Ultrathin anti-veining water-based paint for sand core of cold box, preparation method and application of ultrathin anti-veining water-based paint

Abstract

The invention provides an ultrathin vein-proof water-based coating for a cold box sand core, a preparation method and application, and belongs to the technical field of casting coatings. The coating comprises a phenolic resin / styrene-acrylic emulsion composite normal-temperature binder, a glass powder / bentonite high-temperature binder, a hydroxymethyl cellulose suspending agent, a quartz powder / kaolin / graphite refractory aggregate and a mica powder / iron oxide molten filler, an ultrathin uniform coating of 0.2-0.4 mm is achieved through a gradient melting sealing mechanism, the coating suspension rate is high, the sand core strength is high, and the service life of the sand core is prolonged. And the coating has the characteristics of thermal shock resistance, low VOC (volatile organic compound) and environmental protection, and is particularly suitable for efficient protection of complex castings such as automobile engine cylinder blocks and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of casting coatings, and in particular to an ultra-thin anti-veining water-based coating for cold box sand cores, a preparation method and an application thereof. Background Art

[0002] Cold-box casting technology, due to its high core-making efficiency and excellent dimensional accuracy, is widely used in the production of complex castings such as automotive engine cylinder blocks and cylinder heads. However, during the molten iron pouring process, the high temperature (800°C) on the sand core surface causes a phase change and expansion of the silica sand, leading to cracking and formation of micron-sized fissures in the sand core. Molten metal, under pressure, penetrates these cracks, forming raised metal residue (i.e., veining defects) after solidification. Statistics show that veining defects cause scrap rates as high as 8% to 15% in thin-walled, complex castings such as cylinder water jackets and turbine casings produced using the cold-box process. The subsequent cleanup costs account for 12% to 20% of the total casting cost, severely limiting production efficiency.

[0003] Currently, the industry mainly uses the following two types of technologies to address veining issues, but both have significant technical defects: 1. Coated sand modification technology The expansion of the sand core is suppressed by coating the surface of silica sand with resin and anti-veining additives (such as iron oxide and glass powder). However, this technology has the following drawbacks: (1) High cost: Resins and additives in coated sand modification technology account for 5% to 8%, and the cost per ton is 3 to 5 times higher than that of ordinary sand; (2) Insufficient inhibition of molten iron penetration: The coated sand modification technology can only alleviate shallow penetration less than 0.2 mm, and it is difficult to effectively block deep penetration greater than 0.5 mm caused by high-pressure molten iron (0.5 MPa) in thick-walled castings; (3) Environmental risks: Harmful gases such as formaldehyde and phenol are released during the resin curing process, and the cost of waste gas treatment accounts for 8% to 10% of the total production cost.

[0004] 2. Solvent-based anti-seepage coating Relying on high temperature sintering of organic solvent-based coatings to form an isolation layer, but its inherent defects are significant: (1) It is easy to cause imbalance in coating performance: Solvent-based anti-seepage coatings need to be applied thickly (≥0.5mm) to prevent seepage, but thick coating will lead to a decrease in sand core strength and reduced air permeability; The thermal conductivity of a single quartz powder-based coating is high and cannot delay the temperature rise of the sand core; (2) It is easy to cause high temperature bonding failure: Ordinary bentonite binders will pulverize above 1000℃, causing a sharp drop in the high-temperature impermeability of the coating; (3) Bringing environmental pollution: The VOC emission of solvent-based paint exceeds 50g / L, which does not meet environmental protection requirements.

[0005] In recent years, water-based coatings have gradually replaced solvent-based products, but there is still a contradiction between coating thickness and performance. Due to the insufficient suspension stability of water-based coatings and the 24-hour sedimentation rate greater than 5%, it is easy to cause coating omissions and skinning when applied thinly. Thick coating will lead to a decrease in sand core strength and deterioration of air permeability, which in turn leads to casting defects. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention aims to provide an ultra-thin anti-veining water-based coating for cold box sand cores, which has ultra-thin and uniform film-forming ability, gradient temperature adaptive sealing mechanism and high suspension stability, as well as a preparation method and application.

[0007] One of the objects of the present invention is to provide an ultra-thin anti-veining water-based coating for cold box sand cores, the anti-veining water-based coating comprising the following raw materials in parts by weight: 1~2 parts of room temperature adhesive 20~40 parts of high temperature adhesive 2~5 parts of suspension agent 0.1~0.5 parts of penetrant 0.1~0.5 parts of defoaming agent 0.03~0.1 parts of preservatives 15~35 parts of refractory aggregate 10 to 20 parts of molten filler, and 20~40 parts water

[0008] Wherein, the room temperature binder is a composite of phenolic resin and styrene acrylic emulsion; The high-temperature adhesive includes 200-400 mesh glass powder, calcium-based bentonite liquid and sodium-based bentonite liquid.

[0009] The suspending agent includes hydroxymethyl cellulose solution.

