EP2110448A2 - Method and circulation oven for heating workpieces - Google Patents

Abstract

Heat treatment of a workpiece in a continuous furnace (10) comprises transporting it through the furnace to the point where a section (22) of it projects outside the furnace. The conveyor (30) is then stopped and the section (21) of the workpiece inside the furnace is further treated before the conveyor is started again. An independent claim is included for a continuous furnace for carrying out the method which has a conveyor fitted with a control system for stopping and starting it.

Description

The invention relates to a method for heating at least one workpiece in a furnace, in which the workpiece is heated by heating means. The invention further relates to an associated furnace for carrying out the method.

In the field of production and treatment of molded components, it is customary to produce moldings specifically with desired material properties. For example, in the automotive industry, components such as control arms, B-pillars, or automotive bumpers are cured by complete heating followed by quenching. This may be followed by an incentive procedure for a fee. In various applications of automotive engineering, however, it is advantageous that molded components have different material properties in different areas. For example, it may be provided that a component in one area should have a high strength, but in another area a higher ductility in relation to it.

For example, in order to realize molded components which satisfy different stresses in several regions, it is possible to join components with different properties. Furthermore, components can be reinforced by additional sheets. Also suitable is the annealing of previously fully cured mold components at the appropriate locations to achieve higher ductility regions. However, this leads to intolerable changes in shape in the component.

In addition, it is possible to treat molded components already during production in such a way that regions with different material properties are produced. Here are formed areas with different structures, and the Production of molded components having at least two structural regions, various methods and devices are known from the prior art. For example, the heating of components with induction current is known. However, this is to be expected with high costs and a non-uniform heating.

Further, the European patent application discloses EP 1 426 454 A1 a method for producing a molded component having at least two structural areas of different ductility and a continuous furnace for carrying out the method. Here, a semifinished product to be heated is transported as a blank or preformed component through a continuous furnace, which comprises two juxtaposed zones in which different temperature levels are set. As a result, the component is heated in the oven to two different temperatures and then subjected to a thermoforming process and / or a hardening process. In this case, a more ductile microstructure arises in the higher-heated region of the component, while a solid or high-strength microstructure sets in the less heated region.

The German Utility Model DE 200 14 361 U1 describes a method for producing a B-pillar with different microstructure ranges, in which the B-pillar is heated in an oven and austenitized with it, and then cured in a cooled mold. When heating in the oven large areas of the board or the semi-finished product used are isolated against the effect of temperature, so that sets in the shielded areas no martensitic material structure with high strengths. However, this represents an unsafe process, since in the case of a malfunction heat can penetrate into the covered areas and thus these areas are heated to hardening temperature.

The known methods are not suitable in particular for mass operation with a cycle time of about 15 seconds and given in motor vehicle requirements for process safety because they can not ensure the prescribed hardness profile in the component permanently.

The object of the invention is therefore to provide a method for heating components, which allows the formation of areas with different material properties in the component in subsequent process steps. The object of the invention is also to provide a device for carrying out the method.

According to the invention, this object is achieved by a method having the features of independent claim 1. Advantageous developments of the method will become apparent from the dependent claims 2-10. The object is further achieved by an oven according to claim 11. Advantageous embodiments of this furnace will become apparent from the subclaims 12-17.

The inventive method is used to heat at least one workpiece in an oven, wherein the workpiece is heated by heating means. After an entire workpiece has been heated by the heating means in a first step, according to the invention a movement of the workpiece out of the oven so far that a first portion of the workpiece is still within the furnace, while a second portion of the workpiece is outside of the furnace , In this position, the workpiece is held for a predetermined period of time and then the entire workpiece is moved out of the oven.

In one embodiment of the invention, at least one workpiece is heated in a continuous furnace, and the workpiece is thereby moved by a transport device through the continuous furnace. After the forward side of a workpiece in the transport direction has passed through the heating path of the continuous furnace, moving the workpiece by the transport device so far out of the heating section of the continuous furnace, that a first portion of the workpiece is still within the heating, while a second portion of the workpiece is already outside the heating zone. The movement of the transport device is interrupted at this position of the workpiece for a predetermined period of time, and then carried out a re-moving the entire workpiece by the transport device from the heating section of the continuous furnace out.

In one embodiment of the invention, the first portion of the workpiece is heated by the inventive method to a temperature T ₁ , which is below the hardening temperature of the material of the workpiece, while the second portion of the workpiece is heated to a temperature T ₂ , the hardening temperature of the Material of the workpiece corresponds. In this case, upon movement of the forward side of the workpiece in the transport direction through the heating path of the continuous furnace, the entire workpiece can be heated to a temperature below the hardening temperature of the material of the workpiece, while the second portion of the workpiece within the heating further on to a temperature T. _{2 is} heated, which corresponds to the hardening temperature of the material of the workpiece, when the first portion of the workpiece is located outside the heating path.

