Casting device and method
A improved method and apparatus are provided for casting objects. The apparatus includes a molten metal or liquid retaining container with a bottom feed outlet, a casting chamber with a bottom feed inlet, and a connecting portion through which molten metal or liquid from the container portion flows into the casting mold. The melt flows from the melt container to the casting chamber through the hollow connecting portion by movement of the relative positions of the melt container and the casting chamber, allowing for a controlled casting method with a minimum of turbulence.
The present invention relates in general to the casting of objects, and more particularly to those metal castings that must meet strict quality criteria in which precise, reproducible control of the mold filling rate at all times during melt flow is critical for the manufacture of the desired final product.
Traditional methods of casting such as casting by hand are used to this day, particularly in industries where complex parts are created in small numbers under strict quality standards. In such methods the molten metal is poured into a mold from above or flowed into a mold through an single or multiple entrance ports, or gates, in the mold. It has long been recognized, however, that the quality of a final casting product, particularly those cast with metal and metal alloys, depends largely upon the ability of the casting devices and methods to precisely control the pouring rate and/or flow rate during the filling of the mold.
Turbulence, a direct consequence of high melt flow velocity and/or a lack of control of melt flow velocity, is associated with the mixture of gases into the casting material, and often causes the separation of materials, such as ceramics, that are applied to or embedded in mold casting surfaces. The unwanted inclusion of both gases and the above impurities into the mold material causes the gases and impurities to become trapped in the final cast product, reducing the stability and quality of the casting and often results in castings that must be rejected due to those impurities.
The turbulence associated with the pouring and flowing of melt material is also primarily responsible for the unwanted mixing of impurities found on the surface of the melt material into the material being flowed into the mold. That problem is compounded when methods that flow melt material into the top of a mold from the melt source are employed; such methods allow surface impurities to be carried into the mold.
Turbulence is associated with high velocity, large flow channels and low kinematic viscosity. In casting processes requiring very high quality final products, turbulence may result in significant costs of manufacture due to a decreased number of acceptable final products. See, e.g., P. R. Beely, Foundry Technology, The Butterworth Group, London, England (1972). Of the factors associated with turbulence, velocity is the greatest contributor, and therefore most efforts to reduce turbulence focus on controlling the melt flow velocity into the receiving mold. In order to control melt flow (and thereby reduce turbulence), the current invention utilizes volume control, not velocity, and therefore can be understood as a direct application of Bernoulli's Theorem to the problem of turbulence. Bernoulli's Theorem states that the total energy of unit weight of fluid is constant throughout a system. The Theorem also reveals that the head of metal in a casting system is a significant source of casting complications. The present invention eliminates changes in melt material head height during casting, further eliminating problems associated with melt flow.
Methods of overcoming the problems associated with turbulence, and in particular the issue of controlling velocity, have included controlling the flow of the molten metal into the top of a mold (primarily via controlling the flow rate and/drop height), or using a bottom feed method. Of those solutions, the bottom feed method has gained favor and is a better solution to the problem of turbulence because the melt material may be introduced into the mold in a strictly controlled manner; the upward displacement of melt into the mold results in much less turbulence than pouring the melt material into the mold under gravity, and the velocity of the melt being fed into the mold may be better controlled. As a result, upward displacement of melt into a mold allows for higher quality castings.
However, in order to flow material through the bottom gate or gates of a mold, the melt material must be flowed against gravity. Traditionally, three methods of flowing melt product through bottom gates into a mold have been applied: utilizing gas pressure (positive pressure applied to the melt in the source container and/or drawing a vacuum on the mold container); using a pump to force the molten liquid to flow against its hydrostatic head into the mold; or using a gravity feed utilizing the hydrostatic head of a volume of melt material. Each of the above methods, while a feasible and commonly used solution, has significant drawbacks.
