Very often, if you want to make or repair heater do-it-yourself electric furnaces, a person has many questions. For example, what diameter to take the wire, what should be its length, or what power can be obtained using a wire or tape with given parameters, etc. With the right approach to solving this issue, it is necessary to take into account quite a lot of parameters, for example, the strength of the current passing through heater, operating temperature, type electrical network and others.

This article provides reference data on the materials most common in the manufacture of heaters. electric ovens, as well as the methodology and examples of their calculation (calculation of heaters for electric furnaces).

Heaters. Materials for the manufacture of heaters

Directly heater- one of the most important elements of the furnace, it is he who performs heating, has the highest temperature and determines the performance of the heating installation as a whole. Therefore, heaters must meet a number of requirements, which are listed below.

Requirements for heaters

Basic requirements for heaters (heater materials):

Heaters must have sufficient heat resistance (scaling resistance) and heat resistance. Heat resistance - mechanical strength at high temperatures. Heat resistance - resistance of metals and alloys to gas corrosion at high temperatures (the properties of heat resistance and heat resistance are described in more detail on the page).
Heater in an electric furnace must be made of a material with high electrical resistivity. talking plain language the higher electrical resistance material, the more it heats up. Therefore, if you take a material with less resistance, then you need a heater of greater length and with a smaller cross-sectional area. Not always a sufficiently long heater can be placed in the furnace. It should also be taken into account that the larger the diameter of the wire from which the heater is made, the longer term his service . Examples of materials with high electrical resistance are chromium-nickel alloy, iron-chromium-aluminum alloy, which are precision alloys with high electrical resistance.
A low temperature coefficient of resistance is an essential factor when choosing a material for a heater. This means that when the temperature changes, the electrical resistance of the material heater doesn't change much. If the temperature coefficient of electrical resistance is large, to turn on the furnace in a cold state, it is necessary to use transformers that initially give a reduced voltage.
The physical properties of the heater materials must be constant. Some materials, such as carborundum, which is a non-metallic heater, can change their properties over time. physical properties, in particular electrical resistance, which complicates the conditions of their operation. To stabilize the electrical resistance, transformers with a large number of steps and a voltage range are used.
Metallic materials must have good technological properties, namely ductility and weldability, so that they can be made into wire, tape, and from the tape - heating elements of complex configuration. Also heaters can be made from non-metals. Non-metallic heaters are pressed or molded into a finished product.

Materials for the manufacture of heaters

The most suitable and most used in the production of heaters for electric furnaces are precision alloys with high electrical resistance. These include alloys based on chromium and nickel ( chromium-nickel), iron, chromium and aluminum ( iron-chromium-aluminum). The grades and properties of these alloys are discussed in “Precision alloys. Marks». Representatives of chromium-nickel alloys are grades Kh20N80, Kh20N80-N (950-1200 °С), Kh15N60, Kh15N60-N (900-1125 °С), iron-chromium-aluminum - grades Kh23Yu5T (950-1400 °С), Kh27Yu5T (950-1350 °С ), X23Yu5 (950-1200 °C), X15Yu5 (750-1000 °C). There are also iron-chromium-nickel alloys - Kh15N60Yu3, Kh27N70YuZ.

The alloys listed above have good heat resistance and heat resistance properties, so they can work at high temperatures. good heat resistance provides a protective film of chromium oxide, which forms on the surface of the material. The melting temperature of the film is higher than the melting temperature of the alloy itself; it does not crack when heated and cooled.

Let us give a comparative description of nichrome and fechral.
Advantages of nichrome:

good mechanical properties at both low and high temperatures;
the alloy is creep-resistant;
has good technological properties– plasticity and weldability;
well processed;
does not age, non-magnetic.

Disadvantages of nichrome:

high cost of nickel - one of the main components of the alloy;
lower operating temperatures compared to Fechral.

Advantages of fechral:

cheaper alloy compared to nichrome, tk. does not contain ;
has better heat resistance than nichrome, for example, Fechral X23Yu5T can operate at temperatures up to 1400 ° C (1400 ° C is the maximum operating temperature for a heater made of wire Ø 6.0 mm or more; Ø 3.0 - 1350 ° C; Ø 1.0 - 1225 °С; Ø 0.2 - 950 °С).

Fechral Disadvantages:

brittle and fragile alloy, these negative properties are especially pronounced after the alloy has been at a temperature of more than 1000 ° C;
because fechral has iron in its composition, then this alloy is magnetic and can rust in a humid atmosphere at normal temperatures;
has low creep resistance;
interacts with fireclay lining and iron oxides;
Fechral heaters elongate significantly during operation.

Also comparison of alloys fechral and nichrome produced in the article.

Recently, alloys of the Kh15N60Yu3 and Kh27N70YuZ types have been developed; with the addition of 3% aluminum, which significantly improved the heat resistance of alloys, and the presence of nickel virtually eliminated the disadvantages of iron-chromium-aluminum alloys. Alloys Kh15N60YuZ, Kh27N60YUZ do not interact with chamotte and iron oxides, they are quite well processed, mechanically strong, not brittle. The maximum operating temperature of the X15N60YUZ alloy is 1200 °C.

In addition to the alloys listed above based on nickel, chromium, iron, aluminum, other materials are also used for the manufacture of heaters: refractory metals, as well as non-metals.

Among non-metals for the manufacture of heaters, carborundum, molybdenum disilicide, coal, and graphite are used. Carborundum and molybdenum disilicide heaters are used in high-temperature furnaces. In furnaces with a protective atmosphere, carbon and graphite heaters are used.

Among refractory materials, tantalum and niobium can be used as heaters. In high temperature vacuum and protective atmosphere furnaces, molybdenum heaters and tungsten. Molybdenum heaters can operate up to a temperature of 1700 °C in vacuum and up to 2200 °C in a protective atmosphere. This temperature difference is due to the evaporation of molybdenum at temperatures above 1700 °C in vacuum. Tungsten heaters can operate up to 3000 °C. In special cases, tantalum and niobium heaters are used.

