Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
  • B22C1/26—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of carbohydrates; of distillation residues therefrom
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
  • B22C1/186—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents contaming ammonium or metal silicates, silica sols
  • B22C1/188—Alkali metal silicates

Definitions

• the invention relates to a method for producing casting molds for metalworking according to claim 1.
• Casting molds for the production of metal bodies are essentially produced in two versions.
• the so-called cores or forms form a first group. From these, the casting mold is assembled, which essentially represents the negative mold of the casting to be produced.
• a second group consists of hollow bodies, so-called feeders, which act as equalizing reservoirs. These absorb liquid metal, with appropriate measures being taken to ensure that the metal remains in the liquid phase longer than the metal that is in the casting mold that forms the negative mold. If the metal solidifies in the negative mold, liquid metal can flow out of the compensating reservoir to compensate for the volume contraction that occurs when the metal solidifies.
• Casting molds consist of a refractory material, for example quartz sand, the grains of which are bonded by a suitable binder after the casting mold has been formed, in order to ensure sufficient mechanical strength of the casting mold.
• a refractory base material that has been treated with a suitable binder is therefore used for the production of casting moulds.
• the refractory basic molding material is preferably in a free-flowing form, so that it can be filled into a suitable hollow mold and compacted there.
• the binder creates a solid bond between the particles of the basic molding material, so that the casting mold has the required mechanical stability.
• Casting molds have to meet various requirements. During the casting process itself, they first have to have sufficient stability and temperature resistance to accommodate the liquid metal in the hollow mold formed from one or more (partial) casting molds. After the start of the solidification process, the mechanical stability of the casting mold is ensured by a solidified metal layer that forms along the walls of the cavity. The material of the casting mold must now decompose under the influence of the heat emitted by the metal in such a way that it loses its mechanical strength, i.e. the cohesion between individual particles of the refractory material is broken. This is achieved, for example, by the binder decomposing under the influence of heat. After cooling, the solidified casting is shaken, which ideally causes the material of the casting molds to crumble back into fine sand that can be poured out of the cavities of the metal mold.
• Both organic and inorganic binders can be used to produce the casting molds and can be hardened by cold or hot processes.
• Cold processes are processes which are carried out essentially at room temperature without heating the casting mold.
• the hardening usually takes place through a chemical reaction, which is triggered, for example, by passing a gas as a catalyst through the mold to be hardened.
• the mold material mixture is heated to a sufficiently high temperature after shaping heated, for example, to expel the solvent contained in the binder or to initiate a chemical reaction through which the binder is cured, for example, by crosslinking.
• organic binders are often used in which the curing reaction is accelerated by a gaseous catalyst or which are cured by reaction with a gaseous curing agent. These methods are referred to as "cold box” methods.
• Ashland cold box process An example of the production of casting molds using organic binders is the so-called Ashland cold box process. It is a two-component system. The first component consists of a solution of a polyol, usually a phenolic resin. The second component is the solution of a polyisocyanate. So according to the U.S. 3, 409, 579 A the two components of the polyurethane binder are reacted by passing a gaseous tertiary amine through the mixture of molding base material and binder after molding. The curing reaction of polyurethane binders is a polyaddition, ie a reaction without splitting off by-products such as water. Other advantages of this cold box process include good productivity, dimensional accuracy of the molds, as well as good technical properties such as mold strength, pot life of the mold base and binder mixture, etc.
• Heat-curing organic processes include the hot-box process based on phenolic or furan resins, the warm-box process based on furan resins and the Croning process based on phenolic novolak resins.
• hot-box and warm-box processes liquid resins are processed into a molding mixture with a latent hardener that only becomes effective at elevated temperatures.
• basic mold materials such as quartz, chrome ore, zircon sands, etc. are coated at a temperature of approx. 100 to 160°C with a phenol novolak resin that is liquid at this temperature. Hexamethylenetetramine is added as a reaction partner for later curing.
• shaping and curing takes place in heatable tools that are heated to a temperature of up to 300°C.
• binder systems In order to avoid the emission of decomposition products during the casting process, binders based on inorganic materials or at most a very small proportion of organic ones must be used connections included. Such binder systems have been known for some time. Binder systems have been developed which can be cured by introducing gases. Such a system is for example in GB 782 205 described, in which an alkali water glass is used as a binder, which can be cured by introducing CO 2 . In the DE 199 25 167 will describe an exothermic feeder mass that contains an alkali silicate as a binder. Furthermore, binder systems have been developed which are self-curing at room temperature. Such a system based on phosphoric acid and metal oxides is, for example, in U.S.
• inorganic binder systems are also known which are cured at higher temperatures, for example in a hot tool.
• hot-curing binder systems are, for example, from U.S. 5,474,606 known, in which a binder system consisting of alkali water glass and aluminum silicate is described.
• inorganic binders also have disadvantages compared to organic binders.
• the casting molds made with water glass as a binder have relatively low strength. This leads to problems in particular when the casting mold is removed from the tool, since the casting mold can break. Good strength at this point is particularly important for the production of complicated, thin-walled molded parts and their safe handling.
• the reason for the low strength is primarily that the casting molds still contain residual water from the binder. Longer dwell times in the hot, closed mold are only of limited help, since the water vapor cannot escape to a sufficient extent.
• Casting molds made with water glass as a binder often show poor decay after metal casting.
• the binder can vitrify under the influence of the hot metal, so that the casting mold becomes very hard and can only be removed from the casting with great effort. Attempts have therefore been made to add organic components to the mold material mixture, which burn under the influence of the hot metal and, due to the formation of pores, facilitate the disintegration of the casting mold after casting.
• core and molding sand mixtures which contain sodium silicate as a binder.
• glucose syrup is added to the mixture added.
