WO2008095510A1 - Crust breaker for breaking through a crust formed on a metal molten pool - Google Patents

Abstract

The invention proposes a crust breaker for breaking through a crust (17) formed on a metal molten pool (18), comprising a fluidic double-acting cylinder (10), the piston rod (14) of which is equipped with an impact element (16), and to the two working chambers (12, 13) of which separated by a piston (11) optionally a higher (P2) and a lower fluid pressure (P1) can be applied by means of a valve arrangement (33, 36). The cylinder (10) is equipped with a distance measuring device (24). A monitoring means serves for monitoring a predefinable path-time course, or a predefinable course of speed during the forward movement of the impact element (16) in the direction of the crust (17). A controller (30) serves for switching from the lower to the higher fluid pressure beginning with a definable deviation from the predefined course and is connected to the valve arrangement (33, 36) for this purpose.

Description

 FESTO AG & Co, D-73734 Esslingen

Crust breaker for piercing the crust formed on a molten metal bath

The invention relates to a crust crusher for piercing the crust formed on a molten metal bath, with a fluidic, double-acting cylinder, the piston rod is provided with a shock element and both of which are separated by a piston separate working chambers by means of a valve assembly optionally with a higher and a lower fluid pressure can be acted upon ,

For example, in melt furnaces for the production of raw aluminum, such crust breakers or crust breaker cylinders are used to locally break up an oxide layer forming over the melt. At these points, the raw material aluminum oxide is replenished after treated raw aluminum has been removed. This process takes place approximately every two minutes. In fact, however, no crust has yet formed in this period, which must be pierced. The cylinder thus does not have to apply the maximum force in these cases and can be operated at a lower pressure. An impact element or a shock lance, which is attached to the piston rod of the cylinder, immersed in the breaking of the crust each time in the melt. Residues and alumina are deposited on this lance. These must, if they exceed a certain thickness, be stripped off again, otherwise the impact lance is getting heavier. This is usually done by a fixed steel ring or a pipe that surrounds or the shock lance. Again, a higher force of the cylinder is needed again, and this process occurs only sporadically, that is, the higher force is not required regularly.

In either case, ie breaking the crust and / or stripping the deposits, the position along the stroke of the cylinder where the higher force is needed can not be accurately predicted. The position of the crust depends on the level of the molten bath and can vary in practice by 30 cm. Similarly, the location at which deposits form on the shock lance depends on the fill level of the molten bath, since the lance then dips more or less deeply into the liquid aluminum.

In a Krustenbrecher known from DE 202006002727 Ul of the type mentioned is almost the entire stroke of the cylinder for the reasons mentioned drive through with the higher force, and only when reaching the end positions, which are scanned by sensors, is to reduce the air consumption to a switched lower pressure level. Nevertheless, the pressure which is present during the almost entire stroke movement and designed to break the crust leads to a relatively high air consumption or fluid consumption, which is not least caused by leaks in the fluidic system. An object of the present invention is to reduce fluid consumption in a crust breaker cylinder by applying the higher pressure only when needed.

This object is achieved by a crust breaker with the features of claim 1.

The advantages of the invention are in particular that the cylinder is normally operated only with the minimum necessary operating pressure, so that the desired extension and retraction times are being met. If the cylinder hits an obstacle, in particular the crust, the speed is reduced or the extension movement stops. This is detected by exceeding a definable deviation from the given path-time course or speed profile. Only in this case is then applied the higher pressure, which is designed to pierce the crust. A particular advantage results from the fact that can be switched to the higher pressure level at any point of the cylinder stroke, without the distance of the crust breaker from the molten metal or the crust must be known. Has not formed a new crust or only a relatively thin crust since the last shock process, the specified deviation from the predetermined course is not exceeded, and a switch to the higher pressure level does not occur. Overall, this leads to a very high fluidic saving effect, in particular an air saving effect.

The measures listed in the dependent claims advantageous refinements and improvements of claim 1 crust breaker are possible. Since, according to the invention, any obstacle can be detected by reducing the driving speed and optionally exceeding the specified deviation, this also applies to the backward movement of the pushing element, which can possibly detect residues on the pushing element when hitting a stripping device, which, depending on the circumference, can be overcome require the higher pressure. Such, in particular tubular or annular stripping device is expediently provided for stripping the metal from the molten metal stuck to the repelling element.

