KR20090054921A - Systems for centrifugally casting highly reactive titanium metals - Google Patents

Abstract

A system for centrifugally casting high reactive titanium metal is provided to prevent a crucible from being cracked by fusing metal charge with a cold wall crucible. A system for centrifugally casting high reactive titanium metal comprise: a cold wall conduction crucible(10) accepting titanium metal charge and having a removable floor plate(16) and a plurality of induction coils; a power source heating up the titanium metal charge within the conduction crucible and obtaining the molten metal; a heated second crucible(32) catching the molten metal when the molten metal falls down from the induction crucible; and a centrifugal casting device(36) producing the casting part by maintaining the second crucible and accelerating the second crucible and applying power in a centrifugal direction within a casting mold(38). The titanium metal charge comprises the titanium-aluminide alloy.

Description

System for Centrifugal Casting of Highly Reactive Titanium Metals {SYSTEMS FOR CENTRIFUGALLY CASTING HIGHLY REACTIVE TITANIUM METALS}

Embodiments described herein relate generally to systems for centrifugally casting highly reactive metals. More specifically, the embodiments described herein describe a system for centrifugally casting highly reactive titanium alloys, in particular titanium aluminide alloys.

Turbine engine designers are constantly looking for new materials with improved properties to reduce engine weight and achieve higher engine operating temperatures. Titanium alloys (Ti alloys), in particular titanium aluminide-based alloys (TiAl alloys), have a promising combination of low temperature mechanical properties such as room temperature ductility and toughness, as well as high medium temperature strength and creep resistance. For this reason, TiAl alloys have the potential to replace the nickel-based superalloys currently used to fabricate numerous turbine engine components.

Vacuum Arc Re-melting (VAR) is one technique commonly used to melt Ti alloys. VARs generally include causing an arc between a titanium alloy electrode and a material of the same alloy (eg, electrode end) disposed in a water-cooled copper crucible. A molten pool is formed and the electrode gradually melts. If enough molten metal is available, the electrodes can be separated and the crucible is tilted to pour the metal into the mold for casting parts.

VAR technology can have some disadvantages. Titanium electrodes used in the VAR process can be expensive due to the high price of titanium billets / forgings and the high labor costs associated with forming electrodes from proven scrap or revert materials. In addition, the requirements for prealloy electrodes can make it difficult and expensive to produce non-standard alloys. Moreover, the need to use water-cooled crucibles can limit the degree of overheating that can be achieved in metals, which can also affect flowability, which makes it difficult to fill thin wall castings. In addition, there is the highest temperature that causes arcing in the metal, and a high temperature gradient exists in the molten metal. This can also affect the filling of the mold and create an inferior temperature gradient in the solidification casting.

In view of the foregoing problems associated with VAR technology, another method that may be employed when melting the Ti alloy is Vacuum Induction Melting (VIM). VIM has been developed to handle specialty alloys and new alloys containing reactive elements such as titanium and aluminum that cannot be melted and cast in air. As the use of such alloys continues to increase, VIM is becoming more common as a result.

Vacuum induction melting generally involves heating the metal in the crucible made of a non-conductive refractory oxide alloy until the metal charge in the crucible melts in liquid form. In this technique, a solid titanium alloy material is placed in a cold metal hearth, usually made of copper, and melted in an inert atmosphere using a very intense heat source such as an arc or plasma. The melt pool will initially form on the inside and top surfaces of the titanium charge and the titanium near the adjacent wall of the copper furnace remains solid. This "skull" of solid titanium produced includes liquid titanium metal free of contaminants. For a general discussion of cold wall induced melting, see US Pat. No. 4,654,858 to Rowe.