[0010] The refractory aggregate comprises one or more of 200-800 mesh quartz powder, 320 mesh smelted bauxite powder, 320 mesh calcined kaolin, 320-600 mesh mullite powder and graphite powder; The molten filler includes 320 mesh mica powder and / or iron oxide powder. Preferably, the high-temperature adhesive comprises 2 to 4 parts of glass powder, 7 to 15 parts by mass of calcium-based bentonite liquid, and 12 to 20 parts by mass of sodium-based bentonite liquid.

[0011] Preferably, the mass ratio of the glass powder, calcium-based bentonite liquid and sodium-based bentonite liquid is 1:2-5:4-7.

[0012] Preferably, the mass ratio of the hydroxymethyl cellulose solution to the sodium bentonite solution is 1:3-8.

[0013] Preferably, the refractory aggregate comprises 600 mesh quartz powder, 320 mesh kaolin and flake graphite.

[0014] Preferably, the refractory aggregate comprises 5-15 parts by mass of 600-mesh quartz powder, 5-15 parts by mass of 320-mesh kaolin and 2-6 parts by mass of flake graphite.

[0015] Preferably, the molecular weight distribution M of the phenolic resin is W :M N ≤2.

[0016] Preferably, the preparation method of the room temperature adhesive includes: First, 1 part of phenol is added by mass and melted at 43° C., and then 0.17-0.3 parts of sodium hydroxide solution and 0.2-1.36 parts of water are added, and the mixture is kept at 45° C. for 25 minutes, wherein the sodium hydroxide solution is a sodium hydroxide aqueous solution with a mass percentage of 25%; Then, the first portion of formaldehyde is added, the first portion of formaldehyde is 1.2-1.36 parts by mass and then kept at 45-50°C for 30 minutes, then heated to 87°C at a rate of 0.46-0.53°C / min, then heated to 95°C at a rate of 0.3-0.35°C / min, and kept at this temperature for 25 minutes; Then, the temperature was lowered to 82°C at a rate of 0.4-0.45°C / min, and a second portion of formaldehyde was added, with the second portion of formaldehyde being 0.3-0.34 parts. After holding the temperature for 15 minutes, the temperature was raised to 92-96°C at a rate of 0.33-0.47°C / min, and the temperature was held for 20 minutes. Then, cool to below 40°C, add 20 parts of water and mix, then add 1 to 4 parts of styrene acrylic emulsion and mix.

[0017] Preferably, the penetrant comprises alkylphenol polyoxyethylene ether (JFC).

[0018] Preferably, the defoaming agent comprises polydimethylsiloxane emulsion.

[0019] Preferably, the preservative comprises 1,2-benzisothiazolin-3-one (BIT-10).

[0020] A second object of the present invention is to provide a method for preparing an ultra-thin anti-veining water-based coating for cold box sand cores, the preparation method comprising: S1 adds 20-30% of the total water volume, controls the temperature to 25-30°C, stirs at 250-350 rpm, and sequentially adds room temperature binder, sodium bentonite solution, calcium bentonite solution, hydroxymethyl cellulose solution, penetrant, defoamer and preservative, and continues stirring for 15-25 minutes; S2: adding the solid components of the raw materials, including refractory aggregate, molten filler and glass powder, and stirring at a speed of 800-1200 rpm for 50-70 minutes; Add the remaining water to S3 and stir at a speed of 400-600 rpm for 60 min. Then reduce the speed to 300 rpm and stir for 45 minutes to exhaust.

[0021] A third object of the present invention is to provide an application of an ultra-thin anti-veining water-based coating for cold box sand cores, wherein the coating thickness is 0.2 to 0.4 mm.

[0022] The beneficial effects of the present invention include: The ultra-thin anti-veining water-based coating for cold-box sand cores disclosed in this invention successfully addresses the technical issues of thin coatings in cold-box casting, such as poor suspension stability, which can lead to coating leaks and skinning. This invention establishes a four-dimensional synergistic system of suspension, penetration, bonding, and sealing: First, hydroxymethyl cellulose and sodium bentonite work together to form a three-dimensional suspended network structure through hydrogen bonds and electrostatic effects. When the solid content reaches 50%, the 24-hour sedimentation rate can still be maintained at ≤1%, ensuring the uniformity of the 0.2~0.4mm ultra-thin coating, breaking through the technical difficulties of thin coating, missing coating, and skinning of traditional water-based coatings.

[0023] Second, the shear-thinning property of hydroxymethyl cellulose in the present invention imparts thixotropic fluidity, and the penetrant synergizes the microchannel effect of sodium bentonite and calcium bentonite, and is combined with fine-grained solid components to fill the micropores of the sand core, so that the penetration depth of the coating reaches more than 1.5 mm, forming a deep mechanical interlocking with the sand core.

[0024] Third, the rigid backbone of the phenolic resin and the flexible segments of the styrene-acrylic emulsion form a semi-interpenetrating network, giving the ultra-thin coating both crack resistance and high-temperature adaptability. Furthermore, hydrogen bonds with the hydroxymethyl cellulose in the suspended network further stabilize the dispersion, while its carbonized backbone provides structural support for high-temperature sealing. This gives the ultra-thin coating both high adhesion and crack resistance.

