ABC of glass – technology, terminology, know-how
Unlike standard moulds, which can be used by any bottling company, bespoke moulds are developed exclusively for one customer. The shape, design and finish are created as part of a specific marketing concept.
A method of making hollow glass that was invented in 1925 and is still used to this day. In the blow-and-blow process, the feeder machine forms the molten glass into a long gob of glass which is guided along a channel into the parison or "blank" mould. There it is pre-blown using compressed air to form the parison and the neck is formed before the process is completed in the blow mould.
The invention of this device brought about a revolution in the art of glassmaking. It consists of a tube about 1.2 to 1.6 m long, with a mouthpiece at one end. With the other end, the glassblower picks up the gob of molten glass, turns, swirls and rolls the cooling mass about and blows air into it. Ever since it was first invented in the 1st century BC in Syria, glassmakers have been able to make thin-walled glasses and blow them into all kinds of different shapes.
The CO2 footprint is an environmental parameter that provides information about a product's total CO2 emissions throughout its life-cycle. The figure is calculated using an environmental life-cycle assessment model which maps the entire lifespan of a packaging product from the raw materials right through to recycling. In glass manufacture, the factors for the calculation are: the weight of the glass container, the proportion of used glass in its production, the transport distance to the bottling company, transport by road or rail, and the national recycling rate.
Cold end/hot end
These terms describe the start and finish of the glassmaking process at the glassworks. At the hot end – e.g. the start – gas burners heat the mixture of quartz sand, soda, lime and cullet (broken used glass) in the melting furnaces. After shaping, the bottles are cooled down before, at the cold end, they go through the various stages of Quality testing.
Glass is coloured either in the furnace or in a subsequent process in the forehearth or feeder. Different colouring processes are used for more flexibility in meeting customers' needs and to offer a wide spectrum of colours. In the traditional process of furnace colouring, the colouring components are mixed into the molten glass that is made up of quartz sand, soda, lime, dolomite and used glass. Depending on the colour, the proportion of used glass may be as high as 90%. For smaller production volumes and special colours, glassmakers add the colour concentrate to the molten glass in the feeder.
This term refers to all hollow glass items that are used for packaging, storing, preserving or transporting drinks or other liquids, foodstuffs, and chemical, pharmaceutical and cosmetic substances.
In the annealing furnace, the glass jars and bottles, still glowing red-hot, are gradually cooled down. This slow cooling process is necessary to release any tension in the material. The surface is then treated to protect it from scratches.
The cradle-to-cradle concept describes a waste-free system in which all materials are a permanent part of natural cycles or closed technical cycles. Possible materials for such cycles include, along with glass, compostable textiles, fully reusable raw materials, and pure plastics or metals that can be used an unlimited number of times for the same purpose.
Making glass requires very high temperatures that are normally generated using gas as the energy source. Inside the furnace, the mixture of used glass and primary raw materials is heated to about 1600° Celsius. Precisely because so much energy is needed for glass production, glassmakers have a special responsibility. Technological innovations and corporate decisions that are made with sustainability in mind result in improved energy efficiency. One approach is to increase the proportion of used glass. There is a linear correlation between the proportion of used glass and the energy savings that are made: for every 10% of used glass, 3% of the energy and 7% of the CO2 emissions are saved.
It has to be the right decision, both ecologically and economically, to work for continuous improvement in the environmental balance of glass-making. Reusing used glass has hugely improved the environmental balance of glass production in just a few decades: in the last 25 years, thanks to recycling and technological innovations, the European glass packaging industry has reduced its CO2 emissions and waste production by 70%.
Environmental sustainability describes a political and social aspiration to maintain species diversity and promote climate protection, so as to preserve nature and the environment for future generations. It is one of the three pillars of sustainability.
It is through the different kinds of finishing process that glass containers are given their unmistakeable appearance so that they can support a company's marketing strategy. Reliefs, labelling, coating, screen printing and sleeves can all turn a product into a premium packaging item.
Finite element method
Critical to ensuring the high stability of lightweight glass is the design phase that comes before the actual production. Using special software, the glass designers break down the glass container into smaller units. This allows the structural behaviour to be more easily analysed than for the complete article. On their computer screens, they identify those parts of a container that are subject to particular stresses. Often only minor adjustments to the geometry of the container are required to eliminate those stresses. Thanks to this method, lightweight glass containers can be easily manufactured, filled and stored with no loss of quality.
In 1867, Friedrich Siemens, a gas engineer in Dresden, introduced a technical innovation which speeded up the industrialisation of glass production: the continuous bassin (tank) furnace. These tank furnaces still consist today of a melting end and a working end and are operated continuously day and night. It was a milestone in the mechanical production of glass containers.
Glass is made from natural elements. The main component is quartz sand (70%). Soda (14%) reduces the melting point of the quartz sand, while lime and dolomite (14%) give glass its hardness, shine and durability. It also contains refining agents (2%).
