LOW LEAD BRASS ALLOY AND METHOD FOR PRODUCING PRODUCT COMPRISING THE SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to environmentally-friendly brass alloys and methods for producing products comprising the brass alloys.

2. Description of Related Art

Brasses include copper, zinc and a small amount of impurities, wherein copper and zinc are usually present at a ratio of about 7:3 or 6:4. It is known that brasses contain lead (mainly ranging from 1 to 3 wt %) to improve the properties thereof by achieving the desirable mechanical property at the industrial level. Thus, brasses become important industrial materials which are widely applicable to products such as metallic devices or valves used in pipelines, faucets and water supply/drainage systems.

However, as the awareness of environmental protection increases and the impacts of heavy metals on human health and environmental pollutions become important public issues, it is a tendency to restrict the usage of lead-containing alloys. Various countries such as Japan, the United States of America, etc, have sequentially amend relevant regulations, and put intensive efforts to lower lead contents in the environment by particularly demanding that no molten lead shall leak from the lead-containing alloy materials used in products such as household electronic appliances, automobiles and water systems to drinking water and lead contamination shall be avoided during processing. Thus, there exists an urgent need in the industry to develop a lead-free brass material, and find an alloy formulation that can substitute for lead-containing brasses while having desirable properties like the casting property, machinability, corrosion resistance and mechanical properties.

Several lead-free copper alloy formulations have been reported. In examples where silicon (Si) is added in brass alloys as a major ingredient instead of lead, TW421674, U.S. Pat. No. 7,354,489, US20070062615, US20060078458 and US2004023441 disclose lead-free copper alloy formulations that have poor machinability due to the conventional technologies applied. Further, another lead-free alloy formulation, such as the one disclosed in CN10144045, contains aluminum, silicon and phosphorus as major alloy elements. Although such alloy formulation can be used for casting, it has poor machinability as well as significantly low processing efficiency compared with that of lead-containing brasses. Therefore, the alloy formulation is not suitable for mass productions. Moreover, CN101285138 and CN101285137 disclose lead-free alloy formulations in which phosphorus as a major alloy element, but the application of the alloy formulations to casting is prone to cause defects like cracks and slag inclusions.

Alternatively, there are also publications in which bismuth (Bi) is added in brass alloys as a major component to replace lead. For example, U.S. Pat. No. 7,297,215, U.S. Pat. No. 6,974,509, U.S. Pat. No. 6,955,378, U.S. Pat. No. 6,149,739, U.S. Pat. No. 5,942,056, U.S. Pat. No. 5,653,827, U.S. Pat. No. 5,487,867, U.S. Pat. No. 5,330,712, US20060005901, US20040094243, U.S. Pat. No. 5,637,160 and US20070039667 disclose that the bismuth contents in the aforesaid alloy formulations cover a range from 0.5 wt % to 7 wt %. In addition to bismuth, each of the alloy formulations contains different elemental components and specific proportions. Further, U.S. Pat. No. 6,413,330 discloses a lead-free copper alloy formulation containing bismuth, silicon and other components at the same time, and CN101440444 also discloses a lead-free brass alloy with high zinc content. However, due to the high silicon content and low copper content of alloys, molten alloys have poor fluidity, such that it is difficult to fill in the mold cavity of a metallic mold completely, thereby causing casting defects like misrun. Further, CN101403056 discloses a lead-free brass alloy in which lead is replaced by bismuth and manganese, but the high bismuth content is likely to cause defects like cracks and slag inclusions, and the combination of low bismuth content and high manganese content leads to high degrees of hardness, resistance to chip breaking, and poor machinability.

Since the sources of bismuth is scarce and the price of bismuth is expensive, replacement of lead with higher bismuth content productions of lead-free brasses causes exorbitant product costs which is adverse to commercialization. Further, problems like poor casting property and ineffectiveness to improve material embrittlement are observed in the aforesaid brass alloy formulations.

Further, there are also publications disclosing improved production process of lead-free copper alloys or improved lead stripping processes. For example, U.S. Pat. No. 5,904,783 discloses a method for reducing lead leaching into a fluid supply by treating a brass alloy with sodium and potassium at a high temperature. TW491897 discloses a production process for a brass alloy containing 1 to 2.6 wt % of bismuth. However, conventional lead stripping processes can only reduce leaching of the lead in contact with water surface during immersion of a lead-containing product in water, and therefore the lead content of raw materials cannot be reduced to less than 0.3 wt %.

