An effective means for improving the explosive spalling resistance of a refractory castable or monolithic is to add organic fibers to the formulation. It has been reported that the composition and concentration of fibers are not as important as melting temperature of the fiber, since organic fibers after melting increase permeability at certain temperature and thereby reducing the explosive spalling tendency of the castables and monolithics. The fibers generally used for this purpose are Polypropylene fibers, Polyester staple fibers, etc.
Bottom-line: Both organic and Stainless Steel fiber reinforced refractory castables and other monolithic refractories provide substantial increase in service life and therefore, a considerable reduction in refractory maintenance cost and furnace down-time.
There are several benefits of adding steel fibers in refractory castables and some other monolithic refractories. Steel fiber reinforced refractory castables are very resistant to the tendency of the material to fall apart on thermal cycling. Stainless steel fibers greatly improve the flexural strength of the castable. And this added increase in ductility contributes significantly to the thermal shock and spalling resistance of refractory castables. The fibers generally used are in size varying between 0.1 to 0.4 mm2 in cross-section and 20-40 mm in length.
For monolithic refractories SS (stainless steel) is used either high chrome or high chrome nickel steels available in the market with different grades (Refer to our another article Categories and Types of Stainless Steels: Compositions and Properties). One reason commonly reported that the thermal shock resistance of castables is greatly increased through addition of Stainless Steel fibers is because these fibers act as crack arresters, preventing cracks propagating. This is also possible that the micro cracks caused by a mismatch in thermal expansion coefficients of refractory matrix and fibers dissipate energy from larger cracks propagating as a result of thermal stress.
However percentage of these fibers added is very important because of two reasons:
One of the most effective ways of improving the mechanical and thermal properties of refractory castables and other monolithic refractories is adding stainless steel fibers and organic fibers in suitable proportions to these products respectively.