Method and apparatus for inhibiting springback in a laminated wood curved beam

Abstract

The present application relates to a kind of method and device for inhibiting glue wood arc beam rebound in gluing wood structural member processing technical field, comprising the following steps: laminate group blank is bent and pressurized on forming die;Pressure soaking is kept under initial pressure;Part of radial pressure is removed to maintain pressure, to keep the most outside board unit grain strain value substantially constant as target stress relaxation, make internal elastic strain energy partially dissipate;Second pressurization to solidification pressure pressure soaking solidification;Synchronous staged radial pressure removal, obtain finished product.The present application fundamentally reduces the residual elastic potential energy in the internal component after solidification by constant strain stress relaxation process, while avoiding the risk of glue layer slip by optimizing pressure maintenance coefficient, significantly improve the forming precision and gluing quality of arc beam;Synchronous staged pressure release mode improves operation safety and process stability;Device integrates heating temperature control function, adapts to normal temperature and heating solidification two modes, adjust flexible, strong adaptability.

Description

Technical Field

[0001] This invention relates to the field of glulam structural component processing technology, and in particular to a method and apparatus for suppressing the springback of glulam curved beams. Background Technology

[0002] Glulam (glulam laminated timber) structures have gained increasing popularity in modern timber construction due to their advantages such as energy efficiency, environmental friendliness, lack of size limitations, and flexible design. Curved glulam beams, in particular, are favored by architects for their ability to create spacious interiors and streamlined architectural forms.

[0003] However, curved glued laminated timber (GLLT) components commonly face a technical challenge during fabrication—springback after pressure release. GLLT curved beams are typically formed using a process of applying glue to multiple layers of wood veneers, bending them using a template, and then curing them under pressure. Due to the inherent viscoelastic properties of wood, some elastic strain energy is temporarily "frozen" inside the component during the bending process. Once curing is complete and the external pressure is removed, this elastic potential energy is released, causing the component's curvature to decrease and spring back towards a straighter direction. This springback problem directly affects the component's shape accuracy, ranging from increasing the difficulty of on-site installation and adjustment to, in severe cases, rendering the component unusable.

[0004] The industry has conducted extensive research and proposed a variety of technical solutions to address the springback problem of curved glued laminated timber.

[0005] One type of technical solution adopts the concept of "over-bending compensation," which uses empirical formulas to pre-determine the curvature radius and utilizes the rebound amount to offset the over-bending. For example, patent CN106239681B discloses a rebound compensation method that determines the curvature radius based on the wood moisture content and the number of plywood; patent CN106239680B further considers the influence of wood density and provides calculation formulas for the curvature radius of low-density and medium-density woods respectively; patent CN106182223B optimizes the spacing and sequence of distributed pressure application based on over-bending compensation. The essence of this type of method is "pre-determining the rebound amount and passively adapting," and its compensation effect depends on the precise control of many variables such as wood properties, plywood configuration, and environmental parameters. In actual production, it is difficult to control the rebound deviation within the ideal range.

[0006] Another type of technical solution focuses on improving the plastic forming ability of wood. By adjusting the moisture content of the wood and the temperature and humidity of the processing environment, the wood is made more susceptible to plastic deformation during bending, reducing the proportion of elastic deformation and thus lowering the rebound driving force. For example, patent CN106378849B discloses a forming method based on wood plasticity, which increases the moisture content of the wood to 16%-20%, and the temperature and humidity of the processing environment to above 30℃ and above 80%, respectively, allowing the wood to be bent and formed directly according to the designed curvature in a higher plastic state. Although this method simplifies the preparation parameters, the gluing of wood at high moisture content faces the risks of delayed adhesive curing and reduced bonding strength, and requires a long moisture content adjustment period after forming, thus limiting production efficiency.

