Sealed units everything you need to know about how glass is made, and the different types of glass and glass coatings and how they have changed the industry forever.
Glass, as we know it today, was invented in 1959, and is known as the ‘float glass process’. Before this, glass panes were made using molten glass that was then moulded and polished to remove the imperfections. The move to the float glass process eliminated the step of polishing the glass which reduced the amount of labour needed to make glass, bringing the costs of glass down significantly and making it more affordable for the average consumer.
Sealed units the Modern Glass Manufacturing Process – “Float Glass”
The raw materials that make up modern-day sealed units are quartz (60%), soda and sulphate (20%), and limestone and dolomite (20%). These raw materials are crushed and made into a blend that combines this mixture with recycled scrap glass. The blend is melted in a furnace at a temperature of around 1600°C resulting in a chalk-natron-silicate glass.
The mixture is then refined and cooled to 1200°C in a conditioning basin, after which it is spread evenly over the surface of a liquid tine bath. The molten glass ‘floats’ on top of the liquid tin due to the tin’s inherent surface tension and density. As the molten glass moulds to the surface of the liquid tin, the temperature of the tin bath is reduced from 1000°C to 600°C and the glass forms a solid sheet that can be lifted off the tin. Most of the glass produced around the world is float glass and can range in thickness from 2mm to 25mm with standard dimensions of 3.21m x 6m.
Float glass has a slight green tint which is most noticeable along the edges of the glass. It’s caused by ferric oxide that occurs naturally in the raw materials. To achieve colour-neutral glass, the raw materials need to be low in ferric oxide or, alternatively, the raw materials will need to undergo a chemical bleaching process. If you have a preference for tinted glass, this can be done with chemical additives that can produce green, blue, red, bronze and grey-coloured glass during productions. In general, this is a resource-intensive process, and coloured glass is generally reserved for specialised products.
Advances in Sealed Unit Glass Coatings
When light, energy and heat wavelengths hit the float glass, some will be reflected, some absorbed and others transmitted. Glass coatings are the ideal way to control and manipulate light wavelengths as it is possible, for example, to use a glass coating to reflect infrared wavelengths (heat) while letting through visible light wavelengths (in the form of daylight).
Sealed Unit Production and Application of Glass Coatings
There are two primary techniques for producing float glass coatings:
Hardcoating Sealed Units
Sealed unit hardcoating (chemical pyrolysis) is done during the glass production process where metal oxides are baked into the surface of the glass. They are hard wearing and extremely durable but limited in scope due to their simple structure.
Vacuum deposition (magnetron-sputtering) is the second glass coating process where metal oxides are deposited on the glass in a smooth, controlled sequence. The coating machine has vacuum chambers that are designed to apply a layer of the material onto the surface of the glass using an electrode.
Types of Glass Coatings
Modern-day float glass sealed units come in a range of different types, shapes and sizes, but the most exciting area of innovation is undoubtedly glass coatings. Depending on the application, glass coatings can improve thermal insulation, glass strength, noise reduction and more.
The most important types of glass coatings include:
Thermal insulation (increasing the efficacy of other forms of insulation such as double and triple glazing)
Noise control (along with pane thickness and insulating structure)
Thermally Insulated Sealed Units
As the need for more thermally efficient buildings takes centre stage, glass has an important role to play. Increasingly, consumers are concerned with having a home that is more thermally efficient, without compromising on the ingress of natural light.
There are several reasons that a driving the need for more effective thermal insulation:
Stricter building codes necessitate the incorporation of thermally efficient sealed units, with a prescribed minimum efficiency.
The upfront investment in a solution that will reduce energy costs going forward is appealing for property owners. Advances in the last 30 years have made it more affordable to purchase and install high-tech insulated glass making thermal glass accessible to more people.
With the growing awareness around environmental sustainability in the building industry, owners, architects and builders have begun to seek out solutions that will allow them to construct sustainable, environmentally friendly buildings. Glass is an important part of this as it has the potential to significantly impact heating and cooling costs.
Along with all the other benefits of thermally efficient glass is the simple truth that better thermal insulation increases the comfort of those using the building. Choose the correct sealed unit and temperatures can be kept constant without sacrificing the benefits of natural light.
Insulated Sealed Unit Glass Options
Thermally efficient sealed units are made by combining two (or more) panes of float glass with a spacer to create an insulating glass unit (IGU). This unit effectively reduces the loss of conditioned air, meaning that heading expenses are reduced in colder months, and cooling expenses during the hotter months.
