A large-section insulation mandrel formed by one-time pultrusion to avoid thermal stress cracking and a preparation method thereof

Abstract

The present invention discloses a one-time pultruded large-section insulating core rod for avoiding thermal stress cracking and a preparation method thereof, including a rod body with a diameter of 280-400 mm. The center position of the rod body is an inner ring part, a middle ring part located outside the inner ring part, and an outer ring part located outside the middle part. Glass fibers are axially distributed in the inner ring part, the middle ring part, and the outer ring part, and epoxy resin and a curing agent are filled between the glass fibers; the epoxy resin in the inner ring part contains a first curing accelerator; the epoxy resin in the middle ring part contains a second curing accelerator; the epoxy resin in the outer ring part contains a third curing accelerator; the first curing accelerator is imidazole; the second curing accelerator is triphenylphosphine; the third curing accelerator is tetrabutylphosphonium bromide. By selecting different curing accelerators, the curing rates of the epoxy resins at different positions are different, and the curing temperatures are different, so that the inner part is cured first and the outer part is cured last, so that the thermal stress will not concentrate, and effective heat transfer is achieved, so that no cracks will be generated inside the core rod.

Description

Technical Field

[0001] The invention relates to the field of ultra-high voltage power transmission and transformation, and more particularly to a large-section insulating core rod formed by one-time pultrusion and avoiding thermal stress cracking, and a preparation method thereof. Background Art

[0002] Insulators are key components involved in ultra-high voltage power transmission and transformation projects. The core component, the insulating core rod, is a composite insulating rod formed by cross-linking and curing under a certain temperature and pressure with epoxy resin as the matrix and glass fiber as the reinforcement. In the field of ultra-high voltage power transmission and transformation, with the increase of transmission and transformation voltage, the requirements for the voltage and related mechanical properties of the supporting insulators are getting higher and higher, and the diameter requirements of the insulating core rods used are also getting larger and larger. At present, the ultra-high voltage DC and AC transmission and transformation voltage has reached 800-1000kV. At the same time, the core rod diameter that meets the electrical and mechanical performance requirements must reach φ280-300mm, and in order to avoid the influence of the core rod's internal interface, it must be pultruded in one step. The biggest technical difficulty of the one-time molding process of large-diameter insulating core rods is the problem of thermal stress cracking caused by the asynchronous curing reaction of the rod surface and the core part during the pultrusion process. The reaction of the medium-temperature curing resin system mainly relies on the surface heat transfer of the mold. When the diameter becomes larger, the outer epoxy resin of the core rod is first cured by heat and releases heat. The heat flow conducted by the mold is superimposed, and the inner layer curing reaction is gradually triggered toward the core along the radial direction until the predetermined curing degree is reached. In this process, with the curing of the outer layer, the matrix changes from liquid phase to solid phase, forming a rigid cross-linked body structure, and its heat conduction capacity also deteriorates accordingly. At the same time, the heat released by the reaction will be superimposed on the heat flow introduced by the mold, and further transferred to the core part, thereby triggering more intense reaction heat release along the radial direction. Since the body structure that is cured first near the surface has poor thermal conductivity, the reverse heat conduction is blocked, and the maximum heat accumulation is bound to occur in the center of the rod. With the reaction heat release of the matrix resin in the center, the phenomenon of heat accumulation will be further aggravated, and even lead to the occurrence of exposure and burning. In this way, the different temperatures and reaction start times at different parts of the core rod along the radial direction will make the cross-linking density of the matrix at different parts different, and the curing shrinkage will also produce considerable differences, thus leading to the generation of thermal stress. When the accumulation of thermal stress reaches a certain level, it will be released outward in the form of local cracks. This is the reason why large-diameter core rods produced by single-stage pultrusion produce stress cracking, and ultimately lead to breakdown of insulators under ultra-high voltage during service. Summary of the invention

[0003] In view of the shortcomings of the prior art, the object of the present invention is to provide a large-section insulating core rod formed by one-time pultrusion and avoiding thermal stress cracking.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] An insulating mandrel with a large diameter and heat release avoidance characteristics, comprising a rod body, the diameter of the rod body being 280 - 400 mm. The center position of the rod body is an inner ring part, a middle ring part located outside the inner ring part, and an outer ring part located outside the middle part. Glass fibers are axially distributed in the inner ring part, the middle ring part, and the outer ring part, and epoxy resin and a curing agent are filled between the glass fibers;

[0006] The epoxy resin in the inner ring part contains a first curing accelerator;

[0007] The epoxy resin in the middle ring part contains a second curing accelerator;

[0008] The epoxy resin in the outer ring part contains a third curing accelerator;

[0009] The first curing agent accelerator is imidazole;

[0010] The second curing agent accelerator is triphenylphosphine;

[0011] The third curing agent accelerator is tetrabutylphosphonium bromide.

