RO119960B1 - Process for obtaining controlled atmosphere, for thermochemical treatment - Google Patents

Abstract

The invention relates to a process for obtaining a controlled atmosphere, for thermochemical treatments, directly inside the furnace, from a mixture of carbon dioxide with pit gas, propane or ammonia, in a proportion determined depending on the thermochemical treatment, performed so that the obtained thermochemical treatment atmosphere should contain 49-50% CO, by using pit gas and 58-59% CO, by using propane, in the case of carburizing at 900-950 C and hardening by quencing, at 850 C and -1.5-2.5%C, respectively, in the case of oxynitrocarburizing at 540-580 C.

Description

The invention relates to a process for producing the directly controlled atmosphere, for thermochemical treatments directly in the furnace, from gas mixtures (methane gas, carbon dioxide, ammonia, nitrogen) depending on the type of technological process.

At present, in general, the controlled atmosphere, used to carry out the thermochemical and thermal treatments is composed of the support gas produced in the generator, of methane gas or organic liquids (exogas, endogas) and the gas for enrichment in the furnace, this classic process presenting the disadvantage of a consumption high energy and methane gas, at the generator, consumption of special materials (catalyst, refractory materials, etc.) and increased energy and technological gas consumption, due to the long duration of technological process, with increased risks of explosion, fire and pollution.

The classical atmosphere of thermochemical treatment, currently known, based on endogas and methane or propane gas, has a carbon oxide content of about 22 ... 23% and 33% for the atmosphere obtained from organic liquids.

It is known a process for obtaining a controlled atmosphere by thermochemical treatment, composed of 50 ... 61.5% CO and 38.5 ... 50% H ₂ or 47 ... 59.7% CO, 37.3 ... 47% H ₂ and

3 ... 6% NH ₃ , which, in order to obtain carbon monoxide and hydrogen, decomposes hydrocarbons saturated with 1 ... 4 carbon atoms in the molecule, using as a reducing agent carbon dioxide, in the presence of a catalyst from nickel heated to 1123 ... 1373 ° K (ES 2019030).

This process has the disadvantage of using a nickel catalyst.

The process according to the invention for obtaining the controlled atmosphere for thermochemical treatments eliminates this disadvantage, in that it performs in the furnace the controlled atmosphere of methane or propane gas and carbon dioxide, from which a gas with a high oxide content can be obtained. carbon, 48 ... 58%, at elevated temperatures (9OO ... 95 ° C), used for accelerated carburization and heating, and carbon dioxide mixed with ammonia gives an oxy-nitrocarbon atmosphere. at temperatures of 540., 575'C.

The advantages of the process according to the invention are:

- shortening the duration of technological processes by 30 ... 60% compared to the carburizing or nitriding processes commonly applied in industry;

- reducing the duration of the technological process; reducing energy and technological gas consumption, protecting the working environment and the environment, increasing the operating life of the furnaces;

- the rapid obtaining, directly in the oven, of the controlled atmosphere necessary for the technological process without generator, so without additional energy supply, without additional consumption of special materials (catalyst, refractory steel, refractory bricks, etc.);

- the gases necessary for the technological process are easily used, from the cylinders (propane, ammonia, carbon dioxide, nitrogen) or from the network (methane gas);

- allows a wide range of thermochemical and thermal treatments to be carried out, in a controlled atmosphere: carburizing, carbonitriding, oxynitrocarbon, nitriding, respectively normalization, heating, recovery.

The invention is presented in detail below, in connection with the figure showing the scheme of the installation of the process according to the invention.

By the process according to the invention, the controlled atmosphere of the thermochemical treatment is obtained directly in the furnace, from gaseous mixtures of carbon dioxide and methane (or propane) or ammonia (or nitrogen) gas, for the thermochemical treatments of carbide, carbonitration, oxinitrocarbon, nitration, as well. and for normalization or recovery heat treatments. --2

RO 119960 Β1

With the aid of the installation shown schematically in the figure, the technological gases are distributed 1 from a gas cabinet 1, to the furnace 2, provided with two retorts A, B, where various compositions of controlled atmospheres can be formed, for the application of a wide range of processes. 3 logic techniques, such as:

