Vacuum Melting in a Titanium Foundry
The emergence of the titanium foundry in the 20th century was a vast transformation from the small casting operations that took place over 5,000 years ago in the forerunners of the modern foundry.
The demand for titanium aerospace castings drove this transformation to improve aircraft design and fuel rapid development of titanium casting techniques. The current boom in drone and other UAS development has only added to titanium’s importance and demand, and the modern titanium foundry is consequently always searching for improved titanium melting and casting technologies. FS Precision’s titanium foundry currently utilizes a technique known as Vacuum Arc Remelting (VAR) to achieve high quality and cost-effective castings.
The Melting Process in a Titanium Foundry
The cornerstone of almost any titanium foundry, and the FS Precision VAR process, is a water-cooled copper crucible – or container – used for melting titanium. Copper has both excellent thermal and electrical conduction, both of which are crucial for the melting operation. Prior to melting, the crucible is charged with a small amount of solid titanium located at the bottom of the container.
A large bar of titanium – known as the electrode – often in the form of a long cylinder is driven downward into the crucible, towards the solid titanium at the bottom. DC current is then applied to the crucible, which causes an arc between the electrode and the solid titanium at the base. This arc carries as much as 11,000 amps or more of current, and rapidly heats and melts the electrode.
As the tip of the electrode in contact with the arc melts, the entire 27-inch-long electrode is slowly driven downward to maintain a steady melt rate. Once sufficient quantity of molten titanium has been collected – within approximately 3 minutes – it is poured into the mold to produce the final titanium investment castings.
While this melting process may seem perfectly suited for our titanium foundry, casting titanium alloys presents a unique challenge. Titanium alloys will react spontaneously in the presences of oxygen. This reaction becomes particularly violent at temperatures above 2,190 degrees F. To minimize this reaction, the entire titanium melting and pouring process must occur in an environment without oxygen. Hence, titanium foundry systems incorporate vacuum chambers in their casting systems.
Image courtesy of the Furnace Source
The need for evacuated environment to produce titanium castings might appear to be a very complicated challenge. In fact, there are very few certified titanium casting foundries in the world because of this challenge related to titanium reaction with oxygen.
It is this extreme reactivity of titanium itself, however, that makes titanium castings so good at preventing seawater corrosion. For the same reasons, titanium castings are used frequently to prevent chemical corrosion.
If you would like to learn more, watch our investment casting video or read our article describing the titanium investment casting process.
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FS Precision is one of the largest titanium casting suppliers in the world, and is an emerging global leader for structural investment castings for fixed wing, rotary wing, space launch systems. Our AS9100D certified investment casting foundries are located in the USA and Taiwan.
Learn more About FS Precision AS9100D titanium aerospace castings.