Device and method for preparing short fiber unidirectional distribution annular gradient density preform

Abstract

The invention discloses a device and a method for preparing a short fiber unidirectional distribution annular gradient density preform, and belongs to the technical field of short fiber preforms. The device comprises a short fiber preform mold, the short fiber preform mold is driven by a centrifugal power module to rotate around a centrifugal shaft, carbon fiber slurry in the short fiber preform mold separates carbon fibers to the circumferential direction away from the centrifugal shaft under the action of centrifugal force, and the carbon fibers are distributed in an annular gradient density mode; and performing directional freezing and shaping on the centrifuged carbon fiber slurry through a freezing and shaping module communicated with the short fiber preform mold, and finishing orientation of the carbon fibers in the shaping process so as to obtain an annular structure in which the carbon fibers are distributed unidirectionally. According to the method, unidirectional fiber distribution of the annular carbon fiber preform is realized in a manner of combining centrifugal forming and directional freeze drying, and the problem that in the prior art, unidirectional distribution of short fibers in an annular part in the axial direction cannot be realized is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of short fiber preforms, and in particular relates to a device and a method for preparing a short fiber unidirectionally distributed annular gradient density preform. Background Art

[0002] Chopped carbon fiber reinforced metal matrix composites have the advantages of low cost, strong processability, and flexible forming methods. Compared with continuous fiber reinforced metal matrix composites, they have broader application prospects. Although chopped carbon fibers have a strengthening effect on the mechanical properties of the metal matrix, the short fibers are often randomly distributed in the matrix, and the fibers at a large angle to the load direction are difficult to play a role in load transfer, making it difficult to improve the performance of chopped carbon fiber reinforced metal matrix composites. Therefore, the preparation of a chopped carbon fiber preform with a unidirectional distribution configuration (or the realization of a directional arrangement of chopped carbon fibers) is a key issue that needs to be solved urgently.

[0003] In the currently disclosed method for preparing a unidirectionally distributed short carbon fiber preform, the short carbon fibers are unidirectionally distributed in the preform by extrusion, and then a pressure infiltration method is used to prepare a short carbon fiber reinforced magnesium-based composite material with unidirectional distribution. However, due to the limitation of the preform structure, the disclosed preparation method cannot be implemented for other shapes, such as a gradient density distribution short fiber preform with a ring structure. Summary of the invention

[0004] Technical issues to be solved:

[0005] In order to avoid the shortcomings of the prior art, the present invention provides a device and method for preparing a short fiber unidirectional distribution annular gradient density preform. Based on the structural characteristics of the annular preform, the device uses centrifugal force to advance the carbon fibers in the carbon fiber slurry in the tangential direction of the motion trajectory, so that the carbon fibers gradually move away from the center along the direction of the centrifugal force under the action of the centrifugal force, thereby forming a gradient density annular structure, and then the unidirectional arrangement of the carbon fibers is achieved through the directional freezing method of the shaping module; the present invention adopts a combination of centrifugal forming + directional freeze-drying to achieve unidirectional distribution of fibers in the annular gradient density carbon fiber preform, which solves the problem that the prior art cannot achieve unidirectional distribution of short fibers in the annular part along the axial direction.

[0006] The technical solution of the present invention is: a device for preparing a short fiber unidirectionally distributed annular gradient density preform, comprising a short fiber preform mold, wherein the short fiber preform mold is driven by a centrifugal power module to rotate around a centrifugal axis, so that the carbon fiber slurry inside the short fiber preform separates the carbon fiber to a circumferential direction away from the centrifugal axis under the action of centrifugal force, presenting an annular gradient density distribution; the carbon fiber slurry after centrifugal treatment is shaped by a shaping module connected to the short fiber preform mold, and the carbon fiber is oriented during the shaping process to obtain an annular gradient density configuration in which the carbon fiber is unidirectionally distributed.

[0007] A further technical solution of the present invention is that the short fiber preform mold includes an inner cavity for accommodating carbon fiber slurry, and the profile of the inner cavity peripheral wall is consistent with the shape of the outer peripheral surface of the annular preform to be prepared.

[0008] A further technical solution of the present invention is: the short fiber preform mold includes a mold cavity and a centrifugal mold cover and a centrifugal seat encapsulated at the upper and lower ends thereof, the inner bottom surface of the centrifugal seat is coaxially opened with a countersunk hole and a center through hole, the aperture of the countersunk hole is larger than the inner diameter of the mold cavity, and an isolation layer is arranged between the upper orifice of the countersunk hole and the mold cavity, and the inner cavity containing the carbon fiber slurry and the bottom countersunk hole and the center through hole are isolated by the isolation layer; the centrifugal seat is fixedly connected to the centrifugal shaft of the centrifugal power module.