SUMMARY OF THE INVENTION

In view of the above, an aspect of the present invention is to develop a low lead brass alloy material and improved process of the same.

In order to attain the above and other aspects, the present invention provides an environmentally-friendly low lead brass alloy, comprising 0.05 to 0.03 wt % of lead (Pb), 0.3 to 0.8 wt % of aluminum (Al), 0.01 to 0.4 wt % of bismuth (Bi), 0.1 to 0.15 wt % of microelements and more than 97.5 wt % of copper (Cu) and zinc (Zn), wherein copper is in an amount ranging from 58 to 70 wt % of the lead brass alloy.

In one embodiment, the low lead brass alloy of the present invention comprises copper and zinc in a total amount ranging from 97.5 to 99.54 wt %, and preferably more than 98 wt %. In another embodiment, copper is in an amount ranging from 58 to 70 wt % of the total weight of the low lead brass alloy. Copper present in the aforesaid amounts can provide excellent toughness and processability. In a preferred embodiment, copper is in an amount preferably ranging from 62 to 65 wt %.

In the low lead brass alloy of the present invention, lead is in an amount ranging from 0.05 to 0.3 wt %. In a preferred embodiment, lead is in an amount ranging from 0.1 to 0.25 wt %, and preferably ranging from 0.15 to 0.25 wt %.

In the low lead brass alloy of the present invention, aluminum is in an amount ranging from 0.3 to 0.8 wt %. In a preferred embodiment, aluminum is in an amount ranging from 0.4 to 0.7 wt %, and preferably in an amount ranging from 0.5 to 0.65 wt %. Addition of adequate amounts of aluminum can increase the fluidity of a copper liquid, and improve the casting property of the alloy material.

In the low lead brass alloy of the present invention, bismuth is in an amount less than 4 wt %. In a preferred embodiment, bismuth is in an amount ranging from 0.01 to 0.4 wt %, preferably ranging from 0.05 to 0.3 wt %, and more preferably ranging from 0.1 to 0.2 wt %.

The microelements comprised in the low lead brass alloy of the present invention in an amount ranging from 0.1 to 0.15 wt % can be rare earth elements and/or unavoidable impurities, wherein the rare earth elements comprise cerium, scandium, yttrium and lanthanide elements. The rare earth elements can be used alone or in a combination of at least two elements. Addition of adequate amounts of rare earth elements (such as cerium (Ce)) can significantly refine the as-cast microstructure of an alloy material, induce changes in the relative amounts and crystal morphologies of α and β phases after recrystallization annealing, and form impurity particles with elements such as lead, thereby improving the distribution of the impurities in an alloy material as well as the physical property and processability of an alloy. In one embodiment, the rare earth element is cerium, which is in an amount ranging from 0.1 to 0.15 wt %.

The low lead brass alloy of the present invention further comprises phosphorus (P) in an amount less than 0.8 wt %. In a preferred embodiment, phosphorus is in an amount ranging from 0.4 to 0.8 wt %. Addition of adequate amounts of phosphorus can increase fluidity of melt, thereby improving the weldability of copper and an alloy. Phosphorus has high solid solubility in copper and CuP has low surface energy, so that the surface tension of copper can be lowered, thereby facilitating precipitation of bismuth in the form of particles.

In the present invention, Bi is used to replace Pb for maintaining the machinability of brass. Pb phase is face-centered cubic lattices with a lattice constant of 4.949×10⁻¹⁰m, and Pb has extremely low solid solubility in Cu. Hence, Pb is always present in a Cu alloy in the form of a single phase. Bi phase is rhombohedral lattices with a lattice constant of 4.7457×10⁻¹⁰m, and Cu and Bi in solid states are not mutually dissolvable. Therefore, a small amount of Bi can lead to the presence of a single Bi phase in the structure. Bi is constantly distributed on a grain boundary of brass in the form of a continuous brittle thin film, and generates hot shortness as well as cold shortness. Bi is segregated on the grain boundary by two mechanisms, as shown in FIG. 8.

