JP4219720B2 - Manufacturing method of casting mold - Google Patents

Description

【００１６】
ところで、これら無機硫酸化合物は、含有する結晶水の量により発現する強度にかなり差が出る。例えば、図２は、硫酸マグネシウムの水和量と鋳型強度の関係を示し、以下のような実験により得られたものである。即ち、耐火性粒状物としてフラタリー珪砂１００重量部を用い、これに硫酸マグネシウム・７水和物３重量部と水とを添加して鋳物砂とした。造型は直径30mm、高さ50mmの試験片をJIS Z 2601に定められる試験片搗き固め機を用いて3回搗き固めて成型し試験片とした。そして、出力700Wのマイクロ波を照射して試験片を乾燥させた。
【００１７】
この際、乾燥時間（マイクロ波の照射時間）を調整することにより試験片中の硫酸マグネシウムが含有する結晶水量を変化させて、夫々の試験片の圧縮強度を測定した。試験片中の硫酸マグネシウムの結晶水量の算出は、マイクロ波乾燥後の試験片をさらに300℃で硫酸マグネシウムが完全に無水和物となるまで乾燥させ、この乾燥前後で減った試験片の重量を、試験片内の硫酸マグネシウムが含有する結晶水の量とみなし、添加した硫酸マグネシウムの量からモル比により算出した。
【００１８】
硫酸マグネシウムの水和物は１，４，７及び１２水和物であるが、図２で示すように、約１〜６水和物のものが鋳型用として利用可能であり、さらに、強度が発現する好ましい範囲は１〜５水和物である。従って、乾燥状態で鋳型内の硫酸マグネシウムが１〜５水和物相当の結晶水を含有することが望ましい。さらに望ましくは、硫酸マグネシウムが２〜４水和物相当の結晶水を含有することが望ましい。
【００１９】
ところで、この水溶性の粘結剤を完全に溶解させるために、耐火性粒状物に相当量の水を添加する必要があるが、鋳物砂内部に含まれる水分により鋳物砂の流動性が悪くなり、次の充填工程において成形型に鋳物砂を充填するのが困難になる。そこで、この粘結剤被覆工程において、耐火性粒状物に対して水に加えてアルコールを添加することで、耐火性粒状物の表面張力を低下させて、成型型への鋳物砂の充填性を向上させる。
【００２０】
また、耐火性粒状物としては、図５のような珪砂の他、各粒子の表面に多数の気孔が形成されているために、これら気孔に水分を吸着させることが可能な、セラビーズ（図６（ａ），（ｂ）参照）等の吸水性を有する種々の耐火性粒状物を用いることもできる。このような吸水性の耐火性粒状物を用いて鋳物砂を作製した場合には、粘結剤を溶解させるために耐火性粒状物に加えられた水分の一部が、各粒子の気孔内に吸着されて粒子の表面に付着する水分が減少することになり、鋳物砂の流動性が改善され、次の充填工程における成形型への充填性が向上する。
【００２１】
次に、充填工程において、ブローイング造型により成形型内に鋳物砂を充填する。図３に示すように、水分除去工程で水分の少なくとも一部を除去された鋳物砂Ｓを成形型１の中子成形キャビティ２内に吹き込む。ここで、成形型１は、通気性を有するセラミック型であり、上下に２分割された型分割体１ａ，１ｂで構成され、成形型１は、マイクロ波を透過する合成樹脂製のケース部材３で覆われている。鋳物砂Ｓをキャビティ２内に充填する際には、成形型１の上側に設置したブローヘッド４内に加圧エアを作用させ、ブローノズル５を介して成形型１の内部に形成された中子成形キャビティ２内に鋳物砂Ｓを吹き込み、このキャビティ２内に鋳物砂Ｓを加圧充填して鋳物砂Ｓで所定の形状に造型する。
【００２２】
そして、乾燥工程において、鋳物砂にマイクロ波を照射して鋳物砂を乾燥させて鋳型を作る。図４に示すように、この乾燥工程においては、鋳物砂Ｓを充填した成形型１に対して均等にマイクロ波が照射されるようにスターラー６を回転させつつ、マグネトロン７からマイクロ波を所定時間照射する。このマイクロ波は成形型１を透過してキャビティ２内の鋳物砂Ｓに作用する。ここで、前記水分補給工程において水分を補給された鋳物砂Ｓ内には、自由水と無機硫酸化合物の結晶水という２つの状態で水分が存在するが、自由水の方が結晶水よりも誘電率が高いため、自由水が結晶水よりも先に蒸発しやすくなり、鋳物砂Ｓ内の無機硫酸化合物が少なくとも一部の結晶水を含有する状態を維持しつつ鋳物砂Ｓ内の自由水を蒸発させる。
【００２３】
鋳物砂内の水分が蒸発して発生した水蒸気は、吸引ポンプ８により吸引フード９、吸引ホース１０を介して成形型１の外部へ排出される。このようにして鋳物砂を乾燥させることで、乾燥状態において粘結剤の無機硫酸化合物が結晶水を含有することになって強度が発現するため、乾燥により得られる鋳型の強度を十分に確保することができる。
【００２４】
ここで、成形型１は通気性を有するセラミック型であり、蒸発した水分が成形型１から均等に外部へ放出されるため、無機硫酸化合物が含有する結晶水の量のばらつきを極力抑えて、得られた鋳型の強度を均一化することができる。
尚、キャビティ２を形成する成形型１は、セラミック型に限らず、合成樹脂製の型など、マイクロ波を透過するものであれば、他の材質のものでも使用できる。
【００２５】
次に、前述したように、粘結剤被覆工程において耐火性粒状物として吸水性の耐火性粒状物を使用した場合、あるいは、耐火性粒状物に水に加えてアルコールを添加して鋳物砂を作製した場合に、鋳物砂の充填性がどのように改善されるかを実験により検証した。
【００２６】
まず、耐火性粒状物として、図５に示すような表面に気孔のない珪砂（ウェドロン珪砂）と、図６〜図９に示すような、各粒子の表面が凸凹状に形成されており多数の気孔を有する吸水性の耐火性粒状物とを夫々使用し、これら耐火性粒状物に水だけを添加した場合について説明する。吸水性の耐火性粒状物としては、セラビーズ（図６）、セラミックビーズ（図７）、２種類のオーリチック砂１，２（図８、図９）を使用した。ここで、セラビーズやセラミックビーズは、カオリン、アルミナ等の微粒子を焼結して粒状としたものである。また、オーリチック砂は、生型で使用される生型砂より全粘土粉を除去したものであり、珪砂の回りに粘土が焼結してガラス状になったものが付着している。
【００２７】
そして、まず、これら耐火性粒状物の吸水性について実験した。図５の珪砂及び図６〜図９の吸水性の耐火性粒状物を夫々水中に１時間浸してから、ろ紙により表面の付着水を取り除き、その後、110℃で２時間乾燥させて、乾燥前後の重量の変化量から吸着水分量を求めた。その結果を表２に示す。
【００２８】
【表２】

