TYPES OF METAL CANS THROUGHOUT THE HISTORY

The world of metal packaging is like a tree, like a dense tree that grows as branches grows, each of these branches would be the different types of packaging and their manufacturing technologies. Over time some of them become old and dry, represent the models that are becoming obsolete and stop being sued. But others are appearing while the tree grows, new developments are incorporated into the market. Thus the life cycle of the tree continues, presenting a different aspect as it progresses in its life. The same could be said about the environment of the boats.

With its somewhat proverbial image, it seems that the “cans” are always the same, that they do not change with time. It is very common to think that the typical tomato canister or the traditional can of sardines have not changed over the years and the one we buy now in the supermarket is the same as the one our grandparents bought in the “grocery store”. But it is not true, the packaging evolves and the current little resembles those that began to be manufactured almost two centuries ago.

The present work deals with the different types of cans that since its invention have been marking the history of canning. Some are just memories and are only found among the curiosities of collectors, some of them with a long life still in use and others being almost newcomers already pushing with the strength of youth. They all form the branches of this centenary tree.

 

I.- THOSE THAT WERE AND ARE NO LONGER

We will describe in this chapter the cans that have already gone down in history, those that were used by the first generations of canners, who fulfilled their mission but for different reasons have disappeared from the market

 

1º.- APPLIED WITH SOLDED AND AGUJERED LID

It is the first type of can known professionally. It began to be manufactured in the first half of the 19th century. Practically it corresponded with the patented one by Peter Durand in 1810 and that was manufactured for the first time by Bryan Donkin and John Hall in 1813 in England. Its configuration was cylindrical and although developed in the United Kingdom, it soon spread throughout North America and Western Europe. Let’s see what it consisted of and how it was made:

  • It consisted of “three pieces” – this description will accompany from now on the packages composed of three elements – body, bottom and lid.

 

  • The body of the can, cut by hand from a sheet of tin, was bent over a cylindrical mandrel, taking its shape. Their lateral ends were superimposed by 7 to 10 mm and this zone was soldered manually along the joint generatrix. This technique was designated by the name of “overlapped seam”.

 

  • Shortly thereafter, the body was rolled up by passing it through a pair of rollers and a bending sheet, it was the first type of manual winding machine.

 

  • The bottom and lid, slightly convex to increase its resistance to internal pressure, were constructed from disks also cut by hand and with a diameter greater than that of the can in a couple of cm.

 

  • On the end of the same mandrel and by beating the edges were folded forming a skirt that fitted externally on the ends of the body, being the same of a few millimeters in height. The assembly was then welded also manually.

 

  • The lid had a hole about 38 mm in diameter, by which the canner introduced the packaged product, then covering it with a larger disk, also welded on the lid.

 

Drawing of a primitive overlapping can with a welded and perforated lid

Later – in the middle of the XIX century – rudimentary welding machines were developed, consisting of tin alloy baths, in which the end of the can was introduced with the lid – or the bottom – placed making it turn inclined, so that only submerged the bottom of the edge. As the assembly rotated, the entire perimeter of the lid-body joining area was progressively impregnated with welding.

Its manufacturing rate was very small, depending on the skill of the operator. At the beginning, when the whole process was handmade, it barely passed a few tens per person per day. Later, with the incorporation of the first elementary machines, productions of 1000 cans / operator / day were reached.

His life was extinguished with the nineteenth century, coinciding with the consolidation of the engargolado and soldier packaging, which allowed a higher manufacturing rate.

 

2º.- GOLDEN AND SOLDIER

In the second half of the nineteenth century this new type of packaging was developed, although it took a few decades to completely banish the previous one. It had a long life, since it was of normal use until the “seventies” of the twentieth century. The need to eliminate the tin and lead alloy – with which its side seam was welded – for sanitary reasons, meant its disappearance.

  •        The important step contributed by the new technique was to form hooks in reverse disposition – so that they could be linked – in the edges to be joined of the body. Once joined, they were soldered using a manual soldering iron. They gave more rigidity and security to the seam.

Section of a stitched seam

  • It also meant a saving of material, since the length of the hooks was 2 to 3 mm. each. That type of union received the name of agraphated or engargolada seam.

 

  • This work of forming hooks, was initially done in a folder, but soon gave way to more complex machines, which in a first operation doubled the ends, and in a second hooked and riveted the hooks on a bigornia. Thus the body remained cylindrically formed. These machines, which were manually operated, received the name of sequestering machines.

 

  • Towards the end of the century, a new generation of equipment appeared, which were capable of doing all these operations automatically, from a pile of cut bodies. They were given the name of “bodymaker” and in Spanish “formadora”.

 

  • To reduce the thickness at the ends of the welded seam, – and thus facilitate the closure of the lid – the corners of the outer hook were cut at an angle and those of the inner hook were incised. Actually – in a more complex operation that omitted the details – the ends of the seam were not scribbled but overlapping.

 

  • Soon after they placed the formers, the equipment that applied the molten tin-lead alloy on the seam. These equipments provided the welding on the outside of the seam, rubbing it against the generatrix of a steel roll of stepped profile that turned semi-submerged in a bath of the same. For its function, this machine was called “welder”.

 

  • The rest of operations – blinking and closing – were done with the same current techniques.

This manufacturing process already allowed to obtain cans in a non-cylindrical way. To do this, it was given the appropriate shape to the anvil on which the body was shaped at the moment of riveting its hooks.

The manufacturing speeds of the last equipment that was in operation were really high, reaching 500 cans / minute, being its mechanics of great precision.

 

3º.- ENGARGOLADO WITH THERMOPLASTIC CEMENT

It is a variant of the previous system. It began to be used at the beginning of the 20th century and although in a very limited way, it continues to be used today.

  • Its origin was propitiated in the fact that certain types of cans, which were intended to contain products that did not require an autoclave – for example: paints, oils, varnishes … – served as simple hermetic cans. Therefore, at no time of their use they were subjected to internal pressure or elevated temperatures.

