Hollow glass
As hollow glass refers to glass containers that can be filled by their shape. This sets them apart from all other types of glass. Hollow glass products are ubiquitous in everyday life. In the broadest sense, they are consumer goods (such as beverage bottles or canning jars ) or objects of daily use (such as drinking glasses or glass lamps).
The majority of hollow glass is made from soda lime glass. Exceptions are crystal glass and lead crystal and a number of different glasses for special purposes.
history
The first known hollow glass bodies were made in Egyptian times by overlaying a mold core made of sand with viscous glass melt. However, the actual beginning of the manufacture of hollow glass did not begin until the invention of the glassmaker's pipe around 200 BC. To assume. The technique of shaping glass with a pipe has been preserved to this day in a further developed form. Even the functionality of modern automatic blow molding machines is derived from the manual technology of the glassmaker, albeit hardly recognizable.
See also: Chapter hollow glass in the main article glass
Manufacturing
Hollow glass is created using different manufacturing processes. The three most important are: mouth blow molding, machine blowing or pressing.
Mouth blow molding
The glassmaker's pipe is a 1.5 m long steel pipe with a wooden handle and a mouthpiece at one end. The other end forms the widening called the “navel”, which absorbs a gob of glass when it is immersed in the viscous glass melt. By turning and swiveling the pipe, the adhering glass is prevented from dripping while it is cooling. Depending on the amount of glass required, the glass gob can be dipped into the melt again and more glass can be picked up. Briefly blowing it into the pipe creates a first hollow body, the parison . Its outer shape can be influenced by rolling (rolling) in a hollowed out beech wood soaked with water or on an iron plate, whereby the surface of the glass gob becomes increasingly tough as it cools.
During the subsequent reheating in the oven while turning and swiveling the pipe, the temperature differences that have arisen in the tub are compensated for before the article takes on its final shape. The final blow-molding is completely free for very individual hollow body shapes, only with the use of certain aids such as fulling wood, pliers, etc. More often, however, is blown into a mold, which enables the production of a large number of identical hollow bodies. In the molds soaked with water, in contact with the turned glass, a separating vapor cushion forms, which allows the hollow body to be blown out evenly and thinly through slowed cooling. The result is a brilliant surface, similar to that with a free blow-out, which no other shaping process can achieve. Attaching and shaping another gob of glass to a handle or stem or foot, knocking it off the pipe, putting it in the cooling furnace and separating the blown cap are further steps before a usable hollow glass is created. The process is used in the production of sophisticated glass for everyday use (e.g. goblet glasses) and technical items with small numbers or difficult shapes that are made by specialized workers ( glassmakers ).
Machine blow molding process
The development of mechanical manufacturing processes led in 1903 by Michael Owens to the first blow molding machine. The invention of the drop feeder by Karl E. Pfeiffer (1911) formed the basis for the development of improved carousel machines such. B. the Roirant machine and the IS machine in the 1920s. Characteristic of the IS machine - now the most widely used machine for producing hollow glass articles - the series arrangement of 4 up to today maximum of 20 stations is similar ( English individual sections ) in a machine. The production speed per finished form rose from 17.5 to 90 articles / h and is 900 and more with modern machines. Machine blowing allows the production of a large number of glasses such as beverage bottles and canning jars in large numbers at low costs.
Press
In addition to the blow molding process, the pressing process is of considerable importance for shaping. In contrast to blowing, the glass gob is in contact on all sides with the metallic mold material during pressing. The mold usually consists of three parts, namely the (hollow) mold, the punch that fits into the mold with a gap corresponding to the desired glass thickness, and finally the cover ring that seals the exit between the punch and the mold. For pressing, a drop is fed into the mold and pressed out by the punch pneumatically or hydraulically inserted through the cover ring until the total volume between the mold parts corresponds to the amount of glass fed in. After solidification, the stamp is pulled out again. Usual automatic presses consist of rotary tables with 4 - 20 or more attached molds, which are gradually transported to the removal point via loading, pressing, cooling and other processing stations. Typical press articles are, for example, fireproof household glassware , mugs, lighting fixtures and glass parts of television picture tubes.
Modern IS machines often work according to the combined press-blow process: the parison is formed in the preform using the pressing process, while the final form is formed in a blow molding process.
Usage
The most common and most useful for consumers and industry alike is to differentiate between the intended use of hollow glass: container glass (= glass packaging, i.e. beverage bottles, canning glass, medicine and packaging glass), utility glass (drinking glasses and other glassware for the table, kitchen and home) and hollow glass ( Glass blocks , etc.). Medical-technical hollow glass and lamp glass mainly fall under the group of special glasses and are therefore not listed here.
Container glass (glass packaging)
This term encompasses all hollow glass goods that are used for the packaging, storage, preservation and transport of beverages and other liquids (e.g. perfume), food, chemical, pharmaceutical and cosmetic substances. Container glass is manufactured exclusively in glassworks . This distinguishes it from vials and ampoules, which are assigned to the field of hollow glass processing and require semi-finished products produced in the glassworks, usually glass tubes , as the starting product.
