US20090301682A1

US20090301682A1 - Casting furnace method and apparatus

Info

Publication number: US20090301682A1
Application number: US12/133,923
Authority: US
Inventors: Curtis A. Proske; Timothy P. Uno; Marc W. Bird
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2008-06-05
Filing date: 2008-06-05
Publication date: 2009-12-10
Also published as: WO2009149168A3; WO2009149168A2

Abstract

A system for casting comprising a mold for forming molten metal; a support for supporting the mold and transferring heat to and from the mold; and a furnace operable to substantially surround the mold through a preheat cycle, a heat cycle, and a cooling cycle. The furnace preferably moves vertically down to surround the mold for the preheat, heat, and cooling cycles and moves up and away from the mold after the cooling cycle is complete. In an alternative embodiment, the furnace may be replaced with a cooling can just before initiation of the cooling cycle. The support is preferably stationary and provides directional cooling for the mold during the cooling cycle.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The inventions disclosed and taught herein relate generally to metal casting; and more specifically relate to an improved method and apparatus for casting metal.
2. Description of the Related Art
U.S. Pat. No. 3,810,504 teaches a “[m]ethod and apparatus for improving the production rate of directionally solidified castings employing an annular mold having one or more molding cavities therein and a pair of heat radiating elements disposed concentrically with the mold, one being located inside and the other being located outside the mold, the heat radiating elements being arranged so that no temperature gradient exists across the mold. A pair of heat sinks is provided, the heat sinks being coaxial with the two heat radiating elements. Means are provided for causing relative movement between the annular mold and the heat radiating elements and the coaxially aligned heat sinks. The annular mold is positioned on a highly heat conductive pedestal or chill. The mold is preheated by the heat radiating elements to a temperature above the solidification temperature of the metal to be cast. After casting, the solidification of the metal progresses upwardly from the chill and the relative movement between the annular mold and the heat radiator-heat sink combination causes the solidification innerface to occur at or near the boundary between the heat radiators and the heat sinks. A baffle is advantageously positioned at this boundary to prevent heat being radiated from the heat radiators to the heat sinks. The solidified metal in passing through the heat sinks radiates heat uniformly to the heat sinks so as to prevent a lateral or radial thermal gradient across the mold during solidification of the metal therein.”
U.S. Pat. No. 3,915,699 teaches “[a] sintered metal die or mold having formed therein an internal channel for conducting a heat transfer medium therethrough, and a method for producing same. The method includes the steps of disposing sintering powder, such as iron, copper, tungsten carbide or titanium carbide, in a frame or box, about a pattern made of an infiltrant metal, such as copper, lead, cobalt, nickel, iron or alloys thereof, having a lower melting point than that of the sintering powder, the pattern corresponding in configuration to that of the cavity surface of the desired channel for the heat transfer medium and being positioned within the sintering powder in the position desired for the channel, heating the powder together with the pattern to sintering temperature, whereby to sinter the powder and infiltrate the infiltrant metal forming the pattern into the powder, and cooling so as to obtain a sintered metal die or mold having an internal channel whose configuration complements that of the pattern surface.”
U.S. Pat. No. 4,162,700 teaches “a process and mechanisms for controlling the temperature and heat balance of molds. More particularly, this invention relates to molds with built-in devices for heating and cooling various regions within molds. These devices are so constructed that each device is capable of heating and cooling independent of the other devices. The intensity of heating and cooling of these devices can be varied by regulating the flow of the heating/cooling medium in impulses for variable intervals of time. Prior to filling of the mold, the mold is heated to the desired working temperature by injecting a heated medium into the various heating/cooling devices. During or immediately after filling the mold, the flow of the heated medium to the device furthest from the casting riser (feeder) is discontinued and is replaced by a flow of cooling medium. When the material within the mold in the immediate vicinity of this device is solidified, the flow of cooling medium to this device is decreased or stopped. The remaining heating/cooling devices are then sequentially activated in the same manner as the first with activation occurring in a direction toward the casting riser. Thus, solidification is controlled in a directional manner so that it progresses from the region in the mold furthest from the casting riser toward the riser.”
U.S. Pat. No. 4,247,735 teaches “[a] Joule effect electric furnace for goldsmith, dental and the like melting processes comprises a graphite crucible which constitutes by itself an electric resistance element suitable for the Joule effect heating and is connected to an electric power supply.”
U.S. Pat. No. 6,003,587 teaches “[a] casting furnace for forming a large size turbine blade at a high casting rate using a casting alloy which has a single crystal structure or a columnar crystal structure, includes a main tank 2 in which a mold M is placed. A heater 6 heats the periphery of a mold M to a predetermined temperature. The heater is then vertically raised relative to the mold M while a cooling liquid metal immerses and cools the periphery of the heated mold M below the heater. The surface height of the cooling liquid metal is raised according to the rising of the heater.”
U.S. Pat. No. 6,651,728 teaches “[a] method of casting metal articles includes providing an array of article molds. The article molds are filled with molten metal. The molten metal is solidified in the article molds. During solidification of the molten metal, a plurality of solidification control elements function as heat sinks and radiation baffles. The solidification control elements are disposed between the article molds as the molten metal solidifies.”
GB810294 teaches “[a] mould is moved with respect to a molten metal supply source and is charged at successively higher levels of the mould cavity, each charge flowing upwardly in that cavity. A permanent, two-part mould 4, FIGS. 1 and 2, defining a cavity 8 for an air-foil section, has gates 12 at different levels, and risers 11. The mould is surrounded by a crucible 15 which has valve-plates 16, movable by handles 19, for opening and closing discharge-ports 17, and which plates may be pressed against the mould to form a fluid-tight seal by hydraulic cylinders 18. A heating-coil 14 surrounds the crucible, and a cooling-device 20 is secured to the bottom of the crucible. In operation, a mould on the base-plate 2 is preheated by the coil 14, the plates 16 are raised to allow molten metal to enter the mould through the lowermost gates 12, and the crucible is then progressively raised to cause the metal to flow through the other gates 12 in succession. The cooling-device 20 being raised with the crucible, the solidification of the metal in the mould progresses from the bottom upwardly. Alternatively the crucible or cooling-device may be stationary, and the mould moved. In a modification, FIGS. 4, 4 a, the molten metal is contained in the hollow walls of a structure having a stepped base 30 a. The mould 4 has gates 12 at different levels which correspond with gates 16 in said hollow walls, so that metal flows through the gates 12 in succession as the mould is moved from one step to the next. Stepped cooling walls 31 cause a progressive cooling of the mould. Alternatively the crucible and cooling-walls may be moved past a static-mould. Making aircraft; brazing.—Two cast portions 35, 36, FIG. 5, of an airfoil section, e.g. of aluminum alloy, are joined by placing aluminum brazing compound between the abutting machined faces, and heating in a brazing furnace or by high-frequency heating. Alternatively, the portions with the brazing compound between are squeezed together in a close-fitting die heated to approximately 400-500 F.”
GB191302484 teaches “[p]iping is prevented in ingots by gradual cooling from the bottom upwards, the metal in the upper portion being maintained liquid by electric currents induced in the metal by alternating current in a coil surrounding the mould. An annular furnace with a refractory casing A, FIG. 3, may be raised relatively to the mould during cooling. In a modification, a stationary furnace has a number of coils 1 . . . 20, FIG. 4. Current is supplied to a zone of coils, say 1 . . . 6 at the beginning of the operation. After a time, the coil 1 is switched out and the coil 7 in, and so on.”
The inventions disclosed and taught herein are directed to an improved method and apparatus for metal casting.