[0007] In summary, existing technologies for dealing with the springback problem of curved glued laminated timber either rely on empirical springback compensation calculations or passively adapt by changing the state of the wood. There is no technical solution yet that can actively reduce elastic strain energy through a controllable stress relaxation process to obtain high-precision curved glued laminated timber beams. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention discloses a method and apparatus for suppressing the springback of glued laminated timber curved beams.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for suppressing the springback of glued laminated timber curved beams, comprising the following steps:

[0011] Step 1: Provide a plywood assembly blank formed by stacking multiple wood plywood units;

[0012] Step 2: Place the layer plate blank on a forming mold with a preset radius of curvature, and apply radial pressure to bend it to fit the mold arc surface of the forming mold;

[0013] Step 3: Maintain the radial pressure for a first time period to allow the adhesive to impregnate; the first time period is 3 to 10 minutes;

[0014] Step 4: Remove part of the radial pressure to the holding pressure, and maintain it at the holding pressure for a second time period, with the goal of keeping the longitudinal strain value of the outermost layer unit in the layer assembly basically constant, so that the elastic strain energy generated by bending inside the layer assembly is partially dissipated through the stress relaxation effect; the second time period is 15 to 30 minutes.

[0015] Step 5: Apply radial pressure a second time to the curing pressure, and maintain the pressure at this curing pressure until the adhesive is completely cured;

[0016] Step 6: Simultaneously and gradually remove radial pressure to obtain glued laminated timber curved beams.

[0017] As a preferred technical solution, the step four of keeping the strain value of the outermost layer plate unit basically constant is achieved by monitoring the strain value of the outermost layer plate unit in real time and dynamically adjusting the holding pressure with the strain value as a feedback signal.

[0018] The term "basically constant" means that during the second time period, the fluctuation range of the monitored strain value does not exceed a preset threshold; wherein, the preset threshold is ±2% of the monitored strain value.

[0019] As a preferred technical solution, the maintaining pressure P2 and the initial pressure P1 when step two is completed satisfy: P2=k·P1, where k is the pressure maintaining coefficient, and the value range is 0.4 to 0.6.

[0020] As a preferred technical solution, the curing pressure P3 satisfies: P3 = (1.05~1.10)·P std , where P std The recommended curing pressure for the adhesive used.

[0021] As a preferred technical solution, the synchronous graded removal of radial pressure in step six includes: starting from the curing pressure P3, all pressure points are simultaneously removed to the first intermediate pressure and maintained for a first interval time, and then simultaneously removed to the second intermediate pressure. This graded operation is repeated until the pressure is completely removed.

[0022] As a preferred technical solution, step seven is also included: after the adhesive has fully cured or during the curing process, apply axial pressure along the length of the glued laminated timber curved beam and maintain the axial pressure for 16 to 24 hours.

[0023] In a second aspect, the present invention provides an apparatus for suppressing the springback of glued laminated timber curved beams for implementing the above-described method, comprising:

[0024] The base has multiple guide grooves spaced along its length and arranged along its width.

[0025] A forming mold has multiple mold modules that are arranged one-to-one with guide grooves. Each mold module includes a sliding block and an arc-shaped support plate. The arc-shaped support plate is hinged to the side of the sliding block and is located outside the base.

[0026] A radial pressing mechanism has multiple radial pressing units that correspond one-to-one with the mold module, and an arc-shaped pressure plate is hinged to the bottom of each radial pressing unit.

[0027] The strain monitoring unit is used to measure the parallel tensile strain generated on the outer surface of the outermost layer plate unit during bending in real time.

[0028] The control system is connected to the radial pressurization unit and the strain monitoring unit, and is configured to perform the above-described method.

[0029] As a preferred technical solution, a pressure detection unit is provided between the radial pressurization unit and the arc-shaped pressure plate, and the pressure detection unit is connected to the control system signal.

[0030] As a preferred technical solution, it further includes a heating unit for heating the inner arc surface of the glued laminated timber curved beam and a temperature detection unit for measuring the temperature of the outer arc surface of the glued laminated timber curved beam; both the heating unit and the temperature detection unit are connected to the control system signal.

[0031] As a preferred technical solution, both ends of the base are provided with axial pressing mechanisms, which include:

[0032] The slide rail pair is located at the end of the base.

