What happens to extruded clinker when heated. History and current trends of clinker

Clinker tiles are a facing material that has long been actively used in the construction industry. As early as the beginning of the 19th century, the material was used for laying roads in Holland, immediately after which it began to be used in Russia and Western Europe.

According to historians, the technology for the production of clinker tiles dates back to the 15th century, when people noticed that during the firing of clay bars, they acquire completely different properties (properties of porcelain stoneware).

The kilns in which firing was carried out consisted of only one entrance and a small room. Clay bars of various shapes were laid inside it, after which the entrance was laid for several days. The brick inside, under the influence of high temperature, acquired the necessary physical properties.

Clinker tiles are produced mainly from natural material - clay. As a variety of colors, natural dyes are used. Clay for firing should have a high level of refractoriness, and have a minimum amount of various impurities.

Today, there are deposits of high-quality clinker suitable for the manufacture of clinker facing material in Poland, Germany, Spain, Holland and other countries.

Technology for the production of clinker tiles

At the present time, the production technology of clinker tiles does not differ fundamentally from the production technology in medieval Europe. Although experts in this field distinguish 2 types of production:

• extruding
• semi-dry pressing

Clinker tiles are fired at high temperatures. If, for example, during the firing of ordinary clay products, the material is affected by about 800-900 ° C, then in clinker kilns the operating temperature is 1100-1400 ° C.

Due to this temperature regime, the material changes its physical state, becoming more
durable. At the same time, the consumption of energy carriers is 4 times higher than the need, rather than in the processing of clay products in the usual way.

Extrusion method of production involves the use of special equipment - an extruder. The device is presented in the form of a screw meat grinder, into which wet plastic clay is fed. After its grinding, molding is carried out using a vacuum press. After drying, this blank is sent to the kiln for firing. Clinker material after extrusion is characterized by high density, strength, resistance to abrasion, mechanical and chemical influences.

Semi-dry pressing method also involves the pressing process on special equipment. However, unlike extrusion, raw materials are placed in a kiln without pre-drying. As a result of this production method, the clinker product has a low density, due to which it significantly weakens its strength.

The semi-dry pressing method is needed in order to obtain clinker products with low thermal conductivity. And in some cases, such products are valued much more than, for example, resistance to mechanical or chemical stress.

Equipment for the production of clinker tiles

For the production of high-quality clinker products, special equipment is used. In the process of technological processing, clay passes through an extruder, a special device for pressing and creating the necessary shape (machines are tape, vacuum, rotary, lever), pre-drying chambers and a firing oven.

The molds for shaping, in which wet plastic clay is placed, have a matrix layer that provides the highest possible level of tightness and thermal insulation to the output material.

The main equipment for the production of clinker tiles, of course, is the kiln. Such a room is a kind of tunnel about 150 m long. It has sources of heating in the form of an open fire.

Clinker elements are fed in special trolleys that move through the kiln at a rather low speed. Thus, there is a gradual heating and firing of clay. Such kilns operate continuously, which allows firing a large number of products.

Clinker production does not require significant energy consumption. The high cost of the finished material can only be justified by the cost of delivering the material (clay) from the deposits. But the price is more than offset by the performance of the material. It is this indicator (price-quality) that makes the use of clinker very popular in various areas of the construction industry.

Technical and operational characteristics of clinker

With the help of high-temperature processing, clinker tiles get most of their positive characteristics. The material has practically no pores, therefore it does not allow moisture to pass through and provides high waterproofing to the room. Mold and bacteria do not accumulate in the walls, so the service life of such walls is much longer than usual.

Clinker tiles are immune to alkalis and acids, so they are often used for facing residential buildings. Such material is frost-resistant, which is why it is often used in the construction of building facades in regions with low temperature conditions (clinker can withstand up to 50-80 frosty seasons). Compared to ordinary brickwork, on which light traces appear after 1-2 winter periods, clinker tiles retain their original appearance for a long time.

Clinker has a number of advantages:

• low moisture absorption;
• environmental friendliness;
• a wide variety of colors;
• high strength and frost resistance;
• unlimited service life.

This facing material is very often used together with thermal insulation, obtaining an ideal coating for building facades. Such panels are called thermal panels, and are currently already very popular.

• What is clinker?
  The clinker material is an environmentally friendly, high-strength material, in the manufacture of which only natural factors are involved: one hundred percent clay, water, fire (temperature).

  Clay firing has deep

  national traditions in the countries of Western Europe - Italy, Holland, Germany.
  Currently in Germany there are seed companies with a century and a half of industrial history - Korzilius, Interbau, Stroher, Feldhaus Klinker.

