Propeller blade

Abstract

To provide a propeller blade excellent in productivity and formability.SOLUTION: A propeller blade is provided, having a skin which defines an outer shape of the propeller blade. The skin includes sandwich structure in which a porous layer is interposed between a plurality of fiber-reinforced resin layers, and in a portion where the sandwich structure is included, the porous layer is formed by means such as disposing a foamable sheet on the side closer to the skin from the thickness central plane and causing the foamable sheet to foam. The distance (T1) from a surface on the propeller blade outer surface side of the skin to a surface on the propeller blade outer surface side of the porous layer, and the distance (T2) from a surface on the propeller blade inner surface side of the skin to a surface on the propeller blade inner surface side of the porous layer, satisfy the following equation (1): T1<T2 (1).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a propeller blade.

Background Art

[0002] A propeller blade has an airfoil shape and obtains thrust by pushing air backward as it rotates around a drive shaft. To efficiently push air backward, the propeller blade has a complex shape in which the angle of attack and the chordwise length change from the root to the tip.

[0003] Reducing the weight of the propeller blade contributes to an increase in the payload and the flight range of an aircraft. Therefore, a high-strength and high-rigidity fiber-reinforced material is used as a structural material. However, since the propeller blade has a complex shape as described above, its molding difficulty is high, and mass production at a high build rate is difficult.

[0004] On the other hand, in recent years, many aircraft having a large number of propeller blades, such as Urban Air Mobility (UAM) and drones, have been actively developed, and it is necessary to produce propeller blades at a higher build rate than before in the future.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, aircraft with a large number of propeller blades have been developed for UAM and drones. In these aircraft, due to the need to increase the flight range and time, there is a high need for weight reduction, especially for propeller blades with a large number of blades per aircraft. To meet this need for weight reduction, fiber-reinforced composite materials with high specific strength and high specific stiffness are applied to the propeller blades.

[0007] When manufacturing a propeller blade made of a fiber-reinforced composite material, if a prepreg in which a reinforcing fiber base material is impregnated with a resin is used in advance, fiber twisting during molding can be suppressed, and weight variation of the molded product can also be suppressed, and a high-quality propeller blade can be produced.

[0008] Generally, when manufacturing a propeller blade using a fiber-reinforced composite material, the fiber-reinforced composite material is heat-cured in a mold. When heat-curing the fiber-reinforced composite material, it is necessary to apply pressure, but it is difficult to control the molding pressure only by the amount of the molding material charged into the mold, and it is necessary to provide some pressure-applying means.

[0009] In response to such problems, for example, Patent Document 1 discloses a method of charging foamed particles into the interior of a propeller blade to produce a porous core, and at the same time, pressurizing the fiber-reinforced composite material of the skin by the expansion pressure of the foamed particles. On the other hand, since heat is applied to a normal propeller blade from a molding die, for example, in a thick part such as the root part of the propeller blade, gelation of the skin starts before the expansion of the foamed particles, and pressurization is carried out after the start of gelation, and in some cases, a good molded product cannot be obtained.

[0010] As for the use of a porous body for a propeller blade, there are also other forms shown in Patent Document 2 and Patent Document 3. These documents show a skin having a sandwich structure in which a porous body is sandwiched between fiber-reinforcing materials, and a structure in which the skin is locally reinforced with a porous body. On the other hand, in these documents, it is not considered to utilize the expansion pressure during the molding of the porous body as the molding pressure of the fiber-reinforcing material.

[0011] As described above, although it has been shown that the expansion pressure during the formation of the porous core inside the propeller blade can be utilized as the forming pressure of the fiber-reinforced material of the skin when forming the propeller blade made of the fiber-reinforced composite material, there are still problems.

[0012] Therefore, in the present invention, when utilizing the expansion pressure during the formation of the porous body as the forming pressure of the fiber-reinforced composite material, a suitable propeller blade is shown, and a propeller blade excellent in productivity and formability is provided.

Means for Solving the Problems

[0013] In order to solve such problems, the present invention adopts the following means. [1] A propeller blade having a skin that forms the outer shape of the propeller blade, wherein the skin includes a sandwich structure in which a porous layer is sandwiched between a plurality of layers of fiber-reinforced resin layers, and in the portion including the sandwich structure, the distance (T1) from the outer surface side surface of the skin of the propeller blade to the outer surface side surface of the porous layer and the distance (T2) from the inner surface side surface of the skin of the propeller blade to the inner surface side surface of the porous layer satisfy the following formula (1).

[0014] T1 < T2 (1) [2] In the portion including the sandwich structure, when the thickness of the skin is T 100 the distance (Tpc) from the outer surface side surface of the skin of the propeller blade to the center plane of the porous layer satisfies the following formula (2), and the propeller blade according to [1] above, wherein T1 and T2 satisfy the following formulas (3) and (4).

