MIL-DTL-25421C
3.2 First article approval. Unless otherwise specified in the contract or order
(6.2), the laminated plastic materials furnished under this specification shall be
products which have been approved under the first article inspection prescribed
herein (4.3).
3.3 Materials. Materials used in the laminates shall be as follows:
3.3.1 Glass fiber base.
3.3.1.1 Cloth. The cloth shall be continuous filament glass cloth in accordance
with Tables I and II and the requirements of SAE AMS-C-9084.
3.3.1.2 Mat, short fibers. The short fiber mat shall conform to the requirements
of MIL-M-43248, Grade A.
3.3.1.3 Mat, nonwoven continuous filament. The nonwoven continuous
filament mat shall be as described in Tables I and II.
3.3.2 Resin. The laminating resin shall conform to the requirements of MIL-R-
9300. Types I and II resin of MIL-R-9300 shall be used for Types I and II, laminated
material, respectively, of MIL-P-25421. Any electrical or nonelectrical grade of resin
under MIL-R-9300 may be used for any class of laminated material of MIL-P-25421,
provided the finished laminate product conforms to the requirements for the
applicable class and type under MIL-P-25421 and the requirements for the specific
part or end item.
3.3.3 Fillers. Finely divided, inert, inorganic fillers may be used in mat
laminates only, provided other applicable requirements of this specification are met
by the laminates.
3.4 Finished product. The finished laminated product shall conform to the
following requirements:
3.4.1 Physical properties. The minimum Barcol hardness value and the
minimum and maximum values for specific gravity and for resin content of the
laminated materials shall be as specified in the process specification or data sheet.
3.4.2 Mechanical properties. The mechanical properties of the laminated
materials shall conform to the requirements of Tables I and II when tested in
accordance with Table VI.
3.4.3 Electrical properties. Except as may be specified otherwise for Class 3 in
contract or order (6.2, 6.3), the electrical properties of Class 2 and Class 3 laminated
materials shall conform to Table III when tested in accordance with Table VI. There
shall be no electrical requirements for Class 1 material.
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