EP0424621B1 - Method for manufacturing a plate for sliding gate valve used in metallurgy - Google Patents

Abstract

The invention relates to a method of manufacturing a plate for a sliding gate valve arranged at the outlet of a vessel intended for holding molten metal, in which a plate body (3) of refractory material is surrounded with a heated steel collar (1) and the latter is allowed to shrink onto a circumferential surface (2) of the plate body by cooling. To avoid cracks in the plate body, e.g. during initial casting, the collar used according to the invention is of a steel grade, an excess length (equals the difference between the outside diameter of the plate to the inside diameter of the cold collar) and of a wall thickness such that the compressive stresses which occur in the plate material during shrink fitting, though lower than the compressive strength of the plate material, are higher than the tensile stresses to be expected in the plate material due to the thermal shock loading of the plate body upon initial casting. <IMAGE>

Description

The invention relates to a method for producing a closure plate for a slide closure arranged on the spout of a container intended for receiving the molten metal, in which a plate body made of refractory material is surrounded by a heated tensioning band made of steel and this is cooled down on the peripheral surface of the plate body shrinking.

Such a method is known for example from DE 33 04 938 C1. In order to avoid the effect of shrinkage forces, which can be of different magnitudes, on the plate body, a hardenable mortar layer is first spread on the peripheral surface of the plate body and then the plate body provided with the mortar layer is surrounded by a steel ring and this is shrunk on. During the cooling down of the steel ring the excess mortar is squeezed out up and down; the mortar remaining between the steel ring and the plate body hardens at the same time due to the temperature effect of the steel ring. In this case, no forces are transmitted from the tensioning strap to the plate body.

A problem with such and other state-of-the-art closure plates for slide closures is the formation of cracks in the plate material, in particular due to the thermal shock stress during casting, since the temperature gradients occurring in the plate material and the tensile stresses induced thereby are greatest. The crack formation not only reduces the durability of the closure plate and thus impairs the safety of a slide closure arranged, for example, on the spout of a metallurgical ladle, but also increases the risk of oxygen and nitrogen being sucked in, as a result of which the quality of the molten metal, e.g. a molten steel suffers during pouring.

It is therefore an object of the present invention, using the method mentioned at the outset, to provide a closure plate in which crack formation in the plate body is largely avoided or at least considerably reduced.

This object is achieved in the method of the type mentioned at the outset by using a tensioning band whose steel quality, its excess length (equal to the difference from the outer circumference of the closure plate to the inner circumference of the cold tensioning band) and its wall thickness are dimensioned such that they shrink in the plate material compressive stresses occurring are less than the compressive strength of the plate material, but are greater than the tensile stresses to be expected as a result of the thermal shock loading of the plate body when cast in the plate material. "Cold" here means room temperature.

By shrinking the, for example, red-hot heated steel strip, according to the invention, precisely defined external forces are applied to the plate body, which generate compressive stresses in the plate body, which in turn compensate for the stresses that occur during casting to such an extent that the latter does not exceed the tensile strength of the refractory material of the plate body. On the other hand, since the compressive stresses generated by the shrinking of the tightening strap do not exceed the compressive strength of the plate material, the shrinking of the tightening strap does not affect the plate material. By avoiding or considerably reducing the formation of cracks in the plate material according to the invention, the wear behavior of the closure plate is improved and its service life is increased, the safety of the casting process is increased and the quality of the molten metal, in particular the molten steel, which is poured out of the container, Improved because no bad gases are sucked in due to the lack of cracks.

In order to avoid any impairment of the plate body due to the shrinking of the tensioning band, the tensioning band is preferably selected with regard to steel quality and dimension such that the compressive stresses occurring due to the shrinking in the plate material are not significantly greater than approximately 75% of the compressive strength of the plate material.

With conventional refractory plate materials, such as refractory ceramics or refractory concrete, the compressive stresses should preferably be in the order of magnitude between 30 and 70 N / mm², in particular 50 to 60 N / mm².

According to a further feature of the invention, it is proposed that a tensioning strap be used, the steel quality and dimensions of which are selected such that the tensile stresses occurring in the tensioning strap do not exceed the yield strength of the steel from which the tensioning strap is made by shrinking. In this way, only elastic deformations of the tension band arise when shrinking on.

