EP2035167A1

EP2035167A1 - Feeder with insulation insert

Info

Publication number: EP2035167A1
Application number: EP07765051A
Authority: EP
Inventors: Udo Skerdi; Henning Rehse
Original assignee: AS Luengen GmbH and Co KG
Current assignee: AS Luengen GmbH and Co KG
Priority date: 2006-07-04
Filing date: 2007-07-04
Publication date: 2009-03-18
Also published as: DE102006030875A1; WO2008003478A1

Abstract

The invention relates to a feeder for metal casting with a feeder head that encloses a compensation space (4) that is open to the environment via at least one compensation opening (5), characterized by the fact that the compensation space (4) is at least partially lined with an insulation layer (2, 10), which prevents direct contact between the liquid metal and the material of the feeder head (1) when said liquid metal flows into the compensation space (4).

Description

SPEISER WITH INSULATED INSERT

The invention relates to a feeder for metal casting with a feeder head, which encloses a compensation cavity, which is open to the outside via at least one compensation opening.

In the production of metal castings in the foundry, liquid metal is poured into the mold cavity of a casting mold. When solidifying, the volume of the filled metal decreases. Therefore, so-called feeders are regularly used in or on the casting mold in order to compensate for the volume deficit on solidification of the casting and to prevent voids formation in the casting. The feeders are connected to the casting or vulnerable casting area and are usually located above or on the side of the mold cavity. They include a compensation cavity, which is connected via a compensation opening with the mold cavity of the mold and initially receives liquid metal. At a later time, when the metal solidifies in the mold cavity, the liquid Metal is released from the compensation cavity to compensate for the volume deficit of the casting. It is therefore essential that the metal in the compensating cavity of the feeder solidifies at a later time than the metal in the mold cavity of the mold.

In the production of metal castings, a model is initially produced which substantially corresponds in shape to the metal casting to be produced. Feeders and feeders are attached to this model. Subsequently, the model is surrounded in a molding box with molding sand. The molding sand is compacted and then cured. After curing, the mold is removed from the molding box. The casting mold has a mold cavity or, if the casting mold is made up of a plurality of partial pieces, a part of the mold cavity which essentially corresponds to a negative mold of the metal casting to be produced. After the casting mold has possibly been assembled, liquid metal is introduced into the mold cavity of the casting mold. The inflowing liquid metal displaces the air from the mold cavity. The air escapes through openings provided in the mold or through porous sections of the mold, for example through the wall of a feeder. The feeders therefore preferably have a sufficient porosity, so that on the one hand during the filling of the liquid metal can flow into the feeder and on the other hand, during cooling and solidification of the metal in the mold cavity of the mold, the still liquid metal can flow from the feeder into the mold cavity of the mold ,

EP 0 888 199 B1 describes feeders which may have exothermic properties or insulating properties and which are obtained by a cold-box process. For this purpose, a feeder mixture is poured into a feeder mold. The feeder mixture comprises an oxidizable metal and an oxi- or an insulating refractory material or mixtures of these materials and an effective binder amount of a chemically reactive cold box binder. The feeder mixture is formed into an uncured feeder which is then contacted with a vaporous curing catalyst. The hardened feeder can then be removed from the mold. Hollow aluminum silicate microspheres may be used as the insulating refractory material. By using such microspheres of aluminum silicate, the feeders receive a low thermal conductivity and thus a very pronounced insulating effect. Furthermore, these feeders have a very low weight, so that they can be easily handled and transported on the one hand and on the other not so easy to fall off the model when this is tilted, for example.

EP 0 913 215 B1 describes a method for producing feeders and other feed and feed elements for casting molds. To this end, a composition comprising hollow aluminosilicate microspheres having an alumina content of less than 38% by weight, a binder for cold box curing, and optionally a filler, wherein the filler is not in fibrous form, is formed by blowing into a mold box shaped uncured molded product. This uncured molded product is contacted with a suitable catalyst, whereby the molded product cures. The cured molded product can then be removed from the molding box. The feeders obtained by this method also have a pronounced insulating effect and a low weight.

The feeders described above contain, as a refractory filling material, aluminum silicate microbubbles which are bonded by an organic polymer as a binder. When filling the liquid metal, the organic binder decomposes - A -

under smoke and odor development. Since the smoke in addition to the odor nuisance can also develop a harmful effect, the air must be sucked over the mold and cleaned. Due to the decomposition of the binder, the feeders lose their strength and disintegrate. In the processing of the molding sand, which is released by the disintegration of the mold again, the lumpy riser must be separated by sieving and disposed of.

From WO 00/73236 A2 an exothermic feeder composition is known, which contains aluminum and magnesium, at least one oxidizing agent, a SiÜ ₂ -containing filler and an alkali silicate as a binder. Further, the feeder mass contains about 2.5 to 20 wt .-% of a reactive alumina having a specific surface area of at least about 0.5 m ² / g and an average particle diameter (D ₅ 0) of about 0.5 to 8 microns. The feeder mass is practically free of fluoride-containing fluxes. By using such a feeder mass for the production of feeders, so-called "hollow firing", which is probably due to vitrification of the SiO ₂ -containing fillers with alkali compounds, can be clearly suppressed.

