A full-wrapping type blade root remanufacturing method for high-load steel box girder retired blades

Abstract

The application discloses a kind of high bearing steel box girder full-wrapping type decommissioned blade root remanufacturing methods, belong to wind power equipment remanufacturing technical field.The method includes: cutting off the original blade root of decommissioned blade, keep blade main body with complete blade tip;The exposed upper and lower beam plate is cut into two ends wide, narrow in the middle to form a mechanical interlocking bowtie-shaped section;Iron core is bonded between beam plate to form a whole assembly;The assembly is embedded in the U-shaped steel box girder with slot, and the lower side is embedded and bonded, the side gap is filled and bonded, and the upper side is embedded and bonded, and then welded to seal the box, to form a full-wrapping connection structure;Finally, glass fiber cloth is laid by hand at the joint to form a reinforcing layer, and a through hole is drilled to implant a high-strength anchor rod for anchoring.The application can realize high-reliability root remanufacturing of decommissioned blades, and the flange interface can be adapted to any hub.

Description

Technical Field

[0001] This invention belongs to the technical field of wind power equipment remanufacturing and retired wind turbine blade recycling. Specifically, it relates to a method for remanufacturing the blade root of retired blades by fully wrapping it with a high-load-bearing steel box girder. By removing the original composite material blade root and reconstructing the blade root connection structure by fully wrapping the end of the beam plate with a high-strength steel box girder, the retired blades can be adapted to wind turbine hubs of different specifications with high reliability and reuse, which meets the relevant national standards for remanufacturing of mechanical products. Background Technology

[0002] Wind turbine blades are the core wind-catching components of wind turbine generators. They are mainly made of glass fiber reinforced epoxy resin matrix composite (GFRP) through vacuum injection molding. The main beam, which includes upper and lower beam plates, bears more than 80% of the total load of the blade and is the most critical load-bearing structure of the blade.

[0003] The disposal of large quantities of decommissioned blades is both an environmental challenge and an industrial opportunity for efficient resource utilization.

[0004] Among the existing technologies for disposing of decommissioned blades, landfilling and incineration cause serious pollution and waste resources; mechanical crushing and recycling is a material-level downgrade that completely destroys the aerodynamic performance and structural value of the blades; pyrolysis and chemical recycling technologies have low maturity and high costs, making it difficult to achieve high-value utilization of decommissioned blades.

[0005] The most valuable utilization method is to directly reuse the blades as a whole. However, the original blade root connection structure (embedded bolt sleeve, T-bolt, etc.) of retired blades is customized for the hub interface of specific wind turbine models. When retired blades are used for wind turbines of different specifications, the original blade root interface cannot be matched with the new hub, which becomes the core bottleneck of overall reuse.

[0006] To address the interface mismatch issue, some existing solutions opt to discard the original blade root and fabricate a new metal flange connection, but these solutions generally suffer from the following technical defects: Firstly, the steel-composite bonding interface has insufficient strength. Planar lap bonding is often used, relying solely on the shear strength of a single adhesive layer. The bonding area is limited, making it prone to interfacial debonding failure under long-term alternating wind loads, resulting in poor fatigue performance.

[0007] Secondly, stress concentration is severe. The elastic modulus of steel and composite materials differ greatly, and the stiffness at the junction changes abruptly, which easily leads to severe stress concentration and accelerates crack initiation and propagation.

[0008] Third, mechanical connections can easily damage the substrate. Simple bolt-through connections can cut the composite material fibers, causing hidden defects such as delamination and splitting, which in turn weakens the strength of the beam and slab itself and results in insufficient connection reliability.

[0009] Fourth, the overall stiffness and torsional resistance are poor. Due to the lack of a reasonable internal filling and external wrapping structure, the torsional and bending stiffness of the modified blade root section is insufficient, making it prone to deformation and instability under complex loads.

[0010] Therefore, the industry urgently needs a remanufacturing method that can achieve high-strength, high-rigidity, and high-reliability connections between composite beams and metal blade roots. This method would solve the interface mismatch problem, ensure the long-term operational safety of the connection nodes, and enable retired blades to meet remanufacturing standards and be safely downgraded and reused. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention provides a method for reconstructing the root of decommissioned blades using a fully enclosed high-load-bearing steel box girder. The method employs a composite structure consisting of a high-strength steel box girder fully enclosing the beam plate and filling it with an internal iron core. This is combined with bow-tie interlocking, four-sided wrapping bonding, stepped layering transition, and through-reinforcement anchoring to construct a multi-load-bearing system, significantly improving connection strength, stiffness, and reliability.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for reconstructing the root of a decommissioned blade with a fully enclosed structure in a high-load-bearing steel box girder, comprising the following steps: S1 Blade Body Cutting: Determine the total length of the blade after modification based on the installed parameters of the target wind turbine, cut off the original blade root along the cutting line and discard it, and retain the blade body with complete blade tip and continuous aerodynamic shape.

[0013] Completely remove the original composite blade root that is incompatible with the target hub interface to free up installation space for the reconstruction of a standardized steel blade root; at the same time, fully preserve the aerodynamic shape of the blade body and the main beam load-bearing structure, inheriting the blade's highest-value aerodynamic and structural performance. This fundamentally solves the core bottleneck of the original blade root interface mismatch; the blade body retains 100% of the original design's aerodynamic parameters, ensuring that the power generation efficiency after modification does not show a significant decrease. This procedure is applicable to all decommissioned wind turbine blades with intact main structures and no structural damage. Regardless of the original blade root interface form and size specifications, interface reconstruction can be achieved by cutting off the original blade root.

[0014] The length of the blade body retained after cutting is 6 to 15 meters. This length range corresponds to the commonly used blade length of 100kW to 1MW distributed wind turbines and is the mainstream adaptation range for the downgrading and reuse of retired large megawatt blades. The original airfoil curve, torsion angle distribution, and chord length distribution aerodynamic parameters of the blade are completely preserved, which is the core prerequisite for ensuring the power generation efficiency of the blade after modification.

[0015] S2 end structure pretreatment: The leading edge skin, trailing edge skin and web plate within a set length range are cut off along the axial direction towards the blade tip at the cut end of the blade body, exposing the upper beam plate and lower beam plate arranged opposite each other within this length range, and the surface of the beam plate is polished and cleaned.

