TOOL INSERT, MOULD TOOL OR CORE TOOL AND METHOD FOR PRODUCING MOULDS OR CORES

Abstract

The present invention relates to the selection of materials for methods for producing moulds (2) or cores (2) for foundry purposes. When selecting the core box material, a special ceramic, such as for example silicon carbide or silicon nitride, is used instead of metals such as steel or aluminium. It is essential for the inventionthat a material (7) for receiving the mixture (9) is introduced into a housing (3), the material consisting of silicon carbide or silicon nitride, that electrical energy is supplied to the material (7) by way of electrodes (10) arranged in/on the housing (3) and in this way heat is supplied, leading to curing of the mixture (9). This allows longer service lives to be achieved for the core boxes as a result of low abrasive wear.

Claims

1. A tool insert comprised of a material for mold or core tools for producing foundry cores with at least one cavity for holding a molding material mixture, wherein, in application, heat is supplied to the material by means of current, which causes a curing of the moulding-material mixture: characterized in that the specific electrical resistance of the material is between 0.5 ohmmeters and 200 ohmmeters at an operating temperature of 150 C. to 180 C., the heat conductivity of the material is at least 0.56 W/(m*K), the tool insert is comprised of at least two parts having at least one direct electrically conductive contact surface without an electrically insulating intermediate layer in the assembled state and wherein the material comprises a contact surface for the electrically conductive connection to the respective electrode of a mold or core tool.

2. The tool insert according to claim 1, characterized in that it comprises a sintered insert.

3. The tool insert according to claim 1, characterized in that, for the escape of water vapour or gases, the tool insert is porous and contains ventilation slits for the escape of water vapor or gases.

4. The tool insert according to claim 1, characterized in that, the material is a special ceramic and thereby, the insert is also suitable for operation in mold or core tools having an external heater.

5. A mold or core tool for producing molds moulds or cores for foundry purposes, wherein at least one tool insert according to claim 1 is inserted into a housing, the housing comprises at least two parts, which are movable together or apart respectively at the beginning and upon completion of a cycle process.

6. A method for producing molds or cores for foundry purposes by means of adapting the specific electrical resistance of a tool insert to the specific electrical resistance of a mixture comprising of at least one molding material, in particular, foundry sand, and at least one water-containing inorganic binder curable by means of heat, and which has an electrical conductivity of at least 5.Math.103 S/m. wherein: (1) at least one tool insert according to claim 1 made of an electrically conductive material for holding the molding-material mixture is introduced into an electrically non-conductive housing, wherein the electrical conductivity of the material at an operating temperature between 150 and 180 C. is between 0.5 ohmmeters and 200 ohmmeters, (2) electrical energy and thus heat is supplied to the tool insert via electrodes that are arranged in parallel in/on the housing, which cures the mixture, (3) wherein the housing and the tool insert are respectively comprised of at least two separable parts, which are moved together or apart from each other respectively at the beginning and upon completion of the cycle process, and wherein the moved-together parts of the tool insert form a direct electrically conductive contact surface without an intermediate insulating layer, (4) holes for ejection pins are provided within the tool, belonging to at least one electrode as well as to at least one part of the housing for removing the cores, (5) both the tool as well as the electrodes and at least one part of the housing are one or more of: porous or ventilation slits are present for the escape of water vapor or gases, and (6) the mold(s) or the core(s) are pressed out of the tool and removed by means of ejection pins after curing of the mixture and moving apart the housing parts.

Description

[0115] On a schematic level respectively, the figures show

[0116] FIG. 1 a cross-sectional illustration through a mould or core tool according to the invention,

[0117] FIG. 2 a phase diagram with a qualitative view of an introduced electrical power and a related resistance in a core or a mould,

[0118] FIG. 3 a view of the heating by means of an existing electrical method without adapting the specific resistance of the core-box material to the sand/binder mixture.

[0119] FIG. 4 illustration of a possible core-box design

[0120] FIG. 5 attachment of the material with insulating housing and base plate,

[0121] FIG. 6 Illustration of vent and discharge holes

[0122] In accordance with FIG. 1, a mould or core tool 1 according to the invention for producing moulds 2 or cores 2 for foundry purposes, a housing 3 that is electrically insulated from the machine, which consists of two parts 4, 5, which are connected to each other via a separation level 6. The housing is attached to a base plate 12.

[0123] The housing 3 is made of plastic, insulating ceramics or other non-conductive material and takes up a conductive material 7. The material 7 forms a mould to hold a mixture 9, from which the core 2 or the mould 2 is formed after curing. The material 7 can, for example, be a ceramic material. According to the invention, the specific electrical conductivity of the mixture 9 and the specific electric conductivity of the material 7 are thereby at least approximately identical in strength, for example, they no longer differ like in phase 2 in FIG. 2 so that, in the material 7 and the mixture 9, essentially the same specific electrical conductivity and the same specific electrical resistance prevail. The mould or core tool 1 according to the invention furthermore possesses at least two electrodes 10, which are arranged in parallel to one another. A device 8 is provided to regulate and control the voltage supplied to the electrodes 10.

