graphite refractory bricks
Graphite refractory bricks are made of carbonaceous materials and added with a suitable amount of binder to make high temperature and neutral refractory.
Material products. The raw materials of graphite refractory bricks include anthracite, coke and graphite, as well as pitch, tar and anthracene oil binders. Anthracite has less volatile matter and compact structure. When producing graphite refractory bricks, it is often used as aggregate, metallurgical coke is added, and pitch is used as binder.
The technical requirements of graphite refractory bricks are generally carbon content ≥92%; mechanical strength ≥25MPa; ash content ≤8%. The external dimensions are strictly required, and general products must undergo certain mechanical processing.
Quality introduction of graphite refractory bricks
1. Has extremely high refractoriness
Does not melt or soften. Only when the temperature is very high, there will be volatilization (>3000℃). But this temperature cannot be reached in a blast furnace.
2. High compressive strength.
Its compressive strength can reach 250～500kg/cm2, which is similar to sticky brick. However, the compressive strength of clay bricks can reach up to 1000kg/cm2.
3. The softening point under load is much higher than that of clay bricks. Generally, the load softening temperature of clay bricks is 1400℃, while the load softening temperature of graphite refractory bricks does not exist (that is, the softening point is extremely high), but it must be pointed out that this is only for high-quality graphite refractory bricks with low ash content.
4. The slag resistance is very good, except for the slag containing high FeO, no slag can play a corrosive effect.
5. It has high abrasion resistance, and its abrasion resistance is not inferior to clay bricks.
6. It is not infiltrated by iron and slag (iron slag can not be stained on graphite refractory bricks), so there is less chance of nodulation and damage due to iron and slag. Therefore, in the past, graphite refractory bricks were built on the furnace body, thinking that this might reduce the chance of nodulation (because generally furnace nodules are generated at the furnace body), but the results prove that if the operation is not normal, there will still be furnace nodules. .
7. The expansion coefficient is small. This is one of the characteristics of graphite refractory bricks, other refractory materials are far inferior to it. Rapid cooling at high temperatures will not cause cracks. This is an extremely desirable property for certain parts that are easily damaged due to cracks (such as the furnace bottom). Therefore, the furnace bottom bricks are mostly made of graphite refractory bricks.
8. The thermal conductivity is much higher than that of clay bricks, especially graphite bricks. But its effects can be beneficial or harmful. Large heat loss is a negative effect, but it is advantageous to easily generate slag in the lower part. When the lower part of the blast furnace is built with graphite refractory bricks, it can be cooled without cooling water, but only with air for natural cooling, and even some smaller blast furnace hearths do not need to be cooled at all. But generally the cooling water tank is still used, because sometimes the graphite refractory bricks are of poor quality and the hearth is easily destroyed. If there is no cooling water tank, the slag leakage accident will occur. At the same time, the installation of the cooling water tank is not very troublesome. Cooling water tanks are still used when using graphite refractory bricks.
The manufacture of graphite refractory bricks generally uses coke (<10 mm) with a small particle size and less ash content, and 16-18% coal tar is added and mixed uniformly. At the same time, it is crushed to 6 mm, and then press-formed. At the same time, the porosity is reduced. Finally, it is roasted in a sealed furnace for several days and nights at a roasting temperature of 1000°C. There should be no air gaps in this furnace; sand is used to cover the bricks during firing to completely isolate the bricks from air and heat the bricks by conduction. High fuel consumption and low output are the reasons for the high price of graphite refractory bricks.
Properties of graphite refractory bricks
Graphite refractory bricks have good thermal stability, low thermal expansion coefficient, high temperature resistance, corrosion resistance of various acids, alkalis, salts and organic solvents, but they are easily oxidized in an oxidizing atmosphere.
The graphite refractory bricks are dark gray and shiny. The well-fired graphite refractory bricks will not stain the hands and will have a crisp sound when struck with a small hammer. High refractoriness and load softening temperature, good thermal shock resistance; not wetted by molten slag, molten iron, etc., almost not corroded by all acid-base salts and organic chemicals, good slag resistance, high temperature stability, high mechanical strength, Good wear resistance, good electrical and thermal conductivity.
In addition, carbon is easy to oxidize. Whether it is the calcination of raw materials, the calcination of products, and the use of products, all must be carried out in a reducing atmosphere.
Application of graphite refractory bricks
Graphite refractory bricks are not only widely used in the metallurgical industry, but also in aluminum electrolytic cells. In addition, it is widely used in pickling tanks and electroplating tanks in the electroplating industry, dissolution tanks in the paper industry, reaction tanks and storage tanks in the chemical industry, autoclaves in the petrochemical industry, ferroalloy industrial furnaces (or equipment linings), acid solutions , Lye tank lining and pipeline, and smelting non-ferrous metals (such as aluminum, lead, tin, etc.) furnace lining.
Because of the above-mentioned properties of graphite refractory bricks, they are widely used in masonry bottoms and hearths of blast furnaces. In recent years, the scope of use has been continuously expanded, and graphite refractory bricks have also begun to be used in the furnace body and the lower part of the furnace body. It can increase the continuous operation time of the blast furnace and prolong the service life.
The performance of refractory materials for blast furnace hearth is one of the key factors affecting the life of blast furnace.
In the development of refractory materials for blast furnace hearths, one is to improve the performance and structure of graphite refractory bricks, and use hot-pressed graphite refractory bricks with high thermal conductivity, high purity, and micro-pores to overcome alkali corrosion, carbon deposition, molten iron penetration, etc. Factors caused damage to the hearth; the second is the use of new hearth materials. The “ceramic cup” technology developed by the French company Savoi has now been accepted and adopted worldwide. So far, 21 blast furnaces have adopted the “ceramic cup” technology, with a maximum volume of 5000 m3 of blast furnaces. There will be another one by 1997 11 seats were put into use. The remarkable feature of the “ceramic cup” technology is that it greatly reduces the damage caused by molten iron penetration, reduces heat loss, and moves the 800℃ isothermal layer that easily causes embrittlement of graphite refractory bricks to the ceramic cup masonry layer, eliminating the increase in molten iron temperature and The premature damage of the tap hole area caused by the increase of the molten iron flow, thereby increasing the life of the hearth.