Classification, application, ratio of raw materials and damage mechanism of blast furnace mud

Clay is an amorphous functional refractory material, used in the process of plugging the taphole of the ironmaking blast furnace. The composition of gun mud can be divided into two parts: refractory aggregate and binder. Refractory aggregate refers to refractory raw materials such as corundum, mullite, coke gemstone and modified materials such as coke and mica, which are used to improve the refractoriness, high temperature performance and slag resistance of gun mud; the binder is water, tar pitch or phenolic Organic materials such as resin can also be mixed with SiC, Si₃N₄, expansion agents and additives to improve the physical properties and product quality of the gun mud.

According to the different binders, gun mud can be divided into two categories: water gun mud and waterless gun mud. Domestically, medium and small blast furnaces (<2000m³) with low top pressure and low level of intensified smelting use water blasting mud; while large and medium blast furnaces (>2000m³) with high top pressure and high level of intensive smelting are generally used Anhydrous cannon mud. Many foreign blast furnaces represented by Japanese blast furnaces generally use high-quality anhydrous gun mud, and are equipped with special opening methods and opening machines.

The water cannon mud is usually made of clay, coke powder, bauxite clinker and tar pitch as the main materials, and then mixed and stirred with water as a binder. Water cannon mud is a kind of cannon mud that was used in large quantities in the early days, but because of its relatively small bulk density, its ability to resist scouring of iron slag solution is weak, it is easy to cause insufficient hole depth when used on large and medium blast furnaces and runaway during tapping. Phenomena such as coke, iron tapping and venting and unclean iron slag will affect the normal production of the blast furnace. So far, due to the low cost of water gun mud, many medium and small blast furnaces (<2000m³) are still improving their composition and working hard to adapt to the smelting environment, and their unit consumption is above 1.2kg·t⁻¹.

Anhydrous gun mud generally uses corundum, high alumina bauxite, clay, sericite, pitch, silicon carbide, coke powder, etc. as raw materials, and tar, resin, etc. as binders. The bulk density of corundum and high alumina bauxite is relatively large, and they play the role of supporting the skeleton in the gun mud, which is the foundation of the gun mud strength, which greatly improves the ability of the gun mud to resist the scouring of the iron slag solution; the coke powder has good reduction It can protect other carbon components, maintain the reducing atmosphere of the blast furnace taphole, and has good thermal conductivity, which can be quickly sintered and has a certain sintering strength; silicon carbide has small thermal expansion coefficient, good thermal conductivity, and excellent thermal shock resistance, which can improve The refractoriness, volume stability, high temperature strength and erosion resistance of gun mud; clay and asphalt improve the plasticity of gun mud; sericite improves the sintering strength and plasticity of gun mud. Anhydrous gun mud has the advantages of no dampness, high strength, stable taphole depth, small taphole changes in the tapping process, etc., and will not cause a large flow.

The main factors affecting the performance and quality of blast furnace clay are raw materials, binders, additives and production processes.

Blast furnace taphole clay must have the following properties:

(1) Easy to open holes. When the tap hole needs to be tapped, the sintered gun mud in the tap hole can be easily drilled through the hole and tapped in time;

(2) It is easy to block the tap hole. When the tap hole is completed, the tap hole can be blocked in a short time, and sufficient mud volume is ensured to maintain a stable tap depth;

(3) Good adhesion. The new gun mud driven into the tap hole must have good adhesion with the old gun mud in the hole to make the new and old gun mud form a whole to prevent the existence of gaps. Iron seepage, slag seepage, impact on tapping and safety accidents in front of the furnace;

(4) Good sinterability. The shot mud can be sintered to different degrees in the three temperature stages of low temperature, medium temperature and high temperature. The iron hole is blocked in time and a large enough mud bag is formed in the hearth. Play the role of protecting the hearth lining bricks.

(5) It has good jet scouring and corrosion resistance, so that the tap hole diameter is not sharply enlarged, and the tapping time is guaranteed to be 150 to 180 minutes/time, which reduces the labor intensity in front of the furnace and reduces the consumption of materials in front of the furnace.

The main damage mechanism of blast furnace mud

Thermal stress damage. When the iron is tapped, the center of the iron hole is drilled by a drill bit, and hot molten iron and molten slag flow out of the iron hole, so that the iron hole can withstand high temperature above 1500 ℃. When the iron slag is discharged and the iron hole is re-blocked with gun mud, the old gun mud contacts the newly plugged gun mud, and the temperature drops rapidly from 1500°C to about 200°C. This repeated action generates huge heat inside the old gun mud. Stress can easily lead to arc-shaped cracks with the iron hole as the center.

Thermal chemical attack. Prolonged contact with molten iron and molten slag can cause chemical reactions to cause erosion of the mud. The reaction generates a low-melting mineral phase, which is lost with the scouring of the molten iron slag during the tapping period, which enlarges the hole diameter of the tap hole, causing the molten iron to rush out of the tap hole quickly, affecting the stability of the tap hole.

The biggest weakness of the current blast furnace mud is that the iron mouth expands quickly and the resistance to hot metal erosion is insufficient, which causes the molten iron in the hearth of the blast furnace to be unclean, affects the output, and is not conducive to the smooth movement of the blast furnace. In addition, it is difficult to open the iron hole, which causes the iron hole to be unable to open on time and affects the normal iron casting. Therefore, many large-scale blast furnaces at home and abroad use the plunger method or are equipped with opening machines with strong positive and reverse impact capabilities to solve the problem of difficult opening of blast furnace mud. Under normal circumstances, after the blast furnace is finished, the surface of the original gun mud seeps into the iron slag. After the new gun mud is plugged into the iron hole, a barrier is formed at the junction of the old and the new gun mud, which is not conducive to bonding. As a result, the molten iron in the blast furnace will enter along the gap between the new and old gun mud, resulting in a slag-iron penetration area in the middle of the gun mud. The formation of the slag-iron penetration area also increases the difficulty of the taphole opening to a certain extent. The iron gate is not easy to open, which can easily lead to major safety production accidents. At home and abroad, great attention is paid to the on-site operability of blast furnace taphole mud.