EP2992116B1 - Method and device for heat treating elongated products - Google Patents

Description

The invention relates to a method for the heat treatment of long products, in particular metallic long products such as wires, sheets or the like made of steel, the long product being passed through an oven with at least one heating device for heating an atmosphere and an inlet and an outlet, the long product being passed through the Inlet can be introduced into the oven and can be carried out through the outlet thereof, and the heated product is used to heat the long product passed through the oven, the atmosphere in the oven being conducted in a circuit with lateral flow of the long product passed through the oven, characterized in that that the atmosphere is guided in a meandering loop around the long product, with the long product being flown from above and below.

Furthermore, the invention relates to a device for the heat treatment of long products, in particular metallic long products such as wires, sheets or the like made of steel, comprising at least one furnace with at least one heating device for heating an atmosphere and an inlet and an outlet along which the long product enters the furnace is insertable and executable from it, with the heated atmosphere the long product passed through the furnace can be heated, the atmosphere in the furnace with lateral flow of the long product passing through the furnace being feasible in a cycle, characterized in that the cycle as a meandering loop and is formed in a meandering manner around the transport path in the area of the side flow against the long product, so that the long product is flowed from above and below.

In the production of long metal products such as wires, sheets or other flat products made of steel, heat treatment steps are often used as intermediate steps or final steps in a process chain. For example, metallic wires provided with a layer of copper and zinc are heat-treated in diffusion furnaces in order to convert the layer of copper and zinc to brass. This can then be done in a unit downstream of the diffusion furnace stress relieving at temperatures of up to 800 ° C. For many long products alone, the stress relieving process step alone is a necessary intermediate step in order to form a semifinished product with suitable mechanical parameters, for example for a subsequent forming process. In the prior art, heat treatment processes for long products and devices for their execution are known DE 695 09 097 , WO 2011/094775 and DE 38 02 476 known for example.

Heat treatment of steel wires for the purpose of diffusion in areas close to the surface and the formation of suitable surface layers, as well as stress relief annealing can be carried out in different ways according to the prior art:

Resistance heating (so-called Joule heating) creates an electrical contact with the wire, which subsequently represents resistance. The wire is then energized so that the wire heats up and heat flows from the inside out. However, this method has several disadvantages. First, it is necessary to make electrical contact with the wire. So-called contact fires can occur at the contact points, which favors the formation of martensite. This martensite formation can in turn lead to wire cracks due to the hard and brittle structure of the martensite. On the other hand, resistance heating is difficult to regulate, especially with regard to a temperature range. Finally, such a method is mainly suitable for stress relief annealing, but not very well for near-surface diffusion, because the heat in the wire flows from the inside to the outside.

It is also possible to achieve inductive heating of a wire by means of one or more coils in a continuous process. In this method, the heat flows from a wire surface into the inside of the wire. A disadvantage of this, however, is that the wire must always be in the center of a coil for precise temperature control. Otherwise there may be inhomogeneities in the structure of the wire. If several coils are provided one after the other, which is the rule in particular in the case of continuous processes for achieving a required temperature and thus a conversion, these problems can hardly be overcome.

Another process is the so-called fluidized bed process. This process is characterized by good heat transfer, but the media used, such as salt or sand, have a corrosive and / or abrasive effect. In particular in a subsequent process step such as drawing a wire, an abrasive portion on the surface of the drawn wire also affects the devices and their components, e.g. B. drawing dies, extremely disadvantageous.

Finally, it is also known for stress relief annealing to use lead baths or salt baths. However, such baths, in addition to a possible loss of lead in lead baths and a so-called "entrainment" of lead, have the particular disadvantage that speeds for carrying out a long product are limited. A high level of economy cannot therefore be achieved.

The object of the invention is to provide a method of the type mentioned at the outset with which heat treatment processes of long products, in particular steel wires, can be carried out effectively and with high quality in a continuous process.

Another object of the invention is to provide a device suitable for this.

The procedural object of the invention is achieved if, in a method of the type mentioned at the outset, the atmosphere in the furnace is circulated with the side flow of the long product passed through the furnace.