【００２９】
表２において、珪砂中の水分は、珪砂の表面に付着している水分量であると考えられるが、その珪砂の水分量に対して、気孔を有する吸水性の耐火性粒状物の水分量は２倍以上であり、気孔を有する耐火性粒状物に水分が吸着されていることがわかる。
【００３０】
次に、吸水性の耐火性粒状物を用いた鋳物砂の圧縮強度と充填性について実験した。ここで、前述の吸水性実験で１時間水中に浸した後の珪砂及び吸水性の耐火性粒状物に、粘結剤としての硫酸マグネシウム・７水和物を1.425重量％及びリン酸二水素ナトリウムを0.075重量％と、所定量の水を加えて粘結剤を溶解させ、これらを混練して全体の水分量が0.5〜2.0重量％となるような鋳物砂を作製した。そして、この混練砂を３回ラミングしてφ３０ｍｍ×５０ｍｍの圧縮試験片を形成し、出力７００Ｗのマイクロ波により１分加熱して硬化させ、冷却後に強度測定を行った。
【００３１】
また、充填性の確認については、前記の鋳物砂を、ブロー成形機を用いてブロー圧20psi（約0.14Mpa）、ブロータイム0.5秒でブローイングして鋳型密度を求め、この値と、JISZ2601の試験片搗き固め器を用いて３回ラミングして成型した圧縮試験片の密度の比率から、以下のようにして充填率を算出した。
充填率（％）＝（JISZ2601によるラミング後の密度／ブロー成型後の密度）×100
これら圧縮強度及び充填性に関する実験の結果を表３に示す。
【００３２】
【表３】

【００３３】
表３より、予め吸水させた吸水性を有する耐火性粒状物を用いた場合には、気孔を有さない珪砂を用いた場合に比べて鋳物砂の充填性が向上していることがわかる。しかし、セラミックビーズやオーリチック砂を用いた鋳物砂では、水分量が多く粘結剤が十分に溶解して各粒子に被覆されていると考えられる状態でも強度が不足しており、吸水性の耐火性粒状物の中では、セラビーズが最も実用に適していると思われる。従って、以下の実験では、吸水性を有する耐火性粒状物としてセラビーズを使用する。
【００３４】
以上の実験では、予め吸水させた耐火性粒状物に粘結剤と水とを加えて鋳物砂を作製したが、乾燥した珪砂及びセラビーズを、粘結剤（硫酸マグネシウム・７水和物1.425重量％、リン酸二水素ナトリウム0.075重量％）を溶解させた水溶液中に１時間浸してからろ紙により表面の付着水を取り除き、その後、110℃で２時間乾燥させて吸着水溶液量を測定し、さらに、その吸着水溶液中の吸着水分量を求めた。その結果を表４に示す。この場合でも、珪砂に対してセラビーズの吸着水分量は２倍以上であり、気孔を有するセラビーズに粘結剤の水溶液及び水分が吸着されていることがわかる。
【００３５】
【表４】

【００３６】
さらに、表４の吸水性実験と同様にして１時間水溶液中に浸した後の珪砂及びセラビーズを用いて、全体の水分量が0.5〜2.0重量％となるように鋳物砂を作製して、圧縮強度を測定するとともに充填率を算出すると、表５のようになる。
【００３７】
【表５】

【００３８】
表５より、気孔を有するセラビーズでは珪砂に比べて充填性が向上していることがわかる。また、粘結剤が十分に溶解するだけの水分量を与えると、圧縮強度はやや低めではあるが実用には耐えうる。
【００３９】
以上の実験により、耐火性粒状物にセラビーズを用いることにより、鋳物砂の充填性がある程度改善されることがわかる。しかし、気孔内の空隙が全体の体積の１０％弱もあるとされているセラビーズに対して、実際に吸着された水分量はかなり少ない（0.38重量％）。これは、水の表面張力が高いために、気孔内に十分に水が浸透しないことが原因と考えられる。そこで、表面張力の低いアルコールを水と混ぜて混合溶液（水とアルコールの混合比率：７５対２５、または、５０対５０）を作り、この混合溶液中にセラビーズを浸して前述の実験と同様にして混合溶液の吸着量を測定し、測定された吸着量と混合溶液の混合比率とにより吸着水分量を求めた。その結果を表６に示す。
【００４０】
【表６】

【００４１】
表６より、水にセラビーズを浸透させた場合に比べて、水とエタノールの混合溶液、あるいは水とメタノールの混合溶液にセラビーズを浸透させた場合には、セラビーズへの吸着水分量が１．５倍程度増加しており、アルコールを添加することによりセラビーズに水分が吸着しやすくなることがわかる。
【００４２】
さらに、水とアルコールの混合溶液を吸着させたセラビーズを用いた鋳物砂の、圧縮強度及び充填性について実験を行った。ここで、圧縮強度の測定に関しては、水とアルコールの混合溶液を吸着させたセラビーズに、粘結剤（硫酸マグネシウム・７水和物1.425重量％、リン酸二水素ナトリウム0.075重量％）と所定量の水を加えて粘結剤を溶解させ、これらを混練して全体の水分量が0.5〜2.0重量％となるような鋳物砂を作製した。そして、この鋳物砂を密閉容器中で60℃に昇温し、80℃の金型中で３回ラミングして、φ２８ｍｍ×５０ｍｍの試験片を作製した。また、充填性に関しては、前述の水のみを吸着させた実験（表３）と同様にして鋳物砂の充填率を求めた。その結果を表７に示す。
【００４３】
【表７】