[0016] By removing the skin and web within the connecting section, the upper, lower, and left / right sides of the upper and lower beams are fully exposed, providing a complete and clean bonding substrate for the subsequent full-wrap bonding of the steel box girder. In this design, the web of the connecting section is removed to create internal space for the insertion of an iron core, ensuring a complete and tight fit between the inner wall of the steel box girder and the beam surface. With the beam completely exposed on all four sides, wraparound bonding on all four sides can be achieved, maximizing the bonding area and providing a structural foundation for the full-wrap connection.

[0017] The axial length of the skin and web removed is 300-800mm, which can be flexibly adjusted according to the load level of the target wind turbine, taking into account both connection strength and structural weight; grinding and cleaning remove residual resin, contaminants and surface aging layer from the beam and plate surface, exposing a clean fiber-reinforced composite material surface, avoiding interface contamination that leads to a decrease in bonding strength, and ensuring the interface bonding strength of subsequent bonding.

[0018] S3 Bowtie Tenon Processing: The exposed upper and lower beam ends are cut into bowtie symmetrical cross-section structures that are wide at both ends and narrow in the middle.

[0019] By processing the ends of traditional equal-width beams and slabs into bow-tie-shaped sections, several advantages are achieved: First, a concave waist structure is formed, which, when embedded into the corresponding groove, enables axial mechanical interlocking, creating the first line of mechanical locking defense and changing the failure mode of single bonding. Second, the bonding perimeter is maximized within a limited axial length, significantly increasing the total bonding area. Third, the load is smoothly transferred through two beveled transitions, avoiding stress concentration caused by abrupt changes in the cross-section. The bonding perimeter of the bow-tie-shaped section can be increased by 40% to 60% compared to a rectangular section of equal width, with a corresponding increase in bonding area. The concave waist structure forms a natural mechanical barrier, which can distribute a large amount of load under axial tension. Even if the adhesive layer experiences local failure, the connection can still be maintained through mechanical interlocking, greatly improving safety redundancy.

[0020] The minimum width of the bowtie-shaped symmetrical section is 50% to 70% of the original width of the beam and slab. This ratio range takes into account both the mechanical locking effect and the structural strength of the beam and slab itself. If the width is narrowed too much, the strength of the beam and slab section will be weakened excessively. If the width is narrowed too little, the mechanical locking effect will not be obvious. The two ends of the wide section and the middle concave section are connected by two beveled transition sections to ensure a smooth transition of load. After cutting, the edges of the bowtie shape are rounded with a radius of 3 to 5 mm. The purpose is to remove the sharp corners and burrs generated by cutting, eliminate stress concentration sources, and avoid cracking and delamination defects at the edges when under load.

[0021] S4 Iron Core Assembly Bonding: Prepare an iron core that matches the gap between the beam and the plate. Apply epoxy structural adhesive to the upper and lower surfaces of the iron core and the inner wall of the beam and plate. Bond and fix the iron core in the gap between the upper and lower beam and plate. After pressure curing, form an integral assembly of beam and plate-core.

[0022] Firstly, pre-bonding the iron core to the beam and slab in the open space as an integral assembly ensures the concentric positioning accuracy of the iron core and the beam and slab, avoiding problems such as inability to insert, misalignment, and skewness caused by first placing the beam and slab into the closed box and then inserting the iron core. Secondly, the iron core completely fills the cavity between the beam and slab, transforming the original cavity section into an approximately solid section, which can effectively transfer inter-story shear force and significantly improve the shear resistance and overall stiffness of the joint. Thirdly, the iron core provides a reliable internal anchoring base for subsequent through-type rebar anchoring, significantly improving the anchoring force and reliability of the rebar.

[0023] The beam and the inner core are bonded together as a rigid whole, with high assembly and positioning accuracy. The cross-sectional bending, shear and torsional stiffness are greatly improved, providing a stable composite matrix for the subsequent full-wrap connection of the box girder.

[0024] The iron core is a solid steel structure with a strength of Q355 or higher, ensuring its own load-bearing strength. The surface is provided with annular grooves to increase the bonding area and improve the interfacial bonding force. The axial length of the iron core is consistent with the overlap length of the beam and plate, and the thickness matches the spacing between the upper and lower beams and plates, completely filling the gaps between the beams and plates and ensuring uniform support throughout the entire length. The curing conditions are 60℃ for 6 hours or room temperature for 72 hours, which matches the epoxy structural adhesive curing process commonly used in the wind power industry, ensuring that the adhesive layer performance is fully utilized.

[0025] S5 Steel Box Girder Prefabrication: Prepare steel box girders with connecting flanges. The box girders are first welded into a U-shaped structure with a top opening, consisting of a lower plate and two side plates, with the upper plate reserved for later installation; a lower plate groove adapted to the bowtie-shaped cross section is opened on the inner side of the lower plate, and an upper plate groove adapted to the bowtie-shaped cross section is opened on the inner side of the upper plate.

[0026] High-strength steel box girder is the main load-bearing structure of the new blade root. The strength and elastic modulus of steel are far superior to those of composite materials, fundamentally improving the structural strength and load-bearing capacity of the blade root section. The separate manufacturing method, which involves first fabricating the U-shaped opening structure and then sealing the top plate, is to leave room for top operations, ensuring that pressure can be applied to all internal bonding surfaces and quality can be observed. This avoids the problems of inability to construct internal bonding and uncontrollable quality after the box body is closed. The steel box girder provides extremely high structural stiffness and strength, with a load-bearing capacity far exceeding that of the original composite material blade root. The separate design ensures the workability and quality control of internal bonding, significantly reducing construction difficulty and increasing the yield rate.