Preferably, the workpiece is moved into the continuous furnace through an input port after a cover has temporarily cleared this input port, and the workpiece is moved out of the continuous furnace through an exit port after a cover has temporarily released that exit port. The cycle times of the covers of the input and output ports are suitably adapted to the cycle times of the transport device.

It may further be provided that the cover of the exit opening only partially releases this exit opening, in order to move the second section of the workpiece out of the continuous furnace, and the cover of the exit opening then releases the exit opening to a greater extent than before, around the workpiece then move completely out of the continuous furnace out, wherein the different degrees of opening of the cover of the outlet opening are also adapted to the cycle times of the transport device. By only partially opening the cover, the heat loss can be reduced.

In one embodiment of the invention, at least two workpieces are simultaneously moved by means of at least one transport device side by side through the continuous furnace and thereby heated on a heating section of heating means. On In this way, the throughput of the furnace can be increased. In particular, in order to adapt the cycle times of the furnace to the capacities of downstream stations, it can be provided that the transport movement of at least one first workpiece is interrupted, while at least one second workpiece is moved by the transport device as far out of the heating section of the continuous furnace, that a first portion of the workpiece is still within the heating path, while a second portion of the workpiece is already outside the heating section. At this position, the transport movement of the at least one second workpiece is interrupted for a predetermined period of time until it is moved out of the heating path of the continuous furnace. Subsequently or in parallel, the transport movement of the at least one first workpiece resumes and the at least one first workpiece moves out of the heating path of the continuous furnace so that a first subarea of this workpiece is still within the heating section, while a second subarea of this workpiece already outside the heating section. The transport movement is interrupted at this position of the at least one first workpiece for a predetermined period of time, and there is a movement of the at least one first workpiece from the heating section of the continuous furnace out.

Interrupting the transport movement of individual workpieces can be achieved, for example, by moving each of the workpieces by means of a separate transport device through the continuous furnace, and interrupting the transport movement of the at least one first workpiece by interrupting the movement of the associated transport device, while resuming the transport movement the at least one first workpiece is performed by resuming the movement of the associated transport device. In an alternative embodiment, all workpieces are moved through the continuous furnace by means of a common transport device, and the transport movement of the at least one first workpiece is interrupted by decoupling the at least one first workpiece from the transport device, while the resumption of the transport movement of the at least one first workpiece by coupling the at least one first workpiece is made to the transport device.

In order to enable decoupling of individual workpieces from the transport device, a roller conveyor may be provided as the transport device, for example, on which the workpieces simultaneously move side by side through the heating path of the continuous furnace. The decoupling of at least one first workpiece from the roller conveyor may then take place by raising the workpiece to a position in which the workpiece is not in contact with the roller conveyor while coupling the at least one first workpiece to the roller conveyor by lowering the workpiece to a position, in which the workpiece again has contact with the roller conveyor and is moved by this in the transport direction. This raising and lowering of a workpiece can be done by one or more plungers, which are arranged below the workpieces and move clocked up and down. The upward movement of at least one plunger can cause the lifting of a workpiece from below, while the downward movement of at least one plunger causes the lowering of a workpiece. This movement of the plunger is expediently controlled by a control device.

Also included in the invention is a continuous furnace for heating at least one workpiece, in which the workpiece can be moved through the continuous furnace by a transport device and can be heated by heating means on a heating path. According to the invention, the transport device has means for moving the workpiece far enough out of the heating path of the continuous furnace that a first subarea of the workpiece is still within the heating path, while a second subarea of the workpiece is already outside the heating section. The movement of the transport device is interruptible at this position of the workpiece for a predetermined period of time, which is controlled by a control device.

Preferably, the continuous furnace has an inlet opening and an outlet opening, which are temporarily closed with a respective cover, wherein the cycle times of the release of the input and output openings are adapted to the cycle times of the transport device. The transport device may be a roller conveyor on which a workpiece moves through the continuous furnace becomes. The cover of the outlet opening preferably allows different degrees of opening of the outlet opening in order to open the cover only as far as it is necessary for the respective workpiece at a time. As a result, unnecessary heat losses of the furnace can be avoided.

In one embodiment of the invention, a plurality of workpieces are movable simultaneously and side by side by means of at least one transport device through the continuous furnace and thereby heated on a heating section of heating means. In this case, at least one transport device can be provided with means which allow a workpiece to move as far out of the heating section of the continuous furnace that a first subregion of the respective workpiece is still within the heating section, while a second subregion of the respective workpiece is already outside the heating section located. The movement of the at least one transport device is interruptible at this position of the respective workpiece for a predetermined period of time, and the continuous furnace further comprises means for temporarily interrupting the transport movement of workpieces during the passage of the furnace.

