What is refractory cement? What are the precautions in the use of refractory cement? Rongsheng REFRACTORY CEMENT FACTORY will provide you with high-quality refractory inorganic binders, including refractory cement, aluminum dihydrogen phosphate, etc. Next, we will introduce the use nature of refractory cement in refractory materials.
What is refractory cement?
Cement with refractoriness not less than 1580℃. The different compositions can be divided into aluminate refractory cement, low calcium aluminate refractory cement, calcium magnesium aluminate cement, and dolomite refractory cement.
Historical data show that with the discovery and understanding of the heat resistance of calcium aluminate, the yield of calcium aluminate in Europe in 1913 had a rapid increase. In the 1920s, indestructible refractory casting materials began to take their own steps of development. In the late 1980s and 1990s, new pouring techniques gradually emerged. The pump and flow gating technology with low cement castables is introduced. Then came wet spray or jet technology. In these technological changes, refractory cement was produced.
Refractory cement is also called aluminate cement. Aluminate cement is made of bauxite and limestone as raw materials, calcined with calcium aluminate as the main component, the alumina content of about 50% of clinker, and then grinding into hydraulic cementitious materials. Aluminate cement is often yellow or brown, but also gray. The main mineral composition of aluminate cement is calcium aluminate and another aluminate, and a small amount of dicalcium silicate.
The use nature of refractory cement in refractories
Aluminate cement is a kind of binder (permanent binder) that can be combined at room temperature and high temperature. The refractoriness of amorphous refractories is very important. In general, the higher the Fe2O3 in cement, the lower its fire resistance. The type and content of calcium aluminate affect the fire resistance of cement. Practice shows that ordinary high aluminum cement is used at less than 1300℃, high aluminum cement (bauxite cement) is used at less than 1500℃, and low calcium high aluminum cement (high aluminum cement) is used at higher than 1600℃ temperature.
Aluminate cement often refers to calcium aluminate as the main component of cement. Calcium aluminate cement is the basic binder of amorphous refractories, especially cast refractories. The properties of aluminate cement mainly depend on its mineral composition. The main mineral composition of aluminate cement, calcium aluminate (CA), has a high hydrohard activity, the setting is not fast but hardening is very rapid, and the hardening time is not more than one day. It is the main source of the strength of high aluminum cement, especially the early strength. Calcium dialuminate (CA2) has a slow hydration hardening, low strength in the early stage, and high strength in the later stage. Dodecalcium heptaaluminate (C12A7) has the characteristics of quick hydration and rapid condensation, but the strength is not high. In ordinary high alumina cement containing inclusions, impurities affect the hardening effect of the cement and its strength.
Calcium aluminate cement contains these 5 kinds of calcium aluminate minerals, which will be along with the hydration reaction and show an intense heating phenomenon. The temperature of common high-alumina cement (53~55% A12O3) reaches the peak after 5~8h, reaching 80~90℃. The temperature of advanced high alumina cement containing 70% A12O3 reaches the peak value after 10~12h and that of 80% A12O3 after 8~10h. The temperature is 80C and 70C respectively.
The heating temperature and the time to reach the highest temperature of single castable of different kinds of high aluminum cement are determined by the heating characteristics and content of calcium aluminate. Therefore, the calorific value of high aluminum cement will also change due to the different calcium aluminate contents. If too much high aluminum cement containing C12A or CAF as the main component is added to the cast refractory, it will cause cracks and surface spalling due to intense evaporation of water in the castable hardening body due to concentrated heat. Therefore, the choice of cement dosage and quality is very important.
Precautions for the use of refractory cement
- At a room temperature of 350 degrees, it is most likely to cause local bursting, and special attention should be paid to slow baking. If there is still a lot of steam bubbling up after 350 degrees of insulation, the heating rate should still be slowed down.
- in the condition of poor ventilation, water is not easy to discharge, to appropriately extend the holding time.
- When baking with heavy oil, it is necessary to strictly prevent heavy oil from spraying on the surface of the furnace lining to prevent local bursts.
- When using wood to bake, direct contact with the flame often causes local heating to be too rapid, which should be protected.
- the newly poured refractory cement, at least after 3d can be baked.
- the cooling of refractory cement furnace lining should also be slow to avoid forced ventilation.