Increasing regulatory requirements and consumer demand mean that there are new, better alternatives to the traditional aluminium spacers entering the market. The most promising and popular of these are slimline stainless-steel profiles. They offer similar diffusion capabilities and mechanical stability compared to the aluminium spacers but offer significantly reduced heat conductivity.
There are also a number of additional techniques that can improve the thermal insulation performance of the glass, including:
Triple Glazed Sealed Units
Triple glazing uses an additional glass pane and spacer in the creation of the insulating glass unit. It’s typically used in projects that require high levels of insulation for sustainability certification.
Gas in the Interspace
The interspace (the space between the panes of glass in an IGU) is hermetically sealed and can be filled to 90% of capacity with an inert gas that offers additional thermal insulating properties. The most popular is argon with krypton being used less frequently due to its scarcity and the associated cost. If argon is used, the interspace needs to be between 15 and 18mm for optimum thermal insulation efficiency, whereas krypton only needs 10 to 12mm and offers better insulating results.
A low-emissivity coating is an energy-efficient sputter coating that can be applied to the panes of glass to increase the level of thermal insulation by preventing heat from escaping through the window to the cold outdoors. It improves the energy efficiency of your home, reduces the amount of energy used, and saves on heating bills.
Warm Edge Spacer Bars
Made with stainless steel and polypropylene, warm edge spacer bars can improve the thermal performance of an IGU. The polypropylene has a low thermal conductivity coefficient, reducing heat loss at the edges of the unit, with steel used to strengthen the spacer and the tight fit of the unit. Warm edge spacers are a significantly superior option than aluminium which is highly conducive to heat.
Solar Protection Glass
Modern buildings continue to make use of more and more glass, and this is largely due to the advent of solar protection glass which mitigates the greenhouse effect. This means that during hot periods, such as summer, rooms can heat up to the point where they become uncomfortable to be in as uncoated glass transmits the solar heat wavelengths. Solar protection glass prevents this as well as reducing cooling costs throughout the year by reflecting and filtering the sun’s rays by allowing light into the room without the accompanying visual glare.
Solar control glass is essentially glass with a special coating that both absorbs and reflects heat and filters light for reduced glare. There are many different types, including tinted, reflective and neutral.
The primary benefits of solar protection glass are:
Cooling a building is significantly more expensive than heating and, with solar glass, the costs of air conditioning are limited. This is done without compromising on natural light as large windows can still be incorporated into the design of the building, which also negates the need for high levels of artificial lighting.
Reducing the amount of cooling power and lighting helps to reduce the ecological footprint of the building.
Solar (heat) energy is usually the cause of an overheated room, particularly in summer. Sun protection glass allows for the maximum ingress of light, where living and working areas are open and spacious, without the often-associated negative heat. This means that it is possible to have a function, comfortable interior, that is the right temperature and brightly lit with natural light.
Solar Protection Glass Options
There are a variety of solar glass control solutions depending on the level of solar control you need which are manufactured by tinting and/or applying a metallic coating. While there are both online and offline coating options, online coating is considered to be the best option as it allows for a greater range of performance without impacting the appearance of the glass.
The SHGC (Solar Heat Gain Coefficient) is a number between 0 and 1 that measures a window’s ability to transmit solar energy. The lower the number, the greater the window’s ability to insulate against solar heat. Solar control glass is not only a stand-alone solution, and can be incorporated into a double glazing window that has self-cleaning, Low E and decorative solutions as well. In particular, the combination of solar control glass with Low E thermal insulation in a single, double glazing unit offers the ideal solution for year-round temperature comfort and control.
Noise Control Glass
Noise pollution across the UK continues to rise, particularly in high traffic areas, along transportation routes and around airports. Heathrow, for example, could soon be hosting an additional 300 flights every day that exceed the maximum noise pollution limits with the development of new supersonic planes.
It’s an issue that can, in part, be addressed by glass and glazing innovations as there is a growing awareness of the impact that noise can have on our health. The WHO has stated that frequent noise exposure impacts work performance causes hearing damage and can have cardiovascular effects. Worryingly, the report found that 30% of people living in the EU are routinely exposed to noise levels that have adverse health effects.
Noise control glass offers a solution that makes it possible to control a wide variety of sounds that would normally be transported through the air and solid objects from outside into our homes.
Introducing glazing Noise Control Glass Options
The three different methods for reducing the way that noise travels through glass include:
If traffic noise or a busy pedestrian road is a concern, it may be preferable to choose thicker panes of glass. In general, the thicker the pane of glass, the greater the noise reduction benefits.
