The present invention provides an improved process for
production of metal castings such as intake manifold

castings.
The present practice in foundries is to use a shell sand

core for casting. Sand core is a poor conductor of heat. As
a result, when molten metal is introduced into the sand core,
heat dissipation through the walls of the sand core is very
slow. Therefore, molten metal in heavy and isolated casting

areas remains hotter for a longer time than in other areas of

the casting. This results in shrinkage/porosity problem In

order to solve this problem, the casting area in which
shrinkage occurs has to be fed with molten metal from

additional feeders, or this area has to be cooled faster. In
many cases, it is hot possible to use additional feeders or
risers So, in prior art faster cooling, called 'chilling'

was adopted. It is also known in the prior art to provide an
aluminium paint coating on sand cores where porosity is
likely to appear. But this has not been found to be
satisfactory. Further, in the case of heavy castings where

the section is very heavy, such a method does not solve the
problem of porosity
The object of the present invention is to provide a
process for production of metal castings which eliminates the
occurrence of shrinkage/porosity, especially in heavy
castings The present invention envisages to eliminate, or

at least minimize shrinkage problems in complicate castings

in permanent gravity/tilting gravity molds usxng shell sand
cores.
Accordingly, the present invention provides an improved
process for production of metal castings, said process
comprising:
(a) placing in a casting mold a shell sand core having the

pattern of the metal casting to be produced;
(b) introducing molten metal into the casting mold,
(c) allowing the molten metal to cool to form the metal
casting; and
(d) removing the metal casting from the casting mold;
characterized by:
(i) cutting out portions of the shell sand core
corresponding to the portions of the casting having
defects, to form shell sand core portions;
(II) dressing each shell sand core portion to the shape of a
chill to be produced;
(III) positioning a said shell sand core portion in a casting
mold and pouring molten metal into the mold to produce
a chill mold,
(IV) pouring molten metal into the chill mold to produce a
chill;
(v) repeating steps (iii) and (iv) for each shell sand core
portion to produce chills,
(vi) shot blasting the chills by methods known per se to make
the surfaces thereof rough;

(vii) preheating the chills to about 100 to 150°C;
(vxii) positioning the chills of step (vii) at appropriate
positions in a shell core mold mounted in a shell core
shooting machine,
(IX) injecting resin-sand mixture into the shell sand core
mold and curing the mixture to produce a chill core
comprising a shell sand core embodying said chills;
(x) placing the chill core in said casting mold and
thereafter pouring molten metal into the casting mold to
produce said metal casting.
It is preferable to make the chills of aluminium,
instead of cast iron or steel for the following reasons:
(a) Molten aluminium is readily available in the foundry and
hence economical;
(b) Latent heat of aluminium is 93 cal/g, as compared to
latent heat of 63.7 cal/g of iron; so, aluminium chills
formed can absorb more heat than iron;
(c) Thermal conductivity of Al is 0.5 cal/cm /cm2/S/cc) ,
which is 3 times more than that of iron; so, chilling
effect of aluminium chill is three times faster than
that of iron chill,
(d) The chills can be produced by mass production, with the
help of simple molds which are prepared using the
casting portion itself as the pattern;
The invention will now be described by way of
illustration with reference to the accompanying drawings,
wherein

Fig. 1 shows an intake manifold casting with prior art
process;
Fig. 2 shows shrinkage porosity observed in the casting of
Fig. 1;
Figs. 3 and 4 show close-up view of the shrinkage porosity
and air leak in the casting of Fig. 1;
Fig 5 shows a casting having a chill in the area of
shrinkage porosity according to a first embodiment of the
present invention;
Fig. 6 shows a close-up view of the casting produced by the
first embodiment of the present invention;
Fig. 7 shows a graph of air leak in a casting without chills
and a casting with chills according to the present invention;
Fig. 8 shows an intake manifold casting produced by a second
embodiment of the method of the present invention;
Figs. 9 and 10 show a close-up view of a casting of prior art
surrounded by sand core on three sides;
Figs 11 and 12 show close-up views of a casting produced by
the second embodiment of Fig. 8;
Fig. 13 shows graph of air leak without chills and with
chills.
Fig. 1 shows an intake manifold produced by known
processes. In this case, molten metal is fed from a main
riser 1 into a casting mould 2 filled with sand core 3. When
the casting is removed from the mould 2, it is observed that
there is shrinkage 4 Fig. 2 shows the shrinkage 4 in a

