KR20120125235A - Salt-based cores, method for the production thereof and use thereof - Google Patents

Abstract

When die-casting a workpiece with metal to retain the cavity contained within the workpiece, the core inserted inside the die must meet high requirements for dimensional stability when filling the mold with molten metal and can be easily removed from the cavity. It should be possible. Therefore, in accordance with the present invention, salt-based cores are provided that can be prepared by molding and compacting a core material mixture, the core materials comprising one or more salts, one or more binders and optionally auxiliary materials such as additives, fillers, wetting agents and catalysts. Wherein the salts, binders and optionally used auxiliary materials of the core material mixture are inorganic and the core materials are soluble in water as a solvent.

Description

Salt-based cores, methods for their preparation and uses thereof {SALT-BASED CORES, METHOD FOR THE PRODUCTION THEREOF AND USE THEREOF}

FIELD OF THE INVENTION The present invention relates to salt-based cores, methods of making salt-based cores as well as the use of such cores, wherein the use of such cores is for example to leave a solid residue behind. It is a space holder for cavities used in the manufacture of die-cast metal workpieces, preferably in connection with permanent mold die-casting technology, which can be easily and completely removed from the workpiece.

Cores used to die cast metal workpieces, i.e., to maintain cavities when filling the die with molten metal, require high requirements. These cores should be easily manufactured and dimensionally stable, have a precise shape, and the materials used to make the cores as well as the solvents used to dissolve the materials should not be detrimental to the quality of the die casting and environmentally Must be safe, and should not pose a health hazard.

Although the precision of the surface and shape of the cavity in the material requires special requirements, the core surface must be particularly smooth and accurate in shape, and furthermore, the core is completely dissolved in a suitable solvent, leaving behind any solid residue. It should be possible to completely remove the core from the cavity in the workpiece without. For example, core residues containing insoluble components, such as quartz sand, can cause damage to the surface awaiting finishing or result in precipitation of aggregates such as, for example, core residues, resulting in a common set of diesel-generating sets. This will block the injector nozzles of the rail system.

It is therefore an object of the present invention to provide a salt-based core of minimum porosity, good surface grade and optimum strength, which is easily and completely removed from the workpiece after die casting of the core.

A further object of the present invention is to produce such cores by means of an optimal easy and cost-effective molding method, preferably by a so-called dry-pressing process.

To date, it has not been possible to produce salt-based cores by so-called dry forming processes that can withstand mechanical stress as well as excessive heat generated when molten metal flows around the core without subsequent sintering or recrystallization processes. In other words, it produces a salt-based core that must have high strength on the one hand and easily be removed from these dies on the other hand while at the same time providing optimum good quality smooth surface properties for casting without leaving residue behind. So-called dry forming methods have not been used to date.

According to the invention, this problem is achieved by the method described in claim 22 as well as in claim 1. Advantageous embodiments of the invention are described in the dependent claims.

The cores according to the invention consist of salts, binders and optionally further auxiliary materials such as fillers, additives, wetting agents and catalysts. These cores are preferably provided in workpieces cast by a gravity die casting process, for example, with a nonmagnetic metal such as aluminum, brass or copper. The core according to the invention consists of materials which can be completely removed from the cavity of the workpiece without leaving any residue using water, which is the preferred solvent for environmental protection reasons.

The cores according to the invention have the advantage of being constructed of a material which, if properly treated, does not exhibit any environmentally harmful gaseous reactions during the manufacturing or casting process. Casting quality is improved because cracking products of organic binders do not occur during casting operation, thereby avoiding casting errors such as shrinkage holes, gas pockets, etc., which may occur due to core gases. When removing the cores from the workpiece, no residues are produced that may require special treatment to dispose of the residues. Depending on the composition of the materials, the materials may be recovered from the liquid phase by the application of suitable processes such as, for example, salt recovery by spray drying or evaporation.

All compositions of core materials can be compacted using conventional mechanical or hydraulic presses. The complexity of the core shape determines the manufacturing parameters as well as the design and structural form of the tools and presses for making the core.

