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= Steel_and_tin_cans =
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Introduction
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A steel can, tin can, tin (especially in British English, Australian
English, Canadian English and South African English), or can is a
container made of thin metal, for distribution or storage of goods.
Some cans are opened by removing the top panel with a can opener or
other tool; others have covers removable by hand without a tool. Cans
can store a broad variety of contents: food, beverages, oil,
chemicals, etc. In a broad sense, any metal container is sometimes
called a "tin can", even if it is made, for example, of aluminium.
Steel cans were traditionally made of tinplate; the tin coating
stopped the contents from rusting the steel. Tinned steel is still
used, especially for fruit juices and pale canned fruit. Modern cans
are often made from steel lined with transparent films made from
assorted plastics, instead of tin. Early cans were often soldered with
neurotoxic high-lead solders. High-lead solders were banned in the
1990s in the United States, but smaller amounts of lead were still
often present in both the solder used to seal cans and in the
mostly-tin linings.
Cans are highly recyclable and around 65% of steel cans are recycled.
History
======================================================================
The tin canning process was conceived by the Frenchman Philippe de
Girard, who had British merchant Peter Durand patent the idea in 1810.
The canning concept was based on experimental food preservation work
in glass containers the year before by the French inventor Nicholas
Appert. Durand did not pursue food canning, but, in 1812, sold his
patent to two Englishmen, Bryan Donkin and John Hall, who refined the
process and product, and set up the world's first commercial canning
factory on Southwark Park Road, London. By 1813 they were producing
their first tin canned goods for the Royal Navy. By 1820, tin
canisters or cans were being used for gunpowder, seeds, and
turpentine.
Early tin cans were sealed by soldering with a tin-lead alloy, which
could lead to lead poisoning. Automated soldering machines started to
arrive in the 1870s and steel started to displace iron as a material
for the cans at the very end of the 19th century. Locking side seam
was invented by Max Ams in 1888, giving the rise to a "sanitary can"
design, where the solder was found only on the outside of the can and
never touched the food. The modern three-piece design dates back to
1904 (Sanitary Can Company of New York).
In 1901 in the United States, the American Can Company was founded, at
the time producing 90% of the tin cans in the United States. It bought
out the Sanitary Can Company of New York in 1908, and the three-piece
design displaced all other cans by the early 1920s. The can saw very
little change since then, although better technology brought 20%
reduction in the use of steel, and 50% - in the use of tin (the modern
cans are 99.5% steel).
Canned food in tin cans was already quite popular in various countries
when technological advancements in the 1920s lowered the cost of the
cans even further. In 1935, the first beer in metal cans was sold; it
was an instant sales success. The production of these three-piece cans
by the American Can Company stopped for World War II due to lack of
material, after the war the first two-piece cans with no side seams
and a cone top were introduced. The use of aluminum started in 1958
with Primo beer.
About 600 different types of cans were used in the early 21st century,
with the most popular being the three-piece design with side seam and
two double-seamed ends, followed by the two-piece construction with
sides and bottom drawn as one piece.
Description
======================================================================
Most cans are right circular cylinders with identical and parallel
round tops and bottoms with vertical sides. However, in cans for small
volumes or particularly-shaped contents, the top and bottom may be
rounded-corner rectangles or ovals. Other contents may suit a can that
is somewhat conical in shape.
Fabrication of most cans results in at least one 'rim'--a narrow ring
slightly larger than the outside diameter of the rest of the can. The
flat surfaces of rimmed cans are recessed from the edge of any rim
(toward the middle of the can) by about the width of the rim; the
inside diameter of a rim, adjacent to this recessed surface, is
slightly smaller than the inside diameter of the rest of the can.
Three-piece can construction results in top and bottom rims. In
two-piece construction, one piece is a flat top and the other a
deep-drawn cup-shaped piece that combines the (at least roughly)
cylindrical wall and the round base. Transition between wall and base
is usually gradual. Such cans have a single rim at the top. Some cans
have a separate cover that slides onto the top or is hinged.