  

  A wide range of ceramic products is produced from clinker - facade tiles, floor tiles, steps, skirting boards, corners, decors, paving stones - intended for interior and exterior cladding of facades, columns, various architectural forms, paths, etc.
  The main characteristics and advantages of the clinker material are:
  - rough, embossed, non-slip surface (anti-slip);
  - frost resistance;
  - high strength;
  - high resistance to chemical compounds, engine oil, etc.;
  - high functionality, allowing to veneer and pave almost any surface;
  - aesthetic, stylish appearance.

• Delivery of material to the object
  We have delivery. To clarify the cost of delivery, please contact the transport department. The transport department will need the detailed address and phone number of the recipient.
  ATTENTION! Delivery is carried out to the entrance - you need to unload the goods on your own.
• Is there delivery to the regions?
  We can help organize the delivery of clinker to the regions in the following way. If the client is already working with a transport company, we can undertake to contact this company and explain where to find us. If it is necessary to deliver clinker from our warehouse to the warehouse of a transport company, we can carry out such delivery with billing for transport services to the client.

EXTRUSION CLINKER CERAMIC TILE (clinker -?).

Recently, when selling ceramic tiles in Moscow, there has been a practice of using the terms clinker, clinker tiles, extrusion tiles, etc. as synonyms. This use of terms is justified only because it is easier to say "clinker" than, for example, "extrusive ceramic clinker tiles". In fact, it is a mixture of terms and categories.

Clinker ceramic tiles are tiles obtained from raw slate clays (clay has a special mineralogical composition) by pressing or extrusion, followed by long-term high-temperature firing. Sometimes clinker is called ceramic stone. Clinker tiles are “hardened” within 40 hours (ordinary tiles are fired for at least 45 minutes, max - 2 hours). Firing is carried out at a temperature of 13000C - 13900C (for comparison - porcelain stoneware, one of the most durable types of ceramic tiles, is fired at a temperature of 11

extrusion Clinker tiles are produced using a special machine - an extruder (from Latin Extrudo - “I squeeze out”, in everyday life it is a meat grinder or a confectionery syringe) by squeezing plastic raw clay through a shaping hole, the cross section of which corresponds to the configuration of the finished product. Products can be of the most complex shape (hence the connection with steps, this method is most often used for their production). Manufacturing technology of clinker tiles by pressing similar to the method of making ordinary tiles and hardly requires further explanation.

Both technologies make it possible to produce an excellent durable material, however, extruded clinker tiles are superior in performance to any “pressed” tiles (including ordinary porcelain stoneware), which explains their ever-growing popularity.

Features of extrusion clinker (advantages and disadvantages):

The high density of the material and, as a result, its frost resistance justifying the use in our climate zone.

· Surface clinker extrusion products has high anti-slip properties: such tiles are safe - it is difficult to slip on them.

· Strength(due to strength the material itself and at the expense thick finished product - up to 2.5 cm.) determines the advantage of laying on the floor compared to porcelain stoneware in areas of high traffic and with difficult operating conditions. For example, as steps - porcelain stoneware steps, as a rule, are much thinner than clinker ones. Thick stoneware steps are of course also produced, only they are too expensive to be widely used. The reverse side of these qualities of clinker is that thick heavy material will require more expenses for its delivery to the place of use.

· Variety of design solutions products from extruded clinker (due to new technologies for clinker surface treatment) - for every taste. If you want steps under terracotta - here you are, if you want wooden ones - please, or you can put a funny drawing on the riser:

https://pandia.ru/text/78/094/images/image002_102.jpg" width="213" height="102 src=">.jpg" align="left" width="166" height="93 ">look at the photo above! And porcelain stoneware steps are often less reliable, not only because of their small thickness, but also because they are composite. That is, they are glued together from two elements: an ordinary rectangular tile and a rounded part that looks like a cornice. Of course, solid steps are also produced from porcelain stoneware (an example of such a step is in the figure), but they are much more expensive than extrusion clinker ones. And - note: the rounded part the composite step is not made of porcelain stoneware, but of clinker! Such clinker cornice-like rounded elements are produced by the Exagres factory, for example, and are commercially available as a separate product. The end elements are supplied with metal embedded plates, which, in our opinion, make it possible to achieve a stronger cement-adhesive base, a corner element and a rectangular part of the step than in a finished porcelain stoneware composite step, where the tile and the rounded part are simply glued together.

