A universal lost foam coating for cast steel and cast iron and a preparation method and application thereof

Abstract

The application provides a universal lost foam coating for cast steel and cast iron and a preparation method and application thereof, and relates to the technical field of lost foam casting. Raw materials of the lost foam coating include quartz powder, kaolin and iron liquid nodularizing slag micro powder, the iron liquid nodularizing slag micro powder is obtained by calcining treatment of iron liquid nodularizing slag, and the iron liquid nodularizing slag is obtained by nodularizing and slagging treatment of iron liquid in a nodular cast iron process; the mass percentage of the iron liquid nodularizing slag micro powder in the raw materials is 4-17%, the mass ratio of the quartz powder to the iron liquid nodularizing slag micro powder is 4-16:1, and the mass ratio of the kaolin to the iron liquid nodularizing slag micro powder is 0.6-3:1. The lost foam coating has suitable air permeability, high crack resistance and bending strength in a wide temperature range, can be simultaneously applied to cast iron and cast steel, realizes universal design of the coating, and reduces production cost while improving resource recycling rate.

Description

A general-purpose lost foam coating for cast steel and cast iron, its preparation method and application Technical Field

[0001] This invention relates to the field of lost foam casting technology, and in particular to a general-purpose lost foam coating for cast steel and cast iron, its preparation method, and its application. Background Technology

[0002] Lost foam casting is a novel casting method. Compared to sand casting, it offers advantages such as lower production costs, more flexible design, and cleaner production, making it widely used in the production of complex castings. Lost foam coatings play a crucial role in the lost foam casting process, preventing mechanical and thermochemical sand adhesion to the castings, increasing the rigidity of the foam model, preventing deformation during embedding, and facilitating the rapid release of thermal decomposition gases from the lost foam model.

[0003] However, for foundries that handle both cast iron and cast steel orders, the selection and management of lost foam coatings presents a significant challenge. Cast iron (especially ductile iron) coatings typically require the addition of graphite to utilize its high-temperature lubricity and resistance to molten iron wetting; while cast steel coatings strictly prohibit the use of graphite to prevent surface carburization, and instead primarily employ light-colored aggregates such as quartz sand and bauxite. Because the two are not interchangeable, existing technology lacks a universal lost foam coating suitable for both cast iron and cast steel. This necessitates two independent coating systems on the production line, which can easily lead to material mixing and batch quality incidents such as carburization in cast steel parts or sand adhesion in cast iron parts.

[0004] In addition, traditional graphite coatings for cast iron also suffer from serious workshop pollution and black, dirty cleaning. Although there are graphite-free "white coatings" on the market, most of them improve performance by adding expensive mullite and zircon powder, which is costly. Moreover, under the significantly different casting temperatures of cast iron (about 1350~1450℃) and cast steel (about 1500~1600℃), it is difficult to achieve both good permeability and high crack resistance and flexural strength.

[0005] The slag from the spheroidizing treatment of molten iron in ductile iron production (mainly composed of SiO2-MgO-CaO-RE2O3 and desulfurization products) is usually stored as solid waste, and the rare earth resources contained therein have not been effectively utilized.

[0006] Therefore, there is an urgent need to develop a lost foam coating that combines low cost, environmental friendliness, and versatility. Summary of the Invention

[0007] This invention provides a general-purpose lost foam coating for cast steel and cast iron, its preparation method, and its application, in order to solve the above-mentioned problems existing in the prior art.

[0008] In a first aspect, the present invention provides a general-purpose lost foam coating for cast steel and cast iron. The raw materials of the lost foam coating include quartz powder, kaolin, and slag powder for molten iron spheroidizing treatment. The slag powder for molten iron spheroidizing treatment is obtained by calcining slag for molten iron spheroidizing treatment. The slag for molten iron spheroidizing treatment is obtained by spheroidizing and removing slag from molten iron in the ductile iron casting process.

