Glass manufacturing involves two main methods: the float glass process for flat products, and glass blowing to produce bottles and other containers.
Production of glass containers
Glass container factories
Generally speaking, modern glass container factories operate in three phases: raw material preparation, hot process, and cold post-processing. In the first, the raw materials are stored and dosed; In the second, the glass is melted in ovens and the containers are shaped using special machines; and in the third the product is inspected and packed to be shipped.
hot process
The following table shows typical viscosity set point values applicable to large-scale glass production and for laboratory melted glass:[1].
One of the initial steps in the glass manufacturing process is the processing of raw materials, which are usually stored in large silos (fed by truck or rail), with capacity for up to 5 days of production. Some systems include sieving of materials; its inspection, sampling and analysis; dried, or preheated (in the case of recycling). Automated or manual, these facilities weigh and measure the materials, mixing them using hoppers, conveyor belts, and scales to feed the ovens. Loads of materials are prepared according to the different desired characteristics (colors and qualities). The availability and purity of the materials determine the conditions of each batch.
In the hot process is where different shapes are given to molten glass. To maintain their temperature, the ovens are fed slowly. They usually operate with natural gas or fuel oil, with temperatures of up to 1,575 °C,[3] limited only by the quality of the material of the oven itself and the composition of the glass. The types of ovens used usually have oxygen supply to improve their performance. Their production capacity is usually measured in metric tons per day.
There are currently two primary methods of manufacturing glass containers: the method used only for narrow-neck containers, and the method used for conical-shaped jars and containers.
Aluminum and Glass Installations
Introduction
Glass manufacturing involves two main methods: the float glass process for flat products, and glass blowing to produce bottles and other containers.
Production of glass containers
Glass container factories
Generally speaking, modern glass container factories operate in three phases: raw material preparation, hot process, and cold post-processing. In the first, the raw materials are stored and dosed; In the second, the glass is melted in ovens and the containers are shaped using special machines; and in the third the product is inspected and packed to be shipped.
hot process
The following table shows typical viscosity set point values applicable to large-scale glass production and for laboratory melted glass:[1].
One of the initial steps in the glass manufacturing process is the processing of raw materials, which are usually stored in large silos (fed by truck or rail), with capacity for up to 5 days of production. Some systems include sieving of materials; its inspection, sampling and analysis; dried, or preheated (in the case of recycling). Automated or manual, these facilities weigh and measure the materials, mixing them using hoppers, conveyor belts, and scales to feed the ovens. Loads of materials are prepared according to the different desired characteristics (colors and qualities). The availability and purity of the materials determine the conditions of each batch.
In the hot process is where different shapes are given to molten glass. To maintain their temperature, the ovens are fed slowly. They usually operate with natural gas or fuel oil, with temperatures of up to 1,575 °C,[3] limited only by the quality of the material of the oven itself and the composition of the glass. The types of ovens used usually have oxygen supply to improve their performance. Their production capacity is usually measured in metric tons per day.
blow and blow
press and blow
In both methods, a stream of molten glass at its plastic temperature (1,050–1,200 °C) is cut with a shear blade to form a solid cylinder of glass, called a "gob", with the predetermined weight needed to make a bottle. Both processes begin with the drop descending by gravity, guided through feeders and hoppers to the blowing or pressing pre-molds depending on the method, whose two halves are closed and sealed at the top using a separator.
In the blowing and blowing process, the glass is first blown through an upper valve, forcing it to descend towards the three-piece mouth mold, while it is imprisoned in the neck mold, where the details of the mouth of the container are shaped (the ring to hold the plates or the helical grooves of the screw closures),[4] then the plug or needle is removed, allowing a first breath of compressed air to pass through which will give rise to a preform. Thanks to an inversion arm (invert in English), the preform is sent to the finishing mold after rotating 180°, where thanks to the second blow, a fully formed container will result.
