Special coating for low-pressure mold of large-size thin-wall aluminum alloy casting and casting process

Abstract

The invention discloses a special coating for a low-pressure mold of a large-size thin-wall aluminum alloy casting and a casting process. The special coating for the mold comprises the following components in parts by weight: 30-40 parts of organic silicon resin, 3-5 parts of a suspending agent, 40-50 parts of heat insulation aggregate, 2-3 parts of a lubricating agent and 1-2 parts of a dispersing agent. The casting process comprises the following steps: preheating the mold to 180-220 DEG C; a mold cavity is coated with the paint, and a coating is formed after curing; closing the mold; casting preparation: preparing metal raw materials into molten metal; pouring is conducted, specifically, a mold cavity is filled with molten metal; and solidification and demolding are conducted, specifically, solidification is conducted after pouring is finished, and a casting is taken out after mold opening. According to the invention, the formula of the coating is adjusted, and a specific casting process is designed, so that the key parameters of the casting process are accurately controlled while the excellent coating performance of the coating is guaranteed, and batch production of high-quality castings is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy casting, and in particular relates to a special coating for a low-pressure mold of a large-size thin-walled aluminum alloy casting and a casting process. Background Art

[0002] With the rapid development of modern industry, especially in the field of high-end equipment, the demand for large-size thin-walled aluminum alloys is growing. Such castings face many difficulties in the casting process due to their complex structure, thin walls (usually 2-8mm thick), and large size (single-side length exceeds 1000mm).

[0003] In order to prevent adhesion of castings and improve the surface quality of castings, coatings are applied inside the cavity. However, the coatings used in traditional low-pressure casting molds are difficult to meet the molding requirements of large-sized thin-walled aluminum alloy castings. Ordinary coatings have poor fluidity when filling large-sized cavities, resulting in uneven coating thickness, and castings are prone to defects such as cold shut and insufficient pouring. Thin-walled parts cool quickly, and the poor thermal insulation of the coating will aggravate the rapid solidification of the molten metal and affect the integrity of the casting. At the same time, conventional casting processes cannot accurately control the filling speed and pressure of the molten metal. Given the complex solidification characteristics of large-sized thin-walled parts, internal quality problems such as shrinkage cavities and shrinkage porosity are easily caused, which seriously restricts the product qualification rate and performance.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The purpose of the present invention is to provide a special coating for low-pressure molds of large-size thin-walled aluminum alloy castings and a casting process, wherein the coating has excellent coating performance and good fluidity.

[0006] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0007] A special coating for low-pressure molds of large-size thin-walled aluminum alloy castings comprises the following components by weight: 30-40 parts of silicone resin, 3-5 parts of suspending agent, 40-50 parts of heat-insulating aggregate, 2-3 parts of lubricant and 1-2 parts of dispersant.

[0008] In one or more embodiments of the present invention, the suspending agent is sodium carboxymethyl cellulose.

[0009] In one or more embodiments of the present invention, the thermal insulation aggregate is hollow ceramic microspheres.

[0010] In one or more embodiments of the present invention, the hollow ceramic microspheres are spherical and have a diameter of 20 to 80 μm.

[0011] In one or more embodiments of the present invention, the lubricant is graphite powder.

[0012] In one or more embodiments of the present invention, the dispersant is sodium hexametaphosphate.

[0013] Another specific embodiment of the present invention provides a technical solution as follows:

[0014] A casting process comprises the following steps:

[0015] Preheat the mold to 180-220°C;

[0016] The above-mentioned large-size thin-wall aluminum alloy casting low-pressure mold special coating is applied to the mold cavity and formed into a coating after curing;

[0017] Mould closing;

[0018] Pouring preparation: turning metal raw materials into molten metal;

[0019] Pouring: Filling the molten metal into the mold cavity;

[0020] Solidification and demoulding: After pouring, solidification is carried out. After solidification, the mold is opened to take out the casting.

[0021] In one or more embodiments of the present invention, the coating thickness is 0.3-0.5 mm.

[0022] In one or more embodiments of the present invention, the specific pouring operation is: pushing the molten metal into the mold cavity at 0.01-0.02 MPa; when the molten metal fills 50-60% of the volume of the cavity, increasing the pressure to 0.03-0.04 MPa; when the molten metal fills 90-95% of the volume of the cavity, reducing the pressure to 0.005-0.01 MPa.

