Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2001-06-19
2003-09-02
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C428S553000
Reexamination Certificate
active
06613121
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a sintered material and a composite sintered contact component. More particularly, the present invention relates to a Cu—Al-based sintered material and a composite sintered contact component manufactured by use of the Cu—Al-based sintered material. The Cu—Al-based sintered material is obtained by increasing the sinterability of Al-bronze alloys widely used as copper alloys having excellent hardness, wear resistance, high-temperature oxidation resistance and corrosion resistance, and therefore is suited for use in manufacture of products with good dimensional accuracy.
BACKGROUND ART
Al-bronze alloys are widely used as copper alloys having high hardness, wear resistance, high-temperature oxidation resistance and corrosion resistance. However, when producing an Al-bronze alloy component from sintered material, abnormal expansion occurs during a sintering process, making it difficult to compress the material. For this reason, Al-bronze cast alloys and particularly, Cu—Al—Fe—Ni—Mn alloys are most commonly used and these alloys are stipulated as “AlBC1-4” by Japan Industrial Standard.
Related prior art is disclosed in Japanese Patent Publication (KOKAI) Gazette Nos. 56-152901 (1981) and 56-152902 (1981) according to which, 0.1 to 10 wt % Ti or 0.05 to 1.0 wt % P is added for the purpose of encouragement of sintering, thereby achieving Cu—Al-based sintered materials excellent in strength and toughness.
For example, bronze and lead-bronze based materials such as Cu—Sn—Pb are often used as copper-based sintered bearing materials, and double-layered sintered contact components in which one of such sintered materials is integral with an iron backing are well known. Such contact components are commonly used for the rollers incorporated in the base carrier of construction machines.
Also, steel bushings, to which carburization or induction hardening focused upon wear resistance has been applied, are commonly used in grease-lubricated circumstances as bearings (e.g., implement bushings for construction machines) used under higher bearing pressure and lower speed conditions. In particularly these implements, lubrication is getting worse under high bearing pressure, making an unpleasant abnormal noise in operation. Attempts to prevent abnormal noise have been made by use of high strength brass bushings or bushings made by further applying lubricant coating treatment to the above-described steel bushings.
An Al-bronze-based, double-layered, sintered contact component used in a high bearing pressure condition is disclosed in Japanese Patent Publication (KOKAI) Gazette No. 5-156388 (1993). According to this publication, an Al-bronze-based sintered alloy powder sheet, in which 3 to 8 wt % graphite (as a solid lubricating element), 5 to 13 wt % Al, 3 to 6 wt % Fe and 0.1 to 1.5 wt % Ti are dispersed, is bonded to a steel plate with a phosphor-bronze bonded layer therebetween, and at that time, pressure is applied during sintering at 800 to 950 degrees centigrade to provide high density for the Al-bronze-based sintered layer while firm bonding is ensured. In the sintered layer of the double-layered sintered contact component disclosed in the above publication, Ti is added in the form of hydrogenated Ti (TiH), while the Al
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coating of the Al powdery layer is reduced by hydrogen generated during sintering to increase sinterability. The sintered layer contains 18 to 25% by volume of voids and these voids are impregnated with a lubricant, thereby forming a contact component.
Al-bronze alloys widely used as high-strength, wear resistant copper-based alloys, however, have revealed the disadvantages that Al
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suspends during dissolution, causing poor fluidity and that they cause violent gas absorption, leading to a high coefficient of coagulation/contraction. For this reason, it is difficult to form sound cast products from Al-bronze alloys. Accordingly, a need exists for easy development of Al-bronze sintered alloys. However, as disclosed by Mitani et al. (“Revised and Enlarged Edition of Powder Metallurgy” pp. 79-82; pp. 258-260 issued by Corona Publishing Co., Ltd. (Sep. 10, 1985)), sound products having good compactness and dimensional accuracy cannot be produced from Cu—Al-based sintered materials since considerable expanding phenomenon emerges during sintering.
Hashimoto et. al. have reported an Al adding process in which compaction is carried out by sintering a Cu—Al-based alloy powder containing 6.54 wt % Al or 9.92 wt % Al at a high temperature of 1,000 degrees centigrade (“Powder and Powder Metallurgy”, Vol. 29, No. 6, p. 211 (1982)). This process also suffers from the problem that an extremely strong degree of springback occurs when a compact particularly formed from a mixture of electrolytic Cu and alloy powder is taken out of a die with the result that the green compact is substantially broken.
In addition, as pointed out in the above report written by Mitani et. al., the techniques disclosed in the aforesaid Japanese Publication Nos. 56-152901, 56-152902, which use a mixed powder or alloy powder containing, as a master alloy powder, a sintered material having a high concentration of Al (6 to 9 wt %), is directed to avoiding eutectic reaction at a temperature of 548 degrees of centigrade shown in the Cu—Al phase diagram, but have revealed such a problem that tendency for the springback of the compact is high and the alloy powder is hard, which make it difficult to increase compact density. Especially, a higher degree of springback leads to damage to the compact when it is removed from the die, resulting in a considerable increase in the percentage of defective products.
It is conceivable that springback may be reduced by sintering a compact in which the sintered material structure is adjusted to consist of an alpha single phase region by use of the above-described Cu—Al alloy powder and by utilizing the sinter promoting action of Ti and P which occurs during sintering. However, where a compact formed from Al or an Al alloy powder is sintered, the eutectic reaction is involved in sintering so that the sinter promoting action of Ti and P cannot be utilized without arrangement and as a result, there arises a need for an addition of other elements as a third element and its effect has to be studied.
This is apparent from the fact that as disclosed in Japanese Patent Publication No. 5-156388, a Cu—Al-based sintered contact material, in which 0.1 to 1.5 wt % TiH is added to a powder blend containing a pure Al powder to improve sinterability, has 18 to 25% by volume of voids in heat-sintering at a pressure of 5 kg/cm
2
or less so that sufficient compactness cannot be achieved. Of course, the compactness of the sintered body can be achieved by applying increased pressure like the hot-press, but the application of increased pressure is disadvantageous in view of productivity as well as cost performance and, moreover, causes difficulty in producing sintered products of more intricate shape.
The double-layered sintered contact component of Japanese Patent Publication No. 5-156388 in which an Al bronze based sintered contact material containing 3 to 8 wt % graphite is integrally bonded to a metal backing with a phosphor bronze layer therebetween cannot avoid the increased cost of the sintering and/or sinter bonding process during which pressure is applied to cope with the above-described emergence of abnormal expansion during sintering. In addition, sinterability further decreases in the case of sintered metal bodies containing large amounts of solid lubricant such as graphite, and it is obvious that if high density and high hardness cannot be achieved in the sintered material, wear rapidly occurs in applications to implement bushings for construction machines which are subjected to use under an extremely high bearing pressure condition or a condition susceptible to a shortage of lubricant.
The Cu—Sn—Pb lead bronze based sintered contact materials, which are commonly used for manufacturing rollers of the base carrier of construction machines,
Takayama Takemori
Tanaka Yoshikiyo
Komatsu Ltd.
Mai Ngoclan
Rader & Fishman & Grauer, PLLC
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