Electrical Casting

Epoxy resin has is in use since the 1980s, for the transformer, instrument transformer, insulator and other electrical products as main insulating materials, in voltage range of 10 kV to 35 kV. The processing method – casting involves pouring the epoxy resin materials into the assembled work-piece mold. Such mould is cured and upon de-moulding the finished product is achieved. The epoxy casting process is a dominant insulation method which helps to achieve miniaturisation, achieve lightweight and low noise in the electrical product. Twin has fully automated and proven machines for the process of development of normal pressure casting, full vacuum casting and automatic pressure gelation (APG).

Twin’s Machines come with advanced vacuum degassing pumps and thin-film degassing to ensure highest quality of de-aerating, resulting in lower number of bubbles during casting, and higher quality of products. The casting speed is generally controlled at 1.5-2 kg/min so as not to obstruct gas vent. The castable mix is poured and put into Casting gate of die set continuously and slowly. The process can be controlled to ensure complete filling and avoid any possibility of solidification at the Casting gate, formation of air pockets inside the mould or large incomplete filling formed internally.

Twin’s Machines for the electrical casting applications deliver several unique results for you such as bubble free casting, better electrical insulation and mechanical properties, higher product yield and lower product cost and labor intensity.

Atmospheric Casting

Atmospheric casting involves dispensing of the mixed resins under atmospheric pressure. The degassing of materials to be mixed is critical and is carried out in the tanks. The prevention of sedimentation from the filler addition is also a concern in the casting/ potting of transformer coils. Epoxy Resins are pre-heated in separate tanks to a temperature of 80℃-120℃. The materials are vacuum degassed and continuously stir with thin-film degassing to ensure bubble-free mix. Accelerant is added to final mixing tank. The material is mixed before dispensing and casted into moulds under atmospheric pressure.

Vacuum Casting
Vacuum Casting of Epoxy resins involves several steps. The first step is preheating a formula mix containing epoxy resin, curing agent, functional aids, inorganic powder filler, since these materials have a tendency to absorb moisture in the air during transportation and storage and reduce product insulation. The preheating also helps in improved fluidity.
Typically, Silica powder is dried under 120℃ before adding it to the resin and curing agent. Epoxy Resins are pre-heated in separate tanks to a temperature of 80℃-120℃. The materials are vacuum degassed and continuously stir with thin-film degassing to ensure bubble-free mix. Accelerant is added to the final mixing tank. The material is mixed before dispensing. The mix is poured under vacuum, according to the complexity of cavity of die set in a flow controlled to 1.5-2 kg/min.

Automatic Pressure Gelation (APG)
The automatic pressure gelation (APG) process is a well established and indispensable method for producing all kind of insulating parts for the high voltage engineering industry. Twin’s offers an end-to-end solution which involves feeding of clamping machines using central or portable resin mix supply systems. Twin’s Machines can supply materials to up to 8-12 APG clamping stations, at a time and process up to 2 Tons of mix per day. The Machines includes built-in system for silica handling, preheating and blending and offers shrinkage compensation for void free castings with shorter cycle times.