GB1601902A

GB1601902A - Low pressure casting installation

Info

Publication number: GB1601902A
Application number: GB9774/78A
Authority: GB
Original assignee: Pont a Mousson SA
Current assignee: Pont a Mousson SA
Priority date: 1977-03-21
Filing date: 1978-03-13
Publication date: 1981-11-04
Also published as: DK126578A; AU3437078A; CH618903A5; EG17409A; FR2384568A1; AU512332B2; IT7867616A0; DK164395B; BR7801700A; DK164395C; IT1107172B; ES468185A1; CA1102995A; FR2384568B1; BE865086A

Description

(54) LOW PRESSURE CASTING INSTALLATION (71) We, PoNT-A-MoUssoN S.A., a Societe Anonyme organised and existing under the laws of France, of 91 Avenue de la Liberation, 54000 Nancy, France, 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: The present invention relates to a casting installation for the bottom casting of liquid metal at low pressure, the installation comprising a mould cavity, a vertical supply pipe, and at least one casting inlet connecting the pipe to the mould cavity.

The invention relates in particular, but not exclusively, to the casting of lamellar or spheroidal graphite cast iron.

It is known that casting at low pressure is frequently carried out in sand moulds, in particular in order to obtain certain metallic structures in the castings. This is the case for example when one wishes to produce rough castings of spheroidal graphite cast iron, which contain no hydrocarbons, in the rough cast state, without requiring subsequent heat treatment.

This result is due essentially to the re fractory nature of the sand forming a thermal barrier which prevents the phenomenon of chilling of the cast metal.

One also benefits from the permeability of the sand to gas.

Thus, moulds comprising walls of sand prevent foundry defects and reduce wastage.

The method of casting at low pressure is also known, according to which the mould is filled under pressure with metal supplied via a vertical pipe, the pressure is maintained until the metal in the inlet has solidified, then the pressure is released. The inlet is designed so that the metal in it solidfies after a period of time which is slightly greater than the time necessary for supplying the mould cavity with an adequate quantity of molten metal in order to obtain a sound casting. The cross-section of the inlet is much less than that of the pipe, such that in practice all the metal contained in the pipe re-descends into the casting ladle when the pressure is released.

However, the fact that this known method uses conventional sand moulds, which are not reinforced, introduces drawbacks: owing to the fact that the filling pressure is maintained for a prolonged period of time, the moulds must have relatively high mechanical strength. It is therefore necessary to use sand having a higher proportion of binding agent and/or moulds which are thicker than in the case of casting by simple gravity.

This increases the cost price of the castings, since on the one hand, the moulds, which cannot be re-used, are more expensive to produce and on the other hand, cooling of the castings, is too slow, which considerably reduces the production rate. The time required for the solidification of metal in the inlet also reduces the production rate.

It is an object of the present invention to remedy these drawbacks.

According to the present invention, there is provided a casting installation for the bottom casting of liquid metal at low pressure, comprising a mould cavity, a vertical supply pipe, and at least one inlet connecting the pipe to the mould cavity, the cross-section of the or each casting inlet being smaller than that of the pipe, characterised in that the vertical supply pipe is connected to a mould constituted by a two part metal shell surrounding and supporting agglomerated sand which is shaped to define the mould cavity, a cover of agglomerated sand being located inside the shell over the upper end of the supply pipe, and the or each inlet extending through the cover, the cover preventing liquid metal from flowing out of the upper end of the supply pipe except through the or each inlet.

The installation of the invention provides for rapid cooling of the casting. The mould has high mechanical strength, and a sound casting structure is ensured.

The metal shell gives the mould the necessary mechanical strength and rigidity and the relatively thin agglomerated sand defining the mould cavity may easily be designed to give a relatively rapid, predetermined cooling speed to the cast metal.

The inlet may be formed from agglomerated sand, or may have metal walls in order to increase the cooling of the metal at this point, thus eliminating the thermal barrier constituted by the sand and making it possible to release the pressure more quickly at the end of casting, which increases the production rate.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic sectional view of an installation for casting at low pressure according to the invention; Figure 2 is a partial detailed view in section of a further embodiment according to the invention; Figure 3 is a diagrammatic sectional view of another embodiment according to the invention, comprising cores for moulding two parts at the same time; and Figure 4 is a sectional view on line P4 of figure 3.