Another feature of extrusion clinker is on the reverse side of the tile there is a characteristic profile, called dovetail, which is fundamental improves grip material with a binder solution and, ultimately, with the surface to be coated. Pressed tiles do not have such a profile. The presence of a dovetail also makes it possible to create heat-insulating facade panels lined with extruded clinker - clinker tiles are molded from the “inside out” into expanded polystyrene, which forms a very strong connection with the tile during polymerization. An example of a thermal panel made of clinker tiles and a paneled facade:

Hence - all the variety of areas of application of extrusion clinker tiles. It is widely used for interior and exterior work, both in residential and industrial premises for finishing any surfaces. In a country house, extrusion clinker is laid out on steps, platforms on stairs, in premises “freezing” in winter (warehouses, garages, terraces), in industrial premises they are finished with walls and floors in production areas (clinker is resistant to chemically active substances), spread in places of high traffic (floor in a store, restaurant, workshop, etc.). Extruded clinker tiles are widely used for cladding (and insulation) of facades of any buildings. And let's not forget to mention such an important and specific area of ​​application as swimming pools - with all the variety of special elements necessary to ensure their proper functioning, and convenient to manufacture from clinker using extrusion technology.

Today, the increase in sales of extruded clinker ceramics in Moscow is associated with the understanding of the buyers themselves of the advantages of such tiles, even in comparison with porcelain stoneware.

