Abstract

Introduction

One of the most common technologies used in steel-making industries is Electric Arc Furnace (EAF). The EAF consists of a refractory-lined vessel, covered with a roof. The centre of the roof is called the delta and made of refractory product. Since more than 20 years, TRB is designing and producing deltas for EAF. The delta is composed of a refractory precast shape.

The wear mechanisms of delta roofs are not well known. This is one of the most affected parts of the EAF as it is subject to all kind of stresses, e.g. thermal, chemical and mechanical. The delta bottom surface is exposed to temperature by radiation and slag splashes. It is also exposed to corrosive action of slag and metal oxides. Since the design is also complicated because of the openings of the electrodes, water cooling arrangement etc. it is subjected to considerable mechanical stresses and thermal shocks causing spalling.

Material and methods

In order to contribute to a better knowledge of the processes of degradation, temperature measurements of a delta roof were performed on several campaigns. Measurements were made in different heights and positions using thermocouples. A data logger was used to record temperatures.

Temperature observed during one campaign isn’t very high, reaching a maximum of 700°C at 130 mm of the working lining. Knowing the thermal conductivity of the refractory, we expected the temperature on the hot face to be less than 1150°C. This result was confirmed by post mortem analysis of refractory on the hot face:  mineralogical phases observed after the campaign were formed between 1000°C and 1100°C.

Secondly, numerical simulation using finite element analysis helped us to understand the thermomechanical behaviour of the delta in operation. The results point out some specific location where we found stress concentration due to the cooling system or other process factor.

Results and conclusions

Thus, the instrumentation of delta roof allowed a better correlation between degradations and the process in service conditions.

On the other hand, temperature measurement and numerical simulation allow the development of new solution better armed to withstand against the stress level present in EAF roof.