Patent Application
20080060779
Referring to
In the present methodology, a SOD (slurry-on-demand) casting method casts a low-solid-fraction, namely 10 to 30% by weight solid-fraction alloy. This is in contrast to prior solid-fraction ratios of 40 to 60%. By way of analogy, the noted prior 40 to 60% solid-fraction ratio provides an ice cream-like or jello-like billet, whereas a 10 to 30% solid-fraction ratio provides a soupy milkshake-like or oatmeal-like charge or billet. It is has been found that the latter ratio, namely a low-solid-fraction, namely 10 to 30% solid-fraction, enables usage of a wider array of die cast alloys, including 380, 383, 360, and Mercalloy (commercially produced under such Trademark by Mercury Marine Division, Brunswick Corporation) alloys. The present method provides a SOD, slurry-on-demand, casting method for casting a low-solid-fraction, namely 10 to 30% solid-fraction, alloy, including the steps of heating the alloy to a molten liquid state, e.g. in vessel 10 as above, cooling and stirring the alloy to nucleate and create a partial solid phase of the noted low-solid-fraction, and transferring the alloy while in the partial solid phase of the noted low-solid-fraction to a casting machine, as in the above noted incorporated SOD patents.
In the preferred embodiment of the present method, the alloy includes a pair of constituents of different melting point including a first constituent of a first melting point, and a second constituent of a second lower melting point. During the noted cooling and stirring step, the preferred embodiment of the present method cools the alloy below the first melting point but above the second melting point, whereafter the noted transferring step is performed. The first and second melting points are preferably selected close enough to each other such that during the cooling and stirring step, the solidification of the first constituent is limited to the noted low-solid-fraction until the second constituent begins to solidify, and then the transferring step is performed when the temperature of the alloy is between the noted first and second melting points.
In one preferred embodiment, the alloy is provided by aluminum as the first constituent and silicon as the second constituent. In this embodiment, it is preferred that the silicon content in the molten state increase from 9% to 12%±1% (in one preferred embodiment the latter being 12.6%) during the noted cooling step between the first and second melting temperatures whereby the amount of aluminum transitioning in phase from liquid to solid state is limited to the noted low-solid-fraction, wherein the eutectic composition of the alloy is at the noted 12.6% silicon.
Further in the preferred embodiment, the noted first constituent is nucleated and solidified by magnetic stirring, as in the above noted incorporated SOD patents. Further in the preferred embodiment, the first constituent is nucleated and solidified without introducing a foreign object into the molten alloy. This is in contrast to prior art systems incorporating a rotating cooled rod, e.g. a graphite rod, introduced into a crucible of alloy to initiate the nucleation of solid phase particles.
Further in the preferred embodiment, after the noted heating step, the alloy is transferred while in the molten liquid state to vessel 10, and then the cooling and magnetic stirring step is performed while the alloy is in vessel 10, and then the alloy is transferred in the noted partial solid phase of the noted low-solid-fraction from the vessel to the casting machine.
In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.