In particular, when using feeders which have been solidified with an inorganic binder such as water glass, the problem arises that the liquid metal is first shock-cooled as it enters the balance cavity of the feeder by contact with the wall of the balance cavity. It forms a thin layer of solidified metal on the wall of the compensation cavity, which seals the compensation cavity gas-tight. Therefore, the liquid metal in the compensation cavity can no longer flow, since the lack of or reduced porosity of the feeder head, the air can not flow unhindered in the compensation cavity and adjusts a negative pressure. The invention was therefore an object of the invention to provide a feeder, which allows a reliable feeding of a casting.

This object is achieved by a feeder having the features of patent claim 1. Advantageous embodiments of the feeder according to the invention are the subject of the dependent claims.

In the feeder according to the invention, the compensation cavity in the feeder head is lined at least in sections with an insulating layer. As a result, the liquid metal does not come into direct contact with the material of the feeder head when flowing into the compensation cavity, which usually also consists of the wall of the compensation cavity. Therefore, the liquid metal undergoes no shock-like cooling, so that no thin metal skin forms on the wall of the compensation cavity, which closes the pores of the feeder head and thereby no longer allows air exchange between compensation cavity and environment. Due to the delayed at the moment of penetration of the liquid metal into the compensation cavity heat flow, the feeder head can be heated by the liquid metal, so that the wall of the compensation cavity reaches a temperature which is above the temperature of the melting point of the metal. An insulating layer is thus understood to mean a layer which has a lower thermal conductivity than the material of the feeder head. Due to the insulating layer of the compensation cavity of the feeder head is thus isolated against rapid flow of heat.

There is therefore provided a feeder for metal casting, with a feeder head, which encloses a compensation cavity, which is open via at least one compensation opening to the outside. According to the invention, the compensation cavity is at least sectionally equipped with a heat-insulating layer. clothes, which prevents direct contact between liquid metal and the material of the feeder head when flowing liquid metal into the compensation cavity.

The provided in the inventive feeder in the compensation cavity insulating layer thus acts as a thermal insulation between the liquid metal and the material of the feeder head. The thermal conductivity of the insulating layer is less than the thermal conductivity of the material from which the wall of the compensation cavity or the feeder head is made or the insulating layer itself has exothermic properties. Preferably, the thermal conductivity of the insulating layer is at least 10% less than the thermal conductivity of the material of the feeder head, preferably by at least 20%, particularly preferably by more than 50%. In general, the insulating layer reduces the heat flow from the liquid metal in the compensation cavity into the surrounding feeder head. It is essential that the insulating effect remains at least at the time of flowing liquid metal into the compensation cavity, so that the heat flow from the liquid metal into the feeder head is delayed so far that no skin of metal can form along the wall of the Ausgleichshohlraums , The insulation can be permanently formed, so that the insulating layer may still be present on the wall of the feeder even after casting. However, it is also possible to form the insulating layer of a combustible material which burns on contact with the liquid metal and forms a gas-rich insulating layer for the period of time required for temperature compensation between liquid metal and the material of the feeder head. Such an insulating layer is thus lost during casting.

The feeder according to the invention can in itself take any suitable shape. The feeder can be designed as a cylindrical feeder be, in which the compensation cavity is open on both sides or closed on one side. On the closed side of the compensation cavity, a ventilation opening may be provided. Such feeders can simply be plugged onto the model. It is also possible to design the feeder as a spring mandrel feeder, which can be attached to a model by means of a spring mandrel. It is also possible to use the feeder as a filter feeder, in which a filter insert is provided in the compensation cavity to retain contaminants in the liquid metal. The feeder according to the invention can be made in one piece and in the simplest case have the shape of a tube opened on both sides. The feeder consists in this case only of the feeder head, which comprises the compensation cavity. But it is also possible to perform the feeder in several parts. For example, the feeder may have a feeder head which includes the compensation cavity. In the compensation opening of the compensation cavity, a tubular body may be received, which establishes the connection between the compensation cavity and the mold cavity of the mold. The tubular body may be fixedly or slidably received in the compensation opening.

An essential feature of the feeder according to the invention is that the compensation cavity is at least partially lined with an insulating layer which prevents direct contact between the liquid metal and the wall of the compensation cavity, which is constructed of the material of the feeder head as the liquid metal flows into the compensation cavity , The insulating layer may be formed of a single layer. But it is also possible to arrange several layers one above the other, which together form the insulating layer. The insulating layer preferably adjoins directly to the existing of the material of the feeder head wall of the Ausgleichshohlraums. In order to In order to prevent direct contact between the liquid metal and the wall of the compensation cavity, the insulating layer preferably extends at least as far into the compensation cavity starting at the compensation opening, as corresponds to the penetration depth of the liquid metal. Preferably, at least the walls of the compensation hollow space running around the longitudinal axis of the feeder head are provided with the insulating layer.

