The Ingenious Design of the Aluminum Beverage Can

Summary

The script explores the engineering marvel of the aluminum beverage can, explaining why it's cylindrical, not spherical or cuboid, despite those shapes' theoretical advantages. It details the can's manufacturing process, from blank punching to drawing, redrawing, ironing, and doming, emphasizing the can's efficient material use and rapid production. The script also highlights the can's innovative features, such as the double seam and the stay-on tab, and touches on the importance of recycling, noting that most cans contain a significant amount of recycled material.

Takeaways

• 🔢 Every year, nearly half a trillion cans are manufactured, averaging 15,000 per second.
• 🔍 The can is shaped as a cylinder because it combines the material efficiency of a sphere and the practicality of a cuboid.
• 🛠️ Manufacturing a can involves a process of drawing, redrawing, ironing, and doming to form the can body.
• 🔩 The can's bottom is domed to distribute pressure and reduce the amount of material needed.
• 🏭 The production process is highly automated, with certain steps happening in a fraction of a second.
• ⚙️ The can body is made from a thin aluminum sheet which is punched and shaped into a can.
• 🎨 The can is decorated with a colorful design and has an epoxy lacquer coating on the inside to prevent metallic taste.
• 🌐 The neck of the can is formed through a process called necking, which involves multiple stages to prevent wrinkling.
• 🔗 The double seam is a key feature that ensures a hygienic and secure seal for the can.
• 💨 The internal pressure inside the can strengthens the thin walls, allowing it to support significant weight.
• 🔑 The modern stay-on tab is a result of clever engineering to replace the older pull-tab design, addressing environmental concerns.

Q & A

How many cans are manufactured each year, and how does this rate compare to the speed of production?

Nearly half a trillion cans are manufactured each year, which is about 15,000 cans per second.

Why are cans shaped like cylinders instead of spheres or cuboids?

Cans are shaped like cylinders because spheres, while efficient in material use, are impractical to manufacture and unstable when placed on a surface. Cuboids, while efficient in packing, are uncomfortable to hold and drink from, and have weak points that require thicker walls. Cylinders combine the best of both shapes, offering a balance between material use and practicality.

What is the maximum packing factor of a cylinder-shaped can?

A cylinder-shaped can has a maximum packing factor of about 91%, which is better than a sphere but not as efficient as a cuboid.

How is the initial can shape formed and what is this process called?

The initial can shape is formed by pressing a blank, which is a disk punched from an aluminum sheet, into a cup using a cylindrical punch and a process called 'drawing.'

What is the purpose of re-drawing and ironing in the can manufacturing process?

Re-drawing is used to reduce the diameter of the cup to the final can size, while ironing is used to make the walls thinner and the can taller without changing the diameter.

Why is a dome formed at the bottom of the can?

A dome is formed at the bottom of the can to reduce the amount of metal needed and to distribute some of the vertical load into horizontal forces, allowing the can to withstand greater pressure.

What do the debossed numbers on the dome signify?

The debossed numbers on the dome signify the production line in the factory and the bodymaker number, which is the machine that performs the redrawing, ironing, and doming processes. These numbers help troubleshoot production problems.

How quickly does the can manufacturing process occur?

The last three steps of can manufacturing—re-drawing, ironing, and doming—all happen in one continuous stroke and in only a seventh of a second.

What is the purpose of the spray-coated epoxy lacquer applied to the inside of the can?

The spray-coated epoxy lacquer is applied to the inside of the can to separate the contents from the aluminum walls, preventing the drink from acquiring a metallic taste and keeping acids in the beverage from dissolving the aluminum.

How has the necking process evolved since the 1960s, and what is its significance?

Since the 1960s, the diameter of the can end has become smaller by 6 mm, from 60 mm to 54 mm today. This reduction saves at least 90 million kilograms of aluminum annually, which is significant in the context of the aluminum can industry's massive production volume.

What is the purpose of the double seam in can manufacturing?

The double seam is a hygienic and faster method of sealing the can compared to older welding or soldering techniques. It creates an airtight seal that prevents contamination of the can's contents.