The casting installation of figure 1 comprises a ladle 1 for casting under pressure, of known type, containing liquid spheroidal or lamellar graphite cast iron 2. This ladle is provided with a removable graphite cast iron 2. This ladle is provided with a removable cover 3, fixed in a sealed manner.

A vertical refractory casting tube 4 passes through the cover 3 and its lower part terminates in the vicinity of the bottom of the ladle 1. A conduit 5 for supplying a pressurized gas, for example compressed air, controlled by a valve 6, opens into the ladle 1 through the cover 3, above the maximum level of liquid cast iron 2.

The ladle 1 is placed in a frame 7 having an upper horizontal table 8 able to serve as a support for a mould 9. As known, the top 10 of the refractory casting tube 4 projects slightly above the table 8 of the frame 7.

The mould 9 is in two parts, a lower part 11 and upper part 12, separated at a horizontal median interface 13. It is constituted by a metal shell 14 of outer parallelepipedal shape and a layer 15 of agglomerated sand adhering to the inner wall of this shell. The layer 15 of agglomerated sand defines the mould cavity.

The inner wall of the shell 14 defines a vertical blind cylinder 16 which open at the bottom, and a cavity 17 similar to but larger than the mould cavity. An approximately horizontal channel 18, whose section is less than that of the cylinder 16, connects this cylinder to the cavity 17, on either side of the interface 13.

As a variation, the channel 18 could be inclined and/or located above or below the interface 13.

The wall 16-17-18 is not machined, but on the contrary rough. A series of vents 19 connects this wall to the respectively lower and upper outer sides of each half-shell.

The layer 15 is constituted by agglomerated sand, the sand being mixed for example with a polyisocyanate resin hardened by a chemical reaction carried out cold with a gas containing an amine, by the so-called "cold box" method. This layer 15 of virtually uniform depth, covers the entire wall 16-17-18, the bottom end of the cylinder 16 remaining open. It thus defines a supply pipe 20, connected by an inlet 21 to the mould cavity 22, these three parts having walls consisting of agglomerated sand.

To produce the mould 9, the two halfshells which are themselves rough cast, are placed in a machine for blowing or "drawing" cores, of any suitable known type. The sand/resin mixture is injected through the vents 19, then a cold hardening gas, and then compressed air are passed into the mass moulded in this way, through the same vents 19. The use of a shell which has not been machined, facilitates adhesion of the layer of sand and is very economical. Using this method, it is possible to obtain a thin layer having a thickness, of the order of lOmin, very quickly. It has been found that this method also makes it possible to speed up stripping of the casting and thus to increase the production rate and the rate of re-cycling the shells.

In addition, since the operation is carried out cold, any thermal deformation of the shell is prevented.

The operation of the installation is as follows: A mould 9 is put in position on the table 8 of the frame 7 in order to connect the inlet of the pipe 20 to the upper end 10 of the casting tube 4. The junction may be sealed by any known means, for example by means of a refractory pasty coating as described in French Patent 2 295 808.

The weight 23 is placed on the mould to prevent the upper part 12 of this mould from rising when the metal is cast. For example, the weight 23 may be a plate connected to the piston of a pressing ram.

Air at a given pressure greater than atmospheric pressure is introduced through the pipe 5 above the level of the liquid cast iron 2. Owing to the fact that the mould cavity is empty, the liquid cast iron rises in the tube 4, the pipe 20, passes through the inlet 21 and fills the mould cavity 22. The gases liberated as the cast iron rises escape easily through the pores of the layer of sand 15 and through the vents 19, which are thus used as air holes. This contributes to obtaining a sound casting.

The air pressure necessary for causing the cast iron to rise into the mould cavity is maintained in the pipe 5 for the period of time necessary for filling the cavity 22 of the mould and for solidification of the cast iron located in the casting inlet 21.

The air pressure in the pipe 5 is then released, such that virtually all the liquid cast iron contained in the pipe 20 and the casting tube 4 drops quickly into the ladle, at the most leaving solidified residue on he walls of the pipe 16 and in the inlet 21.

