Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-12-03
2004-06-22
Stoner, Kiley (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S332000, C164S334000
Reexamination Certificate
active
06752198
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process, and to molding apparatus, for the production of composite metal articles comprising bimetallic plate.
Numerous prior art proposals for producing composite metal articles are discussed in U.S. Pat. No. 4,953,612 to Sare et al (filed as PCT/AU84/00123). Those proposals suffer from various disadvantages or limitations, at least some of which are overcome by the teaching of U.S. Pat. No. 4,953,612. The teaching of U.S. Pat. No. 4,953,612 is well suited for the manufacture of a range of composite metal articles comprising a cast component bonded to a substrate component. However, the teaching is less well suited for the production of a composite metal article comprising bimetallic plate, in particular plate which is relatively thin and/or has a relatively large surface area. Thus, the teaching of U.S. Pat. No. 4,953,612 can encounter difficulties, such as uneven bonding, in the production of bimetallic plate in sizes greater than about 300×300 mm, with a thickness of less than about 30 mm and a thickness ratio of about 1:1 or less for cast metal to substrate.
The present invention seeks to provide a process and molding apparatus which enables production of relatively large area, bimetallic plate, such as up to and in excess of 1800×1500 mm, while indications are that plate at least up to 3000×1650 mm is able to be produced.
In the process of the present invention a plate (hereinafter referred to as a “substrate”), which is formed of a first metal, has a component (hereinafter referred to as “cladding”) of a second metal cast against it to form bimetallic plate. The first metal for the substrate may be titanium, nickel or cobalt, a ferrous alloy or a titanium-, nickel- or cobalt-base alloy. The second metal for the cladding may be copper, nickel or cobalt, a ferrous alloy or a copper-, nickel- or cobalt-base alloy. While not necessarily the case, the first and second metals usually are compositionally different. However, where the first and second metals are the same or similar, in being closely related compositionally, this can be to achieve a difference in properties based on microstructure, such as due to the substrate being hot- or cold-worked and the cladding having an as cast microstructure.
As in U.S. Pat. No. 4,953,612, the surface of the substrate against which molten alloy is to be cast to form the cladding needs to be rendered substantially oxide-free. Also, the substrate is preheated and is protected against oxidation by a suitable coating. The coating may be formed from flux which is applied over the substrate surface, and melted to form a protective film during preheating. However, other protective coatings can be used, such as a deposit of a suitable metal formed for example by electroless or electrolytic plating of nickel or another metal, or a non-metallic coating such as of colloidal graphite containing a silicate binder. Depending on the protective coating use, it is either displaced by or alloyed with the alloy cast to form the cladding, facilitating wetting of the substrate surface by the cast alloy.
Also as in U.S. Pat. No. 4,953,612, the molten alloy to form the cladding is poured at a superheated temperature to facilitate the attainment, with preheating of the substrate, of an overall heat energy balance to achieve a diffusion bonding between the cladding and the substrate. The diffusion bond is obtained substantially in the absence of fusion of the substrate surface against which the cladding is cast.
In the production of bimetallic plate, it can be very difficult to achieve a sufficient heat energy balance for good bonding between the cladding and substrate. This is particularly the case where the plate is large in area, and/or relatively thin and/or has a relatively low thickness ratio of cladding to substrate. Under these conditions, it is found that loss of heat energy to the mold becomes a significant factor preventing the attainment of such energy balance, with this loss being from both the preheated substrate and from the molten alloy as it flows over the substrate. This loss can be exacerbated by delays between preheating the substrate and pouring the molten alloy to provide the cladding and/or by an unduly long period during which the molten alloy is poured. Also, it is found that loss of uniformity of heat energy balance, with resultant non-uniformity of bonding, can result from uncontrolled or irregular flow of molten alloy over the substrate, such as to give rise to an unduly long flow path and/or a reducing flow rate for the alloy.
SUMMARY OF THE INVENTION
We have found that substantially improved bimetallic plate can be produced by controlled casting of molten, alloy to provide the cladding. In the process of the invention, the cast alloy is caused to flow across the surface of the substrate along a controlled melt front which is advanced in a manner which, having regard to the temperature to which the substrate is preheated and the superheat temperature of the molten alloy, provides over substantially the entire surface of the substrate a heat energy balance within limits sufficient for achieving a diffusion bond between the cladding and substrate.
While not necessarily the case, the bimetallic plate may be square or other rectangular form. For ease of further description, a rectangular substrate and resultant plate is assumed in the following. Also for ease of description, directions across the substrate are designated as longitudinal, for the direction in which the melt front advances, and lateral for the direction in which the melt front extends transversely with respect to its direction of advance. However, while the substrate and resultant plate may have a longitudinal extent which is greater than its lateral extent, the converse may apply or the longitudinal and lateral extents may be substantially equal. Additionally, while the longitudinal direction of melt front advance can be substantially between longitudinally opposite edges of the substrate, longitudinal melt advance can be over part of the longitudinal extent of the substrate. Moreover, the lateral extent of the melt front and, hence, the width of cladding in that direction, may be over substantially the full lateral extent of the substrate or over a part of that extent.
In the process of the present invention, a controlled melt front is advanced in a manner providing required heat energy balance for bonding by at least one of the following features:
(a) causing the molten alloy to enter a mold cavity, in which the substrate is positioned, through a laterally disposed series of gates providing communication between a runner and the mold cavity, whereby the molten alloy forms a laterally extending melt front, and
(b) causing the melt front to advance longitudinally over the substrate at a rate which is substantially uniform across the lateral extent of the melt front.
The process of the invention preferably utilizes each of features (a) and (b).
Thus, according to the present invention, there is provided a process for the production of a composite bimetallic plate, wherein the process comprises the steps of:
(a) rendering a major surface of a substrate plate formed of a first metal substantially oxide-free;
(b) providing a suitable coating over said oxide-free major surface whereby said major surface is protected against oxidation;
(c) preheating the substrate plate to a sufficient temperature;
(d) positioning the substrate plate in a mold cavity of a mold with said major surface facing upwardly and substantially horizontally to thereby fill a lower portion of the depth of the mold cavity;
(e) securing the substrate plate in the mold cavity; and
(f) casting a cladding of a second metal over said major surface of the substrate plate to form, with the substrate plate, said bimetallic plate wherein said cladding is cast by pouring, at a sufficient superheated temperature, a melt of the second metal for flow of the melt into the mold cavity to fill an upper portion of the depth of the mold cavity,
wher
Bednarz Bernard
Brunton Robert Sidney
Dick Ian Robert
Goss Geoffrey Martin
Heijkoop Teunis
Commonwealth Scientific and Industrial Research Organisation of
Kerns Kevin P.
Ladas & Parry
Stoner Kiley
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