As mentioned above, copper crucibles are most often employed for cold wall induction melting of highly reactive alloys for several reasons. For example, melting and casting from a ceramic crucible can generate significant thermal stress on the crucible, which can result in crucible cracking. Such cracking can reduce crucible life and cause inclusions in the part being cast. In addition, highly reactive TiAl alloys can break ceramic crucibles and contaminate titanium alloys with oxygen and refractory alloys from oxides. Similarly, if a graphite crucible is employed, titanium aluminide can break down a large amount of carbon from the crucible into the titanium alloy, which results in contamination. Such contamination can result in a loss of mechanical properties of the titanium alloy. Copper is less likely to present the aforementioned problems associated with ceramic and graphite crucibles, which is why copper crucibles are typically employed when using cold wall induction melting to melt highly reactive metal alloys.

However, while cooling crucible melting in copper crucibles can provide metallurgical advantages in the treatment of the highly reactive alloys described above, many technical and economical factors, including low overheating, loss of yield due to skull formation, and high power requirements. May have limitations. In particular, the cold wall induction crucible suffers heat loss when the power supply to the crucible is terminated and the metal falls towards the water-cooled copper side of the mold.

One development employed to address the above problems with vacuum induced melting is pouring from the bottom through a nozzle from a cooling furnace melting system. See US Pat. No. 4,546,858 to Loewe and US Pat. No. 5,164,097 to Wang et al. The nozzle material typically employed was copper or brass, considered a good heat conducting material. Graphite and thermal insulation materials have also been mentioned for use as nozzle materials.

The use of nozzles can provide many benefits over other common means, but the use of nozzles is not without problems at all. For example, cold furnace melting and pouring of reactive materials such as titanium at the bottom can result in undesirable melt hardening in the nozzle. In addition, many crucible / furnace systems can struggle to provide the necessary control of liquid flow rate, minimize nozzle corrosion, and minimize melt contamination.

Another development employed to address the foregoing problems associated with vacuum induction melting is levitation melting, which generally involves electromagnetically floating the metal being melted using energy from the induction coil. For a general discussion of flotation melting, see US Pat. No. 5,275,229 to Fishman et al. However, the magnetic induction magnetic field can both heat the metal and keep the molten metal floating in the space within the crucible, but once the power source for the system is turned off, the metal can slide back into the water-cooled crucible before it can be poured. Can be cooled again. This can result in incomplete filling of the mold.

Thus, despite such advances, improved systems are useful for melting high reactive metal alloys, such as TiAl, which allow the alloy to remain molten during pouring and also reduce the incidence of problems associated with conventional melting processes. There remains a need.

Embodiments herein generally receive a titanium metal charge, and a cold wall induction crucible having a plurality of induction coils and a removable bottom plate, and a titanium metal charge in the induction crucible by heating A preheated second crucible that captures the molten metal when the molten metal falls from the induction crucible after the power source obtaining the molten metal and the removable bottom plate are separated and the power source is turned off; A system for centrifugally casting a highly reactive titanium metal comprising a centrifugal casting machine for holding and accelerating a crucible to apply centrifugal force to the molten metal into a mold mold to produce a cast part.

Embodiments herein also generally include a cold wall induction crucible having a titanium metal charge and having a plurality of induction coils and a removable bottom plate, a power source for heating the titanium metal charge in the induction crucible to obtain a molten metal; A preheated second crucible that captures the molten metal when the molten metal falls from the induction crucible after the removable bottom plate is separated and the power source is turned off, and the molten metal from the induction crucible A highly reactive titanium comprising a funnel moving to the second crucible and a centrifugal casting machine for holding and accelerating the second crucible to apply a centrifugal force to the molten metal into a mold mold to produce a cast part. A system for centrifugal casting a metal.

