CN115477532B

CN115477532B - Preparation method of water-soluble precise ceramic core for casting aluminum alloy

Info

Publication number: CN115477532B
Application number: CN202211249829.6A
Authority: CN
Inventors: 李艳磊; 赵龙; 吴国; 张军; 胡继群; 梁长刘
Original assignee: Shanghai Tobacco Machinery Xinchang Foundry Co ltd
Current assignee: Shanghai Tobacco Machinery Xinchang Foundry Co ltd
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2023-04-25
Anticipated expiration: 2042-10-12
Also published as: CN115477532A

Abstract

The application discloses a preparation method of a water-soluble precise ceramic core for casting aluminum alloy, which belongs to the technical field of aluminum alloy casting and comprises the following steps: 1) Preparing corundum glue solution; 2) Preparing phenolic resin; 3) Preparing a GO mixture; 4) Preparing a gel core; 5) Preparing a casting core; 6) Preparing collapsibility powder; 7) And recycling the dispersed powder. Aiming at the problems that the strength of a wet type core formed by the existing inorganic binder or organic binder is low, and the pouring strength is insufficient due to the fact that the hygroscopicity is too strong after sintering, the application constructs the novel inorganic-organic composite gel core which has high bending strength and low hygroscopicity, can be stored for a long time, is overlapped with the pouring temperature rising process of an aluminum alloy casting in the sintering carbonization process, and thoroughly avoids the risk of low strength of the existing core after moisture absorption; the pouring core of this application intensity is higher and easily collapss, and collapsibility powder can be according to the direct recycle of carbon residue volume, and the cost is lower.

Description

Preparation method of water-soluble precise ceramic core for casting aluminum alloy

Technical Field

The application relates to the technical field of aluminum alloy casting, in particular to a preparation method of a water-soluble precise ceramic core for casting aluminum alloy.

Background

With the rapid development of industry, the requirement of the high-precision industrial age is far from being met by a mode of preparing complex and precise workpieces through the combined assembly of traditional simple parts or the material reduction processing of a base material. For aluminum alloy materials, if complex inner cavity or pore canal structures are to be formed, the mold core is required to have higher performance, and the mold core is required to be conveniently demolded in a later period, so that the water-soluble ceramic mold core is generated.

The water-soluble ceramic core has the advantages that after the aluminum alloy casting product is molded, the core can be cleaned only by washing or soaking with water, the hole digging treatment is not needed in the casting cavity, the operation is simple, and the demolding process has no damage to the casting structure; therefore, the application of the water-soluble ceramic core is more and more extensive, and especially, the development of various easily collapsible cores provides an alternative scheme for aluminum alloy components with various complex structures.

However, the following problems still remain with water-soluble ceramic cores: firstly, the intensity of the molded core is lower, secondly, the core is easy to absorb moisture in the air, and the intensity of the core is greatly influenced before casting, so that the requirement in the production of high-precision complex aluminum alloy castings can not be met.

Disclosure of Invention

In order to improve the molding strength of the existing water-soluble ceramic core and reduce the problem of the hygroscopicity of the molded water-soluble ceramic core, the application provides a preparation method of the water-soluble precise ceramic core for casting aluminum alloy.

The technical scheme is as follows:

the preparation method of the water-soluble precise ceramic core for casting the aluminum alloy comprises the following steps:

1) Preparation of corundum glue solution: sieving corundum powder with 700 mesh sieve to obtain large-grain corundum and small-grain corundum, and passing through Al (OH) ₃ And H ₃ PO ₄ The alumina gel solution is prepared by reaction, large-grain corundum is put into the alumina gel solution, and corundum gel solution is obtained after homogenizing and stirring;

2) Preparation of phenolic resin: under stirring, phenol and formaldehyde form a reaction monomer solution, concentrated sulfuric acid and phosphoric acid are prepared into mixed acid, the mixed acid is dripped at room temperature, and the mixed acid is heated, stirred and subjected to reflux reaction, so that a viscous phenolic aldehyde reaction system is obtained;

naturally cooling a phenolic reaction system, standing and aging for 1-2 h, taking supernatant to obtain a solution phase, obtaining a gel phase of a lower viscous colloid, and distilling the gel phase under reduced pressure to obtain viscous phenolic resin;

3) Preparation of GO mixture: GO powder and AlCl ₃ Mixing with 98% concentrated sulfuric acid, homogenizing and stirring to obtain GO dispersion;

Adding GO dispersion liquid into small-grain corundum, forming viscous colloid through a colloid mill made of ceramic materials, pouring solution phase until the viscous colloid is completely disintegrated, pouring the colloid mill middle system into a heating container, stirring and reacting to obtain a suspension viscous system, and standing to remove upper clear solution to obtain a viscous GO mixture;

4) Preparation of gel core: mixing corundum glue solution, GO mixture, phenolic resin, carbon powder and curing agent, homogenizing to obtain slurry, heating the slurry once, filling the slurry into a core mold, and pressing to obtain a primary molding core; heating the core mold for the second time, preserving heat, and pressing for the second time; heating the core mold for three times, and thermally curing to obtain a gel core;

5) Preparation of casting core: heating the gel mold core to 400 ℃ with a heating gradient of 20 ℃/min, heating to 700 ℃ with a heating gradient of 5 ℃/min, and preserving heat for 2 hours to obtain a casting mold core;

casting aluminum alloy at 600-750 ℃ and forming to obtain an aluminum alloy casting;

6) Preparation of the collapsibility powder: soaking the pouring core in hot water, flushing the inner cavity of the aluminum alloy casting with high-speed hot water to obtain a collapsibility powder water mixed solution, and filtering and drying to obtain collapsibility powder;

7) Recovery and use of the collapsibility powder: sampling the collapsibility powder, detecting the residual carbon quantity, and recycling according to the residual carbon quantity:

if the carbon residue is less than or equal to 0.5%, the corundum powder serving as the raw material in the step 1) can be directly replaced;

if the carbon residue is less than or equal to 0.5 percent and less than or equal to 1.5 percent, the corundum powder which is the raw material of the step 1) can be directly replaced, and new carbon powder is not needed to be added in the step 4);

if the carbon residue amount is less than or equal to 1.5 percent and less than or equal to 3 percent, adopting 98 percent concentrated sulfuric acid to wash the collapsibility powder for 2 to 3 times, then washing the collapsibility powder for 2 to 3 times by using clear water, and replacing the raw material corundum powder in the step 1) after drying, wherein new carbon powder is not needed to be added in the step 4), and the usage amount of GO powder in the GO dispersion liquid in the step 3) is reduced;

if the carbon residue is more than 3%, the carbon residue is calcined at high temperature until the carbon residue is 1.5 percent and less than or equal to 3 percent.

