Plant fiber yarn continuous efficient processing equipment and automatic control method

Abstract

The invention relates to continuous and efficient plant fiber yarn processing equipment and an automatic control method. The method comprises the following steps: setting parameters; constant tension establishment: the PLC realizes constant tension conveying based on tension feedback and speed feedforward; pre-infiltration is carried out; performing total immersion modification: running the yarns in a modification tank along a Z-shaped path, and starting ultrasonic oscillation at the same time; performing infrared preheating; washing and liquid squeezing: guiding the yarns into a washing unit to remove residual modified liquid, and then performing secondary liquid squeezing by a liquid squeezing unit to stabilize the moisture content; partitioned drying: performing roller surface contact heating and forced air drying; the tension and the temperature are monitored on line, and when the tension or the temperature exceeds the limit, a PLC conducts automatic linkage correction; cooling and rolling; and linkage control: performing master-slave or synchronous control with downstream pultrusion equipment according to the speed / tension signal. Compared with the prior art, the device has the advantages of realizing efficient and continuous automatic production, improving the efficiency, improving the modification uniformity and penetration depth, improving the product performance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous pretreatment and process control of plant fiber composites, and in particular to a plant fiber yarn continuous efficient treatment equipment and automatic control method. BACKGROUND

[0002] With the deepening of the concept of green and sustainable development, high-performance composites derived from renewable resources have attracted widespread attention. Plant fiber reinforced composites (PFRCs) have the advantages of being renewable, degradable, high specific strength / specific modulus, heat and sound insulation, and have shown application potential in the fields of construction, transportation, automobiles, wind energy, etc. However, plant fibers are composed of cellulose, hemicellulose, lignin, pectin and wax, etc., and the surface is rich in hydroxyl groups, which is strongly hydrophilic. There is natural incompatibility in interfacial wetting and bonding between hydrophobic matrices such as vinyl resin and epoxy resin. Superimposed with the differences and dispersion of fiber sources, PFRCs still face key pain points such as poor interfacial bonding, moisture absorption and swelling leading to reduced durability and large performance fluctuations.

[0003] To improve the interfacial compatibility, existing technologies propose physical methods such as plasma and heat treatment, and chemical methods such as alkali treatment, silanization, acylation / esterification, or biological methods such as enzyme method. Among them, alkali treatment is the most widely used due to its mature process and controllable cost: NaOH can partially remove hemicellulose, lignin and wax layer, expose microfibers, increase surface roughness and mechanical engagement, and reduce hydrophilic groups to improve dimensional stability and interfacial strength. Studies have shown that moderate alkali treatment can improve mechanical properties by 10-30%. However, the traditional immersion route highly depends on diffusion mass transfer, and generally has the following problems: (1) long time, high energy consumption, and difficult to continuously connect downstream processes; (2) difficult to control treatment intensity and uniformity, prone to "excessive modification on the surface / insufficient modification on the inside"; (3) process parameters are not visible and controllable, lacking online monitoring and closed-loop control of tension, solution temperature, etc., with large batch-to-batch fluctuations; (4) risk of heat-sensitive damage and increased hairiness: improper drying process temperature trajectory and stress can cause surface hardening, local thermal degradation and increased hairiness; (5) penetration resistance coupled with the twist structure: complex inter-bundle voids and capillary channels can easily form bubble barriers and limit the entry of modification agents. On the other hand, the poor intrinsic flame retardancy of PFRCs also restricts their structural applications. Existing technologies still lack systematic solutions and process windows for the synergy of "interfacial modification-flame retardant treatment-continuous molding".

[0004] In summary, in order to realize engineering and large-scale application of PFRCs, an industrial continuous production-oriented pretreatment method is urgently needed: an integrated series system capable of completing interface modification, flame-retardant treatment and pultrusion under constant tension conveying; therefore, it is necessary to propose a continuous automatic pretreatment method for plant fiber yarns, strike a balance between efficiency, uniformity and controllability, and build an overall technical path connecting interface modification, flame-retardant treatment and pultrusion process, so as to support the large-scale application of PFRCs in the fields of building, transportation and renewable energy. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a continuous and efficient processing equipment and automatic control method for plant fiber yarns, which realizes efficient and continuous automatic production and improves efficiency; through multiple synergistic mass transfer enhancement, the modification uniformity and penetration depth are improved; intelligent closed-loop control and optimized drying curve are adopted to ensure process stability and inhibit fiber damage; and the product performance is improved.