- efficient carburetor, with short duration (3 ... 4 h, for 1 mm depth of carburetor layer), 5 in atmosphere obtained directly in the furnace of methane gas and carbon dioxide - mixture resulting in a high fuel gas composition, which contains 48 ... 49% CO, for a carbon potential 7: C _pot = 0.9 ... 1.1;

- efficient, short-lasting carburetor, in the atmosphere obtained directly in the furnace, from propane 9 and carbon dioxide - mixture resulting in a high fuel gas composition, containing 57 ... 59% CO, for C _pol . = 0.9 ... 1.1; 11

- carbonitriding at 880 ° C, in an atmosphere obtained directly in the furnace, from methane or propane gas, carbon dioxide and ammonia, from which a gas with a gaseous composition of 47 ... 51% CO, 1 is obtained ... 1.5% CO ₂ , in rest-H ₂ ;

- oxinitrocarbon at temperatures of 540 ... 580Ό, with a short duration (4 ... 6 h), in atmosphere15 obtained directly in the furnace, of ammonia and carbon dioxide, a mixture of which results in a gaseous composition with: 1.5. ..3.0% CO, 2.0 ... 3.0% CO ₂ , 18 ... 24% H ₂ , 3 ... 5% H ₂ 0.0.5 ... 2.0% CH ₄ , at rest -17

NH ₃ ;

- tempering in a controlled atmosphere, obtained directly in the furnace, from methane or propane gas and 19 carbon dioxide, of which a gas composition with:

49 ... 58% CO, 2.0 ... 4.0% CO ₂ , 34 ... 43% H ₂ ; 2.8 ... 3.2% H ₂ O; 0.1 ... 0.3% CH ₄ , for C _pot . = 21

0.5 ... 1.0;

The installation for applying the process, for performing these treatments, consists of 23 of a gas cabinet 1, an oven 2 provided with a thermocouple 3, two retorts A and B, in the lid of which is mounted a fan 4 and the supply system. with technological gases (25 methane gas, propane, carbon dioxide, nitrogen), provided with a sense valve 5, the ammonia entrance taking place separately through the side of the retort, under its lid. The installation also has a system of exhaust and combustion of waste gas 6, the measurement and regulation of the gaseous composition obtained in the retort of the furnace being done by means of an oxygen probe 7 or with 29 gas analyzers (CO ₂ , H ₂ O) via an additional gas analysis route 8, the measurement information is taken over by a programmable automatic and a carbon potential regulator. 31

The development of the technological process, the operation of the installation and the regulation of the gaseous composition obtained in the furnace can be automated through an electrical installation provided 33 with a programmable automatic.

For supplying the furnace with the technological gases in automatic working regime, 35 are provided some electric valves 9, and for manual operation, there are provided some taps 10, the gas flows being measured with some flowmeters 11. 37

On the supply route with carbon dioxide, to prevent the formation of carbon snow, the system 12 is provided for heating and maintaining a constant temperature of 35 ... 40 ° C. 39

The following are examples of embodiments of the process according to the invention.

1. For the hardening by carburation in a controlled atmosphere with a high percentage of CO 41 (49 ... 59%), obtained directly in the furnace, from the mixture of methane or propane gas and carbon dioxide, the following procedure is carried out: at a minimum temperature 750 ° C, through the installation 43 feed carburetor retort A, of furnace 2, with methane or propane gas and carbon dioxide, resulting, at carburetor temperature (900 ... 950 ° C), in the furnace retort, a 45 high carbon dioxide gaseous composition (according to table 1), which provides strong fuel effect on the metal undergoing the process, which results in obtaining the desired depth 47 of carbide layer, in a short time. Based on the composition of the gas in the furnace retort (table 1),

RO 119960 Β1 oxygen probe 7 transmits the information to an existing carbon potential regulator on the international market and will order the shut-off or opening of the methane or carbon dioxide gas valves, depending on the value of the regulated potential.

Using the method proposed in the invention, the depth of a carburetor layer of about 1 mm can be obtained for 3 ... 4 h, at 900 ° C, as opposed to the conventional carburetor with methane endogas, at which the layer depth is obtained. 1 mm, in 6 ... 7 h, so the carburetor life can be reduced by 30 ... 60%, depending on the steel, the working temperature and the type of oven.

