Lead-free copper alloys

Abstract

Disclosed is a lead-free copper alloy with superior properties as compared to currently available lead-free copper alloys which can be produced at lower costs than currently available lead-free copper alloys. The lead-free copper alloy uses a novel combination of tin, nickel and zinc along with selenium and bismuth to avoids the problems associated with leaded copper alloys, while maintaining physical properties comparable to traditional leaded copper alloys. In one embodiment, the lead-free copper alloy described contains from about 7.5 to 10.0 percent by weight zinc, from about 0.8 to 1.5 percent by weight nickel, from about 1.6 to 2.2 percent by weight bismuth, from about 0.04 to 0.35 percent by weight selenium, from about 2.2 to 3.0 percent by weight tin and up to about 0.3 percent by weight iron (maximum), the balance, apart from impurities, being copper. In an alternate embodiment, the lead-free copper alloy described contains from about 5 to 7.5 percent by weight zinc, from about 1.0 to 1.5 percent by weight nickel, from about 1.5 to 2.6 percent by weight bismuth, from about 0.04 to 0.35 percent by weight selenium, from about 5 to 6 percent by weight tin and up to about 0.3 percent by weight iron (maximum), the balance, apart from impurities, being copper.

Description

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to lead-free copper alloys.

BACKGROUND

[0002] In order improve the characteristics of copper alloys, particularly copper alloys used in casting applications, lead has been traditionally added to copper alloys. Among other characteristics, the addition of lead improves the machinability of the copper alloys and improves the pressure tightness of copper alloy. Regarding machinability, the addition of lead facilitates chip formation by acting as a stress raiser for the alloy. The addition of lead also provides a lubricating function to the alloy which minimize the tool wear, thereby decreasing maintenance costs and down time of equipments used to manipulate the copper alloys. In addition, lead inclusion makes the lead much easier to polish, which is desirable in certain applications. However, the addition of lead does decrease the tensile strength of the alloy slightly.

[0003] As a result of these and other properties, leaded copper alloys became the industry standard, especially in plumbing fixtures and pipe fittings used for potable water supplies. The current disclosure relates primarily to copper alloys referred to in the art as leaded red brasses and leaded semi-red brasses. The leaded red brasses typically have a copper content ranging from 82% to 94%, while the leaded semi-red brasses have a copper content ranging from 75% to 82%. The balance of both the leaded red and leaded semi-red brasses is made up predominantly of tin, lead and zinc. The current standard for the copper alloys of the leaded red and leaded semi-red brasses is copper alloy C84400, which is also referred to as alloy 123, leaded semi-red brass or 81-3-7-9. The composition of alloy C84400 is set forth in Table 1. Alloy C84400 replaced alloy C83600, also known as alloy 115, leaded red brass, ounce metal and 85-5-5-5. The composition of alloy C83600 is set forth in Table 1.

[0004] However, it has been recognized that the presence of lead in copper alloys is a cause for concern for several reasons. First, lead has a tendency to leach out of copper based alloys over time, posing a health threat to those who consume material, such as water or foods, which have come into contact with lead containing metals and/or alloys. Second, the use of lead in the manufacturing process of copper alloys has also caused significant health risks for workers exposed to lead in the workplace. Lead particles can volatilize during the manufacturing process and become suspended in the ambient air. Workers subsequently inhale this air and the suspended lead particles, leading to adverse health consequences. In order to combat this problem, workers must wear respirators when lead is used in the manufacturing process. In addition, workers must have their clothing specially laundered to remove the lead contamination. Third, lead also serves as a source of environmental contamination. The air released from the plant must be scrubbed of lead particles by filters so as not to contaminate the surrounding environment with the suspended lead particles. Also, the materials used in the manufacturing process become contaminated with lead to such an extent they are classified as hazardous wastes. As a result, the lead-contaminated materials must be sent to special hazardous waste landfills at great cost to the foundries that use lead as a part of their copper alloys.

