Lined furnace. Furnace lining: essence and purpose, how it is carried out for various furnaces. Lining technology

What is lining, and is it always necessary? Let's try to understand this issue.

Lining - this is a way to protect the walls of the furnace or fireplace from overheating at very high temperatures. The walls of the firebox can crack, and the metal can become excessively hot and collapse over time if the temperatures in the firebox exceed 700-800 degrees Celsius. This usually occurs when burning coal, although pellets can get very hot.

Overheating is not the only effect that negatively affects the walls of a metal or brick firebox. The lining can also have the following functions:

Protection against temperature changes (thermal insulation properties).
Protection against aggressive reagents (acid-resistant lining).
Lining as a facing material.

In general, the lining can create a tight environment inside the firebox and can extend the service life of the stove firebox and the stove/fireplace as a whole.

Negative points of the lining:

The internal lining of the firebox absorbs or reflects part of the radiant heat flows (heat goes into chimney), and, accordingly, the fireplace heats less.
Actually, labor costs and the cost of lining.

In what cases is it impossible to do without furnace lining?

A lining is necessary if you have a metal firebox (cast iron, steel), and the firebox is powerful enough to produce a temperature of 700-800 degrees Celsius. Large fireplaces with a large volume of firewood on one stack, almost all of them, even without coal, are capable of reaching this temperature, and the lining will significantly extend the service life of the fireplace.

For a medium-sized potbelly stove made of cast iron, the task of which is to smolder firewood, a lining is not necessary.

A fireclay firebox also does not require lining: fireclay is a lining in its essence.

Lining the internal surface of the chimney , in addition to protection from high temperatures, it helps smooth the inner surface of the chimney (as a result, combustion products accumulate less in it, and the chimney does not need to be cleaned as often) and seal it.

What materials are the stove/fireplace lining made of?

Furnace lining materials, depending on the degree of protection, are divided into 3 classes:

Class A materials are based on silica. These are artificial materials (bricks made from compressed rocks) and natural materials (rock stones). Such materials are suitable for lining a fireplace portal (these are well-known granite, sandstone, quartz), but for lining the firebox from the inside the thermal protection is weak, since the materials have low thermal conductivity and are prone to cracking.
Class B materials are based on clay and alumina. These are the usual, familiar fireclay refractory bricks and bauxite bricks (burnt bricks made of alumina with an admixture of iron oxide and bauxite). Suitable for lining inside the firebox and can withstand high temperatures.
Class C materials are mixed materials that cannot be classified into the first two classes. These are refractory mortars, coal bricks and basic heels based on hammer scale, ore and slag.

Errors in the execution of the lining

Many craftsmen, when making brick lining, join it flush to the firebox, leaving no gap. The fact is that under the influence of high temperatures, brick and metal expand differently, and such installation can lead to cracking of the lining.

In addition, ordinary bricks used for lining have low thermal conductivity. A metal stove lined with it will be shielded with brick from the environment (the room that needs to be heated), and all the heat will go into the chimney instead of the room.

How are the lining bricks secured inside the firebox?

There are two popular ways to attach bricks inside the firebox:

Using clay.
The bricks are laid on top of each other with intersections, and fastened with metal bolts to each other, for which holes are made in the bricks.

Furnaces are built from fire-resistant materials. But due to the fact that when burning fuel a very high temperature is formed, reaching several hundred degrees, this material is not able to withstand it. To protect the outer walls, a lining is installed inside the furnace.

What is lining

The lining is a brick shell that is installed inside the firebox. It is very resistant to even the highest temperatures. This allows the stove to serve for many years, because it is protected from overheating.

The lining cannot be considered as an independent element, because it closely interacts with the materials from which the stove is lined, and with the internal environment of the firebox in which the combustion process takes place.

The lining can be made not only of brick, but also of other materials. There are three types of refractory substances that differ in their chemical properties as such materials:

Sour.
Basic.
Neutral.

They have different reactions to substances that arise during the combustion of fuel.

The lining is produced only when all engineering calculations have been carried out and the material for it has been selected. Using this calculation, the maximum effect is achieved, taking into account the characteristics of the material and the furnace itself. In addition, the lining protects various oven elements from chemical and mechanical influence.

Methods of heat protection of the furnace

Surface inside the firebox can be protected in two ways:

Using a material with low heat conductivity, which is used to treat the inner surface of the firebox.
Using protective screens that reflect thermal radiation. In this case, the heat from the radiation is removed from the furnace along with the smoke.

It is worth noting that the first method does not provide thermal insulation, but thermal protection. With thermal insulation, the heat generated by the stove remains inside it. And thermal protection protects a certain area of the furnace structure from radiation, removing heat from it. Therefore, thermal insulation materials are used for lining.

