CN114889171A

CN114889171A - Core die and preparation method of unidirectional winding plate

Info

Publication number: CN114889171A
Application number: CN202210545462.6A
Authority: CN
Inventors: 李骏光; 朱和国
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2022-05-19
Filing date: 2022-05-19
Publication date: 2022-08-12

Abstract

The invention discloses a core mould, which comprises a core plate made of a polytetrafluoroethylene flat plate, two straight steel plates and two clamping plates, wherein the core plate is made of a polytetrafluoroethylene flat plate; the two straight steel plates respectively abut against two sides of the core plate in the width direction, the core plate and the two straight steel plates form a winding plate together, and the middle part of the winding plate in the first direction forms a winding area; the two clamping plates are arranged at intervals along a first direction, two ends of the winding plate in the first direction are respectively inserted into the clamping grooves of one clamping plate, and two ends of the core plate in the first direction and two ends of each straight steel plate in the first direction are respectively inserted into the clamping grooves; the first strip hole of through-hole form is all seted up in the both sides in the winding district of every straight steel sheet, and first strip hole is located between winding district and the cardboard. The application also discloses a method for preparing the unidirectional winding plate by adopting the core mould. By the aid of the method, deformation of the core mold can be reduced, and demolding performance of the composite material is improved.

Description

Core die and preparation method of unidirectional winding plate

Technical Field

The invention relates to a core die and a preparation method of a unidirectional winding plate.

Background

The unidirectional fiber reinforced plastic flat plate is a plate-shaped structure similar to a fabric, and is formed by continuously winding single reinforcing fiber yarn bundles in yarn rolls according to a specified interval and sequentially arranging the single reinforcing fiber yarn bundles on a core mold. This is the most basic and intuitive test method for evaluating the performance of reinforced fiber composites.

At present, the molding process of the unidirectional winding plate is mainly divided into a dry method and a wet method, wherein the wet method is to wind fibers soaked with resin on a core mold, and then to mold the unidirectional fiber reinforced plastic plate by a method of pressing and curing through a pressing plate; the dry method adopts dry yarn without impregnated resin to wind on the core mould directly, and then the dry fiber board wound on the core mould is introduced into the resin molding unidirectional fiber reinforced plastic board by adopting the composite material molding process such as vacuum infusion or RTM. Through experimental data analysis in practice, the dry-method forming mode is adopted, data are more stable, and the wet-state forming mode is characterized in that fibers impregnated with resin are placed in air, so that even if the resin is subjected to pre-defoaming operation, air is introduced along with the rotation of a core mold, air bubbles are fully distributed in gaps between tows, the air bubbles cannot be effectively removed in a later pressure forming process, a large number of pores are formed in a formed unidirectional winding plate, the mechanical property of the unidirectional winding plate is poor, and the problem occurs in the sample preparation process, so that the obtained experimental data cannot effectively reflect the real property of the reinforcing fibers. In addition, the wet process has the defects of complex operation process, high pollution, high post-treatment difficulty and the like, so that the usage amount of the wet process is small.

In addition, the dry process also has the following problems: the core mould of the current unidirectional winding plate is composed of a metal plate with the length and width of at least 400mm and the thickness of at least 7mm, the end of the reinforced fiber yarn is pulled out from a yarn roll during sample preparation and is fixed on the core mould, the yarn is wound on the core mould by rotating the core mould, and the distance between every two yarns is kept according to the width of the yarn, so that the yarns are arranged in parallel. After winding, when performing composite molding of core yarn and resin, the following two methods are generally adopted: the first method is that the core mould and the yarn are placed together in a vacuum bag film for vacuum infusion or a closed mould cavity of RTM technology for composite material forming; the second method is to lay a polyester film on the core mould, fix the first layer of yarn layer on the polyester film by means of double-sided adhesive tape, fix the yarn layers with the double-sided adhesive tape, cut the parallel and side-by-side yarns after winding, take the yarns off the core mould together with the film, put them into the vacuum bag film of vacuum infusion or the sealed mould cavity of RTM process, and form the composite material. The first method has the advantages that the tension of the yarn is kept uniform, the formed board surface is flat, but the biggest problem is that the yarn is difficult to separate from a core mould after being compositely formed with resin, the separation process not only causes unknown damage to a sample, but also damages the surface flatness of the core mould, meanwhile, because the time period of the composite forming process is long, generally at least 2 days, but a delivery inspection client may entrust a plurality of groups of winding sample preparation tasks, a detection mechanism has to be provided with a large number of core moulds to ensure the timeliness of sample preparation, which inevitably brings a large amount of cost investment, and the pure metal core moulds with the size and thickness have large weight, and in the operation process, the core moulds are frequently disassembled, which further brings labor cost and potential safety hazards of operators. The second method is a way to solve the disadvantages of the first method, but fixing the fiber by the double-sided adhesive tape cannot ensure that the tension of each yarn is not changed after cutting, which causes unstable data of the sample after composite molding during detection, and especially in the sample preparation condition that multiple layers need to be wound, the double-sided adhesive tape needs to be adhered to each layer, thereby reducing the sample preparation efficiency.

