Efficiency and Temperature Considerations in Induction Re-Heating of Bar, Rod and Slab

This article describes several important design criteria used when designing modern in-line induction heating systems.

Modern techniques for producing long products such as cylindrical and rectangular shaped bars and rods integrate three stages of production-casting, re-heating and rolling-into a continuous line. The goal of re-heating is to provide the bar/rod at the rolling stage with the desired temperature profile across its thickness, diameter and length. In some cases, initial temperature of the product prior to re-heating is ambient. In other cases, the initial temperature is non-uniform due to uneven cooling of the rod/bar as it progresses from the caster.

In the past, gas-fired furnaces were typically used because of the low cost of gas. In recent years, however, bar/rod producers are shifting their preference toward induction heating systems. Gas-fired furnaces require a very long heating tunnel to achieve the desired temperature uniformity. The length presents a great problem in plants due to the limited space between the caster and rolling mill. Also, gas-firing can result in poor bar surface quality (due to scale, decarburization, etc.), and faces environmental restrictions. These factors resulted in heating by induction becoming the popular approach to re-heating bars and rods of both ferrous and nonferrous metals.[1]