DE102017006937A1 - Twin Belt Caster for steel casting with 10-12 m / min casting speed with inductive heating of the casting strip edges and with new casting tape seal against cooling water suitable for high strip temperatures - Google Patents

Abstract

What happens on the first 150 mm path during liquid-steel solidification in the Twin-Belt Caster is particularly important and consequential because the shell thickness of the strand is still very low there (about 1.2-2.5 mm). The form stability on the strand is not yet so stable that a liquid metal outlet in the form of "fins" would be impossible. - "Fins" but can only arise if a casting belt deformation has led locally to a small gap between insulation block chain and casting belt, in the vacant spaces between the support rollers. -This application is based on the idea that the casting strip deformation as a result of temperature differences on the casting belt in the central region (temp. About 220 ° C) and in the edge region (temp. About 30 ° C) arise, after all, a difference of 190 ° C. As a solution heating of the casting tape edge zone via an inductive heating is proposed, which takes place between the casting belts. Associated with this is the laying of the current location for the casting tape sealing against cooling water, which is to be carried out in two places in the future. -Both measures are described and supplemented with sketches.

Description

introduction

For more than 40 years, attempts have been made to develop casting machines with revolving mold walls for steel casting at high casting speeds. -

In particular, the HAZELETT twin-belt caster served as a basis for trials a number of times, including Bethlehem Steel, Oregon Steel and Krupp. The tests failed because the thermal stresses in steel casting are higher than in copper casting, for which the twin-belt caster is successfully used.

In Krupp (1986), uncontrollable deformations on the steel casting belt occurred at the transition to the side boundary blocks, which led to the mold being broken and the casting being broken off. - There were so-called "fins" on the strand, these are "ears" on the cast rectangular billet, which led to the blockage of the caster or the tearing of the insulating block chain. -

1. a) DE 10 2015 001 507.9 (Billet-Caster mit Memory Alloy Gießband);
2. b) DE 10 2015 005 751.0 (Caster mit 2 Klotzketten)
3. c) DE 10 2016 006 566.4 (Caster mit hydrostatischer Führung und Zwischenbehälter).

There are several patent applications dealing with the problem:

1. a) DE 10 2015 001 507.9 (Billet Caster with Memory Alloy Casting Belt);
2. b) DE 10 2015 005 751.0 (Caster with 2 block chains)
3. c) DE 10 2016 006 566.4 (Caster with hydrostatic guide and intermediate container).

• Was während der ersten 150 mm Weg während der Erstarrung im Twin Belt Caster mit den Gießband-Deformationen passiert, ist besonders wichtig, weil dort die Schalendicke des Strangs noch relativ gering ist (ca. 1,2-2,5 mm). Das bedeutet, dass die Strangfestigkeit hier noch nicht so stabil ist, dass ein Flüssigmetall-Austritt unmöglich wäre. Daher ist die Randheizung des Gießbandes in diesem Bereich des Casters von besonderer Bedeutung, weil durch sie die Gießband-Deformation verhindert wird. -

In all experiments with the TBC, the casting belt surfaces in the mold area were protected by a "coating". - Decisive for the current application is the following finding:

• What happens during the first 150 mm path during solidification in the Twin Belt Caster with the casting belt deformations is particularly important, because there the shell thickness of the strand is still relatively small (about 1.2-2.5 mm). This means that the strand strength here is not yet so stable that a liquid metal outlet would be impossible. Therefore, the edge heating of the casting belt in this area of the caster is of particular importance because it prevents the casting belt deformation. -

• Hier ist die Strangschalendicke schon größer und der Strang damit steifer und stabiler, so dass eine Gießband-Deformation nicht zur Finbildung führt! - Erschwerend kommt hinzu, dass man nach der vollständigen Erstarrung des Strangs nicht mehr erkennen kann, dass die Finbildung bei ganz geringer Schalendicke eingeleitet wurde. -

This is different in the second and third thirds of the caster length:

• Here, the strand shell thickness is already larger and the strand thus stiffer and more stable, so that a casting strip deformation does not lead to the formation of fineness! - To make matters worse, that after the complete solidification of the strand can no longer recognize that the fineness was initiated at a very small shell thickness. -

In the present application, therefore, the idea is examined that the leakage of the mold of the twin-belt caster caused by a casting belt deformation, wherein the deformation due to temperature differences of the casting belt in the center of the caster (mold cavity) and the casting tape edge is caused. -

As a solution, it is proposed to significantly reduce the temperature difference between the casting belt center and casting belt edges by controlling the casting belt edges controlled by an inductive heater, at least in the first half of the caster. -

Associated with this is a modified casting tape seal against water, which now has to be designed for higher temperatures.

