Method for preparing a reinforcing coating for lost foam production of heat-resistant cast iron parts

Abstract

The application discloses a preparation method of reinforced coating for heat-resistant cast iron parts produced by an evaporative pattern casting method, and relates to the technical field of functional coating.The application discloses a preparation method of reinforced coating for heat-resistant cast iron parts produced by an evaporative pattern casting method, and comprises the following steps: a suspension agent is immersed and treated with part of a carrier liquid to obtain suspension agent slurry; the suspension agent slurry, refractory aggregate, binder, additive and modifier are ball milled into a paste state, and the remaining carrier liquid is stirred to obtain the reinforced coating; the modifier is composed of KH550 modified nano silicon nitride and core-shell particles with a mass ratio of 7-8:2-3.The coating prepared by the application has air permeability and anti-adhesion sand performance; moreover, the coating layer has the characteristics of high-temperature strength and good thermal shock resistance, and is suitable for the production requirements of high-precision, large-size heat-resistant cast iron parts.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of functional coating technology, in particular to a preparation method of reinforced coating for producing heat-resistant cast iron parts by lost foam casting. BACKGROUND

[0002] The lost foam casting technology is a casting method that a plastic foam model similar in size and shape to the casting is bonded and combined into a model cluster, a special coating for lost foam is brushed and dried, and then buried in dry sand and vibrated to compact the mold, a special sand box is connected to a vacuum device to extract vacuum, and the liquid metal is poured under the condition of maintaining a certain negative pressure in the casting mold, the model is gasified, the decomposition products escape through the coating / mold interface, the liquid metal occupies the position of the model, and the casting is formed after solidification and cooling. Under the action of negative pressure, the liquid metal can easily penetrate into the gap between the dry sand to form mechanical sand sticking. In order to avoid mechanical sand sticking, the surface of the lost foam pattern must be coated with a layer of refractory coating. Unlike general sand casting coating, the coating for lost foam casting is not coated on the mold cavity, but on the foam plastic. When the foam plastic model is replaced by liquid metal, the coating actually plays the role of the mold. A large amount of gas produced by thermal decomposition can only be discharged outside the mold through the gap between the dry sand. During the pouring process of the mold, this layer of refractory coating is between the metal liquid and the mold sand, and plays a very important role in the gasification of the lost foam pattern, the filling of the metal liquid and the formation of the casting.

[0003] Common cast iron and cast steel coatings are suitable for most ordinary cast iron and cast steel parts, but they have certain limitations for special materials, large size and complex shape products. For example, high chromium cast iron, heat-resistant steel, stainless steel and other castings, general coatings mostly use quartz sand as the basic aggregate, the refractoriness and chemical corrosion resistance of the coating are insufficient, and the resistance to high melting point metal liquid erosion and chemical reaction is weak; the coating layer is easily eroded and melted by the metal liquid, resulting in sand sticking and subsurface porosity on the surface of the casting. For large size castings such as heavy machine tool bed and large valve body, the coating prepared by general coating has concentrated shrinkage stress during drying, and the overall strength (room temperature strength and high temperature strength) is insufficient, the coating layer cracks during drying, and the metal liquid pressure easily breaks the cracks during pouring, causing the mold to collapse. For complex shape castings such as multi-cavity valve body and special-shaped pipe fittings, it is difficult for general coating to be uniform in deep cavity and narrow gap, and the balance between local permeability and strength is poor; the local coating layer is easily eroded by the metal liquid, and the thick coating layer is not easy to exhaust, resulting in fire choking and slag inclusion of the casting. The existing coating is difficult to adapt to the lost foam casting process under high precision, large size and high temperature environment. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of reinforced coating for producing heat-resistant cast iron parts by lost foam casting, which solves the following technical problems:

[0005] The conventional coating used in the lost foam casting process is difficult to adapt to large size, high precision and temperature resistance requirements.