• the molding sand mixture processed into a mold is set by passing carbon dioxide gas through it.
• the molding sand mixture contains 1 to 3% by weight of glucose syrup, 2 to 7% by weight of an alkali silicate and a sufficient quantity of core or molding sand.
• molds and cores containing glucose syrup have far better disintegration properties than molds and cores containing sucrose or pure dextrose.
• a binder mixture for solidifying molding sand which consists of an alkali metal silicate, preferably sodium silicate, a polyhydric alcohol and other additives, modified carbohydrates, non-hygroscopic starch, a metal oxide and a filler being provided as additives.
• a non-hygroscopic starch hydrolyzate with a reducing power of 6 to 15%, which can be added as a powder, is used as the modified carbohydrate.
• the non-hygroscopic starch and the metal oxide, preferably iron oxide, are added in an amount of 0.25 to 1% by weight of the amount of sand. If necessary, a lubricant in powder form or as an oil can be added to the binder mixture.
• the binder mixture is preferably cured by using CO 2 or a chemical catalyst.
• a binder composition for the production of casting molds which comprises an alkali metal silicate with a SiO 2 /M 2 O modulus of 2.0 to 3.22 and a polyhydroxy compound.
• the binder is mixed with a refractory mold base material and cured after the mold has been produced by gassing with carbon dioxide.
• Mono-, di-, tri- or tetrasaccharides, for example, are used as polyhydroxy compounds, with no high requirements being placed on the purity of these compounds.
• a mold material mixture for the production of casting molds which, in addition to a refractory mold base material, comprises a binder composition which comprises a mixture of 100 parts of glue obtained from grain, 2 to 20 parts of sugar and 2 to 20 parts of a halogen acid or a salt of a halogen acid .
• a suitable salt is, for example, ammonium chloride.
• the glue is made by partially hydrolyzing starch. To produce a casting mold, the mold material mixture is first brought into the desired shape and then heated to a temperature of at least 175 - 180 °C.
• a molding material mixture for the production of casting molds which, in addition to a refractory basic molding material, comprises a water-containing binder which, in addition to an alkali metal silicate, contains an oxidizing agent which is compatible with the alkali metal silicate and, based on the solution, contains 9 to 40% by weight of an easily oxidizable organic material .
• Nitrates, chromates, dichromates, permanganates or chlorates of the alkali metals, for example, can be used as the oxidizing agent.
• starch, dextrins, cellulose, hydrocarbons, synthetic polymers such as polyether or polystyrene, and hydrocarbons such as tar can be used as easily oxidizable material.
• the mold material mixture can be cured by heating or by gassing with carbon dioxide.
• a mold material mixture for the production of casting molds which, in addition to a refractory mold base material, comprises a binder based on an alkali metal silicate, in particular water glass.
• Amorphous silicon dioxide is added to the binder in a proportion which, based on the solution of the binder, corresponds to 2 to 75%.
• the amorphous silica has a particle size range of about 2 to 500 nm.
• the binder has a modulus SiO 2 : M 2 O of 3.5 to 10, where M is an alkali metal.
• the invention was therefore based on the object of providing a method for producing casting molds for metalworking, which comprises at least one refractory basic molding material and a binder system based on water glass, the molding material mixture containing a proportion of a particulate metal oxide which contains synthetically produced amorphous silicon dioxide is, and which enables the production of casting molds with complex geometry and which can also include, for example, thin-walled sections, whereby after the metal casting the casting obtained should already have a high surface quality.
• the mold material mixture produced as part of the method according to the invention contains a carbohydrate as a further component, the carbohydrate being an oligosaccharide or polysaccharide and the proportion of the carbohydrate, based on the refractory base mold material, being in the range from 0.01 to 0.4% by weight. is selected, and wherein the carbohydrate is added in solid form to the refractory mold base.
• the refractory mold base material must have sufficient dimensional stability at the temperatures prevailing during metal casting.
• a suitable refractory base molding material is therefore characterized by a high melting point.
• the melting point of the refractory basic molding material is preferably higher than 700°C, preferably higher than 800°C, particularly preferably higher than 900°C and particularly preferably higher than 1000°C.
• Quartz or zircon sand for example, is suitable as a refractory base molding material.
• fibrous refractory molding materials are also suitable, such as fireclay fibers.
• Other suitable refractory basic molding materials are, for example, olivine, chrome ore sand, vermiculite.
• Artificial refractory base materials can also be used as refractory base materials, such as aluminum silicate hollow spheres (so-called microspheres), glass beads, glass granules or spherical ceramic base materials known as "Cerabeads ® " or "Carboaccucast ® ". These artificial refractory basic mold materials are produced synthetically or, for example, accumulate as waste in industrial processes. These spherical ceramic mold base materials contain, for example, mullite, corundum and ⁇ -cristobalite in different proportions as minerals. They contain aluminum oxide and silicon dioxide as essential components. Typical compositions contain, for example, Al 2 O 3 and SiO 2 in approximately equal proportions.
• the diameter of the spherical, refractory basic mold materials is preferably less than 1000 ⁇ m, in particular less than 600 ⁇ m.
• These artificial ones Basic molding materials do not have a natural origin and can also have been subjected to a special shaping process, such as in the production of hollow aluminum silicate microspheres, glass beads or spherical ceramic basic molding materials.
• Hollow aluminum silicate microspheres are formed, for example, when fossil fuels or other combustible materials are burned and are separated from the ash produced during combustion.
• Hollow microspheres as an artificial refractory molding material are characterized by a low specific weight. This is due to the structure of these artificial refractory mold bases, which include gas-filled pores. These pores can be open or closed. Closed-pored artificial refractory basic molding materials are preferably used. When using open-pored artificial refractory basic molding materials, part of the binder based on water glass is absorbed in the pores and can then no longer develop a binding effect.