[0009] The raw materials contain 4-17% by mass of slag powder from molten iron spheroidization treatment, the mass ratio of quartz powder to slag powder from molten iron spheroidization treatment is 4-16:1, and the mass ratio of kaolin to slag powder from molten iron spheroidization treatment is 0.6-3:1.

[0010] The universal lost foam coating for cast steel and cast iron of this invention uses spheroidizing slag powder from calcined molten iron as raw material, combined with aggregates (quartz powder and kaolin) in a specific mass ratio, to construct a synergistic reaction system of "waste slag powder-quartz matrix". This effectively replaces the anti-wetting effect of graphite at high temperatures, allowing the coating to adaptively form a dense and tough sintered layer within a wide temperature range (1350-1600℃). This not only makes the coating applicable to both cast iron and cast steel, effectively avoiding batch quality accidents caused by mixing of coatings for cast steel and cast iron, leading to carburization of cast steel parts or sand adhesion in cast iron parts, but also improves the coating's anti-sand adhesion, air permeability, flexural strength, and crack resistance over a wide temperature range. At the same time, it also improves the resource utilization rate of spheroidizing slag from molten iron, reducing costs and environmental pollution.

[0011] Furthermore, rare earth magnesium-silicon-iron alloy spheroidizing agents, such as FeSiMg8RE5, are preferred when spheroidizing molten iron.

[0012] Furthermore, the slag powder from the molten iron spheroidization treatment comprises, by mass percentage: 40-55% SiO2, 8-17% MgO, 10-20% CaO, 5-10% Al2O3, 5-10% FeO / Fe2O3, and 1-3% REO (rare earth oxides), wherein the REO is Ce2O3 and / or La2O3.

[0013] This invention has found that when the mass percentage of REO in the slag powder from molten iron spheroidization treatment is 1-3%, the crack resistance and flexural strength of the coating at high temperatures can be improved.

[0014] Preferably, the mass percentage of REO in the slag powder from the molten iron spheroidization treatment is 1.5-3%.

[0015] In the above scheme, the mechanism of action of the slag in the molten iron spheroidization treatment is as follows:

[0016] CaO in the slag from the spheroidizing treatment of molten iron reacts with SiO2 and Al2O3 in the aggregates (quartz sand and kaolin) at a high temperature of 1350~1450℃ to form a low-melting-point calcium feldspar liquid phase. SiO2 in the aggregates (quartz sand and kaolin) reacts with FeO in the slag to form a low-melting-point fir olivine. These compounds and the resulting eutectic are the basis for achieving wide-temperature-range glazing. At the casting temperature of cast iron, an active liquid phase with good wettability is generated, forming the initial liquid phase. This initial liquid phase effectively wets and encapsulates quartz particles, fills the pores of the coating, promotes the initial densification and glazing of the coating, and forms a preliminary dense glaze layer at a relatively low temperature. This effectively blocks the penetration of molten iron (especially cast iron), prevents sand adhesion, and improves the coating's anti-sand adhesion properties.

[0017] When the temperature rises to the casting range of cast steel (1500–1600℃), rare earth oxides (REO) in the slag from the spheroidizing treatment of molten iron begin to play a crucial role. 3+ With its large ionic radius and high electric field strength, it can reduce the viscosity and surface tension of silicate melt, promote the flow and spreading of the liquid phase, and achieve secondary deep glazing of the coating.

[0018] Simultaneously, kaolin and quartz powder react at high temperatures to form the mullite phase (3Al2O3·2SiO2). Rare earth oxides (REO) in the slag powder from the spheroidizing treatment of molten iron act as highly efficient mineralizers, significantly reducing the activation energy of this reaction and promoting the large-scale, rapid in-situ formation of mullite over a wider temperature range (starting from cast iron temperature). Rare earth ions also strongly inhibit mullite grain coarsening, guiding it to form an interwoven fine-grained network, significantly promoting low-temperature mullite formation and grain refinement. This fundamentally enhances the ceramic skeleton strength of the coating, enabling the coating to achieve stronger ceramic bonding strength at higher temperatures, thus meeting the high-temperature requirements of cast steel.

