JP3963685B2 - Method for producing cast iron member - Google Patents

Description

【００１１】
なお、反応式（１）において、γ、αは、それぞれ、γ−Ｆｅ（オーステナイト）、α−Ｆｅ（フェライト）を表す。
【００１２】
Ａ₁変態点を通過してフェライト組織が生成した成形品５は、ブロア８からの送風により強制的に冷却される。
【００１３】
次に、このような熱処理が施された成形品５のシャフト部３等に対し、旋削加工等の機械加工処理を施す。これにより、寸法精度を有するバランサシャフト１（図３参照）が製造されるに至る。
【００１４】
最後に、バランサシャフト１の硬度を確保するため、該バランサシャフト１に対して軟窒化（ＬＣＮ）処理やガス窒化（ＧＣＮ）処理等の窒化処理を施し、充分な強度や硬度を有する完成製品とする。
【００１５】
【発明が解決しようとする課題】
ところで、近年における環境保護の観点から、自動車等には燃費が良好なことが求められている。そして、これを達成するために、各部材の軽量化が図られている。
【００１６】
バランサシャフト１を軽量化する場合には、より耐摩耗性に優れかつ高強度な材質、例えば、ＦＣＤ７００からバランサシャフト１を構成することが想起される。この場合、略同等の強度・耐摩耗性を有するものであれば、ＦＣＤ４５０からなるバランサシャフト１に比して断面積を小さくすることができるからである。
【００１７】
ＦＣＤ７００からなるバランサシャフト１を製造するためには、ＦＣＤ７００相当の組成の原材料を溶解して溶湯とした上で鋳造作業を行う。しかしながら、このようにして製造されたＦＣＤ７００からなるバランサシャフト１の成形品５は、耐摩耗性が著しく高いため、シャフト部３等に対して旋削加工を施すことが困難であるという不具合がある。
【００１８】
また、ＦＣＤ４５０の原材料とＦＣＤ７００の原材料とでは、組成が互いに相違する。具体的には、ＦＣＤ４５０においては、フェライト組織を生成させるためにＳｉが添加される。これに対し、ＦＣＤ７００においては、パーライト組織を生成させるためにＣｕやＳｎが添加される。したがって、ＦＣＤ４５０からなるバランサシャフト１を製造した後に同一の鋳造装置を使用してＦＣＤ７００からなるバランサシャフト１を製造すると、鋳型のキャビティに残留したＳｉによってフェライト組織が生成してしまうことが懸念される。このような事態が生じると、バランサシャフト１の強度・耐摩耗性を向上させることが困難となる。
【００１９】
このような事態を回避するためには、別の鋳造装置を使用すればよい。しかしながら、この場合、鋳造装置に対する高額の設備投資が必要となるという不都合を招く。
【００２０】
本発明は上記した問題を解決するためになされたもので、耐摩耗性が良好な部位と各種の機械加工を比較的容易に施すことができる部位とを有する鋳鉄製部材を同一の溶湯から製造することが可能な鋳鉄製部材の製造方法を提供することを目的とする。
【００２１】
【課題を解決するための手段】
前記の目的を達成するために、本発明は、パーライト組織を主相とする第１の部位とフェライト組織を主相とする第２の部位とを具備する鋳鉄製部材の製造方法であって、
鋳鉄の溶湯を鋳型内で冷却固化して成形品とする第１工程と、
前記成形品の温度がＡ₁変態点を通過する前に該成形品に対して熱処理を施すことによって、前記第１工程において該成形品に生成したチル組織を分解する第２工程と、
チル組織が分解された前記成形品の少なくとも一部位をパーライト組織が生成する条件下で冷却して第１の部位を設ける一方で、残余の部位をフェライト組織が生成する条件下で冷却して第２の部位を設ける第３工程と、
前記第２の部位に対して機械加工を施すことによって完成製品である鋳鉄製部材とする第４工程と、
を有することを特徴とする。
【００２２】
本発明によれば、チル組織を消失させた後の冷却速度が個別に設定され、これにより高硬度で耐摩耗性が良好な第１の部位と、旋削加工等の機械加工を施すことが比較的容易な第２の部位とを設けるようにしている。このため、特性が互いに異なる部位を有する鋳鉄製部材を組成を特に調整することなく同一の溶湯から容易かつ簡便に製造することができる。
【００２３】
また、主にパーライト組織を含む第１の部位は、実用に際して充分な強度・耐摩耗性を有する。このため、該第１の部位等に対して各種の窒化処理を行う必要も特にない。したがって、鋳鉄製部材を効率よく製造することができる上、窒化処理を行うためのコストを削減することもできる。
【００２４】
なお、上記のようにして製造されるフェライト組織とパーライト組織とを有する鋳鉄製部材の好適な例としては、球状黒鉛鋳鉄からなるものを挙げることができる。
【００２５】
そして、鋳鉄製部材の好適な例としては、自動車等の車輌に搭載される内燃機関用のバランサシャフトを挙げることができる。この場合、強度・耐摩耗性が良好な第１の部位としてジャーナル部を設け、かつ研削加工等を施すことが比較的容易な第２の部位としてシャフト部を設けるようにすればよい。
【００２６】
【発明の実施の形態】
以下、本発明に係る鋳鉄製部材の製造方法につき好適な実施の形態を挙げ、添付の図面を参照して詳細に説明する。
