Note: Descriptions are shown in the official language in which they were submitted.
13~t~ 9
` - 1 - FS 139
MOULDS FOR METAL CASTING AND SEEEVES
CONTAINING fILTERS FOR USE THEREIN
This invention relates to moulds for
metal casting and sleeves containing filters for
use therein.
Moulds such as sand moulds or metal
dies for casting molten metal, usually have a
mould cavity for producing the desired casting
and a running system, usually consisting of a
sprue, one or more runner bars and one or more
ingates,and possibly one or more feeder cavities
located above or at the side of the mould cavity.
During solidification cast metals undergo a
reduction in their volume. For this reason, in
the casting of molten metals into moulds it is
usually necessary to employ feeder heads located
above or at the side of the castings in order to
compensate for the shrinkage which occurs when
the castings solidify. It is common practice to
surround a feeder head with an exothermic and/or
thermally ~nsulated feeder sleeve in order to
reta~n the feeder head metal in the molten state
for as long as possible and thereby to ~mprove
the feeding effect and to enable the feeder head
volume to be reduced to a m~n1mum.
The running system connects the point
of entry of molten metal ~nto the mould w~th the
mould cavity and ensures not only that the mould
cav~y ~s filled w~th mo7ten metal sat~sfactor~ly
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but also that the molten metal flows into the
mould cavity without turbulence. If molten metal
flows into a mould in a turbulent manner, splash-
ing can occur, air can be entrapped in the metal
thus leading to porosity in the casting and when
casting readily oxidisable metals such as aluminium
to oxidation of the metal and the production of
oxide inclusions in the casting. Use of a running
system entails casting more metal than is needed
for producing a particùlar casting itself and it
is not uncommon for the total weight of a casting
running system to be up to about 50X of the total
weight of the metal casting.
It has now been found that the need to
use a running system can be substantially or com-
pletely eliminated by inserting in a mould at the
point of entry of molten metal into the mould
cavity, a sleeve of refractory material having a
ceramic foam fi1ter fixed inside the sleeve.
According to the present invention there
is provided a mould for metal casting comprising
a mould cavity and a sprue communicating directly
with the mould cavity and having located in the
sprue a sleeve of refractory material hav1ng a
cellular ceramic fllter fixed thereln.
Accordlng to a further feature of the
lnventlon there ls provlded for use in a mould
for castlng metal as descrlbed above, a sleeve
of refractory materlal having a cellular ceramic
fllter flxed therein.
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- 3 - FS 139~
As used herein the term sprue means
any passage which is used to provide the sole means
of entry of molten metal into the mould cavity.
The mould of the invention has no
running system apart from the sprue, but in addi-
tion to the mould cavity and the sprue the mould
may also have one or more feeder cavities.
The mould and the sleeve of the
invention may be used for the casting of a variety
of non^ferrous metals, for example, aluminium and
aluminium alloys, aluminium bronze, magnesium and
its alloys, zinc and its alloys and lead and its
alloys, or for the casting of ferrous metals such
as iron and steel.
The mould may be a sand mould pre-
pared to conventional foundry practice or a perma-
nent mould, such as a metal die, for producing
castings by gravity diecasting or by low pressure
diecasting.
The material from which the sleeve
is made must be sufficiently refractory to with-
stand the temperature of the metal to be cast in
the mould. Suitable materials include metals,
ceramic materials, bonded particulate refractory
materials such as silica sand and bonded refractory
heat-insulating materials contatning refractory
fibres. For some applications the sleeve may also
contain exothermic materJals. I
Preferably the sleeve is made
13~45S9
4 - FS 13~T ~
in bonded refractory heat-insulating ~aterial and
is made by dewatering on to a suitable former an
aqueous slurry containing fibrous material and a
binder and optionally particulate ~aterial removing
the sleeve from the former and then heating the
sleeve to remove water and to harden or cure the
binder. Such sleeves can be manufactured
accurately to close tolerances on both their inner
and outer surfaces. This is important because the
outer surface must be such that the sleeve fits
snugly in the sprue of a die or sand ould without
being crushed and without floating of the sleeve
occuring when metal is cast into the die or sand
mould. Accuracy in the size of the inner surface
is important in order to guarantee insertion and
location of the filter. Such sleeves are also
erosion resistant and this ensures that particles
and fibres are not washed from the surface by
metal poured into the sleeve and through the
filter into the mould cavity.
For ease of manufacture the sleeve will
usually be of circular horizontal cross-section
but the horizontal cross-section of the sleeve
may be for example, oval, oblong or square.
