Wire for heating concrete - PNSV wire, laying diagram

As is known, concrete gains full strength in 28 days, but at sub-zero temperatures the process of hardening of the concrete mass undergoes serious changes. The water included in the mortar turns into ice, and the concrete mixture hardens more slowly, which is why the finished building loses some of its strength characteristics, crumbles and collapses. To prevent this from happening, it is recommended to use a special wire for heating concrete - PNSV wire.

Thanks to this heating cable, the hardening time of concrete is reduced to several days (and sometimes hours), which is of no small importance when construction work is carried out in winter.

Warm-up technology

The locations of communications and the location of holes in the concrete surface must be thought out before starting to pour the composition. After installing the system and covering it with a cement mixture, any work on the surface may damage the wires. For example, before diamond drilling into a material, you need to make sure that the hole will not pass through the concrete heating cable.

Rules for laying the system

Before placing the heating system, reinforcement and formwork are installed. Then the PNSV layout is carried out; there should be an interval of 8-20 cm between the turns of wires. The size of the gap depends on the wind, outside temperature and humidity.

The cable is attached with clamps to the fittings, without tension. The optimal radius of bends is more than 25 cm. The current-carrying conductors should not intersect, the distance between them is 1.5 cm, this arrangement avoids short circuits.

The following points must be checked before pouring the solution:

• the temperature of the prepared mixture is above +5 °C;
• there is no ice in the formwork;
• the circuit is connected correctly;
• cold ends have an optimal length.

The PNSV cable comes with instructions, which are important to follow when installing the heating system. There are two options for connecting via busbars - star and delta.

In the first method, three cables of the same type are combined into a node, then the free three contacts are connected to a transformer. The power supply is located at a distance of up to 25 m from the connection point. The area of ​​material that will be heated is protected by a fence.

The system is connected only after the solution has been poured. The use of a heating cable for concrete PNSV includes the following steps:

1. Warming up is underway; the temperature should increase by 10 °C per hour. High speed will disrupt the uniform heating of the material.
2. Heating is carried out at a constant temperature value. Concrete needs to gain half of its technological strength. The optimal temperature is 60 °C, the maximum possible is 80 °C.
3. The material cools slowly. Its cooling rate should not exceed 5 °C per hour, otherwise cracking of the structure will occur.

If all work was carried out correctly, the concrete will reach the appropriate strength grade. After heating, the cable remains in the material and plays the role of an auxiliary reinforcing structure.

VET and KDBS cables can be connected through a socket or panel board to a 220 V network; they are also divided into sections, which prevents overloads. But their cost is significantly higher than PNSV wires.

Concrete can also be heated using a tubular electric heater (TEH) and electrodes. The fittings are inserted into the solution and connected to a power source - a welding machine or other step-down transformer. This option does not require a heating cable, but will require significant energy expenditure. Water acts as a conductor in concrete, and as the material hardens, the resistance will increase.

Calculation of the length of the PNSV

Several factors influence the determination of the length of the PNSV cable. The amount of heat that will be applied to the material for hardening is of great importance. This indicator is affected by thermal insulation, air temperature, shape and size of the structure, and humidity.

The length of the loop should be on average 28−36 m. If the temperature is above -5 °C, then laying is done in increments of 20 cm. When cooling, every 5 degrees the gap between the cores is reduced by 4 cm. At around -15 °C it will be equals 12 cm.

The power consumption of the PNSV cable is also important; it depends on the diameter:

• 1.2 mm - 0.015 Ohm/m;
• 2 mm - 0.044 Ohm/m;
• 3 mm - 0.02 Ohm/m.

To do this, the squared current is multiplied by the resistivity. The total power is found from the product of the obtained value and the total length of the wire. The transformer voltage is calculated in a similar way. The current is multiplied by the resistance to get the operating voltage.

PNSV wire is the cheapest option for heating concrete mix. But its use requires special equipment and relevant knowledge. Thermal insulation also reduces the cost of heating the material and improves the quality of concrete due to uniform cooling.

https://youtube.com/watch?v=Mi9bK_pcfcI

Peculiarities

The instructions for pouring concrete structures and foundations involve carrying out the process under certain conditions. The mixture hardens and gains strength at a relative ambient humidity of 95-100%, temperature from 15 to 20ºС. For concrete, this is a technology generally recognized by building codes.

If the conditions for hardening the mixture are not met, the hardening processes slow down and the duration of the period of strength gain increases. This affects the material at the molecular level. Concrete will not be able to gain the required strength. It will crack and crumble.

Today, chemicals called additives and plasticizers are used. They are added to concrete in order to reduce the hardening threshold of water in the solution. A more effective result is obtained by heating the building material with electricity. The presented process occurs when using transformers, for example, KTPTO, TMOB and many other models.

