Ferroalloy Furnace: A Method for Preventing Early Carbon Lining Failure

Ferroalloy Furnace: A Method for Preventing Early Carbon Lining Failure

Carbon-based linings are the material of choice for most ferroalloy furnace linings. However, as the capacity of submerged arc furnaces (SAFs) continues to increase, the problem of premature lining failure has become prominent. This document outlines a relatively simple yet effective technological solution to address this long-standing industry challenge.

An examination of current carbon furnace lining construction methods reveals three primary techniques:

1.  The Carbon Brick "Seamless" Method

2.  The Carbon Brick Wide-Joint Method

3.  The Cold-Ramming Paste Monolithic Ramming Method

Each method has inherent disadvantages:

   "Seamless" Carbon Brick Method: True seamlessness is unattainable. Molten metal can penetrate through micro-cracks at the brick joints, infiltrate beneath the bricks, and cause them to float, leading to complete lining failure.

   Wide-Joint Carbon Brick Method: This involves machining annular grooves into the sides of carbon bricks, leaving approximately 50mm gaps during construction, which are then filled with cold-ramming paste. The weakness lies in the relatively loose structure of the wide-joint filler, which lacks the density and corrosion resistance of the high-pressure pressed carbon bricks. Consequently, these joints erode prematurely, allowing molten metal to quickly reach the brick bottom and induce failure.

   Cold-Ramming Paste Monolithic Method: The resulting lining structure is less dense than carbon brick, leading to inferior performance and a significantly shorter service life.

Innovative Solution

Through extensive research, the author has developed a novel furnace construction method that synthesizes the advantages of existing techniques. This method leverages the hot-melt properties of carbon paste—solid at room temperature but capable of melting, fusing, and ultimately graphitizing at high temperatures—to address the critical weakness of brick joints. The goal is to prevent early lining failure, thereby extending lining life and overcoming a persistent industry problem. This method has been granted a National Utility Model Patent.

The foundation of this approach is the "seamless" carbon brick method, with special treatment applied to the lining's vulnerable points: the brick joints, categorized as vertical joints and horizontal (flat) joints.

1. Special Treatment of Vertical Joints

The vertical joint treatment involves machining two inverted dovetail sealing grooves around the perimeter of each carbon brick. These grooves are filled with a specially formulated, low-expansion coarse-joint paste. This transforms each carbon brick into a composite structure, consisting of a pre-baked carbon matrix integrated with a continuous belt of self-baking paste material.

After the SAF lining is constructed using the "seamless" masonry method and the furnace is commissioned, the temperature rise causes the pre-installed self-baking paste within the inverted dovetail grooves to melt, fuse, bake, and solidify. This process effectively seals the vertical joints between adjacent bricks, analogous to a sealing ring in mechanical assemblies, thereby blocking molten metal penetration. Crucially, because this sealing element is embedded within the brick body, it is protected from direct wash-out by the molten metal. This allows even the initially loose paste structure to meet practical service requirements.

2. Special Treatment of Horizontal Joints

A typical furnace lining design uses three layers of carbon bricks, resulting in two horizontal joints, with each layer staggered 45° relative to the layer below. Inverted dovetail grooves, wider and shallower than the side grooves, are machined onto the mating surfaces (top and bottom) of the carbon bricks. These, along with the side grooves, are filled with self-baking paste, tamped, and ground smooth.

When the furnace is put into operation, these horizontal grooves form a flat, prismatic mesh. At the intersections of upper and lower brick grooves, the paste fuses together, creating a robust network that integrally joins the upper and lower layers of carbon bricks. This structure ensures that even if molten metal penetrates to the bottom of a brick, it cannot cause the brick to float.

Conclusion

Through differentiated treatment of vertical and horizontal joints, the carbon bricks forming the furnace lining—including wall bricks and tap-hole bricks—are securely interconnected into a cohesive whole. This effectively prevents metal penetration, providing an elegant solution to a longstanding industry challenge.

This method is both simple to implement and highly effective. It warrants attention and adoption within the industry. Its widespread promotion and application are anticipated to significantly extend furnace lining life, substantially reduce production costs, and elevate lining technology to a new level.

We are a professional electric furnace manufacturer. For further inquiries, or if you require submerged arc furnaces, electric arc furnaces, ladle refining furnaces, or other melting equipment, please do not hesitate to contact us at  susan@aeaxa.com