Section III. POTTING, EMBEDDING, AND SEALING

TM 750-245-4

Section III. POTTING, EMBEDDING, AND SEALING

product; therefore, adhesion to the mold is essential. In

9-10. General

embedding, however, a release agent must be applied

In many cases, potting, embedding, and sealing

to the mold before potting. Often, electrical wires with

compounds are identical to adhesive bonding

nonadherent surfaces are encountered. Do not attempt

compounds. More material is used in their application

to abrade or clean electrical wires or sleeved junctions

than in bonding. These compounds are resin which can

near the potted area, since the abrasion may cause

be converted from liquids to solids at room or slightly

short circuits.

elevated temperatures. Normally, these resins will not

be used in field repair except for the potting of plugs,

d. Check each unit to be processed to insure that

jacks, and material containing potting, embedding, and

components are in place and ready for potting or

sealing may be damaged and will have to be inspected

encapsulating. Correct any discrepancies. Aline molds

for defects.

The defects may have originated in

and components in the fixtures and center all wires and

manufacture or they may be the result of handling and

components protruding from a mold uniformly in the

environment in service.

The application of these

cavity.

materials is defined as follows:

e. When so instructed in the technical

a. Potting. The placing of electrical components or

documentation, prime the molds, components,

networks in a metal or plastic container which is then

substrates, or any combination thereof, with suitable

filled with casting resin. The liquid resin then hardens

adhesion-promoting agents, or release agents, as

by cooling or chemical action and the container

applicable. Make sure the primer will not damage the

becomes an integral part of the finished product.

molds, components, substrates, or the potting or

b. Embedding. A process similar to potting except

encapsulating compound. Apply the primer according to

that the components and liquid resin material are cast in

the instructions on the container.

a temporary container which is removed when the resin

hardens.

9-12. Preparing the Potting Compound

c. Sealing. The placement of a small fillet of resin

a. Almost all potting compounds require thorough

sealant over joints or cracks on containers. The sealant

mixing before combining two-part or applying one-part

protects the container from foreign material.

sealants to a substrate. If the resin or accelerator

Sometimes sealants are used for staking (bonding) parts

contains no filler and is transparent, it may not require

together in conjunction with the protection or sealing

extensive mixing.

action.

b. If weighing and mixing of two-part systems are

necessary, follow the instructions on the container.

9-11. Preparing Parts to be Potted

c. Foaming systems, because of their short

a. To achieve maximum adhesion, the adherent

reaction time, must be quickly and thoroughly mixed.

surface must be carefully prepared. Clean all potting

Stir the mixture until it is homogeneous, lighter in color,

areas until they are free from oil, grease, release

and more viscous. Do not overmix or the mixture will

agents, rust, moisture, or fingerprints. Skin grease or

be too stiff to pour.

perspiration deposited on the adherent surface may

reduce adhesion by as much as 75 percent.

9-13. Applying the Potting Compound

b. Thoroughly

clean

the

surface

either

a. Potting compounds can be poured, extruded

mechanically or chemically, depending upon the type of

through sealant guns, (air-pressure activated), dipped,

material and the contaminant to be removed. To

or spread with a knife or spatula.

Each potting

eliminate dirt, scale, rust, and similar contaminants, use

compound or sealant has its own particular procedure

wire brushing, buffing with powdered wire brushes,

for application, depending on the material's viscosity. In

sandpapering, sandblasting, or other types of abrasion.

general, apply material as dictated by the instructions on

Degrease by solvent cleaning before and after abrading

the container. Apply only enough to insure adequate

the surfaces. Remove oils, greases, and most similar

coverage.

contaminants with chemical cleaning agents such as

solvents and detergents. Make sure no solvent remains

b. Be careful not to trap air in the potting or

within the mold cavity.

encapsulating material while putting the material in

sealant guns or other injection apparatus. Pour the

c. While preparing adherent surfaces, consider

material down the inside wall when loading the gun or

which areas do or do not require adhesion. In potting,

cartridge.

the mold or container becomes a part of the finished

9-3