A kind of anti-brightening coating for gearbox casting and its preparation method and application

Abstract

The application provides an anti-exposed coating for a gearbox casting and a preparation method and application thereof, and relates to the technical field of lost foam casting. The raw materials of the lost foam coating include aggregate, alkali-swellable hydrophobically modified acrylate emulsion and fatty alcohol polyoxyethylene ether. The total content of quartz sand and quartz powder in the aggregate is 85-92wt% of the aggregate, the content of the alkali-swellable hydrophobically modified acrylate emulsion is 0.2-0.8wt% of the aggregate, and the mass ratio of the alkali-swellable hydrophobically modified acrylate emulsion to the fatty alcohol polyoxyethylene ether is 0.6-8:1. The coating improves the utilization rate of quartz raw materials and reduces the raw material cost. The synergistic effect of the alkali-swellable hydrophobically modified emulsion and the fatty alcohol polyoxyethylene ether improves the wetting and spreading ability of the slurry with quartz sand and quartz powder as the main aggregate on the surface of the white mold, avoids the local exposure phenomenon during coating, enhances the suspension stability and strength of the slurry, inhibits the aggregate settlement and sagging, and ensures the uniformity of the coating.

Description

Technical Field

[0001] This invention relates to the field of lost foam casting technology, and in particular to an anti-whitening lost foam coating for gearbox castings, its preparation method, and its application. Background Technology

[0002] With the high-quality development of my country's automotive and other industries, the surface quality requirements for gearbox castings are constantly increasing. Consequently, the requirements for the anti-whitening performance of lost foam coatings used in the casting process of gearbox castings are also rising. The quality of the anti-whitening performance of lost foam coatings has become crucial to ensuring the quality of gearbox castings. Excellent anti-whitening lost foam coatings are a prerequisite for ensuring the density and thickness of the surface coating, effectively resisting molten metal penetration and thermal shock during casting, ensuring the complete formation of complex internal and external cavities. This is a core technical element for ensuring the surface quality of castings and improving the yield rate of gearbox castings.

[0003] Gearbox housings, as typical complex thin-walled components, have complex foam model (white model) structures, including numerous bearing seats, reinforcing ribs, internal cavities, and other characteristic parts. These models are typically machine-made, and oil-based or wax-based release agents must be used to ensure smooth demolding. The hydrophobic residual film formed by these release agents on the model surface makes it difficult for traditional water-based coatings to wet and spread. During coating, the slurry is prone to shrinkage at corners, edges, or areas with significant release agent residue, forming dotted or sheet-like white defects. This results in missing coating at the exposed areas, making it susceptible to molten metal penetration during casting, leading to severe casting defects such as sand adhesion and iron spikes, thus reducing the yield rate of lost foam casting of gearbox housings.

[0004] To improve the resistance to whitening, lost foam coatings are often made from raw materials such as bauxite and corundum powder. Although these materials can improve the resistance to whitening to a certain extent, whitening still occurs. Moreover, these raw materials are expensive and cannot meet the demand for lost foam coatings that are both low-cost and have high resistance to whitening.

[0005] Quartz sand, as the cheapest refractory aggregate, is the most direct way to reduce coating costs. However, the application of high proportions of quartz sand (especially coarse sand) presents the following challenges:

[0006] (1) The surface of quartz sand has poor hydrophilicity, and the slurry has poor wettability on the foam model (white model) covered with release agent (wax grease), which easily causes local discontinuity of the coating, exposing the white model body, causing serious white coating exposure, and the exposed white part will become the origin of casting defects such as sand adhesion and iron spikes, affecting the quality of the casting.

[0007] (2) Slow drying speed and easy cracking: The slurry with a high proportion of quartz sand has strong water retention and slow water migration and discharge. The water evaporates unevenly during the drying process and the drying cycle is long. Cracks are easily generated due to the large thermal expansion coefficient of quartz sand, which affects the integrity of the coating and high temperature strength.

[0008] In addition, traditional thickeners often lead to excessively high viscosity of the slurry, resulting in poor flowability during coating and uneven coating in complex structures (such as the inner cavity of bearing housings and reinforcing ribs). On the other hand, excessive pursuit of flowability can lead to sagging on vertical surfaces and aggregate settling, resulting in uneven coating thickness and local air permeability imbalance, which is essentially a kind of hidden whitening or performance defect.

[0009] Therefore, how to effectively improve the wettability, coating uniformity and crack resistance of coatings while increasing the amount of quartz sand to reduce costs has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0010] This invention provides an anti-whitening lost foam coating for gearbox castings, which solves the defects of existing coatings such as high cost, sagging, and severe whitening of the coating.

[0011] In a first aspect, the present invention provides an anti-whitening lost foam coating for gearbox castings, wherein the raw materials of the lost foam coating include aggregate, acrylate hydrophobically modified alkali-swellable emulsion, and fatty alcohol polyoxyethylene ether; the total content of quartz sand and quartz powder in the aggregate is 85-92 wt% of the aggregate, the content of the acrylate hydrophobically modified alkali-swellable emulsion is 0.2-0.8 wt% of the aggregate, and the mass ratio of the acrylate to the fatty alcohol polyoxyethylene ether is 0.6-8:1.

