A method for pressing a carbon composite material on a pipe surface

Abstract

The application relates to the technical field of pipe material film pressing, in particular to a pipe material surface carbon composite material film pressing method, which comprises the following steps: recovering reinforcing fibers and matrix materials from waste materials to form carbon composite materials, curing the carbon composite materials on the pipe material surface according to a preset temperature and pressure rising curve, collecting temperature data and strain data of each detection point at each moment in each curing stage on the pipe material surface; calculating the curing degree and resin viscosity of each detection point at each moment in each curing stage; determining the adjusted pressure at each moment in each curing stage, curing and film pressing the carbon composite materials on the pipe material surface, and evaluating the curing and film pressing effect. Through real-time adjustment of the pressure, the application compensates for the resin flow resistance change caused by temperature and curing degree change in the curing process, effectively avoids problems such as undercuring, overcuring and uneven fiber distribution caused by insufficient or excessively high pressure, and improves the mechanical properties and quality of the pipe material after curing and film pressing.

Description

Technical Field

[0001] This application relates to the field of pipe lamination technology, specifically to a method for laminating carbon composite materials onto the surface of pipes. Background Technology

[0002] Molding refers to the process of applying pressure to a mold or substrate using plastic material or a pre-impregnated resin film, then bonding and shaping it through heating and pressurization. Surface coating significantly enhances the corrosion resistance and wear resistance of pipes. Furthermore, molding improves the sealing and aesthetics of pipes, and effectively prevents direct contact between the medium and the pipe, avoiding material aging or contamination problems.

[0003] Carbon composite materials are composite materials with carbon fiber as reinforcement and carbon or polymer as matrix. They are bonded to the surface of pipes through hot pressing to form a dense, functional coating. Under the stringent requirements of the intelligent manufacturing equipment industry for high-precision, high-reliability composite material products, existing molding processes typically set fixed molding temperatures and pressures based on the product thickness and resin curing rate. This fails to consider the low-temperature edges and localized overheating points that exist during molding, leading to inconsistent resin curing rates and resulting in localized over-curing or under-curing. This makes it difficult to meet the uniformity and consistency requirements of molding on complex pipe structures, resulting in uneven curing of carbon composite materials on the pipe surface. Summary of the Invention

[0004] To address the aforementioned technical problems, a method for laminating carbon composite materials onto the surface of pipes is provided to solve the existing issues. The solution provided in this application is a method for laminating carbon composite materials onto the surface of pipes, comprising the following steps:

[0005] Reinforcing fibers and matrix materials are recovered from waste to form carbon composite materials. The carbon composite materials on the pipe surface are cured according to a preset heating and pressurization curve. Temperature and strain data of each detection point on the pipe surface at each time point during each curing stage are collected.

[0006] Based on the temperature data at each moment, the degree of curing at each detection point at each moment under each curing stage is calculated using the Arrhenius equation. Then, the resin viscosity at each detection point at each moment under each curing stage is calculated using the degree of curing and temperature data.

[0007] By analyzing the deviation of strain data at different detection points at each time point during each curing stage, and combining this with the resin viscosity, the adjusted pressure at each time point during each curing stage is determined. Based on the real-time adjusted pressure, the carbon composite material on the pipe surface is cured and pressed into a film, and the curing and pressing effect is evaluated.

[0008] Preferably, the preset temperature and pressure curve is divided into 4 curing stages, specifically including:

[0009] First curing stage: Heat from room temperature to T1 at a heating rate of ΔT, maintain pressure P1, and hold for X1 hours;

[0010] The second curing stage: the temperature is increased from T1 to T2, the pressure is increased to P2, and the temperature is maintained for 2 hours;

[0011] The third curing stage: the temperature is increased from T2 to T3, the pressure is increased to P3, and the temperature is maintained for 3 hours;

[0012] The fourth curing stage: Heating is turned off, and the mixture is allowed to cool naturally to below T4, with pressure released slowly. Here, ΔT, T1, T2, T3, T4, P1, P2, P3, X1, X2, and X3 are all preset values, and T4... <T1<T2<T3,P1<P2<P3,X1<X2<X3。

[0013] Preferably, the carbon composite material is a carbon fiber cloth-epoxy resin prepreg formed with carbon fiber cloth as reinforcement and epoxy resin as matrix.

