Note: Descriptions are shown in the official language in which they were submitted.
6 ~ :1 8
The present lnvention relates tq the low Rressure
casting o~ metal parts, for example from pig iron, in a mould
compX;~sing a thin-walled form made of a hardened mixture of
sand and res~n.
Low pressuxe casting~ in which ~ound~y ~oulds are
supplied from the bottom at a pressure greater than atmospheric
pressure, but substantially less than 2 bars, is known. The
advantage of the latter is that it facilitates the filling of
forms of complicated shape, which would be poorly filled by
simple gravity casting, and that it lends itseld to automation
in the control of successive casting operations, whilst elimin-
ating troublesome and dangerous operations of handling tilting
casting ladles or casting ladles comprising a stopper-rod.
lS Furthermore, by using suitable means for supplying the mould
and controlliny the pressure (see for example French Patent
No. 7,442,713 in the name of the Applicant published under No.
2,295,808), low pressure cas-ting can eliminate shrinkage-heads
and certain casting appendages.
It is known that low pressure casting is frequently
carried out in sand forms, in particular in order to ob~ain
certain metal structures. This is the case, for example,
when it is desired to produce from spheroidal graphite cast
iron rough-cast parts which have no carbides in the rough-cast
state, without the need for any subsequent thermal trea-tment.
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This result is due essentiall~ to the re~xactory nature
of the sand~ ~hich forms a therm~1 barrier that eliminates a
hardenin~ phenomenon of the cast me~al.
In addition, one thus benefits from the permeability to
gases of the sand.
Thus, moulds with walls consistlng of sand prevent cast-
ing faults and reduce rejects.
Xowever, the use in this method of conventional sand
moulds, which are solid, causes difficulties: on account of the
fact that the filling pressure is maintained for a prolonged per-
iod of time, the moulds must have a relatively high mechanical
strength. It is therefore necessary to use sand comprising a
greater proportion of binding agent and/or moulds which are thic-
ker than in the case of simple gravity casting. But this in-
creases the cost price of the parts, since the moulds, which can
be used only once, are more expensive to produce, and cooling of
the parts becomes too slow, which considerably reduces the pro-
duction rate, if only on account of the delay necessary for the
solidification of the inlet point of the metal into the moulding
cavity.
This is why an attempt has been made to limit the quan-
tity of sand used. In a known solution (see the Applicant's
French Patent No. 77 08 364 published under No. 2,384,568), the
sand form is enclosed in a metal shell. The shell must thus be
` changed for each shape of cast part. In addition, the shell fre-
quently requires
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machining, albeit rough machining.
The object of the present invention is to provide
another solution which is more flexible and more economical,
for casting of this type, thus, ensuring an effective
support for the sand form, and enabling the latter to
withstand the force of the metal under pressure.
According to the present invention there is
provided in a method of low-pressure casting metal parts
in a thin-walled sand form, the improvement comprising
packing the sand form within a mass of magnetisable
particles, compacting the mass prior to casting, and
rigidifying the mass of particles by means of a magnetic
field.
The invention also relates to a mould for use in the
low-pressure casting of metal parts, comprising a closed box having
in an upper part -thereof a closable opening enabling it to be filled
with magnetisable particles, a casting orifice in the bottom of
the box, and a sand form adapted to rest on the bottom of the box
and be packed within the magnetisable particles, said sand fo.rm
having a casting orifice in communication with the casting
orifice in the closed box.
. The invention also relates to a low-pressure
casting installation of metal parts, comprising a
reservoir for molten metal, a substantially vertical
supply pipe in the reservoir, means for supporting a
mould as defined above and pressing the casting orifice
thereof against the upper end of the supply pipe, means
for supplying propellent gas to thP reservoir to force
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molten metal up the supply pipe, and an electro-magnet
which is placed around the mould during a casting operation
to rigidify the magnetisable particles.
The inv~ntion will now be described in mora
detail, by way of example only, with reference to the
accompanying drawings in which:-
Figure 1 is a partial diagrammatic view ofvertical section of an installation according to the
Figure 2 is a partial plan view of this
installation.
The low pressure casting installation illustrated
comprises a casting ladle 1, a frame 2 and a number of
identical moulds 3, of which only one has been shown. The
dimensions of the mould 3 have been exaggerated with respect
to those of the ladle 1 for the sake of clarity.