The cellular ceramic filter may be for
example a honeycomb type of structure hav~ng cells
which extend between two outer surfaces of the
filter or a structure having interconnecting pores
such as a ceram~c foam.
Ceramlc foam f~lters are preferred and
such filters may be made us~ng a known method of
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13~d~SS~
- 5 - FS 1391
making a ceramic form, in which an organic foam,
usually polyurethane foam, is impregnated with an
aqueous slurry of ceramic material containing a
binder, the impregnated foam is dried to remove
water and the dried impregnated foam is fired to
burn off the organic foam to produce a ceramic
foam.
The filter is preferably located at or
adjacent to the lower end of the sleeve. The
filter may be fixed inside the sleeve by means of
an adhesive.
The refractory sleeve may be formed
integrally with the filt~r by forming it around the
lateral surface of the filter. During forming it
is desirable to cover the open faces of the filter
to prevent the material from which the sleeve is
formed from entering the pores of the filter and
blocking them. When the sleeve and filter are to
be used for casting aluminium the cover may
conveniently be aluminium foil which in use is
immediately melted by molten aluminium poured into
the sleeve.
The sleeve may also be formed in two
parts and one end of each of the two parts may be
fixed to a face of the filter, for example, by
means of an adhesive and the lateral surface of the
filter sealed to prevent leakage of molten metal in
use.
13(~4SS9
- 6 - FS 1391
The sleeve may have one or more ledges
or shoulder on its inner sur~ace for locating the
filter in the desired position.
The length of the sleeve may be the
same as or similar to the thickness of the filter
so that the sleeve is in the form of a ring around
the filter. However, it is preferred that the
length of the sleeve is appreciably larger than the
thickness of the filter, so that the molten metal
can be poured into the sleeve, thus avoiding the
possibility of metal leaking into the mould cavity
around the outside of the sleeve. If desired, to
aid filling of the sleeve, the upper end of the
sleeve may be flared in the shape of a funnel.
In order to insert and locate the
sleeve in the sprue of the mould it is preferred
that the outer surface of the sleeve is tapered and
that the sprue has a corresponding taper, the
direction of taper depending on whether the sleeve
is to be inserted in the sprue from above or below.
It is also preferred that the outer surface of the
sleeve or the mould surface surrounding the sprue
has means for holding the sleeve firmly in position
once it has been inserted in the sprue. The means
may be for example protrusions such as ribs on the
lateral surface of the sleeve or protrusions such
as ribs formed on the sprue of a sand mould by the
use of a recessed former during mould production or
in the case of a metal mould or die protrusion such
as ribs ma~chined on the mould or die surface
surrounding the sprue.
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7 FS 1391
The refractory sleeve is preferably
located in the sprue such that the lower end of the
sleeve and the filter are not in contact with the
casting. This can be achieved for example by
incorporating a ledge above the base of the sprue
and seating the sleeve on the ledge.
When a casting requiring a feeder is
produced using the mould and sleeve of the invention
it is possible to locate the sleeve containing the
filter in the feeder cavity and to utilise the
feeder as the sprue. In such applications it will
be usual to use a sleeve which has exothermic and/
or heat-insulating properties as well as being
refractory in order to achieve satisfactory feeding
Of the casting.
By the use of a sleeve of refractory
material having a filter therein and a mould
according to the invention, having no running
system, apart from the sprue, it is possible to
produce castings more economically compared with
conventional practices of sand casting or gravity
diecasting metals because elimination of the running
system significantly reduces the weight of metal
wh;ch must be cast to produce a particular casting
and less fettling of the casting is needed.
The construction of a sand mould or
the design of a die for gravity diecasting is
simplified and both can be made smaller compared to
conventional sand moulds or dies. An existing die
may be modified to produce a mould according to the
invention by blocking off its running system and if
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13~4SS~
- 8 - FS 1391
necessary, machining the sprue of the die to allow
insertion of the sleeve.
Furthermore, metal can be cast at
lower melt temperatures and in the case of gravity
diecasting, at lower die temperatures.
Castings produced in moulds according
to the invention have improved directional
solidification characteristics and are substantially
free-from porosity and inclusions and as a result,
have good mechanical properties such as elongation
and good machinability and are pressure tight.
The invention is illustrated with
reference to the accompanying drawings in which
Figure 1 is a vertical cross-section
of a sleeve according to the invention
Figure 2 is a vertical cross-section
of a conventional sand mould for producing an
aluminium plate casting
Figure 3 is a vertical cross-section
of a sand mould according to the invention for
producing the aluminium plate casting of Figure 2
Figure 4 is a vertical cross-section
of a further embodiment of a mould according to the
invention
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13~45~
- 9 - FS 1391
Figure 5 is a diagrammatic top plan
of an aluminium cylinder head casting produced in a
conventional metal die by gravity diecasting and
Figure 6 is a diagrammatic top plan
of the aluminium cylinder head casting of Figure 5
produced in a mould according to the invention by
gravity diecasting.