[0012] The acrylate hydrophobically modified alkali-swellable emulsion is HASE, and the fatty alcohol polyoxyethylene ether is JFC.

[0013] This coating uses a high proportion (85-92 wt%) of quartz-based raw materials as the core aggregate, significantly reducing raw material costs. The synergistic effect of the acrylate-based hydrophobically modified alkali-swellable emulsion and fatty alcohol polyoxyethylene ether significantly improves the wetting and spreading ability of the slurry on the white mold surface, effectively preventing localized whitening during coating. Simultaneously, the acrylate-based hydrophobically modified alkali-swellable emulsion swells under alkaline conditions to form a three-dimensional network structure, enhancing the suspension stability and strength of the slurry, inhibiting aggregate settling and sagging, and ensuring coating uniformity. The mechanism of action is as follows:

[0014] Fatty alcohol polyoxyethylene ether reduces the contact angle between the slurry and the white mold (foam plastic mold) to an extremely low level, achieving instant spread. Its lipophilic groups are directionally adsorbed on the surface of the foam plastic mold, while its hydrophilic groups are connected to the water phase, reducing interfacial tension and significantly improving the coating's coatability and wettability on the hydrophobic foam model. This helps to ensure that HASE molecules are evenly spread on the surface of the foam plastic mold, avoiding uneven coating thickness caused by local thickener aggregation and solving the interfacial wetting problem.

[0015] The main molecular chain of the acrylate-based hydrophobically modified alkali-swellable emulsion in this coating is poly(acrylic acid-co-methacrylic acid), with hydrophobic alkyl (such as octadecyl) acrylates grafted onto the side chains. When the system pH > 8.5 (provided by an alkaline environment from sodium silicate), the carboxyl groups on the chain undergo deprotonation ionization, producing carboxylate ions (-COO₂). - The negatively charged molecules extend fully due to electrostatic repulsion, increasing the hydrodynamic volume and leading to a significant increase in the low-shear viscosity of the system. This endows the slurry with excellent static suspension ability, preventing the sedimentation of quartz sand and ensuring uniform and stable coating thickness.

[0016] Under the high shear rate of coating application, the extended molecular chains of HASE align along the flow field direction. Simultaneously, the reversible physical cross-linking points (hydrophobic association) formed between molecules through hydrophobic alkyl chains are temporarily disrupted. This results in shear thinning, a significant decrease in viscosity, and excellent slurry fluidity, facilitating leveling and penetration into complex cavities, thus preventing uneven coating and white spots. When coating stops (shear force disappears), the hydrophobic groups rapidly recombine within seconds to tens of seconds through van der Waals forces, restoring the transient network structure. The viscosity quickly recovers, effectively preventing slurry sagging on vertical surfaces and ensuring uniform coating thickness across complex structures.

[0017] Furthermore, the hydrophobic side chains (C14-C16 alkyl groups) of HASE form mixed micelles with the fatty alcohol polyoxyethylene ether adsorbed on the surface of the foam plastic mold. This allows the HASE molecular chains to form more stable physical cross-linking points at the interface, improving the high-temperature flexural strength and crack resistance of the coating and effectively preventing whitening caused by coating shrinkage. When the mass ratio of the acrylate hydrophobically modified alkali-swellable emulsion to the fatty alcohol polyoxyethylene ether is controlled below 0.6, HASE and fatty alcohol polyoxyethylene ether form a large number of micelles, encapsulating the hydrophobic groups of HASE. This leads to a decrease in its hydrophobic association ability, a weakening of the three-dimensional network structure of the system, insufficient static viscosity, and reduced slurry suspension, making it prone to aggregate settling and sagging after coating. When the mass ratio is higher than 8, the content of fatty alcohol polyoxyethylene ether is relatively low, resulting in poor interfacial wetting and spreading effects, increased contact angle, and HASE's inability to be effectively fixed at the interface. After drying, the coating is prone to shrinkage and cracking, leading to whitening defects. Experiments show that when the mass ratio of the two is controlled within the range of 0.6 to 8:1, the wettability, suspension, rheology, high-temperature bending strength and crack resistance are optimally synergistically combined. The coating is complete and continuous, without any white spots or sagging defects, and is suitable for high-precision lost foam casting process requirements, significantly improving the surface quality of castings.

[0018] In summary, the key innovation of this invention lies in the first-time introduction of HASE (a rheology modifier commonly used in high-end latex paints) and JFC (a common wetting agent) in a specific ratio into a high-solids-content, high-shear water-based casting coating. The synergistic effect of these two components successfully resolves the long-standing process contradiction between wettability (avoiding white spots) and anti-sagging properties (ensuring coating uniformity) under conditions of high quartz sand content. This is not a simple material addition, but rather a synergistic design of rheology and interfacial chemistry specifically tailored to the unique working conditions of casting coatings.

[0019] Furthermore, the aggregate also includes asphalt powder and modified starch, wherein the mass ratio of the asphalt powder to the acrylate hydrophobic modified alkali-swellable emulsion is 3.7~35:1, and the mass ratio of the modified starch to the acrylate hydrophobic modified alkali-swellable emulsion is 0.1~1.6:1.

