GB2239201A

GB2239201A - Method and apparatus for producing castings with cavities

Info

Publication number: GB2239201A
Application number: GB8928647A
Authority: GB
Inventors: Todor Iliev Nikiforov; Tencho Koychev Kostov
Original assignee: SO PERIFERNA TECHNIKA
Current assignee: SO PERIFERNA TECHNIKA
Priority date: 1989-12-19
Filing date: 1989-12-19
Publication date: 1991-06-26
Also published as: GB8928647D0; FR2656245A1; DE3941538A1

Abstract

A casting with a cavity is produced from melt which is subject to pressure in a sealed chamber (5) containing a reservoir (6) for melt and a chamber (24) with a casting mould (1). When solidification of melt in the mould has progressed for the required configuration of the casting to be achieved, excess melt is pushed out and back into the reservoir (6) by feeding the or each cavity in the casting directly with a gas with a pressure higher than the pressure over the melt in the reservoir (6). A nozzle (2) in the wall of the mould supplies the gas which is fed from a gas reservoir (9), pressure-reducing valve (8) and conduit including a supply valve (7). Commencement of such supply is initiated by a computer (13) after a time adequate for shell formation. The computer (13) controls the solidification process in the mould using thermocouples (19, 20) to obtain melt and mould temperatures and by regulating mould heating (18) and cooling (15, 16) elements. <IMAGE>

Description

A 9 METHOD AND APPARATUS FOR PRODUCING CASTINGS WITH CAVITIES This

invention refers to a method and an apparatus for use in the foundry industry for producing castings with cavities, and in particular for producing shaped castings.

A method is known for producing hollow items from silicate melts (BG 17065) in which the silicate melt is poured into a prepared collapsable chill mould. At a given moment residual melt is poured out of the mould by inverting the mould. A hollow item is produced from the chilled material with a configuration copying the is forming surfaces of the mould used. The thickness of the wall of the finished item is a function of the time that the melt stays in the casting mould.

A shortcoming of this method is that the turning of the casting mould requires a supplementary energy consumption. Another shortcoming is the prolonged duration of the process since the inversion of the mould has to be effected slowly with a smooth starting and termination due to the presence of big inertia forces and also since the running out of the melt is hampered by the counter movement of air.

An apparatus for casting thin-walled castings with cavities under low pressure is known (FR 2.147.827) in which the melt from the melt reservoir which is disposed in a chamber closed to the atmosphere is fed under a pressure greater than atmospheric pressure through a duct into a pressurised chamber with two conical cavities which are connected with each other and to the said duct. The upper end of the first conical cavity is linked with the casting mould, while the second is connected via a conduit with a valve which has at least four positions. The first position 1# of the valve is connected with a compressed gas source, the second with the gas volume of the chamber enclosing the melt reservoir, the third with the conduit of the second conical cavity of the pressurized chamber and the fourth with the atmosphere.

Both conical cavities of the pressurized chamber have almost equal volumes and are connected by a passage, the cross-section of which is equal to that of the conduit from the reservoir. The volume of the second conical cavity linked to the valve is such that when the casting mould is full the level of the melt in this cavity ought to be beneath a determined level. The upper part of the pressurized chamber at the beginning of the conduit connecting the second conical cavity with the valve has a device for stopping the flow of gas in this cavity when the melt in it has reached a predetermined level.

A disadvantage of this apparatus is that it only allows casting of items only under low pressure and in particular is only suitable for casting thin-walled hollow work-pieces, while at the same time imposing the necessity for a supplementary intermediary chamber under pressure with a valve monitoring the casting phases. Another disadvantage is that the evacuation of the melt from the cavities in the casting is effected by gravity with a counter current influx of air that occupies the volume being freed by the melt. This mode of melt evacuation is of very long duration and thus additionally the cycle of casting is lengthened and the precision of the dimensions of the cavity is reduced. There is also a problem with oxidising of the melt. Also the equipment has a low productivity since the moulding is eliminated after solidification of the melt, which requires considerably more time than the time of casting.

Also-known are a method and an apparatus for 4 k producing castings from metals and alloys by casting with counter- pressure (BG 48717). A drawback of the method is that it is not appropriate for casting shaped cast bodies with cavities with a complicated configuration since it is not possible for the melt to solidify on the upper surface of the mould cavity. Another disadvantage of this method.is that in order to push out the melt from the mould it is necessary to increase the pressure in the chamber in which the casting mould is situated thus causing additional consumption of high pressure gas.

A drawback of the apparatus is that it cannot record the movement of the surface of melt which is running out of the mould under the action of the high pressure gas through the space from the bottom of the cast to the lower end of the casting gate conduit. Thus the danger of escape of this high pressure gas through the melt in the crucible and the spilling of melt along the walls and the cover of the furnace cannot be avoided. Another drawback of the apparatus is that it can not provide for the control of the solidification process producing a blank in the mould. According to one aspect of this invention there is provided a method for producing castings with cavities in which a melt passes through a material conduit under the action of pressure in a sealed chamber between a reservoir for melt and a chamber with a casting mould, and fills up a cavity of a casting mould and begins to solidify, in which the configuration of the casting is formed and the melt is displaced into the said reservoir by supplying a gas under pressure that is higher than that over the melt in the reservoir directly into the interior of the casting.

According to a second aspect of this invention there is provided an apparatus for producing castings with cavities comprising a chamber containing a reservoir for melt connected via a material conduit to a chamber containing a casting mould, the chamber being communicable with a source of gas under a first pressure to drive melt through the conduit thereinto and having a nozzle extending through its wall to a position in the interior thereof through which gas injection at a second pressure higher than the first is to be effected to cause the displacement of melt out of said mould into said reservoir.