Glass is a natural and neutral raw material with outstanding properties that make it ideal for storing high-quality food and drinks. Glass does not form any kind of bond with the contents, does not permit migration and protects the contents as if they were in a safe. The US food regulatory body, the FDA, categorises glass as the only packaging material that is "Generally Recognized As Safe" (GRAS).
Inert, a chemical property
Substances are described as chemically inert (from a Latin word meaning "inactive" or "uninvolved") when they do not react with potential reactants, or only to a vanishingly small extent. Glass is inert: nothing passes from the glass into the product, nothing penetrates from outside through the glass into the product and nothing escapes outside. Glass packaging does not react with the contents, it is gas-proof and taste-neutral.
The main characteristic of lightweight glass bottles is their even, thin walls. Lightweight glass technology guarantees that glass containers have a significant reduction in weight but are just as strong and stable as their heavier predecessors. Glass packaging nowadays is about 40% lighter than it was 20 years ago. The ecological benefits of traditionally produced glass are also retained. Using lightweight glass saves on raw materials, weight and transport costs.
The melting of the mixture takes place at the »hot end of glass production. Inside the furnace, the mixture of used glass and primary raw materials is heated to about 1600° Celsius.
A specific kind of production that allows for greater flexibility, even with small batch sizes. On a multi-gob glass-blowing machine, two, or in some cases even more, glass containers can be made at the same time that differ in their shape and weight. A special sorting machine then automatically forwards the different glass products for their product-specific quality testing and packing.
While the molten glass is still in the blank mould, a plunger is pressed into it to ensure that the walls of the glass container are not only as uniform as possible but also thinner. The technological shift from the traditional process to the narrow-neck-press-and-blow process has enabled the production of thin-walled glass containers – e.g. lightweight glass. Another advantage of this process is that the parison cools down faster during pressing, resulting in higher production rates.
Glass as a raw material also occurs in nature. Glass forms when, at extremely high temperatures - caused, for example, by bolts of lightning, volcanic eruptions or meteorite impacts - quartz sand melts and then the molten mass cools down. This is how the glassy rocks fulgurite, obsidian and tektite are formed.
This is one of the most common processes in industrial hollow glass production. In the press-and-blow process, the gob of glass is delivered from above into the mould and the pressing plunger is inserted from below. Once the gob has dropped into the parison (blank) mould, the mould is closed from above with the parison mould baffle. The plunger rises and shapes the blank mould and the neck. As soon as the plunger is removed from the blank mould, the parison is transferred to the blow mould. In contrast to the blow-and-blow process, in press-and-blow the neck is fully formed at the end.
Before the glass containers are sorted, packed and delivered, they undergo strict, certified test procedures to ensure that the products are of consistently high quality. The weight, contents and dimensions are checked by measurement. Destructive testing is carried out to measure internal pressure, pendulum swing impact and thermal shock, in addition to in-line tests using inspection machines (wall thickness, crack testing, impurity testing, etc.).
The word "recycling", borrowed from English, is derived from the Greek kýklos (cycle) and the Latin prefix re- (back, again). In recycling (reuse, reprocessing), waste products are reused, or their basic materials are processed into secondary raw materials. The goal of a future-proof materials cycle is for all the raw materials to be brought back into the production process after the individual product has reached the end of its life-cycle. Glass goes round in a materials cycle that is 100% closed. It can be endlessly reshaped into new bottles and jars, with no loss of quality. For the production of flint and brown glass, up to 60% recycled glass can be used, and for new green glass, theoretically, as much as 100%. The quality of the material that is collected and how it is processed are vital.
Returnable glass packaging is subjected to greater stress due to the repeated refilling and washing, so it is made heavier, with thicker walls. Glass is ideal for all kinds of bottling and for the recycling cycle. It withstands very high temperatures, is dimensionally stable up to about 500° Celsius and is therefore suitable for all standard bottling processes, such as hot and cold filling, pasteurisation, sterile and aseptic bottling. A returnable bottle can withstand up to 60 cycles.
When it comes out of the furnace, the molten glass is still liquid. Glowing "gobs" of glass are cut off, guided into a channel and fed into the blank mould. In the blow mould, compressed air gives the glass container its final shape. When container glass is being produced, the glass can be shaped by pressing and blowing.
Social responsibility is one of the three pillars of sustainability. The key principles of social sustainability are responsible corporate governance in day-to-day operations, a binding Code of Conduct, comprehensive health and workplace protection, a participative management style and a willingness to meet the social needs of employees.
The first fully automated bottle-blowing machine was invented in 1903 by the American engineer Michael J. Owens. It used the suck-and-blow process, i.e. the gob of glass is sucked into the metal mould and cut off automatically. Nowadays this process has been replaced by press-and-blow or the »narrow-neck-press-and-blow process.
Three pillars model of sustainability
The three pillars model of sustainability regards the economic, environmental and social responsibilities of a company or country as being of equal importance.