 

  • In these cases the agrarian sewing was enough that it used as a sealing element – instead of a tin-lead alloy – a thermoplastic glue.

 

  • This glue is applied fused by means of an injector in the same “formadora”. It was positioned on the inner face of the inner hook, before the hooks were joined and riveted.

 

  • This involved the elimination of the welding machine and a cheapening of the product

 

  • The type of facilities that worked in this way received the name of “general lines” – “general lines” -. Over time, this concept encompassed a wide variety of cans, in various forms – round, rectangular, oblong, etc. -, with different accessories – handles, necklaces, plugs, etc. – and different applications – chemical products, paints, mineral and vegetable oils, etc. -. But all of them with a common denominator: the absence of a process after being filled.

 

Detail of the end of a cemented side seam

The production rates were moderate, without reaching the previous case, this moderation was not caused by technical problems, but by the needs of the target markets: flexibility, reduced runs, variety of formats, etc.

 

4th.- TOP COVERED (CLOSED)

It was one of the most decisive advances in the improvement of the metallic can. He had a progressive gestation. First there was a patent by the American Delawere in 1859. Later several developments took it to practice. Today there are several who attribute the paternity of what supposed the closing of cans – by means of suitable equipment – as it has arrived at our days. Thus it is worth mentioning as participants in its set-up to Europeans EL Bourgine (English), Henrik Jorgen Reinert (Swedish) and others. All of them set up “seamers” capable of achieving a proper top-body union. The truth is that at the end of the 19th century this decisive improvement was industrially available and since then it has been fully in force.

  • The union of the body with the lid and the bottom is carried out from now on in an efficient and fast way, allowing an excellent hermeticity, achieving in addition to speed up the process. This was a big step in this industry.

 

  • For this, the lid modifies its design, changing its configuration. It is provided with a recessed panel in relation to the edge of the can that is called a bucket. It is lodged in a closing plate. The edge of the cover is forming a horizontal plane in the form of “wing” and hence comes its designation. Subsequently part of this plane is folded into a curl, originating a new generation of nominated “curly wing” caps.

 

  •        The wing of the lid is snapped by means of a double hook to the end of the body, – which has also changed its shape, leaving the straight termination by another one in “flange” silhouette – using a pair of rollers (routines) with an adequate profile. The first roller folds the edge of the lid over the body and the second roller firmly crushes both.

Schematic of the latching operation – close – a lid

  • To ensure tightness, previously a rubber has been applied on the area to be closed of the lid.

 

  • This way of closing the cans gave rise a few decades later to a new generation of cans, which received the qualification of “sanitary”. The delay in its use was due to the fact that at the beginning, the resulting union was not totally sealed when closing metal on metal. The development of sealing joints fifteen years later, made possible its full use. These joints – applied on the edge of the lid – initially were cellulose and later rubber.

 

The process, purely mechanical, allowed the automation of the operation, giving rise to some new equipment that starting from bodies and covers already prepared properly, fed them, superimposed and linked them, ejecting the set – can – already finished an evacuation channel. All this every time at higher speeds, getting its increase mainly based on increasing the number of closing heads. The seamers of boats were born, key team between the manufacturers of cans and canners, from then until today.

 

5th.- LEAVING

With the arrival of the “sanitary” can, the automation of the manufacturing process was increased. Not only the closing operation but in the different ways of making the body. Thus the overlapping bodies – which we have already described – maintaining their configuration, changed the way they were built, improving in quality and production cadence. With it they lived a second youth.

  • The production of bodies was now done on rotary machines of step by step advancement – carousel type -. They had a series of arms each equipped with a “comb” gripper that grasped the lateral ends of the body, superimposing them but leaving a space between them to allow the passage of the welding tape.

 

  • The bodies were introduced already curved and their feeding was manual. The welding process was carried out automatically, introducing a tin-lead alloy stripping tape between the areas to be joined, melting it by supplying heat by means of gas burners. Meanwhile, a pressure was applied through the “combs” on the welding area.

 

  • The welding perfection improved significantly when the entire area of ​​welded overlap was left. This technique was very used for short runs of sanitary cans, given the speed of preparation of the format change.

 

  • Although the most usual form of the bodies made by this procedure was the cylindrical one, the system allowed other configurations (rectangular, oval, etc.)

Section of an overlapped seam

Its average speed was 30 cans / minute, although there were versions designed for small sizes of cans (fish) with automatic feeder bodies, which doubled this speed.

The equipment that made this new type of can possible started in the early twentieth century, had a long life – almost three quarters of a century – and was called “circular welders”. Its use was much more widespread in Europe than in North America.

 

6º.- LATERAL OPENING WITH TONGUE

Packaging openers developed with some delay – in the second half of the 19th century – and presented some limitations in their use. For example, its use in cans for solid products – especially meat – the irregular edge left on the open area, once the lid was removed, acted as a stop that made it difficult to extract. In order to try to improve this operation, the first cans of lateral opening with key appeared in the market. Its first application was in the cans for “corned beef”.

 

  • About 15 or 20 mm from the top of the boat, the outer edge of the welded area of ​​the body, was prolonged with a tongue.
  • In the two points of connection of the same with the aforementioned edge were practiced notches, which would be the start of the opening tear.
  • From these notches and parallel to the lid, two incisions were made along the entire outer perimeter of the can. The depth of the same was something more than 1/3 of the thickness of the material. The tear occurred along these incisions.
  • It was frequent that in the area delimited by the two incisions two small cords were added to the outside and parallel to the aforementioned incisions. Its mission was to give rigidity to the torn strip and support the key during the operation.
  • Sometimes the system, instead of presenting two incisions, was increased to four; beginning the tear by the two external ones. If along the route of the tear he withdrew from them, he always converged towards the two interiors that continued the function of facilitating the opening.
  • To make the opening, a small wrench made of steel wire was used – which was supplied with the can, welded to the lid by a drop of solder, being easily peelable – that had a groove; which was introduced in the tongue described.
  • By turning the key on itself, the tongue was folded and with a slight effort began the tearing of the body. Continuing the perimeter advance, the can was split into two asymmetrical half. In other words, the can opened on the body, the lid and bottom remaining intact – an effect similar to that of breaking an egg -. Thus the packaged solid product could be extracted without difficulty.