[0033] An axial pressurizing unit is provided in the sliding part of the slide rail pair, and a pusher plate is provided at the inner end of the axial pressurizing unit.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention employs a multi-stage pressure control process—"initial pressure holding—active partial pressure relief—constant strain relaxation—secondary pressure application"—to actively create stress relaxation conditions before the adhesive is fully cured. Aiming to maintain a essentially constant strain in the outermost layer unit, the invention monitors strain in real time and dynamically adjusts the holding pressure. This allows the elastic strain generated inside the layer assembly due to bending to be fully and controllably dissipated under constant strain conditions through the viscoelastic effect of wood, fundamentally reducing residual elastic potential energy after curing and significantly improving molding accuracy. Furthermore, by controlling the pressure holding coefficient k within a reasonable range of 0.4–0.6, it avoids layer slippage and adhesive layer damage caused by excessive pressure relief, suppressing springback while ensuring the integrity of the bonding interface. Experimental results show that the relative deviation of the radius of curvature of the glued laminated timber arc beam prepared using this method is 0.015%–0.026%, and the bonding strength meets national standards.

[0036] 2. This invention achieves precise control of the bending and forming process by setting a strain monitoring unit in the outermost layer unit to monitor the tensile strain along the grain in real time and using the theoretical target strain value as the criterion for the end of pressurization. During the stress relaxation stage, the pressure is dynamically adjusted using the strain monitoring value as feedback signal, controlling the strain fluctuation range within ±2%, thus quantifying the stress relaxation process. This overcomes the shortcomings of traditional empirical formula compensation methods, which are sensitive to variations in wood properties and have unstable compensation accuracy. It is applicable to layer assembly of different tree species and specifications, significantly improving the adaptability and stability of the process.

[0037] 3. This invention employs a synchronous, staged pressure relief process. By simultaneously and stepwise removing pressure at all pressure points and setting holding times between each pressure level, the internal stress of the glued laminated timber curved beam is smoothly redistributed, avoiding localized damage or excessive rebound caused by sudden stress release. This pressure relief method improves the product yield and is more suitable for industrial mass production.

[0038] 4. The device of this invention integrates a heating unit and a temperature detection unit, enabling the same device to achieve both room temperature curing and accelerated curing by heating. Experiments have shown that production efficiency is increased by more than 55% when using heat curing, while maintaining the same level of accuracy. In addition, by adding an axial pressure curing step after curing, residual stress is further released, interlayer micro-gaps are eliminated, and the long-term shape stability of the component is significantly improved.

[0039] 5. The device provided by this invention adopts a modular design. The position of the mold module can be flexibly adjusted along the guide groove, enabling it to quickly adapt to the production needs of curved beams with different radii of curvature and cross-sectional dimensions. Each pressurizing unit is independently controlled, and in conjunction with the control system, it can realize complex multi-stage pressurization processes. The precise coordination between the heating unit and the temperature detection unit makes this invention highly adaptable to both room temperature curing and accelerated curing by heating, effectively improving production efficiency while ensuring accuracy. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the device for suppressing the springback of glued laminated timber curved beams according to an embodiment of the present invention;

[0041] Figure 2 This is a front view of the device for suppressing the springback of glued laminated timber curved beams according to an embodiment of the present invention, under the conditions of steps two to five.

[0042] Figure 3 This is a rear view of the device for suppressing the springback of glued laminated timber curved beams according to an embodiment of the present invention, in step seven.

[0043] Figure 4 This is a control logic block diagram of the first structure in the device for suppressing the springback of glued laminated timber curved beams according to an embodiment of the present invention;

[0044] Figure 5 This is a control logic block diagram of the second structure in the device for suppressing the springback of glued laminated timber curved beams according to an embodiment of the present invention;

[0045] Figure 6 This is a control logic block diagram of the third structure in the device for suppressing the springback of glued laminated timber curved beams according to an embodiment of the present invention.

[0046] In the diagram: 1. Base; 11. Guide groove; 2. Mold module; 21. Sliding block; 22. Arc-shaped support plate; 3. Radial pressurization unit; 4. Arc-shaped pressure plate; 5. Heating unit; 6. Temperature detection unit; 7. Strain monitoring unit; 8. Control system; 9. Pressure detection unit; 10. Axial pressurization mechanism; 101. Slide rail pair; 102. Axial pressurization unit; 103. Propulsion plate. Detailed Implementation

[0047] The present invention will be explained in detail through the following embodiments. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention. In the description of the present invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," etc., indicating orientation or positional relationships, are only corresponding to the drawings of this application for the convenience of describing the present invention. The terms "end," "side," "end portion," "side part," "lateral," "longitudinal," etc., indicating orientation or positional relationships, are only corresponding to the length and width of the corresponding components. That is, "end portion" indicates the beginning and end areas in the length direction of the corresponding component, and "side part" indicates the beginning and end areas in the width direction of the corresponding component. The term "provided with" should be understood in the art as "provided with" or "assembled with," and does not limit the specific connection method. The term "corresponding" should be understood in the art as being used to describe the relative positional relationship, functional cooperation relationship, or spatial alignment relationship between two components. For the convenience of describing the present invention, it is not intended to indicate or imply that the device or element referred to must have a specific orientation.

