DE102008004911A1 - Method for controlling the secondary cooling of continuous casting plants - Google Patents

Abstract

Known secondary cooling of casting strands with a water-air mixture are controlled either individually or in groups depending on process parameters, such as casting speed, steel quality, format width, with the required water pressure and / or water volume. The associated air proportion is used here as a fixed setting value (air pressure or volume flow). In order to present a novel control for cooling with such two-substance nozzles, which has a variable control of the air content (pressure or volume) as a significant additional component, the invention proposes that the controlled amount of water (13) and the amount of air, the latter for a given nozzle characteristic as air pressure (12), using the determined from process, material and system data (18, 19) heat transfer coefficient (alpha) can be used.

Description

The The invention relates to a method for controlling the secondary cooling one leaving the mold with a viable shell Cast strand of a slab, thin slab, block, Billet, or Vorprofilstranggießanlage, wherein between the guide rollers of the strand guide a water-air mixture as spray water by means of splash water nozzles applied under pressure to the strand surface.

After this the cast strand leaves the mold, the subsequent cooling and solidification in the so-called Secondary cooling zone, which is usually between the roller guide or strand guide is located. Secondary cooling is known as pure water cooling (1-material cooling) and with a water-air mixture (2-material cooling). The necessary for the water-air cooling Spray nozzles are either individually or in groups depending on process parameters, such as Casting speed, steel quality, format width, controlled with the required water pressure and / or volume of water. The associated air content is hereby used as a fixed setting value (Air pressure or volume flow) used.

In the DE 31 27 348 A1 For example, a method and apparatus for cooling a continuously cast slab is described wherein cooling is accomplished indirectly by cooling a plurality of guide rollers with an air-liquid spray. In order to investigate the decisive for the cooling effect particle size of emerging from the air / water nozzle cooling water, the water pressure, the water volume and the air pressure were independently varied in a series of experiments, with particle sizes smaller than 60 microns were achieved. In the case of a limited system length, the slab may alternatively be first subjected to direct cooling by means of an air-liquid spray jet and then to indirect cooling in the subsequent process step.

• – Durchmesser der Öffnungen zwischen 0,5 bis 5 mm,
• – Verhältnis Wasser- zur Luftmenge zwischen 1 bis 30,
• – Luftgeschwindigkeit zwischen 75 m/sec bis Schallgeschwindigkeit,
• – Abstand zur Kühlfläche zwischen 5 mm bis 3 m.

From the DT 25 00 079 a device for cooling continuous casting is known with at least one arranged between the guide rollers trough-shaped Zerstäubungsbühne in the emerging from the openings and intersecting and intersecting water and air jets of water atomized and this is sprayed onto the surface to be cooled. These vary:

• Diameter of the openings between 0.5 to 5 mm,
• - ratio of water to air quantity between 1 and 30,
• - air speed between 75 m / sec to the speed of sound,
• - Distance to the cooling surface between 5 mm to 3 m.

outgoing From the described prior art, it is an object of the invention a novel scheme for cooling with 2-fluid nozzles represent a variable regulation of the proportion of air (pressure or volume) as an essential further component.

The Asked object is with the characterizing features of the claim 1 achieved in that as a controlled variable the Amount of water and the amount of air, the latter for a given nozzle characteristic as air pressure, using the process, material and Plant data determined heat transfer coefficient α used become. Advantageous embodiments of the invention are in the subclaims specified.

The effect of the secondary cooling water application can be defined by the heat transfer coefficient α in W / (m ² K). The heat transfer coefficient α is a proportionality factor that determines the intensity of heat transfer at an interface. It represents a specific characteristic of a configuration of materials to a fluid environment. The heat transfer coefficient α depends, inter alia, on the set air pressure at the nozzle, since with increase of the compressed air pressure increases the total pulse of the cooling medium and thereby the insulating vapor layer is reduced, which forms on the strand surface during the cooling process. As a result, the heat transfer coefficient α or the amount of heat extracted or the effect of the cooling is increased.

to use of the heat transfer coefficient α according to the invention The control parameter is the regulation of the water quantity and the air pressure performed so that a previously determined Heat transfer coefficient α as a constant Value is maintained and a change in the rule setting for example, cost optimization with as much as possible Heat transfer coefficient α performed becomes.