• glass materials are used as the artificial mold raw materials. These are used in particular either as glass beads or as glass granules.
• Conventional glasses can be used as the glass, with glasses having a high melting point being preferred.
• glass beads and/or glass granules made from broken glass are suitable.
• Borate glasses are also suitable.
• the composition of such glasses is given by way of example in the table below. Table: composition of glasses component broken glass borate glass SiO 2 50-80% 50-80% Al2O3 _ 0-15% 0 - 15% Fe2O3 _ ⁇ 2% ⁇ 2% M II O 0 - 25% 0 - 25% M I 2 O 5-25% 1 - 10% B2O3 _ ⁇ 15% Otherwise. ⁇ 10% ⁇ 10% M II : alkaline earth metal, eg Mg, Ca, Ba M I : alkali metal, e.g. Na, K
• glasses listed in the table can also be used whose content of the abovementioned compounds is outside the ranges mentioned.
• special glasses can also be used which, in addition to the oxides mentioned, also contain other elements or their oxides.
• the diameter of the glass spheres is preferably 1 to 1000 ⁇ m, preferably 5 to 500 ⁇ m and particularly preferably 10 to 400 ⁇ m.
• the refractory base mold material is formed by glass materials.
• the proportion of glass material in the refractory basic molding material is preferably chosen to be less than 35% by weight, particularly preferably less than 25% by weight, particularly preferably less than 15% by weight.
• the proportion of glass material in the refractory basic molding material is preferably greater than 0.5% by weight, preferably greater than 1% by weight, particularly preferably greater than 1.5% by weight. , particularly preferably greater than 2 wt .-% selected.
• the preferred proportion of the artificial basic molding materials is at least about 3% by weight, particularly preferably at least 5% by weight, particularly preferably at least 10% by weight, preferably at least about 15% by weight, particularly preferably at least about 20% by weight % by weight, based on the total amount of the refractory basic molding material.
• the refractory basic molding material preferably has a free-flowing state, so that the molding material mixture produced as part of the method according to the invention can be processed in conventional core shooting machines.
• the proportion of the artificial refractory base molding materials in the refractory base molding material is preferably less than 80% by weight, preferably less than 75% by weight, particularly preferably less than 65% by weight.
• the molding material mixture produced as part of the method according to the invention comprises a binder based on water glass as a further component.
• Conventional water glasses can be used as the water glass, as they are already used as binders in molding material mixtures. These water glasses contain dissolved sodium or potassium silicates and can be made by dissolving vitreous potassium and sodium silicates in water.
• the water glass preferably has a SiO 2 /M 2 O modulus in the range from 1.6 to 4.0, in particular 2.0 to 3.5, where M stands for sodium and/or potassium.
• the water glasses preferably have a solids content in the range from 30 to 60% by weight. The solids content refers to the amount of SiO 2 and M 2 O contained in the water glass.
• the molding mixture also contains a proportion of a particulate metal oxide which is synthetically produced amorphous silicon dioxide.
• the average primary particle size of the particulate metal oxide can be between 0.10 ⁇ m and 1 ⁇ m. Because of the agglomeration of the primary particles, however, the particle size of the metal oxides is preferably less than 300 ⁇ m, preferably less than 200 ⁇ m, particularly preferably less than 100 ⁇ m. It is preferably in the range from 5 to 90 ⁇ m, particularly preferably in the range from 10 to 30 ⁇ m and very particularly preferably in the range from 15 to 50 ⁇ m.
• the particle size allows can be determined, for example, by sieve analysis.
• the sieve residue on a sieve with a mesh size of 63 ⁇ m is particularly preferably less than 10% by weight, preferably less than 8% by weight.
• Precipitated silica and/or pyrogenic silica is preferably used as the particulate silicon dioxide.
• Precipitated silica is obtained by reacting an aqueous alkali silicate solution with mineral acids. The resulting precipitate is then separated off, dried and ground.
• Pyrogenic silicic acids are understood as meaning silicic acids which are obtained from the gas phase by coagulation at high temperatures. Pyrogenic silica can be produced, for example, by flame hydrolysis of silicon tetrachloride or in an electric arc furnace by reduction of quartz sand with coke or anthracite to silicon monoxide gas with subsequent oxidation to silicon dioxide.
• the pyrogenic silicas produced by the arc furnace process can still contain carbon.
• Precipitated silica and fumed silica are equally well suited for the mold material mixture produced as part of the process of the invention. These silicas are hereinafter referred to as "synthetic amorphous silicon dioxide".
• the inventors assume that the strongly alkaline water glass can react with the silanol groups arranged on the surface of the synthetically produced amorphous silicon dioxide and that when the water evaporates an intensive bond is produced between the silicon dioxide and the then solid water glass.
• the mold material mixture produced as part of the process according to the invention contains a carbohydrate as an essential further component, the carbohydrate being an oligosaccharide or polysaccharide and the proportion of carbohydrate, based on the refractory base mold material, being in the range from 0.01 to 0.4% by weight. % is chosen, and wherein the carbohydrate is added in solid form to the refractory mold base.
• oligo- or polysaccharides are used.
• the carbohydrate can be used either as a single compound or as a mixture of different carbohydrates. No excessive demands are made on the purity of the carbohydrates used.
• the carbohydrates based on the dry weight, are present in a purity of more than 80% by weight, particularly preferably more than 90% by weight, particularly preferably more than 95% by weight, in each case based on the dry weight.
• the monosaccharide units of the carbohydrates can be linked in any way.
• the carbohydrates preferably have a linear structure, for example an ⁇ - or ⁇ -glycosidic 1,4-linkage.
• the carbohydrates can also be wholly or partly 1,6-linked, such as. B. the amylopectin, which has up to 6% ⁇ -1,6 bonds.
