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heat-resistant organism is used to determine the correct

process time. Often these processes are described in terms

of F values.

F Value. An F value is the time in minutes to heat-

inactivate a given number of certain micro-organism at a

ﬁxed temperature (4). If the temperature is 2501F (1211C)

and the organism is Cl. botulinum, then the F value is

called F

. This value is the number of minutes required to

kill a given population of Cl. botulinum spores at 2501F

(1211C). Combinations of times and temperatures other

than 2501F and F

minutes can inactivate the same

number of spores; temperatures lower than 2501F for

longer time periods or temperatures greater than 2501F

for shorter times have an equal ability to inactivate the

spores. An F

= 2.45 min reduces the population of Cl.

botulinum spores by a factor of 10

(5). In practice, F

values of greater than 3 are used as a safety measure. To

prevent overprocessing (overcooking) of the food, the spore

inactivation (called lethality) is summed up during the

time the coldest spot in the can is coming up to the retort

temperature. Some viscous conduction-heated foods may

never completely reach the common retort temperature of

2501F (1211C) yet still receive the proper F

treatment.

The Food and Drug Administration (FDA) regulations

require that these tests and calculations be carried out

only by recognized authorities (6).

Interest in thermal processes resulted in techniques

that commercially sterilize ﬂuid foods in continuous-ﬂow

heat-exchange systems before packaging (7). The thermal

death calculations described above still apply to these

processes, and proper F values must be achieved (8). The

continuous-ﬂow commercial sterilization procedures have

the advantage that products can be heated and cooled

more rapidly for shorter times with equal lethality. This

can give a higher quality product. These products must be

ﬁlled into presterilized containers (see the Aseptic packa-

ging article).

CANNING OPERATIONS

The canning process requires several unit operations that

normally take place in a set sequence (9).

Product Preparation. As soon as the raw agricultural

product is received at the canning plant, it is washed,

inspected, sorted to remove defective product, and graded.

Often, the edible portion is separated from nonedible as

in the case of peas or corn. Fruits and vegetables are

subjected to a blanching operation by exposing them to

either live steam or hot water at 190–2101F (88–991C).

Blanching serves to inactivate enzymes that would other-

wise cause discoloration or deterioration in the product. It

also softens, cleans, and degases the product. Peeling,

coring, dicing, and/or mixing operations may be carried

out next. These operations prepare the product for ﬁlling

into the can.

Container Preparation. Containers must be washed

thoroughly immediately prior to ﬁlling. Cans are washed

inverted so that any foreign objects and the excess water

can drain out. The container is now ready for ﬁlling.

Accurate and precise ﬁlling is necessary to meet minimum

labeled ﬁll requirements yet leave sufﬁcient headspace for

development of the proper vacuum after closure. Too large

a headspace results in an underweight container, whereas

overﬁlling can result in bulging or domed ends after

processing. Excessive headspace may also suggest that

large amounts of oxygen remain in the can, which accel-

erates product deterioration and can corrosion. Liquid or

semiliquid products including small pieces are ﬁlled by

automated equipment. Larger, more fragile products, such

as asparagus, are packed by hand or by semiautomated

equipment. In most products, brine, broth, or oil is added

along with the product. This liquid excludes much of the

air between the particles and provides for more efﬁcient

heat transfer during thermal processing.

Vacuum. Proper application of the closure after ﬁlling

is one of the most critical steps in the canning operation.

The two-step seaming operation not only must produce

a sound, well-formed double seam at speeds of several

hundred cans per minute but also must produce an

interior vacuum of 10–20 in. Hg (34–68 kPa) (10). This

vacuum reduces the oxygen content, retards corrosion and

spoilage, leaves the can end in a concave shape during

storage, and prevents permanent distortion during retort-

ing. A proper internal vacuum can be achieved by several

methods. Containers that are sealed while the food is at or

near the boiling point develop a vacuum when the product

cools. This preheating or hot ﬁll also serves to sterilize the

container when high-acid foods are packaged. Products

that are cool when ﬁlled can be heated in the container

prior to sealing with the same result as the hot ﬁll. This is

often termed ‘‘thermal exhaust.’’ An internal vacuum may

also be achieved by mechanical means. The ﬁlled, un-

sealed container is fed into a vacuum chamber by means of

an air lock, and the closure is sealed while under vacuum.

This system has the disadvantage that ﬂashing of the

liquid may occur if air is entrapped in the food or high

levels of dissolved air are found in the liquid. The most

common method of producing internal vacuum is by

displacing the air in the headspace with live steam prior

to and during double seaming the cover. The steam in the

headspace condenses and forms a vacuum as the container

cools.

Retorting. In conventional canning operations of low-

acid foods, the sealed containers are next thermally

processed at 2501F (1211C) in retorts. Recent regulatory

agency rule changes allow speciﬁc ﬂexible containers to be

processed at 2751F (1341C).