The importance of glass as a packaging material goes back on the one hand to its diverse formability and design. Company- or brand-typical forms can be created, which have become a fixed term for the product they contain. However, the basic properties of glass as a material are even more important for its use in packaging. Glass is transparent, easy to clean and hygienic, above all it is odorless and inert . This means that glass is absolutely tasteless. It does not release any ingredients, nor does it absorb any flavoring or active substances. This is particularly important for sensitive products such as baby food and medicines, but also for carbonated beverages that do not lose carbon dioxide when packaged in glass. Glass can withstand very high temperatures and is dimensionally stable up to approx. 500 ° C. That is why glass is suitable for all common filling processes, such as cold filling, hot filling, pasteurization , sterile filling or aseptic filling. Reusable glass bottles can be perfectly hygienically cleaned due to the possible high washing temperatures. A disadvantage of glass packaging is that it is relatively heavy. The glass industry takes this into account through continuous efforts to reduce weight. In the case of canning jars, weight savings of approx. 20-25% have been achieved, and disposable beer bottles have even become a third lighter since 1955.
Special features in production
Among the colored glass packaging, green and brown tints are the most common. Green glass, which is still permeable to some of the UV radiation , is obtained by adding chromium (III) oxide . Brown glasses are almost impermeable to UV radiation. The reason for this is the so-called "charcoal yellow" color due to an iron-sulfur chromophore. This is generated by adding iron (II) disulfide , which is either introduced directly into the mixture as pyrite or by adding sodium sulfate (Na 2 SO 4 ) and carbon (as a reducing agent) in the presence of iron. The color can be used for identification as well as light protection or just for aesthetic reasons. In addition to the - mostly native - raw materials that occur almost exclusively in nature, broken glass is now an important raw material for new glass packaging in the manufacture of glasses and bottles . With an average cullet content of 60% to a maximum of 90%, this is the most important raw material in terms of quantity. In this way, new glass is repeatedly created from used glass in a closed cycle.
Economic glass
This ambiguous and often misleading term encompasses the group of hollow glass products that play an essential role in daily use and often have to meet high design standards. In recent times the term utility glass seems to have become more and more common. Another phrase that is more popular in advertising is “glass for the table setting”. The economic glass product family primarily includes all kinds of drinking glasses as well as other table accessories made of glass and articles that are used in the kitchen, apartments and offices. Typical commercial glass products, often also referred to as “gift items”, are also ashtrays and smoking sets, table and floor vases, flower bowls, candle holders and large glass plates. Decorative glasses without function, figurative representations, glass animals and room decorations made of glass also belong to this widely ramified product family.
Hollow glass
Glass blocks , concrete glasses and glass roof tiles together form the hollow glass sector. They are manufactured using the pressing process. The hollow cuboid glass blocks are created by fusing the two pressed halves, whereby the enclosed air experiences a strong pressure reduction as it cools. This results in good thermal insulation properties and sound insulation values of 40 decibels and above. The outer and inner visible surfaces can also be provided with ornamental patterns , light-diffusing matt finishes, colored decorations or sun protection layers . There are also plate-shaped glass blocks. Concrete glasses, which also consist of pressed solid or hollow parts, are used to manufacture components made of reinforced glass concrete, with concrete, steel and glass interacting statically. For example, it is used to make covers for light shafts that can be walked on and also driven on with limited loads. Glass roof tiles are produced in the form of the commercially available clay tiles and concrete roof tiles and must be so thick that they can be walked on (for cleaning) and are resistant to hail.
Web links
- Website action forum glass packaging
- IMACS Users Guide - Bottles / Glass (PDF; 45 kB). 1992 (engl.)
Individual evidence
- ^ A b c Heinz G. Pfaender and Hubert Schröder: Schott Glaslexikon . 5th edition. mvg Verlag, Landsberg am Lech 1997, p. 76 f .
- ^ Heinz G. Pfaender and Hubert Schröder: Schott Glaslexikon . 5th edition. mvg Verlag, Landsberg am Lech 1997, p. 77 f .
- ^ Heinz G. Pfaender and Hubert Schröder: Schott Glaslexikon . 5th edition. mvg Verlag, Landsberg am Lech 1997, p. 81 .
- ^ Heinz G. Pfaender and Hubert Schröder: Schott Glaslexikon . 5th edition. mvg Verlag, Landsberg am Lech 1997, p. 86 .
- ↑ Action forum for glass packaging. Properties. (No longer available online.) Archived from the original on November 13, 2010 ; Retrieved March 9, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Action forum for glass packaging. Recycling. (No longer available online.) Archived from the original on November 14, 2010 ; Retrieved March 9, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Heinz G. Pfaender and Hubert Schröder: Schott Glaslexikon . 5th edition. mvg Verlag, Landsberg am Lech 1997, p. 89 f .
- ^ Heinz G. Pfaender and Hubert Schröder: Schott Glaslexikon . 5th edition. mvg Verlag, Landsberg am Lech 1997, p. 94 f .
