Patent Publication Number: US-3880222-A

Title: Low-pressure casting devices

Description:
United States Patent n 1 Chatourel et al.  
 [ Apr. 29, 1975 LOW-PRESSURE CASTING DEVICES [73] Assignee: Regie Nationale des Usines Renault.  
 Billancourt. France [22] Filed: Oct. 2, I973 [Zll App]. No.: 402,9[3  
 [56] References Cited UNITED STATES PATENTS 3.542.330 ll/l97tl Wirtz H 164/305 3.672.432 6/l972 Widdowson ct al. i i i H l64/l l9 3.717.674 4/1973 Chatourcl ct Lll. lo4/l 19 Primary blmmincr- Donald G. Kelly Assistant Examiner Robert (T Watson Attorney, Agent, or FirmStevens Davis, Miller &amp; Mosher [57] ABSTRACT The purposes of this invention. namely preventing the molten metal from solidifying in the casting tube and manifold of a low-pressure chill-mold casting installation and avoiding any undesired contact between the molten metal and the external air, are achieved by providing a novel structure of the end of the casting tube. wherein said end is connected to a cover of which one opening is coincident with a casting inlet of the mold, said cover being fitted in a corresponding cavity of the chill-mold which communicates with a duct supplying heatng gas; this cavity may have an upward extension lined with a ceramic sleeve for exhausting the gas flame and insulating the chill&#39;mold from said flame Alternatively, the bottom of said cover may enclose one or two filters in the form of adjustable spiral wound steel strips permitting the ingress of neutral gas but not the passage of molten metal. Furthermore, a heated reservoir of vertical cylindrical elongated configuration for the neutral gas is disposed between a solenoid-operated valve and the connection between the casting tube and the manifold. so that closing said valve during a casting operation will cause said reservoir to act as a buffer capacity filled with molten metal to balance the furnace pressure.  
 [0 Claims, 5 Drawing Figures PMENTED APRZS i975 SHEET 2 BF 4 LOW-PRESSI&#39;RE CASTING DEYICES The present imention relates to lovwpressure casting devices of the type intended for chill-molding non ferrous alloys. and more particularly to a specific structure of the casting tube directing the molten metal into the chill-mt-ld.  
  Low-pressure chill-mold casting plants are well known. notably those described and illustrated in the Pat. Nos. 3. 171174 of Apr. l7. I97} and 3.698.47l of Oct. 17. I972. and comprise in general a furnace for melting and maintaining in the molten state the metal in a closed chamber adjacent a chill-mold for casting the parts. and a tube dipping in the liquid metai is usually connected to said chillmoId for transferring the metal from said chamber to the mold when a sufficient gaseous pressure is applied to the closed furnace chamber.  
  According to the technique characterising the mentioned patents cited above. said tube is inclined and constantly heated by e\ternal burners for preventing the liquid metal contained therein from solidifying. so that this escess fluid can flow back into the furnace upon completion of the casting operation. the only metal ha\ing solidified being substantially that left in the mold impressions for constituting the castings. To prc\ent an undesired ovidation of the metal in said casting tube. purging or scavenging neutral-gas is in jectetl therethrough.  
  Ho\\e\er. heating said tube and maintaining the metal in the molten state therein constitute difficult problems. especially in the end portion of the tube which is connected to the chill-mold.  
  In this tube section the access for the heating burner is rather difficult and the flow of metal divided into distributing channels at the casting inlets is less massive. and the losses of heat in the chill-mold. due to the usual cooling thereof. are greater. Now. a satisfactory casting is subordinate to the absence of metal oxidation and also of any premature solidification in said tube section. otherwise the casting tube might become clogged unless its rapid fouling causes defects to develop in the castings as a consequence of the sweeping along of oxide skins deposited during subsequent casting operations.  
  It is the essential object of the present invention to avoid the incomenience set forth hereinabove by providing an improved structure for the end portion of the casting tube which connects this tube to a cover having an aperture coincident with a casting inlet of the chillmold. said cover being fitted in a corresponding cavity of the chillmold which communicates with a duct for supplying heating gas thereto.  