[0006] The object of the present application can be achieved by the following technical solutions:

[0007] The preparation method of the reinforcing coating for producing heat-resistant cast iron parts by lost foam includes the following steps:

[0008] The suspending agent is infiltrated with part of the carrier liquid to obtain a suspending agent slurry;

[0009] The suspending agent slurry, refractory aggregate, binder, additive, and modifier are ball milled into a paste, and the remaining carrier liquid is stirred to obtain the reinforcing coating;

[0010] The modifier is composed of KH550 modified nano silicon nitride and core-shell particles;

[0011] The preparation method of the core-shell particles includes the following steps:

[0012] S1: Iron(II) chloride, iron(III) chloride, polyethylene glycol, and deionized water are added to a reaction bottle and dispersed, porous nano silicon dioxide is added, stirred at room temperature for 0.5-1h, ammonia water is added dropwise, the temperature is controlled at 60-70℃, and the reaction is incubated for 1-3h, then magnetic separation, washing, and drying are performed to obtain modified porous nano silicon dioxide;

[0013] S2: Zinc nitrate, hexamethylenetetramine, deionized water, and anhydrous ethanol are added to a reaction kettle and stirred and dispersed, modified porous nano silicon dioxide is added and ultrasonically dispersed, the temperature is controlled at 85-95℃, and the reaction is incubated for 3-4h, then solid-liquid separation, washing, and drying are performed to obtain core-shell particles.

[0014] As a further scheme of the present application: the ammonia water in S1 is 25wt%-28wt% ammonia water; the addition ratio of iron(II) chloride, iron(III) chloride, polyethylene glycol, deionized water, porous nano silicon dioxide, and ammonia water is 3-4g:6-9g:0.2-0.3g:200-400mL:10g:20-40mL;

[0015] The addition ratio of zinc nitrate, hexamethylenetetramine, deionized water, anhydrous ethanol, and modified porous nano silicon dioxide in S2 is 4-6g:2-3g:200-400mL:100-150mL:10g.

[0016] As a further scheme of the present application: the mass ratio of refractory aggregate: KH550 modified nano silicon nitride: core-shell particles is 100:1-2:4-6.

[0017] As a further scheme of the present application: the preparation method of the KH550 modified nano silicon nitride includes the following steps: 10g of nano silicon nitride and 100-150mL of ethyl acetate are added to a reaction kettle and dispersed, 3-6g of KH550 is added, reflux reaction is performed for 2-4h, centrifugation, washing, and drying are performed to obtain KH550 modified nano silicon nitride.

[0018] As a further scheme of the present application: the binder comprises silica sol, modified phenolic resin, sodium hexametaphosphate; the mass ratio of silica sol to refractory aggregate is 3-6:100; the mass ratio of modified phenolic resin to refractory aggregate is 1-2:100; the mass ratio of sodium hexametaphosphate to refractory aggregate is 0.5-1:100.

[0019] As a further scheme of the present application: the preparation method of silica sol comprises the following steps: 65-70 mL of deionized water, 3-5 g of ethanol, 2-3 g of 25wt%-28wt% ammonia water are added into a reaction kettle for dispersion, 25-30 g of tetraethyl orthosilicate is added dropwise under the condition of controlling the temperature at 30-35℃ and stirring, and then the stirring is continued for 2-3 h, the temperature is controlled at 40-45℃, and the reaction is continued for 0.5-1 h under the condition of stirring, 0.1-0.2 g of sodium hydroxide is added, and the stirring is continued for 15-45 min, and then filtration is performed to obtain silica sol.

[0020] As a further scheme of the present application: the preparation method of modified phenolic resin comprises the following steps: 45-50 g of molten phenol and 0.8-1.2 g of sodium hydroxide are added into a reaction kettle for stirring and dispersion, the temperature is controlled at 45-50℃, 35-40 g of 37wt%-40wt% formaldehyde aqueous solution is added dropwise, the temperature is controlled at 60-65℃, and the reaction is continued for 1-1.5 h, 10-15 g of cardanol and 0.3-0.5 g of triethanolamine are added, the temperature is controlled at 70-75℃, and the reaction is continued for 2-3 h under the condition of stirring, the temperature is controlled at 30-40℃, 5-8 mL of deionized water is added, and the reaction is continued for 0.5-1 h under the condition of stirring, and then suction filtration is performed to obtain modified phenolic resin.

[0021] As a further scheme of the present application: the suspending agent comprises sodium carboxymethyl cellulose, sodium bentonite, xanthan gum; the mass ratio of sodium carboxymethyl cellulose to refractory aggregate is 3-6:100; the mass ratio of sodium bentonite to refractory aggregate is 2-3:100; the mass ratio of xanthan gum to refractory aggregate is 0.2-0.5:100; the loading liquid added in the suspending agent slurry accounts for 30-35% of the total loading liquid in the reinforcing coating.

