EP1745872A2 - Process for handling foundry moulding materials - Google Patents

Abstract

Treatment of foundry molding material (I), comprising core sand bonded with inorganic binder(s), involves separating (I) from the casting in dry form, crushing, screening (to give a predetermined grain size and remove fines) and dividing the sand (hardened by moisture extraction) into two partial streams. One stream is subjected to intermediate storage and the other to wet regeneration, and the stored and regenerated streams are then recombined.

Description

The invention relates to a method for treating foundry mold materials containing core sand and binder.

A method of mixing foundry sand containing core sand and foundries containing organic binders is described EP 0 445 436 B1 in which the mix is conveyed from a mixing space into a mixing space separated therefrom by an installation body, and the mixing got rotation is decelerated in the plane determined by the installation bodies; This achieves a high mixing intensity. It is also described that the mixing effect of mixers with rotating mixing tool can be increased by increasing the mixing tool speed until the friction of the mixture at the mixing container wall is no longer sufficient and the mix follows as a more or less compact mass of the rotary motion of the mixing tool. Thus, the friction, Zerteil- and Umschichtkräfte required for the mixing process are limited. This property is particularly disadvantageous when viscous components are present in the mix.

The collective term "binder" encompasses a product which is capable of combining both similar and different substances. The setting process is carried out by physical drying, by solidification or by a strong increase in viscosity - such as a melting process - or by chemical reactions. For example, bitumen and tar are binders in road construction for aggregates, and in the field of refractories, aluminum phosphates may be used as binders. In the case of building materials, in turn, additives such as sand and gravel are set and cemented by hardening the water-borne binders.

The assignment of binders has changed lately. For example, attempts are being made to replace hitherto customary organic binders in the casting area for cores - and in part also for molds - with inorganic binders which are non-toxic and are hardened without dehumidification by dehumidification. These are, for example, water glass, magnesium sulfate, sodium phosphate and similar substances.

The solidification of a closed sand in a core box of the casting industry sand binder mixture is done by dehumidification; For example, hot core boxes, microwaves or hot air conducted through the sand binder mixture into the core box are used. After pouring the castings, the hard core can be removed from the castings, for example, by shaking, in a water bath or by high pressure water jets.

Of great importance is that the sand then for economic reasons, must be used again for the production of new cores and molds, which has led to a sand cycle. If the cores are dissolved by water, then the entire sand must then be dried again so that it is suitable for transport by means of pneumatic conveying, for storage in silos and for dosing the next round - in other words: it must be free flowing, which requires a drying of the sand.

It is well known to dry sand with heat, thanks to which the sand also heats up. Since the types of binder used, the curing of the sand by heating takes place, remains warm sand for the production of cores i. w. not suitable. For this reason, the sand must be cooled after drying. As considerable quantities of sand circulate - quantities of more than 10 t / h have to be processed - the energy and drying required for drying and cooling and the equipment requirements can make the use of these environmentally friendly binders uneconomic.

With dry coring it has been shown that the sand qualities are no longer sufficient after a few rounds due to increasing binder content and influences of the casting process.

Against the background of these considerations, the inventor has set itself the goal of developing a method that makes it possible to regenerate core sand economically, which is provided with cured by moisture removal inorganic binders. So should then also in the EP 0 445 436 B1 described device can be used efficiently for inorganic binder.

To achieve this object, the teaching of the independent claim; the dependent claims indicate favorable developments. In addition, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of the invention. For given naming ranges should also within the mentioned limits as limits and can be used arbitrarily.

According to the invention, the core sand bonded with inorganic / inorganic binder (s) is separated after the casting process dry from castings formed thereby; lumpy pieces are crushed dry, the core sand is then sieved to a predetermined grain size and unwanted fines fraction removed, after which the cured by moisture removal core sand is divided into two streams. According to the invention, one partial stream is fed to an intermediate storage facility and the other partial flow is regenerated.

According to a further feature of the invention, the partial stream to be regenerated is fed to a reactor with liquid and the introduced sand is treated until the grain surface is sufficiently cleaned of binder residues and products of the casting process; In addition, it is intended to add to the liquid, in particular, water additives, for example sodium hydroxide solution in waterglass binders.

As low it has proven to deposit the free liquid after the cleaning process and to dry the sand of the partial flow; the separation of the free liquid should preferably be carried out on vibrating screens, sieve drums or centrifuges.

According to a further feature of the invention, the intermediate partial flow are combined on the one hand and the other partial flow after its regeneration. In this case, a degree of drying, in which the mixture of the dry intermediate stored partial stream and the wet regenerated Partial flow is free-flowing, proved to be particularly favorable. The remaining moisture content of the mixed two partial streams should preferably not exceed 0.1%.

Furthermore, it should flow through the partial flow with dried, cool air in the fluidized bed or in the flow stream or a flow through the partial flow with heated air of low relative humidity. For example, molecular sieve beads of - in particular hydrophilic - zeolites can be admixed or else grains of silica gel.