In this case, for example, be provided for each of the workpieces a separate transport device with which the respective workpiece is movable through the continuous furnace, the respective transport devices are controlled separately and the temporary interrupting the transport movement of a workpiece by the temporary interruption of the movement of the associated transport device can.

Alternatively, a common transport device is provided for the transport of all workpieces through the continuous furnace, and the continuous furnace has means for the temporary decoupling of individual workpieces from the transport device. In this case, for example, the transport means may be a roller conveyor on which the workpieces are movable through the heating path of the continuous furnace, and the temporary uncoupling of a workpiece from the roller conveyor is effected by lifting the workpiece to a position where the workpiece is not in contact with the roller conveyor , The coupling of a workpiece to the roller conveyor is then carried out by lowering the workpiece to a position in which the workpiece again has contact with the roller conveyor and is movable by this in the transport direction. For raising and lowering a workpiece, one or more plungers may be provided, which are located below the workpieces, wherein the plungers are designed for a clocked up and down movement, and a control device is provided, which controls this upward and downward movement of the plunger.

The invention has the advantage that components with different temperature ranges and thereby also with different structures can be produced by the heating according to the invention, wherein it is a fast process with which short cycle times can be realized. Furthermore, the invention represents a safe process in which there are no undesirable changes in shape of the component and the structure formation can always be reliably adjusted.

For example, sheet metal workpieces can be heated homogeneously in the oven to Austenittemperatur and then moved out with the desired end of the oven door. In the ambient temperature, this sheet metal part cools slowly, and it formed here pearlite and ferrite, while the part located in the furnace continues to dwell on austenite. After about 15-25 seconds, the sheet is quickly moved out of the oven and preferably both molded in a water-cooled press pad and cooled quickly. During this cooling, the hot austenite forms the hard martensite steel and in the cooler part of the sheet soft and plastically deformable pearlite steel with ferrite steel.

Several components can be simultaneously moved side by side through a furnace, which increases the throughput of such a furnace over furnaces, in which components are moved one after the other through an oven and thereby heated. However, since process stations such as presses, which are connected behind the heating of the components, often have limited capacity, in particular by an embodiment of the invention, in which there is a temporary interruption of the movement of individual components, there is the possibility of the discharge of a continuous furnace to adjust the given capacities of downstream stations. So can the Throughput of a furnace can be increased by the simultaneous heating of several components, while the individual output of heated components can be adapted to the availability of downstream stations. It can be ejected so components in the cycle from the oven, where they can be processed by the downstream stations. If the capacities of the downstream stations change, the exhaust stroke of the furnace can be adjusted.

Further advantages, features and expedient developments of the invention will become apparent from the dependent claims and the following description of preferred embodiments with reference to the drawings.

From the pictures shows:

Fig. 1

the step of introducing a workpiece into a continuous furnace;

Fig. 2

the step of heating the entire workpiece within a heating path;

Fig. 3

the step of partially moving a workpiece out of a continuous furnace;

Fig. 4

a workpiece after carrying out the method according to the invention and feeding a new workpiece;

Fig. 5

a second embodiment of a continuous furnace; and

Fig. 6

a third embodiment of a continuous furnace;

Fig. 7

a schematic plan view of several workpieces in a continuous furnace;

Fig. 8

the step of introducing a plurality of workpieces in a continuous furnace;

Fig. 9

the step of simultaneously heating a plurality of workpieces within a heating section;

Fig. 10

the step of partially moving a workpiece out of a continuous furnace and decoupling at least one workpiece from a conveyor;

Fig. 11

a first workpiece after the heating and the coupling of another workpiece back to the transport device;

Fig. 12

a second workpiece after the heating and the coupling of another workpiece back to the transport device;

Fig. 13

a third workpiece after heating and feeding new workpieces into the oven; and

Fig. 14

a schematic view of several workpieces in a continuous furnace.

In Fig. 1 an embodiment of a continuous furnace 10 according to the invention is shown, which has a furnace housing in which as transport means 30 for workpieces 20 preferably a roller conveyor is provided. The workpieces 20 are deposited on the roller conveyor and moved by the driven rollers through the continuous furnace 10. However, any other transport means may be provided. For example, it is possible to provide a transport device are mounted on the workpieces and hanging moved through the oven.

The workpieces can be any components in which other material properties are desired in one end region than in the opposite end region. For example, it may be the B-pillar or a molding for the B-pillar of a motor vehicle, in which the foot of the B-pillar should be relatively ductile, while the rest of the component should have a higher strength. In one embodiment of the method according to the invention, provision is made for a workpiece 20 to be introduced into the furnace 10 in such a way that the end region in which a higher ductility is to be achieved than in other regions lies in front in the transport direction of the workpiece. If the process is carried out in a furnace in which a workpiece is removed from the same opening through which it was introduced into the furnace, the reverse is the case. Then, that end region in which a higher ductility is to be achieved than in other regions, should lie in the transport direction of the workpiece at the rear, when the workpiece is moved into the oven.

