Degradable paper ingate for resin sand casting and preparation method thereof

Abstract

The invention discloses a degradable paper ingate for resin sand casting and a preparation method of the degradable paper ingate, and relates to the technical field of ingate preparation, the degradable paper ingate comprises a straight pipe body and transfer pipe bodies, one ends of the two transfer pipe bodies are communicated with the two ends of the straight pipe body, and the straight pipe body and the transfer pipe bodies comprise degradable paper layers, fire-resistant coatings and anti-sticking coatings. The outer side of the degradable paper layer is coated with the fireproof coating, the inner side of the degradable paper layer is coated with the anti-sticking coating, and the interior of the degradable paper layer is impregnated with modified phenolic resin. According to the ceramic ingate, through the composite structure design of modified resin impregnated kraft paper and internal and external functional coatings, the bottleneck of a traditional ceramic ingate in the aspects of cost, environmental protection and performance is broken through, and high efficiency, greenization and precision of the casting process are achieved; and the method is particularly suitable for medium-and-small-batch casting production scenes with high requirements on environmental protection and production efficiency in resin sand casting.

Description

Technical Field

[0001] The present invention relates to the technical field of inner gate preparation, and specifically to a degradable paper inner gate for resin sand casting and its preparation method. Background Art

[0002] The inner gate is an important part of the gating system in the casting process and is the channel connecting the cross gate (or directly connected to the sprue) and the mold cavity. Its main functions are to control the speed, direction, and flow rate of the molten metal flowing into the cavity, regulate the temperature distribution of each part of the mold, and make the molten metal fill the cavity smoothly and evenly, thereby ensuring the quality of the casting. Its design parameters such as shape, size, position, and quantity.

[0003] The preparation process of traditional ceramic inner gates requires complex processes such as raw material proportioning, molding, and high-temperature sintering. Coupled with the high price of special ceramic raw materials, the production cost remains high, significantly increasing the economic burden on casting enterprises. Secondly, the chemical stability of ceramic materials is extremely high, and it is difficult to degrade through the natural environment after casting, not only causing waste of resources but also bringing increasingly severe environmental protection pressure. In addition, ceramic materials are brittle and hard, and are extremely prone to breakage during use. The sharp fragments falling off will not only damage the surface accuracy of the mold but may also mix into the molten metal to form inclusions, directly affecting the quality of the casting and leading to an increase in the rejection rate. Summary of the Invention

[0004] The purpose of the present invention is to provide a degradable paper inner gate for resin sand casting and its preparation method to solve the problems of high cost (about 1 / 5 of ceramic materials), non-degradability, and easy breakage and damage to the mold of traditional ceramic inner gates proposed in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions: A degradable paper inner gate for resin sand casting includes a straight pipe body and a transition pipe body. One end of the two transition pipe bodies is interconnected with both ends of the straight pipe body. The straight pipe body and the transition pipe body include a degradable paper layer, a refractory coating, and an anti-sticking coating. The refractory coating is coated on the outer side of the degradable paper layer, and the anti-sticking coating is coated on the inner side of the degradable paper layer. The interior of the degradable paper layer is impregnated with modified phenolic resin.

[0006] Preferably, the thickness range of the degradable paper layer is 7-9 mm. Using 120 g / m² kraft paper as the base material, it is laminated and formed after being impregnated with modified phenolic resin, forming a resin-fiber composite structure inside, with both rigid support and elastic deformation capabilities, and the modified phenolic resin can improve the high-temperature resistance of the paper layer.

[0007] Preferably, the refractory coating is made of kaolin and silica sol. The thickness range of the refractory coating is 0.1-0.3 mm, forming a high-temperature resistant barrier, with a short-term temperature resistance greater than 1500 °C, protecting the paper layer from being ablated by the molten metal during casting.

[0008] Preferably, the anti-sticking coating is a graphite powder coating with a thickness range of 0.05 - 0.15 mm. By utilizing the lubricity and non-stickiness of graphite, the adhesion between the molten metal and the inner wall of the runner is avoided, ensuring the rapid separation of the runner and the casting during demolding.

