Yam, Kit L. (ed.). The Wiley encyclopedia of packaging technology

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Three-piece can manufacture is readily adaptable to

making cans of any diameter and height. The production

equipment is amendable to changes in size and is capable

of production speeds of up 700+ cans per minute when

cans are made as singles. In case of multi-high canmaking,

the bodies are scored to ﬁnal individual height prior to

rolling and welding; subsequently separated outputs of

1200 to 1500 cans per minute are achieved on appropri-

ately designed lines. Where the use of lead/tin solder is no

longer acceptable, the change to welding can be made at

minimal cost on existing lines, because only the equip-

ment that makes the cylinder (the bodymaker) needs to be

changed.

Three-piece manufacture is the choice of the small-to-

medium-sized operation requiring ﬂexibility for producing

can sizes required in relatively modest quantities or

to suit a variety of ﬁll products that require changes

in coating speciﬁcations. This is the salient asset of

three-piece canmaking facilities. It allows the manufac-

ture of various can types, i.e., food, ﬂat and/or carbonated

beverages, aerosols, and general line cans (industrial and

dry products) by adding the adequate complementing

equipment at limited cost to the existing line as long as

the bodymaker can cope with the range of cans to be made.

Two-piece can manufacture is basically suited to a

single can size, which requires outputs of at least 150 to

300 million cans per year. Yearly productions of modern

lines are usually much higher, i.e., in the range of 400 to

500 million per annum. DRD, using precoated sheet or coil

material, is used for food cans and predominently in the

shallower sizes (h/do1). The process is being used, how-

ever, for food cans with an h/d ratio of 1.5 in the popular 3-

in. (7.6 cm) diameter, e.g., 300 406 in the United States

(for explanation of can dimensions: The ﬁrst digit stands

for inches and the two last ones, for sixteenths of inches;

the measures are taken on the ﬁnished can overall in

length and over the double seems in diameter).

The application of enamel to both sides permits the use

of electrolytically chromium coated steel (ECCS), which

has a surface that is too abrasive to be used uncoated

(plain). It does also not offer any corrosion resistance.

Because economics demand the use of the thinnest possi-

ble can stock, the high strength needed dictates the use of

double-reduced (DR) grades. Additional strength is pro-

vided by beading or reforming the can bodies and adapting

the proﬁles of the ends for increased ﬂexibility in the

autoclave, i.e., providing a maximum of expansion volume.

Generally, using two presses with a minimum of per-

ipheral equipment, DRD provides a compact installation

of relatively low capital cost for the achievable outputs.

For that reason, it seems to be a preferred method for self-

manufacture (captive canmaking) of relatively shallow

containers by packers (e.g., tuna ﬁsh cans). However, the

material property requirements and its constance of

drawability are high, and the standard of enameling is

critical to maintain integrity as the metal is formed.

D&I converts a plain coil into a fully ﬁnished can in a

totally integrated, fully automatic process. The high capi-

tal cost of the full range of equipment needed implies

a high volume in a nonﬂuctuating and constant ensured

market. Together with the desirability of keeping the line

running once harmonious operation has been achieved,

this results in a 24-hour per day, 7-day per week operation

with annual production up to planned business feasibility

studies. Basically a single-can-size process, it is best

suited for the production of beverage cans, which are

made worldwide in a few standard sizes for use of high-

speed ﬁlling-closing lines. D&I thin-walled cans are pres-

sure packs (4 to 6 kg/cm

constant pressure in carbonated

drinks cans and much higher in D&I aerosol cans).

Their rigidity derives from the high inside pressure.

Such pressures are currently generated in noncarbonated

ﬁlls by inoculating a speciﬁc quantity of liquid nitrogen

into the headspace of the ﬁlled cans just prior to closing

the cans. This offers more and vast opportunities for light-

weight two-piece D&I cans.

Either tinplate or aluminum is used, usually on a

dedicated line. In recent years, because of the uncertain

economics relating to metal costs, new lines are built as

‘‘swing lines,’’ which basically can handle either metal. It

does nevertheless require some downtime to make the

change over, and lines normally operate continuously on

the one metal.

