JP3794971B2 - Copper alloy tube for heat exchanger - Google Patents
Copper alloy tube for heat exchanger Download PDFInfo
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- JP3794971B2 JP3794971B2 JP2002075152A JP2002075152A JP3794971B2 JP 3794971 B2 JP3794971 B2 JP 3794971B2 JP 2002075152 A JP2002075152 A JP 2002075152A JP 2002075152 A JP2002075152 A JP 2002075152A JP 3794971 B2 JP3794971 B2 JP 3794971B2
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Description
【0001】
【発明の属する技術分野】
本発明は、エアコン及び大型空調機等の熱交換器に使用する銅合金管に関し、特に、ろう付け加熱前及びろう付け加熱後の0.2%耐力及び疲労強度が優れた熱交換器用銅合金管に関する。
【0002】
【従来の技術】
例えば、エアコンの熱交換器は、ヘアピン状に曲げ加工したU字形銅管(以下、銅管という場合は銅合金管も含む)をアルミニウムフィンの貫通孔に通し、前記銅管を治具により拡管することにより銅管とアルミニウムフィンとを密着させ、更に、銅管の開放端を拡管し、この拡管部にU字形に曲げ加工した銅管を挿入し、りん銅ろうにより銅管を拡管部にろう付けする。
【0003】
このため、熱交換器に使用される銅管には、曲げ加工性及びろう付け性が良好であることが要求される。従って、これらの特性が良好であり、更に熱伝導率が良く、適切な強度を有するりん脱酸銅が広く使用されている。
【0004】
上述のような熱交換器の組立に使用されるりん銅ろう(BCuP−2:Cu−6.8〜7.5質量%P)の融点は805℃(液相線温度)であり、ろう付け部は800℃以上の温度に数秒乃至数十秒間加熱されるため、ろう付け部及びその近傍のりん脱酸銅管はその他の部分に比べて結晶粒が粗大化し、軟化により強度が低下した状態となってしまう。
【0005】
ところで、エアコンなどの熱交換器に使用する熱媒体(冷媒)には、HCFC(ハイドロクロロフルオロカーボン)系フロンが広く使用されてきた。しかしながら、フロンによるオゾン層破壊の懸念よりHCFC系フロンの代替冷媒としてHFC(ハイドロフルオロカーボン)系フロンが使用されるようになってきた。HFC系フロンを冷媒に使用した熱交換器において、HCFC系フロンを使用した場合と同じ伝熱性能を維持するには、運転時の凝縮圧力をHCFC系フロンの1.5倍以上に大きくする必要がある。
【0006】
また、エアコンの価格を下げるために、伝熱管である銅管に対しては質量低減の要求が強まり、銅管の薄肉化が進んでいる。このため、従来から使用されているりん脱酸銅管については、疲れ強さが低いことが問題となっている。また、このような熱交換器の機内配管には更に大きな圧力が作用するため、機内配管に使用される銅管には、強度及び疲れ強さに対する要求が更に厳しいものとなっている。
【0007】
このような要求に応えるべく、0.2%耐力と疲れ強さが優れた銅合金管として、例えば、Co:0.02乃至0.2質量%、P:0.01乃至0.05質量%、C:1乃至20ppmを含有し、残部がCu及び不可避的不純物からなり、不純物の酸素が50ppm以下である熱交換器用電縫溶接銅合金管(特開2000−199023)が提案されている。また、Fe:0.005乃至0.8質量%、P:0.01乃至0.026質量%、Zr:0.005乃至0.3質量%及びO:3乃至30ppmを含有し、残部はCu及び不可避的不純物からなる組成を有する熱交換器用継目無銅合金管(特公昭58−39900号)も提案されている。
【0008】
【発明が解決しようとする課題】
前記の従来の銅合金管は、Coのりん化物又はZr等が夫々析出することにより、強度と疲れ強さを向上させている。このような析出型銅合金に、所定の強度と疲れ強さを持たせるためには、銅合金管の製造工程において、焼入れ、加熱温度及び加熱速度等の加工熱処理条件を狭い範囲で制御することが必要になり、前述の製造条件のばらつきは製造される銅合金管の特性の不安定さに繋がるため、加熱温度及び加熱速度のばらつきが発生しないように、生産設備の改造及び新設等に新たな投資が必要になる。
【0009】
また、前記析出型銅合金においては、600℃程度までの加熱では優れた耐熱性を有するが、ろう付けの高温加熱条件では析出物が固溶してしまい結晶粒が急成長するため、耐力及び疲労強さの低下は固溶型の銅合金よりむしろ大きくなる場合がある。このため、組立てた熱交換器においては、目標とする耐力及び疲れ強さを保持できなくなってしまう。
【0010】
本発明はかかる問題点に鑑みてなされたものであり、ろう付け性、ろう付け加熱後の耐力及び疲れ強さが優れた熱交換器用銅合金管を提供することを目的とする。
【0011】
【課題を解決するための手段】
