Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND SHOOT-MOULDING MACHINE FOR THE MANUFACTURE OF
MOULD PARTS, SUCH AS CASTING CORES, FOR CASTING MOULDS FOR
THE CASTING OF MOLTEN METAL
The invention relates to a method and shoot-moulding
machine for the manufacture of mould
parts, such as casting cores, for casting moulds for the
casting of molten metal.
With the conventional manufacture of casting cores
intended for the casting of light metal heats, as a rule a
resin-bonded mould material is poured into the hollow
cavity of a mould tool which determines the final shape of
the casting core mould part which is to be produced. The
mould tool exhibits in this situation a number of shooting
openings, sufficient for the uniform filling of the
cavity, through which the filling with the mould material
takes place. In order to fill the mould tool, a "shooting
nozzle" is introduced into each of these shooting
openings, via which the mould material is then shot in.
The shooting nozzles are as a rule carried together on a
height-adjustable "shooting head plate", which ensures the
movement of the core box into and out of the shooting
position.
In known devices, the nozzles are usually supplied via
what is referred to as a "shooting hood", which covers the
shooting head plate on its side turned away from the mould
tool, and is filled with mould material. To shoot in the
moulding sand, the mould material contained in the
shooting hood is abruptly subjected to uniform pressure by
means of a gas, generally air, by means of a pressure
cylinder, so that it is driven through the shooting
nozzles into the mould tool.
In order to create the final strength required for the
mould parts which are to be produced, there is the
possibility on the one hand of incurring a chemical
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reaction by catalytic means in the mould material by the
addition of suitable media. With this so-called "Cold Box
Method", a hardened moulded part is obtained as a result
of the chemical reaction. This cannot, however, be
conducted back into the cycle for the materials used for
the manufacture of the moulded part.
As an alternative, the hardening can be initiated with the
use of suitable binding agents by the application of heat.
To carry out this method, referred to as the "Hot Box
method", known shoot-moulding machines for the manufacture
of mould cores are equipped with heating units in order to
heat the mould tool. The hardening of the mould material
is in this case brought about by the application of heat
in the mould tool.
Because the use of organic binding agents can lead to
burdens on the workplace and the environment, it is a
matter of concern that the organic binding agents used
hitherto for the manufacture of casting cores should be
replaced by such mould materials as are bonded by
inorganic binding agents, such as binding agents based for
example on water glass. A method which allows for the use
of mould materials composed in this manner for the
manufacture of core formed bodies is known from EP 0 917
499 B1.
According to this known method, a mould material is first
manufactured by the mixing of an inorganic refractory
mould sand with an inorganic binding agent on a water
glass base. This mould material is then filled into a
temperature-controlled mould tool, which is subjected to
underpressure during the filling. The temperature/dwell
time of the mould material after the closure of the mould
tool is adjusted in this situation in such a way that a
skin shell which is stable in shape and ... of bearing is
formed on the core formed body. When the core formed body
has reached this state, the mould tool is opened and the
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core form removed. Immediately after this, the core foamed
body is subjected to complete drying under the effect of
microwaves. In this way, moisture is drawn by physical
means out of the mixture filled into the mould tool. As a
result, by means of this dehydration process a hardening
of the core formed body is achieved while still in the
mould tool, which at least makes it possible for it to be
handled in the further processing steps.
In practice, a number of deficiencies have become apparent
with the carrying out of the known method in conventional
devices equipped with a device for the heating of the
mould tool. These are expressed, for example, in an
undesirable premature hardening of the mould materials in
the components of the shoot-moulding machine, which are
affected by the heat irradiating from the mould tool.
These components are in particular the shooting nozzles
and shooting hood, which even when in a waiting position
are heated to a temperature which is critical for the
commencement of the hardening of the mould material
because of dehydration. The premature hardening of the
mould material leads, for example, to crust formation in
the shooting hood on the surface of the mould material, so
that the mould material can no longer be introduced in the
proper manner into the mould tool, resulting in the
incomplete filling of the mould tool and the clogging of
the shooting nozzles. Mould material which hardens by
itself in the shooting nozzles also leads to the clogging
of the nozzles, with the result likewise that a uniform
and proper filling is no longer guaranteed.
The object of the invention is to provide a method and
device with which moulded parts for casting moulds can be
manufactured, reliably and with reduced susceptibility to
faults, from a mould material containing an inorganic
binding agent.
