A carbon fiber tow spreading performance quantitative test system and method

Abstract

This application relates to the field of carbon fiber performance testing technology, and in particular to a quantitative testing system and method for carbon fiber tow spreading performance. To overcome the problems of long cycles, low efficiency, inconsistencies with actual prepreg production processes, and potential damage to carbon fibers in existing online and offline testing, qualitative and quantitative testing, this system is based on the mechanical vibration spreading principle for carbon fiber spreading. It uses a laser sensor as the width measuring device to test the carbon fiber tow width, and is equipped with an image analyzer for real-time image capture. This testing system can comprehensively test and characterize the influence of multiple parameters on carbon fiber tow spreading performance, objectively and accurately evaluate carbon fiber tow spreading performance, is applicable to different types of carbon fibers, causes minimal damage to carbon fibers, and has high testing efficiency.

Description

Technical Field

[0001] This application relates to the field of carbon fiber performance testing technology, and in particular to a quantitative testing system and method for carbon fiber tow stretching performance. Background Technology

[0002] Carbon fiber, with its superior properties such as high specific strength and high specific modulus, has become an indispensable key strategic material in both defense and civilian fields. Carbon fiber exists in the form of tows, each tow containing thousands of monofilaments. Depending on the number of monofilaments, it is classified into types such as 3K, 6K, 12K, 24K, and 48K, where K represents thousands of monofilaments. The carbon fiber tows are bound together by a sizing agent. Unidirectional carbon fiber tape prepreg is an important intermediate product in the preparation of carbon fiber reinforced resin matrix composites, formed by compounding carbon fiber and resin through a one-step or two-step process.

[0003] In the preparation of carbon fiber prepreg, the carbon fiber tow should possess good spreading (or spreading, fiber spreading, filament spreading, fiber opening) properties. Ideally, the carbon fiber filaments should be parallel and fully spread to ensure sufficient impregnation of the carbon fiber with the resin, resulting in a composite material with uniform thickness and fiber volume fraction distribution. In reality, carbon fiber tows are difficult to spread or have poor spreading uniformity due to sizing, interlacing between filaments, and tow reversal. Poorly spread fiber tows are prone to uneven tow spacing and gap defects during prepreg preparation, leading to uneven composite material thickness and uneven carbon fiber volume fraction distribution, resulting in a large dispersion of the composite material's mechanical properties. Therefore, spreading performance is an important process performance indicator for carbon fiber, which is of great significance for both carbon fiber production and use.

[0004] Currently, there is no unified quantitative testing device, method, or standard for testing the spreading performance of carbon fiber tow in China. In the prepreg production process, most tests still rely on manual observation and experience to explore and determine the spreading process parameters, which cannot objectively and accurately evaluate the spreading performance of carbon fiber tow. Therefore, a quantitative testing device and method that can reflect the spreading performance during the carbon fiber prepreg preparation process will help to achieve real-time and accurate measurement of key parameters such as the spreading width and uniformity of carbon fiber tow, thereby improving the quality control level of the carbon fiber prepreg production process and the ability to evaluate carbon fiber quality. Summary of the Invention

[0005] This application provides a quantitative testing system and method for the stretching performance of carbon fiber tow to solve the problems mentioned in the background art.

[0006] In a first aspect, this application provides a quantitative testing system for the spreading performance of carbon fiber tow, including a spreading unit and a measuring unit. The spreading unit includes a spreading roller group, which, according to the carbon fiber movement direction, includes, from front to back, a guide roller, an upper and lower vibrating roller, a front lifting roller, a front left and right vibrating roller, a lifting roller, a rear left and right vibrating roller, and a rear lifting roller. The measuring unit includes a laser sensor. The spreading unit is used to spread carbon fiber based on the mechanical vibration spreading principle, and the measuring unit is used to test the width of the carbon fiber tow.

[0007] Furthermore, the guide roller is a roller that passes through the yarn guide hole and before the upper and lower vibrating rollers. It is used to prevent the fiber bundles coming out of the yarn guide hole from sticking together, deforming or twisting due to vibration during the up and down vibration.

[0008] Furthermore, the upper and lower vibrating rollers are used for heating and vibrating up and down according to a set frequency and amplitude, thereby changing the tension of the fiber bundle and making the fiber bundle thinner.

[0009] Furthermore, the front left and right vibrating rollers and the rear left and right vibrating rollers are used for heating and vibrating left and right according to a set frequency and amplitude to widen the fiber bundles left and right.

[0010] Furthermore, the front lifting roller, the lifting roller, and the rear lifting roller are used to adjust their up and down positions via a servo motor, thereby changing the wrap angle of the fiber bundle on the vibrating roller.