Two piece steel cans can be made by "drawing" to form the bottom and
sides and adding an "end" at the top: these do not have side seams.
Cans can be fabricated with separate slip-on, or friction fit covers
and with covers attached by hinges. Various easy opening methods are
available.
In the mid-20th century, a few milk products were packaged in nearly
rimless cans, reflecting different construction; in this case, one
flat surface had a hole (for filling the nearly complete can) that was
sealed after filling with a quickly solidifying drop of molten solder.
Concern arose that the milk contained unsafe levels of lead leached
from this solder plug.
Advantages of steel cans
======================================================================
A number of factors make steel cans useful containers for beverages.
Steel cans are stronger than cartons or plastic, and less fragile than
glass, protecting the product in transit and preventing leakage or
spillage, while also reducing the need for secondary packaging.
Steel and aluminium packaging offer complete protection against light,
water and air, and metal cans without resealable closures are among
the most tamper-evident of all packaging materials. Food and drink
packed in steel cans has equivalent vitamin content to freshly
prepared, without needing preserving agents. Steel cans also extend
the product's shelf-life, allowing longer sell-by and use-by dates and
reducing waste.
As an ambient packaging medium, steel cans do not require cooling in
the supply chain, simplifying logistics and storage, and saving energy
and cost. At the same time, steel's relatively high thermal
conductivity means canned drinks chill much more rapidly and easily
than those in glass or plastic bottles.
File:Fransk Linolja - 2021.jpg|A can of French linseed oil
File:Canned-air.jpg|Compressed gas with dispensing valve
File:Trevqrp.png|Flip-top can with hinged cover
File:Ronsonol Lighter Fluid.JPG|Can of lighter fluid
File:Yellow oil can.JPG|Special can for dispensing oil
File:Camp fuel.jpg|Camp stove fuel in "F-Style" can
File:Alkydharzlack.jpg|Paint can with double friction cover (plug)
File:Assorted biscuits Khong Guan.JPG|Can with slip-on cover
File:Boite de cirage Baranne ouverte.jpg|Can of shoe polish
File:Ridgways Assam Tea tin pic3.JPG|Tea tin
Tin
=====
No cans currently in wide use are composed primarily or wholly of tin.
Until the second half of the 20th century, almost all cans were made
of tinplate steel. The steel was cheap and structurally strong, but
prone to rust; the tin coating prevented the wet food from corroding
the steel. Corrosion-resistant coatings on almost all steel food cans
are now made from plastic, not tin. Some manufacturers use Vitreous
enamel, instead.
Dissolution of tin into the food
==================================
Tin is corrosion resistant, but acidic food like fruits and vegetables
can corrode the tin layer. Nausea, vomiting, and diarrhea have been
reported after ingesting canned food containing 200 mg/kg of tin. A
2002 study showed that 99.5% of 1,200 tested cans contained below the
UK regulatory limit of 200 mg/kg of tin - an improvement over most
previous studies, which was largely attributed to the increased use of
fully lacquered cans for acidic foods. They concluded that the results
do not raise any long term food safety concerns for consumers. The two
non-compliant products were voluntarily recalled.
Evidence of tin impurities can sometimes be indicated by discolored
food (pears, for example), but lack of color change does not guarantee
that a food is not tainted with tin.
Lead
======
Lead is harmful to health in any quantity, and more lead is more
harmful than less lead. Infants and children are more severely
affected, as lead harms brain development.
In November 1991, US can manufacturers voluntarily eliminated lead
seams in food cans. Imported food cans continued to include lead
soldered seams.
In 1995, the US FDA issued a rule prohibiting lead soldered food cans,
including both domestic and imported food cans. Unfortunately, the FDA
did not give a definition of "lead solder", or a quantitative limit to
permissible lead levels, and some solders and tin linings used on tin
cans still contained significant amounts of lead. In 2017,
quantitative limits were set, but they are high enough to permit
intentionally adding lead, and the FDA measurements show measurable
levels of lead in many US canned foods in the 2010s.
Plastic linings
=================
Many metal food cans are lined with plastic, to prevent the food from
corroding the can.