[0006] The purpose of the present application can be achieved by the following technical solutions: The present application provides a continuous and efficient automatic control method for processing plant fiber yarns, characterized by comprising the following steps: S1, parameter setting: setting the preheating temperature, pulling speed, solution concentration and drying temperature curve on the PLC+HMI platform, and enabling batch recording; the PLC+HMI platform is an automatic control man-machine interface platform; S2, constant tension establishment: threading the yarn to be processed into the equipment, and realizing constant tension conveying based on tension feedback and speed feedforward of the PLC; realizing tension closed-loop stability based on tension feedback and speed feedforward of the PLC; S3, pre-wetting: pre-wetting the yarn with water or diluent; to reduce the surface tension, improve the subsequent modification liquid wetting and immersion; S4, full immersion modification: the yarn runs along the "Z" path in the modification tank, and the ultrasonic oscillation is turned on at the same time; S5, infrared preheating: using an infrared preheating synergy unit to preheat the surface layer of the yarn near the surface of the modification tank; to reduce the near-surface viscosity, improve the fluidity and capillary penetration, and avoid overall overheating; S6, rinsing and liquid squeezing: guiding the yarn into the rinsing unit to remove residual modification liquid, and then using the liquid squeezing unit for secondary liquid squeezing to stabilize the moisture content; S7, zoned drying: the yarn enters the zoned preheating and multi-section synergistic drying unit, and is heated and air-dried by roller surface contact according to the temperature trajectory of "slow temperature rise-constant speed devolatilization-mild setting", and the temperature of each zone and the surface temperature of the yarn are monitored in real time; S8, process adaptive correction: online monitoring of tension and temperature, when the tension or temperature is out of limit, PLC automatically links to correct the traction speed, roll gap, infrared power and drying power; S9, cooling and winding: the dried yarn is cooled and wound under constant tension; the roll diameter, tension and length information are recorded to form a batch data report; S10, linkage control: master-slave or synchronous control is performed according to the speed / tension signal with the downstream pultrusion equipment.

[0007] Further, in S4, the "Z" guide path length of the full immersion solution modification tank is 2m±0.5m. The modification tank is lengthened and deepened to increase the effective immersion time.

[0008] Further, in S4, the ultrasonic oscillator has a power of 200W and a frequency of 20kHz.

[0009] Further, in S5, the power of the infrared preheating coordination unit is 1000W, and it is arranged at a position 100±10mm above the liquid surface.

[0010] Further, in S6, the extrusion unit includes a pair of gap-adjustable counter-rollers, and the roll gap adjustment accuracy is ≤0.1mm, which is used to control the liquid carrying rate of the yarn, and the control deviation is ≤±5%.

[0011] Further, in S7, the multi-section coordination drying unit includes at least four contact heating rollers and two hot air chambers, and can operate according to a temperature gradient curve of "slow temperature rise-constant speed devolatilization-mild setting".

[0012] Further, in S8, the online monitoring signals include yarn tension, traction speed, preheating and drying temperature detection.

[0013] Further, in S8, the PLC uses feedforward-feedback compound control and PID adjustment to control the conveying tension fluctuation to be ≤±5%.

[0014] Further, in S4, the modification liquid is a sodium hydroxide aqueous solution with a mass fraction of 6%-10%; in S2, the traction speed is 80-120mm / min; and in S7, the drying temperature is 80-120℃.

[0015] The application also provides a plant fiber yarn continuous and efficient processing equipment using the automatic control method, which is characterized in that it includes, in sequence along the yarn running direction: a yarn supply frame and a guide system; a traction and constant tension unwinding unit, which is internally provided with a load sensing traction roller; a pre-soaking unit; a full immersion solution modification tank, which is lengthened and deepened and is provided with a "Z" guide path, and is further provided with an ultrasonic oscillation unit at the tank bottom. An infrared preheating unit is arranged above the liquid surface of the full-immersion solution modification tank. A rinsing unit and a squeezing unit; A multi-stage cooperative drying unit adopts a combination of roller surface heating and air blowing drying. A cooling guide and constant tension winding unit; An online monitoring system for monitoring yarn tension, pulling speed and temperature, and a PLC+HMI control platform for receiving online monitoring signals and performing multivariate closed-loop coordinated control on the pulling and constant tension unwinding unit, ultrasonic oscillation unit, infrared preheating unit, squeezing unit and multi-stage cooperative drying unit to realize seamless connection with downstream pultrusion equipment.