To increase the efficiency or in a rapid process-related change in the cooling is the control of the amount of water and the air pressure then carried out so that as soon as possible from the originally set heat transfer coefficient α deviating higher or lower heat transfer coefficient α is achieved.

• – Gießgeschwindigkeit
• – Stahlqualitäten
• – Formatabmessungen
• – Durchflusswerte
• – Düsenkennlinie
• – Ventilkennlinien
• – Druckwerte
• – Temperaturen
• – Oberflächenzieltemperaturen
• – Erstarrungszielwerte
• – Minimaler Energieaufwand
• – Ausnutzung des max. Regelbereiches
• – eine bestimmte oder max. Kühlleistung

The method according to the invention is carried out for adjusting or regulating individual spray water nozzles or spray water nozzles combined in groups of individual regions and / or subregions of a common strand guide, the air quantity or the air pressure being advantageously changed for regulation for a given amount of water. The water control value determining the water quantity and the air control value determining the air pressure are calculated in a process computer from the process parameters and system parameters, whereby, in addition to the heat transfer coefficient α, the following criteria are taken into account for calculating the control values, for example:

• - Casting speed
• - Steel qualities
• - Format dimensions
• - Flow values
• - nozzle characteristic
• - Valve characteristics
• - Pressure values
• - temperatures
• - Surface target temperatures
• - solidification target values
• - Minimal energy consumption
• - utilization of the max. control range
• - a certain or max. cooling capacity

• – Verbesserung der erzeugten Oberflächenqualität der Bramme durch eine gezielte bzw. genauere Steuerung der Strangerstarrung in der Strangführung,
• – gezielte Einstellung der Strangoberflächentemperatur (Temperaturprofil) in Gießrichtung,
• – gezielte Einstellung der Strangoberflächentemperatur (Temperaturprofil) quer zur Gießrichtung (bzw. über die Gießproduktbreite),
• – gezielte Regelung der Strangerstarrung (Wärmeabfuhr über die Sekundärkühlung) zur Verbesserung der Oberflächen und Innenqualität des Gießproduktes,
• – Regelung/Einstellung eines bestimmten prozessabhängigen Wasser-/Luftverhältnisses (Druck oder Volumen/Menge),
• – Einstellung einer Kühlleistung über Kennlinien für Wasserdruck/-menge und Luftdruck/-menge,
• – Einstellung einer Kühlleistung durch geeignetes Verhältnis zwischen Wasserdruck/-menge und Luftdruck/-menge, so dass das Spritzbild optimal ist,
• – Einstellung einer Kühlleistung durch geeignetes Verhältnis zwischen Wasserdruck/-menge und Luftdruck/-menge, so dass der Impuls optimal ist,
• – Regelung einer Kühlleistung durch geeignetes Verhältnis zwischen Wasserdruck/-menge und Luftdruck/-menge in Richtung größter Wirksamkeit,
• – Einstellung einer maximalen Kühlleistung unter Berücksichtigung der gegebenen bereitgestellten Energie durch vorliegende Wasserdrücke/Wasservolumen und/oder vorliegende Luftdrücke/Luftvolumen zur Maximierung der Produktion,
• – Einstellung einer optimalen Kühlleistung unter Berücksichtigung der gegebenen bereitgestellten Medien (vorliegende Wasserdrücke/Wasservolumen und/oder vorliegende Luftdrücke/Luftvolumen) zur Minimierung des Medienverbrauches bei der Erzeugung von Luft- und Wasserdrücken bzw. deren Volumen.