[0020] To further improve the anti-sagging properties of the coating, asphalt powder and modified starch (CMS, carboxymethyl starch) were introduced. Asphalt powder, acting as an auxiliary binder, has a certain affinity for the wax grease on the white mold surface due to its hydrophobic components. This not only promotes the anchoring of the coating on the white mold surface and enhances interfacial bonding, reducing uneven thickness caused by slurry slippage during coating and significantly improving the room temperature flexural strength of the coating, but also improves the wettability of the white mold, preventing white spots. Furthermore, its carbonization at high temperatures forms a carbon network, further enhancing high-temperature flexural strength. Modified starch, after dissolving in water, forms a high-viscosity colloid that synergistically thickens with HASE. This viscosity has a coating effect on aggregate particles, causing them to adhere together. This prevents the slurry from easily shrinking when encountering localized hydrophobic points, effectively preventing defects such as localized cracking and white spots in the coating. The synergistic effect of acrylate hydrophobically modified alkali-swellable emulsion (HASE), fatty alcohol polyoxyethylene ether, asphalt powder and modified starch can further optimize and improve the coating's resistance to whitening, sag, coating uniformity, flexural strength and crack resistance.

[0021] To further enhance the coating's adaptability under extreme conditions or optimize specific performance, it is preferable to selectively add one or more auxiliary functional additives to the core synergistic system composed of HASE and JFC. The addition of these auxiliary functional additives is not a necessary condition for resolving the core contradiction of wetting-anti-sagging, but rather aims to further supplement and fine-tune the interfacial bonding strength or application rheology of the coating.

[0022] Furthermore, the auxiliary functional additives include, but are not limited to, interface reinforcing agents and rheology modifiers, wherein the content of the interface reinforcing agent is 0.05 to 0.3 wt% of the aggregate, and the content of the rheology modifier is 0.05 to 0.2 wt% of the aggregate.

[0023] Preferably, the interface reinforcing agent includes polyvinylpyrrolidone (PVP). PVP is a highly polar polymer that can be simultaneously adsorbed onto the surface of hydrophilic aggregates and the surface of hydrophobic foam models, acting as a molecular bridge. This enhances the adhesion between the coating and the model substrate, reduces the risk of interface peeling due to drying shrinkage, and further consolidates the anti-whitening effect.

[0024] Furthermore, the rheology modifier includes castor oil-based derivatives, which are commonly used nonionic rheology modifiers that can produce a synergistic thixotropic effect with HASE. This helps the coating to have better flowability at high shear rates (facilitating leveling) and to recover structural viscosity more quickly at low shear rates (resisting sagging), thereby optimizing the coating uniformity of complex structures. In the system composed of HASE and JFC, the high-temperature flexural strength of lost foam coatings can also be effectively improved.

[0025] Preferably, the castor oil-based derivative includes one or more of hydrogenated castor oil (such as Thixatrol ST), polyamide-modified castor oil (such as Crayvallac PF), and 12-hydroxystearic acid.

[0026] When adding any auxiliary functional additives, it should be ensured that they have good compatibility with the core components HASE and JFC, and their dosage should be controlled within the reasonable range described in this invention, so as to avoid interfering with the synergistic effect of the core components and introducing negative effects.

[0027] Furthermore, the raw materials also include a binder, the content of which is 2 to 4 wt% of the aggregate.

[0028] Furthermore, the adhesive is composed of sodium silicate and polyvinyl alcohol in a mass ratio of 1.5 to 6:1.

[0029] Polyvinyl alcohol and sodium silicate work synergistically to form a film rapidly at lower temperatures, locking the coating structure, preventing cracking, and further improving initial strength. In the system of this invention, the use of a binder composed of sodium silicate and polyvinyl alcohol can achieve a better synergistic effect in improving high-temperature crack resistance and high-temperature flexural strength.

[0030] Furthermore, the particle size of the quartz sand is 100-140 mesh, the particle size of the quartz powder is 200-300 mesh, and the mass ratio of the quartz sand to the quartz powder is 1-2:1. Controlling the particle size of the quartz sand within the above range provides a stable pore structure, which not only facilitates the migration and discharge of moisture during the coating drying process but also improves the air permeability of the coating.

[0031] Furthermore, the aggregate also includes kaolin, the particle size of which is 300-350 mesh, and its content is 5-8 wt% of the aggregate.

[0032] Furthermore, the raw materials also include calcium lignosulfonate and carboxymethyl cellulose, wherein the content of calcium lignosulfonate is 0.2-0.5 wt% of the aggregate, and the content of carboxymethyl cellulose is 0.05-0.15 wt% of the aggregate. The introduction of acrylate-based hydrophobically modified alkali-swellable emulsion (HASE) into the coating can reduce the amount of carboxymethyl cellulose used, achieving excellent anti-sagging properties in a low-volume carboxymethyl cellulose system, reducing the binding of water by hydrophilic colloids, promoting water migration, improving drying efficiency, and reducing the risk of cracking.

