EP0179050A2 - Furnace for heat-treating light metal bars - Google Patents

Abstract

For the heat treatment of light metal bars (3), a step conveyor for the individual bars (3) lying transversely to the conveying direction is provided in a furnace chamber (2) between a product inlet and a product outlet. In order to ensure an advantageous heat treatment, the step conveyor consists of at least two vertical conveying sections (4a, 4b), which are connected to one another and connected by a transfer (13) with opposite conveying directions, whereby between the conveying section (4a) adjoining the material inlet and the immediately adjacent one Conveyor section (4b) a vertical partition (14) is provided.

Description

The invention relates to a furnace for the heat treatment of light metal bars, consisting of a furnace chamber through which hot gas flows, in which a step conveyor is provided between the goods inlet and a goods outlet for the individual bars lying transversely to the conveying direction.

For the extrusion of profiles or tubes made of light metal, it is generally assumed that extruded round bars, which must be subjected to a heat treatment known as homogenization annealing in order to compensate for casting heterogeneities that occur during continuous casting. The treatment temperature for the most commonly used alloys is around 560 - 580 ° C. After this homogenization temperature has been reached, the bars must be kept at this temperature in order to ensure the time required for the diffusion processes. If the bars are heated for this purpose in a continuous furnace, which has the advantage over the heating of a stack of bars in a chamber furnace above all the same heat treatment of all bars, the walking beam conveyor must receive a corresponding number of bars for a desired throughput so that the individual bars not only brought to the homogenization temperature within the continuous furnace, but can also be kept at this temperature for a predetermined time, which is generally several hours. However, the comparatively large number of ingot receptacles requires a large furnace length, which in turn means a large furnace space pulls, so that there is an unfavorable ratio of the furnace output to the furnace volume. Since the bars of the walking beam conveyor are mainly subjected to bending due to the bars on them, these bars must be supported accordingly. However, these supports for the walking beams which penetrate the furnace housing require passage openings which allow the supports to move in the conveying direction in accordance with the step length of the walking beam conveyor, so that despite the attempts to seal these passage openings in a heat-insulating manner, increased heat losses are to be expected, due to the large length of the furnace are significant from the start.

The endeavors to shorten the length of such continuous furnaces have resulted in the furnace space to be passed being divided into two differently heated zones in the conveying direction, namely a heating zone and a zone in which the treatment temperature reached is maintained. Since, due to this subdivision of the furnace space, the ingots can be heated to the treatment temperature with hot gases that have been overheated compared to this treatment temperature, the heating time can be reduced considerably and the length of the heating zone can be shortened accordingly. Nevertheless, the space required for such continuous furnaces remains large, so that it has been proposed to heat the ingots to the required treatment temperature in separate tunnel furnaces, which, however, significantly increases the investment and construction costs.

The subjected to a heat treatment billet must be reheated prior to extrusion to achieve a certain ductility, whereby the required heating temperatures about 50 to 100 ^* C below the treatment temperature for the homogenization. This heating of the bars before the extrusion generally takes place in separate furnaces, which entails an additional expenditure of energy. It is therefore obvious that the homogenization glu hen the ingot immediately before pressing in order to save the subsequent warming up to the pressing temperature. The merging of the homogenization annealing and the warming up for the pressing process in a common continuous furnace, however, generally fails because of the large space requirement of such a furnace, because the space available is limited, particularly in existing extrusion plants.

Finally, in order to be able to convey light metal bars for heat treatment through a furnace, it is known (DE-PS 752 031) to use a revolving, vertical chain conveyor, the conveyor chains of which have supporting links for receiving the light metal bars. Compared to step conveyors, chain conveyors of this type have the considerable disadvantage that the conveying speed must inevitably remain the same over the entire conveying path and that the bars in the area of the upper deflection wheels have to be lifted from the support links and must be newly caught during the transition from the chain strands leading up to the chain strands leading downwards. In addition, the known furnaces with such vertical chain conveyors can only offer a uniform treatment temperature for all the ingots located in the furnace chamber, so that a division of the furnace chamber into a heating zone and a heat treatment zone is not possible.

The invention is therefore based on the object to avoid these deficiencies and to improve a furnace for the heat treatment of light metal ingots of the type described above in such a way that the space required for the continuous furnace is substantially reduced so that the individual ingots while maintaining an advantageous efficiency of the heat treatment required in each case can be subjected and that the step conveyor between the product inlet and the product outlet of the furnace does not require expensive covering of through openings in the furnace housing.

The invention achieves the stated object in that the step conveyor is arranged in a shaft-like furnace space and in a manner known per se from at least two vertical conveying lines arranged next to one another and connected to one another by a transfer line is set and that at least between the conveyor line adjoining the material inlet and the immediately adjacent conveyor line a vertical partition dividing the shaft-like furnace space is provided.

