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METAL PACKAGING
CANS & CONTAINERS

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Introduction
• Metal packaging plays an important role in the process of food preservation.

• The common expression used to describe such a process is “canning”.

• Canned food has become an important part of the human diet in developed countries during the past century.

• It is of particular value in those parts of the world where no or limited refrigeration exists for storing food.

• It is a means of safely preserving foodstuffs without microbiological deterioration.

• Metal packaging has a double function as a protection against any external influence on the foodstuff during
heat treatment and storage and as a sales and information pack.

• The basic requirement for such a package is the hermetic tightness of the container.

• The food, which is sterilised by the heat process, ought to be protected against any re-infection with
microorganisms or any other kind of influence from the outside.

• This rather complex requirement is often described as “container integrity”.

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Applications of metal packaging
• Food is packed into a wide range of containers, some of which consist of all metal whilst others have metal
components.

• Different types of metal packaging include:

• Beer and soft drink cans

• Food cans

• Drums and pails

• Aerosol containers

• Tubes

• Open trays

• Caps and closures (e.g. lids on glass jars and bottle tops)

• Lids (e.g. for yoghurt and butter containers).

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• Most food cans are for wet products such as meat, fish, vegetables, fruit, rice, milk-based and recipe products, and
all these need to be heat processed immediately after filling to sterilise the food for long shelf life, usually a
minimum of three years.

• Drinks cans may contain carbonated or non-carbonated liquids.

• Many drinks require low level heat processing, such as pasteurisation, to ensure adequate shelf life of the product.

• Aerosols contain fillings ranging from personal care and toiletries through foodstuffs to household, paint and
building products.

• Dry products include powdered foods, tea leaves, wrapped foods (candies, sweets), and non-food items.

• Many of these are highly decorated containers and used as promotional containers where they may be secondary
packages containing, for example, a glass bottle of spirits.

• Cans for general line technical products are designed to hold liquids, mostly for household or industrial use.

• This range of containers includes tapered and parallel sided drums of up to 50 litre capacity.
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Aerosol for food products

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Advantages of metal packaging
• Steel cans are stronger than cartons or plastic, and less fragile than glass, protecting the product in transit and
preventing leakage or spillage, while also reducing the need for secondary packaging.

• Steel and aluminium packaging offer 100% barrier protection against light, water or moisture and air →
safeguarding flavour, appearance , vitamin content and quality from factory to final consumer → no need of
preserving agents

• Metal cans without resealable closures are among the most tamper-evident of all packaging materials.

• Steel cans extend the product’s shelf-life, allowing longer sell-by and use-by dates and reducing waste.

• As an ambient packaging medium, steel cans do not require cooling in the supply chain, simplifying logistics
and storage, and saving energy and cost.

• Steel’s relatively high thermal conductivity means canned drinks chill much more rapidly and easily than those
in glass or plastic bottles.
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• recyclable,

• easy conversion into various shapes,

• Ability to withstand high heating temperatures,

• rigid structure,

• transportation to long distances and unique decorating possibilities

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Disadvantages of metal packaging
• Global warming due to carbon dioxide emission from metal manufacturing units

• Leaching of harmful toxic chemicals from containers to food and depletion of resources.

• Expensive compared to other packaging materials.

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Forms of metal packaging
• Used in 3 forms – Rigid, Semi-rigid and Flexible.

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Metal container shapes

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METALS USED FOR FOOD PACKAGING
1. Aluminium

2. Stainless Steel

3. Coated steel

a) Tinplate (ETP)

b) Tin-free steel (TFS) or electrolytically chromium/chromium oxide coated steel (ECCS)

c) Polymer coated steel

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1. Aluminium

• Aluminium, with 8.8% of earth’s crust, is the most abundant metallic constituent.

• Aluminium production process involves the conversion of alumina to aluminium hydroxide (Al(OH)3) in a
solution of sodium hydroxide at 175 degC.

• The insolubles are filtered off and soluble Al(OH)3 precipitated as white fluffy solid.

