EP2570503B1 - Method and device for heating a pre-coated steel circuit board - Google Patents

Description

The invention relates to a method for heating a precoated steel plate for the production of a thermoformed component according to the features in the preamble of claim 1 and a device for heating a precoated steel plate for the production of a thermoformed component according to the features in the preamble of claim. 4 ,

The production of thermoformed components is based on the plastic deformation of mostly flat semi-finished products. Compared to the cold forming at room temperature, the previous heating, in particular of metallic semi-finished products, contributes to the fact that they do not receive any undesirable solidification with reduced toughness in the forming area. In addition, the heating overall facilitates the targeted change in shape of the semifinished product, since any shear or fracture fractures are largely prevented by the reduced in the heated state strengths of the material used.

Especially in the automotive industry, steel blanks form the basis for the manufacture of bodywork or structural components. In addition to the necessary protection against corrosion arises from an ecological and economic point of view, an increasing demand for high-strength components, which have a very favorable ratio of strength to weight. Their mechanical resistance leaves Increase in a known manner by the material is cured by heating and subsequent rapid cooling. The causative change in position of the carbon atoms in the metal lattice begins when the austenitizing temperature is reached, with the subsequent cooling resulting in a martensitic hardening structure and thus significantly increasing the strength of the formed component. The cooling rate required for this depends on the particular alloy used.

In connection with the use of steel thin-walled blanks, economic molding or press-hardening have become established as a method of hot-working sheet metal. Here, the heated board is placed in a molding tool, in which it is formed and cured by cooling. To prevent decarburization and oxidation of the steel during heating, it may be done in a controlled atmosphere, for example under nitrogen. In contrast, the heating can also take place in ambient air, provided that the board receives a suitable coating before being heated.

By the US 2007/163685 A1 For example, there is known a method of heating a precoated steel sheet for the manufacture of a thermoformed component wherein the coated sheet is heated in an oven and the atmosphere within the furnace is controlled by the supply of pretreated air. The air is pretreated by drying before being fed, preferably by reducing its hydrogen content below 1% and limiting the dew point to a maximum of 10 ° C.

By the DE 26 36 639 A1 a heat treatment furnace belongs to the state of the art. This is suitable for heating of pre-coated blanks made of steel for the production of thermoformed components. The furnace comprises at least one supply line, which is connected to a heatable interior of the furnace, wherein the supply line between a drying arrangement, a compressor and the interior of the furnace is arranged. The interior is pretreated via the drying arrangement air through the feed line fed.

From the EP 1 013 785 B1 is a method for heating a precoated board made of steel, wherein the coating of aluminum or an aluminum alloy, for example, of aluminum and silicon. The board provided with the coating is first heated in an oven, whereby at least partially an intermetallic alloy layer is formed on the board. The alloy layer is formed between the surface of the board and the coating arranged thereon. The heating takes place at a temperature between 750 ° C and 1200 ° C, wherein the atmosphere in the interior of the furnace due to the oxidation barrier formed by the coating requires no control. Subsequent cooling of the thermoformed component increases its mechanical hardness properties.

The corrosion and decarburization of the steel prevented by the coating and in particular by the intermetallic alloy formed prevents the formation of scale, which leads to rapid wear of the shaping tools. In addition, the intermetallic alloy forms a lubricating function, especially at high temperatures, which facilitates the forming.

Basically, the passive corrosion inhibiting property of oxides on the surface of metals is known. In order to obtain their positive property on the surface of the coating, the access of atmospheric oxygen during heating is desired. On the other hand, the nitrogen naturally contained in ambient air together with the coating formed of aluminum or of an alloy of aluminum and silicon forms extremely hard deposits which adhere to the forming tool. In order not to reduce the quality of the components to be manufactured with respect to their surface, appropriate tool cleaning is required. In addition to the resulting inevitable downtime, set-up and maintenance times, the hard deposits require a grinding of the forming tool areas, which significantly increases their wear. Due to the heated furnace atmosphere, the oxygen content contained therein is at least partially reduced, whereby the formation of the desired oxide layer on the coating is at least limited. So can the attachment of the Coating on the mold counteracting oxide layer does not form completely, which contributes to the additional formation of deposits.

