JP3647029B2 - Drawing method of iridium or iridium alloy wire - Google Patents

Description

【数５】

【数６】

【００１７】
本発明の数４〜数６により定められる品質保証領域を図４に示す。この図４では、上述した加工可能温度上限が数４に、表面荒れ発生温度線が数５に、そして、割れ発生温度線が数６に対応する。尚、加工可能温度下限線は、数４と数６との交点より低い断面減少率で交錯しないことが本発明者等の検討から明らかとなっているので、加工可能温度下限線は品質保証領域を規定することはない。また、本発明者によれば、従来のバーナー加熱による加工における条件は図４のａ点近傍の温度、加工率で示され、本発明の品質保証領域の範囲外にある。
【００１８】
本発明によれば、加工温度を加工率との関連から適正な範囲とすることで、高品質の線材の引抜き加工が可能となる。また、本発明によれば最大限の加工率（数４及び数６の交差点であり約３０％である）での加工を行なうことができ、１回の加工による断面減少効果に優れ効率的な加工が可能である。これは、上述のように所望の線径の線材を製造するためには引抜き加工を複数回繰り返し加工することとなるが、本発明によれば、１回当たりの加工率を最大限に設定することでその加工パス数を最小とすることが可能となる。
【００１９】
また、本発明に係る加工方法における線材の加熱温度は従来のものより低くなることから、線材と接触するダイスに与えるダメージを低減することができダイスの寿命の長期化を図ることができる。
【００２０】
ところで、複数回繰り返し加工を行ない細径の線材を製造する際には、加工する材料によっては各加工パス間で中間焼鈍を行なう必要がある場合がある。これは、引抜き加工を数回繰り返すことで加工硬化が進展し、材料割れを生じることがあることから、数パス加工後に中間焼鈍することで材料に回復現象を生じさせ再び加工可能な状態にするものである。そして、この中間焼鈍は引抜き加工時の加熱温度が低い程、頻繁に行う必要が生じてくるが、中間焼鈍工程を頻繁に行うことは全体の加工時間を増大させることとなる。そこで、本願発明における加工温度のうちより好ましい範囲としては、Ｔ＝７５０の線より上の領域、即ち、７５０℃以上で再結晶が生じない温度範囲とするのが好ましい。かかる範囲とすることで中間焼鈍の実施回数を極力減らすことができるからである。尚、この中間焼鈍の要否及び焼鈍温度は、合金種により加工硬化挙動ならびに回復挙動が異なることから、合金種により異なる。例えば、イリジウム−白金合金では１０００℃〜１１００℃の中間焼鈍が必要であり、イリジウム−ロジウム合金においても場合によっては９００℃〜１０００℃の中間焼鈍が必要となることがある。
【００２１】
尚、本発明における加工速度（引き抜き速度）については、特に限定されるものではない。例えば、従来のバーナー加熱による加工の加工速度は０.５〜１.０ｍ／ｍｉｎであるが、本発明でもこの速度での加工が可能であるが、加工条件を適正化していることから、従来の加工速度より高速での加工も可能である。そして、好ましい加工速度は１.０〜３.０ｍ／ｍｉｎである。
【００２２】
一方、本発明は引抜き加工時の温度を従来よりも低くし、更にその下限値の好ましいものを約７５０℃とすることから、比較的狭い温度範囲で加工することを特徴とするものである。従って、本発明においては、加工温度の制御を適正に行なうことが重要となる。一方、従来の引抜き加工で行われているバーナーの火炎では加工温度が高くなりすぎ、本発明で目的とする温度域での制御は困難である。そこで、本発明者等は加熱温度を従来より低く設定することができ、且つその制御が容易な手法として通電加熱法、即ち、被加工材である線材に電流を流すことにより線材を加熱し加工するのが好ましいとする。
【００２３】
この加熱方法は線材に電流を流すことで発生する抵抗熱を加工のための熱源とするものであるが、このときの線材温度は印加する電流を調整することで設定することができる。従って、この通電加熱法によれば、従来のバーナー加熱に比べて加工温度を低めに設定することができ更に安定させることができる。そして、これにより加工条件を適切な範囲で維持することができるため、高品質の線材を効率的に製造することができる。
【００２４】
この線材の通電加熱は、具体的には、一対の電極を線材に接触させて通電することによりなされるが、線材がダイスを通過する前に所定温度になるよう通電する必要がある。この場合、双方の電極をダイス入口側に設置しこれらを線材に接触させて通電しても良いが、好ましいのは、一方の電極をダイスの入口側に離隔設置し他方の電極はダイスの出口側で且つダイスに近接させるのものである。双方の電極をダイス入口側に配した場合、線材の加熱がダイスに導入される前に終了してしまい、加工途中に温度低下が生じ予定されていた加工条件での加工ができないからである。また、他方の電極をダイスの出口側で且つダイスに近接させるのは他方の電極をダイスから離して設置すると加工終了後も線材が加熱されるため線材の破断が生じることがあるからである。ここでの出口側電極とダイス出口面との間隔は１００ｍｍ以下とするのが好ましい。但し、最も効率的に線材を通電するためには、このダイス出口側の電極をダイスに接触させた状態で配置して電流がダイスを通過する状態とし、電極及びダイスの双方により線材を通電するようにするのが特に好ましいものである。