By adopting the technical scheme, the method firstly utilizes the fusion (90-100 ℃) bonding effect of phenolic resin (different from the existing gel injection molding method) on the basis of low temperature (40-50 ℃) of inorganic adhesive-aluminum dihydrogen phosphate (aluminum glue for short), utilizes the difference of fluidization temperatures of the two, carries out secondary bonding and secondary molding, and carries out shaping by utilizing the thermosetting effect (140-150 ℃) of the phenolic resin to obtain the gel core without secondary trimming; compared with the traditional organic binder, the carbonization effect in the sintering process of the phenolic resin can effectively reduce the shrinkage rate in the sintering process of the gel core and ensure the strength of the casting core after sintering and molding in the sintering process; graphene is added to improve the strength of the gel mold core and the pouring mold core; carbon powder is added to properly increase the porosity of the casting core.

Preferably, in the step 1), the mass ratio of the aluminum gel solution to the large corundum is 0.2-0.25:1.

By adopting the technical scheme, the size limit of the large-grain corundum and the small-grain corundum is 20 mu m, wherein the large-grain corundum accounts for about 60 percent, the small-grain corundum accounts for about 40 percent, the large-grain corundum is easy to settle, and the small-grain corundum is difficult to settle, so that the large-grain corundum and the small-grain corundum are subjected to distinguishing treatment: the large corundum is mixed with an inorganic binder-aluminum glue solution with higher viscosity, so that the strong acid aluminum dihydrogen phosphate is uniformly coated outside the large corundum.

The corundum selected in the application adopts fused corundum powder, wherein alpha-Al ₂ O ₃ The content exceeds 95 percent, the melting point is 2030 ℃, and the density is 3.99 to 4.00g/cm ³ Compact structure, good heat conduction performance, small thermal expansion coefficient and stable chemical property. It is an amphoteric oxide, is usually weak alkaline or neutral at high temperature, has strong acid-base resistance, does not change under the action of oxidant, reducing agent or various metal liquids, and has good chemical stability.

The aluminum paste solution was prepared by using Al (OH) ₃ And H ₃ PO ₄ The specific operation method for preparing the aluminum glue is to prepare the aluminum glue according to Al (OH) ₃ And H ₃ PO ₄ The molar ratio of (2) is 1:3.1-1:3.2, and a small amount of distilled water is used for weighing the dosage, and Al (OH) is firstly used for preparing the catalyst ₃ Mixing, and slowly mixingAl (OH) ₃ Adding the hydrosol into a beaker filled with phosphoric acid, stirring while adding, heating to 60 ℃ in a water bath kettle, and continuously stirring for 2 hours until no precipitate exists, thus obtaining transparent, colorless and odorless aluminum dihydrogen phosphate [ Al (H) ₂ PO ₄ ) ₃ ]A viscous liquid; directly adding large-grain corundum into an aluminum glue solution at 60 ℃, and homogenizing and stirring to obtain the corundum glue solution.

Preferably, the specific preparation process of the phenolic resin in the step 2) is as follows: slowly adding 85% phosphoric acid into 98% concentrated sulfuric acid under stirring, wherein the mass ratio of the 98% concentrated sulfuric acid to the 85% phosphoric acid is 1:1, preparing mixed acid, taking formaldehyde aqueous solution with the molar ratio of phenol to formaldehyde of 1:0.8-0.9 to form reaction monomer solution, dropwise adding the mixed acid at room temperature for 10min until the mass ratio of the reaction monomer solution to the mixed acid is 1:0.36-0.61, heating to 100 ℃, stirring for 3-5 min, heating to 135-145 ℃, and carrying out reflux reaction for 1-2 h to obtain a viscous phenolic reaction system;

naturally cooling the phenolic reaction system to room temperature, standing and aging for 1-2 h, drawing the supernatant to obtain a solution phase, obtaining a gel phase of the lower viscous colloid, and distilling the gel phase under reduced pressure at 80 ℃ to obtain the viscous phenolic resin.

By adopting the technical scheme, the acid catalysis is utilized to synthesize the thermoplastic phenolic resin, the concentrated sulfuric acid is utilized to catalyze, the phosphoric acid is utilized to replace phenolic hydroxyl groups, 2-3 phenolic molecular chains can be crosslinked, the phenolic resin of second-order preliminary gel is formed, and the phenolic resin is stable and can be stored for 2-3 months under normal temperature and normal pressure in a sealing way; the gel phase generated by cooling, standing and aging according to a phenolic aldehyde reaction system has a melting point of 90-100 ℃ and can be used as an organic binder for forming corundum particles; and the rest of unreacted monomers or phenolic intermediates with molecular weight less than 300 can be used for mixing small corundum and graphene oxide particles after being subjected to oxidation reaction and crosslinking by adopting hot concentrated sulfuric acid to make the phenolic intermediates be primarily tackified.

Preferably, the mixture ratio of each component in the GO dispersion in the step 3) is as follows: GO powder, alCl ₃ And 98% concentrated sulfuric acid in the mass ratio of 0.09-0.12 to 0.2-0.3 to 1.

By adopting the technical scheme, the method utilizesAlCl in concentrated sulfuric acid ₃ The GO intercalation reaction can be carried out, so that the GO is expanded and the surface is provided with ions, the GO dispersion liquid can be in a stable suspension state for a long time (50-100 h), no obvious sedimentation effect is achieved, and the mixing with the small corundum is facilitated.

Preferably, the specific preparation process of the GO mixture in step 3) is as follows: adding GO dispersion liquid into small-grain corundum, wherein the mass ratio of the GO dispersion liquid to the small-grain corundum is 0.1-0.15:1, forming viscous colloid through a colloid mill made of ceramic materials, pouring solution phase, pouring the viscous colloid into the mixer until the viscous colloid is completely disintegrated, pouring a colloid mill system into a heating container, stirring and reacting for 1-2 h at 130 ℃ to obtain a suspension viscous system, and standing to remove upper-layer clear solution to obtain a viscous GO mixture;

By adopting the technical scheme, the phenolic resin in the solution phase is unreacted and continuously subjected to concentrated sulfuric acid oxidation in the GO dispersion liquid, molecular chains grow and carry out crosslinking reaction, so that the viscosity of the system is increased, and the reaction is carried out on the surfaces of GO and granular corundum in situ, so that the viscosity of the system is improved; at the same time AlCl ₃ Under the acid heating reaction, the produced AlO ₂ ^～ The mixture is adhered to the surfaces of GO and small corundum particles, so that the chargeability of suspended particles is improved, a colloid system is promoted to be formed, and clear liquid with phosphoric acid and sulfuric acid is removed after aging, so that a viscous GO mixture is finally obtained.

Preferably, the proportion of the gel core in the step 4) is as follows: the corundum glue solution, the GO mixture, the phenolic resin, the carbon powder and the curing agent are mixed according to the mass ratio of 1 (0.56-0.62), 0.15-0.18, 0.008-0.010 and 0.015-0.025, wherein the curing agent is hexamethylene tetramine which is most commonly used.

By adopting the technical scheme, the corundum particles with different particle sizes are respectively treated by using the inorganic binder and the organic binder which are both acidic and the viscous corundum solution, the GO mixture and the phenolic resin, and the mixed water content (including the potential water content generated by dehydration of the components such as aluminum dihydrogen phosphate, sulfuric acid, phosphoric acid, phenolic curing and the like after heating and the free water contained in each system) is not more than 10 percent by virtue of scientific proportioning design, and the phenolic resin also contains 20 percent of swelling solvent, and not more than 2 percent of mixture content, so that the low-pressure injection requirement of the core is met; and the porosity of the final casting mold core is 27-35% by the gas generated by decomposing the carbon powder graphene and the phenolic resin, meanwhile, various gas components are different in volatilization temperature, and holes are formed for multiple times to form a reticular hole structure, so that the risk of collapsing the internal structure of the mold core due to too fast release of the gas in the sintering process is avoided.