Calculation of heaters of electric furnaces

Usually, the initial data for are the power that the heaters must provide, the maximum temperature required for the implementation of the corresponding technological process (tempering, hardening, sintering, etc.) and the size of the working space of the electric furnace. If the furnace power is not set, then it can be determined by the rule of thumb. During the calculation of heaters, it is required to obtain the diameter and length (for wire) or cross-sectional area and length (for tape), which are necessary for manufacture of heaters.

It is also necessary to determine the material from which to make heaters(this item is not considered in the article). In this article, chromium-nickel precision alloy with high electrical resistance is considered as a material for heaters, which is one of the most popular in the manufacture of heating elements.

Determining the diameter and length of the heater (nichrome wire) for a given furnace power (simple calculation)

Perhaps the simplest option heater calculation of nichrome is the choice of diameter and length at a given power of the heater, the supply voltage of the network, as well as the temperature that the heater will have. Despite the simplicity of the calculation, it has one feature, which we will pay attention to below.

An example of calculating the diameter and length of the heating element

Initial data:
Device power P = 800 W; mains voltage U = 220 V; heater temperature 800 °C. Nichrome wire X20H80 is used as a heating element.

1. First you need to determine the current strength that will pass through the heating element:
I=P/U \u003d 800 / 220 \u003d 3.63 A.

2. Now you need to find the resistance of the heater:
R=U/I = 220 / 3.63 = 61 ohms;

3. Based on the value obtained in paragraph 1 of the current passing through nichrome heater, you need to select the diameter of the wire. And this moment is important. If, for example, at a current strength of 6 A, a nichrome wire with a diameter of 0.4 mm is used, then it will burn out. Therefore, having calculated the current strength, it is necessary to select the appropriate value of the wire diameter from the table. In our case, for a current strength of 3.63 A and a heater temperature of 800 ° C, we select a nichrome wire with a diameter d = 0.35 mm and cross-sectional area S \u003d 0.096 mm 2.

General rule wire diameter selection can be formulated as follows: it is necessary to choose a wire whose permissible current strength is not less than the calculated current strength passing through the heater. In order to save the material of the heater, you should choose a wire with the nearest higher (than the calculated) allowable current.

Table 1

Permissible current passing through a nichrome wire heater, corresponding to certain heating temperatures of the wire suspended horizontally in calm air of normal temperature

Diameter, mm	Cross-sectional area of nichrome wire, mm 2	Heating temperature of nichrome wire, °C
		200	400	600	700	800	900	1000
		Maximum allowable current, A
5	19,6	52	83	105	124	146	173	206
4	12,6	37,0	60,0	80,0	93,0	110,0	129,0	151,0
3	7,07	22,3	37,5	54,5	64,0	77,0	88,0	102,0
2,5	4,91	16,6	27,5	40,0	46,6	57,5	66,5	73,0
2	3,14	11,7	19,6	28,7	33,8	39,5	47,0	51,0
1,8	2,54	10,0	16,9	24,9	29,0	33,1	39,0	43,2
1,6	2,01	8,6	14,4	21,0	24,5	28,0	32,9	36,0
1,5	1,77	7,9	13,2	19,2	22,4	25,7	30,0	33,0
1,4	1,54	7,25	12,0	17,4	20,0	23,3	27,0	30,0
1,3	1,33	6,6	10,9	15,6	17,8	21,0	24,4	27,0
1,2	1,13	6,0	9,8	14,0	15,8	18,7	21,6	24,3
1,1	0,95	5,4	8,7	12,4	13,9	16,5	19,1	21,5
1,0	0,785	4,85	7,7	10,8	12,1	14,3	16,8	19,2
0,9	0,636	4,25	6,7	9,35	10,45	12,3	14,5	16,5
0,8	0,503	3,7	5,7	8,15	9,15	10,8	12,3	14,0
0,75	0,442	3,4	5,3	7,55	8,4	9,95	11,25	12,85
0,7	0,385	3,1	4,8	6,95	7,8	9,1	10,3	11,8
0,65	0,342	2,82	4,4	6,3	7,15	8,25	9,3	10,75
0,6	0,283	2,52	4	5,7	6,5	7,5	8,5	9,7
0,55	0,238	2,25	3,55	5,1	5,8	6,75	7,6	8,7
0,5	0,196	2	3,15	4,5	5,2	5,9	6,75	7,7
0,45	0,159	1,74	2,75	3,9	4,45	5,2	5,85	6,75
0,4	0,126	1,5	2,34	3,3	3,85	4,4	5,0	5,7
0,35	0,096	1,27	1,95	2,76	3,3	3,75	4,15	4,75
0,3	0,085	1,05	1,63	2,27	2,7	3,05	3,4	3,85
0,25	0,049	0,84	1,33	1,83	2,15	2,4	2,7	3,1
0,2	0,0314	0,65	1,03	1,4	1,65	1,82	2,0	2,3
0,15	0,0177	0,46	0,74	0,99	1,15	1,28	1,4	1,62
0,1	0,00785	0,1	0,47	0,63	0,72	0,8	0,9	1,0

Note :

if the heaters are inside the heated liquid, then the load (permissible current) can be increased by 1.1 - 1.5 times;
when the heaters are closed (for example, in chamber electric furnaces), it is necessary to reduce the load by 1.2 - 1.5 times (a smaller coefficient is taken for a thicker wire, a larger one for a thin one).

4. Next, determine the length of the nichrome wire.
R = ρ l/S ,
where R - electrical resistance of the conductor (heater) [Ohm], ρ - electrical resistivity of the heater material [Ohm mm 2 / m], l - conductor (heater) length [mm], S - cross-sectional area of the conductor (heater) [mm 2 ].

Thus, we get the length of the heater:
l = R S / ρ \u003d 61 0.096 / 1.11 \u003d 5.3 m.

