Inorganic coated sand for preventing the sticking of sand to a casting and maintaining high flowability of a pore and a method for producing the same

Abstract

The present application relates to a kind of inorganic coating sand for preventing casting sand and keeping pore high fluidity and its preparation method.The method is: sequentially grinding, particle size screening to Inner Mongolia sand, to obtain screened sand;It is heated, and adding alkali phenolic resin is stirred evenly, to obtain modified sand;It is cooled, and then sequentially adding inorganic binder, inorganic powder and stirring evenly, to obtain inorganic binder sand;It is filled into sand shooting hopper and sprayed to mold, after completion, it can be heated to mold drum hot air heating.The method relative to traditional coated sand and cold core sand, inorganic binder sand casting process has no gas generated by the decomposition of organic matter, can effectively avoid the pore defect of aluminum alloy casting;And Inner Mongolia sand is ground and screened, and the angular coefficient and concentration are optimized, the fluidity of inorganic binder sand is greatly improved, and the surface of sand particle is weak alkaline, can effectively avoid the case that the surface of sand particle is weak acid and causes inorganic bonding system to weaken, further consolidate the strength of inorganic binder sand core.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy casting, specifically relating to an inorganic coated sand that prevents sand from sticking to castings and maintains high porosity and its preparation method. Background Technology

[0002] Lightweighting of automobiles is an important development direction for the automotive industry. Therefore, the market demand for aluminum alloy automotive parts in my country is increasing daily. For example, key aluminum alloy components such as engine cylinder heads, new energy motor housings, subframes, and H-arms are in short supply. These aluminum alloy castings are mostly produced using gravity casting processes, with metal molds for the outer cavity and sand core molds for the inner cavity. Therefore, the performance of the sand core is crucial.

[0003] Patent application number 2021110128868 discloses a method for preparing high-strength, low-gas-emission coated sand. The method involves modifying thermosetting phenolic resin with polysulfone resin, adding the resulting polysulfone-modified thermosetting phenolic resin as a binder to mixed sand, adding hexamethylenetetramine and barium carbonate as curing agents to the mixture, continuing mixing, and finally adding calcium stearate as a lubricant to mix the sand before discharge. The resulting sand is then crushed and sieved to obtain a high-strength, low-gas-emission coated sand. This coated sand exhibits slow gas generation. During metal casting, the gas generation rate only significantly increases after the molten metal has been poured and a thin metal shell has solidified on the surface. This prevents most of the gas from entering the molten metal, significantly reducing the porosity defect rate of the casting. However, this modification process is relatively complex and can only alleviate the rate of organic matter decomposition, not completely eliminate the gas generated by organic matter decomposition, resulting in significant porosity defects in the casting.

[0004] Patent application number 202010896384 discloses a method for preparing acid-based cold box resin for casting and its application, belonging to the category of casting molding sand binders. The cold box resin uses an acidic curing gas source, such as acetic acid or oxalic acid, which decomposes naturally and is non-toxic and harmless, thus preventing defects such as hot cracking and burrs in castings. The self-hardening sand of the cold box resin has low gas evolution and good collapsibility. However, further analysis reveals that although this cold box resin minimizes gas evolution, significant casting porosity defects still exist. Acetic acid and oxalic acid release irritating odors during core-making and casting, which is extremely environmentally unfriendly.

[0005] Patent application number 2019102254804 discloses an inorganic binder for casting, comprising an alkali metal silicate, a surfactant, a modulus adjuster, a preservative, a modifier, and a solvent; the alkali metal silicate is at least one of sodium silicate, potassium silicate, and lithium silicate; the surfactant is an anionic surfactant; the modulus adjuster is a strong alkali; the solvent is deionized water; the preservative is one or a combination of potassium sorbate, ethylparaben, propylparaben, and sorbic acid; the modifier is one or a combination of sodium hexametaphosphate, sodium tripolyphosphate, dipotassium hydrogen phosphate, dextrin, and silica; and the inorganic binder for casting is an alkaline aqueous solution. This inorganic binder has low viscosity, low gas evolution, low cost, and low VOC emissions. However, this patent only mentions one synthesis scheme for the inorganic binder and does not consider the flow properties during use, nor does it address issues such as nozzle clogging and sand adhesion.

