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layer) but is less resistant to corrosion than tinplate.

TFS is not used in three-piece cans, because it cannot

be soldered by traditional techniques, nor in DWI

two-piece cans because its hard and rough surface

makes drawing operations in uncoated metal imprac-

ticable. Therefore, TFS is frequently used for can ends

and DRD two-piece cans.

0009 Aluminum is a light metal, easy to work through-

out most of the conventional can-forming processes.

Aluminum is used for two-piece containers only, DWI

and singly or multiply drawn cans, but it is also

formed into easy-open ends. Aluminum cans may

also be formed by impact extrusion, this type of can

normally being used for monobloc aerosols.

0010 Aluminum body stock is available in a range of

thicknesses from 0.25 to 0.30 mm, whereas end

stock covers the range from 0.30 to 0.38 mm. Most

commercial applications of aluminum require special

properties that the pure metal cannot provide. There-

fore, alloying agents are added to impart strength,

improve formability, and influence corrosion charac-

teristics. A wide range of alloys are commercially

available for packaging applications, depending on

the container design and fabrication method being

used. The alloys are identified by four-digit numbers

where the value of the first digit indicates the alloy

type and the principal alloying ingredient. For

example: 2xxx for copper, 3xxx for manganese,

4xxx for silicon, and 5xxx for magnesium. Series

1xxx represents aluminum with 99.00% or higher

purity. Commercially pure aluminum (types 1100

and 1050) is used for the manufacture of foil and

extruded containers since it is the least susceptible to

work hardening. For rigid packaging, the alloy elem-

ents used are manganese and magnesium (alloy types

3004 and 5184). When the aluminum surface is ex-

posed to the atmosphere, a layer of aluminum oxides

is naturally formed, which protects the metal from

further oxidation. This self-protecting characteristic

gives the aluminum its high resistance to corrosion,

unless it is exposed to some substance that destroys

this passivation layer. Aluminum will corrode on con-

tact with products with a pH lower than 4 or higher

than 9, and when used for manufacturing cans for

food and beverage products, it is always coated with a

organic lacquer in the internal surface.

Manufacturing Processes

0011Steel and aluminum are initially in coil form, so sheet

cutting is often the first manufacturing process. This

operation can be performed by the can-maker if coil

cut-up lines are available in the plant. Otherwise,

material must be acquired already in sheet form.

Sheets to be used for the production of can ends or

round DRD cans are scroll-cut (Figure 4). This is a

method used to cut coil into sheets in a pattern, which

reduces metal wastage. It enables circular blanks to

be packaged more densely: skeleton scrap is reduced

by a third compared with straight-cut sheet.

Three-piece Cans

0012Starting with metal sheets, rectangular in format and

with dimensions suiting the can body size (Figure 5a),

Differential coating (identification on heavier coated side)

D 8.4/5.6

D 11.2/5.6

D 2.8/1.1

[mm]

D 5.6/2.8

D 11.2/2.8

D 8.4/2.8

25.4

38.0

38.0 12.7

50.8

38.0

25.4

12.7

Equal coating

E 2.8/2.8

E 5.6/5.6

E 8.4/8.4

E 11.2/11.2

fig0003 Figure 3 Tin coating weights.

826 CANNING/Cans and their Manufacture

the sheets are coated on the side that will become the

internal surfaces of the finished cans (Figure 5b). This

special lacquer protects the can itself from corrosion

and limits the interaction between the contents and

the metal. However, welding margins should be left

uncoated since the polymeric nature of the lacquer

would influence the electric current passage through

the metal (see details below). The lacquer is cured as

sheets pass in an oven (Figure 5c). The sheet may also

be printed for decoration on the other side, unless a

paper label is to be used.

0013The sheets are fed into a slitter, where they are cut

into body can blanks (Figure 5d). The blank is then

fed to the forming rolls, which generate a cylinder

with the edges of the side seam (Figure 5e). The

cylinder edges are welded by squeezing them together

whilst passing an electric current through them

(Figure 5f). This heats up the metal sufficiently for a

sound join to be made. To protect the weld seam, a

coating is applied immediately after the can body

exits the welder, in both sides of the side seam

(Figure 5g). Powder coating is usually applied electro-

statically to the interior of the side seam.

