JP2002220630A - Strip for welded heat exchanger tube, and welded heat exchanger tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strip for a welded heat exchanger tube consisting of copper or a copper alloy, which can prevent welding failure and spatter in welding, and to provide a welded heat exchanger tube made by means of welding the strip. SOLUTION: A method for manufacturing the strip comprises melting and casting the copper or the copper alloy, hot rolling, cold rolling, continuous annealing, then, furthermore cold rolling and continuous annealing, and winding it up. In this time, in the above copper or the copper alloy, [H]2×[O] is to be 40, when content of hydrogen is to be 1.0 ppm or less, content of oxygen is to be 50 ppm or less, the content of hydrogen is to be [H] (ppm), and the content of oxygen is to be [O] (ppm). A method for manufacturing the welding heat exchanger tube includes groove rolling the strip, curving it to a widthwise direction, and high frequency welding it after butting edges of a widthwise direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding heat transfer tube made of copper or a copper alloy used as a material of a welding heat transfer tube and a welded heat transfer tube formed by welding this material. The present invention relates to a welding heat transfer tube strip and a welding heat transfer tube that suppress occurrence of welding defects such as blow holes during high frequency welding.

[0002]

2. Description of the Related Art Conventionally, as a heat transfer tube used in a heat exchanger, an inner grooved tube made of copper or a copper alloy and manufactured by rolling is used. However, recently, it has been required to improve the heat transfer performance of the heat exchanger and to change the refrigerant due to environmental problems, and to further improve the heat transfer performance of the heat transfer tube. In order to improve the heat transfer performance of the heat transfer tube, it is effective to form a groove having a complicated shape on the inner surface of the heat transfer tube. However, since it is difficult to form such a complicated-shaped groove in the rolling process, a groove made of copper or a copper alloy is groove-rolled to form a groove on at least one surface of the strip, and this groove is formed. 2. Description of the Related Art Welded pipes with an inner groove manufactured by high-frequency welding of strip materials have come to be used in many cases.

[0003]

However, the prior art has the following problems. In the manufacturing process of the above-described welded pipe, poor welding and poor welding such as blow holes and spatter may occur during welding. Welded pipes with poor welds may leak,
It cannot be used as a heat transfer tube because cracks are caused by secondary processing such as hairpin bending, tube expansion and flaring. Spatter generated during welding remains in the tube. If a welded tube with spatter remaining in such a tube is incorporated into a heat exchanger, the compressor of the heat exchanger may be damaged, so that a welded tube with a large amount of spatter cannot be used as a heat transfer tube.

[0004] In the above-mentioned process of manufacturing a welded pipe with an inner groove, after a raw material (strip) is welded and formed into a pipe, it remains in the pipe before forming an aligned winding coil (LWC: Level Wound Coil). The amount of spatter to be performed is measured, and the material having a large amount of residual sputter is discarded. Further, after the aligned winding, continuous annealing is performed, and then an airtight test of the welded pipe is performed. When a leak (leakage) occurs, the entire LWC is discarded as waste. Then, only the LWC in which no leak occurred becomes a product,
Shipped to customer. As described above, when welding defects such as poor welding, poor welding such as blow holes, and spatter occur during welding, there is a problem in that the yield of the welded heat transfer tubes is reduced and the manufacturing cost of the welded heat transfer tubes is increased.

Conventionally, it has been known that rolling conditions, welding conditions, and shapes and dimensions of strips affect welding defects and the occurrence of spatters. In some cases, poor welding and spatter may occur. For this reason, it is not possible to completely prevent poor welding and generation of spatter only by adjusting welding conditions and the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a strip for a heat transfer tube made of copper or a copper alloy and capable of reliably preventing poor welding and spatter during welding. It is an object to provide a welded heat transfer tube formed by welding a strip.

[0007]

A strip member for a welded heat transfer tube according to the present invention is rolled in the width direction and welded at its edges in the width direction so that the longitudinal direction and the axial direction coincide with each other. In a strip made of copper or a copper alloy as a raw material, the hydrogen content is 1.0 ppm or less, the oxygen content is 50 ppm or less, the hydrogen content is [H] (ppm), and the oxygen content is [O] ( ppm), [H] ² × [O] is 40
It is characterized by the following.

In the present invention, by limiting the hydrogen content and the oxygen content in the copper or copper alloy to the above-mentioned ranges, poor welding and poor welding such as blow holes during welding of the heat transfer tube strip can be obtained. Sputtering can be prevented.