The mechanisms responsible for segregation of Bi on the grain boundary can be explained by two mathematical models, which are illustrated in FIG. 8 by McLean's Model and Hofmann-Ertewein's Model. FIG. 8A shows a model where volumes are expanded and the model is based on the rule that Bi atoms diffuse from a bullion into the grain boundary (i.e. Fick's Law), and FIG. 8B shows a dislocation pipe diffusion model to illustrate the mechanism and the model is based on the rule that liquid Bi flows into a dislocation pipe, which acts as a delivery pipe to transfer the liquid Bi to the grain boundary (i.e. dislocation diffusion mechanism). The diffusion rate of the latter diffusion mechanism is 105 times higher than that of the former diffusion mechanism. When the precipitation of Bi is based on the dislocation-pipe diffusion model, double phase regions of Cu solid solution and L (liquid Bi) are formed, and in turn leading to the formation of the so-called thin-filmed Bi, thereby significantly increasing the material embrittlement. To improve the situation, a rapid cooling approach is applied when the temperature is lowered to below 750° C., causing the dislocation and diffusion of the double phase regions to disappear and preventing Bi from segregating on the gain boundary so as to avoid the material embrittlement.

In the present invention, phosphorus is further added to the brass alloy for reducing the surface tension thereof. This makes the ratio of the surface tension of the included angle between heterogeneous phases and the surface tension of the included angle between homogenous phases approximate to 0.5. If a dihedral angle is greater than 60 degrees, Bi in the brass alloy formulation will precipitate in the form of Bi particles. The machinability of the alloy material is increased to an extent that it does not generate casting defects therein.

In one embodiment, the low lead brass alloy of the present invention comprises 0.05 to 0.3 wt % of lead, 0.3 to 0.8 wt % of aluminum, 0.01 to 0.4 wt % of bismuth, 0.1 to 0.15 wt % of microelements (i.e. rare earth elements and/or unavoidable impurities), less than 0.8 wt % of phosphorus, and 98 to 99.54 wt % of copper and zinc, wherein Cu is in an amount ranging from 58 to 70 wt %.

In another embodiment, the low lead brass alloy of the present invention comprises 62 to 65 wt % of copper, 0.05 to 0.25 wt % of lead, 0.5 to 0.75 wt % of aluminum, 0.2 to 0.3 wt % of bismuth, less than 0.8 wt % of phosphorus (and the total amount of aluminum and phosphorus is less than 1.4 wt %), 0.1 to 0.15 wt % of cerium and residual zinc, and less than 0.1 wt % of unavoidable impurities.

Further, the present invention provides a method for producing a product comprising a low lead brass alloy, comprising the steps of: (a) preheating the low lead brass alloy and foundry return to a temperature ranging from 400° C. to 500° C.; (b) melting the low lead brass alloy and the foundry return to boiling to form a molten copper liquid; (c) preheating the mold to 200° C. and placing sand core into the mold; (d) casting the molten copper liquid into the mold at a temperature ranging from 1010 to 1060° C. to obtain a casting part; and (e) releasing the casting part from the mold.

The method of the present invention can further comprise a step of preparing the sand core by mixing one or more selected from the group consisting of rounded sand having particle diameters respectively ranging from 40 to 70 meshes, 50 to 100 meshes and 70 to 140 meshes with a resin and a curing agent, wherein the resin is a urea formaldehyde resin and/or a furan resin. The sand core used in the method of the present invention must be sufficiently dried to lower the number of void defects.

In one embodiment, a sand washing treatment is performed prior to step (a), so as to remove sand and iron wires.

In another embodiment, the weights of the lead-free copper bullion and the foundry return are at a ratio ranging from 6:1 to 9:1, preferably ranging from 6:1 to 8:1, and more preferably 7:1.

Step (b) of the present invention can further comprise the step of adding refining slag, wherein the refining slag is preheated to a temperature above 400° C. prior to the addition.

In an embodiment, the refining slag is added in an amount ranging from 0.1 to 0.5 wt %, preferably ranging from 0.15 to 0.3 wt %, and more preferably 0.2 wt % based on the total weight of the lead-free copper bullion and the foundry return. In step (b), the refining slag can be added singly or by separate fractions.

In step (d) of the present invention, the casting of the molten copper liquid can be gravity casting. The casting temperature in step (d) needs to be maintained at a range from 1010° C. to 1060° C. Casting is performed by batches, wherein the casting amount is about 1 to 2 kilograms in every batch, and the casting time is about 3 to 8 seconds.

