Welcome to the technical information page. This page aims to provide you with an in depth knowledge of the glass and glazing industry. Learn all about float glass, toughened glass, mirrors, sand blasted glass, energy glass and much more. Enjoy. Double Glazed Sealed Units.  In single glazing as an example, because glass is a good conductor of heat, the single pane does not insulate well, and if it is warm as toast indoors and freezing cold outdoors, the glass temperature in single glazing will be somewhere between the two, i.e. still very cold.
Enter ’double glazing’.
Unlike glass, air is a poor conductor of heat, and so double glazing works by having two panes of glass held apart by a ’spacer bar’ with an ’air gap’ between, and then sealed up around the perimeter, hence the name ’sealed unit’.
The purpose is to join two panes of Glass with an aluminium spacer in between. The spacer contains a Hygroscopic material which absorbs water vapour in the air, thus creating dry air in between. The Glass can either be Laminated, Toughened or ordinary, depending on the application.
What you can do about misted up double glazed sealed units:
In the trade we say that the double glazed sealed unit has ’broken down’. This means that the perimeter edge seal has lost it’s integrity and that it is letting in moisture somewhere. The moisture itself is hard to spot at first, sometimes becoming only visible as the Sun or another heat source ’draws’ the moisture up. Typically the moisture will be drawn in as the atmospheric pressure changes, and it will build up eventually condensing into water inside the sealed unit. This can sometimes look like a fish tank with several inches of water inside that cannot escape, and quite funny when it is in a door and the water sloshes about!
The only answer is to replace the double glazed sealed units with new ones. That almost always means little or no alteration or disruption to the framework as the glass sealed unit is designed to be removable and replaceable.
How are the two panes of glass ’stuck’ together - and does it matter:
The life of a double glazed sealed unit is primarily dependant on the method and materials used to bond the two panes of glass together, followed a close second by the design of the framework it is fitted into, and it is also dependant on the way it is fitted into its framework. With the best will in the world, manufacturers of double glazed sealed units may endeavor to make their units last a lifetime, but in the real world premature failure is all too common.
The picture shows a sealed unit being ’gunned up’. The circular table can be rotated by the operator by a foot pedal.
Very large sealed units are best gunned up on a table that supports the glass over a much wider area to ensure that the bottom pane is not deformed by the weight.
Let’s start with ’Hermetically’ sealed units. Good word isn’t it?, sounds very impressive and a ’must have’, and this description is often used by manufacturers who use the ’hot - melt’ method because it is efficient to make, and when made it can be handled and used almost straight away.
Glass bonded together using either ’two part polysulphide’ or 2-part polyurethane, although technically still ’hermetically sealed’, is the product of a more laboured manufacturing process, and may need to be laid flat to cure overnight. We feel the 2-part mix is the better seal but the price of them reflects this.
How Long Should Sealed Units Last?:
All sealed units installed by Impact Glazing are guaranteed from breaking down (misting up) for five years from date of installation. As stated above, how long a sealed unit lasts depends on the quality of the manufacturer and the quality of installation, making sure all sealed units are blocked correctly (toe + heel where appropriate) and the right glazing compound is used (in wooden windows).
From the early days of Kettering and corby glass that we started in 1979, we have customers to this day that had sealed units made and installed by us and have still not misted up 18 years on. Sealed units should last at least 5 years, any less is very poor.
We would highly recommend not using silicone in any way to glaze sealed units in wooden windows! We have seen this many times before and as silicone is a very strong substance it can eat away at the seal of the unit and cause premature failure within a short space of time. Back to top Toughened Glass Achieved by heating annealed glass to approx 620°C within a furnace at which point it begins to soften, this is then cooled rapidly. When broken, Toughened Glass fractures into small pieces (called dice). As these particles do not have sharp edges and dagger points of normal broken glass it is generally regarded as Safety Glass.
Toughened Glass must be cut to a size and have any other processes (drilling, polishing etc.) completed before toughening because attempts to ’work’ the glass after will cause it to shatter.
PLEASE NOTE
Glass that has been toughened cannot be cut or drilled. Care must be taken with edges and especially corners on toughened glass as these are the most vunerable parts. Toughened glass is up to five times stronger than normal glass.
SAFETY GLAZING MATERIAL
Doors and side panels over 900 mm wide, not less than B2 6206 Class B. Doors and side panels up to 900 mm wide, not less than B2 6206 Class C. Low level glazing mostly B2 6206 Class C.