Several distinct types of commercially manufactured

retorts are available for thermally processing canned food

(11). Although all, by necessity, operate at pressures above

15 psi (103 kPa), the design characteristics of each type are

considerably different. At least six design variables exist:

(a) discontinuous (batch) types versus continuous con-

tainer processing, (b) the heating medium used to transfer

heat to the container, (c) the agitation or nonagitation

of containers during processing, (d) the layout of the

188 CANNING, FOOD

pressure vessel (vertical vs horizontal), (e) the method

used to load and unload the containers from the retort,

and (f) the cooling procedures used after thermal

processing.

A—Water line. O—Water spreader.

B—Steam line. P—Safety valve.

C—Temperature control. Q—Vent valve for steam

processing.

D—Overﬂow line. R—Pressure gauge.

—Drain line. S—Inlet air control.

—Screens. T—Pressure control.

F—Check valves. U—Air line.

G—Line from hot

water storage.

V—To pressure control

instrument.

H—Suction line and manifold. W—To temperature control

instrument.

I—Circulating pump. X—Wing nuts.

J—Petcocks. Y

—Crate support.

K—Recirculating line. Y

—Crate guides.

L—Steam distributor. Z—Constant ﬂow oriﬁce valve.

M—Temperature-controller

bulb.

—Constant ﬂow oriﬁce

valve used during come-up.

N—Thermometer. Z

—Constant ﬂow oriﬁce

valve used during cook.

The simplest retorts are batch (discontinous) retorts

that use pure steam as the heating medium and do

not have provisions for mixing (agitation) of the con-

tainer contents during processing. These retorts are

termed still retorts (Figure 1). Temperature inside still

retorts is maintained by automatic control of the steam

pressure.

Loading and unloading the containers from discontin-

uous still retorts are accomplished by preloading contain-

ers into crates, baskets, cars, or trays. ‘‘Crateless’’ systems

randomly drop containers into the retort vessel, which is

ﬁlled with water to act as a cushion and prevent container

drainage (Figure 2). The water is drained prior to proces-

sing. The orientation of the retort depends on the type

of container handling system. Systems that use crates

or baskets and the crateless systems, by necessity, use

vertical vessels, whereas car handling necessitates a

horizontal orientation.

Glass, semirigid, and ﬂexible containers must be pro-

cessed in still retorts that have been designed to accom-

modate the fragility of these containers at retort

temperatures and pressures. These retorts operate at

pressures greater than the 15 psi (103 kPa) of steam

required to reach 2501F (1211C) to counterbalance the

internal pressure developed in the container. This is

termed ‘‘processing with overpressure.’’ The pressure

buildup inside individual containers during processing

would result in the loss of seal integrity in heat-sealed

containers (see the Sealing, heat article) and could loosen

the covers of glass containers or permanently distort

semirigid plastic containers. Four design changes in still

retorts must be made to process with overpressure:

1. Either steam or air overpressure must be automati-

cally controlled. Pressures of 25–35 psi (172–241 kPa)

are typical.

2. Control of the retort temperature must be indepen-

dent of retort pressure.

3. Mixed heating media of either steam—air, water–

air, or water–steam are used in place of pure steam.

Heat transfer is less efﬁcient in these mixed-heating

media. For this reason, some means of circulating or

Figure 1. Vertical still retort (21 CFR, Part 113).

Figure 2. FMC crateless retort system. (Courtesy of FMC Corporation, Food Processing Machinery Division.)

CANNING, FOOD 189

mixing the heating medium is necessary. For steam–

air mixtures, fans may be provided. Water–air and

water–steam systems use circulating pumps.

4. Provisions to prevent stress on the containers

caused by motion during processing are made.

These designs may be incorporated into either vertical

or horizontal retorts depending on how the containers are

handled. Glass containers are typically loaded into crates

or baskets for processing in vertical water–air or water–

steam retorts. Flexible retortable pouches are often loaded

into trays and cars (which also serve to maintain the

proper shape of the pouch) and moved into horizontal

retorts for water–steam or steam–air processing (see

Figure 3).

Still retorts, whether designed for metal cans or other

containers, are batch (discontinous) systems. The hydro-

static retort is technically a still retort (product is not

agitated) that continuously processes containers. The

retort operates at a constant temperature (and pressure)

as the containers are carried through the retort by a

continuously moving chain (Figure 4). The required

15 psi (103 kPa) of steam pressure inside the retort (or

steam dome) is maintained by two columns of water,

which also serve as pressure locks for incoming and out-

going containers. These columns of water (called feed and

discharge legs) must be greater than 37 ft (11.3 m) high to

maintain at least a minimum 15-psi (103-kPa) steam

pressure. Hydrostatic retorts have the highest through-

puts; are efﬁcient in their use of ﬂoorspace, steam, and

water; can process a variety of container sizes and types

(including ﬂexible); and are highly automated. They have

the disadvantage of high capital costs and are therefore

applicable only to high-volume operations.

The heating time necessary to ensure that the coldest

spot in the container receives the proper lethality depends

somewhat on the consistency of the product. For viscous

products such as canned pumpkin and baked beans, the

primary heat-transfer mechanism is conduction. Products

that have a thin consistency or are packed with brine

(canned peas) are heated by convection. The transfer of

heat to the center of the container can be greatly facili-

tated if internal mixing occurs in the can during retorting.

