A composite material tube forming method using heat expansion adhesive

Abstract

The present invention relates to a composite material pipe forming method using a heat expansion adhesive, which belongs to the technical field of composite material pipe manufacturing, and is used to solve the problem that the pipe is prone to defects such as delamination and pores, and the inner wall of the pipe is uneven, including: coating the surface of a hollow rigid core mold with an expansion adhesive film; coating the surface of the expansion adhesive film with fiber prepreg; after coating the prepreg, pre-expanding the expansion adhesive film; placing the hollow rigid core mold, the expansion adhesive film and the fiber prepreg in a female mold for heating and forming, and obtaining a composite material pipe. The technical solution provided by the present invention avoids defects such as delamination and pores of composite products in the manufactured pipe, and improves the quality of pipe forming.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material pipe manufacturing, and in particular relates to a composite material pipe forming method using thermal expansion adhesive. Background Art

[0002] Thermal expansion adhesive is a resin adhesive that can expand by heating. Thermal expansion adhesive is used in industry to provide pressure and manufacture composite pipe fittings.

[0003] Usually, the heat expansion adhesive is preformed into a core mold, and then the prepreg is directly wrapped on the core mold made of the heat expansion adhesive. Finally, the tubular composite is formed by the foamed expansion adhesive.

[0004] However, the pipes using the above technical solution are prone to defects such as delamination and pores, and the inner wall of the pipe is uneven. Summary of the invention

[0005] Based on the above analysis, the present invention aims to provide a composite material tube forming method using a thermal expansion adhesive to solve the problem that the tube is prone to defects such as delamination and pores and the inner wall of the tube is uneven.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a composite material tube forming method using a thermal expansion adhesive, comprising:

[0008] Wrapping the surface of the hollow rigid core mold with an expansion rubber film;

[0009] Wrapping fiber prepreg on the surface of the expansion adhesive film;

[0010] After wrapping the prepreg, pre-expand the expansion adhesive film;

[0011] The hollow rigid core mold, the expansion adhesive film and the fiber prepreg are placed in a female mold and heated to form a composite material pipe.

[0012] Furthermore, the expansion temperature of the expansion adhesive film is 50° C. to 170° C., the volume expansion coefficient is 2 to 30, and the expansion pressure is 0.2 to 4 MPa.

[0013] Furthermore, the expansion adhesive film is prepared from one or more materials selected from epoxy compounds, polyurethane compounds, polymethacrylic acid compounds and unsaturated polyester compounds.

[0014] Furthermore, the rigid core mold is made of a metal material, a resin material or a resin-based composite material;

[0015] Wherein, the curing temperature of the resin material is higher than 100°C; and the glass transition temperature of the resin-based composite material is higher than 150°C.

[0016] Furthermore, there is a process gap between the inner wall of the female mold and the prepreg;

[0017] The process gap does not exceed the thickness of the expansion adhesive film.

[0018] Further, when the cross section of the hollow rigid core mold is circular, the ratio of the wall thickness of the hollow rigid core mold to the cross-sectional diameter is not less than 1:20;

[0019] When the cross-section of the hollow rigid core mold is rectangular, the ratio of the wall thickness of the hollow rigid core mold to the length of any side of the cross-section is not less than 1:20.

[0020] Furthermore, the pre-expansion heating temperature is 100° C.-130° C., and the heating time is 0.5 h-2 h.

[0021] Furthermore, the expansion adhesive film is in sheet form.

[0022] Furthermore, after coating the surface of the hollow rigid core mold with the expansion adhesive film, the method further comprises:

[0023] The surface of the prepreg is covered with a release cloth.

[0024] Furthermore, the step of placing the hollow rigid core mold, the expansion adhesive film and the fiber prepreg into a female mold and heating and molding the hollow rigid core mold comprises:

[0025] Put the hollow rigid core mold, the expansion adhesive film and the fiber prepreg into a female mold and put it into an oven;

[0026] Preheat at 60℃-70℃ for 20min-30min;

[0027] Raise the temperature to 95℃-105℃ and maintain the temperature for 20min-30min;

[0028] Raise the temperature to 145°C-155°C and maintain the temperature for 2h-3h.

