Glass Sheets
| Infobox on Glass Sheets | |
|---|---|
| Example of Glass Sheets |  |
| Facts | |
| Origin | - |
| Stowage factor (in m3/t) | 1,42/1,98 m3/t (cases) |
| Humidity / moisture | - |
| Ventilation | - |
| Risk factors | See text |
Glass Sheets
Description
Broad sheet is a type of hand-blown glass. It is made by blowing molten glass into an elongated balloon shape with a blowpipe. Then, while the glass is still hot, the ends are cut off and the resulting cylinder is split with shears and flattened on an iron plate. (This is the forerunner of the cylinder process). The quality of broad sheet glass is not good, with many imperfections. Due to the relatively small sizes blown, broad sheet was typically made into leadlights.
Other methods for making hand-blown glass included blown plate glass, crown glass, polished plate glass and cylinder blown sheet glass. These methods of manufacture lasted at least until the end of the 19th Century. The early 20th century marks the move away from hand-blown to machine manufactured glass such as rolled plate glass, machine drawn cylinder sheet glass, flat drawn sheet glass, single and twin ground polished plate glass and float glass.
Flat glass, sheet glass, or plate glass is a type of glass, initially produced in plane form, commonly used for windows, glass doors, transparent walls, and windshields. For modern architectural and automotive applications, the flat glass is sometimes bent after production of the plane sheet. Flat glass stands in contrast to container glass (used for bottles, jars, cups) and fiberglass (used for thermal insulation and optical communication). Most flat glass is soda-lime glass, produced by the float glass process.
Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Modern windows are made from float glass. Most float glass is soda-lime glass, but relatively minor quantities of specialty borosilicate and flat panel display glass are also produced using the float glass process.
Fiberglass (also called glass-reinforced plastic, GRP, is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass.
Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favourable when compared to metals, and it can be easily formed using moulding processes. The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinylester) or thermoplastic. Common uses of fiberglass include high performance aircrafts (gliders), boats, automobiles, baths, hot tubs, water tanks, roofing, pipes, cladding, casts, Surfboards, and external door skins.
Shipment / Storage
Glass sheets are usually shipped in crates or cases.
Much breakage can be avoided by ensuring that, where the sizes of the glass sheets are large, the crates or cases are stiffened sufficiently so as not to bend when being handled or slung. If the case is not fitted with skids/cleats but is still to be pushed about by fork-lift trucks in ship’s hold during loading and stow-tightening operations, the lower part of the cases should be faced with a hardwood batten to reduce the risk of fork prongs penetrating the case and contents.
Glass must be packed securely within the case to prevent movement, this chocking can be achieved by generous use of wood wool, polystyrene, etc., packing materials. Usually the glass stands on strips of material proud of the base of the case. The support material must not compress unduly when the case is mishandled, for example snatch lifted/dropped, otherwise scratching or breakage may result. Where large sheets are concerned, they should be slung and handled on their edges. In all circumstances, to avoid breakage, packages of glass should be kept in an upright position and never allowed to lie on the flat.
A common form of damage to glass is staining, and a frequent cause is either dampness in the packing when shipped or dampness which has been absorbed by the packing during transit. When glass is shipped overseas in cases, however, it will normally be interleaved with paper or other interleavants and either the glass block will be wrapped in paper/polythene or the case will be so lined to prevent moisture ingress.
There are various methods by which stains may be removed but they all require long and laborious treatment by at least semi-skilled labour and so are seldom economically justifiable for ordinary glass products. No treatment can remove severe stain, and even light stain cannot be removed so successfully that the glass could be subsequently silvered.
One suggestion is that the glass be polished with red Iron Oxide another that a suspension of precipitated chalk in 2% solution of ammonia be rubbed on the glass, the glass finally being cleared by rubbing with a 5% solution of chromic acid. It is suggested that this latter treatment be confined to figured glass. It is also suggested that buffing might offer some improvement if used for figured glass, provided that a very soft cloth buff is used which will penetrate the grooves in the pattern. Some improvement could, however, be obtained as a general rule by scrubbing the surface with a fairly hard brush, the brush being dipped in a solution of Acetic Acid.
For commercial purposes a good vinegar would be quite satisfactory. The acetic acid or vinegar will dissolve the small amounts of lime and soda which hold the silica fairly firmly on the surface of the glass and, providing that the staining has not gone too far, will effect a considerable improvement in the appearance.
The treatment of rolled figured glass or window glass with hydrofluoric acid, as a means of removing stain, is not recommended. The hydrofluoric acid will dissolve the stain material, which is mainly silica, but it will tend to produce a light grey etching over the whole surface. The greyness will depend on the exact composition of the glass, on the strength of the hydrofluoric acid and the length of time which it is in contact with the glass surface. The process is dangerous, because even very dilute hydrofluoric acid can cause severe injury to the skin; also, unless the process is very carefully controlled, the etching can produce a sufficiently noticeable grey for the condition of the glass to be worse than at first, except that the grey might be more uniform over the whole surface.
Float glass is used extensively in the building industry for windows and building facades. It is shipped in wooden crates with inner packaging of wood wool, polystyrene, straw or other soft packing. The quality of the crates is crucial and they must be of solid stout construction to protect what is a delicate cargo.
Risk factors
- Glass is prone to stain damage resulting from dampness working into the packing. Whilst stains can be removed it can restrict its future use.
- Due to the fragility of the cargo, proper securing is essential to prevent damage.
- Care must be taken to avoid uneven distribution of weight on container floors resulting from point loading of crate pads or skids.
- In the event of cargo being “out of gauge” any rail or road movements should be checked for bridge clearances.
- Float/sheet glass must never be stowed flat and must always be on end.