Furthermore, the incompletely developed and thus partially releasing aluminum oxide layer leads to increased dust formation, which leads to increased wear due to abrasion, in particular in the guided and / or stored components of the forming tool. Consequently, for example, the guides of slides and brakes of the forming tool also subject to increased wear. Due to the uncontrolled atmosphere within the furnace this has a corresponding proportion of water in the form of water vapor, which results from the exchange with the ambient air. The splitting of the water by the thermal load within the furnace leads to an increased proportion of hydrogen, which undesirably promotes any hydrogen embrittlement of the steel. The advantageous from an economic point of view small openings of the furnace for its loading and the removal cause that only a small proportion of atmospheric oxygen enters the furnace, which also the formation of the advantageous oxide layer is limited to the coating.

As a result, the otherwise advantageous heating of pre-coated boards still offers room for improvement.

The invention is, starting from the prior art, the object of the invention to improve a method and apparatus for heating a precoated steel plate to form an alloy layer for the production of thermoformed bodywork and structural components to the effect that the wear of the thermoforming tool by deposits and abrasion reduced and sufficient oxidation of the coating is simultaneously made possible with reduced risk of hydrogen embrittlement economically.

The solution of the procedural part of the object according to the invention in a method for heating a precoated steel plate for the production of a thermoformed component according to the features of claim 1.

The solution of the objective part of the object according to the invention in a device for heating a precoated steel plate for the production of a thermoformed component according to the features of claim 4.

Advantageous developments are the subject of the respective dependent claims.

Hereafter, a method for heating a precoated steel plate for the production of a thermoformed component, in particular for the production of a thermoformed body or structural component, first shown, wherein the provided with a coating board in an oven to a temperature of 700 ° C to 950 ° C is heated. As a result of the heating, an intermetallic alloy layer is formed on the board at least in some areas. According to the invention, the atmosphere within the furnace is controlled by the supply of pretreated air, the air being pretreated by drying before being fed, the air being heated to a temperature of 100 ° C to 500 ° C after its drying, and dried Air is supplied to the furnace under pressure, wherein the pressure of the dried air is set to a value between the atmospheric pressure and including 8 bar and the dew point of the dried air to a value of -40 ° C to -10 ° C is set.

The particular advantage consists in the reduction of the proportion of dissolved water in the form of water vapor within the furnace atmosphere. Since less splittable water is thus present in the atmosphere of the furnace, consequently, the elimination of hydrogen is also reduced. By reducing the proportion of hydrogen in the furnace atmosphere of any hydrogen embrittlement of the steel plate is reduced by penetrating into the material hydrogen. Compared to the supply of nitrogen, the supply of dried ambient air increases the proportion of oxygen within the furnace atmosphere, thereby improving the desired formation of the oxide layer on the coating. The thus well-formed oxide layer reduces the adhesion of the coating on the forming areas of the forming tool. Furthermore, by the well formed oxide layer whose detachment and the resulting dust formation is reduced, so that the associated abrasion moving and stored parts of the forming tool is reduced.

The coating is preferably an aluminum coating, in particular an aluminum-silicon coating. In the context of the invention, the precoated board is heated to a temperature of 700 ° C to 950 ° C, in particular to a Austenitisierungstemperatur AC3, and cured after the forming in the forming tool by cooling. Even if the cooling can take place outside the forming tool, the cooling is preferably carried out within the forming tool.

Preferably, the board is made of a steel alloy with a carbon content of 0.15 wt .-% to 2.0 wt .-%. In particular, a steel alloy, which has the following proportions of its alloying partners in terms of percent by weight, is suitable for the board: Carbon (C): 0.18 wt% to 0.30 wt% Silicon (Si): 0.10 wt% to 0.70 wt% Manganese (Mn): 1.00% by weight to 2.50% by weight Chrome (Cr): 0.10 wt% to 0.80 wt% Molybdenum (Mo): 0.10 wt% to 0.50 wt% Titanium (Ti): From 0.02% to 0.05% by weight Boron (B): 0.002 wt% to 0.005 wt% Aluminum (Al): 0.01% by weight to 0.06% by weight Sulfur (S): maximum 0.01% by weight Phosphorus (P): maximum 0.025% by weight Rest: Iron, incl. Impurities caused by melting

Alternatively, the invention provides that the board has, for example, the following proportions of its alloying partners: Carbon (C): 0.19% by weight to 0.25% by weight Silicon (Si): 0.15% by weight to 0.50% by weight Manganese (Mn): 1.10% by weight to 1.40% by weight Phosphorus (P): maximum 0.025% by weight Sulfur (S): maximum 0.015% by weight Chrome (Cr): maximum 0.35% by weight Molybdenum (Mo): maximum 0.35% by weight Titanium (Ti): From 0.02% to 0.05% by weight Boron (B): 0.002 wt% to 0.005 wt% Aluminum (Al): 0.02 wt.% To 0.06 wt.% Rest: Iron, incl. Impurities caused by melting