[0048] Please refer to the instruction manual appendix. Figure 1-6 The present invention provides the following technical solutions:

[0049] Example 1: A method for suppressing the springback of glued laminated timber curved beams, employing methods such as... Figure 1-4 The illustrated apparatus is implemented by including the following steps:

[0050] Step 1: Material preparation and billet assembly

[0051] Standard-grade Douglas fir or Scots pine timber with a moisture content controlled within the range of 10%±2% was selected and processed into laminates with a thickness of 35mm and a width of 150mm. The laminates were then finger-jointed to increase length and width laterally, creating laminate units of the required length and width. A cold-curing resorcinol-formaldehyde resin adhesive was applied to one side of each laminate unit at a rate of 300g / m². The adhesive-coated laminate units were then assembled according to the design sequence to form the laminate preform to be pressed. During assembly, the outermost laminate unit (the tension side during bending) was designated as the "strain monitoring layer," and strain monitoring units 7 (resistance strain gauges in this embodiment) were attached to its outer surface along the grain direction.

[0052] Specifically, at the mid-span and 1 / 4 span positions on the outermost layer unit, three resistance strain gauges are attached along the grain direction (wood fiber direction or length direction) of the layer unit. The sensitive grid direction of the resistance strain gauges is parallel to the grain direction of the layer unit, which is used to accurately measure the tensile strain along the grain generated on the outer surface of the layer unit during bending.

[0053] Step 2: Initial pressure application and bending shaping

[0054] The sheet assembly is placed on the forming mold. The forming mold consists of multiple mold modules 2 arranged at equal intervals along the length (X-axis) of the base 1. The arc-shaped support plate 22 of each mold module 2 is pre-adjusted to the mold curvature radius R. mold The corresponding precise height forms a continuous curved surface of the mold. The radius of curvature R of the mold curved surface. mold With the target radius of curvature R target The following proportional relationship must be satisfied:

[0055] R mold =R target ×(1-δ)

[0056] Wherein, δ is the bending coefficient of the mold, and its value ranges from 0.001 to 0.003. In this embodiment, δ = 0.0025 is used.

[0057] The radial pressurization mechanism is activated, and multiple independently controlled radial pressurization units 3 (servo hydraulic cylinders are used in this embodiment) operate synchronously, with their arc-shaped pressure plates 4 moving downwards to contact the surface of the laminate assembly. The control system 8 steadily increases the pressure at a rate of 0.2 MPa / s. During the pressurization process, the control system 8 reads the strain value from the strain monitoring unit 7 in real time. When the strain value reaches the theoretically calculated target value ε... set When the pressure is reached, the control system 8 stops pressurizing and locks the current pressure, which is recorded as the initial pressure P1.

[0058] Target strain value ε set The thickness t of the outermost layer plate unit and the radius of curvature R of the mold arc surface are determined by... mold Determined, the calculation formula is: ε set =t / (2×R mold )=t / (2×R target ×(1-δ))

[0059] In this embodiment, t = 35 mm; R target =8000mm; δ=0.0025. Calculated ε set =0.002193≈2.19‰.

[0060] Step 3: Initial pressure holding and adhesive layer impregnation

[0061] The initial pressure P1 is maintained for a first time period t1 to allow the adhesive to fully impregnate the wood surface. In this embodiment, t1 = 4 minutes.

[0062] Step 4: Active partial stress relief and constant strain stress relaxation

[0063] After the initial pressure holding is completed, the control system 8 controls each radial pressurizing unit 3 to begin depressurization. The depressurization process proceeds at a rate of 0.5 MPa / s until the pressure drops to the holding pressure P2. The holding pressure P2 satisfies: P2 = k·P1

[0064] Where k is the pressure maintenance coefficient, which is usually 0.4 to 0.6. In this embodiment, k = 0.50. That is, the maintenance pressure P2 is 50% of the initial pressure P1.