In the method of the present invention, releasing of the mold is performed 10 or 15 seconds after the casting or till the casting is not red and hot. In a preferred embodiment, the casting part released from the mold is cooled by natural cooling.

The method of the present invention can further comprise the following steps after step (e): cooling the mold and maintaining the temperature of the mold ranging from 180 to 220° C.; and cleaning the mold (for example, by blowing compressed air onto the surface of the mold) and spreading a small amount of graphite liquid on the surface of the mold (for example, spraying with a sprayer) for the next casting.

In an embodiment, the mold is immersed in and cooled with graphite liquid for 3 to 8 seconds. The graphite liquid is preferably maintained at a temperature ranging from 25 to 40° C., and the specific weight of the graphite liquid ranges from 1.02 to 1.10.

RIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the solidified state of a molten low lead brass of the present invention;

FIG. 2 shows the morphology of a specimen of a low lead brass of the present invention viewed under a scanning electronic microscope (SED) and a quantitative analysis performed on the elements present in a microscopic region by using an X-ray energy dispersive spectroscope (EDS);

FIG. 3A shows the metallographic structural distribution of the specimen of the low lead brass of the present invention;

FIG. 3B shows the metallographic structural distribution of a specimen of a lead-free bismuth brass;

FIG. 3C shows the metallographic structural distribution of a specimen of a C85710 lead brass;

FIG. 4A shows material cracking in the specimen of a lead-free bismuth brass;

FIG. 4B is an enlarged view showing cracks in the specimen of a lead-free bismuth brass;

FIG. 5A shows the metallographic structural distribution after performing a test of dezincification corrosion resistance on the specimen of a lead-free bismuth brass;

FIG. 5B shows the metallographic structural distribution after performing a test of dezincification corrosion resistance on the specimen of a low lead brass according to the present invention;

FIG. 6A shows the chip breaking from a lead-free bismuth brass;

FIG. 6B shows the chip breaking from a C85710 lead brass;

FIG. 6C shows the chip breaking from a low lead brass of the present invention;

FIG. 7 is a schematic diagram showing the production of a product comprising the low lead brass according to the present invention; and

FIGS. 8A and 8B illustrate mechanisms for segregating bismuth in an alloy on a grain boundary.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description of the present invention is illustrated by the following specific examples. Persons skilled in the art can conceive the other advantages and effects of the present invention based on the disclosure contained in the specification of the present invention.

Unless otherwise specified, the ingredients comprised in the low lead brass alloy of the present invention are all based on the total weight of the alloy, and are expressed in weight percentages (i.e. wt %).

The present inventors found that when a high bismuth content (i.e. more than 1 wt %) is added to the brass alloy conventionally, at the micro level, thin liquid Bi films are easily formed in the grain of the brass alloy, and later generate continuously flaky bismuth by segregation on the grain boundary to mask it, so that the mechanical strength of the alloy breaks down and the hot shortness and cold shortness of the alloy in turn increase, thereby causing material cracking. Nevertheless, according to the low lead brass alloy formulation of the present invention, only less than 0.4 wt % of bismuth is needed. This can solve material cracking, and achieve the required material characteristics (such as machinability) of lead brasses (such as conventional C85710 lead brasses) without the likeliness to cause product defects likes cracks and slag inclusions. Hence, the amount of bismuth used in the low lead brass alloy of the present invention can be significantly decreased. This is effective in lowering the production costs of low lead brass alloys, and extremely advantageous in commercial-scale productions and applications.

Moreover, according to the low lead brass alloy formulation of the present invention, the lead content of the alloy can be lowered to a range from 0.05 to 0.3 wt %, to conform to the stipulated international requirement for the leads contents in water pipelines. Hence, the low lead brass alloy according to the present invention is applicable to applications to manufacturing of faucets and laboratory components, water pipelines and water supply systems.

In one embodiment, the low lead brass alloy of the present invention comprises 0.05 to 0.3 wt % of lead, 0.3 to 0.8 wt % of aluminum, 0.01 to 0.4 wt % of bismuth, 0.1 to 0.15 wt % of microelements (i.e., rare earth elements and/or unavoidable impurities) and 97.5 to 99.54 wt % of copper an zinc, wherein copper is in an amount ranging from 58 to 70 wt %.

The present invention is illustrated in details by the exemplary examples below. Example 1:

In the example 1, the ingredients (the unit weight percentages) of the low lead brass alloy of the present invention are as follows:

Cu: 62.51
Zn: 35.72
Pb: 0.177
Bi: 0.154
Al: 0.478
P: 0.52
Sn: 0.183
Ce: 0.114.