The dried air is fed to the furnace under overpressure. By setting the desired overpressure, the desired amount of pretreated air, especially dried air, which is fed to the furnace can be controlled. The pressure of the dried air, when fed into the furnace, can be adjusted to a value between the atmospheric pressure and 8 bar inclusive. Preferably, the pressure of the dried air to be supplied to the furnace is adjusted to a value between the atmospheric pressure and 6 bar inclusive. By specifying the air pressure, more precisely the overpressure, of the dried air to be supplied, it is ensured that a specific amount of desired elements, in particular oxygen (O ₂ ), is present during the heating of the precoated board. In addition, in particular at an overpressure of 6 bar of existing in a known manner network pressure existing compressed air lines can be used without any compressed air higher compression to the to realize desired feed into the oven. As a result, it is possible to resort to devices and setting variables that are generally available. The advantage lies in the least possible effort and thus economic use of existing components and sizes.

Another advantage of the overpressure is seen in the displacement of ambient air as well as any combustion products from the furnace atmosphere. Thus, especially at high ambient temperatures, the thereby provided with an increased amount of moisture ambient air displaced in an advantageous manner from the furnace atmosphere out. By further tracking of controlled in their moisture content air thus the desired furnace atmosphere is set.

In addition to controlling the atmosphere by adding nitrogen (N ₂ ), any existing infrastructure can also be reduced, resulting in low operating costs as a result. This would, for example, any existing nitrogen treatment and a corresponding filtration superfluous.

By drying the air, its dew point is set to a value of -40 ° C to -10 ° C. Basically, a good economy is achieved at a value for the dew point of the dried air of at least - 10 ° C. The range for the value of the dew point of the dried air between -40 ° C and -10 ° C, in principle, a good quality in accordance with justified costs for the associated effort is achieved.

The dew point itself gives the value for the temperature at which the moisture dissolved in the air as water vapor precipitates as condensate. The ability of air to absorb water in the form of water vapor depends on its overall temperature. Thus, in particular in the summer months with a correspondingly high air temperature, their absorption capacity for moisture is increased. In other words, warm air is able to absorb more moisture, whereas cold air may contain less moisture. Thus, with 100% saturation of the air with steam in warm air, more water is contained than in cold air.

Regardless of the temperature of the air can thus be reduced by the drying of the respective dew point.

The air to be supplied to the oven is heated after it has dried. If necessary and depending on the design, the air can also be heated during its drying. In principle, the air can also be heated before it is dried. The air is heated to a temperature of 100 ° C to 500 ° C. The advantage is in the approximation of the temperature of the supplied air to the temperature within the furnace. As a result, otherwise inevitably occurring temperature fluctuations within the furnace atmosphere are largely avoided. In addition, the furnace can be operated more economically, since the furnace atmosphere is not or only slightly cooled down by the supply of heated air. As a result, the required heating power is less than the supply of unheated air.

In particular, in the supply of unheated air, the furnace atmosphere in the region of the supply of air to the surrounding air within the furnace lower temperature, whereby the heating of the board can delay unfavorably. Advantageously, for this purpose, the energy of the exhaust air, in particular the exhaust gas of the furnace is used, which is withdrawn for example via a suitable heat exchanger and the supplied air is supplied in the form of heat. The configuration may, for example, be such that the exhaust air line, in particular the exhaust air line of at least one burner of the furnace has a heat-transmitting coupling with the supply line for the pretreated air. For this purpose, the supply line of the pretreated air can be peripherally in contact with the exhaust air line, for example, in which the supply line is arranged around the exhaust air duct around or parallel to this. As a result, the heat of the exhaust air can be transmitted via the respective walls of the lines in contact with each other at least partially to the air to be supplied.

Alternatively, the supply line for the pretreated air, for example, at least partially disposed within an exhaust duct of at least one burner of the furnace. By doing the whole circumference completely with heated Exhaust air surrounded feed line as large as possible heat transfer between the exhaust air and the pretreated air can be achieved.

