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Select Lamination Steel: Insulation Specifications

The classification of insulating coatings for electrical lamination steels is listed in ASTM designation A 976-03, available from ASTM International (www.astm.org), one of the world's largest standards development organizations.

Most of the prototype die-cast copper rotors have been produced using laminations having either a C-0 or C-1 coating. A C-0 coating is a naturally formed oxide on the lamination steel surface, while the C-1 coating is a user-formed oxide created by an oxidizing furnace atmosphere. Additional information about these coatings is reproduced from ASTM A 976-03 in Table 3.3.1 below.

Electrical testing of copper rotors produced using these two types of insulation coatings demonstrated that they are compatible with the higher temperatures associated with copper die-casting.

**Table 3.3.1:** Information about the C-0 and C-1 insulating coatings for lamination steels.
Coating Name	Coating Description/Characteristics
C-0	Oxide that is formed on the steel surface during mill processing. This layer is thin, tightly adherent, and provides sufficient insulating quality for most small cores. The oxide layer will withstand normal stress-relief annealing temperatures. The insulation quality is affected by the oxidizing potential of the user's anneal, that is, the oxidized surface condition may be enhanced by controlling the atmosphere to be more or less oxidizing to the surface.
C-1	User-formed oxide that is created on the steel surface by contact with an oxidizing atmosphere at the end of the heat treating cycle. This coating usually is bluish to gray in color and used for various electrical steel applications.
Extracted, with permission, from ASTM A 976-03, "Standard Classification of Insulating Coatings for Electrical Steels by Composition, Relative Insulating Ability and Application", copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM (www.astm.org).