Molding sand for large castings and application thereof
By adding water-like talc crumblers to the coated sand, the problems of insufficient dissolution efficiency and poor environmental adaptability of the existing cured sand during casting are solved, and efficient dissolution and cleaning of coated sand are achieved, and there is no significant impact on the high-temperature performance and strength of coated sand.
Patent Information
- Application Number
- CN202510079824.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-18
- Publication Date
- 2025-05-13
AI Technical Summary
The existing crushing agents are insufficient in the casting process, poor environmental adaptability, their impact on the strength of the coated sand and potential environmental pollution problems, making it difficult to effectively clean the sand core and sand forms in the castings.
Hydrtalcite-like is used as the crumble agent, and the general formula is [M2+1-xM3+x(OH)2]x+(An-)x/n·yH2O, and is added to the coating sand to improve the crumble rate and cleaning efficiency.
The collapse rate of the coated sand is significantly improved, the cleaning efficiency of the coated sand after casting is improved, and the high-temperature performance and strength of the coated sand is maintained.
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Figure CN119973033A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of coated sand materials, and in particular relates to molding sand for large castings and application thereof. Background Art
[0002] Coated sand, as an advanced foundry sand, has a pre-coated layer of cured binder film, such as phenolic resin film, on its surface. This pre-coated sand can maintain excellent high temperature strength and dimensional stability during the casting process, and is suitable for producing high-quality castings. The preparation of coated sand usually includes raw sand, binder, curing agent, lubricant and other ingredients. The binder is evenly coated on the surface of the sand through a specific process to form a thin and hard film.
[0003] In the casting process, sand cores and sand molds must be effectively removed after the casting solidifies in order to facilitate subsequent processing of the casting. Traditional sand cores and sand molds are often difficult to quickly and thoroughly crush and separate, which not only increases the workload of cleaning castings and prolongs the production cycle, but also reduces production efficiency and increases costs. Therefore, the development of efficient and environmentally friendly disintegrators has become an urgent need in the foundry industry.
[0004] At present, the disintegrators used in the market mainly include inorganic salts, organic compounds and their derivatives. For example, a composition consisting of nitrate, chloride, cresol, sodium fluorescein, ethanol and water has been reported to be used to produce easily disintegrated coated sand. These disintegrators can cause the molecular chains of phenolic resin coated sand to break at high temperatures, so that the sand core and sand mold will automatically collapse after the casting cools, making it easy to clean.
[0005] Although existing disintegrators have improved the disintegration performance of coated sand to a certain extent, they still have some limitations, such as insufficient disintegration efficiency, poor environmental adaptability, impact on the strength of coated sand, and potential environmental pollution problems. In addition, the amount and type of disintegrator added have a significant impact on the final performance of coated sand, and further optimization is needed to balance the disintegration performance with other requirements of the casting process. Researchers are also committed to developing new disintegrators to improve disintegration efficiency and reduce environmental impact without affecting the high temperature performance and strength of coated sand. Summary of the invention
[0006] In view of the above technical problems, this application proposes molding sand for large castings and its application, and the specific technical solutions are as follows:
[0007] The present application provides a large casting molding sand, comprising aggregate, binder, curing agent and disintegrating agent, wherein the disintegrating agent is a hydrotalcite-like substance, and the general formula is [M 2+ 1-x M 3+ x (OH) 2 ]x +(A n- ) x / n ·yH 2 O.
[0008] Preferably, the hydrotalcite-like substance does not exceed 5.5‰ of the mass of the binder, and the amount of hydrotalcite-like substance added is not zero.
[0009] Preferably, the hydrotalcite-like substance does not exceed 4.5‰ of the mass of the binder.
[0010] Preferably, a lubricant is also included.
[0011] Preferably, in the hydrotalcite-like substance, M 2+ Including Mg 2+ 、Zn 2+ , Fe 2+ , Cu 2+ 、Co 2+ .