【００２７】
本実施の形態に係る鋳鉄製部材の製造方法のフローチャートを図１に示す。この製造方法は、鋳鉄の溶湯を鋳型内（キャビティ）で冷却固化して成形品とする第１工程Ｓ１と、前記成形品に対して熱処理を施して該成形品に生成したチル組織を分解する第２工程Ｓ２と、前記成形品にパーライト組織を含む第１の部位およびフェライト組織を含む第２の部位を設ける第３工程Ｓ３と、前記第２の部位に機械加工を施すことによって完成製品である鋳鉄製部材とする第４工程Ｓ４とを有する。
【００２８】
この製造方法につき、それを遂行する鋳造装置との関係で、鋳鉄製部材として図３に示すバランサシャフト１を製造する場合を例示して具体的に説明する。
【００２９】
鋳造装置１０は、図２に示すように、注湯ステーション１２と、固定金型１４および可動金型１６を有する金型成形装置１８と、矯正・切断装置２０と、熱処理炉２２とを備える。なお、可動金型１６は、金型成形装置１８を構成するシリンダ２３の作用下に固定金型１４に対して接近または離間自在である。
【００３０】
金型成形装置１８の上方には、ブロースモーク装置２８が上下方向に変位自在に設けられている。また、金型成形装置１８の下流側上方には、ワーク取出ロボット３０が水平方向に移動自在に設けられている。これらブロースモーク装置２８およびワーク取出ロボット３０は、支持台３１によって支持されている。
【００３１】
注湯ステーション１２は、溶解炉３２と、加圧注湯炉３４と、該加圧注湯炉３４から導出された溶湯を受け取って金型成形装置１８のキャビティに導入する取り鍋２４とを有し、このうち、溶解炉３２は、架台３６上に設置されている。
【００３２】
本実施の形態に係る製造方法を行うに際しては、まず、原材料を溶解して溶湯とする。すなわち、原材料として鋼屑や返り材、銑鉄等を溶解炉３２に収容した後、該溶解炉３２を周囲から加熱してこれらを溶解させる。
【００３３】
ここで、原材料の組成は、ＦＣＤ４５０に相当する組成とＦＣＤ７００に相当する組成との中間、すなわち、ＦＣＤ５００やＦＣＤ６００に相当する組成とすることが好ましい。この場合、成形品５を冷却させる際にパーライト組織およびフェライト組織を容易に生成させることができるからである。しかしながら、特にこれに限定されるものではなく、ＦＣＤ７００に相当する組成であってもよいし、ＦＣＤ４５０に相当する組成であってもよい。この場合、成形品５にフェライト組織およびパーライト組織を生成させるには、冷却速度をより厳密に制御するようにすればよい。
【００３４】
溶解炉３２は、傾動動作させることが可能である。すなわち、溶解炉３２の上方に突出形成された湯口部３８の下端部には、シリンダ４０のロッド４２が連結されている。また、溶解炉３２の底部には、該底部の中央から湯口部３８の方に偏在して支軸４４が連結されている。このため、溶解炉３２は、ロッド４２が上下動することに追従して、支軸４４との連結箇所を支点として傾動動作する。溶湯を搬送取り鍋４６内に注湯する場合には、ロッド４２を下降動作させることにより湯口部３８を搬送取り鍋４６に指向して傾動動作させればよい。
【００３５】
図示しないクレーンのフック４８に支持された搬送取り鍋４６は、前記クレーンの作用下に加圧注湯炉３４に指向して搬送される。そして、搬送取り鍋４６が図示しない第１傾動機構によって傾動動作することにより、該搬送取り鍋４６内の溶湯が漏斗５０を介して加圧注湯炉３４の内室５２に注湯・貯留される。
【００３６】
加圧注湯炉３４には、内室５２の圧力を上昇させるガスを導入するためのガス供給管５４が連結されている。すなわち、このガス供給管５４からＡｒ等の不活性ガスが供給されることに伴って内室５２内の圧力が上昇し、その結果、該内室５２に貯留されていた溶湯が、加圧注湯炉３４の出湯部５６に設けられた湯路５８に導入され、最終的に出湯部５６の出湯口５９から導出される。上記したように、導出された溶湯は、取り鍋２４内に注湯される。
【００３７】
取り鍋２４はロードセル６０上に載置されており、該取り鍋２４内の溶湯量はロードセル６０の作用下に所定量に制御される。すなわち、取り鍋２４内に注湯された溶湯の重量の測定値がロードセル６０に予め設定された設定値に一致したとき、該ロードセル６０と電気的に接続された図示しない制御部からの制御信号により、ガス供給管５４に介装されたバルブ（図示せず）が閉止される。これに伴い加圧注湯炉３４の内室５２へのガスの供給が停止され、その結果、加圧注湯炉３４の出湯口５９から溶湯の導出が停止される。
【００３８】
この取り鍋２４は、図示しない第２傾動機構によって傾動動作させることが可能である。この傾動動作に伴い、金型成形装置１８を構成する湯口６４を介して、取り鍋２４内に導入された所定量の溶湯が金型成形装置１８のキャビティに注湯され、第１工程Ｓ１が開始される。なお、金型成形装置１８の固定金型１４と可動金型１６とが型締めされる前には、ブロースモーク装置２８によって、キャビティ面に離型剤が予め塗布される。
【００３９】
金型成形装置１８のキャビティに導入された溶湯は、１０００℃／分程度の冷却速度で冷却され、最終的に表層部のみが固化して成形品５となる。この成形品５における固化した表層部には、セメンタイト（Ｆｅ₃Ｃ）からなるチル組織が形成されている。