*
*Update on can lining changes
*Industry explainer These linings can leach contaminants into the
canned food. Some of these contaminants are substances with known
health harms, though whether they are ingested in canned food in
levels sufficient to cause harms is not known.
*UK Food Standards Agency is unsure of harms to humans.
*Review finding canned food consumption is a predictor of urine BPA.
*Market survey of the materials in can linings, including BPA-free
substitutes.
*Review discussing migration of contaminants in canned food from can
materials
*Update on can lining changes
*Washington State, in the US, looking at improving the safety of can
linings., and specifically
Among other substances, the plastic linings in food cans often contain
bisphenol A (BPA). Pregnant women who eat more canned food have higher
levels of BPA in their urine.
Other constituents in can linings, including newer BPA-free can
linings, have also been identified as having known health harms.
*Market survey of the materials in can linings, including BPA-free
substitutes.
*Review discussing migration of contaminants in canned food from can
materials
*Update on can lining changes
*Industry explainer
**an industry-run market survey showing only some cans imported to the
US now contain BPA, as of 2020.
*Washington State, in the US, looking at improving the safety of can
linings., and specifically
Bisphenol-A
=============
Bisphenol-A (BPA) is a controversial chemical compound present in
commercially available tin can plastic linings and transferred to
canned food. The inside of the can is coated with an epoxy coating, in
an attempt to prevent food or beverage from coming into contact with
the metal. The longer food is in a can, and the warmer and more acidic
it is, the more BPA leaches into it. In September 2010, Canada became
the first country to declare BPA a toxic substance. In the European
Union and Canada, BPA use is banned in baby bottles.
The FDA does not regulate BPA (see BPA controversy#Public health
regulatory history in the United States). Several companies, like
Campbell's Soup, announced plans to eliminate BPA from the linings of
their cans, but have not said which chemical they plan to replace it
with. (See BPA controversy#Chemical manufacturers reactions to bans.)
Canada
========
In 2016, BPA was common in food can linings in Canada. , Health
Canada's Food Directorate concluded that "the current dietary exposure
to BPA through food packaging uses is not expected to pose a health
risk to the general population, including newborns and infants". They
also stated that, as some animal studies had shown effects from low
levels of BPA, they were seeking to make BPA levels in food packaged
for infants and newborns (especially formula). They also cited a WHO
review.
UK
====
In modern times, the majority of food cans in the UK have been lined
with a plastic coating containing bisphenol A (BPA). The coating
prevents acids and other substances from corroding the tin or
aluminium of the can, but leaching of BPA into the cans contents was
investigated as a potential health hazard. The UK Food Standards
agency currently considers can-derived BPA levels to be acceptable,
but is investigating its safe-level thresholds; it currently has a
temporary threshold for BPA, .
US
====
A 2016 market survey using Fourier-transform infrared spectrums to
identify materials, found BPA and other substances known to have
health harms were common in food can linings in the US. A similar
survey done by food can manufacturers in 2020 found BPA only in some
imported cans; it did not discuss potential harms from lining
substances other than BPA.
*Market survey of the materials in can linings, including BPA-free
substitutes.
**CBC report on same
*Update on can lining changes
*Industry explainer
**an industry-run market survey showing only some cans imported to the
US now contain BPA, as of 2020.
*Washington State, in the US, looking at improving the safety of can
linings., and specifically
Labels
========
A can traditionally has a printed label glued to the outside of the
curved surface, indicating its contents. Some labels contain
additional information, such as recipes, on the reverse side. Labels
are sometimes printed directly onto the metal before or after the
metal sheet is formed into the individual cans.
Traditionally, labels were glued on with casein glue, which dissolved
easily in hot water. Some other glues may make the label harder to
remove for recycling.
Standard sizes
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Cans come in a variety of shapes and sizes. Walls are often stiffened
with rib bulges, especially on larger cans, to help the can resist
dents that can cause seams to split.