本発明に係る熱交換器用銅合金管は、Sn:0.1乃至1.0質量%、P:0.005乃至0.1質量%、O:0.005質量%以下及びH:0.0002質量%以下を含有し、残部がCu及び不可避的不純物からなる組成を有し、平均結晶粒径が30μm以下であることを特徴とする。
【0012】
この熱交換器用銅合金管において、更に、Zn:0.01乃至1.0質量%を含有することが好ましい。また、850℃で30秒間加熱した後の平均結晶粒径が100μm以下、0.2%耐力が40N/mm2以上、疲れ試験において繰り返し応力を92MPaとしたとき、繰り返し数n=107回で破断しない疲労強度を有することが好ましい。
【0013】
なお、平均結晶粒径は、銅合金管の軸方向に平行の断面について、JISH0501に定められた切断法により、肉厚方向の平均結晶粒径を測定し、これを管軸方向に任意の10箇所で測定してそれらの平均を平均結晶粒径とした。0.2%耐力は、JISZ2241に準拠して求めた。疲れ強さは、JISZ2273に準拠した疲れ試験方法を使用して求めた。
【0014】
【発明の実施の形態】
以下、本発明について詳細に説明する。本発明者等がろう付け性、ろう付け加熱後の耐力及び疲れ強さが優れた熱交換器用銅合金管を開発すべく種々実験研究した結果、銅合金管のSn含有量、P含有量、酸素含有量、水素含有量、平均結晶粒径を適切に規定することにより、ろう付け性、ろう付け加熱後の耐力及び疲れ強さが優れた銅合金管を得ることができることを見出した。
【0015】
以下、本発明の銅合金管の組成の数値限定理由について説明する。
【0016】
Sn(錫):0 . 1乃至1 . 0質量%
Snが1.0質量%より多く含まれると、鋳塊における凝固偏析が激しくなる。製造工程において、熱間押出時の加熱温度及び加熱時間が十分でないと鋳塊の偏析が製品においても十分に解消されず、製品管の組織不均一による機械的性質の低下及び耐食性の低下を招きやすい。このような現象を防止するためには、熱間押出前の加熱温度又は/及び加熱時間を増加させる必要があり、生産コストの増大を招く。また、Snが1.0質量%より多く含まれると、ろうの濡れ広がり性も低下するので、Snの含有量は1.0質量%以下とする。一方、Snが0.1%未満であると、ろう付け加熱後の0.2%耐力及び疲労強度が不十分となる。このため、Snは0.1質量%以上含有させる。
【0017】
P(リン):0 . 005乃至0 . 1質量%
脱酸を主目的として添加するPは、0.1質量%より多く含まれると、熱間押出時に割れが発生しやすくなると共に、応力腐食割れ感受性が大きくなり、熱交換器としての信頼性を低下させる。一方、Pが0.005質量%未満の場合は、脱酸不足によりSnの酸化物が大量に発生し、鋳塊の健全性を低下させ、熱間押出が難しくなる。従って、Pの含有量は0.005乃至0.1質量%とする。
【0018】
酸素(O):0.005質量%以下
酸素が0.005質量%より多く含まれると、形成されたSn及びCuの酸化物が鋳塊に巻込まれ、鋳塊の健全性を低下させる。また、製造時の焼鈍工程において水素脆化を発生させやすくし、ろうの濡れ広がり性、0.2%耐力及び疲労強度も低下させる。従って、酸素の含有量は0.005質量%以下とする。
【0019】
水素(H):0 . 0002質量%以下
水素が0.0002質量%より多く含まれると、熱間押出時の割れ、焼鈍時の膨れが発生しやすくなり、製品歩留りが低下する。従って、水素の含有量は0.0002質量%以下とする。
【0020】
Zn:0 . 01%乃至1 . 0質量%
Znを添加することにより、銅合金管の熱伝導率を大きく低下させることなく、強度、耐熱性及び疲れ強さを向上させることができる。また、Znの添加により、抽伸加工時及び転造加工時等の工具磨耗を低減させることができ、溝付きプラグの寿命を延命させる効果がある。Znの含有量が0.01質量%以下では、上述の効果が十分でない。一方、Znが1.0質量%より多く含まれると、応力腐食割れ感受性が高くなり、応力腐食割れの可能性が懸念される。従って、Znを添加する場合は、Znの含有量は0.01乃至1.0質量%とする。
【0021】
その他、Cu、Sn及びPの含有量の合計、又は、Cu、Sn、P及びZnの含有量の合計が、99.95質量%以上であることが望ましい。特に、これらの合計が99.98質量%以上であることが更に望ましい。
【0022】
また、本発明の銅合金管に含まれるPと金属間化合物を形成して、母相中に析出するFe、Ni、Co、Mn、Mg、Cr、Ti、Zr及びAg等の元素の合計含有量は、これらの合計値が0.03質量%以下であることが望ましく、更に、0.02質量%以下であることがより望ましい。
【0023】
なお、Al、Si、Pb、S、Li、Se、As、Ca及びInは、合計で0.01質量%以下までなら、含有させても本発明の銅合金管の耐熱性、疲れ強さなどの特性を劣化させることはない。
【0024】
次に、本発明の銅合金管の平均結晶粒径及び諸特性の限定理由について説明する。
【0025】
平均結晶粒径
平均結晶粒径は、銅合金管の軸方向に平行の断面について、JISH0501に定められた切断法により、肉厚方向の平均結晶粒径を測定し、これを管軸方向に任意の10箇所で測定してそれらの平均を平均結晶粒径とした。
【0026】
この平均結晶粒径が30μmを超えると、エアコン等の熱交換器の組立工程で銅合金管をヘアピン曲げ加工する際に、曲げ部に割れが発生しやすくなる。従って、平均結晶粒径は30μm以下とすることが必要である。なお、この平均結晶粒径は20μm以下であることがより望ましい。また、測定される10箇所の結晶粒径は夫々平均値の±20%以内であることが望ましい。
