Types of fire-resistant glasses

The increased use of glazing in buildings, together with building code requirements in the fire-rated glass sector which have seen rapid changes, have lead to the development of new types of fire glasses.

Generally, any type of glass that can withstand the fire test and therefore resist passage of smoke, flames and hot gases, is considered "fire-resistant glass". These glasses are then further categorised and rated according to special criteria. Typically, the rating is based on how long a particular type and size of glass will withstand fire. Classifications range from 20 minutes up to 3 hours. Ordinary flat glass cannot withstand extreme temperatures, and breaks at around 120° C. Fire-resistant glass must be able to withstand 870° C for a selected period of time and remain in its frame. Immediately following this extreme heat, the glass is exposed to ?The Hose Stream Test?. In this test, water is used to rapidly cool the hot glass to test its ability to withstand thermal change. The purpose of this test is to test a real situation in which water from a sprinkler system shatters glass intended to function as a barrier, and thus permits smoke and fire to spread and escalate to the next level. The three most important factors in connection with the choice of fire-protection glass are: - type of protection (class E- and class EI) - duration of protection (e.g. 15, 30 or 60 minutes), - frame construction to be used (wood, aluminum or steel). Class E involves protection against smoke and flames while class EI also offers protection against fires spreading heat radiation. On the market today they are several fire-resistant glass products such as wired glass, ceramic glass, fire-rated tempered and special laminated glass.

article source http://www.glassonweb.com

Today’s challenges of automotive glass manufacturers

Automotive glass manufacturers are forced to face great challenges daily. Especially now since world financial crisis had almost immediate impact on the industry. The slowing economy drives the new vehicle sales down with out exception in each continent. To Remain competitive, more than ever now all manufacturers from largest multinational corporations to smaller private companies are seeking ways to cut costs, improve efficiency and production yields – at least they should be, by now.

Ever rising energy prices are making each windscreens production cost higher and when we add on top of this all the costs arising from waste pieces, used working hours, and possibly extended development periods, the margin per piece simply comes smaller and smaller. Without continuous efforts to boost up the yield, productivity, efficiency, and quality, company will end up losing ground to its competitors. Well trained, professional and committed staff is a key factor when companies fight their way through these rough times. THE PROCESS From raw glass warehouse, to cutting table, grinding, washing, long pair powdering and short pair to printing, short pair is dried and finally glasses are paired again. After this so called “cold-end” of the process is done and the glass is half way in the process chain. It is amazing how much these processing methods still vary today. It is common to see glasses hand cut and separating powder applied manually while in the other hand larger more developed companies use completely automated production lines with robots and automatic measuring. Although these companies are set to aim different markets, both can make profitable business. With out any deeper knowledge on the cold-end part everyone can understand that a lot can be done wrong and many to cut costs and improve efficiency. Automatic quality control monitoring is available for the manufacturing lines, but due to the costs the quality is still monitored by the operators. From these processes grinding and powdering can cause breakages and defects later, in and after bending process. Therefore it is important to monitor these processes carefully. After the “cold-end” the process chain continues with bending the most demanding process of the complete chain. After bending follows pvb assembly, vacuum and autoclaving. This article will focus more on the “hot-end” part of the process chain. MANUFACTURING CHALLENGES - Bending the most important part of the process Every day larger and more complex shapes in car windscreens come more common. Although every part of the process play their important role in the final product, it is clear that bending is the most important and demanding part. Without successful bending results the complete process fails. So called cielo and panoramic type windscreens with deep cross curvatures, tight wing shapes and small installation angle, together with thin, coloured, glass pair combinations create an “equation” that needs careful and professional care while it’s been developed into production. Bending these difficult windscreens with basic gravity bending furnaces is everything else than simple. The key issue will be – How to achieve perfect optical quality. Challenge is obvious, even to meet the optical requirements of the ECE 43 regulations and it is common that the car manufacturer has its own standards. These manufacturer standards have a tendency to be far more demanding than the ECE optical regulations. Hand in hand with this optical challenge comes the complex shape. Deep cross curvatures are sometimes some what tricky to handle. The “profile” of centre section of the glass easily contains “flat” or “reverse” parts. In other words the cross curvature is not smooth and continuous, as part or parts of the windscreen is left “flat” or has “reverse bending”. These “flat and reverse” areas cause problems in “wiperbility” and in worst case these defects will cause reflections on the optical examination. Due to the challenging characteristics of the windscreen and quality requirements the bending trials can get uncomfortable while the perfect heating configurations and tooling settings are being searched for long periods of time and often without any encouraging results. After a while the work can come into a halt. Correct heating configuration and advanced tooling are highly important, but it is also necessary to realize that good optical quality cannot be reached if the process chain from cutting until final inspection is not in order. The latest model serial gravity bending furnaces are equipped with wide range of features, but still the challenge is real. The biggest advantage on new furnaces is the well improved heating element controls and endless possibilities of adjustments. In fact so many that an average shift operator does not know half of the parameters and the functions behind. Older furnaces have their limits when it comes to producing the windscreens for latest car industry innovations, and we are not talking only about the physical limitation set by the chamber size. Coloured, thin glass pair combination and a complex shape can prove out to be impossible to manufacture without up to date machinery. Unfortunately investing into a new furnace can be too expensive. Similar challenges are faced with coach, special vehicle and bus windscreen manufacturing. Biggest challenge for this segment of windscreens is the wing and corner shapes. Today most of the single chamber and serial furnaces for larger windscreens are equipped with bottom heating and position/out put power controls. These technical features enable faster and uniform heating for both short and long glass pair and a precise heating radiation control only to the areas where the radiation needs to be applied. Bottom heating further eliminates possible optical defects. Large windscreens with long and tight wing shapes together with deep cross curvature are difficult to bend to the final shape. Deformations on edge shapes and reverse bending are common problem when the glass has been forced to its shape. To achieve competitive results advanced mould tooling is very important. Advanced mould tooling allows perfect control of the windscreen from the beginning of the bending process until the very end. With different mechanical solutions the mould and glass can be controlled so that no external manipulation of the glass is necessary. Such control of the glass and mould eases reverse bendings and shape deviations on the corner areas. Generally, with both; serial and single chamber furnaces, complex bus and special vehicle windscreens are bent manually using only the basic automatic functions such as automatic heating element configuration during the bending and final bending. Other functions weight controls, slight adjustments on temperature balance and finally release to cooling (Glass Ready) are all controlled by the operator(s) during the process. Manual operating is time consuming but in some cases cannot be avoided, simply because the technology available today does not make it possible. Since the process is controlled manually it is obvious that certain level of skill is a must to successful operation. The bending is very unforgiving, and one mistake can be fatal to the end product. Well trained and committed staff is major factor in this process and the yield levels and quality can be improved to a completely new level with continuous and efficient development of the bending practises QUALITY - a true strength ECE 43 regulations determine the basic guide lines regarding the checks on conformity of production, but it leaves a lot for the manufacturer it self to decide how to measure and control the end product. When compared the manufacturers ARG windscreen manufacturing quality control measures vary widely from next to nothing to basically thorough 100 % inspections. For example: Some companies are checking all windscreens immediately after bending with the checking fixture and document the shape and size variations carefully while others still are not using no checking fixtures at all. In OEM segment the practice does not vary so widely although clear variation on quality control measures is still there. Strict quality control measures after each process are easy way to improve the yield levels and save costs when only the good parts are processed. Once again the production line staff is in a key role – they must be committed to the perfect quality idea. INDEPENDENT EXTERNAL VIEW – way to easier solutions? In every aspect of the business, companies are using consulting, coaching, training and advising when their own internal development and technical departments face a situation when there’s simply no new ideas and the work comes to stand still. Most of the times the external view is sought even before the actual stand still situation is faced. In these situations external professional view, can probably pin point the weakest spots and determine worst “reefs” to be avoided. Problems can be caused simply because the matters are looked from “too close proximity” and instead of seeing the complete picture, everyone is focused into one minor detail, “thinking inside the box”. Thinking outside of the box normally generates innovative and novel ideas. Sometimes neutral external “variable” can change a lot. Broader view, different approach, professional experience, and purely neutral opinions based only to the facts gathered, can lighten up the situation for all, in completely different perspective. Doesn’t really matter if it is a technical problem or matter of working practises – the “external variable” can be a way to easier solution. In technical problems the working pattern is very much like doctor and patient relation. The reasons are sought according to the patient’s report of the symptoms. Doctor examines the process and after analysing the observations he explains the cause and consequences and suggests possible treatments. All this is done under professional confidentiality. Since the automotive windscreens manufacturing process chain still contains a lot of “manual” and “automated manual” work it is clear that the skills and commitment of the manufacturing staff play a crucial role on the continuous development. Both multinational corporations or private companies targeting the local markets need “tools” to overcome and improve their daily practises. Efficient and necessary “tool” can be change of attitude, practical training, technical advising or possibly new machinery, but sometimes hiring help out side is necessary to define the correct solutions. article source http://www.glassonweb.com

