EP0028267A1 - Apparatus for drying foundry moulds and cores - Google Patents

Abstract

1. Apparatus for drying wet casting moulds and cores (3 to 6) which are produced according to the vacuum process and covered with films (10) of plastics material, liquid coatings being applied to the films (10) of plastics material, the casting moulds and cores (3 to 6) being subjected to a vacuum during drying and the gases and vapours formed being sucked away, characterized in that the coating consists of a black wash, the apparatus (1, 2, 16) comprises a reflector plate (15) towards the ground for receiving the casting moulds and cores (3 to 6) to be dried and a hood-shaped reflector shield (17) which receives the devices producing the microwaves, and devices are provided in the drying apparatus (1, 2, 6) for producing a vacuum in the casting moulds and cores (3 to 6).

Description

The invention relates to a method and a device for drying moist molds and cores and to the sizes applied to them, in particular to sizes applied to plastic films of foundry molds produced by the vacuum molding process.

The drying of foundry molds and cores takes a considerable amount of time, especially when moist parts in green sand molds or molds that have to be hardened by thermosetting binders have to be dried. But the drying of sizes also takes a relatively long time and is a decisive factor in determining the work cycle, especially for foundry molds that are manufactured using the vacuum molding process.

For the production of foundry molds after the vacuum forming method, a thin _P is first lastikfolie pulled over a model and sucked by vacuum thereon. Then this film is sprayed with a size, which is crucial to improve the Surface quality of the product to _G ußstückes contributes. These sizes are offset generally with alcohol or water and have been absolutely be dried prior to introduction of the _F ormsandes to avoid subsequent casting defects.

For drying the sizing is generally an _H eißluftgebläse, the extensive mechanical devices requires as air generator, air supply and exhaust fans, air caps and pipes and chimneys to the resulting gases and vapors to dissipate.

This drying time determines the work cycle of the machine, since it is considerably longer than the other work steps.

The invention has for its object to propose a method and an apparatus for drying casting molds and cores, the bezw. which on the one hand considerably reduces the drying time and on the other hand the drying of the size applied to plastic films even after the foundry mold sand has been introduced, i.e. after completion of the foundry mold.

This object is achieved in that the foundry molds or cores are dried by microwaves and that the molds and cores are exposed to a vacuum and the gases and vapors that occur are extracted.

When drying with microwaves, only the moist parts of the molds and cores or the sizes are heated directly, while the plastic film and also the other parts of the foundry mold remain cold. This way of drying foundry molds is extreme for two reasons economically. On the one hand, the energy consumption remains very low compared to conventional drying methods and on the other hand the drying time is reduced by a factor of 10. In particular for foundry molds which are produced by the vacuum molding process, this means that the drying time is no longer decisive for the cycle time of the machine. In addition, this new process allows the foundry molds to be dried after completion. ie outside the machine. In a conventional drying, this was not possible, because at the relatively low drying temperatures the time required for heating the inner parts of the _G ießereiform so long that an effective drying can not be achieved in reasonable times. When using higher drying temperatures, there is a risk of damage to the plastic film that keeps the shape airtight.

Further advantageous refinements of the invention, in particular the design of a device for drying foundry molds and cores, can be found in the subclaims.

An embodiment of the invention is described below with reference to the drawing. 1 and 2 each show a drying device according to the invention during the drying process of foundry molds produced by the vacuum process.

In Fig. 1, two foundry mold boxes 1, 2 are shown in section, the annular vacuum channels 3,4 have, which can be connected to a vacuum line, not shown, via vacuum connections 5, 6. The vacuum channels 3, 4 have openings 7, 8 which point towards the inside of the foundry mold box and are so large that no foundry mold sand can penetrate into the channels 3, 4. Both of the mold box 3 as well as the _G ießereiformkasten 4 are on the closed one side with a plastic film 9 and are on the opposite side in each case by a plastic film 10, which are kept pressed by the external air pressure against the filled in the casting mold boxes loose, binderless foundry molding sand 11 . A size 12 is applied to the foils 10 and is to be dried in the present exemplary embodiment. A core 14 is inserted in the interior of the cavity 13 of the casting mold.

To dry the size 12, the foundry mold boxes are placed on a reflector plate 15 of a microwave drying device, designated overall by 16. The reflector plate 15 has the same circumferential contour as the foundry mold boxes 2, 3, which provides complete shielding downwards and to the sides. A reflector screen 17 is placed on the upper foundry mold box halves 1, the circumferential contour of which also corresponds to the circumferential contour of the foundry mold boxes 1, 2. The microwave transmitters 18 are arranged in the reflector screen 17. The electrical connections have been omitted for simplicity.

The drying process takes place as follows: The foundry mold sand 11 in the two mold halves is constantly evacuated via the evacuation lines 5, 6. On the one hand, this is necessary so that the loose, binder-free Sand foundry mold remains dimensionally stable. After switching on the microwave drying device, the microwaves penetrate the plastic films 9, 10 unhindered and are reflected on the reflector plate 15. Lateral exit of the microwaves is prevented by the mold boxes 1, 2. The energy contained in the microwaves causes the moisture molecules in the size 11 to vibrate, as a result of which the latter is heated and evaporated. The resulting vapors are suctioned off directly via the evacuation lines 5, 6, so that, on the other hand, it is prevented that after cooling, the steam condenses again in the foundry mold and can lead to casting errors.

The embodiment of FIG. 2 differs from that of FIG. 1 in that the reflector screen 17 includes the mold boxes. In order to evacuate the foundry molds, vacuum lines going through the reflector plate 15 are connected to the vacuum connections.

However, it is also conceivable to design the drying device as an oven with a closable loading opening.

Claims (3)

1. A method for drying moist molds and cores and on these applied sizes, in particular of sizes applied from plastic films of foundry molds produced by the vacuum process, characterized in that the drying of the molds or cores is carried out by microwaves and that the molds and cores during drying are exposed to a negative pressure and the gases and vapors are extracted. 2. Device for drying foundry molds according to one of claims 1 to 3, characterized in that the device (16) from a bottom reflector plate (15) for receiving the foundry molds and cores to be dried and from a hood-shaped reflector screen (17) exists, which receives the microwave generating devices and that devices for generating a negative pressure in the foundry molds and cores (3 to 6) are present in the drying device (16). 3. Apparatus according to claim 3 for use in frame-shaped mold boxes, in particular for foundry molds produced by the vacuum molding process, characterized in that the reflector plate (15) and the reflector screen (17) have the same peripheral contours as the mold boxes (1, 2) and that the interior of the mold boxes (1, 2) and thus the molds and cores are evacuated via vacuum lines (3, 4) and connections (5, 6) attached to the mold boxes.

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