【００２５】
一方、ダイス入口側に離隔設置する電極の位置は、ダイスから４５０〜５５０ｍｍ上流側とするのが好ましい。後述するように、この引き抜き加工では線材に潤滑剤を塗布するのが好ましいが、この電極の設置位置をあまりにダイスに近くすると、線材温度が直ちに上昇し塗布した潤滑剤が沸騰してしまい，均一に塗布することができなくなるからであり、また、塗布作業のためのスペースが確保できなくなるからである。更に、温度測定のスペース確保ならびに線材温度コントロールをなるべく容易にするため電極の設置間隔がある程度必要となるからである。尚、このダイス入口側に離隔配置される電極の材質は、カーボンを用いるのが好ましい。
【００２６】
そして、本発明に係る引抜き加工方法においては、線材の加熱に加えて、ダイスも加熱して加工を行うことがより好ましい。ダイスを加熱することにより加工途中の線材の温度低下を抑制することができるため、これにより線材の破断を確実に防止することができるからである。このダイスの加熱温度としては、４００〜７００℃の範囲とするのが好ましく、ダイス外周に電気ヒーターを設置しこれにより行なうことができる。
【００２７】
更に、この引き抜き加工においては、加工後の線材の品質の確保、加工効率の確保のために、線材に潤滑剤を塗布した後加工するのが好ましい。この潤滑剤としては、主成分がカーボンであるカーボン系潤滑材を適用するのが好ましい。カーボン潤滑剤は本発明における温度下において劈開し微細に粉砕することで滑らかとなり、線材に傷を発生させることなく加工を補助できるからである。この点、カーボン系潤滑剤は、大気中でＣＯならびにＣＯ_２へと酸化されることにより消費されてしまい、従来の引き抜き加工における加工温度（１３００℃）ではその酸化速度が非常に速く使用が困難である。そのため従来法では、上述のように窒化ホウ素系の潤滑剤を適用しているが、窒化ホウ素系の潤滑剤は揮発はしないものの硬く、劈開することなく線材を傷つけることがある。従って、本発明はカーボン系潤滑剤の使用を可能としたことにより傷の発生しない高品質の線材を製造することができるというメリットもある。
【００２８】
また、本発明により実現されるカーボン系潤滑剤の適用により、線材の品質向上と共にダイス寿命のさらなる向上というメリットもある。従来法で使用されている窒化ホウ素系潤滑剤は、セラミックスの１種でありダイスに対して研磨作用があるが、カーボン系潤滑剤にはかかる研磨作用はないからである・
【００２９】
【発明の実施の形態】
以下に本発明の好適な実施形態を図面と共に示す。
【００３０】
第１実施形態：本実施形態では、イリジウム合金としてイリジウム−白金合金（Ｉｒ−５％Ｐｔ）よりなる線材を製造した。イリジウム２０９ｇと白金１１ｇとを秤量、混合し、これをＡｒアーク炉にて溶解し、イリジウム合金インゴットを製造した。そして、このイリジウム合金インゴットを１５００℃で熱間鍛造した。加工後のインゴットの寸法は１０ｍｍ角、長さ９０ｍｍとした。次にこの角材を１３００℃に加熱した溝付ロールに通過させることにより熱間圧延して断面径を更に減少させた後、大気雰囲気で１４００℃、３０分焼鈍した後、熱間スエージングを行った。スエージング加工は、鍛造機としてロータリースエージャーを用い、加工温度を１３００℃とし、加圧周期５０Ｈｚとした。このスエージング加工による総合加工率は７５％で、加工後のイリジウム合金線材は直径３.１０ｍｍの断面円形のものとなった
【００３１】
そして、熱間スエージング加工後のイリジウム合金線材を引抜き加工により細線とした。引抜き加工は、図５で示すような方法にて行なった。図５において被加工材である線材１は、ダイス上流側のロール電極２とダイス３の出口側の電極を兼ねるダイス保持板４とにより通電加熱されダイス３を通過することで加工される。線材温度は赤外線放射温度計により測定されその値をもとにプログラム式コントローラー５で線材に印加する電気量を調節している。また、通電ロール２を通過した線材には潤滑剤６を塗布した後にダイスに送り込む。ダイス３は電気ヒーター７により６５０℃に加熱されている。尚、本実施形態では、ダイスと通電ロールとの間隔を５２０ｍｍとし、加熱温度は１０００℃となるよう通電量を制御している。
【００３２】
そして、この装置により、ダイス１パスにおける平均断面減少率１７.５％とし、伸線速度を１.０〜２.３ｍ／ｍｉｎ間に設定してダイス孔径を順次減少させて合金線材を繰り返し引抜き加工し、最終的に径０．６ｍｍの細線とした。尚、この繰り返し引抜き工程を行なうに当たっては、２〜４パス毎に中間焼鈍（１１００℃、３０ｍｉｎ）を行なっている。
【００３３】
そして、この製造したイリジウム−白金合金線材につき、材料組織及び欠陥の有無を検査したところ、材料組織はほぼ均一であり、微小なものも含め欠陥がないことが確認された。
【００３４】
比較例：第１実施形態に対する比較として、従来の方法によりイリジウム−白金合金線材を製造した。従来法によるイリジウム合金線材の製造は、図６の製造装置により行なっており、バーナー８としてプロパン燃焼バーナーを用いた。また、潤滑剤は窒化ホウ素系潤滑剤を塗布している。