[0023] Compared with the prior art, the present invention ensures that the coating has excellent coating performance by designing the coating and the supporting casting process, accurately controls the key parameters of the casting process, and realizes mass production of high-quality castings. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0025] A specific embodiment of the present invention provides a special coating for low-pressure molds of large-size thin-walled aluminum alloy castings, comprising the following components in weight: 30 to 40 parts of silicone resin, 3 to 5 parts of suspending agent, 40 to 50 parts of insulating aggregate, 2 to 3 parts of lubricant, and 1 to 2 parts of dispersant.

[0026] Specifically, the silicone resin is phenolic resin. The silicone resin is selected as a binder. It has excellent high temperature resistance and can withstand the pouring temperature of aluminum alloy liquid (680-750°C). After curing, it can form a tough bonding network and firmly adhere to the mold surface, providing basic strength and adhesion for the coating and preventing the coating from peeling off.

[0027] In terms of specific dosage, by weight, the silicone resin can be 30 parts, 32 parts, 35 parts, 37 parts, 39 parts or 40 parts, the suspending agent can be 3 parts, 3.5 parts, 4 parts, 4.5 parts or 5 parts, the insulating aggregate can be 40 parts, 42 parts, 43 parts, 45 parts, 47 parts, 48 ​​parts or 50 parts, the lubricant can be 2 parts, 2.3 parts, 2.5 parts, 2.8 parts or 3 parts, and the dispersant can be 1 part, 1.2 parts, 1.5 parts, 1.7 parts or 2 parts. The prepared coatings can meet the molding requirements of large-size thin-walled aluminum alloy castings by combining different weight portions of silicone resin, suspending agent, insulating aggregate, lubricant and dispersant.

[0028] Furthermore, the suspending agent is sodium carboxycellulose. By utilizing the water-soluble and colloidal properties of sodium carboxycellulose, the various components of the coating can be evenly dispersed and suspended, avoiding precipitation and stratification, ensuring that the performance of the coating is consistent each time it is applied, and facilitating the precise control of the coating thickness and quality. In addition to sodium carboxycellulose, other substances with water-soluble and colloidal properties can also be used.

[0029] Furthermore, the insulating aggregate is hollow ceramic microspheres, preferably, the hollow ceramic microspheres are spherical, with a diameter of 20 to 80 microns.

[0030] Specifically, the hollow structure inside the hollow ceramic microspheres can give them excellent thermal insulation, which can effectively slow down the heat dissipation rate of aluminum alloy liquid in thin walls and optimize the solidification rate. The spherical appearance is conducive to the flow of coating, making the coating uniform and flat, and can adapt to the complex surface of large-sized mold cavities. In addition to hollow ceramic microspheres, other aggregates with thermal insulation properties can also be used.

[0031] Furthermore, the lubricant is graphite powder, and preferably, the particle size of the graphite powder is 200 meshes.

[0032] Specifically, graphite can form a lubricating film at high temperatures, which can reduce the friction between the aluminum alloy liquid and the mold, facilitate filling, reduce defects such as scratches and sticking on the casting surface, and gradually improve the surface finish.

[0033] Furthermore, the dispersant is sodium hexametaphosphate, which can assist the suspending agent in breaking up the agglomeration of the components, further refine the paint particles, improve the overall stability of the paint, make the paint delicate and smooth, and facilitate spraying and brushing operations. In addition to sodium hexametaphosphate, other substances that play a dispersing role can also be selected.

[0034] Furthermore, a method for preparing a special coating for a low-pressure mold of a large-size thin-walled aluminum alloy casting comprises the following steps 1-4.

[0035] Step 1: Take an appropriate amount of deionized water and slowly pour the silicone resin into the deionized water, stirring while pouring, with a stirring speed of 200-300 r / min and a water temperature maintained at 40-50°C until the silicone resin is completely dissolved to form a uniform binder solution. Step 1 is intended to activate the activity of the silicone resin and prepare for subsequent reactions.

[0036] Step 2: Add the suspending agent and dispersing agent to the binder solution in sequence, increase the stirring speed to 400-500 r / min, and stir for 20-30 minutes to ensure that the suspending agent and dispersing agent are fully dissolved and dispersed, thus laying the foundation for a stable dispersion system for the subsequent addition of thermal insulation aggregate.

[0037] Step 3, slowly add the insulating aggregate to the mixed solution of step 2, stirring at 100-200 r / min while adding to prevent the aggregate from splashing and agglomerating; after the insulating aggregate is added, stir at 600-800 r / min for 30-40 minutes to ensure that the insulating aggregate is fully wrapped by the silicone resin and evenly dispersed.

