SAG is committed to manufacture highest quality float glass products in accordance with ASTM standards. The quality policy covers all process, production technologies and business practices employed to deliver world-class products & services.
All SAG products-Clear Float Glass, Tinted & Online coated Glass range are manufactured under licensed technology from Vitro (formerly PPG USA) and designed to meet the global quality standards form Architectural & Automotive glazing application through all secondary process like mirror coating. Offline sputter Coating, Heat Treatment, Bending & Lamination etc, as recommended / specified for the end application.
SAG products are backed with quality certification for recommend applications and EFG reserves the right to upgrade, Improve, or replace the product range keeping in tune with changing design standards & improving performance requirements.
One of the effects of the fracture characteristics of tempered glass is the occurrence of what are known as ‘spontaneous fractures’. These are fractures of the tempered glass due to no immediately obvious reason.
The causes of fracture of tempered glass, listed in order of likelihood, are as follows:
- Impact damage (deliberate or accidental)
- Damage before installation (during handling)
- Poor installation (tight glazing, missing setting blocks)
- Poor design (insufficient clearances, structural movement)
- Inclusions in the glass (e.g. nickel sulphide)
This is the most common cause of breakage of tempered glass, often from a deliberate impact (e.g. throwing stones). It is; however, difficult to identify, because the ‘star’ pattern seen in fractured annealed glass is overwhelmed by the innate fracture pattern of the tempered glass, which also often falls from the frame. The impacting object may be small (a pebble or air gun pellet) and may not end up in the vicinity of the broken glass fragments.
Edge damage often occurs when the glass is being handled. While the majority of such damage either causes instant failure or is insignificant, some edge damage can lead to delayed fracture.
Tempered glass is manufactured in such a way that the outer surface has a built-in compressive stress while the interior of the glass has a compensating built-in tensile stress. Since glass always breaks from tensile stresses at the surface, tempered glass is stronger because the built-in compressive stress has to be overcome. However, if a crack does occur and penetrates to the inner tensile stress zone, the tempered glass will fracture violently and disintegrate into smaller particles.
It is possible for edge damage, e.g. from impact or edge chips, to penetrate close to the inner tensile zone, but without causing complete fracture. In many cases of such damage the tempered glass will remain in a stable state permanently, but, on occasion the damage is such that it destabilize the built-in stresses around the damaged area to an extent which can allow a static fatigue mechanism to operate and which causes complete fracture to occur at some time after the initial damage was caused. The time of fracture could be from a few seconds up to several months after damage. This type of occurrence is relatively rare; most tempered glass fractures at the time it is damaged or not at all.
Most framing systems are designed so that the glass is adequately supported giving no local high spots or stress concentrations on the glass. However, poor installation, or later attachments to the frame (e.g. blinds), may create local high spots or stress concentrations which may, under repeated wind loads, cause weakness to arise in the tempered glass, eventually leading to fracture.
While poor glazing is the cause of some fractures, bad design may make it impossible to install the glass correctly. Bolted fixings without sufficient tolerance allowance, or holes too small to get bushes in, are prime examples. Some framing systems may have inherent faults, such as protruding screw heads or rivets and even structural movement of lightweight structures like space frames may take up the edge clearance allowed round the glass if not properly assessed and allowed for in the design.
Of the various causes of ‘spontaneous fracture’, only that associated with the presence of foreign particles in the glass is more likely to cause fracture in tempered glass than in other forms of glass, because they can disturb the very high built-in stresses in tempered glass.
While there are several (rare) types of foreign particles which may cause ‘spontaneous fracture’, one type in particular, Nickel Sulphide, is directly associated with the tempering process.
In 1962, Ballantyne of the CSIRO (Building Research, Melbourne) published a report indicating that the cause of many spontaneous breakages was nickel sulphide (NiS). NiS is a complex material, which undergoes a phase change (a change in crystalline structure), at 380oC, which is accompanied by a change in volume. The a-NiS, which is stable above 380oC, has a smaller volume than the b-NiS, which is stable below 380oC.
The tempering process in glass requires the glass to be heated to around 620oC followed by rapid cooling. Any NiS in the glass is converted to the a phase at the higher temperature, but the rapid cooling does not allow time for the conversion back to the b phase. The NiS is thus ‘frozen’ into the tempered glass in an unstable form.
Over a period of time the a phase slowly converts back to the b phase, the conversion being accompanied by an increase in volume of 2%-4%. If a particle (inclusion) of NiS is sufficiently large and is in the central (tensile stress) zone of the tempered glass, then the expansion caused by the conversion can exert sufficient excess stress to cause a crack to propagate, leading to disintegration of the pane.
