JP3871966B2 - Vanishing model casting method - Google Patents

Description

【００１６】
式（１）の変数のうち、模型の平均の断面積Ｓと模型の高さＨは、鋳物形状から固定される値となるので、溶湯の通路の断面積Ｓｃ、湯口の長さＺが変更可能な変数となる。鋳込時間ｔの調整は、これら２つの変数を含む他の条件を調整することで行われる。発生気体による背圧は溶湯の乱れを抑える効果があり、この発生気体の生成、排出は鋳込時間に及ぼす影響が大きいため、消失模型鋳造法における鋳込時間ｔのｔ_∞に対する比ｔ／ｔ_∞が適切な範囲、すなわちａ＜ｔ／ｔ_∞＜ｂ（ａ、ｂ：常数）にあると湯乱れが抑えられるものと考えられる。
【００１７】
上記式（１）で表される空隙鋳造における鋳込時間ｔ_∞は、例えば、「講座・現在の金属学材料編１０ 鋳造凝固」（日本金属学会、１９９２、Ｐ３２）に記載されている通り、空隙鋳造の鋳込時間の計算式としてよく知られている。
【００１８】
式（１）において、ｃは流量係数（単位なし）であり、「鋳造工学」（産業図書、１９９５年、Ｐ１１２）によれば、通常０．２〜０．８程度の値となる。ｃは溶湯の通路の形状に応じて決まるが、本方法においてはｃ＝０．３とする。ｇは重力加速度（ｍ／ｓ²）である。Ｓは模型の平均断面積で、形状が複雑な場合、例えば模型の体積を模型の最大高さで割ることで求めることができる。Ｓ_cは溶湯の通路の断面積（ｍ²）であり、通路の最狭部の断面積を用いるのが好ましい。また、Ｓ_cとして通路最狭部の断面積に代えて、湯口や湯道、せきのいずれかの総断面積を用いてもよい。Ｚは湯口の長さ（ｍ）で、溶湯の落差を表すものである。受口の深さを湯口長さとあわせてＺとしてもよく、好ましくは受口における実際の湯面の位置からせきまでの落差である。Ｈは模型の高さ（ｍ）である。
【００１９】
なお、式（１）は押上方案を想定しており、せきを模型最下部に設置すると仮定して上記パラメータを定義した。せきの位置が模型最下部でない場合、あるいは最上部の場合、「講座・現在の金属学材料編１０ 鋳造凝固」（日本金属工学会、１９９２、Ｐ３１〜３２）を参考に、模型の高さをせきより上の部分と下の部分に分けて、上型と下型の充填時間を別々に求めて、それらを合計することで空隙鋳造の鋳込時間ｔ_∞を求める。すなわち、せきから受口の湯面位置までの高さをＺ、模型の底部からせきまでの高さをＨ₁、せきから模型の上面までの高さをＨ₂とする。せきより下の下型部が充填される時間ｔ₁は
【００２０】
【数４】

【００２１】
である。ここでV₁は下型空洞部（模型部分）の体積（ｍ³）である。せきより上の上型部が充填される時間ｔ₂は、式（１）と同様に、
【００２２】
【数５】