【0027】
850℃に30秒間加熱した後の平均結晶粒径
この850℃に30秒間加熱したときの平均結晶粒径の測定法は、前述のとおりである。850℃に30秒間加熱することは、ろう付け時の加熱条件を想定しており、この加熱により平均結晶粒径が100μmを超えると、熱交換器のろう付け部及びその近傍において疲れ強さが低下し、エアコン等の運転時に高い圧力が必要なHFC系フロンを冷媒に使用すると、使用中に銅合金管の破壊が発生しやすくなる。従って、850℃に30秒間加熱した後の平均結晶粒径は100μm以下とすることが望ましい。なお、この平均結晶粒径は80μm以下であることが更に望ましい。
【0028】
850℃に30秒間加熱した後の0 . 2%耐力
銅合金管を850℃に30秒間加熱した後、JISZ2241に準拠した方法により引張り試験を行ない、オフセット法により0.2%耐力を算出する。850℃に30秒間加熱した後の0.2%耐力が40N/mm2未満であると、運転圧力が高いHFC系フロン系の冷媒を使用したときに、銅合金管に疲労破壊が起こりやすい。従って、850℃に30秒間加熱した後の0.2%耐力が40N/mm2以上であることが望ましい。
【0029】
850℃に30秒間加熱した後の疲れ強さ
銅合金管を850℃に30秒間加熱した後、JISZ2273に定められた疲れ試験方法により疲れ強さを測定する。この試験材の銅合金管を850℃に30秒間加熱した後、銅合金管の両管端を固定して92MPaの両振り応力を付与する。この場合に、繰り返し数107回未満で破断した場合は、運転時に高い圧力が必要なHFC系フロンを冷媒に使用する熱交換器では、その信頼性が低下する。従って、850℃に30秒間加熱した後の疲れ強さとして、繰返し応力92MPaで疲労試験を行ったとき、繰り返し数が107回以上であることが望ましい。
【0030】
以下、本発明の銅合金管の製造方法の一例について説明する。なお、この製造方法は、平滑管又は内面溝付管等の銅合金管を製造するものである。
【0031】
まず、原料の電気銅を木炭被覆の元で溶解し、銅が溶解した後、Sn及びZnを所定量添加し、更に、脱酸を目的として15質量%のPを含有する銅合金を添加する。このように、成分調整が終了した後、半連続鋳造により所定の寸法のビレットを作製する。
【0032】
得られたビレットを加熱炉で加熱し、熱間押し出しを行なう。熱間押出前に、ビレットを750乃至950℃に0.1乃至2時間程度保持して均質化による偏析改善を行うことが望ましい。その後、ビレットの温度を750℃乃至850℃とし、熱間押出を行う。水中押出し又は押出し後の水冷により、表面温度が100℃になるまでの冷却速度が1.5℃/秒以上となるように冷却することが望ましい。この急冷により、焼鈍時の混粒組織の発生を抑制でき、平均結晶粒径が30μm以下で、且つ結晶粒の大きさにバラツキが少ない粗管を作製することができる。
【0033】
この押出し後、圧延加工を行なう。このときの加工率を92%以下とすることにより、圧延時の製品不良を低減できる。
【0034】
そして、圧延後、抽伸加工を行なって所定の寸法の素管を製造する。このときの加工率は35%以下にすることにより、抽伸時の製品不良を低減できる。
【0035】
その後、所定寸法の素管に、更に抽伸加工を行って平滑管を製作する。又は、所定寸法の素管を焼鈍し、溝付転造加工を行って内面溝付管を製作する。
【0036】
得られた平滑管又は内面溝付管に焼鈍処理を施すことにより、熱交換器用銅合金管が得られる。
【0037】
【実施例】
以下、本発明の実施例の平滑管又は内面溝付管について、その特性を、本発明範囲から外れる比較例と比較した結果について説明する。
【0038】
第1の実施例(平滑管)
供試材を、以下の工程により作成した。
▲1▼電気銅を原料とし、溶湯中に所定のSnを添加し、更に必要に応じてZnを添加した後、Cu−P母合金を添加することにより、所定組成の溶湯を作製した。
▲2▼鋳造温度1200℃で、直径300×長さ3000mmの鋳塊を半連続鋳造した。
▲3▼鋳塊より長さ475mmのビレットを切り出した。
▲4▼ビレットを加熱して900℃に到達した後、1.5時間保持し、均質化処理した。
▲5▼冷却したビレットをインダクションヒーターで加熱し、830℃に到達した後、3分間保持し、その後熱間押出しにより、外径94mm、肉厚10mmの押出し粗管を作製した。
▲6▼押出し粗管を圧延し、外径38mm、肉厚2.1mmの圧延粗管を作製した。
▲7▼圧延粗管を抽伸し、加工率35%以下で外径9.52mm、肉厚0.3mmまで抽伸した。
▲8▼焼鈍炉にて抽伸素管を焼鈍し、供試材とした。
▲9▼この供試材について、ろう付け加熱を想定し、供試材を850℃の塩浴炉に30秒間保持した。
【0039】
試験項目は以下のとおりである。
▲1▼成分:供試材より所定量の試料を採取し、組成を分析した。
▲2▼平均結晶粒径:前述の方法により測定した。
▲3▼曲げ試験:供試材より長さ1000mmの管を10本採取し、ピッチ25mmでヘアピン曲げ加工を行い、曲げ部の割れの有無を確認した。
▲4▼0.2%耐力:前述の方法により測定した。
▲5▼疲労試験:前述の方法により試験した。繰り返し数107回で割れが発生しない限界の曲げ応力と、92MPaの応力付加時の割れの有無を確認した。
