Bent glass has been used for building purposes since the early nineteenth century, yet this is still a modern and dynamic product that has far from exhausted its potential. Today the use of bent glass is steadily increasing along with other uses of glass in modern architecture. Safety glass now accounts for a growing proportion of all production. With the continuing advances in glass technology, the improving safety properties and energy economy of glass and the new methods available for producing bent glass, the future market prospects for bent glass are promising indeed. This article looks at some of the new uses and applications that are open to bent glass and explores its development prospects.

Use of glass increasing in building and construction

The use of glass in public buildings and office complexes has steadily increased over the past few decades, and the trend looks set to continue. Glass is an inexpensive material which offers many superior properties in different applications. It is environmentally friendly and fully recyclable, an increasingly important consideration with the growing emphasis on life-span thinking.

There is a strong trend in modern architecture towards transparent structures, which allow natural light to enter buildings and on other hand open up the natural landscape to end-users inside. Glass creates an airiness, provides a sense of space that can only be achieved with larger glass sizes and in lighter support structures.

Modern glass technology has done away with the need for any compromises in terms of energy economy. Different types of coating and insulating glass structures mean that modern glazing applications can be so designed that they meet even the most stringent thermal insulation requirements (which in glass structures are typically expressed in the K-value). Ideally, glass surfaces and glass walls will allow a suitable amount of warmth in, but keep the hottest sunshine out the building.

Bent glass is a powerful tool of aesthetic design. Curved surfaces help effectively to tone down the coldness and hardness that is usually associated with glass. They also bring large glass surfaces alive and help the building stand out of the mass, a value widely acknowledged among architects and end-users. Bent glass can be used as part of the building facade, or to make up the whole facade. In the case of offices and business premises, facades are an integral part of the corporate image.

Tempered bent glass now available

A growing proportion of all bent glass is processed to make safety glass. Bent laminated glass has the same safety features as flat safety glass. Shattered safety glass remains firmly in place: it does not drop out its frame, no sharp pieces are left lying around and there is no gaping hole in the surface. Bent laminated glass has long been available in the marketplace. The basic unit is made by laminating two sheets of glass together with a PVB film. Bent glass can also be laminated to different impact, burglary and bullet resistant categories. Laminated bent glass is ideally suited for different kinds of railing applications in staircases and elevated walkways, skylights, elevator doors, revolving doors and display windows, particularly in cases where both safety and aesthetic considerations matter.

The mechanical and thermal resistance of tempered glass is four to five times greater than that of ordinary glass. Upon breaking it shatters into small pebble-like pieces. Availability of tempered bent glass used to be limited, as was the size in which it could be produced, but modern technology means that it is now possible to bend and temper glass surfaces up to four metres in length. This has increased the use of tempered bent glass in facades and in interior architecture, for instance.

Lamination of bent tempered glass allows us to combine different safety properties. Skylights, for example, are traditionally made by using insulating glass elements, with a load-bearing tempered glass sheet on top and a laminated sheet that does not shatter underneath. In applications where an insulating glass element is not needed or where it is not feasible, this structure has been replaced by laminating two tempered or heat-strengthened glasses together. A typical application might be a glass ceiling or a railing glass.

More and more applications

Bent glass has been used primarily in public buildings, office complexes and in the facades of corporate facilities. Typical building projects where bent glass is used include airports, exhibition areas, museums, concert halls and shopping arcades. There are two main categories of application, i.e. interior and exterior architecture:

The specific type of glass required for different applications is usually determined by building regulations. Work to develop these regulations and safety glass norms is continuing to progress, which will certainly facilitate the task of making the right choice. It is indeed crucial that for each application a type of glass is chosen that best meets the requirements for that particular application. Although the choice of structure is ultimately the responsibility of the authority concerned, the glass professionals may nonetheless suggest a better alternative.

For instance, the norm for staircase applications is usually tempered glass, even though it is known it will drop out of its frame upon breakage and leave a gaping hole in the railing. For such applications laminated glass, or for bolt-secured railings tempered laminated glass, might well be a more sensible choice: this would protect users from falling pieces of glass and keep the railing intact even upon breakage.

Removing the obstacles

Perhaps the main obstacle to the wider use of bent glass is that both architects and building contractors are not well enough informed. The design and manufacture of a bent glass structure requires special expertise, which remains quite rare in these professions. On the other hand a bent glass structure is always an individual, unique product. Standardised solutions are mainly found in applications that are produced in longer runs, such as revolving doors and elevators. In facades, each structure has to be designed and usually submitted for approval separately, which not only requires special expertise and experience but also raises the cost of building. However it has to be said that most glass benders have done an excellent job in providing architects with the information they need. This is indeed the best address for users who need to know about bent glass and its uses: glass benders can always provide a full and comprehensive information package.

Previously the price of glass structures was also pushed up by the fact that the frames and in many cases the load-bearing structures had to be separately designed for curved glass. For instance, the bending of aluminium profiles is a slow manual process, which obviously adds to the cost of the final product. However new stretch forming methods have very much alleviated this problem. At the same time new bolt-secured glass structures, for instance, have allowed for more flexible adaptation to curved glass.

The image of curved glass has long been tainted by quality problems that have now been largely eliminated with new advanced furnaces and mould technologies; this is true at least of laminated glass. Most glass benders today are capable of producing bent laminated glass with superior optical and design properties. Combined moulds and optimal temperature control in electric furnaces have been among the key factors in this development.

Architects, however, are not always content with the optical properties of tempered curved glass. Curved building glass used to be manufactured with roller hearth furnaces, where the end product tends to suffer from waviness caused by the use of rollers and from the overheating that was necessary to compensate for the cooling required during bending. We are now getting rid of this problem, too, with the introduction of new furnaces in which the bending is done inside the furnace.

In relative terms the production costs of curved tempered glass are lower than those for curved laminated glass. The tempering process requires heating and cooling in any case; the extra costs come mainly from the time required by bending and bender amortisations. For curved laminated glass, the whole bending process is added on top of this and the processing times are considerably longer. In other words the recent technological advances in production methods and the increased production capacity are set to open up whole new prospects for the use of curved glass with cheaper prices, improved technical properties and better availability.

To be continued …