Taking the prior art explained heretofore as a starting
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point, this object is solved by a method for the
manufacture of moulded parts for casting moulds for the
casting of molten metal,
Wherein, in a shoot-moulding machine, with the aid of
filling elements such as shooting nozzles and
shooting hood, a mould material containing an
inorganic binding agent is filled into a cavity of a
mould tool which determines the shape of the mould
part which is to be manufactured,
- Wherein heat is supplied to the mould material filled
into the mould tool, over a hardening period in order
for the mould material to solidify due to the
extraction of moisture,
and
- Wherein, during the hardening period, at least the
filling elements of the shoot-moulding machine, which
contains mould material, and which are in a stand-by
position during this hardening period and are heated
concomitantly by the radiated heat given off by the
mould tool, are maintained at a moisture content
level which prevents the solidifying of the mould
material.
On the other hand, the object described heretofore is
solved by a shoot-moulding machine for the manufacture of
mould parts for casting moulds for the casting of light
metal materials,
- with a mould tool having a cavity, which determines
the shape of the mould part which is to be
manufactured,
- with a heating device for heating the mould tool,
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- with filling elements for the introduction of mould
material into the mould tool, wherein the mould tool
can be moved relative to the filling elements and/or
the filling elements can be moved relative to the
mould tool, out of a filling position in which they
are arranged closely adjacent to one another for the
filling of the mould tool, into a stand-by position
in which they are positioned distant from one
another, and
- with a moistening device which, with the filling
elements located in the stand-by position, keeps
those filling elements moist which contain mould sand
and which lie in the radiation range of the heat
emitted from the mould tool.
For preference, in this situation the mould tool is
additionally capable of being moved backwards and forwards
between a filling station and a removal station.
Particularly well-suited are a method according to the
invention and a shoot-moulding machine according to the
invention for the manufacture of casting cores for the
casting of light metal melts, which in practice represent
by far the largest proportion of the casting mould parts
manufactured in the manner under consideration here.
According to the invention, during the hardening of the
mould material filled into the heated mould tool, those
parts are deliberately kept moist which are heated by the
radiant heat from the mould tool up to a temperature at
which the undesirable premature and therefore disruptive
hardening of the mould material could set in. In this way,
the extraction of water from the mould material which
could otherwise occur in or at these parts as a result of
the heating is counteracted, and the solidification of the
mould material in the critical parts of the shoot-moulding
machine will therefore be prevented. The parts which are
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particularly affected by the heating are in this case
typically the shooting nozzles or the shooting hood
required for supplying the shooting nozzles, with the
shooting plate or other supply channels conducting mould
materials connected to it.
Given that these parts are deliberately kept moist during
the dwell time required for the hardening of the mould
parts in the mould tool, this prevents, for example, both
the formation of crust in the shooting hood as well as the
clogging of the shooting nozzles due to the solidifying
mould material. Tn this way, also mould materials
containing inorganic water-based binding agents can be
reliably used for mould parts for casting operations. The
mould parts obtained are characterised by high strength
and after use can be conducted back into the circle of the
materials used for the manufacture of the mould.
The moistening of the parts heated by the heat emitted by
the mould tool and consequently at risk with regard to the
solidification of the mould material can be effected
according to a first variant of the invention by at least
one of the filling elements being subjected at least
temporarily to a moist atmosphere during the hardening
period. This embodiment of the invention is particularly
well-suited for avoiding the hardening of mould material
in the shooting hood, if a moist atmosphere is
specifically maintained in the hood. The moisture content
of the atmosphere, formed for preference by air as the
carrier gas, can in this situation be adjusted with no
problem to the particular circumstances. It is
conceivable, for example, for the moisture content of the
atmosphere surrounding the shooting nozzles in the stand-
by position to be adjusted in such a way that condensation
forms on the shooting nozzles and, as a result, the
solidification of mould material contained in the shooting
nozzles or adhering to them will be reliably avoided.
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As an alternative or supplement to a moistening by the
maintaining of an atmosphere of specific humidity it can
be of advantage for at least one of the filling elements
to be cooled at least temporarily during the hardening
period. Such a specific cooling process can also induce
the formation of condensation. This embodiment of the
invention is therefore particularly well-suited for the
protection of the shooting nozzles against clogging by
solidified mould material. In addition or as an
alternative to this, the shooting air itself can be
moistened, in order to prevent the drying or hardening of
the mould material right from the outset.