Can with tongue

As it has already been said, it was the “corned beef” the first product that used this system, with a type of can of prismatic or truncated-pyramidal form. Later it was applied to the whole range of solid or pasty meat products – mortadelas, “chopek” … – and of various shapes: cylindrical, rectangular …. This way of opening was linked from its beginning to overlapping side seam cans or also entangled – engargolada -. In this second type of seam, the area of ​​the tongue should be overlapped, since the edge could not be folded to form the outer joining hook. The procedure was very complex, similar to the one used for the aerosol cans, which had a seam divided into several overlapping and alternately engargolados sections.

With the advent of electric welding technology, its realization was complicated both by the way of welding and by the effort necessary to initiate the tearing, so that after a life of almost a century, it has practically disappeared from the market.

 

7º.- NORWEGIAN OPENING

In the northern area of ​​Europe, a very important application of packaging was the fish canning industry. This conserve demanded cans of little height and a rectangular base to allow horizontal positioning of the fish – so as not to deteriorate it. Norway – which was where this system originated – also had a strong tradition in the semi-conserve of fish. Semi-preserved products are those products that have been prepared prior to packaging and therefore do not undergo any process inside the can. For its conservation, it is required to resort to cold during its useful life inside the can. This is the case of typical anchovies or smoked.

This last market developed a new form of openness. It was characterized by the following:

 

  • It used rectangular cans, in which the body and the bottom were normal.
  • The lid had a tongue on one of the smaller sides as an extension of the wing of said lid.
  • On the panel of the lid and parallel to the profile of the tray, an external incision was made that connected with the base of the tongue
  • When closing the lid, there was logically no lid hook in the area of ​​the tongue. When closing, there was only an effect similar to a “false closing” (failure in the closure when the lid and body hooks do not fit together), therefore, although the pressure in this area was intended to be strong, no a 100% water tight seal could be guaranteed.
  • Therefore, this system was not valid for processable products. Hence its use only in semiconservas.
  • The can was opened with the help of a key that was supplied loose – in cartons – or welded to the bottom of the can, fixed to it by a drop of solder.
  • As you can see, the system was similar to the one used for a lateral opening with a key, transferring to the lid what in the other was done on the body. This was so because in the body, being of very low height, there was no space to mount this means of opening.

Rectangular inlay can with tab for Norwegian opening

The Norwegian opening was widely used in Northern and Western Europe (Norway, Sweden, Denmark, France, Spain and Portugal) but with the arrival of the easy opening lid, it became obsolete.

 

8º.- DECOLLAGE

Europe at the beginning of the 20th century continued to create its own style of boats. A very interesting example of this was the development in France during this period of “decollage” type packaging. These cans were used exclusively for fish, since they, due to their low height, made the use of the classic can opener very uncomfortable. The difference between them was not so much in the form, which could be round, rectangular or oval (although the non-round predominated) but in the way of opening.

  • In these cans, the lid had a tongue, which was positioned well in a corner or in the center of one of the smaller sides thereof.

 

  • This lid, instead of being joined to the body by a conventional closure was welded to it.

Boat to decollage  

  • For this purpose, a pair of superposed flat and parallel surfaces formed on the edge of the lid and at the end of the body. That is, the lid had a flat wing and the body had a flange – also flat – towards the inside

 

  • On the outer surface of the body, the weld alloy was applied by means of a semi-submerged roller train in a molten alloy tank.

 

  • In the next step, both surfaces were joined together and the whole was consolidated. To do this, the lid-body assembly was passed, subjected to a strong pressure, through a tunnel with a high temperature. Thus, the alloy previously applied on the flange of the body was remelted, producing a firm union of both. This equipment was called “rectilinear welder”.

 

  • The “decollage” cans were the first ones that did not need a classic opener for their opening, although they had to be provided with a small wrench made of wire to separate the lid. The key was inserted into the tongue and making it turn on itself was taking off the lid.

 

  • For the manufacture of these cans it was possible to start from bodies with side seams overlapped or engargolada.

Detail of the body-lid welding area of ​​a decollege can

Manufacturing speeds depended on the type of seam used. So in lines of overlap was 60 cans / minute and engargolado lines could reach 220. Almost all of French origin.

It was a first conatus easy to open and enjoyed great acceptance in France, Spain, Portugal and North Africa. They had a long life, as they continued to be used in the preserved fish market until well into the ’70s of the 20th century. Its disappearance was linked to the prohibition of the use of the tin-lead alloy as welding for sanitary reasons.

 

9º.- “CONOWELD” WELDING

In the “60s” of the twentieth century, health knowledge verified the negative incidence of lead in the body, beginning to apply limitations in its use for those cases that could be ingested by man. For this reason, soon began to question the use of tin-lead alloys as welding in the sewing of cans for food. The industry began to study alternative systems to solve this situation.

In principle, in the USA – 1970 – a solution was found that had the great advantage of being able to continue using the previously modified equipment. This made the conversion of the facilities cheaper. It consisted in transforming the old “bodymakers” (manufacturing) of the body of the can, incorporating to them an electric welding equipment and thus, changing the seaming system engargolada (interlaced of two hooks) and welded by tin-lead alloy by an overlapped seam and electrically welded. The serious problem to be solved was that the low temperature of fusion of the tin in relation to the steel, caused that before reaching the sufficient temperature to weld the two edges of the body of the can already the tin of the coating of the tin plate had melted, contaminating the welding electrodes. This caused that their life was very short, making the procedure unfeasible.

