WO2014173494A1

WO2014173494A1 - Method for regulating a thaw point temperature of a heat treatment oven

Info

Publication number: WO2014173494A1
Application number: PCT/EP2014/000892
Authority: WO
Inventors: Matthias Bors
Original assignee: Linde Aktiengesellschaft
Priority date: 2013-04-25
Filing date: 2014-04-03
Publication date: 2014-10-30
Also published as: EP2796570A1

Abstract

The present invention relates to a method for regulating a thaw point temperature of a heat treatment oven (100) for a heat treatment of workpieces (102), and to a heat treatment oven (100) for a heat treatment of workpieces (102), wherein nitrogen and air are supplied to the heat treatment oven (100) and an amount of supplied nitrogen based on an actual value for the thaw point temperature determined in the heat treatment oven (100) is determined in such a way that the actual value of the thaw point temperature is regulated toward a target value via the amount of supplied nitrogen determined.

Description

description

Method for controlling a dew point temperature of a heat treatment furnace

The invention relates to a method for controlling a dew point temperature of a heat treatment furnace for a heat treatment of workpieces, wherein the heat treatment furnace is operated with at least one fuel gas-oxygen burner, and a heat treatment furnace for a heat treatment of

Workpieces.

State of the art

In the heat treatment of workpieces, especially metals, certain material properties can be generated by exposing the workpieces to certain temperatures or temperature gradients. Methods of heat treatment, for example, the annealing, curing or tempering, with which the structure of a metal, so the arrangement of the crystallites contained, can be selectively influenced. Properties such as hardness, toughness, cold workability or microstructure homogeneity of the workpieces can be planned in this way. For example, the components of UHS steel (ultra-high-strength steel) can be austenitized in heat treatment plants and then molded in a press and simultaneously cooled and hardened. Components with a strength> 1450MPa can be manufactured in this way.

In such heat treatment plants usually an atmosphere of air is used because the workpieces are usually coated with zinc or AISi and thus have a protection against oxidation. However, in the past workpieces have been found in the form of cracking in the past. One possible cause of this damage can be an increased proportion of diffusible

Hydrogen in combination with the high strength and the high

Be the residual stress state of the workpieces, wherein the hydrogen is produced from the moist ambient air in the heat treatment furnace.

When burning fuel gas with oxygen, essentially H ₂ 0 and C0 _{2 are formed} . Being a fuel gas-oxygen burner in a heat treatment furnace used, produced during its operation significant amounts of water vapor, whereby the formation of hydrogen is promoted in the oven.

The object which now arises to those skilled in the art is to provide a way to prevent the formation of hydrogen in heat treatment furnaces and associated damage to workpieces manufactured in the heat treatment furnaces.

This object is achieved by an inventive method for controlling a dew point temperature of a heat treatment furnace for a heat treatment of workpieces and by a heat treatment furnace according to the invention for a heat treatment of workpieces according to the independent claims. In the course of a method according to the invention are the

Heat treatment furnace nitrogen and air supplied, whereby a nitrogen-air atmosphere is generated in the heat treatment furnace. The amount of nitrogen supplied is determined based on an actual value of the dew point temperature determined in the heat treatment furnace. The actual value of the dew point temperature is controlled by this specific amount of nitrogen supplied to a desired value. The target value of the dew point temperature is expediently chosen such that no or hardly formation of hydrogen can occur.

The invention is suitable for all types of heat treatment furnaces or heat treatment systems. In particular, the heat treatment furnace can be designed as a rotary drum furnace, a roller hearth furnace or a chamber furnace. Advantages of the invention

The invention is based on the recognition that an atmosphere of a

Heat treatment furnace made of nitrogen and air has particular advantages.

In particular, it has been recognized within the scope of the invention that said

Atmospheric composition has significant advantages over a pure nitrogen atmosphere. True, a pure nitrogen atmosphere in one

Heat treatment furnace formation of hydrogen and thus the uptake of

Preventing hydrogen into the workpieces and damage to the workpieces, however, a nitrogen atmosphere favors the formation of a fine silicon nitride layer on the fabricated workpieces, which in turn increased to an increased Wear of tools that are used to process the finished workpieces (for example, during the forming of heat-treated sheets).