[0033] Further, the lost foam coating comprises the following raw materials in parts by weight: 50-60 parts of quartz sand, 35-42 parts of quartz powder, 5-8 parts of kaolin, 3-7 parts of asphalt powder, 0.2-0.8 parts of acrylate hydrophobic modified alkali-swellable emulsion, 0.1-0.3 parts of fatty alcohol polyoxyethylene ether, 0.5-1.5 parts of modified starch, 1.5-3.0 parts of sodium silicate, 0.5-1.0 parts of polyvinyl alcohol, 0.2-0.5 parts of calcium lignosulfonate, and 0.05-0.15 parts of carboxymethyl cellulose.

[0034] In a second aspect, the present invention provides a method for preparing the above-mentioned anti-whitening lost foam coating for gearbox castings, comprising the following steps: first dissolving the fatty alcohol polyoxyethylene ether and calcium lignosulfonate in water, adjusting the pH to 9-10, and then adding other raw materials and mixing them evenly.

[0035] Further, the preparation method includes the following steps: first, dissolve the fatty alcohol polyoxyethylene ether and calcium lignosulfonate in water, adjust the pH to 9-10, then add other raw materials except sodium silicate, stir at high speed of 2500 rpm for 18 min, then add sodium silicate, and stir at low speed of 1000 rpm for 30 min.

[0036] Furthermore, the mass ratio of the raw material to water is 1:0.45 to 0.55.

[0037] A third aspect of the present invention provides the above-described anti-whitening lost foam coating for gearbox castings or the application of the above-described lost foam coating in casting gearbox castings.

[0038] The beneficial effects of the lost foam coating for gearbox castings, its preparation method, and its application provided by this invention are as follows: The lost foam coating of this invention uses quartz raw materials as the core aggregate, which significantly improves the utilization rate of quartz raw materials and greatly reduces the raw material cost; and through the synergistic effect of hydrophobic alkali-swellable emulsion and fatty alcohol polyoxyethylene ether, it not only significantly improves the wetting and spreading ability of the slurry on the surface of the white foam, effectively avoiding local white exposure during coating, but also enhances the suspension stability and strength of the slurry, inhibits the sedimentation and sagging of aggregates, ensures the uniformity of the coating, and solves the problem of white exposure and uneven flow in lost foam coatings with high quartz sand content. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 These are the test results of the high-temperature crack resistance of the lost foam coatings in Examples 1-5.

[0041] Figure 2 The graphs show the test results of the high-temperature crack resistance of the lost foam coatings in proportions 1 to 6.

[0042] Figure 3 These are the test results of the high-temperature flexural strength of the lost foam coatings in Examples 1-5.

[0043] Figure 4 The graphs show the test results of the high-temperature flexural strength of the lost foam coatings in proportions 1 to 6. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0045] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0046] Example 1

[0047] An anti-whitening lost foam coating for gearbox castings, comprising the following raw materials in parts by weight:

[0048] 51 parts of 140-mesh quartz sand, 38 parts of 200-mesh quartz powder, 6 parts of 325-mesh kaolin, 5 parts of 200-mesh asphalt powder, 0.5 parts of acrylate hydrophobic modified alkali-swellable emulsion (HASE, model HASE-60), 0.2 parts of fatty alcohol polyoxyethylene ether (JFC, model JFC-4, CAS No.: 71060-57-6), 1 part of modified starch (CMS, carboxymethyl starch), 2.5 parts of sodium silicate, 0.8 parts of polyvinyl alcohol (PVA 17-88), 0.3 parts of calcium lignosulfonate, and 0.08 parts of carboxymethyl cellulose (CMC).

[0049] This embodiment also provides a method for preparing the above-mentioned lost foam coating, the steps of which are as follows: first, dissolve the fatty alcohol polyoxyethylene ether and calcium lignosulfonate in 52 parts of water, adjust the pH to 9-10, then add other raw materials except sodium silicate, stir at high speed of 2500 rpm for 18 min, then add sodium silicate, and stir at low speed of 1000 rpm for 30 min.

[0050] Example 2

[0051] An anti-whitening lost foam coating for gearbox castings, comprising the following raw materials in parts by weight:

[0052] The following ingredients were used: 55 parts 140-mesh quartz sand, 32 parts 200-mesh quartz powder, 8 parts 325-mesh kaolin, 6.3 parts 200-mesh asphalt powder, 0.8 parts acrylate hydrophobically modified alkali-swellable emulsion (HASE-60), 0.3 parts fatty alcohol polyoxyethylene ether (JFC, model JFC-4), 1.5 parts modified starch (CMS, carboxymethyl starch), 1.5 parts sodium silicate, 0.5 parts polyvinyl alcohol (PVA 17-88), 0.5 parts calcium lignosulfonate, and 0.15 parts carboxymethyl cellulose. The preparation method was the same as in Example 1.

[0053] Example 3

[0054] An anti-whitening lost foam coating for gearbox castings, comprising the following raw materials in parts by weight:

[0055] The ingredients are: 60 parts 140-mesh quartz sand, 35 parts 200-mesh quartz powder, 5 parts 325-mesh kaolin, 6.7 parts 200-mesh asphalt powder, 0.2 parts acrylate hydrophobically modified alkali-swellable emulsion (HASE-60), 0.1 parts fatty alcohol polyoxyethylene ether (JFC, model JFC-4), 0.5 parts modified starch (CMS, carboxymethyl starch), 1.5 parts sodium silicate, 0.5 parts polyvinyl alcohol (PVA 17-88), 0.2 parts calcium lignosulfonate, and 0.05 parts carboxymethyl cellulose. The preparation method is the same as in Example 1.

