Recently, the study of coreless-type low frequency furnace is being made increasingly, but little work has been done on the erosion of lining. With this in mind, authors have made the study of the dry process lining for 1.5t low frequency induction furnace to clarity the actual condition of erosion and study the method of understanding it by measuring the degree of erosion and comparing the characteristics by using the tool. The results are as follows :
  (1) Concave or convex deformation is remarkable especially on the basic lining.
  (2) The degree of erosion on the bottom is larger than that on the wall. The difference in between the upper and the lower wall is not remarkable. However, the erosion on the bottom erosion increases correspondingly to the number of melting.
  (3) A new method of study in which the measured point is moved from the top to the bottom in a spiral by a tool and the values are put in increasing order was devised. The merit of this method is in showing the degree of the changes in the lining configuration by the whole gradient of the curve and the movement of the cross point on the 0-line.

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  It has been confirmed by one of the authors that various properties of gray cast iron are improved by reducing sulphur content in the pig iron to the minimum, presumably due to the change of graphite and other structures by the decrease of sulphur content. Generally speaking, when sulphur is contained in the molten pig iron, it tends to decrease the interfacial energy between the molten pig and the austenite, making it easy to precipitate on the graphite piece through the austenite phase.
  It is said, therefore, that as the sulpher content increases, the distance between the graphite pieces becomes so much wider, and the graphite pieces become so much large or coarse. On the contrary, if the sulphur content is reduced to the minimum, the graphite pieces become smaller, thereby if the improving the mechanical proprties. It is also said that sulphur and manganese contained togetrher in the pig iron will form a stable sulphide such as MnS, and that, if their quantity is increased, graphite tends to become larger. The effect of sulphur content on the mechanical properties of the gray cast iron may vary depending upon the quantity of manganese simultaneously contained, and also may be influenced by the silicon content, which is an element that accelerates graphitization. After studying these relations, it has been verified that sulphur content being the main factor giving great influence to the mechanial properties, the lower the sulphur content, is the better the mechanical properties are.

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  By adding a small amount of boron, cast iron with a characteristic microstructure (fine mottled structure) can be prodused. In order to clarify the process by which such a characteristic structture can be obtained, authors studied the changes in microstructure and the cooling curve, when different amounts of boron were added to Fe-C and Fe-C-Si-Mn melts. Moreover, cast specimens which were composed of three cylindrical parts with different diameters (40, 20, 10mm) were made from cast iron with various boron contents, and the number or the shape of austenite-graphite entectic cells was counted. The results obtained can be summarized as follows :
  (1) By adding boron to a hypoeutectic cast iron melt, the primary austenite arrest temperature in the cooling curve can be lowered, and the carbon content of the eutectic liquid can presumably be lowered also.
  (2) When the amount of boron is increased, the progress of austenite-graphite eutectic solidification slows down; and in mid-progress, austenite-carbide-eutectic solidification takes place.
  (3) As boron content increases, the structure of Fe-C-B alloy changes from a normal gray cast iron structure to a white cast iron structure. As an intermediate structure, white cast iron structure contatining fine graphite eutectic cells or irregularly shaped lump graphite can be observed. In Fe-C-Si-Mn-B alloy, a greater amount of graphite can be observed compared to Fe-C-B alloy, and a fine mottled structure with flake graphite and carbide can be obtained.
  (4) Addition of boron increases the number of austenite-graphite eutectic cells and tends to make the shape of the cells irregular.
  (5) Boron seems to slow down the growth rate of austenite-graphite eutectic cells, and seems to be enriched in the remaining liquid as eutectic solidification proceeds.
  These results would explain the specific process and microstructure of boron containing cast iron.

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  In an earlier study, the authors observed various changes of spheroidal graphite cast iron heated repeatedly in high vacuum up to the final stage of growth and elucidated the inner structural changes of the cast iron with the increase in irreversible expansion.
  In this investgation, an identical experiment was tried on flake cast iron which is easily affected by the heating atmosphere because of the shape of the flake graphite. From these experiments, a new clue to clarifying the effect of heating atmosphere was found, which is one of the most important variables associated with the growth characteristics of cast iron. The results obtained were summarized as follows ;
  (1) Growth increased continuously and reached teh maximum value of 19.4% after 235 heating cycles, and it was observed that the growth to the final stage was due to the mechanism of irreversible graphite migration.
  (2) The growth process up to the final stage was divided into four stages. In the first stage (up to the linear growth of 5%) the growth rate decreased rapidly; in the second stage (up to 11%) the cast iron grew at a constant rate; in the third stage (up to 19%) gorwth was saturated and reached the maximum value; and in fourth stage the cast iron contracted slightly.
  (3) When the growth reached a value of 5%, the structure of cast iron became porous. As a result, growth was restricted by the intermediate measuring of length in air carried out between heatings in high vacuum.

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  In order to study the adaptability of sorbitol, which is an organic matter with hydrophile radical, for a molding sand binder the following experiments were carried out : (1) various properties of cement-sorbitol self hardening molding sand, using sorbitol as a binder, (2) improvements in properties of molding sand by adding sorbitol using to molasses-cement type fluidized molding sand, (3) some experiments which support chelating reaction of cement and sorbitol.
  The following points became evident from the results of the above experiments :
  (1) Sorbitol chelates with the mineral composition of cement.
  (2) When once hardened sand is shattered to pieces, compounded and then mulled again together with water, it tends to herden gradually.
  (3) Sorbitol, cement and moisture are closely related to each other and the herdening time can be contorolled by adjusting the quantity of each of these materials.
  (4) The strength necessary for sand mold can be obtained from sorbitol when it is used as a binder for self-hardening molding sand.
  (5) Fluidization can be obtained with low moisture. Besides it extends the life of the fluidized bench.
  (6) Residual moisture within sand mold is under 2.0% after leaving for 24 hours. Accordingly, the time necessary for drying will be reduced.
  (7) Sand burning or penetration is rare even in thick casting.
  (8) Sand collapsibility can be improved.

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