Vacuum-assisted preforming device for pultrusion processes of composite materials

Abstract

A vacuum-assisted preforming device for pultrusion processes of composite materials, characterized in that it comprises a fiber guide plate for the layer-by-layer passage of fiber bundles, an impregnation tray for receiving resin, resin press rollers for squeezing out excess resin, and a vacuum-assisted preforming template, which are arranged sequentially in the pultrusion direction; wherein the vacuum-assisted preforming template has a preforming template cavity, a vacuum cavity is provided in a section of the preforming template cavity of the vacuum-assisted preforming template, a vacuum extraction opening is formed above the vacuum cavity, a semipermeable membrane is arranged at the vacuum extraction opening which allows the passage of gas but blocks the passage of resin, and the vacuum extraction opening is externally connected to a vacuum generating device.

Description

Technical area

[0001] The present utility model relates to the technical field of pultrusion forming of composite materials and refers in particular to a vacuum-assisted preforming device for pultrusion processes of composite materials. State of the art

[0002] With its key advantages such as continuous production, high automation, excellent product straightness, and high quality stability, the pultrusion process has become one of the main methods for manufacturing high-performance composite materials and is widely used in numerous key fields. For example, in the wind energy industry, pultruded main support sheet produced by this process has become the preferred material for the main support beams of large rotor blades. It significantly improves the bending stiffness, structural efficiency, and fatigue life of the blades while considerably reducing manufacturing costs. In the aerospace industry, pultruded, lightweight, and high-strength beam and girder structural components contribute to weight reduction and increased aircraft efficiency.In the rail transport industry, pultruded profiles are used to manufacture lightweight body components and interior parts. Furthermore, pultruded composite materials also demonstrate great application potential and high value in areas such as new energy vehicles (e.g., structural reinforcement beams for battery packs), high-quality sporting goods (e.g., carbon fiber racket frames), shipbuilding, and component reinforcement (e.g., CFRP rods).

[0003] Currently, pultrusion with an impregnation tank is the predominant method in this field. Its basic process is typically as follows: Reinforcing fiber bundles (for example, carbon fiber or glass fiber bundles) are fed into the impregnation tank for resin impregnation after combing through a fiber divider plate. They are then pulled by a traction mechanism, pass successively through a resin press roller and a pre-forming unit, and finally enter a heated curing die to complete the resin curing and forming process. The pre-forming unit (also called a pre-forming template), located between the impregnation and curing stages, plays a crucial role in this process.Their main task is to squeeze out excess resin and trapped air bubbles from the fiber bundles, and to provisionally integrate and compact the slightly loose fiber bundles after impregnation until they approximate a cross-sectional shape that corresponds to the final product shape. In this way, a preform with a more stable structure and more precise geometric dimensions is provided for the subsequent heat curing phase.

[0004] Nevertheless, the existing conventional pre-forming equipment and processes exhibit the following problems: 1. Insufficient efficiency in air bubble removal: Existing preforming equipment relies primarily on mechanical pressure to remove air bubbles and excess resin. While this method is effective to some extent against larger air bubbles, it is hardly effective at removing microscopic (micrometer-sized) air bubbles and dissolved gases both within the resin and between fiber bundle layers or within the fiber bundles themselves. These remaining micropores become stress concentration points and potential sources of failure during the subsequent curing phase. They are among the main factors leading to high void content in the final product, thereby significantly impairing the shear strength between layers, compressive strength, fatigue life, and other key performance characteristics and the long-term durability of the composites. 2. Difficulties in controlling the resin quantity and distribution uniformity: The amount of resin in the fiber bundles upon entering the preforming die is usually controlled indirectly by adjusting the pressure of the resin press roller. However, due to differences in the distribution of the fiber bundles across the cross-section, uneven tension, and the rheological properties of the resin itself (e.g., thixotropy), this pressing method can hardly ensure that excess resin is removed uniformly and consistently across the entire cross-section and along the longitudinal direction of the fiber bundles. This directly leads to the occurrence of both areas with excess resin ("resin-rich areas") and areas with insufficient resin ("resin-poor areas") in the preform.This not only causes an uneven stress distribution inside the product, but can also cause shrinkage deformation during curing, thus affecting the dimensional stability and the uniformity of the product's mechanical properties. 3. Low impregnation efficiency with high-viscosity resin systems: With the increasing demands on the performance of composite materials, high-performance resin systems (e.g., high-toughness epoxy resins, bismaleimide resins, cyanate resins) are widely used due to their excellent mechanical properties and temperature resistance. However, these resins often exhibit high viscosity at room temperature or lower preheating temperatures. Conventional impregnation and preforming processes rely primarily on the resin's flowability and the limited compression effect. With high-viscosity resins, the resin's resistance to penetration within the fiber bundles increases, and the impregnation rate slows considerably. Even with extended impregnation time or additional pressure during the preforming phase, complete and thorough fiber impregnation is difficult to achieve.Instead, "dry spots" or micropores that are not filled with resin are more likely to form. This ultimately significantly impairs the overall reliability and quality of the product. 4. Lack of Means for Active Resin and Gas Control: The current pre-forming process is essentially passive and depends on the impregnation state of the fiber bundles themselves and the subsequent pressing. With incomplete impregnation or a large number of air bubbles, the system itself lacks an active and efficient physical mechanism to actively control the resin and thus thoroughly fill the interfiber spaces or effectively draw gas from deeper layers.

