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Glass Performance – What does it mean and how is it measured.

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What is glass performance? Most of us have a sense of what the term “performance” means when we are talking about cars, computers, phones or cameras, but how can a seemingly inanimate object or material have performance?

The key is in understanding what is trying to be achieved or controlled when considering glass performance. The role glass is generally tasked with performing in a building or even a vehicle is to provide protection from outside elements (i.e. rain, wind, cold or heat), while at the same time providing transparency (a good view), and maintaining structural integrity against wind and possibly even earthquake. In order to meet these requirements, glass needs to be able to control the following elements:

  1. Solar Radiation (visible sunlight as well as artificial lighting)
  2. Temperature (cold and heat)
  3. Moisture (rain and condensation)
  4. Structural loads (wind and seismic)
  5. Sound (exterior and interior noise control)

In this article we are going to focus on the first two elements (Solar Radiation and Temperature), as Moisture and Structural loads are as much a function of the framing and gasketing systems and we will cover sound control in an upcoming Gazette article.Visible light is a small portion of the electromagnetic spectrum that ranges between 380 nm to 780nm or 400 and 790 terahertz (hertz is a measurement of the frequency of a wave pattern). Other forms (wavelengths) of solar energy that glass is designed to control is Infrared (heat) and Ultraviolet (which causes fadin

The primary metrics that we are concerned with in measuring glass performance are:

  • Visible Light Transmittance (VLT)
  • U-value (inverse of R-value)
  • Solar Heat Gain Coefficient (SHGC)

 

Visible light transmittance (VLT) is measured in the form of a percentage of the total visible light (total being 100%). The amount of visible light passing through a glass medium will be a percentage of the total (i.e. SN68 Clear IG has a VLT of 68%).

U-value is a measure of the resistance to heat transfer through the glass measured in Heat Units/Time per temperature differential between inside and outside (i.e. Btu/hr.ft2. °F or W/m2 °K).

Solar Heat Gain Coefficient (SHGC) is a measure of the total solar radiation (solar gain in the form of heat) passing directly through the glass and what is absorbed and re-radiated by the glazing (i.e. SNX51/23 has a SHGC of 23).
The typical objective of the glass designer is to achieve high Visible Light, while at the same time providing a low U-value (low heat transfer) and a low SHGC (low solar heat gain). This is typically achieved through coatings on the glass (low-e or reflective) coatings (silver typically being the active coating) as well as the substrate tints (i.e. blue, green, grey or bronze) or lack of body tint (i.e. low iron). We look forward to getting more in depth in future Gazette articles. If you would like to learn more about this topic, feel free to approach me at any time.

Air Side & Tin Side

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Did you know that there is an airside and a tin side to all float glass? Clear glass is not actually the same on both sides, even though to the naked eye they look identical.

During the production of float glass, one side of the molten glass comes into contact with a bath of molten tin. Traces of tin or tin oxide are deposited on the surface of glass as it is removed from the molten tin bath. This surface of the glass is identified as the tin side. The opposite side of the glass is denoted as the airside. The Tin side is actually a smoother surface compared to the air side on a microscopic level.

So why is the important in our manufacturing processes? There are 3 areas where this matters.

  • Tempering: The tin side should always be down so that the smoother surface is what comes into contact with the conveyor rollers. This produces higher quality tempered glass as the air side surface would be more susceptible to picking up debris or ending up with heat stain.
  • Frit: Always apply frit to the air side as the residual tin from the tin side will react negatively with the frit and cause the color to change slightly.
  • SGP Lamination: SGP bonds much better to the surface that has the tin compared to the airside surface. When laminating SGP we always try to bond the tin side to the tin side. If that is not possible, then we need to use the adhesion promoter so that the interlayer will bond properly. This is only for the SGP. PVB bonds equally for both he tine and the air sides.

How can you tell the difference? All you need to do is shine a tin tester (it is just a black light) on the surface to tell them apart. The short-wave UV radiation causes the tin to glow with a fluorescent (milky white) light. When the lamp is placed on the tin-side and viewed through the glass, a fluorescent glow will be observed. With the lamp on the non-tin side and viewed thought the glass only the violet UV light will be seen. This is because the float glass does not transmit the UV light and the tin coating on the opposite side of the glass is not exposed to the UV radiation.

Heat-Soaked Glass

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How is heat-soaked glass different from tempered glass?

The how is fairly straight forward, heat soaking is a process that checks for seemingly invisible nickel sulphide inclusions in the glass by heating it to 290 degrees Celsius and controlled cycle. If it goes through the cycle and does not explode, then it passed the test. This Can only be done after the glass is fully tempered and it is not 100% effective but does greatly reduce the risk of potential field breakage. In summary, this is an additional but completely separate process from tempering the glass and would never do it with heat strengthened glass.

