Metal cans. Who invented tin cans What are tin cans made of?

At the end of the XVIII century, Napoleon Bonaparte decided to conquer Europe. The planned conquest campaigns required new ways of storing provisions. And then Napoleon announced that whoever finds a way to keep food fresh for a long time will receive a solid monetary reward.

Many experts thought about this question, but the confectioner and chef Nicolas Francois Appert turned out to be the most successful. He came to the conclusion that if food is placed in sealed packaging and then subjected to heat treatment, then they can be stored for a very long time.

The hypothesis turned out to be correct. Products prepared in the manner proposed by Apper were stored long time and after that they turned out to be not only suitable for consumption, but also of very high quality. Appert used ceramic or glass jars to store food, which were hermetically sealed. The method invented by Apper saved the Napoleonic soldiers from a lot of problems with cooking that arose during military campaigns.

In 1809, Napoleon awarded Apper a cash prize and awarded him the title of "Benefactor of Mankind".

Invention of the tin can

Subsequently, the Englishman Peter Durand improved the invention of Upper. In 1810, he patented his own design of tin cans. Such containers for storing canned food were much more convenient than glass and ceramic vessels.

Of course, the first tin cans differed significantly in appearance from modern ones. These containers had very thick walls; their inner surface was covered. They were made by hand, and the lid of the jars was not very convenient. They opened such canned food with a hammer and chisel.

Over time, America became the center of the canning industry. They began to produce special ones there, on which it was possible to make tin cans in an automated way. Already in the second decade of the XIX century in the United States mass-produced canned fish and fruits. It was here that the tin can acquired its familiar look, familiar to everyone today.

Interestingly, the Americans thought of inventing a can opener only in the middle of the 19th century.

In 1870, the first cannery appeared in Russia. He produced several types of canned food, which were intended for the needs of the army. Fried beef, porridge and meat with peas enclosed in cans enjoyed great success with consumers.

“Soup in a saucepan came right on the steamer from Paris; they will open the lid - steam, which cannot be found in nature." Gogolevsky Khlestakov did not just "fill in", but talked about canned food that came into fashion among the nobility in the 30s of the 19th century, which were then expensive, and which he himself, Apparently you didn't have to try.

The history of food preservation began in 1809, when a French culinary Nicolas Upper , inspired by an award promised fifteen years earlier for suggesting a method that allows food to be stored for a long time, considered that he had achieved the required results, and claimed his invention. The French government committee for art and industry, after checking, found his method of preservation acceptable, and himself Napoleon presented him with a prize in 1810. In the same year in the UK Peter Durand a method of preserving food was patented, similar to Apper's - only instead of a glass jar in Britain they used a tin.

Since then, a metal can has become the main container for many canned goods: fish, meat, meat and vegetable, dairy, vegetable - and has long been called nothing other than "canning".

EARLY XIX CENTURY

Methods for coating iron with a layer of tin in order to protect it from corrosion were known in Ancient Rome. Now thin steel, coated on both sides with tin, is called tin. In the 13th century, Southern Germany became the center of tinsmithing in Europe. Kitchen utensils were made there, as well as the first tin containers, in particular, snuff boxes. With the imposition of high import duties on tinplate in 1706, Britain became the leading producer of tinplate in Europe over the next hundred years. So the use of cans for food preservation in this country is not accidental.

The first industrial canning industry arose in the city of Berdmosy (Great Britain) in 1812. It is quite understandable that, like most inventions, the canning innovation immediately began to be used in military interests. The first canned goods were used to supply the army and navy. Canned foods have ensured the success of many long expeditions. But there were cases when tin cans also served as the cause of the death of the military and researchers. Lead contained in the solder used to seal the cans sometimes got inside and mixed with the contents. Naturally, this caused poisoning of those who consumed the canned product. The danger was also the second component of solders - tin. At low temperatures ordinary white tin can go into another allotropic modification- gray tin, while breaking up into small crystals. This is what caused the death of the second Antarctic expedition. Robert Scott in 1912. The seams of the cans were soldered, and the expedition was left without food and fuel. But the death of courageous people forced to pay attention to this metal problem, called "tin plague".

