U.S. patent application number 16/436634 was filed with the patent office on 2019-12-12 for shaped parts made of a corrosion-resistant and machinable copper alloy.
This patent application is currently assigned to Gebr. Kemper GmbH + Co. KG Metallwerke. The applicant listed for this patent is Gebr. Kemper GmbH + Co. KG Metallwerke. Invention is credited to Andreas Hansen.
Application Number | 20190376162 16/436634 |
Document ID | / |
Family ID | 66826940 |
Filed Date | 2019-12-12 |
United States Patent
Application |
20190376162 |
Kind Code |
A1 |
Hansen; Andreas |
December 12, 2019 |
SHAPED PARTS MADE OF A CORROSION-RESISTANT AND MACHINABLE COPPER
ALLOY
Abstract
The present invention concerns a copper alloy, its use and a
process for the manufacture of mouldings, and the mouldings made
therefrom.
Inventors: |
Hansen; Andreas; (Reichshof,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gebr. Kemper GmbH + Co. KG Metallwerke |
Olpe |
|
DE |
|
|
Assignee: |
Gebr. Kemper GmbH + Co. KG
Metallwerke
Olpe
DE
|
Family ID: |
66826940 |
Appl. No.: |
16/436634 |
Filed: |
June 10, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 9/02 20130101; C22F
1/08 20130101; B21D 22/022 20130101; C22C 9/04 20130101 |
International
Class: |
C22C 9/02 20060101
C22C009/02; B21D 22/02 20060101 B21D022/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 2018 |
DE |
102018004702.5 |
Claims
1. Copper alloy suitable for the manufacture of shaped parts by a
process comprising at least one hot forming operation, the alloy
having the following composition in % by weight: Sn: 2 to 6% Zn: 0
to 5% S: 0.05 to 0.6% Pb: less than 0.25 Ni: less than 0.6 Sb: less
than 0.2 and optionally phosphorus to a maximum of 0.06% by weight,
B to a maximum of 0.03% by weight, Zr to a maximum of 0.03% by
weight, and unavoidable impurities, and the balance being Cu.
2. A shaped article manufactured by a process comprising at least
one hot forming operation, the alloy having the following
composition in % by weight: Sn: 2 to 6% Zn: 0 to 5% S: 0.05 to 0.6%
Pb: less than 0.25 Ni: less than 0.6 Sb: less than 0.2 and
optionally phosphorus to a maximum of 0.06% by weight, B to a
maximum of 0.03% by weight, Zr to a maximum of 0.03% by weight, and
unavoidable impurities, and the balance being Cu.
3. Process for the production of shaped parts from a copper alloy,
wherein the alloy has the following composition in % by weight: Sn:
2 to 6% Zn: 0 to 5% S: 0.05 to 0.6% Pb: less than 0.25 Ni: less
than 0.6 Sb: less than 0.2 and optionally phosphorus to a maximum
of 0.06% by weight, B to a maximum of 0.03% by weight, Zr to a
maximum of 0.03% by weight, and unavoidable impurities, and the
balance being Cu; said process comprising the steps of: at least
one hot forming operation of the copper alloy to produce a shaped
article
4. A copper alloy according to claim 1, wherein the sum of
impurities does not exceed 0.25% by weight.
5. A copper alloy according to claim 1, characterized in that the
tin content is 2 to 4% by weight.
6. A copper alloy according to claim 1, characterized in that the
zinc content is 0 to 3% by weight.
7. A copper alloy according to claim 1, characterized in that the
sulfur content is 0.1 to 0.45 wt. %.
8. A copper alloy according to claim 1, wherein the alloy does not
contain elements of the group Al, Si, Sb, Te, Se, C and Bi and/or
wherein the alloy does not contain Pb.
9. The process according to claim 3 further comprising the step of
machining after the at least one hot forming.
10. (canceled)
11. A shaped product, comprising a copper alloy, wherein the alloy
has the following composition in % by weight: Sn: 2 to 6% Zn: 0 to
5% S: 0.05 to 0.6% Pb: less than 0.25 Ni: less than 0.6 Sb: less
than 0.2 and optionally phosphorus to a maximum of 0.06% by weight,
B to a maximum of 0.03% by weight, Zr to a maximum of 0.03% by
weight, and unavoidable impurities, and the balance being Cu.
12. The shaped product of claim 11, wherein the sum of impurities
does not exceed 0.25% by weight.
13. The shaped product of claim 11, wherein the tin content is 2 to
4% by weight.
