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Mil Specs & Varnishes

Jack Hasson, Northeast RSM

Impregnating varnishes for various insulating applications may fall under several industrial specifications. One set of specifications, Military Specifications (commonly called MIL Specs) may be called-out in the production design for motors or other equipment using electrical windings for military applications. The manufacturer or re-builder needs to understand these specs and how they impact the choice of varnish and the application method.

Military Specification MIL-I-24092 (D) Insulating Varnishes and Solventless Resins for Application by the Dip Process categorizes varnishes by type (solvent containing solventless or water based) curing process (baking or air dry) and thermal class. For example if the design spec calls for MIL-I-24092/3 - Insulating Varnish, solvent containing, baking, semi-rigid, for dip processing, Grade CBH, 180 to 200 thermal class, HI-THERM® BC-346-A would be a suitable varnish to meet the requirements. Likewise if the design called for MIL-I-24092/7 - Insulating Resin, solventless, baking, semi-rigid, for dip processing, Grade SH, 155 to 200 thermal class DOLPHON® CC-1105 would prove to be an excellent product to meet these criteria.

Military Specification MIL-I-24092 does not determine pass/fail criteria for the various insulating varnishes or resins, it does however, specify the tests that are to be performed on product.

Military Specification MIL-M-17060E (SH) this specification covers the requirements for 60 Hz, three phase, integral-horsepower, alternating current motors for shipboard use. MIL-M-17060E is a manufacturing "process" specification outlining the production methods and steps needed to build a motor to meet the requirements of MIL-M-17060E. This specification stipulates that the wound components be vacuum pressure impregnated using a thixotropic, 100% epoxy varnish. DOLPHON® CC-1118-LV, an epoxy product, is used in production operations meeting the above mentioned specification.

One requirement in MIL-M-17060E is a salt water submersion test. In this test, sample coils are manufactured per design and treated in a VPI system with the epoxy resin. After processing, the test coil is immersed in sea water to determine the effectiveness of the manufacturing process and the epoxy resin. This requirement can be difficult to achieve with a standard epoxy varnish. DOLPHON® CC-1152 a very flexible, 100% highly thixotropic, epoxy resin, has been formulated to meet or exceed the sea water immersion requirements of MIL-M-17969E.

Several manufacturers and re-builders of motors for the Navy use DOLPHON® CC-1118 LV and CC-1152 to meet the performance needs of these demanding and critical applications aboard ships and submarines. When manufacturing electrical equipment to meet Military Specification or for Military applications call you local John C. Dolph representative.

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