Thermosetting material forming die and method for tensile property test

Abstract

The invention discloses a thermosetting material forming die and method for tensile property testing. The thermosetting material forming die comprises a forming cavity and a heating and bubble discharging assembly. The height of the forming cavity is greater than the length of the thermosetting material test piece; the heating and bubble discharging assembly comprises a heating device and a heat conducting plate; the heating device is arranged at the bottom of the forming cavity; the heat conduction plate is a rear mold plate of the forming cavity. The thickness limiting frame, the thickness standard steel block and the thermosetting material test piece are vertically cut, and the left-right-center three-section track glue injection mode is adopted, so that the uniformity and consistency of the thickness of the thermosetting material test piece are ensured; meanwhile, bubble generation is reduced from the source through control over the glue filling temperature and negative pressure of the glue gun, in addition, bubble generation is further guaranteed through control modes such as the forming mold temperature, the glue injection temperature, the glue injection mode and vacuum heating exhaust, and then burrs and microcracks are reduced. According to the method, the initial gas content can be reduced by 90% or above, the porosity of a sample is stably smaller than or equal to 0.3%, and one-time forming with the controllable thickness and without bubbles and flashes inside is achieved.

Description

Technical Field

[0001] This invention relates to the field of thermosetting polymer performance testing technology, and in particular to a molding die and method for thermosetting materials used in tensile performance testing. Background Technology

[0002] Thermosetting resin-based composites are widely used as coatings, structural adhesives, and advanced composite matrices due to their excellent mechanical strength, stability, chemical resistance, and heat resistance. They occupy an irreplaceable position in fields such as automotive lightweighting, aerospace main load-bearing components, electronic packaging, and building reinforcement. These resins undergo cross-linking reactions with curing agents such as amines, acid anhydrides, or phenols to form a three-dimensional network thermosetting structure. However, this high degree of cross-linking also leads to significant intrinsic brittleness; once cracks initiate, they propagate rapidly, resulting in sudden brittle fracture. Therefore, accurately obtaining their tensile strength, elastic modulus, and elongation at break is a primary step in evaluating formulation design, process optimization, and service safety.

[0003] Quasi-static tensile testing, as the most fundamental method in materials mechanical characterization, is also applicable to thermosetting systems. However, because epoxy resin is non-redeemable after curing, only an "in-situ molding-direct testing" mode can be used, meaning the sample quality depends entirely on the mold structure and preparation process. Existing technologies generally face the following challenges: 1. Metal mold cavities have high surface energy, requiring external spraying of release agent, which can easily cause surface contamination and penetrate into the weak interface layer.

[0004] 2. Insufficient venting at the parting line makes the edges prone to stress concentration, leading to burrs and microcracks. Specifically, when molten material is injected into the mold cavity (plastic, metal, rubber, etc.), if the air / gas inside the cavity cannot be released in time, it will cause gas stagnation, compression, or localized heating, resulting in localized obstruction of melt flow and uneven cooling. This leads to the formation of microcracks, precipitation holes, or stress concentration, causing burrs or rough edges. Furthermore, it also causes uneven shrinkage or cracking of the material after cooling. Therefore, "insufficient venting" follows a logical chain: delayed gas release → melt flow disturbance / imperfect cooling → mechanical / thermal / structural stress concentration → burrs and microcracks.

[0005] 3. In conventional processes, operators often pour the preheated resin material directly into an open mold and rely on the material's own leveling to form the sample. Because thermosetting materials are highly sensitive to temperature, local viscosity differences and uneven shrinkage may occur during casting and curing, which can easily lead to excessive differences in sample thickness, excessive internal air bubbles, and even delamination at the interface.

[0006] 4. Uneven temperature-pressure coupling during the curing stage leads to a gradient in the crosslinking density distribution, which ultimately manifests as a large dispersion coefficient in tensile data (e.g., >10%) and a measured strength lower than the theoretical eigenvalue.

