WO2000048769A1

WO2000048769A1 - Ascending pipe for molten metals

Info

Publication number: WO2000048769A1
Application number: PCT/EP2000/000952
Authority: WO
Inventors: Johannes Seyer; Helmut Feuer; Gerhard WÖTTING
Original assignee: Cfi Ceramics For Industry Gmbh & Co. Kg
Priority date: 1999-02-19
Filing date: 2000-02-07
Publication date: 2000-08-24
Also published as: AU2907300A; DE19906982A1

Abstract

The invention relates to an ascending pipe (1) for molten metals and to a holder (16, 17) pertaining thereto. The ascending pipe is held by means of a clamping effect which can be especially produced by metal wedges (15) that engage with grooves (20). The metal wedges are pressed against the ascending pipe by a holder which is screwed together. A seal (19) is arranged between the ascending pipe and the lower holder element (16). Said seal is pressed against the ascending pipe (1) by the holder.

Description

Riser pipe for molten metal

The present invention relates to a riser pipe, preferably made of sintered ceramic material, for molten metals with a coupling area which can interact with a holder of the riser pipe. The invention further relates to a holder for risers for molten metals.

Riser pipes made of sintered ceramic material for molten metals are e.g. in the low-pressure mold casting process for light metal melts, in particular for

Aluminum and aluminum alloys used (DLN 1725 sheet 2). In this process, the light metal melt is located in a sealed, thermally insulated container, from which the melt is fed into the metallic form (mold) via a riser pipe. If necessary, there may be an intermediate pipe between the riser pipe and the mold. To carry the

Molten metal is pressed riser pipe and possibly intermediate pipe against the mold, and the space above the molten metal is pressurized. As a result, the metal level in the riser pipe rises and the molten metal is conveyed into the mold.

The holder with which the ceramic riser pipe is held in the molten metal and pressed against the mold must meet the following requirements:

1. Holding and positioning the riser pipe;

2. absorbing the axial forces that arise when the riser pipe and mold move together;

3. Sealing the overpressure in the furnace chamber from the ambient pressure; 4. Fulfillment of functions 1 to 3 even with different thermal expansion of the holder and tube;

5. Fulfillment of functions 1 to 4 even at maximum application temperature (temperatures of typically are on the outer surface of the holder

300 to 400 ° C measured).

According to the prior art, the riser pipes are attached to the holder via a flange on the ceramic pipe. This flange can be rectangular or conical, terminal or non-terminal. There are also special forms

Combinations of the variants mentioned.

A related application for conveying liquid material is in a holder for metering riser pipes. The pipes are often poured into a metal pipe with refractory cement. However, this holder does not meet the above requirements for riser pipe holders in connection with molten metal.

The holders for riser pipes known from the prior art have various disadvantages. When using a right-angled flange, e.g. the axial forces that can be borne by the holder are limited, since these lead to tensions in the connection area between the flange and the riser pipe, which can ultimately lead to cracks and destruction of the pipe. A limitation of the axial forces also means that the contact pressure between the mold (or intermediate tube) and the riser is limited, which may can lead to inadequate sealing at this point.

A higher axial load is possible with conical flanges, but there are displacements within the holder due to different thermal expansions of the riser pipe and the holder. These shifts must be compensated for by the elasticity of the intermediate seals, which places special demands on their material properties.

The object of the present invention is to avoid the disadvantages described and to provide a riser pipe and a holder for a riser pipe which can absorb high axial forces and in which no sealing problems occur, in particular not due to different thermal expansions of the riser pipe and holder or by varying axial loads.

This object is achieved by a riser pipe for molten metal, which preferably consists of sintered ceramic material and which has a coupling area which can interact with a holder of the riser pipe. In contrast to the prior art, the coupling area in the riser pipe according to the invention, however, consists of depressions in the outer surface of the riser pipe.

The riser pipe according to the invention is fastened by clamping it in a holder. This means that forces running radially to the riser pipe axis act on the circumference of the riser pipe and that this is held thereby.

In a secondary embodiment of the invention, the coupling area on the riser pipe is formed by roughening the outer surface. Due to this roughening, the coupling area with a corresponding e.g. cooperate roughened surface on a bracket such that the bracket clamps the riser pipe and thereby holds.

The described ascending pipes according to the invention have in common that they can be manufactured more easily than the known ascending pipes with a rectangular or conical flange. The risers according to the invention do not have such a flange, but at most a recess (groove) or roughening of the surface. The outer shape of the riser pipe is therefore cylindrical without protruding elements. These risers can therefore also be produced, for example, by an extrusion process. Further advantages of these risers result from their interaction with holders according to the invention, which are described below.