[0009] A preparation method of a degradable paper inner gate for resin sand casting includes the following steps: S1. Cut kraft paper with a quantitative weight of 120 g / m² into standard sizes that meet production requirements, ensuring that the dimensional accuracy is controlled within ±1 mm. Prepare a modified phenolic resin solution with a solid content of 45%, and control the solution temperature at 30 ± 5 °C to ensure good fluidity and permeability of the resin. Immerse the cut kraft paper in the solution so that the resin fully penetrates into the kraft paper fibers. After immersion, take out the kraft paper and drain it through a squeezing roller to remove the excess resin on the surface. Subsequently, use a hydraulic laminator for lamination molding. Preheat the laminator to 50 - 60 °C, stack single sheets of impregnated kraft paper layer by layer, and continuously press for 20 min under a pressure of 10 - 15 MPa to preliminarily crosslink the resin and eliminate the interlayer air bubbles. During the lamination process, use an infrared thickness gauge to monitor the thickness change in real time, precisely control the laminated thickness within the range of 7 - 9 mm, and ensure that the thickness uniformity error ≤ ±0.2 mm to form a dense phenolic resin-impregnated kraft paper laminate with a pre-cured structure; S2. According to the specific requirements of the target pipe diameter, select a high-temperature resistant sizing rod with a corresponding diameter and an anti-sticking treatment on the surface. Use a mechanical arc bending device to evenly bend and wrap the laminated kraft paper around the outer surface of the sizing rod, ensuring that the paper layer is tightly attached to the rod body without defects such as wrinkles and air bubbles. Send the wrapped sizing rod into a box-type hot air circulation heating chamber through an orbital conveying system for high-temperature baking. During this period, the modified phenolic resin undergoes a crosslinking reaction, causing the laminated kraft paper to cure and form a rigidly supported tubular shell. After the shell cools to room temperature, separate the sizing rod from the paper tube through a demolding mechanism to obtain a preliminarily formed tubular shell with a smooth inner wall; S3. Use a spraying device to evenly coat the outer side of the degradable paper layer 3 in the tubular shell with a refractory slurry made by mixing kaolin and silica sol in a mass ratio of 3:1. During the spraying process, control the pressure of the spray gun at 0.4 - 0.6 MPa, and keep the distance between the spray gun and the paper layer surface at 150 - 200 mm to ensure uniform coating thickness, with a target thickness of 0.15 mm and the thickness deviation controlled within ±0.02 mm. Subsequently, send the degradable paper layer 3 with the refractory slurry coated on the outside into a hot air circulation drying furnace for pre-drying treatment. Make the air in the furnace flow evenly through the air blowing system to quickly remove the moisture on the coating surface. Then, send it into a box-type drying furnace for high-temperature curing to cause the silica sol in the coating to undergo a gelation reaction, and the kaolin particles to bind tightly, forming a dense refractory coating 4 to complete the processing and curing of the refractory coating 4; S4. Use a spraying device to coat the inner side of the degradable paper layer 3 in the tubular housing with an anti-sticking slurry prepared by mixing graphite powder with a small amount of water-based binder. During spraying, control the pressure of the spray gun at 0.2 - 0.3 MPa, and keep the distance between the spray gun and the surface of the paper layer at 200 - 250 mm to ensure that the thickness of the anti-sticking coating is uniform, with a target thickness of 0.1 mm and the thickness deviation controlled within ±0.01 mm. Subsequently, send the degradable paper layer 3 with the anti-sticking slurry coated on the inner side into a hot air circulation drying furnace for low-temperature drying treatment.

[0010] Preferably, the soaking duration in step S1 ranges from 8 - 10 min.

[0011] Preferably, the high-temperature baking temperature in step S2 is 180 °C, and the baking time ranges from 30 - 35 min.

[0012] Preferably, the temperature range of the pre-drying treatment in step S3 is 50 - 80 °C, the pre-drying treatment time ranges from 15 - 20 minutes, and the pre-drying wind speed ranges from 0.5 - 1 m / s.

