Patent Application
20130042989
The invention relates to a method for producing molds or cores, in particular for foundry purposes, wherein molding compound or sand and at least one binder which is at least predominantly inorganic, water-soluble and/or hygroscopic are mixed by means of a mixing apparatus, and wherein this mixture is fed to at least one sand storage unit of a core or mold production apparatus with the aid of a feed device.
The invention furthermore relates to an apparatus for producing molds or cores, in particular for foundry purposes, having a mixing apparatus for mixing molding compound or sand and a binder which is at least predominantly inorganic, water-soluble and/or hygroscopic, and having a feed device for conveying the mixture to a sand storage unit of a core or mold production apparatus.
Such a method and a comparable apparatus are known from practice and have proved suitable.
It may be the case, however, that moisture originally present in the binder escapes during the mixing operation and also thereafter, such that the mixture dries out and becomes incrusted in places, which on the one hand can make it harder to forward and feed the mixture to the core or mold production apparatus and on the other hand can contaminate the mixing apparatus and also the downstream feed device and the sand storage unit. The mold production apparatus itself, too, can be blocked by a clumped mixture. Rejects, a stop in production, and a high level of cleaning expenditure for the overall system—from the mixing apparatus to the mold production apparatus—may be the consequence.
To date, these problems have been reduced by short cleaning intervals, by cooling the mixture or, if appropriate, by increasing the binder content, i.e. by additional expenditure.
The object is therefore that of providing a method and also an apparatus of the type mentioned in the introduction in which premature drying-out and incrustation of the mixture and the associated contamination of the mixing apparatus and/or of the feed device and/or sand storage unit are largely avoided.
To achieve this object, the method defined in the introduction provides for the mixture-free region of the mixing apparatus, at least at times, and/or the mixture-free region of the feed device located between the mixing apparatus and the core or mold production apparatus and/or the mixture-free region of the sand storage unit downstream of the feed device and upstream of the core or mold production apparatus to be moistened or kept moist. The moistening establishes a high atmospheric humidity in said regions, which can prevent or reduce evaporation or escape of moisture from the mixture. Therefore, the mixture is unable to harden or dry out or form crusts either completely or in parts. Instances of contamination of the mixing apparatus and/or of the feed device and/or of the sand storage unit, but also of the core or mold production apparatus, can thus be reduced and/or the required cleaning intervals can be prolonged. This fact can have a particularly positive effect on the productivity of the core and mold production process, and in addition the cleaning intervals can be prolonged and the cleaning costs can be lowered.
It is particularly favorable here if the mixture-free region of the mixing apparatus is moistened or kept moist at least at times at least during the mixing operation. Primarily as a result of the mixing operation, moisture could escape from the mixture into the mixture-free region. By moistening the mixture-free region, it is easily possible to prevent moisture from escaping from the mixture, drying it out, settling on parts of the mixing apparatus and contaminating the mixing apparatus.
In addition, it may be favorable if evaporation or escape of moisture from the mixture is reduced or prevented by virtue of the fact that the atmospheric humidity above the mixture is kept high by feeding in moisture, in particular is kept at approximately 70% to 100%, preferably at approximately 80% to 100%. Such atmospheric humidity values minimize the moisture gradients between the mixture and the air surrounding the mixture, as a result of which the release of moisture from the mixture to the air by evaporation and associated, undesirable hardening of the mixture can be prevented to the greatest possible extent.
It is possible here that the liquid which serves for moistening or the water which serves for moistening is atomized by means of ultrasound to form a suspendable aerosol and fed to the mixing apparatus and/or to the feed device and/or to the sand storage unit. The suspendable aerosol here contains such small liquid constituents that they can evaporate directly and increase the atmospheric humidity without condensing beforehand and without being deposited as a condensate in the mixing apparatus and/or the feed device and/or the sand storage unit. The size of the liquid particles produced by ultrasound can lie in the order of magnitude of 0.01 mm or below. At the same time, a sufficiently high atmospheric humidity, which can prevent the sand/binder mixture from drying out, is achieved. Both the mixing operation and the feeding and the storage of the sand/binder mixture can be effected reliably.
The aerosol or the quantity of this suspendable aerosol and the magnitude of the volumetric flow provided with the aerosol can be set by changing the pulse packets emitted by the ultrasound generator(s) and/or by changing the voltage of the ultrasound generator(s). In this way, it is possible to adapt the quantity of the suspendable aerosol, with which the mixing apparatus and/or the sand storage unit are moistened, to the existing conditions such as atmospheric humidity, magnitude of the volume to be moistened and ambient temperature.
