HK1251625A1

HK1251625A1 - Copper alloy for heat exchanger tube

Info

Publication number: HK1251625A1
Application number: HK18111018.5A
Authority: HK
Inventors: Parker M. Finney; Larz Ignberg; Anders Kamf; Tim Goebel; Eric Gong; Ed Rottman
Original assignee: Virtus Precision Tube, Llc
Priority date: 2009-07-10
Filing date: 2018-08-27
Publication date: 2019-02-01
Also published as: MY173128A; WO2011005926A1; BR112012000607A2; EP2451604A1; US20110005739A1; EP2451604B1; CA2767242C; BR112012000607A8; MX2012000544A; JP2015178679A; JP6087982B2; US20160363397A1; CA2767242A1; MX340861B; ES2649557T3; JP2012532990A; CN107739880A; EP2451604A4; CN102470471A; BR112012000607B1

Abstract

An alloy comprising copper, nickel, tin and, optionally, phosphorus which can be used in, for example, a copper alloy tube for heat exchangers that provides excellent fracture strength and processability for reducing the weight of the tube and for use in high pressure applications with cooling media such as carbon dioxide.

Description

Copper alloy for heat exchanger tubes

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of a patent application having application number 201080031914.4 on 7/8/2010 and entitled "copper alloy for heat exchanger tube" claiming priority from U.S. provisional patent application No. 61/224671 filed on 7/10/2009, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates generally to copper alloys and the use of copper alloys in heat exchanger tubes. In particular, the present invention relates to a high strength copper alloy tube having suitable pressure rupture strength and workability properties. The alloy is suitable for reduced thickness and therefore is useful in existing Air Conditioning and Refrigeration (ACR) heat exchangersMaterial savings when replacing and adaptation to use of e.g. CO₂Such as a heat exchanger for a cooling medium.

Background

The air conditioning heat exchanger may be comprised of a U-shaped copper tube bent into a hairpin shape and fins made of aluminum or aluminum alloy plate.

Therefore, copper tubes for heat exchangers of the above-mentioned type require suitable thermal/electrical conductivity, formability and brazing properties.

HCFC (hydrochlorofluorocarbon) -based fluorocarbons have been widely used for cooling media for heat exchangers such as air conditioners. However, HCFCs have a strong tendency to deplete ozone, so for environmental reasons one chooses other cooling media. "Green refrigerants", e.g. natural cooling medium CO₂Have been used in heat exchangers.

With CO₂As a cooling medium, it is necessary to increase the condensation pressure during operation in order to maintain the same heat exchange performance as HCFC-based fluorocarbons. In heat exchangers, the pressure of the cooling medium (pressure of the fluid flowing in the heat exchanger tubes) is used, usually in the Condenser (CO)₂Air cooler in (1) becomes maximum. In this condenser or air cooler, for example, the condensation pressure of R22 (an HCFC-based fluorocarbon) is about 1.8 MPa. On the other hand, CO₂The cooling medium needs to have a condensation pressure (supercritical state) of about 7 to 10 MPa. Therefore, the operating pressure of the novel cooling medium is increased as compared with that of the conventional cooling medium R22.

Since the pressure is increased and some loss of strength occurs due to brazing during the formation of some pipes, conventional copper materials must be made thicker, which increases the weight of the pipes and thus the material costs associated with the pipes.

There is a need for a heat exchanger tube having high tensile strength, excellent processability and good thermal conductivity, suitable for heat exchangeSmall wall thickness, thereby reducing material costs of ACR heat exchangers, and is suitable for use with applications such as CO₂The need for the new "green" cooling medium of (a) withstands high pressure applications.

Disclosure of Invention

The present invention provides a copper alloy for a heat exchanger tube, which has, for example, high tensile strength, excellent workability, and good thermal conductivity.

In one aspect, the invention is a copper alloy composition comprising the following components, wherein the percentages are by weight. The composition includes copper (Cu), nickel (Ni), and tin (Sn). In one embodiment, the composition of the alloy is 99 wt.% copper, 0.5 wt.% nickel, and 0.5 wt.% tin, which may be expressed as CuNi (0.5) Sn (0.5). In another embodiment, the nickel is present in a range of 0.2% to 1.0%, the tin is present in a range of 0.2% to 1.0%, and the remainder includes Cu and impurities. The composition optionally includes 0.01% to 0.07% phosphorus.

In another aspect, the invention provides a pipe for ACR applications comprising the copper alloy composition. In yet another aspect of the invention, the alloy composition is formed into a pipe for ACR applications.

Drawings

FIG. 1 is a graphical representation of the relative metal value per foot versus copper value for alloy C122 currently in use having a standard wall thickness as compared to the reduced wall thickness of the CuNi (0.5) Sn (0.5) alloy of the present invention.

