EP2176016B1 - Method and device for equalization of the heat transfer of a cast product during the solidification thereof on a metal conveyor belt of a horizontal strip casting system - Google Patents

Description

The invention relates to a method and a device for close-to-near-net casting of rectangular metal strands and subsequent further processing to metal strips by the DSC process (direct strip casting) in a horizontal strip casting, wherein the molten metal by means of a melt delivery system on a cooled at the bottom horizontally encircling Metal conveyor belt is poured and solidifies the liquid cast product on this metal conveyor belt during its transport to the pre-band, which is then conveyed to a driver after leaving the metal conveyor belt - mechanically clamped for example by smoothing / driving rollers. The structure with smoothing / driving rollers is not absolutely necessary, the structure can also be realized without these roles.

Due to the unequal heat dissipation in the solidification process of the DSC method under inert atmosphere cast without casting powder tape, the top of the belt is cooled only by convection with the ambient atmosphere and by heat radiation, while its bottom in direct contact with a cooled Metal conveyor belt is stationary, the band already deformed during solidification and then first up and then down.

At the beginning of the cooling, the lowermost material layer of the band contracts most strongly due to very large temperature gradients. The entire band curves upwards in the middle, with very high stresses being introduced in the upper layer. Since these stresses are greater than the yield stress, they degrade in the course of solidification by elongation (flow) again, resulting in an opposite curvature of the Band center down gives. As a result, the lower layer remains initially elongated, the upper one shortened.

If the temperature of the strip over the strip thickness then compensates for the now-reduced cooling of the underside of the strip when leaving the strip, which is normally not guided on its upper side, from the moving metal conveyor belt, the thermal expansion also equals itself. The upper shortened and the lower elongated band areas now cause a backward curvature, whereby the band edges bulge upwards. However, the stresses occurring below or below the yield point, so that no or a very small regression of the curvature can be observed by flow processes. The upward curvature remains and results in a bowing of the narrow sides of the tape and also of the tape head similar to a ski.

In the further course of transport of the band, the degree of freedom of these warping in the longitudinal direction due to the weight of the horizontally transported on the subsequent roller conveyor belt and / or by one or more after the metal conveyor belt following drive or smoothing rollers is limited, the first band top and then the entire band mechanically clamp and force river-downwards to plane-parallel run. This restriction of the degree of freedom then leads to the fact that the stresses present in the band must be dissipated in non-clamped areas, which is why the band narrow sides first bulge up after leaving the metal conveyor belt. This behavior extends back into the region of the metal conveyor belt, so that the solidifying belt partially no longer has contact with the metal conveyor belt and thus the cooling medium with the result of an inhomogeneous temperature distribution across the width of the belt, which is profiled like a rain gutter.

To counter this problem and to avoid the effect of the profiling of the pre-strip in the casting area and the threading in the Ensuring downstream aggregates is provided in the WO 2006/066552 A1 proposed to arrange a guide element at the end of the primary cooling zone and before the start of the usual secondary cooling zone. As a rule, the guide element consists of several above and below the pre-strip in top to top or mutually offset roles.

In a particular arrangement of the rollers, the pre-strip is guided into a plane lying above the casting line in order to absorb the elongation of the underside of the pre-strip by the upward movement thereby carried out. Also, a roller assembly in which the sub-band undulating passes through the set of rollers is possible, but has not been used.

A disadvantage of the WO 2006/066552 A1 known method is that by the metal conveyor belt subsequent guide element a sweeping influence on the thermal processes on the metal conveyor belt is only incomplete possible.

From the publication JP 06 007900 A For example, an apparatus and a method for continuous casting of thick slabs is known, in which the molten metal is poured onto a metal strip. In the course of the strand guide, a heater for heating the strip edges is disposed between a secondary cooling and a rolling stand before the slab enters the rolling stand.

The WO 2006/066552 relates to a method and an apparatus for horizontal strip casting of steel, wherein a cooled conveyor belt having pulleys at its two ends, further comprising an adjoining housed roller conveyor.

Based on the known prior art, the invention is based on the objective task that the device and the method for near-net-shape casting of strands of metal should be improved so that deformation of the metal strip are avoided as much as possible, especially in the area of the conveyor belt ,

The stated object is achieved by the method with the features of claim 1. Characteristic of the inventive method is that to avoid a possible up to the pouring of the casting rear buckling of the strip edges and to homogenize the heat transfer to the cast product during its solidification on the metal conveyor belt when leaving the conveyor belt abruptly reduced cooling of the underside of the pre-strip is compensated What is additionally cooled in an area immediately behind the conveyor belt, the underside of the Vorbandes.

