DE202018106268U1 - Tool for producing molds or cores by electrical resistance heating of a plastic-based material - Google Patents

Abstract

Mold or core tool (1) for producing organic or inorganic molds (2) or cores (2 '); wherein at least one tool insert (7) of the tool insert is at least partially electrically conductive and a specific electrical resistance of the material (7) of the tool insert is chosen so that it is passed through a heated electric current and causes curing of the molding material mixture (9) in the cavity; characterized in that the material of the tool insert comprises a plastic.

Description

Technical area

The present invention relates to the production of moldings or cores in the field of foundry and plastics processing. In particular, the invention relates to a mold or core tool having a tool insert for producing organic or inorganic molds or cores.

Background of the invention

From the WO 2003/013761 A1 is a generic method is known in which as an inorganic binder magnesium sulfate is used, which is dispersed in water and / or dissolved and then mixed with foundry sand. Subsequently, this mixture of a molding material, that is, for example, foundry sand and the binder containing water, introduced into the mold or core tool and cured there by heating. By using an inorganic binder leakage of environmentally damaging gases when curing the mixture should be avoided. This application is based in part on the patent application DE 24 35 886 A1 from 1974 for hardening of sand cores by "passing an electric current".

In the mentioned document WO 2003/013761 A1 it is stated that the energy required for curing is provided by means of electricity. The electricity is applied via two or more electrodes to "at least partially electrically conductive, mutually insulated parts of the separable mold or core tools". Said application does not consider the differences between the electrical resistivity properties of the core tool and the electrical resistivity properties of the sand binder mixture. It uses "mutually isolated parts of the separable mold or core tools".

From the DE 37 35 751 A1 a gas-permeable mold for the production of cast and core molds made of hardenable molding sand is known, wherein the tool consists of heteroporous constructed, open-pore material and wherein the wall of the mold a first, adjacent to the molding sand fine-pored layer region of 0.2-2 mm thickness, 75-95% of the theoretical material density and pore diameter <50 microns, to which a second, massive area in the form of a large-pored supporting skeleton of <80% of the theoretical material density and a mean pore diameter <100 microns adjoining the material fit.

From the DE 24 35 886 A1 A method of making foundry molds or cores by introducing a mixture of aggregate and binder into a mold or core box and heating the mixture is known, wherein the heating is effected by passing an electric current through the mixture. From the EP 3 103 562 A1 a template is known, which has a frame-shaped or box-shaped, preferably slightly tapered down, design with a circumferential wall and a box-shaped configuration also has a bottom.

Mold or core tools for inorganic processes are mainly made of metal such as steel or aluminum. From the patent DE 24 35 886 A1 It is known that in this case the materials used for heating the tools or the tool inserts medium current in many cases on ceramic or ceramic-based material mixtures, some of which additional components are added. For example, these admixtures are intended to adapt physical properties of the mixture, for example melting temperature, specific electrical resistance, strengths and other properties, to the respective applications. In this case, the adaptation to the electrical conductivity of the sand-binder mixture to be used takes place. Especially for areas where forms are to be made of non-conductive materials, the previously known methods are often not suitable.

Disclosure of the invention

The present invention therefore deals with the problem of providing for an apparatus of the generic type an improved or at least one alternative embodiment which overcomes in particular the disadvantages known from the prior art. This problem is solved according to the invention by the subject matters of the independent claims. Advantageous embodiments are the subject of the dependent claims.

The present invention is based on the general idea that it would be desirable to provide an alternative, in particular to the materials used for the tool, in particular the tool insert. There is therefore proposed a mold or core tool for the production of inorganic molds or cores. This molding tool has at least one tool insert with at least one cavity for receiving a molding material mixture. This means that the tool insert is intended to come into direct contact with the molding material mixture and to define this by the execution of the cavity in its shape. Additionally or alternatively, the tool insert can be heated by means of current and heated by direct contact with the molding material mixture, the molding material mixture.

For example, a molding material mixture may be a mixture of a base material such as sand, and various additives such as binders, electrolytes, water, and the like. The molding material mixture may, according to one example, be electrically conductive and heat up when flowing through an electric current due to its specific electrical resistance. A material of the tool insert is at least partially electrically conductive and a specific electrical resistance of the material of the tool insert is selected such that it heats when passing an electric current and causes a hardening of the molding material mixture in the cavity. In other words, an electrical current flows through the material of the tool insert, for example by electrodes, which are arranged on the outer sides of the tool insert. Due to the specific electrical resistance, heat develops which, via direct contact with the molding material mixture in the cavity, causes heating of this molding material mixture.

Depending on the nature of the molding material mixture, the heating caused by the tool insert causes hardening of the molding material mixture in the cavity. It is known to the person skilled in the art that the necessary temperatures must be matched to the composition of the molding material mixture in order to be able to ensure reliable curing at the prevailing temperatures of the tool insert. The peculiarity of the present invention can be seen in that the material of the tool insert comprises a plastic.

This feature is based on the following considerations: In addition to the known uses of conductive ceramics and similar materials or blended materials also conductive high performance plastics can be used. Due to the development of novel production processes, it is also possible to produce such electrically conductive plastics at acceptable economic conditions. Here, plastics can offer a number of advantages over the known ceramic-based materials. One aspect is that different temperature resistance curves are desirable for different applications. Plastics may have a different course compared to known ceramic materials and thus meet the possible applications. In comparison to high-performance ceramics, the progress of the plastic samples can have a flatter curve with significantly lower initial resistance. According to one example, individual ceramic samples may have a resistance of up to 8000 ohm-meters at 20 ° C and then fall sharply upon temperature rise to about 20 to 30 ohm-meters at 200 ° C. Other embodiments of such plastics begin at an initial resistance of about 200 ohm meters at 20 ° C and then run almost linearly to 20 to 30 ohm meters at 200 ° C. If the electrical conductivity, according to one example, is between 0.01 ohmmeter and 300 ohmmeter at a temperature of 150 ° C to 200 ° C, plastic may be used as the material.

