The present invention relates to an apparatus and a method for casting metal and metal alloys. The present invention is also directed to preforms and other articles produced by the method and/or apparatus of the present invention.
In certain applications, components must be manufactured from large diameter metal or metal alloy preforms which are substantially free of defects. (For ease of reference, the term “metallic material” is used herein to refer collectively to unalloyed metals and to metal alloys.) One known method for producing high quality preforms is spray forming, which is generally described in, for example, U.S. Pat. Nos. 5,325,906 and 5,348,566. Spray forming is essentially a “moldless” process using gas atomization to create a spray of droplets of liquid metal from a stream of molten metal. Spray forming, however, suffers from a number of disadvantages that make its application to the formation of large diameter preforms problematic. Furthermore, an unavoidable byproduct of spray forming is overspray, wherein a portion of the metal spray misses the developing preform altogether or solidifies in flight without attaching to the preform. Average yield losses due to overspray in spray forming can be 20-30%.
Another method for producing high quality preforms is nucleated casting, which is generally described in, for example, U.S. Pat. Nos. 6,496,529 and 7,154,932. Nucleated casting is essentially a process involving using gas atomization to create a spray of droplets of liquid metal and depositing the droplet spray into a mold. In various circumstances, portions of the droplet spray, i.e., the overspray, may accumulate on a top surface of the mold. In some instances, the overspray accumulated on the mold's top surface bonds with a preform being cast within the mold. In these circumstances, the nucleated casting process may have to be stopped in order to remove the overspray, and this may result in scrapping the preform. Accordingly, there are drawbacks associated with certain known techniques in which preforms are cast from a droplet spray. Thus, a need exists for an improved apparatus and method for nucleated casting of metallic materials.
In one form of the invention, a nucleated casting apparatus can include an atomizing nozzle configured to produce a droplet spray of a metallic material, a mold configured to receive the droplet spray and form a preform therein, and a gas injector which can limit, and possibly prevent, overspray from accumulating on the mold. In various embodiments, the gas injector can be configured to produce a gas flow which can impinge on the droplet spray to redirect the droplet spray away from a side wall of the mold. In at least one such embodiment, the gas flow can push the droplet spray into the mold, thereby reducing the amount of the droplet spray which accumulates on top of the side wall. In various embodiments, the droplet spray may be directed by the atomizing nozzle in a generally downward direction, whereas the gas flow may be directed in a generally upward direction such that the gas flow forms a physical barrier, ‘curtain’, or ‘fence’ surrounding the perimeter of the mold and biases the droplet spray to a preferred path.
The reader will appreciate the foregoing details and advantages of the present invention, as well as others, upon consideration of the following detailed description of embodiments of the invention. The reader also may comprehend such additional advantages and details of the present invention upon carrying out or using the invention.
The features and advantages of the present invention may be better understood by reference to the accompanying drawings in which:
In various embodiments, the present invention includes a process for casting a metallic material, such as 100Cr6, 1% C, 1.5% Cr AISI 52100 steel, for example. The process can include melting and refining the metallic material and subsequently casting the material to create a preform by a nucleated casting technique. Melting and refining the material may be accomplished by, for example, electroslag remelting (ESR) or vacuum arc remelting (VAR). The process can also include transferring the molten refined material to a nucleated casting apparatus through a passage so as to protect it from contamination. The passage may be that formed through a cold induction guide (CIG) or another transfer apparatus. Such exemplary devices and methods are disclosed in U.S. Pat. No. 6,496,529, entitled REFINING AND CASTING APPARATUS AND METHOD, which issued on Dec. 17, 2002, U.S. Pat. No. 7,154,932, entitled REFINING AND CASTING APPARATUS, which issued on Dec. 26, 2006, and U.S. patent application Ser. No. 11/564,021, entitled REFINING AND CASTING APPARATUS AND METHOD, which was filed on Nov. 28, 2006, the disclosures of which are hereby incorporated by reference herein. Other suitable devices and methods, however, can be used to provide a molten metallic material in connection with the devices and methods described below.