14. The shaped product of claim 11, wherein the zinc content is 0
to 3% by weight.
15. The shaped product of claim 11, wherein the sulfur content is
0.1 to 0.45 wt. %.
16. The shaped product of claim 11, wherein the alloy does not
contain elements of the group Al, Si, Sb, Te, Se, C and Bi and/or
wherein the alloy does not contain Pb.
Description
[0001] This invention concerns a copper alloy, its use and a
process for the production of mouldings, as well as the mouldings
made from it.
STATE OF THE ART
[0002] Water is a valuable raw material and indispensable for daily
use. Therefore, when drinking water is taken from the supply
system, it has to be microbiologically so that its subsequent
consumption does not lead to any human illness. In order to achieve
this, high demands are placed on materials that come into direct
contact with drinking water. Copper is the noblest commodity
material and is regarded as an indispensable material in industry
and technology for water-bearing systems. Copper has bacteriostatic
properties and also offers excellent corrosion resistance. Copper
also shows positive properties in shaping. Copper casting alloys
are easy to cast and the high strength and toughness of the
material also make it particularly suitable for plastomechanical
forming.
[0003] However, it is precisely this plastic deformability that
causes problems during machining. Here, homogeneous copper
materials tend to form long chips. This type of chip inhibits the
work sequence during fully automatic turning or drilling and leads
to heavy wear on the tool cutting edges. The chip formation of
copper is often the limiting factor in mechanical machining and
therefore has a direct influence on the economic efficiency of the
workpieces.
[0004] Gunmetal belongs to the group of copper casting alloys and
is characterised by the combination of good castability with
optimum machinability and high strength. Due to its good corrosion
resistance, gunmetal is particularly suitable for water-bearing
systems such as fittings and sanitary technology. Common gunmetal
alloys contain tin to increase strength and corrosion resistance.
Zinc is added as a cost-effective substitute for copper. In order
to be able to process the products made of gunmetal economically at
all, the heavy metal lead is added, which acts as a chip breaker in
the alloy and makes machining possible on CNC machines and
conventional automatic lathes.
[0005] If the drinking water stagnates over a longer period of time
in commercially available lead-containing fittings, there is a
possibility that lead may be released into the tap water through
metal ion migration. High lead concentrations are considered
harmful to health. For this reason, ever stricter requirements are
being imposed worldwide on the lead content of materials that come
into contact with drinking water. Within Germany, too, the lead
content has been reduced to 10 .mu.g lead/I since Jan. 12, 2013 via
the statutory drinking water ordinance. The pressure to further
reduce lead content in drinking water has increased worldwide and
will continue to grow. For example, legal requirements from the USA
require that lead contents in copper alloys must not exceed an
average lead content of 0.25%, irrespective of the actual lead
concentration in drinking water.
[0006] The ideal gunmetal would be free of lead and other
questionable substances, with the same or better efficiency in
production and without impairing corrosion resistance, high
mechanical strength and good processability.
[0007] EP 2290114 A1 describes a lead-free gunmetal alloy with 4 to
6 wt. % tin, 4 to 6 wt. % zinc and less than 0.25 wt. % lead. Wth
this alloy, lead-free components can be produced by means of
casting processes. However, the subsequent mechanical processing to
create the functional surfaces of these components is not taken
into account. Without lead, the specified composition shows a
homogeneous .alpha.-MK microstructure which tends to form long
chips and cannot be machined economically. The presupposed casting
process also requires a higher material input for the production of
the moulded part than alternative forming processes. The US
2012/0082588 A1, the EP 2 241 643 A1, the EP 3 225 707 A1 and the
U.S. Pat. No. 9,181,606 B2 reveal copper alloys.
[0008] EP 2 872 660 B1 describes a forming process for a lead-free
gunmetal alloy. A process for preconditioning a gunmetal alloy
containing 2 to 8% by weight tin, 2.5 to 13% by weight zinc and
less than 0.25% by weight lead which is suitable for hot pressing
and exhibits a homogeneous structure at the end of the hot pressing
process is described. Hot forming enables the economical production
of shaped parts with low material input. Although the process
sequence up to the shaping of the blank is explained, the
subsequent machining process necessary for the elaboration of
functional surfaces of the components is not taken into account.
Due to the chemical composition and the subsequent hot forming, a
homogeneous microstructure is created and here, too, the absence of
a chip breaker can be expected to result in long chip formation
during machining, which makes economic machining of the components
more difficult.
