Molding sand powder for casting and processing technology thereof

Abstract

The present invention provides a foundry sand powder and a processing technology thereof, belonging to the field of the foundry industry. The present invention uses hydrophobic bentonite, coal powder, silicate, and starch as main components, and modifies calcium silicate. The calcium silicate is used in combination with anion-modified starch. By introducing the hydrophobic component, the water content of the sand powder is effectively reduced, the compaction rate is increased, and the strength of the sand powder is ensured to meet requirements during use.

Description

Technical Field

[0001] The invention belongs to the field of casting industry, and in particular relates to casting sand powder and a processing technology thereof. Background Art

[0002] Sand casting is a method of producing castings in sand molds. Steel, iron, and most nonferrous alloy castings can be produced using this method. Because the molding materials used in sand casting are inexpensive and readily available, and the molds are simple to manufacture, sand casting is adaptable to single-piece, batch, and mass production. It has long been a fundamental process in foundry production. The quality of sand castings is closely related to the quality of the sand powder used. Poor sand powder quality results in significant casting rejects. Statistics show that molding and core-making costs account for half of a casting's total cost, with 60% of casting rejects caused by these factors. 70% of welding defects in castings are related to the molding and core-making materials.

[0003] The quality of molding sand powder has a vital impact on the quality of castings produced by casting. However, the existing ordinary casting sand powder has too high water content, which will cause dilution and softening of the clay film. At the same time, the molding sand powder has a low compaction rate and cannot be well coated, resulting in a decrease in wet compressive strength.

[0004] Therefore, how to modify the components of the molding sand powder, introduce hydrophobic components, effectively reduce the water content of the molding sand powder, and increase the compaction rate to ensure that the strength of the molding sand powder can meet the requirements when used has become a direction that needs to be focused on. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a casting sand powder and its processing technology, aiming to solve the problems that the existing casting sand powder has too high water content, causing dilution and softening of the clay film, and at the same time, the molding sand powder has a low compaction rate and cannot be well coated, resulting in reduced wet compressive strength.

[0006] The present invention uses hydrophobic bentonite, coal powder, silicate and starch as main components, and modifies calcium silicate. At the same time, it is used together with anion-modified starch. By introducing the hydrophobic component, the water content of the molding sand powder is effectively reduced, and the compaction rate is increased, so as to ensure that the strength of the molding sand powder can meet the requirements when used.

[0007] The technical solutions of the present invention are as follows:

[0008] A first aspect of the present invention provides a molding sand powder for casting, comprising, by weight, 60 to 70 parts of hydrophobic bentonite, 15 to 26 parts of coal powder, 5 to 10 parts of silicate, and 3 to 8 parts of starch.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0010] As a preferred technical solution of the present invention, the preparation method of the hydrophobic bentonite is:

[0011] In parts by weight, 30 parts of bentonite and 5 parts of hexadecyltrimethylammonium bromide were added to 200 parts of deionized water, stirred evenly, and then oscillated at 150 r / min for 4 hours using a constant temperature digital oscillator at 60°C. After the oscillation was completed, the mixture was centrifuged, and the centrifugal precipitate was dried at 50°C for 12 hours and ground to obtain hydrophobic bentonite.

[0012] After conventional bentonite is modified with hexadecyltrimethylammonium bromide cationic modifier, hexadecyltrimethylammonium bromide combines with the surface of bentonite particles, changing the surface of bentonite particles from hydrophilic to hydrophobic, reducing affinity to water, and effectively reducing the water content of molding sand powder.

[0013] As a preferred technical solution of the present invention, the silicate is selected from any one of magnesium silicate, calcium silicate, aluminum silicate, and iron silicate, or a combination of at least two thereof.

[0014] As a preferred technical solution of the present invention, the calcium silicate is modified calcium silicate; the preparation method of the modified calcium silicate is:

[0015] (1) In parts by weight, 10 parts of calcium silicate were added to 100 parts of deionized water, and the mixture was stirred for 0.5 h to obtain a suspension. A hydrochloric acid solution with a mass concentration of 5% was added dropwise to the suspension, and the mixture was reacted at a pH of 5 for 2 h. After the reaction was completed, the mixture was filtered, and the filter residue was dried to obtain acidified calcium silicate.