▲6▼ろう付け試験: 長さ300mmの供試材の管を軸方向に半割にし、内面側に直径1.6mm、長さ10mmのりん銅ろう(BCuP−2)を載せ、窒素気流中で850℃に10分間保持して、ろうの拡がり長さを測定した。なお、加熱前に測定した酸化膜の厚さは全て500nm以下であった。
【0040】
以上の試験結果を下記表1及び表2に示す。No.3乃至5及び11は本発明の実施例であり、No.1,2、6乃至10、12乃至14は比較例である。また、表1は、ろう付けを想定した加熱を行う前の特性であり、表2は、ろう付けを想定した850℃で30秒の加熱を行った後の特性である。表中の下線が引いてある項目は、本発明の範囲外の数値であることを示す。
【0041】
【表1】
【0042】
【表2】
【0043】
実施例No.3乃至5及び11は、いずれも優れた曲げ加工性及びろうの広がり性を有し、且つ850℃も30秒間加熱した後も結晶粒の粗大化が少なく、耐力の低下が小さいため、疲れ強さが優れている。
【0044】
比較例No.1は、従来のりん脱酸銅管であるが、850℃に30秒間の加熱により、疲れ強さが大きく低下した。
【0045】
比較例No.2は、スズの含有量が0.1%より少ないため、850℃で30秒の加熱により疲れ強さが大きく低下した。
【0046】
比較例No.6は、スズの含有量が1.0%より多いため、ろうの広がり性が低下した。
【0047】
比較例No.7は、リンの含有量が0.005%より少ないため、ろうの広がり性が低下した。
【0048】
比較例No.8は、リンの含有量が0.1%より多いため、熱間押出時に微細な割れが発生し、供試材の製作を中止した(組成は押出素管で調査した)。
【0049】
比較例No.9は、酸素の含有量が0.005%より多いため、ろうの広がり性が低下した。
【0050】
比較例No.10は、水素の含有量が0.0002%より多いため、熱間押出時に微細な割れが発生し、供試材の製作を中止した(組成は押出素管で調査した)。
【0051】
比較例No.12は、亜鉛の含有量が1.0%より多いため、ろうの広がり性が少し低下し、別に行った耐応力腐食割れ試験の結果、応力腐食割れに至る時間が実施例No.1と比較して50%に低下した。
【0052】
比較例No.13及び14は、共に平均結晶粒径が30μmより大きく,且つ混粒組織となったため曲げ試験で割れが発生した。これらについては疲労試験を行わなかった。
【0053】
第2の実施例(内面溝付管)
表1の比較例No.1、実施例No.3、4及び11の組成を有する圧延素管を使用し、以下に示す方法で内面溝付管を製造した。なお、▲1▼乃至▲6▼の工程は平滑管の場合と同様である。
▲7▼圧延粗管を抽伸し、溝付転造用の素管を製作した。
▲8▼溝付転造用素管をインダクションヒーターにより中間焼鈍した。
▲9▼焼鈍した溝付転造用素管に溝付転造加工を行い、外径が9.52mm、底肉厚が0.26mmの内面溝付管を製作した。この内面溝は、内部フィン高さが0.2mm、リード角が18°、内部フィン数:55である。製作した内面溝付管を焼鈍、供試材とした。
試験項目は、平滑管の場合と同様である、但し、ろう付け試験は行わなかった。
【0054】
試験結果を下記表3及び表4に示す。なお、表3及び表4において、比較例No.15は、表1、2の比較例No.1の組成であり、表3、4の実施例No.16、17、18は夫々表1、2の実施例No.3、4、11の組成である。また、表3は、ろう付けを想定した加熱を行う前の特性であり、表4は、ろう付けを想定した850℃で30秒間の加熱を行った後の特性である。表中の下線が引いてある数値は、本発明の範囲外の数値であることを示す。
【0055】
【表3】
【0056】
【表4】
【0057】
実施例No.16乃至18は本発明の銅合金管であり、いずれも優れた曲げ加工性及びろうの広がり性を有し、且つ850℃で30秒加熱後も結晶粒の粗大化が少なく、耐力の低下が小さいため、疲れ強さが優れたものである。
【0058】
これに対し、比較例No.15は、従来のりん脱酸銅管であるため、850℃で30秒の加熱により疲れ強さが大きく低下している。
【0059】
【発明の効果】
以上詳述したように本発明によれば、銅合金管のSnの含有量を0.1乃至1.0質量%、Pの含有量を0.005乃至0.1質量%、酸素の含有量を0.005質量%以下及び水素の含有量を0.0002%以下とし、平均結晶粒径を30μm以下とすることにより、ろう付け性、ろう付け加熱前及びろう付け加熱後の耐力及び疲労強度が優れた銅合金管が得られる。更に、Znの含有量を0.01乃至1.0%にすることによって、これらの特性を更に向上させることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a copper alloy tube used for a heat exchanger such as an air conditioner and a large air conditioner, and in particular, a copper alloy for a heat exchanger excellent in 0.2% proof stress and fatigue strength before and after brazing heating. Regarding the tube.
