Moisture-resistant method for ester-hardened sodium silicate-bonded sand

Abstract

The invention belongs to the technical field of sodium silicate self-hardening sand, and particularly relates to a moisture-resistant method of ester-hardened sodium silicate sand, which is characterized by comprising the following steps: before sand mixing, putting a mixture of organic ester and bentonite into an ultrasonic tank for ultrasonic pretreatment, adding the mixture into crude sand, and uniformly mixing and stirring, and finally, adding water glass, and uniformly mixing to prepare the ester-hardened water glass sand. The ester-hardened sodium silicate sand comprises the following components in parts by weight: 100 parts of crude sand, 3 to 3.5 parts of sodium silicate, 0.5 to 0.7 part of organic ester and 0.4 to 0.7 part of bentonite. The preparation method has the beneficial effects that through ion exchange between multivalent ions (calcium, magnesium and the like) bentonite and sodium ions in the water glass, due to the existence of organic ester in bentonite layer gaps, the sodium ions in the water glass and bentonite calcium ions cannot be directly exchanged, so that the reaction speed is greatly reduced, and sufficient molding time is reserved. The adverse effect of air humidity on a sand mold is reduced, and the tensile strength of a sample in 24 h is larger than 0.6 Mpa in the environment with the relative humidity being 95% or above.

Description

Technical Field

[0001] This invention belongs to the field of water glass self-hardening sand technology, and particularly relates to a moisture-resistant method for ester-hardened water glass sand. Background Technology

[0002] Sand casting is a casting method that uses sand molds as casting templates. The basic raw materials for making sand molds are foundry sand and molding sand binders (except for the V-process). To ensure that the sand molds and cores have sufficient strength and do not deform or break during handling, mold assembly, and pouring of molten metal, molding sand binders are generally added to the foundry sand to bind the loose sand particles together. Silica sand is the most commonly used molding sand for foundry. Special sands such as zircon sand, chromite sand, and corundum sand are also used when there are special requirements in the casting process. Commonly used binders in casting include water glass, resin, and clay.

[0003] Ester-cured water glass self-hardening sand is a sand casting process that uses water glass as a binder and organic esters as a curing agent to harden the sand mold (sand core). This process allows for the recycling of used sand, making it one of the least environmentally polluting casting processes. The basic process of ester-cured water glass sand is: raw sand + binder (water glass) + curing agent (organic ester) → mixed and filled into a mold, which automatically hardens and solidifies over time. Removing the mold yields the desired sand mold. The strength of this sand mold is affected by various conditions, including raw materials (raw sand, binder, curing agent), equipment (sand mixer), process (feeding ratio, sequence, mixing time, etc.), and external conditions (temperature, humidity).

[0004] The hardening principle of ester-hardened water glass sand is as follows: On the one hand, when water glass and organic esters (such as triacetin) are mixed, the organic esters hydrolyze into acids and alcohols. The acids promote the polymerization of small water glass molecules, thus hardening the sand, mainly affecting the initial stage of hardening. On the other hand, water glass undergoes dehydration and condensation hardening, which mainly affects the later stages. When the humidity in the environment is too high, dehydration hardening will be affected, leading to a significant reduction in the final strength of the sand mold and affecting the casting quality. Polyvalent metal ions can also harden water glass sand, but the reaction between polyvalent metal ions and water glass is usually too rapid, and there is insufficient time for sand mixing, filling, and molding in production, so it is rarely used in casting.

[0005] Chinese invention patent application number 201310472575.9 discloses a moisture-resistant, CO2-blown hardening water glass sand and its preparation method. It is made from the following raw materials in parts by weight: 70-80 parts recycled sand, 25-35 parts potassium feldspar, 3-5 parts triacetin, 4-8 parts modified water glass, 5-10 parts diatomaceous earth, 3-6 parts red mud, 2-3 parts zinc carbonate, 1.5-2.5 parts lithium hydroxide, 1-2 parts ammonium alum, 4-6 parts water-soluble phenolic resin, 2-3 parts No. 20 machine oil, and 0.5-1.5 parts tridecafluorooctyltrimethoxysilane. This water glass sand exhibits excellent moisture resistance; in an environment with a relative humidity above 95%, the tensile strength of the 24-hour sample is greater than 0.5 MPa. Summary of the Invention