[0022] As a further scheme of the present application: the loading liquid is water; the refractory aggregate comprises bauxite clinker powder, zirconium powder, graphite powder, flaky graphite powder;

[0023] Each hundred mass parts of the refractory aggregate contains 60-65 parts of bauxite clinker powder, 25-30 parts of zirconium powder, 4.6-6.4 parts of graphite powder, and 3.2-4.2 parts of flaky graphite powder;

[0024] The mass ratio of the loading liquid to the refractory aggregate is 70-82.4:100.

[0025] As a further scheme of the present application: the auxiliary agent comprises a surfactant, a defoaming agent, an oxidizing agent, and a preservative; the mass ratio of the surfactant to the refractory aggregate is 0.2-0.4:100; the mass ratio of the defoaming agent to the refractory aggregate is 0.1-0.2:100; the mass ratio of the oxidizing agent to the refractory aggregate is 0.3-0.5:100; and the mass ratio of the preservative to the refractory aggregate is 0.1-0.2:100.

[0026] As a further scheme of the present application: the surfactant is one or more of polyoxyethylene alkyl alcohol ether, fatty alcohol polyoxyethylene ether, and sodium salt of succinic acid neo-fatty sulfonate, mixed in any ratio; the defoaming agent is one or more of n-octanol and n-pentanol, mixed in any ratio; the preservative is sodium benzoate; and the oxidizing agent is iron oxide.

[0027] The present application has the following beneficial effects:

[0028] (1) Fire resistance and erosion resistance

[0029] The present application uses bauxite clinker powder, zirconium powder, graphite powder, and flaky graphite powder to form the refractory aggregate; the bauxite clinker powder is used as the basic aggregate, has high refractoriness and good chemical stability, ensures the basic structural stability of the coating at high temperature, and resists the erosion of the metal liquid; the zirconium powder has low thermal expansion rate, can reduce the shrinkage stress of the coating during drying and pouring, reduce the cracking of the coating, and improve the sticking problem; the graphite powder and the flaky graphite powder synergistically enhance the high-temperature lubricity and the anti-metal penetration ability of the coating, prevent the oxidation of the iron liquid, and relieve the subsurface porosity defect. The present application also uses KH550 modified nano silicon nitride and core-shell particles, which not only strengthen the high-temperature strength, but also fill the gaps between the aggregates to improve the density of the coating, and the micro-pores formed can balance the air permeability and the strength, and give the coating the fire resistance, erosion resistance, and thermal shock resistance.

[0030] (2) Bonding and anti-cracking

[0031] The present application constructs an organic-inorganic bonding system, and adds silicon sol and modified phenolic resin in the coating to synergistically act; the silicon sol can firmly adhere the coating to the foam mold at room temperature, and the rigid structure formed by the silicon sol solidification at high temperature forms a Si-O-C composite structure with the residual carbon of the modified phenolic resin, and forms a low-temperature eutectic with Al2O3 and ZrO2 in the refractory aggregate, which significantly improves the high-temperature strength of the coating and avoids the collapse of the coating during pouring; the modified phenolic resin effectively enhances the bonding force at room temperature, slowly solidifies during drying, reduces the shrinkage stress concentration, and reduces the risk of cracking of the coating.

[0032] (3) Dispersion and coating hanging property

[0033] The application adds a suspending agent in the coating in cooperation with a surfactant, sodium carboxymethyl cellulose, xanthan gum and sodium bentonite effectively improve the thixotropy of the coating, solve the uneven coating problem of complex shape castings, adapt to the coating of complex shape castings, and adapt to deep cavities and narrow seams.

[0034] (4) Prevention and control of blowhole and sand sticking

[0035] After the pores of the porous silica inside the core-shell particles prepared by the application are filled with ferroferric oxide, the permeability of the coating can be improved, the gas generated by the gasification of the foam model can be efficiently discharged, and the blowhole defects of the castings can be solved; the surface-coated zinc hydroxide can enhance the bonding force between the coating and the refractory aggregate, and can form a stable isolation layer at high temperature to prevent the metal liquid from penetrating into the sand to cause sand sticking. In combination with modified nano silicon nitride, the high temperature strength and thermal shock resistance of the coating are targetedly improved. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0037] The preparation method of the KH550 modified nano silicon nitride in Example 1 includes the following steps:

[0038] 10 g of nano silicon nitride and 100 mL of ethyl acetate were added into a reaction kettle for dispersion, 3 g of KH550 was added, and reflux reaction was performed for 2 h. After centrifugation, washing and drying, the KH550 modified nano silicon nitride was obtained.