Why is the beverage can pressurized?

The internal pressure in a beverage can creates strength in the thin walls, allowing the can to support weight and maintain its shape without needing additional structural support like corrugations.

What is the function of the tab on the end of the can?

The tab on the end of the can is used to open the can by venting it and creating an opening for consumption. It has evolved from the pull-tab to the modern stay-on tab to prevent litter and injury from sharp edges.

Outlines

00:00

🔵 Can Design and Manufacturing

The paragraph discusses the manufacturing of cans and the engineering behind their design. It explains why cans are cylindrical rather than spherical or cuboid, despite the latter two options having certain advantages. Cans are made from aluminum sheets, and the process begins with a 'blank' that is drawn into a cup shape. This cup is then re-drawn to the correct diameter and ironed to achieve the desired height and wall thickness. The bottom of the can is domed to distribute pressure and reduce material use. The manufacturing process is rapid, with the final stages of re-drawing, ironing, and doming happening in quick succession. The paragraph also touches on the importance of the can's design for efficient packing and transportation.

05:04

🔩 The Evolution of Can Necking and Seams

This paragraph delves into the process of forming the can's neck and the development of the double seam, which is a key feature for sealing the can. The necking process involves multiple stages to prevent the aluminum from wrinkling. The paragraph also highlights the reduction in can end diameter over time, which has led to significant material savings. The double seam is described as a hygienic and efficient method of sealing compared to older methods, and the paragraph explains how the seam is created and the importance of precision in its manufacture. The internal pressure within the can is also discussed, explaining how it strengthens the can and allows for thinner walls.

10:06

🔨 The Stay-On Tab and Can Lifecycle

The final paragraph discusses the history and engineering of the can's opening mechanism, specifically the pull-tab and its evolution into the stay-on tab. It explains the mechanical advantage used by the tab and how the internal pressure of the can assists in the opening process. The paragraph also touches on the environmental impact of cans, mentioning the high percentage of recycled material used in modern cans and providing resources for further learning about can manufacturing and recycling.

Keywords

💡Cylinder

A cylinder is the shape chosen for modern beverage cans because it combines the structural advantages of a sphere with the practical packing efficiency of a cuboid. Cylinders offer stability, are easier to manufacture, and can withstand the internal pressure of the beverage while minimizing the amount of material used. The video highlights how a cylinder strikes a balance between strength and efficient use of space.

💡Dome

The dome is the concave bottom of the can, designed to reduce material use while still providing structural integrity. The dome allows the can to withstand high internal pressures by distributing vertical loads into horizontal forces. This ensures the can remains strong despite its thin walls, preventing it from buckling under pressure.

💡Redrawing

Redrawing is a process in can manufacturing where a cylindrical punch is used to resize a larger cup into a smaller one with the desired diameter for the can. This stage is crucial to forming the final shape of the can, ensuring the proper size before the walls are thinned through ironing. It is one of the high-speed processes used to efficiently mass-produce cans.

💡Ironing

Ironing is the stage in can manufacturing where the walls of the can are made thinner and the can is elongated to its final height. The cup passes through several ironing rings that progressively reduce the wall thickness while maintaining the same diameter. This process is necessary to make the can lightweight without compromising its strength.

💡Necking

Necking refers to the process of shaping the top of the can to taper inward, allowing the smaller can end to be fitted securely. This stage requires multiple steps to avoid wrinkling the thin aluminum. The reduction in can end diameter over the years has saved substantial amounts of aluminum across billions of cans produced.

💡Double Seam

The double seam is a precise, hygienic way to seal the top of the can to the body, ensuring an airtight closure. The seam is formed by curling the end of the can cover around the body flange and pressing the metals together. The video emphasizes the importance of this design in creating a reliable and safe seal that prevents contamination or gas escape.

💡Pressurization

Pressurization refers to the internal pressure inside the can, which strengthens the thin walls and prevents the can from collapsing. The internal pressure is usually caused by carbon dioxide in sodas or nitrogen in non-carbonated drinks. This pressure ensures that the can remains rigid and can support weight, despite its thin aluminum construction.

