Why does the refractory castable used for the furnace nozzle of a tilting furnace fall off?

A tilting furnace is a movable furnace body with a refractory lining that can operate continuously. The furnace cover and furnace nozzle of this type of furnace are generally made of refractory castable, while other parts are lined with refractory bricks.

The refractory castable lining on the furnace cover is 80 mm thick, with V-shaped anchors. After pouring, the castable needs to be baked before it can be put into operation. However, many manufacturers apply the refractory castable directly onto the furnace nozzle without baking and put it into use immediately. This method is widely adopted because it simplifies on-site construction.

To be used properly, the refractory castable for the furnace nozzle must meet certain technical requirements. Specifically, its maximum particle size should not exceed 6 mm. The castable for the furnace cover, by contrast, has a maximum particle size of 8 mm. If the furnace-cover castable is applied directly to the nozzle without baking, it is very likely to fall off. So how can this problem be prevented?

First, the furnace nozzle must be cleaned thoroughly before applying the castable. If the surface is not properly cleaned, the castable will likely fall off within a few days of use. Second, the binder must be added during mixing. Without the binder, the castable lacks flowability and will fail to bond firmly, leading to spalling within a few days. Third, if the water addition is not properly controlled, this can also cause the castable to fall off.

The best approach is to use a trowelling mix instead of castable at the furnace nozzle. A trowelling mix is more convenient to apply. Since the binder used in a trowelling mix is different from that in a standard castable, a specialized mix with better flowability and workability can be formulated specifically for furnace-nozzle applications. That said, the furnace nozzle must still be cleaned thoroughly beforehand — otherwise, spalling will still occur. In addition, it is recommended to commission the lining after low-temperature baking. Rapid heating during commissioning is also acceptable, but the initial temperature should not be too high.

If refractory castable is used at the furnace nozzle, its particle size must be properly controlled. After construction, it should be properly baked before being put into operation. This is the most effective way to extend the service life of the lining.