[0014] Preferably, the formula for calculating the degree of cure α is: Where A is the frequency factor, E a Let R be the activation energy of the reaction, T be the temperature data, t be the curing time, which is the time interval from the start of heating to time t, and exp be an exponential function with the natural constant as the base.

[0015] Preferably, the activation energy and frequency factor are calculated using the Kissinger method.

[0016] Preferably, the formula for calculating the resin viscosity η is: Where η0 is the initial viscosity of the resin at room temperature, and E a α is the activation energy of the reaction, R is the gas constant, T is the temperature data, α is the degree of curing, β is the curing sensitivity coefficient, is a constant, and exp is an exponential function with the natural constant as the base.

[0017] Preferably, determining the adjusted pressure at each time step of the curing stage includes:

[0018] For each curing stage, the difference between the preset target strain value and the strain data at each detection point at each time point is recorded as the strain deviation;

[0019] Calculate the average value of the product of resin viscosity, strain deviation, and preset adjustment coefficient at all detection points at each time point;

[0020] The initial pressure is recorded as the pressure at each moment of each curing stage in the preset heating and pressurization curve.

[0021] The adjusted pressure is the result of combining the initial pressure and the average value.

[0022] Preferably, the strain deviation is the difference between the preset target strain value and the strain data of each detection point at each time step in each curing stage.

[0023] Preferably, the fusion process involves calculating the sum of the initial pressure and the average value, which is used as the adjusted pressure.

[0024] Preferably, the evaluation of the curing and pressing effect includes: measuring the curing uniformity by differential scanning calorimetry; measuring the porosity by gravimetric method; measuring the interlaminar shear strength by testing the maximum shear stress that the carbon composite material can withstand between layers; and measuring the outer diameter accuracy of the pipe by high-precision calipers.

[0025] This application has at least the following beneficial effects:

[0026] This application calculates the degree of curing by measuring temperature changes at different test points on the pipe surface. This is beneficial because it considers the degree of resin cross-linking at different test points. Furthermore, based on the degree of curing, the resin viscosity is calculated, which is beneficial because it assesses the curing process and reflects the resin flow during curing. Secondly, by analyzing the deviation of strain data at different test points at each curing stage and combining it with the resin viscosity, the adjusted pressure at each time point in each curing stage is determined. Based on the real-time adjusted pressure, the carbon composite material on the pipe surface is cured and pressed, and the curing and pressing effect is evaluated. This is beneficial because the strain deviation at the test points assesses the compaction state and the resistance to resin flow. By adjusting the pressure in real time, changes in resin flow resistance caused by temperature and degree of curing during the curing process are compensated, ensuring uniform compaction of the carbon composite material. This effectively avoids problems such as under-curing, over-curing, and uneven fiber distribution caused by insufficient or excessive pressure, improving the mechanical properties and quality of the pipe after curing and pressing. Attached Figure Description

[0027] The following description, in conjunction with the accompanying drawings, provides a more detailed explanation of a carbon composite material pressing method for pipe surfaces according to this application.

[0028] Figure 1 A flowchart illustrating the steps of a carbon composite material lamination method for pipe surfaces provided in this application embodiment;

[0029] Figure 2 A flowchart illustrating the steps of the method for obtaining the adjusted pressure at each time point in each curing stage provided in the embodiments of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description of a carbon composite material pressing method for pipe surfaces, in conjunction with the accompanying drawings and embodiments, is provided. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] Please see Figure 1 The diagram illustrates a flowchart of a method for pressing carbon composite material onto a pipe surface according to an embodiment of this application. The method includes the following steps:

[0033] Step 1: Recover reinforcing fibers and matrix materials from waste materials to form carbon composite materials. Cure the carbon composite materials on the pipe surface according to the preset heating and pressurization curve. Collect temperature and strain data at each detection point on the pipe surface at each time during each curing stage.