Benefits of warming up

The use of a warm-up transformer is a common technique in the winter construction process. Electricity consumption and additional costs for technical concreting are compensated by the advantages of the presented methodology. These include the following facts:

1. Possibility of carrying out construction work all year round.
2. Increased productivity due to no downtime.
3. Meeting deadlines for the construction of the facility.
4. Transport and equipment are used rationally.
5. Ready-made concrete structures comply with existing standards.
6. The strength of the cement mixture improves.
7. No additional costs for the purchase of expensive plasticizers and chemical additives against concrete freezing.

Thanks to the listed factors, warm-up transformer units are used during the construction process, for example, TSDZ-80, KTPTO-80 and other varieties.

PNSV wire

A universal and affordable way to warm up concrete in winter using a high-resistance cable and a step-down transformer. When linking the frame from the reinforcement, a heating cable is laid; the size and shape of the structure does not matter.

This heating method is applicable both at the construction site and for home builders. Let's tell you in a little more detail how to heat a concrete mixture with a PNSV wire at home.

After reinforcing the frame of the structure or laying the beacons under the self-leveling floor, the wire is laid in a snake no closer than 20 centimeters from each other (the optimal laying step). The length of one loop ranges from 28-36 meters. A welding machine can be used as a voltage source. The connection diagram in this case will look like this:

The nuance of warming up is that the PNSV cannot be connected without being covered with a solution, because Without heat absorption due to the high temperature outdoors, it will burn out. To avoid burnout, switch to an aluminum cable, leaving the output ends of the PNSV heating wire 10 cm out of solution. The manufacturer recommends a current in the cable of 11-17 amperes, which can be controlled with current clamps. We talked about how to use current clamps in a separate article.

For home construction, a PNSV with a diameter of 1.2 mm is sufficient. Its characteristics:

• resistance 0.15 Ohm/m;
• operating current immersed in solution 14-16 amperes;
• laying temperature from -25 to 50 °C.

Wire consumption per cube of concrete is 60 linear meters. The temperature to which concrete is heated is 80 °C, it is controlled by any thermometer. The rate of temperature rise of the solution should not exceed 10 degrees per hour. To avoid pointless expenses on electricity bills, the heated area is covered with any material that prevents the heating of the atmosphere, for example, covered with sawdust. To obtain an excellent result, the concrete mixture is also heated before pouring; the temperature of the mixture should not be lower than +5 °C. Following these instructions, you can warm up concrete in winter with your own hands. The technology is labor-intensive, but even an inexperienced person can do it. How to lay a heating cable in the foundation is described in the video tutorial:

Heating the foundation with wire

By the way, instead of the PNSV wire, you can also use the BET cable to heat the concrete. The video below briefly describes the instructions for installing the heating conductor:

How heating with BET cable works

The article does not indicate all methods of heating concrete in winter. There are induction, infrared and other methods, but we do not consider them due to their low prevalence and complexity. We gave a general idea of ​​the technology for constructing concrete structures, and the possibility of home craftsmen using methods for heating screeds and walls. By the way, the use of PNSV wire is possible not only during the heating of the structure under construction, but also after that. It can be used as a ready-made warm floor or anti-ice on stairs or sidewalks. Short sections are connected through a step-down transformer from 400 to 1500 watts. To connect directly to a 220 volt network, the length of the wire will be more than 120 meters.

That's all I wanted to tell you about why concrete is needed to be heated in winter and how to do it using heat guns, electrodes or PNSV wire. We hope our instructions were clear to you. You can get more information by watching the video tutorials in the article.

We also recommend reading:

• Heating of tracks with a heating cable
• How to save energy at home
• How to choose a heat gun by power
• Temporary power supply for construction site

Parameters, scope of application

The properties are determined by the requirements of TU 16.K71-013-88, OKP code 35581304. Used for warming up:

• Monolith, reinforced concrete in the construction of industrial facilities;
• Objects, buildings, structures of industrial complexes for various purposes, construction mechanisms;
• Can be used in heating systems for domestic and industrial building structures.

The PNSV marking indicates the design, area of ​​use, materials: “P” heating wire, single “C” steel conductor, insulated with polychlorine “B” vinyl.

Basic, defining indicators are shown in the table:

The physical and chemical characteristics of the materials give the parameters values ​​that ensure:

• Lack of reaction when interacting with water, chemically active aqueous solutions of salt, alkalis, the solution concentration of which reaches 20÷30%;
• Strength that allows bending on a roller, the size of which is equal to ten wire diameters, without loss of mechanical properties for at least three cycles;
• Possibility to operate in constant long-term heating modes or pulsed, short-term repeated heating modes.

When performing installation work, you need to take into account the following restrictions:

1. Bending is carried out with a radius less than five diameters;
2. Crossing at any angle or touching in the heated volume is not allowed;
3. It is prohibited to place wires no closer than 15 cm from each other.

