A drying method for carbon fiber prepreg

Abstract

The present invention provides a method for drying carbon fiber prepregs, which includes the following steps: feeding the carbon fiber substrate after impregnation into a horizontal oven for drying and curing; a feed port and a discharge port are respectively provided on both sides of the horizontal oven; a shielding tube with a heating function is provided at a position adjacent to the feed port and a position adjacent to the discharge port; a temperature sensor, an electric heating tube and a control component are provided inside the horizontal oven; the shielding tube, the temperature sensor and the electric heating tube are all electrically connected to the control component; the control component includes a PID controller, a PID parameter adjustment controller and an environmental parameter prediction controller. The present invention cooperates with the precise temperature control of the shielding tube and the control component to synergistically improve the thermal efficiency and temperature control level, so that the hot air flow field inside the horizontal oven is evenly distributed, thereby improving the uniformity of impregnation and curing of the carbon fiber prepreg.

Description

Technical Field

[0001] The invention relates to a method for producing carbon fiber prepreg, in particular to a method for drying carbon fiber prepreg, and belongs to the technical field of carbon fiber manufacturing. Background Art

[0002] Carbon fiber prepreg is made by combining carbon fiber yarn, a thermosetting resin matrix, and release paper through processes such as pretreatment, impregnation, drying, and lamination. During the preparation process, carbon fiber prepreg requires drying to remove the solvent and solidify the resin. This is usually accomplished in a drying device, typically a hot air oven. Traditional hot air ovens use electric heating tubes or other heating elements to heat air to a certain temperature. A fan then generates hot air, which is evenly blown toward the material through an air duct and outlet to dry it.

[0003] In the carbon fiber prepreg production line, commonly used hot air ovens include horizontal, furnace and box types. The horizontal oven has a feed port and a discharge port on both sides, and is equipped with a conveyor belt, which can realize the continuous production of carbon fiber prepreg and improve the production efficiency of carbon fiber prepreg. Therefore, it is widely used.

[0004] However, the feed port and discharge port of the horizontal oven are both connected to the external environment. The connected parts will destroy the hot air flow field distribution inside the horizontal oven, increase the difficulty of temperature control inside the horizontal oven, and thus increase the uneven distribution of the hot air flow field inside the horizontal oven, resulting in differences in heat transfer of the carbon fiber prepreg after impregnation in different parts of the horizontal oven, and the heat accumulation in different parts of the carbon fiber prepreg is not exactly the same. At this time, if the temperature and air volume control of the hot air oven fluctuate and deviate, it will easily lead to different degrees of resin curing in different parts of the carbon fiber prepreg. The resin in the overheated area will be over-cured, while the resin in the area with insufficient heat will not be fully cured. All of these will lead to reduced mechanical properties of the carbon fiber prepreg and defects such as fracture and deformation. Summary of the Invention

[0005] Based on the above background, the object of the present invention is to provide a method for drying carbon fiber prepreg to improve the uniformity of impregnation and curing.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for drying carbon fiber prepreg, the method comprising the following steps:

[0008] The carbon fiber substrate after impregnation is sent into a horizontal oven for drying and curing; a feed port and a discharge port are respectively provided on both sides of the horizontal oven, and a shielding tube with a heating function is provided at a position adjacent to the feed port and a position adjacent to the discharge port of the horizontal oven. A temperature sensor, an electric heating tube and a control component are provided inside the horizontal oven, and the shielding tube, the temperature sensor and the electric heating tube are all electrically connected to the control component, and the control component includes a PID controller, a PID parameter adjustment controller and an environmental parameter prediction controller.

[0009] Preferably, the mathematical expression of the output control quantity of the PID controller is:

[0010] T con =aT out +(1-a)ΔT t ;

[0011] Where: T con is the temperature output control quantity of the PID controller, T out is the temperature feedback output control quantity of the PID controller, ΔT t is the predicted temperature change, a is the temperature feedback control weight parameter, 0 <a<1。

[0012] Preferably, the temperature feedback output control quantity of the PID controller is determined by a proportional parameter, an integral parameter, and a differential parameter, and the proportional parameter, the integral parameter, and the differential parameter are determined by the output parameters of the PID parameter adjustment controller.

[0013] Preferably, the PID parameter adjustment controller is used to run a PID parameter adjustment model, and the PID parameter adjustment model is a neural network model consisting of an input layer, a hidden layer and an output layer.

[0014] Preferably, the input layer includes a first node corresponding to the temperature value in the hot air oven collected by the temperature sensor, the hidden layer includes multiple second nodes, and the output layer includes three third nodes, which correspond to the proportional parameter, integral parameter and differential parameter respectively. The value of the output layer serves as the output parameter of the PID parameter adjustment controller.

[0015] Preferably, the environmental parameter prediction controller is used to run a temperature parameter prediction model, and the output parameter of the environmental parameter prediction controller is the predicted temperature change. Through the environmental parameter prediction controller, a feedforward control method is introduced and combined with the existing feedback control method of the PID controller.

