DE10316140B3 - Device for hot dip coating a steel strip comprises a container having two parallel pipes in its lower region forming a gap for the vertical passage of the steel strip - Google Patents

Abstract

Device for hot dip coating a steel strip comprises a container (3) having two parallel pipes (7) in its lower region forming a gap (8) for the vertical passage of the steel strip. A rotating shaft (5) with permanent magnets (6) is arranged in each pipe. The container has two weirs (9) in its upper region forming a wall of the container.

Description

The invention relates to a device for hot-dip coating a metal strand, in particular of a steel strip in which the metal strand is melted by one Coating metal-receiving container can be passed vertically, being in the bottom of the container a magnetic restraint for melted Coating metal is arranged, which has two rotatable shafts, on the circumference of which a number of permanent magnets are arranged.

For the coating of steel strips in particular is hot dip coating adequately known. The liquid Coating metal, for example zinc, placed in a container, through which the strip to be coated is passed. Through adhesion and Cohesive forces are liable the coating metal on the belt.

usual Metal dip coating systems for metal strips have a maintenance-intensive part on, namely the coating vessel with the equipment inside. The surfaces the metal strips to be coated have to cleaned of oxide residues before coating and for connection be activated with the coating metal. For this reason become the belt surfaces before coating in heat processes in a reducing atmosphere treated. Since the oxide layers are removed chemically or abrasively beforehand, be with the reducing heat process the surfaces activated in such a way that they are metallically pure after the heating process available.

With the activation of the belt surface, however, increases the affinity of these tape surfaces for the surrounding atmospheric oxygen. To prevent atmospheric oxygen get back to the strip surfaces before the coating process can, the tapes in a diving trunk introduced into the dip coating bath from above. Because the coating metal in liquid Form is present and you get the gravitation together with blow-off devices would like to use the following processes to adjust the coating thickness however a band touch until complete To prevent solidification of the coating metal, the strip must Coating vessel in vertical Direction to be redirected. That happens with a role that in liquid metal running. Through the liquid Coating metal is subject to heavy wear and tear Cause of downtimes and with it failures in production.

Due to the desired low support thickness of the coating metal, which are in the micrometer range can, high demands are placed on the quality of the belt surface. The means the surfaces too the band leader High quality rolls have to be. Malfunctions these surfaces to lead generally damage on the belt surface. This is another reason for frequent downtimes the plant.

To avoid the problems that related to the in liquid Solutions are known for coating metal running rollers who use a coating vessel open at the bottom, that in the lower area a guide channel for vertical Band implementation upwards and for sealing an electromagnetic Insert closure. These are electromagnetic Inductors with pushing back, pumping or constricting electromagnetic alternating or traveling fields work that the Coating vessel down caulk.

Such solutions are in WO 96/03533 A1 and described in WO 01/71051 A1. There are electromagnetic Inductors are used in the bottom area of the coating vessel to keep the melted Prevent coating metal from going through the gap for the metal strand flow out.

As an alternative to electromagnetic restraint systems it is from the article “Electromagnetic Induction Pump on Permanent Magnets for Pb / Bi Melt "by I. Bucenieks et al. as well as from the article “Free Surface Instabilities in MHD Seals "by J. Valdmanis et al., Both dated Institute of Physics of the University of Latvia, Salaspils, known, a magnetic restraint for the Use hot dip coating based on permanent magnets. There are two rotors that are parallel on both sides of the metal strand are arranged to each other, on their circumference with a number of permanent magnets provided the radially outward in their polarity alternate. By rotating the rotors in the sense that in the area of the gap-shaped passage for the Metal strand is opposed to the movement of gravity, there is the retention effect.

When the permanent magnets rotate the moving field sequence of the magnetic field strength is simulated, where compared to the electromagnetic solution a much shorter height and a smaller effective area is achieved. This proves to be favorable in terms of ferromagnetic Attraction of the metal strand during the Operating as it is possible will, just about the guy ratios to guide the tape stably and available through the to effectively seal standing magnetic materials.

In the light of the aforementioned prior art, the object of the invention is the coating vessel for the melt to further dip-coat a metal strand in such a way that when using the magnetic retention device based on permanent magnets, effective operation becomes possible, which leads to high-quality, coated metal strands and which does not pose any problems even in the event of malfunctions.

The solution to this problem by Invention is characterized in that the container in in its lower area two tubes arranged parallel to each other which are positioned so that they have a gap for the vertical Form passage of the metal strand, with one in each of the tubes rotatable shaft is arranged with permanent magnets, and that the container has two weirs in its upper area, which form a wall of the container.