[0005] In response to these and other concerns, the Environmental Protection Agency and the Occupational Safety and Health Administration have imposed safety regulations concerning the use of lead in the workplace. For example, foundries that use lead in their copper alloys are required to monitor the lead content in the ambient air and must monitor the level of lead in their employees to make certain the level of lead in their bloodstreams does not exceed established standards. These regulations cost the manufactures substantial amounts of money and time to ensure compliance. Despite these issues, many foundries still employ lead containing copper alloys, such as C84400. The primary reason for the continued use of lead containing alloys is cost and compatibility of lead-free copper alloys that are currently available. In most cases, the use of currently available lead-free copper alloys is limited to foundries that produce castings for use with potable water where the lead content of the castings has been limited by law to low levels.

[0006] Therefore, a lead-free copper allows having substantially the same properties as the lead containing alloys would be useful. If a commercially viable, lead-free copper alloy could be developed, the risk to workers and the environment would be significantly minimized. In addition, the cost of production would be lowered.

[0007] Despite numerous attempts to find substitutes for lead containing alloys, there still exists a need for a lead-free copper alloy with improved characteristics. The primary focus of such efforts has been to substitute one or more elements for lead. For example, bismuth has been used as a lead replacement with some success. Bismuth is located next to lead on the periodic table of the elements, has many of the same physical properties as lead and is essentially non-toxic. However, the addition of bismuth alone leads to a brittle alloy and the problems associated therewith. However, several alloys containing bismuth as a lead substitute have been produced (see for example, U.S. Pat. No. 4,879,094 to Rushton). In addition, the cost of bismuth has raised concern about its effectiveness as a substitute for lead.

[0008] To combat these problems, bismuth has been used in combination with one or more elements to provide a lead substitute with more desirable characteristics. For example, bismuth has been combined with graphite, titanium, manganese, chromium, mischmetal, silicon, sulfur and selenium (see U.S. Pat. No. 5,614,038 to King and U.S. Pat. No. 5,330,712 to Singh).

[0009] However, despite these efforts, a cost effective lead-free copper based alloy with the desired properties has not been produced. The present disclosure provides such a solution.

SUMMARY

[0010] The present disclosure describes a lead-free copper alloy with superior properties as compared to currently available lead-free copper alloys. In addition, the lead-free copper alloy of the present disclosure can be produced at lower costs than currently available lead-free copper alloys. The lead-free copper alloy described uses primarily a combination of selenium and bismuth along with novel combinations of tin, nickel and zinc. As a result, the alloy of the present disclosure avoids the problems associated with leaded copper alloys, while maintaining physical properties comparable to traditional leaded copper alloys.

[0011] In one embodiment, the lead-free copper alloy described contains from about 7.5 to 10.0 percent by weight zinc, from about 0.8 to 1.5 percent by weight nickel, from about 1.6 to 2.2 percent by weight bismuth, from about 0.04 to 0.35 percent by weight selenium, from about 2.2 to 3.0 percent by weight tin and up to about 0.3 percent by weight iron (maximum), the balance, apart from impurities, being copper.

[0012] In an alternate embodiment, the lead-free copper alloy described contains from about 5 to 7.5 percent by weight zinc, from about 1.0 to 1.5 percent by weight nickel, from about 1.5 to 2.6 percent by weight bismuth, from about 0.04 to 0.35 percent by weight selenium, from about 5 to 6 percent by weight tin and up to about 0.3 percent by weight iron (maximum), the balance, apart from impurities, being copper.

[0013] The lead-free copper alloy of the present disclosure may be used for the manufacture of a wide variety of cast goods. One class of such cast goods includes, but is not limited to, fittings, such as, but not limited to, valves, check valves, foot valves and meters for the transport of potable water, or fixtures and other components for use with potable water. However, the lead free copper alloy disclosed may be used for the manufacture of other cast goods as well. As a result of the composition of the lead-free copper alloy of the present disclosure, its physical properties are comparable to leaded copper alloys such that the lead-free copper alloy can be easily machined and manipulated and can be used without requiring extensive modification to casting methods or processes. In addition, the lead-free copper alloy of the present disclosure can be produced at lower cost than currently available lead-free copper alloys.