[0039] The preparation method of the silica sol includes the following steps:

[0040] 70 mL of deionized water, 5 g of ethanol and 3 g of 25wt% ammonia water were added into a reaction kettle for dispersion. 30 g of tetraethyl orthosilicate was added dropwise under the condition of controlling the temperature to 30℃ and stirring. After 3 h of heat preservation and stirring, the temperature was controlled to 45℃, and the reaction was performed under the condition of heat preservation and stirring for 1 h. 0.2 g of sodium hydroxide was added, and the stirring reaction was continued for 45 min. Filtration was performed to obtain the silica sol.

[0041] The preparation method of the modified phenolic resin in Example 2 includes the following steps:

[0042] Put 45 g of molten phenol, 0.8 g of sodium hydroxide into the reaction kettle and stir to disperse, control the temperature at 45℃, drop 35 g of 37wt%-40wt% formaldehyde aqueous solution, control the temperature at 60℃, keep the reaction for 1h, add 10 g of cardanol, 0.3 g of triethanolamine, control the temperature at 70℃, keep the reaction for 2h under stirring condition; control the temperature at 30℃, add 5 mL of deionized water, keep the reaction for 0.5h under stirring condition, and then filter to obtain the modified phenolic resin.

[0043] The preparation method of the core-shell particle comprises the following steps:

[0044] S1: Put 3 g of ferrous chloride, 6 g of ferric chloride, 0.2 g of polyethylene glycol (PEG-6000), 200 mL of deionized water into the reaction bottle and disperse, add 10 g of porous nanosilica, stir at room temperature for 0.5h, drop 20 mL of 25wt% ammonia water, control the temperature at 60℃, keep the reaction for 1h, and then separate, wash and dry by magnetic separation to obtain the modified porous nanosilica;

[0045] S2: Put 4 g of zinc nitrate, 2 g of hexamethylenetetramine, 200 mL of deionized water, 100 mL of anhydrous ethanol into the reaction kettle and stir to disperse, add 10 g of the modified porous nanosilica and ultrasonic dispersion, control the temperature at 85℃, keep the reaction for 3h, and then separate, wash and dry by solid-liquid separation to obtain the core-shell particle.

[0046] The preparation method of the modified phenolic resin comprises the following steps:

[0047] Put 47 g of molten phenol, 1 g of sodium hydroxide into the reaction kettle and stir to disperse, control the temperature at 45℃, drop 40 g of 37wt% formaldehyde aqueous solution, control the temperature at 60℃, keep the reaction for 1.5h, add 10 g of cardanol, 0.4 g of triethanolamine, control the temperature at 70℃, keep the reaction for 3h under stirring condition; control the temperature at 30℃, add 8 mL of deionized water, keep the reaction for 0.5h under stirring condition, and then filter to obtain the modified phenolic resin.

[0048] The preparation method of the core-shell particle comprises the following steps:

[0049] S1: Put 3 g of ferrous chloride, 6 g of ferric chloride, 0.2 g of polyethylene glycol (PEG-6000), 200 mL of deionized water into the reaction bottle and disperse, add 10 g of porous nanosilica, stir at room temperature for 0.5h, drop 20 mL of 25wt% ammonia water, control the temperature at 60℃, keep the reaction for 1h, and then separate, wash and dry by magnetic separation to obtain the modified porous nanosilica;

[0050] S2: 5 g of zinc nitrate, 2.5 g of hexamethylenetetramine, 300 mL of deionized water, 100 mL of anhydrous ethanol were added into a reaction kettle and stirred and dispersed, 10 g of modified porous nanosilica was ultrasonically dispersed, the temperature was controlled at 90℃, and the reaction was kept for 3.5 h, solid-liquid separation, washing, and drying were performed to obtain the core-shell particles.

