Apparatus For Molding Thin Layers

Abstract

The invention is applied to the molding of articles having thin walls and in particular to the molding of radiator elements, caps, cases, frames, pipe members, cylinder heads, in which the molding apparatus comprises a mold which is open at its lower end, a compression chamber having two cavities connected at their upper portion respectively to the opening of the mold and to a source of compressed gas, and at their lower portion to a delivery conduit and a furnace into the bath of molten material in which the delivery conduit dips and which can be put under gas pressure by a pipe member.

Description

The present invention relates to the field of casting metals, alloys and plastics and more particularly to apparatus for molding in thin layers.

It is known to mold an article having thin walls by filling a metal mold with a metal, alloy or a synthetic resin, cooling the layer which is in contact with the wall of the mold until solidification occurs, then removing the excess of liquid material. This results in articles having thin walls of uniform or variable thickness, for example hollow articles, without using a core.

The method is performed in an artisan manner, filling and emptying being effected manually.

It is an object of this invention to provide an apparatus for molding thin layers, which permits precise control of the heat exchange between a liquid material and the walls of a mold, and which lends itself to automation.

The apparatus according to the invention comprises a mold which is open at its lower end and which is provided at its upper part with a device for the discharge of gas and, in its walls, at least one cooling means, and a closed low-pressure casting furnace in which the crucible contains a fusion bath and in which the internal volume above the crucible is occupied by a gas under pressure, said furnace being placed below the lower opening of the mold. Between the mold and the furnace is a compression chamber comprising two cavities which are connected at their upper ends respectively to the lower opening of the mold and to a pipe member which goes laterally out of the chamber, while, at their lower ends, the cavities are connected together and to a delivery conduit which extends into the furnace and with the lower end dipping into the bath. A valve comprises at least four pipe members of which a first is connected to a source of compressed gas, a second is connected to the gas volume of the furnace, a third is connected to the lateral pipe member issuing from the compression chamber, and finally a fourth is in communication with the atmosphere, and at least one movable member which is capable, during a first machine stopped phase, of ensuring closure of all the pipe members; then, during a second phase of filling the mold by the liquid material in the furnace, of connecting the first pipe member to the second; then, during a third phase of solidification of the layer against the wall of the mold and discharge of the excess of liquid material from the mold to the furnace, of connecting the second pipe member to the third pipe member; and finally, during a fourth phase, of bringing to atmospheric pressure the assembly comprising the mold, the compression chamber and the furnace, of connecting together the second, third and fourth pipe members.

The above defined invention is described by means of examples illustrated by the accompanying drawings.

FIGS. 1 and 2 are diagrammatic views of the assembly comprising the furnace, the compression chamber and the mold. In the construction shown in FIG. 1, injection is effected obliquely, whereas in the construction shown in FIG. 2 injection is effected vertically.

FIG. 3 is a diagrammatic view of the entire apparatus.

FIG. 4 is a sectional view showing the valve in greater detail.

FIG. 5 is a sectional elevational view showing the compression chamber in cross-section.

FIGS. 6 to 9 are sectional views diagrammatically showing the apparatus in the positions respectively corresponding to the four phases.

FIG. 10 is a top plan view of a radiator element fabricated with the apparatus of this invention.

FIG. 11 is a cross-sectional view taken along the line XI--XI of FIG. 10.

FIG. 12 is a cross-sectional view of the upper half of the mold and the molded element in place.

The apparatus for molding thin layers comprises a furnace 1, a compression chamber 2 and a mold 3, which are placed one above the other in the order specified, and a valve 4.

The casting furnace, which is of the low-pressure type, comprises a crucible 12 in a hermetically closed chamber 11 which is capable of being put under pressure by means of a gas input pipe member 13. The crucible contains the material to be molded, in the form of a bath 14 of molten material.

The compression chamber 2 comprises a body 21 within which are provided two cavities 22 and 23. The cavity 22 has an upper opening 24 communicating with an opening 34 in the lower part of the mold 3. In its upper portion, the cavity 23 is connected to a pipe member 25 which extends laterally out of the body 21. In their lower portions, the two cavities 22 and 23 are connected together and lead to a delivery conduit 26, the lower end of which is immersed in the bath 14 contained in the crucible 12. The conduit 26 can be set obliquely, as in FIG. 1, or vertically, as in FIG. 2.