[0006] It is important to note that inorganic binders are based on modified water glass and consist of multiple components including activators (hardeners), crosslinking agents, rheology modifiers, and dispersants. During core making, the sodium silicate in the modified water glass forms silica gel under the action of CO2 or high-temperature dehydration, thus providing bonding strength. Surveys of foundry enterprises show two problems with inorganic sand during use: 1) it requires high aggregate fluidity, easily causing nozzle blockage during core making; 2) it is sensitive to aggregate pH; if the sand grain surface is weakly acidic, the inorganic sand core strength is low, and sand adhesion easily occurs during casting. This invention provides a high-fluidity inorganic coated sand that prevents sand adhesion and porosity in aluminum alloy castings. It effectively improves the strength and fluidity of inorganic sand and significantly reduces the sand adhesion and porosity defect rate of aluminum alloy castings compared to traditional coated sand and cold box processes.

[0007] Traditional coated sand and cold box process sand cores both use sand as aggregate and organic resin as binder. During the casting process, due to insufficient high temperature resistance and large gas generation, the castings are prone to sand adhesion and porosity defects. According to statistics, the scrap rate caused by sand adhesion and porosity defects in castings can exceed 50% in severe cases.

[0008] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides an inorganic coated sand that prevents sand from adhering to castings and maintains high fluidity of pores, and its preparation method.

[0010] The present invention provides a method for preparing inorganic coated sand that prevents sand adhesion to castings while maintaining high fluidity of pores. The preparation method includes the following steps:

[0011] (1) Grind and screen the Inner Mongolia sand in sequence to obtain screened sand;

[0012] (2) The sieved sand is heated and alkali phenolic resin is added and stirred evenly to obtain modified sand;

[0013] (3) Cool the modified sand, then add inorganic binder and inorganic powder in sequence and stir evenly to obtain inorganic binder sand;

[0014] (4) The inorganic binder sand is loaded into the sand-shooting hopper and sprayed into the mold. After completion, hot air is blown into the mold to heat it.

[0015] Preferably, the weight ratio of the Inner Mongolian sand, alkali-phenolic resin, inorganic binder, and inorganic powder is 100:0.2-0.9:1-3:0.5-1.5. Through repeated verification by the inventors, when the proportion of alkali-phenolic resin is too high, the gas generation increases accordingly, causing porosity in the casting; when the proportion of alkali-phenolic resin is too low, the strength is insufficient, and the sand core is prone to breakage and scrap. When the proportion of inorganic binder is too high, the collapsibility is poor, making casting cleaning difficult; when the proportion of inorganic binder is too low, the strength is insufficient. When the proportion of inorganic powder is too high, the usable time is shortened, core making nozzles become clogged, and the sand core is loose; when the proportion of inorganic powder is too low, the sand core solidifies slowly, resulting in high production energy consumption.

[0016] Preferably, in step (1), 100 parts by weight of Inner Mongolian sand with a specification of 50 / 100 mesh is taken and ground for 20 to 50 seconds at 360 to 1200 r / min. After grinding, the Inner Mongolian sand is subjected to particle size sieving to remove Inner Mongolian sand with a particle size of more than 20 mesh, and the content of Inner Mongolian sand with a particle size of less than 140 mesh is controlled to be ≤2%, and the concentration of the 50 / 100 three-sieve is ≥92%, so as to obtain sieved sand.

[0017] Preferably, in step (1), 100 parts by weight of Inner Mongolia sand with a specification of 50 / 100 mesh is taken and ground for 20 to 50 seconds at 360 to 1200 r / min. After grinding, the Inner Mongolia sand is sieved to remove particles larger than 20 mesh, and the content of particles smaller than 140 mesh is controlled to be ≤2%, and the concentration of the 50 / 100 three-sieve is ≥92%, so as to obtain sieved sand.

[0018] Preferably, in step (2), the screened sand is heated to 120-180°C, put into a sand mixer, and 0.2-0.9 parts by weight of alkali phenolic resin is added and stirred for 10-60 seconds to obtain modified sand.

