DE2935840A1 - Pouring head for continuous casting molds - Google Patents

Description

A ZinatnuM

** ental 7 / ii.Au *. _3 ^ 293584Q

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• I. Sep 1979

Z / II

ACCIAIERIE DI PIOMBINO S.p.A. Reeietenza 2 PICMBINO (Leghorn) Italy

Casting head for continuous casting molds

The present invention relates to a casting head for continuous casting, in particular for casting high quality steels and other cast metals calmed with aluminum «

The continuous casting of steels killed with aluminum or titanium has always given rise to problems for the following reasons!

(A) Shrinkage of the pouring block placed in the device distributing the steel to the various pouring lines as a result of the deposition of aluminum in the cast stone mouth. This requires the use of large pouring stones and the setting and closing of overflow channels «which, in addition to height,

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operational difficulties and the constant presence of technicians are necessary. This led to the choice of a calibrated pouring stone and the feeding of aluminum in the form of a wire into the mold · Although in the last-mentioned procedure, the problem of the shrinkage of the pouring stones is solved because steel flows through them that has been calmed only with silicon or very little aluminum (maximum 0.007%), so it is with regard to the metallurgical requirements (complete dissipation »control of the austenitic grain, reduction of the formation of cavities) inadequate, and it makes the surface quality and the structure of the semi-finished products is insufficient for subsequent use as so-called carbon and special steels, and for the following reasons:

(a) The aluminum wire inserted into the mold does not have enough time to diffuse into the steel _y because of the rapid solidification of the same, this leads to aluminum-rich areas on or below the surface, which causes damage to the subsequent rolling train and leads to a lack of homogenization in addition to a non-uniform and undesirably large austenite grain "

(b) The inclusions of aluminum oxide and silicon aluminates, which result from the reaction of the aluminum with the oxygen in the air and the oxygen still bound in the steel, do not have sufficient time to separate because the high kinetic energy of the cast steel carries these inclusions deeply and makes them difficult to separate, so that these inclusions remain trapped as slag inclusions both on and below the surface, what more causes unacceptable defects in the subsequent rolled product and makes the possible treatment of the cast semi-finished product ineffective.

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(c) Albeit the aluminum feed and casting speed remains unchanged, the formation of aluminum metal changes with the oxidation of the steel, whereby the steel its composition becomes non-uniform between different casting processes »

(B) Various methods have been patented to reduce the oxidation of the steel during the casting process, e.g. Submerged pouring stones rait the supply of powder at the free pole of the steel in the mold and the protection of the pouring stream by means of inert gases, liquid oxygen or the like. All these arrangements undoubtedly led to better results, In addition to increasing costs, they also worsened the working conditions of the workers and caused considerable losses operational problems. In particular, in the case of the immersed sprues, the feeding of the aluminum wire even more difficult, and overflow channels are required in the ladle, and it can only be done in the case of ingot molds for products with a thickness of more than 140 mm can be used. This technique also requires special care on the part of the workers in order to to keep the steel level always above the outlet opening of the pouring stone, otherwise it will be in the steel during solidification Slag inclusions would result, which would result in an interruption of the pouring lines.

(C) Regardless of the type of calming of the steel and the use of immersed or non-immersed pouring stones and other measures to prevent oxidation, it is known that the at a high rate of the distribution device coming steel streams in relation to the mold must be precisely centered in order to prevent solidification errors or interruptions in the casting line. In particular in machines that have multiple casting lines

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it is difficult to do so because of the deformation of the ladle due to the thermal effect.

It is also known that the high kinetic energy of the casting jets penetrating deep into the mold bath Floating and separation of the non-metallic inclusions made more difficult.

From the above brief summary of the prior art, the ideal conditions for continuous Continuous casting of high-quality steels and other steels that have been killed with aluminum, i.e .:

1) The steel must be in a reduced state as much as possible, with a homogeneous chemical composition, especially as regards the aluminum, and with the lowest possible slag content. The aluminum must therefore be supplied beforehand and in such a way that that it has enough time to distribute itself evenly in the steel and that the reduction products have enough time, to separate themselves for the most part.

2) The kinetic energy of the molten steel in the mold must be as small as possible, which simplifies the deposition of the remaining non-metallic inclusions, reduces the labor and re-pouring of the solidification front, and the centering of the casting becomes less critical.