Referring to Figure 1 a sleeve 1 made
in refractory heat-insulating material has an outer
surface 2 which tapers from the bottom 3 of the
sleeve to the top 4. The inside of the sleeve 1
has a ledge 5 at the bottom 3 of the sleeve 1 on
which there is fixed a ceramic foam filter 6. In
use the sleeve 1 is inserted into a mould sprue
having a taper corresponding to that of the outer
lateral surface 2 of the sleeve 1.
Referring to Figure 2 a sand mould 11
having a mould cavity 12 for producing an aluminium
plate casting has a pouring bush 13, a running
system comprising a sprue 14, a well 15, a runner
bar 16 and an ingate 17 and a feeder cavity 18.
The feeder cavity 18 is lined with a cylindrical
heat-insulating feeder sleeve 19 made in bonded
fibrous and non-fibrous particulate refractory
material.
In use molten metal is poured into
the pouring bush 13 and flows through the running
system and into the mould cavity 12 and the feeder
ca~ity 18.
13~45S~
lo - FS 1391
Referring to Figure 3 a sand mould 21
for producing an aluminium plate casting identical
to that to be produced in Figure 2 has a mould
cavity 22 and a sprue 23. The mould has no pouring
bush and no running system. The sprue 23 is lined
with a refractory heat-insulating sleeve 24 made in
bonded fibrous and non-fibrous particulate
refractory material and the sleeve 24 has a ceramic
foam filter 25 located adjacent its lower end 26.
In use molten metal is poured into the sprue 23 and
flows through the ceramic foam f;lter 25 into the
mould cavity 22. Pouring ceases when the sprue 23
is full of molten metal.
Moulds of the type shown in Figure 2
1s and Figure 3 were used to produce aluminium plate
castings measuring 26 cm x 26 cm x 2 cm. The total
weight of metal cast using the Figure 2 mould was 5 kg
and t~e total.weight of metal cast using the Figure
- 3 mould was 3 kg. Using a mould according to the
invention therefore gave a saving of 2 kg in the
total weight of metal cast.
Referring to Figure 4 a sand mould 31
for producing a plate casting has a mould cavity 32
and a sprue 33 having an upper part 34 and a lower
part 35. The lower part 34 is formed by a tapered
former which has longitudinally extending recesses
in its lateral surface and the recesses form ribs
36 on the surface of the mould material surrouoding
the lower part 35. A sleeve 37 having a ceramic
foam filter 38 fixed therein as shown in Figurel
is inserted into the lower part 35 of the sprue 33
i3~45S9
~ FS 1391
and is held firmly in place by the ribs 36. In use
molten metal is poured into the upper part 34 of
the sprue 33 and the metal passes through the
ceramic foam filter 38 into the mould cavity 32.
Referring to Figure 5 an aluminium
cylinder head casting 41 produced in a gravity die
having four cylinders 42 and two valve ports 43 per
cylinder has a running system consisting of a sprue
44 connected via runner bars 45 and ingates 46 to
the cylinder head and three cylindrical feeders 47
and an elongate feeder 48. The casting 41 is
produced by pouring molten aluminium into the
sprue 44 so that it flows through the running
system into the die cavity and the feeder cavities.
~eferring to Figure 6 an identical
aluminium cylinder head casting 51 to that shown in
Figure 5 having four cylinders 52 and two valve
ports 53 per cylinder has three cylindrical feeders
54A, 54B, 54C and an elongate feeder 55 but no
running system. Prior to production of the casting
a refractory sleeve made in bonded fibrous and
non-fibrous particulate refractory material and
having a ceramic foam filter fixed inside the sleeve
at one end was inserted into the cavity of the
gravity die for producing the central feeder 54B of
the three cylindrical feeders so that the bottom
end of the sleeve containing the ceramic foam filter
was just above the top of the die cavity. The
casting 51 was produced by pouring molten a1uminium
into the cavity for feeder 54B so that it passed
through the sleeve and the filter into the die
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- 12 - FS 1391
CdVity and the other feeder cavities. The total
weight of the casting shown in Figure 5 was 19.0 kg
made up of 10.5 kg for the cylinder head itself,
6.0 kg for the feeders and 2.5 kg for the running
system. The total weight of the casting shown in
Figure 6 was 16.5 kg thus resulting in a saving of
cast metal of 2.5 kg compared with the Figure 5
casting.
