A process for drying wet paperboard with equalizing balls

Abstract

This invention belongs to the field of electrical insulation component manufacturing technology and discloses a drying process for wet cardboard covering a pressure equalizing ball. The process involves wrapping a cleaned pressure equalizing ball with cut wet cardboard, then placing it in a low-temperature vacuum drying oven. The vacuum level is gradually reduced at 50-60°C until the cardboard moisture content drops to 8%-12%. The cardboard is then transferred to a high-temperature hot air drying oven at 105-110°C until the moisture content is ≤1%. After finishing, the product is obtained. This invention effectively solves the oxidation problem on the visible parts of the pressure equalizing ball, resulting in stable product quality and high work efficiency, eliminating the need for subsequent sanding.

Description

Technical Field

[0001] This invention belongs to the field of electrical insulation component manufacturing technology, specifically relating to a drying process for wet paperboard coated with equalizing balls. Background Technology

[0002] The equalizing sphere is a key electric field control component in high-voltage power equipment (such as transformers, ultra-high voltage transmission lines, GIS equipment, etc.). Its core function is "voltage equalization"—that is, by optimizing the electrode structure, the high-voltage electric field is distributed more evenly in the insulating medium, avoiding local field strength concentration that could lead to air breakdown or surface flashover, thereby ensuring the safe and stable operation of the equipment.

[0003] These components are mostly made of aluminum alloy due to their lightweight, good conductivity, and ease of molding. During the manufacturing process, wet cardboard (such as insulating cardboard or prepreg cardboard) is often wrapped around the surface of the equalizing ball to enhance insulation performance or serve as a structural support layer. The entire assembly then undergoes a hot-pressing and drying process to remove moisture and achieve curing.

[0004] However, in traditional drying processes, wet paperboard rapidly releases a large amount of water vapor at high temperatures. This vapor reacts violently with the aluminum alloy surface (located in externally visible areas such as the inner wall and flange of the equalizing sphere; the contact area between the pulp and the equalizing sphere is a closed space, where no oxidation occurs), producing aluminum oxides such as aluminum oxide (Al₂O₃). This reaction has the following hazards:

[0005] 1. Obvious color difference: The oxidized area darkens in color (turns grayish or black), creating a visual difference with the unoxidized area and affecting product consistency;

[0006] 2. Disruption of electric field uniformity: Uneven oxide layer thickness leads to increased surface roughness, local electric field distortion, and weakens the "equalization" function;

[0007] 3. Reduced insulation performance: Oxides may become conductive paths or defects, affecting the insulation quality of the cardboard-metal interface;

[0008] 4. Post-processing pollution is serious: Currently, the main method to remove the oxide layer is manual sandpaper grinding. However, the grinding process produces metal powder and oxide particles, which can easily contaminate the insulating paperboard, causing potential breakdown risks. In addition, it is labor-intensive, inefficient, and inconsistent.

[0009] Therefore, there is an urgent need for a process to inhibit oxidation reactions at the source, replacing the outdated "oxidize first, then polish" approach. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a drying process for wet paperboard covered with equalizing balls. This process overcomes the defects in the prior art, can effectively solve the oxidation problem of the visible parts of the equalizing balls, and produces products with stable quality and high work efficiency, without the need for subsequent sanding.

[0011] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0012] A drying process for wet paperboard coated with an equalizing ball bearing includes the following steps:

[0013] a. Pretreatment: Cut the wet cardboard (with a moisture content of about 50%) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0014] b. After impregnating (soaking) the insulating cardboard (cellulose substrate) with water, wrap it around the surface of the equalizing ball, and then tighten it with elastic cloth to drain the water;

[0015] c. Place the coated pressure-equalizing ball in a low-temperature vacuum drying oven and dry it for 4 to 8 hours at 50 to 60°C and a vacuum of 2000 Pa to 15000 Pa (until the moisture content of the cardboard drops to 8% to 12%, the specific time depends on the thickness of the cardboard, the number of coating layers and the initial moisture content); then slowly depressurize and restore it to normal pressure.

[0016] d. Transfer the equalizing balls to a high-temperature hot air drying oven and dry them at 105-110℃ for 1-6 hours (until the moisture content of the cardboard is ≤1%). After fine finishing, the finished equalizing balls are obtained.

