EP0126532A1

EP0126532A1 - Method for the production of hollow foundry cores

Info

Publication number: EP0126532A1
Application number: EP84302157A
Authority: EP
Inventors: Anatol Michelson
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-03-30
Filing date: 1984-03-29
Publication date: 1984-11-28
Also published as: CA1205613A; BR8401558A; AU2610584A; AU546308B2; KR840007838A

Abstract

A method for the production of hollow foundry sand cores in which binder coated sand is cured in the patten cavity (17) of a core box (10) using an amine catalyst gas to form a hollow sand core, and uncured binder coated sand is discharged and recovered from the cavity of the hollow sand core. Fresh binder coated sand and recovered binder coated sand are volumetrically metered alternately to a blow head (40) so that at no time is there a mixture of the two sands in the blow head.

The metered binder coated sand in the blow head (40) is blown by compressed air through an investment aperture in the top of the core box into the core pattern cavity (17).

After gassing, any uncured binder coated sand is discharged and recovered from hollow sand cores while fresh binder coated is being metered to the blow head. Metering of fresh binder coated sand is discontinues after a predetermined period of time equivalent to aout 1/10 to about 1 /3 of the bench life of the binder coated sand. At this point, metering of recovered binder coated sand to the blow head is commenced and continued until essentially all of the sans is consumed in hollow core formation. The metering of fresh binder coated sand is then recommenced and the procedure repeated.