This design of the container for the melted Coating metal will have significant advantages in operation and achieved especially in the emergency running properties of the system. Furthermore results optimal flow in the coating metal, so that a depletion of individual alloy elements is excluded. The quality of the coated metal strand is very high.

According to a further development, it is provided that the weir is formed by an essentially flat plate, which at an angle of 0 ° to 45 ° against the Vertical is inclined. As a result, the flow in the Coating metal optimized in a simple way.

Furthermore, the weir can be closed have the open and can be kept closed. For the shutdown of the system, this enables especially in the event of a power failure, optimal operating and Safety conditions. The closure can be on the side facing away from the container are fluidly connected to a process. Furthermore can the weir an overflow for melted Have coating metal, the one facing away from the container Fluidly connected to a process.

To the level of the melted Coating metal in the container A bath level regulation can be able to keep at a predetermined value be provided.

Means of adjustment are advantageous the gap provided by relative movement of the two tubes. In order to can determine the optimal width of the passage gap for the metal strand can be set.

The wall of the container in The area of the end faces of the pipes is preferred by flat plates educated. It can then be provided that the distance between the flat plates essentially corresponds to the width of the metal strand.

After all, it has proven to be beneficial it turns out if there is a supply line for supply of the container with coating metal through at least one flat plate and opens into the area of the gap.

In the drawing, embodiments of the Invention shown. Show it:

1 schematically the section through a hot-dip coating vessel with two shafts with permanent magnets,

2 schematically the construction of a hot-dip coating system,

3 the facility according to 2 with subsequent mill stand and

4 an alternative design of the system according 3 ,

In 1 part of a hot-dip coating system can be seen, namely a container 3 with molten coating metal 2 is filled up to a desired level. Through the container 3 occurs the metal strand to be coated 1 in the form of a steel band vertically through it. This takes place in the direction of movement T, which in the present case is directed from top to bottom. However, the metal strand can 1 Alternatively, move upwards for coating.

The wall of the container 3 is first through two pipes 7 formed, which are arranged parallel to each other. Above the pipes 7 two weirs close 9 which are aligned at an angle α to the vertical. In 1 is not seen on the two faces of the tubes 7 flat wall panels are arranged. The pipes 7 who have favourited Weirs 9 and the wall plates arranged on the end face define the receiving space of the container 3 for the coating metal 2 ,

So that the molten coating metal 2 not down from the container 3 flows out, the procedure is as follows: The two pipes 7 are by means 13 provided, each a translational movement of the tubes 7 allow in the horizontal direction (see double arrow), the two tubes 7 always stay parallel to each other. Both pipes 7 form a gap 8th leading to the passage of the metal strand 1 serves. The pipes 7 form part of a magnetic restraint 4 that the lower part of the container 3 forms. For this purpose are in the pipes 7 waves 5 arranged, which are provided with - not shown - drive means. The waves 5 each have an even number of permanent magnets on their circumference 6 which are rod-shaped and perpendicular to the plane of the drawing in 1 extend. The permanent magnets are in the radially outer area 6 arranged with alternating polarity over the circumference. The south poles of the permanent magnets 6 are denoted by S, the north poles by N.

By rotating the waves 5 In the direction of the arrow, the magnetic force generates an upward restraining force in the gap which counteracts gravity 8th which the coating metal 2 in container 3 restrains.

The container 3 is via a supply line 14 with molten coating metal 2 provided. The supply line opens 14 above the area of the gap 8th in the container 3 one, at the front through the - not shown - flat side boundary plate.

The weirs 9 each have a closure 10 which is drawn with solid lines in the closed position; the open position is indicated by dashed lines. Is the clasp 10 closed, the molten coating metal 2 remains in the container 3 , With the shutter open 10 it can over the the metal strand 1 facing outer surfaces of the pipes 7 drain off and so to a drain 11 with which it can be caught. Exceeding a maximum level of the molten coating metal 2 in the container 3 is caused by an overflow 12 prevented. Coating metal can be applied in the same way 2 the end 11 reach.

The start-up and operation of the hot-dip coating system is carried out as follows:
To start up the system, the drives (not shown) for the two shafts are first used 5 activated. Both waves 5 turn synchronously in the entered direction of rotation. By means 13 to adjust the gap 8th the two pipes 7 on the for the metal strand to be coated 1 necessary distance traveled. The container comes from the side 3 via the supply line 14 then with molten coating metal 2 filled. The metal strand is already running 1 in the direction of movement T. Is the container 3 up to a desired level with coating metal 2 filled, the metal strand is coated in a known manner 1 with coating metal 2 , By the movement of the waves 5 in the pipes 7 becomes the coating metal 2 moved, from the area of the gap 8th away and along the outer peripheral surface of the tubes 7 up. Through the weirs 9 becomes the coating metal 2 deflected and by the movement of the metal strand 1 as well as directed downwards again by gravity. The possible flow is in 1 in the left half of the container 3 outlined. The movement of the coating metal 2 in the manner explained has the consequence that there is an intensive flow in the container 3 formed. The coating metal 2 is in the container 3 vigorously circulated so that individual alloy elements do not become poor due to a lack of bath movement.