A further embodiment of the invention which is
particularly easy to implement but nevertheless effective
is characterised in that at least one of the filling
elements which is heated concomitantly is brought at least
temporarily in contact with a moisture carrier during the
hardening period. This moisture carrier can be an
absorbent material which is soaked with liquid, in
particular water, such as a sponge or cloth. Practical
tests have revealed that if such a moisture carrier is
docked against shooting nozzles which are in the stand-by
position, the solidification of mould material contained
in the nozzles is reliably avoided.
If, in the course of the hardening time, a hot gas, for
preference heated air, flows through the cavity in the
mould tool at least temporarily, which is introduced dry
and is drawn off loaded with moisture, the progress of the
hardening of the mould part contained in the mould tool
can be specifically improved. In this case, after the
filling of the mould tool with mould material, during the
period of time required for the hardening of the formed
body and in addition to the heat introduced via the mould
tool itself, a hot, dry gas flow is conducted through the
mould. In this way, on the one hand the gases incurred in
the course of the hardening will be conducted out of the
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mould tool. On the other hand additional heat will be
introduced into the mould part. In this situation, this
heat does not penetrate slowly via the shell of the mould
part into its interior, but is actively conveyed by the
gas flow into the interior of the core of the mould part.
As a result, a rapid and uniform core hardening is thus
achieved. The influence of even strongly fluctuating
thickness values of the core will in this way be
minimised. Moulded parts obtained with the application of
this variant of the proceeding according to the invention
therefore already have a particularly high and
homogenously distributed strength as early as when they
are removed from the mould tool. At the same time, in this
way cycle times can be achieved in the manufacture of
casting cores which are not higher than the times which
are required for the manufacture of corresponding casting
cores from mould materials containing organic binding
agents, in particular artificial resins.
Further advantageous embodiments of the invention are
described in the dependent claims and are in the following
explained in greater detail in connection with the
embodiment described on the basis of the drawing. These
show in diagrammatic form, in a partially sectional
representation:
Fig. 1 A hoot-moulding machine for the manufacture of
casting cores in a first operational position;
Fig. 2 The shoot-moulding machine represented in Fig. 1
in a second operational position.
The shoot-moulding machine 1 for the manufacture of
casting cores K according to the "Hot Box method" exhibits
a mixer 3. Mixed in the mixer 3 is a mould material F
consisting of an inorganic refractory mould sand and a
binding agent based on water glass.
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This mould material F is introduced into a filling hopper
4 arranged beneath the mixer 3, from which it is conducted
to a shooting cylinder 5 positioned beneath the filling
hopper 4. The shooting cylinder 5 shoots the filling
material F into a shooting hood 6, connected to it and
widening downwards in its width and depth from the
shooting cylinder 5, the shooting hood being closed on its
underside by a shooting head plate 7. Formed into the
shooting head plate 7 are a large number of mounts, not
represented, in each of which a shooting nozzle 8 is
located.
The shooting nozzles 8 extending in the direction of the
cope 9 of a mould tool 10 are arranged in accordance with
the shooting holes 11 formed in the cope 9. The shooting
holes 11 open into a cavity 12, which is formed by
corresponding recesses formed in the cope 9 and the drag
box 13 of the mould tool 10. Further elements not
represented here can be constituent parts of the moulding
machine 1.
The shape of the casting core K which is to be
manufactured is determined by the cavity 12. Venting
openings 14 are formed in the drag box 13, by means of
which the air displaced by the mould material F when it is
filled into the cavity 12 escapes. If required,
corresponding venting openings, not represented here, are
located in the cope. The cope 9 and the drag box 13 of the
mould tool can be heated in a controlled manner by means
of a heating device 15.
Provision is made for positioning devices, not shown, in
order to move the core box with the shooting holes 11 to
the shooting nozzles 8 into a shooting position, in which
they are located in the shooting holes 11 of the mould
tool 10. In this situation, together with the shooting
nozzles 8, the shooting head plate 7 secured firmly to
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them, the shooting hood 6, the shooting cylinder S, and
the hopper 4 are all brought together (Fig. 1).