As already indicated, these containers are manufactured in two stages. The molds of the first stage make up all the details of the mouth of the container, but the body is initially much smaller than its final measurement. These partially finished vessels are called "parisons", although they are immediately blown into their final shape.
Regarding the mechanism, the "rings" are sealed at the bottom by a plunger. With the first blow, the drop takes its position, and the plunger is withdrawn slightly, to allow the surface of the container to smooth out. This blowing from the bottom through the plunger creates the "parison", leaving the neck of the container at the bottom of the mold. The closure is lifted and the spaces are opened, now rotating the mold 180 degrees. With the neck of the container now located up, the shape of the container is completed by the second blowing.
In the compression and blowing process, the "parison" is formed by a long metal plunger that rises and propels the glass outward to fill the ring and molds.[4][5]
The process then continues as above, with the parison transferred to the mold of the final shape, and the glass blown into the mold.
Immediately afterwards, the glass container is extracted from the mold by a special mechanism, and is placed on a platform where it is cooled with air currents. Finally, the bottles are transported at a controlled temperature to undergo the annealing process.
After the forming process, some containers—particularly those intended to contain alcoholic products—are subjected to a treatment to improve the chemical resistance of their interior, called dealkalization, generally by injecting a sulfide or a gas mixture containing fluorine when the glass is at high temperatures. The gas is typically applied to the container with the air used in the blowing process, or through a nozzle that directs a stream of gas to the mouth of the bottle. The treatment makes the container more resistant to alkali dissolution, which can cause increases in the pH of the product, and degradation of the container in some cases.
When glass cools, it solidifies and contracts. Uneven cooling causes weak glass due to internal residual stresses. An annealing oven (known in the industry as Lehr) heats containers to approximately 580°C and then gradually cools them over a time that depends on the thickness of the glass (between 20 and 6000 minutes).
Cold post-processing
In the cold post-processing, a polyethylene coating spray is applied to improve abrasion resistance and reduce friction, the containers are labeled, inspected for possible defects, and packed into containers for shipment.
Glass containers are 100% inspected; Automatic machines, or sometimes people, inspect each container to detect a series of defects (such as small cracks or inclusions of refractory brick remains from the kiln, or large, defectively cast sand granules), removing the failed containers to be melted again. Removing these containers is especially important because these defects increase the danger of glass breakage. For example, these elements can generate significant amounts of thermal stress, causing the container to destroy explosively when heated.
Other defects include bubbles (called blisters in English), excessively thin walls, or the manufacturing defect known as tears. In the squeeze and blow system, if a plunger and its mold are out of alignment, or have been heated to the wrong temperature, the glass will stick to anything and end up tearing.
In addition to rejecting defective containers, the inspection team prepares statistical studies that are provided to the forming machine operators. Computer systems collect the information necessary to locate molds where failures are occurring. This is possible because each mold marks the containers it produces with a point code. Operators also carry out a series of checks manually on packaging samples, typically visual and dimensional checks.
Sometimes packaging factories offer services such as labeling. There are many labeling technologies available. Specific to glass is the application of a ceramic glaze. This is a silkscreen applied to the container with a Coca-Cola enamel paint.
Glass containers are packaged in various ways. In Europe, pallets with between 1,000 and 4,000 containers each are common. They are formed with automatic machines (palletizers) that arrange and stack the containers in superimposed layers separated by support sheets. Other possibilities include boxes and even hand-loaded bags. Once the containers are packed, the new packages are labeled and stored.
Glass containers typically receive two surface coatings, one in the hot processing, just before annealing, and one in the cold processing, just after annealing. In the first process, a very thin layer of tin (IV) oxide is added using a safe organic or inorganic compound, tin chloride. "Tin (IV) chloride") Tin-based systems are not the only ones used, but they are the most common. Titanium chloride "Titanium (IV) chloride") or organic titanates are also used. In all cases the coating makes the glass surface more adhesive to the second cold coating, typically a layer of polyethylene wax, applied via a water-based emulsion. This makes the glass slippery, avoiding snags and stops on the conveyor belts that move the containers through the production line. The resulting invisible combined coating provides the container with a virtually scratch-resistant surface. These coatings are often called hardeners (due to the reduced damage they provide), although a more correct definition might be protective coatings.