[0056] Example 4

[0057] A lost foam coating for gearbox castings that resists whitening is formulated based on Example 1, with the addition of polyvinylpyrrolidone (PVP) as an interface reinforcing agent.

[0058] It is composed of the following raw materials in parts by weight: 51 parts of 140 mesh quartz sand, 38 parts of 200 mesh quartz powder, 6 parts of 325 mesh kaolin, 5 parts of 200 mesh asphalt powder, 0.5 parts of acrylate hydrophobic modified alkali-swellable emulsion (HASE-60), 0.2 parts of fatty alcohol polyoxyethylene ether (JFC, model JFC-4), 1 part of modified starch (CMS), 2.5 parts of sodium silicate, 0.8 parts of polyvinyl alcohol (PVA 17-88), 0.3 parts of calcium lignosulfonate, 0.08 parts of carboxymethyl cellulose (CMC), and 0.15 parts of polyvinylpyrrolidone (PVP).

[0059] The preparation method is the same as in Example 1.

[0060] Example 5

[0061] A lost foam coating for gearbox castings that resists whitening is formulated based on Example 1, with the addition of castor oil derivatives as rheology modifiers.

[0062] The product is composed of the following raw materials in parts by weight: 51 parts 140-mesh quartz sand, 38 parts 200-mesh quartz powder, 6 parts 325-mesh kaolin, 5 parts 200-mesh pitch powder, 0.5 parts acrylate hydrophobically modified alkali-swellable emulsion (HASE-60), 0.2 parts fatty alcohol polyoxyethylene ether (JFC, model JFC-4), 1 part modified starch (CMS), 2.5 parts sodium silicate, 0.8 parts polyvinyl alcohol (PVA 17-88), 0.3 parts calcium lignosulfonate, 0.08 parts carboxymethyl cellulose (CMC), and 0.10 parts castor oil derivative, which is 12-hydroxystearic acid (12-HSA). 12-hydroxystearic acid (12-HSA) is a representative substance among castor oil derivatives, with the chemical structure CH3(CH2)5-CH(OH)-(CH2). 10 -COOH, with a molecular weight of 300.48. Its molecular chain contains long-chain alkyl, hydroxyl, and carboxyl groups, which can self-assemble into a three-dimensional network structure through intermolecular hydrogen bonds, giving the coating system thixotropic and anti-sagging properties.

[0063] The preparation method is the same as in Example 1.

[0064] Comparative Example 1

[0065] This comparative example is basically the same as Example 1, except that no acrylate-based hydrophobic modified alkali-swellable emulsion is added.

[0066] Comparative Example 2

[0067] This comparative example is basically the same as Example 1, except that fatty alcohol polyoxyethylene ether is not added.

[0068] Comparative Example 3

[0069] This comparative example is basically the same as Example 1, except that: 0.1 parts of acrylate hydrophobic modified alkali-swellable emulsion (HASE-60) were used.

[0070] Comparative Example 4

[0071] This comparative example is basically the same as Example 1, except that: 1 part of acrylate hydrophobic modified alkali-swellable emulsion (HASE-60) was used.

[0072] Comparative Example 5

[0073] This comparative example is basically the same as Example 1, except that: 0.2 parts of acrylate hydrophobic modified alkali-swellable emulsion (HASE-60) and 0.5 parts of fatty alcohol polyoxyethylene ether (JFC, model JFC-4) were used.

[0074] Comparative Example 6

[0075] This comparative example is basically the same as Example 1, except that: 0.63 parts of acrylate hydrophobic modified alkali-swellable emulsion (HASE-60) and 0.07 parts of fatty alcohol polyoxyethylene ether (JFC, model JFC-4) were used.

[0076] This invention uses lost foam coating prepared in the examples and comparative examples to produce gearboxes (workpiece material is QT600-3 ductile iron, pouring temperature is 1380℃). The gearbox preparation steps are as follows: the coating is uniformly coated on the surface of the gearbox foam model using a flow coating process, the coating thickness is 1mm, the model is then dried at 50℃ for 3h, followed by sand embedding and vacuum pouring, and cooling.

[0077] Meanwhile, the performance of the anti-whitening lost foam coatings for gearbox castings prepared in the embodiments and comparative examples was tested, and the test results are shown in Tables 1 to 3. Figures 1-4 As shown.

[0078] Table 1. High-temperature air permeability (in cm⁻¹) of the lost foam coatings prepared in the examples and comparative examples. 4 / g·min)

[0079]

[0080] As shown in Table 1, the high-temperature air permeability of the lost foam coatings corresponding to Examples 1-5 is higher than that of Comparative Examples 1-6, indicating that the lost foam coating of the present invention has excellent high-temperature air permeability.

