Vacuum infusion method for cork wood shell of wind power blade

Abstract

The invention provides a vacuum infusion method for a balsa wood shell of a wind turbine blade, belongs to the field of wind turbine blades, is used for infusing resin on the balsa wood shell through vacuum negative pressure, and comprises the steps that S1, a mold is cleaned, and the surface of the cleaned mold is coated with a release agent; s2, glass fiber cloth, cork wood core materials, top glass fiber cloth, an isolating membrane and demolding cloth are laid; s3, laying of a resin pipeline; s4, constructing a vacuum infusion system; and S5, vacuum pouring is carried out, demolding is carried out after vacuum pouring is finished, a glue inlet of the resin pipeline is located in the center of the mold cavity, and glue outlets are located in the two sides of the mold cavity. According to the method, the glue feeding route of a traditional vacuum infusion process is changed, the flowing distance of the resin is shortened, and the time that the glass fiber cloth is surrounded by the resin is delayed, so that the glass fiber cloth is more uniformly infiltrated by the resin; the problems that bubbles exist in grooves and holes of a balsa wood shell subjected to traditional vacuum infusion, and a glass fiber panel is whitened, wrinkled and white spots exist are solved.

Description

Technical Field

[0001] The invention belongs to the field of wind turbine blades, and in particular relates to a vacuum infusion method for a balsa wood shell of a wind turbine blade. Background Art

[0002] With the continuous consumption of traditional energy and the increasing pressure on environmental protection, the demand for clean and renewable energy is becoming more and more urgent. As a renewable and pollution-free natural resource, wind energy has been emerging in the field of electricity. As a medium for directly converting wind energy into electrical energy, wind turbines have attracted attention from countries around the world. As a key component of wind turbines, wind turbine blades directly affect the performance, reliability and manufacturing cost of the entire system. At present, the molding process used for wind turbine blades is mainly vacuum infusion molding, which effectively avoids the shortcomings of hand lay-up process such as low production efficiency, serious environmental pollution, high labor intensity and poor product quality stability. It is suitable for the production of large-sized and irregular-shaped products, and can effectively ensure the efficiency and quality of blade molding.

[0003] However, the vacuum infusion molding process has strict requirements. The raw materials, vacuum infusion process and balsa wood processing technology will cause the balsa wood shell after vacuum infusion molding to produce bubbles, white spots and other quality defects, such as Figure 10-12 The figure shows a schematic diagram of common quality defects. These quality defects need to be restored or reinforced, which increases the manufacturing cost of the blade and reduces the quality of the blade. Summary of the invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a vacuum infusion method for a balsa wood shell of a wind turbine blade, so as to solve the product defect problem caused by the existing vacuum infusion process.

[0005] In order to achieve the above object, the technical solution provided by the present invention is as follows: A vacuum infusion method for a balsa wood shell of a wind turbine blade is provided, which is used to infuse resin on the balsa wood shell by using vacuum negative pressure. The method comprises: S1: Clean the mold and apply a release agent on the cleaned mold surface; S2: Laying fiberglass cloth, balsa wood core material, top fiberglass cloth, isolation film and release cloth; S3: Laying of resin pipelines; S4: constructing a vacuum infusion system; S5: Vacuum infusion and demoulding after completion. Wherein, the resin inlet of the resin pipeline is located at the center of the mold cavity, and the glue outlet is located on both sides of the mold cavity.

[0006] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the technical feature that the resin inlet section and the resin outlet section of the resin pipeline are parallel.

[0007] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical feature: the glue outlet is provided with a pressing sheet for balancing the pressure.

[0008] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical feature: the cross section of the pressed sheet is a trapezoid.

[0009] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical feature: the pressing sheet is provided with openings for ensuring smooth passage of resin.

[0010] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical features: S2 comprises: S2.1: After the release agent is applied, lay the bottom guide net, bottom isolation film and bottom release cloth in order; S2.2: Lay the lower layer of fiberglass cloth, balsa wood core material, and top layer of fiberglass cloth in sequence; S2.3: Lay the top layer of release cloth, top layer of isolation film and top layer of guide net in sequence.