The solution found was to remove the tin from the area to be welded prior to the welding station. The equipment developed for this type of sewing was formed as follows:

–          It was based on a conventional trainer.

–          Of the same one of eliminated the part of formation of hooks and the station of engargolado complete – wings, bigornia and matillo – was modified.

–          In the old hook-forming area, small “strawberries” were incorporated which, rotating at high speed, scraped the tin from the extreme areas of the body – solder-free solder reserves.

–          An electric welding equipment was installed on the arch of the former.

–          In the old area of ​​engargolado the welding electrodes were mounted, consisting of a pair of adequately profiled copper rollers that rotated synchronized with the advance of the body.

Thus a finished body was obtained that could continue its advance through the rest of the machines -which had not been modified- until its total completion. Therefore, conventional lines were affected in the modification of the former and in the elimination of the welder by tin-lead alloy.

 

Its advantages were:

–          Removal of tin-lead solder alloy.

–          Economy of material when removing the hooks from the seam.

–          Greater space for welding, reducing reserves.

–          Elimination of the operation – of the equipment – of alloy welding

The packaging obtained had a very similar appearance to the one we are now accustomed to with the electric welding techniques put in place by the Soudronic house, with two appreciable differences: 1) larger lithography reserves; 2º) “Steel” color of the same, due to the absence of tin and the presence of the trace that the “strawberries” – starting tools – had left on their surface.

Obviously it was essential the outer and inner rebarnizado of the area of ​​the welding in the absence of protective tin to avoid the rapid oxidation of steel.

The conoweld welding was not consolidated in part because the transformation of the equipment was not easy and being a development of a metal company – Continental Can – was not available to the market in general. The appearance shortly after the technology developed by Soudronic, which brought more advantages, relegated it to a marginal situation. However, it continues to be used as the only solution to be able to weld bodies of cans made with TFS, since it allows to eliminate the surface chromium in the welding zone.

 

10º.- MIRASEAM

While Continental Can was developing the “conoweld”, the other major American multinational, American Can, was fine-tuning its own procedure to achieve similar goals, that is, to find a solution to the elimination of tin-lead alloy welding. He found it in the welding “miraseam”. This consisted of making an overlapping type of welding, gluing the superimposed parts with a special cement. This cement was a thermoplastic polyamide (plastisol) applied in a thin layer.

Its advantages were analogous to those already indicated for “conoweld” welding. The manufacturing speed was lower than that of a traditional bodymaker and also required a rebarnizado of the union stuck.

Old promotional “meraseam” can

The development that initially captured the interest of the market, soon saw its penetration in the same limited by the appearance of the electric welding that gathered more advantages than this development. It only had an important acceptance in the Japanese market for unprocessed products, drinks type. Its use disappeared in the last decade of the 20th century.

 

11º.- BOX BANDE

It was the last conatus to facilitate the opening of a can, before the easy to open ring covers burst. It was also a French development carried out at the beginning of the “seventies” of the twentieth century. It was a very interesting type of opening, which, unlike the previous ones, did not require a key or any instrument to open the boat. It was an invention that came late to the market, because shortly after its implementation, the legislation that prohibited the use of tin-lead alloys came into force, leaving it out of play. If not for that, it would have had a lot of acceptance and possibly many years of validity. Its essential characteristics were the following:

  • The bottom of the can was conventional.
  • The body, engargolado and obtained by the classic system, incorporated a reduction of diameter in the end to unite with the cover. That is to say, it underwent a notching process, analogous to the current stackable cans. This reduction in diameter was made at a height of approximately 8 mm. and the decrease in the value thereof was twice the thickness of the lid material. At this end of the body no tab was formed for the closure, but remained straight.
  • The cover consisted of a panel and a vertical side skirt of the same height as the reduced part of the end of the body, on which it adjusted smoothly, since its internal diameter coincided with that of the notched part of the body. In other words, it acted as a cover closing to external pressure. The outer diameter of the lid coincided with that of the exterior of the body, that is to say there was a continuity along the height of the can,
  • Once the cover was mounted on the body, a metal tape – very thin and flexible – was applied to cover the joint area. Therefore this tape covered the contact circumference between the lower edge of the skirt of the lid and the shoulder of the notch of the body.
  • This tape had a tin-lead alloy applied on its inner face. Applying heat to the assembly the alloy was melted, welding the lid to the body through the tape and also achieving a tight seal. The tape had a length greater than the development of the body, leaving the excess part loose, in the form of a tongue
  • The team that performed the operation of joining the body-cap, applying the tape and welding the assembly, had a circular, rotating design, step by step, in a horizontal plane. All this very sophisticated and complex.
  • For the opening it was enough to pull firmly from the free end of the tape, it was peeled off and then the lid could be removed by hand. It was a process similar to opening a pack of cigarettes.

Can with opening type “box bande”

There was no place to develop a certain variety of equipment. Those that were available were devised by Franpac – the inventor of the system -. The maximum speed reached was 200 cans / minute.

 

II.- THOSE WHO WERE AND CONTINUE

There is a group of cans that have been in use for a long time – some of them are much earlier than some of those written in the previous chapter and are no longer used – they enjoy good health and due to their good qualities they will continue to provide service to the consumer during time In this second chapter we will detail the most significant ones.

 

1º.- EMBUTIDO

The appearance of double effect and long stroke presses allowed the manufacture of a new type of packaging very different from the previous ones. This happened already at the beginning of the 20th century. It is the embossed or “two pieces” boat. It consists of two elements: the cover – normal and therefore equal to that used for the “three pieces” – and the body that incorporates the bottom.

  • The body is actually an extension of the bottom, made with the same material and in the same production operation. For this, the metal has to have special characteristics, such as greater ductility and less hardness so that it can withstand a drawing process without breaking.