The invention provides that the introduced during the heating of the board in the oven and this passing volume flow of the dried, in particular dried and heated air is set to 2.5 times the furnace volume per hour. The air introduced into and passing through the oven is pressurized with respect to the desired volumetric flow rate. The furnace used can be, for example, a chamber furnace and a rotary kiln or a roller hearth furnace. For economical production, a continuous furnace is preferably used. As a result, the pressing tool can be continuously equipped with heated steel blanks.

In this case, an inserted in the continuous furnace board passes through this by means of a transport unit, for example in the form of transport rollers, wherein the board is heated in the furnace atmosphere and maintained at temperature.

The volume flow of the dried air introduced into the oven and passing through it during the heating of the board is adjusted in particular to 3 times the furnace volume per hour. Preferably, the volume flow passing through the oven is adjusted to 6 times the oven volume per hour. By continuously passing the oven with dried air flow rate ensures that only the desired atmosphere is present within the furnace, as in particular the existing pressure and the associated flow effectively prevents any ingress of ambient air.

The invention provides that the atmosphere within the furnace is set to the following values of its proportions: Nitrogen (N2): less than or equal to (≤) 85% by volume, preferably 78% by volume; Oxygen (O2): from 10% by volume to 21% by volume, preferably from 15% by volume to 21% by volume, especially 21% by volume;

Water vapor (H2O steam): less than (<) 3 vol.% And
a residue consisting of carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), hydrogen (H2) and impurities dependent on the starting material and its coating

The distribution of nitrogen at 78% by volume and oxygen at 21% by volume corresponds to the content of normal ambient air. The proportion of oxygen in the dried air can be increased, for example, by the supply of pure oxygen. Since the content of oxygen in the furnace atmosphere is reduced for example by the formation of the oxide layer and any combustion processes, even the supply of dried air leads to an increase in the oxygen content. The supply of dried air also reduces the proportion of nitrogen which is increased within the furnace atmosphere.

The invention relates to a method for heating a precoated steel plate to form an alloy layer for the production of thermoformed body and structural component, which reduces the wear of the thermoforming tool by deposits and abrasion and economically sufficient oxidation of the coating with reduced risk of hydrogen embrittlement possible. In particular, the use of mostly existing compressed air in this case represents a very cost-effective way to control the furnace atmosphere. Thus, the sole drying of the compressed air to be supplied to the furnace brings about the described advantages, which in particular lead to the formation of a sufficient oxide layer, which in turn prevents or at least significantly reduces any deposits in the shaping areas of the forming tool. In addition, the risk of hydrogen embrittlement is significantly reduced, which is due to the reduced proportion of water in the form of water vapor within the supplied air. Furthermore, the well-formed oxide layer on the coating reduces their detachment, whereupon the possible formation of dust and the associated signs of wear of the forming tool are minimized.

Furthermore, in the context of the invention, a device for heating a precoated steel plate for the production of a thermoformed component is shown. The components to be manufactured are in particular thermoformed bodywork or structural components. The device comprises a furnace and at least one supply line, which is connected to a heatable interior of the furnace. According to the invention, the feed line is arranged between a drying arrangement and the interior of the furnace. As a result, air which can be pretreated via the drying arrangement can be supplied to the interior of the furnace through the supply line.

The reduced by drying proportion of water in the form of water vapor within the furnace atmosphere reduces the risk of hydrogen embrittlement of the steel plate. In addition, the furnace atmosphere is enriched in terms of its oxygen content with oxygen from the pretreated ambient air, which is otherwise reduced within the furnace atmosphere, in particular by the high temperatures.

Advantageously, the drying arrangement is connected to an air compressor. As a result, the air compressed by the air compressor in a thus controllable amount is hineinleitbar through the dry assembly through the supply line into the interior of the furnace. In other words, the air compressor is used to direct a determinable volume of dried air in the form of a volume flow in the interior of the furnace. As a result, the required amount of proportions of the dried air, in particular oxygen, regulated.

The drying arrangement has at least two drying containers, through which the air to be passed into the oven flows. Through the use of at least two dry containers they can be alternately flowed through with the required air. The exchangeable flow through the two drying containers causes the non-traversed drying container can be dried with respect to the moisture collected therein, for example by heating. As a result of the alternating feeding of the two drying containers with air to be dried, this can be continuously provided for feeding into the oven.