[0011] Furthermore, the yarn spreading unit also includes a mold temperature controller, which is used to control the temperature of the yarn spreading roller assembly.

[0012] Furthermore, the measuring unit also includes an image analyzer, which is used to record and measure the gap width of the carbon fiber after the yarn is unfurled, with a measurement accuracy of ±0.01mm.

[0013] Furthermore, it also includes an unwinding unit, which includes a yarn drum, a yarn guide rod, a yarn guide plate, and a yarn guide wheel; the unwinding unit is used to place carbon fibers and actively unwind the yarn.

[0014] Furthermore, it also includes a winding unit, which includes a shaping roller, an air-expanding take-up shaft, a chuck, and an adjusting seat; the winding unit is used to provide power for automatic winding, to continuously move the carbon fiber and collect the unfolded carbon fiber bundle, and has an automatic stop function when the preset length is reached.

[0015] Secondly, this application provides a quantitative testing method for the stretching performance of carbon fiber tow, which is implemented by the quantitative testing system for the stretching performance of carbon fiber tow as described above; The quantitative testing method for the stretching performance of carbon fiber tow includes: The carbon fiber passes through the guide roller, upper and lower vibrating rollers, front lifting roller, front left and right vibrating rollers, lifting roller, rear left and right vibrating roller, and rear lifting roller in sequence. Set the carbon fiber tow stretching process parameters, including speed, temperature, tension, wrap angle, vibration frequency, and amplitude; After starting the test system and running the carbon fiber bundle for at least 2m, the measuring unit records the width of the carbon fiber bundle before and after the yarn is unrolled 20 times at 0.5m intervals. Calculate the average width of the unfolded filament bundle before unfolding, denoted as L1, accurate to 0.1mm; calculate the average width of the unfolded filament bundle after unfolding, denoted as L2, accurate to 0.1mm.

[0016] The above-mentioned technical solution of this application has the following advantages: The quantitative testing system and method for carbon fiber tow spreading performance provided in this application are based on the principle of mechanical vibration spreading of carbon fiber, using a laser sensor as the width measuring device to test the width of the carbon fiber tow, and simultaneously equipped with an image analyzer for real-time image capture. This testing system can comprehensively test and characterize the influence of multiple parameters on the spreading performance of carbon fiber tow, can objectively and accurately evaluate the spreading performance of carbon fiber tow, is applicable to different types of carbon fiber, causes minimal damage to the carbon fiber, and has high testing efficiency. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of the quantitative testing system for the stretching performance of carbon fiber tow provided in the embodiments of this application; Figure 2 This is a schematic diagram of the structure of the unwinding unit provided in the embodiments of this application; Figure 3 This is a schematic diagram of the structure of the yarn spreading roller assembly provided in the embodiments of this application; Figure 4 This is a schematic diagram of the structure of the winding unit provided in the embodiments of this application; Figure 5 This is a schematic diagram of the structure of the measurement unit provided in an embodiment of this application.

[0019] Reference numerals: 1—Unwinding unit; 2—Front width measuring device; 3—Carbon fiber bundle; 4—Yarn spreading unit; 5—Guide roller; 6—Upper and lower vibrating rollers; 7—Front lifting roller; 8—Front left and right vibrating rollers; 9—Lifting roller; 10—Rear left and right vibrating rollers; 11—Rear lifting roller; 12—Rear width measuring device; 13—Image analyzer; 14—Setting roller; 15—Twist-up unit; 16—Wrapping angle; 1-1—Yarn barrel; 1-2—Yarn guide rod; 1-3—Yarn guide plate; 1-4—Yarn guide steel wheel; 4-1 Upper and lower vibrating roller motor; 4-2 Left and right vibrating roller motor; 4-3 Lifting roller motor; 4-4 Vibrating drag wheel; 5-1 Manual displacement table; 5-2 Laser emitter (upper sensor); 5-3 Laser receiver (lower sensor); 15-1—Air-expanded take-up shaft; 15-2—Clamp; 15-3—Adjusting seat; 15-4—Servo motor. Detailed Implementation

[0020] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and processes are omitted so as not to obscure the description of this application with unnecessary detail.

[0021] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0022] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized. "A plurality" means "two or more."

[0024] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application.

[0025] This application provides a quantitative testing system for the spreading performance of carbon fiber tows. It enables the spreading of carbon fiber tows under a certain tension through mechanical vibration and heating, automatically measuring the width of the tow before and after spreading. It can perform spreading tests on carbon fiber tows of specifications such as 3K, 6K, 12K, 24K, and 48K. It mainly consists of five parts: an unwinding unit, a spreading unit, a measuring unit, a winding unit, and a control unit. See the structural diagram for details. Figure 1 .