The supply of coating metal 2 in the container 3 can be done in the amount corresponding to that by the coated metal strand 1 back out of the container 3 is promoted. Alternatively, there is the option of more coating metal 2 in the container 3 to promote, so this overflow 12 can drain again; in the right half of the figure 1 the level that then appears in the container is dashed 3 outlined. For the former case, in which only the coating metal removed 2 is replaced again, the use of a bath level control is recommended, which maintains a desired predetermined level.

There are particular advantages of the system when shutting down the system or in the event of a fault:
The case of shutdown or malfunction is due to the special shape of the pipes 7 easy and effective to do. For this, the closures 10 the weirs 9 open. The promotion of the coating metal 2 now continues on the outer wall of the pipes 7 along so that the coating metal 2 in the process 11 arrives. Special safety devices under the area of the gap 8th (Channel area) in the event of shutdown and malfunction are not required here, which is indispensable in the classic vertical process. The power failure is equally unproblematic, since flywheel masses and an uninterruptible power supply with low power make it possible to wait for the short time before the emergency power diesel starts.

By the rotational movement of the waves 5 in the pipes 7 is the surface area of the permanent magnets 6 on the continuous metal strand 1 only briefly. Despite the high field strength of the permanent magnets 6 the attraction is not sufficient to the metal strand 1 distract from its normal path. Should this happen due to a lack of tension in the metal strand 1 the case, you have the option of moving the two pipes 7 from the metal bar 1 away or by adjusting the rotational speed of the shafts 5 to control the attraction within certain limits. The limit for the movement of the waves 5 or pipes 7 from the metal strand 1 away is given by the fact that the tightness of the system must be guaranteed. The control is over a parallel displacement of the pipes 7 and also possible through a one-sided shift. Zero and first order belt run disturbances can thus be checked perfectly. Other forms of belt run disturbances are not expected due to the short height.

The further design of the entire coating system is based on 2 to 4 shows where alternative possibilities are shown.

As can be seen from these figures, the container 3 via the supply line 14 from a larger storage vessel with molten coating metal 2 provided. The container 3 is on the side with an oven system 15 connected via which the metal strand 1 the container 3 is fed. The connection is designed to be gas-tight, including a lock 16 can be used. The furnace system 15 is a classic band upstream, for the removal of the scale on the metal strand used 1 provides. The strip pickling line can be operated using the turbulence process or the vario process. The furnace system 15 firstly, preheats the metal strand 1 for the coating process, on the other hand, the reducing atmosphere in the furnace for a clean metallic surface is a prerequisite for good adhesion of the coating metal 2 taken care of. On the one hand there is the possibility of the metal strand 1 coming from below through the container 3 to promote, as it corresponds to the classic case. However, as an alternative to this, one has the device for collecting the coating metal that is not required 2 in the event of an accident, the possibility of the metal strand 1 coming from above down through the container 3 to promote, as is provided in the exemplary embodiments. In this case, the waves take over 5 with the permanent magnets 6 also the task of stripping the coating metal 2 to adjust the pad thickness.

For the classic case of guiding the metal strand 1 from the bottom up through the container 3 In the case of inversion casting, problems can arise with the heating of the metal strand 1 result in temperatures at which the metal strand 1 for connection to the coating metal 2 becomes slightly doughy and the necessary tensile force to pass on the metal strand 1 can no longer be applied, which would tear the tape. Here the reverse band guidance from top to bottom through the container proves itself 3 as beneficial. Because there are no special precautions to catch the coating metal 2 in the event of an accident, it is possible to cool the coated metal strand after a short distance 1 immediately a horizontal mill stand 17 to use for the first forming, as this in 3 is illustrated. After this reshaping, there is no longer a solidification structure, and the strength of the metal strand can now be increased 1 make a diversion in the horizontal direction. Classic roll stands can be used for final forming into the desired finished strip thickness 1 are used (not shown).