Roasting is the final technological operation of clinker production. During the firing process, clinker is obtained from a raw mixture of a certain chemical composition, consisting of four main clinker minerals.
The composition of clinker minerals includes each of the initial components of the raw mixture. For example, tricalcium silicate, the main clinker mineral, is formed from three molecules of CaO, the oxide of the limestone mineral, and one molecule of SiO2, the oxide of the clay mineral. Similarly, the other three clinker minerals are obtained - dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. Thus, for the formation of clinker, the minerals of one raw material component - limestone and the minerals of the second component - clay must chemically react with each other.
Under normal conditions, the components of the raw mixture - limestone, clay, etc. are inert, that is, they do not react with one another. When heated, they become active and begin to mutually exhibit reactivity. This is explained by the fact that with an increase in temperature, the energy of moving molecules of solids becomes so significant that mutual exchange of molecules and atoms between them is possible with the formation of a new compound. The formation of a new substance as a result of the reaction of two or more solids is called a solid phase reaction.
However, the rate of a chemical reaction increases even more if some of the materials are melted, forming a liquid phase. Such partial melting is called sintering, and the material is called sintered. Portland cement clinker is fired to sinter. Sintering, i.e., the formation of a liquid phase, is necessary for a more complete chemical assimilation of calcium oxide CaO by silica SiO2 and, in this case, obtaining tricalcium silicate.
Partial melting of clinker raw materials starts at 1300°C. To accelerate the reaction of formation of tricalcium silicate, the clinker firing temperature is increased to 1450°C.
As installations for the production of clinker, thermal units of various designs and operating principles can be used. However, rotary kilns are mainly used for this purpose, they produce approximately 95% of clinker from the total output, 3.5% of clinker is obtained in shaft kilns and the remaining 1.5% - in thermal units of other systems - sintering grates, clinker burning reactors in a suspended state or in a fluidized bed. Rotary kilns are the main heating unit for both wet and dry clinker production.
The rotary kiln calciner is a drum lined inside with refractory materials. The drum is mounted with an inclination on roller bearings.
From the raised end, liquid slurry or granules enter the drum. As a result of the rotation of the drum, the sludge moves to the lowered end. Fuel is fed into the drum and burns from the side of the lowered end. The incandescent flue gases formed in this process move towards the material to be fired and heat it. The burned material in the form of clinker leaves the drum. Coal dust, fuel oil or natural gas are used as fuel for a rotary kiln. Solid and liquid fuels are fed into the furnace in the atomized state. The air required for fuel combustion is introduced into the furnace along with the fuel, and is additionally supplied from the furnace cooler. In the refrigerator, it is heated by the heat of hot clinker, while cooling the latter. The air that is introduced into the furnace along with the fuel is called primary, and the air received from the furnace cooler is called secondary.
The incandescent gases formed during the combustion of fuel move towards the material being fired, heat it, and cool themselves. As a result, the temperature of the materials in the drum increases all the time as they move, and the temperature of the gases decreases.
The broken nature of the temperature curve of the material shows that when the raw mixture is heated, various physicochemical processes occur in it, in some cases inhibiting heating (sloping sections), and in others contributing to sharp heating (steep sections). The essence of these processes is as follows.
Raw sludge, which has ambient temperature, entering the furnace, is exposed to a sharp effect of the high temperature of the flue gases and heats up. The temperature of the exhaust gases in this case decreases from about 800-1000 to 160-250 ° C.
When heated, the sludge first liquefies, and then thickens and, with the loss of a significant amount of water, turns into large clods, which, upon further heating, turn into grains - granules.
The process of evaporation from the sludge of water mechanically mixed with it (drying of the sludge) lasts approximately up to a temperature of 200 ° C, since the moisture contained in the fine pores and capillaries of the material evaporates slowly.
By the nature of the processes occurring in the sludge at temperatures up to 200 ° C, this zone of the furnace is called the evaporation zone.
With further advancement, the material enters the region of higher temperatures and chemical processes begin to occur in the raw mixture: at temperatures above 200-300 ° C, organic impurities burn out and the water contained in clay minerals is lost. The loss of chemically bound water by clay minerals (dehydration) leads to a complete loss of clay of its binding properties and pieces of sludge crumble into powder. This process lasts up to temperatures of approximately 600-700 ° C.
In essence, the processes occurring in the temperature range from 200 to 700 ° C, this zone of the furnace is called the heating zone.
As a result of the stay of the raw mixture in the region of such a temperature, calcium oxide is formed, therefore this zone of the furnace (up to a temperature of 1200 °) is called the calcination zone.
The temperature of the material in this zone increases relatively slowly. This is explained by the fact that the heat of flue gases is spent mainly on the decomposition of CaCO3: to decompose 1 kg of CaCO3 into CaO and CO2, 425 kcal of heat is required.
The appearance of calcium oxide in the raw mixture and the presence of high temperature causes the beginning of the chemical interaction of silicon, aluminum and iron oxides in the clay with calcium oxide. This interaction proceeds between oxides in the solid state (in solid phases).
Reactions in solid phases develop in the temperature range of 1200-1300 ° C. These reactions are exothermic, that is, they proceed with the release of heat, which is why this zone of the furnace was called the zone of exothermic reactions.
The formation of tricalcium silicate occurs already in the next section of the furnace in the area of ​​​​highest temperatures, called the sintering zone.
In the sintering zone, the most fusible minerals are melted. In the resulting liquid phase, 2CaO-Si02 is partially dissolved and saturated with lime to 3CaO-Si02.
Tricalcium silicate has a significantly lower ability to dissolve in the melt than dicalcium silicate. Therefore, as soon as its formation has taken place, the melt becomes supersaturated with respect to this mineral and tricalcium silicate precipitates from the melt in the form of tiny solid crystals, which then, under given conditions, are able to increase in size.
The dissolution of 2CaO-Si02 and the absorption of lime by it does not occur immediately in the entire mass of the mixture, but in its separate portions. Therefore, for a more complete assimilation of lime by two-calcium silicate, it is necessary to withstand materials for a certain period at a sintering temperature (1300-1450 ° C). The longer this exposure will be, the more complete the binding of lime will occur, and at the same time the 3CaO-Si02 crystals will become larger.
However, it is not recommended to keep the clinker at the sintering temperature for a long time or to cool it slowly; Portland cement, in which 3CaO - SiO2 has a fine crystalline structure, has a higher strength.
The holding time of the clinker depends on the temperature: the higher it is in the sintering zone, the faster the clinker is formed. However, with an excessively high, and most importantly, a sharp increase in temperature, a lot of melt is quickly formed and the fired mixture can begin to clump. Large grains formed in this case are more difficult to heat up and the process of transition of C2S to C3S is disturbed. As a result, the clinker will be poorly fired (there will be little tricalcium silicate in it).
To speed up the process of clinker formation, as well as in cases where it is necessary to obtain clinker with a high content of 3CaO-Si02, some substances are used (calcium fluoride CaF2, iron oxide, etc.), which have the ability to reduce the melting point of the raw mixture. Earlier formation of the liquid phase shifts the process of clinker formation to lower temperatures.
During the sintering period, sometimes all the lime in the mixture does not have time to be completely assimilated by silica; the process of this assimilation proceeds more and more slowly due to the depletion of the mixture in lime and 2CaO Si02. As a result, clinkers with a high saturation factor, which require maximum lime assimilation in 3CaO SiO2, will always have free lime.
1-2% free lime does not affect the quality of Portland cement, but its higher content causes uneven changes in the volume of Portland cement during hardening and is therefore unacceptable.
The clinker from the sintering zone enters the cooling zone (VI), where cold air flows towards the clinker.
The clinker leaves the cooling zone with a temperature of 1000-1100 ° C and for final cooling it is sent to the furnace cooler.