[0026] The unwinding unit consists of a yarn drum, a yarn guide rod, a yarn guide plate, and a yarn guide wheel. The unwinding unit is used to hold one spool of carbon fiber and for active yarn unwinding. See details. Figure 2 After the carbon fiber yarn is released from the yarn bobbin, it passes sequentially through the guide rod and guide plate, with the path level adjusted by the guide steel wheel. The height adjustment of the guide steel wheel is ±20mm, and the surface treatment is matte hard chrome plating. Each yarn bobbin can carry a carbon fiber yarn weight of 5kg~9kg. The carbon fiber yarn bobbin is fixed on the yarn release frame and actively releases the yarn. Tension is provided by a servo motor in reverse rotation. The servo motor adjusts the output torque in real time based on the tension feedback detection data to ensure that the carbon fiber filament tension is consistent with the set value (i.e., unwinding will only be successful when the tension of the traction filament is greater than the set tension value; if the traction force is too small, unwinding will not be possible). The tension of the unwinding unit is adjustable, with a damping range of 0.5N~10N and an index value of 0.1N.

[0027] The yarn spreading unit is the core system, consisting of a yarn spreading roller assembly and a mold temperature controller. It unfolds the carbon fiber tow through mechanical vibration and heating. The yarn spreading roller assembly is a multi-axial mechanical vibration yarn spreading device, composed of one guide roller, one upper and lower vibrating roller, three lifting rollers, and two left and right vibrating rollers. Following the direction of carbon fiber movement, from front to back, the sequence is: guide roller, upper and lower vibrating roller, front lifting roller, front left and right vibrating rollers, lifting roller, rear left and right vibrating roller, and rear lifting roller. See details... Figure 3Each roller is made of stainless steel with a chrome-plated surface. Each roller is detachable for easy replacement of those with damaged plating. Each roller has a diameter of φ100mm, a working length ≤200mm, and a surface roughness of 1.9μm±0.2μm. Each vibrating roller has vibration and heating functions, and its height can be adjusted to change the wrap angle. The vibrating rollers are driven by servo motors and, via vibrating drag wheels (manually adjustable scales of 2mm, 3mm, 4mm, 6mm, and 8mm), achieve up-down and left-right yarn spreading, with a vibration frequency ≤300 / min. The lifting rollers are driven by servo motors, allowing each roller to move up and down within a range of ±60mm. The oil-type mold temperature controller operates at RT-120℃ with a temperature accuracy of ±2℃, uniformly controlling the temperature of the spreading roller assembly. The functions of each roller in the spreading roller assembly are as follows: Guide roller: This roller guides the fiber bundles through the yarn guide holes before passing over the upper and lower vibrating rollers. It prevents the fiber bundles exiting the yarn guide holes from sticking together, deforming, or twisting due to vibration during the up-and-down vibration.

[0028] Upper and lower vibrating rollers: heated and vibrating up and down according to a set frequency and amplitude, changing the tension of the fiber bundle through the up and down vibration, making the fiber bundle thinner.

[0029] Left and right vibrating rollers: heated and vibrating left and right according to the set frequency and amplitude to widen the fiber bundles to the left and right.

[0030] Lifting roller: The up and down position is adjusted by a servo motor to change the wrap angle of the fiber bundle on the vibrating roller.

[0031] Rewinding Unit: The rewinding unit provides power for automatic rewinding, continuously moving the carbon fiber and collecting the unwound carbon fiber bundle. It features an automatic stop function upon reaching a preset length. It mainly consists of a setting roller, an air-expanding take-up shaft, a chuck, and an adjusting seat. See details... Figure 4 The winding uses an air-expanding take-up shaft, which can support the inner diameter of the paper tube φ76mm. The servo motor drives the winding via a reducer. The parallelism with the shaping roller (which causes less wear on the fibers) is adjusted by a manual adjustment seat, with an adjustment range of ±35mm.