0014The cans are passed through a flanger, where the

top and bottom of the can are flanged outwards to

accept the ends (Figure 5h). Ends, produced else-

where, are seamed to the can bodies to close one

end (called the ‘maker’s end’) of every can (Figure 5i).

0015Depending on the can design, cans are passed

through a beader, where the walls of the cans have

circumferential beads formed (Figure 5j). Beading of

the can body wall, although reducing the top-load

resistance of the can, allows for a reduction in wall

thickness without sacrificing paneling performance.

0016Testing is performed with high-pressure air to

detect pinholes and poor seams on every can, and

the finished can bodies are then transferred to the

warehouse to be automatically palletized before

delivery to the filling plant.

DWI Two-piece Cans

0017Aluminum or steel coil (Figure 6a) is lubricated with a

thin film of oil and then fed continuously through a

cupping press (Figure 6b), which stamps and draws

disks into cups at a rate of more than 1500 cans per

(a) (b) (c) (d) (e)

(f) (g) (h) (i) (j)

fig0005 Figure 5 Three-piece can-manufacturing process.

Scroll-cut sheet

Straight-cut sheet

Width across coil

Length

of cut

sheet

Length

of cut

sheet

(b)

(a)

fig0004 Figure 4 Comparison between scroll and straight cut sheet.

CANNING/Cans and their Manufacture 827

minute. Each cup is rammed through a series of tung-

sten carbide rings for drawing and ironing. This pro-

cess redraws the cup to smaller diameter and thins

the walls, whilst increasing the height leading to

untrimmed cans (Figure 6c).

0018 Trimmers remove the surplus irregular edge and

cut each can to a precise specified height (Figure 6d).

The trimmed can bodies are passed through washers

(Figure 6e) for removal of all traces of lubricant

and then dried in preparation for internal and exter-

nal coatings. The clean cans are coated externally

(Figure 6f) with a clear or pigmented base coat,

which forms a good surface for the printing inks.

The cans pass through a hot air oven to dry the

lacquer (Figure 6g).

0019 The next step is the application of the print

design in up to six colors, and a varnish, by a highly

sophisticated printer/decorator (Figure 6h). A coat

of varnish is also applied to the base of each can

by the rim coater (Figure 6i). The cans pass through

a second oven, which dries the ink and the

varnish. Spray machines apply an internal coating of

protective lacquer (Figure 6j) to maintain product

quality, and the cans are then dried in the final oven

(Figure 6k).

0020The cans are passed through a necker/flanger

(Figure 6l), where the diameter of the body is reduced

(necked in), and the tops of the cans are flanged out-

wards to accept the ends after the cans have been filled.

0021Every can is tested at each stage of manufacture. At

the final stage, they pass through a light tester, which

automatically rejects any can with pinholes or frac-

tures (Figure 6m). Cans are then moved to the ware-

house for palletizing and delivery to the filling plant

together with the ends.

DRD Two-piece Cans

0022This process is similar to the DWI process, except that

the final height and diameter of the container are

produced by sequentially drawing cups to a smaller

diameter, i.e., causing metal to flow from the base to

the wall of the container rather than ironing the con-

tainer wall. The wall and base thickness of DRD cans,

as well as the surface area, are identical to the original

blank, as opposed to the DWI cans, where the wall

thickness is much lower than the base thickness

(Figure 7).

0023The process starts with blanking and cupping, in

which cups are produced from prescrolled sheets,

lacquered, and/or decorated. The cups then go

(a) (b) (c) (d)

(e) (f) (g) (h)

(i) (j) (k) (l)

(m) (n) (o) (p)

fig0006 Figure 6 Two-piece DWI can-manufacturing process.

828 CANNING/Cans and their Manufacture

through the first drawing operation, where they are

drawn by a punch through a die. The cups produced

at this stage may undergo a similar redraw process for

further diameter reduction as the height is progres-

sively increased (Figure 7b).

