EP1759787A1 - Process for the treatment of foundry moulding material - Google Patents

Abstract

Treatment of foundry mold materials, containing core sand and binder involves subjecting the core sand (Sk) bonded with inorganic binder(s), while still hot after casting, to dry separation (A1) from the casting (M1), dry crushing (B1) and subdivision (E1) into two hot partial streams (T1, T2).

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. In particular, it should be possible to regenerate the core sand after the casting, before the core sand could cool down.

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 bound with inorganic / inorganic binder (s) is dry-separated after a casting process in still tempered state from castings formed thereby, dry-comminuted, and the tempered core sand is subdivided into two partial streams. The one partial stream is buffered according to the invention and the other partial stream is regenerated. For this purpose, it has proved to be advantageous that, after the division process, the partial stream to be regenerated is fed to a liquid-containing reactor and the introduced sand is wet-regenerated until the grain surface has been sufficiently cleaned of binder residues and products of the casting process; then this partial stream is mixed with the other partial stream. In this case, the second partial flow is dried according to the invention by the heat of the first partial flow.

According to another feature of the method according to the invention, the first partial flow is cooled by the heat of vaporization of the moisture of the second partial flow.

In the context of the invention, the first partial stream is passed through the heating of the second partial stream to the mixing temperature of the merged partial streams after cooling of the second partial stream and the second partial stream is subjected to a wet regeneration by its introduction into the reactor. In addition, a cleaning of the grain surface of the introduced sand of binder residues and products of the casting process should be done by means of a liquid, in particular by water.

To assist the dissolution process, additives can be added to the water in a suitable amount, for example sodium hydroxide solution with waterglass binder.

The cleaning process can be mechanically supported according to the invention, for example by agitators, oscillations or ultrasonic radiators; The processes triggered by these stations can also be used in combination.

The introduced with the tempered sand in the liquid heat increases the cleaning intensity in the reactor. The bath temperature of the reactor should be controlled by means of a cooling device or with supplied fresh water.

Drained water can be cooled and, after removing the substances dissolved in the water, returned to the reactor as fresh water. Arising swaths are removed.

It has proved to be favorable to carry out the treatment batchwise or continuously.

The amount of withdrawn for wet regeneration part or sand flow should be at least so large that after the combination of the two streams after the wet regeneration of that partial flow results in a sufficiently high sand quality for new casts. In this case, the amount of the partial flow is limited by the heat content of the first subset, through which - as described - the wet-regenerated partial flow is to be dried.

According to further features of the invention has at a sand temperature of about 200 ° C, the second partial stream - at a humidity of about 4% after wet regeneration - a share of about 40% of the total amount of sand. Also, to increase the second part of this current before addition to the first partial flow by means of sieve, centrifuge or the like. Facilities are deprived of free water.

Overall, there is an economically favorable Regenerierverfahren for tempered inorganically bound foundry sands.

Fig. 1, 4:

jeweils einen schematisierten Stammbaum zu einer Sandaufbereitung;

Fig. 2, 5:

Verfahrensschritte zu einem Bereich des Stammbaumes der Fig. 1 bzw. der Fig. 4;

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, 4:

in each case a schematized family tree for a sand preparation;

Fig. 2, 5:

Method steps to a region of the family tree of Fig. 1 and Fig. 4;

3:

further method steps in the area of FIG. 2.

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

Figures 1 to 3 of the drawing is a process for the regeneration of cold sands to be taken, which are bound with inorganic binders; the regeneration of the core sand takes place in several steps:

• Dry separation in station A bound sand (reference S) of castings (reference M).
• Dry chopping of the lumpy parts of stream S in station B.
• A sieving process to sieve the sand to the desired grain size (station C).
• The removal of unwanted fines in zone D.
• The sharing of the amount of sand in the region of the zone E in two sand or streams, one of which is fed as a sand stream S ₁ an intermediate storage, whereas the other stream S _{2 is} to be regenerated.
• The regeneration of the sand or partial stream S ₂ in zone F.
• The merging and mixing of the two sand or partial streams S ₁ , S ₂ in zone G.

In this case, the amount of withdrawn for the regeneration sub-stream S _{2 should} be selected so that after merging the two sand or 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 :

The treatment of 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.

F ₄ :

The drying of the sand.

As far as sub-step 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 chosen so that the mixture of the completely dry sand or partial stream S _{1 of} the intermediate storage and the wet-regenerated sand or partial stream S _{2 is} free-flowing; Thus, the composite of two sand or 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 surface of the sand grain (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 or partial 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.

The family tree of Fig. 4 illustrates another method, namely the regeneration of the core sand after the casting, before the core sand is cooled.

For this purpose, in station A _1, the sand S _k separated from the castings M _l as well as comminuted in station _B1. For this purpose, the entire still temperate amount of sand in zone E _{1 is divided} into two partial streams T ₁ , T ₂ . The first partial flow T _{1 of} the sand S _k is temporarily buffered in zone K, the second partial flow T ₂ is wet-regenerated in a reactor NR, metered into zone Q and subsequently mixed again into the first partial flow T ₁ in zone G ₁ .

