High Alumina Cement Applications
- To Form non load-bearing salt-resistant material
- To Form expansive and self stressedcement
- To produce scagliola
- To Form heat-resistant concrete, refractory castable, and unshaped refractory
High Alumina Cement Manufacturing Process
There are usually two kinds of methods, sintering or melting. These are the main methods to produce high alumina cement:
Rotary Kiln Sintering for High Alumina Cement Manufacturing Process（Sintering Method）
In china, bauxite has lower content of iron, which can be sintered under more complex temperature environment. So it is proper to use rotary kiln as producing method of high alumina cement. Rotary kiln sintering method by using bituminous coal as fuel, has the characteristics of low production cost, high production efficiency and easy quality stability. It is widely used in china.
Key process of sintering method in rotary kiln are:
- Step 1: select high quality bauxite and limestone as raw materials,
- Step 2: match them with certain proportion and mill into powder in ball grinding mill.
- Step 3: After that, sinter the powder in rotary kiln.
- Step 4: Grinding the finished chamotte in ball mill again, and finish the procedure.
When industrial alumina and high quality limestone are used as raw materials, white calcium aluminate cement can be produced by using ashless fuels such as natural gas and diesel or heavy oil. Because of its low content of impurities, white calcium aluminate cement is widely used to prepare high-grade refractory castable.
In the sintering process of raw materials, CA minerals are firstly formed by solid phase reaction. Because the high reactivity of limestone after decomposition, a small amount of C12A7 minerals will appear. But with the increase of temperature, the reaction rate of Al2O3 and SiO2 in bauxite increases, and the mineral in clinker will be gradually balanced according to the design, and finally C12A7 will disappear. The main mineral phases of the clinker minerals are CA, followed by CA2 and C2AS, Impurities Fe2O3 and TiO2 which forms C2F and CT. Therefore, the high alumina cement produced by rotary kiln will not have C12A7 when finely calcined (which is also a mineral that better not to appear in high alumina cement for chemical building materials).
The control of ingredients, sintering process and the mineral composition of cement are very important, in the manufacture process of high alumina cement for chemical building materials.
Arc Furnace Melting for High Alumina Cement Manufacturing Process (Melting Method)
- Step 1: Use bauxite and limestone as raw materials,
- Step 2: reckon the mix portion, mix,
- Step 3: melt the raw materials in an arc furnace,
- Step 4: control cooling to form chamotte.
- Step 5: finish with high alumina cement by grinding the ball mill to the required fineness
The arc furnace melting method is suitable for producing high alumina cement with high content of CaO. The content of CaO in the clinker produced by rotary kiln is generally less than 35%. If the content of CaO is too high, the ability of chamotte to bear ranging temperature will become narrow, resulted in difficulty in operation. By using arc furnace melting method, cement with higher content of CaO(That is, higher content of CA) can be produced, thus obtaining high alumina cement with higher strength in the early stage。
In addition, bauxite can also be used in melting method as raw material to produce cement with higher content of Fe2O3.
The key technology of producing high alumina cement in arc furnace, is to choose high quality bauxite and limestone. Try to master the oxidation atmosphere during the melting process. Because in the reducing atmosphere, FeO is formed which will produce a multicolored mineral called Pleochroite. The chemical formula of Pleochroite is: （Ca，Na，K，Fe2+）A(Fe3+，Al)B (Al2O7)5 (AlO4)6-x （Si，TiO2)x. The formation of Pleochroite will have a harmful effect on the performance of high alumina cement, which leads to the increase of C12A7 content, and makes it difficult to control the setting and hardening process of high alumina cement.
Moreover, cooling conditions can have a huge impact on the performance of high alumina cement in the melting method. Therefore, control cooling is also an important process.
Reverberatory Melting Method for High Alumina Cement Manufacturing
Same as arc furnace melting method, reverberatory method is also suitable for the production of high calcium content and high iron content cement. Likely, the reverberatory method also requires strict control on the atmosphere and cooling process to ensure stability of the product.