Preferably, the molding temperature of the gel core in step 4) is controlled as follows: heating corundum glue solution to 40-50 ℃ for one time, sequentially adding GO mixture, phenolic resin, carbon powder and curing agent, continuously heating to maintain the temperature of the mixed system to 40-50 ℃, homogenizing to obtain slurry, filling the slurry into a core mold by low-pressure injection, and pressing under 10-15 Mpa to obtain a primary molding core; heating the core mould to 90-100 ℃ for 10-20 min, and pressing for the second time under 10-15 Mpa; and heating the core mold for three times to 150 ℃, and thermally curing for 5-15 min to obtain the gel core.

By adopting the technical scheme, the basic fluidity of the swelling phenolic resin (the mixture of the first-order thermoplastic phenolic resin and the second-order phosphoric acid modified phenolic resin) produced by the reaction is utilized by three-stage temperature control, and the primary molding is carried out at the fluidization temperature of the inorganic binder of 40-50 ℃; under the melting point condition of phenolic resin, the fluidity of the primary molding core is improved, secondary hot pressing is carried out, internal bubbles generated by mixing are broken, the compaction density is improved, and secondary fusion bonding is realized; and (3) performing thermosetting setting under the action of a curing agent.

Preferably, the preparation of the casting core in step 5): installing a gel mold core in a casting box, heating the gel mold core to 400 ℃ at a heating gradient of 20 ℃/min, heating to 700 ℃ at a heating gradient of 5 ℃/min, and preserving heat for 2 hours to obtain a casting mold core; and (3) pouring the aluminum alloy at 600-750 ℃ and forming to obtain the aluminum alloy casting.

By adopting the technical scheme, the carbonization temperature range of the phenolic resin is 400-700 ℃, the carbonization temperature is quickly increased, free water, solvent and water vapor generated by dehydration of each component are continuously evaporated in the process, and a through air hole channel is formed in the core; after the carbonization temperature is reached, the temperature is raised slowly, carbonization is carried out, heat preservation is carried out, oxygen cannot be touched in time to be completely decomposed after carbonization, graphite-like or other amorphous carbon simple substances occupy phenolic resin in situ, and the supporting effect is achieved on the internal structure of the core; graphene is added for bridging, so that the strength of the core is further improved; and the casting core that this application utilized phenolic aldehyde carbomorphism temperature and aluminum alloy melt casting temperature to be close characteristics, and the casting core that forms after the carbomorphism can directly pour, avoids current water-soluble ceramic core preparation back hygroscopicity too strong and leads to the defect that the intensity is insufficient before pouring.

Preferably, the hot water temperature for soaking the pouring core and flushing the aluminum alloy casting in the step 6) is 60-80 ℃, and the collapsibility powder with the water content of less than 5% is obtained after filtering and drying.

Through adopting above-mentioned technical scheme, because phenolic resin carbomorphism back, add the bridging effect of graphene oxide, make the pouring core of this application after pouring use, intensity still be higher than current other cores, lead to its collapsibility slightly to reduce, so adopt hot water (60 ~ 80 ℃) of higher temperature to soak and wash.

Preferably, the carbon residue in the step 7) is the weight of the unit weight of the collapsible powder containing simple substance carbon, the simple substance carbon comprises added carbon powder, graphene oxide main body and carbon generated by phenolic resin carbonization, the carbon residue is 1.5 percent less than or equal to 3 percent, the carbon generated by phenolic resin carbonization comprises active carbon powder and graphite, the active carbon powder and the graphite can be burnt in the air at 700-900 ℃, in the calcination process, the graphite is continuously deflated to cause internal porosity, the subsequent interlayer expansion of the graphite is facilitated, 98 percent concentrated sulfuric acid is adopted to wash the collapsible powder for 2-3 times after calcination, clean water is used for 2-3 times, and the collapsible powder washed by the clean water is dried to the water content of <5 percent, so that the collapsible powder can be returned for use.

By adopting the technical scheme, the casting core used for the primary casting is added with the carbon powder and the graphene oxide, and graphite or amorphous carbon formed by carbonizing the phenolic resin after casting is high-activity carbon simple substance, so that the phenolic resin has reutilization value and the graphene has bonding phenomenon, so that 98% concentrated sulfuric acid elution treatment is needed; therefore, the method classifies the collapsibility powder according to the residual carbon amount, replaces a high-cost recovery method of direct complete calcination in the prior art, replaces carbon components in the subsequent gel mold core as appropriate, and saves cost.

The high-temperature calcination in the step 7) specifically means that the collapsibility powder with carbon residue of more than 3% is calcined for 5-60 min at 800 ℃, and excessive carbon powder and carbon generated by phenolic resin carbonization are burnt until the carbon residue of 1.5% < 3%.

By adopting the technical scheme, the carbon generated by phenolic resin carbonization comprises active carbon powder and graphite, the active carbon powder and the graphite can be burnt in the air at 700-900 ℃, and in the calcination process, the graphite is continuously deflated to cause internal loosening, so that the subsequent interlayer expansion of the graphite is facilitated, and 98% concentrated sulfuric acid is used for washing the collapsed powder for 2-3 times after calcination; 1.5 percent of the collapsibility powder with the carbon residue less than or equal to 3 percent is eluted by concentrated sulfuric acid, the concentrated sulfuric acid is used for eluting the bonding interface between corundum particles and carbon particles, meanwhile, the concentrated sulfuric acid and the acidolysis corundum particles thereof generate trace aluminum sulfate, the expanded graphite generated by sintering graphene and the graphite generated by carbonizing phenolic resin are subjected to intercalation expansion, the collapsibility powder obtained by drying can directly replace the raw material corundum powder in the step 1), new carbon powder is not needed to be added in the step 4), and the GO powder in the GO dispersion in the step 3) can be reduced as appropriate.

Preferably, the eluent obtained by washing the collapsibility powder with 98% concentrated sulfuric acid in the step 7) replaces the 98% concentrated sulfuric acid adopted in the step 3), and the eluent is mixed with GO powder to prepare a new GO dispersion liquid for preparing a GO mixture.

By adopting the technical scheme, the eluted concentrated sulfuric acid can also be used as a solvent for graphene oxide instead of using, aluminum ions are generated in the dissolution process, and the consumption of GO dispersion liquid is saved.

Preferably: washing the collapsibility powder washed by 98% concentrated sulfuric acid in the step 7) with clear water for 2-3 times, mixing clear water washing liquid with the upper layer clear solution in the step 3) for adjusting the viscosity and the water content of the aluminum colloid solution, the phenolic reaction system, the viscous phenolic resin and the viscous GO mixture and the viscous colloid in the step 3), and storing the rest in a sedimentation tank for collecting and treating waste sand, metal scraps and the like in a factory area to be used as a dilute acid dissolution tank.