[0007] Recent studies have shown that the specimen method has an even greater impact on test results than the crosslinking density itself. However, existing methods mostly focus on the formulation or post-machining stages, failing to address the four major challenges of mold sticking, venting, pressure equalization, and rapid heating and cooling at the mold source. Therefore, developing a high-precision, low-defect, and repeatable mold and its supporting method specifically designed for thermosetting material tensile specimens has become an urgent need to achieve accurate evaluation of material properties and data traceability. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a molding die and method for thermosetting materials used in tensile performance testing. This molding die and method can reduce the initial gas content by more than 90%, stabilize the porosity of the sample to ≤0.3%, and achieve one-time molding with "controllable thickness, no internal bubbles, and no flash".

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A molding die for thermosetting materials used in tensile property testing includes a molding cavity and a heating and defoaming assembly.

[0010] The height of the molding cavity is greater than the length of the thermosetting material specimen.

[0011] The heating and defoaming assembly includes a heating device and a heat-conducting plate.

[0012] The heating device is located at the bottom of the molding cavity.

[0013] The heat-conducting plate is at least one large vertical sidewall of the molding cavity and is connected to the heating device.

[0014] The molding cavity includes a bottom frame, a front template, a rear template, a thickness limiting frame, and a sealing and clamping assembly.

[0015] The bottom frame is a U-shaped frame with the opening facing upwards; the thickness limiting frame is also a U-shaped frame with the opening facing upwards, and its thickness is equal to the thickness of the thermosetting material specimen.

[0016] The front template, thickness limiting frame, and rear template are stacked sequentially from front to back, with their bottoms extending into the bottom frame, and both sides are sealed and clamped by sealing clamping components.

[0017] The heating device is embedded in the bottom of the U-shaped groove of the base frame. The front template is a heat-resistant glass plate, and the rear template is a heat-conducting plate.

[0018] A method for molding thermosetting materials for tensile property testing includes the following steps.

[0019] Step 1, Filling the glue gun: Preheat the glue gun cartridge to the set temperature T1, and at the same time preheat the liquid thermosetting material to be filled to the set temperature T2 and evacuate it; then, fill the preheated and evacuated liquid thermosetting material into the preheated glue gun cartridge; wherein, T1 > T2.

[0020] Step 2: Preheat the molding cavity to the set temperature T1.

[0021] Step 3, Glue Injection: Move the glue gun nozzle to a distance of [distance missing] from the top surface of the molding cavity. a At a height of mm, the glue gun reciprocates along the length of the molding cavity using a three-segment trajectory of "left → right → center" until the molding cavity is filled; the dwell time at each trajectory point is specified. t Second.

[0022] Step 4, Heating and Exhausting: Transfer the molding cavity filled with liquid thermosetting material to a vacuum heating box that has been preheated to the set temperature T1, and evacuate it under negative pressure.

[0023] Step 5, Curing: Remove the molding cavity from the vacuum heating chamber, heat the de-bubbling component to cool the molding cavity, and solidify the liquid thermosetting material in the molding cavity to form a solid thermosetting material block.

[0024] Step 6, specimen cutting: Demold the solid thermosetting material block from the molding cavity and cut off the two sides in the height direction. Then, cut out several thermosetting material specimens as needed; each thermosetting material specimen is cut along the height direction of the solid thermosetting material block.

[0025] In step 1, T1 = 60℃. By adjusting T2 and the vacuum pressure, the viscosity of the liquid thermosetting material to be filled is stabilized at 0.8–1.2 Pa·s.

[0026] In step 2, the inner sidewall of the molding cavity is coated with an ultra-thin PTFE isolation layer with a thickness not exceeding 0.02 mm.

[0027] In step 3, a =0.5mm, when the glue gun is injecting glue at the left section trajectory point, the glue gun nozzle is 2mm away from the left side wall of the molding cavity; when the glue gun is injecting glue at the right section trajectory point, the glue gun nozzle is 2mm away from the right side wall of the molding cavity.

[0028] In step 3, the glue gun dispenses glue at a constant pressure of 0.25–0.35 MPa and a constant flow rate of 1.5–2.0 mL / s, with a dwell time at each trajectory point. t =30 seconds.

[0029] In step 4, the method of vacuum heating box negative pressure evacuation is as follows: the vacuum heating box is preheated to 60°C, first evacuated to a slight negative pressure of -15 kPa, and after a set time, the negative pressure is maintained at -8 kPa, so as to avoid damage to the thermosetting material structure and continuously carry out the trapped small air bubbles.