[0012] As a further improvement of the present invention,

[0013] The dosage of the first curing accelerator is 0.5% - 5% of the sum of the masses of the epoxy resin and the curing agent in the inner ring part;

[0014] The dosage of the second curing accelerator is 0.5% - 5% of the sum of the masses of the epoxy resin and the curing agent in the middle ring part;

[0015] The dosage of the third curing accelerator is 0.5% - 5% of the sum of the masses of the epoxy resin and the curing agent in the outer ring part.

[0016] As a further improvement of the present invention,

[0017] The curing agent is methyltetrahydrophthalic anhydride.

[0018] As a further improvement of the present invention,

[0019] The mass ratio of the epoxy resin to the curing agent is 1:1.

[0020] As a further improvement of the present invention,

[0021] The glass fiber accounts for 75 - 80% of the total mass of the rod.

[0022] As a further improvement of the present invention,

[0023] The cross-sectional areas of the inner ring part, the middle ring part, and the outer ring part are the same.

[0024] As another object of the present invention, there is provided a method for preparing a large cross-section insulating mandrel by one-step pultrusion molding to avoid thermal stress cracking.

[0025] Step 1: Mix epoxy resin, curing agent and the first curing accelerator, and place them in the first impregnation tank; mix epoxy resin, curing agent and the second curing accelerator, and place them in the second impregnation tank; mix epoxy resin, curing agent and the third curing accelerator, and place them in the third impregnation tank.

[0026] Step 2: Divide the glass fiber into three strands, and pass them through the first impregnation tank, the second impregnation tank, and the third impregnation tank respectively.

[0027] Step 3: Pass the impregnated glass fiber through a preforming device. The glass fiber passing through the first impregnation tank is located at the central position, the glass fiber passing through the second impregnation tank is located on the circumferential outer side of the glass fiber passing through the first impregnation tank, and the glass fiber passing through the third impregnation tank is located on the circumferential outer side of the glass fiber passing through the second impregnation tank to form a rod.

[0028] Step 4: Place the rod in a heating mold and carry out continuous curing and molding.

[0029] As a further improvement of the present invention,

[0030] In step 4, the temperature of the heating mold is 120°C to 200°C.

[0031] As a further improvement of the present invention,

[0032] The heating mold in step 4 has several heating zones, and the temperature from the rod entering the heating mold to leaving the heating mold is an increasing temperature in sequence.

[0033] As a further improvement, the temperature from the rod entering the heating mold to leaving the heating mold is 120°C, 140°C, 160°C, 180°C, and 200°C in sequence.

[0034] In the present invention, the glass fiber mainly uses alkali-free and twist-free glass fiber yarn, and enters the molding mold in a closely fitting manner. Only epoxy resin, curing agent, and curing accelerator are filled in the gaps. During the actual measurement, the glass fiber can reach 75-80%. As the key point of the present invention, different curing accelerators are selected, so that the curing rates and temperatures of the epoxy resin at different positions are different, so that the internal part cures first and the external part cures last, so that the thermal stress will not concentrate, and the heat transfer is effective, so that no cracks will occur inside the mandrel. And the cross-sectional areas of the inner ring part, the middle ring part, and the outer ring part are set to be the same, mainly to make the heat release more uniform.

[0035] Advantages of the present invention: In the present invention, the inner ring part uses imidazole, which has a relatively small curing range and cures quickly. The curing reaction terminates at 156°C. The outer ring part uses tetrabutylphosphonium bromide, which has a relatively large curing range and the curing reaction terminates at 181°C, requiring a relatively high temperature to terminate. The middle ring part uses triphenylphosphine, and its curing reaction ends at 162°C. Therefore, after the inner ring part is completely cured, the middle ring part cures, and finally the outer ring part cures, thus forming a curing range difference, which can completely conduct the internal heat out. After cooling, no cracks will occur, so it is applicable to large-diameter insulating mandrels. Description of the Drawings

[0036] Figure 1 is the process flow chart of the embodiment of the present invention;

[0037] Figure 2 is the schematic cross-sectional view of the rod in the embodiment of the present invention;

[0038] Figure 3 is the cross-sectional view of the rod prepared in the embodiment of the present invention;

[0039] Figure 4 is the cross-sectional view of the rod prepared in the comparative example of the present invention;

[0040] Figure 5 is the DSC test result diagram of the present invention.

[0041] Reference Signs:

[0042] 1, first dipping tank; 2, second dipping tank; 3, third dipping tank; 4, preforming device; 5, heating mold; 6, inner ring part; 7, middle ring part; 8, outer ring part. Detailed Embodiments

[0043] The present invention will be further described in detail below with reference to the embodiments given in the drawings.