The invention provides that the supply line is arranged at least in a central region of the interior of the furnace. In particular, when using a continuous furnace this design includes two openings, with an opening serve the feed of the continuous furnace and the other opening of the removal of the heated semi-finished product. In the vicinity of the two openings, an exchange of ambient air with the furnace atmosphere is possible. As a result, the proportion of oxygen in the interior of the furnace is increased in the region of the openings relative to the furnace section located between the openings. As a result of the arrangement of the supply line in a central region of the interior, a virtually constant proportion of oxygen in the interior of the furnace can be achieved. The resulting positive effects on the formation of the oxide layer on the coating thus come into play over the entire run length of the furnace.

The furnace has at least one exhaust duct, via which any exhaust gases of at least one burner can be diverted. The exhaust duct is preferably arranged outside the interior of the furnace. Advantageously, the exhaust air line is at least partially in communication with the supply line for the air. The exhaust duct is at least partially thermally coupled to the supply line. The thermal coupling can be done for example via a heat exchanger. Also, the supply line may be at least partially integrated in an exhaust duct. The advantage consists in an at least partial transfer of the heat of the exhaust air, whereby the air to be supplied to the interior of the furnace is heated.

In particular, the structural separation within the heat exchanger no exchange of the respective fluids. As a result, a suitable temperature, in particular a heating of the supplied air is possible without additional energy. Here, the supplied air can be heated to 100 ° C. In principle, the heating of the air before, during or after their drying can take place. By the exhaust air to be supplied to a temperature of 100 ° C to 950 ° C, preferably heated to a temperature of 100 ° C to 700 ° C, in particular to a temperature of 100 ° C to 500 ° C. Depending on the design of the heat exchanger, the supplied air can also be heated to a temperature of 100 ° C to 200 ° C.

Preferably, the furnace is a continuous furnace in which at least two are located between the drying assembly and the interior of the furnace arranged supply lines are provided. The distance between the at least two supply lines basically depends on the length of the continuous furnace. With regard to a typical continuous furnace, a distance of the feed lines of 2.0 m to 3.0 m from each other is preferred in the context of the invention. In principle, more supply lines can be arranged, which are arranged closer together, for example, with a correspondingly smaller cross-section. The aim is to obtain the most uniform possible supply of dried air in the interior of the furnace. Here is a constant possible composition of the air, more closely the furnace atmosphere, in the foreground.

In order to obtain a composition of the furnace atmosphere which is as constant as possible and independent of the respective temperature of the air to be dried, the invention provides that the furnace has at least one dew point sensor. The dew point sensor can be arranged, for example, within a supply line. Advantageously, the at least one dew point sensor is arranged in the interior of the furnace to detect the real composition of the furnace atmosphere with respect to its dew point. For this purpose, the dew point sensor is coupled to the drying arrangement. The coupling serves to control, in particular the exchange of information between dew point sensor and dry arrangement. In other words, the detected measured quantity by the dew point sensor serves to regulate the drying effect of the drying arrangement with respect to the air flowing through it. For this purpose, the dew point sensor can transmit measured values to the drying arrangement at certain intervals, the drying effect of which is set by means of suitable control, for example.

Of course, the measurement of the dew point sensor can also be carried out continuously, so that the dry arrangement also undergoes a continuous adjustment of its efficiency. The dew point sensor may be, for example, a humidity sensor or a humidity sensor. The nominal dew point of the furnace atmosphere is thus regulated by the combination of dew point sensor and dry arrangement.

The dry arrangement may be, for example, a refrigeration dryer or an IR dryer. The drying arrangement is preferably in order an adsorption dryer. This may for example comprise a desiccant of activated alumina, which has a continuously high adsorption capacity and a good regeneration capacity.

Although the drying arrangement can be time-controlled, it is advantageously capacity-controlled in order to enable the required regulation of the desired dew point. The control of the degree of dryness can take place over all phases of the drying cycle, such as the adsorption, the pressure relief and the regeneration of the desiccant and the pressure build-up.

Advantageously, the furnace has at least two temperature zones. In this case, the temperature zones can be arranged in the direction of passage of the furnace and / or transversely to the direction of passage of the furnace. In this case, temperature zones arranged in the direction of travel can also be supplemented by temperature zones arranged transversely to the passage direction. The mutually different temperature zones serve to enable a partial thermoforming of the steel plate, if necessary. Here, targeted individual areas of the board are brought to the required temperature in order to adjust the required properties of the material in the subsequent thermoforming, in particular by press hardening.