[0027] The steel box girder is made of Q355 or higher strength steel to meet the strength and fatigue requirements of wind power structures. The cross-section is rectangular box-shaped, and the axial length is 1.2 to 1.5 times the length of the exposed beam plate, ensuring sufficient overlap length and strength reserve. The contours of the lower and upper plate grooves are 3 to 5 mm larger than the outer contour of the bow-tie beam plate, forming a uniform bonding gap to provide filling space for the resin adhesive and ensure uniform adhesive layer thickness. The groove depth is two-thirds of the beam plate thickness, ensuring sufficient embedding depth and mechanical locking effect while retaining the base material thickness at the bottom of the steel plate, avoiding the weakening of the steel plate body strength due to excessive groove depth. The connecting flange is welded to the flange end of the box girder, and the flange bolt hole parameters are customized to match the target wind turbine hub interface, which can be adapted to hub interfaces of any specification, completely eliminating the limitations of the original blade root interface.

[0028] S6 Lower side interlocking and bonding: Insert the beam-core integral assembly into the top opening of the U-shaped box beam, embed the lower beam into the corresponding groove, apply adhesive and apply pressure to cure, and achieve the lower bow tie-shaped interlocking and bonding.

[0029] First, the lower bonding surface is fixed as a positioning benchmark for the overall assembly, ensuring the relative positional accuracy of the beam and the box girder. Simultaneously, a bow-tie interlocking joint achieves a dual connection of chemical bonding and mechanical locking on the lower side. The lower side positioning is precise and reliable, and the bonding quality is controllable, providing a stable benchmark for subsequent bonding of the sides and top, preventing assembly misalignment.

[0030] The adhesive used in this step is a special epoxy structural adhesive for wind turbine blades. After curing, the tensile shear strength is not less than 25MPa. This type of adhesive has good bonding compatibility with composite material matrices and steel, and has excellent aging resistance and fatigue resistance. It is the standard material for structural bonding in the wind power industry. The bonding process uses tooling to apply pressure and squeeze out excess adhesive to ensure that the adhesive layer is uniform and free of air bubbles, thereby improving the stability of the bonding quality.

[0031] S7 Side Gap Filling and Bonding: Inject epoxy structural adhesive into the gaps between the left and right sides of the beam-plate assembly and the inner wall of the box girder side plate, apply pressure and cure to achieve full side bonding.

[0032] By filling the gap between the side panels of the filler beam and the side panels of the box girder, full bonding on both sides is achieved, expanding the bonding surface from the top and bottom to all four sides, further increasing the total bonding area and significantly improving the torsional bearing capacity of the joint. The total bonding area is greatly increased, and a circumferential bonding constraint is formed, significantly enhancing the shear and torsional resistance of the joint and improving the overall structural integrity.

[0033] The adhesive used in this step is also a special epoxy structural adhesive for wind turbine blades, with a tensile shear strength of not less than 25MPa after curing. The adhesive is injected slowly from the bottom up to ensure that the gaps are completely filled with adhesive and there are no air bubbles. After the adhesive is injected, a side pressure tool is used to apply appropriate pressure to squeeze out excess adhesive and ensure that the adhesive layer is dense and uniform.

[0034] S8 Upper side inlay bonding: Cover the box girder upper plate with the top opening, so that the upper beam plate is embedded in the upper plate groove, apply glue and pressurize to cure, realize the upper bow tie-shaped inlay bonding, and complete the full wrap bonding of the beam plate around the whole side.

[0035] The upper plate is then closed and the upper bow tie is joined and bonded, ultimately forming a fully enclosed bonding system that surrounds the beam on all four sides. This maximizes the bonding area and mechanical locking effect, completing the full constraint of the steel box girder on the beam end. This achieves a fully enclosed connection between the steel box girder and the beam end, with the bonding surface encircling the entire beam, optimizing both load-bearing capacity and structural integrity.

[0036] The adhesive used in this step is a special epoxy structural adhesive for wind turbine blades, with a tensile shear strength of not less than 25MPa after curing. After sealing, pressure is applied using a vertical tool to squeeze out excess adhesive and ensure that the adhesive layer is uniform and free of air bubbles.

[0037] S9 Box Girder Welded Enclosure: After all adhesive layers have cured, the top plate is welded and fixed to the side plates on both sides to form a closed steel box section.

[0038] After welding, the box girder forms a complete closed box section, where the moment of inertia and torsional stiffness reach their maximum values, resulting in the strongest overall structural integrity. Simultaneously, welding permanently fixes the top and side plates, creating a mechanically enclosed constraint that further enhances structural reliability. The bending and torsional stiffness of the closed box section is significantly higher than that of the open section, resulting in a substantial improvement in overall structural strength and stability, enabling it to withstand more complex alternating loads.

[0039] use Gas shielded welding is a highly efficient welding method that produces good weld formation and stable quality. After welding, non-destructive testing is performed on the weld to ensure that there are no defects such as cracks, porosity, or slag inclusions, and that the weld quality meets the relevant standards.

[0040] S10 Joint Lay-up Reinforcement: At the joint surface of the steel box girder and the exposed composite material of the blade body, multiple layers of glass fiber cloth are laid by hand and coated with resin adhesive. After curing, a glass fiber hand lay-up reinforcement layer is formed.

[0041] The significant difference in elastic modulus between steel and composite materials can easily lead to abrupt changes in stiffness and severe stress concentration at the interface. Glass fiber composites, with a modulus between that of steel and the original matrix composite, can form a gradual modulus transition zone through stepped layup, effectively alleviating interfacial stress concentration, achieving smooth load transfer, and inhibiting crack initiation and propagation. The stress concentration factor at the interface is significantly reduced, the fatigue life of the joint is greatly improved, and the overall structural integrity of the steel-composite interface is significantly enhanced.

[0042] The fiberglass cloth is a ±45° biaxial cloth. This orientation of the fiber cloth can effectively bear the interfacial shear and peel loads, resulting in the best reinforcement effect. A total of 4 to 8 layers are laid, with the size of each layer increasing by 20 to 30 mm to form a stepped overlap structure, achieving a gradual transition in stiffness and avoiding the generation of new stress concentration points. After each layer is laid, an epoxy resin adhesive is applied and compacted to remove air. The total thickness after curing is 2 to 4 mm, ensuring that the fibers are fully impregnated and free from defects such as bubbles and insufficient adhesive.

[0043] S11 Through-type anchoring: Drill through holes at the overlapping parts of the connection area, penetrating the steel plate of the box girder, the adhesive layer, the composite material beam plate and the iron core, insert high-strength anchor rods and inject anchoring adhesive to cure, forming a through-type mechanical anchoring.