What makes glass transparent?

Glass is something we use every day, a transparent material produced by melting a mixture of sand, calcium, oxide, and other raw materials and then cooling the resulting product. But have you ever wondered what makes glass transparent? Why can we see through window and not through the frame that enclose it?

In general most liquids and gases like water, air, natural gas, cooking oil, or rubbing alcohol are transparent, while solid materials like wood, metal, ceramics, etc. are opaque. That is because of a difference between the molecular structure of solids, liquids and gases. When a substance is in its solid state, molecules are ordered in a regular lattice just like bricks stacked neatly on top of one another, being virtually impenetrable for light waves. The molecules of an substance in the liquid stage are disordered and are not rigidly bound. This causes the disordered stacking of the molecules, creating gaps and holes that allow portions of light waves to pass through. The greater the gaps in molecular organization the easier it is for light to pass through. As glass in neither liquid nor solid, because its molecules are motionless (like a solid) but random in configuration (like a liquid), glass exists in a solid yet transparent state.

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http://www.glassonweb.com

Why a hose stream test is critical for testing fire glass

The options in fire-rated glass have expanded greatly in recent years. Where architects and designers were once limited to traditional wired glass in relatively small sizes, today they can choose from a range of glazing that offers superior fire protection and the chance to incorporate entire walls of glass without compromising safety.