[0015] 0.2 × T 100 ≦ Tpc ≦ 0.45 × T 100 (2) T1 ≧ 0.05 × T 100 (3) T2 ≧ 0.30 × T 100 (4) [3] The propeller blade according to [1] or [2] above, wherein the thickness (Tp) of the porous layer satisfies the following formula (5).

[0016] Tp ≦ 0.30×T 100 (5) [4] The propeller blade according to any one of [1] to [3] above, wherein the density of the porous layer is 0.1 g / cm 3 or more and 0.5 g / cm 3 or less. [5] The propeller blade according to any one of [1] to [4] above, wherein T1 is 0.2 mm or more. [6] The propeller blade according to any one of [1] to [5] above, wherein the plurality of fiber-reinforced resin layers are fiber-reinforced resin layers using a thermosetting resin, and the curing time of the thermosetting resin used in the fiber-reinforced resin layer existing on the outer surface side of the propeller blade with respect to the porous layer is longer than the curing time of the thermosetting resin used in the fiber-reinforced resin layer existing on the inner surface side of the propeller blade with respect to the porous layer. [7] The propeller blade according to any one of [1] to [6] above, wherein the skin is supported by a porous core. [8] A method for manufacturing a propeller blade having a skin that forms the outer shape of the propeller blade, wherein the skin includes a plurality of sheet-like fiber-reinforced composite material precursor sheets (sheet A) and at least one resin sheet (sheet B) having thermal expansibility that becomes a porous layer after expansion. The method includes a step of preparing (step 1), a step of laminating sheet A and sheet B and installing them in a mold with sheet B sandwiched by sheet A (step 2), and a step of heating sheet A and sheet B in the mold, thermally expanding sheet B to form a porous layer, and using the pressure generated at that time to pressurize and cure / mold the laminated sheet A (step 3). The method for manufacturing a propeller blade is manufactured through at least these steps, and after molding, the distance (T1) from the surface on the outer surface side of the propeller blade of the skin to the surface on the outer surface side of the porous layer and the distance (T2) from the surface on the inner surface side of the propeller blade of the skin to the surface on the inner surface side of the porous layer satisfy the following formula (1).

[0017] T1 < T2 (1) [9] The manufacturing method of the propeller blade according to [8] above, wherein the volume change rate before and after forming the sheet B exceeds 100% and is 400% or less.

[10] A method for manufacturing a propeller blade according to [8] or [9] above, which comprises preparing a porous core, and performing step 2 by laminating sheet A and sheet B so as to enclose the porous core.

[11] The manufacturing method of the propeller blade according to any one of [8] to

[10] above, wherein step 2 is performed by installing the laminated sheet A and sheet B in a preheated mold after laminating sheet A and sheet B.

[12] The manufacturing method of the propeller blade according to any one of [8] to

[11] above, wherein the expansion start temperature of sheet B is 20°C or more lower than the heating temperature in step 3.

[13] The manufacturing method of the propeller blade according to any one of [8] to

[12] above, wherein the expansion start temperature of sheet B is lower than the temperature indicating the lowest viscosity of the resin which is a component of sheet A.

[14] The manufacturing method of the propeller blade according to any one of [8] to

[13] above, wherein sheet B contains thermally expandable microcapsules, and thermal expansion and pressurization are performed by utilizing the expansion of the thermally expandable microcapsules.

[15] A method for manufacturing a propeller blade according to any one of [8] to

[14] above, which comprises preparing a resin sheet not containing reinforcing fibers, and performing step 2 by laminating the resin sheet not containing reinforcing fibers on the outer surface side of the propeller blade of sheet A. [Effect of the Invention]

[0018] According to the present invention, it is possible to provide a propeller blade that achieves high mechanical properties while achieving high productivity. The propeller blade of the present invention is particularly suitable for aircraft that use a large number of propeller blades such as UAM and drones. [Brief Description of the Drawings]

[0019]

Figure 1

Mode for Carrying Out the Invention

[0020] The propeller blade according to the present invention has an airfoil shape and obtains thrust by pushing air backward by rotating around a drive shaft. Generally, a propeller blade has a skin shaped into an airfoil shape, and has a solid structure having a porous core inside, or a structure in which the inside of the skin is a hollow structure and the skin is connected in the thickness direction of the wing, and a reinforcing structure such as a shear web extending in the wing length direction is provided.

[0021] In the present invention, a structure in which a fiber-reinforced composite material is shaped into a propeller shape is a structure in which at least the fiber-reinforced composite material forms a part of the skin structure of the propeller blade. Here, the skin is a thin plate-like member having the airfoil shape of the propeller blade.

[0022] Here, the fiber-reinforced composite material is a material obtained by embedding reinforcing fibers in a resin. As the form of the reinforcing fibers, for example, there are forms of continuous fibers and forms of short fibers, and any form may be used in the present invention. Also, regarding the form of the base material of the reinforcing fibers, there are forms oriented in one direction, woven forms, NCF (non-crimp fabric) forms, forms in which short fibers are randomly oriented, etc., but the present invention is not limited to any form.