THREE-PIECE CAN MANUFACTURE

The manufacturing process of three-piece cans is as

follows: cut up coil stock into rectangular sheets; coat

and/or decorate sheets; slit into rectangular blanks; form

cylinders and side seam (soldered or nonsoldered, or

welded side seams); inside and/or outside side seam strip-

ing (lacquer or powder application and curing); separate

cylinders in case of multi-high cylinders; neck and or bead

if appropriate; expand or reshape or reform cylinders if

appropriate; form ﬂanges at both extremities; ﬁt maker’s

end; organized visual inspection or/and automatic leak

testing; and casing or palletizing (see Figure 3).

Figure 2. Scrolled sheet showing layout of blanks and scrolled

edges for material utilization. 1, Primary scrolling used when

cutting coil into sheets for coating. 2, Secondary scrolling used for

cutting sheets into strips for feeding into the shell press.

728 METAL CANS, FABRICATION

Cans for corrosive or delicate products (carbonated

beverages or red fruit, etc.) are internally spray coated

and cured prior to applying the maker’s end. This coat is

called ‘‘top coat,’’ whereas the ‘‘bottom coat’’ is applied on

the ﬂat sheet in roller coaters and cured in wicket ovens.

Both bottom and top coats can be spray coats with or

without intermediate curing (spray–spray–cure or spray–

cure–spray–cure).

Slitting. Large rectangular sheets of can body stock,

precoated if required on one or both sides by roller coating

techniques, are slit by pairs of circular knives (3) on

tandem slitters, ﬁrst logitudinally into strips in which

the width corresponds with the development of the can

bodies, and then transversely into rectangular blanks of

the appropriate size corresponding with the can height,

respectively, with the allowance to form the welding over-

lap (or the lock side seam in case lap-locked side seamed

cans are made, soldered, or nonsoldered or cemented).

Because welded cans have considerably less overlap

(0.4 to 0.8 mm) at the side seam than soldered cans (side

seam allowance), slitting demands more rigorous preci-

sion (dimensions and right angles) than is needed for

soldered can blanks. Circular slitting cutters can be posi-

tioned accurately by applying internal pressure at the

bore of the cutter hubs to expand them so as to move freely

on the slitter shaft (4). The said hubs can also be blocked

on the shafts by screw jammed wedges or by application of

hydraulic pressure (compressed grease) inside the hub.

Any of these proven methods must apply the needed

jamming pressure perfectly symetrically to avoid distort-

ing the setting (narrow slitting gap, usually 5% of the body

stock thickness) or/and cause wabbling of the slitter

knives’ cutting edges.

Bodymaking, Soldered Cans. The solder alloys com-

monly used consist of 98% lead and 2% tin. As more and

more countries impose lower limits of lead content in food,

the soldered can is being phased out in Western countries,

if not being banned altogether as in the United States.

Nevertheless, many soldering lines around the world will

continue in operation for some time. The machine consists

of a ‘‘bodymaker,’’ which feeds single blanks from the feed

hopper, and then scores (in case of multi-high can bodies),

ﬂexes, and forms the blanks into cylinders after slit and

clip notching and hooking. The bodymaker is coupled to

the side seamer, i.e., the soldering attachment where the

joint is soldered and wiped off the excess of solder accu-

mulated at the outside of the side seam.

Blanks are still commonly transferred manually from

the slitter blank collector, although equipment exists for

automatic transfer. In the ﬁrst case, a visual check for

quality and eventual rejects is possible, whereas sophisti-

cated devices check automatically any miscut blanks

and trigger the programmed intervention. The prepared

hooks, or edges, as prepared and formed in the hooking

station(s) of the bodymaker are interlocked on the forming

horn and are compressed in the horn spline groove by the

bumping steel. For high-speed operation, the body cylin-

der is usually formed by a pair of wings. (The term ‘‘wing

form bodymaker’’ contrasts with ‘‘roll form bodymaker,’’

which is a former American Can Co. technique.) In this

technique, bodies are rolled and consecutively notched

and hooked in the rolled shape.) Liquid ﬂux is applied

on one or both hooks prior to engage and bump the side-

seam on the forming horn.