• The cost of aluminium is higher as compared to almost all coated steels and mostly preferred for seamless
containers because of its inability to get welded.

• Aluminium is mainly used as light weight packaging material in its pure form for sea foods, soft-drink cans,
pet foods etc. while addition of manganese enhances its strength.

• It is also used for making foil, cans, laminated and metallized packaging material in combination with paper
and plastics.

• Aluminium is used for food packaging application in different forms like collapsible tubes, bottles, caps,
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closures, retort pouches, laminated and metallized films.
• Aluminium is considered to be the best material for recyclability because of its easy conversion to new
products but foils from recycled aluminium usually contain pinholes and its non-magnetic property creates
segregation glitches.

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2. Stainless Steel

• Stainless steel is the iron alloy which possess extensive corrosion resistance and chemical inertness property
due to chromium content (normally above 11%).

• Although, chromium is highly active metal but in contact with atmospheric oxygen, it forms an inert layer of
chromium oxide (Cr2O3) on steel surface leading to its auto-passivation against corrosion.

• Stainless steel, owing to its corrosion resistance and inertness, is used in food industry as a packaging material
and for development of food processing and storage equipment.

• Stainless steel is costly as compared to aluminium and tin therefore it is mainly used for returnable containers
in food packaging (kegs for beer, wine and soft drinks).

• However, for large storage or transport containers, stainless steel is the leading material.

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3. Coated steel

• Several alloys of iron are called as steels, with all of them having carbon content ranging between 0.2 and 2%
which binds the iron atoms in rigid lattice and contributes to mechanical properties of steels, especially
exceptional tensile strength.

• The alloys of iron used for food packaging applications can be categorized as ‘carbon steel’ with carbon
content not exceeding 1%.

i. Tin plate,

ii. tin free steel and

iii. polymer coated steels

• are the three majorly used coated steel for food packaging applications.

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Note: This diagram is only for easy understanding
a) Tin plate

• Tin plate is the most important coated steel used in food packaging applications.

• Tin plate usually refers to steel (base steel) coated with tin on each side.

• Historically, dipping was used for coating and it was known as hot-dipped tin plate, but now electroplating is
most commonly used (known as electrolytic tin plate) because of its ability to have coatings of different
thickness on both sides.

• The process of tin plate production involves: tinning which involves covering of steel base plate with thin layer
of tin; flow melting comprising thermal treatment above tin’s melting point (260–270 degC) and rapid
quenching in water leading to formation of tin iron compound (FeSn2); chemical passivation in a sodium
dichromate electrolyte generating tin and chromium oxides on the surface thus providing more stability and
resistance to atmosphere; coatings with oily lubricant such as dioctyl sebacate and acetyl tributyl citrate for
resistance against scratch, environmental corrosion and finally passage of tin plate sheets through container
forming machines.
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• Tin plate is cheaper and heavier than aluminum, recyclable, has magnetic property which helps in its easy
segregation, easy to decorate, impermeable to moisture and gases, and also withstands high temperature of
product processing which makes it suitable for sterile products including beverages for longer storage.

• However, it requires surface coatings as it may react with food.

• According to the Bureau of Indian Standards, the tin plate for food and drink cans should have tin plate of
0.15–0.49 mm thickness and coated on both sides either by dipping or electro-deposition.

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b) Tin free steel (TFS)

• Tin free steel or electrolytically chromium/chromium oxide coated steel (ECCS) is similar to tin plate except non-
involvement of flow melting and chemical passivation during its production.

• The production process involves dual electroplating of chromium and chromium sesquioxide and finally coating with an
oil such as butyl stearate oil.

• ECCS is slightly less expensive as compared to tin plate and more susceptible to corrosion in acidic environment because
of absence of sacrificial tin layer and therefore usually coated.

• Conversely, it is more acceptable for protective enamel coatings than tin plate because of low melting point (232 degC).

• The use of TFS is less as compared to tin plate and mainly utilized for food can ends, crown caps, and vacuum closures for
glass containers.

• Removal of coatings as a prerequisite for welding of TFS hinders its extensive usage for single use containers and
recyclability.

