Inorganic water-soluble binder system

Abstract

A composition for manufacturing cores used in shaping or metal casting processes. This composition includes particulate refractories and a binder composition. The binder composition includes at least one alkali metal silicate, potassium carbonate, and at least one pozzolan additive. The cores formed from this composition have high strength and are water dispersible.

Description

Technical Field

[0001] The present invention relates to a composition for use as a core in a casting or molding process, a core comprising the composition, a casting mold comprising the core, and a method for manufacturing a molded article using the core. In particular, the present invention relates to a core that can be washed out from the internal cavities of a cast or molded article using water.

Background Art

[0002] In the gravity casting method, molten metal (or metal alloy) is poured into a pre-formed mold cavity that defines the outer shape of the casting, and the molten metal fills the mold cavity by the force of gravity. The shape of the hollow or internal cavities within the casting may generally be defined by disposable cores made of cured resin-bonded sand. During casting, the resin binder within the core is thermally decomposed by the extreme heat from the molten metal, and the core decomposes when the molten metal cools and solidifies, allowing it to be easily shaken out from the finished casting. The use of cured disposable resin-bonded sand cores is also commonly applied to low-pressure sand casting, gravity sand casting, and low-pressure die casting.

[0003] However, in die casting processes where the metal is cooled very rapidly or in die casting processes where the walls of the casting are relatively thin, the cores may not be exposed to enough heat for the binder to decompose during the casting process, making it very difficult to remove the cores after the casting has solidified. Examples of such die casting processes include high-pressure die casting, semi-solid casting (such as rheocasting and thixocasting), and squeeze casting. In such processes, the cores are exposed to much lower temperatures for only a limited time, which is insufficient to thermally decompose conventional resin binders.

[0004] In conventional high-pressure die casting (HPDC), molten metal is injected into the mold cavity at high pressure at high speed and held under compressive force until the metal solidifies. The molds used in die casting can be made of metal (such as steel) to withstand high pressures and metal velocities and are usually reusable. In addition to the very fast filling time of the molten metal, the casting walls are thin and an active cooling system is used in the mold, resulting in a very fast solidification time.

[0005] Semi-solid casting is a type of HPDC. By injecting the metal (or metal alloy) into the mold in a semi-solid state rather than a fully molten state, the kinematic viscosity and metal fluidity are improved, realizing advantages such as thin-wall design, reduction of porosity, surface finish, elongation, fatigue, and improvement of tool life. In rheocasting, the metal is cooled from a fully molten state to a semi-solid state before injection, while in thixocasting, solid metal is partially melted to become a semi-solid state.

[0006] It is desirable to use cores to form internal shapes in die casting applications, but there are problems. At the low times and temperatures of HPDC, the thermal decomposition of the binder is low, making it difficult to remove the sand after casting. Conventional cores do not have sufficient strength to withstand the pressures and metal velocities involved in many applications and may be crushed in such use. Therefore, conventional resin-bonded cores are not suitable for use in most high-pressure die casting processes. There are alternative methods to form internal cavities in HPDC, but they are not widely adopted due to process complexity and cost issues.

[0007] One alternative technology is to form cores from soluble salts. However, this technology is costly except for very niche applications. A further solution to the above core strength and removability problems is to use a mold or core sand and an organic polymer binder. It is possible to achieve cores and molds with good strength and water solubility, but a common problem is that volatile organic compounds (VOCs) are generated when the organic binder thermally decomposes, especially in molding processes that require particularly long cycle times. VOCs pose risks to foundry workers and also have an adverse impact on other environments.

[0008] Efforts have also been made to use conventional core technologies for HPDC applications, and it is possible to some extent to achieve the strength required to resist the forces during filling and solidification. However, it is extremely difficult to remove these cores by applying a high mechanical impact load to the parts. Since the parts are thin-walled and the initial casting strength is weak, damage and cracks occur in the castings, and many fragments from the cores remain in the cavity.

[0009] The present invention seeks to reduce or improve the above-mentioned problems associated with removing internal cores from cast or molded parts, or at least to provide a useful alternative.