In this example, nichrome wire Ø 0.35 mm is used as a heater. In accordance with "Wire made of precision alloys with high electrical resistance. Specifications" nominal value electrical resistivity of nichrome wire brand X20N80 is 1.1 Ohm mm 2 / m ( ρ \u003d 1.1 Ohm mm 2 / m), see table. 2.

The result of the calculations is the required length of the nichrome wire, which is 5.3 m, diameter - 0.35 mm.

table 2

Determining the diameter and length of the heater (nichrome wire) for a given furnace (detailed calculation)

The calculation presented in this paragraph is more complex than the one above. Here we will take into account the additional parameters of the heaters, we will try to figure out the options for connecting heaters to the network three-phase current. Calculation of the heater will be carried out on the example of an electric furnace. Let the initial data be the internal dimensions of the furnace.

1. The first thing to do is to calculate the volume of the chamber inside the oven. In this case, let's take h = 490 mm, d = 350 mm and l = 350 mm (height, width and depth, respectively). Thus, we get the volume V = h d l \u003d 490 350 350 \u003d 60 10 6 mm 3 \u003d 60 l (a measure of volume).

2. Next, you need to determine the power that the furnace should give out. Power is measured in Watts (W) and is determined by rule of thumb: for an electric oven with a volume of 10 - 50 liters, the specific power is 100 W / l (Watts per liter of volume), with a volume of 100 - 500 liters - 50 - 70 W / l. Let us take the specific power of 100 W/l for the furnace under consideration. Thus, the power of the electric furnace heater should be P \u003d 100 60 \u003d 6000 W \u003d 6 kW.

It should be noted that with a power of 5-10 kW heaters are usually made in single phase. At high powers, for uniform loading of the network, the heaters are made three-phase.

3. Then you need to find the strength of the current passing through the heater I=P/U , where P - heater power, U - the voltage on the heater (between its ends), and the resistance of the heater R=U/I .

There may be two options for connecting to the electrical network:

to home network single-phase current- then U = 220 V;
to the industrial network of three-phase current - U = 220 V (between neutral wire and phase) or U = 380 V (between any two phases).

Further, the calculation will be carried out separately for single-phase and three-phase connections.

I=P/U \u003d 6000 / 220 \u003d 27.3 A - the current passing through the heater.
Then it is necessary to determine the resistance of the furnace heater.
R=U/I \u003d 220 / 27.3 \u003d 8.06 ohms.

Figure 1 Wire heater in a single-phase current network

The desired values of the wire diameter and its length will be determined in paragraph 5 of this paragraph.

With this type of connection, the load is distributed evenly over three phases, i.e. 6 / 3 = 2 kW per phase. So we need 3 heaters. Next, you need to choose the method of connecting the heaters (load) directly. There can be 2 ways: “STAR” or “TRIANGLE”.

It is worth noting that in this article the formulas for calculating the current strength ( I ) and resistance ( R ) for three-phase network written in a non-classical way. This is done in order not to complicate the presentation of the material on the calculation of heaters with electrical terms and definitions (for example, phase and line voltages and currents and relations between them). With a classic approach and calculation formulas three-phase circuits can be found in specialized literature. In this article, some mathematical transformations carried out on classical formulas are hidden from the reader, and this does not have any effect on the final result.

When connecting type “STAR” the heater is connected between phase and zero (see Fig. 2). Accordingly, the voltage at the ends of the heater will be U = 220 V.
I=P/U \u003d 2000 / 220 \u003d 9.10 A.
R=U/I = 220 / 9.10 = 24.2 ohms.

Figure 2 Wire heater in a three-phase current network. Connection according to the "STAR" scheme

When connecting type “TRIANGLE” the heater is connected between two phases (see fig. 3). Accordingly, the voltage at the ends of the heater will be U = 380 V.
The current passing through the heater is
I=P/U \u003d 2000 / 380 \u003d 5.26 A.
Resistance of one heater -
R=U/I \u003d 380 / 5.26 \u003d 72.2 ohms.

Figure 3 Wire heater in a three-phase current network. Connection according to the scheme "TRIANGLE"

4. After determining the resistance of the heater with an appropriate connection to the electrical network choose the diameter and length of the wire.

When determining the above parameters, it is necessary to analyze specific surface power of the heater, i.e. power dissipated per unit area. The surface power of the heater depends on the temperature of the heated material and on the design of the heaters.

Example
From the previous calculation points (see paragraph 3 of this paragraph), we know the resistance of the heater. For a 60 liter oven with single-phase connection it is R = 8.06 ohms. As an example, take a diameter of 1 mm. Then, in order to obtain the required resistance, it is necessary l = R / p \u003d 8.06 / 1.4 \u003d 5.7 m of nichrome wire, where ρ - the nominal value of the electrical resistance of 1 m of the wire in [Ohm / m]. The mass of this piece of nichrome wire will be m = l μ \u003d 5.7 0.007 \u003d 0.0399 kg \u003d 40 g, where μ - weight of 1 m of wire. Now it is necessary to determine the surface area of a piece of wire 5.7 m long. S = l π d \u003d 570 3.14 0.1 \u003d 179 cm 2, where l – wire length [cm], d – wire diameter [cm]. Thus, 6 kW should be allocated from an area of 179 cm 2. Solving a simple proportion, we get that power is released from 1 cm 2 β=P/S \u003d 6000 / 179 \u003d 33.5 W, where β - surface power of the heater.

The resulting surface power is too high. Heater will melt if it is heated to a temperature that would provide the obtained value of surface power. This temperature will be higher than the melting point of the heater material.

The above example is a demonstration of the wrong choice of wire diameter, which will be used to manufacture the heater. In paragraph 5 of this paragraph, an example will be given with the correct selection of the diameter.

For each material, depending on the required heating temperature, the permissible value of the surface power is determined. It can be determined using special tables or graphs. Tables are used in these calculations.