[0030] In step 2, the front template of the molding cavity is a heat-resistant glass plate; in step 4, the heat-resistant glass plate is oriented toward the observation port of the vacuum heating box, and the bubble situation in the liquid thermosetting material is observed in real time during the heating and exhaust process; when bubbles are observed in the liquid thermosetting material, the bubbles are discharged from the liquid thermosetting material by increasing the negative pressure value of the vacuum heating box.

[0031] In step 5, the heating defoaming component cools the molding cavity in sections at a cooling rate of 3 ℃ / s, thereby controlling the cooling and solidification of the liquid thermosetting material in the molding cavity and inhibiting the expansion of pores and bubbles caused by the chemical shrinkage of the liquid thermosetting material.

[0032] This invention offers the following advantages: By employing a thickness limiting frame, a thickness standard steel block, vertical cutting of the thermosetting material specimen, and a three-stage trajectory injection method ("left → right → center"), it ensures the uniformity of the thermosetting material specimen's thickness. Simultaneously, by controlling the glue gun's filling temperature and negative pressure, it reduces foaming at the source. Furthermore, by controlling the molding mold temperature, injection temperature, injection method, and vacuum heating and venting, it further minimizes bubble formation, thereby reducing burrs and microcracks. This invention can reduce the initial gas content by over 90%, stabilize the sample porosity at ≤0.3%, and achieve one-time molding with "controllable thickness, no internal bubbles, and no flash." Attached Figure Description

[0033] Figure 1 A schematic diagram of the structure of a thermosetting material molding die for tensile property testing according to the present invention is shown.

[0034] Figure 2 A schematic diagram of the dispensing machine in this invention is shown.

[0035] Figure 3 A schematic diagram showing the structure of multiple molding dies mounted on the insert is displayed.

[0036] Figure 4 A schematic diagram of the dumbbell-shaped thermosetting material specimen is shown.

[0037] Figure 5 A schematic diagram of the structure of a traditional flow mold is shown.

[0038] Figure 6 The image shows physical images of several thermosetting material specimens obtained after cutting according to the present invention.

[0039] Among them are: 10. Molding cavity; 11. Base frame; 12. Front template; 13. Thickness limiting frame; 14. Rear template; 20. Sealing clamping assembly; 21. Clamp; 22. Sealing strip; 23. Clamping screw; 30. Standard thickness steel block; 40. Glue dispensing machine; 41. Three-dimensional moving frame; 42. Glue gun; 43. Glue application table; 431. Mold limiting plate; 44. Molding mold; 45. Insert; 50. Thermosetting material specimen; 51. Thickness test point at the narrowest point. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

[0041] In the description of this invention, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of the components, and therefore should not be construed as a limitation of this invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of this invention.

[0042] like Figure 1 and Figure 3 As shown, a molding die for thermosetting materials used for tensile property testing, also known as molding die 44, includes a molding cavity 10, a heating and defoaming assembly, and a thickness standard steel block 30.

[0043] The height of the molding cavity is greater than the length of the thermosetting material specimen, which means that the thermosetting material specimen can be cut vertically.

[0044] The molding cavity includes a bottom frame 11, a front template 12, a thickness limiting frame 13, a rear template 14, and a sealing and clamping assembly 20.

[0045] The bottom frame is a U-shaped frame with the opening facing upwards.

[0046] The front template, thickness limiting frame, and rear template are stacked sequentially from front to back, with their bottoms extending into the bottom frame, and both sides are sealed and clamped by sealing clamping components.

[0047] The thickness limiting frame is also a U-shaped frame with the opening facing upwards, and its thickness is equal to the thickness of the thermosetting material specimen, thereby ensuring the thickness of the thermosetting material specimen.

[0048] The thickness tolerance of the above-mentioned molding cavity is preferably controlled within ±0.01 mm, the parallelism of the sample edge is ≤0.02 mm, and the surface roughness Ra is ≤0.1 µm, which fully meets the high precision requirements of ISO 527-2 1BA and eliminates the apparent modulus deviation caused by uneven thickness.

[0049] The sealing clamping assembly preferably includes a clamp 21, a sealing strip 22, and a clamping screw 23.

