The tuyere area is one of the weakest links within the blast furnace hearth. High-quality, water-free ramming mass, combined with proper tuyere operation and maintenance practices, plays a critical role in improving the working environment at the iron tapping area, reducing maintenance requirements for the tuyere, enhancing front-end production efficiency, cutting costs while boosting profitability, and ultimately extending the lifespan of the blast furnace. Only by selecting a ramming material that perfectly matches the furnace’s specific needs—and consistently applying sound operational and maintenance habits—can operators achieve optimal performance and maximize benefits. Therefore, the quality of the water-free ramming mass is absolutely essential for ensuring stable, long-term blast furnace operations.

The operational period from a blast furnace's ignition and start-up to its shutdown for maintenance is referred to as one "furnace campaign." During different phases of the furnace campaign, the working conditions at the tuyere—particularly the performance of the ramming mass—can vary significantly, leading to varying priorities in terms of mud formulation requirements. To ensure effective use of the ramming mass, each batch must meet specified performance criteria within a defined range, avoiding deviations that fall outside critical upper or lower limits. By analyzing and summarizing the unique characteristics of blast furnaces at different campaign stages along with their corresponding mud requirements, users should carefully select ramming masses that best align with the specific needs of their furnaces.

I. Early Stage of Furnace Operation

When the furnace was first started, both wind temperature and wind pressure remained relatively low, resulting in molten iron and slag that were unusually viscous. The blast furnace has two critical requirements: First, the slag and iron must be efficiently drained away without delay; second, moisture trapped inside the furnace—particularly in the mud pack and various masonry structures—needs to be expelled through the tuyere. To meet these demands, the tuyere must be opened swiftly and precisely on schedule. As a result, the accuracy of tuyere opening has become the primary metric for evaluating operations at the furnace front. Failure to open the tuyere promptly and reliably can easily lead to a "wind stoppage," jeopardizing the entire startup process—or even worse, causing a complete blockage of the tuyere, leaving all furnace-startup efforts hopelessly behind schedule.

In recent years, thanks to advancements in blast furnace ironmaking technology and the growing expertise gained from numerous startup experiences, the time required from ignition to full production has been steadily decreasing—now often reaching full capacity within just three to five days under optimal conditions. Additionally, water-based gunning materials have been phased out during startup; instead, dry gunning materials are now used right from the moment ignition begins. Meanwhile, the process of moisture removal from the refractory lining within the tuyere area remains gradual, as it takes a considerable amount of time for all internal moisture to fully evaporate. During the initial startup phase, the focus should be on transitioning smoothly from blast furnace ignition and commissioning to establishing a stable airflow regime, ensuring that the hearth remains actively and consistently operational.

Figure 1: Condition of the iron tapping area during early furnace operation

The iron tapping area during the initial stages of furnace operation is shown in Figure 1. In recent years, most newly built blast furnaces have incorporated a mud-pack platform—either poured or rammed—directly beneath the iron tap. At the start of production, this mud pack remains remarkably stable, preventing erosion of the tap bricks and keeping the hearth activity relatively low. As a result, the requirements for the gunning material in terms of erosion resistance and tap depth are relatively modest, making it easier to maintain an optimal tap depth. To keep the hearth actively functioning, it’s crucial to promptly open the tap and efficiently discharge both slag and molten iron. Achieving high tap-opening accuracy and consistency places specific demands on the gunning material: it must be easy to apply, allow for precise opening, and minimize spattering during the process.

During the initial stages of furnace startup, the mud gun equipment is in its running-in phase, leading to lower temperatures in both the gun chamber and the iron-running area. Additionally, the temperature of the iron tapping channel remains insufficient, resulting in increased resistance when pushing the mud forward. As a result, the actual mud-pushing pressure often falls below the designed value. Consequently, the mud gun's Marsh value during this period should be kept below the standard level. However, simply increasing the bonding agent dosage to reduce the Marsh value is not advisable, as it could prolong the coking time of the mud and leave the gun with inadequate strength even after opening.

After the blast furnace is tapped and iron begins to flow, moisture gradually escapes from the hearth refractories. As the masonry expands or contracts under high temperatures, gaps may form—cracks that can easily allow gas to leak into the tap hole area. Moreover, a gunning mix with a high binding agent dosage but slow coking behavior not only fails to effectively prevent gas leakage during tapping—it actually exacerbates spattering at the tap hole, worsening the working conditions in front of the furnace and increasing the physical strain on operators. During the initial stages of furnace operation, finding the right balance between reducing the mash value of the gunning mix and accelerating its coking process presents a significant challenge for technicians specializing in gunning materials. In the early days after startup, gas leakage through the tap hole can disrupt iron tapping, making it crucial to promptly enhance the performance of the gunning mix. To meet customer demands more efficiently and quickly, gunning mix manufacturers must continuously innovate and adapt to these evolving needs.

To address the issue of gas leakage from the iron tapping opening during the initial furnace start-up phase, the mud composition can be optimized by selecting a splash-suppressing type of ramming mass. With its excellent operational performance, outstanding resistance to erosion, and appropriately controlled coking rate, the splashing phenomenon will gradually diminish—and eventually cease altogether.