The invention also relates to a holder for a riser for molten metals, which is designed so that with it a dosable and radial with respect to the riser axis clamping force can be exerted on the outer surface of the riser. Such a holder allows a riser pipe to be used without a protruding flange. Such a riser pipe is much easier to manufacture than one with a flange. The strength of the holder can be adjusted as desired by the adjustable radial clamping force.

The clamping force in the holder mentioned is preferably transmitted via metal wedges. Their material and shape can be selected to match the riser pipe.

Furthermore, it is possible to clamp the riser pipe at different positions (heights) by means of different geometries of the metal wedges, so that a variable height adjustment results in a simple manner. In the prior art, however, the vertical position of a riser pipe is always determined by the fixed flange on the riser pipe.

The holder according to the invention can in particular consist of a lower element in the direction of the riser pipe axis and an associated upper element, the axial distance of which can be variably adjusted. The lower and / or the upper element has a surface which is inclined to the riser pipe axis and which corresponds to the

Wedge surface of the metal wedge cooperates such that the metal wedge is moved radially towards the riser pipe when the distance between the upper and lower element is reduced. By varying the distance between the upper and lower element, the clamping force with which the pipe is held by the metal wedges can be metered. It is preferred that the inclined surface is attached to the lower element, since in this case an after axial load on the riser directed downwards, which is transferred to the metal wedge, allows the metal wedge to slide closer to the riser along the inclined surface, so that the clamping effect is increased still further. Such a bracket is therefore reinforced by itself if necessary (axial load).

In a secondary configuration of a holder according to the invention, in which there is a seal between the holder and the riser pipe, the contact pressure of the seal on the outer surface of the riser pipe can be set to a minimum value which is independent of the axial load.

In the riser pipe holdings according to the prior art, there is a seal between the bracket and the outer surface of the flange of the riser pipe. The position of this seal, which is oriented parallel or optionally obliquely to the riser pipe axis, means that axial loads on the riser pipe are transferred to the seal, at least with partial components. On the one hand, this can lead to an enormous load on the seal, on the other hand the contact pressure and thus the sealing effect is determined by the axial load. With a low axial load, the sealing effect is also low. In the holder according to the invention, however, the contact pressure of the seal between the holder and the riser pipe can be set to a minimum value regardless of the axial load. This guarantees that there is an adequate seal even with low axial loads, so that no gases can escape into the environment from the pressurized furnace chamber.

In a special embodiment of the last-mentioned holder, the seal is arranged between the outer surface of the riser pipe and a surface of the holder running parallel to it, the said surfaces preferably running parallel to the riser pipe axis. Since the axial loads run in the direction of the riser pipe axis by definition, no component of these loads (except due to friction) can affect the seal and the opposite surface of the

Transfer bracket. The contact pressure of the seal is therefore almost completely - o -

dependent on the axial load on the riser pipe. This guarantees an adequate seal of the furnace chamber even if there are variable axial loads or if there are displacements within the holder due to different thermal expansions.

In the following the invention is explained by way of example with the aid of the figures.

Figure 1 shows a riser pipe according to the prior art with a rectangular flange.

Figure 2 shows a riser pipe according to the prior art with a conical flange.

Figure 3 shows an embodiment of the riser pipe and holder according to the invention.

1 shows a section through the holder 2 of a riser pipe 1. The

Riser pipe comes from a light metal melt located below (not shown), which is located in a room with the furnace cover 7. The mold 4 or an intermediate pipe is located (schematically indicated) above the riser pipe 1. The riser pipe 1 shown has a flange 3 projecting at right angles, which is received all around by the holder 2.

This type of riser pipe holder represents the most common variant. The mechanical clamping means that only a limited axial force 9 can be applied, since tensile stresses are induced on the attachment 8 of the flanges, which can lead to cracks. The axial force is created by coupling the

Casting mold (mold) on the riser pipe. The fact that only a limited force can be applied includes the risk that metal melt can escape or air can flow in between the mold 4 and the riser pipe 1 due to insufficient pressing of the seal 5. Furthermore, it has been shown in practice that fluctuations in the compressibility of the seals 6 on the flange of the riser

Cracks and leaks occur. It should also be noted that an axial Force that is transmitted to the riser pipe 1 leads to compression of the lower seal 6, while the upper seal 6 on the flange is relieved accordingly. This means that leaks can occur around the upper seal.