[0044] By using through-type anchor bolts, the four-layer structure of steel box girder, resin adhesive layer, composite material beam plate and iron core is mechanically connected into one, providing a second mechanical load-bearing defense line independent of the adhesive layer. Even if the adhesive layer ages or fails due to fatigue, the anchor bolt can still bear the load independently, forming a dual protection system of chemical bonding and mechanical anchoring, which greatly improves the safety redundancy of the node.

[0045] The safety redundancy of the connection nodes is significantly improved, possessing fail-safe characteristics, preventing overall failure under extreme conditions, and significantly enhancing long-term operational reliability. The through holes are arranged in a matrix, with 2-4 rows, 3-6 holes per row, and a hole diameter of 16-25mm. The number and density can be flexibly adjusted according to the load level. High-strength anchor bolts use HRB400 or higher strength steel bars to ensure their own load-bearing strength. Epoxy anchoring adhesive is used for anchoring and curing, ensuring reliable anchoring force, good durability, and excellent adhesion to both steel and composite materials.

[0046] S12 Finished product finishing and inspection: This involves the remanufacturing of the steel blade roots from retired blades. The finished products undergo visual finishing, dimensional inspection, and non-destructive testing to ensure the quality of the remanufactured products meets relevant standards and design requirements. This guarantees the quality of products leaving the factory, eliminates hidden defects, and meets the safety requirements for installed operation.

[0047] The beneficial effects of this invention compared to the prior art are: 1. This invention employs a closed steel box girder to fully enclose the ends of the beam slab, filled with an iron core, forming a composite section of "outer steel, inner solid". The tensile strength and elastic modulus of high-strength steel are approximately 5 to 8 times that of glass fiber composite materials, resulting in a stronger load-bearing capacity. The bending and torsional moments of inertia of the closed box girder section are significantly greater than those of the thin-walled annular section of the original composite blade root, leading to higher load-bearing efficiency. Combined with the internal solid iron core filling, the distortion risk of the hollow section is completely eliminated, further enhancing the section stiffness. The ultimate bending moment bearing capacity of the reconstructed blade root can reach more than 2.1 times the design requirement, and the torsional stiffness is increased several times, completely solving the problem of insufficient connection strength of the composite blade root. It can adapt to higher load operating conditions with ample safety reserves.

[0048] 2. The beam ends of this invention are machined into a bow-tie shaped cross-section, which, together with the upper and lower interlocking grooves and side fillers, forms a four-sided bonding system. Ordinary planar overlaps only bond on one side, limiting the bonding area; this solution bonds on all four sides, significantly increasing the total bonding area. Simultaneously, the concave waist structure of the bow-tie cross-section mechanically interlocks with the groove, and under axial tension, the concave waist sidewalls and groove walls form a mechanical barrier, distributing a large portion of the axial load and changing the failure mode of single-layer shear. The static strength of the joint bonding is more than double that of planar overlaps, and it possesses natural mechanical locking capabilities, significantly enhancing the interface's resistance to peeling and slippage, and greatly improving the connection reliability under long-term alternating loads.

[0049] 3. This invention first bonds the iron core to the beam plate in an open space to form an integral assembly, and then places the entire assembly into the U-shaped box girder. If the beam plate is placed into the box girder first and then the iron core is inserted, the internal operating space is narrow, alignment is difficult, and problems such as iron core misalignment, skewness, or even inability to be inserted are prone to occur. Pre-assembling the core in the open space provides ample operating space and precise alignment, effectively ensuring the concentricity of the iron core and the beam plate and the bonding quality. The assembly and positioning accuracy is high, the construction difficulty is low, the product consistency is good, and the quality risks caused by internal component misalignment are avoided, resulting in stronger stability for mass production.

[0050] 4. In this invention, the bottom, side, and top surfaces are bonded sequentially in a U-shaped open state. All bonded layers are cured before welding and sealing the box. If a closed box is welded first, pressure cannot be applied to the internal bonded surfaces, and the adhesive layer filling status cannot be observed, easily leading to hidden defects such as insufficient adhesive and air bubbles. The step-by-step sealing process ensures that all bonded surfaces are in an open and operable state, allowing for full observation of the adhesive layer status and pressure venting, making the bonding quality completely controllable. The adhesive layer quality on all four sides is uniform and controllable, significantly reducing the rate of hidden defects such as insufficient adhesive and air bubbles, significantly improving the stability of bonding quality, and resulting in a higher finished product qualification rate.

[0051] 5. The iron core of this invention completely fills the gap between beams and slabs, bonding them integrally. The original beam-slab structure was a hollow cavity, with inter-story shear force transmitted solely through the web, resulting in weak shear resistance and susceptibility to cross-sectional distortion. The solid iron core effectively transmits inter-story shear force between upper and lower beams and slabs, effectively adding internal shear-resistant components. Furthermore, the solid cross-section's resistance to instability is far superior to that of a hollow cross-section. The shear resistance of the joints is increased by more than 100%, with high cross-sectional stiffness, no risk of cavity distortion, and excellent structural stability under complex alternating loads.

[0052] 6. This invention employs a stepped glass fiber layup reinforcement at the junction, bridging the steel side and the composite material side. The significant difference in elastic modulus between steel and composite materials leads to a severe abrupt change in stiffness when directly joined, with the stress concentration factor reaching 2-3 times that of a uniform cross-section, easily inducing fatigue cracks. The modulus of the glass fiber reinforcement layer lies between the two, and the stepped layup achieves a gradual transition in modulus, dispersing localized stress over a larger area and significantly reducing the stress concentration factor. The stress concentration factor at the junction is reduced by more than 40%, the fatigue life of the joint is extended by more than 30%, effectively suppressing the initiation and propagation of interface cracks, resulting in stronger long-term operational reliability.

[0053] 7. This invention features a matrix-type through-type anchor bolt structure consisting of four layers: steel plate, adhesive layer, beam plate, and iron core. Resin bonding is a chemical connection, which carries the risk of long-term aging and fatigue degradation; through-type rebar anchoring is a purely mechanical connection, unaffected by adhesive layer aging, and can independently bear loads. The two form a dual load-bearing system of "chemical and mechanical," meaning that failure in either method will not lead to overall connection failure. The connection node possesses excellent failure safety characteristics; even if the adhesive layer ages and is damaged, the anchor bolt can still maintain the connection without overall detachment, significantly improving safety redundancy and adapting to harsh conditions such as typhoons and extreme gusts.