The housing of the furnace 10 is preferably closed and has only an inlet and an outlet opening, can be introduced through the workpieces 20 on one side in the oven and on another side again out of it can be moved. The openings are each closed with covers 12 and 13. The covers may be, for example, oven slides, which can be pushed in front of the openings to temporarily close or release them. The oven slides are moved by a controllable drive.

Preferably, the covers 12 and 13 move upwardly to release the respective oven opening so that a workpiece can be moved into the oven, for example on a roller conveyor. The workpieces 20 can also be stored manually or by robots on the transport device. Alternatively, the workpieces can be transported on a further transport device to the furnace 10 and transferred to the transport device 30 of the furnace.

The covers 12 and 13 may also release the respective oven opening by sideways movement, or the covers move downwardly to release the upper portion of an opening. This is advantageous, for example, if a conveyor is provided as a transport device, which moves workpieces hanging through the oven. In a suspended transport, the suspensions should be arranged so that the front end of a workpiece can protrude from the furnace while the remainder is still inside the furnace.

Preferably, at least the cover 13 at the outlet opening of the furnace 10 release different degrees of opening. For example, the cover 13 can be controlled by a drive so that it completely or only partially releases the outlet opening. Thus, the covers can only be opened as far as necessary, which prevents unnecessary heat loss.

In the interior of the furnace suitable heating means 11 are arranged, with which the workpieces 20 can be heated when passing through the furnace on the conveyor. Such heating means are known from the prior art and will not be explained in detail. Also, all other required components for operating the furnace are not the subject of the invention and can be selected by the skilled person suitable.

The individual method steps of the method according to the invention and further possible embodiments will now be explained with reference to the figures. How out Fig. 1 As can be seen, opens the cover 12 of the input opening and a workpiece 20 is moved by the transport device 30 in the oven In Fig. 2 If the cover 12 is already closed again and the workpiece 20 moves on the transport device 30 through the heating path of the furnace, which is formed by the heating means 11. In this case, the workpiece 20 is heated to a temperature which is expediently below the hardening temperature of the material of the workpiece 20. For example, if the hardening temperature of the workpiece is about 700 ° C, the heating means 11 and the passage time of the leading edge of the workpiece 20 are selected by the heating path so that the workpiece 20 is heated to a temperature of 700 ° C.

Conveniently, the length of the furnace 10 and the transport speed of the transport means 30 is selected accordingly so that the workpiece is moved continuously through the furnace and has set the desired temperature in the workpiece, as soon as the leading edge of the workpiece 20, the heating line completely to the end has passed through the furnace. Alternatively, it may also be provided to temporarily increase the movement of the transport device interrupt to keep the workpiece within the heating distance for a certain period of time.

Subsequently, the cover 13 releases the exit opening of the furnace 10, so that a part of the workpiece can be moved out of the furnace. The cover 13 does not have to be completely opened for this purpose, but can for example only release the lower region of the outlet opening, as shown in FIG Fig. 3 is shown. As soon as this portion 22 of the workpiece 20 is outside the furnace and thus outside the heating path, the movement of the transport device 30 is interrupted for a certain period of time. Outside the furnace 10 holding devices may be provided which support the workpiece 20.

In the period of the stoppage of the transport device 30, the first portion 21 of the workpiece 20, which is still within the furnace and thus in the range of the heating means 11, further heated to a temperature corresponding to at least the hardening temperature of the material of the workpiece. For example, this portion 21 is heated to a temperature above 700 ° C, while the second portion 22 of the workpiece outside the furnace is not further heated. In both subsections, different temperatures thus occur due to the different residence time of the regions in the furnace.

Depending on the ambient conditions outside the furnace 10, the second portion 22 outside the furnace 10 cools slightly, so that it must have previously been heated in the oven to a temperature at which, despite slight cooling at the end of the process, a temperature T ₁ adjusts the material only a partial structural change, so that this area remains relatively ductile in the subsequent rapid quenching. In the first sub-area 21, however, a higher temperature T _{2 is} set by the longer heating within the heating section, which causes a complete structural change and thus austenitization. During the subsequent quenching, higher strengths thus arise in this first region. In principle, however, no complete microstructure change has to take place in this area either. The Temperature and thus the degree of structural change should only be higher than in the second portion 21 in order to achieve the desired differences in the material properties.