Suitable core materials for the core according to the invention include, in particular, salts of alkali and alkaline earth metal elements such as sodium chloride, potassium chloride and magnesium chloride; In particular, salts and nitrates of alkali and alkaline earth metal elements such as potassium sulfate, magnesium sulfate, as well as ammonium salts such as ammonium sulfate in particular. Water soluble examples of these core materials are preferred. If these materials do not react with each other and do not adversely affect the desired properties, they can be used as mixtures and also individually, in practice the core material is any material during the manufacture of the core which adversely affects the free removal of its residues. Must not undergo conversion of. In general, all salts that can be easily melted with a melting point or melting point higher than the temperature of the liquid metal melt are convenient for use. The core material can be easily and simply divided according to the desired particle size of the core material, similar to sand. The particle size distribution chosen and the degree of compaction chosen in particular affect the surface properties of the core. The smaller the particle size, the smoother the surface. In general, the degree of demanding compaction is as high as possible, which can be achieved by mixing different salts and, if necessary, additional materials as mixtures with different particle size curves, for example with two or three particle size distributions.

According to the invention, the particle size is preferably in the range of 0.01 mm to 2 mm, depending on the core material, the desired surface grade and the shape precision of the workpiece to be cast. Depending on the degree of compaction, the particle size fractions of 0.01 mm to 0.29 mm, 0.3 mm to 1.3 mm and / or 1.31 mm to 2.0 mm are mixed in different proportions.

In addition, fillers that can be completely removed using water as solvent can replace some of the salts without negatively affecting the density and strength of the core. According to the invention, up to 30% by weight salt can be replaced by the corresponding filler. The particle size of the filler is suitably controlled by the particle size and / or particle size distribution of the salt.

Preferably, by a dry forming process, in order to ensure the required stability of the core after the forming process, a suitable binder / bonding agent and / or a suitable binder system is added to the salt prior to the compacting step. Selectable binders are all binder / binding agents that can provide good wettability for salts and can be removed with water after the curing process, leaving no residue behind, and a mixture of these materials is placed inside the core destroyed by the compaction. It must be able to be formed. Suitable binders / binding agents are generally inorganic phosphates, inorganic borates, silicate compounds or mixtures of these binding agents, provided they can be removed using water as a solvent without leaving residue. Inorganic phosphates that can be used are, for example, alkaline phosphates or ammonium phosphates, monoaluminum phosphates, boron phosphates or sodium polyphosphates. Preferred binders / binding agents consist of water soluble silicates such as water soluble water glass with water glass modules of 1 to 5, and water glass with different water glass modules may also be present as a mixture. The amount added depends on the water glass module used and is from 0.5% to 15% by weight, preferably from 5% to 8% by weight, depending on the wetting properties. It is also possible to use special binder mixtures to achieve the necessary properties such as strength and dimensional stability for subsequent die-casting processes.

The properties of the mixtures according to the invention, including salts, if necessary, auxiliary materials such as additives, fillers, wetting agents and / or catalysts and binders and / or binder systems, can be influenced by the intended addition of the additives. In addition, these mixtures can easily remove these additives or their reaction products from the cavity of the workpiece without leaving any residue using water as solvent and can adversely affect the casting step and cause casting errors. The clue applies that gases should not be generated during the die-casting process. Depending on the composition of the core material, these additives may be, for example, surface active agents, additives affecting the concentration of the mixture, lubricants, de-clumping additives, gelling agents, for example heat Additives suitable for altering the thermal-physical properties of the core, such as conductivity, additives that prevent metals from sticking to the core, additives that result in good homogeneity and miscibility, additives that improve lifetime, additives that prevent premature cure, dies -An additive which prevents the formation of fumes and condensation during the casting operation, as well as additives which accelerate the curing process. These additives are known to those skilled in the art with respect to the manufacture of conventional cores. The amount these materials are added depends on the form and composition of the core material.

In order to ensure the required strength of the core after the dry forming step, it may be necessary to initiate and accelerate the curing step by applying a catalyst which is adjusted accordingly according to the composition of the core material.

It has been surprisingly found that it acts as a catalyst for the curing step, especially by the addition of fine particulate salts, preferably by the addition of powder salts having a particle size of less than 100 nm.

If a gaseous catalyst according to the invention is used, in particular the core material, preferably carbon dioxide or gas, for the hardening and drying of the core after the dry forming step can still be blown into the sealed die. The pressure is up to 5 bar.

Thermal follow-up to the core is also possible at temperatures up to 500 ° C.

The core material consists of salts and binders as well as additives such as fillers, additives and catalysts, if necessary, and the fillers and binders are inorganic materials. All materials can be mixed homogeneously using mixing apparatus known in the art. The amount of binder and additional material added should be selected according to the purpose of use of the core as it can determine not only the surface grade of the core but also the density and strength.