[0025] Fourth, the anti-veining water-based coating of the present invention also achieves gradient sealing through temperature response: at 600-800°C, calcium-based bentonite forms anorthite, providing medium-temperature bonding compensation. At 800-1000°C, the glass powder softens, forming a primary sealing layer, while the mica powder dehydrates, providing a viscous flow medium. At 1000-1200°C, the iron oxide and quartz powder sinter and densify. During each of these stages, the sodium-based bentonite expands and contracts, forming a closed-loop protection system with the dynamic flow of the molten filler.

[0026] The components of the anti-veining water-based coating described in the present invention work synergistically to achieve ultra-thin, uniform coating (0.2-0.4 mm). A gradient molten filler is used to form a dynamic sealing layer at high temperatures, addressing the veining defect problem caused by molten iron penetrating into sand core cracks during cold-box casting. This coating also overcomes technical issues associated with traditional coatings, such as decreased sand core strength and solvent contamination caused by thick coatings. The coating is particularly suitable for protecting the surface of sand cores in complex internal cavity castings, such as automotive engine blocks and cylinder heads. DETAILED DESCRIPTION

[0027] In the following description, certain specific details are included to provide a thorough understanding of each disclosed embodiment. However, one skilled in the relevant art will recognize that the embodiments can be implemented without one or more of these specific details and with other methods, components, materials, etc.

[0028] Unless otherwise required herein, throughout the specification and claims that follow, the words "include" and "comprising" should be interpreted in an open, inclusive sense, ie, "including but not limited to."

[0029] Reference throughout this specification to "one embodiment" or "an embodiment" or "a preferred embodiment" or "certain embodiments" means that the specific referenced elements, structures, or features described in connection with that embodiment are included in at least one embodiment. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" or "in a preferred embodiment" or "in certain embodiments" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the specific elements, structures, or features may be combined in any suitable manner in one or more embodiments.

[0030] In the technical solution provided by the present invention, "ultra-thin" means that the thickness of the coating after the coating is applied and physically dried and cured is 0.2~0.4mm.

[0031] According to a first aspect of the present invention, there is provided an ultra-thin anti-veining water-based coating for cold box sand cores, the anti-veining water-based coating comprising the following raw materials in parts by mass: 1~2 parts of room temperature adhesive 20~40 parts of high temperature adhesive 2~5 parts of suspension agent 0.1~0.5 parts of penetrant 0.1~0.5 parts of defoaming agent 0.03~0.1 parts of preservatives 15~35 parts of refractory aggregate 10 to 20 parts of molten filler, and 20-40 parts water; Wherein, the room temperature binder is a composite of phenolic resin and styrene acrylic emulsion; The high temperature adhesive includes 200-400 mesh glass powder calcium-based bentonite liquid and sodium-based bentonite liquid; The suspending agent includes hydroxymethyl cellulose solution and bentonite; The refractory aggregate comprises one or more of 200-800 mesh quartz powder, 320 mesh smelted bauxite powder, 320 mesh calcined kaolin, 320-600 mesh mullite powder and graphite powder; The molten filler includes 320 mesh mica powder and / or iron oxide powder. In the present invention, phenolic resin and styrene-acrylic emulsion are used as room-temperature binders. The phenolic resin provides the coating with a rigid skeleton and initial bonding strength, and after high-temperature carbonization, it forms a porous skeleton, providing an attachment base for the molten filler. Simultaneously, the flexible segments of the styrene-acrylic emulsion can fill the brittle defects of the phenolic resin, effectively preventing cracking of the thin coating. The two hydrogen bonds form a semi-interpenetrating network, which can balance strength and toughness.

[0032] Preferably, the mass ratio of the phenolic resin to the styrene acrylic emulsion is 0.7-3.4:1.

[0033] The room temperature adhesive is, for example, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts or 2 parts, and any point value between any two of the above. The room temperature adhesive is preferably 1.6 parts.

[0034] The high-temperature binder includes glass powder, sodium-based bentonite liquid, and calcium-based bentonite liquid. The high-temperature binder is, for example, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 36 parts, 38 parts, 39 parts, or 40 parts, or values therebetween, and preferably 30 parts.

[0035] Glass powder has a softening point of 780-820°C. Upon melting, it forms a continuous glass phase, sealing microcracks on the sand core surface. Calcium bentonite forms anorthite at 600-700°C, providing a medium-temperature transition bond and effectively mitigating thermal stress cracking. Sodium bentonite expands at high temperatures, providing expansion and contraction compensation, and forms a closed-loop protection loop with the dynamic flow of the molten filler.

[0036] Specifically, the sodium bentonite liquid is a sodium bentonite aqueous solution with a mass percentage of 5%.

[0037] The preparation method of the sodium bentonite liquid comprises: adding 5 parts of sodium bentonite and 95 parts of water, first stirring at a low speed of 200-400 rpm for 30 minutes, then stirring at a high speed of 800-1200 rpm for 60 minutes, and standing for 24 hours.

[0038] The calcium-based bentonite liquid is a calcium-based bentonite aqueous solution with a mass percentage of 10%.

[0039] The preparation method of the calcium-based bentonite liquid comprises: adding 10 parts of calcium-based bentonite and 90 parts of water, first stirring at a low speed of 200-400 rpm for 30 minutes, then stirring at a high speed of 800-1200 rpm for 60 minutes, and standing for 24 hours.