DETAILED DESCRIPTION

[0014] A lead-free copper alloy with superior properties is described. Two alternate embodiments of the lead-free copper alloy are specifically described below and are referred to as KE88 and KE22. As a result of this unique formulation, the lead-free copper alloy of the present disclosure avoids the problems associated with leaded copper alloys, while maintaining physical properties very similar to traditional leaded copper alloys. The term lead-free as used in the present disclosure describes an alloy that contains a level of lead less than 0.2% by weight. The lead-free copper alloy described herein employs a combination of bismuth and selenium (along with unique combinations of other components) in the place of lead. In the selenium hypo-eutectoid, the bismuth concentration can range from about 1.6 to 2.2 weight percent in KE88 to 1.5 to 2.6 weight percent in KE22, while the selenium concentration may be 0.04 to 0.35 percent by weight in both embodiments. The resulting bismuth to selenium ratio ranges from about 5 to 1 and higher.

[0015] The lead-free alloys EnviroBrass I (also known as alloy C89510) and II (also known as alloy C89520) (see U.S. Pat. No. 5,614,038) also use a combination of bismuth and selenium as a substitute for lead. However, the selenium content of EnviroBrass I and II is significantly higher than the lead-free copper alloy of the present disclosure. For EnviroBrass I, the bismuth concentration ranges from 0.5 to 1.5% by weight and the selenium concentration ranges from 0.35 to 0.75% by weight. For EnviroBrass II the bismuth concentration ranges from 1.6 to 2.2% by weight and the selenium concentration ranges from 0.8 to 1.1% by weight. For both EnviroBrass I and II the bismuth to selenium ratios are not higher than 4.3 to 1.

[0016] The selenium may be added as a bismuth/selenium compound or a selenium/copper compound to avoid problems associated with the use of free selenium. In addition, the time selenium is maintained in the molten state should be minimized. Selenium is noted to have certain toxic effects, similar to those encountered with lead. For example, selenium is reactive with oxygen and volatile. When selenium is added to copper based alloys, the selenium fumes, releasing free selenium into the ambient air. In one embodiment, the bismuth/selenium compound is Bi2Se3. Additional bismuth may be added as elemental bismuth.

[0017] One embodiment of the lead free copper alloy disclosed is set forth in Table 2 and referred to as KE88 contains from about 7.5 to 10.0 percent by weight zinc, from about 0.8 to 1.5 percent by weight nickel, from about 1.6 to 2.2 percent by weight bismuth, from about 0.04 to 0.35 percent by weight selenium, from about 2.2 to 3.0 percent by weight tin and up to about 0.3 percent by weight iron, the balance, apart from impurities, being copper.

[0018] An alternate embodiment of the lead free copper alloy disclosed is set forth in Table 2 and referred to as KE22, contains from about 5 to 7.5 percent by weight zinc, from about 1.0 to 1.5 percent by weight nickel, from about 1.5 to 2.6 percent by weight bismuth, from about 0.04 to 0.2 percent by weight selenium, from about 5 to 6 percent by weight tin and up to about 0.3 percent by weight iron, the balance, apart from impurities, being copper.

[0019] EnviroBrass I and EnviroBrass II differ significantly from the lead-free copper alloy described herein. The composition of EnviroBrass I and II is given in Table 2. As shown in Table 2, the zinc content of EnviroBrass I and II ranges from 4 to 6% by weight, while the zinc content of KE88 and KE22 range from 7.5 to 10% by weight and 5 to 7.5% by weight, respectively. In addition, the specifications for EnviroBrass I and II do not specify a range of nickel, but state that nickel content should be held at a maximum of 1% by weight. In contrast, the nickel content of KE88 and KE 22 is specified to be in the range of 0.8 to 1.5% by weight and 1.0 to 1.5% by weight, respectively. The tin content of EnviroBrass I and II is specified in the range of 4.0 to 6.0% by weight and 5.0 to 6.0% by weight, respectively. However, the tin content of KE88 is specified to be in the range of 2.2 to 3.0% by weight and the tin content of KE22 is specified in the range of 5.0 to 7.5%. Finally, as discussed above, the selenium concentration in KE88 and KE22 is lower than in either EnviroBrass I or II, with the result being a higher bismuth to selenium ration in KE88 and KE22. The concentrations of nickel and zinc in the KE88 and KE 22 can be varied to produce customized lead-free copper alloys as might be desired for various applications.