Fig. 2 is a graphical representation of tensile strength and electrical conductivity of the alloys tested as a function of Ni and Sn content. Sn has a greater influence on both strength and conductivity.

Fig. 3(a) - (c) are various views of a tubing according to an embodiment of the present invention. FIG. (a) is a perspective view; FIG. (b) is a cross-sectional view of the tubing shown in FIG. (a) taken along the longitudinal axis; FIG. (c) is a cross-sectional view of the tubing shown in FIGS. (a) and (b) viewed along an axis perpendicular to the longitudinal axis.

Detailed Description

The present invention provides high strength alloys that can, for example, reduce wall thickness, thereby reducing the costs associated with existing ACR tubing; and/or can provide an ACR pipe that can withstand exposure to a cooling medium such as CO₂Associated increased pressure. By "high strength" is meant that the alloy and/or the pipe made from the alloy has at least the levels of tensile strength and/or burst pressure and/or cyclic fatigue failure described herein. Copper alloys can save materials and costs, reducing environmental impact and energy consumption.

To provide a copper alloy for heat exchanger tubes and to enable the use of such as CO for the heat exchanger tubes₂Such as cooling media, the alloy selected should have suitable material properties and good workability. Important material properties include, for example, burst pressure/strength, ductility, thermal/electrical conductivity, and cyclic fatigue. The characteristics of the alloys and/or tubes described herein are suitable so that they can withstand the ACR working environment.

High tensile strength and high burst pressure are advantageous pipe properties because they define the working pressure that the pipe can withstand before failing. For example, the higher the burst pressure, the stronger the tube structure, or for a given minimum burst pressure, the alloy of the present invention can be made into thinner walled tubes. There is a correlation between tensile strength and burst pressure. The alloy and/or the pipe comprising the alloy has a material tensile strength of, for example, at least 38ksi (kilopounds per square inch). The tensile strength of the material can be measured by methods known in the art, such as ASTM E-8 test protocol. In various embodiments, the alloy and/or the tube comprising the alloy has a material tensile strength of 39, 40, 41, or 42 ksi.

The ductility of the alloy and/or the tubing made from the alloy is an advantageous property because in one embodiment, the tubing needs to be bent 180 degrees to a hairpin shape without cracking or wrinkling in order to be coiled for use. Elongation is an indicator of the ductility of a material. The alloy and/or the pipe comprising the alloy has an elongation of e.g. at least 40%. Elongation can be measured by methods known in the art, such as ASTM E-8 test protocol. In various embodiments, the alloy and/or the pipe comprising the alloy has a minimum elongation of 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%.

Thermal/electrical conductivity is an advantageous property because it is related to heat transfer capability and, therefore, is a factor that affects the efficiency of ACR coils. Thermal/electrical conductivity is also important for pipe forming. The alloy and/or the pipe comprising the alloy has a minimum electrical conductivity of, for example, 35% IACS. Conductivity can be measured by methods known in the art, such as ASTM E-1004 test protocol. In various embodiments, the alloy and/or the pipe comprising the alloy has a minimum electrical conductivity of 36%, 37%, 38%, 39%, 40%, 45%, 50%, 55%, 60%, or 65% (IACS).

The alloy and/or pipe has at least the same resistance to cyclic fatigue failure as, for example, the currently used alloys such as C122, as shown in table 2. Further, the alloy and/or pipe has at least the same resistance to one or more of corrosion (e.g., galvanic corrosion and formicary corrosion) as, for example, currently used alloys such as C122.

In one embodiment, the pipe comprising the alloy of the present invention has improved softening resistance (which may be important for brazing) and/or increased fatigue strength compared to standard copper pipe, such as pipe made with C122.

In one embodiment, the pipe shown in fig. 3(a) - (C) comprising the alloy of the present invention has a reduced wall thickness t (compared to a pipe comprising a conventional alloy, e.g., C122), has the same or improved burst pressure and/or cyclic fatigue properties as a pipe comprising a conventional alloy, e.g., C122. For example, the wall thickness of the inventive tubing is minimized relative to standard tubing, such as C122, which reduces the overall material cost, but the burst pressure of the two tubing is the same. In various embodiments, the wall thickness is at least 10%, 15%, or 20% thinner than the C122 tubing, but the two tubing have the same burst pressure. Burst pressure can be measured by methods known in the art such as CSA-C22.2, 140.3, article 6.1 strength test, UL207, article 13. Cyclic fatigue can be measured by methods known in the art such as CSA-C22.2, 140.3, fatigue test No. 6.4, UL207, No. 14.

The alloys of the present invention may be made according to methods known in the art. Controlling the temperature may be important during the alloy manufacturing process and/or the pipe forming process. Controlling the temperature may be important to keep the elements in solution (to prevent precipitation) and to control particle size. For example, if the treatment is incorrect, the thermal/electrical conductivity may increase and the formability may decrease.