【００４０】
得られた成形品５は、可動金型１６が固定金型１４から離間して型開きが行われた後、ワーク取出ロボット３０に把持される。このワーク取出ロボット３０が水平方向に移動することに伴い、成形品５が矯正・切断装置２０に搬送される。この矯正・切断装置２０では、成形品５に対してトリミング等が施される。
【００４１】
その後、成形品５は、移載ロボット６６の作用下に搬送され、熱処理炉２２内に導入される。この熱処理炉２２において、第２工程Ｓ２、すなわち、成形品５に対する熱処理が施される。
【００４２】
以上の過程において、成形品５の内部が未凝固で高温の溶湯であるため、成形品５の温度がＡ₁変態点を下回ることはない。換言すれば、成形品５は、該成形品５の温度がＡ₁変態点を通過する前に金型成形装置１８のキャビティから取り出され、かつ熱処理炉２２内に導入される。
【００４３】
この熱処理は、成形品５の表層部に生成したチル組織（Ｆｅ₃Ｃ）をパーライト組織に変態させるためのものである。すなわち、成形品５の表層部に存在するチル組織に対して熱を加えると、チル組織がオーステナイト（γ−Ｆｅ）および黒鉛へと分解する。なお、熱処理の温度や時間は、チル組織が分解するような条件に設定すればよく、例えば、９３０℃で３０分間保持という条件に設定することができる。
【００４４】
このようにしてチル組織が分解された成形品５を熱処理炉２２から取り出した後、第３工程Ｓ３において、パーライト組織を主に含み高硬度で耐摩耗性が良好なジャーナル部２（第１の部位）と、フェライト組織を主に含み旋削加工を施すことが比較的容易なシャフト部３（第２の部位）とが設けられるように冷却処理を施す。すなわち、例えば、成形品５のジャーナル部２のみに冷却速度が２００℃／分以上となるような流量で圧縮エアを吹き付け、該ジャーナル部２を強制的に冷却する。その一方で、ジャーナル部２以外の箇所には圧縮エアの吹き付けを行わず、大気中で空冷する。なお、未凝固の状態であった成形品５の内部の溶湯は、この冷却処理が施される最中に完全に冷却固化する。
【００４５】
以上から諒解されるように、本実施の形態においては、チル組織を消失させた後の冷却速度を部位に応じて個別に設定することにより、原材料（溶湯）の組成を特に調整することなく、高硬度で耐摩耗性に優れるジャーナル部２と旋削加工等を施すことが比較的容易なシャフト部３とを設けるようにしている。このため、溶湯の組成に応じて金型成形装置１８を個別に用意する必要がない。したがって、高額の設備投資が必要となることもない。
【００４６】
最後に、第４工程Ｓ４において、シャフト部等に対して旋削加工等の機械加工を施すことにより、寸法精度を有する完成製品としてのバランサシャフト１が得られるに至る。
【００４７】
このバランサシャフト１においては、ジャーナル部２がパーライト組織を含むので充分な強度・耐摩耗性を有する。このため、該ジャーナル部２に対してＬＣＮ処理やＧＣＮ処理を行う必要も特にない。したがって、バランサシャフト１を効率よく製造することができるとともに、ＬＣＮ処理やＧＣＮ処理を行うためのコストを削減することができるという利点もある。
【００４８】
なお、上記した実施の形態では、鋳鉄製部材としてバランサシャフト１を製造する場合を例示して説明したが、それ以外のものであってもよいことはいうまでもない。
【００４９】
また、本実施の形態に係る製造方法においては、鋳造時に金型が使用されているが、成形品にチル組織が生成する条件下で鋳造が行われるのであれば、特にこれに限定されるものではない。
【００５０】
【発明の効果】
以上説明したように、本発明に係る鋳鉄製部材の製造方法によれば、部位に応じて互いに異なる冷却速度を設定することにより、パーライト組織を含む部位とフェライト組織を含む部位とが混在する鋳鉄製部材を得るようにしている。このため、組成を特に調整することなく、耐摩耗性が良好な部位を有する一方で、旋削加工等の機械加工を比較的容易に施すことが可能な部位を有する鋳鉄製部材が得られるという効果が達成される。したがって、組成に応じて鋳造装置を個別に用意する必要がないので、高額な設備投資が必要となることもない。
【００５１】
また、パーライト組織を含む部位は高硬度で耐摩耗性が良好であるので、窒化処理を行う必要は特にない。このため、窒化処理を行うためのコストを削減することもできる。
【図面の簡単な説明】
【図１】本実施の形態に係る鋳鉄製部材の製造方法のフローチャートである。
【図２】本実施の形態に係る鋳鉄製部材を遂行する鋳造装置の概略全体構成図である。
【図３】バランサシャフトの概略全体斜視図である。
【図４】熱処理炉にて成形品に熱処理を施している状態を示す概略縦断面図である。
【符号の説明】
１…バランサシャフト ２…ジャーナル部（第１の部位）
３…シャフト部（第２の部位） ４、２２…熱処理炉
５…成形品 ６ａ〜６ｅ…加熱域
８…ブロア １０…鋳造装置
１２…注湯ステーション １４…固定金型
１６…可動金型 １８…金型成形装置
２０…矯正・切断装置 ２４…取り鍋
３２…溶解炉 ３４…加圧注湯炉
４６…搬送取り鍋 ５２…内室