This is no small feat: To achieve a fire rating of more than 20 minutes, heated glass is subjected to a mandatory hose stream test as specified in test standards such as the National Fire Protection Association’s (NFPA) Standards on Fire Test for Window and Glass Block Assemblies. While some have questioned the ongoing necessity of the hose stream test, the NFPA standards clearly state: “The hose stream test provides a method for evaluating the integrity of constructions and assemblies and for eliminating inadequate materials or constructions. The cooling, impact, and erosion effects of the hose stream provide important tests of the integrity of the specimen being evaluated.” Why should architects, glaziers and building code officials be aware of the importance of the hose stream test? Because one manufacturer now sells a 60-minute “fire-rated” product that does not and cannot pass the mandatory hose stream test. To the unsuspecting eye, a 45- or 60-minute fire-rated label on the glass that says “…without hose stream…” may not raise suspicions – unless you know that the hose stream is a mandatory procedure required by North American test standards. To selectively decide what portions of required test procedures one chooses to complete can be dangerous. Fire-Glass Testing The hose stream test is part of a series of tests that begins with heat testing of the glass. Manufacturers seeking a fire rating take their products to an independent testing facility, such as Underwriters’ Laboratories. The lab installs multiple pieces of the glass in a frame and wall assembly, which is then placed in a large furnace. A fire is then ignited on one side of the widow assembly, with temperatures attempting to replicate a “real world” fire. Following a standard time/temperature curve, at five minutes temperatures approach 1,000 F. and are nearly 2,000 F. at 180 minutes. The length of time the glass remains intact in the furnace will correspond to the final fire rating it receives (ranging from 20 minutes to 3 hours). The goal of this testing is to determine how long the glass can remain in place and be expected to act as a barrier to a real life fire. If glass fails under the intense heat and vacates the frame, the flames and deadly smoke will be free to travel throughout a building. If glass successfully survives the fire test and the manufacturer is seeking a rating greater than 20 minutes, the glass is immediately put through a second type of test. While the glass and framing system is still hot from the furnace, it is sprayed with water from a fire hose at a pressure of at least 30 PSI. Most glass cannot tolerate drastic temperature differences such as this. If one area of the glass and framing system is hot while another is cool, it creates stress on the glass, known as thermal shock. Since part of the glass is expanding and part is contracting at the same time, the glass will shatter and vacate the frame. The hose stream test is a critical way to measure how glass will respond to temperature differences. The glass must remain intact in order to pass and offer protection. Interestingly, it doesn’t have to be a fire hose to prove the point. One manufacturer tested a 20-minute rated product with a simple garden hose. While the hot glass was able to withstand approximately 1,500 F., it quickly shattered when the light spray was applied. Continuing Need for Hose Stream Test Why is the hose stream test important? In the case of a real world fire, there’s a good chance glass and framing systems that have been exposed to the heat of flames will also be subjected to water from a fire hose, sprinklers or fire extinguishers. If the glass can’t withstand thermal shock, it will fall out of the frame, leaving an opening for fire or smoke to spread. In the United States, all fire-rated glazing products with ratings greater than 20 minutes are required to pass the hose stream test (Canada requires the hose stream test for all ratings). Building and fire codes are very clear on why the hose stream test is critical, and in recent years, proposals to eliminate the test have been soundly defeated. Last year, the manufacturer marketing a product that cannot pass the hose stream test sought to eliminate the hose stream test requirements from two portions of the fire-rated glass test standards in the International Code Councils’ (ICC) building safety and fire prevention codes. The ICC’s Fire Safety Code Development Committee, comprised of code officials, fire marshals and other experts, rejected these proposals after careful review of the issues presented in open public hearings. In its rejection of one of the proposals, the Committee stated that removal of the hose stream test requirement “…would reduce the level of life safety which the code has generally required and provided.” In its decision on the other proposal, the Committee noted that the issue has been debated a number of times and that “it has always been defeated.” (2006 ICC Public Hearing Results, FS121-06/07 and FS107-06/07). By its actions, the ICC has repeatedly validated the importance of the required hose stream test for life and property safety. When choosing fire-rated glazing materials, it is critical to make sure that the product in question meets or exceeds all the testing standards. Otherwise, you may be taking a serious risk or increasing your liability. For openings with fire ratings of greater than 20 minutes, always insist on glass that has passed the mandatory hose stream test, and beware of products that acknowledge they have not passed the required test. There’s no need to compromise when life and property safety could be at stake. About the author: Jerry Razwick is founder and president of Technical Glass Products (TGP), a distributor of specialty glass and framing as well as architectural products. He has been a glass factory agent in foreign and domestic markets for over 25 years. Mr. Razwick has served on the Industry Advisory Committee for Underwriters Laboratories, Inc. and is an active member of AIA, CSI, NGA and GANA

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http://www.glassonweb.com

Windows of the future

We spend millions of dollars every year to heat our homes and businesses. That is why it is so important to understand the role that windows play in how buildings use energy. In older homes, windows are often one of the largest sources of heat loss in winter due to their low insulating ability and high air leakage rates. Windows are also generally the major source of unwanted heat gain in the summer. As a result, windows are typically net energy losers, and can be responsible for 25 to 50 percent of the energy used to heat and cool homes. However, improved windows, combined with proper consideration of their placement and other details, can result in windows that provide a net energy gain.

Windows Windows were once little more than holes cut in walls to let light and air into rooms. Today they bring beauty and light, warmth and cooling breezes into homes while providing a sense of openness and space. On the down side, windows can also let in the winter chill or the summer heat. They can make a home drafty, uncomfortable, and energy inefficient. Fortunately, modern windows make the most of the benefits of windows while minimizing the drawbacks. Single-pane glass has been replaced by multi-panes separated by insulating materials. Frames are made of new, more energy efficient materials. Even the glass itself has been coated to reflect heat. Windows of the future New technologies are producing increasingly energy efficient windows. Already on the market are “super-windows”, boasting triple layer designs, with two low-E coatings and spaces filled with mixtures of argon or krypton gases. A new generation of windows, however, is being called “smart windows” because they adapt to changing conditions. A few “smart windows” are already commercially available, and others are being developed in research labs. These windows change properties - like their shading coefficients and visible transmittances - in response to either an electric charge or an environmental signal such as a change in light level. Depending on the mechanism that initiates the change in the window, these “switchable glazings” fall into four categories: electrochromic, liquid crystal, thermochromic, and photochromic. By GlassOnWeb editorial staff Photochromic Windows: See The Difference Sunlight Reactive Thermo Windows are the ultimate “smart” window.  They are perfect for any application, architectural or residential. Photochromic glass automatically changes from a clear glass to a tinted glass with the rays of the sun.  There is no electricity or knobs required.  As the sun sets, the glass will lighten up returning to it’s clear state.  This will continue each time the sun is shining on the glass without fatigue unlike film tints and coatings.  It also costs a fraction of the price of other smart windows currently available on the market. Other glass reflects the harmful ultra violet rays that go back into the Earth’s ozone and are a great contributor to the global warming problem.  Photochromic glass absorbs the UV rays helping to protect our planet.  In doing this, it reduces the heat transferring into the building and reduces energy consumption and air conditioning costs. In architectural applications, the automatically tinting glass will create privacy on sunny bright days.  It will also protect expensive office furnishings with it’s 100% UV protection and stop the glare on computer screens and projectors.  It can be made in a variety of colours making each application unique. In residential applications, homeowners will be able to enjoy the sight out of their windows, protect their furnishings, and save on their energy costs all without curtains or blinds. With Sunlight Reactive Thermo windows, as the glass changes from light to dark with the sunlight, you can see the difference. For more information Please visit our website at:www.photochromicwindows.com By Christopher Crawford

World Demand for Flat Glass

According to a study from the Freedonia Group, production of flat glass is projected to increase 5.2 percent per year through 2008 to 48.3 million metric tons, of which around 34 million metric tons will be high quality float glass.

