Note: Descriptions are shown in the official language in which they were submitted.
21 89400
PATENT
Attorney Docket
No. 9003-79
(A 96 512 M US)
TITLE
Process And Device For Coating Foundry
Molds And/Or Foundry Cores With Powder
BACKGROUND OF THE INVENTION
The invention concerns a process for coating
foundry molds and/or foundry cores made of a fireproof
component, especially sand and preferably a liquid binding
component, with a powder to create a barrier between the
mold or the core and the casting material against gases
penetrating into the hardening casting.
The invention furthermore concerns a device for
implementing the process with a receptacle for the foundry
mold(s) and/or foundry core(s) and a mixture of a granular
base material and powder.
The foundry industry works with molds and cores
which must meet a series of technological requirements in
order to be able to withstand the casting material which
consists of liquid metal or i-ron. The foundry forms
and/or cores (referred to herein more generally as casting
molds or casting cores) consist of a fireproof component,
mostly sand with a suitable granularity, for example
quartz, zirconium, chromite-sand, etc., and at least one
liquid binding component which brings about the solidity
of the shaped mold or core by chemical hardening. Modern
binders for this purpose are manufactured on the basis of
a synthetic resin. Their hardening takes place with the
aid of a suitable, usually organic hardener. When the
mold is filled with metallic melts, hydrocarbons of the
solidified binder polymers on the metal/mold or core
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boundary are partially decomposed, whereby gases arise.
These gases should not be allowed to remain in the
metallic casting, because its mechanical properties will
be diminished by this. Further sources of gas in the mold
or core are condensed alcohols, solvents and/or water.
For this reason, it is already known to
counteract the penetration of such gasses into the
hardening casting by applying coatings to the surfaces of
the casting mold and/or core which will contact the
metallic casting.
Furthermore, spreading a powder to form a
protective layer on molds and cores is known from
DE 27 24 705. Of course, there exists in this regard the
problem of obtaining a good adhesion, for which reason a
vacuum must simultaneously be generated in the mold or the
core, so that the powder can be sucked into the mold or
the core. This represents a considerable expenditure,
whereby it is moreover difficult and hardly conceivable to
place a mold or even a core under low pressure in such a
manner that a sprinkled powder can be sucked evenly into
the interior.
Charging particles triboelectrically (by
friction), grounding the substrate, and bringing the
charged particles into contact with the grounded substrate
are known from EP 0 024 067 for coating substrates which
in use come into contact with molten metals. Chargeable
particles are thus needed for such a coating and a
corresponding electrotechnical expenditure must be
assumed.
SUMMARY OF THE INVENTION
There thus exists the object of creating a
process and a device as well of the type mentioned in the
beginning, with which a powder for creating a barrier
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between the mold or the core on the one hand and the
casting material on the other can be applied to the mold
or the core in a sufficiently durable and stable manner,
without having to place these parts to be coated with
powder under vacuum, and without having to
triboelectrically charge the particles serving as a
coating.
To accomplish this objective, the process
according to the invention is characterized by the powder
being mixed with a granular mineral base material or sand,
and the powder from this mixture of dry, granular mineral
base material and powder being flowed around the casting
mold and/or core to coat it.
Thus, a powder is not simply sprinkled or spread
on the parts to be coated, but a mixture of this powder
with a granular bulk material, preferably sand, is
produced in a surprising manner, and the parts to be
coated are washed with it. This leads to the result that
powder adhering to the grains of the granular base
material mixture are intensively transferred to the
casting form or core and are carried into its surface, so
that the surface pores are largely closed, and the
roughness of these parts is also considerably diminished.
By closing the surface pores, the escape of gas from the
mold or the core is prevented during the casting process
in the first hardening phase. The granular base material
or sand grains belonging to the mixture do not remain
stuck on the mold or the core, since they are dry, so that
they serve to a certain extent as carriers for the powder,
on the one hand, and as mechanical aids in coating and
carrying in, on the other.