[0012] Preferably, in the hydrotalcite-like substance, M 3+ Including Al 3+ , Fe 3+ .
[0013] Preferably, in the hydrotalcite-like substance, A n- Including SO 4 2- ,PO 4 3- , organic anions, borate ions, molybdate ions, fluorosilicate ions, and amine hydrochlorides.
[0014] Preferably, in the hydrotalcite-like substance, A n- It is amine hydrochloride.
[0015] On the other hand, the present application provides an application of molding sand for large castings, wherein any of the above-mentioned molding sand is used to make a mold to cast molten metal to make a metal casting.
[0016] The beneficial effect of the present invention is that after adding the hydrotalcite-like substance into the coated sand, the collapse rate of the coated sand is significantly improved, which is beneficial to improving the cleaning efficiency of the coated sand after the casting is completed. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 Shown is a defect diagram of a product cast using the coated sand of Example 10. DETAILED DESCRIPTION
[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments.
[0019] The molding sand for large castings described in the present application comprises aggregate, binder, curing agent and disintegrating agent, as well as other additives such as lubricant which can be optionally added according to specific manufacturing requirements.
[0020] Aggregate: It is the main component of coated sand, usually natural silica sand or other refractory sand, such as zircon sand, chromite sand, etc.
[0021] Binder: Phenolic resin is a commonly used binder.
[0022] Curing agent: The curing agent is usually hexamethylenetetramine (urotropine). Sometimes the curing agent is prepared as an aqueous solution and added to the mixture in a certain proportion.
[0023] Disintegrator: Disintegrator is a hydrotalcite-like substance with the general formula [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Mg 2+ 、Zn 2+ , Fe 2+ , Cu 2+ 、Co 2+ , M 3+ Including Al 3+ , Fe 3+ , and A n- Not for CO 3 2- , A n- Including common SO 4 2- ,PO 4 3- .
[0024] In some cases, A n- It also includes some organic anions, borate ions, molybdate ions, and fluorosilicate ions that can enter the interlayer through intercalation. Except for amine hydrochloride, the recorded some organic anions should be limited to ion types that will not form gas by the hydrotalcite itself or by reaction at high temperature, such as sulfonate ions and alcoholate ions.
[0025] The difference of amine hydrochloride is that amine hydrochloride will generate ammonia when heated. Ammonia is an alkaline gas that can neutralize the acidic groups in phenolic resin, which will interfere with the cross-linking process of the resin and weaken the bonding properties of the resin. Ammonia can also penetrate into the cross-linking network of the resin, causing the resin to swell, thereby reducing its mechanical strength.
[0026] In the following embodiments and comparative examples of the present application, aggregate, binder, curing agent, lubricant and disintegrator and component system are used for exemplary description, wherein the aggregate is natural silica sand (commercially available), the binder is phenolic resin (commercially available), the curing agent is hexamethylenetetramine (commercially available), the lubricant is calcium stearate (commercially available), and the disintegrator is hydrotalcite (commercially available).
[0027] In addition, the present application provides a method for preparing molding sand, which comprises:
[0028] (1) heating natural silica sand to a predetermined temperature and mixing the mixture with a phenolic resin, and using the temperature of the natural silica sand to melt the solid phenolic resin to obtain a first mixture;
[0029] (2) dissolving hexamethylenetetramine in water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0030] (3) Add the hydrotalcite-like substance and calcium stearate to the second mixture and mix well.
[0031] As an illustration of the above method, the target heating temperature of natural silica sand can be set at 130±30°C according to the prior art, phenolic resin is added within 50 seconds after the natural silica sand reaches the target temperature, curing agent aqueous solution is added within 25 seconds after the addition of phenolic resin, and hydrotalcite and calcium stearate are added within 60 seconds after the addition of curing agent aqueous solution.
[0032] According to an exemplary molding sand of the prior art, the contents (mass fractions) of the various components are as follows:
[0033] 95 parts of aggregate, 5.5 parts of binder, 0.6 parts of curing agent, and 0.2 parts of lubricant.