[0040] The suspending agent includes hydroxymethyl cellulose liquid. The entanglement effect of the long-chain molecules of hydroxymethyl cellulose cooperates with the lamellar support structure of sodium bentonite to form a three-dimensional suspended network structure. The hydroxymethyl cellulose and sodium bentonite work together to make the coating have excellent thixotropy, and work together with the penetrant to effectively improve the penetration performance of the coating.

[0041] The suspending agent is, for example, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, 3 parts, 3.2 parts, 3.4 parts, 3.8 parts, 4 parts, 4.2 parts, 4.4 parts, 4.6 parts or 5 parts, and any point value between any two of the above.

[0042] Specifically, the hydroxymethyl cellulose solution is a hydroxymethyl cellulose aqueous solution with a mass percentage of 2%.

[0043] The preparation method of the hydroxymethyl cellulose solution comprises: dissolving 2 parts of hydroxymethyl cellulose in 98 parts of water, stirring at a low speed of 200-400 rpm for 30 minutes, then stirring at a high speed of 800-1200 rpm for 60 minutes, and then standing for 24 hours.

[0044] The penetrant is, for example, 0.1 part, 0.2 part, 0.3 part, 0.4 part or 0.5 part, and any value between any two of the above. The penetrant is preferably 0.3 part.

[0045] The defoamer is used to eliminate defects such as pores and pinholes in the coating, improve the density of the coating, and reduce the risk of overflow during coating application. The defoamer is, for example, 0.1 part, 0.15 part, 0.2 part, 0.25 part, 0.3 part, 0.35 part, 0.4 part, 0.45 part, or 0.5 part, or any value therebetween, and preferably 0.2 part.

[0046] The preservative is used to extend the shelf life of the coating while preventing microbial degradation of coating components, which can lead to viscosity loss or precipitation. The preservative is present in amounts of, for example, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1 parts, or values in between. The preservative is preferably present in an amount of 0.05 parts.

[0047] The refractory aggregate comprises one or more of 200-800 mesh quartz powder, 320 mesh slaked bauxite powder, 320 mesh calcined kaolin, 320-600 mesh mullite powder and graphite powder.

[0048] The refractory aggregate is, for example, 15 parts, 16 parts, 17 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts or 35 parts, and any point value between any two of the above. The refractory aggregate is preferably 30 parts.

[0049] The refractory aggregate can optimize the particle grading at multiple scales, which is beneficial to forming a multi-scale thermal insulation barrier, prolonging the sand core heating time, maintaining the integrity of the coating structure at high temperatures, enhancing the compressive strength of the coating, reducing porosity, and improving the anti-seepage effect.

[0050] The molten filler includes 320 mesh mica powder and / or iron oxide powder. The molten filler is, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, or 20 parts, or any value therebetween, and preferably 15 parts.

[0051] The molten filler can cover the surface defects of the sand core when it is melted, and when a few cracks appear, it can further penetrate into the deep cracks of the sand core to form a three-dimensional protection.

[0052] Preferably, the molten filler comprises 320 mesh mica powder and iron oxide powder.

[0053] Preferably, the 320 mesh mica powder is 10 to 15 parts, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, and the point value between any two of the above, preferably 13 parts; the iron oxide powder is 1 to 3 parts, for example, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts or 3 parts, and the point value between any two of the above, preferably 2 parts.

[0054] In this method, mica powder dehydrates and softens at 800°C, allowing it to flow and fill microcracks in the sand core. Iron oxide powder, after melting at 1200°C, reacts with quartz powder to form a FeO·SiO2 glass phase, forming a dense isolation layer. The mica powder and iron oxide melt in stages, achieving dynamic sealing. The reaction of iron oxide with the core silica sand also strengthens interfacial bonding, reducing the risk of coating spalling.

[0055] The present invention successfully solves the technical problems of easy coating leakage and skinning when thinly coating water-based coatings in cold box casting due to poor suspension stability through multi-component and multi-scale collaborative design.

[0056] The anti-veining water-based coating of the present invention achieves gradient sealing through temperature response during application: at 600-800°C, calcium-based bentonite forms anorthite, providing medium-temperature bonding compensation. At 800-1000°C, the glass powder softens, forming a primary sealing layer, while the mica powder dehydrates, providing a viscous flow medium. At 1000-1200°C, the iron oxide and quartz powder sinter and densify. During each of these stages, the sodium-based bentonite expands and contracts, forming a closed-loop protection loop with the dynamic flow of the molten filler.

[0057] In a preferred embodiment of the present invention, the high-temperature binder includes 2 to 4 parts by mass of glass powder, 7 to 15 parts by mass of calcium-based bentonite liquid, and 12 to 20 parts by mass of sodium-based bentonite liquid.

