The commonly used insulating materials with their properties and uses are described as below.
Cork
It is derived from the bark of oak trees. It is ground, sized and baked in moulds. When ground and baked, the natural resin in the cork binds the material into homogeneous mass, which can be pressed into flexible sheets or boards etc. It is available in the form of granulated cork, slab cork and re-granulated baked cork. It is light in colour, porous in structure, not affected by moisture, possesses low thermal conductivity, easily compressible. Cork sheets and boards are used for insulating walls and ceilings, for pipes carrying steam or hot water, for scientific apparatus, for refrigeration and cold storage insulation.
Glass wool
Glass wool is a form of fibrous glass with short and fine fibres, scattered in various directions. It is available in the form of loose fibres, mats, blocks etc. It is fibrous in structure, lighter in weight, having good tensile and dielectric strength, possesses low thermal conductivity, durable. It is used for insulation of pipes, bends, valves, panel insulation for all types of industrial equipment, thermal and sound insulation of aircrafts, for thermal y insulated partition walls, for boilers, ovens, cylinder or pipe insulation etc.
Fibreglass
Fibreglass is the fibrous insulation material by virtue of the maximum resistance offered for the heat transfer through the system by millions of air cells formed by laying fibres having lower thermal conductivity. The fibrous insulation materials are the most suitable and efficient ones among the wide range of insulation materials available all over the world. The fibreglass offers the advantages as listed below:
- Fibreglass serves a dual purpose of providing thermal as well as sound insulation, when applied to ceilings and walls.
- Its capital cost is low and reduces the operating cost of air conditioned plant due to its low thermal conductivity and less wear and tear.
- It will not settle even under prolonged vibrations.
- It is non-hygroscopic.
- It is light in weight and easy to handle, cut and install.
- It is sufficiently strong to take the loads generally considered in air conditioning applications.
- Fibreglass crown is non-inflammable.
Rock wool
Rock wool is produced from flint rock containing some calcareous matter. In the absence of such a natural rock, flint and lime are mixed in the requisite proportions and melted In a furnace at temperature of about 1700°C. This molten material is then formed into small globules by means of steam jet. These globules are then drawn Into very fine fibres by hurl ng them in a large container. These fibres of wool are then formed into boards or blankets (to be used as insulators). It can also be pressed, rolled and secured between fabric of wire-netting of brass or copper. It is available in the various forms such as loose fibres, mattresses, mats, boards or felts, rigid or semi-rigid slabs. It is soft and flexible, heat and sound proof. It is used for heat and sound insulation purposes, for electric insulation.
Slag wool
Slag wool is an aggregate of fine filaments of slag produced by blowing air through a stream of blast furnace slag. It is available in the form of loose fibres. It is used for heat insulation in high temperature furnaces.
Asbestos
Asbestos is a mineral fibre composed of hydrous silicate of magnesia with a small amount of iron oxide and alumina. Asbestos sheets or boards consist of natural asbestos fibres mixed with a binding agent (usually cement) and then rolled in the form of sheets or boards. It is flexible, resistant to high temperature, fire-proof, unaffected by acids and fumes, resistant to corrosion, excellently resists heat and electricity. It is used for heat and sound insulation of buildings, for insulation of furnaces.
Thermocole
Thermocole is a type of polystyrene made by direct extrusion of the foam from raw materials. It is much lighter in weight, has much lower thermal conductivity, highly resistant to moisture, odourless, chemically stable and resistant to fungus attack, fully resistant to water, salt, soaps and bleaching agents, possesses good shock-protecting properties. It is used for insulation in refrigerators, cold storages, air conditioning, chilled pipelines, for industrial insulation and insulation for buildings etc.
Celotex
Celotex is an excellent example of a fireproof fibre wall board, in which, bagasse (sugarcane after juice is removed), is a principal ingredient. In the manufacture of Celotex, the fibres are cooked to dissolve all soluble matter and then waterproofing chemicals are added. The final product is an odourless light material.
Plastic foams
In modern air conditioning buildings, foamed plastics are finding rapidly growing application. Key considerations in selecting plastic foam as insulating material are thermal conductivity, compressive strength, water vapour transmission, dimensional stability and method of installation.
Polystyrene foams (PUF)
These foams can be supplied in any desired shape for large production runs. It is available in the form of foamed sheet or pipe covering. It is used:
- As thermal insulation in cold storage rooms, tanks and vessels.
- As a core for sandwich panels, encased in materials ranging from aluminium and steel to plywood.
- As temporary structural framework for placing and curing permanent shell material. The frame work then remains bonded to the permanent shell as insulation and vapour barrier, and as an interior finishing base.
Urethane foam
Urethane is known as super insulation in air conditioning industry. These materials are somewhat more expensive than polystyrene, but because of economy of labour in their application, they are the predominant plastic foam. Rigid urethane foam is used for insulating ducts, pipes, walls, roofs, basements and certain walls in wide variety of new and existing structures. It is the only insulating material that can be sprayed as a liquid to reach virtually inaccessible areas. Urethane foam possesses high thermal resistance to the heat flow. It can lower heating or cooling costs of the buildings particularly in electrically heated buildings, where effective insulation is required to make operative cost competitive with other fuel system.
Phenolics or Phenolic foam
Phenolics is probably the most flame resistant cellular material developed so far. Phenolic foam is readily bonded to a Wide range Of materials like concrete, glass, steel etc. by means of commercially available adhesives. Owing to their high thermal resistance, phenolic foams are recommended as insulating materials for flat roofs. They are also used as cores for sandwich panels.