Concept of pull-tab can

Typical carbonated soft drink cans are made of two pieces, one making up the sides and bottom, and the lid on top. Lids are commonly made of a different alloy than the aluminum sides and base because the flat shape provides less resistance to pressure than the concave bottom and rounded sides.

The first beverage cans were opened via puncture with a “church key” can opener.

In 1959, Ermal Fraze devised a can-opening method that would come to dominate the canned drink market. His invention was the "pull-tab". His first version used a lever that pierced a hole in the can. Unfortunately, this design produced a sharp opening, sometimes injuring the drinkers. Later he created the familiar pull-tab version, which had a ring attached at the rivet for pulling, and which would come off completely to be tossed aside.

His idea was patented by the United States government in 1963. Pittsburgh Brewing Company in Pittsburgh was the first company utilize Fraze’s design.

A pull-tab consists of a metal ring which, along with a wedge-shaped portion of the can top, is completely separated from the can when pulled to create an opening.

A variety of styles of pull-tabs evolved over the next 20 years or so, many of which pulled off completely and caused a great deal of environmental pollution. The version of the pop tab known today began to appear on beverage cans around 1980.
Concept of pull-tab can

Defect of can: Springers and Flippers

Cans are an excellent and durable container. However, they are potentially dangerous if they have been processed incorrectly or the can fails in storage.

Care also not to overfill the cans, since this may result in the development of springers or flippers. Dangers arise from canned goods as a result of changes in the contents, defects in the canning, impurities from the can or the use of representative and coloring agents.

By pressing the ends of a can with fingers, it will detect flippers and springers and soft and hard swells. Springer - a can with one end permanently bulged. When sufficient pressure is applied to this end, it will flip in, but the other end will flip out.

Flipper is a can that normally appears flat; A slight distension of one end of the container where outside pressure will return the end to a normal position but will cause the other end to flip out. Flippers result from a lack of vacuum.

This condition is actually the beginning of a hydrogen swelling or due to an insufficient exhaustion or over-filling beyond the capacity of the can. Flippers or springers are most frequently caused by inadequacies of vacuum and headspace, and only rarely by microbial spoilage.
Defect of can: Springers and Flippers

Metal can defect

Draw and redraw of can manufacture

There are essentially two methods for manufacturing two-piece cans:
*Draw-redraw
*Drawn and wall-ironed, sometimes called drawn and ironed

Drawing or draw redraw is mainly but not exclusively, used for manufacturing shallow cans with use of tinplate, TFS or aluminium. Some tall cans are made from steel with use of this process; examples are 0.5 kg cans in Europe and tall tapered cans, for salmon, made in the USA.

Draw and redraw can technology involves cutting a blank from a previously lacquered sheet, drawing the blank through a die, thus forming a cup, and redrawing the cup to form a can of desired height and diameter.

These operations are typically performed on a press. In this process, the punch-die clearance is always at least as great as the thickness of the ingoing material. This technology is largely used in the packaging of fruits, vegetables, baby foods and soups and prepared foods dispense from vending machines.
Draw and redraw of can manufacture

Draw and iron can

The draw-iron can was developed to compete with aluminum alloys for pressurized beverages containers, which have become the highest growth market for cans, due to their popularity for dispensing drinks. In the draw and iron technique, the can is made in two steps.

A disc is blanked from sheet stock, and drawn into a cup. The can is lengthened or deepened by ironing the sides in a stretching operation that reduces wall thickness to about one third of its original gauge.

The drawn and ironed can is then washed clean of lubricant lithographed, interior spray-coated, necked-in and flanged. A two-piece cup-like can ready to receive contents and a double seam end is the resulting product.
Draw and iron can

Innovation of cans

Appert canning technique was improved by the work of British scientists Bryan Donkin and John Hall. They created the first tinned canned food in 1812.

The first cans were handmade of steel coated with tin. Durand’s early process produced 10 cans per day; modern can-making machines can produce 1000 or more per minutes.

