Before castables are installed, palladium nails must be welded to secure the castable. The choice of palladium nails and the quality of the welding can directly impact the lifespan of the castable. Many castables experience direct fragmentation during use or collapse during cooling, often due to issues with the palladium nails. Today, we will discuss the material, shape, installation, and inspection considerations for palladium nails.

Palladium nails are generally made of two materials: 1Cr18Ni9Ti and Cr25Ni20. Cr25Ni20 is primarily used in high-temperature, demanding environments, such as the kiln mouth, grate cooler front wall, and a section of low wall. 1Cr18Ni9Ti is sufficient for other locations, saving costs.

Palladium nails come in various shapes, including V-shaped and Y-shaped. V-shaped palladium nails are primarily used in areas with thin castable thickness, such as spray nozzles. Generally, V-shaped palladium nails are suitable for castables with a thickness of no more than 100 mm. Y-shaped nails are used in other areas where the castable is thicker. If the castable is thicker than 300mm, branches must be welded to the Y-shaped nails. The nail height should be sufficient to provide a protective layer against the castable thickness, generally 20-30mm. For V-shaped nails, due to the relatively thin castable, it's best to have the two legs of the nail at different heights to prevent the nail head from blowing off flush with the heat. Generally, the high leg should be three-quarters of the castable thickness, and the low leg should be two-thirds. Some nails have curved legs, and some companies use nuts to secure the nails on the pulverized coal injection pipes. This prevents the nail from expanding during heat rise without affecting its connection to the pipe body.

Welding the nails is crucial. First, choose the appropriate welding rod material. For Cr25Ni20 palladium nails, it's best to use A407 welding rods. This rod's composition of Cr26 and Ni21 closely matches the palladium nail's material, ensuring consistent high-temperature properties. Before welding, the rods should be baked at 250°C for one hour and kept warm in a heat-insulating container during welding. During welding, the welding current should be adjusted between 70 and 120A. For 1Cr18Ni9Ti palladium nails, it's best to use A132 or A137 welding rods; A102 and A107 should not be used. If welding 1Cr18Ni9Ti palladium nails on ordinary steel, use 307 or E309 welding rods. Using the wrong rod material for palladium nails can easily cause problems. When welding, ensure a full weld, welding all three sides of the palladium nail leg. Avoid welding at the bend to prevent damage, which can easily break the nail during use. Also, be sure to remove any debris from the base metal weld joints, including any rusted areas. It's best to polish them clean with a grinding wheel. Inspection of palladium nails involves two steps. The first is to check for cracks at the bend before welding. Palladium nails are typically machine-bent. If the material is poor or the bending speed is high, cracks can form at the bend, seriously affecting strength. In many cases, the nail falls off along with the castable, leaving only a small section welded to the base. Therefore, careful inspection is essential; any cracked nails should be discontinued. The second step is to inspect the weld quality after completion. This is typically done by tapping with a small hammer, paying careful attention to the direction of the strike and avoiding excessive force in the direction of the bend. Once the weld quality is inspected, asphalt paint can be applied. A plastic cap is generally recommended for the palladium nail head. Palladium nails expand the most toward the head, so sufficient clearance is essential.

If these steps are followed, large pieces of castable material will generally not fall off, and the castable's lifespan can be guaranteed to a certain extent.