【００３５】
そして、第１実施形態と同様の圧延、スエージングにより製造したイリジウム合金線材について、ダイス１パス当たりの平均断面減少率９.７％とし、伸線速度を０.５〜０.７ｍ／ｍｉｎ間で設定して複数回繰り返し引抜き加工した。尚、この比較例における加工率、伸線速度は第１実施形態のものより低く設定したが、これはバーナー加熱による加工温度（約１３００℃）が高すぎるために、第１実施形態と同じ加工率等で加工を行なうと、線材表面に荒れ、皺が発生すると共に線材破断が発生し易いことからこれより低い値としたものである。また、このバーナー加熱による引抜き加工では、加工温度が１３００℃と高いことから中間焼鈍を行なう必要はないため、行なっていない。
【００３６】
この比較例における引抜き工程でも製造された線材に破断や大きな欠陥はなかったが、この比較例においては、線材表面に荒れ，皺が生じ、これを除去するために加工途中で線材表面を研磨しなければならなかった。また、比較例は加工温度が高温であり、そのために使用した窒化ホウ素系潤滑材の粒子が劈開しないために線材表面に潤滑剤粒子によるスクラッチが観察された。
【００３７】
また、破断が生じないとはいっても、これは破断が生じないように加工条件を制限したことによるものである。そして、このように制限された加工条件下では同じ径の線材を製造するためのパス数（加工数）が第１実施形態よりも大きくなり、第１実施形態では１.８８倍のパス回数が必要となった。また、全加工時間も比較例は大きく、第１実施形態では中間焼鈍の時間を考慮しても比較例は中間焼鈍がないにもかかわらず１.７６倍の時間を要した。従って、第１実施形態の引抜き加工方法は高品質の線材をより短いパス数、時間で製造可能であることが確認できる。
【００３８】
第２実施形態：本実施形態では、イリジウム合金としてイリジウム−ロジウム合金（Ｉｒ−２０％Ｒｈ）よりなる線材を製造した。イリジウム１６０ｇとロジウム４０ｇとを秤量、混合し、これをＡｒアーク炉にて溶解し、イリジウム合金インゴットを製造した。
【００３９】
このイリジウム合金インゴットを第１実施形態と同様に、熱間鍛造、熱間スェージングを行なった。ここでの加工条件は、鍛造温度は１５００℃とし、熱間スェージングは、加工温度を１３００℃とし、加圧周期５０Ｈｚとした。そして、スエージング加工により直径３.１０ｍｍの断面円形のイリジウム合金線材とした。
【００４０】
そして、第１実施形態と同様、通電加熱によりダイス１パスの平均断面減少率１７.５％，伸線速度１.０〜２.３ｍ／ｍｉｎ間で設定し引抜き加工を行なった。 尚、白金―ロジウム合金の場合、中間焼鈍を行なう必要がないので行なっていない。
【００４１】
この結果製造された線材は第１実施系他と同様良好な品質のものであり、ほぼ均一な材料組織であり、欠陥がないことが確認された。
尚、このイリジウム―ロジウム合金についても、比較例１のように従来法であるバーナー加熱による引抜き加工を行なったが、この場合の加工パス数は第２実施形態の２.０倍であった。そして、全加工時間も第２実施形態の３.７６倍であった。従って、イリジウム―ロジウム合金線材の製造にあたっても本発明は効率に優れた加工方法であることがわかった。
【００４２】
【発明の効果】
以上説明したように本発明によれば、割れや組織的不均一等の欠陥を有しない極めて優れた品質のイリジウム又はイリジウム合金線材を効率的に製造することができる。そのため、本発明により製造されるイリジウム又はイリジウム合金線材は、点火プラグ用電極等のような今後の需要の拡大が予測され、品質基準の厳格な機能材料としての用途への適用が期待できる。
【図面の簡単な説明】
【図１】イリジウム合金線材の常温及び高温での引き抜き加工時の破断状況を示す図。
【図２】イリジウム合金線材を引き抜き加工する際の加工可能領域を示す図。
【図３】イリジウム合金線材を引き抜き加工する際の品質保証領域を示す図。
【図４】本発明に係る引き抜き加工条件を詳細に示す図。
【図５】第１及び第実施形態の通電加熱法によるイリジウム合金の引き抜き加工工程を示す図。
【図６】従来のバーナー加熱によるイリジウム合金の引き抜き加工工程を示す図。
【符号の説明】
１ イリジウム合金線材
２ ロール電極
３ ダイス
４ ダイス保持板
５ プログラム式コントローラー
６ 潤滑剤
７ 電気ヒーター
８ バーナー
９ 火炎[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a processing method for reducing a cross-sectional area of a wire made of iridium or an iridium alloy by drawing. More specifically, the present invention relates to a production method for efficiently producing high-quality iridium or iridium alloy wire without defects.