In Figure 2 is another variant for a holder of risers after the

State of the art. There is a conical flange 11 at the end of the riser pipe 1. The inclined surface of this flange lies on an appropriately inclined surface of the holder 10 via an intermediate seal 12. This variant is usually very solid in the flange area and a high axial load (> 100kN) is possible. A secure seal between the mold 4 and the riser pipe 1 can thereby be achieved. Due to the different thermal expansion between the holder 10 and the tube 1, the tube moves downward by typically 0.2 mm while the axial force remains the same. If the mold does not follow this movement, this distance must be compensated for by the elasticity of the seals 12, 13. This leads to corresponding demands on the material properties of these seals. It should also be noted that a component of the axial force 9 acts on the seal 12 between the outer surface of the riser pipe 1 (or its flange 11) and the holder 10. This means that the contact pressure of this seal and thus the sealing effect depend on the axial load on the riser pipe 1. In particular, an insufficient axial load can lead to inadequate tightness.

FIG. 3 shows an ascending pipe according to the invention with an associated holder according to the invention. In a known manner, the riser pipe 1 leads from the molten metal through the furnace cover 7 to the mold 4 or an intermediate pipe. Furthermore, in a known manner, there is a seal 14 between the mold 4 or the intermediate tube and the riser tube 1, the tightness of which is guaranteed by a correspondingly large axial force 9.

Unlike the known holders, the riser pipe 1 according to the invention, however, has no flange. Rather, it is flanged without a "clamp bracket" - o -

hold. The riser pipe 1 has a recess 20 which, for example, as a groove can run around the entire pipe. There can also be several such grooves at different distances on the pipe, so that the pipe can be clamped in different places and thus at different heights without any problems.

Metal wedges 15 engage in the groove 20. The metal wedges 15 shown in section can e.g. extend around the tube as a 4-part ring.

The metal wedges 15 are in turn enclosed by a holder which consists of a lower element 16 and an upper element 17. The lower element 16 has a surface 21 inclined relative to the riser axis, which cooperates with the wedge surface of the metal wedge 15 in such a way that a shortening of the distance between the lower element 16 and the upper element 17 pushes the wedge inwards - in the direction of the riser axis - and thus for one increased radial pressure on the riser. The clamping bracket of the riser pipe can thus be made virtually any size by generating a correspondingly high clamping pressure. In order to be able to bring about the adjustable reduction in distance between the lower element 16 and the upper element 17, both are designed as elements which can be screwed together.

In the holder according to the invention, unlike in the prior art, the seal 19 is further arranged between the outer surface of the riser pipe 1 and the holder 16 in such a way that it is located between two surfaces running parallel to the riser pipe axis. This has the effect that no axial load is transmitted to the seal 19 from the riser pipe - except through friction. The contact pressure of the seal 19 on the riser pipe 1 is rather determined solely by how firmly the seal 19 is pressed by the holder 16. A contact pressure is thus ensured even without axial load in the riser pipe 1, which ensures sufficient sealing by the seal 19. Irrespective of this, an axial load occurring in the riser pipe 1 further increases the sealing effect. The seal 19 then receives a part of the axial pressure from above via the metal wedges 15 and the interposed metal disks 18, which leads to an additional compression of the seal 19 and thus to an increase in the sealing effect.

The separation of the functions holding / positioning and sealing with the arrangement according to the invention allows the usual tolerances for the dimensions of the holder and the riser pipe and for the compressibility of the sealing material. The positioning by means of the metal wedges allows an exact and safe positioning of the riser pipe. The independently attached seal 19 ensures the necessary gas tightness. The entire construction allows high axial forces 9, so that a secure sealing between the riser pipe 1 and the mold 4 (or intermediate pipe) is achieved.

The riser pipe 1 shown in FIG. 3 has a groove 20. This has the function of increasing the frictional force between the riser pipe 1 and the metal wedge 15. This effect could also be achieved by other measures, such as rough or structured surfaces of the riser pipe and / or metal wedge.

The tubes with flange known from the prior art are significantly more complex to manufacture than the tubes without flange according to the invention. The isostatic pressing or slip casting molding processes are usually used for the production of risers. On the other hand, other shaping processes are conceivable for the production of the flangeless pipes according to the invention, which are generally not used for pipes with a flange (e.g. extrusion).

