(like casting) or objects with inherent voids (like motor coils) to prevent accumulation of undesired

elements like dust, dirt, chemicals or water. Impregnation of objects improves its physical properties

and also tends to improve overall parameters of the equipment/component wherein use. For Ex. a

varnish impregnated coil improves the overall insulation resistance of the motor and hence the life of

the motor is improved.

Different chemicals are used in the process of the impregnation. These chemicals can be classified

as epoxy, varnish and resins. Impregnation process itself can be classified in different types like

flood impregnation, dip impregnation, vacuum impregnation, vacuum pressure impregnation, trickle

impregnation, hot roll dipped impregnation. At NACH we have expertise in manufacturing all these types

of the impregnation systems.

Flood impregnation and dip impregnation are simple impregnation processes often used in the low

voltage small frame electrical motors. In flood impregnation the resin/varnish is flooded in the chamber

where the preheated coils (electric motor stator or wound rotor) are placed. The coils are kept for

soaking in varnish for a certain period and then taken off to the baking oven. The varnish is stored in

a cold chamber or vessel called the storage tank. Typically temperatures for maintaining the varnish/

resins is 15 deg C to 10 deg C. In dip impregnation, coils are dipped in a tank that contains varnish and

kept for a certain time.

Vacuum pressure impregnation is a special process designed to impregnate the motor coils or some

castings that are used in critical applications. Vacuum pressure Impregnation often called the VPI

process impregnates the coils or metal castings under vacuum. Impregnation under vacuum prevents

advent of external moisture that may be accumulated in the voids of the coil or may be absorbed in

insulation. Vacuum impregnated coils are free of moisture that result good electrical properties.

In case of metal impregnation, vacuum impregnation results good adhesion of the chemical with the

surface. Metal impregnation process that involves impregnation of castings is often accompanied by

additional processes like cleaning of castings jobs, chemical treatment for better adhesion etc. Often

epoxy is used for porosity sealing of the castings.

In a vacuum pressure impregnation plant, there are two tanks, one is the impregnation chamber and the

other is the storage tank used to store the varnish/resin. In resin impregnation system, often storage

tanks require cold storage of level up to 10 Deg C to 15 Deg C. Alternately a epoxy impregnation system

demands hot storage, since the curing of epoxy occurs at room temperature. Distinct manufacturers

for epoxy like Alantas (formerly Dr Beck), Huntsman (formerly CIBA), Von Roll, Vantico Ltd. suggest

methods for vacuum pressure impregnation with indication of different processes like vacuum, soaking,

maintaining pressure, amount of pressure etc for better results.

In a typical vacuum pressure impregnation system for motors, preheated coils are kept in the

impregnation tank and vacuum is drawn. After a certain period resin is introduced in the impregnation

tank in controlled manner and filled till the top of the coil stack. Dry air or nitrogen pressure is applied in

the chamber for better penetration of the resin in the voids and this is maintained for a stipulated time.

Later the resin is withdrawn to the storage tank. Almost in all the impregnation processes the resin or

varnish transfer from tank to tank is achieved by pressure difference in the two tanks or by gravity flow

of the varnish.

In trickle impregnation or a hot rolled impregnation process, the resin is introduced on the motor coil

in a very controlled fashion. The coils are heated by use of its own resistance. This type of methods are

used where resin costs are higher or usage of resins/chemicals have limitations.

At NACH we have the expertise to develop the vacuum impregnation systems for different resins. NACH

can manufacture VPI systems as per guidelines and specifications defined by resin manufacturers.

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