[0002]
[Prior art]
Iridium and alloys containing iridium as a main component (iridium-platinum alloy, iridium-rhodium alloy, etc.) have been conventionally used as crucibles and insoluble electrodes because of their high melting point, high hardness, and high corrosion resistance. In recent years, it has attracted attention that its oxidation resistance and electrical properties have unique properties, and its use in other fields is also being studied in the future. Examples of recent use of iridium alloys include electrodes for ignition plugs for internal combustion engines such as automobiles, and pin tips for dot printers. Thus, the application range of iridium alloys is expanding, for example, in terms of spark plug electrodes, iridium has a high melting point among platinum group metals, and therefore has low volatility loss and excellent spark oxidation resistance. It is based on.
[0003]
In order to apply such a spark plug to an application such as an electrode, a thin wire is used, and the wire is cut into an appropriate length. The wire is manufactured by forging, rolling, or the like. It is made by drawing this from (bar material).
[0004]
Iridium and iridium alloys are high melting point materials (the melting point of iridium is 2400 ° C. or higher), and are relatively brittle and difficult to process at room temperature. Therefore, hot processing is usually applied. It is. This also applies to the drawing process. In the conventional iridium alloy drawing process, a drawing process at a high temperature of about 1300 ° C. is performed. FIG. 6 schematically shows a drawing process of a conventional iridium alloy wire. The iridium wire 1 as a workpiece is coated with a lubricant 6 before being processed, and is heated by a flame 9 of a burner 8. The heated wire passes through the die 3 and becomes a wire having a smaller wire diameter. Then, when it is desired to make the wire diameter of the wire intended for processing smaller, this process is repeated. This conventional drawing process is a widely practiced method because the wire can be brought to a predetermined processing temperature by a simple heating means such as heating by a burner.
[0005]
[Problems to be solved by the invention]
By the way, the iridium alloy wire manufactured as described above is required to be free from defects such as scratches, wrinkles, cracks, and structural nonuniformity, and to have a constant wire diameter. It has become increasingly severe. For example, there is a remarkable improvement in the performance of automobile engines in recent years, but a highly reliable spark plug is indispensable for improving the performance of engines. And even if the electrode with cracks has a very small defect, it may cause the discharge characteristics to become unstable, shortening its life more than expected, and reducing its reliability. Therefore, a wire having no defects is required.
[0006]
In order to meet such requirements, the conventional manufacturing conditions and manufacturing methods can be substantially satisfied for the original purpose of reducing the cross-sectional area of the wire, but the quality is not necessarily sufficient. In particular, it can be said that establishment of a high-precision molding technique free from defects is required in consideration of higher quality standards that will be required in the future.
[0007]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method capable of forming a high-quality wire material that is more efficient and has no defects in a method of drawing a wire material made of iridium or an iridium alloy.
[0008]
[Means for Solving the Problems]
In order to solve such a problem, the present inventor first decided to optimize processing conditions when hot drawing iridium. In general, as conditions for material processing, selection of processing temperature and processing rate (section reduction rate in drawing processing) is important. In this regard, in the case of iridium, the processing temperature is conventionally set high in consideration of the melting point and toughness at room temperature as described above. Therefore, the present inventors first examined the state change of the workpiece depending on the processing temperature in the iridium drawing process, and obtained the following knowledge.
