Metal treatment – Stock – Copper base
Reexamination Certificate
2001-11-13
2002-07-02
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Copper base
C420S477000, C420S479000, C420S480000, C420S481000, C420S482000, C420S483000
Reexamination Certificate
active
06413330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lead-free free-cutting copper alloys.
2. Prior Art
Among the copper alloys with a good machinability are bronze alloys such as that having the JIS designation H5111 BC6 and brass alloys such as those having the JIS designations H3250-C3604 and C3771. These alloys are enhanced in machinability by the addition of 1.0 to 6.0 percent, by weight, of lead, and provide an industrially satisfactory machinability. Because of their excellent machinability, those lead-contained copper alloys have been an important basic material for a variety of articles such as city water faucets, water supply/drainage metal fittings and valves.
However, the application of those lead-mixed alloys has been greatly limited in recent years, because lead contained therein is an environmental pollutant harmful to humans. That is, the lead-contained alloys pose a threat to human health and environmental hygiene because lead is contained in metallic vapor that is generated in the steps of processing those alloys at high temperatures, such as in melting and casting operations. There is also a concern that lead contained in water system metal fittings, valves, and other components made of those alloys will dissolve out into drinking water.
For these reasons, the United States and other advanced countries have been moving to tighten the standards for lead-contained copper alloys, drastically limiting the permissible level of lead in copper alloys in recent years. In Japan, too, the use of lead-contained alloys has been increasingly restricted, and there has been a growing call for development of free-cutting copper alloys with a low lead content.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a lead-free copper alloy which does not contain the machinability-improving element lead, yet is quite excellent in machinability and can be used as safe substitute for the conventional free cutting (easy-to-cut) copper alloy that has a high lead content, with concomitant environmental hygienic problems. The lead-free copper alloy of the present invention also permits recycling of chips without problems. Thus, the present invention presents a timely answer to the mounting call for restriction of lead-containing products.
It is an another object of the present invention to provide a lead-free copper alloy that has high corrosion resistance as well as excellent machinability, and is suitable as basic material for cutting works, forgings, castings, and other applications, thus having a very high practical value. The cutting works, forgings, castings, and other applications include city water faucets, water supply/drainage metal fittings, valves, stems, hot water supply pipe fittings, shaft and heat exchanger parts.
It is yet another object of the present invention to provide a lead-free copper alloy with high strength and wear resistance as well as machinability. This lead-free copper alloy is suitable as basic material for the manufacture of cutting works, forgings, castings, and other uses requiring high strength and wear resistance such as, for example, bearings, bolts, nuts, bushes, gears, sewing machine parts, and hydraulic system parts. Hence, this embodiment of the present invention has a very high practical value.
It is a further object of the present invention to provide a lead-free copper alloy with excellent high-temperature oxidation resistance as well as machinability, which alloy is suitable as basic material for the manufacture of cutting works, forgings, castings, and other uses where high thermal oxidation resistance is essential, e.g., nozzles for kerosene oil and gas heaters, burner heads, and gas nozzles for hot-water dispensers. Hence, this embodiment of the present invention too has a very high practical value.
The objects of the present inventions are achieved by provision of the following copper alloys:
A lead-free free-cutting copper alloy with an excellent machinability, which is composed of 69 to 79 percent, by weight, of copper, more than 3.0 to 4.0 percent or less, by weight, of silicon, and the remaining percent, by weight, of zinc, wherein the percent by weight of copper and silicon in the copper alloy satisfy the relationship; 55≦X−3Y≦70, wherein X is the percent, by weight, of copper, and Y is the percent, by weight, of silicon; and the copper alloy has a metal construction comprising multiple phases integrated to form a composite phase, wherein the composite phase is an &agr; phase matrix having a total phase area comprising not more than 5% of a &bgr; phase, and 5-70% of the total phase area is provided by at least one phase selected from the group consisting of a &ggr; phase, a &kgr; phase, and a &mgr; phase. For purpose of simplicity, this copper alloy will be hereinafter called the “first invention alloy”.
Lead does not form a solid solution in the matrix but instead disperses in a granular form to improve the machinability of an alloy. Silicon enhances the easy-to-cut property of an alloy by producing a gamma phase (in some cases, a kappa phase) in the structure of metal. That way, both act to improve alloy machinability, though they are quite different in their respective contributions to the properties of the alloy. On the basis of that recognition, silicon is added to the first invention alloy in place of lead so as to bring about a high level of machinability meeting industrial requirements. That is, the first invention alloy is improved in machinability through formation of a gamma phase with the addition of silicon.
The addition of less than 2.0 percent, by weight, of silicon cannot form a gamma phase sufficient to provide industrially satisfactory machinability. With increases above 2.0 weight-percent in the addition of silicon, the machinability improves. But with the addition of more than 4.0 percent, by weight, of silicon, the machinability will not improve proportionally. A problem is, however, that silicon has a high melting point and a low specific gravity and is also liable to oxidize. If silicon alone is fed in a simple substance into a furnace in an alloy melting step, silicon will float on the molten metal and be oxidized into oxides of silicon (or silicon oxide), hampering production of a silicon-containing copper alloy. In making an ingot of silicon-containing copper alloy, therefore, silicon is usually added in the form of a Cu—Si alloy, which boosts the production cost. In the light of the cost of making the alloy, too, it is not desirable to add silicon in a quantity exceeding the saturation point where machinability improvement levels off, i.e., 4.0 percent by weight. Experimentation has shown that when silicon is added in an amount of more than 3.0 percent and up to and including 4.0 percent, by weight, it is desirable to hold the content of copper to 69 to 79 percent, by weight, in consideration of its relation to the content of zinc in order to maintain the intrinsic properties of the Cu—Zn alloy. For this reason, the first invention alloy is composed of 69 to 79 percent, by weight, of copper and more than 3.0 percent and up to and including 4.0 percent, by weight, of silicon. It is stressed that the range of silicon content included, by weight, in the composition of the first invention alloy excludes 3 percent, by weight, of silicon. The addition of silicon, as specified above, improves not only the machinability but also the flow of the molten metal in casting, strength, wear resistance, resistance to stress corrosion cracking, high-temperature oxidation resistance. Also, the ductility and dezincification resistance will be improved to some extent.
A lead-free free-cutting copper alloy, also with an excellent machinability, which is composed of 69 to 79 percent, by weight, of copper; 2.0 to 4.0 percent, by weight, of silicon; at least one element selected from among 0.02 to 0.4 percent, by weight, of bismuth, 0.02 to 0.4 percent, by weight, of tellurium, and 0.02 to 0.4 percent, by weight, of selenium; and the remaining percent, by we
Griffin & Szipl, P.C.
Ip Sikyin
Sambo Copper Alloy Co., Ltd.
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