• the amount of carbohydrate is selected to be relatively small, with the proportion of carbohydrate, based on the refractory base molding material, being selected in the range from 0.01 to 0.4% by weight.
• the aim is to keep the proportion of organic components in the mold material mixture as low as possible, so that the development of smoke caused by the thermal decomposition of these organic compounds is suppressed as far as possible. It will therefore Relatively small amounts of carbohydrate are added to the mold material mixture, whereby a significant improvement in the strength of the casting molds before casting or a significant improvement in the quality of the surface of the casting can be observed
• a high proportion of carbohydrates does not bring about any further improvement in the strength of the casting mold or the surface quality of the casting.
• the proportion of carbohydrate in the mold material mixture is preferably in the range from 0.2 to 0.4% by weight.
• the carbohydrate is used in underivatized form.
• Such carbohydrates can conveniently be obtained from natural sources such as plants, for example grain or potatoes.
• the molecular weight of such carbohydrates obtained from natural sources can be reduced, for example, by chemical or enzymatic hydrolysis, for example in order to improve the solubility in water.
• underivatized carbohydrates which are made up only of carbon, oxygen and hydrogen
• derivatized carbohydrates in which, for example, some or all of the hydroxyl groups are etherified with, for example, alkyl groups.
• Suitable derivatized carbohydrates are, for example, ethyl cellulose or carboxymethyl cellulose.
• low molecular weight hydrocarbons such as mono- or disaccharides can already be used. Examples are glucose or sucrose.
• oligo- or polysaccharides are claimed as carbohydrates. The beneficial effects are observed when using oligo- or polysaccharides. An oligo- or polysaccharide is therefore used as the carbohydrate.
• the oligo- or polysaccharide has a molar mass in the range from 1,000 to 100,000 g/mol, preferably 2,000 and 30,000 g/mol.
• the carbohydrate has a molar mass in the range from 5,000 to 20,000 g/mol, a significant increase in the strength of the casting mold is observed, so that the casting mold can be easily removed from the mold and transported during manufacture. Even when stored for a longer period of time, the casting mold shows very good strength, so that storage of the casting molds required for series production of castings, even for several days in the presence of atmospheric moisture, is easily possible.
• the resistance to the effects of water which is unavoidable, for example, when applying a wash to the casting mold, is also very good.
• the polysaccharide is preferably made up of glucose units, which are particularly preferably linked in an ⁇ - or ⁇ -glycosidic manner in a 1,4-linked manner.
• the carbohydrate is particularly preferably selected from the group consisting of cellulose, starch and dextrins and derivatives of these carbohydrates.
• Suitable derivatives are, for example, derivatives which are wholly or partially etherified with alkyl groups.
• other derivatizations can also be carried out, for example esterifications with inorganic or organic acids.
• a further optimization of the stability of the casting mold and the surface of the casting can be achieved if special carbohydrates and here particularly preferably starches, dextrins (hydrolyzate product of starches) and their derivatives are used as additives for the mold material mixture.
• special carbohydrates and here particularly preferably starches, dextrins (hydrolyzate product of starches) and their derivatives are used as additives for the mold material mixture.
• starches such as potato, corn, rice, pea, banana, horse chestnut or wheat starch can be used as starches.
• modified starches such as pregelatinized starch, thin-boiling starch, oxidized starch, citrate starch, acetate starch, starch ethers, starch esters or else starch phosphates. There is no restriction in the choice of strength per se.
• the starch can, for example, be of low viscosity, medium viscosity or high viscosity, cationic or anionic, soluble in cold water or soluble in hot water.
• the dextrin is particularly preferably selected from the group of potato dextrin, corn dextrin, yellow dextrin, white dextrin, borax dextrin, cyclodextrin and maltodextrin.
• the mold material mixture preferably additionally comprises a phosphorus-containing compound.
• a phosphorus-containing compound Both organic and inorganic phosphorus compounds can be used here.
• the phosphorus in the phosphorus-containing compounds is preferably present in oxidation state V.
• the stability of the casting mold can be further increased by adding phosphorus-containing compounds. This is particularly important when the liquid metal hits a sloping surface during metal casting and exerts a high erosive effect there due to the high metallostatic pressure or can lead to deformations, particularly of thin-walled sections of the casting mold.
• the phosphorus-containing compound is preferably in the form of a phosphate or phosphorus oxide.
• the phosphate can be in the form of an alkali or alkaline earth metal phosphate, with alkali metal phosphates and in particular the sodium salts being particularly preferred. In principle, ammonium phosphates or phosphates of other metal ions can also be used. However, the alkali metal or alkaline earth metal phosphates mentioned as preferred are easily accessible and are available inexpensively in any desired amounts. Phosphates of polyvalent metal ions, especially trivalent metal ions, are not preferred. It has been observed that when using such phosphates of polyvalent metal ions, in particular trivalent metal ions, the processing time of the mold material mixture is shortened.
• the phosphorus oxide is preferably present in the form of phosphorus pentoxide.
• phosphorus tri- and phosphorus tetroxide can also be used.
• the phosphorus-containing compound can be added to the mold material mixture in the form of the salts of fluorophosphoric acids.
• the salts of monofluorophosphoric acid are particularly preferred here.
• the sodium salt is particularly preferred.
• organic phosphates are added to the mold material mixture as a phosphorus-containing compound.
• a phosphorus-containing compound Preference is given here alkyl or aryl phosphates.
• the alkyl groups preferably contain 1 to 10 carbon atoms and can be straight-chain or branched.
• the aryl groups preferably contain 6 to 18 carbon atoms, and the aryl groups can also be substituted by alkyl groups.
• Phosphate compounds derived from monomeric or polymeric carbohydrates such as glucose, cellulose or starch are particularly preferred.