Assuming known sand-binder mixtures, so these required resistance ranges in the working temperature range of 150 ° C - 200 ° C despite different initial resistance at 20 ° C and the use of plastics can be achieved as part of the material of the tool insert. In this case, a flatter resistance temperature curve may allow for easier control of the process as well as significantly lower warm-up times of the tool insert at the start of the process. The underlying principle is that lower initial resistances at room temperature lead to faster warm-up times. The required working temperatures of, for example, sand binder mixtures as well as of other molding and core materials for shaping or curing determine which electrically conductive plastics can be used.

An advantage of the use of plastics can be seen in the fact that, compared with the known ceramic-based materials, a considerably less expensive hard machining is possible. This can, for example, enable mass production of standardized dimensions particularly cost-effectively. For this it may be advantageous for companies to keep a stock of standardized tooling semi-stock in stock to then manufacture the finished tool if necessary by means of hard machining.

In one embodiment of the invention, the plastic of the tool insert is a plastic from the group of polyether ketones. According to another embodiment, the plastic is a PEEK polyether ketone. PEEK plastic has a lower melting temperature and lower deformation temperature than the previously used sintered ceramics. In this case, for example, a maximum permanent working temperature for an exemplary PEEK composition may be approximately 260 ° C. Therefore, these tools can be used accordingly for binders and molding materials which require a correspondingly lower curing temperature such as 150 ° C to 220 ° C.

In addition to the PEEK materials, according to one example, PI, PAI, PEKEKK, PEK, LCP, PPS, PES, PPSU, PEI, PSU, PPP, PC-HT, ETFE, PCTFE, PVDF come into question, since these materials are in continuous use of over 150 ° C can be used. This allows the curing of inorganic sand-binder mixtures or other molding materials which require lower temperatures. The plastics to be used are to be selected according to the material properties. Each of the plastic classes offers its own fundamental advantages. The electrical properties of the plastics can be adjusted with the help of additives. Furthermore, the strength of plastics can be reinforced by means of carbon fibers (CFRP applications). Therefore, it depends on the overall characteristics and aspects. The basic considerations for selecting a suitable plastic may be melting temperature, strength and cost. An extract from possible plastics is shown in the following list. A / B / A Acrylonitrile / butadiene / acrylate, copolymer A / MMA Acrylonitrile / methyl methacrylate, copolymer APE Aromatic polyester ASA Acrylester-styrene-acrylonitrile BR Butadiene Rubber CA cellulose acetate CN cellulose nitrate COC Cyclic olefin copolymer C-PET polyethylene terephthalate CR Chloroprene rubber CSM chlorosulfonated polyethylene CSM Chlorosulfonyl-polyethylene rubber ECB Ethylene copolymer bitumen EP epoxy resin EPDM EPDM rubber EPM Ethylene-propylene copolymer (rubber) ETFE ETFE EVA, EVM ethylene vinyl acetate FEP Fluorinated copolymer FFKM, FFPM Perfluorinated rubber FKM, FPM Fluoro-polymer rubber FVMQ Fluoro-silicone rubber HD-PE Polyethylene, high-density HIPS High impact polystyrene, copolymer HNBR Hydrogenated nitrile rubber IIR butyl rubber IR Isoprene rubber LCP Liquid Crystal Polymer LD-PE Polyethylene, low-density LLDPE Polyethylene, linear low density MF Melamine-formaldehyde resin MVQ, VMQ Silicone rubber NBR Acrylonitrile-butadiene rubber PA polyamide PA 11/12 Polyamide 11/12 PA 6 Polyamide 6 PA 6 G oil-containing Polyamide G + oil PA 6 cast Polyamide casting PA 6.6 Polyamide 6.6 PAEK Polyethyl ether ketone PAI polyamide-imide PAN polyacrylonitrile PBI polybenzimidazole PBT polybutylene terephthalate PC polycarbonate PCT polycyclohexylenedimethylene PCTFE polychlorotrifluoroethylene PE polyethylene PE 1000 Polyethylene 1000 PE 500 Polyethylene 500 PE-C, CM Chlorinated polyethylene PEEK polyetheretherketone HDPE Polyethylene, high density PE-HMW Polyethylene, high molecular weight, high molecular weight PEI polyetherimide PEK polyether ketone LDPE Polyethylene, low density LLDPE Polyethylene, linear, low density PE-MD Polyethylene, medium density PEN polyethylene PES polyether sulfone PET polyethylene terephthalate PETG Polyethylene terephthalate + glycol PETP polyethylene terephthalate PE-UHMW Polyethylene, ultra-high molecular weight, very high molecular weight PF Phenol-formaldehyde resin PFA Perfluoroalkoxylalkane / perfluoroalkoxy copolymer PFPE perfluoropolyether PI polyimide PIB polyisobutene PMI polymethacrylamide PMMA polymethylmethacrylate POM Polyoxymethylene, polyacetal POM + slip Polyacetal + lubricant PP polypropylene PPA polyphthalamide PP-C Polypropylene, copolymer PPE polyphenylene ether PP-H Polypropylene, homopolymer PPO polyphenylene oxide PPS polyphenylene sulfide PPY polypyrrole PS polystyrene PS-E Polystyrene, expandable PSU polysulfone PTFE polytetrafluoroethylene PU polyurethane PURE Polyurethane, polyester elastomer PVA polyvinyl alcohol PVAC polyvinyl acetate PVC polyvinylchloride PVDC polyvinylidene PVDF polyvinylidene fluoride PVF polyvinyl fluoride SAN Styrene-acrylonitrile SBR Styrene-butadiene TPE Thermoplastic elastomers UF Urea-formaldehyde resin

In addition, the use of plastic-based tooling materials may allow more cost-effective repair and subsequent costly modifications of tool inserts due to lower hardness. Solely due to the greater expense required for repairs and modifications and the greater hardness of previous ceramic-based materials, plastic-based materials can offer a distinct advantage here.