A sensor for the melt level may be mounted to the material conduit in the apparatus.

An advantage of the method of this invention is that conditions are created for improving the casting structure due to its thorough building by controllable directed solidification of the melt along with an optimal compensation of the volume deficiency from the liquid phase that fills up the casting cavities. Another advantage is that when the use of single cores is avoided economy of materials, energy, labour for the manufacture of the cores and elimination from the castings can be realised. Furthermore the work of the casting machine operator is facilitated and productivity is increased due to a decrease in the operation of core setting. Also, the production of rejects as a result of breaking or collapsing of sand cores as well as of the escaping of gases is avoided.

Further advantages of the method and apparatus are that they can be based on existing equipment for casting with counter-pressure and that the regulation of the temperature conditions of the mould which controls the solidification of the casting and the forming of cavities therein can be monitored by microcomputer.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made to the accompanying drawing which is a 1 A 1 cross section through a preferred form of apparatus embodying the invention.

The apparatus according to the accompanying drawing comprises a nozzle 2 that is mounted in a casting mould 1 and which communicates at one of its ends with a cavity 3 in a casting 100 Its other end is connected, via a controllable valve 4, with a sealed chamber 5 in which is placed a reservoir 6 for melt.

The nozzle 2 is also linked by means of the controllable valve 7 and pressure redgcing valve 8 to a reservoir 9 for pressurized gas to which is attached a manometer 10. A sensor 12 for melt level which is connected to a microcomputer 13 is mounted on the material conduit 11. Also linked to the microcomputer 13 are controllable valves 14 which are connected to mobile metal cores 15 and the cooling elements 16 via conduits for the cooling liquid. Also connected with the computer is a commutator 17 which controls an electric heating element 18 inserted in the casting mould 1 and thermocouples 19 and 20. The reservoir 9 for pressurized gas is connected through the valves 21, 22, and 23 with both sealed chambers of the apparatus, i.e. chamber 5 and chamber 24 in which the mould is located while the latter are linked through valve 25.

Escape valve 26 is attached to chamber 24.

The operation of the apparatus is as follows: with valves 21, 22, 23 and 25 open and valve 7 closed the filling of both sealed chambers 5 and 24 with pressurized gas from reservoir 9 begins. When the preset operational pressure is reached in both chambers the valves 22. 23 and 25 are closed. Now valve 26 is opened and the gas from chamber 24 escapes into the atmosphere and the pressure therein begins to diminish until a preset value is reached, after which valve 26 is closed. Under the action of the higher pressure existing in chamber 5 the melt from reservoir 6 fills the casting mould 2 completely through the material conduit 11. According to a preliminary preset programme and based upon the information received from the thermocouple 19 which records the temperature of the melt in reservoir 6 as well as upon information from a system of thermocouples 20 which record the temperature in the separate zones of the casting mould, the microcomputer 13 switches the feeding of cooling liquid to the mobile metal cores 15 and to the coolers 16 on or off via the valves 14. It also switches the electric heating elements 18 on or off via the commutator 17. Thus the microcomputer 13 controls the temperature conditions in the casting mould and hence the solidification of melt, so that after the elapse of a predetermined time period the melt takes up the configuration of the casting. Thereafter the microcomputer 13 transmits a signal for opening valve 7 causing gas with a pressure preset by the pressure reducing valve 8 and higher than that in chamber 5, to enter the casting cavity 3 via the nozzle 2. Under the effect of this higher pressure gas the melt is driven away from the casting cavity 3. When the surface of the melt reaches the level sensor 12 the latter transmits a signal to the microcomputer 13 which releases a command for closing valve 7 so that the flow of the high pressure gas is discontinued. A command for opening the second controllable valve 4 is also given so that the pressure over the surface of the melt in the material conduit is equalized with the pressure in chamber 5 and thus the melt continues to return to the reservoir 6 under only the effect of its own weight. Thus the spilling of melt is avoided.

I

Claims

1. A method for producing castings with cavities in which a melt passes through a material conduit under the action of pressure in a sealed chamber between a reservoir for melt and a chamber with a casting mould, and fills up a cavity of a casting mould and begins to solidify, in which the configuration of the casting is formed.and the melt is displaced into the said reservoir by supplying a gas under a pressure that is higher than that over the melt in the reservoir directly into the interior of the casting.

2. A method as claimed in claim 1, wherein supply of said gas under pressure is continued until melt in the reservoir reaches a predetermined monitored level in a conduit connecting the reservoir with the casting mould.

3. A method as claimed in claim 1 or 2 which is utilised in the production of silicate castings.

4. A method for producing castings with cavities substantially as hereinbefore described with reference to the accompanying drawing. 25

5. An apparatus for producing castings with cavities comprising a chamber containing a reservoir for melt connected via a material conduit to a chamber containing a casting mould, the chamber being communicable with a source of gas under a first pressure to drive melt through the conduit thereinto and having a nozzle extending through its wall to a position in the interior thereof through which gas injection at a second pressure higher than the first is to be effected to cause the displacement of melt out of said mould into said reservoir.

6. An apparatus as claimed in claim 5.

additionally comprising means for monitoring the level of melt in said material conduit.

7. An apparatus for producing castings with cavities, substantially as hereinbefore described with reference to, and shown in, the accompanying drawing.

8. A casting, whereinever produced by the method claimed in any use of claims 1 to 4.

PubUshed 1991 at 7lie Patent Office. State House. 66171 High Holbom. London WC3R47P. Further copies may be obtained from Sales B. Unit 6, Nine Mfle Point Cwmfelinfach. Cross Keys. Newport NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.