 

  • The press where this operation is carried out needs:
  1. A) A greater stroke of the car, of the order of three times the height of the can to be manufactured, which allows sufficient travel to stuff and eject the boat.
  2. B) A lower device – under the table – that generates a pressure as uniform as possible along the advance of the drawing to ensure the ironing of the metal and thus prevent the formation of wrinkles to deform it. This is what we might call a “double effect”, although this designation is also used for secondary actions in other types of presses.
  •        The used die has analogies with the one used up to now for the manufacture of flat wing covers, but of greater height and with higher demands in precision and quality of materials. Its design allowed the can to be punched in its final dimensions, including its flange but with an irregular finish on its edge and in oversize.

Rectangular inlay can

  • A production line consists of:
  1. a)  )   A main press, which had to meet the aforementioned characteristics where starting from material cut into bands with manual feed and later automatic, the can was die-cut.
  2. )   An auxiliary press that trimmed the excess material from the edge, leaving the finished body with its corresponding tab to measure.
  • Years later – in the second half of the twentieth century – dies were developed capable of doing in a single press the two operations of drawing and trimming but they were useful for frequent and complicated maintenance so they were not fully successful. On the contrary, it was generalized the use of double, double – punching tools – capable of punching two cans per press stroke, expanding with time to a greater number of punches.

To be able to count on materials of sufficient properties and with presses and suitable tools, the metal industry soon offered in the 20th century this type of can that had some advantages over the previous ones such as: Lower risk of leakage by eliminating the closure of the bottom, simplicity in manufacturing equipment, simple technology …

On the contrary, it also had certain limitations. The materials and processes were only able to reach drawing heights approximately equal to half the diameter of the can. This forced to center its use in small boats, of low height. Also the use of the raw material was lower.

However, the new packaging was very useful for a range of products sold in small contents: food such as fish or pates; other more general uses such as cosmetics and pharmacy. So much so that continues to be used in modern times.

The normal production rates for this type of packaging were – and is – 60 hits / minute of press, which must be multiplied by the number of “punches” that the die has.

 

2º.- CLOSURE TO FRICTION

Certain uses of packaging involve only partially using the product it contains, and must be designed to keep the part that will be consumed later in good condition. In other words, it must be possible to close the boat again. Logically they must be products that do not decompose once opened with the passage of certain time. Let’s give some examples: milk powder, butters and jellies in food; waxes, paints and varnishes in general-purpose products.

All have in common that they are prepared before canning and therefore the can is not subjected to any treatment that generates internal pressure.

Also, in almost all cases, an instrument – spoon, brush – is needed for its use.

To all these conditions, a type of can complied with the type of “general lines” that began to be manufactured very soon by the metal industry. It treats of the cans with closing to friction or also called to pressesure.

It is a four-piece boat. The background and the body can be defined as normal or usual in other uses, but the lid is broken down into two elements:

  1. a) A ring – or ring – that is attached to the body by a normal closure and that has a large central hole.
  2. b)   A plug that adapts to the hoop hole

 

Ring-stopper assembly of a simple friction closure

To attach the plug on the ring requires a certain effort – or pressure – as it fits tightly into it. The friction force originated between them keeps them firmly united. From this effect derives its name.

Within this model of packaging, according to the design of the part in contact between ring and stopper, has given rise to several types of closure under pressure.

In the oldest, the friction is done on a single vertical wall. It was the one defined by the hoop hole, which had a skirt several millimeters high, on which the outer wall of the stopper was fitted. The risk of loss of tightness existed, since any failure or imperfection in this wall broke it.

That is why its improvement was sought with double pressure closure. In it the sealing area has a “U” shape, therefore there are two vertical surfaces that rub, the two walls of the “U”. For this, both the ring and the stopper must be given this form. At the bottom of the “U” there is no contact between the two.

Ring-stopper assembly of a double friction closure

These two elements are made in several operations in special press dies, at least two in each case. Because of the double folding of the material it is required that it be the same of a low hardness.

There is a variety of this type of closure where a new improvement is provided, consisting of achieving a third adjustment surface, resulting in what is called “triple friction”. This third closing is done by adding a half-round to the cap, concentric to the “U” and smaller diameter than it. The inner edge of the ring is embedded in this half-round. Sometimes, to improve this third contact a joint – compound – is applied in this half reed so that the edge of the ring is keyed in it, achieving a perfectly hermetic closure.

 

 

 

Example of triple friction closure

The invention of the “triple friction” closure was subsequent to the others and took place in the United States in the middle of the 20th century. This presents some advantages in relation to the other types, in addition to the improvement of the airtightness, as it is to prevent the exposed steel edge – without tin protection – from coming into contact with the product. For products that contain water, it is important because it eliminates the possibility of iron oxide formation, which can affect the presentation.

A variant of the closure to fraction consists of applying a warranty seal under the hoop. This seal is usually made of aluminum foil and its mission is to ensure the inviolability of the product, since to access it requires tearing it.

Its use is indicated for food contents of great sanitary responsibility such as powdered milk for babies and dietetic products.

There are special equipment that punches the seal from aluminum coil and inserts it on the ring previously manufactured. The ring-seal assembly is placed on the body by means of a normal closure, although the seamer has to have a special feeder for these elements.

All these types of closures raise the price of the can in relation to a normal lid for obvious reasons:

     Greater consumption of raw materials as they are one or two pieces more.

     Use of more expensive raw materials, due to special hardness

     Manufacturing of the most complex components – several operations – and slow

However, its advantages for certain uses are so evident that its use is widespread.

There is still another type of pressure closure very different from the previous ones. This is the “external pressure closure”. In the ring is removed and the plug fits directly on the upper part of the body.

In this case the end of the body is adequately reinforced by means of a folding of its edge normally towards its interior. This provides sufficient rigidity to maintain a “mouth” on which the cap fits. The latter consists of a simple panel with an outer skirt, which acts as a closing surface. Sometimes the lid and the body are joined by means of hinges.