[0017] Preferably, in step c, the transformer condition is that the initial vacuum level is the highest, and the vacuum level is decreased sequentially.

[0018] Preferably, the drying process is monitored indirectly in steps c and d by weighing or a humidity sensor.

[0019] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0020] This invention utilizes a segmented drying technology combining "low-temperature vacuum + high-temperature hot air" to avoid the severe oxidation caused by the superposition of "high temperature + high humidity" in traditional processes. The combination of "low-temperature vacuum + high-temperature hot air" not only improves drying efficiency but also ensures good density of the pulp insulation, enhancing electrical and mechanical properties. This results in clean and uniformly colored external parts of the equalizing ball, eliminating the need for subsequent polishing. It also improves product consistency and long-term operational reliability. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of step a, surface cleaning, in Embodiment 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of step a, cutting the wet cardboard, in Embodiment 1 of the present invention;

[0023] Figure 3 This is a schematic diagram of step b, the coating process, in Embodiment 1 of the present invention;

[0024] Figure 4 This is a schematic diagram of step b, the draining process, in Embodiment 1 of the present invention;

[0025] Figure 5 This is a schematic diagram of step c, low-temperature vacuum drying, in Embodiment 1 of the present invention;

[0026] Figure 6 This is a schematic diagram of step d, high-temperature hot air drying, in Embodiment 1 of the present invention;

[0027] Figure 7 This is a schematic diagram of the external appearance of the product after refinement in step d of Embodiment 1 of the present invention;

[0028] Figure 8 This is a schematic diagram of the internal structure of the product after refinement in step e of Embodiment 1 of the present invention;

[0029] Figure 9 This is a schematic diagram of the internal structure of the product according to Embodiment 1 of the present invention;

[0030] Figure 10 This is a schematic diagram of the internal structure of the product according to Embodiment 2 of the present invention;

[0031] Figure 11 This is a schematic diagram of the internal structure of the product according to Embodiment 3 of the present invention;

[0032] Figure 12 This is a schematic diagram of the internal structure of the product according to Embodiment 4 of the present invention;

[0033] Figure 13 This is a schematic diagram of the internal structure of the product according to Embodiment 5 of the present invention;

[0034] Figure 14 This is a schematic diagram of the internal structure of the product in Comparative Example 1 of the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] The following experiment was conducted using insulating paperboard (cellulose substrate) with an initial moisture content of 50% (mass fraction).

[0037] Example 1

[0038] a. Pretreatment: Cut the wet cardboard (with a moisture content of about 50%) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0039] b. Soak the insulating cardboard in deionized water until it is easy to shape, then wrap it around the surface of the pressure equalizing ball (5mm thick); then tighten it with an elastic cloth to drain the water;

[0040] c. Place the coated pressure-equalizing balls in a low-temperature vacuum drying oven and dry them at 60°C under vacuum conditions of 15000Pa for 1 hour, 7500Pa for 1 hour, and 2000Pa for 2 hours (until the moisture content of the cardboard drops to 8%). Then slowly depressurize and restore to normal pressure.

[0041] d. Transfer the equalizing balls to a high-temperature hot air drying oven and dry them at 110°C for 1 hour (until the moisture content of the cardboard is 0.8%). After fine finishing, the finished equalizing balls are obtained.

[0042] Example 2

[0043] a. Pretreatment: Cut the wet cardboard (with a moisture content of about 50%) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0044] b. Soak the insulating cardboard in deionized water until it is easy to shape, then wrap it around the surface of the pressure equalizing ball (7.5mm thick), and then tighten it with an elastic cloth to drain the water;

[0045] c. Place the coated pressure-equalizing balls in a low-temperature vacuum drying oven and dry them at 50°C and a vacuum of 15000Pa for 1 hour, then at a vacuum of 7500Pa for 1 hour, and then at a vacuum of 2000Pa for 2.5 hours (until the moisture content of the cardboard drops to 11%). Then slowly depressurize and restore the pressure to normal.

[0046] d. Transfer the equalizing balls to a high-temperature hot air drying oven and dry them at 105℃ for 1.5 hours (until the moisture content of the cardboard is 0.9%). After fine finishing, the finished equalizing balls are obtained.

