Mineral wool

Mineral wool close-up.
Mineral wool under microscope
Building joint with incomplete firestop made of mineral wool packing that still requires topcaulking.
Common insulation applications in an apartment building.
Mineral wool pipe covering applied to a steel pipe for a fire test.

Mineral wool, also known as mineral fiber, mineral cotton, mineral fibre, man-made mineral fibre (MMMF), and man-made vitreous fiber (MMVF), is a general name for fiber materials that are formed by spinning or drawing molten minerals (or "synthetic minerals" such as slag and ceramics).[1] Specific mineral wool products are rock (stone) wool and slag wool. Europe also includes glass wool which, together with ceramic fiber, are completely man-made fibers. Applications of mineral wool include thermal insulation (as both structural insulation and pipe insulation), filtration, soundproofing, and hydroponic growth medium.

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".[2] A method of making mineral wool was patented in the United States in 1870 by John Player[3] and first produced commercially in 1871 at Georgsmarienhütte in Osnabrück Germany. The process involved blowing a strong stream of steam or 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.[3]

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 fibres with a typical diameter of 6 to 10 micrometers. Mineral wool may contain a binder, most often phenolic but for environmental reasons now sometimes replaced by food-grade starch, and an oil to reduce fiber emission and improve moisture sensitiveness.

Usage

Though the individual fibers conduct heat very well, when pressed into rolls and sheets, their ability to partition air makes them excellent heat insulators and sound absorbers.[4][5] 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.

Mineral wools will provide a structure for bacterial growth if allowed to become wet.

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.

Heat resistance of mineral wool[6]
Material Temperature
Glass wool 230 - 260 °C
Stone wool 700 - 850 °C
Ceramic fiber wool 1200 °C

In hydroponics

Mineral wool products can hold large quantities of water and air that aid root growth and nutrient uptake in hydroponics; their fibrous nature also provides a good mechanical structure to hold the plant stable. The naturally high pH of mineral wool makes them initially unsuitable to plant growth and requires "conditioning" to produce a wool with an appropriate, stable pH.[7]:16

Safety of material

Precautions need to be taken when handling a fiber product, as it can irritate the eyes, skin, and respiratory tract. A summary of occupational health and safety information is provided by OSHA (USA).

The International Agency for Research on Cancer (IARC) has reviewed the carcinogenicity of man-made mineral fibres in October 2002.[8] The IARC Monograph's working group concluded only the more biopersistent materials remain classified by IARC as "possibly carcinogenic to humans" (Group 2B). These include refractory ceramic fibres, which are used industrially as insulation in high-temperature environments such as blast furnaces, and certain special-purpose glass wools not used as insulating materials. In contrast, the more commonly used vitreous fibre wools produced since 2000, including insulation glass wool, stone wool, and slag wool, are considered "not classifiable as to carcinogenicity in humans" (Group 3).

High biosoluble fibres (HT-fibres) are produced that do not cause damage to the human cell. These newer materials have been tested for carcinogenicity and most are found to be noncarcinogenic, or to cause tumours in experimental animals only under very restricted conditions of exposure. The IARC Monograph's working group "elected not to make an overall evaluation of the newly developed fibres designed to be less biopersistent such as the alkaline earth silicate or high-alumina, low-silica wools. This decision was made in part because no human data were available, although such fibres that have been tested appear to have low carcinogenic potential in experimental animals, and because the Working Group had difficulty in categorizing these fibres into meaningful groups based on chemical composition."[9]

See also

References

  1. ↑ "Man-made mineral fibre (MMMF) is a generic name used to describe an inorganic fibrous material manufactured primarily from glass, rock, minerals, slag and processed inorganic oxides. The MMMF produced are non-crystalline (glassy, vitreous, amorphous)." Recommendation from the Scientific Committee on Occupational Exposure Limits for man made-mineral fibres (MMMF) with no indication for carcinogenicity and not specified elsewhere
  2. ↑ Spon, Ernest. Workshop Receipts ... London: E. & F. N. Spon, 18831892. Page 439
  3. ↑ 3.0 3.1 "Mineral Wool or Mineral Cotton", Appleton's Annual Cyclopedia and Register of Important Events of the Year 1891. New Series vol. 16. New York: 1892. 528. Print.
  4. ↑ Weiner, Ethan. Acoustic Treatment and Design for Recording Studios and Listening Rooms. "Without question, the most effective absorber for midrange and high frequencies is rigid fiberglass."http://www.ethanwiner.com/acoustics.html#rigid%20fiberglass.
  5. ↑ Houghton, Matt. Sound On Sound. "What is the best density for a good, fairly wide-spectrum absorber? . . .try looking for mineral wool in the region of 45-75kg/m3." http://www.soundonsound.com/sos/oct10/articles/qa-1010-2.htm
  6. ↑ "Competition Commission Alternatives to Glass Mineral Wool" (PDF). 090820 competition-commission.org.uk, 2.2 Mineral Wools
  7. ↑ Tom Alexander; Don Parker (1994). The Best of Growing Edge. New Moon Publishing, Inc. ISBN 9780944557013.
  8. ↑ IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 81 (2002), Man-made Vitreous Fibres (PLEASE NOTE: Some manufacturers of insulation products have cited this volume while making erroneous claims that "IARC scientists confirm safety of mineral wool insulation". These claims are just false. The findings in this volume are not a determination of non-carcinogenicity or overall safety.)
  9. ↑ IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 81 (2002), Man-made Vitreous Fibres, Overall evaluation, p. 339

External links

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