For any further processing of the core material into the usable core, the type of core material available is of fundamental importance. If the core material in solid form as desired by the present invention is desired, it is very important as to whether the core material will be clumped or prevented from clumping and whether the core material will be in free flowing form. Only a free flow form of the material mixture can automatically and completely fill the so-called filling shoes, which are used in connection with the dry forming method as a preferred forming method according to the invention. Therefore, free flowing mixtures of water glass used as salt and binder material according to the invention as well as free flowing mixtures of any other additives to be mixed are particularly preferred as core materials.

The preparation of the core materials takes place separately from the manufacturing processes and, if necessary, a convenient protection method should be provided to prevent clumping and premature curing. For example, depending on the composition of the core material, preparation, transportation and storage must be under protective gas atmosphere or vacuum.

The composition and properties of the core have a significant impact on the quality of the metal casting.

Salt-based cores based on sodium chloride prepared according to the invention usually have a density of between 1.5 g / cm 3 and 1.9 g / cm 3, preferably between 1.2 g / cm 3 and 1.8 g / cm 3, as determined by the buoyancy method. . This corresponds to a porosity of 10% to 35%, preferably 5% to 25%. Bending strength as measured according to VDG leaflet P73 ranges from 400 N / cm 3 to 1500 N / cm 3.

Using the examples, the most important features will be summarized later. The features shown relate to cores not applied by the coating.

This embodiment uses a core made of NaCl with additional additives such as release agents, cure retardants and wetting agents, among other additive materials, namely water glass binders, and others. The core was formed on a hydraulic press applying a pressure of 50 to 120 bar, followed by thermal workup over a 60 minute course at a temperature of 200 ° C. to support curing. The core is particularly well suited for use in connection with aluminum gravity die-casting. In order to withstand the temperatures and forces that may occur during the casting process, the core must be dimensionally stable. Mechanical properties of the core were determined for samples having the following dimensions: 180 mm long, 22 mm wide and 22 mm high. Bending strengths as measured according to VDG leaflet P73 (February 1996) are 400 and 1500 N / cm 3.

The surface of the core may not be cleaned or damaged during the ingress of metal. Therefore, the core needs to have a corresponding surface strength, and the porosity of the core can also play an important role. In this embodiment the porosity is 30.

After the die casting has completely cured, the core must be removed. During this step, it is important that the core dissolve completely and easily without leaving any solid residue behind (Note: When the present invention uses the term “water soluble” or “dissolved” it necessarily refers to dissolution of chemical meaning). Not). An important aspect is that the components of the cores according to the invention can be easily and completely removed from the cavity of the workpiece without leaving behind any residues. The die dissolution rate of the core according to the invention naturally depends not only on the material of the core but also on the pretreatment and size of the core. For pure salts, cores with dimensions of 22 mm × 22 mm × 180 mm were cast over a course of 1-2 minutes with hot water, as demonstrated in the composition of the binder and filler for the test part in the deviation experiment. It can be seen from that it can be washed completely.

Based on the above, the idea according to the invention applies to the salt-based cores as follows.

? A salt-based core that can be prepared by molding and compacting a core material mixture from which a core material is selected from a mixture comprising one or more salts, one or more salts and, if necessary, auxiliary materials such as additives, fillers, wetting agents and catalysts, The salt, binder and, if necessary, auxiliary materials used are inorganic materials, these core materials are soluble in water as solvent, and the core material mixture is molded and compacted into the core by a dry forming method.

Preferred Cores

? Salt-based cores comprising salts having a melting point or melting point above the temperature of the liquid metal flowing around the core;

? Chlorides of alkali and alkaline earth metal elements, in particular sodium chloride, potassium chloride, and / or magnesium chloride; Sulfates and nitrates of alkali and alkaline earth metal elements, in particular potassium sulfate and / or magnesium sulfate; Ammonium salts, in particular ammonium sulfate; Or a salt-based core comprising a mixture of these salts as a salt;

? Salt-based cores comprising sodium chloride as salt;

? Salt-based cores using salts with particle sizes ranging from 0.01 mm to 2 mm;

? Salt-based cores using salts of two or three particle size distributions;

? Salt-based cores using salts with a particle size distribution of 0.01 to 0.29 mm, 0.3 to 1.3 mm and / or 1.31 to 2.0 mm;

? Salt-based cores using such inorganic phosphates, inorganic borates, silicate compounds or mixtures of these binders as binders, which can be removed by water without leaving any residue behind;

? Salt-based cores using such alkali or ammonium phosphate, monoaluminum phosphate, boron phosphate, sodium polyphosphate or mixtures of these binders as binders, which can be removed by water without leaving any residue behind;

? Salt-based cores using water soluble silicate compounds, preferably water glass as binder;

? Salt-based cores using as a binder a water glass having a water glass module of 1 to 5 and / or a water glass mixture having a different water glass module;