The use according to the invention of a nitrogen-air atmosphere for regulating the dew point temperature of the heat treatment furnace prevents or at least reduces the formation of hydrogen in the heat treatment furnace and thus damage to finished workpieces. On the other hand, the reduced nitrogen content in the atmosphere of the heat treatment furnace reduces the reaction of nitrogen with the workpieces compared to the pure nitrogen atmosphere, thereby forming a silicon nitride layer on the workpieces and thus the associated increased wear of tools for machining the workpieces prevented or at least reduced.

By the inventive supply of the determined amount of nitrogen, the ratio of the nitrogen-air atmosphere in dependence on the actual value of the

Dew point temperature changed. Thus, eventually the dew point temperature is changed. For the purposes of the invention, the dew point temperature in the

Heat treatment furnace can be adjusted accordingly flexible and reliable. The use of a fuel gas oxygen burner for the heat treatment furnace significantly affects the dew point temperature in the heat treatment furnace.

In particular, in a discontinuous operation of the fuel gas-oxygen burner, the dew point temperature can change greatly within a short time. By the supply according to the invention of nitrogen and, if appropriate, of additional air, increases in the dew point temperature can be counteracted quickly and efficiently, and the dew point temperature can be regulated to the desired desired value.

The invention is furthermore particularly suitable as a measure for a so-called Flue Gas Management System for reducing exhaust-induced water fractions in heat treatment furnaces.

Advantageously, dried air is supplied to the heat treatment furnace. In this case, only the dried air or a mixture of (ambient) air and dried air can be supplied to the heat treatment furnace. By the reduced Proportion of water in dried air can further prevent the formation of hydrogen from the air in the heat treatment furnace.

The heat treatment furnace preferably has at least one chamber or zone. For example, chambers can be physically separated units of the heat treatment furnace. For example, zones can also be called

different areas are formed within a chamber, which have no fixed boundary to each other. In particular, different temperatures prevail in the different chambers or zones and in particular different process steps of the heat treatment of the

Off workpieces. Accordingly, different dewpoint temperatures can prevail in the different chambers or zones.

The regulation according to the invention of the dew point temperature is carried out for the at least one chamber or zone. Depending on the length and size of the

Heat treatment plant, the inventive scheme of

Dew point temperature can be performed over the entire heat treatment furnace as a zone or the heat treatment furnace can be divided into several zones, for each of which the inventive control of

Dew point temperature is carried out separately. In particular, the

The dew point temperature control according to the invention is carried out individually and independently of each other for each chamber or zone. The dew point temperature of each chamber or zone can be suitably regulated to a separate, individual desired value. The amount of nitrogen introduced is determined on the basis of the actual value of the dew-point temperature detected in the respective chamber or zone and on the basis of the individual desired value of the dew-point temperature determined for the respective chamber or zone.

Preferably, in addition to the amount of nitrogen, an amount of supplied air based on the determined in the heat treatment furnace actual value of

Dew point temperature is determined such that the actual value of the dew point temperature is controlled by the specific amount of nitrogen supplied and supplied air to the target value. The dew point temperature can thus be regulated even more flexible. Furthermore, thus, the ratio of the nitrogen-air mixture in the heat treatment furnace can be set more flexible and optionally on different workpiece materials are adjusted. Preferably, an upper limit of the dew point temperature is determined by the amount of air supplied / Alternatively or additionally, a lower limit of the dew point temperature is preferably determined by the amount of nitrogen supplied. The set target value is then within the range of lower and upper limit.

In a preferred embodiment of the invention, the dew point temperature to target values between -5 ° C and -60 ° C, in particular between -10 ° C and -40 ° C, regulated. The dew point temperature can be controlled by means of the method according to the invention on the one hand to target values less than a minimum possible dew point temperature for a pure air atmosphere of about -10 ° C. On the other hand, the dew point temperature can be controlled to target values greater than a dew point temperature for a pure nitrogen atmosphere of about -60 ° C.

