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GLASS CONTAINER INDUSTRY
THE HISTORY OF GLASS:
The first man-molded glass may have appeared around 7,000 B.C. in the form of beaded jewelry made from natural glass such as obsidian, rock crystal, agate, or onyx. It wasn't until 1,500 B.C. that the first glass containers were produced. Thousands of years later, in 1608, America's glass container industry was born when English settlers in Jamestown, Virginia, built a glass-melting furnace. By 1880, more than 25 percent of the glass made in America was used for common bottles.
Glass containers remained something of a luxury, with the industry dependent on the skill and availability of its glassblowers. The invention of the first completely automatic glass bottle-blowing machine. This machine made it possible to mass produce bottles and jars of uniform height, weight, and capacity. High-speed filling and packing lines soon followed. Glass containers entered the modern age, with today's machines capable of producing over 1,000,000 bottles a day!
THE PROCESS:
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Step 1: Glass Melting. The furnace melts cullet
(crushed, recycled glass), sand, soda ash, limestone, and other raw
materials together. Molten glass usually ranges in temperature between
2,300 and 2,800° F. A Furnace Control Room houses the computer which
monitors and controls furnace temperature.
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Step 2: Container Forming. The Refiner
distributes the molten glass to the fore hearth, which brings the
temperature of the molten glass to a uniform level. A Shearing and
Distribution System cuts molten glass from the fore hearth into
uniform gobs and sends them to an I.S. (Individual Section) Forming
Machine that forces the molten gobs into the mold shape. The glass
temperature drops further in the Forming Machine to below 2,100° F.
Formed glass containers leave the machine, crossing a cooling plate
where they are cooled rapidly to below 900° F. The glass has now
passed from liquid to solid form.
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Step 3: Container Conditioning. The
formed containers are loaded into an Annealing Lehr, where their
temperature is brought back up close to the melting point, then
reduced gradually to below 900° F. This reheating and slow cooling
eliminates the stress in the containers making them stronger and shock
resistant.
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Step 4: Surface Treatment. The temperature of
the containers is reduced to between 225 and 275° F. Cold End Sprays
then apply an exterior coating to the bottles to increase line
mobility, and reduce abrasions to maintain the inherent strength of
the container.
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Step 5: Automatic Inspection. The Fast Cooling
Section then brings container temperatures down to about 100° F -
cool enough to touch by hand. The manufactured containers then pass
through a series of instruments that physically and optically test the
containers. Rejected containers are recycled back into the furnace.
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Step 6: Product Handling & Packaging. A
Case Packer then packs the containers in corrugated cases for
shipment. The cases are then sent to the Case Palletizer, where they
are stacked in a prearranged pattern to increase stability for
shipment. A strapper fits plastic bands around the stacked boxes for
added stability and, finally, the Stretch Wrap Unit covers the stacked
boxes with plastic wrap. Containers can also be sent to a Bulk
Palletizer that stacks the individual containers in 5 to 15 layers,
depending upon the size of the container. These Bulk loads are also
strapped for stability and sent through the Stretch Wrap Unit and
covered with plastic wrap for shipment.
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portions of this page by:
© 2003 Owens-Illinois. All rights reserved.
GLASS TECHNOLOGY TERMS:
Annealing Point. The temperature at which internal stresses in glass are significantly reduced. In the annealing operation, glass is gradually cooled from above the annealing point temperature to below the strain point temperature. This slow cooling relieves residual thermal stresses that would develop if the glass were allowed to cool in an uncontrolled manner.
Batch. The mixed raw materials used in manufacturing glass that have been blended and proportionally mixed for delivery to the glass furnace.
Blank. Usually refers to a glass parison that is formed during the first step of glass molding. The piece is then transferred to a lamp worker or glass blower for final shape configuration.
Blister. A gaseous inclusion or bubble in the glass.
Blow Mold. Usually a metal mold used to form a piece of glass from a hot gob.
Borosilicate Glass. A high silicate glass that has at least 5% boron oxide.
Contraction Coefficient. The fractional change in length of a piece of glass per degree change in temperature on cooling from the annealing point to ambient temperature.
Cullet. Waste or broken glass. Clean cullet is always used in the batch.
Density. Mass per unit volume measured in grams per cubic centimeter.
Distribution. The wall thickness or the evenness of the glass distribution throughout the container.
Etch. To attack the glass surface with a strong chemical agent, usually hydrofluoric acid. Usually used in decorating glass.
Finish. The part of a bottle which holds the cap, stopper or closure. The area that has the threads (generally a shortened term for thread finish). The first part made on an automatic machine, but the last part (or finish) to be made when bottles were hand blown. On labware, may refer to an interchangeable ground joint.
Forming. The shaping of hot glass.
Glassblowing. The shaping of glass using air pressure.
Gob. A portion of hot glass that is delivered from the furnace for forming.
Hard Glass. A glass with a high softening point or high viscosity (usually borosilicate).
Hot End. A manufacturing term for the area of a glass manufacturing plant where molten glass is processed.
Lampworking. Flame re-working of a blank or tubing cane, typically on a lathe.
Lehr. A long belt-fed, tunnel-shaped oven used to heat glass to the annealing point and then slowly cool it to room temperature to remove any residual thermal stresses in the glass. Can also be a large oven where glass is manually loaded and unloaded (batch lehr).
Linear Coefficient of Expansion. The fractional change in length of a piece of glass per degree change in temperature. The coefficient of expansion generally indicates the thermal endurance of the glass. Glasses with a low linear coefficient of expansion can be subjected to greater rapid temperature changes with less chance of fracture than glasses with a high coefficient of expansion. (Generally, Type I glasses have a lower COE than Type III).
Melt. The amount of glass that is melted at one time.
Mold Mark. The mark in the bottom of the container that denotes the manufacturer.
Pressed Glass. Glassware that is formed by pressing a gob between a mold and a plunger.
Soda-Lime (or Soft) Glass. A glass with a substantial portion of lime in the formula.
Softening Point. Temperature at which a thread or rod of glass rapidly deforms under its own weight.
Strain Point. The temperature at which thermal residual stresses become permanent upon cooling. Temperatures above the strain point will introduce permanent stresses that can cause or contribute to fracture. At temperatures below the strain point, the glass can be temporarily heated and cooled without introducing permanent stress. The strain point can be considered the maximum service temperature.
Tank. The furnace that melts the raw materials into molten glass. Temperatures in the tank vary depending on the glass type being melted, but are typically in excess of 1,200°C.
Temper. The degree of residual stress in annealed glass as measured using polarized light techniques.
Weathering The attack on glass surface by atmospheric elements.
RAW
MATERIALS FOR GLASS MANUFACTURING:
CONSUMPTION
RATIO OF RAW MATERIAL (IN TERM OF QUANTITY)
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