[0019] Rare earth oxides (REO, taking Ce2O3 as an example) in the slag powder from spheroidizing treatment of molten iron can dissolve into the mullite (3Al2O3·2SiO2) lattice at high temperatures (1500–1600℃). 3+ Partially replaces Al 3+ The site causes lattice distortion, which can pin grain boundaries and inhibit grain coarsening, thereby improving the thermal stability and high-temperature bending strength of the coating in cast steel.

[0020] Rare earth elements (RE) in the slag powder from the spheroidizing treatment of molten iron react with harmful impurities (such as S and P) that segregate from the molten metal or coating to the grain boundaries, generating high-melting-point stable compounds. This reaction promotes the transformation of harmful impurities such as low-melting-point sulfides and phosphorus eutectics that embrittle the grain boundaries into high-melting-point, highly stable compounds (such as Ce2O2S and LaPO4), achieving deep purification of the ceramic phase grain boundaries and fundamentally eliminating the source of brittle fracture. The synergistic effect of grain boundary purification and grain boundary strengthening significantly improves the high-temperature creep resistance, toughness, and thermal shock stability of the coating, enhancing its crack resistance when subjected to the intense thermal cycling caused by alternating production of cast iron and cast steel.

[0021] Furthermore, the small amount of residual metallic iron particles or FeO / Fe2O3 contained in the slag powder from the spheroidizing treatment of molten iron can undergo a reduction reaction at high temperatures with carbonaceous impurities in the coating (from the pyrolysis of the binder) or with carbon diffused from the interface of the cast iron parts, generating trace amounts of CO gas. This CO gas can form dispersed micron-sized closed pores during coating application. These pores complement and synergize with the main pore network formed by aggregate accumulation, serving as thermal stress buffers and auxiliary venting channels, enabling the coating to adapt to different alloy systems and pouring temperatures, thus improving permeability.

[0022] Furthermore, the particle size of the slag powder from the molten iron spheroidization treatment is 200–325 mesh, and / or the calcination temperature is 900–1000℃, and the calcination time is 2–3 hours. Calcination treatment can effectively remove residual carbon and sulfur and stabilize the phase, reducing the risk of carburization and cracking.

[0023] Preferably, the particle size of the slag powder from the molten iron spheroidization treatment is 325 mesh.

[0024] Further, the quartz powder comprises coarse quartz powder and fine quartz powder in a mass ratio of 1:2 to 3, wherein the coarse quartz powder has a particle size of 100 to 140 mesh and the fine quartz powder has a particle size of 200 to 300 mesh; and / or, the kaolin has a particle size of 300 to 350 mesh.

[0025] By controlling the particle size of quartz powder, kaolin, and slag powder from molten iron spheroidization treatment within the above-mentioned range, the densest packing can be achieved, which improves coating density and flexural strength while satisfying air permeability.

[0026] Preferably, the coarse quartz powder has a particle size of 100 mesh or 140 mesh, and the kaolin has a particle size of 325 mesh.

[0027] Furthermore, the raw materials also include a composite binder, wherein the mass ratio of the composite binder to the slag powder from the molten iron spheroidization treatment is 0.1 to 0.7:1; and / or, the composite binder is composed of silica sol and sodium carboxymethyl cellulose in a mass ratio of 4 to 15:1.

[0028] This invention has found that, in the system of this invention, a composite binder composed of silica sol and sodium carboxymethyl cellulose is used, and the mass ratio of the composite binder to the slag powder from the spheroidizing treatment of molten iron is controlled within the above-mentioned range. This effectively controls the CO content formed, keeping it within a suitable range. This effectively overcomes defects such as porosity, sand inclusion, carburization, and the inability to effectively discharge gasification products from the mold on the surface of the casting during casting. It can further improve air permeability, achieve better air permeability, and improve the application effect of the coating.

[0029] Furthermore, the raw materials also include one or more of lithium-based bentonite, water-reducing agents, and defoamers.