By according to the invention in the region of the metal conveyor belt end from the top of the cast product and here in particular on the belt edges pressure enforced by the complete contact of the underside of the cast product with the metal conveyor belt, connected to the additional cooling of the Vorbandunterseite, can be an optimization and homogenization of the heat transfer from the metal conveyor belt to the cast product over the entire casting width and achieve a heat balance within the Vorbandes after leaving the metal conveyor belt.

The required pressure is applied for this purpose by acting on the entire width of the cast product pressure roller or by acting only on the band edges partial pressure rollers. The pressure rollers are preferably driven separately and cooled inside. According to the invention, the required pressure can also be applied by a circumferential pressure belt resting on the entire width of the cast product, which likewise can be driven and cooled separately.

In combination with the pressure on the cast product cooling of the Vorbandunterseite is performed in a defined area immediately behind the metal conveyor belt according to the invention, this defined area over the entire width of the Vorbandes and in the presence of smoothing / blowing rollers up to can extend this. This cooling is done by an open spray cooling, for example with water, and / or by a closed cooling by means of a circulating cooled cooling belt, which is similar to the metal conveyor belt in contact with the Vorbandunterseite. According to the invention, it is also possible to arrange a circulating cooling belt at the same time on the pre-strip top side in order to guide the pre-strip and to cool it in a differently adapted manner.

Further details and advantages of the invention are explained in more detail below by way of exemplary embodiments illustrated in schematic drawing figures.

Fig. 1

das Layout einer Gießanlage mit ihren wesentlichen Komponenten,

Fig. 2a

einen vergrößerten Teilausschnitt der Fig. 1 mit offener Spritzkühlung,

Fig. 2b

einen vergrößerten Teilausschnitt der Fig. 1 mit umlaufenden Kühlbändern,

Fig. 3a

eine Draufsicht auf einen Teilausschnitt der Fig. 1 nach dem Stand der Technik,

Fig. 3b

Querschnitte durch das Gussprodukt/Vorband nach dem Stand der Technik,

Fig. 4a

die Draufsicht der Fig. 3 mit einer Druckrolle,

Fig. 4b

Querschnitte durch das Gussprodukt/Vorband mit eingesetzter Druckrolle,

Fig. 5

die Draufsicht der Fig. 3 mit Teildruckrollen,

Fig. 6

die Draufsicht der Fig. 3 mit einem Druckband.

Show it:

Fig. 1

the layout of a casting plant with its essential components,

Fig. 2a

an enlarged part of the Fig. 1 with open spray cooling,

Fig. 2b

an enlarged part of the Fig. 1 with circulating cooling belts,

Fig. 3a

a plan view of a partial section of Fig. 1 According to the state of the art,

Fig. 3b

Cross sections through the cast product / Vorband according to the prior art,

Fig. 4a

the top view of Fig. 3 with a pressure roller,

Fig. 4b

Cross sections through the cast product / pre-strip with inserted pressure roller,

Fig. 5

the top view of Fig. 3 with partial pressure rollers,

Fig. 6

the top view of Fig. 3 with a pressure band.

In the FIG. 1 is a side view of a strip casting 1 according to the DSC method shown with its essential components. In the casting direction (in the drawing from left to right), this system consists of the actual casting machine 2 with the ladle 2 ', a distributor channel 3, a melt delivery system 3' and a circulating metal conveyor belt 7. The from the ladle 2 'through the distribution channel 3 after Downstream molten metal is applied by the melt delivery system 3 'in a certain thickness on the cooled metal conveyor belt 7 as a cast product 4. The length of the metal conveyor belt 7 is designed so that the residence time of the cast product 4 on the metal conveyor belt 7 is sufficient for its extensive solidification to the pre-strip 5. The metal conveyor belt 7, which has only a thickness of about 1 mm, for example, is driven and guided by two deflection rollers 8, 9 and, for example, a tensioning roller 10. For lateral delimitation of the cast product 4 on the metal conveyor belt 7, a follower dam block chain 15 is arranged on each side of the metal conveyor belt 7. To the metal conveyor belt 7 close for transport and safe guidance of fully solidified Vorbandes 5 smoothing / driving rollers 14, which mechanically clamp the Vorband and promote to a driver 16, from where it is then fed to its further processing.

In this state-of-the-art strip casting machine 1, according to the invention, a pressure roller 11 is arranged above the cast product 4 in the region of the deflection roller 8 located at the end of the metal conveyor belt 7. By means of this pressure roller 11 resting on the cast product 4, a maximum contact of at least the strip edges of the cast product 4 with the metal conveyor belt 7 can be forced by a correspondingly exerted pressure on the cast product 4.