[0020] Increasing the zinc content increases fluidity of the alloy. Increasing the nickel concentration increases the physical properties of the alloy, similar to that seen when tin concentrations are increased. However, when considering the price of raw materials, nickel is a more cost effective alternative to tin. Increasing the nickel concentration also increases the soundness of the castings, which will result in fewer scrapped castings.

[0021] In addition to copper, zinc, tin, nickel, bismuth and selenium, the lead-free copper alloy described is open to the inclusion of those elements commonly occurring in conventional casting alloys. These include iron, antimony, sulphur, phosphorous, aluminum, manganese and silicon. These elements are generally present in a total amount less than 1% by weight. In addition, the lead-free copper alloy described may contain incidental impurities, generally present in an amount less than 0.5% by weight.

[0022] The lead-free copper alloy of the present disclosure may be used for the manufacture of cast goods, such as pipe fittings for the transport of potable water, or fixtures and other components for use with potable water. As a result of the composition of the lead-free copper alloy of the present disclosure, its physical properties are similar to leaded copper alloys such that the lead-free copper alloy can be easily machined and manipulated. As a result of its low cost and excellent physical properties, the lead-free copper alloys of the present disclosure will provide a significant benefit to the foundry industry. Importantly, the physical properties (such as, but not limited to, fluidity and shrinkage) are similar to leaded copper alloys, such as, but not limited to, C84400, existing patterns and other equipment may be used with no modification or risering.

[0023] The following examples illustrate selected attributes of one embodiment of the alloy of the present disclosure. The examples below are not meant to be inclusive, but to illustrate certain properties of the embodiments of the lead-free copper alloy disclosed herein.

EXAMPLE 1

Production of KE88 and KE22

[0024] The lead-free copper alloy of the present disclosure is produced as described below. This is only 1 embodiment and other methods may be used, with the method below shown only as way of example. Both KE88 and KE 22 are produced using essentially the same method, and with the same raw materials, with only the percentage of the raw materials being different as dictated by the composition of the 2 embodiments.

[0025] Copper and zinc may be obtained from a variety of sources. In one embodiment, at least a portion of the raw materials are obtained from scrap. For example, copper and zinc may be obtained from prime production scrap including, but not limited to, gilding metal (95% CU 5% Zn), commercial bronze (90% copper 10% Zn) and cartridge brass (70% Cu 30% Zn). Copper may also be obtained from brass mill grade copper scraps and copper chops. Some of the material described above may also be coated with tin, providing tin to the mixture. Tin may also be derived from phos bronze. Nickel may be obtained from sources such as cupro nickel, ranging from about 90% Cu, 10% Ni to 70% Cu, 30% Ni. The inclusion of the raw material from scrap sources has several advantages, including lower costs per pound for the raw materials and lower melt losses.

[0026] The raw material stock should be melted and tested for conformation to the desired analysis. The analysis should confirm the relative percentage of the elements, and confirm that the levels of trace elements such as lead, iron, silicon, aluminum, sulfur and antimony are below the maximum allowable percentages. The levels of the trace elements may be decreased by dilution, and in some cases, may be reduced by refining.

[0027] The final concentrations of copper, zinc, tin and nickel may be adjusted with additions of the unalloyed metals. After the final adjustments are made, the bismuth and selenium are added. In one embodiment, bismuth is added as elemental bismuth and selenide is added as a bismuth tri-selenide compound (Bi2Se3). It is preferred that bismuth tri-selenide be added last and that total time in the molten phase be limited. Selenium is both reactive with oxygen and volatile. As a result, the selenium may be released as a gas fume, creating safety concerns similar to those caused by lead.