[0054] 8. The connecting flange of this invention is custom-welded to the end of the box girder according to the target hub parameters. This completely eliminates the size limitations of the original blade root interface. The outer diameter, thickness, number of bolts, hole diameter, pitch circle, and other parameters of the flange can be flexibly designed according to the target hub. The modified blade can be adapted to wind turbine hubs of any model and power, with a wide range of applications, fundamentally solving the reuse problem of mismatched original blade root interfaces.

[0055] 9. This invention fully preserves the blade body, including the blade tip, inheriting 100% of its aerodynamic parameters such as airfoil, torsion, and chord length. The blade's power generation capacity is determined by its aerodynamic shape design, with the tip contributing over 60% of the total wind capture. Both fragmentation and short-cutting solutions would damage the aerodynamic shape, while this solution fully preserves the original blade's aerodynamic design value. The modified blade's power generation efficiency can reach over 95% of that of a new blade of the same specification, with a reuse value far exceeding that of material-level recycling, resulting in significant economic benefits.

[0056] 10. This invention reuses the main components of retired blades throughout the entire process, adding only a steel structure and a small amount of bonding and layup materials. The process is environmentally friendly and pollution-free, and the final product performance meets the standards. It meets the core requirements of the "General Technical Requirements for Remanufacturing of Mechanical Products" (GB / T 28618-2012), which states that "remanufactured products should have performance no lower than new products, make full use of old parts, and be energy-saving and environmentally friendly," and is a typical high-end remanufacturing technology. Compared with manufacturing new blades of the same specifications, it can save more than 80% of material and energy consumption, has no secondary pollution, and conforms to the dual-carbon goals and the direction of circular economy development. Attached Figure Description

[0057] The present invention will now be further described with reference to the accompanying drawings.

[0058] Figure 1 A schematic diagram of the main structure of the leaf after the original leaf root has been removed; Figure 2 This is a schematic diagram of the beam plate and blade tip structure in this invention; Figure 3 This is a side view of the present invention; Figure 4 for Figure 3 Sectional view of section AA; Figure 5 This is the front view of the present invention.

[0059] In the diagram: 1 is the blade body, 2 is the blade tip, 3 is the upper beam plate, 4 is the lower beam plate, 5 is the lower plate of the box girder, 6 is the side plate of the box girder, 7 is the upper plate of the box girder, 8 is the connecting flange, 9 is the upper plate groove, 10 is the lower plate groove, 11 is the iron inner core, 12 is the resin adhesive layer, 13 is the glass fiber hand-laid reinforcement layer, and 14 is the high-strength anchor bolt. Detailed Implementation

[0060] The following is in conjunction with the appendix Figure 1 To be continued Figure 5 The present invention will be further described in detail with reference to specific embodiments. This embodiment takes the remanufacturing of a 1.5MW decommissioned wind turbine blade into a blade adapted for a 200kW distributed wind turbine as an example, and elaborates on the process parameters, key points of operation, connection principles and technical effects of each process. All process parameters and structural features correspond completely to the claims. The purpose, use and expected effect of each step are explained in detail during the implementation process.

[0061] The original decommissioned blades were 38m long, with a main beam constructed of unidirectional glass fiber reinforced epoxy resin. The original blade roots were connected using pre-embedded bolt sleeves (36 M36 bolts, pitch circle diameter 1600mm). Ultrasonic non-destructive testing revealed no structural damage such as cracks, delamination, or debonding on the blade body, meeting the requirements for remanufacturing. The target wind turbine hub interface uses 12 M20 bolts, with a pitch circle diameter of 680mm, and the redesigned total length is 12m.

[0062] Step 1: Cutting the main body of the blade Based on the target wind turbine power rating, hub interface dimensions, and nacelle installation space, the total length of the modified blade was determined to be 12m. A 12m measurement was taken from the original blade root end to the blade tip in a 2-way direction, and a circular cutting line was marked using a laser line marker to ensure that the cutting line was perpendicular to the blade axis.

[0063] A diamond wire saw is used for water-cooled cutting along the cutting line, with the linear speed controlled at 15–20 m / s and the feed rate controlled at 5–10 mm / min. Deionized water is used for continuous cooling throughout the process to prevent resin degradation and fiber interface debonding caused by high cutting temperatures, ensuring the integrity of the composite material at the cut. After cutting, the end face is ground and finished to ensure that the perpendicularity error of the cut end face is ≤2 mm / m.

[0064] After cutting, the original blade root section is removed and discarded, and the 12m long blade body 1 is retained, which has a complete blade tip 2. All aerodynamic parameters such as the original airfoil curve, twist angle distribution, and chord length distribution are completely retained.

[0065] This step completely removed the original composite blade root with mismatched interface, fully preserving the aerodynamic and structural value of the blade, laying the foundation for the remanufacturing and installation of the new steel blade root; the cutting precision meets the requirements of subsequent assembly, and there is no risk of end face tilting.

[0066] Step 2: End structure pretreatment Measure 500mm from the cut end face of the blade body 1 along the axial direction towards the blade tip 2 to mark the boundary of the pre-treatment area. Use an angle grinder with a diamond cutting disc to remove the leading edge skin, trailing edge skin, and web of this area in layers. The thickness of each layer is controlled at 2-3mm to avoid excessive cutting force in a single operation, which could cause tearing of the main beam fibers and delamination damage.

[0067] After the excision was completed, the upper beam plate 3 and the lower beam plate 4, which are arranged parallel to each other, were exposed. The upper surface, lower surface, and left and right sides of the beam plates were all exposed, with no skin or web residue. Then, all surfaces to be bonded were dry-ground with 80-grit alumina sandpaper, and the roughness was controlled at Ra25-50μm to form a rough micro-interface, which improved the mechanical interlocking force and interfacial bonding strength during bonding. After sanding, the dust was blown away with high-pressure clean air, and then the surface was wiped with anhydrous ethanol to remove residual resin, contaminants and surface aging layer, exposing a clean fiber-reinforced composite material surface.