[0029] The present invention can achieve one of the following beneficial effects:

[0030] 1. During the heating and forming process, the expansion adhesive film is sandwiched between the outer surface of the hollow rigid core mold and the fiber prepreg. Since the core mold is hollow, one side of the expansion adhesive film can be heated from the inside of the core mold. At the same time, the other side of the expansion adhesive film can also be heated through the fiber prepreg. Compared with the existing solid expansion adhesive core mold, the sheet-like expansion adhesive film is thinner, so it can reach the expansion temperature more quickly, thereby avoiding defects such as delamination and pores in the composite product, and improving the quality of pipe forming.

[0031] 2. In the prior art, a set of core molds is prefabricated for each pipe diameter. In the present invention, the expansion rubber film is in sheet form. When manufacturing pipes of different diameters, the radial size of the pipe can be controlled by controlling the number of layers of the expansion rubber film wrapped on the core mold, so that a core mold of a certain size can be used to manufacture pipes of various sizes, thereby reducing the types of prefabricated core molds and further reducing production costs.

[0032] 3. The present invention only winds the expansion rubber film on the core mold, while in the prior art, the core mold is a solid expansion rubber core mold made of heat expansion rubber. Therefore, under the condition of producing pipes with the same diameter, the amount of expansion rubber used in the present invention is less, thereby saving production costs.

[0033] 4. After the tube is formed, the expansion glue film on the inner wall of the tube is a hollow columnar structure, and after the tube is formed, the expansion glue is also a hollow columnar structure. Compared with the solid expansion glue core mold in the prior art, the expansion glue with a hollow columnar structure is more convenient to extract, for example, by mechanical means to hang the expansion glue out from the inner wall of the tube. At the same time, under the same conditions, the amount of expansion glue used in the hollow columnar structure is less than that of the solid expansion glue core mold, so it is easier to remove the internal expansion glue, and there is almost no expansion glue left on the inner wall of the tube.

[0034] 5. The strength and hardness of the expansion rubber are not enough. When manufacturing a solid expansion rubber core mold, the surface of the expansion rubber core mold is prone to unevenness, which will cause unevenness on the inner wall surface of the pipe, thereby forming quality defects. The core mold of the present invention can be made of metal, non-metal composite materials and resin materials, which ensures the strength and hardness of the core mold, so that the expansion rubber wrapped on the hollow rigid core mold expands to the same degree, thereby preventing unevenness and quality defects on the inner wall surface of the pipe.

[0035] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0037] Figure 1 It is a schematic structural diagram of a hollow rigid core mold, an expansion adhesive film and a fiber prepreg before heating and molding provided in an embodiment of the present invention.

[0038] Explanation of the reference numerals: 1 - fiber prepreg; 2 - expanded adhesive film; 3 - hollow rigid core mold. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] Currently, there are two methods for manufacturing composite pipes: the first is the traditional method, and the second is to use the expansion characteristics of thermal expansion glue to make pipes.

[0041] Traditional composite pipe manufacturing processes include: pultrusion, tube winding, winding, airbag, autoclave, molding, etc. These methods all have some problems, such as pultrusion cannot achieve multi-angle layering, tube winding and winding have slightly poor density, airbag molding may cause waste due to air bag leakage, autoclave and molding costs are too high, and there is a possibility of local fiber buckling and accumulation.

[0042] Thermal expansion adhesive is a resin adhesive that expands after heating and has been widely used in the fields of vehicles, aerospace, etc. The general process of using thermal expansion adhesive to manufacture composite pipe fittings is to preform a core mold first, and then directly wrap the prepreg on the core mold and heat and cure it. This molding method has the following defects:

[0043] 1. During the heating and molding process, if the prepreg is heated in advance, the prepreg resin may gel and solidify in advance, seriously affecting the quality of the product. In the existing process, during molding, the heat needs to pass through the mold and prepreg before it can be transferred to the expansion glue. Considering that the core mold is solid, the time for the expansion glue to reach the expansion temperature is further extended. Therefore, when the prepreg has begun to solidify, the expansion glue core mold has not yet reached the required pressure expansion temperature, which causes defects such as delamination and pores in the composite product, seriously affecting the molding quality.

[0044] 2. In the prior art, for the same pipe diameter, two sets of molds are required for forming, namely, a pipe forming mold and a core forming mold. For different pipe diameters, more types of molds are required, thereby increasing the manufacturing cost of the pipe.