Construction markets will grow the fastest based on expanding global fixed investment: consequently, demand in the already dominant architectural glass sector will register the best gains.  The market for architectural glass is forecast to grow 5.4 percent per year through 2008 to US$53 billion: it will benefit from the greater use of value-added glazing products (such as laminated, tempered, mirrored glass, and, above all, double-glazed insulating glass units, which have become more and more popular in developed countries).  Asia will continue to offer strong annual gains, with growth especially strong in China and India. The US market for fabricated flat glass is forecast to outpace the global average, although actual gains in metric tonnage and square meters are expected to remain slightly above the average. Western Europe will continue to post the weakest sales growth, hindered by below average economic growth.  article source http://www.glassonweb.com

Windscreens Go Deeper, Wider, Steeper, Spherical

Breaking new ground with designs that are original and appealing is a daily challenge for car designers. One limitation on their creativity may be the constraints placed by the materials used in the design.

New glass technologies have brought significant advances in design; windshields have gone from being flat to curved, and now they can be spherical with wrap-around corners. Many practical issues still pose a challenge; visibility during the day and at night, comfort and safety, to name a few.  As a result, car designers today are including more and more glass in their cars. They are looking for aerodynamic efficiency, driving comfort and safety, as well as optimum structural stability and an attractive appearance. This has led to higher and wider windscreens, and steeper inclinations. And more glass overall in the car body.  TECHNOLOGY  For deep sags (> 30 mm), it has almost been the rule to use a press bender. This is certainly justified in long OEM series, but for short OEM series and replacement windscreens, it reduces manufacturing flexibility. Glassrobots has designed its innovative, reliable TFA FuzzyBend™ range of windscreen bending furnaces to be flexible enough for short and long runs in OEM and ARG production. With the new TFA 3evolution™ furnace, windscreens with sags of up to 32 mm are also produced with the reliable Glassrobots gravity bending control method. Using the TFA 3evolution™, it is possible to manufacture these windscreens, which manufacturers used to think required a press bender. Windscreen manufacturers can then decide whether they do short, long or replacement series. With the TFA 3evolution™, they at least have the right furnace.  The tooling for a press bender is also very expensive, which makes it uneconomical and unsuitable for producing replacement windscreens. Since more and more new windscreen models are being produced, it was time to design a reliable and flexible furnace for this ARG market. Complex, wrap-around corners, increased cross-bending and larger glass sizes are typical features of modern windscreen design.  The outstanding, distortion free quality and dimensional accuracy of the end product, as well as the higher capacity, derive from the following innovative features of the TFA 3evolution™ furnace:  • New enhanced bending programme based on percentage control of heating elements with the proven and patented FuzzyBend™ control system  • Bottom heating elements with individual control for different models  • Special second level heating zone  • Customised heating elements for making the most demanding windscreen shapes  • Optimised arrangement of moving parts  All this is backed up by the experience and proven technology of Glassrobots, such as:  • Vertically Adjustable Heating Elements, VAHE™, to focus heat in difficult areas in the bending section  • 5-part heating elements in the bending sections, instead of the normal 3-part elements  • Temperature Balancing System, TBS™, consisting of an extra pyrometer in the bending sections, guarantees symmetrical heating. The glass temperature is measured systematically and if variations are detected, the control system automatically adjusts the heating pattern.  • Side Heaters enhance the heating of the side areas. They are normally installed in the pre-bending and bending sections.  • MirrorPattern™ (patent pending) eliminates the negative effect in mixed production of thermal inertia from the heating pattern for the previous glass.  • GlassButler™, remote diagnostic software that enables our technicians to be in direct contact via a modem link with the client’s process computers.  • Condition Monitoring and Maintenance System, CMMS™, a preventive maintenance feature that minimizes downtime and maximizes hours of operation.  RECENT DELIVERIES  Trakya Cam Sanayii A.S. Oto Cam Fabrikasi, a member of the Sisecam Group in Turkey, acquired its second car windscreen bending furnace from Glassrobots in just two and a half years. Sisecam is the biggest glass producer in Turkey. The Sisecam Group, one of the first public enterprises in Turkey, is quoted on the Istanbul Stock Exchange.  Gilan Glass Industries, Iran, is one of the largest OEM suppliers in Iran. They have one plant operating in Rashd in northern Iran. Capacity requirements have increased, and GGI is building a new plant in southern Iran. To better serve OEM car suppliers, GGI chose the new Glassrobots furnace, with an option for a second one.  The innovative details characteristic of Glassrobots furnaces were the main reason why these clients chose aGlassrobots furnace. And there are more to come, with windshield manufacturers queuing up for this fantastic product.  FUTURE INNOVATIONS  Much has been achieved, but even more remains to be done, to satisfy the ever-increasing demands of windscreen benders, or ultimately the car designers and makers. Future models will probably make even greater demands on the bending and laminating process. The use of solar-control glass, heated windscreens, integrated antenna systems, advanced display systems etc. is becoming more common, but research on these and other issues is going on all the time.  It is not just windshields that are undergoing considerable changes in design. Windscreens today may even continue directly into a roof window that is also laminated. Some car models now have laminated side lites. These provide better sound insulation, improve security against break-ins and safety in roll-over accidents, and of course give a wide range ofcolour options. But they cost five times more for the carmakers.  In order to meet future requirements and develop the new technology for them, the windscreen processor and furnace manufacturer have to work together and come up with new ideas to give them an edge over the competition. The key factors in success will continue to be cost efficiency, process quality and control and, above all, product quality.  article source http://www.glassonweb.com

Photos: Glassrobots Oy Last review: July, 2008

Windshield Lamination Process Secrets

The complex nature of lamination defects; individual processing conditions, and different materials create a situation where the only working solutions are individually adjusted processing parameters.