[0034] Example 1
[0035] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0036] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0037] 0.01 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0038] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(An- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0039] Example 2
[0040] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0041] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0042] 0.015 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0043] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0044] Example 3
[0045] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0046] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0047] 0.02 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0048] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0049] Example 4
[0050] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0051] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0052] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0053] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0054] Example 5
[0055] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0056] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0057] 0.03 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0058] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0059] Example 6
[0060] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0061] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0062] 0.035 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0063] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0064] Example 7
[0065] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0066] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0067] 0.04 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0068] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0069] Example 8
[0070] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0071] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0072] 0.045 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0073] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0074] Example 9
[0075] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0076] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0077] 0.05 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed evenly.
[0078] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0079] Comparative Example 1
[0080] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0081] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0082] Add 0.2 g of calcium stearate to the second mixture and mix well.
[0083] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For SO 4 2- .
[0084] The collapsibility of the coated sands of Examples 1 to 9 and Comparative Example 1 was tested, and the room temperature flexural strength, hot flexural strength, ignition loss and melting point were also tested. The test results are shown in Table 1.
[0085] Table 1: Collapse rate, room temperature flexural strength, hot flexural strength, ignition loss and melting point of Examples 1 to 9 and Comparative Example 1
[0086]
[0087] Combining the test results of Examples 1 to 9 and Comparative Example 1, it can be seen that after adding hydrotalcite-like substances to the coated sand, the disintegration rate of the coated sand is significantly improved, indicating that the addition of hydrotalcite-like substances is beneficial to improving the cleaning efficiency of the coated sand after casting; and as the amount of hydrotalcite-like substances added increases, the improvement in disintegration becomes more obvious. At the same time, the loss on ignition of the coated sand is basically maintained at about 1.5%, and the melting point is basically maintained at about 105°C; however, when the amount of hydrotalcite-like substances added exceeds 5.5‰ of the mass of the binder, it is not conducive to maintaining the mechanical properties of the coated sand, such as room temperature flexural strength and hot flexural strength.
[0088] The general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ is a divalent metal ion, M 3+ It is a trivalent metal ion, and the whole is in a layered double metal hydroxide state, with anions between the layers and crystal water between the layers. The following changes will occur in the hydrotalcite of this structure during heating:
[0089] (1) Dehydration stage: At a relatively low temperature (approximately between 100°C and 200°C), hydrotalcite-like materials will first lose interlayer crystalline water due to the evaporation of water molecules;
[0090] (2) Anion decomposition and metal oxidation stage: As the temperature increases, at about 300°C to 400°C, the interlayer anions begin to react with the metal cations to form metal oxides;
[0091] (3) Complete decomposition stage: At higher temperatures (about 500°C or above), the hydrotalcite-like structure is completely destroyed, all interlayer anions are expelled, and metal cations are completely converted into metal oxides.
[0092] The application environment in this application is the production of large steel castings (such as forklift counterweights), and the casting temperature is basically over 1000°C, so that the zinc-aluminum sulfate-type hydrotalcite in the coated sand will lose interlayer crystallization water under this temperature condition, and further react to generate a part of zinc oxide, aluminum oxide and sulfate. Finally, the hydrotalcite structure is completely destroyed, all interlayer anions are expelled, and metal cations are completely converted into metal oxides. The final product is mainly zinc oxide, aluminum oxide and possible sulfate or other residues.
[0093] Under the high temperature conditions of casting, the metal ions on the surface of the generated metal oxide can serve as active centers to adsorb phenolic resin molecules, reduce the activation energy of the reaction, thereby making the decomposition reaction easier and promoting the bond breaking of the phenolic resin molecules; on the other hand, the generated alkaline metal oxide has the effect of catalyzing the breaking of cross-linked bonds in the resin structure, thereby accelerating the decomposition of the phenolic resin.
[0094] Example 10
[0095] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0096] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0097] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0098] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For CO 3 2- .
