Formaldehyde-free varnishing on stator core sheets to prevent formaldehyde emissions

Formaldehyde has been identified as a hazardous gas and a number of European countries have set limits on the tolerated concentrations of it in working areas. Alstom tested and analyzed the standard varnishes in use for the past 20 years and compared them to newly developed varnishes. Alstom´s study showed that the new varnishes are far below the limits required by various public authorities. Specifically, varnishes based on melamine and phenolic resins emit some formaldehyde while polyester based varnishes have no substantial emissions and are therefore formaldehyde-uncritical. This paper presents comparison results of the distribution of bound and released formaldehyde on stator sheets between conventional and new varnishes. The study also demonstrated the need for close co-operation between the varnish, steel and stator-core-sheet suppliers because tests on specific mechanical, chemical, electrical and thermal conditions are very complex. Alstom has been working on the topic of formaldehyde emissions for over ten years. The company began working on the subject when the varnish used for the insulation coating between the stator lamination sheets was identified as source of formaldehyde (methyl aldehyde CH2O) emissions. As a result, Alstom decided to perform initial measurements on site in Germany in 2004. The emission level measured on site reached approximately 30 ppm. Such emissions were observed in machines from several manufacturers (OEM´s). Subsequent investigations by complete quantity gas analysis have indicated that formaldehyde was present. Precursors are often used as crosslin king agents in the melamine varnishes. The heating process of the machine initiates chemical reactions which release formaldehyde emissions.