Problems and solutions in the use of taphole clay

Problems and solutions in the use of taphole clay

For steel mills, perfect waterless taphole clay should meet the following requirements: easy to make clay, easy to open, easy to maintain the iron taphole depth, the iron tapping time meets the requirements of blast furnace, no splashing and no smoke during the iron tapping process, etc.

In fact, it is impossible for any supplier of Anhydrous taphole clay and taphole clay technicians to perfectly meet all the above requirements at the same time. If you are not careful when using taphole clay, it is easy to encounter the following problems: difficulty in making clay, hard spots at the front end of the iron taphole, leaks at the iron taphole, shallow depth of the iron taphole, short tapping time, large tides of clay when opening, or even rockets, and long splashing time. Usually, various problems are not completely isolated, but often have linkage, that is, once a problem occurs, it is often accompanied by several other problems. For example, when the taphole clay lacks plasticity, it may also produce the following problems: difficulty in making clay, hard shells at the front end of the iron taphole, or a high probability of leaks at the iron taphole, and difficulty in opening leads to oxygen burning, which damages the iron taphole channel and results in short tapping time. The author believes that the quality of waterless taphole clay is often only a fine line apart. The taphole clay that seems to have a messy result may become more ideal by slightly adjusting the process formula, and vice versa.

The main factors that determine the effect of anhydrous taphole clay include three major aspects: production formula, production process control, and coordination for on-site use. In addition, there are many small factors that affect the quality and effect of taphole clay. Saying that these factors are "small" does not mean that they are unimportant. On the contrary, some very small factors sometimes cause fatal harm and make the application of taphole clay a mess.

This article focuses on the common problems and solutions in the application of taphole clay.

1. Difficulty in clayding or failure to clay

If external factors such as equipment failure and blocked iron taphole passage are excluded, the reason for failure to clayding is mostly due to insufficient plasticity, accompanied by the dispersion and drying of the clay squeezed out of the gun head after the gun is removed. The direct causes may be: the asphalt quality is too poor, its β-resin content is low; the asphalt addition is insufficient; the Marshal value is controlled too high; the clay binder is of poor quality or the addition amount is too small.

Solution: During on-site operation, temporary countermeasures can be taken according to actual conditions, such as increasing or decreasing the intensity of the baking gun, adding waste oil and other lubricants into the clay gun; appropriately adjusting the particle grading, increasing the proportion of aggregate; increasing the amount of asphalt; adding liquid binder, reducing the Maxwell value of the gun clay; changing the type of clay or increasing the amount of clay.

Before changing any parameters, first find out whether the difficulty in making clay is slightly difficult or not at all, whether it is occasional difficulty or general difficulty. The adjustment intensity should be determined based on the specific degree to avoid going from one extreme to another.

2. High probability of iron taphole leakage

Iron taphole leakage refers to the phenomenon that during the opening process, the hole is not drilled through and slag iron is seen halfway through. Sometimes, after the iron taphole is broken, it basically does not affect the normal iron tapping, but affects the depth of the iron taphole; sometimes after iron leakage, the iron taphole cannot tap normally, and slag iron flutters out little by little. In this case, it is difficult to burn the iron taphole with oxygen. The oxygen pipe enters the channel and quickly melts due to heat, and is often forced to block the taphole again.

The reasons for the high probability of leakage are usually: 1) Poor plasticity of clay, insufficient clay addition, insufficient amount of organic binder, etc., which lead to lack of plasticity of the gun clay and loose iron taphole channel; 2) The gun clay is too soft, resulting in the iron taphole channel and clay bag being not dense after plugging, and the gun clay shrinks too much at high temperature; 3) The total amount of expansion agent in the gun clay is improperly controlled, resulting in excessive changes in the gun clay line; 4) The sintering strength of the gun clay is too high, and leakage occurs due to mechanical impact during the opening process.

Solution: As a temporary solution for blast furnace operation, if the plasticity of the taphole clay is poor, consider baking the taphole appropriately; if the taphole clay is too soft, do not bake it, and you can also pump water into the clay taphole to cool it down to prevent the taphole clay from being overheated; when plugging the taphole, use the method of segmented clay beating and inching clay replenishment; reasonably adjust the total amount of expansion agent in the formula; slow down the sintering speed of the taphole clay and reduce the opening strength; change the type of clay, select the appropriate viscosity and fineness, and control the reasonable amount of clay added; reasonably control the amount of asphalt and tar binder and the Maxwell value of the taphole clay.