In the recent past, stoves were made mainly from ordinary bricks, which very quickly became unusable under the influence of high temperatures. Then, for quite a long time, bricks with a denser structure began to be used instead. Fireclay bricks are currently gaining popularity. It is made from clay, which is mixed with baked clay powder and then fired at high temperatures.

Fireclay brick is an ideal option for lining furnace structures. It differs from ordinary bricks in its excellent heat-insulating properties. Lining involves lining the inner surface of the furnace with just such a brick.

Brick kiln lining

Lining brick oven has some features. It should not be laid too close to bricks, which are elements of external walls. The fact is that the stove gets very hot and cracking occurs under the influence of high temperatures. The hot inner layers push the cold outer layers out of their places. The outer walls, which maintain the shape of the oven, begin to diverge to the sides due to the impact of the expanded inner layers. Bricks become covered with cracks, and some may even collapse. This may allow carbon monoxide to enter the room.

The situation can be aggravated by the fact that the clay used to connect the outer layer of bricks has little adhesion and, when heated, expands more than the brick itself. As a result of overheating, the seam is destroyed.

That is why, when constructing a furnace structure, a plastic solution is used and then tested. To do this, two bricks are connected to each other using this mortar and fired at high temperature. This tests the solution's adhesion, expansion and cracking. If everything is fine, the solution can be used for the entire structure.

When lining metal furnaces attention should be paid to the fact that metal under the influence of high temperatures expands stronger than a brick. Therefore, it is necessary to make a gap for thermal expansion between the lining layer and the metal furnace walls, otherwise when the metal is heated, the lining is often destroyed. To seal the gap, use basalt wool in the form of a sheet or strands. If the stove is not located in a residential building, asbestos can be used instead of basalt wool.

Metal stoves are often lined with brick both outside and inside to improve heating of the stove and its safety. However this method is considered erroneous, because:

Brick is characterized by low thermal conductivity and high heat capacity, as a result of which the heat arising from the combustion of fuel remains inside the firebox and goes away along with the smoke.
In this case, the stove surface is deprived of air access to remove heat, which leads to burnout of the walls. As a result, carbon monoxide may enter the room, which is life-threatening.

Thus, the lining of the furnace is done to ensure that it does not collapse due to exposure to high temperatures. The most important thing is to use high-quality material so that the stove can last for a long time.

Stoves intended for heating residential premises can have different shapes, sizes, etc. design features. Based on the purpose and technical characteristics, decide on the need to line the fireboxes.

It is not recommended to cover the fireboxes of small household stoves that operate in normal mode - this way they better cope with the tasks of heating the room with low fuel consumption.

Furnace lining may be required for the following types of products:

Furnaces designed for long-term use.
Stoves that use high-calorie fuel.
Large household ovens.
Fire chambers of Russian stoves, which are used for cooking.
Furnaces in which smoke channels are located along the walls of the firebox.

The fireboxes of the fire chambers of Russian stoves are lined with red brick; for other types of stoves, refractory bricks are used.

The furnace lining can be internal or external. The inner one serves to protect the stove firebox from overheating, the outer one is intended to give a decent appearance.

The interior decoration is made of fireproof materials that can withstand high temperatures for a long time. The brick is laid on edge along the walls of the firebox, while the refractory brickwork is joined to the main firebox masonry with one vertical seam, but is not tied together. This method allows you to protect the walls of the firebox from overheating and significantly extends the life of the stove.

Depending on the purpose of the furnace, protective screens capable of absorbing radiant fluxes can be used for finishing. If the stove is used for cooking, such screens are installed inside the firebox, where they help quickly warm up the flue gases or air supplied to the firebox. For the same purpose, the internal walls of the firebox can be lined with fire-resistant materials with low thermal conductivity. Screens installed outside are designed to create the required level of thermal protection. In other words, this finish guarantees heat retention inside the oven, preventing overheating of the outer surface.

For the exterior decoration of household stoves, the most various materials. The simplest and most practical way of exterior cladding is stove plastering. It is this type of finishing that is most often used for lining the walls of domestic stoves.

Often, brick or decorative panels made of natural or artificial materials are used to decorate the outside of the stove. Traditionally, stoves are decorated with tiles, but this is one of the most expensive methods. Ready-made tiles can be purchased in specialized stores, but for correct installation such registration will require a specialist. Without certain skills, it is quite difficult to correctly make a frame for a household stove.

Lining a furnace with your own hands is almost impossible if you do not have certain skills and abilities. Correct design requires experience and knowledge of the basics of stove laying, as well as knowledge of basic physics. Laying a stove requires a responsible approach, which is impossible without special skills. A properly built stove can serve not only as a piece of furniture, but also as a guarantee of coziness and comfort in the home.

Video

We invite you to watch a video about lining the outside of the furnace.

