The Ingenious Design of the Aluminum Beverage Can

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the ingenious design of the aluminum

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beverage gap every year nearly a half

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trillion of these cans are manufactured

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that's about 15,000 per second so many

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that we overlook the cans superb

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engineering let's start with why the can

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is shaped like it is why a cylinder an

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engineer might like to make a spherical

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can it has the smallest surface area for

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a given volume and so it uses the least

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amount of material and it also has no

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corners and so no weak points because

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the pressure in the can uniformly

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stresses the walls but a sphere is not

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practical manufacture and of course

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it'll roll off the table

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also when packed as closely as possible

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only seventy four percent of the total

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volume is taken up by the product the

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other twenty six percent is void space

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which goes unused when transporting the

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cans or in a store display an engineer

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could sell this problem by making a

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cuboid shaped cam it sits on a table but

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it's uncomfortable to hold and awkward

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to drink from and well easier to

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manufacture those sphere these edges are

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weak voids and require very thick walls

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but the cuboid surpasses the sphere and

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packing efficiency it is almost no

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wasted space although with the sacrifice

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of using more surface area to contain

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the same volume as the sphere so to

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create a can engineers use a cylinder

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which has elements of both shapes from

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the top it's like a sphere and from the

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side it's like a cuboid a cylinder has a

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maximum packing factor of about 91

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percent not as good as the cuboid bit

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better than the sphere most important of

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all the cylinder can be rapidly

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manufactured the can begins as this disc

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called a blank punch from an aluminum

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sheet about three tenths of a millimeter

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thick the first step starts with a

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drawing die on which sits the blank and

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then a blank holder that rests on top

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well look at a slice of the die so we

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can see what's happening a cylindrical

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punch presses down on the die forming

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the blank into a cup this process is

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called drawing this cup is about 88

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millimeters in diameter larger than the

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final can

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so it's redrawn that process starts with

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this white cup and uses another

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cylindrical punch and a redrawing die

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the punch presses the cup through the

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redrawing die and transforms it into a

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cup with a narrower diameter which is a

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bit taller this redrawn Cup is now the

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final diameter of the can 65 millimeters

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but it's not yet tall enough a punch

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pushes this redrawn Cup through an

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ironing ring the cup stays the same

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diameter as it becomes taller on the

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walls thinner if we watch this process

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again up close you see the initial thick

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wall and then the thinner wall after

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it's ironed ironing occurs in three

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stages

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each progressively making the walls

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thinner and the kam taller after the cup

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is ironed the dome on the bottom is

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formed this requires a convex doming

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tool and a punch with a matching concave

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indentation as the punch presses the cup

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downward into the doming tool the cup

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bottom then deforms into a dome that

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dome reduces the amount of metal needed

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to manufacture the can the dome bottom

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uses less material than if the bottom

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were flat a dome is an arch revolved

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around its inner the curvature of the

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arch distributes some of the vertical

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load into horizontal forces allowing a

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dome to withstand greater pressure than

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a flat beam on the dome you might notice

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two large numbers these de bas numbers

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are engraved on the doming tool the

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first number signifies the production

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line in the factory and the second

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number signifies the body maker number

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the body maker is the machine that

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performs the redrawing ironing and

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doming processes these numbers help

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troubleshoot production problems in the

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factory in that factory the

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manufacturing of can takes place at a

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tremendous rate these last three steps

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redrawing ironing and doming all happen

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in one continuous stroke in an only 1/7

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of a second the punch moves at a maximum

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velocity of 11 meters per second and

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experiences a maximum acceleration of 45

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G's this process runs continuously for

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six months for around a hundred million

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cycles before the machine needs

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servicing now if you look closely at the

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top of the cam body you see that the

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edges are wavy and uneven these

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irregularities occur during the forming

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to get a nice even edge about six

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millimeters is trimmed off of the top

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with an even top

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Han could now be sealed but before that

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sealing occurs a colorful design is

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printed on the outside the term of art

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in the industry is a decoration the

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inside also gets a treatment a spray

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coated epoxy lacquer separates the cans

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contents from its aluminum walls this

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prevents the drink from acquiring a

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metallic taste and also keeps acids in

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the beverage from dissolving the

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aluminum the next step forms the cans

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neck the part of the can body that

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tapers inward this necking requires 11

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stages the forming starts with a

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straight walled cannon the top has

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brought slightly inward and then this is

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repeated further up a Ken wall until the

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final diameter is reached the change in

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neck size at each stage is so subtle

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that you can barely tell a difference

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between one stage in the next each one

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of these stages works by inserting an

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inner die into the can body then pushing

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an outer dyeing called the necking

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sleeve around the outside the necking

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sleep attracts the inner diary tracks

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and the can moves to the next stage the

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neck has drawn out over many different

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stages to prevent wrinkling or pleading

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of the thin aluminum since the 1960's