A scanning electron microscopy (SEM) and an X-ray energy dispersive spectroscope (EDS) are used to analyze the morphology, composition and mechanism of a specimen of the brass. Results are shown in FIGS. 1 and 2 and Table 1. As shown in the microscopic image in FIG. 2, spot A is α phase and high in copper content, and has a small amount of bismuth in grains; spot B is β phase and high in zinc content, and does not contain bismuth; and spot C is a grain boundary, and has more bismuth precipitated therefrom to form soft spots which are prone to chip breaking, thereby increasing the machinability of the material. Analyses of the compositions of spots A, B and C of the specimens of the low bismuth brass are shown in FIG. 1.

TABLE 1

Analysis of energy dispersion spectra (atomic percentage)

A (α)
B (β)
C

Cu
63.03
51.91
61.09

Zn
24.31
42.87
35.1

Bi
0.09
0
2.37

Pb
0.25
0.17
0.04

Al
0.67
0.53
0.1

P
8.01
1.76
0.26

Test Example 1

Under the same producing and operating conditions, the low lead brass alloy (examples 2 to 4) of the present invention, lead-free bismuth brass alloy (comparative examples 1 to 4), H-59 lead brass alloy (comparative examples 5 and 6), and high phosphorus lead brass alloy (comparative example 7) were used as materials to produce the same product. The processing characteristics of each alloy and the yield of production at each stage were compared, wherein the yield is defined as follows:

yield of production=the number of non-defective products/the total number of products×100%

The yield of production reflects the qualitative stability of the production. High qualitative stability ensures normal production.

TABLE 2

Statistical data of the products

high
the low lead

phosphorus
brass of the

lead-free bismuth brass
C85710 brass
lead brass
present invention

comparative
comparative
comparative
comparative
comparative
comparative
comparative
example
example
example

category
example 1
example 2
example 3
example 4
example 5
example 6
example 7
2
3
4

measured Cu
62.48
62.57
63.01
61.96
61.5
61.1
62.29
63.35
61.12
62.51

content (%)

measured Al
0.513
0.556
0.563
0.555
0.607
0.589
0.537
0.515
0.531
0.524

content (%)

measured Pb
0.0075
0.0042
0.0067
0.0047
1.47
1.54
0.117
0.182
0.151
0.143

content (%)

measured Bi
0.762
0.549
0.312
0.147
0.0119
0.0089
0.125
0.117
0.149
0.116

content (%)

measured P
0.0024
0.0083
0.0074
0.0041
0.0002
0.0002
0.947
0.435
0.584
0.721

content (%)

yield in
71%
78%
85%
88%
96%
95%
83%
93%
92%
92%

casting

yield
84%
82%
81%
77%
99%
99%
97%
98%
99%
97%

in mechanical

processing

yield
89%
88%
90%
91%
92%
94%
94%
96%
95%
95%

in casting

polishing

total yield
53.1%
56.3%
62.0%
61.7%
87.4%
88.4%
75.7%
87.5%
86.5%
84.8%

As shown in FIG. 2, when lead-free bismuth brass is used as a material for product casting, more casting defects are found in the obtained casting part. Thus, the total yield of production is lower than 70%. The higher the bismuth content, the lower the yield. The major defects observed in the casting part in which lead-free bismuth brass is used as material are voids, slag inclusions, cracks, misrun and shrinkage. The defective products with the above defects comprise 72% of the total number of defective products. Specifically, the fluidity of the molten copper liquid of the lead-free bismuth brass is low and the filling of the mold is poor, such that the casting part is prone to misrun. Cracking is likely to occur in the casting part, and some minor cracks are not found until the final polishing step. Slag inclusions and voids are likely to occur in the casting part. Further, the machinability of lead-free bismuth brass is poor, such that problems like vibration and adhesion are likely to occur, thereby causing low yield during subsequent mechanical processing.

