Metal

Cans & Containers

 Metal packaging form

Steel - is one of the older packaging material.

- originally used for round, square, and rectangular boxes and canisters
(shortened to “can”).
- tea & tobacco – products packaged in tin-plated, mechanically seamed
or soldered steel containers with friction or hinged lid.

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- Metal packaging form provides sanitary food cans.
- Thermal processing of food packed into hand-soldered cylindrical metal
cans started in the early 1980s & developed into a major industry.

Advantages:

1. Being relatively inexpensive.

2. Capable of being thermally processed.
3. Rigid.
4. Easy to process on high-speed lines.
5. Readily recyclable.
6. Offers total gas & light barriers.
- Originally, all steels containers were
fabricated from flat sheets that were
cut to size, bent to shape &
mechanically clinched or soldered
to hold the final shape of THREE -
PIECE CAN (construction of a sidewall
& top and bottom ends).
- Now , ways of drawing metal
(shaping metal by pushing it through a
die) were developed to produce TWO- Three-piece (left) & two-piece (right) can
construction.
PIECE CAN (construction have a body
& bottom in a single piece with a
separate attached end).
 Shallow drawn containers with
friction or slip covers were used
for pastes, greases & other Shallow drawn
semisolid products. containers with
friction or slip Two-piece cans. Left steel can,
 Later, two-piece shallow drawn covers right aluminium can. Steel can
cans with double-seamed be shallow drawn, aluminium
(folded) bends were used for can be deep drawn.
sardines.
 Two-piece vs. Three-piece cans

Advantages:
-Two-piece cans
 reduced material usage
 improved appearance
 elimination of a possible leakage location.

-Three-piece cans can easily be changed in length & diameter.

Disadvantages:
-Two-piece cans require more elaborate tooling that is dedicated to
one can form.
 Two-piece cans

- Improvement in metallurgy & processing methods of

making two-piece cans allowed:

 Deeper draw
 Multiple draws
 Draw-and-iron process (walls of drawn container
were made thinner by an ironing step)
 Common types of metal

Common metals used as packaging material such as:

 Low carbon steel-are the most common form of steel, containing

approx. 0.05 to 0.15% of carbon.
 Tin (Sn), a chemical element belonging to the carbon family, Group 14
(IVa) of the periodic table). Tin is widely used for plating steel cans used
as food containers, in metals used for bearings, and in solder.
 Lead (Pb).
 Aluminium (Al).
 Common types of metal

- Tin, lead & aluminium can be formed into tubular shapes by impact
extrusion. The advancement in impact extrusion technology allows
production of heavier-gauge aluminium containers e.g. Pressurised
aerosol.

- Collapsible tube- originally made from tin & lead, but now using
Aluminium.

- Except for small number of applications requiring chemical properties

of tin or lead.
 Common metal
container shapes

The most common metal container shapes include:

 Three-piece steel sanitary food cans.
 Aerosol cans made by two methods: (1) Three-piece sheet cans with a
welded body & two ends, & (2) one-piece, impact extruded aluminium
cans necked-in to accept the valve cup.
 Steel or aluminium two-piece, drawned-and-ironed beverage cans.
 Two-piece steel or aluminium cans made by drawing or by draw and
redraw. Full opening, ring pull-top cans are used for fish products, canned
meats & dips. Double seamed, conventional-top cans are used for many
canned food products.
 Common metal container shapes -
continued
 Canned with hinged lids, usually steel, used for medications, confections,
small parts & novelties.
 Flat round cans of drawn steel or aluminium with slip covers. Used for
ointments, confections, shoe polish & novelties.
 Three-piece steel or aluminium ovals, typically fitted with a dispensing
spout & used for oils.
 Traditional pear-shaped, three-piece steel ham cans.
 Oblong, steel three-piece F-style cans. The “F” name comes from Flit
insecticides.
 Oblong, key-opening cans, three-piece steel, used for luncheon meat
products.
 Three-piece square-breasted steel cans. Larger design are used for the
talcum, bath & baby powder products. Smaller cans, used for spices & dry
condiments.
 Can-making steel
- The name “tin can” is not strictly correct, since low-carbon steel is the
predominant can-making material.

- Bare steel corrodes readily when in contact with moisture & other
corrosive agents, & unprotected steel or black plate can be used only
for noncorrosive products such as waxes, oils or greases.