The high demands on the quality of the rolled Product can only be adjusted with the help of a precisely working roll gap setting and regulation. The expected rolling forces are small. About the relationship Rolling force to frictional force in the horizontal adjustment system rolling mill to improve and thus undesirable stick-slip effects To avoid in the adjusting movements, low-friction sealing systems should be used for the Positioning cylinders as well as hydrodynamic bearings or rolling element bearings for the guides the chocks be used.

The has a special meaning Train balance between the coating cell and the first roll stand. The Location of the flow sheath in the nip varies with variations in thickness and strength of the incoming product. So the resulting changes do not lead to a strip break in the rolling speed, they must speed changes adjusted or the tape buffered.

If you arrange the first roll stand horizontally Part of the system, arises in the deflection zone between vertical and horizontal part an arch, which on the one hand as a tape storage can be used for buffering, on the other hand, the deflection of the strip from the ideal line to regulate the drives of the rolling stands.

An illustration of this can be found in 4 , The metal strand 1 after coating after deflection must be sufficiently solidified and the deflection bend 18 be chosen large enough. A pair of roles 19 that is below the container 3 and is located above the deflection, holds transverse forces and moments from the rolling stand 20 due to the applied band tension in the metal strand 1 be introduced from the weakest point of the coated metal strand 1 in the vertical part of the plant. The roles too 19 must be sufficiently far below the container 3 be attached so that the metal strand 1 solidified there enough and through the contact on the rollers 19 no undesired and undefined rolling is caused.

On the other hand, the vertical part of the metal strand may 1 below the container 3 before the deflection, do not become too long, so that the weight of the coated metal strand is not 1 leads to demolition at the critical point. The bow of the metal strand that lowers as the speed decreases 1 should be as good as possible for strain relief through a roller conveyor 21 be intercepted.

Only vertical mill stands are horizontal Part of the system used exclusively conventional systems for the roll gap setting are used.

1

metal strand (Steel strip)

2

coating metal

3

container

4

magnetic Restraint

5

wave

6

permanent magnets

7

pipe

8th

gap

9

weir

10

shutter

11

procedure

12

overflow

13

medium to adjust the gap

14

supply line

15

furnace system

16

lock

17

rolling mill

18

reversing curve

19

roller pair

20

rolling mill

21

roller conveyor

α

angle

S

South Pole of the permanent magnets

N

North Pole of the permanent magnet

T

movement direction

Claims (10)

Device for hot-dip coating a metal strand ( 1 ), in particular a steel strip in which the metal strand ( 1 ) by the molten coating metal ( 2 ) receiving container ( 3 ) can be passed vertically, whereby in the lower area of the container ( 3 ) a magnetic restraint ( 4 ) for molten coating metal ( 2 ) is arranged, the two rotatable shafts ( 5 ), on the circumference of which a number of permanent magnets ( 6 ) are arranged, characterized in that the container ( 3 ) in its lower area two tubes arranged parallel to each other ( 7 ) positioned so that they have a gap ( 8th ) for the vertical passage of the metal strand ( 1 ), whereby in each of the tubes ( 7 ) one rotating shaft each ( 5 ) with permanent magnets ( 6 ) is arranged and that the container ( 3 ) two weirs in its upper part ( 9 ) which has a wall of the container ( 3 ) form. Device according to claim 1, characterized in that the weir ( 9 ) is formed by a substantially flat plate, which is arranged at an angle (α) of 0 ° to 45 ° inclined to the vertical. Device according to claim 1 or 2, characterized in that the weir ( 9 ) a closure ( 10 ) that can be kept open and closed. Device according to claim 3, characterized in that the closure ( 10 ) on the container ( 3 ) fluid side facing away with a drain ( 11 ) is connected. Device according to one of claims 1 to 4, characterized in that the weir ( 9 ) an overflow ( 12 ) for molten coating metal ( 2 ) which is attached to the container ( 3 ) fluid side facing away with a drain ( 11 ) is connected. Device according to one of claims 1 to 5, characterized by a bath level control with which the level of the molten coating metal ( 2 ) in the container ( 3 ) can be kept at a predetermined value. Device according to one of claims 1 to 6, characterized by means ( 13 ) to adjust the gap ( 8th ) by relative movement of the two tubes ( 7 ). Device according to one of claims 1 to 7, characterized in that the wall of the container ( 3 ) in the area of the end faces of the pipes ( 7 ) is formed by flat plates. Apparatus according to claim 8, characterized in that the distance between the flat plates substantially the width of the metal strand ( 1 ) corresponds. Apparatus according to claim 8 or 9, characterized in that a supply line ( 14 ) to supply the container ( 3 ) with coating metal ( 2 ) extends through at least one flat plate and into the area of the gap ( 8th ) flows out.