Furnace lining is a special finishing of product surfaces to protect against possible damage during operation resulting from thermal, mechanical, chemical and other effects. The lining of furnace equipment is designed to extend the service life of the walls and other parts of the firebox.

Features of protective finishing of furnaces

When using the oven regularly, all materials from which it is made are exposed to very high temperatures. They depend on the combustion temperatures of specific substances that are used as fuel. Of course, the walls of the stove are made of refractory materials, but extreme thermal effects change their structure and properties, which leads to gradual destruction. It is to protect against such influences that the lining is used.

The lining will be the best internal protection of your fireplace from burnout and other damage.

In what cases is it used?

If we are talking about a small fireplace that is used periodically - for heating country house on a day off or cooking in the fresh air (barbecue), then additional protection is not needed. In such cases, if damage occurs, it is minimal and will not damage the device in the near future.

Mandatory lining will be required for the following types of combustion products:

Large household and industrial.
Intended for very long-term use - for example, constant heating of a home.
Heat chambers, which are arranged for regular cooking in “Russian” and other similar stoves.
Fuel units, the smoke channels of which are located directly along the walls of the firebox.
In cases of using high-calorie fuel with an exceptionally high combustion temperature.

Types of lining

Lining work is carried out directly inside the firebox of metal, stone and brick devices. This can be done in different ways depending on what effect is expected and what goals are to be achieved:

It is possible to use special protective screens with heat-insulating effect. They will influence the percentage of heating of the flue gases, absorbing a significant part of the radiant heat fluxes and removing most of the heat through the chimneys.
The use of materials that will absorb most of the thermal impact - fire-resistant with low thermal conductivity, slowing down the heating process of the firebox materials and excluding their direct contact with fire.

Lining work in a brick firebox is carried out by laying out brickwork

ATTENTION! Heat-insulating screens significantly reduce heat transfer, so they are not used for fireboxes intended for heating rooms.

Methods of execution

The lining of the fireplace is usually carried out using so-called “fireclay” materials - specially processed substances and their mixtures with the inclusion of firing elements, which destroy the plastic properties and lead to sintering of their particles, as well as other refractory products. It can be:

Hewn stone made from natural rock such as sandstone or quartz, or conglomerate, resistant to particularly high temperatures.
Ready-made fireclay bricks, from which the inner wall is laid. Their fire-resistant properties are achieved thanks to a special manufacturing technology with the addition of powder from pre-fired clay and other substances that improve the properties of the final product. Protection made from such bricks is very popular, as it can withstand almost any temperature of a heating furnace and is relatively cheap.
Roll materials, plates and mats:
- basalt fiber;
- vermiculite boards;
- kaolin in the form of paper or cardboard, consisting of the mineral white clay.
Solutions and substances used to cover the walls of the furnace:
- fireclay, which is fire-resistant concrete with the addition of a waste component,
- mullite - silicate liquid glass mixtures with various composition variations.

Vermiculite finishing can be an excellent alternative to brick and stone

Comparison table of lining materials

IMPORTANT! In production conditions - in metallurgical and other enterprises where hot processing of raw materials and finished products is used, furnace protection is most often made of stone or fireclay brick. In “cramped” home conditions, alternative options are more acceptable.

My own master

Of course, to install a lining layer in a home fire, you can resort to the services of specialists, but with some work skills and appropriate knowledge, this operation can be carried out independently.

Brick lining

Do-it-yourself furnace lining from fireclay bricks is carried out taking into account the following features:

The brick is carefully laid out “edge to edge”, without shifting the masonry elements relative to each other, along all the walls of the internal firebox.
The seams between individual bricks are filled with a mortar based on fireclay and clay.
If the main masonry is also made of brick, then the lining and main layers are joined using one vertical seam, but without dressing.
If the material of the firebox itself is metal (cast iron or steel), then a small gap must be left between its walls and the masonry, designed for thermal expansion of the metal, otherwise regular heating and cooling may soon destroy it.

Finishing with fireclay bricks occurs according to the scheme - along all walls with a gap, taking into account the expansion of materials

ATTENTION! Internal furnace masonry from fire-resistant red brick is also possible, but it is impossible to mix types of bricks (fireclay plus fire-resistant), since they have different indicators of linear expansion and thermal conductivity, which will make the building short-lived.

Old fireclay brick masonry is subject to regular inspection and repair of worn areas, which is carried out by grouting with a mortar of fireclay and aluminous cement.