[0002]
[Prior art]
For example, a heat exchanger of an air conditioner passes a U-shaped copper tube bent into a hairpin shape (hereinafter referred to as a copper tube also includes a copper alloy tube) through an aluminum fin through-hole and expands the copper tube with a jig. In this way, the copper tube and the aluminum fin are brought into close contact with each other, and the open end of the copper tube is expanded, and a U-shaped bent copper tube is inserted into the expanded portion. Braze.
[0003]
For this reason, it is requested | required that the copper pipe | tube used for a heat exchanger should have favorable bending workability and brazing property. Accordingly, phosphorous deoxidized copper having good characteristics, good thermal conductivity, and appropriate strength is widely used.
[0004]
Phosphor copper brazing (BCuP-2: Cu-6.8 to 7.5% by mass P) used for assembling the heat exchanger as described above has a melting point of 805 ° C. (liquidus temperature), and brazing Since the part is heated to a temperature of 800 ° C. or more for several seconds to several tens of seconds, the brazed part and the phosphorous deoxidized copper pipe in the vicinity thereof are coarser than the other parts, and the strength is reduced due to softening End up.
[0005]
By the way, HCFC (hydrochlorofluorocarbon) chlorofluorocarbon has been widely used as a heat medium (refrigerant) used in a heat exchanger such as an air conditioner. However, HFC (hydrofluorocarbon) -based chlorofluorocarbon has been used as an alternative refrigerant for HCFC-based chlorofluorocarbon because of the concern about the destruction of the ozone layer by chlorofluorocarbon. To maintain the same heat transfer performance as when HCFC-based chlorofluorocarbon is used in a heat exchanger that uses HFC-based chlorofluorocarbon as a refrigerant, it is necessary to increase the condensation pressure during operation to at least 1.5 times that of HCFC-based chlorofluorocarbon. There is.
[0006]
In addition, in order to reduce the price of air conditioners, there is an increasing demand for reducing the mass of copper tubes that are heat transfer tubes, and the copper tubes are becoming thinner. For this reason, the phosphorus deoxidized copper pipes conventionally used have a problem of low fatigue strength. In addition, since a larger pressure acts on the in-machine piping of such a heat exchanger, the copper pipes used for the in-machine piping are more demanding for strength and fatigue strength.
[0007]
In order to meet such demands, for example, Co: 0.02 to 0.2 mass%, P: 0.01 to 0.05 mass%, as a copper alloy tube having excellent 0.2% proof stress and fatigue strength , C: 1 to 20 ppm, the remainder being made of Cu and inevitable impurities, and the oxygen of the impurities is 50 ppm or less, an electric resistance welded copper alloy pipe for heat exchanger (Japanese Patent Laid-Open No. 2000-199023) has been proposed. . Further, Fe: 0.005 to 0.8 mass%, P: 0.01 to 0.026 mass%, Zr: 0.005 to 0.3 mass%, and O: 3 to 30 ppm, with the balance being Cu. In addition, a seamless copper alloy tube (Japanese Patent Publication No. 58-39900) for heat exchangers having a composition consisting of inevitable impurities has also been proposed.
[0008]
[Problems to be solved by the invention]
In the conventional copper alloy tube, Co phosphide or Zr is precipitated to improve strength and fatigue strength. In order to give such a precipitation-type copper alloy the prescribed strength and fatigue strength, the heat treatment conditions such as quenching, heating temperature, and heating rate should be controlled within a narrow range in the copper alloy tube manufacturing process. As the above-mentioned variations in manufacturing conditions lead to instability in the characteristics of the copper alloy tubes to be manufactured, new production facilities have been remodeled and newly installed to prevent variations in heating temperature and heating speed. Investment is required.
[0009]
In addition, the precipitation type copper alloy has excellent heat resistance when heated to about 600 ° C., but the precipitates dissolve in a high temperature heating condition of brazing, and crystal grains grow rapidly. The decrease in fatigue strength may be greater than in a solid solution type copper alloy. For this reason, in the assembled heat exchanger, the target yield strength and fatigue strength cannot be maintained.
[0010]
This invention is made | formed in view of this problem, and it aims at providing the copper alloy tube for heat exchangers which was excellent in brazability, the yield strength after brazing heating, and the fatigue strength.
[0011]
[Means for Solving the Problems]
The copper alloy tube for a heat exchanger according to the present invention has Sn: 0.1 to 1.0 mass%, P: 0.005 to 0.1 mass%, O: 0.005 mass% or less, and H: 0.0002. It is characterized by containing a mass% or less, the remainder having a composition consisting of Cu and inevitable impurities, and having an average crystal grain size of 30 μm or less.
[0012]
This copper alloy tube for heat exchangers preferably further contains Zn: 0.01 to 1.0% by mass. When the average crystal grain size after heating at 850 ° C. for 30 seconds is 100 μm or less, the 0.2% proof stress is 40 N / mm 2 or more, and the repeated stress is 92 MPa in the fatigue test, the number of repetitions is n = 10 7 times. It is preferable to have fatigue strength that does not break.
[0013]
In addition, the average crystal grain size is determined by measuring the average crystal grain size in the thickness direction with respect to a cross section parallel to the axial direction of the copper alloy tube by a cutting method defined in JISH0501, and measuring the average crystal grain size in the tube axis direction. The average was measured as the average crystal grain size. The 0.2% proof stress was determined according to JISZ2241. The fatigue strength was determined using a fatigue test method based on JISZ2273.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. As a result of various experimental studies by the present inventors to develop a copper alloy tube for heat exchangers with excellent brazeability, yield strength after brazing heating and fatigue strength, the Sn content, the P content, It has been found that a copper alloy tube excellent in brazeability, yield strength after brazing heating and fatigue strength can be obtained by appropriately defining the oxygen content, hydrogen content, and average crystal grain size.
