Mineral wool (also known as stone wool, mineral cotton, mineral fiber, man-made mineral fiber (MMMF), and man-made vitreous fiber (MMVF)) is any fibrous material formed by spinning or drawing molten mineral or rock materials such as slag and ceramics. It was first manufactured in the 19th century. Applications include thermal insulation (as both structural insulation and pipe insulation), filtration, soundproofing, and hydroponic growth medium. Mineral wool can cause irritation to the eyes, skin and lungs, especially during its manufacture and installation.
History Slag wool was first made in 1840 in Wales by Edward Parry, "but no effort appears to have been made to confine the wool after production; consequently it floated about the works with the slightest breeze, and became so injurious to the men that the process had to be abandoned". A method of making mineral wool was patented in the United States in 1870 by John Player and first produced commercially in 1871 at Georgsmarienhütte in Osnabrück Germany. The process involved blowing a strong stream of air across a falling flow of liquid iron slag which was similar to the natural occurrence of fine strands of volcanic slag from Kilauea called Pele's hair created by strong winds blowing apart the slag during an eruption.
In 1936 Spun Rock Wools Limited of Thorold Ontario Canada registered a trademark for Spun Rock Wool, a “Fibrous Insulating Material manufactured from rock and in loose, sheet, or pad form.” Using rock to produce wool insulation material was started in Thorold in 1934. November 1, 1934 according to the registration document UCA8090. Spun stone wool was made by heating natural dolomite shale to 3,000 °F (1,650 °C) and pouring the white hot liquid onto a whirling disc known as a “spinner.”
According to a mineral wool manufacturer, the first mineral wool intended for high-temperature applications was invented in the United States in 1942 but was not commercially viable until approximately 1953. More forms of mineral wool became available in the 1970s and 1980s.
Properties Classification temperature is the temperature at which a certain amount of linear contraction (usually two to four percent) is not exceeded after a 24-hour heat treatment in an electrically heated laboratory oven in a neutral atmosphere. Depending on the type of product, the value may not exceed two percent for boards and shaped products and four percent for mats and papers. The classification temperature is specified in 50 °C (90 °F) steps starting at 850 °C (1,560 °F) and up to 1,600 °C (2,910 °F). 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 high-temperature mineral wool (AES and ASW) is typically 100 to 150 °C (180 to 270 °F) below the classification temperature. Products made of polycrystalline wool can generally be used up to the classification temperature.
Types There are several types of high-temperature mineral wool made from different types of minerals. The mineral chosen results in different material properties and classification temperatures.
Alkaline earth silicate wool (AES wool) consists of amorphous glass fibers that are produced by melting a combination of calcium oxide (CaO−), magnesium oxide (MgO−), and silicon dioxide (SiO2). Products made from AES wool are generally used in equipment that continuously operates and in domestic appliances. Some formulations of AES wool are bio-soluble, meaning they dissolve in bodily fluids within a few weeks and are quickly cleared from the lungs. Alumino silicate wool (ASW), also known as refractory ceramic fiber (RCF), consists of amorphous fibers produced by melting a combination of aluminum oxide (Al2O3) and silicon dioxide (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 exceeding 900 °C (1,650 °F) for equipment that operates intermittently and in critical application conditions (see Technical Rules TRGS 619). Polycrystalline wool (PCW) consists of fibers that contain aluminum oxide (Al2O3) at greater than 70 percent of the total materials and is produced by sol–gel method from aqueous spinning solutions. The water-soluble green fibers obtained as a precursor are crystallized by means of heat treatment. Polycrystalline wool is generally used at application temperatures exceeding 1,300 °C (2,370 °F) and in critical chemical and physical application conditions. Kaowool is a type of high-temperature mineral wool made from the mineral kaolin. It was one of the first types of high-temperature mineral wool invented and has been used into the 21st century. It can withstand temperatures close to 1,650 °C (3,000 °F).
Manufacture Stone wool is a furnace product of molten rock at a temperature of about 1600°C through which a stream of air or steam is blown. More advanced production techniques are based on spinning molten rock in high-speed spinning heads somewhat like the process used to produce cotton candy. The final product is a mass of fine, intertwined fibers with a typical diameter of 2 to 6 micrometers. Mineral wool may contain a binder, often a terpolymer, and an oil to reduce dusting.
Applications Though the individual fibers conduct heat very well, when pressed into rolls and sheets, their ability to partition air makes them excellent insulators and sound absorbers. Though not immune to the effects of a sufficiently hot fire, the fire resistance of fiberglass, stone wool, and ceramic fibers makes them common building materials when passive fire protection is required, being used as spray fireproofing, in stud cavities in drywall assemblies and as packing materials in firestops. Other uses are in resin bonded panels, as filler in compounds for gaskets, in brake pads, in plastics in the automotive industry, as a filtering medium, and as a growth medium in hydroponics. Mineral fibers are produced in the same way, without binder. The fiber as such is used as a raw material for its reinforcing purposes in various applications, such as friction materials, gaskets, plastics, and coatings.
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