Several advantages are realized with a method according to the invention. A particularly effective heating of the long product through the furnace can be achieved by the lateral flow. Since heating to a desired temperature range can be achieved over a short distance, the furnace used can also have a short overall length. This in turn means that only a small volume of the furnace needs to be heated. In addition, because the atmosphere is circulated, energy expenditure is minimized. The flow towards the side of the continuously guided long product also leads to long quality products to be treated. Overall, this results in an economically effective process which also leads to a high quality of the long product being treated.

In order to achieve a directed flow towards the side, the atmosphere can be guided onto the long product with guide means. The flow direction of the atmosphere towards the long product can be set in a targeted manner using the guide means.

Provision can be made for baffles to be used as a guide for the lateral flow of the long product in order to guide the atmosphere in the circuit as directed as possible and with simultaneous flow against the long product. In particular, it can be provided that the long product is flown to the side with a plurality of guide means above and below the long product passed through the furnace. It is expedient for the long product to flow from above and below, in particular alternately, at an angle of 45 ° to 135 °, preferably approximately vertically.

In the area of the continuous passage of the long product, the invention provides for the atmosphere to be guided in a meandering loop around the long product. As a result, it is possible in a simple manner, in particular if guide plates are provided as guide means, to achieve a desired lateral flow of the guided long product in a small space. Simultaneously, the meandering loop can be integrated into the circuit or represent part of the same.

In order to be able to fine-tune the lateral inflow of the long product in one or more areas of the furnace, even with given guide means and thus basically the predetermined flow direction, it can advantageously be provided that the inflow of the long product is arranged with actuating means arranged above and below a transport path of the long product , in particular flaps, is regulated.

It is particularly advantageously provided that the atmosphere is heated to a first temperature in a preheating zone and to a second temperature in a subsequent heating zone. This enables a targeted temperature setting for the purpose of loading the long product. It is even more important that part of the atmosphere between the preheating zone and the subsequent heating zone can also be removed and conducted in a separate circuit. This makes it possible to connect a post-treatment unit to the furnace, in which part of the second, separate circuit is located. The removed part of the atmosphere is then led into a post-treatment unit connected to the furnace. The long product can be kept in the post-treatment unit with the removed part of the atmosphere in a predetermined temperature range. The temperature range in the aftertreatment unit is then essentially set by heating in the preheating zone, which completely passes through the atmosphere. The removed part, with the temperature set in the preheating zone, is then fed into the aftertreatment unit. The remaining part of the atmosphere is heated to a second temperature in the subsequent heating zone and then used for the side flow or loading of the long product passed through the furnace. For this purpose it can also be provided that a quantity of the removed part of the atmosphere with one between the preheating zone and the subsequent heating zone arranged adjusting means is set. This allows a ratio of the proportions of the portions of the atmosphere passed through the furnace on the one hand and the post-treatment unit on the other to be set precisely.

If two circuits are provided, it is preferred that the removed part of the atmosphere at the end of the own circuit is brought together with a part of the atmosphere circulated in the furnace along the circuit. The two sub-streams then in turn reach the preheating zone, after which, after heating to the first temperature, a split into sub-streams takes place for the first or second, separate circuit.

In principle, a method according to the invention can be operated in countercurrent. However, it is preferred that the atmosphere in the area of the long product is conducted in the same direction as the long product. This results in favorable temperature management because the long product is still at a low temperature in the area of the inlet, but the atmosphere there is at the highest temperature. This enables the long product to be heated quickly.

In accordance with the above, the method is usually implemented in such a way that the long product is continuously fed through the furnace.

The further object of the invention is achieved if, in a device of the type mentioned at the outset, the atmosphere in the furnace can be conducted in a circuit with lateral flow against the long product passed through the furnace.

A device according to the invention is distinguished by the fact that, due to the lateral flow provided in the furnace, the furnace is short and thus has a small volume. This in turn means that only a small volume can be kept at temperature with the atmosphere. Energy expenditure is therefore minimized. In addition, the lateral flow of the long product also results in a high quality of a long product treated in this way.

Guide means are preferably provided with which the atmosphere can be conducted onto the long product. In this way, a desired lateral flow against the long product can be achieved in a simple manner.