A particularly expedient configuration of the method according to the invention is provided in the fact that the suspendable aerosol is formed and conducted via one or more lines to the mixing apparatus and/or to the feed device and/or to the sand storage unit. The aerosol is therefore produced outside the mixing, feed and/or the sand storage unit. No additional installation space is therefore required in the mixing, feed and/or the sand storage unit for the production of the aerosol. Nevertheless, it is possible to provide a sufficiently high atmospheric humidity, such that it is possible to avoid drying out of the sand/binder mixture without, however, feeding in too much liquid, as a result of which in particular the binder could possibly be washed out or dissolved.
To achieve the object, the apparatus defined in the introduction is characterized in that the mixing apparatus and/or the feed device and/or the sand storage unit are provided with a moistening device, which acts upon the interior thereof or opens out into the interior thereof. With the aid of the moistening device, it is possible to produce and maintain the desired atmospheric humidity in a particularly simple manner, such that the risk of drying out on account of a loss in moisture of the mixture in the mixing apparatus and/or in the feed device and/or in the sand storage unit can be reduced. This can favorably reduce the contamination of the mixing apparatus and/or of the feed device and/or of the sand storage unit, but also of the downstream core or mold production apparatus.
It is possible here for the moistening device to have at least one ultrasound generator in the form of an ultrasound atomizer for water or for a liquid containing water in particular. The invention therefore takes advantage of the fact or knowledge that ultrasound atomizers can atomize water or a water-containing liquid in such a manner that the individual droplets may be smaller than 20 one-thousandths of a millimeter or even smaller than 10 one-thousandths of a millimeter, such that they pass over into atmospheric humidity and are not deposited, or are deposited scarcely, as a film of moisture on parts of the mixing apparatus and/or of the feed device and/or of the sand storage unit.
It is particularly favorable here if the ultrasound atomizer(s) and a liquid reservoir belonging thereto are arranged spatially separate from the mixing apparatus and/or from the feed device and/or from the sand storage unit and are connected to the region(s) to be moistened via at least one tubular or hose line. Tests have shown that the suspended aerosol which is formed from water or from a water-containing liquid by an ultrasound atomizer can be transported without any problems over a plurality of meters through such a line in order to provide, at the desired location, sufficiently moist air which prevents the mixture of sand or molding compound and binder from drying up in particular in the mixing apparatus itself, the feed device and/or the sand storage unit, without however excessively soaking said mixture. The liquid reservoir with the ultrasound generator(s) can thus advantageously be arranged at a location of the mold or core shooting machine or close to this machine, where sufficient space therefor is available.
It is particularly expedient here if the mixing apparatus, the feed device and the sand storage unit are each connected to the moistening device via a tubular or hose line. Using tubular or hose lines provided separately for the individual apparatus regions, it is possible for moist air to be conducted into the mixing apparatus, the feed device and/or the sand storage unit in a manner tuned individually to the individual process steps. It is thus possible with even greater reliability to prevent the sand/binder mixture from losing moisture in one of the aforementioned regions, drying out and contaminating the latter.
A development of the apparatus according to the invention can provide for the number of ultrasound atomizers to at least correspond to the number of tubular or hose lines, and for at least one ultrasound atomizer to be provided for each tubular or hose line. With at least one ultrasound atomizer for each tubular line, it is possible that, even with different atmospheric humidity values in the regions to be moistened, a sufficient quantity of liquid can be atomized and fed to the respective regions, in order to prevent the mixture from drying out and becoming incrusted.
In addition, it may be expedient if a fan or a pressurized gas connection is arranged, in particular, above the liquid surface in the liquid reservoir in order to transport the moisture or the aerosol from the ultrasound atomizer(s) to the mixing apparatus and/or feed device and/or sand storage unit. Although the aerosol could flow to the mixing apparatus and/or feed device and/or sand storage unit primarily in the case of relatively short lines on account of its own pressure, a fan or a pressurized gas connection can improve this flow or else make it possible for there to be a greater distance between the ultrasound atomizer and the regions of the apparatus to be supplied with moist air. Furthermore, a fan and/or a pressurized gas connection can overcome differences in height between the ultrasound atomizer and said regions of the apparatus at the core shooting device. Above all, the aerosol can also be conveyed upward, such that the ultrasound atomizer with the liquid reservoir can also be arranged at a greater depth, where sufficient space therefor is generally available. In addition, it is advantageous in the case of such an arrangement that a condensate which possibly forms on the inner walls of the tube or of the hose in which the aerosol is transported can flow back downward into the liquid reservoir.