Summary of the Invention

[0010] Composition

[0011] According to a first aspect of the present invention, there is provided a composition for producing cores for use in a molding or metal casting process. The composition may include particulate refractory material. The composition may include a binder composition. The binder composition may include at least one alkali metal silicate. The binder composition may include potassium carbonate. The binder composition may include at least one pozzolan additive.

[0012] The inventors of the present invention have found that cores produced from the composition of the first aspect have sufficient strength to withstand the forces experienced during the casting or molding process, but can be washed from the internal cavities of the casting or molded part using only water. In particular, this composition does not require mechanical force to remove the cores from the molded part, and provides a high-quality surface finish and a high degree of cleanliness of the internal cavities. To avoid misunderstanding, as used herein, the term "solubility" refers to the solubility of the binder composition. With respect to the cured cores formed from the composition, the discussion of "dissolubility" is intended to refer to the water dispersibility of the cured cores. It will be understood that particulate refractories are generally water-insoluble.

[0013] In some embodiments, the neutrons produced using the composition are water-soluble even after being heated to at least 200 °C. In some embodiments, the neutrons produced using the composition are water-soluble after being heated to a temperature of 200 - 350 °C.

[0014] The binder may comprise 1.5 - 35 wt% based on the weight of the particulate refractory. In some embodiments, the composition comprises at least 2 wt%, at least 3 wt%, at least 4 wt%, at least 5 wt%, at least 6 wt%, at least 7 wt%, at least 8 wt%, at least 9 wt%, at least 10 wt%, at least 11 wt%, at least 12 wt%, at least 13 wt%, at least 14 wt%, at least 15 wt%, at least 16 wt%, at least 17 wt%, at least 18 wt%, at least 19 wt%, or at least 20 wt% of the binder composition based on the weight of the particulate refractory material. In some embodiments, the composition comprises 35 wt% or less, 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less, 5 wt% or less, or 2 wt% or less of the binder composition based on the weight of the particulate refractory. In some embodiments, the binder composition comprises 0.5 - 30 wt%, 1 - 20 wt%, 2 - 15 wt%, or 2 - 10 wt% of the binder composition based on the weight of the particulate refractory.

[0015] The binder composition may be an inorganic binder composition. Such embodiments are advantageous because they can avoid the generation of VOCs due to the binder burning or thermally decomposing upon contact with the molten metal.

[0016] Alkali metal silicate

[0017] At least one alkali metal silicate may comprise 1 to 15 wt% based on the weight of the particulate refractory. At least one alkali metal silicate may comprise at least 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, or at least 14 wt% based on the weight of the particulate refractory. In some embodiments, at least one alkali metal silicate may comprise 14 wt% or less, 13 wt% or less, 12 wt% or less, 11 wt% or less, 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, or 2 wt% or less, or may comprise the particulate refractory.

[0018] In some embodiments, at least one alkali metal silicate comprises sodium silicate. In some embodiments, at least one alkali metal silicate comprises potassium silicate. In a series of embodiments, at least one alkali metal silicate comprises sodium silicate and potassium silicate.

[0019] The alkali metal silicate may be an aqueous solution. The aqueous solution can have a solids content of 30 to 50 wt%. In some embodiments, the solids content may be 32 to 48 wt%, 34 to 46 wt%, 35 to 45 wt%, 36 to 44 wt%, or 38 to 42 wt%. The solids may be about 40 wt%.

[0020] In some embodiments, the binder composition may further comprise 1 to 3 wt% water based on the particulate refractory.

[0021] Pozolan additive

[0022] In the present invention, the composition contains at least one pozzolan additive. The pozzolan additive is typically a fine powdery substance. The at least one pozzolan-based additive may contain 0.5 to 10 wt% based on the weight of the particulate refractory. In some embodiments, the at least one pozzolan additive contains at least 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, or 9 wt% based on the weight of the particulate refractory. In some embodiments, the at least one pozzolan particulate refractory is 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less based on the weight of the particulate refractory.

[0023] The inventors have found that a small amount of pozzolan additive enhances the strength of the cores produced from this composition. More desirably, the composition of the present invention has a significantly lower proportion of pozzolan additive than conventional binder systems.

[0024] The at least one pozzolan additive can be selected from the group consisting of silica fume, fly ash, rice husk ash, diatomaceous earth, volcanic ash, metakaolin, and mixtures thereof. The at least one pozzolan additive may contain spherical particles and / or cenospheres. In a preferred embodiment, the at least one pozzolan additive contains silica fume.