The chamber 2 preferably is formed of cast iron of current quality, used for the manufacture of metal molds for gravity casting. It is fluid-tight and coated internally with a white, insulating and refractory coating of a known type.

In the construction, as illustrated in FIG. 5, it is made in two parts: the body 211 proper, and a base portion 212 which carries the delivery conduit 26. The upper body portion 211 terminates at its upper part in a thermal joint 213: this joint, and also the joint which connects the two parts of the chamber, is machined to permit a plastic joint made of asbestos of very small thickness, to be set in position, in order more easily to ensure sealing and to give an effective thermal joint. Heating elements 215, for example gas burners or electrical resistances, are disposed either on the outside of the body or in recesses 214 provided for that purpose, in order to keep the assembly at a temperature which is slightly higher than that of the liquid material used to mold the article.

The two cavities 22 and 23 in the chamber 2 can be of substantially equal volumes. The aperture, by way of which they are in communication in their lower part, can be of a cross-section equal to the cross-section of the delivery conduit 26. In its upper portion, the cavity 23 is provided with a discharge pipe member 25 which can be closed by the valve 4, it being necessary for the level of liquid material to remain below the point of connection of the pipe member 25. This point is monitored by a safety device for stopping injection, for example in the case of a leak at the valve 4. When the material to be molded is an electrical conductor (for example aluminum and alloys thereof), the safety device can comprise two conductors 27 which the material brings into electrical contact, in the event of an excessive rise in level, thus causing closure of the valve 4, by way of an electrically operated valve (not shown).

The shape of the cavity 25 is preferably conical, so that the volume of gas in its "full mold" position is such that the surface of the liquid is a short distance, such as substantially 2 centimeters, below the electrical contact, which is itself located a short distance, such as about 2 centimeters, below the pipe member 25. This residual volume is determined by a simple application of the law of Mariotte, from the height of maximum filling of the mold and the specific weight of the liquid material. This calculation determines the volume of the cavity 23 corresponding to the largest article which can be molded with the machine in question, and it obviously remains applicable for smaller dimensions.

The mold 3 comprises a body 31 of which the inward surface defines an internal volume 33. In its lower portion, it is formed with an opening 34 connected to the upper opening 24 of the cavity 22 of the compression chamber 2, while in its upper portion, it is provided with an air flow passage 35.

This mold preferably is formed of separate portions which are referred to as shells, which are adjusted along preferential planes, in most cases horizontal and vertical, as determined by a study of heat exchange phenomena. Some of these portions comprise autonomous circuits 36 for cooling by circulation of a fluid. They are assembled by means of thermal insulating joints or air spaces permitting orientation of the temperature gradient of the molten metal filling the mold at the moment of cooling and the beginning of solidification, by the action of the cooling circuit in each respective shell. This produces the desired pellicular layer, with thicknesses which are of greater or lesser dimension, depending on the intensity of cooling.

The mold can comprise the components known in the molding art: plugs, dismantlable members, sliders, slideways, and ejectors. Whenever possible, the discharge aperture is of rounded shape, which permits the excess of metal easily to be cut off and enables the article rapidly to be closed by a disc which is secured by adhesive or welding, for example by friction-turning, or by any other process.

The various members and components of the mold can be provided with actuating means, such as jacks which enable them to be separated, when removing the article from the mold, and returned to their operative position, at the moment of molding.

The air flow passages 35 are provided with a filter for the discharge of air from the mold. This filter, which is known per se, permits the gas to pass, but prevents the passage of the liquid material to be molded by solidification thereof. For example, use can be made of dehydrated alumina in compressed powder form.