[0051] Example 4 The preparation method of the modified phenolic resin comprises the following steps:

[0052] 50 g of molten phenol and 1.2 g of sodium hydroxide were added into a reaction kettle and stirred and dispersed, the temperature was controlled at 50℃, 40 g of 37wt% formaldehyde aqueous solution was added dropwise, the temperature was controlled at 65℃, and the reaction was kept for 1.5 h, 15 g of cardanol and 0.5 g of triethanolamine were added, the temperature was controlled at 75℃, and the reaction was kept for 3 h under stirring conditions, 8 mL of deionized water was added, the reaction was kept for 1 h under stirring conditions, and filtration was performed to obtain the modified phenolic resin.

[0053] The preparation method of the core-shell particles comprises the following steps:

[0054] S1: 4 g of ferrous chloride, 9 g of ferric chloride, 0.3 g of polyethylene glycol (PEG-6000), and 400 mL of deionized water were added into a reaction bottle and dispersed, 10 g of porous nanosilica was added, stirring was performed at room temperature for 1 h, 40 mL of 25wt% ammonia water was added dropwise, the temperature was controlled at 70℃, and the reaction was kept for 3 h, magnetic separation, washing, and drying were performed to obtain the modified porous nanosilica;

[0055] S2: 6 g of zinc nitrate, 3 g of hexamethylenetetramine, 400 mL of deionized water, and 150 mL of anhydrous ethanol were added into a reaction kettle and stirred and dispersed, 10 g of modified porous nanosilica was ultrasonically dispersed, the temperature was controlled at 95℃, and the reaction was kept for 4 h, solid-liquid separation, washing, and drying were performed to obtain the core-shell particles.

[0056] Example 5 The preparation method of the reinforced coating for producing heat-resistant cast iron parts by using the lost foam method comprises the following steps:

[0057] 4.4 g of sodium carboxymethyl cellulose, 2.1 g of sodium-based bentonite, 0.5 g of xanthan gum, and 25 g of water were treated by immersion to obtain a suspension slurry;

[0058] The suspension agent slurry, 63 g of bauxite clinker powder (400 mesh), 28 g of zirconium powder (500 mesh), 5.2 g of graphite powder (325 mesh), 3.8 g of flaky graphite powder (200 mesh), 4.5 g of the silica sol prepared in Example 1, 1.5 g of the modified phenolic resin prepared in Example 2, 0.8 g of sodium hexametaphosphate, 0.3 g of polyoxyethylene alkyl alcohol ether (PO-10), 0.2 g of n-octanol, 0.4 g of iron oxide, 0.1 g of sodium benzoate, 1.5 g of the KH550 modified nano silicon nitride prepared in Example 1, and 5 g of the core-shell particle prepared in Example 2 were ground into a paste, and 50 g of water was added and stirred to obtain a reinforcing coating.

[0059] Example 6 A method for preparing a reinforcing coating for heat-resistant cast iron parts produced by the lost foam process, comprising the following steps:

[0060] The suspension agent slurry was obtained by treating 4.4 g of sodium carboxymethyl cellulose, 2.1 g of sodium-based bentonite, and 0.5 g of xanthan gum with 25 g of water.

[0061] The suspension agent slurry, 63 g of bauxite clinker powder (400 mesh), 28 g of zirconium powder (500 mesh), 5.2 g of graphite powder (325 mesh), 3.8 g of flaky graphite powder (200 mesh), 4.5 g of the silica sol prepared in Example 1, 1.5 g of the modified phenolic resin prepared in Example 3, 0.8 g of sodium hexametaphosphate, 0.3 g of polyoxyethylene alkyl alcohol ether (PO-10), 0.2 g of n-octanol, 0.4 g of iron oxide, 0.1 g of sodium benzoate, 1.5 g of the KH550 modified nano silicon nitride prepared in Example 1, and 5 g of the core-shell particle prepared in Example 3 were ground into a paste, and 50 g of water was added and stirred to obtain a reinforcing coating.

[0062] Example 7 A method for preparing a reinforcing coating for heat-resistant cast iron parts produced by the lost foam process, comprising the following steps:

[0063] The suspension agent slurry was obtained by treating 4.4 g of sodium carboxymethyl cellulose, 2.1 g of sodium-based bentonite, and 0.5 g of xanthan gum with 25 g of water.