[0032] Measurement Unit: The measurement unit consists of two laser sensors (one before and one after the carbon fiber tow is unfurled) and one image analyzer. The laser sensors automatically identify and record the width of the carbon fiber tow before and after unfurling, with a single measurement range of 250mm and an accuracy of ±0.1mm. The width-measuring laser sensors are a pair, one above the other; the upper sensor emits red light, and the lower sensor receives it. The maximum distance between the upper and lower sensors is 300mm (meaning that the sensor will not receive light beyond a distance of 300mm), with a repeatability of 5µm. The sensors are made of aluminum alloy and include a manual displacement stage (located next to the sensors, allowing simultaneous movement of both sensors) with an adjustment range of 60mm. The position can be adjusted to suit products in different locations. See details. Figure 5The image analyzer is used to record and measure the gap width of carbon fiber after yarn unfolding, with a measurement accuracy of ±0.01mm. It has quantitative measurement and analysis software and a data processing system.

[0033] Control Unit: The operating system adopts a touchscreen + PLC control method. For convenient operation and control of each device, independent touchscreen control is used. The overall equipment has both manual and automatic modes. The independent control panel has functions for setting, adjusting, displaying, storing, and outputting the unit's technical parameters. All fault information is displayed and recorded in real time. Audible and visual prompts are given when the set temperature, speed, and time are reached, and when the process ends. Audible and visual alarms are also given when the set temperature and speed are reached, or when the temperature and speed exceed the allowable range. It has a self-diagnostic function, providing real-time alarms for various faults during operation, using audible and visual methods, and indicating the fault location.

[0034] The following is a description through specific embodiments.

[0035] Example This embodiment provides a quantitative testing system for the stretching performance of carbon fiber tow, comprising five parts: an unwinding unit, a spreading unit, a measuring unit, a winding unit, and a control unit.

[0036] The unwinding unit consists of a yarn drum, a yarn guide rod, a yarn guide plate, and a yarn guide wheel.

[0037] The yarn spreading unit is the most crucial system, consisting of a yarn spreading roller assembly and a mold temperature controller. The yarn spreading roller assembly is a multi-axial mechanical vibration yarn spreading device, consisting of one guide roller, one upper and lower vibrating roller, three lifting rollers, and two left and right vibrating rollers. According to the direction of carbon fiber movement, from front to back, they are: guide roller, upper and lower vibrating roller, front lifting roller, front left and right vibrating roller, lifting roller, rear left and right vibrating roller, and rear lifting roller.

[0038] The winding unit consists of a shaping roller, an air-expanded take-up shaft, a chuck, and an adjusting seat.

[0039] The measurement unit consists of two laser sensors and an image analyzer.

[0040] The control unit's operating system uses a touchscreen + PLC control method. To facilitate the operation and control of each device, independent touchscreen control is used. The overall equipment has two modes: manual and automatic.

[0041] Carbon fiber tow width test procedure: Place the yarn canister -- Unwind -- Measure the width before spreading -- Spread the yarn -- Measure the width after spreading -- Rewind.

[0042] The method for measuring the spreadability of carbon fiber tow using the quantitative testing system for carbon fiber tow spreadability described above is as follows: Step 1: Install carbon fiber bundles: After the carbon fiber is released from the yarn drum, it passes through the yarn guide rod and the yarn guide plate in sequence, and is released in the unwinding unit; then it passes through the guide roller, upper and lower vibrating rollers, front lifting roller, front left and right vibrating rollers, lifting roller, rear left and right vibrating roller, rear lifting roller, shaping roller, and air-expanded take-up shaft in sequence.

[0043] Step 2: Set the carbon fiber tow broadening process parameters: These mainly include parameters such as speed, temperature, tension, wrap angle, vibration frequency, and amplitude, which vary depending on the type of carbon fiber and sizing agent.

[0044] Step 3: Carbon fiber tow spreading performance test: Start the test system. After the carbon fiber tow has been running for at least 2m, use the width measuring device to record the width of the carbon fiber tow before and after spreading 20 times at 0.5m intervals.

[0045] Step 4: Calculate the average width of the unfolded filament bundle before unfolding, denoted as L1, accurate to 0.1mm; calculate the average width of the unfolded filament bundle after unfolding, denoted as L2, accurate to 0.1mm.

[0046] This application provides a quantitative testing system for the spreading performance of carbon fiber tow. The system is based on multi-axis mechanical vibration to spread the carbon fiber tow. The carbon fiber tow runs under a certain unwinding tension and speed, and is spread by a spreading roller under certain temperature, frequency, and amplitude. A laser sensor measures the width of the carbon fiber tow before and after spreading, and an image analyzer is used to photograph and analyze the width of the carbon fiber gaps after spreading. This quantitative testing system can quantitatively and accurately evaluate the spreading performance of carbon fibers. Its main improvements are: (1) It can realize the spreading of carbon fiber bundles under controllable conditions of multiple factors such as linear speed, tension, wrap angle between carbon fiber and metal roller, amplitude, vibration frequency, and temperature, and accurately monitor the spreading performance of carbon fibers; (2) It can realize the full automation of the process of automatic tension control, spreading, measurement, and winding, and monitor the process parameters in real time; (3) It can reflect the actual prepreg production process, and use the system to accurately analyze the influence of process parameters on the spreading performance of carbon fibers, and accurately guide the setting and adjustment of prepreg production process parameters; (4) It has a wide range of applications (it can be adapted to the spreading performance testing of various types of carbon fiber bundles such as 3K, 6K, 12K, 24K, and 48K), and the testing process is efficient and causes little damage to the fibers.