Table 1

Highly fuel gaseous compositions, with high% carbon oxide

Gases used Τ ', c % CO ₂ % CO ₂ % CH ₄ % H ₂ (PR.'C) O ₂ (mV) cp ch ₄ / co ₂ 900 ... 950Ό 49 ... 50 0.7 ... 0.5 0.5 ... 0.2 48 ... 48.5 +5 ... + 2 1110 ... 1095 0.85 1.1 ... C ₃ H ₈ / CO ₂ 900 ... 950 ° C 58 ... 59 1.1 ... 0.9 0.25 ... 0.1 38 7 ... + 6

2. For the hardening by hardening in a controlled atmosphere obtained directly in the furnace, from gaseous mixtures of CH ₄ / CO ₂ or C ₃ H ₈ / CO ₂ , as for example with the atmospheres presented in table 2, proceed as in example 1, being different only the proportion of gas entering the furnace, depending on the desired value for the carbon potential (C _pot ).

Table 2

Gaseous compositions used as protective atmospheres for tempering

Gases used R.C % co ₂ % CO ₂ % ch ₄ % h ₂ (PR.'C) θ2 (mV) C _P CH ₄ / CO ₂ 850 ° C 49.5 2.75 0.55 44.5 23 1060 0.6 C ₃ H ₈ / CO ₂ 850 ° C 58.5 3.8 0.2 35 21 1095

The gaseous compositions, presented as an example in table 2, have the advantage that they are obtained directly in the furnace, during the heating process, in order to austenitize, the metal parts, being possible to produce different compositions characterized by different carbon potentials.

3. For oxinitrocarbon hardening, in an atmosphere obtained from ammonia and carbon dioxide, directly in the oven, at the treatment temperature (55O ... 6OO ° C), with a gaseous composition within the limits shown in the example in table 3, retort B, which is mounted in the furnace 2 and is supplied with ammonia and carbon dioxide through the installation shown in the figure, using the ammonia and carbon dioxide feed routes, to form a gaseous composition similar to the one presented in table 3, which provides obtaining a nitrocarbon layer in a short maintenance time (generally 4 ... 6 h), depending on the type of steel subjected to the hardening process and the characteristics of the obtained layer.

Table 3

Gaseous compositions used for nitrocarbons, obtained from ammonia and carbon dioxide

T'.C Gases used Oven composition,% Dissociation degree% CO CO ₂ ch ₄ h ₂ ^ 20 (PR'c) n ₂ nh ₃ 570 N H / CO ;, 1.5 ... 2.5 2 ... 3 0.6 ... 2.0 18 .... 24 +28 ... + 35 6 ... 8 change 35 ... 40

RO 119960 Β1

For example, in order to obtain a 0.25 mm layer for 42MoCr 11 steel, the duration of the process 1 can be 3 ... 4 h, in the case of oxinitrocarbon in an atmosphere of ammonia and carbon dioxide, compared with the duration of 30. .40 h, required in the case of classical nitriding in ammonia, which 3 can also be achieved with the installation in the figure, using the ammonia route.

The regulation of the process takes place based on the measurement of the gas flows with the flowmeters 11 and 5, the measurement of the dissociation degree resulted in the retort of the furnace at the process temperature, with a classical dissociometer, mounted on the gas analysis path 8, modifying the value of the ammonia flow rate of 7 for the classification. value in the range 30 ... 40%, depending on the temperature of the process, the type of steel and the requirements of the parts. 9 depending on the practical needs, the installation allows the use of nitrogen in the furnace, for heating, normalization, return to the protective atmosphere, using the nitrogen route from the installation. 11

The nitrogen path in the plant can be used as a technological gas or as a purge gas, in case of damage, to prevent fires or explosions, the nitrogen electric fan 9 being 13 of the ND type (normally open), the air path being necessary for the well operation. oxygen.

Claims (1)

15 Claim Process for obtaining the controlled atmosphere, for thermochemical treatments directly in the furnace, from a mixture of carbon dioxide with a hydrocarbon or ammonia gas, characterized in that it is used as hydrocarbon gas, the methane or propane gas, in proportion determined according to the treatment. made thermochemically, so that the atmosphere of thermo-21 chemical treatment obtained contains 49 ... 50% CO, by the use of methane gas, and 58 ... 59% CO, by the use of propane, in the case of carburization at 900 .. .950 * 0 and of the hardening by tempering at 850 ° C and, 23 respectively -1.5 ... 2.5% C, in the case of oxinitrocarbon at 54O ... 58O ° C.