GB1595732A

GB1595732A - Pouring tubes for casting metals under gas pressure

Info

Publication number: GB1595732A
Application number: GB3614/78A
Authority: GB
Original assignee: BUSCHER KG
Current assignee: BUSCHER KG
Priority date: 1977-01-28
Filing date: 1978-01-30
Publication date: 1981-08-19
Also published as: FR2378591B1; IT7819718A0; ES466941A1; IT1091820B; BR7800528A; FR2378591A1

Description

(54) IMPROVEMENTS IN OR RELATING TO POURING TUBES FOR CASTING METALS UNDER GAS PRESSURE (71) We, BUSCHER KOMMAN DITGESELLSCHAFT, a German body corporate, of Wulfrather Strasse 56, 5620 Velbert 7, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to pouring tubes for casting metals under gas pressure. Such a pouring tube may be used in low pressure casting equipment and may comprise a pipe in the form of several concentric shells, with its lower end immersed in moten metal and having a border region between two shells being connected to the exterior by way of at least one outwardly directed hole.

Gas-tight pouring tubes manufactured from ceramic materials are known, but are mechanically extremely susceptible to fracture and are therefore unsatisfactory for rough foundry practice and are furthermore elaborate and expensive to manufacture. It is also difficult to manufacture all necessary shapes and sizes of pouring tube from the said material.

Pouring tubes of steel or cast iron are also known. Molten aluminium in particular reacts relatively strongly with such materials. It has therefore already been attempted to protect the pouring tube from metal attack by carefully applied smooth linings. It has, however, been shown that the smooth lining does not withstand the mechanical stresses or temperature changes.

A pouring tube consisting of several concentric shells is known, the region of which, lying between two shells, is filled with sand and is vented through an outwardly directed vent passing through a flange, so that the air which is trapped inside the inner of the two shells, which is gas permeable, can escape outwards with the molten metal rising in the pouring tube during casting, without penetrating into the pipe duct. The outer of the two shells which border the region is in the form of a steel pipe which is jacketed with a refractory ceramic material, which because of the fact that its coefficient of expansion is different from that of steel quickly fractures and crumbles away. Because of this, the steel pipe is provided with outwardly projecting support elements which grip into the refractory material. The expense of manufacturing such a steel pipe is particularly high, and the danger of fracture and crumb - ing of the outer ceramic layer is still not able to be completely prevented.

Finally, there are various materials such as argillaceous graphite or silicon carbide used for pouring tubes, which are resistant to molten metals and are easy to form into pouring tubes but have the great disadvantage of being to a greater or lesser extent gas permeable, or become gas permeable to an increasing degree during operation due to the burning away of their material components, so that during the casting operation air is able to pass through the pipe wall into the pipe duct and from here into the casting mould. All attempts to provide such materials with a refractory lining which is impermeable to gas have so far been unsuccessful.

According to one aspect of the invention there is provided a pouring tube for use in casting metals under gas pressure, comprising a pipe in the form of a plurality of concentric shells with a border region between two shells being connected by way of at least one outwardly directed hole to the exterior, the border region comprising an air gap and the two shells which border the air gap comprising non-metallic refractory material which is permeable to gas or which becomes permeable to gas following use, the said two shells being joined together at least at the lower end of the pouring tube in a manner tight against molten metal.

According to another aspect of the invention, there is provided a pouring tube for use in casting metals under gas pressure, comprising a pipe in the form of a plurality of concentric shells with a border region defined by two shells being connected by way of at least one outwardly directed hole to the exterior, the two shells comprising non-metallic refractory material which is permeable to gas or which becomes perme able to gas following use, the said two shells being joined together at least at the lower end of the pouring tube in a manner tight against molten metal, the inner of the said two shells bordering directly on the outer of the said two shells and including the border region within itself.