Moreover, when the low lead brass of the present invention is used as a raw material in the test group, the yield is the best (i.e. higher than 90%), and the material fluidity of the low lead brass is close to that of the conventional C85710 lead brass. After performing optimization of the casting art, an equiaxed dendritic crystal phase structure with low occurrence of embrittlement is obtained after the casting part solidifies. While ensuring the machinability, the above structure ensures that defects like cracking is not prone to occur, so that the entire material can suffice the production requirements. Among them, high phosphorus content is likely to cause casting defects in brass alloys, and lower yield. Therefore, the phosphorus content of the low lead brass of the present invention should not be more than 0.8%. Further, the corrosion resistance of the low lead brass of the present invention is improved compared with the lead-free high bismuth brass in comparative examples 1 and 2.

Test Example 2

A specimen of a brass material was placed under a metallographic microscope to examine the structural distribution of the material. The results magnified at 100-fold is shown in FIG. 3.

The measured values of the ingredients of the low lead brass in example 1 were Cu: 63.35 wt %, AI: 0.515 wt %, Pb: 0.182 wt %, Bi: 0.117 wt %, P: 0.425 wt %. The structural distribution of the low lead brass is shown in FIG. 3A, wherein an equiaxed dendritic crystal phase structure is shown, and the material is prone to chip breaking and can provide good machinability due to the grains shown as dendritic phases. Further, the crystal phase structure has low occurrence of embrittlement, thereby not being likely to have defects like cracks.

FIG. 3B shows a structural distribution in comparative example 1, the measured values of the major ingredients of the lead-free bismuth brass are Cu: 62.48 wt %, Al: 0.513 wt %, Pb: 0.0075 wt %, Bi: 0.762 wt % and P: 0.0024 wt %. When bismuth content is high, more heterogeneous nucleation sites are formed and nucleation rates are high; and when the composition of a phase is over cooling, the grains formed are mainly dendritic and rarely massive crystals. Hence, bismuth segregates on the grain boundary and generates continuously flaky bismuth, so that the mechanical strength of the material breaks down and the hot shortness and cold shortness are increased, thereby causing the material to crack.

FIG. 3C shows the structural distribution in comparative example 6, wherein the measured values of the ingredients of the C85710 lead brass were Cu: 61.1 wt %, Al: 0.589 wt %, Pb: 1.54 wt %, Bi: 0.0089 wt % and P: 0.0002 wt %. a phase of the alloy is round-shaped and has good toughness, and thus it is not likely to have defects like cracks.

Among them, the specimen of the lead-free high bismuth brass in comparative example 1 cracked naturally after casting. FIG. 4A shows cracks of the specimen, and FIG. 4B shows results of an observation of the specimen under a stereo microscope. As shown in FIGS. 4A and 4B, sites with higher bismuth contents were likely to have bigger gaps along the direction of the grain boundary, thereby lowering the mechanical strength.

Test Example 3

A dezincification test was performed on the brass alloys in examples 3 and 4 to examine the corrosion resistance of brass. The dezincification test was performed according to the standards set forth in Australian AS2345-2006 “Anti-dezincification of copper alloys”. Before a corrosion experiment was performed, a novolak resin was used to make the exposed area of each brass be 100 mm², the specimens were ground flat using a 600# metallographic abrasive paper following by washing using distilled water, and the specimens were baked dry The test solution was 1% CuCl₂solution prepared before use, and the test temperature was 75±2° C. The specimens and the CuCl₂solution were placed in a temperature-controlled water bath to react for 24±0.5 hours, and the specimens were removed from the water bath and cut along the vertical direction. The cross-sections of the specimens were polished, and then the depths of corrosion thereof were measured and observed under a digital metallographic microscope. Results are shown in FIG. 5.

As shown in FIG. 5, the average dezincified depth of the lead-free low bismuth brass (Bi: 0.147%) in comparative example 4 was 324.08 mm; and as shown in FIG. 5B, the average dezincified depth of the low lead brass (Bi: 0.149%) of the present invention was 125.36 mm. The above results proved that low lead brass of the present invention had better dezincification corrosion resistance.

Test Example 4

A mechanical property test was performed on the brass alloys according to the standards set forth in IS06998-1998 “Tensile experiments on metallic materials at room temperature”. Results are shown in Table 3.

TABLE 3

Results of the mechanical property test

mechanical property

tensile strength (Mpa)
elongation (%)

Type of material
1
2
3
4
5
average
1
2
3
4
5
average

Comparative
372
358
349
367
375
364.2
15
14
11
12
10
12.4

example1

Comparative
356
337
363
374
367
359.6
12
11
13
13
12
12.2

example5

As shown in Table 3, the tensile strength and elongation of the low lead brass alloy of the present invention were comparable to those of the C85710 lead brass. This means that the low lead brass of the present invention has the same mechanical property as that of the C85710 lead brass, indicating that the C85710 lead brass can be replaced by the low lead brass of the present invention in manufacturing of products.

