Injection molding apparatus and injection molding method for long fiber reinforced composites

Abstract

The application relates to the technical field of injection molding equipment, in particular to injection molding equipment and an injection molding method for long-fiber reinforced composite materials. The injection molding equipment comprises a felt placing assembly, a felt feeding assembly, an injection assembly and a mold assembly. The injection assembly comprises a first-stage pre-plasticizing mechanism and a second-stage injection mechanism. The first-stage pre-plasticizing mechanism comprises a first-stage barrel, a first-stage screw and a first-stage driving component. The first-stage barrel comprises a front conveying section and a rear conveying section, and a heater is arranged on the outer side of the rear conveying section. The second-stage injection mechanism comprises a second-stage barrel, a second-stage screw, a second-stage driving component and an injection driving component. The outer side of the second-stage barrel is provided with a heater, and the second-stage barrel comprises a compression section and a metering section. The bottom surface of the screw groove of the second-stage screw in the compression section adopts a wave-shaped structure. The injection molding equipment can realize automatic and continuous injection molding, ensure the uniform dispersion of fibers in the composite material, maximize the length of the fibers and obtain long-fiber reinforced composite materials with excellent performance.

Description

Technical Field

[0001] This invention relates to an injection molding equipment and injection molding method for long fiber reinforced composite materials, belonging to the technical field of injection molding equipment. Background Technology

[0002] In the field of composite materials, fiber-reinforced structures are classified according to the morphology of the reinforcing phase, including continuous fiber-reinforced composites, long fiber-reinforced composites, and short fiber-reinforced composites. Continuous fiber-reinforced composites are those where the two ends of the fiber are located at the boundaries of the composite material, exhibiting anisotropy. Short fiber-reinforced composites are those where short fibers (generally <6mm in length) are randomly arranged in the matrix, exhibiting isotropy. Currently, continuous fiber-reinforced composites, with their excellent properties of lightweight, high specific strength, and high specific modulus, firmly occupy the "performance-first" fields such as aerospace and high-end sporting goods, such as the fuselage skin of the Airbus A350 and high-end golf club shafts. Short fiber-reinforced composites, on the other hand, are widely used in the "mass-production-first" markets such as automotive parts and electronic appliance housings, thanks to their efficient injection molding and extrusion processes and moderate cost, such as car hoods and laptop casings. Both types of composites, in their balance between performance and cost-effectiveness, meet specific needs and form clear application boundaries.

[0003] Long fiber reinforced composites (fiber length 6mm-100mm) break through this inherent boundary, exhibiting unique advantages. Their fiber length can, to some extent, form a load transfer path similar to continuous fibers, providing mechanical properties far exceeding those of short fibers, making them suitable for industrial components with high strength requirements. Furthermore, because they do not require complex layup processes, production costs are significantly lower than those of continuous fiber composites. In addition, the length of the long fibers reduces the agglomeration problems that are prone to occur with short fibers in finished products, and also improves the low interlaminar shear strength defect of continuous fibers, achieving a balanced optimization of properties in all directions. This provides new solutions for lightweight automotive structural components, mass production of high-end sports equipment, and other fields.

[0004] However, conventional injection molding processes for long fiber reinforced composites present numerous technical challenges. For instance, long fibers are difficult to disperse evenly in thermoplastic resins. Furthermore, the plasticization process of thermoplastic granules involves conveying, compression, melting, and mixing in a screw, inevitably accompanied by strong shearing. This high-intensity melt shearing severely damages the fibers, drastically reducing their retention length in the final part and significantly impacting the reinforcement effect. Conversely, suppressing melt shearing hinders melt mixing and fiber dispersion, leading to fiber agglomeration and severely affecting the part's appearance and mechanical stability. To address the issue of uneven dispersion of long fibers in thermoplastic resins, a fiber mat with uniformly dispersed long fibers and thermoplastic resin can be prepared using an opening machine, feeding machine, carding machine, and pre-punching machine. This fiber mat can then be used for injection molding. However, existing injection molding equipment often fails to meet application requirements; currently, ordinary long fiber injection-reinforced injection molding machines can only retain a maximum fiber length of 20 mm in the finished product. Patent application CN109203405A discloses a method for direct injection molding of long-fiber online reinforced polypropylene. The production apparatus includes: a primary screw extruder, a secondary twin-screw extruder, an injection molding system, a mold-locking system, and a sequential dispersing rack. The primary screw extruder is equipped with a feed hopper. The first feed inlet of the secondary twin-screw extruder is connected to the extrusion die of the primary screw extruder. The injection molding system is connected to the extrusion die of the secondary twin-screw extruder. The mold-locking system is connected to the injection molding system. The sequential dispersing rack is located at the second feed inlet of the secondary twin-screw extruder. Fibers pass through the sequential dispersing rack and enter the secondary twin-screw extruder through the second feed inlet. While this method can increase the fiber length in the composite material to some extent, the uniformity between the fiber and the thermoplastic polymer is relatively low, thus limiting the fiber addition ratio in the composite material. Patent application CN116890428A discloses a dedicated injection molding machine for direct injection molding of continuous fiber-reinforced thermoplastics. It includes a fiber feeding system that feeds pre-heat-treated continuous fibers and chopped fibers from an upper feed port and a side feed port located in the middle of the barrel to the second-stage screw feeding zone. The first-stage screw is used for melting, plasticizing, and conveying the thermoplastic resin, while the second-stage screw is used for dispersing and mixing the molten resin with the reinforcing fibers. Three small parts at the screw head are used for anti-reverse flow during plasticizing and injection, reducing friction and extending service life. However, the continuous two-stage screw configuration of this injection molding machine prevents the use of fiber felt for continuous feeding injection molding. During injection, the fiber felt will break, and long fibers will be damaged, affecting the smooth production process of continuous injection molding. This also leads to a decrease in the performance of the final composite injection molded material, and the performance of the long fiber reinforced composite material cannot be fully realized.

[0005] Therefore, developing an injection molding equipment and injection molding method can effectively balance the retention length and dispersion state of fibers in the part and realize continuous injection molding production to obtain high-performance long fiber reinforced composite materials, which is of great value. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an injection molding equipment and method for long fiber reinforced composite materials. Using fiber mats with uniformly dispersed fibers and thermoplastics as raw materials, the injection molding equipment and method can automate and continuously carry out the injection molding process, and ensure uniform dispersion of fibers in the composite material, maximizing the retention length of fibers in the final part, ultimately obtaining a long fiber reinforced composite material with excellent performance.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: an injection molding equipment for long fiber reinforced composite materials, the injection molding equipment comprising:

[0008] A felting assembly; a fiber felt made of a blend of aramid long fibers and thermoplastic resin long fibers is placed on the felting assembly.

