CN102831991B - Method for manufacturing epoxy-cast insulators - Google Patents

Abstract

The invention relates to a method for manufacturing epoxy cast insulators, comprising the following steps: surface treatment of metal inserts, preparation of castables, mold loading of metal inserts, pouring, curing and demoulding, wherein the step of surface treatment of metal inserts includes inserts Sand blasting, insert cleaning and insert gluing, where the insert cleaning is carried out in the following order: (1) Sodium hydroxide solution erosion at 90±5°C for 5-20s; (2) Hot water washing at 90±5°C for 3-20 seconds 15s; (3) Washing in cold water at 25±5°C for 3-15s; (4) Washing in nitric acid at 25±5°C for 5-20s; (5) Washing in cold water at 25±5°C for 3-15s; (6) Sulfuric acid at 25±5°C Mix pickling for 5-15 minutes; (7) Wash in cold water at 25±5°C for 3-15s; (8) Wash in hot water at 90±5°C for 3-15s; (9) Soak in cold water until the insert is taken out before loading. The invention improves the bonding force between the metal insert and the resin matrix, and its bonding force is increased by about 50% compared with the conventional surface treatment process, and its bonding strength can reach 55MPa.

Description

Manufacturing method of epoxy cast insulator

technical field

The invention relates to a method for manufacturing an epoxy casting insulator.

Background technique

For high-voltage switchgear, its voltage level mainly depends on the various electrical and mechanical performance indicators of the insulator. The higher the voltage level, the more stringent the requirements for the insulator. At present, the mechanical performance indicators of the insulator are measured by the water pressure damage strength. . For large insulators, such as pot insulators for 1100kV GIS (diameter 934mm, depth 365mm, weight 140kg), it is required to have excellent mechanical properties under the premise of satisfying its electrical properties, that is, the hydraulic pressure failure strength must meet the specified design requirements , while the water pressure failure strength is determined by the strength and toughness of the insulator body. Under the condition of a certain design size of the insulator, the curing method in the epoxy casting production is the key to determine the strength and toughness of the insulator body.

At present, the conventional manufacturing methods of epoxy cast insulators mainly include the following processes: mold preparation, surface treatment of inserts such as center conductors, preparation of castables, insert molding, pouring, curing and demoulding. The key link of the performance index. The curing process generally has three main stages: continuous heating, heat preservation and cooling. The curing temperature and the length of the curing time directly affect the microstructure formation and shrinkage of the casting. If the curing temperature is too high or Rapid temperature rise will lead to porosity and even shrinkage cavity, which will affect the mechanical properties of castings.

There are two main curing methods for epoxy castings currently used: single-stage curing and two-stage curing. The corresponding curing degree DSC curves are shown in Figure 1. The curve at the bottom end, from the curve shown in the figure, we can know that the single-stage curing generally chooses a relatively low curing temperature, and the curing degree is increased by lengthening the time. Therefore, the curing degree of the insulator using the single-stage curing is generally low, and the curing process Among them, the glass transition temperature is low, and there is an obvious curing exothermic peak; while the two-stage curing is due to the large temperature difference between the first stage and the second stage, which can easily lead to excessive curing in the second stage. The glass transition temperature is high during the curing process, and the inflection point is not obvious. For insulators cast by the above two curing methods, when the curing degree is too low, the insulator body is soft and flexible, but its strength is relatively small; while the insulator is strong but also brittle if the curing degree is too high, which increases the Risk of cracking.

From the DSC curves of single-stage curing and two-stage curing in Figure 1, it can be seen that the strength and toughness of the insulator are directly related to the curing degree of epoxy pouring. It is necessary to ensure that the insulator has high strength and good toughness. The production of large insulators by using the above two curing methods for epoxy castings obviously cannot meet the requirements for its mechanical properties, which means that the curing process requires a new curing method. , which poses a new topic for the epoxy casting process of insulators.

In addition, the bonding force between the metal insert of the center conductor of the pot insulator and the resin matrix also has a certain influence on the hydraulic failure strength of the insulator, so in the casting production process of the pot insulator, the metal inserts such as the center conductor must be surfaced before casting In order to improve the bonding force between the metal insert and the resin matrix, the conventional surface treatment methods currently used are sandblasting and ultrasonic cleaning of the metal insert. This treatment method is simple and cannot meet its requirements for large pot insulators. Requirements for the bonding force between the insert and the resin.

