Copper-based sliding alloy

Details Copper-based sliding alloy Copper-based sliding alloy

1999-04-01

2001-10-16

Zimmerman, John J. (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Having metal particles

C428S564000, C428S677000, C419S011000, C419S013000, C419S014000, C419S019000, C075S231000, C075S232000, C075S236000, C075S243000, C075S246000, C420S474000, C420S475000, C420S491000, C384S901000, C384S912000, C384S913000

Reexamination Certificate

active

06303235

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a copper-based sliding alloy excellent in wear resistance and, more particularly, to a copper-based sliding alloy applied to sliding bearings, valve plates and the like.
A technique related to copper-based sliding alloys with increased wear resistance is disclosed in JP-A-4-88137.
In this conventional technique, a sliding alloy is obtained by mixing solid lubricants, such as graphite, molybdenum disulfide and lead, and hard particles of SiC, SiO
2
, Si
3
N
4
, Al
2
O
3
, TiC, WC, TiN, etc. with copper alloy powder and by hot extruding the mixture. It is disclosed that a sliding alloy excellent in wear resistance and anti-seizure property is obtained by blending appropriate amounts of these lubricants and hard particles in a well-balanced manner.
However, higher performance such as sliding property has been required in recent sliding materials. In the above conventional technique which involves dispersing lubricants and hard particles in a matrix of copper, anti-seizure property is obtained from solid lubricants and wear resistance is obtained from hard particles. Wear resistance and anti-seizure property are improved by the contents of solid lubricants and hard particles. For this reason, anti-seizure property deteriorates when the content of hard particles is raised to increase wear resistance, whereas wear resistance deteriorates when the content of solid lubricants is raised to improve anti-seizure property. Therefore, there have existed limitations to the improvement of these properties.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a copper-based sliding alloy excellent in wear resistance and anti-seizure property, which is obtained by dispersing a phase of lead in a matrix of copper and locating hard particles in the dispersed lead phase.
According to one aspect of the present invention, there is provided a copper-based alloy which comprises a phase of 2 to 30 wt. % lead, 0.1 to 6 vol. % hard particles having an average particle size of 5 to 25 &mgr;m, and a matrix selected from the group consisting of copper and copper alloy. The above hard particles are included in the lead phase, which is dispersed in the matrix.
The copper alloy preferably contains 0.5 to 15 wt. % tin. The effect of tin on an increase in alloy strength cannot be obtained when the tin content is less than 0.5 wt. %. Furthermore, when the tin content exceeds 15 wt. %, many Cu—Sn compounds are formed, making the copper alloy brittle. Further, in this case thermal conductivity also decreases, resulting in a decrease in anti-seizure property.
The matrix may be strengthened by adding at least one kind selected from the group consisting of nickel, iron, aluminum, zinc and manganese in amounts of up to 40 wt. % in total to the copper alloy. Furthermore, wear resistance may be increased by adding the solid lubricants of MOS
2
, WS
2
, BN and graphite that have self-lubricity.
Lead forms a lead phase dispersed in the matrix of the copper alloy, which lead phase brings about wear resistance and anti-seizure property. The improvement in anti-seizure property cannot be expected when the lead content is less than 2 wt. % because it becomes impossible for such Pb phase to contain hard particles therein. Furthermore, strength decreases when the lead content exceeds 30 wt. %. Therefore, the lead content should be 2 to 30 wt. % and, preferably 5 to 25 wt. %.
It is desirable that the lead phase be uniformly dispersed. Lead is present in discontinuous granular form when its content is low, whereas it is present in continuous network form when its content is high. However, either of the two forms is good.
Oxides, nitrides, carbides, etc. of such metals as SiC, SiO
2
, Si
3
N
4
, Al
2
O
3
, TiC, WC and TiN may be used as hard particles and the average particle size may be 5 to 25 &mgr;m. When the average particle size exceeds 25 &mgr;m, it is difficult to make hard particles included in the lead phase especially with low lead contents and hard particles have a strong tendency to attack a mating member with which the copper-based alloy mates. When the average particle size is less than 5 &mgr;m, it is difficult to disperse hard particles. For these reasons, the average particle size of hard particles may be 5 to 25 &mgr;m and preferably 8 to 20 &mgr;m. Especially when the average particle size is in the range of 10 to 18 &mgr;m, it is easy to make hard particles included into the lead phase and, at the same time, hard particles exhibit such an action as to make the sliding surface of the mating member smooth by leveling its roughness.
Hard particles are present in such a manner that they are embraced in the lead phase dispersed in the matrix of the copper alloy. Therefore, as shown in
FIG. 4
, a soft lead phase
3
serves as a cushion on the sliding surface, and the attack on the mating member by a hard particle
2
exposed on the surface of a matrix
1
is reduced.
When there is no hard particle
2
in the lead phase
3
, lead is apt to be carried away onto the sliding surface during sliding as shown in FIG.
5
. In the present invention, however, the carrying-away of lead is prevented by the presence of the hard particle
2
. Even when the hard particle is carried away, another hard particle is again captured by the lead phase because of its embeddability and, therefore, abrasive wear is reduced.
Because hard particles are incorporated into the lead phase, wear resistance is excellent and anti-seizure property is improved. For this reason, the quantity of hard particles, which depends on the lead content, is preferably 0.1 to 6 vol. %. When the quantity of hard particles is less than 0.1 vol. %, the presence of hard particles is not effective in improving wear resistance. When the quantity of hard particles exceeds 6 vol. %, hard particles that are not embraced by the lead phase increase and their attack on the mating member increases. The quantity of hard particles, i.e., 0.1 to 6 vol. %, which varies depending on the composition and lead content of the copper alloy, corresponds to about 0.03 to 2.2 wt. % when it is converted to weight % in the case of SiC, for example.
The powder sintering method is desirable as a method for producing the alloy of the present invention. In a case of a hot extrusion method, the lead phase is elongated in the extrusion direction, with the result that an orientation is generated and, at the same time, it occurs such an undesirable state as hard particles are less apt to be embraced by the lead phase.
In addition to alloy powder, mixed powder may be used as copper-based powder. A green compact-sintering method is preferable for sliding materials composed of a copper-based sliding alloy alone, which sliding materials are used for valve plates and shoes of hydraulic pump and motor, for example. In a sliding material formed by bonding a copper-based sliding alloy to a back metal, such as a sliding bearing, a sintering method is preferable in which sintering is performed after disposing a raw material powder onto the back metal. A sliding material with increased strength can be obtained when the density thereof is increased by performing rolling before and/or after the sintering thereof.
In the present invention, a copper-based sliding alloy having superior wear resistance can be obtained because the copper-based alloy consists of a phase of 2 to 30 wt. % lead, 0.1 to 6 vol. % hard particles having an average particle size of 5 to 25 &mgr;m, and a matrix selected from the group consisting of copper and copper alloy. The above hard particles are included in the lead phase, which is dispersed in the matrix.


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patent: 5256494 (1993-10-01), Tanaka et al.
patent: 5279638 (1994-01-01), Asada et al.
patent: 5326384 (1994-07-01), Asada et al.
patent: 5938864 (1999-08-01), Tomikawa et al.
patent: 2045806 (1980-11-01), None
patent: 04-088137 (1992-03-01), None
patent: 10-46272 (1998-02-01), None
patent: 10-46271 (1998-02-01), None

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