For example, in order to maintain the desired grain size and prevent the formation of precipitates during alloy manufacture and/or pipe forming, a short heat treatment is performed during production to maintain the temperature of the alloy and/or pipe between 400 ℃ and 600 ℃ and to allow the temperature to rise and fall rapidly (e.g., 10-500 ℃/sec).

The alloy and/or the pipe made of said alloy preferably have the desired grain size. In one embodiment, the particle size is 1-50 μm, including all integers between 1-50 μm. In another embodiment, the particle size is 10-25 μm. In yet another embodiment, the particle size is 10-15 μm. Particle size can be measured by methods known in the art, such as ASTM E-112 test protocol.

The alloy compositions of the present invention include the following components, wherein the relative amounts of the alloy components are expressed in weight percent. Weight percent ranges include all fractions of a percentage within the stated range (including, but not limited to, tenths and hundredths of a percentage).

In one embodiment, the composition comprises copper, nickel, tin, and optionally phosphorus. The nickel content ranges from 0.2% to 1.0%, more specifically from 0.3% to 0.7%; tin ranges from 0.2% to 1.0%, more specifically from 0.3% to 0.7%; the remainder comprising copper and impurities. In one embodiment, the composition of the alloy is CuNi (0.5) Sn (0.5). In another embodiment, the composition of the alloy is CuNi (0.5) Sn (0.5) P (0.020).

The impurities may be, for example, natural impurities or impurities brought in during the treatment. Examples of impurities include, for example, zinc, iron, and lead. In one embodiment, the impurity content is up to 0.6%. In other various embodiments, the impurity content is up to 0.5%, 0.45%, 0.3%, 0.2%, or 0.1%.

The optional amount of phosphorus ranges from 0.01% to 0.07%, more specifically from 0.015% to 0.030%, or is 0.02%. Without intending to be bound by any particular theory, it is contemplated that the inclusion of phosphorus in the alloy in appropriate amounts can affect the flow characteristics and oxygen content of the metal, thereby improving the solderability of the alloy, but that the addition of too much phosphorus can result in a poor grain structure and cause unwanted precipitation.

In one embodiment, the composition consists essentially of Cu, Ni, and Sn within the ranges described above. In another embodiment, the composition consists essentially of Cu, Ni, Sn, and P within the ranges described above. In various embodiments, the addition of components other than copper, nickel, tin (and phosphorus in the case of the second embodiment) does not result in an adverse change in properties of the alloy of the present invention, such as burst pressure/strength, ductility, thermal/electrical conductivity, and cyclic fatigue, of more than 5%, 4%, 3%, 2%, or 1%.

In one embodiment, the alloy composition consists of Cu, Ni, Sn, and P within the above ranges. In another embodiment, the alloy composition consists of Cu, Ni, Sn, and P within the above ranges.

The alloy of the present invention can be used in various processes, such as cast and roll, extrusion or roll and weld. Processing requirements include, for example, brazeability. Brazing is used when joining pipes as described below.

In the roll welding process, the alloy is typically cast into a rod, rolled into a thin gauge, heat treated, cut to the desired size, embossed, formed into tubing, welded, annealed, and packaged. In the cast-rolling process, the alloy is typically cast into a "parent" tube, drawn to the desired size, annealed, machined to form an internal groove, sized, annealed, and packaged. In an extrusion process, the alloy is typically cast into a solid billet, reheated, extrusion pressed, drawn and slotted to final dimensions, annealed, and packaged.

In one aspect, the present invention provides a pipe comprising a copper-nickel-tin alloy (as described herein). In one embodiment, the tubing has an outer diameter of 0.100 to 1 inch, including all fractions of an inch between 0.100 and 1 inch; the tubing has a wall thickness of 0.004-0.040 inches, including all fractions of an inch between 0.004-0.040 inches. One advantage of the present invention is that thinner walled tubing can be used for ACR applications. This results in a reduction of material costs (see fig. 1).

In one embodiment, the tubing comprising a copper-nickel-tin alloy (as described herein) is used in ACR applications. The tubing is preferably sufficiently thermally/electrically conductive (e.g., such that the tubing can be joined by welding) and formable (e.g., capable of being formed into a shape, such as being bent after the tubing is formed). In addition, the tubing is desirably of suitable properties such that the internal channel of the tubing is reinforced.