[0013] Preferably, the high-temperature curing temperature range in step S3 is 120 - 150 °C, and the curing time ranges from 20 - 30 min.

[0014] Preferably, the temperature range of the low-temperature drying treatment in step S4 is 25 - 30 °C, and the low-temperature drying treatment time ranges from 120 - 180 min.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. Through the composite structure design of "modified resin-impregnated kraft paper + inner and outer functional coatings", this solution breaks through the bottleneck of traditional ceramic inner runners in terms of cost, environmental protection, and performance, realizing the high-efficiency, green, and precision of the casting process, and is particularly suitable for the production scenarios of small and medium-sized batch castings with high requirements for environmental protection and production efficiency in resin sand casting.

[0016] 2. In the present invention, the degradable paper layer is composed of natural plant fibers (kraft paper) and decomposable modified phenolic resin, which can be naturally degraded or incinerated (without harmful gas emissions) after being discarded, solving the environmental protection pain points of non-degradability and difficult treatment of traditional ceramic runners.

[0017] 3. In the present invention, after the degradable paper layer is cured at 180°C, a "resin-fiber" composite structure is formed, with a flexural strength ≥ 30 MPa and a temperature-resistant decomposition temperature ≥ 200°C. In combination with the 0.15 mm kaolin-silica sol refractory coating on the outer side, it can effectively resist the high-temperature impact of molten metal, prevent the rapid carbonization of the paper layer, ensure the stable shape of the runner during the casting process, and reduce casting defects caused by the deformation of the runner. The 0.1 mm graphite powder anti-sticking coating on the inner side utilizes the low friction coefficient and high-temperature non-stickiness of graphite to reduce the adhesion force between the molten metal and the inner wall of the runner by 80%. When demolding, the inner runner separates from the casting with "zero adhesion", the residual amount of the casting gate is reduced by 90%, and the subsequent grinding and cleaning workload is reduced by 60%, significantly improving the post-treatment efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. is a three-dimensional structural schematic diagram of a straight pipe body and a transition pipe body in the degradable paper inner runner for resin sand casting of the present invention; Figure 2 FIG. is a schematic diagram of the positional relationship between the degradable paper layer, the refractory coating, and the anti-sticking coating in the degradable paper inner runner for resin sand casting of the present invention; Figure 3 FIG. is a flow chart of the preparation method of the degradable paper inner runner for resin sand casting of the present invention.

[0019] In the figure: 1, straight pipe body; 2, transition pipe body; 3, degradable paper layer; 4, refractory coating; 5, anti-sticking coating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] Example 1: Refer to Figure 1 and Figure 2 As shown: The degradable paper inner runner for resin sand casting includes a straight pipe body 1 and a transition pipe body 2. One end of the two transition pipe bodies 2 is interconnected with both ends of the straight pipe body 1. The straight pipe body 1 and the transition pipe body 2 include a degradable paper layer 3, a refractory coating 4, and an anti-sticking coating 5. The refractory coating 4 is coated on the outer side of the degradable paper layer 3, and the anti-sticking coating 5 is coated on the inner side of the degradable paper layer 3. The interior of the degradable paper layer 3 is impregnated with modified phenolic resin. The degradable paper layer 3 is made of kraft paper, with a thickness of 8 mm. The refractory coating 4 is made of kaolin and silica sol, with a thickness of 0.15 mm. The anti-sticking coating 5 is a graphite powder coating, and its thickness ranges from 0.1 mm.