The range of the PNSV model range is wide. Specific values ​​of geometric dimensions are determined by the technical conditions of the manufacturer in accordance with the requirements of the relevant GOST. The trend in the dependence of parameters on the nominal diameter of the core is laid down in TU 16.K71-013-88, illustrated by the table:

Technical data

Structure

PNSV cable element diagram

The heating wire for concrete has a simple structure:

1. A steel core consisting of a single wire, capable of conducting electric current and having a round shape. Its diameter can be from 1.2 mm to 3 mm.
2. An insulation layer usually made of polyvinyl chloride or polyethylene.

Performance characteristics

Has high resistance to temperature changes. It does not lose its qualities and is able to work properly in the range from -60 degrees Celsius to +50, which in the case of our climate means always.

Low temperature makes the core shell less elastic and prone to fracture

• Polyethylene or PVC coating provides high water-repellent properties and can withstand exposure to a twenty percent salt solution and thirty percent alkali.
• When laying the cable, you will probably have to roll and bend it. If you overdo this, the metal wire may break off inside the insulating sheath. To prevent this from happening, the bending radius should not be less than twenty-five millimeters.

An example of the correct installation of a heating wire with your own hands

The instructions also require maintaining a minimum distance between wire elements of at least fifteen millimeters. Overheating can lead to damage to the insulating coating, followed by a short circuit. Sufficient indentation will save you from worrying about this.

Maintain the required gap between the heating elements even with such a chaotic arrangement

• During operation, the cable must operate in intermittent or long-term mode.
• The connection to the power supply must be made with “cold” ends and the soldering points must be taken outside the heating area.

Electrical indicators

1. The resistance of the product in question depends on the thickness of its section, decreasing as it increases:

• 1.2 mm – 0.15 Ohm;
• 1.4 mm – 0.1 Ohm;
• 2 mm – 0.025 Ohm;
• 3 mm – 0.005 Ohm.

1. The supplied AC voltage is allowed up to 380 V.
2. The power supply in this case is considered most suitable around 65 V.
3. The amount of heat generated depends on the presence of reinforcement in the structure:

• Reinforced concrete mass - 30-35 watts per linear meter.
• Ordinary concrete without metal inserts - 35-40 watts per linear meter.

1. The required heating cycle is usually three days.

Warming up concrete with PNSV wire

Professional construction is a process that does not stop in any weather: neither in rain, nor in snow, nor in severe frost. One of the main components of any construction process is concrete, for accelerated hardening of which various technologies, methods and devices are used. The most common technical means for accelerating the process in this way are: heating the concrete solution and structures made from it using special thermoelectric construction mats (TEMS) and wires for heating the concrete.

Characteristics and features of the wire

To heat concrete, in most cases, a wire marked PNSV is used, which stands for: “heating wire, steel core, vinyl sheath.” In some cases, PTPG 2x1.2 is used. The PNSV cable for electrical heating of concrete consists of a steel core, in some cases additionally galvanized, with a diameter that can vary from 1.2 to 3 mm. On top it is covered with an insulating shell made of polyvinyl chloride or its subtypes. This type of insulation allows you to avoid fractures and kinks of the internal veins, and also protects against fires. A cable for heating concrete, depending on the core diameter and electrical resistance, can withstand a load of 80-160 watts per meter. PNSV type wire is optimally used for heating monolithic concrete, for example, when pouring foundations or walls.

Another distinctive feature of the heating cable is the presence of so-called cold ends. These are special branches that extend beyond the concrete surface. For them, APV wires are used, connecting the heating cable PNSV and the supply line from the heating transformer.

Heating wires are fixed to the reinforcement frame and supplied with current through step-down transformers, consisting of several stages, which allows you to change the level of surface heating depending on the ambient temperature. The most common heating substations are SPB-80 or KTPTO-80/86, each of which can heat about 20-30 m3 of concrete solution. The stations are connected to a three-phase network with an operating voltage of 380V, with mandatory grounding of the housing and the neutral (zero-phase) wire.

New warm-up method

More recently, it has become possible to heat concrete using a cable without a transformer. This became possible using BET thermal cable technology, capable of withstanding up to 40 W per linear meter and operating from a network with a voltage of 220V. A nichrome shielded thread is used as a heating element, ensuring a constant temperature of +80 °C and uniform heating of the solution. This cable is suitable for any type of foundation, be it a strip grillage or a monolithic one.

Wire prices

To expand the temperature range of cable use from -60 to +50 °C, as well as to increase the strength characteristics of the insulating layer, primary raw materials (primary) are used. The prices at which you can buy PNSV wire today for heating concrete made from such raw materials are presented in the table below:

How to heat concrete?

To warm up concrete, a certain sequence must be followed:

1. During the first two hours, the heating rate of the concrete composition should not exceed 10 °C per hour;

2. In the future, it is necessary to ensure that the temperature does not exceed +80 °C.

3. The last stage is cooling, and the temperature should not drop by more than 5 degrees per hour.

In the event that a separate heating station is used, a “star” connection diagram is suitable, designed for heating small areas. Installation must be carried out according to the technological map of the facility.

Connection diagram, heating equipment

Heating of poured concrete is carried out only by powerful contractors on large objects. The method is expensive and requires highly qualified workers and special equipment. The transformer heating substation provides power to the heating wiring with reduced voltage and makes it possible to use a large current of reduced voltage.