[0009] A further technical solution of the present invention is that the inner cavity peripheral wall is square, circular or has peripheral protrusions / grooves in a circular array.

[0010] A further technical solution of the present invention is: the centrifugal power module includes a centrifugal shaft, a transmission assembly and a motor, and the rotational torque output by the motor is transmitted to the centrifugal shaft through the transmission assembly, driving the centrifugal shaft to rotate around the axis.

[0011] A further technical solution of the present invention is: the centrifugal shaft is provided with a through hole along the axial direction, the top end of the centrifugal shaft is coaxially connected with the central through hole of the centrifugal seat, and the through hole of the centrifugal shaft is connected with the inner cavity of the counterbore of the centrifugal seat through the central through hole of the centrifugal seat, and the through hole opening at the bottom end is connected with the shaping module to pass the medium used for shaping into the inner cavity of the counterbore.

[0012] A further technical solution of the present invention is: the outer shape of the mold cavity is cylindrical, the top of its inner cavity is a circular surface with an internal thread, which is connected to the centrifugal mold cover through threads, and the outer circumferential surface of its bottom is provided with an annular protrusion; the main body of the centrifugal seat is a disc structure, and an annular boss is provided at the circumferential outer edge of the top surface of the disc, the inner diameter of the annular boss is consistent with the outer diameter of the annular protrusion of the mold cavity, the bottom end of the mold cavity is embedded in the annular boss, and the bottom of the mold cavity and the centrifugal seat are pressed and fixed by a mold pressure ring and bolts; the isolation layer is pressed between the bottom surface of the mold cavity and the disc surface of the centrifugal seat to separate the mold cavity from the countersunk inner cavity on the centrifugal seat.

[0013] A further technical solution of the present invention is: the shaping module comprises a liquid nitrogen delivery pipe, a liquid nitrogen nozzle, a liquid nitrogen boosting pipe, a boosting pump, and a liquid nitrogen bottle which are connected in sequence; the outlet end of the liquid nitrogen delivery pipe is sealed and connected to the through hole opening at the bottom end of the centrifugal shaft; the liquid nitrogen is passed from the liquid nitrogen bottle into the liquid nitrogen boosting pipe through the boosting pump, and then sprayed out through the liquid nitrogen nozzle, through the liquid nitrogen delivery pipe and the through hole of the centrifugal shaft, into the sink hole inner cavity of the centrifugal base, and then the low temperature is transferred to the carbon fiber slurry through the isolation layer, so as to complete the directional freezing shaping of the carbon fiber slurry.

[0014] A further technical solution of the present invention is: the isolation layer is copper foil.

[0015] A method for preparing a short fiber unidirectional distribution annular gradient density preform, the specific steps are as follows:

[0016] The chopped carbon fiber, dispersant and deionized water are mixed in a mass ratio of 10:0.2:500, stirred to obtain a uniformly dispersed carbon fiber slurry, and the slurry is injected into a short fiber preform mold;

[0017] The centrifugal power module is started to drive the short fiber preform mold to rotate through the centrifugal shaft, and the short chopped carbon fibers in the carbon fiber slurry move away from the centrifugal shaft under the action of centrifugal force to form short chopped carbon fibers with an annular gradient density distribution; the rotation speed of the centrifugal shaft is 1500-3000 r / min;

[0018] After the short-cut carbon fibers are distributed in an annular gradient density, the shaping module is turned on to pass liquid nitrogen into the short-fiber preform mold to perform directional freezing shaping on the carbon fiber slurry in the short-fiber preform mold;

[0019] After the carbon fiber slurry is completely frozen to an ice crystal state, the shaping module and the centrifugal power module are closed;

[0020] The carbon fiber slurry frozen into an ice crystal state is taken out and subjected to a vacuum freeze-drying treatment to remove moisture from the carbon fiber, thereby obtaining a ring-shaped preform in which the fibers are distributed in one direction.