3) The steel melt in the mold must be protected against oxidation in order to prevent inclusions, oxidation of the aluminum metal and the formation of pores in the mold To prevent surface.

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4) To prevent pore formation, it is ideal if the solidification takes place under the pressure of an inert gas or under the ferrostatic pressure.

5) To minimize the effects of the oscillating movements of the mold on the product it is ideal * when the solidification begins under the pressure of an inert gas or under a hood made of liquid steel.

These five requirements are met by the method according to the invention

The main feature of the invention is to arrange a pouring head between the ladle and the mold, which is rigidly connected to the mold and oscillates together with it «

Further details, advantages and features of the invention emerge from the following description and the drawing, express reference is made to all details not described in the text. Show it:

Fig. 1 is a vertical section through a first embodiment of the invention,

FIG. 2 is a plan view of the casting head according to FIG. 1,

3 shows a vertical section through a second embodiment of the invention,

Fig. 4 is a plan view of the casting head according to Fig. 3, and

5 is a diagram to illustrate the relationship between that prevailing in the mold

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Pressure and the diameter of the pouring stone of the pouring head for one explained in the description Embodiment of the invention, with the ordinate parallel to the pressure in the mold the steel level in the mold and the proportional values of an electrical signal are plotted which makes the level available for adjustment.

In the first embodiment shown in FIGS. 1 and 2, the steel killed only with silicon is of a The pouring ladle 1 is poured into a basin 4 of a pouring head through a pouring stone 2, which has one of the desired pouring speed has a corresponding calibrated diameter, with an immersed tube 3 contacting the pouring stream with air prevented. If necessary, an aluminum wire is fed into the basin 4 through a pipe 5, the feed device is generally known and is not shown in the drawing.

In this basin 4 the complete dissolution of the aluminum and its homogenization with the steel is achieved thanks to the good turbulence present in this, which was caused by the pouring stream emerging from the pipe 3, and because the steel has suffered practically no temperature loss.

At the same time, the reduction products come into contact with the slag layer 6 and are absorbed therein. A first deposition of non-metallic inclusions is thus brought about. The steel then flows into an overflow 7 Basin 8 of the casting head, which has a projection made of heat-resistant material of the cooled mold that is already in use 9 forms. Even the free pole of the steel in the basin 8 is protected against oxidation by the slag layer protected and is kept warm by this.

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In fact, the steel in the basin 8 remains liquid, while the solidification begins when the steel with the water-cooled Parts of the mold come into contact, thereby achieving:

- The complete elimination of the negative effects of electrical energy of kinetic energy of molten steel and their possible inaccurate centering;

- the best hydrodynamic conditions so that the non-metallic inclusions are suitable for excretion to the Surface have required time;

- the beginning of solidification under the pressure of a liquid ferrostatic hood, which causes the formation of pores prevents the poles of the oscillatory motion of the mold substantially eliminated and the elimination of the solidified Skin from the mold is delayed, which increases its cooling effect and consequently the thickness of the skin at the outlet the mold is enlarged.

Through this pouring head, the relationship between the mold and the steel fed from the ladle enables:

- Casting with an immersed pouring stone or better with a steel protected against oxidation with uniform and very small cross-section;

- a swirling of the steel in the mold, whereby its connection with the basin 4 tangential to the basin 8 is. This technique can only be used when the surface quality is more important than the internal quality. In In this case, no covering powder is applied to the free top of the basin 8;

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- the attachment of possible cores in the mold, which are suitable for coupling tubular semi-finished products;

- the loading of one, two or more molds with a single pouring stone of the ladle.

This embodiment requires:

- Minor modifications in the upper area of the existing molds to change the arrangement of the seal 10 for the cooling water! those in the present position with the steel would come into contact to eliminate the oil delivery system and the shut-off ring of the copper pipe to support the mold with stainless steel for high temperatures or with another suitable material that is partially cooled by contact with water-cooled areas with the liquid steel can come into contact without any damage, which at the same time ensures a steady transition between the hot and cold zones of the system are preserved;

- A ring 12 made of refractory material (carbon, silicon nitride, etc.), so that a stable physical transition can be achieved between the medium temperature ring 11 and the hot body of the pouring head;

- the placement of a control device on the casting head for the steel level (thermocouple, infrared rays, etc.) automatically adjust the take-off speed of the semi-finished product;

- As an alternative to the previous paragraph, the steel level can also be adjusted by manually acting on the withdrawal speed of the pinch rollers, i.e. the device for removing the ingot from the mold.