[0099] Embodiment 11
[0100] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0101] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0102] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0103] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- NO 3 - .
[0104] Example 12
[0105] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0106] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0107] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0108] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- For PO 4 3- .
[0109] Embodiment 13
[0110] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0111] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0112] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0113] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- It is the borate ion.
[0114] Embodiment 14
[0115] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0116] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0117] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0118] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- It is the benzoate ion.
[0119] Embodiment 15
[0120] 95 g of natural silica sand was heated to 150° C. and mixed with 5.5 g of phenolic resin to obtain a first mixture;
[0121] Dissolving 0.6 g of hexamethylenetetramine in 2 ml of water to obtain a curing agent aqueous solution, and then uniformly mixing the curing agent aqueous solution with the first mixture to obtain a second mixture;
[0122] 0.025 g of hydrotalcite and 0.2 g of calcium stearate were added to the second mixture and mixed well.
[0123] In this embodiment, the general formula of hydrotalcite is [M 2+ 1-x M 3+ x (OH) 2 ] x +(A n- ) x / n ·yH 2 O, where M 2+ Including Zn 2+ , M 3 + For Al 3+ , A n- It is diethylamine hydrochloride ion (amine hydrochloride ion).
[0124] The hydrotalcite-like substances used in the above-described embodiments are all prepared by co-precipitation method, and the specific method is as follows:
[0125] Prepare the required metal salt, alkaline source and anion to be intercalated;
[0126] Dissolving a metal salt in deionized water to form a metal salt solution of a certain concentration;
[0127] Slowly add an alkali source to the metal salt solution while continuously stirring to control the pH of the solution;
[0128] During the addition of the alkali source, the solution is kept stirred at a certain temperature, usually between 60°C and 100°C;
[0129] After the precipitation is completed, continue stirring and keep the constant temperature for a period of aging;
[0130] After aging is completed, the precipitate is collected by filtration, and the precipitate is washed several times with deionized water or alcohol to remove attached impurities and unreacted alkali;
[0131] The washed precipitate is dried in an oven, usually at around 100°C, until the water is completely removed.
[0132] The specific preparation method is provided by way of example with zinc-aluminum sulfate-type hydrotalcite, and the method is as follows:
[0133] (1) Zinc nitrate Zn(NO 3 ) 2 6H 2 O and aluminum nitrate Al(NO 3 ) 3 9H 2 O was dissolved in deionized water at a molar ratio of 2:1 to obtain a metal salt solution, ensuring that the solution was completely clear without precipitation;
[0134] (2) using sodium hydroxide as the alkali source and sodium sulfate as the sulfate source;
[0135] (3) Under magnetic stirring, slowly add the metal salt solution dropwise to the beaker containing the alkaline source while controlling the pH value between 8 and 10; the temperature is usually controlled at 70-90°C and maintained using a heating plate or oil bath; the stirring rate is generally set at 300-500 rpm to ensure that the solution is fully mixed;
[0136] (4) After the addition is completed, continue stirring and aging at the set temperature for more than 8 hours;
[0137] (5) dispersing the initially formed hydrotalcite in a sodium sulfate solution, and then stirring for a certain period of time at room temperature or under heating conditions to promote sulfate ions to enter the interlayer space;
[0138] (6) filtering out the precipitate using a Buchner funnel or a vacuum filter; washing the precipitate multiple times with deionized water or ethanol to remove residual alkali and ions that do not participate in the reaction;
[0139] (7) drying the washed precipitate in an oven at 100-110° C. until the water is completely removed;
[0140] Optionally, the dried hydrotalcite is calcined in a muffle furnace at 200-300° C. for 1-2 hours to enhance its thermal stability and improve its structural integrity.
[0141] The collapsibility of the coated sands of Examples 1 to 9 and Comparative Example 1 was tested, and the room temperature flexural strength, hot flexural strength, ignition loss and melting point were also tested. The test results are shown in Table 2.