• Moreover, its low cost over tinplate makes it the best choice for drums used in bulk storing and transportation of finished
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products.
c) Polymer coated steel

• Various efforts for the passivation of steel against corrosion has led to the utilization of conducting polymers
like polyaniline, polythiopen and polypyrrole for coating steel cans.

• Studies on utilization of polyethylene terephthalate (PET) and polypropylene (PP) as coatings on deep drawn
cans had indicated good effectiveness as well as no solvent emission during process.

• Polymer coated steels are highly abrasion and corrosion resistant with outstanding appearance and moisture
barrier properties.

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COATINGS FOR METAL PACKAGING
• Coating materials are applied to the metal surfaces either in liquid or solid form (as powders, laminates or hot
extrusions).

• This may be done prior to the metal forming operations, i.e. as coil or cut sheet, or after forming when the container
or end has a three-dimensional shape.

• Liquid coatings may be applied by roller coating or airless spray and generally form part of the can-making
operation.

• Figure 8.6 describes the process of roller coating the top side of a metal sheet while Fig. 8.7 shows how lacquer is
applied by airless spray to the inside surfaces of a seamless can.

• During heat curing the coated product passes through a tunnel oven where the liquid carriers are first evaporated
leaving the residual resin to be cured, by chemical cross-linking, into a hard but flexible surface.

• Typically the total time for this operation is approximately 20 minutes.

• Ultraviolet curing is achieved by passing the wet surface of the metal sheet under a UV lamp at high speed.

• This creates an instant cure.

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 Air-less spray coating method
Roller coating method

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• Powder coatings are 100% resin and contain no solvent or water carriers. Application is by spraying the dry
powder followed by heat curing as part of the can-making operation. This process allows heavier coating
weights to be applied than can be achieved by a single coat of liquid.

• Polymer films, whether as laminates or direct extrusions, are normally applied by the metal manufacturer, as
the most efficient way of achieving this is in a coil-to-coil operation.

• New systems are being developed which use pre-coated tin-free steel or aluminium for two-piece can
manufacturing, either drawn or drawn and ironed.

• These systems may be single- or multi-layer polymers but in all cases are based on polyethylene terephthalate
(PET).

• The main advantage of these systems is that all the processes of applying the polymers to the metal substrate
take place under controlled conditions in the factories of the metal manufacturers.

• These then simplify the can-making process, eliminating can washing and in-line internal and external coating
operations.
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• Many metal packagings (typically cans, containers, caps & closures) are normally coated on one or both sides.

• The inside (food contact) coating is referred to as an internal coating, lacquer or enamel and the outside as
external coating, enamel, ink or varnish.

• Unlike many other applications, can coatings are normally thermally processed (stoved or baked).

• Unlike many other industries, practices vary widely – both geographically and on a company-by company
basis.

• For various reasons, some countries or companies will use a particular type of metal, can or coating for a
specific end use, whilst other countries or companies may use alternatives for the same end use.

• A single can may consist of different metals and a number of different or similar internal coatings.

• Metal packaging is coated for many reasons;

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Internal (food contact) coatings:

• Provide protection of the contents from the metal – e.g. iron pick-up in beer or discolouration of some dark-
coloured fruits, such as plums and strawberries, due to metal contact

• Provide protection of the metal can from the contents of the can – e.g. acidic soft drinks (which may corrode
uncoated metal) or some fish, meats and soups (which may cause sulphur staining).

External (non-food contact) coatings:

• Provide protection of the metal from the environment – e.g. atmospheric corrosion

• Support decoration, labelling and consumer information

• Influence mobility (friction) of the article during filling operations – e.g. beverage cans can only be filled with
an external decoration, which provides the necessary friction (mobility) to pass through the filling head.

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• Coatings influence the manufacturability of the can:

• By reducing tool wear for tin-free steel (TFS) substrates.

Tin on the surface of steel (electrolytic tinplate – ETP) “lubricates” the metal during deformation, whereas steel
without a tin layer is very abrasive and the presses used for forming would rapidly wear out.