[0005] The existence of these technical bottlenecks has become a key factor limiting the development of high-performance and more reliable pultruded composite products, as well as the improvement of production efficiency. Therefore, a pressing core problem in this technology area is how to more actively and efficiently remove microscopic air bubbles during the pre-forming phase, control the resin quantity and distribution more precisely, and significantly improve the thorough impregnation of fibers with high-viscosity resins. Content of the utility model

[0006] To solve the aforementioned technical problems, the present utility model aims to provide a vacuum-assisted preforming device for pultrusion processes of composite materials. This device can effectively remove microbubbles in resin and fiber bundles, effectively control the uniform distribution of the resin content, and significantly promote the thorough impregnation of fibers with high-viscosity resin.

[0007] In order to achieve the above technical objective and the aforementioned technical effects, the present utility model is implemented by the following technical solution: A vacuum-assisted preforming device for pultrusion processes of composite materials comprises a fiber guide plate for the layer-by-layer passage of fiber bundles, an impregnation tray for receiving resin, resin press rollers for squeezing out excess resin, and a vacuum-assisted preforming template, which are arranged sequentially in the pultrusion direction; wherein the vacuum-assisted preforming template has a preforming template cavity, a vacuum cavity is provided in a section of the preforming template cavity of the vacuum-assisted preforming template, a vacuum extraction opening is formed above the vacuum cavity, a semipermeable membrane is arranged at the vacuum extraction opening which allows the passage of gas but blocks the passage of resin, and the vacuum extraction opening is externally connected to a vacuum generating device.

[0008] Furthermore, the vacuum cavity is located near the inlet area of ​​the preforming template cavity.

[0009] Furthermore, the vacuum generation device includes a vacuum pump, wherein the vacuum pump is connected to the vacuum extraction port via a vacuum suction line.

[0010] Furthermore, the vacuum generation device also includes a vacuum container, the vacuum container being connected to the vacuum suction line and the vacuum pump.

[0011] Furthermore, the vacuum-assisted preforming device for pultrusion processes also includes a preforming plate, wherein the preforming plate is arranged between the resin press rollers and the vacuum-assisted preforming template, and preforming openings for the passage of the impregnated fiber bundles are formed on the preforming plate, which serve for the further alignment of the fiber bundles and the pressing out of excess resin.

[0012] Furthermore, the preforming plate is fixed to the inset end of the vacuum-assisted preforming template via a template carrier.

[0013] Furthermore, the vacuum-assisted preforming device for pultrusion processes also includes a resin collection tray, wherein the resin collection tray is arranged between the impregnation tray and the vacuum-assisted preforming template and serves to collect the resin squeezed out of the fiber bundles.

[0014] Furthermore, the semipermeable membrane is embedded in the vacuum extraction opening. The semipermeable membrane is a polytetrafluoroethylene membrane, a glass fiber composite filter membrane, or a sintered metallic porous membrane. At least two groups of resin press rollers are arranged in the pultrusion direction.

[0015] The advantages of the present utility model are as follows: 1. A vacuum cavity is provided in the preforming template cavity of the preforming template of the present utility model; the vacuum cavity cooperates with the semipermeable membrane in the vacuum extraction port and the externally connected vacuum generation device to create a negative pressure environment in the cavity of the preforming template. Under the influence of the sustained vacuum-induced negative pressure, the micrometer-sized microbubbles within the fiber bundles and between the fiber layers, as well as the gases dissolved in the resin, which are difficult to remove by mechanical pressing, are efficiently deposited.The gas can be smoothly drawn through the semipermeable membrane, while the liquid resin is effectively retained in the cavity of the preforming template by the semipermeable membrane; this significantly reduces the content of residual gases in the preform, thus reducing the porosity of the cured product, minimizing internal defects in the composites, eliminating stress concentration points, and thereby improving the mechanical properties of the composite products.

