Stock material or miscellaneous articles – All metal or with adjacent metals – Laterally noncoextensive components
Reexamination Certificate
2002-11-01
2004-06-22
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Laterally noncoextensive components
C428S553000, C428S674000, C428S677000, C384S912000
Reexamination Certificate
active
06753092
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer material for manufacturing a plain bearing etc. and a manufacturing method of the same, and more particularly to a multilayer material whose obverse material bonded to a backing material has an orientated dendrite structure and a manufacturing method of the same.
As conventional manufacturing methods of a multilayer material for a bearing having such a structure as a copper-based bearing alloy which is an obverse material is bonded to a steel strip which is a backing material, there are a sintering method and a continuous-strip casting method.
In the sintering method, a copper alloy powder to be sintered for forming a copper-based bearing alloy is spread at a predetermined thickness onto a steel strip, they being then heated in a reducing atmosphere at 850°-900° C. so that a primary sintering thereof may be performed, thereafter they being subjected to rolling so that the density of the copper alloy powder layer may become 100%, and then they are subjected to a second sintering under the same sintering conditions as above, thereby completing the multilayer material.
In the continuous-strip casting method, a steel strip is bent into an L shape at both sides thereof so that a channel (groove) shape may be formed, it being then preheated in a reducing atmosphere up to 1,000° C., a molten copper alloy being poured into the channel while cooling the poured copper alloy from the back side thereof by oil-quenching the back side of the steel strip, thereby unidirectionally solidifying the poured copper alloy, then the L-shaped bent portions at both of the channel sides being removed by cutting while removing unnecessary portions on the copper alloy surface by grinding, and at the final step the steel strip made to have a martensitic structure by the oil-quenching is softened by heating at 800° C., whereby the multilayer material is completed.
In the sintering method, it is necessary to prepare facilities for the primary and secondary sintering, rolling, etc., and in the continuous-strip casting method it is also necessary to prepare facilities for forming the channel, preheating, etc. Thus, each of the methods requires a very long production line.
Further, in the sintering method there is such problems as a bonding strength between the copper alloy layer (obverse material) and the steel strip (backing material) is low and as the copper alloy structure becomes coarse in grain size together with the decrease in the strength due to the secondary sintering. On the other hand, in the continuous-strip casting method, there are such problems as the steel strip is hardened due to the quenching performed at the back side of the steel strip although the bonding strength between the copper alloy and the steel strip becomes high and as the copper alloy structure becomes coarse in grain size together with decrease in the strength due to a tempering performed thereafter for the softening thereof.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above problems of the prior art, and an object of the invention is to provide a multilayer material having a densified and fine structure and a high strength, and a manufacturing method of the same.
According to the first aspect of the invention, there is provided a multilayer material comprising a backing material and an obverse material of a metal different from the backing material, the obverse material being bonded to the backing material, the obverse material being provided with a rapidly solidified dendrite structure extending substantially vertically to the backing material, a grain size not more than 0.02 mm in a cutting plane in parallel to the backing material surface and/or a dendrite arm spacing not more than 0.02 mm in another cutting plane vertical to the backing material.
According to the second aspect of the invention, there is provided a method of producing the multilayer material comprising the steps of: spreading on a backing material a powder of a metal different from the backing material; irradiating the metal powder with laser beams having an energy density of 10-100 kW/cm
2
so that the metal powder is locally melted, while shifting successively the laser beams; and cooling just after the melting the melted portion from the back side of the backing material so that the melted portion is rapidly cooled and solidified.
A laser is suitable for the local heating, and good bonding between the obverse material and the backing material can be obtained by locally heating and melting the metal powder for bonding the melted metal to the backing material, and this local heating and melting can make the thermal influence on the other portions small. Insofar as the locally heated zone is concerned, the cooling of the heated portion can be more readily controlled. As regard the laser, it is preferred to use a semiconductor laser having a superior conversion efficiency of energy.
On the other hand, the copper-based alloy is one of materials having superior characteristics as a bearing alloy, and has a good wettability to a steel back metal and a superior bondability to steel back metal. Oxides present on the surfaces of copper-based alloy powder can reduce the reflection of the laser beam and can enhance the beam absorbency. The wavelength of the laser beams emitted from the semiconductor laser is 0.8-1.1 &mgr;m, which provides the enhanced absorbency for the copper-based alloy. That is, the combination of the copper-based alloy with the semiconductor laser is most preferable for the practice of the present manufacturing method.
In the multilayer-manufacturing method of the invention, a metal powder
11
is spread, as shown in
FIG. 2
, onto a backing material
10
, and then the metal powder is irradiated with laser beams
5
a
. The metal powder in the portion irradiated with the laser beam
5
a
is instantaneously melted upon absorption of the laser beams
5
a
and changes into a sphere
11
a
by surface tension, as shown in
FIG. 3
, where the heating rate because of the laser beams becomes 800° C./sec or more. The molten portion in the state of the sphere
11
a
is, at the next moment, spread on the surface of the backing material
10
by gravity and is changed into a semi-sphere
11
b
, as shown in
FIG. 4
, while being cooled from the bottom side of the semi-sphere
11
b
through the backing material
10
, so that the solidification proceeds upwards from the bottom side and a dendrite structure comes to extend vertically from the backing material
10
.
Thus, in the method of the invention, the bimetal material (multilayer material) can be produced by the steps of spreading the metal powder onto the backing material, melting it by the laser beams, and quenching it, so that it becomes unnecessary to provide such facilities for the primary sintering, secondary sintering, rolling, etc. as to be used in the conventional sintering method, or it becomes unnecessary to provide such large-scale facilities for melting the metal and for cooling much amount of molten metal poured onto the steel strip as to be used in the continuous-strip casting method, whereby it becomes possible to shorten the production line. Further, since the metal powder spread on the backing material is locally melted rapidly and is successively cooled rapidly, the structure of the obverse material is densified and fine.
In the multilayer-manufacturing method of the invention, the energy density of the laser beams for bring about proper melting and solidifying conditions is made to be 10-100 kW/cm
2
. In a case where the energy density is less than 10 kW/cm
2
, the metal powder spread on the backing metal is not melted, whereas in another case where an energy density is more than 100 kW/cm
2
, even the backing material is melted, resulting in failure in forming the bimetal. Thus, in the energy density range of 10 to 100 kW/cm
2
, it becomes possible to obtain the bimetal of the obverse material and the backing material while keeping the proper bonding state between them.
In the mult
Fujita Masahito
Inoue Eisaku
Shibayama Takayuki
Browdy and Neimark , P.L.L.C.
Daido Metal Company Ltd.
Jones Deborah
Savage Jason L.
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