[0009]
Fig. 1 shows the rupture when iridium alloy is drawn at room temperature and high temperature. First, when it is processed at low temperature (room temperature), the iridium alloy wire as shown in Fig. 1 (a) Although breakage occurs, the breakage at this time occurs in the die. The cause of the occurrence of breakage at normal temperature is that the plastic working resistance of the wire in the die is greater than the tensile force of the wire near the die outlet. In this case, by heating the wire and softening the wire, the plastic working resistance can be reduced and the occurrence of breakage can be prevented.
[0010]
On the other hand, even when the processing temperature is high, the wire may be broken. As shown in FIG. 1B, the fracture at this time occurs not after the die but after passing through the die, but this does not cause fracture in the die due to a decrease in processing resistance due to heating. This is because the material strength after passing through the die is smaller than the tensile force. And as a factor of this material strength reduction, recrystallization occurs in the material by heating to high temperature, the result of grain boundary strength decreases due to factors such as crystal grain growth and segregation of impurities to the grain boundary, embrittlement, This is probably because the strength of the entire material is reduced.
[0011]
Considering the above behavior at the time of drawing at low and high temperatures, the drawing of the iridium alloy requires heating, but the temperature needs to be within a range where recrystallization does not occur. That is, it is considered that there is a predetermined range (workable region) in the workable temperature of the iridium alloy, and there are upper and lower limits that form this range.
[0012]
On the other hand, this processable temperature range is not uniformly determined, but is considered to vary depending on the processing rate. That is, since the machining resistance increases as the machining rate increases, it is considered that the lower limit value of the machining temperature shifts to the high temperature side as the machining rate increases as shown in FIG. 2 (line (2) in FIG. 2). On the other hand, regarding the upper limit value, it is considered that the recrystallization temperature decreases due to the increase in the processing rate, and the upper limit value also decreases in connection with this (line (1) in FIG. 2).
[0013]
As described above, in the drawing process of the iridium wire, there is a processable temperature range corresponding to the processing rate, which fluctuates. On the other hand, the processable region merely indicates whether or not processing can be performed without causing breakage, and does not indicate a range in which a high-quality wire without defects can be processed. That is, at the processing temperature near the lower limit value, it is considered that there is a region where micro-cracking occurs although fracture does not occur due to the relationship between processing resistance and material strength. Further, at the processing temperature near the upper limit value, the recrystallization described above appears not only inside the material but also on the surface, which causes a rough surface of the material. Therefore, it is necessary to consider the recrystallization temperature which changes with the change of the processing rate as the upper limit value of the processing temperature. Therefore, it can be said that there is a quality assurance area for ensuring good quality in the workable area.
[0014]
FIG. 3 shows a quality assurance region derived from these processable temperatures and defect occurrence temperatures. The inventors of the present invention have intensively studied that the defect-free wire can be manufactured by processing under the conditions in the quality assurance area, and have determined the boundary line of the quality assurance area.
[0015]
That is, in the drawing method according to the present application, when the processing rate in one pass of the die is X (%) and the wire heating temperature at the die entrance is T (° C.), the processing rate in the region surrounded by the following formula, It is characterized by processing at a heating temperature.
[0016]
[Expression 4]

[Equation 5]

[Formula 6]

[0017]
FIG. 4 shows the quality assurance area defined by the equations 4 to 6. In FIG. 4, the upper limit of the workable temperature described above corresponds to Equation 4, the surface roughness occurrence temperature line corresponds to Equation 5, and the crack occurrence temperature line corresponds to Equation 6. In addition, since it has become clear from the study by the present inventors that the lower limit line for workable temperature does not cross at a cross-section reduction rate lower than the intersection of Equation 4 and Equation 6, the lower limit line for workable temperature is a quality assurance area. Is not prescribed. Further, according to the present inventor, the conditions for processing by conventional burner heating are indicated by the temperature and processing rate in the vicinity of point a in FIG. 4 and are outside the range of the quality assurance region of the present invention.
[0018]
According to the present invention, it is possible to draw a high-quality wire by setting the processing temperature within an appropriate range in relation to the processing rate. In addition, according to the present invention, it is possible to perform processing at the maximum processing rate (the intersections of Equations 4 and 6 and about 30%), and the cross-section reduction effect by one processing is excellent and efficient. Processing is possible. In order to manufacture a wire having a desired wire diameter as described above, the drawing process is repeatedly performed a plurality of times. According to the present invention, the processing rate per process is set to the maximum. This makes it possible to minimize the number of machining passes.
[0019]
Moreover, since the heating temperature of the wire in the processing method according to the present invention is lower than the conventional one, damage to the die in contact with the wire can be reduced, and the life of the die can be prolonged.