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The second embodiment shown in FIGS the invention does not make any changes to the mold and the device for determining the level in the mold and no special heat-resistant materials are required either.

In this embodiment, the outflow from a pouring stone is turned on by applying a suitable counter pressure the place where the pouring stone opens, the counter pressure and consequently the outflowing amount by an electric Signal is automatically regulated, which is supplied by the device determining the level in the mold.

This possibility of being able to adjust the flow rate of a pouring stone in a very large range, with the this feeding watering head can be arbitrary, makes it possible to provide this watering head with a pouring stone, its Diameter is much larger than it is necessary for the required casting speed, so that he through the Effect of aluminum can shrink without its output decreasing.

Referring to Figures 3 and 4, the silicon (or less than 0.007% aluminum) killed steel poured from the furnace into the ladle 1, which is provided with a pouring stone 2 which is calibrated so that it gives a flow rate required for the desired casting speed. This flow rate is:

Q _t - K S _t
whereby:

Q _t = flow rate of the pouring stone of the ladle in cm / min

K »outflow constant

2 S. = cross section of the ladle pouring stone in cm

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g = 981 cm / sec

t = 60 seconds

H _t = ferrostatic height in the ladle in cm.

Immediately or through the immersed tube 3, which any Preventing the steel from coming into contact with air, the steel enters a basin 104 of the pouring head, creating a seal 112 causes the seal between the casting head and the mold. This is the place where the aluminum wire is placed if necessary through the pipe 5 and the already known (not shown in the drawing) device. The full Dissolution of the aluminum and its homogenization with steel as well as a first separation of the non-metallic inclusions takes place in the basin 104 as in the first embodiment.

The steel then passes through an overflow 107 into a basin 108 of the casting head, where it is non-conductive and protected against oxidation by means of a powder coating 106. A second deposition of non-metallic inclusions takes place in the basin 108. The basin 108 is provided with a pouring stone 109, the cross section S _{M of which is} considerably larger than the cross section S of the pouring stone 2 of the pouring ladle.

The steel then flows through the pouring block 109 into the mold 110, in which a pressure HL as a result of the displacement and The heating of the pre-existing air is generated as soon as the steel completes the head of the wrong block forms. This pressure - partially that by the valve of the adjustment device for the counterpressure prevailing in the mold escapes to the outside, whereby the valve is completely open in this step - is the one penetrating into the mold Steel by partially closing the pouring stone 109

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blocks, and this leads to the formation of a liquid casting head HM in the casting head.

In the meantime, the level of the steel in the mold rises, and when it reaches a predetermined lower level, which is controlled by a level adjuster 111 then the steel actuates this device, which in turn sets the counter pressure HL in the mold and causes the cast block to be removed by actuating the pinch rollers.

The moment the HL € HM condition is obtained, any gurgling through the pouring stone 109 ceases and the automatic adjustment of the steel flow as a function of HL and HM is obtained.

From this moment on, the only requirement to prevent this gurgeine is that the pressure HL is smaller than the ferrostatic pressure HM. This is obtained automatically if the setting of the Pressure HL as a function of the steel level in the mold was taken into account and when the entire system upstream of the mold (pouring head and ladle) was designed. Indeed, there must be an increase in the steel level in the watering head correspond to an increase in the steel level in the mold. The flow rate of the pouring stone 9 actually results as follows:

QM - KS _M - V 2g where:

QM = flow rate of the pouring head pouring stone in cm / min «ferrostatic height in the pouring head in cm, = Pressure in the mold in cm of steel

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By equating the outflow Q of the discharge block ladles _fc with the outflow QH results ι

κ s _t VIg VhJ. Τ - κ s _M from which results:

₁₄₁ HS ²

S _t _- and Hj ₁ »H ₁ +

_t _- and Hj ₁ »H ₁₄ + - ₂

V ^H t ^S M

The direct link between HH and H is now

The following are, for example, the diameters of the ladle spout and the pouring head spout as well as the maximum constriction of the watering head spout is calculated « in which its flow rate does not change for a practical case of continuous casting.

