literature review how can is processed
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1.0HOW A CAN IS PROCESSED
1.1Types of Can ProcessingThere are two types of can processing, namely two-piece can processing and three-piece can
processing. Both processes will be described here. The main difference for two-piece and three-piece
can is that in two-piece can processing, the body is formed first before printing and coating is done.
Meanwhile, in three-piece can processing, the printing and coating is done first before the body is formed.
Two-piece can processing is a modern way to process can compared to three-piece can processing [1].
TWO-PIECE CAN PROCESSING [2]
Cup Blanking and Drawing: Aluminium or steel sheet usually arrives in manufacturing plant in huge
coils. The sheet is fed continuously from an uncoiler into a cupping press which cuts out thousands of
discs per minute and forms them into shallow cups. Surplus material will be recycled.
Bodymaking and Trimming: In the bodymaker, the cup is placed in front of a moving ram which forces
it through a series of precision rings, each a little smaller than the previous one. This reduces the
thickness of the metal (wall ironing) and as a result, the can gets taller. At the end of the stroke, the base
is formed and the can is removed from the ram. The trimmer cuts off the can to the correct height. The
surplus material is then recycled.
Cleaning and Drying: Trimmed cans pass through highly efficient washer to remove lubricants used
during the previous processes and to prepare the can surface for coating and printing. Cans are then dried
in an oven.
Basecoating: Cans may be externally coated with a white or clear acrylic lacquer depends on customers
requirements. Cans are dried in a pin oven.
Printing and Varnishing: Highly sophisticated decorators are used to print colours to the can. Up to
six colours can be printed onto the can in the same operation. This depends on the customers design. A
clear over-varnish is sometimes added to protect the can and give a glossy finish. Cans are then dried in a
pin oven.
Inner Spraying: The inner side of each can is sprayed with a coating. This special layer is used to
protect the product in the can from interaction with the metal.
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Necking: Cans are passed through a necker or flanger which gives then the characteristics of neck shape.
The diameter of the top of the can is reduced or necked-in. The top of the can is flanged outwards to
enable the end to be seamed on after the cans are filled.
Testing: Cans are quality tested at each stage of manufacture. At the final stage, the can is put through a
series of additional tests, including a light test and internal and external inspection cameras. Any
defective cans are automatically rejected.
Packing: The cans are packed on to pallets which are then either sent to our warehouse for storage or
transported directly to the customers for filling.
THREE-PIECE CAN PROCESSING [3]
Shearing: The large coil of metal which arrives at the manufacturing plant is cut into sheets at the rate of
approximately 160 sheets per minute. The irregular ends of the sheets are designed for the maximum
number of ends per sheet.
Inner Coating: An inner protective coating is placed on the sheets and cured.
Printing: The sheets are decorated with customers design and then an overcoat of varnish is placed on
the decorated sheet and cured.
Body Forming:Body blanks are fed into a bodymaker where they are formed into cylinders and joined attheir side seams by solder, cement or weld.
Flanging: The formed cylinders come from the bodymaker to the flanger. Here the metal on both ends is
rolled to form a flange on each end of the can. This flange will at a later time accept double seaming.
Spray Coating: A final coating is placed on the interior surface of the can. This is a specially
compounded protective coating.
Baking: The final interior coating is baked and cured through a funnel type oven where the time-
temperature cycle must be controlled carefully.
Testing: A 100 per cent quality control inspection for any micro leak is given to every can.
Packing: Cans are packed into cartons or placed on pallets for delivery to customers.
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1.2Can Processing In Production LineThe processes which are used in production to produce can is more complex compared to the
description in Section 1.1. In a factory, the production line is divided into stations and different
processes are carried out in each station. Below is the detailed description for each station [4].
Station 1: Blanking and Deep Drawing
The tin plate strip is unwound, its surface coated with a thin film of
lubricant and the strip continuously conveyed to the deep-drawing
press.
At first a blank is cut out at each individual tool of the press; the
drawing ram then presses this blank through the draw ring to form a
cup. The tool is made up of 9 to 10 individual tools which are
arranged next to each other and behind each other.
Station 2: Wall Ironing and End Forming
The cup is conveyed to the wall-ironing machine from the top. The
ram first pushes it through the redraw ring to reduce its diameter to
the punch diameter whilst retaining the sheet thickness. The cup is
held by a blank holder to prevent puckers.
There is a gap between the punch and the wall-ironing rings 1 to 4
immediately after the redraw ring where the wall thickness of the can
is reduced by "ironing" the tin plate and consequently lengthening the
can.
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At the end of this stroke, the punch with the can comes into contact
with the base panelling tool and the can base is formed. When the ram
is withdrawn, the can is removed from the punch by a stripper and
conveyed out of the machine via an unloader belt.
Station 3: Trimming
In the trimming machine the can is held by a vacuum plate, set in
rotation and then moved axially until it reaches the required trimming
height. Then the movable cutter unit is guided to the can.
Whilst the can rotates precisely once, the can rim between the upper
and lower cutter is cut off burr-free at the required height. The rings
cut off are removed by vacuum, pressed into bales and returned to
the tin plate production facility.
Station 4: Washing
The wall-ironing lubricant used in the can forming process is
removed prior to coating the can internally and externally. The cans
are transported to the washer on a wide belt and conveyed through
several washing chambers upside down.
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In this way the outside of the can is rinsed with tap water supplied
through the jets located at the top and the inside of the can by the jets
located at the bottom. Immediately downstream of the washing unit,
the can is dried with dry air at a temperature of approx. 200 in the
drying oven.
Station 5: Outside Coating
The cans are coated on the outside as protection against corrosion
and in order to apply a decorative design. White, gold or
transparent coating as well as aluminium-coloured coating can be
used according to customer specifications. Generally the coatings
are water-based.