Its use is indicated to contain products that do not require sealing, such as: chocolates, sweets, pastries, etc.

Curiously, this type of closure was the first used in the manufacture of packaging. In fact, its first application dates back to the eighteenth century, long before the discovery of Nicolas Appert. It was used in the small tin boxes that the English aristocrats kept in the pocket of their waistcoats and contained monkfish to suck.

 

3º.- BRASS

Metal cans lend themselves to multiple uses. In addition to the most common such as to contain processed foods, household products or beverages, they are also used as cans for liquids.

A subject unrelated to this work would be the large capacity drums, which although their manufacturing process is similar, the raw material is different and they deviate from our course. But there is an intermediate link between cans and drums, which is the making of “brass”, which are cans of a certain capacity – between one and twenty liters approximately – that if they enter fully into this matter. In them, both the raw material and manufacturing equipment are part of the metal industry.

Its utilities are very varied. They are consumed in markets such as: lubricating oils, vegetable oils for food, chemical products, paints and varnishes for professionals, preserves of olives, etc.

They can be classified into two large groups:

  1. a) Brass of total opening. Fundamentally to contain paintings. In them, the upper part acts as a lid, being able to open without destroying it, allowing its later use. This type of opening leaves the entire mouth of the body free, allowing the introduction of a tool such as a roller or a brush to paint. The skirt of the cover is divided into a certain number of tabs that are graphed on the outer rim of the mouth of the body, achieving a hermetic seal thanks to the use of a special compound – very spongy – applied on a channel of the cover in the closing area.

In commerce this type of packaging is called “pails” and for its manufacture there are specialized lines. Its normal shape is that of inverted truncated cone, which allows it to be stacked one inside the other when empty. This saves a lot of storage space and transportation, a factor that is important due to their high capacity. The frustoconical shape is achieved by expanding the body that has initially been cylindrically formed. . These cans due to their weight, are provided with a handle for transport. It is usually made from wire to plastic and is fixed to the sides of the body by means of two opposed supports called “orejones”.

  1. b) Brass with neck. To contain liquids. In these, the lid that is the same as the bottom and that is attached to the body by a standard closure, is equipped with a neck through which the liquid is poured. This neck is closed with a cap that also incorporates a guarantee seal.

There are a variety of types of necklaces: metallic, plastic, mixed … and also various ways to fix them to the lid: welded, pressure … The latter defines the filling and closing system of the can by the packer.

In the case of welded metal beads, the package is delivered with the same placed and filled through it, then covering it by means of the cap-seal. It is a procedure that is used less and less.

 

 

 

 

Brass with neck and handle

In the case of cans with plastic necks, two options are commonly presented: a)

The package is delivered with the lid, already equipped with neck, placed. In this case the packer fills the bottom and closes it by means of a conventional seamer. b) The brass is supplied with the bottom and the cover already placed, but the latter without neck. It is filled by the hole intended to receive the neck and subsequently it is mounted on it.

Plastic necks are usually telescopic, so when they are not used they can be picked up, not exceeding in this position the edge of the closure. This allows the cans to be stacked without the neck posing an obstacle.

Brass with neck are almost always rectangular, which saves space. They are also provided with a wire handle fixed by means of a hinge, which allows it to remain in the “lying down” position, facilitating its stacking.

The manufacture of brass with neck follows the usual technique of the other cans, having only of particular: 1) the preparation of the housing hole thereof. This supposes an additional operation of punching in the cover once finished. 2º) The welding of the handle to the lid, which is done by the technique of spot welding.

There are other brass variants of the above, such as those intended to contain olives, which have a handle or neck, closing and opening like a normal can.

 

4th.- CAPS FOR BOTTLES

The covers for bottles are a very specialized product within the metal industry. They have the raw material in common with the packaging, but its manufacture is very different. Within the market of covers for bottles and jars of glass there is a great variety, certain types have already gone down in history. Without pretending to be exhaustive, we will mention some of them that continue to be used.

Crown plug : It is the oldest, dating back to 1892. They are the popular “plates” used in beer bottles and drinks. Initially, it is formed by a metallic shell with a series of corrugations and a cork disk that made a tight seal. Currently the cork has been replaced by a sealing compound, a distant relative of that used in can closures.

Section of a crown cap

The crown plug was a big step in the packaging of carbonated drinks because it allowed – besides getting a tight seal – to facilitate the automation of the processes.

Its manufacture is carried out on lines basically formed by:

     A multipunzón press – at least of fifteen punches – that punches the shells and that is fed by whole leaves.

     A team applied the rubber by injecting a drop of it, subsequently molded to the appropriate configuration.

     A compound drying oven.

The crown plug has suffered a significant reduction in consumption with the expansion of beverage cans.

 

4th.- CAPS FOR BOTTLES

The covers for bottles are a very specialized product within the metal industry. They have the raw material in common with the packaging, but its manufacture is very different. Within the market of covers for bottles and jars of glass there is a great variety, certain types have already gone down in history. Without pretending to be exhaustive, we will mention some of them that continue to be used.

 

Crown plug : It is the oldest, dating back to 1892. They are the popular “plates” used in beer bottles and drinks. Initially, it is formed by a metallic shell with a series of corrugations and a cork disk that made a tight seal. Currently the cork has been replaced by a sealing compound, a distant relative of that used in can closures.

Section of a crown cap

The crown plug was a big step in the packaging of carbonated drinks because it allowed – besides getting a tight seal – to facilitate the automation of the processes.

Its manufacture is carried out on lines basically formed by:

     A multipunzón press – at least of fifteen punches – that punches the shells and that is fed by whole leaves.

     A team applied the rubber by injecting a drop of it, subsequently molded to the appropriate configuration.

     A compound drying oven.

The crown plug has suffered a significant reduction in consumption with the expansion of beverage cans.

