Patent Publication Number: US-3874440-A

Title: Moulds for producing light alloy and other castings

Description:
United States Patent 1191 Voisin 1451 Apr. 1, 1975 1 MOULDS FOR PRODUCING LIGHT ALLOY AND OTHER CASTINGS [75] Inventor: Albert S. Vosin, Neuilly-Sur-Seine,  
 France [731 Assignee: Societe Anonyme dite: Etablissements, A. Voisin, Puteaux, France 22 Filed: Dec. 17, 1973 211 App]. No.: 425,126  
 [30] Foreign Application Priority Data Dec. 15, 1972 France 72.44828 [52] U.S. Cl. 164/306, 164/113 [51] Int. Cl B22d 17/00 [58] Field of Search 164/306, 309, 316, 319,  
 [56] References Cited UNITED STATES PATENTS 2,210,544 8/1940 Galloway 164/62 2,825,107 3/1958 Schueler 164/61 X 3,160,930 12/1964 Fisher 164/316 3,270,383 9/1966 Hall 164/120 3,457,985 7/1969 Wilson..... 164/155 3,777,801 12/1973 Tenner 164/337 Primary Examiner-Francis S. Husar Assistant Examiner-John S. Brown Attorney, Agent, or Firm-Lewis H. Eslinger; Alvin Sinderbrand 57 ABSTRACT A mould for producing light alloy or other castings comprises a base plate which supports a number of pattern-defining elements. A tank is attached to the base plate and is arranged to contain molten metal which is fed into the tank through a pipe having a flow control valve. Injection tubes extend between the interior of the tank and the pattern, and the interior of the tank is arranged for connection to a source of pressure or to a source of vacuum.  
 12 Claims, 6 Drawing Figures PATENTEB APR 1 I975 SHEET 2 0F 3 PRODUCING LIGHT ALLOY AND BACKGROUND OF THE INVENTION l.-Field of the Invention The present invention relates to a mould for the production of castings, and more particularly to a mould for the production of light alloy castings by means of the so-called low-pressure&#34; moulding process.  
 2. Description of the Prior Art The low pressure moulding process is of use in casting aluminium since it offers many advantages as compared to gravity moulding, in particular an improvement in the quality of the workpieces, a reduced number of the feed ducts for the moulds, and an improved metallic structure.  
 Hitherto these advantages have been partially negated by shortcomings occurring upon application of the process. These are of several kinds. Firstly, it has been necessary to position the mould above or close to the furnace which keeps the metal in a molten state. This leads to prohibitive bulk which diminishes the accessibility of the mould. Such an arrangement eliminates any possibility of applying base-mounted systems of ejection and extraction control which are made use of in gravity-fed moulds, and the casting must be extracted from the lower part of the mould by pulling the casting upwardly at the risk of warping, or else it must be secured to the upper part of the mould by means of projecting portions, the casting being deposited on a receiving plate after it has been ejected from the upper part of the mould. Moreover, the feed of molten metal to the mould occurs by means of a tube extending into the furnace and connecting the metal bath to the cavity of the pattern with the result that the volume of metal contained within the tube outside the bath will become.  
 relatively greater as the level drops.  
  The application of pressure on the bath of meta within the furnace is suspended when solidification has progressed up to the level of the feed passage of the mould. Consequently, the metalcontained in a single injection tube falls. This metal is colder than that of the bath, and thus cools and agitates the latter whilst forming oxides. This is increasingly troublesome when the level ofthe bath within the furnace drops, since the volume of cooler metal becomes relatively greater. Moreover, this arrangement imposes the need for frequent adjustment of the overpressure to be applied above the bath to ensure correct filling of the mould as a function of the drop in the level of the bath. At low levels, this overpressure reaches values which initiate a hammer effect within the feed ducts and within the pattern of the mould, which impairs the stability of the cores.  
  Further, the feed to the mould through a single injection tube commonly occurs into a limited space of the mould. This arrangement is disadvantageous in that overheating of an area of the mould is caused which leads to a rise in the temperature of the infeed aperture, and thus to a delay in the solidification of the metal and to a reduction of the moulding rate.  