In addition, the design of the twin-belt caster must be changed in various details, which are described in the episode. -

However, a perfectly uniform adaptation of the casting belt temperatures in the middle region and at the edge is not possible in practice and also not necessary.

However, it is already a big step forward if the temperature difference between the center of the casting strip and the casting strip edge can be made smaller by the measures described in the application. -

Even with copper casting with the Twin Belt Caster, there are the temperature differences between the center of the casting strip and the casting strip edge, but without negative consequences.

Because at the lower melting point of 924 ° C for copper compared to 1650 ° C for steel, the entire temperature level at the casting belt is significantly lower, so that there is no "fining" during copper casting. -

The measures described for the steel casting are only a compromise, because in the area of the casting tape in the insulating block area direct heating is not possible.

If the heat comes from the front and back, however, a rapid temperature balance is likely at the casting line in the insulating block area.

II. State of the art

The technique most commonly used today for billet continuous casting of steel is to use a vertical casting machine for 3 m / min with an oscillating mold, whereby a shell of about 10 mm is produced on the strand. -

The strand is guided in an arc and cooled, and then deflected in the horizontal (R = 9 m) and further treated and divided to complete Strangerstarrung with water-spray cooling. -

It is a hall for about 11 m height strand guidance and cooling needed. For the aggregates for strand redirection and fragmentation heavy mechanical engineering is necessary (expensive).

In addition: Without reheating, hot rolling on smaller cross sections is not possible.

It is clear that a horizontal billet caster with 10 m / min casting speed would bring great benefits. The low overall height would save on investment costs, and the option of inline rolling without reheating would save a lot of energy. -

III. solution

As explained in the introduction, a casting strip deformation could be caused by temperature differences of the casting belt in the mold cavity of the caster (about 220 ° C) and on the casting tape edge (about 30 ° C). -

This temperature difference of about 190 ° C must be significantly reduced.

It is proposed to make an edge heating of the casting tapes above and below in the mold area by a powerful electric induction heating. This is intended to reduce the risk of deformation of the casting belts between the support rollers. -

The water cooling in the previous type with high flow velocity should continue to be used. The caster length is divided into different sections; old heated water is removed and new cold water is supplied. -

The new induction heater sits at the point in the caster between the upper and lower casting belt, where formerly the casting tape seal next to the Dämmblock chain had their place. -

1. 1. ein neuer Platz gefunden werden (neben dem Gießband); und
2. 2. die Dichtung an die hohen Temperaturen des Gießbandes an dieser Stelle angepasst werden.

Therefore, for the new casting tape seal

1. 1. find a new place (next to the casting belt); and
2. 2. The gasket adapted to the high temperatures of the casting belt at this point.

Solutions are proposed for both tasks, and the proposals are explained through sketches.

IIIa) Pictures directory

Image 1:

Strand with "fins" for 70 × 180 mm ²

Picture 2:

Twin Belt Caster (TBC) in side view

Picture 3:

Twin Belt Caster in vertical section

Picture 4:

Mold cavity of the TBC, cut with casting belts above and below

Picture 5:

Partial longitudinal section of the TBC with new seal and with induction heating

Picture 6:

Position of the induction heating to heat the casting strip edges

Picture 7:

Vertical section Caster with induction heating and new seal

Picture 8:

Induction heating for the casting tape edges in section and top view

Picture 9:

Holder for sealing strips

Picture 10:

Table for high temperature sealing materials

Picture 11:

Temperature distribution at the casting belt (example)