💡Tab Mechanism

The tab mechanism is a key feature of modern beverage cans that allows the can to be opened easily without detaching the tab. It operates first as a second-class lever to vent the can and then as a first-class lever to fully open it. This design solves the problem of littering and safety concerns associated with older pull-tabs, which were often discarded after opening.

💡Epoxy Lacquer

Epoxy lacquer is a coating applied to the inside of the can to prevent the beverage from reacting with the aluminum, which could alter the taste or cause corrosion. This coating is essential for maintaining the quality and safety of the drink inside, particularly for acidic beverages like soda.

💡Recycling

Recycling is a major theme in the video, highlighting that modern aluminum cans are made with about 70% recycled material. The can's design and material efficiency make aluminum highly recyclable, and this contributes to significant savings in energy and raw materials, with a measurable impact on environmental sustainability.

Highlights

Nearly a half trillion cans are manufactured annually, averaging about 15,000 per second.

Cans are cylindrical for practical manufacturing and handling, despite spheres having the smallest surface area.

Spherical cans are impractical due to rolling off tables and inefficient packing, occupying only 74% of volume.

Cuboid-shaped cans are easier to manufacture than spheres but have weak edges and require thicker walls.

Cylinders are chosen for cans as they combine the benefits of both spheres and cuboids, with a 91% packing factor.

The can manufacturing process begins with a disk called a 'blank' punched from an aluminum sheet.

The 'drawing' process forms the blank into a cup, which is then re-drawn to the final can diameter.

Ironing the cup makes the walls thinner and the can taller in three stages, maintaining the diameter.

The dome bottom of the can is formed using a doming tool, reducing material use and enabling greater pressure resistance.

Debossed numbers on the dome are for production line and bodymaker identification, aiding in quality control.

Cans are manufactured at a high rate with the last three steps happening in under a second.

The can's edge is evened by trimming 6mm off the top to prepare it for sealing.

Cans are coated with epoxy lacquer on the inside to prevent metallic taste and protect from beverage acids.

The can's neck is formed through an eleven-stage process to prevent wrinkling in the thin aluminum.

The can end diameter has shrunk by 6mm since the 1960s, saving at least 90 million kilograms of aluminum annually.

Modern cans use a hygienic double seam for securing the end, avoiding contamination.

Pressurized cans are strong due to the internal pressure keeping the thin walls in tension.

The pull-tab was invented in the 1960s, but environmental concerns led to the modern stay-on tab.

The stay-on tab uses a second class lever mechanism initially, then switches to a first class lever post-venting.

Aluminum cans contain about 70% recycled material, highlighting their sustainability.

Transcripts

Every year nearly a half trillion of these cans are manufactured—that’s about 15,000

per second — so many that we overlook the can’s superb engineering. Let’s start

with why the can is shaped like it is. Why a cylinder? An engineer might like to make

a spherical can: it has the smallest surface area for a given volume and so it uses the least

amount of material. And it also has no corners and so no weak points because the pressure

in the can uniformly stresses the walls. But a sphere is not practical to manufacture.

And, of course, it’ll roll off the table. Also, when packed as closely as possible only

74% of the total volume is taken up by the product. The other 26% is void space, which

goes unused when transporting the cans or in a store display. An engineer could solve

this problem by making a cuboid-shaped can. It sits on a table, but it’s uncomfortable

to hold and awkward to drink from. And while easier to manufacture than a sphere, these

edges are weak points and require very thick walls. But the cuboid surpasses the sphere

in packing efficiently: it has almost no wasted space, although at the sacrifice of using

more surface area to contain the same volume as the sphere. So, to create a can engineers

use a cylinder, which has elements of both shapes. From the top, it’s like a sphere,

and from the side, it’s like a cuboid .A cylinder has a maximum packing factor of about

91% -- not as good as the cuboid, but better than the sphere. Most important of all: the

cylinder can be rapidly manufactured. The can begins as this disk —called a “blank”—

punched from an aluminum sheet about three-tenths of a mm thick. The first step starts with

a “drawing die,” on which sits the blank and then a “blank holder” that rests on

top. We’ll look at a slice of the die so we can see what’s happening. A cylindrical

punch presses down on the die, forming the blank into a cup. This process is called “drawing.”

