EP0774312A1 - Process and apparatus for coating foundry moulds and/or cores with a powder - Google Patents

Abstract

The method concerns coating of foundry moulds and/or cores (2) with a powder, in order to produce a barrier against gases which otherwise would enter into the casting. The powder is mixed with a granular base material or sand, and the mould (and or core) is coated by washing it with the resultant, dried mixture. Also claimed is an appts. for implementation of the proposed method.

Description

The invention relates to a method for coating foundry molds and / or foundry cores from a refractory component, in particular sand and preferably a liquid binder component with a powder to form a barrier between the mold or the core and the casting material against gases penetrating into the solidifying cast body.

The invention further relates to a device for performing the method with a receptacle for the foundry mold (s) and / or foundry cores and a mixture of a granular base material and powder.

In the foundry industry, molds and cores are used which have to meet a number of technological requirements in order to be able to withstand the casting material made of liquid metal or iron. The foundry molds or cores consist of a refractory component, usually sand with a suitable grain size - e.g. quartz, zircon, chromite sand, etc. - and at least one liquid binder component that chemically hardens the shape or core of the molded form causes.

Modern binders are made from synthetic resin. They are hardened using a suitable, usually organic hardener. When the mold is filled with a molten metal, hydrocarbons of the solidified binder polymer are partially decomposed at the metal / mold or core boundary, resulting in gases. These gases must not remain in the cast metal body, because this will impair its mechanical properties. Further gas sources are alcohols, solvents and / or water condensed in the form or in the core.

It is therefore already known to counteract the penetration of such gases into the solidifying cast body by applying size to the contact surfaces of the foundry mold or the core with the metallic cast body.

It is also known from DE 27 24 705 to sprinkle molds and cores with a powder forming a protective layer. However, there is the problem of achieving good adhesion, which is why a negative pressure should be generated in the mold or the core at the same time so that the powder can be sucked into the mold or the core. This represents a considerable effort, and it is also difficult and hardly imaginable to place a mold or even a core under negative pressure in such a way that a scattered powder is sucked evenly into the interior.

From EP 0 024 067 it is known to triboelectrically charge particles for coating substrates which come into contact with molten metal in use, to ground the substrate and to bring the charged particles into contact with the grounded substrate. For such a coating, therefore, chargeable particles are required and a corresponding electrical engineering effort must be made.

There is therefore the task of creating a method and also a device of the type mentioned at the beginning, with which a Powder to form a barrier between the mold or the core on the one hand and the casting material on the other hand can be applied to the mold or the core in a sufficiently permanent and firm manner without subjecting the powder-coated parts to negative pressure or having to triboelectrically charge the particles used for coating .

To achieve this object, the method according to the invention is characterized in that the powder is mixed with a granular mineral base material or sand and that the foundry mold and / or the foundry core for coating with the powder is washed by this mixture of dry granular mineral base material and powder.

A powder is therefore not simply sprinkled or coated on the parts to be coated, but surprisingly a mixture of this powder with a granular bulk material, preferably sand, is produced, and the parts to be coated are thus washed around. This leads to the fact that the powder adhering to the grains of the granular basic mixture is transferred intensively to the foundry mold or the core and introduced into the surface thereof, so that the surface pores are largely closed and the roughness of these parts is considerably reduced. Closing the surface pores prevents gas from escaping from the mold or core during the casting process in the first solidification phase. The granular base materials or grains of sand belonging to the mixture do not adhere to the mold or the core, since they are dry, so that they serve as a carrier for the powder on the one hand and also as mechanical application and insertion aids.

It is particularly expedient for the process of washing around the mold or core if the mixture of base material and powder is loosened to form a flowable mass in the area of the foundry mold (s) and / or the foundry core (s). It is in itself known that granular and / or powdery masses or goods can be loosened so that they get a similar flow behavior as a liquid.