  Possibly. this cavity may comprise an upward extension and. within this extension. at chimney-forming ceramic pipe for exhausting the flame. the latter being thus isolated from the chill-mold.  
  In another form of embodiment of this invention the heating duct consists only of the lateral surface of the aforesaid cover having a pervious bottom and receiving therethrough the flow of neutral scavenging gas. said bottom being however impervious to the liquid metal. To this end. this bottom has a circular configuration and consists of at least one turn ofthin steel sheet about a central winding shaft. the degree of tightening of this shaft determining the amplitude ofthe gap left between adjacent turns of said sheet and therefore the gas permeability of the dc\ice. the very moderate thickness of (ill the steel sheet affording a considerable length of wound sheet permitting the passage of gas and imparting the necessary porosity to the filter thus constituted.  
  The covers according to this invention. when inserted into the chill-mold at the end of the casting tube and surrounded directly by the heating gas. are thus heated uniformly and regularly in a closed chamber. thus ensuring a satisfactory heat distribution. This sheathing consisting only of combustion gas without any atmospheric air prevents the ingress of air into the tube by gas perviousness through red-hot walls. which is the major inconvenience of external burners. Moreover. any air introduction is definitely prevented by the scavenging of neutral gas when the molten metal has withdrawn from its highest point in the casting tube. which is the gas-pervious bottom of the cover.  
  As the metal withdraws. it is replaced automatically with neutral gas and the latter is discharged through the same bottom and through the casting inlet or inlets of the chill-mold during the subsequent metal injection.  
  As a result. the casting system operates without any fouling and the chill-molds are supplied with very clean metal. so that spotless castings are obtained. The neutral gas output is easily adjusted by the degree of tightening of said wound steel sheet forming a filter about its central shaft which is locked against rotation in the proper position to this end.  
  A typical form of embodiment of the invention will now be described by way of example with reference to the attached drawings. in which:  
  FIG. 1 illustrates in sectional view one end of the casting tube according to this invention:  
  FIG. IA is a detail view showing on a smaller scale the casting tube of this invention. which is connected through a manifold to the bottom of the chilLmold;  
  FIG. 2 illustrates a similar end portion but provided with a pervious bottom and means for supplying neutral gas;  
  FIG. 3 illustrates a modified embodiment of the structure of FIG. 2 and FIG. 4 shows a modified arrangement of the preceding structures.  
  In FIG. I. an injection mold I secured to the stationary plate 2 of an injection press is shown in its open po sition. A casting tube or pipe 3 extending from a melting furnace (not shown) is connected via a manifold 3. opening into a cover 4 located in a cavity in the bottom ofthc mold to each casting inlet 5 coincident with a lateral aperture 6 of said cover 4.  
  A duct 7 for supplying heating gas. generally in the form of the flame of a gas burner. opens into the gap 8 left between said cover 4 and its assembling cavity in mold l, which gap extends above said cover 4 to constitute a chimney 9 for exhausting the gas flame. This chimney may be lined with a ceramic sleeve 10 limiting the heat exchanges between the flame and the mold structure 1.  
  In FIG. 2. showing the chill-mold I in its closed position. the cover 4 has substantially the shape of an open sleeve receiving at its upper end a pervious bottom consisting of an assembling ring ll having a central core 12 engaged by a winding shaft 13 about which a strip of steel sheet l4 retained by a hub-forming cover [5 fitting in said ring 1] is adapted to be wound. The neutral gas. usually nitrogen. is introduced through the orifice l6 into the assembling cavity 17 of cover 4 under an overpressure sufficient for causing the gas to flow through the steel strip turns into cover 4. manifold 3 and tube 3 as the metal withdraws into the furnace subsequent to the injection operation. After opening the mold and stripping the casting. the neutral gas will escape through the casting inlets 5. thus preventing the ingress of external air into the manifold and tube. and blowing the air out from the mould impressions after the closing of the chill-mold. and before the nest injection step. so that the contact between the metal and the air is kept to a minimum.  
  By way of example. the filter-forming plug may consist of a winding made of three meters of steel sheet strip with a clearance of the order of 0.1 to (1.05 mm between adjacent turns. thus giving a cross-sectional passage area of lit) to Bill) square mm for the gas.  