[0015]
Hereinafter, the reason for limiting the numerical value of the composition of the copper alloy tube of the present invention will be described.
[0016]
Sn (tin).. 0 1 to 1 0 wt%
When Sn is contained more than 1.0 mass%, solidification segregation in the ingot becomes intense. In the manufacturing process, if the heating temperature and heating time at the time of hot extrusion are not sufficient, segregation of the ingot will not be sufficiently eliminated in the product, leading to deterioration of mechanical properties and corrosion resistance due to uneven structure of the product pipe. Cheap. In order to prevent such a phenomenon, it is necessary to increase the heating temperature or / and the heating time before hot extrusion, leading to an increase in production cost. Further, when Sn is contained in an amount of more than 1.0% by mass, the wettability of the wax is also lowered, so the Sn content is 1.0% by mass or less. On the other hand, if Sn is less than 0.1%, the 0.2% proof stress and fatigue strength after brazing heating will be insufficient. For this reason, Sn is contained by 0.1 mass% or more.
[0017]
P (phosphorus):.. 0 005 to 0 1%
When P added for the main purpose of deoxidation is contained in an amount of more than 0.1% by mass, cracking is likely to occur during hot extrusion, and the susceptibility to stress corrosion cracking is increased, thereby improving the reliability as a heat exchanger. Reduce. On the other hand, when P is less than 0.005 mass%, a large amount of Sn oxide is generated due to insufficient deoxidation, the soundness of the ingot is lowered, and hot extrusion becomes difficult. Therefore, the P content is set to 0.005 to 0.1 mass%.
[0018]
Oxygen (O): 0.005% by mass or less If oxygen is contained in an amount of more than 0.005% by mass, the formed Sn and Cu oxides are wound into the ingot, thereby improving the soundness of the ingot. Reduce. In addition, hydrogen embrittlement is likely to occur in the annealing process during production, and the wettability of brazing, 0.2% proof stress and fatigue strength are also reduced. Accordingly, the oxygen content is set to 0.005 mass% or less.
[0019]
Hydrogen (H):. 0 When 0,002 wt% or less <br/> hydrogen is contained more than 0.0002 wt%, cracking during hot extrusion, becomes swollen during annealing is likely to occur, the product yield is lowered . Accordingly, the hydrogen content is set to 0.0002 mass% or less.
[0020]
Zn:.. 0 01% to 1 0 wt%
By adding Zn, the strength, heat resistance and fatigue strength can be improved without greatly reducing the thermal conductivity of the copper alloy tube. In addition, the addition of Zn can reduce tool wear during drawing and rolling, and has the effect of extending the life of the grooved plug. When the Zn content is 0.01% by mass or less, the above-described effects are not sufficient. On the other hand, when Zn is contained more than 1.0 mass%, the stress corrosion cracking sensitivity becomes high, and there is a concern about the possibility of stress corrosion cracking. Therefore, when Zn is added, the Zn content is 0.01 to 1.0 mass%.
[0021]
In addition, it is desirable that the total content of Cu, Sn and P or the total content of Cu, Sn, P and Zn is 99.95% by mass or more. In particular, the total of these is more preferably 99.98% by mass or more.
[0022]
Moreover, the total content of elements such as Fe, Ni, Co, Mn, Mg, Cr, Ti, Zr and Ag formed in the parent phase by forming an intermetallic compound with P contained in the copper alloy tube of the present invention The total amount of these is preferably 0.03% by mass or less, and more preferably 0.02% by mass or less.
[0023]
In addition, even if Al, Si, Pb, S, Li, Se, As, Ca, and In are added up to 0.01% by mass or less, the heat resistance, fatigue strength, etc. of the copper alloy tube of the present invention are included. It does not degrade the characteristics.
[0024]
Next, the reasons for limiting the average crystal grain size and various characteristics of the copper alloy tube of the present invention will be described.
[0025]
Average crystal grain size The average crystal grain size is determined by measuring the average crystal grain size in the thickness direction of the cross section parallel to the axial direction of the copper alloy tube by the cutting method defined in JISH0501. Measurements were made at any 10 locations in the axial direction, and the average of these was taken as the average crystal grain size.
[0026]
When the average crystal grain size exceeds 30 μm, cracks are likely to occur in the bent portion when the copper alloy tube is subjected to hairpin bending in the assembly process of a heat exchanger such as an air conditioner. Therefore, the average crystal grain size needs to be 30 μm or less. The average crystal grain size is more preferably 20 μm or less. Further, it is desirable that the measured crystal grain sizes at 10 locations are within ± 20% of the average value.
[0027]
Average crystal grain size after heating to 850C for 30 seconds The method for measuring the average crystal grain size when heated to 850C for 30 seconds is as described above. Heating to 850 ° C. for 30 seconds assumes the heating conditions at the time of brazing. If the average crystal grain size exceeds 100 μm due to this heating, the fatigue strength is increased at the brazed portion of the heat exchanger and in the vicinity thereof. If HFC-based chlorofluorocarbon, which requires a high pressure during operation of an air conditioner or the like, is used as a refrigerant, the copper alloy tube is likely to be broken during use. Accordingly, the average crystal grain size after heating at 850 ° C. for 30 seconds is desirably 100 μm or less. The average crystal grain size is more desirably 80 μm or less.
