Thermal Breakage in Glass


There are many instances where the glass panes in a building tends to crack for itself. This could be attributed to various factors like poor quality glazing, but there is also another factor which causes such breakage and is called thermal breakage. Thermal breakage in glass mainly happens due to the high difference in temperature between two points in a single glass pane, resulting in expansion and contraction in the same pane.

The temperature difference as mentioned above could be a result of many factors, such as difference of temperature between inside and outside, solar intensity in the region where building is located, type of glass (whether it is tinted, reflective, etc.), thickness of the glass, internal ventilation, type of glazing done, partial shade on glass, etc. Of all these factors, solar intensity plays a major role and it differs with geographical location, building orientation, seasons, etc. Continue reading

Optical Distortion in Tempered or Toughened Glass


In my previous post on Glass Tempering or Toughening Process, I had mentioned how the process is executed and the physics involved (Refer Back). Also a brief mention how the toughened glass quality is assessed after it breaks, this is very important because safety is the reason for we spend on tempering. There are also other issues in terms of quality when glass is tempered. These are mainly optical distortion, roller marks, waviness and bend, edge strength, coating burns, fragmenting, burns, spontaneous breakage, etc.

High Optical Distortion

Quality of tempered glass mainly depends on the quality of equipments used and the quality control procedures adopted. Optical Distortion , is mainly a blurred appearance in images when seen through the glass, as well as on the reflection on the glass. This quality issue in tempered glass is common to all types of glasses. Even though minor levels of optical distortion is present in most of the tempered glasses, but it gets magnified when the quality is that poor and the glass is applied on high rise building facades. The minor level optical distortion is inherent on tempered glass, considering the fact that glass nearly reaches it’s softening point as it is heated up to a temperature of 726 degrees, and also the fact that this glass moves in rollers, therefore it is also called roller wave distortions. Such distortions could be easily identified in reflective and low-e coated glasses. Roller wave distortions could be easily controlled by adopting suitable technology and quality control procedures (use of forced convection furnaces instead of radiation furnaces). Continue reading

Laminated Glass: Myths and Facts


There are major defects happening with laminated glass, if the process is not executed properly. Most prominent of such problems is de-lamination. This happens mainly due to the poor bonding between the glass and PVB sheet. In my previous post on laminated glass basics, I had mentioned about the clean facility requirement for lamination process, if this is not followed in the facility, there are chances for dust to stick on to the PVB and at a later stage, resulting in de-lamination. Waviness in the glass is also another reason for de-lamination: waviness in the glass can happen mainly due to poor quality tempering and even in annealed glass which has high amount of  inherent waviness. De-lamination mainly occur at the edges where chemical bonding is weaker. De-lamination may also happen when the unit is over exposed to water, mason errors (like improper cutting), applying poor quality sealants, etc. Continue reading

Laminated Glass Basics

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Laminated glass is made by sandwiching Poly vinyl butryl (PVB) sheet in between two pieces of glass. Laminated glass offers more safety because when the glass breaks, it keeps sticking on to the PVB sheet in the middle. Apart from … Continue reading

Glass Tempering or Toughening Process

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Annealed float glass when breaks is a safety hazard, just because it breaks into sharp pieces and can injure. Imagine, if an annealed glass applied to a window in the 6th floor of a building, and if it breaks by … Continue reading

What is Float Glass?

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Initially, window glasses were made by cutting from large discs of Crown glass. Crown glass is nothing but a large globe of glass, made by blowing molten glass into a crown or a hollow globe. The crown glass is further reheated and spinned out of the globe into large discs, which were then flattened using centrifugal force. These glasses were then cut into desired sizes. There were other methods of making glass as well, like the blown plate, broad sheet, polished plate and cylinder blown sheets, which were all in practice up till the end of the 19th century. 20th century witnessed more advanced processes like rolled plate, machine drawn cylinder sheet, flat drawn sheet, single and twin ground polished plate and float glass. Continue reading

A Glass Is a Glass Is Not Just a Glass!!!

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To be honest, my exposure to glass and glazing industry is brief, and the same was my knowledge about glass. Glass never had more than a decorative value in my mind, as it had to be for me since I was from a decorative product segment (paints). It was just after I got inducted into this industry that I had to invent this statement- “A Glass is a Glass is not just a Glass!!!”.

At first, I realized that there are different types of glasses being manufactured, each with different chemical properties and functions. But I could superficially assimilate the knowledge and as a new comer, it was enough for me to classify them as Soda-lime glass, lead glass, borosilicate glass and glass fibre. Since I’m only concerned with glass as a building material, I would be writing only about flat glass. Flat glass industry includes both float glass and sheet glass manufacturers. Basic difference between these two are the process by which they are made. Sheet glass is made by using iron rolling pins to flatten the molten glass and to get it into desired shape, and further grind and polish it to make it clear. Float glass on the other hand is flattened by making the molten glass to float over molten tin. I also learned that the float glass manufacturing process was invented by Alastair Pilkington and Kenneth Bickerstaff in 1957. Continue reading