[0025] In some embodiments, the at least one pozzolan additive has a D50 particle size of 20 μm or less, 10 μm or less, 5 μm or less, 2 μm or less, 1 μm or less, 0.5 μm or less, or 0.1 μm or less. In some embodiments, the at least one pozzolan additive has a D50 particle size of at least 0.01 μm, at least 0.05 μm, at least 0.1 μm, or at least 0.5 μm. In some embodiments, the at least one pozzolan additive has a D50 particle size of 0.01 μm to 50 μm, 0.01 to 20 μm, 0.01 to 10 μm, 0.01 μm to 5 μm, or 0.01 μm to 2 μm.

[0026] Potassium carbonate

[0027] Potassium carbonate may contain 0.125 to 10 wt% based on the weight of the particulate refractory. In some embodiments, potassium carbonate may contain at least 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.75 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, or 9 wt%. In some embodiments, potassium carbonate may contain 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.75 wt% or less, 0.5 wt% or less, 0.4 wt% or less, 0.3 wt% or less, or 0.2 wt% or less. The inventors have found that the addition of potassium carbonate to the composition improves the solubility of the seeds formed from the composition.

[0028] Surfactant

[0029] In a series of embodiments, the composition further comprises at least one surfactant. The at least one surfactant can be selected from the group consisting of anionic surfactants, cationic surfactants, nonionic surfactants and amphoteric surfactants, and mixtures thereof. Types of surfactants suitable for use in the present invention include sulfates, methosulfates, linear alcohol sulfates, sulfonates, sulfosuccinates, phosphate esters, glucosides, and mixtures thereof. In particular, the at least one surfactant can be selected from the group consisting of 2-ethylhexyl sulfosuccinate, 2-ethylhexyl sulfate, dodecylbenzene sulfonate, nonylphenol sulfate, sodium lauryl sulfate, 3-ethylhexyl phosphate ester, undecylamidopropyltrimethylammonium methosulfate, alkyl polyglycol ether ammonium methosulfate, 2-ethylhexyl glucoside, hexyl glucoside, and mixtures thereof. In a preferred embodiment, the surfactant comprises sodium ethylhexyl sulfate.

[0030] The inventors of the present invention have found that a binder composition having a high surface tension reduces the fluidity of the composition, and by adding a small amount of surfactant to reduce the surface tension of the binder composition, the fluidity of the composition can be significantly increased. Consequently, the increase in the fluidity of the composition results in cores with improved strength for the reasons described above.

[0031] Particulate refractory

[0032] The particulate refractory may be a natural refractory. The refractory may be a synthetic refractory. In some embodiments, a plurality of refractory materials may be used.

[0033] In some embodiments, the particulate refractory includes sand. The sand may be any type of sand suitable for use in refractory applications, such as quartz sand. In some embodiments, the particulate refractory can include any one or more conventional refractories such as oxides, carbides, nitrides of elements such as silicon, aluminum, magnesium, calcium, and zirconium. Suitable refractories include, but are not limited to, quartz, cordierite, chromite, zircon, alumina, etc. In some embodiments, the particulate refractory includes spherical particles and / or cenospheres such as fly ash. In some embodiments, the particulate refractory includes a mixture of sand and spherical particles and / or cenospheres, such as a mixture of sand and fly ash.

[0034] In embodiments where both the particulate refractory material and the pozzolanic additive include spherical particles and / or hemispheres, both the particulate refractory material and the pozzolanic additive may include the same type of spherical particles and / or hemispheres, such as fly ash. Alternatively, the particulate refractory material and the pozzolanic additive may include different types of spherical particles and / or hemispheres. For example, the particulate refractory material may include fly ash, while the pozzolanic additive may include silica fume. In embodiments where the particulate refractory and the pozzolanic additive both include the same type of spherical particles and / or spherulites, it will be understood that the D50 particle size of the particulate refractory is greater than the D50 particle size of the pozzolanic additive and that the particulate refractory is different from the pozzolanic additive.

