Glass Manufacturing Process
From Sand To Sophistication
Since the beginning, when the earth itself was formed in the fiery forge of cosmic activity, nature has given us a substance that today forms an integral part of our lives – glass.
We don't know how glass was discovered. It may have been after a chance lightning strike in a patch of sand, or by prehistoric nomads who found the hard, shiny, magical material in the ashes of their fire. But while it may have been discovered by chance, the manufacturing process continues to be perfected over centuries through sheer human and technical ingenuity.
Today, glass touches our lives in so many ways and is recognised as a trusted, versatile, and 100% recyclable packaging choice.
Consol Glass has been synonymous with glass packaging for over 65 years and is Africa's leading glass packaging manufacturing company.
Join us on a journey as we explain the glass making process; a magical, passion filled process to produce nature's packaging.
Making glass requires the correct recipe for a perfect result. Glass starts its life as a range of raw materials combined in a very specific ratio. The recipe calls for:
- soda ash
- limestone and
- other ingredients, such as iron and carbon which provide colour
Another important ingredient in the glass manufacturing process is cullet or recovered glass, obtained from recycling centres and bottle banks. Cullet usage can vary quite considerably, with as much as 40% utilization per batch. Its inclusion in production is most important, as it means that less virgin raw materials are used. It also melts at a lower temperature, enabling us to reduce emissions and save energy.
Consol has invested an estimated R240 million in equipment and cullet processing plants, to facilitate the glass recycling process.
Raw materials are stored in large silos, from where they are measured and delivered to batch mixers, according to pre-programmed recipes. Consol's batch houses are among the most modern in the world and use leading-edge technology to ensure that the mixed material or "batches" delivered to our furnaces meet our stringent quality standards.
The batch is continuously fed into the furnace, which is the beginning of what is known in the glass industry as the "hot end". And hot it is indeed: the temperature of a furnace is approximately 1 500° C. Operating 24 hours a day, 7 days a week, it is no surprise that a furnace has a limited lifespan, lasting between 8 to 10 years, before requiring a rebuild.
It takes some 24 hours for a batch of raw materials to be converted into molten glass. Red-hot liquid glass is continuously drawn from the furnace through a submerged throat.
From the furnace, the molten glass makes its way to the refiner area, where it is cooled to approximately 1 200° C. Maintaining the correct temperature is extremely important, not just to keep the flow of the molten glass correct, but also because it influences the quality of the end product.
From the refiner, the forehearths deliver glass to the individual bottle-making machines.
Having been conditioned for bottle-making by careful temperature control in the refiner and forehearths, the molten glass enters the feeder and flows through cavities in an orifice plate. Streams of glass are cut into gobs of a predetermined weight – exactly as much as is needed to make a single bottle. These gobs are then guided into the individual moulds of the bottle-making equipment, as part of a process known as forming
Bottles are formed in two moulding stages:
In the first stage the gob of glass falls into a blank mould to produce a parison. The opening of the bottle is moulded into its finished shape during this stage, but the body of the container is initially much smaller than its final size.
There are two primary methods of making a glass container. The first, known as the Blow-Blow process, is used for narrow-neck containers. In this process, compressed air is blown into the molten gob to create a cavity while it is in the blank mould and this results in a hollow and partly formed container. This is then transferred to the second moulding stage. Compressed air is used again in the second stage to blow mould the final shape.
The second process, known as the Press-Blow method, is used for jars and tapered narrow-neck containers. Here, a metal plunger instead of air is used to press a cavity into the gob in the blank mould before compressed air is used to form the container in the blow mould.
The newly formed bottle is then removed from the mould and transferred by conveyer to the annealing oven or lehr. The external surface of the bottle is first coated with a thin layer of tin oxide to strengthen it. In the lehr it is cooled from 600° C to 100° C in a controlled manner. Doing so prevents uneven cooling, relieves stresses within the bottle and ensures that it is stable and safe to handle. This process takes anything between 30 minutes and 2 hours. When the bottle exits the lehr it is cooled and this is referred to as the "cold end" of the plant.
Before leaving the annealing lehr, the bottles external surface is coated with polyethylene wax to protect the surface of the glass and prevent scuffing between bottles.
All glass containers manufactured by Consol undergo multiple tests and inspections to ensure that they comply with strict quality standards.
From here the bottles undergo further visual inspection by sophisticated, high-resolution camera equipment, as well as trained specialists. Rejected containers are sent to the recycling operation to be turned into cullet and re-enter the production process.
At Consol we pride ourselves on our commitment to manufacturing excellence, quality and the safety of our employees, customers and consumers. We are committed to achieving and maintaining compliance across all relevant standard specifications, and undergo regular audits accordingly.
OHAS 18001: 2007 – an international occupational health and safety management system specification
ISO 14001: 2004 – an environmental management system
ISO 9001: 2008 – recognised standard for quality management
HACCP Sans 10030 (2007)
FSSCISO 22 000 - Food Safety Certification
We offer a range of added value decorative solutions, which further enhance the creativity of the bottle making process. Some of these added service offerings include forehearth coloring, embossing, debossing, coating, sleeving, decorating and labeling.
These offerings create a range of brand building possibilities for our customers glass products.
With the manufacturing process completed, the bottles are individually coded with production date and time, packed on pallets and covered with protective shrink-wrapping before being dispatched to our customers.
Through various retail channels, the containers we manufacture make their way into the homes and hands of consumers, who continue to enjoy the benefits of consuming products in glass. They are, in turn, encouraged to reuse or recycle glass packaging, and to make use of glass collection points and bottle banks.
This recycled glass makes its way back to Consol's factories, where it is turned into cullet and re-enters the manufacturing process; testimony indeed to its infinite closed loop recyclability. We remain committed to driving glass recycling and take responsibility for purchasing all glass collected from post-consumer waste, to ensure a sustainable future for our planet.
The glass manufacturing process combines science and the passion and skill of our staff, who remain dedicated to producing glass packaging of the highest quality, for the food, beverage, pharmaceutical, cosmetics and tableware industries.
With factories nationally and a production rate of close to one million tonnes of glass annually, Consol is well placed to maintain its leadership position and fulfill our vision to be the supplier and pack of choice across Africa.
The versatility and unquestionable style of glass makes it the packaging of choice for consumers. And, being 100% impermeable, glass is also the healthy choice, preserving both the taste and the natural goodness of its contents.