[0023] Examples of the reinforcing fiber include organic fibers such as aramid fiber, polyethylene fiber, and poly(paraphenylene benzoxazole) (PBO) fiber, inorganic fibers such as glass fiber, carbon fiber, silicon carbide fiber, alumina fiber, chilaro fiber, basalt fiber, and ceramic fiber, metal fibers such as stainless steel fiber and steel fiber, and other fibers such as boron fiber, natural fiber, and modified natural fiber. Among them, carbon fiber is preferred in the present invention. Among these reinforcing fibers, it is lightweight and has particularly excellent properties in terms of specific strength and specific modulus, and is also excellent in heat resistance and chemical resistance. Furthermore, polyacrylonitrile (PAN)-based carbon fiber, from which high-strength carbon fiber is easily obtained, is more preferred.

[0024] Examples of resins used for fiber-reinforced composite materials include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins, cyanate resins, etc., and thermoplastic resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate (PTT) resin, polyethylene (PE) resin, polypropylene (PP) resin, styrene resins, polyoxymethylene (POM) resin, polyamide (PA) resin, polycarbonate (PC) resin, polymethyl methacrylate (PMMA) resin, polyvinyl chloride (PVC) resin, polyphenylene sulfide (PPS) resin, polyphenylene ether (PPE) resin, modified PPE resin, polyimide (PI) resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, polysulfone (PSU) resin, modified PSU resin, polyethersulfone resin, polyketone (PK) resin, polyarylene ether ketone resin (PAEK), polyarylate (PAR) resin, polyether nitrile (PEN) resin, phenolic resins, phenoxy resins, fluorine-based resins such as polytetrafluoroethylene resin, and furthermore, thermoplastic elastomers such as polystyrene-based resins, polyolefin-based resins, polyurethane-based resins, polyester-based resins, polyamide-based resins, polybutadiene-based resins, polyisoprene-based resins, fluorine-based resins, etc., and copolymers, modified products, and thermoplastic resins blended with two or more of these may also be used. Further, examples of the polyarylene ether ketone resin (PAEK) include polyether ketone (PEK), polyether ether ketone (PEEK), polyether ether ketone ketone (PEEKK), polyether ketone ketone (PEKK), polyether ketone ether ketone ketone (PEKEKK), polyether ether ketone ether ketone (PEEKEK), polyether ether ether ketone (PEEEK), and polyether diphenyl ether ketone (PEDEK), etc., and copolymers, modified products, and resins blended with two or more of these may also be used.

[0025] The propeller blade of the present invention is a propeller blade having a skin that forms the outer shape of the propeller blade, and the skin is characterized by including a sandwich structure in which a porous layer is sandwiched between a plurality of layers of fiber-reinforced resin layers.

[0026] The porous layer in the present invention refers to a resin layer containing voids. As the form of the voids, an independent bubble structure in which each void forms a closed space or a continuous bubble structure in which a plurality of voids are combined may be used, but from the viewpoint of the mechanical properties of the propeller blade, an independent bubble structure is desirable. Further, the voids may be simply in a state where the voids are scattered in the resin, may be formed by dispersing microcapsules in the resin layer, or may be in a state where the voids are formed by the springback of a web made of short fibers. Further, the porous layer may contain a filler or reinforcing fibers as necessary.

[0027] Further, the porous layer may be provided over the entire area of the propeller blade or may be provided only in a partial area of the propeller blade. When provided only in a partial area of the propeller blade, it is particularly preferable to provide it at a location that is difficult to apply a molding pressure during molding, for example, at a location that forms a vertical wall during molding at the root of the propeller blade.

[0028] The resin constituting the porous layer is not particularly limited. For example, thermosetting resins such as epoxy resin, unsaturated polyester resin, vinyl ester resin, phenol resin, epoxy acrylate resin, urethane acrylate resin, phenoxy resin, alkyd resin, urethane resin, maleimide resin, cyanate resin, etc., and polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate (PTT) resin, polyethylene (PE) resin, polypropylene (PP) resin, styrene resin, polyoxymethylene (POM) resin, polyamide (PA) resin, polycarbonate (PC) resin, polymethyl methacrylate (PMMA) resin, polyvinyl chloride (PVC) resin, polyphenylene sulfide (PPS) resin, polyphenylene ether (PPE) resin, modified PPE resin, polyimide (PI) resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, polysulfone (PSU) resin, modified PSU resin, polyether sulfone resin, polyketone (PK) resin, polyarylene ether ketone resin (PAEK), polyarylate (PAR) resin, polyether nitrile (PEN) resin, phenol resin, phenoxy resin, fluororesin such as polytetrafluoroethylene resin, and furthermore, thermoplastic elastomers such as polystyrene resin, polyolefin resin, polyurethane resin, polyester resin, polyamide resin, polybutadiene resin, polyisoprene resin, fluororesin, etc., their copolymers, modified products, and thermoplastic resins blended with two or more of these may also be used. Further, as the polyarylene ether ketone resin (PAEK), for example, polyether ketone (PEK), polyether ether ketone (PEEK), polyether ether ketone ketone (PEEKK), polyether ketone ketone (PEKK), polyether ketone ether ketone ketone (PEKEKK), polyether ether ketone ether ketone (PEEKEK), polyether ether ether ketone (PEEEK), and polyether diphenyl ether ketone (PEDEK), etc., their copolymers, modified products, and resins blended with two or more of these may also be used.