５４…ガス供給管 ６０…ロードセル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cast iron member, and more particularly, to a method for producing a cast iron member capable of easily and simply producing a cast iron member having portions having different characteristics.
[0002]
[Prior art]
FIG. 3 shows a balancer shaft 1 made of FCD450 (JIS standard for spheroidal graphite cast iron, the same applies hereinafter) constituting an internal combustion engine for vehicles such as automobiles. The balancer shaft 1 is manufactured as follows, for example. That is, first, a raw material having a composition corresponding to FCD450 is melted to obtain a molten metal. As raw materials, steel scraps, return materials (design parts such as gates or scraps of hot water, cast iron members produced as defective products, etc.), pig iron and the like are used.
[0003]
Next, the molten metal is poured into a mold such as a sand mold or a mold and then cooled and solidified. By this cooling and solidification, a molded product having a shape having a journal portion 2 and a long shaft portion 3 substantially corresponding to the balancer shaft 1 is obtained. The cooling rate at this time is generally about 240 ° C./min for the sand mold and about 1000 ° C./min for the mold, although it depends on the type of mold.
[0004]
As can be understood from this, the cooling rate of the molten metal can be remarkably increased by using the mold. In other words, the use of the mold has an advantage that the balancer shaft 1 which is a molded product, and thus a finished product, can be efficiently manufactured.
[0005]
However, when the molten metal is cooled and solidified in such a high cooling rate, a chill structure made of cementite (Fe ₃ C) is formed in the surface layer portion of the molded product. The chill structure has a high hardness, and therefore the wear resistance of the surface layer portion of the molded product is excessively improved. In order to use the molded product as the balancer shaft 1, it is necessary to perform machining processing such as turning on the surface layer portion such as the shaft portion 3 in the molded body to finish the surface layer portion. As a result of improving the wear resistance, it is difficult to perform this turning process.
