Method for forming large size thin-walled arcuate foam articles

Abstract

A method for molding large-size thin-walled arc-shaped foam products for aerospace fairings is disclosed: S1. A cavity mold is made of breathable steel with a porosity of 22%-26%, an average pore diameter of 7-35μm, and a thickness of 5-15mm. The cavity thickness of the cavity mold is 5-20mm, and the inner surface area of ​​the cavity mold is 5000-10000cm². 2 The molding process involves several steps: S2 involves weighing and calculating the pre-expanded expandable polystyrene particles and filling them into the cavity of the mold from step S1; S3 involves injecting steam into the cavity of the mold through the air inlets using a two-step steam pressurization method, with the steam temperature at 95-105℃ and the pressure at 0.8-1 MPa; S4 involves reducing the steam pressure to 0.5-0.8 MPa after pressurization and maintaining the pressure for 60-80 seconds to allow the pre-expanded particles in the mold to expand and fuse together. After cooling, the product is demolded. This molding method produces large-size, thin-walled, arc-shaped foam products with mechanical strength and density uniformity that meet the requirements for the front and inverted cone sections of aerospace fairings.

Description

Technical Field

[0001] This invention belongs to the field of polymer foam product manufacturing, specifically relating to a molding method for large-size thin-walled arc-shaped foam products used in aerospace fairings. Background Technology

[0002] Polymer foam is a type of polymer material formed by dispersing a large number of gas micropores in solid plastic. It has excellent properties such as light weight, high specific strength, ability to absorb impact loads, and good heat insulation and sound insulation. It is currently widely used in industry, agriculture, construction, transportation and other fields, but it has not yet been well applied in fairings in the aerospace field.

[0003] In the field of aerospace fairings, reference Figure 1 The foam product is the front cone section of the fairing ( Figure 1 (left side) and inverted cone segment ( Figure 1 (Right side) The foam products of the front and inverted cone sections of the fairing are characterized by large size, thin walls, and large curvature. Traditional polystyrene foam molding methods are not suitable for producing such large-sized, thin-walled, curved components.

[0004] Thin-walled, large-size polystyrene foam products with a foam thickness of less than 100mm are typically formed by post-processing of the foam blocks. The specific forming method is as follows: First, flat foam blocks are produced in a foam molding machine. These uniformly formed flat foam blocks can then be cut into the desired shape using resistance wire. However, when cutting into such shapes… Figure 1 When making foam products for the front cone or inverted cone section of the fairing, due to their large-sized, thin-walled, arc-shaped structure, cutting and molding results in rough product surfaces and reduced mechanical properties.

[0005] To avoid the aforementioned problems through integrated mold foaming, traditional polystyrene foam molds typically have one inlet and one outlet. High-temperature, high-pressure steam is injected through the inlet, forming a steam flow within the mold, heating the foam microspheres, and finally exiting through the outlet. Before exiting, a certain pressure and temperature must be maintained within the mold; otherwise, the surface of the foam microspheres cannot melt and expand, thus "compacting" the foam. When producing large-sized, thin-walled, curved foam products using this traditional integrated mold molding method, the mold cavity is also thin, long, and curved. The heat from the steam flow within the mold is absorbed and attenuated as the distance increases, resulting in inconsistent steam pressure and temperature across different sections of the mold. Furthermore, the poor steam flow within the cavity mold of this size and shape easily leads to localized heat accumulation, causing excessively high local pressure and temperature. All of this causes inconsistent expansion rates of the foam particles, ultimately resulting in foam products with uneven texture. Such products with uneven density do not meet the high requirements of aerospace fairing foam products. Summary of the Invention

[0006] Based on the content in the background art, in order to avoid the problems of rough surface and reduced mechanical properties of large-size thin-walled arc-shaped foam products formed by cutting and processing foam blocks, or to avoid the problem of uneven density in the traditional mold integral foaming process, this invention provides another molding method for large-size thin-walled arc-shaped foam products. The mechanical strength and density uniformity of the foam products obtained by this molding method meet the performance design requirements of the front cone section and the inverted cone section foam products of aerospace fairings.