Baffles are expediently provided as guide means for the lateral flow of the long product. This allows the atmosphere to be circulated in a particularly effective manner and in particular in terms of flow technology to the long product to be treated.

A large number of guide means is expediently provided in the furnace above and below a transport path of the long product. This means that a long product passed through the furnace can alternately be exposed to the atmosphere from above and below. The guide means are preferably oriented such that an angle of attack for the long product is 45 ° to 135 °, preferably approximately 90 °.

In particular, it can be provided that the circuit in the area of the lateral flow against the long product is meandering around the transport path. This enables a compact design of the furnace to be achieved with the desired side flow of the long product.

Adjustment means for regulating the flow of the long product can be provided above and below the transport path in order to gradually vary the atmosphere around the long product.

It is particularly expedient that a preheating zone is provided for heating the atmosphere to a first temperature and a subsequent heating zone for heating the atmosphere to a second, higher temperature. For this purpose, at least one heating device can be arranged in the preheating zone and in the heating zone. In this context, at least one adjusting means can be arranged between the preheating zone and the heating zone, with which a part of the atmosphere carried in the circuit can be branched off, and a separate circuit is provided in which the branched part of the atmosphere can be guided. This makes it possible to establish a second circuit, which is provided, for example, for an aftertreatment unit, in particular for stress relieving can. On the one hand, the entire atmosphere can then be brought to a first temperature in the preheating zone. This first temperature is decisive for the removed part that is led into the aftertreatment unit. The remaining part of the atmosphere passes through a second heating device and is brought to a second, higher temperature, which is required in the furnace for the lateral flow of the long product. Accordingly, an aftertreatment unit can be connected to the furnace and the removed part of the atmosphere can be passed through the aftertreatment unit in a separate circuit in order to keep the long product in a predetermined temperature range.

• Fig. 1 eine schematische Darstellung einer erfindungsgemäßen Vorrichtung im Querschnitt;
• Fig. 2 eine perspektivische Ansicht einer Vorrichtung gemäß Fig. 1.

Further features, advantages and effects of the invention result from the exemplary embodiments presented below. In the drawings, to which reference is made, show:

• Fig. 1 a schematic representation of a device according to the invention in cross section;
• Fig. 2 a perspective view of a device according to Fig. 1 .

example 1

In 1 and 2 A device 1 according to the invention is shown in more detail. The device 1 comprises an oven 2 and an aftertreatment unit 13 arranged downstream of the oven 2.

The furnace 2 has an inlet 5 and an outlet 6. A long product L can be introduced along a transport path 9 via the inlet 5, which is provided with several flaps. The long product L is usually a wire, in particular a metallic wire such as a steel wire. In principle, however, other long products L such as rods, sheets or strips, in particular those made of a metallic material such as steel, can also be guided along the transport path 9 or treated in the furnace 2. At an end opposite the end with the inlet 5, the oven 2 has the outlet 6 mentioned, in the region of which the long product L, which is generally continuously guided through the oven 2, is moved out of it again. In the area of the inlet 5 and, if appropriate, the outlet 6, a plurality of flaps which are movable in the direction of the transport path 9 are provided, which on the one hand the Completely gas-tightly close furnace 2 in the area of inlet 5 and outlet 6, but on the other hand also allow the long product L to be drawn in for the first time with a somewhat more voluminous pulling device if the furnace 2 is initially loaded with the long product L. If a plurality of long products L guided in parallel are provided, they are guided through the oven 2 at a distance from one another.

