[0001] The present invention relates to a method for the production of hollow foundry sand
cores.
[0002] 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.
[0003] 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.
[0004] 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..
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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°.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
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°.