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