Contents of the invention

The object of the present invention is to provide a method for manufacturing epoxy cast insulators capable of improving the bonding force between metal inserts such as central conductors and epoxy resin matrix.

In order to achieve the above object, the present invention adopts the following technical scheme: the method for manufacturing epoxy cast insulators, including the following steps: surface treatment of metal inserts, preparation of castables, metal insert molding, casting, curing and demoulding, wherein the metal inserts The surface treatment steps include insert sandblasting, insert cleaning and insert gluing, where the insert cleaning is carried out in the following order:

(1) Erosion with sodium hydroxide solution at 90±5°C for 5-20s;

(2) Wash in hot water at 90±5°C for 3-15s;

(3) Wash in cold water at 25±5°C for 3 to 15 seconds;

(4) Nitric acid washing at 25±5°C for 5-20s;

(5) Wash in cold water at 25±5°C for 3 to 15 seconds;

(6) Mixed pickling with sulfuric acid at 25±5°C for 5 to 15 minutes;

(7) Wash in cold water at 25±5°C for 3-15 seconds;

(8) Wash in hot water at 90±5°C for 3 to 15 seconds;

(9) Soak in cold water until the insert is removed before loading the mold.

Further, in the step (6), the pickling solution used in sulfuric acid mixed pickling is a mixed solution of sulfuric acid and nitric acid, a mixed solution of sulfuric acid and chromic acid, or a mixed solution of sulfuric acid, nitric acid, and chromic acid.

Furthermore, after demolding, there is a stress relief step, which is to keep the demolded insulator at a temperature of 145±3°C for 4±0.5h.

The curing method in the present invention divides the curing process into three stages (hereinafter the curing method of the present invention is referred to as three-stage curing), and its degree of curing can be qualitatively evaluated by the DSC curve shown in Figure 1. In Figure 1, The three-stage curing corresponds to the curve in the middle. From the comparison of the three curves in Fig. 1, it can be clearly explained that the present invention makes the continuous temperature rise in the curing process gentle, and the duration Appropriate, the glass transition temperature is moderate during the curing process, the inflection point is obvious, and there is no exothermic peak. The three-stage curing makes the pouring process have a more suitable degree of curing than the single-stage curing and two-stage curing. The following table is for the three curing methods. Data from strength and toughness tests performed on cast samples:

                                                

Through the comparison of the test data in the above table and the electron microscope pictures in Figure 2 and Figure 3, the single-stage solidified grains are coarse and uneven, and easy to yield, resulting in low strength and high elongation at break; the two-stage solidified material is brittle, Brittle cracks lead to low strength and low elongation at break; compared with pot insulators using single-stage curing, the three-stage curing pot insulator has uniform and fine grains, which greatly improves the compactness and Uniformity, which further improves the overall strength of the insulator. Compared with single-stage curing and two-stage curing, the castings obtained by using three-stage curing also have higher toughness and excellent comprehensive mechanical properties. . The three-stage curing method makes it possible to produce large pot insulators that meet the requirements of use. The pot insulators manufactured by the method of the present invention are 934mm in diameter, 365mm in depth, and 140kg in weight. After 10 times of cold and heat cycle tests, the water The crushing strength is as high as 4.4MPa. In addition, the breakdown strength per unit thickness of the insulator can reach 35kV/mm, which ensures the electrical performance of the insulator.

The present invention adopts 0.05MPa pressurization measures at the initial stage of heat preservation in the first stage of three-stage curing, which can reduce defects such as shrinkage marks caused by curing shrinkage of castings, which is of great significance for large castings.

In the present invention, a surface treatment process combining sandblasting, cleaning and gluing is adopted for metal inserts such as the central conductor of an insulator. Since the cleaning process uses repeated cleaning steps of different solutions, not only can the surface layer substances of the inserts such as the central conductor be removed, At the same time, it can also make the surface of the sandblasted insert uniform and dense, thereby improving the bonding force between the central conductor and the resin matrix; using conventional sandblasting plus ultrasonic cleaning, the bonding strength of the resin and metal is only 25MPa The bonding strength between the metal insert and the resin of the present invention can reach about 55MPa, which is about 50% higher than the conventional surface treatment process, laying a foundation for improving the hydraulic damage performance of pot insulators. the

In the present invention, stress relief treatment at 145±3°C/4h is adopted after demoulding, which fully releases the curing internal stress of the pot insulator, and the time is appropriate, without causing brittle changes.