greater detail.
It is known to apply aluminium paint 5 (Fig. 3) on the
sand core at places where the casting is likely to have
shrinkage. Even when such aluminium paint is used, in the
case of heavy castings or castings of complicated shapes, the
shrinkage cannot be eliminated. It is seen from Fig. 4 that
when drilling is carried out, air leak (6) is observed.
In order to overcome this problem, the present invention
proposes use of chills embodied in the shell sand core.
First of all a casting is produced by the known
processes. Then, the areas of shrinkage porosity in the
casting are identified. Thereafter, the shell core portion
corresponding to these areas are cut from the shell sand
core. Thus, the shell sand core 3 itself is used as the
pattern Each shell core portion is dressed and shaped to
the desired shape of the chill to be produced. Each shell
core portion should preferably be of a size at least twice
the size of the defective area, (preferably two to three
times the size of the defective area), so that the chill does
not get melted by the molten metal during casting. A shell
core portion is placed in a casting mold and metal is poured
into the mold. After cooling, the metal solidifies to form a
chill mold. The cavity in the chill mold is preferably
coated with dycote. Metal is poured into the chill mold and
allowed to cool and solidify to form a chill. During
pouring, the temperature of the molten metal is preferably

kept below 700°C. The chill is removed from the casting
mold. Burrs and fleshes on the chill are removed by methods
well known in the art. Thereafter, the chill is shotblast by
methods known per se. These steps are repeated for each
shell core portion.
The chills are then preheated to about 100 to 150°C and
placed at appropriate positions in a shell sand core mold of
a shell core shooting machine. Resin-sand mixture is
injected into the shell core mold and cured to form a chill
core comprising shell sand core embodying the chills. The
chill core is positioned in the casting mold. Thereafter the
molten metal is introduced into the casting mold. After
cooling the metal casting is taken out. When the sand is
knocked out of the casting mold, the chills also drop,out and
can be re-used
Figs. 5 and 6, it can be seen that chill core comprises
shell sand core 3 with sand core portions 7 corresponding to
the identified defective area encast therewith. From Fig.
6, it can be seen that the casting 8 produced does not have
any porosity even after drilling operation is carried out.
For checking air leak, tapped holes were drilled in the
castings produced by known process and the process according
to the present invention From the graph shown in Fig. 7, in
the case of a casting made without the use of chill core, it
can be seen that the air leak was quite high. But when chill
core was used according to the present invention, there was a
dramatic elimination of air leak, indicating that the casting

had no shrinkage porosity.
Fig. 8 shows an intake manifold casting produced with
shell sand core 3 on three sides. When no chill core was
used, an area 4 having shrinkage porosity was identified.
The shrinkage was observed in the casting area formed by sand
cores from three sides. This was due to poor conductivity of
the sand cores. This caused shrinkage/ porosity in the
identified area.
In Fig. 9, the aluminium casting portion 9 has a central
sand core 31 and also sand cores 32, 33 and 34. From Fig.
10, it can be seen that a portion 91 of the casting is
surrounded by sand cores 32, 33, 34. Due to poor
conductivity of the sand cores, area 4 of shrinkage porosity
is formed. This cannot be eliminated-even by application of
aluminium paint, especially in the case of heavy castings.
In order to overcome this problem, chills 7 made as
earlier described are encast with the sand cores at the
places where porosity is observed. This is shown in Fig. 11.
From Fig. 12 is can be seen that porosity is almost
eliminated.
Air leak tests were carried out on castings produced by
known method and - castings produced by the method of the
present invention As can be seen from Fig. 13, air leak was
high in castings produced by known methods, whereas there was
very little air leak in castings produced with chill cores
according to the present invention
The present invention is very useful in producing

aluminium castings having complicated shapes with no
.shrinkage or the least1 shrinkage.