[0050] The sealing strip is preferably U-shaped, fitted tightly against the inner wall of the thickness limiting frame, and its thickness is greater than that of the thickness limiting frame.

[0051] The aforementioned clamp preferably has three parts: a bottom clamp and a side clamp.

[0052] In this embodiment, the two U-shaped sidewalls of the bottom frame are preferably flexible to form a bottom clamp, which clamps the bottom of the front template, the thickness limiting frame and the rear template by clamping screws 22.

[0053] Preferably, the aforementioned side clamps have two parts, which respectively clamp the two sides of the front template, the thickness limiting frame, and the rear template, and are clamped by several clamping screws 22. During the clamping process, a thickness standard steel block 30 is inserted into the top of the molding cavity. The thickness of the thickness standard steel block 30 is equal to the thickness of the thermosetting material specimen, thereby further ensuring the consistency of thickness in various parts of the thermosetting material specimen. Furthermore, the thickness standard steel block 30 avoids the subsequent glue injection trajectory points.

[0054] like Figure 4 The diagram shows a schematic of a dumbbell-shaped thermosetting material specimen. When the dumbbell-shaped thermosetting material specimen is type 1, 2, or 3, the thickness at the narrowest point of the specimen is typically required to be 2.0 mm ± 0.2 mm. When the dumbbell-shaped thermosetting material specimen is type 4, the thickness at the narrowest point of the specimen is typically required to be 1.0 mm ± 0.1 mm. The thickness at the narrowest point of the specimen is usually taken as... Figure 4 The average of three measurements taken at 51 test points at the three narrowest points in the middle.

[0055] like Figure 5 As shown, in the prior art, the traditional flow mold is usually laid flat, and the preheated resin material is poured directly into the traditional flow mold, relying on the material itself to level out and form. Since thermosetting materials are highly sensitive to temperature, local viscosity differences and uneven shrinkage will occur during the casting and curing process, which can easily lead to excessive differences in sample thickness, excessive air bubbles inside, and even delamination at the interface.

[0056] The aforementioned heating and defoaming assembly includes a heating device and a heat-conducting plate.

[0057] The heating device is located at the bottom of the molding cavity, preferably embedded in the bottom of the U-shaped groove of the bottom frame (not shown in the figure), and preferably can heat up at a heating rate of 5°C / s.

[0058] The heat-conducting plate is at least one large vertical sidewall of the molding cavity, that is, one or two of the front template and the rear template. In this embodiment, the rear template is preferred, and its bottom is connected to the heating device so as to conduct heat quickly; the front template is a heat-resistant glass plate.

[0059] This invention uses a dispensing machine to perform the dispensing operation on the above-mentioned molding mold, such as... Figure 2 As shown, the glue dispensing machine 40 includes a three-dimensional moving frame 41, a glue gun 42, and a glue dispensing table 43.

[0060] The aforementioned three-dimensional moving frame 41 is located on top of the glue application table and can drive the glue gun 42 to move in three dimensions.

[0061] The top center of the above-mentioned glue-applying station is provided with a mold limiting plate 431, which has a limiting groove for placing and limiting the molding mold 44.

[0062] like Figure 3 As shown, several molding dies are detachably mounted side-by-side on the insert 45. The insert is detachably mounted on the glue application table via the limiting groove of the mold limiting plate 431. In this embodiment, five molding dies are arranged side-by-side on the insert, which can meet the automated production of 30 samples, thus improving efficiency.

[0063] A method for molding thermosetting materials for tensile property testing includes the following steps.

[0064] Step 1, Filling the glue gun: Preheat the glue gun cartridge to a set temperature T1, and simultaneously preheat the liquid thermosetting material to be filled to a set temperature T2, preferably using vacuum planetary mixing or ultrasonic treatment to create a vacuum; then, fill the preheated and vacuumed liquid thermosetting material into the preheated glue gun cartridge; wherein, T1 > T2. In this embodiment, T1 = 60℃, T2 = 40~50℃; by adjusting T2 and the vacuum pressure (the initial vacuum pressure is approximately −60 kPa), the initial gas content of the liquid thermosetting material to be filled is significantly reduced, and the viscosity is stabilized at 0.8–1.2 Pa·s, which is beneficial for subsequent laminar flow filling and thus reduces foam generation at the source.