- Normally a coating is needed to protect the steel:

 Dipping black plate sheets into baths of molten tin (known as
“tinned canister”).

 Today, black plate is electrolytically tin-plated, allowing substantial

reductions in the amount of tin used, as well as offering the ability to
put different thicknesses of tin on either side of a steel sheet. Thin tin
layer  0.38 µm.
 Can-making steel
 Electrolytic chrome-coated steel (ECCS) use chrome & chrome
oxide for corrosion protection.
o ECCS is also known as tin-free steel (TFS).
 Advantage:
1. ECCS is more economical than tinplate.
 Disadvantages
1. ECCS has gray appearance rather than bright reflectance of
tinned steel.
2. However, the chrome must be removed to weld the body can.
Therefore, ECCS is most often used for can ends or for
drawing, where weldability is not the requirement.
 Three-piece steel cans
- Steel three-piece can bodies can be mechanically seamed, bonded
with adhesives, welded or soldered.
-Aluminium cannot be soldered or welded economically.
-Welded sanitary three-piece can bodies are, therefore, only made on
steel.
-Mechanical seaming, or clinching, would be used only for containers
intended for dry products, where hermetic seal is not important.
 Three-piece steel cans
- Adhesive bonding, or cementing, uses a thermoplastic (or other)
adhesive extruded onto a hot can blank. The blank is shaped into a cylinder
on a body former, the hot thermoplastic adhesive is applied, & the seam is
“bumped” & quickly chilled to set the bond.

- Soldered cans (solders: 97.5% lead & 2.5% tin)

The engaging hooks are bent into the can blank similar to that for a
mechanical seam. Molten lead-or tin-based solder is flowed into the seam.
Lead extraction by food products is always a potential problem. Soldered
food cans no longer permitted in North America, but, some soldering is still
done for non-food applications.

- Welded cans- strong & eliminate potential lead hazards.

The body sheet is formed into a tube with a slight overlap along the joint –
then passed between 2 continuous copper wire electrodes; an electrical
current heats and fuses the metal.
Welded seam: about 30% thicker than the two base metal sheets.
 Three-piece
steel cans

Three-piece can
production.

-All three-piece can bodies are pressure-tested & have the ends flanged to
receive the can top & bottom ends.
-The can maker plies one can end & sends the other end to the user for
double seaming after the can is filled.
 Three-piece
steel cans
- Sanitary food cans that may be thermally processed in a retort have
beads pattern embossed into the can sidewalls.
 Sidewall beading pattern serves to improve resistance to collapse
because of external pressure.
- This prevent paneling during pressure differentials encountered
during retorting & enables the can to withstand an internal vacuum.

 Sidewall beading offers advantages:

 requires more material
 reduces top-to-bottom compression strength
 complicates labeling
 Three-piece
steel cans

Can-end
embossing
pattern.

- Can ends intended for thermal processing are stamped with a series of circular
expansion panels.
- This allows the ends to move so that the contents inside the can are able to
expand & contract without bulging or otherwise distorting the can.

- The chuck panel is designed to give the proper clearance to the double-seaming
chuck used to seal the can end to the body.

- Can-end compound applied around the perimeter that acts curl as a caulk or
sealant when the end is mated & double-seamed to the can body.
 Three-piece steel cans

- Double-seaming is the attachment of the can end to the body. It involves two
curling steps.
- The first operation roller rolls the cover hook around the body hook and the
second operation roller tightens the two hooks to provide a double seam.
 Two-piece drawn cans
There are 3 methods of making steel or
aluminium two-piece cans:
 Draw
 Draw and redraw (D&D)
 Draw and iron (D&I)

Straight lines on a blank (left) become

distorted in different directions when
Draw process drawn into a can (right).

- A shallow profile can – whose height is less than its diameter – can be
drawn (stamped) directly from a circular metal blank.
- The metal blank is drawn through a die & re-formed into a new shape.
- The thickness of the finished can sidewall & bottom remain essentially as in
the original blank. The process is sometimes referred to as “shallow draw”.
- Blanks for drawn cans may be decorated prior to drawing
 Two-piece drawn cans
Draw-and-redraw process
- A single-draw operation is limited in how far the metal can be reshaped.
- Cans having a height equal to or greater than the can’s diameter will
usually require a second draw, is called the “draw-and-redraw” process.
- The first draw produces a shallow cup. The second draw reduces the
diameter as the can is deepened.
- Cans having a height significantly greater than the can diameter would
require a third draw.
- If the container is to be thermally processed, sidewall beads are rolled
into the walls in a separate step.
- Body flanges for engaging the can end are rolled on in a manner similar
to that used in three-piece can manufacturing.
 Two-piece
drawn cans
The manufacturing
sequence for a
necked D&I can.