[0034] This embodiment takes ductile iron pipe as an example. Ductile iron pipe is usually used in water supply and drainage, gas transmission and other fields. The pipe has high requirements for wear resistance and corrosion resistance. By pressing a film on the surface of the pipe, its wear resistance and corrosion resistance can be enhanced and its service life can be extended.

[0035] First, the pipe surface is pretreated to enhance interfacial adhesion, specifically including:

[0036] Surface cleaning: Soak the pipe in acetone or anhydrous ethanol for 5 to 15 minutes, and wipe it with a lint-free cloth to remove oil, dust and other impurities from the surface of the pipe.

[0037] Sandblasting: The surface of the pipe is sandblasted with 80-120 mesh alumina sand to achieve a surface roughness of Ra1.6-3.2μm, which enhances the adhesion. The surface roughness can be measured using a portable surface roughness measuring instrument.

[0038] Coupling agent treatment: Dilute silane coupling agent KH-550 with ethanol to a concentration of 2%, apply it evenly to the surface of the sandblasted pipe, and dry it at room temperature for 1 hour to form an interface transition layer.

[0039] Secondly, waste materials containing carbon fiber reinforcement or carbon or polymer matrix composites are collected, such as waste from the aerospace, automotive, and wind power industries. The reinforcing fibers and matrix materials are recovered from these wastes to form carbon composites, which are composites with carbon fiber reinforcement and carbon or polymer matrix. In pipe surface lamination, carbon fiber reinforced resin matrix composites (CFRP) or carbon / carbon composites (C / C) are commonly used. For example, carbon fiber cloth is impregnated with epoxy or phenolic resin to form a prepreg, which is then hot-pressed onto the pipe surface to form a dense, functional coating. These materials not only possess the high strength and high modulus characteristics of carbon fiber but also achieve a strong bond with the pipe through the matrix material (such as resin or carbon-based materials), making them particularly suitable for applications in the intelligent manufacturing equipment industry requiring high temperature resistance, corrosion resistance, or lightweighting.

[0040] Ductile iron pipes reinforced with a carbon composite prepreg enhance pipe performance through the prepreg curing process. Prepreg is a semi-finished material made by pre-impregnating and curing fiber-reinforcing materials, such as carbon fiber, glass fiber, and aramid fiber, with a resin matrix, such as epoxy resin, polyester resin, or bismaleimide resin, to a semi-cured state. Therefore, the curing reaction of the resin is the primary process during compression molding. The curing reaction of thermosetting resins refers to the process by which linear, flowable resins undergo complex chemical reactions under curing agent and heating conditions to form a stable, infusible, and non-soluble solid resin structure.

[0041] In this embodiment, the carbon composite material uses carbon fiber cloth-epoxy resin prepreg, wherein the carbon fiber cloth provides high strength and wear resistance, and the epoxy resin has good adhesion and chemical corrosion resistance. The thickness of the prepreg is selected as 0.10-0.25 mm, and the carbon fiber volume fraction is selected as 50%-60%. As other embodiments, implementers can choose according to the actual situation.

[0042] The prepreg is cut using a CNC cutting machine according to the pipe size, and then laid up in a certain way. The layup width is W = πD + Δw, the layup length is L = L + 2Δl, D is the diameter of the pipe, L is the length of the pipe, Δw represents the width allowance (10mm in this embodiment), and Δl represents the length allowance (20mm in this embodiment), meaning there is a Δl allowance at both ends of the pipe.

[0043] Secondly, the layup can be divided into circumferential layers and axial layers. The circumferential layer refers to the fiber direction laid along the tangent direction of the pipe circumference (i.e., a ring direction perpendicular to the pipe axis), usually in a closed ring or spiral winding, mainly resisting the circumferential tensile stress caused by the internal pressure of the pipe, providing radial stiffness and burst resistance. The axial layer refers to the fiber direction laid along the pipe axis, at an angle of 0° or a small angle (±5°~15°), mainly bearing axial loads, providing longitudinal stiffness and tensile and compressive resistance. Laying is carried out by alternating circumferential and axial layers, with the specific layup steps as follows:

[0044] Transition layer laying: On the surface of ductile iron pipe, lay chopped carbon fiber felt or glass fiber surface felt, and use a rubber roller to compact it from the center to the edge to remove air bubbles. The edge extends 10mm beyond the pipe end to fill the micropores on the cast iron surface, uniformly transfer stress, and reduce the risk of interface peeling.