NiS is a contaminant in the glass. Sulphur compounds are unavoidable, but the nickel can be reduced by careful control. Sources of nickel contamination have been found in the raw materials, the fuels, and the component parts of the melting tank structures and the steel components of equipment in the melting tanks. Reputable glass manufacturers have taken action to reduce nickel contamination over the 30 years since NiS was shown to be a cause of spontaneous fracture. The occurrence of NiS in glass is now considerably lower (by at least an order of magnitude) than it was in the 1960’s
For example, When Pilkington first assessed the occurrence of NiS in their UK manufactured glass, in 1965, the occurrence of critical NiS particles was around 1 in 500kg of glass produced. By 1988, the occurrence of critical NiS particles in their UK manufactured float glass was down to less than 1 in 13000kg.
NiS inclusions are difficult to detect. The size of the inclusions is below the limits for extraneous particles detectable by quality control systems in glass manufacturing plants. They are relatively infrequent and there is no easy method of finding a NiS inclusion other than at the origin of a fracture, which has been caused by one.
Three main factors have a considerable effect on breakage due to NiS inclusions.
- The rate of conversion from the a phase to the b phase is temperature dependent. At higher temperatures the chemical reaction of the conversion will proceed at a faster rate. Thus glass which is subjected to higher service temperatures will show higher initial rates of breakage due to NiS This will affect especially solar control glasses and spandrel panels, which tend to show comparatively higher rates of breakage.
- The volume of the NiS inclusion must be sufficiently large. In practise, NiS inclusions, which have caused breakage, have been measured with sizes between 0.04mm and 0.45mm in diameter. The size of inclusion will also affect the time needed to generate failure stress, since, in a larger inclusion, total conversion is not necessary to develop a critical volume increase.
- The initial central stress in the tempered glass also contributes to the probability of breakage. The higher the built-in stress, the smaller is the size of inclusion required to cause fracture. Theoretical studies indicate that inclusions larger than 0.04mm diameter are required to fracture fully tempered glass.
The effect above can be used to construct a further process, which has been called heat soak testing. This essentially requires the glass to be heated to a high temperature (but less than 380℃) and left for a period of time long enough to fracture a large proportion of the panes which may otherwise fracture in service.
Saudi American Glass strongly recommends that all Tempered Glass is Heat Soak Tested in order to greatly reduce the risk of Spontaneous Breakages resulting from Nickle Sulphide Inclusions ( NiS ).
|4mm thick||1220 x 2440mm **|
|5mm thick||2440 x 3050mm **|
|6mm, 8mm, 10mm, 12mm thick||2440 x 6000mm|
|Minimum||300mm x 300mm|
|4mm thick||1220 x 2440mm **|
|5mm thick||2440 x 3050mm **|
|6mm, 8mm, 10mm thick||2440 x 6000mm|
|≤ 10mm thick||300mm x 300mm|
|Architectural||2400mm x 4300mm|
|Bullet Resistant||3000mm x 2000mm*|
|Bullet Resistant with polycarbonate||2050mm x 3000mm*|
|Minimum (with tempered glass)||500mm x 500mm|
|K-Lite Coatings||3210mm x 6000mm (≤ 12mm thick substrate)|
|Minimum tempered||400mm x 800mm|
|Minimum annealed||100mm x 150mm|
|O/A IGU (width x height)||2500mm x 3700mm*|
|Minimum||300mm x 300mm|
Annealed glass is glass which, immediately after it has solidified into the required form, while still at high temperature, is slowly cooled in a carefully controlled temperature regime in order to reduce to a minimum the internal stresses in the glass. The resulting glass can be worked. It is, in fact, ‘ordinary’ glass as taken from the production line and stored in stock plates.
These plates will be subsequently cut to size, and the cut sizes may be then treated as required, e.g. by tempering.
Saudi American Glass Safe T Lam® laminated glass consists of two or more panes of float glass bonded together by heat and pressure with one or more sheets of a tough flexible pvb (polyvinylbutyral) interlayer, sandwiched permanently between the glass sheets.
When laminated glass is broken the glass fragments remain attached to the pvb interlayer and are thus prevented from causing serious injury that may occur with non laminated annealed glass. Laminated glass is regarded as a safety glass and safety glazing material.
The performance of Safe T Lam® laminated safety glass can be varied by changing the number, thickness and type of each of the glass components and the number and thickness of the pvb interlayers.
Tempered glass is produced by heating annealed glass to approximately 650oC, at which point it begins to soften. The surfaces of this heated glass are then cooled rapidly.