Disclosure of Invention

In order to solve the problems, the invention firstly provides a core die which comprises a core plate, two straight steel plates and two clamping plates; the core plate is made of a polytetrafluoroethylene flat plate, the length of the core plate extends along a first direction, the width of the core plate extends along a second direction, and the first direction is vertical to the second direction;

the two straight steel plates respectively abut against two sides of the core plate in the width direction, the core plate and the two straight steel plates form a winding plate together, and the middle part of the winding plate in the first direction forms a winding area;

the two clamping plates are arranged at intervals along a first direction, one side of each clamping plate, which faces the other clamping plate, is provided with a clamping groove, one side of each clamping plate, which faces away from the other clamping plate, is provided with a connecting block, and each fixing block is provided with a connecting through hole;

the two ends of the winding plate in the first direction are respectively inserted into the clamping grooves of one clamping plate, the winding plate is detachably connected to the two clamping plates through bolts, and the two ends of the core plate in the first direction and the two ends of each straight steel plate in the first direction are respectively inserted into the clamping grooves;

the first strip hole of through-hole form is all seted up in the both sides in the winding district of every straight steel sheet, and first strip hole is located between winding district and the cardboard.

The advantage of the mandrel of this configuration is two-fold, the first being: because the original core mould is integrally formed by steel, the core mould is easy to deform due to tension when the resin impregnated yarn is solidified at the later stage when the core mould is designed to be too thin, the core mould is increased in weight when the core mould is designed to be too thick, the operation is inconvenient, the cost is increased, and meanwhile, the steel core mould is not easy to demould the composite material. The improved core mould consists of a core plate, straight steel plates and clamping plates, wherein the straight steel plates and the clamping plates form an outer frame surrounding the core plate, so that the outer frame can be designed to be thicker and the integral rigidity is improved, the influence of the yarn tension on the deformation of the core mould in the later curing process is effectively prevented, and the core plate is a polytetrafluoroethylene flat plate, so that the weight can be effectively reduced, and meanwhile, the natural advantage of polytetrafluoroethylene is that the demoulding convenience can be effectively ensured due to the non-adhesiveness of colloids such as resin.

Further, for the stability that improves the structure, every straight steel sheet both ends all are connected to two splint through bolt detachably on, and the both ends of core also are connected to two splint through bolt detachably.

Secondly, the application also discloses a preparation method of the unidirectional winding plate, which comprises the following steps:

(1) winding a fiber yarn in a winding region of the mandrel of claim 1 or 2 to form a yarn winding mandrel, the wound fiber yarn being formed into a fiber preform;

(2) horizontally placing a bottom plate on an operation table, adhering a lower sealing adhesive tape on the upper surface of the bottom plate to form a lower adhesive tape frame in a rectangular frame shape, and then laying lower demolding cloth on the bottom plate surrounded by the lower adhesive tape frame;

(3) laying a lower resin flow guide net on the lower demoulding cloth;

(4) horizontally placing the yarn winding core mould on a lower resin flow guide net, and arranging a lower gasket between the core plate and the bottom plate in a cushioning manner, wherein the lower gasket is supported on the outer side of the winding area;

