Final Inspection, Cured Potting Compound

TM 750-245-4

Fahrenheit above the intended maximum service

b. Avoid testing potted or sealed assemblies.

temperature of the cured compound.

Instead, if tests are required to determine that the

(2) Polysulfides. Avoid heat curing these

assembly is properly potted, provide test samples of the

same material. Choose standard test specimens to

materials at temperatures higher than 120 degrees

satisfy this requirement whenever practical, taking care

Fahrenheit, because the cured potting compound will

to repeat the curing and potting methods employed

gas or become foamlike in appearance. Do not use

during the original procedure. If the test specimen fails,

heat lamps.

try to determine the specific cause of failure. Some of

(3) Epoxies.

Allow mixed epoxies which

the predominant causes of failure are listed below:

have generated exothermic heat to return to or below

(1) Poor surface preparation of substrates.

cure temperature before starting the cure cycle.

(2) Potting compound not properly mixed.

(3) Incorrect ratio of resin to hardener (the

9-16. Final Inspection, Cured Potting Compound

ratio is sometimes reversed).

a. Inspect the potting compound to determine if it

(4) Each unit container not premixed.

is smooth, continuous, and properly cured. Poorly

potted parts may be recognized by: air voids on the

(5) Potting compound shelf-life exceeded

surface and throughout the potted unit; potting material

(this can result from incorrect shelf-life markings).

burned or bubbly from excessive heat or localized heat;

(6) Potting compound not suited for the job.

compound soft or tacky from under-curing, discrepant

(7) Substrates not suitable for potting

shelf-life, or lack of heat; substance cracked because of

because of configuration or type of material.

thermal shock or exothermic reactions, or streaked

because of inadequate mixing.

9-5