[0081] The results of high-temperature crack resistance of lost foam coating at 1200℃ are as follows: Figure 1 and Figure 2 As shown, by Figure 1 and Figure 2 It can be seen that the lost foam coatings corresponding to Examples 1 to 5 did not show cracks after high-temperature heating, but Comparative Examples 1 to 6 all showed cracks, especially Comparative Examples 1 and 2, which had larger cracks. This indicates that the addition of acrylate hydrophobic modified alkali-swellable emulsion and fatty alcohol polyoxyethylene ether has a significant impact on the high-temperature crack resistance of the coating.

[0082] The results of the high-temperature flexural strength of lost foam coatings at room temperature and 1300℃ are shown in Table 2. Figure 3 and Figure 4 As shown.

[0083] Table 2. High-temperature flexural strength of the lost foam coatings prepared in the examples and comparative examples.

[0084]

[0085] As shown in Table 2, the high-temperature flexural strength of the lost foam coatings corresponding to Examples 1-5 at 1300℃ is higher than 10MPa, and is also higher than that of Comparative Examples 1-6, indicating that the lost foam coating of the present invention has excellent high-temperature flexural strength.

[0086] The coating pass rate of lost foam coating is shown in Table 3.

[0087] Table 3 shows the coating pass rates of the lost foam coatings prepared in the examples and comparative examples.

[0088]

[0089] As shown in Table 3, the coating qualification rate of the lost foam coatings corresponding to Examples 1 to 5 is significantly higher than that of the comparative examples. Moreover, the coating is uniform, without any white showing, and there is no dripping during coating, indicating that the lost foam coating of the present invention has excellent anti-white showing and anti-dripping properties.

[0090] The above results indicate that the lost foam coating of the present invention not only has good air permeability, crack resistance and flexural strength at high temperatures, but also excellent resistance to whitening and sagging, which meets the requirements for casting gearbox-type castings.

[0091] The test methods for the high-temperature air permeability, high-temperature crack resistance, high-temperature flexural strength, and coating pass rate of the lost foam coatings prepared in the above embodiments and comparative examples are as follows:

[0092] Test Example 1: High-Temperature Air Permeability Test of Lost Foam Coating

[0093] 1. Tools: NBD-M1700-22TI box furnace; ZTY intelligent air permeability tester; 101-2BS electric thermostatic drying oven; stainless steel ring with inner diameter Φ50mm and thickness 1.80mm (two flat, non-warped surfaces free of oxide scale, adhesives, and other foreign matter); stainless steel ring fixing base plate; stainless steel pressure ring; high-temperature sleeve device.

[0094] 2. Test Procedure

[0095] (1) Add water to the lost foam coating to be tested and stir. The stirring speed should not exceed 1000 rpm. After stopping the addition of water, stir at 500 rpm for 20 minutes to obtain a paste coating for later use. Stir the paste coating for 5 minutes before use and cover the coating bucket tightly with a plastic cover after use.

[0096] (2) Fix the stainless steel ring that meets the requirements to the special base plate with screws. Apply plastic tape evenly, flatly and tightly to the flat surface of the base plate.

[0097] (3) Applying coating:

[0098] a. Spread the paste-like coating evenly inside three stainless steel rings, with the first layer of coating approximately 0.9 mm thick, and dry at 100°C for about 1.5 hours. If the sample has cracks after drying, touch up with the paste-like coating and then dry again.

[0099] b. After the sample is dried without cracks, apply a second layer of coating until it is flush with the surface of the ring. Let it stand at room temperature for 10-15 minutes, then dry at 100℃ for 1.5 hours. If cracks appear on the sample after drying, apply a paste-like coating and then dry again.

[0100] c. After the sample is dried without cracks, apply a third coat of paint and smooth it out. Let it stand at room temperature for 10-15 minutes, then dry it at 100℃ for 1.5 hours.

[0101] d. After the sample is dried, it is demolded. The demolded sample should have smooth surfaces on both sides, no protrusions or cracks, and a thickness of 1.80±0.04mm.

[0102] e. If there is a gap at the junction of the stainless steel ring and the coating, fill the gap with water glass. Let it stand at room temperature for at least 10 minutes before testing. Samples not to be tested immediately should be stored in a desiccator until testing.

[0103] (4) Connect the uncoated side (bottom) of the sample to the sleeve, place a stainless steel pressure ring on the coated side, and fix the sample to the high temperature sleeve with stainless steel screws and nuts (pay special attention to strictly prohibit fixing to the normal temperature sleeve).

[0104] (5) Place the fixed sample in the NBD-M1700-22TI box furnace with a high temperature sleeve, and use the ZTY intelligent air permeability tester to measure the air permeability of the sample at different temperatures.

[0105] Temperature setting procedure: Start heating from room temperature, increasing the temperature by 10°C per minute. Test the air permeability at room temperature before heating, then measure again at 150°C. From 600°C onwards, test the air permeability of the sample every 10°C. If the sample cracks, the experiment ends; if the sample does not crack, heat to 850°C and end the experiment. The air permeability at 800°C is the standard. If cracking or warping and leakage occur before 800°C, the sample must be prepared and tested again.

