Creating glass containers can be accomplished by one of two different processes &#; the Blow and Blow, or the Press and Blow process. Each process is chosen based on the kind of glass bottle being made. All glass bottles start out as raw materials. Silica (sand), soda ash, limestone, and cullet (furnace-ready, recycled glass) are combined into a specific mixture based on the desired properties of the bottle. The mixture is then melted at high temperatures in the furnace until it becomes a molten material, ready for formation. The type of glass this mixture will produce is known as soda-lime glass, the most popular glass for food and beverages.
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Glass Forming Methods
Molten glass gobs are cut by a perfectly-timed blade to ensure each gob is of equal weight before it goes into the forming machine. The weight of a gob is important to the formation process for each glass container being made. The molded glass is created by gravity feeding gobs of molten glass into a forming machine, where pressure forms the neck and basic shape of the bottle. Once the neck finish and the general glass bottle shape has been achieved, the form is known as a parison. To achieve the final container shape, one of two processes are used.
Press and Blow Process
The Press and Blow process is the most commonly used method in glass bottle manufacturing. It uses an individual section (IS) machine, which is separated into varying sections to produce several containers of the same size simultaneously. The molten glass is cut with a shearing blade into a specific gob size. The gob falls into the machine by force of gravity. A metal plunger is used to push the gob down into the mold, where it starts to take shape and become a parison. The parison is then transferred into the blow mold and reheated so that the parison is soft enough to finish off the dimensions of the glass. Once the parison is reheated to blowing temperature, air is injected to blow the container into shape. Press and blow methods are typically used for manufacturing wide-mouth bottles and jars as their size allows the plunger into the parison.
Blow and Blow Process
The Blow and Blow process is used to create narrow containers. It also requires an IS machine, where gobs of molten glass are gravity fed into the mold. The parison is created by using compressed air to form the neck finish and basic bottle shape. The parison is then flipped 180 degrees and reheated before air is again injected to blow the container into its final shape. Compressed air is once again used to blow the bottle into its desired shape. Blow and Blow methods are best used for glass bottle manufacturing requiring different neck thicknesses.
Finishing the Process
Regardless of the process used, once the bottle has been completely formed, it is removed from the mold and transferred to the annealing lehr. The lehr reheats the bottes to a temperature of about 1,050 degrees Fahrenheit then gradually cools them to about 390F. This process allows the glass to cool at an even rate - eliminating internal stresses in the glass that could lead to cracking or shattering. Bottles are then subjected to careful inspections to ensure they meet quality control guidelines. Any bottles showing imperfections, including bubbles, cracks, or misshapen areas, are removed from the line and used as cullet. All remaining bottles are sorted according to size and type. The bottles are then packaged on pallets and prepared for shipping.
For an infographic on the glass manufacturing process, click here: Infographic - From Grit to Glass, How Are Glass Bottles Made.
View the video: From Grit to Glass: How Glass Bottles are Made
What is Type III glass? Are there other types of glass? This is a classification of glass for containers which has been adopted by different Pharmacopoeias in order to establish a more appropriate use of glass in containers according to their contents. There is glass type I, type II, and type III.
Type I is a borosilicate glass (known as Neutral) with a high hydrolytic stability suitable for containing injectable products.
Type II derives from type III: thanks to a special ammonium sulfate treatment of the internal surface, this type achieves a similar hydrolytic stability to type I and is suitable for containing acid or neutral products (e.g., infusion solutions).
Type III is a soda-lime glass with a low alkali content and good hydrolytic stability, suitable for containing preparations that are not in aqueous or alkaline sensitive solutions.
There is another type of glass which is suitable for containing food products and known as Type A Glass (soda-lime glass) which does not require any specific hydrolytic resistance, unlike type III.
Are tumblers, household objects, windows, etc. all made of the same type of glass as pots, jars, and bottles? There are different types of glass which are all manufactured by the same process of melting raw materials, based on silicon, soda, and potassium, in a furnace. These various types of glass meet different requirements. For instance:
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What are the main components of glass? The main components of the glass batch are:
When was glass first used as an industrial packaging material? The ancient Romans used glass to store their wine, but industrial production with mass volumes did not begin until the late s.
What is the difference between ordinary glass and crystal? Glass is a generic term that includes different types of the same material. Crystal is a particular type of glass principally made up of lead, barium, and zinc which are all substances that increase the refraction index responsible for its shine. The batch used to produce crystal always requires slightly lower melting temperatures than glass for bottles. Moreover, crystal is not as hard as traditional glass and therefore it can be more easily engraved.
What are the main features that differentiate special bottles from standard bottles? There isn&#;t any real classification in this respect. A standard glass bottle is one that is usually manufactured by a glass factory and that can be used by many different customers. It is generally produced in large quantities compared to the average production of a glass factory.