Can sizes in the United States have an assortment of designations and
sizes. For example, size 7/8 contains one serving of half a cup with
an estimated weight of 4 ounces; size 1 "picnic" has two or three
servings totalling one and a quarter cups with an estimated weight of
10 ounces; size 303 has four servings totalling 2 cups weighing 15
ounces; and size 10 cans, most widely used by food services selling to
cafeterias and restaurants, have twenty-five servings totalling 13
cups with an estimated weight of 103 ounces (size of a roughly 3 pound
coffee can). These are U.S. customary cups, not British Imperial
standard.
In the United States, cook books sometimes reference cans by size. The
Can Manufacturers Institute defines these sizes, expressing them in
three-digit numbers, as measured in whole and sixteenths of an inch
for the container's nominal outside dimensions: a 307 × 512 would thus
measure 3 and 7/16" in diameter by 5 and 3/4" (12/16") in height.
Older can numbers are often expressed as single digits, their contents
being calculated for room-temperature water as approximately eleven
ounces (#1 "picnic" can), twenty ounces (#2), thirty-two ounces (#3),
fifty-eight ounces (#5), and one-hundred-ten ounces (#10 "coffee"
can).
Can Name !! (inches) !! Capacity (U.S. fluid ounces) !! No. 2 can
equivalent !! Typical products
6Z 2 × 3 6.08 0.295
8Z Short 2 × 3 7.93 0.386
8Z Tall 2 × 3 8.68 0.422
No. I (Picnic) 2 × 4 10.94 0.532
No. 211 Cylinder 2 × 4 13.56 0.660
No. 300 3 × 4 15.22 0.741 Cranberry Sauce, Pork & Beans
No. 300 Cylinder 3 × 5 19.40 0.945
No. I Tall 3 × 4 16.70 0.813
No. 303 3 × 4 16.88 0.821 Fruits, Vegetables, Soups
No. 303 Cylinder 3 × 5 21.86 1.060
No. 2 Vacuum 3 × 3 14.71 0.716
No. 2 3 × 4 20.55 1.000 Juices, Soups, Vegetables
Jumbo 3 × 5 25.80 1.2537
No. 2 Cylinder 3 × 5 26.40 1.284
No. 1.25 4 × 2 13.81 0.672
No. 2.5 4 × 4 29.79 1.450 Fruits, Vegetables
No. 3 Vacuum 4 × 3 23.90 1.162
No. 3 Cylinder 4 × 7 51.70 2.515
No. 5 5 × 5 59.10 2.8744 Fruit Juice, Soups
No. 10 6 × 7 109.43 5.325 Fruits, Vegetables
In parts of the world using the metric system, tins are made in 250,
500, 750 ml (millilitre) and 1 L (litre) sizes (250 ml is
approximately 1 cup or 8 ounces). Cans imported from the US often
have odd sizes such as 3.8 L (1 US gallon), 1.9 L (1/2 US gallon), and
946 ml (2 US pints / 1 quart).
In the UK and Australia, cans are usually measured by net weight. A
standard size tin can holds roughly 400 g; though the weight can vary
between 385 g and 425 g depending on the density of the contents. The
smaller half sized can holds roughly 200 g, typically varying between
170 g and 225 g.
Fabrication of cans
======================================================================
Rimmed three-piece can construction involves several stages;
* Forming a tube and welding or soldering the seam of the sides
* Joining the bottom end to the tube
* Printing or attaching labels to the can
* Filling the can with content; sterilization or retorting is
required for many food products
* Joining the wall and top "end".
Double seam rims are crucial to the joining of the wall to a top or
bottom surface. An extremely tight fit between the pieces must be
accomplished to prevent leakage; the process of accomplishing this
radically deforms the rims of the parts. Part of the tube that forms
the wall is bent, almost at its end, turning outward through 90
degrees, and then bent further, toward the middle of the tube, until
it is parallel to the rest of the tube, a total bend of 180 degrees.