[0006]
Therefore, next, heat treatment for eliminating the chill structure is performed on the molded product 5 in the heat treatment furnace 4 shown in FIG.
[0007]
In this heat treatment furnace, heat treatment for eliminating the chill structure is performed in the first and second heating zones 6a and 6b. Specifically, each temperature of the first and second heating zones 6a and 6b is set to about 980 ° C. As the molded product 5 passes through the first and second heating zones 6a and 6b, the chill The structure is decomposed into austenite (γ-Fe) and graphite and disappears. The speed of the conveyor 7 is set so that one molded product 5 passes through the first and second heating zones 6a and 6b in about 30 minutes.
[0008]
Next, with respect to the molded product 5 that has passed through the first and second heating zones 6a and 6b, the third to fifth heating zones 6c to 6e whose temperatures are respectively set to about 920 ° C., about 850 ° C., and about 820 ° C. Ferritic treatment is applied at. That is, the molded article 5 is gradually cooled in the third to fifth heating zone 6C～6e, it passes through the A ₁ transformation point finally the fifth heating zone 6e. As a result, a ferrite structure is generated in the molded product 5.
[0009]
Here, the A ₁ transformation point is defined as the starting temperature of the eutectoid reaction represented by the following reaction formula (1), and the value is 723 ° C. according to Hansen's Fe—C equilibrium diagram. .
[0010]
[Expression 1]

[0011]
In the reaction formula (1), γ and α represent γ-Fe (austenite) and α-Fe (ferrite), respectively.
[0012]
The molded product 5 that has passed through the A ₁ transformation point and has formed a ferrite structure is forcibly cooled by air blown from the blower 8.
[0013]
Next, a machining process such as a turning process is performed on the shaft portion 3 and the like of the molded product 5 subjected to such heat treatment. As a result, the balancer shaft 1 (see FIG. 3) having dimensional accuracy is manufactured.
[0014]
Finally, in order to ensure the hardness of the balancer shaft 1, the balancer shaft 1 is subjected to a nitriding treatment such as soft nitriding (LCN) treatment or gas nitriding (GCN) treatment to obtain a finished product having sufficient strength and hardness. To do.
[0015]
[Problems to be solved by the invention]
By the way, from the viewpoint of environmental protection in recent years, automobiles and the like are required to have good fuel efficiency. And in order to achieve this, weight reduction of each member is achieved.
[0016]
In the case of reducing the weight of the balancer shaft 1, it is conceived that the balancer shaft 1 is made of a material having higher wear resistance and higher strength, for example, FCD700. In this case, the cross-sectional area can be reduced as compared with the balancer shaft 1 made of FCD450 as long as it has substantially the same strength and wear resistance.
[0017]
In order to manufacture the balancer shaft 1 made of the FCD 700, a casting operation is performed after a raw material having a composition equivalent to the FCD 700 is melted to form a molten metal. However, the molded product 5 of the balancer shaft 1 made of the FCD 700 manufactured in this way has a problem that it is difficult to turn the shaft portion 3 and the like because the wear resistance is remarkably high.
[0018]
In addition, the FCD450 raw material and the FCD700 raw material have different compositions. Specifically, in FCD450, Si is added to generate a ferrite structure. On the other hand, in FCD700, Cu or Sn is added to generate a pearlite structure. Therefore, if the balancer shaft 1 made of the FCD 700 is manufactured using the same casting apparatus after the balancer shaft 1 made of the FCD 450 is manufactured, there is a concern that a ferrite structure is generated by Si remaining in the mold cavity. . When such a situation occurs, it becomes difficult to improve the strength and wear resistance of the balancer shaft 1.
[0019]
In order to avoid such a situation, another casting apparatus may be used. However, in this case, there is an inconvenience that a large capital investment is required for the casting apparatus.
[0020]
The present invention has been made in order to solve the above-mentioned problems. A cast iron member having a portion having good wear resistance and a portion capable of performing various machining operations relatively easily is manufactured from the same molten metal. It aims at providing the manufacturing method of the member made from cast iron which can do.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a method for producing a cast iron member comprising a first part having a pearlite structure as a main phase and a second part having a ferrite structure as a main phase ,
A first step of cooling and solidifying a cast iron melt in a mold to form a molded product;
By performing heat treatment on the molded article before the temperature of the molded product passes through the A ₁ transformation point, and a second step of decomposing the chilled structure generated in the molded article in the first step,
At least a part of the molded product in which the chill structure is decomposed is cooled under the condition that the pearlite structure is generated to provide the first part, while the remaining part is cooled under the condition that the ferrite structure is generated. A third step of providing two sites;
A fourth step of forming a cast iron member, which is a finished product, by machining the second part;
It is characterized by having.