The forming machines are largely driven by compressed air. Factories usually have several large compressors to provide the necessary compressed air. Ovens, compressors and molding machines generate considerable amounts of heat, and are usually cooled with water. Hot glass that is not used in the forming machine (called cullet) is diverted and usually cooled with water, and sometimes even processed and crushed in a water immersion system. Often there are several cooling towers shared by the different systems, sized so that they can be maintained without having to stop the manufacturing plant.
Marketing
Glass container manufacturing in the developed world is a mature market business. Annual sales growth for the industry as a whole generally follows population growth. It is also a geographic business; The product is heavy and large volume, and the necessary raw materials (sand, soda ash and limestone) are generally readily available, therefore it is advisable to locate production facilities close to your markets. A glass furnace can handle productions of hundreds of tonnes, and it is simply not practical to close it every night, or indeed for any short period of less than a month. The factories therefore operate 24 hours a day and 7 days a week. This means there is little room to increase or decrease production rates. Kilns are very expensive and complex installations, requiring planning of at least 18 months. Given this fact, and the fact that there are typically more products than production lines, this means that the containers being sold have been previously stored. The production challenge is to be able to forecast demand in the short term (from 4 to 12 weeks) and especially in the long term (from 24 to 48 months). Factories are generally sized to meet the demand of a city; In developed countries, each factory can normally cover the needs of an area of 1 to 2 million people. A typical factory can produce 1 to 3 million containers per day.
Despite its positioning as a mature market product, glass enjoys a high level of consumer acceptance and is perceived as premium packaging.
Life cycle of glass containers
Glass containers are completely recyclable and glass industries in many countries maintain policies, sometimes at the behest of governments, of maintaining a high price of used containers to ensure high return rates. Return rates of 95% are not uncommon in the Nordic countries (Sweden, Norway, Denmark and Finland). Naturally, glass containers can also be reused, and in developing countries this is common, although the environmental impact of washing them is uncertain. Factors to consider here are the chemicals and fresh water used in washing, and the fact that a single-use container can be manufactured much lighter, using less than half the glass (and therefore energy) of a multi-use container. Another significant factor in the consideration of reuse in the developed world is the producer's concern about the risk and responsibility for the product derived from using a component (the reused container) of unknown and difficult to assess safety. Compared to other types of packaging (plastic, cardboard, aluminum) it is surprising to point out; but there are still no conclusive studies about the life cycle of glass.
float glass process
Float glass is what is made by depositing the molten material on a bed of also molten metal, usually tin, although lead and various low-melting alloys were used in the past. This method gives the glass sheet a remarkably uniform thickness and very flat surfaces. Modern windows are made of float glass. Most float glass is ordinary silica glass, although borosilicate glass[6] occasionally and glass for flat-screen televisions is routinely produced using this method,[7] also known as the Pilkington process (it was invented by the British Alastair Pilkington in the 1950s).
Environmental impacts
Environmental impact
Like all highly concentrated industries, glass factories cause moderately high local environmental impacts, as well as global impacts. This situation is aggravated because they are businesses linked to mature markets and have often been located in the same place for long periods of time, which in many cases means that they have become located on residential land due to the growth of cities. The main impacts in these residential areas are noise, the use of drinking water, water pollution, the emission of NOx and SOx, air pollution, and the generation of dust.
Shaping machines generate considerable noise. When operated by compressed air, they can produce noise levels of up to 106 dB(A). How this noise affects the environment depends strongly on the factory design. Another noise production factor is the movement of trucks. A typical factory processes on the order of 600 tons of material per day, which in turn means the output of an equivalent amount of finished product from the factory.