[0035] In some embodiments, the particulate refractory has a D50 particle diameter of at least 20 μm, at least 50 μm, at least 100 μm, at least 250 μm, or at least 500 μm. In some embodiments, the particulate refractory has a D50 particle diameter of 2 mm or less, 1 mm or less, or 500 μm or less. In some embodiments, the particulate refractory has a D50 particle diameter of 20 μm to 2 mm, 50 μm to 2 mm, or 50 μm to 1 mm.

[0036] Neutron

[0037] According to a second aspect of the present invention, there is provided a neutron for use in a shaping or metal casting process, comprising the composition of the first aspect of the present invention. The neutron may be coated with a surface coating. The surface coating may be any coating suitable for refractory applications and may include one or more of boron nitride, silicate, titania, alumina, zirconia, alumina, aluminum silicate, or mixtures thereof. In some embodiments, the surface coating may be a sealant.

[0038] The neutrons may be water-dispersible. The neutrons may be configured such that the solidified neutron composition decomposes in water such that a cylinder of the solidified neutron composition having a maximum height of 80 mm and a maximum diameter of 50 mm disintegrates in less than 10 minutes when immersed in water. Preferably, the solidified neutrons disintegrate in less than 5 minutes, less than 4 minutes, less than 3 minutes, less than 2 minutes, less than 1 minute, less than 45 seconds, less than 30 seconds, or less than 15 seconds. The water may be at a temperature of 20°C. In some embodiments, the water may be at least 30°C, 40°C, 50°C, or 60°C. In some embodiments, the water may be less than 100°C, such as less than 90°C, less than 80°C, less than 70°C, less than 60°C, or less than 50°C. The water can be stirred at a speed of at least 60 rpm. The water may be stirred at less than 150 rpm.

[0039] In some embodiments, the solidified neutron composition may have a flexural strength of at least 250 N / cm 2 In some embodiments, the solidified neutron composition is at least 500 N / cm 2 , at least 750 N / cm 3 or at least 1000 N / cm 2 of flexural strength. If possible, a higher flexural strength is preferred to reduce the likelihood of the neutrons cracking during casting.

[0040] In some embodiments, the cylinder of the solidified neutron composition disintegrates in water in less than 10 minutes after being heated to a temperature of 200 - 350°C.

[0041] Mold

[0042] According to a third aspect of the present invention, a mold containing the neutrons of the second aspect is provided. The mold may be for manufacturing a molded article by metal casting, and the neutrons are for defining an internal cavity of the molded article.

[0043] The mold may be any of high pressure die casting, semi-solid casting, and squeeze casting.

[0044] Method

[0045] According to a fourth aspect of the present invention, a method for manufacturing a molded article by high-pressure die casting or semi-solid casting is provided. This method may include mixing a composition according to the first aspect to form a mixture. The method may include molding and curing the mixture to produce a core for the shape of the internal cavity of the molded article. The method includes assembling the core with a mold for high-pressure die casting or semi-solid casting such that the mold and the core together define a casting cavity. The method includes injecting molten metal or semi-solid metal into the casting cavity until the cavity is filled. The method consists of cooling and solidifying the molten metal or semi-molten metal to form the molded article, and the core is accommodated within the internal cavity of the molded article. The method may include removing the molded article including the core from the mold. The method may include removing the core from the internal cavity by flushing with water.

[0046] The method may further include coating the core with a surface coating before assembling the core with the mold.

[0047] The step of molding and solidifying the mixture may include drying the mixture. The step of molding and solidifying the mixture may include compressing the mixture into a core mold. The step of molding and curing the mixture can be carried out using a core injection device. The step of molding and curing the mixture to produce the core includes producing the core by an additive manufacturing process or a 3D printing process.

[0048] In a further aspect of the present invention, the use of a composition according to the first aspect in a molding process or a metal casting process is provided.

Examples

[0049] Example 1 - Comparative example First, the following composition was prepared:

[0050]

Table 1

Table 1

[0051] The comparative compositions C1 - C3 are examples of the compositions described in the international application PCT / EP2021 / 079512. Composition 1 was formed by first mixing an alkali metal silicate with water and then mixing this solution with a mixture of a pozzolan additive, potassium carbonate, and fine particles. Subsequently, neutrons were formed using a Laempe L1 neutron shooter at an injection pressure of 4 bar, an injection time of 1 second, and a neutron box temperature of 140°C. All neutrons were cured with hot air (120°C), and different purge times were set according to the size and shape of the produced neutrons.