In the FIG. 2a , an enlarged part of the Fig. 1 , is in addition to the pressure roller 11, which acts from the top with a certain pressure on the cast product 4, this in combination according to the invention carried out additional cooling the underside of the pre-strip 5 in the form of spray cooling 17 is located. This cooling is adjusted so that it acts only in a defined area, which can extend over the entire width of the pre-strip 5 and in the illustrated embodiment extends from the end of the metal conveyor belt 7 to the first of the lower smoothing / driving rollers 14.

An alternative cooling of the pre-strip 5 in the form of a closed cooling is in the FIG. 2b shown. This cooling, which also takes place only in a defined area immediately behind the deflection roller 8, is performed with a circulating cooling belt 19, 19 '. Here, as in the spray cooling 17 of Fig. 2a represented only the underside of the pre-strip 5 by a cooling belt arranged there 19 and / or optionally also the Vorbandoberseite by a arranged on the upper side of the pre-strip 5 further cooling belt 19 'are cooled.

For better clarity of the pressurization of the cast product 4 according to the invention, the strip casting machine 1 is shown in FIGS. 3 to 6 FIGS. 1 and 2 shown in a perspective plan view.

The FIG. 3a shows by way of example a part of the strip caster 1 from the distributor trough 3 / melt delivery system 3 'to the end of the metal conveyor belt 7 according to the prior art. On the metal conveyor belt 7, on which the strip beginning of a cast product 4 is located, different cross-sectional lines A, B, C are shown. The line "A" represents a cross section through the cast product 4 in the front half of the metal conveyor belt 7, the line "B" shows a cross section through the cast product 4 at the end of the metal conveyor belt 7 and the line "C" represents a cross section through the solidified Vorband 5, which rests after leaving the metal conveyor belt 7 on a roller table 7 '. In a strip casting machine 1 according to the prior art the cast product 4 dissolves from its base, the metal conveyor belt 7, and bulges steadily with its band edges 6. This warping begins in the form of a wedge-shaped bulge region 18 with an increasing amount approximately in the region of the cross-section line "A", so that finally, after leaving the metal conveyor belt 7 (in the region of the cross-section line "C"), the drawn final state is established.

In the FIG. 3b will that be in the Fig. 3a described high buckling of the band by the resulting at the respective cross-sectional lines band cross sections shown more clearly. In the cross-section line "A" is the not completely solidified cast product 4, due to its weight and its existing plastic properties with complete contact still on its base, the metal conveyor belt 7, on. In the cross-section line "B", the band edges 6 of the now no longer plastic cast product 4 have detached from the metal conveyor belt 7, the cast product 4 now has a slightly arcuate cross-section. In the cross-section line "C", the warping of the strip edges 6 has progressed further and the cross-section of the fully solidified pre-strip 5 resting on a roller conveyor 7 'extending the metal conveyor belt 7 has approximately the shape of a rain gutter.

In the FIG. 4a the change in the warping of the strip edges 6 occurring as a result of the use of a pressure roller 11 arranged in the region of the cross-section line "B" is shown. The bulge region 18 of the band edges 6 begins only from the cross-sectional line "B" with a significantly reduced absolute amount. Accordingly, the pressure roller 11 also acts backwards, with the effect of suppressing the bulging of the band edges 6, back to the region of the cross-sectional line "A". The further forward bowing of the band edges 6 to the cross-sectional line "C" can not be completely suppressed by the pressure roller 11, but is significantly lower than in the Fig. 3a without pressure roller 11. The object of the invention to ensure complete contact of the cast product 4 with its base, the metal conveyor belt 7 is thus completely fulfilled by the use of the pressure roller 11.

The resulting by the use of the pressure roller 11 at the corresponding cross-sectional lines band cross sections are in the FIG. 4b shown. As with the pressure roller 11, in the case of the cross section line "A", the cast product 4 lies flat on the metal conveyor belt 7, but also in the cross section line "B" laid at the end of the metal conveyor belt 7. Only after leaving the metal conveyor belt 7 then results in a low Bandkantengewölbung, but can be compensated by the inventive additional cooling of the Vorbandunterseite.

In the FIG. 5 are used as an alternative to the pressure roller 11 in the same area at the end of the metal conveyor belt 7 partial pressure rollers 12 as a printing device, which act exclusively on the belt edges 6. The effect achieved by this measure, as is clear by the marked bulge region 18, with the operation of a pressure roller 11 is quite comparable.

Another alternative to the pressure rollers 11 and partial pressure rollers 12 is the use of a printing tape 13, which corresponds to the FIG. 6 acting on a larger area of the cast product 4 with pressure. The bulge area 18 resulting here is therefore somewhat smaller than in the previously described pressure rollers 11, 12.

The invention is not limited to the illustrated embodiments, but may also be carried out with respect to the applied printing devices and devices for additional cooling with deviating from the description of aggregates, if the inventive method also hereby possible.

