Slab reheating

As discussed earlier, slab reheating in the conventional strip process route is achieved by burning natural gas or other fuels in a reheat furnace. In the thin slab casting route, equalization of slab temperature is usually achieved in a natural-gas-combusted tunnel furnace. The common feature in these processes is that the slab is oxidizing in an atmosphere containing a mixture of several gas species. Normally, the furnaces are operated under air-rich combustion conditions, i.e. more than sufficient amounts of air are used to react with the fuels introduced to the furnaces, and therefore, when in equilibrium, the... 

Annealed Metal. A slab 40 mm. thick at an initial temperature of 450° is reduced to the required thickness by hot rolling, without intermediate reheating, and is finally annealed at 350°. 

Cameras observe slabs or billets as they are set on "walking beams" to be moved through reheat furnaces. They also monitor the center of the furnaces for proper distance between slabs and to be sure slabs are held properly before they are lifted from the furnace and placed on the rolling or forge line. In these applications, a lens with a forward-oblique 45° direction of view often furnishes a useful perspective as it views the material within the furnace (see Figure 16.9). 

For application in steel reheating furnaces, uniform temperature distribution in the entire furnace section is achieved due to dispersed flame in addition to the advantages of energy saving and low NO. Skid marks of the slab can be diminished with the dispersed flame in a steel reheating furnace. Example of skid mark reduction is shown in Figure 21.22. 

Fig. 5.22. Eight-zone reheat furnace, side sectional view with an aerial perspective view inset at top right. This furnace has longitudinal firing in all but zones 5 and 6, which are roof fired. Billets or slabs move from left to right, and poc move from right to left. An unfired preheat zone is left of zones 1 and 2.

These one-way-fired pits were fired with blast furnace gas, coke oven gas, natural gas, or heavy oil. With the number of these pits in operation, it is a wonder that more data are not available concerning their deficiencies. They were built to supply primary mills which rolled ingots into slabs, rounds, and bars, all to be reheated and rolled into finished products, but they had temperature differences longitudinally and top to bottom. 

The steel ingot obtained from the furnace is reheated to provide uniform temperature for further processing or hot forming. The ingot steel is generally processed in a blooming mill or slab mill to form plates, sheets, strip, skelp, and bars. 

W. Beck, Comparison of Carbon Steel, Alonized Type 304 for Use as Dummy Slabs in Reheat Furnace Operation, Alon Processing, Inc., Tarentum, PA... 

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