• By assisting tooling for aluminium substrates.

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TYPES/FORMS OF METAL PACKAGING
• Rigid Metal packaging used for foodstuffs can be arbitrarily divided into

• cans,

• pails and drums,

• aerosol containers,

• tubes,

• trays,

• closures and lids.

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I. CAN
• There are distinct types of cans and ends (or lids).

• The lids are always attached after filling the can with foodstuffs, thus the packers and fillers purchase empty
cans and lids and seam the lids onto the cans.

• Cans consist of either two or three separate components (“two-piece cans” and “three-piece cans”); while
three-piece cans are composed of a cylinder, a top and a bottom end, two-piece cans have the wall and bottom
formed out of one piece and a separate top.

• Their sizes range from very small (a few grams) to catering pack sizes (typically for contents of 2–10 kg).

• Impact extruded cans are also known as single piece cans.

• So, cans can be classified into Single piece, 2 piece and 3 piece cans.

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1. Single piece cans or Impact extruded cans [and tubes]:

• The process of impact extrusion is restricted to containers made from aluminium only as it is not possible to form
steel cans in this way.

• Historically, this process has been used for aerosols, rigid and collapsible tubes.

• In recent years shaped bottles for drinks have been introduced where the forming process has been based on that
used for aerosol production.

• In this process a thick disc equal in diameter to the outside of the finished container is punched out from aluminium
plate.

• The disc thickness is such that its mass/volume is equal to that of the untrimmed can body.

• The disc is placed in the bottom of a die and a reciprocating punch having maximum diameter equal to the inside
diameter of the container is driven into the disc at high speed.

• The cold metal is forced out of the die block and flows up the side of the punch until the end of the stroke.

• This process is described in Fig. 8.18.

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• The same process is used for forming collapsible tubes.

• However, in this case the base of the die is modified to allow formation of the tube nozzle with or without a
sealing membrane and the starting disc shape is also modified as shown in Fig. 8.19.

• Further manufacturing steps, including coating and printing, are similar to those used for DWI drinks cans.

• The only exception to this is that necking and flanging are replaced by a multi-step forming process, to shape
the top of the container from full body diameter to that required to accommodate the ultimate can closure
device, as shown in Fig. 8.20.

• This could be a flange on which to crimp an aerosol valve mechanism, a rolled edge to accept a crown end or a
screw neck to accept a ROPP™ (roll-on pilfer proof) cap.

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• Components or parts of a can.

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• Three-piece cans are mainly used for food, but may be used for some non-carbonated beverages, particularly fruit
juices.

• They were the original cans, consisting of a bottom (end), walls (body) and lid.

• They are made with Electrolytic tin plate (ETP) only being used for the body, in order to facilitate welding, whilst
TFS or ETP could be used for the ends or possibly aluminium if an easy-open end (lid) is used.

• Three piece cans are easier to form in any combination of height and diameter, providing mixed specification cans
with ease.

• Firstly, the cut sheets of metal are coated, printed and rolled as per the requirement and longitudinal sides of the flat
metal sheet is joined either by soldering or welding.

• However, soldering is usually avoided for food cans because of concerns related to migration of lead from tin/lead
solder into foods.

• Welding is preferred for side seaming in food industries, which not only overcomes safety concerns of soldering but
also reduces the metal usage as overlapping is a prerequisite for welding which requires less metal as compared to
interlocking for soldering.
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• After the formation of round hollow structure (cylindrical body) by side seaming, necking and flanging for
beverage cans and beading and flanging for food cans are performed.

• Necking usually refers to reducing the diameter of flat ends in perfectly cylindrical seamed body to concave
ends thus offering metal usage reduction.

• The beading treatment of food cans gives spherical curves (corrugations) to the round structure of can for extra
strength required during retorting of food products.

• Flanging refers to creation of outward flanges (hooks) for better fitting of can lids.

• Can ends (lids) are attached mechanically using double seaming process, involving interlocking of flange and
lid’s edge.