[0016] Compared with the prior art, the present application has the following advantages: (1) Realize efficient continuous automatic production and improve efficiency. The pretreatment (such as alkali treatment) of traditional plant fiber yarns is mostly carried out by intermittent soaking method, which is time-consuming and low in efficiency, and is difficult to connect with continuous forming processes such as pultrusion. The present application integrates yarn feeding, pre-soaking, modification, rinsing, drying and winding processes in one continuous production line, and uses constant tension traction to realize continuous and efficient treatment. The present equipment can directly control the downstream pultrusion equipment through speed / tension signals, support one-key start and stop, and realize the full-process continuous and large-scale production of plant fiber composites.

[0017] As shown in the examples, the total processing time is greatly shortened from about 270 minutes (soaking for 120 minutes + rinsing for 30 minutes + drying for 120 minutes) of the traditional soaking method to about 45 minutes (soaking for 20 minutes + rinsing for 5 minutes + drying for 20 minutes), and the efficiency is improved by about 6 times. (2) By multiple synergistic mass transfer enhancement, the modification uniformity and penetration depth are improved. The internal structure of plant fiber yarn bundle is complex, and traditional methods are prone to cause "excessive modification on the surface and insufficient penetration inside". The present application adopts a triple synergistic mass transfer enhancement scheme of "physical path lengthening + ultrasonic cavitation + infrared directional preheating", which improves the modification effect. A "Z" type guide path about 2 meters long is arranged in the full immersion modification tank, which significantly increases the contact area and immersion time of the yarn and the modification liquid, ensuring the basic treatment intensity. Ultrasonic transducers (200W, 20kHz) are arranged at the bottom of the tank, which can effectively impact and break the bubble barrier inside the yarn bundle through cavitation effect, reduce the capillary resistance, and forcefully promote the modification liquid to enter the internal fiber bundle. An infrared preheating device (1000W) is arranged above the liquid surface to directionally heat the surface layer of the yarn just out of the liquid surface. The viscosity of the near-surface liquid is selectively reduced, and the fluidity and capillary penetration force are improved, thereby further promoting the migration of the modification liquid to the inside, while avoiding the risk of heat-sensitive damage to the whole yarn caused by overheating.

[0018] (3) Intelligent closed-loop control and optimized drying curve are adopted to ensure process stability and inhibit fiber damage. The process parameters are parameterized, and multi-variable closed-loop cooperative control is realized through PLC+HMI platform, and a scientific partition drying strategy is designed, which takes into account the treatment efficiency and fiber protection. The system online monitors key parameters such as yarn tension, pulling speed, and temperature in each region. The PLC adopts a compound control algorithm of feedforward (speed) + feedback (tension), which can automatically correct the pulling speed, squeezing roller gap, infrared power or drying power when the monitored tension or temperature exceeds the limit, so that the tension fluctuation is stably controlled within ±5%, improving the stability and batch consistency of the treatment. The multi-section cooperative drying unit (at least four contact heating rollers + two hot air chambers) follows an optimized temperature trajectory. This gradient heating method avoids the hardening of the yarn surface caused by rapid evaporation of water, which in turn causes the surface fibers to stick and become brittle, and also avoids the fiber damage caused by excessive internal steam pressure, effectively inhibiting the increase of hairiness and the risk of thermal degradation during the treatment process.

[0019] (4) Improve product performance. The interface performance of the treated plant fiber yarn and its composite material is significantly improved. In the example, sisal yarn is taken as an example, and under the optimal process parameters (NaOH 8%, pulling speed 90 mm / min, drying temperature 100°C): Yarn body performance improvement: the tensile strength of the treated yarn is improved to 311.62 MPa, which is better than that of the untreated yarn (285.75 MPa) and the yarn treated by traditional soaking method (293.82 MPa).