LIST OF REFERENCE NUMBERS

(1)

Upper endless casting belt made of steel

(2)

lower endless casting belt made of steel

(3)

Curved insulation block chain

(4)

Liquid steel sprue made of FF material

(5)

Deflection drum above

(6)

Deflection drum below

(7)

Induction heating right (picture 3)

(8th)

Induction heating left (picture 3)

(9)

Insulating block chain right (picture 3)

(10)

Insulating block chain left (picture 3)

(11)

Stand as a holder for parts 5 + 6 (picture 3)

(12)

Mold cavity formed by casting tapes and insulating block chains (Fig. 3)

(13)

upper seal of the casting belt on the right (picture 4)

(14)

Lower seal of the casting tape on the right (picture 4)

(15)

Upper seal of the casting belt on the left (picture 4)

(16)

lower seal of the casting belt on the left (picture 4)

(17)

Support rollers above (picture 5)

(18)

Support rollers below (picture 5)

(19)

upper flat gasket for casting belt (Photo 5)

(20)

lower flat gasket for casting belt (Picture 5)

(21)

Inductor for heating the casting tape edge (Photo 5)

(22)

Induction heater right for casting belt (Picture 6)

(23)

Holder for induction heating (Figure 6) and side guide of the insulating block chain

(24)

Holder for flat gasket (Photo 7)

(25)

Wave seal against water (Photo 7)

(26)

Bearing for support roller with seal (Photo 7)

(27)

Holding part for inductor and side guide for insulating block chain (9) (Picture 7 + 8)

(28)

Coil for copper inductor (Photo 7)

(29)

Steel part holder for part 27 (picture 7)

(30)

Air gap at the top between the inductor and the belt (Figure 8)

(31)

Air gap at the bottom between the inductor and the belt (Figure 8)

(32)

Vertical connection line in the inductor (Figure 8)

(33)

upper carriage (frame)

(34)

lower carriage (frame)

(35)

sealed bearing for support roller (18)

(36)

Upper casting tape edge on the right

(37)

Lower casting tape edge on the right

(38)

Joint seal (Photo 9)

(39)

Mount for seal joint (Figure 9)

(40)

Length of the sealing strip

list of figures

• In picture 1 the strand cross-section is shown in the formation of the fins. The strand shell is still very thin. One recognizes "fins", strand accretions due to the compliance of the mold in the 4 corners of the rectangular strand. The "fins" are thus a sign of the mold's leakage in the area between the casting belt and the insulating block chain. Probably between each 2 support rollers there was a casting strip deformation due to the high thermal load during steel casting. -
• image 2 shows the Twin Belt Caster in the side view. You can see the endless upper casting belt between 2 drums ( 5 ) and also the lower endless casting belt between 2 deflection drums ( 6 ). Between the casting belts runs the endless, curved Dämmblock chain ( 3 ); all at synchronous speed. You can also see the ceramic sprue ( 4 ) for feeding the liquid steel into the caster.
• image 3 shows the TBC in a vertical section. It can be seen that the deflection drums have waves in a housing ( 11 ) are stored. You can also see the insulation block chains ( 9 ) and ( 10 ) and next to it the new induction heaters for the band edges ( 36 ) and ( 37 ). -
• In picture 4 is a vertical section to see on the mold cavity ( 12 ) and an upper support roller ( 17 ) and a lower support roll ( 18 ) to be shown. In addition, the new seal above ( 13 and 15 ) in the upper carriage, the new seal below ( 14 and 16 ) in the lower carriage. -
• image 5 shows a longitudinal section of 5 support rollers ( 17 = above) and ( 18 = below) in the edge area. Here is the new seal ( 19 = above and 20 = bottom), in which case a manufacturing length = 480 mm is assumed. In addition, 4 inductor elements ( 21 ), which are arranged between the casting belts.
• In picture 6 is again a vertical section to see on the location of the new seal ( 13 and 14 ) as well as the arrangement of the conductor loops ( 22 ) is shown for the inductive heating, which is located between the casting belts next to the Dämmblock chain.
• image 7 shows the holder for the right side ( 24 ) for the flat gasket and the bracket ( 23 ) for the inductor for heating the band edge, which consists of a steel part ( 29 ) and a copper body ( 27 ) consists of the conductor loops ( 22 ). The same arrangement, but not shown, exists for the left side of the caster. Also shown is a sealing ring ( 25 ) against water and a sealed bearing ( 26 ) for the support rollers ( 17 = above) and ( 18 = below). Part ( 27 ) also includes the lateral guide for the insulating block chains ( 9 ) and ( 10 ).
• In picture 8th is the inductive heating ( 7 ) again on average ( 7 ) and in the development with the conductor loops ( 7 ). Here you can also see the holder ( 23 ) for the inductor. The inductor is through an air gap ( 30 ) above and through an air gap ( 31 ) at the bottom of the casting belt. -
• image 9 shows the holder for the sealing strips ( 13 and 14 ) with the joints ( 38 ) for the seal.
• image 10 shows a table with the high-temperature materials from the company Freudenberg for the sealing strips. Here are 6 materials for service temperatures between 230 ° C and 120 ° C specified.
• In picture 11 the desired temperature distribution for the casting belt with the center and the two band edges is shown. In this sketch, the casting tape edges are evenly heated up to half of the caster at approx. 200 ° C. The temperature difference between center and edge is about 20 ° C and is harmless. -