Other innovations include quick-opening cans with pull tabs, as are used for soft drinks, sardines and nuts; cans that are opened with a slotted key that comes with the can, as are used for sardines and cured hams; pasteurized cans that use a propellant to dispense whipped cream and cheese spreads; and extruded or drawn cans, as are used for soft drinks, tuna and sardines.

The extruded cans has several advantages over the conventional can, a major one being the elimination of the bottom and side seams, which reduces the probability of seam failures eliminates the use of lead, (used in side seam) and permits more stable stacking in shelves, requiring somewhat less vertical space.

Two basic types of allowed metals are used in food packaging: steel and aluminium. Steel is used primarily to make rigid cans, where aluminium is used to make cans as well as thin aluminium foils and coatings.

Until a few years ago nearly all steel used for cans was coated with a thin layer of tin to inhibit corrosion; hence, the name ‘tin can’.
Innovation of cans

Lacquer

Various lacquers have been developed for lining cans, especially for preventing food discoloration that could occur as a result of interactions between the food and the can.

Internal coating eliminates the food-metal interaction during storage while the external protects the can from abrasion and corrosion.

Three-piece food cans are made from lacquered tinsheets. The lacquer is roller-coated the sheet at a rate of 3000 – 5000 sheet per hour.

The cured lacquer shows a film thickness of 3-6 microns – in other words a very thin film.

It also aids in forming of cup and provides base for decoration.
Lacquer

Aluminium beverage can

The aluminium beverage is familiar to almost everyone. In 1960s, three-piece tinplate can was replaced by aluminium by the introduction of easy-open ring pull can tops made out of aluminium attached to a tinplate can body and around the same time, the all-aluminium beverage can was introduced.

The first complete aluminium beverage can was introduced in 1964. These first aluminium cans were produced by impact extrusion, but very soon these process was abandoned and replaced by the ‘drawn and ironed’ can.

Aluminium beverage cans are made basically of two alloys AA3004 (1.05 Wt% Mg, 1.25 Wt% Mn) and AA5182 which forms the harder can end-pieces or lids.

Aluminum’s light weight, allied to it stability and strength, are among the reason for its successful penetration of the drinks packaging sector.

Its light weight means that it can be easily transported and stored, while consumers have found in aluminium a convenient, yet quality package with high scrap value.

Aluminium beverage can internal surface are protected by a coating of lacquer to avoid contamination of the food from possible dissolution of the aluminum and also to protect the aluminium from pitting or corrosion by the contents.
Aluminium beverage can

Can coatings

The term ‘can coating’ embraces paints for use on a vast variety of decorated metals for packaging purposes.

This includes cans of all kinds, including food cans and aerosol cans, collapsible tubes and caps and closures of many kinds. Cans can be considered as a single material, consisting of a metal substrate with an organic lacquer.

Container coatings were historically called metal decorating coatings, since a major portion of the business was in coating flat sheets, followed by lithographic printing and a finishing varnish (clear top coat) to protect the ink.

The field now usually referred to as container or can coatings. Most cans are food or beverage containers, and one of the key requirements is that there be no possibility of introducing toxic compounds into the foods or beverages.

The interior coating of cans is very important because it prevents the metal from reacting with the ingredients of the filling goods.

The can exterior is painted to prevent corrosion, but also for decorative reason. Accordingly, the requirements for can coatings are extreme in many ways. They include printability and block and scratch resistance yet sufficient elasticity to permit forming and drawing without damage to the paint.
Can coatings

Hermetically sealed container

The preservation of food safety and quality in packaged foods depends on hermetically sealed packages.

The term hermetic refers to a container that is sealed completely against the ingress of gases and vapors. The package can be considered as an air or liquid tight container.

Such a container, as long as it remains intact, will also impervious to bacteria, yeasts, molds and dirt from dust and other sources.

The most common hermetic containers are rigid metal cans and glass bottles, although faulty closures can make them non-hermetic. Canned food can be defend as thermally processed shelf-stable foods in hermetically sealed containers, regardless of the type of container (metal, plastic, paper, etc) or how the thermal process was delivered.