[0020] The interface bonding strength is significantly enhanced: the interface shear strength of the yarn and the resin is increased to 18.62 MPa, which is much higher than 13.58 MPa of the untreated, indicating that the interface bonding quality is greatly improved after modification.

[0021] The surface quality and wettability are optimized: the hairiness index (H) is reduced from 13 to 9, indicating that the fiber surface is smoother and the mechanical damage is small; the resin impregnation degree (I) is increased from 57% to 70%, proving that the pores inside the yarn are better filled, and the subsequent resin wettability is excellent. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Flow chart of automatic control method for continuous and efficient treatment of plant fiber yarn; Figure 2 Physical flow chart of automatic control method for continuous and efficient treatment of plant fiber yarn; Figure 3 Schematic diagram of hairiness index (H value) detection principle; Figure 4 Schematic diagram of process for measuring resin impregnation degree of sisal yarn by weighing method; Figure 5 Schematic diagram of preparation of tensile specimen of sisal dry yarn and impregnated yarn; Figure 6 Schematic diagram of single sisal yarn pull-out test principle; Figure 7 Comparison of treatment time and mechanical properties of sisal yarn under different pretreatment methods; Figure 8 Response surface plots of the effects of NaOH concentration and pulling speed on (a-c) hairiness index and (d-f) resin impregnation degree at different drying temperatures: (a, d) 80℃; (b, e) 100℃; (c, f) 120℃. DETAILED DESCRIPTION

[0023] The present application will be described in detail below in conjunction with the drawings and specific examples. In this technical solution, if the component model, material name, connection structure, control method, algorithm and other features are not explicitly stated, they are considered as common technical features disclosed in the prior art.

[0024] Example 1 The present application provides an automatic control method for continuous and efficient treatment of plant fiber yarn, as shown in Figure 1 , 2 characterized in that it comprises the following steps: S1, parameter setting: set the preheating temperature, pulling speed, solution concentration and drying temperature curve on the PLC+HMI platform, and enable batch recording; the PLC+HMI platform is an automatic control man-machine interface platform; S2. Constant tension establishment: The yarn to be processed is threaded into the equipment, and the PLC realizes constant tension conveying based on tension feedback and speed feedforward; the PLC realizes tension closed-loop stabilization based on tension feedback and speed feedforward. S3. Pre-wetting: Pre-wetting the yarn with water or diluent to reduce surface tension and improve the wetting and penetration of subsequent modifying solutions. S4, Full Immersion Modification: The yarn runs along a "Z" path in the modification tank while ultrasonic oscillation is activated; S5. Infrared preheating: The infrared preheating co-unit is used to preheat the surface layer of the yarn near the liquid surface of the modification tank in a directional manner to reduce the viscosity of the near-surface layer, improve fluidity and capillary penetration, and avoid overall overheating. S6. Rinsing and squeezing: The yarn is introduced into the rinsing unit to remove residual modified liquid, and then the squeezing unit performs a second squeezing to stabilize the wet content. S7. Zoned Drying: The yarn enters the zoned preheating and multi-segment synergistic drying unit, and is subjected to roller contact heating and blower drying according to the temperature trajectory of "slow temperature rise - constant speed devouring - gentle setting". The temperature of each zone and the yarn surface temperature are monitored in real time. S8. Process adaptive correction: Online monitoring of tension and temperature. When tension or temperature exceeds the limit, the PLC automatically corrects the traction speed, roller gap, infrared power and drying power. S9. Cooling and winding: The dried yarn is cooled and wound up under constant tension; the roll diameter, tension and length information are recorded to form a batch data report; S10, Linkage Control: Controls downstream pultrusion equipment in a master-slave or synchronous manner based on speed / tension signals.

[0025] In a specific embodiment, in S4, the length of the "Z"-shaped guide path in the modification tank of the fully immersed solution is 2m ± 0.5m. The modification tank is lengthened and deepened to increase the effective immersion time.

[0026] In a specific implementation, the ultrasonic oscillation in S4 uses an ultrasonic transducer with a power of 200W and a frequency of 20kHz. There is one transducer.

[0027] In a specific implementation, in S5, the infrared preheating coordination unit has a power of 1000W and is positioned at a liquid level of 100±10mm.

