As the core link in the production process of pressed polymer insulators for low voltage overhead insulated conductors, the pressing process affects its mechanical strength and stability throughout all aspects of material fusion, structural molding and performance. First of all, temperature control during the pressing process is one of the key factors affecting material performance. During pressing, the polymer raw material needs to reach a specific melting state to fully combine with fillers, reinforcing fibers and other components. If the temperature is insufficient, the raw material cannot be completely melted, which will lead to uneven mixing of the components and form local stress concentration points, making it easy for the insulator to break from these weak parts when it is subjected to mechanical loads; while too high a temperature may cause the degradation of the polymer molecular chain, weaken the strength of the material itself, and even cause defects such as surface carbonization and internal bubbles in the insulator after molding, which seriously affects its mechanical stability.
The uniformity and size of the pressure applied also play a decisive role in the mechanical properties of the insulator. During the pressing process, the pressure needs to be evenly transmitted to all parts of the mold to ensure that the internal structure of the insulator is dense and consistent. If the pressure distribution is uneven, it may cause density differences in different areas of the insulator, such as insufficient compaction in some parts and more pores, while other parts have fiber breakage or excessive material flow due to excessive pressure. This structural unevenness will cause the stress distribution of the insulator to be unbalanced when subjected to tensile, compressive or bending loads, which is easy to cause local deformation or cracking. In addition, the size of the pressure needs to match the characteristics of the raw materials. If the pressure is too small, the material cannot be tightly combined and the mechanical strength is insufficient; if the pressure is too large, it may exceed the tolerance of the mold and equipment, causing mold wear or equipment failure, and may also have an adverse effect on the molecular structure of the material.
The length of the pressing time is also a process parameter that cannot be ignored. Sufficient pressing time can ensure that the polymer raw material is fully melted, flows and fills the mold cavity, so that a good interface bonding is formed between the reinforcing material and the matrix resin. If the pressing time is too short, the raw materials will not have enough time to fully react and solidify, and there may be incompletely fused areas inside the insulator, resulting in a decrease in mechanical strength, especially when subjected to dynamic loads, which is prone to delamination or cracking; while if the pressing time is too long, the material may be over-cured, the polymer molecular chain may be over-crosslinked, the toughness of the material may be reduced, and the insulator may become brittle and hard, and it may easily break when subjected to impact or vibration, affecting its long-term stability.
The design and processing accuracy of the mold have a direct impact on the effect of the pressing process and the mechanical properties of the insulator. A reasonable mold structure can ensure the uniform distribution of pressure and temperature during the pressing process, and facilitate the flow and exhaust of the raw materials. For example, whether the flow channel design of the mold is smooth will affect the filling speed and filling uniformity of the raw materials. If the flow channel is too narrow or there are sharp angles, the flow of the raw materials may be blocked, forming eddies or retention areas, bubbles or weld marks, and these defects will become the weak links in the mechanical properties of the insulator. In addition, the surface roughness and dimensional accuracy of the mold are also crucial. A rough mold surface may cause scratches or unevenness on the surface of the insulator, which not only affects the appearance, but may also cause cracks due to stress concentration during use; insufficient mold dimensional accuracy will cause the geometric dimensions of the insulator to not meet the design requirements, affecting its installation and coordination with wires, hardware and other components, and thus affecting the stability of the overall mechanical structure.
The control of the cooling process in the pressing process also has a significant impact on the internal stress and mechanical properties of pressed polymer insulators for low voltage overhead insulated conductors. After the pressing is completed, the insulator needs to be cooled and shaped. The speed and uniformity of the cooling rate will affect the generation and distribution of internal stress in the material. If the cooling rate is too fast, the temperature difference between the surface and the inside is too large, which is easy to form a large internal stress inside the insulator. This internal stress may gradually release during long-term use, causing the insulator to deform or crack; while the cooling rate is too slow, it will extend the production cycle and reduce production efficiency. In addition, the uniformity of the cooling process is also very important. Uneven cooling may cause inconsistent shrinkage rates in different parts of the insulator, resulting in warping or distortion, affecting its mechanical strength and installation accuracy.
The pretreatment and mixing process of raw materials are interrelated with the pressing process and jointly affect the mechanical properties of insulators. Before pressing, polymer raw materials usually need to be dried to remove moisture and volatiles. Otherwise, during the pressing process, the moisture will be vaporized by heat and form bubbles inside the insulator, reducing the mechanical strength. At the same time, the dispersion uniformity of reinforcing materials such as glass fiber and carbon fiber also depends on the mixing process. If the mixing is uneven, the fibers may agglomerate or have inconsistent orientation during the pressing process, resulting in significant differences in the mechanical strength of the insulator in different directions, affecting its stability. For example, the area where the fibers agglomerate may lack toughness due to excessive local strength, while the area where the fibers are sparsely distributed becomes a weak point of strength and is easily damaged when subjected to force.
The stability and repeatability of the pressing process are also important factors to ensure the mechanical strength and stability of the insulator. In large-scale production, performance fluctuations of the pressing equipment and slight changes in process parameters may lead to quality differences between different batches of products. For example, if there is an accuracy deviation in the temperature control system of the equipment, the actual temperature of different batches of insulators during the pressing process may not match the set temperature, thereby affecting the curing degree and mechanical properties of the material. Therefore, strict process management and equipment maintenance are required to ensure the stability of the pressing process, so that each batch of insulators can maintain consistent mechanical strength and stability and meet the reliability requirements of the power system for insulating components. From raw material preparation to molding and cooling, the fine control of the pressing process is the key to improving the mechanical properties of pressed polymer insulators for low voltage overhead insulated conductors. Only when all factors work together can high-quality products with excellent mechanical strength and stability be produced.