[0058] In the present invention, 2 to 4 parts of calcium bentonite liquid cooperate with 12 to 20 parts of sodium bentonite liquid to form an expansion gradient compensation mechanism, avoiding the coating warping or powdering caused by excessive use of a single bentonite. 2 to 4 parts of glass powder cooperate with sodium bentonite and calcium bentonite to ensure the balance between the molten glass phase and the expansion filling, thereby improving the high-temperature impermeability pressure. The glass powder is, for example, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, 3 parts, 3.2 parts, 3.4 parts, 3.6 parts, 3.8 parts or 4 parts, the calcium bentonite liquid is, for example, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, and the sodium bentonite includes 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, as well as points between any two of the above.

[0059] Preferably, the mass ratio of the glass powder, calcium-based bentonite liquid and sodium-based bentonite liquid is 1:2-5:4-7, preferably 1:3.6:5.3.

[0060] In the present invention, when the mass ratio of glass powder, calcium-based bentonite liquid and sodium-based bentonite liquid is 1:2~5:4~7, on the one hand, the components can accurately and synergistically offset the high-temperature shrinkage stress and avoid cracking of the coating; on the other hand, it is beneficial to optimize the melt viscosity, ensuring that the molten phase can flow to fill the cracks without excessively flowing and causing the coating to become thinner.

[0061] Preferably, the glass powder is 200 mesh.

[0062] In a preferred embodiment of the present invention, the mass ratio of the hydroxymethyl cellulose solution to the sodium bentonite solution is 1:3-8, for example, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5 or 1:8, and any value between the above two. Preferably, the mass ratio of the hydroxymethyl cellulose solution to the sodium bentonite solution is 1:4-7, more preferably 1:5.3.

[0063] In the present invention, the mass ratio of hydroxymethyl cellulose liquid to sodium bentonite liquid is 1:3-8, which can balance the flexible winding of HEC and the rigid support of bentonite, thereby further reducing the suspension sedimentation rate and stabilizing the viscosity of the coating. It can avoid excessive viscosity caused by excessive hydroxymethyl cellulose and prevent network embrittlement caused by excessive bentonite.

[0064] In a preferred embodiment of the present invention, the refractory aggregate includes 200-800 mesh quartz powder, 320 mesh kaolin and flake graphite.

[0065] In the present invention, on the one hand, quartz powder is used to delay heat conduction, kaolin is used to reflect radiant heat, and graphite can promote uniform heat dissipation, thereby promoting the formation of a three-dimensional thermal insulation barrier; on the other hand, the particle grading of quartz powder and kaolin can reduce porosity, and flake graphite enhances density, which is beneficial to enhancing the anti-seepage pressure of the coating; on the third hand, the composite phase of kaolin and flake graphite can inhibit the phase change expansion of the sand core, which is beneficial to reducing the thermal shock spalling rate.

[0066] In a preferred embodiment of the present invention, the refractory aggregate includes 5 to 15 parts by mass of quartz powder, 5 to 15 parts by mass of kaolin and 2 to 6 parts by mass of flake graphite.

[0067] Preferably, the quartz powder is 600 mesh and the calcined kaolin is 320 mesh.

[0068] In this invention, 600-mesh quartz powder serves as the primary aggregate, forming a tightly packed skeleton. The parallel flaky structure of 320-mesh kaolin forms a continuous reflective layer, which reacts with the quartz powder at 1000°C to form mullite. The lamellar lubrication of graphite reduces internal stress in the coating. At high temperatures, it reacts with iron oxide to form an Fe3C phase, further enhancing the mechanical anchoring effect of the molten filler on cracks. However, excessive amounts of graphite may reduce refractory properties, while excessive amounts of kaolin may increase brittleness.

[0069] In the present invention, the 600 mesh quartz powder is, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, preferably 10 parts; the 320 mesh kaolin is, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, preferably 10 parts; the flake graphite is, for example, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts or 6 parts, and the point value between any two of the above, preferably 4 parts.

[0070] Preferably, the refractory aggregate includes 10 parts of 600 mesh quartz powder, 10 parts of 320 mesh kaolin and 4 parts of flake graphite.

[0071] In a preferred embodiment of the present invention, the molecular weight distribution M of the phenolic resin is W :M N ≤2. The molecular weight distribution M of the phenolic resin W :M N For example, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.

[0072] In the present invention, the molecular weight distribution M of the phenolic resin is W :M N ≤2, the molecular chains are orderly arranged, increasing the contact area with the sand core surface, which helps enhance coating uniformity and room-temperature bonding strength. The phenolic resin described herein exhibits a narrow molecular weight distribution during pyrolysis at 400-600°C, which increases the synchronization of carbonization reactions and forms a continuous porous carbon skeleton, thereby enhancing high-temperature compressive strength. Furthermore, this uniform carbon skeleton provides a stable attachment base for the glass powder melt, improving melt phase coverage and crack filling depth.

