Sheet metals and their importance in today’s industry

The sheet metal has been used since ancient times. At the beginning, it was produced by primitive techniques that included hand-fed batons powered by water. Today, advanced production techniques are used, including the rolling of metal blocks by means of rollers with different spacing.

With this processing method, plates of different thicknesses can be produced, which can be divided into:

• Fine sheet metals – up to 1 mm thickness
• Thin sheet metals – from 1 to 2,75 mm thickness
• Medium sheet metals – from 3 to 4,75 mm thickness
• Thick sheet metals – from 5 to 60 mm thickness

One of the most famous sheet metals used daily in almost all households is aluminum foil. In addition to this, one of the most popular sheet metals are golden leaves whose thickness can be just around 0.005 mm.

Sheet metal types

Today there are many different types of sheet metals that find their application in different industries. Generally, the sheet metals can be divided into:

• Construction sheets
• Ship sheets (plates)
• Car sheets (plates)
• Coal sheets
• Transformation sheets
• Other types of sheets

In addition to the mentioned division, the sheets can also be observed from the aspect of the construction, ie their shape. Thus, for example, we can nowadays find ribbed sheets that are primarily intended for roofing. Furthermore, smooth, bent or corrugated sheets can also be applied.

The sheets can furthermore be divided according to the way they are produced, ie processed. According to this division there are annealed sheets, soft and hard sheets, as well as normalized sheets.

Metal sheet processing

Depending on its properties, metal sheet can be processed in many different ways. Along with laser cutting, as one of  as one of the most economical cutting techniques, plasma and oxy fuel gas cutting are also offered on the market.

However, what you should pay attention to when cutting with laser is the reflection that can cause damage to the laser cutter.

In addition to being cut, there is often a need for sheet bending. This type of treatment is carried out by means of special blades or presses which, under certain pressure with the help of plastic deformation, form a sheet according to the desired and required shape.

The application of sheets in the industry

The sheets are in the industry used for the production of various products starting from cans in the food industry to the manufacture of various machine parts.

In addition, sheets made of stainless steel are used in the process industry, ie in the industry where the demands on the construction materials are exceptionally large.

One of the most important metal sheets used in the industry is the white (steel) sheet. The white sheet is obtained by cold rolling and is coated with a tin of 0.01 mm thickness, which gives it resistance.

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The importance of metal in today’s industry

Today’s world is unimaginable without the metal structures whose application spreads from the car industry to building bridges. Although concepts such as iron, metal, and steel are being used every day, the question arises as to whether there is a difference between them? One of the common mistakes that appears daily is to equalize or use the terms iron, metal, and steel as synonyms.

However, there is a certain difference in the aforementioned terms, ranging from the conceptual definition itself to the way in which steel or iron is obtained in the first place.

What’s the difference between metal iron and steel?

What are metals?

Metals, ie, metallic elements are the chemical elements that got their name thanks to the metal link through which the atoms in the crystal grid are connected. Looked through the prism of chemistry, metals found in nature can be found in pure form, without any additives. Furthermore, each metal has its physical and chemical properties that shape its behavior.

In addition to the above-mentioned division, metals can be divided into precious, semi-precious and common metals. The classification of metals with respect to the preciousness depends on its corrosion resistance. Precious metals are therefore resistant to all types of corrosion while the common metals are on the other hand subject to corrosive action.

All metals have a glossy surface and excellent processing properties. However, due to the reflexive properties, there are problems with laser cutting.  Mainly, in nature, they can be found most often in a solid state, except mercury which is liquid.

Is there a difference between metal and steel?

There is. Due to its chemical properties, stainless steel can’t be classified as metal, but as alloy. Thus, metals as such in their structure don’t have any admixtures as opposed to the steel which has.

However, despite the fact that steel is not a metal, it possesses properties that have metals. For example, steel plates can have a glossy surface just like metals. Observed through the prism of the properties, steel is a good electric power and heat generator just like all metals. Nonetheless, because of its composition, it can’t  be placed in the metals category, in a periodic system of elements.

And what about the difference between iron and steel?

Željezo se kao takvo može klasificirati kao sirovina koje se upotrebljava u izradi kako slitina tako i komponenti poput vijaka. Sukladno tome i činjenici da čelik ima udio željeza do čak 99% izvire glavna razlika između ova dva elementa.