A preferred pouring tube is easy to manufacture, is refractory and resistant to molten metals, has a long life and a relatively high insusceptibility to fracture during the casting operation, and prevents penetration of gas through the pipe wall and into the pige duct.

lt is possible to manufacture gas-tight pouring tubes for metal casting under gas pressure from refractory materials which are resistant to molten metals, easily worked, inexpensive and relatively insensitive to impact, and which in particular after a certain time of use become relatively permeable to gas.

In the case of pouring tubes used for the gas-tight conveying of molten metals into a mould, no harm can result if air penetrates from the outside into the pipe during the casting operation, provided it is ensured that the air pressure is annulled within the pipe wall and thus during the casting operation no air can reach the pipe duct through the pipe.

The air fed into the melting chamber of a low pressure casting apparatus for pushing the molten metal up through a preferred pouring tube into a casting mould can indeed penetrate into the outer wall region of the pouring tube until it reaches the air gap, but from here it is led off to the outside, without it being able to penetrate into the molten metal in the pipe duct.

It can be of advantage to build up a pressure of inert gas in the pipe duct via the inner air gap of the pouring tube at the end of the casting operation as the air pressure in the melting chamber falls, so as to provide a gas cushion above the descending molten metal in the pouring tube to prevent its contact with the indrawn air, so that the molten metal is protected from oxidation. The pressure of inert gas, e.g. nitrogen, fed into the pipe duct through the air gap can then be determined or adjusted such that the molten metal is pushed downwards out of the pouring tube and is thus substantially freed from metal residues adhering to the pouring tube, at the same time making it possible to scavenge the molten metal in the melting chamber with the inert gas so as to flush out oxides from the molten metal in known manner.

A particularly simple preferred pouring tube consists of an argillaceous graphite pipe, the inner wall of which is lined with a layer of a fibrous ceramic material, which serves as a gas reservoir during the casting operation. This means that during the casting operation, air which penetrates into the pouring tube is taken up by the fibrous ceramic material. Thus during the casting operation air does not enter the molten metal in the pouring tube, a condition which would lead to rejection of the casting.

After the casting operation, the air stored in the fibrous ceramic material reaches the pipe duct together with the metal column descending in the pouring tube, and can escape to the outside through the open mould.

In this case, the inner wall of the pouring tube, this latter being of a material which is permeable to air or which becomes permeable to air during use, is lined with a layer of material which possesses two essential properties.

Firstly, it consists of a refractory or high temperature resistant material which is especially suitable for conveying molten metals, as used in low pressure casting. Secondly, the pipe lining possesses a storage capacity for the air which penetrates through the porous outer wall, such that during the casting operation substantially no air passes into the molten metal in the pouring tube and into the mould.

A preferred pouring tube is particularly simple to manufacture. In this respect, the outer pipe can be manufactured first and then the inner pipe inserted into the outer pipe, it then being sufficient to cement the inner pipe at both ends to the outer pipe.

However, the outer pipe can also be constructed around the inner pipe. In this respect, the outer pipe can be cast around the inner pipe from a foundry concrete, so that the pipes are internally in contact with each other over their entire lengths.

The invention will be further described, by way of example with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a low pressure casting apparatus comprising a preferred pouring tube; and Figures 2 to 6 illustrate further preferred pouring tubes.

A low pressure casting apparatus comprises furnace 1, in which a crucible 2 constructed of refractory material and comprising a base 3 is disposed. The crucible 2 is surrounded by heating elements 4. The furnace 1 is closed by a furnace roof 5. A preferred pouring tube 6 extends through a central aperture in the furnace roof 5 and projects into the crucible filled with a molten metal 7 to a point close to the crucible bottom. At its top end, the pouring tube 6 comprises a flange-type head 8, by which it covers the central aperture in the furnace roof 5. The pouring tube 6 comprises a pipe duct 9, through which the molten metal in the crucible 2 is raised by pressure into a mould 11. In addition, the interior of the furnace 1 is connected via a connection 10 to a source of compressed air for building up a determined air pressure over the molten metal. A distance piece 12 is used for connecting the mould 11 to the pouring tube 6.