[0007] A method for molding a large-size thin-walled arc-shaped foam product for aerospace fairings is disclosed, which includes the following steps:

[0008] S1. A cavity mold is made of breathable steel with a porosity of 22%-26%, an average pore diameter of 7-35μm, and a thickness of 5-15mm. The cavity thickness of the cavity mold is 5-20mm, which determines the thickness of the foam product. The inner surface area of ​​the cavity mold is 5000-10000cm². 2 The cavity mold is provided with multiple air inlets, and the pores on the ventilated steel can play the role of air outlet. Therefore, the cavity mold made of ventilated steel does not need to be provided with additional air outlets.

[0009] The cavity mold design made of such breathable steel has a reasonable design for air permeability and pressure holding performance, and can act as a pressure regulator in the following foam molding process.

[0010] S2. Based on the design density requirements of the final molded foam product, the specific design density is 30 kg / m³. 3 Calculate and weigh the pre-expanded polystyrene particles (pre-expanded 15 times, initial particle size of 0.6 mm), and fill them into the cavity of the mold described in step S1.

[0011] S3. A two-step steam pressurization method is used to inject steam into the cavity of the mold through the air inlet. The temperature of the injected steam is 95-105℃ and the pressure is 0.8-1Mpa.

[0012] S4. After pressurization, reduce the pressure of the injected water vapor to 0.5-0.8 MPa and maintain the pressure for 60-80 seconds to allow the pre-foamed particles in the cavity mold to expand and fuse together. After cooling, demold to obtain the product. During this pressure-holding molding process, the cavity mold can utilize the micro-permeability of the breathable steel metal. Its micropores can absorb some condensate and "block" the pores to form a pressure-holding effect. In addition, if the pressure is too high, the absorbed condensate will be discharged from the pores of the breathable steel, and the pressure at that point will automatically decrease. That is, the cavity mold made of breathable steel metal can act as a pressure regulator during the foam molding process, which can avoid the accumulation of heat and the resulting local pressure being too high. This keeps the pressure and temperature in the cavity mold balanced, and keeps the expansion rate of the foam particles in all places consistent. After foaming and demolding, a large-size thin-walled arc-shaped foam product with uniform texture can be obtained. Its mechanical strength and density uniformity meet the performance design requirements of the front cone and inverted cone sections of the aerospace fairing foam products.

[0013] Preferably, the cavity mold has multiple synchronous air inlets evenly distributed on both sides, with 10-15 synchronous air inlets on each side, and each synchronous air inlet covering an area of ​​3000-4000 mm². 2 This synchronous air inlet design allows the pressure inside the mold cavity to rise quickly and evenly to the equilibrium pressure.

[0014] Preferably, a pressure sensor and a temperature sensor are also installed inside the cavity of the mold to monitor changes in pressure and temperature.

[0015] Preferably, the two-step steam pressurization involves first injecting steam for 1-3 seconds and then stopping, allowing the steam to condense in the pores of the permeable steel. After an interval of 3-5 seconds, steam is injected again into the mold cavity for 10-12 seconds for pressurization. Because the condensed water temporarily blocks the micropores of the permeable steel, the secondary steam pressurization will cause the pressure inside the mold cavity to rise initially. When the pressure becomes too high, some water droplets in the pores of the permeable steel are expelled from the mold, allowing the steam pressure to be released from the pores of the permeable steel until the pressure inside the mold cavity no longer increases and reaches equilibrium. This steam pressurization method allows the pressure and temperature inside the cavity to quickly reach the required equilibrium point, minimizing the risk of uneven pressure and temperature caused by excessive travel distance and heat absorption attenuation in the initial stage.

[0016] Through the above technical solutions, the present invention has at least the following beneficial effects:

[0017] The molding method for a large-size thin-walled arc-shaped foam product of aerospace fairing described in this application is the first in the polystyrene foaming industry to use a cavity mold made of breathable steel metal for foam molding. The cavity mold utilizes the micro-permeability of breathable steel metal, and its micropores can absorb some condensate and "block" the pores to form a pressure-holding effect. In addition, if the pressure is too high, the absorbed condensate will be discharged from the pores of the breathable steel, and the pressure at that point will automatically decrease. That is, the cavity mold made of breathable steel metal can act as a pressure regulator in the foam molding process, which can avoid excessive local pressure and keep the pressure and temperature in the cavity of the cavity mold balanced.