According to the invention, the surface-wet grains of sand of the partial stream to be regenerated are treated in a dry reactor. For this purpose, the sand should be mixed with grains of a substance that absorbs the moisture of the sand grain surface, in particular with grains of a large inner surface of porous materials.

Preferably, the grains of sand and the moisture-absorbing grains are separated after a reaction time, in which latter the mixture rests or in which it is agitated. Depending on the properties of the grains used, the reaction time to absorb the moisture from the sand surface is between 10 seconds and a few minutes.

According to a further feature of the invention, the moisture absorbed is removed from those drying grains outside the sand cycle.

In another embodiment of the invention, the wet sand grains are brought into contact with fibrous substances whose fibers absorb the moisture of the sand grains; after separation of the sand from the fibrous substances or the like by pressing, air purging. be dried so that they can be used again to absorb moisture from sand grains.

The fibrous materials - for example felts, scrims and fabrics made of organic and mineral fibers, in particular aramid fibers - can be used in the form of conveyor belts, drum linings or parts to be mixed with the sand and separated again from it. Moreover, the treatment of the grains of sand batchwise or - preferably - continuously.

Instead of fibrous substances, bodies and webs of open-cell foams, e.g. made of polyurethane foam.

The particular advantage of this approach is that the sand remains cold and expensive heating and cooling facilities are not needed.

Thus, this method involves regenerating core binder bonded with inorganic binders which has been cured by moisture removal and works without heating the sand grains during regeneration. For the necessary process steps simple devices can be used with low energy consumption and low wear.

Fig. 1:

den schematisierten Stammbaum zu einer Sandaufbereitung;

Fig. 2:

Verfahrensschritte zu einem Bereich des Stammbaumes der Fig. 1;

Fig. 3:

weitere Verfahrensschritte in dem Bereich der Fig. 2.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing; show in it

Fig. 1:

the schematized family tree for a sand preparation;

Fig. 2:

Method steps to an area of the family tree of Fig. 1;

3:

further method steps in the area of FIG. 2.

• Trockene Trennung gebundenen Sandes von Gussstücken (Bezugszeichen A).
• Trockene Zerkleinerung der stückigen Teile (Bezugszeichen B).
• Einen Siebvorgang zum Sieben des Sandes auf die gewünschte Korngröße (Bezugszeichen C).
• Das Entfernen von unerwünschten Feinteilen in Zone D.
• Das Teilen der Sandmenge im Bereich E in zwei Teilströme, deren einer als Teilstrom S₁ einem Zwischenlager zugeführt wird, wohingegen der andere Teilstrom S₂ zu regenerieren ist.
• Die Regenerierung des letztgenannten Teilstromes in Zone F.
• Das Zusammenführen und Vermischen der beiden genannten Teilströme in Zone G.

The drawing shows that the regeneration of the core sand takes place in several steps:

• Dry separation of bonded sand from castings (reference A).
• Dry comminution of the lumped parts (reference B).
• A sieving process to sieve the sand to the desired grain size (reference C).
• The removal of unwanted fines in zone D.
• The sharing of the amount of sand in the region E into two partial streams, one of which is supplied as a partial stream S _{1 to} an intermediate storage, whereas the other partial stream S _{2 is} to be regenerated.
• The regeneration of the latter part of the stream in zone F.
• The merging and mixing of the two mentioned sub-streams in zone G.

In this case, the amount of withdrawn for the regeneration sub-stream S _{2 should} be chosen so that after merging the two streams S ₁ , S ₂ in the long-term cycle sufficiently good sand properties. Any resulting sand losses can be compensated with new sand and the regeneration effect can be supported.

• F₁: Das Einbringen des regenerierten Sandstromes S₂ in einen Reaktor mit Flüssigkeit.
• F₂: Das Behandeln des eingebrachten Sandes über einen bestimmten Zeitraum, der es ermöglicht, die Kornoberfläche ausreichend von Binderresten und Produkten des Gussvorganges zu reinigen.
• F₃: Das Abscheiden von freiem Wasser beispielsweise auf Schwingsieben oder in Siebtrommeln.
• F₄: Das Trocknen des Sandes.

The above-mentioned regeneration process in zone F contains the following substeps according to FIG. 2:

• F ₁ : The introduction of the regenerated sand stream S ₂ in a reactor with liquid.
• F ₂ : treating the introduced sand over a certain period of time, which makes it possible to sufficiently clean the grain surface of binder residues and products of the casting process.
• F ₃ : The separation of free water, for example on vibrating screens or in screening drums.
• Q ₄ : The drying of the sand.

As far as the partial section F ₂ is concerned, the cleaning of the introduced sand takes place in a liquid; as such, water is suitable. To assist the dissolution process, additives can be added to the water in a suitable amount, for example sodium hydroxide solution with waterglass binder. This cleaning process can be mechanically supported, for example, by stirrers, oscillations and ultrasonic radiators. The treatment may be batchwise or continuous.

