Method for heating a metal component to a target temperature and corresponding roller hearth furnace

Abstract

The method for heating a metal component to a target temperature, in which the component has a preliminary coating and is passed through a furnace that has at least four zones, which can be respectively adjusted to an individual zone temperature, wherein the component is passed successively through at least an initial heating zone, a plateau zone, a peak heating zone and an end zone and wherein the initial heating zone is adjusted to an initial heating temperature, the plateau zone is adjusted to a plateau temperature, the peak heating zone is adjusted to a peak temperature and the end zone is adjusted to the target temperature, the plateau temperature being chosen such that the temperature of the component in the plateau zone lies in a band around a melting temperature of the preliminary coating which is characterized in that the peak temperature lies by at least 100 K above the target temperature.

Claims

1. A method comprising heating a metal component to a target temperature, in which the component has a preliminary coating and is passed through a furnace that has at least four zones, which can be respectively adjusted to an individual zone temperature, wherein the component is passed successively through at least an initial heating zone, a plateau zone, a peak heating zone and an end zone and wherein the initial heating zone is adjusted to an initial heating temperature, the plateau zone is adjusted to a plateau temperature, the peak heating zone is adjusted to a peak temperature and the end zone is adjusted to the target temperature, the plateau temperature being chosen such that the temperature of the component in the plateau zone lies in a band around a melting temperature of the preliminary coating which is characterized in that the peak temperature lies at least 100 K above the target temperature, the method further comprising forming a first intermediate zone between the initial heating zone and the plateau zone, a first intermediate zone temperature of which lying between the initial heating temperature and the plateau temperature, and forming at least one second intermediate zone between the plateau zone and the peak heating zone, the at least one second intermediate zone having a second intermediate zone temperature, which is between the plateau temperature and the peak temperature.

2. The method of claim 1, wherein the preliminary coating is formed from a material comprising aluminum and silicon.

3. The method according to claim 2, wherein the component in the initial heating zone is passed over rollers which are made of quartz material.

4. The method according to claim 2, in which the component is passed over rollers which are formed from a ceramic material in at least one of the following zones: a) the plateau zone; b) the peak heating zone; and c) the end zone.

5. The method according to claim 1, wherein the component in the initial heating zone is passed over rollers which are made of quartz material.

6. The method according to claim 1, in which the component is passed over rollers which are formed from a ceramic material in at least one of the following zones: a) the plateau zone; b) the peak heating zone; and c) the end zone.

7. The method of claim 1 further comprising press hardening the metal component in a press hardening device, after the metal component has been heated to the target temperature.

8. The method according to claim 7, wherein the metal component between the heating and the press hardening is supplied to at least one temperature control unit in which the temperature of at least a portion of the metal component is changed.

9. A roller hearth furnace for heating a metal component having a preliminary coating to a target temperature in which the component can be passed on rollers from an access through the roller hearth furnace to an exit, further comprising at least four heating means through which an individual temperature in a zone around the heating means is adjustable, and a control means for individually controlling at least four of the heating means, wherein the control means is suitable and intended in a manner for controlling the heating means and is determined that at least the following zones can be formed from the access to the exit in this order: an initial heating zone which can be adjusted to an initial heating temperature, a first intermediate zone, a plateau zone which can be adjusted to a plateau temperature, a second intermediate zone, a heatable peak heating zone which can be adjusted to a peak temperature, and an end zone which can be adjusted to the target temperature, wherein the first intermediate zone is between the initial heating zone and the plateau zone and which can be adjusted to a first intermediate zone temperature which is between the initial heating temperature and the plateau temperature, wherein the second intermediate zone is between the plateau zone and the heatable peak heating zone and which can be adjusted to a second intermediate zone temperature which is between the plateau temperature and the peak temperature, the control means and the heating means being suitable for setting the plateau temperature to be in a band around a melting temperature of the preliminary coating and setting the peak temperature to be at least 100 K above the target temperature.

10. The roller hearth furnace according to claim 9, in which in the initial heating zone rollers made of quartz material are configured.

11. The roller hearth furnace according to claim 9, in which rollers are formed from a ceramic material in at least one of the following zones: a. the plateau zone; b. the peak heating zone; and c. the end zone.