The individual temperature zones can be set, for example, by locally independent and different temperature settings. Furthermore, the individual temperature zones can be set and regulated in an advantageous manner, at least in regions, by the supply line of the pretreated air. Of course, a combination of temperature control and air supply is possible. In particular, the supply of the pretreated air allows a feasible within a very short time adaptation of local temperature conditions, since the temperature is usually below the temperature of the furnace atmosphere. Depending on the configuration, the regulation of individual temperature zones can thus be effected by the individual and, for example, increased local supply of pretreated air.

On the other hand, if necessary, the feed line of the pretreated air can be designed such that it has as long a path as possible, for example by an alternating installation, in the area of the exhaust air, in particular the exhaust air line of the Brenners has. Hierdruch takes place a heat transfer from the exhaust air, more precisely the exhaust gas, to the supply line and thus to the air guided therein, whereupon it heats up. In this way, an undesired heat loss of the furnace atmosphere, in particular an undesirable cooling in the supply lines to the interior of the furnace can be at least partially compensated. In other words, this results in the desired heating of the pretreated air before it is passed into the interior of the furnace.

If necessary, by the arrangement of the leads according to atmospheric zones may be formed in the interior of the furnace.

It is envisaged that at least one of the temperature zones is adjustable with respect to their temperature via the supply line of the air. In this case, the temperature zone is arranged in the region of the feed line, so that the temperature zone can be set at least in regions by the supply of the air. Depending on the volume of the temperature zone whose respective temperature is adjustable both on the amount and on the temperature of the air to be supplied.

The invention thus provides a device for heating a precoated steel plate to form an alloy layer for the production of thermoformed body and structural components, which significantly reduces the wear of the thermoforming tool by any deposits and abrasion. In particular, the controlled supply of atmospheric oxygen allows sufficient oxidation of the coating, which reduces the adhesive effect of deposits on the forming areas of the forming tool. In addition, the risk of hydrogen embrittlement is reduced by the reduced proportion of water in the form of water vapor in the furnace atmosphere.

Thus, existing ovens and conventional compressed air networks can be used, with only a supplement by a dry arrangement and any supply lines to the interior of the furnace are necessary. In particular, the reduction of any deposits on the thermoforming tool as well as the resulting dust from the dusting reduce the overall maintenance effort. In addition, the committee will also be involved in ceramic rolls as part of Transport device in continuous furnaces reduced, since the tendency for deposition is reduced by the well-formed oxide layer on the coating.

Figur 1

einen erfindungsgemäßen Durchlaufofen in Kombination mit einem Umformwerkzeug in einer Seitenansicht;

Figur 2

den erfindungsgemäßen Ofen aus Figur 1 mit der Zufuhr von getrockneter Luft dienenden Komponenten in gleicher Darstellungsweise sowie

Figur 3

eine Variante des erfindungsgemäßen Ofens der Figuren 1 und 2 mit geänderter Zufuhr der vorbehandelten Luft in gleicher Darstellungsweise.

The invention will be explained in more detail with reference to some schematically illustrated in the drawings embodiments. Show it:

FIG. 1

a continuous furnace according to the invention in combination with a forming tool in a side view;

FIG. 2

the furnace according to the invention FIG. 1 with the supply of dried air serving components in the same representation as well as

FIG. 3

a variant of the furnace of the invention Figures 1 and 2 with modified supply of pretreated air in the same way.

FIG. 1 schematically shows a longitudinally extending furnace 1 in the form of a continuous furnace. The furnace 1 has at its end in each case an opening, wherein with reference to the illustration of FIG. 1 right opening an entrance 2 and the input 2 opposite opening form an outlet 3 of the furnace 1. In the area of the outlet 3 of the furnace 1, a forming tool 4 is arranged. The forming tool 4 comprises an upper die 4a and a lower die 4b, between which a precoated board 5 is deformable.

For this purpose, the forming tool 4 is located between the upper die 4a and the lower die 4b forming area 4c, within which the reshaping board 5 can be inserted.

Between the furnace 1 and the forming tool 4, a manipulator 6 is arranged in the form of a robot arm. The furnace 1 is used to heat the precoated board 5 made of steel, which is first introduced via the input 2 in the furnace 1 and this passes in the direction of the output 3. On its way through the furnace 1, more precisely through its furnace atmosphere, the coated board 5 is heated in a manner not shown to an austenitizing temperature of 700 ° C to 950 ° C. By the Heating of the board 5 forms an intermetallic alloy layer between the coating of the board and the surface of the board. Due to the oxygen present in the furnace atmosphere, the oxidation of the coating takes place, which thus forms an oxide layer on its surface. The coating is preferably aluminum, in particular an aluminum-silicon alloy.