【００２３】
である。ｔ_∞は、ｔ_∞＝ｔ₁＋ｔ₂と計算される。すなわち、式（１−１）により計算される。
【００２４】
【数６】

【００２５】
また、ｔ_∞を、式（１−２）のように
【００２６】
【数７】

【００２７】
で算出する方法もある。ここで、Ｖは上型と下型をあわせた空洞部（模型部分）の体積（ｍ³）である。なお、精度の点で式（１−１）がより好ましい。これらの式でもｃは０．３とする。
【００２８】
消失模型鋳造法における溶湯充填の制御は、良質な鋳物を得る上で重要であるが、実際の作業現場においては作業者の経験に基づき、塗型剤の通気度や厚みなどを調節して発生気体の通気性を制御している。しかし、実際にどのように制御すると残渣欠陥がなく品質の良い鋳物が製造できるか明確になっていない。これに対して、本発明では、空隙鋳造における鋳込時間ｔ_∞（秒）との対比により定めた溶湯の鋳込時間ｔ（秒）に基づいて、例えば１．１＜ｔ／ｔ_∞＜７を満たすような鋳造方案で鋳造を実施することにより、溶湯充填の制御が適正化され、種々の発泡模型を用いても鋳型内での溶湯の乱れを抑えつつ速やかな充填が実現され、残渣欠陥の少ない品質の良好な鋳物が得られる。すなわち、本発明は、消失模型鋳造法における明確な作業指針を提供できるため、当業界において非常に有用である。
【００２９】
本発明の消失模型鋳造法は、鋳型を減圧して塗膜を通じてのガス排出を促進する、いわゆる減圧法や、外気に連通するガス排出通路を通じてガス排出を行う鋳造法など、いずれにも適用できる。しかし、より残渣欠陥の抑制が可能な外気に連通するガス排出通路を設ける鋳造法、更にはガス排出通路に排出気体抑制手段を設け且つ模型内に湯口及びガス排出通路に連通する貫通孔を形成する鋳造法が好ましい。
【００３０】
本発明の消失模型鋳造法の一例を図１に基づいて説明する。図１中、鋳型は鋳枠４と鋳枠４の内部の鋳物砂７と鋳物砂７に埋設された模型１等からなり、模型１に連通した受口５が左上方に設けられている。模型１は、発泡ポリスチレンによって製品と同一形状に形成されており、貫通孔２が設けられている。鋳物砂７は５．５号硅砂であり、粘結剤を適量含有させてある。鋳型の形成は、まず、模型１の表面に耐火性に優れた塗型剤３を塗布し、その後充分乾燥させる。そして鋳枠４に湯口６および湯道１０を形成した後、模型１を固定し鋳物砂７で埋設し、受口５を設置する。その際、貫通孔２の内部は空間にしておき、貫通孔２を湯道１０に連通させると共に、貫通孔２に連通する排出管を設け排出通路８とする。排出通路８となる排出管はセラミック製で、排出気体抑制手段としてバインダーで成型されたアルミナ等の耐火物粒子９が充填され、貫通孔２と大気とを連通させるように鋳物砂７に埋設される。
【００３１】
受口５から溶湯を注湯すると、溶湯は湯口６および湯道１０を通って模型１に到達し、模型１を溶融させて、鋳型内に溜る。一方、排出通路８からは、溶湯によって溶融、燃焼された模型１の気体の排出が確認されるが、耐火物粒子９が充填されているので、気体の放出が調整される。
【００３２】
以下に本発明の好ましい一態様である図１に示される鋳造法におけるｔの制御方法について説明する。なお、減圧鋳造法においては、塗膜の通気性や減圧度によりｔの制御が一般に可能である。図１のように、排出気体抑制手段を設け、その通気性や設置度合い（設置数、設置位置等）により、溶湯の鋳込時間ｔ（秒）を制御することが好ましい。ここで、排出気体抑制手段とは、該手段を設けることで発生気体を外部に徐々に放出し得る通気性を有する手段であり、耐火物粒子及びその層、背圧弁、中空細管からなることが好ましく、さらには、溶湯の吹き出し防止の点から耐火物粒子及びその層、背圧弁が好ましく、更にはススのろ過の機能も兼ねられる点から耐火物粒子及びその層が好ましい。
【００３３】
排出気体抑制手段の通気性は、充填する耐火物粒子の粒径、充填厚み、排出通路の直径などを変更することで調整できる。中空細管を排出気体抑制手段に用いる場合は、その直径と長さを変更することで調整できる。通気性の調整によって、鋳型内の背圧が変わり、それによって溶湯の充填の制御が可能になる。なお、貫通孔や排出気体抑制手段を設けなくても、塗型剤の通気度を変更したり、膜厚を調整したりして、溶湯の充填制御を行う方法もある。
【００３４】
本発明において、排出気体抑制手段として用いられる通気性のある耐火物層としては、バインダー等を添加して耐火物粒子を成型させたものや、ウレタンフォームにセラミックススラリーを浸漬しその後焼成した、いわゆるセラミックスフォームフィルター等を使用することもでき、好ましくは前者である。耐火物粒子の平均粒径は０．１〜１０ｍｍ、更に０．５〜５ｍｍが好ましく、金属又はその酸化物の粒子、例えばアルミナ、珪砂、ジルコン砂、クロマイト砂、合成セラミック砂等が挙げられる。耐火物は、排出通路の断面積、形状にもよるが、厚さが０．５〜２０ｃｍ、更に１〜１０ｃｍとなる量で充填されることが好ましい。中空細管を排出気体抑制手段とする場合は内径０．１〜５ｃｍ、長さ３０ｃｍ〜５ｍ、更には内径０．５ｃｍ〜２ｃｍ、長さ４０ｃｍ〜２ｍで、金属等の耐火性のある材質で構成されるものが好ましい。
【００３５】
また、背圧弁とは、気体の流れ方向の圧力を弁の前側（気体流路の上流）に比して後側（気体流路の下流）を低く設定できる弁のことであり、バネ式低圧バルブ、ニードル式等何れを用いてもよく、これらを排気通路に設置することで排出気体抑制手段が形成される。
【００３６】
模型は、合成樹脂発泡体からなるものが使用される。合成樹脂発泡体としては、ポリスチレン、ポリメタクリル酸メチル、又はこれらの共重合体等の発泡体が用いられる。
【００３７】