Advantageously, a pressure adjusting device for the speed of the pushing element predetermining lower fluid pressure is provided in order to adjust this speed can.

In an expedient embodiment, the valve assembly consists of a first valve for switching between the high and the lower fluid pressure and a second valve for acting either the first or the second working chamber with the preselected fluid pressure. As a result, only a very small number of valves is needed, namely two in particular.

Preferably, means for forming the actual speed are provided as a time derivative of the path signal of the distance measuring device and arranged in particular in the electronic control device. In a first embodiment, the path measuring device can be designed as a microwave measuring system in a working chamber of the cylinder for measuring the distance between the piston and a cylinder end wall. In a further embodiment, the distance measuring device may also have a arranged in or on the piston rod resistance measuring element, which can be tapped off by at least one electrical pick-off element. In view of the high temperatures that occur, the displacement measuring system is preferably designed as an encapsulated displacement measuring system.

In an advantageous manner, a measuring arrangement for detecting the immersion process of the impact element into the molten metal can also be provided for measuring the electrical connection between the molten metal or the electrically conductive container for this on the one hand and the impact element or the associated piston rod on the other. In conjunction with the displacement measuring system, the distance between the crust breaker and the crust or the underlying molten metal can thereby be measured.

The electronic control device can also be integrated in or on the cylinder in a compact design.

In order to achieve higher speeds of the operations or the movement of the shock element, the electronic control device has means for setting the higher fluid pressure at the beginning of the piston movement and for switching to the lower fluid pressure after completion of the acceleration phase.

An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description. Show it: FIG. 1 shows an illustration of a crust breaker arranged above a molten metal and the corresponding electrical and fluidic circuit as an exemplary embodiment of the invention,

FIG. 2 shows a signal diagram for explaining the mode of action upon impact and immersion of the impact element of the crust breaker into the molten metal bath and

Figure 3 is a corresponding signal diagram for the return movement.

The crust breaker shown in FIG. 1 consists essentially of a fluidic, double-acting cylinder 10, the interior of which is divided by a piston 11 into two working chambers 12, 13. From the piston 11, a piston rod 14 extends sealingly through an end wall 15 of the cylinder 10 and carries at its free end a shock element 16 designed as a shock lance for piercing a crust 17, which usually forms on a molten metal bath 18, for example may be an aluminum molten bath. The molten metal bath 18 is located in a bath

20 container 19 from a metal higher than the melting of the molten metal.

At the piston rod passage owning end wall 15 of the cylinder 10, a tubular stripping device 20 is attached or fixed, in which the shock element

25 16 is slidable with little play. The free end of the stripping device 20, which is remote from the end wall 15, has a scraping edge 21, by means of which the deposits 22 of the crust 17 possibly remaining in the stripping device 20 during the return movement of the pushing element 16 can be caught

3o or the molten metal are stripped off. Instead of a tubular stripping device 20 may for example also occur an annular stripping device.

At the second end wall 23 of the cylinder 10, which is remote from the first end wall 15, a rod-shaped resistance measuring element 24 is mounted centrally, which extends from there into a longitudinal channel 25 in the interior of the piston rod 14. The resistance measuring element 24 may be made of or coated with a resistance material, or a foil resistance element is attached thereto. Within the piston 11, a pick-off element 26 is arranged as a tap for the resistance measuring element 24. This may be a slip ring arrangement or other elastic grinding elements. The tapping element 26 can of course also be arranged outside the piston 11. A further tapping element 27 in or on the first end wall 15 ensures the electrical connection between the electrically conductive piston rod 14 and the electrically conductive first end wall 15. The tapping element 27 in the first end wall 15 and the second end wall 23 attached end region of the resistance element 24 can be tapped resistance value is a measure of the position of the piston 11 and thus of the shock element 16 and is fed via lines 28, 29 of an electronic control device 30.

The distance measuring device essentially formed by the resistance measuring element 24 may for example also be designed according to DE 29713825 U1 and then does not need the second pick-off element 27. Furthermore, other known path measuring devices instead of the described Wegmessvor- direction occur. For example, a measuring element movable in the piston rod 14, similar to the resistance measuring element 24, may have magnetizations or other markings. sen, which are digitally palpable. Such markings can also be attached directly to the piston rod 14 and tapped there. Furthermore, in the working chamber 12 or in the other working chamber 13, an ultrasonic or microwave-based distance measuring device for measuring the distance between the piston 11 and the respective end wall 15 or 23 may be provided. Other known potentiometric Wegmessvorrichtungen can be used accordingly.