【００４４】
表７からわかるように、水とアルコールの混合溶液を吸着させたセラビーズを用いた場合には、水だけを吸着させた場合に比べて明らかに充填性が向上している。これは、水に比べて混合溶液の表面張力が低く、気孔内に水分が浸透しやすくなってセラビーズの各粒子の表面に付着する水分が減少することに加え、各粒子の表面においても表面張力が低下して各粒子の流動性が増すことに起因していると考えられる。
【００４５】
さて、以上の実験においては、耐火性粒状物として、セラビーズ等、各粒子が吸水性を有する耐火性粒状物を用いていたが、珪砂に粘結剤と水とアルコールとを加えて鋳物砂とした場合においても、強度及び充填性が改善されるかどうかを検証した。
【００４６】
まず、珪砂またはセラビーズに、硫酸マグネシウムとリン酸二水素ナトリウムからなる粘結剤と、水または水とエタノールの混合溶液を加えて鋳物砂とし、この鋳物砂を密閉容器中で60℃に昇温し、80℃の金型中で３回ラミングし、３０秒硬化させて、φ２８ｍｍ×５０ｍｍの試験片を作製した。尚、水だけを添加した場合には、ラミング後にエアパージを１５秒行って表面の水分を除去した。エタノールを添加した場合にはエアパージは行わなかった。これは、エタノールを添加した場合には水だけを添加した場合に比べて試験片の硬化が速かったためであるが、エタノールの比熱が水の比熱に比べて小さいことも影響していると思われる。その結果を表８に示す。
【００４７】
【表８】

【００４８】
珪砂に水とエタノールの混合溶液を加えて鋳物砂を作製した場合には、水のみを加えて鋳物砂を作製した場合に比べて充填性が向上している。さらに、エタノールの添加量が0.1重量％の場合では、添加した粘結剤の量にかかわらず鋳物砂の圧縮強度も向上している。
さらに、他の種類のアルコールとして、メタノール、イソプロピルアルコール（ＩＰＡ）を添加した場合、さらに、参考としてトルエンを添加した場合の、鋳物砂の圧縮強度と充填率を表９に示す。
【００４９】
【表９】