[0021] Beneficial Effects

[0022] The beneficial effects of the present invention are as follows: the device of the present invention can realize the preparation of annular gradient density chopped carbon fiber preforms with a unidirectional distribution configuration through centrifugal forming + directional freezing + vacuum freeze drying. In the device, the short fiber preform mold is designed in a layered manner, wherein the mold cavity serves as a container for the carbon fiber slurry, and the inner cavity of the countersunk hole of the centrifugal seat serves as a container for the shaping medium. The two substances are separated, and copper foil is used as a partition layer to achieve lossless transmission of low temperature; the centrifugal shaft of the centrifugal power module couples the transmission and liquid nitrogen supply into one, which can simultaneously achieve stable transmission of centrifugal force and directional transmission of liquid nitrogen while simplifying the structure. Further advantages are as follows:

[0023] (1) No chemical substances such as binders are added during the preparation of the preform, so no impurities are introduced to affect the performance of the final composite material.

[0024] (2) The wall thickness of the annular preform can be controlled by adjusting the centrifugal speed.

[0025] (3) Based on the influence of centrifugal action on the fiber distribution space and directional freezing on the fiber orientation, the present invention realizes the rapid preparation of annular short-cut carbon fiber preforms with a unidirectional distribution configuration, which can greatly improve the performance of the composite material along the fiber distribution direction; wherein, liquid nitrogen is sprayed onto the copper foil at the bottom of the carbon fiber slurry cavity, which can make the carbon fiber slurry freeze into an ice crystal state from bottom to top. At this time, the fibers are arranged along the growth direction of the ice crystals, that is, unidirectionally arranged carbon fibers are obtained; by changing the position of the liquid nitrogen cavity in the short fiber preform mold, the direction of the elastic unidirectional arrangement can be changed.

[0026] (4) By changing the size and shape of the mold cavity, rapid prototyping of large-sized or variable-section annular chopped carbon fiber preforms with a unidirectional distribution configuration can also be achieved.

[0027] (5) In the preparation method of the present invention, the rotation speed of the centrifugal shaft is limited to 1500-3000 r / min. 3 ) is slightly higher than the density of water (1.0g / cm 3 ), at this speed, the uniformity of the carbon fiber after centrifugation can be guaranteed, and the carbon fiber has a gradient density distribution along the radial direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of a device for preparing an annular gradient density chopped carbon fiber preform with a unidirectional distribution configuration according to an embodiment of the present invention.

[0029] Figure 2 and Figure 3 1 is a microstructure diagram of an annular gradient density carbon fiber preform with a unidirectional distribution configuration at different positions of Example 2 of the present invention, Figure 2 To be close to the outer circle of the ring, Figure 3 To get close to the inner circle of the annular part (pyrolytic carbon is deposited on the prepared annular preform, and liquid resin is infiltrated by vacuum negative pressure method. After the resin is solidified, samples are taken to observe the fiber distribution law by scanning electron microscopy).

[0030] Figure 4 is a scanning electron micrograph of Example 3 of the present invention.

[0031] Description of the accompanying drawings: 1-centrifugal mold cover, 2-mold cavity, 3-mold pressure ring, 4-centrifugal seat, 5-centrifugal shaft, 6-upper bearing end cover, 7-upper sealing gasket, 8-bearing seat, 9-upper angular contact ball bearing, 10-bearing positioning sleeve, 11-lower angular contact ball bearing, 12-lower sealing gasket, 13-lower bearing end cover, 14-bracket, 15-base, 16-small synchronous pulley, 17-lower elastic retaining ring , 18-small pulley key, 19-liquid nitrogen delivery pipe, 20-liquid nitrogen nozzle, 21-liquid nitrogen booster pipe, 22-boosting pump, 23-liquid nitrogen bottle, 24-shaft end retaining ring, 25-large synchronous pulley, 26-large pulley positioning sleeve, 27-motor, 28-large pulley key, 29-synchronous belt, 30-lower double-lip sealing ring, 31-upper elastic retaining ring, 32-upper double-lip sealing ring, 34-copper foil, 35-carbon fiber slurry. DETAILED DESCRIPTION

[0032] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0034] The chopped carbon fiber preform with a unidirectional distribution configuration prepared based on the prior art has a single shape and cannot obtain a chopped carbon fiber preform with an annular structure. The present invention provides a device for preparing a short fiber unidirectional distribution annular gradient density preform, including a short fiber preform mold, wherein the short fiber preform mold is driven by a centrifugal power module to rotate around a centrifugal axis, so that the carbon fiber slurry inside the short fiber preform is separated into a circumferential direction away from the centrifugal axis under the action of centrifugal force, and presents an annular gradient density distribution; the carbon fiber slurry after centrifugal treatment is shaped by a shaping module connected to the short fiber preform mold, and the carbon fiber is oriented during the shaping process to obtain an annular gradient density configuration in which the carbon fiber is unidirectionally distributed.