According to a first preferred embodiment, the insulating layer is formed by a sizing. Since sizing can be made in such a way that they contain only small amounts of combustible compounds, this embodiment has the advantage that only a slight evolution of gas or smoke occurs on contact with the liquid metal. The sizing has insulating properties and is applied in a conventional manner to the wall of the compensating cavity, for example by spraying or brushing on. The insulating sizing contains as essential constituents a carrier liquid, such as water or alcohols, for example ethanol or propanol, or alcohol / water mixtures, an insulating material, such as materials containing cavities, for example hollow microspheres, in particular aluminosilicate microcubes, or diathomite, or materials with a platelet or rod-shaped structure, such as ceramic or mineral fibers, layered minerals, such as mica, pyrophyllite, talc, wollastonite, and usually a binder, to ensure a secure fixation of the sizing layer on the wall of the compensation cavity. Conventional binders can be used for this, such as bentonites, starch, aluminum or silicon oxide sols, or also cellulose. The skilled person can fall back here on his knowledge from the production of sizings and select appropriate binder. In addition, other conventional constituents can be used in the size, such as biocides, thickeners, flow agents, wetting agents, antifoams or dispersants. Of the The skilled person can refer here to the usual components for finishing. The sizing may also contain combustible substances, such as wood flour, to improve the porosity of the sizing layer. The solid constituents of the size preferably have a particle size of less than 150 .mu.m, particularly preferably less than 75 .mu.m, in order to enable a uniform structure and layer thickness of the sizing layer. The proportion of the insulating material is preferably selected in the range of 10 to 70 wt .-%, based on the liquid size, ie including the carrier liquid. The optional further ingredients contained in the size are chosen in the usual proportions. So far as provided in the sizing, suspending agents, such as hectorite, bentonite, attapulgite, kaolin, clay or carboxymethylcellulose in proportions of 0.05 to 5.0 wt .-%, biocides in a proportion of 0.01 to 1 wt. %, Dispersant in a proportion of 0 to 1 wt .-%, binder in a proportion of 0.5 to 2.5 wt .-%, wetting agent in an amount of 0 to 1 wt .-% and defoamer in one Used proportion of 0 to 1 wt .-%, wherein the proportion is formed to 100 wt .-% each of the carrier liquid. After application, the sizing is dried to remove portions of solvents that would otherwise cause the sizing layer to flake on contact with the liquid metal. If necessary, the feeders can also be heated to an elevated temperature, for example in the range from 60 to 130 ^° C. The thickness of the sizing layer depends on its insulating effect as well as the type of liquid metal used for the casting or its melting point. The sizing layer preferably has a thickness of 0.1 to 2 mm, preferably 0.5 to 1 mm.

According to a preferred embodiment, the size is carried out as an exothermic size. In this embodiment, the sizing contains, in addition to the components already mentioned, preferably still an oxidizable metal, such as magnesium, aluminum or silicon, and a suitable oxidizing agent, such as an alkali metal nitrate or an alkali metal perchlorate. The proportion of the oxidizable metal is preferably selected in the range of 10 to 60 wt .-% and the proportion of the oxidizing agent preferably in the range of 2 to 20 wt .-%. The oxidizable metal is preferably incorporated in the form of a powder in the sizing, wherein the particle size of the powder is preferably less than 150 microns, preferably less than 75 microns. Due to the exothermic properties of the sizing, the formation of a metal skin on the wall of the compensation cavity is reliably prevented.

According to another embodiment, the insulating layer is formed of a combustible material. Upon contact with the liquid metal, the insulating layer burns and thus prevents the formation of a solid metal layer on the walls of the balance cavity during the time that the material of the feeder head in the vicinity of the balance cavity has heated to the temperature of the liquid metal.

As combustible materials, all materials can be used per se, which burn evenly on contact with the liquid metal, so show no sudden voluminous gas evolution, which could lead to splashing of the liquid metal. The combustible materials can also be filled with non-combustible compounds, so that the structure of the insulating layer is maintained even during combustion. The proportion of non-combustible constituents is preferably greater than 20% by weight, preferably in the range from 30 to 80% by weight, more preferably from 40 to 60% by weight, based on the weight of the insulating layer. Suitable non-combustible materials are known, for example, as fillers for cardboard or plastics. Exemplary components are sand, talc, clays or chalks. Particularly preferred is the combustible material selected from cardboard, paper, wood, cellulose and plastic. These materials are easily accessible and can be formed into any shape, so that a tailor-made lining of the compensation cavity is possible. An insulating layer of said materials can be made by, for example, making a paste or slurry of the materials with which the wall of the balance cavity is covered. For this purpose, the combustible material can be ground into a fine form and provided for example in the form of wood chips or a fine plastic granules.