[0065] Step 2: Preheat the molding cavity to the set temperature T1=60℃. In this embodiment, the inner sidewall of the molding cavity is coated with an ultra-thin PTFE isolation layer with a thickness not exceeding 0.02mm to ensure that the sample can be demolded without damage, and the number of times it can be reused after spraying is greater than 100 times. In addition, it can also avoid the generation of gas sources by the evaporation of liquid release agent, while reducing interface defects and secondary gas entrainment.

[0066] Furthermore, this invention features a low surface energy design with a 30–50 µm PTFE coating, a water contact angle ≥110°, a release force <0.2 N / cm, and no peeling during 200 ℃ cycling, eliminating liquid release agent residue. XPS analysis showed no Si or F contamination, ensuring reliability for subsequent bonding, coating, or microscopic analysis.

[0067] Step 3, Glue Injection: The glue gun nozzle is moved to a position preferably close to the top surface of the molding cavity. a At a height of 0.5mm, the glue gun is preferably used to reciprocate servo-dispense glue along the length of the molding cavity using a constant pressure of 0.25–0.35 MPa and a constant flow rate of 1.5–2.0 mL / s, following a three-segment trajectory of "left → right → center" until the molding cavity is filled; wherein the dwell time at each trajectory point is preferably... t =30 seconds, to avoid turbulent air entrainment and dead zone stagnation.

[0068] Furthermore, when the glue gun is injecting glue at the left segment trajectory point, the distance between the glue gun nozzle and the left side wall of the molding cavity is preferably 2mm; when the glue gun is injecting glue at the right segment trajectory point, the distance between the glue gun nozzle and the right side wall of the molding cavity is preferably 2mm.

[0069] Step 4, Heating and Exhausting: Transfer the molding cavity filled with liquid thermosetting material to a vacuum heating box that has been preheated to the set temperature T1, and evacuate it under negative pressure.

[0070] The above-mentioned vacuum heating box negative pressure evacuation method is as follows: the vacuum heating box is preheated to 60°C, first evacuated to a slight negative pressure of -15 kPa, and after a set time, the negative pressure is maintained at -8 kPa, so as to avoid damage to the thermosetting material structure while continuously bringing out the trapped small air bubbles.

[0071] Furthermore, the heat-resistant glass plate of the molding mold is positioned towards the observation port of the vacuum heating chamber. During the heating and exhaust process, the bubble situation in the liquid thermosetting material is observed in real time. When bubbles are observed in the liquid thermosetting material, the negative pressure value of the vacuum heating chamber is increased to expel the bubbles from the liquid thermosetting material.

[0072] Step 5, Curing: Remove the molding cavity from the vacuum heating chamber, heat the de-bubbling component to cool the molding cavity, and solidify the liquid thermosetting material in the molding cavity to form a solid thermosetting material block.

[0073] Furthermore, the heating and defoaming component allows the molding cavity to be cooled in sections at a cooling rate of 3 °C / s, so that the liquid thermosetting material in the molding cavity is cooled and solidified in a controlled manner, thereby suppressing the expansion of pores and bubbles caused by the chemical shrinkage of the liquid thermosetting material.

[0074] In this embodiment, it is preferable to also perform cooling and curing according to a step curve, specifically: 60 ℃×10 min → 80 ℃×30 min → 120 ℃×90 min → 3 ℃ / s cooling to 25 ℃. This step curve setting allows it to cross the gel point within the same temperature journey, resulting in a more consistent chemical reaction progress.

[0075] Step 6, specimen cutting: Demold the solid thermosetting material block from the molding cavity and cut off the two sides in the height direction. Then, cut out several thermosetting material specimens as needed; each thermosetting material specimen is cut along the height direction of the solid thermosetting material block.

[0076] This invention can reduce the initial gas content by more than 90%, and stabilize the porosity of the sample to ≤0.3%, achieving one-time molding with "controllable thickness, no internal bubbles, and no flash".

[0077] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A molding die for thermosetting materials used in tensile property testing, characterized in that: Includes a molding cavity and a heating and defoaming assembly; The height of the molding cavity is greater than the length of the thermosetting material specimen; The heated defoaming assembly includes a heating device and a heat-conducting plate; The heating device is located at the bottom of the molding cavity; The heat-conducting plate is at least one large vertical sidewall of the molding cavity and is connected to the heating device.