The mould 11 rests on a base-plate 13, which is fixed to guide columns 14. The mould is made in two parts, and the top part 15 is connected via connection pieces 16 to a guide plate 17 which is guided on the guide columns 14. The guide plate 17 is connected via lifting bars 18 to a lifting device consisting of a lifting cylinder 19 and a cross-beam 20. By means of the lifting device, the lifting bars and guide plate, the top part 15 of the mould can be raised and lowered. The guide columns 14 are connected together by a girder 21 for reinforcement.

Figure 2 shows a preferred pouring tube 6 which can be used in a low pressure casting apparatus. This pouring tube comprises an inner pipe 22 and an outer pipe 23 which is slid thereover. The inner pipe 22 and outer pipe 23 have grooves in both end regions.

These grooves serve to form a seal against molten metal by means of a refractory cement material 24 or a similar sealing material, and together form a type of labyrinth seal. Such a labyrinth seal is however not necessary in every case. In this respect, it can be sufficient to insert a refractory sealing material, which does not need to be gastight, into the concentric air gap 26 between the mutuallv inserted pipers, these not being provided with any seal grooves. The air gap 26 is connected to a vent 27, which extends e.g. radially outwardly through the wall of the outer pipe 23.

At its top end, the outer pipe 23 comprises a flange-type head 28, at the end of which there is a concentric projection of cone frustum shape. The distance piece 12 sits on this projection, as shown in Figure 1.

The vent 27 is located in the flange-type head 28, so that it extends above the furnace roof 5. The pouring tube 6 is made gas-tight at that surface of its head which rests on the furnace roof 5, e.g. by means of asbestos cord between it and the roof. It is apparent that the distance piece 12 can also be made in one piece with the pouring tube 6.

As the drawing also shows, the inner pipe 22 preferably has a smaller material thickness than the outer pipe 23. Without in any way limiting the invention, the ratio of the wall thickness of the inner to the wall thickness of the outer pipe can, for example, be 1:1.25. Furthermore, the concentric air gap 26 can for example be 0.2 to 5 mm and preferably 1 mm wide.

On the end face of the lower end of the pouring tube 6, there is a notch 30. This notch 30 connects the pipe duct 9 to the outside of the pouring tube 6.

Figures 3 and 4 show two further embodiments of a preferred pouring tube 6. In this case, the pouring tube 6 preferably comprises a one-piece pipe member which encloses the concentric air gap 26 in its centre. Such a pouring tube can, for example, be manufactured by incorporating, during its formation, a material such as a wax layer or cardboard in the position where the air gap is to be situated. When the pouring tube is fired, this material is burnt out, so leaving a hollow space.

As can be seen in the left hand half of Figure 3 and the right hand half of Figure 4, the inner wall 32 can be thinner than the outer wall 33, or alternatively the two walls can have approximately the same wall thickness, as shown in the right hand half of Figure 3 and the left hand half of Figure 4.

With regard to the pouring tube shown in Figure 3, this substantially corresponds to the embodiment of Figure 2. Different wall thicknesses give an advantageous saving of material.

The pouring tube of Figure 4 is again formed in one piece. However, the axially extending air gap 26 is, during manufacture, closed at the lower end only of the pouring tube, whereas it is open at the upper end.

This embodiment can have constructional advantages. The upper open end of the air gap 26 is closed by means of a seal 34 of heat-resistant material. The lower opening 9' of the duct 9 extending in the pouring tube 6 is of funnel shape to give flow advantages. In this embodiment, the upper end of the pouring tube, on which the distance piece 12 rests, is convex in shape, and the flange-type head 28 tapers downwardly conically. For this reason, the vent 27 in the head 28 extends not radially but inclined upwardly.

In the embodiment of the pouring tube shown in Figure 2, the inner pipe 22 advantageously consists of a fibrous ceramic material which has a very low ability for being wetted by the molten metal, and a high gas permeability. In contrast, the outer pipe 23 consists for example of argillaceous graphite, silicon carbide or a refractory sundry concrete.