Water usually cools furnaces, compressors and leftover molten glass. Water use in factories varies widely; but it is usually around one cubic meter for each ton of molten glass. Of this cubic meter, half evaporates in cooling processes and the rest is discharged as wastewater.
Many factories use water with emulsified oil to cool and lubricate the mechanisms that handle molten glass*.* This emulsion contaminates the water evacuated from the factories, although they are normally equipped with purification systems of varying effectiveness.
Nitrogen oxides are a natural product of the combustion of gases in the atmosphere, and are consequently produced in large quantities by glass furnaces. Some factories in urban areas with particular air pollution problems mitigate them by using liquid oxygen. Even so, the logic of this measure is questionable, due to the carbon cost of (1) not using regenerators and (2) liquefying and transporting oxygen.
Sulfur oxides are produced in the glass melting process. By manipulating the dosage of raw materials, a limited attenuation of this effect can be achieved; Alternatively, gas purification systems can be used.
The raw materials that make up glass are granular or powdery materials. Systems to control dust formation are often difficult to maintain, and given the large quantities of materials moved each day, it is enough for even a small proportion to enter the air to constitute a considerable problem. Furthermore, the transfer of glass containers on the production line (due to friction or breakage) produces suspended glass particles.
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[7] ↑ No todo el vidrio plano para pantallas de televisor es producido por el proceso de flotación.
There are currently two primary methods of manufacturing glass containers: the blow and blow method used only for narrow-neck containers, and the press and blow method used for conical-shaped jars and containers.
In both methods, a stream of molten glass at its plastic temperature (1,050–1,200 °C) is cut with a shear blade to form a solid cylinder of glass, called a "gob", with the predetermined weight needed to make a bottle. Both processes begin with the drop descending by gravity, guided through feeders and hoppers to the blowing or pressing pre-molds depending on the method, whose two halves are closed and sealed at the top using a separator.
In the blowing and blowing process, the glass is first blown through an upper valve, forcing it to descend towards the three-piece mouth mold, while it is imprisoned in the neck mold, where the details of the mouth of the container are shaped (the ring to hold the plates or the helical grooves of the screw closures),[4] then the plug or needle is removed, allowing a first breath of compressed air to pass through which will give rise to a preform. Thanks to an inversion arm (invert in English), the preform is sent to the finishing mold after rotating 180°, where thanks to the second blow, a fully formed container will result.
As already indicated, these containers are manufactured in two stages. The molds of the first stage make up all the details of the mouth of the container, but the body is initially much smaller than its final measurement. These partially finished vessels are called "parisons", although they are immediately blown into their final shape.
Regarding the mechanism, the "rings" are sealed at the bottom by a plunger. With the first blow, the drop takes its position, and the plunger is withdrawn slightly, to allow the surface of the container to smooth out. This blowing from the bottom through the plunger creates the "parison", leaving the neck of the container at the bottom of the mold. The closure is lifted and the spaces are opened, now rotating the mold 180 degrees. With the neck of the container now located up, the shape of the container is completed by the second blowing.
In the compression and blowing process, the "parison" is formed by a long metal plunger that rises and propels the glass outward to fill the ring and molds.[4][5]
The process then continues as above, with the parison transferred to the mold of the final shape, and the glass blown into the mold.
Immediately afterwards, the glass container is extracted from the mold by a special mechanism, and is placed on a platform where it is cooled with air currents. Finally, the bottles are transported at a controlled temperature to undergo the annealing process.
After the forming process, some containers—particularly those intended to contain alcoholic products—are subjected to a treatment to improve the chemical resistance of their interior, called dealkalization, generally by injecting a sulfide or a gas mixture containing fluorine when the glass is at high temperatures. The gas is typically applied to the container with the air used in the blowing process, or through a nozzle that directs a stream of gas to the mouth of the bottle. The treatment makes the container more resistant to alkali dissolution, which can cause increases in the pH of the product, and degradation of the container in some cases.