For high temperature furnaces(at a temperature of more than 700 - 800 ° C) the allowable surface power, W / m 2, is equal to β add \u003d β eff α , where β eff - surface power of heaters depending on the temperature of the heat-receiving medium [W / m 2 ], α is the radiation efficiency factor. β eff is selected according to table 3, α - according to table 4.

If a low temperature oven(temperature less than 200 - 300 ° C), then the allowable surface power can be considered equal to (4 - 6) · 10 4 W / m 2.

Table 3

Effective specific surface power of heaters depending on the temperature of the heat-receiving medium

Heat-receiving surface temperature, °C	β eff, W/cm 2 at heater temperature, °C
Heat-receiving surface temperature, °C	800	850	900	950	1000	1050	1100	1150	1200	1250	1300	1350
100	6,1	7,3	8,7	10,3	12,5	14,15	16,4	19,0	21,8	24,9	28,4	36,3
200	5,9	7,15	8,55	10,15	12,0	14,0	16,25	18,85	21,65	24,75	28,2	36,1
300	5,65	6,85	8,3	9,9	11,7	13,75	16,0	18,6	21,35	24,5	27,9	35,8
400	5,2	6,45	7,85	9,45	11,25	13,3	15,55	18,1	20,9	24,0	27,45	35,4
500	4,5	5,7	7,15	8,8	10,55	12,6	14,85	17,4	20,2	23,3	26,8	34,6
600	3,5	4,7	6,1	7,7	9,5	11,5	13,8	16,4	19,3	22,3	25,7	33,7
700	2	3,2	4,6	6,25	8,05	10,0	12,4	14,9	17,7	20,8	24,3	32,2
800	-	1,25	2,65	4,2	6,05	8,1	10,4	12,9	15,7	18,8	22,3	30,2
850	-	-	1,4	3,0	4,8	6,85	9,1	11,7	14,5	17,6	21,0	29,0
900	-	-	-	1,55	3,4	5,45	7,75	10,3	13	16,2	19,6	27,6
950	-	-	-	-	1,8	3,85	6,15	8,65	11,5	14,5	18,1	26,0
1000	-	-	-	-	-	2,05	4,3	6,85	9,7	12,75	16,25	24,2
1050	-	-	-	-	-	-	2,3	4,8	7,65	10,75	14,25	22,2
1100	-	-	-	-	-	-	-	2,55	5,35	8,5	12,0	19,8
1150	-	-	-	-	-	-	-	-	2,85	5,95	9,4	17,55
1200	-	-	-	-	-	-	-	-	-	3,15	6,55	14,55
1300	-	-	-	-	-	-	-	-	-	-	-	7,95

Table 4

Wire spirals, half-closed in the grooves of the lining

Wire spirals on shelves in tubes

Wire zigzag (rod) heaters

Let us assume that the temperature of the heater is 1000 °C, and we want to heat the workpiece to a temperature of 700 °C. Then, according to table 3, we select β eff \u003d 8.05 W / cm 2, α = 0,2, β add \u003d β eff α \u003d 8.05 0.2 \u003d 1.61 W / cm 2 \u003d 1.61 10 4 W / m 2.

5. After determining the permissible surface power of the heater, it is necessary find its diameter(for wire heaters) or width and thickness(for tape heaters), as well as length.

The wire diameter can be determined using the following formula: d - wire diameter, [m]; P - heater power, [W]; U - voltage at the ends of the heater, [V]; β add - allowable surface power of the heater, [W/m 2 ]; ρt - resistivity of the heater material at a given temperature, [Ohm m].
ρ t = ρ 20 k , where ρ 20 - electrical resistivity of the heater material at 20 °C, [Ohm m] k - correction factor for calculating the change in electrical resistance depending on temperature (by ).

The length of the wire can be determined by the following formula:
l - wire length, [m].

We select the diameter and length of the wire from nichrome Х20Н80. The specific electrical resistance of the heater material is
ρ t = ρ 20 k \u003d 1.13 10 -6 1.025 \u003d 1.15 10 -6 Ohm m.

Household single-phase current network
For a 60 liter stove connected to a household single-phase current network, it is known from the previous calculation steps that the power of the stove is P \u003d 6000 W, voltage at the ends of the heater - U = 220 V, permissible surface heater power β add \u003d 1.6 10 4 W / m 2. Then we get

The resulting size must be rounded up to the nearest larger standard. Standard sizes for nichrome and fechral wire can be found in. Appendix 2, Table 8. In this case, the nearest larger standard size is Ø 2.8 mm. Heater diameter d = 2.8 mm.

Heater length l = 43 m.

It is also sometimes required to determine the mass of the required amount of wire.
m = l μ , where m - mass of a piece of wire, [kg]; l - wire length, [m]; μ - specific gravity (mass of 1 meter of wire), [kg/m].

In our case, the mass of the heater m = l μ \u003d 43 0.052 \u003d 2.3 kg.

This calculation gives the minimum wire diameter at which it can be used as a heater under given conditions.. From the point of view of material savings, such a calculation is optimal. In this case, wire of a larger diameter can also be used, but then its quantity will increase.

Examination
Calculation results can be checked in the following way. A wire diameter of 2.8 mm was obtained. Then the length we need is
l = R / (ρ k) \u003d 8.06 / (0.179 1.025) \u003d 43 m, where l - wire length, [m]; R - heater resistance, [Ohm]; ρ - nominal value of electrical resistance of 1 m of wire, [Ohm/m]; k - correction factor for calculating the change in electrical resistance depending on temperature.
This value is the same as the value obtained from another calculation.

Now it is necessary to check whether the surface power of the heater we have chosen will not exceed the allowable surface power, which was found in step 4. β=P/S \u003d 6000 / (3.14 4300 0.28) \u003d 1.59 W / cm 2. Received value β \u003d 1.59 W / cm 2 does not exceed β add \u003d 1.6 W / cm 2.

Results
Thus, the heater will require 43 meters of X20H80 nichrome wire with a diameter of 2.8 mm, which is 2.3 kg.