  In this case. the chimneys 9 for exhausting the heating flames are disposed at other locations of the heating circuit 7. as shown in FlG. 3 illustrating on the other hand another arrangement for supplying neutral gas which. instead of being connected indirectly to the chill-mold via a manifold. as in the preceding case. is connected directly through a simple seat or gasket [8. from an internal supply passage 19 formed in the sta tionary press plate 2. Thus. by simply tightening a screw it is possible to obtain the desired fluid tightness through the engagement of the nozzle 23 with said seal 18. With this arrangement any external unions and like couplings. and therefore the risks ofdamages arising therefrom. are definitely eliminated. while freeing the space around the chill-mold. FIG. 3 also shows a possible modification ofthe neutral-gas pcrvious bottom of cover 4. which consists of a pair of steel sheet strip windings 14 formed as in the preceding example about a winding and adjustment shaft 13 but mounted directly in a shoulder formed in the bottom of cover 4 and retained by a circlip 21. A perforated spacer plate 22 disposed between the two windings 14. will prevent these from slipping axially and being distorted. thus maintaining them flat by using particularly simple means. in combination with the fitting of the outer diameters of said windings in the shoulder by means of said resilient circlip 2l.  
  In another embodiment of this invention the supply of neutral scavenging gas through filter means into the cover is replaced by a supply obtained by using a buffer reservoir connected to the casting tube downstream and in close vicinity of the casting system.  
  FIG. 4 illustrates in vertical section one end of the casting tube equipped with means for supplying neutral gas thereto.  
  ln HO. 4 the half-mold l is rigidly connected to the stationary plate 2 of the injection press. The casting tube 3 extending from the melting furnace (not shown) is connected via a manifold 3, opening into the cover 4 located in a cavity at the bottom of the chill-mold to each casting inlet 5 coincident with a lateral opening 6 of cover 4.  
  The reservoir 24 containing neutral gas has a cylindrical configuration and is disposed vertically; it is connected at its bottom to the casting tube 3 adjacent the ports connecting this tube 3 to the manifold 3 At its upper portion the reservoir 24 comprises. at a level markedly higher than that ofthe half-mold l. a pipe for supplying neutral gas to this reservoir. which is connected in turn to a solenoid-operated valve 26. The side walls of reservoir 24 are heated by means of gas burn ers 27.  
 This device operates as follows:  
  When starting the operation of the casting machine. and before accomplishing the first casting operation. the solenoid-operated valve 26 supplying the neutral gas is opened. This gas. generally nitrogen. fills the reservoir 24. flows up into the casting tube 3 and manifold 3.. and through the cover 4; then. it flows through the lateral opening 6 and casting inlet or port 5. escapes through the half-mold 1, thus purging the air contained in the device. due to the higher pressure of the neutral gas. which is of the order of 20 g/sq.cm. After this purging operation. the two half molds l are closed. the furnace is pressurized and at the same time the solenoidoperated valve supplying neutral gas is closed. When the furnace is pressurized (under a pressure of the order of l()() to g/sq.cm.. the molten metal rises in the casting tube 3. then. via manifold 3, and along the same path as that described hereinabove in connection with the neutral gas. the molten metal penetrates into the half-molds l and scavenges the neutral gas which can escape through the residual openings. At the same time. the molten metal penetrates into the reservoir 24 and compresses the neutral gas therein. due to the closed condition of valve 26.  
  Under no circumstances the column of molten metal balancing the furnace pressure in reservoir 24 should be allowed to reach as far as the solenoid-operated valve 26, to avoid damaging the latter. and this accounts for the vertical position of the elongated cylindrical reservoir 24 and also for the position of said valve 26. Moreover. since the metal contained in this reservoir 24 must remain liquid. the side walls of this reservoir 24 are heated by means of burners 27.  