A circuit K1 is provided in the interior of the furnace 2, in which an atmosphere 4 is circulated. For this purpose, a fan 15 is provided, which draws in the atmosphere 4 and in an upper region of the circuit K1 first of all to a heating device 3 of a preheating zone 11 and then to a heating zone 12. In the preheating zone 11, the atmosphere 4 is preheated to a first temperature. As will be explained later, only part of the atmosphere 4 is then conveyed to a downstream heating device 3 or the heating zone 12. From there, the atmosphere 4 is diverted so that it is conveyed in the area of the inlet 5 in the same direction as the long product L. Thereafter, guide means 7 are provided, which lead the atmosphere 4 alternately from above and below to the long product L passed through the furnace 2. The guide means 7 form a meandering loop 8, as shown in FIG Fig. 1 can be seen. The guide means 7 can in particular be formed from guide plates 71, 72, 73. In principle, it would be possible for the middle guide plates 72, 73 shown between outer guide plates 71 to be deleted without replacement, but it has proven to be expedient to provide a plurality of intermediate guide elements in order to achieve a homogeneous flow of the long product L through the atmosphere 4. The circuit K1 is therefore widened in the region of a first curvature of the loop 8 and two intermediate guide plates are provided. As a result, one intermediate baffle is sufficient to achieve a desired homogeneous flow of the long product L. Of course, it is also possible that several intermediate baffles are provided in the individual sectors. How from Fig. 1 it can also be seen that the guide plates 71, 72, 73 are arranged such that there is essentially an approximately vertical flow of the long product L through the atmosphere 4. As a result, the long product L can be brought to the desired temperature particularly quickly, because the heat transfer is very effective and the furnace 2 can thus be constructed to be particularly short. However, it is not absolutely necessary that the in Fig. 1 shown vertical angle is set. Deviations from this, in particular in the angular range from 45 ° to 135 °, are possible. Furthermore, in In the area of the guide plates 71, 72, 73 or the loop 8, which extends around the long product L in the area of the furnace 2, several adjusting means 10 are also provided, with which a fine adjustment of the atmosphere 4 in the respective sector can be achieved. Like the flaps discussed with regard to the inlet 5, these adjusting means 10 are also movably mounted, so that the long product L can be drawn in when the system is started up. At the end of the meandering course of the loop 8, the fan 15 connects, which in turn leads the atmosphere 4 back to the preheating zone.

As mentioned, only part of the atmosphere 4 is led from the preheating zone 11 to the heating zone 12. Part of the atmosphere 4 is fed to a second circuit K2 by means of a further adjusting means 14, in particular a flap. This circuit K2 leads to the aftertreatment unit 13, where the preheated atmosphere 4, which is set to a first temperature with the heating device 3 of the preheating zone 11, serves for stress relieving of the long product L. The post-treatment unit 13 can, but is not mandatory, have several sections, into each of which portions of the atmosphere 4 are led. It is also conceivable that additional heating devices 3 are provided in the aftertreatment unit 13 in order to set locally desired temperatures. It is also possible that 13 temperature sensors are arranged in the aftertreatment unit, which regulate the heating device 3 in the area of the preheating zone 11 by measuring the temperature. The circuit K2 is designed in such a way that the atmosphere 4 led into the area of the long product L in the aftertreatment unit 13 is returned to the fan 15, so that ultimately the two recirculated partial flows of the atmosphere 4 from the circuit K1 and the circuit K2 in turn result in the total circulated atmosphere 4 results. In a method according to the invention, a long product L is passed through the furnace 2. This process can in particular be a heat treatment for the purpose of diffusion, for example after-treatment of a brass layer on a steel wire. The long product L is guided through the furnace 2 and passes through the meandering loop 8, with a lateral flow of the long product L with the atmosphere 4 brought to a second temperature by the heating device 3 of the heating zone 12 in several successive areas. The inflow from the side results in an effective heat transfer, the long product L being heated from the outside like a wire. This enables the desired diffusion conversion to be carried out in a short way.

After passing the outlet 6, the long product L is guided into the aftertreatment unit 13, the atmosphere 4 circulated in the second circuit K2 ensuring that the long product L is annealed with low stress.

By using the two circuits K1, K2 in the area of the furnace 2 or the aftertreatment unit 13 coupled with the preheating zone 11 and the heating zone 12 and the distribution of the mass flows through the actuating means 14, the furnace 2 together with the aftertreatment unit 13 can achieve a high quality of heat-treated Long products L are operated energetically effectively.

Example 2

In this example, the procedure is as in Example 1, but using several strips as long products L. The belts are arranged vertically, so that optimal stacking or use of space in the oven 2 results. By setting it up vertically, in contrast to arranging the belts horizontally, sag is minimized. An obliquely inclined arrangement of the tapes is also possible in order to promote circulation of the atmosphere around the tapes and thus heating them. Like the wires in Example 1, the ribbons are spaced apart so that the atmosphere between the long products L can pass through.