The Why is a bit more technical and has to do with microscopic impurities in the glass we get from the float plant. Nickle Sulfide (NiS) inclusions are extremely rare, especially in float glass manufactured in North America, but can cause fully tempered glass to spontaneously exploded years after it was installed depending on the application, this can have serious safety implications if someone is standing below.

The NiS inclusions can slowly grow over time to the point where they are pushing out on the glass with enough force to break the glass and spontaneous breakage occurs. Fully tempered glass does not just break in one spot, the entire piece explodes. Heating the glass and folding it for 2 hours at 290 degrees Celsius will expedite the growth of any NiS inclusions and if they are present, the glass should break within the testing cycle.

When designing using glass, you can reduce the risk of breakage due to NiS inclusions by specifying heat strengthened glass, heat soaking fully tempered glass or laminated glass.

Heat Treated Glass

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Which image shows a Fully Tempered glass, and which is a Heat strengthened glass? (A/B) If you answered A as a fully tempered glass, and B as heat strengthen glass then you are correct! Did you know that both are produced in the same tempering ovens and even heated to the same temperature? The difference is how fast they are quenched or cooled with air?

The difference between the two types of glass are as follows.

With tempered glass, the cooling process is accelerated to create higher surface compression in the glass of at least 10,000 psi. This is the process that makes the glass four to five times safer than annealed glass. As a result, tempered glass is less likely to experience a thermal break. With heat-strengthened glass, the cooling process is slower, which means the compression strength is lower at 3500-7500 psi. In the end, heat-strengthened glass is approximately twice as strong as annealed glass. Although heat -strengthen glass is not as strong as fully tempered glass, it has the advantage that glass fragments are more similar in size and shape to annealed glass fragments. The fragments tend to stay in the opening longer than fully tempered glass particles when broken which prevents the glass from falling in injuring someone.

 

Graphics by Guardian Glass

How Glass is Made

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The Difference Between Primary and Secondary Glass Manufacturing

This entry will give a short description of both primary (how flat glass is made) and secondary glass manufacturing processes (how flat glass is processed) and a description of what the tin side of float glass is and how it affects certain processes.

Primary glass manufacturing is the mixing and melting of finely ground glass ingredients to make float glass as shown in the picture. It is called float glass because once the glass mix has melted, the molten glass is floated on top of a pool of molten tin (called the float or tin bath). This is done to ensure that the glass is perfectly flat. Molten glass will naturally pool to a thickness of approximately 6mm or ¼” thick. By controlling the speed at which the molten glass travels over the tin, the thickness can be changed. Increase the speed and the glass becomes thin, slow the speed down and the glass becomes thicker. Once the glass is cooled through the annealing process, it is cut into large sheets and sold to secondary glass manufacturers.

Secondary glass manufacturing is the cutting of glass to required sizes, drilling holes, polishing the edges, applying ceramic frit to the glass surface, tempered and/or made into sealed units, whatever is required by the customer.

Knowing which side of float glass was in contact with the tin bath is important when cutting the glass to size. Glass is always scored on the non tin side (air side) because it breaks more cleanly. Ceramic frit will change colour (white will look burnt) if applied to the tin side rather that the air side. Casting or slumping float glass over a mold tin side down, will result in cloudy glass. Lifting glass using suction cups on the tin side can cause ghost like images of the suction cups to appear when water (rain or condensation) is present on the tin surface.

Garibaldi Glass Completes Inaugural Point Supported Glass Structural Wall

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At Garibaldi Glass we are excited about completion of our first “Point Supported Glass Structural Wall”. The project at 1st & Main Street in Portland, Oregon was Garibaldi Glass first venture along with “Nupress Facades” to produce IG Units for a Point Supported Structural Wall. The finished product has been met with a resounding job well done, and the reward of additional projects. At Garibaldi Glass we see the demand from Architects to build more “Point Supported Glass Structural Walls” in the future.

At Garibaldi Glass our partnership with “Nupress Facades” and now certification of our production processes with “Nupress Facades” point supported systems, allows Garibaldi Glass to expand our markets and our core competency in these markets. At Garibaldi Glass we also have the capabilities to “Heat Soak Test” all glass substrates used in “Point Supported Glass Structural Walls” if the customer requires the additional security. All Heat Soak Testing is done to current EU Standards.

General Contractor: Hoffman Construction

Architect: GBD Architects

Glazer: Mountain Glass

Fabricator: Garibaldi Glass Industries Inc.

About Garibaldi Glass Industries Inc.

Garibaldi Glass Industries Inc. (est. 1966) is a leading architectural glass fabricator in the Pacific Northwest. GGii’s custom fabrication and high‐performance architectural glass products include quality insulated units, spandrel, tempered glass, laminated glass, Ceramic frit application according to your specific design pattern, colour, and glass type request (Silk‐screen or hand‐applied), structural doors and entrances. The family‐owned glass business is located in Burnaby, B.C., Canada.

