MOLD, METHOD OF PRODUCING MOLD AND CASTING METHOD

Abstract: Disclosed are a porous calcia mold containing not less than 40 wt% CaO, a mold containing 95 to 10 wt% CaO and 5 to 50 wt% graphite, a mold containing not less than 40 wt% CaO, not more than 5 wt% low-eutectic temperature oxide and not more than 40 wt% high-eutectic temperature oxide, and a mold provided with a layer containing not less than 40 wt% CaO on the surface which comes into contact with a molten metal. A method of producing a porous mold by baking a molded body obtained by a slip casting method or an injection molding method, and a method of producing a mold by baking a molded body (1) while bringing a member for preventing the deformation of a molded body (2) into contact with the molded body (1) are also disclosed. In addition, a method of casting a highly active metal, a high-melting point metal, or an alloy containing such a metal by using one of the above-described molds, and a casting method comprising the steps of placing a bottomless porous calcia mold on a metal chill plate, pouring a molten metal by top-pouring and gradually solidifying the molten metal from the lower part while insulating the riser are also disclosed.

Description: The present invention relates to a casting method using a mold containing calcia (CaO). From US-A-2 876 122 a method of making a calcia mold is known comprising compacting calcia particles, containing no more than 20% fused magnesia, not more than 3% fused silica, not more than 2% of oxide other than calcia, magnesia and silica, and not more than 0.5% of material other than oxide and thereafter sintering by firing the article throughout a temperature of at teast 120°C. When an active metal such as titanium and zirconium is poured into such a conventional mold, a mold reaction occurs and in the case of a magnesium containing and/or zirconium containing mold oxygen will be set free which contaminates the surface of the casting. Such a contamination of the surface of a casting requires a step of removing the contaminated layer from the surface, thereby rendering the manufacturing process complicated and costly. From US-B-5 11 885 a mold is known comprising portions which are open at the base of the mold. The base rests on a spacer that in turn rests on a chill plate. It is an object of the invention to provide a mold which is capable of casting an active metal such as titanium and zirconium or an alloy containing such an active metal and is capable of producing a highly purified casting free from carbon, oxygen, nitrogen and other contaminations. This object is solved by the features as indicated in claim 1. Since the mold is porous and has high heat retaining properties and because the mold has a metal chill plate at the bottom, the molten metal solidifies directionally, so that the yield of the product is high. With the inventive method the active metal does not react on the mold even if it is cooled very slowly, since the mold is mainly composed of calcia. The invention will be explained in accordance with the drawing. Figure 1 is an explanatory side elevational view of an embodiment according to the present invention; and Figure 2 is an explanatory side elevational view of a further embodiment according to the inventive method. Figs. 1 and 2 are respectively side elevational views of preferred embodiments of the casting method. In the embodiment shown in Fig. 1 a bottomless calcia mold 31 (having a cylindrical configuration and the cavity has a slightly tapered configuration toward the lower side in this embodiment) is placed on a metal chill plate 32, and a riser sleeve 33 of the same calcia is placed on the upper side of the mold 31. The metal chill plate 32 in Fig. 1 is a single-sheet plate, and the central part of the upper surface is recessed in this embodiment for receiving the calcia mold 31 (the recessed portion is not essential). The embodiment shown in Fig. 2 has the same structure as that of the embodiment in Fig. 1 except that an insulating member 34 is used in place of the calcia riser sleeve 33. In the present invention, a molten metal is poured into the bottomless calcia mold 31 by top-pouring. The poured molten metal is cooled by the metal chill plate 32 and gradually solidified from the lower part. The cooling speed is higher than that of a calcia mold having no metal chill plate, so that the position of the shrinkage cavity becomes higher. Further, the riser of the mold is insulated by the calcia riser sleeve 33 or the insulating member 34, whereby the position of the shrinkage cavity become even higher. In the present invention, the calcia riser sleeve 33 and the insulating member 34 may incorporate a heating medium, or the calcia riser sleeve 33 and the insulating member 34 may have a structure which is capable of heating so as to retain the heat of the riser of the mold by providing heat therefor. It will be possible to make the position of the shrinkage cavity still higher by heating in this way. In the method of the present invention, a calcia mold which is made by molding a calcia particulate molding material together with an appropriate non-aqueous binder, and baking the molded body is preferably used. The calcia particulate molding material preferably contains not less than 60 %, more preferably not less than 80 % calcia. Especially in the case of pouring highly active molten metal such as pure chromium, chromium alloy, pure titanium and titanium alloy (especially high titanium alloy), a high-purity calcia mold containing not less than 90 % calcia is preferably used. As the metal chill plate 32, ordinary steel plate, cast iron plate, copper plate and the like are preferable. In the case of using a metal chill plate of a water-cooling system, a copper plate is preferable. As the material of the riser sleeve 33, calcia, graphite, and a refractory material containing an exothermic ingredient are preferable. A graphite insulating member facilitates the heating and the heat retaining of the riser of the mold by electrically heating or induction heating. When a calcia insulating member is used, if the member is made of metal powder which is mixed, molded and baked, heat retaining is also possible by induction heating. It is preferable that the calcia mold has a porosity of 30 to 70 vol%, more preferably about 40 to 50 vol%. As an experiment, a chromium alloy was poured in accordance with the embodiments shown in Figs. 1 and 2. The dimensions of the mold 31, the metal chill plate 32 and the insulating member 34 are described in Figs. 1 and 2. The riser sleeve 33 was an insulating sleeve made of calcia which was the same material as that of the mold. The metal chill plates 32 in Figs. 1 and 2 were made of copper. As a result of pouring the chromium alloy, the shrinkage cavity in Fig. 1 was produced at a position 1.4 cm deep from the top surface of the mold, and the shrinkage cavity in Fig. 6 at a position 0 cm deep from the top surface of the mold 31. The next experiment was carried out for comparison. A chromium alloy was poured in the same way as in the method shown in Fig. 2 except that the bottom part of the mold 31 was closed by a calcia refractory material in place of the metal chill plate 32. As a result, the shrinkage cavity was produced at a position of 2.8 cm deep from the top surface of the mold.

Claims: A casting method comprising the steps of: placing a bottomless porous calcia mould (31) having a porosity of 30 to 70 vol% on a metal chill plate (32) pouring a molten metal by top-pouring; and gradually solidifying said molten metal from a lower part while insulating the riser of said mould. A method according to claim 1, wherein said calcia mould contains not less than 60wt% CaO.

Inventors: DEGAWA, TORU, FUJIWARA, KOZO, HASHIMOTO, AKIO, OKUYAMA, GEN, SATO, TAKASHI, UCHIDA, SEIJU
Applicants: MITSUI ENGINEERING & SHIPBUILDING CO., LTD
Application year: 1987
Main classification: B22C1
IPC codes: B22C1, B22C9