Example 3

In this example, the procedure is as in Example 1, but using several strips as long products L. In contrast to Example 1, however, the meandering loop 8 is rotated by 90 °, so that the flow does not occur essentially vertically from above and below, as in Example 1, but from the left and right. As long products L, tapes in particular can be treated with this arrangement, although possible applications of this arrangement are not limited to tapes.

Claims (15)

1. A method for heat treating long products (L), particularly metallic long products (L), such as wires, metal sheets or the like, made from steel, the long product (L) being guided through a furnace (2) using at least one heating device (3) for heating an atmosphere (4) and an inlet (5) and an outlet (6), it being possible to insert the long product (L) into the furnace (2) through the inlet (5) and guide the long product out of the same through the outlet (6), and the long product (L) guided through the furnace (2) being heated using the heated atmosphere (4), the atmosphere (4) in the furnace (2) being guided in a circuit (K1), with lateral flow around the long product (L) guided through the furnace (2), characterized in that the atmosphere (4) is guided in a meandering loop (8) around the long product (L), wherein the long product (L) is flowed around from above and below.
2. The method according to claim 1, characterized in that the atmosphere (4) is guided onto the long product (L) using guide means (7).
3. The method according to claim 1 or 2, characterized in that baffle plates (71, 72, 73) are used as guide means (7) for the lateral flow around the long product (L).
4. The method according to one of claims 1 to 3, characterized in that the long product (L) is flowed around laterally above and below using a multiplicity of guide means (7).
5. The method according to claim 4, characterized in that the long product (L) is flowed around from above and below at an angle of 45° to 135°, preferably approximately perpendicularly.
6. The method according to one of claims 1 to 5, characterized in that the flow around the long product (L) is regulated using control devices (10), particularly flaps, arranged above and below a transport path (9) of the long product (L).
7. The method according to one of claims 1 to 6, characterized in that the atmosphere (4) is heated to a first temperature in a preheating zone (11) and to a second temperature in a subsequent heating zone (12).
8. The method according to claim 7, characterized in that a part of the atmosphere (4) is discharged between the preheating zone (11) and the subsequent heating zone (12) and guided in a separate circuit (K2).
9. A device (1) for heat treating long products (L), particularly metallic long products (L), such as wires, metal sheets or the like, made from steel, comprising at least one furnace (2) with at least one heating device (3) for heating an atmosphere (4) and an inlet (5) and an outlet (6), along which the long product (L) can be inserted into the furnace (2) and guided out of the same, it being possible to heat the long product (L) guided through the furnace (2) using the heated atmosphere (4), it being possible to guide the atmosphere (4) in the furnace (2) in a circuit (K1), with lateral flow around the long product (L) guided through the furnace (2), characterized in that the circuit (K1) is constructed as a meandering loop (8) and to run in a meandering manner around the transport path (9) in the region of the lateral flow around the long product (L), so that the long product (L) is flowed around from above and below.
10. The device (1) according to claim 9, characterized in that guide means (7) are provided, using which the atmosphere (4) can be guided onto the long product (L).
11. The device (1) according to claim 9 or 10, characterized in that baffle plates (71, 72, 73) are provided as guide means (7) for the lateral flow around the long product (L).
12. The device (1) according to one of claims 9 to 11, characterized in that a multiplicity of guide means (7) are provided above and below a transport path (9) of the long product (L) in the furnace (2).
13. The device according to claim 12, characterized in that the guide means (7) are aligned for a flow angle for the long product (L) of 45° to 135°, preferably an approximately perpendicular flow angle.
14. The device (1) according to one of claims 9 to 13, characterized in that control devices (10) are provided above and below the transport path (9) for regulating the flow around the long product (L).
15. The device (1) according to one of claims 9 to 14, characterized in that a preheating zone (11) is provided for heating the atmosphere (4) to a first temperature and a subsequent heating zone (12) is provided for heating the atmosphere (4) to a second, higher temperature.

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