1	“Refractories for The End User” Refractory Principles and Simple Rules of Thumb for Problem Solving Jim Conrad Fedmet Refractories
2	Chemical Reactions Most all refractory reactions are simple acid/base reactions The exception is the role of fluxes Refractory oxides are generally classified as one of these 3 types Acid, base or flux
3	Refractory Oxides Crystals of oxidized metallic elements. Each pure oxide or compound has a unique crystalline shape and properties. Crystals can react at high temperatures to combine with other crystals (sintering). If these new compounds are refractory, they’re called spinels. If they’re not refractory, they’re called glass-forming, and contribute to slag.
4	Acid Oxides Silica (SiO2): melts at 3133F. Occurs naturally as sand and quartz. Part of most other minerals like bauxite, olivine, etc. Alumina (Al2O3): melts at 3722F. Occurs naturally as clay and bauxite.
5	Basic Oxides Lime (CaO): melts at 4660F. Occurs naturally as limestone, and is part of dolomite. Magnesite (MgO): melts at 5070F. Occurs naturally as periclase and is in olivine and dolomite.
6	Acid/Base Reactions CaO + Al2O3 = Calcium aluminate. Melts at 2600F. MgO + Al2O3 = Spinel. Melts at 3875F. CaO + SiO2 = Di- or Tri-Calcium silicate. Melts at 3497F. MgO + SiO2 = Olivine. Melts at 3362F.
7	Acid/Acid and Base/Base These can happen because one element is a stronger acid or base than the other. They are easily decomposed in the presence of a complimentary acid or base. MgO + CaO = Dolomite. Melts at 4658F. Al2O3 + SiO2 = Mullite. Melts at 3362F.
8	Fluxes A non-refractory oxide that can enter the crystal structure and lower its melting point (refractoriness) by altering the bonds. FeO/Fe2O3: melts at 2586F. MnO2: melts at 1950F. K2O: melts at 1200F (red heat). Na2O: melts at 1200F (red heat). F: melts at 1200F (red heat). Cl: melts at 1200F (red heat).
9	Inert oxides Neither acid nor base. Have very few possible reactions due to the stability of the pure oxide. Zirconia: melts at 4892F. Chrome: melts at 4226F.
10	Exotic additives Additives to refractories that aren’t oxides at all. Carbon: doesn’t melt. Can remove oxygen from an oxide (called reduction) and turn it back into a metal. Also subject to oxidation. Carbides and nitrides: react similarly to carbon. Also subject to oxidation, but worry about hydration too.
11	Refractory Systems Based on compatibility of the oxides- acid/base, acid/acid and base/base reactions- with the slag present in the operation. Additives of inert or non-oxides can be made to repel fluxes and slag components. Sacrifical metallic additions can be made to retard oxidation and form carbides to lower permeability of gasses like oxygen.
12	Slags Classified by their major components and the ratios of acid to base. Due to its beneficial reactions with undesirable elements in metals (sulfur, phos, etc.), CaO is a common component in metals processing. CaO is also very reactive and forms non-refractory (glassy) compounds with acids. These are slag-forming and cause erosion to the rest of the refractory.
13	Slag Basicity In silica-rich slags, this is calculated by % CaO / %SiO2 = V In alumina-rich slags, this is calculated by % CaO / (% Al2O3 + % SiO2) = Vm
14	Refractory Selection Avoid putting an oxide in contact with a slag high in other oxides that form glasses with the dominant oxide in the refractory. Be aware of which fluxes attack which oxides and minimize the potential for problems. If circumstances require using a chemically less-than-ideal oxide, consider using additives to protect or enhance the system.
15	Refractory Selection Cont. Other points to consider are mechanical: Thermal shock resistance Heat transfer Abrasion Erosion Hot strength Flexing Expansion
16	Mechanical Considerations All refractories expand when heated, but they reach a point where they soften and then shrink before turning to a liquid. This is referred to as creep and is reported as the temperature at which this softening occurs. The higher the creep value, the higher the refractoriness.
17	Mechanical Points, Cont. Another property to consider is thermal conductivity. This is reported as BTU/SF/HR2. The higher the number, the more heat is lost through the lining. Carbon in the form of graphite is the highest conductor. Air is the worst conductor. Denser refractories generally conduct more heat.