Description of drawings

Fig. 1 is the comparison of DSC curves of single-stage curing, two-stage curing and three-stage curing insulator curing degree of the present invention;

Figure 2 is a 4000 times electron microscope image of the microstructure of the pot insulator formed by the single-stage curing method after epoxy pouring;

Fig. 3 is the 4000 times electron microscope picture of the pot insulator microstructure formed according to the three-stage curing method of the present invention after epoxy pouring;

Fig. 4 is three sections curing temperature-time graphs among the present invention;

Fig. 5 is a flow chart of Embodiment 1 of the method for manufacturing an epoxy cast insulator according to the present invention.

Detailed ways

The embodiment of the epoxy cast insulator manufacturing method provided by the present invention is as follows

Embodiment 1: As shown in Figure 5, the method for manufacturing an epoxy cast insulator includes the following steps:

1. Mold preparation: mainly consists of mold treatment, surface treatment of metal inserts such as center conductors, insert molding and mold pre-baking;

2. Preparation of castables: After the resin pre-baking, curing agent pre-baking and filler pre-baking are completed, the ingredients are prepared, and then statically mixed; this step is the same as the corresponding conventional step;

3. Vacuum pouring: the same as the conventional pouring method;

4. Curing: The curing step is three-stage curing. The three-stage curing consists of three stages in the following order, as shown in Figure 4. The first stage: the temperature is continuously raised from room temperature to 105°C within 2 hours, and kept for 15 hours. The first 6 hours of 15 hours are kept at 0.05MPa pressure; then enter the second stage: continue to heat up from 105°C to 150°C within 1 hour, and keep warm for 15 hours; then enter the third stage: continue to heat up from 150°C to 155°C within 1 hour ℃, and keep warm for 5h;

5. Demoulding;

6. Stress relief treatment: The stress relief step is to keep the demoulded insulator at a temperature of 145°C for 4 hours.

Among them, the surface treatment of metal inserts such as the center conductor in step 1 consists of insert sandblasting, insert cleaning and insert glue coating in sequence, and the insert cleaning step is carried out in the following order:

(1) Corroded by sodium hydroxide solution at 90°C for 12s; since the uneven porous structure is formed on the surface of the metal insert after sandblasting, and there is an oxide layer on the surface of the insert, use sodium hydroxide solution after sandblasting. The oxide layer is eroded, and the hot lye can expand the micropores on the surface of the insert, ensuring that the oxide layer on the surface of the insert can be completely eroded;

(2) Wash in hot water at 90°C for 9 seconds; using hot water at the same temperature as the lye can keep the micropores on the surface of the insert in the original expanded state without shrinkage, and it is convenient to remove the residual lye and impurities attached to the outer surface of the hole wash away;

(3) Wash in cold water at 25°C for 9s; further clean the residue on the surface of the insert to improve the surface cleanliness;

(4) Nitric acid washing at 25°C for 12s; this step uses nitric acid for acid-base neutralization to remove the alkali-etched layer on the surface of the insert;

(5) Wash in cold water at 25°C for 9s; this step washes away the residual liquid and impurities attached to the surface of the insert;

(6) Mixed pickling with sulfuric acid at 25°C for 9 minutes; the pickling solution can be a mixed solution of sulfuric acid and nitric acid, a mixed solution of sulfuric acid and chromic acid, or a mixed solution of sulfuric acid, nitric acid, and chromic acid; this step is to eliminate inserts The burrs and peaks on the surface make the surface of the insert uniform and consistent, so as to improve the bonding force with the resin;

(7) Wash in cold water at 25°C for 9s; remove residual acid and impurities attached to the surface of the insert;

(8) Wash in hot water at 90°C for 9s; use hot water to wash again in the state of hole expansion, and thoroughly remove the residue on the outer surface of the hole;

(9) Soak in cold water until the insert is removed before loading the mold. If the surface of the insert treated by the above steps is in contact with air for a certain period of time, it will be easily oxidized, and the resulting oxide layer will reduce the bonding force with the resin. Therefore, before pouring and molding, soak the insert in cold water to isolate the air and prevent Oxidized until the Insert is molded out of the water when ready to pour.