As a result, on the one hand, the drying of the second subset T ₂ by the heat of the first subset T ₁ and on the other cooling the first subset T ₁ by the heat of vaporization of the moisture of the second subset T ₂ and the heating of the sand of the second subset T ₂ the mixing temperature of the merged subsets T ₁ , T ₂ after cooling the second subset T ₂ by the regeneration process.

After combining the two subsets T ₁ , T ₂ , the sand in zone R is cooled to use temperature.

The screening and the removal of fines, that is a sighting, can be carried out before the separation into two partial streams T ₁ , T ₂ in the region of the zone E ₁ or preferably after their combination or cooling, as shown in FIG. 4 with the stations C ₁ and Z indicates.

NR 1:

Einbringen des Teilstromes T₂ in einen Reaktor mit Flüssigkeit.

NR 2:

Behandeln des eingebrachten Sandes des Teilstroms T₂, bis dessen Kornoberfläche ausreichend von Bindemittelresten und Produkten vom Gussvorgang gereinigt ist.

NR 2.1:

Die Reinigung des eingebrachten Sandes des Teilstroms T₂ erfolgt in einer Flüssigkeit.

The wet regeneration of the second partial stream T ₂ is carried out according to FIG. 5 in the following method steps:

NUMBER 1:

Introducing the partial flow T ₂ in a reactor with liquid.

NO. 2:

Treating the introduced sand of the partial stream T ₂ until its grain surface is sufficiently cleaned of binder residues and products from the casting process.

NR 2.1:

The cleaning of the introduced sand of the partial flow T ₂ takes place in a liquid.

As a liquid in zone NR 2.1, for example, 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.

The cleaning process can be mechanically assisted, e.g. by - also combined - use of agitators, oscillations or ultrasonic radiators.

The tempered sand of the partial flow T _{2 introduced} into the liquid heat increases the cleaning intensity in the reactor NR. The bath temperature of the reactor NR can be controlled by means of a cooling device or with supplied fresh water.

Drained water can be cooled. After removing the substances dissolved in the water, it can be recycled to the reactor NR as fresh water. Arising swaths are removed.

The treatment is carried out batchwise or continuously.

The amount of partial stream T ₂ removed for wet regeneration should be at least so great that, after the union of the two partial streams T ₁ , T ₂ or after the wet regeneration of the partial flow T ₂ results in a sufficiently high sand quality for new casts.

The amount of the partial flow T ₂ is limited by the heat content of the amount of the first partial flow T ₁ , through which - - as described - the wet-regenerated substream T _{2 is to be} dried.

Thus, for example, at a sand temperature of 200 ° C, the partial flow T ₂ , which has a humidity of 4% after wet regeneration, have a share of about 40% of the total amount of sand.

To increase the partial flow T ₂ , the partial flow T ₂ by means of a sieve, a centrifuge or similar. Free water systems are withdrawn before the partial flow T _{2 is added to} the partial flow T ₁ again.

Sand losses can be compensated with new sand and so the regeneration effect can be supported.

Claims (12)

Process for treating foundry mold materials containing core sand and binder,
characterized,
that bound with inorganic / inorganic binder / n core sand (S _k ) after a casting process in still tempered state of thereby resulting castings (M ₁ ) dry separated, dry crushed and divided the tempered core sand into two streams (T ₁ , T ₂ ) becomes (Station E ₁ ). A method according to claim 1, characterized in that after the division process, a partial stream (T ₁ ) is buffered. A method according to claim 1 and 2, characterized in that after the division process to be regenerated partial stream (T ₂ ) a liquid-containing reactor (NR) supplied and the introduced sand is wet regenerated until the grain surface is sufficiently cleaned of binder residues and products of the casting process , after which this partial flow is mixed with the other partial flow (T ₁ ) (station G ₁ ). A method according to claim 3, characterized in that the second partial flow (T ₂ ) by the heat of the first partial flow (T ₁ ) is dried. A method according to claim 3 or 4, characterized in that the first partial flow (T ₁ ) is cooled by the heat of vaporization of the moisture of the second partial flow (T ₂ ). Method according to one of claims 3 to 5, characterized in that the first partial flow (T ₁ ) is carried out by heating the second partial flow (T ₂ ) to the mixing temperature of the merged partial flows after cooling of the second partial flow. Method according to one of claims 3 to 6, characterized by a wet regeneration of the second partial stream (T ₂ ) by its introduction into the reactor (NR). A method according to claim 7, characterized by a cleaning of the grain surface of the introduced sand of binder residues and products of the casting process, wherein preferably the cleaning of the introduced sand by means of a liquid, in particular with water, is carried out and the liquid to assist the dissolution process in particular additives are added For example, sodium hydroxide solution with water glass binder. A method according to claim 7 or 8, characterized in that at least one agitator and / or vibrations and / or ultrasonic beams are used for mechanical support for the cleaning process. Method according to one of claims 7 to 9, characterized in that the bath temperature of the reactor (NR) is controlled by at least one cooling device and / or supplied fresh water. Method according to one of claims 1 to 10, characterized in that at a sand temperature of about 200 ° C, the second partial stream (T ₂ ) at a humidity of about 4% after wet regeneration has a share of about 40% of the total amount of sand. Method according to one of claims 1 to 11, characterized in that the second partial stream (T ₂ ) before addition to the first partial stream (T ₁ ) by means of sieve, centrifuge or the like. Facilities free of water is withdrawn.

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