According to a particularly preferred embodiment, the insulating layer is formed as a sleeve, which can be inserted into the compensation cavity. This makes it possible to assemble the feeder according to the invention easily and quickly by inserting the sleeve into the compensating cavity. As such, the sleeve may be made of any material which meets the requirement for insulation at least on entry of the liquid metal into the balance cavity. For example, the sleeve may be made of an insulating inorganic material. However, from the viewpoint of cost and handleability, it is preferable to make the sleeve of a combustible material, particularly one of the above-mentioned preferred combustible materials. Particularly preferred sleeves of cardboard, paper or cellulose are used. Such sleeves are easy to manufacture and still have some flexibility so that they can be inserted without difficulty through the compensation opening in the compensation cavity. The wall thickness of the sleeves in turn depends on the material used and on the size of the compensation cavity. It is chosen so that a sufficient insulating effect is achieved, so when penetrating the liquid metal in the compensation cavity at the Wall of the compensation cavity does not form a solid metal layer and the sleeve has sufficient stability so that they can be handled well, so for example, can be easily inserted into the compensation cavity of the feeder head. The wall thickness of the sleeves is preferably selected in the range of 0.05 to 3 mm, particularly preferably 0.1 to 2 mm. The sleeves may be formed as a tube. But it is also possible to first provide a sheet of the combustible material, such as a sheet of paper, and then to form a tube, which is then inserted into the compensation cavity. The tube can also be fixed with an adhesive connection.

Glue-free papers or boards are particularly preferably used, since these show a low smoke development.

The sleeve preferably has a length such that it covers at least the region of the compensation cavity which is filled with liquid metal during casting. Preferably, the sleeve has a longitudinal extent, which corresponds at least to the longitudinal extent of the compensation cavity, so that the sleeve can be inserted so far into the compensation cavity that it comes to rest on the compensation opening opposite end of the compensation cavity to the plant. When inserting the sleeve in the compensation cavity, this can then not fall into the compensation cavity but reliably covers the adjoining the compensation opening area of the compensation cavity.

In a further embodiment, the length of the sleeve, ie its extension in the direction of the longitudinal axis, chosen to be greater than the longitudinal extent of the compensation cavity. If the sleeve is completely inserted into the compensation hollow space, in this case it projects beyond the end of the compensation opening formed by the compensation opening. If such a feeder attached to a model, the sleeve is initially not fully inserted into the compensation cavity and can on get up this way on the model or the foot of a feather thorn. After the model has been wrapped in a molding box with molding sand, the molding sand is compacted. The feeder head is moved towards the model, whereby the sleeve pushes into the compensation cavity. In this embodiment, the diameter of the compensation opening corresponds to the diameter of the compensation cavity. The outer diameter of the sleeve substantially corresponds to the diameter of the compensation opening, so that the sleeve can be displaced into the compensation cavity.

According to a further embodiment of the feeder according to the invention, the compensation cavity on the side of the compensation opening has a larger diameter than at the opposite end of the compensation opening. In this way, a correspondingly shaped sleeve can be very easily inserted into the compensation cavity. Particularly preferably, the compensation cavity has a conical shape. The difference between the diameter at the respective ends of the compensation cavity is chosen so large that the sleeve can be used easily in the compensation cavity. Preferably, the difference in the diameter of the compensation cavity at its ends between 2 and 20%, preferably selected between 5 and 10%.

The material from which the feeder head is made corresponds to the materials used in the manufacture of feeders. Essentially, the material for the feeder or feeder head comprises a granular refractory material and a binder.

As refractory material, for example, aluminum silicates may be used, for example, fibrous refractories, or zirconia sand. Furthermore, synthetically produced refractory fillers can also be used, such as, for example, lit (Al ₂ SiO ₅ ). In the selection of the refractory material initially there are no restrictions.

However, the feeder head is particularly preferably made of a material which acts insulating against heat loss. Particular preference is given in the material of the feeder head insulating refractory materials are used, which have a low thermal conductivity. Preferably, the thermal conductivity of the insulating refractory is 0.04-0.25 W / mK.

The refractory material of the feeder head therefore preferably comprises at least a portion of a refractory material which has cavities and which is highly heat-insulating by the gas enclosed in the cavities. Particularly preferably, the material of the feeder head comprises a proportion of refractory hollow microbeads. Such refractory hollow microspheres preferably have a shell of an aluminum silicate. They can be obtained, for example, from fly ash, which is separated in industrial plants from combustion exhaust gases. The microholes have a diameter of preferably less than 3 mm, more preferably less than 1 mm. The wall thickness of the hollow microspheres is preferably 5 to 20% of the diameter of the hollow microspheres. The composition of the aluminum silicate microbeads may vary within wide ranges. Preferably, the aluminum content, calculated as Al ₂ O ₃ and based on the weight of the hollow microspheres, is between 25 and 75%, preferably 30 and 50%. The proportion of hollow microspheres based on the weight of the material from which the feeder head is made is preferably greater than 30%, preferably greater than 40%, more preferably in the range of 60 to 95%, particularly preferably in the range of 65 to 90% by weight .-% chosen.