[0006] The purpose of this invention is to provide a moisture-resistant method for ester-cured water glass sand, overcoming the shortcomings of the prior art. In response to the influence of seasonal air humidity, the invention introduces polyvalent ions of bentonite to harden the water glass, replacing the dehydration hardening process. The bentonite is pre-impregnated with organic ester to slow down the reaction rate between metal ions and water glass, thus avoiding the adverse effects of excessive summer air humidity on the strength of the sand mold.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for moisture-resistant ester-cured water glass sand involves pre-treating an organic ester and bentonite mixture in an ultrasonic tank before mixing the sand. The pre-treatment allows the organic ester to impregnate and coat the bentonite. The mixture is then added to the original sand and stirred until homogeneous. Finally, water glass is added and mixed until homogeneous to produce ester-cured water glass sand. The components in the ester-cured water glass sand are in the following weight ratios: 100 parts original sand, 3-3.5 parts water glass, 0.5-0.7 parts organic ester, and 0.4-0.7 parts bentonite.

[0008] Furthermore, the organic ester is any one or a combination of two or more of triacetin, propylene carbonate, and ethylene glycol diacetate.

[0009] Furthermore, the raw sand is any one or a combination of two or more of silica sand, alumina sand, and ceramsite sand, with a particle size of 40 / 70 mesh or 50 / 100 mesh.

[0010] Furthermore, the bentonite is calcium-based bentonite or magnesium-based bentonite, with a particle size of 200-1250 mesh and a sieve residue of less than 0.2%.

[0011] Furthermore, the ultrasonic pretreatment is performed at an ultrasonic frequency of 20kHz-40kHz for a processing time of 5-10 minutes.

[0012] Furthermore, the mixing speed is 120-150 rpm, and the mixing time is 1-5 minutes.

[0013] Furthermore, the modulus of the water glass is 2.0-2.4, and the viscosity at 25°C is 180 mPa·s.

[0014] The working principle of this invention is based on the ion exchange between polyvalent ions (calcium, magnesium, etc.) in bentonite and sodium ions in water glass, achieving polyvalent ion hardening of the water glass. However, the hardening rate of polyvalent ions is too fast, resulting in insufficient usable time for molding. By using a sand mixing process of pre-treated bentonite with organic esters, followed by the addition of water glass, the presence of organic esters in the bentonite interlayers prevents direct exchange between sodium ions in the water glass and calcium ions in the bentonite, thus significantly reducing the reaction rate and solving the problem of excessively rapid polyvalent ion hardening. Furthermore, the strength of water glass hardened by polyvalent ions is unaffected by moisture, thereby reducing the adverse effects of air humidity on the sand mold.

[0015] Compared with the prior art, the beneficial effects of the present invention are: Ultrasonic pretreatment can disperse bentonite particles and enhance the adsorption performance of bentonite for metal ions. By utilizing the cavitation effect and mechanical vibration of ultrasound, ultrasound can expand the interlayer spacing of bentonite, promote the dispersion of montmorillonite particles, enhance their adsorption or binding ability with other substances, and promote the dispersion of montmorillonite particles. The application of water glass self-hardening sand is realized through ion exchange between multivalent ions (calcium, magnesium, etc.) in bentonite and sodium ions in water glass. Calcium-based bentonite is common in the market and inexpensive, which helps to reduce the cost of sand casting. By employing a sand-mixing process involving raw sand, organic esters, and bentonite premixed before adding water glass, the presence of organic esters in the bentonite interlayers prevents direct exchange between sodium ions in the water glass and calcium ions in the bentonite, thus significantly reducing the reaction rate and allowing sufficient molding time. This reduces the adverse effects of air humidity on the sand mold; in an environment with relative humidity above 95%, the tensile strength of the 24-hour sample exceeds 0.6 MPa. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the specific embodiments used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the specific embodiments described below are some embodiments of the present invention. For those skilled in the art, other specific embodiments can be obtained based on these specific embodiments without creative effort.