In various embodiments, referring to
In various circumstances, at least portions of droplet spray 26, i.e., the overspray, can accumulate on top surface 28 of mold 20. This overspray can become welded to a preform, such as preform 30, for example, being cast within mold 20 as the overspray solidifies. In such circumstances, the overspray can, as described in greater detail below, inhibit the proper formation of preform 30. In various embodiments, referring to
As illustrated in
Referring to
As described above and referring to
In various embodiments, gas injector 32 and mold 20 can define passageway 38 such that it completely circumscribes, or extends around the entire perimeter of, mold 20. In at least one embodiment, passageway 38 can include one continuous opening, or gap, 39 surrounding mold 20 such that gas flow 34 exiting passageway 38 can completely circumscribe, or enclose, droplet spray 26. In such embodiments, referring to
In various embodiments, referring to
The following actual examples confirm advantages provided by the apparatus and method of the present invention.
Referring to
Further to the above, Test Sample B, referring to
Test Sample C, similar to Test Sample A, included a gap having an axis oriented at a 60 degree angle with respect to the horizontal. As illustrated in Table 1, the thickness of the gap of Test Sample C, however, was much narrower than the gap of Test Sample A. Referring to
As outlined in Table 1, it was also observed that a larger gap can produce a larger and/or faster gas flow. In at least one such embodiment, a faster gas flow can impart more momentum and/or energy to the droplet spray and re-direct the droplets further away from the sidewall of the mold than a slower gas flow. In various embodiments, it was observed that, for a given test sample, the velocity of the gas exiting the gap was substantially proportional to the pressure of the inert gas within the plenum of the coupon. In at least one embodiment, the relationship between the gas velocity and pressure was linearly proportional. Furthermore, referring to
Referring to
In at least one evaluation, Test Samples G, H, and J were exposed to a droplet spray for approximately 25 seconds and an inert gas was supplied to the gas injectors at approximately 1.9 bar. As illustrated in
While an approximately 67 degree angle was determined to be optimal for these particular test samples, the optimal angle in other embodiments may be different and may be dependent upon the distance between the nozzle and the top of the mold, the diameter of the mold, and the configuration of the droplet spray. In at least one embodiment, the droplet spray may be rastered and/or oscillated relative to the mold wherein, in such embodiments, the optimal gap axis angle may be selected based on an average and/or median configuration of the droplet spray, for example. In various circumstances, including evaluations utilizing Test Sample H, for example, the inert gas flow produced by at least one gas injector impinged on the droplet spray so significantly that it overly disrupted the spray cone and caused portions of the droplet spray to accumulate on adjacent test samples. In view of the above, it was determined that the pressure and velocity of such gas flows could be controlled, or reduced, to prevent such gas injectors from producing an overly-disruptive gas flow.
Referring to
Referring to
Referring to
In various embodiments, a gas injector, or at least a portion thereof, can be polished with a surface grinder or drill, where the surface grinder or drill can include a rotating wheel configured to be moved over the surfaces of the gas injector. In such embodiments, a rotating wheel comprised of large grit particles, such as 80 grit, for example, can be initially used and, thereafter, wheels having smaller grit particles, such as 240 grit, for example, can be successively used until a ‘soft wheel’ is used. In at least one embodiment, the gas injector can be positioned against a rotating wheel extending from a stationary machine. In either event, the surfaces of the gas injector can then be wet polished with a rotating wheel and/or a fine polishing media. In various circumstances, the surfaces can also be manually polished with a natural brush and at least one polishing paste in order to attain the desired surface finish. In various embodiments, the gas injectors can be electro and/or chemical polished in addition to or in lieu of the mechanical polishing described above. In such embodiments, the surfaces can be polished such that they have a surface roughness, either Ra and/or Rq, of approximately 1.9 μm, approximately 0.8 μm, approximately 0.4 μm, approximately 0.1 μm, and/or approximately 0.012 μm, for example.
As illustrated in
In various examples, referring to the photomicrographs illustrated in
As can be seen from Table 3, the polished surfaces exhibited the smoothest, or least rough, surfaces and the as-rolled surfaces exhibited the roughest surfaces. As described above, droplet overspray was observed to be less likely to accumulate on gas injectors having polished surfaces than gas injectors having non-polished surfaces. Furthermore, grinding or machining the surfaces of the gas injectors and/or mold side walls can reduce the roughness of the surfaces as compared to as-rolled surfaces. In such embodiments, as a result, the ground or machined surfaces can reduce the amount of overspray which accumulates thereon as compared to as-rolled surfaces. In such embodiments, the surfaces can be machined or ground such that they have a surface roughness, either Ra and/or Rq, of approximately 6.3 μm, approximately 3.2 μm, approximately 1.6 μm, approximately 0.2 μm, approximately 0.1 μm, approximately 0.05 μm, and/or approximately 0.025 μm, for example.