[0068] This step precisely separates the load-bearing components from the non-load-bearing components, resulting in a clean and complete beam-slab bonding substrate, providing sufficient and reliable bonding surfaces for subsequent four-sided full-wrap bonding.

[0069] Step 3: Processing the bowtie-shaped tenon A bow-tie shaped cutting template is drawn according to the design dimensions and fixed to the beam surface for positioning. A CNC diamond cutting machine is used to cut the ends of the upper beam slab 3 and lower beam slab 4, with dimensional errors controlled within ±1mm. The parameters of the finished bow-tie symmetrical cross-section are as follows: the end closest to the cut end retains its original width of 300mm; after moving 200mm inward along the axial direction, the width narrows to a minimum of 180mm (60% of the original width); then extends 200mm outward, expanding the width to 220mm; the final cut length is 500mm, forming a bow-tie shape that is wide at both ends and concave in the middle; the bevel angle of the narrowing section is approximately 16°, and the bevel angle of the expanding section is approximately 5.7°, with a smooth transition between the two bevel angles.

[0070] After cutting, use a special chamfering tool to round all the edges of the bow tie shape with a radius of 5mm. This removes sharp corners, burrs, and micro-cracks caused by cutting, eliminates stress concentration sources, and prevents cracking and delamination from occurring on the edges under load.

[0071] The processed bowtie-shaped beams and slabs have both a large bonding area and mechanical interlocking function, providing a core structural foundation for subsequent high-strength interlocking connections; they have high dimensional accuracy, good edge quality, and no risk of stress concentration.

[0072] Step 4: Bonding the iron inner core assembly The iron inner core 11 is made of Q355B hot-rolled steel plate with finished dimensions of 860×260×490mm. The surface is machined with multiple annular grooves with a depth of 2mm and a spacing of 10mm to increase the bonding surface area and improve the mechanical interlocking force and bonding strength of the interface.

[0073] Huntsman 1568 wind power-specific epoxy structural adhesive was selected and prepared according to the specified weight ratio A:B=10:3. After mechanical stirring and uniform mixing, vacuum degassing was performed. The resin adhesive was evenly applied to the upper and lower surfaces of the iron inner core 11 and the inner walls of the upper beam plate 3 and lower beam plate 4, with the adhesive thickness controlled between 0.3 and 0.5 mm. After the adhesive was applied, the iron inner core 11 was smoothly inserted into the gap between the upper and lower beam plates, and its position was adjusted to ensure uniform gaps and axial alignment.

[0074] A specialized hydraulic tooling is used to apply a uniform pressure of 0.2–0.3 MPa along the thickness direction, causing excess adhesive to be evenly squeezed out from the gaps, ensuring a uniform adhesive layer thickness, removing air bubbles, and avoiding defects such as insufficient adhesive or porosity. The adhesive is then cured at room temperature for 72 hours under a fixed fixture to fully cure and form the resin adhesive bonding layer 12. Finally, the upper beam plate 3, the iron inner core 11, and the lower beam plate 4 are bonded together as a strong, integrated assembly.

[0075] After curing, the assembly is inspected by appearance and tapping to confirm that the bond is tight and there are no loose or hollow areas.

[0076] After this step is completed, the iron core and the beam form a rigid whole, which not only ensures the positioning accuracy of subsequent assembly, but also transforms the original hollow section into an approximately solid section, greatly improving the section's shear, bending and torsional stiffness. At the same time, the iron core provides a reliable internal anchoring base for subsequent rebar installation, which can significantly improve the anchoring effect of the rebar installation.

[0077] Step 5: Prefabrication of steel box girders The steel box girder is fabricated using Q355B steel plate, with a finished cross-sectional dimension of 900×300mm, a steel plate wall thickness of 16mm, and an axial length of 750mm. First, the lower plate 5 of the box girder is connected to the side plates 6 of the box girder on both sides using... Gas shielded welding is used for U-shaped opening structures. The welding current is 180–220A, and the welding voltage is 28–32V. Post-weld stress-relief tempering is performed to reduce residual welding stress and deformation, ensuring the dimensional accuracy of the box girder. The upper plate 7 of the box girder is fabricated separately and will not be welded at this time.

[0078] A CNC milling machine is used to machine a lower plate groove 10 on the inner surface of the lower plate 5 and an upper plate groove 9 on the inner surface of the upper plate 7. The groove outline is perfectly matched with the bow-tie shaped beam plate. The overall size of the groove is 4mm larger than the beam plate to form a uniform bonding gap. The groove depth is two-thirds of the beam plate thickness to preserve the strength of the bottom substrate of the steel plate.

[0079] Flange 8 is welded to the flange end of the box girder. The flange has an outer diameter of 800mm and a thickness of 25mm. Twelve φ22mm bolt holes are drilled using a CNC drilling machine. The pitch circle diameter is 680mm, which perfectly matches the target wind turbine hub interface. After welding, the flange end face is machined to ensure that the flatness of the end face is ≤0.5mm.

[0080] The prefabricated U-shaped box girder has a constraint benchmark at the bottom and sides, and the reserved top opening provides ample operating space for internal assembly and bonding construction; the trough has high processing precision and can be precisely fitted with the bowtie-shaped beam plate.

[0081] Step 6: Lower side embedding and bonding Apply epoxy structural adhesive evenly to the lower plate groove 10, with an adhesive thickness of 0.3–0.5 mm. Smoothly insert the beam-core assembly (with the bonded iron core) into the top opening of the U-shaped box girder, accurately embedding the lower beam 4 into the lower plate groove 10. Adjust the axial position and coaxiality of the assembly, ensuring uniform gaps around the perimeter. Then, apply 0.2 MPa pressure using a vertical tool to evenly expel excess adhesive.

[0082] Curing at room temperature for 24 hours while the fixture is in place completes the lower bowtie-shaped interlocking bonding.

[0083] The lower adhesive surface serves as the positioning reference for the overall assembly, ensuring accurate fixation and uniform adhesive layer, thus providing a stable positioning foundation for subsequent bonding of the sides and top. The bow tie-shaped interlocking achieves a dual connection of chemical bonding and mechanical locking on the lower side.