[0009] EP 1 801 250 A1 describes low-migration components made of a
copper alloy with a relatively high content of Si, in addition to
lower but significant proportions of Mn, Al and Zr. Similar copper
alloys are also disclosed in WO 2007/068470.
[0010] Despite the many copper alloys now known in the state of the
art, it is still a challenge to specify gunmetal copper alloys
which, on the one hand, manage without the use of lead (Pb), which
is problematic from an environmental and health point of view, and,
on the other hand, enable forming processes without impairing the
mechanical properties and corrosion resistance. The provision of
copper alloys which show good hot formability (i.e. without any
significant drop in mechanical properties) and are also preferably
easy to machine has proved to be particularly challenging.
Task of the Present Invention
[0011] Due to the above-mentioned disadvantages in the state of the
art, it is the task of the present invention to indicate a copper
alloy which overcomes these disadvantages. In particular, a copper
alloy that comprises as few components as possible, is lead-free or
essentially lead-free and can also dispense with expensive metal
components and/or metal components that are difficult to mix in
would be desirable.
Short Description of the Invention
[0012] This task is solved by the copper alloy according to claim
1, its use according to claim 2, and the process for the production
of moulded parts according to claim 3. Preferred designs are
indicated in the subclaims and in the following description. The
moulded parts manufactured using the copper alloy described here
are also subject to stress.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present invention is described in the following first of
all with regard to the alloy in accordance with the invention.
However, it is clear to the skilled person that the preferred
designs described in this context can also be applied to the
described use, the described manufacturing process and the
described moulded parts and must also be regarded as preferred
designs for these aspects of the invention.
[0014] This invention makes it possible to produce shaped parts
with high mechanical strength, high dimensional stability and high
corrosion resistance from a gunmetal alloy, which has a chip
breaker in its microstructure, by means of hot forming with low
material input. These parts can then also be subjected to economic
machining after hot pressing. The hot-formable gunmetal alloy of
the present invention does not require elements such as Al, Si, Pb,
Sb, Te, Se, C and Bi to form a chip breaker in the microstructure
and is therefore easily reusable.
[0015] The present invention thus provides a copper alloy which has
the following composition in % by weight, in particular for the
production of shaped parts from at least one hot forming process
followed by machining:
Sn: 2 to 6%
Zn: 0 to 5%
S: 0.05 to 0.6%
[0016] Pb: less than 0.25 Ni: less than 0.6 Sb: less than 0.2%,
optionally further containing phosphorus to a maximum of 0.06% by
weight, B to a maximum of 0.003% by weight, Zr to a maximum of
0.03% by weight and unavoidable impurities, the sum of the
impurities preferably not exceeding 0.25% by weight, and the
remainder being Cu.
[0017] As stated above, in particular, the alloy invented does not
contain elements of the group Al, Si, Sb, Te, Se, C and Bi and, in
preferred forms, does not contain Pb either.
[0018] Preferred contents of alloy components to be used in
accordance with the invention are as follows, whereby these are
disclosed and claimed individually as well as in each combination
in accordance with the invention (in each case again in % by
weight):
Sn: 2 to 4%, in embodiments 2 to less than 3.5%, such as 2 to 3.25
Zn: 0 to 3%, in embodiments 0 to less than 1.5%, in particular 0.1
to less than 1.5% S: 0.1 to 0.45% and, in embodiments, 0.1 to less
than 0.25%, such as 0.1 to 0.2%. Ni: less than 0.5%, such as from 0
to 0.4%, from 0 to 0.25%
[0019] The copper content in the alloy is preferably 88 wt. % or
more, more preferably 90 wt. % or more.
[0020] It has been shown unexpectedly that the copper alloys
disclosed here can overcome the known disadvantages from the state
of the art. In particular, semi-finished and intermediate products
made of copper alloys can be subjected to hot forming very well.
Despite the frequent degradation of strain hardenings during hot
forming (typically at temperatures of about 600 to 950.degree. C.),
the alloy according to the invention makes it possible to produce
shaped parts (which may then be further processed, e.g. by
machining) which still have excellent mechanical properties and do
not show any degradation of corrosion resistance.
