Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
2000-09-27
2002-10-29
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C164S486000, C164S481000
Reexamination Certificate
active
06471796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method and apparatus for continuously casting molten aluminum into a plate-shaped bearing alloy by belt casting means, and more particularly to such a casting method and apparatus in which crystals can be prevented from being coarsened.
2. Description of the Prior Art
As an apparatus for continuously casting a metal which melts at a relatively low temperature, for example, aluminum, aluminum alloys, zinc, etc., a belt casting machine has been known in which casting is carried out between a pair of endless belts. In the known belt casting machine, each belt is passed over or around a plurality of rollers. A horizontal or slightly inclined casting space is defined between substantially horizontal portions of the belts. The belts are driven by driving rollers so as to travel while being cooled by a cooling system. A molten metal is supplied into the casting space to be cooled by the belts, thereby solidifying into the shape of a plate. Plate-shaped materials are continuously fed out of the casting space. The aforesaid belt casting machine of the movable casting mold type is superior in a casting speed and accordingly in the productivity to a continuous casting machine of the fixed casting mold type.
A bearing lined with an aluminum bearing alloy, which is referred to as “aluminum alloy bearing,” is generally used for engines of automobiles or industrial machines. The aluminum alloy bearing is manufactured sequentially through steps of casting, rolling, cladding, heat treatment and machining. More specifically, molten metals are cast into the shape of a plate. The cast plate is rolled in the rolling step. The cast plate is then cladded on a steel sheet so that a bimetal is made. The bimetal is annealed so that the bonding strength between the cast plate and the steel sheet is improved. Thereafter, the bimetal is machined to be finally formed into a semi-cylindrical or cylindrical bearing.
Manufacturers of engine bearings have used the aforesaid belt casting machine for continuously casting the aluminum alloy into the cast plate to thereby improve the productivity. In the belt casting machine, however, a cooling rate for the cast plate is low since the casting speed is high. Thus, the belt casting machine assumes that a slow cooling state is obtained. As a result, coarsening and segregation of crystals such as crystallized Sn and Si are easy to occur in the aluminum alloy containing Sn, Si, etc. Further, in an aluminum alloy containing various elements for improvement of the bearing characteristic, too, crystals of the intermetallic compound are easy to be coarsened and to be segregated. The plasticity of the alloy is reduced when the crystals are segregated or coarsened in the aluminum alloy. As a result, cracks occur in the alloy in the subsequent rolling and cladding steps where plastic deformation processing is executed. Further, decrease in the fatigue strength and wear resistance of the alloy as the bearing characteristics reduces the effect of addition of various elements for the improvement of the bearing characteristics.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention is to provide a method and apparatus for continuous casting of aluminum bearing alloy in which coarsening and segregation of the crystals can be prevented when the aluminum bearing alloy is continuously cast into the shape of a plate.
According to a first feature of the invention, it is provided a method of continuous casting of a molten aluminum bearing alloy in which a casting space is defined between substantially parallel opposed portions of a pair of travelling endless belts and the molten aluminum bearing alloy is supplied into the casting space to be continuously cast into the shape of a plate. The method comprises the step of controlling a cooling rate &Dgr;T during solidification of the aluminum bearing alloy so that the cooling rate &Dgr;T ranges between 3 and 6° C./sec. where &Dgr;T=(T−500)/t, T is a temperature when the casting of the aluminum bearing alloy starts, and t is a cooling time in sec. between start of casting and the time when the temperature of the aluminum bearing alloy decreases to 500° C.
According to the above-described method, the cooling rate of 3 to 6° C./sec. is higher than one of the conventional belt casting machine, that is, 1 to 2° C./sec. When the aluminum alloy is solidified at such a high cooling rate, the crystal is not coarsened nor segregated. Further, occurrence of cracks can be prevented in the subsequent rolling and cladding. Additionally, the bearing characteristics can be prevented from being reduced.
In a second feature, the aluminum bearing alloy comprises, by mass, 3 to 40% Sn, 0.5 to 7% Si, 0.05 to 2% Fe, and the balance of Al and unavoidable impurities, and a ternary intermetallic compound of Al—SI—Fe is crystallized. In a third feature, the aluminum bearing alloy comprises, by mass, 3 to 40% Sn, 0.5 to 7% Si and 0.05 to 2% Fe and at least one or more of 0.01 to 3% each of Mn, V, Mo, Cr, Co, Ni and W, and the balance of Al and unavoidable impurities and a multi-element intermetallic compound of Al—SI—Fe containing said at least one or more of Mn, V, Mo, Cr, Co, Ni and W is crystallized.
In a fourth feature, the aluminum bearing alloy comprises at least one or more of 0.01 to 2% each of B, Ti and Zr. In a fifth feature, the aluminum bearing alloy comprises at least one or more of 0.1 to 5% each of Cu, Mg and Zn.
The technical background of the development of the aforesaid novel aluminum alloy will now be described. With recent development of high performance engines, engine bearings necessitate further improvement in the fatigue strength and wear resistance. Regarding the fatigue strength, elements such as Cu, Mn and V are added to the aluminum alloy to strengthen the latter. For the purpose of improvement in the wear resistance, JP-A-58-64332 discloses that Si is added to the aluminum alloy and the size and distribution of Si particles crystallized in the aluminum alloy are controlled. Further, JP-A-58-67841 discloses that Mn, Fe, Mo, Ni, etc. are added to the aluminum alloy so that an intermetallic compound between Mn etc. and Al is crystallized in the aluminum alloy. These two cases propose an improvement in the conformability and anti-seizure property of the aluminum alloy, thereby improving the wear resistance.
The above-noted JP-A-58-64332 and JP-A-58-67841 disclose that a desired effect can be achieved when the sizes of Si particles and the intermetallic compound range between 5 &mgr;m and 40 &mgr;m, respectively. Generally, hard particles contained in Al are uniformly distributed to be used for strengthening the aluminum alloy, and the effect is larger as the size of particles becomes small. In the aforesaid two cases, however, when the size of Si and the intermetallic compound is controlled so as to range between 5 &mgr;m and 40 &mgr;m, the strength of the Al matrix and accordingly the fatigue strength of the Al alloy are reduced as the size of Si and the intermetallic compound is relatively large. Thus, the anti-seizure property cannot be improved when crystallized particles are rendered small for improvement in the fatigue strength. On the other hand, the fatigue strength cannot be improved when the crystallized particles are rendered large for improvement in the anti-seizure property and accordingly in the wear resistance.
The inventors developed an Al alloy by crystallizing a ternary intermetallic compound of Al—SI—Fe or a multi-element intermetallic compound containing Al—SI—Fe as the base. The Al alloy can improve the anti-seizure property and wear resistance without reduction in the fatigue strength. The ternary intermetallic compound of Al—SI—Fe and the multi-element intermetallic compound containing Al—SI—Fe as the base are exceedingly stable, and its basic shape is not changed even by the heat treatment after cladding with a back metal. More specifically, Si crystallizes as a eutectic in the form like a thr
Fujita Masahito
Kagohara Yukihiko
Shibayama Takayuki
Yamamoto Koichi
Browdy and Neimark , P.L.L.C.
Combs Morillo Janelle
Daido Metal Company Ltd.
Wyszomierski George
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