According to a further preferred embodiment, the material of the feeder head comprises a refractory material having an open-pored structure. Due to the open-pored structure receives the Speiser a very good gas permeability, so that the air in the Ausgleichshohlraum when penetrating the liquid metal can escape largely unhindered or when the liquid metal flows out of the compensating cavity when dining again, can flow largely unhindered back into the mold cavity of the mold.

By a porous refractory having a continuous open pore structure is meant a refractory having a sponge-like structure which extends throughout the entire volume of the grain. Such an open-pored structure can be recognized, for example, on a micrograph of a grain, possibly under microscopic magnification. Whereas in the case of the abovementioned hollow microspheres, in each case a single "pore" is surrounded by a substantially gas-tight envelope and therefore no simple gas exchange between the cavity of the hollow microspheres and the environment is possible, the open-pored refractory material is traversed by passages which allow gas exchange of the individual pores enable with the environment. The proportion of pores in the entire volume of the porous open-celled substance is preferably very high. Preferably, the porous refractory material has a pore volume of at least 50%, preferably at least 60%, in particular at least 65%, based on the total volume of the porous refractory. The pore volume can be determined, for example, by mercury intrusion.

The porous refractory materials having an open-pore structure contained in the material of the feeder head preferably have a density of less than 0.5 g / ml, preferably less than 0.4 g / ml, particularly preferably 0.05 to 0.4 g / ml. The feeders according to the invention therefore advantageously have a low weight in this embodiment. The feeders can for example be plugged onto a model and fall because of Their low weight does not decrease when the model or the form is turned.

Suitable porous refractory materials are, for example, pumice stone, expanded slate, perlite, vermiculite, boiler sand, foam lava or expanded concrete, and mixtures thereof.

The molding compound from which the feeder head is made preferably has a gas permeability of at least 150, preferably more than 200, in particular more than 300. The gas permeability is a standard in the foundry industry characteristic of the porosity of moldings or molding sands. It is usually determined on devices of the company Georg Fischer AG, Schaffhausen, Switzerland.

The gas permeability of the porous refractory material used can be determined in the following manner:

a) Preparation of a specimen:

About 100 g of porous refractory material to be tested, adjusted to a center grain of about 0.3 mm, are mixed in a mixer with 20 g of water glass (solids content about 30%, modulus SiO ₂ / Na ₂ O about 2 , 5) mixed. The mixture is poured into a sleeve having an inner diameter of 50 mm. The sleeve is used in a Georg Fischer rammer. The mixture is compressed in the ram by three strokes. The sleeve with the compacted molding compound is removed from the ram and the molding compound is cured by blowing carbon dioxide through the molding compound for about 3 seconds from the open ends of the sleeve. The cured specimen can then be pushed out of the sleeve. After the specimen has been pushed out, its height is measured. This should be 50 mm. If the specimen does not have the desired height, it must be fitted with an adapted th amount of the molding compound another test specimen can be produced. The test specimen is then dried in an oven at 18O ⁰ C to constant weight.

b) Gas permeability test

The gas permeability test is carried out with a type PDU permeability testing apparatus from Georg Fischer Aktiengesellschaft, 8201 Schaffhausen, Switzerland.

The test specimen prepared as described under (a) is inserted into the precision test specimen tube of the apparatus and the gap between specimen and test specimen tube is sealed. The test specimen tube is inserted into the test apparatus and determines the gas permeability Gd. The gas permeability number Gd indicates how much cm ^{3 of} air passes through a cube or cylinder of 1 cm ² cross-section in one minute at a pressure of 1 cm water column. The gas permeability is calculated as follows:

Gd = (Q-h) / (F • p • t)

where:

Gd: gas permeability number

Q: air volume flowing through (2000 cm ³ ); h: height of the test piece

F: cross-sectional area of the test piece (19.63 cm ³ ); p: pressure in cm water column; t: flow-through time for 2000 cm ^{3 of} air in minutes.

p and t are determined; all other values are constants set by the tester. Pumice is particularly preferably used as a porous refractory material. Pumice is a naturally occurring rock glass, ie it has essentially an amorphous structure without recognizable crystals. Pumice has a low specific gravity of up to about 0.3 g / cm ³ . It has a very high pore volume of up to 85%. Due to its high porosity, the pumice has a very high gas permeability.

As the pumice, it is preferable to use a material from a natural source ground to a suitable grain size. The grain size of the ground pumice is preferably less than 1.5 mm, more preferably less than 1 mm. The grain size can be adjusted, for example, by sieving or air classification.

In addition to the porous refractory material, in particular pumice, the molding composition for the production of the feeder head preferably contains a proportion of a reactive alumina. The reactive aluminum oxide preferably has the following properties:

Al ₂ O ₃ content> 90%

Content of OH groups <5% specific surface area (BET) 1 to 10 m ² / g average particle diameter (D ₅₀ ) 0.5 to 15 μm

The addition of a reactive alumina gives the feeder head better strength.

