During construction, contractors tend to leave a part of a wall open, in which a window is inserted later. This becomes even trickier when the windows have to be inserted around the corner. To facilitate this, window manufacturers connect two window panes using a metal rail. Alternately they use glue to fix the two panes together.
Both these methods have some shortcomings and eventually lead to distorted view of surroundings both from inside and outside the building.
Today, there are various kinds of machines available to bend the glass panes. However, it is difficult to achieve that perfect 90 degree angle through such conventional methods. Also the glass often loses optical quality in such bending processes. In order to bend a glass pane, a finished glass pane must be reheated and softened. Since the glass disc is in metal molds in the machine, the glass can deform at the support points. In the cold glass then weak impressions remain visible, which later stand out when you are close to the window. In addition, waves form on the glass surface as a result of the forming process. As a result, the pane later reflects light differently on flat surfaces. The reflections of objects such as signs or trees then appear distorted on the glass facade in the curved areas, just as the view from inside to outside looks disturbingly distorted.
Researchers from the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg have now developed a new method for achieving the required angular glass fronts: they can bend glass panes with almost sharp edges – for example, by 90 degrees. So they put the corner right in the glass. “We have received a lot of positive feedback from architects,” says Tobias Rist, a Fraunhofer IWM glass forming expert and head of the glass forming and processing group.
Since the research team has already generated so much interest in this product from the user community, across industries, they are looking at moving from prototype stage to the mass scale production, by partnering with the right companies.
The IWM team uses a self-developed special oven for this process. During the bending process, not the entire pane is heated so much that it softens, but only the area in which the glass is to be bent. This is done by a laser, whose intense radiation is guided along the bending line on the mirror. The oven is preheated to around 500 degrees and thus stays just below the temperature at which glass softens. “The laser only has to heat the glass at the appropriate point by a few degrees to the glass transition point so that we can bend,” explains Tobias Rist.
To bend the glass correctly, gravity is used by the team. The glass is placed without any support below, such that as the laser heats the glass along the bending line, the glass bends down by itself due to gravity. Since not the entire disc is heated to softening, no pressure points arise at the support points. The glass pane remains perfectly smooth except at the bending point. In addition, it was possible to create several panes of matched bending radii, then turning them into sandwich structures to assemble into composite, safety and insulating glass panes.