Since both types of defects are difficult to detect, it is desirable to use an improved or different manufacturing process. It is well known in the industry that the VAR process, even with the inclusion of premelt procedural requirements and post-production nondestructive test (NDT) inspections has proven unable to completely exclude hard alpha inclusions and has shown only a minimal capability for eliminating HDIs. Of these, the worst defects are usually high in nitrogen and generally result from titanium burning in the presence of oxygen such as atmospheric air during production. Hard alpha defects are titanium particles or regions with high concentrations of the interstitial alpha stabilizers, such as nitrogen, oxygen, or carbon.
High-density inclusions, also called HDIs, are particles of significantly higher density than titanium and are introduced through contamination of raw materials used for ingot production where these defects are commonly molybdenum, tantalum, tungsten, and tungsten carbide. However, high density inclusions and hard alpha inclusions were still sometimes present presenting the risk of failure of the component-a risk that is to be avoided due to the nature of use of many titanium components such as in aircraft engines. The quality, tolerances, reliability, purity, structural integrity and other factors of these parts are critical to the performance thereof, and as such have required very high quality, advanced materials such as ultra-pure titanium or titanium alloys.įor decades, titanium usage was only where critical to meet very high quality, tolerances, reliability, purity, structural integrity and other factors because of the high cost of the manufacturing process which was typically a vacuum arc re-melting (VAR) process. Specifically, the invention is a method and apparatus for optimizing melting using a combination of plasma torches and direct arc electrodes, each of which is extendable and retractable into the melting environment and moveable in a circular pivoting or side to side linear motion.įor many decades, aircraft engines, naval watercraft hulls, high tech parts for machinery and other critical component users have used substantial amounts of titanium or titanium alloys or other high quality alloys in the engines, the hulls, and other critical areas or components. More particularly, this invention relates to a plasma cold hearth melting method and apparatus for providing a titanium ingot of commercial quality. This invention relates to the melting of titanium or titanium alloys in a plasma cold hearth furnace.
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