The lap-lock assembled bodies are fed out of the body-

maker and picked up synchroneously and individually by

the clamping pawls of the soldering chain. The side seam

area is preheated by ribbon gas burners before passing

over a longitudinal solder roll where solder is applied. The

presolder ribbon burners preheat the side seam, and by

appropriate setting of the ‘‘bow and counter bow’’ burners

the side seam is kept as straight as possible. When

applying solder, post-solder ribbon burners ensure that

the solder is ‘‘sweat’’ into the capillary gaps of the side

seam, after which a rotating wiper mop removes excess

solder, mainly in the form of blobs. Any solder splashes

Figure 3. Three-piece can manufacture. Sheet-coating line: 1, sheet feeder; 2, roll coater; 3, oven; 4, cooler; and 5, unloader and sheet

stacker. Can line: 6, slitter; 7, blank feed; 8, bodymaker; 9, side seamer; 10, ﬂanger; 11 beader; 12, end seamer; and 13, tester. End line: 14,

sheet feeder; 15, secondary scroll shears; 16, shell press; and 17, compound liner. Courtesy of Metal Box Ltd.

METAL CANS, FABRICATION 729

toward the inside of the can bodies have to be avoided.

Rotary solder splash shields provide for this.

The can is then cooled by air jets before conveying to

the downstream ﬁnishing operations. As lead contamina-

tion has become an increasing concern, the wiper mop

unit has been the subject of considerable improvement to

contain the lead dust generated by its operation, particu-

larly at high-speed canmaking operation. By its nature,

the process requires the use of tinplate, although black-

plate had been soldered during World War II in the United

States. To ensure sound soldering, a minimum ‘‘solder-

ability’’ has to be ensured: rugosity of the steel base, a

minimum of alloyed and free tin, oxidation, and so on. The

line operator’s skill and experience will overcome most of

the material inherent drawbacks, the major one of which

is the ﬂuctuation of stiffness of the steel base of the blanks

(open or thick laps).

Bodymaking, Welded Cans. The side seam is made by a

resistance-welding process using the ‘‘lost-wire-electrode’’

principle (5) as well as The Canmaker June 1996 issue

Evolution of a bodymaker by Sigfried Frei, Frei AG

Switzerland. Body blanks are fed from the bottom of the

feed hopper and then transferred through double blank

detectors; then, the blanks are scored for eventual multi-

high can bodies and ﬂexed into the forming rolls (See

Figure 4).

The two laps of the rounded cylinder are butted in the

grooves of the Z-bar, and the cylinders are pushed along

the Z-bar by one or more driven chains provided with

pawls. Upon perfect radial centering in the Z-bar, the

cylinders are introduced into the welding rolls at the same

speed as the said rolls are driven at. The actuating

mechanism of the reciprocating introduction pusher pawls

are designed so as to guarantee that pushing speeds are

accurately matching the peripheral roller electrodes

speed. Only the outer electrode is driven.

Overlap accuracy over the full length of the side seam,

which is also dependent on gauge and temper of the plate,

has to be controlled as to avoid bodymaker jams and

wrecks or mainly irregularly welded side seams. The two

overlapping edges of the cylinders are bonded by a-c

resistance continuous nugget welding using approxi-

mately 4000 to 7000 A at 8 to 5 V. Both overlapping edges

must be free of contamination, each one on both sides

(lacquer splashes or traces) to eliminate variations of

resistance, which would lead to welding faults as well as

eventual copper wire ruptures.

A signiﬁcant amount of energy is lost in heating other

parts of the welder, such as welding arms and electrodes,

which need water cooling. In high humidity, this can lead

to problems with condensation. Thermostatically con-

trolled cooling media, even on upper acceptable limits of

operation temperature, should avoid reaching dew points.

Each resistance welding spot, which is called a nugget,

is achieved by one half of the a-c wave cycle. Welding

current supply to the electrodes and welding speed are

limited because the nuggets should overlap longitudinally

to ensure a homogenous side seam over the full length of

the side seam. To achieve higher welding speeds of up to

120th per minute, higher welding current frequencies

have to be generated via an alternator or static transfor-

mers. Other sinuosoidal waveforms are applied and

contribute to reaching high welding speeds coping with

different canstock surface conditions.

Earlier systems used a large overlap (2 to 3 mm) and

raised the steel temperature to the melting point by

applying welding roller pressure to forge weld the metal.