? Salt-based cores comprising 0.5% to 15% by weight of the binder moiety;

? A salt-based core comprising a binder moiety in the range of 0.5% to 15% by weight, depending on the wet behavior and the water glass module;

? A salt-based core comprising, as a binder, 0.5 wt% to 15 wt% of water glass moieties adjusted according to the particle size distribution and controlled by the water glass module;

? Salt-based cores with a catalyst added as auxiliary material;

? Salt-based cores comprising, in particular, fine particulate salts, preferably powder salts of particle sizes of less than 100 nm as catalyst;

? Two or three particle size distributions, and particularly preferred particle size distributions of 0.01 to 0.29 mm, 0.3 to 1.3 mm and / or 1.31 to 2.0 mm, wherein the binder is a water glass, and if a catalyst is required, additives, fillers, wetting agents and Salts comprising in particular fine particulate salts, preferably powder salts with a particle size of less than 100 nm, comprising further auxiliary materials such as additional catalysts, and wherein the mixture of core materials comprises free flowing sodium chloride as salt- Family cores;

? Salt-based cores heat treated after molding;

? Salt-based cores heat treated after molding at a temperature of 500 ° C .;

? Salt-based cores having a density between 1.5 g / cm 3 and 1.9 g / cm 3, preferably between 1.2 g / cm 3 and 1.8 g / cm 3;

? Salt-based cores having a porosity of 10% to 40%, preferably 5% to 25% after molding;

? Salt-based cores having a bending strength in the range of 400 N / cm 2 to 1500 N / cm 2 after molding;

The idea according to the invention is also

? The same applies to a method for producing a salt-based core, wherein the core comprises a core material selected from at least one salt, at least one binder, and if necessary, auxiliary materials such as additives, fillers, wetting agents and / or catalysts. The material mix is uniformly mixed in the non-liquid form, formed into a core and compacted by a dry forming process.

Preferred methods provide the following.

? Mixing salts of particle size with different distribution curves, preferably two or three particle distributions;

? Uniformly mixed and, if necessary, additional auxiliary materials are added to form a core and compacted by a dry forming method; Chlorides selected from alkali metal and alkaline earth metal elements, in particular sodium chloride, potassium chloride, and / or magnesium chloride; Sulfates and nitrates of alkali and alkaline earth metal elements, in particular potassium sulfate and / or magnesium sulfate; As well as ammonium salts, in particular ammonium sulfate; Or salts which are mixtures of these salts;

? A core material selected from the range of 0.01 mm to 2 mm depending on the metal of the metal workpiece to be cast, the desired surface grade of the workpiece to be cast, and the precision of the shape, formed into a core and pressed by a dry forming method;

? A core material that is uniformly mixed into the free-flowing mixture, formed into a core and to be compacted by a dry forming method.

The cores according to the invention can be used as place holders inside a cavity, for example, during the production of parts by metal casting, preferably by gravity diecasting technology.

Claims (27)