[0016] (2) In parts by weight, 10 parts of acidified calcium silicate were added to 150 parts of anhydrous ethanol and dispersed uniformly, and then 30 parts of ammonia water and 20 parts of deionized water were added, stirred for 0.5 h, and then 6 parts of dodecyltriethoxysilane were added. The mixture was reacted at 80° C. for 6 h. After the reaction was completed, the mixture was filtered, and the product was washed three times by centrifugation with anhydrous ethanol and vacuum dried at 60° C. for 12 h to obtain modified calcium silicate.

[0017] By pretreating calcium silicate with hydrochloric acid, a large number of silanol groups can be stimulated to form acidified calcium silicate on the surface of calcium silicate. The rich silanol groups in the acidified calcium silicate can undergo a grafting reaction, and the low-surface-energy substance dodecyltriethoxysilane is introduced for microencapsulation modification. Dodecyltriethoxysilane forms hydrophobic groups on the surface of calcium silicate particles and is coated on the surface of calcium silicate particles with a nanolayer structure, which greatly increases the contact angle of the modified calcium silicate, improves the hydrophobic properties, and reduces the water content of the molding sand powder.

[0018] As a preferred technical solution of the present invention, the starch is anionically modified starch; the preparation method of the anionically modified starch is:

[0019] In parts by weight, 10 parts of α-starch and 15 parts of triethanolamine were weighed and added to 100 parts of deionized water, stirred and dissolved for 1 hour, and then 0.5 parts of epichlorohydrin were added to react for 2 hours. After the reaction was completed, 6 parts of acrylic acid and 0.2 parts of ammonium persulfate were added, and the mixture was reacted at 70°C for 4 hours to obtain a starch mixture; 1 part of 3-sulfopropyl hexadecyldimethylammonium, 0.5 parts of calcium chloride, and 7.5 parts of epichlorohydrin were added to the starch mixture, and the mixture was reacted at 60°C for 10 hours. After the reaction was completed, the mixture was filtered and the filter residue was dried to obtain anionic modified starch.

[0020] Anionic modified starch carries negatively charged groups, while cetyltrimethylammonium bromide in hydrophobic bentonite carries a strong positive charge. The two attract each other to form a complex, increase hydrogen bond points, and form a strong bond, thereby increasing the strength and compactness of the molding sand powder. In addition, anionic starch contains amino and carboxyl groups, which can react with the silanol groups in modified calcium silicate to form an interconnected network structure, thereby increasing the area of ​​the bonding bridge and improving the strength and compactness of the molding sand powder.

[0021] A second aspect of the present invention provides a process for processing casting sand powder, comprising the following steps:

[0022] Hydrophobic bentonite, coal powder, silicate and starch are sequentially added into a roller sand mixer to form a semi-finished product, stirred to obtain a mixture, crushed to 200-300 meshes, and packaged to obtain molding sand powder for casting.

[0023] Preferably, the stirring time is 0.2 to 0.5 h.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention performs hydrophobic modification on bentonite and introduces modified calcium silicate with hydrophobic groups. By changing the surface of an important component of the molding sand powder from hydrophilic to hydrophobic, the affinity for water is reduced, thereby effectively reducing the water content of the molding sand powder.

[0026] (2) The anionic modified starch of the present invention can serve as a bridge to connect the hydrophobic bentonite and the modified calcium silicate. On the one hand, the negatively charged groups of the anionic modified starch are complexed with the positive charges of the hydrophobic bentonite. On the other hand, the amino and carboxyl groups in the anionic starch can combine with the silanol groups in the calcium silicate to form a network interpenetrating structure, which reduces the fluidity of each component in the molding sand powder, increases the volume shrinkage, and effectively improves the compaction rate. At the same time, the network interpenetrating structure can also serve as a support for the molding sand powder, thereby increasing the wet compressive strength. DETAILED DESCRIPTION

[0027] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0028] The sources of some components in the Examples and Comparative Examples are as follows:

[0029] Bentonite, CAS No. 1302-78-9; coal powder, JYP-2107070154, purchased from Shanghai Baoding Energy Co., Ltd.; calcium silicate, CAS No. 10101-39-0; α-starch, CAS No. 9005-84-9.