As soon as at least the desired temperature T _{2 has been set} in the first subregion 21, the workpiece 20 can be removed from the furnace, as shown in FIG Fig. 4 is shown. The cover 13 can be further raised to increase the degree of opening, so that the workpiece 20 can be completely removed. The workpiece is now outside the furnace 10 with the desired temperatures T ₁ and T ₂ and can be supplied to further process steps. For example, it can be fed manually or by robotics to a quench bath or a forming press.

In a further embodiment of the invention, the entire workpiece is heated in the oven to a temperature corresponding to the hardening temperature of the respective material. As soon as the second subarea 22 of the workpiece is outside the heating zone, it cools to a temperature below the hardening temperature, while the first subarea 21 of the workpiece within the furnace is kept at the hardening temperature. Even so, different temperatures occur in both subareas.

As an alternative to a closed continuous furnace with housing, the method according to the invention can also be carried out with a transport device 30 which moves workpieces only through a heating section enclosed by a housing, in which the heating means is arranged. This is for example in Fig. 5 shown. In this case, it is not a closed oven, but by separating slide 12 and 13, only the region of a heating section is defined in which takes place at the transport means 30 heating by heating means 11.

The cycle times of the respective covers 12 and 13 are adapted to the residence time of the workpiece 20 in the oven, to the speed of the transport device 30 and also to the period of standstill of the transport device 30. Also, the different degrees of opening, in particular the cover 13 at the Exit opening, are also adapted to the steps in the inventive method. Thus, for example, the cover 13 of the outlet opening of the furnace 10 opens and then the movement of the transport device 30 is interrupted. After that, the cover 13 may possibly also slightly lower again. However, before the transport device 30 and thus the workpiece set in motion again, the cover 13 must open again. Simultaneously with this, the cover 12 can release the input opening to receive another workpiece. With this procedure, cycle times of 15 seconds can be achieved for the heating of workpieces.

In one embodiment of the invention, no continuous furnace is provided for heating the workpieces, but a furnace has only one opening through which workpieces are inserted and removed again. This design of a furnace is shown schematically in FIG Fig. 6 shown. A workpiece is stored in the oven 10 and optionally moved with a transport device 30 into the interior of the furnace. After the workpiece 20 has been heated to a temperature below the hardening temperature of the material of the workpiece, the cover 14 at least partially releases the furnace opening and the workpiece 20 is moved out of the oven so far that a first portion 21 is still within the furnace, while a second portion 22 is outside the furnace. In this position, the workpiece is held until the first portion 21 has been further heated to the desired temperature. Subsequently, the workpiece 20 is completely removed from the oven and the next workpiece can be treated.

Of course, not only one workpiece can be heated with the method according to the invention, but several workpieces can be treated simultaneously. This is in Fig. 7 illustrated by way of example in a schematic plan view. In this process, three workpieces 20, 20 'and 20 "are moved side by side on a transport device 30 through an oven, and at the end of the oven also portions of all workpieces protrude out of the oven to further heat the respective other sections of the workpieces within the oven is it further, that one or more workpieces are moved on a workpiece carrier through the oven.

If several workpieces are moved simultaneously through a continuous furnace, it can be provided in one embodiment of the invention that the movement of individual workpieces is temporarily interrupted in order to adapt the output of the furnace to the capacities of downstream stations. This will be explained below with reference to Figures 8-14 be explained.

Like from the Fig. 8 As can be seen, the workpieces are deposited on the roller conveyor 30 and simultaneously moved side by side by the driven rollers through the continuous furnace 10. Also in this embodiment of the invention, any other transport means may be provided. Furthermore, a separate transport device can be provided for each workpiece and the movements of these transport devices can be controlled separately from one another. For example, a plurality of roller conveyors can be arranged next to one another, with one workpiece being deposited on each roller conveyor.

In Fig. 9 If the cover 12 is already closed again and the workpieces 20, 20 'and 20 "move simultaneously on the transport device 30 through the heating path of the furnace, which is formed by the heating means 11. In this case, a heating of the workpieces 20, 20' and 20th "to a temperature which is below the hardening temperature of the material of the workpiece 20. If the hardening temperature of the workpiece, for example, at about 700 ° C, the heating means 11 and the lead time of the front edges of the workpieces 20, 20 'and 20 "are selected by the heating so that the workpieces 20, 20' and 20" on a Heat the temperature below 700 ° C.

After this common heating of the workpieces 20, 20 'and 20 ", the transport movement of at least one of the workpieces is temporarily interrupted If a separate transport device is used for each workpiece, this can be done simply by temporarily interrupting the movement of the relevant transport device. If a common transport device for all workpieces is used, a temporary Interruption of the transport movement of individual workpieces by the temporary decoupling of the respective workpiece carried by the transport device. The decoupling can be realized in different ways depending on the embodiment of the transport device. Out Fig. 10 For example, it can be seen how two of the workpieces 20 'and 20 "are temporarily decoupled from the conveyor 30 by being lifted by plungers 40 and 41 so that they no longer contact the conveyor 30. In other types of conveyors than a roller conveyor For example, decoupling may be accomplished by unlatching workpieces from a transport device into which they have been previously hung.