12. The roller hearth furnace according to claim 9, in which shielding means are formed between at least two adjacent zones.

Description

(1) The invention and the technical environment will be explained in more detail with reference to the figures. It should be noted that the invention should not be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects from the facts explained in the figures and to combine them with other components and/or insights from other figures and/or from the present description. They show schematically:

(2) FIG. 1 a roller hearth furnace which is operated according to the inventive method;

(3) FIG. 2 a temperature control in the roller hearth furnace;

(4) FIG. 3 an example of a temperature control assumed to be known;

(5) FIG. 4 an example of a temperature control according to the present invention;

(6) FIG. 5 another example of a roller hearth furnace;

(7) FIG. 6 a first example of a device for the heat treatment of components; and

(8) FIG. 7 a second example of a device for the heat treatment of components.

(9) FIG. 1 schematically shows a roller hearth furnace 1, in which a method for heating a metal component 2 to a target temperature 3 is carried out. The corresponding temperatures are shown schematically in FIG. 2. For this purpose, the metal component 2 is passed through an access 4 into the roller hearth furnace 1. In the roller hearth furnace 1, the metal component 2 is passed over rollers 5 through the roller hearth furnace 1 to the exit 6.

(10) In the present case, the metal component 2 has an Al/Si preliminary coating 7, which is flat and formed mostly on both sides of the metal component 2. In the direction of movement 8 of the metal component 2, an initial heating zone 9, a plateau zone 10, a peak heating zone 11 and an end zone 12 adjoin the access 4. In operation, the initial heating zone 9 is adjusted to an initial heating temperature 13, the plateau zone 10 is adjusted to the plateau temperature 14, the peak heating zone 11 is adjusted to a peak temperature 15 and the end zone 12 is adjusted to the target temperature 3 (heated). For this purpose, heating means 16 are formed, which are designed here as jet pipes. The individual jet pipes each include gas burners that burn into a closed (ceramic) pipe, so that the combustion exhaust gases are not introduced into the furnace in order to prevent the hydrogen embrittlement of the metal, which may be promoted by the exhaust gases of the combustion, in particular of moist exhaust gas.

(11) The number and design of the individual heating means 16 are shown as examples. This means that in each zone 9, 10, 11, 12 a different number of heating means 16, each heating means 16 of different strengths and/or in each case different heating means 16, such as partially electric heating means 16 and partially jet pipes, can be designed as heating means 16. The same also applies to the rollers 5, which can be formed in different numbers and/or at different intervals and/or from different materials in each zone 9, 10, 11, 12. To carry out the method, the heating means 16 are connected to a control means 17, by means of which the operation of the heating means 16 can be controlled or regulated and which is suitable and intended for the corresponding activation of the heating means 16. In addition, at least individual (driven) rollers 5 can also be connected to the control means 17.

(12) Shielding means 27 are formed between zones 9, 10, 11, 12, which in particular reduce or prevent a longitudinal flow between adjacent zones 9, 10, 11, 12. As an alternative or in addition, the shielding means 27 can be designed in such a way that they reduce or prevent thermal radiation between adjacent zones 9, 10, 11, 12. The shielding means 27 are formed in the present example as internals reducing the open cross section of the roller hearth furnace 1, the height of which can vary.

(13) In the present example, the rollers 5 in the initial heating zone 9 are made of a quartz material, while the rollers in the plateau zone 10, the peak heating zone 11 and the end zone 12 are made of a ceramic material. The rollers 5 in the initial heating zone 9 are preferably made of quartz material in order to be able to absorb the thermal loads on the rollers 5 due to the large temperature difference between the (hot) rollers 5 and the (cold) metal component 2.

(14) The heating means 16 are regulated, for example, in such a way that, for a component made of a boron manganese steel marketed as “Usibor® 1500” or “MBW® 1500+AS” and which has an Al/Si preliminary coating 7, in the initial heating zone 9 as the initial heating temperature 13 a temperature of approximately 840 to 860° C., in particular of 850° C. is set, in the plateau zone 10 as plateau temperature 14 a temperature of approximately 630° C. to 670° C., in particular of 650° C. is set with a band of +/−20° C. around the melting temperature of the preliminary coating 7, in the peak heating zone 11 as the peak temperature a temperature of about 1080 to 1120° C., in particular 1100° C. is set, and in the end zone 12 as the target temperature 3 a temperature of 870 to 940° C. is set.