[0016] The design of the semipermeable membrane can prevent the resin from being sucked into the vacuum system; this avoids problems such as contamination of the vacuum equipment by resin, reduction of suction power, fluctuations in the vacuum level or even vacuum failure, and allows for the maintenance of a consistently stable vacuum environment.

[0017] 2. The vacuum-induced negative pressure environment in the pre-forming template of the present utility model can exert a uniform "suction effect" on the resin-containing fiber bundles as a whole, leading to a change in the resin's flow behavior. In contrast to purely mechanical pressure, which can lead to local resin accumulation (resin-rich areas) or resin deficiency (resin-poor areas), the vacuum-induced negative pressure can enable a balanced migration and redistribution of the resin within the fiber bundles and across their cross-section. On the one hand, it helps to "draw off" excess resin from the enriched areas; on the other hand, it directs the resin to the resin-poor areas with insufficient impregnation (for example, the core of the fiber bundles) for filling.This vacuum-driven effect significantly improves the uniformity of resin distribution within the preform and the accuracy of fiber volume fraction control before it enters the curing mold. The result is not only a more uniform stress distribution within the product and improved dimensional stability, but also reduces the risk of curing variations caused by uneven resin distribution and ultimately ensures high consistency of properties between different product batches.

[0018] 3. High-performance composite materials (for example, in the wind energy or aerospace industries) frequently employ highly viscous resin systems such as high-strength epoxy resins or bismaleimide resins. Conventional preforming methods rely on the resin's flowability and limited pressure, resulting in low permeation efficiency for these resins and easily leading to unimpregnated "dry spots" and microporous defects. The vacuum-assisted preforming of the present utility model effectively solves this problem. The vacuum-induced negative pressure environment in the preforming jig of the present utility model actively reduces the ambient pressure inside the resin system, thereby significantly reducing the flow resistance of the high-viscosity resin as it penetrates the microscopic spaces between dense fiber bundles (especially at the intersection points of multilayer fibers).This creates a strong suction effect for the impregnation process of the high-viscosity resin and significantly accelerates the capillary permeation rate and depth of the resin between the fibers (i.e., the capillary effect). As a result, even under conditions of rapid tensile movement, thorough, rapid, and uniform impregnation of the high-viscosity resin system can be achieved. Unimpregnated dry spots and micropore defects caused by insufficient impregnation are effectively eliminated, thus significantly improving the quality integrity and operational reliability of the final product. Furthermore, the presence of the semipermeable membrane ensures that this negative pressure-induced suction effect acts continuously and stably on the resin-fiber system without being affected by resin extraction.

[0019] 4. The present utility model transforms the conventional pre-forming process, which relies on passive pressure, into an active and controllable integrated process of "suction-impregnation-gas removal." The "vacuum-induced suction" and the upstream "mechanical pressure of the resin press rollers" act synergistically, forming a doubly optimized mechanism of "physical pressure for resin removal and large bubble removal + vacuum-induced negative pressure for deep removal of microscopic bubbles / improved impregnation." This mechanism enables the continuous, rapid, and stable production of high-performance composite profiles with extremely low porosity, uniform resin distribution, and thorough fiber impregnation. Description of the attached drawings Fig. Figure 1 is a schematic representation of the structure of a vacuum-assisted preforming device for pultrusion processes of composite materials of the present utility model; Fig. Figure 2 is a schematic representation of part of the structure of the vacuum-assisted preforming device for pultrusion processes of composite materials of the present utility model; Fig. Figure 3 is a further schematic representation of part of the structure of the vacuum-assisted preforming device for pultrusion processes of composite materials of the present utility model; and Fig. Figure 4 is a schematic representation of the cooperation between a vacuum-assisted preforming template and a vacuum generating device of the present utility model.

[0020] The following designations apply: 1-Fiber guide plate; 101-Fiber guide opening; 2-Impregnation tray; 3-Resin press roller; 4-Vacuum-assisted preforming template; 401-Preforming template cavity; 402-Vacuum cavity; 403-Vacuum extraction opening; 5-Resin collection tray; 6-Preforming plate; 601-Preforming opening; 7-Template carrier; 8-Semipermeable membrane; 9-Vacuum pump; 10-Vacuum container; and 11-Vacuum suction line. Examples of implementation

[0021] The technical solutions of this utility model are described clearly and completely below with reference to specific embodiments; it is obvious that the described embodiments are only a part of the embodiments of this utility model and do not represent all embodiments. Based on the embodiments of this utility model, all further embodiments that a person skilled in the art in the field could achieve without inventive work fall within the scope of protection of this utility model.