I was inspired writing this article after I concluded that majority of my windshield production related cases included findings causing lamination defects and encouraged further more after seeing lines performing under conditions that were not supposed to produce even one good piece of laminated glass. In my experience the producers sometimes over look the conditions that contribute to reduced lamination process performance. The lamination process is in key-role in complete windshield production unit performance and it’s results and quality are directly linked with bending and pre-processing activities. In this article I will review the lamination process and most common lamination defect. LAMINATION PROCESS Lamination defects are typically within the top 5 waste (scrap) reasons in production of laminated windshields. Dominating lamination process in production of windshields contains the following process cycle: PVB Assembly -> 2. Vacuum conveyor (cold and hot)-> 3. Autoclave Alternatives are existent such as vacuum boxes, but the processing principles remain. The entire process seems simple, however following the basic guide lines of clean environment work and common processing parameters alone is not enough to maintain and improve the production yield levels. Without perfectly adjusted processing parameters the process can result with high number of re-autoclaved and waste pieces due to lamination defects. Waste created at this stage of production chain is particularly expensive and re-autoclaved pieces create workflow to unnatural direction. Furthermore re-autoclaved pieces are especially harmful for productivity as the autoclave is typically the bottleneck in laminated glass production lines, due to the limited capacity and long process cycle taking up to 4 hours. TYPICAL LAMINATION DEFECT Defect known as “bubbles” is probably the dominating lamination defect caused by air left between the glass sheets. This lamination defect is controversial: the bubbles do not appear every time when a little air is left between the laminate or when gapping between the glass pairs is monitored. The defect seems to arise when few contributing factors are existent. The fact that there seems to be no single dominating factor that ultimately creates this defect makes the elimination difficult. The “Bubble”-defect appears in different sizes and locations. Typically the defect appears as “bubble”-areas in the very edges of the glass, while also larger individual bubbles appear: both in edges as well more towards to the middle section. Larger “bubbles” appearing in the very edge of glass can be commonly fixed with re-autoclave cycle adding clips that help sealing the glass edges. However larger bubbles in the inner parts of the glass, typically between the glass corner and mould hinge line can be impossible to fix. WHY BUBBLES APPEAR? There are several conditions in each processing stage that can affect the lamination performance. Pre-Processing Cutting size variations will cause severe difficulties in positioning of the glass pair in the lamination. Default in positioning of glass pairs in PVB assembly will cause unwanted gapping between the glass   sheets. Extensive amount of separating powder will cause minor surface variations in the glass pairs inner surfaces reducing adhesion of the PVB and glass. Poor washing water characteristics can affect the adhesion. Therefore the hardness of the water is monitored. Gapping between glass pairs created during bending process is also potentially increasing the risk of defects. Gapping between the glass sheets created due to temperature difference between the glass sheets or mould issues will contribute to appearing bubbles. Gapping affect is very product dependent, however gapping < 0,8 mm is usually not considered to cause “bubbles”. In any case gapping is a contributing factor and together with other contributing factors will create circumstances where the “bubble”-defect is more likely to appear. Lamination process conditions: Lamination clean environment conditions; temperature, and relative humidity should be in suitable levels. PVB storage should also maintain correct temperature and relative humidity. Cold-Suction of the laminate is also in important role. The cold-suction time should be sufficient enough to relive almost all the air from the glass before the edges are sealed. Usually most common reason for appearing bubbles is processing default in the very beginning of the heat treatment (hot-vacuum) enabling the glass edge to close too early. The hot de-airing phases heating should be conducted gradually and evenly so that the glass edges do not seal before all air is relieved from the sandwich Autoclaving process  The autoclaving process is the final real treatment process of a typical windshield that will define the lamination and end product quality. The process temperature and pressure curves can be controlled in great detail with modern autoclaves. Correct temperature and pressure set points are required to gain perfect results. With wrong set points the bubbles can appear days after the process. HOW TO PREVENT BUBLES DEFECT? Start with perfecting the pre-processing activities; cutting size, washing water quality control, bending process controls and quality. Follow to lamination activities controlling and measuring all the actions carefully: Releasing the PVB, careful positioning at assembly, sufficient cold-vacuum, controlled heating in hot-vacuum, correct actions with vacuum ring assembly and disassembly, and finally perform perfectly adjusted autoclave process with correct heating and pressure curves. When all production activities are well documented, staff performs according to production instructions and process parameters are repeated to perfection the identification of all variations is considerably easier. Safety Glass Experts provides services to study your current production activities performing a complete production Present State Evaluation. The evaluation will provide you complete, objective, external experts assessment and findings of your production current status. This information enables efficient approach solving any production defects, reducing waste, improving efficiency and line personnel know-how. CONCLUSIONS Processing conditions and used materials vary; therefore the followed process guidelines must be adapted to individual situations. Lamination process conditions must be well controlled to enable adjustments and identification of process variations when defects appear. Lamination process includes various minor details that potentially affect the results and results are linked with bending and pre-processing quality. Mastering these details is essential. Manufacturers suffering from any lamination difficulty will receive immediate solutions through our Remote Expert Service or on-site visits conducted by our experts. Safety Glass Experts International Oy Ltd Talviseisaus 2 D 8 FI-20400 Turku Finland Phone: +358 400 979 300 Fax: +358 2 6518 2539 Email: info@sge.fi Web: www.sge.fi All graphics, photographs, and text appearing in this article belong to Safety Glass Experts International Oy Ltd. Redistribution or commercial use is prohibited without express written permission.

Photos: http://www.sge.fi Last review: January, 2011

Glass Manufacturing)..Installing Channel Glass )

A Popular daylighting system for interior or exterior glass walls, channel glass – such as Pilkington Profilit™, available from Technical Glass Products (TGP), Kirkland, Washington – provides a sleek, modern look for commercial or industrial buildings and homes. The glass is available in a variety of colors and textures with varying translucency, allowing for the passage of natural light without loss of privacy. This very versatile product can be installed vertically or horizontally and is available in lengths up to 23 feet, with either tempering or filming options available to meet impact safety requirements.