模型には塗型剤により塗型層が形成される。塗型の通気性は鋳込時間ｔに影響する因子の一つである。塗型剤としては、市販のもののほか、粒径１０μｍ以下の耐火性骨材を含有するものも使用可能である。これにより、塗型膜の表面平滑性が向上し、鋳物の表面平滑性も向上する。塗型剤中の耐火性骨材としては、例えば黒鉛、ジルコン、マグネシア、アルミナ、シリカなどがある。また塗型剤の粘結剤として、水系ではポリアクリル酸ナトリウム、澱粉、メチルセルロース、ポリビニルアルコール、アルギン酸ナトリウム、アラビアガム等の水溶性高分子や酢酸ビニル系等の各種の樹脂のエマルションを、またアルコール系ではアルコール可溶もしくは分散する各種樹脂を添加するのが、塗型強度の点から好ましい。添加量は耐火性骨材１００重量部に対し、好ましくは０．５〜１０重量部である。
【００３８】
鋳造に用いる鋳物砂としては、石英質を主成分とする珪砂の他、ジルコン砂、クロマイト砂、合成セラミック砂等の新砂又は再生砂が使用される。鋳物砂は粘結剤を添加せずに用いることもでき、その場合には充填性が良好であるが、強度が必要な場合には、粘結剤を添加し、硬化剤により硬化させるのが好ましい。
【００３９】
上記した本発明によれば、鋳物砂内に合成樹脂発泡体製模型を埋設してなる鋳型に溶湯を注湯し、該溶湯によって前記模型を消失させながら製品を鋳造する消失模型鋳造法であって、当該鋳造法のための鋳造方案から鋳型の内圧のかからない空隙鋳造における鋳込時間ｔ_∞（秒）を求め、このｔ_∞に基づいて前記溶湯の鋳込時間ｔ（秒）を決定する消失模型鋳造法が提供される。
【００４０】
また、本発明によれば、鋳物砂内に合成樹脂発泡体製模型を埋設してなる鋳型に溶湯を注湯し、該溶湯によって前記模型を消失させながら製品を鋳造する消失模型鋳造法であって、暫定的に決定された鋳造方案から鋳型の内圧のかからない空隙鋳造における鋳込時間ｔ_∞（秒）を求め、このｔ_∞から目標とすべき溶湯の鋳込時間ｔ（秒）を定め、ｔ_∞とｔの比較結果に基づいて最終的な鋳造方案を決定し、当該最終的な鋳造方案に基づいて鋳造を行う消失模型鋳造法が提供される。
【００４１】
【発明の効果】
本発明によれば、品質の優れた鋳物が得られる条件を簡易に決定できる消失模型鋳造法が提供される。
【００４２】
【実施例】
実施例１
図２に示す発泡ポリスチレン製の発泡模型を図１のようにセットして消失模型鋳造を行った。その際、湯口系の設置は図４のようにした。模型の空洞部１、３の大きさは、横２００ｍｍ×縦１３０ｍｍ、深さ２７５ｍｍ、空洞部２の大きさは、横２００ｍｍ×縦１４０ｍｍ、深さ２７５ｍｍであった（外枠、仕切部の厚み２５ｍｍ）。
【００４３】
また、この模型における貫通孔の形成の様子を図３に、模型の設置位置を図４に、それぞれ模式的に示した。フィルターを２本設置する場合は図４（ａ）の貫通孔（ａ）、（ｄ）に、４本設置する場合は図４（ａ）の貫通孔（ａ）〜（ｄ）に、１２本設置する場合は図４（ｂ）に示すように設置した。図４（ｂ）でも貫通孔（ａ）〜（ｄ）が形成され、更に破線で示すように貫通孔が形成されている。湯道とせきは発泡ポリスチレンによって形成されており、湯道とせきの内部には互いに連通する貫通孔が形成されている。この貫通孔は、湯口に連通させると共に模型内部の貫通孔にも連通している。せきは６ヶ所であり、各せきの断面積の合計をＳ_cとして採用した。
【００４４】
鋳造は表１の鋳造方案で行った。鋳造の際、表２に示すフィルターを、排出気体抑制手段を備えた排出通路として、表１のように用いた。
【００４５】
模型の表面には７０ボーメの塗型剤を塗布し、乾燥後、造型を行った。なお、塗型剤の組成は、シリカ粉（平均粒径８μｍ）４０重量％、鱗状黒鉛１０重量％、酢酸ビニル系バインダー５重量％、水４０重量％、非イオン界面活性剤０．５重量％、ベントナイト４．５重量％であった。また、鋳鉄の材質はＦＣ−２５０、鋳込温度は１４００℃であった。本実施例の鋳造材料である鋳鉄は、注湯温度である１４００℃において密度は６７００ｋｇ／ｍ³である。
【００４６】
鋳込時間ｔは、タッチセンサーを用いて計測した。タッチセンサーとは溶湯の導電性を利用して、ある場所における溶湯の到達を知るもので、その一例が、小林武、糟谷良和：鋳物Vol.64, p.794 (1992) に掲載されている。
【００４７】
ｔ／ｔ_∞の値と鋳物品質を評価した結果を表１に示す。ここで、残渣欠陥は、鋳物上面をフライス盤により切削し残渣欠陥がなくなる深さである。表１の結果から、ｔ／ｔ_∞が１．１超７未満の範囲にある場合は、残渣欠陥が抑制されたことがわかる。この結果から、ｔ／ｔ_∞がこの範囲にある場合は、溶湯の充填が適度に制御され鋳型内の溶湯の乱れがなく、模型熱分解物を巻き込むことがないものと推察される。従来のように、鋳物メーカー等における作業者が、経験や勘に基づいて実施例１に記載された発泡模型の鋳造を行うと、木型法に比べて高い不良率となることが予想されるのに対し、本発明に準じて鋳造を行えば、木型法並みの不良率まで低減できるものと考えられる。
【００４８】
なお、表１の試験Ｎｏ．１におけるｔ_∞の算出方法を示す。試験Ｎｏ．１において、ｃ＝０．３、重力加速度ｇ＝９．８［ｍ／ｓ］、湯口高さＺ＝０．７［ｍ］、せき断面積Ｓ_c＝３．６１×１０^-3［ｍ²］、模型の高さは０．３［ｍ］である。模型の平均断面積は、実際にＮＣ加工された模型に基づいて決定した。各実験の平均模型重量が０．６［ｋｇ］であり、模型密度２０［ｋｇ／ｍ³］を用いて、平均模型体積は０．６／２０＝０．０３［ｍ³］となる。なお、模型密度２０［ｋｇ／ｍ³］は発泡倍率５０倍にあたる。得られた模型体積を模型高さ０．３［ｍ］で割ることで、平均断面積０．１［ｍ²］を得る。以上より、試験Ｎｏ．１のｔ_∞は
【００４９】
【数８】

