X Международная студенческая научная конференция Студенческий научный форум - 2018

Insulation materials (also heat insulation, thermal insulation, or heat insulator), a material or article used for heat insulation of buildings, structures, industrial equipment, and transportation vehicles. Insulating materials have low thermal conductivity (less than 0.2 watt per [m·°K]), high porosity (70–98 percent), and low density and strength (their compressive strength is 0.05–2.5 meganewtons per sq m).

The main indicator of the quality of an insulating material is the thermal conductivity. However, determination of this indicator requires considerable labor and special equipment; therefore, the indicator used in practice—the grade of insulating material—is the dry density expressed in kilograms per cubic meter (kg/m3). This gives an adequate approximation of the thermal conductivity of the material. Nineteen grades of heat insulators are distinguished, with values ranging from 15 to 700. Insulating materials must be protected against moisture during use; upon saturation with water, their thermal conductivity increases severalfold.

Insulating materials are used primarily to insulate enclosing members and such equipment as industrial furnaces, heating units, refrigeration chambers, and pipelines. They may be rigid (boards, blocks, bricks, casings, and segments), flexible (blankets, bats, and rope), loose-fill (granular and powdered), or fibrous. Insulating materials are subdivided into organic, inorganic, and mixed, depending on the raw material used.

Predominant among the organic insulating materials are those obtained by processing noncommercial wood and by-products from woodworking (fiberboard and chipboard sheets), agricultural waste products (strawboard, reed board), peat (peat board), and other local organic raw materials. These materials usually have low water resistance and are readily biodegradable. The gas-filled plastics (expanded, porous, cellular, and other types) do not have these shortcomings; they are highly effective organic insulators, with densities of 10–100 kg/m3. Low refractoriness is characteristic of most organic insulating materials, and consequently they are not usually used at temperatures above 150°C. Materials of mixed composition, such as fibrolit and arbolit, which are produced from a mixture of a mineral cement and an organic filler such as wood chips or shavings, are more refractory.

The inorganic insulating materials include mineral wool and articles made from it (among the latter the solid and highly rigid mineral wool sheets are very promising), lightweight and cellular concretes (primarily gas and foamed concrete), foam glass, fiberglass, and articles made of expanded perlite. Articles made of mineral wool are obtained by processing melts of rock or metallurgical slags, mainly blast-furnace slags, into a vitreous fiber. The density of articles made of mineral wool is 75–350 kg/m3.

Inorganic insulating materials used as installation materials are made with asbestos (asbestos millboard, paper, and felting), mixtures of asbestos and mineral cements (asbestos-diatomaceous, asbestos-tripoli, asbestos-lime-alumina, and asbestos-cement articles), or expanded rock (vermiculite and perlite). For insulating industrial equipment and installations that operate at temperatures above 1000°C (for example, metallurgical, heating, and other types of furnaces and boilers), lightweight refractories are made in discrete units such as bricks or blocks of various shapes from refractory clays or highly refractory oxides. The manufacture of fibrous insulating materials from refractory fibers and mineral cements is also promising; their thermal conductivity at high temperatures is 25–50 percent lower than that of traditional materials with cellular structure.

Fiberglass

Fiberglass (or fiber glass) -- which consists of extremely fine glass fibers -- is one of the most ubiquitous insulation materials. It's commonly used in two different types of insulation: blanket (batts and rolls) and loose-fill and is also available as rigid boards and duct insulation.

Manufacturers now produce medium- and high-density fiberglass batt insulation products that have slightly higher R-values than the standard batts. The denser products are intended for insulating areas with limited cavity space, such as cathedral ceilings.

High-density fiberglass batts for a 2 by 4 inch (51 by 102 millimeter [mm]) stud-framed wall has an R-15 value, compared to R-11 for "low density" types. A medium-density batt offers R-13 for the same space. High-density batts for a 2 by 6 inch (51 by 152 mm) frame wall offer R-21, and high-density batts for an 8.5-inch (216-mm) spaces yield about an R-30 value. R-38 batts for 12-inch (304-mm) spaces are also available.

One unconventional fibrous insulation product combines two types of glass, which are fused together.

As the two materials cool during manufacturing, they form random curls of material. This material may be less irritating and possibly safer to work with. It also requires no chemical binder to hold the batts together, and even comes in a perforated plastic sleeve to assist in handling.