For example, the popular KTPTO substation with an oil-filled three-phase transformer TMTO-80 has the following basic technical characteristics:

Additionally, it can automatically or manually regulate the heating of concrete in the range of 0÷100°C. Other functions of the substation not related to heating will not be considered now.

Heating sections can be connected to the transformer using a single-phase or three-phase star or delta circuit. Three-phase heaters make the network load more uniform.

By turning on the required number of sections in parallel, sufficient power is obtained to heat the required area.

Laying scheme

The main requirement is uniform heating; there should be no cold zones. The minimum distance between adjacent wires for heating concrete is 15 mm, the maximum is selected taking into account the characteristics and external conditions. The optimal horizontal gap is considered to be 20-40 cm, vertically - 8-10, it is not recommended to exceed it. The entire volume of the mixture and the main dimensions of the structures are taken into account.

The simplest design is a “snake” with a bending radius of at least 5 working diameters for PNSV and 10 for PTPG. It is placed along the reinforcement without tension (ideally with fixation with plastic clamps), overlaps and exits to the surface (the recommended distance to the edges is from 20 mm), the integrity of the insulation is monitored. Direct contacts of bare areas with mesh or metal rods cause a short circuit; in particularly dangerous places, laying with pieces of bitumen-impregnated paper or roofing felt is provided.

An unregulated wire is connected to a step-down transformer, special attention is paid to the cold ends, the current supply conductors must have a lower resistivity value than the heating ones, aluminum meets this requirement. When choosing a "triangle" circuit, the wires are divided into three equal groups, connected in parallel and combined into three output points

When distributing the load with a “star”, three segments of equal length at one end will be connected into one node, the rest - to the power station. All contacts are reliably insulated; for these purposes, double-sided electrical tape or heat-shrinkable tubes are used. The power of the transformer for heating is determined by the calculation; on average, 1 kW is required for 0.4-1 m3 of concrete.

Laying KDBS follows the same principle, but in slightly larger increments (consumption is 4 lm per 1 m2 along a screed or horizontal plane) and with direct connection to an outlet. It is completely immersed in concrete, only the supply terminal remains outside. Despite the higher cost of the cable and the increase in power consumption to 1.5 kW per 1 m3, this type provides the most uniform heating and stable performance characteristics. Once dry, it is simply cut off and left in the concrete. KDBS is selected for critical areas, when carrying out urgent repairs, with a large number of individual monolithic elements, or the need to use a vibrator. It is easier to install it for people without experience; the factory parameters exclude overheating or burnout.

Basic rules of heating technology:

• The minimum temperature of the poured composition is +5 °C.
• Power is supplied exclusively to wires buried in concrete, ideally through a voltage stabilizer.
• Due to cracking of the insulation, installation is not recommended at temperatures below -15 °C.
• The process is carried out with power control: smooth heating for the first 2 hours, maintaining within 50-60 °C for at least 3-4 days, gradual cooling.

Heating cable price review

Single- and double-core cables are sold in coils:

Prices for self-regulating cable in sections, respectively, are:

Concrete heating technology

System installation

The work is performed in the following order:

• First of all, you need to clean the surface of debris and various sharp parts that can damage the wire.
• Then the reinforcement or reinforcing mesh is laid, and the reinforcement is welded.
• Then the wire is installed. The easiest way is to lay it with a snake. Its value will depend on the area of ​​the fill and the length of the cable. At the same time, do not forget that laying wires on top of each other is strictly prohibited; in addition, you must ensure that the cable does not come into contact with the formwork and does not protrude beyond the surface of the concrete.

Wire installation

The optimal distance between cables is considered to be no more than 15 centimeters, especially if there is a long wire and the filling area is small.

Next, you need to check the system for functionality - connect it to electricity and make sure that the cable heats up. It is imperative to control the current power.

Do not exceed the indicators indicated by the manufacturer on the wire. If the system will be operated without a transformer that allows you to reduce the current, then PTPZh brand wire should be used, since it is more powerful.

• After this, you need to disconnect the cable and let it cool.
• The final stage is pouring the area with concrete.

Cable installation diagram

As we can see, installing a concrete heating system with wire is in many ways similar to installing a heated floor. Moreover, this cable can be used for these purposes as well. The only thing is that in this case it is more expedient to make a heating element from wire threads and wrap it with insulating material.

If a separate power station is used, then it is better to use a “star” connection diagram. It is more efficient than the “snake” and is well suited for heating small areas.

Star scheme

Procedure for heating concrete

Instructions for heating concrete with a cable are as follows:

• After the area is completely filled with concrete, the heating system starts. In this case, the rate of temperature increase should be no more than ten degrees Celsius in two hours.
• Next, the main warm-up period begins. At this stage, you need to ensure that the temperature does not reach 80 degrees Celsius.
• The final stage is cooling. The rate of temperature decrease should be no more than five degrees per hour.

