Thermal stress developed in castings during solidification and subsequent cooling is closely connected with hot tear and dimensional accuracy of the castings. At high temperatures thermal stress results in gradual plastic deformation, namely, creep. As well known, there is a relation between the stress and the creep rate.
  In casting thermal shrinkage causes creep. In this case, even if the casting has a simple form, cooling will not occur uniformly. Besides mold or core will restrain it from free shrinkage. These unequal cooling and difficulty in shrinkage result in developing plastic deformation as the casting cools down. The creep rate ε is given as a function of the cooling rate (−Ṫ) and coefficient of thermal expansion α.
  For example, in case a casting of rod form is fixed at its both ends, the creep takes place at a rate of (−αṪ) in the lengthwise direction of the rod. If a plate casting is fixed at its border, the creep takes place similarly at a rate of (−αṪ) but the stress is expressed by a function of (−2αṪ). The stress developed in the crust of solidifying casting of plate form is compressive in the side near the mold wall but changes to be tensile with the distance from the mold. Namely, there is a neutral plane in the crust on which the stress changes from compression to tension.
  Stresses developed in a sphere casting are influenced by the conditions of liquid core at its center. If the core has neither feeding channel nor cavity, the radial stress increases with the approach of the center, it becoming the maximum at the center. The tangential stress is compressive near the surface, while it changes to be tensile with the approach of the center. The magnitude of the stresses can be estimated by solving simultaneous equations of the creep in relation to the thermal shrinkage of casting, if such conditions as distributions of temperature and cooling rate, material constants and so on are preliminaly given.

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  The curing rate of binders used for self curing molds is retarded depending upon the composition of silica sand. Paticularly, as the curing rate of furan resin binders is accelerated by acid catalysers, it is said that the curing rate is retarded as the value of PH of silica sand increases.
  The relationship between the composition of silica sand and curing rate of furan resin binders was examined in the present study. It was found that the ferrous oxide in silica sand was an important determinant. Furthermore, when the ferrous oxides take the form of Fe₃O₄ and FeO the retardation was observed to be even more remarkable.

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  White iron of various nitrogen content were crushed into sizes smaller than 100 mesh, and were electrolyzed by a special apparatus for isolation of cementite. The electrolyte was 0.5N-HCI and the anode potential was −0.2 V against calomel electrode.
  Nitrogen content of white iron and isolated cementite was analysed. In samples B and C, the nitrogen addition was in a molten state. The acid-soluble nitrogen in the cementite was 5-6 times as much as in the white iron. Acid-insoluble nitrogen was about two times as much. It is considered that the isolated cementites are almost all eutectic cementites. During primary solidification, nitrogen concentrates in the molten iron and in parts forms Si₃N₄. On eutectic solidification, a part of the Si₃N₄ is enveloped by the eutectic cementite and residual nitrogen in the molten iron enters into the cementite.
  Next, the isolated cementite was graphitized in vacuum. There was very little graphitization in annealing at 800° and 850°C. Therefore, the isolated cementite was annealed at 900°, 925° and 950°C and free-carbon in the cementite was determined. From the relation between the time of annealing and the degree of graphitization, it was observed that nitrogen in the cementite actually disturbs graphitization. The activation energy of nucleation increases with nitrogen content (Fig.1).
  The n value in y=1−exp(−t/k₁) ⁿ and the m value in y/1-y=k₂t ^m are very close to 1. Therefore, the growth of graphite is controlled by a diffusion process.