• Where food cans are going to be heat processed (retorted) after filling and where the can height is greater than
its diameter, it is usually necessary to form circumferential beads in the can body wall to increase the hoop
strength to resist implosion of the can during the earlier part of the process.
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Note: These diagrams – only for understanding

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 So, cans can be

• Short or tall

• Any shape

• 2 piece or 3 piece,

• with or without wall beads

• with plain end or easy-open end.

Note: These diagrams – only for understanding

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Note: These diagrams – only for understanding

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2. Two-piece cans (drawn cans)

• Most of the drawn cans find usage in the beverage as well as the food industry.

• Drawn cans are also widely used for packing sweets, and these are usually closed with a slip lid.

• Both steel and aluminium substrates can be used.

• A punch is used to deform a disc of metal.

• Two-piece cans are formed from a blank of metal into a can without a lid.

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Note: These diagrams – only for understanding

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 • Drawn cans are differentiated by the method used to form them:
1. Single drawn
2. Drawn and redrawn (DRD)
3. Drawn and wall-ironed (DWI)

• Single drawn cans:

• For shallow cans, a single drawing operation is required.

• Examples are folded aluminium baking trays and takeaway containers.

Note: These diagrams – only for understanding

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• Drawn and redrawn cans (DRD):

• For production of a deeper can, the drawing operation may be repeated (redrawing) in a second station with
appropriate sized tooling; however, as for the first draw, the surface area of the deeper can and the wall
thickness of wall and base will still be unchanged from that of the original disc of metal.

• The redrawing process sequence is shown in Fig. 8.14.

• The full process sequence of making DRD cans is shown in Fig. 8.15.

• The DRD process may also be used to form taper wall flanged cans as well as aluminium or steel taper thin
wall trays to which heat sealed foil lids are applied.

• Some drawn cans have a larger diameter at the top than at the bottom.

• The tapered shape enables them to slide into each other for transport, thereby minimising the costs of
transporting large quantities of air for large distances.

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• Thickness of the initial cup and the final cup/can will be same.
• Diameter is changed/reduced.

Note: This diagram – only for understanding

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• Drawn and wall-ironed (DWI) cans:

• These cans are used for beer and beverages (B&B).

• The number of DWI B&B cans manufactured and filled in the EU is more than double that for food cans, by
whatever manufacturing technique.

• They are made from either aluminium or steel.

• Soft drinks are normally cold-filled and carbonated thereby generating a positive pressure, which serves the
multiple purpose of displacing headspace oxygen, producing the characteristic “fizz” and, importantly,
providing abuse resistance and strength to the thin walled DWI can.

• Post-processing is minimal.

• Beers are normally pasteurized after filling.

• This involves heating to about 65°C for 20–30 min and then cooling.

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Note: This diagram – only for understanding
• To produce a DWI can, a drawn cup is further processed to make a cylinder by deforming the sides of the cup by
stretching it through dyes of decreasing diameter (“wall ironing”).

• The wall thickness of the can is reduced by “ironing” the metal and consequently lengthening the can.

• The process of making a DWI can is similar for aluminium and steel.

• Steel beverage cans utilize more coating and processing options than aluminium ones.

• The cans are washed (four to six times) in a multi-stage washer.

• At this stage, various treatment chemicals can be used in the washers; these may differ for aluminium and steel cans.

• The washing serves to remove any lubricant from the wall ironing process.

• Aluminium cans may also undergo a pre-treatment during the washing process to improve the adhesion of the
coatings.

• The last wash is normally with deionized water to create a contaminant-free surface for coating. After drying, the
cans are externally decorated.

• The final stage is the application of the internal lacquer, which is spray-applied and cured in an oven.
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• Internal diameter of the initial cup and final can remains same.
• Thickness is reduced . Initial thickness of the cut-round disc is very important.

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VIDEOs for 1 piece, 2 piece and 3 piece can production
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CAN END
• The base of a three-piece can will always be a plain end (non-easy-open).

• For food cans, the top may be either plain (requiring an opening tool), full aperture easy-open or peelable
membrane design.