[0016] Preferably, the mathematical expression of the temperature parameter prediction model is:

[0017] ΔT t =α1ΔT t-1+α2ΔT t-2 +ε t +β1ε t-1 +β2ε t-2 +β3ε t-3 +γH t ;

[0018] Where: ΔT t is the predicted temperature change; α1 and α2 are AR coefficients used to express ΔT t and its timing lag value ΔT t-1 and ΔT t-2 The relationship between t is a random disturbance term, which is used to represent other unmodeled factors affecting the temperature change; β1, β2 and β3 are MA coefficients, which are used to represent ΔT t and the random perturbation term ε t The time lag value ε t-1 , ε t-2 , ε t-3 relationship; H t is the temperature of the shielding tube; γ is H t The regression coefficient of H t ΔT t degree of impact.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The present invention provides a method for drying carbon fiber prepregs. Shielding tubes with a heating function are provided at the feed port and the discharge port of a horizontal oven to effectively compensate for the heat loss caused by the openings and improve the thermal efficiency of the oven. A PID controller is used to accurately control the internal temperature of the oven. The PID parameter adjustment controller dynamically optimizes the PID parameters according to changes in the drying process to improve the temperature control effect. An environmental parameter prediction controller is used to increase feedforward control to predict and compensate for the effects of various disturbances in advance. The precise temperature control of the shielding tube and the control components are coordinated to synergistically improve the thermal efficiency and temperature control level, so that the hot air flow field inside the horizontal oven is evenly distributed, thereby improving the uniformity of the impregnation and curing of the carbon fiber prepregs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0022] Figure 1 It is a structural schematic diagram of the hot air drying oven in the present invention.

[0023] In the figure: 1. Horizontal oven; 2. Feed inlet; 3. Discharge outlet; 4. Shielding tube; 5. Temperature sensor; 6. Electric heating tube; 7. Control components. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the scope of protection of the present invention.

[0025] In the present invention, unless otherwise specified, all parts and percentages are by weight. The equipment and raw materials used are commercially available or commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are all universal standard parts or components known to those skilled in the art. Their structures and principles are known to those skilled in the art through technical manuals or routine experimental methods.

[0026] The following detailed description of the embodiments of the present invention is made in conjunction with the accompanying drawings. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, one or more embodiments may be implemented by those skilled in the art without these specific details.

[0027] An embodiment of the present invention discloses a method for drying carbon fiber prepreg, which includes the following steps: feeding the carbon fiber substrate after impregnation into a horizontal oven for drying and curing. Particularly, a feed port and a discharge port are provided on both sides of the horizontal oven, and a belt conveyor is provided inside the horizontal oven between the feed port and the discharge port. The belt conveyor is a prior art and is used to transport carbon fiber prepreg, and the specific structure will not be described in detail. The horizontal oven is provided with a shielding tube with a heating function at a position adjacent to the feed port and a position adjacent to the discharge port. A temperature sensor, an electric heating tube and a control component are provided inside the horizontal oven, and the shielding tube, the temperature sensor and the electric heating tube are all electrically connected to the control component.

[0028] The shielding tube is an electric heating tube with a similar structure to an electric heating tube, but with smaller dimensions. It acts as a heat shield, reducing heat loss from the inlet and outlet, and providing compensatory heating for the carbon fiber prepreg passing through it. A gap exists between the bottom of the shielding tube and the surface of the horizontal oven's belt conveyor to accommodate the carbon fiber prepreg, preventing interference with material transportation.

[0029] There are six temperature sensors, four of which are evenly spaced above the belt conveyor of the horizontal oven, and the other two are located above the belt conveyor near the feed port and the discharge port, respectively. The temperature sensors are all infrared temperature sensors, which can more accurately measure the temperature of the carbon fiber prepreg carried on the surface of the belt conveyor, as well as the temperature of the carbon fiber prepreg at the feed port and the discharge port.

[0030] Although adding the shielding tube improves the heat shielding effect and reduces heat loss, it also increases the complexity of temperature control inside the horizontal oven. Therefore, the control components of the horizontal oven have been adjusted accordingly.

[0031] The control components include PID controller, PID parameter adjustment controller and environmental parameter prediction controller. The mathematical expression of the output control quantity of the PID controller is:

[0032] T con =aT out +(1-a)ΔT t ;

[0033] Where: T con is the temperature output control quantity of the PID controller, T out is the temperature feedback output control quantity of the PID controller, ΔT t is the predicted temperature change, a is the temperature feedback control weight parameter, 0 <a<1。

[0034] Among them, the temperature feedback output control quantity of the PID controller is determined by the proportional parameter, integral parameter, and differential parameter, and the proportional parameter, integral parameter, and differential parameter are determined by the output parameters of the PID parameter adjustment controller.

[0035] The PID parameter adjustment controller is used to operate a PID parameter adjustment model. The PID parameter adjustment model is a neural network model consisting of an input layer, a hidden layer, and an output layer. The input layer includes a first node corresponding to the temperature value inside the hot air oven collected by a temperature sensor. The hidden layer includes multiple second nodes. The output layer includes three third nodes, each corresponding to a proportional parameter, an integral parameter, and a differential parameter. The value of the output layer serves as the output parameter of the PID parameter adjustment controller. The number of second nodes is greater than the number of first nodes and the number of third nodes, respectively, and is set to 6 in this embodiment. The neural network model is essentially a three-layer feedforward neural network model. The connection weights between each layer are optimized by collecting data and performing model training.