  The feed of the pattern cannot be accurately controlled by means of this arrangement. Accordingly, if this feed occurs into volumes equipped with cores, it causes the drenching&#34; of the latter.  
 SUMMARY OF THE INVENTION According to the present invention, there is provided in a mould for producing castings, a base plate, patterndefining elements supported on the base plate, means defining a tank for molten metal, the tank being attached to the base plate, a plurality of injection tubes communicating the interior of the tank with the interior of the pattern defined by said elements, first pipe means extending into the tank beneath the level of a bath of molten metal therein, said first pipe means being closable and being arranged to feed molten metal into the tank, second pipe means communicating with the interior of the tank above the bath of molten metal therein, said second pipe means being arranged for connection to a source of pressurized fluid whereby to pressurize the interior of the tank, and for connection to a source of vacuum whereby to create a reduced pressure in the interior of the tank.  
  Further according to the present invention, there is provided in a mould for producing castings, a base plate, pattern-defining elements supported on the base plate, means defining a tank for molten metal, the tank being attached to the base plate, a plurality of injection tubes communicating the interior of the tank with the interior of the pattern-defined by said elements, first pipe means extending into the tank, said first pipe means being closable and being arranged to feed molten metal into the tank, second pipe means communicating with the interior of the tank, said second pipe means being arranged for connection to a source of pressurized fluid whereby to pressurise the interior of the tank.  
  Preferably, the tank is larger than the base plate of the mould but is separated therefrom by a gap of several centimetres to insulate the base plate and to prevent heat transmission by conduction and, possibly, to permit aircooling. The tank contains a volume of metal corresponding to the sum of the workpiece volume and its feed system colume, and to a complementary volume which, at the lowest level, forms the bath within the tank.  
 BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which:  
  FIG. 1 is a cross-section of a mould in accordance with the present invention;  
  FIG. 2 is a fragmentary section, to an enlarged scale, showing an injection tube and an ejection rod of the mould;  
 FIG. 3 is a section taken on line III-III of FIG. 1;  
  FIG. 4 is a fragmentary section, to an enlarged scale, taken in the direction of the arrow F in FIG. 3; and  
  FIGS. 5 and 6 are fragmentary cross-sections of a modified form of mould having multiple patterns.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS The mould shown in FIG. 1 is formed from several parts, comprising an outer case 1 between which are clamped upper checks 2, lower checks 3, and an upper steel core 4 equipped with a pin 4a. In the embodiment shown, these. elements are intended, in cooperation with sand cores 5, to form a pattern for a motor car engine cylinder-head, and are held in position by means of a base plate 6. A cover 7 of a tank 8 is fastened to the base plate 6 and a device 8a is arranged to keep the tank 8 hermetically sealed to the cover 7 whilst allowing rapid disassembling of the tank. It will be noted that a gap 6a is left between the base plate 6 and the cover 7, contact between the said base plate and cover being established at particular points only. At the level of its cover, the tank 8 has a greater surface area that the lower surface of the pattern, and contains a predetermined volume of liquid metal 9 corresponding to at least the metal volume required to fill the pattern, plus a complementary volume corresponding to the volume required to fill the tank to a lower level 9a. A chamber 10 is defined between the surface of the molten metal bath thus formed in the tank 8, and the cover 7. By means of a pipe 11 the chamber 10 can be selectively placed in communication with a source of fluid (preferably air) under controlled pressure and with a vacuum source (not shown).  
  The tank 8 and its cover 7 are equipped with heating elements 12 and 13, which are inserted into the thickness of the cover 7 between the ejection rods 15, and into the walls of the tank 8, respectively. These heating elements are preferably in the form of electrical resistances.  
  An ejection system 14 equipped with ejection rods 15 is located beneath the tank 8. Movable pins 16, required to assemble the pattern, are installed on a system l7 displaceable in the vertical direction. A plurality of injection tubes 18, which provide communication between the pattern and the tank 8, are arranged to pass through the base plate 6 and the cover 7 and extend into the tank 8.  