Embodiment 2: The manufacturing method of the epoxy cast insulator of this embodiment differs from that of Embodiment 1 in that: the cleaning step of the metal insert in step 1 is carried out in the following order:

(1) Corrosion with sodium hydroxide solution at 95°C for 5s;

(2) Wash in hot water at 95°C for 3 seconds;

(3) Wash in cold water at 30°C for 3 seconds;

(4) Wash with nitric acid at 30°C for 5s;

(5) Wash in cold water at 30°C for 3 seconds;

(6) Mixed pickling with sulfuric acid at 30°C for 5 minutes; the pickling solution can be a mixed solution of sulfuric acid and nitric acid, a mixed solution of sulfuric acid and chromic acid, or a mixed solution of sulfuric acid, nitric acid, and chromic acid;

(7) Wash in cold water at 30°C for 3 seconds;

(8) Wash in hot water at 95°C for 3 seconds;

(9) Soak in cold water until the insert is removed before loading the mold.

In addition, in step 4, the curing is composed of three stages in the following order. The first stage: the temperature is continuously raised from room temperature to 102°C within 1.5 hours, and the temperature is kept for 15.5 hours. The first 6 hours of this 15.5 hours of heat preservation are 0.05MPa Keep warm; then enter the second stage: continue to heat up from 102°C to 147°C within 0.5h, and keep warm for 15.5h; then enter the third stage: continue to heat up from 147°C to 152°C within 0.5h, and keep warm for 5.5h.

In step 6, the stress relief step is to keep the molded casting at 142° C. for 4.5 hours.

Embodiment 3: The difference between the method for manufacturing epoxy cast insulators in this embodiment and Embodiment 1 is that the cleaning step of the metal insert in step 1 is carried out in the following order:

(1) Erosion with sodium hydroxide solution at 85°C for 20s;

(2) Wash in hot water at 85°C for 15s;

(3) Wash in cold water at 20°C for 15s;

(4) Wash with nitric acid at 20°C for 20s;

(5) Wash in cold water at 20°C for 15s;

(6) Mixed pickling with sulfuric acid at 20°C for 15 minutes; the pickling solution can be a mixed solution of sulfuric acid and nitric acid, a mixed solution of sulfuric acid and chromic acid, or a mixed solution of sulfuric acid, nitric acid, and chromic acid;

(7) Wash in cold water at 20°C for 15s;

(8) Wash in hot water at 85°C for 15s;

(9) Soak in cold water until the insert is removed before loading the mold.

In addition, in step 4, the curing consists of three stages in the following order. The first stage: the temperature is continuously raised from room temperature to 108°C within 2.5 hours, and the temperature is kept for 14.5 hours. Keep warm; then enter the second stage: continue to heat up from 108°C to 153°C within 1.5h, and keep warm for 14.5h; then enter the third stage: continue to heat up from 153°C to 158°C within 1.5h, and keep warm for 4.5h.

In step 6, the stress relief step is to keep the molded casting at 148° C. for 3.5 hours.

Step 4 in the above three embodiments, the first 6h of the first stage of the three-stage curing in the heat preservation process adopts 0.05MPa pressurized heat preservation measures, all of which are to reduce the shrinkage marks and other defects caused by the curing shrinkage of the insulator. Large insulators are more important, while small insulators can be kept warm without pressurization.

The method for manufacturing epoxy cast insulators of the present invention, wherein the surface treatment method for metal inserts such as central conductors, is particularly suitable for the production of large basin-type insulators, and the basin-type insulators produced by the method of the present invention have a gap between the central conductor metal inserts and the resin The bonding strength can reach about 55MPa, and its bonding force is increased by about 50% compared with the conventional surface treatment process, which lays the foundation for the improvement of the water pressure damage performance of the pot insulator. the

Claims (9)