[0029] In the present invention, the density of the porous layer is 0.1 g / cm 3 or more and preferably 0.5 g / cm 3 or less. With such a density, while achieving weight reduction, a good expansion pressure can be imparted during the formation of the fiber-reinforced composite material of the skin. As a method for measuring the density, it can be measured according to JIS Z 8807:2012, Methods for Measuring the Density and Specific Gravity of Solids, or it can also be calculated by cutting out the porous layer into a certain shape, measuring the weight, and then dividing the weight of the porous layer by the volume. When measuring the weight of the sample in water in JIS Z 8807, the surface is covered in advance with tape or the like whose specific gravity and weight have been measured so that water does not enter the pores of the porous layer, and the measurement can be carried out by removing the influence of the tape from the measurement results.

[0030] Further, the skin of the propeller blade of the present invention includes a sandwich structure in which a porous layer is sandwiched between a plurality of fiber-reinforced resin layers. The sandwich structure in the present invention is, for example, as shown in FIG. 1, a structure in which at least one layer of fiber-reinforced resin layers (101, 102) are arranged on the inner layer side and the outer layer side of the porous layer, respectively, and the porous layer (103) is sandwiched therebetween. By adopting such a structure, the skin rigidity can be increased and the weight of the propeller blade can be reduced.

[0031] Also, when forming the fiber-reinforced composite material of the propeller blade with the expansion force of the inflatable body, for example, conventionally, the expansion pressure during the foam molding of the porous core encapsulated in the skin was used for the molding. However, when using the expansion pressure during the foam molding of the porous core, since it takes time for the heat applied from the outside of the mold to reach the inside of the propeller blade, high-rate production was difficult. Therefore, the present invention arranges a layer (conveniently referred to as the "thermal expansion layer") having thermal expansibility and becoming a porous layer after expansion at a location closer to the outer layer side of the propeller blade where heat is more easily transmitted from the mold, so that heat is transmitted to the thermal expansion layer and expansion starts at an early stage when heat begins to be transmitted to the fiber-reinforced material, and the expansion pressure is transmitted at an early stage, enabling high-rate production.

[0032] Thus, when considering forming the fiber-reinforced composite material of the propeller blade by utilizing the expansion pressure during the formation of the porous layer, the propeller blade of the present invention has a sandwich structure with a porous layer that generates expansion pressure disposed on the skin of the propeller blade.

[0033] In a conventionally known sandwich structure, the porous layer is disposed on the neutral axis, and it is recommended that the fiber-reinforced resin layers sandwiching the porous layer have the same thickness respectively.

[0034] On the other hand, the propeller blade of the present invention is characterized in that the distance (T1) from the outer surface side surface of the skin of the propeller blade to the outer surface side surface of the porous layer and the distance (T2) from the inner surface side surface of the skin of the propeller blade to the inner surface side surface of the porous layer satisfy the following formula (1).

[0035] T1 < T2 (1) In this way, by disposing the porous layer not on the neutral axis of the skin but closer to the outer layer side of the skin, heat is more likely to be transferred from the mold during molding, which is preferable. Here, the thickness of the skin is obtained as the length of the line segment connecting the inner layer side surface of the skin to the outer layer side surface of the skin at the minimum distance. Also, the thickness from the inner layer surface of the target porous layer to the inner layer surface of the skin and the thickness from the outer layer surface of the target porous layer to the outer layer surface of the skin are measured along the above-mentioned line segment. When a plurality of porous layers exist in the skin, in the present invention, it is necessary to satisfy the relationship of the formula (1) using T1 and T2 obtained based on the porous layer located on the outermost layer of the skin.

[0036] Also, in the propeller blade of the present invention, when the thickness of the skin is T 100 it is preferable that the distance (Tpc) from the outer surface side surface of the skin of the propeller blade to the center plane of the porous layer satisfies the following formula (2), and T1 and T2 satisfy the following formulas (3) and (4). 0.2×T 100 ≦Tpc≦0.45×T 100 (2) T1≧0.05×T100 (3) T2 ≧ 0.30 × T 100 (4) The central plane of the porous layer is determined as the set of midpoints of line segments that connect the inner layer side surface of the skin to the outer layer side surface of the skin at the minimum distance. Further, the distance (Tpc) from the outer surface of the propeller blade of the skin along the line segment to the central plane of the porous layer can be measured. In the example of FIG. 1, Tpc is equal to T1 + 1 / 2Tp. When a plurality of porous layers are present in the skin, in the present invention, Tpc is determined based on the porous layer located in the outermost layer of the skin.