• Historically, tapered rectangular solid meat cans have employed a key opening device to separate the two
scored body sections; these are now gradually being replaced by containers having rectangular panel full
aperture easy-open ends.

• For drink cans, the top is usually referred to as a stay-on-tab (SOT), enabling the opening tab and pierce-open
end section to be retained on the can.

• The SOT end has largely superseded the traditional ring-pull end.

• Ring pull end created littering problems as the small metal pieces were thrown away and also used to hurt
people.
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Non-easy-open/plain/penny lever/pry-off lever end

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Pull ring end

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Stay-on-tab (SOT) end or Easy-open end (EOE)

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Full aperture easy-open ends

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Peelable membrane design

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Can with key opening device

• The key tab is an integral part of the end curl which is die formed.
• The key is usually spot welded to the end panel.
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Can with key opening device

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Mechanical seaming of ends onto can bodies

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Testing of cans
• 2 types – In-line, as part of the manufacturing process and Off-line, in a laboratory.
• Examples of in-line processes are pressure or light testing for cracks and pinholes, video inspections of can
internal surfaces or external decoration.
• They are part of manufacturing process.

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 The following are examples of off-line tests usually carried out:

• Dimensions – height, diameter, wall thickness range, flange width

• Strength – axial compression, resistance to implosion (food cans), base dome buckle (drinks cans)

• Coating integrity – weight, continuity (freedom from pinholes), adhesion

• Ends (in addition to above tests), deflection due to internal pressure changes, lining compound placement and
weight

• Easy-open ends, additional tests to determine ‘pop’ and ‘pull’ loads to open and tear the tab, rivet strength and
integrity.

https://industrialphysics.com/product/buckle-burst-tester-aerosol-cans/
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The most common defects that may be found in metal packaging components are:

• all can bodies – low tin coating weight, badly formed flanges

• coated surfaces – pinholes, poor adhesion, undercuring, underfilm staining, cracks in coating after necking in
drink cans and after curling can ends

• three-piece can bodies – poor weld strength, badly formed/incomplete weld

• two-piece draw and wall ironed can bodies – pinholes in body or flange area

• can ends (plain) – lining compound incorrect weight and bad placement

• can ends (easy-open) – broken/leaking rivets, residual score out of specification, pop and pull loads out of
specification.

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DECORATING PROCESSES
• Printing – conventional offset, Dry offset, Digital
• For 2 piece cans – image is initially distorted if to be printed before forming.

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II. METAL CLOSURES
• Metal closures for fitting to glass and plastic containers are highly specialised products.

• Because of the different strength requirements, the closures for drinks containers are made from aluminium,
whilst those for processed food are made from steel.

• It will be seen that the threads on closures can be formed during the initial metal-forming process, or as an off-
line moulding process, or during the filling/closing process or even during the (food) heat processing
operation.

• In all cases, the dimensions (finish) of the neck of the glass/plastic container need to be specified very
accurately and, for this reason, the specifications are usually set by the closure manufacturer and not the
container maker.

• Outlines of all the closures discussed below are shown in Fig. 8.32.

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1. Roll-on pilfer proof (ROPP™) caps

Paperboard and foamed plastics laminated

with Al foil or plastic films are used as wad.

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2. Composite closure

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3. Twist-off closures / lug closure

• They include lugs or protrusions on the inner edge, designed to engage with an interrupted thread on the
container neck.

• They are secured by placing on the container, exerting a downward force and twisting so that the lugs slide
under the thread to hold the cap in place.

• Often fitted with a pop-up vacuum bottom which indicated whether there is still vacuum inside the head space.
This provides both tamper evidence and safety feature.

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4. Press-twist (PT) closures or Push-on twist-off closures

• Usually made from a tinplate shell, injected with a soft thermoplastic sealing compound.

• The pdt is hot-filled into the container (usually glass) which has an interrupted thread, and the closure is applied.

• As the pdt cools, a partial vacuum is developed, pulling the metal closure down onto the finish of the container.

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5. Crown cork closures

• Widely used on glass bottles of beer and other carbonated beverages.