Another advantage of plastics can be seen in the fact that used tool inserts can be recycled after the end of the useful life and can be reshaped again. For this purpose, common recycling processes can be used to reuse the plastics for injection molding, hot compression molding or extruder processes for the production of new tool inserts.

According to one example, a surface of the tool bit is ground to reduce a surface resistance of the tool bit. This may be particularly advantageous when electrodes abut the tool insert.

• - PI - Polyimide: dies sind Kunststoffe mit sehr guten Festigkeitswerten, welche als Duroplaste oder Thermoplaste zum Einsatz kommen können. Besonders positiv sind die hohen Dauereinsatztemperaturen bis ca. 230 °C und Kurztemperaturen bis zu 400 °C.
• - PAI - Polyamidimid: Kunststoffe, welche mit zu den thermisch stabilsten Kunststoffen zählen. Weiterhin ist die besondere Abriebfestigkeit und Chemiekalienbeständigkeit von Vorteil, die auch eine Verwendung bei über 220°C Dauertemperaturbeständigkeit sicherstellt.
• - PEEK sowie PEK, PAEK, PEKEKK, PEKK, PEEEK, PEEKK: Diese Kunststoffe gehören zu der Gruppe der Polyetheretherketone und weisen einen teilkristallinen Charakter auf. Die besondere Hochtemperaturfestigkeit zeichnen diese Kunststoffe auch für Anwendungen in Temperaturbereichen > 200 °C aus. Zudem sind ebenfalls die mechanischen Eigenschaften vorteilhaft. Besonders die hohe Steifigkeit, hohe Festigkeit sowie günstiges Abriebverhalten machen diese Materialien auch für Gießereianwendungen anwendbar. Allerdings können die Herstellungskosten im Vergleich zu anderen Kunststoffen höher liegen.
• - LCP: Die Abkürzung steht für flüssigkristallines Copolyester und stammt aus dem englischsprachige Akronym für Liquid Crystal Polymer. Diese Kunststoffe zeigen eine sehr hohe Steifigkeit und Dimensionsstabilität selbst bei hohen Temperaturen. Zudem ist die Wärmeausdehnung im Vergleich zu anderen Kunststoffen gering.
• - PPS - Polyphenylensulfid: Kunststoffe, welche mittels Glasfasern verstärkt werden können. Besonders die gute elektrische Leitfähigkeit und die hohe Temperaturbeständigkeit stellen einen Vorteil für diesen Kunststoff dar.
• - PSU - Polysulfon: Kunststoffe zeichnen sich durch gute Wärmebeständigkeit und gute mechanische Eigenschaften bis ca. 180 °C aus.
• - PPSU - Polyphenylsulfon: Amorphe Hochleistungskunststoffe, welche eine besonders gute Schlagfestigkeit für Industrieanwendungen aufweisen können.

In the following, selected plastic classes will be briefly introduced.

• - PI polyimides: these are plastics with very good strength values, which can be used as thermosets or thermoplastics. Particularly positive are the high continuous use temperatures up to approx. 230 ° C and short temperatures up to 400 ° C.
• - PAI - polyamideimide: plastics, which are among the most thermally stable plastics. Furthermore, the particular abrasion resistance and chemical resistance is an advantage, which also ensures use at over 220 ° C continuous temperature resistance.
• - PEEK and PEK, PAEK, PEKEKK, PEKK, PEEEK, PEEKK: These plastics belong to the group of polyetheretherketones and have a semi-crystalline character. The special high-temperature strength also distinguishes these plastics for applications in temperature ranges> 200 ° C. In addition, the mechanical properties are also advantageous. In particular, the high rigidity, high strength and favorable abrasion behavior make these materials also applicable for foundry applications. However, the manufacturing costs can be higher compared to other plastics.
• - LCP: The abbreviation stands for liquid-crystalline copolyester and comes from the English acronym for liquid crystal polymer. These plastics show very high rigidity and dimensional stability even at high temperatures. In addition, thermal expansion is low compared to other plastics.
• - PPS - polyphenylene sulfide: plastics which can be reinforced by glass fibers. Especially the good electrical conductivity and the high temperature resistance are an advantage for this plastic.
• - PSU - Polysulfone: Plastics are characterized by good heat resistance and good mechanical properties up to 180 ° C.
• - PPSU - Polyphenylsulfone: amorphous high performance plastics, which can have a particularly good impact resistance for industrial applications.

In one embodiment, the tool bit has one or more layers of a semi-material. For use in series operation, it may be useful to use standard blocks of the required plastic for the tool inserts. In the hitherto used ceramics hitherto a hard working has already been recommended before sintering or slight modifications after sintering due to the Mohs hardness. Since plastics have a lower hardness, the hard machining can advantageously be done only when needed, since the effort and the required machinery and equipment, such as CNC equipment in the local workshops are often already available. As a result, standard blocks can be stored at the production site and worked into the finished form if necessary. This can advantageously reduce costly downtime and reduce inventory costs for tool replacement. Another advantage results from the lower cost compared to a hard machining of ceramics, which can be economical for very large quantities, but is usually not the best choice for small series and prototypes.

An advantage over the hard machining are the better economic possibilities for repairing tool inserts or the adaptation of tool inserts with frequently required adjustment of the core geometries. Cost-effective modifications to tool inserts, e.g. Vent holes, core brands, Auswerststößel etc. are economically feasible with the invention described herein, since it may be cheaper in the ceramic-based process under certain circumstances, to produce a new ceramic than to rework an existing ceramic.

Another advantage of the use of plastics arises from the fact that some ceramic mixtures, although the electrical conductivity for curing the molding material at working temperatures, but at room temperature have a relatively high initial resistance of> 7500 ohms. If this ceramic mixture is used, this leads to longer warm-up times since at the beginning the temperature rises more slowly when applying the voltage than with ceramics with, for example, an initial resistance of 1000 ohm meters. This effect thus leads to longer warm-up phases at the beginning of the production and thus to a slightly lower productivity.

