Sliding bearing and its production method

Details Sliding bearing and its production method Sliding bearing and its production method

2000-07-07

2001-10-30

Koehler, Robert R. (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

C205S149000, C205S238000, C205S261000, C384S912000, C428S643000, C428S644000, C428S650000, C428S674000, C428S675000, C428S680000, C428S926000, C428S935000, C508S103000

Reexamination Certificate

active

06309759

ABSTRACT:

BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a sliding bearing, more particularly to a sliding bearing which comprises; a bearing-alloy layer referred to as the lining and consisting of copper-lead alloy or an aluminum alloy; and an overlay, which consists of a soft-alloy plating layer and is deposited on the lining to impart compatibility; and a Ni plating barrier layer and the like occasionally formed between the lining and the overlay. The present invention also relates to a method for producing the sliding bearing.
2. Description of Related Art
The sliding bearing described above is used mainly for the journal portion of a crankshaft, or the big end of a connecting rod of an internal combustion engine. Lead alloys are mainly used as the overlay and, occasionally, tin alloys.
One of the present applicants has succeeded in improving the composition of the lead overlay alloy as seen in German Patent No. 3000379 and improving the crystal orientation as seen in Japanese Unexamined Patent Publication (kokai) No. 8-20893.
Since lead is an environmental pollutant, discontinuance of its use or reduction in the amount of its use is requied. A development for avoiding the use of lead as the overlay is directed towards bonding such tribological material as MoS
2
with resin to form the overlay film. In addition, one of the present applications proposed in European Patent Publication No. 0795693A2 a Cu—Ag alloy which may not necessitate an overlay.
Incidentally, bismuth is a low-melting point metal as lead is. Bismuth is harder and more brittle than lead. Specifically, the hardness Hv
0.2
of lead is 5, while the hardness Hv
0.2
of bismuth is 10. The electro-plating, which is frequency used in the formation of an overlay, hardens the resultant layer due to absorption of hydrogen. That is, the hardness Hv
0.2
of electro-plated lead is 10, while the hardness Hv
0.2
of conventionally electro-plated bismuth is approximately 20. Such property of bismuth is inappropriate to attain fatigue resistance and compatibility of the sliding material. Bismuth has, therefore, not been used for the sliding material.
Meanwhile, the low-melting property of bismuth is utilized in the bismuth-based soldering alloy or the bismuth-based core of a mold. Bismuth is also used for semiconductor material, electronic material, optical recording media (for example, Japanese Unexamined Patent Publication No. 4-51742), and magnet material (Mn—Bi magnet). This recording medium is prepared by sputtering.
The present inventors made extensive researches into the replacement of lead with bismuth, in an attempt to utilize the better corrosion resistance of bismuth in acidic solution than that of lead and to avoid the toxicity of lead.
SUMMARY OF INVENTION
It is an object of the present invention to discover bismuth material which exhibits the fatigue resistance and compatibility required for an overlay, and to provide an improved sliding bearing.
It is also an object of the present invention to provide a method for producing a sliding bearing which comprises a bismuth or bismuth-alloy overlay, the crystals of which are so oriented that the fatigue resistance and compatibility are outstandingly improved as compared with essentially random-oriented bismuth crystals or essentially, or completely, single crystalline bismuth crystals.
The present invention involves a discovery that the hard and brittle properties of bismuth can be ameliorated to such a level that they present no serious problem by means of controlling the orientation of bismuth crystals.
The sliding bearing proposed by the present invention comprises a lining and a bismuth or bismuth-alloy overlay formed on the lining with or without the intermediary of a barrier layer, characterized in that the relative ratio of the X-ray diffraction intensity I
[hkl]
defined below satifies the following (a) and (b):
(a) the relative ratio of the X-ray diffraction intensity I
[hkl]
of planes other than {012} is from 0.2 to 5 times as high as the ratio of the X-ray diffraction intensity I
[012]
, namely, 0.2I
[012]
≦I
[hkl]
≦5I
[012]
(b) the relative ratio of the X-ray diffraction intensity I
[hkl]
of three or more planes other than {012} falls within a range from 0.5 to 2 times as high as the relative ratio of the X-ray diffraction intensity I
[012]
, namely, 0.5I
[012]
≦I
[hkl]
≦2I
[012]
.
The definition of the relative ratio of the X-ray diffraction intensity I
[hkl]
is as follows: the {hkl} planes of bismith crystals of standard powder samples having random orientation indicate the X-ray diffraction intensity Rp (hkl); the {hkl} planes of bismuth crystals of said bismuth or bismuth-alloy overlay indicate the X-ray diffraction intensity R
O/L
(hkl); the ratio of both intensities is expressed by K (hkl)=R
O/L
(hkl)/Rp (hkl); the ratio K (012), namely, K (hkl) of the {012} plane and the K (hkl) of the X-ray diffraction intensity at the {hkl} plane are converted to the ratio of the X-ray diffraction intensity I
[hkl]
=K(hkl)/K(012).
The method for producing a sliding bearing according to the present invention comprises the steps of:
preparing a backing metal in the form of a strip;
preparing a lining in the form of a strip consisting of one material selected from the group consisting of an aluminum bearing-alloy and a copper bearing-alloy;
bringing said lining into contact with an electrolytic solution which contains methanesulfonic acid and bismuth methane sulfonate; and,
cathodically depositing bismuth on said lining.
Another electrolytic solution may contain sulfuric acid and bismuth sulfate.
In one aspect of the present invention, there is provided use of bismuth or bismuth alloy satisfying the conditions (a) and (b) mentioned above to an overlay of a sliding bearing.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention is described hereinafter in detail.
Bismuth is a rhombohedral crystal which is equivalent to a hexagonal crystal. Generally, the Miller index of the hexagonal crystal is expressed by four parameters (h, k, i, l). Here, h, k and i indicate the a
1,2,3
axes, respectively. The symbol “l” indicates the index of the c axis. Since the relationship h+k=−i is established in the Bi crystal, the parameter i is omitted, and the three parameters (h k l) are used to define the lattice planes of a bismuth crystal.
The Bi or Bi alloy layer is collectively referred to as the “Bi layer” except for the description of their composition. The Bi layer has an intermediate orientation between the completely random one such as that of the fine powder and a particular orientation such as that of the single crystal.
The orientation is evaluated as follows.
First, the Bi crystals having completely random orientation such as the powder are subjected to the X-ray diffraction. The resultant diffraction intensity of the respective planes is Rp (hkl). Likewise, the Bi crystals of an overlay are subjected to the X-ray diffraction. The resultant diffraction intensity of the respective planes is R
O/L
(hkl). Then, their ration K (hkl)=R
O/L
(hkl)/Rp (hkl) is calculated. In the case of K (hkl) )
1
, it turns out that the Bi crystals of an overlay are oriented in (hkl).
Note that there are two K (hkl) of the Bi crystals, i.e., K(hkl) of {012} and K(hkl) of the planes other than {012}. Their relative magnitude is calculated as the ratio I
[hkl]
=K(hkl)/K (012). If I
[hkl]
≡0, it turns out that a {012} single crystal is formed. On the other hand, if I
[hkl]
>>1, it turns out that (hkl) crystals are intensely oriented. If K (012)=1, and K (hkl)=1, the Bi crystals are random or are completely non-oriented. In this case, I
[hkl]
is 1 for each (hkl) plane. ON the contrary, even if I
[hkl]
is 1 for s

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