The use of gas pressure to force the molten material to flow against its hydrostatic head requires atmospherically-controllable conditions, usually obtained by atmospherically sealing the entire casting process area or sealing and pressurizing the feeding chamber. In the alternative, the mold may be subjected to partial atmospheric evacuation. In any of those methods, however, complicated systems must be utilized and continuously monitored in order to control the casting process. Further, changes in gas pressures can adversely impact the quality of the final cast product, and involve further time delays in the casting process. Finally, high pressure systems cannot be used as high pressure increases the velocity of melt material, which in turn increases the turbulence in the receiving mold. This process both produces and traps gas made by the process itself. The pressure differentials, therefore, must be kept low which decreases flow rate and therefore increases the time necessary for a single casting event. Trapped gas and hollow gating may be eliminated with the invention disclosed herein.
Pumping of the melt material into a mold usually is accomplished by utilizing electromagnetic pumps. Such pumps, however, are expensive to install and costly to maintain, largely because the pumps must exist in the extreme environment of molten metal. Further, pumping is often too cumbersome and expensive to be utilized in casting small amounts of high quality products. Finally, electromagnetic pumps cannot be utilized in systems for the casting of non-ferrous metals, such as titanium.
As an alternative, the melt material may be fed into the mold by utilizing the hydrostatic head of the melt material in a holding or feeding chamber, such as is incorporated in the invention of Tooley et al., U.S. Pat. No. 6,619,373. In such methods, however, the flow rate can only be controlled by maintaining the hydrostatic head through constant filling and the incorporation of what is often a complicated valve mechanism.
Finally, in all three methods, back-flow of melt material from the mold into the feeding system must be avoided by either maintaining the pressure differential, which slows the casting process by requiring a cooling period before the mold can be removed, or through the use of a check-valve of some sort. In either case, controlling the flow of material becomes more complex and costly, and slows the production rate of cast material.
Numerous attempts have been made to overcome all of the above problems. For example, many foundries utilize a bottom feed method that includes the steps of allowing the metal to solidify within the mold cavity and then removing the mold from a feeding relationship with the source of molten metal. A majority of the time involved in that casting method is occupied with waiting for the metal to solidify in the mold cavity before the source of metal can be taken out of the feeding relationship. Solutions to this problem have generally been complex and costly, such as the pressure technique taught by Smith, U.S. Pat. No. 4,733,714. The present invention overcomes the problems associated with isolating the receiving mold from the feed source by simultaneously flowing the melt material into the mold while removing the melt material source from the feeding relationship with the mold. The mold may therefore be removed and replaced by another sooner than is possible in other current methods, decreasing casting delays.
As noted above, for bottom feed casting methods, it is important to provide some means to prevent a back-flow of melt material into the feeding means or device. The instant invention removes this problem entirely by changing the positions of the mold and the feed chamber such that, for back-flow to occur, the metal in the mold would have to flow against gravity.
The present invention overcomes the problems currently experienced in bottom-feed and top-feed methods by providing a simple, rapid, and easily-controllable method and device for casting objects that requires few or no moving parts, no artificial pressure or pumping of molten material as well as significantly limiting turbulence in casting and reducing the delays in the casting process. In addition, through the combination of reducing or eliminating turbulence and flowing melt material down through the bottom gate of the melt chamber and up through the bottom gate into the mold (bottom feeding), the present invention reduces or completely eliminates unwanted mixing of those surface impurities into the final cast product. The impurities float to the top when the metal is melted; these impurities do not leave the original melt, and can be kept from entering the gating or the receiving mold.
SUMMARY OF THE PRESENT INVENTIONThe present invention provides an apparatus and method for casting objects that overcomes existing problems associated with casting metals. Impurities are isolated and remain in the melt chamber rather than being introduced into the final cast product. In particular, the instant device provides a method of bottom-feeding a mold without the use of pressure differentials, mechanical pumping, or the complex machinery and control systems associated with both. It is a further intention of the present invention to allow such simple yet easily controllable bottom-feeding to be applied to small scale batch production as well as large scale multiple mold processes.
More specifically, the present invention contemplates apparatus for the bottom-fill casting which comprises: a melt chamber, a mold, a connecting means between the melt chamber and the mold, and a means of changing the position of the melt chamber and the mold relative to each other such that the molten material flows from the melt chamber into the mold. The apparatus may further comprise valves at the feed inlets and outlets of the mold and melt chamber. The apparatus may also further comprise a plurality of molds into which melt material may be flowed simultaneously.