Another advantage results from the increased impact resistance of plastics compared to ceramics. This allows a waiver of additional devices on the core shooting system to avoid permanent damage when closing the tool parts by impact. Another advantage of the use of plastics arises from the fact that so far the conductivity of sand-binder mixtures after evaporation of the water content decreases and thus the residual heat can be produced only limited in the core.

The geometric shape of the workpiece determines the appropriate dimensions for the tool insert. In this case, a standardization of the semi-finished materials may be useful, since this is a good compromise between cost and effort and flexibility in terms of different tool uses. Through the use of plastic-based materials can be moved by the lower cost of hard machining this compromise in the direction of higher flexibility at the same or lower cost. The above-mentioned advantages of plastics over high performance ceramics also allow cost-effective production of prototypes since, according to one example, the plastic materials can be provided as semi-materials in the form of blocks. These blocks of semi-finished materials can thus be quickly machined using industry-standard CNC equipment to produce molds and cores for prototypes.

According to one embodiment of the invention, one of the materials of the tool insert comprises sintered ceramic. In other words, a combination of different materials, including common ceramic-based materials in combination with one or more plastics can be used. Advantage here can be a combination of each favorable properties, for example, to produce a certain temperature-resistance curve or to allow the absorption of impact effects by a plastic to protect the underlying ceramic.

According to one example, the tool insert consists of at least two materials. The tool insert forms a contact surface to a second tool insert. This is the case, for example, in common molds when two opposing or oppositely arranged tool inserts to move towards each other and the cavities forms a substantially closed volume for the molding material mixture. In this case, the material of the contact surface is selected such that it has at 200 ° C a substantially same resistance as the second material (eg the sintered ceramic). So here can be done using a 2 , plastic-based material a comparable electrical resistance as in previously used sintered ceramic (first material) can be used. According to one example, the material of the tool insert is interchangeable. As a result, for example, the material itself is not fixed and permanently connected to an outer wall of the tool insert, but can be changed depending on the application with little effort, for example, to extend the overall life of the tool

According to one embodiment, the material, for example PEEK plastic, of the tool insert has a carbon and / or other additives for setting an electrical conductivity. In other words, this can be used to adjust the specific electrical resistance of the material. Carbon can be added to the material in the form of nanoparticles, for example. In particular, an admixture with plastics such as PEEK, CFK or PAI can take place.

According to one embodiment, electrodes for feeding the electric current into the material of the tool insert are arranged laterally on the forming or core tool. This can for example allow a spatial arrangement of the tool as a whole, for example, much less space. In addition, the lateral arrangement may allow a more effective flow of electrical current from one side of the tool bit to the opposite side. According to one example, in an overall arrangement, individual molds or cores are each supplied with electrical current via a pair of electrodes for heating. For larger or more complex shapes, it is also possible, according to another example, to arrange a plurality of pairs of electrodes. In addition, a lateral arrangement of the electrode pairs per mold half also allows a flow of current and thus a heating with the tool open.

According to one example, the electrodes are laid per tool part with several cavities after a grid and can be controlled individually. The respective pairs of electrodes must be applied parallel to the tool halves. Thus, the positive effect can be achieved that even with different degrees of shapes or cores, the current flow of each core can be optimally controlled individually to allow a uniform and simultaneous curing of all cavities.

In one example, both lateral electrode pairs per tool half and electrode pairs are applied, as known from the prior art.

In one embodiment, the tool bit is configured to receive external heat to shorten the warm-up phase when the electrical resistivity of the tool insert material is greater than 100 ohm-meters at 20 ° C. In other words, a state is described here in which, due to the comparatively high specific electrical resistance at the beginning, only inadequate Heat for warming up the tool insert arises and thus a duration for heating would be disproportionately long. Therefore, heat is transferred to the tool bit, for example via an external heat source, to accelerate the warm-up operation. At higher temperatures, the electrical resistivity decreases and a larger amount of heat is generated, which can eventually make the supply of external heat superfluous.

According to one embodiment of the invention, the forming or core tool has a device for measuring energy consumption, temperature and / or electrical resistance. These quantities can be used in particular for process control and quality assurance. For example, these variables are measured during a process cycle and compared with historical measurement data. In one example, these may be temperature-time curves. As a result, for example, the strength of an electric current for heat generation can be controlled in order to ensure a consistently high quality of the mold produced.

According to one example, temperature sensors are arranged insulating in the tool insert in order not to negatively influence the conductivity and the desired electrical current in the tool. According to one example, when using several electrode pairs, an energy consumption, resistance and possibly temperature can be detected in each case. This may allow determination of average values of energy and electrical resistance per mold in continuous production operation. This allows conclusions to be drawn on a quality of the form.

In a further embodiment of the invention, the forming or core tool has an evaluation unit. Wherein the evaluation unit is configured to generate a control signal when the power consumption, the temperature and / or the electrical resistance value falls below or exceeds a defined threshold value. This may be particularly advantageous if in an exemplary application, an automatic ejection or a signal function is provided, which sorted out forms with very different energy consumption as rejects or for subsequent manual control.

According to one embodiment of the invention, the molding material mixture is heated by means of the method and can thus also be introduced into cavities in injection molding processes or processed in extruder processes. In other words, the device described here can be applied to a method in the field of plastics processing. Examples include known methods such as injection molding, hot press melting or the extruder process.

According to one embodiment, the tool insert is designed to receive electrically non-conductive molding mixtures. This may mean that, for example, plastics, which usually have an extremely low or no electrical conductivity, are suitable as starting material for the mold to be produced. This can be done according to an example such that the tool itself is heated by electric current, even if the molding material is not or only slightly electrically conductive.

