Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The inven-tion relates to a method oE producing frozen
casting moulcls or cores of a granular material and a binder in a
mould chamber or a core box, comprising the use of a Ereezable
binder which is in a gas or liquid state a-t posi-tive temperatures
calculated in degrees cen-tigrade.
The specification of the IJni-ted States Patent 4,150,70
-teaches a method in which the mould sand is admixed with a
controlled quantity of water which after moulding is frozen to
iee in a certain depth from the surface tha-t is caused to eontaet
molten metal e.g. by placing a layer of so-called dry ice or
spraying liquid nitrogen on the surface. This gives a very strong
mould surface which retains its strength and shape until the
surface of the metal has solidified. As the metal gives off its
heat, the water melts and evaporates so that the mould begins
collapsing without the use of mechanical means, practically no
srnoke is developed in the casting process, and the mould sand can
be reused right away.
An article in the Russian Magazine Liteinoe Proizvodsto,
1975, No. 5, P.21-22, describes the freezing of a sand mould
containing 3 to 7 percent water by means of a coolan-t that
circulates through the evaporator in a cooling system and through
mould.
Freezing of the added water is by nature a rather slow
process r and consequently it takes a relatively long time from
the moment when the moulding process is finished until the mould
has frozen deep enough to be able to resist the effect of molten
metal for a sufficien-tly long time, and this in -turn causes the
overall mould procduction to become considerably more time-consuming
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than the convellti.ona:L moulcl manufact-lring processes.
The object Or the inven-tion is to overcome -this drawback
of the known embod.iments of -the presen-t methocl, and -this objec-t
is achieved by the present inven-tion. Thus -the presen-t inventior
provides a method of producing frozen casting moulds or cores,
which method comprises:
a) providi.ng a granular material;
b) providing a binder material that is in a fluid
state,
c) cooling the binder material to a tempera-ture below
its freezing point to form fine particles;
d) mixing the granular material and the cooled,
particulate binder material -to form a homogeneous, easy flowing
mixture; and
e) compressing the resulting mixture to bind together
th.e granular mate:rial to form a mould or core.
In this embodiment par-t or the entire necessary cooling
may have been effected in advance, i.e. before the moulding
process, so that the molten metal may be poured into the mould
immediately after the termination of the moulding process. This
provides for such a great production rate that the method may be
used in connection with fast working automa-tic machines for the
production of casting moulds with or without cores, e.g. of the
type disclosed in the applicants' Danish Patent Specification No.
87,~62 to obtain the high operation rate of these machines.
When the binder has been frozen before the moulding
process, it may be expedient that additionally at least one of the
tools and/or materials which the binder is caused to contact in
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the moulding process or in the mould and which may con-tain a binder
previously used, has been cooled below the freezing poin-t of the
binder or to a temperature slightly above said freeæing point.
The mould binder may have been cooled before -the mould
manufacturing process so that it is presen-t in the form of fine,
dendritic particles, e.g. snow, in the mould material, and a
compression during the moulding process may entail that the binder
obtains part of or its entire binding capacity depending upon the
temperature conditions at the -time of the mould manufacturing
process.
The mould binder used may also have been cooled before
the mould manufacturing process so that it is present in the form
of a finely divided powdered material, e.g. ice in the mould
material, and a compression during the moulding process may entail
that the binder obtains part of or its entire binding capacity
depending upon the temperature conditions at the time of the mould
manufacturing process.
When a suitable mixture of granular material and snow or
broken ice is compressed in a mould box, the snow or the ice may
thus be caused to bind the grains of the material toyether to
impart a cohesive force to the mould or the core sufficient for
it to resist the effect from liquid metal which is poured down
into the finished mould with or without cores. A corresponding
effect can be achieved by injecting one of the mentioned mixture
of mould material into a core box with a sufficiently great force
and at a sufficiently great rate.
The precooled binder in the form of pulverized material
may also be combined with liquid gas. This permits -the temperature
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of the mould mater,ial to be reduced to a very low value before and
during the moulding process and during the immediately following
casting process. The mixture must be homophenols and easy flowing.
Actually, there is nothing -to prevent -the use of
conventional setting binders. Thus, -to form a binder there may
be used water glass and liquid carbon dioxide or a mixture of
polyisocyanate and phenol resin which is activated by precooled,
liquid dimethylethyl amine or triethyl amine. This provides Eor
a reduction in the use of an environmentally harmful binder.
To obtain a better resistance to the heat effect of -the
molten metal and thereby a delay in the hea-ting of -the mould or
the core in the casting process, the granular material used for
the formation of the mould or the core may have been deep-frozen
in advance.
Additionally, the process ingredients may have been
deep-frozen in advance by means of an admixed freezing agent,
and the freezing agent used may expediently be liquid gas. The
use of an inert gas, obviates any risk of chemical attacks on
the equipment used for the process or for chemical reactions
with the casting metal.
The required cooling may also be effected or be supported
by deep-freezing the parts of the appara-tus which the mould
material contacts during the moulding process. In the production
of casting moulds, particularly the pattern board which contacts
the same mould surface as the molten metal does later, may have
been deep-frozen in advance and a core box deep-frozen in
advance may be used in the production of cores. Also, the core
box with the co~e or cores may be cooled simultaneously and
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additionally e.cJ. with ]iquid cJas.
A specific embodiment of -the method of the invention in
the production of casting moulds comprises the use of deep-Erozen
disposable patterns of a material which evaporates when heated
and this material may expediently have been deep-frozen ancl
formed. Such patterns may be produced currently in a particular
bifurcate pattern mould box corresponding -to a conventional core
box and be placed in a closed chamber, following which the space
between the pattern and the walls of the chamber is filled with
the moulding material which is cooled by the pattern and may
additionally have been cooled in advance as mentioned above. After
the moulding proeess is finished the pattern evaporates rapidly
owing to the heat received. This obviates the inconvenient
development of gas, which otherwise takes place in the moulding
of disposable patterns. This embodiment of the method results in
particularly accurate eas-tings beeause the inaccuracies which in
the conventional mould manufacturing process result from wear on
the pattern board caused by shootings of sand, are avoided.
Moreover, bifurcation of the mould box is not required when readily
evaporable patterns are used.
The invention also relates -to a plant for carrying out
the disclosed method, which plant comprises an apparatus for the
produetion of casting moulds or an apparatus for the production
of eores, wherein the apparatus or at least one part thereof is
contained in a cooling chamber. Aceording to the invention, the
neeessary temperature eonditions may be readily and eonstantly
maintained so that valuable produetion time is no-t lost in
waiting for eooling.
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When the plan-t is connected to a casting plan-t having
melting apparatus, a considerable saving in energy may be achieved
by an arrangement such that waste heat from the melting apparatus
is used for the operation of the cooling sys-tem of -the cooling
chamber.
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