[0009] A welded heat transfer tube according to the present invention is a welded heat transfer tube made of copper or a copper alloy manufactured by welding circumferential edges, wherein the copper or copper alloy has a hydrogen content of 1.0 ppm.
Hereinafter, when the oxygen content is 50 ppm or less, and the hydrogen content is [H] (ppm) and the oxygen content is [O] (ppm), [H] ² × [O] is 40 or less. It is characterized by having.

In the present invention, by limiting the hydrogen content and the oxygen content in copper or a copper alloy to the above ranges, it is possible to prevent poor welding at welding, poor welding such as blowholes, and generation of spatter. Can be. This makes it possible to obtain a welded heat transfer tube having good airtightness and no spatter remaining in the tube. In addition, the welded heat transfer tube of the present invention may be an inner grooved tube or a smooth tube.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive experiments and research conducted by the present inventors to solve the above-mentioned problems, poor welding and generation of spatter are caused by the amount of hydrogen contained in copper or copper alloy constituting the strip. And oxygen content. Hereinafter, the reasons for limiting the numerical values of the components of the present invention will be described.

Hydrogen content: 1.0 ppm or less When copper or a copper alloy undergoes a phase change from a liquid to a solid, the amount of hydrogen dissolved in the copper or copper alloy is significantly reduced. For this reason, the hydrogen dissolved in the liquid state in the copper or copper alloy tends to become a hydrogen gas at the time of solidification and be discharged from the copper or copper alloy. At this time, if the solidification rate is high, the hydrogen gas that has not been discharged is trapped in the solid copper or copper alloy. Blowholes and pinholes are generated by the trapped hydrogen gas, and the bonding strength of the welded portion is reduced, so that poor welding tends to occur. Further, spattering in which granular copper or copper alloy is discharged together with discharge of hydrogen gas from the liquid is likely to occur. When the hydrogen content of copper or a copper alloy exceeds 1.0 ppm, the above-described blowholes, pinholes, poorly welded portions, spatters, and the like are likely to be formed in the welded portion. This is because the hydrogen atoms present in the solid copper or copper alloy diffuse at high speed in the crystal grain boundaries of copper or copper alloy as the temperature rises due to welding, and the dissolved copper or copper alloy It is considered that hydrogen gas is formed in the alloy to cause the above-described phenomenon during solidification. Therefore, the hydrogen content in the copper or copper alloy is set to 1.0 ppm or less. The hydrogen content in copper or copper alloy is desirably 0.7 ppm or less.
More preferably, it is 5 ppm or less.

Oxygen content: 50 ppm or less In copper or a copper alloy, oxygen is present as a solid solution in the parent phase or in the form of an oxide of copper (Cu ₂ O) or an alloy element. Usually, the dissociation pressure of copper oxide is extremely low, so that blow holes and the like are not easily formed in the welded portion with oxygen alone. However, due to heating and melting at the time of welding, oxygen in copper or a copper alloy reacts with H, S, C, Zn, or the like existing in the atmosphere around the molten portion or the welded portion, and respectively reacts with steam, SO ₂ , CO ₂ , By forming ZnO or the like, a blow hole and a poor welding portion are formed in a welded portion, and spatter is generated. If the oxygen content in the copper or copper alloy exceeds 50 ppm, the amount of blowholes formed in the welded portion, poorly welded portions, and spatter generated by welding increases. Therefore, the oxygen content is set to 50 ppm or less. The oxygen content is desirably 40 ppm or less, and 30 pp.
m is more preferable.

[H] (ppm) hydrogen content, oxygen content
When the amount is [O] (ppm), [H] ² × [O]:
40 or less Normally, copper or copper alloy strips produced by thermomechanical processing of copper or copper alloy melt-cast in air contain a certain amount of hydrogen and oxygen, the amount of which is usually determined by the melting atmosphere. , [H] ² × [O] are constant. When making a welded pipe using such copper or copper alloy strip,
Depending on the value of [H] ² × [O], hydrogen gas and steam gas are generated at the time of welding, and blow holes, pin holes, poor welding, spatter, and the like are likely to occur. Even when the hydrogen content is 1.0 ppm or less and the oxygen content is 50 ppm or less, if the value of [H] ² × [O] exceeds 40, poor welding and blow holes are likely to occur during welding, and The amount of spatter also increases. Therefore, [H] ² ×
[O] is 40 or less. [H] ² × [O] is
It is desirably 30 or less, and more desirably 20 or less.

