Glass Basics

How Glass Is Made

Until the middle of the 20th century, glass panes were produced by drawing or moulding molten glass, and then polishing out the imperfections. In 1959, the float glass process was invented, eliminating the need to polish and therefore reducing the labour required. The float glass process is how our plants across various geographies make their glass.

The float glass process begins with a mixture of raw materials, including about 60% quartz, 20% soda and sulphate, and 20% limestone and dolomite. Huge agitators crush and then process these materials into a mixture. A blend comprising of roughly 80% of this mixture and 20% of recycled scrap glass is fed into the furnace and melted at about 1600°C. The result is a chalk-natron-silicate glass. After refining the molten mixture, the molten glass is fed into the conditioning basin and left to cool to approx. 1200°C before flowing over a refractory spout into a liquid tin bath.

Molten glass spreads evenly over the surface of this liquid tin bath, “floating” on top of the liquid tin with its inherent surface tension and density, which is heavier than the density of liquid glass. As a result, the molten glass smoothly and evenly moulds itself to the surface shape of the liquid tin. Reducing the temperature in the tin bath from approx. 1000°C to approx. 600°C turns a viscous mass of molten glass into a solid glass sheet that can be lifted right off the surface of the tin bath at the end of the floating process.

How glass is made

Properties of Glass

Normal float glass has a slightly greenish tint. This colouring can mainly be seen along the edge of the glass and is caused by the naturally existing ferric oxide in the raw materials. By selecting extremely ferric oxide-poor raw materials, or by undergoing a chemical bleaching process, the melt can be turned into an absolutely colour-neutral, extra white glass.

Tinted glass can be produced using coloured mass. Chemical additives in the mixture allow green, grey, blue, reddish and bronze coloured glass to be produced during certain production floating line periods. Changing glass colour in the vat naturally means a considerable amount of work and increased cost due to scrap and loss in productivity. Thus, it is only produced for special campaigns.

Most of today’s glass production is float glass, with thickness usually ranging from 2mm to 12 mm and a standard size of 3660mm x 2440mm that is used for further processing.

The Need for Glass Coatings

The physical definitions of light, energy and heat are described by defined wavelengths of the electromagnetic spectrum. When wavelengths hit an object, certain wavelengths are reflected, absorbed and transmitted through the object. Coatings are applied to float glass in order to manipulate which wavelengths are reflected, absorbed and transmitted to serve functional and aesthetic requirements.

For example, designing glass coatings that reduces solar heat requires controlling the radiation emitted by the sun that strikes the earth. Our glass coatings are designed to reflect the infrared wavelengths (solar heat) while at the same time transmitting the visible light wavelengths (daylight) through the glass.

Applying Coatings to Glass

Float glass coatings are produced in huge quantities, primarily in 2 techniques. One is the chemical pyrolysis process, also called hardcoating, which occurs online during glass production on the float line. Metal oxides are permanently baked onto the surface, and are very hard (hardcoating) and resistant, but their properties are very limited due to their simple structure.

Gujarat Guardian Limited focuses on the second coating process called vacuum deposition process or magnetron-sputtering. Magnetron sputtering deposits metal oxides onto glass perfectly smoothly in a sequence designed to achieve outstanding optical and thermal properties. Glass is sent to into a coater with vacuum chambers each designed to apply a layer that material to the glass.

The material (which is a metal plate) that is going to be deposited on the glass surface is mounted on an electrode that has a high electrical potential. Electrode and material are electrically isolated from the wall of the vacuum chamber. The strong electrical field (fast electrons) ionize the sputter gas argon. The accelerated argon ions are able to break off material from the target by colliding with it, which then comes into contact with the glass, where it is deposited onto the surface evenly.

how glass is coated

Thermal Insulation

Architects and consumers are demanding greater thermal insulation of their building envelopes to satisfy economic, ecological and comfort requirements. Gujarat Guardian Limited is working tirelessly to enhance building performance without sacrificing the natural light people desire. The motivations behind greater thermal insulation are:

Building owners and managers are willing to invest in solutions that will reduce their energy costs. Technological advances of the last three decades have produced systems and equipment that can coat high-tech insulating glass with razor-thin, neutral coatings using low-cost processes. This technology is now applied to millions of square meters of glazed areas of windows and facades.

