鋳造法における最近の進歩

抄録

The object of the present lecture is to give a general idea of the progress made in recent years in the process of sand moulding and thereby to call up the interest of the members of the Japan Institute of Metals for general founding of metals. From the nature of this plan the author has endeavored mainly to make clear the principle of various processes of making moulds.
In the first section the nature of molding sand is discussed, giving mineral analysis of natural sands and studying the thermal expansion of quartz and feldspar, the main ingredients of sands. They expand linearly 1.4 per cent on heating them to 1200°C. Various casting defects such as rat tails, buckling and seabbing are caused by this expansion, especially by the abnormal expansion due to the α—β transformation of silica sand at 575°C, and also by the acute temperature gradient from the hottest mold skin to the coldest buck sand.
In the second section the natures of clay and bentonite are discussed. The process of making sand mold is after all the process of binding of sand grains and the recent progress has been made by studying how to utilize organic and inorganic binders. As inorganic binders we use clay and bentonite which develope their binding action by electrochemical action of their colloidal particles. However minute their particles may be, they have no bonding action without the aid of OH ions in their crystal structure. They are merely non-bonding ashes if they are dehydrated at high temperatures. In the case of organic binders the binding action is caused by resin-aus polymers. The drying of core oils and the curing of shell mold resins are the examples of this type. We have another group of binders such as ethyl silicate and water glass. In this group the bonding of silica sands is made by the gelling action of Si(OH)₄ deposited from alcoholic or aquaus solution. In any case, organic or inorganic, the viscosity of binders, the setting time and the strength after setting are the main items in actual molding practice.
Standing on these viewpoints, the author describes the crystalline nature of clayey minerals, their thermal contraction, their dehydration and recrystallization, referring to many papers from various sources.
In the 3rd section he discusses the drying phenomena of core oils, the mechanism of which is not yet clarified but in final analysis, the binding action of baked core oil is nothing but the binding action of resinous polymers.
In the 4th section the author discusses the shell molding process. It has been generally known that many modern synthetic resins were used as binders for glass fibers, rock wools and compound plates. The Croning process is not an inconicevable method if we imagine the past utilisation of resins as binders.
In the 5th section he explains the lost wax process, which is an oldest art of oriental founding. In ancient time, molders engraved wax, enbedded it in loam mold, melted out the wax pattern by heating, and thereafter they poured bronze. We have many bronze articles which could not be produced except by this process. The modern investment castings are manufactured by sand mold-bound by ethylsilicate solution, the silicic acid Si(OH)₄ being the binder of this process.
In the 6th and the last section he describes the recent development of CO₂ process. The polymerised silicic acid, deposited by the decomposition of sodium silicate by the action of CO₂ gas, is again a gelatinous binder of silica sand.
In conclusion the author emphasises that there are so many processes introduced into practice under the cooperation of chemistry. Every process has its own field of application, the classical process using sand and clay having the widest and the investment casting using wax pattern and ethyl silicate having its special field of practical application. And if we suppose that the shell molding process, for example, is applic