In addition, another thing that affects the significant difference between steel and iron are its properties. That is just why stainless steel (inox) is corrosion-resistant, has good thermal conductivity and properties that make it one of the most widely used constructional metals .

Iron is an important raw material for component making

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The emergence of stainless steel alloy

Today’s world of construction, car industry, mechanical engineering and many other branches can hardly be imagined without inox or stainless steel. Inox was created in 1821 when French Berthier added 1.5% chromium to steel, in order to make cutlery. During the 20th century, the approach to the development of steel production technology was systematical; and a number of new ways and techniques have that have greatly contributed to and enhanced the production of the same have been discovered.

The importance of this material is reflected in the fact that during 2011, a total of 1 490.06 million tonnes of steel was produced in the world, and this figure is increasing over the years. The leading stainless steel manufacturer is China, followed by Japan, the United States and India. The special importance of stainless steel is that it can be completely recycled and the proportion of recycled stainless steel is up to 80%.

Chemical composition of inox

As it has already been said, in the production of stainless steel, a certain percentage of chromium or nickel is added to the mentioned. These materials make steel resistant to corrosion. Chromium, whose share can rise up to 20% is added to the iron and carbon. In addition to chromium, nickel is added to the mixture as well. However, different standards in stainless steel production require different proportions of chemical elements. For example, the steel of the standard X13 NiCr Si 35-16 contains up to 37% nickel and 17% chromium while other elements such as nitrogen come in a proportion of a 0.11% maximum. However, the most important metal in the chemical composition is chrome, which creates an oxidized layer on the steel surface, that protects it against corrosion and external influences.

Production process

The process of stainless steel production begins with loading the recycled material by large cranes or magnets into containers that are then transported to the high furnaces. In high furnaces, with the addition of nickel, or chromium, recycled steel is left to melt. There are different stoves that can be used in this process, and among the best is an electric furnace which produces the best and the fines steel as well. However, prior to the melting, the steel should be grinded or cleaned from impurities to make the quality as good as possible.

The production process is continued in the refining furnace after melting. Since molten steel itself contains many other chemical elements, these elements need to be removed, which is achieved by the refining process, after which the molten steel flows from the refining furnace and is formed into pieces of about 64 meters long. These pieces are further rolled to finally obtain a rolled steel strip that then goes to further purification, or where a protective layer is formed through the contact of chromium and atmosphere. After that, the steel is shaped or cut according to customer’s requirements, and later pipes, fences, and other things can be made of it.

Apart from the fact that steel can be produced by recycling an old steel, it can also be produced by the purification of crude iron, which is a process that in some segments differs from the production process done with recycled steel.

High furnaces

The process of steel production, as well as of other metals, happens in high furnaces. The electric furnace serves for the melting of the steel and is made on the basis of the electrical arc or induction. The electric arc-based blades function in a way that a high temperature is being created between the electrode and the metal by means of electric energy, and that’s how the steel melts. There are several basic reasons why an electric furnace is used, and the main reasons are an easy achievement of high temperature, an easier control of the chemical composition, no combustion product, and much less coating on the stove itself is being consumed.

Types of stainless steels

There are different types of stainless steels or inox, which can be divided into:

• Ferritic stainless steels – This kind of stainless steel contains 13 to 17% of chromium. This kind of steel is highly resistant to acids, is very soft, possesses the properties of the magnet but there is a problem of poor weldability

• Austenitic inox – the chromium content in this type of steel ranges from 15 to 20%. Its main characteristics are self-magnetism, bigger deformation in welding, plasticity and good properties at low temperatures

• Austenitic ferrite inox– chromium content ranges from 22 to 24%. This kind of steel is often used in mining, ie petroleum, petrochemical and chemical industry

• Martensitic inox – inox which has an increased carbon content, and is mainly used in the production of tools

• Soft martensitic inox – these steels are high-strength. They are used to make parts that are in an environment where unclean air is well present

Stainless steel processing techniques

Inox as one of the most common metals in today’s industry has various processing techniques. However, to make the positions made of stainless steel, processable, it is necessary to cut them. One of the most economical cutting techniques is laser cutting. In addition to laser cutting, inox can be cutted with the following techniques:

• Plasma cutting
• Water jet cutting
• Autogenous cutting
• Cutting steel by using cutting plates

However, of all the above mentioned cutting metal processing techniques, laser inox cutting represents a technique in which the ratio of the cutting quality, the speed and the economy of the cutting is the best.