According to one example, a molding material mixture having electrically conductive additives, such as e.g. Carbon provided to achieve a conductivity. This enables a continuous flow of current. The advantage, especially in the case of inorganic sand-binder mixtures, is that even after evaporation of the moisture, a residual conductivity remains in the sand-binder mixture and thus, even in the last phase of the heating, electricity can be used directly in the sand core to heat the sand core. Thus, even with non-conductive materials can be dispensed with an external heat generation and energy consumption can be greatly reduced.

In one embodiment, the tool insert with the cavity is designed to heat the respective surfaces of at least two plastic bodies in order to effect a connection of the two plastic bodies when a melting temperature is reached. This means that, especially in plastics processing, two molding materials of the same or different material can be bonded upon reaching a melting temperature. For this it may be sufficient to sufficiently heat the respective surfaces. This can be done by means of the heated by power tool insert and the heat transfer enabled thereby.

In one embodiment, the tool insert forms at least two regions, wherein the material of the tool insert of the one region has a different electrical resistivity than the material in the other region. In other words, different materials are used for the tool insert in spatially, for example, adjacently arranged areas. This can cause different temperatures in the respective areas during a manufacturing process can be achieved.

list of figures

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings. It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention. Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

• 1 eine Schnittdarstellung durch ein erfindungsgemäßes Form- oder Kernwerkzeug,
• 2 ein Phasendiagramm mit qualitativer Darstellung einer eingebrachten elektrischen Leistung und eines zugehörigen Widerstandes in einem Kern oder einer Form,
• 3 eine Darstellung der Erwärmung mittels elektrischen Verfahren ohne Anpassung des spezifischen Widerstandes des (Kernkasten-) Materials an das Sand-Bindergemisch (Mischung),
• 4 eine Darstellung einer möglichen Kernkastenausführung,
• 4A eine Kernkastenausführung mit Kontaktflächen,
• 5 eine Befestigung des Materials mit isolierendem Gehäuse und Grundplatte,
• 6 eine Darstellung von Entlüftungs- und Ausstoßbohrungen mit einer Ansicht von oben (6 a.)), einer Ansicht von vorne (6 b.)) und einer Seitenansicht
• (6 c.)), und 7 ein Beispiel eines Querschnitts durch ein Spritzgießwerkzeug zur Herstellung von Kunststoff-Formen.

It show, each schematically:

• 1 a sectional view through an inventive mold or core tool,
• 2 a phase diagram with a qualitative representation of an introduced electrical power and an associated resistance in a core or a mold,
• 3 a representation of the heating by means of electrical methods without adaptation of the specific resistance of the (core box) material to the sand-binder mixture (mixture),
• 4 an illustration of a possible core box design,
• 4A a core box design with contact surfaces,
• 5 an attachment of the material with insulating housing and base plate,
• 6 a representation of venting and ejection holes with a top view ( 6 a .)), a view from the front ( 6 b .)) and a side view
• ( 6 c .)), and 7 an example of a cross section through an injection mold for the production of plastic molds.

Detailed description of the figures

According to the 1 has an inventive mold or core tool 1 for the production of organic or inorganic forms 2 or cores 2 ' , a housing electrically insulated towards the machine 3 on, the two parts 4 . 5 exists that has a dividing plane 6 connected to each other. The housing 3 is on a base plate 12 attached. The housing 3 is formed of plastic, insulating ceramic or other non-conductive material and takes an at least partially electrically conductive material 7 on. The material 7 forms a mold for receiving a mixture 9 , from which, after curing, the core 2 ' or the shape 2 is formed. The material 7 has a plastic here. In this case, according to one example, the specific electrical conductivity of the mixture 9 and the electrical resistivity of the material 7 be at least approximately the same size, so that in the material 7 and the mixture 9 substantially the same specific electrical conductivity and resistivity. The mold or core tool according to the invention 1 also has at least two electrodes 10 , which are arranged parallel to each other in the example shown here. Provided is a facility 8th for regulating or controlling the electrodes 10 supplied voltage. Because here the specific electrical conductivity of the material 7 of the core 2 ' or the form 2 approximately the specific electrical conductivity of the mixture 9 in phase 2 from 2 is equivalent, is a relatively uniform passage of electrical energy through the mixture 9 possible. But the mixture can also be completely non-conductive, so for example, an organic compound such as plastics or plastic mixtures, if heat is needed for shaping.

With the molding or core tool according to the invention 1 can be a form 2 or a core 2 ' or a casting core 2 ' , to produce at the highest quality level, because due to the at least nearly the same electrical conductivity of the mold 2 or the core 2 ' used mixture 9 and the material 7 a smooth passage of electrical current through the material 7 and the mixture 9 and thus a uniform heating and curing of the mixture 9 can be done regardless of the respective geometric dimensions of the mold 2 or the core 2 ' ,

The mold is made 2 or the core 2 ' as follows: First, after the material selection mentioned in the first construction, the at least partially electrically conductive material 7 in the housing 3 of the mold or core tool 1 introduced and forms a negative mold for the later form 2 or the later core 2 ' forming mixture 9 , Subsequently, the material 7 over the electrodes 10 electrical energy and thus heat supplied, resulting in a curing of the molding material mixture 9 leads. A curing of the mixture 9 can in particular by evaporating water from the mixture 9 take place, the mixture 9 For example, may contain an inorganic binder, water and foundry sand.

That in the mix 9 (For example, a sand-binder mixture or a plastic mixture) used inorganic binder may be water-soluble, but at least contain water. With the method and with the molding or core tool according to the invention 1 can be a particularly uniformly heated and thus also particularly uniformly cured and thus homogeneous casting core or core 2 ' or shape 2 create and this regardless of the respective geometric dimension of the core 2 ' or the form 2 , because due to the here preferably exemplified same electrical conductivity of the mixture 9 for the core 2 ' and the material 7 the electric current does not seek shorter ways, as was the case with previously known from the prior art form or core tools. This often meant that due to the geometric dimensions of the core 2 ' or the form 2 conditional electrical paths these may not have cured uniformly so far and thus had areas with complete curing and only partial or no curing, whereby the quality of the molds or cores produced so far with the previous mold or core tools was often unsatisfactory.

