Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PRODUCING LOW LEAD BRASS ALLOY AND PRODUCT
COMPRISING THE SAME
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to methods for producing brass alloys
environmentally-friendly and products comprising the same, and more
particularly,
to a method for producing a low lead brass alloy and a product comprising the
same.
2. Description of Related Art
Major components of brasses are 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, and thus the 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 issues like environmental
pollutions
become major focuses, 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, putting 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
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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 up to the
present. In examples where silicon (Si) is added in brass alloys as a major
ingredient instead of lead, TW421674, US7354489, 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 by CN10144045,
contains aluminum, silicon and phosphorus as major alloy elements. Although
the
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 CNIO1285137 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, US7297215,
US6974509, US6955378, US6149739, US5942056, US5653827, US5487867,
US5330712, US20060005901, US20040094243, US5637160 and US20070039667
disclose that the bismuth contents in the aforesaid alloy formulations covers
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,
US6413330 discloses a lead-free copper alloy formulation containing bismuth,
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silicon and other components at the same time, and CNIO1440444 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, CNI01403056 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.
Because 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,
US5904783 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 I to 2.6 wt%o 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 below 0.3
wt%.
SUMMARY OF THE INVENTION
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According to an aspect of the invention, there is provided a low lead brass
alloy,
comprising:
0.05 to 0.3 wt% of lead;
0.5 to 0.8 wt% of aluminum;
0.01 to 0.1 wt% of bismuth;
0.1 to 0.15 wt% of microelements; and
more than 97.85 wt% of copper and zinc, wherein the copper is in an amount
ranging from 58 to 70 wt%;
wherein the phosphorus is in an amount ranging from 0.4 to 0.8 wt%.
According to another aspect of the invention, there is provided a method for
producing a product comprising the low lead brass alloy of claim 1, comprising
the
following steps:
preheating the low lead brass alloy and foundry return to a temperature
ranging from
400 C to 500 C ;
melting the low lead brass alloy and the foundry return to boiling to form a
molten
copper liquid;
preheating a mold to 200 C and placing sand core into the mold;
casting the molten copper liquid into the mold at a temperature to obtain a
casting part,
wherein the temperature ranges from 1010 to 1060 C; and
releasing the casting part from the mold.
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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 0.1 wt% of bismuth (Bi),
0.1 to
0.15 wt% of microelements and more than 98.65 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 another aspect, 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%.
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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 strongly refine the as-cast
microstructure of an alloy material, induce changes in the relative amounts
and
crystal morphologies of a and (3 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 an aspect, 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 surface low, 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 the purpose of
maintaining the machinability of brass. Pb phase is face-centered cubic
lattices with
a lattice constant of 4.949 x 10-10 in, 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 x 10-10 m, and Cu and
Bi in
solid states are essentially not mutually dissolvable. Therefore, a small
amount of Bi
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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 uses 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, thereby avoiding the material
embrittlement.
In the present invention, phosphorus is further added to the brass alloy to
reduce 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 to be approximate to 0.5. If a
dihedral
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angel 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 an aspect, 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 aspect, 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.
According to the aspects of the present invention, the present invention
provides a method for producing a product comprising a low lead brass alloy,
comprising the steps of: preheating the low lead brass alloy and foundry
return to a
temperature ranging from 400 C to 500 C; melting the low lead brass alloy and
the
foundry return to boiling to form a molten copper liquid; preheating the mold
into
200 C and placing sand core into the mold; casting the molten copper liquid
into the
mold at a temperature to obtain a casting, wherein the temperature ranges from
1010
to 1060 C; and releasing the casting part from the mold.
The method of the present invention can further comprise a step for
preparing the sand core by mixing one or more selected from the group
consisting
of rounded sand having particle diameters 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
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urea formaldehyde resin and/or a furan resin. The sand core used by the method
of
the present invention must be sufficiently dried to lower the number of void
defects.
In an aspect, a sand washing treatment is performed prior to the step of
preheating the low lead brass alloy and foundry return to a temperature
ranging
from 400 C to 500 C, so as to remove sand and iron wires.
In another aspect, 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 of melting the low lead brass alloy and the foundry return to boiling to
form a molten copper liquid 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%,
of the total weight of the lead-free copper bullion and the foundry return. In
the step
of melting the low lead brass alloy and the foundry return to boiling to form
a
molten copper liquid, the refining slag can be added singly or by separate
fractions.