This results in a shorter processing time and higher

quality product.

Retorts that are designed to increase convection heat-

ing by container motion during processing are termed

agitating retorts. Both end-over-end and axial rotation

are used, but the latter predominates. Glass, semirigid,

and ﬂexible containers are not agitated because of fragi-

lity. Agitating retorts may be either batch or continuous

types. Continuous retorts predominate because they have

Figure 3. FMC convenience foods sterilizer, showing water ﬂow

and pouch restraints. (Courtesy of FMC Corporation, Food Pro-

cessing Machinery Division.

Figure 4. Flow diagram of a hydrostatic sterilizer for canned

foods. (Courtesy of FMC Coporation, Food Processing Machinery

Division.)

Figure 5. Cutaway view of a continuous rotary cooker–cooler’s

turning wheel and interlock. (Courtesy of FMC Corporation, Food

Processing Machinery Division.)

190 CANNING, FOOD

greater efﬁciency and throughout but are less easily

adapted to changes in container size.

The continuous rotary cooker–cooler (see Figure 5) has

become widely used for large-volume operations in which

convection-heated products such as vegetables in brine

are packed in metal cans. This system feeds individual

cans into and out of the pressurized vessels by means of

rotary pressure lock valves. Cans are rotated around the

inside of the vessel’s shell by means of an inner rotating

reel and a series of spiral channel guides attached to the

shell (Figure 5). This system provides for intermittent

agitation of the cans by providing rotation about the can

axis during a portion of the reel’s rotation inside the

vessel. This system has the disadvantage that container

size cannot be easily changed.

Regardless of retort design, consideration must be

given to cooling containers after processing. For glass,

ﬂexible, and semirigid containers, cooling with overpres-

sure is necessary. These containers would fail because of

the internal pressure developed during heating should the

external pressure drop. Even metal cans may buckle and

panel if brought to atmospheric pressure while the con-

tents are at 2501F (1211C). In batch-type still retorts,

overriding air pressure with water cooling is used. Hydro-

static retorts (continuous still retorts) cool containers by

removing heat from the water in the discharge leg. If more

cooling is necessary, an additional cooling section is added

and cool water is cascaded over the containers. Contin-

uous agitating (rotary) systems cool under pressure by

transferring containers to pressurized cooling vessels by

means of rotating transfer valves (Figure 6). The second-

stage vessels are maintained at elevated air pressures

while the containers are cooled with water. A third-stage

atmospheric cooler may also be incorporated.

In addition to the pressurized heating and cooling

vessels, all retort systems require a set of precise instru-

ments and controls. Regulations require a direct reading

mercury-in-glass thermometer as well as temperature

Figure 6. Transfer valve between cooking and cooling vessels of a continuous cooker–cooler.

R Rotor containing can pockets and ejector paddles. PW1 Downstream water pressure gauge.

SV Forespace steam valve. O Oriﬁce for ﬂow control.

M Microcooling chamber. Overﬂow Release line for excess air or water.

F Forespace for pressure equilization. S1 Steam line.

D Water dam. C Check valve.

G Splash guard. PSI Pressure vacuum gauge.

Air Pressure regulated air supply. 1. Hot can.

V Vestibule. 1a. Valve-leading edge.

AV1 Forespace regulated air inlet valve. 2. The can receive some water splash.

AV2 Microcooling space air inlet valve. 3.–7. The cans are fully exposed to water ﬂow.

PAI Forespace air pressure gauge. 7a. Valve-trailing edge.

PA2 Microcooling space air pressure gauge. 8. Can is about to leave microcooler valve.

Water Water inlet and perforated distributor. 9.–12. Cans are subject to sprays of water.

WV Water inlet regulator valve. 13. Drain pocket.

PW2 Upstream water pressure gauge.

(Courtesy of FMC Corporation, Food Processing Machinery Division.)

CANNING, FOOD 191

recording devices. A continuous temperature controller

must be installed. For retorts that use pure steam, this

may be a pressure controller; processing with overpres-

sure requires a direct temperature controller. Retorts

require reliable sources of steam, air, and water. A pres-

sure reading device is required as well as an accurate

recording timing device so that the scheduled process can

be insured and the proper records maintained. All instru-

ments must undergo periodic calibration.

REGULATION

The canning of foods is carefully regulated by the FDA, or

in the case of canned meats and poultry, the United States

Department of Agriculture (USDA). These agencies recog-

nize the serious public health implications of improperly

processed foods. The FDA has developed a complete set of

regulations commonly referred to as the Good Manufac-

turing Practices (GMPs) for canning foods. These regula-

tions govern the type of equipment used to can foods and

the procedures, the frequency of inspection of containers

and equipment, and the records that must be kept, and

they provide for the ﬁling of individual processes prior to

production. The regulations pertaining to food canning are

contained in Title 21 of the Code of Federal Regulations

(CFR) under the following sections: (a) 21 CFR Part 108,

‘‘Emergency Permit Control’’; (b) 21 CFR Part 113, ‘‘Ther-

mally Processed Low-acid Foods Packaged in Hermetically

Sealed Containers’’; and (c) 21 CFR Part 114, ‘‘Acidiﬁed

Foods.’’