• the use of a phosphorus-containing organic component as an additive is advantageous in two respects. On the one hand, the necessary thermal stability of the casting mold can be achieved through the phosphorus content and, on the other hand, the surface quality of the corresponding casting is positively influenced by the organic content.
• Both orthophosphates and polyphosphates, pyrophosphates or metaphosphates can be used as phosphates.
• the phosphates can be prepared, for example, by neutralizing the corresponding acids with a corresponding base, for example an alkali metal base such as NaOH or possibly also an alkaline earth metal base, it not necessarily having to be saturated with metal ions for all the negative charges on the phosphate ion.
• Both the metal phosphates and the metal hydrogen phosphates and the metal dihydrogen phosphates can be used, such as Na 3 PO 4 , Na 2 HPO 4 and NaH 2 PO 4 .
• the anhydrous phosphates as well as hydrates of the phosphates can also be used.
• the phosphates can be introduced into the mold material mixture both in crystalline and in amorphous form.
• Polyphosphates are understood to mean, in particular, linear phosphates which comprise more than one phosphorus atom, the phosphorus atoms each being connected via oxygen bridges. Polyphosphates are obtained by dehydrating condensation of orthophosphate ions to form a linear chain of PO 4 tetrahedra, each connected at corners. Polyphosphates have the general formula (O(PO 3 ) n ) (n+2)- , where n is the chain length. A polyphosphate can contain up to several hundred PO 4 tetrahedra. However, preference is given to using polyphosphates with shorter chain lengths. n preferably has values from 2 to 100, particularly preferably 5 to 50. Higher condensed polyphosphates can also be used, ie polyphosphates in which the PO 4 tetrahedra are connected to one another via more than two corners and therefore exhibit polymerization in two or three dimensions.
• Metaphosphates are understood as meaning cyclic structures which are made up of PO 4 tetrahedra which are each connected via corners. Metaphosphates have the general formula ((PO 3 ) n ) n- where n is at least 3. n preferably has values from 3 to 10.
• Both individual phosphates and mixtures of different phosphates and/or phosphorus oxides can be used.
• the preferred proportion of the phosphorus-containing compound, based on the refractory base molding material, is between 0.05 and 1.0% by weight. If the content is less than 0.05% by weight, there is no significant influence on the dimensional stability of the casting mold. If the content of the phosphate exceeds 1.0% by weight, the tear strength of the mold decreases sharply.
• the proportion of the phosphorus-containing compound is preferably chosen to be between 0.10 and 0.5% by weight.
• the phosphorus-containing compound preferably contains between 0.5 and 90% by weight of phosphorus, calculated as P 2 O 5 . If inorganic phosphorus compounds are used, they preferably contain 40 to 90% by weight, particularly preferably 50 to 80% by weight, of phosphorus, calculated as P 2 O 5 . If organic phosphorus compounds are used, they preferably contain 0.5 to 30% by weight, particularly preferably 1 to 20% by weight, of phosphorus, calculated as P 2 O 5 .
• the phosphorus-containing compound can be added to the mold material mixture in solid or dissolved form.
• the phosphorus-containing compound is preferably added to the mold material mixture as a solid. If the phosphorus-containing compound is added in dissolved form, water is the preferred solvent.
• a further advantage of adding phosphorus-containing compounds to molding material mixtures for the production of casting molds was found that the molds disintegrate very well after metal casting. This applies to metals that require lower pouring temperatures, such as light metals, especially aluminum. However, better disintegration of the mold was also found in iron casting. With iron casting, higher temperatures of more than 1200°C act on the casting mold, so that there is an increased risk of the casting mold vitrifying and thus worsening the decay properties.
• Iron oxide was also considered as a possible additive as part of the investigations carried out by the inventors on the stability and disintegration of casting molds.
• iron oxide is added to the mold material mixture, an increase in the stability of the casting mold is also observed in metal casting.
• the addition of iron oxide can also potentially improve the stability of thin-walled sections of the casting mold.
• the addition of iron oxide does not bring about the improvement in the disintegration properties of the casting mold after metal casting, in particular iron casting, that is observed when phosphorus-containing compounds are added.
• the molding material mixture produced as part of the method according to the invention represents an intensive mixture of at least the components mentioned.
• the particles of the refractory basic molding material are preferably coated with a layer of the binder.
• evaporating the water present in the binder approximately 40-70% by weight, based on the weight of the binder
• firm cohesion between the particles of the refractory base mold material can then be achieved.
• the binder ie the water glass and the particulate metal oxide, in particular synthetic amorphous silicon dioxide, and the carbohydrate is preferably contained in the mold material mixture in a proportion of less than 20% by weight, particularly preferably in a range from 1 to 15% by weight .
• the proportion of the binder refers to the solids content of the binder. If solid refractory basic molding materials are used, such as quartz sand, the binder is preferably present in a proportion of less than 10% by weight, preferably less than 8% by weight, particularly preferably less than 5% by weight. If refractory basic molding materials are used which have a low density, such as the hollow microspheres described above, the proportion of binder increases accordingly.
• the particulate metal oxide in particular the synthetic amorphous silicon dioxide, is preferably contained in a proportion of 2 to 80% by weight, preferably between 3 and 60% by weight, particularly preferably between 4 and 50% by weight, based on the total weight of the binder %.
• the ratio of water glass to particulate metal oxide, especially synthetic amorphous silicon dioxide can be varied within wide ranges. This offers the advantage of improving the initial strength of the casting mold, i.e. the strength immediately after removal from the hot tool, and the moisture resistance without significantly affecting the final strengths, i.e. the strengths after the casting mold has cooled, compared to a water glass binder without amorphous silicon dioxide. This is of great interest, especially in light metal casting.