It is particularly appropriate for the process
of washing the mold or the core if the mixture of base
material and powder is loosened up into a mass which can
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flow in the vicinity of the casting mold(s) and/or the
casting core(s). It is known E~E se that granular and/or
pulverized masses or materials can be so loosened up that
they acquire a flow behavior similar to a liquid.
It is especially beneficial if the base
material-powder or sand-powder mixture is loosened up by
vibrations or sound or a carrier medium, especially
compressed air, or a combination of these. Cores or molds
situated in the vicinity of the base material-powder
mixture are then washed around by this loosening up of
this mixture, so that the powder from the mixture can be
at least partially transferred to the surface of the mold
or the core and rubbed and carried into the surface owing
to the granular components of the base mixture. The
desired permanent coating with powder results in this way,
without the molds or cores having to be exposed to a low
pressure, which would have to act from the surface into
the interior in order to carry the powder into the
surface.
It is especially favorable that the powder which
covers the grains of the base material or sand of the
mixture is transferred by friction to the surface of the
casting mold or casting core, and especially carried into
the surface pores. This leads at the same time to a
smoothing of the surface so that even the structure of the
mold or core is improved, and the exactness of the
subsequent cast piece can be elevated. This working in of
powder components into the pores of the casting molds
and/or cores yields the desired barriers against released
gases.
A productive, space-saving, energy-saving, and
technologically beneficial procedure for treating the
surfaces of casting molds and cores results above all with
the combination of individual or several of the procedural
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.
steps described previously, which process is in a position
to replace the previously customary coating of layers or
sprinkling with powder, without a loss in quality in the
casting. In fact, the powder can be conveyed into the
surface pores so that these are closed to the greatest
extent, thus forming a good barrier against escaping gases
at least during the casting and first hardening phase,
whereby at the same time the surface roughness of the mold
or core is reduced, and the quality of the casting can
also be improved thereby. The washing of the mold or the
core with the mixture of base material or sand and powder
can at the same time also take place, for example in the
manner of a fluidized bed without problems.
It is especially economically beneficial if the
mixture consisting of base material or sand and powder is
used several times (i.e., recycled), and powder is again
admixed with this mixture from time to time. With the
previously described process, the base material or sand
partially deposits the powder adhering to it on the mold
or core so that the powder proportion in the mixture thus
gradually diminishes. The base material or sand remains
unchanged, and consequently only powder needs to be
admixed to the mixture from time to time in order to be
able to coat further molds or cores with it.
The device for implementing this process already
mentioned at the beginning is chiefly characterized by
vibrators and/or sources of sound and/or a compressed air
system being attached to the receptacle for the mold(s)
and/or cores(s) in order to loosen up and fluidize the
base material-powder mixture situated in the receptacle
together with one or several molds and/or cores. It is
thus sufficient to accommodate molds or cores together
with the base material-powder mixture in a suitable
receptacle, and then to loosen the mixture up with
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vibrators, sound sources and/or compressed air situated on
the receptacle such that this mixture in a sense flows
around the parts to be coated, so that the powder
components from this mixture can be worked into the
surface of the forms or cores in the manner already
described.
The receptacle can have a bottom on which the
mixture directly lies and on which the casting mold and or
the casting core can be laid. This provides an especially
simple container, in which the washing of the molds or
cores with the base material-powder mixture can take
place.
A modified specific embodiment can consist of
installing in the receptacle a gas-permeable plate, a net
or the like above the bottom for laying the mold and/or
core upon it, or mounting a supporting device for the
molds or cores on the bottom of the receptacle. In this
way, the mold and/or core can be positioned within the
container somewhat higher than the bottom, so that an even
better washing with powder, and therewith a better coating
is made possible.
A compressed air dryer, and if necessary a
pressure reducer, can be installed in the compressed air
supply to the receptacle. In this way, it is assured that
the compressed air serving to fluidize or to create a
fluidized bed within the receptacle contains the requisite
dryness, so that the base material-powder mixture is not
impeded by moisture in being set in motion or loosened up.
