Patent Application
20160130684
The present invention relates to a material for use in a member for water works, which is made of a copper alloy and in which the level of lead leaching is not more than a stipulated value.
JIS H5120 CAC406, a bronze alloy which has been conventionally used for parts in materials and equipment for water works and in feed water supply system, contains from 4.0 to 6.0% by weight of lead, and the lead leaching therefrom into the tap water has been frequently observed. Therefore, in order to reduce the amount of toxic lead leaching, the production of a copper alloy containing a reduced amount of lead, or a lead-free copper alloy which contains no lead has been investigated.
However, when a copper alloy is produced without or with a reduced amount of lead, the castability, machinability and/or the water pressure resistance of the resulting copper alloy are reduced, thereby causing the leaking of water, when the alloy is used in a valve, for example. Therefore, an alloy has been investigated, in which not only the content of lead is reduced, but also the deterioration of functional properties, such as a decrease in the water pressure resistance, is prevented as much as possible, as compared to the alloy containing lead.
For example, the below-identified Patent Document 1 describes a bronze alloy, which contains from 0.5 to 6% by weight of Bi and from 0.05 to 3% by weight of Sb, to compensate for the reduced lead content. Particularly, Example 7 therein describes that a bronze alloy which contains 1.5% by weight of Sn; 17.5% by weight of Zn, 0.7% by weight of Bi, 0.06% by weight of Sb, 0.003% by weight of P, and 0.8% by weight of Ni, and in which the content of Pb is reduced to 0.1% by weight, provided suitable results.
Further, the below-identified Patent Document 2 describes a copper alloy for use in a member for water works, which exhibits suitable properties despite a reduced lead content, as a result of containing from 2.0 to 3.0% by weight of Ni, and from 0.5 to 1.1% by weight or less of Bi (claim 1, etc.).
In addition, the below-identified Patent Document 3 describes a bronze alloy which contains from 1.5 to 2.5% by mass of Bi and from 0.1 to 0.5% by mass of Ni.
Patent Document 1 JP 2889829 B
Patent Document 2 JP 4866717 B
Patent Document 3 JP 4294793 B
However, recent researches have reported the results which suggest an undeniable possibility that the Ni, which is contained in the alloy disclosed in Example 7 of Patent Document 1 and the alloy disclosed in Patent Document 2, could cause an allergy. Therefore, from now on, it is considered that reducing the Ni content as much as possible is preferred, even in the material for use in a member for water works. On the other hand, since the bronze alloy disclosed in Patent Document 3 contains too high an amount of Bi despite a low Ni content, it has been found that, when subjected to sand casting, the resulting casting is prone to shrinkage cavities and tends to have reduced mechanical properties.
Accordingly, an object of the present invention is to provide a copper alloy for use in a member for water works, which has not only a reduced lead content and the lowest possible Ni content, but also a reduced Bi content, and which still exhibits suitable properties.
The present invention has solved the above mentioned problems by adopting the following constitution.
A copper alloy comprising: less than 0.5% by mass of Ni; 0.2% by mass or more and 0.9% by mass or less of Bi;
12.0% by mass or more and 20.0% by mass or less of Zn; 1.5% by mass or more and 4.5% by mass or less of Sn; and 0.005% by mass or more and 0.1% by mass or less of P;
wherein the total content of Zn and Sn is 21.5% by mass or less, and the balance is a trace element(s) and Cu.
In other words, the present invention provides a blending ratio which allows for production of a copper alloy in which: the content of Ni is reduced in addition to reducing the content of Pb to prevent adverse effects to health; the occurrence of shrinkage cavities can be prevented during the sand casting even though the content of Bi is reduced; and, at the same time, the influence of reduced Bi content can be compensated so that the alloy is able to exhibit sufficient mechanical properties.
Further, if the content of Zn is too high, in particular, the solid solubility of Sn is reduced to result in an increased concentration of Sn in the residual liquid phase during the solidification, and as a result, the crystallization of β-phase due to peritectic reaction is more likely to occur. Eventually, eutectoids of α+δ phases, composed of α-phases scattered in hard δ-phases, are generated between dendrites, resulting in a reduction in the material strength of the alloy, and a tendency thereof to develop casting defects. It has been discovered that, this effect is synergistically aggravated by the presence of Bi, which is also not solid-solubilized in Cu, but dispersed. Therefore, by adjusting the total content of Zn and Sn to a range in which Sn is allowed to solid-solubilize in Cu, while reducing the Bi content, it is possible to provide a copper alloy which has sufficient strength and which is less prone to casting defects under such an environment.