The reactive aluminum oxide is preferably, based on the weight of the molding material from which the feeder head is prepared, in a proportion of more than 2 wt .-%, preferably more than 5 wt .-% in the molding composition of the invention. In addition to the insulating refractory material, the material of the feeder head may also comprise at least one refractory filler, which preferably has a relatively low SiO ₂ content. Preferably, the refractory filler has an SiO ₂ content of less than 60% by weight, preferably less than 50% by weight, particularly preferably less than 40% by weight. Due to the low proportion of SiO ₂ , the risk of vitrification is counteracted, as a result of which casting defects can be avoided. Preferably, the material of the feeder head contains no SiO ₂ as a mixture component, so it is free of, for example, quartz sand. The SiO ₂ content contained in the molding composition is therefore preferably in bound form as aluminum silicate.

Particularly preferably, the refractory filler is at least partially formed from chamotte. Fireclay is understood to mean a highly fired (double-fired) clay which has a dimensional stability up to a temperature of about 1500 ^° C. In addition to amorphous portions, chamotte, the crystalline phases of mullite (3Al ₂ O ₃ ^• 2SiO ₂₎ and cristobalite (SiO ₂₎ contained. The chamotte is also preferably ground to a particle size of less than 1.5 mm, preferably less than 1 mm. Through the chamotte obtained from the molding compound feeder a very high temperature resistance and strength.

The proportion of fireclay on the refractory filler is preferably chosen to be high. Preferably, the proportion of chamotte, based on the weight of the refractory filler, at least 50 wt .-%, more preferably at least 60 wt .-%, and most preferably at least 70 wt .-%. In a particularly preferred embodiment, the refractory filler is formed essentially only of chamotte. The chamotte is preferably contained in ground form in the material of the feeder head. The particle size here is preferably less than 1.5 mm, particularly preferably less than 1 mm. The chamotte preferably has a high proportion of aluminum oxide. The chamotte preferably contains at least 30% by weight of aluminum oxide, particularly preferably at least 35% by weight and very particularly preferably at least 40% by weight. The alumina is preferably in the form of aluminum silicates.

The proportion of the refractory filler, based on the weight of the material of the feeder head is preferably between 5 and 60 wt .-%, particularly preferably 8 to 50 wt .-%. The fractions of the refractory filler do not include the proportions of pumice and reactive alumina.

In addition to the components already mentioned, the material of the feeder head may contain other constituents in conventional amounts. For example, an organic material may be included, such as e.g. Wood flour. In the manufacture of the feeder head, the organic material is advantageously present in a form in which it does not contain any liquid constituents, e.g. Water glass, absorbs. For example, in the manufacture of the feeder head, the wood meal may be first sealed with a suitable material, such as water glass, so that the pores are closed. The presence of the organic material will further reduce the cooling of the liquid metal upon first contact with the wall of the balance cavity.

The material of the feeder head is preferably almost free of fluoride-containing fluxes. The fluoride content is preferably less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight, calculated as sodium fluoride.

The percentages which indicate the proportions of the individual components in the molding compound for the feeder head, in each case based on the weight of the molding material in a dry state. The composition of the molding material for the production of the feeder head can be varied according to requirements. For the production of insulating feeders, the amounts of porous refractory, in particular pumice, refractory filler and reactive alumina are preferably selected within the following ranges:

refractory porous 15 to 90% by weight,

Fabric (pumice) preferably 60 to 80% by weight refractory 5 to 50% by weight, filler preferably 8 to 20% by weight reactive 5 to 30% by weight,

Alumina preferably 8 to 20% by weight

If an organic material, such as wood flour, is contained, this is preferably contained in a proportion of 5 to 20 wt .-%, preferably 8 to 12 wt .-%.

As binders for curing the feeder mixture, any desired binders can be used. Thus, organic polymers can be used as binders, which are cured by suitable methods. Examples of binders based on organic polymers are cold box binders, hot box binders or resin binders.

When using a cold-box binder, it is preferably selected from the group of phenol-urethane resins activated by amines, epoxy-acrylic resins which can be activated by SO ₂ , alkaline phenolic resins characterized by CO ₂ or Methyl formate can be activated, as well as water glass, which can be activated by CO ₂ . The person skilled in the art is aware of such cold-box binders. Such binding Demittelsysteme are described for example in US 3,409,579 or US 4,526,219.

Water glass is particularly preferably used as a binder. Conventional water glasses can be used as the water glass, as they are already used as binders in molding mixtures for the foundry industry. These water glasses contain dissolved sodium or potassium silicates and can be prepared by dissolving glassy potassium and sodium silicates in water. The water glass preferably has a modulus M ₂ O / SiO ₂ in the range of 2.0 to 3.5, where M is sodium and / or potassium. The water glasses preferably have a solids content in the range of 20 to 50 wt .-%. Furthermore, solid water glass can also be used for the production of the feeder head. For the proportions of the molding material for the production of the feeder head only the solids content of the water glass are considered in each case.

