Any raw material with high-quality bauxite and high-quality lime as raw materials, mixed in a certain proportion to form an appropriate amount of raw material, after sintering, the clinker with aluminate as the main component is ground into fine powder, and made into a fire-resistant clinker Hydraulic cementitious material, called refractory cement, its refractoriness is not less than 1580 degrees Celsius.
It is also called high temperature cement. Cement with special materials used in the preparation of high-temperature (fire-resistant) concrete. There are:
① Low-calcium aluminate refractory cement with pure bauxite and limestone as the main raw materials, including Secar cement in France.
② Dolomite high-temperature cement made by adding dolomite as the main raw material and adding apatite and iron ore.
③Use materials that can produce chemical reaction and harden at high temperature, such as refractory sulfate, borate and phosphate as high-temperature cement.
Technology Classification
(1) Aluminate refractory cement
Usually 4 parts (by mass) low-calcium aluminate refractory cement clinker and 1 part high-alumina cement clinker are mixed and ground into a kind of refractory cement. Compared with low-calcium aluminate refractory cement: higher early strength, similar refractoriness, and the same purpose.
(2) Low calcium aluminate cement
Cement with a refractoriness not less than 1580°C. According to different composition, it can be divided into aluminate refractory cement, low calcium aluminate refractory cement, calcium magnesium aluminate cement and dolomite refractory cement. Refractory cement can be used to cement various refractory aggregates (such as corundum, calcined high alumina bauxite, etc.) to make refractory mortar or concrete, which is used as lining in cement rotary kilns and other industrial kilns.
Where high-quality bauxite and high-quality white limestone are used as raw materials, mixed into a certain proportion of raw materials with appropriate ingredients, after sintering, the resulting clinker with low-calcium aluminate as the main component is ground into fine powder and made into a fine powder. This kind of hydraulic cementitious material with fire resistance is called low calcium aluminate refractory cement.
Low lime aluminate refractory cement is a kind of aluminate cement made by mixing high quality bauxite and limestone in proper proportion, after sintering and grinding. Its composition is generally: alumina accounts for 70%, calcium oxide accounts for 19% to 23%, silica <4%, iron oxide <1.5%. The mineral composition is dominated by monocalcium dialuminate, accounting for 60% to 70%, and its refractoriness is above 1650℃. Compared with high alumina cement, the main differences are: high alumina content, low calcium oxide content, low early strength, high refractoriness, etc. It can be mixed with refractory aggregates (such as calcined bauxite, high alumina brick fragments, etc.) with a refractoriness above 1770°C to make refractory concrete or refractory mortar, which can be used as the lining of cement rotary kilns and other industrial kilns.
Its uses include:
1. It can be formulated into refractory concrete or refractory mortar with refractory materials with refractoriness above 1770℃, such as calcined bauxite, high alumina brick fragments, etc., and used as refractory lining in some high temperature kilns and some long-term exposure to the atmosphere High-temperature engineering with the effect of rainwater erosion.
2. It can be formulated with light aggregate to make heat-insulating coagulation and heat-resistant coagulation.
3. Ding and asbestos are formulated into asbestos-cement products with insulation and heat resistance.
(3) Calcium magnesium aluminate cement
Calcium magnesium aluminate cement is a kind of aluminate cement made by mixing high-quality bauxite and dolomite in proper proportion, sintering and grinding. The composition of calcium magnesium aluminate cement is generally as follows: alumina accounts for 66% to 74%, calcium oxide accounts for 13% to 18%, and magnesium oxide accounts for 10% to 13%. There are trace amounts of silicon dioxide and iron oxide. The mineral composition consists of calcium aluminate and calcium dialuminate accounting for 45%-60%, and spinel accounting for 35%-50%. The refractoriness is above 1650℃.
Compared with low-calcium aluminate cement, calcium magnesium aluminate cement has the following advantages: resistance to slag and metal melt chemical attack; in the case of the same alumina content, due to the presence of spinel, High refractoriness; less mixing water, low porosity after hardening of cement, small calcination shrinkage; less strength loss when heated to 1100°C for dehydration. Calcium magnesium aluminate cement and fused white corundum are prepared into concrete, which can be used as the lining of cement rotary kilns and other industrial kilns.
Baking and technical requirements
Refractory cement refers to cement with a refractoriness of not less than 1580°C. It uses bauxite and limestone as raw materials and is calcined to obtain clinker with calcium aluminate as the main component and about 50% alumina content. Made of hydraulic cementing material. It can be used to cement various refractory aggregates (such as corundum, calcined high alumina bauxite, etc.) to make refractory mortar or concrete, which is used as lining for cement rotary kilns and other
industrial kilns.
Matters needing attention when baking refractory cement lining:
(1) The 350℃ stage at room temperature is most likely to cause local bursts. Pay special attention to slow baking. If there is still a lot of steam coming out after heat preservation at 350°C, the temperature rise rate should still be slowed down.
(2) Under the conditions of poor ventilation and difficult to discharge water vapor, the heat preservation time should be extended appropriately.
(3) When baking with heavy oil, it is necessary to prevent heavy oil from spraying on the surface of the furnace lining to prevent local bursting.
(4) When using wood for baking, direct contact with the flame will often cause local heating up too quickly, which should be protected.
(5) For the newly poured refractory cement, it can be baked at least 3 days later.
(6) The refractory cement lining should also be cooled slowly to avoid forced ventilation.
skills requirement:
(1) The finer the cement particles, the larger the specific surface area, the faster and more adequate the hydration reaction, and the higher the early and late strength. National regulations: The specific surface area should be greater than 300 square meters per kilogram, otherwise it is unqualified.
(2) In order to ensure that there is sufficient time during construction to complete various processes such as mixing, transportation, and molding, the initial setting time of cement should not be too short; after the construction is completed, it is hoped that the cement can harden as soon as possible to produce strength, so the final setting time It should not be too long. Its initial setting time shall not be earlier than 45 minutes, and its final setting time shall not be later than 390 minutes.
(3) The uniformity of the volume change of the cement paste during the setting and hardening process is called the volume stability of the cement. If the volume changes unevenly, that is, the volume stability is poor, it is prone to warping and cracking, which reduces the quality of the project and even causes accidents.