The cans are spaced by an intake wheel and drawn on to the coating
mandrel of the mandrel wheel by means of a vacuum. They are then
set in rotation around their own axis by the rotation belt. The
coating film on the coater cylinder is then transferred to the cans
positioned on the rotating coating mandrels. The coated cans are
then blown off the coating mandrels and transported to the drying
oven on a magnetic conveyor belt. The coating is pumped from a
coating container to the engraved cylinder which transfers the
appropriate quantity to the rubber-coated coating cylinder from
where it is transferred to the cans.
Station 6: Printing
The externally coated cans are spaced by the intake wheel, as in the
coating machine, and drawn on to the mandrel wheel mandrels by
means of a vacuum. The mandrels are set in rotation around their
own axis by a rotation belt.
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The can positioned on the mandrel rolls synchronously over the
blanket and absorbs the complete decorative design with all the ink
colours from it. The individual colours are transferred by the inking
units to the blankets via ink boxes, various rollers and the clich
cylinder with mounted printing plate. The high pressure printing
clichs only absorb ink in the parts in which they are raised.
Therefore each inking unit presses one colour ink onto the rubber
blanket. Prior to the can coming into contact with the blanket, all the
ink colours are on the rubber blanket entering the inking section;
here the printed image is mirror-inverted. The inks are transferred to
the can by rolling the can over the rubber blanket and the printed
image becomes positive. The printed cans are then blown off the
mandrels and conveyed to the drying oven by a magnetic conveyor
belt.
Station 7: Drying
The drying oven is basically divided into 3 zones (2 heating zones
and 1 cooling zone). The heating zones serve to heat the cans and to
evaporate the fluid constituents as well as to cross link the coating
and the printing ink. The air in the heating zones is recirculated to
reduce the amount of fresh air which has to be heated.
The exhaust air is supplied to the thermal incineration unit where the
exhaust gases from the oven are incinerated to carbon dioxide and
water without any residue. After leaving the heating zone, the cans
are conveyed to the cooling zone and are adapted to the ambienttemperature.
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Station 8: Initial Internal Coating
Inside the internal coating machine, the can is conveyed to a coating
turret and positioned on a vacuum plate. It is set into rotation and
passes two spray guns, the first one which coats the lower section of
the body and the second the body and the base.
When the spray guns have applied the required amount of coating,
the can is conveyed via a discharge belt to a collective conveyer andto the internal coating drying oven connected downstream.
Station 9: Necking In
The diameter of the can which is still cylindrical needs to be reduced
in the upper section to accommodate the smaller end. During thenecking in process the can is loaded on to a lifter and the axial
movement of the lifter presses the open edge into the outer tool.
There the upper rim of the can is bent inwards and the diameter
cylindrically reduced by approx. 1 mm. The lifter is then withdrawn,
the can is pushed out of the tool using compressed air and conveyed
to the next station. There the diameter is reduced further following
the same procedure. A total of 15 stations are required in order to
obtain the required final diameter.
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Station 10: Flanging
The flange is required in order to seal the filled can securely to the
end. The flange is produced in the 16th station of the necking in and
flanging unit.
The can is again loaded on to a lifter and pressed axially on to a
flanging head.
The open end of the can is bent outwards by the rotation of the
three rollers of the flanging head spaced around the circumference
and the flange is formed according to the geometry of the neck
roller.
Station 11: End Coating
The metallic bright can end is coated from the outside in the end
coating machine. The cans are conveyed via the intake turret to the
working turret. Each of the 6 magnetic chucks picks up one can at
the flange and sets it in rotation around its own axis.
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Six spray guns rotate synchronously with the working turret and
spray-coat the base of the respective allocated cans.
Station 12: Second Internal Coating
Depending on the application for which the can is intended, it is then
given a second internal coating. The procedure for the second internal
coating is identical to the first.
Station 13: Testing For Holes and Internal Cracks
We test all the cans produced for holes and flange cracks. These
two types of defect can occur due to the great degree to which the
tin plate is formed. Each can is picked up by a support spindle and
immediately moved in an axial direction until the open side has
reached the flange seal.
It is then conveyed passed a series of lights by the turret wheel.
That means that light is shed on to the body of the can. If a hole or a
flange crack allows light into the inside of the can, then the sensor
on the open side of the can reacts in such a manner that this
defective can is ejected whilst the machine is operating at full
speed.
Station 14: Testing For Internal Defects
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This test is a continuous 100% test of the inside of the can. It
is performed by a CCD line scan camera system comprising
five cameras.Camera no. 5 monitors the end and the lower
section of the can. Cameras nos. 1, 2, 3 and 4 concentrate on
the respective internal section of the can allocated to them.
The images from the five cameras are compared with a specified
image in the computer system connected downstream. As soon as
one of the five camera images does not correspond to the specified
data in the computer system, then the can is removed from the can
flow via a blow-off station.
Station 15: Palleting
The palleting unit assembles the cans in up to 23 layers to a
package unit almost 3 m high. The palleting process starts
by picking up an empty pallet. Layers of cans and interim
layers are pushed on to the pallet until the required number
of layers has been reached.
A cover frame made of steel forms the top layer. Plastic
strips are wrapped around the package criss-crossing twice in
order to make it stable for transport.
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REFERENCES:
[1] http://www.cannedfood.co.uk/microsite/teachers/lesson_zone/making_cans/intro.html
[2] http://www.rexam.com/sectors/index.asp?pageid=74
[3] http://www.cancentral.com/howMade.cfm
[4] http://www.ball-europe.com/382_717_ENG_PHP.html?parentid=791
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