Hereinafter, embodiments of the present invention will be specifically described. The strip material for a welded heat transfer tube according to the present embodiment is manufactured by melting and casting copper or a copper alloy, hot rolling, cold rolling and continuous annealing, and then cold rolling, continuous annealing and winding. Examples of copper or copper alloy include oxygen-free copper, a copper alloy obtained by adding an alloying element to oxygen-free copper, phosphorus deoxidized copper described in C1201, C1220, and C1221 of JIS H3100, C192
10 and C194, a Cu-Fe-P-based alloy, a Cu-Fe-P-Sn-based alloy, Cu-Ni-Si
Alloys, Cu-Co-P alloys, Cu-Cr alloys, Cu-Zr alloys and the like can be used. In these copper or copper alloys, the hydrogen content is 1.0 ppm or less, the oxygen content is 50 ppm or less, and the hydrogen content is [H] (pp
m), when the oxygen content is [O] (ppm),
[H] ² × [O] is 40 or less. Further, it is preferable that the content of S is 30 ppm or less and the content of C is 10 ppm or less for the above-described reason. Furthermore, the thickness of the oxide film formed on the surface of the copper or copper alloy strip is 10 nm or less in order to reduce blow holes, poor welding, spattering, etc., and to prevent discoloration of the copper tube after production. It is desirable.

The thickness of the copper or copper alloy strip in the present invention is not particularly limited. However, there is no problem if the thickness of the butt-welded end is about 0.1 to 1.5 mm. In addition,
If necessary, the strip may be subjected to groove rolling to form grooves on one or both sides of the strip.

Next, a method for manufacturing the welded heat transfer tube of this embodiment will be described. Using the above-mentioned strip as a raw strip, this strip is curved into an arc shape in the width direction by roll forming, and the edges in the width direction of the strip are abutted. At this time, if a groove is formed on one surface of the strip, the strip is curved so that the groove forming surface is the inner surface. Next, the joined edges are formed into a tubular shape by high frequency welding. After welding, the welded pipe is cooled, sized and reduced to a predetermined outer diameter. Then, continuously coil (level wound coil: LW
C) and annealing is performed. Thereby, a welding heat transfer tube having a predetermined outer diameter can be manufactured.

In the welding heat transfer tube of this embodiment, since the content of hydrogen and the content of oxygen are limited to the above-mentioned predetermined ranges in the material copper or copper alloy, poor welding, blow holes and spatter Does not occur.
Therefore, a welded heat transfer tube having good airtightness, no leak, and no spatter remaining in the tube can be obtained.

[0019]

The effects of the embodiment of the present invention will be specifically described below in comparison with a comparative example outside the scope of the claims. First, a description will be given of a method for manufacturing a welded heat transfer tube formed from the strip and a material for a welded heat transfer tube in Examples and Comparative Examples. First, the phosphorous deoxidized copper is melted and cast to a thickness of 1
An ingot having a length of 50 mm, a width of 600 mm and a length of 4500 mm was produced. Next, this ingot was hot-rolled, cold-rolled, further cold-rolled after continuous annealing, again continuous-annealed, wound around a traverse coil while slitting, and the sheet thickness was 0.5 mm.
A strip having a width of 25 mm and a length of 5000 m was produced.
At this time, the hydrogen content and the oxygen content in the strip were changed by changing the degree of drying of the melted raw material, the amount of charcoal at the time of melting, and the like.

The content of P in the copper alloy used in this example and the comparative example is 0.016 to 0.027 mass%.
Was within the range. Further, as a result of analyzing other main elements, it was found that Fe: 0.0003 to 0.0015% by mass, N:
i: 0.0003 to 0.0023 mass%, Co: 0.0
002 to 0.0017 mass%, Sn: 0.0005 to
0.0026 mass%, Zn: 0.0006 to 0.001
5% by mass, Al: 0.0002 to 0.0012% by mass,
Mn: 0.0002 to 0.0011% by mass, Cr: 0.
0001 to 0.0005% by mass, Pb: 0.001 to
0.005% by mass, S: 0.0002 to 0.0013% by mass, Bi: 0.00005 to 0.0003% by mass, A
s: 0.0001 to 0.0003 mass%, Sb: 0.0
001-0.0006 mass%, C: 0.00005-
0.0003% by mass. In addition, the thickness of the oxide film on the surface of the strip measured before performing the groove rolling was 2 to 6 nm.