0024 There is a linear relationship between the max-

imum height to which a container can be drawn in a

single operation and its diameter. The taller the can,

the more drawing operations are required. Also,

single-reduced steels can be drawn more than

double-reduced, which can be used in lower gauges

for the same strength.

0025 The bottom end is the thickest region and governs

the material gauge, often resulting in an excessive side

wall thickness. Typically, a prelacquered tinplate and

TFS with a thickness of 0.2 mm, is used for the DRD

process. DRD cans are currently used in the pack-

aging for food rather than beverages, where a greater

wall thickness is required to withstand pressure rever-

sals. The body is beaded, and TFS is used more than

tinplate because a better enamel adhesion is achieved

with the former.

Ends

0026 The can end is designed for optimum deformation

behavior during the food-heating process, thereby pre-

venting permanent distortion: it should resist the high

relative internal pressure achieved in the heating pro-

cess that tends to deform the can ends outwards, and it

must also be sufficiently flexible to return to its original

profile as the internal pressure becomes slightly nega-

tive inside the processed can. This behavior depends on

the metal thickness, the profile of the expansion rings,

and the countersink depth (Figure 8).

0027The scroll-cut sheet, previously lacquered, is fed

through a press that stamps the ends. After stamping,

the edges are curled and passed through a lining ma-

chine, which applies a precise amount of a sealant com-

pound around the inside of the curl. This sealant assists

the formation of a hermetic seal by providing a gasket

between adjacent layers of metal in the double seam.

0028Easy-open ends are produced, from a previously

stamped shell (Figure 9a), in a press comprising four

basic operations: a bubble-like structure is drawn

(Figure 9b), a cylindrical button is drawn from

the bubble (Figure 9c), the score line is performed

(Figure 9d), and the tab is attached at the rivet station

by compression of the button, the tab being formed

on a separate operation (Figure 9e). In this way, the

tab is affixed to the end without any loss of end

integrity. Figure 9 illustrates the basic operations.

Double Seaming

0029The end is joined to the can body by a double-seaming

operation that is carried out in two stages (Figure 10):

in the first operation, the end curl and the body

flange are brought together and rolled inwards so

that the end hook is well tucked up underneath

the body hook. The shape of the seaming roll deter-

mines the contour of the seam at the end of this stage;

in the second operation, the seam is tightened by a

second set of seaming rolls. The final quality of

the double seam is defined by its length, thickness,

and the extent of the overlap of the end hook with

the body hook (Figure 11). Rigid standards are laid

down for an acceptable degree of overlap and seam

tightness.

Welding Side Seams of Three-piece Cans

0030The side seam is made by a resistance-welding pro-

cess, using the lost-wire-electrode principle. After the

can body blank has been formed into a cylinder over

(a)

(b)

fig0007 Figure 7 Comparison between (a) DRD and (b) DWI processes.

From Bakker M and Eckroth D (1986) The Wiley Encyclopedia of

Packaging Technology. New York: John Wiley with permission.

Seaming panel

Bead

Second expansion

panel

Center panel

First expansion

panel

fig0008Figure 8 Can end profile.

CANNING/Cans and their Manufacture 829

the welding arm, the overlapping seam (0.4 mm for

most cans) passes between two copper weld rolls

where the weld is formed (Figure 12).

0031The two layers in the seam are squeezed together

between the upper weld roll located outside the can

body and a smaller-diameter inner weld roll. An al-

ternating current is passed to the upper roll, and high

electrical resistance causes the interface temperature

to rise rapidly to at least 900



C, resulting in solid-

phase bonding. As the can body moves continuously

between the two weld rolls, a spot weld is created at

each peak of the alternating current. By adjusting the

frequency of the current to the linear speed of the can

body, the correct number of spot welds per unit of can

length can be achieved. In a good weld, the individual

spots should merge into a continuous weld. Although

the welded seam is free from the danger of lead pick-

up, the weld has to be effectively coated to prevent

any traces of iron being picked up by some types of

beverages and acidic foods. The external side of the

seam is also coated for protection.