[0019] Preferably, in step (3), the modified sand is cooled to 10-40°C, 1-3 parts by weight of inorganic binder are added first, and the mixture is stirred for 30-60 seconds; then 0.5-1.5 parts by weight of inorganic powder are added, and the mixture is stirred for 20-60 seconds to obtain inorganic binder sand.

[0020] Preferably, in step (4), the inorganic binder sand is loaded into the sand-shooting hopper and sprayed into the mold. The sand-shooting pressure is 0.3-0.6 MPa and the venting time is 1-3 s. After completion, hot air at 100-200°C is blown into the mold for 20-60 s. The mold heating temperature is 150-200°C. After completion, the mold is ready.

[0021] Preferably, the free phenol in the alkali phenolic resin is ≤8 wt.%, the free aldehyde is ≤5 wt.%, the solid content is ≥73 wt.%, and the pH is 8-9.

[0022] Preferably, the inorganic binder contains ≥35 wt.% sodium silicate, ≤2 wt.% phosphorus pentoxide, and ≤60 wt.% water.

[0023] Preferably, the inorganic powder contains 90-95 wt.% silica, 3-5 wt.% aluminum oxide, 1-2 wt.% chromium oxide, and ≤2 wt.% other oxides.

[0024] Based on the same technical concept, another aspect of the present invention is to provide an inorganic coated sand prepared by the above method that prevents sand from sticking to castings and maintains high fluidity of pores.

[0025] The beneficial effects of this invention are as follows:

[0026] The preparation method described in this invention, compared to traditional coated sand and cold-core sand, eliminates the gas generated by the decomposition of organic matter during the inorganic binder sand casting process, effectively preventing poor porosity in aluminum alloy castings. Furthermore, the inner lining sand undergoes grinding and sieving, optimizing the angularity coefficient and concentration (angularity coefficient optimized from ≤1.3 to ≤1.1, and three-screen concentration optimized from ≥80% to ≥90%), significantly improving the fluidity of the inorganic binder sand. Additionally, the optimized inner lining sand is coated and modified with alkaline phenolic resin, resulting in a smoother surface and enhanced properties. The inorganic binder adheres well to the surface of the sand grains. The weakly alkaline surface of the sand grains effectively prevents the weakening of the inorganic bonding system caused by a weakly acidic surface, further strengthening the strength of the inorganic binder-bonded sand core. Finally, the inorganic binder of this invention uses sodium silicate (its aqueous solution is commonly known as water glass) as a base material. During the core-making process, the sodium silicate in the modified water glass forms a silica gel under the action of CO2 or high-temperature dehydration, thus possessing bonding strength. Furthermore, the inorganic binder emits no VOCs during the core-making and casting processes, making it environmentally friendly. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] In the examples, the raw materials used are expressed in "parts by weight". In the actual preparation process, the proportions can be adjusted according to the actual amount used, which is a common practice for those skilled in the art. For example, when the amount used is small, 100 parts by weight can represent 100g; when the amount used is large, 100 parts by weight can represent 1000g, that is, the amount used can be increased or decreased proportionally according to the needs.

[0029] Example 1

[0030] This embodiment provides a method for preparing inorganic coated sand that prevents sand adhesion to castings while maintaining high porosity and fluidity. The method includes the following steps:

[0031] (1) Take 100 parts by weight of Inner Mongolia sand with a specification of 50 / 100 mesh, grind it for 20s under the condition of grinding wheel speed of 360r / min, and then sieve the Inner Mongolia sand to remove particles larger than 20 mesh, control the content of particles smaller than 140 mesh to be 1.0%, and the concentration of 50 / 100 three-sieve is ≥95% to obtain sieved sand.

[0032] (2) The screened sand is heated to 120°C, put into a sand mixer and 0.2 parts by weight of alkali phenolic resin is added and stirred for 10 seconds to obtain modified sand; wherein, the free phenol in the alkali phenolic resin is 7 wt.%; the free aldehyde is ≤3 wt.%; the solid content is ≥75 wt.%; and the pH is 8.2.

