Metal fusion bonding – Process – Specific mode of heating or applying pressure
Reexamination Certificate
2000-12-19
2002-08-27
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Process
Specific mode of heating or applying pressure
C029S017300
Reexamination Certificate
active
06439451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of making an aluminum alloy plate for bearing by cladding a bonding layer comprising a pure aluminum or an aluminum alloy excluding Sn onto a bearing alloy layer comprising an aluminum alloy.
2. Description of the Prior Art
In making a bearing lined with an aluminum alloy (aluminum alloy bearing), a bearing alloy layer comprising an aluminum alloy containing Sn is generally bonded to a back metal with a bonding layer being interposed therebetween, so that a bimetal is made. The bonding layer comprises a pure aluminum or an aluminum alloy. The bimetal is then machined into an aluminum alloy bearing. The bonding layer is bonded to the bearing alloy layer prior to bonding of the bearing alloy layer to the back metal. The bonding layer is cladded onto the bearing alloy layer when bonded thereto. More specifically, a plate formed into the bearing alloy layer and a plate formed into the bonding layer are passed between a pair of flat rolls so that the plates are rolled down at a large reduction ratio such that the bonding layer is cladded onto the bearing alloy layer.
The aluminum alloy bearing is generally used for engines of automobiles or industrial machines since it has excellent fatigue resistance, wear resistance, etc. However, with recent advancement in the performance of engine, the bearing has necessitated a further improvement in the fatigue strength, wear resistance, etc. The bearing aluminum alloy has been changed from a relatively soft Al—Sn system to a hard Al—Sn—Si system or Al—Sn—Si—Mn system in order that the requirement may be met.
However, the bearing aluminum alloy of hard Al—Sn—Si system or Al—Sn—Si—Mn system has a low rolling workability of the aluminum alloy. Accordingly, there is a possibility that crack may occur when the bonding layer is cladded onto the bearing alloy layer. The crack occurs in both widthwise edges of the aluminum alloy plate formed into the bearing layer.
When a bonding layer plate is cladded on a bearing alloy layer plate so that both are bonded together, a higher bonding strength is ensured as the reduction ratio becomes high. Accordingly, the bonding layer plate is cladded on the bearing alloy layer plate at a reduction ratio of 40 to 50% when a relatively soft Al—Sn alloy is used for the bearing alloy layer. The reduction ratio is defined as [(plate thickness prior to rolling—plate thickness after rolling)/plate thickness prior to rolling]×100.
However, the Al—Sn—Si alloy or Al—Sn—Si—Mn alloy, each of which serves as the bearing alloy layer and has a low rolling workability, cannot withstand pressurization or cladding at such a high reduction ratio as mentioned above in order that occurrence of crack may be prevented for increase in the yield. Accordingly, since the bonding layer is cladded onto each layer of these bearing alloys at a low reduction ratio, the bonding strength between the bearing alloy layer and the bonding layer becomes insufficient.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a method of making an aluminum alloy plate for bearing in which even when an aluminum alloy having a low rolling workability is used for the bearing alloy layer, the bonding layer can be cladded onto the bearing alloy layer at a high reduction ratio while occurrence of crack is prevented, so that an aluminum alloy plate for bearing having a sufficient bonding strength can be made.
To achieve the object, the present invention provides a method of making an aluminum alloy plate for bearing which is made by cladding a bonding layer comprising a pure aluminum or an aluminum alloy excluding Sn onto a bearing alloy layer comprising an aluminum alloy. The method comprises the steps of fitting a concave portion of a first roll in a convex portion of a second roll, the first roll having both axial ends with large diameter portions respectively, the second roll having both axial ends with small diameter portions respectively, and passing superposed plates formed into the bearing alloy layer and the bonding layer respectively through a roll gap defined between the concave and convex portions and closed by the large diameter portions of the first roll so that the plates are rolled down at a reduction ratio of not less than 50% while both widthwise ends of each plate is restricted by the large diameter portions of the first roll respectively such that the bonding layer is cladded onto the bearing alloy layer.
According to the above-described method, the axial large diameter portions of the first roll closing both ends of the roll space restrict the widthwise ends of each plate, thereby preventing widthwise extension of each plate. Consequently, since occurrence of crack is reduced, both layers can be rolled down at a high reduction ratio of not less than 50% even when the aluminum alloy having a low rolling workability is used for the bearing alloy layer, whereupon the bonding strength between the plates can be increased.
In a first preferred form, a cast plate quenched at 3 to 6° C./sec. by a belt casting machine is used as the plate made into the bearing alloy. The belt casting machine performing casting between a pair of endless belts is known in the art. The known belt casting machine has a casting space defined to be horizontal or slightly inclined between substantially horizontal portions of the belts. The belts are driven to travel while being cooled. A molten metal is supplied into the casting space and cooled by the belts to be solidified into the shape of a plate. The solidified metal is then fed out of the casting space continuously.
The aforesaid belt casting machine of the movable mold type has a higher casting speed and productivity than continuous casting machines of the fixed mold type. Accordingly, even bearing manufacturers employ belt casting machines to cast aluminum alloy plates for a bearing alloy layer. However, the conventional belt casting machines have low cooling rates such that a cast plate is gradually cooled. As a result, since crystals become easy to coarsen or segregate, the rolling workability and bearing characteristic are deteriorated.
In view of the above-described problem, the inventors developed a belt casting machine with a water sprayer. A cast plate fed out of the casting space is quenched at a cooling rate of 3 to 6° C./sec. by water sprayed from the water sprayer so that the crystals are prevented from coarsening. However, since the machine carries out the belt casting method although being provided with the water sprayer, the casting speed becomes high but the cooling rate becomes low. Accordingly, it is difficult to completely prevent the crystals from being coarsened. Thus, the bearing alloy plate made by the belt casting machine with the water sprayer fairly improves a rolling workability but is still difficult to roll. Particularly when the plate contains Si, the cladding using ordinary flat rolls results in occurrence of crack on the widthwise edges of the plate.
The bonding layer can be cladded onto the bearing alloy plate cast by the belt casting machine by the method of the present invention without occurrence of crack, although the plate is fairly difficult to roll. In the casting by the above-described belt casting machine, Sn and Si segregate and an intermetallic compound with aluminum coarsens or segregates when the cooling rate is below 3° C./sec. As a result, the plastic workability such as rolling workability is reduced such that the fatigue resistance and wear resistance both as the bearing characteristics become unstable. When the cooling rate exceeds 6° C./sec., quenching results in segregation on the surface of the plate, whereupon milling the surface of the plate becomes difficult.
In the present invention, the following two novel aluminum alloys are particularly suitable as the bearing alloy layer on which the bonding layer is cladded. One is a novel aluminum alloy comprising, by mass, 3 to 40% Sn, 0.5 to 7% Si, 0.05 to 2% Fe, and balance of Al and un
Fujita Masahito
Kagohara Yukihiko
Shibayama Takayuki
Yamamoto Koichi
Browdy and Neimark
Daido Metal Company Ltd.
Elve M. Alexandra
McHenry Kevin
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