Refractories

Thermal cycling, thermal shock, mechanical impact or vibration can all cause cracking, which in turn can lead to premature failure and substantial cost penalties. Achieving maximum refractory service life at a minimum cost is therefore a key element in the efficient operation of these processes, and in enabling companies to maximize their competitive edge.

The addition of Ribtec's Rapidly Solidified (RS) steel fibers to castable, gunning and moldable refractories inhibits crack formation (Figure 1) and transforms the conventional refractory from a brittle material to a tough and tenacious composite (Figure 2) exhibiting dramatic improvements in service life.

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Ribtec's direct spun stainless fibers are fully annealed and therefore more pliable and ductile. This is of particular benefit during the mixing cycle and when the refractory composite is installed. These pliable fibers are not only more user friendly than the stiff "needle-like" cut fibers, but also have better flow characteristics. Dispersion is further aided by the optimum Aspect Ratio design which guarantees rapid fiber separation during the mixing phase.

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RS fiber also has a major influence on the cost of the sprayed linings. On impact with a sprayed surface, the majority of ductile fibers contained within a mix stay in place, whereas a high proportion of the stiff drawn wire fibers rebound, resulting in a very expensive waste material. Rebound loss of RS fibers is typically 50% less than that of drawn wire fibers.

The rough cast surface texture and irregular profile of Ribtec RS guarantees "mechanical interlock" with the refractory matrix (Figure 3). The unique "kidney shaped cross-section" (Figure 4) provides a higher specific surface area for bonding than round or flat fibers, and is free of surface lubricants which are often present on chopped wire and slit sheet fiber and which prevents bonding.

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Ribtec RS stainless steel fibers are spun directly from the melt using the company's advanced Melt Extraction (ME) and Melt Overflow (MO) processes. Rapid cooling of the fiber during manufacture (equivalent to 50,000°C per second) "freezes" the metallurgical structure, capturing it in an optimum state to resist high temperature corrosion - a state which is impossible for conventionally cast steel to match.

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As Ribtec produces its own high quality steels, we have developed a range of alloys to cope with the full diversity of service temperatures, operating conditions, combustion gases, etc. When coupled with the benefits of RS processing, Ribtec's alloys provide outstanding high temperature durability and substantially outperform other "equivalent" fiber types on the market with similar Cr and Ni additions.

Our 3/4 or 1 inch long fiber is a popular choice for addition to pre-blended dry refractory castables and gunning mixes. For on-site mixing and for precast shapes our 1-3/8 inch fiber is a preferred choice, imparting even greater performance benefits for the same cost (Figure 6). For special applications, other lengths and diameters are also available.

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Cost savings are the main reason for adding stainless steel fibers. In all areas of high thermal and mechanical shock, fibers will at least double refractory life.

Ribtec's low cost/high performance RS fibers provide the quickest payback. Our quality product costs substantially less because we produce our molten steel and spun fiber on-line in one fully integrated manufacturing plant. Ribtec is able to keep fiber manufacturing costs to a minimum, which is reflected in the very competitive prices Ribtec charges.

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It is essential to include sufficient fiber in the mix to prevent the micro-cracks which develop under thermal stress from propagating into visible cracks which lead to premature refractory failure. International experience has proven that the most cost-effective fiber addition for enhanced serviceability, irrespective of fiber type used, is 1% by volume. (This is equivalent to 3-4% by weight for most non-insulating refractory mixes.)

In an endeavor to trim initial costs, a few refractory suppliers have been tempted to use fiber contents as low as 2% by weight. This is contrary to the current trend towards the use of higher fiber dosage levels (up to 6% by weight) to maximize service life (see Figure 2). Manufacturers of expensive drawn stainless wire fibers often promote 2% fiber addition in an effort to present their product as "competitive". This approach is in reality a false economy, since the associated reduced service life of the composite makes the low fiber containing refractories work out significantly more costly over their shorter service life.

Attempts to support the argument for "low fiber addition" by simple laboratory tests of strength and toughness are misleading and do not reflect "real life conditions".

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Ribtec understands refractory users need immediate product availability to minimize delays in repairs and downtime costs. Ribtec's range of products are therefore available from stock for prompt delivery worldwide. Supported by its international network of local distributors built up over 20 years, Ribtec has developed an unrivalled reputation for service and delivery. Ribtec's distributors are available to offer expert advice on how to get the best results from fibers in refractories.

• Tailor made, low cost stainless steel alloyed fibers to meet all applications.
• Specialized packaging designed to minimize handling costs and to meet specific customer requirements.
• Unrivalled in-depth knowledge of steel fiber technology and economic refractory fiber applications.

Put simply, no other manufacturer can match Ribtec's service.

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