By the method of the invention, an extended controllability of the heat transfer coefficient at given fixed further process parameters is achieved with a minimization / optimization of water and / or air consumption values and an extended adjustability of the desired strand surface temperature in the form of a targeted cooling of the casting strand. In summary, the following advantages can be achieved with the method of the invention:

• - Improvement of the surface quality of the slab produced by a targeted or more precise control of Strangerstarrung in the strand guide,
• - targeted adjustment of the strand surface temperature (temperature profile) in the casting direction,
• - targeted adjustment of the strand surface temperature (temperature profile) transversely to the casting direction (or over the cast product width),
• - targeted control of strand solidification (heat removal via secondary cooling) to improve the surface and internal quality of the cast product,
• - regulation / adjustment of a specific process-dependent water / air ratio (pressure or volume / quantity),
• - Setting a cooling capacity over characteristic curves for water pressure / quantity and air pressure / quantity,
• Setting a cooling capacity by a suitable ratio between water pressure / quantity and air pressure / quantity, so that the spray pattern is optimal,
• Setting a cooling capacity by a suitable ratio between water pressure / quantity and air pressure / quantity, so that the momentum is optimal,
• - Regulation of a cooling capacity by a suitable ratio between water pressure / quantity and air pressure / quantity in the direction of greatest effectiveness,
• Setting a maximum cooling capacity taking into account the given energy provided by present water pressures / volumes and / or present air pressures / volumes to maximize production,
• - Setting an optimal cooling capacity taking into account the given media provided (present water pressures / water volume and / or present air pressures / air volume) to minimize the media consumption in the generation of air and water pressures or their volume.

Further Advantages and details of the invention are given below in schematic drawings illustrated embodiments explained in more detail.

It demonstrate:

1 a schematic diagram of the control concept according to the invention,

2 a control scheme with integrated heat transfer coefficient α.

In the 1 is shown as a schematic diagram of the control concept of the invention. In the figure on the left becomes a part of a vertically arranged cast strand 3 by laterally spaced guide rollers 5 supported. Between the guide rollers 5 there is one spray nozzle each 1 , which spray water for cooling on the Gießstrangoberfläche cone-shaped 2 aufdüst. In the right part of the 1 is the control concept for an exemplary spray nozzle 1' located. Determined or established process parameters 18 and plant parameters 19 For example, the surface temperature, product quality, and water / air ratio become a process computer 4 fed and of this, taking into account achievable goals, such as a maximum cooling effect with minimal energy consumption, and after Be calculation of the required heat transfer coefficient α to the required water control value 16 or air control value 17 converted. With these values, then from the existing water supply 6 or air supply 7 the spray water nozzle 1' respectively supplied amount of water or air quantity controlled by the water control valve 10 and the air control valve 11 ,

This control is controlled by one in front of the water control valve 10 or air control valve 11 arranged water volume flow rate meter 14 or air volume flow rate meter 15 , as well as one after the water control valve 10 or air control valve 11 arranged water pressure gauge 8th or air pressure gauge 9 ,

In the 2 the control diagram according to the invention based on the heat transfer coefficient α is shown as a diagram. In the diagram are the air pressure 12 in cash over the amount of water 13 plotted in l / min and plotted on a defined nozzle characteristic curve and applicable for three different operating conditions heat transfer coefficient curves α1, α2 and α3. Any possible as a rule working point 20 designated point on one of the heat transfer coefficient curves corresponds to a very specific control ratio of water quantity 13 and air pressure 12 , The control possibilities resulting from this representation are as follows, where α1 <α2 <α3:

The rule operating point 20 will be according to the direction of movement 21 shifted along the heat transfer coefficient curve α1. This corresponds to a control with a constant heat transfer coefficient α, as it is carried out for cost optimization, for example. With a required quick change of the cooling setting becomes the control operating point 20 in the direction of displacement 22 shifted to another heat transfer coefficient curve, then on in the direction of displacement 21 , with now changed, but constant heat transfer coefficient α, the amount of water 13 and the air pressure 12 be managed.

