Glass Manufacture – Two Main Methods
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Glass production
Glass production involves two main methods – the float glass process, which produces sheet glass, and glassblowing which produces bottles and other containers.
Contents
1 Glass container production
1.1 Glass container factories
1.2 Hot end
1.2.1 Furnace
1.2.2 Forming process
1.2.3 Forming machines
1.2.4 Internal treatment
1.2.5 Annealing
1.3 Cold end
1.3.1 Inspection equipment
1.3.2 Secondary processing
1.3.3 Packaging
1.3.4 Coatings
1.3.5 Ancillary processes – compressors & cooling
1.4 Marketing
1.5 Lifecycle impact
2 Float glass process
3 Environmental impacts
3.1 Local environmental impacts
3.2 Global environmental impact
4 See also
5 References
6 External links
Glass container production
Glass container factories
Broadly, modern glass container factories are three-part operations: the batch house, the hot end, and the cold end. The batch house handles the raw materials; the hot end handles the manufacture proper — the furnaces, annealing ovens, and forming machines; and the cold end handles the product-inspection and -packaging equipment.
Hot end
The following table lists common viscosity fixpoints, applicable to large-scale glass production and experimental glass melting in the laboratory:[1]
log10(η, Pa*s)
log10(η, P)
Description
Melting Point (glass melt homogenization and fining)
Working Point (pressing, blowing, gob forming)
Flow Point
Littleton Softening Point (Glass deforms visibly under its own weight. Standard procedures ASTM C338, ISO 7884-3)
Dilatometric Softing Point, Td, depending on load[2]
Deformation Point (Glass deforms under its own weight on the μm-scale within a few hours.)
11-12.3
12-13.3
Glass Transition Temperature, Tg
Annealing Point (Stress is relieved within several minutes.)
Strain Point (Stress is relieved within several hours.)
Furnace
Batch feed (doghouse) of a glass furnace
The hot end of a glassworks is where the molten glass is formed into glass products, beginning when the batch is fed into the furnace at a slow, controlled rate. The furnaces are natural gas- or fuel oil-fired, and operate at temperatures up to 1,575oC. [3] The temperature is limited only by the quality of the furnaces superstructure material and by the glass composition.
Forming process
Glass container forming
There are, currently, two primary methods of making a glass container: the blow and blow method used for narrow neck containers only, and the press and blow method used for jars and increasingly narrow neck containers. In both cases a stream of molten glass, at its plastic temperature (1050oC-1200oC), is cut with a shearing blade to form a cylinder of glass, called a gob. Both processes start with the gob falling, by gravity, and guided, through troughs and chutes, into the blank moulds, two halves which are clamped shut and then sealed by the “baffle” from above. In the “blow and blow” process, the glass is first blown through a valve in the baffle, forcing it down into the three piece “ring mould”, which is held in the “neckring arm” below the blanks, to form the “finish”, or top of the parison. The “rings” are sealed from below by a short plunger. After the “settleblow” finishes, the plunger retracts slightly, to allow the skin thats formed to soften, before counterblow” air blows up through the plunger, to create a parison, or pre-container. The baffle raises, the blanks open, and the parison is inverted in an arc to the “mould side” by the “neckring arm”, which holds the “parison” by the “finish”. As the “neckring arm” reaches the end of its arc, two mould halves close around the “parison”, the “neckring arm” opens slightly to release the “finish” then reverts to the blank side. Final blow applied through the “blowhead” blows the glass out, in to the mould, to make the final container shape. In the case of press and blow process, the parison is formed with a long metal plunger, which rises up and presses the glass out, to fill the ring and blank moulds. The process then continues as before, with the parison being transferred to the mould, and the glass being blown out into the mould. The container is then picked up from the mould by the “take-out” mechanism, and held over the “deadplate”, where air cooling helps cool down the still soft glass, until finally, the bottles are swept onto a conveyor, ready for annealing.
Forming machines
IS machine during bottle production
The forming machines hold and move the parts that form the container. Generally powered by compressed air, the mechanisms are timed to coordinate the movement of all these parts so that containers are made.
The most widely used forming machine arrangement is the individual section machine (or IS machine). This machine has a bank of 5-20 identical sections, each of which contains one complete set of mechanisms to make containers. The sections are in a row, and the gobs feed into each section via a moving chute, called the gob distributor. Sections make either