Limestone alone as a flux is not sufficient to give adequate protection to the melt, mainly because it's main fluxing ingredient calcium oxide is formed only after carbon dioxide is driven off from calcium carbonate at 825 deg c. On the other hand cupolux melts and reacts at a much lower temperature.
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">
style="height:250px;">