[0018] Specifically, by designing the cavity thickness, inner surface area, number and area of ​​air inlets, as well as the thickness, pore diameter, and porosity of the permeable steel in the cavity mold, the permeability and pressure holding performance of the cavity mold made of permeable steel metal are reasonably designed. Combined with the two-step steam pressurization molding method, the pressure and temperature at various points within the cavity mold can quickly reach the required equilibrium point and be automatically adjusted to maintain uniformity. The resulting large-size thin-walled arc-shaped foam products have mechanical strength and density uniformity that meet the requirements of the front cone and inverted cone sections of aerospace fairing foam products. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the foam products for the front cone section and the inverted cone section of the fairing. Detailed Implementation

[0020] The present invention will be further illustrated by the following embodiments, but the application of the present invention is not limited to the embodiments described.

[0021] Example 1

[0022] A method for molding a large-size thin-walled arc-shaped foam product for an aerospace fairing includes the following steps:

[0023] S1. A cavity mold is made of breathable steel with a porosity of 23%, an average pore diameter of 25μm (with a deviation of ±2μm), and a thickness of 10mm. The specific material type of the breathable steel is PM-35. The cavity thickness of the cavity mold is 12mm, which determines the thickness of the foam product. The inner surface area of ​​the cavity mold is 7500cm². 2 The cavity mold is provided with multiple air inlets, and the pores on the ventilated steel can play the role of air outlet. Therefore, the cavity mold made of ventilated steel does not need to be provided with additional air outlets.

[0024] The cavity mold has multiple synchronous air inlets evenly distributed on both sides, with 12 synchronous air inlets on each side, and each synchronous air inlet covering an area of ​​3500 mm². 2This synchronous air inlet design allows the pressure inside the mold cavity to rise quickly and evenly to the equilibrium pressure.

[0025] The cavity mold design made of such breathable steel has a reasonable design for air permeability and pressure holding performance, and can act as a pressure regulator in the following foam molding process.

[0026] The cavity of the mold is also equipped with a pressure sensor and a temperature sensor to monitor changes in pressure and temperature.

[0027] S2. Based on the design density requirements of the final molded foam product, the specific design density is 30 kg / m³. 3 Calculate and weigh the pre-expanded polystyrene particles (pre-expanded 15 times, initial particle size of 0.6 mm), and fill them into the cavity of the mold described in step S1.

[0028] S3. A two-step steam pressurization method is adopted. Water vapor is injected into the cavity of the mold through the air inlet. The temperature of the injected water vapor is 98℃ and the pressure is 0.9Mpa. The water vapor is injected for 2 seconds and then stopped, so that the water vapor condenses in the pores of the ventilated steel. After a 4-second interval, water vapor is injected into the mold again for 11 seconds to pressurize it. Because the condensed water temporarily blocks the micropores of the ventilated steel, the pressure in the mold cavity will rise first when the pressure is too high. When the pressure is too high, some water droplets in the pores of the ventilated steel are discharged from the mold, so that the steam pressure can be released from the pores of the ventilated steel until the pressure in the cavity of the mold cavity no longer increases and reaches equilibrium. This steam pressurization method can quickly reach the required equilibrium point in the cavity pressure and temperature, and minimize the pressure and temperature unevenness caused by excessive travel and heat absorption attenuation in the initial stage.

[0029] S4. After pressurization, reduce the pressure of the injected water vapor to 0.65 MPa and maintain the pressure for 70 seconds to allow the pre-foamed particles in the cavity mold to expand and fuse together. After cooling, demold to obtain the product. During this pressure-holding molding process, the cavity mold can utilize the micro-permeability of the breathable steel metal. Its micropores can absorb some condensate and "block" the pores to form a pressure-holding effect. In addition, if the pressure is too high, the absorbed condensate will be discharged from the pores of the breathable steel, and the pressure at that point will automatically decrease. That is, the cavity mold made of breathable steel metal can act as a pressure regulator during the foam molding process, which can avoid the accumulation of heat and the resulting local pressure being too high. This keeps the pressure and temperature in the cavity mold balanced, and keeps the expansion rate of the foam particles in all places consistent. After foaming and demolding, a large-size thin-walled arc-shaped foam product with uniform texture can be obtained. Its mechanical strength and density uniformity meet the performance design requirements of the front cone and inverted cone sections of the aerospace fairing foam products.