BRIEF SUMMARY OF THE INVENTION

A system for casting comprising a mold for forming molten metal; a support for supporting the mold and transferring heat to and from the mold; and a furnace operable to substantially surround the mold through a preheat cycle, a heat cycle, and a cooling cycle. The furnace preferably moves vertically down to surround the mold for the preheat, heat, and cooling cycles and moves up and away from the mold after the cooling cycle is complete. In an alternative embodiment, the furnace may be replaced with a cooling can just before initiation of the cooling cycle. The support is preferably stationary and provides directional cooling for the mold during the cooling cycle.
A method for casting metal in a mold comprising placing solid metal ingots in the mold; placing the mold on a support; lowering a furnace to surround the mold on the support; transferring heat from the support and furnace to the mold, thereby melting the metal ingots; transferring heat from the mold to the support using a cooling system integral to the support; and raising the furnace away from the mold after the mold has been cooled. The support is preferably stationary, such that the furnace moves vertically down to surround the mold for preheat, heat, and cooling cycles and moves up and away from the mold after the cooling cycle is complete.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates of a cross sectional view of a particular embodiment of a casting apparatus utilizing certain aspects of the present inventions with a furnace above a mold support;

FIG. 2 is a flow chart showing the operation of certain aspects of the present inventions;

FIG. 3 illustrates of a cross sectional view of the casting apparatus with the furnace lowered down to the mold support for preheat and heat cycles; and

FIG. 4 illustrates of a cross sectional view of the casting apparatus utilizing certain aspects of the present inventions during a cooling cycle.