II. Stable Production Period

When wind temperature and pressure reach design levels—and especially as the air distribution system stabilizes, leading to rational airflow distribution in the blast furnace, uniform temperature profiles, and abundant, steady thermal energy—the hearth area becomes actively operational. This marks the transition of the blast furnace into its stable production phase.

Once the blast furnace enters its stable production phase, large volumes of molten, scorching slag and iron are continuously discharged from the tuyere. High hot blast temperatures, oxygen-enriched coal injection, and high-pressure differential operations have led to particularly severe erosion in the tuyere area. As a result, establishing a robust mud pack to protect the furnace wall and ensuring smooth, efficient slag and iron discharge have become the core tasks. To achieve this, the tuyere depth qualification rate, full wind-blowing plugging rate, and slag-iron tapping efficiency are now the primary performance indicators evaluated during front-of-furnace operations.

Highly productive blast furnaces require iron-blowing mud that is easy to maintain, ensuring low probabilities of iron leakage or blowout during tapping. Once the tap hole is opened, there should be no wet mud spattering, allowing for smooth iron flow and complete slag-iron discharge. Currently, most steelmakers operate at high smelting intensities, with daily production far exceeding design capacity. As a result, the equipment used for opening and sealing the tap holes at the furnace front often limits the full potential of the iron-blowing mud. When combined with lower strength, slower coking rates, and excessive proportions of recycled materials in the mud, these conditions typically enable easy initial opening of the tap hole. However, after tapping begins, the depth of the tap hole tends to decline rapidly—sometimes even eroding and wearing away into the furnace wall itself. To address this issue, an ideal iron-blowing mud should feature a controlled process: starting with a gentle blast of air, gradually increasing the airflow as tapping progresses, leading to a slow but steady buildup of spatter until the final stages of iron discharge.

Maintaining a stable iron tap depth isn’t achieved overnight—it requires the consistent quality of gunning material over the long term. The quality of the gunning material should remain stable, without significant fluctuations caused by variations in raw material batches, seasonal changes, or temperature shifts. During periods of stable production, suppliers should be chosen based on their cost-effectiveness rather than simply opting for the lowest bid.

III. Late Stage of Furnace Operation

The blast furnace operates continuously under high-intensity smelting conditions, creating an especially harsh working environment around the iron tapping hole. Molten iron and slag from other parts of the hearth circulate in a "circulatory" pattern toward the tapping opening. Under the "stirring" action of the tuyere swirling zone, these molten materials form a "vortex" just ahead of the tapping hole’s passage. The rapidly flowing slag and iron then violently erode the clay lining and the tapping channel itself, eventually widening the channel into a flared, trumpet-like shape—severely damaging both the clay lining and the tapping hole’s internal structure. The condition of the tapping area during the later stages of furnace operation is illustrated in Figure 2.

1. Refractory bricks for the furnace wall; 2. Taphole channel; 3. Slag layer on the furnace wall; 4. Old mud pack; 5. Mud pack eroded and altered by molten iron and slag during tapping; 6. New ramming material; 7. Coke; 8. Furnace wall; 9. Taphole mud sleeve; 10. Taphole frame. L, taphole depth; K, red spot (hard shell); α, taphole angle.

Figure 2: Condition of the iron tapping area in the later stages of furnace operation

As shown in Figure 2, after the tuyere has been in operation for a period of time, both the ceramic cup and carbon bricks become increasingly thinned due to slag and iron erosion. Eventually, only the mud pack formed by the ramming material after plugging and the slag crust remain to protect the cooling stave. When a proper mud pack fails to form—or if the existing mud pack is too thin—water temperatures near the tuyere rise sharply, turning the tuyere area into the most vulnerable and critically damaged part of the blast furnace body. Therefore, maintaining an appropriate tuyere depth becomes absolutely critical during the later stages of blast furnace operation. Improper maintenance of the tuyere can lead to abnormal operating conditions, causing the remaining refractory lining to completely spall away, ultimately resulting in damage to the cooling stave. In severe cases, this could even trigger catastrophic incidents such as a breakthrough of the hearth.

In the later stages of furnace operation, it is essential to enhance the slag-resistant ability of the gunning material. The goal is to ensure that, after each iron tapping, the remaining amount of gunning material in the mud pack exceeds both the volume lost due to drifting out of the tap hole and the amount eroded or washed away during the process. A sufficiently thick mud pack can more effectively protect the hearth wall around the tap hole, thereby maintaining safe and stable operations in ironmaking production.

If the earlier use of poor-quality ramming mass resulted in ineffective iron tap maintenance and abnormal water temperature differences across the cooling stave in the iron tap area, it is advisable to promptly switch to vanadium-titanium ramming mass. After the vanadium-titanium ramming mass is packed into the iron tap, the vanadium-titanium compounds within it form TiN and TiC near the tap, reinforcing and protecting the furnace lining. Practical applications across multiple blast furnaces have demonstrated that combining vanadium-titanium ramming mass with the simultaneous addition of titanium ore or titanium wire for comprehensive furnace protection can quickly restore the cooling stave water temperature difference back to safe, acceptable levels.