The latest welders use a small overlap as mentioned (0.4

to 0.8 mm) with metal temperatures just below the melt-

ing point and increased roll pressure to forge the two laps

together. To ensure reproducible welding conditions over

the full length of all double seams produced, the electrode

contact is made by endless copper wire wrapping around

both welding rolls and moving the cylinders at the preset

welding speed. Any contamination of the welding electro-

des by tin pick-up is thus continuously removed from the

contact area. After use on both sides of the proﬁled wire, it

is either chopped or rewound for recycling.

Having dealt effectively with the problem of tin con-

tamination of the copper wire electrodes, the system

paradoxically requires a minimum of tin coating on the

can stock, around 0.09 lb/bb on both sides (1.2 g/m

on one

side.) Table 1 shows the comparison of properties of

various materials wherein nr 25 and nr 10 stocks have

respectively tin coatings of 2.8 and 1 g/m

on one side. TFS

or ECCS materials, as well as blackplates, are poorly

weldable if at all under acceptable production conditions.

They have to be ‘‘edge cleaned,’’ i.e., the oxide ﬁlms have to

be abrased from the four sides of the overlapping edges of

the side seam. Edge cleaning has, however, never found

reliable solutions apart from edge cleaning by ‘‘edge

milling’’ as practiced by the Continental Can Company

in their Conoweld Technique. This system used welding

rolls without an intermediate copper wire, but it is now of

less importance in high-speed canmaking, mainly because

of the frequent need for changing the electrode rolls.

The integrity and quality of the seam weld is usually

tested by visual and mechanical means (e.g., Ball test). For

a more detailed examination, weld cross and longitudinal

metallographic inspection will reveal any sign of separa-

tion between laps, cavities and so on. Radiographical

examinations are also used for quality inspections.

Welders have been ﬁtted with ‘‘weld monitors’’ to monitor

welded seam quality continually. Usually, these monitors

rely on measurements of voltage or current ﬂuctuations

between the welding electrodes. Welded seams, as well as

single nuggets, made outside the preset limits are de-

tected, and the faulty cans are ejected. Other monitoring

systems have been explored for enhanced performance

and were based on weld temperature or on the ﬁnal

thickness of the forge-welded overlapped side seam.

Renewed effort went into welding the side seam by

means of a laser beam (6). The principle of can welding by

a laser was demonstrated in the late 1970s, but welding

speeds seemed to be too low to justify commercial exploi-

tation. The technique was then discarded. Positive results

of other ongoing research and development (R&D) work

on the subject in the United States, Europe, and Japan are

not known. Apart from the elimination of costly copper

wire, the method offers pure butt welding with advan-

tages to double seaming of the ends, necking, as well as

730 METAL CANS, FABRICATION

Figure 4. (a) Fundamentals of electric canbody welding. (b) Longitudinal section of a welded seam showing overlapping weld nuggets

(40 ). (c) Longitudinal section of a welded seam showing separated weld nuggets (40 ). (d) Section through elements involved directly at

the welding station.

METAL CANS, FABRICATION 731

versatile decoration such as wrap-around printing. The

copper-wire-welded seam and the plain welding margin in

case of lacquered insides of the cylinder interrupt an

otherwise smooth inside enameled (or plain) surface.

The welded seam contains exposed iron and iron oxide

as well as eventual traces of copper besides tin at either

side of the weld. To protect the product from contamina-

tion and/or the weld from attack by the product that still

results in contamination of the product, the side seam

needs to be coated in most cases.

The formation of iron oxide can be avoided by neutral

gas welding, in which case the weld area is isolated from

the atmosphere by neutral gas jets such as nitrogen and a

small percentage of hydrogen. This can be done at the

inside and/or at the outside of the side seam.

Bodymaking, Cemented Cans. Cans used only for dry or

otherwise neutral products, such as powders of speciﬁc

natures, mineral or/and vegetable oils as well as many

industrial products. Melted organic cements are injected

into the inner hook of lap-locked side seams and, after

engaging and ﬂattening the side seam, they act as sea-

lents. Before the almost universal use of two-piece cans

for high-output beverage-can production, one method for

making them was to cover the longitudinal edges of the

blanks with a nylon strip, which was fused after forming

the cylinder. The process has a many of proprietary names

(eg, Miraseam and A-seam). An advantage was the com-

plete protection of the raw-cut edges of the blank. It could

only be used with precoated TFS, because the melting

point of tin is close to the fusion temperature of the plastic.

Even tapered corned beef cans were made in this way.