[0064] The suspension agent slurry, 63 g of bauxite clinker powder (400 mesh), 28 g of zirconium powder (500 mesh), 5.2 g of graphite powder (325 mesh), 3.8 g of flaky graphite powder (200 mesh), 4.5 g of the silica sol prepared in Example 1, 1.5 g of the modified phenolic resin prepared in Example 4, 0.8 g of sodium hexametaphosphate, 0.3 g of polyoxyethylene alkyl alcohol ether (PO-10), 0.2 g of n-octanol, 0.4 g of iron oxide, 0.1 g of sodium benzoate, 1.5 g of the KH550 modified nano silicon nitride prepared in Example 1, and 5 g of the core-shell particle prepared in Example 4 were ground into a paste, and 50 g of water was added and stirred to obtain a reinforcing coating.

[0065] Comparative Example 1 A method for preparing a core-shell particle, comprising the following steps:

[0066] Into the reaction kettle were added 5 g of zinc nitrate, 2.5 g of hexamethylenetetramine, 300 mL of deionized water, 100 mL of anhydrous ethanol, which were stirred and dispersed, 10 g of porous nanosilica was ultrasonically dispersed, the temperature was controlled at 90°C, and the reaction was kept for 3.5 h, solid-liquid separation, washing, and drying were performed to obtain the core-shell particles.

[0067] The preparation method of the core-shell particles of Comparative Example 2 comprises the following steps:

[0068] Into the reaction bottle were added 3 g of ferrous chloride, 8 g of ferric chloride, 0.3 g of polyethylene glycol (PEG-6000), 300 mL of deionized water, which were dispersed, 10 g of porous nanosilica was added, stirring was performed at room temperature for 0.5 h, 30 mL of 25wt% ammonia water was added dropwise, the temperature was controlled at 65°C, and the reaction was kept for 2 h, magnetic separation, washing, and drying were performed to obtain the core-shell particles.

[0069] Comparative Example 3, compared with Example 6, only the core-shell particles prepared in Example 3 added in Example 6 were replaced by an equal amount of the core-shell particles prepared in Comparative Example 1, and the remaining components and preparation method were completely consistent with Example 6.

[0070] Comparative Example 4, compared with Example 6, only the core-shell particles prepared in Example 3 added in Example 6 were replaced by an equal amount of the core-shell particles prepared in Comparative Example 2, and the remaining components and preparation method were completely consistent with Example 6.

[0071] Comparative Example 5, compared with Example 6, only the modified phenolic resin prepared in Example 1 added in Example 6 was deleted, and the remaining components and preparation method were completely consistent with Example 6.

[0072] Comparative Example 6, compared with Example 6, only the KH550 modified nanosilicon nitride prepared in Example 1 added in Example 6 was replaced by an equal amount of nanosilicon nitride, and the remaining components and preparation method were completely consistent with Example 6.

[0073] Performance detection

[0074] (1) Suspension stability: 100 mL of paint was poured into a measuring cylinder, sealed and left to stand for 24 h and 48 h, and the height of the supernatant and the height of the bottom sediment layer were measured respectively; the test results are shown in Table 1;

[0075] (2) Thixotropy detection: the viscosities (η1, η2) of the paint at rotational speeds of 6 r / min and 60 r / min were measured by a rotational viscometer, and the thixotropic index TI = η1 / η2 was calculated; the test results are shown in Table 1;

[0076] Table 1: Statistical table of paint stability detection data

[0077]

[0078] From Table 1, the coating prepared in the application has a 24h clear liquid height ≤5mL, and a precipitate layer height ≤3mL; it is shown that the suspended agent in the coating prepared in the application has effective synergistic effect, and the aggregate is avoided from agglomeration; the coating prepared in the application is high, which shows that the coating is thick when standing and thin when stirring, and is not easy to flow after coating, and the complex shape casting is not leaked, and the problem of uneven coating of the complex shape casting is solved, and the coating is suitable for the complex shape casting, and is suitable for deep cavity and narrow gap.

[0079] (3) Normal temperature bonding strength: the foam mold (size 50mmx50mmx10mm) is immersed in the coating, dried at 60℃ to constant weight (coating thickness 1.0mm), and the maximum pulling force of the coating from the surface of the foam mold is measured by using a pulling force testing machine to determine the bonding strength, and the detection results are shown in Table 2;

[0080] (4) High temperature residual compressive strength: the coating is made into a test block of Φ25mmx50mm, dried at 60℃, and then put into a muffle furnace, heated to 800℃, and kept for 1h, and then cooled to room temperature, and then the high temperature residual compressive strength is measured by using a compressive strength testing machine, and the detection results are shown in Table 2;

