Pore-Free and Perfectly Insulated - Vacuum impregnation seals castings and high voltage coils

Pore-Free and Perfectly Insulated - Vacuum impregnation seals castings and high voltage coils

Suede shoes are protected from moisture using impregnation. But many technical components also require a protective coating that is as dense as possible. Vacuum makes this perfect.

Small pores can have a devastating effect on technical components: the oil sump on the engine block or the high-performance generator in the power plant can lead to loss of function and total failure.

Inevitable pore formation

The oil sump is usually made of cast metal. Despite careful production, small pores can develop during casting and further processing. Such material faults make the sump leaky and thus unusable. It is also essential that they do not occur with other cast parts such as brake cylinders, pump housings or valves.

Electric motors and generators are much more complex and composed of different materials. Here, too, pores can be fatal, especially in coils and windings. Air inclusions between the wires and the insulation can cause increased resistance, reduced breakdown voltage, partial discharges and even complete destruction of high-voltage components.

So the pores somehow need to be removed. To achieve this, cavities remaining in cast parts and coils are filled with synthetic resin. However, it is not sufficient to apply the impregnation only externally, as is the case with suede shoes because the pores and spaces are tiny and can also be deep inside the parts.

Penetration made easy

Vacuum transports the sealing material into all gaps. First, the parts are heated. Residual moisture evaporates and the synthetic resin becomes more liquid. The work piece is then placed in a vacuum chamber in which a "dry" vacuum extracts vapor and air. The impregnating agent is now run from a container into the evacuated chamber. Atmospheric pressure forces the mass into the smallest pores of the target object.

If necessary, this "moist" vacuum is maintained for a while until the work piece is completely penetrated. In the finishing process, excess residues are removed and the impregnation is solidified by hot polymerization. The penetration of coils and windings in electrical components reaches almost one hundred percent; cast parts are permanently pressure-tight after this treatment.

For vacuum impregnation and similar processes in which a liquid mass is to penetrate into cavities and gaps, space must first be created there. However, just one cubic centimeter of air contains about 30,000,000,000,000,000,000 gas atoms. They are in the way when you want to fill a cavity with something else. In an open environment, a liquid with a much higher density will effortlessly displace the gas. However, the smaller the cavities, the more likely it is that "dead ends" are formed in which the atoms are trapped. The trapped air cannot escape.

Only vacuum with its suction effect ensures that even the smallest cavities are emptied and that the penetrating medium no longer encounters obstacles in the form of gas atoms in the air. Suction of the air has another effect: in the evacuated chamber the air pressure is close to zero, while "outside" the air column of the atmosphere weighs around 10,000 kilograms on every square meter of surface area. This force can now act unhindered in the direction of the vacuum. It is sufficient to press even viscous and sticky masses into the smallest cavities.

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