There are two kinds of corundum castables that we often see, one is corundum refractory castable, and the other is corundum mullite refractory castable.
Corundum castables are made of refractory products with corundum Al2O3 content greater than 90%, corundum as the main crystal phase, and appropriate amount of dispersant, coagulant, stainless steel fiber, and a strict formula. It has many points such as good high temperature strength, wear resistance and erosion resistance, high thermal conductivity, thermal shock resistance, corrosion resistance, good sealing performance, rapid setting and early strength.
A refractory castable prepared with corundum as aggregate and powder plus some binders. It has higher mechanical strength and anti-abrasion performance than high alumina refractory castable and mullite refractory castable, but its thermal shock resistance is slightly worse. Mainly used as lining materials for boilers, blast furnace hot-blast stoves, heating furnaces, ceramic kilns, etc.
The corundum contained in the preparation of corundum refractory castables is a trigonal crystal system, and the crystal form is generally short columnar. The corundum itself also has high thermal conductivity and electrical insulation properties, excellent chemical stability and resistance to reducing agents. Therefore, corundum is an advanced refractory raw material for unshaped refractories. Corundum is generally made of industrial alumina or bauxite after sintering or electrofusion. Therefore, all artificial corundum is used in industry. The density and hardness of artificial corundum are relatively large, so the use effect is also more significant.
Corundum and mullite castables are made of dense corundum and mullite as aggregates, and white corundum powder, α-Al2O3 micropowder and mullite powder as fine powder.
Performance characteristics of corundum and mullite castable: It has the common advantages of corundum and mullite castable; high temperature strength, thermal shock resistance and structural peeling resistance; good thermal shock resistance, high load softening temperature, high temperature creep The rate of change is small, and the chemical corrosion resistance is good.
The mullite contained in corundum mullite refractory castables is relatively small in nature, and the mullite raw materials used in industry are artificially synthesized, with high purity and relatively high density. , Good structure, low creep rate, low thermal expansion, good thermal shock resistance and strong chemical resistance. It is widely used in the refractory industry, and it is developing relatively quickly. However, if you use corundum and molai In terms of stone ratio, the hardness and true density of corundum are much better than that of mullite.
A formula technology patent of corundum mullite castable
Recipe 1:
A corundum mullite castable, which is characterized in that the castable is composed of the following components:
55-70% of corundum particles with a particle size of 0.05-1mm
Fine corundum powder with particle size less than 0.06mm 7-15%
8-11% of mullite particles with a particle size of less than 1mm
6-10% α-Al2O3 fine powder with a particle size of less than 3μm
1-3% SiO2 powder with particle size less than 1μm
Quicklime 2-4%
Iron oxide red 2-4%
Cement 3-5%
Compound admixture 0.5-1.5%,
The above components are based on 100% of the mass percentage.
Recipe 2:
60% of corundum particles with a particle size of 0.05-1mm
11% of corundum fine powder with particle size less than 0.06mm
9% of mullite particles with a particle size of less than 1mm
Α-Al2O3 fine powder with particle size less than 3μm 7%
SiO2 powder with a particle size of less than 1μm 2% quicklime 3% iron oxide red 3% cement 4% composite admixture 1%.
The chemical composition requirements of the corundum described in formula one and formula two are: Al2O3≥99.0%; the chemical composition requirement of mullite is: Al2O3+SiO2≥97.0%; the SiO2 micropowder uses imported micropowder, and its composition requirements are: ：SiO2≥97.5%; the cement is at least one of silicate or calcium aluminate cement; the composite admixture is composed of citric acid aqueous solution, chemically pure trisodium phosphate solution and lignin sulfonic acid Calcium solution is mixed according to the ratio of 2-3.5:1.25-1.5:1-2.
The preparation method includes the following steps:
(1) Pre-mixing of the matrix powder: fine corundum powder, α-Al2O3 powder, SiO2 powder, quicklime, red iron oxide, cement, composite admixtures according to the set ratio, put them in a ball mill and mix for 30-50 minutes. Make SiO2 micropowder and Al2O3 micropowder fully mixed evenly, and the mixed matrix powder shall be sealed and stored for later use;
(2) Put the weighed corundum particles, mullite particles and the pre-mixed matrix powder into a forced mixer and mix for 5-15 minutes, add 5-8% of the total weight of the material, mix and stir evenly , Inject into a clean and fixed mold, place it on a vibrating table for vibration molding or use a vibrating rod to vibrate in layers, and wait until the surface is flooded;
(3) Curing for 2～4 days after casting and demoulding, and then drying at 100～120℃ for no less than 24 hours. After the moisture is fully discharged, the product is fired in a dry kiln at 1600℃. Products can be used after being sorted and packaged.