Description

The present invention relates to a method for the production of hollow foundry sand cores.
In the cold box process for making solid foundly sand cores as described in U.S. Patent 3,409,579, a charge of a mixture of sand and a binder comprising a phenolic resin and a polyisocyanate is shaped in the pattern cavity of a core box. The resultant shaped sand mass is then subjected at room temperature to the action of a tertiary amine catalyst introduced under sufficient pressure to penetrate the sand mass, whereby an instantaneous cnre of the binder is effected and a solid sand core formed. In practice, the process is conducted as a highly automated procedure-in which binder coated sand is invested from a blow head into a core box enclosing a core pattern through which the amine gas-is passed, and-the resultant cured solid sand core then removed from the opened core box.
Notwithstanding the acceptance of the cold box process by the foundry industry and notwithstanding the commercial success that it has enjoyed in most of the industrialized countries of the world over-the past several years, there are certain disadvantages to the process. The most apparent disadvantage is that the cores produced by the process are solid weighing as much as three or four times similar hollow cores produced by the well known Croning shell process. Raw material costs for the cold box process are, accordingly, correspondingly greater than for the shell process, and handling of the cores produced by the process is more difficult because of their greater weight. Solid sand cores, moreoser, inherently lack the permeability and collapsibility properties of hollow sand cores that are so important in metal casting.
As currently practiced, the shell process for producing hollow sand cores, involves subjecting a mixture of sand coated with a hexamethylenetetramine-containing phenolformaldehyde resin to the curing action of heat in the range of 400-480°F for a time sufficient to effect a cure of the resin. Unfortunately, there are also disadvantages associated with the shell-process-most of which are related to the high temperature curing step. Among these may be mentioned the need for excessive cure times, high fuel costs, the need for heat resistant core boxes, as well as less than - desirable foundry working conditions..
More recently, it has been proposed to use the cold-box concept to form hollow sand cores in an effort to gain the advantages of both procedures without suffering their respective disadvantages. As disclosed in U.S. Patent 4,232,726 issued-in the name of Anatol Michelson-, the resultant cold hollow-core forming procedure comprises investing, or charging, a binder coated sand to the cavity of a gas permeable core pattern surrounded by a gas impermeable core box. The charged sand mass is then cured by introducing a gaseous amine catalyst at ambient temperature and under pressure into the space enclosed by the gas permeable gas pattern and the gas impermeable core box. The amine catalyst penetrates the core pattern throughout its entire contour and enters the sand mass to a distance determined by the equilibrium condition eventually reached between the pressure of the gaseous amine and of the air in the sand mass of the core pattern cavity. Curing of the binder occurs as the sand mass is penetrated by the amine gas, the extent of penetration determining the depth of cure. Once pressure equilibrium is reached, residual gaseous amine is evacuated from the core box, uncured binder coated sand removed from the cavity of the hollow sand core, and the core box opened to effect separation of the hollow sand core from the core pattern.
Disclosed in U.S: Patent 4,291,740 also issued in the name of Anatol Michelson, is a process and apparatus for-conducting the cold hollow core forming- procedure disclosed in U.S. Patent 4,232,726 in a continuously automated manner. As described therein, the- cold hollow core forming process comprises a plurality of basic steps conducted in sequence including (a) transferring binder coated sand from an upper feed hopper to a blow head, and from the latter to the cavity of a core pattern through an investment aperture in the core box top, whereby-a-charge of sand is shaped in the core pattern cavity; (b) sealing the core box and core pattern; (c) gassing the shaped sand mass by introducing an amine catalyst at ambient temperature and under pressure into the enclosed space formed between the core pattern and the core box to cure the binder and form a hollow core; (d) rotating the core box through 180° and discharging uncured binder coated sand, by means of gravity and compressed air, from the cavity of the hollow core into a lower feed hopper for recycle; (e) again rotating the core box, this time through 90°, to permit extraction of the hollow core from the pattern, as by means shown in U.S. Patent 4,204,569 issued in the name of the inventor hereof; and (f) closing the core box and rotating it another 90° to its original position for the start of another production cycle. A complete production cycle conducted in accordance with the described process requires about 30 seconds.
While clearly providing advantages over existing sand-core forming procedures, the described cold hollow core process is subject to its own disadvantages. One such disadvantage, for instance, concerns the vaporization of the solvent used for the two component binder system. To the extent that the solvent is lost by vaporization, the binder coated sand becomes correspondingly less useable, until-a degree of solvent loss can occur which-can render the binder coated sand totally unuseable. When practicing the described cold hollow core process, it has been the practice to charge binder coated sand to the blow' head in a quantity several times greater in volume than the volume of the core pattern cavity. Since only the equivalent of sand corresponding to the volume of the core pattern cavity is invested from the blow head into the cavity in each core production cycle, a substantial quantity of binder coated sand remains in the blow head to be exposed to the compressed air used in investing, as sand is charged to the pattern cavity during successive production cycles. The consequence of this exposure to pressurized air is compounded, moreover, as recovered uncured binder coated sand is recycled, mixed with fresh sand, returned to the blow head and subjected to repeated exposures to the investing compressed air during successive production cycles.