DETAILED DESCRIPTION

The Figures described above and the written description of specific structures and functions below are not presented to limit the scope of what Applicants have invented or the scope of the appended claims. Rather, the Figures and written description are provided to teach any person skilled in the art to make and use the inventions for which patent protection is sought. Those skilled in the art will appreciate that not all features of a commercial embodiment of the inventions are described or shown for the sake of clarity and understanding. Persons of skill in this art will also appreciate that the development of an actual commercial embodiment incorporating aspects of the present inventions will require numerous implementation-specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such implementation-specific decisions may include, and likely are not limited to, compliance with system-related, business-related, government-related and other constraints, which may vary by specific implementation, location and from time to time. While a developer's efforts might be complex and time-consuming in an absolute sense, such efforts would be, nevertheless, a routine undertaking for those of skill this art having benefit of this disclosure. It must be understood that the inventions disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Lastly, the use of a singular term, such as, but not limited to, “a,” is not intended as limiting of the number of items. Also, the use of relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like are used in the written description for clarity in specific reference to the Figures and are not intended to limit the scope of the invention or the appended claims.
Particular embodiments of the invention may be described below with reference to block diagrams and/or operational illustrations of methods. It will be understood that each block of the block diagrams and/or operational illustrations, and combinations of blocks in the block diagrams and/or operational illustrations, can be implemented by analog and/or digital hardware, and/or computer program instructions. Such computer program instructions may be provided to a processor of a general-purpose computer, special purpose computer, ASIC, and/or other programmable data processing system. The executed instructions may create structures and functions for implementing the actions specified in the block diagrams and/or operational illustrations. In some alternate implementations, the functions/actions/structures noted in the figures may occur out of the order noted in the block diagrams and/or operational illustrations. For example, two operations shown as occurring in succession, in fact, may be executed substantially concurrently or the operations may be executed in the reverse order, depending upon the functionality/acts/structure involved.
Applicants have created a system and method for casting comprising a mold for forming molten metal; a support for supporting the mold and transferring heat to and from the mold; and a furnace operable to substantially surround the mold through a preheat cycle, a heat cycle, and a cooling cycle. The furnace preferably moves vertically down to surround the mold for the preheat, heat, and cooling cycles and moves up and away from the mold after the cooling cycle is complete. The support is preferably stationary and provides directional cooling for the mold during the cooling cycle.
FIG. 1 is an illustration of a system 10 for casting metal. The system 10 is especially well adapted to form drill bits, of the type used in oil and gas drilling operations, but may be well suited to the formation of many other cast products. The system 10 of the present invention preferably includes a mold 12 for forming molten metal, a furnace 14 for melting the metal in the mold 12, and a support 16 upon which the mold 12 rests. The mold 12 is preferably conventional and comprises a box or container 18 filled with casting sand, or some other casting material, 20. The bit is formed by melting a matrix of metal pellets, or ingots, 22 in a void 24 of the casting sand 20. More specifically, the bit is preferably comprised of a matrix of tungsten carbide powders and a copper alloy binder. Typically, during bit fabrication, the tungsten carbide powder is not melted, but rather suspended in the molten copper alloy binder. In other words, the molten copper binder impregnates the matrix of tungsten carbide powder to form the bit.
In one embodiment, the furnace 14 is an electric furnace comprising one or more resistance heating coils 26. The coils 26 are preferably embedded within sidewalls 28 of the furnace 14. The coils 26 may also be embedded in a roof, or ceiling, 30 of the furnace 14. The sidewalls 28 and roof 30 of the furnace 14 form a heating camber 32. The heating chamber 32 is preferably sized to substantially surround the mold 12.
While in the preferred embodiment the furnace 14 uses resistance heating, the furnace 14 may use induction heating in alternative embodiments. In still other embodiments, the furnace 14 may use gas or some other fuel to provide heat. Finally, the furnace 14 may use a combination of heating techniques.
The furnace 14, in the preferred embodiment, is raised and lowered vertically by a hoist (not shown), or any other suitable means of transporting the furnace 14. In this manner, the furnace 14 can be lowered onto the support 16 and substantially surround the mold 12 during formation of the bit. Once the bit has cooled, or before cooling, as will be discussed in greater detail below, the furnace 14 can be raised, thereby providing access to the newly formed bit.
The support 16 preferably supports the mold 12 in a stationary position throughout preheat, heat, and cooling cycles, as will be discussed in greater detail below. Because the support 16 and mold 12 remain stationary, with the furnace 14 moving to and away from them, more consistent casting is promoted. This technique may also provide for safer and more efficient casting, as it does not require any handling of hot molds or molten metal.