The embodiment also generally includes a cold wall induction crucible containing a titanium aluminide charge and having a plurality of induction coils and a slidably removable bottom plate, and molten titanium aluminide by heating the titanium aluminide charge in the induction crucible. And a preheated second crucible that captures the molten titanium aluminide when the molten titanium aluminide falls from the induction crucible after the removable bottom plate is separated and the power source is turned off. A niobium funnel for moving the molten titanium aluminide from the induction crucible to the second crucible, and the second crucible about 0.5 after the molten titanium aluminide falls into the second crucible. From stationary for seconds to about 2 seconds, and And a centrifugal casting machine for accelerating the second crucible from about 1 second to about 2 seconds to about 100 rpm to about 600 rpm to apply a centrifugal force to the molten titanium aluminide into a casting mold to produce a cast part. A system for centrifugally casting highly reactive titanium metals.

These and other features, embodiments, and advantages will become apparent to those skilled in the art from the following disclosure.

According to the system for centrifugally casting the highly reactive titanium metal of the present invention, it is possible to keep the alloy in a molten state during pouring, and also to reduce the occurrence of problems associated with conventional melting processes.

While the embodiments described herein relate generally to systems for centrifugally casting highly reactive metals, particularly titanium alloys and titanium aluminide alloys, into net shape components, the following description should not be limited thereto.

According to the description herein below, a cold wall induction crucible 10 having a body 12 may be provided as shown in FIG. 1. Body 12 may be made of any metal having good thermal and electrical conductivity, such as, for example, copper. Body 12 may be water-cooled to prevent copper from melting during heating of the crucible. More specifically, copper generally melts at about 1,900 ° F. (about 1,038 ° C.), TiAl melts at about 2,600 ° F. (about 1,427 ° C.), and copper in the crucible will form a low melting eutectic with titanium. Can be. This can be prevented from occurring by water-cooling the crucible. Water cooling inlets 24 and outlets 26 may be used to circulate the cooling water through a plurality of channels 28 located around the body 12. Body 12 may be of any shape desired and suitable for use in induction melting, but body 12 may be generally formed of a hollow cylinder. The body 12 may have a plurality of induction coils 14 positioned around it, and the plurality of induction coils 14 may be heated using the power source 21. Coil 14 may act as a heat source to melt and maintain a molten metal charge disposed in the crucible as described below.

Crucible 10 may also have a movable bottom plate 16 as shown in FIG. 1. Like crucible 10, bottom plate 16 may comprise any metal having good thermal and electrical conductivity, and in one embodiment may include copper. The bottom plate 16 may also be water cooled, and may have a plurality of induction coils 14 disposed below and which help to melt and maintain the molten metal charge placed in the crucible 10. . In addition, an electrically insulating plate 19 may surround the bottom plate 16 to help maintain heat at the bottom of the crucible 10. As described below, the bottom plate 16 is separated from the body 12 in a variety of ways, including but not limited to sliding, rotation, and dropping (such as shown in FIGS. 2 and 3). Can be.

In use, a metal charge 18 comprising a highly reactive alloy may be disposed inside the body 12 of the crucible 10 as shown in FIG. 1. In one embodiment, the metal charge 18 may comprise a titanium alloy, more specifically titanium aluminide alloy, including lumps, ingots, granules, plates, powders and the like. It may take any suitable form including but not limited to a mixture of. Those skilled in the art will vary from about 1 pound (about 454 grams) to about 3.5 pounds (about 1,588 grams) in one embodiment, although the amount of metal charge 18 disposed in the crucible 10 may vary depending on the intended use. It will be appreciated that in other embodiments, from about 1.25 pounds (about 567 grams) to about 3.3 pounds (about 1,497 grams) of metal charge 18 can be used to make precision shaped low pressure turbine blades as described below. .