[0047] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application.

[0048] It should be clarified that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. This application is not limited to the specific structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0049] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A carbon fiber tow spreadability quantitative test system, characterized by, The device includes a yarn spreading unit and a measuring unit. The yarn spreading unit includes a yarn spreading roller group, which, in accordance with the direction of carbon fiber movement, includes, from front to back, a guide roller, an upper and lower vibrating roller, a front lifting roller, a front left and right vibrating roller, a lifting roller, a rear left and right vibrating roller, and a rear lifting roller. The measuring unit includes a laser sensor. The yarn spreading unit is used to spread carbon fiber yarn based on the principle of mechanical vibration yarn spreading, and the measuring unit is used to test the width of the carbon fiber bundle.

2. The carbon fiber tow spreadability quantitative test system according to claim 1, wherein, The guide roller is a roller that passes through the yarn guide hole and before the upper and lower vibrating rollers. It is used to prevent the fiber bundles coming out of the yarn guide hole from sticking together, deforming or twisting due to vibration during the up and down vibration.

3. The carbon fiber tow spreadability quantitative test system according to claim 1, wherein, The upper and lower vibrating rollers are used for heating and vibrating up and down according to a set frequency and amplitude. The up and down vibration changes the tension of the fiber bundle, making the fiber bundle thinner.

4. The carbon fiber tow spreadability quantitative test system according to claim 1, wherein, The front left and right vibrating rollers and the rear left and right vibrating rollers are used for heating and vibrating left and right according to a set frequency and amplitude to widen the fiber bundles left and right.

5. The quantitative testing system for the stretching performance of carbon fiber tow as described in claim 1, characterized in that, The front lifting roller, the lifting roller, and the rear lifting roller are used to adjust their up and down positions via a servo motor, thereby changing the wrap angle of the fiber bundle on the vibrating roller.

6. The quantitative testing system for the stretching performance of carbon fiber tow as described in claim 1, characterized in that, The yarn spreading unit also includes a mold temperature controller, which is used to control the temperature of the yarn spreading roller assembly.

7. The quantitative testing system for the stretching performance of carbon fiber tow as described in claim 1, characterized in that, The measuring unit also includes an image analyzer, which is used to record and measure the width of the carbon fiber gap after the yarn is unfurled, with a measurement accuracy of ±0.01mm.

8. The quantitative testing system for the stretching performance of carbon fiber tow as described in claim 1, characterized in that, It also includes an unwinding unit, which comprises a yarn drum, a yarn guide rod, a yarn guide plate, and a yarn guide wheel; the unwinding unit is used to place carbon fibers and actively unwind the yarn.

9. The quantitative testing system for the stretching performance of carbon fiber tow as described in claim 1, characterized in that, It also includes a winding unit, which includes a shaping roller, an air-expanding take-up shaft, a chuck, and an adjustment seat; the winding unit is used to provide power for automatic winding, to pull the carbon fiber to move continuously and to collect the carbon fiber bundle after it is spread out, and has an automatic stop function when the preset length is reached.

10. A quantitative testing method for the broadening performance of carbon fiber tow, characterized in that, This is achieved using the quantitative testing system for the stretching performance of carbon fiber tow as described in any one of claims 1 to 9; The quantitative testing method for the stretching performance of carbon fiber tow includes: The carbon fiber passes through the guide roller, upper and lower vibrating rollers, front lifting roller, front left and right vibrating rollers, lifting roller, rear left and right vibrating roller, and rear lifting roller in sequence. Set the carbon fiber tow stretching process parameters, including speed, temperature, tension, wrap angle, vibration frequency, and amplitude; After starting the test system and running the carbon fiber bundle for at least 2m, the measuring unit records the width of the carbon fiber bundle before and after the yarn is unrolled 20 times at 0.5m intervals. Calculate the average width of the unfolded filament bundle before unfolding, denoted as L1, accurate to 0.1mm; calculate the average width of the unfolded filament bundle after unfolding, denoted as L2, accurate to 0.1mm.

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