[0033] (3) The modified sand is placed in a fluid cooling tank and cooled to 20°C. Two parts by weight of inorganic binder are added and stirred for 30 seconds. Then, one part by weight of inorganic powder is added and stirred for 20 seconds to obtain inorganic binder sand. The inorganic binder contains 40 wt.% sodium silicate, 59 wt.% water, and ≤1 wt.% phosphorus pentoxide. The inorganic powder contains 95 wt.% microsilica, 3 wt.% aluminum oxide, 1 wt.% chromium oxide, and 1 wt.% other oxides.

[0034] (4) The inorganic binder sand is loaded into the sand shooting hopper, the sand shooting pressure is 0.6 MPa, the venting time is 2 s, the sand is filled into the mold, and hot air at 200°C is blown in for 30 s. The mold is heated to 180°C to make a sand core.

[0035] In the subsequent stage, molten aluminum can be poured at a temperature of 750°C to obtain the finished casting.

[0036] Example 2

[0037] This embodiment provides a method for preparing inorganic coated sand that prevents sand adhesion to castings while maintaining high porosity and fluidity. The method includes the following steps:

[0038] (1) Take 100 parts by weight of Inner Mongolia sand with a specification of 50 / 100 mesh, grind it for 50s under the condition of grinding wheel speed of 1200r / min, and after grinding, Inner Mongolia sand is screened to remove particles larger than 20 mesh, control the content of particles smaller than 140 mesh to be 1.0%, and the concentration of 50 / 100 three-screen ≥96% to obtain screened sand;

[0039] (2) Heat the screened sand to 180°C, put it into a sand mixer and add 0.9 parts by weight of alkali phenolic resin and stir for 60 seconds to obtain modified sand; wherein, the free phenol in the alkali phenolic resin is 8%, the free aldehyde is ≤4wt.%, the solid content is ≥76wt.%, and the pH is 9.

[0040] (3) The modified sand is placed in a fluid cooling tank and cooled to 40°C. 3 parts by weight of inorganic binder are added and stirred for 60 seconds. Then 1.5 parts by weight of inorganic powder are added and stirred for 60 seconds to obtain inorganic binder sand. The inorganic binder contains 40 wt.% sodium silicate, 59 wt.% water, and ≤1 wt.% phosphorus pentoxide. The inorganic powder contains 95 wt.% microsilica, 3 wt.% aluminum oxide, 1 wt.% chromium oxide, and 1 wt.% other oxides.

[0041] (4) The inorganic binder sand is loaded into the sand shooting hopper, the sand shooting pressure is 0.3 MPa, the venting time is 3 s, the sand is filled into the mold, and hot air at 200°C is blown in for 60 s. The mold is heated to 180°C to make a sand core.

[0042] In the subsequent stage, molten aluminum can be poured at a temperature of 750°C to obtain the finished casting.

[0043] Comparative Example

[0044] Comparative Example 1: Compared with Example 1, Comparative Example 1 did not involve a grinding process, but all other operations were the same as in Example 1.

[0045] Comparative Example 2: Compared with Example 1, Comparative Example 2 did not involve a sieving process, but other operations were the same as in Example 1.

[0046] Comparative Example 3: Compared with Example 1, Comparative Example 3 uses alkali-free phenolic resin to modify the surface of sand particles, and other operations are the same as in Example 1.

[0047] Comparative Example 4: Cores were made using the existing coated sand process, with the same amount of binder added and the same casting conditions as in Example 1.

[0048] Comparative Example 5: Cores were made using the existing cold box process, with the same amount of binder added and the same casting conditions as in Example 1.

[0049] To demonstrate the technical effects of the present invention, tests were conducted on Example 1 and Comparative Examples 1 to 5. The test methods were as follows:

[0050] The test of sand core strength, flowability, and gas generation should refer to standard JB / T8583-2008.

[0051] Core production yield: Prepare 100 identical sand cores and calculate the yield.

[0052] Casting yield: 100 castings were cast, and the sand adhesion rate and porosity were calculated.

[0053] The test results are shown in Table 1.

[0054] Table 1. Physicochemical Properties

[0055]

[0056]

[0057] The data shows that when the grinding process is removed, the sand core strength of Comparative Example 1 decreases by 15%, the fluidity increases by 21%, the gas generation remains unchanged, the core yield decreases by 18%, the casting sand adhesion scrap rate increases by 4%, and the casting porosity scrap rate increases by 1%.

