Saturday, 26 December 2015

Types of Glass

Types of glass:

The glass may be broadly classified as:

  1. Soda-Lime Glass (or) Crown Glass
  2. Potash Lime Glass
  3. Potash Lead Glass
  4. Flint Glass
  5. Pyrex (or) Heat resistant Glass
  6. Common Glass and 
  7. Special Glass

1. Soda Lime Glass: It is the cheapest quality of glass. It is mainly a mixture of sodium silicate and calcium silicate. It's composition, like that of most glass, is not rigidly fixed, but can be varied both as to the amount of ingredients and chemical compounds used. It is fusible at low temperature. In the fusion condition it can be Blown (or) Welded easily. It is colourless, clean and clear state. They are resistant to water not to the acids.
It is used as window panes and for the laboratory tubes and apparatus. 

2. Potash Lime Glass: It is mainly a mixture of potassium silicate and calcium silicate and potassium carbonate. It is also known as hard glass. It fuse at high temperature. It is used in the manufacture of glass articles which have to withstand high temperatures.

3. Potash Lead Glass: It is mainly a mixture of potassium silicate and lead silicate. It possesses bright lustre and great refractive power. It is used in the manufacture of artificial gems, electric bulbs, lenses, prisms etc.,

4. Flint Glass: Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). It contains varying proportion of lead oxide to make it suitable for varying purposes. Lead provides brilliance and high polish which makes the glass available for special purposes. Liquifies at lower temperature than Soda-lime glass and has better lustre.

5. Pyrex or Heat resistant glass: Both Soad-lime and Flint glass are unavailable to withstand sudden temperature changes, Because of their large coefficients of thermal expansion. The basic oxides that they contain make them susceptible to chemical attack by water and acids. Elimination of the basic oxides and inclusion of boron oxide produce a glass that is very resistant to thermal shock and to attack by water and acids.

6. Common Glass: It is mainly a mixture of sodium silicate, calcium silicate and iron silicate. It is brown, green or yellow in colour. It is mainly used in the manufacture of medicine bottles.

7. Special Glasses: Properties of glasses can be suitably altered by changing basic ingredients and adding few more ingredients. It has now emerged as versatile material to meet many special requirement in engineering. The following is the list of some of the special glasses:

  (a) Annealing glass

          To prevent glass articles becoming too brittle and falling into pieces at the slight shock they are annealed. Annealing is a process of slowly cooling hot glass to relieve internal stresses after it was formed. The process may be carried out in a temperature controlled Klin known as Lehr. The longer the annealing period, the better the quality of glass.

(b) Plate glass
          It is made by pouring white hot glass over an iron table and rolling it to a uniform thickness under heavy roller. It is stronger and more transparent to sheet glass. Plate glass includes transparent, transluscent, opacue and structural glasses. 

(c) Fluted glass
          When there are corrugation on one side of the plate glass then it is known as fluted glass. The other side is wavy but smooth. The light is admitted without glare of the sun.
(d) Fibre glass or wool glass
          Glass fiber (or glass fibre) is a material consisting of numerous extremely fine fibers of glass. The usual composition of Fibre glass is that of a soda-lime but it may be varied for different purposes. The glass fibre are made by letting the moltan glass drop through tiny orifices and blowing with air or steam to attenuate the fibres. They have high tensile strengths, upto about 2800 N/mm2.
          Glass wool is an insulating material made from fibres of glass arranged using a binder into a texture similar to wool. The process traps many small pockets of air between the glass, and these small air pockets results in high thermal insulation properties. Glass wool is produced in rolls or in slabs, with different thermal and mechanical properties. It may also be produced as a material that can be sprayed or applied in place, on the surface to be insulated. 
          The modern method of producing glass wool is the invention of Games Slayter.

(e) Foam glass

          Foam glass, is lightweight, opaque glass material having closed-cell structure.  It is prepared from powdered glass to which is added the desired quantity of carbon or any gas which makes the mass porous and light in weight. It is light enough to float in water and has been used as a substitute for cork, but it's main uses are for thermal and sound insulation. It is impervious to moisture, most fumes and vermin. This glass is water-proof also. It can be easily cut and worked with common masonry tools.

(f) Bullet proof glass
          Bullet proof glass (also known as ballistic glass, transparent armor, or bullet-resistant) is a type of strong but optically transparent material that is particularly resistant to being penetrated when struck. This glass is made of several layers of plate glass and alternate layers consist of venyl-resign plastic. The outer layers of plate glass are made thinner than the inner layers. The thickness of this type of glass may vary from 15 mm to 75 mm. 
          Overall, bullet-proof glass is generally used to protect employees and objects of great value in banks, government buildings, convenience stores, liquor stores, jewelry stores, post offices, churches and schools. It has other uses, including protecting cars and transportation units.
(g) Structural glass
          Structural glass is the glass that is used as a building material. This type of glass is available in the form of glass-crete square blocks, or tiles in thickness varying from 5 to 30 mm. It is most typically used as transparent glazing material in the building envelope including windows in the external walls. Glass is also used for internal partitions and as an architectural feature. When used in buildings, glass is often of a safety type, which include reinforced, toughened and laminated glasses. 

(h) Glass blocks
          Glass block also known as glass brick, is an architectural element made from glass. These consist of two halves so fused together as to form a hollow inside. Glass bricks provide visual obstruction while admitting light. A recent innovation in the manufacture of glass blocks is the insulation of argon gas within the hollow centre of glass wall blocks. This advancement in production technique has resulted in a glass block which is able to offer significantly improved thermal insulation properties.
(i) Wired glass
          It is glass reinforced with wire netting or similar strengthening material embedded in it during manufacture. That is why it is called as reinforced glass. Wired glass has an impact resistance similar to that of normal glass, but in case of breakage, themesh retains the pieces of glass. This product is traditionally accepted as a low-cost fire-resistant glass.
Wired glass is produced by continuously feeding wire mesh from a roller into the molten glass ribbon just before it undergoes cooling. A steel wire mesh is sandwiched between two separate ribbons of semi-molten glass, and then passed through a pair of metal rollers which squeeze the "sandwich of glass and wire" together. Wired glass may be further processed by grinding and polishing both surfaces, producing "polishing wired glass". 

(j) Ultraviolet ray glass
          Ultraviolet (UV) light is an electromagnetic radiation with a wavelength from 400 nm to 10 nm, Shorter than that of visible light but longer than X-Rays. These glasses transmit UV rays effectively even though it is not in the direction of the rays of sun. It is made from the raw mixture with minimum admixtures of iron, titanium and chrome.
(k) Perforated glass
    “There are two kinds of perforated glass : one having he perforations manufactured in the glass, the other having them afterwards cut. The later is the best, as the former break very readily". 

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