[0037] When the porous layer is formed at a position closer to the outer layer as described above, from the time when the porous layer starts to expand until the expansion is completed and the internal pressure is applied, it can be quickly completed. Not only can a propeller blade without defects be obtained at a fast cycle time, but also the rigidity of the outermost surface of the molded product can be ensured, and damage to the propeller blade during foreign object collision can be prevented. Defects in the present invention are, for example, voids contained in the fiber-reinforced resin layer, which occur when sufficient pressure is not applied during molding. When a plurality of porous layers are present in the skin, the position of each porous layer is measured, and if the outermost porous layer is within the above range, the effects of the present invention can be obtained. Therefore, in the present invention, the object can be achieved if at least the porous layer located in the outermost layer is within the above range.

[0038] Further, in the propeller blade of the present invention, it is preferable that the thickness (Tp) of the porous layer satisfies the following formula (5).

[0039] Tp ≦ 0.30 × T 100 (5) The thickness (Tp) of the porous layer is determined by measuring the distance from the inner layer surface of the porous layer to the outer layer surface of the porous layer along a line segment that connects the inner layer side surface of the skin to the outer layer side surface of the skin at the minimum distance. In the present invention, by setting the thickness of the porous layer within such a range, as the porous body becomes thicker, the effect of suppressing heat conduction to the inner layer of the porous layer is reduced, and furthermore, morphological collapse from the preform shape due to volume change during the expansion molding of the porous layer can be suppressed. When a plurality of porous layers are present in the skin, Tp shall be determined as the sum of the thicknesses of all the porous layers.

[0040] Also, in the propeller blade of the present invention, it is preferable that T1 is 0.2 mm or more. If T1 is 0.2 mm or more, the rigidity of the outermost surface of the molded product can be ensured, and damage to the propeller blade during foreign object collision can be prevented. Also, when there is a fiber-reinforced resin layer of fabric on the outer layer of the porous layer, it is preferable because it can withstand various loads with a small thickness.

[0041] Also, in the propeller blade of the present invention, the plurality of fiber-reinforced resin layers are fiber-reinforced resin layers using a thermosetting resin, and the curing time of the thermosetting resin used for the fiber-reinforced resin layer present on the outer surface side of the propeller blade with respect to the porous layer is preferably longer than the curing time of the thermosetting resin used for the fiber-reinforced resin layer present on the inner surface side of the propeller blade with respect to the porous layer. With such a configuration, gelation of the fiber-reinforced resin layer located on the outer layer of the porous layer, which is easily heated by the mold, can be suppressed, and a propeller blade with few defects can be obtained.

[0042] Also, in the propeller blade of the present invention, it is preferable that the skin is supported by a porous core. With such a configuration, it can be arranged in the mold while maintaining the preform shape of the fiber-reinforced resin layer, and also, the expansion pressure of the porous body in the propeller blade skin layer can be supported from the inner layer of the skin, and internal pressure can be applied, and a propeller blade with few defects can be obtained.

[0043] In addition, the method for manufacturing a propeller blade of the present invention includes a step of preparing a plurality of sheet-shaped fiber-reinforced composite material precursor sheets (hereinafter referred to as "sheet A") and at least one resin sheet having thermal expansibility and becoming porous after thermal expansion (hereinafter referred to as "sheet B") (step 1), a step of laminating the sheet A and the sheet B and installing them in a mold with the sheet B sandwiched by the sheet A (step 2), a step of heating the sheet A and the sheet B in the mold, thermally expanding the sheet B to form a porous layer, and using the pressure generated at that time to pressurize the laminated sheet A to cure and form it (step 3). The method for manufacturing a propeller blade is manufactured through at least these steps, and after molding, the distance (T1) from the skin's propeller blade outer surface side surface to the porous layer's propeller blade outer surface side surface and the distance (T2) from the skin's propeller blade inner surface side surface to the porous layer's propeller blade inner surface side surface satisfy the following formula (1).

[0044] T1 < T2 (1) Examples of the sheet-shaped fiber-reinforced composite material precursor sheet include, but are not limited to, a prepreg in which a reinforcing fiber base material is impregnated with resin in advance and is in a semi-cured state. The resin sheet having thermal expansibility and becoming porous after thermal expansion is not particularly limited. For example, those in which microcapsules having thermal expansibility are dispersed in the resin, those containing a short fiber web and expanding the volume of the sheet by its springback action, and those containing a component that generates gas by a chemical reaction can be mentioned. Examples of such materials include Toray MicroPly (trademark) EM-3 manufactured by Toray Advanced Composites, Inc., the foamed resin sheet HPS-28K manufactured by Sun Yurek Co., Ltd., and the expansion adhesive sheet TB1652 manufactured by Three Bond Co., Ltd.

[0045] Preparing sheet A and sheet B is step 1. In this step 1, it is preferably carried out to cut out sheet A and sheet B into the shape of the skin of the propeller blade. The number of sheet A and sheet B to be prepared is determined by the lamination structure.