Preferably, the amount of nitrogen at high speed is the

Heat treatment furnace supplied. Thereby, a homogeneous nitrogen-air atmosphere can be generated in the heat treatment furnace. The detection of the actual value of the dew point temperature and thus the analysis of the dew point temperature can thus be carried out more reliably and precisely. Furthermore, the dew point temperature in particular and the temperature of the

Heat treatment furnace generally be set homogeneously and without significant local variations. In particular, a Carbojet process is used to supply the amount of nitrogen. The Carbojet process and associated Carbojet nozzles or Carbojet lances are sold by the applicant. Small amounts of nitrogen are injected at high speeds of up to 250-300 m / s into individual areas of the heat treatment furnace. By means of the Carbojet process, the accuracy of analyzers as well as homogeneous gas and temperature distribution can be further improved. For a detailed description of a Carbojet method, reference is made by way of example to the document DE 10 2008 009 818 A1.

Preferably, the heat treatment furnace by means of at least one

premixing fuel gas-oxygen burner, in particular at least one Hydrogen-oxygen burner, operated. Premixing fuel gas oxygen burners are characterized by a particularly high heat transfer efficiency. A burner head of the premixing fuel gas oxygen burner while a gas mixture of fuel gas and oxygen is already supplied and not only generated in the corresponding burner head. Premixing burners produce particularly hard flames that are suitable for larger surface areas, too

Depressions or other irregularities may have melted. Corresponding burners are also known as so-called Hydropox burners and are sold under this brand name by the applicant. For a detailed description of the Hydropox burner, see for example the data sheet "HYDROPOX®. Optimal glass surface treatment with pre-mixing hydrogen / oxygen burners. "The applicant referenced.

The use of a premixing fuel gas oxygen burner for the

Heat treatment furnace affects the dew point temperature in the

Heat treatment furnace considerably. By means of the invention, the dew point temperature of a heat treatment furnace with premixing fuel gas-oxygen burner can be controlled simply and reliably. It should be noted that the invention is not limited to the use of premixing fuel gas-oxygen burners, but is also suitable for the use of, for example, external mixing burners. Alternatively or additionally, for example, the use of an oxyfuel burner is possible. In contrast to conventional combustion processes, an oxy-fuel burner does not use air, but rather an oxygen-rich gas, in particular (virtually) pure oxygen as oxidizer.

Advantageously, the workpieces are rapidly heated in the heat treatment furnace for the heat treatment. This procedure is known as "Rapid Heating". Since workpieces for a "rapid heating" process in a short time to very high

Temperatures are heated, in particular premixing fuel gas oxygen burner, in particular Hydropox burner, are suitable for a "rapid heating"

Method. The rapid heating significantly affects the dew point temperature within the heat treatment furnace. Therefore, the invention is particularly suitable for a "rapid heating" process. In the heat treatment furnace, locally different material properties are preferably produced by local heat treatment. This procedure is generally known as "tailored properties". For example, certain areas of a workpiece may be press-hardened, and other areas may be formed such that they have ductility and thus can absorb more energy by plastic deformation.

Possibilities for the production of "tailored properties", ie of such locally different properties, can be, for example, a targeted influencing of alloy components of corresponding semi-finished products, a production of so-called "tailored welded blanks", ie blanks which are made of different materials, partial (local) Heating by means of inductive or conductive heating technologies, a partial tempering of certain areas of the press hardening tools by local heating, a partial tempering of press-hardened components and / or masking of certain component areas

Warming (and thus austenitization) to suppress.

Thus, in different areas or zones of the

Heat treatment furnace in which the respective different properties of the workpieces are produced, different temperatures and different dew point temperatures prevail. By means of the method according to the invention, the dew point temperatures of the individual zones can be regulated in a particularly simple manner independently of each other.