Because of the shape of the system, it can achieve very tight radiuses or can be used in serpentine applications. Intermediate vertical mullions are generally not required for vertical installations. Additional benefits include strong thermal performance, sound transmission control and adaptability to seismic code requirements. Given the distinctive nature of channel glazing, some specific guidelines must be followed for proper installation. While not difficult or complex, the steps differ from more traditional glazing materials. The following guidelines provide general instructions for installing the product in exterior vertical applications. As with any specialty glazing, consult the supplier’s documentation for specific installation instructions, including procedures for horizontal or interior installations. Preparing the Structural Opening Prior to fitting, the supporting structure must be checked to ensure that it is square, plumb and in plane. The support jambs must be plumb. All surfaces should be checked to ensure that they are suitable for attachment and conform to the contract documents. Measuring and Attaching Aluminum Frames Measure the opening sizes and cut the head, sill and jamb sections. Miter or cope and butt the joints at the head. Cope and butt joints at the sill. When measuring the frames, take into account the caulking bead clearance requirements and shim with the appropriate-sized horseshoe-type plastic glazing shim. Expansion properties of the aluminum frame should be taken in to consideration. Consult the supplier for specific details. To attach the aluminum frames to the structure, place all fasteners approximately 12 to 18 inches on center (300 to 450 mm), or as recommended by the engineer of record. Fasteners should be located no closer than 6 inches from the corner joints. Couple frame members exceeding 24 feet in length with an expansion joint material as supplied by TGP. The specific type of fastener required depends on whether the supporting structure is concrete, steel or wood. Refer to manufacturer’s table for typical types of fasteners for the various applications. At all head/jamb mitered corner joints, install aluminum corner keys and internally seal corners with approved silicone. At sill/jamb coped and butted corner joints, a screw boss is provided for corner assembly. After assembly, care must be taken to internally seal all joints. Cut and fit plastic inserts into the head, jamb and sill sections of the frame. The vinyl inserts at the jamb should be fitted to the full daylight height of the opening and clip securely into the frame. The horizontal head and sill vinyl comes pre-cut to length to match the glass sizes and should be place intermittently (to match glass placements) in the sill and head of the frame. Finally, insert foam baffles into exterior weep holes. Cutting channel glass Tempered glass and annealed (at customer’s option) glass can be provided cut to length. If glass is desired, or required, to be cut on site, the following procedures should be followed: • Place the glass channel on a flat surface, preferably cushioned with felt or other suitable materials. With the flanges pointed upward, channel glass channels can be cut by hand or by special saw. There should be a minimum glass bite allowance of ¾ inches (20mm) for the head and jamb and ½ inches (13mm) for the sill. The flange cut (jamb) channels must have a bite or at least ¾ inches (20mm). To cut by hand: • Use a cutting template or straight edge to ensure a straight cut. • Begin by scoring the flange furthest away, starting at the corner and working upwards; return back to the corner of origin and start the cut across the face of the glass and continue up the flange closest to the cutter in one continuous motion. • Make a light glancing blow to the top edge of the flange opposite the cut on each side of the glass channel. • Place the glass-cutting tool under the glass channel and apply light pressure to the flanges of the glass to snap it cleanly across the cut line. • Ensure that the ends of the channels are free from chips, cracks or bad cuts (pay particular attention to the quality of the cut at the corners, there should be no notches or shark’s teeth in this area). Seam the ends of the glass with a disc or belt sander specifically designed for glass edging, taking special care to smooth any irregularities caused by cutting. Installing Glass Before installation, clean all internal surfaces of the glass with an alcohol-based glass cleaner. Apply the 166 flange gaskets on each flange of every channel. The gasket application is most effective if the material is stored in a shaded location prior to installation. The gasket should be held ½ inch from the end of the flange on one end and flush with the edge of the flange on the opposite end (e.g. a 96-inch channel would have a 95-½ inch 166 flange gasket). The recessed portion of the gasket is always applied to the bottom end of the channel. Installation of the glass channels can begin at either the center point of the opening or at either end. Shop drawings are typically provided to indicate starting point and number of channels to be used for a specific elevation. Consult TGP for the size of joint between the channels. Typically, these joints are 1/8 inch, but the size can sometimes vary depending on the requirements of the contract documents. The jamb channels at either end of the glazed opening must have a minimum glass coverage of ¾ inch (20mm), or as otherwise specified. The flange cut/jamb channels are typically inserted prior to the installation of the last full-size channel. Pocket glaze the channels by inserting into the plastic liners located in the head and then lowering the glass down onto the corresponding plastic insert located in the sill. Suction cups are typically used to aid with this procedure. To ensure that the spacing between the channels is consistent, place 1/8-inch plastic shims at the head and sill of each channel as it is being installed. Sealing the System Prior to the application of any sealant, check glass joints for consistency and plumb. Install special channel glass shims across internal and external joints and seal all glass-to-glass and glass-to-aluminum joints with approved silicone sealant. For 1/8-inch glass-to-glass caulk joints, it is not necessary to use backer rod. The caulk joint at the perimeter of the frame should be packed with the properly sized backer rod and the approved, specified sealant should now be applied to the perimeter joint. Although the installation process for channel glass such as Pilkington Profilit involves some specific steps and techniques that differ from standard glass, experienced glaziers can install the product without hassle using these basic guidelines.  By Ms. Tysen Gannon and Mr. Peter Alberini Tysen Gannon is the product manager for Pilkington Profilit, a channel glass offered by Technical Glass Products (TGP), Kirkland, Washington. Peter Alberini is the technical sales manager for TGP. www.tgpamerica.com 1-800-426-0279

Glass Manufacturing)..Glass Tempering: Issues and Concerns)

Tempered glass has traveled a long distance, since inception of its production by vertical method, transition to sophisticated horizontal tempering equipments and now tempering of the most sophisticated glass types and designs, but this journey was not as smooth as it sounds, glass processors faced a plethora of problems during this transition stages (and a chunk of them are still facing). We will examine various issues related to glass tempering in this article.

