Coercimeter for Non-destructive Measurement of the Coercivity of Steel Sheets

A special instrument has been built to measure the coercivity directly on steel sheets without having to cut samples. It will be used to perform the 8000 coercivity measurements which will be needed during the production of the ll'OOO ton of steel sheets for the LEP dipole magnets. The coercimeter allows local and directional coercivity measurements to be made on a steel sheet with an accuracy of 3 % and a reproducibility of better than 1 %. The permeability can also be measured with similar precision. I INTRODUCTION The 3304 dipole magnets of LEP require the production of ll'OOO tons of 1.5 mm thick decarburized steel sheet. As explained in a previous paper [ 1 ] , th is steel , besides having a low coercivity and a high permeability, must also have a very low spread of coercivi ty. The maximum dispersion of ± 11 A m", guaranteed by the manufacturer, is s t i l l too large and a controlled mixing of the steel is necessary. To this end, about 8000 coercivity measurements wi l l have to be performed during production. For such a large number of measurements, classical permeameters (ring or Epstein frame) requiring preparation of samples are excessively timeand steel-consuming, hence the idea to build a "coercimeter" measuring the coercivity direct ly on the steel sheets without having to cut samples.