The solution of the stated task to provide a variable control, which has as the essential additional component of the spray water nozzle supplied air content, is represented by the representation of 2 thus clearly stated.

The following is a numerical example of a basic setting of spray nozzles for dual-fluid cooling (water / air) for continuous casters: General limit values for a 2-fluid nozzle Water pressure adjustment range: 0.5 ... 12 bar Air quantity at the nozzle: 1 ... 20 Nm ³ / h Amount of water: 0.05 ... 40 l / min Barometer: 0.5 ... 6 bar Heat Transfer Coefficient (HTC): 0.5 ... 1000 W / (m ² K) Infeed system with sufficient volume or quantity typical network values Water pressure: 14 bar Barometer: 4 bar Basic setting (related to a specific nozzle) setpoints Amount of water: 8 l / min Barometer: 2 bar (at the nozzle) Result (actual value) Water pressure: 3.5 bar Air flow: 6 Nm ³ / h Heat transfer coefficient: 150 W / (m ² K) (determined)

Variant setting (related to a specific nozzle), water quantity is reduced compared to the basic setting (energy optimization through less water use). Control approach (the heat transfer coefficient with 150 W / (m ² K) should be maintained: setpoints Amount of water: 6 l / min Barometer: 3 bar (at the nozzle) Result (actual value) Water pressure: 3 bar Air flow: 10 Nm ³ / h

1

Spritzwasserdüse

2

splash

3

cast strand

4

process computer

5

leadership

6

water supply

7

air supply

8th

Water pressure gauge

9

Luftdruckmesser

10

Water control valve

11

Air control valve

12

air pressure

13

amount of water

14

Water flow-meter

15

Air volume flow meter

16

Water control value

17

Air control value

18

process parameters

19

system parameters

20

Rule operating

21

displacement direction of the operating point at constant α

22

displacement direction the operating point at different α heat transfer coefficient

• - nozzle characteristic
• - Valve characteristics
• - Pressure values
• - temperatures
• - Surface target temperatures
• - solidification target values
• - Minimal energy consumption
• - utilization of the max. control range
• - a certain or max. cooling capacity

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3127348 A1 [0003]
• - DT 2500079 [0004]

Claims (7)

Method for controlling the secondary cooling of a cast strand leaving the mold with a load-bearing shell ( 3 ) a slab, thin slab, block, billet or Vorprofilstranggießanlage, wherein between the guide rollers ( 5 ) the strand guide a water-air mixture as a spray ( 2 ) by means of spray nozzles ( 1 ) is applied under pressure to the strand surface, characterized in that as a controlled variable the amount of water ( 13 ) and the amount of air, the latter for a given nozzle characteristic as air pressure ( 12 ), using the process, material and plant data ( 18 . 19 ) heat transfer coefficients (α) are used. Method according to claim 1, characterized in that the regulation of the amount of water ( 13 ) and the air pressure ( 12 ) while maintaining a heat transfer coefficient (α). Method according to claim 2, characterized in that the regulation of the amount of water ( 13 ) and the air pressure ( 12 ) is performed so that as soon as possible, a different higher or lower heat transfer coefficient (α) is achieved. A method according to claim 1, 2 or 3, characterized in that the spray water nozzles ( 1 ) are regulated separately and / or in groups of individual areas and / or subareas of a common strand management separately. A method according to claim 4, characterized in that for regulation at a given amount of water ( 13 ) the amount of air or the air pressure ( 12 ) is changed. Method according to one or more of claims 1 to 5, characterized in that the amount of water ( 13 ) determining water control value ( 16 ) and the air pressure ( 12 ) determining air control value ( 17 ) in a process computer ( 4 ) from the process parameters ( 18 ) and system parameters ( 19 ) is calculated. A method according to claim 6, characterized in that in addition to the heat transfer coefficient (α) for calculating the control values ( 16 . 17 ), for example, the following criteria are considered: casting speed steel grades format dimensions flow rates