By adopting the technical scheme, the dilute acid waste liquid in the production process is recycled, and the water consumption is saved.

In summary, the present application includes at least one of the following beneficial technical effects:

1. the novel gel core with inorganic and organic combination is high in bending strength and low in moisture absorption rate, can be stored for a long time, is overlapped with the pouring temperature rising process of an aluminum alloy casting in the sintering carbonization process, and thoroughly avoids the risk of low strength of the existing core after moisture absorption.

2. The phenolic resin sintering process is utilized to carbonize and occupy the in-situ pore canal of the binder, so that the strength of the core is gradually enhanced in the sintering process, no obvious defect exists on the surface of the core, and the strength of the core is further enhanced through the bridging of graphene oxide.

3. The pouring core of this application intensity is higher and easily collapss, and collapsibility powder can be according to the direct recycle of carbon residue volume, and the cost is lower.

Drawings

FIG. 1 is a process flow diagram of a method for preparing a water-soluble precision ceramic core for casting aluminum alloy according to the present application.

Detailed Description

The present application is described in further detail below in conjunction with fig. 1.

Preparation example A1:

preparation of corundum glue solution:

100kg of fused corundum powder is taken, and 60.2kg of large-grain corundum and 39.6kg of small-grain corundum are obtained after sieving by a 700-mesh sieve;

weigh 3kg Al (OH) ₃ 99.5% of industrial high-purity Al (OH) is selected ₃ Adding 0.15kg distilled water to obtain Al (OH) with particle size of 800 mesh ₃ Mixing evenly, taking 14kg of 85% H ₃ PO ₄ ，Al(OH) ₃ And H ₃ PO ₄ The molar ratio of (3) to (3) is 1:3.16, and the Al (OH) is uniformly mixed ₃ Hydrosol additionAdding into beaker filled with phosphoric acid, stirring while heating to 60deg.C in water bath, and stirring for 2 hr until no precipitate is present to obtain transparent colorless and odorless aluminum dihydrogen phosphate [ Al (H) ₂ PO ₄ ) ₃ ]Viscous liquid, test pH 1.7, weighing about 17.1kg;

taking 10kg of large-grain corundum, adding 2kg of aluminum cement solution, and homogenizing and stirring to obtain corundum cement A1.

Preparation example A2:

the same as in preparation A1 except that 10kg of large-grain corundum was used, 2.3kg of alumina cement solution was added thereto, and the mixture was homogenized and stirred to obtain corundum cement A2.

Preparation example A3:

the same as in preparation A1 except that 10kg of large-grain corundum was used, 2.5kg of alumina cement solution was added thereto, and the mixture was homogenized and stirred to obtain corundum cement solution A3.

Preparation example B1:

preparation of phenolic resin:

adopting a pilot-scale reaction kettle, weighing 10kg of phenol, weighing 6.59kg of 40% formaldehyde aqueous solution to form a reaction monomer solution, slowly adding 5.0kg of 98% concentrated sulfuric acid into 5.0kg of 85% phosphoric acid to prepare mixed acid, dripping the mixed acid into the reaction monomer solution within 10min, heating to 100 ℃, stirring for 35min, heating to 135 ℃, and carrying out reflux reaction for 1h to obtain a viscous phenolic reaction system;

naturally cooling the phenolic reaction system to room temperature, standing and aging for 1h, and drawing supernatant to obtain 12.29kg of solution phase; the gel phase of the lower layer viscous colloid is obtained, the gel phase is distilled under reduced pressure at 80 ℃ to obtain viscous phenolic resin, and 9.9kg of the viscous phenolic resin is weighed.

Preparation example B2:

preparation of phenolic resin:

adopting a pilot-scale reaction kettle, weighing 10kg of phenol, weighing 7.02kg of 40% formaldehyde aqueous solution to form a reaction monomer solution, slowly adding 4.1kg of 98% concentrated sulfuric acid into 4.1kg of 85% phosphoric acid to prepare mixed acid, dripping the mixed acid into the reaction monomer solution within 10min, heating to 100 ℃, stirring for 5min, heating to 145 ℃, and carrying out reflux reaction for 2h to obtain a viscous phenolic reaction system;

naturally cooling the phenolic reaction system to room temperature, standing and aging for 2 hours, and drawing supernatant to obtain 13.6kg of solution phase; the gel phase of the lower layer viscous colloid is obtained, the gel phase is distilled under reduced pressure at 80 ℃ to obtain viscous phenolic resin, and 10.3kg of the viscous phenolic resin is weighed.

Preparation example B3:

preparation of phenolic resin:

adopting a pilot-scale reaction kettle, weighing 10kg of phenol, weighing 7.41kg of 40% formaldehyde aqueous solution to form a reaction monomer solution, slowly adding 3.3kg of 98% concentrated sulfuric acid into 3.3kg of 85% phosphoric acid to prepare mixed acid, dripping the mixed acid into the reaction monomer solution within 10min, heating to 100 ℃, stirring for 4min, heating to 140 ℃, and carrying out reflux reaction for 1.5h to obtain a viscous phenolic reaction system;

naturally cooling the phenolic reaction system to room temperature, standing and aging for 1.5h, and drawing the supernatant to obtain 15.5kg of solution phase; the gel phase of the lower layer viscous colloid is obtained, the gel phase is distilled under reduced pressure at 80 ℃ to obtain viscous phenolic resin, and 11.3kg of the viscous phenolic resin is weighed.

Preparation example C1:

preparation of GO mixture:

10kg of 98% concentrated sulfuric acid is taken and added with 0.9kg of GO powder and 3kg of AlCl ₃ (99% Industrial high purity grade AlCl) ₃ ) And (3) homogenizing and stirring for 2 hours, observing no obvious sedimentation and agglomeration after overnight, obtaining GO dispersion liquid, and detecting no obvious sedimentation for 100 hours.

Taking 10kg of small-grain corundum, adding 1.5kg of GO dispersion liquid, passing through a colloid mill made of ceramic materials to form viscous colloid, pouring 2.5kg of solution phase obtained in preparation example B1 until the viscous colloid is completely disintegrated, pouring a system in the colloid mill into a heating kettle, stirring and reacting for 1h at 130 ℃ to obtain a suspension viscous system, and standing to remove upper clear solution to obtain a viscous GO mixture; preparation example C2:

preparation of GO mixture:

10kg of 98% concentrated sulfuric acid is taken and added with 1.2kg of GO powder and 2kg of AlCl ₃ (99% Industrial high purity grade AlCl) ₃ ) Homogenizing and stirring for more than 2 hours, and observing no obvious sedimentation and agglomeration after overnight to obtain GO fractionThe dispersion liquid has no obvious sediment after detection for more than 100 hours.