Protective Organic Coatings

0032The primary function of interior can coatings,

enamels or lacquers, is to prevent any interaction

between the can and its contents, although some

enamels have special properties, and others are used

merely to improve the appearance of the pack. Exter-

ior can coatings may be used to provide protection

against the environment, as well as for decoration and

product labeling.

(a)

(b)

(c)

(d)

(e)

Sealant

Score line

Rivet

Ring tab

fig0009 Figure 9 Easy-open end production.

Lining compound

Can end

Flange on can body

(a)

(c)

Profile of roller die

Lining compound

Lining

compound

Lining

compound

Profile of roller die

Former

(d)

(b)

fig0010 Figure 10 Double-seaming: (a) and (b) first seaming operation;

Seam length

End-hook legth

Overlap

Seam thickness

Countersink depth

Body-hook length

Body-plate thickness

End-plate

thickness

fig0011Figure 11 Main components of a double seam.

830 CANNING/Cans and their Manufacture

0033 Internal lacquers must be inert, must provide a

good barrier, and must also have a good mechanical

resistance, as well as thermal resistance if the product

is to be thermally processed. The lacquer must

comply with the regulations for materials intended

for food contact, i.e., only approved substances that

had sustained successful migration or extraction tests

and that do not impart any flavor to the contents,

may be used.

0034 The barrier provided by the lacquer depends on its

chemical composition and on its porosity (which

must be as low as possible) and which in turn depends

on the thickness of the lacquer. Control of the amount

of lacquer applied, usually measured in terms of the

mass of dry film per area of metal sheet, is very

important since a thin layer will not cover the surface

completely, and a layer that is too thick will lead to

brittleness, lack of flexibility, and poor adhesion, as

well as being uneconomical.

0035 The lacquer must be resistant to mechanical solici-

tations during can and ends manufacturing oper-

ations, as in the case of three-piece cans and most

DRD two-piece cans that are produced from a pre-

coated metal sheet. Flexibility and adhesion are also

important characteristics of lacquers, as during

retorting, the can tends to deform, due to a pressure

imbalance.

0036 The lacquer is usually applied by roller coating to

the metal in the flat form sheet or coil before fabrica-

tion. Spraying is used for coating the internal surface

of DWI two-piece cans that cannot be produced

from prelacquered sheets, owing to the considerable

amount of metal deformation and surface disruption

occurring during ironing operations. Powder coating,

where the resin is applied dry in the form of a fine

powder, usually under the direction of an electrostatic

field, is used for the protection of welded side seams

(internal side), where heavy coatings are required.

A postfabrication repair lacquering is applied to

cans used to pack products with very demanding

protection requirements, to compensate for natural

application imperfections and layer damage during

can fabrication.

0037After application, the lacquer must be dried by

solvent removal, oxidation, and/or heat polymeriza-

tion. This process is usually performed in a forced

convection oven using hot air up to 210



C for up to

15 min. Recent developments include resin formula-

tions, which need lower temperatures and shorter

curing times, often through the use of ultraviolet

radiation (these ultraviolet-curing resins are virtually

solvent-free).

0038The more common chemical families of protective

lacquers are the phenols, epoxy, polyesters, and vinyl.

The resins are rarely used pure. They are modified

and/or combined with other resins and additives that

confer specific characteristics. Table 3 summarizes

the major lacquers’ characteristics and applications.

0039Phenolic resins are produced by the action of for-

maldehyde on phenol and are characterized by having

a high degree of reticulation enhancing barrier, hard-

ness and chemical inertia, but limited flexibility due

to the presence of the bulge phenolic ring.