【００５０】
となる。
【００５１】
【表１】

【００５２】
＊１：湯口比は、湯口：湯道：せきの面積比率である。
＊２：フィルターは下記表２に示されるものである。
【００５３】
【表２】

【図面の簡単な説明】
【図１】本発明の消失模型鋳造法の一例を示す概略図
【図２】実施例１で用いた模型の概略図
【図３】実施例１で用いた模型の貫通孔の形成位置を示す概略図
【図４】実施例１の鋳型における模型、湯口及び湯道の位置関係を示す概略図
【符号の説明】
１ 模型
２ 貫通孔
８ 排気通路
９ 耐火物粒子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a disappearance model casting method.
[0002]
[Prior art]
The disappearance model casting method is also called a full mold method, and is a process of using a model made of synthetic resin foam as a mold while being embedded in foundry sand, and has many advantages such as easy casting. On the other hand, casting defects are likely to occur due to thermal decomposition of the model. In particular, when filling is slow, the model does not completely decompose and vaporize due to a drop in the temperature of the molten metal, resulting in residual defects. Conversely, if the filling is too fast and the molten metal in the mold is disturbed, It gets caught in and causes residue defects.
[0003]
To give a guide to the casting speed from the viewpoint of disassembling the model, Toru Tsujidon: JACTNEWS, page 15693 (1997) is disclosed, and the molten metal surface in the mold should rise at a speed of about 1 cm / s. It is said that. As a method for controlling the residual defects, a method for adjusting the outgassing by a gas seal film set to an appropriate film thickness and controlling the molten metal (Japanese Patent Laid-Open No. 2-268934), or providing a hollow portion inside the model A method for reducing the generated gas and applying pressure to prevent the coating from collapsing (Japanese Patent Laid-Open No. 2000-140994) is disclosed.
[0004]
[Problems to be solved by the invention]
As described above, in the disappearance model casting method, it is important to realize rapid filling while suppressing the turbulence of the molten metal in the mold, but the setting of absolute casting speed and the conventionally proposed residual defect The improvement method alone cannot be said to be sufficient, and the conditions for improving the casting quality according to various methods such as the size and shape of the casting and other casting conditions have not been clarified.
[0005]
Accordingly, if the conditions under which residual defects are reduced and excellent quality castings can be easily determined, it is considered that the utility value in this industry is extremely high.
[0006]
[Means for Solving the Problems]
The present invention is a vanishing model casting method in which a molten metal is poured into a mold formed by embedding a synthetic resin foam model in foundry sand, and the product is cast while the model is lost by the molten metal. The present invention relates to a disappearance model casting method in which a casting time t (second) of the molten metal is determined based on a casting time t _∞ (second) in void casting in which no internal pressure is applied.
[0007]
Further, according to the present invention, a casting time t _∞ (second) in void casting that does not require the internal pressure of the mold is obtained from a tentatively determined casting method, and a casting time to be targeted based on this casting time t _∞. The present invention relates to a casting method determination method in the disappearance model casting method in which t is defined and a final casting method is determined so as to give the casting time t.
[0008]
Further, the present invention is a disappearing model casting method in which a molten metal is poured into a mold formed by embedding a synthetic resin foam model in foundry sand, and the product is cast while the model is lost by the molten metal, The present invention relates to a disappearance model casting method in which a casting time t (second) of the molten metal and a casting time t _∞ (second) in void casting that does not apply the internal pressure of the mold satisfy 1.1 <t / t _∞ <7.
[0009]
For example, as described in "Mechanical Engineering Handbook B2" (Maruzen) p.12 (1987), the casting method is a pouring gate that pours molten metal into the mold, a hot water / cooling metal that prevents sink marks, etc. It is a general term for design and setting of pouring temperature. Furthermore, in the present invention, the design of the means for discharging the gas in the mold including the gas generated by the thermal decomposition of the model is also called a casting method. Examples of the means for discharging the gas include a gas discharge passage communicating with the coating film and the outside air, and an exhaust gas suppressing means provided in the discharge passage. In the disappearance model casting method, the casting time is affected by this casting method. Conventionally, the casting defines the casting design empirically been performed, the present invention defines a casting time t of the target based on the t _∞, adjusting the casting design to achieve this . By such a method, in the present invention, conditions for reducing residual defects and obtaining a casting of excellent quality can be easily determined. This is a new finding by the present invention different from the conventional one.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, in order to realize rapid filling while suppressing turbulence of the molten metal in the mold, casting is performed on the basis of the casting time t _∞ in the void casting that does not require the inner pressure of the mold in consideration of the size and shape of the model. Time t is determined.
[0011]
In the present invention, the casting time t is the time from when the molten metal passes through the cough and starts to flow into the model until the molten metal is filled to the top surface of the product. Further, when it is difficult to specify the time at which the molten metal flows into the model, the time at which the pouring is started may be substituted. Similarly, when it is difficult to specify the time at which the product top surface is filled, the time at which the molten metal reaches the hot water or fried food can be substituted.
[0012]
In general, when t / t _∞ is small, the molten metal in the mold is disturbed, and thus a residue defect tends to occur. When t / t _∞ is large, filling of the molten metal is inhibited and the residual defect tends to become prominent. . Note that the theoretical optimum value of t / t _∞ is 1 when deaeration promotion or the like by decompression is not performed. The characteristic of the present invention is that the casting time t of the actual disappearance model casting method is determined with reference to the casting time t _∞ at the time of void casting by the corresponding casting method, and the ratio t / t to t _∞ is t /. it is preferred to be judged by t _∞, further _{a <t / t ∞ <b} (a, b: constant) as is determined in accordance with the scheme, the optimal range is specifically 1.1 <t / t _∞ <7, preferably 1.5 <t / t _∞ <6, more preferably 1.5 <t / t _∞ <3.
[0013]
In the present invention, after satisfying the range of t / t _∞ , the speed v at which the molten metal surface rises in the mold is set to 1 <v <4, further 1.4 <v <3, particularly 1.8 <. It is further desirable that v <2.9 [cm / s].
[0014]
t _∞ means casting time in the air gap casting does not take the pressure of the mold (i.e. back pressure) may actually seek performed void cast in the same casting design and evaporative pattern casting method carrying out, but to calculate Simple and preferable. As an example of calculating by calculating the t _∞, and a method according to the following formula (1).
[0015]
[Equation 3]