This completes the concrete heating process. If the instructions are strictly followed, the material will be able to achieve the required level of strength even in conditions of very low temperatures.

Operating principle of the device

There are several types of thermal fuses that perform the same functions, but differ in design:

• Disposable fuses. Inside the element there is a wire made of a low-melting alloy - Rose (+94°C.) or Wood (+60-68.5°C). The filler is quartz sand, which absorbs molten metal and extinguishes the arc that appears when the device is triggered.
• Self-resetting fuse. This is a polymer thermistor with a nonlinear change in resistance with increasing temperature. In a cold state, it is close to 0 and does not affect the operation of the circuit. When the temperature is exceeded, the resistance of the element increases, and it disconnects the transformer winding from the network. After cooling, the fuse returns to its original state.
• Bimetallic thermostats. The housing of these devices contains contacts and a bimetallic strip. When heated, it bends and opens the contact. There are two types - small-sized with flexible leads that are installed inside the windings and more massive ones that have terminals for connection and are placed outside the device on the magnetic core or radiator of the output transistors.

Wire Requirements

The PNSV heating cable must comply with the parameters that have a direct impact on the functional qualities:

• Bandwidth. For houses and apartments, a current of 16 A is sufficient; if installation on an industrial scale is necessary, the figure must be increased.
• Section diameter. Its resistance to heat depends on the thickness of the cable; a wire that is too thin for heating concrete will burn out when the temperature increases to a certain limit. The recommended value for private use is 1.2 mm.
• Cold ends. This is the name given to the taps from the main core, which are located outside and connected to the power source. They are usually made of aluminum, the cross-sectional diameter of which is larger than the heating cable for pouring concrete in winter. The ideal option is the APV-4 wire.

Don't forget about the required wire length. Taking into account the thickness of the section, the heating cable for heating concrete should be calculated based on the average value of 55 m of heater per 1 m3 of solution.

Using PNSV wire after hardening

Heating cable sections laid in a concrete structure remain in it forever and do not lose their resistive properties. Therefore, it makes sense to use them to improve the comfort of your stay. Often, the PNSV wire is specially laid in a concrete floor screed. However, this is not the best solution, although it is the most budget-friendly.

When placing the heating element under the floor covering, possible obstacles to the dissipation of the generated heat should be taken into account. In living rooms, these are places where cabinet furniture is installed, the base of which fits tightly to the floor. Local overheating zones appear in them.

With prolonged use, the wire gradually becomes thinner and eventually breaks. Replacing it is extremely difficult, as it requires removing the floor covering and destroying the concrete screed.

The solution to the problem is to use a self-regulating heating wire. Its design consists of two copper cores, between which there is a so-called thermal matrix - a semiconductor element whose conductivity changes as it heats up. The higher the temperature, the higher the resistance. This causes the current flowing through this area to decrease, causing it to cool down.

Such a heating element works at any size - from a piece a few centimeters long to a multi-meter section. It can be crossed with others similar to it (this is strictly forbidden to do with a PNSV wire due to the danger of melting the insulation and causing a short circuit). The main disadvantage of self-regulating heating wire is the cost. It is several times higher than a single-core resistive one.

https://youtube.com/watch?v=ITujT-WErts

Warming up the poured concrete mass using the PNSV heating cable allows you to reduce the time to achieve 80% of the structural strength from seven days to two to three days and not stop work with the onset of cold weather. However, the technology of this process is quite complex; usually its scheme is developed for each specific case. Therefore, do not be seduced by its apparent simplicity. Contact professionals, and in their absence, thoroughly study the issue yourself.

Heating concrete with a 220 volt cable: features

To ensure that the solution poured into the formwork sets properly, a KDBS is used - a 220-volt heating cable for concrete. This is a two-core resistive heating cable, complemented by a connecting wire and a connector for connecting to the mains.

It is effective in the temperature range from +5*C to -30*C and can be used not only for monolithic work, but also for temporary heating of the entire construction site.

Heating concrete using a heating cable has many advantages:

1. The concreting process at low temperatures accelerates, and the concrete does not freeze.
2. It is possible to maintain a high pace of construction work, reducing time and labor costs.
3. This is an economical solution that does not require significant financial investments.
4. Installation of a heating cable for concrete does not require the use of special equipment, is carried out without a technological map and can be carried out directly by specialists from a construction company.
5. To connect the line, a step-down transformer is not needed, since the concrete is heated with a 220-volt wire.
6. The maximum cable heating temperature is 60*C, which provides optimal conditions for concrete hardening. It does not overheat and does not boil, which means that so-called “sinks” and voids are not formed in it, reducing its strength.
7. Heating of concrete at 220 V is carried out using heating sections, which guarantee uniform heating over the entire area of ​​the poured structure.
8. The use of KDBS is absolutely safe, since the high-strength insulating coating reliably protects the steel core from mechanical damage.