• high initial strengths are desired so that after the casting mold has been produced it can be transported without any problems or assembled with other casting molds.
• the final strength after curing should not be too high in order to avoid problems with the binder breaking down after casting, i.e. the basic mold material should be able to be easily removed from cavities in the mold after casting.
• the basic molding material contained in the molding material mixture produced as part of the method according to the invention can contain at least a portion of hollow microspheres.
• the diameter of the hollow microspheres is usually in the range of 5 to 500 ⁇ m, preferably in the range of 10 to 350 ⁇ m, and the thickness of the shell is usually in the range of 5 to 15% of the diameter of the microspheres.
• These microspheres have a very low specific weight, so that the casting molds produced using hollow microspheres have a low weight.
• the insulating effect of the hollow microspheres is particularly advantageous.
• the hollow microspheres are therefore used in particular for the production of casting molds if these are to have an increased insulating effect.
• Such casting molds are, for example, the feeders already described in the introduction, which act as a compensating reservoir and contain liquid metal, with the metal being kept in a liquid state until the metal filled into the hollow mold has solidified.
• Another area of application for casting molds that contain hollow microspheres are, for example, sections of a casting mold that correspond to particularly thin-walled sections of the finished casting mold. The insulating effect of the hollow microspheres ensures that the metal in the thin-walled sections does not solidify prematurely and thus block the paths within the casting mold.
• the binder due to the low density of these hollow microspheres, is preferably used in a proportion in the range of preferably less than 20% by weight, particularly preferably in the range from 10 to 18% by weight.
• the values relate to the solids content of the binder.
• the hollow microspheres preferably have sufficient temperature stability so that they do not soften prematurely and lose their shape during metal casting.
• the hollow microspheres preferably consist of one aluminum silicate. These hollow aluminum silicate microspheres preferably have an aluminum oxide content of more than 20% by weight, but can also have a content of more than 40% by weight.
• Such hollow microspheres are manufactured, for example, by Omega Minerals Germany GmbH, Norderstedt, under the names Omega-Spheres ® SG with an aluminum oxide content of approx. 28-33%, Omega-Spheres ® WSG with an aluminum oxide content of approx. 35-39% and E- Spheres with an aluminum oxide content of approx. 43% on the market. Corresponding products are available from PQ Corporation (USA) under the name “ Extendospheres® ”.
• hollow microspheres which are made of glass are used as the refractory base molding material.
• the hollow microspheres consist of a borosilicate glass.
• the borosilicate glass has a boron content, calculated as B 2 O 3 , of more than 3% by weight.
• the proportion of hollow microspheres is preferably chosen to be less than 20% by weight, based on the mold material mixture.
• a small proportion is preferably selected. This is preferably less than 5% by weight, preferably less than 3% by weight, and is particularly preferably in the range from 0.01 to 2% by weight.
• the mold material mixture produced as part of the method according to the invention contains at least a proportion of glass granules and/or glass beads as the refractory base molding material.
• the mold material mixture contains an oxidizable metal and a suitable oxidizing agent.
• the oxidizable metals preferably make up a proportion of 15 to 35% by weight.
• the oxidizing agent is preferably added in a proportion of 20 to 30% by weight, based on the mold material mixture.
• Suitable oxidizable metals are, for example, aluminum or magnesium.
• Suitable oxidizing agents are, for example, iron oxide or potassium nitrate.
• Binders that contain water result in poorer flowability of the molding mixture compared to binders based on organic solvents.
• the flowability of the mold material mixture can deteriorate further as a result of the addition of the particulate metal oxide.
• This means molds with narrow passages and multiple diversions are harder to fill.
• the molds have sections with insufficient compaction, which in turn can lead to casting defects in the casting.
• the mold material mixture produced as part of the method according to the invention contains a proportion of a lubricant, preferably a flaky lubricant, in particular graphite, MoS 2 , talc and/or pyrophillite.
• lubricants in particular graphite
• complex shapes with thin-walled sections can also be produced, with the casting molds consistently having a consistently high density and strength, so that essentially no casting defects are observed during casting.
• the amount of the added flake-form lubricant, in particular graphite is preferably 0.05% by weight to 1% by weight, based on the refractory base molding material.
• the mold material mixture produced as part of the method according to the invention can also include other additives.
• internal release agents can be added, which facilitate the detachment of the casting molds from the mold. Suitable internal release agents are, for example, calcium stearate, fatty acid esters, waxes, natural resins or special alkyd resins.
• silanes can also be added to the mold material mixture.
• the molding material mixture produced as part of the process according to the invention contains an organic additive which has a melting point in the range from 40 to 180° C., preferably 50 to 175° C., ie is solid at room temperature.
• Organic additives are understood as meaning compounds whose molecular structure is made up predominantly of carbon atoms, ie organic polymers, for example. The addition of the organic additives can further improve the quality of the surface of the casting. The mechanism of action of the organic additives has not been clarified.
• the inventors assume that at least part of the organic additives burns during the casting process, creating a thin gas cushion between the liquid metal and the basic mold materials forming the wall of the casting mold and thus a reaction between the liquid metal and the basic mold material is prevented.
• the inventors also assume that some of the organic additives form a thin layer of so-called lustrous carbon under the reducing atmosphere prevailing during casting, which also prevents a reaction between the metal and the basic mold material.
• an increase in the strength of the casting mold after curing can be achieved by adding the organic additives.
• the organic additives are preferably used in an amount of 0.01 to 1.5% by weight, more preferably 0.05 to 1.3% by weight, more preferably 0.1 to 1.0% by weight, respectively based on the refractory mold material added.
• the proportion of organic additives is preferably chosen to be less than 0.5% by weight.