In the production of the feeder head, the hardening of the offset with water glass as a binder refractory materials by conventional methods. The curing can be carried out by passing carbon dioxide through the blank of the feeder head, wherein the curing is preferably carried out at room temperature. But it is also possible to heat the blank of the feeder head, for example, to temperatures of 120 to 200 ⁰ C. To accelerate the curing, hot air can be passed through the blank of the feeder head. The temperature of the air blown is preferably from 100 ⁰ C to 180 ° C, particularly preferably from 120 ⁰ C to 150 ⁰ C. After the first curing, the feeder heads can be dried or, for example in an oven or by irradiation with microwaves.

As a particular advantage in this embodiment, the feeder during the casting process because of the heat resistance of the water glass under the action of heat of the liquid metal not destroyed. In the reprocessing of the mold, therefore, the feeders can be recovered and the compensation cavity can be provided with a new layer of the insulating material. For this purpose, the compensation cavity can be re-coated with a suitable size after appropriate cleaning or it can be inserted a new sleeve in the compensation cavity.

The advantages of the invention are particularly evident when the feeder according to the invention is designed as an insulating feeder. However, it is also possible to carry out the feeder according to the invention as an exothermic feeder, which ignites on contact with liquid metal and thereby ensures a delay in the solidification of the metal in the feeder. For this purpose, the material of the feeder head contains an oxidizable metal, in particular aluminum and / or magnesium and / or silicon, as well as an oxidizing agent. The oxidizable metals and the oxidizing agent are preferably present in finely divided form. As the oxidizing agent, for example, iron oxide and / or an alkali nitrate such as sodium or potassium nitrate can be used.

An exemplary exothermic molding composition may contain the following proportions:

Aluminum 20 to 35 wt .-%, preferably 25 to 30 wt.

Magnesium 1 to 15 wt.%, Preferably 2 to 10 wt.

Oxidizing agent 8 to 20% by weight, preferably 10 to 15% by weight reactive 4 to 20% by weight,

Alumina preferably 10 to 18 wt.

refractory porous 15 to 40% by weight,

Fabric (pumice) preferably 20 to 30% by weight of fire-resistant 5 to 30% by weight,

Filler preferably 8 to 20 wt.

The feeder according to the invention is in itself prepared by conventional methods. First, a molding compound is prepared which comprises at least one refractory granular material and a binder. This molding material is processed into a blank by the molding material is shot, for example, in a core shooting machine by means of compressed air in a suitable form. Preferred refractory materials and other components have already been explained in connection with the material of the feeder head. Suitable binders were also already explained in the material of the feeder head. Particularly preferably, water glass is used as the binder. After curing, the insulating layer is introduced into the compensation cavity. If a size is used, it can be applied by conventional methods. The sizing can be sprayed or painted on. The sizing may also be applied by dipping. If the insulating sizing is introduced in the form of a sleeve in the compensation cavity, the sleeve is inserted into the compensation cavity. Subsequently, the Install according to the invention Speiser in a conventional manner in a mold.

The feeder according to the invention is suitable for metal casting, in particular aluminum casting.

The invention will be explained in more detail below with reference to examples and the attached figures. Showing:

1 shows a longitudinal section through a feeder according to the invention and through a corresponding feeder head and a sleeve made of an insulating material.

2 shows a longitudinal section through a further embodiment of the feeder according to the invention.

Fig. 1 shows a longitudinal section through a feeder according to the invention and by its individual components, the feeder head 1 and an insert 2 made of an insulating material. The feeder head 1 shown in Fig. 1 c has a tubular shape. The feeder wall 3 is constructed of a refractory material containing, for example, aluminum silicate microbubbles to improve the insulating properties of the feeder. The feeder wall 3 surrounds a compensation cavity 4, which is bounded on one side by a compensation opening 5. At the compensation opening 5 arranged opposite end there is a ventilation opening 6. The diameter of the compensation opening 5 is selected to be larger than the diameter of the ventilation opening 6, so that the feeder head has a conical shape.

The sleeve 2 is made of a combustible material, such as cardboard. The shape of the sleeve 7 is matched to the shape of the compensation cavity 4 of the feeder head. The sleeve comprises a cardboard wall 7, which has sufficient strength to to allow a temperature compensation between liquid metal and feeder head. The sleeve has at its one end an outer diameter which corresponds substantially to the diameter of the compensation cavity at the end to the compensation opening 5, and at its other end 8 an outer diameter which substantially corresponds to the diameter of the compensation cavity 4 at the end of the ventilation opening 6. The sleeve 2 can therefore be suitably inserted into the compensation cavity 4 of the feeder head 1. After the sleeve 2 has been inserted into the feeder head 1, the feeder 9 with the compensation opening 5 'with the mold cavity of a mold (not shown) can be connected. When pouring the liquid metal in the compensation cavity 4 ^{1 it} comes into contact with the sleeve 2, which burns under the action of heat. As a result, the liquid metal does not come into direct contact with the wall of the feeder head 1, so that it does not cool in a shock-like manner and solidifies into a thin skin.