Consumer and industry awareness for environmental sustainability have grown rapidly within the building industry. Due to its natural ingredients and superior energy-balancing properties, glass is a key element to reduce heating and cooling costs and to achieve the goals of globally recognized certification programs for building sustainable and environmentally friendly buildings.

Better thermal insulation reduces unpleasant drafts from glazing areas, without sacrificing the benefits of daylight that make people feel better and more productive.

Insulating Glass

To achieve thermal insulation properties, two or more float glass panes are combined with a spacer to form an insulating glass unit (IGU). This reduces the loss of conditioned air—reducing heating expenses in colder months and air conditioning costs in warmer ones.

Until very recently, the majority of IGUs has been produced using aluminium spacers. Increased requirements have created thermo-technically improved alternatives that are gaining ground in insulating glass production. Extremely thin stainless steel profiles possessing considerably reduced heat conductivity as compared with aluminium are the most frequent alternative. They are similar to aluminium, however, in terms of their mechanical stability and diffusion capability.

Insulating glass can increase its thermal insulation performance using three additional techniques:

Low-E coatings
Sputter coatings designed to increase thermal insulation, such as many Guardian® SunGuard® coatings, can be applied to surface #2 or #3 (depending on climate).

Gas in the interspace
The resulting hermetically sealed interspace is often filled with especially high thermal insulating inert gas. The width of the pane interspace depends on the inert gas that is used. Argon is used most often, krypton more rarely. To reach its optimum thermal insulation efficiency, argon needs an interspace of 15 - 18 mm; krypton needs only 10 - 12 mm for better insulating results. The interspace is usually filled to 90% capacity. Krypton is many times more expensive than argon since it is more rare.

Especially for projects where sustainability certification is a priority, triple-glazing (using 3 glass lites) enhances thermal insulation performance even further.

Solar Protection Glass

Modern architecture continues to use more and more glass, largely thanks to advances in solar protection glass. Solar protection glass reduces the greenhouse effect that mainly occurs in summer due to that fact that rooms can heat up to the point that they become unpleasant to be in, while dramatically reducing a building’s operating cost throughout the year. Solar protection glass offers:

Financial savings
Solar protection glass minimizes the amount of heat energy that penetrates a building, limiting the extreme costs of air conditioning, since it costs much more to cool the interior of a building than to heat it. Large window and facade surfaces allow a great deal of light deep into a building’s interior, thereby avoiding excessive use of artificial lightning.

Ecological benefits
Energy is saved by reducing the amount of cooling power use or reducing the phases of artificial light – helping to reduce human impact on the environment. ln this context, it is a logical consequence to certify these types of sun protection glass products according to prestigious and approved certification systems for sustainable constructions , such as to LEED and GRIHA.

Solar energy can be leading cause of overheated room, which make occupants uncomfortable. Today’s architecture – which strives to create living and working areas that are close to nature and are open and spacious – has shifted away from this opaque way of construction towards transparency. Therefore it is essential to master the essential parameters of the sun protection using glass to create a functional and comfortable interior.

Noise control glass

Sound is normally transported both through the air and through solid objects. The intensity of the variability in pressure is called sound pressure and can be extremely variable, from the ticking of a clock to the crack of a gunshot. Three methods are used to control a wide variety of sounds:

Pane thickness
The rule of thumb is that the thicker the pane per surface unit is, the greater the noise reduction. Therefore, insulation efficiency increases as glass thickness rises.

Insulating structure
Double- or triple-insulating glass is a mass-spring-mass system: Both outer panes (masses) are separated from each other by the air or gas that fills the interspace. The interspace muffles the vibrations from the outer pane before they reach the inner second pane, with the rule being the bigger the interspace, the more effective the noise reduction. But this is only possible to a limited degree, since this process also reduces thermal insulation.

The noise-reducing effect of thicker, heavier glass may be further optimized by using a flexible interlayer (PVB) to connect two single panes of glass. With this solution, the thickness and space weight remain the same; the pane, however gets “softer” and thus increases its insulating capacity in terms of sound waves.