When glass cools, it solidifies and contracts. Uneven cooling causes weak glass due to internal residual stresses. An annealing oven (known in the industry as Lehr) heats containers to approximately 580°C and then gradually cools them over a time that depends on the thickness of the glass (between 20 and 6000 minutes).
Cold post-processing
In the cold post-processing, a polyethylene coating spray is applied to improve abrasion resistance and reduce friction, the containers are labeled, inspected for possible defects, and packed into containers for shipment.
Glass containers are 100% inspected; Automatic machines, or sometimes people, inspect each container to detect a series of defects (such as small cracks or inclusions of refractory brick remains from the kiln, or large, defectively cast sand granules), removing the failed containers to be melted again. Removing these containers is especially important because these defects increase the danger of glass breakage. For example, these elements can generate significant amounts of thermal stress, causing the container to destroy explosively when heated.
Other defects include bubbles (called blisters in English), excessively thin walls, or the manufacturing defect known as tears. In the squeeze and blow system, if a plunger and its mold are out of alignment, or have been heated to the wrong temperature, the glass will stick to anything and end up tearing.
In addition to rejecting defective containers, the inspection team prepares statistical studies that are provided to the forming machine operators. Computer systems collect the information necessary to locate molds where failures are occurring. This is possible because each mold marks the containers it produces with a point code. Operators also carry out a series of checks manually on packaging samples, typically visual and dimensional checks.
Sometimes packaging factories offer services such as labeling. There are many labeling technologies available. Specific to glass is the application of a ceramic glaze. This is a silkscreen applied to the container with a Coca-Cola enamel paint.
Glass containers are packaged in various ways. In Europe, pallets with between 1,000 and 4,000 containers each are common. They are formed with automatic machines (palletizers) that arrange and stack the containers in superimposed layers separated by support sheets. Other possibilities include boxes and even hand-loaded bags. Once the containers are packed, the new packages are labeled and stored.
Glass containers typically receive two surface coatings, one in the hot processing, just before annealing, and one in the cold processing, just after annealing. In the first process, a very thin layer of tin (IV) oxide is added using a safe organic or inorganic compound, tin chloride. "Tin (IV) chloride") Tin-based systems are not the only ones used, but they are the most common. Titanium chloride "Titanium (IV) chloride") or organic titanates are also used. In all cases the coating makes the glass surface more adhesive to the second cold coating, typically a layer of polyethylene wax, applied via a water-based emulsion. This makes the glass slippery, avoiding snags and stops on the conveyor belts that move the containers through the production line. The resulting invisible combined coating provides the container with a virtually scratch-resistant surface. These coatings are often called hardeners (due to the reduced damage they provide), although a more correct definition might be protective coatings.
The forming machines are largely driven by compressed air. Factories usually have several large compressors to provide the necessary compressed air. Ovens, compressors and molding machines generate considerable amounts of heat, and are usually cooled with water. Hot glass that is not used in the forming machine (called cullet) is diverted and usually cooled with water, and sometimes even processed and crushed in a water immersion system. Often there are several cooling towers shared by the different systems, sized so that they can be maintained without having to stop the manufacturing plant.
Marketing
Glass container manufacturing in the developed world is a mature market business. Annual sales growth for the industry as a whole generally follows population growth. It is also a geographic business; The product is heavy and large volume, and the necessary raw materials (sand, soda ash and limestone) are generally readily available, therefore it is advisable to locate production facilities close to your markets. A glass furnace can handle productions of hundreds of tonnes, and it is simply not practical to close it every night, or indeed for any short period of less than a month. The factories therefore operate 24 hours a day and 7 days a week. This means there is little room to increase or decrease production rates. Kilns are very expensive and complex installations, requiring planning of at least 18 months. Given this fact, and the fact that there are typically more products than production lines, this means that the containers being sold have been previously stored. The production challenge is to be able to forecast demand in the short term (from 4 to 12 weeks) and especially in the long term (from 24 to 48 months). Factories are generally sized to meet the demand of a city; In developed countries, each factory can normally cover the needs of an area of 1 to 2 million people. A typical factory can produce 1 to 3 million containers per day.