[0009] Felt feed assembly;

[0010] An injection assembly includes a first-stage pre-plasticizing mechanism and a second-stage injection mechanism. The first-stage pre-plasticizing mechanism includes a first-stage barrel, a first-stage screw located within the first-stage barrel, and a drive component for rotating the first-stage screw. The first-stage barrel includes a front conveying section and a rear conveying section, with a heater located on the outer side of the rear conveying section. The second-stage injection mechanism includes a second-stage barrel communicating with the rear conveying section, a second-stage screw located within the second-stage barrel, a drive component for rotating the second-stage screw, and a drive component for reciprocating injection motion of the second-stage screw. A heater is located on the outer side of the second-stage barrel, which includes a compression section and a metering section. The bottom surface of the screw groove of the second-stage screw located in the compression section has a wavy structure.

[0011] Mold assembly; the metering section is connected to the mold assembly via a nozzle.

[0012] Furthermore, the felt-releasing assembly includes a felt cylinder and a braking component that provides tension to the fiber felt. The fiber felt is wound on the felt cylinder, and the felt cylinder is connected to the braking component via a connecting shaft.

[0013] Furthermore, the felt feeding assembly includes an active roller, a passive roller, a roller gear, and a screw gear; the screw gear is fixedly installed with the first-order screw, the screw gear meshes with the roller gear, the roller gear is fixedly installed with the active roller on the active shaft, the active roller and the passive roller together clamp the fiber felt, and the rotation of the active roller drives the passive roller to rotate, causing the fiber felt to be fed into the front conveying section of the injection assembly.

[0014] Furthermore, the pitch of the first-stage screw located in the front conveying section is less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw and the first-stage barrel located in the front conveying section is less than the thickness of the fiber felt.

[0015] The pitch of the first-stage screw located in the rear conveying section is not less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw located in the rear conveying section and the first-stage barrel is less than the gap between the tooth crest of the first-stage screw located in the front conveying section and the first-stage barrel.

[0016] Furthermore, the length of the first-order screw in the front conveying section accounts for 20-40%, and the length of the first-order screw in the rear conveying section accounts for 60-80%.

[0017] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is (20-50%): (25-60%): (10-30%).

[0018] Furthermore, when the thermoplastic resin long fiber is made of polycarbonate or rigid polyvinyl chloride, the length of the second-stage screw in the compression section accounts for 25-40% of the total working length of the first-stage and second-stage screws; when the thermoplastic resin long fiber is made of polyetheretherketone or polyphenylene sulfide, the length of the second-stage screw in the compression section accounts for 40-60% of the total working length of the first-stage and second-stage screws.

[0019] When the thermoplastic resin long fiber is a heat-sensitive material, the length of the second-stage screw in the metering section accounts for 10-20% of the total working length of the first-stage screw and the second-stage screw; when the thermoplastic resin long fiber is not a heat-sensitive material, the length of the second-stage screw in the metering section accounts for 20-25% of the total working length of the first-stage screw and the second-stage screw.

[0020] Furthermore, the screw groove depth of the second-order screw located in the metering section is (0.03-0.1)*D, where D is the diameter of the second-order screw.

[0021] Furthermore, the radius of the fillet of the wave structure on the bottom surface of the spiral groove is not less than 0.5 mm, the amplitude of the wave structure is 1 / 6 to 1 / 3 of the maximum depth of the spiral groove, and the wavelength of the wave structure is 0.5 to 2.5 times the lead.

[0022] From the inlet to the outlet direction of the second-stage barrel, the screw groove volume of the second-stage screw in the compression section gradually decreases.

[0023] Furthermore, the aramid long fiber has a length of 30 mm to 80 mm;

[0024] The total weight of the aramid long fiber and the thermoplastic resin long fiber is calculated as 100, and the weight ratio of the aramid long fiber and the thermoplastic resin long fiber is (10-40):(60-90).

[0025] This invention also discloses an injection molding method for long fiber reinforced composite materials, wherein the injection molding method comprises: using the injection molding equipment described in this invention to perform injection molding of the long fiber reinforced composite material.

[0026] Fiber felt is placed on the felt-laying assembly, and the fiber felt is fed to the injection assembly through the felt-feeding assembly. Through the rotation of the first-stage screw and the second-stage screw, the fiber felt material is conveyed from the first-stage barrel to the second-stage barrel.

[0027] The fiber felt first enters the rear conveying section through the front conveying section, where it is preheated and melted. Then it enters the compression section, where it is mixed, compressed, and pressurized for degassing. Finally, it enters the metering section for further mixing and homogenization. The double injection molding motion of the second-stage screw injects the mixed material into the mold assembly through the nozzle.

[0028] The beneficial effects of this invention are:

[0029] The injection molding equipment described in this invention, through the reasonable coordination between the felt feeding assembly, the felt infeed assembly, the injection assembly, and the mold assembly, can improve the fiber retention length in long fiber reinforced composite materials, increase the uniformity of fiber distribution, reduce the risk of fiber agglomeration, and improve the quality of long fiber reinforced composite materials; it can also improve the degree of automation, realize continuous injection molding production, improve injection molding efficiency, and optimize assembly dimensions to reduce space occupancy.

[0030] Specifically, in the injection molding equipment described in this invention, by setting a first-stage pre-plasticizing mechanism and a second-stage injection mechanism, the fiber felt is pre-plasticized in the first-stage barrel, compressed and degassed in the second-stage barrel, and the injection action is completed by the movement of the second-stage screw. The first-stage screw does not participate in the reciprocating injection action, so that the fiber felt will not be cut off due to the screw injection action, improving the degree of automation and ensuring the continuity of injection molding. The felt feeding assembly and felt unloading assembly ensure continuous automatic feeding of the fiber felt, realizing automatic production after the felt cylinder is installed until the fiber felt on the felt cylinder is exhausted. Furthermore, the speed of the felt feeding assembly is adjustable, improving injection molding efficiency.

[0031] Specifically, in the injection molding equipment described in this invention, the appropriate matching of the length ratios of the front conveying section, the rear conveying section, the compression section, and the metering section can achieve uniform mixing while avoiding damage to the materials inside the fiber felt, ensuring the production of high-quality long fiber reinforced composite materials, and enabling smoother continuous injection molding production.

[0032] The injection molding equipment and method described in this invention use a uniformly dispersed fiber mat of aramid long fibers and thermoplastic resin long fibers as raw materials. It eliminates the screw mixing structure, reduces shearing action, and mitigates fiber breakage caused by melt shearing, maximizing the fiber retention length in the final part. The bottom surface of the screw groove in the screw compression section adopts a wavy design to reduce the risk of fiber agglomeration and improve the quality of the injection molded products.