[0106] Test Example 2: High-Temperature Crack Resistance Test of Lost Foam Coating

[0107] 1. Instruments and tools: long-handled pliers, NBD-M1700-22TI box furnace, 101-2BS electric constant temperature drying oven, refractory bricks, vernier calipers, hot melt glue gun, 80×20×120mm white mold, 40×20×120mm white mold, S-shaped hook, wallpaper knife.

[0108] 2. Test Procedure

[0109] (1) Make three white T-shaped cross-section molds with a diameter of 80 / 40×120mm and a thickness of 10-20mm, and connect them with hot melt glue; then cut off the six edges of the white T-shaped cross-section molds with a utility knife; then fix the white molds with S-shaped hooks.

[0110] (2) Add water to the lost foam coating to be tested and stir. The stirring speed should not exceed 1000 rpm. After stopping the addition of water, stir at 500 rpm for 20 minutes to obtain a paste coating for later use. Stir the paste coating for 5 minutes before use and cover the coating bucket tightly with a plastic cover after use.

[0111] (3) Immerse the white model into the stirred coating to a height of about 100 mm. Place the coated sample in a drying oven and dry at 50°C for 2 hours. Repeat the immersion coating 3 times to ensure that the coating thickness of the sample is 1.50 to 1.80 mm.

[0112] (4) Observe whether there are cracks on the surface of the yellow mold, and use a hacksaw blade to cut the uncoated mouth along with the coating.

[0113] (5) Heat the NBD-M1700-22TI box furnace to 1200℃ and hold it at that temperature. Open the furnace door and quickly use long-handled pliers to clamp the yellow mold and place it into the furnace. Hold it at 1200℃ for 3 minutes. Take it out and immediately observe the state of the mold shell cracks with a magnifying glass and take a picture. The observation must be performed when the mold shell is light yellow to red when it is just taken out. If the color darkens, it is invalid.

[0114] The crack grade for evaluating high-temperature crack resistance is based on the following criteria:

[0115] Level 1: The surface is smooth and free of cracks, or has only very fine cracks;

[0116] Level 2: The surface has dendritic or net-like fine cracks, and the crack width is less than 0.5 mm;

[0117] Level 3: The surface has dendritic or network cracks, the crack width is less than 1 mm, the cracks are relatively deep, and there are no through coarse cracks in the transverse (and horizontal circumferential) or longitudinal direction.

[0118] Level 4: The surface has dendritic or network cracks, the crack width is greater than 1mm, and there are coarse through cracks in the transverse and longitudinal directions.

[0119] Test Example 3: High-Temperature Flexural Strength Test of Lost Foam Coating

[0120] 1. Instruments and tools: paint mixer, standard sample mold, electric heating blast constant temperature drying oven, 1700℃ box-type high temperature electric furnace, XQY-Ⅱ intelligent sand strength tester, vernier caliper, long-handled pliers, high temperature resistant 77 ceramic boat or 60×30 square boat.

[0121] 2. Test Procedure

[0122] (1) Add water to the lost foam coating to be tested and stir. The stirring speed should not exceed 1000 rpm. After stopping the addition of water, stir at 500 rpm for 20 minutes to obtain a paste coating for later use. Stir the paste coating for 5 minutes before use and cover the coating bucket tightly with a plastic cover after use.

[0123] (2) Preparation of standard sample molds and base plates:

[0124] a. The test standard sample mold is free from deformation, the parting surface fits tightly, the cavity surface is flat without protrusions, and plastic tape is applied to prevent sticking.

[0125] b. Apply plastic tape evenly, smoothly, and tightly to the flat surface of the base plate;

[0126] c. Place the standard sample mold firmly onto the base plate using plastic tape and secure it with tape.

[0127] (3) Coating and drying:

[0128] a. Spread the paste-like coating evenly into the three cavities of the mold, with the first layer of coating being approximately 3mm thick. Place the mold at 50℃ and dry for 3 hours. If the sample has cracks after drying, touch up with the paste-like coating and then dry again.

[0129] b. After the sample is dried without cracks, apply a second coat of paint approximately 3 mm thick. Let it stand at room temperature for 10–15 minutes, then dry at 50°C for 3 hours. If cracks appear on the sample after drying, apply a paste-like paint to repair them and then dry again.

[0130] c. After the sample is dried without cracks, apply a third layer of coating slightly higher than the top plane of the mold, place it at room temperature for 10-15 minutes, and then dry it at 50℃ for 3 hours.

[0131] d. After the sample is dried, flatten the upper surface of the sample with a scraper, turn it over to check the bottom surface, repair any defects, and demold after drying at 50°C for 1 hour.

[0132] e. Test sample dimensions: width 22.36±0.2mm, thickness 11.18±0.2mm, length 70mm, no cracks.

[0133] Dry at 50℃ for more than 8 hours before testing. Samples not to be tested immediately should be stored in a desiccator until testing. Each group consists of three samples.

[0134] (4) Place two of the dried samples upright on the ceramic boat on the bottom plate of the high-temperature furnace (to facilitate heating of the lower side of the sample), add a door plug and close the furnace door.

[0135] (5) Set the heating curve of NBD-M1700-22TI box furnace: start heating from room temperature, increase the temperature by 10℃ per minute, and hold at 1300℃ for 1 hour (if not starting heating from room temperature, the holding time needs to be extended to 2 hours to ensure that the temperature of the center part of the sample is consistent with the surface temperature).