By the device 8th In particular, the voltage can be increased or decreased, whereby a cycle time for the production of the mold 2 or the core 2 ' is controllable. The base plate of the tool 12 takes the case 3 or the parts 4.5 as well as the material 7 on, and insulated screws 13 and angles 14 provide for a fastening. Insulating screws 13 can also be replaced by quick release systems to allow for easier and faster removal. The material "floats" on the electrode 10 and the electrode 10 is done by alignment bolts 15 held in their position. If required, the tool halves or tool inserts can be equipped with additional positioning aids to ensure optimum alignment of the tool halves.

In 2 is the typical course of the electrical resistance and the introduced electrical power of a conductive heated molding material mixture 9 of any inorganic sand / binder mixture. The qualitative relationships described below are also based on organic or plastic-based mixtures 9 applicable. This may result in more advantageous courses, the example of a sand-binder mixture described below is intended merely as an example. After switching on the voltage, the resistance drops significantly within a very short time (phase 1 : Capacitive load). Then the phase begins 2 the slowly decreasing electrical resistance in the course of the curve (increase of the charge carriers). During this time, the power consumed by the sample also increases continuously until charge carriers evaporate due to the temperature reached. The resistance is now rising very fast (phase 3 ).

For the choice of the electrical resistivity (Rho) of the material for a later form, the time before the rise of the electrical resistance of the sample is in phase 3 optimal, since here the greatest achievement can be introduced (shortly before end phase 2 ). This is in 2 With 1 1 designated. Furthermore, there are also specific electrical resistances resulting from the calculation of the values within the phase 2 arise, conceivable.

The electrical resistivity of the tested mixtures 9 changes during the heating process. It is below 100 ° C at about 85 ohm meters and falls under further warming 25 Ohmmeter at over 130 ° C. With further warming, the resistivity increases dramatically. Then, however, the energy required to expel the water from the binder, which leads to curing, in the sand-binder mixture 9 available.

According to another example, the inorganic binder may be replaced by other binder types or plastics, provided that they are electrically conductive and require heat for curing and have the other required properties. For optimal selection of electrically conductive materials for this process is after the determination of the temperature-resistance curve of the mixture 9 the determination of the material 7 based on the required resistivity possible. Based on the specific resistance of the molding material mixture 9 a material composition must be determined by means of test series which has a suitable electrical resistivity at a certain temperature. This particular temperature depends on the optimum temperature of the binder or molding material needed to cure the best.

As another example, the mixture 9 be modified by electrically conductive additives. This makes it possible to increase the conductivity and to adapt the temperature-resistance curve. Thus, the efficiency of the process can be positively influenced even after any water components have evaporated. Carbon shares of 2-5% have proven to be particularly positive

As another example, the inorganic binder may be modified by other molding materials such as e.g. Plastic are replaced, even if they are electrically non-conductive but need heat to cure and have the other required properties. The optimum choice of electrically conductive materials for this process is not dependent on the temperature-resistance curve of the molding material in this application. Instead, the material can be selected for fast and efficient heating. Advantageously, materials with an electrical resistance between 0.05 ohmmeter and 50 ohm meters have been found.

In our experiments with sand-binder mixtures, tested binders required temperatures of about 150 ° C to about 180 ° C to cure. The area around the optimal resistance was determined by means of a temperature-resistance curve (see above) by approx. 25 ohmmeters. Consequently, the tested binder mixture requires 9 a material 7 with a resistivity of about 25 ohm meters at 150-180 ° C. In principle, it may be advantageous to the specific resistance of the material 7 equal to the optimum resistivity for the sand-binder mixture 9 adjust. Should be in the implementation of the specific resistance of the material 7 above that of the sand-binder mix 9 lie, this tends to cause warming from the center of the nucleus 2 in the direction of the core box material 7 because here the current finds the path of lesser resistance.

Should be in the implementation of the specific resistance of the material 7 be lower than in the sand binder mixture 9 , so the heating of the core box material tends to occur 7 towards sand core center. Similarly, the course of the temperature-resistance curve of the material should 7 Similar to the temperature-resistance curve of the sand-binder mixture 9 , The smaller the deviation of both curves, the more effective the process.

The most critical step is the production of the material 7 , The material 7 requires on the opposite side of the contouring surface a direct contact surface with the respective electrode. In experiments, it has been recommended to just grind the contact surface in order to achieve a very good contact between the electrode 10 and the material 7 to enable. This leads to the desired effect of keeping the contact resistance low.

As in 4 The electrode should be shown 10 while floating on the back of the material part. This is necessary because the material of the electrodes 10 has a different thermal expansion than the core box material. For this purpose, two pins can be attached in the back of the material, which are the electrodes 10 hold in position during the production process. Due to the parallel arrangement of the electrodes 10 can be a comparatively uniform passage of electrical energy through the material 7 and the mixture 9 be achieved, which in turn results in benefits in terms of uniform heating and uniform curing.

A possible embodiment also sees an introduction of the electrodes 10 in the material 7 in front. In this case, no pins would be needed for alignment. The electrodes 10 as well as the material 7 will then be received by means of a recess in an insulating material. The attachment of the multilayer levels can by means of anchoring in the base plate 12 of the tool. For the attachment can angle 14 with screw connections 13 used as in 5 exemplified. In order to enable a quick exchange of individual materials, quick-release systems can be used instead of screws.

The fixing screws 13 should be made of non-conductive material to conduct electricity to the housing 3 to avoid. In addition, if necessary in the material 7 , in the electrodes 10 as well as in the housing 3 vents 17 Provide (nozzles) to allow the escape of gases or water vapor. Hardening gases or water vapor can, as in existing processes using core marks (nozzles) from the sand core 2 ' (Core) and the material 7 , the electrodes 10 and the casing 3 about holes 17 be dissipated. Alternatively, the material may also be porous and thus allow the escape of gases or water vapor.