This cup is about 88 mm in diameter—larger than the final can — so it’s re-drawn.

That process starts with this wide cup, and uses another cylindrical punch, and a “redrawing

die.” The punch presses the cup through the redrawing die and transforms it into a

cup with a narrower diameter, which is a bit taller. This redrawn cup is now the final

diameter of the can—65 mm—but it’s not yet tall enough. A punch pushes this redrawn

cup through an ironing ring. The cup stays the same diameter, as it becomes taller and

the walls thinner. If we watch this process again up close, you see the initial thick

wall, and then the thinner wall after it’s ironed. Ironing occurs in three stages, each

progressively making the walls thinner and the can taller. After the cup is ironed, the

dome on the bottom is formed. This requires a convex doming tool and a punch with a matching

concave indentation. As the punch presses the cup downward onto the doming tool: the

cup bottom then deforms into a dome. That dome reduces the amount of metal needed to

manufacture the can. The dome bottom uses less material than if the bottom were

flat. A dome is an arch, revolved around its center. The curvature of the arch distributes

some of the vertical load into horizontal forces, allowing a dome to withstand greater

pressure than a flat beam. On the dome you might notice two large numbers. These debossed

numbers are engraved on the doming tool. The first number signifies the production line

in the factory, and the second number signifies the bodymaker number -- the bodymaker is the

machine that performs the redrawing, ironing and doming processes. These numbers help troubleshoot

production problems in the factory. In that factory the manufacturing of a can takes place

at a tremendous rate: these last three steps— re-drawing, ironing and doming—all happen

in one continuous stroke and in only a seventh of a second. The punch moves at a maximum

velocity of 11 meters per second and experiences a maximum acceleration of 45 Gs. This process

runs continuously for 6 months or around 100 million cycles before the machine needs servicing.

Now, if you look closely at the top of the can body, you see that the edges are wavy

and uneven. These irregularities occur during the forming. To get a nice even edge, about

6 mm is trimmed off of the top. With an even top the can can now be sealed. But before

that sealing occurs a colorful design is printed on the outside—the term of art in the industry

is “decoration.” The inside also gets a treatment: a spray-coated epoxy lacquer

separates the can’s contents from its aluminum walls. This prevents the drink from acquiring

a metallic taste, and also keeps acids in the beverage from dissolving the aluminium.

The next step forms the can’s neck — the part of the can body that tapers inward. This

“necking” requires eleven-stages. The forming starts with a straight-walled can.

The top is brought slightly inward. And then this is repeated further up the can wall until

the final diameter is reached. The change in neck size at each stage is so subtle that

you can barely tell a difference between one stage and the next. Each one of these stages

works by inserting an inner die into the can body, then pushing an outer die—called the

necking sleeve—around the outside. The necking sleeve retracts, the inner die retracts, and

the can moves to the next stage. The necking is drawn out over many different stages to prevent wrinkling,

or pleating, of the thin aluminum. Since the 1960’s, the diameter of the can end has

become smaller by 6 mm — from 60 mm to 54 mm today. This seems a tiny amount, but the

aluminum can industry produces over 100 billion cans a year, so that 6 mm reduction saves

at least 90 million kilograms of aluminum annually. That amount would form a solid cube

of aluminum 32 meters on a side—compare that to a 787 dreamliner with a 60 meter wingspan.

Now, after the neck has been formed the top is flanged; that is, it flares out slightly

and allows the end to be secured to the body, which brings us to the next brilliant design

feature: the double seam. On older steel cans manufactures welded or soldered on the ends.

This often contaminated the can’s contents. In contrast, today’s cans use a hygienic

“double seam,” which can also be made faster. This can is cut in half so you can

see the cross-section of the double seam. To create this seam, a machine uses two basic

operations. The first curls the end of the can cover around the flange of the can body.