The plungers 40 and 41 are located below the workpieces and perform a clocked up and down movement, which is controlled by a control device. The plunger can be guided by gaps between the individual rollers of the roller conveyor and so one or more workpieces clocked raise and lower again. In the in Fig. 3 In this embodiment, two workpieces 20 'and 20 "are decoupled from the roller conveyor while a remaining workpiece 20 is moved on, but the invention is not limited to this embodiment but, for example, two workpieces can be moved while only one workpiece is decoupled, or other number of workpieces other variations are possible.

Subsequently, the cover 13 releases the exit opening of the furnace 10, so that a part of the further moving workpiece 20 can be moved out of the furnace. As soon as this portion 22 of the workpiece 20 is outside the furnace and thus outside the heating zone, the movement of the transport device 30 is interrupted for a certain period of time, for example 15-25 seconds, for this workpiece 20.

As soon as at least the desired temperature T _{2 has been set} in the first subregion 21, the workpiece 20 can be removed from the furnace, as shown in FIG Fig. 11 is shown. Subsequently or already while the first workpiece 20 is being driven out of the oven, the transport movement of at least one of the remaining workpieces 20 'resumed. In the embodiment of Fig. 11 the respective workpiece 20 'is again coupled to the transport device 30 by the associated plunger perform a downward movement and settle the workpiece again on the transport device 30, which transports it to the furnace exit.

For this workpiece 20 ', the explained steps of partially continuing the heating are repeated, while the remaining workpiece 20' is further decoupled from the transport device 30, as shown in FIG Fig. 12 is shown. If the workpiece 20 'removed from the oven, and the plunger of the workpiece 20 "are lowered and also for this workpiece 20" 20 partial continuation of the heating can be done at the end of the furnace. At this time, new workpieces may already be introduced into the oven through the entrance opening of the oven as shown in FIG Fig. 13 is shown, so that repeat the described method steps.

The cycle times of the respective covers 12 and 13 are adapted to the residence time of the workpiece 20 in the oven, to the speed of the transport device 30 and also to the period of standstill of the transport device 30. The upward and downward movement of the plungers is also adapted to these parameters, wherein the actuation of all components preferably takes place by means of a common control device.

In the Fig. 14 FIGURE 11 is a top view of how three workpieces 20, 20 'and 20 "are heated by the oven 10. The workpieces were previously placed side-by-side on the roller conveyor 30 and moved through the oven to above rams 40, 41, 42 , 43, 44 and 45, wherein for decoupling of each workpiece there are for example two plungers each which can raise and lower a workpiece at two points, the plungers being arranged in spaces between the individual rollers of the roller conveyor, so that they are arranged between the rollers Rolls can be pulled out Fig. 14 the activated plungers 40 and 41 are shown filled in black, wherein these activated plungers have lifted the workpiece 20 "and thus decoupled it from the movement of the roller conveyor 30. The currently not activated plungers 42, 43, 44 and 45 are white. This applies to the associated plunger of the workpiece 20, which has already been removed from the oven and for the associated plunger 42 and 43 of the workpiece 20 ', which currently undergoes a partial continuation of the heating at the end of the furnace. In order to be able to perform the timing of the individual plungers, sensors may be provided within the furnace, which determine the position of the workpieces on the transport device 30 and transmit to a control device which performs a suitably adapted control of the upward and downward movement of the plunger. The plungers can be designed in different ways to safely lift and lower workpieces.

10

Ofen, Durchlaufofen

11

Heizmittel

12

Abdeckung Eingangsöffnung; Trennschieber

13

Abdeckung Ausgangsöffnung; Trennschieber

14

Abdeckung

20,20',20"

Werkstück

21,21',21"

Erster Teilbereich eines Werkstücks mit höherer Temperatur

22,22',22"

Zweiter Teilbereich eines Werkstücks mit niedrigerer Temperatur

30

Transporteinrichtung, Rollenförderer

40,41

Stößel (aktiviert)

42,43,44,45

Stößel (deaktiviert)

LIST OF REFERENCE NUMBERS

10

Oven, continuous furnace

11

heating

12

Cover entrance opening; separating slide

13

Cover outlet opening; separating slide

14

cover

20,20 ', 20 "

workpiece

21,21 ', 21 "

First part of a workpiece with a higher temperature

22,22 ', 22 "

Second part of a workpiece with lower temperature

30

Transport device, roller conveyor

40.41

Plunger (activated)

42,43,44,45

Plunger (deactivated)

Claims (17)