Another disadvantage to the described cold hollow core process lies in the fact that no physical means are provided in the investment aperture, either during investing of sand or during gassing of the sand, for defining the top of the sand mass charged to the core pattern cavity. As a result, when the core-box-is sealed and gassed,-the-gas will penetrate- at random around and under the base of the investment sleeve into the investment aperture causing the formation of a core top, or "print", as the case may be, that is trough, uneven and of uncertain configuration.
Finally, it should be noted that the cold hollow core process described in U.S. Patent 4,191,170 calls for discharging uncured binder coated sand from the cavity of the formed-hollow core -through the investment aperture for recycle to the upper feed hopper. To accomplish this, the core box is rotated through 180° thereby permitting the uncured binder coated sand to discharge. The means necessarily required to carry out sand discharge in this manner are very complex and costly since they must include a "cradle" or "cage" in which to mount the core box for rotation, mechanism for effecting rotation, conveyors for the recovered sand, and the like.
There has remained, therefore, a need for improving the above described cold hollow core forming process. It is a principal object of this invention to fulfill this need. It is a further object of this invention to provide a process for advancing, or conducting, binder coated sand through the various mechanical elements employed in conducting the process, in an effective manner. It is still a further object of this invention to minimize exposure of binder coated sand to the solvent vaporizing effect of pressurized air used in the cold hollow core process thereby reducing the waste of sand. Still another object of this invention, in one form thereof, is to conduct the process so as-to produce a hollow-core whose top or "print", as the case may be, is smooth, even and of predetermined and final dimensions.
The invention is a method for forming hollow sand cores which comprises investing a charge of binder coated sand into the cavity of a gas permeable core pattern surrounded-by a gas impermeable core box as conventionally done. Unlike previous practice, however, in which a quantity of sand equivalent to several times the voiume of the core-pattern cavity is charged to the blow head, a quantity of -binder coated sand is metered to the blow head, in accordance with the present invention, which is no greater than that which is essentially equivalent to the volume of the core pattern cavity. From the blow head, the binder coated sand is invested in the cavity of the core pattern through an investment aperture in the core box top formed by an investment sleeve. Unlike previous practice, the protrusion, if any, of sand into the investment aperture and, accordingly, the definite, predetermined configuration of the top or "print", as the case may be, of the resultant hollow core is established by the positioning of the blow plate of the blow head in the investment aperture.
Once the sand has been charged to the core pattern cavity, the core box is sealed by a seal head placed in the investment aperture at the sand level predetermined by earlier placement-of the blow plate during sand investment. The core box is then gassed by-introducing amine catalyst at ambient temperature and under pressure into the enclosed space between the core pattern and the core box the air from-which space has been evacuated. After curing of the binder coated sand to a selected depth in the core pattern,-: the core box is unsealed and, without rotation of the core-box, uncured binder coated sand-is removed from the hollow core cavity through the investment - aperture, and the hollow core then separated from the opened core box.
Successive hollow core production cycles are conducted in the same manner using fresh binder coated sand, uncured binder-coated-sand being recovered from the cavity of the hollow core produced in each cycle. At a selected point in time in the hollow core production procedure, usually governed by the bench life of the sand coated binder or by the capacity of the equipment for storing and recycling uncured binder coated sand, the metering of fresh binder coated sand to the blow head is discontinued. At this selected point in time, the metering of recovered uncured binder coated sand to the blow head is commenced and successive hollow core production cycles are conducted in the same manner as done heretofore with fresh binder coated sand, uncured binder coated sand being recovered from the cavity of the hollow core produced in each cycle. Recovered uncured binder coated sand is recycled and metered to the blow head until insufficient sand is recovered to produce a hollow core. At this point, fresh binder coated sand is again metered to the blow head and successive production cycles conducted as heretofore, the alternating use of fresh binder coated sand and recovered uncured binder-coated sand being observed so long as the production procedure is conducted. At no time during-the production procedure are fresh binder coated sand and recovered uncured binder coated sand metered to the blow head simultaneously.
In the drawings, which illustrate that which is presently regarded as the preferred mode of carrying out the invention:

Fig. 1 is a schematic of a cold hollow core box assembly for use in the method for producing hollow foundry cores according to this invention.
Fig. 2 illustrates-an embodiment for metering binder coated sand to a blow head.
Fig. 3 illustrates the blow head in investing relationship with the core box for investing binder coated sand into the cavity of the core pattern through the core box investment aperture.
Fig. 4 illustrates the core box sealed by appropriate sealing means and the core box ready for gassing with amine catalyst.
Figs. 5 and 6 illustrate an embodiment for recovering uncured binder coated sand from the cavity of a hollow core formed in the core box without rotation of the core box through 180°.

Turning now to Fig. 1 of the drawings, reference numeral 10 indicates a core box for use in the production of hollow foundry sand cores in accordance with the method of the present invention. Core box 10 comprises a pair of gas impermeable sections 11, 12 supporting gas permeable core pattern sections 13, 14. When brought together along parting line 15, core pattern sections 13, 14 form core pattern 16 defining a core pattern cavity 17 which communicates with the exterior of core box 10 through an investment aperture 18 defined by investment sleeve 19. Also formed by-the assemblage of core pattern sections 13, 14 is an enclosed flow space 20 situated between core box 10 and core pattern 16. Core box 10 is provided with a pair of ports 21, 22 in its wall which communicate-with fllow space 20. Port 21 is connected through suitable valve means 23 to an exhaust fan or scrubber means in one position of the valve, and with the atmosphere in another position of the valve. Port 22 is connected through similar valve means 24 with a source of compressed air in one position of the valve, and with a source of amine catalyst gas in another position of the valve.
In the production method of the present invention, a metered quantity of binder coated sand is charged by means of compressed air through investment aperture 18 into core pattern cavity 17 as air is exhausted from the core box through flow space 20 and port 21. When sand investment is completed, core box 10 is sealed and gaseous amine catalyst introduced at ambient temperature and under pressure through port 22 into flow space 20. The amine gas penetrates the gas permeable walls 13, 14 of core pattern 16 and the binder coated sand in core pattern cavity 17, thereby catalyzing the cure of binder with which it comes in contact, the depth of cure in core pattern cavity 17 being governed by the equalization of the pressures of the amine gas and the air in the sand in core pattern cavity 17. Upon completion of curing, core box 10 is purged of residual amine gas through flow space 20, port 21 and valve means 22, and core box 10 unsealed. Without rotating core box 10, uncured binder coated sand is then recovered from the cavity of the hollow core, and core box 10 then opened to permit extraction of the hollow core.
As earlier described,-one of the disadvantages to the cold hollow core process arises from the practice-of charging binder coated sand so as to fill the entire volume of the blow head, i.e. several times the volume of the core pattern cavity. Inasmuch -as each investment of sand into the core pattern cavity from the blow head-is essentially no greater than the volume of the core pattern cavity, it necessarily follows that a considerable quantity of-sand remains in the blow head to be subjected to the deleterious effect of the compressed air used in successive sand investments to the core pattern cavity. Since recovered uncured binder coated sand is recycled to the blow head in admixture with fresh binder coated sand, the exposure of any particular increment of sand to the compressed air used in the blow head can be considerable. As a consequence, sand can become unuseable because of vaporization of its solvent content through exposure to the compressed air and, accordingly, must be discarded.
In accordance with the present invention, the exposure of sand to compressed air in the blow head is minimized and the waste of sand reduced, by metering to the blow head only so much fresh binder coated sand as is essentially equivalent in volume to the volume of the core pattern cavity. The metered volume of sand is then invested in the core pattern cavity and a hollow core formed. Uncured binder coated sand is recovered and collected without-mixing it with fresh sand. Successive production cycles are conducted in the same manner using-only fresh binder coated sand, the uncured binder coated sand from each cycle being recovered and collected. At a selected point in the procedure, the metering of fresh sand to the blow head is discontinued. This point will be governed either by the bench life of the recovered uncured binder coated sand, or by the size-of the system for collecting recovered sand. The bench life of the binder coated sand is that length of time required for the binder to sufficiently cure in the absence of amine catalyzation so as to render it unuseable in the production of hollow cores. The point at which the metering of fresh binder coated sand to the blow head is discontinued should preferably be about 1/10 to 1/3 of the bench time. If the capacity of the system used in practice of the procedure to collect recovered uncured binder coated sand is less than that capable of accepting the quantity of sand recovered in that length of time, then the length of time should be adjusted to accommodate the collection system capacity. Preferably, of course, the collection system capacity should be designed to complement the 1/10 to 1/3 of the bench life period of time.
