An expandable sand core coating and a process for its preparation

Abstract

The application discloses an expandable sand core coating, and the coating comprises the following components in percentage by weight: 20-50% of aggregate, 5-15% of bulking agent, 1-10% of suspending agent, 0.1-1% of thickening agent, 0.5-3% of binder, 0.1-1% of defoaming agent, 0.1-1% of wetting agent and 40-60% of carrier liquid, wherein the aggregate is refractory aggregate, and the bulking agent is a mixture of sodium nitrate and activated carbon powder. When the coating is used in low-pressure casting, sodium nitrate reacts with activated carbon powder to generate carbon dioxide and nitric oxide under the action of aluminum liquid, and the two gases are not dissolved in the aluminum melt, so that the two gases are not easy to form invasive pores, can be discharged through the sand core, and the two gases can also prevent hydrogen-containing gas in the sand core from invading the aluminum melt, thereby avoiding hydrogen pores and the like. The discharge of the gas makes the coating layer loose, so that the coating layer is easy to peel off during cleaning. Therefore, the expandable sand core coating can solve the defects of mechanical sand sticking, coating adhesion and pores.

Description

Technical Field

[0001] This invention relates to the field of coating equipment technology, and more specifically, to an expandable sand core coating and its preparation process. Background Technology

[0002] Aluminum alloy water-cooled motor housings are core components of new energy vehicles, characterized by their light weight, high airtightness requirements, high cooling efficiency, and the impurity-free nature of the water-cooled internal cavity. Due to the complex structure of the water-cooled internal cavity, high-strength coated sand is required to manufacture the sand core. However, coated sand generates a large amount of gas, and because the sand core is completely encased in the casting, the high temperature and long duration during casting easily lead to problems such as mechanical sand adhesion, coating adhesion, and air leakage due to pores in the internal cavity.

[0003] Currently, the casting industry mainly uses low-pressure casting technology. The surface of the inner cavity sand core is covered with water-based coating. The coating is the main means to solve mechanical sand adhesion and prevent defects such as porosity. Subsequently, the sand core in the water-cooled casing is first burned and then mechanically vibrated to remove the sand. However, current aluminum alloy casting coatings cannot solve the problem of mechanical sand adhesion, especially coating adhesion. Because existing coatings easily adhere to the inner wall of the casing water channel and have high adhesion strength, they cannot be removed by simple vibration sand removal. The coating that cannot be removed will fall off during customer use, blocking the water channel circulation and causing machine failure. Summary of the Invention

[0004] The purpose of this invention is to provide an expandable sand core coating and its preparation process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: an expandable sand core coating, the coating comprising the following components by weight percentage: 20-50% aggregate, 5-15% expander, 1-10% suspending agent, 0.1-1% thickener, 0.5-3% binder, 0.1-1% defoamer, 0.1-1% wetting agent and 40-60% carrier liquid, wherein the aggregate is refractory aggregate containing graphite powder, and the expander is a mixture of sodium nitrate and activated carbon powder.

[0006] Preferably, the aggregate is a mixture of graphite powder and one or more of quartz powder, talc powder, bauxite powder, and zirconium oxide.

[0007] Preferably, the suspending agent includes one or more of sodium bentonite, tert-bentonite, organo-bentonite, and attapulgite.

[0008] Preferably, the thickener includes one or more of sodium carboxymethyl cellulose, polyvinyl butyral, polyacrylamide, and gelatin.

[0009] Preferably, the defoamer is one or more of organosilicon emulsion, fatty acid, and fatty acid ester.

[0010] Preferably, the wetting agent is one or more of ethoxyethylene ethers, alcohols, and fatty acid salts.

[0011] Preferably, the carrier liquid is water and alcohol, and the alcohol includes one or more of methanol, ethanol, and propanol.

[0012] Preferably, the binder includes organic and inorganic binders, wherein the inorganic binder includes one or more of sodium silicate, silica sol, aluminum dihydrogen phosphate, calcium silicate, aluminum sol, and zirconium sol; and the organic binder includes one or more of dextrin, starch, phenolic resin, pulp waste liquor, and PVA.

[0013] A preparation process for an expandable sand core coating includes the following steps:

[0014] 1) First, add the required carrier liquid to the material tank, turn on the agitator and stir at a speed of 500-1000 rpm;

[0015] 2) Add the suspending agent and stir for 1-3 hours to allow the suspending agent to fully swell;

[0016] 3) Add thickener and continue stirring for 1-2 hours. After the solution is homogeneous, add binder and continue stirring for 30-60 minutes.

[0017] 4) Add refractory aggregate and expander and stir for 1-2 hours.