[0030] Furthermore, the lithium-based bentonite constitutes 0.8% to 2.1% of the raw material by mass.

[0031] And / or, the water-reducing agent is 0.08~0.3% by mass in the raw material;

[0032] And / or, the defoamer is 0.04 to 0.12% by mass in the raw material.

[0033] Further, the lost foam coating comprises the following raw materials in parts by weight: 70-80 parts quartz powder, 10-15 parts kaolin, 5-15 parts slag powder from molten iron spheroidization treatment, 1.0-1.8 parts lithium-based bentonite, 2.2-3.5 parts composite binder, 0.1-0.25 parts water-reducing agent, and 0.05-0.1 parts defoamer.

[0034] Preferably, the water-reducing agent can be a conventional water-reducing agent in the prior art, such as a polycarboxylate water-reducing agent.

[0035] Preferably, the defoamer can be a conventional defoamer in the prior art, such as an organosilicon.

[0036] In a second aspect, the present invention provides a method for preparing the above-mentioned general-purpose lost foam coating for cast steel and cast iron, comprising the following steps: dissolving the raw materials in water at a mass ratio of raw materials to water of 1:0.45 to 0.55.

[0037] A third aspect of the present invention provides the application of the above-described general-purpose lost foam coating for cast steel and cast iron, or the general-purpose lost foam coating for cast steel and cast iron prepared by the above-described preparation method, in cast iron and / or cast steel.

[0038] The beneficial effects of the universal lost foam coating for cast steel and cast iron, its preparation method, and its application provided by this invention are as follows: This invention uses spheroidized slag powder from calcined molten iron as raw material, combined with aggregates (quartz powder and kaolin) in a specific mass ratio, to construct a synergistic reaction system of "waste slag powder-quartz matrix". This effectively replaces the anti-wetting effect of graphite at high temperatures. The coating exhibits good anti-sand adhesion, suitable air permeability, and high crack resistance and flexural strength over a wide temperature range. It can be applied to both cast iron and cast steel, realizing the universal design of the coating, reducing production costs while improving the recycling rate of resources. 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 shows the test results of the high-temperature crack resistance of the lost foam coatings in Examples 1-5.

[0041] Figure 2 shows the test results of the high-temperature crack resistance of the lost foam coatings of Examples 1 to 4.

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

[0043] Figure 4 shows the test results of the high-temperature flexural strength of the lost foam coatings in Examples 1 to 4. 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] The following are the raw material information used in the examples and comparative examples:

[0047] Polycarboxylate superplasticizer: Commercially available polycarboxylate dispersants suitable for water-based casting coatings can be used, such as BASF MasterCast series;

[0048] Silicone defoamer: Evonik TEGO Foamex 810.

[0049] The slag from the spheroidizing treatment of molten iron in the following examples and comparative examples is obtained by spheroidizing and slag removal of molten iron in the ductile iron casting process. Rare earth magnesium silicon iron alloy spheroidizing agent is used when spheroidizing molten iron.

[0050] Example 1

[0051] A general-purpose lost foam coating for cast steel and cast iron comprises the following raw materials in parts by weight: 50 parts coarse quartz powder (140 mesh), 25 parts fine quartz powder (200 mesh), 12 parts kaolin (325 mesh), 13 parts slag powder from molten iron spheroidizing treatment (300 mesh, REO content 2.1%), 1.5 parts lithium-based bentonite, 2.8 parts silica sol, 0.3 parts CMC (sodium carboxymethyl cellulose), 0.18 parts polycarboxylate superplasticizer, and 0.08 parts organosilicon defoamer.

[0052] This embodiment also provides a method for preparing the above-mentioned lost foam coating, the steps of which are as follows: First, lithium-based bentonite is dispersed in water, then iron spheroidization treatment slag powder, coarse quartz powder, fine quartz powder, and kaolin are added, and finally silica sol, CMC, polycarboxylate superplasticizer, and organosilicon defoamer are added, and the mixture is stirred at high speed to ensure that all raw materials are fully dispersed. The mass ratio of raw materials to water is 1:0.5.