• Typically made from heavy gauge metal with suitable coatings on both sides.

• They have a sealing wad inside the closure which may be crown cork or a compressible plastic or a liner of soft
plastic material around the inner circumference of the cap.

• The closure is pre-formed and then placed over the neck of the container, often using magnets, and the outer
circumference is compressed around the lip of the bottle and the edges tucked under a retaining ring on the lip to
secure the closure in place.

• Ideally suitable to withstand internal pressure of carbonated beverages.

• High seal integrity.

• Bottle opener is required to remove the closure.

• Once removed the closure is deformed and cannot be re-applied.

• Cheap closure and suitable for high volume, high speed production.

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III. DRUMS AND PAILS
• Drums and pails are in essence large three-piece steel cans.

• They are supplied empty, with bungs in the “lid” for the customer to fill.

• They are not subjected to any processing when filled.

• Drums tend to refer to larger volume containers of typically 100–220 l whilst pails normally refer to 5–25 l
containers.

• There are different grades of drums depending upon the intended contents and method of transportation.

Video

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IV. TUBES
• Metallic tubes are extruded from a slug of metal (mostly aluminium).

• Not all tubes are internally lacquered, particularly toothpaste tubes.

• Many tubes are no longer based on metal.

• Only those tubes with contents necessitating minimal interaction with oxygen are metal based.
Video

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V. TRAYS AND FOILS
• Rigid and semi-rigid aluminium trays for food application are based on rolled aluminium (with different
alloys) of a thickness in the range 70–300 μm.

• In some cases, containers with polyolefin laminate structures together with polyurethane adhesives are used for
the food contact side of the tray to provide retort resistance.

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VI. AEROSOLS
• Aerosol is a pressurized container.

• The products contained in an aerosol pack may range from liquid, through wax containing polishes, upto
highly viscous fluid such as hand cream.

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Applications of aerosol package

• Pharmaceutical – anti-sprain sprays, foot spray, etc.

• Cosmetic – perfumes, hair-sprays, shaving cream, etc.

• Industrial application – insecticides, paints, garden chemicals, fly sprays, oven cleaners, etc

• Only a few foodstuffs, such as canned whipping cream, are packaged in an aerosol.

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 Characteristics and advantages of aerosol package
• Uses a pressurized container → self-energized package
• Provides means for controlled dispensing
• Protects contents from oxidation (due to pressure inside container)
• Even the last drop of product can be dispensed → minimum wastage
• Desired characteristics like spray, droplets or foam can be obtained.

Limitations of aerosol package

• Atmospheric pollution due to fine spray or cloud
• Gas leakage
• Higher package cost due to valve, actuator and cap

Most aerosol paints have a metal, glass or plastic ball called a pea inside of the can, which is used to mix the paint when
the can is shaken, helping to deliver a better flow through the nozzle.
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Aerosol Can
• Aerosol containers are generally made of glass, metals (e.g., tin plated steel, aluminum, and stainless steel),
and plastics.

• The selection of the container for a particular aerosol product is based on its adaptability to production
methods, compatibility with the formulation, ability to sustain the pressure necessary for the product, the
design and aesthetic appeal, and the cost.

• The metal cans used for aerosol containers can be 3 piece, 2 piece or single piece.

• Single piece or impact extruded cans are most commonly used.

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Actuator (a), aluminum aerosol cans (b, c), glass aerosol can (d) and valve (e)
• Glass containers would be the preferred container for most aerosols.

• Glass presents fewer problems with respect to chemical compatibility with the formulation compared to metal
containers and is not subject to corrosion.

• Glass is also more adaptive to design creativity and allows the user to view the level of contents in the container.

• However, glass containers must be precisely engineered to provide the maximum pressure safety and impact
resistance.

• Therefore, glass containers are used in products that have lower pressures and lower percentages of propellants.

• When the pressure is below 25 psi and less than 50% propellant is used, coated glass containers are considered safe.

• Glass containers range in size from 15 to 30 mL and are used primarily with solution aerosols.

