I. Flow Mechanism and Molding Method
1. Self-Flowing Castables: Flow and deaerated by their own gravity, requiring no external vibration. The slurry is in a suspended state, with the aggregate encapsulated by a continuous phase, exhibiting an overall "liquid" behavior.
2. Refractory Castables: Belong to a vibration molding system. High friction between aggregates necessitates external vibration to rearrange particles and expel air bubbles; molds are also required to maintain shape.
II. Aggregate Gradation and Morphology
1. Self-Flowing refractories Castables: Use near-spherical, rounded aggregates, with a strictly controlled upper limit of 5mm particle size, occasionally relaxed to 8mm. High roundness and low water absorption reduce internal friction and improve rollability.
2. Refractory cement Castables: Irregular aggregate morphology with sharp edges; gradation range 0–10 mm, with special varieties allowing up to 25mm. Coarse-grained skeletons impart higher load-bearing temperatures and high-temperature strength to materials, but reduce fluidity.
III. Matrix Composition and Slurry Characteristics
1. Self-flowing Castables: High matrix proportion; the synergistic effect of ultrafine powder, dispersant, and suspending agent gives the slurry "Bingham fluid" characteristics in a static state, with low yield value and moderate plastic viscosity. Aggregates remain dispersed, allowing for overall self-leveling.
2. Refractory Castables: Relatively less matrix; particle contact is mainly point-to-surface. Vibration is needed to break the "arch bridge" structure, forming a dense packing. The system is more dependent on aggregate strength; therefore, its room-temperature and high-temperature mechanical properties are usually higher than those of self-flowing materials of the same material.
IV. Water Addition and Construction Control
1. Self-flowing Castables: Higher water addition than traditional vibratory castables. Excess water activates the dispersant, causing the ultrafine powder to produce a dual effect of filling and lubrication, further reducing the yield value; however, high-efficiency water-reducing agents and setting control agents are needed to prevent segregation.
2. Refractory material Castables: The amount of water added must be strictly controlled. Excessive water will cause particle segregation and bleeding during vibration, leaving interconnected pores after baking, significantly reducing strength and corrosion resistance.
V. Molds and Working Environment
1. Self-flowing refractory Castables: No complex support is required; only simple baffles or paper templates are needed. Pumping or self-flowing nozzles can be used to fill high or narrow areas, reducing labor intensity and construction time.
2. Refractory Castables: Full-size molds must be made according to the furnace shell shape, and the molds must have sufficient rigidity to resist the lateral pressure of vibration. Demolding time and turnover efficiency directly affect the construction cycle.
VI. Application Areas and Thickness Requirements
1. Self-flowing Castables: Suitable for thin-walled lining areas (<100mm), geometrically complex or manually vibratory dead corners, local repairs, and emergency repairs requiring rapid furnace drying.
2. Refractory cement Castables: Used in large-area load-bearing areas of the working layer, typically designed with a thickness ≥100mm. The thick structure resists slag erosion and thermomechanical stress, ensuring long-term operation.
VII. Material Expansion and Development Trends
Self-flowing castables are not a single-variety concept, but rather can achieve "self-flowing" designs on various matrices such as high-alumina, corundum-spinel, magnesia, and silicon carbide. By adjusting the dispersion-suspension-thixotropic ternary system, they can meet the differentiated requirements for purity, erosion resistance, and thermal shock resistance under different furnace atmospheres (oxidation, reduction, vacuum).
With the rise of new construction methods such as pumping, spraying, and 3D printing, self-flowing materials have become an important branch of low-labor, high-efficiency, and green refractory materials, while traditional vibratory castables continue to maintain an irreplaceable position under thick-layer, high-load conditions. The two complement each other, jointly driving the development of kiln lining technology towards "functional zoning and precise matching.