Drying the active part of the transformer in a chamber without vacuum

With this drying method, the active part of the transformer is placed in a well-insulated chamber (Figure 1), which is made of wooden frames and panels covered with plywood sheets with an air gap. The inside of the chamber is sheathed with sheet asbestos and on top of it with sheets of roofing steel. The joints between the panels are insulated with asbestos. Another camera design can be used. The distance between the walls of the chamber and the active part of the transformer must be at least 180 - 200 mm. An exhaust hole is made at the top of the chamber to remove vapors released during drying. The active part is most often heated using blowers. You can also use electric ovens or steam coils.

Figure 1. Drying a transformer in a chamber using a blower1 – fan; 2 – heater; 3 – spark arrester; 4 – insulated chamber; 5 – adjusting gate; 6 – thermometers; 7 – thermocouples in the winding

To speed up drying, it is advisable to use two blowers, supplying hot air from them into two holes located in the lower part of the chamber, along its diagonal. With one blower, for uniform drying, air from it should also be supplied to two holes diagonally in the chamber. A fabric filter is installed on the suction pipe of the blower, and a spark arrester (metal mesh) is installed on the pressure pipe. The hot air stream should not be directed at the winding or yoke insulation.

The amount of air Qb, m3 supplied to the drying chamber in 1 minute should be 1.5 times the volume of the chamber Qcam.

The power of electric blower furnaces, kW, should be equal to:

P = 0.07 × Qв × Gр × (t2 – t1) ,

where Gr is the specific heat capacity of air, taken equal to 0.273 cal/kg×deg; t1 – ambient air temperature, °C; t2 – temperature of air entering the chamber, °C.

Example. Chamber volume 2 × 3 × 2 m = 12 m3, t1 = 20 °C, t2 = 100 °C. Determine the power of the blower.

Volume of air supplied to the chamber:

Qв = 1.5 × Qkam = 1.5 × 12 = 18 m3.

Blower power

P = 0.07 × 18 × 0.273 × (100 – 20) = 18.7 kW.

The temperature of the incoming air and the temperature in the chamber should not exceed 105 °C. The temperature of the exhaust air should not be lower than 80 – 90 °C. At a lower temperature of the exhaust air, the chamber should be insulated more thoroughly.

When the insulation temperature of the active part of the transformer rises above 105 °C, the temperature of the incoming air should be reduced by increasing the opening of the blower gate, and if it is fully open, periodically turning it off.

For transformers with a voltage of 35 kV and higher, after heating the active part to a steady-state temperature on the winding (105 ° C), it is advisable to speed up drying by quickly reducing the temperature of the outer layers of insulation by turning off the electric furnaces of the blower and supplying cold air (use the so-called thermal diffusion). When the chamber is rapidly cooled, the inner layers of insulation do not have time to cool down much and their temperature will be higher than the temperature of the outer layers. Thus, the decrease in temperature across the layers will coincide with the direction of moisture removal, which will significantly speed up the drying process. The temperature of the internal layers can be approximately considered equal to the temperature of the magnetic core. The temperature difference between the outer and inner layers of insulation must be at least 15 - 20 ° C and last for 15 - 25 hours. It is recommended to reduce the temperature on the outer layers of insulation to 50 – 40 °C and on the magnetic core to 70 – 65 °C. After the end of the thermal diffusion cycle, the active part is heated to the previous temperature and the insulation resistance values ​​before and after thermal diffusion are compared. Depending on the results obtained, a decision is made to apply a repeated thermal diffusion cycle or to terminate drying.

After drying, the active part is inspected (pressing the windings, tightening fasteners, etc.), which is then lowered into the tank and filled with oil.

Carrying out treatment of concrete after heating

Many builders wonder whether it is possible to manipulate cutting or drilling concrete after it has gained strength. This question is due to the fact that at the time the heating stops, the structure has not yet acquired brand strength. The answer to this question can be positive, but with some reservations. Although cutting is possible, it is unacceptable to produce impact loads. The most suitable solution for this is the use of diamond tools. So, if you use diamond drilling at this stage, the holes in the concrete will have smooth edges and cracks will not appear. Moreover, if you drill through the concrete body using a diamond bit, then you will not have to change the tool at the moment of breaking through the reinforcement, which is true for reinforced concrete.

Types of heating wires

The modern market provides a wide range of such products with different performance characteristics.

The cable heating the concrete must have good insulation, otherwise a short circuit or fire may occur. A good insulating layer helps prevent kinks and fractures. As a rule, such products have one current-carrying core, but they are also found with two conductors.

Types of wire for heating concrete and their features:

• PNSV is the most accessible and well-known type. It has an attractive price, starting from 1 ruble per meter. Reusable use is possible, but can only be used with a transformer.
• The PTPZh wire is similar in technical characteristics to the PNSV, but it has two cores.
• KDBS - two-wire in sections. Expensive. Can be used without a transformer. Very easy to install and install. Applies once.
• VET - with two steel wires. Economical. You can work with it without a transformer.

https://youtube.com/watch?v=ITujT-WErts

In addition to products that heat concrete structures, there are series of heating wires used for other purposes. They can be resistive or self-regulating. Resistive conductors include the simplest ones, which are used in the construction of heated floors, as well as for heating pipes with a diameter of up to 40 mm. Large pipes and roof heating are carried out using a self-regulating cable, which independently regulates heating without sensors, reacting to temperature changes.