0040Epoxy resins are produced by polymerization of

bisphenol A with glycerol epichlorohydrine. Epoxy

is highly reactive, allowing for combination with

other resins, and it has a good chemical resistance. It

is very flexible because of its linear structure, without

reticulation, and it is often combined with phenolics

giving the epoxy-phenolic family, one of the most

widely used families of resins for lacquering. A

three-dimensional structure is formed during curing,

either by straight blending of a solid epoxy resin with

a solid phenolic resin or by condensation of a mixture

of two resins in appropriate solvents. Epoxy-phenolic

lacquer combines the good adhesion properties of the

epoxy resin with the high chemical resistance proper-

ties of the phenolic resin. The balanced properties of

fig0012 Figure 12 Welding side seam of a three-piece can: 1, blank feed; 2, wire fed; 3, welding rolls (electrodes); 4, copper wire (welding

contact); 5, used wire. From Bakker M and Eckroth D (1986) The Wiley Encyclopedia of Packaging Technology. New York: John Wiley, with

permission.

CANNING/Cans and their Manufacture 831

epoxy-phenolic coatings have made their use almost

universal in food-can applications. Epoxy may also

be combined with amines to produce epoxy-urea and

with fatty acids to produce epoxy-esters.

0041 Vinyl coatings are based on copolymers of vinyl

chloride and vinyl acetate. They can be used with or

without pigmentation, and they can be blended with

alkyd, epoxy, and phenolic resins to enhance their

performance. Their main disadvantage is the high

sensitivity to heat and retorting processes, restricting

their application to cans that are hot-filled and to beer

and beverage products.

0042 Vinyl organosol coatings are dispersions of PVC

(homopolymer), sometimes reinforced with soluble

thermosetting resins, such as epoxy or phenolic, to

enhance thermal resistance and adhesion. Plasticizers

are also added to aid film formation. These coatings are

typically white due to the addition of titanium dioxide.

0043 Polyesters have an excellent resistance to high tem-

peratures and are often used for can external coating.

When used for heat-processed foods, they are modi-

fied with phenolic resins and often white pigmented

with titanium dioxide.

0044 The choice of lacquer depends on the nature of the

food and the can to be used. Products that contain

sulfur-containing amino acids require sulfur-resistant

lacquers to prevent staining of tinplate surfaces.

Sulfur compounds may break down during heat pro-

cessing to release sulfides, which react with tin to

form brown–violet tin sulfide (SnS) that affects the

global can surface or with iron to form iron sulfide

(FeS) in spots where, due to lacquering and tin-

coating imperfections, iron may be in contact with

the food. These compounds do not affect the product

safety or quality but are suspicious to the consumer.

To overcome this problem, lacquers offering a good

physical barrier, such as phenolic or epoxy-phenolic,

are used. In addition, these are pigmented with zinc

oxide, which reacts preferentially with the sulfur

compounds, thus acting as a chemical barrier.

Lacquers may also be pigmented with aluminum

powder or white pigments, to obscure any tin sulfide

that might be formed.

0045Acidic foods require a very good protection to

prevent can corrosion. A vinyl organosol with a high

thickness, pigmented with aluminum powder or

titanium dioxide, or a double coating of epoxy-

phenolic plus vinyl organosol may be used for this

purpose.

0046Beer and other drinks susceptible to flavor contam-

ination by metallic traces require very good protec-

tion as well. DWI cans are coated after fabrication,

usually with two coats of lacquer: epoxy-phenolic

plus vinyl, epoxy-urea plus vinyl or a double layer

of epoxy-urea.

See also: Canning: Principles; Food Handling; Quality

Changes During Canning; Packaging: Packaging of

Liquids; Packaging of Solids

Further Reading

Bakker M and Eckroth D (1986) The Wiley Encyclopedia

of Packaging Technology. New York: John Wiley.

Robertson GL (1993) Food Packaging Principles and

Practice. New York: Marcel Dekker.

Soroka W (1995) Fundamentals of Packaging Technology.

Herndon, VA: Institute of Packaging Professionals.

