Picture Galleries > Making Chilled Iron Wheels > tram wheel 4.jpg

This shows a 'chill'.  The idea of this is that a ring of 'chills' which have a 'negative of the desired wheel profile on them are placed in a ring as part of the sand mould.  When the molten iron hits the 'chill' it solidifies quickly and the crystalline structure of the wearibg surface is altered so that it becomes very hard.  If broken open the 'chilled' portion is white in colour compared to the grey of the rest of the casting.