Simple Solutions That Work! Issue 5

Free Energy of Formation values for each complex compound present. This liquid glass or slag phase will nucleate and grow on the deposited buildup because the surface of the initial buildup or solid slag phase is similar to the liquefied slag or glass phase attempting to precipitate out of solution. The order of precipitation of ceramic compounds can be predicted by thermodynamic calculations but this is extremely difficult due to the complex chemistry of the systems involved. This concept has seemingly been verified by observation of the order, orientation andmorphology of buildups observed in previous research. Another factor in the formation of buildup can be considered similar to the general principles of ceramic crystallization. At the melting point of a ceramicmaterial (or any material), the Gibbs’s Free Energy of Formation ( G f ) for a given quantity is the same whether it is crystalline or liquid. At lower temperatures, the crystalline form that has a lowest free energy, will precipitate out first. However, this does not readily happen unless there are nucleation sites. In the absence of nuclei, crystallization does not occur unless the system is cooled to a point below a critical temperature at which crystallization is spontaneous. Unfortunately, very little is known about the thermodynamic properties of the complex systems involved so it is not possible to develop a method to predict critical temperatures for this crystallization theory. However the behavior of this formation can be compared to other ceramic formations. A mechanical explanation of buildup formation: Prominent research has proven the mechanisms for the formation of alumina buildup in pouring tubes and referred to three basic conditions that had to be satisfied: (1) particles have to come in contact with the refractory surface, (2) particles have to adhere to the refractory surface, and (3) particles have to adhere to each other so as to sinter and form a network. This work explained the importance of metal velocity, especially in areas close to the surface where flow velocity is a function of the frictional force between the refractory surface and the molten metal. If the metal flow is kept at a high velocity and not allowed to remain in an idle or slow-moving state, the tendency for buildups to occur is usually reduced. Stirring action of an inductor is pronounced when the inductor is placed on high power. This “stirring action” refers to the actual metal flow through the inductor channels. Whether in a single loop or a double loop inductor, the molten metal is superheated within the inductor channels and enters the upper body through the throat. Circulation of Molten Metal in a Channel Induction Furnace In either inductor case, the “stirring action” is not as well defined when thefurnace is lefton lowholdpower such as during an idle weekend operation. During these periods, the areas of minimal flow occur in the boat section (the transition section between the channels at the top of the inductor) or in the refractory areas in the throat that are adjacent to the molten metal stream emanating from each channel. These represent the “dead” zones where metal does not circulate as effectively as it does within the channel. The mechanical mechanism for buildup can be further supported by sedimentation of the insoluble oxides in the lowflow areas. This is helpful in explaining initial buildup. 35