【００５０】
メタノール、ＩＰＡを添加した場合においても、水のみを加えた場合に比べて充填性が向上し、アルコールの添加量が0.1重量％の場合においては圧縮強度も１割以上上昇している。但し、トルエンを添加した場合には充填性についての効果は認められない。
尚、エタノールやメタノール、ＩＰＡ等のアルコールの添加量が多い場合には、鋳物砂を乾燥して鋳型を硬化させる際に、アルコールが急激に気化して鋳型が崩れやすくなる虞があるため、乾燥工程においては、鋳物砂の加熱を緩やかに行って鋳物砂の温度を急激に上げないようにすることが望ましい。
【００５１】
ところで、表８、表９において、耐火性粒状物に、0.1重量％程度のアルコールを水とともに加えると、水のみを加えた場合に比べて圧縮強度が大きくなっている。これは、次のような要因によるものと考えられる。
【００５２】
前述したように、硫酸マグネシウム等の無機硫酸化合物を主体とする粘結剤を用いた鋳物砂は、無機硫酸化合物が結晶水を有する水和物の状態で強度が発現する。ところで、例えば、硫酸マグネシウムは、温度により、無水和物から１２水和物までの種々の状態で存在し、-3.8〜1.8℃では１２水和物、1.8〜48.3℃では７水和物、48.3〜68℃では６水和物、200℃以上で無水和物となる。そして、最も強度が発現する２〜４水和物となるのは、80℃前後の温度にある場合と考えられる。
【００５３】
ところで、メタノール、エタノール、ＩＰＡの沸点は、夫々65.6℃、78.3℃、82.7℃であるため、図１０に示すように、水とアルコールを混合させた混合溶液を加熱していくと、80℃前後の温度で気液平衡の状態となり、この80℃前後の温度状態がしばらく続くことになる。従って、乾燥工程において、耐火性粒状物に粘結剤と水とアルコールを加えて作製した鋳物砂を乾燥する際に、鋳物砂の温度が80℃前後となる可能性が高くなり、乾燥後の鋳型内の硫酸マグネシウムが２〜４水和物の状態で存在しやすくなる。
【００５４】
以上説明した鋳造用鋳型の製造方法によれば、次のような効果が得られる。
１）粘結剤被覆工程において、水に加えてアルコールを耐火性粒状物に加えることで、耐火性粒状物の各粒子の表面の表面張力が低下するため、成形型への鋳物砂の充填性を向上させることができる。また、アルコールを適量加えることにより鋳型の強度を向上させることも可能になる。
【００５５】
２）粘結剤被覆工程において、耐火性粒状物として各粒子が吸水性を有する耐火性粒状物を用いることで、粘結剤を溶解させるために加えられた水分の一部が、耐火性粒状物の各粒子に吸収され、各粒子の表面に存在する水分の量が減少するため、各粒子の表面張力が低下して鋳物砂の充填性が向上する。
【００５６】
次に、前記実施形態に種々の変更を加えた変更形態について説明する。
１］粘結剤被覆工程において耐火性粒状物に加えるアルコールとしては、前述のメタノール、エタノール、ＩＰＡの他、プロピルアルコール、ブチルアルコール、アミルアルコール、アリルアルコール等、他の低級アルコールを用いてもよい。さらに、高級アルコールを用いても同様の効果が得られる可能性がある。
【００５７】
２］前記実施形態では、耐火性粒状物として珪砂単独、あるいは、吸水性を有するセラビーズを単独で使用しているが、複数種類の耐火性粒状物を混合して使用してもよい。
３］乾燥工程における、鋳物砂の乾燥方法としては、前述のマイクロ波や過熱蒸気による乾燥の他、鋳型に温風を供給してその熱により水分を蒸発させる方法、金型を加熱してその中に鋳物砂を充填して硬化させる方法、成形型内に鋳物砂を充填させた後に減圧して水分を蒸発させる方法などを適用できる。さらに、これらの方法を組み合わせて適用してもよい。
【００５８】
４］鋳物砂あるいは粘結剤には、鋳造欠陥を防止するために通常鋳物砂に添加されるベンガラ、鉄粉、石炭粉、黒鉛粉、木粉、タルク、澱粉、穀物粉、シリカフラワー、ジルコンフラワー、オリビンフラワーなどを所定量配合できる。
【００５９】
さらに、鋳物砂あるいは粘結剤には、型への充填性を改善するために、無機潤滑剤として二硫化タングステン、二硫化モリブデン、有機潤滑剤として炭化水素系、ポリアルキレングリコール、シリコーン系、フッ素系、フェニルエーテル、リン酸エステル潤滑剤を所定量配合できる。
さらに、鋳型にはアルコール性塗型、水性塗型、粉末塗型、表面安定剤、ひけ防止用テルル粉末などの通常、鋳型表面に塗布する造型材料を用いることができる。
【００６０】
【発明の効果】
請求項１の発明によれば、粘結剤被覆工程において、水に加えてアルコールを鋳物砂用耐火性粒状物に加えるので、鋳物砂用耐火性粒状物の各粒子の表面の表面張力が低下するため、成形型への鋳物砂の充填性を向上させることができる。
【００６１】
請求項２の発明によれば、粘結剤被覆工程において鋳物砂用耐火性粒状物に加えられた水分の一部が、鋳物砂用耐火性粒状物の各粒子に吸収されて、各粒子の表面に存在する水分の量が減少するため、各粒子の表面張力が低下して鋳物砂の充填性が向上する。
【００６２】
請求項３の発明によれば、無機硫酸化合物に硫酸マグネシウムが含まれ、この硫酸マグネシウムは水に対する溶解性が良好であるため、硫酸マグネシウムを含む粘結剤を用いることで水溶性の鋳造用鋳型を製造することができ、注湯後に水を加えるだけで鋳型を崩壊させて粘結剤を回収することも容易になる。
【００６３】
請求項４の発明によれば、乾燥工程において鋳物砂にマイクロ波を照射して鋳物砂を乾燥させるので、鋳物砂内の無機硫酸化合物が少なくとも一部の結晶水を含有する状態を維持しつつ水を除去することが可能になり、鋳型の乾燥状態において無機硫酸化合物を水和物の状態で存在させて、鋳型の強度を発現させることができる。
【００６４】
請求項５の発明によれば、乾燥工程で鋳物砂を乾燥する際に、蒸発した水分を通気性のセラミック型から均等に外部へ放出させることができるため、鋳型の強度を均一化することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る水溶性鋳造用鋳型の製造方法を示す工程図である。
【図２】硫酸マグネシウム水和物と圧縮強度の関係を示す図である。
【図３】充填工程における鋳物砂の型への充填作業を説明する説明図である。
【図４】乾燥工程におけるマイクロ波による乾燥作業を説明する説明図である。
【図５】電子顕微鏡による珪砂の粒子全体の写真である。
【図６】セラビーズの粒子の写真であり、（ａ）は粒子全体の写真、（ｂ）は粒子表面を拡大した写真である。
【図７】セラミックビーズの粒子の写真であり、（ａ）は粒子全体の写真、（ｂ）は粒子表面を拡大した写真である。
【図８】オーリチック砂（オーリチック砂１）の粒子の写真であり、（ａ）は粒子全体の写真、（ｂ）は粒子表面を拡大した写真である。
【図９】別のオーリチック砂（オーリチック砂２）の粒子の写真であり、（ａ）は粒子全体の写真、（ｂ）は粒子表面を拡大した写真である。
【図１０】水とアルコールの混合溶液の温度変化を示す図である。
【符号の説明】
Ｓ 鋳物砂
１ 成形型
２ キャビティ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a casting mold, and particularly relates to a method using a water-soluble binder.
[0002]
[Prior art]
Conventionally, as a casting mold manufacturing method, casting sand is made by adding a water-soluble binder and water to a refractory granule for casting sand, and then molding the mold by filling this molding sand into a mold. There is a method for obtaining a mold. For example, as a water-soluble binder, a method for producing a water-soluble casting mold using a binder mainly composed of an inorganic sulfate compound such as magnesium sulfate which is easily soluble in water has been proposed (for example, , See Patent Document 1).
[0003]
[Patent Document 1]
JP-A-53-119724 (page 1-2)
[0004]
[Problems to be solved by the invention]
In the mold manufacturing method described in Patent Document 1, in order to reliably coat the surface of the refractory granular material for foundry sand with a water-soluble binder, an amount of water capable of dissolving the binder is used. It is necessary to add it together with the binder. In other words, since the foundry sand is in a so-called wet sand state containing moisture, the casting sand has low fluidity. When it is filled, the filling property is deteriorated. And, when filling the casting mold obtained by molding the foundry sand, filling defects are likely to occur, and casting defects such as seizure defects, sand bite defects, cracking defects and deformation may occur during casting. is there.
[0005]
An object of the present invention is to improve the fluidity of the foundry sand and improve the filling property of the foundry sand into the mold.
[0006]
[Means for Solving the Problems]
The method for producing a casting mold according to claim 1 is a casting mold producing method for producing a casting mold by molding casting sand. A binder coating process for forming a molding sand by adding a binder, water and alcohol to the refractory granule for molding sand to coat the molding sand, a filling process for filling the molding sand with a molding mold, and a molding mold And a drying step of drying the foundry sand filled in the container.
[0007]
In this casting mold manufacturing method, in the binder coating step, a refractory granule for foundry sand is added by adding a binder mainly composed of a water-soluble inorganic sulfuric acid compound and water to the refractory granule for foundry sand. Cover the object with a binder dissolved in water to make foundry sand. Here, as the binder, one kind of a combination of various sulfuric acid compounds exhibiting water solubility such as magnesium sulfate, aluminum sulfate, sodium sulfate, potassium sulfate, nickel sulfate, or a combination of a plurality of kinds can be used. Then, after the molding sand is filled into the mold in the filling step, the molding sand filled in the molding die is dried in the drying step, thereby completing the production of the mold.
[0008]
By the way, in the binder coating step, in order to dissolve the binder, water is added to the foundry sand, so that the filling property of the foundry sand is deteriorated. If the amount is reduced, the binder mainly composed of inorganic sulfate compound may not be sufficiently coated on the surface of each particle of the refractory granular material for foundry sand, and sufficient strength may not be developed in the mold. Therefore, in the binder coating step, by adding alcohol to the refractory granule for foundry sand in addition to water, the surface tension of the surface of each particle of the refractory granule for foundry sand is reduced, and the mold is formed. Improves the filling property of the foundry sand.
[0009]
The method for producing a casting mold according to claim 2 is characterized in that, in the invention according to claim 1, each particle of the refractory granule for foundry sand has water absorption. Therefore, a part of the water added to the refractory granule for foundry sand in the binder coating process is absorbed by each particle of the refractory granule for foundry sand, and the amount of moisture present on the surface of each particle. Therefore, the surface tension of each particle is lowered, and the filling property of the foundry sand into the mold is improved.
[0010]
The method for producing a casting mold according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the inorganic sulfate compound contains magnesium sulfate. Magnesium sulfate has a good solubility in water, so a water-soluble casting mold can be produced by using a binder containing magnesium sulfate, and the mold is destroyed by simply adding water after pouring. Thus, it becomes easy to recover the binder and repeatedly use the binder.
[0011]
According to a fourth aspect of the present invention, there is provided a casting mold manufacturing method according to the first to third aspects of the invention, wherein in the drying step, the casting sand is irradiated with microwaves to dry the casting sand. Generally, when the foundry sand is dried in the drying process, the strength of the mold is higher when the inorganic sulfate compound is present in a hydrated state having crystal water than when it is present in the anhydrous form. . Therefore, when the casting sand is irradiated with microwaves in the drying process, the moisture in the casting sand has a higher dielectric constant than the crystallization water of the inorganic sulfate compound, and therefore, it easily evaporates before the crystallization water. Water can be removed while maintaining a state containing at least a part of crystal water, and the inorganic sulfate compound can be present in a hydrated state in the dry state of the template.
[0012]
According to a fifth aspect of the present invention, there is provided a casting mold manufacturing method according to the first to fourth aspects, wherein the mold is a ceramic mold having air permeability. Therefore, when the foundry sand is dried in the drying step, the evaporated water can be evenly discharged from the breathable ceramic mold to the outside, so that the strength of the mold can be made uniform.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. The present invention is an example applied to a method for producing a water-soluble casting mold in which a casting sand is molded to produce an aluminum alloy casting mold.
As shown in FIG. 1, this water-soluble casting mold manufacturing method comprises a binder and water mainly composed of a water-soluble inorganic sulfate compound in a refractory granule for foundry sand (hereinafter referred to as a refractory granule). And alcohol are added to the refractory granular material to form a molding sand by coating the binder, a filling process to fill the molding sand with the molding sand, and the molding sand filled in the molding mold is dried. And a drying process.
[0014]
First, in the binder coating step, a binder mainly composed of a water-soluble inorganic sulfuric acid compound and water in an amount capable of dissolving the binder are added to and mixed with refractory granules such as silica sand. The foundry sand is made by coating the surface of the refractory granular material with a binder dissolved in water. Here, it is desirable that the inorganic sulfuric acid compound contained in the binder has a melting point of 770 ° C. or higher, which is an average pouring temperature of aluminum alloy casting, and is easily soluble in water. Specifically, it is magnesium sulfate, aluminum sulfate, sodium sulfate, nickel sulfate, manganese sulfate, etc. shown in Table 1. By using a binder mainly composed of such easily soluble inorganic sulfate compounds, the mold can be destroyed by simply adding water after pouring to recover the binder, and the binder can be used repeatedly. It becomes easy.
[0015]
[Table 1]