[0044] Refer to Figures 1 to 5 as shown

[0045] Embodiment:

[0046] A large-diameter insulating mandrel with heat release prevention characteristics includes a rod body with a diameter of 300 mm. The center position of the rod body is an inner ring part, a middle ring part located outside the inner ring part, and an outer ring part located outside the middle part. The inner ring part, middle ring part, and outer ring part are all axially distributed with glass fibers, and epoxy resin and curing agent are filled between the glass fibers; the cross-sectional areas of the inner ring part, middle ring part, and outer ring part are the same.

[0047] The epoxy resin in the inner ring part contains a first curing accelerator;

[0048] The epoxy resin in the middle ring part contains a second curing accelerator;

[0049] The epoxy resin in the outer ring part contains a third curing accelerator;

[0050] The first curing accelerator is imidazole;

[0051] The second curing accelerator is triphenylphosphine;

[0052] The third curing accelerator is tetrabutylphosphonium bromide.

[0053] The dosage of the first curing accelerator is 1% of the sum of the masses of the epoxy resin and the curing agent in the inner ring part;

[0054] The dosage of the second curing accelerator is 1% of the sum of the masses of the epoxy resin and the curing agent in the middle ring part;

[0055] The dosage of the third curing accelerator is 1% of the sum of the masses of the epoxy resin and the curing agent in the outer ring part.

[0056] The curing agent is methyltetrahydrophthalic anhydride.

[0057] The mass ratio of the epoxy resin to the curing agent is 1:1.

[0058] The glass fiber accounts for 78% of the total mass of the rod.

[0059] Step 1: Mix the epoxy resin, the curing agent and the first curing accelerator, and place them in the first dipping tank; mix the epoxy resin, the curing agent and the second curing accelerator, and place them in the second dipping tank; mix the epoxy resin, the curing agent and the third curing accelerator, and place them in the third dipping tank;

[0060] Step 2: Divide the glass fiber into three strands, and pass them through the first dipping tank, the second dipping tank and the third dipping tank respectively;

[0061] Step 3: Pass the glass fiber after dipping through a preforming device. The glass fiber passing through the first dipping tank is located at the central position, the glass fiber passing through the second dipping tank is located on the circumferential outer side of the glass fiber passing through the first dipping tank, and the glass fiber passing through the third dipping tank is located on the circumferential outer side of the glass fiber passing through the second dipping tank to form a rod;

[0062] Step 4: Place the rod in a heating mold and carry out continuous curing and forming.

[0063] The temperature of the heating mold in Step 4 is 120°C to 200°C.

[0064] The heating mold in Step 4 has several heating zones, and the temperature increases sequentially from the time when the rod enters the heating mold to the time when it leaves the heating mold.

[0065] The temperatures from when the rod enters the heating die to when it leaves the heating die are 120°C, 140°C, 160°C, 180°C, and 200°C in sequence.

[0066] Comparative example:

[0067] Prepare a rod with a diameter of 300 mm:

[0068] Step 1: Mix epoxy resin, methyltetrahydrophthalic anhydride, and tetrabutylphosphonium bromide, and place them in the first sizing bath, the second sizing bath, and the third sizing bath; the mass ratio of epoxy resin, methyltetrahydrophthalic anhydride, and tetrabutylphosphonium bromide is 50:50:1.

[0069] Step 2: Divide the glass fiber into three strands, and pass them through the first sizing bath, the second sizing bath, and the third sizing bath respectively.

[0070] Step 3: Pass the sized glass fiber through a preforming device. The glass fiber passing through the first sizing bath is located at the central position, the glass fiber passing through the second sizing bath is located on the circumferential outside of the glass fiber passing through the first sizing bath, and the glass fiber passing through the third sizing bath is located on the circumferential outside of the glass fiber passing through the second sizing bath to form a rod.

[0071] Step 4: Place the rod in a heating die for continuous curing and forming.

[0072] The temperatures from when the rod enters the heating die to when it leaves the heating die are 120°C, 140°C, 160°C, 180°C, and 200°C in sequence.

[0073] After testing, in this example and the comparative example, the total mass of the glass fiber reaches 78%.

[0074] Testing:

[0075] I. Observe the cross-sections of the example and the comparative example.

[0076] Refer to Figure 3 and Figure 4 , where Figure 3 is the cross-section of the rod prepared in the example of the present invention, with a uniform surface and no cracks, while Figure 4 is the one prepared in the comparative example. It can be seen that there are a large number of turtle cracks on the surface. After the diameter becomes larger, due to the inability of the internal heat to dissipate, thermal stress is generated, resulting in internal cracks.