[0065] This embodiment provides two parallel implementation methods:

[0066] Implementation Method 1: Each radial pressurization unit 3 is equipped with a pressure detection unit 9 (such as a pressure sensor). During the depressurization process, the control system 8 depressurizes at a rate of 0.5 MPa / s and reads the feedback value of the pressure detection unit 9 in real time until the feedback value of the pressure detection unit 9 reaches the maintenance pressure P2.

[0067] Implementation Method 2: The displacement-pressure relationship curve of the radial pressurization unit 3 under standard operating conditions is pre-calibrated through experiments, and the curve is stored in the control system in the form of a data table or fitting function. During depressurization, the control system 8 estimates the current pressure value based on the current displacement value of the arc-shaped pressure plate 4 through the displacement-pressure relationship curve, and uses the estimated value as a feedback signal to control the depressurization process until the estimated pressure value reaches the maintenance pressure P2.

[0068] After depressurization, the stress relaxation period begins. During this stage, the control system 8 uses the strain value fed back in real time by the strain monitoring unit 7 as a basis, and fine-tunes the radial pressurization unit 3 to keep the monitored strain value basically constant within the second time period t2. t2 is typically 15 to 30 minutes; in this embodiment, t2 is 20 minutes, and through the dynamic adjustment of the control system 8, the fluctuation range of the monitored strain value is controlled within ±2%. This process achieves constant strain stress relaxation, allowing the elastic strain energy inside the laminate assembly to be effectively dissipated through the viscoelastic properties of wood.

[0069] Step 5: Secondary pressurization and final curing

[0070] After the stress relaxation period ends, the control system 8 controls the radial pressurization unit 3 to apply pressure again. The pressure is increased from P2 to the curing pressure P3. The curing pressure P3 is: P3 = (1.05~1.10)·P std

[0071] Where Pstd Recommended curing pressure for the selected adhesive (P in this example) std =1.0MPa), in this embodiment, P3 = 1.08MPa. The adhesive is cured under curing pressure P3. This embodiment uses a room temperature curing method, with the ambient temperature controlled at 20±2°C, relative humidity at 65±5%, and a pressure holding curing time of no less than 10 hours.

[0072] Step Six: Synchronous Staged Depressurization

[0073] After curing, synchronous staged depressurization is performed. Specifically, firstly, all radial pressure units 3 are depressurized from the curing pressure P3 to a first intermediate pressure of 0.8 MPa at a rate of 0.2 MPa / s, and held for 30 seconds; then, they are synchronously depressurized to a second intermediate pressure of 0.4 MPa, and held for 30 seconds; finally, the pressure is synchronously and completely released. After depressurization, a glued laminated timber curved beam is obtained.

[0074] To achieve higher precision in shape stability, this embodiment adds a preferred step after depressurization: Step Seven: Post-processing with axial pressure applied to the end.

[0075] (1) Complete the full depressurization as per step six;

[0076] (2) Move the depressurized glued laminated timber arc beam into the rear side of the base 1 and place it on the arc-shaped support plate 22 on the rear side of the base 1;

[0077] (3) Start the axial pressure unit 102 at both ends of the base 1 so that the corresponding push plate 103 can smoothly contact the end faces of both ends of the glued laminated timber arc beam;

[0078] (4) The control system 8 controls the axial pressure units 102 at both ends to apply axial pressure synchronously. The pressure value is 0.3-0.6MPa (based on the average compressive stress gauge of the end face of the glued laminated timber arc beam). In this embodiment, the pressure value is set to 0.4MPa.

[0079] (5) Under this axial pressure, maintain curing for 16 to 24 hours; in this example, it is 20 hours.

[0080] (6) After the curing period is over, slowly release the axial pressure (pressure release rate 0.25~0.35MPa / s) and remove the glued laminated timber curved beam.

[0081] Experimental results: The glued laminated timber curved beam prepared by the above method, after three-dimensional scanning measurement, has an average actual radius of curvature of 8001.2 mm, which is close to the designed radius of curvature R. target The absolute value of the deviation of 8000mm is only 1.2mm, and the relative deviation is only 0.015%.