The weight 23 is then removed and the mould 9 is removed from the installation, since cooling and stripping of the casting will be continued outside the installation.

Owing to this installation and in particular owing to the mould 9 having a layer of sand 15 reinforced by a shell 14, the mould 9 is very rigid. In fact, the shell 14 gives the mould 9 increased mechanical strength, thus preventing any danger of cracking the sand.

It is thus possible to cast parts of more complicated shape and to produce in the foundry casting details sometimes of small dimensions.

This great rigidity of the composite mould 9 is also advantageous for dimensional accuracy of the casting, for producing a sound casting and for reducing wastage. In fact, expansion of the sand under the pressure of the cast iron and thermal expansion is limited by the shell 14 fulfilling the function of a rigid corset, which explains the accuracy of the dimensions of the casting. A composite mould of this type also benefits from the porosity of the sand and its refractory nature making it possible to eliminate occlusions of gas and the effect of surface hardening, which explains the soundness of the casting.

Furthermore, the technique of casting under pressure for which this rigidity of the composite mould is particularly well-suited makes it possible either to cast parts from metals having a high melting point at a temperature lower than when casting by gravity (for example at approximately 1320"C instead of approximately 1420"C for the cast iron), which speeds up cooling and consequently increases the production rate, or to cast thinner parts than when casting by gravity, at the same temperature (for example approximately 1420"C).

Furthermore, the consumption of agglomerated sand is much less than in the case of prior art moulds made completely of agglomerated sand and this results in an appreciable saving in sand and time, as shown by the following example: Example: In order to cast a manhole for a road, one uses a layer of sand 15 having a depth of the order of 10mm, which for the weight of the rough cast part of 70kg, limits the consumption of sand to 60 kg instead of 100kg for a mould consisting entirely of agglomerated sand. For a rate of binding agent of 0-06% by weight of ASHLAND resin sand number 606 + 0-6% by weight ASHLAND resin sand No. 306, the numerical data are: - filling pressure of the cast iron: 0-8 bars; - time for the increase in pressure: 18 secs; time for filling the composite mould: 2 5 secs; - stripping of the casting: 20 to 30 minutes after the beginning of blowing of the mould, instead of 11 hours in the case of conventional moulding.

Thus, with respect to the use of solid moulds, it is possible to reduce all the time occurring in a cycle for low pressure moulding: the filling time, since the presence of the metal reinforcement 14 makes the sand mould sufficiently rigid and strong to withstand a rapid intake of cast iron; - the time during which the pressure is maintained, since, owing to the slight depth of the layer of sand, the metal cools relatively quickly and consequently a supply sufficient for compensating for shrinkage as well as solidification of the inlet, which is slightly later by construction, are obtained quickly.

The two above-mentioned periods of time relate to the presence of the mould on the table 8 and shortening of the latter makes it possible to speed up the casting rate.

But in addition, the other times relating to the overall installation are also reduced: - the cooling time before stripping, owing to the thinners of the sand; - the time for producing a mould from two half shells owing to the small volume of sand used.

Consequently, for mass production, it is possible to use only a small number of metal shells which are re-cycled quickly, the arrangement constituting a "modular" installation of relatively low bulk. The advantage consists of great flexibility of the equipment, the number of "modules" being able to be modified easily as required.

According to the variation of figure 2, with the aim of increasing the production rate still further, a casting inlet lined with metal 21a is used instead of a sand lined inlet. Metal "inserts" 24, for example of cast iron, copper or steel, are fixed to the shell 14, at the location of the casting inlet, for example eliminating part of the layer of sand at this point. Cooling of the casting inlet 21a is thus accelerated with respect to cooling of the cast iron contained in the mould cavity 22 and the cast iron is trapped more quickly therein, which for a given cross section of the inlet 21a, makes it possible to release the pressure in the pipe 5 sooner, so that the cast iron drops back in the pipe 21 and tube 4, without any danger of suction of the cast iron contained in the cavity 22.