Test Example 5

A test was performed according to the standards set forth in NSF 61-2007a SPAC for the allowable precipitation amounts of metals in products, to examine the precipitation amounts of the metals of the brass alloys in aqueous environments. Results are shown in Table 4.

TABLE 4

Precipitation amounts of metals in the products

comparative

example 5

Upper limit of

(after a lead

standard value
comparative
stripping

Element
(ug/L)
example 5
treatment)
example 1

lead (Pb)
5.0
19.173
0.462
0.281

bismuth (Bi)
50.0
0.011
0.006
0.023

aluminum (Al)
5.0
0.093
0.012
0.146

As shown in FIG. 4, various metal precipitation amounts of the low lead brass of the present invention were lower than the upper limits of the standard values, and therefore, the low lead brass of the present invention conforms to NSF 61-2007a SPAC. Further, the low lead brass of the present invention clearly had a lower precipitation amount of the heavy metal, lead, than that of the C85710 lead brass. Thus, the low lead brass of the present invention is more environmentally friendly, and more beneficial to human health.

Test Example 6

A machinability test was performed on the low lead brass in example 1, the lead-free bismuth brass in comparative example 1 and the C85710 lead brass in comparative example 5, respectively, on a lathe. The machinability test was set at the following conditions: 2 mm of feed amount, 950 rpm of rotating speed, and 0.21 mm/rev of charging amount. Results are shown in FIGS. 5 and 6.

TABLE 5

Results of the machinability test on the brasses in example 1,

comparative examples 1 and 5

comparative
comparative

example 1
example 5
example 1

Category
1#
2#
1#
2#
1#
2#

machining energy u
979.84
998.32
809.93
816.72
839.78
832.43

(N/mm²)

machining
Ff (N)
178.34
162.49
95.47
100.54
118.65
104.82

resistance
Fp (N)
42.72
37.23
23.31
21.72
28.69
24.62

Fc (N)
349.31
336.89
212.97
231.83
254.26
227.36

machining forms
chips broke were curvy
chips broke were
chips broke were

and continuously
needle-shaped and
needle-shaped or flaky

formed
disintegrated
and disintegrated

In the machinability tests, machining resistance of the lead-free bismuth brass was the highest in axial direction (Ff), longitudinal direction (Fp) and normal direction (Fc), and the machining resistance of the low lead brass of the present invention was closer to that of the conventional C85710 lead brass. The machining energy was also maximum for the lead-free bismuth brass, and closer to that of the conventional C85710 lead brass.

Moreover, as shown in FIG. 6, due to the distribution of lead on the brass substrate by dispersing soft spots, the chips broke from C85710 lead brass were disintegrated and round-shaped or needle-shaped and had good machinability (see FIG. 6B); the chips broke from the low lead brass of the present invention were similar to that of the C85710 lead brass (see FIG. 6C); and the chips broke from the lead-free bismuth brass was flaky and had poor machinability (see FIG. 6A).

It can be elucidated from each of the above test examples that the machinability of the lead-free bismuth brass material is poorer than that of the conventional C85710 lead brass, and is prone to have cutting problems like vibration and adhesion, thereby causing the yield in the subsequent mechanical processing to be overly low. Thus, lead-free bismuth brass is not a suitable replacement of a lead brass alloy. Further, when the lead-free bismuth brass material is used in manufacturing of products, slag inclusions, voids and cracks are likely to occur in casting parts. Cracks are often not found until the polishing step is reached, and production costs are higher. Hence, the lead-free bismuth brass is not suitable for industrial applications.

The low lead brass alloy of the present invention has a mechanical property (for example, machinability) comparable to that of the C85710 lead brass and is better than that (for example, tensile strength and elongation) of the conventional C85710 lead brass, and the yield of production and mechanical processing of the casting parts are also good. Further, the precipitation amount of lead from the low lead brass of the present invention is significantly lowered, thus it is an extremely suitable alloy material to replace conventional lead brasses.

Test Example 7

Brasses, of the present invention, for use in faucets were cast environmentally friendly as shown in FIG. 7.