[0052] The solubility of the binder was evaluated by immersing the cured neutrons in water and rotating them at the temperatures and rotation speeds shown in the above table. The binder solubility was judged as "excellent" if it dissolved within 5 seconds regardless of the temperature when the neutrons were immersed in water. Neutrons that dispersed in water within 5 - 45 seconds were rated "good", within 45 - 120 seconds were "moderate", within 120 - 600 seconds were "poor", and those that took more than 600 seconds were "insoluble".

[0053] The comparative compositions C1 and C3 were found to have excellent flexural strength of about 800 N / cm 2 . C1 also had good solubility. In the test of rotating at 60 rpm in water at 20°C, the binder dissolved in 20 - 40 seconds, and at 65°C and 150 rpm, it dissolved within 15 seconds. C3 had good solubility and dissolved in 15 - 45 seconds in water at 65°C and 150 rpm, but its solubility was poor at 20°C and 60 rpm, usually taking 240 - 260 seconds.

[0054] The comparative composition C2 had equivalent flexural strength of about 800 N / cm 2 , but the binder composition did not dissolve in water within 600 seconds. Therefore, it was judged not suitable for use in forming neutrons for the molding process because the neutrons could not be efficiently removed from the molded product.

[0055] The bending strength and solubility of C1 and C3 are acceptable for use in HPDC and other casting processes. However, in order to obtain the required strength, it was necessary to contain a relatively large amount of pozzolan additive respectively. Silica fume A is a by-product of zirconia production and is known to contain heavy metal contaminants. In particular, the presence of lead and nickel may lead to wastewater pollution during the cleaning of molding sand in some molding processes, so additional processes are required to prevent water pollution.

[0056] Example 2 - Influence of alkali metal silicate content In order to evaluate the influence of the content of alkali metal silicate on the properties of the neutrons, the following compositions were prepared.

[0057]

Table 2

[0058] The alkali metal silicate, MTR6099 / 17, is a mixture of sodium silicate (90 wt% Crystal 230, PQ Corporation BV, Eysden, the Netherlands), potassium silicate (5.0 wt% Kasil 1841 PQ Corporation BV, Eysden, the Netherlands), water (4.5 wt%) and DSK40 (0.5 wt% Brenntag BV, Enschede, the Netherlands). Without wishing to be bound by theory, it is considered that the reduction of surface tension due to the presence of the surfactant improves the fluidity of the composition and thus the compression, density and mechanical strength of the obtained neutrons.

[0059] The neutrons were formed in the same manner as in Example 1. As a result of the tests, it was found that increasing the content of the alkali metal silicate slightly increased the bending strength. When the content of the binder with respect to the fine particles was very high, loss of structure was observed. When the content of the alkali metal silicate was 20 wt%, the composition became a wet paste and it was impossible to form neutrons.

[0060] In all cases, the solubility of the neutrons in hot tap water (about 65 °C) was good and was not affected by the increase in strength associated with the increase in the content of alkali metal silicate.

[0061] Example 3 - K 2 CO 3 Influence of content K 2 CO 3 To evaluate the influence of the content of on the properties of the neutrons, the following compositions were prepared.

[0062]

Table 3a

[0063] In the compositions shown in Table 3a, it has been shown that even a small amount of potassium carbonate improves the solubility of the binder compared to the prior art. Increasing the potassium carbonate does not seem to improve the strength or solubility of the neutrons. At the highest level of potassium carbonate tested (10 wt%), defects were found in the neutrons. Without wishing to be bound by theory, it is thought that the low fluidity of Composition 8 at high potassium carbonate levels leads to such defects and, therefore, higher levels of potassium carbonate were not tested.

[0064]

Table 3b

[0065] In the compositions of Table 3b, an equal amount of water was added to the potassium carbonate to dissolve the potassium carbonate before mixing with the alkali metal silicate, pozzolan additive and fine particles. The neutrons were formed in the same manner as in Example 1.

[0066] This test shows that the presence of potassium carbonate significantly improves the solubility of the binder composition and thus the water dispersibility of each neutron formed from the composition. However, as supported by Table 3a, K2 CO 3 Even when the level was increased, the solubility did not increase further. It was found that even at a low potassium carbonate content (e.g., 0.5 wt%), the solubility was improved compared to the composition without potassium carbonate.