[0035] Specifically, the short fiber preform mold includes an inner cavity for accommodating carbon fiber slurry, and the profile of the peripheral wall of the inner cavity is consistent with the shape of the outer peripheral surface of the annular preform to be prepared.

[0036] Specifically, the short fiber preform mold includes a mold cavity and a centrifugal mold cover and a centrifugal seat encapsulated at the upper end thereof. The inner bottom surface of the centrifugal seat is coaxially provided with a countersunk hole and a center through hole. The aperture of the countersunk hole is larger than the inner diameter of the mold cavity, and an isolation layer is arranged between the upper orifice of the countersunk hole and the mold cavity. The inner cavity containing the carbon fiber slurry and the bottom countersunk hole and the center through hole are isolated by the isolation layer; the centrifugal seat is fixedly connected to the centrifugal shaft of the centrifugal power module.

[0037] Specifically, the inner cavity peripheral wall is square, circular, or has peripheral protrusions / grooves in a circular array.

[0038] Specifically, the centrifugal power module includes a centrifugal shaft, a transmission assembly and a motor. The transmission assembly transmits the rotational torque output by the motor to the centrifugal shaft, driving the centrifugal shaft to rotate around the axis.

[0039] Specifically, the centrifugal shaft has a through hole in the axial direction, the top end of which is coaxially connected to the central through hole of the centrifugal seat, and the through hole of the centrifugal shaft is connected to the inner cavity of the sink hole of the centrifugal seat through the central through hole of the centrifugal seat, and the through hole opening at the bottom end is connected to the shaping module, so that the medium used for shaping is passed into the inner cavity of the sink hole.

[0040] Specifically, the outer shape of the mold cavity is cylindrical, and the top of its inner cavity is a circular surface with an internal thread, which is connected to the centrifugal mold cover through threads, and the outer circumferential surface of its bottom is provided with an annular protrusion; the main body of the centrifugal seat is a disc structure, and an annular boss is provided at the circumferential outer edge of the top surface of the disc, and the inner diameter of the annular boss is consistent with the outer diameter of the annular protrusion of the mold cavity. The bottom end of the mold cavity is embedded in the annular boss, and the bottom of the mold cavity and the centrifugal seat are pressed and fixed by a mold pressure ring and bolts; the isolation layer is pressed between the bottom surface of the mold cavity and the disc surface of the centrifugal seat to separate the mold cavity from the countersunk inner cavity on the centrifugal seat.

[0041] Specifically, the shaping module includes a liquid nitrogen delivery pipe, a liquid nitrogen nozzle, a liquid nitrogen boosting pipe, a boosting pump, and a liquid nitrogen bottle which are connected in sequence. The outlet end of the liquid nitrogen delivery pipe is sealed and connected to the through hole opening at the bottom end of the centrifugal shaft. The liquid nitrogen is passed from the liquid nitrogen bottle into the liquid nitrogen boosting pipe through the boosting pump, and then sprayed out through the liquid nitrogen nozzle, and sequentially passes through the liquid nitrogen delivery pipe and the through hole of the centrifugal shaft into the countersunk cavity of the centrifugal base, and then the low temperature is transferred to the carbon fiber slurry through the isolation layer, so as to complete the directional freezing shaping of the carbon fiber slurry.

[0042] Specifically, the isolation layer is copper foil.

[0043] The present invention provides a method for preparing a short fiber unidirectional distribution annular gradient density preform, and the specific steps are as follows:

[0044] Step 1: Mix chopped carbon fiber, dispersant and deionized water in a mass ratio of 10:0.2:500, stir to obtain a uniformly dispersed carbon fiber slurry, and pour it into a short fiber preform mold;

[0045] Step 2: Start the centrifugal power module, drive the short fiber preform mold to rotate through the centrifugal shaft, and the chopped carbon fibers in the carbon fiber slurry move away from the centrifugal shaft under the action of centrifugal force to form chopped carbon fibers with an annular gradient density distribution; the rotation speed of the centrifugal shaft is 1500-3000 r / min;

[0046] Step 3: After the chopped carbon fibers are distributed in an annular gradient density, the shaping module is turned on, and liquid nitrogen is passed into the short fiber preform mold to perform directional freezing shaping on the carbon fiber slurry in the short fiber preform mold;

[0047] Step 4: After the carbon fiber slurry is completely frozen to an ice crystal state, the shaping module and the centrifugal power module are closed;

[0048] Step 5: Take out the carbon fiber slurry frozen into an ice crystal state, and dry it to remove moisture from the carbon fiber, thereby obtaining a ring-shaped preform in which the fibers are distributed in one direction.