The valve 4 comprises a valve body 48 having at least four pipe members. In the embodiment illustrated, it has five such members, in the order 41 to 45, in which the second and fourth pipe members are connected together and play the same part. They are separated only for reasons of ease of construction. The movable valve member is a rotor 46 provided with a cut-out portion 47 which permits some adjacent pipe members to be brought into communication with each other, as will be described in detail hereinafter. The first pipe member 41 is connected to a source of compressed gas, for example air or even nitrogen or any other neutral gas. The second pipe member 42 and the fourth pipe member 44 are connected to the pipe member 13 for the feed of compressed gas into the chamber of the furnace 3. The third pipe member 43 is connected to the pipe member 25 of the cavity 23 of the compression chamber 2. Finally, the fifth pipe member 45 is connected to the ambient atmosphere.

The phases which comprise a casting cycle will now be described.

In a first phase, referred to as machine stopped, all the pipe members of the valve 4 are closed. The mold 33, the cavities 22 and 23 of the compression chamber and the delivery conduit 26 are empty and are at atmospheric pressure (FIG. 6). The mold can therefore be opened for the operations of surface preparation, molding and removal from the mold.

In a second phase, referred to as mold filling, the mold is closed, the pipe members 41 and 42 of the valve 4 are in communication, while the other pipe members remain closed (FIG. 7). Compressed gas passes into the low-pressure furnace 1 and the liquid material rises in the delivery conduit 26, then into the cavities 22 and 23 of the compression chamber, and finally into the mold (FIG. 7). The air contained in the mold is discharged through the air flow passages 35 which are then closed by the solidified metal. In the cavity 23, which is closed by the closed pipe member 43, the liquid alloy compresses the gas, and the safety device 27 prevents any mishap by causing stoppage of injection in the case of leakage of the valve 4. A manometer can be provided, as shown in FIG. 5, in order to check for any slight leaks.

In a third phase, referred to as solidification of the layer adjacent to the surface of the mold and discharge of the excess of liquid magerial in the mold to the furnace, the pressure is first maintained for the period necessary to form the crust which is solidified against the walls 32 of the mold 3. The walls 32 of the mold 3 can be cooled by circulating a cooling fluid, as shown in FIG. 3. As soon as the pellicular layer 30 has reached the required thickness, the valve 4 is moved into the position shown in FIG. 8; the pipe members 42 and 43 are brought into communication with each other, while the other pipe members remain closed. The pressures are equalized, as between the furnace 1 and the cavity 23, gas escapes through the cavity 23 into the mold and permits the liquid material contained in the mold to be returned to the furnace. At that time, the pressure of the gas in the installation is different from the ambient atmospheric pressure.

In a fourth and last phase, referred to as putting the assembly under atmospheric pressure, the valve is moved into the position shown in FIG. 9, whereby the pipe members 43, 44 and 45 are brought into communication with each other, while the pipe members 41 and 42 are closed. The interior of the furnace 1 and the cavity 23 are brought into communication with the ambient air, to which the pipe member 45 is open. The mold is then opened, the article 30 is removed and the mold is reclosed.

Another production cycle can begin.

All the operations described hereinbefore, including opening and closing the mold, and the movements of all the components, plugs, dismantlable members, slideways, ejectors, etc. of the mold, can be made automatic in accordance with a predetermined program, so that no human intervention is required in manufacture of the article.

It is recommended that the materials used should have a short solidification period (eutectic or weakly alloyed alloys) if a pleasing appearance is desired for the internal surface of the article.

The above described apparatus can be used for the production of any article having thin walls. The following can be mentioned by way of example: radiator elements, covers, cases, frames,mechanical parts such as pipe members, or cylinder heads, for example for heat engines.

Described hereinafter is the production of a domestic radiator element 6 of aluminum alloy, in which the walls 66 define a central passage 61 and two lateral passages 62 and 63 (FIGS. 10 and 11). At their upper and lower ends, the three passages are in communication by way of an upper passage 64 and a lower passage 65 respectively, and can be brought into communication with the passages of adjacent elements by means of four pipe members, comprising two upper members 641 and 642 and two lower pipe members 651 and 652, which are positioned in the central region of the corresponding passage 64 and 65. The element is molded with the lower end 655 open, but with the pipe members 641, 642, 651 and 652 closed.