[0022] In this embodiment, the straight pipe body 1 and the adapter pipe body 2 form a split flow channel system. The two realize the diversion of molten metal through the communication end, adapting to the multi-angle flow channel layout of complex molds. Its variable cross-section structure adopts a tapered flow channel design, and the elastic deformation of the paper material is used to compensate for metal shrinkage. The degradable paper layer 3 uses 120 g / m² kraft paper as the base material, is impregnated with modified phenolic resin and then laminated into a shape with a thickness of 8 mm, forming a resin-fiber composite structure inside, with both rigid support and elastic deformation capabilities, and the modified phenolic resin can improve the high-temperature resistance of the paper layer; the refractory coating 4 is coated on the outer side of the paper layer, which is prepared by mixing kaolin and silica sol in a mass ratio of 3:1, with a thickness of 0.15 mm, forming a high-temperature resistant barrier, and its short-term temperature resistance is greater than 1500 °C, protecting the paper layer from being ablated by molten metal during casting; the anti-adhesion coating 5 is coated on the inner side of the paper layer, using a graphite powder coating with a thickness of 0.1 mm. Utilizing the lubricity and non-adhesiveness of graphite, it avoids the adhesion of molten metal to the inner wall of the flow channel, ensuring the rapid separation of the flow channel and the casting during demolding; The degradable paper layer 3 is made of kraft paper, which can be naturally degraded or incinerated without harmful gas emissions after being discarded, solving the environmental protection problem of non-degradable ceramic runners and conforming to the green manufacturing trend of the casting industry; Through the composite structure design of "modified resin impregnated kraft paper + internal and external functional coatings", this solution breaks through the bottleneck of traditional ceramic inner runners in terms of cost, environmental protection and performance, realizing the high-efficiency, green and precision of the casting process, and is especially suitable for the production scenarios of medium and small batch castings with high requirements for environmental protection and production efficiency in resin sand casting.

[0023] Embodiment 2: The usage method of the degradable paper inner runner for resin sand casting includes the following steps: S1. Cut the kraft paper with a quantitative of 120 g / m² into standard sizes that meet production requirements, ensuring that the dimensional accuracy is controlled within ±1 mm. Prepare a modified phenolic resin solution with a solid content of 45%, and control the solution temperature at 30 ± 5 °C to ensure good fluidity and permeability of the resin. Immerse the cut kraft paper in this solution for 8 - 10 min, so that the resin fully penetrates into the kraft paper fibers. After soaking, take out the kraft paper and drain it through a squeeze roller to remove the excess resin on the surface. Subsequently, use a hydraulic laminator for lamination. The laminator is preheated to 50 - 60 °C, stack the single-layer impregnated kraft paper layer by layer, and continuously press it under a pressure of 10 - 15 MPa for 20 min to preliminarily crosslink the resin and eliminate the interlayer bubbles. During the lamination process, use an infrared thickness gauge to monitor the thickness change in real time, and precisely control the laminated thickness within the range of 7 - 9 mm, ensuring that the thickness uniformity error ≤ ±0.2 mm, forming a dense phenolic resin impregnated kraft paper laminate with a pre-cured structure; S2. According to the specific requirements of the target pipe diameter, select a high-temperature resistant sizing rod with a corresponding diameter and an anti-sticking treatment on the surface. Use a mechanical arc-bending device to evenly bend and wrap the laminated kraft paper around the outer surface of the sizing rod, ensuring that the paper layer is closely attached to the rod body without defects such as wrinkles and bubbles. Feed the wrapped sizing rod into the box-type hot air circulation heating chamber through the track conveying system. Set the temperature of the heating chamber to 180 °C, and start the air blowing device to make the internal temperature uniformity error ≤ ±5 °C. Conduct high-temperature baking at this temperature for 30 - 35 minutes. During this period, the modified phenolic resin undergoes a cross-linking reaction, causing the laminated kraft paper to cure and form a rigidly supported tubular shell. After the shell cools to room temperature, separate the sizing rod from the paper tube through the demolding mechanism to obtain a preliminarily formed tubular shell with a smooth inner wall; S3. Use a spraying device to evenly coat the outside of the degradable paper layer 3 in the tubular shell with a refractory slurry made by mixing kaolin and silica sol in a mass ratio of 3:1. During the spraying process, control the pressure of the spray gun to be 0.4 - 0.6 MPa, and keep the distance between the spray gun and the surface of the paper layer at 150 - 200 mm to ensure uniform coating thickness. The target thickness is 0.15 mm, and the thickness deviation is controlled within ±0.02 mm. Subsequently, feed the degradable paper layer 3 with the refractory slurry coated on the outside into the hot air circulation drying furnace for pre-drying treatment. Set the temperature of the pre-drying treatment to 50 - 80 °C, the time of the pre-drying treatment to 15 - 20 minutes, and the pre-drying wind speed to 0.5 - 1 m / s. Make the air in the furnace flow evenly through the air blowing system to quickly remove the moisture on the surface of the coating. Then, feed it into the box-type drying furnace for high-temperature curing. Set the high-temperature curing temperature to 120 - 150 °C and the curing time to 20 - 30 minutes, causing the silica sol in the coating to undergo a gelation reaction and the kaolin particles to bind tightly to form a dense refractory coating 4, completing the processing and curing of the refractory coating 4; S4. Use a spraying device to coat the inside of the degradable paper layer 3 in the tubular shell with an anti-sticking slurry prepared by mixing graphite powder and a small amount of water-based binder. During spraying, control the pressure of the spray gun to be 0.2 - 0.3 MPa, and keep the distance between the spray gun and the surface of the paper layer at 200 - 250 mm to ensure uniform anti-sticking coating thickness. The target thickness is 0.1 mm, and the thickness deviation is controlled within ±0.01 mm. Subsequently, feed the degradable paper layer 3 with the anti-sticking slurry coated on the inside into the hot air circulation drying furnace for low-temperature drying treatment. Set the temperature of the low-temperature drying treatment to 25 - 30 °C and the time of the low-temperature drying treatment to 120 - 180 minutes. Slowly dry at this temperature to avoid damaging the lubricating structure of graphite due to excessive temperature, causing the anti-sticking slurry on the inside to cure into an anti-sticking coating 5, completing the processing and curing of the anti-sticking coating 5.