Word "clinker" today it is familiar to everyone who has ever thought about building their own house or in general with a construction site for “you”. However, there are dozens of interpretations of this concept, many of which have nothing to do with real clinker. From various sources, you can hear that clinker is a ceramic brick, an artificial ceramic stone, a rough uneven brick for “handmade”, a flexible plastic profile with a “brick-like” relief, and so on and so forth.

According to the Russian Architecture Dictionary (1995), clinker is a brand of high-strength brick for paving roads and flooring in industrial buildings. Taking advantage of the gullibility of buyers, unscrupulous sellers very often appeal to this concept, seeking to increase the interest of customers in their own products. One thing is invariable - they try to pass off a variety of building materials for clinker, attributing to them unique indicators of frost resistance, environmental friendliness and special strength (up to M1000).

Meanwhile, clinker today is a certain standard of clay, from which, in the process of the most complex production certified by German legislation, building materials such as facing bricks, brick-like facade tiles, floor and terrace tiles, as well as steps of the highest quality are made.

The material acquires this quality due to the selected - special refractory - clays included in its composition. Raw materials for clinker materials are mined in quarries between England and Holland. This layer of clay, which came to the surface during the ice age, does not contain lime impurities. And that is why the surface of a brick made from it does not lose color over time and “efflorescence” and whitish spots do not form on its surface.

In addition to raw materials, the standard defines the conditions and process of production. Let's make a reservation right away, ceramic products produced in the process of "dry" pressing are not clinker. In special molds under a giant press, clay dust is pressed in an almost dry granular state (moisture content - no more than 4-5%), and then fired also at temperatures of 1000-1200 °. This is how porcelain stoneware is produced - no less spectacular and wear-resistant facing material, however, demonstrating completely different properties. The water absorption of porcelain stoneware is very low, however, for example, in terms of vapor permeability, it is completely opaque, unlike clinker. During dry pressing, disordered particles with large voids appear in the structure of the material, which accumulate water for a long time, which means that they destroy the tile itself at low temperatures.

How to distinguish extruded ceramics from dry-pressed ceramics?

It is by the stamping grid, which is available on the reverse side of any ceramic tile created by the "dry" pressing method, that a ceramic product made by the dry pressing method can be distinguished from clinker. Clinker tiles have longitudinal stripes on the reverse side.
Clinker material is produced only by extrusion, or wet molding. By analogy with how it happens in the production of noodles, the raw material is “squeezed out” from a large compartment through nozzles of the desired shape of the future profile. At the same time, about 15% moisture is still in the mass. Then the mass is cut to a certain format, sent for drying and for a long, more than 36 hours, firing in a tunnel kiln over 100 meters long at the highest temperature of about 1300 degrees until complete sintering, however, without vitrifying the surface. Such a production standard, which involves the use of a specific material and technical process conditions, makes it possible to create a high-density, finely porous, but homogeneous material without large voids and cavities. A homogeneous structure with capillary channels allows you to quickly and easily remove the penetrated moisture to the surface of the tile in the form of water vapor.

It is the structure that provides the high performance characteristics of the clinker. And it makes products made of it surprisingly vapor-permeable, frost-resistant, wear-resistant and immune to the effects of aggressive, including chemical, environments. Low water absorption characterizes both glazed and unglazed types of clinker products - from leading German manufacturers, such as Feldhaus klinker, the ratio is less than 2%. It is the low water absorption that makes it possible to use clinker both for paving streets and for finishing the facades of houses and interiors, with a normal and humid environment.

Various technologies for the production of ceramic products determine the properties of fastening such a material to the surface. So, the reverse side of the pressed tile has a very dense, smooth, partially even "glazed" surface. It allows only a slight inclusion of auxiliary substances and elements for a small adhesion to adhesive solutions. Under conditioned temperature loads, such a tile breaks off quite easily. Given the low vapor permeability of porcelain stoneware, it is this feature of this facing material that leads to the fact that it is not recommended to glue dry-pressed ceramics directly onto the walls of buildings without creating a ventilated facade.
The reverse side of extruded ceramics, on the contrary, is textured and rough. Adhesive crystals penetrate into the open pores of the reverse side of such a tile, which provides a large bonding area, which means optimal adhesion.

Which ceramics to choose? The most important thing is to divide products into product groups based on their differences.