The operation of the apparatus comprising a pouring tube as shown in Figure 1, 2, 3 or 4 is as follows. An air pressure of e.g. 0.5 bars is built up and maintained in the furnace 1, which is closed in a known gas-tight manner. By means of this air pressure, the molten metal in the crucible is pushed upwards through the pouring tube 6 and into the mould 11. During this, the molten metal in the crucible must not fall below a determined minimum level. The air then tends to penetrate into the gas-permeable outer wall, e.g. of argillaceous graphite. The air however is not able to reach the duct, and thus is unable to reach the molten metal located therein, because the air pressure is reduced to atmospheric pressure through the air gap 26 in the pouring tube, the air being able to escape through the vent 27, 35 into the free atmosphere. Thus spoiled castings due to the penetration of air into the molten metal in the pouring tube are impossible.

When the air pressure in the furnace 1 is reduced after a casting operation, a gas pressure can be built up in the air gap 26 in the pouring tube wall, e.g. using nitrogen fed through the line 35 and vent 27. For this purpose, a change-over valve, not shown, can be connected to the line 35, so that it connects the line 35 to atmosphere in one position, and to a source of pressurised nitrogen in the other position.

If nitrogen is fed in this manner into the air gap 26 at that point in time, as stated, when the casting mould is full and the pressure in the furnace has fallen, nitrogen penetrates through the gas-permeable inner pipe 23, which is preferably of a fibrous ceramic material, into the duct in the pouring tube, and pushes the molten metal therein downwards oui of the pouring tube, so that the pouring tube becomes freed of adhering metal residues. At the same time, by further feeding nitrogen, the molten metal becomes scavenged with nitrogen, which escapes through the molten metal and into the hollow compartment above the molten metal at atmospheric pressure, so removing oxides.

The notch 30 at the lower end of the pouring tube 6 (Figure 2) and/or the funnelshaped recess (Figure 4) facilitate the well regulated exit of the nitrogen. It is apparent that, instead of nitrogen, another inert gas could be used.

Each of the pouring tubes 6 shown in Figure 5 and 6 comprises an outer pipe 23 of a material which is permeable to gas or which becomes permeable to gas during use, preferably argillaceous graphite, silicon carbide or refractory foundry concrete, and an inner pipe 22 of a refractory or high temperature resistant gas-permeable material, preferably a fibrous ceramic material, which as previously stated serves as a gas reservoir during the casting operation. In the example, the inner pipe is cemented at both ends to the outer pipe with no air gap between the pipes. It is apparent that the upper and lower end of the pouring tube can have any required shape. In the examples, pouring tubes with flange-type heads 28 are chosen, on the front end of which there is a concentric, cone frustum projection, on which a distance piece is disposed to connect the pouring tube to the casting mould, as shown in Figure 1.

The heads 28 of the pouring tubes shown in Figures 5 and 6 comprise at least one vent 27, connected to the inner pipe 22. A line 35 is connected to the vent 27 and leads to a change-over device 31. In a first position of the change-over device, the inner pipe is vented via the vent 27 and line 35, and in a second position the line 35 is connected to a pressurised gas source 32, so that, after the casting operation, nitrogen for example can be pushed therethrough into the inner pipe, so that it enters the duct interior and pushes the molten metal downwards from the pouring tube. By this means, the inner wall of the inner pipe is substantially freed from metal residues. The molten metal can also be scavenged with nitrogen, in order to wash out the oxides.

The expressions "inner pipe" and "outer pipe" are not to be understood as being limited to two mutually inserted individual pipes which are previously separately manufactured. Thus, the expression "inner pipe" also includes a layer of a determined thickness with which the inner wall of the outer pipe is lined. Likewise, the expression "outer pipe" also includes a layer of a determined thickness with which the inner pipe is externally jacketed.