1. The method for manufacturing epoxy cast insulators is characterized in that: comprising the following steps: metal insert surface treatment, preparation of castable, metal insert mold loading, pouring, curing and demoulding, wherein: The curing step has three stages: in the first stage, the temperature is continuously raised from room temperature to 105°C within 2 hours and kept for 15 hours, and the first 6 hours of this 15-hour heat preservation are held at 0.05MPa under pressure; in the second stage, the temperature is continuously raised from 105°C within 1 hour Keep warm at 150°C for 15 hours; in the third stage, continue to heat up from 150°C to 155°C within 1 hour and keep warm for 5 hours; The surface treatment steps of metal inserts include insert sandblasting, insert cleaning and insert glue coating, where the insert cleaning is carried out in the following order: (1) Erosion with sodium hydroxide solution at 90±5°C for 5-20s; (2) Wash in hot water at 90±5°C for 3-15s; (3) Wash in cold water at 25±5°C for 3 to 15 seconds; (4) Nitric acid washing at 25±5°C for 5-20s; (5) Wash in cold water at 25±5°C for 3 to 15 seconds; (6) Mixed pickling with sulfuric acid at 25±5°C for 5 to 15 minutes; (7) Wash in cold water at 25±5°C for 3 to 15 seconds; (8) Wash in hot water at 90±5°C for 3 to 15 seconds; (9) Soak in cold water until the insert is taken out before loading the mold. 2. The method for manufacturing epoxy cast insulators according to claim 1, characterized in that: in the step (6), the pickling solution used in sulfuric acid mixed pickling is a mixed solution of sulfuric acid and nitric acid, sulfuric acid and chromic acid mixed solution of sulfuric acid, nitric acid, and chromic acid. 3. The method for manufacturing epoxy cast insulators according to claim 1 or 2, characterized in that: after demoulding, there is a step of stress relief, and the step of stress relief is to place the insulator after demoulding at a temperature of 145±3°C Keep for 4±0.5h. 4. The method for manufacturing epoxy cast insulators is characterized in that it includes the following steps: surface treatment of metal inserts, preparation of castables, mold loading of metal inserts, pouring, curing and demoulding, wherein: The curing step has three stages: in the first stage, the temperature is continuously raised from room temperature to 102°C within 1.5 hours and kept for 15.5 hours. 102°C to 147°C for 15.5 hours; the third stage: 147°C to 152°C within 0.5 hours for 5.5 hours; The surface treatment steps of metal inserts include insert sandblasting, insert cleaning and insert glue coating, where the insert cleaning is carried out in the following order: (1) Erosion with sodium hydroxide solution at 90±5°C for 5-20s; (2) Wash in hot water at 90±5°C for 3-15s; (3) Wash in cold water at 25±5°C for 3 to 15 seconds; (4) Nitric acid washing at 25±5°C for 5-20s; (5) Wash in cold water at 25±5°C for 3 to 15 seconds; (6) Mixed pickling with sulfuric acid at 25±5°C for 5 to 15 minutes; (7) Wash in cold water at 25±5°C for 3 to 15 seconds; (8) Wash in hot water at 90±5°C for 3 to 15 seconds; (9) Soak in cold water until the insert is taken out before loading the mold. 5. The method for manufacturing epoxy cast insulators according to claim 4, characterized in that: in the step (6), the pickling solution used in sulfuric acid mixed pickling is a mixed solution of sulfuric acid and nitric acid, sulfuric acid and chromic acid mixed solution of sulfuric acid, nitric acid, and chromic acid. 6. The method for manufacturing epoxy cast insulators according to claim 4 or 5, characterized in that: after demoulding, there is a step of stress relief, and the step of stress relief is to place the insulator after demoulding at a temperature of 145±3°C Keep for 4±0.5h. 7. The method for manufacturing epoxy cast insulators, which is characterized in that it includes the following steps: surface treatment of metal inserts, preparation of castables, mold loading of metal inserts, pouring, curing and demoulding, wherein: The curing step has three stages: in the first stage, the temperature is continuously raised from room temperature to 108°C within 2.5 hours and kept for 14.5 hours. Continue to heat up from 108°C to 153°C for 14.5 hours; in the third stage, continue to heat up from 153°C to 158°C within 1.5 hours and hold for 4.5 hours; The surface treatment steps of metal inserts include insert sandblasting, insert cleaning and insert glue coating, where the insert cleaning is carried out in the following order: (1) Erosion with sodium hydroxide solution at 90±5°C for 5-20s; (2) Wash in hot water at 90±5°C for 3-15s; (3) Wash in cold water at 25±5°C for 3 to 15 seconds; (4) Nitric acid washing at 25±5°C for 5-20s; (5) Wash in cold water at 25±5°C for 3 to 15 seconds; (6) Mixed pickling with sulfuric acid at 25±5°C for 5 to 15 minutes; (7) Wash in cold water at 25±5°C for 3 to 15 seconds; (8) Wash in hot water at 90±5°C for 3 to 15 seconds; (9) Soak in cold water until the insert is taken out before loading the mold. 8. The method for manufacturing epoxy cast insulators according to claim 7, characterized in that: in the step (6), the pickling solution used in sulfuric acid mixed pickling is a mixed solution of sulfuric acid and nitric acid, sulfuric acid and chromic acid mixed solution of sulfuric acid, nitric acid, and chromic acid. 9. The method for manufacturing epoxy cast insulators according to claim 7 or 8, characterized in that: after demolding, there is a stress relief step, the stress relief step is to place the demolded insulator at a temperature of 145±3°C Keep for 4±0.5h.