Safety glass

A component must be reliable if it is going to be safe to use. Glass manufacturers recognized this fact more than 100 years ago, and apply this principle to glass manufacturing today. A wide range of safety glass is available that is used either individually or in combination with other types of glass in building construction. The three main types of glass are tempered safety glass, laminated safety glass and heat-strengthened glass.

Fully tempered glass
Tempered glass offers four to five times greater tensile strength than annealed glass of the same thickness, and can therefore handle much higher suction or blunt impact forces. However, should failure occur due to overloading, the glass will fracture into a mass of loosely connected pieces that pose a lesser risk of injury than the sharp-edged shards produced by shattered conventional glass.

Fully tempered glass is resistant to shocks from soft, deformable objects like the human body. At 6mm thick, fully tempered glass is especially suitable for use in large surface glass applications in gyms and sports halls.

Heat-soaked tempered glass
In float glass there are extremely low quantities of nickel sulfide (NiS) crystals that are inevitably introduced into the glass via the raw materials. The extremely fast cooling off period during the tempering process “freezes” the NiS particles in a high temperature crystal modification. When heat is later applied through solar energy absorption, for example, this crystal structure may change because the volume of the crystals increases. This may cause the glass to suddenly burst apart as soon as the particles exceed a critical size. All safety relevant glazing and panes such as façade glass that are exposed to high temperature alterations must be subjected to the additional heat-soak test.

Laminated safety glass
Laminated safety glass is a key component in modern architecture. The permanent connection of two or more glass panes with sticky, elastic, highly tear-resistant polyvinyl-butyral (PVB) makes a multi-functional element from the glass, which can handle high static forces and constructive tasks in addition to its given transparency.

The safety effect of laminated safety glass is based on the extremely high tensile strength of the PVB interlayer and its excellent adhesion to the adjacent glass surface. In situations of mechanical stress such as shock, impact or influence from other forces breaking the glass, the fragments adhere to the PVB layer, so that the laminated safety glass will usually retain its stability under load. This leaves the glazed opening closed, which sharply reduces the risk of injury due to chips adhering. Depending on the use of laminated safety glass, multiple PVB interlayers can be placed between two glass panes to meet needs that have tougher requirements.

Design Options

For centuries, generations have used glass for filling “light holes” in massive outer walls. This has drastically changed in the last three decades. Today glass itself forms and shapes the space and creates room enclosures, thus creating transparent architecture that allows people to feel close to nature. A glass’s finish on a façade always influences its reflective properties, which can range from being produced so that the glass is very reflective, reflects an overall color, or has a weak reflection.

Screen-Print technique
The screen-print which is mainly dedicated for painting partial areas and used for specific design colour which joins firmly with the glass surface and coating in the following tempering process. This technology is adopted for larger quantities and is ideal for parapet glasses components is less suitable for larger areas and homogeneous painting.

Design glasses
Transparent elements can become more and more visual and functional decoration façets. From etching and shot blasting over the ceramic screenprint up to laminated glass with inside foils, the design can be a decorative ornament or symbol or also an all over illustration or matting.

Screen-print directly onto the glass
The one colour screen-print directly onto the glass has a long tradition. The enamel or ceramic paint which is a mixture of small milled glass and joining colour pigments is pressed with a scraper through the open parts of the sieve onto the glass.

Transfer colour print on glass
The transfer print offers an alternative to achieve a multi colour print instead of the single colour screen-print. Also enamel and ceramic colours can be transferred via digital print on transfer foils and can thus reproduce multi colour motives. These printed foils will then be fixed on glasses that are going to be tempered. During the tempering process these transfer foils will burn residue-free and the painted colours will join as previously described.

Coloured foils in laminated glass
Within the same lamination process exists a large pallet of different colour foils, which can be combined of to achieve each imaginable colour in laminated glass.

Bent architectural glass
Architects and designers love to interrupt straightness, corners and curves with soft curves. In the applications of the building envelope, glass is generally bent through a thermal gravity process. A glass pane is laid over a bending form and in the bending oven heated up to 550 - 620℃. After having reached the softening point the pane descends (through gravity) slowly into the bending mould and adopts its shape. The following cooling down defines the shape of the glass. Slow cooling, free from residual stress, produces a glass which can be further processed, whereas fast cooling creates a partial or fully tempered glass which is not applicable for further processing.