(5) a first bottom plate hole corresponding to the first strip hole is formed in the bottom plate, the yarn winding core mold is locked on the bottom plate through the first strip hole and the first bottom plate hole by the first locking bolt, the core plate is tightly pressed on the lower gasket and is bonded on the lower adhesive tape frame, and the clamping plate is removed;

(6) covering a resin flow guide net on the fiber prefabricated body, placing an upper gasket on the upper surface of the core plate and sticking an upper sealing adhesive tape to form a rectangular frame-shaped upper adhesive tape frame, wherein the upper adhesive tape frame surrounds the outer side of the winding area; arranging a glue injection conduit and an air exhaust conduit at two ends of the core plate in the second direction respectively, and communicating the air exhaust conduit with a vacuum pump;

the upper resin flow guide net is positioned in a space surrounded by the upper adhesive tape frame;

(7) placing the coated steel plate on the upper resin guide net, pressing the coated steel plate on the upper gasket, and bonding the coated steel plate on the upper rubber strip frame;

(8) covering the vacuum film bag on the film-coated steel plate, and sealing the vacuum film bag on the bottom plate;

(9) closing the glue injection conduit, starting a vacuum pump, vacuumizing the vacuum film bag until negative pressure is set, then opening the glue injection conduit, injecting resin into the vacuum film bag through the glue injection conduit, and infiltrating the resin into the fiber yarns to form an infiltrant;

(10) and (3) putting the infiltrant into an oven for curing, and respectively preparing the infiltrant on two sides of the core plate into samples to be detected after the curing is finished.

Furthermore, in order to avoid the curling of the lower resin diversion net and the upper resin diversion net and influence the pouring of resin, the lower gasket is placed on the lower resin diversion net, and the upper resin diversion net covers the upper gasket.

Further, for the stability of guaranteeing to support, all be provided with gasket and lower gasket in the both sides of the first direction in winding district.

Furthermore, the coated steel plate comprises a steel flat plate and a polytetrafluoroethylene film bonded on the surface of the steel flat plate. This design can avoid laying drawing of patterns cloth on last resin water conservancy diversion net, utilizes the dull and stereotyped surperficial polytetrafluoroethylene film of steel as drawing of patterns cloth, improves the convenience of operation.

Furthermore, in order to improve the detachability of the infiltration body, the bottom plate is prepared by polytetrafluoroethylene plates.

In this application, when preparing the sample that awaits measuring, the fibre yarn twines on the core all the time, has kept the tension of fibre yarn, utilizes water conservancy diversion net from top to bottom to promote resin impregnation speed, has improved the impregnation effect of resin simultaneously, because the core adopts the dull and stereotyped preparation of polytetrafluoroethylene, and utilizes the tectorial membrane steel sheet can peel off fibre yarn and the combined material that the resin formed smoothly from the core, improves the shaping quality of combined material sample effectively.

At present, the manufacture of the mold core of the unidirectional winding plate has higher requirements, a whole steel core mold needs to be ensured to have uniform and flat thickness and smooth chamfer, and rust prevention treatment is needed, so the manufacturing cost is higher, but in the actual use process, the core mold is easy to wear, deform and rust due to the complex use environment, the precision of the core mold is reduced, and the quality of a detection sample is influenced. In this application, adopt the combination concatenation formula mandrel of steel vertical bar and polytetrafluoroethylene flat board, when can utilize the rigidity of steel vertical bar to guarantee fibre yarn winding tension, because polytetrafluoroethylene material durability has still prolonged the life of mandrel.