[0030] Example 2

[0031] A method for molding a large-size thin-walled arc-shaped foam product for an aerospace fairing includes the following steps:

[0032] S1. A cavity mold is made of breathable steel with a porosity of 26%, an average pore diameter of 7μm (with a deviation of ±2μm), and a thickness of 5mm. The specific material type of the breathable steel is PM-35. The cavity thickness of the cavity mold is 5mm, which determines the thickness of the foam product. The inner surface area of ​​the cavity mold is 5000cm². 2 The cavity mold is provided with multiple air inlets, and the pores on the ventilated steel can play the role of air outlet. Therefore, the cavity mold made of ventilated steel does not need to be provided with additional air outlets.

[0033] The cavity mold has multiple synchronous air inlets evenly distributed on both sides, with 10 synchronous air inlets on each side, and each synchronous air inlet covering an area of ​​4000 mm². 2 This synchronous air inlet design allows the pressure inside the mold cavity to rise quickly and evenly to the equilibrium pressure.

[0034] The cavity mold design made of such breathable steel has a reasonable design for air permeability and pressure holding performance, and can act as a pressure regulator in the following foam molding process.

[0035] The cavity of the mold is also equipped with a pressure sensor and a temperature sensor to monitor changes in pressure and temperature.

[0036] S2. Based on the design density requirements of the final molded foam product, the specific design density is 30 kg / m³. 3 Calculate and weigh the pre-expanded polystyrene particles (pre-expanded 15 times, initial particle size of 0.6 mm), and fill them into the cavity of the mold described in step S1.

[0037] S3. A two-step steam pressurization method is adopted. Water vapor is injected into the cavity of the mold through the air inlet. The temperature of the injected water vapor is 95℃ and the pressure is 0.8Mpa. The water vapor is injected for 1 second and then stopped, so that the water vapor condenses in the pores of the ventilated steel. After a 5-second interval, water vapor is injected into the mold again for 10 seconds to pressurize it. Because the condensed water temporarily blocks the micropores of the ventilated steel, the pressure in the mold cavity will rise first when the pressure is too high. When the pressure is too high, some water droplets in the pores of the ventilated steel are discharged from the mold, so that the steam pressure can be released from the pores of the ventilated steel until the pressure in the cavity of the mold cavity no longer increases and reaches equilibrium. This steam pressurization method can quickly reach the required equilibrium point in the cavity pressure and temperature, and minimize the pressure and temperature unevenness caused by excessive travel and heat absorption attenuation in the initial stage.

[0038] S4. After pressurization, reduce the pressure of the injected water vapor to 0.5 MPa and maintain the pressure for 80 seconds to allow the pre-foamed particles in the cavity mold to expand and fuse together. After cooling, demold to obtain the product. During this pressure-holding molding process, the cavity mold can utilize the micro-permeability of the breathable steel metal. Its micropores can absorb some condensate and "block" the pores to form a pressure-holding effect. In addition, if the pressure is too high, the absorbed condensate will be discharged from the pores of the breathable steel, and the pressure at that point will automatically decrease. That is, the cavity mold made of breathable steel metal can act as a pressure regulator during the foam molding process, which can avoid the accumulation of heat and the resulting local pressure being too high. This keeps the pressure and temperature in the cavity mold balanced, and keeps the expansion rate of the foam particles in all places consistent. After foaming and demolding, a large-size thin-walled arc-shaped foam product with uniform texture can be obtained. Its mechanical strength and density uniformity meet the performance design requirements of the front cone and inverted cone sections of the aerospace fairing foam products.

