Raw Materials from Steel Industry

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About 70% of all Refractory Products are used un the steel industry.

Raw materials are more & more expensive and scarce.

For this reason Refractory Manufactures find difficult to control the price of their products.

All of this take us in two topics of study:

1.- Recycling of raw materials.

2.- Production of synthetic high valued, raw materials.

Interesting article written by:

F.Richter, H. Seifer “Refractory Raw Materials from the Steel Industry”,refractories worldforum 5 (2013) [1] 83-86

http://www.refractories-worldforum.com/

 

Why slag may appear adhered to the lining?

The slag adhered to the silicon lining carries an inefficient running of the furnace. It can be low or high melting point.

Low melting point. When the furnace works at low temperatures silicon oxide is formed and it sticks to the walls of the lining as:

Si metal + O2 > SiO2 slag

High melting point. Slag difficult to eliminate are formed because these have higher melting point than the own lining:

2 FeO oxidized load + Si metal > 2 Fe + Si O2 slag.

Al metal >Al2O3 + SiO2 lining >Al2O3 SiO2 mullitic slag.

What can happen?

In any of two cases the furnace loses capacity, increases the risk of cracks forming, presents and irregular melting with distinct areas of magnetic behaviour , in short the life of the furnace decreases.

What to do?

It is indispensable to analyse the reason of this regrowth.

With low point of melting slag, raise the metal level and proceed to raise the temperature up to eliminate it. With high point of melting slag, it is indispensable to analyse the load and used additives. Often high concentrations of Si appear in FeSi causing of this problem.

 

Why does Zn appear against the mica during the demolition of the lining?

The presence of Zn in the demolition is associated with its presence in the used load and with the incorrect melting of the same one in the furnace of induction.

The Zn  volatilizes at 919 ºC going from solid form (of galvanic sheets) to gas. In gas form it penetrates in the pores of the lining and having found its isotherm of solidification at 419 ºC solid form happens again.

What happen?

If coils are in poor condition Zn can be resposible for arches between turns.

What to do?

– Improve the densification of the lining.

– Proceed to change the way fo providing the metallic load. The galvanized package should be introduced once the furnace has enough metal and temperature.

 

 

What is the difference between acid and boric oxide?

Boric acid is the hydrated form (it contains water) of boric oxide (anhydrous form or free water). Boric acid H3BO3 at low temperature (less than 150ºC) decomposes to boric oxide (B2O3) and water (H2O) representing approximately 44% by weight.

This means thta when we have 10 kg of boric acid in a lining it will descompose releasing 4,4 kg of water.

This fact should be taken into account when the suitable percentage and the definition of the curve of sintered are chosen.

From the point of view of thermal behaviour the major dispersion of boric acid makes that the lining presents a better light mechanical resistance than the similar percentage in boric oxide.

Why do small black balls appear in the lining when it is demolished?

Carbon monoxide produced of the oxidation of the carbon of the metal spreads across the porous zones of the silicon lining where it dissociates itself depositing coal.

2C metal + O2 (air) >2 CO (gas) > C + O2

What can happen?

It does not have effect on the refractoriness of the mass. However, in old or poorly conditioned coils it can cause arches between turns.

What to do?

– Avoid overheating.

– Do not put the graphite into the empty furnace.

– Increase the density of the area by improving material quality and / or vibration.