[0033] Specifically, the bottom surface of the screw groove in the screw compression section adopts a wave-shaped design, which periodically changes the volume of the screw groove, causing the fiber felt to repeatedly experience the "compression-expansion" state during its forward movement. The gas trapped inside is more easily released and discharged. The change in the depth of the screw groove leads to a high flow rate and strong shear at the crest of the material, and a slow flow rate and more filling at the trough, forming a strong turbulent mixing effect, reducing the risk of fiber agglomeration and improving the quality of injection molded products.

[0034] More specifically, conventional smooth screw channels rely on heat conduction and screw shearing through the "barrel wall → melt boundary layer → solid fiber layer" for melting. However, for high-viscosity, low-thermal-conductivity materials or highly filled materials (such as those with a fiber weight content of over 30%), the heat conduction efficiency is low, and the solid fiber layer is prone to incomplete melting. In this invention, the convex structure of the wavy screw channel directly separates the solid fiber layer from the melt layer. The convex area exerts a squeezing effect on the solid fiber layer, increasing the contact area between the solid fiber and the high-temperature barrel wall, thus accelerating heat absorption. The concave area forms a local vortex zone, allowing unmelted solid fibers to repeatedly contact the melt in the vortex, preventing undissolved solid fibers from entering the metering section. This is particularly suitable for the melting and homogenization of highly filled materials. The wavy spiral channel bottom structure can divide and disperse the fibers, breaking up existing fiber agglomerates. In conventional smooth spiral channels, fiber agglomerates move in laminar flow along the channel with the melt, and it is difficult to effectively tear apart the tightly packed agglomerates by the shear force of the screw alone (the relative movement between the channel wall and the melt). However, the raised structure of the wavy spiral channel directly obstructs and compresses the melt flow: when the melt containing agglomerates flows through the raised section, the agglomerates are physically divided by the raised section: larger fiber bundles are "split" into smaller bundles by the edge of the raised section; at the same time, the "narrow gap" formed by the raised section and the channel wall generates local high pressure, forcing the agglomerates to be squeezed and dispersed in the gap, which is especially suitable for materials with severe initial agglomeration (such as PA66 and PP with fiber content ≥30%). Furthermore, the wavy structure of the spiral groove bottom can create a vortex and circulation effect, allowing the fibers to be fully wetted by the melt and preventing new agglomeration. Another important reason for fiber agglomeration is insufficient melt wetting; the surface of the aramid long fibers is not completely coated by the thermoplastic resin melt, resulting in friction between the aramid long fibers, making them prone to re-entanglement. The concave area of ​​the wavy spiral groove bottom will form a local vortex: the thermoplastic resin melt will generate a circulating flow (rather than unidirectional laminar flow) in the concave area, and the aramid long fibers will repeatedly turn and collide in the vortex, increasing the contact area with the thermoplastic resin melt and accelerating the wetting of the aramid long fibers by the thermoplastic resin. The vortex can also break the aramid fiber settling layer (in conventional spiral grooves, the fiber density is slightly higher than that of the melt, which easily forms a concentrated layer at the bottom of the spiral groove, aggravating agglomeration), allowing the aramid long fibers to be evenly dispersed in the thermoplastic resin melt, reducing new agglomeration caused by local enrichment.

[0035] The injection molding equipment described in this invention no longer adopts the traditional single long screw structure. Instead, through optimized design, the felt feeding assembly and the felt infeed assembly are set on the first-stage pre-plasticizing mechanism. The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are arranged vertically, which achieves a significant reduction in overall size, reduces space occupancy, and is more suitable for industrial use. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the injection molding equipment for long fiber reinforced composite materials described in the embodiment;

[0037] Figure 2 This is an internal cross-sectional view of the injection molding equipment for long fiber reinforced composite materials described in the embodiment;

[0038] Figure 3 This is a schematic diagram of the felt-laying assembly described in the embodiment;

[0039] Figure 4 This is a schematic diagram of the internal structure of the felt feeding assembly described in the embodiment;

[0040] Figure 5 This is a schematic diagram of the first-order pre-plasticizing mechanism described in the embodiment;

[0041] Figure 6 This is a schematic diagram of the second-order injection mechanism described in the embodiment;

[0042] Figure 7 This is an unfolded and sectional view of the wave-shaped spiral groove.

[0043] Figure 8 This is a schematic diagram of a conventional injection molding machine;

[0044] In the diagram, 1. Felt feeding assembly; 2. Felt infeed assembly; 3. Injection assembly; 4. Mold assembly;

[0045] 11. Felt cylinder; 12. Braking component; 13. Connecting shaft; 14. Brake;

[0046] 21. Driven roller; 22. Driven roller; 23. Roller gear; 24. Screw gear; 25. Drive shaft; 26. Driven shaft; 27. Gearbox;

[0047] 31. First-order pre-plasticizing mechanism; 32. Second-order injection mechanism;

[0048] 311. First-stage barrel; 312. First-stage screw; 313. First-stage drive unit; 314. Front conveyor section; 315. Rear conveyor section;

[0049] 321. Second-stage barrel; 322. Second-stage screw; 323. Second-stage drive unit; 324. Injection driving unit; 325. Compression section; 326. Metering section; 327. Nozzle;

[0050] 5. Heater; 6. Mounting bracket. Detailed Implementation

[0051] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0052] 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 invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0053] like Figures 1-2 As shown, an injection molding equipment for long fiber reinforced composite materials is disclosed. The injection molding equipment includes: a felt unwinding assembly 1, a felt feeding assembly 2, an injection assembly 3, and a mold assembly 4. The felt unwinding assembly 1 performs the function of unwinding the fiber felt, the felt feeding assembly 2 performs the function of automatically and continuously introducing the fiber felt, the injection assembly 3 performs the functions of conveying, plasticizing, storing and injecting, and the mold assembly 4 performs the function of injection molding into the finished part.

[0054] Specifically, a fiber felt made of a blend of aramid long fibers and thermoplastic resin long fibers is placed on the felt-laying assembly 1.

[0055] The injection assembly 3 includes a first-stage pre-plasticizing mechanism 31 and a second-stage injection mechanism 32. The first-stage pre-plasticizing mechanism 31 performs the functions of winding fiber felt and partial plasticizing, while the second-stage injection mechanism 32 performs the functions of complete plasticizing, material storage and injection.