Typical problems occurring during the heating process Heating is the most typical stage of glass tempering; a lot depend on this stage to bring out the product of high standard. Quality of tempered glass is very much influenced by the heating process used in the furnace. Non-uniform heating causes deformation of the glass in the quenching process. The most common problem is caused by rapid heating of the lower surface of the glass due to conduction of the heat from the ceramic rollers. The resulting expansion of the lower surface bows the glass edges upwards and the glass moves on the rollers like a boat, resulting in damage called “centre line haze”. Other non-uniform heating results include overheated edges, which cause deformation known as bistable saddle and may result in breaking of edges during the heating process. Coated Glass- A challenge for processors The continuing move towards better energy efficiency in buildings is  providing a strong push for the application of coated glass. Sputtered (off-line) low-E or solar control coatings are becoming standard in countries where climates are sunny the whole year or cold in winter and warm in summer. For glass processors with traditional technology this has meant a need to adopt somewhat slower  tempering processes because of longer heating time. At the same time processors are hard pressed to boost their production capacity  without compromising the aim for outstanding quality with all glass types. Problems are far more severe when processing coated Low-E and reflective glasses. In addition to the problem of conductive heat from the rollers, the coating on the upper surface of the glass reflects the radiation from the upper heating elements, whereas the lower heating elements heat the glass twice, because the radiation from below penetrates the glass and is reflected back from the coated upper surface. Uneven heat distribution may in turn occur when variable loads are run into the furnace one after another. When it enters the furnace, the cold glass absorbs the heat from the roller bed. Due to thermal inertia, the previous glass leaves the area where it has been oscillating cold, and consequently the next batch enters a roller bed which may have excess heat on the edges and a cold area in the middle. This can be partly compensated by adjusting the cross-sectional heat so that it only heats the loaded area. Non-uniform heating may also result in cold streaks in the direction of the glass. Here the uneven temperature caused by the resistance elements gives rise to iridescence which is most clearly seen in a polarisation test, but may also be visible to the naked eye. The glass itself may also cause problems in heating. Radiant heat is differently absorbed in printed areas of the glass than in plain glass. The same applies to shaped glass lites. These problems may adversely affect the shape or flatness of the end-product, its optical qualities or the surface of the glass. Uniformity in heating is achieved by compensating the temperature difference by profiled heating; hence the key importance of having the option of profiled heating. Convection for coated glass and speed "Heat is transferred to the glass in three different ways: by radiation, conduction and convection. Regardless of the type of furnace, these three ways of heat transfer are always present. They can be further analysed into the following parts: 1. Radiation Direct radiation Indirect radiation 2. Conduction from the ceramic rollers . 3. Convection – It can be classified in three categories. Natural convection. Assisted convection by using compressed air. Forced convection. The extent to which each of these contributes to the heating process depends upon the type of furnace, the type of glass and the phase of the heating process. In traditional furnaces the main source of heat transfer is conduction from the rollers (in the initial phases of heating) and then radiation. In full convection furnaces, the heat predominantly transfers through convection. Convection must play a major role if coated glasses are to be heated effectively. In order to overcome these problems, machinery manufacturers are on the constant lookout for new solutions that are based on the use of convection. Convection is seen as a must for any production line where coated glass is made. As well as helping to improve the quality of the end product, convectional heating has another important advantage over radiant systems, namely heating speed. Tempering systems based on radiant furnaces heat up the float glass at speeds of about 40 sec/mm of thickness. With convectional heating, heating times can be reduced to 25-30 sec/mm of thickness, increasing output and productivity by up to 40-50%! As Low-E and other coated glass types require much longer heating times in a radiant furnace, productivity is increased even more. "(quoted from the article Convection gives the advantage, by Juha Karisola) Disadvantages of Forced Convection There are three negatives of forced convection tempering. First, it is difficult to control the convection currents inside the furnace and requires proper design in the equipment and operator skill. Secondly, forced convection tempering consumes about 10% more electricity due to indirect heating through air-jets. Additionally, forced convection machines are also more expensive to buy as well as maintain. Edge Quality and Toughned Glass Edge quality plays an important role during fabrication, shipping and installation of float glass products in automotive and architectural applications.  The tempering process induces transient tensile stresses during early portion of tempering both on the surface and edges of float glass.  Depending on the temperature and viscosity of glass these stresses may or may not be relieved by viscous relaxation before the permanent beneficial stresses begin to build in. In view of good quality of float glass the temporary tensile stresses can be sustained by the surfaces but not necessarily by the edges. Indeed, the edge quality which depends on the type of edge finish is inferior  to that of tin and air side surfaces. Consequently, premature fracture may initiate at these edges if the combination of temporary tension and flaw severity is unbearable. Such a premature breakage occurs when the glass temperature is not high enough and the quench  rate is too high. Glass breakage during tempering cuts down productivity and at the same time reduces glass quality. Chinese Processing Machinery- Boon and Bane No doubts that China is the most vibrant economy of the world, this day and Chinese glass industry is giving sleepless nights to the glass producers and processors worldwide, but alas this vibrant economy and its machinery producers have failed significantly when it comes to glass tempering machines, you can count on your fingers a few quality machine manufacturers ( I bet you wont exhaust even one hand ), but ironically Chinese tempering machines are mushrooming in every corner of the world, be it the most sophisticated market of North America , Western Europe or the developing countries like India, Vietnam or African countries. These Cheap machines are finding the market in most unlikely places, I mentioned this matter to a few glass processors in my country and invariably the answer was lower initial cost, however none of the processor mentioned that there is a problem with quality (though the plant managers have a different story to tell). One doesn’t have to look very far, the way tempering machine manufacturers mushroomed in China, in a very short span of time tells the story itself. Look back five years back, there were five manufacturers of tempering machines in China, today you can count three dozens, and majority of them with hardly any R & D and selling at a cost nearly one third of European manufacturers . Though the lower initial cost has helped a lot of processors and new processors have bought these machines and has added to the volume of processed glass but in majority of the cases at the cost of quality. In my country has high as 75% of the tempering machines used are of Chinese origin.  By Seema Gahlaut article source http://www.glassonweb.com

Glass Manufacturing).Glass-Ceramics )

Ordinary glass is non-crystalline. Glass-ceramics however, are manufactured through the controlled crystallization of a specially formulated glass.

