Glass fire department doors can be very large and use more glass than smaller commercial applications. With so much glass in the frame and so many options to choose from, it is important to know and understand some of the qualities different glass options offer. Tempered glass is one of the most commonly used glass types on glass fire department doors since it is considered safety glass. Tempered units are subject to a byproduct of the manufacturing process called Roller Wave Distortion.
What is Distortion?
On flat glass such as non-heat treated float glass a reflected object is seen as normal with light rays reflecting at equal angles. On heat treated tempered units where the glass is curved, light waves bounce off the varying angles and this causes the reflected image to appear different.
Concave surfaces make reflected images look shorter and thinner while convex surfaces cause reflections to appear stretched. These two effects are common in heat treated glass with roll wave distortion.
Tempered glass units are heat-treated in an oven and contain waves created when the glass comes in contact with rollers during the tempering process. This is known in the industry as roller wave distortion and can be view when looking at a reflected object on the glass surface from a distance. It does not noticeably affect the clarity of images when looking through the glass.
The process of heating glass followed by cooling it will always cause distortion to some degree. When heated, glass will sag between the carrier rollers in the furnace. After heating, the unit passes through a rapid cooling process that results in a heat-strengthened or fully tempered glass. This process results in a slight deviation from optically flat glass called roller wave distortion. Although glass thickness and size can affect the amount of distortion, the actual distortion cannot be eliminated.
Roller wave distortion is not considered a defect in the manufacturing process of tempered or heat treated glass units.