[0039] Example 3

[0040] A method for molding a large-size thin-walled arc-shaped foam product for an aerospace fairing includes the following steps:

[0041] S1. A cavity mold is made of breathable steel with a porosity of 22%, an average pore diameter of 35μm (with a deviation of ±2μm), and a thickness of 15mm. The specific material type of the breathable steel is PM-35. The cavity thickness of the cavity mold is 20mm, which determines the thickness of the foam product. The inner surface area of ​​the cavity mold is 10000cm². 2 The cavity mold is provided with multiple air inlets, and the pores on the ventilated steel can play the role of air outlet. Therefore, the cavity mold made of ventilated steel does not need to be provided with additional air outlets.

[0042] The cavity mold has multiple synchronous air inlets evenly distributed on both sides, with 15 synchronous air inlets on each side, and each synchronous air inlet covering an area of ​​3000 mm². 2 This synchronous air inlet design allows the pressure inside the mold cavity to rise quickly and evenly to the equilibrium pressure.

[0043] The cavity mold design made of such breathable steel has a reasonable design for air permeability and pressure holding performance, and can act as a pressure regulator in the following foam molding process.

[0044] The cavity of the mold is also equipped with a pressure sensor and a temperature sensor to monitor changes in pressure and temperature.

[0045] S2. Based on the design density requirements of the final molded foam product, the specific design density is 30 kg / m³. 3Calculate and weigh the pre-expanded polystyrene particles (pre-expanded 15 times, initial particle size of 0.6 mm), and fill them into the cavity of the mold described in step S1.

[0046] S3. A two-step steam pressurization method is adopted. Water vapor is injected into the cavity of the mold through the air inlet. The temperature of the injected water vapor is 105℃ and the pressure is 1Mpa. After injecting water vapor for 3 seconds, the injection is stopped, allowing the water vapor to condense in the pores of the ventilated steel. After a 3-second interval, water vapor is injected into the mold again for 12 seconds to pressurize it. Because the condensed water temporarily blocks the micropores of the ventilated steel, the pressure in the mold cavity will rise first due to the secondary steam pressurization. When the pressure is too high, some water droplets in the pores of the ventilated steel are discharged from the mold, allowing the steam pressure to be released from the pores of the ventilated steel until the pressure in the cavity of the mold cavity no longer increases and reaches equilibrium. This steam pressurization method can quickly reach the required equilibrium point in the cavity pressure and temperature, minimizing the pressure and temperature unevenness caused by excessive travel and heat absorption attenuation in the initial stage.

[0047] S4. After pressurization, reduce the pressure of the injected water vapor to 0.8 MPa and maintain the pressure for 60 seconds to allow the pre-foamed particles in the cavity mold to expand and fuse together. After cooling, demold to obtain the product. During this pressure-holding molding process, the cavity mold can utilize the micro-permeability of the breathable steel metal. Its micropores can absorb some condensate and "block" the pores to form a pressure-holding effect. In addition, if the pressure is too high, the absorbed condensate will be discharged from the pores of the breathable steel, and the pressure at that point will automatically decrease. That is, the cavity mold made of breathable steel metal can act as a pressure regulator during the foam molding process, which can avoid the accumulation of heat and the resulting local pressure being too high. This keeps the pressure and temperature in the cavity mold cavity balanced, and keeps the expansion rate of the foam particles in all places consistent. After foaming and demolding, a large-size thin-walled arc-shaped foam product with uniform texture can be obtained. Its mechanical strength and density uniformity meet the performance design requirements of the front cone and inverted cone sections of the aerospace fairing foam products.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Based on the present invention, and through the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0049] Comparative Example

[0050] This comparative example demonstrates the use of traditional molds to integrally mold large-sized, thin-walled, curved foam products, and is used to compare with Example 1 to illustrate the superiority of the cavity mold designed in this invention. The specific molding method is as follows:

[0051] The conventional mold is made to have the same size and shape as the cavity mold in Example 1. Of course, in addition to the air inlet, the mold is also equipped with an air outlet.

[0052] Expandable polystyrene particles (initial particle size 0.6 mm) were obtained by pressure impregnation using pentane as a foaming agent (8 wt%). These particles were then pre-expanded 15 times in high-temperature steam to form soft small balls, which were then cured for later use. The final foam product was designed to have a density of 30 kg / m³. 3 Weigh the pre-expanded foam balls and fill them into the mold. Then quickly introduce steam (98℃, 0.9Mpa, 15s) to increase the pressure. Then reduce the pressure to 0.65MPa and hold for 70s to allow the foam to form. After cooling, demold.

