In the production of silicone rubber cables, ensuring a tight bond between the conductor and the insulation layer is crucial for improving the overall performance of the cable. This bond directly affects not only the electrical insulation performance of silicone rubber cables but also their mechanical strength, resistance to environmental aging, and long-term operational stability. Achieving this requires a comprehensive approach encompassing multiple dimensions, including conductor surface treatment, insulation material selection, extrusion process optimization, cooling and curing control, quality inspection and feedback, and production environment management.
Conductor surface treatment is the first step in ensuring a tight bond. The presence of oil, oxide layers, or impurities on the conductor surface significantly weakens the adhesion between the silicone rubber insulation layer and the conductor. Therefore, rigorous cleaning of the conductor is necessary before production. This typically involves chemical cleaning or mechanical abrasion to remove surface contaminants, followed by sandblasting or plating to increase surface roughness and create a micro-textured structure. This structure enhances the mechanical interlocking effect between the silicone rubber and the conductor, resulting in a stronger bond between the insulation layer and the conductor after curing.
The choice of insulation material directly affects the bonding effect. As an insulating material, silicone rubber must possess excellent flowability, adhesion, and elasticity to ensure it can fully fill the microscopic gaps on the conductor surface during extrusion. Simultaneously, the material formulation design must balance processing performance and bonding strength, for example, by adding coupling agents or tackifiers to improve the chemical compatibility between silicone rubber and the conductor metal surface. Furthermore, the material's hardness, elastic modulus, and other physical properties must match the conductor's characteristics to avoid stress concentration leading to interface delamination.
Optimizing the extrusion process is crucial for ensuring bonding strength. During extrusion, silicone rubber must uniformly coat the conductor under high temperature and pressure to form a dense, defect-free insulating layer. This process requires strict control of parameters such as extrusion temperature, screw speed, and traction speed: excessively high temperatures may cause silicone rubber decomposition or excessive flowability, forming flow marks or bubbles; excessively low temperatures will increase the material viscosity, making it difficult to fully fill the conductor surface. At the same time, precise matching of screw speed and traction speed is necessary to ensure the uniformity of the insulating layer thickness, avoiding reduced bonding strength due to localized areas of excessive thinness or thickness.
Controlling cooling and curing is critical to the stability of the bonding strength. After extrusion, silicone rubber undergoes a cooling and curing stage to transform the insulating layer from a molten state into an elastic solid. During this process, the cooling rate must be moderate: too rapid a rate may lead to stress concentration within the insulating layer, causing cracking or peeling; too slow a rate may cause excessive material flow, resulting in an unclear bonding interface. A segmented cooling method is typically used: first, low-temperature air cooling or water cooling rapidly reduces the surface temperature, followed by natural cooling or isothermal curing to release internal stress and ensure a stable bond between the insulating layer and the conductor.
Quality inspection and feedback are the last line of defense for ensuring bonding strength. During production, online monitoring equipment is used to monitor parameters such as the thickness, eccentricity, and surface quality of the insulating layer in real time, combined with sampling tests to test the bonding strength. For example, peel tests or tensile tests are used to assess the adhesion between the insulating layer and the conductor, or the microstructure of the bonding interface is observed under a microscope. If the bonding strength is found to be substandard, process parameters must be adjusted immediately or the material replaced to avoid batch defects.
Production environment management is equally crucial. Silicone rubber is sensitive to dust, moisture, and chemicals in the environment. If the production workshop is contaminated, impurities may become embedded in the bonding interface, reducing bonding strength. Therefore, it is necessary to maintain workshop cleanliness, control temperature and humidity, and avoid contact with oil or corrosive substances during the insulation extrusion process. Furthermore, the skill level of the operators directly affects the bonding effect; training is required to ensure they are proficient in the extrusion process and equipment operating procedures.