The technique creates a state of high compression in the outer surfaces of the glass and, as a result, although most other characteristics remain unchanged, the bending strength is increased by a factor of four or five times that of annealed glass.
When broken, the tempered glass fractures into small pieces (called dice). As these particles do not have the sharp edges and dagger points of broken annealed glass, it is regarded as a safety glass and safety glazing material.
Tempered glass must be cut to size and have any other processing, such as edge polishing or hole drilling, completed before tempering, because attempts to ‘work’ the glass after tempering will cause it to shatter.
Tempered glass carries a small risk of “spontaneous fracture” which can occur a long time after the glass is produced and has been installed. The heat soak process involves heating up the already tempered glass to a high temperature, typically (280oC +/- 10oC) and keeping it at this temperature for a period of time long enough to fracture a large proportion of the panes which may otherwise have fractured in service.
Heat strengthened glass is produced by a similar process to that used for tempered glass. However, the strength developed is about half that of tempered glass and it is therefore sometimes referred to as “Semi tempered glass”. Heat strengthened glass is not generally considered to be prone to spontaneous fracture and does not therefore require heat soak testing.
The product is ideal for use where thermal over-stressing of annealed glass is predicted and where the safety characteristics of tempered glass are not required. It does not meet the criteria for safety glazing because its breakage pattern resembles that of annealed glass. When broken, correctly heat strengthened glass exhibits fracture patterns running to the edge of the glass pane thus leaving no substantial islands of unsupported glass to fall from the building.
Wired glass is not float glass, but is manufactured by a continuous casting and rolling system which effectively laminates a fully welded steel mesh between two layers of molten glass. Wired glass can be supplied with a rough cast (Nominal 7mm thick) obscuring finish that is achieved during manufacture or it can have both surfaces polished flat and parallel to give a clear (Nominal 6mm thick)glass appearance.
Wired glass is designed for use in fire rated glazing systems where the glass is securely clamped at the edges. In the event of fire the glass may crack and even soften but is retained in the frame by the wire mesh.
Standard wired glass is not a safety glazing product, there are however wired glass products that incorporate a heavier wire mesh that is designed to achieve a safety glass rating in accordance with the requirements of various international safety glazing standards.
Light Transmittance (Tv) is defined as the amount of light transmitted to the indoor environment divided by the intensity of incident daylight radiation.
Visible Light Reflectance (Rv) is the amount of visible light reflected from the glass surfaces the two values of visible light reflectance are determined:
- The visible reflectance as perceived from outside the building, Routv.
- The visible reflectance as perceived from inside the building, Rinv.
Solar Energy Reflectance (Re) is the proportion of solar radiation at near normal incidence that is reflected by the glass back into the atmosphere.
Solar Energy Absorptance (Ae) is the proportion of solar radiation at near normal incidence that is absorbed by the glass.
Direct Solar Energy Transmittance (Te) is the proportion of solar radiation at near normal incidence that is transmitted directly through the glass.
Solar Factor (SF) is the total solar energy transmission also referred to as the g Value in Europe, or as the Solar Heat Gain Coefficient (SHGC) in the USA. The Solar Factor is the proportion of solar radiation at near normal incidence that is transferred through the glazing by all means. It is composed of the direct transmittance, also known as the short wave component and the part of the solar absorptance that is released inwards by long wave radiation and convection, known as the long wave component.
Shading Coefficient (SC) is derived by comparing the total solar energy transmittance of the glazing with a clear float glass having a total solar energy transmittance of 0.87.
This corresponds to float glass of thickness 3-4mm. The shading coefficient may be divided into two components: the short wave shading coefficient which is the solar transmittance divided by 0.87, and the long wave shading coefficient, which is the inward flowing fraction of the absorbed solar energy, (qi) divided by 0.87.
The U value, or thermal transmittance, is defined as the steady state density of heat transfer rate per temperature difference between the environmental temperatures on each side in the absence of solar radiation in W/m2K. The U value is defined for the transparent centre of glass part of the glazing. (To convert W/m2K to Btu/ft2/h/oF ÷ 5.6783)
Relative Heat Gain (RHG) is the amount of heat gained through the glass, taking into consideration the U value and the shading coefficient. Using ASHRAE standard environmental conditions is calculated as follows.
- Metric RHG = (Summer U- value x 7.8oC) + (Shading coefficient x 630 W/m2)
- Imperial RHG = (Summer U- value x 14oF) + (Shading coefficient x 200 Btu/ft2)
Ultra Violet Transmission (Tuv) is the proportion of solar radiation at wavelengths between 300nm and 380nm that is transmitted through the glass.