[0056] like Figures 5-6 As shown, the first-stage pre-plasticizing mechanism 31 includes a first-stage barrel 311, a first-stage screw 312 located inside the first-stage barrel 311, and a first-stage driving component 313 that drives the first-stage screw 312 to rotate; the first-stage barrel 311 includes a front conveying section 314 and a rear conveying section 315, and a heater 5 is provided on the outer side of the rear conveying section 315; the second-stage injection mechanism 32 includes a second-stage barrel 321 communicating with the rear conveying section 315, a second-stage screw 322 located inside the second-stage barrel 321, a second-stage driving component 323 that drives the second-stage screw 322 to rotate, and an injection driving component 324 that drives the second-stage screw 322 to perform reciprocating injection molding motion; a heater 5 is provided on the outer side of the second-stage barrel 321, and the second-stage barrel 321 includes a compression section 325 and a metering section 326; the bottom surface of the screw groove of the second-stage screw 322 located in the compression section 325 adopts a wave-shaped structure;

[0057] The first-stage barrel 311 is located above the second-stage barrel 321. The screw head of the first-stage screw 312 faces the outlet of the first-stage barrel 311. The outlet of the first-stage barrel 311 is connected to the inlet of the second-stage barrel 321. A nozzle 327 is fixedly connected to the outlet of the second-stage barrel 321 through a flange. The screw head of the second-stage screw 322 faces the nozzle 327. The metering section 326 is connected to the mold assembly 4 through the nozzle 327.

[0058] Specifically, such as Figure 3As shown, the felt-releasing assembly 1 includes a felt cylinder 11 and a braking component 12 that provides tension to the fiber felt. Fiber felt is wound on the felt cylinder 11, and the felt cylinder 11 is connected to the braking component 12 via a connecting shaft 13.

[0059] The braking component 12 can apply a certain braking force to maintain a certain tension in the fiber felt, ensuring the uniformity of the felt feeding at the rear end. After the fiber felt is used up, the felt cylinder 11 can be easily replaced. The felt feeding assembly 1 is mounted on the bracket 14, which provides support for the felt cylinder 11 and the braking component 12.

[0060] More specifically, the braking component 12 is a magnetic powder brake, but it is not limited to using a magnetic powder brake; any device that can provide tension to the fiber felt is acceptable.

[0061] Specifically, such as Figure 4 As shown, the felt feeding assembly 2 includes an active roller 21, a passive roller 22, a roller gear 23, and a screw gear 24. The screw gear 24 is fixedly installed with the first-order screw 312. The first-order drive component 313 drives the first-order screw 312 and the screw gear 24 to rotate synchronously. The screw gear 24 is meshed with the roller gear 23, and the screw gear 24 drives the roller gear 23 to rotate. The roller gear 23 is fixedly installed with the active roller 21 on the active shaft 25. The active roller 21, the active shaft 25, and the roller gear 23 together form an active shaft 25 system. The rotation of the active shaft 25 system is achieved by the rotation of the roller gear 23. The passive roller 22 is installed on the passive shaft 26. The active roller 21 and the passive roller 22 together clamp the fiber felt. The rotation of the active roller 21 drives the passive roller 22 to rotate, causing the fiber felt to be fed into the front conveying section 314 of the injection assembly 3, thereby achieving continuous feeding of the fiber felt.

[0062] More specifically, both the roller gear 23 and the screw gear 24 are installed inside the gearbox 27.

[0063] Specifically, the pitch of the first-stage screw 312 located in the front conveying section 314 is less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw 312 and the first-stage material cylinder 311 located in the front conveying section 314 is less than the thickness of the fiber felt; through the connection between the first-stage driving component 313 and the first-stage screw 312, rotational power is transmitted to the first-stage screw 312, and the first-stage screw 312 can wind the fiber felt introduced by the felt feeding assembly 2 around the outer circumference of the first-stage screw 312 to realize the conveying of the fiber felt.

[0064] The pitch of the first-stage screw 312 located in the rear conveying section 315 is not less than the width of the fiber felt. The gap between the tooth crest of the first-stage screw 312 and the first-stage barrel 311 located in the rear conveying section 315 is smaller than the gap between the tooth crest of the first-stage screw 312 and the first-stage barrel 311 located in the front conveying section 314. Upon entering the rear conveying section 315, the fiber felt falls into the screw groove, and the heater 5 pre-plasticizes the fiber felt during conveying.

[0065] More specifically, the first-order drive component 313 is a motor, but it is not limited to a motor. Any power component that can drive the first-order screw 312 to rotate is acceptable.

[0066] The second-order drive component 323 is a motor, but it is not limited to a motor. Any power component that can drive the second-order screw 322 to rotate is acceptable.

[0067] The injection driving component 324 is a hydraulic cylinder, but it is not limited to a hydraulic cylinder. It can be any cylinder that can drive the second-order screw 322 to perform reciprocating injection motion.

[0068] Specifically, the first-stage screw 312 accounts for 20-40% of the length of the front conveying section 314, and 60-80% of the length of the rear conveying section 315. The front conveying section 314 and the rear conveying section 315 realize the conveying, pushing and preheating of the fiber felt. In the rear conveying section 315, it is necessary to ensure that the thermoplastic resin long fibers in the fiber felt can be heated to the melting point. For crystalline thermoplastic resin long fibers, the rear conveying section 315 can be longer, followed by non-crystalline thermoplastic resin long fibers. When the thermoplastic resin long fibers are heat-sensitive materials, the length of the rear conveying section 315 is set to the shortest.

[0069] The ratio of the total length of the first-order screw 312 in the front conveying section 314 and the rear conveying section 315, the length of the second-order screw 322 in the compression section 325, and the length of the second-order screw 322 in the metering section 326 is (20-50%): (25-60%): (10-30%).

[0070] Compression section 325 mixes, compresses, and pressurizes the thermoplastic resin material to remove fumes. The raw materials passing through this section are almost completely melted.

[0071] The metering section 326 ensures that the thermoplastic resin material is completely melted and the temperature is uniform, resulting in uniform mixing. A longer metering section 326 results in better mixing, but if it is too long, the melt may remain in place for too long, leading to thermal decomposition. If it is too short, the temperature may be uneven. Therefore, setting the length ratio of the metering section 326 appropriately is more conducive to the smooth progress of the injection molding process.

[0072] Furthermore, when the thermoplastic resin long fiber is made of polycarbonate or rigid polyvinyl chloride, the length of the second-stage screw 322 in the compression section 325 accounts for 25-40% of the total working length of the first-stage screw 312 and the second-stage screw 322; when the thermoplastic resin long fiber is made of polyetheretherketone or polyphenylene sulfide (high viscosity, low conductivity, high additives, etc. thermoplastic materials), the length of the second-stage screw 322 in the compression section 325 accounts for 40-60% of the total working length of the first-stage screw 312 and the second-stage screw 322.