Industrial three-phase current network
You can also find the diameter and length of the wire required for the manufacture of furnace heaters connected to a three-phase current network.

As described in point 3, each of the three heaters has 2 kW of power. Find the diameter, length and mass of one heater.

STAR connection(see fig. 2)

In this case, the nearest larger standard size is Ø 1.4 mm. Heater diameter d = 1.4 mm.

Length of one heater l = 30 m.
Weight of one heater m = l μ \u003d 30 0.013 \u003d 0.39 kg.

Examination
A wire diameter of 1.4 mm was obtained. Then the length we need is
l = R / (ρ k) \u003d 24.2 / (0.714 1.025) \u003d 33 m.

β=P/S \u003d 2000 / (3.14 3000 0.14) \u003d 1.52 W / cm 2, it does not exceed the permissible.

Results
For three heaters connected according to the “STAR” scheme, you will need
l \u003d 3 30 \u003d 90 m of wire, which is
m \u003d 3 0.39 \u003d 1.2 kg.

Connection type “TRIANGLE”(see fig. 3)

In this case, the nearest larger standard size is Ø 0.95 mm. Heater diameter d = 0.95 mm.

Length of one heater l = 43 m.
Weight of one heater m = l μ \u003d 43 0.006 \u003d 0.258 kg.

Examination
A wire diameter of 0.95 mm was obtained. Then the length we need is
l = R / (ρ k) \u003d 72.2 / (1.55 1.025) \u003d 45 m.

This value almost coincides with the value obtained as a result of another calculation.

Surface power will be β=P/S \u003d 2000 / (3.14 4300 0.095) \u003d 1.56 W / cm 2, it does not exceed the permissible.

Results
For three heaters connected according to the “TRIANGLE” scheme, you will need
l \u003d 3 43 \u003d 129 m of wire, which is
m \u003d 3 0.258 \u003d 0.8 kg.

If we compare the 2 options discussed above for connecting heaters to a three-phase current network, we can see that “STAR” requires a larger diameter wire than “TRIANGLE” (1.4 mm vs. 0.95 mm) in order to achieve a given furnace power of 6 kW. Wherein the required length of the nichrome wire when connected according to the “STAR” scheme is less than the length of the wire when connecting the “TRIANGLE” type(90 m vs. 129 m), and the required mass, on the contrary, is more (1.2 kg vs. 0.8 kg).

Spiral calculation

During operation, the main task is to place the heater of the calculated length in the limited space of the furnace. Nichrome and fechral wire are wound in the form of spirals or bent in the form of zigzags, the tape is bent in the form of zigzags, which allows you to fit more material (along the length) into working chamber. The most common option is the spiral.

The ratios between the pitch of the spiral and its diameter and the diameter of the wire are chosen in such a way as to facilitate the placement of the heaters in the furnace, ensure their sufficient rigidity, to the maximum extent possible exclude local overheating of the turns of the spiral itself and at the same time not hinder the heat transfer from them to the products.

The larger the diameter of the spiral and the smaller its pitch, the easier it is to place heaters in the furnace, but with an increase in diameter, the strength of the spiral decreases, and the tendency of its turns to lie on top of each other increases. On the other hand, with an increase in the frequency of winding, the shielding effect of the part of its turns facing the products on the rest increases and, consequently, the use of its surface deteriorates, and local overheating may also occur.

Practice has established well-defined, recommended ratios between the wire diameter ( d ), step ( t ) and the diameter of the spiral ( D ) for wire Ø 3 to 7 mm. These ratios are as follows: t ≥ 2d and D = (7÷10) d for nichrome and D = (4÷6) d - for less durable iron-chromium-aluminum alloys, such as fechral, etc. For thinner wires, the ratio D and d , as well as t usually take more.

Conclusion

The article discussed various aspects related to calculation of electric furnace heaters- materials, calculation examples with the necessary reference data, references to standards, illustrations.

In the examples, methods for calculating only wire heaters. In addition to wire from precision alloys, tape can also be used for the manufacture of heaters.

The calculation of heaters is not limited to the choice of their sizes. Also it is necessary to determine the material from which the heater should be made, the type of heater (wire or tape), the type of location of the heaters and other features. If the heater is made in the form of a spiral, then it is necessary to determine the number of turns and the pitch between them.

We hope that the article was useful to you. We allow its free distribution provided that the link to our website http://www.site is maintained.

If you find any inaccuracies, please let us know by e-mail [email protected] website or using the Orfus system by selecting the misspelled text and pressing Ctrl+Enter.

Bibliography

Dyakov V.I. "Typical calculations for electrical equipment".
Zhukov L.L., Plemyannikova I.M., Mironova M.N., Barkaya D.S., Shumkov Yu.V. "Alloys for heaters".
Sokunov B.A., Grobova L.S. "Electrothermal installations (electric resistance furnaces)".
Feldman I.A., Gutman M.B., Rubin G.K., Shadrich N.I. "Calculation and design of heaters for electric resistance furnaces".
http://www.horss.ru/h6.php?p=45
http://www.electromonter.info/advice/nichrom.html

Modern technology puts serious demands on the indicators of compliance of its composite materials with real working conditions. One of the high-tech alloys is nichrome. Wire and devices containing it are resistant to aggressive operating conditions.

Discovery history

The alloy is a compound of nickel and chromium, with variations in the addition of iron, manganese, aluminum, silicon.

Initially had two ways of origin. The roots lie in scientific research regarding and modification of their properties. Ni and Cr are components of high-quality corrosion-resistant and heat-resistant steels.

As a two-component alloy of nickel and chromium, it was discovered in 1906 in the USA. Today, its various modifications are used, including three-component ones based on iron.

Basic properties

The material for modern heating technology for domestic and industrial purposes is, of course, nichrome wire. Its properties correspond to the highest technological requirements.