BRIEF DESCRIPTION OF THE
SEVERAL VIEWS OF THE DRAWINGS
The foregoing summary, as well as the following
detailed description of preferred embodiments of the
invention, will be better understood when read in
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conjunction with the appended drawings. For the purpose
of illustrating the invention, there are shown in the
drawings embodiments of a device for carrying out the
process of the invention, which are presently preferred.
It should be understood, however, that the invention is
not limited to the precise arrangements and
instrumentalities shown. In the drawings:
Fig. 1 is a longitudinal section of a device in
the starting position for coating casting molds and/or
casting cores with a powder having a receptacle for this
purpose, and for a mixture of a granular base material and
powder, wherein vibrators, sound sources and a compressed
air system are connected to the receptacle for loosening
up the mixture containing the powder;
Fig. 2 is a longitudinal section in accordance
with Fig. 1 during processing of the casting molds or
cores with the base material-powder mixture;
Fig. 3 is a modified specific embodiment in
which a gas-permeable plate is mounted within the
receptacle for laying the molds and/or cores upon it above
a first plate of the receptacle, again in the starting
position;
Fig. 4 is the receptacle in accordance with Fig.
3 during treatment of casting molds and/or cores with the
powder-base material mixture.
Fig. 5 is a schematic and enlarged view of the
surface of a casting mold or a core from the base material
components of the core or mold sand with binding
components therebetween prior to treatment with the base
material-powder mixture; and
Fig. 6 is a representation corresponding to Fig.
5 after coating with the powder.
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DETAILED DESCRIPTION OF THE INVENTION
In the following description corresponding parts
of the various devices are designated with identical
reference numbers even if they deviate in their function
or form.
The respective device represented in each of
Figs. 1 to 4 has above all a receptacle 1 in which casting
molds or cores 2 can be placed together with a base
material-powder mixture 3. The base material can be sand,
for example.
The receptacle 1 is provided with vibrators 4
and/or sound sources 5 and/or a compressed air system 6,
with which the powder-base material mixture 3 can be
brought into motion and loosened up, so that it flows
around the molds and cores 2 lying on or above it first
according to Fig. 1 and also in accordance with Fig. 3.
In the embodiment according to Figs. 1 and 2 a
gas-permeable plate 7 is fastened over the bottom of the
receptacle 1, which permits the introduction and uniform
distribution of the compressed air supplied by the
compressed air system 6 over the entire horizontal cross
section of the receptacle 1. This plate 7 is mounted for
this purpose between fastening elements 8. Its
interstices or openings are smaller than the mean grain
size of the mineral base material contained in the
powder-base material mixture 3, so that the intervening
space between the bottom and this plate'7 remains free of
this mixture 3. In this connection, one sees in Fig. 1
the starting position in which the molds and cores 2 lie
upon the powder-base material mixture, which for its part
is piled up on the plate 7.
How the molds and cores 2 are coated with powder
is depicted in Fig. 2. The mixture is loosened by turning
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on the vibrators 4 or the sound sources 5. In addition,
the compressed air system 6 can be turned on. The mixture
3 is thereby fluidized and loosened up practically as in a
fluidized bed, so that the molds and the cores 2 are
washed by it, such that the powder found in the mixture
can be deposited on these parts 2.
The compressed air system 6 consists of a
compressed air source 9, a compressed air dryer 10, and a
pressure reducer 11, as well as conduits, valves and
connections, as schematically indicated.
The individual particles and components of the
powder-base material mixture 3 come into intensive motion
by the loosening up and consequently flow around all
contact surfaces of the casting molds or cores 2. The
kinetic energy of the mixture 3 serves for creating
friction and for introducing the powder into the pores of
the casting molds and/or cores 2. The roughness of the
casting molds and/or cores 2 is considerably reduced as a
result of this treatment.
If one compares Figs. 5 and 6, one recognizes
the surface of a casting mold or of a core 2 in greatly
enlarged and schematic presentation before treatment in
accordance with Fig. 5 and after treatment according to
Fig. 6. One recognizes the base components 30 therein,
which can be grains of sand, for example, and binder
components 31 arranged in between.