Part 108 stipulates that food-canning plants must

the FDA. This section also contains provisions for issuing

emergency permits to ﬁrms that the FDA believes do not

fully meet the regulations. Part 113 is the most extensive

section and details the equipment, procedures, process

controls, establishment of correct process, critical factors,

and necessary records for canning low-acid foods. This

section also details the procedures to be used in evaluating

the integrity of the double seams. Part 114 describes the

GMP requirements for packaging high acid foods

(pHr4.6). This section includes general provisions as

well as speciﬁc requirements for production and process

control.

The USDA’s Food Safety and Inspection Service (FSIS)

has regulatory authority over canning poultry and meat

products and has promulgated a series of regulations

under Title 9 of the CFR. Current FSIS regulations are

considerably more general than FDA regulations and

have not kept pace with changes in canning technology.

Meat and poultry canning operations are subject to con-

tinuous inspection in a manner similar to other FSIS-

regulated plants. These regulations are contained in sec-

tions 318.11 and 381.49, which deal with the cleaning of

empty containers, inspection of ﬁlled containers, coding,

use of heat-sensitive indicators (see Indicating devices),

and incubation of processed products. In 1984, FSIS

proposed a more detailed set of regulations similar to

those promulgated by the FDA for canning low-acid foods.

The sections of the CFR that deal, in part, with meat and

poultry canning, and related requirements will be 9 CFR

308, 318, 320, and 381.

TRENDS

The food-canning industry has undergone substantial

changes, most notably in the area of containers (12).

Changes are ongoing in the retort systems. Rotation,

oscillation, gentle motion, and shaka are the various

terms used by vendors to promote their particular system.

The major trends are in the uses of semirigid and ﬂexible

pouches.

The industry is increaingly using the ﬂexible pouch and

semirigid containers, taking advantage of the thinner

proﬁle of these containers that can result in faster heating

and higher quality food. Also the shipping cost of the

empty can and glass jars to the retort facility is becoming

more of an issue.

Metal as well as glass cans will have increasing com-

petition from plastics and composite materials (14).

Development of thermal processes in which the food is

commercially sterilized before packaging is ongoing. This

allows food to be thermally processed in continuous-ﬂow,

heat-exchange systems that can result in higher quality

products and allow the use of less expensive containers

based on paperboard or thin plastics. This technology is

used for juices, drinks, and milk. Recent products include

soups, stews, and vegetables (8).

BIBLIOGRAPHY

J. H. Hotchkiss, ‘‘Canning Food,’’ in The Wiley Encyclopedia of

Packaging Technology, 1st edition, Wiley, New York, 1986, pp.

86–91; 2nd edition, 1997, pp. 123–128.

1. S. R. Friedman in W. C. Simms, ed., The Packaging Encyclo-

pedia—1984, Cahners Publishing, Boston, MA, 29(4), 334

(1985).

2. A. Lopez, A Complete Course in Canning, 11th edition, Book 1,

The Canning Trade, Inc., Baltimore, MD, 1981, p. 9.

3. I. J. Pﬂug and W. B. Esselen in J. M. Jackson and B. M. Shinn,

eds., Fundamentals of Food Canning Technology, AVI Pub-

lishing, Westport, CT., 1979, pp. 10–94.

4. N. N. Potter, Food Science, 3rd edition, AVI Publishing,

Westport, CT, 1978, pp. 177–193.

5. Ref. 2, p. 330.

6. Establishing Scheduled Processes, Code of Federal Regula-

tions, Title 21, Part 113.83, U.S. Government Printing Ofﬁce,

1983, Washington, DC, p. 112.

7. D. Wernimont, Food Eng. 55(7), 87 (1983).

8. A. A. Teixeira and J. E. Manson, Food Technol. 37(4), 128

(1983).

9. Ref. 4, pp. 550–557.

10. Ref. 2, pp. 217–219.

11. Canned Foods: Principles of Thermal Process Control, Acid-

iﬁcation and Container Closure Evaluation, 4th edition, The

Food Processors Institute, Washington, DC, 1982, p. 162.

12. B. J. McKernan, Food Technol. 37(4), 134 (1983).

192 CANNING, FOOD

13. ‘‘Welded Can Expected to Capture 3-Piece Can Market,’’ Food

Prod. Manage. 104(12), 12 (1982).

14. J. Haggin, Chem. Eng. News. 62(9), 20 (1984).

General References

A. Lopez, A Complete Course in Canning, 11th edition, Books 1

and 2, The Canning Trade, Inc., Baltimore, MD, 1981, pp. 556.

J. M. Jackson and B. M. Shin, Fundamentals of Food Canning

Technology, AVI Publishing, Westport, CT, 1979, pp. 406.

Canned Foods: Principles of Thermal Process Control, Acidiﬁca-

tion and Container Closure Evaluation, 4th edition, The Food

Processors Institute, Washington, DC, p. 246.