[0028] In a specific embodiment, in S6, the squeezing unit includes a pair of rollers with adjustable gap, the roller gap adjustment accuracy being ≤0.1mm, used to control the liquid carrying rate of the yarn, with a control deviation of ≤±5%.

[0029] In a specific implementation, S7, the multi-segment synergistic drying unit includes at least four contact heating rollers and two hot air chambers, and can operate according to a temperature gradient curve of "slow heating-constant speed devolatation-mild shaping".

[0030] In a specific implementation, S8 includes online monitoring signals such as yarn tension, traction speed, preheating and drying temperature detection.

[0031] In a specific implementation, in S8, the PLC uses feedforward-feedback composite control and PID regulation to control the conveying tension fluctuation within ≤±5%.

[0032] In a specific embodiment, in S4, the modified liquid is a sodium hydroxide aqueous solution with a mass fraction of 6%-10%; in S2, the traction speed is 80-120 mm / min; and in S7, the drying temperature is 80-120℃.

[0033] This invention also provides a continuous and efficient processing device for plant fiber yarns, using the above-mentioned automatic control method, characterized in that the process includes, in sequence along the yarn running direction: Yarn supply frame and guiding system; The traction and constant tension unwinding unit has a built-in load-sensing traction roller; Pre-wetting unit; The fully immersed solution modification tank is lengthened and deepened and equipped with a "Z"-shaped guide path, and the bottom of the tank is equipped with an ultrasonic oscillation unit. An infrared preheating coordination unit is positioned above the liquid surface of the fully immersed solution modification tank; Rinsing unit and squeezing unit; The multi-stage synergistic drying unit uses a combination of roller heating and forced-air drying. Cooling guide and constant tension winding unit; The system includes an online monitoring system for monitoring yarn tension, traction speed, and temperature. The PLC+HMI control platform receives the online monitoring signals and performs multi-variable closed-loop coordinated control on the traction and constant tension unwinding unit, ultrasonic oscillation unit, infrared preheating coordination unit, liquid extrusion unit, and multi-segment coordinated drying unit, achieving seamless integration with downstream pultrusion equipment.

[0034] Example 2 Objects and Specifications Yarn type: Natural plant fiber yarn (taking sisal as an example, it can be used in the same way as flax, jute, etc.).

[0035] Linear density and twist: 1200 tex, 95 tpm as an example (also applicable to 60-150 tpm).

[0036] Parallel inputs: 4 (expandable to 4-16).

[0037] The continuous and efficient processing equipment for plant fiber yarn includes, in sequence along the yarn running direction: Yarn supply frame and guiding system; The traction and constant tension unwinding unit has a built-in load-sensing traction roller; Pre-wetting unit; The fully immersed solution modification tank is lengthened and deepened and equipped with a "Z"-shaped guide path, and the bottom of the tank is equipped with an ultrasonic oscillation unit. An infrared preheating coordination unit is positioned above the liquid surface of the fully immersed solution modification tank, at a distance of 50-150 mm from the liquid surface.

[0038] Rinsing unit and squeezing unit; The multi-stage synergistic drying unit uses a combination of roller heating and forced-air drying. Cooling guide and constant tension winding unit; Online monitoring system and PLC+HMI control platform Typical process window (can be fine-tuned according to yarn specifications and target effect); Modifying solution: NaOH aqueous solution with a mass fraction of 6%-10% (preferably 8%).

[0039] Traction speed: 80-120 mm / min (preferably 90 mm / min).

[0040] Preheating temperature: 40-60℃ (preferably 40℃).

[0041] Drying temperature: 80-120 ℃ (Example three: 90 / 100 / 90 ℃).

[0042] Ultrasound: 200 W, 20 kHz (1-2 units can be connected in parallel, example 1 unit, continuous or 40% duty cycle).

[0043] Infrared preheating: 1000 W, approximately 100 mm from the liquid surface (directional irradiation of the liquid surface and the area where the yarn exits the liquid).

[0044] Tension setting: 2.5-3.5 N (taking 3.0 N as an example), fluctuation control ≤ ±5%.

[0045] Automatic control methods for continuous and efficient processing of plant fiber yarns, such as Figure 1 , 2 As shown, it includes the following steps: S1. Parameter Setting and Recipe Loading On the HMI, select "Formulation - Plant Fiber Yarn - 1200 tex - 95 tpm - Continuous Pretreatment", set the preheating temperature, traction speed, solution concentration and drying temperature on the platform, enable the "Response Surface Optimization" module, and enable batch recording.