The support 16 may be constructed of graphite, ceramic, and/or silicon carbide and/or may include a ceramic coating to prolong service life in an oxidizing environment and/or control thermal expansion and contraction. The support 16 may include both heating and cooling subsystems. The heating subsystem preferably matches the technology used in the furnace 14. Therefore, in the preferred embodiment, the support 16 preferably includes one or more resistive heating coils 34.
In one embodiment, the support's 16 cooling subsystem comprises a number of cooling passageways 36, through which a cooling medium may pass. In this manner, the cooling medium extracts heat from the support 16, thereby extracting heat from the mold 12 and bit. Thus, the cooling subsystem effects directional cooling of the bit. The cooling medium may be a gas, such as air or nitrogen, or liquid, such as water or liquid nitrogen. The cooling medium may be completely inert or may comprise a refrigerant.
Rather than, or in addition to, the cooling passages 36, the cooling subsystem may comprise one or more nozzles 38 (as shown in FIG. 4) that spray the cooling medium onto the support 16 and/or the mold 12 directly. While not preferred, the nozzles 38 may spray onto the furnace 14, as well. The cooling medium used in conjunction with the nozzles 38 may be the same as the cooling medium associated with the passages 36. Alternatively, the passages 36 and nozzles 38 may use different cooling mediums.
Other and further embodiments utilizing one or more aspects of the inventions described above can be devised without departing from the spirit of Applicant's invention. For example, rather than including both the heating and cooling subsystems within the support 16, they may be interchangeably coupled with the support 16. Additionally, nitrogen may be induced into select components of the system to prevent oxidation. Further, the various methods and embodiments of the casting system can be included in combination with each other to produce variations of the disclosed methods and embodiments. Discussion of singular elements can include plural elements and vice-versa.
First, now referring also to FIG. 2, solid metal matrix is placed within the mold 12 and the mold 12 is placed on the support 16, as shown in steps A and B. Now referring also to FIG. 3, the furnace 14 is lowered onto the support 16, surrounding the mold 12, as shown in step C. The preheat cycle is begun, as shown in step D, to controllably raise the temperature of the heating chamber 32, and thereby the mold 12 and metal ingots. The preheat cycle may comprise energizing any of the coils 26,34 of the furnace 14 and/or support 16. For example, the preheat cycle may comprise energizing select coils 26 from the furnace 14. Alternatively, the preheat cycle may comprise energizing select coils 34 from the support 16. The preheat cycle may last for a predetermined period and/or until the mold 12 reaches a predetermined temperature. The preheat cycle may be tightly controlled to follow a temperature versus time profile.
After the preheat cycle, the furnace 14 is preferably left in place upon the support 16 and surrounding the mold 12 for the heat cycle, as shown in step E. During the heat cycle, all of the coils 26,34 from the furnace 14 and support 16 are preferably energized to melt the binder in the mold 12. The heat cycle may last for a predetermined period, until the mold 12 reaches a predetermined temperature, until the binder is completely molten, and/or some combination thereof.
After the heat cycle, the furnace 14 is preferably left in place upon the support 16 and surrounding the mold 12 for the cooling cycle, as shown in step F. Now referring also to FIG. 4, during the cooling cycle, all of the coils 26,34 from the furnace 14 and support 16 are preferably de-energized. Additionally, the support's 16 cooling subsystem is preferably activated. Specifically, a cooling medium 40 is preferably passed through the passages 36 and/or sprayed through the nozzles 38, thereby extracting heat from the support 16 and/or furnace 14. This in turn extracts heat from the mold 12 and bit therein. The cooling cycle may last for a predetermined period and/or until the mold 12 reaches a predetermined temperature. The cooling cycle may be tightly controlled to follow a temperature versus time profile.
Once the cooling cycle is complete, the furnace 14 may be raised up and away from the mold 12, as shown in step G. At this point, the bit has been fully cast and cooled. In the preferred embodiment, there is no movement during the preheat, heat, and cooling cycles. Thus, the system 10 and method of the present invention provides greater safety and dramatically reduces the cost of the furnace 14, as well as providing a more accurate processing time, resulting in better bit integrity and metallurgy by eliminating jarring of the mold and/or sloshing of the molten metal during the casting process. However, in alternative embodiments, the furnace 14 may be raised before the cooling cycle is complete, or even begun.
The order of steps can occur in a variety of sequences unless otherwise specifically limited. The various steps described herein can be combined with other steps, interlineated with the stated steps, and/or split into multiple steps. Similarly, elements have been described functionally and can be embodied as separate components or can be combined into components having multiple functions.
For example, in an alternative embodiment, the furnace 14 is raised after the heat cycle and before the cooling cycle. A cooling can may be lowered onto the support 16 and surrounding the mold 12, taking the place of the furnace 14 during the cooling cycle. The cooling can is preferably an insulated metal container having an open bottom end.
The inventions have been described in the context of preferred and other embodiments and not every embodiment of the invention has been described. Obvious modifications and alterations to the described embodiments are available to those of ordinary skill in the art. The disclosed and undisclosed embodiments are not intended to limit or restrict the scope or applicability of the invention conceived of by the Applicants, but rather, in conformity with the patent laws, Applicants intend to fully protect all such modifications and improvements that come within the scope or range of equivalent of the following claims.