NOT LESS THAN 6mm ANNEALED GLASS
Note: Areas of annealed glass less than 0.5m2 and not greater than 250mm in width must not be less than 6mm in thickness, except in the case of traditional leaded lights and copper lights. 
 Back to top Laminated Glass Manufactured by assembling two panels of glass which are sandwiched together with PVB. This is, therefore, a composite high performance product which combines the material properties of the glass with the unique properties of PVB such as adhesion to glass, elasticity and impact resistance.
There are two types of laminated glass: PVB and resin laminated glass:
- PVB laminated glass is two or more sheets of glass which are bonded together with one or more layers (PVB) under heat and pressure to form a single piece.
- Resins laminated glass is manufactured by pouring liquid resin into the cavity between two sheets of glass which are held together until the resin cures.
When broken it will still remain integral due to the plastic between the glass, remaining safe even when broken. Although it will break or crack easier than toughened glass, it has a better security aspect as a much greater force is needed to break the plastic.
- The glass may break, but the plastic innerlayer will remain overall integrity and continue to act as a barrier, withstanding blows from heavy objects such as bricks, hammers, crowbars etc.
- 6.4mm thickness is the most widely used giving a Class B performance to BS 6206: 1981.
- Resists manual penetration and provides some security protection in addition to safety.
- Protects against break-ins by preventing or slowing down burglary attempts.
* Please note laminated glass is also available in the thickness of 4.4mm*
Back to top Low E Energy Glass  This glass has a microscopic metal coating which reflects heat back into the room. Double Glazed Units which incorporate this glass offer up to 33% better insulation than conventional insulating glass units, therefore reducing heating bills.
What is Document L?
Document L came into force in April 2002. Under Document L, all replacement windows have to be double glazed with a Low-E glass, and meet a certain U-value. The term 'windows' applies to the frame and double glazed unit combined. If only the double glazed unit is changed in existing windows, this can be done on a like for like basis.
For more information on Document L Contact Us
K Glass Brochure click here Back to top Mirrors Mirrors are commonly made of glass with a smooth, polished surface that forms images by the reflection of rays and light. Mirrors are exceptionally useful and practical devices and are commonly used in every area of daily life.
The original method of making glass mirrors consists of depositing a coating of metal, mostly silver, on the surface of clear or body-tinted glass. A layer of copper, which is in turn protected by a painted backing, usually protects this deposit. The silver gives the mirror its reflective properties.
Back to top Anti - Reflective Glass Anti-reflective glass is float glass with a specially-designed coating which reflects a very low % of light. It offers maximum transparency and optical clarity, allowing optimum viewing through the glass at all times. The clarity of vision makes anti-reflective glass suitable for all applications where glass should be transparent.
Exteriors: shop fronts and commercial frontages, glazing where vision is important, particularly at night time(panoramic restaurants, air traffic control towers, petrol station windows) etc.
Interiors: high quality picture framing, display cabinets and interior display windows, dividing screens in cinema projection rooms, television studios, machine control rooms etc.
Back to top Wired Glass Wired glass is a product in which a wire mesh has been inserted during production. It has an impact resistance similar to that of normal glass, but in case of breakage, the mesh retains the pieces of glass. This product is traditionally accepted as low-cost fire glass.
A steel wire mesh is sandwiched between two separate ribbons of semi-molten glass, and then passed through a pair of metal rollers which squeeze the "sandwich of glass and wire" together.
Georgian Wired Polished Plate (G.W.P.P. - clear), and Georgian Wired Cast (G.W.C. - obscure) provide an added safety and security to your glazing when you need it.
This glass will hold back smoke and flames for a minimum of 30 minutes, and up to 2 hours in the higher specified types.
A visible wire mesh is inside the 6mm or 7mm glass providing safety and security.
- If hit with sufficient force the glass will break, but remains held in place by the wire, reducing risk of injury.
- Conforms to BS 6206: Class C.
- Available in clear for observation, or obscure for privacy.
- A visible deterrant to thieves and vandals.
- Capable of holding back flames and smoke for up to 2 hours.
Pyroshield is a registered name of Pilkington glass.
