The service life of the kiln mouth refractory castable has a crucial impact on the operation cycle of the entire cement production line. During the use of the rotary kiln kiln mouth castable, in addition to the high temperature above 1400 ℃, it also needs to withstand the impact of rapid cooling and hot air flow, high temperature cement clinker wear and high temperature harmful gas alkali corrosion and other mechanical stress, thermal stress and chemical erosion The use conditions are very harsh, and the kiln mouth castables must have good thermal shock resistance, wear resistance and alkali resistance. At present, corundum-mullite, corundum-spinel and steel fiber reinforced refractory castables are widely used in kiln mouth castables. In order to improve the erosion resistance and thermal shock resistance of kiln mouth castables, they are often Add some silicon carbide. The kiln mouth castable can form an integral lining, but because it is a brittle material, it is difficult to adapt to a certain degree of deformation like a brick rotary kiln cylinder, and it is easy to crack under the action of stress. The toughness is very beneficial to improve its service life. Black corundum is a gray-black crystal with α-Al2O3 and iron-aluminum spinel as the main mineral phases. It has the characteristics of high toughness, high temperature resistance and stable thermomechanical properties, and is mostly used in abrasives. In view of the performance characteristics of black corundum and the performance requirements of kiln mouth castables, this paper is based on corundum-mullite kiln mouth castables, using black corundum as part of the raw materials, and studies the effect of black corundum with different particle sizes and its addition on the kiln mouth. Influence of castable properties.
1.1 Raw materials and test plan
The main raw materials used in the test are: sintered mullite (2.73g·cm-3, particle size includes 8-5, 5-3, 3-1mm), brown corundum (3.92g·cm-3, particle size includes 3-1, ≤1, 0.074mm), black corundum (3.71g·cm-3, particle size includes 3～1, ≤1, 0.074mm), silicon carbide (particle size includes ≤1, 0.074mm), α-Al2O3 powder, silicon dioxide Micropowder and calcium aluminate cement, admixtures include water reducer and explosion-proof fiber.
1.2 Sample preparation and performance testing
Mix all kinds of raw materials evenly in proportion, add 5.6% (w) of water, and then shake and shape, and cure for 24 hours at room temperature before demoulding. After the samples are treated at different temperatures, the bulk density of the samples (YB/T5200-1993 ), compressive strength (GB/T5072-2008), flexural strength (GB/T3001-2007), linear change rate (GB/T5988-2007).
results and analysis
2.1 Influence of different addition amounts of black corundum on the performance of kiln mouth castables
With the increase of the addition amount of black corundum ≤1mm, the bulk density of the sample shows a downward trend, which is caused by the lower bulk density of black corundum than that of brown corundum. Taking into account the particle gradation factor, when the content of ≤1mm black corundum increased to 25% (w) in the test, no silicon carbide ≤1mm was added to the sample, which was equivalent to ≤1mm black corundum replacing all ≤1mm brown corundum and ≤1mm. Silicon carbide of ≤1mm, and the bulk density of black corundum is greater than that of silicon carbide, so the bulk density of the sample is improved.
The flexural strength at room temperature of the samples with ≤1mm black corundum added 5% (w) after different temperature treatment is higher than that of the samples without black corundum, and the addition amount (w) of ≤1mm black corundum is between 5% and 20%. Within the range of %, with the increase of the amount of black corundum added, the change trend of the flexural strength of the sample after holding at 110 °C for 24 h is not obvious. This is because the strength of the sample at 110 °C for 24 h is mainly composed of cement binder. supply. After 1100℃ for 3h and 1350℃ for 3h, the room temperature flexural strength of the samples showed a trend of increasing first and then decreasing. The flexural strength was mainly affected by the degree of bonding between the matrix and the aggregate, and the fracture process was mostly aggregates. The destruction of the particles themselves, rather than the pull-out effect of the particles from the matrix, the change in flexural strength reflects the strength of the bond between the matrix and the aggregate.
The compressive strength at room temperature of the samples with 5% (w) of black corundum ≤1mm was lower than that of the samples without black corundum. With the increase of the amount of black corundum added, the compressive strength at room temperature first increased and then decreased. The compressive strength of the samples treated at 110℃ for 24h is affected by the action of the binder and the degree of close packing. Under the condition of the same mass ratio, the addition of black corundum causes changes in the degree of close packing, thereby causing changes in the compressive strength. Under the test conditions, when the addition amount (w) of ≤1mm black corundum is about 10%, the compressive strength of the sample at room temperature is the highest after being kept at 1100℃ for 3h and 1350℃ for 3h, which is related to the degree of reaction in the sample. It is related to the close packing of particles [7]. As a heterogeneous material, the flexural strength of castables is more easily affected by microstructures such as cracks and inhomogeneities than compressive strength.
The linear shrinkage of the sample with ≤1mm black corundum added 5% is significantly higher than that of the sample without black corundum, indicating that there is an obvious sintering reaction in the sample. The changes of the sample lines after heat treatment at 1100℃ for 3h showed shrinkage characteristics, and the shrinkage rate gradually decreased as the black corundum addition (w) increased in the range of 5% to 20%. The samples treated at 1350 °C for 3 h show the characteristics of shrinkage first and then expansion within the range of ≤1mm black corundum addition (w) of 5% to 20%, which is related to the phase reaction in the sample [ 8], indicating that the black corundum first generates a low melting point liquid phase in the sample to cause volume shrinkage, and with the increase of the black corundum content, a new phase is generated to expand, and the specific phase needs further analysis and confirmation. ≤1mm black corundum addition amount (w) of 25% of the sample line changes fluctuated, mainly because black corundum replaced silicon carbide, silicon carbide will also affect the line changes of the sample, silicon carbide partially under high temperature conditions Oxidation occurs to generate silicon dioxide, and then the reaction generates mullite, which produces a certain degree of volume expansion effect. It also shows that the volume effect of silicon carbide on the sample is greater than that of black corundum. The volume expansion effect also leads to the decrease of the normal temperature compressive strength of the samples treated at 1350 ℃ for 3 h with the increase of the addition amount of black corundum. The flexural strength at room temperature and the compressive strength at room temperature are easily affected by microscopic defects. In comparison, the change of the permanent heating line as a macro evaluation index can more objectively reflect the state of the sample after sintering. Considering the use of the kiln mouth castable Conditions, thermal shock resistance, strength and other performance requirements, the addition amount (w) of ≤1mm black corundum is about 15%.