• Suitable organic additives are, for example, phenol-formaldehyde resins such as novolaks, epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins or epoxidized novolaks, polyols such as polyethylene glycols or polypropylene glycols, polyolefins such as polyethylene or polypropylene, copolymers Olefins such as ethylene or propylene and other comonomers such as vinyl acetate, polyamides such as polyamide 6, polyamide 12 or polyamide 6,6, natural resins such as gum rosin, fatty acids such as stearic acid, fatty acid esters such as cetyl palmitate , Fatty acid amides, such as ethylenediaminebisstearamide, and metal soaps, such as stearates or oleates of monovalent to trivalent metals.
• the organic additives can be both pure substance as
• the mold material mixture produced as part of the method according to the invention contains a proportion of at least one silane.
• suitable silanes are aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes, methacrylsilanes, ureidosilanes and polysiloxanes.
• silanes examples include ⁇ -aminopropyltrimethoxysilane, ⁇ -hydroxypropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, ⁇ -mercaptopropyltrimethoxysilane, ⁇ -glycidoxypropyltrimethoxysilane, ⁇ -(3,4-epoxycyclohexyl)-trimethoxysilane, 3-methacryloxypropyltrimethoxysilane and N- ⁇ (aminoethyl)- ⁇ - aminopropyltrimethoxysilane.
• silane Based on the particulate metal oxide, typically about 5-50% by weight of silane is used, preferably about 7-45% by weight, particularly preferably about 10-40% by weight.
• the casting molds made with the mold material mixture made as part of the method of the invention surprisingly show good disintegration after casting, especially in the case of aluminum casting.
• casting molds can be produced which also show very good disintegration in iron casting, so that the molding material mixture can easily be removed from narrow and angled sections of the casting mold after casting can be poured out again.
• the use of the moldings produced from the mold material mixture produced as part of the method according to the invention is therefore not limited to light metal casting.
• the casting molds are generally suitable for casting metals. Such metals are, for example, non-ferrous metals, such as brass or bronze, and ferrous metals.
• the procedure is generally such that first the refractory mold base material is introduced and then the binder is added with stirring.
• the water glass and the particulate metal oxide, in particular the synthetic amorphous silica, and the carbohydrate itself can be added in any order.
• the carbohydrate can be added in dry form, for example in the form of starch powder.
• the solid carbohydrate is added to the refractory base material.
• the binder is provided as a two-component system, with a first liquid component containing the water glass and a second solid component containing the particulate metal oxide.
• the solid component can also include, for example, the phosphate and optionally a lubricant, preferably in the form of flakes.
• the carbohydrate is added to the mold material mixture in solid form and this can also be added to the solid component.
• the refractory base mold material is placed in a mixer and the solid component(s) of the binder is then preferably added first and mixed with the refractory base mold material.
• the mixing time is chosen so that the refractory basic molding material and the solid binder component are thoroughly mixed.
• the mixing time depends on the amount of molding material mixture to be produced and on the mixing unit used.
• the mixing time is preferably chosen to be between 1 and 5 minutes.
• the liquid component of the binder is then added, preferably with further agitation of the mixture, and the mixture is then further mixed until a uniform layer of the binder has formed on the grains of the refractory basic molding material.
• the mixing time depends on the quantity of molding material mixture to be produced and on the mixing unit used.
• the duration for the mixing process is preferably chosen to be between 1 and 5 minutes.
• a liquid component is understood to mean both a mixture of different liquid components and the totality of all liquid individual components, with the latter also being able to be added individually.
• a solid component is understood to mean both the mixture of individual or all of the solid components described above and the totality of all solid individual components, with the latter being able to be added to the mold material mixture together or one after the other.
• the liquid component of the binder can also be added to the refractory basic molding material first and only then the solid component of the mixture can be added.
• 0.05 to 0.3% water based on the weight of the basic molding material, is first added to the refractory basic molding material and only then are the solid and liquid components of the binder added.
• a surprisingly positive effect on the processing time of the mold mixture can be achieved. The inventors assume that the water-removing effect of the solid components of the binder is reduced in this way and the curing process is delayed as a result.
• the mold material mixture is then brought into the desired shape.
• Conventional methods are used for shaping. For example, can the mold material mixture is shot into the mold using a core shooter with the aid of compressed air.
• the mold material mixture is then hardened by supplying heat in order to evaporate the water contained in the binder. Water is extracted from the mold material mixture when it is heated. The removal of water presumably also initiates condensation reactions between silanol groups, so that crosslinking of the water glass occurs.
• the cold hardening processes described in the prior art for example by introducing carbon dioxide or by polyvalent metal cations, difficultly soluble compounds are precipitated and the casting mold is thus strengthened.
• the molding material mixture can be heated, for example, in the mold. It is possible to fully harden the casting mold in the mold. However, it is also possible to harden the casting mold only in its edge region, so that it has sufficient strength to be able to be removed from the mold. The casting mold can then be fully cured by removing more water from it. This can be done in an oven, for example.
• the hardening of the casting molds can be accelerated by blowing heated air into the mold.
• rapid removal of the water contained in the binder is achieved, as a result of which the casting mold is solidified within periods of time suitable for industrial use.
• the temperature of the blown air is preferably 100°C to 180°C, more preferably 120°C to 150°C.
• the flow rate of the heated air is preferably adjusted so that the mold hardens in periods of time suitable for industrial use.
• the periods depend on the size of the molds being made.
• the aim is curing in less than 5 minutes, preferably less than 2 minutes. However, longer periods of time may be required for very large molds.
• the water can also be removed from the mold material mixture by heating the mold material mixture by irradiating it with microwaves.
• the irradiation of the microwaves is preferably carried out after the casting mold has been removed from the mold.
• the casting mold must already have sufficient strength. As already explained, this can be brought about, for example, in that at least one outer shell of the casting mold is already cured in the mold.