[0045] Circumferential layer laying: Lay the prepreg along the circumferential direction according to the cut size, align the edges with the pipe axis, and stagger the joints of adjacent circumferential layers by ≥50mm to avoid circumferential stress concentration.

[0046] Axial layer laying: Lay the prepreg along the axial direction of the pipe according to the cut size, covering the surface of the circumferential layer, with an overlap width of ≥15mm to ensure tight bonding between layers.

[0047] Alternating layering: The layers are laid alternately in the order of "circumferential layer, axial layer, circumferential layer, axial layer, ...", with a total of 8 to 12 layers.

[0048] After every 2-3 layers, compact the surface with a rubber roller at a pressure of 0.3-0.5 MPa, moving the roller from the center outwards to drive air bubbles to the edges. After laying the layers, trim any excess material at the ends, leaving a 10mm allowance for subsequent mold sealing.

[0049] A polytetrafluoroethylene (PTFE) film is covered on the outer surface of the pipe after the prepreg has been laid to prevent the prepreg from sticking to the mold and to facilitate demolding. Then, a two-piece steel mold is placed in, the mold seams are aligned, and it is fixed with bolts. The outside of the mold is wrapped with a heat insulation layer, such as asbestos cloth, and connected to heating and pressure devices.

[0050] Multiple embedded slots are made on the inner surface of the mold. The fiber Bragg grating sensor (FBG) is placed in the slots with high-temperature adhesive and the surface is covered with a transparent high-temperature resistant film, such as polyimide, to ensure that the sensor is flush with the mold surface and does not affect the mold compaction. A sealed wire hole is provided on the side of the mold, and the optical fiber is led out through the armored protective tube and connected to an external demodulator.

[0051] Taking carbon fiber cloth-epoxy resin prepreg as an example, the prepreg on the pipe surface is cured according to a preset temperature and pressure curve. The entire curing process is divided into four curing stages, as follows:

[0052] The first curing stage is the low-temperature degassing stage: the temperature is increased from room temperature to T1 at a rate of ΔT, the pressure is maintained at P1, and the temperature is maintained for X1 hours to remove volatile components; where ΔT is 5℃ / min, T1 is 60℃, P1 is 0.5MPa, and X1 is 0.25 hours, or 15 minutes.

[0053] The second curing stage is the resin flow and impregnation stage: the temperature is increased from T1 to T2, the pressure is increased to P2, and the temperature is maintained for X2 hours to allow the resin to melt and flow, impregnate the fiber and remove microbubbles; where T2 is 80℃, P2 is 2MPa, and X2 is 0.5 hours, or 30 minutes.

[0054] The third curing stage is the curing and cross-linking stage: the temperature is increased from T2 to T3, the pressure is increased to P3, and the temperature is maintained for X3 hours to allow the curing agent to fully react and form a three-dimensional cross-linked structure; where T3 is 120℃, P3 is 5, and X3 is 2 hours.

[0055] The fourth curing stage is the cooling and depressurization stage: turn off the heating, allow it to cool naturally to below T4, and slowly release the pressure at a rate ≤1MPa / min, where T4 is 50℃;

[0056] Each fiber optic grating sensor in the embedded slot is recorded as a detection point. The temperature and strain data of each detection point on the surface of the pipe at different times during each curing stage are collected in real time by the temperature and strain sensors built into the FBG.

[0057] In this embodiment, embedded grooves are formed at 45° intervals along the circumference of the inner surface of the mold and at 100mm intervals along the axial direction of the mold. The embedded grooves are 2mm deep and 3mm wide. The sampling frequency of the sensor is 10Hz. As other implementation methods, the implementer can set them according to the actual situation.

[0058] Thus, the temperature and strain data of each detection point at each time point during each curing stage are obtained.

[0059] Step 2: Based on the temperature data at each time point, calculate the degree of curing at each detection point at each time point under each curing stage using the Arrhenius equation, and calculate the resin viscosity at each detection point at each time point under each curing stage using the degree of curing and temperature data.