[0022]
According to the present invention, the cooling rate after the disappearance of the chill structure is individually set, thereby comparing the first part having high hardness and good wear resistance with machining such as turning. A second portion that is easy to handle is provided. For this reason, the cast iron member which has a site | part from which a characteristic mutually differs can be manufactured easily and simply from the same molten metal, without adjusting a composition in particular.
[0023]
In addition, the first part mainly including the pearlite structure has sufficient strength and wear resistance in practical use. For this reason, it is not particularly necessary to perform various nitriding treatments on the first part or the like. Therefore, the cast iron member can be efficiently manufactured and the cost for performing the nitriding treatment can be reduced.
[0024]
In addition, as a suitable example of the cast iron member having the ferrite structure and the pearlite structure manufactured as described above, one made of spheroidal graphite cast iron can be cited.
[0025]
A preferable example of the cast iron member is a balancer shaft for an internal combustion engine mounted on a vehicle such as an automobile. In this case, the journal portion may be provided as the first portion having good strength and wear resistance, and the shaft portion may be provided as the second portion that is relatively easy to perform grinding or the like.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the method for producing a cast iron member according to the present invention will be described and described in detail with reference to the accompanying drawings.
[0027]
FIG. 1 shows a flowchart of a method for manufacturing a cast iron member according to the present embodiment. In this manufacturing method, the cast iron melt is cooled and solidified in a mold (cavity) to form a molded product, and the molded product is subjected to heat treatment to decompose the chill structure generated in the molded product. A second step S2, a third step S3 in which a first part including a pearlite structure and a second part including a ferrite structure are provided in the molded product, and a finished product by machining the second part. And a fourth step S4 for making a cast iron member.
[0028]
This manufacturing method will be specifically described by exemplifying a case where the balancer shaft 1 shown in FIG. 3 is manufactured as a cast iron member in relation to a casting apparatus that performs the manufacturing method.
[0029]
As shown in FIG. 2, the casting apparatus 10 includes a pouring station 12, a mold forming apparatus 18 having a fixed mold 14 and a movable mold 16, a correction / cutting apparatus 20, and a heat treatment furnace 22. The movable mold 16 can be moved toward or away from the fixed mold 14 under the action of the cylinder 23 constituting the mold forming apparatus 18.
[0030]
A blow smoke device 28 is provided above the mold forming device 18 so as to be freely displaceable in the vertical direction. In addition, a workpiece picking robot 30 is provided in the upper part on the downstream side of the mold forming apparatus 18 so as to be movable in the horizontal direction. The blow smoke device 28 and the workpiece picking robot 30 are supported by a support base 31.
[0031]
The pouring station 12 includes a melting furnace 32, a pressurized pouring furnace 34, and a ladle 24 that receives the molten metal derived from the pressurized pouring furnace 34 and introduces the molten metal into the cavity of the mold molding apparatus 18. Among these, the melting furnace 32 is installed on the mount 36.
[0032]
In performing the manufacturing method according to the present embodiment, first, the raw materials are melted to form a molten metal. That is, after steel scraps, return materials, pig iron and the like are stored in the melting furnace 32 as raw materials, the melting furnace 32 is heated from the surroundings to melt them.
[0033]
Here, the composition of the raw material is preferably an intermediate between the composition corresponding to FCD450 and the composition corresponding to FCD700, that is, a composition corresponding to FCD500 or FCD600. In this case, when the molded product 5 is cooled, a pearlite structure and a ferrite structure can be easily generated. However, the composition is not particularly limited to this, and may be a composition corresponding to FCD700 or a composition corresponding to FCD450. In this case, in order to generate a ferrite structure and a pearlite structure in the molded article 5, the cooling rate may be controlled more strictly.
[0034]
The melting furnace 32 can be tilted. That is, the rod 42 of the cylinder 40 is connected to the lower end portion of the gate 38 that is formed to protrude above the melting furnace 32. A support shaft 44 is connected to the bottom of the melting furnace 32 so as to be unevenly distributed from the center of the bottom toward the gate portion 38. For this reason, the melting furnace 32 tilts with the connecting portion with the support shaft 44 as a fulcrum, following the vertical movement of the rod 42. When pouring the molten metal into the transport ladle 46, the pouring gate 38 may be tilted toward the transport ladle 46 by moving the rod 42 downward.