[0067] A further advantage is that the flexural strength is improved even at a relatively low level of potassium carbonate. Without wishing to be bound by theory, the presence of potassium carbonate is understood to be able to improve the chemical bond between individual sand grains. This effect was also observed with H33 sand (see Table 3a above), and the strength increased up to about 3 wt%. As the concentration increases, the stability decreases and the strength also decreases.

[0068] Example 4 - Effect of pozzolan additive To evaluate the influence of the pozzolan content and composition on the properties of the mortar, the following compositions were prepared.

[0069]

Table 4a

[0070] As a result of the tests, it was found that both silica fume and microsilica had a large positive effect on the flexural strength of the mortar. Fly ash had a less significant effect on the strength compared to the example without pozzolan additive, and the respective values were found to be approximately the same within the error range. The sample weight of the mortar without pozzolan additive was the lowest among the tested mortars, indicating the worst compaction of the mortar and thus the lowest density.

[0071]

Table 4b

[0072] Compositions 16 - 18 show that the high strength achievable with the use of fumed silica and microsilica is replicated with alternative fumed silica and microsilica products and is not limited to a single supplier or product. Compositions 19 and 20 show that the flexural strength increases significantly as the content of the pozzolan additive increases. However, the increase in pozzolan content significantly reduces the solubility of the neutrons.

[0073] Example 5 - Effect of refractory fine particles To evaluate the effect of the type of refractory particulate material on the properties of the neutrons, the following compositions were prepared.

[0074]

Table 5

[0075] These tests show that similar results are reproducible with alternative particulate refractories. Compositions 21 - 23 are synthetic sands commonly used in casting applications where high strength is required.

[0076] While not wishing to be bound by theory, the presence of the pozzolan additive is thought to aid the fluidity of the mixture, and the smaller the particle size of the pozzolan additive, the better the packing of the neutrons and thus the higher the density, resulting in improved strength. Since the synthetic sands tested were spherical, it was necessary to lower the addition rate of the binder composition to obtain similar strength. Effective neutrons could not be obtained using porous bars (small spherical expanded glass beads), presumably because of their very low density. These test results show that the use of synthetic sands and synthetic spherical ceramic particles together with the binder composition can provide the desired neutrons for the molding process.

[0077] Example 6 - Effects of various alkali silicates To evaluate the effect of the type of alkali silicate on the properties of the neutrons, the following compositions were prepared.

[0078]

Table 6

[0079] Table 6 shows the effects of various types of alkali silicates on the quality and water solubility of the cores formed from the compositions. MTR 6099 / 17 based on sodium silicate * 、the use of both Crystal 230M and Crystal 230M2 has been found to have excellent performance. Composition 29 contains Kasil 1841M containing 5 parts by weight of potassium silicate, 20% by weight of water, and 0.5% by weight of surfactant. When only potassium silicate was used in Composition 29, the mechanical strength decreased slightly and the water solubility also decreased, but both were within the acceptable range.

[0080] Compositions 28 and 30 differ only in that Composition 28 contains a small amount of surfactant (the alkali silicate component contains 0.5 wt% of DSK40). In the absence of DSK40, it was found that the sample weight and mechanical strength of the cores formed from the composition were low. Composition 27 containing a mixture of both sodium silicate and potassium silicate showed good performance in the solubility test, providing a lower viscosity and good fluidity compared to Compositions 28 and 30 containing only sodium silicate. Without wishing to be bound by theory, it is believed that the result of containing a small amount of surfactant and potassium silicate leads to lower viscosity and better fluidity, resulting in higher compression and density of the formed cores, and thus higher flexural strength.

[0081] Example 7 - Effect of recycled sand The effect of regenerating particulate matter was investigated.

[0082]

Table 7

[0083] For composition 31, as a benchmark, a fresh sample of LA32 that had not been used previously was employed. In composition 32, the fine particles LA32 were recycled and recycled five times. These results indicate that the use of recycled fine particles did not significantly affect the weight or strength of the formed neutrons and thus did not have an adverse effect on the performance of the binder system.