During the drying process, the degree of drying is selected so that the mixture of the completely dry sand stream S _{1 of} the intermediate storage and the wet-regenerated sand stream S _{2 is} free-flowing; Thus, the composite of two streams S ₁ , S ₂ sand stream can be handled with the usual facilities of a foundry.

According to FIG. 3, several processes are alternatively used for the above-described process step F ₄ of sand drying, ie the treatment of the sand grains with moist surfaces in a drying reactor, in which the sand grains do not or only very slightly heat; on the one hand there is a flow with dried cooler air in the fluidized bed or in the flow stream (step F _4.1 ), on the other hand, a flow of slightly heated air with low relative humidity in the air flow or fluidized bed (step F _4.2 ). Or the sand is mixed with grains of a substance that absorbs the moisture from the sand grain surface (step F _4.3 ).

The sand is mixed with grains of a substance, which absorbs the moisture from the sand grain surface. For example, the grains consist of porous materials with a large internal surface area. After a sufficient reaction time, in which the mixture can be moved or rest, the grains of sand and the moisture-absorbing grains are separated, for example by sieving, if their dimension is greater than that of the grains of sand. So the drying takes place without heating the sand. The dried sand is added to the untreated sand stream S ₁ . The residual moisture is distributed over the total sand amount.

The drying grains outside the sand cycle are deprived of the absorbed moisture.

Another way, shown by way of example, to reduce the surface moisture of the sand grains sufficiently, is to bring the wet sand grains with fibrous substances in contact. The fibers absorb the moisture of the grains of sand and, when the sand has been separated from the fibrous materials, are dried, for example, by squeezing, air purging or similar steps, so that they can regain moisture from grains of sand.

Claims (17)

Process for treating foundry mold materials containing core sand and binder,
characterized,
that the core sand bound with inorganic / inorganic binder / n dry is separated after a casting process of resulting castings and pieces are dry crushed, the core sand is sieved to a predetermined grain size and unwanted fines are removed, after which cured by sanding core sand in two Partial streams (S ₁ , S ₂ ) subdivided and fed to a partial flow of an intermediate storage and the other is regenerated. A method according to claim 1, characterized in that the partial stream to be regenerated (S ₂ ) fed to a reactor with liquid and the introduced sand is treated until the grain surface is sufficiently cleaned of binder residues and products of the casting process. A method according to claim 2, characterized in that the liquid, in particular water, additives are added, for example, sodium hydroxide solution in water glass binder. A method according to claim 2 or 3, characterized in that after the cleaning process, the free liquid deposited and the sand of the partial stream (S ₂ ) is dried, wherein optionally the deposition of the free liquid on vibrating screens or screening drums is performed. Method according to one of claims 1 to 4, characterized in that the intermediate stored partial flow (S ₁ ) and the other partial flow (S ₂ ) are brought together after its regeneration. A method according to claim 4 or 5, characterized by a degree of drying in which the mixture of the dry temporarily stored partial stream (S ₁ ) and the wet regenerated partial stream (S ₂ ) is free-flowing, wherein the degree of moisture is preferably at most 0.1%. A method according to claim 6, characterized by a flow through the partial stream (S ₂ ) with dried, cool air in the fluidized bed or in the flow stream or characterized by a flow through the partial stream (S ₂ ) with heated air of low relative humidity in the stream or fluidized bed. Method according to one of claims 4 to 7, characterized in that the surface wet sand grains of the partial stream to be regenerated (S ₂ ) are treated in a dry reactor. A method according to claim 8, characterized in that the sand is mixed with grains of a substance which absorbs the moisture of the sand grain surface. A method according to claim 9, characterized by the admixture of molecular sieve beads of zeolites, in particular of hydrophilic zeolites or characterized by grains of silica gel. A method according to claim 9 or 10, characterized by grains of porous material having a large inner surface. Method according to one of claims 9 to 11, characterized in that the grains of sand and the moisture-absorbing grains are separated after a reaction time in which the mixture rests, wherein the reaction time for receiving the moisture is preferably about 10 seconds and five minutes. Method according to one of claims 9 to 11, characterized in that the grains of sand and the moisture-absorbing grains are separated after a reaction time in which the mixture is moved, wherein the reaction time for receiving the moisture is preferably about 10 seconds and five minutes. Method according to one of claims 10 to 13, characterized in that the drying grains of silica gel outside the sand cycle, the absorbed moisture is removed. Method according to one of claims 4 to 8, characterized in that the wet sand grains are brought into contact with fibrous substances whose fibers absorb the moisture of the sand grains, optionally felts, scrims or fabrics of organic and mineral fibers are used, in particular aramid fibers. A method according to claim 15, characterized in that after separation of the sand from the fibrous materials, these by pressing, air purging or the like. dried to the extent that the moisture of sand grains can be absorbed by them. Method according to one of claims 4 to 8, characterized in that the wet sand grains are brought into contact with webs and / or bodies of open-cell foams, in particular with polyurethane foam, which absorb the moisture of the sand grains.

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