Specific electrical resistance: within 1100-1400 Ohm * m.
The melting temperature is about 1400˚С, which allows it to function at 800-1100˚С. The maximum allowable value for work depends on the composition. So, the iron content reduces it to 850-900˚С, for a pure two-component it is 1100˚С.
Density: 8000-8500 kg/m 3 .
High strength (σ in =650-700 MPa); performance is maintained in an acidic aggressive environment and significant temperatures.
Good ductility together with exemplary hardness allows for rolling and drawing.

Distinctive characteristics

Among the most popular electrical products on the market is nichrome wire. of this component of electric heating technology is exceptionally high, which makes it possible to have a wide demand.

An important feature of the metal is its resistance to high-temperature oxidation under normal and aggressive conditions. Chromium plays a key role here. The element forms an appropriate oxide film on the surface, which performs a protective function. She is also responsible for the respective dark color material, which is replaced by a characteristic white-gray upon mechanical removal of the oxidized layer.

It is worth noting that direct contact with acids still destroys it, even more than corrosion-resistant tungsten.

The two-component alloy has no magnetic characteristics. They arise for its multicomponent modifications, however, they have weakened indicators.

Nichrome wire is rigid, does not lend itself to simple force influence.

We systematize information on how to identify nichrome wire, mainly how to distinguish it from outwardly similar materials:

White color of the new metal, dark - previously worked out.
Negative or minimal magnetism.
Rigidity.
Destruction under the action of acids, resistance to oxidation under the influence of high temperatures.

Brand nomenclature

Existing brands differ in composition, they represent an assortment of nichrome alloy. The wire has a wide use, which is determined by the individual properties of each.

Group 1 - resistor material: X20N80, X20N73YUM-VI, N80HYUD-VI, X15N60.
Group 2 - metal for heating elements for domestic and industrial purposes with increased heat resistance characteristics: Kh20N80-N-VI, Kh15N60-N, KhN70Yu-N, Kh20N80-N, KhN20YUS.
group 3 - for operation at temperatures up to 900˚С: Н50К10, Х25Н20.

In this case, the diameter of the nichrome wire of the first group is 0.009-0.4 mm, and for the second - 0.2-7.5 mm.

"Kindred" are kantals or fechrals - alloys of chromium, aluminum and iron. They are also characterized by high electrical resistance, resistance to heat in the range of 1250-1400 ° C, but less reliability, although low cost (Kh23Yu5, Kh13Yu4, Kh23Yu5T, Kh27Yu5T, Kh15Yu5).

Deciphering stamps

The properties and purpose of nichrome products are determined by their chemical composition. Let's consider the main ones.

Kh20N73YUM-VI: chromium - 20%, nickel - 73%, aluminum - 3%, molybdenum - 1.5%, manganese - up to 0.3%, titanium - up to 0.05%, iron - 2%, carbon - up to 0.05%; smelted using the vacuum induction method;
KhN70Yu-N: Cr - 27%, Ni - 70%, Al - 3%, Mn - up to 0.3%, Cs - up to 0.03%, Ba - up to 0.1%, Fe - up to 1.5% , C - up to 0.1%; designed for electric heating elements;
ХН20ЮС: Cr - 20%, Ni - 20%, Al - 1%, Zn - up to 0.2%, Ca - up to 0.1%, Si - 2.5%, Fe - 50%, C - up to 0, 08% - for industrial furnace heaters.

Product types

The choice of any alloy, which is characterized by high-quality technological and mechanical characteristics, must be justified and regulated. Especially when it comes to high cost. Nichrome wire is such a high-tech and expensive material. GOST 8803-89, 12766.1-90, 12766.3-90, 12766.4-90 defines the requirements, features of marking and application. In accordance with the standards and depending on the type, the metal is commercially available in the form of wire or strips, the choice of which depends on the diameter, section, length, and features of use.

The corresponding rental is the starting point for the industrial production of tape zigzags, wire spirals.

Technical specifications

When choosing products from nichrome, it is important to consider the following features:

nominal resistivity;
diameter, section and weight;
actual resistance and operating temperature limits depending on physical parameters.

The nominal values of the main parametric characteristic are determined by GOST and depend on the brand and composition.

The diameter of the nichrome wire determines its cross section, the weight of the coil and the corresponding objective resistance.

Thus, the weight of the wire (nichrome) per 100 meters of products is directly proportional to its dimensions, and the diameter and cross-sectional area are inversely proportional to the actual resistance.

The operating temperature depends not only on the chemical composition, but also on the parametric characteristics.

brand	Working temperature, ˚С
	product diameter, mm

The diameter of the wire produced by manufacturers is presented in the range of 0.05-12 mm, and the diameter of the tape - 0.15-3.2 mm.

Application

Quality always justifies the cost. The same applies to nichrome alloy. Wire and tape made from this material are widely used in areas where any other metal could not replace them. High oxidation resistance, high quality mechanical characteristics, including for aggressive environments, high-temperature working conditions - all this allows it to be used in various fields.

In industry:

Thermocouples of metallurgical electric heating furnaces.
Structural elements for induction metal-smelting equipment.
Industrial ventilation dryers.
Details of boilers and heat exchangers.
Electrical production: resistors and rheostats.
Some electrodes for welding.
Single-core and multi-core electrical wires.

It is the main structural element for all modern household appliances:

heating elements in electric kettles, boilers, boilers, heaters.
Heating elements in hair dryers, curling irons, irons.
Car candles and heating systems.
E-Sigs.

Perhaps the price is the only drawback of the nichrome material. Two-component nickel-chrome wire will be more expensive. The content of iron and the reduction in the amount of nickel, in turn, regulate a lower cost, but do not provide the same opportunities as X20H80. The choice depends on the technical needs.

When choosing products from nichrome, it is important to operate with information about the chemical composition of the brand of interest, its electrical conductivity and resistance, the physical characteristics of the diameter, cross section, and length. It is also important to be interested in documentation of compliance, as well as to be able to visually distinguish an alloy from its “competitors”. Properly selected material is the key to the reliability of equipment and technology for its use.