Review of popular transformers

When choosing an electrical installation, you must take them into account:

• Design features.
• Power and number of voltage stages.
• How does the winding cool down? There are models with dry insulation, in which cooling occurs naturally (due to direct heat exchange with air), and there are also oil transformers that cool the winding using mineral oils. In addition, today there are units with a forced cooling system.

Let's consider a list of models that best meet these requirements.

https://youtube.com/watch?v=AXgOIRKILLlc

KTPTO 80-86

The KTPTO concrete heating station is a three-phase transformer for frozen soil and concrete mortar, with a power of 80 kW and a supply voltage of 380 V. The unit has an oil cooling system. The KTPTO transformer operates in automatic mode, so the operator does not need to constantly compare the readings of air temperature and heating power. The station operates in a temperature range from -40 to + 10 degrees. The area that the transformer is capable of heating is up to 40 m3.

If we talk about the advantages of the KTPTO 80 concrete heating transformer, the unit stands out:

• a fairly simple device;
• possibility of connecting third-party equipment.

Among the disadvantages of the unit:

• the dimensions of the station are too large;
• heavy weight (because of this, the transformer can only be moved on a skid).
• equipment requires maintenance every 3 months.

But today more modern stations have appeared on sale, which are compact and lighter in weight. Moreover, in modified models you can adjust the temperature both manually and automatically.

The cost of the transformer ranges from 125,000 to 180,000 rubles.

SPB-20

This three-phase concrete heating station has a dry-type cooling system and a rated power of 20 kW. The temperature range at which the unit performs its functions is from -40 to +5 degrees.

The SPB-20 concrete heating station is more suitable for small construction projects with an area of ​​up to 20 m3, so it is recommended to use it for self-construction of buildings.

The advantages of the equipment include the following:

• facilitated wheeled transportation;
• increased reliability and protection against power surges.

Among the disadvantages:

During the adjustment process under network load, switches sometimes break down.

The cost of the station ranges from 49,000 to 61,000 rubles. You can also find a lower power model on sale - SPB-10, which will cost from 20,000 to 25,000 rubles. There are also more powerful units, for example, SPB-35 - SPB-100, but their use is rational only when we are talking about large areas. In addition, their cost will be from 60,000 to 160,000 rubles.

TSDZ-63/0.38

The next three-phase power unit, providing a power of 63 kW, is equipped with a forced ventilation system (built-in fan). The transformer is capable of operating in a wider temperature range from -45 to +20 degrees. In this case, the unit operates in uninterrupted mode.

Among the advantages:

• light weight, compact;
• equipped with an automatic switch.

Among the disadvantages, users highlight:

Frequent breakdowns of the cooling system, due to which the entire installation ceases to function.

TSDZ-63/0.38 costs from 61,000 to 79,000 rubles.

TSDZ-80/0.38 UZ

This mobile station also heats concrete mortar and frozen soil. The unit also has a forced cooling system, which operates thanks to two fans installed on the rear of the unit.

Positive sides:

• compactness;
• light weight;
• possibility of automated operation;
• high level of protection, due to which it is impossible to regulate the voltage during operation of the equipment.

However, this transformer has one significant drawback - if the station breaks down, it will be impossible to repair it.

The cost of a power transformer ranges from 70,000 to 100,000 rubles.

TSZP-80/0.38

This mobile unit is equipped with a natural cooling system. Its distinctive feature is that the concrete is heated by a transformer in 6 modes from 45 to 100 V.

The main advantages of the station:

• convenient transportation;
• compact size and light weight;
• possibility of self-repair.

There is only one drawback - the automation does not always work stably.

Such a power unit costs from 58,000 rubles.

Method of heating reinforced concrete

The main advantage of this technology over other heating methods is the absolute absence of heat loss, since thermal energy remains in the surrounding concrete mass. The costs of heating the cable and transferring heat into the body of the concrete structure are minimal compared to other heating technologies.

The next, undoubtedly, big advantage is the ease of implementation of this method. After calculations, it is enough to select the right heating element, connection and installation diagram, select the appropriate voltage, and the final result can be achieved without resorting to the services of builders and electricians.

The technology itself consists of several stages, the first of which is the construction of formwork or a form of the corresponding structure, into which the reinforced frame, heating wire will be laid and concrete will be poured, which must be compacted with an in-depth vibrator before applying voltage to the circuit.

Pouring the solution into the prepared form

https://youtube.com/watch?v=Mi9bK_pcfcI

Some features that PNSV or KDBS have, which are used to warm up the concrete mass, allow the circuit to more efficiently convert voltage electricity into heat, the main thing is to calculate everything correctly. This heat warms the concrete, speeding up its setting and hardening.