The outer edge of the flat piece is bent against this toward the
middle of the tubular wall, until parallel with the wall, turning
inward through 90 degrees. The edge of bent portion is bent further
through another 90 degrees, inward now toward the axis of the tube and
parallel to the main portion of the flat piece, making a total bend of
180 degrees. It is bent far enough inward that its circular edge is
now slightly 'smaller' in diameter than the edge of the tube. Bending
it yet further, until it is parallel with the tube's axis, gives it a
total bend of 270 degrees. It now envelops the outward rim of the
tube.
Looking outward from the axis of the tube, the first surface is the
unbent portion of the tube. Slightly further out is a narrow portion
of the top, including its edge. The outward-bent portion of the tube,
including its edge, is still slightly further out. Furthest out is the
90-degree-bent portion of the flat surface.
The combined interacting forces, as the portion of the flat surface
adjacent to the interior of the tube is indented toward the middle of
the tube and then outward 'forward' the axis of the tube, and the
other bent portions of the flat piece and the tube are all forced
'toward' the axis of the tube, drives these five thicknesses of metal
against each other from inside and out, forming a "dry" joint so tight
that welding or solder is not needed to strengthen or seal it.
Illustrations of this process can be found on pages 20-22 of the FAO
Fisheries Technical Paper 285 "Manual on fish canning".
Steel for can making
======================
The majority of steel used in packaging is tinplate, which is steel
that has been coated with a thin layer of tin, whose functionality is
required for the production process. The tin layer is usually applied
by electroplating.
Two-piece steel can design
============================
Most steel beverage cans are two-piece designs, made from 1) a disc
re-formed into a cylinder with an integral end, double-seamed after
filling and 2) a loose end to close it. Steel cans are made in many
different diameters and volumes, with opening mechanisms that vary
from ring pulls and tab openers, to wide open mouths.
Drawn-and-ironed (DWI) steel cans
===================================
The process of re-forming sheet metal without changing its thickness
is known as 'drawing'. Thinning the walls of a two-piece can by
passing it through circular dies is called 'ironing'. Steel beverage
cans are therefore generally referred to as drawn-and-ironed, or DWI,
cans (sometimes D&I). The DWI process is used for making cans
where the height is greater than the diameter, and is particularly
suited to making large volumes of cans of the same basic
specification.
Steel can wall thicknesses are now 30% thinner and weigh 40% less than
30 years ago, reducing the amounts of raw materials and energy
required to make them. They are also up to 40% thinner than aluminium.
Magnetic properties
=====================
Carbon steel is magnetic. For beverage packaging this is unique. This
allows the use of magnetic conveyor systems to transfer empty cans
through the filling and packing processes, increasing accuracy and
reducing potential spillage and waste. In recycling facilities, steel
cans may be readily separated from other waste using magnetic
equipment including cross-belt separators, also known as overband
magnets, and drum magnets.
Opening cans
======================================================================
The first cans were heavy-weight containers that required considerable
force to open, with instructions directing to use a hammer and chisel;
during the war of 1812, British soldiers resorted to bayonets and
knives to get them open. After an introduction of much thinner cans in
the 1850s, specialized opening tools became a practical possibility,
and were introduced in 1855 (Robert Yeates) and 1858 (Ezra J. Warner).
The latter unwieldy design saw limited use by soldiers in the American
Civil War. A push-lever opener similar to modern ones was introduced
in 1860 ("Bull's Head"), and one with a cutting wheel was invented in
1870 (William W. Lyman). A serrated wheel, which became common in
rotating can openers, was first used by the Star Can Opener Company in
1925.
While beverage cans or cans of liquid such as broth can be
punctured--as with a church key--to pour out the contents, solid or
semisolid contents require removing one end of the can. This can be
accomplished with a heavy knife or other sharp tool, but can openers
are safer, easier, and more convenient.
Some cans, such as those used for sardines, have a specially scored
lid so that the user can break out the metal by the leverage of
winding it around a slotted twist-key. Until the mid-20th century,
some sardine tins had solder-attached lids, and the twist-key worked
by forcing the solder joint apart.
The advent of pull tabs in beverage cans spread to the canning of
various food products, such as pet food or nuts (and non-food products
such as motor oil and tennis balls). The ends are known as 'easy open'
lids because they open without any tools or implements. An additional
innovation developed specifically for food cans uses a tab that is
bent slightly upwards, creating a larger surface area for easier
finger access.