[0018] 5) Add defoamer and wetting agent and continue stirring for 1 hour.

[0019] 6) Adjust the Baumé degree to 60-90 by adding carrier liquid. After the Baumé degree is qualified, discharge the material to complete the coating preparation.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] During low-pressure casting, sodium nitrate reacts with activated carbon powder under the action of molten aluminum to produce carbon dioxide and nitric oxide (nitric oxide). These two gases are insoluble in the molten aluminum, thus preventing the formation of intrusive pores and allowing them to escape through the sand core. Simultaneously, these gases also prevent hydrogen-containing gases from the sand core from intruding into the molten aluminum, avoiding hydrogen porosity. The escaping of these gases makes the coating layer looser, making it easier to peel off during cleaning. Therefore, the expandable sand core coating can solve defects such as mechanical sand adhesion, coating adhesion, and porosity. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a performance test diagram of one embodiment and a comparative example of the present invention.

[0024] Figure 2 This diagram illustrates the difference between the coating adhesion thickness examples and the comparative examples. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0026] This invention provides an expandable sand core coating, comprising the following components by weight percentage: 20-50% aggregate, 5-15% expander, 1-10% suspending agent, 0.1-1% thickener, 0.5-3% binder, 0.1-1% defoamer, 0.1-1% wetting agent, and 40-60% carrier liquid, wherein the aggregate is refractory aggregate, and the expander is a mixture of sodium nitrate and activated carbon powder.

[0027] The aggregate is a mixture of graphite powder and one or more of quartz powder, talc powder, bauxite powder, zirconium oxide, and graphite powder.

[0028] The suspending agent includes one or more of sodium bentonite, tert-bentonite, organo-bentonite, and attapulgite.

[0029] Preferably, the thickener includes one or more of sodium carboxymethyl cellulose, polyvinyl butyral, polyacrylamide, and gelatin.

[0030] The defoamer is one or more of the following: silicone emulsion, fatty acid, and fatty acid ester.

[0031] The wetting agent is one or more of oxyethylene ethers, alcohols, and fatty acid salts.

[0032] The carrier liquid is water and alcohol, and the alcohol includes one or more of methanol, ethanol, and propanol.

[0033] The binder includes organic and inorganic binders, wherein the inorganic binder includes one or more of sodium silicate, silica sol, aluminum dihydrogen phosphate, calcium silicate, aluminum sol, and zirconium sol; and the organic binder includes one or more of dextrin, starch, phenolic resin, pulp waste liquor, and PVA.

[0034] Example 1

[0035] An expandable sand core coating is prepared through the following process steps:

[0036] 1) First, add 40% of the total mass of the carrier liquid to the material tank, turn on the agitator and stir at a speed of 500 rpm;

[0037] 2) Add 3% sodium-based bentonite suspending agent and stir for 1.2 hours to allow the suspending agent to fully swell;

[0038] 3) Add 0.2% sodium carboxymethyl cellulose and continue stirring for 1 hour. After the solution is homogeneous, add the binder and continue stirring for 30 minutes.

[0039] 4) Add a mixture of 20% graphite powder, 5% sodium nitrate and activated carbon powder and stir for 1 hour.

[0040] 5) Add 0.2% defoamer and 0.1% wetting agent and continue stirring for 1 hour.

[0041] 6) Adjust the Baumé degree to 60 by adding carrier liquid. After the Baumé degree is qualified, discharge the material to complete the coating preparation.

[0042] Example 2

[0043] An expandable sand core coating is prepared through the following process steps:

[0044] 1) First, add 45% of the total mass of the carrier liquid to the material tank, turn on the agitator and stir at 700 rpm;

[0045] 2) Add 1.5% sodium-based bentonite suspending agent and stir for 2 hours to allow the suspending agent to fully swell;

[0046] 3) Add 0.3% sodium carboxymethyl cellulose and continue stirring for 1 hour. After the solution is homogeneous, add the binder and continue stirring for 40 minutes.

[0047] 4) Add a mixture of 45% quartz powder, 5% sodium nitrate and activated carbon powder and stir for 1 hour.

[0048] 5) Add 0.5% defoamer and 0.3% wetting agent and continue stirring for 1 hour.

[0049] 6) Adjust the Baumé degree to 70 by adding carrier liquid. Once the Baumé degree is qualified, discharge the material to complete the coating preparation.

[0050] Example 3

[0051] An expandable sand core coating is prepared through the following process steps:

[0052] 1) First, add 60% of the total mass of the carrier liquid to the material tank, turn on the agitator and stir at 1000 rpm;

[0053] 2) Add 3% sodium-based bentonite suspending agent and stir for 3 hours to allow the suspending agent to fully swell;

[0054] 3) Add 0.3% sodium carboxymethyl cellulose and continue stirring for 1 hour. After the solution is homogeneous, add the binder and continue stirring for 60 minutes.