Taking 10kg of small-grain corundum, adding 1kg of GO dispersion liquid, forming viscous colloid through a colloid mill made of ceramic materials, pouring 2kg of solution phase obtained in preparation example B2 until the viscous colloid is completely disintegrated, pouring a colloid mill middle system into a heating kettle, stirring and reacting for 2 hours at 130 ℃ to obtain a suspension viscous system, and standing to remove upper clear solution to obtain a viscous GO mixture; preparation example C3:

Preparation of GO mixture:

10kg of 98% concentrated sulfuric acid is taken and 1.1kg of GO powder and 2.5kg of AlCl are added ₃ (99% Industrial high purity grade AlCl) ₃ ) Homogenizing and stirring for more than 2 hours, observing no obvious sedimentation and agglomeration after overnight, obtaining GO dispersion liquid, and detecting no obvious sedimentation for more than 100 hours.

Taking 10kg of small-grain corundum, adding 1.2kg of GO dispersion liquid, passing through a colloid mill made of ceramic materials to form viscous colloid, pouring 2.2kg of solution phase obtained in preparation example B3 until the viscous colloid is completely disintegrated, pouring a system in the colloid mill into a heating kettle, stirring and reacting for 1.5 hours at 130 ℃ to obtain a suspension viscous system, and standing to remove upper clear solution to obtain a viscous GO mixture;

example 1:

preparation of gel core: the radius of the inner cavity hole is 15mm, the radius of the outer cylinder is 60mm, the wall thickness is 45mm, and the height is 150 mm.

Taking 4kg of corundum glue solution of preparation example A1, heating to 40 ℃ in a water bath, preserving heat, sequentially adding 600g of phenolic resin of preparation example B1, 2.48kg of GO mixture of preparation example C1, 40g of carbon powder and 60g of hexamethylenetetramine, mixing and homogenizing to obtain slurry, filling the slurry into a core mold through low-pressure injection, and pressing under 10-15 Mpa to obtain a primary molding core;

Heating the core mold to 100 ℃ for a second time, preserving heat for 10min, and pressing for a second time under 10-15 Mpa;

the core mold was heated three times to a temperature of 150℃and thermally cured for 5 minutes to obtain a gel core, which was weighed to be 6.78kg. The gel core was placed in a dust-free air atmosphere at 25 ℃ and 70% humidity, and tested for hygroscopicity and wet strength.

Preparation of casting core: heating the gel mold core to 400 ℃, heating to 700 ℃ with a heating gradient of 5 ℃/min, and preserving heat for 2 hours to obtain a casting mold core; the casting cores obtained by calcination were tested for porosity and dry strength.

Collapsibility test: adopting a casting temperature of 650 ℃, casting Al-10Si-0.3Mg, after the casting core is molded, air-cooling to about 100 ℃ to obtain an aluminum alloy casting, and taking the defect rate of less than 0.3% as a qualification; soaking the pouring core in hot water at 80 ℃, flushing the inner cavity of the aluminum alloy casting with hot water at 80 ℃ under the impact pressure of 2Mpa to obtain a collapsibility powder water mixed solution, and filtering and drying to obtain collapsibility powder;

testing carbon residue rate of the collapsed powder:

because the gel cores prepared each time have different mixing uniformity, phenolic resin carbonization environments of all areas cannot be completely the same, even the gel cores with the same components have fluctuation of the pore structures and the porosities, and the carbon residue rates of the obtained collapsibility powder are different, so that the gel cores need to be treated differently;

1g of powder is sampled and dispersed, calcined for 2 hours at 800 ℃, and after natural cooling, 968mg of dry powder is directly tested, the residual carbon rate is 2.4%, so that the original dispersed powder is repeatedly eluted for 2 times by 98% concentrated sulfuric acid, the obtained eluent is tested to have the weight concentration of aluminum sulfate of 9.2% and the water content of 3.4%, and the eluent can be directly used for dispersing GO powder, so that new GO dispersion liquid is prepared; washing the dispersed powder eluted by concentrated sulfuric acid with clear water for 2 times, wherein the dispersed powder dried at 60 ℃ under vacuum of <1Pa has no obvious caking, and the water content is controlled within 5%;

recovery test: taking 10g of obtained collapsed powder, carrying out intense crushing and stirring by 10% dilute sulfuric acid, standing to obtain suspension and precipitate, centrifuging and drying the suspension, detecting that the suspension contains 48.6mg of active carbon and 25.3mg of graphene oxide particles, testing the content of the active carbon to be 0.486% and the content of the GO to be 0.253%, considering that a small amount of active carbon and graphene oxide particles still exist in the precipitate, the collapsed powder with the proportion can completely replace the raw corundum powder in the step 1), the new carbon powder is not needed to be added in the step 4), and the GO powder consumption in the GO dispersion in the step 3) can be reduced by 70%.

Example 2:

preparation of gel core: the radius of the inner cavity hole is 15mm, the radius of the outer cylinder is 60mm, and the height of the outer cylinder is 150 mm.

Taking 4kg of corundum glue solution of preparation example A1, heating to 45 ℃ in a water bath, preserving heat, sequentially adding 660g of phenolic resin of preparation example B1, 2.36kg of GO mixture of preparation example C1, 36g of carbon powder and 80g of hexamethylenetetramine, mixing and homogenizing to obtain slurry, filling the slurry into a core mold through low-pressure injection, and pressing under 10-15 Mpa to obtain a primary molding core;

heating the core mould to 95 ℃ for the second time, preserving heat for 15min, and pressing for the second time under 10-15 Mpa;

the core mold was heated three times to 145℃and thermally cured for 10min to give a gel core weighing 6.76kg. The gel core was placed in a dust-free air atmosphere at 25 ℃ and 70% humidity, and tested for hygroscopicity and wet strength.

Collapsibility test: adopting a casting temperature of 650 ℃, casting Al-10Si-0.3Mg, after the casting core is molded, air-cooling to about 100 ℃ to obtain an aluminum alloy casting, and taking the defect rate of less than 0.3% as a qualification; soaking the pouring core in hot water at 60 ℃, flushing the inner cavity of the aluminum alloy casting with hot water at 60 ℃ under the impact pressure of 2Mpa to obtain a collapsibility powder water mixed solution, and filtering and drying to obtain collapsibility powder;

Testing carbon residue rate of the collapsed powder:

1g of the powder is sampled and calcined at 800 ℃ for 2 hours, 968mg of dry powder is directly tested after natural cooling, and the carbon residue rate is 3.2%, so that the original powder is calcined for 36 minutes to obtain the powder with the carbon residue rate of 1.8%, the powder is repeatedly eluted for 3 times by 98% concentrated sulfuric acid, and the eluent is tested to have the weight concentration of aluminum sulfate of 11.1% and the water content of 2.7%, and can be directly used for dispersing GO powder, so that a new GO dispersion liquid is prepared; washing the dispersed powder eluted by concentrated sulfuric acid with clear water for 3 times, wherein the dispersed powder dried at 60 ℃ under vacuum of <1Pa has no obvious caking, and the water content is controlled within 5%;

recovery test: taking 10g of obtained collapsed powder, carrying out intense crushing and stirring by 10% dilute sulfuric acid, standing to obtain suspension and precipitate, centrifuging and drying the suspension, detecting that 45.1mg of active carbon and 28.1mg of graphene oxide particles are contained in the suspension, testing the content of the active carbon to be 0.451%, and the content of the GO to be 0.281%, wherein small amount of active carbon and graphene oxide particles are still considered in the precipitate, the collapsed powder with the proportion can completely replace the raw corundum powder in the step 1), new carbon powder is not needed to be added in the step 4), and the GO powder consumption in the GO dispersion in the step 3) can be reduced by 80%.