It is thus possible for the solidification time of the inlet to approach the period of time during which the cavity is supplied with metal, leading reliably to a sound casting. It is thus possible for example to reduce the period of time during which the filling pressure is maintained, for the same casting, from approximately 40 seconds in the case of the sand lined inlet 21 to approximately 15 seconds in the case of the metal lined inlet 21a.

As a variation, instead of using inserts 24, the channel 18 of the shell may itself constitute the metal inlet 21a. It is also possible to provide graphite inserts 24.

Naturally, with a metal inlet 21a, the structure of the solidified cast iron in the inlet is hardened, but this does not impair the quality of the casting in the cavity 22.

The variation of the mould of figures 3 and 4 advantageously makes it possible to cast two parts simultaneously, without producing a burr, this without these parts being attached to each other at the time of stripping.

In this example, a frame 25 of a manhole for a road and its cover 26 are cast simultaneously.

One uses a mould 9a in two parts 1 la and 12a, which is essentially similar to that of figure 1.

The frame 25 is cast in the lower part 1 la and the cover 26 in the upper part 12a.

An inner mass of sand 27, forming a core, produces the inner shape of the frame 25 and the shape of the lower side of the cover 26. The outer shape of the frame 25 as well as that of the other sides of the cover 26 are produced by the sand layer 15.

The supply pipe 20 is provided at its upper end with a radial protuberance 28 forming a supply basin at which point two horizontal inlets 29 and 30 originate, one for the frame 25, the other for the cover 26. The inlets 29 and 30 are separated by a core 31 of agglomerated sand in the shape of a plate and do not meet. The edge of this plate opposite the pipe 20 rests on the mass of sand 27, whereas its side are received in shoulders 32 of the lower half mould 1 la and sandwiched between these shoulders and the upper half mould 12a.

It should be noted that it is not absolutely necessary for the inlets 29 and 30 to be horizontal, nor parallel: they may be slightly inclined, convergent, divergent or in the form of a siphon.

Figure 3 shows the level N of the liquid cast iron 2 at the time when the air pressure in the pipe 5 has been released. The cast iron falls back in the pipe 20 at the most leaving only traces in the basin 28 and in the pipe 20 itself. Small quantities of solidified cast iron remain in the inlets 29 and 30, which are separated from each other. The castings 25 (frame) and 26 (cover) may thus be stripped independently, without any connection produced by casting.

This advantageously results in an improvement in the ratio of the weight of casting/ weight of metal solidified in the mould. Time is also saved during casting, since two parts are cast at the same time and after casting, since it is no longer necessary to detach the two parts one from the other and energy is also saved due to the presence of a common supply pipe 20.

On condition of retaining the core 31, it is also possible to replace all or part of the sand walls of the inlets 29 and 30 by metal inserts or by the wall of the shell 14a itself.

It should also be noted that in the case of static casting by simple gravity, it would be possible to cast the frame and cover of a manhole for a road in the same mould, but it would not be possible to obtain castings which are not attached by casting connections.

In fact, the latter would remain full of cast iron, since, contrary to the technique of moulding at low pressure, cast iron is not removed from the supply pipes after casting.

Naturally, the invention may also be applied to the casting of aluminium or other metals.

WHAT WE CLAIM IS:- 1. A casting installation for the bottom casting of liquid metal at low pressure, comprising a mould cavity, a vertical supply pipe, and at least one inlet connecting the pipe to the mould cavity, the cross-section of the or each casting inlet being smaller than that of the pipe, characterised in that the vertical supply pipe is connected to a mould constituted by a two part metal shell surrounding and supporting agglomerated sand which is shaped to define the mould cavity, a cover of agglomerated sand being located inside the shell over the upper end of the supply pipe, and the or each inlet extending through the cover, the cover preventing liquid metal from flowing out of the upper end of the supply pipe except through the or each inlet.

2. A casting installation according to claim 1, wherein the inlet is constituted by agglomerated sand surrounded by the shell.

3. A casting installation according to claim 1, wherein the walls of the inlet are metallic.

4. A casting installation according to claim 3, wherein the walls of the inlet are constituted by the shell.

5. A casting installation according to claim 3, wherein the walls of the inlet are constituted by at least one metal part fixed in a passage in the shell.