Method for heating at least one workpiece (20; 20 '; 20 ") in an oven (10) in which the workpiece (20; 20';20") is heated by heating means (11),
characterized,
the following steps take place after an entire workpiece (20; 20 '; 20 ") has been heated by the heating means in a first step: Moving the workpiece (20; 20 '; 20 ") far enough out of the oven (10) that a first portion (21; 21';21") of the workpiece (20; 20 '; 20 ") is still within the Oven (10) is located while a second portion (22; 22 '; 22 ") of the workpiece (20; 20';20") is located outside the oven (10); Holding the workpiece (20; 20 '; 20 ") in this position for a predetermined period of time; and Moving the entire workpiece (20; 20 '; 20 ") out of the oven (10). Method according to claim 1,
characterized,
that at least one workpiece (20; 20 '; 20 ") is heated in a continuous furnace (10) and the workpiece (20; 20';20") is moved through a continuous furnace (10) by a transport device (30) a heating section is heated by heating means (11), the following steps taking place after the side of a workpiece (20; 20 '; 20 ") lying in the transport direction has passed through the heating section of the continuous furnace (10): Moving the workpiece (20; 20 '; 20 ") out of the heating path of the continuous furnace (10) by the transport device (30) so that a first subregion (21; 21';21") of the workpiece (20; '; 20 ") is still within the heating zone, while a second subarea (22; 22';22") of the workpiece (20; 20 '; 20 ") is already outside the heating zone; - interrupting the movement of the transport device (30) at this position of the workpiece (20; 20 '; 20 ") for a predetermined period of time; - Moving the entire workpiece (20: 20 ', 20 ") by the transport device (30) from the heating section of the continuous furnace (10) out. Method according to one of the two claims 1 and 2,
characterized,
that the first part region (21; 21 '; 21 ") of the workpiece (20; 20';20") by the process to a temperature T ₁ is heated, which is below the hardening temperature of the material of the workpiece (20; 20 '; 20 ") while the second portion (22; 22 ';22") of the workpiece (20; 20'; 20 ") is heated to a temperature T ₂ equal to the hardening temperature of the material of the workpiece (20; 20 ';"). Method according to one of claims 2 to 3,
characterized,
in that, when the transport side of the workpiece (20; 20 '; 20 ") moves in the direction of travel of the continuous furnace (10), the entire workpiece (20; 20';20") is heated to a temperature below the hardening temperature the second part region (22, 22 ', 22 ") of the workpiece (20, 20', 20") within the heating path is further heated to a temperature T ₂ which corresponds to the hardening temperature of the material of the workpiece (20; 20 '; 20 ") when the first portion (21; 21';21") of the workpiece (20; 20 '; 20 ") is outside the heating path. Method according to one of claims 2 to 4,
characterized,
that at least two workpieces (20, 20 ', 20 ") are moved simultaneously by means of at least one transport device (30) side by side through the continuous furnace (10) and thereby heated by heating means (11) on a heating path. Method according to claim 5,
characterized,
the following steps take place after the sides of the workpieces (20; 20 '; 20 ") lying in front in the direction of transport have partially or completely passed through the heating path of the continuous furnace (10): Interrupting the transport movement of at least one first workpiece (20 ', 20 "), while at least one second workpiece (20) is moved out of the heating section of the continuous furnace (10) by means of the transport device (30) such that a first partial region (21 ) of the workpiece (20) is still within the heating zone, while a second partial area (22) of the workpiece (20) is already located outside the heating zone; - interrupting the transport movement at this position of the at least one second workpiece (20) for a predetermined period of time; - Moving the at least one second workpiece (20) from the heating section of the continuous furnace (10) out; - Resumption of the transport movement of the at least one first workpiece (20 ', 20 ") and moving the at least one first workpiece (20', 20") far out of the heating path of the continuous furnace (10) out, that a first portion (21 '; 21 ") of the workpiece (20 ', 20") is still within the heating path, while a second portion (22'; 22 ") of the workpiece (20 ';20") is already outside the heating path; - interrupting the transport movement at this position of the at least one first workpiece (20 ', 20 ") for a predetermined period of time; Moving the at least one first workpiece (20 ', 20 ") out of the heating path of the continuous furnace (10). Method according to claim 6,
characterized,
in that each of the workpieces (20; 20 '; 20 ") is moved through the continuous furnace (10) by means of a separate transport device, and interrupting the transport movement of the at least one first workpiece (20';20") in step a) by interrupting Movement of the associated transport device takes place while the resumption of the transport movement of the at least one first workpiece (20 ', 20 ") in step d) takes place by resuming the movement of the associated transport device. Method according to claim 6,
characterized,