For a very long time, tin cans were made by hand from thick tin. Seams were soldered with tin. To open the then tin can, it was necessary to have the appropriate tool, for example, a hammer and chisel, and decent physical strength. It hardly corresponds to reality that got into the book T. Heina and on the Internet, the legend that a tin can with roast veal was unharmed on two expeditions William Perry 1820s due to unsuccessful attempts to open it. One must think that the majority of sailors then were strong men, and a chisel or chisel would have been found on the ship. Rather, its existence was simply forgotten. But the fact that this jar was opened only in 1938 is absolutely real. Research, and then feeding of laboratory animals, showed that the product, which had been in the jar for more than a hundred years, was perfectly preserved.

MIDDLE AND END OF THE XIX CENTURY

The production of jars by hand was a laborious process and, moreover, did not meet the ever-existing consumer demand for accurate container sizes. Therefore, tinsmiths, whose artels began to settle around large canning industries, began to invent small-scale mechanization devices aimed at both. The greatest influence on the development of the production of cans was made by a number of inventions made in the world canning centers - the United States and Britain - in the late 40s of the 19th century. Among the inventors, it is impossible not to mention the Englishman Henry Evans, who in 1846-49. made several inventions, the main of which was the formation of blanks (in professional slang - blanks) of cylindrical cans using rollers. Many of his inventions eventually made it possible to create machines for the production of prefabricated cans. It is worth adding that in 1866 another step towards the creation of machines was taken - a method for automatically sealing the seam of the can body was patented.

Can manufacturers were also helped by the successes of metallurgy in the second half of the 19th century, which began with inventions Henry Bessemer , which contributed to the production of low-carbon steel. From it began to receive thinner tin. And thin tin gave greater accuracy in the dimensions of the manufactured cans, facilitating the work of tinsmiths and mechanizing their work. It has become easier to open banks. However, the surge in the invention of can openers of various designs, which occurred in the second half of the 50s - in the 60s of the XIX century, simplified the opening even more.

True, thin tin also gave rise to a problem: during the heat treatment of canned food in sealed cans, the pressure arising inside began to inflate the cans. The problem was solved by the appearance on the bottoms and lids of cans (they are called ends in professional terminology) of concentric grooves-reliefs, which ensure their swelling when the pressure in the can changes and the restoration of its original position when the canned food cools.

But on the other hand, the use of thin tin made it possible, when fixing the ends stop welding. At the end of the 1880s, a seam called a double seam was invented, which is still mainly used today, and the first equipment for rolling lids and bottoms of cans with such a seam appeared. And from the mid-1890s, the edges of the blanks began to be sealed into a lock to obtain a longitudinal seam of the body. True, it was not possible to refuse from soldering the seam. But the possibility of solder material getting inside the cans was reduced to a minimum, and the cans were processed better before filling. The very first lines for the manufacture of metal cans with a greater or lesser degree of automation began to appear at the turn of the 80s and 90s of the XIX century.

Separately, we note that in the last decade of this century, the design of a prefabricated tin can with a soldered seam was finally formed, which still exists, and until the 60s was the only one.

XX CENTURY

The first half of the 20th century, during which more and more sophisticated equipment for the production of cans and canning products was created, did not contribute anything to the design of a metal can.

Unless an aerosol package was created, the same can was used as a container. But here the invention was more about an aerosol valve than a container. There is evidence that aerosol packaging was developed in Norway in 1922. But its widespread use began much later, during World War II, when the United States Army, which fought on tropical islands, needed a convenient container for the delivery, storage and spraying of chemicals that destroy insects.

Although canned soups in cans have been produced since the beginning of the 19th century, the idea to use this packaging for drinks did not appear until 1935. Since 1958, cans have been made from aluminum, which were originally used exclusively as containers for drinks. Aluminum and its alloys were first used in canning containers in 1960, but then only to create easy-to-open lids. But four years later, cans were stamped out of it. At the same time, tin cases began to be made. Thus, 1964 is the year of the appearance of a new type of metal can for preservation, a can consisting of two parts: a body made together with a bottom, and a lid. Such a bank began to be called whole.

The end of the 60s introduced changes in the production technology of prefabricated cans: in the manufacture of longitudinal seams, instead of sealing the edges into a lock and sealing, they began to use welding with the edges located in a joint. Such a can became known as a team with a welded seam or a team welded.

OUR DAYS AND PROSPECTS

Despite the increasing use of the easier-to-manufacture whole cans, prefabricated cans continue to be actively used in the canning sectors of the food industry. The advantages of prefabricated cans are in a larger range of their capacity. For example, GOST 5981, which defines the shape, design and dimensions of this container, has 35 standard sizes of round prefabricated cans with a capacity of 70 to 9550 cm3, while for whole cans the maximum capacity reaches 353 cm3 for round and 1500 cm3 for oval.