When tin prices were a multiple of the current ones, using

TFS was most cost-attractive solution. Cost cutting

in metal packagings is therefore not an exclusive pre-

sent-day problem. The bodymaker used to make the

nylon-bonded cans was an adaptation of the soldering

conﬁguration.

Completing the Body. The plain cylinder must be furn-

ished with a ﬂange at each extremity of the cylinder or

otherwise odd-shaped body for attachment of the closure.

For food processed in and with the can, where the can may

be subjected to external pressure especially at the cooling

phase of the autoclaving cycle, or remain under internal

vacuum during storage, the cylinder wall may be ribbed or

beaded for radial strength. Beading proﬁles and distribu-

tion along the can body are to be designed so as to reach

the desired proportion of radial against axial resistance of

the cans.

Cylinders for shallow containers, especially those that

cannot be made on bodymakers because of limited mini-

mum cylinder height, may be made ‘‘multi high,’’ i.e., in a

length suitable for two or three cans to obtain maximum

efﬁciency from the forming machine. The welding speed

remains unchanged thereby whereas the mechanical mo-

tions are divided by 2 or 3. Two techniques are used for

parting the multi-high bodies into their double or triple

components by breaking the score line or by cutting

peripherally the unscored bodies.

TWO-PIECE CAN MANUFACTURE

Metal Forming Methods. Both methods of making two-

piece cans use metal-forming principles that depend on

Table 1. Comparison of Properties of Various Materials

Properties

Material Section structure Weldability

Lacquer

adhesion

Iron Pickup Value

(IPV)

Filiform corrosion

(FFC)

LITEWEL-N Cr

  

Ni-Sn-Fe

Base steel

#25 Tin plate Cr





FeSn

Base steel

#10 Tin plate Cr



FeSn

Base steel

TFS Cr

 

Base steel

Low-nickel-plated steel Cr

 

Base steel



Excellent



Good D Normal x Poor Cr

: Chromium oxide Cr

: Chromium metal

Source: NKK Technical Bulletin—The Steel Canstock Guide by Elizabeth Parr, Shefﬁeld, UK.

732 METAL CANS, FABRICATION

the properties of metal to ‘‘ﬂow’’ by rearrangement of the

crystal structure under the inﬂuence of compound stresses

without rupturing the metal.

Drawing. In drawing, as applied to can manufacture, a

ﬂat sheet is formed into a cylinder or other section, such as

oblong, e.g., ﬁsh cans, by the action of a punch drawing it

through a circular or different shaped die. See Figure 5

showing the basic tool parts involved and the stresses and

strains occuring in the material. Some thickening toward

the upper part of the drawn element is inevitable, but the

process is essentially one of diameter reduction at constant

metal thickness and volume so that the surface area of the

drawn part is practically equal to the surface area of the

blank from which is has been formed. This factor forms the

basis of design, in particular the calculation of metal use.

The amount of diameter reduction achievable, i.e., from

blank to cup diameter, is governed by the properties of the

material, the surface friction interactions between the

tooling and the material inﬂuenced by the tool, and mate-

rial surface conditions and lubrication. The blankholder

force is an additional factor that adds to the drawing force

which the material has to stand between punch and draw

radii. Drawing has been the subject of much research. One

of the classic relationships is shown in Figure 6.

The diameter of the cup produced in the initial draw

may be reduced even more by a similar redraw operation

with a draw sleeve ﬁtting between the punch and the

Figure 6. Limiting draw ratio. The maximum blank diameter

which can be drawn into a cup without metal failure. The

relationship illustrate the signiﬁcance of sheet thickness (gauge).

D = blank diameter; d = punch diameter; s = sheet gauge. Courtesy

of International Tinplate Conference, 1976.

Figure 5. Basic stresses and strains. Courtesy of ALCOA Form-

ing Aluminum.

Figure 7. Reduction in diameter is accompanied by a corre-

sponding increase in height. Courtesy of Styner O Bienz, Nieder

Wangen/Bern Switzerland.

METAL CANS, FABRICATION 733

Figure 8. (a) Typical lay out of medium production of DRD cans. Courtesy of Ferembal Nancy/France. (b) Sequence of DRD fabrication

steps (c) Typical 401 206 DRD can with end (for ref. only).