Once the mould material F has been shot into the mould
tool 10, the moulding machine 1 is moved into the stand-by
position, in which the tips of the shooting nozzles 9 are
arranged at a distance interval above the mould tool 10
(Fig. 2). This stand-by position is maintained by the
shooting nozzles 8 until the mould material F contained in
the cavity 12 of the mould tool 10 has hardened to form
the casting core K as a result of the dehydration which
results as a consequence of the heating of the mould
material F in the mould tool. If no air flow L is
conducted by over-pressure or low-pressure through the
mould tool 10, in order to improve the hardening process,
then the gases incurred in the course of the hardening
will escape from the mould tool 10 automatically via the
holes 11 and the venting openings 14.
A moistening device 16 is connected to the shooting hood
6, by means of which moist air can be conducted into the
interior of the shooting hood 6. In addition to this, a
sponge 17 is secured on a plate 18, which with the
shooting nozzles 8 located in the stand-by position can be
moved beneath the shooting nozzles 8 and raised in such a
way that the sponge 17 presses against the shooting
nozzles 8 and fully surrounds at least their lower
section, which exhibits the nozzle opening. In addition to
this, a nozzle 19 is allocated in each case to the
shootting nozzle 8, by means of which, with the shooting
nozzles 8 in the stand-by position, the moist air
delivered from the moistening device 16 is blown onto the
shooting nozzles 8.
The moisture content of the moist air introduced into the
shooting hood 6 in the stand-by position and blown against
the shooting nozzles 8 is determined in such a way that
the mould material cannot be dehydrated. In this way the
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risk can be reliably prevented of the mould sand F still
contained in the shooting hood 6 and the shooting nozzles
8 in the stand-by position solidifying as a result of the
heating and the extraction of the water, to which the
parts in question are subjected due to the radiant heat W
emitted from the hot mould tool 10 both during the filling
process (Fig. 1) as well as in the stand-by position (Fig.
2) which they occupy for longer.
In this situation, the sponge 17 pressed against the
shooting nozzles 8 in the stand-by position also
specifically ensures that no clogging of the nozzle
apertures of the shooting nozzles 8 occurs as a result of
clogging mould material F. The formation of condensation
in the area of the shooting nozzles 8 can be further
supported by the shooting nozzles 8 being cooled in the
stand-by position with the aid of a cooling device, not
shown here. This cooling process also reliably prevents
the temperature in the interior of the shooting nozzles 8
rising to a level which is critical for the solidification
of the mould material F. The moistening of the outside of
the shooting nozzles 8 guarantees that no solidified mould
sand F becomes baked onto the shooting nozzles 8.
In order to achieve an improved process of the hardening
of the casting core K in the mould tool 10, a device 20 is
provided which exhibits an air delivery connection 21 and
suction extraction connection 22. During the hardening
time required for the hardening of the casting core K,
with the shooting nozzles 8 in the stand-by position, the
air delivery connection 21 of the device 20 is coupled to
the shooting holes 1 and the suction extraction connection
22 of the device 20 is coupled to venting openings 14 of
the mould tool 10 (Fig. 2). In this situation, a hot, dry
air flow L is constantly conducted into the mould tool 10
via the air delivery connection 21. This air flow L flows
through the casting core K contained in the mould tool 10
being in the process of hardening, and is drawn off via
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the venting openings 14 of the mould tool 10. In this way
also the interior of the core is uniformly heated, so that
the moisture contained in the casting core K as a whole
escapes more rapidly.
At the same time, the air flow L extracted via the suction
extraction connection 22 conveys the gases incurred in the
course of the heating of the casting core K in a targeted
and rapid manner out of the mould tool 10. The more
homogenous heat distribution attained in the casting core
K by the air flow L accordingly has the effect of
incurring a shortened hardening time, with improved
strength of the casting core K obtained being achieved at
the same time.
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REFERENCE FIGURES
1 Shoot-moulding machine for the manufacture of casting
cores
3 Mixer
4 Filling hopper
Shooting cylinder
6 Shooting head
7 Shooting head plate
8 Shooting nozzle
9 Cope
Mould tool
11 Shooting holes
12 Cavity
13 Drag box
14 Venting openings
Heating device
16 Moistening device
17 Sponge
18 Plate
19 Nozzle
Device for producing and suction extraction of the
air flow L
21 Air delivery connection
22 Suction extraction connection
D Thickness of the casting core K
F Mould material
K Casting core
L Dry air flow
W Radiant heat