[0073] When the thermoplastic resin long fiber is a heat-sensitive material, the length of the second-stage screw 322 in the metering section 326 accounts for 10-20% of the total working length of the first-stage screw 312 and the second-stage screw 322; when the thermoplastic resin long fiber is not a heat-sensitive material, the length of the second-stage screw 322 in the metering section 326 accounts for 20-25% of the total working length of the first-stage screw 312 and the second-stage screw 322.

[0074] Specifically, the screw groove depth of the second-order screw 322 located in the metering section 326 is (0.03-0.1)*D, where D is the diameter of the second-order screw 322. The deeper the screw groove depth, the greater the conveying capacity, but the screw strength must be considered. The shallower the screw groove depth of the metering section 326, the higher the plasticizing heat generation and mixing performance index. However, if the metering screw groove depth is too shallow, the shear heat and self-generated heat will increase, and the temperature rise will be too high, causing discoloration or scorching of thermoplastic resins, which is especially unfavorable to heat-sensitive resin materials.

[0075] Specifically, such as Figure 7 As shown, the radius of the rounded corners of the wave structure in the spiral groove is not less than 0.5mm, and the amplitude of the wave structure is 1 / 6 to 1 / 3 of the maximum depth of the spiral groove (the amplitude of each wave structure is calculated based on the maximum depth of the spiral groove in the next wavelength); the wavelength of the wave structure is 0.5 to 2.5 times the lead; if there are sharp corners in the recessed area of ​​the wave structure, it will form a dead corner for the material, and the fibers will accumulate in the dead corner, which will lead to more serious local agglomeration. Therefore, a high-quality wave design needs to make a "rounded corner transition" (the radius of the rounded corner between the bottom of the recess and the edge of the protrusion is ≥0.5mm) to avoid dead corners.

[0076] From the inlet to the outlet direction of the second-stage barrel 321, the screw channel volume of the second-stage screw 322 in the compression section 325 gradually decreases. In the compression section 325, the thermoplastic resin gradually melts, and the screw channel volume decreases accordingly (achieved by gradually shallowing the screw channel depth) to correspond to the decrease in the geometric volume of the thermoplastic resin; otherwise, the material would not be compacted, heat transfer would be slow, and venting would be poor.

[0077] More specifically, in practical applications, the structural dimensions of the bottom surface of the corresponding wave-shaped spiral groove can be designed according to the length of the aramid long fibers.

[0078] Specifically, the aramid long fiber has a length of 30 mm to 80 mm.

[0079] Preferably, when the length of the aramid long fibers in the fiber felt is 30mm-40mm, the amplitude of the wave structure is 1 / 6 to 1 / 4 of the maximum depth of the spiral groove; the wavelength of the wave structure is 1.5 to 2.5 times the lead. When the length of the aramid long fibers in the fiber felt is 40mm or more, the amplitude of the wave structure is 1 / 4 to 1 / 3 of the maximum depth of the spiral groove; the wavelength of the wave structure is 0.5 to 1.5 times the lead.

[0080] Preferably, the screw channel volume of the second-stage screw 322 in the compression section 325 gradually decreases according to the following principle: the melting difficulty, thermal stability, and viscosity characteristics of the resin directly determine whether a "slow gradual change" or a "rapid gradual change" is needed. This is the primary consideration in designing the speed of screw channel volume change. For refractory resins (high melting temperature / slow melting rate): the screw channel volume needs to change slowly. For heat-sensitive resins (easily thermally decomposed): the screw channel volume needs to change slowly. For high-viscosity resins (poor melt flowability): the screw channel volume needs to change slowly. Furthermore, for high compression ratios and large aspect ratios, the screw channel volume tends to change slowly; for low compression ratios and small aspect ratios, the screw channel volume tends to change rapidly.

[0081] Specifically, the total weight of the aramid long fiber and the thermoplastic resin long fiber is calculated as 100, and the weight ratio of the aramid long fiber and the thermoplastic resin long fiber is (10-40):(60-90).

[0082] More specifically, in this embodiment of the invention, the aramid long fiber is a aramid long fiber that has undergone crimping treatment, and the length of the aramid fiber is 30 mm-80 mm; the thermoplastic resin long fiber is a long fiber that has undergone crimping treatment, and the length of the thermoplastic resin long fiber is 30 mm-80 mm; wherein the crimping treatment is as follows: after oiling and humidifying, a preheating process is performed, and then mechanical crimping is performed for shaping, and the degree of crimping is controlled by the pressure of the crimping roller, with the crimp degree controlled at 10%-15%.

[0083] More specifically, the first-order drive component 313 and the second-order drive component 323 are installed according to conventional installation methods, as long as they can achieve smooth rotational movement of the first-order screw 312 and the second-order screw 322 respectively; the injection driving component 324 is installed according to conventional installation methods, as long as it can enable the second-order screw 322 to perform reciprocating injection movement relative to the second-order barrel 321.

[0084] The entire injection molding equipment is fixedly installed by the fixing frame 6. In actual production, the structure of the mold assembly 4 is selected according to the injection molding shape and size requirements.

[0085] This invention also discloses an injection molding method for long fiber reinforced composite materials, wherein the injection molding method comprises: using the injection molding equipment described in this invention to perform injection molding of the long fiber reinforced composite material.

[0086] Fiber felt is placed on the felt-laying assembly 1, and the fiber felt is fed to the injection assembly 3 through the felt-feeding assembly 2. Through the rotation of the first-stage screw 312 and the second-stage screw 322, the fiber felt is conveyed from the first-stage barrel 311 to the second-stage barrel 321.

[0087] The fiber felt first enters the rear conveying section 315 through the front conveying section 314, where it is preheated and melted. Then it enters the compression section 325, where it is mixed, compressed, and pressurized for degassing. Finally, it enters the metering section 326 for specific mixing and homogenization. The second-stage screw 322's injection molding motion injects the mixed material into the mold assembly 4 through the nozzle.

[0088] More specifically, the injection molding process is as follows:

[0089] A felt cylinder 11 wound with fiber felt is placed on the connecting shaft 13 of the felt-releasing assembly 1, and the braking component 12 provides tension to the fiber felt; the active roller 21 and the passive roller 22 clamp the fiber felt together, and the first-stage driving component 313 drives the first-stage screw 312 and the screw gear 24 to rotate synchronously. The screw gear 24 drives the roller gear 23 to rotate, and at the same time drives the active roller 21 and the passive roller 22 to rotate, so that the fiber felt is fed into the first-stage pre-plasticizing mechanism 31 of the injection assembly 3.