[0024] From the perspective of cost, the core raw materials are kraft paper and modified phenolic resin. The raw material cost is only 1 / 5 of that of traditional ceramic internal runners, and there is no need to rely on high-price special ceramic raw materials, significantly reducing the material procurement cost of foundry enterprises. From the perspective of environmental protection, the degradable paper layer 3 is composed of kraft paper and decomposable modified phenolic resin. After being discarded, it can be naturally degraded or incinerated (without harmful gas emissions). During the natural degradation process, it can be gradually decomposed into glucose by cellulase secreted by microorganisms (such as fungi and actinomycetes) in the natural environment, and finally converted into CO2 and water. The degradation period is about 6-12 months. The modified phenolic resin can achieve a decomposition rate of 80% in the soil within 3 years by introducing hydrolyzable groups (such as ester bonds), avoiding the permanent non-degradability of traditional thermosetting resins. From the perspective of performance, after the degradable paper layer 3 is cured at 180°C, a "resin-fiber" composite structure is formed. The bending strength of pure kraft paper is about 15 MPa, which is increased to more than 30 MPa after impregnation, approaching that of low-density engineering plastics. It can withstand the lateral pressure of molding sand and the impact force during the flow of molten metal during casting. The original ignition point of kraft paper is about 230°C, and the cross-linked structure formed after the curing of the modified phenolic resin raises the decomposition temperature to more than 200°C. Combined with the 0.15 mm refractory coating on the outside, a double protection of "matrix temperature resistance + coating heat insulation" is formed: when the molten metal is poured, the surface temperature of the refractory layer reaches 1200°C, but the temperature inside the paper layer can be controlled below 180°C, ensuring that the runner maintains a stable shape during the 3-5 minute pouring process. The shrinkage defect rate of the casting is reduced from 12% to less than 4%, avoiding the collapse risk of traditional paper runners; the 0.1 mm graphite powder anti-sticking coating 5 on the inside utilizes the low friction coefficient and high-temperature non-stickiness of graphite. Graphite is chemically stable at high temperatures (≤1600°C) and does not react with iron-based and aluminum-based molten metals, avoiding the problem of the reaction between SiO2 and iron liquid in ceramic runners to generate FeO impurities. During demolding, the separation force between the internal runner and the casting is reduced from 50-100 N of ceramic runners to 10-20 N, enabling "zero tapping" demolding. The gate residue is reduced from an average of 5 mm to less than 0.5 mm, saving 60% of the post-treatment grinding time and avoiding damage to the casting surface caused by mechanical tapping.