[0016]
Of the variables in equation (1), the average cross-sectional area S and the height H of the model are fixed values from the casting shape, so the cross-sectional area Sc of the molten metal passage and the length Z of the gate are changed. It becomes a possible variable. The casting time t is adjusted by adjusting other conditions including these two variables. The back pressure due to the generated gas has the effect of suppressing the turbulence of the molten metal, and the generation and discharge of this generated gas has a large effect on the casting time, so the ratio t / t of the casting time t to t _∞ in the disappearance model casting method. _{When ∞} is in an appropriate range, that is, a <t / t _∞ <b (a, b: constant), it is considered that hot water turbulence can be suppressed.
[0017]
The casting time t _∞ in the void casting represented by the above formula (1) is, for example, as described in “Course / Current Metallographic Materials 10 Casting Solidification” (Japan Institute of Metals, 1992, P32) It is well known as a formula for calculating the casting time of gap casting.
[0018]
In the formula (1), c is a flow coefficient (no unit), and is usually about 0.2 to 0.8 according to “Casting Engineering” (Industry Books, 1995, P112). Although c is determined according to the shape of the molten metal passage, in this method, c = 0.3. g is a gravitational acceleration (m / s ² ). S is an average cross-sectional area of the model, and when the shape is complicated, it can be obtained, for example, by dividing the volume of the model by the maximum height of the model. S _c is the cross-sectional area (m ² ) of the molten metal passage, and the cross-sectional area of the narrowest portion of the passage is preferably used. Further, instead of the cross-sectional area of the passage at the narrowest portion as S _c, sprue or runner may be using the total cross-sectional area of either of the weir. Z is the length (m) of the gate and represents the drop of the molten metal. The depth of the receiving port may be Z together with the length of the pouring gate, and is preferably a drop from the actual position of the hot water surface to the cough at the receiving port. H is the height (m) of the model.
[0019]
Note that equation (1) assumes a push-up plan, and the above parameters are defined on the assumption that a cough is installed at the bottom of the model. If the position of the cough is not at the bottom of the model, or if it is at the top, refer to “Course / Current Metallurgy Materials 10 Casting and Solidification” (Japan Metal Engineering Society, 1992, P31-32), in portions and the lower part of the Sekiyori, seeking filling time of the upper and lower molds are separately obtains the casting time t _∞ void casting by summing them. That is, the height from the cough to the hot water surface position of the receiving port is Z, the height from the bottom of the model to the cough is H ₁ , and the height from the cough to the top surface of the model is H ₂ . The time t ₁ when the lower mold part below the cough is filled is:
[Expression 4]

