Preconditioners & Cover Material
Preconditioners are typically used in grey iron when aluminum levels are too low. Preconditioners are added to increase the aluminum levels to increase the nucleation sites to form type A graphite. If the nucleation levels are too low, you will have a poor graphite matrix. Preconditioners are added when the heat is ready to pour, and the extra aluminum will increase the nucleation sites, resulting in better graphite.
Cover material is used for ductile iron. This is placed over the magnesium alloy to delay the reaction time. One to one and a half percent cover material is typically used based on the weight of the metal. However, you can add too much cover material, which will delay the reaction until the ladle is almost full. This can cause poor treatment and spitting or bubbling the metal out of the ladle. You want your reaction to start when the ladle is half to two-thirds full. If the mag alloy reacts as soon as you pour metal in, you do not have enough cover material, or your alloy pocket is improperly placed or sized.
Carpenter Brothers can assist you in determining what preconditioner you should be using and how much cover material to use. We can also with the design and placement of your alloy pocket.