In an advantageous embodiment of the invention, the heat treatment furnace is used for a region-wise austenitization. This procedure is commonly known as tailored austenitizing. Analogous to a "tailored properties" process, different zones of the heat treatment furnace can also have different temperatures and different temperatures in a "tailored austenitizing" process

Have dew point temperatures. Therefore, the method according to the invention is also particularly suitable for controlling the dew point temperatures in the course of a tailored austenitizing process. The invention further relates to a heat treatment furnace for a heat treatment of workpieces. Embodiments of the heat treatment furnace according to the invention will be apparent from the above description of the

Method according to the invention in an analogous manner and from the underlying embodiment, wherein the features shown there can also be used alone or in other combinations.

The invention and its advantages will now be explained with reference to the accompanying drawings. In this shows

Figure 1 schematically an embodiment of an inventive

Heat treatment furnace for a heat treatment of workpieces and Figure 2 schematically shows an embodiment of a method according to the invention as a block diagram.

A preferred embodiment of a heat treatment furnace according to the invention for a heat treatment of workpieces is shown schematically in FIG. 1 and designated by 100. The heat treatment furnace is in this example as a

Roller hearth furnace 100 formed.

On a plurality of rollers 103, workpieces 102 are transported through the roller hearth furnace 100 (from left to right in FIG. 1).

The roller hearth furnace 100 has two zones (101 a and 101 b), the

Heat treatment technology are separated from each other. In the two zones 101 a and 101 b, two different process steps of the heat treatment of the workpieces 102 take place. The zone 101 a has a premixing fuel gas oxygen burner 105 (shown only schematically). The premixing

Fuel gas oxygen burner 105 is in this example as premixing

Hydrogen-oxygen burner, in particular as a Hydropox burner trained. The Hydropox burner 105 generates in the zone 101 a a comparatively high

Temperature. When passing through the zone 101a, workpieces 102 are first heated to a high temperature in a short time, in particular according to a "Rapid The workpieces 102 then pass through the holding zone 101 b and are homogenized therein.

To prevent that in the zones 101 a and 101 b of humid

Ambient air forms hydrogen, which can be absorbed in the workpieces 102 and thus contributes to cracking in the workpieces 102 is the

Roller hearth furnace 100 adapted to an embodiment of a

to carry out inventive method, which is shown in Figure 2 schematically as a block diagram. In the course of this, the dew point temperature in each of the zones 101 a and 101 b is regulated separately from one another.

For this purpose, each of the zones 101a and 101b respectively comprise measuring instruments 110a and 110b, which are connected to a computing unit 120, in particular a control unit, for example a control cabinet, indicated by reference numeral 1 10. In method step 201, by means of Measuring instruments 1 10a and 1 10b each an actual value of the dew point temperature of the zones 101 a and 101 b determined.

Based on the determined actual values of the dew point temperature for the zones 101 a and 101 b, an amount of dried air and an amount of nitrogen are determined in the control unit 120 in step 202. Thus, a nitrogen-air mixture is determined, which forms the atmosphere of the respective zone 101 a and 101 b of the roller hearth furnace 100. Depending on the proportion of air or nitrogen content of the nitrogen-air mixture, the dew point temperature of the respective zone is changed. The amount of dried air and the amount of nitrogen are determined such that the actual value of the dew point temperature of the respective zones 101 a and 101 b is regulated to a predetermined desired value. The desired values for the two zones 101 a and 101 b may be the same or different.

The control unit 120 is connected to a gas control unit 130, indicated by reference numeral 125. The gas control unit leads the specific amount

Nitrogen and dried air to the zones 101 a and 101 b to. For that, the

Roller hearth furnace 100, a container for dried air 140 and a container for nitrogen 150, which are respectively connected via lines 141 and 151 to the gas control unit 130. The line 151 includes an evaporator 160. The gas control unit 130 is connected via lines 130a and 130b to the zones 101 a and 101 b and At step 203, the zones 101a and 101b, respectively, are supplied with the amount of dried air and nitrogen. The quantities of dried air and nitrogen can in each case be supplied via separate lines to the zones 101a or 101b or via one or more common lines per zone. If the amounts of nitrogen and dried air to the zones 101 a and 101 b fed via separate lines, the amounts of nitrogen can be supplied to the chambers 101 a and 101 b in particular via a high-speed Carbojet method.