Physical properties

specific electrical resistance - 1.05 ÷ 1.3 Ohm mm² / m (depending on the grade of alloy)
density - 8200-8500 kg/m³
melting point - 1100-1400 °C
working temperature - 800-1100 °C
specific heat capacity - 0.45 kJ/(kg K) at 25 °C
tensile strength - 0.65-0.70 GPa

Application

Nichrome has high heat resistance in an oxidizing atmosphere (up to 1250 ° C), high electrical resistivity (1.05-1.4 Ohm mm² / m), and has a minimum temperature coefficient of electrical resistance. It has increased heat resistance, creep resistance, ductility, keeps its shape well. Nichrome is an expensive alloy, but given its durability and reliability, the price does not seem excessive.

Nichrome is widely used:

for the manufacture of heating elements in high-temperature electric furnaces, roasting and drying furnaces, various electrical devices of thermal action;
as a heat-resistant (heat-resistant) alloy and chemically resistant alloy in certain aggressive environments;
in parts operating at high temperature, resistor elements, rheostats;
as a sublayer and heat-resistant coating for thermal spraying.

The high plasticity of nichrome allows it to be subjected to welding, turning, drawing, stamping and other types of machining.

International names of nichromes

Nichrome H20H80- Cr 20%, Ni 80%. Resistivity - 650 Ohms/cmf , melting point - 1200 °C.

Analogues: NiCr80/20, Ni80Cr20, Chromel A, N8, Nikrothal 8, Resistohm 80, Cronix 80, Nichrome V, HAI-NiCr 80, euronichrome.

Nichrome Х15Н60- Ni 60%, Cr 16%, Fe 24%. Resistivity - 675 Ohms/cmf, melting point - 1390 °C.

Analogs: NiCr60/15, Ni60Cr15, Chromel C, N6, Nikrothal 6, Nikrothal 60, Cronifer II, Alloy C.

Alloy Х20Н80

Nichrome Kh20N80 - nichrome alloy of the following composition: (73-78%); (19-21%); (one %); (0.7%); the rest. Sometimes the alloy is alloyed with rare earth metals to achieve a longer life.

Nichrome Х20Н80, especially wire, are the most liquid assortment of nichrome. Nichrome tape and strip remain less sold than wire, but are more in demand than rods and sheets. It is generally accepted that the Kh20N80 brand contains about 20% chromium and 80% nickel, but this does not quite correspond to GOST, which allows microalloying of precision alloys to improve their consumer characteristics.

Notes

Links

Nichrome- article from the Great Soviet Encyclopedia (3rd edition)
GOST 10994-74. Precision alloys. Marks. Archived from the original on August 23, 2011. Retrieved September 7, 2009.. (see also GOST)
Maltsev I. M. Technology of tribological tape electrosintered powder materials // International scientific and technical journal. - 2003. - No. 1. - S. 60-66.
Pyatin Yu. M. and others. Materials in instrument making and automation. - 2nd ed. - "Engineering", 1982. - 528 p.
Kasatkin A. G. Basic processes and apparatuses of chemical technology . - 2nd ed. - M .: Editorial office of chemical literature, 1938. - S. 170-171.
Kudryavtsev I. V. Materials in mechanical engineering. Choice and application / Khimushkin F.F., Zhukov L.L. and others. - M .: "Engineering", 1968. - T. 3 (Special steels and alloys). - S. 304-319. - 448 p. - 30,000 copies.

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Synonyms:

See what "Nichrome" is in other dictionaries:

Nichrome ... Spelling Dictionary

- (from nickel and chromium) Ni alloys (base) with Cr (15-30%) alloyed with Si (up to 1.5%), Al (up to 3.5%), micro-additives of rare earth elements. In ferronichromes, part of Ni is replaced by Fe (over 20%). High heat resistance and electrical resistivity.… … Big encyclopedic Dictionary

Exist., number of synonyms: 2 alloy (252) ferronichrome (2) ASIS synonym dictionary. V.N. Trishin. 2013 ... Synonym dictionary

nichrome- — [Ya.N. Luginsky, M.S. Fezi Zhilinskaya, Yu.S. Kabirov. English Russian Dictionary of Electrical Engineering and Power Industry, Moscow, 1999] Electrical engineering topics, basic concepts of EN nichrome ... Technical Translator's Handbook

nichrome- an alloy of nickel and chromium ... Dictionary of abbreviations and abbreviations

Nichrome- - the general name for a group of heat-resistant alloys of nickel (65 80%) with chromium (in addition, silicon, aluminum, micro-additives of rare earth metals can be included in nichrome). Due to the combination of high heat resistance and electrical ... ... Encyclopedia of terms, definitions and explanations of building materials

NICHROME- chromium-nickel alloy containing 65-80% nickel, 15-30% chromium, sometimes with additives of silicon, aluminum; has high heat resistance and electrical resistivity. It is used for the manufacture of rheostats and various heating ... ... Great Polytechnic Encyclopedia

Nichrome- chromium-nickel alloy (65-80% Ni, 15-30% Cr, sometimes with additions of Si, Al and other elements), characterized by high heat resistance and electrical resistivity. They are used for the manufacture of heating elements in ... ... Encyclopedic Dictionary of Metallurgy

The general name for a group of heat-resistant alloys of nickel (65-80%) with chromium (15-30%). N. was first patented in 1905 by A. Marsh in the USA. AT different countries a large number of varieties of N. are produced, alloyed, as a rule, with Si (up to 1.5%), Al (up to 3.5%) ... Great Soviet Encyclopedia

BUT; m. An alloy of nickel and chromium, which has high heat resistance and electrical resistivity (used for the manufacture of heating elements). ◁ Nichrome, oh, oh. * * * Nichrome (from nickel and chromium), Ni alloys (base) with Cr (15 30%) ... encyclopedic Dictionary electronic book

Kh15N60 and Kh20N80 are the most commonly used chromium-nickel precision alloys. As already mentioned, they are distinguished by high electrical resistance. Nickel is the main metal in this alloy. There is a lot of it in nichrome - as much as 55-78 percent. He is almost as good as chromium, which in nichrome is 15-23 percent. In addition to nickel and chromium, nichrome also contains iron, titanium, phosphorus, aluminum, manganese, sulfur, carbon, and silicon.