[0022] As in the Fig. 1 to Fig.As shown in Figure 4, the present utility model provides a vacuum-assisted preforming device for pultrusion processes of composite materials, which is arranged upstream of the heating and curing template. This vacuum-assisted preforming device for pultrusion processes comprises a fiber guide plate 1, an impregnation trough 2, resin press rollers 3, and a vacuum-assisted preforming template 4, which are arranged sequentially in the pultrusion direction.

[0023] Several fiber guide openings 101 for the passage of fibers are distributed on the fiber guide plate 1, and several fiber guide plates 1 are provided. The impregnation tank 2 contains resin. At least two groups of resin press rollers 3 are arranged in the pultrusion direction, and each group of resin press rollers 3 comprises several resin press rollers 3 arranged one above the other, which serve to squeeze out excess resin. One of the groups of resin press rollers 3 is located above the impregnation tank 2, so that the fiber bundles can be completely immersed in the resin of the impregnation tank 2.

[0024] A resin collection tray 5 is also provided between the outlet of the impregnation tray 2 and the vacuum-assisted preforming template 4. This tray serves to collect the resin squeezed out of the fiber bundles. This prevents the resin from dripping and contaminating production equipment and the working environment, maintains cleanliness, and allows for resin reuse, thus reducing costs.

[0025] A preforming plate 6 is provided between the resin press rollers 3 and the vacuum-assisted preforming template 4. The preforming plate 6 is fixed to the inlet end of the vacuum-assisted preforming template 4 via a template carrier 7. Preforming openings 601 are formed on the preforming plate 6 for the passage of the impregnated fiber bundles. These openings serve to further arrange the fiber bundles and to expel excess resin. This further reduces the looseness of the fibers before they enter the vacuum-assisted preforming template 4, improves the order of the fiber bundles upon entry into the vacuum cavity 402, and facilitates a uniform effect of the subsequent vacuum-induced negative pressure. The vacuum-assisted preforming template 4 consists of an upper template and a lower template.The upper template has an upper template cavity, and the lower template has a lower template cavity; the upper template cavity and the lower template cavity together form the preforming template cavity 401. A vacuum cavity 402 is provided in a section of the preforming template cavity 401 of the vacuum-assisted preforming template 4. Above the vacuum cavity 402 (i.e., on the upper template), a vacuum extraction port 403 is formed, and the vacuum extraction port 403 is externally connected to a vacuum generating device. A semipermeable membrane 8 is embedded in the vacuum extraction port 403, which allows the passage of gas but blocks the passage of resin.The vacuum generating device comprises a vacuum pump 9 and a vacuum reservoir 10; the vacuum pump 9 is connected to the vacuum reservoir 10 via a vacuum suction line 11, and the vacuum reservoir 10 is in turn connected to the vacuum discharge port 403 via the vacuum suction line 11. The vacuum pump 9 provides the core driving force to establish and maintain a stable vacuum environment in the vacuum cavity 402. The vacuum reservoir 10 dampens fluctuations in the vacuum, maintains pressure stability in the vacuum cavity 402, reduces the switching frequency of the vacuum pump 9, extends its service life, saves energy, and reduces noise.

[0026] The vacuum cavity 402 is located near the inlet area of ​​the preforming template cavity 401, so that the effect of the vacuum-induced negative pressure is exerted on the impregnated fiber bundles in the initial phase of their entry into the preforming template cavity 401. At this point, the fiber bundles are relatively loose and contain a high proportion of bubbles, which enables efficient and timely removal of the vast majority of bubbles and dissolved gases and prevents them from penetrating deep into the preforming template cavity 401 where they could be difficult to remove.

[0027] Preferably, a polytetrafluoroethylene membrane, a glass fiber composite filter membrane, or a sintered metallic porous membrane is used as the semipermeable membrane 8. These membranes exhibit excellent gas permeability, corrosion resistance to resin solvents, liquid repellency (difficult to wet by resin and therefore not easily clogged), thermal stability, and mechanical strength. Consequently, they can operate stably in the pultrusion process environment over the long term and ensure reliable gas-liquid separation.

[0028] The working process of the vacuum-assisted preforming device for pultrusion processes of composite materials is as follows: After the fiber bundles (e.g., carbon fiber bundles or glass fiber bundles) are unwound from a fiber reel stand, they are guided precisely through the fiber guide openings 101 on several groups of fiber guide plates 1 according to a predefined path to achieve longitudinal separation and transverse alignment. This prevents the fibers from crossing and tangling and creates a structural basis for subsequent uniform impregnation. The smoothed fiber bundles are then immersed in the resin liquid (e.g., epoxy resin or polyester resin) of the impregnation bath 2 for thorough impregnation; the surface and spaces of the fiber bundles are coated and filled with resin.