[0046] S2, threading and establishing constant tension The four yarns are passed sequentially through the yarn frame and the guiding system into the tension-sensing traction roller. The PLC uses a combination of feedforward (speed) and feedback (tension) control to establish constant tension. Once the tension stabilizes at 3.0 N ± 5%, the next step is initiated.

[0047] S3, Pre-wetting Pre-wetting the yarn in room temperature water or a diluent reduces surface tension and opens capillary channels, creating conditions for subsequent wetting and penetration of the modifying solution. The yarn should be immediately immersed in the modification tank after pre-impregnation to prevent surface drying.

[0048] S4, Full Immersion Modification + "Z" Path Delay The yarn enters the extended and deepened modification tank, running along a 2-meter "Z"-shaped guide path to prolong the residence time and increase the contact area; the tank temperature is kept constant according to the set parameters (e.g., 20-60℃). Taking a linear speed of 90 mm / min as an example, the theoretical residence time is approximately 2000 mm / 90 mm·min. -1 ≈22 min (can be adjusted by path length and speed to meet different modification intensities); turn on the 200 W / 20 kHz ultrasonic transducer at the bottom of the tank (duty cycle can be set to 0%, period 10 s on / 15 s off) to form cavitation in the yarn bundle to break the bubble barrier, reduce capillary resistance and promote liquid entry; the ultrasonic temperature rise is limited by the tank temperature sensor, and the duty cycle is automatically reduced or paused if the limit is exceeded.

[0049] S5, Infrared Directional Preheating and Viscosity Reduction A 1000 W infrared device is turned on at a distance of about 100 mm above the liquid surface to perform directional preheating of the surface liquid and the outlet area, thereby reducing the near-surface viscosity, improving fluidity and capillary penetration, and preventing overall overheating. When the surface temperature reaches the upper limit threshold, the PLC automatically reduces the infrared power.

[0050] S6, Rinse / Squeeze to neutralize For scenarios with high alkalinity residue, the solution enters the rinsing / neutralization unit (pure water, effluent pH 7.0±0.5), followed by a second squeezing to stabilize the moisture content and prevent excessive subsequent drying and evaporation load.

[0051] S7, Zoned Preheating and Multi-Stage Drying The yarn is dried by roller contact heating and blower in tandem with the curve of "slow heating-constant rate volatilization-gentle setting". Example temperature zone: 90 / 100 / 90℃; temperature sensors are installed in each zone to monitor the yarn surface temperature, limit the heating rate and peak value, and inhibit surface hardening, thermal degradation and re-fuzzing.

[0052] S8, Process Adaptive Correction During operation, tension and temperature are monitored online. When tension or temperature exceeds the limit, the PLC automatically adjusts the traction speed, roller gap, infrared power, and drying power.

[0053] S9. Cooling, setting, and winding After drying, the yarn is guided and cooled to a set temperature and automatically wound up under constant tension; batch information such as roll diameter, tension, length and timestamp is recorded and an electronic report is generated.

[0054] S10, Linked with the pultrusion line When connected to downstream pultrusion equipment, it can achieve master-slave or synchronous control based on speed / tension signals, and supports one-button start / stop and acceleration / deceleration ramp synchronization to avoid material accumulation and breakage.

[0055] Detection and evaluation methods (examples) Hairiness Index (H): The hairiness index of sisal yarn was determined using an automatic yarn hairiness tester YG173A (Suzhou Changfang, China). Instrument specifications are as follows... Figure 3 As shown. This index reflects the surface roughness and microfibrillation degree of plant fiber yarn, and has a direct impact on resin wetting and penetration, as well as the mechanical interlocking of the fiber / matrix interface. During the test, the yarn passes through the laser scanning area under constant tension and constant yarn speed: the incident laser is scattered by the protruding fibers on the yarn surface, while the main filament bundle is suppressed because it does not reflect light; the scattered light is collected by the objective lens and converted into an electrical signal by the optical sensor. The hairiness index H is defined as the sum of the projected lengths of all protruding fibers on a unit length of yarn (1 m). It should be noted that the recorded length is the projection value of the optical system on the detection plane, not the actual fiber length in the three-dimensional space of the yarn. Each group of samples was measured 5 times independently under standard climatic conditions (20±2℃, 65±5% RH), and the mean and standard deviation were reported.

