Refractory linings in kilns, hot blast stoves and exhaust ducts fail in predictable ways: the hot face cracks, backup insulation absorbs heat it was never designed for, and the shell reaches temperatures that endanger personnel. Ceramic Fiber addresses this because it delivers low thermal conductivity at high temperature in a form that can be shaped, layered and anchored without the joints that complicate dense brick.
One property explains most of the interest: conductivity stays roughly constant as temperature rises, unlike insulating firebrick, whose conductivity climbs with mean temperature. The trade-offs are equally clear: low thermal mass, no structural strength, poor resistance to abrasion, impact and flame impingement, and particle release from disturbed exposed surfaces.
Selection starts with the working temperature of the hot face, not the average furnace temperature, and continues with cycle length. Short cycling furnaces tolerate a lower grade than a continuous-duty kiln, while a vessel exposed to molten metal splash needs a hard face rather than bare fiber. Confirm the declared classification temperature, the fiber chemistry, and whether the product is a blanket, a module or a finished board.
| Grade family | Continuous service temperature | Typical density | Thermal conductivity | Best suited to |
|---|---|---|---|---|
| Standard alumina-silicate blanket | 1050–1260 °C | 64–128 kg/m³ | 0.12–0.30 W/m·K | General furnace backup insulation |
| High-alumina blanket | 1260–1425 °C | 96–160 kg/m³ | 0.15–0.35 W/m·K | High duty cycles, vibration-prone ducts |
| Alumina or mullite fiber board | 1425–1600 °C | 200–350 kg/m³ | 0.25–0.40 W/m·K | Machined linings facing gas flow |
| Higher-grade alumina fiber | 1600–1650 °C | 150–300 kg/m³ | 0.15–0.35 W/m·K | Hot blast furnace bustle pipes |
| Compressed fiber module | Set by parent grade | 96–160 kg/m³ | Rises after compression | Anchored linings on curved surfaces |
A workable rule is to specify a classification temperature at least 100 °C above the calculated hot face temperature, leaving headroom for local fluctuations, uneven gas distribution and the temperature rise after a shutdown. Never mix grades within one continuous layer: the denser grade becomes a heat path and the soft grade collapses into gaps. Separate temperature zones with a designed expansion joint, and confirm the chemistry suits the atmosphere.
In rotary kilns, tunnel kilns and hot blast furnaces, Ceramic Fiber is rarely used at the hot face against the burden or the gas stream. Dense brick or castable is retained where mechanical wear, chemical attack and slag adhesion are severe. The fiber sits behind that dense layer as backup insulation, and takes over where geometry prevents a thick dense lining: the charging end of a rotary kiln, door seals, burner ports, flue transitions and hot blast stove bustle pipework.
Unanchored fiber will not stay in place; the anchor system holds its shape and resists gravity and gas flow. The usual arrangement is stainless or alloy studs welded to the shell, each carrying a self-locking washer that grips the blanket when tightened. Module construction compresses the blanket between anchor and shell, so it holds its shape and can be removed without dismantling the lining. Keep anchor spacing consistent and allow for expansion near openings. Weld studs only to clean, prepared steel and verify them by pull test; coat them where condensation is possible, since a corroding anchor releases the lining long before the fiber is spent. Hardware inside the hot zone must match the service temperature of that zone.
Pipes and ducts are where Ceramic Fiber shows the clearest economic return, because a small thickness reduction translates into a smaller support structure and lower heat loss. Most hot duct work uses a segmented blanket with a facing of aluminum foil, sheet or board to protect the fiber from airflow erosion and mechanical damage. Horizontal runs need banding at regular spacing, and every flange or damper needs a removable section for inspection.
| Service | Typical temperature | Recommended construction | Typical thickness | Critical installation point |
|---|---|---|---|---|
| Hot flue and exhaust duct | 200–600 °C | Segmented blanket with foil or board facing | 60–120 mm | Keep the facing away from the gas stream |
| Removable pipe jacket | 250–700 °C | Segmented blanket, mesh and fiber wrap | 50–100 mm | Split the jacket so flanges stay accessible |
| Steam or hot water header | 120–300 °C | Blanket with a weather protection sheet | 50–80 mm | Overlap the vapor barrier at every joint |
| Cold surface pipework | Below 100 °C | Fiber with sealed barrier and cladding | 40–80 mm | Seal the barrier against condensation |
| Kiln car and deck | 300–900 °C | Board or module over a protective deck | 40–75 mm | Protect the fiber from load and spillage |
Cut the blanket slightly oversize and compress it into the joint so no gas path remains, and tighten the banding without crushing the fiber. A seam pulled open during installation lets hot gas wash the fiber surface and degrades it quickly.