The upper part of the mold is shown in FIG. 12. The shell portions of the mold touching parts of the radiator element, the walls of which are of minimal thickness, are not provided with cooling means, while the shell portions touching parts of the element in which the walls are of greater thickness, are provided with cooling means. Thus, the shell portions 3111, 3112, 3121, 3122, 3131 and 3132 which respectively touch the thin walls 6611, 6612, 6621, 6622, 6631 and 6632 do not comprise any cooling system. On the other hand, the shell por-tions 3141, 3142, 3151 and 3152 which respectively touch the thick walls 6641, 6642, 6651 and 6652 comprise cooling systems 3611, 3612, 3621 and 3622. The lower part of the mold is identical, being replaced by the outflow aperture of circular cross-section.

Each shell portion is movable separately by means of a hydraulic or pneumatic jack.

After casting with the apparatus and in accordance with the method of this invention, as described hereinbefore, it is only necessary to cut of saw off the pipe members 641, 642, 651 and 652 along the lines 600 shown in FIG. 11, and to close the casting opening 653 by a closure member which is welded or crimped into place.

This method therefore produces thin walls which are incapable of being achieved with another method, and also maximum structural delicacy, without any casting defect such as shrinkage holes, blow holes or the like, and with, at most, very small shrinkage cracks.

It will be understood that changes may be made in the details of construction and operation without departing from the spirit of the invention, especially as defined in the following claims.

Claims

I claim:

1. Apparatus for molding thin layers, which permits a precise control of the heat exchange between a liquid material and the walls of a mold, and which lends itself to automation, the apparatus comprising a mold which is open at its lower end and which is provided in its upper portion with a device for the discharge of gas, and at least one cooling means within its walls, a closed low-pressure casting furnace and a crucible therein for containing a fusion bath, and in which the internal volume above the crucible is adapted to be occupied by a gas under pressure, said furnace being placed below the lower opening of the mold, characterized by a compression chamber positioned between the mold and the furnace and comprising two cavities and connected at their upper ends respectively to the lower opening of the mold and a pipe member which extends laterally out of the chamber, the lower ends of the cavities being connected together, a delivery conduit which connects with the cavities and extends into the furnace end of which the lower end dips into the bath, and further characterized by a valve comprising at least four pipe members of which a first is connected to a source of compressed gas, a second is connected to the gas volume of the furnace, a third is connected to the lateral pipe member issuing from the compression chamber, and finally a fourth is in communication with the atmosphere, and at least one movable member which, during a first machine stopped phase, closes all the pipe members, during a second phase of filling the mold with the liquid material from the furnace connects the first pipe member to the second, then, during a third phase of solidification of the layer against the wall of the mold and discharge of the excess of liquid material from the mold to the furnace, connects the second pipe member to the third pipe member and finally, during a fourth phase of bringing to atmospheric pressure the assembly comprising the mold, the compression chamber and the furnace, connects together the second, third and fourth pipe members.

2. Apparatus as claimed in claim 1 in which the delivery conduit is oblique.

3. Apparatus as claimed in claim 1 in which the delivery conduit is vertical.

4. Apparatus as claimed in claim 1 in which the compression chamber comprises a chamber body proper and a base portion which carries the delivery conduit.

5. Apparatus as claimed in claim 1 in which the compression chamber comprises heating means permitting it to be raised to a temperature higher than that of the liquid material which passes through it.

6. Apparatus as claimed in claim 1 in which the two cavities of the compression chamber are of substantially equal volumes.

7. Apparatus as claimed in claim 1 in which the aperture by way of which the two cavities are in communication at their lower ends, is of a section substantially equal to the that of the delivery conduit.

8. Apparatus as claimed in claim 1 in which the cavity of the compression chamber is provided, in its upper portion connected to the lateral pipe member and below the outlet of the pipe member, with a safety device for stopping injection of gas when the liquid material reaches a given level.

9. Apparatus as claimed in claim 8 in which the cavity connected to the lateral pipe member is of conical shape and its volume is such that, when the mold is full, the surface of the liquid material lies below the level detected by the safety device.