[0073] In a preferred embodiment of the present invention, the preparation method of the room temperature adhesive comprises: First, 1 part of phenol is added by mass and melted at 43° C., and then 0.17-0.3 parts of sodium hydroxide solution and 0.2-1.36 parts of water are added, and the mixture is kept at 45° C. for 25 minutes, wherein the sodium hydroxide solution is a sodium hydroxide aqueous solution with a mass percentage of 25%; Then, the first portion of formaldehyde is added, which is 1.2 to 1.36 parts and then kept at 45-50°C for 30 minutes, then heated to 87°C at a rate of 0.46-0.53°C / min, and then heated to 95°C at a rate of 0.3-0.35°C / min, and kept at this temperature for 25 minutes; Then, the temperature was lowered to 82°C at a rate of 0.4-0.45°C / min, and a second portion of formaldehyde was added, with the second portion of formaldehyde being 0.3-0.34 parts. After holding the temperature for 15 minutes, the temperature was raised to 92-96°C at a rate of 0.33-0.47°C / min, and the temperature was held for 20 minutes. Then, cool to below 40°C, add 20 parts of water and mix, then add 1 to 4 parts of styrene acrylic emulsion and mix.

[0074] In the present invention, a staged temperature-controlled polycondensation, secondary formaldehyde addition, and low-temperature lamination process achieve a narrow molecular weight distribution and controlled branching of the phenolic resin. This allows it to form a hydrogen-bonded network with the styrene-acrylic emulsion, resulting in an ultra-thin coating with both high strength and high toughness. The phenolic resin also helps maintain the coating's viscosity stability. Furthermore, the carbonized skeleton formed at high temperatures can form an interpenetrating network with the molten filler, thereby increasing compressive strength and crack-filling thickness.

[0075] In a preferred embodiment of the present invention, the penetrant comprises alkylphenol polyoxyethylene ether (JFC).

[0076] Preferably, the defoaming agent comprises polydimethylsiloxane emulsion.

[0077] Preferably, the preservative comprises 1,2-benzisothiazolin-3-one (BIT-10).

[0078] According to a second aspect of the present invention, there is provided a method for preparing an ultra-thin anti-veining water-based coating for cold box sand cores, the preparation method comprising: S1 adds 20-30% of the total water volume, controls the temperature to 25-30°C, stirs at 250-350 rpm, and sequentially adds room temperature binder, sodium bentonite solution, calcium bentonite solution, hydroxymethyl cellulose solution, penetrant, defoamer and preservative, and continues stirring for 15-25 minutes; S2: adding the solid components of the raw materials, including refractory aggregate, molten filler and glass powder, and stirring at a speed of 800-1200 rpm for 50-70 minutes; Add the remaining water to S3 and stir at a speed of 400-600 rpm for 60 min. Then reduce the speed to 300 rpm and stir for 45 minutes to exhaust.

[0079] In a preferred embodiment of the present invention, in step S2, the solid component is added in three times: First add other refractory aggregates except graphite powder and stir for 5-10 minutes; Then add the molten filler and stir for 10-20 minutes; Finally, add glass powder and optionally graphite powder and stir for 20-30 minutes; In step S2, the stirring speed is 800-1200 rpm.

[0080] In the present invention, quartz powder and calcined kaolin are added for the first time. Quartz powder is used as the main aggregate and has a higher density. Its priority addition can avoid sedimentation caused by insufficient suspension force in the later stage. The calcined kaolin has a flaky structure and is interspersed in the gaps between the quartz powder, initially forming a "brick-mud" dense structure, increasing the bulk density. High-speed shearing breaks up the quartz powder agglomerates, and at the same time, the kaolin flakes are arranged in parallel, forming a prototype structure that reflects thermal radiation.

[0081] Mica powder and iron oxide powder are added for the second time. The layered structure of the mica powder is peeled off under high-speed stirring, which increases the thixotropy of the suspension system. The iron oxide powder particles are evenly dispersed through the eddy current effect to avoid precipitation. During the high-speed stirring process, water between the mica layers is released to form a pre-hydrated layer, preparing for high-temperature dehydration and viscosity flow.

[0082] Glass powder and flake graphite are added for the third time. Glass powder is added last as a low-density lightweight particle and is evenly distributed by the buoyancy of the suspended network. The lubricity of flake graphite can reduce the internal friction heat during high-speed stirring and prevent local overheating from causing pre-curing of the resin. The subsequent stirring for 20 to 30 minutes can ensure full contact between the glass powder and the molten filler and pre-construct a high-temperature reaction interface.

[0083] According to a third aspect of the present invention, there is provided an application of an ultra-thin anti-veining water-based coating for cold box sand cores, characterized in that the coating thickness is 0.2-0.4 mm.

[0084] Specifically, after dust removal on the surface of the sand core, the coating is applied by dipping, spraying or brushing, and then allowed to stand at 120-150°C for 20-30 minutes to allow the coating surface to dry and undergo physical curing. The coating thickness after physical curing is controlled at 0.2-0.4 mm.

[0085] Then, during mold pouring, the heat of the molten iron is used to further trigger the dynamic step sealing of the coating.