[0124] According to the invention, now, the specific electrical conductivity of the material 7 of the core 2 or of the mould 2 approximately correspond to the specific electrical conductivity of the mixture 9 in phase 2 in FIG. 2, whereby a comparably even channelling of electrical energy through the mixture 9 is possible.

[0125] With the mould or core tool 1 according to the invention, a mould 2 or a core 2 or a foundry core 2 can be produced at the highest level of quality possible since, due to the at least approximately same electrical conductivity of the mixture 9 and the material 7 used for the mould 2 or the core 2, an even channelling of electrical current through the material 7 and the mixture 9 and thereby, an even heating and curing of the mixture 9 can take place and that being independent of the respective geometrical dimensions of the mould 2 or of the core 2.

[0126] Thereby, the mould 2 or core 2 is produced as follows: First, after the aforementioned selection of materials during the first construction, the electrically conductive material 7 is inserted into housing 3 of the mould or core tool 1 and forms a negative mould for the mixture 9 forming the later mould 2 or the later core 2. Subsequently, electrical energy and thereby heat is supplied to the material 7 via the electrodes 10, which result in a curing of the mixture 9. A curing of the mixture 9 thereby takes place, in particular, by means of evaporating water from the mixture 9, wherein the mixture 9 can, for example, contain an inorganic binder, water and foundry sand.

[0127] The inorganic binder used in the mixture 9 can be water soluble, but at least contain water and is, in any case, electrically conductive. Using the method according to the invention and the mould or core tool 1 according to the invention, a particularly evenly heated and thereby also particularly evenly cured and therefore more homogeneous foundry core or core 2 can be created and that being independent of the respective geometrical dimensions of the core 2 or of the mould 2, since, the electrical current does not seek out any shorter routes due to the preferably identical electrical conductivity of the mixture 9 for the core 2 and of the material 7, as has been the case up until this point with known mould or core tools known from prior art. Up until this point, this had resulted in the fact that, due to the electrical paths caused by the geometrical dimensions of the core 2 or the mould 2, under certain circumstances, up until this point, these had not been evenly cured and, therefore, had regions that were fully cured and regions that were only partially or not cured at all, whereby the quality of the moulds or cores manufactured up and to this point using the mould or core tools up until this point were often unsatisfactory.

[0128] By means of the device 8, in particular, the voltage can be increased or decreased, whereby a cycle time for producing the mould 2 or the core 2 can be controlled.

[0129] The base plate of the tool (12) takes up the housing (3) and the parts (4, 5) as well as the material (7) and insulation screws (13) and brackets (14) provide for an attachment. Insulation screws 13 can also be replaced by rapid-clamping systems to make easier and faster expansion possible.

[0130] The material floats on the electrode and electrode is held in its position by alignment pins (15).

[0131] In the following, Tables 1 is included for the sake of a better understanding. Thereby, Table 1 shows a plurality of measurement series with different sand/binder mixtures. Thereby, the findings entail that the specific electrical conductivity depends on the desired sand/binder mixture and that it can be influenced by varying additives and/or by changing the percentage of the components it consists of The stronger the electrically conductive proportion is in the sand/binder mixture, the lower the specific electrical resistance in the sand/binder mixture is.

[0132] Therefore, the approach described in the above is used to determine the specific electrical property of the desired sand/binder mixture. However, this method can also be used if the sand/binder mixture has not yet defined. In this case, an attempt can be made to specifically influence the specific electrical property of the sand/binder mixture, for example, by means of varying the additives in order to improve the efficiency of the method.

[0133] See Table 1: Sand/binder mixture measurement tables

TABLE-US-00001 TABLE 1 Sand/binder mixtures measurement series Lowest measured Specific Surface, Height, resistance electrical Specific test body test body (optimum point) resistance Measurement series sand heat cm.sup.2 cm.sup.2 ohm [ohm cm] Water glass 2% 0.835 J/g*K 6.1 2 1080 3294 Water glass 3% 0.835 J/g*K 6.1 2 1130 3447 Water glass 3% and 0.835 J/g*K 6.1 2 588 1793 graphite 0.5% Water glass 3%, 0.835 J/g*K 6.1 2 529 1613 graphite, 1%, measurement series 1 Water glass 3%, 0.835 J/g*K 6.1 2 498 1519 graphite, 1%, measurement series 2 Water glass 4%, 0.835 J/g*K 6.1 2 523 1595 measurement series 1 Water glass 4%, 0.835 J/g*K 6.1 2 584 1781 measurement series 2 Water glass 10% and 0.835 J/g*K 6.1 2 12.78 39 graphite 5.0% Innotek Binder by ASK 0.835 J/g*K 6.1 2 781 2383 Cordis binder by Httenes 0.835 J/g*K 6.1 2 683 2083 Albertus Foundry binder 0.835 J/g*K 9.6 3.5 499 1371 (undisclosed)