This copper alloy may also contain a trace element(s) in addition to the above mentioned elements. However, it is necessary that the total content of the trace element(s) be within the range in which the effect of the present invention is not impaired. The total content is preferably less than 3.0% by mass, and more preferably less than 1.0% by mass. Further, the content of one trace element is preferably less than 1.0% by mass, and more preferably, less than 0.4% by mass. Still more preferably, the content is not more than the amount contained as an unavoidable impurity(ies), because the resulting copper alloy can be expected to have stable properties. Particularly, it is preferred that the content of Pb be less than 0.25% by mass, in order to prevent Pb leaching. In addition, the content of unavoidable impurity(ies) is preferably less than 0.5% by mass, and more preferably, less than 0.1% by mass.
If the copper alloy according to the present invention contains 0.0003% by mass or more and 0.006% by mass or less of B, as a trace element which is not an impurity, the flowability of molten metal, in particular, of the copper alloy can be significantly improved.
According to the present invention, it is possible to provide a copper alloy, which has sufficient mechanical properties, which is less prone to shrinkage cavities during sand casting, and which can be easily handled, while reducing the content of Pb, and also the content of Ni, which is suspected to cause an allergy; and to produce a member for water works in which safety is further secured.
The present invention will now be described in detail.
The present invention relates to a copper alloy for use in a member for water works, in which the content of Pb, Ni, and Bi is reduced.
In the above mentioned copper alloy, it is necessary that the content of Ni be less than 0.5% by mass. Preferably, the Ni content is less than 0.3% by mass. It is unclear as to the conditions under which Ni causes an allergy due to leaching. However, the upper limit of Ni leaching, as measured by the leaching test into water, is determined by WHO to be 0.07 mg/L or less, and there is a potential risk that this requirement may not be met, if the copper alloy contains 0.5% by mass or more of Ni. Much of the information regarding the adverse effects of Ni remains unclear, and thus, at this moment, it is considered that a lesser Ni content is more desirable.
In the above mentioned copper alloy, it is necessary that the Bi content be 0.2% by mass or more. Preferably, the Bi content is 0.3% by mass or more, more preferably, 0.4% by mass or more. Although the reduction in the physical properties of the alloy, as a result of reducing the content of Pb, can be compensated by incorporating Bi, if the Bi content is less than 0.2% by mass, the reduction in the machinability becomes unignorable, and shrinkage cavities are more likely to occur in the resulting casting, when subjected to sand casting. In order to reliably avoid these problems, Bi content is preferably 0.3% by mass or more. On the other hand, it is necessary that the Bi content be 0.9% by mass or less. Preferably the Bi content is 0.8% by mass or less. Since Bi is not solid-solubilized in Cu, but dispersed, a higher Bi content is more likely to cause a reduction in the tensile strength. If the Bi content exceeds 0.9% by mass, the dispersed Bi leads to a marked tendency of the alloy to develop shrinkage cavities during the sand casting, and the reduction in the tensile strength will be unignorable.
In the above mentioned copper alloy, it is necessary that the Zn content be 12% by mass or more. Preferably, the Zn content is 13% by mass or more. A Zn content of less than 12% by mass results in a tendency to produce curled machining chips, thereby reducing the machinability. Increasing the Zn content produces an effect of reducing the Ni leaching. On the other hand, it is necessary that the Zn content be 20% by mass or less. Preferably the Zn content is 19% by mass or less, more preferably, 16% by mass or less. Too high a Zn content not only causes a reduction in mechanical properties, but also increases zinc residue, thereby complicating the casting.
In the above mentioned copper alloy, it is necessary that the Sn content be 1.5% by mass or more. Preferably, the Sn content is 2.0% by mass or more. A Sn content of less than 1.5% by mass results in a tendency to produce curled machining chips, as in the case of the Zn content, thereby reducing the machinability. On the other hand, it is necessary that the Sn content be 4.5% by mass or less. Preferably, the Sn content is 4.3% by mass or less, more preferably, 3.0% by mass or less. This is because too high a Sn content results in a reduced elongation and/or occurrence of shrinkage cavities during the sand casting.