The Need for Oversized Glass Guidelines with Roland Rossman at IGMA 2018 Winter Conference

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The Insulating Glass Manufacturers Alliance 2018 Winter Conference, set in the picturesque desert of Tucson, Arizona at the Loews Ventana Canyon Resort focused on the technical components that are critical to the growth of the insulating glass industry. On the first day of the event, IGMA spoke about certification programs pertaining to the industry and established task groups to provide support for industry questions related to oversized glass guidelines. In the video above, watch our very own Roland Rossman, Projects Leader at Garibaldi Glass share his expertise on the need for oversized glass guidelines.

Garibaldi Glass Wins Gold Award for British Columbia’s Manufacturer & Supplier

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November 15, 2017 – Garibaldi Glass Industries Inc. took home the top prize in the Manufacturer & Supplier category at the (VRCA) Vancouver Regional Construction Association’s 29th Annual Awards of Excellence held at the Vancouver Convention Centre on October 25th.

Garibaldi Glass was selected for the award based on providing design-assist services paired with project management for the iconic Nordstrom Redevelopment of the old Sears space at Pacific Centre Mall located in downtown Vancouver. Through Design Assist with James Cheng Architects, Garibaldi Glass, Guardian Industries and Inland Glass & Aluminum, Garibaldi supplied over 134,000 sq. ft. of insulated glass units using Guardian SNR43 and IS20, the latest “soft coat” low E technology.

“On behalf of all of us at Garibaldi, it was definitely a team effort to be honored with this award. With all of the great opportunities in the marketplace, it comes down to our project management team and everybody working together,” said Carey Mobius, President and CEO, Garibaldi Glass Industries Inc.

Winning this award, emphasizes and confirms Garibaldi’s successful Design Assist and Project Management and streamline manufacturing processes allowed the project to be completed on time and on budget.

ABOUT GARIBALDI GLASS

Garibaldi Glass is a privately owned, architectural glass fabrication facility serving local and international markets. Since 1966, Garibaldi Glass has grown to become the premier source of innovative glass solutions, currently employing over 220 employees working in our 160,000 square foot facility in Burnaby, BC. As we look towards our next 50 years, we are eager to continue our journey to excellence through the continuous improvement of our products and processes to be the leading custom glass fabricator on the West Coast of North America.

Phantom Circles on Glass

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From time to time a customer will see the appearance of circular marks on glass under certain climate and/or lighting conditions. Like crop circles, they mysteriously appear and disappear and many people are unsure of where they come from or how they are made.

Under certain lighting conditions (i.e. sun light at a very specific angle) or climatic conditions (rainwater running down the glass or fogged shower glass), one or more circles may become visible. They do not obstruct vision through the glass but simply show a contrast when looking at the reflectance of the glass surface when compared to the rest of the glass or as a resist area where rain water will not run down evenly but around the circular area or as a circular image on fogged shower glass.

These circular marks will usually measure anywhere from 12 “ to 3” in diameter. They can originate during the original manufacturing process or the secondary manufacturing of the finished glass. During all glass manufacturing processes, glass sheets can be moved from one location to another by the use of suction cups.

Although the suction cups are made of a very soft rubber like material, they can abrade the glass surface on a microscopic level. This can be further exaggerated if the glass is being lifted by its “tin” side (see “How Glass is Made – The Difference Between Primary and Secondary Glass Manufacturing”), an imperceptible amount of the tin residue is removed. The result is that under the circumstances described earlier, the “ghost” of one or more of the suction cups may become visible.

If the end user finds the appearance disturbing, applying a very mild abrasive such as cerium oxide onto a wet, clean rag and rubbing the effected area vigorously, will possibly remove the appearance. It is very important to carefully clean the glass area affected before applying the abrasive.

In conclusion, this is an industry wide phenomenon. It is not considered a defect since it is not constant in appearance and does not impact the performance of the glass and is not recognized by any industry standards. It is important to note that it is almost impossible duplicate this phenomenon in the industrial manufacturing environment on a cost effect basis.

Innovation

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Wikipedia states: “Innovation is the development of new customers’ value through solutions that meet new needs, inarticulate needs, or old customer and market needs in new ways. This is accomplished through different or more effective products, processes, services, technologies, or ideas…”

At Garibaldi Glass, innovation is one of our core values and with good reason. Whether undertaking the challenges of developing and manufacturing the special phosphoresent vent covers for the Shangri-La Hotel in Vancouver, or the fritted shadow box sealed units for the Surrey Memorial Hospital project in Surrey, British Columbia, innovation has allowed us to help our customers realize satisfactory, cost effect solutions to complex challenges. A willingness to listen carefully to a customer’s desires and using the cumulative knowledge of our staff, there are few challenges we can’t find solutions to. The only challenges we have not been able to solve, normally involve changing the laws of physics and when has the budget not been blown before the glass requirements have been finalized? Not only can we usually find a solution, we endeavor to do them in the most cost effective ways possible.