High-temperature mineral wool (HTMW) is a type of mineral wool (a wool-like material made from mineral fibers), created for use as high-temperature insulation - usually for use in industrial furnaces and foundries - generally defined as being resistant to temperatures above 1000°C. The first variety, aluminium silicate fiber, was developed in the 1950s. They are used primarily as insulation for furnaces and foundries.
Due to the costly production, and limited availability compared to regular mineral wool, HTMW products are used almost exclusively in high temperature industrial applications and processes.
Video High-temperature mineral wool
History
According to a manufacturer of HTMW, the first HTMW, known as Refractory Ceramic Fiber was invented in the United States in 1942, but was not commercial viable until approximately 1953. More forms of mineral wool become available in the 1970s and 1980s
Maps High-temperature mineral wool
Definitions
Classification temperature
The classification temperature is defined as the temperature at which a linear shrinkage of a certain amount (usually 2-4%) is not exceeded after a 24-hour heat treatment in the electrically heated laboratory oven and in a neutral atmosphere. Depending on the type of product, the value may not exceed the following limits: 2% for boards and shaped products, 4% for mats and papers. The classification temperature is specified in 50 °C steps (starting at 850 °C and up to 1600 °C). The classification temperature does not mean that the product can be used continuously at this temperature. In the field, the continuous application temperature of amorphous HTMW (AES and ASW) is typically 100-150 °C below the classification temperature. Products made of Polycrystalline Wool can generally be used up to classification temperature.
Wool
Wool is an ordered accumulation of fibres of varying length and diameter. HTMW fulfills this definition and is therefore covered by the term "wool". Amorphous AES and ASW are produced by melting the raw materials in a melting pot by means of electrical resistance melting. The jet of melt discharged from the pot is accelerated in a blowing or spinning process and pulled into fibres with different length / diameter ratios, and then formed into wool.
Types of HTMW
There are several types of HTMWs made from different types of mineral, and with different properties and temperatures that they can withstand. Below are some common types:
Alkaline earth silicate wool (AES wool)
AES Wool consists of amorphous glass fibres, which are produced by melting a combination of CaO-, MgO-, SiO2 and ZrO2. Products made from AES are generally used in continuously operating equipment and domestic appliances. AES wool has the advantage of being biosoluble; if inhaled it will generally stay in the body only a couple of weeks, reducing the chances of causing silicosis.
Alumino silicate wool (ASW)
Alumino silicate wool also known as "refractory ceramic fibre" (RCF), are amorphous fibres produced by melting a combination of Al2O3 and SiO2, usually in a weight ratio 50:50 (see also VDI 3469 Parts 1 and 5, as well as TRGS 521). Products made of alumino silicate wool are generally used at application temperatures of greater than 900°C and in intermittently operating equipment and critical application conditions (see Technical Rules TRGS 619).
Polycrystalline wool (PCW)
Polycrystalline wool consists of fibres containing greater than 70 wt.% Al2O3; they are produced by a "sol-gel method" from aqueous spinning solutions. The water-soluble green fibres obtained as a precursor are crystallized by means of heat treatment. Polycrystalline wool is generally used at application temperatures greater than 1300 °C and in critical chemical and physical application conditions, also at lower temperatures.
Kaowool
Kaowool is a type of HTMW made from the mineral Kaolin. It was one of the first types of HTMW invented and has continued use into the 21st century. It can withstand temperatures close to 3,000° F (1649° C).
Uses
HTMW is used primarily for insulation and lining of industrial furnaces and foundries to improve efficiency and safety. It is also used to prevent the spread of fire.
The use of HTMW enables a more lightweight construction of industrial furnaces and other technical equipment as compared to other methods such as fire bricks, due to it's high heat resistance capabilities per weight, but has the disadvantage of being more expensive than other methods.
Comparison of the mass of different wall linings:
- Lightweight lining (no HTMW): 500-1000 kg/m³
- Heavyweight lining (no HTMW): 1500-3500 kg/m³
- Lining with HTMW: 160-300 kg/m³
Health and environmental impact
Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) is a European Union regulation of 18 December 2006. REACH addresses the production and use of chemical substances, and their potential impacts on both human health and the environment. A Substance Information Exchange Forum (SIEF) has been set up for each type of HTMW; AES, ASW and PCW have been registered before the first deadline of 1 December 2010 and can therefore be used on the European market.