In Fig. 2 is a longitudinal section through an embodiment of the feeder according to the invention is shown, in which the compensation cavity 4 is closed on one side. The feeder wall 3 is again made of a refractory material, for example, comprises a proportion of Aluminiumiumsilikatmikrohohlkugeln or ground pumice and which has been cured with water glass as a binder. The feeder wall 3 defines a compensating cavity 4, the walls of which are lined with a size coat 10. The sizing layer 10 contains aluminum powder and an oxidizing agent and therefore has slightly exothermic properties. The compensation cavity 4 is open to one side to a compensation opening 5, via which the compensation cavity with the mold cavity of a mold (not shown) can be connected. The compensation opening 5 opposite a ventilation opening 11 is arranged, through wel- Air escape from the compensation cavity 4 and can flow into this.

Analytical methods:

Determination of specific surface area:

The BET surface area is determined on a fully automatic nitrogen porosimeter from the company Micromeritics, type ASAP 2010, in accordance with DIN 66131.

Pore volume:

The porosity is determined by mercury porosimetry according to DIN 66133.

Average particle diameter (dso):

The mean particle diameter was determined by laser diffraction on a Mastersizer S, Malvern Instruments GmbH, Herrenberg, DE according to the manufacturer.

Elemental analysis:

The analysis is based on a total analysis of the materials. After dissolution of the solids, the individual components are treated with conventionally specific analytical methods, e.g. ICP analyzed and quantified.

Determination of density:

The powdery porous refractory material is charged in one go into a previously weighed 1000 ml glass cylinder which has been cut off at the 1000 ml mark. After the debris cone has been stripped off and any material left on the cylinder has been removed, the cylinder is weighed again. The weight gain corresponds to the density. Example 1 :

Tubular feeders were produced from a molding material mixture of the following formulations:

Table 1: Formulation for the production of feeders (aluminum silicate hollow microspheres)

Table 2: Formulation for the preparation of feeders (pumice stone)

: Solids content: 50% by weight, modulus SiO ₂ / Na ₂ O: 2.2

The molding material mixtures were shot into a mold at room temperature and cured there for 90 seconds by passing carbon dioxide through. Subsequently, the feed blanks were dried for 5 hours in an oven at 180 ° C. Tubular feeders having a length of 150 mm, an outer diameter of 59 mm and an inner diameter of 40 mm were obtained.

The compensation cavity of the feeders was lined with the following materials:

Paper sleeves (wall thickness 0.09 mm) Cardboard sleeves (wall thickness: 2 mm) Cellulose sleeves (wall thickness: 1 mm)

Furthermore, two insulating sizes were prepared, the formulation of which is given in Tables 3 and 4.

As a comparison, a feeder of the same dimensions was used but a cold-box binder was used for curing and its balance cavity was not lined with an insulating layer.

The feeders were each installed in a mold and made an aluminum casting. In each case, the smoke development was assessed on a scale of grades, with the strongest smoke being rated with the grade 6 and the lowest amount of smoke with the rating being 1.

Table 3: Formulation for insulating sizing

Table 4: Formulation for exothermic size:

After casting, the casting was removed from the mold and the buttock remaining on the casting was evaluated. A smooth surface was judged to be grade 1, while a clear formation of depressions on the surface of the buttock was rated grade 6. The results are summarized in Table 5.

Table 5: Results of aluminum casting

The results are consistent with feeders containing hollow microspheres as a refractory and those containing pumice refractory.

Claims

1. Feeder for metal casting with a feeder head, which encloses a compensation cavity (4) which is open to the outside via at least one compensation opening (5), characterized in that the compensation cavity (4) at least in sections with an insulating layer (2, 10 ), which prevents the direct contact between liquid metal and the material of the feeder head (1) when flowing liquid metal into the compensation cavity (4).

2. feeder according to claim 1, characterized in that the insulating layer of a sizing layer (10) is formed.

3. A feeder according to claim 2, characterized in that the sizing layer (10) has exothermic properties.

4. A feeder according to claim 1, characterized in that the insulating layer (2, 10) is formed of a combustible material.

5. feeder according to claim 4, characterized in that the combustible material is selected from cardboard, paper, wood, cellulose and plastic.

6. Feeder according to one of the preceding claims, characterized in that the insulating layer is formed as a sleeve (2) which can be used in the compensation cavity (4).

7. A feeder according to claim 6, characterized in that the sleeve (2) protrudes from the compensation opening (5) of the compensation cavity (4).

8. Feeder according to one of the preceding claims, characterized in that the compensating cavity (4) has a conical shape.

9. Feeder according to one of the preceding claims, characterized in that the material of the feeder head comprises a proportion of refractory hollow microspheres.

10. A feeder according to any one of claims 1 to 7, characterized in that the material of the feeder head comprises a refractory material having an open-pore structure.

11. Feeder according to one of the preceding claims, characterized in that the feeder material comprises an inorganic binder.

12. A feeder according to claim 10, characterized in that the inorganic binder is water glass.