[0049] Specifically, the stirring speed in step 1 is 800-1500 r / min.

[0050] Specifically, in step 2, the rotation speed of the centrifugal shaft is 1500 to 3000 r / min.

[0051] Specifically, the freezing time in step 3 is 30 to 120 seconds.

[0052] Specifically, the drying time in step 5 is 24 to 72 hours.

[0053] The above technical solution is further described below in conjunction with the accompanying drawings:

[0054] Reference Figure 1As shown, the present embodiment is a forming device for an annular gradient density chopped carbon fiber preform with a unidirectional distribution configuration, including a centrifugal mold cover 1, a mold cavity 2, a mold pressure ring 3, a centrifugal seat 4, a centrifugal shaft 5, an upper bearing end cover 6, an upper sealing gasket 7, a bearing seat 8, an upper angular contact ball bearing 9, a bearing positioning sleeve 10, a lower angular contact ball bearing 11, a lower sealing gasket 12, a lower bearing end cover 13, a bracket 14, a base 15, a small synchronous pulley 16, a lower elastic retaining ring 17, a small pulley key 18, a liquid nitrogen delivery pipe 19, a liquid nitrogen nozzle 20, a liquid nitrogen booster pipe 21, a booster pump 22, a liquid nitrogen bottle 23, a large pulley key 28, a shaft end retaining ring 24, a large synchronous pulley 25, a large pulley positioning sleeve 26, a motor 27, a synchronous belt 29, a lower double-lip sealing ring 30, an upper elastic retaining ring 31, an upper double-lip sealing ring 32, a copper foil 33, and a carbon fiber slurry 34.

[0055] The centrifugal mold cover 1 is connected to the mold cavity 2 by threads, the copper foil 33 is connected to the bottom of the mold cavity 2 by sealant, and the carbon fiber slurry is leak-free after sealing. The mold cavity 2 is fixed by a mold pressure ring 3 and a centrifugal seat 4, and the mold pressure ring 3 and the centrifugal seat 4 are fixedly connected by bolts. A cavity is left between the mold cavity 2 and the centrifugal seat 4 for liquid nitrogen freezing;

[0056] The centrifugal seat 4 is connected to the centrifugal shaft 5 by threads, and the centrifugal shaft 5 is a hollow structure; the upper angular contact ball bearing 9 and the lower angular contact ball bearing 11 are positioned by a sleeve 10, and the upper angular contact ball bearing 9 and the lower angular contact ball bearing 11 are placed in the bearing seat 8, and the upper bearing end cover 6 and the lower bearing end cover 13 are installed at both ends of the bearing seat, which are respectively used to position the outer rings of the upper angular contact ball bearing 9 and the lower angular contact ball bearing 11, and the inner ring of the lower angular contact ball bearing 11 is positioned by an elastic retaining ring 31, and the upper bearing end cover 6 and the lower bearing end cover 13 are sealed with the bearing seat by an upper sealing gasket 7 and a lower sealing gasket 12 respectively; the upper bearing end cover 6 and the lower bearing end cover 13 are sealed with the centrifugal shaft 5 by an upper double-lip sealing ring 32 and a lower double-lip sealing ring 30 respectively, and the bearing end cover and the bearing seat are fixed by screws; the small synchronous pulley 16 is connected to the centrifugal shaft 5 by a screw; the upper bearing end cover 16 and the lower bearing end cover 13 are sealed with the centrifugal shaft 5 by an upper double-lip sealing ring 32 and a lower double-lip sealing ring 30 respectively, and the bearing end cover and the bearing seat are fixed by screws; the small synchronous pulley 16 and the centrifugal shaft The spindle 5 is connected with a flat key 18 and is positioned axially with an elastic retaining ring 17; the lower bearing end cover 13 is embedded in the bracket 14 and fixed with screws. The bracket 14 is fixed on the base 15. A hollow groove is opened at one end of the bracket for installing a synchronous belt 29 and a liquid nitrogen booster pipe 21; the large synchronous pulley 25 is connected to the motor shaft with a flat key 24, and is positioned axially with a shaft end retaining ring 24 and a large pulley positioning sleeve 26. The motor drives the large synchronous pulley 25 to rotate, and drives the small synchronous pulley 16 to rotate through the synchronous belt 29, drives the centrifugal shaft 5 to rotate, and then drives the mold cavity 2 to rotate; the liquid nitrogen delivery pipe 19 extends into the hollow inner cavity of the centrifugal shaft, does not contact the hollow inner cavity of the centrifugal shaft, the liquid nitrogen nozzle 20 is connected to the liquid nitrogen booster pipe 21, the booster pump 22, and the liquid nitrogen bottle 23 in sequence, and the liquid nitrogen nozzle 20 extends into the liquid nitrogen delivery pipe 19.

