Measurement of Distribution of Charged Metal in the Mould by Activable Tracer Method

Abstract

It would be helpful to the understanding of the behavior of molten metal in a mold and the elucidation of its “run”, an important factor in the making of castings, to determine the distribution of each portion of molten metal and its mixing state caused by convection during its solidification process. In this study, the distribution of molten metal in a mold was investigated by the activable tracer method, with a real casting part. Au and Ir were used as the tracer elements, which were not originally included in the casting material and highly sensitive to the neutron activation method. In the preliminary experiment with a simpler mold, it was revealed that 0.005% addition was sufficient for either Au or Ir to be fully detected after 5 hr irradiation with a neutron flux of 2×10¹¹n/cm²/sec, followed by 24 hr of cooling and that the sampling for radiation detection should be carefully made because of incomplete mixing state of molten metal even in a preferred area. The mold in the experiment was a sand mold for the production of a cylinder head of an automotive engine. Molten metal was poured in three charges. The first charge contained Au, the second Ir and the third no tracer. About 10 g of sample was taken from each appropriate part of the casting, and subjected to the irradiation by neutrons with a flux of 2×10¹¹n/cm²/sec. The content percents of the first and second charges were determined from the measurement of the photo-peak area of gamma-rays at 0.41 (Au) and 0.31 (Ir) MeV, respectively. The remainder was assigned to the third charge.
From these observations, it was clarified that the first charge settled in the lower part in the mold, farthest from the sprue runner. The second and third charges tended to solidify in more upper layers. However, in some portions in the mold was definitely observed some degree of mixing by convection.