2. The molding die for thermosetting materials used in tensile property testing according to claim 1, characterized in that: The molding cavity includes a bottom frame, a front template, a rear template, a thickness limiting frame, and a sealing and clamping assembly; The bottom frame is a U-shaped frame with an upward opening; The thickness limiting frame is also a U-shaped frame with the opening facing upwards, and its thickness is equal to the thickness of the thermosetting material specimen. The front template, thickness limiting frame and rear template are stacked in sequence from front to back, with their bottoms extending into the bottom frame, and sealed and clamped on both sides by sealing and clamping components. The heating device is embedded in the bottom of the U-shaped groove of the base frame. The front template is a heat-resistant glass plate, and the rear template is a heat-conducting plate.

3. A molding method for thermosetting materials used in tensile property testing, characterized in that: Includes the following steps: Step 1, Filling the glue gun: Preheat the glue gun cartridge to the set temperature T1, and at the same time preheat the liquid thermosetting material to be filled to the set temperature T2 and evacuate it; then, fill the preheated liquid thermosetting material to be filled into the preheated glue gun cartridge after evacuation; wherein, T1 > T2. Step 2: Preheat the molding cavity to the set temperature T1; Step 3, Glue Injection: Move the glue gun nozzle to a distance of [distance missing] from the top surface of the molding cavity. a At a height of mm, the glue gun reciprocates along the length of the molding cavity using a three-segment trajectory of "left → right → center" until the molding cavity is filled; the dwell time at each trajectory point is specified. t Second; Step 4, Heating and Exhausting: Transfer the molding cavity filled with liquid thermosetting material to a vacuum heating box that has been preheated to the set temperature T1, and evacuate under negative pressure; Step 5, Curing: Remove the molding cavity from the vacuum heating box, heat the de-bubbling component to cool the molding cavity, and solidify the liquid thermosetting material in the molding cavity to form a solid thermosetting material block; Step 6, specimen cutting: Demold the solid thermosetting material block from the molding cavity and cut off the two sides in the height direction. Then, cut out several thermosetting material specimens as needed; each thermosetting material specimen is cut along the height direction of the solid thermosetting material block.

4. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 1, T1 = 60℃. By adjusting T2 and the vacuum pressure, the viscosity of the liquid thermosetting material to be filled is stabilized at 0.8–1.2 Pa·s.

5. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 2, the inner sidewall of the molding cavity is coated with an ultra-thin PTFE isolation layer with a thickness not exceeding 0.02 mm.

6. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 3, a =0.5mm, when the glue gun is injecting glue at the left section trajectory point, the glue gun nozzle is 2mm away from the left side wall of the molding cavity; when the glue gun is injecting glue at the right section trajectory point, the glue gun nozzle is 2mm away from the right side wall of the molding cavity.

7. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 3, the glue gun dispenses glue at a constant pressure of 0.25–0.35 MPa and a constant flow rate of 1.5–2.0 mL / s, with a dwell time at each trajectory point. t =30 seconds.

8. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 4, the method of vacuum heating box negative pressure evacuation is as follows: the vacuum heating box is preheated to 60°C, first evacuated to a slight negative pressure of -15 kPa, and after a set time, the negative pressure is maintained at -8 kPa, so as to avoid damage to the thermosetting material structure and continuously carry out the trapped small air bubbles.

9. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 2, the front template of the molding cavity is a heat-resistant glass plate; in step 4, the heat-resistant glass plate is oriented toward the observation port of the vacuum heating box, and the bubble situation in the liquid thermosetting material is observed in real time during the heating and exhaust process; when bubbles are observed in the liquid thermosetting material, the bubbles are discharged from the liquid thermosetting material by increasing the negative pressure value of the vacuum heating box.

10. The method for molding thermosetting materials for tensile property testing according to claim 3, characterized in that: In step 5, the heating defoaming component cools the molding cavity in sections at a cooling rate of 3 ℃ / s, thereby controlling the cooling and solidification of the liquid thermosetting material in the molding cavity and inhibiting the expansion of pores and bubbles caused by the chemical shrinkage of the liquid thermosetting material.

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