[0020]
By the way, when manufacturing a thin wire rod by repeatedly processing a plurality of times, depending on the material to be processed, it may be necessary to perform an intermediate annealing between each processing pass. This is because work hardening progresses by repeating the drawing process several times, and material cracking may occur. Therefore, intermediate annealing after several pass processing causes a recovery phenomenon in the material and makes it ready for processing again. Is. The intermediate annealing needs to be performed more frequently as the heating temperature during the drawing process is lower. However, frequently performing the intermediate annealing process increases the overall processing time. Therefore, a more preferable range of the processing temperatures in the present invention is preferably a region above the line T = 750, that is, a temperature range in which recrystallization does not occur at 750 ° C. or higher. It is because the frequency | count of implementation of intermediate annealing can be reduced as much as possible by setting it as this range. Note that the necessity of the intermediate annealing and the annealing temperature differ depending on the alloy type because the work hardening behavior and the recovery behavior differ depending on the alloy type. For example, an iridium-platinum alloy requires intermediate annealing at 1000 ° C. to 1100 ° C., and an iridium-rhodium alloy may require intermediate annealing at 900 ° C. to 1000 ° C. in some cases.
[0021]
The processing speed (drawing speed) in the present invention is not particularly limited. For example, the processing speed of processing by conventional burner heating is 0.5 to 1.0 m / min. Although processing at this speed is possible in the present invention, the processing conditions are optimized, so that Machining at a speed higher than the machining speed is possible. A preferable processing speed is 1.0 to 3.0 m / min.
[0022]
On the other hand, the present invention is characterized by processing at a relatively narrow temperature range because the temperature at the time of drawing is lower than that of the prior art and the preferable lower limit is about 750 ° C. Therefore, in the present invention, it is important to appropriately control the processing temperature. On the other hand, in the flame of a burner performed in the conventional drawing process, the processing temperature becomes too high, and it is difficult to control in the temperature range intended by the present invention. Therefore, the present inventors can set the heating temperature lower than in the prior art, and as an easy control method, an electric heating method, that is, the wire is heated and processed by passing an electric current through the wire that is the workpiece. It is preferable to do this.
[0023]
In this heating method, resistance heat generated by passing an electric current through the wire is used as a heat source for processing. The wire temperature at this time can be set by adjusting the applied current. Therefore, according to this energization heating method, the processing temperature can be set lower than that of the conventional burner heating, and can be further stabilized. And since processing conditions can be maintained in an appropriate range by this, a high quality wire can be manufactured efficiently.
[0024]
Specifically, the heating of the wire is performed by bringing a pair of electrodes into contact with the wire and energizing. However, the wire needs to be energized to reach a predetermined temperature before passing through the die. In this case, both electrodes may be placed on the die entrance side, and these may be brought into contact with the wire and energized. However, it is preferable that one electrode is placed separately on the die entrance side, and the other electrode is the die outlet. On the side and close to the die. This is because when both electrodes are arranged on the die entrance side, heating of the wire ends before being introduced into the die, and the processing under the processing conditions in which the temperature is lowered during processing cannot be performed. The reason why the other electrode is placed on the exit side of the die and close to the die is that if the other electrode is placed away from the die, the wire is heated even after the processing is completed, and the wire may be broken. It is preferable that the space | interval of an exit side electrode here and die | dye exit surface shall be 100 mm or less. However, in order to energize the wire most efficiently, the electrode on the die outlet side is placed in contact with the die so that the current passes through the die, and the wire is energized by both the electrode and the die. It is particularly preferable to do so.
[0025]
On the other hand, it is preferable that the position of the electrode spaced apart on the die entrance side is 450 to 550 mm upstream from the die. As will be described later, in this drawing process, it is preferable to apply a lubricant to the wire. However, if the electrode is placed too close to the die, the wire temperature immediately rises and the applied lubricant boils and becomes uniform. It is because it becomes impossible to apply | coat to this, and the space for an application | coating operation | work cannot be ensured. Further, it is necessary to provide a certain space between the electrodes in order to secure a space for temperature measurement and control the wire temperature as much as possible. In addition, it is preferable to use carbon as the material of the electrode spaced apart on the die entrance side.
[0026]
In the drawing method according to the present invention, it is more preferable to perform processing by heating the die in addition to heating the wire. This is because, by heating the die, the temperature drop of the wire during the processing can be suppressed, so that the breakage of the wire can be surely prevented. The heating temperature of this die is preferably in the range of 400 to 700 ° C., and an electric heater can be installed on the outer periphery of the die to perform this.
[0027]
Furthermore, in this drawing process, it is preferable to apply the lubricant to the wire and then process it in order to ensure the quality of the processed wire and the processing efficiency. As this lubricant, it is preferable to apply a carbon-based lubricant whose main component is carbon. This is because the carbon lubricant becomes smooth when cleaved and finely pulverized at the temperature in the present invention, and the processing can be assisted without causing scratches on the wire. In this respect, the carbon-based lubricant is consumed by being oxidized into CO and CO ₂ in the atmosphere, and its oxidation rate is very fast and difficult to use at the processing temperature (1300 ° C.) in the conventional drawing process. It is. Therefore, in the conventional method, the boron nitride-based lubricant is applied as described above. However, the boron nitride-based lubricant does not volatilize but is hard and may damage the wire without cleaving. Therefore, the present invention has an advantage that a high-quality wire without scratches can be produced by making it possible to use a carbon-based lubricant.