To detect the position at which the impact element 16 has broken through the crust 17 on the molten metal bath 18, the series connection of a lamp 31 with a voltage source 32 between the pick-off element 27 and the bath tank 19 is connected. After breaking through the crust 17, the shock element 16 reaches the molten metal and thereby closes the circuit, so that the lamp 32 lights up. Of course, instead of a lamp, another optical or acoustic signaling device can occur. The resulting signal is fed back via the line 29 of the electrical control device 30, so that the position measurement present at this time is a measure of the position of the crust breaker relative to the molten metal bath 18.

The lamp 31 and the external voltage source 32 can of course also be realized by a corresponding circuit in conjunction with the electronic control device 30, in which case only the resistance value between the pick-off element 27 and the bath container 19 is detected.

For actuating the cylinder 10, a lower pressure P 1 of a first pressure source 34 or a higher pressure P 2 of a second pressure source 35 can be preset via an electrically controllable 3/2 way valve 33. The because by the valve position of the directional control valve 33 predetermined working pressure is alternatively supplied by means of a second 5/2 way valve 36 to one of the two working chambers 12, 13, while at the same time the other working chamber venting 5 tet. The two-way valves are controlled by the electronic control device 30. The lower pressure Pl is chosen so that the piston 11 moves in the unloaded state at the desired speed. To change this speed, an adjustable throttle 37 acts between the first pressure source 34 and the directional control valve 33. The higher pressure P2 is selected such that it exerts a force on the piston 11 sufficient to produce a crust 17 pierced with maximum thickness. Again, a corresponding throttle 36 or i5 other pressure adjustment device for varying the pressure P2 may be provided.

The operation of the described Krustenbrecheranordnung will be explained below with reference to the signal diagrams shown in Figures 2 and 3.

20 For the forward movement of the piston 11 and the shock element 16 to the molten metal 18 through the working chamber 12 is acted upon by corresponding valve positions of the directional valves 33, 36 with the lower pressure Pl. The shock element 16 thereby moves initially unhindered until

25 to the crust 17. The corresponding path-time course (w-t

History) is stored as a setpoint curve Sv in the electronic control device 30. This setpoint curve continues linearly as if there were no crust 17 or other obstruction in the movement of the pushing element. Along these

30 ser setpoint curve Sv a tolerance band Tv is formed, the in

Figure 2 is shown as dashed lines. The movement of the shock element 16, so the motion actual value Iv, as dash-dotted line is shown, initially follows substantially the setpoint curve Sv. If the impact element 16 reaches the crust 17 and the force caused by the lower pressure P1 does not suffice to pierce this crust, the movement of the impact element 16 is inhibited, and the movement actual value Iv leaves the tolerance band Tv. This is detected or detected in the electronic control device 30 by target-actual comparison, and by reversing the directional valve 33, the higher pressure P2 is then given, the lo is sufficient to pierce the crust 17. If no crust has yet formed at the time the shock element 16 is reached, or if it is so thin that the lower pressure P1 is also sufficient for penetration, then the actual movement value Iv does not leave the tolerance band Tv, and there is no switching over to the higher pressure P2.

The setpoint curve Sv can be stored, for example, within the scope of a learning cycle in the electronic control device 30. The desired-actual comparison can be done most simply by a speed comparison. This means that a desired speed profile is stored and compared with the respective actual speed during the movement. The actual speed can be detected by time derivative of the path signal of the distance measuring device.

During the rearward movement of the impact element 16 away from the molten metal bath 18, deposits 22 made of the metal of the molten metal bath 18 or of the crust 17 on the impact element 16 may remain, which are scraped off by means of the stripping device 20. The conditions in the backward movement are shown in FIG. Instead of the setpoint curve Sv, the setpoint curve Sr occurs here, instead of the tolerance band Tv the tolerance band Tr occurs here, and instead of the motion actual value Iv, the actual movement value Ir occurs. The movement takes place next again with the lower pressure Pl, with which the other working chamber 13 is acted upon. If any remaining deposits 22 reach the stripping device 20, then the force can not be sufficient by means of the lower pressure P1 to carry out the stripping process. In this case, in turn, the movement is inhibited, and the movement actual value Ir moves outside the tolerance band Tr. This in turn causes a switch to the higher pressure P2, which is sufficient to perform the stripping process. If there are no or only slight deposits on the impact element 16, then the lower pressure Pl can be sufficient for the stripping process, and there is no switchover to the higher pressure P2.