[0053] The slag powder from the spheroidizing treatment of molten iron comprises, by mass percentage: 50% SiO2, 16.9% MgO, 16% CaO, 7% Al2O3, 8% FeO, and 2.1% REO (rare earth oxides), wherein the REO is Ce2O3 and La2O3 in a mass ratio of 1:1.

[0054] The preparation method of the iron spheroidizing treatment slag powder includes: calcining the iron spheroidizing treatment slag at a temperature of 950℃ for 2.5h, and then pulverizing it to 300 mesh.

[0055] Example 2

[0056] A general-purpose lost foam coating for cast steel and cast iron comprises the following raw materials in parts by weight: 55 parts coarse quartz powder (140 mesh), 20 parts fine quartz powder (200 mesh), 10 parts kaolin (325 mesh), 15 parts slag powder from molten iron spheroidizing treatment (300 mesh, REO content 2.1%), 1.6 parts lithium-based bentonite, 2.4 parts silica sol, 0.7 parts CMC (sodium carboxymethyl cellulose), 0.25 parts polycarboxylate superplasticizer, and 0.1 parts organosilicon defoamer. Its preparation method is the same as in Example 1.

[0057] Example 3

[0058] A general-purpose lost foam coating for cast steel and cast iron comprises the following raw materials in parts by weight: 50 parts coarse quartz powder (140 mesh), 30 parts fine quartz powder (200 mesh), 10 parts kaolin (325 mesh), 10 parts slag powder from molten iron spheroidizing treatment (300 mesh, REO content 2.1%), 1.0 part lithium-based bentonite, 2.2 parts silica sol, 1 part CMC (sodium carboxymethyl cellulose), 0.1 part polycarboxylate superplasticizer, and 0.05 parts organosilicon defoamer. Its preparation method is the same as in Example 1.

[0059] Example 4

[0060] This embodiment is basically the same as embodiment 1, except that the mass percentage of REO in the slag powder from the molten iron spheroidization treatment is 1%.

[0061] Example 5

[0062] This embodiment is basically the same as embodiment 1, except that the mass percentage of REO in the slag powder from the molten iron spheroidization treatment is 3%.

[0063] Comparative Example 1

[0064] This comparative example is basically the same as Example 1, except that no iron spheroidization treatment slag powder is added.

[0065] Comparative Example 2

[0066] This comparative example is basically the same as Example 1, except that the weight of the slag powder from the spheroidizing treatment of molten iron is 21 parts.

[0067] Comparative Example 3

[0068] This comparative example is basically the same as Example 1, except that the mass percentage of REO in the slag powder from the molten iron spheroidization treatment is 0.5%.

[0069] Comparative Example 4

[0070] This comparative example is basically the same as Example 1, except that the mass percentage of REO in the slag powder from the molten iron spheroidization treatment is 5%.

[0071] This invention uses a universal lost foam coating for cast steel and cast iron to simultaneously produce a tractor differential housing (workpiece material is QT600-3 ductile iron, pouring temperature is 1380℃) and a cast steel bracket (ZG270-500, pouring temperature is 1560℃). The preparation steps of the differential housing and cast steel bracket are as follows: the lost foam coating is uniformly coated on the surface of the foam model with a coating thickness of 1.5mm. Then the model is placed in a 50℃ drying oven for 8 hours, followed by sand embedding and vacuum pouring, and cooling.

[0072] Meanwhile, the present invention also tested the high-temperature air permeability, high-temperature crack resistance, and high-temperature flexural strength of the general-purpose lost foam coatings for cast steel and cast iron prepared in the examples and comparative examples. The test results are shown in Tables 1-2 and Figures 1-4.

[0073] The results of the high-temperature air permeability of the lost foam coating are shown in Table 1:

[0074] Table 1. High-temperature air permeability of lost foam coatings prepared in the examples and comparative examples.