  Upon completion of the casting operation. the pressure is allowed to expand in the furnace. The liquid metal flows by gravity into the casting tube 3. thus freeing the cover 4, manifold 3 and reservoir 24. and causing the compressed gas to expand gradually from the pipe 25 and in said reservoir. This gradual expansion prevents the occurrence of the detrimental hammering (fluid shock) caused by the simultaneous opening of said valve 26 supplying neutral gas and of said halfmolds i. It also permits of properly scavenging the walls before the neutral gas re-introduced through the solenoid-operated valve 26 fills the casting device and escapes through the casting inlets 5, thus preventing the ingress of external air into the assembly comprising the tube 3 and manifold 3 while purging the mold impressions after the closing of said molds for performing the next casting operation. It is thus clear that with the device of this invention the possibility of allowing the molten metal to contact atmospheric air is minimized.  
  By way of example. in a typical construction according to the teachings ofthis invention, the volume of reservoir 24 is about 1.600 cubic cm for the above-defined pressure values. i.c.. about 20 g/sq.cm for the neutral gas and Hill to 150 g/sq.cm. for pressurizing the furnace.  
  Although a specific form of embodiment of this in vention has been described hereinabove and illustrated in the accompanying drawing. it will readily occur to those skilled in the art that various modifications and changes may be brought thereto without departing from the scope of the invention as set forth in the appended claims.  
 We claim:  
  l. A low-pressure casting device for chill-casting parts from non-ferrous alloys comprising:  
 a chill-mold located adjacent a melting furnace but at a higher elevation.  
 mold impressions in the chill-mold corresponding to the parts to be cast.  
 means defining a casting inlet in said mold impressions.  
 a casting tube connecting the melting furnace to said chill-mold.  
 means for supplying neutral gas to the chill-mold.  
 a cover member fitted in a corresponding cavity of the chill-mold. said cover member having an opening coincident with the casting inlet of said mold impressions.  
 said casting tube being connected to said cover member for communication with said cavity of the chillmold. and  
 said cavity communicating with a duct in the chillmold forming a gas burner and connected to a heating gas supply.  
  2. A low-pressure casting device according to claim l. wherein said heating gas supply duct opens into a gap left between said cover member and its assembling cavity formed in the chill-mold. said gap having an extension in the form of a chimney permitting the escape of the gas flame. said chimney being lined if desired with a ceramic sleeve.  
  3. A low-pressure casting device according to claim 1. wherein said cover member has substantially the shape of an open sleeve receiving at its upper end a pervious bottom consisting of an assembling ring with a central hub engageable by a winding shaft about which a steel sheet strip retained by a hub-forming cover is wound. said hub cover fitting in said ring. the neutral gas being introduced through the turns of said strip would in said cover. the manifold and casting tube. during the withdrawal of the metal into the furnace after the casting injection. the neutral gas escaping through the casting inlets of the mold when the latter is open.  
  4. A low-pressure casting device according to claim 3. wherein said winding is adjustable by rotating said central shaft about which the steel sheet strip is wound.  
  5. A low-pressure casting device according to claim 3. wherein it comprises a double winding of steel sheet strip retained by a distance-piece forming perforated plate disposed between said windings and fitted directly in said cover.  
  6. A low-pressure casting device according to claim I. wherein the supply of neutral gas not connected indirectly through a tube to the chill-mold is connected directly thereto through a seal from an internal supply passage formed in the stationary plate of the injection press.  
  7. A low-pressure casting device according to claim 1. wherein neutral purging gas is supplied to said chillmold with the assistance of a buffer reservoir connected to the casting tube downstream and adjacent the chill-mold cover member.  
  8. A low-pressure casting device according to claim 7, wherein said supplying means comprises a solenoidoperated valve. and said reservoir has a cylindrical elongated configuration and is disposed vertically with its upper end being connected through a pipe to said solenoid-operated valve for supplying neutral gas to the chill-mold. said valve being located at such level with respect to said reservoir that the column of molten metal balancing the furnace pressure cannot reach said valve.  
  9. A low-pressure casting device according to claim 8. further comprising: means for opening said solenoidoperated valve supplying neutral gas to the chill-mold simultaneously with an opening of said chill-mold. the gradual expansion of the compressed neutral gas in the buffer reservoir safely preventing the occurrence of any fluid shock likely to be caused by this simultaneous opening.  
  10. A low-pressure casting device according to claim 7, wherein the lateral walls of said buffer reservoir are heated by means of gas burners for maintaining the molten metal in the liquid state when said reservoir is filled with molten metal.