In the above mentioned copper alloy, it is necessary that the total content of Zn and Sn be 21.5% by mass or less. Preferably, the total content is 21.0% by mass or less. If the amount of Zn solid-solubilized in Cu is too high, the solid solubility of Sn is reduced to result in an increased concentration of Sn in the residual liquid phase during the solidification, and as a result, the crystallization of β-phase due to peritectic reaction is more likely to occur. Eventually, α+δ phases, composed of α-phases scattered in hard δ-phases (Cu31Sn8), are generated between dendrites, resulting in a reduction in the tensile strength. Further, the presence of Bi dispersed in the vicinity of the α+δ phases, during the generation thereof, leads to a synergistic reduction in the tensile strength of the alloy. In addition, when the casting is carried out under the conditions of low solidification rate, such as when producing a thick wall casting or sand casting, there is a potential risk that the resulting casting may develop casting defects during the final solidification, such as a defect referred to as “tin sweat”, a state where Sn exudes from the surface of the alloy as if it is sweating, or shrinkage cavity defects. If the total content of Zn and Sn exceeds 21.5% by mass, the reduction in mechanical properties and occurrence of casting defects will be unignorable.
In the above mentioned copper alloy, it is necessary that the P content be 0.005% by mass or more. Preferably, the P content is 0.01% by mass or more. Since P produces a deoxidizing effect, too low a P content reduces the deoxidizing effect during the casting, resulting not only in an increased occurrence of gas defects, but also in a decreased flowability of molten metal due to oxidation of the molten metal. On the other hand, it is necessary that the P content be 0.1% by mass or less. Preferably, the P content is 0.05% by mass or less. If the P content is too high, P reacts with water in the mold to increase the occurrence of gas defects and shrinkage cavity defects in the resulting casting, and the mechanical properties thereof are also reduced. On the other hand, since the above mentioned copper alloy contains a high amount of Zn, gas absorption is reduced due to the degassing effect of Zn. This allows for production of a casting with little casting defects, even if the P content is low as compared to a representative bronze alloy, JIS H5120 CAC406.
The above mentioned copper alloy may contain another trace element(s), as the balance, in addition to Cu. It is necessary that the total content of the trace element(s) be within the range in which the effect of present invention is not impaired. The content is preferably less than 1.0% by mass, more preferably, less than 0.5% by mass. This is because, if too much unexpected elements are incorporated in the alloy, even if the above mentioned elements are contained within the above mentioned ranges, there is a potential risk that the physical properties of the alloy may be deteriorated. Further, the content of one trace element is more preferably less than 0.4% by mass. Still more preferably, the content is not more than the amount contained as unavoidable impurity(ies), because the resulting alloy can be expected to have stable mechanical properties.
Among the above mentioned trace elements, the content of Pb, which is considered as an impurity, is preferably less than 0.25% by mass. Pb is an element whose leaching from the alloy should be prevented as much as possible, and if the amount of Pb leaching exceeds 0.25% by mass, it will be difficult to satisfy the reference leaching value in the leaching test. The Pb content is preferably less than 0.1% by mass, and the lower the better.
Among the above mentioned trace elements, the content of each of the unavoidable impurities, which are unavoidably incorporated into the alloy due to the problems associated with the raw materials or the production process, is preferably less than 0.4% by mass, more preferably, less than 0.2% by mass, and still more preferably, less than the detection limit. Examples of such impurities include Fe, Mn, Cr, Zr, Mg, Ti, Te, Se, Cd, Si, Al, and Sb. Among those in particular, the content of Se and Cd, which are known to be toxic, is each preferably less than 0.1% by mass, more preferably, less than the detection limit.
Among the above mentioned unavoidable impurities, the content of Si is preferably less than 0.01% by mass, more preferably, less than 0.005% by mass. Too high a Si content tends to increase the occurrence of shrinkage cavities, resulting in a failure to produce a decent casting.
Among the above mentioned unavoidable impurities, the content of Al is preferably less than 0.01% by mass, more preferably, less than 0.005% by mass. Too high an Al content, as with the Si content, tends to increase the occurrence of shrinkage cavities, resulting in a failure to produce a decent casting.
Among the above mentioned unavoidable impurities, the content of Sb is preferably less than 0.05% by mass, more preferably, less than 0.03% by mass, and most preferably, less than the detection limit. Since Sb tends to form Cu—Sn—Sb-based intermetallic compounds, which tend to reduce the toughness of the alloy, there is a risk that the mechanical properties of the alloy may be reduced.
On the other hand, if the alloy contains 0.0003% by mass or more of B, as one of the above mentioned trace elements, the flowability of molten metal during the casting can be improved. Preferably, the B content is 0.0005% by mass or more, since the flowability of molten metal can further be improved. On the other hand, a B content of more than 0.006% by mass leads to a sharp drop in the tensile strength, and an increased occurrence of shrinkage cavities. Therefore, the B content is preferably 0.006% by mass or less. Further, if the B content is 0.003% by mass or less, the flowability of molten metal can be improved, without causing deterioration of the mechanical properties and/or occurrence of casting defects.