[0021]
It is. Here, V ₁ is the volume (m ³ ) of the lower mold cavity (model part). The time t ₂ during which the upper mold part above the cough is filled is the same as in the formula (1).
[0022]
[Equation 5]

[0023]
It is. t _∞ is calculated as t _∞ = t ₁ + t ₂ . That is, it is calculated by the equation (1-1).
[0024]
[Formula 6]

[0025]
Further, t _∞ is expressed by the following equation (1-2):
[Expression 7]

[0027]
There is also a method of calculating by. Here, V is the volume (m ³ ) of the hollow portion (model portion) of the upper die and the lower die. In addition, Formula (1-1) is more preferable in terms of accuracy. In these formulas, c is 0.3.
[0028]
Control of molten metal filling in the disappearance model casting method is important for obtaining a high quality casting, but in actual work sites, it is generated by adjusting the air permeability and thickness of the coating agent based on the experience of the worker. The gas permeability is controlled. However, it has not been clarified as to how to actually produce a casting with good quality without residual defects. On the other hand, in the present invention, for example, 1.1 <t / t _∞ <7 based on the casting time t (second) of the molten metal determined by comparison with the casting time t _∞ (second) in the void casting. By performing casting with a casting method that satisfies the requirements, the molten metal filling control is optimized, and even with various foamed models, rapid filling is realized while suppressing turbulence of the molten metal in the mold, and residual defects A good casting with low quality can be obtained. That is, the present invention is very useful in the industry because it can provide a clear working guideline in the disappearance model casting method.
[0029]
The vanishing model casting method of the present invention can be applied to any of a so-called decompression method in which the mold is depressurized to promote gas discharge through the coating film, and a casting method in which gas is discharged through a gas discharge passage communicating with the outside air. . However, a casting method that provides a gas discharge passage that communicates with the outside air that can further suppress residue defects, and further, a gas discharge passage is provided in the gas discharge passage and a through hole that communicates with the gate and gas discharge passage is formed in the model. A casting method is preferred.
[0030]
An example of the vanishing model casting method of the present invention will be described with reference to FIG. In FIG. 1, the mold includes a casting frame 4, a casting sand 7 inside the casting frame 4, a model 1 embedded in the casting sand 7, and the like, and a receiving port 5 communicating with the model 1 is provided in the upper left. The model 1 is formed in the same shape as the product by foamed polystyrene, and is provided with a through hole 2. The foundry sand 7 is No. 5.5 dredged sand and contains an appropriate amount of binder. In forming the mold, first, a coating agent 3 having excellent fire resistance is applied to the surface of the model 1 and then sufficiently dried. And after forming the sprue 6 and the runner 10 in the casting frame 4, the model 1 is fixed, it embed | buries with the foundry sand 7, and the receiving port 5 is installed. At this time, the inside of the through hole 2 is left as a space, and the through hole 2 communicates with the runner 10 and a discharge pipe that communicates with the through hole 2 is provided as the discharge passage 8. The discharge pipe serving as the discharge passage 8 is made of ceramic, filled with refractory particles 9 such as alumina molded with a binder as an exhaust gas suppressing means, and embedded in the foundry sand 7 so as to communicate the through hole 2 with the atmosphere. The
[0031]
When molten metal is poured from the receiving port 5, the molten metal reaches the model 1 through the gate 6 and the runner 10, melts the model 1, and accumulates in the mold. On the other hand, from the discharge passage 8, it is confirmed that the gas of the model 1 melted and burned by the molten metal is discharged, but since the refractory particles 9 are filled, the release of the gas is adjusted.
[0032]
Hereinafter, a control method of t in the casting method shown in FIG. 1 which is a preferred embodiment of the present invention will be described. In the vacuum casting method, t can generally be controlled by the air permeability of the coating film and the degree of vacuum. As shown in FIG. 1, it is preferable to provide exhaust gas suppression means and control the casting time t (seconds) of the molten metal according to the air permeability and the degree of installation (number of installations, installation positions, etc.). Here, the exhaust gas suppressing means is a means having air permeability capable of gradually releasing the generated gas to the outside by providing the means, and may be composed of refractory particles and a layer thereof, a back pressure valve, and a hollow thin tube. Further, refractory particles and their layers and back pressure valves are preferable from the viewpoint of preventing molten metal from blowing out, and refractory particles and their layers are preferable from the viewpoint of also functioning as a soot filtering function.
[0033]
The air permeability of the exhaust gas suppressing means can be adjusted by changing the particle size of the refractory particles to be filled, the filling thickness, the diameter of the discharge passage, and the like. When a hollow thin tube is used as the exhaust gas suppressing means, it can be adjusted by changing its diameter and length. By adjusting the air permeability, the back pressure in the mold is changed, thereby allowing the filling of the molten metal to be controlled. In addition, there is a method in which the filling control of the molten metal is performed by changing the air permeability of the coating agent or adjusting the film thickness without providing the through hole and the exhaust gas suppressing means.
[0034]
In the present invention, as a breathable refractory layer used as an exhaust gas suppression means, a so-called refractory particle formed by adding a binder or the like, or a ceramic slurry immersed in urethane foam and then fired, so-called A ceramic foam filter or the like can also be used, and the former is preferable. The average particle diameter of the refractory particles is preferably 0.1 to 10 mm, more preferably 0.5 to 5 mm, and examples thereof include metal or oxide particles such as alumina, silica sand, zircon sand, chromite sand, and synthetic ceramic sand. Although it depends on the cross-sectional area and shape of the discharge passage, the refractory is preferably filled in an amount of 0.5 to 20 cm, more preferably 1 to 10 cm. When a hollow thin tube is used as the exhaust gas suppression means, the inner diameter is 0.1 to 5 cm, the length is 30 cm to 5 m, the inner diameter is 0.5 cm to 2 cm, and the length is 40 cm to 2 m. Are preferred.
[0035]
The back pressure valve is a valve that can set the pressure in the gas flow direction lower on the rear side (downstream of the gas flow path) than the front side of the valve (upstream of the gas flow path). Any of a valve, a needle type and the like may be used, and the exhaust gas suppressing means is formed by installing these in the exhaust passage.