The electrodes 10 require a power supply, which is connected to the external cabinet and thus an electric control 8th allows. The electric control 8th must be adapted to the core box as well as the procedure. The electric control 8th The task takes over the core box by means of power supply and electrodes 10 to provide sufficient electricity. For new systems, the electric control 8th (Facility 8th ) are scheduled accordingly. When converting existing systems to the new method, it may be possible to modify and adapt existing switchgear. It is important that the energy input into the material 7 over electrodes 10 he follows. In this case, AC or DC is conceivable.

The control of the power supply must be the maximum short-term load of the selected material 7 and the resistance-temperature curve of the material 7 and the sand binder mixture 9 consider. The electric control 8th is to be chosen so that the highest possible power input by means of high voltage occurs, however, the maximum short-term load limit is never exceeded to damage the material 7 to prevent and thus ensure an economic process. The power input and related heat development in the sand-binder mixture 9 depends on the specific resistance and the applied voltage. Therefore, with regulation of the voltage, the power input and the temperature can be controlled. In addition, the core box may have temperature sensors to avoid heating beyond the prescribed working range of the binder, as too high a temperature would otherwise adversely affect the bonding force.

The electric control 8th It also regulates the different process steps of the core shooting machine. In doing so, special care must be taken when moving the core box parts together so that the merge happens at an adjusted speed to avoid a shock effect in the core box material and thus a possible permanent damage. For core tools with multiple sand cores 2 can either have one electrode pair per sand core 2 ' used or a pair of electrodes which all sand cores 2 covering the complete core box. It should be noted that during the heating process, the controller should be chosen so that all sand cores 2 but can never harden in the desired cycle time, the temperature never in the sand core 2 ' rises above the point where the binders lose their binding power.

The regular production process is divided into three processes. The first process describes the commissioning of the system after a short or long standstill. One feature during this process is that the material 7 not yet reached the planned operating temperature. The heating of the core box or of the tool insert takes place as well as in the typical production process. The parts 4 . 5 are brought together from their initial position and form a contact surface 18. In 4A an embodiment is shown where, in addition to those in 4 shown opposing contact surfaces 18 are provided. These contact surfaces comprise a material selected to have, at 200 ° C, an essentially similar electrical resistance as sintered ceramic according to one example.

If now the two parts 4 . 5 move towards each other, they come with their respective contact surfaces 18 indirect mechanical and thus electrical contact. According to one example, these contact surfaces 18 may be exchangeable and thus different electrical properties of the respective filler mixture 9 and / or the material 7 be adjusted.

Subsequently, the molding material mixture 9 to be shot in the core box. This may, according to one example, also be an electrically non-conductive or organic substance such as, for example, plastic. In the next step, the energy is supplied by electricity thanks to the electric control 8th , Due to increased specific resistances of the material 7 The warm-up process takes a little longer than the regular production cycle times. During the warm-up process, the material usage heats up slowly and as the temperature rises, the resistivity of the material decreases 7 , The more the resistance drops, the faster the material heats up 7 continue on the principle of resistance heating. Because the heat input in the first forms 2 Not under optimal conditions, increased rejects may occur during this process.

As soon as the desired operating temperature at the tool insert has been reached, the actual production process begins. The process parameters can be described as follows. The material 7 the core box or the tool insert has the operating temperature and thus the optimum specific resistance of the molding material mixture 9 , The core box parts 4 . 5 have moved apart and the cavity is empty. In the first step, the core box parts 4 . 5 closed and then the molding material mixture 9 shot in the core box. The specific resistance depends on the temperature of the molding material mixture 9 , The mixture 9 may be at room temperature or already preheated.

Once the molding material mixture 9 was shot into the core box, the direct contact surface cools the molding material mixture 9 of the core box material. This increases the resistance of the core box material or material of the tool insert in the short term 7 , At the same time thanks to the heat absorption, the specific resistance of the molding material mixture 9 falls. Since, as described above, the temperature-resistance curves of the material 7 and the molding material mixture 9 Similar, the deviation of the resistivity remains limited.

The electric control 8th activates the flow of current and this leads to a flow of current through the material 7 as well as through the sand core 2 ' or the shape 2 , With increasing warming now takes the resistance of the molding material mixture 9 as well as in the material 7 until the optimum resistance is reached. At this moment the performance entry is optimal. The molding material mixture 9 has now heated from the starting temperature to about 100 to 130 ° C depending on the size within a few seconds. Once by evaporation of the water content in the molding material mixture 9 the free charge carriers are reduced, the resistivity of the molding mixture begins abruptly 9 to rise. At this moment, the flow of current is within the sand core 2 reduced. To the desired optimum operating temperature for the molding material mixture 9 To achieve this, the remaining heat energy must now be transferred via the core box material 7 as in existing procedures.

The particular advantage of the method is therefore particularly in the heating of the molding material mixture 9 from the temperature at injection up to about 130 ° C by the principle of resistance heating by means of current flow within the sand core 2 , The further advantage is the efficient heating of the material 7 and thus the heat supply in the phase of 130 ° C up to the desired operating temperature of the molding material mixture 9 , Required ejector bolts 16 for ejecting the sand core from the cavity, as in 6 shown are in the designated ejection holes 16 ' attached and allow the release of the molds 2 from the material 7 ,

The third process describes the cooling phase before a break or shutdown. In this phase, the core box can simply cool down in the extended state and is then available again at any time for the first process step. Mold surface prevents what would be the case, for example, when curing by means of external heat (for example, oil heating).

In 7 is a schematic representation of an injection mold 20 shown in sectional view. Here, in particular, it should be shown that the general method for producing molds and cores by means of electric current and resistance heating can also be transferred to other fields of application, for example in plastics processing. In general, the tool described here according to the invention can be transferred to fields of application and methods which have the following features in common. First, these processes require heat to produce molds or cores. In addition, the production of these shapes and cores based on contour-bound forms, so for example cavities. Furthermore, the processes in question require a molding material mixture 9 (here as the core 2 shown), which may be conductive or non-conductive and which is introduced into the cavity.