Special bottles may refer to those with a particular shape, not square or round, but may also refer to those designed especially for a particular customer and sold exclusively to that customer.
From the point of view of the technological production, there is absolutely no difference between these two articles, but special bottles always require a particular expertise when the production starts, in printing brand names, dealing with irregularities in the shape or creating a heavy base, or because they are unstable on the conveyor belts.
Sometimes when a glass bottle or glass jar breaks you can see that the glass thickness is not uniform. Why is this? The glass container is formed in the blow mold by a blow-blow process. The stretching of the glass is therefore influenced by the temperature of the glass batch. The reduction in glass thickness is often more evident in bottles and usually appears at two-thirds of the bottle height, going down towards the bottom, which corresponds to the height of the parison. So a certain amount of difference in the thickness is a natural physical feature, provided it does not affect the solidity of the container.
Many bottles have a very thick glass bottom. What is this for and how is it made? The extra thick glass on the bottom of bottles is primarily for aesthetic reasons to make the bottle look more valuable, and in the case of clear glass, to enhance the transparency and purity of the bottle. Technically, the concentration of glass on the bottom of the bottles is achieved by creating a special preparatory mold (parison) with a higher glass mass than a normal bottle that does not get deformed during the first blowing process.
Who collects glass for recycling and who uses it? Glass is collected by companies appointed by the individual municipalities. The collectors treat the glass cullet in special industrial plants that wash it, break it into very small pieces, and separate off the impurities. The recycled glass is then sold to glass factories that mix it in with the batch formula.
Is glass &#;biodegradable?&#; What impact does glass have on the environment? No. Glass is a mineral and the labels on glass containers generally state &#;please dispose of responsibly&#;. Over time, the glass will tend to &#;return to sand&#;, especially if it is thrown away on beaches, in the sea, or wherever it may be repeatedly moved by natural elements.
How much recycled glass should be used in production? There is no technically fixed quantity. Cullet can be used as a support to the melting of the raw materials since it melts at a lower temperature and thus offers significant economic and environmental advantages (less energy consumption). For extra-flint glass, in particular, the quantity of glass cullet is kept as low as possible (10%) in order to avoid impurities appearing in the recycled material.
Another solution is for the producer to use cullet exclusively from their own recycled product. Some glass factories that produce colored glass can use 60% or more of cullet since any color impurities in the cullet will not have a significant impact on the final result. It is also possible to manufacture new containers using only cullet, but in this case, it is important to adopt special strategies to keep complete control of the material in order to ensure the homogeneity of the molten materials.
Is it possible to recycle glass that is already a product of recycling? Glass recycling can be repeated indefinitely; a 600 gram container will produce another container of the same weight without any loss. The original &#;mineral&#; does not change: the process of melting to the semi-liquid form is repeated (some people would define glass as a highly viscous liquid), the shape is changed, it solidifies as it cools, and is then used again.
Is it possible to detect glass packaging with recycled content? No. When &#;cullet&#; is melted, it returns to its original purity as if it was &#;new glass&#;.
Since glass objects are thrown indiscriminately into glass banks regardless of their color, what color is the final recycled glass product? A recycled glass of mixed colors is generally used to produce dark glass (green, antique green, or yellow). Cullet (crushed and mixed) is used in the normal mixture of raw materials, with the addition of colorants that guarantee a uniform final result. Melting takes place at over °C and at this stage there is a viscous, perfectly homogeneous and purified mixture.
Why are glass water bottles returned and how are they reused? This is a question of relative cost, balancing the cost of water with the cost of the glass bottle, as these are both &#;low cost&#; items. It is necessary to take into account the cost of returning the bottle to the filling plant, as well as the cost of the necessary processing before it can be reused: such processing is quite complex in terms of equipment and water consumption for washing in order to ensure the completely hygienic condition of the bottle independently from its previous use.
Why shouldn&#;t lids be reused? Because the mastic used for the lid, the material which allows the &#;air-tight&#; seal, doesn&#;t have the same elasticity after the first use. The &#;threads/lugs&#; that ensure the coupling of the lid to the jar finish become deformed after the first use.
If glass containers should be &#;cleaned&#; before they are used by the food industry, what is the most efficient cleaning method? Glass containers arrive at the end of the uninterrupted production chain clean and packaged. Before using the container, the filling company must ensure that no internal contamination has occurred during storage and unpacking. A washing or blowing procedure is generally adopted on the production line. The blowing procedure &#; which is the most commonly used &#; is carried out by a machine placed in between the depalletizer and the product filler, which blows air forcefully into the inverted container. In this way, the combination of air pressure and gravity together eliminate any impurities which may have been introduced during the storage or unpacking phases.
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