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Химия Pressing
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Fusion Draw

Schematic representation of horizontal tempering furnace

The tin side of the glass is in contact with the bath (and enriched with tin) and it is contacted by the rollers. None of this happens to the top side.

Concentration and penetration of tin have been measured extensively on both faces (tin and atmosphere sides.

A major change to the float process was the introduction of on-line coatings. As the glass ribbon moves continuously, high deposition rates are required (60–100nms).

The first manufactured coatings (low-E glazing) were tin oxide (SnO2) which was deposited from an organotin compound and oxygen.

Fusion draw was invented by Corning in the 1960s for automotive applications.

With this process, the glass sheet is formed from a continuous glass flow delivered by a refractory piece called an ‘isopipe’. Glass flows out laterally along the two sides of the pipe. These two flows later join downwards to form the glass sheet. The control of the thickness is carried out with rollers that do not contact the central part of the sheet.

An important characteristic of this process is that the external faces of the sheet are not mechanically damaged since they are not in contact with any tool. In fact, the two glass surfaces that were in contact with the refractory are fused together when they join. This process allows production of sheets of 1m2 with an excellent control of thickness down to 0.5mm.

This is an important point to reduce flat display panel weight. Moreover, no polishing of the glass is necessary since the process delivers excellent glass surface quality.

Pressing is used for widened containers (plates, cups and glasses) and also for producing thicker cross-sections for automotive lenses. The gob of molten glass is loaded in a mould, the plunger is lowered and forces the glass to spread and fill the mould. Pressing can be performed with free sides (without a ring) when dimension tolerance is acceptable. The size of the plate or glass is then determined by the parison temperature and the pressing force. Patterns on the mould surface allow for imprinting the glass object and make it look more attractive and more expensive than it is.

For more dimensional control, the mould is closed by a ring allowing for production of automotive headlight lenses with high-precision shape. An automatic machine comprises 6 to 16 different moulds allowingfor high production yield.

Fibre Process

Glass fibre production tools are very different when considering optical fibres, rovings or glass wool. Processes differ in the way drawing force is applied and three drawing modes are distinguished: tensile drawing, gas friction drawing, and centrifugal drawing.

Nowadays, processes employ either tensile or centrifugal drawing gas friction being combined with centrifugal drawing.

(Fibre drawing process)

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