As the positions of the melt chamber and the mold(s) are changed relative to each other, the melt flows out of the melt chamber, through the connecting means, and into the receiving mold(s). The positions of the melt chamber and the mold may be changed manually or, if greater control and reproducibility of flow rate is desired, the positions may be changed through the use of mechanical means.
The bottom ports in both the melt chamber and the mold may further comprise check valves, creating a mechanical isolation of the mold from the melt source once the mold has been filled fully with molten material, allowing the mold to be removed without the need to wait for a cooling period. If multiple products are desired to be cast under identical feed conditions and from the same quality of melt material (such as a single batch of alloy), a single melt chamber may be utilized to feed a plurality of molds.
A positive feed angle above the horizontal and in the direction of flow from the melt source to the mold further reduces the problems associated with the movement of gas trapped with the melt material. A slight angle on the mold itself may also reduce gas-trapping effects associated with melt material flows. The positive angle in the direction of feed flow may also be achieved by changing the position of the entire assembly. Further, a greater level of control over the feeding process, and a reduction of the inclusion of trapped gases, may be had by changing the positive feed angle simultaneously or in conjunction with changing the relative positions of the melt chamber and the mold(s) are changed. The feed angle is imparted through an angle in the connecting means such as a hollow, high-temperature tube between the melt chambers. Although the angle may be from close to 180° down to close to 0°, experimental use has shown that a feed angle close to or at 45° is the most advantageous for the method wherein the apparatus has a fixed structure and there are no moveable joints either connecting the melt chambers to the connecting tube or in the connecting tube itself. For other applications, the specific most advantageous angle may be in the above-noted range; i.e., from 180° to 0° depending upon the melt material, feed tube configuration including diameter and length, mold and casting configuration and characteristics, environmental and monetary concerns, etc.
It is contemplated that the present invention may be utilized inside of a furnace, or may have melt material fed directly into it from a furnace. The melt chamber itself may also comprise a heat source and/or serve as the furnace, further reducing the complexity of the casting operation.
Finally, the connecting means may be created utilizing a variety of materials and components. A high temperature flexible feed tube or hose is preferred, as it reduces the complexity of the device and the number of possible failure points. However, feed tubing that comprises sealed joints that allow rotation of the melt chamber and the mold(s) relative to each other may also be utilized.
In one embodiment of the present invention, the positions of the melt chamber and the mold are changed relative to each other through manual manipulation.
In another embodiment, the positions of the melt chamber and the mold are changed relative to each other through mechanical means.
In another embodiment, either or both of the melt chamber and mold are molds of the desired final cast such that, after serving as the melt chamber for one casting, the melt chamber then becomes the mold for the second casting, allowing alternate castings to be made in rapid succession without resetting the apparatus.
In another embodiment, a melt chamber feeds a plurality of molds, allowing simultaneous casting of multiple molds of equal quality.
In another embodiment, the connecting means between the melt chamber and the mold(s) comprises a flexible tubing material suitable to flow a high temperature material without a requirement for joints or points of rotation in the connecting means.
In another embodiment, the connecting means between the melt chamber and the mold(s) comprises a jointed feed-tube suitable to flow a high temperature material.
In another embodiment, the present invention further comprises isolation valves located at the bottom feed ports in the melt chamber and the mold(s).
In another embodiment, the present invention comprises changing the angle of the flow path so that there is a positive angle above the horizontal in the direction of melt flow.
In another embodiment, the impurities in the melt material float to the top when the metal is melted; these impurities never leave the original melt, nor enter the gating or the receiving mold.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the embodiment of the invention illustrated in
This invention has been described in connection with a preferred embodiment thereof, and it should be clear to one skilled in the art that modifications and changes therein may be made by one skilled in the art without departing from the spirit and scope of the invention. The details of the present invention as described are illustrative only, and do not limit the scope of the present invention as claimed below.
Claims
1. An apparatus for casting metal products comprising:
- one or more first melt chambers with inlet/outlet ports; and
- one or more second melt chambers with inlet/outlet parts; and
- a connecting means between said one or more first melt chambers and said one or more second melt chambers connected to said one or more first melt chambers and said one or more second melt chambers at said inlet/outlet ports.
