The resistance to heat-check of cast metal materials generally used at high temperatures was examined. Sixteen kinds of cast alloy metal were tested and compared under two thermal patterns with an apparatus designed by the authors.
  From the test results, it was recognized that the appearance of heat-check differed remarkably among various materials, and moreover that heat-check formed under these testing conditions could be classified into three types according to their appearance.
  Since the resistance to heat-check differed among various materials, it was difficult to make a simple analyses of the results. However, the resistance to heat-check of these sixteen kinds of cast alloy could be evaluated and fundametal data necessary for future improvements in heat-check resistance were obtained. It must be emphasized that each material should be tested under conditions simulating actual service.

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  The constitution and porosity changes on heating, wettability on steel surfaces and moisture absorption were investigated on metal mold casting washes using 20% aluminum dihydrogen phosphate solution (PH≃1.5) as a bonding material. Different amounts of chromium phosphate, were added into the solution for the modification of the wash composition. A comparative investigation was made for metal mold casting washes using 15% water glasssolution (Na₂O/SiO₂ mol ratio=1: 2.1) as another bonding material.
  The results can be summarized as follows :
  (1) Aluminum trimeta- and/or ortho-phosphates are the major constituents of phosphate washes whem the washes are heated up to temperatures of 700-1,000°C.
  (2) A non-crystalline state is easily attained by a heat treatment of phosphate washes modified by a suitable amount of chromium cation. The temperature range of the achievement is increased with increasing the cation content.
  (3) The crystallization of water glass washes at temperatures below the solidification range can be explained by the concepts of crystal nucleation and growth of super-cooled liquid.
  (4) The porosity of phosphate washes is largely increased on heating the washes modified by the chromium cation (>about 0.02 mol per 100g. of 20% dihydrogen phosphate solution) from 300 to 1,000°C. The porosity is increased with increasing the cation content, and with decreasing the content of silica flour included as an aggregate. The temperature range for the attainment of maximum porosity is 700-800°C.
  (5) The porosity of water glass washes decreases when the washes are heated to the crystallization temperature range.
  (6) The matrix of porous phosphate washes (max. porosity : about 98%) is the noncrystalline solid including finely dispersed pores (dimension??0.1mm). The effectiveness of this matrix in the prevention from chilling a cast iron can be explained by the concept of heat conduction in the system solid and pore components.
  (7) The contact angle on a steel surface is smaller for the aluminum dihydrogen phosphate bonding agent than for the water glass bonding agent. The decrease in the angle with time is larger for the former than for the latter : This suggests the easier formation of chemical bonds and leads to give an increased adhesion at the interface of metal mold and wash in the former.
  (8) The moisture absorption by the modified phosphate washes is comparatively small. This leads to decrease in the defects caused by water vapor excessively evolved from washes during the casting. process.
  The above results suggests the superiority in both thermal insulation and durability of the modified aluminum phosphate washes for the metal mold casting of cast iron.

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  When dicalcium silicate powder is added to sodium silicate solution, a gelling reaction takes place. In this investigation, the relationship between the chemical reaction of these calcium salts and the strength after self-hardening of the sodium silicate is reported, using 2CaO•SiO₂, Ca(OH)₂ and CaSiO₃ as additives to sodium silicate solution. Materials used in the experiments included the following :
  (1) The powdered 2CaO•SiO₂ used in all mixes was analysed as 50.4%CaO, 27.0%SiO₂ and 22.6% others. It was furnished with a fineness of 100% minus 200 mesh and 80 to 90% minus 350 mesh.
  (2) The mixtures were made with sodium silicates having a 3.2 and 2.5SiO₂/Na₂O ratio.
  (3) The ratio of sodium silicate solution weight to powdered 2CaO•SiO₂ weight was 2.
Properties measured were :
  (1) compressive strength
  (2) shutter toughness
  (3) retained moisturs content
The hardening conditions of each were :
  (1) In the atmosphere at room temperature
  (2) In the sealed box at room temperature
(3) drying for 3 hours at 105°C.
The conclusions are as follows :
  The strength after self-hardening decreased with the increase in Ca(OH)₂ and CaSiO₃ cotent in the mixture, as well as with the dilution of the concentration of the sodium silicate solution, but it was not much influenced by the amount of retained moisture. This is because congelations retaining 11% moisture develop compressive strength of 140 kg. per sq. cm. after curing for 5 days in the sealed box. This strength can be matched by congelations retaining 5% moisture in the atmosphere. The sodium silicate solution is dehydrated or dried so that the sodium silicate glass is left as the bonding material.

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  In order to investigate the effects of silicon carbide addition to cast iron, experiments were made with a low frequency induction furnace of 500kg capacity lined with fused silica. The experiments were devided into two series. One was the silicon carbide addition series in which silicon carbide was used for composition control and the other was the ferro-silicon series in which ferro-silicon was added for composition control. The quality of melt was examined by comparing the melts in the two series. Heats were repeated five times in both series. In order to study the effect of accumulation of the additives 0.7% in case of silicon carbide and 0.65% in case of ferro-silicon were added to the charging materials in each heat which consisted of 80% scrap returned from the previous heat and 20% steel scrap. These amount of additions were decided so that the same silicon content will be maintained in each melt, and the carbon content was controlled with a carburization material. The first heats in both series were made with the starting blocks which had been prepared by another heat so that they had identical heredity and chemical composition.
  Mechanical properties, structure of graphites and character of shrinkages were mainly examined through these experiments and the following conclusions were obtained :
  1) Mechanical strength increased by the addition of silicon carbide. In the case of ferro-silicon addition the same phenomena were also observed.
  2) The graphite structures of silicon carbide added melt was mainly the A type, but those of ferro-silicon addition were a mixture of A, D and E type graphites. Therefore the silicon carbide added iron would be of better quality than the ferro-silicon added iron.
  3) The silicon carbide added melt showed skin formation type of solidification. On the other hand, the ferro-silicon added melt showed mushy type solidification. This is why the silicon carbide added iron showed less swelling and became a more compact casting. Shrinkage was found to be concentrated in the hot spots in castings and, therefore, risers may be used effectively in this case.

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  This paper considers the machinability of pearlite cast iron on SiC addition. The test pieces were cast from 80% returned material and 20% steel scrap with an addition of either 0.7%SiC or 0.65%FeSi. The following results were obtained.
  (1) On lathe turning, the machinability of cast iron was improved by repeated melting with SiC addition. The tangential cutting force showed little change by SiC addition, but the axial and radial forces showed considerable decrease. This indicates that the frictional force between the chip and the top rake surface of the tool is rather small.
  (2) There was only a slight effect on the crater wear of carbide tool with SiC, some debrises welded onto the bottom of crater with FeSi. This shows that there is a rather large friction between chip and top rake surface.

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