• the flowability of the mold material mixture produced as part of the method according to the invention can be improved by the addition of, preferably platelet-shaped, lubricants, in particular graphite and/or MoS 2 and/or talc.
• Talc-like minerals such as pyrophyllite can also improve the flowability of the molding mixture.
• the flake-form lubricant, in particular graphite and/or talc can be added to the mold material mixture separately from the two binder components.
• the mold material mixture can also include other organic additives, as already described. These further organic additives can be added at any time during the production of the mold material mixture.
• the total amount of organic additives, ie including the carbohydrate, is preferably selected to be less than 0.5% by weight, based on the refractory base molding material.
• the organic additives are preferably added as a powder or as short fibers, with the mean particle size or the fiber length preferably being chosen such that it does not exceed the size of the refractory particles of the basic molding material.
• the organic additives can particularly preferably be sieved through a sieve with a mesh size of about 0.3 mm.
• the particulate metal oxide and the organic additive(s) are preferably not added separately to the molding sand but are premixed.
• the mold material mixture contains silanes or siloxanes, they are usually added in the form that they are worked into the binder beforehand.
• the silanes or siloxanes can also be added to the basic molding material as a separate component.
• the method according to the invention is suitable per se for the production of all casting molds customary for metal casting, ie for example cores and moulds. Casting molds that include very thin-walled sections can also be produced particularly advantageously.
• the method according to the invention is suitable for the production of feeders, in particular when insulating refractory basic molding material is added or when exothermic materials are added to the molding material mixture produced as part of the method according to the invention.
• the casting molds produced from the mold material mixture produced as part of the method according to the invention or with the method according to the invention have a high strength immediately after production, without the strength of the casting molds after hardening being so high that difficulties in removing them after production of the casting of the mold occur. It was found here that the casting mold has very good disintegration properties both in the case of light metal casting, in particular aluminum casting, and in the case of iron casting. Furthermore, these casting molds have a high stability at elevated humidity, i.e. the casting molds can surprisingly also be stored for long periods of time without any problems. As a particular advantage, the casting mold has a very high stability under mechanical stress, so that even thin-walled sections of the casting mold can be realized without them being deformed by the metallostatic pressure during the casting process.
• the casting mold produced by the method according to the invention is generally suitable for metal casting, in particular light metal casting. Particularly advantageous results are obtained with aluminum casting.
• Georg Fischer test bars were used to test the molding mixture produced. Georg Fischer test bars are cuboid test bars with the dimensions 150 mm x 22.36 mm x 22.36 mm.
• the components listed in Table 1 were mixed in a laboratory blade mixer (Vogel & Schemmann AG, Hagen, DE). For this purpose, the quartz sand was initially introduced and the water glass was added with stirring. A sodium water glass which contained potassium was used as the water glass. The modulus is therefore given as SiO 2 : M 2 O in the following tables, where M indicates the sum of sodium and potassium. After the mixture was stirred for one minute, the amorphous silica and/or carbohydrate, if any, were added with continued stirring. The mixture was then stirred for a further minute;
• the molding material mixtures were transferred to the storage bunker of an H 2.5 hot-box core shooter from Röperwerk-Giessereimaschinen GmbH, Viersen, DE, whose mold was heated to 200° C.;
• the mold material mixtures were introduced into the mold using compressed air (5 bar) and remained in the mold for a further 35 seconds;
• hot air (2 bar, 120° C. on entry into the mold) was passed through the mold for the last 20 seconds;
• the mold was opened and the test bar was removed.
• test bars were placed in a Georg Fischer strength tester equipped with a 3-point bending device (DISA Industrie AG, Schaffhausen, CH) and the force which caused the test bars to break was measured.
• Example 1.1 shows that adequate hot strength cannot be achieved without the addition of amorphous silicon dioxide or a carbohydrate.
• the shelf life of the cores produced with mold material mixture 1.1 also shows that process-reliable series core production is not possible with this.
• the hot strength can be increased by adding amorphous silicon dioxide (Examples 1.2 and 1.3), so that the cores have sufficient strength to be processed further directly after the core production.
• the addition of amorphous silica improves the shelf life of the cores, especially at high relative humidity.
• carbohydrate compounds, in particular dextrin compounds Example 1.4
• the cores produced have an improved shelf life.
• the combined addition of amorphous silicon dioxide and dextrin shows particularly high immediate strength and a further optimized shelf life.
• the final strengths are also significantly increased compared to the other mixtures.
• the use of ethyl cellulose (Example 1.6) or a potato starch derivative (Example 1.7) in combination with amorphous silicon dioxide also enables process-reliable core production.
• Even adding just 0.1% potato dextrin (mixture 1.8) has a positive effect on the immediate strength and storage stability of the kernels (compared to mixture 1.3)
• Georg Fischer test bars of the molding material mixtures 1.1 to 1.8 were installed in a sand casting mold in such a way that three of the four long sides come into contact with the cast metal during the casting process. Casting was carried out with a type 226 aluminum alloy at a casting temperature of 735°C. After the mold had cooled down, the sand was removed from the casting using high-frequency hammer blows. The castings were assessed with regard to the remaining sand adhesions.
• the cast section of mixture 1.1 shows very strong sand adhesions.
• the carbohydrate-containing mold material mixture (mixture 1.4) has a positive influence on the casting surface quality.
• the cast sections of mixtures 1.5, 1.6 and 1.7 also show hardly any sand adhesions, which confirms the positive influence of the carbohydrates (here in the form of dextrin and ethyl cellulose) on the cast surface quality in these cases as well. Even the addition of just 0.1% dextrin (Mixture 1.8) brings about a significant improvement in surface quality compared to the carbohydrate-free comparison (mixture 1.3).

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