Note that, the values of the content of the elements as described in the present invention denote the values of the content of elements in the resulting casting or forging, not the content thereof in the raw materials.
The balance of the above mentioned copper alloy is Cu. The copper alloy according to the present invention can be produced by a common method for producing a copper alloy. When producing a member for water works using the thus obtained copper alloy, a common casting method (such as sand casting) can be used. For example, a member for water works can be prepared by a method in which an alloy is melted using an oil furnace, gas furnace, or high frequency induction melting furnace, and then cast using molds in various shapes.
Examples in which the copper alloy of the present invention was actually produced will now be described. Firstly, the testing methods for copper alloy will be described.
For each of the alloys, a Type A sample defined in JIS H5120 and having the shape as shown in
The tensile strength was evaluated as follows: “∘” . . . 195 MPa or more; and “x” . . . less than 195 MPa.
The elongation was evaluated as follows: “∘” . . . 15% or more; and “x” . . . less than 15%.
Note that, these threshold values are reference values for JIS H5120 CAC406 generally used in a member for water works.
The evaluations for the drilling test and the lathe machining test as described below were combined to determine the overall evaluation of the machinability. The overall evaluation of the machinability was carried out according to the following standards: those evaluated as “⊚” in the drilling test and evaluated as “∘” in the lathe machining test were defined as “⊚”; those evaluated as “∘” in both the drilling test and the lathe machining test were defined as “∘”; those having at least one “Δ” evaluation were defined as “Δ”; and those having at least one “x” evaluation were defined as “x”.
For each of the alloys, the drilling test using a drilling machine was carried out. The drilling test was carried out using each of the samples formed by machining to a size of 20 mm diameter×10H (mm height), and using a drilling machine, under the conditions as shown in Table 1. Evaluation was carried out as follows. The time required to drill a 5 mm hole in each of the samples was measured, and those with the results of 5 seconds or less were evaluated as “⊚”; those with the results of more than 5 seconds and 10 seconds or less are evaluated as “∘”; those with the results of more than 10 seconds and 15 seconds or less are evaluated as “Δ”; and those with results exceeding 15 seconds are evaluated as “x”.
For each of the alloys, the shape of machining chips, which were obtained when the alloy was subjected to lathe machining to produce the test specimen for the tensile test, was examined to evaluate the machinability. The lathe machining was carried out under the following conditions: the tool used: high-speed steel; rotational speed: 700 rpm, cut depth: 2 mm, and feed rate: 0.07 mm/rev. Then machining chips produced were collected, and categorized based on their shapes, as shown in
Each of the copper alloys of Examples and Comparative Examples was heated and melted, and then cast using a spiral-shaped test mold shown in
For each of the alloys, liquid penetrant test was performed using a step-shaped sample, and evaluation of casting defects was performed. “−” in the Table denotes that the evaluation was not carried out. Specifically the test was carried out as follows. A step-shaped CO2 mold as shown in
Materials containing each of the elements were mixed, and melted in a high frequency induction melting furnace, followed by casting using a CO2 mold to produce samples each having the composition as shown in Table 2. All the values of the content of the elements are expressed in % by mass, and are values measured in the resulting casting after the production. A conventionally used bronze material containing lead, JIS H5120 CAC406, was used as Comparative Example 11, which was used as a reference material for the comparison of physical properties. The content of each of the elements in Comparative Example 11 is also shown in the Table. The following tests were carried out for each of the resulting copper alloys. Note that, the content of each of Sb, Al, Si, and Fe was less than the detection limit, in each of Examples and Comparative Examples shown the Table 2. The content of “0” in the Table means that the content is less than the detection limit. The overall evaluation was carried out according to the following standards: those having “⊚” or “∘” evaluation in all the tests performed were defined as “∘”; those having as least one “Δ” evaluation in any of the tests were defined as “Δ”; and those having as least one “x” evaluation in any of the tests were defined as “x”.
