Metal treatment – Stock – Copper base
Reexamination Certificate
2000-04-04
2001-08-28
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Copper base
C420S496000
Reexamination Certificate
active
06280541
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates to a seamless copper alloy pipe having high 0.2% proof strength and fatigue strength which is mainly used for a heat transfer pipe of a heat exchanger and especially relates to said pipe which can be used as a heat transfer pipe when HFC-type fluorocarbon is used as a heating medium.
Discussion of the Background:
In general, a seamless pipe of phosphorus deoxidized copper has been used as a heat transfer pipe of a heat exchanger. In order to assemble the pipe of phosphorus deoxidized copper above to a heat transfer pipe of a heat exchanger, at first, said pipe should be cut to predetermined length and be formed to U character form by bending. After that, this U character formed pipe is passed into through holes of aluminum or aluminum alloy fins which are arranged in parallel and these fins are fixed on said pipe in parallel by extending a inside diameter of said pipe to pass through a plug or to load liquid pressure.
Moreover, the end of the U character formed pipe above is extended by flare forming and re-flare forming which is extending again the already flare formed end of the pipe and these extended ends are combined with other U character formed pipes by inserting one end of a not-extended U character formed pipe into the other extended end of pipe and soldering each other using a phosphorus copper solder.
After extending the end of pipe, when the end of U character formed pipe of usual phosphorus deoxidized copper is heated in soldering, crystal growth of copper alloy at heated area arises and, as a result, the strength of said heat influenced area which adjoins at soldered part may falls remarkably. As a seamless copper alloy pipe for a heat exchanger to prevent crystal growth above by soldering, a seamless copper alloy pipe made of phosphorus deoxidized copper with adding Fe is known. As such a conventional seamless copper alloy pipe being made of phosphorus deoxidized copper in which Fe is added as an indispensable component, for example, the following compositions are known. That is, a seamless copper alloy pipe for a heat exchanger being made of copper alloy comprising: the total amount of 0.005 to 0.8 weight % of Fe, 0.01 to 0.026% of P, 0.005 to 0.3% of Zr, 3 to 30 ppm of oxygen and remainder Cu (refer to Japanese Patent Laid-Open Nos. 39900/1983) and one comprising: 0.01 to 1.0 weight % of Fe, 0.005 to 0.6% of at least of one element selected from Cr, Si, Mn, As, Ni and Co, 0.005 to 0.6% of at least of one element selected from P, Ca and Mg, 0.004 to 0.04% of oxygen and remainder Cu (refer to Japanese Patent Laid-Open Nos. 156719/1977).
These seamless copper alloy pipes are assembled as heat transfer pipes of a heat exchanger and are filled up with a heating medium. The heat exchanger is operated by loading and opening wide condensation pressure to a heating medium. HCFC-type fluorocarbon has formerly been used as a heating medium above but HFC-type fluorocarbon is recently become to use since HCFC-type fluorocarbon contributes braking an ozone layer of earth and there are no fear about HFC-type fluorocarbon.
SUMMARY OF THE INVENTION
However, the condensation pressure at the time of using HFC-type fluorocarbon as a heating medium needs to be made larger than that of using the conventional HCFC-type fluorocarbon as a heating medium. For example, when R-22 which is typical one in HCFC-type fluorocarbon is used as a heating medium for a heat exchanger, it is enough that the condensation pressure of HCFC-type fluorocarbon in heat transfer tube is 20 kgf/cm
2
. However, when R-410a which is typical one in HFC-type fluorocarbon is used as a heating medium, the condensation pressure in heat transfer pipe needs 31 kgf/cm
2
and this value is 1.5 times or more from the former value. Under the environment in which such high condensation pressure was loaded periodically, there were problems that cracks arose and broke the heat transfer pipe to become the possible cause of a trouble in long time use since 0.2% proof strength and fatigue strength of former heat transfer pipe were not enough, and that the characteristics of heat exchanger fell since the size of the heat transfer pipe largely changed because of shortage of 0.2% proof strength.
Means for Solving the Problems
In viewpoint of the above, the present inventors proceeded the research for the development of a seamless copper alloy pipe for a heat exchanger which is consisted by a copper alloy having excellent 0.2% proof strength and fatigue strength and the following knowledge was obtained.
(a) When Co was independently added 0.02 to 0.2% to phosphorus deoxidized copper, 0.2% proof strength and fatigue strength of copper alloy increased extremely, and electrical conductivity also increased.
(b) When carbon was added 1 to 20 ppm to phosphorus deoxidized copper with the addition of 0.02 to 0.2% of Co, 0.2% proof strength and fatigue strength of copper alloy furthermore increased.
(c) The content of P is preferably 0.01 to 0.5% and furthermore, an oxygen content as an unavoidable impurity is preferably regulated to 50 ppm or less.
The present invention was achieved based on the results set forth above and characterized as follow.
(1) A seamless pipe having high 0.2% proof strength and fatigue strength for a heat exchanger, the seamless pipe being made of copper alloy comprising: a total amount of 0.02 to 0.2 weight % of Co, 0.01 to 0.05% of P, remainder Cu, and unavoidable impurities and, as said impurities, the total oxygen content in said alloy is regulated to 50 ppm or less.
(2) A seamless pipe having high 0.2% proof strength and fatigue strength for a heat exchanger, the seamless pipe being made of copper alloy comprising: a total amount of 0.02 to 0.2 weight % of Co, 0.01 to 0.05% of P, 1 to 20 ppm of C, remainder Cu, and unavoidable impurities and, as said impurities, the total oxygen content of said alloy is regulated to 50 ppm or less.
In order to manufacture this seamless copper alloy pipe for a heat exchanger of the present invention, at first, usual electrolytic copper is melted under reducing atmosphere to make a molten low oxygen copper and next, Co and a mother alloy of Co and P are added to said molten copper to make a molten copper alloy. Furthermore, after adding predetermined amount of carbon as a mother alloy of Co and C to the molten copper alloy above if needed, said molten copper alloy is casted to make a columnar ingot.
This columnar ingot above is heated to a predetermined temperature within the range from 850° C. to 1050° C. and is formed by a extrusion into water. Furthermore, cold working and annealing are done to make a seamless copper alloy pipe for a heat exchanger having a predetermined cross-sectional size.
There is described next the reason why the composition of the copper alloy for a seamless pipe of a heat exchanger according to the invention is defined as above.
(a) Co
Co is dissolved into the matrix of phosphorus deoxidized copper or forms phosphorous compound phases and is an effective component which enhances 0.2% proof strength and fatigue strength of copper alloy above. When the Co content is over 0.2%, electrical conductivity of copper alloy above becomes less than 70% IACS and thermal conductivity falls. Whereas, when the Co content is less than 0.01%, a desired effect is not obtained. Therefore, the Co content is determined to 0.02% to 0.2% and preferably 0.04% to 0.1%.
(b)P
P has the work which makes crystal grain finer by coexisting with Co and therefore, enhances 0.2% proof strength and fatigue strength. When the P content is over 0.05%, electrical conductivity of copper alloy above decreases remarkably. Whereas, when the P content is less than 0.01%, a desired effect is not obtained. Therefore, the P content is determined to 0.01% to 0.05% and preferably 0.015% to 0.04%.
(c) Oxygen
Oxygen is contained as an unavoidable impurity. When the oxygen content is over 50 ppm, a coarse oxide is formed in copper alloy above and, as a result, 0.2% proof strength and fatigue strength are decreased. The
Saito Yutaka
Sudo Yuichiro
Yamaji Tetsuo
Ip Sikyin
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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