Professional builders know and understand the difference between heating wire and cable, and individual developers will find it useful to have an idea about this, which will help them use the technology correctly and more efficiently. The heating method using a cable is more expensive for the following reasons:

1. Heating of reinforced concrete is carried out by connecting the circuit to a reduced voltage through a special step-down transformer in order to prevent the leakage of dangerous voltage into the structure through wet metal reinforcement in the event of accidental damage to the insulation.
2. The heating KDBS can be connected to a network of at least 220V. Optimally - 220V or 380V without reducing the mains voltage.

Connecting PNSV or KDBS is easier in terms of organizing the workflow - connections are made through special couplings, and the cable does not need to be shortened or extended. But a heating cable is more expensive than a wire, so in individual construction it is used at the discretion of the owner. Another disadvantage of cables is that they cannot be reused.

KDBS for heating concrete

Wire differences:

1. Externally, a wire can be distinguished from a cable by the following characteristics: a wire usually has one core, a cable has two or more.
2. The wire has nominal temperature limits when heating concrete – ± 55°C.
3. Maximum current – ​​16 A.
4. The cross-section is 0.6-3 mm, which allows you to bend the wire in any direction and use complex laying patterns. You can use a special calculator to calculate the wire cross-section.
5. Wire consumption for heating 1 m3 of concrete solution is 50-55 m.

Operating principle and types of wires

The description of the operating features of conductors of this type is that they are connected to the electrical network through step-down transformers. The wires are laid in the thickness of the concrete mass and, heating up with the passage of current, maintain the required temperature regime. Laying occurs at the reinforcement stage. The cables are attached to the fitting sections.

Laying the wire together with reinforcement

Important! The concrete solution hardens completely in 26-28 days. In the cold season at sub-zero temperatures, the water included in the solution freezes

Hardening of the concrete mixture slows down. When temperatures change (as they rise), the ice melts again. There is no need to talk about the quality of concrete.

PNSV cable and similar products can help get rid of the problem and maintain the temperature of the solution within acceptable limits. The use of this technology makes it possible to reduce the setting and hardening time of concrete by 5-6 times. In this case, the structure of the solution does not change, the concrete does not crack or swell.

Types of heating wires used for heating concrete compositions:

• CDBS;
• VET;
• PNSV.

A cable that has two cores and is used for sectional concrete is KDBS. The advantage of this model is its direct connection to 220 V. There is no need to use a step-down transformer. Laying is carried out according to the required pattern, without cutting, using couplings.

Attention! Dismantling the KDBS after the concrete has hardened is impossible; it itself costs from 60 to 280 rubles per linear meter. Heating cable KDBS

Heating cable KDBS

VET is a Finnish cable with two cores, which similarly allows you to connect yourself to a 220 V network using a special plug and does not require transformation of the supply voltage. Used at temperatures up to -250C. Conductor consumption – 5 l.m. (linear meters) per 1 cubic meter of heated volume, but not less than one kilowatt per 1 m3.

For your information. The price of BET ranges from 76 to 530 rubles per linear meter. It is worth considering that the shorter the product length, the higher the cost.

PNSV is a single-core wire. It can be used several times. When connecting, if the total length of the conductor does not withstand the supply voltage of 220 V, it is necessary to use a step-down transformer.

Recommendations for use

Sections 40 KDBS are economically and technologically feasible to use in the following typical areas:

• pouring a large number of small-sized monolithic structures and elements;
• critical fillings that require uniform heating of the reinforcement grids without boiling or burning out;
• production of columns, walls, etc. without the involvement of specialized teams for the monolith;
• using a vibrator;
• supplying concrete mixture from a mixer;
• urgent large-scale work in which it is impossible to regulate the heating power;
• the need for a large number of heating stations at the same time.

Read with this

• Cable current cross-section
• Warming up concrete in winter: goals, common methods and pouring without heating
• Using PVC wire according to the characteristics and description
• Pugnp and punp wires: characteristics, differences, prohibition of use
• Wire cross-section for home wiring: how to calculate correctly
• Technical parameters and scope of application of heat-resistant wire RKGM
• Which cable to choose for installation outdoors (over the air and in the ground)
• Wire pv-1: description and characteristics
• Which wire is better: single-core or stranded
• Wiring diagram and installation of electrical wiring in the kitchen

Delivery

Delivery to your door

We deliver goods by partner vehicles throughout Rostov-on-Don and the Rostov region. The cost of delivery within the city is from 500 rubles. up to 1500 rub.

In the Rostov region, we offer delivery by partner transport and transport companies. The price of delivery within the region is calculated depending on the remoteness of the settlement and the parameters of the cargo. Indicate your delivery address in your order or call us and we will help you calculate the cost.

Calculators for independently calculating shipping costs:

Delivery costs are calculated depending on the weight and dimensions of the cargo. These parameters are indicated in the technical specifications of the product.