[0028] After the addition of the bismuth and selenium, a final analysis is conducted to confirm the percentages of the raw materials are in the desired range. Once the analysis is conducted, pour off of ingot should begin. The time taken to pour the ingot should be kept to a minimum to avoid fluctuation in the concentration of zinc and selenium. A sample may be taken for analysis at the end of the ingot pour to confirm the entire production conforms to the specification.

EXAMPLE 2

Formulation of One Embodiment of KE88

[0029] In one embodiment (the physical properties of which are given in Example 4), the KE-88 alloy comprises 86.11 percent by weight copper, 2.42 percent by weight tin, 7.88 percent by weight zinc, 1.08 percent by weight nickel, 1.99 percent by weight bismuth, 0.34 percent by weight selenium and 0.07 percent by weight iron and 0.11 percent by weight lead. This embodiment was produced as described in Example 1.

EXAMPLE 3

Formulation of One Embodiment of KE22

[0030] In one embodiment (the physical properties of which are given in Example 4), the KE-88 alloy comprises 85.26 percent by weight copper, 5.1 percent by weight tin, 6.3 percent by weight zinc, 1.0 percent by weight nickel, 1.9 percent by weight bismuth, 0.3 percent by weight selenium, 0.03 percent by weight iron and 0.11 percent by weight lead. This embodiment was produced as described in Example 1.

EXAMPLE 4

Comparison of Physical Properties

[0031] Table 3 below gives selected physical properties of KE88 and KE22 and compares these properties to EnviroBrass II, FederalAlloy I-844 and the leaded copper alloy C84400. As can be seen, the properties of both KE88 and KE22 are similar to the currently used copper alloys 1 TABLE 3 Comparison of Selected Physical Properties UTS (Ksi) YS 0.5% (Ksi) % Elongation 123 leaded semi- 29.0 13.0 18.0 red brass/C84400 KE88 28.0 13.0 12.0 KE22 30.0 20.0  6.0 EnviroBrass II 21.0 18.0  6.0 C89520 FederalAlloy I-844 29.0 13.0 Not determined C89831

EXAMPLE 5

Raw Materials Cost Comparison

[0032] As a result of the unique composition of the lead-free copper ally described, the raw material costs of the alloy are significantly reduced as compared to conventional lead-free copper alloys (see Table 4). The raw material cost of the metals used in the various alloys was compared at mid-year 2002, after allowing for melt loss during production. As can be seen, KE88 can be produced at a raw materials cost of 67.927 cents/pound and KE22 can be produced at a raw materials cost of 73.851 cents/pound. This is compared to a raw materials cost of 81.999 cents/pound for EnviroBrass II. The raw materials cost of the leaded copper alloy C84400 is 51.602 cents/pound. Therefore, from a raw materials standpoint, use of KE88 results in a cost savings of 14.072 cents/pound and the use of KE22 results in a cost savings of 8.148 cents/pound as compared to EnviroBrass II. 2 TABLE 4 Raw Material Cost Comparison of Selected Copper Alloys (allowing for metal loss during production) Raw Materials Cost Cost Savings (in cents/pound as Alloy (in cents/pound) compared to EnviroBrass II) EnviroBrass II 81.999 C89520 KE88 67.927 14.072 KE22 73.851  8.148 123 leaded semi-red 51.602 brass/C84400

[0033] 3 TABLE 1 Composition of the prior art leaded copper alloys. Concentration is expressed % of material by weight, giving maximum and minimum ranges or as maximum concentrations by weight. C83600 C84400 Copper 84.0-86.0 78.0-82.0 Tin 4.0-6.0 2.3-3.5 Lead 4.0-6.0 6.0-8.0 Zinc 4.0-6.0  7.0-10.0 Nickel ≦1.0 ≦1.0