[0021] Furthermore, it has been shown that the formed parts
obtained in this way (i.e. after hot forming) can also be further
processed in an economical manner, since in particular the
undesired formation of long chips is avoided. It can thus be seen
that, despite the processes involved in hot forming, chip breaking
components are still present in the microstructure of the alloy,
although the alloy according to the invention dispenses with
typical chip breaking components such as Pb or Si. So the invention
at hand provides a copper alloy with an excellent balance of
desired properties. It is therefore possible to produce shaped
parts from this alloy, in particular by hot forming, possibly
combined with further processing steps as described here, without
having to fear any reductions in the other desired properties of
the copper alloy and its suitability for use in hot forming.
[0022] The alloy in accordance with the invention can thus be used
advantageously for the manufacture of shaped parts, whereby these
manufacturing processes include hot forming, possibly combined with
other machining processes, such as subsequent machining.
[0023] In order to maintain the desired properties of the copper
alloy described here, the individual alloy components alone and in
their interaction allow good and reproducible control of the alloy
properties.
[0024] Tin acts in the alloy as a solid solution hardener and thus
increases tensile strength, yield strength and hardness, but
reduces elongation at break. Furthermore, tin increases the
corrosion resistance, whereby the corrosion resistance increases
with increasing tin contents. During the production of the blanks
for hot forming it could be recognized that strong segregations
occur in the microstructure due to tin, which lead to the formation
of zone crystals during solidification. At the beginning of
solidification, copper crystals with a lower tin content are
precipitated and the residual melt is enriched with a tin content
that is higher than the average content of the alloy. Deviating
from the stable copper-tin state diagram, a eutectoid may be
present in the microstructure at room temperature at contents of
more than 7 wt. % tin (.alpha.+.delta.); under equilibrium
conditions, this eutectoid is only formed at max. 15.8 wt. % tin.
The possible .delta. phase crystallizes in the kfz lattice and
should therefore be easily deformable, but the phase has a brittle
behavior due to its voluminous elementary cell of 416 atoms. This
makes the subsequent hot forming process more difficult. The
eutectoid can be removed by heat treatment at high temperatures
with sufficient time (.alpha.+.delta.), but heat treatment requires
a lot of energy.
[0025] There is also a risk of grain enlargement of the
microstructure during treatment. This would lead to a reduction in
elongation, making the subsequent hot forming process more
difficult. With a content of 2 to 6 wt. % tin, especially preferred
2-4 wt. % tin, a high mechanical strength with high elongation is
guaranteed and the formation of eutectoid (.alpha.+.delta.) in the
cast state is avoided.
[0026] Sulphur is almost insoluble in solid copper and the original
properties of the material, such as corrosion resistance, are not
affected by the addition of sulphur. Due to its insolubility in
solid copper, sulphur leads to a constitutive behaviour that
influences the solidification process of copper-tin alloys in a
similar way to lead. Unlike lead, however, at the end of
solidification sulphur is not present in the microstructure as an
element, but in the form of an intermetallic metal-sulphur compound
which is evenly distributed in the microstructure. It could be
recognized that this phase is incoherent and brittle in the
microstructure and thus generates a chip breaking mechanism.
[0027] The properties of the sulphides influence the mechanical,
plastic behaviour of the gunmetal material. The influence is
determined by the amount of sulfide phases in the material. From
sulphur contents above 0.6% by weight, the stress transmitting
.alpha.-Cu matrix is so strongly affected by the sulphides that a
hot pressing process is very difficult. The sulphur content of 0.05
wt. % to 0.6 wt. %, particularly preferably 0.1 wt. % to 0.45 wt.
%, ensures that sufficient sulphide inclusions are present in the
microstructure to produce a chip breaking mechanism and ensure a
hot forming process.
[0028] Zinc is added to the alloy as an economic substitute for
copper. It has been recognised that there is a close relationship
between the zinc content and the sulphur content over the time and
the type of distribution of sulphide formation. The higher the zinc
content, the earlier the sulphide inclusions form in the
microstructure during casting solidification. If the zinc content
is above 5% by weight, the sulphide formation is shifted to
temperatures in the range of the solidification temperature of the
gunmetal alloy. In this temperature range there are still high
molten parts in the casting structure which are connected to each
other in places.
[0029] A high zinc content then leads to early formation of the
sulphides. These sulfides are inhomogeneous and concentrated in the
microstructure and thus make the hot pressing process more
difficult due to a local weakening of the .alpha.-MK matrix. If the
zinc content is low, the formation is shifted to lower temperatures
and the sulphides are present in former residual melt areas
separately from each other and homogeneously distributed. The zinc
content of 0 to 5% by weight, particularly 0 to 3% by weight zinc,
ensures that sulphide formation at higher temperatures is
avoided.
