Abstract
When metal is cut and ground with a grinder, chips are heated by friction and oxidation, and scattered, which look like sparks. The temperature varies depending on the particle properties with changing in time accordingly. It is difficult to obtain quantitative information simultaneously such as each particle size, unsteady velocity, and temperature varying over 1000 K. In the present study, we developed a new framework for estimating the particle size of pure iron sparks by fitting the equation of motion to the trajectory of the time-resolved images, and for calculating the spark temperature by solving the unsteady thermal equation. The validity is convinced through the comparison with the high-speed images, SEM images, and temperature measurement results. We succeeded in finding the time-dependent changes in temperature and heat balance, which are closely related to the colors of sparks, starting from the grinder to the end. The heat production by surface oxidization deteriorates as the spark decelerates due to the aerial drag force. The heat dissipation of heat transfer is dominantly affected by the spark temperature rather than the boundary layer thickness. The effect of the heat of fusion is insignificant in the temperature change.