[0090] The first-stage screw 312 winds the fiber felt introduced by the felt feeding assembly 2 around the outer periphery of the first-stage screw 312, realizing the conveying of the fiber felt from the front conveying section 314 to the rear conveying section 315. The fiber is pre-plasticized in the rear conveying section 315, and the thermoplastic resin long fiber is heated to the melting point. Then the material in the rear conveying section 315 is conveyed to the second-stage injection mechanism 32.

[0091] The material enters the compression section 325 of the two-stage injection structure. Within the compression section 325, the thermoplastic resin material is mixed, compressed, and pressurized for degassing through the combined action of the wave-shaped screw groove of the second-stage screw 322 and the heater 5. The raw material in this section is almost completely melted. The second-stage drive component 323 drives the second-stage screw 322 to rotate, conveying the material from the compression section 325 to the metering section 326. The metering section 326 ensures that the thermoplastic resin material is completely melted and that the temperature and mixing are uniform. Simultaneously, the injection drive component 324 drives the second-stage screw 322 in reciprocating motion, and the material in the metering section 326 enters the mold assembly 4 through the nozzle 327 to complete the injection molding process.

[0092] The injection molding machine described in this embodiment of the invention can improve the fiber retention length in long fiber reinforced composite materials, increase the uniformity of fiber distribution, reduce the risk of fiber agglomeration, and improve the quality of long fiber reinforced composite materials; it can also improve the degree of automation, realize continuous injection molding production, improve injection molding efficiency, and optimize assembly dimensions to reduce space occupancy. Figure 8 The conventional injection molding equipment has a structure that cannot achieve continuous injection molding of long fiber reinforced composite materials. Moreover, the injection process can cause the fiber mat to break and the aramid long fibers to be damaged, making it impossible to produce high-quality long fiber reinforced composite materials.

[0093] Specific embodiments of preparing aramid long fiber reinforced thermoplastic resin matrix composites using the injection molding equipment described in this invention are as follows:

[0094] Example 1

[0095] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0096] S1. Preparation of blended yarn strips:

[0097] Using a textile industry cleaning and combing equipment, 51mm long aramid fibers (para-aramid fibers, denier 1.5D) and 51mm long PPS fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 40:60.

[0098] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 330 r / min, the secondary roller speed at 700 r / min, and the doffer speed at 5 r / min; the drawing frame combines and drafts eight slivers, with a total draft ratio of 8.5 times and a back zone draft ratio of 1.2 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0099] S2. Preparation of fiber felt:

[0100] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.3 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 160℃.

[0101] S3, Melt Mixing and Injection Molding:

[0102] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0103] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0104] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0105] The first-order screw accounts for 25% of the length in the front conveying section and 75% of the length in the rear conveying section.

[0106] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 30%:50%:20%.

[0107] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0108] Rear conveying section: The temperature rises to 310℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-order screw changes from 25mm to 50mm.

[0109] Compression section: Temperature maintained at 320℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 1.0 times the lead.

[0110] Metering section: The temperature is maintained at the same level as the compression section, the pitch is 50mm, the conveying is stable, and the melt pressure is established.

[0111] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0112] Injection pressure: 160MPa;

[0113] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0114] Mold temperature: 80℃;

[0115] Cooldown time: 30 seconds.

[0116] Example 2

[0117] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0118] S1. Preparation of blended yarn strips:

[0119] Using a textile industry cleaning and combing equipment, 51mm long aramid fibers (para-aramid fibers, denier 1.5D) and 51mm long PA6 fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 40:60.

[0120] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 350 r / min, the secondary roller speed at 750 r / min, and the doffer speed at 7 r / min; the drawing frame combines and drafts up to 6 slivers, with a total draft ratio of 8 times and a back zone draft ratio of 1.1 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0121] S2. Preparation of fiber felt:

[0122] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.2 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 110℃.

[0123] S3, Melt Mixing and Injection Molding:

[0124] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0125] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0126] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0127] The first-order screw accounts for 30% of the length in the front conveying section and 70% of the length in the rear conveying section.

[0128] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 50%:30%:20%.

[0129] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0130] Rear conveying section: The temperature rises to 240℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-stage screw changes from 25mm to 50mm.

[0131] Compression section: Temperature maintained at 250℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 1.0 times the lead.

[0132] Metering section: The temperature is kept consistent with that of the compression section, the pitch is 50mm, the feed is stable, and the melt pressure is established.

[0133] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0134] Injection pressure: 140 MPa;

[0135] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0136] Mold temperature: 80℃;

[0137] Cooldown time: 30 seconds.

[0138] Example 3

[0139] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0140] S1. Preparation of blended yarn strips:

[0141] Using a textile industry cleaning and combing equipment, 51mm long aramid fibers (para-aramid fibers, denier 1.5D) and 51mm long PP fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 40:60.

[0142] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 450 r / min, the secondary roller speed at 800 r / min, and the doffer speed at 10 r / min; the drawing frame combines and drafts eight slivers, with a total draft ratio of 9 times and a back zone draft ratio of 1.5 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0143] S2. Preparation of fiber felt:

[0144] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.1 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 80℃.

[0145] S3, Melt Mixing and Injection Molding:

[0146] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0147] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0148] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0149] The first-order screw accounts for 30% of the length in the front conveying section and 70% of the length in the rear conveying section.

[0150] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 40%:40%:20%.

[0151] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0152] Rear conveying section: The temperature rises to 210℃, and the thermoplastic resin melts and impregnates the aramid filament fibers through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-order screw changes from 25mm to 50mm.

[0153] Compression section: Temperature maintained at 230℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 1.0 times the lead.

[0154] Metering section: The temperature is maintained at the same level as the compression section, the pitch is 50mm, the conveying is stable, and the melt pressure is established.

[0155] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0156] Injection pressure: 120MPa;

[0157] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0158] Mold temperature: 80℃;

[0159] Cooldown time: 30 seconds.

[0160] Example 4

[0161] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0162] S1. Preparation of blended yarn strips:

[0163] Using a textile industry cleaning and combing equipment, 80mm long aramid fibers (para-aramid fibers, denier 1.5D) and 80mm long polyamide 66 fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 10:90.

[0164] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 300 r / min, the secondary roller speed at 700 r / min, and the doffer speed at 5 r / min; the drawing frame combines up to 7 slivers and drafts them, with a total draft ratio of 10 and a back zone draft ratio of 1.5, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0165] S2. Preparation of fiber felt:

[0166] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.3 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 90℃.

[0167] S3, Melt Mixing and Injection Molding:

[0168] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0169] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0170] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0171] The first-order screw accounts for 40% of the length in the front conveying section and 60% of the length in the rear conveying section.