When the metering of fresh binder coated sand to the blow head is discontinued at the point referred to above, the metering of the recovered uncured binder coated sand to the blow head is commenced in the same manner. As before, uncured binder coated sand is recovered from each production cycle, collected and recycled for metering to the blow head. Only when the quantity of recovered binder coated sand is no longer sufficient to form a hollow core, is the metering of recovered sand discontinued to the blow head and the metering of fresh binder coated sand recommenced. The procedure of alternatively metering fresh and recovered sand to the blow head is then repeated. At no time in the practice of the process are fresh and recovered sand mixed and metered to the blow-head.
In accordance with the practice of the process of this invention, therefore, it can-be readily - recognized that the disadvantage of the cold hollow core-process-described above is substantially minimized, if not totally eliminated. Since the charging of binder coated sand to the blow head is precisely metered in accordance with the volume of the core pattern cavity, only a single volume of sand, is subjected to the investing compressed air during each investment of the core pattern cavity. Moreover, since there is no mixing of fresh sand and recovered sand, and since fresh sand and recovered sand are alternately metered to the blow head, the period of time that any particular increment of sand remains in the system in which the procedure is conducted, is reduced to a preferred and acceptable level.
Referring to Fig. 2, there is shown a metering device 30 for charging a volumetrically measured quantity of binder coated sand to blow head 40 comprising a metering drum 31 having a chamber 32 defined by the drum ends, longitudinal wall members 33 and bottom plate 34.- Adjusting means 35 for modifying the position of bottom plate 34 and - consequently varying the volume of chamber 32 are provided to accommodate varying sizes of core patterns 16 that may be used in core box 10. _; Metering drum 31 is mounted for rotation on axle 36, which-supports member 37. In operation, metering device 30 is fed with binder coated sand from feed hopper 38 to fill chamber 32, drum 31 then being rotated clockwise so as to place chamber 32 over the top-of blow head 40. As metering device-31 is rotated, its sand content is confined in chamber-32 by means-of stationary cylinder wall 39 until chamber 32 is properly positioned over the top of blow head 40, at which time the volumetrically measured quantity of binder coated sand is discharged from chamber 32 into blow head 40.
The volumetrically measured quantity of binder received by blow head 40 is then transferred to core pattern cavity 17 by being blown by compressed air through investment aperture 18. This transfer is accomplished by moving and stationing blow head 40, by means not shown, under air cup 41 shown in Fig. 3. Air cup 41 which is connected to a pneumatic cylinder, see Fig. 5, then engages blow head 40 moving it downwardly in axial alignment with-core box 10 along its axis 15 and in sealed relationship with the top thereof by means of sealing element 42. The charge of binder coated sand is then blown from blow head 40 through investment aperture 18 into core pattern cavity 17. If there is to be no core print on the hollow core, then blow plate 44 will be made precise in its length to that of investment sleeve 19 so that there will be no protrusion of sand into investment aperture 18. On the other hand, if there is to be a core print, then the length of blow plate - 44 is correspondingly reduced to conform to the desired length of print. In either event, the placement of blow plate 44 within aperture sleeve 19, - coupled with the placement of a gas permeable disk within aperture sleeve 19 during gassing, as will be subsequently discussed, will assure a definite and predetermined configuration to the hollow core at the point of aperture 18.
On completion of the investment of sand and removal of blow head 40 from core box 10, the same cup 41 with its cylinder 78, as shown in Fig. 5, brings sealing means 50 provided with sealing head 51, as shown in Fig. 4, into alignment with axis 15 of core box 10. Sealing head 51 is provided with a gas permeable disk 52 which, by virtue of the action of cup 41, is caused to contact the upper surface of the binder coated sand charge in core pattern cavity 17, rather than the top of aperture sleeve 19 as previously practiced. Sealing head 51 is tightly sealed against the top surface of core box 10 by means of sealing element 54.
Gas permeable disk 52 holds the sand in core pattern cavity 17 down against the force of the catalyst gas pressure which otherwise would tend to throw sand out of cavity 17 into investment aperture 18. Accordingly, disk 52 serves to provide a hollow core whose configuration in the area of its aperture will be definite and predetermined. Disk 52, moreover, cooperates with escape space 57 in sealing head 51 by permitting air contained in the sand to retreat, or escape, into space 57 when amine catalyst is introduced under pressure into flow space 20 - forcing air in the sand away from core pattern sections 13, 14. In this respect, escape space 57 can be varied in size as, for example, by the placement therein of spacer rings or fillers, whereby ,the thickness of the hollow core can be correspondingly varied. Finally, gas permeable disk 52 also serves to allow compressed air to enter core pattern cavity 17 during the exhausting of core box 10.
As shown in Fig. 4, sealing head 51 is also provided with means 56 communicating with a source of negative pressure applied to core pattern cavity 17 during amine gassing. Sealing head 51 is further provided with means 55 communicating with a source of compressed air for facilitating the purging of core box 10 of residual amine after gassing.
