The Bell System is recognized as the conventional, foundational mechanism for charging raw materials, or burden, into the blast furnace.
This system, typically employing a double-bell (or cup and cone) structure, serves two critical functions. First, it acts as a high-pressure airlock, sequentially opening the small bell then the large bell to prevent pressurized blast furnace gas from escaping the top.
Second, and equally vital, the rotation and timing of the bells control the radial burden distribution of coke and ore inside the shaft. While newer bell-less top (BLT) systems offer finer control, the integrity of the bell system's seal and its impact on gas flow remain central to stable, efficient iron production.