Specialty metals and metal alloys, such as titanium, titanium alloys and nickel based super alloys, can be produced by a process known as cold hearth melting. In cold hearth melting, a heat source, such as a plasma torch or an electron beam is used to heat raw materials into a molten material. U.S. Pat. No. 6,019,812 and U.S. Pat. No. 7,137,436 disclose exemplary prior art cold hearth systems. In these systems, the hearth is made of a thermally conductive material, such as copper, and can include a fluid cooling system for maintaining the hearth in solid form. Typically the hearth is held stationary during the melting process, and can be configured as a chute for transferring the molten material for further processing. Usually there is no mixing in the hearth other than gravity induced currents resulting from density differences in the molten material. Also, the heat source is a stationary element, which does not provide even heating of the molten material in the hearth.
Due to the high cost of producing these specialty metals and metal alloys, purity and quality are of critical importance. It is thus desirable to eliminate any contaminants from the ingots produced during the cold hearth melting process. For example, in the case of titanium, hard alpha inclusions, such as oxygen, nitrogen, and carbon, sometimes form in titanium ingots. These inclusions, which are often introduced during the cold hearth melting process, provide points of weakness and potential failure in articles formed from the ingot, such as turbine blades and medical prosthesis. The elimination of these contaminants provides a significant challenge to manufacturers of specialty metals and metal alloys.
Another challenge for manufacturers of specialty metals is the optimization of process conditions to accommodate particular raw materials and products. In general, cold hearth melting requires expensive systems and large energy expenditures. However, prior art systems may not be suitable for processing different types of raw materials and different products. Similarly, energy can be wasted if the systems and processes are not well suited to the raw materials and products. It would thus be advantageous for a cold hearth system and process to be able to accommodate different raw materials and different process parameters with minimal energy expenditures. In addition, it would be advantageous for a system and process to be able to accommodate different types of products. For example, in addition to metal ingots, specialty metals and metal alloys can be produced as metal powders. However, most prior art cold hearth systems and processes do not interface efficiently with conventional atomization systems and processes. Similarly, most prior art cold hearth melting systems do not interface efficiently with conventional roll casting systems and processes.
In view of the deficiencies in conventional cold hearth systems and processes, the present disclosure is directed to an improved cold hearth metallurgical system and an improved process for producing metals and metal alloys. However, the foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.