Example 3:

Taking 4kg of corundum glue solution of preparation example A1, heating to 50 ℃ in a water bath, preserving heat, sequentially adding 720g of phenolic resin of preparation example B1, 2.24kg of GO mixture of preparation example C1, 32g of carbon powder and 100g of hexamethylenetetramine, mixing and homogenizing to obtain slurry, filling the slurry into a core mold through low-pressure injection, and pressing under 10-15 Mpa to obtain a primary molding core;

heating the core mould to 90 ℃ for the second time, preserving heat for 20min, and pressing for the second time under 10-15 Mpa;

the core mold was heated three times to a temperature of 140℃and thermally cured for 20 minutes to obtain a gel core, which was weighed to be 6.80kg.

Collapsibility test: adopting a casting temperature of 650 ℃, casting Al-10Si-0.3Mg, after the casting core is molded, air-cooling to about 100 ℃ to obtain an aluminum alloy casting, and taking the defect rate of less than 0.3% as a qualification; soaking the pouring core in hot water at 70 ℃, flushing the inner cavity of the aluminum alloy casting with hot water at 70 ℃ under the impact pressure of 2Mpa to obtain a collapsibility powder water mixed solution, and filtering and drying to obtain collapsibility powder;

Testing carbon residue rate of the collapsed powder:

1g of the powder is sampled and calcined at 800 ℃ for 2 hours, after natural cooling, 968mg of dry powder is directly tested, the carbon residue rate is 3.8%, so the original powder is calcined for 45 minutes to obtain powder with the carbon residue rate of 2.7%, the powder is repeatedly eluted for 3 times by 98% concentrated sulfuric acid, and the eluent is tested to have the weight concentration of aluminum sulfate of 12.3% and the water content of 3.5%, and can be directly used for dispersing GO powder, so that new GO dispersion liquid is prepared; washing the dispersed powder eluted by concentrated sulfuric acid with clear water for 3 times, wherein the dispersed powder dried at 60 ℃ under vacuum of <1Pa has no obvious caking, and the water content is controlled within 5%;

recovery test: taking 10g of obtained collapsed powder, carrying out intense crushing and stirring by 10% dilute sulfuric acid, standing to obtain suspension and precipitate, centrifuging and drying the suspension, detecting that the suspension contains 51.2mg of active carbon and 31.3mg of graphene oxide particles, testing the content of the active carbon to be 0.512%, and the content of the GO to be 0.313%, wherein a small amount of active carbon and graphene oxide particles are still considered in the precipitate, and the collapsed powder with the proportion can completely replace the raw corundum powder in the step 1), wherein new carbon powder is not required to be added in the step 4), and new GO powder is not required to be added in the GO dispersion in the step 3).

Comparative test group:

comparative example 1:

the procedure was the same as in example 3, except that the gel core was prepared without adding carbon powder.

Comparative example 2:

the procedure is as in example 3, except that the gel core is prepared without the addition of hexamethylenetetramine.

Comparative example 3:

the procedure was the same as in example 3, except that the gel core was prepared without adding carbon powder and hexamethylenetetramine.

Recovery test group:

example 4:

the recovered collapsibility powder obtained in example 1 is used for replacing corundum, 700 mesh screening is carried out, new large-grain corundum and new small-grain corundum are obtained, 4kg of corundum glue solution is obtained by the new large-grain corundum through the preparation example A1, the GO mixture is obtained by the new small-grain corundum through the preparation example C1, water bath heating is carried out to 50 ℃, heat preservation is carried out, 720g of phenolic resin in the preparation example B1, 2.24kg of GO mixture in the preparation example C1 are sequentially added, 100g of hexamethylenetetramine is added, wherein the original required amount of GO dispersion used by the GO mixture is 15.5gGO powder, and only 4.67g is needed. And calcining the prepared gel core to obtain a casting core, and performing a collapsibility test after casting to test each performance.

Example 5:

the recovered collapsibility powder obtained in example 1 is used for replacing corundum, 700 mesh screening is carried out, new large-grain corundum and new small-grain corundum are obtained, 4kg of corundum glue solution is obtained by the new large-grain corundum through the preparation example A1, the GO mixture is obtained by the new small-grain corundum through the preparation example C1, water bath heating is carried out to 50 ℃, heat preservation is carried out, 720g of phenolic resin in the preparation example B1, 2.24kg of GO mixture in the preparation example C1 are sequentially added, 100g of hexamethylenetetramine is added, wherein the original required amount of GO dispersion used by the GO mixture is 15.5gGO powder, and only 3.1g is needed. And calcining the prepared gel core to obtain a casting core, and performing a collapsibility test after casting to test each performance.

Example 6:

the recovered collapsibility powder obtained in example 1 is used for replacing corundum, 700 mesh screening is carried out, new large-grain corundum and new small-grain corundum are obtained, 4kg of corundum glue solution is obtained by the new large-grain corundum through the preparation example A1, the GO mixture is obtained by the new small-grain corundum through the preparation example C1, water bath heating is carried out to 50 ℃, heat preservation is carried out, 720g of phenolic resin of the preparation example B1, 2.24kg of GO mixture of the preparation example C1 are sequentially added, 100g of hexamethylenetetramine is added, and no new GO powder is added into GO dispersion used by the GO mixture. And calcining the prepared gel core to obtain a casting core, and performing a collapsibility test after casting to test each performance.

Cross test groups were prepared:

example 7:

in the embodiment 3, the components of the gel core are marked as A1B1C1, so that the combination test of each preparation test is tested, in the embodiment, 4kg of corundum glue solution of the preparation example A1 is adopted, water bath heating is carried out to 50 ℃ and heat preservation is carried out, 720g of phenolic resin of the preparation example B2, 2.24kg of GO mixture of the preparation example C2 are sequentially added, 32g of carbon powder and 100g of hexamethylenetetramine are added, and the mixture is mixed and homogenized to obtain slurry, wherein the obtained gel core is marked as A1B2C2.

Example 8:

similar to example 7, using 4kg of corundum glue solution of preparation example A1, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B3, 2.24kg of GO mixture of preparation example C3, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, and the gel core is marked as A1B3C3.

Example 9:

similar to example 7, using 4kg of corundum glue solution of preparation example A2, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B1, 2.24kg of GO mixture of preparation example C1, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, and the gel core is marked as A2B1C1.

Example 10:

similar to example 7, using 4kg of corundum glue solution of preparation example A2, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B2, 2.24kg of GO mixture of preparation example C2, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, and the gel core is marked as A2B2C2.

Example 11:

similar to example 7, using 4kg of corundum glue solution of preparation example A2, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B3, 2.24kg of GO mixture of preparation example C3, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, and the gel core is marked as A2B3C3.

Example 12:

similar to example 7, using 4kg of corundum glue solution of preparation example A3, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B1, 2.24kg of GO mixture of preparation example C1, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, and the gel core is marked as A3B1C1.

