Alumina ramming mass
Alumina ramming mass is a semi-dry, bulk refractory material formed by ramming. It is usually composed of high-alumina granules and fine powders in a certain gradation and adding an appropriate amount of binder. It is characterized by poor fluidity and must be vigorously rammed during molding to obtain a justifiable structure. This bulk material can be used to construct the overall lining of industrial kilns and is a widely used refractory material.
1. Raw materials
In the parts with high service temperature and severe chemical erosion, first-grade high alumina bauxite clinker with high Al2O3 content and good calcination is usually used as aggregate, and the critical particle is generally 8mm; Or fused corundum powder, the particle size is less than 0.088mmo, and the natural particles less than 4mm can be used. Sometimes, in order to make the ramming material have a certain plasticity, improve the construction performance, and avoid overpressure delamination and high temperature spalling, high plasticity clay is added.
Alumina ramming mass usually use phosphoric acid or aluminum sulfate as a binder. When phosphoric acid is used as a binder, during the storage process, due to the reaction between phosphoric acid and the activated alumina material in the ramming material, a water-insoluble aluminum orthophosphate is precipitated and coagulated and modified, which loses plasticity and is difficult to construct. Therefore, to prolong the shelf life of the ramming material? Appropriate preservatives must be added to try to prevent or delay the occurrence of coagulation and hardening. Oxalic acid is usually used as a preservative.
2. the ramming process
Henan Hongtai Kiln Refractory Co., Ltd. generally recommends that the raw materials be bred in the ratio of coarse: medium: fine = 20: 40: 40, plus 12~14% of industrial phosphoric acid with a specific gravity of 1.26 as a binder. The ingredients are mixed in a mixer for 6 minutes and discharged. The particle size composition of the mud is: >5mm 17~27%; 5~0.088mm 30~45%; <0.088mm 35~40%. The muddy material can be used after about 16 hours.
If ramming the ladle, place the steel inner tube in the ladle before ramming. Using a tamping machine with a wind pressure of 490kPa, the white bag is beaten from the bottom to the upper part. After each beat is about 100mm thick, the surface is peeled off and then the material is added, and it is rammed with a hammer and a half hammer to ensure the density. Immediately demould after ramming, and the surface of the rammed parts is smooth. Use gas to bake, and heat up slowly. At the beginning, under a small fire below 200 ℃, slowly increase the gas flow after baking for 16 hours, and slowly bake at about 400 ℃ for more than 16 hours. To about 600~700℃, the total baking time is about 48h. At this time, the free water and crystal water on the surface of the ramming piece have been removed, and the surface is dark red, and it can be put into use.