(15) FIG. 3 shows, in contrast, a temperature profile assumed to be known, in which the zone temperature 18 and the component temperature 19 are shown. Several zones are also formed here. The (cold) metal component 2 first crosses an initial heating zone with an initial heating zone temperature 13, then a plateau zone with a plateau temperature 14 and then an end zone with a target temperature 3. Accordingly, the component temperature 19 follows a curve from a start temperature to the target temperature 3.

(16) FIG. 4 shows an example of a temperature profile with zone temperature 18 and component temperature 19 according to the method proposed here. In addition to the initial heating zone temperature 13, plateau temperature 14 and target temperature 3, the zone temperature here also shows the peak heating zone 11. Comparing the component temperature 19 in this example with the component temperature 19 as shown in FIG. 3, the component temperature 19 reaches the target temperature 3 faster in the method proposed here than in the method assumed to be known, as shown in FIG. 3.

(17) FIGS. 4 and 5, which show a further embodiment of a roller hearth furnace 1, further show the formation of intermediate zones. A first intermediate zone 20 is formed between the initial heating zone 9 and the plateau zone 10, the first intermediate zone temperature 21 of which lies between the initial heating temperature 13 and the plateau temperature 14. The first intermediate zone 20 reduces or prevents heat exchange between the initial heating zone 9 and the plateau zone 10, so that a more precise control of the furnace temperature in the zones 9, 10 is possible. Furthermore, the zone temperature 18 in FIG. 4 shows two second intermediate zones 22 between the plateau zone 10 and the peak heating zone 11, which have two second intermediate zone temperatures 23. These serve to define the peak heating zone 11 and the plateau zone 10 more precisely. For the rest, reference is made to the above description of FIG. 1.

(18) FIG. 6 shows a device 24 for heat treatment of a metal component 2 with a roller hearth furnace 1 and a press hardening unit 25.

(19) For example, it is possible to select the target temperature 3 in the roller hearth furnace 1 so that it is at or above the AC1 temperature (i.e. the temperature at which the formation of austenite begins during a heating process), or even above the AC3 temperature (the temperature at which the conversion of ferrite to austenite ends during a heating process) of the corresponding material of the metal component 2, that at least a proportion of martensite is formed in the metal component during the subsequent press hardening.

(20) Optionally, at least one temperature control unit 26 is formed between the roller hearth furnace 1 and the press hardening unit 25 (see FIG. 7), which, after the metal component 2 has rapidly been heated up in the roller hearth furnace 1, allows the temperature of areas of the metal component 2 to be adjusted differently, in particular to heat partial areas and to cool other parts.

(21) Alternatively, a method can be chosen in which the target temperature 3 is chosen so that it is below the AC3 or even AC1 temperature and then in a subsequent temperature control unit 26 in at least a partial area of the metal component 2 the temperature is increased above the AC1 or AC3 temperature, while the temperature in at least one other partial area of the metal component 2 is left below the AC1 or AC3 temperature. In this way, metal components 2 can be produced which, after press hardening, have areas of different structures or strengths.

LIST OF REFERENCE NUMBERS

(22) 1 roller hearth furnace

(23) 2 metal component

(24) 3 target temperature

(25) 4 access

(26) 5 roller

(27) 6 exit

(28) 7 preliminary coating

(29) 8 direction of movement

(30) 9 initial heating zone

(31) 10 plateau zone

(32) 11 peak heating zone

(33) 12 end zone

(34) 13 initial heating temperature

(35) 14 plateau temperature

(36) 15 peak temperature

(37) 16 heating means

(38) 17 control means

(39) 18 zone temperature

(40) 19 component temperature

(41) 20 first intermediate zone

(42) 21 first intermediate zone temperature

(43) 22 second intermediate zone

(44) 23 second intermediate zone temperatures

(45) 24 heat treatment device

(46) 25 press hardening unit

(47) 26 adjusting station

(48) 27 shielding means