2. The apparatus of claim 1, wherein said inlet/outlet ports in said first melt and second melt chambers are located at the bottom of the said melt chambers.
3. The apparatus of claim 2, wherein said inlet/outlet ports further include valves.
4. The apparatus of claim 1, wherein said one or more first melt chambers are moveable relative to said one or more second melt chambers.
5. The apparatus of claim 4, further comprising mechanical means for changing the position of said one or more first and one or more second melt chambers relative to one another.
6. The apparatus of claim 4, wherein the positions of said one or more first and one or more second melt chambers are moved vertically with respect to one another.
7. The apparatus of claim 4, wherein the positions of said one or more first and one or more second melt chambers are moved rotationally with respect to one another about a horizontal axis running longitudinally through said apparatus.
8. The apparatus of claim 1, wherein the position of said melt chambers includes a positive feed angle between said one or more first melt chambers and said one or more second melt chambers in the direction of melt material flow.
9. The apparatus of claim 8, wherein said melt chambers further include a positive feed angle in the direction of melt flow from said inlet into the receiving melt chamber.
10. An apparatus for casting metal products comprising: one or more first melt chambers with inlet/outlet ports:
- and one or more second melt chambers with inlet/outlet parts: and
- a connecting means between said one or more first melt chambers and said one or more second melt chambers connected to said one or more first melt chambers and said one or more second melt chambers at said inlet/outlet ports, wherein said connecting means is a hollow rigid tube of a high-temperature heat resistant material.
11. The apparatus of claim 1, wherein said connecting means is moveably connected to said one or more first and one or more second melt chambers.
12. The apparatus of claim 1, wherein said one or more second melt chambers are molds for casting objects.
13. The apparatus of claim 4, wherein said apparatus further comprises mechanical means to rotate the said one or more first melt chambers and said one or more second melt chambers about a horizontal axis with respect to one another.
14. The apparatus of claim 1 wherein said melt chambers further comprise heating means.
15. The apparatus of claim 1, wherein said one or more first melt chambers feeds a plurality of second melt chambers.
16. An apparatus for casting metal products comprising;
- one or more first melt chambers with inlet/outlet parts;
- one or more second melt chambers with inlet/outlet ports wherein said one or more second melt chambers are moveable with respect to each other; a connecting means between the said one or more first melt chambers and said one or more second melt chambers wherein said connecting means is connected to said one or more first melt chambers and said one or more second melt chambers at said inlet/outlet ports; a positive melt materials feed angle from said one or more first melt chambers to said or more second melt chambers; and said one or more first melt chambers and said one or more second melt chambers comprise one or more casting molds.
17. The apparatus of claim 16 wherein said one or more first melt chambers and said one or more second melt chambers are moveable vertically with respect to one another.
18. An apparatus for casting metal products comprising; one or more first melt chambers with inlet/outlet parts, one or more second melt chambers with inlet/outlet ports wherein said one or more second melt chambers are moveable with respect to each other; a connecting means between the said one or more first melt chambers and said one or more second melt chambers wherein said connecting means is connected to said one or more first melt chambers and said one or more second melt chambers at said inlet/outlet ports: a positive melt materials feed angle from said one or more first melt chambers to said or more second melt chambers: and said one or more first melt chambers and said one or more second melt chamber comprise one or more casting molds; and wherein said connecting means is a rigid hollow tube.
19. A method of casting metal products by transferring molten metal from a first melt chamber to a second melt chamber through bottom inlet/outlet ports, said method comprising the steps of: filling one or more first melt chamber with a desired amount of molten metal; moving said one or more first melt chamber vertically with respect to one or more second melt chamber such that said molten metal flows from the first melt chamber into said second melt chamber leaving a volume of molten metal in said one or more first melt chambers.
20. The method of claim 19 wherein surface impurities are not transferred into said second melt chamber.
Type: Application
Filed: Feb 18, 2005
Publication Date: May 18, 2006
Inventor: Robert Howard (Newport News, VA)
Application Number: 11/060,445
International Classification: B22D 35/04 (20060101);
