In a steel plant, the raking process (most commonly referred to as slag raking or de-slagging) is the mechanical method used to physically scrape and remove the floating layer of slag from the surface of molten iron or steel. As slag is less dense than molten metal, it floats to the top, much like oil on water. Raking is the brute-force, physical extraction of this layer.

Raking typically occurs at specific stages in the steelmaking process where the metal is held in a ladle. A very common location is right after the Hot Metal Desulfurization station (before the molten iron goes into the Basic Oxygen Furnace/BOF) or at the Ladle Metallurgy Furnace (LMF).

The process uses a massive piece of equipment called a de-slagging machine with a long, robust, hydraulically or pneumatically driven arm which literally drags or “rakes” the viscous, crusty slag over the lip of the ladle so it falls into a waiting slag pot below. 

The Role of Thermal Imaging in Raking

This is exactly where the Long-Wave Infrared (LWIR) cameras provide immense value. During the raking process, the operator controls the mechanical arm, often dealing with blinding glare, heavy smoke, and extreme heat. It can be very difficult for the human eye to see exactly when all the highly emissive slag has been successfully raked off, or if the rake is dipping too deep and accidentally pulling out valuable liquid metal.

By aiming a thermal camera at the ladle during the raking process, the operator gets a clear, real-time visual contrast on their monitor.  They can see exactly where the “hot/bright” slag remains and when the surface is completely clear, ensuring a highly efficient and clean de-slagging operation without wasting good steel. The processing or image acquisition happens only within the duration between IN and OUT signals of boom. This occurs for 3-4 seconds when no boom could be seen inside the ladle free board. Within this time only, the images are being captured for processing.