[0060] During the molding process, uneven heating of the pipe surface can lead to low-temperature spots at the edges and localized overheating spots, causing inconsistent resin curing rates and resulting in localized over-curing or under-curing. When the localized temperature of the pipe surface is too high, causing the curing rate to increase too rapidly, the resin viscosity rises rapidly, inhibiting flow. In this case, the pressure needs to be increased to overcome the viscosity resistance, promote compaction, and avoid localized over-curing. Conversely, when the localized temperature of the pipe surface is too low, and the curing rate is lower than expected, the pressure can be appropriately reduced to prevent uneven fiber distribution caused by excessive resin flow.

[0061] During the pressure curing process of pipes using a preset temperature and pressure curve, the curing of thermosetting resin is a process of forming a three-dimensional network structure through intermolecular cross-linking reactions, and its reaction rate is directly proportional to the concentration of uncured resin. Based on the Arrhenius equation, the relationship between the curing reaction rate and temperature can be obtained, and the calculation process for the degree of curing can be derived.

[0062] The reaction rate constant k is described by the Arrhenius equation:

[0063]

[0064] Where k is the reaction rate constant, A is the frequency factor reflecting the collision frequency of resin molecules, and E... a Let E be the activation energy of the reaction, i.e., the minimum energy required for the resin curing reaction; R be the gas constant, a fixed value taken as 8.314; and T be the temperature data. a A and B are calculated using the Kissinger method. The Arrhenius equation and the Kissinger method are well-known techniques and will not be elaborated here.

[0065] For most thermosetting resins, the curing mechanism is described using an autocatalytic reaction model, as follows:

[0066]

[0067] in, α is the curing reaction rate, k is the reaction rate constant, and α is the degree of curing.

[0068] Therefore, it can be deduced that:

[0069]

[0070] Integrating both sides, we get: ln(1-α)=-k×t. Therefore, the formula for calculating the degree of curing α can be derived as:

[0071]

[0072] Where t is the curing time, which is the time interval from the start of heating to time t, and exp[] and exp() are both exponential functions with the natural constant as the base.

[0073] While the degree of curing reflects the extent of resin crosslinking, it cannot directly characterize the dynamic changes in the resin's physical state. Resin viscosity is a key parameter affecting its flow, molding, and compaction, while the degree of curing only reflects the progress of the chemical reaction and does not relate to the influence of molecular chain entanglement and crosslinking network formation on viscous behavior. Directly controlling pressure based on the degree of curing easily overlooks the nonlinear response of viscosity to temperature and pressure. For example, while increasing temperature accelerates curing, it may temporarily reduce viscosity; excessive curing can lead to a sudden increase in viscosity, hindering flow and resulting in large errors in flow compaction simulations and lag in parameter adjustment.

[0074] Based on the above analysis, resin viscosity significantly affects resin flow. During the entire curing process of thermosetting resins, it is difficult to directly measure resin viscosity. However, by using the viscosity model for 3501-6 epoxy resin provided in publicly available data regarding the relationship between resin viscosity, degree of cure, and temperature, the resin viscosity can be calculated to reflect the changes in resin viscosity during the curing process. Specifically:

[0075]

[0076] Where η is the resin viscosity, reflecting the resin flow resistance, and η0 is the initial viscosity of the resin at room temperature, measured by a viscometer. E a R is the activation energy of the reaction, T is the gas constant, α is the degree of curing, β is the curing sensitivity coefficient, and α is a constant, which is the influence factor of the degree of curing on viscosity, reflecting the viscosity growth rate caused by the crosslinking reaction.

[0077] It should be noted that the viscosity model of epoxy resin is a known technology; the initial viscosity η0 of the resin at room temperature is measured by a viscometer, and the curing sensitivity coefficient β is obtained by performing a resin curing experiment under laboratory conditions, measuring the resin viscosity and its corresponding degree of curing in real time, and fitting the resin viscosity and degree of curing. In this embodiment, the curing sensitivity coefficient β for epoxy resin 3501-6 is 14.1 according to the reference. In other implementation methods, the implementer can set the value according to the actual resin used.