A square block with a side length of 140 is poured under the following conditions at a speed of 1.55 m / min:

Htm = »minimum water level in the ladle» 32 cm HtH = maximum water level in the ladle »36 Uranium «minimum water level in the pouring head = 20 cm HmR = average water level in the watering head »25 cm HIm β minimum pressure in the mold = 0 cm molten steel HLH = maximum pressure in the mold * Hmm * 20 cm molten steel S. (0 _t ) = cross section (diameter) of the ladle casting block

SmH {0 H) s maximum cross-section (diameter) of the casting headm

pouring stone

Smm (0mm) ■ minimum cross-section (diameter) of the pouring head pouring stone

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Q = steel inflow in cm / min

2 2

S β cross section of the cast block in cm = 14

P = weight of the cast block per η in g

Y ■ specific gravity of the liquid steel = 7 g / cm

Y, = specific gravity of the solidified steel = 7.6 g / cm

V = desired casting speed = 1.55 m / min

The steel weight of the cast block per m is: P ■ Sc χ 100 χ Y ₁ »14 ² χ 100 χ 7.60 = 148960 g

The volume of liquid steel to be cast per minute is:

Q = ZJLZ

Y 7

During the project planning it is sufficient to use the pouring ladle pouring stone for the minimum water level (Htm) in the ladle to estimate even a possible necking to be able to meet the same. This results in:

Q ■ KS _t \ f ~ 2q V ^Htm * ^t ~ ^K i ^s t V ^ ™ where:

K K. = KV2g t = 2657.67 (whereby from the experimental Data K = I and t = 60 seconds is assumed. It follows:

S. « 9 -, -. - this results in: 0. = \ J

^r K ₁ VStm ^r V

_4Q

: _λ yfmm

S = -2 £ iZ22. 2.194 cm ² 0. = 167 cm accordingly

2657.67 3Ϊ

about 17 mm.

The cross-section (diameter) of the pouring stone with which the pouring head must be provided, so SmM (0mM) is for a

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Maximum pressure HLM in the mold is calculated, which is equal to or slightly less than the minimum steel level (Hmm) in the pouring head (which enables the above condition to be achieved, which is necessary for Hmm to be 7 Hl to prevent any gurgling during the average level height (HmR) is calculated as follows:

SmM « τ— . from which it follows, because Q must be constant:

- HLM

^S t " ^K l * V ^H tm ^{= SmM} * ^K l

SmM ■ 2.194 \ / --— = 5.55 cm, 0 M = 2.65 cm

The minimum cross-section (diameter) that the pouring stone of the pouring head can assume, i.e. Smm (0 ^ _n ) * although the flow rate Q is kept constant, must be calculated from the minimum level of the steel (Hmm) in the pouring head, which reflects the most unfavorable condition , and for the minimum pressure in the mold, which is zero. It follows:

_t V - as - «U - K V

Hmm-HLm ^Y Hmm-HLm

1.88 cm

The notation A ^ _m ~ 0 _m ^M - ^ m _n results in: 26.5 - 18.8 - 7.7 mm

In the case under consideration, this means that the pouring stone of the pouring head has a diameter of 7.7 mm, that is 29% without reducing the flow rate.

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whereby the pressure in the mold goes from a maximum pressure of 20 cm steel column (which corresponds to 0.14 kg / cm) to zero decreased.

As an example, only the case in question is shown in the diagram according to FIG. 5, from which the necessary Relationship between the steel level in the mold and the pressure HL in the mold is shown. When the pouring stone of the casting head has a diameter of 26.5 mm, then the level in the mold is - 8 cm, and the level measuring device shows about 2.2 volts, which must correspond to a pressure of 13,720 KPa in the mold. If the diameter of the pouring stone is the The ladle is reduced to 19 mm, then the level in the mold is approximately - 11.5 cm, and the level measuring device shows approximately 6.1 volts, which corresponds to a pressure in the mold of approximately 4.100 KPa. In this case the calibration was made between the steel level and the pressure in the mold, the apparently made a purely linear relationship, considering a change in the level within 5 cm. Obviously, the range of change can be expanded or narrowed depending on the needs and the sensitivity that the system should have.