[0086] Example The present application will be further described in detail below in conjunction with the embodiments. It will be understood that the specific embodiments described herein are only used to explain the relevant invention and are not intended to limit the invention. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0087] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, typical but non-limiting embodiments of the present invention are as follows: 1. Preparation of room temperature adhesive 1. Examples 1 to 6, Examples 8 to 12, and Comparative Examples 1 to 2 were prepared using the following method: First, add 1 part of phenol by mass and melt it at 43°C, then add 0.24 parts of 25% sodium hydroxide aqueous solution and 0.2-1.36 parts of water, and keep it at 45°C for 25 minutes; Then, the first portion of formaldehyde was added, which was 1.28 parts. After keeping the temperature at 45-50°C for 30 minutes, the temperature was increased to 87°C at a rate of 0.5°C / min, and then the temperature was increased to 95°C at a rate of 0.32°C / min and kept for 25 minutes. Then, the temperature was lowered from 95°C to 82°C at a rate of 0.43°C / min, and a second portion of formaldehyde (0.32 parts) was added. After holding the temperature for 15 minutes, the temperature was raised to 94°C at a rate of 0.4°C / min and held for 20 minutes. Then, cool to below 40°C, add 20 parts of water and mix, then add 3 parts of styrene acrylic emulsion and stir and mix thoroughly.

[0088] Gel permeation chromatography (GPC) was used to measure the molecular weight distribution of phenolic resin. w / M n =1.78.

[0089] 2. Example 7 uses the following preparation method: First, add 1 part of phenol by mass and melt it at 43°C, then add 0.24 parts of 25% sodium hydroxide aqueous solution and 0.2-1.36 parts of water, and keep it at 45°C for 25 minutes; Then, 1.6 parts of formaldehyde was added, and the mixture was kept at 45-50°C for 30 minutes, and then the temperature was increased to 95°C at a rate of 1°C / min and kept for 25 minutes; Then, cool to below 40°C, add 20 parts of water and mix, then add 3 parts of styrene acrylic emulsion and stir and mix thoroughly.

[0090] Gel permeation chromatography (GPC) was used to measure the molecular weight distribution of phenolic resin. w / M n =2.3.

[0091] 2. Preparation of Hydroxymethyl Cellulose Solution 2 parts of hydroxymethyl cellulose were dissolved in 98 parts of water by mass, stirred at a low speed of 300 rpm for 30 minutes, then stirred at a high speed of 1000 rpm for 60 minutes, and then allowed to stand for 24 hours.

[0092] 3. Preparation of sodium bentonite solution Add 5 parts of sodium bentonite and 95 parts of water, stir at a low speed of 200-400 rpm for 30 minutes, then stir at a high speed of 800-1200 rpm for 60 minutes, and let it stand for 24 hours.

[0093] 4. Preparation of calcium-based bentonite liquid Add 10 parts of calcium bentonite and 90 parts of water, stir at a low speed of 200-400 rpm for 30 minutes, then stir at a high speed of 800-1200 rpm for 60 minutes, and let it stand for 24 hours.

[0094] The mass ratios of Examples 1-12 and Comparative Examples 1-2 are shown in Table 1.

[0095] Table 1 Mass ratio of Examples 1-12 and Comparative Examples 1-2

[0096] The preparation method of the anti-veining coating described in each embodiment and comparative example is: S1 adds 20-30% of the total water volume, controls the temperature to 25-30°C, stirs at 300 rpm, and sequentially adds room temperature binder, sodium bentonite solution, calcium bentonite solution, hydroxymethyl cellulose solution, penetrant, defoamer and preservative, and continues stirring for 20 minutes; S2 was added into the solid components of each raw material three times, and then 600 mesh quartz powder and 320 mesh calcined kaolin were added first, and stirred at 1000 rpm for 10 min, then 320 mesh mica powder and iron oxide powder were added, and stirred at 1000 rpm for 15 min, and finally 200 mesh glass powder and flake graphite powder were added, and stirred at 1000 rpm for 25 min; S3 was added with the remaining water, and the mixture was stirred at 500 rpm for 60 min, and then the speed was reduced to 300 rpm and stirred for 45 min to exhaust.

[0097] In step S2, the solid component is added in three times: First add 600 mesh quartz powder and 320 mesh calcined kaolin or 320 mesh cooked bauxite powder, stir for 5-10 minutes; Then add 320 mesh mica powder and iron oxide powder and stir for 10-20 minutes; Finally, add 200 mesh glass powder and flake graphite powder and stir for 20-30 minutes; In step S2, the stirring speed is 800-1200 rpm.

[0098] After the anti-veining coating was prepared, the viscosity, density, and suspension rate of the anti-veining coating obtained in each example and comparative example were tested, wherein: the viscosity test was performed using a 4 mm diameter flow cup to measure the flow time; the density was tested using a Baume meter; and the suspension rate was tested according to the coating sedimentation section of the standard GB / T 6753.3-1986.

[0099] The cold core is then coated using a dip coating method. The coating must be uniform and free of surface defects such as overflow and pores. After the coating is physically cured, its thickness is tested. The physical curing method involves standing the coating at 120-150°C for 20-30 minutes to allow the coating to dry. The coating is tested according to the film thickness measurement section of ISO 2808-2019.

[0100] Next, tests for core strength, veining defects, spalling after physical curing, and spalling during chemical curing are required. Core strength is tested according to JB / T 8583-2016, Casting Sand Core Strength; veining defects are tested according to ASTM E2868-2019 (X-ray Inspection of Castings); and spalling after physical curing is tested according to JB / T 8583, with the absence of cracks considered a pass.