[0075]

[0076] As shown in Table 1, the high-temperature air permeability of the lost foam coatings corresponding to Examples 1-5 is significantly higher than that of Comparative Examples 1-4, indicating that the lost foam coating of the present invention has excellent high-temperature air permeability, meeting the requirements of cast steel and cast iron.

[0077] The results of the high-temperature crack resistance of the lost foam coating at 1500℃ are shown in Figures 1 and 2. As can be seen from Figures 1 and 2, the lost foam coatings corresponding to Examples 1-5 did not show cracks after high-temperature heating, but Comparative Examples 1-4 all showed cracks, especially Comparative Examples 1 and 2, where the cracks were larger. This indicates that the amount of slag powder used in the spheroidizing treatment of molten iron has a significant impact on the high-temperature crack resistance of the coating. The lost foam coating of this invention has excellent high-temperature crack resistance and can simultaneously meet the requirements of both cast steel and cast iron.

[0078] The results of the flexural strength of the lost foam coating at room temperature and high temperature of 1300℃ are shown in Table 2, Figure 3 and Figure 4.

[0079] Table 2. High-temperature flexural strength of the lost foam coatings prepared in the examples and comparative examples.

[0080]

[0081] As shown in Table 2, the high-temperature flexural strength of the lost foam coatings corresponding to Examples 1-5 at 1300℃ is all higher than 9.1 MPa, and also higher than that of Comparative Examples 1, 3, and 4. Compared with Example 1, the flexural strength of Comparative Example 2 is slightly lower than that of Example 1, indicating that excessive addition of slag powder from molten iron spheroidizing treatment can also affect the high-temperature flexural strength of the lost foam coating. The lost foam coating of the present invention has excellent high-temperature flexural strength, which can meet the requirements of both cast steel and cast iron.

[0082] In summary, the above results indicate that the lost foam coating of the present invention has excellent high-temperature permeability, high-temperature crack resistance and high-temperature flexural strength. Under the significantly different casting temperatures of cast iron and cast steel, it has excellent permeability, high crack resistance and high flexural strength, which can simultaneously meet the requirements of cast steel and cast iron.

[0083] The test methods for the high-temperature air permeability, high-temperature crack resistance, and high-temperature flexural strength of the lost foam coatings in the above embodiments and comparative examples are as follows:

[0084] Test Example 1: High-Temperature Air Permeability Test of Lost Foam Coating

[0085] 1. Tools: NBD-M1700-22TI box furnace, ZTY intelligent air permeability tester, 101-2BS electric constant temperature drying oven, stainless steel ring with inner diameter Φ50mm and thickness 1.80mm (two flat, non-warped surfaces free of oxide scale, adhesive and other foreign matter), stainless steel ring fixing base plate, stainless steel pressure ring, high temperature sleeve device.

[0086] 2. Test Procedure

[0087] (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.

[0088] (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.

[0089] (3) Applying coating:

[0090] 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.

[0091] 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, touch up with a paste-like coating and then dry again.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] (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).

[0096] (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.

[0097] 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, end the experiment at 850°C. The air permeability at 800°C is the standard. If cracking or warping and leakage occur before 800°C, a new sample must be prepared and tested.

[0098] Test Example 2: High-Temperature Crack Resistance Test of Lost Foam Coating

[0099] 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.

[0100] 2. Test Procedure

[0101] (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.

[0102] (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.

[0103] (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 1.50-1.80 mm.

[0104] (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.

[0105] (5) Heat the NBD-M1700-22TI box furnace to 1500℃ 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 1500℃ 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.

[0106] The crack grade for high-temperature crack resistance is evaluated according to the following criteria:

[0107] Level 1: The surface is smooth and without cracks, or has only very fine cracks;

[0108] Level 2: The surface has dendritic or net-like fine cracks, and the crack width is less than 0.5 mm;

[0109] 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.

[0110] 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.

[0111] Test Example 3: High-Temperature Flexural Strength Test of Lost Foam Coating

[0112] 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.

[0113] 2. Test Procedure

[0114] (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.