As earlier discussed herein, another principal disadvantage to the cold hollow core process as described is the necessity to rotate the core box through 180° in order to discharge uncured binder coated sand from the cavity of the hollow core through the investment aperture, a procedure that- involves complex and costly equipment to effect. This
disadvantage is eliminated by effecting the discharge of uncured binder coated sand through the investment aperture-of the core box while the core box is in a non-rotated, i.e., upright, position by causing the uncured binder coated sand to-travel a path under-the force of compressed air upwardly and away from-the investment aperture to a point at which it can flow freely under the force of gravity to a sand separation and collection means. In order to minimize-the exposure-time of the binder coated sand to the effect of the-compressed air, the path of travel of the sand while under the influence of the compressed air is as short as possible and, accordingly, will preferably take the form of a curved path through more than 90° and the direction of which is essentially reversed from the point of discharge from the investment aperture to the point of deposit in the separation and collection means.
Turning now to Figs. 5 and 6, there is shown an embodiment for conducting the discharge of uncured binder coated sand
comprising a sand discharge tube 60 adapted to be sealably engaged about investment aperture 18 of core box 10 by means of sealing member 61 located in sand discharge head 62. Discharge head 62 is connected to three guide rods 63 which slide in two supporting plates 64, 73, both of which are attached to .discharge tube 60. Under the force of springs 72, plate 76, which is attached to the upper ends of rods 63, is normally pushed upwardly, thus disengaging discharge head 62 from-core box 10. When air cup 41 presses plate 76 downwardly, it causes discharge head 62 to seal core box 10 with sealing member 61. The top of discharge head-62 can freely slide inside the end of discharge tube 60. A sand separator is rigidly mounted beneath the outside end-of discharge tube 60 and comprises a housing 68, a pivotally mounted screen 69, a fine sand discharge duct 70 and lump sand discharge duct 71.
After gassing of core box 10 is complete and core box 10 is unsealed by removal of sealing head = 51, sand discharge tube 60 is rotated by cylinder 67 and connecting means 66 so as to position discharge head 62 under air cup 41 which urges it toward core box 10 against the tension of spring means 72 to sealably secure it to core box 10 around investments aperture 18 by means of sealing element 61. Compressed air is then introduced into flow space 20 by means of valve 24^-and port 22 under sufficient pressure to convey uncured binder coated sand from the cavity of the hollow core in core pattern cavity 17 through investment aperture 18 and along the bent or curved path provided by discharge tube 60 and deposit it in the upper chamber 68 of the vibrating screen separator. Fine sand passes through screen 69 and fine discharge 70 into fine sand collector 74. After separation of all fine sand is completed, screen 69 is pivoted to discharge lump sand through lump discharge duct 71 and into lump sand collector 75. The vibrating sand separator is provided with a deflector 77 to direct fine sand away from lump discharge duct 71 and into fine discharge duct 70.
In practicing the method of producing hollow foundry sand cores in accordance with this invention, a charge of binder coated sand equivalent to essentially one volume of the core pattern cavity is metered into the blow head. The blow head is then brought into sealed relationship with the core box and the metered volume of sand blown into the core pattern cavity through the investment aperture, the blow plate being positioned within the investment sleeve at such point as will produce the desired configuration at the aperture of the hollow core, which configuration may, if required, be in the form of a core print. The core box is then sealed with a gas permeable disk in contact with the sand in the core pattern cavity and the sand gassed with an amine catalyst to cure the binder. The depth of cure within the core pattern cavity will be determined by the equilibrium pressure reached between the amine gas and the air in the sand, which equilibrium pressure may be varied by applying a negative pressure to the core pattern cavity. After curing is complete, the core box is purged of residual amine gas and uncured binder coated sand recovered by causing it to flow upwardly under the force of compressed air through the investment aperture, and then to follow a bent or curved path thereafter to be deposited in a screen separator and collected. The hollow core thus formed is then removed from the core box.
The above procedure is repeated in successive core production cycles using fresh binder coated sand in each cycle until a period of time has elapsed equivalent to about 1/10 to 1/3 the bench time of the binder coated sand. At that point in time, the metering of fresh sand to the blow head is discontinued, the metering of recovered sand to the blow head commenced, and the production procedure conducted in the-same manner as-before. Recovered sand is continually metered to the blow head in a quantity equivalent to about the volume of the core pattern cavity for each production cycle until essentially all of the sand introduced during the time period equivalent to 1/10 to 1/3 of the bench life of the binder-coated-sand is consumed in hollow core production. Only at this point; is fresh binder coated sand again metered to the blow head for the commencement of the production of hollow cores as before. The alternating use of fresh and recovered binder coated sand in the method of this invention is an essential feature thereof. At no time are fresh and recovered binder coated sands admixed for charging to the blow head.