[0082] As a control, a glued laminated timber curved beam prepared using the exact same materials, molds, and adhesives, but omitting step four (i.e., one-time pressure curing), had an average actual radius of curvature of 8017.6 mm. This indicates that after depressurization, the glued laminated timber curved beam exhibited significant springback (straightening), with its radius of curvature exceeding the design value by 17.6 mm, a relative deviation of 0.22%.

[0083] Example 2, a method for suppressing the springback of glued laminated timber curved beams, differs from Example 1 in that: heat curing is used in step 5 to shorten the production cycle.

[0084] Step 5

[0085] After the secondary pressurization to the curing pressure P3 (1.08 MPa), heating unit 5 and temperature detection unit 6 are activated. Heating unit 5 is used to heat the inner arc surface of the glued laminated timber curved beam; temperature detection unit 6 is used to detect the glue layer temperature in real time from the outer arc surface and feed it back to control system 8. Control system 8 has a built-in PID temperature control module, which controls the temperature rise according to the following program.

[0086] (1) Gradient heating first stage: The temperature of the adhesive layer is uniformly raised to 40℃ at a heating rate of 0.5℃ / min;

[0087] (2) Heat preservation stage: keep warm at 40℃±2℃ for 60 minutes to allow the adhesive to fully gel;

[0088] (3) Gradient heating second stage: The temperature of the adhesive layer is raised to 65℃ at a heating rate of 0.5℃ / min;

[0089] (4) Final curing stage: Keep warm at 65℃±2℃ for 180 minutes to allow the adhesive to fully cure.

[0090] Comparison of results: By using the heat-accelerated curing method, the total pressure-holding curing time was reduced from 10 hours for room temperature curing to 4.5 hours, increasing production efficiency by more than 55%. Measurements showed that the final radius of curvature of the heat-cured beam was 8002.1 mm, with a springback deviation of 0.026%, which is at the same precision level as the room temperature curing method (deviation 0.015%), fully meeting the requirements of high-precision engineering. This embodiment demonstrates that the method of the present invention has good adaptability to both room temperature curing and heat-accelerated curing.

[0091] Example 3, as Figure 1-2 and Figure 4 As shown, a device for suppressing the springback of a glued laminated timber curved beam includes a base 1, a forming mold, a radial pressure mechanism, a resistance strain gauge 7, and a control system 8.

[0092] The base 1 is a rectangular steel platform, and multiple guide grooves 11 are spaced apart along the length of the base 1 and arranged along its width.

[0093] The forming mold provides an arc-shaped support surface for bending the plywood assembly. The forming mold has multiple mold modules 2, each corresponding to a guide groove 11. Each mold module 2 includes a sliding block 21 and an arc-shaped support plate 22. The sliding block 21 is slidably installed within the corresponding guide groove 11 and its position can be adjusted along the extension direction of the guide groove 11 (i.e., the width direction of the base 1) to accommodate glulam curved beams with different radii of curvature. After adjustment, its position can be fixed using bolts or other fasteners.

[0094] The arc-shaped support plate 22 is hinged to the side of the sliding block 21 via a pin and is located on the outer side of the base 1. Its working surface is a smooth arc surface. The working surfaces of each arc-shaped support plate 22 are connected sequentially after adjustment to form a continuous designed arc surface, constituting the mold arc surface of the forming mold. The hinged connection allows the arc-shaped support plate 22 to adaptively adjust its tilt angle according to the bending angle of the glued laminated timber arc beam. By adjusting the horizontal position of each sliding block 21, the radius of curvature of the mold arc surface can be precisely controlled.

[0095] The radial pressurizing mechanism includes multiple radial pressurizing units 3 (servo hydraulic cylinders are used in this embodiment) that correspond one-to-one with the mold module 2, and are fixedly installed on the crossbeam (not shown in the figure) above the frame 1. Each radial pressurizing unit 3 has an arc-shaped pressure plate 4 hinged to the piston rod end, and the arc-shaped pressure plate 4 is used to apply pressure evenly to the surface of the layer assembly blank during pressurization.

[0096] The strain monitoring unit 7 is used to measure the tensile strain along the grain generated on the outer surface of the outermost layer plate unit during bending. In this embodiment, a resistance strain gauge is attached to the outer surface of the outermost layer plate unit to measure the tensile strain along the grain generated during bending in real time.