Recent Developments in Can

Design

M de F Filipe Poc¸ as, Escola Superior de

Biotecnologia, Universidade Cato

lica Portuguesa,

Portugal

Short History of the Can

0001Metal cans have been on the marketplace since the

early nineteenth century, and this early-born pack-

aging system keeps its relevant position in the food

packaging area owing to constant developments and

tbl0003 Table 3 Application and characteristics of lacquers

Family Application Flexibility Adhesion Resistance to

heat-processing

Phenolic Fruits, vegetables, meat: very good barrier Bad Bad Very good

Epoxy-phenolic Wide use, can be pigmented with Al, ZnO; characteristics

depending on formulation

Good Good Good

Vinylics Beverages Excellent Good Bad

Organosols Large use in two-piece cans Very good Very good Good

Acrylics Pigmented with TiO

Good Very good Medium

Epoxy-urea Beverages Good Good Medium

Polyesters Pigmented with TiO

Medium Good Good

832 CANNING/Recent Developments in Can Design

innovation to meet the demands from the food and

beverage industry, distribution, and the consumer.

Recent developments in can design include light-

weighting, shaping cans, double seams, the use of

polymer coated metals, and new can opening features.

0002 The start of the history of the can is attributed to

Nicholas Appert as a result of the method he developed

for storing and sterilizing food using glass bottles. This

was followed by the registration of the first patent, by

Peter Duran, for food processing using iron and tin

containers. Since then, the modern can has evolved

from a simple cylinder with two flat ends into a sophis-

ticated package, with a design that incorporates

features to improve performance, convenience, and

appearance, as well as to reduce costs. Environmental

protection has also played a role as a driving force in

can design, particularly in issues related to the reduc-

tion of metal and energy usage, and air emissions and

liquid effluents on can-manufacturing operations.

Table 1 summarizes the major landmarks on food

and drink can history, and Figure 1 shows, as an

example, changes in Coca-Cola beverage can design

over decades. These include changes in the easy-open

end, can body neck-in, and innovations in can shape.

Lightweighting

0003Lightweighting means the reduction in the amount of

material used in the can-making process. This may be

achieved at the expense of a reduction in the metal

thickness and/or improvements in can construction,

leading to savings on the metal sheet surface required

for each can. Statistics show that lightweighting is a

fact. For example, over the last 20 years, a typical

33 cm

steel beverage can has become on average

30% lighter (Figure 2). In general, the steel thickness

of the can body has decreased by around 4.5 mm per

year, and the steel thickness of can ends has decreased

by 2 mm per year, i.e., a 40 and 18% reduction, re-

spectively, in thickness over the last 20 years.

0004Downgauging has been possible through the use of

double-reduced steels and through can wall beading.

Double-reduced steel has suffered a second cold-

reduction process, between annealing and tinplating,

where the thickness is reduced by about 35%,

whereas the elastic limit of the steel has increased to

more than 500 N mm

2

. Therefore, double-reduced

steels have additional strength although at the ex-

pense of their ductibility and formability properties.

This process allows for a 3/100 mm reduction in steel

thickness without compromising mechanical per-

formance. Double-reduced steels have been used for

can bodies and more recently for can ends.

0005Beading has the effect of reinforcing the side wall,

thus allowing for a reduction in metal thickness

without compromising paneling performance. The

tbl0001 Table 1 Brief history of can making

Period Innovation

1809 Nicolas Appert wins Napoleon’s prize for his method of

processing food

1810 Peter Durand patents the idea of using tinplate for

making a container

1853 The canned condensed milk is introduced

1900s The first can with soldered side-seamed and double-

seamed ends is produced

1930s Cans for beer and soft drinks appear

1942 Electroplating for applying tin coating is introduced

1940s The draw–redraw process is developed

1947 Draw-wall-ironing aluminum cans are introduced

1959 The Soudronic Company is founded (side-seam welding

machines)

1962 Aluminum easy-open ends for beverage cans are

produced

1965 Tin-free steel is available

1975 The Wima (wire mash) welding system is developed by

Soudronic

fig0001 Figure 1 Coca-Cola beverage can design over decades. From

Group Ltd. Reprinted with permission.

1960 1970 1980 1990 2000

Year

g/can

fig0002Figure 2 Weight of a 33 cm

steel beverage can. Source: Apeal.