The ladle 1 comprises a container 4 of large
dimensions containing liquid metal 5 and comprising an
oblique filling spout 6 closed by a lid 7. A vertical
supply pipe 8 of refractory material passes through the
upper wall of this container. It descends virtually to
the bottom of the lattPr and projec~s thereabove over a
short length, where it is surrounded by a reinfoxcing
~0
5 -
11B~8~
nozzle 9 of general frustoconical shape. The upper end of the
pipe 8 is conta.ined in.the same horizontal plane ~ as the fla~
upper side of the nozzle 9.
A pipe 10 co.mmunicating with the inside of the container
4 may be connected, under the control of a v~l~e 11, either to
a source of compressed gas, for example compressed air, or to the
outlet.
The frame 2 comprises four telescopic uprights 12 pro~
vided with helical springs 13. The uprights 12 support a hori-
zontal table 14 pushed permanently upwards by the springs 13.
Fixed below the table 1~ are vibrating devices 15, whereas an
electro-magnet 16 of U shape comprising two parallel sides or
arms 17 connected by a coil 17a is positioned on this table.
The table 14 comprises a frustoconical orifice 18 mating
with the outer surface of the nozzle 9. In the lower position of
the table, the orifice 18 bears on this surface and the upper side
of the table is contained in the plane P described above.
The frame also comprises a retractable vertical jack 19
located at a slightly higher level,strai~ht above the ladle 1.
The mould 3 is constituted by a box 20, sand form 21,
and a mass of particles 22. The box and mass 22 are common to
all the moulds, in contrast to the sand form 21.
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The box 20 is a para:Llelepipedal metal box whereof the
length is s]ightly less than the distance separating ~he two
sides 17 of the electro-magnet 16. I'he base of this box h~s a
frustoconical opening 23, which .is convergent in the downwards
direction, whereas its upper wall constitutes a removable lid
or pressing plate 24. The opening 23 opens to the ou-tside in a
xebate 25 of slight depth.
The sand form 21 is in the form of a thin-walled shell
consisting of a hardened mixture of sand and theremosetting re-
sin, such as an isocyanate resin or a phenol-formaldehyde resin.
This shell, divided into two halves along a horizontal interface
Q, defines with an inner core 2~, a moulding cavity 27 in the
shape of a part to be cast, which is for example a gate-valve
body.
The lower half-shell comprises a tubular extension 28,
which defines a main conduit or inlet 29 of the same diameter
as the pipe 8. Externally, this projection is frustoconical and
fits the opening 23 in the box. When it is fitted in this open-
ing, its end face is flush with the bottom of the rebate 25.
The conduit 29 comrnunicates with the moulding cavity solely
through a small horizontal conduit or secondary inlet 30.
2~ Externally, the shell 21 has annular stiffening or streng-
thening projections, one of which, bearing the reference numeral
31, is at a distance from the extension
~ 8 -- .
28. ~.~en the shell is pl~ced i~ the box 20, which leaves
a considerable clearc~ce on all sides, the pro3ection ~1
rests on the botto~l of this bo~, possibly throu~h the
intermedi.ary of a wedge 32 as illustrated. ~he shell is
thus perfectly positioned, in ~ stable man~er, without
the sand being subjected to excessive stress~ ~he space
remaining free in the box 20 is filled with the mass 22
constituted by compressed ma~netisable iron shot~ the
grain si.ze of which is 17/10 mm for exaL~pleO
. ~
~e operation of this installation is as follows.
At the beginnin~, the casting ladle 1 containing
liquid metal 5, for example pig iron, is kept under a
moderate air press~re, for examp].e of ~he order of 1 bar,
through the conduit 10. Under the effect of thi~
pressure, the pig iron is`located in the suppl-~ pi.pe 8
at a level ~ substantially lower than the lev~l of t;he
outlet operling o.f this pipe. rrhe tablc ~14 is in the
upper position unde~ the action of the springs 13~ -the
jack 19 being retracted as i.s the lid 24. ~he LatJGer
-may moreover be integral with the piston rod of the
jack 19.
An adhesive sealing washer ~3, for example of the
type described in the c~orementioned ~rench Pate~t No. ..