CANS, ALUMINUM

TERRE REINGARDT

Ball Corporation, Westminster,

Colorado

N. F . NIEDER

Amheuser-Busch

Updated by Staff

INTRODUCTION

Over 98% of all aluminum cans are drawn-and-ironed

(D & I) cans used for beer and soft drinks (see Cans,

fabrication; Carbonated-beverage packaging). The other

1–2% is accounted for by small shallow-draw food cans. In

the United States, production of aluminum beverage cans

has reached about 100 billion/yr (1). Virtually all beer cans

are aluminum, and 100% of all soft-drink cans are alumi-

num. Until 1965, the three-piece soldered can was the only

can used for beer and beverages (see Cans, fabrication;

Cans, steel). It was generally made of 75-lb per base box

(16.8 kg/m

) tinplate (see Tin-mill products). Aluminum

does not have the strength of steel per unit weight and

cannot be soldered. Therefore, early in the development of

the aluminum can, attention was focused on improving

the properties of aluminum and perfecting two-piece D & I

technology. More recently, the emphasis has been on

saving metal, because the cost of metal is the single

largest component of ﬁnal product cost. One of the chief

reasons for the success of aluminum cans has been their

scrap value for recycling (see Energy utilization; Recy-

cling). This article pertains to the technical developments

that have led to today’s aluminum beverage can.

HISTORICAL DEVELOPMENT

The signiﬁcant developments took place in the late 1960s.

Earlier, in 1958, Kaiser Aluminum attempted to make a

7-oz (207-mL) aluminum can using a 3003 soft-temper

aluminum of the type used for aluminum-foil production,

but the effort was not a commercial success. In the

universe of aluminum alloys, the 3-series alloys contain

a small percentage of manganese as the principal alloying

element. The success of the aluminum can depended on

the development of the 3004 alloy for the can body, which

contains manganese along with a slightly lower amount of

magnesium. (The softer 5182 alloy for can ends contains a

higher amount of magnesium.) Reynolds Metals Co. began

making production quantities of 12-oz (355-mL) seamless

D & I cans in 1964 using a 3004 alloy. The walls of these

ﬁrst cans were straight, with a top diameter of ‘‘211’’:

in. (68.26 mm). The starting gauge was 0.0195 in.

(0.495 mm); can weight was 41.5 lb/1000 (18.8 kg/1000).

Reynolds introduced the ﬁrst necked-in cans (see

Figure 1) in 1966, reducing the top diameter from 211

to 209, that is, 2

in. (65.09 mm). This represented a

breakthrough in technology and container performance,

particularly as it is related to cracked ﬂanges. Cracked

ﬂanges were a serious problem in both double-reduced

tinplate and straight-walled aluminum cans. The intro-

duction of carbide knives at the slitter essentially elimi-

nated cracked ﬂanges on tinplate cans. Eliminating them

on aluminum cans required a change from die ﬂanging to

spin ﬂanging, and necking-in before ﬂanging, which does

not stretch the metal beyond its elastic limits.

In 1968, a new harder-temper (H19) 3004 alloy was

introduced for aluminum cans. Although the 3004–H19

combination had been available since the 1950s for other

purposes, it was not until 1968, when Alcoa and Reynolds

were in commercial production with full-hard-temper can

sheet, that it could be used to effect signiﬁcant weight

reductions. Weight/1000 cans decreased from 41.5 lb

(18.8 kg) in the mid-1960s to 34 lb (15.4 kg) in the mid-

1970s and to less than 30 lb (13.6 kg) in the mid-1980s.

Both 3004–H19 and 3014-H19 are used today.

Gauge reductions have increased the point where de-

sign techniques have become critical to sustaining the

can’s ability to hold the product. With few exceptions, U.S.

brewers pasteurize beer in the can. This generates high

internal pressures, and most cans used for beer must be

designed so that they have a minimum bottom buckle

Figure 1. A necked-in can.

CANS, ALUMINUM 193

strength of 85–90 psi (586–620 kPa), depending on the

carbonation level. Brewers were asking for cans with

minimum column strength (i.e., vertical crush) of 300 lbf

(1330 N).

A revolution has taken place in bottom proﬁles (see

Figure 2). The original D & I bottom had a rather generous

bottom-heel radius. In order to meet the 90-psi (620 kPa)

minimum bottom buckle-strength requirement, a 211 can

with this conﬁguration would have to be made with a

starting gauge of 0.016–0.0165 in. (406–419 mm). The next

proﬁle development, basically the Alcoa B-53 design, is

widely used throughout the beer industry today because

it allows the starting gauge to go as low as 0.013 in.

(330 mm), in most cases without sacriﬁcing the 90-psi (620-

kPa) minimum bottom buckle strength. The Alcoa B-80

proﬁle allows starting-gauge reduction to B0.0126 in.

(B320 mm).

An ‘‘expandable bottom’’ design might permit use of a

0.010-in. (254 mm) starting gauge for pasteurized product.

