Studies have been made on the shrinkage cavity formation in extra hypereutectic spheroidal graphite irons with high silicon content cast in metallic molds. Increasing silicon content to 3.0 to 3.3% in specimens containing 3.4 to 3.6%C (carbon equivalent 4.5 to 4.6) for preventing chill formation yielded sound castings. When carbon equivalent exceeded about 4.6% by increasing silicon content above 3.3% , however, shrinkage cavities were formed in areas which were judged to be hot spots. Observation of graphite morphology of the specimens with shrinkage cavities revealed presence of large spheroidal graphites, about 10 counts or more per mm². The shrinkage area increased with an increase in the number of the large graphites. It was reasoned that large primary graphites were generated during the spheroidizing treatment and kept in the melt up to the time of pouring, which resulted in less graphite crystallizing during freezing in the mold.

View full abstract

  Experimental studies were carried out on a riserless casting system utilizing feeding effect through the gating system. In order to get a sound casting, it is necessary that the molten melal is fed through the entire course of shrinkage of the molten metal in the casting, because if a shrinkage cavity is once formed, even though it may later be refilled by the expanding metal in the eutectic solidification process, the refilled area can not be expected to be fully sound. Until the fraction of solid metal in the sprue reaches 0.4 there will be a sufficient feeding effect through the gating system, provided that there is no excessive solidification in the runner and ingate.

View full abstract

  The purpose of this paper is to present an on-line moldability control system for the mulling process of molding sand. A microcomputer-aided equipment for water supply has been developed to improve the reliability of an actuator part of the system. Dynamic analysis has been done on the mulling process of molding sand with bentonite(clay) ratio 6 to 10%. An auto-tuning PID control algorithm is presented to provide a consistent control quality of sand whose conditions tend to vary widely from batch to batch. The system proved feasible through laboratory experiments with respect to both control precision and mulling time saving.

View full abstract

  Gray cast iron, high manganese cast iron, high phosphorus cast iron and the latter with some alloying additions were tested by a high speed friction tester to study the influence of alloying elements on friction and wear characteristics of the irons. Test pieces of the cast irons were pressed against a rotaing disk made of a steel for train wheel, with friction speed from 7 to 42 m/s and pressure from 0.55 and 0.75 MPa. It was found that phosphorus addition improves the frictional coefficient and chromium addition stabilizes the friction coefficient at high speed.

View full abstract

  Vanadium carbide layers formed on grey or ductile cast irons when immersed in molten borax baths containing vanadium are as dense as those formed on steels. Since the growth rate of VC layers on graphites in the cast irons is smaller than that on the matrix, pits are formed on the graphites in the beginning of the growth when VC layers are thin. But these pits disappear gradually with the growth of VC layers. The growth rate of VC layers on spheroidal graphites in ductile cast iron is smaller than that on artificially made bulk graphites. Initially growth rate of VC on spheroidal graphite is slower at the center of graphite than at the edge. Intermediate iron carbide layers containing small amount of V and Cr form between the matrix and VC layers and between the matrix and graphites which are in contact with the VC layers.

View full abstract

  Dynamic fracture toughness of heavy-wall nodular iron castings for containers was evaluated mainly by CAI system (Computer Aided Instrumented Chapy Impact Testing System), an evaluation system developed by the authors. The elastic-plastic fracture toughness value (J_d) and the stable crack growth toughness value (T_mat) were successfully evaluated by the system. Furthermore, β_IC method and impact response curve method have been applied in the transition region and low temperature region, respectively. As a result, it was found that these methods give dynamic fracture toughness values near the lower boundary values as obtained by the conventional test method. Incidentally elastic-plastic fracture toughness is generally known to be affected by the specimen size. The valid condition for the specimen size determined under dynamic loading condition was on the severer side than that of ASTM E813. Constant J_d value was obtained by using the side grooved Charpy type specimen with the thickness of 20mm, the net thickness being 16mm.

View full abstract

  Relationship between the structure of cast irons and the ultrasonic velocity was investigated with the following results :
  (1) Ultrasonic velocity V was quite sensitive to the structure of cast iron.
  (2) Velocity V was influenced by the graphite structure in that V increased with an increase in spheroidization ratio or graphite shape factor and with a decrease in size, nodule number and area fraction of graphite. Correlation between these factors and V was close when structure and phase ratio of the matrix were kept similar.
  (3) V was also influenced by the matrix structure in such a way that V increased with an increase in matrix hardness when graphite structure was kept similar. Various heat treatments to change the matrix resulted in decrease in V as compared with the structure after casting.
  (4) Structure of cast iron can be quantitatively assessed by measuring the ultrasonic velocity V, provided that the manufacturing history of the iron is known.

View full abstract