If we compare prefabricated cans with a welded and soldered seam, then the first one has the full advantage. The technology itself is based on their manufacture on continuous equipment, which is a priori more productive. In addition, there is a technology when the body of a welded can is made larger in height, and then cut into several bodies of the required height. In addition to being less convenient in production, a can with a soldered seam loses in terms of safety: as shown by studies conducted by specialists from the Institute of Research and Development of the Federal Institute of Chemistry of the Federal Reserve, in some cans with a welded seam, after two years of storage of canned meat, a noticeable amount of tin and lead coming there from the solder is found. The content of these substances increased as the shelf life increased. In welded cans, the migration of harmful substances exceeding allowable norms was not observed even after five years of storage. The fact that there is no future for prefabricated cans with a soldered seam became clear back in the early 80s of the last century. Even in the mentioned standard, the permissible period for the use of brazed cans in our country was stipulated - their use should have ended in 1993. Later, a change was made to the standard, and the phrase about limiting the use of such cans disappeared. Soldered cans continue to be used in the domestic canning industry. But the time of existence of the can, the design of which is more than a hundred years old, is ending.

The question of how to protect food from spoilage has occupied mankind since ancient times. At first, food was saved for oneself or one's family, then the problem became more global - it was necessary to make supplies for long-term storage - for armies, expeditions. At first, only drying was used. Meat or fish was dried in the sun, sometimes rubbed between stones and dried the resulting powder, mixing it with spices. This mixture was stored in leather bags for more than six months.

More than 200 years ago, an invention was made that radically changed the idea of ​​mankind about the possibilities of food storage and greatly simplified the life of professional chefs and ordinary housewives around the world.

The first canned food produced by man was found during excavations of the tomb of Pharaoh Tutankhamen in Egypt. Products were stored in the bowels of the earth for about 3 thousand years. It was roasted and embalmed olive oil ducks in a clay bowl, the oval halves of which were held together with resinous putty. Canned food of this quality has withstood the test for thousands of years and has retained relative suitability for food (there is evidence that ducks were edible for animals). They would be the envy of many of today's canned food.

The Roman senator Marcus Porcius Cato the Elder was one of the earliest "canners". In his book On Agriculture, he wrote: “If you want to have grape juice all year round, then pour it into an amphora, grind the cork and lower the amphora into the pool. Take it out after 30 days. The juice will stand for a whole year ... "

M.V. Lomonosov in 1763, while organizing an expedition to explore the polar regions and the Northern Sea Route, ordered: “Making dried soup with and without spices, one and a half pounds of each variety.” That is, two centuries ago, the soup concentrate traveled across Russia by land and the Arctic Ocean to Kamchatka.

Needham, an Irishman, stubbornly boiled lamb gravy in a corked bottle, but after a day or two it was full of germs again.

The Italian Spallaziani saw his mistake and corked the bottle hermetically - after boiling the product remained fresh and usable for several days.
The Frenchman Nicolas Francois Appert, a man far from pure science, but a good practitioner, learned about the experiments.

In 1795, about to conquer all of Europe, Napoleon Bonaparte announced that a cook who found a way to keep food fresh for a long time would be rewarded with 12,000 francs. Scientific disputes between two scientists, Needham and Spallanzani (the first argued that microbes arise from inanimate matter, and the second argued that each microbe has its own progenitor) led the French chef and confectioner Nicolas Francois Appert, far from science, to the idea that hermetically sealed products and subjected to heat treatment, can be stored for a long time. His assumption turned out to be correct, and the products prepared by him in this way, after long-term storage, were recognized as high quality. It took him more than ten years to prove a fact known to all modern housewives - if glass or ceramic jars are filled with jam, broth or fried meat, tightly corked, and then boiled in water for a long time, then the contents of the jars will not deteriorate and remain completely edible for about a year . The invention was immediately put on stream for the constantly fighting Napoleonic army.

In 1809, Apper was awarded for his invention state prize and the title of "Benefactor of Humanity". Later, this enterprising gentleman opened a shop "Miscellaneous food in bottles and boxes" on one of the streets of Paris, where he sold manufactured supplies in sealed and hermetically sealed bottles. The store operated a small factory for the production of canned food. Later, Apper, already a "Benefactor of Humanity", wrote the book "The Art of Preserving Plant and Animal Substances for a Long Period". Apper's method was scientifically substantiated almost sixty years later, in 1857 at a conference of the Society of Naturalists. Louis Pasteur, then an unknown young scientist, made a presentation that there are microbes in nature that cause the process of putrefaction, leading to spoilage of products. For the life of these organisms, special conditions are necessary - a certain temperature, high humidity, the presence of oxygen and, most importantly, the absence of antibiotic substances in the product. It is worth violating these conditions - and the microbes die. It is on this provision that the methods of preservation are based - sterilization and pasteurization.