[0030] Investigations have shown that the copper alloy according to
the invention has a special suitability for use in a manufacturing
process for shaped parts due to its specific composition, which
process comprises at least one hot forming. Due to the special
composition of the alloy, further processing steps can be carried
out after hot forming without any problems, for example subsequent
machining.
[0031] A hot forming process in accordance with the invention can,
for example, be a hot pressing process. According to the invention,
however, other hot forming processes are also possible which are
known to the specialist. The blank is heated to 600.degree. C. to
950.degree. C. before hot forming, for example a hot pressing
process. From 600.degree. C., the yield strength is sufficiently
low to plastically deform the gunmetal material using a hot forming
process. According to the invention, hot forming can be carried out
at any suitable temperature within the above temperature window,
for example 700 to 900.degree. C. The respective temperature is
selected by the specialist depending on the type of moulded part,
the desired speed of forming, etc.
[0032] It was recognized that in the given temperature range also
the atomic bonds of the sulfides become weaker, so that dislocation
movements in these superstructures are facilitated. In this
temperature range, the phases lose their brittleness and become
deformable and thus do not inhibit the hot forming process.
Immediately after forming, a dynamic recrystallization of the
.alpha.-MK matrix takes place, which removes the previously cast
zone solid solution with different tin concentrations and ensures a
homogeneous concentration across the cross-section and thus
constant mechanical characteristics and corrosion properties.
[0033] After the deformation process at room temperature, however,
the sulphides are distributed again in the microstructure and are
brittle, so that they act as chip breakers. It was possible to
determine that even with thermoformed moulded parts with low
sulphur contents of 0.05 wt. % or more, jerking of the tool occurs
during mechanical machining due to temporally changed friction
between chip and tool. These changed friction conditions are due to
the inhomogeneous microstructure which, after the hot pressing
process, consists of a copper-containing .alpha.-MK matrix with
sulphides embedded in it. Shear bands are produced in the chip due
to the jerky sliding, which lead to lamellar chips and shear chips
and break in the further course of the machining process when
discharged via a chip guide step in the tool. This prevents long
chips and enables economical machining.
[0034] In order to enable the hot pressing process envisaged in the
invention, the average grain size in the cast state should not
exceed 2 mm. The necessary measures to ensure such an average grain
size are known to the expert. Grain refinement is possible, for
example, by using chemical additives such as zirconium and boron up
to contents of 0.005 to 0.03% by weight or other alternative
processes to grain refinement such as electromagnetic stirring,
ultrasonic excitation, vibration, gas injection or by means of
strong subcooling of the melt during casting.
[0035] The copper alloy described above is particularly suitable
for use in the manufacture of shaped parts, the manufacture
comprising at least one hot forming operation. It can also be used
for the production of shaped parts, in which at least one hot
forming operation is followed by further processing steps, such as
subsequent machining. The corresponding manufacturing process is
particularly suitable for the manufacture of components, e.g. media
pipes, e.g. gas or water pipes, and components to be connected,
e.g. fittings, etc. Fittings that are particularly in focus are
components of domestic plumbing pipe systems, including pipes,
fittings, end caps and connectors. The basic process steps for the
manufacture of such moulded parts are known to the specialist and
will therefore not be described in detail here.
[0036] In this context, it is essential to note that the specific
composition of the copper alloy to be used, as described above,
means that there is no drop in mechanical properties and corrosion
resistance even after hot forming. In addition, it has been shown
that both before and after hot forming, the parts obtained can be
subjected to other machining processes without any problems. In
particular, machining is possible as the problematic and
undesirable formation of long chips is avoided. In this way, a
moulded part can be produced in an economic manner (in particular
since the other desirable properties of the copper alloy, such as
good hot working properties, inertness to substances in contact
with the parts, in particular drinking water, and corrosion
resistance, are not affected). In this context, it should be
particularly emphasized that the advantages of this invention
described here are achieved, although the use of the components Pb,
Si etc., which are otherwise often considered necessary in the
state of the art, is dispensed with.
[0037] This unexpected advantage of the copper alloy described here
enables its economic use in the manufacture of the moulded parts
described above.
Example
[0038] From a lead-free gunmetal, a shaped part for the drinking
water installation was produced in a fine grain state by means of
hot forming with subsequent machining. This showed that after the
hot pressing process chip breakers were present in the
microstructure of the alloy, so that economic fully automated
mechanical processing was possible.
* * * * *