At the latest when removing the board 5 through the outlet 3 from the furnace 1, this is heated to Austenitisierungstemperatur. The board 5 is detected in a manner not shown by the manipulator 6 and inserted into the forming area 4 c of the forming tool 4. Subsequently, in a likewise not shown manner, the deformation of the board 5, wherein the upper die 4 a is approximated to the lower die 4 b by means of pressing force. Subsequently, the board 5 still located in the forming area 4c of the forming tool 4 is cooled to harden it.

In order to cool the formed blank 5 within the forming tool 4 at a speed dependent on the respective alloy, the upper die 4a and / or the lower die 4b have cooling means (not shown). Thus, for example, integrated cooling lines can be provided which can be flowed through by a cooling fluid in order to absorb and remove the heat present in the upper die 4a and / or the lower die 4b.

In practice, a continuous feeding of the furnace 1 with precoated boards 5 via the input 2. Thus, continuously heated austenitizing at boards 5 at the output 3 of the furnace 1 are available, which is inserted via the manipulator 6 in the forming tool 4 and formed therein be press-hardened.

FIG. 2 shows the oven 1 the FIG. 1 with more details. Outside the furnace 1, a drying arrangement 7 is arranged with at least one drying container, not shown. The drying arrangement 7 is connected to an interior 1a of the furnace 1 via a central supply line 8 with further supply lines 8a arranged at a distance A from one another. Furthermore, the furnace 1 several dew point sensors 9, which are connected via cable 10 with a controller 11. The controller 11 is composed of a measuring module 11a and a default module 11b and a control module 11c. In principle, the connection between dew point sensor 9 and control 11 can also be wireless.

The distance A is dependent on the burners used and not shown in detail, in particular their performance and the corresponding burner tube thickness. In the present case, the distance A is preferably from 0.5 m to 2.5 m. The distance A may result, for example, from three times the particular burner tube thickness used. For example, with the use of 50 kW burners with a respective burner tube thickness of 50 cm, a distance A of 1.5 m could result.

Between the supply line 8 and the drying assembly 7, a controller 12 is arranged, via which the the interior 1a of the furnace 1 to be supplied amount of dried over the drying assembly 7 air is adjustable. The control module 11 c of the controller 11 is also connected via a cable 13 to the controller 12. In addition, the drying assembly 7 is connected via a cable 14 to the control module 11 c of the controller 11. In principle, the connection of the controller 12 and / or the drying arrangement 7 with the controller 11 can also be wireless. Of course, the communication of the controller 12 and / or the drying arrangement 7 with the controller 11 can take place via a suitable BUS system.

FIG. 3 shows an alternative embodiment of a furnace 1 b, which extends from the furnace 1 of Figures 1 and 2 differs with respect to the supply of pretreated air in its interior 1c. The central supply line 8, which is connected to the drying arrangement 7 via the controller 12, likewise has supply lines 8b arranged at a distance A from one another, which are connected to the interior 1c of the oven 1b. In order to heat the pretreated air prior to its introduction into the interior 1c of the furnace 1b, the supply lines 8b are arranged alternately and / or spirally around a hot exhaust duct 15 of a burner, not shown. The supply lines 8b act as a heat exchanger, so that the pretreated air is heated in the region of the exhaust duct 15 within the supply lines 8b before it is introduced into the interior 1 c. Thus, the anyway Existing heat can be used to preheat the pretreated air without using more energy to the desired temperature.

In practice, the dew point sensors 9 serve to detect the current dew point of the furnace atmosphere contained in the interior 1a, 1c of the furnace 1, 1b. The detected values are transmitted via the cable 10 to the measuring module 11 a of the controller 11. The desired value stored in the control 11 in the default module 11b is compared with the actual values transmitted to the measuring module 11a and measured by the dew point sensors 9 as a controlled variable. If an adjustment is necessary, the controller 12 is controlled via the cable 13 and / or the drying assembly 7 as actuators via the cable 14 by the control module 11 c of the controller 11 to the volume flow of dried air into the interior 1a, 1c and / or to adjust the dry performance of the dryer assembly 7.