[0011] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical features: S5 comprises: S5.1: Use a vacuum pump to evacuate the glue outlet to -950mbar; S5.2: Close the air extraction valve to maintain pressure; S5.3: inject resin from the injection port; S5.4: Demould after the resin is cured.

[0012] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical features: S5.3 further includes preheating the mold before injecting the resin, the preheating temperature being 60°C. The curing temperature of the resin in S5.4 is 60°C-80°C.

[0013] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical features: S5.3 also includes mixing a curing agent into the resin and performing vacuum degassing treatment before injecting the resin, and the vacuum degassing time is 40min-60min.

[0014] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention also has the following technical feature: in S5.3, when the resin is injected into the glue inlet, the regulating valve of the infusion flow rate is half-open.

[0015] The vacuum infusion method for the balsa wood shell of a wind turbine blade provided by the present invention improves the vacuum infusion process. More importantly, it changes the glue feeding route of the traditional vacuum infusion process, shortens the flow distance of the resin, and delays the time when the glass fiber cloth is surrounded by the resin, thereby making the resin infiltration of the glass fiber cloth more uniform, solving various problems of bubble defects in the grooves and holes of the balsa wood shell of the traditional vacuum infusion, whitening, wrinkles, and white spots on the glass fiber panel. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 : A schematic diagram of a perfusion circuit of the perfusion method provided by the present invention; Figure 2 : A schematic diagram of a perfusion circuit of a perfusion method provided by the prior art; Figure 3 : Schematic diagram of the third perfusion circuit used as experimental comparison; Figure 4 : Schematic diagram of the fourth perfusion circuit used as experimental comparison; Figure 5 : Schematic diagram of the fifth perfusion circuit used as experimental comparison; Figure 6 : A schematic diagram of a cross-sectional view of a tablet used in the perfusion method provided by the present invention; Figure 7 : Schematic diagram of common tablet cross section; Figure 8 : Schematic diagram of the openings on the tablet used in the perfusion method provided by the present invention; Fig. 9 : Reaction mechanism diagram of epoxy resin and amine curing agent; Fig.10 : Schematic diagram of bubble defects in vacuum infusion of balsa wood shell in the prior art; Fig.11 : Schematic diagram of whitening defects of vacuum infusion of balsa wood shell in the prior art; Fig.12 : Schematic diagram of white spot defects in vacuum infusion of balsa wood shell in the prior art. DETAILED DESCRIPTION

[0018] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments are combined with the accompanying drawings to specifically illustrate the segmented wind turbine blade provided by the present invention.

[0019] In the description of the embodiments of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the invention.

[0020] In addition, the terms "first", "second", "third", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] The terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0022] Uneven flow of epoxy resin in glass fiber cloth and balsa wood shell can easily lead to white spot defects. The power of vacuum infusion comes from the pressure gradient. The flow direction of resin is from the glue inlet to the glue outlet. The resin flow can be seen as flowing in the pores between the flow cutoff and the fiber yarn bundles on a macroscopic level. On a microscopic level, it refers to the flow inside the fiber yarn bundle. The two work together to complete the flow of resin in the product. During the vacuum infusion process, the resin flow rate in the balsa wood shell groove is faster than the resin infiltration rate in the glass fiber cloth, which makes the local resin flow uneven. Glass fibers in certain areas will be surrounded by resin, and the pressure will be reduced, causing the resin to lose the power of infiltration. If the encirclement behavior occurs late and the surrounded area is small enough, the glass fiber cloth will avoid the occurrence of defects or reduce the severity of defects through its own capillary effect. However, once the two exceed a certain tolerance range, it will inevitably lead to the occurrence of defects, namely white spots.

[0023] A vacuum infusion method for a balsa wood shell of a wind turbine blade is used to infuse resin on the balsa wood shell by using vacuum negative pressure. The method comprises: S1: Use a flexible scraper to clean the mold surface and apply a release agent on the cleaned mold surface; S2: Laying fiberglass cloth, balsa wood core material, top fiberglass cloth, isolation film and release cloth; S3: Laying of resin pipelines; S4: Construct a vacuum infusion system: apply a circle of sealant around the laid core material, and use vacuum bag film and sealant to construct a vacuum system; S5: Vacuum infusion and demoulding after completion. Wherein, the resin inlet of the resin pipeline is located at the center of the mold cavity, and the glue outlet is located on both sides of the mold cavity.