From roll material

Benefits of use roll materials(as well as plates and mats) is that they take up very little space and do not “steal” the total volume required for fuel loading and smoke passage. The standard thickness of most of them does not exceed 1 cm (for example, thick kaolin cardboard can be up to 7 mm thick). To spend necessary work, you need to remember that:

The amount of materials required for lining is calculated taking into account their linear expansion when heated.
In some cases, it is possible to lay the canvas in 2 layers, but for domestic needs this is not at all necessary.
Individual plates are fastened with reinforcement elements - metal pins, which are inserted into pre-made grooves.
When finishing with refractory mats or plates, the sequence of their attachment should be followed: first the bottom is covered, then the side surface, and then the “ceiling” of the combustion chamber.

INTERESTING! Many modern factory-made furnaces already have a lining layer on the walls of the combustion chambers and do not require additional processing. In particular, steel units are often treated with vermiculite.

Interior finishing can be done with basalt cardboard

Coating with solutions

Coating with refractory solutions gives an even thinner layer of lining. This method is characterized by the following nuances:

To prepare solutions, dry compositions of fireclay, mullite or corundum mixtures are usually used, which are then diluted with water to the desired consistency.
After application, the solution must be fired under natural conditions (while the oven is operating) or using a blowtorch. In the second case, work is carried out until a hard crust appears.

IMPORTANT! The advantage of the mortar method is also the creation of absolutely monolithic surfaces, which provide better protection of materials from the effects of fire. However, such a monolith will require repairs faster than stone and brickwork.

Pre-thought-out stove protection will guarantee warmth and comfort for many years

How long will a new lining last?

Any coating can wear out over time. Even the most durable lining layer inside your firebox can gradually lose its initial tightness. To save it, keep the following in mind:

The internal protection of the furnace needs to be periodically checked for integrity. Damage must be repaired in a timely manner with solutions prepared from a mixture of fireclay and clay.
Surfaces that are initially made of higher quality will last much longer (an even sealed layer of uniform thickness without cracks or other damage).

ATTENTION! Installation of lining is a complex engineering task that is best entrusted to knowledgeable people, that is, carry out the work under the guidance of a specialist or leave it completely in the hands of professionals. High-quality performance of this important work will allow you to forget about repairing the hearth for a long time.

Video: furnace firebox lining

The inner walls of the firebox are exposed to very high temperatures. Such loads lead to their destruction, even if they have a high degree of fire resistance. It is for their protection that it is carried out furnace lining fireclay materials, namely brick or mortar. The physical properties of fireclay give it the ability to withstand temperatures up to 1300ºC. This is enough for high-quality protection of the firebox made of any material. However, internal protection rules must be observed, since a violation of the technology leads over time to the collapse of the furnace.

Lining materials

In addition to fireclay, there are mullite mixtures that can withstand ultra-high temperatures. Pure mullite melts at 1800ºC, but solutions or heat-insulating mats made from its fibers are used for lining. The mats are resistant to temperatures up to 1600ºC. Mullite is often included in fireclay materials.

For household use, fireclay is produced in the form of bricks or a mixture. In the first case, it is used for lining furnaces with metal or brick fireboxes and brick casings. The solution is used to protect the firebox lined with refractory clay. Both materials are the most accessible and inexpensive, and therefore the most popular.

However, new technologies have made it easier to repair old working furnaces and protect new units. Today, manufacturers offer special adhesives, mastics, and coatings that can be applied even during fuel combustion. They have a pasty consistency and consist of fireclay microscopic fibers. The compositions also include binding additives. Used for sealing cracks and continuous surface coating.

There are adhesives and mastics that only need to be applied in a 1 mm layer. In addition to bricks, mats and coatings, other materials are produced for lining furnaces of all types and purposes. They are packaged in rolls for ease of use and are available in the following products:

kaolin paper (rolls with a layer thickness of up to 5 mm),
kaolin cardboard (canvas thickness up to 7 mm),
kaolin wool (easily torn, used in the form of lumps or pieces).

Lining rules

The internal walls of the firebox are protected taking into account the expansion of materials from exposure to open fire. That is why a gap of 5-10 mm is always left between fireclay bricks. Before starting work, a material calculation is made. Its standard dimensions are 250x150x65 mm. Sometimes stove makers lay it in 2 layers. In everyday life, it is not necessary to make a double layer of furnace lining. It should be known that the total thickness of the lining is determined by the following factors:

The fireclay elements are secured to each other using metal pins. To do this, grooves are made in their walls by cutting, then a rod is inserted into them. Thus, it is a reinforcement detail that guarantees the fixation of the material. The sequence of lining work is as follows: first, fireclay bricks are laid on the bottom of the firebox, then on the side walls, ending with the upper horizontal part.

It is important to know that you cannot use 2 types of bricks at the same time: fireclay and fire-resistant red. Despite the fact that clay is heat-resistant, they have different degrees of thermal conductivity and linear expansion. This will eventually lead to cracks in the red brick and reworking of all the work. A special mixture is used for masonry. It also contains fireclay fibers, and this equalizes the degree of its expansion with the properties of brick.