[0172] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 50%:30%:20%.

[0173] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0174] Rear conveying section: The temperature rises to 250℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-stage screw changes from 25mm to 50mm.

[0175] Compression section: Temperature maintained at 260℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 3 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 0.5 times the lead.

[0176] Metering section: The temperature is kept consistent with that of the compression section, the pitch is 50mm, the feed is stable, and the melt pressure is established.

[0177] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0178] Injection pressure: 140 MPa;

[0179] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0180] Mold temperature: 80℃;

[0181] Cooldown time: 30 seconds.

[0182] Example 5

[0183] A method for preparing an aramid long fiber reinforced thermoplastic resin-based composite material:

[0184] S1. Preparation of blended yarn strips:

[0185] Using a textile industry cleaning and combing equipment, 38mm long aramid fibers (para-aramid fibers, denier 1.5D) and 38mm long PPS fibers (denier 2D, purchased from Guangzhou Longta Chemical Fiber) are blended at a mass ratio of 30:70.

[0186] The carding and combing equipment sequentially performs the following processes: In the carding machine, the fiber raw material is opened by a beater; the carding machine uses the carding cloth of the cylinder and the flats to fully mix the aramid long fibers and thermoplastic resin long fibers, with the cylinder speed at 330 r / min, the secondary roller speed at 700 r / min, and the doffer speed at 5 r / min; the drawing frame combines and drafts eight slivers, with a total draft ratio of 8.5 times and a back zone draft ratio of 1.2 times, forming a uniform blended yarn. The linear density of this yarn is controlled at 3000 tex, and the breaking strength is ≥15 cN / tex.

[0187] S2. Preparation of fiber felt:

[0188] The blended yarn is fed into the airflow dispersion chamber and the preheating chamber in sequence through the conveying guide roller and the spiral pushing mechanism. The spiral pushing mechanism conveys the blended yarn to the airflow dispersion chamber at a uniform speed of 20 r / min. In the airflow dispersion chamber, compressed air of 0.3 MPa is used to break the yarn into single fibers under the impact of the airflow to obtain fiber mat (the width of the fiber mat is 50 mm). The preheating chamber raises the fiber temperature to 160℃.

[0189] S3, Melt Mixing and Injection Molding:

[0190] The fiber felt is sequentially fed into the first-stage pre-plasticizing mechanism and the second-stage injection mechanism for conveying and melting, and then enters the mold assembly for injection molding;

[0191] The first-stage pre-plasticizing mechanism and the second-stage injection mechanism are respectively equipped with a first-stage screw and a second-stage screw; the fiber felt first enters the rear conveying section through the front conveying section of the first-stage pre-plasticizing mechanism, where it is preheated and melted, and then enters the compression section of the second-stage injection mechanism, where it is mixed, compressed and pressurized to exhaust air, and then enters the metering section to be mixed evenly before injection molding.

[0192] The length-to-diameter ratio of the first-order screw and the second-order screw is 24:1, and the compression ratio of the fiber felt raw material in the injection molding equipment is 2.5:1.

[0193] The first-order screw accounts for 30% of the length in the front conveying section and 70% of the length in the rear conveying section.

[0194] The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is 35%:45%:20%.

[0195] Front conveyor section: transports the fiber felt to the rear conveyor section;

[0196] Rear conveying section: The temperature rises to 310℃, and the thermoplastic resin melts and impregnates the aramid filament fiber through shearing and conduction; from the beginning of the front conveying section to the end of the rear conveying section, the pitch of the first-order screw gradually changes from 25mm to 50mm.

[0197] Compression section: Temperature maintained at 320℃, mixing residence time approximately 45s; screw diameter 50mm, groove depth gradually decreasing from 7.5mm to 3.0mm; the amplitude of the groove wave structure is 1 / 6 of the maximum groove depth (the amplitude of each wave structure is calculated based on the maximum groove depth within the next wavelength); the wavelength of the wave structure is 2.5 times the lead.

[0198] Metering section: The temperature is maintained at the same level as the compression section, the pitch is 50mm, the conveying is stable, and the melt pressure is established.

[0199] During injection molding, the uniformly mixed material is injected into the mold assembly, and the molding parameters are set as follows:

[0200] Injection pressure: 160MPa;

[0201] Pressure holding pressure: 80MPa, pressure holding time: 20s;

[0202] Mold temperature: 80℃;

[0203] Cooldown time: 30 seconds.

[0204] Comparative Example 1

[0205] The composite material was prepared using the same method as in Example 1, except that the bottom surface of the screw groove of the second-order screw in the compression section of Comparative Example 1 was a smooth screw groove (not a wavy structure), and the other process conditions were the same as in Example 1.

[0206] Comparative Example 2

[0207] The composite material was prepared using the same method as in Example 1, except that: in this Comparative Example 2, the lengths of the first-stage screw and the first-stage barrel were increased, and a compression section with the same proportional length as in Example 1 was placed in the first-stage barrel; only the metering section was retained in the second-stage barrel, and other process conditions were the same as in Example 1.

[0208] Comparative Example 3

[0209] The composite material was prepared using the same method as in Example 1, except that: in Comparative Example 3, the length ratio of the compression section was shortened; in Comparative Example 3, the ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section was 50%:20%:30%; and other process conditions were the same as in Example 1.

[0210] Comparative Example 4

[0211] The composite material was prepared using the same method as in Example 1, except that the length ratio of the extended compression section in Comparative Example 4, the ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section in Comparative Example 4 were 20%:70%:10%, and other process conditions were the same as in Example 1.

[0212] All composite materials used in the above embodiments and comparative examples were injection molded into samples with the same structural dimensions. The tensile sample dimensions were based on GB / T 1040.3-2022, and the bending sample dimensions were based on GB / T 9341-2008. Performance tests were performed on these injection-molded samples, and the specific test results are shown in Table 1 below. The test methods involved were in accordance with ISO 527 standard.

[0213] Table 1 Performance Test Results

[0214]

[0215] The experimental data above show that the aramid long fiber reinforced thermoplastic resin matrix composite samples prepared by the injection molding equipment and injection molding method described in Examples 1-5 have superior tensile strength and flexural modulus properties. Moreover, through improvements in process conditions and equipment structure, mass production of aramid long fiber reinforced thermoplastic resin matrix composites by injection molding can be achieved, with improved production efficiency and reduced costs compared to continuous fiber composites. In terms of performance balance, the appropriate length of the long fibers avoids the problems of short fiber agglomeration and interlaminar defects in continuous fibers, thereby improving the interlaminar shear strength of the composite material and effectively expanding the application boundaries of the composite material.