[0028]
0 After heating for 30 seconds to 850 ° C.. After heating for 30 seconds to 2% proof stress <br/> copper alloy tube 850 ° C., subjected to tensile test by a method based on JISZ2241, 0.2% yield strength by the offset method Is calculated. When the 0.2% proof stress after heating at 850 ° C. for 30 seconds is less than 40 N / mm 2 , fatigue failure tends to occur in the copper alloy tube when an HFC-based refrigerant having a high operating pressure is used. Therefore, it is desirable that the 0.2% yield strength after heating at 850 ° C. for 30 seconds is 40 N / mm 2 or more.
[0029]
Fatigue strength after heating to 850C for 30 seconds After heating the copper alloy tube to 850C for 30 seconds, the fatigue strength is measured by the fatigue test method defined in JISZ2273. The copper alloy tube of this test material is heated to 850 ° C. for 30 seconds, and then both ends of the copper alloy tube are fixed and a swing stress of 92 MPa is applied. In this case, when the fracture occurs after the number of repetitions of less than 10 7 times, the reliability of the heat exchanger that uses HFC-based Freon, which requires a high pressure during operation, as the refrigerant is lowered. Accordingly, as the fatigue strength after heating at 850 ° C. for 30 seconds, when the fatigue test is performed with a repeated stress of 92 MPa, the number of repetitions is desirably 10 7 times or more.
[0030]
Hereinafter, an example of the manufacturing method of the copper alloy pipe of the present invention will be described. In addition, this manufacturing method manufactures copper alloy tubes, such as a smooth tube or an internally grooved tube.
[0031]
First, raw electrolytic copper is melted under charcoal coating, and after copper is dissolved, a predetermined amount of Sn and Zn is added, and a copper alloy containing 15% by mass of P is added for the purpose of deoxidation. . In this way, after the component adjustment is completed, a billet having a predetermined size is produced by semi-continuous casting.
[0032]
The obtained billet is heated in a heating furnace and subjected to hot extrusion. Prior to hot extrusion, it is desirable to improve segregation by homogenization by holding the billet at 750 to 950 ° C. for about 0.1 to 2 hours. Thereafter, the billet temperature is set to 750 ° C. to 850 ° C., and hot extrusion is performed. It is desirable that the cooling is performed so that the cooling rate until the surface temperature reaches 100 ° C. is 1.5 ° C./second or more by extrusion in water or water cooling after extrusion. By this rapid cooling, generation of a mixed grain structure during annealing can be suppressed, and a rough tube having an average crystal grain size of 30 μm or less and less variation in crystal grain size can be produced.
[0033]
After this extrusion, a rolling process is performed. By setting the processing rate at this time to 92% or less, product defects during rolling can be reduced.
[0034]
Then, after rolling, drawing processing is performed to manufacture a raw tube having a predetermined size. By setting the processing rate at this time to 35% or less, product defects during drawing can be reduced.
[0035]
Thereafter, a smooth pipe is manufactured by further drawing the base pipe having a predetermined size. Alternatively, an inner-grooved pipe is manufactured by annealing a raw pipe having a predetermined size and performing grooved rolling.
[0036]
A copper alloy tube for a heat exchanger is obtained by subjecting the obtained smooth tube or internally grooved tube to an annealing treatment.
[0037]
【Example】
Hereinafter, the result of having compared the characteristic with the comparative example which remove | deviates from the range of this invention about the smooth tube of the Example of this invention or the inner surface grooved pipe is demonstrated.
[0038]
First embodiment (smooth tube)
A specimen was prepared by the following process.
{Circle around (1)} Using molten copper as a raw material, a predetermined Sn was added to the molten metal, and Zn was further added as required, and then a Cu—P master alloy was added to prepare a molten metal having a predetermined composition.
(2) An ingot having a diameter of 300 × length of 3000 mm was semi-continuously cast at a casting temperature of 1200 ° C.
(3) A billet having a length of 475 mm was cut out from the ingot.
(4) The billet was heated to reach 900 ° C. and then held for 1.5 hours for homogenization.
(5) The cooled billet was heated with an induction heater, reached 830 ° C., held for 3 minutes, and then hot extruded to produce an extruded rough tube having an outer diameter of 94 mm and a wall thickness of 10 mm.
(6) The extruded rough tube was rolled to produce a rolled rough tube having an outer diameter of 38 mm and a wall thickness of 2.1 mm.
(7) The rolled rough tube was drawn and drawn to an outer diameter of 9.52 mm and a wall thickness of 0.3 mm at a processing rate of 35% or less.
(8) The drawing tube was annealed in an annealing furnace to obtain a test material.
{Circle around (9)} The specimen was held in a salt bath furnace at 850 ° C. for 30 seconds assuming brazing heating.
[0039]
The test items are as follows.
(1) Component: A predetermined amount of a sample was taken from the test material, and the composition was analyzed.
(2) Average crystal grain size: measured by the method described above.
(3) Bending test: Ten tubes having a length of 1000 mm were sampled from the test material and subjected to hairpin bending at a pitch of 25 mm to confirm the presence or absence of cracks in the bent portion.
(4) 0.2% proof stress: measured by the method described above.
(5) Fatigue test: Tested by the method described above. The bending stress at the limit at which cracks do not occur at the number of repetitions of 10 7 times and the presence or absence of cracks when a stress of 92 MPa was applied were confirmed.