[0024] In the above embodiment, in order to solve the problem of uneven epoxy resin flow, the glue inlet is set at the center of the mold cavity, which shortens the flow distance of the resin and delays the timing for the glass fiber cloth to be surrounded by the resin, thereby making the resin infiltration of the glass fiber cloth more uniform. The glue outlet is located on both sides of the mold cavity. The glue outlet on both sides balances the vacuum pressure on both sides, making the vacuum pressure distribution more uniform, and the resin can flow evenly to avoid the formation of cavities in the groove.

[0025] like Figure 1-Figure 5 As shown, different laying methods of resin pipelines are changed, and the technical effects brought by different laying methods are tested. The specific test results are shown in Table 1: Table 1: Effects of different resin pipeline laying methods Pipe layout Preform layer number Filling time (seconds / S) and effect Figure 1 4 layers 290s, good perfusion effect Figure 2 4 layers 600s, white spots appear near the glue outlet Figure 3 4 layers 250s on one side near the glue outlet and no white spots, the other side cannot be filled Figure 4 4 layers 1000s, large area of ​​white spots Figure 5 4 layers 305s, small white spots From the table above, we can see that to obtain faster and more uniform mold filling, the glue inlet should be set in the center of the mold cavity to minimize the flow distance of the resin. Leaning to the left or right will increase the resin flow distance on the other side, thereby increasing the mold filling time. In the balsa wood shell, due to the large number of grooves and holes, the resin flow uniformity is poor. If the glue injection pipe is set to the left or right, the probability of white spots will increase. According to the size of the shell, the laying of the middle glue inlet pipeline can be increased. In some embodiments, the resin inlet section and the resin outlet section of the resin pipeline are parallel. The resin inlet section and the resin outlet section of the resin pipeline are arranged in parallel to avoid dry spots caused by uneven resin flow.

[0026] In some embodiments, the glue outlet is provided with a pressing sheet for balancing the pressure. If the glue outlet is arranged on the upper surface of the light wood shell, obvious wrinkle defects will be generated. Therefore, a pressing sheet is used to balance the downward pressure. The pressing sheet can be made of hard plastic or hard closed-cell foam, and the thickness of the pressing sheet is 2-3 mm.

[0027] In some embodiments, the cross section of the tablet is a trapezoid. In the above embodiments, the cross section of the tablet is set to be a trapezoid, which has better dispersion of downward pressure than the tablet with a common rectangular cross section.

[0028] like Figure 6-Figure 7 As shown, it is a schematic diagram of the cross-sectional shape of different tablets. Different tablets are used and other process conditions remain unchanged for vacuum infusion. The results are shown in Table 2: Table 2: Vacuum infusion effect of tablets with different cross sections Cross-sectional shape of tablets Preform layer number Infusion Effect rectangle 4 layers There are wrinkle defects Trapezoid 4 layers No wrinkles As shown in the table above, because there are angled edges on both sides of the trapezoid, the applied force is spread through these edges to the rest of the structure, effectively dispersing the downforce.

[0029] In some embodiments, the pressing sheet is provided with openings for ensuring smooth passage of the resin. The setting of the pressing sheet will block the flow of the resin to the bottom of the pressing sheet, resulting in the formation of white spots in the area below the pressing sheet due to poor infiltration, such as Figure 8 As shown, a hole is opened above the tablet, and after passing through the hole, the resin can flow smoothly to the area below the tablet.

[0030] In some embodiments, the S2 includes: S2.1: After the release agent is applied, lay the bottom guide net, bottom isolation film and bottom release cloth in order; S2.2: Lay the lower layer of fiberglass cloth, balsa wood core material, and top layer of fiberglass cloth in sequence; S2.3: Lay the top layer of release cloth, top layer of isolation film and top layer of guide net in sequence.