  The cover 7 has projections 70 through which extend the passages for the tubes 18; the projections 71: encircle the tubes 18 in order to distribute heat along the portion of the tubes which is not located in the tank whereby to maintain their temperature at a level substantially equal to that of the tank.  
  FIG. 2 shows the tank 8 with an injection tube 18 and an ejection rod 15. The bottom 8b of the tank is shaped adjacent the passage for the rod 15. in such manner as to come into contact with the cover 7 and to form a casing or housing 19 around the rod 15. The rod 15 thus passes through the tank 8 to contact the workpiece moulded within the pattern without being in contact with the bath of molten metal with the tank. Identical casings are situated at the points of passage of all the ejection rods 15 with which the mould is equipped, as well as at the points of passage of the pins 16.  
  The submerged end portions of the tubes 18 are situated adjacent to the bottom of the tank into which the liquid metal is fed by gravity. A chamfer 21 is produced at the lower end portion of the tubes 18. The volume of liquid metal 9 remaining in the tank 8 at the lowest level of the bath should, after the charging of the pattern, surround the still submerged end portions of the tubes 18, in such manner that the overpressure prevailing within the chamber 10 and acting on the surface 9a of the bath is sufficient to keep the metal within the pattern until it solidifies.  
  As shown in FIG. 3, a funnel 22 for feeding the molten metal into the tank 8 leads into the tank through a pipe 22a the lower end of which lies beneath the lower of, alignment with the funnel 22 whereby to open or close the infeed passage thus provided for the molten metal. When the valve 23 is being closed, the valve is displaced on a sloping surface 240 which causes it to bear against the walls of the housing 29 thus sealing the tank 8 hermetically without contact with the metal. The metal comes from a source which is not illustrated and can be in the form of a manually charged opening, or a furnace from which extends a metal feed pipe connected to the funnel 22.  
  As shown in FIG. 3 the bottom 8b of the tank 8 slopes downwardly towards a drainage hole 25 sealed by means of a removable plug 26. A sensor 27 is installed on the mould and is immersed in the metal bath in order to ascertain its level. The sensor is arranged to transmit a control signal to the valve 23 in order to shut off the funnel 22 when the level of the bath reaches that which is required. A pyrometer 28 is provided to determine the temperature of the bath. During injection of the metal into the pattern, the removal of the air and gases originating from the combustion of the sand cores which are enclosed, should be as rapid as the inflow of the metal, and for this purpose and independently of the conventional draught devices, sheet steel (suction) strainers 30 are provided in the gap between the bot-,  
 tom of the mould and the cover of the tank; alternatively for example an automatic device can be provided on the upper core, which device, upon the opening and closing of the mould, effects alternating displacement, with a stroke of approximately 10 mm, of pins 31 which, by their displacement, prevent obstruction caused by fouling.  
  FIG. 4 shows to an enlarged scale the funnel 22, the pipe 22a, and the housing 29 formed in the cover 7 in which the valve 23 is arranged to slide. Control over the displacement of the valve 23 can be made dependent upon the signal emitted by the sensor 27.  
  After initiating the displacement of the valve 23, the sensor 27 can control the infeed of air under pressure into the portion 10 of the tank 8 above the molten metal by means of controllable pressure regulators appropriate for automatic reproduction of the operating process. The device operates in a simple manner. Once the different elements of the mould have been placed in position, the operation consists in feeding into the tank 8 through the open funnel 22, a volume of metal at least equivalent to the volume of the workpiece which is to be produced, plus that of the feed head (runner, discard head, dead head, and so forth), the sensor 27 ensuring that the lower bath level is always maintained. Once this volume is reached, the sensor 27 previously set for the corresponding level, acts on the valve 23 to close the funnel 22. It then initiates the inflow of gas (for example air) under pressure which is fed through the pipe 11 into the portion 10 of the tank 8. An overpressure is applied throughout the free surface of the bath of metal contained in the tank 8, with the result that the metal is caused to rise in the injection tubes 18 and thus to fill the pattern. The overpressure is maintained while the metal of the workpiece is solidifying. The inflow of compressed gas is controlled by means of an automatic control system for regulating the pressure which controls the speed of infeed of the metal, to a higher pressure for rapid filling of the pattern, and to a lower pressure for its retention during the period of solidification.  