734 METAL CANS, FABRICATION

inside diameter of the cup. The said draw sleeve acts as a

blankholder. The rule of constant area and volume deter-

mines that the reduction in diameter is accompanied

by a corresponding increase in height (see Figure 7). The

redraw operation can be repeated in several drawing

stages, provided the progressive reductions fall between

deﬁnite limits to avoid metal failure. Draws can be made

‘‘through the die,’’ and the drawn part be stripped from the

punch at the end of the press stroke below the die or the

press stroke can be limited so as to leave the drawn part

with a ﬂange. In this case, the drawn part is extracted

from the die and is retained by the punch (friction and

vacuum), and ultimately it is stripped from the punch for

transfer or evacuating from the press. The stroke of the

press has to be adapted accordingly. In the latter case, it is

usually equal to 2.5 times the cylinder height as drawn.

Figure 8(c) shows a typical drawn can provided with a

stacking or/and label retaining bead if canstock is not

decorated. Figure 8(b) is the sequence of operations from

the blank to the ﬁnished can, and Figure 8(a) is a typical

schematic layout of a DRD can production line of medium

production capacity.

Wall Ironing. In pure ironing, as used in the D&I

process, a cylindrically drawn cup is redrawn by the

ironing punch and therefore precisely ﬁts the said punch

diameter. The redrawn cup is then forced axially through

a set of ironing die rings, whose diameters, which are

progressively decreasing, create a gap with the punch that

is smaller than the wall thicknesses of the redrawn cup

and the consecutive wall thicknesses from t1 to t4; see

Figure 9(a) whereon the stated wall thicknesses are

related with the punch and rings radii differences.

The process, which is similar to impact extrusion, thus

results in a reduction in wall thicknesses at a constant

diameter excepted for t3 where the punch diameter is

recessed so as to form the ‘‘thick wall.’’ t4 is the ‘‘thin wall’’

that is reduced from 0.22 mm for t0 down to 0.07 mm. Here

too, the governing principle is the constant metal volume.

In other words, the volume of the metal in the ironed can

body (prior to trimming) is equal to the ingoing cup

and consequently to the original blanked disk. Note the

sequence of operations in Figure 10. The amount of

reduction at each stage is determined by the material

properties, governed by the needs to avoid metal failure.

The high friction, under extreme surface pressure mainly

at the outer surface of the ironed can body, makes special

demands during lubrication, which is combined with

copious ﬂood cooling to maintain the critical punch-to-

die gap.

A similar effect can be obtained in drawing if the gap

between the draw die and the punch is less than that of

the metal being drawn. It is common practice to keep this

gap equal to the nominal thickness of the canstock to

control thickening caused by diameter reduction. This

process is called sizing. The drawing gap can be reduced

even more to produce a deﬁnite thinning of the wall,

relative to the base material as a combination of drawing

and ironing, or thinning. Special lacquering is primordial

in this case.

D&I Can Manufacturing. The procedure of producing

D&I cans is schematically as follows: unwind the plain

coil; lubricate; conduct blanking and cup drawing; redraw;

execute wall ironing; perform dome forming; trim body to

correct height; wash and surface treat (if appropriate as

for aluminum); implement dry or wash coat; and cure.

Then for beverage cans, the process is as follows: base coat

outside and cure (if appropriate; decorate and cure); coat

inside and cure (eventually a double coat); and neck and

ﬂange open end (in the case of a tinplate, the order of the

last two operations may be reversed). For food cans, the

process is as follows: wash coat outside; neck and/or ﬂange

as appropriate and if body is not beaded; body beading;

and coat inside (in some lines the order of the two last

Figure 9. (a) Schematic of wall ironing principal Courtesy of:

Tin-plate and modern canmaking technology by E. Morgan (b)

Ironing DWI can body and stresses on the material. Courtesy of

Rasselstein AG Germany.

METAL CANS, FABRICATION 735

operations is reversed). The closures,orends, are made

from precoated sheets or coil on multi-die presses, which

are proﬁled in such a way that internal pressure will not

cause any permanent deformation (peaking) in the chuck

wall radius area. Their turned down edge of the ﬂange

(crown shaped or plain) is curled so as to allow stacking

and automatic handling and assist the formation of the

double seam. A sealing compound is nozzle injected onto

the spinning ends and then placed and centrifuged so as to

form a gasket in the ﬁnished double seam (see Figure 11).