[0045] 3. The amount of expansion glue required to directly manufacture the core mold with expansion glue is very large, which increases the cost of the pipe manufacturing process.

[0046] 4. In the prior art, since the core mold is made of expansion rubber, after the pipe is formed, the expansion rubber in the inner diameter of the pipe is difficult to remove, which will form dead weight, that is, a large amount of expansion rubber remains on the inner wall of the pipe.

[0047] 5. In the prior art, since the expansion rubber itself has insufficient strength and hardness, when the expansion rubber is used to make a columnar core mold, the surface of the expansion rubber core mold is prone to unevenness. As a result, during the pipe forming process, the expansion degree of each part of the expansion rubber core mold will be uneven, resulting in an uneven inner wall surface of the pipe, which in turn causes quality defects.

[0048] In order to solve the above problems, an embodiment of the present invention provides a composite material tube forming method using a thermal expansion adhesive, comprising the following steps:

[0049] Step 1: Cover the surface of the hollow rigid core mold with an expansion adhesive film.

[0050] In the embodiment of the present invention, in order to provide a better support for the expansion glue and avoid the problem of uneven inner surface of the pipe, a hollow rigid core mold is designed, which is a cylindrical structure with a thickness of not less than 2 mm, preferably greater than 5 mm; the preparation material of the core mold includes one of a metal material (such as an aluminum alloy), a resin material and a resin-based composite material, such as one of the metal materials, one of the resin materials or one of the resin-based composite materials; wherein the curing temperature of the resin material is greater than 100°C; the glass transition temperature of the resin-based composite material is greater than 150°C, and the preferred solution is higher than 180°C. Among them, the resin material includes: bisphenol A, bisphenol F, polysulfone, alicyclic epoxy resin, epoxy-modified cyanate, bismaleimide and other resins. The resin material also includes: cured bisphenol A, bisphenol F, polysulfone, alicyclic epoxy resin. Among them, the curing agent includes: dicyandiamide, acid anhydride, polyurea, aniline and other curing agents. The resin-based composite material material is a composite material with any of the above resin materials as the matrix.

[0051] In the embodiment of the present invention, in order to achieve uniform and low-defect products, the expansion adhesive film is set in a sheet shape. After the expansion adhesive is made into a sheet shape, the expansion adhesive is evenly distributed in a plane, thereby ensuring that the expansion adhesive is evenly distributed during heating and molding, thereby ensuring the flatness of the inner wall of the pipe. In addition, the sheet-shaped expansion adhesive has better flexibility and is easier to curl into a cylindrical structure on the hollow rigid core mold, and better fits with the hollow rigid core mold, further ensuring the flatness of the inner wall of the pipe.

[0052] In order to prevent the expansion glue from overflowing during the subsequent heating and molding process, the cylindrical structure formed by the expansion glue film does not cover the two ends of the hollow rigid core mold. After covering the expansion glue film, the two ends of the hollow rigid core mold are exposed by 10mm-15mm respectively.

[0053] In the embodiment of the present invention, in order to ensure the rigidity of the hollow rigid core mold, the ratio of the wall thickness of the hollow rigid core mold to the cross-sectional size is controlled. Specifically, when the cross-section of the hollow rigid core mold is circular, the ratio of the wall thickness of the hollow rigid core mold to the cross-sectional diameter is not less than 1:20. When the cross-section of the hollow rigid core mold is rectangular, the ratio of the wall thickness of the hollow rigid core mold to the length of any side of the cross-section is not less than 1:20.

[0054] Step 2: Wrap the fiber prepreg on the surface of the expansion adhesive film.

[0055] In an embodiment of the present invention, the thickness of the expansion adhesive film is 2-3 mm, and the materials for preparing the expansion adhesive film include: epoxy compounds, polyurethane compounds, polymethacrylate compounds and unsaturated polyester compounds. The expansion temperature of the expansion adhesive film is 50°C to 170°C, the volume expansion rate is 2 to 30, and the expansion pressure is 0.2 to 4MPa. Preferably, the expansion adhesive begins to expand at 110°C, and the maximum expansion rate can reach 8 to 30 times the original volume. The expansion adhesive can reach the maximum expansion rate at 130°C, and the maximum expansion pressure is about 3MPa.

[0056] In the embodiment of the present invention, after the fiber prepreg is wrapped on the expansion adhesive, the thickness is 1-3 mm.