The self-adjustment of the pressure in the mold as a function of the steel level in the mold can be obtained in any suitable way, for example by an electropneumatic system _P. The gas to be used can be any inert gas or nitrogen.

The pressure in the mold can obviously also be adjusted manually, in which case the operator does Ausflussrentil operated in such a way that the level indicator is always in the center of the variable area controlled by the system remains.

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In both cases, the withdrawal speed of the cast block can be constant or self-adjusting around a nominal value are made by the steel level in the mold as it is currently used.

In the case of self-adjustment of the pressure, however, a constant take-off speed is preferable, while im If the pressure is set manually, a self-adjusting pull-off speed is preferable.

The casting according to the embodiment shown in FIGS allows to achieve:

- A considerable reduction in the negative effects of the kinetic energy of the molten steel]

- perfect centering of the molten steel;

- better hydrodynamic conditions for the dissolution and homogenization of the aluminum with steel and for the separation the surface contamination both in the casting head and in the mold;

- a start of solidification under a pressure which opposes the formation of pores and also the influence of the Oscillation movements of the mold are reduced and the separation of the solidified skin from the mold is delayed, as a result of which the cooling effect of the mold is increased, which leads to the above mentioned advantages;

- A protection of the steel layer in the mold against oxidation by an inert atmosphere;

the addition of small amounts of lubricating oil that does not burn because of the inert atmosphere;

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- The pouring of aluminum steel through pouring stones with a large diameter, regardless of the cross-section to be poured and the casting speed, which solves the well-known problem of the constriction of the pouring stone;

- The possibility of charging one , two or more molds with a single ladle pouring stone.

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Claims (6)

Patent claims: 1. Casting head for continuous casting molds for cooling high-quality steels that have been killed with silicon or aluminum or other cast metals, consisting of two chambers open at the top, the first chamber having a pouring stone of a ladle with steel pacified with silicon (or with a maximum of 0.007% aluminum) / while the second Chamber is provided with a lower channel in order to load a continuous casting mold located below, characterized in that that between the first and the second chamber (4 and 8: 104 and 108) a horizontal channel (7; 107), preferably is arranged below the level of the liquid metal contained in the two chambers and that a device (5) is connected to the first chamber (4; 104) for supplying predetermined amounts of aluminum. 2. Casting head according to claim 1, characterized in that the channel (12) formed in the bottom of the second chamber (8) a horizontal cross-section to transfer the liquid metal from the second chamber into the mold (9) below sf area which is substantially equal to or slightly smaller than the cross-sectional area of the mold and the second chamber, a seal (11) being arranged between the bottom of the second chamber and the upper edge of the mold is. 3. Watering head according to claim 1, characterized in that the channel formed in the bottom of the second chamber (108) for transferring the liquid metal from the second chamber into the 030011/0915 The mold (110) underneath consists of a pouring stone (109) with a diameter exceeding the supply requirement at the desired speed, the supply of which is controlled by the back pressure of an inert gas which enters the space between the level of the metal in the mold and the ground of the casting head is initiated that between the bottom of the second chamber (108) and the upper edge of the mold (110) a seal (112) is arranged and that a device
for supplying a pressure medium, preferably an inert gas, is provided, the pressure of the inert gas being variable,
in order to keep the level of the liquid metal in the mold constant regardless of the flow rate through the pouring stone (109) of the second chamber (108) of the casting head. 4. Watering head according to claim 3, which is a continuous
self-regulating supply of the liquid metal into the mold enables the level of the metal in the same to be controlled within wide limits, regardless of the flow rate of the pouring stone
keep constant, characterized in that the self-regulation is obtained automatically by changing the
Pressure of the inert gas from the existing system to the control
of the metal in the mold (110) is made dependent. 5. Casting head according to one of the preceding claims, characterized in that the the first chamber (104) with the
second chamber (108) connecting channel (107) to the periphery of the
second chamber is directed tangentially. 6. Casting head according to claim 1 to 4, characterized in that the first chamber (4) with the second chamber ^ 8) connecting Channel (7) runs in the direction of the line connecting the central areas of the two chambers. 030011 / 091S