Compounds are either solvent based (hexane) or water

based, which are, respectively, drying by evaporation

of the solvent or by heat drying (hot air or various

radiations).

The components of a D&I line are shown in Figure 12.

The coils are shipped with the axis vertical, for safety and

to avoid damage to the laps. A down ender is used to bring

the axis horizontal and to transfer the coil to a coil car for

distribution to one of several dereelers (unwind stands),

each feeding one cupping press or cupper. Dereelers may

be dual and engineered in such a way that coil changes are

rapid either when coils are ﬁnished or if one has to be

removed for being defective. The coil is passed through a

lubricator where lubricant is applied by dipping in a tank;

the excess is removed in a couple of rubber-covered rolls.

The lubricant is constantly recirculated for ﬁltering, tem-

perature control, and bacteriological control. It is essential

that lubricants, coolant-lubricants and washing chemicals

be compatible and form a system possibly supplied by

the same manufacturer. The steel coils are additionally

and continuously inspected to detect pinholes and surface

defects (visual inspection), and to monitor the gauge

thickness, which is interlocked to stop the cupper when

out-of-speciﬁcation material is detected. The cupper (7) is

a double-action press used to blank and draw the cups

under a perfectly controlled blankholder force. Blanking

the disk and drawing the cup are two consecutive phases

in one stamping cycle or press stroke.

Depending on coil width, as many as 12 cups may be

produced in one working stroke. The cuppers can be

designed with top drives (Minster) or underdrive (Stan-

dun). Cups are produced at speeds of up to 200 strokes per

minute.

The cupping process demands great precision because

of (a) extremely narrow drawing gaps of 10% in excess of

the material thickness, the between punch and die. Ma-

terials currently used have a thickness of 0.009’’ (0.24 mm)

and canstock will undoubtedly become thinner still in the

future. (b) Shreds (intervals) between two adjacent cuts of

blanks is about 0.04 in. (1 mm). (c) All press and tool parts

must be perfectly aligned, ﬂat, parallel, and/or concentric.

The cups should show no wrinkling or measurable or

visual differences all around the walls. This is fundamen-

tal for successful ironing. The wall ironer (bodymaker in

the United States) (8, 9) converts the cups into a cylinder

with the correct preestablished and correct thickness

distribution along the wall and dome shapes (the base)

to resist elevated internal pressure. Figure 9(a) shows the

arrangement of the ironing tool set as it is basically used

in all ironers. At the end of the stroke, at the moment the

punch reciprocates after the front dead point of the ram,

spring-loaded stripper ﬁngers, assisted by compressed air

fed through the ram to the punch nose, strip the can body

from the punch into a discharge conveyor, which transfers

the cans sideways to the trimmer. For the alledged base of

constance of metal volume, the length of the cans will vary

with the tolerances of the material and toolings. The top

end of the cylinder will be more or less wavy, earing, which

is caused by speciﬁc characteristics of the canstock as long

as toolings and alignments, as well as ironer stability,

cannot be incriminated.

Ironers run at about the same speed as the cuppers, so

that one wall ironer is needed for every tool or ‘‘out’’ in the

cupper. In practice, one ironer was added as a stand by to

bridge short interventions on the machine or/and clear

jams, and so on. Newer generations of ironers run faster

than the cupper and twin-ram machines allow to half the

number of ironers in the canmaking line. Stand by must

still be available as the loss of output is doubled during

down time in case of twin-ram machines. The tooling uses

inserts of carbides or/and ceramics in the ironing dies

together with carbide or ceramic punches when steel cans

Figure 11. Double-seam closure. Showing ﬁxing of end to cylin-

der, and function of lining compound: 1, end curl, folding round

ﬂange on cylinder, 2, lining compound; 3, seam overlap; 4,

cylinder; and 5, end.

Figure 10. Stages in forming a D&I body. 1, Circular blank; 2,

cup; 3, redraw; 4, ﬁrst ironing stage; 5, second ironing stage; 6,

third ironing and dome forming (note thickening at top where

ﬂange is to be formed); and 7, trimmed body.

736 METAL CANS, FABRICATION

are fabricated. Good quality tool steels are adequate for

aluminum cans. Associated with every ironer is a trimmer

to which the eared bodies are transferred positively held

by the base either magnetically or by vacuum. Rail (sickel

knife) or roller trimmers are used.