[0081] (5) Air permeability: the dried coating test block (thickness 1.0mm, area 50cm 2 ) is placed in the instrument, 0.02MPa pressure is applied, the air flow through the test block per unit time is measured, and the detection results are shown in Table 2;

[0082] Table 2: Statistics table of coating layer physical and chemical performance detection data

[0083]

[0084] From Table 2, the organic-inorganic synergistic bonding in the coating prepared in the application is effective, and the coating layer is firmly attached. The modified nano silicon nitride added in the coating has a high temperature strengthening effect, and the skeleton formed by the solidification of the silica sol is effective, the coating layer does not collapse and crack at high temperature, and can resist the pressure of the metal liquid. The core-shell particles added in the coating of the application construct an effective air guide channel, which does not sacrifice the density of the coating layer, and can quickly discharge the generated gas to reduce the casting porosity defect.

[0085] (6) Fire resistance and erosion resistance: the dried coating test block (20mmx20mmx5mm) is put into a muffle furnace, heated to 1450℃ (heat-resistant cast iron pouring temperature), kept for 30min, and then cooled to observe whether the test block is molten, cracked or powdered; the coating is coated on the inner wall of a graphite crucible (thickness 1.0mm), dried, and then poured into 1450℃ heat-resistant cast iron liquid, kept for 10min, and then cooled to observe the wetting condition of the coating and the metal liquid, and measure the erosion layer thickness, and the detection results are shown in Table 3;

[0086] (7) Drying shrinkage: The paint was coated on the surface of a foam mold with a size of 100mmx100mmx5mm, the wet film thickness (h1) was measured, the dry film thickness (h2) was measured after drying at 60℃ for 8h, and the drying shrinkage = (h1-h2) / h1x100% was calculated. The test results are shown in Table 3;

[0087] (8) Sand sticking rate: The area of defects such as sand sticking, pitting, pinhole and the like on the surface of the casting was recorded, and the sand sticking rate = (sand sticking defect area / casting total surface area)x100% was calculated. The test results are shown in Table 3;

[0088] (9) Surface roughness: The surface roughness of the casting was measured by a surface roughness meter. The test results are shown in Table 3;

[0089] Table 3: Casting coating and casting performance test data statistics table

[0090]

[0091] As shown in Table 3, the refractory aggregate, modified nano silicon nitride and core-shell particles in the paint prepared by the application synergistically build an effective refractory system to isolate the metal liquid and meet the demand for corrosion resistance of heat-resistant cast iron parts. The low shrinkage property of the modified phenolic resin and the low expansion coefficient of the zirconium powder are synergistically effective, and the stress concentration is small during drying of the coating, so that there is no risk of cracking of large-size castings. The paint prepared by the application is used as a reinforcing coating to coat the surface of a foam mold, and has excellent sand sticking resistance, and the surface quality of the prepared casting is good, and the subsequent processing amount is reduced.

[0092] The above describes one embodiment of the application in detail, but the content described is only a preferred embodiment of the application and cannot be considered as limiting the scope of the implementation of the application. Any equivalent changes and improvements made in the scope of the application should still belong to the patent coverage of the application.

Claims

1. A method for preparing reinforcing coatings for lost foam casting of heat-resistant cast iron parts, characterized in that, Includes the following steps: The suspending agent is wetted with a portion of the carrier liquid to obtain a slurry of suspending agent; The slurry, refractory aggregate, binder, additives, and modifier are ball-milled into a paste, and the remaining carrier liquid is added and stirred to obtain the reinforced coating. The modifier is composed of KH550 modified nano-silicon nitride and core-shell particles; The preparation method of core-shell particles includes the following steps: S1: Add ferrous chloride, ferric chloride, polyethylene glycol and deionized water to a reaction flask and disperse them. Add porous nano-silica and stir at room temperature for 0.5-1h. Add ammonia dropwise and control the temperature at 60-70℃. Keep the reaction at this temperature for 1-3h. Separate by magnetic separation, wash and dry to obtain modified porous nano-silica. S2: Add zinc nitrate, hexamethylenetetramine, deionized water, and anhydrous ethanol to a reaction vessel and stir to disperse. Add modified porous nano-silica and disperse by ultrasonication. Control the temperature at 85-95℃ and keep the reaction at this temperature for 3-4 hours. Separate the solid and liquid, wash, and dry to obtain core-shell particles.

2. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 1, characterized in that, S1 contains 25wt%-28wt% ammonia; the addition ratio of ferrous chloride, ferric chloride, polyethylene glycol, deionized water, porous nano silica, and ammonia is 3-4g: 6-9g: 0.2-0.3g: 200-400mL: 10g: 20-40mL. The addition ratio of zinc nitrate, hexamethylenetetramine, deionized water, anhydrous ethanol, and modified porous nano-silica in S2 is 4-6g: 2-3g: 200-400mL: 100-150mL: 10g.

3. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 1, characterized in that, The refractory aggregate, KH550 modified nano-silicon nitride, has a core-shell particle mass ratio of 100:1-2:4-6.

4. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 1, characterized in that, The binder includes silica sol, modified phenolic resin, and sodium hexametaphosphate; the mass ratio of silica sol to refractory aggregate is 3-6:100; the mass ratio of modified phenolic resin to refractory aggregate is 1-2:100; and the mass ratio of sodium hexametaphosphate to refractory aggregate is 0.5-1:

100.

5. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 4, characterized in that, The preparation method of the silica sol includes the following steps: 65-70 mL of deionized water, 3-5 g of ethanol, and 2-3 g of 25 wt%-28 wt% ammonia water are added to a reaction vessel and dispersed. Under the control of temperature 30-35℃ and stirring, 25-30 g of tetraethyl orthosilicate is added dropwise. The mixture is kept warm and stirred for 2-3 h. Under the control of temperature 40-45℃ and stirring, the reaction is kept warm for 0.5-1 h. 0.1-0.2 g of sodium hydroxide is added, and the reaction is continued to be stirred for 15-45 min. The mixture is then filtered to obtain the silica sol.

6. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 4, characterized in that, The preparation method of the modified phenolic resin includes the following steps: 45-50g of molten phenol and 0.8-1.2g of sodium hydroxide are added to a reaction vessel and stirred and dispersed. The temperature is controlled at 45-50℃. 35-40g of 37wt%-40wt% formaldehyde aqueous solution is added dropwise. The temperature is controlled at 60-65℃ and the reaction is maintained at this temperature for 1-1.5h. 10-15g of cashew nut shell powder and 0.3-0.5g of triethanolamine are added. The temperature is controlled at 70-75℃ and the reaction is maintained at this temperature for 2-3h under stirring. The temperature is controlled at 30-40℃. 5-8mL of deionized water is added and the reaction is maintained at this temperature for 0.5-1h under stirring. The mixture is then filtered to obtain the modified phenolic resin.

7. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 1, characterized in that, The suspending agent includes sodium carboxymethyl cellulose, sodium bentonite, and xanthan gum; the mass ratio of sodium carboxymethyl cellulose to refractory aggregate is 3-6:100; the mass ratio of sodium bentonite to refractory aggregate is 2-3:100; the mass ratio of xanthan gum to refractory aggregate is 0.2-0.5:100; the carrier liquid added to the suspending agent slurry accounts for 30-35% of the total carrier liquid in the reinforcing coating.

8. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 1, characterized in that, The carrier liquid is water; the refractory aggregate includes bauxite clinker powder, zircon powder, graphite powder, and flake graphite powder. Each 100 parts by weight of refractory aggregate contains 60-65 parts of bauxite clinker powder, 25-30 parts of zircon powder, 4.6-6.4 parts of graphite powder, and 3.2-4.2 parts of flake graphite powder. The mass ratio of the carrier liquid to the refractory aggregate is 70-82.4:

100.

9. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 1, characterized in that, The additives include surfactants, defoamers, oxidants, and preservatives; the mass ratio of the surfactant to the refractory aggregate is 0.2-0.4:100; the mass ratio of the defoamer to the refractory aggregate is 0.1-0.2:100; the mass ratio of the oxidant to the refractory aggregate is 0.3-0.5:100; and the mass ratio of the preservative to the refractory aggregate is 0.1-0.2:

100.

10. The method for preparing the reinforcing coating for lost foam casting of heat-resistant cast iron parts according to claim 9, characterized in that, The surfactant is one or more of polyoxyethylene alkyl alcohol ether, fatty alcohol polyoxyethylene ether, and sodium succinate sodium salt mixed in any proportion; the defoamer is one or more of n-octanol and n-pentanol mixed in any proportion; the preservative is sodium benzoate; and the oxidant is iron oxide.

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