[0031] There are often white spots on the bottom of the balsa wood shell. This is mainly because the balsa wood shell is close to the mold in a vacuum environment, so that the resin flows faster in the bottom groove than the infiltration speed between the isolation film / release cloth / glass fiber cloth, causing the glass fibers near the groove to be infiltrated with resin in advance, forming enveloping white spots. In the above embodiment, a guide net is added under the bottom isolation film. After the guide net is added at the bottom, the resin flows faster on the guide net, thereby increasing the soaking speed between the bottom isolation film / release cloth / glass fiber cloth and improving the occurrence of white spot defects at the bottom.

[0032] In some embodiments, the S5 includes: S5.1: Use a vacuum pump to evacuate the glue outlet to -950mbar; S5.2: Close the exhaust valve to maintain pressure. The pressure maintenance requirement is: after 15 minutes, the pressure loss is no more than 25mbar; S5.3: inject resin from the injection port; S5.4: Demould after the resin is cured.

[0033] In some embodiments, S5.3 further includes preheating the mold before injecting the resin and keeping the mold warm for 60 minutes, the preheating temperature is 60°C, and the curing temperature of the resin in S5.4 is 60°C-80°C.

[0034] In some embodiments, the balsa wood shell is dried before vacuum infusion, the moisture content of the balsa wood shell does not exceed 8%, the drying temperature is set at 50-60°C, and the drying time is greater than 8 hours. The effects of different drying temperatures and drying times on the balsa wood shell are shown in Table 3 below: Table 3: Effect of drying temperature and drying time on balsa wood shell Balsa Wood Number Drying temperature / ℃ Drying time / h Effect after shell infusion 1# 50 ＜8 The balsa wood shell has many bubble defects and a large range of implosion defects. 2# 55 ＜8 The balsa wood shell has many bubble defects and a small range of implosion defects. 3# 60 ＜8 The balsa wood shell has many bubble defects and a small range of implosion defects. 4# 50 ＞8 The balsa wood shell has small bubble defects and no implosion defects 5# 55 ＞8 The balsa wood shell has small bubble defects and no implosion defects 6# 60 ＞8 The balsa wood shell has small bubble defects and no implosion defects The main reason for the whitening of the panel is the explosion of the resin. The manufacturing of wind turbine blades generally uses a mixed system of epoxy resin and amine curing agent, which belongs to the ring-opening bulk polymerization reaction. Fig. 9 As shown, the reaction process includes three stages: chain initiation, chain growth, and chain termination. The stage with the fastest reaction rate and the most intense heat release is the chain growth stage, which is also the resin cross-linking and curing stage. When the moisture content in balsa wood is too high, the rapid accumulation of temperature during the curing process of epoxy resin may cause water to produce hydrogen ions and hydroxide ions, which promotes the ring opening rate of epoxy groups, aggravates the chain growth rate, and generates more reaction heat. In addition, there are loose structures such as tree cores and water cores in balsa wood. During the vacuum infusion process, the resin will invade the interior of the wood fiber tube package in large quantities. Due to the low thermal conductivity characteristics of the balsa wood closed-cell tube package structure, the reaction heat will be difficult to remove in time, resulting in a rapid increase in the resin temperature. When the temperature is too high, the resin reaction is too intense and explosion occurs, which eventually leads to the generation of whitening defects. In addition, the cracking of the balsa wood produced during the processing of the balsa wood shell will lead to a large amount of resin enrichment, and the reaction heat will accumulate in the resin enrichment area, resulting in the generation of whitening defects. Therefore, in the above two embodiments, the moisture content and temperature of the balsa wood shell are respectively limited.

[0035] The mold is preheated and kept warm for a period of time, so that the air and residual moisture in the wood fiber tube wall of the balsa wood shell are further released. The effects of preheating temperature and holding time on the balsa wood shell are shown in Table 4: Table 4: Effect of preheating temperature and holding time on balsa wood shell Balsa Wood Number Preheating temperature / ℃ Insulation time / min Effect after shell infusion 1# 50 20 The balsa wood shell has more bubble defects and a smaller range of implosion defects. 2# 50 40 The balsa wood shell has many bubble defects and no implosion defects. 3# 50 60 The balsa wood shell has small bubble defects and no implosion defects 4# 60 20 The balsa wood shell has many bubble defects and no implosion defects. 5# 60 40 The balsa wood shell has small bubble defects and no implosion defects. 6# 60 60 The balsa wood shell has no obvious bubble defects and no implosion defects If the curing temperature of the resin is too high, the resin curing reaction will be violent and explosion will occur. If the curing temperature is too low, the resin will cure slowly or incompletely.