[0038] Step 4, finally add the lubricant, stir at 300-400 r / min for 10-15 min, so that the lubricant is evenly mixed in the mixed liquid, and obtain the special coating for low-pressure molds of large-size thin-walled aluminum alloy castings.

[0039] Furthermore, the obtained special coating for low-pressure mold of large-size thin-walled aluminum alloy castings is filtered through a 200-mesh filter to remove impurities and large particles to ensure smooth coating.

[0040] Another specific embodiment of the present invention provides a casting process, comprising steps (1)-(5).

[0041] (1) Mold pretreatment: Clean the low-pressure casting mold to remove impurities such as oil, rust, and residual old coatings. After cleaning, sandblasting can be used to roughen the mold surface and enhance the adhesion of the paint. Subsequently, preheat the mold to 180-220°C to dissipate water vapor and create a suitable temperature environment for coating, which helps the coating to cure quickly and make the coating fit tightly to the mold.

[0042] Among them, sandblasting the mold is a conventional operation in the art, and the spraying material such as copper ore sand, quartz sand, corundum, iron sand, etc. can be sprayed onto the surface of the mold.

[0043] (2) Paint coating: Use high-pressure airless spray equipment to evenly spray the paint on key areas such as mold cavities and risers, and areas with thinner product walls. The spray gun pressure is 0.4-0.6MPa, the spray distance is 20-30cm, and the coating thickness is controlled at 0.3-0.5cm. For complex corners and thin-walled areas, manual brushing is used to ensure that the coating is complete, the thickness is accurate, and there is no missing paint or sagging.

[0044] (3) Mold closing and casting preparation: After coating is completed and the coating is cured, the mold is closed and the mold sealing is checked. Metal raw materials are loaded into the low-pressure casting furnace. The present invention uses aluminum alloy raw materials, which are commercially available. The temperature is increased and melted, refined and degassed, and the aluminum liquid temperature is controlled to be 700-730°C. The composition meets the design requirements of the casting. After refining, it is left to stand for 15-20 minutes to make the aluminum liquid composition and temperature uniform and stable.

[0045] (4) Low-pressure pouring: Turn on the low-pressure casting equipment and push the aluminum liquid to rise slowly with a starting pressure of 0.01-0.02 MPa into the mold cavity. In the early stage of filling, low pressure and low speed are used to avoid turbulent air entrainment. When the aluminum liquid fills 50-60% of the volume of the cavity, gradually increase the pressure to 0.03-0.04 MPa to speed up the filling and ensure that the thin-walled parts are completely filled. When the aluminum liquid fills 90-95% of the volume of the cavity, reduce the pressure to 0.005-0.01 MPa and end smoothly to reduce the impact and splash of the aluminum liquid.

[0046] (5) Solidification and demoulding: After pouring, the pressure is maintained for 3 to 5 minutes, and the residual heat of the mold and the ambient temperature are used to promote the solidification of the aluminum liquid, following the principle of thin wall first and thick wall follow-up solidification; after solidification, the mold is opened to remove the casting, and the demoulding temperature of the casting is controlled at 200 to 300°C to prevent deformation and cracking of the casting due to excessive temperature difference. After demoulding, the casting is subjected to stress relief annealing to eliminate residual stress and improve dimensional stability and mechanical properties.

[0047] Specifically, the stress relief annealing treatment is a conventional treatment method, and the temperature can be selected to be 200-300°C.

[0048] The present invention is further described in detail below in conjunction with specific embodiments.

[0049] Example 1

[0050] In parts by weight, take 35 parts of phenolic resin, 4 parts of sodium carboxymethyl cellulose, 45 parts of hollow ceramic microspheres, 2.5 parts of graphite powder and 1.5 parts of sodium hexametaphosphate, take 1 part of deionized water, heat to 40°C and keep warm, add phenolic resin into the deionized water, stir while pouring, and stir at a speed of 200r / min until the phenolic resin is completely dissolved to prepare a binder solution.

[0051] Sodium carboxymethyl cellulose and sodium hexametaphosphate were added to the binder solution and stirred at 400r / min for 25min. At a stirring speed of 100r / min, hollow ceramic microbeads were slowly added. After the addition was completed, the mixture was stirred at 700r / min for 35min. Finally, graphite powder was added and stirred at 400r / min for 15min. The prepared coating was filtered through a 200-mesh filter to remove large particle impurities, and the finished product, a special coating for low-pressure molds of large-sized thin-walled aluminum alloy castings, was obtained.