[0018] The components of the embodiments of the invention described and shown in the specific embodiments herein can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the specific embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0019] The bentonite in the following embodiments of the present invention is a non-metallic mineral with montmorillonite as the main mineral component. Montmorillonite has a 2:1 crystal structure consisting of two silicon-oxygen tetrahedra sandwiching a layer of aluminum-oxygen octahedra. Due to the presence of certain cations, such as Ca and Mg, in the layered structure formed by the montmorillonite unit cells, and the unstable interaction between these cations and the montmorillonite unit cells, it is easily exchanged by other cations, thus exhibiting good ion exchange properties. The organic ester is any one or a combination of two or more of triacetin, propylene carbonate, and ethylene glycol diacetate. The raw sand is any one or a combination of two or more of silica sand, granulated sand, and ceramsite sand, with a particle size of 40 / 70 mesh or 50 / 100 mesh. The bentonite is calcium-based bentonite or magnesium-based bentonite, with a particle size of 200-1250 mesh and a sieve residue of less than 0.2%. The water glass has a modulus of 2.0-2.4 and a viscosity of 180 mPa·s at 25°C.

[0020] Example 1 A method for moisture resistance of ester-cured water glass sand involves pre-treating a mixture of 0.5 parts organic ester and 0.5 parts bentonite in an ultrasonic tank before sand mixing. The ultrasonic frequency is 20 kHz, and the treatment time is 10 minutes. This pre-treatment process ensures the organic ester completely impregnates and coats the bentonite. The mixture is then added to 100 parts of raw sand (silica sand) and stirred evenly at a mixing speed of 120 rpm for 2 minutes. Finally, 3 parts of water glass are added and mixed evenly to produce ester-cured water glass sand. In Example 1, the ester-cured water glass sand treated in this method exhibited a tensile strength of 0.61 MPa after 24 hours in an environment with a relative humidity above 95%.

[0021] Example 2 A method for moisture resistance of ester-cured water glass sand involves pre-treating a mixture of 0.5 parts organic ester and 0.7 parts bentonite in an ultrasonic tank before sand mixing. The ultrasonic frequency is 20 kHz, and the treatment time is 10 minutes. This pre-treatment process ensures the organic ester completely impregnates and coats the bentonite. The mixture is then added to 100 parts of raw sand (precious pearl sand) and stirred evenly at a mixing speed of 150 rpm for 2 minutes. Finally, 3 parts of water glass are added and mixed evenly to produce ester-cured water glass sand. In Example 2, the tensile strength of the treated ester-cured water glass sand sample was 0.76 MPa after 24 hours in an environment with a relative humidity above 95%.

[0022] Example 3 A method for moisture resistance of ester-cured water glass sand involves pre-treating a mixture of 0.5 parts organic ester and 0.7 parts bentonite in an ultrasonic tank before sand mixing. The ultrasonic frequency is 20 kHz, and the treatment time is 5 minutes. This pre-treatment process ensures the organic ester completely impregnates and coats the bentonite. The mixture is then added to 100 parts of raw sand (ceramsite sand) and stirred evenly at a mixing speed of 120 rpm for 2 minutes. Finally, 3 parts of water glass are added and mixed evenly to produce ester-cured water glass sand. In Example 3, the tensile strength of the treated ester-cured water glass sand sample was 0.71 MPa after 24 hours in an environment with a relative humidity above 95%.

[0023] Example 4 A method for moisture resistance of ester-cured water glass sand involves pre-treating a mixture of 0.5 parts organic ester and 0.7 parts bentonite in an ultrasonic tank before sand mixing. The ultrasonic frequency is 40 kHz, and the treatment time is 10 minutes. This pre-treatment process ensures the organic ester completely impregnates and coats the bentonite. The mixture is then added to 100 parts of raw sand (silica sand) and stirred evenly at a mixing speed of 120 rpm for 2 minutes. Finally, 3 parts of water glass are added and mixed evenly to produce ester-cured water glass sand. In Example 4, the treated ester-cured water glass sand exhibited a tensile strength of 0.69 MPa after 24 hours in an environment with a relative humidity above 95%.