It is on this provision that the methods of preservation are based - sterilization and pasteurization. Although the palm in meat preservation belongs to a talented Frenchman, this method of preserving food was brought to mind by another person - the Englishman Peter Duran. He invented and patented tin cans that are more convenient than glass containers.

Naturally, they were much different from modern ones - they were made by hand and had an uncomfortable lid. The British acquired a patent for the production of canned food according to the Upper method and from 1826 supplied their army with canned meat. True, in order to open such a jar, the soldiers had to use not a knife, but a hammer and a chisel. However, not France or England, but America very quickly became the world center of the canning industry. In Baltimore, they began to produce a variety of machines for the automated production of cans. Beginning in 1819, canned lobster and tuna were produced in the United States, and fruits were also canned. It was here that cans took on the form that is now known to each of us. Things were going so well that the production of canned food became an extremely profitable business - factories for the production of cans appeared, new items were literally swept off the shelves. And in 1860, again, the can opener was invented in the United States.

In Russia, of course, they knew about the French invention. In 1821, the St. Petersburg and Moscow public vividly discussed the report of the Russian Archive magazine about how turtle soup, poured into cans, was delivered from the East Indies to London shops. Despite the awareness, the first cannery appeared in Russia only in 1870. The main customer, of course, was the army. Five types of canned food were produced in St. Petersburg: fried beef, stew, porridge, meat with peas and pea soup.

Celebrating the 200th anniversary of the invention, the Japan Canning Society has released an exclusive batch of canned food that is said to be exactly the same as what Napoleonic soldiers ate. Japanese experts have made five types of canned food according to Apper's recipes. In particular, the Japanese repeated soldier's consommé, vegetable stew, pot-au-fee boiled beef soup, bean melange with mushrooms and strawberry dessert. These canned goods were ceremonially opened and tasted at the Tokyo headquarters of the canning society.

A tin of roast veal made in 1924 returned untouched from two sea voyages. She got into the museum, lay there until 1938, and scientists finally became interested in her. “The condition of the meat looks impeccable, large pieces look like veal was cooked the other day,” the researchers reported.

They noted the bright pink color of the meat and the presence of white oily mucus, and the analysis showed that the canned food was better preserved than expected. For ten days this meat was fed to young healthy rats, who ate greedily and without consequences, and once fed to a cat, with which nothing happened either. With current technology and scientific advances, which canned food manufacturer would dare to test the expiration date like this?

And one more thing: in 1966 in the USSR, an elderly citizen entered the All-Union Research Institute of the Canning Industry and put a can of canned food on the table with the inscription “Peter and Paul Cannery. Stewed meat. 1916". Andrei Vasilyevich Muratov, the owner of this can, received it at the front during the First World War. The analysis and subsequent tasting showed that the "Meat Stew" was excellently preserved, despite the fact that it had lain in the jar for 50 years!

The current canned food that makes up the diet of astronauts on the orbital station, of course, differs from army provisions. And opening another tube or a jar of pate, not every cosmic long-liver will remember Apper, the benefactor of mankind, but the value of a simple tin can does not become less important from this.

“Tin has outlived its “bronze age” and has become the metal of a tin can” - this is a quote from Academician A.E. Fersman’s excellent essay on tin, from the book “Entertaining Geochemistry”. The title of the essay follows the title of this chapter.

Really, known to man Since ancient times, tin has been used for thousands of years as the main additive to copper. The great alloy - bronze - was obtained as a result of this union.

But the Bronze Age has passed. Bronzes have become one of the widely used, but by no means the main alloys. And tin has found other uses. It made friends with iron, more precisely, with tin, thin sheets of rolled iron. Thousands of applications has such a sheet. And one of the most important is to be a container of a canned product, in other words, a tin can.

Tin has a significant resistance to chemical attack. It does not react with water, it dissolves very slowly in dilute acids, only when heated to 150 degrees does it begin to oxidize with atmospheric oxygen. All this fully satisfies the high requirements that can be made to the metal that covers the inside of the tin of a can that comes into contact with food intended for humans. That is why tin covers the inner surface of cans.

