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HEAT-INSULATING AND ACOUSTIC MATERIALS

Materials with low thermal-conductivity, assigned for the thermal insulation of building constructions, industrial equipment and pipelines are called heat-insulation materials. Application of heat-insulation materials is one of the most important directions of reduction material capacity of construction and decreasing of fuel consumption.

Application of materials with low thermal-conductivity in enclosing structures, for example in large-panel dwelling-houses, enables to reduce the charges of steel and cement in 1.5-2 times as compared to structures without thermal insulation.

Application of the light-weight brick walls with effective heat insulation in place of the continuous bricking allows substantially shortening the need in bricks, cement and lime, reducing weight of structures and transport expenses.

Charges of thermal energy for houses heating are increased in inverse proportion to resistance of the wall heat transfer. This property depends on the density of materials used.

Three-layer wall structures are widespread in construction. These structures (panels, shells, etc.) consist of thin external layers, which are made from strength material, and heat-insulating middle layer. Such structures differ by relatively low weight and prefabricability that allows executing construction works in any time of the year. Asbestos cement, aluminium alloys, zinc-coated steel, waterproof plywood and other sheet materials can be used for facing of panels. There is a positive experience of application of three-layer reinforced concrete panels. Heat-insulating materials based on the local raw materials can be used for filling of framed external walls and internal partitions and also for ceiling heating.

The insulation of thermal equipment, technological apparatus and pipelines at construction of thermal power-stations results in reduction in 20-25 times of thermal charges.

Characteristic feature of heat-insulating materials is a type of initial materials. Depending on it there are inorganic and organic materials.

According to their form heat-insulating materials are divided into piece, roll and loose; according to character of structure - on hard, flexible and friable.

Density and heat-conductivity are basic properties which characterize efficiency of heat-insulating materials.

Also an important value has limiting temperature of application, strength, deformation, fire-proofness, biostability, vapour permeability, etc.

Materials with the average density up to 600 kg/ m3 can be used as heat-insulation. However, effective heat-insulation materials must have the average density no more than 400 kg/ m3. Some of them (gas-filled plastics, mineral wool products based on synthetic binders, etc.) can be considerably lighter (no more than 50-100 kg/ m3).

According to thermal conductivity heat-insulating materials can be divided into three classes: low heat-conducting – up to 0.06, middle – 0.06-0.115 and high – 0.115-0.175 W/(m·K). For high porous materials heat-conductivity is similar to the heat-conductivity of air – 0.025 W/(m·K).



Reduction of pores sizes deteriorating heat transfer positive influences on heat-reflecting properties of materials. Also complication of chemical composition and formation of amorphous structure of materials improve heat-reflecting properties.

It follows to take into account that in operational conditions thermal conductivity of heat-insulating materials is in arcwise increase with growth of temperature.

The limiting temperature of application is an important operating property of heat-insulating materials. For example, limiting temperature of application of expanded perlite and vermiculite is 900 °C, mineral wool – 600°C, porous concrete – 400-700°C, and gas-filled plastics – 60-180 ° C.

Strength of heat-insulating materials must be sufficient for their warehousing, transporting, installation and application during required term. The compressive and bending strength for the most widespread heat-insulating materials is in the range of 0.1-1.5 MPa.

Range of application of heat-insulating materials depends on their fireproofness, biostability, chemical resistance, water absorbtion, gas and vapour impermeability and number of other properties.

Acoustic materials are used for providing of required auditory perception and reduction of sound level in apartments (sound-absorbing materials) or their sound-proofing (sound-insulating materials). Application of acoustic materials has positive influence on health of people and promotes increasing of the labour productivity.

The same as heat-insulating, acoustic materials are characterized by high porosity. Materials with the connected pores are characterized by good sound-absorbing properties. Their basic features are low values of dynamic module of elasticity and accordingly speed of sound distribution.


Date: 2015-12-18; view: 923


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