[0136] (6) Start the XQY-Ⅱ intelligent sand strength tester 10 minutes before the end of the heat preservation time, check and confirm that the tester is normal and test the room temperature bending strength of one sample.

[0137] (7) When the heat preservation time ends, immediately open the furnace door, use long-handled pliers to take out one of the test blocks, close the furnace door, and quickly place the red-hot sample on the support to start the test. The time from opening the furnace door to taking out the sample to the end of the test should not exceed 30 seconds, otherwise it will be considered invalid.

[0138] Test Example 4: Test of the coating pass rate of lost foam coating

[0139] N (usually N≥20, 20 in this test example) gearbox foam models (white models) to be coated were randomly selected. Coating was performed according to the same process parameters (flow rate 100–200 mm / s, immersion time 10–15 seconds). After coating, the models were allowed to stand for t minutes (t=2), and then visually inspected or tested using instruments under a standard light source.

[0140] Criteria for judging qualified parts (must be met simultaneously):

[0141] No exposed white: No part of the model surface has any visible exposure of the original foam color.

[0142] No dripping: No teardrop or curtain-like marks formed by paint flowing down on the vertical or inclined surfaces of the model;

[0143] No buildup: There is no excessive local thickness caused by abnormal paint buildup in complex structures such as the inner cavity, corners, and reinforcing ribs of the model.

[0144] Calculation formula: Coating pass rate (%) = Number of models that meet the above standards / Total number of models participating in the test × 100%.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lost foam coating for gearbox castings that prevents whitening, characterized in that, The raw materials of the lost foam coating include aggregates, acrylate-based hydrophobic modified alkali-swellable emulsions, and fatty alcohol polyoxyethylene ethers. The total content of quartz sand and quartz powder in the aggregates is 85-92 wt%, the content of the acrylate-based hydrophobic modified alkali-swellable emulsions is 0.2-0.8 wt%, and the mass ratio of the acrylate-based hydrophobic modified alkali-swellable emulsions to the fatty alcohol polyoxyethylene ethers is 0.6-8:

1. The aggregates also include asphalt powder and modified starch. The mass ratio of the asphalt powder to the acrylate-based hydrophobic modified alkali-swellable emulsions is 3.7-35:1, and the mass ratio of the modified starch to the acrylate-based hydrophobic modified alkali-swellable emulsions is 0.1-1.6:

1.

2. The anti-whitening lost foam coating for gearbox castings according to claim 1, characterized in that, The raw materials also include a binder, the content of which is 2 to 4 wt% of the aggregate, and the binder is composed of sodium silicate and polyvinyl alcohol in a mass ratio of 1.5 to 6:

1.

3. The anti-whitening lost foam coating for gearbox castings according to claim 2, characterized in that, The raw materials also include an interface reinforcing agent or a rheology modifier, wherein the content of the interface reinforcing agent is 0.05 to 0.3 wt% of the aggregate, and the content of the rheology modifier is 0.05 to 0.2 wt% of the aggregate.

4. The anti-whitening lost foam coating for gearbox castings according to claim 1, characterized in that, The quartz sand has a particle size of 100-140 mesh, the quartz powder has a particle size of 200-300 mesh, and the mass ratio of the quartz sand to the quartz powder is 1-2:

1.

5. The anti-whitening lost foam coating for gearbox castings according to claim 2, characterized in that, The aggregate also includes kaolin, the particle size of which is 300-350 mesh, and its content is 5-8 wt% of the aggregate.

6. The anti-whitening lost foam coating for gearbox castings according to claim 5, characterized in that, The raw materials also include calcium lignosulfonate and carboxymethyl cellulose, wherein the content of calcium lignosulfonate is 0.2 to 0.5 wt% of the aggregate, and the content of carboxymethyl cellulose is 0.05 to 0.15 wt% of the aggregate.

7. The anti-whitening lost foam coating for gearbox castings according to claim 6, characterized in that, The raw materials include the following parts by weight: 50-60 parts of quartz sand, 35-42 parts of quartz powder, 5-8 parts of kaolin, 3-7 parts of asphalt powder, 0.2-0.8 parts of acrylate hydrophobic modified alkali-swellable emulsion, 0.1-0.3 parts of fatty alcohol polyoxyethylene ether, 0.5-1.5 parts of modified starch, 1.5-3.0 parts of sodium silicate, 0.5-1.0 parts of polyvinyl alcohol, 0.2-0.5 parts of calcium lignosulfonate, and 0.05-0.15 parts of carboxymethyl cellulose.

8. The method for preparing the anti-whitening lost foam coating for gearbox castings according to any one of claims 1 to 7, characterized in that, The process includes the following steps: first, dissolve the fatty alcohol polyoxyethylene ether and calcium lignosulfonate in water, adjust the pH to 9-10, and then add other raw materials and mix them evenly.

9. The application of the anti-whitening lost foam coating for gearbox castings as described in any one of claims 1 to 7, or the lost foam coating prepared by the method described in claim 8, in the casting of gearbox castings.

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