[0077] II. DSC test;

[0078] 1. Take 50 g of epoxy resin, 50 g of methyltetrahydrophthalic anhydride, and 1 g of imidazole and mix them for DSC test;

[0079] 2. Take 50 g of epoxy resin, 50 g of methyltetrahydrophthalic anhydride, and 1 g of triphenylphosphine for DSC test;

[0080] 3. Take 50 g of epoxy resin, 50 g of methyltetrahydrophthalic anhydride and 1 g of tetrabutylphosphonium bromide for DSC testing. Refer to Figure 5 , in this embodiment, three curing accelerators are mainly used. For the glass fibers in different parts, epoxy resins with different curing agents are used. After DSC testing, the curing range of imidazole is 130°C to 156°C, and the half-peak width is 14.5°C. The curing range of triphenylphosphine is 124°C to 162°C, and the half-peak width is 21.3°C. The curing range of tetrabutylphosphonium bromide is 124°C to 181°C, and the half-peak width is 27.6°C. When judging the starting temperature, tangents are made on both sides at the position of the half-peak width in the DSC curve, and the intersection positions with the X-axis are judged as the starting temperature and the ending temperature. In this embodiment, imidazole is used in the inner ring part, and its curing range is small and the curing is fast. The curing reaction terminates at 156°C. While tetrabutylphosphonium bromide is used in the outer ring part, and its curing range is large and the curing is slow. The curing reaction terminates at 181°C, and it requires a higher temperature to terminate. And triphenylphosphine is used in the middle ring part, and its curing reaction ends at 162°C. Therefore, after the inner ring part is completely cured, the middle ring layer is cured, and finally the outer ring layer is cured. In this way, a curing range difference is formed, and the internal heat can be completely conducted out. After cooling, no cracks will be generated, so it is applicable to large-diameter insulating mandrels.

[0081] The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking, comprising a rod body with a diameter of 280 - 400 mm. The central position of the rod body is an inner ring part, a middle ring part outside the inner ring part, and an outer ring part outside the middle part. Glass fibers are axially distributed in the inner ring part, middle ring part, and outer ring part, and epoxy resin and a curing agent are filled between the glass fibers. Characterized in that: The epoxy resin in the inner ring part contains a first curing accelerator; The epoxy resin in the middle ring part contains a second curing accelerator; The epoxy resin in the outer ring part contains a third curing accelerator; The first curing accelerator is imidazole; The second curing accelerator is triphenylphosphine; The third curing accelerator is tetrabutylphosphonium bromide.

2. The large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to claim 1, characterized in that: The dosage of the first curing accelerator is 0.5% - 5% of the sum of the mass of the epoxy resin and the curing agent in the inner ring part; The dosage of the second curing accelerator is 0.5% - 5% of the sum of the mass of the epoxy resin and the curing agent in the middle ring part; The dosage of the third curing accelerator is 0.5% - 5% of the sum of the mass of the epoxy resin and the curing agent in the outer ring part.

3. The large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to claim 1, characterized in that: The curing agent is methyltetrahydrophthalic anhydride.

4. The large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to claim 1, characterized in that: The mass ratio of the epoxy resin to the curing agent is 1:

1.

5. The large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to claim 1, characterized in that: The glass fibers account for 75 - 80% of the total mass of the rod.

6. The large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to claim 1, characterized in that: The cross-sectional areas of the inner ring part, middle ring part, and outer ring part are the same.

7. The preparation method of the large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to any one of claims 1 to 6, characterized in that: Step 1: Mix epoxy resin, a curing agent, and the first curing accelerator, and place them in a first impregnating bath; mix epoxy resin, a curing agent, and the second curing accelerator, and place them in a second impregnating bath; mix epoxy resin, a curing agent, and the third curing accelerator, and place them in a third impregnating bath; Step 2: Divide the glass fibers into three strands, and pass them through the first impregnating bath, the second impregnating bath, and the third impregnating bath respectively; Step 3: Pass the impregnated glass fibers through a preforming device. The glass fibers passing through the first impregnating bath are located at the central position, the glass fibers passing through the second impregnating bath are located on the circumferential outer side of the glass fibers passing through the first impregnating bath, and the glass fibers passing through the third impregnating bath are located on the circumferential outer side of the glass fibers passing through the second impregnating bath to form a rod; Step 4: Place the rod in a heating mold for continuous curing and forming.

8. The preparation method of the large-section insulating core rod formed by one-time pultrusion to avoid thermal stress cracking according to claim 7, characterized in that: In the fourth step, the temperature of the heating die is 120°C to 200°C.

9. The method for preparing a large cross-section insulating core rod by one-time pultrusion molding to avoid thermal stress cracking according to claim 8, characterized in that: In the fourth step, the heating die has several heating zones, and the temperature increases sequentially from the time when the rod enters the heating die to the time when it leaves the heating die.

10. The preparation method of the large cross-section insulation mandrel by one-time pultrusion molding for avoiding thermal stress cracking according to claim 9, characterized in that: The temperatures from the time when the rod enters the heating die to the time when it leaves the heating die are 120°C, 140°C, 160°C, 180°C, and 200°C in sequence.

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