We all come in contact with glass every single day. It is the product used for the window pane in your room, the screen on the device with which you are reading this, and the windshield of the vehicle that must have conveyed you somewhere today. Indeed, the glass is of immense importance to us- talk about bottles for storing drinks and other products, bulbs and so many other innumerable things. But has any one of you guys ever bothered to think about how the history of the glass much less how it is produced? Anyway, we’ve got your back!
The truth is that nobody really knows how glass was first discovered. Several unproven theories abound one of which is specifically interesting because it speculates that glass may have been accidentally discovered by ancient humans after chance lightning must have struck a patch of sand and transformed it to glass. In any case, irrespective of how it was discovered, the good thing is that the manufacturing processes of glass have over the centuries been perfected, and as a matter of fact continue to be; all thanks to several scientific breakthroughs. So what do these processes entail? Please read on below.
THE RAW MATERIALS: Just as it is the case with the production of anything, the making of glass requires the correct combination of the right materials [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][recipes] in order to achieve the perfect result. In other words, the production of glass requires the combination of some raw materials in the right ratio. The needed raw materials will include the following:
- sand
- 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 this will mean that less virgin raw materials are used. Cullet also can melt at a lower temperature, enabling factory workers to considerably reduce emissions by saving energy.
MELTING: After preparing the raw materials and dividing them into batches, it is then fed into a furnace. Mind you, the furnace is indeed hot with the temperature as high as 1 500° C. Usually, furnaces operate 24 hours a day, 7 days a week- continuously with stopping; so it is not surprising why its temperature can be quite as hot. Anyway, it takes 24 hours for a batch of raw materials to be converted into molten glass. The red-hot liquid glass is then continuously drawn from the furnace through a submerged throat, passing through the refiner area, where it is cooled to approximately 1 200° C. Please note that maintaining the correct temperature is extremely important as this determines the quality of the final products.
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 molding stages: In the first stage the gob of glass falls into a blank mould to produce a parison. The opening of the bottle is molded 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 molding 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…
*This post has been partly adapted
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