Determination of live clay in foundry greensand by sodium-selective electrode

The rapid determination of 'live' clay in greensand is an essential procedu re for the efficient running of a foundry production line, since progressiv e calcination of the clay binder during casting affects mould competence an d quality of finish. A new method for assessing the active fraction of clay in foundry sand is described that is based on the response of an ion-selec tive electrode (ISE) to sodium ions liberated from the clay by ammonium ion s. The method possesses advantages of speed and objectivity over the Methyl ene Blue titration method presently employed in foundries. Results appear t o be unaffected by the presence of coal dust in greensand.