Once the metal charge 18 is placed inside the crucible 10, the cover 20, which may be made of the same material as the material of the crucible 10 in one embodiment, is placed on top of the body 12. And held in place by the cover ring 22 to ensure that the crucible 10 is sealed. The power source 21 may be turned on and in one embodiment the metal charge 18 may melt when a suitable temperature is achieved that may be from about 2,700 ° F. to about 2,835 ° F. (about 1,480 ° C. to about 1,557 ° C.). . Those skilled in the art will understand that the electromagnetic field generated by the induction coil causes the metal charge to heat itself internally due to the resistive heating caused by the current in the metal charge. As the metal charge 18 begins to melt, the resulting molten metal 30 floats in the body 12 of the crucible 10 so that the molten metal (as long as the powder is being supplied to the crucible 10) 30 does not come into contact with the inside of the main body 12. This suspension of molten metal 30 can prevent the formation of a skull.

At the same time as melting the metal charge in the induction crucible 10, the second crucible 32 or the like holding the device can be preheated using any suitable means such as, but not limited to, microwave or radiant energy. The second crucible can be made of graphite or ceramic and can optionally have a metal liner such as for example niobium. The second crucible 32 can assist in the transport of the molten metal to a casting mold without losing any overheating of the molten metal generated during induction melting in the induction crucible 10. More specifically, the second crucible 32 is at least about 1,832 ° F. (about 1,000 ° C.), and in one embodiment when the second crucible 32 comprises niobium, from about 1,832 ° F. to about 2,200 ° F. Up to about 1,200 ° C.) and up to at least about 1,980 ° F. (about 1,082 ° C.), in one embodiment from about 1,980 ° F. to about 2,400 ° F. (about 1,082 ° C. to about 1,316 ° C.) when the second crucible comprises ceramic. Preheated up to < RTI ID = 0.0 > Preheating can help prevent thermal shock and cracking of the second crucible 32, which will enable reuse of the second crucible. The preheated second crucible 32 can then be placed on a rotating arm 34 of the centrifugal casting machine 36 and located below the induction crucible 10 as schematically shown in FIG. 3. have. Any conventional centrifugal casting machine such as, for example, Linn High-Therm Titancast 700 (Germany) or SEIT Supercast (Italy) is suitable for use herein.

The removable bottom plate 16 may then be separated from the body 12 of the crucible 10 as described above. In the embodiment shown in FIGS. 2 and 3, the bottom plate 16 can be slidably separated from the crucible 10 using any suitable mechanism, such as but not limited to a track or guide. Although the bottom plate 16 has been separated, the molten metal 30 is retained in the body 12 of the crucible 10 as shown in FIG. 2 until the electromagnetic field generated by the induction coil 14 is further processed. You can keep it floating.

When the power source 21 is turned off, the molten metal 30 is dropped from the induction crucible 10 and into the preheated second crucible 32 via the niobium funnel 33, and the second crucible 32. ) May remain stationary in the casting machine 36 long enough for the molten metal 30 to complete its movement into the second crucible 32, and in one embodiment may be from about 0.5 seconds to about 2 seconds. . Once the movement of the molten metal 30 is complete, the second crucible 32 can be accelerated rapidly (about 1 second to about 2 seconds) at a maximum speed that can be about 100 rpm to about 600 rpm. The casting machine 36 can apply centrifugal force to the molten metal 30 from the second crucible 32 into the casting mold 38 through the port 40, the port 40 being a slit, a hole, a tube. Or a combination thereof. This rapid conveyance from the second crucible 32 to the casting mold 38 results in a tangential time of less than about 5 seconds between the two. This short tangential time not only significantly reduces heat loss but also helps to ensure that there is no undesirable reaction between the molten metal and the graphite or ceramics used to construct the second crucible 32. give.

The casting mold 38 may include any ceramic precision casting system that provides an inert face coat and a thermal insulating backing material. For example, in one embodiment, the casting mold 38 may include a cotton coat that includes an oxide. As used herein, "oxide" refers to a composite selected from the group consisting of scandium oxide, yttrium oxide, hafnium oxide, lanthanide and combinations thereof. Lanthanides (also known as "rare earth" composites) are also known as lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, promethium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, and dysprosium oxide. And oxides selected from the group consisting of holmium oxide, erbium oxide, ytterbium oxide, lutetium oxide and combinations thereof. The casting mold 38 may comprise a backing comprising a refractory material selected from the group consisting of aluminum oxide, zirconium silicate, silicon dioxide, and combinations thereof in a colloidal silica suspension.