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  A study was carried out to elucidate factors influencing the structure of white cast irons solidified directionally in a mold with a copper chill block at the bottom. The results obtained are summerized as follows:
  (1) In hypo-eutectic alloys, primary austenite crystallizes as a columnar dendrite. The cooling rate at the beginning of the austenite crystallization, Vs, the local solidification time of the austenite crystallization, t_s, and the average cooling rate from casting temperature to 1000°C, Vm, at a position in a ingot are individually expressed as a function of the height from the bottom of the ingot to the position, h.
  (2) The width between the stalks, Z, and the arm spacing, Za, of the columnar dendrite of primary austenite in the hypo-eutectic iron-carbon alloy are related to Vs, t_s or Vm and carbon content.
  (3) An Addition of less than 1% of third elements such as silicon, manganese, phosphours and sulphur into the hypo-eutectic iron-carbon alloy has no effect on Z and Za of the columnar dendrite.
  (4) The lamellae in ledeburite which is one of lamellar eutectics tend to grow straight without changing the growth direction even in the case with the cellular solid-liquid interface. In such a growth mode lamellar structure becomes unstable at the locally undercooled region where cellular groove is formed and hence it is assumed that the lateral growth of the rod-like austenite from the lamellae must occur at its region. This morphology of ledeburite is called “dendritic” eutectic. It becomes clearer when the condition is such as to promote the development of cellular interface. Sucha condition is created by solidifying under smaller temperature gradient and using an alloy containing a third element of smaller distribution coefficient.
  (5) Since the third element with distribution coefficient of k<1 segregates on the ledeburite colony boundaries, impurities such as phosphorus and sulphur which have very small distribution coefficient form phosphide and sulphide on the boundaries.
  (6) The crystallographic relationship between cementite and austenite in ledeburite is not unique. However, it is found that there is the following relationship:
  lamellar interface//(001)θ//plane of austenite within 15 ° from {951}_r, and growth direction//
  [010]θ
  (7) In iron-carbon alloys the colony. size of ledeburite, Z_E, is inversely proportional to the square root of the cooling rate immediately after the solidification of ledeburite, V_E, and slightly increases with increasing carbon content.
  (8) In the presence of silicon, phosphorus or sulphur as the third element in the nearly eutectic alloys, the relationship between Z_E and V_E described in (7) is maintained, but in the case of manganese this relationship does not hold. The ledeburite colony size increases with increase in the content of the third element such as silicon, phosphorus and sulphur. The coasening effect of the third element for ledeburite colony size becomes larger with smaller distribution coefficient.
  (9) When the eutectic alloy solidified directionally is annealed at a temperature within austenite temperature range without eutectoid reaction after solidification, the rod-like austenite in ledeburite either becomes spherical or disappears, while lamellar austenite remains with little variation in shape. The graphitization of cementite in annealing starts at the colony boundaries.

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  The thermal resistance of a coating layer on the metal mold was measured. The coating material was composed of basic material (diatomaceous earth, zircon flour and graphite) and binder water glass (3.2mol ratio) diluted with water. A coating layer is formed when the coating material is decomposed on the heated surface of the metal mold on spraying.
  Measurement of thermal resistance was made under a steady state at comparatively low temperature using a solid metal in place of a molten metal. The results obtained were as follows.
  (1) The reproducibility of the values obtained for thermal resistance was very high. The thermal resistance of diatomaceous earth was highest followed by zircon flour and graphite was lowest.
  (2) The thermal resistance of diatomaceous earth decreased with the rise in the mean temperature of the coating layer, and that of zircon flour also decreased when the coating layer was thicker than 0.2mm. But it remained the same in zircon flour with a coating layer thinner than 0.2mm and in graphite.
  (3) In each of the coating layers, there was a linear increase in the thermal resistance with the increase in the thickness of the coating layer.
  (4) The thermal conductivity was in the order of 10^-4 (cal/cm sec°C) in each of the coating layer.
  (5) In the measurement of thermal diffusion by modified Ångström method, it is necessary to consider how samples should be prepared.

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  Radio active bentonite containing 30 or 15%CaCO₃ was used to investigate the mixing process of dry sand and clay. After some period for mixing, samples were collected and their cpm were measured. The degree of mixing was determined from the standard deviation of cpm in the samples.
  Results obtained are as follows :
  1. In order to obtain a uniform mixture of sand and bentonite, both crushing and mixing are required. Crushing is performed so that bentonite lumps may be broken down into fine powder.
  2. The uniformity of the mixture decreases as the bentonite content in the mixture increases.
  3. It is difficult to obtain a uniform mixture of coarse sand and bentonite because excess mixing tends to separate bentonite in the mixture, but uniformity can easily be obtained with fine sand.
  4. The optimum mixing period is 1 min. for coarse sand, and 2 min. for fine sand.

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