[0057] Step 3: After wrapping the prepreg, pre-expand the expansion adhesive film, that is, heat the expansion adhesive film at a temperature of 100°C-130°C, a heating time of 30min-2h, and a pre-expansion rate of 5%-50%. Pre-expansion can effectively ensure that the expansion adhesive is fully expanded before the prepreg is formed during heating and molding.

[0058] In the embodiment of the present invention, the structures of the hollow rigid core mold, the expanded adhesive film and the fiber prepreg obtained after step 2 are as follows: Figure 1 It should be noted that Figure 1 It only reflects the hollow rigid core mold, expansion glue film and fiber prepreg from inside to outside before thermoforming. In practice, the two ends of the expansion glue film do not completely cover the two ends of the hollow rigid core mold, while the fiber prepreg completely wraps the two ends of the hollow rigid core mold, so that the expansion glue film will not overflow when expanding, thus ensuring the effect of subsequent expansion and pressurization of the expansion glue.

[0059] Step 4: Place the hollow rigid core mold, the expansion rubber film and the fiber prepreg into a female mold and heat and shape them to obtain a composite material pipe.

[0060] In the embodiment of the present invention, the specific process steps and process conditions of heating forming are:

[0061] Put the hollow rigid core mold, the expansion adhesive film and the fiber prepreg into a female mold and put it into an oven;

[0062] Preheat at 60℃-70℃ for 20min-30min;

[0063] Raise the temperature to 95℃-105℃ and maintain the temperature for 20min-30min;

[0064] Raise the temperature to 145°C-155°C and maintain the temperature for 2h-3h.

[0065] In the embodiment of the present invention, in order to prevent the pipe from adhering to the mold, a layer of release cloth is coated on the surface of the prepreg before thermoforming.

[0066] In the embodiment of the present invention, when the expansion adhesive film expands, it will squeeze the fiber prepreg, so that the fiber prepreg forms a tube that matches the size of the inner wall of the female mold. In actual production, in order to obtain the target tube diameter, a sufficient amount of expansion adhesive needs to be used to provide a sufficiently large pressure, and at the same time, a process gap that matches the amount of the expansion adhesive film needs to be set so that the expanded expansion adhesive film can fill the process gap, thereby squeezing the prepreg onto the inner wall of the female mold and finally forming a tube. Here, the process gap is the gap between the inner wall of the female mold and the prepreg, and the process gap usually does not exceed the thickness of the expansion adhesive film.

[0067] Step 5: After cooling to room temperature, open the mold, take out the whole sample, pull out the aluminum tube, and cut off the uneven areas at both ends.

[0068] In order to illustrate the feasibility of the above-mentioned embodiment, the present invention provides the following embodiments:

[0069] Example 1

[0070] Step 1: Use aluminum alloy 50×50×1000mm, 3mm wall thickness profile as a rigid core mold, and first apply a release agent on the outer surface.

[0071] Step 2: Wrap the outside of the aluminum alloy tube with 2mm thick expansion adhesive film, leaving about 10mm of space at both ends.

[0072] Step 3: The T300 plain weave prepreg completely wraps the aluminum tube and the expansion adhesive film. The thickness of the plain weave is about 2 mm.

[0073] Step 4: pre-expand the expansion adhesive film at a temperature of 130°C for 30 minutes.

[0074] Step 5: Place the female mold. The inner cavity of the female mold has a size of about 58×58×1000 mm. The female mold is a hollow structure. The plain cloth, the expansion rubber film and the hollow rigid core mold are all set in the hollow part. The hollow part of the female mold ensures that both sides of the expansion rubber film can be heated at the same time.

[0075] Step 6: Close the mold, put it into an oven, preheat it at 60°C for 20 minutes, heat it to 100°C, keep it warm for 20 minutes, then heat it to 150°C and keep it warm for 2 hours.

[0076] Step 7: After cooling to room temperature, open the mold, take out the whole sample, pull out the aluminum tube, cut off the uneven areas at both ends of the carbon tube, and grind the edges to obtain the product.

[0077] Example 2

[0078] The difference between Example 2 and Example 1 is that a layer of polytetrafluoroethylene mold release cloth is wrapped on the outer surface of the expanded adhesive film after step 4 and before step 5. The rest is the same as Example 1.

