This case study involves the replacement of a cast-in-place refractory nose ring in each of two rotary kilns that produce pebble lime. In one case, a nose ring was designed for a kiln that is 3.0 m in dia. and 45.7 m in length and has a discharge opening of 2.6 m of steel inside. The kiln in the second case is 4.6 m in dia. and 47.2 m long with a discharge opening of 3.8 m dia.
One difference in the two cases involves the geometry of the shell at the actual point of discharge. The geometry of the shell at the discharge of the 3.0 m dia. kiln was truly conical. The geometry of the shell of the 4.6 m dia. kiln incorporated a very short cylindrical portion at the discharge. This cylindrical mounting surface made the design of the nose ring to be installed much simpler.
Allied Mineral Products’ METAL-ROK® 70M was used to make the set of precast refractory shapes that comprised each nose ring system. METAL-ROK 70M is a fine grain, mullite-based material containing a significant concentration of uniformly distributed metallic fibres.
Due to the nature of the product’s composition and unique design, it can only be supplied in the form of precast shapes. However, it is the casting of the material in the shop under controlled conditions, that gives the product its properties.
METAL-ROK 70M is a low water, low cement refractory material with high density and low porosity. With the addition of carefully chosen metallic fibres, the material becomes a workhorse in application. METAL-ROK 70M has excellent mechanical toughness and hot strength, as well as superior resistance to both abrasion and thermal shock.
Producing the shapes
Two steel backer plates, appropriately cut and shaped, are welded together to form the foundation of the shapes. Stainless steel anchoring is welded to the backer plates. These welded steel substrates are then placed in carefully constructed forms of steel, wood, or hard foam, depending upon the nature of the application. The METAL-ROK 70M material is then cast into the moulds, onto the steel, and allowed to set up. Once set, the shapes are separated from the forms and are then pre-fired under controlled conditions in curing furnaces.
The precast, pre-fired shapes were palletised, protected from moisture, and shipped to site. Onsite, with existing refractory materials removed as necessary, the precast METAL-ROK 70M shapes were welded into place one at a time to form each nose ring system. In the case of the 3.0 m dia. kiln, the nose ring was made up of 22 individual precast shapes, each weighing approximately 109 kg. The nose ring on the 4.6 m dia. kiln had 36 shapes, each weighing about 70 kg.
- Reduced kiln system down-time as a result of a simpler installation than alternate nose ring designs and a much more aggressive, shorter heat-up schedule.
- The unique physical properties of METAL-ROK 70M offered design options that eliminate the need for the alloy steel castings previously required for the structural support of cast-in-place design approaches.
- Service life is in excess of six years, with no maintenance or repair required.
Read the article online at: https://www.worldcement.com/special-reports/23102019/taking-shape/
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