CANNING/Recent Developments in Can Design 833

retorting process of thermal processed food induces

positive and negative pressures within the can at

different stages. The can must withstand high internal

pressures that occur when the product is heated,

this resistance being mostly conferred by the expan-

sion rings of the can ends. It must also withstand

external pressure to paneling owing to the pressure

difference during the early stages of retorting, while

there still is a slight vacuum inside the can, and the

steam pressure acts outside the can. Circumferential

beads on the walls greatly increase can resistance to

implosion. However, beading also reduces the resist-

ance to vertical load, which is important during

filling, storage, and handling, and so a compromise

between beading profile, pitch, and depth must be

achieved. Beading, thickness, and hardness of the

metal sheet are three variables that the can designer

may use to optimize the can performance. Figure 3

shows how these three factors can be combined in the

design of a specific can.

0006 Beading was first introduced in 1970 and was com-

monly used in 1975–80. More recently, a new beading

design was developed by Hoogovens and Impress

Metal – The Varybead (Figure 4). This design has a

constant bead depth of 0.4 mm and a varying bead

pitch from 3.67 mm at the extreme ends of the 20

beads to 2.68 mm in the middle. The end beads

control the mode of axial collapse, and the middle

smaller beads maximize the paneling resistance.

0007 Aluminum drink cans have also been reduced in

weight. The number of cans produced from a kilo-

gram of aluminum increased by 35% between 1975

and 1995. Figure 5 shows the net weight of aluminum

required to make 1000 cans from 1990 to 2000.

Lightweighting has been possible by decreasing the

starting gauges of the aluminum coil (Figure 6), by

improvements in the draw-wall-iron process, and by

using smaller diameter can ends, which is related to

the can body neck-in. Downgauging of the aluminum

coil requires refinement in dome design as the starting

gauge of the metal determines the can bottom dome

thickness, critical to the performance of the can in

terms of its resistance to internal pressure.

Thickness − 0.26 mm

Hardness − Standard

No beading

Thickness − 0.21 mm

Hardness − Standard

Beading

Thickness − 0.17 mm

Hardness − High

Beading

fig0003 Figure 3 Relationship between beading and metal thickness and hardness in can design.

fig0004Figure 4 New beading design – the Varybead. From The Can-

Ltd. Reprinted with permission.

Can

End

1990 1992 1994 1996 1998 2000

Year

9.5

10.5

11.5

0.5

1.5

2.5

3.5

kg/1 000

fig0005Figure 5 Number of cans and ends produced per kilogram of

aluminum. Source: Alcoa.

834 CANNING/Recent Developments in Can Design

Double Seam

0008A double-seam fixes the end to the can body and

provides a hermetic seal. It is one of the most critical

elements in the safety of canned shelf-stable foods,

and great effort is devoted to controlling the double

seam dimensions, in compliance with rigorous

standards and tight tolerances.

0009Developments to reduce costs have led to smaller

seam profiles. The Microseam was developed by Kra-

mer in Brazil, and has a structure similar to the con-

ventional double seam. However, the dimensions of

the seam height, body, and cover hooks are 50% of a

conventional seam. The design is only possible when

using double-reduced steel (0.16 mm or less) for can

body and ends. When applied to a 73-mm-diameter

three-piece can, it allows for the end diameter before

seaming to be reduced from 88.5 to 81.5 mm, and the

blank body height to be reduced from 98.7 to

93.5 mm (Figure 7). The main advantages claimed

1980 1985 1990 1995 2000

Year

0.2

0.25

0.3

0.35

0.4

Thickness, mm

fig0006 Figure 6 Starting gauges of aluminum coil for beverage cans.

Source: Redicon Corporation.

Φ 78.63

Φ 82.50

88.5

81.5

4.935

2.0

3.2

Φ 72.63

0.88

1.08

0.16

Φ 77.565

1.0

1.5

1.0

1.6

3.2

2.0

3.0

0.16

0.22

1.6

(a) (b)

fig0007 Figure 7 Comparative dimensions of (a) conventional and (b) microseam three-piece can double-seam. From The CanMaker

CANNING/Recent Developments in Can Design 835