Cans can be made with easy open features. Some cans have screw caps
for pouring liquids and resealing. Some have hinged covers or slip-on
covers for easy access. Paint cans usually have a lid with an
interference fit, removable and replaceable any number of times so the
paint may be stored between uses.
File:Dosenoeffner.silber2.png|Mechanism of a can opener
File:Euroshopper canned marrowfat peas.jpg|Can that requires a can
opener
File:Tomato soup in a can pull open top.jpg|Soup can with a ring-pull
tab
File:Can(Easy Open Can).JPG|Opened can with a ring-pull tab
File:Corned-beef-1.jpg|Keyed side opening
File:Sardines in a can.jpg|Easy open sardine can
File:POE Stay-on tab.jpg|Stay-on tab
Recycling and re-use
======================================================================
Steel from cans and other sources is the most recycled packaging
material. Around 65% of steel cans are recycled. In the United States,
63% of steel cans are recycled, compared to 52% of aluminium cans. In
Europe, the recycling rate in 2016 is 79.5%.
Most can recycling occurs at the smelters, but individual consumers
also directly reuse cans in various ways. For instance people can
create functional and decorative items for their home, from organizing
tools to making garden decor.
Steel recycling
=================
From an ecological perspective, steel may be regarded as a closed-loop
material: post-consumer waste can be collected, recycled and used to
make new cans or other products. Each tonne of scrap steel recycled
saves 1.5 tonnes of CO2, 1.4 tonnes of iron ore and 740 kg of coal.
Steel is the world's most recycled material, with more than 85% of all
the world's steel products being recycled at the end of their life: an
estimated 630 million tonnes of steel scrap were recycled in 2017,
saving 945 million tonnes of CO2.
Steel can recycling
=====================
A steel can can be recycled again and again without loss of quality;
however, for the food grade steel it's required to remove tin from the
scrap metal, which is done by way of electrochemistry: the tin is
leached from a high pH solution at low negative voltage.
Recycling a single can saves the equivalent power for one laundry
load, 1 hour of TV or 24 hours of lighting (10W LED bulb).
Steel beverage cans are recycled by being melted down in an electric
arc furnace or basic oxygen furnace.
Most steel cans also carry some form of recycling identification such
as the Metal Recycles Forever mark, Recyclable Steel, and the Choose
Steel campaign logo. There is also a campaign in Europe called Every
Can Counts, encouraging can recycling in the workplace.
Smaller carbon footprint
==========================
All beverage packaging creates CO2 emissions at every stage in the
production process, from raw material extraction, processing and
manufacture through to recycling. However, steel cans are an
ecological top performer, as cans can always be recycled. The steel
industry needs the used cans and will use them in the production of
new steel product. By recycling the cans and closing the loop, CO2
emissions are dramatically reduced. There is also the potential for
higher global steel recycling rates as consumers become more aware of
the benefits.
See also
======================================================================
* Albion metal
*Can collecting
* Drink can
* Oil can
* Tin box
* Tin can wall
General references, further reading
=====================================
*
[
https://www.tinplategroup.com/wp-content/uploads/2019/08/Guide-toTinplate.pdf
Guide to Tinplate]
*
* Soroka, W, 'Fundamentals of Packaging Technology', Institute of
Packaging Professionals (IoPP), 2002,
* Yam, K. L., 'Encyclopedia of Packaging Technology', John Wiley &
Sons, 2009,
*
External links
======================================================================
*[
https://archive.today/20121209102331/http://www.steeluniversity.org/content/html/eng/default.asp?catid=116&pageid=2081272389
Steeluniversity Packaging Module]
*[
https://web.archive.org/web/20081211190321/http://www.steel.org/AM/Template.cfm?Section=PDFs2&TEMPLATE=%2FCM%2FContentDisplay.cfm&CONTENTFILEID=1919
Steel industry fact sheet on food cans]
*
License
=========
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License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Steel_and_tin_cans