[0097] The strain monitoring unit 7 is connected to the control system 8 via wires, transmitting real-time strain data to the control system 8 to provide a basis for the control system 8 to determine whether the wood has reached the plastic tensile strain threshold.

[0098] The control system 8 employs a PLC controller, with signals connected to the radial pressurization unit 3 and the strain monitoring unit 7. The control system 8 is configured to execute the aforementioned methods, namely, to achieve constant strain stress relaxation control based on strain feedback, and to perform synchronous graded pressure relief and other functions according to a preset program.

[0099] In this embodiment, the guide groove 11 is located on the front side of the base 1 (i.e., a structure used only for mounting the single-sided mold module 2). Therefore, the entire device only has an arc-shaped support plate 22 arranged on the front side of the base 1. In this embodiment, the base 1 can be arranged horizontally, vertically, or at an angle.

[0100] Example 4, as shown in 1-3, is a device for suppressing the springback of glued laminated timber curved beams. This example differs from Example 3 in that:

[0101] In this embodiment, the guide groove 11 is a through groove that penetrates the base 1 along the thickness direction. This means that the guide groove 11 exists not only on the front side of the base 1, but also extends to its back side (or reverse side). Based on this structure, two sets of molding molds can be symmetrically arranged on the front and back sides of the base 1.

[0102] Preferably, in this embodiment, the base 1 is vertically arranged, that is, the base 1 is provided with molding molds on both the front and rear sides.

[0103] Specifically, at the front of the base 1, a sliding block 21 is slidably mounted on the front portion of the guide groove 11, and an arc-shaped support plate 22 is hinged to the front side of the sliding block 21, forming a first set of molding molds. At the rear of the base 1, another sliding block 21 is slidably mounted on the rear portion of the guide groove 11, and another arc-shaped support plate 22 is hinged to the rear side of the sliding block 21, forming a second set of molding molds.

[0104] Example 5, as Figure 5 As shown, a device for suppressing the springback of glued laminated timber curved beams is provided in this embodiment, which adds a heating unit 5, a temperature detection unit 6 and a pressure detection unit 9 to the basis of embodiment three or four.

[0105] The heating unit 5 is embedded inside the arc-shaped pressure plate 4. In this embodiment, a resistance heating film is used to heat the inner arc surface of the glued laminated timber arc beam.

[0106] Temperature detection unit 6 is located on arc-shaped support plate 22. In this embodiment, a temperature sensor is used to collect temperature from the outer arc surface of the glued laminated timber arc beam.

[0107] The pressure detection unit 9 is located between the arc-shaped pressure plate 4 and the piston rod. In this embodiment, a pressure sensor is used to collect the radial pressure value in real time and feed it back to the control system 8.

[0108] Heating unit 5, temperature detection unit 6 and pressure detection unit 9 are all connected to control system 8. Control system 8 has a built-in PID temperature control module and pressure control module.

[0109] Example 6, as Figure 1-3As shown in Figure 6, a device for suppressing the springback of glued laminated timber curved beams is provided in this embodiment, based on any one of embodiments three to five. An axial pressing mechanism 10 is added to both ends of the base 1. The axial pressing mechanism 10 includes a slide rail pair 101 and an axial pressing unit 102. The slide rail pair 101 (e.g., a linear guide rail and a slider) is located at the end of the base 1 and is arranged along the width direction of the base 1. The axial pressing unit 102 (e.g., a hydraulic cylinder or a pneumatic cylinder) is located on the sliding part of the slide rail pair 101. A pusher plate 103 is provided at the inner end of the axial pressing unit 102 (i.e., the end facing the center of the base).

[0110] Structures, components, and connection methods not described in detail in this invention are all prior art known to those skilled in the art unless otherwise specified. It is obvious to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that the invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the invention. Therefore, the above embodiments should be regarded as exemplary and non-limiting in all respects. The scope of this invention is defined by the appended claims rather than the foregoing description, and therefore all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within this invention.