It is particularly favorable if the base powder mixture or sand powder mixture is loosened up by vibration or sound or a carrier medium, in particular compressed air, or the combination thereof. Cores or molds located in the area of the basic material powder mixture are then washed by this mixture so that the powder from the mixture is at least partially released to the surface of the mold or core and rubbed into and introduced into it by the granular constituents of the basic mixture can be. The desired permanent coating with powder is thus obtained without the molds or cores having to be subjected to a vacuum which would have to be effective from the surface thereof in order to introduce the powder into the surface.

It is particularly favorable that the powder covering the grains of the base material or sand of the mixture is transferred to the surface of the foundry mold or the foundry core by friction on it and is in particular introduced into the pores of the surface. At the same time, this leads to a smoothing of the surface, so that even the structure of the shape or the core can be improved and the accuracy of the later casting can be increased. This incorporation of the powder components into the pores of the foundry molds or cores results in the desired barrier for separated gases.

Especially when combining one or more of the above-described process steps, this results in a productive, workplace-friendly, energy-saving and technologically expedient process for the surface treatment of foundry molds and cores, which is able to apply the size or powder coating with powder without loss of quality to replace on the casting. In fact, the powder can be introduced into the surface pores so that they are closed as far as possible, i.e. form a good barrier against escaping gases at least during the casting and first solidification phase, at the same time reducing the surface roughness of the mold or the core and thus also the quality of the casting can be improved. Flushing around the mold or the core with the mixture of base material or sand and powder can easily be done, for example, in the manner of a fluidized bed.

It is particularly economical from an economic point of view if the mixture consisting of base material or sand and powder is used several times and powder is added to this mixture from time to time. In the method described above, the base material or sand partially releases the powder adhering to it to the mold or core, so that the proportion of the powder in the mixture gradually decreases. The base material or sand remains unchanged, so powder only needs to be added to the mixture from time to time in order to coat other shapes or cores.

The device for carrying out this method already mentioned at the outset is characterized in particular by the fact that vibrators and / or sound sources and / or a compressed air system are connected to the container belonging to it, around which in the container together with one or more shapes and / or cores loosen up and fluidize the basic powder mixture. It is therefore sufficient to place molds or cores together with the basic powder mixture in a suitable container and then loosen them up with the vibrators, sound sources and / or compressed air on the container so that this mixture flows around the parts to be coated, so that the Powder components from this mixture can be incorporated into the surface of the molds or cores in the manner already described.

The receptacle can have a bottom on which the Mixture immediately lies on which the foundry mold and / or the foundry core can be placed. This results in a particularly simple container in which the basic powder mixture can be washed around the molds or cores.

A modified embodiment can consist in that a gas-permeable plate, a net or the like is arranged above the bottom for placing the mold and / or the core in the receiving container or that a support device for the molds or cores is arranged on the bottom of the receiving container. As a result, the shape and / or core can be stored somewhat higher than the base within the container, so that an even better flushing with the powder and thus a better coating is made possible.

A compressed air dryer and optionally a pressure reducer can be arranged in the compressed air supply to the receptacle. This ensures that the compressed air used to fluidize or create a fluidized bed within the container maintains the necessary dryness so that the raw material-powder mixture cannot be prevented from being stirred up or loosened by moisture.

Fig.1

einen Längsschnitt einer Vorrichtung zur Beschichtung von Gießereiformen und/oder Gießereikernen mit einem Pulver mit einem Aufnahmebehälter dafür und für eine Mischung aus einem körnigen Grundstoff und Pulver, wobei an dem Behälter Vibratoren, Schallquellen und ein Druckluftsystem zur Auflockerung der das Pulver enthaltenden Mischung angeschlossen sind, in Ausgangsstellung,

Fig.2

den Längsschnitt gem. Fig.1 während der Behandlung der Gießereiformen oder Kerne mit der Grundstoff-Pulver-Mischung,

Fig.3

eine abgewandelte Ausführungsform, bei welcher innerhalb des Behälters noch eine gasdurchlässige Platte zum Auflegen der Formen und/oder Kerne oberhalb einer ersten Platte des Aufnahmebehälters angeordnet ist, wiederum in Ausgangsstellung,

Fig.4

den Behälter gem. Fig.3 während der Behandlung der Gießereiformen bzw. -kerne mit dem Pulver-Grundstoff-Gemisch,

Fig.5

in schematisierter und vergrößerter Darstellung die Oberfläche einer Gießereiform oder eines Kernes aus den Grundstoffkomponenten des Kern- bzw. Formsandes mit dazwischen befindlichen Binderkomponenten vor der Behandlung mit dem Grundstoff-Pulver-Gemisch sowie

Fig.6

eine der Fig.5 entsprechende Darstellung nach der Beschichtung mit dem Pulver.