In addition, as the winding composite forming time needs 2-4 days, the core mould can be reused only after the unidirectional winding plate is demoulded, therefore, in order to ensure the sample preparation efficiency of the unidirectional winding plate, a plurality of sets of core moulds are arranged, the acquisition cost and the management cost of the core moulds are increased, meanwhile, the traditional core mould can be deformed under the influence of stress shrinkage and the like of the cured composite material after being repeatedly used, the combined splicing type core mould of the steel straight strip and the polytetrafluoroethylene flat plate bears the stress mainly at the bolt position of the steel straight strip, the steel straight strip and the composite forming platform, since the deformation can be resisted by widening, thickening and thickening the dimensions of these portions, although the conventional core mold can resist the deformation by thickening the dimensions, but the monoblock steel flat plate thickening can also cause the increase of weight in addition to the great promotion that causes the cost, influences experimenter's operation. On the other hand, the demolding success rate of the unidirectional winding plate not only affects the working efficiency of a laboratory, but also more importantly, the cost of some reinforced fibers is very high, and the detection cost is improved due to the failure of demolding. The core plate made of polytetrafluoroethylene material is adopted to replace the traditional steel core mold, so that the demolding success rate can be effectively improved.

Drawings

Fig. 1 is a schematic view of the structure of the core mold.

Fig. 2 is a view from a-a in fig. 1.

Fig. 3 is an exploded view of fig. 1.

Fig. 4 is a state diagram at the time of producing the unidirectional winding sheet.

Fig. 5 is a top view of fig. 4.

Detailed Description

Referring to fig. 1 to 3, the structure of the core mold will be described first, in which the first arrow 910 points to indicate a first direction, the second arrow 920 points to indicate a second direction, and the first direction is perpendicular to the second direction.

A core mould comprises a core plate 13, two straight steel plates 12 and two clamping plates 11; the core 13 is made of a teflon plate, the length of which extends in a first direction and the width of which extends in a second direction.

The two straight steel plates respectively abut against two sides of the core plate in the width direction, the core plate and the two straight steel plates form a winding plate together, the middle part of the winding plate in the first direction forms a winding area 131, and in fig. 1, the area between the first dotted line 135 and the second dotted line 136 is the winding area.

In the first direction, the length of each straight steel plate is the same as that of the core plate, and the straight steel plates are flush with one end of the core plate facing the same direction.

Two splint set up along first direction interval, have all seted up a draw-in groove 111 in one side of each splint orientation another splint, all are provided with a connecting block 113 in one side that each splint deviate from another splint, have all seted up two connect the through-hole 114 on each fixed block.

The both ends on the first direction of winding board insert the draw-in groove of a splint respectively, and the bolt is connected winding board detachably on two splint, and the draw-in groove is inserted respectively to the both ends on the first direction of core and the both ends on every straight steel sheet first direction equally divide.

Specifically, in this embodiment, the first core plate holes 132 are disposed on both sides of the first direction of the core plate, and the second bar plate holes 125 are disposed on both ends of the first direction of each straight bar steel plate. First clamp plate hole 112 of first core plate hole 132 of intercommunication is all seted up on every splint to and the second clamp plate hole 115 of intercommunication second plate hole 125, and first bolt is connected to two splint with the both ends detachably of core plate through first clamp plate hole and first core plate hole on, and the both ends detachably of every straight strip steel sheet is connected to two splint through second clamp plate hole and second strip plate hole to the second bolt. I.e. the bolts detachably connect the winding plate to the clamping plates.

First strip hole 121 of through-hole form is all seted up in the both sides in the winding district of every straight steel sheet, and first strip hole 121 is located between winding district and the cardboard.

Referring to fig. 4 and 5, the method for manufacturing the unidirectional winding board is illustrated, wherein the upper resin flow guiding net, the upper rubber strip frame, the upper gasket and the coated steel plate are removed in fig. 5 for clarity. The preparation method comprises the following steps:

(1) the core mold is connected to a chuck of a unidirectional sheet winding machine through a connecting through hole, a fiber yarn is wound in a winding region of the core mold to form a yarn winding core mold 100, and the wound fiber yarn is formed into a fiber preform. The prior art unidirectional board winding machine can be used for winding the fiber yarn in the embodiment, and specifically, in the embodiment, the unidirectional board winding machine adopts equipment disclosed in patent No. ZL 202121543411.7 entitled "sample preparation device for reinforcing fiber density", and specifically, the two connecting blocks 113 of the core mold are respectively clamped on a first clamp and a second clamp, that is, the first clamp and the second clamp are the above-mentioned chucks. Since the reinforced fiber density sample preparation device adopts the form of the holder, a connecting through hole on the connecting block 113 is not needed, and it can be understood that when the chuck on the unidirectional plate winding machine adopts the form of a pin to fix the core mold, the pin needs to be connected to the chuck of the unidirectional plate winding machine through the connecting through hole.