18	Observations of Stresses / Wear mechanisms Spalling: when a refractory fails under a load, and the hot face shears off due to pressures exceeding the strength of the brick. This is always a localized phenomenon, at least at the beginning. Corrosion: due to chemical attack. Usually an over-all phenomenon at the slag/metal interface. Can be worse in spots where adds are made and high concentrations of fluxes are present. Erosion: caused by movement of liquids, solids and even gasses across a refractory surface. Always localized.
19	Addressing Mechanical Stresses There are options available to deal with these potential problems: Improve hot modulus and/or elastic modulus. Improve volume stability. Modify lining design to tighten or loosen the lining as necessary. Add anti-oxidants to retard oxidation, increase MOR and reduce abrasion losses.
20	Electric Arc Furnace Electrical energy Chemical energy Water leaks Oxidation Post-combustion Thermal Cycling Scrap Charging
21	Slag foaming in the EAF Keeps the arc buried and away from the sidewall refractory Reduces oxidation of the lining and the electrodes Insulates the bath Promotes favorable reactions like phos and sulfur removal Reduced emissions
22	Arc Flare The electrical arc is very hot and packs a lot of energy. The flame front of the plasma is many times hotter than the melting point of any refractory. Arc can also physically damage linings that it hits through abrasion .
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24	High power, long arc: meltdown
25	Low power, short arc: refining
26	Maintenance Considerations
27	Maintenance Considerations
28	Other maintenance issues Water panel leaks Water hydrates magnesite Steam is more reactive than water Water reacts to form magnesium hydroxide This new crystal is larger and pushes the brick apart from the inside out Visibly identifiable by smell of acetylene or black crumbly brick
29	Other maintenance issues Burners Oxygen must be balanced so that there is little extra oxygen in the furnace (lean) This burns the carbon from the brick and weakens it and reduces its slag resistance Visibly evident by brown crumbly brick
30	Other maintenance issues Hot repair Bottom must be fritted to maintain the banks and fill holes from boring Thin spots should be gunned as needed to balance the lining wear
31	Other maintenance issues Cold repair Tapholes will need regular replacement Door jambs may require periodic repair Water leaks will have to be dug out and replaced Brick under burners may need constant repair Bottoms can be also repaired cold
32	Design Furnaces come in all different sizes and configurations Conventional runner furnaces EBT (eccentric bottom tap) HOT (horizontal opening taphole) Shaft (vertically preheated scrap) Consteel (horizontally preheated scrap) AC (alternating current) DC (direct current)
33	EBT with a stadium
34	EBT with a shiner bottom
35	Ladles Thermal Cycling Electrical Energy (LMF) Stirring Alloying/refining Tapping Flexing
36	Spalling
37	Ladle Design Round Obround Oval Retaining systems Plug vs Full Bottom Flat vs sloped bottom- yield
38	Designs
39	Stirring Corrosion Erosion Abrasion Localized Metallurgical need
40	Slag compatibility Look at the ladle lining as a System Address dominant wear mechanism in each area Start with chemical and work toward mechanical concerns
41	Tundish Safety Cleanliness Homogenization Performance Cycling Covers Slags
42	Troubleshooting a lining. Get digital pictures. Show high-wear areas and phenomena like spalls, cuts, washes. Do a detailed tear-out profile. Look for any operational anomalies- water leaks, extended outages, new grades, new processes, new operators, etc. Pull a slag sample from the hot-face of the lining if available.
43	Proper Refractory Installation Dry Clean Tight Straight / flat Don’t reverse any keys Stagger cuts Remove all steel penetration Backfill as necessary Fully spike and vibrate bottoms
44	Taphole installation Straight Centered Tight joints Backfill surround block fully
45	EAF Bottom installation 1 bag at a time, no more than 6 inches thick Spike to de-air Vibrate to densify Tin over when done to minimize scrap penetration
46	When repairing EAF Clean surfaces- no slag or steel Remove cracked or broken brick Remove all hydrated or badly oxidized brick Backfill as necessary to fill voids
47	Ladle Installation Start level and flat Keep joints tight Sweep debris from bed joints Ram small volumes to prevent voids Maintain safety linings
48	Summary There are many factors that have to be considered in every case for proper refractory application. Chemical concerns are the first priority. A lot of accurate slag data is required to make good choices. Mechanical problems are hard to predict. But, they will manifest themselves in predictable ways, and they must be addressed methodically.
49	Summary, cont’d Steel is very fluid and will find the smallest void Linings must be tight and properly configured Hydrated and oxidized brick are not going to hold up in the furnace or ladle and will wear very fast When in doubt, tear it out.
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