  The control system comprises a control box Il a having regulator dials Ilh; the control box lIa can be programmcd to effect the cyclic operations offilling, pressure retention and mould stripping; The control box Ila may also receive a signal transmitted by the sensors 27 for control of the level of the bath of metal and can actuate a negative pressure system to cause the withdrawal of the still molten metal sprues, thus reducing metal wastage and the time for solidifying. Accordingly, there is a residual metal volume corresponding substantially to the level marked by the line 9a. The portion 10 of the tank 8 is finally vented, the-valve 23 is displaced, and the tank 8 receives liquid metal again. In the meantime, the mould is opened and the ejection rods raise the workpiece which is then removed manually or automatically. The mould is closed again after insertion of other cores, and the production of another workpiece may be initiated.  
  The mould particularly described has many advantages. Firstly, since the surface area of the upper end of the tank 8 is greater than the surface area of the lower end of the pattern, it is easy to install between the pattern and the tank a large number of injection tubes 18 whereby it is possible on the one hand to provide direct feed for all the large portions of the workpiece, thus ensuring effective sprue stripping, whilst leaving the isotherms&#34; open during the cooling action and, on the other hand, to conduct the injecting operation correctly in such manner that the sand cores are not subject to deterioration or crumbling.  
  This multiplication of the injection tubes thus renders it possible to feed the pattern through its entire bottom surface, which improves the metallurgical quality of the workpiece thus produced, while preventing the formation of hot spots which are necessarily established in the flows of metal into the pattern.  
 The solidification can advantageously be accelerated by the presence of a cooling fluid on the base plate of the mould, and which may be circulated within the gap 6a between the cover and the base plate 6. The projections 71! surrounding the injection tubes 18 keep the tubes at the temperature of the cover 7 in order to prevent premature solidification of the metal contained in the injection tubes at the level of the portion 10 of the tank 8 and of the gap 6a, since such solidification would have the result of forming a solid plug in this part of the tube prior to the solidification of the metal of the pattern in contact with the base plate.  
  Moreover, the aforesaid gap 60 provides an advantageous discharge position for degassing holes as illustrated beneath the plate 30. The problem of the degassing of the cores situated in the bottom of the mould is thus resolved.  
  Further the mould accepts no more than a small volume of molten metal spread over a large surface. Accordingly, the tank is relatively small in height. This offers the possibility of making use of the same systems for ejection of the workpiece or for actuation of the pins, as for gravity moulding, which need merely traverse the height of the tank. Moreover, this small height permits the formation of the housings 19 which permit passage of the rods through the tank without contact with the molten metal.  
  The molten metal does not remain within the tank 8 since it is almost totally injected into the pattern immediately upon being fed into the mould, and it is sufficient to provide a heating action to prevent the metal dropping back into the bottom of the tank following application of a vacuum or venting after solidification, at the temperature of the mould during operation. For the same reason, the tank need not be made of refractory material, since it need not withstand very high temperatures, a protective coating being adequate.  
  The small volume of the metal injected and the small length of the injection tubes permit the application of a very small and easily controllable overpressure. The force of inflow of the metal into the pattern thus amounts to a minimum and obviates the need to construct a robust pattern.  
  Since the tubes 18 have tapered end portions 21 the presence of the tubes can readily be separated from the metal which may have solidified in the cavities, for example when dismantling the tank.  
  Accordingly, it is apparent that the mould is compact and easily accessible. The mould stripping operations may thus be performed very easily and rapidly in vertical or lateral directions. In particular, the fact that the workpiece is ejected from the mould by means of the rods 15, that is to say by thrust, as well as the extraction of the pins which are difficult to strip from the mould, prevent thefaults incurred in conventional techniques according to which the workpieces are pulled out of the mould, causing warping and incipient crazing.  
  The mould also permits extensive mechanisation of the production of workpieces by low-pressure moulding. It is possible to install a number of moulds of this kind on a chain or turntable movable past a station at which the moulds are filled with liquid metal.  