[0028]
In addition, the application of the carbon-based lubricant realized by the present invention has an advantage of improving the quality of the wire and further improving the die life. This is because the boron nitride lubricant used in the conventional method is a kind of ceramics and has a polishing action on the die, but the carbon lubricant does not have such a polishing action.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0030]
First Embodiment : In this embodiment, a wire made of an iridium-platinum alloy (Ir-5% Pt) is manufactured as an iridium alloy. Iridium 209 g and platinum 11 g were weighed and mixed, and dissolved in an Ar arc furnace to produce an iridium alloy ingot. The iridium alloy ingot was hot forged at 1500 ° C. The dimensions of the ingot after processing were 10 mm square and 90 mm long. Next, after passing this square bar through a grooved roll heated to 1300 ° C. and hot rolling to further reduce the cross-sectional diameter, annealing was performed at 1400 ° C. for 30 minutes in an air atmosphere, and then hot swaging was performed. It was. In the swaging process, a rotary swagger was used as a forging machine, the processing temperature was 1300 ° C., and the pressurization cycle was 50 Hz. The overall processing rate by this swaging processing was 75%, and the iridium alloy wire after processing became a circular cross-section with a diameter of 3.10 mm.
And the iridium alloy wire after hot swaging was made into a thin wire by drawing. The drawing process was performed by the method shown in FIG. In FIG. 5, the wire 1 that is a workpiece is processed by being heated and passed through the die 3 by a roll electrode 2 on the upstream side of the die and a die holding plate 4 that also serves as an electrode on the outlet side of the die 3. The wire temperature is measured by an infrared radiation thermometer, and the amount of electricity applied to the wire is adjusted by the programmable controller 5 based on the measured value. Moreover, after applying the lubricant 6 to the wire rod that has passed through the energizing roll 2, it is fed into the die. The die 3 is heated to 650 ° C. by the electric heater 7. In this embodiment, the energization amount is controlled so that the distance between the dice and the energizing roll is 520 mm and the heating temperature is 1000 ° C.
[0032]
With this device, the average cross-section reduction rate in one pass of the die is set to 17.5%, the wire drawing speed is set between 1.0 and 2.3 m / min, and the die hole diameter is sequentially reduced, and the alloy wire is repeatedly drawn. Processed and finally made a fine wire with a diameter of 0.6 mm. In this repeated drawing process, intermediate annealing (1100 ° C., 30 min) is performed every 2 to 4 passes.
[0033]
And when this manufactured iridium-platinum alloy wire was inspected for the material structure and the presence or absence of defects, it was confirmed that the material structure was almost uniform and there were no defects including minute ones.
[0034]
Comparative Example : As a comparison with the first embodiment, an iridium-platinum alloy wire was manufactured by a conventional method. Production of the iridium alloy wire by the conventional method is performed by the production apparatus of FIG. 6, and a propane combustion burner is used as the burner 8. The lubricant is a boron nitride lubricant.
[0035]
And about the iridium alloy wire manufactured by the same rolling and swaging as 1st Embodiment, it was set as the average cross-section reduction rate per die | dye of 9.7%, and the wire drawing speed was between 0.5-0.7 m / min. It was set at, and was repeatedly drawn multiple times. The processing rate and the wire drawing speed in this comparative example were set lower than those in the first embodiment, but this is the same processing as in the first embodiment because the processing temperature (about 1300 ° C.) by the burner heating is too high. If the processing is performed at a rate or the like, the surface of the wire is roughened, wrinkles are generated, and wire breakage is likely to occur. Further, the drawing process by the burner heating is not performed because the processing temperature is as high as 1300 ° C., so that it is not necessary to perform the intermediate annealing.
[0036]
In the comparative example, there was no breakage or large defect in the wire produced in the drawing process. However, in this comparative example, the surface of the wire was roughened and wrinkled, and the surface of the wire was polished in the middle of processing to remove this. I had to. Further, in the comparative example, the processing temperature was high, and the particles of the boron nitride-based lubricant used for that purpose were not cleaved, and scratches due to the lubricant particles were observed on the surface of the wire.