[0029] The resin press rollers 3 exert pressure on the fiber bundles to squeeze out excess resin that accumulates on the surface of the fiber bundles, as well as trapped large bubbles; the squeezed-out resin is collected in real time by the resin collection tray 5.

[0030] The impregnated fiber bundles, freed of excess resin, are then inserted into the preforming openings 601 of the preforming plate 6. As the fiber bundles pass through the preforming openings 601, they are restricted, and further arrangement of the fiber bundles and extrusion of resin take place.

[0031] After the fiber bundles have passed through the preforming plate 6, they are drawn at a constant speed by a pulling mechanism into the preforming template cavity 401 of the vacuum-assisted preforming template 4. The vacuum cavity 402 of this preforming template is externally connected to a vacuum generating device via the vacuum extraction port 403. As the fiber bundles enter the area corresponding to the vacuum cavity 402, the semipermeable membrane 8 in the vacuum extraction port 403, under the action of the vacuum pump 9, creates a stable negative pressure environment in the preforming template cavity 401. This negative pressure environment actively draws out deep microbubbles and dissolved gases from the fiber bundles (the gas is drawn out through the semipermeable membrane 8, while the resin is blocked) and simultaneously promotes the migration and distribution of resin within the fiber bundles.The fiber bundles are progressively compressed through the preforming template cavity 401, and finally a dense, bubble-free preform with uniform resin distribution is ejected. The preform is transported by the pulling mechanism to a downstream heating and curing template, where the resin curing is completed; after cooling and mold fixing, the high-performance composite profile end product is manufactured.

[0032] It is obvious to those skilled in the field that the present utility model is not limited to the details of the exemplary embodiments given above and that the present utility model can be realized in other concrete forms without departing from its spirit or its fundamental features. Therefore, the exemplary embodiments are to be regarded in every respect as illustrative and not limiting. The scope of protection of the present utility model is defined by the appended claims, not by the foregoing description; therefore, it is intended that all modifications falling within the meaning and scope of the equivalent features of the claims are to be included in the present utility model. Furthermore, it should be understood that although the present description is presented according to embodiments, each embodiment does not necessarily contain only one independent technical solution.This description is provided for clarity only; experts in the field should consider the description as a whole, and the technical solutions in the individual embodiments can also be appropriately combined to form further embodiments that are understandable to experts in the field.

Claims

[1] A vacuum-assisted preforming device for pultrusion processes of composite materials, characterized by , comprising a fiber guide plate for the layer-by-layer passage of fiber bundles, an impregnation tray for receiving resin, resin press rollers for squeezing out excess resin, and a vacuum-assisted preforming template, which are arranged sequentially in the pultrusion direction; wherein the vacuum-assisted preforming template has a preforming template cavity, a vacuum cavity is provided in a section of the preforming template cavity of the vacuum-assisted preforming template, a vacuum extraction opening is formed above the vacuum cavity, a semipermeable membrane is arranged at the vacuum extraction opening which allows the passage of gas but blocks the passage of resin, and the vacuum extraction opening is externally connected to a vacuum generating device. [2] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 1, characterized by , that the vacuum cavity is located near the inlet area of ​​the preforming template cavity. [3] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 1, characterized by that the vacuum generating device includes a vacuum pump, wherein the vacuum pump is connected to the vacuum extraction port via a vacuum suction line. [4] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 3, characterized by , that the vacuum generating device further comprises a vacuum vessel, wherein the vacuum vessel is connected to the vacuum suction line and the vacuum pump. [5] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 1, characterized by, that it further comprises a preforming plate, wherein the preforming plate is arranged between the resin press rollers and the vacuum-assisted preforming template and preforming openings for the passage of the impregnated fiber bundles are formed on the preforming plate. [6] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 5, characterized by that the preforming plate is fixed to the inset end of the vacuum-assisted preforming template via a template carrier. [7] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 5, characterized by , that it further comprises a resin collection tray, wherein the resin collection tray is arranged between the impregnation tray and the vacuum-assisted preforming template and serves to collect the resin squeezed out of the fiber bundles. [8] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 1, characterized by that the semipermeable membrane is inserted into the vacuum extraction opening. [9] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 1, characterized by that the semipermeable membrane is a polytetrafluoroethylene membrane, a glass fiber composite filter membrane, or a sintered metallic porous membrane. [10] The vacuum-assisted preforming device for pultrusion processes of composite materials according to claim 1, characterized by that at least two groups of resin press rollers are arranged in the pultrusion direction.

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