Next, the hydrogen content and the oxygen content of the strip were measured. Hereinafter, the measurement method will be described. After the strip was wound around a traverse coil, two measurement samples were collected for each strip, and the hydrogen content and the oxygen content were measured by the following quantitative methods. As a result of the measurement, in the two samples, the measured value of the hydrogen content was 0.05.
ppm or more and the measured oxygen content is 2p
When the difference was not less than pm, two more samples were taken and measured, and the average value of the central two measured values in a total of four measured values was adopted.

The quantitative measurement of hydrogen was carried out by an inert gas melting-thermal conductivity method described in JISZ2614 “General rules for the determination of hydrogen in metallic materials”. The sample was placed in a quartz crucible, the sample was melted in a stream of inert gas, and hydrogen contained in the sample was extracted together with other gases. next,
The extracted gas was collected in a container having a fixed capacity and provided with a thermal conductivity cell, and the change in thermal conductivity due to hydrogen was measured to calculate the amount of hydrogen. As a measuring instrument, a hydrogen analyzer RH-402 manufactured by LECO was used.

The quantitative measurement of oxygen was carried out by an inert gas melting-infrared absorption method described in JISZ1067 "General rules for the method of determining oxygen in copper". A sample is placed in a graphite crucible, the sample is melted by impulse heating in an inert gas stream, and oxygen contained in the sample is converted to carbon monoxide (C).
Extracted with other gases as O). The extracted gas was led to an infrared detector using an inert gas as a carrier, and the amount of oxygen was calculated from the degree of infrared absorption. The measuring instrument is O, N simultaneous analyzer EMGA manufactured by Horiba Ltd.
Model -650A was used. Table 1 shows the hydrogen content and the oxygen content of the strip thus measured.

Next, a welding heat transfer tube was manufactured using the above-mentioned strip. Groove rolling was performed on the strip after being wound on the above-mentioned traverse coil to form a groove on one surface of the strip. For groove rolling, six grooved grooved rings are combined so that the directions of leads of adjacent grooved rings are different from each other,
A grooved roll configured by arranging flat rolls without grooves at both ends of the combined six grooved rings was used. The grooved ring had a lead angle of 30 °, a groove depth of 0.25 mm, a crest angle of 30 °, and a groove pitch of 0.45 mm as viewed from a cross section including the axis of the grooved ring.

Next, this strip was roll-formed so as to be curved in an arc shape in the width direction so that the groove forming surface was on the inside, and the edges in the width direction of the strip were abutted. Next, the joined edges were welded by high-frequency induction heating to form a tubular shape. At this time, the high-frequency frequency in the high-frequency welding is 600 kHz, the welding speed is 120 m / min,
The outer diameter of the tube after welding was about 8 mm. The temperature during welding was 15 to 25 ° C., and the relative humidity was 60 to 85%. After welding, the welded pipe was cooled and sized to reduce the outer diameter of the pipe to 7 mm.

With respect to the welded heat transfer tube manufactured as described above, the amount of spatter in the tube was measured. Hereinafter, a method for measuring the amount of spatter in the tube will be described. As a sample,
In each LWC after diameter reduction and before LWC winding, each LWC
The length from the beginning of the winding of C, that is, 10 mm from the end of the welding
Ten tubes of 00 mm each were collected. The inside of the collected welding heat transfer tube was washed away with water, and the washed water was filtered with filter paper to collect spatter, and the amount of spatter in the tube was determined from the change in weight of the filter paper. Table 1 shows the measurement results of the sputter amount in the tube.

Next, the LWC after diameter reduction was aligned and wound up, and then subjected to continuous annealing. Next, the LWC is made so that the inner tube end and the outer tube end of the LWC can be taken out of the container.
The whole was housed in a vacuum vessel equipped with a helium leak detector. Next, the inside of the vacuum container was evacuated to a degree of vacuum of about 1.3 × 10 ⁻⁵ Pa. Thereafter, the inside of the LWC is taken out from the end of the LWC inner tube which has been taken out of the container.
The vacuum was evacuated for more than one minute, and then the end of the LWC inner tube was closed with a valve or the like. Next, helium was injected into the LWC from the end of the LWC outer tube, and a helium leak detector installed in the vacuum vessel was used to continuously check the presence or absence of a leak of the LWC for 30 minutes or more, and the airtightness was evaluated. . Table 1 shows the evaluation results. The LWC in which the leak was detected was discarded.

A sample was taken from the welded portion of a part of the welded heat transfer tube where the leak and the spatter occurred, and the cross section of the welded portion was observed with an optical microscope. Further, the generated spatter was observed with an optical microscope.