Despite its positioning as a mature market product, glass enjoys a high level of consumer acceptance and is perceived as premium packaging.
Life cycle of glass containers
Glass containers are completely recyclable and glass industries in many countries maintain policies, sometimes at the behest of governments, of maintaining a high price of used containers to ensure high return rates. Return rates of 95% are not uncommon in the Nordic countries (Sweden, Norway, Denmark and Finland). Naturally, glass containers can also be reused, and in developing countries this is common, although the environmental impact of washing them is uncertain. Factors to consider here are the chemicals and fresh water used in washing, and the fact that a single-use container can be manufactured much lighter, using less than half the glass (and therefore energy) of a multi-use container. Another significant factor in the consideration of reuse in the developed world is the producer's concern about the risk and responsibility for the product derived from using a component (the reused container) of unknown and difficult to assess safety. Compared to other types of packaging (plastic, cardboard, aluminum) it is surprising to point out; but there are still no conclusive studies about the life cycle of glass.
float glass process
Float glass is what is made by depositing the molten material on a bed of also molten metal, usually tin, although lead and various low-melting alloys were used in the past. This method gives the glass sheet a remarkably uniform thickness and very flat surfaces. Modern windows are made of float glass. Most float glass is ordinary silica glass, although borosilicate glass[6] occasionally and glass for flat-screen televisions is routinely produced using this method,[7] also known as the Pilkington process (it was invented by the British Alastair Pilkington in the 1950s).
Environmental impacts
Environmental impact
Like all highly concentrated industries, glass factories cause moderately high local environmental impacts, as well as global impacts. This situation is aggravated because they are businesses linked to mature markets and have often been located in the same place for long periods of time, which in many cases means that they have become located on residential land due to the growth of cities. The main impacts in these residential areas are noise, the use of drinking water, water pollution, the emission of NOx and SOx, air pollution, and the generation of dust.
Shaping machines generate considerable noise. When operated by compressed air, they can produce noise levels of up to 106 dB(A). How this noise affects the environment depends strongly on the factory design. Another noise production factor is the movement of trucks. A typical factory processes on the order of 600 tons of material per day, which in turn means the output of an equivalent amount of finished product from the factory.
Water usually cools furnaces, compressors and leftover molten glass. Water use in factories varies widely; but it is usually around one cubic meter for each ton of molten glass. Of this cubic meter, half evaporates in cooling processes and the rest is discharged as wastewater.
Many factories use water with emulsified oil to cool and lubricate the mechanisms that handle molten glass*.* This emulsion contaminates the water evacuated from the factories, although they are normally equipped with purification systems of varying effectiveness.
Nitrogen oxides are a natural product of the combustion of gases in the atmosphere, and are consequently produced in large quantities by glass furnaces. Some factories in urban areas with particular air pollution problems mitigate them by using liquid oxygen. Even so, the logic of this measure is questionable, due to the carbon cost of (1) not using regenerators and (2) liquefying and transporting oxygen.
Sulfur oxides are produced in the glass melting process. By manipulating the dosage of raw materials, a limited attenuation of this effect can be achieved; Alternatively, gas purification systems can be used.
The raw materials that make up glass are granular or powdery materials. Systems to control dust formation are often difficult to maintain, and given the large quantities of materials moved each day, it is enough for even a small proportion to enter the air to constitute a considerable problem. Furthermore, the transfer of glass containers on the production line (due to friction or breakage) produces suspended glass particles.
Find more "Aluminum and Glass Installations" in the following countries: