Evaluation of Formaldehyde Release From ASTM C6 Coating of Non-Oriented Electrical Steel

The formaldehyde released from ASTM C6 (A976) coating of non-oriented grain (NOG) electrical steel was measured based on the desiccator method used to evaluate formaldehyde release from wood panels. The C6 varnishes are applied as insulation of the stator core NOG sheets and they are based on melamine or phenolic resins, which contain precursors of formaldehyde used as crosslinking agents. The component is released during and after the curing process, which can be harmful to humans and, at very high concentrations, is correlated with cancer. Therefore, manufacturers of large rotating electrical machines are concerned about any potential formaldehyde release during the operation. In addition, they are supporting the development of new formaldehyde-free varnishes. A methodology has been developed for the determination of formaldehyde emissions of NOG coated sheets based on the desiccator method. The formaldehyde released at temperatures of 60, 80 and 120 °C from the cured coatings, of a classical C6 varnish based on melamine and/or phenolic resin and a formaldehyde free varnish, was measured by ultraviolet-visible spectroscopy using the colorimetric method with acetylacetone (Hantzsch reaction). An increase in the formaldehyde release was observed by increasing the temperature. In addition, the effect of the curing conditions on the stability of the varnish film was evaluated by thermal analysis, which showed that the thermal performance of the product is dependent on these parameters.