[0079] Example 3

[0080] The difference between Example 3 and Example 1 is that the material of the hollow rigid core mold is any one of bisphenol A, bisphenol F, polysulfone, alicyclic epoxy resin, epoxy modified cyanate, bismaleimide and the like. The rest is the same as Example 1.

[0081] Example 4

[0082] The difference between Example 4 and Example 1 is that the material of the hollow rigid core mold is a resin-based composite material with any one of bisphenol A, bisphenol F, polysulfone, alicyclic epoxy resin, epoxy-modified cyanate, bismaleimide and the like as the matrix. The rest is the same as Example 1.

[0083] Comparative Example

[0084] Step 1: Cut the expansion glue, fiber prepreg cloth and embedded pipe.

[0085] Step 2: Put the embedded tube wrapped with expansion glue into the core mold, heat it to 80℃ and maintain it for 15 minutes. At this temperature, the expansion glue will expand slightly in advance and fill the core material cavity. Cool and demould to remove the preformed core material.

[0086] Step 3: Wrap the fiber prepreg cloth around the preformed core material to obtain a preform, put it into a molding mold, close the mold and heat it to a molding temperature of 150°C for 15 minutes; cool, demold and take out the part to obtain the arm of the carbon fiber robotic arm.

[0087] It can be seen from step 2 of the comparative example that the prior art requires that the expansion glue be placed in the core mold forming mold. Since the expansion glue itself is not strong and hard enough, when the expansion glue is filled in the core mold forming mold and compacted, it is easy to have too much local expansion glue, and cause the expansion degree of each part of the expansion glue to be inconsistent during the subsequent pre-expansion process, and finally cause the surface of the expansion glue core mold to be uneven. In the embodiment of the present invention, based on the characteristics of insufficient strength and hardness of the expansion glue, the expansion glue is made into a sheet. From a process point of view, it is easier to maintain the flatness of the surface when the expansion glue is made into a sheet, and the sheet shape is more conducive to the expansion glue being wound on the rigid core mold.

[0088] It should be noted that the above scheme only takes the square tube as an example and provides a specific operation method. For tubes of other shapes, it is only necessary to make the core mold into the corresponding shape, and other operations are the same as those for square tubes.

[0089] The above are only preferred specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A composite material tube forming method using a heat expansion adhesive, characterized in that: include; Wrapping the surface of the hollow rigid core mold with an expansion rubber film; Wrapping fiber prepreg on the surface of the expansion adhesive film; After wrapping the prepreg, the expansion adhesive film is pre-expanded; it is placed in a female mold and heated to form a composite material pipe; the pre-expansion includes: heating the expansion adhesive film at a temperature of 100°C-130°C, a heating time of 30min-2h, and a pre-expansion rate of 5%-50%; the expansion temperature of the expansion adhesive film is 50°C-170°C, the volume expansion rate is 2-30, and the expansion pressure is 0.2-4MPa; the preparation material of the expansion adhesive film is one or more of epoxy compounds, polyurethane compounds, polymethacrylic compounds and unsaturated polyester compounds; The process steps and process conditions of the heating forming are: The heating and molding is carried out in an oven; there is a process gap between the inner wall of the female mold and the prepreg; the process gap does not exceed the thickness of the expansion adhesive film; preheating is carried out at 60°C-70°C for 20min-30min; Raise the temperature to 95℃-105℃ and maintain the temperature for 20min-30min; Raise the temperature to 145°C-155°C and maintain the temperature for 2h-3h.

2. The method according to claim 1, characterized in that: The hollow rigid core mold is made of metal material, resin material or resin-based composite material; Wherein, the curing temperature of the resin material is higher than 100°C; and the glass transition temperature of the resin-based composite material is higher than 150°C.

3. The method according to claim 1, characterized in that When the cross section of the hollow rigid core mold is circular, the ratio of the wall thickness of the hollow rigid core mold to the cross section diameter is not less than 1:20; When the cross-section of the hollow rigid core mold is rectangular, the ratio of the wall thickness of the hollow rigid core mold to the length of any side of the cross-section is not less than 1:

20.

4. The method according to claim 1, characterized in that: The expansion adhesive film is in sheet form.

5. The method according to any one of claims 1 to 4, characterized in that: After coating the surface of the hollow rigid core mold with the expansion adhesive film, the method further comprises: The surface of the prepreg is covered with a release cloth.

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