In the prior art, shrinkage was a problem. Although use
of aluminium paint can be adopted, it cannot fully eliminate
the problem of shrinkage porosity. Further use of aluminium
paint with alcohol entails higher cost of production. Also,
when air-cleaning the mould, aluminium paint particles fly
around and form a pollution hazard around the foundry.
Further, use of aluminium paint does not solve the problem of

shrinkage in heavier castings and castings having complicated
shapes.
In the present invention, chill cores are used. These
have high heat conduction property. As a result, fine grain
size is obtained in the castings. In heavier castings,
shrinkage can be minimized to a great extent. Also, this
eliminates the use of additional feeders or risers and thus
greatly reduces the cost of production. Further in certain
cases, it may not be possible to provide such additional
feeders or risers. In addition, chill cores can be made in
the same foundry where the castings are made. Thus the
process according to the invention is very economical. In
addition, the chills can be taken out of the shell sand core
after casting and re-used.

Although the chills can be made of any metal having a

good thermal conductivity, aluminium chills are preferred.

The present invention is very economical for production of
aluminium castings of heavy sections or complicated shapes

WE CLAIM
I An improved process for production of metal castings, said process comprising
(a) placing in a casting mold of shell sand coie having the pattern of the metal
casting to be produced,
(b) intoductng molten metal into the casting mold,
(c) allowing the molten metal to cool to foi in the metal casting, and
(d) removing the metal casting fiom the casting mold, characterized by.
(1) cutting out portions of the shell sand core (3) corresponding to the portions (7)
of the casting having defects, to form shell sand core portions,
(ii) dressing each shell sand core portion to the shape of a chill to be produced,
(iii) positioning a said shell sand core portion in a casting mold and pouring molten
metal into the mold to produce a chill mold,
(IV) pouring molten metal into the chill mold to produce a chill,
(v) repeating steps (iii) and (iv) for each shell sand core portion to produce chills,
(vi) shot blasting the chills by methods known per se to make the surfaces thereof
rough,
(vu) preheating the chills to about 100 to 150° C,
(viii) positioning the chills of step (vu) at appiopriatc positions in a shell sand core
mold mounted in a shell core shooting machine,
fix) injecting resin-sand mixture into the shell sand core mold and cuting the
mixture to produce a chill core comprising a shell sand core embodying said chills,
(x) placing the chill core in said casting mold and thereafter pouing molten metal
into the casting mold to produce said metal casting (8)
2. A process as claimed in claim 1, wherein said chills are made of aluminum
3 A process as claimed in claim 3 or 2, wherein in step (ii), the chills are formed to
have a size at least twice, preferably two to three times, the size of the area which is pione to
shrinkage porosity

4 A process as claimed in any of claims 1 to 2, wherein in step (iv), prior to pouring
metal into the chill mold, the cavity in the mold is coated with dycote
5 A process as claimed in any of claims 1 to 4, wherein in step (iv), the temperature of
the molten metal is maintained below 700° C

ABSTRACT

IMPROVED PROCESS FOR THE PRODUCTION
OF METAL CASTINGS
The invention discloses an improved process for production of metal casting, wherein the
shrinkage porosity on solidification of the metal in the mold is avoided or minimised by (1)
cutting out portions of the shell sand core (3) corresponding to the portions (7) of the casting
having defects, to form shell sand core portions, (11) dressing each shell sand core portion to
the shape of a chill to be produced, (iii) positioning a said shell sand core poition in a casting
mold and pouring molten metal into the mold to produce a chill mold, (IV) pouring molten
metal into the chill mold to produce a chill, (v) repeating steps (iii) and (iv) for each shell
sand core portion to produce chills, (vi) shot blasting the chills by methods known per se to
make the surfaces thereof rough, (vii) preheating the chills to about 100 to 150° C, (viii)
positioning the chills of step (vii) at appropriate positions in a shell sand core mold mounted
in a shell core shooting machine, (ix) injecting resin-sand mixture into the shell sand core
mold and curing the mixture to produce a chill core comprising a shell sand core embodying
said chills, (x) placing the chill core in said casting mold and thereafter pouring molten metal
into the casting mold to produce said metal casting (8)