First, the alloy CAC406 used as the reference material, which is shown in Table 2 as Comparative Example 11, will be described. The alloy CAC406 has mechanical properties such as a tensile strength of 195 MPa or more, and an elongation of 15% or more, as specified in JIS. Since CAC406 contains 5.38% by mass of Pb, Comparative Example 11 exhibited good machinability as shown in Table 2 and
Next, Comparative Example 1 and Examples 1 to 4 shown in the first group in Table 2 will be described. These alloys were prepared to have a varying Zn content, with the contents of other elements being as close to each other as possible. The results for the machinability test are shown in Table 2 and
Next, Comparative Example 2, and Examples 2 and 5 to 8 shown in the second group in the Table 2 will be described. These alloys were prepared to have a varying Sn content with Example 2 having roughly an intermediate value, and with the contents of other elements being as close to each other as possible, and they are arranged in the order based on the Sn content. As with the above, the results for the machinability test are shown in Table 2 and
Next, Example 5, Example 2, Example 3, and Comparative Example 3 shown in the third group in Table 2 will be described, which are arranged in the order based on the total content of Zn and Sn. Since in the alloy of Comparative Example 3, the total content of Zn and Sn is 22.37% by mass, which is greater than 21.5% by mass, it had a problem in the tensile strength, despite good machinability. This is considered to be due to excessive α+δ phases being generated in the alloy, combined with the synergetic adverse effect of Bi, causing a decrease in the tensile strength. To investigate these effects metallographically, texture observation and elemental analysis were carried out by SEM-EDS analysis, using JSM-7000, manufactured by JEOL Ltd. The results of both analyses are shown in
Next, Comparative Example 4, Examples 9 and 10, Example 2, Examples 11 and 12, and Comparative Example 5, shown in the fourth group in Table 2 will be described. These alloys were prepared to have a varying P content with Example 2 having roughly an intermediate value, and with the contents of other elements being as close to each other as possible, and they are arranged in the order based on the P content. As with the above, the results for the machinability test are shown in Table 2,
Next, Comparative Example 6, Example 13, Example 2, Examples 14 and 15, Comparative Examples 7 to 9, shown in the fifth group in Table 2 will be described. These alloys were prepared to have a varying Bi content with Example 2 having roughly an intermediate value, and arranged in the order based on the Bi content. As with the above, the results for the machinability test are shown in Table 2 and
The alloys of Examples 16 to 18 and Comparative Example 10 were prepared to have a composition similar to that of Example 2, to which B as a trace element was added. As with the above, the results for the machinability test are shown in Table 2 and
The alloys of Examples 19 to 22 were prepared to have a composition similar to that of Example 2, to which Ni as a trace element was added. It was shown that, if the Ni content was less than 0.5% by mass, the properties required for the alloy according to the present invention can be obtained.
Ni-containing copper alloys each having the blending ratio as shown in Table 3 were prepared, in the same manner as described above. The leaching test was carried out for these alloys in accordance with JIS S3200-7 “Equipment for water supply service. Test methods of effect to water quality”. Specifically, square rod samples having a size of 28×28×100 mm are cast using alloys each having the blending ratio shown in Table 3, which are then machined to a size of 25×25×10 mm. After washing the thus obtained samples, leaching test is carried out using a leachate. Washing is performed for 1 hour using tap water, followed by washing with water for 3 times. Then one end of a sample pipe was stopped hermetically with a plug wrapped with a polyethylene film washed with water, and the interior of the sample pipe was filled with a leachate having a temperature of 23 degrees Celsius and then sealed. The resultant was allowed to rest for 16 hours, while maintaining the liquid temperature. The sample solution is then collected into a bottle made of hard glass, which has been washed with nitric acid first and then washed with water.
The composition of the leachate used in the leaching test is as follows. First, to 900 mL of water, 1 mL of sodium hypochlorite solution (hydrochloric acid concentration: 0.3 mg/mL), 22.5 mL of sodium hydrogen carbonate solution (0.04 mol/L), 11.3 mL of calcium chloride solution (0.04 mol/L) are added, followed by further addition of water, to prepare a solution having a final volume of 1 L. The pH of the resulting solution is adjusted using hydrochloric acid and sodium hydroxide solution, to obtain a leachate having a pH of 7.0±0.1, hardness of 45±5 mg/L, alkalinity of 35±5 mg/L, and residual chlorine of 0.3±0.1 mg/L.
The Ni concentration in the collected sample solution is measured, and the measured value is defined as the amount of Ni leaching. However, since the reference value for Ni leaching is not specified in JIS S3200-7, the guideline value defined by World Health Organization (WHO) was used as the reference value, and the Ni leaching was evaluated as follows: those having the Ni content of 0.07 mg/L or less is evaluated as “∘”; and those having the Ni content of greater than 0.07 mg/L is evaluated as “x”.
The alloys of Examples 23 to 25 have the Ni content of less than 0.5% by mass, and Comparative Example 12 has the Ni content exceeding the upper limit. Ni leaching test was carried out for these copper alloys. In Comparative Example 12, the amount of Ni leaching exceeded 0.07 mg/L.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-123582 | Jun 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/082481 | 12/3/2013 | WO | 00 |