In contrast to the current dome proﬁles, an expandable

bottom is essentially a ﬂat bottom with small pods located

near the perimeter to provide stability to the pressurized

can, reduce drag, and increase mobility. A totally ﬂat

bottom would drag too much on the ﬁlling line. The

‘‘expandable’’ bottom is designed to ﬂex outward during

pasteurization, relieving some of the generated pressure.

Sidewalls are still being redesigned (see Figure 3). In

the 1970s, the so-called nominal thinwall (i.e., the area of

the can that has been thinned most) generally ranged

from 0.0052 to 0.0053 in. (132–135 mm). More recent

versions of the D & I can have reduced the nominal

sidewall to 0.0045 in. (114 mm). A reduction of this magni-

tude represents substantial cost reduction. It also means a

corresponding reduction in the overall column strength

(vertical crush) of the can, not below the minimum 300 lbf

(1330 N) but in terms of overall operating average. Col-

umn strength is very critical to the brewers, who ship long

distances by truck and rail. Extensive testing by the can

companies and the beer and beverage industry in general

has shown that the 300-lbf (1330-N) minimum is satisfac-

tory. Because of the reduction in body-wall thickness,

dents that were acceptable before have now become

critical owing to their inﬂuence on reducing the can’s

column strength. Can makers and brewers are monitoring

their handling systems for empty and full cans to mini-

mize denting wherever possible.

In the 1980s, can suppliers reduced costs further by

double ‘‘necking-in’’ (see Figure 4). These conﬁgurations

reduced costs primarily because of the diameter reduction

of the lid. In 1984, further activity with respect to necking-

in began to occur. Cans with three or four die necks are

now being run commercially (see Figure 4). In Japan, a

can with eight necks was tested. Metal Box (UK) intro-

duced a spin-neck can (see Figure 4), which essentially

produced the same 206 top diameter as the triple- or

quadruple-neck can, that is 2

in. (60.33 mm).

Another advantage of aluminum is the ‘‘split gauge.’’

The industry used to sell coils in 0.0005-in. (12.7-mm)

increments, for example, 0.0130 in. (330 mm), 0.0135 in.

(343 mm), etc. A new pricing structure introduced in 1983

allows can-stock buyers to order gauge stock in 0.0001-in.

(2.54-mm) increments. A can manufacturer can reduce

costs by taking advantage of these slight gauge reduc-

tions. In addition, there has been a change in the gauge

tolerance as rolled by the aluminum mills. In the 1970s,

the order gauge was subject to a 70.0005-in. (12.7 mm)

tolerance; today, it has been reduced to 0.0002 in. (5.1 mm).

This permits further gauge reduction because it allows the

can manufacturer to reduce the order gauge without

changing the minimum bottom buckle strength.

CURRENT DEVELOPMENT

Today 100% of all U.S. soft-drink cans and 95% of all beer

cans are fabricated from aluminum (1). The industry has

moved from 206-diameter necks on 211-diameter bodies to

Figure 2. Can-bottom proﬁles: A, original bottom proﬁle; B,

Alcoa B-53, V-bottom proﬁle; C, Alcoa B-80. (Courtesy of Alcoa.)

Figure 3. Design elements.

Figure 4. Double-, triple-, quadruple-, and spin-neck can.

194 CANS, ALUMINUM

204- and 202-diameter necks. These diameter changes

have reduced the metal gauge and net weight from

0.0108 in. and 7.3 lb/1000 for 206 ends to 0.0088 in. and

5.3 lb/1000 for 202 ends. The primary development is with

the 202 can ends, 200 is also being developed. Wide mouth

cans openings are now being marketed that lower metal

use by 10% (1). Resealable cans are being marketed in

France. A small amount of plastic will be used at the

opening and will not affect recycling (2).

Net can weights have also been reduced from approxi-

mately 30 lb/M at 0.0125 in. to 23 lb/M at 0.0108 in. This

has been accomplished primarily by creating new stron-

ger dome geometry, along with dome postreforming

technology to improve performance criteria, such as

dome buckle, drop resistance, and dome growth. These

new dome designs are more difﬁcult to manufacture, but

provide improved performance and stacking at reduced

gauges. Alcoa is lightweighting by using the thinnest

aluminum possible. Finite element modeling helps with

design prototypes (3). Can body gauging down has re-

sulted in a 25–30% reduction in metal use (4).

Can sidewalls have been further reduced from 0.0045

in. down to 0.0038 in. nominal, and the number of die

necks utilized to produce ﬁnished necks has increased to

as many as 14 for the 202 diameter (4). Multidie necks

combined with spin necking are still popular for all three

neck diameters, and several canmakers are using multidie

necking with spin ﬂow necking.

BIBLIOGRAPHY

Terre Reingardt, and N. F. Nieder, ‘‘Cans, Aluminum’’ in The

Wiley Encyclopedia of Packaging, 2nd edition, John Wiley &

Sons, New York, 1997, pp. 132–134.

Cited Publications

1. All About Cans, Can Manufacturers Institute, www.cancen-

tral.com, accessed July 2008.

2. ‘‘Coca-Cola’s Resealable Can,’’ Ball Packaging Europe,

www.ball-europe.com, March 27, 2008.