Example 13:

similar to example 7, using 4kg of corundum glue solution of preparation example A3, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B2, 2.24kg of GO mixture of preparation example C2, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, and the gel core is marked as A3B2C2.

Example 14:

similar to example 7, using 4kg of corundum glue solution of preparation example A3, heating to 50 ℃ in a water bath and keeping the temperature, 720g of phenolic resin of preparation example B3, 2.24kg of GO mixture of preparation example C3, 32g of carbon powder and 100g of hexamethylenetetramine are sequentially added, and the mixture is mixed and homogenized to obtain a slurry, wherein the gel core is marked as A3B3C3.

Performance test: in each embodiment, five gel core samples are designed, casting cores are respectively manufactured, and after casting, a collapse test is carried out to obtain collapse powder. The following parameters were taken as the middle 3 values in the 5 groups of samples, the arithmetic average was taken, and table 1 was entered for comparison:

1) Moisture absorption δ of gel core: placing the gel core in a dust-free air environment with 25deg.C and 70% humidity, wiping off water drops on the inner and outer surfaces of the gel core with dry sponge after 10 days, weighing to obtain wet weight M _{Wet state} Drying at 100deg.C under 1Pa for 1 hr to obtain dry weight M _Dry Moisture absorption δ= (M) _{Wet state} -M _Dry )/M _Dry 。

2) Wet strength sigma of gel core _{Wet state} : standard samples of 50mm were prepared and tested for room temperature flexural strength using a microcomputer controlled electronic universal tester (New three Si, CMT 4503) according to HB 5353.2-2004. The gauge length is 30mm, the loading rate is 0.5mm/min, and the bending strength sigma of the gel core is tested _{Wet state} 。

3) Volume shrinkage ratio s of gel core and casting core: gel core height h by caliper test ₀ The height of the casting core is h ₁ ，s＝(h ₀ -h ₁ )/h ₀ 。

4) Dry strength sigma of casting core _Dry And (3) preparing a gel core with the diameter of 30mm, calcining to obtain a casting core standard sample, and testing the room-temperature bending strength by adopting a microcomputer-controlled electronic universal tester (New three Si, CMT 4503) according to HB 5353.2-2004. The gauge length is 30mm, the loading rate is 0.5mm/min, and the bending strength sigma of the casting core is tested _Dry 。

5) Porosity K of casting core _a : the dry weight is measured by a drainage method to be m _Dry The casting core of (2) is placed in the air for more than 30min, and the weight m is measured _{Air flow} Soaking in 0deg.C ethanol for 5min, removing surface water drop, and measuring wet weight m _{Wet state} Apparent porosity K _a ＝(m _{Air flow} -m _Dry )/(m _{Wet state} -m _Dry )。

6) Collapse time t of casting core: the casting core sample is soaked in hot water at 80 ℃ until the strength is 0, and the time is the collapse time t.

7) Carbon residue C test of the collapsed powder: sampling 1g of collapsibility powder, calcining at 800 ℃ for 2h, naturally cooling, and directly testing the mass m of the dry powder _Powder (in g), c=m _Powder /1*100％。

Data analysis, as shown in table 1 below:

TABLE 1 Performance test of cores and collapsibility powders of the present application

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I. In comparative examples 1-3, as the mixture of phenolic resin and GO increases, the strength of the gel core increases, which is beneficial to improving the storage time of the gel core, so that the gel core can be manufactured in a large scale, the defect of lower strength before pouring caused by the fact that the moisture absorption rate of the core manufactured by other existing binders is too high is avoided, and the gel core is a hydrophobic resin consolidated object, has strong water resistance and higher strength and cannot deform after long-term storage;

the strength of the corresponding casting core is slightly improved, on one hand, the bridge connection reinforcing principle of the pore canal and the graphene oxide is mainly filled through the carbonization action of phenolic resin, and on the other hand, the filling action of the small-grain corundum is adopted, so that the grains are relatively compact, and the high-pressure and impact strength can be borne;

but correspondingly, as the mixture of the phenolic resin and the GO increases, the total amount of corundum occupies smaller amount, small particles and larger total amount, so that the structure is more compact, the shrinkage is reduced, the porosity is reduced, the increase of binder components is beneficial to the increase of the porosity, and the porosity fluctuates;

However, the collapse time increases and the carbon residue rate increases, so this application requires a trade-off between collapse efficiency and core strength.

II. Comparing example 3 with examples 4-6, which are recovery and reuse of the collapsed powder, the performance of each aspect is similar to that of example 3 in the case that the process steps and the total carbon ratio are maintained at a level, which shows that recovery and reuse of the collapsed powder in the application is completely feasible, and the cycle number is not changed for 20 times in the case that the carbon residue ratio of the recovered collapsed powder is maintained to be less than 3%, and no data display is performed. And the strength of the casting core is even slightly improved, and the reinforcing effect similar to clinker can be generated, and the principle demonstration of whether the clinker effect is still lacked is provided.

III, comparative example 3 and comparative examples 1-3, without adding carbon powder, cause a significant decrease in porosity, slightly increase in strength, without adding a curing agent, and significantly decrease in gel core strength, cause a curing process in a subsequent sintering temperature increasing process, cause a high shrinkage rate and risk of hole collapse, so the casting core strength is very low.

IV, comparative example 3 and examples 7-14, which are cross tests, the alumina gel content was gradually increased from preparation A1-A3, the formaldehyde ratio was gradually increased from preparation B1-B3, the phosphoric acid and sulfuric acid amounts were reduced, and the GO powder content was increased and then reduced from preparation C1-C3.

Examples 3, 7 and 8 compare the properties, with less phenolic resin cross-linking, and less gel core strength, with less phosphoric and sulfuric acid, but with more GO powder, the strength of the casting core can be significantly improved.

In comparison of the properties of examples 3, 9 and 12, the strength of the gel core and the casting core was increased and then decreased as the aluminum gel content was increased, wherein the inorganic binder was mixed with the organic binder to replace each other, and the inorganic binder had an influence on the phenolic resin coating and the carbonization environment, so that the inorganic binder should be moderate.

The best core performance is example 10, wherein the aluminum glue and phenolic resin are moderate in dosage, the carbon powder is least in dosage, the curing agent and GO are larger in dosage, and the mold core can be used as a conclusive proportioning adjustment scheme. The gel core obtained by each embodiment of the application has the performance far higher than that of the existing wet core formed by simply adopting an inorganic binder or an organic binder (the bending strength is about 3.5 Mpa), and the obtained casting core has higher strength (the bending strength is about 8 Mpa), so that the concept that the gel core with a firmer structure is used for replacing the existing wet core to prepare the high-strength casting core is proved to be completely feasible, the gel core can be stored for a long time after being manufactured, and the gel core can be calcined and made into holes before being cast, and is combined with the die heating process in the aluminum alloy casting process, so that the risk of lower strength of the existing core after moisture absorption is thoroughly avoided. The phenolic resin sintering process is utilized to carbonize and occupy the in-situ pore canal of the binder, so that the strength of the core is gradually enhanced in the sintering process, no obvious defect exists on the surface of the core, and the strength of the core is further enhanced through the bridging of graphene oxide. The pouring core of this application intensity is higher and easily collapss, and collapsibility powder can be according to the direct recycle of carbon residue volume, and the cost is lower.