[0057] Method Example 1:

[0058] This embodiment is an operation method of a device for preparing an annular chopped carbon fiber preform with a unidirectional distribution configuration:

[0059] Step 1: First, chopped carbon fiber, dispersant, and deionized water are mixed in a ratio of 10:0.2:500, stirred at a speed of 800-1500 r / min to obtain a uniformly dispersed carbon fiber slurry 34, poured into the mold cavity 2, and the centrifugal mold cover 1 is installed and tightened.

[0060] Step 2: Control the motor 27 to drive the large synchronous pulley 25 to rotate, and drive the small synchronous pulley 16 to rotate through the synchronous belt 29. The small synchronous pulley 16 rotates at 1500-3000r / min through the centrifugal shaft 5, driving the mold cavity 2 to rotate, and then subjecting the carbon fiber slurry 34 to centrifugal action. Since the density of carbon fiber is greater than that of water, the carbon fiber is distributed in an annular gradient density in the mold cavity 2 under the centrifugal action.

[0061] Step 3: After the carbon fiber is in an annular gradient density distribution, the liquid nitrogen bottle 23 and the booster pump 22 are turned on to eject the liquid nitrogen through the liquid nitrogen booster pipe 21 and the liquid nitrogen nozzle 20. The liquid nitrogen is sprayed to the bottom of the copper foil 33 through the liquid nitrogen delivery pipe 19 under high pressure to make it in a low temperature state, thereby freezing the carbon fiber slurry 34 from the bottom to the top in a directional manner, and the freezing time is 3 to 120 seconds. After the carbon fiber slurry 34 is completely frozen to an ice crystal state, the liquid nitrogen bottle 23 and the booster pump 22 are turned off, and the motor 27 is turned off.

[0062] Step 4: Disassemble the mold pressure ring 3, the mold cavity 2, and the centrifugal mold cover 1 in sequence, and take out the carbon fiber slurry frozen into an ice crystal state.

[0063] Step 5: Place the carbon fiber slurry ice crystals obtained in step 4 into a freeze dryer and dry for 24 to 72 hours to remove moisture from the carbon fiber, thereby obtaining a ring-shaped preform in which the fibers are distributed in one direction.

[0064] Method Example 2:

[0065] The specific steps of the method for preparing an annular chopped carbon fiber preform having a unidirectional distribution configuration by using the preform preparation device in this embodiment are as follows:

[0066] Step 1: Preparation of carbon fiber slurry.

[0067] 12 g of T700 chopped carbon fiber with an average length of about 400 μm and 500 ml of 0.04% sodium polyacrylate solution (dispersant) were mixed, stirred at a speed of 1000 r / min for 15 min using a mechanical stirrer, poured into the mold cavity 2, and the centrifugal mold cover 1 was installed.

[0068] Step 2: Centrifuge.

[0069] The motor 27 is controlled to rotate, and the speed of the centrifugal shaft is 2000 r / min. The fibers are subjected to centrifugal action and are distributed in an annular gradient density along the mold cavity 2. At this time, the fibers are in a three-dimensional random distribution state.

[0070] Step 3: Directed Freezing.

[0071] The liquid nitrogen bottle 23 and the booster pump 22 are turned on, and liquid nitrogen is sprayed to the bottom of the copper foil 33 for 60 seconds, so that the carbon fiber slurry is directionally frozen from bottom to top into an ice crystal state. At this time, the fibers are arranged along the growth direction of the ice crystals.

[0072] Step 4: Preform drying.

[0073] The preform in the ice crystal state is taken out, placed in a freeze dryer and dried for 36 hours, and then taken out to obtain a ring-shaped preform with unidirectionally distributed fibers.

[0074] Step 5: Pyrolytic carbon deposition.