The properties of nichrome are determined by nickel and chromium. Nickel has the ability to dissolve a variety of metals in itself, and at the same time remain very ductile. In liquid and gaseous media, it easily resists corrosion. As mentioned many times, it is resistant to high temperatures. Chromium is also heat-resistant, has hardness and high resistance to corrosion processes. So it turns out that chromium itself is endowed with all these positive qualities.

Resistance to elevated temperatures determines the impressive operating temperatures of nichrome. Nichrome belonging to the X20H80 brand can withstand up to 1200 degrees Celsius (here we also pay attention to the diameter of the wire), for nichrome belonging to the X15H60 brand - the maximum temperature is up to 1125 Celsius. The figures are given in accordance with GOST 12766.1-90. How much influence the percentage of nickel in the composition of the alloy, we conclude from this characteristic. The higher the percentage of nickel in nichrome, the greater the heat resistance of nichrome.

Another quality that makes nichrome a widely demanded metal is its high ductility. Plasticity can be attributed to technological features, which indicate what kind of processing the material can be subjected to without damage - this is either turning, or welding, gilding, stamping, and so on). Due to the excellent plasticity of nichrome, it is possible to manufacture products of this kind from it, such as, for example, nichrome tape or nichrome wire, and some other types of very thin wire. How is nichrome wire made? By drawing.

The most important physical features of nichrome include the presence of a small coefficient of electrical resistance and high electrical resistivity. These features, and even coupled with heat resistance, allow nichrome to be the material from which wires are made, as well as tapes for the production of various heating elements.

Nichrome X20H80 and nichrome X15H60 (, nichrome tape) are most often used in electrical engineering. This alloy is taken to create wire-wound resistors (and there are also tape resistors); rheostats in appliances, for heating; electric heaters, electric heating elements that function for a long time in air with temperatures up to 1250 degrees Celsius. And nichrome is also successfully used in the manufacture of electrothermal equipment, which must be very reliable. Nichrome X15H60 is also used in the production of non-precision resistors.

Nichrome is the general name for alloys whose two main components are chromium and nickel. The original version of the alloy contained 20% chromium and 80% nickel. Currently, there are 10 variants of this alloy, each of which has a different ratio of additional impurities - aluminum, titanium, silicon, molybdenum, iron or manganese.

The properties of nichrome directly depend on the proportions of the main and additional metals in the alloy. The most common nichrome product is wire, which is widely used in modern industry.

Nichrome wire: description and main characteristics

Nichrome wire is a metal cord that is produced in different lengths, thicknesses (from a fraction of a millimeter to several centimeters) and sections: round, oval, square or trapezoidal.

The most common type of cross section is round, since such a wire has the maximum ratio of the cross-sectional area to its perimeter. The weight of the product directly depends on the composition of its alloy and the diameter itself.

Nichrome has a rare combination of properties that make it simply an exceptional alloy, the only analogue of which, fechral, is much inferior to it in all respects.

The heat resistance of this material can reach up to 1400 degrees Celsius (two-component alloy). The maximum allowable exposure temperature depends on the composition of the alloy. Also, this wire does not change its shape under the influence of heat and does not sag.

Nichrome wire has high resistance electric current, which means that this metal will require significantly less than a similar one without loss in the amount of heat generated. Therefore, devices that use nichrome wire will have smaller dimensions and weight.

The two-component alloy has no magnetic properties. They occur only when iron is added, but have very weak performance.

Nichrome is not subject to corrosion, resistant to aggressive environments, due to which it has an almost unlimited service life. Nichrome wire has good ductility and excellent shape, while having high strength and hardness, is not afraid of mechanical stress.

The composition of the metal alloy varies the performance of these characteristics. The photo shows the main options for winding nichrome wire.

The use of nichrome wire

The use of nichrome wire is very extensive, due to its versatility. In industry, it is used to create laboratory equipment, resistance units, resistors, rheostats, various heating devices, electric furnaces and kilns for roasting and drying, in welding machines. Wire with a cross section of several centimeters can be used for the manufacture of automatic welding and even ropes.

There are elements of nichrome wire in many household items - toasters, hair dryers, heating systems for windows and rear-view mirrors in cars, household heaters, vapes and even shoe insoles.

Very often, this wire is also used for home-made equipment - cutters and electric jigsaws (for wood and foam), soldering irons and devices for burning wood, home forges.

The choice of nichrome wire

How to choose the wire you need specifically for your needs? For different purposes, items with different alloy compositions, diameters and cross sections are used, so here, first of all, it is necessary to focus on the marking of the wire.

Marking H indicates that this wire is used in the manufacture of heating elements not exceeding 0.2 mm in diameter.

Marking C indicates that this product is suitable for the production of resistance elements of various mechanisms.

The TEN marking indicates the applicability of this product for the production of tubular electric heaters.

The marking also indicates the operating temperatures that are maximum for a particular alloy and its resistivity.

Operating Temperatures/Resistivity:

Х20Н80 up to 1200 degrees Celsius — Х20Н80 — 1.12 Ohm*mm/m
Х15Н60 up to 1125 degrees Celsius — Х15Н60 — 1.13 Ohm*mm/m
KhN20YUS up to 1100 degrees Celsius - KhN20YUS - 1.02 Ohm*mm/m
KhN70Yu up to 1200 degrees Celsius - KhN70Yu - 1.30 Ohm*mm/m

Above in the text are indicators for wire with a thickness of more than 3 mm. The larger the wire diameter, the greater the value of these indicators.

Be sure to pay attention to the availability of technical documents from the manufacturer, on the basis of which this wire was made - GOST or TU. Only these documents can guarantee that you are purchasing a quality product, the characteristics of which will not be lower than those declared by the manufacturer.