[0056] Resin Impregnation Degree (I): To quantitatively characterize the resin penetration performance of sisal yarn, this study used a gravimetric method to determine the resin impregnation degree (I) of the yarn. Figure 4 As shown. The specific steps are as follows: First, clean the surface impurities of the sisal yarn of the predetermined length with a brush, and place it in an oven at 105℃ for 2 hours to remove residual moisture and soluble impurities. Then, weigh its initial mass using an analytical balance and record it as W. initial Next, completely immerse the yarn in the vinyl ester resin that has been uniformly mixed with the curing agent, and keep it for 10 minutes to ensure that the fiber bundle is fully impregnated with resin. After removing it, hang the yarn vertically until no more resin drips. Then place it in an oven and cure it at 120°C for 1 hour. After cooling to room temperature, weigh it again and record the mass as W. impregnated Each sample was measured five times, and the average value was taken as the result. The formula for calculating the resin impregnation degree (I) is as follows: I ; Tensile properties: The diameters of the dry sisal yarn and the glazed sisal yarn were measured under an optical microscope. Then, the selected dry sisal yarn and glazed sisal yarn were bonded to a paper frame. The paper frame was cut along the centerline for each test. The prepared tensile specimens of the dry sisal yarn and glazed sisal yarn are shown below. Figure 7 As shown. Tensile properties of sisal dry yarn under different pretreatment process parameters were tested according to ASTM D2256 standard. The gauge length was 250 mm and the loading rate was 30 mm·min. −1 Fifteen yarns were tested in each group, and the mean and standard deviation were calculated. The tensile properties of sisal-impregnated yarn under pretreatment parameters were tested according to ASTM D4018-99 standard, with a gauge length of 150 mm and a loading rate of 2 mm·min. −1 Each group of 15 yarns was tested, and the mean and standard deviation were calculated.

[0057] Interfacial shear properties: After the prepared single sisal yarn is pulled out of the test sample and dried, the interfacial strength of the sisal yarn is tested, and the applied force and displacement are recorded. The test principle is as follows: Figure 6 As shown. An electronic universal testing machine (model EMC 204C, USA) with a 500N sensor was used, with a gauge length of 10 mm and a tensile speed of 1 mm / min. Each group had no fewer than 15 valid samples, and the mean and standard deviation were calculated.

[0058] Representative results (taking the preferred conditions of this embodiment as an example) Under the conditions of 8% NaOH mass fraction, traction speed of 90 mm / min, preheating at 40℃, and drying at 100℃, compared with the unoptimized intermittent soaking route, the continuous pretreatment of the present invention achieves the following effects (see...). Figure 5 ) The processing time was significantly reduced: the total continuous processing time was about 45 min (immersion 20 min + rinsing 5 min + drying 20 min), which was much shorter than the soaking method's 270 min (120 + 30 + 120 min), and the overall efficiency was improved by 6 times. Mechanical and interfacial improvements: The tensile strength of the impregnated yarn increased to 311.62 MPa (285.75 MPa for untreated yarn and 293.82 MPa for impregnation); the interfacial shear strength increased to 18.62 MPa (13.58 MPa for untreated yarn and 17.39 MPa for impregnation). Quality indicators improved: Feather index H decreased from 13 to 9; resin impregnation degree I increased from 57% to 70%.

[0059] Operational stability: Conveying tension fluctuation ≤ ±5%, stable multi-end parallel continuous operation, and seamless connection with downstream pultrusion line speed.

[0060] Combined with response surface analysis (see) Figure 8 Under drying conditions at 100 °C, H reaches a low point in the region of approximately 8-9 wt% NaOH and approximately 95-110 mm / min traction speed, while I reaches a high value in the region of approximately 8.5-9.0 wt% NaOH and approximately 100-110 mm / min traction speed. The selected example parameters (8%, 90 mm / min, 100 °C) are near the above-mentioned preferred range, balancing fuzz suppression and impregnation enhancement; if further extreme values ​​are required, the concentration can be fine-tuned to 8.5-9.0 wt% or the speed to 100-110 mm / min without sacrificing H.