Draw-and-iron (D&I) process

-Carbonated beverage cans are made by D&I process.
-A blank disc is first drawn into a wide cup (step 2).
-In a separate operation (step 3), the cup is redrawn to the finished can diameter
& pushed through a series of ironing rings, each minutely smaller in diameter
than the previous one. The rings “iron”, or spread, the metal into a thinner sheet
than the original disk.
 Draw-and-iron (D&I) process - continued

In the D&I process, the second draw & ironing stages occur in one
continuous movement. The punch finishes its stroke against the bottoming
tool.
 Draw-and-iron (D&I) process - continued
- The bottom of a D&I can has the same thickness as the starting disc;
however, the sidewalls are considerably reduced in thickness & the
metal area of the final can is greater than that of the initial disk.

- Necking operations reduce the diameter of the can top, thereby

reducing the end-piece diameter. This results in significant metal
savings, since the end piece is much thicker than the sidewalls.

- The thin walls of D&I can restrict its use to applications where it will
not be thermally processed & that will lend support to the walls.
Carbonated beverage cans, where the internal pressure of the carbon
dioxide keeps the walls from denting, is the primary application.

- Noncarbonated juice cans rely on internal pressure created by inert

nitrogen gas introduced into the container.
 Impact
extrusion

Impact extrusion sequence.

- A metal slug is located on a shaped striking surface.

- A punch strikes the slug with great force.
- Under the enormous impact pressure, the metal flows like a liquid
straight up along the outside of the striking punch, forming a round
cylindrical shape. Tube height can be up to 7 times its diameter.
 Impact extrusion
- The tube’s shoulders & tip are formed as part of the process.
- Tube with a dispensing hole will have a hole in the slug, while tubes that
need a dispenser with a thin web of metal over the opening will start with
a solid slug. Embossed shoulders are another option.
- The force of impact work hardens Al & makes it stiff.
- Collapsible tubes are annealed to remove the stiffness.
- The tubes are trimmed to length, threads are turned into the neck, then
sent for finishing.
- Dimensions given for impact-extruded tubes –
 refers to undecorated & unfilled tube
 As the outside diameter & the body length from the shoulder to the
open end.
Tube dimensioning.
Examples of impact-extruded tube tips.
 Impact extrusion
- Some commonly used tips:

 The round end (the most common tip)

 Screw-eye openings
 Nasal tips
 Mastitis tips
 Neckless tubes
 Grease tips
 Advantages of Metal Tubes vs.
Laminate & Plastic Collapsible Tubes
1. They are absolute barriers to all gases & flavors.

2. They have the best dead-fold characteristic (ability to flattened or rolled

up). This feature is particularly important for some pharmaceutical
applications, where air suck-back into the partly empty tube could
contaminate the contents or expose the product to oxygen.

3. They can be decorated in a manner that takes advantage of their metallic

character.

4. They have a wide range of internal lining options because of the metal’s
ability to withstand high curing temperatures.

5. By using heavier slugs, strong cylinders can be made by impact

extrusion. These cylinders hold special greases & has a major application
for aerosol products.
 Impact extrusion- Aluminium

- Tube’s are normally coated with a white enamel base & then
cured.
- Tube are printed by dry offset (offset letterpress), similar to
any round container.
- Using heavier slugs, strong cylinders can be made by
impact extrusion. These cylinders hold special
greases & chaulk.
- A major application is for aerosol products (sleek &
seamless appearance). For aerosol, the cylinders are
not annealed. The sidewall is trimmed to length, turned
down & curled over to accept the spray nozzle base.
 Structural consideration in
cans/drums/pails
- Buckling is characterised - Buckling stress of a
by a sudden sideways smooth cylinder can be
deflection of a structural estimated by:
member.
- Cans most often fails
because of applied
stacking stress causing
the sidewall of the can to
buckle.
Structural consideration in
cans/drums/pails
Structural consideration in
cans/drums/pails
Structural consideration in
cans/drums/pails