3. ‘‘Heavy Duty Light Weighting,’’ www.psc.edu/science/alcoa,

accessed July 2008.

4. Aluminum Beverage Can Innovations, Aluminum Can Council,

Washington, D.C.

CANS, COMPOSITE

M. B. EUBANKS

Sonoco Products Company

Updated by Staff

INTRODUCTION

The ‘‘composite can’’ is broadly deﬁned as a can or container

with body and ends made of dissimilar materials. In

commercial practice the composite can has several more

focused descriptions: cylindrical or rectangular shape; rigid

paperboard (or plastic) body construction; steel, aluminum,

or plastic end closures; generally employing inside liners

and outside labels; and generally delivered with one end

attached and one end shipped separately to be attached by

the user. Today the most common form is the cylindrical

paperboard can with a liner, a label, and two metal ends.

There are other packaging forms similar to traditional

composite cans that are sometimes called composites,but

which are more closely related to folding cartons. These are

single-wrap ﬁber cans made from blanks and mainly

designed for the users’ in-plant production (see Cans,

Composite, Self-Manufactured).

The composite can is not a new package. Early applica-

tions included refrigerated dough and cleansers. As tech-

nology improved, motor oil and frozen juice concentrates

were converted to composites. In the last decade, snack

foods, tobacco, edible oils, shortening, powdered bev-

erages, pet foods, and many other items have been added

to the list. Figure 1 illustrates some of the products

currently available in composite cans.

Since their introduction, composite cans have generally

been marketed and used as a lower-cost packaging form

relative to metal, plastic, and glass. This emphasis has

overshadowed other positive attributes such as the fre-

quent use of recycled materials, weight advantages, noise

reduction, improved graphics, and design ﬂexibility. Be-

cause of its early applications in cleansers and oatmeal,

the composite can once suffered from a low performance

image associated with the term ‘‘cardboard can.’’ This

term cannot begin to describe the current and potential

properties of the paperboard and other materials that go

into today’s composite cans.

By utilizing the best combination of materials, compo-

site-can construction ensures optimum presentation and

mechanical strength as well as hermetic protection. The

choice of materials and production techniques for can

components offers packaging solutions that are ﬂexible

and cost effective for mass consumption and luxury pro-

ducts as well as for numerous industrial applications.

Composite cans are normally available in diameters of

1–7 in. (3–18 cm) and heights of 1–13 in. (3–33 cm). Dimen-

sional nomenclature for composites has been adapted from

Figure 1. Examples of composite cans in commercial use.

CANS, COMPOSITE 195

metal cans, and nominal dimensions are expressed in

inches and sixteenths of an inch (see Cans, Steel). Hence,

a 404 diameter can has a nominal diameter of 4

in.

(10.8 cm). Likewise, a height of 6

in. (16.8 cm) is

expressed as 610, and so on.

MANUFACTURING METHODS

Composite-can bodies are produced by two basic methods:

spiral winding and convolute winding. Figure 2 shows

a schematic drawing of the spiral process. Multiple

webs including a liner, body plies, and label are treated

with adhesive and wound continuously on a reciprocating

mandrel. The resulting tube is trimmed and the can

bodies are passed on to ﬂanging and seaming stations.

Figure 3 depicts the convolute process, wherein a pattern

is coated with adhesive and entered onto a turning

mandrel in a discontinuous process. Trimming and ﬁn-

ishing operations for the convolute and spiral systems

are virtually the same. Most composite-can manufac-

turers favor the spiral process in situations where

long production runs and few line changeovers are

involved.

BODY CONSTRUCTION

Paperboard

The primary strength of the composite can is derived from

its body construction, which is usually paperboard (see

Paperboard). Body strength in composite cans is an attri-

bute that has improved over the years and can be varied to

meet many application demands.

In the early years of composite can development, it was

common for can manufacturers to start with a readily

available body stock such as kraft linerboard or tube-

grade chip. These boards are adequate for most applica-

tions, but new boards with special qualities have also been

developed for more demanding end-use requirements.

Research and development efforts in the combination

paperboard ﬁeld encompass a number of areas of exper-

tise. Examples are (a) engineering mechanics concepts

used to develop structural criteria and to develop tests

to ensure that the paperboards possess the necessary

resistance to bending, buckling, and creep; (b) surface

chemistry used to predict the resistance of the board to

penetration of adhesives, coatings, and inks and, similarly,

protection from environmental conditions such as rain,

high humidity, and freezing temperatures; and (c) process

engineering used to optimize paperboard manufacturing

and converting and to assist in quality assurance pro-

grams (see Speciﬁcations and Quality Assurance).

The scientiﬁc and engineering efforts have, in many

instances, supplemented the artisan-like judgment of

yesterday’s papermaker. However, in many cases the

new technological approaches have been blended with

the papermaker’s art to achieve the best of both worlds.

As a result, the following advances have taken place:

super-high-strength board that can be converted into

composite cans with reasonable wall thicknesses that

can resist implosion when subjected to near-perfect va-

cuum; resin-treated paperboards that retain their struc-

tural integrity when thoroughly wet; chemically treated

paper that resists penetration by water over long time

intervals; and paperboards that can be distorted, rolled,

and formed in high-speed converting equipment without

‘‘creeping’’ back to their original shape.