The second operation presses the folds of metal together to form an air-tight seal.

While the operations themselves are simple, they require high precision. Parts misaligned

by a small fraction of a millimeter cause the seam to fail. In addition to the clamping

of the end and can body, a sealing compound ensures that no gas escapes through the double

seam. The compound is applied as a liquid, then hardens to a form a gasket. The end,

attached immediately after the cans is filled, traps gases inside the can to create pressures

of about 30 psi or 2 times atmospheric pressure. In soda, carbon dioxide produces the pressure;

in non-carbonated drinks, like juices, nitrogen is added. So why is a beverage can pressurized?

Because the internal pressure creates a strong can despite its thin walls. Squeeze a closed,

pressurized can—it barely gives. Then squeeze an empty can—it flexes easily. The cans

walls are thin—only 75 microns thick—and they are flimsy, but the internal pressure

of a sealed can pushes outwards equally, and so keeps the wall in tension. This tension

is key: the thin wall acts like a chain — in compression it has no strength, but in tension

it’s very strong. The internal pressure strengthens the cans so that they can be safely stacked

—a pressurized can easily supports the weight of an average human adult. It also

adds enough strength so that the can doesn’t need the corrugations like in this unpressurized

steel food can. While initially pressurized to about 2 atmospheres, a can may experience

up to 4 atmospheres of internal pressure in its lifetime due to elevated temperatures;

and so the can is designed to withstand up to 6 atmospheres or 90 psi before the dome

or the end will buckle. Why is there a tab on the end of the can? It seems a silly question—how

else would you open it? But originally cans didn’t have tabs. Very early steel cans

were called flat tops, for pretty obvious reasons. You use a special opener to puncture

a hole to drink from, and a hole to vent. In the 1960’s, the pull-tab was invented

so that no opener was needed. The tab worked like this: you lift up this ring to vent the

can, and pull the tab to create the opening. Easy enough, but now you’ve got this loose

tab. The cans ask you to “Please don’t litter” but sadly, these pull tabs got tossed

on the ground, where the sharp edges of the tabs cut the barefeet of beachgoers—or they

harmed wildlife. So, the beverage can industry responded by inventing the modern stay-on

tab. This little tab involved clever engineering. The tab starts as a second class lever; this

is like a wheelbarrow because tip of the tap is the fulcrum and the rivet the load — the

effort is being applied on the end. But here’s the genius part: the moment the can vents

the tab switches to a first class lever which is like a seesaw: where the load is now at

the tip and the fulcrum is the rivet. You can see clearly how the tab, when working

as a wheelbarrow, lifts the rivet. In fact, part of the reason this clever design works

is because the pressure inside the can helps to force the rivet up, which in turn depresses

the outer edge of the top until it vents the can and then the tab changes to a seesaw lever.

Looking from the inside of the can, you can see how the tab first opens near the rivet.

If you tried to simply force the scored metal section into the can using the tab as a first

class lever with the rivet as the fulcrum throughout you'd be fighting the pressure

inside the can: the tab would be enormous, and expensive. If you’d like to learn more

about the entire lifecycle of the aluminum can, watch this animated video by Rexam that

describes can manufacturing and recycling. A typical aluminum can today contains about

70% recycled material. Also, Discovery’s How It’s Made has some great footage of

the manufacturing machinery. Here are two different stepwise animations of the entire

can forming process. And lastly, these are two detailed animations of the cup drawing

and redrawing processes. The aluminum beverage can is so ubiquitous that it’s easy to take

for granted. But the next time you take a sip from one, consider the decades of ingenious

design required to create this modern engineering marvel. I’m Bill Hammack, the engineer guy.

Thanks to Rexam for providing us with aluminum cans in various stages of production. And

thank you very much to the advanced viewers who sent detailed and useful responses for

this video. We read every single comment. If you’d like you to help out as an advanced

viewer check out www.engineerguy.com/preview. You can see upcoming projects and behind-the-scene

footage. For example, you can see a early drafts of this beverage can video. And you

can sign up there to become an advance viewer. Thanks again.