Thereafter, the edge temperature is slowly reduced in 4 steps from 200 ° C to 120 ° C until the exit of the caster, whereby the temperature difference between the belt center and the edge of the belt is gradually increased from 20 ° C to 188 ° C in order to protect the belt. -

The growing strand shell makes the strand so stable towards the end of the caster that a leak of the mold is no longer to be feared.

For tape deformations, the temperature difference is too small, because in the Dämmblock area the casting tape is getting hotter by contact with the Dämmblock chain, which in turn stores the heat capacitively by the contact with the strand and thus hotter towards the end of the caster becomes.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015001507 [0004]
• DE 102015005751 [0004]
• DE 102016006566 [0004]

Claims (8)

Method and apparatus for the rapid casting of steel billets and steel slabs with a twin-belt caster (TBC), characterized in that the moving casting ribbons have left and right at least a quarter of the TBC length of 4400 mm by stationary elements (7 ) can be heated to inductive heating controllable (Figure 3), wherein the induction heater is arranged laterally in the space between the upper (1) and lower (2) casting belt, and wherein the holder of the induction heater also serves as a side guide for the Dämmblock chain ; Method and device according to Claim 1 , characterized in that the moving casting ribbons edges can be controllably heated left and right on the entire Casterlänge by stationary elements (7) for inductive heating, wherein the temperature distribution in the casting belt according to Figure 11 is selected for center and edge; Method and device according to Claim 1 and 2 , characterized in that the induction heaters (7) operate at a center frequency 1-100 Hz without output transformer and are arranged in the range of the selected heating length in several, about 150 mm long elements (21), which can be regulated differently, and because of the heating of iron belts operate with high efficiency and therefore do not require water cooling; Method and device according to Claim 1 characterized in that there are a total of 4 water seals (13, 15, 14, 16) operating across the entire caster length, the first two in the upper carriage on the right and left sides and the second two in the lower carriage on the right and left side are housed; Method and device according to Claim 1 , characterized in that the new water seals in the hot edge region of the casting belts (about 200 ° C) work, and that the seals are specially designed for this high temperature (Figure 9); Method and device according to Claim 1 , characterized in that the turns (7) of the induction heaters according to Figure 8 are formed horizontally meandering in the region of upper and lower casting belt with only one vertical connection (32); Method and device according to Claim 1 characterized in that the induction heating elements are fastened to the lower carriage by a plurality of brackets (23) and that the inductors are respectively held by a steel part (29) and a copper part (27); Method and device according to Claim 1 , characterized in that on such a caster for steel with casting belt heating not only billet dimensions e.g. 70 × 180 mm ² , but also middle band dimensions can be produced for small batch sizes eg 20 × 525 mm ² or 25 × 400 mm ² or 30 × 350 mm ² with 12 m / min casting speed.

Images