Once the molten metal has been sufficiently moved into the casting mold 38, the centrifugal casting machine 36 can be turned off. In one embodiment, the resulting component, which may be a low pressure turbine blade 42 as shown in FIG. 4, may be removed from the casting mold 38 using conventional means. Because of the use of centrifugal casting, the blade 42 requires very little post-casting treatment. The centrifugal force generated by the casting machine 36 provides for optimized filling of the casting mold 38 by improving the filling of thin sections of the mold, thereby providing precision shaped parts.

Moreover, since the cold wall crucible is used to melt the metal charge, there is little thermal stress on the crucible, and therefore there is little crucible cracking. This allows for both reuse of the crucible and less inclusions in the cast part. In addition, since the contact between the molten metal and the second crucible is limited, the probability that the molten metal will be contaminated from breakage of the crucible is reduced. Less contamination can result in improved mechanical properties of the titanium alloy.

This specification uses examples to disclose the invention, including the best embodiments, and to enable any person skilled in the art to make or use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have components that do not differ from the words of the claims, or if they include equivalent components that are substantially indistinguishable from those of the claims.

1 is a schematic cross-sectional view of one embodiment of a cold wall induction crucible with a metal charge disposed therein according to the description herein.

2 is a schematic cross-sectional view of one embodiment of a cold wall induction crucible having a removed bottom plate and molten metal floating therein according to the description herein.

3 is a schematic cross-sectional view of one embodiment of a centrifugal casting system according to the disclosure herein.

4 is a schematic perspective view of one embodiment of a low pressure turbine blade that is a part that can be cast in accordance with the teachings of the present invention.

Explanation of symbols for the main parts of the drawings

10: cold wall induction crucible 12: body

14 coil 16 removable bottom plate

18: metal charge 19: electrical insulation plate

20: cover 21: power source

22: cover ring 24: water cooling inlet

26: water cooling outlet 28: channel

30 molten metal 32 second crucible

33: funnel portion 34: rotating arm

36: casting machine 38: casting mold

40: port 42: low pressure turbine blade

Claims (20)