By arranging vertical, side-by-side conveyor lines with the opposite conveying direction in a shaft-like furnace space enclosing these conveyor lines, the floor space required for the furnace is first significantly reduced compared to the conventional continuous furnaces with horizontal walking beam conveyors. In addition, the height of the furnace space compared to the required conveying length is at least halved by lining up at least two opposing conveying sections, so that a particularly favorable ratio between the furnace output and the furnace volume is achieved. In addition, the hot gas flow, regardless of whether it runs counter to or in the conveying direction, is guided in a thermally advantageous manner in a vertical direction through the furnace space, which results in a particularly uniform heating of the individual bars. Since the supports for the bars in vertical step conveyors run in the conveying direction and are therefore only moved axially during a conveying movement, the penetrations of these supports through the furnace housing can be carried out in a simple manner in a heat-insulating manner.

The vertical partition between the opposing conveying sections of the vertical step conveyor advantageously separates the furnace space into two vertical flow paths. These flow paths on both sides of the dividing wall can be connected to one another to form a hot gas circuit if the ingots passing through the furnace are to be brought to the pressing temperature after homogenization annealing. If rapid warming up and then maintaining the treatment temperature reached is desired, then a flow path in the region of the furnace inlet becomes available Closing conveyor line used for a hot gas guide, in which the hot gas temperature is above the treatment temperature of the ingot, while the flow path on the opposite side of the partition only requires a hot gas flow that covers the heat losses that occur. Particularly advantageous ratios are achieved if the partition wall is designed to be heat-insulating in order to rule out mutual temperature effects between the two flow paths.

The hot gas flow required to cover the heat losses in the region of the conveyor line or conveyor lines adjoining the inlet-side conveyor line can be branched off in a simple manner from the hot gas flow in the region of the inlet-side conveyor line. To control this branch flow, the dividing wall can preferably have throughflow openings in a wall region which is opposite the transition between the conveying sections separated by the dividing wall in the vertical direction and can be closed by control flaps. The secondary circuit of the hot gas flow for keeping the bars brought to the treatment temperature warm can be controlled according to the respective requirements via the position of the control flaps.

In order to obtain particularly simple constructional conditions for the step conveyor, the conveying lines in the longitudinal direction of the bars can have vertically arranged, rotatably mounted, vertical shafts, which support arms for the bars at a uniform axial distance, some of the shafts being axially immovable and the other shafts around a dimension corresponding to at least the axial distance of the support arms from one another is held axially displaceably. For the gradual conveying of the bars, the axially displaceable shafts have to be raised or lowered by one conveying step so that the bars can be swiveled back into the working position after the support arms swiveled out of the bar path into the working position Support arms of the immovable shafts can be put down. The support arms of the raisable and lowerable shafts are then returned to their starting position after being pivoted out of the bar path in order to be ready for a new conveying step. Since the shafts for the support arms only require support in the axial direction due to their vertical arrangement and the shafts perform at most one axial displacement movement in addition to a rotary adjustment, the Durdhführung of this shaft through the furnace housing can be effectively heat-insulating in a simple manner, which prevents additional heat losses .

Because of the small space requirement of the furnaces according to the invention, these furnaces can be assigned directly to the press systems, so that the bars can be pressed after the homogenization annealing without additional heating. However, these ovens can also be used with advantage as separate heating ovens or as homogenizing ovens. When used as a homogenizing furnace, subsequent cooling of the ingots emerging from the furnace must be ensured. This cooling can be carried out in a particularly simple manner in connection with ovens in which an odd number of conveying sections is provided, a further vertical conveying section following the conveying section assigned to the product outlet in a cooling shaft outside the furnace chamber. The warm ingots discharged from the furnace also pass through the cooling shaft in the vertical direction, which not only ensures a small space requirement for the cooling device, but also results in advantageous flow conditions for the cooling air, the sensible waste heat of which, for example, for space heating or the like. can be exploited. Due to the odd number of conveying sections in the furnace chamber, the conveying section in the cooling shaft results in an even total number of conveying sections, so that a uniform conveying level outside the furnace area can be maintained. Whether the bars are initially down or up are promoted, is irrelevant to the function of the furnace and generally depends on the local conditions.

