In the vacuum casting process of epoxy resin cast dry-type transformers, how can residual air bubbles be controlled to further reduce the probability of partial discharge?
Publish Time: 2026-05-14
In the manufacturing process of epoxy resin cast dry-type transformers, the vacuum casting process is a key step in improving insulation performance and operational reliability. The problem of residual air bubbles directly affects the level of partial discharge, because tiny air gaps can easily form discharge initiation points under a high electric field, thereby accelerating insulation aging and even causing failures.1. Improve the vacuum degassing process to reduce the gas content of raw materialsEpoxy resin and curing agent are prone to entraining trace amounts of air during mixing. If these gases are not sufficiently removed, they will form tiny bubbles after curing. Therefore, high-vacuum degassing treatment is required before casting. By continuously pumping vacuum, the dissolved gas content in the system is reduced, making the resin reach a near-air-free state. At the same time, by extending the degassing time and optimizing the stirring method, the gas escape efficiency can be further improved, reducing the conditions for bubble formation from the source.2. Optimize mixing and stirring methods to reduce secondary air entrapmentDuring the mixing stage of resin and curing agent, improper stirring methods can easily introduce new air. Employing low-shear, low-turbulence mixing processes can effectively reduce air entrainment. Simultaneously, using a closed mixing system under vacuum, maintaining negative pressure throughout the mixing process, significantly reduces the probability of gas ingress, thereby minimizing the source of air bubbles in subsequent casting.3. Controlling the Stability of the Vacuum Casting Environment to Improve Filling QualityDuring casting, the stability of the vacuum level directly affects the bubble escape effect. Excessive vacuum fluctuations can cause previously removed gases to re-emerge. Therefore, precisely controlling the vacuum system to maintain a stable negative pressure in the casting cavity ensures the continuous release of residual gases during resin flow and filling. Optimizing the casting path, allowing the resin to slowly fill from a lower to a higher position, facilitates the smooth upward escape of gases.4. Optimizing Mold Structure to Promote Natural Bubble ExpulsionMold structure design also significantly impacts bubble retention. By incorporating venting channels or micro-venting grooves in key areas of the mold, effective escape paths for residual gases can be provided. Meanwhile, rationally designing the positions of the pouring and venting ports to ensure unidirectional resin flow helps prevent gas from becoming trapped in localized structural dead zones, thus reducing the probability of internal voids.5. Controlling the Curing Process to Prevent Gas Re-releaseDuring the resin curing stage, rapid or uneven temperature changes can cause dissolved gases to re-release, forming microbubbles. Therefore, employing a segmented heating and curing process allows the resin to slowly cross-link and cure, effectively reducing the risk of gas release. Simultaneously, maintaining a slight vacuum environment in the early stages of curing helps to further remove residual micro-gases, thereby improving overall insulation density.In summary, in the vacuum casting process of epoxy resin cast dry-type transformers, effectively controlling residual bubbles and reducing the probability of partial discharge requires systematic optimization from multiple aspects, including vacuum degassing, mixing process optimization, casting environment control, mold structure design, and curing process management. Only by achieving comprehensive gas control and process synergy can the product's insulation performance and long-term operational reliability be significantly improved.