Indicated by reference numeral 204, the process begins again at step 201 with determining the actual values of the dew point temperatures of the zones 101a and 101b of the roller hearth furnace 100. The dew point temperatures are thus continuously monitored and controlled in real time to the predetermined target values.

LIST OF REFERENCES

100 heat treatment furnace, roller hearth furnace

101a heating zone 1

101 b heating zone 2

102 workpieces

103 roles

105 premixing fuel gas oxygen burner, Hydropox burner

110 data connection

10a, 110b measuring instruments

120 arithmetic unit, control unit

125 data connection

130 gas control unit

130a, 130b gas lines

140 containers for dry air

150 containers for nitrogen

160 evaporators

141, 151 gas pipes

201 to 204 method steps

Claims

claims

1. A method for controlling a dew point temperature of a

A heat treatment furnace (100) for heat treating workpieces (102), wherein the heat treatment furnace (100) is operated with at least one fuel gas oxygen burner (105),

characterized in that

- Nitrogen and air are fed to the heat treatment furnace (100) and

an amount of supplied nitrogen based on one in the

Heat treatment furnace (100) determined actual value of the dew point temperature is determined (202) such that the actual value of the dew point temperature is controlled by the determined amount of nitrogen supplied to a desired value.

2. The method of claim 1, wherein the heat treatment furnace (100)

dried air is supplied.

3. The method according to claim 1 or 2, wherein the heat treatment furnace (100)

at least one chamber or zone (101 a, 101 b) and the control of the dew point temperature for the at least one chamber or zone (101 a, 101 b) is performed.

4. The method according to any one of the preceding claims, wherein in addition to the

Amount of nitrogen, an amount of supplied air based on the determined in the heat treatment furnace (100) actual value of the dew point temperature is determined (202) that the actual value of the dew point temperature by the specific amount of supplied nitrogen and supplied air to the target -

Value is regulated.

5. The method according to any one of the preceding claims, wherein an upper limit of the dew-point temperature is determined by the amount of supplied air.

6. The method according to any one of the preceding claims, wherein a lower limit of the dew-point temperature is determined by the amount of supplied nitrogen.

7. The method according to any one of the preceding claims, wherein the

Dew point temperature to target values between -5 ° C and -60 ° C, especially between -10 ° C and -40 ° C, is regulated.

8. The method according to any one of the preceding claims, wherein the amount of

Nitrogen is fed to the heat treatment furnace (100) at high speed.

9. The method according to any one of the preceding claims, wherein the

Heat treatment furnace (100) with at least one premixing fuel gas

Oxygen burner (105) is operated.

A method according to any one of the preceding claims, wherein the workpieces (102) are rapidly heated in the heat treatment furnace (100) for the heat treatment.

1 1. A method according to any one of the preceding claims, wherein in the

Heat treatment furnace (100) locally different properties of the

Heat treatment goods are generated.

12. The method according to any one of the preceding claims, wherein the

Heat treatment furnace (100) is used for a region-wise Austenitisierung.

13. A heat treatment furnace (100) for a heat treatment of workpieces (102), wherein the heat treatment furnace (100) has at least one fuel gas oxygen burner (105),

characterized in that

the heat treatment furnace (100) has means to

to supply air and nitrogen to the heat treatment furnace (130, 130a, 130b, 140, 141, 150, 151) and

- To control an actual dew point temperature of the heat treatment furnace by an amount of supplied nitrogen to a desired value (1 10a, 1 10b, 120, 130, 130a, 130b, 150, 151). A heat treatment furnace (100) according to claim 13, wherein said

Heat treatment furnace has at least one chamber or zone (101a, 101b) and means for regulating an actual dew point temperature of the at least one chamber or zone (101a, 101b) by an amount of supplied nitrogen to a desired value.

A heat treatment furnace (00) according to claim 13 or 14, wherein the

Heat treatment furnace (100) has at least one premixing fuel gas oxygen burner (105).