[0030] Preparation of hydrophobic bentonite: 30 parts by weight of bentonite (CAS No. 1302-78-9) and 5 parts of cetyltrimethylammonium bromide (CAS No. 57-09-0) were added to 200 parts of deionized water, stirred evenly, and then oscillated at 150 r / min for 4 hours at 60°C using a constant temperature digital oscillator. After the oscillation is completed, the mixture is centrifuged. After centrifugation, the precipitate is dried at 50°C for 12 hours and ground to obtain hydrophobic bentonite.

[0031] Preparation of modified calcium silicate: (1) In parts by weight, 10 parts of calcium silicate (CAS No. 10101-39-0) were added to 100 parts of deionized water, stirred for 0.5 h to obtain a suspension, 5% hydrochloric acid solution was added dropwise to the suspension, and the mixture was reacted at pH 5 for 2 h. After the reaction was completed, the mixture was filtered and the filter residue was dried to obtain acidified calcium silicate. (2) In parts by weight, 10 parts of acidified calcium silicate were added to 150 parts of anhydrous ethanol (CAS No. 64-17-5) and dispersed uniformly, and then 30 parts of ammonia water (CAS No. 64-17-5) and 20 parts of deionized water were added and stirred for 0.5 h. Then, 6 parts of dodecyltriethoxysilane (CAS No. 18536-91-9) were added and the mixture was reacted at 80°C for 6 h. After the reaction was completed, the mixture was filtered. The product was washed three times by centrifugation with anhydrous ethanol and vacuum dried at 60°C for 12 h to obtain modified calcium silicate.

[0032] Preparation of anionic modified starch: 10 parts of α-starch (CAS No. 9005-84-9) and 15 parts of triethanolamine (CAS No. 102-71-6) were weighed and added to 100 parts of deionized water, stirred and dissolved for 1 hour, and then 0.5 parts of epichlorohydrin (CAS No. 102-71-6) were added and reacted for 2 hours. After the reaction was completed, 6 parts of acrylic acid and 0.2 parts of ammonium persulfate were added, and the mixture was reacted at 70°C for 4 hours to obtain a starch mixture; 1 part of 3-sulfopropyl hexadecyldimethylammonium, 0.5 parts of calcium chloride, and 7.5 parts of epichlorohydrin were added to the starch mixture, and the mixture was reacted at 60°C for 10 hours. After the reaction was completed, the mixture was filtered and the filter residue was dried to obtain anionic modified starch.

[0033] Example 1

[0034] This embodiment provides a molding sand powder for casting, which comprises, by weight: 70 parts of hydrophobic bentonite, 26 parts of coal powder, 10 parts of modified calcium silicate, and 8 parts of anionic modified starch.

[0035] The processing technology of casting sand powder includes the following steps:

[0036] Hydrophobic bentonite, coal powder, modified calcium silicate, and anionic modified starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.5 h to obtain a mixture, crushed the mixture to 300 mesh, and packaged to obtain molding sand powder for casting.

[0037] Example 2

[0038] This embodiment provides a molding sand powder for casting, which comprises, by weight: 60 parts of hydrophobic bentonite, 15 parts of coal powder, 5 parts of modified calcium silicate, and 3 parts of anionic modified starch.

[0039] The processing technology of casting sand powder includes the following steps:

[0040] Hydrophobic bentonite, coal powder, modified calcium silicate, and anionic modified starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.2 hours to obtain a mixture, crushed the mixture to 200 meshes, and packaged to obtain molding sand powder for casting.

[0041] Example 3

[0042] This embodiment provides a molding sand powder for casting, which comprises, by weight: 65 parts of hydrophobic bentonite, 20 parts of coal powder, 8 parts of modified calcium silicate, and 5 parts of anionic modified starch.

[0043] The processing technology of casting sand powder includes the following steps:

[0044] Hydrophobic bentonite, coal powder, modified calcium silicate, and anionic modified starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.4 hours to obtain a mixture, crushed the mixture to 250 meshes, and packaged to obtain molding sand powder for casting.