The rounded sand having particle diameters ranging from 40 to 70 meshes, 50 to 100 meshes and 70 to 140 meshes, an urea formaldehyde, a furan resin and a curing agent were used as raw materials to prepare sand core using a core shooter, and the gas evolutions of the resins were measured using a testing machine. The obtained sand core must be completely used within 5 hours, or it needs to be baked dry.

The low lead brass alloy of the present invention and the foundry return were preheated for 15 minutes to reach a temperature higher than 400° C., and the two were mixed at a weight ratio of 7:1 for melting in an induction furnace until the brass alloy reached a certain molten state (hereinafter referred to as molten copper liquid). An analysis was performed on a copper alloy sample, and an ingredient analysis was performed using a direct reading. After verifying that the chemical composition of the copper alloy complies with the requirement, casting was performed by coupling a metal gravity casting machine with the sand core and a gravity casting mold. A monitoring system was further used for controlling, so as to maintain casting temperature between 1010 and 1060° C.

In order to avoid reducing the number of casting defects caused by great temperature variations during casting, each charging amount was preferably limited to 1 to 2 kg, and the casting temperature was controlled to between 3 to 8 seconds. The surface of the molten copper liquid and the spoon were cleaned after each charging, and the surface of the molten copper liquid was observed with an eye to avoid an excessive amount of impurities floating thereon, and checking the spoon to avoid adhesion of an excessive amount of oxides thereon. If the casting part is a steel die, a furnace slag cleaning process was performed after casting 5 to 8 molds, and if the casting part is a copper die, a furnace slag cleaning process was performed after casting 20 molds.

When the casting part from each mold was released, the mold was cleaned using an air gun to ensure that the site of the core head is clean. The graphite liquid was spread on the surface of the mold following by cooling by immersion. The temperature of the graphite liquid for cooling the mold was preferably maintained between 30 to 36° C. Before each of the casting, the concentration of the graphite liquid was measured using a hydrometer, so as to control the specific weight of the graphite liquid to between 1.05 and 1.06. The impurities in the water tank must be removed, so as to reduce the defects in the appearances of the casting parts. The graphite liquid was cooled collectively by a central cooling system, passing through a channel to allocate cooling water to each of the water tanks of the gravity casting machine, following by immersing the molds into the water tanks to reach cooling effects.

After the molds were cooled, the molds were opened, the castings were released and the casting heads were cleaned. The temperatures of the molds were monitored, so as to control the temperatures to between 200 and 220° C. to faun casting parts. Subsequently, the casting parts were released. During releasing of molds, the casting parts should be removed and set aside carefully, so as to avoid the casting parts from being destroyed in a red and hot state.

After the molten copper liquid in an induction furnace was completely cast, self-inspection was performed on the cooled casting parts and the casting parts were then cleaned in a sand cleaning drum. Then, an as-cast treatment was performed, wherein a thermal treatment for distressing annealing during casting of as-casts was performed on as-casts to eliminate the internal stress generated by casting. The as-casts were subsequently mechanically processed and polished, so that no sand, metal powder or the other impurities adhered to the cavities of the casting parts. The as-casts were completely enclosed, so as to perform sealing tests on shells and spacers in water. Afterwards, the as-casts were classified for stocking after a product inspection analysis was performed.

By the process of the present invention and taken the 6Ms (i.e., man, machine, material, method, measurement and mother nature) into full considerations, lead-free brass was produced by gravity casting. Production conditions such as temperature and time were strictly specified, so as to effectively control each of the variable factors. Undesirable situations which are usually observable in products were minimized.

In conclusion, the low lead brass alloy of the present invention can improve the casting property of the material, and has good toughness and excellent machinability. These can achieve the required material characteristics of conventional lead brasses while not necessarily lead to production of casting defects. Therefore, the alloy material of the present invention is suitable for applications to subsequent processes. Further, the low lead brass alloy material of the present invention is not likely to generate defects like cracks or slag inclusions, and can significantly lower the amount of bismuth used and effectively lower the production costs of the low lead brass alloy, such that it is extremely advantageous in commercial-scale productions and applications.

Furthermore, the use of the process of the present invention can increase the yields of lead-free brass products.

The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation, so as to encompass all such modifications and similar arrangements.

LOW LEAD BRASS ALLOY AND METHOD FOR PRODUCING PRODUCT COMPRISING THE SAME

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