[0101] The thermal shock test is used to test the peeling during chemical curing. First, the coated sand core (Φ50×50mm) is preheated to 800℃ (the phase transition point of silica sand) and quickly immersed in 1380℃ cast iron melt (simulating pouring). It is kept for 10 seconds and then removed. The sample is then cut and the coating peeling area ratio is measured: peeling rate = peeling area / total coating area × 100%.

[0102] The test results of Examples 1-12 and Comparative Examples 1-2 are shown in Table 2.

[0103] Table 2 Test results of Examples 1-12 and Comparative Examples 1-2

[0104] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. An ultra-thin anti-veining water-based coating for cold box sand cores, characterized in that: The anti-veining water-based coating comprises the following raw materials in parts by mass: 1~2 parts of room temperature adhesive 20~40 parts of high temperature adhesive 2~5 parts of suspension agent 0.1~0.5 parts of penetrant 0.1~0.5 parts of defoaming agent 0.03~0.1 parts of preservatives 15~35 parts of refractory aggregate 10 to 20 parts of molten filler, and 20-40 parts water; Wherein, the room temperature binder is a composite of phenolic resin and styrene acrylic emulsion; The high-temperature adhesive includes 200-400 mesh glass powder, calcium-based bentonite liquid and sodium-based bentonite liquid; The suspending agent includes hydroxymethyl cellulose solution; The refractory aggregate comprises one or more of 200-800 mesh quartz powder, 320 mesh smelted bauxite powder, 320 mesh calcined kaolin, 320-600 mesh mullite powder and graphite powder; The molten filler includes 320 mesh mica powder and / or iron oxide powder.

2. The anti-veining water-based coating according to claim 1, wherein: The high-temperature adhesive includes 2 to 4 parts of glass powder, 7 to 15 parts by mass of calcium-based bentonite liquid and 12 to 20 parts by mass of sodium-based bentonite liquid, and the mass ratio of the glass powder, calcium-based bentonite liquid and sodium-based bentonite liquid is 1:2-5:4-7.

3. The anti-veining water-based coating according to claim 1, wherein: The mass ratio of the hydroxymethyl cellulose solution to the sodium bentonite solution is 1:3-8.

4. The anti-veining water-based coating according to claim 1, wherein: The refractory aggregate comprises 600 mesh quartz powder, 320 mesh kaolin and flake graphite.

5. The anti-veining water-based coating according to claim 1, wherein: The refractory aggregate comprises 5 to 15 parts by mass of 600-mesh quartz powder, 5 to 15 parts by mass of 320-mesh kaolin and 2 to 6 parts by mass of flake graphite.

6. The anti-veining water-based coating according to claim 1, wherein: The molecular weight distribution M of the phenolic resin W :M N ≤2.

7. The anti-veining water-based coating according to claim 1, wherein: The preparation method of the room temperature adhesive comprises: First, 1 part of phenol is added by mass and melted at 43° C., and then 0.17-0.3 parts of sodium hydroxide solution and 0.2-1.36 parts of water are added, and the mixture is kept at 45° C. for 25 minutes, wherein the sodium hydroxide solution is a sodium hydroxide aqueous solution with a mass percentage of 25%; Then, the first portion of formaldehyde is added, which is 1.2 to 1.36 parts and then kept at 45-50°C for 30 minutes, then heated to 87°C at a rate of 0.46-0.53°C / min, and then heated to 95°C at a rate of 0.3-0.35°C / min, and kept at this temperature for 25 minutes; Then, the temperature was lowered to 82°C at a rate of 0.4-0.45°C / min, and a second portion of formaldehyde was added, with the second portion of formaldehyde being 0.3-0.34 parts. After holding the temperature for 15 minutes, the temperature was raised to 92-96°C at a rate of 0.33-0.47°C / min, and the temperature was held for 20 minutes. Then, cool to below 40°C, add 20 parts of water and mix, then add 1 to 4 parts of styrene acrylic emulsion and mix.

8. The anti-veining water-based coating according to any one of claims 1 to 7, characterized in that: The penetrant includes alkylphenol polyoxyethylene ether (JFC), the defoaming agent includes polydimethylsiloxane emulsion, and the preservative includes 1,2-benzisothiazolin-3-one (BIT-10).

9. The method for preparing the ultra-thin anti-veining water-based coating for cold box sand cores according to any one of claims 1 to 8, characterized in that: The preparation method comprises: S1 adds 20-30% of the total water volume, controls the temperature to 25-30°C, stirs at 250-350 rpm, sequentially adds room temperature binder, sodium bentonite solution, hydroxymethyl cellulose solution, penetrant, defoamer and preservative, and continues stirring for 15-25 minutes; S2: adding the solid components of the raw materials, including refractory aggregate, molten filler and glass powder, and stirring at a speed of 800-1200 rpm for 50-70 minutes; Add the remaining water to S3 and stir at a speed of 400-600 rpm for 60 min. Then reduce the speed to 300 rpm and stir for 45 minutes to exhaust.

10. Use of the ultra-thin anti-veining water-based coating for cold box sand cores according to any one of claims 1 to 8, characterized in that: The coating thickness is 0.2~0.4mm.

Images