[0024] Example 5 A method for moisture resistance of ester-cured water glass sand involves pre-treating a mixture of 0.5 parts organic ester and 0.5 parts bentonite in an ultrasonic tank before sand mixing. The ultrasonic frequency is 30 kHz, and the treatment time is 10 minutes. During the pre-treatment, the organic ester completely impregnates and coats the bentonite. Then, the mixture is added to 100 parts of raw sand (silica sand) and stirred evenly at a mixing speed of 150 rpm for 2 minutes. Finally, 3.5 parts of water glass are added and mixed evenly to produce ester-cured water glass sand. In Example 5, the tensile strength of the treated ester-cured water glass sand sample was 0.66 MPa after 24 hours in an environment with a relative humidity of over 95%.

[0025] Example 6 A method for moisture resistance of ester-cured water glass sand involves pre-treating a mixture of 0.7 parts organic ester and 0.5 parts bentonite in an ultrasonic tank before sand mixing. The ultrasonic frequency is 30 kHz, and the treatment time is 10 minutes. This pre-treatment process ensures the organic ester completely impregnates and coats the bentonite. The mixture is then added to 100 parts of raw sand (silica sand) and stirred evenly at a mixing speed of 130 rpm for 3 minutes. Finally, 3 parts of water glass are added and mixed evenly to produce ester-cured water glass sand. In Example 6, the treated ester-cured water glass sand exhibited a tensile strength of 0.63 MPa after 24 hours in an environment with a relative humidity above 95%.

[0026] This invention employs a sand-mixing process involving pretreatment with organic esters and bentonite, followed by mixing with raw sand and then adding water glass. Due to the presence of organic esters in the bentonite interlayers, the exchange rate between sodium ions in the water glass and calcium ions in the bentonite is reduced, thus resolving the conflict between excessively rapid hardening of polyvalent ions and practical production considerations. Furthermore, the strength of water glass undergoing polyvalent ion hardening is no longer affected by moisture, thereby reducing the adverse effects of air humidity on the sand mold. The bentonite content and ultrasonic pretreatment have a significant, reliable, and stable impact on the moisture-proof effect.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for moisture-resistant ester-cured water glass sand, characterized in that, Before mixing the sand, the mixture of organic ester and bentonite is placed in an ultrasonic tank for ultrasonic pretreatment. The pretreatment allows the organic ester to impregnate and coat the bentonite. Then, the mixture is added to the original sand and stirred evenly. Finally, water glass is added and mixed evenly to produce ester-hardened water glass sand. The components in the ester-hardened water glass sand are in the following weight ratios: 100 parts original sand, 3-3.5 parts water glass, 0.5-0.7 parts organic ester, and 0.4-0.7 parts bentonite.

2. The method for moisture-resistant ester-cured water glass sand according to claim 1, characterized in that, The organic ester is any one or a combination of two or more of triacetin, propylene carbonate, and ethylene glycol diacetate.

3. The method for moisture resistance of ester-cured water glass sand according to claim 1, characterized in that, The raw sand is any one or a combination of two or more of silica sand, alumina sand, and ceramsite sand, with a particle size of 40 / 70 mesh or 50 / 100 mesh.

4. The method for moisture resistance of ester-cured water glass sand according to claim 1, characterized in that, The bentonite is calcium-based bentonite or magnesium-based bentonite, with a particle size of 200-1250 mesh and a sieve residue of less than 0.2%.

5. The method for moisture resistance of ester-cured water glass sand according to claim 1, characterized in that, The ultrasonic pretreatment is performed at an ultrasonic frequency of 20kHz-40kHz for 5-10 minutes.

6. The method for moisture resistance of ester-cured water glass sand according to claim 1, characterized in that, The mixing speed is 120-150 rpm, and the mixing time is 1-5 minutes.

7. The method for moisture-resistant ester-cured water glass sand according to claim 1, characterized in that, The water glass has a modulus of 2.0-2.4 and a viscosity of 180 mPa·s at 25°C.