If somebody tries to sell you cheap reflective glass saying it is “Hard Coated”, the first thing you should ask is “Is it spray hard coat or CVD hard coat?”. Spray hard coat could be termed as a primitive and is relatively cheaper, in this one the chemical composition is sprayed over glass which would be in a semi solid stage (online process). Most cases, the coating tends to be uneven and deposition rate would be poor. In most cases the coated side appears yellowish.
CVD (Chemical vapor deposition in atmospheric pressure) on the other hand is far superior and the latest. Here, the chemical composition is vaporised and then allowed to deposit on semi-solid glass (online coating) in a controlled manner, achieving high deposition rate and the coating would be even. In most cases, the coated side would have a silver appearance.
It would be a disaster if spray coated glasses which come at cheap rates are used (especially when it is mis-sold with the name “Hard coated reflective glass”) in buildings. Below are some pictures for reference.
There are typically four different glass types used in glazing products: From weakest to strongest they are: Annealed, Heat Strengthened, Tempered and Laminated.
1. Annealed glass is your basic non-impact glass type. It is used in applications where the required wind load is not so high and safety requirements are not a concern. When annealed glass breaks, it breaks in sharp chards.
2. Heat Strengthened glass is also a non-impact glass. It undergoes a “heat treatment” that increases it’s strength to twice that of annealed glass. It is used in similar applications to annealed glass but where the required wind loads are much higher. When heat strengthened glass breaks, it also breaks in chards.
3. Tempered glass is your basic impact glass. It undergoes a more aggressive “treatment” that increases it’s strength to four times that of annealed glass. It is used in “small missile” impact applications typically installed 30 feet or higher above ground and in safeguard applications. When tempered glass breaks, it breaks into very small cubes.
4. Laminated glass is your typical impact glass. It is a combination of two (usually) of the three previously mentioned glass types that are “laminated” together with an interlayer between them. It is typically used in “large missile” impact applications installed up to 30 feet above ground. When laminated glass breaks, it breaks based on it’s glass type make-up but is held in place by the interlayer…similar to a car’s windshield.
Here’s a short article which describes the right usage of Low-e coated glasses. Towards the last sentence of the article, it has been clearly stated that these glasses are used to prevent heat loss from the building in cold climate. But still the usage of these glasses have been mis-understood and are used in hot and humid climates, believing that they reduce the overall heat entering the building. True that they block long wave infra red radiation entering the building, just like they block them from leaving the building (which is why they are mostly used in cold climate).
Read the article on low-e coated glass here.
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Here’s an interesting article by Rick De La Guardia on how to design safely with glass for today’s threats. This article was featured in US Glass Magazine. (Click on the article image to read more and download the entire edition)
Here’s an interesting find from Glazette.com. This article claims about a new type of glass tempering, called Chemical Strengthening. It is also claimed in the article that these glasses are 6 to 8 times stronger than annealed glass, where as toughened glass is only 4 to 5 times strong. Most amazing fact is that these glasses could be cut after tempering unlike toughened glasses. However, the breakage pattern for these glasses remain almost the same as annealed glass, which obviously affects its acceptance in terms of safety.
Read the full article here.
If somebody says that Glass is a green building material, the straight and honest answer would be a big No! Just because in many high rise green rated buildings, glass has been used extensively, it doesn’t make it a green product in itself. One might have encountered with many architects and glass industry professionals who bluntly promote glass as a green product, then why is this article contradicting that belief? Here is an explanation on why glass is not a green product by itself, but why it is essential for a green rated building. This article is in context of float glass only, which is the most widely used in buildings.
Glass could earn a few green points for the fact that it could be recycled. Broken pieces of glass are added along with the raw materials while glass is manufactured so as to bring down the boiling point and there by reduce the energy consumption. Also if the manufacturing facility is near to the building in construction, that could also fetch a few points for green rating, as the material is locally sourced. Local sourcing of material means less energy consumed for transporting the material.
Glass is extensively used in green buildings to harvest maximum light inside and to reduce energy consumption for internal lighting requirements. When more natural light enters a building, equal amount of heat also enters the building. 50% of the Visual Light Transmittance (VLT) is direct solar energy (ER or DET). So when you are asking for 100% light transmittance, you are getting 50% of heat along with it! If in a building, which is centrally air-conditioned, and if it is clear glass which is being extensively used, energy consumption for internal lighting might get reduced to a significant level, but at the same time energy consumption by the air-conditioner would be enormously escalated. This is where solar control and thermal insulating glasses play a major role.
Solar control glasses let in maximum light and also cuts DET down to a great level. Since 80 to 90% of heat entering a building is solar heat, maximum energy could be saved on lighting and air-conditioning. Apart from direct solar energy, non-solar energy or indirect energy, could also be controlled by using double glazed/ Isulated glass units(DGU / IGU), and thermal insulating glass. A DGU cuts down the heat entering a building due to conduction (glass is a good heat conductor) and convection. A thermal insulating or a low emissivity (Low-e) coated glass can reduce the non-solar heat by cutting down the transmittance of Long Wave Infra Red Radiation (LWIR). LWIR is emitted by objects like trees and furnitures during the night time, which absorb the Short Wave Infra Red Radiation (SWIR). In moderate to cold climate conditions, where heaters are used in buildings, it is better to go for a very low u-value glass, so as to prevent heat loss from the building. In tropical climates, it is better to have a moderate u-value range.
