Epoxy Resin Dry Transformer Vacuum Casting

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Epoxy resin is an organic polymer with two or more cyclic epoxy groups in the molecule.Except for a few, their relative molecular mass is not high.

The characteristics of epoxy resin are: (1)variety of forms. (2)Easy to cure. (3)Strong adhesion.(4) Low contractility. (5) Excellent mechanical properties .(6)After curing, it forms a kind of excellent insulation material with high dielectric properties, resistance to surface leakage, and resistance to arc.(7) Chemical stability. (8) Little stability. (9)Pet-tolerant to mold, etc.

In recent ten years, the production of type transformer in China has developed greatly, and the performance and appearance of the products have been improved greatly. Epoxy resin casting has the characteristics of one-time forming, that is, after the forming cooling hardening can not be recycled, the formed winding does not meet the specified standards or design requirements, it can only be scrapped, can not be reused. The structure of prepouring winding is required to be reliable, the proportion of pouring material is reasonable, and the technology is advanced.

At present, the transformer industry is the use of imported or domestic vacuum pouring equipment.Due to the different structure of vacuum pouring equipment, in the concrete pouring operation process also has its unique.

1. The ingredients
SIMUWU Shanghai Ge Hong Vacuum Technology Co., LTD. Casting material is imported two-component epoxy resin material, the batching process is divided into epoxy resin batching and curing agent batching.

Epoxy resin batching is to suck a certain amount of epoxy resin into the batching tank (low vacuum, premix tank).When the stirring is heated to 50℃, its fluidity reaches the best state. Fillers and pigments are added in accordance with a constant ratio to maintain a vacuum degree of 20~ 30 mbar. When the mixing material is stirred evenly without a large amount of foam and the temperature is 50~ 60℃, the material can be sent to the epoxy resin tank for film degassing.

The curing agent batching process is basically the same as that of epoxy resin. The proportion of curing agent and filler is slightly different according to the different brands and models of raw materials. After batching, the mixture is fed into the curing agent tank for film degidation.

2. The degassing
Film degassing is a widely used degassing method in casting process.The result of degassing will determine the number of bubbles during pouring. The fewer bubbles, the higher the pouring quality.

There is an umbrellal spiral lifting device in both epoxy tank and curing agent tank.During operation, the spiral lifting device lifts the mixture onto the deaeration umbrella. On the top, the mixture flows from the top to the sides of the umbrella. At this time, the mixture forms a very thin material layer on the top.The gas in the mixture is on the canopy. It bubbles into the vacuum tank and is pumped out of the tank by a vacuum pump.During the process, the temperature must be kept within the range of 60~ 65 ℃, and stir for a long time for degassing.

In general, at least 12 h of continuous degassing (which can be adjusted according to the amount of material and the change of season) shall be required to remove as much water and gas as possible from the material.During degassing, the viscosity and bubbles of the mixture on the inside sector of the degassing tank should be paid close attention to through the observation window.

3. Preparation before casting
Before pouring, the wound coil is loaded into the pouring mold and hoisted into the pouring tank.

One end of the mold is properly raised, and the lower end of the mold is filled with a pouring pipe opening. A layer of filter screen is installed between the pouring pipe opening and the mold to filter impurities in the pouring material.

There should be no liquid substances, such as detergent, in the pouring pipe. Before putting it into the winding, it should be properly heated, naturally remove the cleaning agent, dry the pipe, check the lighting in the pouring pot, and close the door.The casting tank heating system is opened, the temperature is set at 80~85℃, the windings in the casting tank are heated, the time is 8~10h, two hours before casting, the vacuum pump of the casting tank is opened.

4. Final mixing and casting process
Calculate the weight of the required mixture according to the quota and quantity of the coil resin to be poured, appropriately relax the allowance, respectively fill the epoxy resin material and curing agent material (equipped with packing) into the final mixing tank according to the 1:1 mass ratio, open the vacuum pump of the final mixing tank for final mixing and stirring.
The final mixing time is generally controlled at about 30 min, and pouring is started after 10 min. The pouring process is manually operated, and the flow rate and flow rate are manually controlled (the speed is generally controlled at 1.5 ~ 2 kg/min according to the size and structure of the mold).

Casting time, final mixing and standing time must be controlled within 2 h
< / p > < p > into, over time, the viscosity of the mixture will increase rapidly, directly affect the quality of the winding pouring and equipment safety, casting process to closely track the viscosity of the outlet of the mixture, bubbles and the temperature displayed by each instrument equipment.

The whole process should be as low viscosity, high vacuum, slow pouring and slow pouring as possible, and it is easy to increase the viscosity of the mixture, which requires operators to carry out long-term practical observation and experience summary.

After the completion of casting, casting parts must be quickly pushed into the curing furnace for curing, to minimize the retention time in the low temperature environment, to avoid the impact of the mold temperature drop, material in the mold flow.

5. Solidification and mold removal
The casting mold must be heated and cured in the curing furnace according to the curing temperature time curve.During the curing process, the temperature in the curing furnace should be guaranteed to be uniform.After curing, the coil shall be removed from the oven, the outer film, splice plate and fixture shall be removed as quickly as possible (within 20 min as possible), the coil shall be hoisted into the furnace again, and the temperature shall be lowered slowly with the furnace.

6. Conclusion
The advantage of full vacuum pouring is that the whole mixing process is in a vacuum state, which can effectively extract the air from the epoxy resin mixture and reduce the bubbles in the mixing.

In grasping the technology of pouring process, the process of different products and raw materials is improved, so as to make the epoxy resin products poured out, beautiful appearance and superior performance, so that the overall product performance of dry transformer meet the customer’s demand.

Editor: Frank Lee
Copyright: SIMUWU vacuum furnace

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