[0078] According to the viscosity model above, temperature and resin viscosity are negatively correlated, and the essence of resin viscosity is the resistance to molecular chain segment movement. Secondly, the degree of curing is positively correlated with viscosity. When the degree of curing increases, resin molecules gradually form a three-dimensional network from a linear structure through cross-linking reactions, hindering chain segment movement and causing viscosity to increase exponentially.

[0079] Thus, the resin viscosity is obtained.

[0080] Step 3: By analyzing the deviation of strain data at different detection points at each time point during each curing stage, and combining it with the resin viscosity, determine the adjusted pressure at each time point during each curing stage. Based on the real-time adjusted pressure, perform curing and pressing on the carbon composite material on the pipe surface, and evaluate the curing and pressing effect.

[0081] Secondly, resin viscosity reflects the curing process, while strain data reflects the compaction state. The compaction state refers to the degree of densification and structural stability of the prepreg under pressure during the composite material curing process. Pressure can affect the penetration and filling of resin between fibers by changing resin viscosity and flow resistance, thus determining the mechanical properties of the cured material.

[0082] During the curing process, pressure promotes resin flow, fills the gaps between fibers, and achieves compaction and densification. However, insufficient pressure can lead to under-compaction in the low-temperature edge zones due to high resin viscosity and high flow resistance, posing a risk of under-curing. Conversely, excessive or uneven pressure can create localized hot spots. These hot spots may experience rapid resin curing and a sudden increase in viscosity, causing flow stagnation and resulting in over-curing or fiber defects. By adjusting the pressure, it is possible to ensure uniform densification of the material during curing, eliminating localized defects caused by uneven temperature or differences in flow resistance.

[0083] When increased viscosity leads to greater flow resistance, increasing pressure pushes the resin towards the lower-temperature edges, enhancing heat conduction and mass exchange in that area. The resin carries heat during flow, mitigating under-curing at low temperatures. Conversely, when local hot spots experience a sudden increase in viscosity due to rapid curing, dynamic pressure matching can prevent over-compaction and avoid over-curing caused by stagnant flow exacerbating local overheating. This dynamic pressure compensation ensures that the resin flow resistance and compaction level are more consistent between the mold edges and the center, indirectly balancing the impact of uneven temperature distribution on the curing rate and eliminating over-curing or under-curing defects caused by temperature differences.

[0084] Based on the above analysis, the pressure is adjusted using resin viscosity and strain data. The flowchart illustrating the method for obtaining the adjusted pressure at each time point during each curing stage, as provided in this embodiment, is shown below. Figure 2 As shown, it specifically includes:

[0085] For each curing stage, the difference between the preset target strain value and the strain data at each detection point at each time point is recorded as the strain deviation;

[0086] In this embodiment, the preset target strain value ranges from 0.008 to 0.025. In this embodiment, the preset target strain value is 0.01. As other implementation methods, the implementer can set it according to the actual situation. Secondly, the difference between the preset target strain value and the strain data of each detection point at each time is recorded as the relative deviation.

[0087] Calculate the average value of the product of resin viscosity, strain deviation, and preset adjustment coefficient at all detection points at each time point;

[0088] It should be noted that the preset adjustment coefficient ranges from 0.0001 to 1. If the preset adjustment coefficient is large, even a small change in resin viscosity or strain deviation will cause a large adjustment in pressure. Conversely, the change in viscosity and strain deviation has a relatively small impact on pressure. In this embodiment, the preset adjustment coefficient is set to 0.1.

[0089] The initial pressure is recorded as the pressure at each moment of each curing stage in the preset heating and pressurization curve.

[0090] The sum of the initial pressure and the average value is used as the adjusted pressure at each time step in each curing stage;

[0091] In this embodiment, the formula for calculating the adjusted pressure at each time step in each curing stage is as follows:

[0092]

[0093] Among them, P m,t The pressure adjusted at time t for the m-th curing stage. Let be the initial pressure of the m-th curing stage at time t. η is the preset adjustment coefficient. m,i,t Let ε be the resin viscosity at time t at the i-th detection point during the m-th curing stage. set ε is the preset strain value. m,i,t Let N be the strain data of the i-th detection point at time t during the m-th curing stage, and N be the total number of detection points.