[0035]
A transport ladle 46 supported by a hook 48 of a crane (not shown) is transported toward the pressurized pouring furnace 34 under the action of the crane. The transport ladle 46 is tilted by a first tilting mechanism (not shown), so that the molten metal in the transport ladle 46 is poured and stored in the inner chamber 52 of the pressurized pouring furnace 34 through the funnel 50. .
[0036]
A gas supply pipe 54 for introducing a gas for increasing the pressure of the inner chamber 52 is connected to the pressurized pouring furnace 34. That is, as the inert gas such as Ar is supplied from the gas supply pipe 54, the pressure in the inner chamber 52 increases, and as a result, the molten metal stored in the inner chamber 52 becomes pressurized molten metal. It is introduced into a hot water passage 58 provided in a hot water discharge section 56 of the furnace 34 and finally led out from a hot water outlet 59 of the hot water discharge section 56. As described above, the derived molten metal is poured into the ladle 24.
[0037]
The ladle 24 is placed on the load cell 60, and the amount of molten metal in the ladle 24 is controlled to a predetermined amount under the action of the load cell 60. That is, when the measured value of the weight of the molten metal poured into the ladle 24 matches a preset value set in the load cell 60, a control signal from a control unit (not shown) electrically connected to the load cell 60 is obtained. As a result, a valve (not shown) interposed in the gas supply pipe 54 is closed. Accordingly, the supply of gas to the inner chamber 52 of the pressurized pouring furnace 34 is stopped, and as a result, the derivation of the molten metal from the hot water outlet 59 of the pressurized pouring furnace 34 is stopped.
[0038]
The ladle 24 can be tilted by a second tilting mechanism (not shown). Along with this tilting operation, a predetermined amount of molten metal introduced into the ladle 24 is poured into the cavity of the mold molding device 18 through the gate 64 constituting the mold molding device 18, and the first step S1 is performed. Be started. In addition, before the fixed mold 14 and the movable mold 16 of the mold forming apparatus 18 are clamped, a release agent is applied in advance to the cavity surface by the blow smoke apparatus 28.
[0039]
The molten metal introduced into the cavity of the mold forming apparatus 18 is cooled at a cooling rate of about 1000 ° C./minute, and finally only the surface layer portion is solidified to become the molded product 5. A chill structure made of cementite (Fe ₃ C) is formed on the solidified surface layer portion of the molded product 5.
[0040]
The obtained molded product 5 is gripped by the workpiece picking robot 30 after the movable mold 16 is separated from the fixed mold 14 and the mold is opened. As the workpiece picking robot 30 moves in the horizontal direction, the molded product 5 is conveyed to the correction / cutting device 20. In the correction / cutting device 20, trimming or the like is performed on the molded product 5.
[0041]
Thereafter, the molded product 5 is conveyed under the action of the transfer robot 66 and introduced into the heat treatment furnace 22. In the heat treatment furnace 22, the second step S <b> 2, that is, the heat treatment for the molded product 5 is performed.
[0042]
In the above process, since the inside of the molded product 5 is an unsolidified and high-temperature molten metal, the temperature of the molded product 5 does not fall below the A ₁ transformation point. In other words, the molded product 5 is taken out of the cavity of the mold molding apparatus 18 and introduced into the heat treatment furnace 22 before the temperature of the molded product 5 passes through the A ₁ transformation point.
[0043]
This heat treatment is for transforming the chill structure (Fe ₃ C) generated in the surface layer portion of the molded product 5 into a pearlite structure. That is, when heat is applied to the chill structure existing in the surface layer portion of the molded product 5, the chill structure is decomposed into austenite (γ-Fe) and graphite. Note that the temperature and time of the heat treatment may be set to conditions such that the chill structure is decomposed, and for example, can be set to a condition of holding at 930 ° C for 30 minutes.
[0044]
After the molded product 5 having the chilled structure thus decomposed is taken out from the heat treatment furnace 22, in a third step S3, the journal part 2 (first first, which mainly contains a pearlite structure and has high hardness and good wear resistance. And a shaft portion 3 (second portion) that mainly includes a ferrite structure and is relatively easy to perform a turning process. That is, for example, compressed air is sprayed only on the journal part 2 of the molded product 5 at a flow rate such that the cooling rate is 200 ° C./min or more, thereby forcibly cooling the journal part 2. On the other hand, compressed air is not blown to the places other than the journal part 2 and air cooling is performed in the atmosphere. In addition, the molten metal inside the molded product 5 which has been in an unsolidified state is completely cooled and solidified during the cooling process.