. 74 42 713, is placed in the reba.te 25 of the bo~ 20,
which is then placed on the table 1~ between the arms o
the electro-magnet 16 c~d positiorled so that its orifice
23 is centered Oll the orifice 18 of this tableO
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A slight clearance, for example of 0.5 n~, not visible in the
drawin~, then e~ists between each arm 17 and the adjacent side
of the bax 20. ~ shell 21 is placed len~thwise on the base of
the box 7 in order tobe ~ppoxted by its pxojection 31 and po-
sitioned and supported by its extension 28.
Despite the weight of the ~ould and of -the electromag-
net, the springs 13 are not completely compressed and thus lift
the table 14 slightly, so that the washer 33 is still not com-
pressed.
Magnetisable iron shot is then poured or blown into thebox 20 in order to fill its lower part, between the shell 21 and
the bottom of the box, as well as its upper part, in order that the
shell is covered completely. The outer shape of the shell 21,
constituted almost e~clusively by rounded surfaces, promotes the
introduction of shot below the shell
Then, the vibrators 15 are set in action, in order to
cause the table 14 to vibrate on its springs 13 and to pack the
mass of shot 22 in a suitable manner~
During this packing o~eration, the level of shot in
~ the box 20 drops. The latter is then topped-up with shot and
packing and refilling are recommenced until the level of shot is
flush with the upper part of the box 2n. When it has been pac-
ked in a suitable manner, the mass of shot 22 has the minimum
of gaps therebetween, in particular in the vicinity of the shell
and the maximum density.
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After vibration and packing, -the electro-m~gnet 16 is
excited, and subjects the ma~s of shot 22 to ~ powerful m~gnetic
field, which rigidifies it. The vibrations are sto~ped immedia-
tely after the shot-fillin~ opexation and be~ore the excitation
of the electro-ma~net.
The mass 22, packed in this way and hardened, provides
an excellent rigid support for the shell 21. The arrangement is
virtually equivalent, from the mechanical point of view, to the
metal shell lined internally with sand and described in the afore-
said French Patent No. 77 08 364.
The pressure plate 24 is then put in position and lower-
ed by the jack 19 in order to press the mould 3 with force against
the vibrating table 14. This compresses the springs 13 and pres-
ses the opening 18 in the table agains-t the nozzle 9. The seal-
ing washer 33 is compressed between the latter and the bottom of
its housing.
For reasons of safety, at least one clamp 34 can be
placed around the mould 3 and the table 13 in order to complete
the inter-locking of these two parts of the installation, which
is now ready for casting.
In order to carry out the latter, the valve 11 is opened
and air, for example at a pressure in the order of 1.2 bars, is
introduced into the container 4 above the liquid pig iron 5.
The pig iron rises, through the pipe 8,
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the main inlet 2~ and the secondary i~let 30 into khe said ~orm,
which it fills completel~. The force which the metal introduced
under pressure exerts on the walls of the shell 21 is counter-
balanced by the resistance offered by the mass of shot 22, which
is packed and rigidified, and bythe pressure plate 24, which pre-
vents rising of the mould 3 above the table 14.
During casting, the magnetic mass 22 remains relatively
cold, in particular in the vicinity of the shell 21, where its
temperature scarcely exceeds 200C owing to thè refractory nature
of the shell, which does not transmit the heat from the cast iron.
In the upper part of the mould, the mass of shot is quite cold.
This mass thus remains magnetic and rigid, since it is far from
the Curie point of 750C at which iron loses its magnetic pro-
perties.
It will be noted that, during casting, no gas is liber-
ated outside the mould 3, although the gases produced are able
to leave the casting form through the porous shell 21 and the
permeable mass of shot 22. It is considered that, since the
mould 3 is completely filled with shot in its upper part and
the mass 22 remains cold, the gases spread out in this mass with
a tendency towards condensation, which prevents them from rising
to the upper end of the mould.
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~3 Af-ter :Eilling the ~ YY~5~ with liquid plg i.rorJ
and after the pres~u.re is maintai~ed for a c~rtai.n
relatively short period of time., correspondin~r to the
solidification of the secondary inlet 30 after a~
adequate supply of pig iron to th.e impression, as
described iIl the said ~rench Patent No- 74 ~2 713, the
pressure ls released in the laclls 1 by supplying through
the conduit 10 a pressure which is less than the casting
pressure b~t,sufficient to restore the pig iro~ solely to
a leval N1 illustrated in broken lineg close to the upper
part of th~ noæzle 9.