[0058] When the screening process was removed, the sand core strength of Comparative Example 2 decreased by 20%, the fluidity increased by 23%, the gas generation increased by 2%, the core yield decreased by 10%, the casting sand adhesion scrap rate increased by 3%, and the casting porosity scrap rate increased by 1%.

[0059] When the alkali-phenolic resin modification process was removed, the core strength of Comparative Example 3 decreased by 40%, the fluidity increased by 15%, the gas generation decreased by 2%, the core yield decreased by 22%, the casting sand adhesion scrap rate increased by 8%, and the casting porosity scrap rate increased by 2%.

[0060] When the existing coated sand process is used for core making and the amount of binder added is the same, the core strength of Comparative Example 4 decreases by 15%, the fluidity increases by 19%, the gas generation increases by 159%, the core making yield increases by 2%, the casting sand adhesion scrap rate increases by 9%, and the casting porosity scrap rate increases by 7%.

[0061] When the existing cold box process is used for core making and the amount of binder added is the same, the sand core strength of Comparative Example 5 decreases by 35%, the fluidity is prolonged by 21%, the gas generation increases by 149%, the core making yield decreases by 1%, the casting sand adhesion scrap rate increases by 11%, and the casting porosity scrap rate increases by 8%.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing inorganic coated sand that prevents sand adhesion to castings while maintaining high porosity and fluidity, characterized in that, The preparation method includes the following steps: (1) Take 100 parts by weight of Inner Mongolia sand with a specification of 50 / 100 mesh, grind it for 20-50 seconds at 360~1200r / min, and after grinding, perform particle size sieving on the Inner Mongolia sand to remove Inner Mongolia sand with a particle size of more than 20 mesh, and control the content of Inner Mongolia sand with a particle size of less than 140 mesh to be ≤2%, and the concentration of the 50 / 100 three-sieve to be ≥92% to obtain sieved sand; (2) The sieved sand is heated and alkali phenolic resin is added and stirred evenly to obtain modified sand; (3) Cool the modified sand, then add inorganic binder and inorganic powder in sequence and stir evenly to obtain inorganic binder sand; (4) The inorganic binder sand is loaded into the sand-shooting hopper and sprayed into the mold. After completion, hot air is blown into the mold to heat it. in: The weight ratio of the Inner Mongolia sand, alkali phenolic resin, inorganic binder and inorganic powder is 100:0.2~0.9:1~3:0.5~1.5; The alkali-phenolic resin contains ≤8 wt.% free phenol, ≤5 wt.% free aldehyde, ≥73 wt.% solid content, and pH 8-9. The inorganic binder contains ≥35 wt.% sodium silicate, ≤2 wt.% phosphorus pentoxide, and ≤60 wt.% water. The inorganic powder contains 90-95 wt.% microsilica, 3-5 wt.% aluminum oxide, 1-2 wt.% chromium oxide, and ≤2 wt.% other oxides.

2. The preparation method according to claim 1, characterized in that, In step (2), the screened sand is heated to 120~180℃, put into a sand mixer and 0.2~0.9 parts by weight of alkali phenolic resin is added and stirred for 10~60s to obtain modified sand.

3. The preparation method according to claim 1, characterized in that, In step (3), the modified sand is cooled to 10~40℃, 1~3 parts by weight of inorganic binder are added first, and stirred for 30~60s; then 0.5~1.5 parts by weight of inorganic powder are added, and stirred for 20~60s to obtain inorganic binder sand.

4. The preparation method according to claim 1, characterized in that, In step (4), the inorganic binder sand is loaded into the sand-shooting hopper and sprayed into the mold. The sand-shooting pressure is 0.3~0.6MPa and the venting time is 1~3s. After completion, hot air at 100~200℃ is blown into the mold for 20~60s. The mold heating temperature is 150~200℃. After completion, it is ready.

5. Inorganic coated sand obtained by any of the preparation methods described in claims 1 to 4, which prevents sand from adhering to castings and maintains high fluidity of pores.

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