There are several ways to carry out such a coating of tin with tin. The hot method has long been known, when a cleaned and degreased product is immersed through a layer of flux into molten tin. The extracted product is already covered with semi-dry.

In case it is necessary to polish one side of the metal sheet, it is cleaned, heated from below and the cleaned side is rubbed with tin and flux. This is done with an ordinary dry and clean rag.

Nowadays, however, these methods of tinning are a thing of the past. Today, tin cans are tinned in galvanic baths.

World tin production is subject to rather sharp fluctuations. So, in 1940, about 250 thousand tons of this metal were mined in the capitalist countries, and in 1952 - only about 170 thousand tons. Perhaps there is no country in the world in which tin would not be considered a scarce metal. And most of this tin goes everywhere to the production of tinplate - the metal of cans.

The lack of tin makes it work in three directions. Geologists are trying to find new deposits of tin stone - tin ores.

Metallurgists are looking for ways to replace tin in alloys, to do without it. And everyone should think about how to save the already mined tin, not to let it die.

Each tin is about half a gram of tin, which can be returned to the production cycle if the tin gets into the scrap, and does not rust under the fence. Extracting tin from old cans is not difficult: after all, tin dissolves in alkalis. Old cans are immersed in them, and then the tin is isolated by electrolysis.

The second very serious item of tin consumption is alloys. After all, this metal is part of bronzes, low-melting alloys, printing alloys, bearing materials. But especially a lot of it goes to the production of solders.

And here are the passport properties of this metal. It melts at 232 degrees, boils at 2430 degrees. Its specific gravity at normal conditions about 7.3 g per cu. see. Tin is soft, it can be scratched with a fingernail. Easily forged and rolled into the thinnest foil.

There was a time when not only spoons and bowls were made of tin, but also buttons for soldiers. They say that in one harsh winter, these buttons suddenly “sick”. More recently, shiny, durable, they were covered with a grayish coating for no reason and crumbled into dust. It seemed that the tin of the buttons had fallen ill with some contagious disease. They even came up with a name for this phenomenon - "tin plague".

And everything was explained very simply. The fact is that the usual tin known to us is stable only at temperatures above minus 13 degrees. Below this temperature, tin recrystallizes, it greatly increases in volume and therefore begins to crumble into dust. This process is especially fast at a temperature of about minus 30 degrees. Apparently, this was the temperature when the buttons of the soldiers' overcoats began to crumble.

Such is the service of the tin man. Although this metal is not the immediate neighbor of copper in the periodic table, I have placed it in this chapter. For too many centuries it has been in a fire-bonded friendship with copper, and its present service to man is too similar to the work of zinc to be able to tear this metal away from its friends and work colleagues.

Copper is the chosen one of electricity.

save metal

The production of non-ferrous metals - we have already seen this in a number of examples - is a complex, expensive, labor-intensive process. Remember: to get one ton of copper, you need to extract 100 tons of ore; to get one ton of nickel, it is necessary to raise 200 tons of ore from the bowels of the earth, and even 300 tons of tin. How much human labor is spent on this! And how it is necessary to save this labor embodied in metal!

Once upon a time, all non-ferrous metal mined was spent only on the production of weapons, tools and household items. Hot copper, gold-like brass, sonorous bronze were also used to make jewelry. Cabins and superstructures of warships were hung with coppers, which the sailors had to fiercely scrub. Bulky and heavy chandeliers, various candlesticks, ventilation grilles, taps, etc. were made from the same materials. Yes, technology did not know a hundred years ago, for example, other materials for the manufacture of all these and many other items.

It is a completely different time - a time when old materials are being replaced by new ones, such as aluminum, plastic and refined wood. And for non-ferrous metals, new important applications are found in those places where no one can replace them at all.

The heart of an electric motor is where the copper should be, not in an ornate doorknob or a candlestick heavy as a mortar.

No, there is no place for precious tin and copper in a bulky bronze ink device!

We must try to keep the pewter items out of the cold. They may die irrevocably.

Why spend precious nickel, which is part of stainless steel, for finishing railway and tram cars, river and marine vessels?

But, of course, when revising the consumption rates for non-ferrous metals, reducing the list of products for which non-ferrous metal is used, we must not allow the quality of products to suffer because of this. Replacement should be made only where it is really expedient.

Non-ferrous metals should be saved not only by replacing them with other materials.