[0037]
Further, even though no breakage occurs, this is because the processing conditions are limited so that the breakage does not occur. The number of passes (the number of processing) for manufacturing a wire with the same diameter becomes larger than that in the first embodiment under the processing conditions limited in this way. In the first embodiment, the number of passes is 1.88 times. It became necessary. Further, the total machining time is also large in the comparative example, and in the first embodiment, even if the intermediate annealing time is taken into consideration, the comparative example requires 1.76 times as long as there is no intermediate annealing. Therefore, it can be confirmed that the drawing method of the first embodiment can manufacture a high-quality wire in a shorter number of passes and time.
[0038]
Second Embodiment : In this embodiment, a wire made of an iridium-rhodium alloy (Ir-20% Rh) was manufactured as an iridium alloy. 160 g of iridium and 40 g of rhodium were weighed and mixed and melted in an Ar arc furnace to produce an iridium alloy ingot.
[0039]
This iridium alloy ingot was subjected to hot forging and hot swaging as in the first embodiment. The processing conditions here were a forging temperature of 1500 ° C., and hot swaging was a processing temperature of 1300 ° C. and a pressurization cycle of 50 Hz. And it was set as the iridium alloy wire with a circular section of 3.10 mm in diameter by swaging.
[0040]
Then, similarly to the first embodiment, the drawing process was performed by setting between an average cross-sectional reduction rate of 17.5% for a die and a drawing speed of 1.0 to 2.3 m / min by energization heating. In the case of a platinum-rhodium alloy, it is not necessary because intermediate annealing is not required.
[0041]
As a result, it was confirmed that the manufactured wire was of good quality as in the first embodiment, the material structure was almost uniform, and there were no defects.
The iridium-rhodium alloy was also drawn by burner heating, which is a conventional method, as in Comparative Example 1, but the number of machining passes in this case was 2.0 times that of the second embodiment. The total processing time was 3.76 times that of the second embodiment. Therefore, it was found that the present invention is an efficient processing method in the production of iridium-rhodium alloy wires.
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to efficiently produce iridium or iridium alloy wire of extremely excellent quality that does not have defects such as cracks and structural inhomogeneities. Therefore, iridium or an iridium alloy wire produced according to the present invention is expected to expand in future demand such as a spark plug electrode, and can be expected to be used as a functional material with strict quality standards.
[Brief description of the drawings]
FIG. 1 is a diagram showing a rupture state of an iridium alloy wire during drawing at room temperature and high temperature.
FIG. 2 is a view showing a workable region when drawing an iridium alloy wire.
FIG. 3 is a view showing a quality assurance region when drawing an iridium alloy wire.
FIG. 4 is a diagram showing in detail the drawing conditions according to the present invention.
FIG. 5 is a diagram showing a drawing process of an iridium alloy by an electric heating method according to the first and second embodiments.
FIG. 6 is a view showing a drawing process of an iridium alloy by conventional burner heating.
[Explanation of symbols]
1 Iridium alloy wire 2 Roll electrode 3 Die 4 Die holding plate 5 Programmed controller 6 Lubricant 7 Electric heater 8 Burner 9 Flame

Claims (10)

A iridium or iridium-platinum alloy containing 5% by weight or less of platinum and the balance iridium or a iridium-rhodium alloy containing 20% by weight or less of rhodium and the balance iridium is heated to form a die. In the method of drawing through
When the processing rate in one die pass is X (%) and the wire heating temperature at the die entrance is T (° C.) , the following formula defines the region surrounded by the following formula, and the processing rate and heating temperature are A method of drawing an iridium or iridium alloy wire, characterized by being set in the region and processed.

Furthermore, the drawing method of the iridium or iridium alloy wire material of Claim 1 processed at T = 750 degreeC or more. The one electrode of the pair of electrodes is disposed apart from the die on the die entrance side, the other electrode is disposed in proximity to the die on the die exit side, and the pair of electrodes are brought into contact with the wire to conduct electricity. The drawing method of the iridium or iridium alloy wire according to 2. 4. The method of drawing an iridium or iridium alloy wire according to claim 3, wherein an electric current is passed through the die by disposing the electrode on the die outlet side in contact with the die, and the wire is energized by the electrode and the die. The method of drawing an iridium or iridium alloy wire according to claim 3 or 4 , wherein a material of the electrode spaced apart on the die entrance side is carbon. The drawing method of the iridium or iridium alloy wire material according to any one of claims 1 to 5 , wherein the die is heated and processed. The method of drawing an iridium or iridium alloy wire according to claim 6, wherein an electric heater is installed on the outer periphery of the die and the die is heated by the electric heater. The iridium or iridium alloy wire drawing method according to claim 6 or 7, wherein the die temperature is heated to 400 to 700 ° C. The method of drawing an iridium or iridium alloy wire according to any one of claims 1 to 8 , wherein the iridium or iridium alloy wire is processed after applying a lubricant between a pair of electrodes. The method of drawing an iridium or iridium alloy wire according to claim 9, wherein a lubricant comprising carbon as a main component is applied.

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