[0084] Step 7: Fill and bond the side gaps After the lower side bonding has initially cured, clean the gaps between the left and right sides of the beam-slab assembly and the inner wall of the box girder side plate 6 to ensure there is no dust or oil. Use a high-pressure caulking gun to slowly inject epoxy structural adhesive into the gaps, starting from the bottom of the gap and moving upwards to ensure the gaps are completely filled with adhesive, expel air, and avoid leaving any air bubbles.

[0085] After the adhesive is applied, apply moderate pressure using a double-sided pressure tool to squeeze out excess adhesive and ensure a dense and uniform adhesive layer. Allow to cure at room temperature for 24 hours to complete full bonding on both sides.

[0086] After the left and right sides are bonded, the bonding surface expands from two sides to three sides, the total bonding area is greatly increased, and the torsional load-bearing capacity of the joint is significantly enhanced; the adhesive layer on the sides is uniform and dense, without any hidden air bubbles or defects.

[0087] Step 8: Upper side embedding and bonding Apply epoxy structural adhesive evenly to the groove 9 of the upper plate, with a thickness of 0.3–0.5 mm. Align the upper plate 7 of the box girder with the position and cover the top of the U-shaped opening, so that the upper beam plate 3 is accurately embedded in the groove 9. Adjust the position of the upper plate to ensure alignment with the side plates and uniform gaps around it. Then, apply pressure of 0.2–0.3 MPa using a vertical tool to squeeze out excess adhesive.

[0088] After curing at room temperature for 72 hours with the fixture in place, the upper bow tie-shaped interlocking bonding is completed, thus achieving full wrapping bonding around the beam and slab.

[0089] With all four sides (top, bottom, left, and right) fully bonded, the steel box girder forms a complete enclosure constraint on the beam ends, maximizing the total bonding area and achieving optimal overall connection integrity and load-bearing capacity. All bonding surfaces are constructed in an open state, ensuring that the adhesive layer quality is controllable throughout the process.

[0090] Step 9: Welding and sealing of box girder After confirming that all adhesive layers have fully cured, remove the fixtures and clean the weld bevels. Gas shielded welding is used to seal the joint between the top plate 7 of the box girder and the side plates 6 of the box girder on both sides, forming a complete closed box section. Multi-layer, multi-pass welding is employed to control the interpass temperature and reduce welding deformation.

[0091] After welding is completed, all welds are subjected to magnetic particle non-destructive testing in accordance with the "Method for Magnetic Particle Testing of Welds" (JB / T 6061-2007). Welds that reach Grade I quality are considered qualified, ensuring that there are no surface defects such as cracks, porosity, or slag inclusions.

[0092] After welding and sealing, the box girder forms a complete closed steel box, and the bending and torsional moments of inertia of the section reach their maximum values, greatly improving the overall structure and stability; the weld quality is qualified, there are no welding defects, and there is no risk of breakage during long-term operation.

[0093] Step 10: Layup reinforcement at the junction First, the surface of the junction area between the steel box girder and the exposed composite material of the blade body 1 is treated: the steel side surface is sandblasted to achieve a cleanliness level of Sa2.5, and the composite material side is lightly ground and roughened; then the surface is cleaned with anhydrous ethanol to remove oil and dust.

[0094] The ±45° biaxial fiberglass cloth was manually laid for reinforcement, with a total of 6 layers. The coverage of each layer increased by 25mm, forming a stepped overlap structure. The layup spanned the steel box girder and the composite matrix, with equal extension lengths on both sides.

[0095] After each layer of fiberglass cloth is laid, a layer of epoxy resin is evenly applied and repeatedly compacted with a scraper and rubber roller to remove air bubbles and ensure the fibers are fully impregnated. Once all layers are laid, allow to cure at room temperature for 72 hours to form the fiberglass hand-laid reinforcement layer 13, with a total thickness of approximately 3mm after curing. After curing, the surface is sanded and smoothed to remove burrs and ensure a smooth appearance.

[0096] The stepped ply creates a transition zone with gradually changing modulus, which effectively alleviates stress concentration at the steel-composite interface caused by modulus differences, reduces the risk of crack initiation, and significantly improves the fatigue performance and structural integrity of the joint.

[0097] Step 11: Through-type rebar anchoring Matrix anchoring hole positions were marked at the overlapping areas of the connection zone, with a total of 4 rows and 4 holes per row. The hole diameter was 20mm, and the center deviation of the hole position was ≤0.5mm. Through holes were drilled using a diamond hollow drill bit at a speed controlled between 300 and 500 rpm, sequentially penetrating the box girder steel plate, resin adhesive layer, composite material beam plate, and iron inner core 11. The entire drilling process was water-cooled to avoid high-temperature damage to the composite material.

[0098] After drilling, blow away any dust from the hole with high-pressure clean air, then wipe the hole wall with acetone-soaked cotton to ensure there is no dust or oil inside. Insert φ18mm HRB400 high-strength anchor rods 14, using epoxy anchoring adhesive pressure injection. The adhesive volume should be 2 / 3 of the hole volume. Insert the anchor rod slowly by rotating it to remove air bubbles. Cure at room temperature for 24 hours until the anchoring adhesive is completely cured, forming a through-type mechanical anchoring structure.

[0099] The through-type anchor bolt mechanically connects the four-layer structure of steel box girder, adhesive layer, composite material beam plate and iron core into one, providing a purely mechanical load-bearing defense line independent of the adhesive; even if the adhesive layer ages or suffers fatigue damage, the anchor bolt can still bear the load independently, the node has failure safety characteristics, and the safety redundancy is greatly improved.

[0100] Step 12: Finished Product Trimming and Inspection The finished product undergoes appearance finishing, dimensional verification, and non-destructive testing: appearance finishing removes excess glue nodules and burrs to ensure a smooth surface; key parameters such as the total blade length and flange interface dimensions are verified to ensure they meet design requirements; ultrasonic testing is used to inspect the bonding interface and the interior of the composite material to confirm the absence of debonding or delamination defects; and sampling pull-out tests are conducted on the rebar to verify that the anchoring force meets the standards.