[0046] Next, the step of laminating Sheet A and Sheet B and installing them in the mold with Sheet B sandwiched by Sheet A is Step 2. In this step, as long as Sheet B is sandwiched by Sheet A at the stage finally placed in the molding die, the installation method is not particularly limited. For installation, a method of installing the pre-laminated Sheet A and Sheet B in the mold, or laminating Sheet A and Sheet B along the mold surface in the mold may be used. Also, regarding these, a member serving as a core can be installed in the mold thereafter. Further, Sheet A and Sheet B can be laminated along the core surface of the member serving as a core and installed in the mold.

[0047] Subsequently, as Step 3, Sheet A and Sheet B are heated in the mold to thermally expand Sheet B to form a porous layer, and at the same time, using the pressure generated at that time, the laminated Sheet A is pressurized to be cured and formed. Examples of the heating method for Sheet A and Sheet B include a method of transmitting heat through the mold.

[0048] By molding such that the thickness from the inner layer surface of the porous layer to the inner layer surface of the skin is thicker than the thickness from the outer layer surface of the porous layer to the outer layer surface of the skin of the propeller blade molded product thus obtained, a molded product with few defects can be obtained with high cycle.

[0049] In addition, in the method for manufacturing a propeller blade of the present invention, it is preferable that the volume change rate before and after the forming of the sheet B exceeds 100% and is 400% or less. Here, the volume change rate is a percentage obtained by Ta÷Tb×100, where Ta is the thickness of the porous layer after expansion and Tb is the thickness of the resin sheet having thermal expansibility before expansion. Ta can be obtained along a line segment connecting the inner layer side surface of the skin to the outer layer side surface of the skin at the minimum distance, excluding the location where the porous layer is interrupted. Further, Tb is obtained by measuring the thickness of the sheet before forming using a thickness gauge. By setting such an expansion range, it is possible to suppress the twist of the preform due to the volume change before and after the forming of the sheet B, and since the space can be filled promptly after the start of expansion and the forming pressure due to expansion can be applied, defects in the formed product can be suppressed.

[0050] In addition, in the method for manufacturing a propeller blade of the present invention, a porous core is prepared, and step 2 is performed by laminating sheet A and sheet B so as to enclose the porous core. This is preferable. When performing molding with the expansion pressure of sheet B, it is necessary to support the pressure from the inner layer side of the skin. At this time, by using a porous core, molding can be performed while suppressing the weight of the propeller blade compared to the case of using a solid core.

[0051] In addition, in the method for manufacturing a propeller blade of the present invention, it is preferable that step 2 is performed by laminating sheet A and sheet B and then placing the laminated sheet A and sheet B in a preheated mold. By using a preheated mold, the temperature rise time of the mold can be shortened, and production can be carried out with high cycle.

[0052] In the method for manufacturing a propeller blade of the present invention, even when the mold is at a high temperature, heat is rapidly transmitted to the porous layer, so the forming pressure accompanying the expansion of the porous layer can be obtained from the initial stage of heat curing, and the forming pressure can be applied before the fiber reinforced resin layer close to the mold is cured, so a formed product with few defects can be obtained.

[0053] Further, in the method for manufacturing a propeller blade of the present invention, it is preferable that the expansion start temperature of Sheet B is 20°C or more lower than the heating temperature in Step 3. Here, the heating temperature refers to the maximum temperature applied during Step 3. When the expansion start temperature of Sheet B is 20°C or more lower than the molding temperature, the expansion pressure due to the expansion of Sheet B can be applied from an early stage of molding, and a molded product with few defects can be obtained, which is preferable.

[0054] Further, in the method for manufacturing a propeller blade of the present invention, it is preferable that the expansion start temperature of Sheet B is lower than the temperature at which the resin, which is a component of Sheet A, exhibits the lowest viscosity. If Sheet B starts to expand before the fiber-reinforced resin layer of the skin reaches the lowest viscosity and an internal pressure is applied to Sheet A, the effect of the expansion pressure can be easily obtained, and a molded product with few defects can be obtained, which is preferable. The temperature at which the resin exhibits the lowest viscosity can be obtained, for example, by raising the temperature at a rate of 20°C to 5°C per minute and measuring the viscosity.

[0055] Further, in the method for manufacturing a propeller blade of the present invention, it is preferable that Sheet B contains thermally expandable microcapsules and that thermal expansion and pressurization are performed by utilizing the expansion of the thermally expandable microcapsules. When using thermally expandable capsules, the resulting porous layer becomes closed cells, which is preferable from the perspective of the mechanical properties of the porous layer, and it also becomes easier to control the volume change rate and the expansion temperature.