With double or triple glazing, the interspace between the glass panes (filled with air or gas) serves to muffle the vibrations ensuring that the noise that enters the outer pane is reduced before it reaches the inner (or second) pane. The bigger the interspace, the more effective the noise reduction will be. There is only a small margin for adjustment here as the spacing has an impact on the thermal efficiency of the IGUs.
Acoustic Laminated Glass
Lamination uses a flexible interlayer (called a PVB) to connect two panes of glass. This has a noise-reducing effect as the panes are insulated against sound waves while the thickness and space weight remain the same. The thickness of the glass within the laminated glass also has a significant impact on transfer of sound through the pane. The inner layer of acoustic laminated glass is a sound reduction acoustic PVB layer. Simply changing a single glass thickness or changing from double-glazing to triple-glazing will only have a small effect on the transmission of noise, while the real benefits come with acoustic lamination. In airports, for example, glass panes will have acoustic laminated glass that is 25mm and more in thickness.
For homes and commercial buildings that need complete safety and security, safety glass can be used to protect against accidental and deliberate damage without compromising on the levels of light that are let in through the glass. Modern safety glazing legislation means that innovations in safety glass can be trusted to withstand extremely high levels of force and protect against personal injury.
Safety Glass Options
In order to rely on glass as an important part of a structural project, it needs to be safe to use. There are three methods for improving the safety of glass that can either be used individually or in combination with other glass types:
Fully Tempered Glass
Fully tempered glass offers four to five times the tensile strength of annealed glass and is, therefore, more able to handle suction or blunt impact forces. Additionally, if the glass fails, it does so into a mass of connected pieces which have a far lower risk of causing injury compared to the jagged shards produced by conventional glass when shattered. It is ideal for large-surface applications such as gyms and sports halls.
Heat-Soaked Tempered Glass
Heat soaking is a method that reduces the chance of spontaneous breakage caused by nickel sulphide in tempered glass. During the heat soaking process, tempered glass is placed in a heat-soaking oven and subjected to a temperature of 290°C for a period of several hours. This causes the nickel sulphide inclusions in the glass to change phase reverting back to the original low-temperature state, which causes the inclusions to expand in volume. If the inclusions are close to the centre of the pane of glass, the volume change will stress the glass to the extent that it breaks. This method is estimated to destroy 95% of glass panes that are contaminated with nickel sulphide, thus significantly reducing the chance of the glass breaking spontaneously on-site.
Laminated Safety Glass
With laminated safety glass, two (sometimes more) panes of glass are permanently connected with PVBs (polyvinyl-butyralfoils). These foils are sticky, elastic and extremely tear-resistant, making them able to withstand high static forces and challenging constructive requirements while remaining completely clear and transparent.
The safety element of laminated safety glass is due to the high tensile strength and excellent adhesion qualities of the connecting layer. And, in the rare cases where extreme shock or impacting forces break the glass, the glass fragments adhere to the PVB layer reducing the chance of injury. In some cases, depending on the use of the laminated safety glass, multiple PVB interlayers can be placed between the glass sheets to meet tougher requirements.
The role of glass has shifted from simply filling light holes to fulfilling the most important roles of forming and shaping the design of a space. And, as building design continues to shift to bring people closer to nature, transparent architecture will continue to play an important role. One aspect of this is the ability to influence the reflective properties of the glass as well as its colour, design and form. With the use of various technologies, it is possible to influence not only the pattern and colour of the glass but also the transparency of the surface as well as the amount of light that is transmitted.
Designer Sealed Unit Glass Options
With a wide variety of designer glass options, the sky is the limit for incorporating creative glass into modern architectural designs. To this end, there are several techniques that add flexible design options:
This is commonly used for partitions, roof glazing and external walls offering a full customisable decorative effect from the dramatic to a simpler design and is commonly used for privacy, light transmission and solar control.
Mirror glass incorporates a reflective silver layer that can be used for applications including walls, doors, and partitions.
Usually, for indoor applications, painted glass coatings offer a highly durable, multi-purpose solution that can be customised according to your design needs.
Textured Sealed Units (Obscure Glass)
This glass form is often used for style aesthetics, privacy or to allow more light into internal rooms. With varying levels of privacy and a wide range of modern, contemporary and traditional designs, it can be used for double glazing as well as internal glass panes.
Bent Architectural Glass
To give architects the freedom to bring their creations to life with corners and curves, bent glass provides the ideal solution. The process of bending happens when a glass pane is laid over a bending form then heated in a bending oven to temperatures of between 550 – 620°C. At the softening point, gravity works to slowly shape the glass around the bending mould. As the glass cools, the shape of the glass is defined.