You should also use a steel strip, the steel quality of which has a low tendency to age. In this way, undesirable plastic deformations of the strap when Shrinkage can also be avoided later in operation.

It is also advantageous to use a steel strip, the steel quality of which has a thermal expansion of no more than about 0.8% at 500 ° C. This ensures that even during operation of the slide fastener, in which the strap can heat up to about 500 ° C operating temperature (depending on the operating time), forces are still exerted on the plate body and the strap is not caused by excessive expansion of the steel slips or just becomes loose.

In order to obtain the most uniform possible introduction of force into the closure plate, the invention also proposes to use a plate body with a circular shape which is known per se. It has been shown that crack formation can best be avoided with the resulting generation of uniform compressive stresses in the plate material.

For the same purpose of evenly generating compressive stresses in the plate material, the measure serves to use a plate body with a smooth or smoothed peripheral surface. This prevents voltage peaks.

For the generation of the compressive stresses, it would in itself be most favorable if the height of the tensioning band were equal to the height of the plate body. However, this made movement of the slide plate in the slide lock impossible. The strap must jump back at least slightly towards the surface of the plate body. To ensure this, but on the other hand to avoid too much work in the manufacture of the closure plate, it is also proposed with the invention that the height of the strap is about 0.5 to 10 mm, preferably about 2 to 4 mm less than the height of the Plate body is.

In order to ensure the uniformity of the compressive stresses as much as possible, the tensioning band should be shrunk on approximately in the middle of the peripheral surface of the plate body, so that the tensioning band is at approximately the same distance from the top and the bottom of the plate body.

wobei:

E_st

= Elastizitätsmodul des Stahls

p

= vorzugebende Druckspannung (Flächenpressung)

d_f

= Paßfugendurchmesser, gleich etwa d_ap

d_ap

= Außendurchmesser des runden Plattenkörpers

d_ip

= Innendurchmesser des runden Plattenkörpers mit einer mittigen Durchflußöffnung

d_as

= Außendurchmesser des kalten Spannbandes

d_is

= Innendurchmesser des kalten Spannbandes

In order to achieve particularly favorable results for the application of uniform compressive stresses on the peripheral surface of the plate body in the desired order of magnitude, the invention also proposes that an excess (equal to the difference between the outer diameter of the closure plate and the inner diameter of the cold one) be used for the steel strip in the case of a round closure plate Strap) chooses according to the following requirement:

in which:

E _st

= Modulus of elasticity of the steel

p

= specified compressive stress (surface pressure)

d _f

= Fitting joint diameter, equal to approximately _ap

d _ap

= Outer diameter of the round plate body

d _ip

= Inner diameter of the round plate body with a central flow opening

T _he

= Outside diameter of the cold strap

d _is

= Inner diameter of the cold strap

Further objectives, features, advantages and possible uses of the present invention result from the following description of an exemplary embodiment with reference to the drawing. All of the described and / or illustrated features, alone or in any meaningful combination, form the subject matter of the present invention, regardless of how they are summarized in the claims or their relationship.

• Fig. 1 in Draufsicht eine nach der Erfindung hergestellte Verschlußplatte und
• Fig. 2 schematisch im Schnitt eine Verschlußplatte gemäß Fig. 1.

Show it:

• Fig. 1 in plan view of a closure plate made according to the invention and
• 2 schematically in section a closure plate according to FIG. 1st

The plate body 3 shown in FIG. 1, made of refractory material, of a closure plate for a slide closure arranged on the spout of a container intended to hold molten metal has a circular shape and is equipped with a central circular cylindrical flow opening 4. However, the invention can also be used with closure plates of a different shape and several flow openings, but the circular shape ensures that the compressive stresses in the plate material are distributed as evenly as possible. On the preferably smooth peripheral surface 2 of the plate body 3, a tension band 1 of wall thickness w is shrunk as a ring and Although according to the invention in such a way that the compressive stresses generated in the plate material are lower than the compressive strength of the plate material, but greater than the tensile stresses to be expected due to the thermal shock load on the plate body 3 when cast in the plate material. When pouring, the hot molten metal suddenly flows out of the container, to the spout of which the slide closure is attached and whose component forms the closure plate as a base and / or slide plate, suddenly through the flow opening 4, which leads to considerable tension in the plate material, which occurs in conventional Closure plates inevitably lead to cracks in the plate body 3. However, due to the tension band 1 shrunk on in the manner according to the invention, these tensile stresses are compensated for by the compressive stresses which arise from the compressive forces applied to the smoothest possible peripheral surface 2 from the outside. In this way, cracking is reliably avoided.