[0142] Table 2: Collapse rate, room temperature flexural strength, hot flexural strength, ignition loss and melting point of Examples 10 to 15 and Comparative Example 1
[0143]
[0144]
[0145] Combining the test results of Examples 10 to 15 and the aforementioned Example 4, it can be seen that after adding hydrotalcite-like substances to the coated sand, the collapse rate of the coated sand is significantly improved, indicating that the addition of hydrotalcite-like substances is beneficial to improving the cleaning efficiency of the coated sand after casting. More notably, when the interlayer anion is diethylamine hydrochloride ion, the collapse rate of the coated sand is greater than that of other embodiments. This is because the diethylamine hydrochloride ion is an amine hydrochloride, which will generate ammonia after heating. Ammonia is an alkaline gas, which can neutralize the acidic groups in the phenolic resin, which will interfere with the cross-linking process of the resin and weaken the bonding performance of the resin. Ammonia can also penetrate into the cross-linked network of the resin, causing the resin to swell, thereby reducing its mechanical strength, and it plays a further synergistic role with the alkali metal generated by the hydrotalcite-like substances.
[0146] However, it should be noted that, when the collapse rate and other properties in Examples 10 and 11 are maintained at the same level, when castings are cast with the coated sand of Examples 10 and 11, it is found that some castings with slightly complex surface structures will form visible sand holes on part of the surface, such as Figure 1 As shown, this phenomenon is rarely seen in the application process of other embodiments. It is speculated that the gas generated by the heating of anions such as carbonate and nitrate, and the rapid expansion of the crystal water lost in the mixed part due to the heating cause the sand mold cavity on the surface of the complex structure to explode and form sand holes.
[0147] The coated sand prepared in this application refers to "Coated Sand for Casting" (JB / T8583-2008), the coating is made into an "8"-shaped standard sample, and after being kept at 800°C for 5 minutes, it is placed on a 20-mesh pendulum machine for 10 seconds, and the coated sand that passes through the sieve is collected and weighed. The ratio of the coated sand to the weight of the coated sand is the collapse rate of the coated sand.
[0148] The coated sand prepared in this application is tested for room temperature flexural strength, hot flexural strength, loss on ignition, average fineness and melting point according to "Coated Sand for Casting" (JB / T8583-2008).
[0149] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them.
Claims
1. Molding sand for large castings, characterized in that: It comprises aggregate, binder, curing agent and disintegrating agent, wherein the disintegrating agent is a hydrotalcite-like substance, and the general formula is [M 2+ 1-x M 3+ x (OH)2] x +(A n- ) x / n ·yH2O.
2. The molding sand for large castings according to claim 1, characterized in that: The hydrotalcite-like substance does not exceed 5.5‰ of the mass of the binder, and the amount of hydrotalcite-like substance added is not zero.
3. The molding sand for large castings according to claim 2, characterized in that: The hydrotalcite-like substance does not exceed 4.5‰ of the mass of the binder.
4. The molding sand for large castings according to claim 1, characterized in that: Also includes lubricant.
5. The molding sand for large castings according to claim 1, characterized in that: In the hydrotalcite-like substance, M 2+ Including Mg 2+ 、Zn 2+ , Fe 2+ , Cu 2+ 、Co 2+ .
6. The molding sand for large castings according to claim 1, characterized in that: In the hydrotalcite-like substance, M 3+ Including Al 3+ , Fe 3+ .
7. The molding sand for large castings according to claim 1, characterized in that: In the hydrotalcite-like substance, A n- Including SO4 2- PO4 3- , organic anions, borate ions, molybdate ions, fluorosilicate ions, and amine hydrochlorides.
8. The molding sand for large castings according to claim 1, characterized in that: In the hydrotalcite-like substance, A n- It is amine hydrochloride.
9. Application of molding sand for large castings, characterized in that: The molding sand according to any one of claims 1 to 8 is used to make a mold for casting molten metal to make a metal casting.