LIST OF REFERENCE NUMBERS

1

strip casting plant

2

casting machine

2 '

ladle

3

tundish

3 '

Melt application system

4

casting product

5

opening act

6

Band edges of the opening band

7

Metal conveyor belt

7 '

Roller table after the metal conveyor belt

8.9

idler pulley

10

idler

11

pressure roller

12

Part pressure roller

13

print ribbon

14

Smoothing / blowing rollers

15

Dam block chain

16

driver

17

open cooling device (spray cooling)

18

Aufwölbungsbereich

19

closed cooling device (below circulating cooling belt)

19 '

closed cooling device (above circulating cooling belt)

1. A Cross section through the cast product in the front half of the metal conveyor belt
2. B Cross-section through the pre-strip at the end of the metal conveyor belt
3. C Cross section through the pre-strip after leaving the metal conveyor belt

Claims (13)

1. Method of casting rectangular strips of metal close to final dimensions and subsequently processing to form metal strips, in accordance with the DSC (Direct Strip Casting) method in a horizontal strip casting plant (1), wherein the metal melt is cast by means of a melt delivery system (3') on a horizontally circulating metal transport belt (7) cooled at the underside and the liquid cast product (4) hardens on this metal transport belt (7) during transport thereof so as to form pre-strip (5) which then after leaving the metal transport belt (7) is conveyed mechanically clamped to a driver (16) and wherein for producing maximum contact of the cast product (4) on the metal transport belt (7) a pressing device (11, 12, 13), which is arranged above the pre-strip (5) in the region of the end of the metal transport belt (7) downstream in the casting direction, is pressed from above onto the cast product (4) hardening to form the pre-strip (5),
   characterised in that
   for avoidance of rearward arching, which is possible in the pouring-out region of the casting machine (2), of the strip edges (6) and for homogenising heat transfer to the cast product (4) during hardening thereof on the metal transport belt (7) compensation is provided for the abruptly reduced cooling of the lower side of the pre-strip (5) on departure from the metal transport belt (7), for which purpose the underside of the pre-strip (5) is additionally cooled in the region directly behind the metal transport belt (7).
2. Method according to claim 1, characterised in that a pressure roller (11) acting over the entire width of the cast product (4) is used as pressing device.
3. Method according to claim 1, characterised in that respective pressure sub-rollers (12) respectively acting on the strip edges (6) of the cast product are used as pressing device.
4. Method according to claim 1, characterised in that a circulating pressure belt (13) acting over the entire width of the cast product (4) is used as pressing device.
5. Method according to claim 2, 3 or 4, characterised in that the pressing devices (11, 12, 13) are separately driven and cooled.
6. Method according to claim 1, 2, 3, 4 or 5, characterised in that the region of additional cooling of the underside of the pre-strip (5) when smoothing/driving rollers (14) are present extends up to these smoothing/driving rollers (14).
7. Method according to claim 6, characterised in that the additional cooling is carried out by an open spray cooling (17) and/or by a closed cooling by means of a circulating cooling belt (19, 19').
8. Device for casting rectangular strips of metal close to final dimensions and subsequent processing to form metal strips in accordance with the DSC (Direct Strip Casting) method in a horizontal strip casting plant (1), wherein the metal melt is cast by means of a melt delivery system (3') on a horizontally circulating metal transport belt (7) cooled at the underside and the liquid cast product (4) hardens on this metal transport belt (7) during transport thereof so as to form pre-strip (5) which then after leaving the metal transport belt (7) is conveyed mechanically clamped to a driver (16) and wherein a pressing device (11, 12, 13) is provided, which is arranged above the cast product (4) in the region of the deflecting roller (8) - which is downstream in casting direction - of the metal transport belt (7) and which is constructed to be able to act by a settable pressure from above on the cast product (4) hardening to form the pre-strip (5),
   characterised by
   a cooling device (17, 19, 19') arranged directly behind the metal transport belt (7) for cooling the underside of the pre-strip (5) over the entire width thereof.
9. Device according to claim 8, characterised in that the pressing device is a driven pressure roller (11) acting over the entire width of the cast product (4).
10. Device according to claim 8, characterised in that the pressing device is a respective pressure sub-roller (12) acting on each strip edge of the cast product (4).
11. Device according to claim 8, characterised in that the pressing device is a circulating pressure belt (13) acting over the entire width of the cast product (4).
12. Device according to claim 8, 9, 10 or 11, characterised in that the cooling is set so that it acts only in a defined region which extends over the entire width of the pre-strip (5) and, when smoothing/driving rollers (14) are present, extends selectably up to these.
13. Device according to claim 12, characterised in that the cooling device (17) is constructed in the form of open spray cooling and/or closed cooling by means of a cooling belt (19, 19') circulating below the pre-strip (5).

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