Regardless of how complex or sophisticated the refractory castable is that is selected for an application, the physical properties of the material can be drastically reduced if care is not taken during the mixing, pouring, and curing processes. Particularly with the use of more complex refractory castables to solve specific wear issues, installation variables become even more critical to the performance of a lining. Unfortunately, lining quality is often compromised by field conditions during material placement. Precast roof panels ready for shipment. Project schedules, crew skill levels, equipment availability, job cost pressures, or other demands can sometimes influence proper refractory installation. Improper water addition, mix time variations, over- or under-vibration, and improper curing can drastically affect material quality. With precast shapes, cast in a controlled shop environment, the physical properties of a castable can be more fully optimized.
Initial drying and firing of a refractory castable is a critical installation variable that can influence lining performance. Precast shapes are typically fired in a digitally-controlled furnace prior to shipment, ensuring that the refractory manufacturer's recommended bake-out schedule is closely followed. Since the shapes are fired slowly from all sides, the moisture is removed through the entire thickness of the shape in a controlled manner. Depending on the temperature to which the shape is fired, this can optimize the physical properties of the material through the entire thickness of the shape, not just the hot face surface. This results in a truly homogeneous lining. Micro-cracking within the shape, which are often introduced during field bake-out but may go unnoticed, may also be reduced since the initial firing is more controlled.
In service, linings composed of precast shapes often see less stresses and cracking, due to the independent, "floating" nature of the lining. The performance of the lining can also be more predictable, resulting in better opportunities to plan for maintenance and repairs.