[0216] A comparison of the data from Comparative Example 1 and Example 1 shows that if the bottom surface of the screw groove of the second-order screw in the compression section is a smooth screw groove (not a wavy structure), the mechanical properties of the prepared long fiber plastic will be reduced because the smooth screw groove leads to uneven fiber dispersion and easy agglomeration.

[0217] The data comparison between Comparative Example 2 and Example 1 shows that if the compression section is set in the first-stage barrel and only the metering section is retained in the second-stage barrel, the mechanical properties of the prepared long-fiber plastic will be reduced because it will cause uneven fiber dispersion and easy agglomeration. At the same time, it will reduce the retention length of the fiber in the final part and affect the reinforcement effect of the composite material.

[0218] A comparison of the data from Comparative Example 3 and Example 1 shows that shortening the length ratio of the compression section reduces the mechanical properties of the prepared long-fiber plastic because it leads to uneven fiber dispersion and easy agglomeration.

[0219] A comparison of the data from Comparative Example 4 and Example 1 shows that if the length ratio of the compression section is extended, the mechanical properties of the prepared long-fiber plastic are reduced because the retention length of the fiber in the final part is reduced, which affects the reinforcement effect of the composite material.

[0220] 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 exhaustively listed. 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.

[0221] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. An injection molding machine for long fiber reinforced composite materials, characterized in that, The injection molding equipment includes: A felting assembly; a fiber felt made of a blend of aramid long fibers and thermoplastic resin long fibers is placed on the felting assembly. Felt feed assembly; An injection assembly includes a first-stage pre-plasticizing mechanism and a second-stage injection mechanism. The first-stage pre-plasticizing mechanism includes a first-stage barrel, a first-stage screw located within the first-stage barrel, and a drive component for rotating the first-stage screw. The first-stage barrel includes a front conveying section and a rear conveying section, with a heater located on the outer side of the rear conveying section. The second-stage injection mechanism includes a second-stage barrel communicating with the rear conveying section, a second-stage screw located within the second-stage barrel, a drive component for rotating the second-stage screw, and a drive component for reciprocating injection motion of the second-stage screw. A heater is located on the outer side of the second-stage barrel, which includes a compression section and a metering section. The bottom surface of the screw groove of the second-stage screw located in the compression section has a wavy structure. Mold assembly; the metering section is connected to the mold assembly via a nozzle; The pitch of the first-stage screw located in the front conveying section is less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw and the first-stage barrel located in the front conveying section is less than the thickness of the fiber felt. The pitch of the first-stage screw located in the rear conveying section is not less than the width of the fiber felt, and the gap between the tooth crest of the first-stage screw located in the rear conveying section and the first-stage barrel is less than the gap between the tooth crest of the first-stage screw located in the front conveying section and the first-stage barrel.

2. The injection molding equipment for long fiber reinforced composite materials according to claim 1, characterized in that, The felt-releasing assembly includes a felt cylinder and a braking component that provides tension to the fiber felt. The fiber felt is wound on the felt cylinder, and the felt cylinder is connected to the braking component via a connecting shaft.

3. The injection molding equipment for long fiber reinforced composite materials according to claim 1, characterized in that, The felt feeding assembly includes an active roller, a passive roller, a roller gear, and a screw gear; the screw gear is fixedly installed with the first-order screw, the screw gear meshes with the roller gear, the roller gear is fixedly installed with the active roller on the active shaft, the active roller and the passive roller together clamp the fiber felt, and the rotation of the active roller drives the passive roller to rotate, causing the fiber felt to be fed into the front conveying section of the injection assembly.

4. The injection molding equipment for long fiber reinforced composite materials according to claim 1, characterized in that, The length of the first-order screw in the front conveying section accounts for 20-40%, and the length of the first-order screw in the rear conveying section accounts for 60-80%. The ratio of the total length of the first-order screw in the front conveying section and the rear conveying section, the length of the second-order screw in the compression section, and the length of the second-order screw in the metering section is (20-50%): (25-60%): (10-30%).

5. The injection molding equipment for long fiber reinforced composite materials according to claim 4, characterized in that, When the thermoplastic resin long fiber is made of polycarbonate or rigid polyvinyl chloride, the length of the second-stage screw in the compression section accounts for 25-40% of the total working length of the first-stage and second-stage screws; when the thermoplastic resin long fiber is made of polyetheretherketone or polyphenylene sulfide, the length of the second-stage screw in the compression section accounts for 40-60% of the total working length of the first-stage and second-stage screws. When the thermoplastic resin long fiber is a heat-sensitive material, the length of the second-order screw in the metering section accounts for 10-20% of the total working length of the first-order screw and the second-order screw; when the thermoplastic resin long fiber is a non-heat-sensitive material, the length of the second-order screw in the metering section accounts for 20-30% of the total working length of the first-order screw and the second-order screw.

6. The injection molding equipment for long fiber reinforced composite materials according to claim 1, characterized in that, The groove depth of the second-order screw located in the metering section is (0.03-0.1)*D, where D is the diameter of the second-order screw.

7. The injection molding equipment for long fiber reinforced composite materials according to claim 1, characterized in that, The radius of the fillet of the wave structure at the bottom of the spiral groove is not less than 0.5 mm, the amplitude of the wave structure is 1 / 6 to 1 / 3 of the spiral groove depth, and the wavelength of the wave structure is 0.5 to 2.5 times the lead. From the inlet to the outlet direction of the second-stage barrel, the screw groove volume of the second-stage screw in the compression section gradually decreases.

8. The injection molding equipment for long fiber reinforced composite materials according to claim 1, characterized in that, The aramid long fiber has a length of 30 mm-80 mm; The total weight of the aramid long fiber and the thermoplastic resin long fiber is calculated as 100, and the weight ratio of the aramid long fiber and the thermoplastic resin long fiber is (10-40):(60-90).

9. An injection molding method for a long fiber reinforced composite material, characterized in that, The injection molding method is as follows: injection molding of long fiber reinforced composite materials using the injection molding equipment described in any one of claims 1-8. Fiber felt is placed on the felt-laying assembly, and the fiber felt is fed to the injection assembly through the felt-feeding assembly. Through the rotation of the first-stage screw and the second-stage screw, the fiber felt material is conveyed from the first-stage barrel to the second-stage barrel. The fiber felt first enters the rear conveying section through the front conveying section, where it is preheated and melted. Then it enters the compression section, where it is mixed, compressed, and pressurized for degassing. Finally, it enters the metering section for further mixing and homogenization. The double injection molding motion of the second-stage screw injects the mixed material into the mold assembly through the nozzle.

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