Publication Date

8-1980

Advisor(s) - Committee Chair

Eugene Hoffman, John Riley, Robert Hall, J.E. Philhours

Degree Program

Department of Physics and Astronomy

Degree Type

Master of Science

Abstract

The Cutler-Hammer plant in Bowling Green, Kentucky,manufactures laminated steel armatures for electrical starters (large relays) on which corrosion occurs only in some regions. The manufacturing process includes a heat treatment step from which the laminations emerge with a non-uniform surface appearance.

Laminations from corroded regions of an armature have red oxide (Fe203) on the edges, while the sides have a black coating of partly-burned cutting-machine oil residue. The purpose of the project was to investigate the mechanisms of this corrosion and why it does not occur uniformly and to suggest practical solutions for the plant.

Emission spectroscopy revealed no great differences in the content of minor constituents, although some elements (Li and Mg) were present in traces only in the surface of corroded samples.

X-ray crystallography indicated that the surface of uncorroded strips has a more complex structure than that of corroded strips. Both samples showed diffraction lines that agreed with standard values for body-centered cubic iron. For the uncorroded sample, X-ray diffraction also showed protective Fe3C, Si02' and other unidentified compounds coating the surface.

In dilute acid the black coating soaked loose from corroded regions and corrosion occurred uniformly over the side surfaces. Uncorroded laminations were somewhat more resistant.

In controlled heat treatment experiments oxygen in the oven atmosphere carried out direct chemical attack on unprocessed lamination surfaces to form iron oxides. Formation of red oxide (Fe203) was at a maximum for 900°F, 60 minutes. At 1100°F, 60 minutes, the laminations tended to form black oxide (Fe304) which is more resistant to further corrosion.

These results suggest that the direct attack of oxygen may begin during the heat treatment in the manufacturing process. If an ovencorroded lamination is riveted beside an uncorroded lamination in an armature, a cell may be set up and further corrosion may occur electrochemically.

As possible remedies, the plant may use lower temperature and longer time, use a reducing atmosphere oven, or replace the heat treatment with a solvent process.

Disciplines

Physical Sciences and Mathematics | Physics

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