From Fig. 2 it can be seen that the height h _{s of} the tension band 1 is less than the height h _{p of} the plate body 3 and the tension band 1 is shrunk onto the plate body 3 in the center with respect to the peripheral surface 2. In this way, on the one hand, the functionality of the closure plate is not impaired, on the other hand, it ensures a uniform generation of compressive stresses in the plate material.

Reference symbol list:

1

Strap

2nd

Circumferential surface

3rd

Plate body

4th

Flow opening

h _s

Height strap

h _p

Locking plate height

d _ap

Outside diameter of the closure plate

d _ip

Inner diameter of the closure plate

T _he

Outside diameter of the cold strap

d _is

Inside diameter of the cold strap

Claims (11)

1. Method of manufacturing a valve plate for a sliding gate valve disposed at the outlet of a vessel intended to accommodate metal melt in which a plate body (3) of refractory material is surrounded with a heated tension band (1) of steel which is permitted to shrink onto the peripheral surface (2) of the plate body (3) whilst cooling, characterised in that a tension band (1) is used whose steel quality, whose excess length (1) - equal to the difference in the external periphery of the valve plate (3) from the internal periphery of the cold tension band (1) - and whose wall thickness (w) are such that the compressive stresses occurring in the plate material due to the shrinkage are smaller than the compressive strength of the refractory plate material but larger than the tensional stresses to be expected in the plate material as a result of the thermal shock stressing of the plate body (3) at the beginning of pouring.
2. Method as claimed in claim 1, characterised in that the compressive stresses occurring in the plate material due to the shrinkage of the tension band (1) are not substantially larger than about 75% of the compressive strength of the plate material.
3. Method as claimed in claim 1 or 2, characterised in that the compressive stresses are of the order between 30 and 70N/mm², preferably 50 to 60N/mm².
4. Method as claimed in one of claims 1 to 3, characterised in that a tension band (1) is used whose steel quality and dimensions are so selected that the tensional forces occurring in the tension band (1) due to the shrinkage do not exceed the elastic limit of the steel.
5. Method as claimed in one of claims 1 to 4, characterised in that a steel band (1) is used whose steel quality has a low tendency to ageing.
6. Method as claimed in one of claims 1 to 5, characterised in that a steel band (1) is used whose steel quality has a thermal expansion of not more than ca. 0.8% at 500°C.
7. Method as claimed in one of claims 1 to 6, characterised in that a plate body (3) with a circular shape is used.
8. Method as claimed in one of claims 1 to 7, characterised in that a valve plate (3) with a smooth or smoothed peripheral surface (2) is used.
9. Method as claimed in one of claims 1 to 8, characterised in that the height (h_s) of the tension band (1) is about 0.5 to 10mm, preferably about 2 to 4mm, less than the height (hp) of the plate body (3).
10. Method as claimed in one of claims 1 to 9, characterised in that the tension band (1) is shrunk approximately centrally onto the peripheral surface (2) of the plate body (3).
11. Method as claimed in one of claims 1 to 10, characterised in that for the tension band (1) with a round plate body (3) an oversize (s) (equal to the difference between the external diameter (d_ap) of the valve plate (3) and the internal diameter (d_is) of the cold steel band (1)) is selected in accordance with the following relationship:

    

    whereby:

    E_st   = modulus of elasticity of the steel

    P   = assumed compressive stress (surface pressure)

    d_f   = fitting gap diameter, equal approximately to d_ap

    d_ap   = external diameter of the round plate body

    d_ip   = internal diameter of the round plate body with a central flow opening

    d_as   = external diameter of the cold tension band

    d_is   = internal diameter of the cold tension band.

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