~he supply of electric current to the electro magnet
16 is -theIl cutr The pressure plata 2~ is raised and
retracted with the jack 19 and the mass of shot 22 is
removed at least p~rtly from the mould 3 which has just
been filled with cast iron. ~his operation takes place
under a hood which is not shown, since it is at thi~ ti.me
that the gases formed {~uri~g caæting and which have been
.r~tained up till then in the upper part of the mass of
shot 22, outside the shell 21, are liberated, probabl~
by evaporationO When this shell has been exposed
suff1.ciently from the mass of shot9 it is removed with
the caæting, stripping of which is then carried out.
~or the subseque~t casting operation~ it is su~'ficient
to introduce a new shell 21 provided with itæ core 26, L
into the remalning shot, in the same box 20 once more
placed cn the table 145` then to complete the operation o~
~illingr wi-th shot, usin~ -t~e shot which has just been
removed from the preceding mould 3 and to carry ~ut
packing and the other successive opera-tions which have
been described. In practice, it is unnece~sary to
remove all the shot after each castingg since the latter
retains its confi~uration to a certain extent, when the
shell 21 is extracted therefrom~
As a n~nerlcal example, l~ o~der to cast a ~alve
body from cast iron having a weight of` 60 kg with a
tubular diameter of 200 mm, the box 20 measuring 850 x
95Q x 500 mm, the mass 22 i5 ~ubjected to a ma~netic
f~ad of 4000 gauss, this field depending on the section
of sho' to be made rigid and thus ~n the distance
between the arms 17 of the electro-magnet. ~he grain
size of the shot is chosen to be sufficientl~r fi~e to
leave the minimum nurnber of gaps, 3ince gaps lsad to ~m
increase in the ma~netic field necessary~ without however
loading the mou]d excessively. '~he cast part o~t~lned
has a skin, i.e. an outer surface condition, of very fine
-20 appe~ra~ce a~d has very accurate dimensions.
Since a low pressure casting process is u~ed 9 liquid
metal which is alway~ ho-t is introduced into the-6s~
and this liquid metal is naver apparent
externally, which guarantees the comfort and safet~r of the
operators who may be in the vicinity of the installation.
Furthermore, the risin~ and falling of the iquid r~etal in
the pipe 8 takes place simply by operati~g the valve 11
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and con.~ection to a sol~ee of suitable p~es~11re or to a
discharge, which can b~ easily autom~ted. Thus, the
supply of liquld metal to the mould has no -troublesome
nor d.angerous ~eat~res, Owing to t-h~ vibrating means 15,
the density o~ the mass 22 is s~fficient to guarr~tee
that there are no loeal gaps in contaet with the shell
eausi.ng locally defec-tive external support for the
latter and consequently a risk o~ deformation and rupture
under the foroe of liquid metal~ despite the fac-t that
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the mass 22 ls made rigld by the magnetic field.
r~he mass of shot 22 :is inter-ehangeable and
eompletely reusable whatever the shape of casting
impression r~.d the eomplementar~r equipment eonstituted
by the vibrato.rs 15 and eleetro-magnet 16 comprise solely
parts whieh are easily avai.lable. ~he method of the
invention i.s -thus very eeonomieal.
~he casting method described is well ~uited -to
producin~ parts of' com~licated shapes. ~he o~l~
limitations as regards volume and weiOht of the castings
which are able to be east are dependent on the power of
the maglietie f-.ield which can be produced bv means of the
el~ctro-magQet 16~ Thus? with a ma~neti.c field of 4000
~auss, one can produee p~rts weig~ing up to 500 kg.
As a variation, the mould 3 eould be filled with
shot and vihrated a.way from the casting station~ o~
ano~her vibra-ting ~.a~le~ In thls case~ the table 149
serving ~olely to reeeive the mould at the casting station
,
1 1 6B ~ 3
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~nd to support the electxo-ma~net 169 would no longer b0
provi.d.ed wit~ vibrati.ng mea~s 15.
In a1l cases, one attempts to ~ive the shell
exte~nal shape which .~aci.litates good distribution o~
the shot, even if the mould.~ng cavit~ doe~ not have
correspondingr shapesO ?.he la-tter ma~ be rounded
surfaces~ as in the example illustrated~ or an~ other
sultable deI~lecting shape according to the technique of
filling the box.
