Refractory Materials Used In the Melting Chamber

The melting chamber is composed of the bath, wall and roof, etc. it is a part of an open hearth. It works at 1700℃ or 1750℃ when blowing oxygen. The linings of the melting chamber are subjected to high temperature, dramatic changes in temperature, corrosion by molten slags, erosion by molten steel and impacts by the machines and materials when loading materials, so the working conditions are harsh. 

The melting batch consists of the bottom and the embankment. It works at 1600℃. It is subjected to temperature changes, mechanical impact and chemical corrosion. The slag line area is damaged fastest, so it is the weak point. Its thickness varies with the loading capacity, generally 560-1040mm. The bottom adopts a composite structure. First, a layer of asbestos is laid on the steel shell, then a layer of fireclay bricks and finally a layer of magnesia bricks. The first layer should be laid on flat and the other two layers are laid on edge or on end. But the top layer should be laid in the direction of the center line of the tapping hole to avoid being damaged when tapping. The structure of the bottom has been changed since 1985. When laying magnesia bricks, a 200mm layer of magnesia sand layer is added. 

 

Before loading, the layer of magnesia sand should be sintered into a dense integral lining to prevent the corrosion by molten steel and molten slag. This layer is composed of high magnesium synthetic sand and high iron synthetic sand with low melting substances as the binding phase. However, oxygen blowing cannot be used in this type of melting chambers to strengthen the smelting. In oxygen smelting open hearths, the magnesia sand layer should be composed of fused magnesia sand and reheated magnesia sand without mineralizing agents. Its service life can reach up to 60 times. Each time after tapping, the slag lines area and the bottom should be supplemented with magnesia sand. 

 

The wall refers to the brick masonry above the door. It is connected with the embankment and roof. It works at 1700℃. The wall structure and divided into the end wall, front wall and back wall. It is dry laid with magnesia bricks. The joints should be no more than 2mm and inserted with a 0.5mm thin iron plate, which can make the brick masonry an entirety after fired at high temperature. 

 

When loading, the front wall withstands the impact and wear by the feeding machine and dramatic temperature changes. So, it has a short service life and requires routine maintenance. When the open hearth is repaired, the front wall will be completely replaced and rebuilt. The back wall may also need partial repair. According to the capacity of the open hearth, 3-5 doors are installed in the front wall for loading and repair. 

 

The roof is to maximize the reflected heat from the flame to the molten bath and control the the flow of combustion gases. The roof is in an arched and suspended structure. It works at 1700℃, or 1750℃ when blowing oxygen. After tapping or during loading and repair, the temperature in the roof will drop a lot, so the roof withstands high temperature and dramatic temperature changes as well as corrosion by molten slags and molten steel and erosion by high temperature gas flow. It is easy to be corroded and flaked. It is the weakest point in the chamber. A entire use cycle is a campaign. It represents the service life of the open hearth and is the number of smelting.  

 

In the last century, the roof was mainly built with magnesia chrome bricks or magnesia alumina spinel bricks. With the emergency of new technologies, middle-grade magnesia alumina bricks and magnesia chrome bricks are developed to meet the requirements and have achieved good results.