The electronic control device 30 is optionally equipped with a display 37 to display position values and other operations during the course of the crust breaker.

The crust breaker shown in FIG. 1 has only one single cylinder 10 with a push element 16. Of course, crust crushers with a plurality of cylinders 10 and thus a plurality of impact elements 16 can be used, in particular for larger molten metal baths 18.

In the vicinity of the molten metal bath 18 are generally higher temperatures due to the molten metal. Temperature-sensitive components and assemblies, such as the Wegmessvorrichtung must therefore be designed accordingly, for example, shielded or encapsulated. The directional control valves 33, 36 and / or the electronic control device 30 can be arranged remotely from the cylinder 10 or integrated in or on it, for example on or in the end walls 15, 23. In order to accelerate the working processes, the respective working chamber 12 or 13 can also be acted upon during an acceleration phase with the higher pressure P2, also in deviation from the above description at the beginning of the forward movement and at the beginning of the backward movement of the pushing element 16 desired movement speed, a switchover to the lower working pressure P2 takes place.

The lower pressure Pl can, for example, be between 1 and 1.5 bar and the higher pressure, for example, about 8 bar. It is a pneumatic pressure, for example air pressure. In principle, of course, a hydraulic fluid and a hydraulic arrangement can be used.

Claims

claims 1. Crust breaker for piercing the crumb (17) formed on a molten metal bath (18), with a fluidic, double-acting cylinder (10), whose piston rod (14) is provided with a push element (16) and both of which are connected by a piston (11 ) separate working chambers (12, 13) by means of a valve arrangement (33, 36) optionally with a higher (P2) and a lower fluid pressure Pl) can be acted upon, characterized in that the cylinder (10) is provided with a distance measuring device (24), in that monitoring means are provided for monitoring a predeterminable travel time or a predefinable speed profile during the forward movement of the push element (16) in the direction of the crust (17), and in that a control device (30) for switching from the lower (Pl) to the higher fluid pressure (P2 ) Is connected to the valve assembly (33, 36) from a definable deviation from the predetermined curve (Sv). 2. Crust breaker according to claim 1, characterized in that the control device (30) is also designed for the corresponding monitoring of the rearward movement of the pushing element. 3. crust breaker according to claim 1 or 2, characterized in that a particular tubular or annular stripping device (20) for on the push element (16) stuck hanging Benes metal or stuck crust parts from the molten metal bath (18) is provided. 4. crust breaker according to one of the preceding claims, characterized in that a pressure adjusting device 5 (36) for which the speed of the pushing element (16) predetermining lower fluid pressure (Pl) is provided. 5. crust breaker according to one of the preceding claims, characterized in that the valve arrangement (33, 36) of a first valve (33) for switching between the high lo (P2) and the lower fluid pressure (Pl) and a second valve (36) for the application of either the first or the second working chamber (12, 13) with the preselected fluid pressure. 6. crust breaker according to one of the preceding claims, i5 characterized in that means for forming the actual speed as a time derivative of the path signal of the path measuring device (24) are provided, in particular in the electronic control device (30). 7. Crust breaker according to one of the preceding claims, characterized in that the position measuring device as a microwave measuring system in a working chamber (12 or 13) of the cylinder (10) for measuring the distance between the piston (11) and a Zylinderstirnwandung (15 or 23) is trained. 25 8. crust breaker according to one of claims 1 to 6, characterized in that the Wegmessvorrichtung (24) has a in or on the piston rod (14) arranged resistance measuring element which can be tapped by at least one electrical pick-off element (26). 9. Crust breaker according to one of the preceding claims, characterized in that a the electrical connection between the molten metal bath (18) or the electrically conductive bath container (19) for this one hand and the shocks element (16) or the associated piston rod (14 ) On the other hand, measuring measuring arrangement for detecting the immersion process of the shock element (16) is provided in the molten metal. 10. Crust breaker according to one of the preceding claims, lo characterized in that the electronic control device (30) is integrated in or on the cylinder (10). 11. crust breaker according to one of the preceding claims, characterized in that the electronic control device (30) comprises means for setting the higher fluid pressure (P2) to i5 the beginning of the piston movement and switching to the lower fluid pressure (Pl) after completion of the acceleration phase.