For the production of glass ceramics, a high density of crystalline nuclei is generated in the molten glass, either by the droplet phase-separation mechanism or by the addition of nucleating agents such as titanium, zirconium, or phosphorus pentoxide. After the nucleation process is carried out for a predetermined time, the crystals are allowed to grow to maturity at an increased temperature. It is also named crystallite glass. Glass-ceramics are useful in thermally hazardous conditions. This 'glassy' material contains crystalline lattices, which give it specific properties. Glass-ceramics are commonly used in thermally hazardous environments, such as in cookware. With lower density like aluminium, glass-ceramics are also used in high precision equipment such as high speed cutting reamers and to cover radar appliances on rockets because some types have the property of near-zero expansion. Some others have a high physical strength and can be machined like metals. Good resistance to erosion and pressure, as well as excellent hardness, also makes glass-ceramics widely used in industrial purposes. Moreover, glass-ceramics are very good electrical insulators. article source http://www.glassonweb.com

Glass Manufacturing)..Furnace Technology - development standstill)

The global recession has created severe problems for the automotive industry. Since the rapid downturn, car windscreen original equipment manufacturers (OEMs) have been forced to lay off employees and even close factories. Warehouse stocks of passenger car windscreens do not need replenishing; furthermore, the weak automotive replacement glass (ARG) market, along with decreasing OEM orders, are not offering enough demand to keep larger production lines in operation. The recession has caused a decrease in the demand of personal vehicles, growing demand for public transportation. Also the need for special vehicles which are used to harvest crops and manage forests has remained steady. These factors ensure the relative stability of this segment of the safety glass market.

A brief review of bus and special vehicle windscreen manufacturing techniques will show that, despite the continuing need for the glass products, the industry’s production technology has not been significantly improved in a decade. There are considerable opportunities to advance the state of the art. Production Technology Gravity bending is the only available method for larger, complex, bus and special vehicle windscreen manufacturing. It is amazing, that heat is the most important factor producing these windscreens efficiently, but the technology is still infact very undeveloped. Today these windscreens are produced mainly in infrared-radiation-heated single-chamber and serial furnaces. In the past, furnaces were equipped with longer heating elements controlled in single rows; currently, the heating element rows are divided into three or even six individually controllable parts which enable more accurate heating. The first automatic serial furnaces were introduced in the 1980s. The furnaces produced in the new millennium are highly automated, featuring temperature-controlled bending with multiple pyrometers, heat balancing, adjustable heating elements and power rates, bottom heating, temperature-controlled glass support, and mold/glass movement controls. Most of these technical features were invented before 2000. Automation of basic furnace functions frees the operators to concentrate on glass loading and other tasks. It also improves efficiency by reducing the work force and decreasing human errors that might affect yield. For example, modern furnaces include a glass center support system, probably introduced during the 1970s, that replaced an outmoded “aluminium stick” system built into the mold. The newer support system is mounted into the mold wagons to reduce pre-bending breakage. Originally manually controlled, the support system’s movement is now determined by the user interface temperature-based settings. Automation allows the operator to control the glass bending according to visual observation; the glass wing can be  bend to into its final form only after it reaches the optimal temperature. Bending with automated controls is probably the only viable method for forming complex bus and special vehicle windscreens without any external manipulation. Furnace Characteristics Single-chamber furnaces remain the most common manufacturing units for several reasons. Investment costs are low compared to those for serial furnaces; one-hour cycles accommodate short production series with frequent mold changes; construction facilitates multiple views into the heating chambers and improves ergonomics for operators who can work from a standing position; and simple construction and mechanics guarantee reliable operation. However, single-chamber furnaces definitely have drawbacks. For example, production capacity is small; on average, these furnaces produce only five to eight parts per eight-hour shift. To facilitate greater production capacity, several single-chamber furnaces must be utilized, requiring extensive floor space. In contrast, serial furnaces require less floor while offering similar production capacity than multiple single-chamber furnaces. Single-chamber furnaces are also not energy-efficient. The heating elements require the same amount of energy for each production cycle, while the hot air released by the cooling process is wasted. Compared to single-chamber furnaces, serial furnaces are much more energy efficient since the lower track’s cooling energy can be harnessed to heat the glass on the upper heating track and also the heat mass left into the chamber can be utilized, in continuos serial production. Both single-chamber and serial furnaces are produced with open and closed wagons. In the single-chamber furnaces, a closed wagon provides the option of pre-heating, assuming a special preheating section is available. This enables shorter cycle times because while the bending chamber is busy, the loaded wagon can be preheated. The disadvantage of a closed wagon is that it often limits working space for loading, unloading, mold tuning, and maintenance during operations. In contrast, an open wagon allows free access to the wagon platform during the loading actions. The windscreen cooling rate is sometimes faster with an open wagon. Due to its construction, an open wagon can also perform better from the windscreens edge compression qualities, since the glass edges are exposed to cold air flow immediately after the final bending. This air flow coming from the bottom of the glass can eliminate possible delamination problems. Production Problems Although furnaces in use today are equipped with modern automation, the process-related problems associated with the older, fully manual furnaces persist. For example, variation in the final product is unavoidable, especially with larger windscreens, since repeatability depends completely on operator actions. The final bending of the large windscreens is still handled manually by an operator controlling the furnace with the user interface. It is very difficult to reproduce the same center sag and edge size when these are estimated visually from a distance and with a limited view into the furnace. Glass temperature can be used only as a reference, since the bending conditions still vary. Another enduring processing issue involves the practice of “sticking” as a way to externally manipulate the glass into its final shape. This method leaves marks that appear as dips, black stripes and lines in the inner surfaces of the windscreens. “Sticking” method enables production of more complex shapes with simple mould tooling and furnace technology and amazingly is in common use by leading European manufacturers. A while a go other manufacturers were simply not able to produce large complex shapes, but this is now changing. New companies in the industry are not using such a method, instead they are determined to produce all the glasses with out any external manipulation. This means careful employment of all the up to date furnace systems and superior mould technology. Development Opportunities Future development should advance the state of the art by improving process controls and making the process further automated leaving only the loading, minor process supervision, process fine tuning, and unloading to the operators. Further research should be conducted with the goals of ensuring energy efficiency, increasing output capacity, improving quality, and addressing ergonomics issues. Windscreen manufacturers’ internal research has led to innovations in mold construction and tooling, process controls, and glass shaping, making it possible to develop and produce the windscreen for the vehicles available today. Recently, some interesting trials have been conducted with high frequency microwaves (HFM), which allow both faster and more precise localized heating of glass. It will be interesting to see what the future furnace technology will offer. article source http://www.glassonweb.com