(6) Brazing test: A 300 mm-long test material tube was halved in the axial direction, and 1.6 mm diameter and 10 mm long phosphor copper brazing (BCuP-2) was placed on the inner surface. Was held at 850 ° C. for 10 minutes, and the spreading length of the wax was measured. Note that the thicknesses of the oxide films measured before heating were all 500 nm or less.
[0040]
The above test results are shown in Tables 1 and 2 below. No. Nos. 3 to 5 and 11 are examples of the present invention. 1, 2, 6 to 10, and 12 to 14 are comparative examples. Table 1 shows the characteristics before heating assuming brazing, and Table 2 shows the characteristics after heating for 30 seconds at 850 ° C. assuming brazing. Items underlined in the table indicate numerical values outside the scope of the present invention.
[0041]
[Table 1]
[0042]
[Table 2]
[0043]
Examples Nos. 3 to 5 and 11 all have excellent bending workability and wax spreadability, and after heating at 850 ° C. for 30 seconds, there is little coarsening of the crystal grains, and the decrease in yield strength is small. Therefore, fatigue strength is excellent.
[0044]
Comparative Example No. 1 is a conventional phosphorous deoxidized copper tube, but the fatigue strength was greatly reduced by heating at 850 ° C. for 30 seconds.
[0045]
In Comparative Example No. 2, since the tin content was less than 0.1%, the fatigue strength was greatly reduced by heating at 850 ° C. for 30 seconds.
[0046]
In Comparative Example No. 6, since the tin content was more than 1.0%, the spreadability of the wax was lowered.
[0047]
In Comparative Example No. 7, since the phosphorus content was less than 0.005%, the spreadability of the wax was lowered.
[0048]
In Comparative Example No. 8, since the phosphorus content was more than 0.1%, fine cracks were generated during hot extrusion, and production of the test material was stopped (the composition was examined with an extrusion tube).
[0049]
In Comparative Example No. 9, since the oxygen content was more than 0.005%, the spreadability of the wax was lowered.
[0050]
In Comparative Example No. 10, since the hydrogen content was more than 0.0002%, fine cracks were generated during hot extrusion, and production of the test material was stopped (composition was investigated with an extrusion tube).
[0051]
In Comparative Example No. 12, since the zinc content is more than 1.0%, the spreadability of the braze is slightly lowered, and as a result of a separate stress corrosion cracking test, the time until stress corrosion cracking is shown in Example No. Reduced to 50% compared to 0.1.
[0052]
Comparative Examples No. 13 and 14 both had an average crystal grain size larger than 30 μm and had a mixed grain structure, so cracking occurred in the bending test. These were not subjected to fatigue tests.
[0053]
Second embodiment (inner grooved tube)
Using the rolling blanks having the compositions of Comparative Example No. 1, Table No. 3, 4 and 11 in Table 1, an internally grooved tube was produced by the method shown below. The steps (1) to (6) are the same as in the smooth tube.
(7) A rolled rough pipe was drawn to produce a raw pipe for grooved rolling.
(8) The grooved rolling element tube was subjected to intermediate annealing with an induction heater.
(9) Grooved rolling was performed on the annealed grooved rolling element tube to produce an internally grooved tube having an outer diameter of 9.52 mm and a bottom wall thickness of 0.26 mm. This inner surface groove has an internal fin height of 0.2 mm, a lead angle of 18 °, and the number of internal fins: 55. The manufactured internally grooved tube was annealed and used as a test material.
The test items were the same as in the case of the smooth tube except that the brazing test was not performed.
[0054]
The test results are shown in Tables 3 and 4 below. In Tables 3 and 4, Comparative Example No. 15 is the composition of Comparative Example No. 1 in Tables 1 and 2, and Examples Nos. 16, 17, and 18 in Tables 3 and 4 are the compositions of Example Nos. 3, 4, and 11 in Tables 1 and 2, respectively. It is. Table 3 shows the characteristics before heating assuming brazing, and Table 4 shows the characteristics after heating for 30 seconds at 850 ° C. assuming brazing. A numerical value with an underline in the table indicates a numerical value outside the range of the present invention.
[0055]
[Table 3]
[0056]
[Table 4]
[0057]
Examples Nos. 16 to 18 are copper alloy tubes of the present invention, both having excellent bending workability and brazing expansibility, and less grain coarsening after heating at 850 ° C. for 30 seconds, Fatigue strength is excellent because the decrease in proof stress is small.
[0058]
In contrast, since Comparative Example No. 15 is a conventional phosphorous deoxidized copper tube, the fatigue strength is greatly reduced by heating at 850 ° C. for 30 seconds.
[0059]
【The invention's effect】
As described in detail above, according to the present invention, the Sn content of the copper alloy tube is 0.1 to 1.0 mass%, the P content is 0.005 to 0.1 mass%, and the oxygen content Is 0.005 mass% or less, the hydrogen content is 0.0002% or less, and the average crystal grain size is 30 μm or less, so that brazing performance, proof stress and brazing strength before and after brazing heating are performed. An excellent copper alloy tube can be obtained. Furthermore, these characteristics can be further improved by setting the Zn content to 0.01 to 1.0%.
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2002
- 2002-03-18 JP JP2002075152A patent/JP3794971B2/en not_active Expired - Lifetime
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US9671182B2 (en) | 2007-10-23 | 2017-06-06 | Kobelco & Materials Copper Tube, Ltd. | Copper alloy tube for heat exchanger excellent in fracture strength |
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