발간논문

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To investigate the effect of surface free energy difference between plain and cerium-treated cast iron, the wettability between iron and graphite was compared by means of contact angle measurements in the two cases, namely, where cerium was preliminarily coated on the graphite surface, and where not coated. The result was such that a significant difference in the contact angles has been shown to exist between the above two cases, indicating the presence of a minimum wettability at a critical concentration of cerium in the iron-graphite interface. It is further noted from X-ray and Laser microprobe analysis that some compounds of nodulizing elements are formed during the melting of the iron samples and these may have a nucleating influence on the formation of graphite nodules. The foregoing results imply that the nodule formation of the graphite may be due to the increase of interfacial energy between melt and graphite by the adsorption of cerium or magnesium vapour on the graphite surface, or to the nucleation of graphite by some compounds of nodulizing elements formed during melting, or both.

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The object of this study was to find an optimum work standard for economic manufacturing of nodular graphite iron in Korea. A 0.5 ton/hr capacity acid lined existing cupola was chosen for melting because the majority of 290 foundries in Korea operate acid lined anthracite fired cupola. Nodular graphite iron costed from the melts resulted from various (imported) coke ratio and air blow rate were examined their microstructure, composition and mechanical properties. The optimum was found to be 14 w/o coke ratio, 24㎥/min blow rate and 0.04% residual magnesium; this was rather cheaper way than a case that uses anthracite fuel in this country.

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In this study, copper coin and copper spoon were mainly investigated as the bronze objects in Koryo-Lee Dynasties. The relationship of composition of base alloy and corrosion film, metallograpy of structure, some of corrosion tests, and reduction techniques of corrosion film etc, were carried out in this study. The composition of bronze objects were mainly Cu, Pb, Zn, and Sn, and these compositions were different by the age produced. Black patina is better protective film compared with green patina, and tendency of its formation is gradually increased by the increasing of Sn content.

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Through the anther`s experiences on manufacturing of over forty paper-making dryers an optimum condition was drawn out. Although the shape of a dryer shell appears very simple, there are lots of difficulties in practical manufacturing such as composition and microstructure control for physical and mechanical requirements of a paper dryer. Sorbite structure is recommended as the most foreign makers prefer. The optimum allowances of shell shrinkage and machining are 8/1000 and l0㎜ out diameter (5㎜ inside dia)respectively. Pouring temperature was recommended to be near 1380℃ with the pouring rate of about 230㎏/sec. The 1:1:1 ratio of sprue, runner and gate and top pouring through 2 or 4 down sprues gave satisfied results of the castings.

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Corrosion of underground water pipe lines under the control of the Seoul City Administration are chiefly attributed to stray currents, soil, water and bacteria, according to this study on the corrosions of the water pipe lines in Seoul City. The stray current corrosion due to leakage current from the street-car rails was most severe in the area near a substation and it is considered possible to determine the location and capacity of a drainer of such current by measuring the potential difference between the pipe and ground involved. The soil corrosivity is dependent upon soil characteristics such as resistivity, pH value and corrosive substance, and a contact between heterogeneous soils accelerates the corrosive effect because of a long cell formed owing to the difference in soil texture. The concentration of hydrogen ions and oxygen dissolved, contents of sulfate and chlorine ions, turbidity and evaporation residues in raw and purified water are the factors exerting corrosive effect, although such factors vary by the location of a water supply basin and by season. The microbic corrosion is basically an electrochemical action in the last analysis, although its degree varies according to the kinds of bacteria, and it is considered that this type of corrosion can be prevented by a cathodic protection technique.

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