In rail trimmers, the end of the canbodies is trimmed

between a mandrel mounted on a rotating turret and a

stationary rail. A certain number of mandrels are ﬁtted

and the turret is in continuous motion.

In the roll trimmer, cans are indexed to a position where

the end is inserted between two rolls and rotated about

their axis while the rolls are closed, one being pivotly

mounted, to perform a peripheral trimming, or cutting,

action. In one widely used machine, the cutting rolls are

mounted in an easily removable cartridge for refurbishing

and precision-setting in a toolroom environment.

After trimming the canbodies to their speciﬁed height,

they are mass conveyed in bulk, in upright position, to a

washer. The cans are conveyed on a ﬂatbed open-mesh

belt, open-end down, through a series of compartments

ﬁtted with spray nozzles above and below. The top con-

veyors are used in each spray compartment to restrain the

cans from falling over. After prewashing with detergents

for removing drawing and ironing lubricants, the cans are

washed, prerinsed, and rinsed with demineralized/deio-

nized water. Aluminum cans commonly receive an etching

treatment to make the surface receptive to organic coat-

ings applied in the ﬁnishing operations. Deionized water

rinse ensures stain-free drying.

Alternatively, the ﬁnal rinse may contain an organic

coating to protect the outside surface of tinplate food cans

underneath the paper label applied by the ﬁller. The

washed and dried cans are now ready for receiving inter-

nal and external ﬁnishes, both structural (necking/ﬂan-

ging and eventual reforming) and protective (coatings and

decoration). The food cans are usually beaded for the thin

wall to stand buckling and/or implosion in the same way

as with three-piece cans. The machinery, however, is

differing in detail because of the presence of the integral

bottom and the absence of side-seam extra thickness as on

three-piece cans. Spin ﬂanging is invariably used to avoid

split ﬂanges in the axial metal grain structure caused by

ironing, although excessive work hardening does not

occur. The top of the beverage cans is necked-in to yield

metal cost savings through the use of smaller diameter

and therefore thinner ends material. The ﬁrst necking

steps may be die-necking operations followed by spin

necking/ﬂanging. This method is ﬁnding increasing appli-

cation (10). When the ﬁrst cans were die necked and spin

ﬂanged from 211 to 209 diameter, they are now necked

down to 202. It creates an aesthetically pleasing neck

proﬁle and contour when cans are spin necked, and this

technique provides with minimal strain on the split-prone

ﬂange and low axial force on the can. For the smaller

necks, such as 211/202, several die prenecks are necessary

when die necking is applied (11). Single-stage prenecks

are currently practiced by spinning. The ﬁnal spin-neck/

ﬂanging operation is done either before or after internal

protection depending on local circumstances. In general,

aluminum requires an enameled surface to prevent pick-

up (galling) on the tooling. In some way, the enamel acts as

a lubricant.

DRD Can Manufacturing. The manufacturing steps are

as follows: cut up the coil into scrolled sheets (eventually

coil coated stock); coat and/or decorate sheets; blank disk

and form cups; redraw once or twice depending on the h/d

ratio of the can; form base (or panel can bottom); trim

ﬂange to applying width; bead (if appropriate); spray coat

(either single or top coat on roller coated material accord-

ing to pack) and cure; and test and palletize. See typical

production setup in Figure 8. As in D&I, a multitool

cupper (7) (Figure 8) is used to cut blanks from wide coils

or scrolled sheets and form them into shallow cups. Their

D/d ratio (blank to cup diameter ratio) as chosen will

inﬂuence the performance of the subsequent draws if cups

are reformed by one or two more draws, which progres-

sively reduce the diameter and increase the height. By

Figure 12. D&I can manufacture. Diagram showing all the equipment that may be required. 1, Uncoiler (dereeler); 2, lubricator, and

optional coil inspection; 3, cupping press; 4 wall ironer (bodymaker); 5, trimmer, 6, can washer; 7, external coater; 8, pin oven, 9, decorator;

10, pin oven, 11, necker–ﬂanger; 12, tester; 13, internal spray machines; 14, curing oven (IBO); 15, optional second spray; and 16, IBO.

Courtesy of Metal Box Ltd.

METAL CANS, FABRICATION 737