Adhesives

The adhesives (see Adhesives) and coatings used in the

manufacture of composite cans have also been improved to

provide better heat and water resistance plus increased

Figure 2. Spiral-wound composite-can fabrication.

Figure 3. Convolute composite-can fabrication.

Table 1. Adhesives Used in Composite-Can Manufacture

Adhesives Properties

Poly(vinyl alcohol–acetate) blends Good initial tack, good runnability, moderate to good water resistance

Dextrin Fast tack, poor water resistance

Animal glue Good tack, vulnerable to insect attack

Polyethylene Requires heat, good dry bond, moderate water resistance

Hot melts Require heat, difﬁcult to handle, good water resistance, good water bond

196 CANS, COMPOSITE

operating efﬁciency. Most product applications require

precision gluing equipment to control the amount and

position of the adhesive on each web. The most commonly

used adhesives in today’s composite can production are

listed in Table 1.

Liners

Like all successful packages, the composite can must

contain and protect the products. For that reason, contin-

uous improvement is sought in liner materials. By com-

bining materials such as LDPE (see Polyethylene, Low-

Density), HDPE (see Film, High-Density Polyethylene;

Polyethylene, High-Density), PP (see Film, Nonoriented

Polypropylene; Film, Oriented Polypropylene; Polypropy-

lene), ionomer (see Ionomers), PVDC (see Vinylidene

Chloride Copolymers), metalized PET, and PE (see Film,

oriented Polyester; Polyesters, Thermoplastic) with alu-

minum foil (see Foil, Aluminum) or kraft (Paper; Paper-

board), the barrier properties of composites can be

matched with a broad range of product requirements

(see Laminating, Multilayer Flexible Packaging). The

polymers may be included as ﬁlm or coatings, or both.

Tables 2, 3 illustrate the physical properties of some of the

more common liner ﬁlms and complete liner constructions.

The laminates shown in Table 3 vary signiﬁcantly in

cost. Depending on can size, the difference in cost per

thousand units can be substantial. The foil-based lami-

nates, which provide virtually 100% water and gas bar-

rier, are becoming quite expensive. If less than total

impermeability is acceptable, it pays to investigate coated-

or plain-ﬁlm alternatives. For example, packers of frozen

juice concentrates have gradually moved away from foil

liners to laminations of PE or ionomer/PE and kraft.

Table 2. Physical Characteristics of Commonly Used Liner Films

Polypropylene

Physical

Characteristics

Oriented Oriented PVDC

Coat

Nonoriented Polyester LDPE Ionomer

Properties

50–MD

(0.5)

Tear strength, gf (N) 3–10

(0.03–

0.10)

3–10 (0.03–

0.10)

300–XD

(3) 12–27

(0.12–

0.27)

50–150

(0.5–

1.5)

50–150

(0.5–

1.5)

Burst strength, psi

(kPa)

55–80 (379–

551)

10–12 (69–83) 10–12 (69–83)

WVTR, g mil/(100 in.

24 h) [g mm/(m

d)]

0.75 [29.5] 0.3–0.5 [11.8–

19.7]

1.5 [59] 1.5 (59) 2.0–3.0 (78.7–

118.1)

2.0–3.0 (78.7–

118.1)

rate, cm

mil/(100

in.

24 h) [cm m/

d)]

160 [630] 1–3 [3.9–11.8] 160 [630] 3.0–4.0 (11.8–

15.7)

500 (1970) 250–300 (985–

1180)

elongation, % 35–475 35–475 550–1000 60–165 100–700 400–800

Product Resistance

b,c

Strong acids G G G G G G

Strong alkalines G G G G G G

Grease and oil G G G G G E

Source: Sonoco Products Company, Hartsville, SC.

gf/mil (0.386 N/mm) thickness.

G = good.

E = excellent.

Table 3. Physical Characteristics of Composite Can Liners

WVTR

at 1001F (37.8 1C) and 90% rh

Composite

Flat Creased O

Permeability

,cm

/(m

d)

100 ga PP/adh/100 ga AF/LDPE/25# MGNN kraft o0.001 o0.001 o0.001

100 ga PP/adh/35 ga AF/LDPE/25# MGNN kraft 0.06 o0.02

12# ionomer/35 ga AF/LDPE/30# XKL kraft 0.01 o0.02

1# PET slipcoat/35 ga AF/casein/25# MGNN kraft 0.09 0.93 o0.001

1# PET slipcoat/35 ga AF/LDPE/25# MGNN kraft 0.06 0.09 o0.001

12# HDPE/20# MGNN kraft 15.35 153

14.4# HDPE/20# MGNN kraft 12.09 126

key: # = lb/ream = 454 g/ream. 100 ga = 0.001 in. = mil = 25.4 mm. MGNN = Machine-grade natural Northern. XKL = extensible kraft linerboard.

ASTM Test Method E 96-80.

ASTM Test Method D 3985.

CANS, COMPOSITE 197