Claims

1. A system for casting comprising:

a mold for forming molten metal;

a support for supporting the mold, the support being operable to transfer heat to and from the mold; and

a furnace operable to substantially surround the mold through a preheat cycle and a heat cycle.

2. The system as set forth in claim 1, wherein the furnace moves vertically.

3. The system as set forth in claim 2, wherein the furnace moves down to surround the mold for the preheat cycle, the heat cycle, and a cooling cycle and moves up and away from the mold after the cooling cycle is complete.

4. The system as set forth in claim 1, wherein the support is substantially stationary, such that the furnace moves toward and away from the support.

5. The system as set forth in claim 1, wherein the support uses resistance heating during both the preheat and heat cycles.

6. The system as set forth in claim 1, wherein the support cools the mold during the cooling cycle using a fluid spray.

7. The system as set forth in claim 1, wherein the support provides directional cooling for the mold during the cooling cycle by receiving cooling medium through passages in the support.

8. The system as set forth in claim 1, wherein the furnace is replaced with a cooling can for a cooling cycle.

9. The system as set forth in claim 1, wherein the furnace uses resistance heating.

10. The system as set forth in claim 1, wherein the support is primarily constructed of a material selected from the group consisting of graphite, ceramic, and silicon carbide.

11. The system as set forth in claim 1, wherein the support includes a ceramic coating.

12. An apparatus for casting metal in a mold comprising:

a substantially stationary support for supporting the mold, the support being operable to transfer heat to the mold using resistance heating and transfer heat from the mold by receiving a cooling medium through passages in the support; and

a vertically moving resistance furnace operable to move down to substantially surround the mold through a preheat cycle, a heat cycle, and a cooling cycle, wherein the furnace moves up and away from the mold after the cooling cycle is complete.

13. A method for casting metal in a mold comprising the steps of:

placing solid metal ingots in the mold;

placing the mold on a support;

lowering a furnace to surround the mold on the support;

transferring heat from the support and furnace to the mold, thereby melting the metal ingots;

transferring heat from the mold to the support using a cooling system integral to the support; and

raising the furnace away from the mold.

14. The method as set forth in claim 13, wherein the support is substantially stationary, such that the furnace moves toward and away from the support and the furnace moves vertically down to surround the mold for preheat, heat, and cooling cycles and moves up and away from the mold after the cooling cycle is complete.

15. The method as set forth in claim 13, wherein the support uses resistance heating during both preheat and heat cycles.

16. The method as set forth in claim 13, wherein the cooling system comprises a fluid spray.

17. The method as set forth in claim 13, wherein the cooling system comprises a cooling medium passing through passages in the support.

18. The method as set forth in claim 13, further including the step of lowering a cooling can to surround the mold for a cooling cycle.

19. The method as set forth in claim 13, wherein the furnace uses resistance heating.

20. The method as set forth in claim 13, wherein the mold is held stationary during preheat, heat, and cooling cycles.