[0055] 4) Add a mixture of 20% quartz powder, 5% sodium nitrate and activated carbon powder and stir for 1 hour.

[0056] 5) Add 1% defoamer and 0.3% wetting agent and continue stirring for 1 hour.

[0057] 6) Adjust the Baumé degree to 70 by adding carrier liquid. Once the Baumé degree is qualified, discharge the material to complete the coating preparation.

[0058] Comparative Example

[0059] An expandable sand core coating is prepared through the following process steps:

[0060] 1) First, add 60% of the total mass of the carrier liquid to the material tank, turn on the agitator and stir at 1000 rpm;

[0061] 2) Add 3% sodium-based bentonite suspending agent and stir for 3 hours to allow the suspending agent to fully swell;

[0062] 3) Add 0.3% sodium carboxymethyl cellulose and continue stirring for 1 hour. After the solution is homogeneous, add the binder and continue stirring for 60 minutes.

[0063] 4) Add a mixture of 35% quartz powder and 5% graphite powder and stir for 1 hour.

[0064] 5) Add 1% defoamer and 0.3% wetting agent and continue stirring for 1 hour. 6) After the Baume degree meets the requirements, discharge the material to complete the coating preparation.

[0065] Performance tests were conducted on the sand core coatings of Examples 1, 2, 3 and the comparative example, and the results are as follows: Figure 1 As shown, the adhesion of Examples 1, 2, and 3 is less than that of the comparative example. In practical applications, this makes it less likely for aluminum and coating to adhere, thus solving the defects of mechanical sand adhesion, coating adhesion, and pore formation.

[0066] Figure 2 The figure shows the difference between the coating adhesion thickness example and the comparative example. It can be seen from the figure that the coating thickness and coating adhesion area ratio of the aluminum surface using the coating of this application are better than those of the comparative example.

[0067] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, the patent owner may make various modifications or alterations within the scope of the appended claims, as long as they do not exceed the protection scope described in the claims of the present invention, they shall be within the protection scope of the present invention.

Claims

1. An expandable sand core coating, characterized in that, The coating comprises the following components by weight percentage: 20-50% aggregate, 5-15% bulking agent, 1-10% suspending agent, 0.1-1% thickener, 0.5-3% binder, 0.1-1% defoamer, 0.1-1% wetting agent, and 40-60% carrier liquid. The aggregate is refractory aggregate; the bulking agent is a mixture of sodium nitrate and activated carbon powder; the aggregate is a mixture of graphite powder and one or more of quartz powder, talc powder, bauxite powder, and zirconium oxide; the suspending agent includes one or more of sodium-based bentonite, tert-based bentonite, organo-bentonite, and attapulgite.

2. The expandable sand core coating according to claim 1, characterized in that: The thickener includes one or more of sodium carboxymethyl cellulose, polyvinyl butyral, polyacrylamide, and gelatin.

3. The expandable sand core coating according to claim 1, characterized in that: The defoamer is one or more of the following: silicone emulsion, fatty acid, and fatty acid ester.

4. The expandable sand core coating according to claim 1, characterized in that: The wetting agent is one or more of oxyethylene ethers, alcohols, and fatty acid salts.

5. The expandable sand core coating according to claim 1, characterized in that: The carrier liquid is water and alcohol, including one or more of methanol, ethanol, and propanol.

6. The expandable sand core coating according to claim 1, characterized in that: The binder includes organic and inorganic binders, wherein the inorganic binder includes one or more of sodium silicate, silica sol, aluminum dihydrogen phosphate, calcium silicate, aluminum sol, and zirconium sol; and the organic binder includes one or more of dextrin, starch, phenolic resin, pulp waste liquor, and PVA.

7. A preparation process for an expandable sand core coating, comprising preparation using any one of the components described in claims 1-6, characterized in that, Includes the following steps: 1) First, add the required carrier liquid to the material tank, turn on the agitator and stir at a speed of 500-1000 rpm; 2) Add the suspending agent and stir for 1-3 hours to allow the suspending agent to fully swell; 3) Add thickener and continue stirring for 1-2 hours. After the solution is homogeneous, add binder and continue stirring for 30-60 minutes. 4) Add refractory aggregate and leavening agent and stir for 1-2 hours; 5) Add defoamer and wetting agent and continue stirring for 1 hour; 6) Adjust the Baumé degree to 60-90 by adding carrier liquid. After the Baumé degree is qualified, discharge the material to complete the coating preparation.

Images