In the step of casting the molten copper liquid into the mold at a temperature
to obtain a casting of the present invention, the casting of the molten copper
liquid
can be gravity casting. The casting temperature in the step of casting the
molten
copper liquid into the mold at a temperature to obtain a casting needs to be
maintained at a range from 1010 C to 1060 C. Regarding the casting step,
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
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or 15 seconds after the casting or in the situation in which 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 the step of releasing the casting part from the mold: cooling the
mold, so
as to maintain 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 aspect, the mold is cooled with graphite liquid by immersing therein 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
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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.
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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 the embodiment, the low lead brass alloy of the present invention
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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%.
In the 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 preferred 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.
After a scanning electron microscopy (SEM) and an X-ray energy dispersive
spectroscope (EDS) are used to analyze the morphology, composition and
mechanism
of formation of a specimen of the brass produced environmentally friendly.
Results
are shown in FIGs. 1 and 2 and Table 1. As shown in the microscopic image in
FIG
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2, spot A is a phase and high in copper content, and has a small amount of
bismuth
in grains; spot B is 0 phase and high in zinc content, and generally 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.
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Table 1. Analysis of energy dispersion spectra (atomic percentage)
A(a) B(f3) 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 I 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
of the
alloys and the non-defectiveness in production at each stage were compared,
wherein the non-defectiveness is defined as follows:
non-defectiveness in production = the number of non-defective products/the
total
number of products x 100%
The non-defectiveness in 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 brass of the
categ ory lead-free bismuth brass 085710 brass phosphorus
present invention
lead brass
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comparative comparative comparative comparativ comparative comparative
comparative exampl exampl exampl
example] example2 example3 e example4 example5 example6 example 7 e2 e3 e4
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 (%)
non-
defectiveness 71% 78% 85% 88% 96% 95% 83% 93% 92% 92%
in casting
non-
defectiveness
84% 82% 81% 77% 99% 99% 97% 98% 99% 97%
in mechanical
processing
non-
defectiveness
89% 88% 90% 91% 92% 94% 94% 96% 95% 95%
in casting
polishing
total non-
53.1% 56.3% 62.0% 61.7% 87.4% 88.4% 75.7 /a 87.5% 86.5% 84.8%
defectiveness
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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 non-defectiveness in production is lower than 70%. The higher the
bismuth
content, the lower the non-defectiveness. 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
non-defectiveness 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 non-defectiveness 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 non-defectiveness.
Therefore, the
phosphorus content of the low lead brass of the present invention should not
be more
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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%, Al: 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 the higher the undercooling of the composition
of a
phase, the grains formed are mainly dendritic and rarely massive crystals.
Hence,
bismuth segregates on the grain boundary and generate 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
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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 I 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 of the
brasses to be 100 mm', 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 % CuC12 solution prepared before use, and
the test
temperature was 75 2 C. The specimens and the CuC12 solution 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
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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
Type of
tensile strength (Mpa) elongation ( )
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
examples
As shown in Table 3, the tensile strength and elongation of the low lead
brass alloy of the present invention were the 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
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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
Element Upper limits comparative comparative example example I
of standard example5 5
values (after a lead stripping
(ug/L) treament)
lead (Pb) 5.0 19.173 0.462 0.281
bismuth (Bi) 50.0 0.011 0.006 0.023
aluminum 5.0 0.093 0.012 0.146
(Al)
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.
CA 02675525 2011-09-08
Test example 6:
A machinability test was performed on the low lead brass in example 1, the
lead-free bismuth brass in comparative example I and the C85710 lead brass in
comparative example 5, respectively, on a lathe. The machinability test was
set at
the following conditions: 2mm 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
example 1
Category examplel 5
1# 2# l# 2# 1# 2#
machining energy u
979.84 998.32 809.93 816.72 839.78 832.43
(N/MMz)
Ff (N) 178.34 162.49 95.47 100.54 118.65 104.82
machining
Fp(N) 42.72 37.23 23.31 21.72 28.69 24.62
resistance
Fc(N) 349.31 336.89 212.97 231.83 254.26 227.36
chips broke were
chips broke were chips broke were
needle-shaped or
machining forms curvy and needle-shaped and
flaky and
continuously formed disintegrated
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
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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 non-defectiveness 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 non-defectiveness in 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.
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Test example 7:
Brasses, of the present invention, for use in faucets were cast
environmentally friendly as shown in FIG 7.
First, 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 and after
each
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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. A 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,
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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.
CA 02675525 2011-09-08
Furthermore, the use of the process of the present invention can increase the
yields and non-defectiveness 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.
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