[0056] Further, in the method for manufacturing a propeller blade of the present invention, a resin sheet not containing reinforcing fibers is prepared, and it is preferable that Step 2 is performed by laminating the resin sheet on the outer surface side of the propeller blade of Sheet A. There are no particular restrictions on the type of resin contained in the resin sheet. When performing molding using the expansion pressure of the porous layer, depending on the molding conditions, the molding pressure may become low and the surface quality of the fiber-reinforced composite material may deteriorate. In such a case, by disposing a resin sheet on the outermost layer of the preform, a molded product having good surface quality can be obtained even at a low pressure.

Examples

[0057] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not construed as being limited to the descriptions of the items of such examples.

[0058] In the following description, the wing length direction from the wing root to the wing tip will be described as the 0° direction, and the wing width direction from the wing leading edge to the wing trailing edge will be described as the 90° direction.

[0059] (Example 1) P707AG-15 carbon fiber unidirectional prepreg manufactured by Toray Composite Materials America, Inc. was prepared and cut into the base material shape of the propeller blade skin to obtain a skin-shaped sheet. At the time of this cutting, a prepreg (prepreg 1) in which carbon fibers were oriented in the 0° direction and a prepreg (prepreg 2) in which carbon fibers were oriented in the 90° direction were prepared.

[0060] Subsequently, F6273C-07M carbon fiber fabric prepreg manufactured by Toray Composite Materials America, Inc., in which a biaxially orthogonal carbon fiber fabric was impregnated with resin, was prepared and cut into the base material shape of the propeller blade skin. By cutting, a prepreg (prepreg 3) in which the orthogonal carbon fibers were oriented in the -45° direction and the +45° direction, respectively, was obtained.

[0061] Subsequently, a microballoon-containing thermosetting epoxy resin film, Toray MicroPly (trademark) EM-3 manufactured by Toray Advanced Composites, Inc., was cut into the skin shape of the propeller blade (film 1).

[0062] Subsequently, Rohacell (registered trademark) 110 IG-F, a polymethacrylimide rigid foam manufactured by Polyplastics Co., Ltd., was machined into the core shape of the propeller blade to obtain a porous core.

[0063] Thereafter, at the root of the blade, the porous core was shaped layer by layer so that it became [Prepreg 3 / Prepreg 1 / Film 1 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 3] from the outer surface side of the propeller blade. This propeller blade has a ply drop structure towards the tip of the blade, and at the tip of the blade, it is [Prepreg 3 / Prepreg 1 / Film 1 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 3] from the outer surface side of the propeller blade.

[0064] The obtained three-dimensional preform was placed in a propeller blade molding die preheated to 130 °C, clamped, and heat-cured molding was carried out.

[0065] Regarding the obtained propeller blade molded product, the skin thickness at the root of the propeller blade was 2.3 mm, the thickness of T1 was 0.37 mm, the thickness of T2 was 1.13 mm, and the thickness of the porous layer was 0.8 mm. Therefore, Tpc was 33% of T. 100 Also, since the film thickness before molding of the porous layer was 0.64 mm, the volume change rate before and after molding of the porous layer was 125%.

[0066] (Example 2) The molding die was shaped with [Prepreg 3 / Prepreg 1 / Film 1], and the core was shaped with Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 3]. After that, the core was placed in the molding die so that the laminated structure at the root of the blade in the molding die became [Prepreg 3 / Prepreg 1 / Film 1 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 3]. This propeller blade has a ply drop structure towards the tip of the blade, and at the tip of the blade, it is [Prepreg 3 / Prepreg 1 / Film 1 / Prepreg 1 / Prepreg 1 / Prepreg 2 / Prepreg 3] from the outer surface side of the propeller blade.

[0067] Thereafter, the propeller blade was molded in the same manner as in the example except that the molding die was put into an oven at 130 °C and heat-cured molding was carried out.

[0068] For the obtained propeller blade molded product, the skin thickness at the root of the propeller blade was 2.3 mm, the thickness of T1 was 0.37 mm, the thickness of T2 was 1.13 mm, and the thickness of the porous layer was 0.8 mm. Therefore, Tpc was 33% of T 100 of it.

[0069] (Comparative Example 1) At the root of the blade, the propeller blade was laminated from the outer surface side of the propeller blade as [Preg 3 / Preg 1 / Preg 1 / Preg 2 / Film 1 / Preg 1 / Preg 1 / Preg 2 / Preg 3], and this propeller blade had a ply drop structure toward the tip of the blade. At the tip of the blade, it was [Preg 3 / Preg 1 / Preg 2 / Film 1 / Preg 1 / Preg 2 / Preg 3] from the outer surface side of the propeller blade. The propeller blade was molded in the same manner as in Example 1 except for the above For the obtained propeller blade molded product, the skin thickness at the root of the propeller blade was 2.14 mm, the thickness of T1 was 0.67 mm, the thickness of T2 was 0.67 mm, and the thickness of the porous layer was 0.8 mm. Therefore, Tpc was 50% of T 100 of it.

[0070] For the propeller blades obtained in the examples and comparative examples, after polishing the cross-section of the propeller blade and observing it with a microscope, voids were not confirmed in Examples 1 and 2, but voids were confirmed in Comparative Example 1.

