Curved Glass

Curved glass and curved elements can be an essential aspect for a design or project, they can provide a feel of openness to a space, providing natural organic shapes to a space or room. Using curved glass is a fantastic way to carry on that design feature in message to all external and internal faces of the design.

All curved glass units are made in kiln baths where the radius of the curve required is cut on water jets into metal templates, forming the shape of the glass curvature. The flat glass is placed over the metal mould and the kiln is heated very quickly, kiln goes from 1-1000 degrees in 7 minutes. Glass then forms to the space of the curve.

Curved glass can be made in one of three distinct ways, creating three main types of curved glass, each suited for different applications:

• Annealed Glass Bends (non-impact resistant)

• Laminated Curved Glass (impact resistant)

• Toughened Curved Glass (impact resistant)

Toughened panes can then be brought together and laminated for a further degree of safety glass used in overhead panels. Toughened curved glass panels can also be heat soaked for a better resistance against Nickel Sulphide Inclusion.

Both toughened and laminated curved glass panels can be brought together to form a double or triple glazed curved glass unit for external uses as well as treating curved units with all manner or performance coatings for a more functional glass piece, such as Low-E coatings, solar control coatings, self-cleaning coatings etc.

The results of glass curving can range from cylindrical single curves, to complex non cylindrical items with tight radius curves and tangents. The maximum glass sizes, angles and radius curves depend on the thickness of glass to be used to allow for tight radius curves and a wide range of applications in architectural, commercial and residential installations.

For glass to be used for most residential or commercial projects it needs to have impact resistance (be a safety glass) and will need to be either toughened, laminated or toughened-laminated curved glass or curved double glazing.

Restrictions on size and shape are applicable, as with most glazed items and panels. The level of these restrictions depend on various factors such as the thickness of glass to be curved, whether it will be toughened or laminated, the radius size, the angle of the curve and whether the curved glass will be cylindrical or non-cylindrical.

The maximum size of glass to be curved is 6m x 3m. It is important to recall a few aspect of circle geometry in measuring the size of a curved glass panel that is wanted.

The distance around the outside of a circle is the circumference. The length of a line drawn completely through a circle is the diameter, while any line extending from the centre of a circle to the circumference is its radius.

The distance around a particular bend is known as its girth or arc. The chord of a bend is the distance from one point of the bend to the other. To measure the depth of the curve, you take half the distance of the chord and measure to the top of the curve.

The maximum angle of curved glass is 90 degrees and with small radius sizes can create very tight curvatures and U-bends for more decorative glass aspects. The same applies for curved double glazing.

How is tempered glass made?

Tempered glass is about four times stronger than "ordinary," or annealed, glass. And unlike annealed glass, which can shatter into jagged shards when broken, tempered glass fractures into small, relatively harmless pieces. As a result, tempered glass is used in those environments where human safety is an issue. Applications include side and rear windows in vehicles, entrance doors, shower and tub enclosures, racquetball courts, patio furniture, microwave ovens and skylights.

To prepare glass for the tempering process, it must first be cut to the desired size. (Strength reductions or product failure can occur if any fabrication operations, such as etching or edging, take place after heat treatment.) The glass is then examined for imperfections that could cause breakage at any step during tempering. An abrasivesuch as sandpapertakes sharp edges off the glass, which is subsequently washed.

Next, the glass begins a heat treatment process in which it travels through a tempering oven, either in a batch or continuous feed. The oven heats the glass to a temperature of more than 600 degrees Celsius. (The industry standard is 620 degrees Celsius.) The glass then undergoes a high-pressure cooling procedure called "quenching." During this process, which lasts just seconds, high-pressure air blasts the surface of the glass from an array of nozzles in varying positions. Quenching cools the outer surfaces of the glass much more quickly than the center. As the center of the glass cools, it tries to pull back from the outer surfaces. As a result, the center remains in tension, and the outer surfaces go into compression, which gives tempered glass its strength.

Glass in tension breaks about five times more easily than it does in compression. Annealed glass will break at 6,000 pounds per square inch (psi). Tempered glass, according to federal specifications, must have a surface compression of 10,000 psi or more; it generally breaks at approximately 24,000 psi.

Another approach to making tempered glass is chemical tempering, in which various chemicals exchange ions on the surface of the glass in order to create compression. But because this method costs far more than using tempering ovens and quenching, it is not widely used.