3. Red iron taphole and hard shell phenomenon

The hard shell phenomenon refers to the last small section of the opening process that is very hard, the drill bit or steel drill cannot drill into it and makes a sound similar to drilling on iron sheet. After the drill rod or steel drill is pulled out, only the drill bit part is red, but the drill rod is not red. The reasons for the formation of the hard shell phenomenon are mostly: insufficient bonding dosage, slightly lack of plasticity of the taphole clay (accompanied by a little effort in clay beating, and the taphole clay squeezed out after the taphole is removed is scattered and dry); excessive coke addition leads to too high porosity of the taphole clay. Since the viscosity of molten iron is very small, it is easier to penetrate into the clay bag from the pores or gaps, and then solidify to form an iron shell.

Red iron taphole means that after the iron taphole is half or 2/3 opened, the channel is red. When the drill bit or steel drill drills to this part, it is heated and the strength decreases, making it difficult to continue drilling. After the drill rod is pulled out, a large part of the front end is red, and the drill rod may even stick or be twisted into a twist. Red iron taphole is actually a serious version of the hard shell and iron seepage phenomenon.

Solution: During on-site operation, the blasting can be appropriately carried out; the amount of asphalt added can be appropriately increased; the tar binder can be increased and the Marscha value can be reduced; if a large amount of metallic silicon materials are added to the formula, the amount added should be reduced.

4. Short tapping time

If the tapping depth is not obviously insufficient or the blast furnace smelting is not smooth, the tapping time will be short. Generally, it is because the ore grade is low, the slag volume is large, the tapping clay is not erosion-resistant enough, and the hole expands rapidly after the slag is seen during the tapping process. Of course, the shallow depth of the tapping hole and the use of a large diameter drill to open the hole will also lead to a short tapping time.

Solution: Increase the proportion of silicon carbide and ferrosilicon nitride; adjust the aluminum-silicon ratio in the taphole clay matrix, mainly by adjusting SiO2 powder, clay and other materials to make the matrix more resistant to slag erosion; appropriately introduce additives such as graphite to improve corrosion resistance; use resins and other binders for taphole clay of super-large blast furnaces, because of its high residual carbon, the taphole clay has more ideal corrosion resistance; changing the ratio to increase the density of the taphole clay can also improve corrosion resistance; break through the conventional system of alumina-silicon carbide-carbon, and study new material systems that are better matched with slag.

5. Insufficient taphole depth

To solve the problem of insufficient taphole depth, several aspects can be taken: 1) Appropriately increase the amount of clay, or even adopt segmented clay, inching clay filling and other operation methods; 2) The plasticity of the taphole clay should be moderate, not too soft or too hard, so as to form a good taphole channel and clay bag; 3) Ensure the appropriate amount of expansion agent to achieve micro-expansion of the taphole clay after high-temperature sintering, which can improve the bonding of new and old taphole clay; 4) Improve the corrosion resistance of the taphole clay, so that the clay bag is not easily eroded by slag iron; 5) Close the tuyere above the taphole, and appropriately reduce the wind pressure of the blast furnace, which is more conducive to maintaining the taphole depth.

When the blast furnace is in the late stage of service, due to the deformation and thinning of the furnace wall, the taphole depth is often difficult to maintain. It is difficult to maintain the taphole depth simply by improving the quality of the taphole clay.

6. Poor quality stability of taphole clay

Because there are too many factors that affect the effect of taphole clay, it is easy to cause the quality stability of taphole clay to be unsatisfactory. Specifically, the use results of one package of taphole clay from another in the same batch are very different; when the formula, process and raw materials have not changed, the use results of this batch of taphole clay are very different from the previous batch.

To improve the quality stability of taphole clay, efforts must be made in many aspects: 1) When designing the formula, reasonably allocate the ratio of aggregate and powder to make it less sensitive to changes in certain factors and more tolerant; 2) Adopt multi-level batching and use less bulk materials, otherwise the particles are prone to serious segregation, resulting in poor stability of the particle ratio and thus huge fluctuations in the amount of oil added; 3) The stability of various indicators such as moisture, fineness, and chemical composition of key raw materials must be strictly controlled; 4) Strictly control the production process parameters, including dry mixing time, clay grinding time, clay outlet temperature, Maxwell value, etc.; 5) When the seasonal temperature changes and the raw materials fluctuate, timely prediction and reasonable fine-tuning of the formula and process parameters should be made; 6) Reasonable planning of details such as packaging and clay trapping.

Welcome to learn more about taphole clay.