In order to bring the required amount of dried air in the interior 1a, 1c, the drying assembly 7 is connected either to a compressed air network not shown here or with an air compressor also not shown. As a result, the drying arrangement 7 is charged with ambient air at a pressure above atmospheric pressure, which is dried via the drying arrangement 7 and fed through the supply lines 8, 8a, 8b into the interior 1a, 1c of the furnace 1, 1b. The pretreated compressed air thus supplied escapes via at least one of the openings of the furnace 1, more specifically the inlet 2 and / or the outlet 3.

Reference numerals:

1 -

oven

1a -

Interior v. 1

1 b -

oven

1c -

Interior v. 1b

2 -

entrance

3 -

output

4 -

forming tool

4a -

upper die

4b -

lower die

4c -

forming region

5 -

coated board

6 -

manipulator

7 -

dry arrangement

8th -

supply

8a -

supply

8b -

supply

9 -

Dew Point

10-

electric wire

11 -

regulation

11a -

measurement module

11b -

default module

11c -

control module

12-

regulator

13-

electric wire

14-

electric wire

15

exhaust duct

A -

Distance between 8a, 8b

Claims (7)

1. Method for heating a pre-coated plate (5) made from steel for the production of a hot-formed component, in particular for the production of a hot-formed body or structural component, wherein the plate (5) provided with a coating is heated in a furnace (1, 1b) to a temperature from 700°C to 950°C, whereby an intermetallic alloy layer is formed at least in regions on the plate (5) and the atmosphere within the furnace (1, 1b) is controlled by the supply of pre-treated air, wherein the air is pre-treated in that it is dried before its supply, wherein the air is heated after its drying to a temperature from 100°C to 500°C and the dried air is supplied to the furnace (1, 1b) under excess pressure, wherein the pressure of the dried air is set to a value between the atmospheric pressure and 8 bar inclusive, and the dew point of the dried air is set to a value from -40°C to -10°C.
2. Method according to claim 1, characterised in that the volumetric flow rate of the dried air passing through the furnace (1, 1b) during the heating of the plate (5) is set to 2.5 times the furnace volume per hour, in particular to 3 times the furnace volume per hour, preferably to 6 times the furnace volume per hour.
3. Method according to claim 1 or 2, characterised in that the atmosphere within the furnace is set to the following values of its components:

   nitrogen (N₂): less than or equal to (≤) 85 vol%, preferably 78 vol%;

   oxygen (O₂): from 10 vol% to 21 vol%, preferably from 15 vol% to 21 vol%, in particular 21 vol%;

   water vapour (H₂O vapour): less than (<) 3 vol% and

   a remainder, consisting of carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), hydrogen (H₂) as well as impurities depending on the starting material and the coating thereof.
4. Device for heating a pre-coated plate (5) made from steel for the production of a hot-formed component, in particular for the production of a hot-formed body or structural component, comprising a furnace (1, 1b) as well as at least one supply line (8, 8a, 8b) which is connected to a heatable interior (1a, 1c) of the furnace (1, 1b) and the supply line (8, 8a, 8b) is arranged between a drying assembly (7) and the interior (1a, 1c) of the furnace (1, 1b), such that air which is able to be pre-treated via the drying assembly (7) is able to be supplied to the interior (1a,1c) through the supply line (8, 8a, 8b), wherein the drying assembly (7) is connected to an air compressor and the air compressed by the air compressor is able to be conducted through the drying assembly (7) via the supply line (8, 8a, 8b) into the interior (1a, 1c) of the furnace (1, 1b) and the drying assembly (7) comprises at least two drying containers, wherein the drying containers are able to be flowed through alternately with the pre-treated air and at least one burner of the furnace (1, 1b) has an exhaust air line (15), wherein the exhaust air line (15) is thermally coupled at least in regions to the supply line (8, 8a, 8b) and the furnace (1, 1b) has at least one dew point sensor (9), wherein the dew point sensor (9) is coupled at least indirectly to the drying assembly (7).
5. Device according to claim 4, characterised in that the furnace (1, 1b) is a continuous furnace and at least two supply lines (8, 8a, 8b) arranged between the drying assembly (7) and the interior (1a, 1c) of the furnace (1, 1b) are provided, wherein the supply lines (8, 8a, 8b) have a distance from 2.0 to 3.0m from one another.
6. Device according to claim 4 or 5, characterised in that the furnace (1, 1b) has at least two temperature zones, wherein the temperature zones are arranged in the through-put direction and/or transversely to the through-put direction of the furnace (1, 1b).
7. Device according to claim 6, characterised in that at least one temperature zone is able to be set in its temperature at least in regions by the supply of the air via the supply line (8, 8a, 8b).

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