• Fig. 1 einen erfindungsgemäßen Ofen zur Wärmebehandlung von Leichtmetallbarren in einem vereinfachten Vertikalschnitt,
• Fig. 2 diesen Ofen in einem Schnitt nach der Linie II-II der Fig. l,
• Fig. 3 eine der Fig. 1 entsprechende Darstellung des Ofenteiles mit einer gegenüber der Fig. 1 abgewandelten Heizeinrichtung für die Heißgase,
• Fig. 4 eine Konstruktionsvariante eines erfindungsgemäßen Ofens in einem Vertikalschnitt,
• Fig. 5 eine weitere Ausführungsform eines erfindungsgemäßen Ofens im Vertikalschnitt und
• Fig. 6 eine teilweise nach der Linie VI-VI der Fig. 5 aufgerissene Draufsicht auf einen Ofen gemäß Fig. 5.

The subject matter of the invention is shown in the drawing, for example. Show it

• 1 shows a furnace according to the invention for the heat treatment of light metal bars in a simplified vertical section,
• 2 this oven in a section along the line II-II of FIG. 1,
• 3 shows a representation of the furnace part corresponding to FIG. 1 with a heating device for the hot gases modified compared to FIG. 1,
• 4 shows a constructional variant of a furnace according to the invention in a vertical section,
• Fig. 5 shows a further embodiment of a furnace according to the invention in vertical section and
• FIG. 6 shows a top view of a furnace according to FIG. 5, partially broken open along line VI-VI of FIG. 5.

1 and 2 consists essentially of a standing furnace housing 1, which encloses a shaft-like furnace chamber 2. In this furnace chamber 2, a step conveyor for bars 3 lying transversely to the conveying direction is provided between an oven inlet (not shown in more detail for reasons of clarity) and an oven outlet, said step conveyor consisting of two vertical conveyor lines 4a and 4b lined up next to one another. These conveying lines 4a and 4b each have vertical shafts 5a and 5b lined up in the longitudinal direction of the bars 3, which are rotatably mounted in the furnace housing 1 and carry support arms 6 for the bars 3 at a uniform, axial distance. While the shafts 5a are only rotatably adjustable in the housing 1 of the furnace, the shafts 5b are additionally displaceably guided in the axial direction, so that the bars 3 are in each case one support step to the next higher or lower one via the support arms 6 of the shafts 5b Support arm 6 can be raised or lowered. In order to be able to move the bars past the support arms 6 of the immovable shafts 5a when lifting or lowering, these support arms with the shafts 5a must be swung out of the bar path. The raised or lowered bars are then placed on the pivoted-back support arms of the immovable shafts 5a, the support arms 6 of the displaceable shafts 5b having to be swung out of the bar path before these shafts are returned to the starting position in order to be able to be moved past the bars. By appropriately coordinating the axial displacement movements and the rotary movements of the shafts 5a and 5b, the bars 3, which are fed to the step conveyor or driven away from the step conveyor via longitudinal roller drives 7 and 8 through the furnace inlet or through the furnace outlet, can be lifted step by step or be lowered.

For the rotary adjustment of the shafts 5a and 5b serve with the shafts non-rotatably connected, arranged outside the furnace housing adjusting arms 9, which are connected to each other via control rods 10 and are driven by an actuator, not shown, for example a cylinder drive, which on the one hand on the furnace housing and on the other hand to the Control rods is articulated. The axial conveying movement of the shafts 5b takes place with the aid of spindle drives 11, which are connected to each other by a common drive shaft 12 for each conveying path.

To transfer the individual bars 3 from the conveyor line 4a to the conveyor line 4b, a transfer line 13 is provided which, according to the exemplary embodiment, consists of drain wedges connected to the shafts 5a, on which the bars placed roll to the subsequent, oppositely moving conveyor line.

Between the two conveyor sections 4a and 4b there is a partition 14 which divides the furnace chamber 2 into two flow paths and which has passage openings in the wall region opposite the transfer line 13 in the vertical direction gen 15 form, which can be covered with the help of control flaps 16.

To generate a hot gas flow, fans 17 are provided which are driven by drives 18 outside the furnace chamber 2 and are arranged in the region of a flow shaft 19 provided inside the furnace housing 1, which is separated from the furnace chamber 2 by a wall 20. With the aid of the blower 17, air can thus be drawn in from the furnace chamber 2 and pressed into the furnace chamber 2 again in the circuit through the flow shaft 19. Since an electrical heating register 21 is provided in the flow shaft 19, the air pressed through the heating register 21 is heated to a corresponding temperature. The bars 3 introduced into the furnace chamber 2 via the roller inlet 7 via the material inlet of the furnace are gradually conveyed upwards by the conveying path 4a and heated to a desired treatment temperature by the hot air which is conducted in opposite directions through the furnace chamber. Since the downward conveying section 4b is thermally insulated from the upward conveying section 4a by the partition 14, heating in the area of the conveying section 4a can be carried out with hot gas which has been overheated compared to the desired treatment temperature, which allows rapid heating. An overheating of the bars is not to be feared because after reaching the treatment temperature, the bars are taken over by the conveyor section 4b, which is located in a secondary circuit of the hot gas flow. The flow conditions in this secondary circuit can be adjusted via the control flaps 16, only the temperature reached having to be maintained by covering the heat losses accordingly. If the temperature of the bars 3 is measured at the end of the conveyor section 4a, the desired end temperature can be set precisely via the temperature of the hot gases.