[0053] The mechanical properties and density uniformity of the foam products in the above embodiments and comparative examples were tested.

[0054] The mechanical properties of foam products are tested in accordance with national standards: flexural strength is tested in accordance with GB / T 8812.1-2007, flexural modulus is tested in accordance with GB / T 8812.2-2007, compressive strength is tested in accordance with GB / T 8813-2008, and tensile strength is tested in accordance with GB / T 9641-1988.

[0055] The density uniformity test method for foam products is as follows: Cut 5cm × 5cm cube samples from the four corners and center of the foam product, measure their load-bearing capacity, and calculate their density. Compare the density of each cube sample with the design density of 30kg / m³. 3 The average of the absolute deviations (i.e., the absolute values ​​of the differences between the density of each sample and the design density, and then the average of them) is used to reflect the uniformity of the density of the foam product material. The smaller the value, the more uniform the density.

[0056] The performance test results are shown in Table 1 below.

[0057] Table 1:

[0058]

[0059] Analysis shows that:

[0060] As shown in Table 1, the large-size thin-walled arc-shaped foam products prepared in each embodiment meet the performance design requirements of the front and inverted cone sections of the aerospace fairing foam products in terms of mechanical strength and density uniformity. This is because the cavity molds made of breathable steel in each embodiment have good pressure holding performance and excellent air permeability. Combined with the two-step steam pressurization molding method described above, the pressure and temperature at various points within the cavity of the cavity mold can quickly reach the required equilibrium point and automatically adjust to maintain uniformity.

[0061] In contrast, when using traditional molds (which drain steam through vents) to integrally mold large-sized thin-walled curved foam products, in addition to the uneven steam pressure and temperature at the front and rear sections due to the long travel distance, the thin, long, and curved mold also hinders steam flow. This leads to localized heat accumulation and excessively high pressure and temperature at those locations. Unlike the cavity molds in the embodiments, the foam cannot release air and reduce pressure in time through the micropores of the breathable steel. As a result, the foam particles expand faster at areas with excessive pressure and temperature, ultimately leading to foam products with uneven density. This uneven texture also affects the overall mechanical properties of the foam product.

Claims

1. A method for molding large-size thin-walled arc-shaped foam products, characterized in that, Includes the following steps: S1. A cavity mold is made of breathable steel with a porosity of 22%-26%, an average pore diameter of 7-35 μm, and a thickness of 5-15 mm. The cavity thickness of the cavity mold is 5-20 mm, and the inner surface area of ​​the cavity mold is 5000-10000 cm². 2 The cavity mold is provided with multiple air inlets; S2. Calculate and weigh the pre-expanded polystyrene particles according to the design density requirements of the final molded foam product, and fill them into the cavity of the mold described in step S1. S3. A two-step steam pressurization method is used to inject steam into the cavity of the mold through the air inlet. The temperature of the injected steam is 95-105℃ and the pressure is 0.8-1Mpa. S4. After pressurization, reduce the pressure of the injected water vapor to 0.5-0.8MPa and maintain the pressure for 60-80 seconds to allow the pre-foamed particles in the mold cavity to expand and fuse together. After cooling, demold to obtain the product.

2. The molding method for a large-size thin-walled arc-shaped foam product according to claim 1, characterized in that: The cavity mold has multiple synchronous air inlets evenly distributed on both sides, with 10-15 synchronous air inlets on each side, and each synchronous air inlet covering an area of ​​3000-4000 mm². 2 .

3. The molding method for a large-size thin-walled arc-shaped foam product according to claim 1, characterized in that: A pressure sensor and a temperature sensor are also installed inside the cavity of the mold.

4. A method for molding a large-size thin-walled arc-shaped foam product according to any one of claims 1-3, characterized in that: The two-step steam pressurization involves first injecting steam for 1-3 seconds and then stopping the injection, allowing the steam to condense in the pores of the breathable steel. After an interval of 3-5 seconds, steam is injected into the mold cavity again for 10-12 seconds to pressurize it.

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