The quality of the seal can readily be ascertained by coating the ampoule with a leak-detection compound or detergent solution, then pacing it in a bell jar of vacuum desiccators and evacuating. Any leaks present will result in an easily seen stream of bubbles.
Hermetically sealed container

Three piece cans

Three piece cans consisting of a can body and two end pieces, are used to seal heat-sterilized foods hermetically as well as for other food products like powders, syrups and cooking oils.

The can wall is formed by welding. Three piece welded cans are only constructed from steel as aluminum is not suitable for welding.

As the material for the can wall, lightly coated Sn-plated steel sheets and Ni-plated steel sheets may be employed.

Two main types of base steel are commonly used in can manufacturing type L and type MR. Type L is very corrosion-resistant and is used in canning of very corrosive products e.g., apple juice, berries, prunes and pickles.

Type MR is more suitable for canning moderately to mildly corrosive products, e.g. grapefruit, peaches, peas, and corn.

In both the two-piece can and the three-piece can the outside surface of the can is provided with printing, in order to appeal to consumers for commercial value of the canned goods.

On the other hand the inside surface of the can is coated with resin so as to ensure the corrosion resistance of the can body.

The coatings and ink are normally dried by passing the sheets through a thermally heated oven where the temperature is in the range 150–205 °C.

Three piece cans usually are delivered to the packer with one end in place and the other shipped separately. After filling, the second end is double-seamed by closing machines, which can change the headspace air to a vacuum or inert gas, if required.

Presently, the three-piece cans are being widely used and other cans like two-piece cans, aluminum cans, and other flexible containers are slowly replacing them.
Three piece cans

Tinplate cans

Tin is the oldest available metals and centuries of use have established its non-toxic nature. Tinplate is the common term for a steel sheet with a protective coating of tin.

This combination of materials gives the following properties: a shiny, metallic appearance, formability, possessing a gas barrier, rigidity and providing adequate protection against corrosion and solderability.

Tinplate, the first material used to make metal cans and canisters, consists of a thin sheet of steel, coated with tin. The purpose of the tin coat is to reduce the risk of corrosion.

Modern tinplate for cans is produced from steel strip with tin applied by continues electro-deposition.

There are three can types:
*The three piece can evolved from original concept
*The two piece draw/redraw can
*The draw/wall-ironed can

The two main advantages of tinplate cans are that they are cheaper than aluminum cans and are also magnetic.

This latter feature enables tinplate cans to be transported through leak-testing baths on magnetized conveyor rather than magnetic pucks having to be individually fitted.
Tinplate cans

Two piece cans

Two piece cans is manufactured by press punching cups from sheets or coils of aluminum or steel. During this cupping operation, a blank is produced from the coil stock and in the same punch stroke, s formed into a shallow cup.

The cups are then forced though a series of rings to iron out and form a full-length can and to form the bottom dome.

Subsequent operations include trimming the can to a specified length, washing to remove drawing lubricants, decorating the exterior of the can with the desired brand level and applying coating to prevent contact of the food or beverage product with the metal substrate.

The product at this stage is a container with sides and a bottom representing one of the pieces of a two-piece can. The lid, secured and sealed after filling, is the second piece.

Since 1970, through the conversion of three to two piece cans and subsequent lightweighting, the weight of a 350 mL tinplate soft drink can has been reduced by 50% to 30g, and that of the inherently lighter two-piece aluminum can by 39% to 13 g.

It is evident that two-piece steel can would eliminate the long seam and one double seam and thus preclude two sources of potential leakage.

Steel is a cheaper metal than aluminum, but it is far more difficult to form. A two –piece steel can could offer the advantages of a two piece aluminum can, but at a lower price.

The two piece can has no side seam and only one double seam, which is more easily formed and controlled because of the absence of a side seam lap juncture.

Seaming by the filler at the top end is considerably easier owing to the absence of a junction of the side seam and the end seam.
Two piece cans