 

Tapas “twist-off”

They are round caps with a diameter generally comprised between 35 to 110 mm. that are provided with nails that allow their fixation on the mouth of francs equipped with threads.

American development, from the “40s” of the last century, have become the most widespread closure in glass jars for jams, mayonnaises, sauces, etc. They are also used for classic preserves such as vegetables, legumes, fruits …

Section of a twist-off lid

 

These covers consist essentially of:

     A central panel almost flat, which has a projection on its outside to accommodate the compound.

     A vertical fault.

     A curled inward edge of the skirt.

     A series of nails – depending on the design and size – formed on this edge.

     Area – coinciding with the mouth of the franc – on which a compound is applied

 

5º.- AEROSOLS

An aerosol is defined as the set of particles suspended in a gas that is called propellant. It can occur in nature, although it is normal to obtain it artificially. It is an ideal way to apply an atomized product evenly on any surface.

The way to generate it using a can was first devised by the Norwegian Eric Rotheim in 1929. The basic idea is to contain in a can a liquefied gas at high pressure and dispersed or dissolved in it a product that is the active or useful component . When the contents of the can are brought into contact with the atmosphere, an escape occurs in the form of a gas that incorporates the active principle in the form of particles. The can always remains under internal pressure, since as it is consumed the liquid phase of it, part of the gas evaporates keeping the interior pressure practically constant

Its massive application did not arrive until the years “40” of the last century when in North America its use was commercialized after the success obtained during World War II during which it was used by the American army to fight the diseases caused by insects in the Pacific.

Its first application was for insecticides but soon spread to lacquers, deodorants, etc … At the end of the “70” there was a strong controversy in its use, since the propellant normally used was composed of ClFDs, which attacked the layer of ozone. The industry little changed the formulations, eliminating these gases and today again enjoys a good prestige in the home, pharmacy, perfumery …

The cans used to contain products that are applied in aerosol form must be designed to withstand high internal pressures. Therefore, the thicknesses of metal used are greater than in other cases. The aerosol cans, in addition to the body, bottom and lid, are provided with a valve mounted on the lid that, when activated, allows the product to be released – mixture of propellant and active component. Most valves have a “fishing tube” that guarantees to take the product from the bottom of the can, where the liquid phase is located. The valve is protected with a plastic cap.

The bottoms and covers, to adequately support the internal pressure, have a spherical cap shape, concave in the case of the bottom and convex in the cover that receives the name of cupola, cupel or cone. In its center there is a hole on which the valve is mounted. There is a wide variety of valve types that adapt to the characteristics of the product and the way it is applied.

 

 

 

Spray type can

The bodies must have a welded seam of high quality to ensure its resistance to internal pressure in addition to its tightness. Precisely for this, before the use of electric welding was generalized, a special type of weld seam was used with lead tin alloy, specific for this type of cans, in which overlapping sections were alternated with other engargolados – agrafados-.

Aerosol cans made of tinplate, usually have a reduction in diameter at their ends, so that once made the closures of the bottom and dome, they are aligned with the rest of the cans. This makes the overall appearance of the packaging more attractive, similar to those produced by aluminum extrusion.

 

III.- THE NEW TECHNOLOGIES

Finally, in this final chapter we will discuss the types of cans that have been developed in the last third of the last century and are now being used massively. They are manufactured with complex technologies and represent the young face of this sector, which will allow to maintain activity in the same in the coming decades, until new advances make them obsolete again.

 

1º.- ELECTRIC WELDING

We have already seen in the previous chapters as the normal system throughout the 20th century of welding the lateral seam of the bodies, welding with tin-lead alloy, began to be seriously questioned by the health authorities due to its contribution of lead to food from the “60” years. Said metal is toxic and difficult to eliminate by the human organism. Soon, the prohibition for alimentary uses of this technique was generalized in most of the countries, being replaced by electric welding.

Electrical welding by points, was a technique commonly applied in the industry in general and had already found some applications in the manufacture of packaging, especially in those for industrial use, as for example in welding the sewing of large capacity drums , soldier of handles and supports of boats for paintings, etc. Let’s see the basics of this technique.

In electric welding, the welding point is obtained between two metal parts without any external contribution other than the passage of an intense current through these parts at the point considered. The welding energy is produced by the resistance that opposes the material to the passage of this current at that point. A continuous welding line is achieved by means of a succession of points that are produced between two metal parts, subjected to the pressure of two circular electrodes, animated by a turning movement. The basic principles of electric welding are contained in Ohm’s law (I = V / R) and in Joule’s law, which determines the amount of heat produced. In the case of an alternating current, each frequency change generates two welding points, one for each semisenosoid, hence the need to increase as much as possible the frequency of this current, reaching up to 500 hertz.

Initially, the first applications based on fixed copper electrodes allowed a low rate of work. Due to the low melting temperature of the tin, it caused these electrodes to be coated with this metal after a few cycles, altering the working conditions. A Swiss company (Soudronic), began the manufacture of some machines that were going to give the ideal solution to these problems. Founded in 1953 in a town near Zurich, Soudronic began to build very simple hand-feed welding machines, which solved the problem of contamination of the electrodes, getting them to be continuously renewed, using a copper wire moved at the same speed as the can to be welded. The success was total and in a few years the technique improved a lot, allowing to put on the market equipment capable of working at the same speed as the old “bodymakers”, and even overcome it. Soudronic became the world leader in this technological change, basing its policy on a great effort in research and development, which led it to patented a number of novelties and improvements, which revolutionized the technique of forming bodies of metal cans.

Detail of an electric welding

The advantages of this new technique in relation to the previous ones are several:

–          Reduction of raw material consumption. The necessary development of the bodies was reduced by at least 6 mm.

–          Reduction of lithography and varnish reserves, which improves packaging presentation

–          Elimination of toxic metals (Lead)

–          Improvement of the mechanical strength of the joint (side seam)

–          It facilitates later operations such as cordoning the bodies.