Back to top Sand Blasted Glass  This is produced by spraying sand at high velocities over the surface of the glass. This gives the glass a translucent surface, which is usually rougher than that obtained by etching. During sandblasting, only the areas that are to remain transparent are masked for protection. The depth and degree of the translucency of the sand-blasted finishing vary with the force and type of sand used. Sand-blasted glass can be used in numerous interior design applications in both residential and commercial settings: doors, shower screens, partitions and interior screens, furniture, etc.
Back to top Self - Cleaning Glass  Self-cleaning glass is an ordinary float glass with a special photocatalytic coating. It is made by chemically bonding and integrating a microscopically-thin surface layer to the exterior surface of clear glass. The integrated coating reacts to the sun’s ultraviolet rays to gradually and continuously break down organic dirt through what is called a photocatalytic effect. In other words photocatalytic means that the active integrated coating on the outside of the glass absorbs the sun’s ultraviolet rays. This causes a reaction on the surface which breaks down dirt and loosens it from the glass.
This type of glass also has hydrophilic properties, meaning that rain flows down the pane as a sheet, washing away the dirt instead of, as with normal glasses, leaving the dirt behind. As a result of these two effects, the special self-cleaning coating keeps the glass cleaner for a longer period than with normal glass in applications where it is exposed to the rain. Back to top Float / Annealed Glass Process Stage 1: Melting and refining
Fine-grained ingredients, closely controlled for quality, are mixed to make batch, which flows as a blanket on to molten glass at 1,500oC in the melter.
Float today makes glass of near optical quality. Several processes - melting, refining, homogenising - take place simultaneously in the 2,000 tonnes of molten glass in the furnace. They occur in separate zones in a complex glass flow driven by high temperatures. It adds up to a continuous melting process, lasting as long as 50 hours, that delivers glass at 1,100oC, free from inclusions and bubbles, smoothly and continuously to the float bath. The melting process is key to glass quality; and compositions can be modified to change the properties of the finished product.
Stage 2: Float bath
Glass from the melter flows gently over a refractory spout on to the mirror-like surface of molten tin, starting at 1,100oC and leaving the float bath as a solid ribbon at 600oC.
The principle of float glass is unchanged from the 1950s. But the product has changed dramatically: from a single equilibrium thickness of 6.8mm to a range from sub-millimetre to 25mm; from a ribbon frequently marred by inclusions, bubbles and striations to almost optical perfection. Float delivers what is known as fire finish, the lustre of new chinaware.
Stage 3: Coating
Coatings that make profound changes in optical properties can be applied by advanced high temperature technology to the cooling ribbon of glass.
On-line chemical vapour deposition (CVD) of coatings is the most significant advance in the float process since it was invented. CVD can be used to lay down a variety of coatings, less than a micron thick, to reflect visible and infrared wavelengths, for instance. Multiple coatings can be deposited in the few seconds available as the glass ribbon flows beneath the coaters. Further development of the CVD process may well replace changes in composition as the principal way of varying the optical properties of float glass.
Stage 4: Annealing
Despite the tranquillity with which float glass is formed, considerable stresses are developed in the ribbon as it cools.
Too much stress and the glass will break beneath the cutter. To relieve these stresses the ribbon undergoes heat-treatment in a long furnace known as a lehr. Temperatures are closely controlled both along and across the ribbon. Pilkington has developed technology which automatically feeds back stress levels in the glass to control the temperatures in the lehr.
Stage 5: Inspection
The float process is renowned for making perfectly flat, flaw-free glass. But to ensure the highest quality, inspection takes place at every stage.
Occasionally a bubble is not removed during refining, a sand grain refuses to melt, a tremor in the tin puts ripples into the glass ribbon. Automated on-line inspection does two things. It reveals process faults upstream that can be corrected. And it enables computers downstream to steer cutters round flaws. Flaws imply wastage; while customers press constantly for greater perfection. Inspection technology now allows more than 100 million measurements a second to be made across the ribbon, locating flaws the unaided eye would be unable to see. The data drives ’intelligent’ cutters, further improving product quality to the customer.
Stage 6: Cutting to order
Diamond wheels trim off selvedge - stressed edges - and cut the ribbon to size dictated by computer.
Float glass is sold by the square metre. Computers translate customers’ requirements into patterns of cuts designed to minimise wastage. Pilkington is developing electronic systems to integrate the operation of manufacturing plants with the order book.
Back to top The information provided in this page is a general guide only and should not be treated as a substitute for detailed technical advice in relation to individual circumstances or particular applications of glass or associated products.
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Glass And Glazing
