LandGlass: White haze at the end of glass sheets in glass tempering

Some more advice from LandGlass about the glass tempering process

According to LandGlass, during the glass tempering process, white haze at the front and back ends of the glass sheet can be caused by different reasons:

  • White haze are likely to appear at two ends of a glass sheet larger than 1.5 square metres with a shape close to a square.

  • After the glass sheet enters the glass tempering furnace, the heating temperature of the upper side of the glass tempering furnace is too high, resulting in the upper surface of the glass heating faster than the lower surface. The glass sheet is arched upward in the process of thermal expansion, leaving only the front and back ends of the glass within 100 to 200 millimetres to be in contact with the ceramic rollers while the middle part of the glass is suspended in the air.

  • Thus, during the oscillating movement, the area within 100 to 200 millimetres near the two ends of the glass sheet bears the entire weight of the glass, causing excessive friction between the glass surface and the rollers, resulting in scratches on the glass surface which is usually called white haze.

The solutions can be:

  • Control the temperature difference between the upper and lower temperatures of the glass tempering machine within 10 degrees Celsius.
  • If the glass tempering furnace employs radiation heating, appropriately reduce the air pressure in the heat balance tube and start-up time coefficient of the tempering furnace.
  • For a convection glass tempering furnace, reduce the speed of the upper convection blower as appropriate.
  • In the meantime, increase the heating temperature of the lower section of the tempering furnace appropriately to reduce the temperature difference between the upper and lower parts.