• Glass containers are generally not used with suspension aerosols because the visibility of the suspended particles
presents an aesthetic problem.

• All commercially available containers have a 20 mm neck finish which adapts easily to metered valves.
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• Tin-plated steel containers are light weight and relatively inexpensive. For some products the tin provides all
the necessary protection. However when required, special protective coatings are applied to the tin sheets prior
to fabrication so that the inside of the container will be protected from corrosion and interaction between the
tin and the formulation. The coating usually is an oleoresin, phenolic, vinyl, or epoxy coating. The tin plated
steel containers are used in topical aerosols.

• Aluminum material is extremely light weight and is less reactive than other metals. Aluminum containers can
be coated with epoxy, vinyl, or phenolic resins to decrease the interaction between the aluminum and the
formulation. The aluminum can also be anodized to form a stable coating of aluminum oxide. Most aluminum
containers are manufactured by an impact extrusion process that make them seamless. Therefore, they have a
greater safety against leakage, incompatibility, and corrosion.

• Stainless steel is used when the container must be chemically resistant to the product concentrate. The main
limitation of these containers is their high cost.

• Plastic containers have had limited success because of their inherent permeability problems to the vapor phase
inside the container.
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Aerosol valve
• The effectiveness of an aerosol depends on achieving the proper combination of product concentrate
formulation, container, and valve assembly.

• The valve mechanism is the part of the product package through which the contents of the container are
emitted.

• The valve must withstand the pressure required by the product concentrate and the container, be corrosive
resistant, and must contribute to the form of the emitted product concentrate.

• The primary purpose of the valve is to regulate the flow of product concentrate from the container.

• But the valve must also be multifunctional and regulate the amount of emitted material (metered valves), be
capable of delivering the product concentrate in the desired form, and be easy to turn on and off.

• Among the materials used in the manufacture of the various valve parts are plastic, rubber, aluminum, and
stainless steel.
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The basic parts of a valve assembly can be described as:

1. Actuator - the actuator is the button which the user presses to activate the valve assembly and provides an
easy mechanism of turning the valve on and off. In some actuators, mechanical breakup devices are also
included. It is the combination of the type and quantity of propellant used and the actuator design and
dimensions that determine the physical form of the emitted product concentrate.

2. Stem - the stem supports the actuator and delivers the formulation in the proper form to the chamber of the
actuator.

3. Gasket - the gasket, placed snugly with the stem, serves to prevent leakage of the formulation when the
valve is in the closed position.

4. Spring - the spring holds the gasket in place and also is the mechanism by which the actuator retracts when
pressure is released thereby returning the valve to the closed position.

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5. Valve or Mounting Cup - the mounting cup which is attached to the aerosol container serves to hold the
valve in place. Because the undersigned of the mounting cup is exposed to the formulation, it must receive
the same consideration as the inner part of the container with respect to meeting criteria of compatibility. If
necessary, it may be coated with an inert material to prevent an undesired interaction.

6. Housing - the housing located directly below the mounting cup serves as the link between the dip tube and
the stem and actuator. With the stem, its orifice helps to determine the delivery rate and the form in which
the product is emitted.

7. Dip Tube - the dip tube which extends from the housing down into the product concentrate serves to bring
the formulation from the container to the valve. The viscosity of the product and its intended delivery to rate
dictate the inner dimensions of the dip tube and housing for a particular product.

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Aerosol systems

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• Two phase (gas and liquid) system:

• Consists of a solution of active ingredients in liquefied propellant or in the vapourized propellant.

• Solvent composed of propellant or mixture of the propellant.

• Co-solvents (alcohol, propylene glycol and polyethylene glycols) are used to enhance the solubility of the
active ingredients.

• 3 phase (gas, liquid and solid or liquid) system:

• Consist of suspension or emulsion of the active ingredients in addition to the vapourized propellants.

• Suspension consists of the active ingredients that may be dispersed in the propellant system with the aid of
suitable excipients such as wetting agents and / or solid carriers such as talc or colloidal silica.

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Note: More information in the pdf