[0034] 4 TABLE 2 Compositions of selected embodiments of the lead-free copper alloy of the present disclosure as compared to selected lead-free copper alloys currently available. Concentration is expressed % of material by weight, giving maximum and minimum ranges or as maximum concentrations by weight. KE-88 KE-22 EnviroBrass I EnviroBrass II Copper 85.5-88.0 85.0-88.0 86.0-88.0 85.0-87.0 Tin 2.2-3.0 5.0-6.0 4.0-6.0 5.0-6.0 Lead ≦0.2 ≦0.2 ≦0.25 ≦0.25 Zinc  7.5-10.0 5.0-7.5 4.0-6.0 4.0-6.0 Nickel 0.8-1.5 1.0-1.5 ≦1.0  ≦1.0  Bismuth 1.6-2.2 1.5-2.6 0.5-1.5 1.6-2.2 Selenium 0.04-0.35 0.04-0.35 0.35-0.75 0.8-1.1

Claims

1. A machinable, lead-free copper alloy comprising:

a. from about 7.5 to 10.0 percent by weight zinc;

b. from about 0.8 to 1.5 percent by weight nickel;

c. from about 1.6 to 2.2 percent by weight bismuth;

d. from about 0.04 to 0.35 percent by weight selenium; and

e. the balance, apart from impurities, being copper.

2. The alloy of claim 1 where the copper is from about 85.5 to 88.0 percent by weight.

3. The alloy of claim 1 further comprising from about 2.2 to 3.0 percent by weight tin.

4. The alloy of claim 3 further comprising up to about 0.3 percent by weight iron.

5. The alloy of claim 4 further comprising up to about 0.2 percent by weight lead.

6. The alloy of claim 1 where the zinc is from about 5.0 to 7.5 percent by weight, the nickel is from 1.0 to 1.5 percent by weight and the bismuth is from about 1.6 to 2.6 percent by weight.

7. The alloy of claim 6 where the copper is from 85.0 to 88.0 percent by weight.

8. The alloy of claim 6 further comprising from about 5.0 to 6.0 percent by weight tin.

9. The alloy of claim 8 further comprising up to about 0.3 percent by weight iron.

10. The alloy of claim 9 further comprising up to about 0.2 percent by weight lead.

11. A machinable, lead-free copper alloy comprising:

a. from about 7.5 to 10.0 percent by weight zinc;

b. from about 0.8 to 1.5 percent by weight nickel;

c. an addition of bismuth and selenium, where the bismuth/selenium weight ratio ranges from about 4.5 to 1 to about 55 to 1; and

d. the balance, apart from impurities, being copper.

12. The alloy of claim 11 where the copper is from about 85.5 to 88.0 percent by weight.

13. The alloy of claim 11 further comprising from about 1.2 to 3.0 percent by weight tin.

14. The alloy of claim 13 further comprising up to about 0.3 percent by weight iron.

15. The alloy of claim 4 further comprising up to about 0.2 percent by weight lead.

16. The alloy of claim 11 where the zinc is from about 5.0 to 7.5 percent by weight, the nickel is from 1.0 to 1.5 percent by weight and the bismuth/selenium weight ratio ranges from about 4.5 to 1 to about 65 to 1.

17. The alloy of claim 16 where the copper is from 85.0 to 88.0 percent by weight.

18. The alloy of claim 16 further comprising from about 5.0 to 6.0 percent by weight tin.

19. The alloy of claim 18 further comprising up to about 0.3 percent by weight iron.

20. The alloy of claim 19 further comprising up to about 0.2 percent by weight lead.

21. The alloy of claim 5 where the copper concentration is about 86.1 percent by weight, the tin concentration is about 2.4 percent by weight, the zinc concentration is about 7.9 percent by weight, the nickel concentration is about 1.1 percent by weight, the bismuth concentration is about 2.0 percent by weight, the selenium concentration is about 0.35 percent by weight, the iron concentration is about 0.07 percent by weight and the lead concentration is about 0.11 percent by weight.

22. The alloy of claim 10 where the copper concentration is about 85.3 percent by weight, the tin concentration is about 5.1 percent by weight, the zinc concentration is about 6.3 percent by weight, the nickel concentration is about 1.0 percent by weight, the bismuth concentration is about 1.9 percent by weight, the selenium concentration is about 0.30 percent by weight, the iron concentration is about 0.03 percent by weight and the lead concentration is about 0.11 percent by weight.