Standardization of the tubes is also an option, since the position of the tube in the clamp bracket can easily be varied. In the variant according to the invention shown in FIG. 3, this could be achieved by a plurality of grooves 20 in the riser pipe 1 and / or a displacement of the "nose" on the metal wedge 15. Another advantage is the easy assembly and disassembly, since the metal bracket does not have to be pushed over the lower part of the riser pipe 1, which is immersed in the molten metal. This fact is particularly advantageous if the lower part of the riser is partially protected (e.g. a fiber mat as in DE

196 39 358-A1) is provided.

The basic principle of the holder according to Figure 3 is that the risers are fixed in the oven with a clamp. In the specially illustrated embodiment, the riser pipe 1 is clamped by the (metal) wedge 15 when the holder 16, 17 is screwed together. An applied axial load 9 leads to a simultaneous hardening of the clamp connection, since a pressure "downwards" on the riser 1 tries to take the metal wedges 15 with them, whereupon they tend to move towards the riser due to the inclined surface 21 on the lower support element 16 and therefore to clamp it increasingly.

An advantageous property of the holder according to the invention also arises from the fact that the seal 19 is attached independently of the mechanical clamping of the riser pipe 1. The arrangement shown in Figure 3 leads to the fact that the seal 19 is pressed when thermal expansion of the holder (relative to the riser 1) occurs. Thermal expansion during operation of the device therefore leads to an increase in the sealing effect.

The risers and / or holders preferably consist of a ceramic, particularly preferably sintered ceramic material. This can mostly be done

SiO ₂ -based materials (e.g. DFS = Dense Fused Silica (DFS), SiC-based materials (e.g. oxide or nitride-bonded SiC, recrystallized or sintered SiC), aluminum titanate-based materials (e.g. aluminum titanate Mullite) materials based on silicon nitride (eg: silicon nitride, SiAlON) or materials based on graphite (eg clay-graphite) are particularly preferred aluminum titanate ceramic is used, for example as described in DE 38 14 079-A1 and DE 4029 166-A1.

The invention is not limited to the holder shown as an example in the figure. Rather, it encompasses all methods for

Fastening a riser pipe in a (low pressure) casting plant, in which the riser pipe is positioned and sealed using a clamping device.

The risers and holders according to the invention can preferably be used in the processing of metal melts in low-pressure and counter-pressure mold casting processes.

reference numeral

1 riser pipe

2 bracket 3 right angle flange

4 mold or intermediate tube

5 seal

6 seal

7 Oven cover 8 kink

9 axial force

10 bracket

11 conical flange

12 seal 13 seal

14 seal

15 metal wedge

16 lower mounting element (screw)

17 upper bracket (screw) 18 metal washer

19 seal

20 groove

21 inclined surface

Claims

claims

1. riser for molten metal, with a coupling area that can cooperate with a holder of the riser, characterized in that the coupling area through depressions in the outer surface of the

Riser pipe is formed.

2. riser for molten metal, with a coupling area that can cooperate with a holder of the riser, characterized in that the coupling area by roughening the outer surface of the

Riser pipe is formed.

3. riser pipe according to claims 1 and 2, characterized in that as the material sintered ceramic material based on silicon carbide, aluminum titanate, silicon nitride, silicon nitride with aluminum fractions

(SiAlON) or graphite is used.

4. Holder for a riser for molten metal, characterized in that the holder (15, 16, 17) is designed so that with it a dosable and radial with respect to the riser axis clamping force can be exerted on the outer surface of the riser (1) .

5. Holder according to claim 3, characterized in that the clamping force is transmitted via metal wedges (15).

6. Holder according to claim 4, characterized in that it consists of a lower element in the direction of the riser pipe axis (16) and an associated upper element (17), the axial distance is variably adjustable, the lower and / or the upper element one has surface (21) inclined to the riser axis, which cooperates with the wedge surface of the metal wedge (15) in such a way that the metal wedge reduces the distance is moved radially towards the riser pipe between the upper and lower element.

7. Holder for a riser for molten metal with a seal arranged between the holder and the riser, characterized in that the contact pressure of the seal (19) on the outer surface of the riser (1) is set to a minimum value independent of the axial load (9) can be.

8. Holder according to claim 6, characterized in that the seal (19) between the outer surface of the riser pipe (1) and a parallel surface of the holder (16) is arranged, said surfaces preferably extending parallel to the riser pipe axis.

9. Use of risers according to claims 1 to 3 and brackets according to claims 4 to 8 for processing metal melts in the low-pressure and counter-pressure die casting process.