[0052] Example 2

[0053] The casting process includes the following steps:

[0054] Take the mold, the single side size of the mold is 600mm and the wall thickness is 3-6mm. After cleaning the mold, sandblast it, and then preheat the mold to 200℃.

[0055] At a pressure of 0.4 MPa and a spray distance of 20 cm, use a spray gun to spray the special coating for the large-size thin-walled aluminum alloy casting low-pressure mold prepared in Example 1 onto the mold cavity, riser and mold parts corresponding to the thin wall of the product. The mold corners are manually brushed to ensure that the coating thickness is 0.4 mm and the coating is complete. The coating is cured by the mold temperature, and the mold is closed after the coating is cured.

[0056] The aluminum alloy raw materials were melted, refined and degassed, the aluminum liquid temperature was controlled at 720°C, and after refining, it was allowed to stand for 20 minutes.

[0057] Turn on the low-pressure casting equipment, push the aluminum liquid up slowly with a starting pressure of 0.015MPa, and let the aluminum liquid enter the mold cavity. When the aluminum liquid fills 55% of the volume of the cavity, gradually increase the pressure to 0.035MPa and continue to fill the aluminum liquid. When the aluminum liquid fills 92% of the volume of the cavity, reduce the pressure to 0.008MPa to fill the cavity with aluminum liquid.

[0058] After pouring, the pressure is maintained for 4 minutes, and the aluminum liquid is solidified by the residual heat of the mold and the ambient temperature. After solidification, the mold is opened to take out the casting, and the demoulding temperature of the casting is controlled at 250°C. After demoulding, the casting is subjected to stress relief annealing to eliminate residual stress. The final casting yield rate reaches 85%, there is no shrinkage cavity or shrinkage inside, and the surface roughness Ra reaches 3.2μm, meeting the high standard requirements of the product.

[0059] In summary, the present invention uses a specific amount of raw material composition to make the prepared large-size thin-walled aluminum alloy casting low-pressure mold special coating have smooth fluidity, excellent coating performance, and high thermal insulation. At the same time, by regulating the casting process, the scrap rate of castings is significantly reduced, and the quality stability is greatly improved, which effectively promotes the development of high-end aluminum alloy castings industry and expands the application prospects of large-size thin-walled aluminum alloy parts.

[0060] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0061] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A special coating for low-pressure molds of large-size thin-walled aluminum alloy castings, characterized in that: The invention comprises the following components in parts by weight: 30-40 parts of organic silicon resin, 3-5 parts of suspending agent, 40-50 parts of heat insulating aggregate, 2-3 parts of lubricant and 1-2 parts of dispersant.

2. The special coating for low-pressure molds of large-size thin-walled aluminum alloy castings according to claim 1 is characterized in that: The suspending agent is sodium carboxymethyl cellulose.

3. The special coating for low-pressure molds of large-size thin-walled aluminum alloy castings according to claim 1 is characterized in that: The thermal insulation aggregate is hollow ceramic microspheres.

4. The special coating for low-pressure molds of large-size thin-walled aluminum alloy castings according to claim 3 is characterized in that: The hollow ceramic microspheres are spherical and have a diameter of 20 to 80 μm.

5. The special coating for low-pressure molds of large-size thin-walled aluminum alloy castings according to claim 1 is characterized in that: The lubricant is graphite powder.

6. The special coating for low-pressure molds of large-size thin-walled aluminum alloy castings according to claim 1 is characterized in that: The dispersant is sodium hexametaphosphate.

7. A casting process, characterized in that: The steps include: Preheat the mold to 180-220°C; The special coating for low-pressure molds for large-size thin-walled aluminum alloy castings according to any one of claims 1 to 6 is applied to the mold cavity and solidified to form a coating; Mould closing; Pouring preparation: turning metal raw materials into molten metal; Pouring: Filling the molten metal into the mold cavity; Solidification and demoulding: After pouring, solidification is carried out. After solidification, the mold is opened to take out the casting.

8. The casting process according to claim 7, characterized in that: The coating thickness is 0.3 to 0.5 mm.

9. The casting process according to claim 7, characterized in that: The specific pouring operation is: push the molten metal into the mold cavity at 0.01-0.02MPa; when the molten metal fills 50-60% of the volume of the cavity, increase the pressure to 0.03-0.04MPa; when the molten metal fills 90-95% of the volume of the cavity, reduce the pressure to 0.005-0.01MPa.