Saving non-ferrous metals is the reduction of machining allowances, and the careful collection and sorting of metal chips, and the fight against waste during remelting and heat treatment, and reducing the weight of the corresponding parts.

At many enterprises producing cast iron alloyed with magnesium, not magnesium scrap and waste are used for this purpose, but primary magnesium.

Very often products, the excellent quality of which would be ensured by a thin coating with an anti-corrosion layer, are entirely made of expensive stainless alloys.

Saving non-ferrous metals is both the collection of non-ferrous metal scrap and the collection of household waste.

Each used tin can is tin no longer needed by the consumer.

Remelting a ton of aluminum scrap requires incomparably less expenditure than producing a ton of primary aluminum.

Protect non-ferrous metal! Spend it only where it is really irreplaceable! - with such an appeal addressed to our people the Central Committee of the Communist Party Soviet Union in December 1959.

This call met with the liveliest response of the entire Soviet people.

Metal tin cans are made mainly from tinplate - thin sheet iron, coated on both sides with a layer of tin (half). Some factories have recently started making cans from aluminum sheet and aluminum alloys.

Until recently, for the manufacture of cans, tinplate with a thickness of 0.24 to 0.32 mm was used, but in last years thinner sheet 0.20-0.22 mm thick has been mastered. The use of thin tin can improve the quality of tin cans, reduce metal consumption by 12-16%, as well as reduce the power of electric motors by 10-12% and extend the service life of tin can equipment.

Depending on the thickness, the tin is divided by numbers. The plate number shows its thickness in hundredths of a millimeter. For example, tin plate No. 25 has a thickness of 0.24-0.27 mm, tin plate No. 28 - 0.27-0.30 mm, etc.

For the manufacture of cans, the following types of tin are used:

1. Hot tin plate, hot rolled and cold rolled first and second grade tin plating.

The amount of tin applied to 200 cm2 of the surface of first class tinplate (or 100 cm2 of sheet tinned on both sides) should be 0.39-0.45 g, second class tinplate - 0.28-0.38 g.

First-class tin is mainly used to make jars for canned crab, intended for very long storage.

2. Hot-tinned, cold-rolled tinplate, ZhK grade, first and second class for tin coating. Due to its good malleability, tinplate is widely used for the manufacture of one-piece stamped cans of various shapes and capacities. The possibility of producing this tin in the form of tapes of various widths determines its rational cutting (stamping of cans and lids) with a minimum amount of waste.

3. Electrolytic tinned white rolled sheet, lacquered, first grade, class I SEL. This tin is made of mild carbon steel, coated on both sides with tin (coating thickness on each side of the tape 0.8-1 microns) and over the tin with varnish or enamel (dry varnish film thickness 8-12 microns).

The lacquer film must be resistant to the action of pure (distilled) water, vegetable oil(at a temperature of 120 ° C), 3% sodium chloride solution, 2% tartaric acid solution, 3% solution acetic acid and standard protein solution (3% gelatin, 1% sodium chloride and 0.2% sodium sulfide). After 2-hour boiling of tin plates in any of the indicated solutions, the varnish film should remain intact and retain its gloss and elasticity.

4. Electrolytic tinned white sheet, unvarnished, first grade and first class. For 200 cm2 of the surface of this tin there should be 0.12-0.15 g of tin. This tin can only be used for the manufacture of stamped jars and lids, subject to the obligatory double coating of them on both sides with hot baked food varnish.

Aluminum cans are produced only from seamless aluminum sheets A-0 and A-00 or its alloys with magnesium and manganese, which makes it possible to reduce the thickness of the metal from 0.4 to 0.3 mm, since the strength of the alloys is higher than the strength of pure aluminum .

Aluminum and its alloys have the same corrosion resistance. The corrosion resistance of aluminum and its alloys is improved by electrochemical anodizing and subsequent varnishing with epoxyphenol varnish 3-30-59.

In foreign countries (GDR), black (without pewter) lacquered tin is also used for the manufacture of cans.

In the USSR, the production of canned fish in cans of lacquered black tin has been mastered at canning factories in the Kaliningrad region and should be used in other enterprises in the future.

During the sterilization of canned food, the protein substances of the fish are partially destroyed with the release of sulfur compounds, which interact with the tin coating (half) on the inner surface of the cans made of tinplate. As a result, tin sulphide (SnS) is formed on the inner surface of the cans in the form of a bluish tint. With increased porosity of the semidry, the formation of iron sulfide (FeS) is possible, which also causes darkening of the inner surface of the cans and even of a part of the product adjacent to their walls.