K-Lite high performance coated glass products are produced to the highest technical standards using state of the art production plant and control systems. Product quality is monitored on a minute by minute basis resulting in quality of product that is second to none in the world.
As with any product, absolute perfection is only something that we can constantly strive to achieve. Minor fault allowances do therefore have to be made and recognized accordingly. The following guidelines set out the criteria that must be observed for the inspection of K-Lite coated glass products as installed.
All K-Lite products should be inspected from a distance of not less than 3 meters from the glass surface in a bright uniform daylight background.
Inspection should involve looking through the glass and not at the glass.
The critical viewing area for inspection is defined as an oval or circle with axes corresponding to the width and height of the glass vision area.
Pinholes of 1.5mm – 2.0mm in diameter on a distribution not exceeding one pinhole per square metre.
- Clusters exceeding 3 pinholes at 1.0mm to 1.5mm within a cluster area of 300mm x 300mm are deemed not acceptable
- Clusters exceeding 5 pinholes at 0.5mm to 1.0mm within a cluster area of 400mm x 400mm are deemed not acceptable.
Minor scratches which are not visually obtrusive when looking through the glass are acceptable.
At a distance of 3 meters from the glass surface at a viewing angle of 45degrees and 90degrees some shading variation and mottling may be noticed. This is deemed normal and acceptable in all coated glass products
K-Lite high performance glass delivered to insulating glass unit manufacturers should be inspected on receipt and any defects reported immediately to Saudi American Glass Factory, for further investigation.
Insulating glass unit manufacturers must handle, process and fabricate K-Lite glass in full accordance with procedures and systems agreed with Saudi American Glass Factory.
Saudi American Glass Technical Services will be happy to recommend the required glass specification for any practical glass floor. Glass dimensions along with uniformly distributed and concentrated design loads for floors and stair treads should be determined from BS 6399: part 1:1996 and forwarded to the Technical Services Department.
Calculations for glass in floors are generally stress limited, but the supporting structure for any glass floor must be limited in its deflection or the stiff glass panes may effectively have their backs broken. Saudi American Glass calculation results therefore detail the deflection limits for glass edges and the required I value for the supporting beams.
illustrates the principles to be adopted when installing four edge supported internal glass floor panels, for pedestrian traffic only. The detail shows that the edges of the glass must be fully supported on 3mm thick shore A 60 hardness (approx) neoprene rubber at least as wide as the glass is thick. The minimum recommended dimension for glass to glass joints is 3mm. Surface jointing sealants should be flexible and durable enough to prevent the ingress of grit or sand toward glass edges.
The preferred general glass specification is SAGF Safe T Lam Glass incorporating thick annealed float suitably supported along all four edges. In certain circumstances annealed glass may not be suitably strong and tempered glass must therefore be used.
Tempered glass is stronger than annealed glass but when broken it instantaneously shatters into many tiny fragments of glass. Such breakage in tempered glass in a floor would therefore result in an instantaneous loss of support to anyone or anything that happened to be stood on the tempered glass floor at the time.
Wherever tempered glass is considered for installation into a floor the load bearing pane of tempered glass must be laminated to an additional and at least equal non load bearing pane to provide continued structural integrity of the floor in the event of glass breakage.
The minimum thickness for tempered glass is 12mm as thinner specifications are not considered to be robust for floors.
Glass floor panels should be checked regularly as damage to glass edges or surfaces will serve to reduce the design strength of the glass.
Glass floor panels should be cleaned regularly with a mild detergent and a soft cloth or mop. Excess water should be removed immediately and the glass surface dried to reduce the risk of slippage. Scraping or cleaning with metal implements is not recommended.
Where laminated glasses comprise different glass thicknesses they should be installed with the thicker glass ply uppermost. It is common practice to laminate a thin tempered wearing pane to walking surfaces, with a suitable anti slip fritted finish. Such wearing panes are not considered in the design strength of the finished glass product.
Approximately 1m2 is usually considered to be a practical maximum area for each pane of glass due to handling considerations
All glasses display two images simultaneously: a transmitted image, and a reflected image. This gives a viewer an effect similar to that of a double exposure in a camera. For a one way vision application it is generally required to have the glass appear fully reflective from one side, and to be a transparent viewing window, with little distraction from reflections, from the other side. This is achieved by balancing the glass properties of Reflection (different from each side for a coated product), Transmission, and relative Light Levels on either side of the glass.