Where a lining must resist handling, vibration, dust or light erosion, Ceramic Fiber is supplied as rigid board rather than blanket. Boards are cut, drilled and machined on site, so anchor holes, slotted patterns and service penetrations can be prepared before the panel is lifted into position. Rigid panels serve as the visible inner layer of a furnace wall or the back-up layer behind a dense hot face, often combined with a low-density blanket for extra thermal resistance.
Ceramic Fiber also appears as a filtration medium rather than as insulation. Felt, blanket and woven elements made from ceramic fibers are used in high-temperature bag filters, candle filter elements and catalytic substrate supports where the gas stream carries dust that would destroy conventional fabric or metal media. Because fibers can be produced with fine diameters and controlled pore structure while retaining mechanical integrity, the same material family serves both a porous filtration layer and a rigid support grid. Media in this service is judged on temperature rating, permeability, basis weight, dust loading behaviour and chemical resistance, and must be specified with the cooling or quenching system that keeps it below its limit.
Start from the dust itself. Fine abrasive dust demands high permeability and a robust support structure, while sticky or corrosive dust usually needs a chemically resistant fiber and careful handling of the collected cake. A filter element is only useful within a defined temperature window, so confirm whether the gas enters hot and is quenched by air or spray, or whether elements must survive an extended cooldown without cracking. Support hardware must also match the service temperature. Fine ceramic fiber dust is a respiratory concern, so handle the media with care.
Most production problems with Ceramic Fiber are installation problems rather than material problems, and a disciplined sequence prevents nearly all of them.
Records kept during installation are the difference between a diagnosis and a guess. Note the fiber grade, the anchor test results and any deviation from the drawing.
Acceptance should follow a fixed order. Visually inspect the hot face for open joints, exposed anchor washers, gaps around penetrations and any area where fiber was cut back to fit. Confirm the facing is continuous and that vapor barrier joints on cold service are sealed. Check installed thickness at defined points and record the readings, since an average hides local thin spots. Before start-up, run a controlled heat-up and watch the shell temperature, since rising metal temperature in the first hours usually points to a thin spot or an open joint. Log the results and measured thicknesses in the installation file for the next shutdown.
Thickness follows the calculated hot face temperature, the required shell surface temperature and the conductivity of the selected grade at mean temperature. As a starting point, 75–150 mm of blanket covers most general kiln backup work, while ductwork often needs less and very large cold shell installations may need more. Because conductivity changes little with temperature, base the design on steady-state calculation and confirm it by shell temperature measurement after the first heat-up cycle.
Only where the service is benign. Bare fiber is unsuitable where the lining faces direct flame impingement, hot material load, abrasive dust, slag adhesion or severe chemical attack, because it has no hot face hardness and no mechanical strength. A common arrangement keeps a thin dense layer at the hot face and places Ceramic Fiber behind it as backup insulation.
The most frequent causes are installation faults rather than material faults: blanket joints pulled open during fitting, gaps left around flanges or dampers, insufficient banding on horizontal runs, facing damaged during handling, and erosion where hot gas leaks through an unsealed joint and washes the fiber surface. The second group is underspecification, where the grade was chosen for an average temperature that the gas exceeds at peak load.
Acceptance normally combines four checks: a visual survey of the hot face for open joints, exposed anchors and unfilled penetrations; a thickness measurement at defined points against the design value; an anchor integrity check confirming that studs are tight and correctly welded; and a controlled heat-up with shell temperature monitoring. Measured thicknesses, anchor results and material certificates should be filed with the installation record.
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