–          Improvement of lid and bottom closures by reducing the thickness of metal in the area of ​​the joint.

At present, this technique has displaced all previously used and is the generalized in the manufacture of three-piece cans.

 

2º.- EASY TAPAS OPENING

The idea of ​​facilitating the opening of a can without having to resort to the typical can opener is not new. Its history goes back many years with the use of covers that in some way favored the opening as the “decollage” type, cans with lateral opening by means of tongue in the body (the typical “corned beef”), opening “Norwegian “,” Box bande “(lateral opening by tape) and others. Most of them we have dealt with before. With the arrival of this new type of tapas to the market, designs are developed that have nothing to do with those and that in all cases eliminate the use of any auxiliary instrument.

It was the year 1959, when in Dayton – North America- Ernie Fraze, a former Alcoa technician, well versed in the properties of aluminum and also an expert in die-cutting, had the first prototype of easy opening covers ready. The first industrial versions are presented beginning of the “sixties” and develop rapidly.

The basic idea was to make an incision on the outer face of the cover that delimited an area of ​​the cap and that would be the one that would come off in the opening. To start this area, a ring was attached to the lid – fixed to it by means of a rivet made with the same material as the lid – that had at its end a pointed area – called a nose – that when raising the ring pushed down the area weakened causing its tear. The shape of the opening had in principle the shape of a water drop and was intended for emptying liquids, occupying only a small part of the total surface.

 

 

Primitive lid design for drinks

Little by little and over several years it began to be used in beverages such as colas and beers, reaching at last a total success.

Soon it was thought of a variant of it that would allow to open the entire surface, destined for food. The first designs ripped the circular panel into a strip shape following a spiral configuration. The incision with the naked eye resembled three concentric “C” s, which, when disengaged, had the appearance of a “pig’s tail”. Over time it was replaced by a simpler one with an incision in the shape of a circle.

Several American companies offered, in a short term, tools and equipment suitable for the manufacture of easy opening covers. The tools required a very high design and precision. To work with them, high reliability presses were required. The material used in the United States was – and still is – aluminum, which is logical in a country where energy is cheap. Europe, where energy is expensive, soon changed to tin in the case of total openness. This meant a reworking of equipment and tools, quite complex. In addition, he applied this technique to non-round shaped covers (rectangular and oval) for the fish market.

The easy-open lid was gaining market safely. Today, 100% of the cans for beverages use these caps and also a very high percentage of food cans.

 

 

3º.- DRD PACKAGING

The sausage packaging presented the serious limitation of its low height, as we have already mentioned. For this reason the markets of great consumption of food preserves, that traditionally used higher formats – for example “1/2 kg.” – were not within reach.

At the beginning of the last third of the 20th century, both the quality of the base steel used in tinplate, as well as the precision of tools and equipment, were at an adequate level to be able to develop a new drawing technique that would overcome the barrier of the low depth of the can. This technology was based on making the stamping step by step, that is, in a staggered way. In each step the diameter is reduced and the height of the piece obtained in the previous one is increased. This technique of successive embossments was called “embutición-rembutición” taking the designation “DRD” of this name expressed in English

The manufacturing is done on multi-station presses, transfer type or circular table. The material is usually fed from coil. Normal press operations are usually:

–          Flat disk cutting from coil
–          First drawing of a sketch from the flat disk
–          Second stuffing – more – to reach the desired diameter and height
–          Configuration of the can’s bottom

Subsequently, the irregular material is cut out from the can edge and the flange is formed on it. You can also cordon off your body, try, etc.

 

 

 

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Due to the great deformation that the material undergoes, it is not possible to lithograph it flat, although it can be varnished, although it is possible to decorate after its formation or to label it. Due to the high cost of lithography installations on shaped packaging and its low versatility, the most widespread solution is that of labeling. This type of cans are capable of supporting both the vacuum and the internal overpressure as the walls maintain a thickness very close to the initial and are designed for foods that need sterilization process.

Market penetration of this type of packaging by countries is uneven. Thus in the United States and Central Europe it is important while in the Mediterranean Zone it is marginal. The reason is not only in the high cost of the installation, but also in the little flexibility of the same for change of format. Therefore, it is justified only for large runs of very common sizes that have application in different or very large markets.

 

4th.- DWI CANS

The second variety of two-piece cans of a certain height are those made with the DWI technique. These acronyms come from the English words “embutido, stretched ironed”, that define the process followed in its manufacture.

In this case, the first operation is the simple drawing of a “cup” of little height and diameter greater than the definitive one. For this, the coil is split and the operation is carried out in a multipunzón press. In the following it is subjected to a series of stretched and pressed, until the final shape is obtained. This stretching and ironing is done in a special machine – which is called a trainer or “bodymaker”, in memory of the primitive three-piece. To achieve the stretching of the material, the “cup” – pushed by an inner mandrel – is passed through a succession of rings, each of which has a slightly smaller diameter than the previous one, causing a rolling of the metal by its external face

This achieves a very thin wall with optimal use of the material. This technique achieves that the residual thickness of the walls of the can is less than one third of its original value. On the contrary, the thickness of the background remains practically unchanged. They are designed to withstand only internal pressure and are the typical beverage cans of the current market.

 

 

 

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The facilities are extremely complex and specialized, with no flexibility, so they are dedicated to the manufacture of a single can size. This is almost always the one used for drinks, 33 cl. of capacity and nominal diameter 65 mm. All the cans used in this market are lithographed, an operation that is carried out after the forming and after a severe washing, for the elimination of the lubricant used necessarily for the stretching and ironing process. The bottled beverages, especially the tails, are highly aggressive towards the metal, so a perfect interior varnish – two layers – is required at the end of the manufacturing process.

The DWI cans are the new wise that has brought a strengthening of the sector when it seemed that it was doomed to languish.

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