[0016]
By the way, these inorganic sulfuric acid compounds have a considerable difference in strength expressed by the amount of crystal water contained. For example, FIG. 2 shows the relationship between the hydration amount of magnesium sulfate and the template strength, and was obtained by the following experiment. That is, 100 parts by weight of flattery silica sand was used as the refractory granular material, and 3 parts by weight of magnesium sulfate heptahydrate and water were added thereto to form foundry sand. Molding was performed by crushing and molding a test piece having a diameter of 30 mm and a height of 50 mm three times using a test piece crushing machine defined in JIS Z 2601. And the test piece was dried by irradiating the microwave of the output 700W.
[0017]
At this time, the amount of crystal water contained in the magnesium sulfate in the test piece was changed by adjusting the drying time (microwave irradiation time), and the compressive strength of each test piece was measured. Calculation of the amount of crystal water of magnesium sulfate in the test piece is calculated by further drying the test piece after microwave drying at 300 ° C. until the magnesium sulfate is completely anhydrous. The amount of crystallization water contained in the magnesium sulfate in the test piece was regarded as the molar ratio based on the amount of magnesium sulfate added.
[0018]
Magnesium sulfate hydrates are 1, 4, 7 and 12 hydrates, but as shown in FIG. 2, those of about 1 to 6 hydrates can be used for the mold, and the strength is The preferred range of expression is 1 to 5 hydrate. Therefore, it is desirable that the magnesium sulfate in the mold contains crystal water corresponding to 1 to 5 hydrate in a dry state. More desirably, the magnesium sulfate contains water of crystallization corresponding to 2 to 4 hydrate.
[0019]
By the way, in order to completely dissolve the water-soluble binder, it is necessary to add a considerable amount of water to the refractory granular material. However, the fluidity of the foundry sand deteriorates due to moisture contained in the foundry sand. In the next filling step, it becomes difficult to fill the molding die with the foundry sand. Therefore, in this binder coating step, by adding alcohol to the refractory granule in addition to water, the surface tension of the refractory granule is reduced, and the filling property of the foundry sand into the mold is improved. Improve.
[0020]
In addition to silica sand as shown in FIG. 5, as the refractory granular material, since many pores are formed on the surface of each particle, Cera beads (FIG. 6) can adsorb moisture to these pores. (Refer to (a) and (b)) and the like, various refractory granular materials having water absorption can also be used. When casting sand is produced using such a water-absorbing refractory granule, a part of the water added to the refractory granule to dissolve the binder is contained in the pores of each particle. The moisture adsorbed and adhering to the surface of the particles is reduced, the fluidity of the foundry sand is improved, and the filling ability to the mold in the next filling step is improved.
[0021]
Next, in the filling step, the molding sand is filled into the mold by blowing molding. As shown in FIG. 3, the foundry sand S from which at least a part of moisture has been removed in the moisture removing step is blown into the core forming cavity 2 of the mold 1. Here, the mold 1 is a ceramic mold having air permeability, and is composed of mold divisions 1a and 1b that are divided into two vertically, and the mold 1 is a case member 3 made of a synthetic resin that transmits microwaves. Covered with. When the molding sand S is filled into the cavity 2, pressurized air is applied to the blow head 4 installed on the upper side of the mold 1, and the inside of the mold 1 is formed through the blow nozzle 5. The foundry sand S is blown into the child forming cavity 2, and the foundry sand S is pressurized and filled into the cavity 2, and is formed into a predetermined shape with the foundry sand S.
[0022]
In the drying step, the casting sand is irradiated with microwaves to dry the casting sand to make a mold. As shown in FIG. 4, in this drying step, the microwave is applied from the magnetron 7 for a predetermined time while rotating the stirrer 6 so that the mold 1 filled with the foundry sand S is evenly irradiated with the microwave. Irradiate. This microwave passes through the mold 1 and acts on the foundry sand S in the cavity 2. Here, in the foundry sand S replenished with water in the water replenishment step, water is present in two states: free water and crystal water of an inorganic sulfate compound. Free water is more dielectric than crystal water. Since the rate is high, free water tends to evaporate earlier than crystallization water, and the free water in foundry sand S is maintained while the inorganic sulfuric acid compound in foundry sand S contains at least a portion of crystallization water. Evaporate.
[0023]
Water vapor generated by evaporation of water in the foundry sand is discharged to the outside of the mold 1 through the suction hood 9 and the suction hose 10 by the suction pump 8. By drying the foundry sand in this manner, the inorganic sulfuric acid compound of the binder contains crystal water in the dry state, and the strength is manifested. Therefore, the strength of the mold obtained by drying is sufficiently ensured. be able to.
[0024]
Here, the mold 1 is a ceramic mold having air permeability, and the evaporated water is evenly released from the mold 1 to the outside, so that variation in the amount of crystal water contained in the inorganic sulfate compound is suppressed as much as possible. The strength of the obtained mold can be made uniform.
The mold 1 for forming the cavity 2 is not limited to a ceramic mold, and any other material can be used as long as it transmits microwaves, such as a synthetic resin mold.
[0025]
Next, as described above, when a water-absorbing refractory granule is used as the refractory granule in the binder coating step, or, in addition to water, alcohol is added to the refractory granule to form foundry sand. When produced, it was verified by experiment how the filling property of foundry sand was improved.
[0026]
First, as a refractory granular material, silica sand having no pores (wedron silica sand) as shown in FIG. 5 and the surface of each particle as shown in FIGS. The case where water-absorbing refractory granules having pores are used and only water is added to these refractory granules will be described. Cera beads (FIG. 6), ceramic beads (FIG. 7), and two types of auritic sands 1 and 2 (FIGS. 8 and 9) were used as the water-absorbing fire-resistant granular material. Here, the cera beads and ceramic beads are formed by sintering fine particles such as kaolin and alumina. Auristic sand is obtained by removing all clay powder from green sand used in the green mold, and clay-sintered clay becomes glassy around silica sand.
[0027]
And first, it experimented about the water absorption of these refractory granular materials. The silica sand of Fig. 5 and the water-absorbing refractory particles of Fig. 6 to Fig. 9 are immersed in water for 1 hour, respectively, and water adhering to the surface is removed with a filter paper, then dried at 110 ° C for 2 hours, The amount of moisture adsorbed was determined from the amount of change in the weight of. The results are shown in Table 2.
[0028]
[Table 2]

