Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2000-08-23
2002-12-10
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
Reexamination Certificate
active
06491437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plain bearing and a producing method thereof.
2. Brief Description of the Art
There has been known a plain bearing in which a bearing alloy layer is provided on a back metal and an overlay layer is provided on the bearing alloy layer thereby providing the bearing with improved properties of conformability and embeddability for foreign substances, the overlay layer consisting of a soft material such as a Pb—Sn alloy. In the case where the bearing alloy layer is of a copper alloy system, there has been provided a hard intermediate layer made of Ni, for example, between the bearing alloy layer and the overlay layer in order to prevent a compositional change of the overlay layer due to diffusion of alloy components of the overlay layer into the bearing alloy layer. Also in the case where the bearing alloy layer is of an aluminum system, there has been provided a hard intermediate layer made of Ni, for example, between the bearing alloy layer and the overlay layer in order to securely bond the both layers. However, in the case where the overlay layer wears to expose the hard intermediate layer over a broad area with the operation of the bearing, a mating shaft becomes to be in direct sliding-contact with the hard intermediate layer resulting in that seizure is liable to occur quickly. Thus, there have been known various techniques which were proposed in order to keep anti-seizure property of the composite plain bearings, according to which the bearing alloy layer is provided with an uneven inner surface and the intermediate layer is formed on the bearing alloy layer so as to follow the uneven inner surface and also have an identical uneven surface thereto, whereby, even if the overlay layer formed on the intermediate layer wears to expose the intermediate layer, the soft overlay layer will partially remain in recesses of the uneven surface of the intermediate layer.
According to an invention of JP-A-60-205014, for example, when producing a composite plain bearing having a back metal, a bearing alloy layer, an intermediate layer and an overlay layer, a spiral groove(s) is formed circumferentially on the inner surface of the bearing alloy layer by the boring machining thereby providing an uneven surface to the bearing alloy layer, and subsequently the intermediate layer and the overlay layer are formed on the bearing alloy layer in this order.
According to another invention of JP-A-62-124321, when producing a composite plain bearing having a back metal, a bearing alloy layer, an intermediate layer and an overlay layer, the inner surface of the bearing alloy layer is subjected to a shot peening treatment with ceramic particles to form an uneven surface, and subsequently the intermediate layer and the overlay layer are formed on the bearing alloy layer in this order.
According to still another invention of JP-A-62-283216, when producing a composite plain bearing having a back metal, a bearing alloy layer, an intermediate layer and an overlay layer, the inner surface of the bearing alloy layer is subjected to an electrolytic etching treatment to form recesses each having 5 &mgr;m of depth, and subsequently the intermediate layer having 0.3 &mgr;m of depth and the overlay layer having 5 &mgr;m of depth are formed on the bearing alloy layer in this order.
But, in the case of the uneven surface formed by the boring machining, because of circumferentially extended parallel grooves thereon, when the overlay layer wears, there will appear a stripe pattern surface state consisting of a combination of linear material zones which extend circumferentially and are parts of the intermediate layer and the overlay layer. Whereas, when a foreign substance enters between the bearing and the shaft, a long scratch is formed on the linear overlay material zones resulting in deteriorated anti-seizure property and/or occurrence of fatigue cracks which might extend circumferentially.
In the case of the uneven surface formed by the shot peening, because the surface of the bearing alloy layer is work-hardened, the bearing can not have desired bearing properties including the sliding-contact property.
Further, in the case of the uneven surface formed by the electrolytic etching, because the etching treatment relies on the characteristics that grain boundaries are preferentially eroded while inter-grains are eroded slowly, the etched surface state is limited to have forms of crystal grains of the bearing alloy, so that it is hard to have deep recesses with around 10 &mgr;m while shallow recesses with not more than around 5 &mgr;m may be possible. Thus, in the case where the intermediate layer is provided between the bearing alloy layer and the overlay layer to have an enough large thickness so as to well exhibit the above mentioned functions thereof, as schematically shown in
FIG. 6
, when a wear loss advances to the depth level Y, the intermediate layer
4
is exposed through the almost overall sliding-contact surface. In order to avoid this, it is necessary to make the intermediate layer extremely thinner. Although the prior art of JP-A-62-283216 teaches to form 0.3 &mgr;m of the intermediate layer, it will be hard to absolutely coat the bearing alloy layer with such a very thin intermediate layer resulting in lack of reliability.
BRIEF SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a plain bearing which can be obtained by an etching treatment with utilization of a mask so that an inner surface of a bearing alloy layer can be an optional form of an uneven surface having a fully deep recess without changing properties of the bearing alloy layer.
According to a first aspect of the invention, there is provided the plain bearing which comprises a back metal, a bearing alloy layer, an intermediate layer and an overlay layer provided on the intermediate layer, wherein the bearing alloy layer has a textured uneven surface formed by the etching treatment and the intermediate layer is formed on the uneven surface of the bearing alloy layer so as to follow the textured uneven surface so that the intermediate layer has also a textured uneven surface.
According to the plain bearing, when the overlay layer wears to expose the hard intermediate layer, there appears a surface state that a number of exposed protrusions of the intermediate layer and the soft overlay layer being filled in the recess coexist because the intermediate layer has the uneven surface, whereby the hard intermediate layer can be prevented to expose through a broad area thereby preventing occurrence of seizure.
Also according to the plain bearing, because the textured uneven surface of the bearing alloy layer can be formed by the etching treatment to have an exactly identical to an etching pattern of the mask, the uneven surface state can be optionally formed.
For example, the protrusions of the textured uneven surface in the intermediate layer as well as the bearing alloy layer may be a form of square, circle or lozenge cross-section, or ridges extending in an optional direction, for example, circumferentially, perpendicularly or obliquely to the circumference.
The mask may be of pad printing, screen printing, a photoresist film and so on.
According to a second aspect of the invention, there is provided a method of producing a plain bearing which comprises a back metal, a bearing alloy layer provided on the inner surface of the back metal, an intermediate layer provided on the bearing alloy layer and an overlay layer provided on the intermediate layer, the method comprising the steps of:
coating the inner surface of the bearing alloy layer with a masking material defining a surface area part of the bearing alloy layer to be etched;
etching the coated inner surface of the bearing alloy layer to form a textured uneven surface comprising a number of protrusions;
removing the coated masking material from the inner surface of the bearing alloy layer;
providing the intermediate layer on the etched inner surface of the bearing allo
Ishikawa Hideo
Kawachi Toshiaki
Shibayama Takayuki
Yamada Tatsuo
Daido Metal Company Ltd.
Footland Lenard A.
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