Regulation (EC) No 1907/2006 of the European Parliament and the Council of 18 December 2006 concerning the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) require manufacturers, importers and Only Representatives of non-European manufacturers to share data on potential health and environmental hazard and provide data to the European Chemicals Agency (ECHA) in a formalized registration process.
ASW/RCF, AES and PCW were registered using a joint registration dossier before the first deadline of 1 December 2010. They can therefore be used on the European market. The registration process required that manufacturers, importers of substances >1 t/year agreed on classification, labelling and uses of ASW/RCF, AES and PCW.
The REACH and the CLP Regulation being based on the principle of self-classification by industry; however prior harmonized classification of substances contained in Annex 1 of Directive 67/548 remains valid and has been transferred to Annex VI of CLP. Classification in Annex VI of the CLP Regulation is the mandatory classification; industry has to evaluate whether additional/stricter classification may apply.
- ASW/RCF is therefore classified as carcinogen category 1B
- AES is exempted from carcinogen classification based on short term in vitro study result
- PCW are not classified; self-classification led to the conclusion that PCW are not hazardous
On 13 January 2010 some of the aluminosilicate refractory ceramic fibres and zirconia aluminosilicate refractory ceramic fibres have been included in the candidate list of Substances of Very High Concern. In response to concerns raised with the definition and the dossier two additional dossiers were posted on the ECHA website for consultation and resulted in two additional entries on the candidate list. This actual (having four entries for one substance/group of substances) situation is contrary to the REACH procedure intended. Aside from this situation, concerns raised during the two consultation periods remain valid.
Regardless of the concerns raised, the inclusion of a substance in the candidate list triggers immediately the following legal obligations of manufacturers, importers and suppliers of articles containing that substance in a concentration above 0.1% (w/w):
- Notification to ECHA -REACH Regulation Art. 7
- Provision of Safety Data Sheet- REACH Regulation Art. 31.1
- Duty to communicate safe use information or responding to customer requests -REACH Regulation Art. 33
Fibrous dust
Based on the total experience with humans and the findings of scientific research (animals, cells), it can be concluded that elongated dust particles of every type have in principle the potential to cause the development of tumours providing they are sufficiently long, thin and biopersistent. According to scientific findings inorganic fibre dust particles with a length-to-diameter ratio exceeding 3:1, a length longer than 5 ?m (0.005 mm) and a diameter smaller than 3 ?m (WHO-Fibres) are considered health-critical.
HTMW processed to products contain fibres with different diameters and lengths. During handling of HTMW products, fibrous dusts can be emitted. These can include fibres complying with the WHO definition. The amount depends on how the material is handled. High concentrations are usually found during removal of after-use HTMW and also during mechanical finishing activities and in the assembly of modules. Where fibre products are mechanically abraded by sawing, sanding, routing or other machining the airborne fibre concentrations will be high if uncontrolled. Dust release is further modified by the intensity of energy applied to the product, the surface area to which the energy is applied, and the type, quantity and dimensions of materials being handled or processed. Dispersion or dilution of dust produced depends on the extent of confinement of the sources and the work area, as well as the presence and effectiveness of exhaust ventilation.
Crystalline silica
Amorphous HTMW (AES and ASW) are produced from a molten glass stream which is aerosolised by a jet of high pressure air or by letting the stream impinge onto spinning wheels. The droplets are drawn into fibres; the mass of both fibres and remaining droplets cool very rapidly so that no crystalline phases may form.
When amorphous HTMW are installed and used in high temperature applications such as industrial furnaces, at least one face may be exposed to conditions causing the fibres to partially devitrify. Depending on the chemical composition of the glassy fibre and the time and temperature to which the materials are exposed, different stable crystalline phases may form.
In after-use HTMW crystalline silica crystals are embedded in a matrix composed of other crystals and glasses. Experimental results on the biological activity of after-use HTMW have not demonstrated any hazardous activity that could be related to any form of silica they may contain.
See Also
Mineral wool
References
External links
- ECFIA - European Association representing the High Temperature Insulation Wool Industry
Source of article : Wikipedia
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