(2) The bottom plate 20 is horizontally placed on the operation table 200, the lower sealing adhesive tape 411 is adhered to the upper surface of the bottom plate 20, the lower sealing adhesive tape forms a lower adhesive tape frame in a rectangular frame shape, and then the bottom plate surrounded by the lower adhesive tape frame is laid with the lower demolding cloth. The bottom plate is made of a polytetrafluoroethylene plate.

(3) A lower resin flow guide net 461 is laid on the lower release fabric.

(4) The yarn winding core mold 100 is horizontally placed on the lower resin flow guide net, and the periphery of the lower resin flow guide net outwards exceeds the outer edge of the fiber preform. A lower spacer 441 is padded between the core plate and the bottom plate and supported outside the winding area. The lower gasket is placed on the lower vertical flow guide net. Lower gaskets are arranged on two sides of the first direction of the winding area.

(5) The bottom plate is provided with a first bottom plate hole corresponding to the first strip hole, the yarn winding core mold is locked on the bottom plate through the first strip hole and the first bottom plate hole by the first locking bolt 43, so that the core plate is tightly pressed on the lower gasket, the core plate is bonded on the lower adhesive tape frame, and the clamping plate is removed.

(6) The fiber preform is covered with a resin flow-guiding net 462, and an upper gasket 442 and an upper sealing tape 412 are applied to the upper surface of the core sheet so that the upper sealing tape forms a rectangular frame-shaped upper tape frame which surrounds the outside of the winding area. And a glue injection conduit 51 and an air extraction conduit 52 are respectively arranged at the two ends of the core plate in the second direction, and the air extraction conduit is communicated with a vacuum pump 53. The upper resin diversion net covers the upper gasket. And upper gaskets are arranged on two sides of the first direction of the winding area.

The upper resin flow guide net is positioned in the space surrounded by the upper adhesive tape frame.

(7) The coated steel plate 45 is placed on the upper resin guide net, and is pressed against the upper gasket and bonded on the upper rubber strip frame.

(8) And covering the vacuum film bag on a film-covered steel plate, and sealing the vacuum film bag on the bottom plate by using a sealing adhesive tape.

In this embodiment, the coated steel sheet includes a steel flat plate and a teflon film bonded to the surface of the steel flat plate.

(9) Closing the glue injection conduit, starting the vacuum pump, vacuumizing the vacuum film bag until negative pressure is set, then opening the glue injection conduit, injecting resin into the vacuum film bag through the glue injection conduit, and infiltrating the resin into the fiber yarns to form an infiltration body. In this embodiment, the resin is epoxy resin.

In this example, the set negative pressure was-0.85 MPa.

Claims

1. A core mould is characterized by comprising a core plate, two straight steel plates and two clamping plates; the core plate is made of a polytetrafluoroethylene flat plate, the length of the core plate extends along a first direction, the width of the core plate extends along a second direction, and the first direction is vertical to the second direction;

2. The mandrel of claim 1,

both ends of each straight steel plate are detachably connected to the two clamping plates through bolts, and both ends of the core plate are also detachably connected to the two clamping plates through bolts.

3. A method for preparing a unidirectional winding plate is characterized by comprising the following steps:

(3) laying a lower resin flow guide net on the lower demoulding cloth;

4. The method according to claim 3,

the lower gasket is placed on the lower resin diversion net, and the upper resin diversion net covers the upper gasket.

5. The production method according to claim 3,

an upper gasket and a lower gasket are arranged on two sides of the first direction of the winding area.

6. The production method according to claim 3,

the coated steel plate comprises a steel flat plate and a polytetrafluoroethylene film bonded on the surface of the steel flat plate.

7. The production method according to claim 3,

the bottom plate is made of a polytetrafluoroethylene plate.