[0045] Example 4

[0046] This embodiment provides a molding sand powder for casting, which comprises, by weight, 70 parts of hydrophobic bentonite, 26 parts of coal powder, 10 parts of calcium silicate, and 8 parts of anionic modified starch.

[0047] The processing technology of casting sand powder includes the following steps:

[0048] Hydrophobic bentonite, coal powder, calcium silicate, and anionic modified starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.5 h to obtain a mixture, crushed the mixture to 300 mesh, and packaged to obtain molding sand powder for casting.

[0049] Comparative Example 1

[0050] This comparative example provides a foundry sand powder comprising, by weight, 70 parts of bentonite, 26 parts of coal powder, 10 parts of calcium silicate, and 8 parts of α-starch.

[0051] The processing technology of casting sand powder includes the following steps:

[0052] Bentonite, coal powder, calcium silicate and α-starch are sequentially added into a roller sand mixer to form a semi-finished product, stirred for 0.5 hours to obtain a mixture, crushed the mixture into 300 meshes, and packaged to obtain molding sand powder for casting.

[0053] Comparative Example 2

[0054] This comparative example provides a foundry sand powder, which comprises, by weight, 70 parts of hydrophobic bentonite, 26 parts of coal powder, 10 parts of calcium silicate, and 8 parts of α-starch.

[0055] The processing technology of casting sand powder includes the following steps:

[0056] Hydrophobic bentonite, coal powder, calcium silicate and α-starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.5 hours to obtain a mixture, crushed the mixture to 300 meshes, and packaged to obtain molding sand powder for casting.

[0057] Comparative Example 3

[0058] This comparative example provides a foundry sand powder, which comprises, by weight, 70 parts of bentonite, 26 parts of coal powder, 10 parts of modified calcium silicate, and 8 parts of α-starch.

[0059] The processing technology of casting sand powder includes the following steps:

[0060] Bentonite, coal powder, modified calcium silicate and α-starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.5 hours to obtain a mixture, crushed the mixture to 300 meshes, and packaged to obtain molding sand powder for casting.

[0061] Comparative Example 4

[0062] This embodiment provides a molding sand powder for casting, which comprises, by weight, 70 parts of hydrophobic bentonite, 26 parts of coal powder, 10 parts of modified calcium silicate, and 8 parts of α-starch.

[0063] The processing technology of casting sand powder includes the following steps:

[0064] Hydrophobic bentonite, coal powder, modified calcium silicate and α-starch are sequentially added to a roller sand mixer to form a semi-finished product, stirred for 0.5 hours to obtain a mixture, crushed the mixture to 300 meshes, and packaged to obtain molding sand powder for casting.

[0065] The properties of the molding sand powder provided in the above embodiments and comparative examples were tested using the following test methods:

[0066] Moisture content: Test in accordance with the requirements of GB / T 2684-2009 Test methods for foundry sand and mixtures.

[0067] Compactness: Test in accordance with the requirements of GB / T 2684-2009 Test methods for foundry sand and mixtures.

[0068] Green compressive strength: Tested in accordance with the requirements of GB / T 2684-2009 Test methods for foundry sand and mixtures.

[0069] The above performance test data is shown in Table 1.

[0070] Table 1 Performance test results

[0071] Water content (%) Compactness rate (%) Wet compressive strength (MPa) Example 1 1.5 49 98 Example 2 1.6 48 97 Example 3 1.5 48 98 Example 4 2.1 44 91 Comparative Example 1 2.8 38 81 Comparative Example 2 2.3 39 82 Comparative Example 3 2.2 39 81 Comparative Example 4 1.6 39 82

[0072] From the above content, it can be seen that the present invention uses hydrophobic bentonite, coal powder, silicate and starch as main components, modifies calcium silicate, and uses it together with anionic modified starch to obtain casting sand powder (Examples 1 to 3), which has a water content of 1.5 to 1.6%, a compaction rate of 48 to 49%, and a green compressive strength of 97 to 98 MPa.

[0073] Compared with Example 1, if modified calcium silicate is not used, the water content increases, and the compaction rate and wet compressive strength decrease (Example 4); compared with Example 1, if anionic modified starch is not used, the compaction rate and wet compressive strength decrease (Comparative Example 4).