To prevent darkening of the inner surface of the cans, reduce the amount of tin passing into the product, and prevent corrosion of the cans, usually tin or finished cans are varnished, and tinplate is sometimes passivated.

The essence of passivation is to create a protective film of tin oxides on the surface of the semidry by treating sheets of tin or finished cans with a solution of an oxidizing agent - sodium or potassium dichromate and caustic soda. The protective oxide film is formed as follows. When a tin plate is immersed in an alkaline solution of an oxidizing agent (sodium bichromate), at first a certain amount of tin dissolves with the formation of stannite and sodium stannate:

Sn + O + 2NaOH -> Na25n02 + H20 Sn + 20-"r 2NaOH -> Na25n03 + H20

The stannite and stannate then react to form tin oxides:

Na25n02 + NaoSnOz -] - 2H20 -» ​​BnOg + SnO + 4KaOH.

As a result of supersaturation of the tin solution layer adjacent to the metal, crystallization centers are formed on the metal surface, which, growing, turn into a continuous oxide film. The protective oxide films formed under the action of oxidizing agents can be divided into three groups depending on the thickness:

Thick - clearly visible films with a thickness of more than 5000 A (1 mmk \u003d 10000 A);

Medium thickness - films found on metal in the form of "temper colors", with a thickness of 400 to 5000 A;

Thin - invisible films, detected only by indirect methods, less than 400 A thick.

Passive oxide films on tinplate belong to the third group of films - invisible films.

The process of passivation of tin (or finished cans) consists of the following operations: degreasing of tin or cans;

Actually passivation - immersion of tin (cans) for a few seconds in an alkaline solution of an oxidizing agent;

Rinsing passivated tin (cans) with cold and then hot water to remove the passivator solution.

Passivation is a simpler and cheaper way to protect tin from corrosion than coating with varnishes and enamels, it significantly increases the resistance of cans to corrosion and in some cases can significantly reduce the tin content in canned food.

One of the new ways to protect cans from corrosion is to apply thin invisible layers of oil lubricant to their surface with the addition of surfactants (0.9-0.1%). The lubricant is applied to the cans in a high-voltage current field in a special chamber. This method of protecting cans from corrosion was developed by TsNIIChermet.

Cans used in fish canning (Fig. 11), depending on their shape and method of production, are divided into five types:

/ - cylindrical prefabricated (with or without a turnkey tongue);

II- cylindrical one-piece stamped;

III- figured one-piece stamped rectangular shape;

IV- figured one-piece stamped oval;

V - figured one-piece stamped elliptical shape.

Characteristics of cylindrical cans are given in table. 14, and figured one-piece stamped - in table. 15.

Table 14

For prefabricated cans with a tongue located on the body, the size I can be 4.8-5.0 mm larger than the size indicated in Table. 15.

For jars with a capacity of 96 to 250 ml, a capacity fluctuation of ± 1% is allowed, for jars with a capacity of 250 to 1000 ml - ± 0.5% and for jars with a capacity of 1000 ml - ± 0.25%.

Whole-stamp cans have only one seam at the junction of the body and lid, while prefabricated cans have three seams - one along the body of the can and two at the junction of the body with the ends (lid and bottom) of the can. Rice.

A longitudinal seam on the body of prefabricated cans is made

To the castle. It consists of four layers of tin (Fig. 12) and must be deepened inside the case and evenly soldered with an alloy of tin (40%) and lead (60%) to ensure the tightness of the case.

For fully stamped cans, the lids, and for prefabricated cans, the bottoms and lids are connected to the body with a double seam, which is a strong tight connection between the lid flange and the can body, consisting of five layers of tin with a layer of sealing material.

As a sealing material, paste is most widely used; rubber rings are also used for figured cans.

Paste with the help of special paste machines is applied to the pre-curved (twisted) ends of the cans. After drying, it is a thin elastic film, which fills the gaps in the seam during the canning process.

The film of the paste should not change during sterilization, should not color the contents of the jar and impart extraneous taste and smell to it.

And scald the ends of the cans covered with paste before use, and therefore are usually limited only to rubbing them.

In addition, during the steam exhaustion of cans filled with the product with pre-rolled lids, the aqueous ammonia paste swells and, during the final seaming of the cans, can flow out of the seam, which leads to a violation of the tightness of the cans and contributes to the spoilage of canned food. These shortcomings are devoid of vulcanized paste.