[0115] (2) Preparation of standard sample molds and base plates:

[0116] 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.

[0117] b. Apply plastic tape evenly, smoothly, and tightly to the flat surface of the base plate;

[0118] c. Place the standard sample mold firmly onto the base plate using plastic tape and secure it with tape.

[0119] (3) Coating and drying:

[0120] 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.

[0121] 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.

[0122] 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.

[0123] d. After the sample is dried, flatten the upper surface of the sample with a scraper, turn it over and check the bottom surface. If there are any defects, repair the defects and demold after drying at 50°C for 1 hour.

[0124] e. Test sample dimensions: width 22.36±0.2mm, thickness 11.18±0.2mm, length 70mm, no cracks.

[0125] 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.

[0126] (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.

[0127] (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).

[0128] (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.

[0129] (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.

[0130] 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 general-purpose lost foam coating for cast steel and cast iron, characterized in that, The raw materials for the lost foam coating include quartz powder, kaolin, and slag powder from molten iron spheroidizing treatment. The slag powder is obtained by calcining slag from molten iron spheroidizing treatment, which is produced during the ductile iron casting process by spheroidizing and removing slag from molten iron. The raw materials comprise 4-17% by mass of the slag powder, with a mass ratio of quartz powder to slag powder of 4-16:1, and a mass ratio of kaolin to slag powder of 0.6-3:

1. The slag powder, by mass percentage, comprises: 40-55% SiO2, 8-17% MgO, and 1% CaO. The composition is 10-20%, Al2O3 5-10%, FeO / Fe2O3 5-10%, and rare earth oxides 1-3%, wherein the rare earth oxides are Ce2O3 and / or La2O3; the particle size of the slag powder from the molten iron spheroidization treatment is 200-325 mesh; the calcination temperature is 900-1000℃; and the calcination time is 2-3 hours.

2. The universal lost foam coating for cast steel and cast iron according to claim 1, characterized in that, The quartz powder comprises coarse quartz powder and fine quartz powder in a mass ratio of 1:2 to 3, wherein the coarse quartz powder has a particle size of 100 to 140 mesh and the fine quartz powder has a particle size of 200 to 300 mesh; and / or, the kaolin has a particle size of 300 to 350 mesh.

3. The universal lost foam coating for cast steel and cast iron according to claim 1, characterized in that, The raw materials also include a composite binder, wherein the mass ratio of the composite binder to the slag powder from the molten iron spheroidization treatment is 0.1 to 0.7:1; and / or, the composite binder is composed of silica sol and sodium carboxymethyl cellulose in a mass ratio of 4 to 15:

1.

4. The universal lost foam coating for cast steel and cast iron according to claim 1, characterized in that, The raw materials also include one or more of lithium-based bentonite, water-reducing agents, and defoamers.

5. The universal lost foam coating for cast steel and cast iron according to claim 4, characterized in that, The lithium-based bentonite is present in the raw material at a mass percentage of 0.8-2.1%; and / or the water-reducing agent is present in the raw material at a mass percentage of 0.08-0.3%; and / or the defoamer is present in the raw material at a mass percentage of 0.04-0.12%.

6. The universal lost foam coating for cast steel and cast iron according to claim 1, characterized in that, The raw materials include the following parts by weight: 70-80 parts quartz powder, 10-15 parts kaolin, 5-15 parts slag powder from molten iron spheroidization treatment, 1.0-1.8 parts lithium-based bentonite, 2.2-3.5 parts composite binder, 0.1-0.25 parts water-reducing agent, and 0.05-0.1 parts defoamer.

7. The method for preparing the general-purpose lost foam coating for cast steel and cast iron according to any one of claims 1 to 6, characterized in that, The process includes the following steps: dissolving the raw material in water at a mass ratio of 1:0.45 to 0.

55.

8. The application of the general-purpose lost foam coating for cast steel and cast iron as described in any one of claims 1 to 6, or the lost foam coating prepared by the preparation method described in claim 7, in cast iron and / or cast steel.

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