  Existing moulds can be equipped with a tank as particularly described in or order to achieve production rates analogous to those obtained in pressure-casting with reduced costs.  
  Moulds comprising several patterns for producing identical workpieces are shown in FIGS. 5 and 6. In FIG. 5, each of these workpieces 31 is fed by means of an injection tube 18 and may be ejected by two rods 15. In FIG. 6, the workpieces 32 comprising a central pin 16, are fed through distribution passages 33 leading from a main passage 34, which is fed by a sufficient number ofinjection tubes 18. The distribution passages 33 open into an annular feed passage 35.  
  The moulds particularly described are especially suitable for light-alloy casting.  
 What is claimed is:  
 1. In a mould for producing castings,  
 a base plate,  
 pattern-defining elements supported on the base plate,  
 means defining a tank for molten metal, the tank being attached to the base plate,  
 a plurality of injection tubes communicating the interior of the tank with the interior of the pattern defined by said elements,  
 first pipe means extending into the tank beneath the level of a bath of molten metal therein, said first pipe means being closable and being arranged to feed molten metal into the tank,  
 second pipe means communicating with the interior of the tank above the bath of molten metal therein, said second pipe means being arranged for connection to a source of pressurized fluid whereby to pressurize the interior of the tank, and for connection to a source of vacuum whereby to create a reduced pressure in the interior of the tank; cover means located beneath said base plate and closing said tank;  
 said cover means including means defining passages therein through which said injection tubes extend and heat-distributing projections on the cover means adjacent the passages.  
 2. A mould according to claim 1 further comprising elongate elements extending through the tank, the  
 tank being shaped to define housings around the elongate elements such that the housings retain the elements out of contact with the molten metal within the tank.  
  3. A mould according to claim 2, wherein the elongate elements are in the form of pins.  
  4. A mould according to claim 2, wherein the elongate elements are in the form of ejection rods.  
  5. A mould according to claim 1, wherein the cover means and the base plate define a space therebetween for the circulation of cooling fluid.  
  6. A mould according to claim 3, wherein the injection tubes each have a lower end portion adjacent the bottom of the tank, the said lower end portions being tapered.  
 7. A mould according to claim 2 further comprising means defining a drainage aperture in the tank, the  
 bottom of the tank sloping downwardly towards the aperture.  
  8. A mould according to claim 1, wherein the first pipe means comprises a pipe portion extending from the top of the tank towards the bottom of the tank, said mould further comprising slide valve means operative to close the upper end of said pipe portion, and  
 housing means, said slide valve means being slidable in the housing means transversely to the axis of said pipe portion.  
 9. A mould according to claim 1 further comprising electrical resistance heating elements, said heating elements being incorporated in the thickness of cover means and of the tank.  
 10. A mould according to claim 8 further comprising temperature-sensing means for sensing the temperature with the tank, and  
 level-sensing means for sensing the level of molten metal within the tank, said level-sensing means controlling said slide valve means.  
  11. A mould according to claim 1, wherein at the level of the cover means, the surface area of the tank is greater than the surface area of the mould.  
 12. in a mould for producing castings,  
 a base plate,  
 pattern-defining elements supported on the base plate,  
 means defining a tank for molten metal, the tank being attached to the base plate,  
 a plurality of injection tubes communicating the interior of the tank with the interior of the pattern defined by said elements,  
 first pipe means extending into the tank, said first pipe means being closable and being arranged to feed molten metal into the tank,  
 second pipe means communicating with the interior of the tank, said second pipe means being arranged for connection to a source of pressurizedfluid whereby to pressurize the interior of the tank; cover means located beneath said base plate and closing said tank;  
 said cover means including means defining passages therein through which said injection tubes extend and heat-distributing projections on the cover means adjacent the passages.  
  UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N Dated l,  
 Inventor(s) Albert S. Voisin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 In the heading, change:  
 [75] Albert S. Vosin [75] Albert S. Voisin Signed and Scaled this twentieth Day of April1976 [SEAL] v RUTH C. M A SON C. MARSHALL DANN Arresting Ojjicer Commissioner uflalenls and Trademarks