Epoxy and resin casting is a foundation of modern electrical equipment manufacturing because it protects, insulates, and shapes critical parts. From tiny sensors to large transformer coils, the right casting method controls heat, moisture, and partial discharges while improving strength and reliability. This guide explains process choices, tooling needs, and quality controls that engineers use every day. By the end, you will understand how to choose a path that suits geometry, volume, and performance targets. Below we explore the Top 10 Epoxy And Resin Casting Methods For Electrical Equipment Components with practical tips and selection notes.
#1 Gravity Pour Casting
Gravity pour casting uses a simple heated mold and a controlled resin pour to make panels, bobbins, spacers, and small housings. Resin is mixed, degassed, and poured into the mold by weight for consistent fill. Gate design, risers, and vents prevent air traps while allowing resin to wet fine features. Thermal control is important because exotherm can cause shrink marks or cracks. Silica or alumina fillers reduce shrinkage and raise thermal conductivity for better heat paths. Use gravity casting when part geometry is moderate, run size is small to medium, and tooling cost must remain low.
#2 Vacuum Degassing With Controlled Pour
Vacuum degassing with a controlled pour improves clarity and electrical strength by removing dissolved air before and during filling. The mixed resin sits under vacuum until it foams and collapses, releasing trapped gases. The mold can be vibrated gently while the pour proceeds to help bubbles escape through vents. A bottom feed sprue reduces turbulence compared with top pouring. This approach is excellent for potted coils, sensors, and connectors where voids would become partial discharge sites. Choose this method to upgrade a standard gravity process without the high capital cost of a full vacuum chamber or pressure gelation system.
#3 Full Vacuum Casting For High Voltage Parts
Full vacuum casting places both resin and mold in a sealed chamber so filling happens at low absolute pressure. The pressure differential pulls resin into fine gaps and around windings while almost eliminating entrapped air. This is the preferred route for cast resin bushings, instrument transformer heads, and complex HV insulators. Preheating molds and coils lowers viscosity and improves wetting. After fill, the chamber is returned to ambient or slight pressure while gelation starts in a controlled oven. Use full vacuum casting when the design must achieve very low partial discharge inception levels and long service life in harsh environments.
#4 Pressure Gelation Casting
Pressure gelation casting fills a heated metal mold and then cures the resin while holding positive pressure, often between 3 bar and 10 bar. Pressure squeezes microbubbles smaller than the critical flaw size and drives resin against inserts and ribs for crisp detail. Cycle times are shorter because the mold is hot and the chemistry is fast. The method supports moderate to high volumes of insulators, coil supports, terminal blocks, and stator end caps. Tooling must include ejection and robust seals to avoid leaks during pressurization. Select pressure gelation when you need dimensional repeatability, faster throughput, and reliable surface finish.
#5 Vacuum Pressure Casting Sequence
Vacuum pressure casting combines the strengths of vacuum and pressure in one sequence. The mold and resin are evacuated during fill to prevent air entrapment, then the chamber is switched to positive pressure for gelation. This dual approach produces dense, void free parts with strong dielectric performance. It is effective for bushings with long creepage paths, current transformer casings, and solid insulated busbar joints. Process windows matter, so teams monitor viscosity, temperature, and pressure ramps closely. Choose this method when failure costs are high and when you must pass partial discharge tests at levels that standard casting cannot consistently meet.
#6 Centrifugal Casting
Centrifugal casting spins the mold around a central axis so inertia pushes resin outward during fill and cure. The force expels bubbles toward the inner diameter while packing resin and fillers against the mold wall. This makes smooth, dense tubes, bushings, surge arrestor housings, and hollow insulators. Engineers control speed, time, and viscosity to avoid gradient settling of heavy fillers. Flexible mandrels or dissolvable cores create internal channels for leads or cooling features. Use centrifugal casting when the design is cylindrical and needs uniform wall thickness, high dielectric strength, and excellent roundness without secondary machining.
#7 Transfer Molding Of Epoxy Compounds
Transfer molding uses a pellet or preheated charge of epoxy molding compound that is forced through runners into a closed mold. The material flows under pressure, then cures into a precise shape with minimal flash. Glass fiber and mineral fillers deliver high strength and good tracking resistance for electrical parts. This method suits coil bobbins, switchgear spacers, busbar supports, and connector bodies at higher volumes. Tooling cost is higher than open molds but cycle time is short and tolerances are tight. Pick transfer molding when you need consistent dimensions, captive inserts, and efficient production with thermoset compounds.
#8 Potting And Encapsulation Casting
Potting and encapsulation fill a case or shell around the device rather than using a separate mold cavity. The assembly sits in its final housing while mixed resin flows in through designed gates. This simplifies handling and creates a sealed unit that resists moisture, vibration, and contamination. Common targets include sensor modules, control boards, ignition coils, and small transformers. Resin selection balances thermal path, flexibility, and flame rating so the unit survives thermal cycling and surge events. Choose potting and encapsulation when you want protection and electrical insulation with minimal tooling and when field service is not required.
#9 Overmolding And Insert Casting
Overmolding and insert casting embed conductors, terminals, cores, or sensors inside resin so the finished part leaves the mold as an integrated assembly. Metal inserts are cleaned, blasted, and preheated to improve adhesion and reduce voids at the interface. Engineers add ribs, holes, or knurls to lock inserts mechanically. Gate placement guides flow around sharp corners and avoids shadowing. These techniques reduce assembly steps and improve dielectric creepage by eliminating gaskets and seams. Select overmolding and insert casting when you want reliable alignment, tamper resistance, and robust strain relief in connectors, bushing terminals, and instrument transformer heads.
#10 Cast Resin Transformer Coil Casting
Cast resin transformer coil casting places dried windings into a sectional mold and fills them with filled epoxy under deep vacuum. The process creates a monolithic coil that resists partial discharge and moisture without an oil tank. Preheating windings removes residual moisture and reduces viscosity for thorough wetting. Silica filled systems control exotherm and shrinkage while boosting thermal conductivity. After gelation, post cure ramps elevate glass transition temperature for higher thermal class ratings. Choose this approach for dry type distribution transformers and reactors where fire performance, low maintenance, and clean rooms are important for the installation environment.