The foregoing is merely a preferred embodiment of the present application, and is not intended to limit the scope of the present application. All technical schemes according to equivalent changes of the structure, shape and principle of the application are covered in the protection scope of the application.

Claims

1. The preparation method of the water-soluble precise ceramic core for casting the aluminum alloy is characterized by comprising the following steps of:

1) Preparation of corundum glue solution: sieving corundum powder to obtain large-grain corundum and small-grain corundum, and passing through Al (OH) ₃ And H ₃ PO ₄ The alumina gel solution is prepared by reaction, large-grain corundum is put into the alumina gel solution, and corundum gel solution is obtained after homogenizing and stirring;

2) Preparation of phenolic resin: preparing mixed acid from concentrated sulfuric acid and phosphoric acid, forming a reaction monomer solution by phenol and formaldehyde, dripping the mixed acid, heating, stirring and carrying out reflux reaction to obtain a phenolic reaction system;

naturally cooling, standing and aging a phenolic reaction system, drawing a supernatant to obtain a solution phase, and carrying out reduced pressure distillation on a gel phase of a lower viscous colloid to obtain viscous phenolic resin;

3) Preparation of GO mixture: GO powder and AlCl ₃ Mixing with concentrated sulfuric acid to obtain GO dispersion;

adding the GO dispersion liquid into small-grain corundum to form a viscous gel, pouring a solution phase into the small-grain corundum until the viscous gel is disintegrated, heating and stirring the mixture to react to obtain a suspension viscous system, and standing the suspension viscous system to remove an upper-layer clear solution to obtain a viscous GO mixture;

4) Preparation of gel core: mixing corundum glue solution, GO mixture, phenolic resin, carbon powder and curing agent, homogenizing to obtain slurry, heating the slurry once, filling the slurry into a core mold, and pressing to obtain a primary molding core; heat preservation after secondary heating and secondary pressing; heating for three times, and thermally curing to obtain a gel mold core;

5) Preparation of casting core: and heating the gel mold core to 400 ℃, then heating to 700 ℃, and preserving heat to obtain the casting mold core.

2. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: in the step 1), the mass ratio of the alumina gel solution to the large-grain corundum is 0.2-0.25:1.

3. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: the specific preparation process of the phenolic resin in the step 2) is as follows:

slowly adding 98% concentrated sulfuric acid into 85% phosphoric acid with the mass concentration, wherein the mass ratio of the 98% concentrated sulfuric acid to the 85% phosphoric acid is 1:1, preparing mixed acid, taking phenol and formaldehyde with the mole ratio of 1:0.8-0.9 to form a reaction monomer solution, dropwise adding the mixed acid at room temperature for 10min to obtain a 40% formaldehyde aqueous solution, heating to 100 ℃, stirring for 3-5 min, heating to 135-145 ℃, and carrying out reflux reaction for 1-2 h to obtain a viscous phenolic reaction system;

Naturally cooling the phenolic reaction system to room temperature, standing and aging for 1-2 h, drawing the supernatant to obtain a solution phase, and carrying out reduced pressure distillation on the gel phase of the lower viscous colloid at 80 ℃ to obtain the viscous phenolic resin.

4. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: the GO dispersion liquid in the step 3) comprises the following components in proportion: GO powder, alCl ₃ And 98% concentrated sulfuric acid in the mass ratio of 0.09-0.12 to 0.2-0.3 to 1.

5. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: the specific preparation process of the GO mixture in the step 3) is as follows: adding the GO dispersion liquid into the small-grain corundum, wherein the mass ratio of the GO dispersion liquid to the small-grain corundum is 0.1-0.15:1, forming a viscous colloid through a colloid mill made of ceramic materials, pouring a solution phase, pouring the viscous colloid into the small-grain corundum until the viscous colloid is completely disintegrated, pouring a colloid mill system into a heating container, stirring and reacting for 1-2 h at 130 ℃ to obtain a suspension viscous system, and standing to remove an upper clear solution to obtain a viscous GO mixture.

6. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: the proportion of the gel core in the step 4) is as follows: the mass ratio of the corundum glue solution to the GO mixture to the phenolic resin to the carbon powder to the curing agent is 1 (0.56-0.62), 0.15-0.18, 0.008-0.010 and 0.015-0.025.

7. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: the molding temperature of the gel core in the step 4) is controlled as follows: heating corundum glue solution to 40-50 ℃ for one time, sequentially adding GO mixture, phenolic resin, carbon powder and curing agent, continuously heating to maintain the temperature of the mixed system to 40-50 ℃, homogenizing to obtain slurry, filling the slurry into a core mold by low-pressure injection, and pressing under 10-15 Mpa to obtain a primary molding core; heating to 90-100 ℃ for the second time, preserving heat for 10-20 min, and pressing for the second time under 10-15 Mpa; heating for three times to 150 ℃, and thermally curing for 5-15 min to obtain the gel mold core.

8. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 1, wherein the method comprises the following steps: the concrete preparation process of the pouring core in the step 5) is as follows: installing a gel mold core in a casting box, heating the gel mold core to 400 ℃ at a heating gradient of 20 ℃/min, heating to 700 ℃ at a heating gradient of 5 ℃/min, and preserving heat for 2 hours to obtain a casting mold core; and (3) pouring the aluminum alloy at 600-750 ℃ and forming to obtain the aluminum alloy casting.

9. A method for preparing a water-soluble precision ceramic core for casting aluminum alloy according to claim 3, wherein: the method also comprises the recycling process of the casting core:

6) Preparation of the collapsibility powder: soaking the pouring core in hot water, flushing the inner cavity of the aluminum alloy casting with hot water to obtain a collapsibility powder water mixed solution, and filtering and drying to obtain collapsibility powder;

if the carbon residue is less than or equal to 0.5%, directly replacing the raw corundum powder in the step 1);

if the carbon residue is less than or equal to 0.5 percent and less than or equal to 1.5 percent, the corundum powder which is the raw material of the step 1) is directly replaced, and new carbon powder is not needed to be added in the step 4);

if the carbon residue amount is less than or equal to 1.5%, washing the collapsibility powder for 2-3 times by adopting concentrated sulfuric acid with the mass fraction of 98%, washing the collapsibility powder for 2-3 times by using clear water, and drying the collapsibility powder to replace the raw material corundum powder in the step 1), wherein in the step 4), new carbon powder is not needed, and the GO powder consumption in the GO dispersion liquid in the step 3) is reduced.

10. The method for preparing the water-soluble precise ceramic core for casting aluminum alloy according to claim 9, wherein the method comprises the following steps: and in the step 7), the eluent obtained by washing the collapsibility powder by using 98% concentrated sulfuric acid is adopted to replace the 98% concentrated sulfuric acid adopted in the step 3), and the eluent is mixed with the GO powder to prepare a new GO dispersion liquid for preparing the GO mixture.