Ceramic fiber — alumino-silicate insulation materials

Alumino-silicate wool

Alumino-silicate wools are chemically neutral and resistant to most acids and bases. They are not resistant to strong alkalis or to hydrofluoric and phosphoric acids.

The position of special mullite wools in high-temperature insulation is undisputed today. These products are characterised by extremely high temperature resistance and excellent properties. Thanks to their higher alumina content, the wools are highly resistant to chemical attack, reducing atmospheres and vacuum.

Alumino-silicate blankets

The blankets are available in needled form, made of alumino-silicate fibres and wool, in various thicknesses and densities.

Advantages:

• very good resistance to thermal shock
• low thermal conductivity
• high chemical resistance
• highly eco-friendly thanks to optimal energy use, hence economical to apply

Their thermal load and insulation properties differ as a function of composition. Ceramic-fibre blankets and papers are recommended for chimney pipe insulation.

Fibre-ceramic paper

Fibre-ceramic paper is made from alumino-silicate fibres and a small amount of inorganic and organic binder in a long sieving process. This produces elastic papers available in thicknesses from 0.5 mm up to 6 mm.

Depending on the type of alumino-silicate fibre used, we distinguish product groups by classification temperature:

• 1260 °C
• 1400 °C
• 1600 °C

Further processing can be done by cutting (into strips of various widths and lengths) or by punching.

Fibre-ceramic papers are used in the following fields:

• as firing underlay
• as a separation layer in sintering processes
• as thermal insulation
• in dentistry

Above 200 °C the organic binder volatilises and the paper's strength drops significantly.

Fibre-ceramic cords and textiles

Fibre-ceramic yarns — the starting product of all fibre-ceramic textiles — are spun into braids from 1260 °C classification alumino-silicate fibres and about 20 % organic fibre (e.g. viscose or cellulose fibres). To increase strength, glass fibres are incorporated into the braids up to a service temperature of 500 °C, and chrome-steel wire up to 1150 °C.

The following textile products can be produced from these braids:

Fibre-ceramic cords

Made of parallel yarns that are twisted together. The number of yarns determines the cord diameter. Because the yarns are not interconnected, fibre-ceramic cords have low shape retention.

Fibre-ceramic gaskets

Made of interwoven fibre-ceramic yarns; available in round and polygonal cross-sections. Thanks to the interweaving, fibre-ceramic gaskets are very dimensionally stable.

Insulating cords

Insulating cords are made by winding fibre-ceramic braids around a soft fibre-ceramic blanket core in narrow or wide bundles, combining the favourable properties of the blanket and the braided cord.

Fibre-ceramic tapes

Tapes are woven from fibre-ceramic yarn to a given width. Depending on the weaving method, we produce tapes 2–3 mm and 4–5 mm thick.

Fibre-ceramic fabric

Fibre-ceramic yarns are processed into fabric by a weaving operation. Width is 1000 mm, standard roll length is 30 m. Fibre-ceramic fabrics can be further processed into fire blankets, welding curtains, etc.

Modules

Strip modules are manufactured from alumino-silicate or alumina wools, or a combination of them. Blanket strips arranged in parallel are pressed to a precise module thickness and tied together with gauze or straps. The strip modules can also be used as felt modules — glued with special adhesive to metal mesh or brick lining. The choice of anchor and adhesive decisively affects the service life of the lining.

Advantages:

• simple installation
• no special tools required
• welded or screwed anchors can be used
• anchor points can be inspected before being covered
• furnace lining irregularities can be easily evened out
• damaged modules are easy to replace
• low maintenance demand when Altra compensating strips are used

Modules are used across all areas of heat-treatment technology, primarily in non-continuously operated furnaces: forging furnaces, ladle lids (steel industry), hardening furnaces, annealing furnaces, porcelain kilns, ferrite furnaces, after-burners, etc.

Felt modules

Felt modules are felt sheets joined parallel to each other and pressed together with an organic adhesive. Before gluing to the refractory lining, a perforated bar is typically used to create a large number of holes on the cold side of the felt module. This produces a better mechanical key between the adhesive and the fibre structure, leading to better adhesion to the furnace wall.

The adhesive's role is to fix the felt modules to the metal mesh or brick lining. The choice of adhesive decisively affects the service life of the lining.

Advantages of bonding:

• fast and easy installation
• energy saving
• protection of the existing brick lining against thermal-cycling spalling

Prothermo Hofmann Ltd. selects and applies the various ceramic-fibre materials with great care so that they are environmentally friendly and that the most optimal refractory and insulating materials are used in our equipment for each technological process.