Two antagonistic properties i. e., higher modulus of elasticity and higher damping capacity are required simultaneously to piano frame with gray iron castings. With a view of improving the quality of present frame, damping capacity, natural frequency and power spectrum of gray cast iron specimen were analyzed by measuring the sound emission when the center of the specimen held at two fixed positions by tungsten wires was hammered on specially designed experimental apparatus. From results obtained, it has been clarified that the changing of matrix to ferritic from pearlitic raises damping capacity, but decreases power spectrum. The changing of matrix to pearlitic or martensitic from ferritic, however, lowers natural frequency which has been thought as the parameter of modulus of elasticity of cast iron.
Velocity field in a low pressure die casting was measured and compared with computer simulation. In the experiment, water was pushed up by gas pressure into transparent molds. The velocity in the water was measured by using nylon particles and laser beam. In the simulation, measured pressure was used for boundry condition. Shape of the water front and velocity in the water were rather well simulated until turbulent occurred.
This paper is intended to clarify sand compaction behavior during blowing molding process. Special attention has been paid to the effect of powder pressure vector on sand compaction. The results show that boundary line which is discontinuous parts in hardness distribution is produced in sand slip zone during blowing, and its appearance is influenced by powder pressure vector. Maximum values of powder pressure are shown to be correlated reasonably with the mold hardness index. This relationship does not depend on experimental conditions; arrangement of obstacle plate, vents, blow pressure value and so on. Maximum powder pressure can be divided into two kinds, namely one is peak pressure by kinetic (impact) energy of sand in early stage of blowing, another is powder pressure by air-flow in steady stage. An algorithm of blowing simulation model is given in accordance with the present results.
Dynamics of sand flow during blowing molding is investigated on the basis of simulations and experiments. The studies have been done on sand flow analysis for two dimensional model of core box ; one has a box-type obstacle in the cavity and another has two obstacle plates in the cavity. In the experiments, we have taken the photograph of sand filling using high-speed camera, and the influence of sand flow on sand filling and compaction has been clarified. This result shows that sand stream analysis in blowing molding is indispensable for reasonable designing of cavity and decision of molding conditions. Further, homogeneous mixing model has been applied to sand flow and simulation done. The simulated results of the flow explains reasonably the real phenomena. The measured and calculated values for arrival time of sand flow are shown to have same tendency. The present flow analysis can be developed into a blowing simulation which is aimed at predicting of final mold property and giving suggestions on optimal design of blowing condition.
The rooling contact fatigue strength tests were performed on austempered spheroidal graphite cast irons with graphite nodules ranging 120 to 800/mm2, by using Nishihara-type wear machine under a light oil lubricant. The irons were austenitized at 1148 K for 3600 s and then austempered at 648 K or 508 K for 7200 s. The relative sliding rate was fixed at 9 %. Rolling contact fatigue limit (F∗) of upper bainite iron decreased from 1400 MPa to 1200 MPa as graphite nodules increased from 120/mm2 to about 300∼350/mm2, and F∗ was almost unchanged with nodule count above 350/mm2. On the other hand, F∗ of lower bainite iron took the maximum value, 1700 MPa, at about 300∼350/mm2. The more graphite nodules, that is, less inter-nodule distance should shorten the fatigue limit, since fatigue crack tended to propagate through graphite nodules. However, the graphite nodules could make crack blunt and retard the crack propagation, especially in lower bainite iron. These functions of graphite nodules should influenece the fatigue limit.
Austempered ductile iron (ADI) exhibits a favorable combination of strength and toughness, and has been used as a substitute material for steel, for example, ball joint sockets and sliding parts of air-conditioner for automobile. ADI contains a large amount of retained austenite which contributes to the improvement of ductility and toughness. The content, distribution and morphology of the retained austenite are affected by the contents of alloying and trace elements. However, the effects of the raw materials and trace and alloying elements have not been clear. In this study, ductile irons were made from high purity pig iron, ordinary pig iron or high purity steel scrap. Manganese up to 0.7% and phosphorous up to 0.1% were added to the irons. Some of them were annealed in order to homogenize alloying and trace elements before austempering. The content, distribution and morphology of the retained austenite and the impact properties were measured. Following results were obtained. By using high purity ductile iron with low Mn content which made from high purity pig iron or high purity steel scrap, the rate of transformation of austenite to bainite is accelarated, and high impact property is obtained in a short period. In ADI with high Mn content, the rate is lowered by the segregation of Mn and the impact value is decreased by the large untransformed Mn-segregated area. High impact values are obtained by Mn-homogenizing anneal and by decreasing of untransformed austenite. In ADI with high phosphorous content, the impact property decreases a little.