A preferred pouring tube may include a one-piece pipe, the inner region of which acts in the previously discussed manner as a gas reservoir, or is connected to a vent, and the outer region of which is directly joined to the inner region. Accordingly the pipe can consist for example of argillaceous graphite, silicon carbide or refractory foundry concrete, the outer region of which has a lower gas permeability than the inner region. For this, the two regions can be manufactured in two steps.

Preferred pouring tubes are also suitable for molten metal feeding apparatus with open casting moulds.

WHAT WE CLAIM IS: 1. A pouring tube for use in casting metals under gas pressure, comprising a pipe in the form of a plurality of concentric shells with a border region between two shells being connected by way of at least one outwardly directed hole to the exterior, the border region comprising an air gap and the two shells which border the air gap comprising non-metallic refractory material which is permeable to gas or which becomes permeable to gas following use, the said two shells being ioined together at least at the lower end of the pouring tube in a manner tight against molten metal.

2. A pouring tube for use in casting metals under gas pressure, comprising a pipe in the form of a plurality of concentric shells with a border region defined by two shells being connected by way of at least one outwardly directed hole to the exterior, the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. air however is not able to reach the duct, and thus is unable to reach the molten metal located therein, because the air pressure is reduced to atmospheric pressure through the air gap 26 in the pouring tube, the air being able to escape through the vent 27, 35 into the free atmosphere. Thus spoiled castings due to the penetration of air into the molten metal in the pouring tube are impossible. When the air pressure in the furnace 1 is reduced after a casting operation, a gas pressure can be built up in the air gap 26 in the pouring tube wall, e.g. using nitrogen fed through the line 35 and vent 27. For this purpose, a change-over valve, not shown, can be connected to the line 35, so that it connects the line 35 to atmosphere in one position, and to a source of pressurised nitrogen in the other position. If nitrogen is fed in this manner into the air gap 26 at that point in time, as stated, when the casting mould is full and the pressure in the furnace has fallen, nitrogen penetrates through the gas-permeable inner pipe 23, which is preferably of a fibrous ceramic material, into the duct in the pouring tube, and pushes the molten metal therein downwards oui of the pouring tube, so that the pouring tube becomes freed of adhering metal residues. At the same time, by further feeding nitrogen, the molten metal becomes scavenged with nitrogen, which escapes through the molten metal and into the hollow compartment above the molten metal at atmospheric pressure, so removing oxides. The notch 30 at the lower end of the pouring tube 6 (Figure 2) and/or the funnelshaped recess (Figure 4) facilitate the well regulated exit of the nitrogen. It is apparent that, instead of nitrogen, another inert gas could be used. Each of the pouring tubes 6 shown in Figure 5 and 6 comprises an outer pipe 23 of a material which is permeable to gas or which becomes permeable to gas during use, preferably argillaceous graphite, silicon carbide or refractory foundry concrete, and an inner pipe 22 of a refractory or high temperature resistant gas-permeable material, preferably a fibrous ceramic material, which as previously stated serves as a gas reservoir during the casting operation. In the example, the inner pipe is cemented at both ends to the outer pipe with no air gap between the pipes. It is apparent that the upper and lower end of the pouring tube can have any required shape. In the examples, pouring tubes with flange-type heads 28 are chosen, on the front end of which there is a concentric, cone frustum projection, on which a distance piece is disposed to connect the pouring tube to the casting mould, as shown in Figure 1. The heads 28 of the pouring tubes shown in Figures 5 and 6 comprise at least one vent 27, connected to the inner pipe 22. A line 35 is connected to the vent 27 and leads to a change-over device 31. In a first position of the change-over device, the inner pipe is vented via the vent 27 and line 35, and in a second position the line 35 is connected to a pressurised gas source 32, so that, after the casting operation, nitrogen for example can be pushed therethrough into the inner pipe, so that it enters the duct interior and pushes the molten metal downwards from the pouring tube. By this means, the inner wall of the inner pipe is substantially freed from metal residues. The molten metal can also be scavenged with nitrogen, in order to wash out the oxides. The expressions "inner pipe" and "outer pipe" are not to be understood as being limited to two mutually inserted individual pipes which are previously separately manufactured. Thus, the expression "inner pipe" also includes a layer of a determined thickness with which the inner wall of the outer pipe is lined. Likewise, the expression "outer pipe" also includes a layer of a determined thickness with which the inner pipe is externally jacketed. A preferred pouring tube may include a one-piece pipe, the inner region of which acts in the previously discussed manner as a gas reservoir, or is connected to a vent, and the outer region of which is directly joined to the inner region. Accordingly the pipe can consist for example of argillaceous graphite, silicon carbide or refractory foundry concrete, the outer region of which has a lower gas permeability than the inner region. For this, the two regions can be manufactured in two steps. Preferred pouring tubes are also suitable for molten metal feeding apparatus with open casting moulds. WHAT WE CLAIM IS:

