Tap Hole Clay Composition

Taphole clay is a plastic material made from various basic materials and a binder. It is used in the tapholes of blast furnaces and submerged arc furnaces. Blast furnaces typically have 2–4 tapholes, while submerged arc furnaces usually have 1–2 tapholes. During the production of molten iron in a blast furnace, taphole clay is used to seal the taphole to support stable production. When the molten iron needs to be discharged, the clay must support controlled drilling while limiting gas leakage. After the tapping process is completed, the taphole must be plugged again with taphole clay. This sequence forms the service cycle of taphole clay. Therefore, taphole clay is a special refractory material mainly used to plug and protect the blast furnace taphole.

Why is composition crucial?

The composition design of blast furnace taphole clay is derived from the stringent and interrelated requirements imposed by blast furnace operating conditions. These requirements can be organised according to the clay’s “storage–construction–service” lifecycle, and each component is specifically designed to meet one or more of these requirements with precision. The formulation is a systematic engineering process, intended to ensure that the taphole clay reliably performs its functions at every stage—from raw materials to completing its sealing mission—thereby supporting the continuous, safe, and efficient operation of the blast furnace. The correspondence between composition and performance is summarised as follows:

Composition Design of Taphole Clay

To explain the logic behind the composition design of taphole clay, we first analyse the operating conditions of the blast furnace taphole and then use these requirements to guide the material selection. The table below systematically presents the correspondence between “taphole requirements – corresponding components – design objectives,” helping you understand the role of each component. The table summarizes common formulation logic and shows how each material system supports the required operating performance. This table provides a basic understanding of the composition of water-free taphole clay. We will discuss the detailed function of each material in the following sections.

Stage	Taphole Requirements	Taphole Clay Components	Taphole Clay Design Objectives
Storage & Handling	1. Good storage stability 2. Plastic and ready-to-use 3. Must remain soft inside the clay gun 4. Must completely fill the taphole	Binders (resin, clay), plasticizers, proper particle size distribution	Provide excellent plasticity, adhesion, and shape retention to ensure the clay maintains a uniform, soft, and dense working state throughout storage, loading into the clay gun, and pressing into the taphole.
Opening & Closing Cycle	5. Must harden within a specified time 6. Must be easy to drill open 7. Must erode at a controlled and uniform rate	Coke, resin and other combustible materials, sintering agents	By controlling the content of combustible materials and sintering rate, the clay hardens promptly after sealing to gain strength, can be drilled smoothly during tapping, and erodes uniformly at a controlled rate, maintaining taphole channel stability.
High-Temperature Service	8. Must resist severe erosion and wear from molten iron and slag 9. Must control the flow of molten iron and slag 10. Protect the taphole and furnace bottom (core function)	Corundum, silicon carbide, ferro-silicon nitride, carbon materials (coke powder, graphite)	Coke, resin, and other combustible materials, sintering agents

Four Material Systems in Tap Hole Clay Composition

Binder System

Main Raw Materials

• Resin
• Pitch
• Oils
• Clay

Main Functions

• Provide good plasticity so that the tap hole clay can be easily injected into the tap hole.
• Provide strong bonding strength so that the new clay can adhere firmly to the existing clay.
• Maintain a soft and workable condition during storage and application.
• Control the curing behaviour so that the clay forms a stable structure after plugging.

Design Objectives

• Ensure smooth injection (Easy Injection)
• Ensure reliable sealing of the taphole (Easy Plugging)
• Prevent oil bleeding during application
• Avoid cracking or brittleness during curing

Matrix System

Main Raw Materials

• Fine refractory materials
• Clay-based materials
• Fine aggregates

Main Functions

• From the continuous structural phase of the tap hole clay.
• Provide appropriate extrusion resistance to ensure stable injection.
• Control the structural stability after curing.
• Regulate the thermal expansion behaviour of the material.

Design Objectives

• Provide optimum resistance to extrusion
• Form a stable structure during curing
• Prevent cracking during the curing process
• Maintain good thermal stability

Aggregate System

Main Raw Materials

• High-alumina aggregates
• Corundum
• Other refractory aggregates

Main Functions

• Form the main skeletal structure of the tap hole clay.
• Provide high-temperature strength and structural stability.
• Control the thermal expansion behaviour of the material.
• Improve the thermal shock resistance.

Design Objectives

• Ensure structural stability at high temperatures
• Prevent cracking during the coking stage
• Maintain stable thermal expansion behaviour
• Provide good high-temperature mechanical properties

Anti-Erosion Material System (SiC / C / Nitrides)

Main Raw Materials

• Silicon carbide (SiC)
• Carbon materials (coke powder, graphite)
• Nitride materials such as silicon nitride or Si₃N₄-bonded materials

Main Functions

• Improve resistance to chemical corrosion from molten iron and slag.
• Enhance erosion resistance under high-velocity molten flow.
• Reduce clay wear during the tapping process.
• Improve high-temperature stability.

Design Objectives

• Provide excellent corrosion resistance
• Improve erosion resistance
• Extend the service life of the taphole channel
• Protect the hearth and taphole refractory lining