[0094] It should be noted that during the curing process, the viscosity of the resin changes with factors such as temperature and degree of curing. Higher viscosity makes resin flow more difficult, requiring greater pressure to propel it and compact it. When the strain deviation is greater than zero, it indicates insufficient compaction at that test point, necessitating increased pressure to further deform the material and achieve the target strain. Conversely, a deviation below zero indicates possible over-compaction at that test point, requiring a reduction in pressure. Therefore, by adjusting the pressure to compensate for changes in resin flow resistance caused by temperature and degree of curing during the curing process, uniform material compaction is ensured. This effectively avoids problems such as under-curing, over-curing, and uneven fiber distribution caused by insufficient or excessive pressure, thereby improving the mechanical properties and quality of the cured material.

[0095] After curing under the adjusted pressure, the mold clamps are loosened for demolding. The pipe is then placed in an oven and kept at 120°C for 2 hours for secondary curing, which further improves the degree of crosslinking and reduces the water absorption rate.

[0096] Furthermore, by setting up three control groups, the pressure adjustment method of this embodiment was compared with the control groups to evaluate the effect of the pressure adjustment method of this embodiment on pipe curing. Specifically:

[0097] Control group 1: The temperature was increased from room temperature to 60°C, and the pressure was maintained at 0.5 MPa for 15 minutes; the temperature was increased to 80°C, the pressure was increased to 2 MPa, and the temperature was maintained for 30 minutes; the temperature was increased to 120°C, the pressure was increased to 5 MPa, and the temperature was maintained for 2 hours.

[0098] Control group 2: The temperature was increased from room temperature to 60°C, and the pressure was maintained at 0.5 MPa for 15 minutes; the temperature was increased to 80°C, and the pressure was increased to 2.5 MPa for 30 minutes; the temperature was increased to 120°C, and the pressure was increased to 8 MPa for 2 hours.

[0099] Control group 3: The temperature was increased from room temperature to 60°C, and the pressure was maintained at 0.5 MPa for 15 minutes; the temperature was increased to 80°C, and the pressure was increased to 3 MPa for 30 minutes; the temperature was increased to 120°C, and the pressure was increased to 10 MPa for 2 hours.

[0100] The differential scanning calorimetry (DSC) method was used to test the composite material. Multiple samples were cut from different positions after the film was pressed. The samples were placed in the differential scanning calorimeter and the curve of heat flow changing with temperature was recorded. The curve was analyzed by software and the degree of curing of each sample was calculated. The range of the degree of curing of all samples was taken as the curing uniformity. Therefore, the curing uniformity corresponding to this embodiment, control group 1, control group 2 and control group 3 can be obtained.

[0101] It should be noted that differential scanning calorimetry is a well-known technique and will not be described in detail here; the smaller the curing uniformity, the smaller the difference in curing degree at different locations, and the better the curing uniformity, and vice versa.

[0102] The porosity is calculated by measuring the dry weight and saturated water absorption weight of the material by gravimetric method. Therefore, the porosity corresponding to this embodiment, control group 1, control group 2 and control group 3 can be obtained.

[0103] It should be noted that the calculation process for porosity is a well-known technique and will not be elaborated upon here; the formula for calculating porosity is as follows:

[0104]

[0105] Among them, G wet For saturated water absorption weight, G dry Let ρ be the dry weight of the material, and ρ be the density of water.

[0106] The interlaminar shear strength of the material is obtained by testing the maximum interlaminar shear stress that the material can withstand according to the ASTM D3846 standard. Therefore, the interlaminar shear strengths corresponding to this embodiment, control group 1, control group 2 and control group 3 can be obtained.

[0107] The deviation between the outer diameter of the pipe after molding and the nominal size is measured using a high-precision caliper or micrometer to obtain the outer diameter accuracy.

[0108] It should be noted that the measurement process for interlaminar shear strength and outer diameter dimensional accuracy is a well-known technique and will not be described in detail here.

[0109] Table 1 shows a comparison of the pipe curing effects provided in this embodiment.