Claims

1. A method for the production of hollow foundry sand cores in which binder coated sand is charged to a blow head (40) and invested through an investment aperture (18) of a core box (10) into a core pattern cavity (17) thereof, the sand in the core pattern cavity is gassed with a catalyst to cure the binder and form a hollow sand core, and uncured binder coated sand is discharged from the cavity of the hollow sand core and recovered, characterised by alternatively charging fresh binder coated sand and recovered binder coated sand to the blow head for investment into the core pattern cavity whereby mixtures thereof in the blow head are avoided, the binder coated sand being charged to the blow head by volumetric metering.

2. A method according to claim 1, further characterised by investing the volumetrically metered binder coated sand into the core pattern cavity (17) through a blow plate (44) extending into the investment aperture (18) of the core box (10); inserting a sand seal (52) in the investment aperture in contact with the sand in the core pattern cavity; providing an escape space outside of the core box communicating with the air contained in the sand in the core pattern cavity; and discharging uncured binder coated sand from the hollow sand core formed in the core pattern cavity through the investment aperture.

3. A method according to claim 2, characterised in that the seal (52) is gas permeable and compressed air is introduced through the permeable seal into the core box (10) during exhausting thereof.

4. A method for the production of hollow foundry sand cores in which binder coated sand is charged to a blow head (40) and invested through an investment aperture (18) of a core box (10) into a core pattern cavity (17) thereof, the sand in the core pattern cavity is gassed with a catalyst to cure the binder and form a hollow sand core, and uncured binder coated sand is discharged from the cavity of the hollow sand core and recovered, characterised by volumetrically metering fresh binder coated sand to the blow head (18) for investment into the core pattern cavity (17) where the binder is cured to form a hollow sand core: discharging and recovering uncured binder coated sand from the cavity of the hollow sand core; forming additional hollow sand cores by metering only fresh binder coated sand to the blow head (40) while recovering uncured binder coated sand discharged from the cavities of the cores; discontinuing the metering of fresh binder coated sand to the blow head at a predetermined time; commencing the volumetric metering of recovered binder coated sand to the blow head to form hollow sand cores while discharging and recovering uncured binder coated sand from the cavities of the cores; continuing the metering of recovered binder coated sand to the blow head until the sand is essentially consumed in hollow core formation; and discontinuing the metering of recovered binder coated sand and recommencing the metering of fresh binder coated sand to the blow head, fresh and recovered binder coated sand at no time being simultaneously metered to the blow head.

5. A method according to claim 4, characterised in that fresh binder coated sand is metered to the blow head (40) for a time period equivalent to about 1/10 to about 1/3 of the bench life of the binder coated sand.

6. A method according to any one of the preceding claims, characterised in that the quantity of binder coated sand metered to the blow head is essentially equivalent to the volume of the core pattern cavity.

7. A method according to any one of the preceding claims, characterised in that the uncured binder coated sand is discharged from the hollow sand core upwardly through the investment aperture (18) the core box (10) by compressed air.

8. A method according to any one of claims 1 to 6, characterised in that uncured binder coated sand is discharged from the hollow sand core through the aperture thereof while the core box (10) is in the same position as during charging.

9. A method according to claim 8, characterised in that the sand is discharged upwardly and is thereafter caused to follow a curved path.

10. A method according to claim 9, characterised in that the curved path is greater than 90°.