Table 1 shows the hydrogen content and oxygen content of the strips in the examples and comparative examples, the airtightness evaluation results of the heat transfer tubes formed by high-frequency welding of these strips, and the measurement results of the spatter amount in the pipes. Show. In Table 1, “hydrogen ² × oxygen” means the square of the hydrogen content (ppm) equals the oxygen content (p
pm). The airtightness was evaluated as good (○) when no leak was observed in the airtight test, and poor (x) when leak was observed in the airtightness test.
Further, the amount of spatter in the tube is 0.06 mg or less per 1000 mm of the sample tube as good (○), and the amount exceeding 0.06 mg is poor (×).

[0030]

[Table 1]

In Table 1, no. 1 to 5 are embodiments of the present invention. Example No. In Nos. 1 to 5, the hydrogen content of the strip was 1.0 ppm or less and the oxygen content was 50 ppm.
ppm or less, and the value of (hydrogen ² × oxygen) is 40
Because of the following, welding defects and spatter did not occur during welding of the strip, and therefore, the airtightness of the welded heat transfer tube was good, and no spatter was observed in the welded heat transfer tube.

On the other hand, No. 1 in Table 1 6 and 7 are comparative examples. Comparative Example No. 6 is (hydrogen ² x oxygen)
Is greater than 40, welding defects and spatters occur during welding of the strip, which causes leaks in the welded heat transfer tubes, and more spatters are present in the welded heat transfer tubes. Also, in Comparative Example No. 7 has a hydrogen content of 1.0p
pm, welding defects and spatters occurred during welding of the strips, and as a result, leaks occurred in the welded heat transfer tubes, and a large amount of spatters existed in the tubes.

FIG. 1 shows Comparative Example No. 6 is an optical microscope photograph (magnification: 150) showing a cross-sectional structure of a welded part No. 6; Figure 1
As shown in FIG. In the weld of No. 6, two lines were observed so as to penetrate the pipe wall along the vertical direction (pipe thickness direction) in FIG. These two wires were not completely joined, and this portion was a poorly welded portion.
Further, many fine holes considered as blow holes were formed along these lines. As described above, the presence of the blow hole and the poor welding portion cannot be determined from the appearance of the welding heat transfer tube. This can be determined by the following. In addition, the comparative example No. In 6, the position where welding failure and welding failure such as blowholes occurred was identified from the leak occurrence position. Therefore, the position of the defective welding portion may be specified by a method using the eddy current inspection device.

FIG. In the welding heat transfer tube of No. 6, the magnification indicating the shape of the spatter remaining in the tube is 15
It is a 0 times optical microscope photograph. Comparative Example No. In the welded heat transfer tubes of Nos. 6 and 7, spatters having a shape as shown in FIG. 2 were observed.

[0035]

As described above in detail, according to the present invention, it is possible to obtain a welded heat transfer tube strip made of copper or a copper alloy and capable of preventing poor welding and spatter during welding. Further, by welding the strip material to produce a welded heat transfer tube, it is possible to obtain a welded heat transfer tube having good airtightness and no spatter remaining in the tube.

[Brief description of the drawings]

FIG. 1 is a drawing-substituting photograph showing a cross-sectional structure of a welded portion in a comparative example of the present invention (optical microscope photograph: magnification of 150).
Times).

FIG. 2 is a drawing-substituting photograph showing the shape of a spatter remaining in a welded heat transfer tube of this comparative example (optical microscope photograph: magnification of 150).

Claims (2)

[Claims] 1. An edge which is rounded in the width direction and whose width direction edges are adjacent to each other.
For welding heat transfer tubes whose longitudinal direction and axial direction match
In the material made of copper or copper alloy, which contains hydrogen,
Weight is 1.0 ppm or less, oxygen content is 50 ppm or less
Below, and the hydrogen content is [H] (ppm), the oxygen content
[O] (ppm), [H] ²× [O] is 4
A strip material for a welded heat transfer tube, characterized by being 0 or less. 2. A welded heat transfer tube made of copper or a copper alloy manufactured by welding circumferential edges thereof, wherein said copper or copper alloy has a hydrogen content of 1.0 ppm or less and an oxygen content of 50 ppm or less.
ppm or less, and when the hydrogen content is [H] (ppm) and the oxygen content is [O] (ppm), [H] ² ×
A welded heat transfer tube having a composition in which [O] is 40 or less.