[0029]
In Table 2, the moisture in the quartz sand is considered to be the amount of moisture adhering to the surface of the quartz sand, but the moisture content of the water-absorbing refractory granular material having pores is the moisture content of the quartz sand. It is 2 times or more and it turns out that the water | moisture content is adsorb | sucked to the refractory granular material which has a pore.
[0030]
Next, it experimented about the compressive strength and the filling property of the foundry sand using a water-absorbing fireproof granular material. Here, 1.425% by weight of magnesium sulfate heptahydrate as a binder and sodium dihydrogen phosphate are added to the silica sand and water-absorbing refractory granules after being immersed in water for 1 hour in the water absorption test described above. 0.075% by weight of water and a predetermined amount of water were added to dissolve the binder, and these were kneaded to produce foundry sand having a total water content of 0.5 to 2.0% by weight. Then, this kneaded sand was rammed three times to form a compression test piece of φ30 mm × 50 mm, heated and cured with a microwave with an output of 700 W for 1 minute, and the strength was measured after cooling.
[0031]
For confirmation of fillability, the casting sand was blown with a blow molding machine at a blow pressure of 20 psi (about 0.14 Mpa) and a blow time of 0.5 seconds to determine the mold density. This value and the JISZ2601 test From the ratio of the density of the compression test pieces molded by ramming three times using a single-sided compactor, the filling rate was calculated as follows.
Filling rate (%) = (density after ramming according to JISZ2601 / density after blow molding) x 100
Table 3 shows the results of experiments regarding the compressive strength and the filling property.
[0032]
[Table 3]

[0033]
From Table 3, it can be seen that when the refractory granular material having water absorption previously absorbed is used, the filling property of the foundry sand is improved as compared with the case where silica sand without pores is used. However, foundry sand using ceramic beads or auritic sand is insufficient in strength even when it is thought that the binder has a high water content and the binder is sufficiently dissolved and coated with each particle. Cera beads seem to be most suitable among practical particles. Therefore, in the following experiment, Cerabeads are used as fire-resistant granular materials having water absorption.
[0034]
In the above experiment, casting sand was prepared by adding a binder and water to a refractory granular material that had been preliminarily absorbed, and dried silica sand and cera beads were combined with a binder (magnesium sulfate 7hydrate 1.425 wt. 1%, sodium dihydrogen phosphate 0.075% by weight) was soaked in an aqueous solution for 1 hour, the surface adhering water was removed with a filter paper, and then dried at 110 ° C. for 2 hours to measure the amount of adsorbed aqueous solution. The amount of adsorbed water in the adsorbed aqueous solution was determined. The results are shown in Table 4. Even in this case, the amount of moisture adsorbed by Cerabeads is twice or more that of silica sand, and it can be seen that the aqueous solution of binder and moisture are adsorbed on Cerabeads having pores.
[0035]
[Table 4]