As an example, in 7 a common injection molding apparatus for the production of plastic molds are shown. Plastics are usually processed under pressure at a temperature above a melting point of the plastic. The plastic, for example, at 50 to 80 be injected bar in the injection mold or in at least one of the cavities. The cavity is part of the injection mold, which is kept at a certain temperature using heat sources. Depending on the application, a cooling mechanism can be used in addition to the heat supply. This is appropriate in cases where excess heat energy already exceeds the molding material mixture 9 is introduced into the tool. Such cooling is here via cooling channels 36 indicated, which is to be regarded as optional however. Furthermore, each is an insulation plate 3 provided with a tool base plate 12 connected is.

An injection mold 20 has two parts or halves 4 . 5 on, which are arranged linearly movable to each other. Via a feed 34 is a molding material mixture 9 (here as a later core 2 shown) in a hot runner system 26 pressed. The injection mold 20 , especially in the field 22 of Hot runner system 26 is made of a conductive or at least partially conductive material 7 produced. This may be, for example, a plastic such as PEEK or a ceramic-based material. Especially when processing plastics with a high working temperature of over 200 ° C is the use of an electrically heated injection mold 20 advantageous because it can normally operate without cooling in continuous operation. Heat is added continuously to the tool by applying current (not shown here) to maintain the temperature at a required level. Lower specific electrical resistance of the material used results in faster and more efficient heating of the tool material. However, there must be sufficient resistance to avoid consumption and thus a short circuit. The electrical resistance should therefore be at least 0.0001 ohmmeter.

In addition, ejectors 16 to eject the finished molds 2 intended. Between the two parts 4 . 5 results in a cavity 32 into which the molding material mixture 9 is introduced and hardens there. The introduction of the molding material mixture 9 via hot runner nozzles 24 , The use of additives in the molding material mixture 9 can then be advantageous if the tools used, so here the injection mold 20 , have a comparable electrically matched resistivity. According to one example, in the injection molding process, the mold or core tool or a tool insert may be made of high performance ceramics such as silicon carbide or of a PEEK material. With the use of electrically conductive additives in the material of the molding material mixture 9 as well as in tooling, a method for producing inorganic cores or molds as set forth above can also be used for organic molds and cores in which heat for molding is advantageous.

As an example, the process is used to make salt cores.

It should also be taken into account in the desired influencing of an electrical conductivity of the materials for the molding material mixture 9 or for the tools a so-called percolation effect. This effect describes the sudden increase in electrical conductivity as soon as a certain amount of charge carrier is present in the volume. Up to this threshold, the conductivity may be approximately linear. When exceeded, the conductivity then increases abruptly. When adding additional charge carriers then takes a linear or predictable course. According to one example, a spacing of the installed components due to creeping stresses must be considered in the design of the mold or core tool.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2003/013761 A1 [0002, 0003]
• DE 2435886 A1 [0002, 0005, 0006]
• DE 3735751 A1 [0004]
• EP 3103562 A1 [0005]

Claims (15)

Mold or core tool (1) for producing organic or inorganic molds (2) or cores (2 '); having at least one tool insert with at least one cavity for receiving a molding material mixture (9); wherein a material (7) of the tool insert is at least partially electrically conductive and a specific electrical resistance of the material (7) of the tool insert is selected such that it heats when passing an electric current and causes curing of the molding material mixture (9) in the cavity ; characterized in that the material of the tool insert comprises a plastic. Mold or core tool (1) according to Claim 1 , characterized in that the plastic of the tool insert is a plastic from the group of polyether ketones. Mold or core tool (1) according to Claim 2 wherein the plastic comprises a PEEK polyether ketone. Shaped or core tool (1) according to one of the preceding claims, characterized in that the tool insert comprises one or more layers of a semi-material. Shaped or core tool (1) according to one of the preceding claims, characterized in that the material of the tool insert comprises sintered ceramic. Mold or core tool (1) according to one of the preceding claims, characterized in that the tool insert forms a contact surface to a second tool insert and the material of the contact surface is selected such that it at 200 degrees Celsius, a substantially same electrical resistance as the sintered ceramic formed. Shaped or core tool (1) according to one of the preceding claims, characterized in that the material of the tool insert comprises carbon and / or other additives for adjusting an electrical conductivity. Shaped or core tool (1) according to one of the preceding claims, characterized in that electrodes (10) for supplying the electric current are arranged in the material of the tool insert laterally on the forming or core tool. Mold or core tool (1) according to one of the preceding claims, characterized in that the tool insert is adapted to receive external heat to shorten the warm-up phase, when the electrical resistivity of the material of the tool insert is more than 500 ohm meters at 20 ° C. Shaped or core tool (1) according to one of the preceding claims, characterized in that the forming or core tool has a device for measuring an energy consumption, a temperature and / or an electrical resistance. Mold or core tool (1) according to Claim 10 , characterized in that the forming or core tool has an evaluation unit; wherein the evaluation unit is configured to generate a control signal when the energy consumption, the temperature and / or the electrical resistance value exceeds or falls below a defined threshold value. Shaped or core tool (1) according to one of the preceding claims, characterized in that the molding material mixture can be introduced into the cavity by means of injection molding, hot-pressing molding or extruder processes. Mold or core tool (1) according to Claim 12 , characterized in that the tool insert is designed to receive electrically non-conductive molding mixtures. Shaped or core tool (1) according to one of the preceding claims, characterized in that the tool insert is designed with the cavity to heat the respective surfaces of at least two plastic body to effect connection of the two plastic body on reaching a melting temperature. Tool insert (1) according to at least one of the preceding claims, characterized in that the tool insert forms at least two regions, wherein the material of the tool insert of the one area has a different electrical resistivity than in the other area.

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