In Fig. 6, these are now covered over and sealed
on their surface with powder particles 32, whereby the
powder particles 32 form a clear barrier against the
outside, so that gases arising in the mold or core 2
during the casting process cannot exit for the time being,
and thus cannot harm the cast workpiece.
The specific embodiment of the device according
to Figs. 3 and 4 largely corresponds to that in accordance
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with Figs. 1 and 2. One simply notes in addition above
the plate 7 a further plate 13, which is perforated and
upon which the casting forms and/or cores 2 can be laid.
Consequently, these have a certain distance from the gas
permeable plate 7 in the starting position and also during
their processing.
The additional plate 13 rests upon damping
elements 12, so that where washing around occurs by
vibration, oscillations can be compensated by these
- 10 damping elements 12 so that the casting forms and/or cores
2 which are situated on the plate 13 cannot be damaged by
such vibrations.
The mixture 3 is also loosened up in this case
after appropriate activation of vibrators and/or sound
sources and/or the compressed air system, so that it flows
around the molds and cores 2 and coats the surfaces with
powder in the manner which has already been mentioned in
connection with the first embodiment, so that a result
corresponding to Fig. 6 can be obtained.
At the same time, the compressed air can be
dried efficiently so that the powder in the mixture 3 is
not made unusable by air moisture. The intensity of the
washing with compressed air can be controlled by means of
the pressure reducer 11. The duration of the washing
depends upon the dimensions of the receptacle 1, on the
geometry of the form or the core, on the granularity of
the base material as well as of the powder, and can be
varied within broad limits.
With both devices, one or several casting molds
and/or casting cores 2 can therefore be coated with a
powder, on the one hand in accordance with Figs. 1 and 2
and on the other hand in accordance with Fig. 3 and 4,
whereby the powder is in the first place mixed with a
granular mineral base material or sand so that the mixture
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-
3 shown in the Figures is already made up. The casting
mold and/or casting core 2 can subsequently be washed to
coat them with the powder from this mixture 3 of dry,
granular mineral base material and powder, so that the
5 larger base material grains pass on the powder adhering to
them to the surface of the molds and cores 2 and to a --
certain extent rub it on and into the surface. By this
means, the surface is smoothed at the same time. Existing
pores are closed so that the desired barrier arises, which
prevents the escape of gas from the mold or the core 2, at
least during the first phase of the casting process, and
thereby prevents damage to the casting.
The powders which may be used in the mixtures
for coating the casting molds and/or cores according to
the present invention include, for example, zirconium
silicate (ZrSiO4), corundum (A12O3), magnesite (MgO),
mullite (3A12O3 2SiO2), olivine (Mg2 SiO4), quartz (SiO2),
chromite (A12O3 Cr2O3 FeO), coke (90~ carbon), graphite
(70-85~ carbon), kaolinite (Al2[(OH)4/Si2O5]), pyrophyllite
(Al2[(OH)2/Si4O1o]), talcum (Mg3[(OH)2/AlSi~Ol0]), and mica
(KAl2[(OH)2/AlSi3O1o]). The powder may be mixed with the
base material, preferably silicate sand, at a ratio of
about 1:10 parts by volume, for example. Typically, the
powder will have a particle diameter in the range of about
0.02-0.06 mm, and the carrier sand (base material) will
have a particle diameter in the range of about 0.16-0.3
mm. The choice of powder for a particular application
will depend upon a number of factors, but above all must
be compatible with the material to be cast, such as steel,
steel alloys, iron, copper alloys, aluminum alloys,
magnesium alloys, etc. -
It will be appreciated by those skilled in the
art that changes could be made to the embodiments
described above without departing from the broad inventive
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~ concept thereof. It is understood, therefore, that this
invention is not limited to the particular embodiments
disclosed, but it is intended to cover modifications
within the spirit and scope of the present invention as
defined by the appended claims.