[0036]
Further, in the same manner as in the water absorption experiment shown in Table 4, casting sand was prepared using silica sand and cera beads after soaking in an aqueous solution for 1 hour so that the total water content was 0.5 to 2.0% by weight, and compressed. When the strength is measured and the filling rate is calculated, Table 5 is obtained.
[0037]
[Table 5]

[0038]
From Table 5, it can be seen that Cerabeads having pores have improved filling properties compared to silica sand. Moreover, if the amount of water is sufficient for the binder to sufficiently dissolve, the compressive strength is somewhat low, but it can withstand practical use.
[0039]
From the above experiment, it can be seen that the use of Cerabeads as the refractory granular material improves the filling property of the foundry sand to some extent. However, the amount of water actually adsorbed is considerably smaller (0.38% by weight) than Cerabeads where the voids in the pores are considered to be less than 10% of the total volume. This is thought to be because water does not sufficiently penetrate into the pores due to the high surface tension of water. Therefore, alcohol with low surface tension is mixed with water to make a mixed solution (mixing ratio of water and alcohol: 75:25 or 50:50), and Cerabeads are immersed in this mixed solution in the same manner as in the previous experiment. Then, the amount of adsorption of the mixed solution was measured, and the amount of adsorbed water was determined from the measured amount of adsorption and the mixing ratio of the mixed solution. The results are shown in Table 6.
[0040]
[Table 6]

[0041]
From Table 6, the amount of adsorbed water on the Cerabead is 1.5% when the Cerabead is infiltrated into the mixed solution of water and ethanol or the mixed solution of water and methanol, compared with the case where Cerabead is infiltrated into water. It can be seen that the water is easily adsorbed to the Cerabeads by adding alcohol.
[0042]
Furthermore, experiments were conducted on the compressive strength and fillability of foundry sand using Cerabeads adsorbed with a mixed solution of water and alcohol. Here, with regard to the measurement of compressive strength, Cerabeads adsorbed with a mixed solution of water and alcohol, a binder (magnesium sulfate heptahydrate 1.425% by weight, sodium dihydrogen phosphate 0.075% by weight) and a predetermined amount The water was added to dissolve the binder, and these were kneaded to prepare foundry sand having a total water content of 0.5 to 2.0% by weight. Then, the foundry sand was heated to 60 ° C. in a sealed container and rammed three times in a mold at 80 ° C. to prepare a test piece of φ28 mm × 50 mm. As for the filling property, the filling rate of foundry sand was determined in the same manner as in the experiment (Table 3) in which only water was adsorbed. The results are shown in Table 7.
[0043]
[Table 7]

[0044]
As can be seen from Table 7, when Cerabeads adsorbed with a mixed solution of water and alcohol are used, the filling property is clearly improved as compared with the case where only water is adsorbed. This is because the surface tension of the mixed solution is lower than that of water, moisture easily penetrates into the pores, and moisture adhering to the surface of each particle of the Cerabeads decreases. It is thought that this is due to the decrease in the fluidity and the increase in the fluidity of each particle.
[0045]
Now, in the above experiment, as the refractory granule, Cera beads and other refractory granule each having water absorbency was used, but by adding a binder, water and alcohol to silica sand, In this case, it was verified whether strength and fillability were improved.
[0046]
First, a binder made of magnesium sulfate and sodium dihydrogen phosphate and water or a mixed solution of water and ethanol is added to silica sand or Cerabeads to form foundry sand. The temperature of the foundry sand is raised to 60 ° C in a sealed container. Then, it was rammed three times in a mold at 80 ° C. and cured for 30 seconds to prepare a test piece of φ28 mm × 50 mm. In addition, when only water was added, the surface water | moisture content was removed by performing air purge for 15 seconds after ramming. When ethanol was added, no air purge was performed. This is because when ethanol was added, the specimen was cured faster than when only water was added, but it seems that the specific heat of ethanol is smaller than that of water. . The results are shown in Table 8.
[0047]
[Table 8]

[0048]
When casting sand is produced by adding a mixed solution of water and ethanol to quartz sand, the filling property is improved as compared with the case where casting water is produced by adding only water. Furthermore, when the added amount of ethanol is 0.1% by weight, the compressive strength of the foundry sand is improved regardless of the amount of the added binder.
Further, Table 9 shows the compressive strength and filling rate of foundry sand when methanol and isopropyl alcohol (IPA) are added as other types of alcohol, and when toluene is added as a reference.
[0049]
[Table 9]