[0036]
A model made of a synthetic resin foam is used. As the synthetic resin foam, a foam such as polystyrene, polymethyl methacrylate, or a copolymer thereof is used.
[0037]
A coating layer is formed on the model by a coating agent. The air permeability of the coating mold is one of the factors affecting the casting time t. As the coating agent, in addition to commercially available ones, those containing a refractory aggregate having a particle size of 10 μm or less can be used. Thereby, the surface smoothness of a coating type film improves, and the surface smoothness of a casting also improves. Examples of the refractory aggregate in the coating agent include graphite, zircon, magnesia, alumina, and silica. In addition, as a binder for coating agents, water-based emulsions of water-soluble polymers such as sodium polyacrylate, starch, methylcellulose, polyvinyl alcohol, sodium alginate, gum arabic, and various resins such as vinyl acetate are used as alcohol. In the system, it is preferable from the viewpoint of coating strength to add various resins soluble or dispersed in alcohol. The addition amount is preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the refractory aggregate.
[0038]
As foundry sand used for casting, new sand or recycled sand such as zircon sand, chromite sand, and synthetic ceramic sand is used in addition to quartz sand mainly composed of quartz. Casting sand can also be used without adding a binder, in which case the filling property is good, but if strength is required, a binder is added and cured with a curing agent. preferable.
[0039]
According to the present invention described above, there is a disappearance model casting method in which a molten metal is poured into a mold formed by embedding a synthetic resin foam model in foundry sand, and the product is cast while the model is disappeared by the molten metal. Then, the casting time t _∞ (seconds) in the void casting without applying the internal pressure of the mold is obtained from the casting method for the casting method, and the casting time t (seconds) of the molten metal is determined based on this t _∞. A model casting method is provided.
[0040]
Further, according to the present invention, there is provided a vanishing model casting method in which a molten metal is poured into a mold formed by embedding a model made of a synthetic resin foam in foundry sand, and the product is cast while the model is lost by the molten metal. Then, the casting time t _∞ (seconds) in the void casting that does not apply the internal pressure of the mold is determined from the tentatively determined casting method, and the casting time t (seconds) of the melt to be targeted is determined from this t _∞ , A vanishing model casting method is provided in which a final casting method is determined based on a comparison result between _t∞ and t, and casting is performed based on the final casting method.
[0041]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the vanishing model casting method which can determine easily the conditions from which the casting with excellent quality is obtained is provided.
[0042]
【Example】
Example 1
The foamed model made of expanded polystyrene shown in FIG. 2 was set as shown in FIG. At that time, the gate system was installed as shown in FIG. The size of the cavity portions 1 and 3 of the model was 200 mm wide × 130 mm long and 275 mm deep, and the size of the cavity 2 was 200 mm wide × 140 mm long and 275 mm deep (the thickness of the outer frame and the partition portion) 25 mm).
[0043]
Moreover, the state of formation of the through hole in this model is schematically shown in FIG. 3, and the installation position of the model is schematically shown in FIG. When two filters are installed, 12 holes are provided in the through holes (a) and (d) of FIG. 4A. When four filters are installed, 12 filters are provided in the through holes (a) to (d) of FIG. When installing, it installed as shown in FIG.4 (b). Also in FIG. 4B, through holes (a) to (d) are formed, and further through holes are formed as indicated by broken lines. The runners and coughs are formed of expanded polystyrene, and through holes communicating with each other are formed in the runners and coughs. The through hole communicates with the gate and also communicates with the through hole inside the model. Cough is six locations, employing a total cross-sectional area of each weir as S _c.
[0044]
Casting was performed according to the casting method shown in Table 1. At the time of casting, the filter shown in Table 2 was used as shown in Table 1 as a discharge passage provided with exhaust gas suppressing means.
[0045]
A 70 Baume coating agent was applied to the surface of the model, dried and molded. The composition of the coating agent was 40% by weight of silica powder (average particle size 8 μm), 10% by weight of scaly graphite, 5% by weight of vinyl acetate binder, 40% by weight of water, and 0.5% by weight of nonionic surfactant. The bentonite was 4.5% by weight. The cast iron material was FC-250, and the casting temperature was 1400 ° C. The cast iron, which is the casting material of the present example, has a density of 6700 kg / m ³ at a pouring temperature of 1400 ° C.
[0046]
The casting time t was measured using a touch sensor. The touch sensor uses the conductivity of the molten metal to know the arrival of the molten metal at a certain location. Takeshi Kobayashi, Yoshikazu Kajitani: Casting Vol.64, p.794 (1992) .
[0047]
Table 1 shows the results of evaluating the value of t / t _∞ and casting quality. Here, the residue defect is a depth at which the upper surface of the casting is cut by a milling machine to eliminate the residue defect. From the results in Table 1, it can be seen that when t / t _∞ is in the range of more than 1.1 and less than 7, residual defects are suppressed. From this result, when t / t _∞ is within this range, it is presumed that the filling of the molten metal is appropriately controlled, the molten metal in the mold is not disturbed, and the model pyrolyzate is not involved. When a worker in a casting manufacturer or the like casts the foamed model described in Example 1 based on experience and intuition as in the past, it is expected that the defect rate is higher than that in the wooden mold method. On the other hand, if casting is performed according to the present invention, it is considered that the defect rate can be reduced to the same level as the wooden method.
[0048]
In addition, test No. of Table 1 The calculation method of _t∞ in 1 is shown. Test No. 1, c = 0.3, gravitational acceleration g = 9.8 [m / s], gate height Z = 0.7 [m], cross-sectional area S _c = 3.61 × 10 ⁻³ [m ² ], The height of the model is 0.3 [m]. The average cross-sectional area of the model was determined based on the model that was actually NC processed. The average model weight of each experiment is 0.6 [kg], and using the model density of 20 [kg / m ³ ], the average model volume is 0.6 / 20 = 0.03 [m ³ ]. A model density of 20 [kg / m ³ ] corresponds to a foaming ratio of 50 times. By dividing the obtained model volume by the model height of 0.3 [m], an average cross-sectional area of 0.1 [m ² ] is obtained. From the above, the test No. T _∞ of 1 is [0049]
[Equation 8]

