Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
2002-10-28
2004-07-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C428S553000, C428S564000, C428S677000, C384S912000
Reexamination Certificate
active
06767648
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a copper-based, sintered sliding material provided with a steel back metal layer, particularly a copper-based, sintered sliding material in which the strength of the steel back metal layer and the bearing characteristics of a sintered layer are enhanced, and relates to a method of producing the same.
In prior arts, a conventional copper-based, sintered sliding material has been, in general, produced by a method comprising the steps of: spreading a Cu-based alloy powder on a steel back metal; performing the primary sintering of them in a reducing atmosphere at a temperature of 800 to 950° C. for about 15 minutes; performing the primary rolling thereof so that a sintered layer may be compacted; performing the secondary sintering thereof under the same conditions as those of the primary sintering; and performing the secondary rolling thereof for the purposes of improving the strength and of adjusting the size thereof. Since this method is suitable for the mass production thereof and makes it possible to produce the sliding material at a low cost, the sliding material has been used to produce bearings used in the industries of a broad range.
Nowadays, there are such a tendency as a housing for mounting a bearing is made of a light alloy such as an aluminum alloy so as to meet the requirement of the light-weight-and-small-size design of a bearing device, and such another tendency as the bearing itself is made to have a thin thickness and a narrowed width for obtaining a low friction. On the other hand, the degree of fixing the bearing onto the housing depends on an interference (i.e. crush height), and it is necessary for the interference to have such a value as a radial stress applied onto the bearing is more than a predetermined level so as to prevent the bearing from being displaced in the housing while another stress occurring in the circumferential direction of the bearing due to the interference is not more than the yield point of the bearing (the steel back metal) so that the bearing may be prevented from being buckled.
SUMMARY OF THE INVENTION
However, as is often the case with a bearing device used in an internal combustion engine for a vehicle, there is such a case as the temperature range of the use of the bearing device is very large, for example, from a below-zero temperature (at the time of non-driving) to about 200° C. (during driving). The inventors of the invention have found that, in this case, since the difference in thermal expansion between the housing made of the light alloy and the bearing becomes large, it is necessary to make the interference large so that the fixing of the bearing may not be loosened even at the high temperature. In the case of making the interference large, there occurs such a fear as, in a bearing having a thin thickness or having a narrow width, the circumferential stress becomes so large that the buckling thereof is caused. Once the buckling occurs, a clearance between a shaft and the bearing is decreased with the result that the seizure thereof is apt to occur, and/or the radial stress applied thereto is decreased with the result that the bearing comes to rotate together with the shaft or that the bearing comes to be separated from the housing or that fretting occurs between the inner face of the housing and the back face of the bearing. On the other hand, the inventors of the invention have also found that, in another case of making the interference small, the radial stress applied to the bearing becomes so small that the above problem such as the rotation of both of the bearing and shaft or the separation of the bearing or the fretting etc. occurs similarly to the case of the buckling.
In order to enhance the buckling resistance of the bearing by increasing the strength of the steel back metal layer, it is thought to make the rolling reduction of a secondary rolling large so that the strength of the steel back metal layer may be raised because of the work hardening thereof. However, in the case of making the rolling reduction large, each of the steel back metal layer and the sintered layer made of Cu or Cu alloy becomes hard in hardness and brittle, so that the bearing comes to crack during the press working applied thereto or becomes inferior in workability. Further, in this case, the sliding performances such as conformability and foreign matter embeddability etc. are deteriorated due to the hardening of the Cu or Cu alloy of which the sintered layer is made, so that the seizure thereof is apt to occur. In addition, the sliding material is subjected to a deformation during the secondary rolling, so that the metal grains thereof come to have much strain. In general, a metal material with strained grains causes a recovery phenomenon even at a temperature less than the recrystallization temperature thereof, so that the strain is relieved although the complete release thereof does not occur. Thus, in a bearing used in an internal combustion engine in which the temperature is raised up to about 200° C., the recovery phenomenon is caused during the use thereof, due to which the circumferential length of the bearing is varied (reduced) when the strain put in the crystal grains at the secondary rolling is relieved, even at such a level of the interference as no buckling occurs at the time when the bearing is initially mounted in the housing so that the same problem as in the case where the bearing is buckled is caused. This problem occurs not only in the housing made of the light metal such as Al alloy but also in the housing made of a steel or a cast steel.
The invention is made in taking the above-explained circumstances of the prior art into consideration, and the first object of the invention is to provide a copper-based, sintered sliding material superior in sliding characteristics and workability in which the amount of decrease in the circumferential length of a bearing made of this sliding material is small when the bearing mounted in a housing is subjected to the use temperature thereof and which can keep a high yield point. The second object of the invention is to provide a method of producing the copper-based, sintered sliding material at a low cost.
According to the first aspect of the invention, there is provided a copper-based, sintered sliding material comprising a steel back metal layer and a sintered layer made of Cu or a Cu alloy which is bonded onto the steel back metal layer, the steel back metal layer having a hardness not less than 160 Hv and an elongation not less than 10%, the sintered layer having a hardness not more than 130 Hv and a grain size not more than 45 &mgr;m.
In this copper-based, sintered sliding material having the above constitution, the sintered layer made of Cu or the Cu alloy has such a relatively soft structure as to be not more than 130 Hv in hardness, so that the sliding characteristics such as conformability and foreign matter embeddability are superior. Further, since the grain size of the Cu or Cu alloy is not more than 45 &mgr;m, the sintered layer has a fine structure, so that the strength thereof becomes high although it is soft, with the result that the sintered layer becomes superior in fatigue resistance. The grain size used herein is measured in accordance with the method for estimating average grain size for wrought copper and copper alloy products which is defined in JIS H 0501.
On the other hand, since the steel back metal layer has the elongation not less than 10%, the strain in the crystal grains thereof is at a low level. Further, since the steel back metal layer has the hardness not less than 160 Hv, the yield point thereof becomes high, and the steel back metal layer can withstand a large circumferential stress when the sliding material is formed into a cylindrical bearing, so that no fear of the buckling of the bearing is caused. In addition, the steel back metal layer is previously subjected to a heat treatment for bringing about the recovery phenomenon thereof, there occurs no fear of decrease in the circumferenti
Fujita Masahito
Inoue Eisaku
Saitou Yasushi
Shibayama Takayuki
Daido Metal Company Ltd.
Jones Deborah
Savage Jason L
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