[0050]
Even when methanol and IPA are added, the filling property is improved as compared with the case where only water is added, and the compressive strength is increased by 10% or more when the amount of alcohol added is 0.1% by weight. However, when toluene is added, the effect on the filling property is not recognized.
When the amount of alcohol such as ethanol, methanol, or IPA is large, when the molding sand is dried and the mold is cured, alcohol may be rapidly vaporized and the mold may be easily broken. In the process, it is desirable to gently heat the foundry sand so that the temperature of the foundry sand does not rise rapidly.
[0051]
By the way, in Table 8 and Table 9, when about 0.1 weight% of alcohol is added to a refractory granular material with water, the compressive strength will become large compared with the case where only water is added. This is thought to be due to the following factors.
[0052]
As described above, foundry sand using a binder mainly composed of an inorganic sulfate compound such as magnesium sulfate exhibits strength in a hydrate state in which the inorganic sulfate compound has crystal water. By the way, for example, magnesium sulfate exists in various states from an anhydrate to a 12 hydrate depending on the temperature, a 12 hydrate at −3.8 to 1.8 ° C., a 7 hydrate at 1.8 to 48.3 ° C., 48.3 It becomes hexahydrate at ˜68 ° C. and becomes anhydrous at 200 ° C. or higher. And it is thought that it is in the temperature of about 80 degreeC that it becomes the 2-4 hydrate which intensity | strength develops most.
[0053]
By the way, since the boiling points of methanol, ethanol, and IPA are 65.6 ° C., 78.3 ° C., and 82.7 ° C., respectively, as shown in FIG. 10, when the mixed solution in which water and alcohol are mixed is heated to about 80 ° C. At this temperature, the gas-liquid equilibrium state is reached, and this temperature state around 80 ° C. will continue for a while. Therefore, in the drying process, when drying the foundry sand prepared by adding a binder, water and alcohol to the refractory granular material, the temperature of the foundry sand is likely to be around 80 ° C. Magnesium sulfate in the mold is likely to be present in a 2-4 hydrate state.
[0054]
According to the casting mold manufacturing method described above, the following effects can be obtained.
1) Since the surface tension of the surface of each particle of the refractory granule is reduced by adding alcohol to the refractory granule in addition to water in the binder coating step, the filling property of the molding sand into the mold Can be improved. It is also possible to improve the strength of the mold by adding an appropriate amount of alcohol.
[0055]
2) In the binder coating step, by using a refractory granule in which each particle has water absorption as a refractory granule, a part of the water added to dissolve the binder is refractory granule. Since the amount of water absorbed by each particle of the object and existing on the surface of each particle is reduced, the surface tension of each particle is lowered and the filling property of the foundry sand is improved.
[0056]
Next, modified embodiments in which various modifications are made to the embodiment will be described.
1] As the alcohol to be added to the refractory granule in the binder coating step, other lower alcohols such as propyl alcohol, butyl alcohol, amyl alcohol, and allyl alcohol may be used in addition to the aforementioned methanol, ethanol, and IPA. . Furthermore, the same effect may be obtained even when higher alcohol is used.
[0057]
2] In the above embodiment, silica sand alone or Cerabead having water absorption is used alone as the refractory granule, but a plurality of types of refractory granule may be mixed and used.
3] As a drying method of the foundry sand in the drying process, in addition to the above-mentioned drying by microwave or superheated steam, a method of supplying warm air to the mold and evaporating moisture by the heat, heating the mold and For example, a method of filling the foundry sand and hardening it, a method of filling the foundry mold with the foundry sand and then depressurizing it, and evaporating water can be applied. Furthermore, these methods may be applied in combination.
[0058]
4] For foundry sand or binder, bengara, iron powder, coal powder, graphite powder, wood powder, talc, starch, cereal powder, silica flour, zircon which are usually added to foundry sand to prevent casting defects A predetermined amount of flower, olivine flower or the like can be blended.
[0059]
In addition, in order to improve mold filling properties, the casting sand or binder has tungsten disulfide and molybdenum disulfide as inorganic lubricants, hydrocarbons as organic lubricants, polyalkylene glycols, silicones, fluorine A predetermined amount of a system, phenyl ether, or phosphate ester lubricant can be blended.
Further, a molding material that is usually applied to the surface of the mold, such as an alcoholic coating, an aqueous coating, a powder coating, a surface stabilizer, or tellurium powder for preventing sink marks, can be used for the mold.
[0060]
【The invention's effect】
According to the invention of claim 1, in the binder coating step, since alcohol is added to the refractory granule for foundry sand in addition to water, the surface tension of the surface of each particle of the refractory granule for foundry sand is reduced. Therefore, the filling property of the foundry sand into the mold can be improved.
[0061]
According to invention of Claim 2, a part of the water | moisture content added to the refractory granule for foundry sand in the binder coating process is absorbed by each particle | grain of the refractory granule for foundry sand, Since the amount of moisture present on the surface is reduced, the surface tension of each particle is lowered and the filling property of the foundry sand is improved.
[0062]
According to the invention of claim 3, since the magnesium sulfate is contained in the inorganic sulfate compound and the magnesium sulfate has good solubility in water, a water-soluble casting mold can be obtained by using a binder containing magnesium sulfate. It is also easy to recover the binder by collapsing the mold just by adding water after pouring.
[0063]
According to the invention of claim 4, since the foundry sand is dried by irradiating the foundry sand with microwaves in the drying step, the inorganic sulfate compound in the foundry sand maintains at least a part of crystal water. It becomes possible to remove water, and the inorganic sulfate compound can be present in a hydrated state in the dry state of the template, thereby expressing the strength of the template.
[0064]
According to the invention of claim 5, when the foundry sand is dried in the drying step, the evaporated water can be discharged from the breathable ceramic mold evenly to the outside, so that the strength of the mold can be made uniform. it can.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a method for producing a water-soluble casting mold according to an embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between magnesium sulfate hydrate and compressive strength.
FIG. 3 is an explanatory diagram for explaining a filling operation of a casting sand mold in a filling step.
FIG. 4 is an explanatory diagram illustrating a drying operation using microwaves in a drying process.
FIG. 5 is a photograph of the entire silica sand particles by an electron microscope.
FIG. 6 is a photograph of Cerabead particles, (a) is a photograph of the whole particle, and (b) is a photograph of the particle surface enlarged.
FIG. 7 is a photograph of particles of ceramic beads, (a) is a photograph of the entire particle, and (b) is a photograph of an enlarged particle surface.
8A and 8B are photographs of particles of auritic sand (auritic sand 1), FIG. 8A is a photograph of the entire particles, and FIG. 8B is a photograph of the particle surface enlarged.
FIG. 9 is a photograph of particles of another auritic sand (auritic sand 2), (a) is a photograph of the whole particles, and (b) is a photograph of an enlarged particle surface.
FIG. 10 is a diagram showing a temperature change of a mixed solution of water and alcohol.
[Explanation of symbols]
S foundry sand
1 Mold
2 cavity

Claims (5)

In a casting mold manufacturing method for manufacturing a casting mold by molding foundry sand,
Binder that forms foundry sand by adding a binder containing water-soluble inorganic sulfuric acid compound and water and alcohol to refractory granules for foundry sand and coating the refractory granules for foundry sand with a binder. A coating process;
A filling process for filling the molding sand with the molding sand;
A drying step of drying the foundry sand filled in the mold,
A method for producing a casting mold, comprising: The method for producing a casting mold according to claim 1, wherein each particle of the refractory granular material for foundry sand has water absorption. The method for producing a casting mold according to claim 1, wherein the inorganic sulfate compound contains magnesium sulfate. The casting mold manufacturing method according to any one of claims 1 to 3, wherein in the drying step, the foundry sand is irradiated with microwaves to dry the foundry sand. The method for producing a casting mold according to any one of claims 1 to 4, wherein the mold is a ceramic mold having air permeability.

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