Exemplary embodiments of a device for carrying out the method according to the invention and the method which can be carried out therewith are described in more detail with reference to the drawing. It shows in a schematic representation:

Fig. 1

2 shows a longitudinal section of a device for coating foundry molds and / or foundry cores with a powder with a receptacle for and for a mixture of a granular base material and powder, vibrators, sound sources and a compressed air system for loosening the mixture containing the powder being connected to the container, in the starting position,

Fig. 2

the longitudinal section acc. 1 during the treatment of the foundry molds or cores with the raw material-powder mixture,

Fig. 3

1 shows a modified embodiment in which a gas-permeable plate for placing the molds and / or cores is arranged above a first plate of the receptacle, again in the starting position,

Fig. 4

the container acc. 3 during the treatment of the foundry molds or cores with the powder-raw material mixture,

Fig. 5

in a schematic and enlarged representation, the surface of a foundry mold or a core made of the basic components of the core or molding sand with intermediate binder components between the treatment with the basic powder mixture and

Fig. 6

a representation corresponding to Figure 5 after coating with the powder.

In the following description, identical parts of the various devices are given identical reference numbers, even if they differ in their function or design.

The device shown in FIGS. 1 to 4 above all has a receptacle 1 in which foundry molds or cores 2 can be inserted together with a basic material / powder mixture 3. The basic material can be sand, for example.

The receptacle 1 is with vibrators 4 and / or sound sources 5 and / or a compressed air system 6, with which the powder-raw material mixture 3 can be set in motion and loosened, so that it initially acc. Fig. 1 and also acc. Fig. 3 washed over it or above molds and cores 2

In the embodiment according to 1 and 2, a gas-permeable plate 7 is attached above the bottom of the receptacle 1, which allows the introduction and uniform distribution of the compressed air introduced by the compressed air system 6 over the entire horizontal cross section of the receptacle 1. This plate 7 is mounted between fasteners 8. Their meshes or openings are smaller than the average grain size of the mineral base material contained in the powder-base material mixture 3, so that the space between the bottom and this plate 7 remains free of this mixture 3. 1 shows the starting position, in which the molds and cores 2 rest on the powder-raw material mixture 3, which in turn is stacked on the plate 7.

2 shows how the molds and cores 2 are coated with powder. The mixture 3 is loosened by switching on the vibrators 4 or the sound sources 5. In addition, the compressed air system 6 can be switched on. As a result, the mixture 3 is fluidized and loosened up practically as in a fluidized bed, so that the molds and cores 2 are washed around by it, that is to say the powder in the mixture can be released to these parts 2.

The compressed air system 6 consists, as indicated schematically, of a compressed air source 9, a compressed air dryer 10, a pressure reducer 11 and of lines, valves and connections.

The loosening causes the individual particles and constituents of the powder-raw material mixture 3 to move intensively and thus wash around all contact surfaces of the foundry molds or cores 2. The kinetic energy of the mixture 3 for friction and for introducing the powder into the pores of the foundry molds or cores 2. As a result of this treatment, the roughness of the foundry molds or cores 2 is considerably reduced.

Comparing FIGS. 5 and 6, the surface of a foundry mold or a core 2 can initially be seen in a greatly enlarged and schematic representation. Fig. 5 before and gladly. Fig. 6 after treatment. Here you can see the raw material components 30, which can be grains of sand, for example, and binder components 31 arranged between them.