One example of a process suitable for the alloy of the present invention is a roll welding process used to form heat exchanger coils comprising the tubing. In the first step, the copper alloy of the present invention is cast into a thick plate, and then subjected to hot rolling and cold rolling to form a flat strip. Soft annealing the cold rolled strip. The soft annealed copper alloy strip is then formed into a heat exchanger tube by a continuous roll forming and welding process. The tube may be internally reinforced prior to the roll-forming and welding process, such as by forming grooves or ribs in the inner wall of the tube, as will be apparent to those of ordinary skill in the art. The tubing can be formed in a continuous rolling and welding process, and the product can be wound into large coils. The large coil can then be moved to another location and cut into smaller sections to form a U-shape or hairpin shape.

To construct the heat exchanger, the hairpin tube is screwed into the through-hole of the aluminum fin, and the clip is inserted into the U-shaped copper pipe to expand the copper pipe, thereby tightly connecting the copper pipe and the aluminum fin to each other. The open end of the U-shaped copper tube is then expanded and a shorter hairpin tube, similarly bent into a U-shape, is inserted into the expanded end. The bent copper tube is brazed to the expanded open end with a brazing alloy to connect to the adjacent hairpin tubing to form the heat exchanger.

The following examples are intended to further illustrate the invention and are not intended to be limiting in any way.

Examples

Copper alloys with different Ni and Sn contents were prepared on a pilot scale and the mechanical and physical properties were measured, see table 1.

The results obtained are plotted against the Ni or Sn content, see FIG. 2. All alloys tested met the required minimum conductivity of 35% IACS. All the alloys tested achieved mechanical properties with a minimum tensile strength of 38 ksi. To meet the required strength and conductivity, the composition should contain both Ni and Sn in an amount of 0.2 wt% to 1.0 wt%.

A material containing a composition of 0.5% Ni and 0.5% Sn [ CuNi (0.5) Sn (0.5) ] was prepared on a full production scale and formed into a pipe using a roll welding process. Tubing with a standard wall thickness (e.g., 0.0118 inches) and 13% thinner wall thickness was prepared. The mechanical properties of the pipes were tested using ASTM and UL (e.g. UL test protocol) and compared to pipes with standard wall thickness prepared with the "currently used" copper alloy C12200. The results are shown in Table 2. The alloy CuNi (0.5) Sn (0.5) of the invention has higher strength and higher burst pressure at standard wall thickness. For the resulting reduced wall thickness tubes, the burst pressure of the alloy of the invention [ CuNi (0.5) Sn (0.5) ] is still higher than C122 with a standard wall thickness.

Mechanical properties and conductivity of the alloys with different Ni and Sn contents tested in Table 1

TABLE 2 comparison of mechanical properties of pipes made of the alloy according to the invention (CuNi0.5Sn0.5) with the existing standard alloy C12200(Cu-DHP)

While the invention has been particularly shown and described with reference to a particular embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

1. A copper alloy for a heat exchanger, the copper alloy comprising:

a)0.3 wt% to 0.7 wt% nickel;

b)0.2 to 1.0 weight percent tin; and

c)0.01 wt% to 0.07 wt% phosphorus;

wherein the balance of the alloy is copper and impurities and the particle size of the copper alloy is 1-50 μm.

2. The alloy of claim 1, wherein tin is present in the alloy in an amount of 0.3 wt.% to 0.7 wt.%.

3. The alloy of claim 1, wherein the nickel is present in the alloy in an amount of 0.5 wt.%, and the tin is present in the alloy in an amount of 0.5 wt.%.

4. The alloy of claim 1, wherein the phosphorus is present in the alloy in an amount of 0.020% by weight.

5. The alloy of claim 1, wherein the alloy has a particle size of 10 to 25 μ ι η.

6. An ACR tube for a heat exchanger, wherein the tube comprises a copper alloy, the copper alloy comprising:

a)0.3 wt% to 0.7 wt% nickel;

b)0.2 to 1.0 weight percent tin; and

c)0.01 wt% to 0.07 wt% phosphorus;

7. The ACR tube of claim 6, wherein the tin is present in an amount of 0.3% to 0.7% by weight.

8. The ACR tube of claim 6, wherein the nickel is present in an amount of 0.5 weight percent and the tin is present in an amount of 0.5 weight percent.

9. The ACR tube of claim 6, wherein the phosphorous is present in the alloy at 0.020% by weight.

10. The ACR tube of claim 6, wherein the alloy has a grain size of 10 to 25 μ ι η.

11. The ACR tube of claim 6, wherein the tube has an outer diameter of 0.100 to 1 inch.

12. The ACR tube of claim 6, wherein the tube has a wall thickness of 0.004 inches to 0.040 inches.

13. The ACR tube of claim 6, wherein the wall thickness of the tube is minimized relative to the wall thickness of a standard C122 tube, thereby reducing the overall material cost, and wherein the tube and the standard C122 tube have substantially the same burst pressure.

14. The ACR tube of claim 13, wherein the wall thickness of the tube is at least 10% thinner than the wall thickness of a standard C122 tube.