As FIG. 3 shows, very different heating devices can be provided for the hot gas generation. To 3, burners 22 are used for this purpose, which achieve a comparatively high efficiency with the aid of a recuperator.

The furnace according to FIG. 4 has no separation shaft for the hot gas generation which is separated from the furnace space 2. Rather, the shaft-like furnace chamber 2 is divided by the partition 14 between the two conveyor sections 4a and 4b into two vertical flow paths connected to form a circuit, through which the hot gas is guided. A burner 23 is used to generate this hot gas, which opens into the furnace area in the floor area and expels the combustion gases at high speed for hot gas circulation. Since the conveyor sections 4a and 4b are not thermally insulated from one another in accordance with this design variant, such a furnace is preferably used only for heating the ingots to a desired temperature, for example to the pressing temperature. Nevertheless, all advantages with regard to the simple design of the conveyor lines and with regard to the small space requirement and the high efficiency are retained.

5 and 6, the step conveyor in the furnace chamber 2 does not have two, but three vertical conveyor sections 4a, 4b and 4c. The ingots 3 introduced into the furnace chamber 2 via the roller table 7 are gradually raised over the conveyor section 4a and heated in countercurrent by a hot gas flow, which is sucked in with the aid of the fan 17 and separated by a wall 20 from the furnace chamber 2 by the electric heating register 21 Flow shaft 19 is pressed in order to be guided downward again from the flow shaft 19 between the partition wall 14 and the wall 20. The bars 3 heated up in the area of the conveyor line 4a in a comparatively short period of time are transferred to the conveyor line 4b after reaching the desired final temperature, which is provided together with the conveyor line 4c in the furnace space 2 divided by the partition wall 14, in which the temperature reached Ingots should be retained to ensure the diffusion processes necessary to compensate for casting heterogeneities. Via the control flap 16, a secondary circuit can be ensured through this separated part of the furnace space, which is just sufficient to compensate for the heat losses that occur. Since two conveyor lines 4b and 4c are provided, the dwell time in this furnace space is comparatively long. After the heat treatment of the ingots 3, the ingots are transferred via the closable furnace outlet 24 to a further conveyor section 25, which is provided outside the furnace housing 1 in a cooling shaft 26 and has the same structure as the other conveyor sections. In this cooling shaft 26, the bars 3 are cooled in countercurrent, the heated cooling air being sucked off with the aid of fans 27. The sensible waste heat of this cooling air can be used for heating purposes, for example.

Since the total number of conveying sections inside the furnace space 2 and outside the furnace space is even, the conveying level of the furnace inlet is reached again by the last conveying section 25, so that additional conveying devices can be omitted.

Claims (5)

1. Furnace for the heat treatment of light metal bars, consisting of a furnace chamber (2) through which high-pressure gas flows, in which a step conveyor for the individual bars (3) lying transversely to the conveying direction is provided between a good inlet and a good outlet, characterized in that the step conveyor in one shaft-like furnace chamber (2) is arranged and consists of at least two adjacent vertical conveying sections (4a, 4b) with an opposite conveying direction, which are interconnected by a transition (13) and that at least between the conveying section (4a) adjoining the material inlet and the immediately adjacent one Conveying path (4b) a vertical partition (14) dividing the shaft-like furnace space (2) is provided. 2. Oven according to claim 1, characterized in that the partition (14) is heat-insulating. 3. Furnace according to claim 1 or 2, characterized in that the partition (14) preferably in a wall region which is opposite the conduit (13) between the conveyor sections (4a, 4b) separated from one another by the partition (14) in the vertical direction, Has flow openings (15) which can be closed by control flaps (16). 4. Oven according to one of claims 1 to 3, characterized in that the conveyor lines (4a, 4b, 4c) in the longitudinal direction of the bars (3) side by side, rotatably mounted, vertical shafts (5a, 5b) which have a uniform, axial distance Support arms (6) for the bars (3), and that part of the shafts (5a) are axially immovable and the other shafts (5b) are held axially displaceable by at least an amount corresponding to the axial distance between the support arms (6). 5. Furnace according to one of claims 1 to 4, characterized in that an odd number of conveying sections (4a, 4b, 4c) is provided and that there is a further vertical conveying section (4c) associated with the material outlet (24). 25) in a cooling shaft (26) outside the furnace chamber (2).

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