different types and dimensional parameter textures on the surface of the composite insulator silicone rubber samples. The surface morphology of the specimens is observed by a three-dimensional morphometer and scanning electron microscope, and the hydrophobicity principles of the specimens are analyzed. The contact angle of the samples with different complex texture surfaces is tested using a contact angle measuring instrument. Consequently, the optimal type and size parameters of complex texture with the best hydrophobicity are obtained. The freezing time of water droplets on the specimen surface is evaluated using a high and low temperature-humidity test chamber to test the freezing time of water droplets on different texture specimen surfaces at -10 ℃. The ice adhesion force on different texture surfaces is also investigated. Furthermore, the anti-icing durability of the specimens is examined by testing the change contact angle and freezing time after repeated icing and de-icing of the specimens.
The textured surface of the specimens prepared by laser processing, without any chemical modification, has good hydrophobicity, and the contact angle of the square + circular texture (Sq+ Ci) surface with the size of 350 μm can reach 154.1° to realize superhydrophobicity (Fig. 4). The study on the anti-icing property shows that the freezing time of the droplet on different complex texture surfaces first increases and then decreases as the size increases. The longest freezing time is reached at the Sq+ Ci texture surface with the size of 350 μm, which is 144 s (Fig. 5). Compared to the original surface with an icing adhesion force of 4.54 N and a freezing time of 72 s, the adhesion forces of the droplet on the three textured surfaces with the optimal size are below 2 N in the same low-temperature condition (Fig. 7). When the environmental temperature change from -4 to -12 ℃, the freezing time of the droplet on the Sq+ Ci texture surface decreases from 355 to 129 s and becomes shorter by about two-thirds, demonstrating that the anti-icing performance of the specimens decreases sharply as the environmental temperature decreases (Fig. 9). Additionally, after 20 times of icing and de-icing, the freezing time of the droplet on the sample surface remains higher than 133 s, indicating that the surface of the silicone rubber processed by laser engraving has good anti-icing durability (Fig. 10).
In this study, the hydrophobicity of silicone rubber can be significantly improved by constructing rough complex microtextures on the surface via laser engraving. The hydrophobicity of the three different complex textures first increases and then decreases as the size increases, and the Sq+ Ci texture with the size of 350 μm has the best hydrophobicity and ice resistance. There is a linear relationship between hydrophobicity and anti-icing performance of different textures. The better the hydrophobicity of the textured surface, the longer the freezing time and better icing resistance due to the slower heat exchange. The surface wear resistance of the textured sample is good. After icing and de-icing, the ice resistance does not decrease too much, and the surface icing can still be delayed to a great extent. After the laser engraving, the textured surface wear resistance of the silicone rubber composite insulator is good, which can be seen from the change in the contact angle and freezing time after multiple icing and de-icing. The textured surface can still delay the surface icing to a large extent. This study has a certain reference value for the design of improving the anti-icing ability of equipment surfaces and provides new ideas for high-efficiency laser processing.