1. A pouring tube for use in casting metals under gas pressure, comprising a pipe in the form of a plurality of concentric shells with a border region between two shells being connected by way of at least one outwardly directed hole to the exterior, the border region comprising an air gap and the two shells which border the air gap comprising non-metallic refractory material which is permeable to gas or which becomes permeable to gas following use, the said two shells being ioined together at least at the lower end of the pouring tube in a manner tight against molten metal.

two shells comprising non-metallic refractory material which is permeable to gas or which becomes permeable to gas following use, the said two shells being joined together at least at the lower end of the pouring tube in a manner tight against molten metal, the inner of the said two shells bordering directly on the outer of the said two shells and including the border region within itself.

3. A pouring tube as claimed in claim 1 or 2, in which the tube comprises only two shells.

4. A pouring tube as claimed in claim 1 or 3, in which the said two shells form a homogeneous one-piece member.

5. A pouring tube as claimed in any one of claims 1 to 3 in which the outer of the said two shells is in the form of an outer pipe and the inner is in the form of an inner pipe.

6. A pouring tube as claimed in any one of the preceding claims, in which the inner of the said two shells serves as a gas reservoir during the casting operation.

7. A pouring tube as claimed in any one of claims 1, 2, 3, 5 and 6, in which the inner of the said two shells has a higher gas permeability than the outer of the said two shells.

8. A pouring tube as claimed in any one of the preceding claims, in which the inner of the said two shells has a low ability for being wetted by molten metal.

9. A pouring tube as claimed in any one of the preceding claims, in which the inner of the said two shells is formed from a fibrous ceramic material.

10. A pouring tube as claimed in claim 4, in which the homogeneous one-piece pipe member consists of argillaceous graphite, silicon carbide or a refractory foundry concrete.

11. A pouring tube as claimed in any one of claims 5, 6, 7 and 8, in which at least the outer of the said two shells consists of argillaceous graphite, silicon carbide or refractory foundry concrete.

12. A pouring tube as claimed in any one of the preceding claims in which the hole is connected to at least one line which may be selectively vented or pressurised with a gas.

13. A pouring tube as claimed in any one of claims 2, 3, 5 to 9, 11 and 12, in which the inner of the said two shells is cemented at least at its two ends to the outer of the said two shells.

14. A pouring tube as claimed in any one of claims 2, 3, 5 to 9, 11 and 12, in which the inner of the said two shells is jacketed with a layer of material which forms the outer of the said two shells.

15. A pouring tube as claimed in claim 14, in which the outer of the said two shells is lined with a layer of material which forms the inner of the said two shells.

16. A pouring tube as claimed in claim 14 or 15, in which the outer of the said two shells is constructed on the inner of the said two shells.

17. A pouring tube as claimed in any one of claims 1 to 15, in which the inner and outer shells consist of the same material but are of different gas permeabilities.

18. A pouring tube for use in casting metals under gas pressure, substantially as hereinbefore described with reference to and as illustrated in any one of Figure 2 to 6 of the accompanying drawings.

19. A metal casting apparatus including a pouring tube as claimed in any one of the preceding claims.