6. A casting installation according to claim 1, wherein two cores are received in the shell to define two separate mould cavities, each mould cavity being connected to the upper part of the pipe by a respective one of two parallel inlets, each inlet extending from the cover of agglomerated sand to its associated mould cavity without meeting the other inlet.

7. A casting installation according to claim 6, characterised in that the cover

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. from approximately 40 seconds in the case of the sand lined inlet 21 to approximately 15 seconds in the case of the metal lined inlet 21a. As a variation, instead of using inserts 24, the channel 18 of the shell may itself constitute the metal inlet 21a. It is also possible to provide graphite inserts 24. Naturally, with a metal inlet 21a, the structure of the solidified cast iron in the inlet is hardened, but this does not impair the quality of the casting in the cavity 22. The variation of the mould of figures 3 and 4 advantageously makes it possible to cast two parts simultaneously, without producing a burr, this without these parts being attached to each other at the time of stripping. In this example, a frame 25 of a manhole for a road and its cover 26 are cast simultaneously. One uses a mould 9a in two parts 1 la and 12a, which is essentially similar to that of figure 1. The frame 25 is cast in the lower part 1 la and the cover 26 in the upper part 12a. An inner mass of sand 27, forming a core, produces the inner shape of the frame 25 and the shape of the lower side of the cover 26. The outer shape of the frame 25 as well as that of the other sides of the cover 26 are produced by the sand layer 15. The supply pipe 20 is provided at its upper end with a radial protuberance 28 forming a supply basin at which point two horizontal inlets 29 and 30 originate, one for the frame 25, the other for the cover 26. The inlets 29 and 30 are separated by a core 31 of agglomerated sand in the shape of a plate and do not meet. The edge of this plate opposite the pipe 20 rests on the mass of sand 27, whereas its side are received in shoulders 32 of the lower half mould 1 la and sandwiched between these shoulders and the upper half mould 12a. It should be noted that it is not absolutely necessary for the inlets 29 and 30 to be horizontal, nor parallel: they may be slightly inclined, convergent, divergent or in the form of a siphon. Figure 3 shows the level N of the liquid cast iron 2 at the time when the air pressure in the pipe 5 has been released. The cast iron falls back in the pipe 20 at the most leaving only traces in the basin 28 and in the pipe 20 itself. Small quantities of solidified cast iron remain in the inlets 29 and 30, which are separated from each other. The castings 25 (frame) and 26 (cover) may thus be stripped independently, without any connection produced by casting. This advantageously results in an improvement in the ratio of the weight of casting/ weight of metal solidified in the mould. Time is also saved during casting, since two parts are cast at the same time and after casting, since it is no longer necessary to detach the two parts one from the other and energy is also saved due to the presence of a common supply pipe 20. On condition of retaining the core 31, it is also possible to replace all or part of the sand walls of the inlets 29 and 30 by metal inserts or by the wall of the shell 14a itself. It should also be noted that in the case of static casting by simple gravity, it would be possible to cast the frame and cover of a manhole for a road in the same mould, but it would not be possible to obtain castings which are not attached by casting connections. In fact, the latter would remain full of cast iron, since, contrary to the technique of moulding at low pressure, cast iron is not removed from the supply pipes after casting. Naturally, the invention may also be applied to the casting of aluminium or other metals. WHAT WE CLAIM IS:-

1. A casting installation for the bottom casting of liquid metal at low pressure, comprising a mould cavity, a vertical supply pipe, and at least one inlet connecting the pipe to the mould cavity, the cross-section of the or each casting inlet being smaller than that of the pipe, characterised in that the vertical supply pipe is connected to a mould constituted by a two part metal shell surrounding and supporting agglomerated sand which is shaped to define the mould cavity, a cover of agglomerated sand being located inside the shell over the upper end of the supply pipe, and the or each inlet extending through the cover, the cover preventing liquid metal from flowing out of the upper end of the supply pipe except through the or each inlet.

7. A casting installation according to claim 6, characterised in that the cover

defines a radially extending cavity with which the two inlets communicate.

8. A casting installation for the bottom casting of liquid metal at low pressure substantially as hereinbefore described with reference to Fig. 1, Fig. 2 or Figs. 3 and 4 of the accompanying drawings.