A system for centrifugally casting highly reactive titanium metals, A cold wall induction crucible containing a titanium metal charge and having a plurality of induction coils and a removable bottom plate, A power source for heating the titanium metal charge in the induction crucible to obtain a molten metal; A preheated second crucible that captures the molten metal when the molten metal falls from the induction crucible after the removable bottom plate is separated and the power source is turned off; A centrifugal casting machine for holding and accelerating the second crucible to apply a centrifugal force to the molten metal into a mold mold to produce a cast part; Highly reactive titanium metal centrifugal casting system. The method of claim 1, The titanium metal charge comprises a titanium aluminide alloy Highly reactive titanium metal centrifugal casting system. The method of claim 1, The bottom plate of the induction crucible is separated using a method selected from the group consisting of sliding, rotating and dropping. Highly reactive titanium metal centrifugal casting system. The method of claim 1, The cast part comprises a low pressure turbine blade Highly reactive titanium metal centrifugal casting system. The method of claim 2, The induction coil of the induction crucible is used to heat the metal charge to a temperature of about 1,480 ° C. to about 1,557 ° C. to obtain the molten metal. Highly reactive titanium metal centrifugal casting system. The method of claim 1, The molten metal is suspended in the induction crucible Highly reactive titanium metal centrifugal casting system. The method of claim 2, The second crucible is heated to a temperature of at least about 1,000 ° C. when the second crucible comprises niobium and to a temperature of at least about 1,082 ° C. when the second crucible comprises ceramic. Highly reactive titanium metal centrifugal casting system. The method of claim 1, The centrifugal casting machine holds the second crucible stationary for about 0.5 seconds to about 2 seconds after the molten metal has dropped into the second crucible, The centrifugal casting machine then accelerates the second crucible from about 100 rpm to about 600 rpm in about 1 second to about 2 seconds to apply centrifugal force to the molten metal into the casting mold to produce the cast part. Highly reactive titanium metal centrifugal casting system. A system for centrifugally casting highly reactive titanium metals, A cold wall induction crucible containing a titanium metal charge and having a plurality of induction coils and a removable bottom plate, A power source for heating the titanium metal charge in the induction crucible to obtain a molten metal; A preheated second crucible that captures the molten metal when the molten metal falls from the induction crucible after the removable bottom plate is separated and the power source is turned off; A funnel for moving the molten metal from the induction crucible to the second crucible, A centrifugal casting machine for holding and accelerating the second crucible to apply a centrifugal force to the molten metal into a mold mold to produce a cast part; Highly reactive titanium metal centrifugal casting system. The method of claim 9, The titanium metal charge comprises a titanium aluminide alloy Highly reactive titanium metal centrifugal casting system. The method of claim 9, The bottom plate of the induction crucible is separated using a method selected from the group consisting of sliding, rotating and falling Highly reactive titanium metal centrifugal casting system. The method of claim 10, The cast part comprises a low pressure turbine blade Highly reactive titanium metal centrifugal casting system. The method of claim 10, The induction coil of the induction crucible is used to heat the metal charge to a temperature of about 1,480 ° C. to about 1,557 ° C. to obtain the molten metal. Highly reactive titanium metal centrifugal casting system. The method of claim 9, The molten metal is suspended in the induction crucible Highly reactive titanium metal centrifugal casting system. The method of claim 10, The second crucible is heated to a temperature of at least about 1,000 ° C. when the second crucible comprises niobium and to a temperature of at least about 1,082 ° C. when the second crucible comprises ceramic. Highly reactive titanium metal centrifugal casting system. The method of claim 9, The centrifugal casting machine holds the second crucible stationary for about 0.5 seconds to about 2 seconds after the molten metal has dropped into the second crucible, The centrifugal casting machine then accelerates the second crucible from about 100 rpm to about 600 rpm in about 1 second to about 2 seconds to apply centrifugal force to the molten metal into the casting mold to produce the cast part. Highly reactive titanium metal centrifugal casting system. A system for centrifugally casting highly reactive titanium metals, A cold wall induction crucible containing a titanium aluminide charge and having a plurality of induction coils and a slidably removable bottom plate, A power source for heating the titanium aluminide charge in the induction crucible to obtain molten titanium aluminide, A preheated second crucible that captures the molten titanium aluminide when the molten titanium aluminide falls from the induction crucible after the removable bottom plate is separated and the power source is turned off; A niobium funnel portion for moving the molten titanium aluminide from the induction crucible to the second crucible, After the molten titanium aluminide has dropped into the second crucible, the second crucible is held stationary for about 0.5 seconds to about 2 seconds, and then the second crucible is held within about 1 second to about 2 seconds. A centrifugal casting machine for accelerating from about 100 rpm to about 600 rpm to produce a cast part by applying a centrifugal force to the molten titanium aluminide into a casting mold; Highly reactive titanium metal centrifugal casting system. The method of claim 17, The induction coil of the induction crucible is used to heat the metal charge to a temperature of about 1,480 ° C. to about 1,557 ° C. to obtain the molten metal. Highly reactive titanium metal centrifugal casting system. The method of claim 17, The second crucible is heated to a temperature of at least about 1,000 ° C. when the second crucible comprises niobium and to a temperature of at least about 1,082 ° C. when the second crucible comprises ceramic. Highly reactive titanium metal centrifugal casting system. The method of claim 17, The cast part comprises a low pressure turbine blade Highly reactive titanium metal centrifugal casting system.

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