[0110] Table 1 Comparison of Curing Effects

[0111]

[0112] As shown in Table 1, when the pressure is adjusted according to the method of this embodiment during the curing process, it can dynamically adapt to changes in resin viscosity and compaction requirements, effectively promoting uniform curing. Higher interlaminar shear strength indicates tight interlaminar bonding, low porosity reflects fewer internal defects, and high outer diameter accuracy indicates precise control over pipe forming, which enhances the performance of the pipe after molding.

[0113] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0114] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application, without departing from the content of the technical solution of this application, shall fall within the protection scope of the technical solution of this application.

Claims

1. A method of carbon composite film pressing on a pipe surface, characterized by, The method comprises the following steps: Recovering the reinforcing fibers and the matrix material from the waste material to form a carbon composite material, curing the carbon composite material on the surface of the pipe according to a preset temperature and pressure rising curve, collecting temperature data and strain data of each detection point at each time point in each curing stage on the surface of the pipe; Based on the temperature data at each time point, the curing degree of each detection point at each time point in each curing stage is calculated through the Arrhenius equation, and the resin viscosity of each detection point at each time point in each curing stage is calculated through the curing degree and the temperature data; The adjusted pressure of each curing stage at each time point is determined by the deviation of the strain data of different detection points at each time point in each curing stage, combined with the resin viscosity, the curing and pressing of the carbon composite material on the surface of the pipe is carried out based on the real-time adjusted pressure, and the effect of the curing and pressing is evaluated; The determination of the adjusted pressure of each curing stage at each time point comprises: For each curing stage, the difference between the preset target strain value and the strain data of each detection point at each time point is recorded as the strain deviation; The average value of the product of the resin viscosity, the strain deviation and the preset adjustment coefficient of all detection points at each time point is calculated; According to the pressure of each curing stage at each time point in the preset temperature and pressure rising curve, the initial pressure is recorded; The adjusted pressure is the fusion result of the initial pressure and the average value; The strain deviation is the difference between the preset target strain value and the strain data of each detection point at each time point in each curing stage; The fusion process is: calculating the sum of the initial pressure and the average value as the adjusted pressure.

2. A method of carbon composite press molding of a pipe surface according to claim 1, wherein The preset temperature and pressure rising curve is divided into four curing stages, which specifically comprises: First curing stage: heating from room temperature to at a heating rate of , pressure is kept , holding time is hours; Second curing stage: temperature from up to , pressure increased to , holding time hours; Third curing stage: temperature from up to , pressure up to , holding time hours; Fourth curing stage: turn off heat, cool naturally to The following, and slowly release the pressure, wherein, , , , , , , , , , , are preset values, and , , .

3. A method of carbon composite press molding of a pipe surface according to claim 1, wherein The carbon composite material is a carbon fiber cloth-epoxy resin prepreg formed by taking carbon fiber cloth as the reinforcing body and taking epoxy resin as the matrix.

4. A method of carbon composite press molding of a pipe surface according to claim 1, wherein Degree of cure The calculation formula is: wherein, is a frequency factor, is a reaction activation energy, is a gas constant, is temperature data, is a curing time, which is a time interval between a time point when heating is started and a time point when the temperature reaches a predetermined temperature, is an exponential function with a natural constant as a base number.

5. A method of carbon composite press forming of a pipe surface according to claim 4, wherein The reaction activation energy and the frequency factor are calculated by the Kissinger method.

6. A method of press-felming a carbon composite material on a surface of a pipe material as set forth in claim 5, wherein Resin viscosity The calculation formula is: wherein, is the initial viscosity of the resin at normal temperature, is the reaction activation energy, is the gas constant, is the temperature data, is the curing degree, is the curing sensitivity coefficient, is a constant, is an exponential function with the natural constant as the base.

7. A method of carbon composite press forming of a pipe surface according to claim 1, wherein The evaluation of the curing and pressing effect comprises: measuring the curing uniformity by differential scanning calorimetry, measuring the porosity by weight method, measuring the interlaminar shear strength by testing the maximum shear stress that the interlaminar of the carbon composite material can withstand, and measuring the outer diameter size accuracy of the pipe by high-precision caliper.

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