In view of the above, it is believed that the tendency for the atomized droplets of metallic materials to accumulate on the as-rolled surfaces, for example, may be the result of, at least in part, a mechanical keying effect or interlocking between the atomized spray droplets and ridges extending from the as-rolled surfaces. While such a mechanical interlocking may occur on the machined and/or polished surfaces, it is believed that such surfaces have smaller and/or fewer ridges and, as a result, the atomized droplets are less likely to adhere to such surfaces. In various embodiments, further to the above, at least a portion of a gas injector and/or mold wall can be coated with a material which can decrease the coefficient of friction between the overspray droplets and the surfaces of the gas injector or mold thereby increasing the possibility that the droplets will not ‘catch’ on the surfaces thereof.
Referring to
During at least several actual examples, it was observed that less overspray accumulated on the top surfaces of test samples which were oriented, or sloped, in a direction substantially parallel to the outside perimeter of the spray cone. Correspondingly, it was also observed that top surfaces oriented in directions which were increasingly closer to being transverse to the outside perimeter of the droplet spray accumulated more overspray thereon. Thus, it is apparent that the top surface of the gas injector preferably should be angled so as to substantially match, if not exceed, the angle of the spray cone in order to reduce the accumulation of overspray. In at least one such embodiment, as described above, the angle of the spray cone was determined to be approximately 67 degrees and, thus, the top surface would be optimally oriented at an approximately 67 degree, or greater, angle with respect to the horizontal, i.e., a plane perpendicular to the axis of the droplet spray.
Embodiments of the present invention are envisioned in which the configuration of passageway 38 can be changed. In various embodiments, referring to
In various embodiments, a gas injector can be integrally formed with a mold. In at least one such embodiment, the mold can include an opening, passageway, and/or plenum formed therein which can be configured to receive an inert gas as described above. In various alternative embodiments, referring to
In various embodiments, referring to
In various embodiments, referring to
In various circumstances, as indicated above, if overspray is permitted to accumulate on mold 20 and it is not sufficiently removed, the overspray may block at least a portion of droplet spray 26 from entering mold 20 and thereby impede the proper formation of preform 30. Furthermore, as described above, the overspray may become welded to preform 30 and prevent preform 30 from being withdrawn relative to side wall 21. Such circumstances can reduce the output and profitability of the nucleated casting process and negatively affect the quality of cast preforms. In view of the above, gas injectors in accordance with the present invention can also be configured to direct a flow of gas which can dislodge overspray which has accumulated on top surface 28, for example, and direct it into mold 20. In at least one embodiment, the gas injectors can be configured to dislodge the overspray from top surface 28 such that it does not fall into mold 20. In either case, the gas injectors can be oriented to direct a gas flow at any suitable angle with respect to the top surface of the mold, for example, including a generally downward direction and/or a direction where the gas flow impinges on the side wall of the mold, for example.
It is to be understood that the present description illustrates those aspects of the invention relevant to a clear understanding of the invention. Certain aspects of the invention that would be apparent to those of ordinary skill in the art and that, therefore, would not facilitate a better understanding of the invention have not been presented in order to simplify the present description. Although the present invention has been described in connection with certain embodiments, those of ordinary skill in the art will, upon considering the foregoing description, recognize that many modifications and variations of the invention may be employed. All such variations and modifications of the invention are intended to be covered by the foregoing description and the following claims.
The present application is a continuation application claiming priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/861,033, filed Aug. 23, 2010 now U.S. Pat. No. 7,963,314, entitled “CASTING APPARATUS AND METHOD”, which application is in turn a continuation application claiming priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 11/949,808, filed Dec. 4, 2007, entitled “CASTING APPARATUS AND METHOD”, which issued as U.S. Pat. No. 7,798,199 on Sep. 21, 2010. The entire disclosures of U.S. patent application Ser. No. 12/861,033 and U.S. Pat. No. 7,798,199 are hereby incorporated by reference herein.
Certain of the research leading to the present invention was funded by the National Institute of Standards and Technology Advanced Technology Program (NIST ATP), Contract No. 70NANB1H3042. The United States may have certain rights in the invention.
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Number | Date | Country | |
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Parent | 12861033 | Aug 2010 | US |
Child | 13108402 | US | |
Parent | 11949808 | Dec 2007 | US |
Child | 12861033 | US |