Claims

1. A method for suppressing springback in glued laminated timber curved beams, characterized in that, Includes the following steps: Step 1: Provide a plywood assembly blank formed by stacking multiple wood plywood units; Step 2: Place the layer plate blank on a forming mold with a preset radius of curvature, and apply radial pressure to bend it to fit the mold arc surface of the forming mold; Step 3: Maintain the radial pressure for a first time period to allow the adhesive to impregnate; the first time period is 3 to 10 minutes; Step 4: Remove part of the radial pressure to the holding pressure, and maintain it at the holding pressure for a second time period, with the goal of keeping the longitudinal strain value of the outermost layer unit in the layer assembly basically constant, so that the elastic strain energy generated by bending inside the layer assembly is partially dissipated through the stress relaxation effect; the second time period is 15 to 30 minutes. Step 5: Apply radial pressure a second time to the curing pressure, and maintain the pressure at this curing pressure until the adhesive is completely cured; Step 6: Simultaneously and gradually remove radial pressure to obtain glued laminated timber curved beams.

2. The method for suppressing springback of glued laminated timber curved beams according to claim 1, characterized in that: The step four, which involves keeping the strain value of the outermost layer plate unit basically constant, is achieved by monitoring the strain value of the outermost layer plate unit in real time and dynamically adjusting the holding pressure using the strain value as a feedback signal. The term "basically constant" means that during the second time period, the fluctuation range of the monitored strain value does not exceed a preset threshold; wherein, the preset threshold is ±2% of the monitored strain value.

3. The method for suppressing springback of glued laminated timber curved beams according to claim 1, characterized in that: The maintaining pressure P2 and the initial pressure P1 at the completion of step two satisfy: P2 = k·P1, where k is the pressure maintaining coefficient, and its value ranges from 0.4 to 0.

6.

4. The method for suppressing springback of glued laminated timber curved beams according to claim 1, characterized in that: The curing pressure P3 satisfies: P3 = (1.05~1.10)·P std , where P std The recommended curing pressure for the adhesive used.

5. The method for suppressing springback of glued laminated timber curved beams according to claim 1, characterized in that: The synchronous graded removal of radial pressure in step six includes: starting from the curing pressure P3, all pressure points are simultaneously removed to the first intermediate pressure and maintained for a first interval time, and then simultaneously removed to the second intermediate pressure. This graded operation is repeated until the pressure is completely removed.

6. The method for suppressing springback of glued laminated timber curved beams according to any one of claims 1-5, characterized in that: It also includes step seven: after the adhesive has fully cured or during the curing process, apply axial pressure along the length of the glued laminated timber curved beam and maintain the axial pressure for 16 to 24 hours.

7. An apparatus for suppressing the springback of glued laminated timber curved beams in carrying out the method according to any one of claims 1-6, characterized in that, include: The base (1) has multiple guide grooves (11) spaced along its length and arranged along its width. The forming mold has multiple mold modules (2) that are arranged one-to-one with the guide groove (11). Each mold module (2) includes a sliding block (21) and an arc-shaped support plate (22). The arc-shaped support plate (22) is hinged to the side of the sliding block (21) and located outside the base (1). The radial pressure mechanism has multiple radial pressure units (3) that correspond one-to-one with the mold module (2), and the bottom of the radial pressure unit (3) is hinged with an arc-shaped pressure plate (4). The strain monitoring unit (7) is used to measure the parallel tensile strain generated on the outer surface of the outermost layer plate unit during bending in real time. The control system (8) is connected to the radial pressurization unit (3) and the strain monitoring unit (7) and is configured to perform the method as described in any one of claims 1-6.

8. The device for suppressing the springback of glued laminated timber curved beams according to claim 7, characterized in that: A pressure detection unit (9) is provided between the radial pressurizing unit (3) and the arc-shaped pressure plate (4), and the pressure detection unit (9) is connected to the control system (8) via signal.

9. The device for suppressing the springback of glued laminated timber curved beams according to claim 7, characterized in that: It also includes a heating unit (5) for heating the inner arc surface of the glued laminated timber curved beam and a temperature detection unit (6) for measuring the temperature of the outer arc surface of the glued laminated timber curved beam; both the heating unit (5) and the temperature detection unit (6) are signal connected to the control system (8).

10. The device for suppressing the springback of glued laminated timber curved beams according to claim 8 or 9, characterized in that: The base (1) is provided with an axial pressing mechanism (10) at both ends, which includes: A slide rail pair (101) is provided at the end of the base (1). An axial pressurizing unit (102) is provided in the sliding part of the slide rail pair (101), and a pusher plate (103) is provided at the inner end of the axial pressurizing unit (102).

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