In Fig. 6, these are now covered and sealed on the surface with powder particles 32, the powder particles 32 forming a clear barrier to the outside, so that gases formed in the mold or core 2 during the casting process cannot initially escape, that is to say the casting workpiece not harm.

The embodiment of the device like. 3 and 4 largely corresponds to the gem. Fig. 1 and 2. Man only recognizes an additional plate 13 above the plate 7, which is perforated and on which the foundry molds or cores 2 can be placed. Thus, in the starting position and also during their treatment, they are at a certain distance from the gas-permeable plate 7.

This further plate 3 is mounted on damping elements 12, so that in the event of a vibration around the vibrations, these damping elements 12 can be compensated so that the foundry molds or cores 2, which are located on the plate 13, cannot be damaged by such vibrations .

In this case too, the mixture 2 is loosened after the corresponding actuation of vibrators and / or sound sources and / or of the compressed air system, so that the latter forms and cores 2 and the surface coated with powder in the manner as already mentioned in the first embodiment, so that a result corresponding to FIG. 6 can be achieved.

The compressed air can be dried efficiently so that the powder in the mixture 3 is not made unusable by atmospheric moisture. The intensity of the flushing with compressed air can be controlled via the pressure reducer 11. The duration of the rinsing depends on the dimensions of the receptacle 1, the shape or core geometry, the grain size of the base material and the grain size of the powder and can be varied within wide limits.

With both devices, on the one hand gladly. 1 and 2 and on the other hand gladly. 3 and 4, one or more foundry molds and / or foundry cores 2 can thus be coated with a powder, the powder being first mixed with a granular mineral base material or sand, so that the mixture 3 already produced in the figures is produced, and then can the foundry mold and / or the foundry core 2 to be coated with the powder of this mixture 3 of dry, granular mineral base material and powder, so that the larger base material passes the powder adhering to them to the surface of the molds and cores 2 and sort of rubs on and into the surface, which smoothes it at the same time. Existing pores are closed, so that the desired barrier is created which, at least during the first phase of the casting process, prevents gas from escaping from the mold or core 2 and thereby damaging the cast workpiece.

Claims (9)

Process for coating foundry molds and / or foundry cores (1) with a powder to form a barrier between the mold or core (2) and the casting material against gases penetrating into the solidifying cast body, characterized in that the powder contains a granular mineral base material or sand is mixed and that the foundry mold and / or the foundry core (2) for coating with the powder is washed around by this mixture (3) of dry granular mineral base material and powder. A method according to claim 1, characterized in that the mixture (3) of base material and powder is loosened to form a flowable mass in the area of the foundry mold (s) and / or the foundry core (s). A method according to claim 1 or 2, characterized in that the raw material powder mixture or sand powder mixture (3) is loosened by vibration or sound or a carrier medium, in particular compressed air, or the combination thereof. Method according to one of claims 1 to 3, characterized in that the powder covering the grains of the base material or sand of the mixture is transferred to the surface of the foundry mold or the foundry core by friction on it and is in particular introduced into the pores of the surface. Method according to one of claims 1 to 4, characterized in that the mixture (3) consisting of base material or sand and powder is used several times and that powder is added to this mixture from time to time. Device for carrying out the method according to one of the preceding claims with a receptacle (1) for the foundry mold (s) and / or foundry cores and a mixture of a granular base material and powder, characterized in that vibrators (4) on the container (1) and / or sound sources (5) and / or a compressed air system (6) are connected in order to loosen and fluidize the basic material powder mixture (3). Apparatus according to claim 6, characterized in that the receptacle (1) has a bottom on which the mixture (3) lies directly, on which the foundry mold and / or the foundry core (2) can be placed. Device according to one of claims 5 or 6, characterized in that a gas-permeable plate (7), a net or the like is arranged above the bottom for placing the mold and / or the core in the receiving container (1) or that a supporting device for the Shapes or cores is arranged on the bottom of the receptacle. Device according to one of claims 5 to 8, characterized in that a compressed air dryer (10) and optionally a pressure reducer (11) are arranged in the compressed air supply to the receiving container (1).

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