Simple Solutions That Work! Issue 5

TWO EXAMPLES OF CAST IRON INSOLUBLE BUILDUP, THE IDENTIFICATION OF COMPONENTS AND FLUX TREATMENTS: Example #1 Treated Ductile Iron Magnesium Fade in Holding Pour ing Applications Since the introduction of ductile iron, foundries have managed the inevitable problem of loss of magnesium, i.e., “mag fade” when holding and pouring treated ductile. Themagnesium fade often creates insoluble build-up which will result in significant capacity loss for ladles / unheated pouring boxes, and inductor/throat failure for operating pressure pour furnaces. Significant downtime can be attributed to insoluble build-up and the required cleaning maintenance. An example of a Magnesium Silicate build-up in the presence of a magnesia matrix is shown below. This is a typical build-up scenario for Magnesium fade in treated ductile iron. Magnesium Silicates, 2MgO·SiO2 (Forsterite) Mel t temp 3,434oF(1890C) , Gform@2,700 oF = -13,017 Cal/ mole 2MgO + SiO2 => 2 MgO·SiO2 From the Gibbs Free Energy of Formation calculation, at 2700 F magnesium silicate is quite stable. (Amoderate low negative value for the G) When holding or pouring treated ductile iron, molten metal temperatures will be less, which would translate into more stability for this compound. In the presence of a flouride-free flux, Calcium Oxide can react as follows: Calcium Oxide on Forsterite, 2CaO · S i O2 +2MgO · S i O2 => 2(CaOMgO)·2SiO2 (Diopside) @2,700°F Melt temp 2,536°F(1,391°C) Gform = -33,922 Cal/mole Whenconsideringbuildupobtained from fading treated ductile iron, the chemical analyses will reflect major presence of MgO along with MgS. While it is impossible to stop this “fade,” how foundries can maintain daily and weekly cleaning can help prolong the service hours of the pouring and treatment equipment. To help to control the insoluble MgO and MgS from “mag fade”, an addition of ½ to 1 pound of flouride-free flux to every ton of molten metal in a treatment vessel or ladle, is an improvement and will allow for increased service life. Example #2 Channel Induction Furnace – throat buildup in cast iron, grey or ductile-base. Many cast iron foundries utilize a channel induction furnace for melting or holding/pouringmolten metal continuously. As charge or molten metal continuously enters into the channel furnace, the presence of slag and insoluble remnants is floating within the metal. When the metal level is dropped to minimum heel level, the likelihood of this slag to reach the throat opening is inevitable. Below is an example of a severe clogging of the throat opening of a typical channel furnace melter. 36