At the ends of the cans there is a corrugated relief, which ensures their elastic deformation during the sterilization of canned food. The shape and dimensions of the relief depend on the configuration and dimensions of the cans, as well as on the thickness of the sheet.

The bottoms of prefabricated cans are marked on presses during their manufacture in can shops. When marking the bottoms, the letter P is applied - the index of the fishing industry, the number assigned to the canned food factory (for example, 144 - the Temryuk fish cannery), and the last digit of the year the canned food was manufactured.

The marking on the bottom of the P1446 can indicates that the canned food was made by the fishing industry at the Temryuk Cannery in 1966.

The lids of the cans are marked on marking machines immediately before the capping of the filled cans. On the covers indicate the serial number of the work shift, the date of manufacture of canned food - the day and month and the assortment sign of canned food.

The month is conventionally denoted by letters of the alphabet: January - A,

February - B, March - C, April - D, May - D, June - E, July - F, August - I, September - K, October - L, November - M, December - H.

Assortment signs of canned food are indicated by numbers; the only exceptions are the assortment signs of canned food from the Far East salmon fish, flounder and sardines.

The marking inscription on the lid of the combined can 214B051 should be read as follows: second shift, March 14, carp in tomato sauce (assortment mark of this canned food 051).

At canning factories that do not have canning shops, as well as on trawlers and other ships that receive empty cans from enterprises, the markings on the lids are affixed in the following order: plant or trawler number, year of canned food production, shift serial number, canned food production date (date and month), assortment sign (number) of canned food. In this case, it is allowed to apply markings in two rows.

Marking on the lid of the can 457

455216IG or --------- denotes: 45 - Kikhchik fish factory

Combine, 7 - 1967, 2 - second shift, August 16-16, G - natural chum salmon in its own juice.

Whole-stamped cans for canned fish are labeled in the following order. When stamping cans, only the letter P is stamped on the bottoms - the index of the fishing industry; and the rest of the markings - the plant number, the last digit of the year of manufacture and others are applied to the covers in two rows.

Marking inscription on the cover of one-piece stamped 1336

At the Makhachkala fish cannery (factory number 133) in 1966 (6); the bottom row - in the first shift (1), January 14 (14A), Caspian sprats with spicy salting (192 - canned food assortment mark).

On the lids of cans of canned crab, produced in export clearance, they stamp or apply thermal

Resistant quick-drying paint the following markings: the first - the number of the floating cannery; the second - the last digit of the year of production of canned food; third - F or A- conditional designation of the variety of canned food; the fourth and fifth are the serial number of the day of production of canned food from the beginning of the season of the given year. Marking inscription on the lids of canned crab premium 45F62 or first grade 41A62 designates: 4 - floating cannery "Vsevolod Sibir

Tsev"; 5 - canned food produced in 1965; F - canned food of the highest grade (Fancy); A - canned food of the first grade (Agreid); 62 - canned food was produced on the 62nd day from the start of the production of canned crab at the Vsevolod Sibirtsev plant in this year.

On the bottom of the cans of canned crab, USSR signs are stamped - canned food is produced in the USSR.

Symbols (numbers) of canning enterprises and assortment signs (numbers) of canned food indicated during marking are unified and approved by leading economic organizations.

Before being put into production, cans are inspected and checked for leaks. On examination, jars with the following defects are rejected: tin influx on the longitudinal seam near the fold; the fold of the body of the can is large; the fold of the can body is bent; oblique can body; the fold of the body of the can is not bent enough (high fold); the shape of the fold circle is deformed; dented flanges or jar body.

Cans with burrs and notches along the fold, rusty and with protruding paste along the seam of the bottom seam are also not allowed into production.

The diameters of the ends and bodies of the cans must exactly correspond to the dimensions established by the standard, otherwise the wrong seam will result when the cans are seamed.

The main requirement for the quality of cans is their tightness.

Banks are checked for leaks on automatic or semi-automatic testers, which are water and air.

In water testers, the test cans are placed in a tank with water and filled with compressed air at a pressure of not more than

1 ati. At the same time, leaky cans are easy to detect by air bubbles escaping through leaks in the seams.

Water testers are very reliable, but their productivity is relatively low, so they are used mainly for selective control of the tightness of cans and periodic control of the operation of air testers.

Air testers are high-performance machines that allow you to control 100-120 cans per minute. With their help, you can check all the cans for leaks.
in the canning industry. A well-adjusted air tester will reject cans that pass more than 8-10 cm3 of air in 30-35 seconds.