A modified embodiment of the invention may provide for the feed device to be at least one movable transport bucket. A movable transport bucket as the feed device makes it possible to transport the sand/binder mixture even over relatively large distances from the mixing apparatus to the sand storage unit of the core or mold production apparatus.
An exemplary embodiment of the invention is described in more detail hereinbelow with reference to the drawing. The single FIGURE shows, in a schematized illustration,
An apparatus, denoted as a whole by 1, for producing molds or cores, in the exemplary embodiment for producing cores for foundry purposes, has a mixing apparatus 20 with a mixing tool 22 for producing a mixture M by mixing molding compound or sand and a binder, a feed device 30 for conveying the mixture M to a sand storage unit 40 with a closure device 42, and also a core or mold production apparatus 50.
For moistening the air in the apparatus 1, use is made of a moistening device 2 with two ultrasound atomizers 60 for water or for a liquid 71 containing water in particular and with a liquid reservoir 70. With the aid of these ultrasound atomizers 60, the liquid 71 can be atomized to form a fine aerosol. This aerosol is indicated by the two mushroom clouds 61 in the interior of the liquid reservoir 70 in the FIGURE.
An embodiment of the apparatus which is not shown may also provide, however, for three ultrasound atomizers 60 to be provided, of which a respective one is assigned to one of the three tubular lines 81, 82 and 83, such that at least one ultrasound atomizer is therefore available for each tubular line 81, 82 and 83 for feeding the liquid into the regions to be moistened. The quantity of moisture can thus be measured and fed individually for the individual regions.
With reference to the FIGURE, it can also be seen that the moistening device 2 with the ultrasound atomizers 60 and the liquid reservoir 70 are arranged spatially separate from the mixing apparatus 20, the feed device 30 and the sand storage unit 40, but are connected to the regions to be moistened via tubular lines 81, 82 and 83, which reach directly from the liquid reservoir 70 into said regions of the apparatus 1, where they supply mixture-free regions 21, 31 and 41 with moist air. In the exemplary embodiment, not only the mixing apparatus 20 but also the feed unit 30 and the sand storage unit 40 at least at times each have a mixture-free region 31 and 41.
A fan 90 and also a pressurized gas connection 10 can additionally be seen in the liquid-free region of the liquid reservoir 70. Either the fan 90 or the pressurized gas connection 10 or preferably both serve for conveying and for transporting the aerosol produced by the ultrasound atomizers 60 via the tubular lines 81, 82 and 83 to the mixing apparatus 20, the feed device 30 and the sand storage unit 40.
Sufficiently moist air above the mixture M is blown via the tubular lines 81, 82 and 83 into the mixing apparatus 20, the feed device 30 and the sand storage unit 40, such that the mixture M cannot harden and dry out in any of the three regions of the apparatus 1, which prevents the contamination of the apparatus 1 and thereby improves the uninterrupted operation of the apparatus 1 and also increases the quality of the sand cores produced.
A modified embodiment of the apparatus 1 which is not shown in more detail can provide for the feed device 30 to be at least one movable transport bucket which can be moved between the mixing apparatus 20 and the sand storage unit 40 with the aid of a railway or with a crane, for example. This can be favorable particularly for crossing relatively large distances between the mixing apparatus 20 and the sand storage unit 40.
To produce molds or cores for foundry purposes from a mixture M of molding compound or sand and at least one binder, the mixture M is mixed by means of a mixing apparatus 20 and fed to at least one sand storage unit 40 of a core or mold production apparatus 50 with the aid of a feed device 30, wherein the mixture-free region 21 of the mixing apparatus 20, at least at times, and/or the feed device 30 located between the mixing apparatus 20 and the core or mold production apparatus 50 and/or the sand storage unit 40 downstream of the feed device 30 and upstream of the core or mold production apparatus 50 are moistened or kept moist by means of a liquid 71, wherein the liquid 71 which serves for moistening is atomized by at least one ultrasound atomizer 60 to form a suspendable aerosol and fed to the mixing apparatus 20 and/or to the feed device 30 and/or to the sand storage unit 40 via tubular lines 81, 82 and 83.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102010018751.8 | Apr 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/001757 | 4/8/2011 | WO | 00 | 10/31/2012 |