[0036] The environmental parameter prediction controller is used to run the temperature parameter prediction model. The output parameter of the environmental parameter prediction controller is the predicted temperature change. Through the environmental parameter prediction controller, the feedforward control method is introduced and combined with the existing feedback control method of the PID controller.

[0037] The mathematical expression of the temperature parameter prediction model is:

[0038] ΔT t =α1ΔT t-1 +α2ΔT t-2 +ε t +β1ε t-1 +β2ε t-2 +β3ε t-3 +γH t ;

[0039] Where: ΔT t is the predicted temperature change; α1 and α2 are AR coefficients used to express ΔT t and its timing lag value ΔT t-1 and ΔT t-2 The relationship between t is a random disturbance term, which is used to represent other unmodeled factors affecting the temperature change; β1, β2 and β3 are MA coefficients, which are used to represent ΔT t and the random perturbation term ε t The time lag value ε t-1 , ε t-2 , ε t-3 relationship; H t is the temperature of the shielding tube; γ is H t The regression coefficient of H t ΔT t The temperature parameter prediction model establishes the relationship between the shielding tube temperature value, the time factor of the temperature change, and other factors and the predicted temperature change. It has a certain feedforward prediction capability. Therefore, when the external environment changes and causes air disturbances, the PID controller can respond to temperature fluctuations more quickly. A certain amount of feedforward control is included in the temperature control.

[0040] The carbon fiber prepreg drying method of the present invention has the following advantages compared with the prior art technical solution of continuously drying carbon fiber prepreg using a traditional horizontal oven or a vertical oven:

[0041] By setting shielding tubes with heating function at the feed inlet and discharge port of the horizontal oven, the heat loss caused by the opening is effectively compensated and the thermal efficiency of the oven is improved;

[0042] The PID controller is used to accurately control the internal temperature of the oven. The PID parameter adjustment controller dynamically optimizes the PID parameters according to the changes in the drying process to improve the temperature control effect. The environmental parameter prediction controller is used to increase feedforward control to predict and compensate for the impact of various disturbances in advance.

[0043] The precise temperature control of the shielding tube and the control components synergistically improves thermal efficiency and temperature control level, making the hot air flow field inside the horizontal oven evenly distributed, thereby improving the uniformity of the impregnation and curing of the carbon fiber prepreg.

[0044] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for drying carbon fiber prepreg, characterized in that: The method comprises the following steps: The carbon fiber substrate after the resin impregnation is sent to a horizontal oven for drying and curing, and the drying temperature is set to 95-100 degrees Celsius; a feed port and a discharge port are respectively provided on both sides of the horizontal oven, and a shielding tube with a heating function is provided at a position adjacent to the feed port and a position adjacent to the discharge port of the horizontal oven. A temperature sensor, an electric heating tube and a control component are provided inside the horizontal oven, and the shielding tube, the temperature sensor and the electric heating tube are all electrically connected to the control component, and the control component includes a PID controller, a PID parameter adjustment controller and an environmental parameter prediction controller; The mathematical expression of the output control quantity of the PID controller is: T con =aT out +(1-a) ΔT t ; Where: T con is the temperature output control quantity of the PID controller, T out is the temperature feedback output control quantity of the PID controller, ΔT t is the predicted temperature change, a is the temperature feedback control weight parameter, 0 <a<1; The temperature feedback output control quantity of the PID controller is determined by a proportional parameter, an integral parameter, and a differential parameter, and the proportional parameter, the integral parameter, and the differential parameter are determined by the output parameters of the PID parameter adjustment controller; The PID parameter adjustment controller is used to run a PID parameter adjustment model, which is a neural network model consisting of an input layer, a hidden layer, and an output layer; The input layer includes a first node corresponding to the temperature value in the hot air drying oven collected by the temperature sensor, the hidden layer includes multiple second nodes, and the output layer includes three third nodes, which correspond to the proportional parameter, the integral parameter, and the differential parameter respectively. The value of the output layer is used as the output parameter of the PID parameter adjustment controller; The environmental parameter prediction controller is used to run the temperature parameter prediction model, and the output parameter of the environmental parameter prediction controller is the predicted temperature change; The mathematical expression of the temperature parameter prediction model is: ΔT t =α1ΔT t−1 +α2ΔT t−2 +e t +β1ε t−1 +β2ε t−2 +β3ε t−3 +γH t ; Where: ΔT t is the predicted temperature change; α1 and α2 are AR coefficients used to express ΔT t and its timing lag value ΔT t−1 and ΔT t−2 The relationship between t is a random disturbance term, which is used to represent other unmodeled factors affecting the temperature change; β1, β2 and β3 are MA coefficients, which are used to represent ΔT t and the random perturbation term ε t The time lag value ε t−1 , ε t−2 , ε t−3 relationship; H t is the temperature of the shielding tube; γ is H t The regression coefficient of H t ΔT t degree of impact.

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