[0036] In some embodiments, S5.3 also includes mixing a curing agent into the resin and performing a vacuum degassing treatment before injecting the resin, and the vacuum degassing time is 40min-60min. The vacuum degassing treatment can remove the bubbles generated during the stirring process. The degassing time is between 40-60min, and the time should not be too long or too short. If the degassing time is too short, the bubbles in the resin cannot be completely eliminated. If the degassing time is too long, the resin begins to undergo a cross-linking reaction, at which time the viscosity of the resin increases and the fluidity decreases, and it is not suitable for infusion.

[0037] In some embodiments, in S5.3, when the resin is injected into the glue inlet, the regulating valve of the injection flow rate is half-opened. The effects of different valve openings on the injection effect of the balsa wood shell are shown in Table 5 below: Table 5 Effect of valve control on filling time and product quality Valve control Resin flow rate Infusion time (min) Balsa wood shell infusion effect 1 / 4 slow 60 The bubbles in the deep grooves and through holes are large, and the defect area is large. There are no white spots on the fiberglass panel. 1 / 3 slow 45 The bubbles in deep grooves and through holes are small, the defect area is small, and there is no white spot on the fiberglass panel 1 / 2 Moderate 30 No bubbles in deep grooves and through holes, no white spots on fiberglass panels 2 / 3 Faster 20 No bubbles in deep grooves and through holes, small white spots on fiberglass panels Fully open quick 15 There are no bubbles in deep grooves and through holes, and large white spots on the fiberglass panel The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A vacuum infusion method for a balsa wood shell of a wind turbine blade, used to infuse resin on the balsa wood shell using vacuum negative pressure, characterized in that: The method comprises: S1: Clean the mold and apply a release agent on the cleaned mold surface; S2: Laying fiberglass cloth, balsa wood core material, top fiberglass cloth, isolation film and release cloth; S3: Laying of resin pipelines; S4: constructing a vacuum infusion system; S5: Vacuum infusion and demoulding after completion. Wherein, the resin inlet of the resin pipeline is located at the center of the mold cavity, and the glue outlet is located on both sides of the mold cavity.

2. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 1, characterized in that: The resin inlet section and the resin outlet section of the resin pipeline are parallel.

3. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 1, characterized in that: The glue outlet is provided with a pressing sheet for balancing the pressure.

4. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 3, characterized in that: The cross section of the pressed tablet is trapezoidal.

5. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 3, characterized in that: The pressing sheet is provided with openings for ensuring smooth passage of resin.

6. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 1, characterized in that: The S2 includes: S2.1: After the release agent is applied, lay the bottom guide net, bottom isolation film and bottom release cloth in order; S2.2: Lay the lower layer of fiberglass cloth, balsa wood core material, and top layer of fiberglass cloth in sequence; S2.3: Lay the top layer of release cloth, top layer of isolation film and top layer of guide net in sequence.

7. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 1, characterized in that: The S5 includes: S5.1: Use a vacuum pump to evacuate the glue outlet to -950mbar; S5.2: Close the air extraction valve to maintain pressure; S5.3: inject resin from the injection port; S5.4: Demould after the resin is cured.

8. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 7, characterized in that: The S5.3 also includes preheating the mold before injecting the resin, the preheating temperature is 60°C, The curing temperature of the resin in S5.4 is 60°C-80°C.

9. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 7, characterized in that: The S5.3 also includes mixing a curing agent into the resin and performing a vacuum degassing treatment before injecting the resin, and the vacuum degassing time is 40 minutes to 60 minutes.

10. The vacuum infusion method for the balsa wood shell of a wind turbine blade according to claim 7, characterized in that: In S5.3, when the resin is injected into the glue inlet, the regulating valve of the injection flow rate is half opened.

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