In short, it is not an isolated pane of glass that is green rated or that helps you gain green points, it is the configuration of glass units installed in your building, based on the window to wall ratio, orientation of the building, total glazing area, energy efficiency of the building, and hours of operation of the building occupants.
(Originally written for Associatedcontent.com)
Soft Coat Glass, otherwise known as vacuum coated or off-line coated glasses, are manufactured by a process which is entirely different from hard coat glass (discussed in last post). The name soft coat is given because of the susceptible nature of the coating to get peeled off (in single glazing/ monolithic application) when compared to hard coat. However, soft coat glasses can offer a very low solar factor when compared to hard coat glasses.
Manufacturing process involves metal particles being deposited on the glass surface inside a vacuum chamber. The process, otherwise known as Magnetron Sputtering Vapor Deposition (MSVD) is sometimes referred to as Cathodic Vapor Deposition. Some glass manufacturers mention it as CVD coating, just to create a confusion with actual Atmospheric Pressure Chemical Vapor Deposition, mis-interpret it and mis-sell it as hard coat.
During the process, the material to be sputtered is loaded in a high voltage electric circuit, which is followed by the feeding of process gas into vacuum chamber, where plasma is formed. An ion discharge takes place inside the chamber, these positive charged ions gets attracted and collide with the material to be sputtered. This process happens at a very high speed and atoms of the material sputtered gets ejected, which gets accumulated on the glass below. Most widely used metals for sputtering are Silver and Titanium.
Soft coat glasses are generally used in double glazed units, with the coated surface at position 2 or 3, so that the coating is kept protected from peeling off. With the advance in technology, soft coat glasses are now made which can also be used in monolithic form (single glazed) with much improved life for the coating, but still the life of the coating cannot match with that of hard coat glass in monolithic applications.
Soft coat glass also has problems while tempering when compared to hard coat glass. It tends to show up a problem called lensing, which happens because the coated surface of the glass reflects Infra Red radiation and heats up differently than the lower surface (which is heated).
° Jushi USA / Gibson Fiberglass announced to have developed ViPro™, a high strength, high modules fiber for reinforcement for composite applications with improved corrosion resistance and physical properties; this product will be fully marketed by end of Q1-2011 and is manufactured by Jushi Fiberglass, Tongxiang Economic Development Zone, Zhejiang, PRC. With three production bases in Tongxiang, Jiujiang, and Chengdu, they have a capacity for 900,000 TPY of fiberglass.
° Guardian Industries Corp. following extensive analysis and strategic planning announces plans to build a float glass manufacturing plant in Krasny Sulin (Rostov region), Russia, with 900 TPD capacity and downstream treatment facilities. The plant is expected to begin operations in mid 2012.
° Saint-Gobain SEFPRO has announced the forthcoming opening of its new manufacturing facility for sintered refractories at its existing production site, SEPR India, in Palakkad. The product range will include sillimanite, andalusite, mullite, high alumina, bonded AZS and zircon for the glass industry and will be made under Savoie Refractaires standards.
° Owens Corning announced that will sell its glass fiber reinforcements plant in Capivari, Brazil to China’s Chongqing Polycomp International Corp. Terms were not disclosed, but the sale is expected to close in Q2-2011. This will not affect OC’s ownership of its fiber reinforcements and fabrics facilities in Rio Claro, Brazil.
° Saudi Advanced Industries Company (SAIC) announced that has begun the float glass operation at its subsidiary Obeikan Glass Company. The plant is located at Yanbu el Bahr, Saudi Arabia, some 350 km north of Jeddah. When fully operational, the plant will produce 800 TPD, under Fives Stein technology.
° Resco of Pittsburgh, PN, on Jan. 20, has announced 2011 products prices increases from 5-15%, up to 20-25% for some specific item, mostly due to raw materials (bauxite, magnesite, graphite, dolomite, etc) price inflation but also freight and labor costs, not anymore absorbable through cost savings. Increases will become effective on March 1st.
Hard coated or pyrolytic coated reflective glasses are those in which the coating is applied when the glass is manufactured,i.e. it is an online coating process. In this process of coating, the glass is fused into the glass at 650-700 degree celcius, and on cooling, the coating becomes a part of the glass.
Primary advantage of hard coated glass is the durability, it could also be handled like normal/annealed glass, could be easily heat strengthened, toughened, laminated or curved. These glasses could also be used in single glazing without any fear of losing the coating. Soft coat glasses (to be discussed in the next post) are susceptible to scratch and degradation over time, and requires special handling, hard coated glasses were invented just to counter this problem. Only disadvantage is the variety of colors available when compared to off line coating. Continue reading
In the previous post, types of heat entering a building was discussed, of which solar heat comprises around 80% and the rest is non-solar heat. It becomes very important to control non-solar heat as well even though it contribute to only 20% heat entering a building, especially in buildings where there is 24 x 7 operations and households, so as to bring down the energy consumption during night time. In this post, non-solar heat and how all to control it will be discussed in detail.
Non-solar heat is mainly transferred in three ways- conduction, convection and radiation, and is measured in terms of U-value (W/m2.K). Continue reading
Glass is used in a building to harvest natural light inside it and there by reducing the internal artificial lighting requirements, in turn saving energy. The two major sources for heat entering the building is solar heat and non-solar heat; solar heat is nothing but the direct solar heat entering the building through visible light, non solar heat is caused by various factors like conduction, convection and radiation. Out of the heat sources, solar heat is the major one and requires more attention, even though the effects of non-solar heat could not be ignored as well, as it plays a major role in certain structures. Continue reading
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
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.
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
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
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