Fiberglass loose-fill insulation is made from molten glass that is spun or blown into fibers. Most manufacturers use 20% to 30% recycled glass content. Loose-fill insulation must be applied using an insulation-blowing machine in either open-blow applications (such as attic spaces) or closed-cavity applications (such as those found inside walls or covered attic floors). Learn more about where to insulate.

One variation of fiberglass loose-fill insulation is the Blow-In-Blanket System® (BIBS). BIBS is blown in dry, and tests have shown that walls insulated with a BIBS system are significantly better filled than those insulated using other forms of fiberglass insulation such as batts.

The newer BIBS HP is an economical hybrid system that combines BIBS with spray polyurethane foam.

Mineral Wool Insulation Materials

The term "mineral wool" typically refers to two types of insulation material:

Rock wool, a man-made material consisting of natural minerals like basalt or diabase.

Slag wool, a man-made material from blast furnace slag (the scum that forms on the surface of molten metal).

Mineral wool contains an average of 75% post-industrial recycled content. It doesn't require additional chemicals to make it fire resistant, and it is commonly available as blanket (batts and rolls) and loose-fill insulation.

Cellulose Insulation Material

Cellulose insulation is made from recycled paper products, primarily newsprint, and has a very high recycled material content, generally 82% to 85%. The paper is first reduced to small pieces and then fiberized, creating a product that packs tightly into building cavities, inhibits airflow, and provides an R-value of 3.6 to 3.8 per inch.

Manufacturers add the mineral borate, sometimes blended with the less costly ammonium sulfate, to ensure fire and insect resistance. Cellulose insulation typically requires no moisture barrier and, when installed at proper densities, cannot settle in a building cavity.

Cellulose insulation is used in both new and existing homes, as loose-fill in open attic installations and dense packed in building cavities such as walls and cathedral ceilings. In existing structures, installers remove a strip of exterior siding, usually about waist high; drill a row of three inch holes, one into each stud bay, through the wall sheathing; insert a special filler tube to the top of the wall cavity; and blow the insulation into the building cavity, typically to a density of 3.5 lb per cubic foot. When installation is complete, the holes are sealed with a plug and the siding is replaced and touched up if necessary to match the wall.

In new construction, cellulose can be either damp-sprayed or installed dry behind netting. When damp sprayed, a small amount of moisture is added at the spray nozzle tip, activating natural starches in the product and causing it to adhere inside the cavity. Damp-sprayed cellulose is typically ready for wall covering within 24 hours of installation. Cellulose can also be blown dry into netting stapled over building cavities.

Plastic Fiber Insulation Material

Plastic fiber insulation material is primarily made from recycled plastic milk bottles (polyethylene terephthalate or PET). The fibers are formed into batt insulation similar to high-density fiberglass.

The insulation is treated with a fire retardant so it doesn't burn readily, but it does melt when exposed to flame.

The R-values of plastic fiber insulation vary with the batt’s density, ranging from R-3.8 per inch at 1.0 lb/ft3 density to R-4.3 per inch at 3.0 lb/ft3 density. Plastic fiber insulation is relatively non-irritating to work with, but the batts reportedly can be difficult to handle and cut with standard tools. In many areas of the United States, plastic fiber insulation might not be readily available.

Natural Fiber Insulation Materials

Some natural fibers -- including cotton, sheep's wool, straw, and hemp -- are used as insulation materials.

Cotton

Cotton insulation consists of 85% recycled cotton and 15% plastic fibers that have been treated with borate -- the same flame retardant and insect/rodent repellent used in cellulose insulation. One product uses recycled blue jean manufacturing trim waste. As a result of its recycled content, this product uses minimal energy to manufacture. Cotton insulation is available in batts with an R-value of R-3.4 per inch. Cotton insulation is also nontoxic, and you can install it without using respiratory or skin exposure protection. However, cotton insulation costs about 15% to 20% more than fiberglass batt insulation.

Sheep’s Wool

For use as insulation, sheep's wool is also treated with borate to resist pests, fire, and mold. It can hold large quantities of water, which is an advantage for use in some walls, but repeated wetting and drying can leach out the borate. The thermal resistance or R-value of sheep's wool batts is about R-3.5 per inch, similar to other fibrous insulation types.

REFERENCES:

Spravochnik po proizvodstvu teploizoliatsionnykh i akusticheskikh materialov. Moscow, 1964.

Kitaitsev, V. A. Tekhnologiia teploizoliatsionnykh materialov, 3rd ed. Moscow, 1973.

Sukharev, M. F. Proizvodstvo teploizoliatsionnykh materialov i izdelii. Moscow, 1973.

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