When one of the two simultaneously observed images is at least 50 times brighter than the other one, only the bright image is perceived. This is the required property on the “subject” side of a transparent mirror where a “subject” seeing the reflected image of themselves and the room, should not be aware of the very faint image of an “observer”.
When one of the images is about 5 times brighter than the other, then the bright image is easily observed with little distraction from the fainter image. This is the required property on the “observer” side of a transparent mirror where the presence of a faint ghost image of the observer is not an issue.
Note the following formula s apply to any glass type, in any installation. For example; even a single pane of clear glass can be seen to act as an effective transparent mirror when the room side lighting is 600 times brighter than the exterior light level. This can be sometimes observed on a dark night in a residence with normal interior lighting when there are no exterior lights.
Two ratios are defined to illustrate the effectiveness of one way vision glass in hiding the observer (Masking Ratio), and the ability of the observer to see the subject (Observation Ratio).
Definition of terms used in the diagram:
- Id = Illumination on the dark side (observer side)
- Ib = Illumination on the bright side (subject side)
- T = Light transmittance through the transparent mirror (equal in either direction)
- Rf = Film side reflectance of the transparent mirror
- Rg = Glass side reflectance of the transparent mirror
The one way vision glass must be installed with the dominant reflective surface towards the subject side. Note also that this side must have the higher level of illumination. The optical ratios are defined as follows:
Masking Ratio: The ability of the transparent mirror to mask, or hide, the observer
Masking Ratio = Ib x Rf (reflected image brightness seen by subject) / Id x T (transmitted image brightness seen by subject)
Observation Ratio: The ease with which the subject can be observed or seen
Observation Ratio = Ib x T (transmitted image brightness seen by observer) / Id x Rg (reflected image brightness seen by observer)
Glazing to provide one way vision should be designed with the following characteristics to give optimum performance:
A successful one way observation application involves the careful use of light levels, direct and indirect illumination, and fabric and wall colour choices.
An 8 to 1 light level is recommended and should be adhered to if possible. Less critical applications may allow lower ratios but the masking and observation properties will be diminished.
SAG can supply one way observation products with improved properties which allow a wall to be completely glazed, from floor to ceiling. With no illumination on the dark side, the light coming through the glass from the bright side will automatically create an 8 to 1 light ratio.
Where an 8 to 1 light ratio cannot be achieved, an additional light of grey glass can be added by either multiple glazing or lamination to obtain a satisfactory Masking Ratio. This will however, reduce the brightness of the observer’s image of the subject.
Subject side lighting should be bright and evenly distributed over all walls and furnishings but should not shine directly onto the one way vision glass. Beyond this lighting may be consistent with decor and function of the room. The intent is to brighten the reflected image seen by the subject. Note: do not shine subject side lights directly onto the glass because they will only illuminate the observer and the observation room behind the transparent mirror.
Observer side lighting should be dim with no open light sources (such as un-shaded high intensity desk lamps), or reflections from bright objects such as chrome furniture, visible in a direct line of sight through the transparent mirror. Opaque lamp shades on the observer side are recommended for best results.
Subject side decor should be bright and light in colour and shade to create a bright reflected image.
Observer side decor should be subdued, dark and uniform. Patterns should be minimized in favour of plain materials.
Bright reflecting chrome furnishings should not be used on the observer side.
Note that if the subjects are very close to the one way vision glass less than 600 mm, it may be easier for them to see an observer especially if the observer is also very close to their side of the one way vision glass. On the observer side, it is important to keep people, objects and light sources (such as lamps, flashlights and lit cigarettes) as far back as possible from the one way vision glass surface.
- Airport Security. Baggage Inspection
- Day Care Centre
- Police Identification Line-up
- Retail Store Anti-Theft Monitoring
- Airport Security. Immigration
- Privacy Screening for Ladies
The use of tinted glasses enhance the effectiveness of one way vision glazing for a given lighting condition by increasing the effective lighting ratio (ELR). Wherever a reduction in the apparent lighting level and colour rendition of the subject room is acceptable to the observer tinted glass may prove to be very effective.
Calculate the maximum visible light transmission of a glass that will provide an ELR of 40 when the subject room light level is 120 Ftc and the observation room light level is 15 Ftc.
Wherever subject and/or observer rooms are exposed to differing degrees of natural daylighting which is of course variable, then some means of varying the effective lighting ratios needs to be introduced to maintain the effectiveness of the privacy screening. The control of internal lighting levels to both subject and observer rooms by means of a rheostat (dimmer switch) can be effective.
As with all coated glass products the one way vision glasses should be checked for compatibility with construction and insulating glass sealants.