[0075] Methane is used as the precursor with a flow rate of 15-24 L / h, and nitrogen is used as the carrier gas with a flow rate of 0.1-0.3 m 3 / h, the deposition temperature is 950-1200℃, and the deposition time is 120min to improve the compressive strength of the preform.

[0076] Step 6: Impregnation with resin.

[0077] The epoxy resin was infiltrated with vacuum negative pressure of 0.6-0.9 MPa. After the infiltration, it was left to stand at room temperature for 24-48 hours. After solidification, a sample was taken from it. An ion sputtering instrument was used to spray gold powder on the sample surface for 20-40 seconds, and a scanning electron microscope was used for observation. Figure 2 and 3 shown.

[0078] Method embodiment 3:

[0079] The specific steps of the method for preparing an annular chopped carbon fiber preform having a unidirectional distribution configuration by using the preform preparation device in this embodiment are as follows:

[0080] Step 1: Preparation of carbon fiber slurry.

[0081] 13 g of XN-100-25M chopped carbon fiber with an average length of about 250 μm and 500 ml of 0.05% sodium polyacrylate solution (dispersant) were mixed, stirred at a speed of 1200 r / min for 30 min using a mechanical stirrer, poured into the mold cavity 2, and the centrifugal mold cover 1 was installed.

[0082] Step 2: Centrifuge.

[0083] The motor 27 is controlled to rotate, and the speed of the centrifugal shaft is 2500 r / min. The fibers are subjected to centrifugal action and are distributed in an annular gradient density along the mold cavity 2. At this time, the fibers are in a three-dimensional random distribution state.

[0084] Step 3: Directed Freezing.

[0085] The liquid nitrogen bottle 23 and the booster pump 22 are turned on, and liquid nitrogen is sprayed to the bottom of the copper foil 33 for 80 seconds, so that the carbon fiber slurry is directionally frozen from bottom to top into an ice crystal state. At this time, the fibers are arranged along the growth direction of the ice crystals.

[0086] Step 4: Preform drying.

[0087] The preform in the ice crystal state is taken out, placed in a freeze dryer and dried for 36 hours, and then taken out to obtain a ring-shaped preform with unidirectionally distributed fibers.

[0088] Step 5: Pyrolytic carbon deposition.

[0089] Methane is used as the precursor with a flow rate of 15-24 L / h, and nitrogen is used as the carrier gas with a flow rate of 0.1-0.3 m 3 / h, the deposition temperature is 950-1200℃, and the deposition time is 150min to improve the compressive strength of the preform.

[0090] Step 6: Composite material preparation.

[0091] Using AZ91D alloy as the matrix, short carbon fiber reinforced magnesium matrix composites were prepared by pressure infiltration process, and the fracture surface was observed by scanning electron microscopy. Figure 4 As shown, the fibers have an obvious unidirectional orientation pattern along the axial direction of the annular member.

[0092] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A device for preparing a short fiber unidirectional distribution annular gradient density preform, characterized in that: The invention comprises a short fiber preform mold, which is driven by a centrifugal power module to rotate around a centrifugal axis, so that the carbon fiber slurry inside the short fiber preform separates the carbon fiber to a circumferential direction away from the centrifugal axis under the action of centrifugal force, and presents an annular gradient density distribution; the carbon fiber slurry after centrifugal treatment is subjected to directional freezing and shaping by a freezing shaping module connected to the short fiber preform mold, and the orientation of the carbon fiber is completed during the shaping process to obtain an annular configuration in which the carbon fiber is unidirectionally distributed.

2. According to claim 1, a device for preparing a short fiber unidirectional distribution annular gradient density preform, characterized in that: The short fiber preform mold comprises an inner cavity for accommodating carbon fiber slurry, and the profile of the peripheral wall of the inner cavity is consistent with the shape of the outer peripheral surface of the annular preform to be prepared.

3. According to claim 1, a device for preparing a short fiber unidirectional distribution annular gradient density preform, characterized in that: The short fiber preform mold includes a mold cavity and a centrifugal mold cover and a centrifugal seat encapsulated at the upper and lower ends thereof. The inner bottom surface of the centrifugal seat is coaxially provided with a countersunk hole and a central through hole. The aperture of the countersunk hole is larger than the inner diameter of the mold cavity, and an isolation layer is arranged between the upper orifice of the countersunk hole and the mold cavity. The inner cavity containing the carbon fiber slurry and the bottom countersunk hole and the central through hole are isolated by the isolation layer; the centrifugal seat is fixedly connected to the centrifugal shaft of the centrifugal power module.