[0045]
As understood from the above, in the present embodiment, by individually setting the cooling rate after the disappearance of the chill structure according to the site, without particularly adjusting the composition of the raw material (molten metal), A journal portion 2 having high hardness and excellent wear resistance and a shaft portion 3 that is relatively easy to perform turning are provided. For this reason, it is not necessary to prepare the mold forming apparatus 18 individually according to the composition of the molten metal. Therefore, expensive capital investment is not required.
[0046]
Finally, in the fourth step S4, the balancer shaft 1 as a finished product having dimensional accuracy is obtained by performing machining such as turning on the shaft portion and the like.
[0047]
The balancer shaft 1 has sufficient strength and wear resistance because the journal portion 2 includes a pearlite structure. For this reason, it is not particularly necessary to perform LCN processing or GCN processing on the journal unit 2. Therefore, there is an advantage that the balancer shaft 1 can be efficiently manufactured and the cost for performing the LCN process and the GCN process can be reduced.
[0048]
In the above-described embodiment, the case where the balancer shaft 1 is manufactured as a cast iron member has been described as an example, but it goes without saying that it may be other than that.
[0049]
Further, in the manufacturing method according to the present embodiment, a mold is used at the time of casting. However, the casting is particularly limited as long as casting is performed under a condition that a chill structure is generated in the molded product. is not.
[0050]
【The invention's effect】
As described above, according to the method for manufacturing a cast iron member according to the present invention, by setting different cooling rates depending on the part, the cast iron in which the part including the pearlite structure and the part including the ferrite structure are mixed. It is made to obtain the member made. For this reason, it is possible to obtain a cast iron member having a portion having good wear resistance without particularly adjusting the composition, while having a portion capable of relatively easily performing machining such as turning. Is achieved. Therefore, it is not necessary to prepare casting apparatuses individually according to the composition, so that no expensive capital investment is required.
[0051]
Further, since the site containing the pearlite structure has high hardness and good wear resistance, it is not particularly necessary to perform nitriding treatment. For this reason, the cost for performing a nitriding process can also be reduced.
[Brief description of the drawings]
FIG. 1 is a flowchart of a method for manufacturing a cast iron member according to the present embodiment.
FIG. 2 is a schematic overall configuration diagram of a casting apparatus that performs a cast iron member according to the present embodiment.
FIG. 3 is a schematic overall perspective view of a balancer shaft.
FIG. 4 is a schematic longitudinal sectional view showing a state in which a molded product is subjected to heat treatment in a heat treatment furnace.
[Explanation of symbols]
1 ... Balancer shaft 2 ... Journal part (first part)
DESCRIPTION OF SYMBOLS 3 ... Shaft part (2nd part) 4, 22 ... Heat processing furnace 5 ... Molded product 6a-6e ... Heating area 8 ... Blower 10 ... Casting apparatus 12 ... Pouring station 14 ... Fixed mold 16 ... Movable mold 18 ... Mold forming device 20 ... Correction / cutting device 24 ... Ladle 32 ... Melting furnace 34 ... Pressurizing pouring furnace 46 ... Conveying ladle 52 ... Inner chamber 54 ... Gas supply pipe 60 ... Load cell

Claims (3)

A method for producing a cast iron member comprising a first part having a pearlite structure as a main phase and a second part having a ferrite structure as a main phase ,
A first step of cooling and solidifying a cast iron melt in a mold to form a molded product;
By performing heat treatment on the molded article before the temperature of the molded product passes through the A ₁ transformation point, and a second step of decomposing the chilled structure generated in the molded article in the first step,
At least a part of the molded product in which the chill structure is decomposed is cooled under the condition that the pearlite structure is generated to provide the first part, while the remaining part is cooled under the condition that the ferrite structure is generated. A third step of providing two sites;
A fourth step of forming a cast iron member, which is a finished product, by machining the second part;
A method for producing a cast iron member, comprising:   2. The method for manufacturing a cast iron member according to claim 1, wherein the cast iron member is made of spheroidal graphite cast iron.   3. The manufacturing method according to claim 2, wherein a balancer shaft for an internal combustion engine mounted on a vehicle is manufactured as the cast iron member, a journal portion of the balancer shaft is formed as the first portion, and the shaft portion is formed. It forms as said 2nd site | part, The manufacturing method of the member made from cast iron characterized by the above-mentioned.

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