in that all workpieces (20; 20 '; 20 ") are moved by means of a common transport device (30) through the continuous furnace (10), and the transport movement of the at least one first workpiece (20';20") is interrupted in process step a) Decoupling of the at least one first workpiece (20 ', 20 ") from the transport device (30), while the resumption of the transport movement of the at least one first workpiece (20', 20") in method step d) by coupling the at least one first workpiece ( 20 ', 20 ") to the transport device (30). Method according to claim 8,
characterized,
in that the transport device (30) is a roller conveyor on which the workpieces (20; 20 '; 20 ") are simultaneously moved side by side through the heating path of the continuous furnace (10), and in that the decoupling of at least one first workpiece (20'; ) from the roller conveyor by lifting the workpiece (20 '; 20 ") to a position where the workpiece (20';20") is not in contact with the roller conveyor while coupling the at least one first workpiece (20 ';") takes place on the roller conveyor by lowering the workpiece (20 ', 20") into a position in which the workpiece (20', 20 ") again has contact with the roller conveyor and is moved by this in the transport direction. Method according to claim 9,
characterized,
that the raising and lowering a workpiece (20 '; 20 ") by one or more rams (40; 41; 42; 43:; 45 44) takes place below the workpieces (20';20") are arranged and timed to move upward and downward, wherein the upward movement of at least one plunger (40; 41; 42; 43; 44; 45) causes lifting of a workpiece (20 '; 20 ") from below, while the downward movement of at least one plunger (40; 41; 42; 43; 44; 45) the Lowering a workpiece (20 ', 20 ") causes, and that this movement of the plunger (40; 41; 42; 43; 44; 45) is controlled by a control device. Continuous furnace (10) for heating at least one workpiece (20,20 ', 20 "), in which the workpiece (20,20', 20") by a transport device (30) through the continuous furnace (10) movable and thereby on a heating line of heating means (11) is heatable,
characterized,
in that the transport device (30) has means for moving the workpiece (20, 20 ', 20 ") far enough out of the heating path of the continuous furnace (10) that a first subregion (21, 21', 21") of the workpiece (20 , 20 ', 20 ") is still within the heating path, while a second portion (22, 22', 22") of the workpiece (20, 20 '; 20 ") is already outside the heating path, and in that the movement of the transport device (30) at this position of the workpiece (20,20 '; 20 ") for a predetermined period of time by a control device is interruptible. Continuous furnace according to claim 11,
characterized,
a plurality of workpieces (20; 20 '; 20 ") can be moved simultaneously and side by side by means of at least one transport device (30) through the continuous furnace (10) and can be heated by heating means (11) on a heating path. Continuous furnace according to claim 12,
characterized,
in that the at least one transport device (30) has means for moving a workpiece (20; 20 '; 20 ") far enough out of the heating path of the continuous furnace (10) that a first subregion (21; 21';21") of the respective one Workpiece (20; 20 ', 20 ") is still within the heating section, while a second portion (22; 22';22") of the respective workpiece (20) is already outside the heating path, and that the movement of the at least one transport device (30) at this position of the respective workpiece (20; 20 '; 20 ") is interruptible for a predetermined period of time, and that the continuous furnace (10) further comprises means for temporarily interrupting the Transport movement of workpieces (20 ', 20 ") during the passage of the furnace (10). Continuous furnace according to claim 13,
characterized,
that for each of the workpieces (20; 20 '; 20 ") has a separate transport means is provided with which the respective workpiece (20; 20';20") through the continuous furnace (10) is movable with the respective transport devices can be controlled separately from each other, and the temporary interruption of the transport movement of a workpiece (20 ', 20 ") can take place by the temporary interruption of the movement of the associated transport device. Continuous furnace according to claim 13,
characterized,
that for the transport of all workpieces (20; 20 '; 20 ") through the continuous furnace (10) has a common transport device (30) is provided, and in that the continuous furnace (10) means for temporarily decoupling of individual workpieces (20';20") from the transport device (30). Continuous furnace according to claim 15,
characterized,
in that the transport device (30) is a roller conveyor on which the workpieces (20; 20 '; 20 ") are movable through the heating path of the continuous furnace (10), and in that the temporary decoupling of a workpiece (20';20") from the Roller conveyor by lifting the workpiece (20 ', 20 ") takes place in a position in which the workpiece (20';20") has no contact with the roller conveyor, while coupling a workpiece (20 ', 20 ") to the roller conveyor through Lowering of the workpiece (20 ', 20 ") takes place in a position in which the workpiece (20', 20") again has contact with the roller conveyor and is movable through this in the transport direction. Continuous furnace according to claim 16,
characterized,
in that for raising and lowering a workpiece (20 '; 20 "), one or more rams (40; 41; 42; 43; 44; 45) are provided, which are located below the workpieces (20';20") Rams (40; 41; 42; 43; 44; 45) are designed for clocked upward and downward movement, and a control device is provided which controls this upward and downward movement of the rams (40; 41; 42; 43; 44; 45 ).

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