[0074] Comparative Example 1 does not adopt the technical innovation of the present invention, so the performance is poor, with a water content of 2.8%, a compaction rate of 38%, and a wet compressive strength of 81 MPa; compared with Comparative Example 1, if hydrophobic bentonite is used, the water content decreases (Comparative Example 2); compared with Comparative Example 1, if modified calcium silicate is used, the water content decreases (Comparative Example 3).

[0075] In summary, the present invention adopts hydrophobic bentonite, coal powder, silicate and starch as main components, and modifies calcium silicate, and uses it together with anion-modified starch. By introducing hydrophobic components, the water content of the molding sand powder is effectively reduced, and the compaction rate is increased, ensuring that the strength of the molding sand powder can meet the requirements when used.

[0076] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed process flow of the present invention, but the present invention is not limited to the above-described detailed process flow, that is, it does not mean that the present invention must rely on the above-described detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A casting sand powder, characterized in that: The invention comprises, by weight: 60 to 70 parts of hydrophobic bentonite, 15 to 26 parts of coal powder, 5 to 10 parts of silicate, and 3 to 8 parts of starch; The starch is anionic modified starch; The preparation method of the anionic modified starch comprises the following steps: weighing 10 parts of α-starch and 15 parts of triethanolamine by weight, adding the mixture to 100 parts of deionized water, stirring and dissolving the mixture for 1 hour, then adding 0.5 parts of epichlorohydrin and reacting the mixture for 2 hours, adding 6 parts of acrylic acid and 0.2 parts of ammonium persulfate after the reaction is completed, and reacting the mixture at 70° C. for 4 hours to obtain a starch mixture; adding 1 part of 3-sulfopropyl hexadecyldimethylammonium, 0.5 parts of calcium chloride, and 7.5 parts of epichlorohydrin to the starch mixture, reacting the mixture at 60° C. for 10 hours, filtering the mixture after the reaction is completed, and drying the filter residue to obtain the anionic modified starch.

2. The molding sand powder for casting according to claim 1, characterized in that: The preparation method of the hydrophobic bentonite is: In parts by weight, 30 parts of bentonite and 5 parts of hexadecyltrimethylammonium bromide were added to 200 parts of deionized water, stirred evenly, and then oscillated at 150 r / min for 4 hours using a constant temperature digital oscillator at 60°C. After the oscillation was completed, the mixture was centrifuged, and the centrifugal precipitate was dried at 50°C for 12 hours and ground to obtain hydrophobic bentonite.

3. The molding sand powder for casting according to claim 1, characterized in that: The silicate is selected from any one of magnesium silicate, modified calcium silicate, aluminum silicate, and iron silicate, or a combination of at least two thereof; The preparation method of the modified calcium silicate is: In parts by weight, 10 parts of calcium silicate are added to 100 parts of deionized water, stirred for 0.5 h to obtain a suspension, a hydrochloric acid solution with a mass concentration of 5% is added dropwise to the suspension, and the mixture is reacted at a pH of 5 for 2 h. After the reaction is completed, the mixture is filtered, and the filter residue is dried to obtain acidified calcium silicate; 10 parts of the acidified calcium silicate are added to 150 parts of anhydrous ethanol and uniformly dispersed, and then 30 parts of ammonia water and 20 parts of deionized water are added, stirred for 0.5 h, and then 6 parts of dodecyltriethoxysilane are added, and the mixture is reacted at 80° C. for 6 h. After the reaction is completed, the mixture is filtered, the product is centrifuged and washed three times with anhydrous ethanol, and vacuum dried at 60° C. for 12 h to obtain modified calcium silicate.

4. A process for processing casting sand powder according to any one of claims 1 to 3, characterized in that: The steps include: Hydrophobic bentonite, coal powder, silicate and starch are sequentially added into a roller sand mixer to form a semi-finished product, stirred to obtain a mixture, crushed to 200-300 meshes, and packaged to obtain molding sand powder for casting.

5. The process for processing casting sand powder according to claim 4, characterized in that: The stirring time is 0.2 to 0.5 h.