[0101] Once all inspections are passed, the steel box girder-enclosed blade root reconstruction of the retired blades is completed.

[0102] The finished product of this embodiment has been verified by finite element analysis. The ultimate bending moment bearing capacity of the box girder is 2.1 times that of the design requirement. After 2000 hours of continuous operation test (including typhoon condition simulation), the connection nodes are not loose or cracked, and the rebar is not pulled out, which is safe and reliable. The measured power generation efficiency reaches more than 95% of the new blade of the same specification. All indicators have met the expectations and meet the remanufacturing standard requirements.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Anyone skilled in the art can implement the present invention smoothly according to the above description. However, any modifications or alterations made by those skilled in the art without departing from the scope of the present invention's technical solution to the disclosed technical content to create equivalent embodiments are still within the protection scope of the present invention's technical solution.

Claims

1. A method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder, characterized in that, Includes the following steps: S1. Cutting the main body of the blade; The original blade root of the retired wind turbine blade is removed, while the blade body with a complete blade tip and continuous aerodynamic shape is retained. S2. End structure pretreatment; The skin and web are cut off axially at the cut end of the blade body to expose the upper and lower beam plates, which are then polished and cleaned. S3. Tenon machining; The exposed upper and lower beams are cut into symmetrical cross-sectional structures that are wider at both ends and narrower in the middle to form a mechanically interlocking structure, hereinafter referred to as the cross-section; S4, Iron inner core assembly bonding; Prepare an iron core that fits the gap between the beam and the plate. Apply epoxy structural adhesive to the upper and lower surfaces of the iron core and the inner wall of the beam. Bond and fix the iron core in the gap between the upper and lower beams. After pressure curing, form an integral assembly of beam and core. S5. Precast steel box girder; Prepare a steel box girder with connecting flanges. The box girder is first welded into a U-shaped structure with a top opening, consisting of a lower plate and two side plates, with the upper plate reserved for later installation. A lower plate groove adapted to the cross-section is opened on the inner side of the lower plate, and an upper plate groove adapted to the cross-section is opened on the inner side of the upper plate. S6. Lower side embedding and bonding; Insert the beam-core assembly into the top opening of the U-shaped box beam, embed the lower beam into the corresponding groove, apply adhesive and apply pressure to cure, and achieve the bottom side splicing. S7, Side gap filling and bonding; Epoxy structural adhesive is injected into the gap between the left and right sides of the beam-slab assembly and the inner wall of the box girder side plate, and then cured under pressure to achieve full side bonding. S8, Upper side embedding and bonding; The upper plate of the box girder is placed over the top opening, so that the upper beam plate is embedded into the upper plate groove. Glue is applied and pressure is applied to cure, so as to realize the upper side embedding and bonding, and complete the full wrapping and bonding of the beam plate around the four sides. S9. Box girder welded and closed; After all adhesive layers have cured, the top plate is welded and fixed to the two side plates to form a closed steel box-shaped cross section. S10, reinforcement at the junction; At the junction of the steel box girder and the exposed composite material of the blade body, multiple layers of glass fiber cloth are laid by hand and resin adhesive is applied. After curing, a glass fiber hand-laid reinforcement layer is formed. S11, Through-type rebar anchoring; Through holes are drilled at the overlapping parts of the connection area, penetrating the steel plate of the box girder, the adhesive layer, the composite material beam plate and the iron core, high-strength anchor rods are inserted and the anchoring adhesive is injected and cured to form a through mechanical anchor. S12. Finished product repair and inspection, and completion of steel blade root reconstruction for retired blades.

2. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, In step S3, the minimum width of the cross section is 50% to 70% of the original width of the beam slab. The two ends of the wide section are connected to the middle concave section through two beveled transition sections. After cutting, the edges are rounded with a radius of 3 to 5 mm.

3. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, In step S4, the iron core is a solid steel structure with a strength of Q355 or higher, and the surface is provided with annular grooves to increase the bonding area; the axial length of the iron core is consistent with the overlap length of the beam and plate, and the thickness matches the spacing between the upper and lower beams and plates, completely filling the gap between the beams and plates; the curing conditions are 60℃ for 6 hours or room temperature for 72 hours.

4. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, In step S5, the steel box girder is made of Q355 or higher strength steel, with a rectangular box section and an axial length of 1.2 to 1.5 times the length of the exposed beam plate; the contours of the lower plate groove and the upper plate groove are 3 to 5 mm larger than the outer contour of the beam plate to form a uniform bonding gap, and the groove depth is two-thirds of the beam plate thickness; the connecting flange is welded to the flange end of the box girder, and the flange bolt hole parameters are customized to match the target wind turbine hub interface.

5. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, The adhesives used in steps S6, S7, and S8 are all epoxy structural adhesives specifically for wind turbine blades, with a tensile shear strength of not less than 25 MPa after curing. Each bonding step uses tooling to apply pressure and squeeze out excess adhesive to ensure a uniform adhesive layer free of air bubbles.

6. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, Step S9 uses Gas shielded welding is used for welding. After welding is completed, non-destructive testing is performed on the weld to ensure that the weld quality is up to standard.

7. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, In step S10, the fiberglass cloth is a ±45° biaxial cloth, and a total of 4 to 8 layers are laid. The size of each layer increases by 20 to 30 mm to form a stepped overlapping structure. After each layer is laid, an epoxy resin adhesive is applied and compacted to remove air. The total thickness after curing is 2 to 4 mm.

8. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, In step S11, the through holes are arranged in a matrix, with 2 to 4 rows and 3 to 6 holes in each row, with a hole diameter of 16 to 25 mm; the high-strength anchor rods are made of HRB400 or higher strength steel bars and are anchored and cured with epoxy anchoring adhesive.

9. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, The axial length of the skin and web removed is 300-800 mm; the surface of the beam and plate is ground and cleaned to remove residual resin and contaminants, exposing a clean fiber-reinforced composite material surface.

10. The method for reconstructing the root of a fully enclosed retired blade in a high-load-bearing steel box girder according to claim 1, characterized in that, The length of the blade body after cutting is 6 to 15 m, and the original airfoil curve, twist angle distribution, chord length distribution and other aerodynamic parameters of the blade are completely preserved.

Images