[0061] The above results show that the present invention significantly improves processing efficiency, uniformity and consistency of subsequent wetting / interface bonding while ensuring mass transfer and thermal safety, and has engineering advantages of continuous operation, traceability and ease of scaling.

[0062] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0063] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for automatic control of continuous and efficient processing of plant fiber yarns, characterized by, The method comprises the following steps: S1, parameter setting: setting preheating temperature, traction speed, solution concentration and drying temperature curve on PLC+HMI platform, and enabling batch record; S2, constant tension establishment: threading the yarn to be treated into the equipment, and realizing constant tension conveying based on tension feedback and speed feedforward of PLC; S3, pre-wetting: pre-wetting the yarn with water or diluent; S4, full immersion modification: the yarn runs along the "Z" path in the modification tank, and the ultrasonic oscillation is started at the same time; S5, infrared preheating: using the infrared preheating cooperative unit to preheat the surface layer of the yarn near the liquid surface of the modification tank; S6, rinsing and squeezing: guiding the yarn into the rinsing unit to remove residual modification liquid, and then using the squeezing unit for secondary squeezing to stabilize the moisture content; S7, zoned drying: the yarn enters the zoned preheating and multi-section cooperative drying unit, and is heated and blown dry by roller surface contact according to the temperature trajectory of "slow temperature rise-constant speed devolatilization-mild setting"; the temperature of each zone and the surface temperature of the yarn are monitored in real time; S8, process self-adaptive correction: when the tension or temperature is out of limit, the traction speed, nip, infrared power and drying power are automatically corrected by PLC; S9, cooling and winding: the dried yarn is cooled and wound under constant tension; the diameter, tension and length information are recorded to form a batch data report; S10, linkage control: master-slave or synchronous control is performed according to the speed / tension signal with the downstream pultrusion equipment.

2. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S4, the "Z" path length of the full immersion solution modification tank is 2m±0.5m.

3. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S4, the ultrasonic vibrator power is 200W, and the frequency is 20kHz.

4. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S5, the power of the infrared preheating cooperative unit is 1000W, and it is arranged at 100±10mm above the liquid surface.

5. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S6, the squeezing unit includes a pair of gap-adjustable counter-rollers, the nip adjustment accuracy is ≤0.1mm, which is used to control the liquid carrying rate of the yarn, and the control deviation is ≤±5%.

6. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S7, the multi-section cooperative drying unit includes at least four contact heating rollers and two hot air chambers, which can run according to the temperature gradient curve of "slow temperature rise-constant speed devolatilization-mild setting".

7. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S8, the online monitoring signals include yarn tension, traction speed, preheating and drying temperature detection.

8. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S8, the PLC uses feedforward-feedback compound control and PID regulation to control the tension fluctuation within ≤±5%.

9. The automatic control method for continuous and efficient processing of plant fiber yarn according to claim 1, characterized in that, In S4, the modification liquid is 6%-10% sodium hydroxide aqueous solution; the traction speed in S2 is 80-120mm / min; and the drying temperature in S7 is 80-120℃.

10. A continuous and efficient plant fiber yarn processing apparatus using the automatic control method according to any one of claims 1 to 9, characterized by, In sequence along the running direction of the yarn, it comprises: yarn supply frame and guide system; traction and constant tension unwinding unit, which is internally provided with a load sensing traction roller; pre-wetting unit; full immersion solution modification tank, which is lengthened and deepened and is provided with a "Z" guide path, and is further provided with an ultrasonic oscillation unit at the tank bottom; infrared preheating cooperative unit, which is arranged above the liquid surface of the full immersion solution modification tank; rinsing unit and squeezing unit; multi-section cooperative drying unit, which adopts the combination of roller surface heating and air blowing drying; cooling guide and constant tension winding unit; The online monitoring system is used for monitoring yarn tension, traction speed and temperature; the PLC+HMI control platform is used for receiving online monitoring signals, and performing multivariate closed-loop coordinated control on the traction and constant tension unwinding unit, ultrasonic oscillation unit, infrared preheating cooperative unit, liquid squeezing unit and multi-section cooperative drying unit, so as to realize seamless connection with downstream pultrusion equipment.

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