[0050]
It becomes.
[0051]
[Table 1]

[0052]
* 1: Yuguchi ratio is the area ratio of Yuguchi: Yudo: Cough.
* 2: The filters are those shown in Table 2 below.
[0053]
[Table 2]

[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a vanishing model casting method according to the present invention. FIG. 2 is a schematic view of a model used in Example 1. FIG. 3 is a diagram showing positions where through holes are formed in the model used in Example 1. Schematic diagram [FIG. 4] Schematic diagram showing the positional relationship between the model, the gate and the runner in the mold of Example 1 [Explanation of symbols]
1 Model 2 Through-hole 8 Exhaust passage 9 Refractory particles

Claims (5)

A vanishing model casting method in which a molten metal is poured into a mold formed by embedding a synthetic resin foam model in foundry sand, and the product is cast while the model disappears with the molten metal, and the void is not subjected to the internal pressure of the mold. A vanishing model casting method in which a casting time t (second) of the molten metal is determined based on a casting time t _∞ (second) in casting. The disappearance model casting method according to claim 1, wherein a casting time t _∞ (seconds) in the void casting is calculated by the following formula (1-1) or (1-2).

The vanishing model casting method according to claim 1 or 2, wherein a speed v at which the molten metal surface rises in the mold is 1 <v <4 [cm / s]. The casting time t _∞ (seconds) in the void casting that does not apply the internal pressure of the mold is determined from the tentatively determined casting method, and the target casting time t is determined based on the casting time t _∞. A method for determining a casting method in the disappearance model casting method, in which a final casting method is determined so as to give a setting time t. A vanishing model casting method in which a molten metal is poured into a mold formed by embedding a synthetic resin foam model in foundry sand, and the product is cast while the model is lost by the molten metal, and the casting time of the molten metal An extinction model casting method in which t (second) and casting time t _∞ (second) in void casting that does not apply the internal pressure of the mold satisfy 1.1 <t / t _∞ <7.

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