ODDP Overflow Down Draw Process®
The method pioneered by Libbey Owens Sheet Glass Co. in the 1920ies. The inventor has been Arthur E. Fowle who has filed the patent in 1925.
The use of this method was to produce automobile windshields for the FORD Motor company.
In this first approach, the glass melt is flowing from a molten reservoir above into the ‘directing member or slab’ shaped refractory block and then overflowing both sides. In the area where the glass melt of both sides joins into a single sheet the area was cooled by air and water mixture.
A method re-invented by Corning in 1961 by Dockerty and Shay and was patented in 1964. The first use of this method was to produce sunglass lenses. The fusion or overflow method is a variation of the slot down draw method but overcome the harmful effects of the slot.
In this advanced approach, over-flowing molten glass flows into a trough shaped fusion block. Overflowing from both sides, it joins into a single sheet as the glass is pulled downward. The substrate surface does not come into contact with metal slot or rollers during film formation. As a result, an improved surface is produced.
The ODDP® furnaces do not require as large of an investment as the Mini float tanks resulting in higher utilization and increased flexibility.
In addition to Corning, also Nippon Electric Glass (NEG) and AvanStrate (formerly NH Techno a 50/50 joint venture of Nippon Sheet Glass, NSG & Hoya; now majority controlled by Carlyle) have adopted this approach after they first used Slot Down Draw process for the TFT LCD Motherglass.
About 75% of each, the TFT and cover glass market substrates are produced by Overflow Down Draw or Fusion Process.
TFT - Display
What is TFT LCD?
TFT LCD (Thin Film Transistor Liquid Crystal Display) has a sandwich-like structure with liquid crystal filled between two glass plates.
TFT Glass has as many TFTs as the number of pixels displayed, while a Color Filter Glass has color filter which generates color. Liquid crystals move according to the difference in voltage between the Color Filter Glass and the TFT Glass. The amount of light supplied by Back Light is determined by the amount of movement of the liquid crystals in such a way as to generate color.
Batch house [mixing]
In the batch house the raw materials are been stored, dosed, weighted and mixed in order to receive the batch for feeding the furnace. For TFT LCD glass 13 materials (cover glass need 9 materials) need to be mixed in defined amount.
Furnace [melting area]
The furnace is made from special refractory material and has to withstand upto 1650 °C melting temperatures. The modern furnace compromise oxy fuel firing (mix of oxygen and neutral gas) with additional electic booting by use of platium electrodes.
DHPS® Direct Heated Platinum System [conditioning area]
In the DHPS® the glass will be refined with temperatures depending on the glass quality of the furnace. Some refiners are working with temperatures up to 1650 °C . After the glass is conditioned (refined, stirred and cooled homogenously) it flows into the trough or sword. Depending on the application, the temperature can range between 1000 °C up to 1200 °C .
Muffle, Trough and Annealer [forming area]
In the Muffle and Trough area the molten glass will flow on both sides of the trough into the Annealer where it meets temperatures of about 700 °C . After the annealing of the glass film took place it will leave the area with approx. 200~300 °C in order to be cross cut in the BOD section.
BOD Vertical cutting line [cutting area]
The glass flim will be cross cut and further processed in the BOD. After trimming of the edges of the glass sheet, a protective film will cover the glass sheet and it will be unloaded from the line for further processing in the cold end area.
Processing line [cold end area]
The glass sheet will run through following station:
Finishing /Precise cutting, Edging and Corner cut
Washing w/ Ultrasonic & Inspection (manual / automatic)