4. The device for preparing a preform with unidirectional distribution of short fibers and annular gradient density according to claim 3, characterized in that: The inner cavity peripheral wall is in the shape of a square, a circle, or a shape in which peripheral protrusions / grooves are arranged in a circular array.

5. The device for preparing a preform with unidirectional distribution of short fibers and annular gradient density according to claim 3, characterized in that: The centrifugal power module includes a centrifugal shaft, a transmission assembly and a motor. The rotational torque output by the motor is transmitted to the centrifugal shaft through the transmission assembly, driving the centrifugal shaft to rotate around the axis.

6. The device for preparing a preform with unidirectional distribution of short fibers and annular gradient density according to claim 5, characterized in that: The centrifugal shaft has a through hole in the axial direction, and its top end is coaxially connected with the central through hole of the centrifugal seat, and the through hole of the centrifugal shaft is connected with the inner cavity of the sink hole of the centrifugal seat through the central through hole of the centrifugal seat, and the through hole opening at the bottom end is connected with the shaping module to pass the medium used for shaping into the inner cavity of the sink hole.

7. The device for preparing a preform with unidirectional short fiber distribution and annular gradient density according to claim 6, characterized in that: The outer shape of the mold cavity is cylindrical, and the top of its inner cavity is a circular surface with an internal thread, which is connected to the centrifugal mold cover through threads, and the outer circumferential surface of its bottom is provided with an annular protrusion; the main body of the centrifugal seat is a disc structure, and an annular boss is provided at the circumferential outer edge of the top surface of the disc, and the inner diameter of the annular boss is consistent with the outer diameter of the annular protrusion of the mold cavity. The bottom end of the mold cavity is embedded in the annular boss, and the bottom of the mold cavity and the centrifugal seat are pressed and fixed by a mold pressure ring and bolts; the isolation layer is pressed between the bottom surface of the mold cavity and the disc surface of the centrifugal seat to separate the mold cavity from the countersunk cavity on the centrifugal seat.

8. The device for preparing a preform with unidirectional short fiber distribution and annular gradient density according to claim 3, characterized in that: The freezing and shaping module comprises a liquid nitrogen delivery pipe, a liquid nitrogen nozzle, a liquid nitrogen boosting pipe, a boosting pump, and a liquid nitrogen bottle which are connected in sequence. The outlet end of the liquid nitrogen delivery pipe is sealed and connected to the through hole opening at the bottom end of the centrifugal shaft. The liquid nitrogen is passed from the liquid nitrogen bottle into the liquid nitrogen boosting pipe through the boosting pump, and then sprayed out through the liquid nitrogen nozzle, through the liquid nitrogen delivery pipe and the through hole of the centrifugal shaft, into the sink hole inner cavity of the centrifugal base, and then the low temperature is transferred to the carbon fiber slurry through the isolation layer, so as to directionally freeze and shape the carbon fiber slurry.

9. The device for preparing a preform with unidirectional short fiber distribution and annular gradient density according to claim 8, characterized in that: The isolation layer is copper foil.

10. A method for preparing a short fiber unidirectional distribution annular gradient density preform, which is implemented by using the short fiber unidirectional distribution annular preform preparation device according to any one of claims 1 to 9, characterized in that The specific steps are as follows: The chopped carbon fiber, dispersant and deionized water are mixed in a mass ratio of 10:0.2:500, stirred to obtain a uniformly dispersed carbon fiber slurry, and the slurry is injected into a short fiber preform mold; The centrifugal power module is started to drive the short fiber preform mold to rotate through the centrifugal shaft, and the short chopped carbon fibers in the carbon fiber slurry move away from the centrifugal shaft under the action of centrifugal force to form short chopped carbon fibers with an annular gradient density distribution; the rotation speed of the centrifugal shaft is 1500-3000 r / min; After the short-cut carbon fibers are distributed in an annular gradient density, the shaping module is turned on to pass liquid nitrogen into the short-fiber preform mold to perform directional freezing shaping on the carbon fiber slurry in the short-fiber preform mold; After the carbon fiber slurry is completely frozen to an ice crystal state, the shaping module and the centrifugal power module are closed; The carbon fiber slurry frozen into an ice crystal state is taken out and dried to remove moisture from the carbon fibers, thereby obtaining a ring-shaped preform in which the fibers are distributed in one direction.

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