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the diameter of the cannon has become

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smaller by six millimeters from 60

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millimeters to 54 millimeters today this

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seems a tiny amount but the aluminum can

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industry produces over 100 billion cans

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a year so that six millimeter reduction

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saves at least 90 million kilograms of

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aluminum annually that amount would form

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a solid cube of aluminum 32 meters on a

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side compare that to a 787 dreamliner

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with a 60 meter wingspan now after the

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neck has been formed the top is flanged

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that is it flares out slightly and

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allows the end to be secured to the body

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which brings us to the next brilliant

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design feature the double seam on older

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steel cans manufacturers welded or

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soldered on the ends this often

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contaminated the cans contents in

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contrast today's cans use a hygienic

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devil seam which can also be made faster

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this can is cut in half so you can see

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the cross-section of the double seam to

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create this scene a machine uses two

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basic operations

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the first curls the end of the can cover

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around the flange of the can body the

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second operation presses the folds of

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the metal together to form an airtight

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seal well the operation themselves are

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simple they require high precision parts

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misaligned by a small fraction of a

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millimeter caused the seam to fail in

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addition to the clamping of the end can

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body a sealing compound ensures that no

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gas escapes through the devil' seen the

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compound is applied as a liquid and

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hardens to form a gasket the end

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attached immediately after the can is

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filled traps gasses inside the can to

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create pressures of about 30 psi or 2

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times atmospheric pressure in soda

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carbon dioxide produces the pressure in

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non-carbonated drinks like juices

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nitrogen is added so why is a beverage

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can pressurized because the internal

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pressure creates a strong can despite

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it's thin walls squeeze a closed

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pressurized can it barely gives then

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squeeze an empty can it flexes easily

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the can walls are thin only 75 microns

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thick and they're flimsy but the

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internal pressure of a sealed can pushes

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outwards equally and so it keeps the

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wall in tension this tension is key the

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thin wall acts like a chain in

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compression it has no strength but in

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tension it's very strong the internal

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pressure strengthens the cans so that

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they can be safely stacked a pressurized

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can't easily supports the weight of an

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average human adult it also adds enough

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strength so the can doesn't need the

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corrugations like in this unpressurized

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steal food camp well initially

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pressurize to about two atmospheres a

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can may experience up to four

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atmospheres of internal pressure in its

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lifetime due to elevated temperatures

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and so the can is designed withstand up

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to six atmospheres or 90 psi before the

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dome or the end will buckle

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why is there a tab on the end of the can

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it seems a silly question how else would

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you open it but originally cans didn't

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have tabs very early steel cans were

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called flat tops for pretty obvious

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reasons you use a special opener to

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puncture a hole to drink from and a hold

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of it in the 1960s the pole tab was

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invented so that no opener

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needed the tab worked like this you lift

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up this ring to vent the can and pull

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the tab to create the opening easy

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enough but now you've got this loose tab

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the cans ask you to please don't litter

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but sadly these pull tabs got tossed on

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the ground with the sharp edges of the

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tabs cut the bare feet of beachgoers or

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they harmed wildlife so the beverage can

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industry responded by inventing the

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modern stay on tab this little tab

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involved clever engineering the tab

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starts as a second class lever this is

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like a wheelbarrow because the tip of

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the tab is the fulcrum and the rivet to

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load the effort is being applied on the

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end but here's the genius part the

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moment the canvas the tab switches to a

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first class lever which is like a seesaw

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where the load is now at the tip and the

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fulcrum is the rivet you can see clearly

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how the tab when working as a

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wheelbarrow lifts the rivet in fact part

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of the reason this clever design works

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is because the pressure inside the can

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helps to force the rivet up which in

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turn depresses the outer edge of the top

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until it Vince the can and then the tab

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changes to a seesaw lever looking from

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the inside of the can you can see how

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the tab first opens near the rivet if

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you try to simply force the scored metal

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section into the can using the tab as a

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first class lever with the rivet of the

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fulcrum throughout you'd be fighting the

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pressure inside the can the tab would be

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enormous and expensive if you'd like to

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learn more about the entire lifecycle of

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the aluminum can watch this animated

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video by wrexham that describes can

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manufacturing and recycling a typical

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aluminum can today contains about 70

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percent recycled material also

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discoveries how it's made as some great

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footage of the manufacturing machinery

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here are two different stepwise

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animations of the entire can farming

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process and lastly these are too

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detailed animations of the cup drawing

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and redrawing processes the aluminum

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beverage can is so ubiquitous that it's

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easy to take for granted but the next

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time you take a sip from one consider

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the decades of ingenious design required

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to create this modern engineering marvel

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I'm bill Hammack the engineer guy

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thanks to Wrexham for providing us with

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aluminum cans in various stages of

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production and thank you very much to

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the advanced viewers who's in detailed

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and useful responses for this video we

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