Industrial Applicability

[0071] The hollow structure according to the present invention, particularly a propeller blade, is a propeller blade having an excellent productivity, a lightweight and high-quality hollow structure, and can be suitably used for propellers of UAM, UAS (Unmanned Aircraft Systems), drones, aircraft, and the like.

Explanation of Signs

[0072] 101: Inner layer fiber-reinforced resin layer 102: Outer layer fiber-reinforced resin layer 103: Porous layer 104: Core part 201: Inner surface side surface of the skin part 202: Outer surface side surface of the skin part

Claims

1. A propeller blade having a skin that forms the outer shape of the propeller blade, wherein the skin includes a sandwich structure in which a porous layer is sandwiched between a plurality of layers of fiber-reinforced resin layers, and in a portion where the sandwich structure is included, the distance (T1) from the outer surface side surface of the skin to the outer surface side surface of the porous layer of the propeller blade and the distance (T2) from the inner surface side surface of the skin to the inner surface side surface of the porous layer of the propeller blade satisfy the following formula (1). A propeller blade. T1 < T2 (1)

2. In the portion including the sandwich structure, when the thickness of the skin is T １００ The propeller blade according to claim 1, wherein the distance (Tpc) from the outer surface side surface of the skin of the propeller blade to the center plane of the porous layer satisfies the following formula (2), and T1 and T2 satisfy the following formulas (3) and (4). 0.2 × T １００ 0.2 × T ≤ Tpc ≤ 0.45 × T １００ (2) T1 ≥ 0.05 × T １００ (3) T2 ≥ 0.30 × T １００ (4)

3. The propeller blade according to claim 1 or 2, wherein the thickness (Tp) of the porous layer satisfies the following formula (5). Tp ≤ 0.30 × T １００ (5)

4. The density of the porous layer is 0.1 g / cm ３ or more and 0.5 g / cm ３ or less. The propeller blade according to claim 1 or 2

5. The propeller blade according to claim 1 or 2, wherein T1 is 0.2 mm or more.

6. The plurality of layers of fiber-reinforced resin layers are fiber-reinforced resin layers using a thermosetting resin, and the curing time of the thermosetting resin used in the fiber-reinforced resin layer existing on the outer surface side of the propeller blade with respect to the porous layer is longer than the curing time of the thermosetting resin used in the fiber-reinforced resin layer existing on the inner surface side of the propeller blade with respect to the porous layer. The propeller blade according to claim 1 or 2.

7. The propeller blade according to claim 1 or 2, wherein the skin is supported by a porous core.

8. A method for manufacturing a propeller blade having a skin that forms the outer shape of the propeller blade, wherein the skin includes a plurality of sheet-shaped fiber-reinforced composite material precursor sheets (hereinafter referred to as "sheet A") and at least one resin sheet having thermal expansibility and becoming a porous layer after expansion (hereinafter referred to as "sheet B"). The method comprises the steps of: preparing the sheets (step 1); laminating sheet A and sheet B and placing them in a mold with sheet B sandwiched by sheet A (step 2); heating sheet A and sheet B in the mold to thermally expand sheet B and form a porous layer, and using the pressure generated during this process to pressurize and cure / mold the laminated sheet A (step 3). The manufacturing method passes through at least these steps. After molding, the distance (T1) from the outer surface side surface of the skin of the propeller blade to the outer surface side surface of the porous layer and the distance (T2) from the inner surface side surface of the skin of the propeller blade to the inner surface side surface of the porous layer satisfy the following formula (1). T1 < T2 (1)

9. The method for manufacturing a propeller blade according to claim 8, wherein the volume change rate of the sheet B before and after molding exceeds 100% and is 400% or less.

10. The method for manufacturing a propeller blade according to claim 8 or 9, wherein a porous core is prepared, and step 2 is performed by laminating sheet A and sheet B so as to enclose the porous core.

11. The method for manufacturing a propeller blade according to claim 8 or 9, wherein step 2 is performed by laminating sheet A and sheet B and then placing the laminated sheet A and sheet B in a preheated mold.

12. The method for manufacturing a propeller blade according to claim 8 or 9, wherein the thermal expansion start temperature of sheet B is 20°C or more lower than the heating temperature in step 3.

13. The method for manufacturing a propeller blade according to claim 8 or 9, wherein the thermal expansion start temperature of sheet B is lower than the temperature at which the lowest viscosity of the resin, which is a component of sheet A, is exhibited.

14. The method for manufacturing a propeller blade according to claim 8 or 9, wherein sheet B contains thermally expandable microcapsules, and thermal expansion and pressurization are performed by utilizing the expansion of the thermally expandable microcapsules.

15. Prepare a resin sheet that does not contain reinforcing fibers, and the step 2 is performed by laminating the resin sheet that does not contain reinforcing fibers on the outer surface side of the propeller blade of the sheet A. The manufacturing method of the propeller blade according to claim 8 or 9.

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