A salt-based core prepared by molding and compacting a mixture of core materials selected from one or more salts, one or more binders and, if necessary, auxiliary materials such as additives, fillers, wetting agents and catalysts,
Wherein the salts, binders, and auxiliary materials used if necessary of the core material mixture are inorganic and soluble in water as a solvent, the core material mixture being molded and compacted into the core by a dry forming method,
Salt-based cores.
The method of claim 1,
Wherein said core material mixture is free flowing,
Salt-based cores.
The method according to claim 1 or 2,
Salts having a melting point or melting point above the temperature of the liquid metal flowing around the core are used,
Salt-based cores.
The method according to any one of claims 1 to 3,
Chlorides of alkali metals and alkaline earth metals, in particular sodium chloride, potassium chloride, and / or magnesium chloride; Sulfates and nitrates of alkali and alkaline earth metals, in particular potassium sulfate and / or magnesium sulfate; Characterized in that ammonium salts, in particular ammonium sulfate or mixtures of these salts, are used as salts,
Salt-based cores.
The method according to any one of claims 1 to 4,
The salt is characterized in that the sodium chloride,
Salt-based cores.
6. The method according to any one of claims 1 to 5,
The particle sizes of the salts used are in the range of 0.01 mm to 2 mm,
Salt-based cores.
7. The method according to any one of claims 1 to 6,
The salts used are characterized by being available in two or three particle size distributions,
Salt-based cores.
The method according to any one of claims 1 to 7,
The salts used are characterized in that they are available in particle size distributions of 0.01 to 0.29 mm, 0.3 to 1.3 mm and / or 1.31 to 2.0 mm,
Salt-based cores.
The method according to any one of claims 1 to 8,
Inorganic borate, which is removable with water without leaving any residue behind; Alkali phosphates or inorganic phosphates such as ammonium phosphate, monoaluminum phosphate, boron phosphate or sodium polyphosphate; Silicone compounds, preferably water glass; Or mixtures of these binders are used,
Salt-based cores.
The method according to any one of claims 1 to 8,
The binder is a mixture of water glass with water glass modules of 1 to 5 and / or water glass with different water glass modules,
Salt-based cores.
11. The method according to any one of claims 1 to 10,
The portion of the binder medium is in the range of 0.5% to 15% by weight,
Salt-based cores.
12. The method according to any one of claims 1 to 11,
The binder portion is characterized in that the range of 0.5% to 15% by weight, depending on the wetting properties and water glass module,
Salt-based cores.
13. The method according to any one of claims 1 to 12,
Characterized in that 0.5% to 15% by weight of the water glass portion, which is adjusted according to the particle size distribution and controlled by the water glass module, is included as a binder,
Salt-based cores.
14. The method according to any one of claims 1 to 13,
A catalyst is added as an auxiliary material,
Salt-based cores.
15. The method according to any one of claims 1 to 14,
The catalyst is characterized in that it is a particularly fine particulate salt, preferably a powder salt, having a particle size of less than 100 nm,
Salt-based cores.
The method according to any one of claims 1 to 15,
The salt is sodium chloride which is preferably available in two or three particle size distributions, particularly preferably in a particle size distribution of 0.01 to 0.29 mm, 0.3 to 1.3 mm and / or 1.31 to 2.0 mm, the binder is a water glass, and The catalyst is a particularly fine particulate salt, preferably a powder salt with a particle size of less than 100 nm, further comprising additional auxiliary materials such as additives, fillers, wetting agents and / or further catalysts as necessary, wherein the mixture of core materials Free-flowing,
Salt-based cores.
The method according to any one of claims 1 to 16 or more than one,
The cores are heat-treated after molding,
Salt-based cores.
The method according to any one or more of claims 1 to 17,
Characterized in that the cores are heat-treated at a temperature of 500 ℃ after molding,
Salt-based cores.
The method according to any one of claims 1 to 18 or more than one,
Wherein said shaped cores have a density of between 1.5 g / cm 3 and 1.9 g / cm 3, preferably between 1.2 g / cm 3 and 1.8 g / cm 3,
Salt-based cores.
The method according to any one of claims 1 to 19, or
Characterized in that the cores have a porosity of 10% to 40%, preferably 5% to 25%,
Salt-based cores.
The method according to any one of claims 1 to 20 or more than one,
The cores are characterized in that they have a bending strength of 400 N / ㎠ to 1500 N / ㎠
Salt-based cores.
In the method for producing a salt-based core,
One or more salts, one or more binders and, if necessary, a mixture of core materials selected from auxiliary materials such as additives, fillers, wetting agents and catalysts, are uniformly mixed in a non-liquid form by a dry forming process, molded into cores and It is characterized by being compacted,
Method of Making Salt-Based Cores.
The method of claim 22,
Characterized in that variable distribution curves, preferably salts of particle size with two or three particle size distributions, are used and mixed,
Method of Making Salt-Based Cores.
24. The method according to claim 22 or 23,
Chlorides such as alkali metals and alkaline earth metals, in particular sodium chloride, potassium chloride, and / or magnesium chloride; Sulfates and nitrates of alkali metals and alkaline earth metals, in particular potassium sulfate and / or magnesium sulfate; as well as ammonium salts, in particular ammonium sulfate or mixtures selected thereof, are uniformly carried out by means of a dry forming process with additional auxiliary materials as necessary Characterized in that it is mixed, molded into a core and compacted,
Method of Making Salt-Based Cores.
25. The method according to any one of claims 21 to 24,
The core material having a particle size in the range of 0.01 mm to 2 mm is used depending on the core material, the desired surface grade and shape precision of the workpiece to be cast from the metal, characterized in that it is molded and compacted into the core by a dry forming process. ,
Method of Making Salt-Based Cores.
26. The method according to any one of claims 21 to 25,
Characterized in that the core materials are uniformly mixed with the free-flowing material mixture, molded into the core and compacted by a dry forming process,
Method of Making Salt-Based Cores.
The method according to any one of claims 1 to 20,
Said salt-based core is used as a common place holder during metal casting, preferably by gravity diecasting technology,
Method of Making Salt-Based Cores.