[0025] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Degradable paper inner runner for resin sand casting, characterized in that: It includes a straight pipe body (1) and a connecting pipe body (2). One end of the two connecting pipe bodies (2) is interconnected with both ends of the straight pipe body (1). The straight pipe body (1) and the connecting pipe body (2) include a degradable paper layer (3), a refractory coating (4), and an anti-sticking coating (5). The refractory coating (4) is coated on the outer side of the degradable paper layer (3), and the anti-sticking coating (5) is coated on the inner side of the degradable paper layer (3). The inside of the degradable paper layer (3) is impregnated with modified phenolic resin.

2. The degradable paper inner runner for resin sand casting according to claim 1, characterized in that: The degradable paper layer (3) is made of kraft paper, and the thickness range of the degradable paper layer (3) is 7 - 9 mm.

3. The degradable paper inner runner for resin sand casting according to claim 1, characterized in that: The refractory coating (4) is made of kaolin and silica sol, and the thickness range of the refractory coating (4) is 0.1 - 0.3 mm.

4. The degradable paper-based ingate for resin sand casting according to claim 1, characterized in that: The anti-sticking coating (5) is a graphite powder coating, and its thickness range is 0.05 - 0.15 mm.

5. Preparation method of degradable paper inner runner for resin sand casting, which uses the degradable paper inner runner for resin sand casting described in any one of the above claims 1-4, characterized in that It includes the following steps: S1. Cut the kraft paper into standard sizes, immerse it in a modified phenolic resin solution with a solid content of 45%, take out the kraft paper after soaking, drain the excess resin on the surface with a squeezing roller, and then use a hydraulic laminator for laminating to make its thickness within the range of 7 - 9 mm. S2. Select a high-temperature shaping rod with a corresponding diameter according to the target pipe diameter, use a mechanical arc-bending device to evenly bend and wrap the laminated kraft paper around the outer surface of the shaping rod, and send it into the interior of a heating chamber for high-temperature baking to cure the laminated kraft paper to form a tubular shell with rigid support. S3. Use a spraying device to evenly coat the refractory slurry on the outer side of the degradable paper layer (3) in the tubular shell. Then, send the degradable paper layer (3) with the refractory slurry coated on the outer side into a hot air circulation drying furnace for pre-drying treatment to remove the moisture on its surface. Next, send the degradable paper layer (3) with the refractory slurry coated on the outer side into a box-type drying furnace for high-temperature curing to cure the refractory slurry on its outer side into a refractory coating (4), completing the processing and curing of the refractory coating (4). S4. Use a spraying device to coat the anti-sticking slurry on the inner side of the degradable paper layer (3) in the tubular shell. Then, send the degradable paper layer (3) with the anti-sticking slurry coated on the inner side into a hot air circulation drying furnace for low-temperature drying treatment to cure the anti-sticking slurry on its inner side into an anti-sticking coating (5), completing the processing and curing of the anti-sticking coating (5).

6. The preparation method of the degradable paper-based ingate for resin sand casting according to claim 5, characterized in that: The soaking duration in step S1 ranges from 8 - 10 min.

7. The preparation method of the degradable paper-based ingate for resin sand casting according to claim 5, characterized in that: The high-temperature baking temperature in step S2 is 180 °C, and the baking time ranges from 30 - 35 min.

8. The preparation method of the degradable paper inner runner for resin sand casting according to claim 5, characterized in that: In step S3, the temperature range of the pre-drying treatment is 50 - 80 °C, the time range of the pre-drying treatment is 15 - 20 minutes, and the pre-drying wind speed ranges from 0.5 - 1 m / s.

9. The preparation method of the degradable paper inner runner for resin sand casting according to claim 5, characterized in that: In step S3, the high-temperature curing temperature range is 120 - 150 °C, and the curing time ranges from 20 - 30 min.

10. The preparation method of the degradable paper-based ingate for resin sand casting according to claim 5, characterized in that: In step S4, the temperature range of the low-temperature drying treatment is 25 - 30 °C, and the time range of the low-temperature drying treatment is 120 - 180 min.

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