An Introduction To Glazing
Glass is a wonder product used extensively in many industries today without even a thought to how it is made and its many uses and applications. Glass has developed from merely glazing windows or repairing broken panes to becoming a very practical and safe product as well as considerably improving the aesthetics of a building. Glass is now used in skylights, balustrades, glass doors, shop fronts, glass bricks and squash courts to mention but a few.
To many, glass has often been perceived as a dangerous product,and if it is used or handled incorrectly, it can very well be. However, the large range of glass products available today include toughened glass and bullet proof glass used for safety purposes in areas that require visibility and safety such as banks, oven doors, fire walls, ballustrades and roofs. The amazing properties of glass lend it to many applications. It can withstand heat and cold, pressure, extensive wear and tear and is waterproof. It is also available in a wide variety of colours and finishes.
The following are AAAMSA/SAGGA recommendations for the application of safety glazing materials in balustrading. It is recommended that any balustrade design is confirmed through testing, or is checked by a structural engineer having the appropriate Professional Indemnity Insurance for compliance with the structural requirements of SABS 0160. A balustrade guarding the edge of any balcony, bridge, flat roof or similar place more than 1 m above the adjacent ground or floor level shall be not less than 1 m in height and shall not have any opening that permits the passage of a 1OOmm diameter ball. These requirements also apply to any interior balcony or any mezzanine floor (SABS 0400 -1990 Part D). Balustrading guarding a swimming pool or swimming bath shall not be less than 1,2m high measured from the ground level, and shall not contain any opening which will permit the passage of a 100mm diameter ball. (SABS 0400 -1990 Part D). Glass in balustrading is often applied having two edge support.
What is glass?
Glass is a solid material giving total through-vision. When other materials such as metal, solidify, they become crystalline, whereas glass (a super cool liquid) is non crystalline. A solid that is transparent!
How is glass made?
Glass is made by mixing raw materials such as sand, limestone, soda, dolomite, felspar and saltcake then heating them together at a temperature of over 1500oC. When the materials are melted, they form a viscous liquid called the quiescent melt. As this melt cools, the viscosity increases until the glass becomes hard. If the liquid cools too quickly, the glass does not have time to release stresses. This process is done by heat treatment and is called annealing.
Silica sand is the main raw material in glass, but very high temperatures are needed to melt it. By adding soda ash, a fluxing agent, the glass can be melted at a lower temperature, but the result is water glass which is soluble in water. Limestone, a stabiliser, is thus added to the silica and soda ash. Cullet (scrap glass) is also added to assist the melting process.
Making Flat Glass (The Float Process)
The float process of glass manufacture was developed by the Pilkington Glass Group (England) in 1959. There are currently over 60 float glass plants operating around the world, some under licence. In the float process, a continuous ribbon of molten glass moves out of a melting furnace (1 500oC) and floats along the surface of a bath of molten tin.
The ribbon is cooled down while still advancing across the molten tin until the surfaces are hard enough for it to progress through the annealing lehr without the rollers marking its bottom surface. The glass produced has a uniform thickness and bright fire polished surface, without the need for further grinding and polishing.
Basic Types Of Flat Glass Used In The Building Industry
Float Glass (also known as annealed or raw glass)
This is the finished product as it comes off the float line. It has a bright, fire-polished surface and is optically virtually distortion free. It is relatively brittle and will break when subjected to a severe blow or load. Float glass break is undesirable - slivers of large pieces may cause injury.
Consists of two or more pieces of float glass, firmly united and alternately one or more interlayers of either liquid resin or polyvinyl butyral. Will crack under impact, but the fracture does not cause the glass to separate from the interlayer, therefore will not cause severe injury.
Normal float glass which has been converted into structural glass by a process of heating and rapid cooling. Process produces a glass 4-5 times stronger than normal float glass of same thickness. Toughened glass (the strongest type of glass available) is more resistant to impact and thermal shock than annealed glass. Fragments are harmless, as they disintegrate into small pieces with blunt edges.
Incorporation of metal fabric in wired glass. Two ribbons of glass converge and meet with a wire netting fed in between them. Wired glass is more brittle than normal glass of same thickness.
As glass ribbon passes between rollers, the pattern/design is pressed onto one surface of glass. By changing the one roller, different patterns are achieved. This glass has the same break pattern properties as normal float glass.
We have a range of glazing contractors, large and small, with the skills and experience to handle any size project.