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Aluminum as one of the main metals in today’s industry

Aluminum is the third most widespread metal on Earth with a percentage of 7.3%. However, for a long time, the world did not know about its existence and its way of production. The Englishman, Sir Humphrey Davy, had discovered his existence exactly 208 years ago, or in 1808, while only in 1854 the first primitive ways of getting this important metal were developed.

Technological processes by which aluminum is produced even today were only discovered in 1886, and the most deserving of it were Paul Herlot and Charles Hall who discovered the production method by electrolysis.

In addition to this finding, it is interesting to note that the aforementioned scientists did not know about the existence and operation of the other, and although they were at the opposite parts of the world, and without any contact, they have managed to develop a completely identical method of production.

Technological process of aluminum production

As has been said before, aluminum is produced using the Hall-Heroult process, or Bayer’s process. The Bayer process consists of obtaining the alumina which is again obtained from the bauxite. In order to produce two tons of aluminum, it is generally necessary to have four tons of bauxite.

Alumina is added to the bath together with the cryolite, and by lowering the anode the electrolysis begins. The anode is usually changed every 20 days due to its increased consumption. Through Electrolysis, alumina is dissolved in the bath, forming various aluminum oxyfluoride ions.

In this way, numerous fluorides are produced and then carried out through the purification system to avoid the atmosphere being contaminated. Apart from the harmful gases produced by the anodes, the problem is the so-called red sludge from which aluminum hydroxide is obtained.

With the development of the technological processes, aluminum production has advanced greatly. The first factories that produced aluminum had cells with a power of 1,000 amperes, while today’s factories supply their cells with a power of as much as 500,000 amperes.

Aluminum as a constructive metal

Aluminum is now used in the construction of various objects or parts. The reason for the application of this metal is its resistance to corrosion, strength and small mass. For this reason, some parts in cars and aircraft are made of aluminum.

Some of the other applications,  in other words items made of aluminum, are:

• Aluminum rods – are commonly used in construction
• Aluminum Sheets – Used in construction, mechanical engineering, dairy production, electrical engineering, food industry
• Other aluminum profiles – used for making frames of; for example desks
• Aluminum alloys – have different applications, from shipbuilding to crafting

Aluminum properties

As it has been said before, aluminum is being applied in numerous industries thanks to its properties, among which the most important are:

• Almost three times lighter than steel
• Good stretch and strength properties
• Excellent properties at low temperatures
• 13 times higher thermal conductivity than stainless steel
• Does not possess magnetic properties
• Good processing
• Excellent resistance to external influences
• Excellent electrical conductivity

Aluminum processing

Because of its features listed above, aluminum is easy to process. However, during processing, beware of heating the aluminum, which is primarily related to welding or grinding.

By heating, aluminum can be deformed, or when welding, with high-temperature development, weld metal porosity may occur. As for the most common welding methods when it comes to aluminum, TIG, MIG, and electro-welding are used.

When grinding aluminum, one should be very careful as it can happen that at an elevated number of turns done by the grinder, the aluminum can become dull. If high gloss is to be achieved, the aluminum should be grinded in several cycles with different grinding plates, and with different pressure on the surface.

One of the methods of aluminum processing is the anodising, or the intentional oxidation of aluminum so that it remains protected against external influences or assumes a certain color. Anodizing is most often carried out in the alkaline bath, by the electrolysis process.

Laser aluminum cutting

Almost all metals have a reflective property, which is especially the case with aluminum. The reflective property of aluminum can cause destruction or damage to the laser, by which the cutting process is being done.

However, what is actually reflection?

Reflection is the property of metals and materials in general, which causes the repulsion of beams (eg light) back to the source, which in the case of laser cutting means the reflection of the laser beam into the optical parts of the laser cutting machine.

Due to the reflexive property of aluminum, prior to cutting, a coating layer preventing reflection is being applied to it.

However, this is not enough because the reflection does not only come from the surface of the aluminum sheet but also from the molten aluminum resulting as an inevitable cutting product.

That’s why, when cutting the aluminum, it is necessary to adjust the cutting parameters, which reduces the reflection to a minimum or completely eliminates it.

Most of today’s laser cutters have a system specially designed for aluminum cutting, which follows the cutting parameters and, after the occurrence of a possible critical reflection, turns off the laser beam and thus prevents possible damage.

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