[0084] Example 8 - Influence of storage conditions Using a series of identical neutrons formed from the above composition 1, various storage conditions and storage periods were investigated. The various conditions were selected to evaluate the effects of exposure under ambient conditions or storage in airtight plastic bags. The initial weights of the sample neutrons were all 426.1 g, and the initial flexural strength was 1009 ± 50 N / cm 2 It was.

[0085]

Table 8a

[0086] The sand neutrons were stored at 25 °C and a relative humidity (RH) of 30% (corresponding to the maximum storage time and typical conditions in a foundry), and an exposure test up to one week (168 hours) was carried out. Additionally, one batch (Example E38) was placed in an airtight plastic bag. In all tests, it was confirmed that the solubility of the neutrons was good, and it was shown that the desirable dissolution characteristics were maintained over a useful product life.

[0087] Next, the experiment was repeated using a composition containing 7 wt% alkali metal silicate and 1.5 wt% potassium carbonate with respect to the weight of the fine particles. The initial sample weight was 419.2 g, and the initial flexural strength was 950 ± 23 N / cm 2 It was. The results are shown in Table 8b.

[0088]

Table 8b

[0089] From these tests, regardless of the amount of potassium carbonate and storage conditions, and even with a storage period of up to 168 hours, the water solubility of the produced neutrons was within the acceptable range. In all cases, the neutrons with 3.0 wt% potassium carbonate added showed slightly higher water solubility. All tests were conducted with tap water (65 °C).

Claims

1. A composition for manufacturing cores used in mold shaping or metal casting processes, comprising granular refractories, and a binder composition, wherein the binder composition comprises at least one alkali metal silicate in an amount of 1 to 15 wt%, potassium carbonate in an amount of 0.125 to 10 wt%, and at least one pozzolan additive in an amount of 0.5 to 10 wt%, and the composition range of the binder composition is based on the weight of the granular refractory.

2. The composition according to claim 1, wherein the binder comprises 1.5 to 35 wt% based on the weight of the granular refractory.

3. The composition according to any one of the preceding claims, wherein the binder composition is an inorganic binder composition.

4. The composition according to any one of the preceding claims, wherein the at least one alkali metal silicate comprises sodium silicate and potassium silicate.

5. The composition according to any one of the preceding claims, wherein the at least one alkali metal silicate is in an aqueous solution and has a solids content of 30 to 50 wt%.

6. The composition according to any one of the preceding claims, wherein the at least one pozzolan additive has a D50 particle size of 20 μm or less.

7. The composition according to any one of the preceding claims, wherein the at least one pozzolan additive comprises silica fume.

8. The composition according to any one of the preceding claims, wherein potassium carbonate is 1 to 6 wt% based on the weight of the granular refractory.

9. The composition according to any one of the preceding claims, further comprising a surfactant, and optionally, the surfactant is sodium ethylhexyl sulfate.

10. The composition according to any one of the preceding claims, wherein the binder composition further comprises water in an amount of 1 to 3 wt% based on the weight of the granular refractory.

11. A core for use in a molding or metal casting process, comprising the composition according to any one of the preceding claims.

12. The core according to claim 11, wherein the core is coated with a surface coating, and optionally, the surface coating comprises boron nitride, silicate, titania, alumina, zirconia, alumina, aluminum silicate, or a mixture thereof.

13. A mold comprising the core according to claim 11 or 12, wherein the mold is for manufacturing a molded article by metal casting, and the core is for defining an internal cavity of the molded article.

14. A method for manufacturing a molded article by high-pressure die casting or semi-solid casting, the method comprising the following steps: (i) mixing the composition according to any one of claims 1 to 10 to form a mixture; (ii) shaping and curing the mixture to produce a core having the shape of the internal cavity of the molded article; (iii) assembling the core and the mold for high-pressure die casting or semi-solid casting, the mold and the core being integrated to define a casting cavity (iv) injecting molten metal or semi-solid metal into the casting cavity until the cavity is filled; (v) cooling and solidifying the molten metal or semi-molten metal to form the molded article; (vi) removing the molded article containing the core from the mold; and (vii) removing the core from the internal cavity by flushing with water.

15. Use of the composition according to any one of claims 1 to 10 in a shaping process or a metal casting process.

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