[0047] Example 3

[0048] a. Cut the wet cardboard (with approximately 50% moisture content) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0049] b. Soak the insulating cardboard in deionized water until it is easy to shape, then wrap it around the surface of the pressure equalizing ball (10mm thick), and then tighten it with an elastic cloth to drain the water;

[0050] c. Place the coated pressure-equalizing balls in a low-temperature vacuum drying oven and dry them at 55°C under vacuum conditions of 15000Pa for 1 hour, 7500Pa for 1.5 hours, and 2000Pa for 2.8 hours (until the moisture content of the cardboard drops to 10%). Then slowly depressurize and restore to normal pressure.

[0051] d. Transfer the equalizing balls to a high-temperature hot air drying oven and dry them at 107.5℃ for 2.5 hours (until the moisture content of the cardboard is 0.9%). After fine finishing, the finished equalizing balls are obtained.

[0052] Example 4

[0053] a. Pretreatment: Cut the wet cardboard (with a moisture content of about 50%) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0054] b. Soak the insulating cardboard in deionized water until it is easy to shape, then wrap it around the surface of the pressure equalizing ball (12.5mm thick), and then tighten it with an elastic cloth to drain the water;

[0055] c. Place the coated pressure-equalizing balls in a low-temperature vacuum drying oven and dry them at 55°C and 15000Pa vacuum for 1 hour, 7500Pa vacuum for 2 hours, and 2000Pa vacuum for 3.5 hours (until the moisture content of the cardboard drops to 10%). Then slowly depressurize and restore to normal pressure.

[0056] d. Transfer the equalizing balls to a high-temperature hot air drying oven and dry them at 107.5℃ for 4 hours (until the moisture content of the cardboard is 0.8%). After fine finishing, the finished equalizing balls are obtained.

[0057] Example 5

[0058] a. Pretreatment: Cut the wet cardboard (with a moisture content of about 50%) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0059] b. Soak the insulating cardboard in deionized water until it is easy to shape, then wrap it around the surface of the pressure equalizing ball (15mm thick), and then tighten it with an elastic cloth to drain the water;

[0060] c. Place the coated pressure-equalizing balls in a low-temperature vacuum drying oven and dry them at 55°C and 15000Pa vacuum for 1.5 hours, 7500Pa vacuum for 2 hours, and 2000Pa vacuum for 4.5 hours (until the moisture content of the cardboard drops to 10%). Then slowly depressurize and restore to normal pressure.

[0061] d. Transfer the equalizing balls to a high-temperature hot air drying oven and dry them at 107.5℃ for 6 hours (until the moisture content of the cardboard is 0.8%). After fine finishing, the finished equalizing balls are obtained.

[0062] Comparative Example 1

[0063] a. Pretreatment: Cut the wet cardboard (with a moisture content of about 50%) according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball (remove oil and dust).

[0064] b. Soak the insulating cardboard in deionized water until it is easy to shape, then wrap it around the surface of the equalizing ball (15mm thick).

[0065] c. Place the coated equalizing balls in a high-temperature hot air drying oven and dry them at 107.5℃ for 22 hours (until the moisture content of the cardboard is 0.8%).

[0066] Results and Analysis

[0067] The production parameters and related performance of the products of Examples 1-5 and Comparative Example 1 were tested (surface condition inspection, materials, etc.), and the results are shown in Table 1. The product status of each process during production and the product status of Examples 1-5 and Comparative Example 1 are shown in Table 1. Figure 1-14 The partial discharge quantity was tested according to the national standard GB1094-85; the oxide film thickness was tested using the split-beam microscopy method for the thickness of aluminum and aluminum alloy anodic oxide films as specified in GB / T8014.3-2005.

[0068] Table 1. Production parameters and relevant product performance of Examples 1-5 and Comparative Example 1.

[0069] Wet paper insulation thickness (mm) Drying time (h) Are there any visible oxides? Possibility of causing excessive partial discharge Oxide film thickness and distribution (μm) Conductivity uniformity Partial discharge quantity (PC) Example 1 5 5 none Extremely low 11.5 Evenly distributed good 1.2 Example 2 7.5 6 none Extremely low 12.3 Uniform distribution good 0.8 Example 3 10 7.8 none Extremely low 15.6 Uniform distribution good 1.3 Example 4 12.5 10.5 none Extremely low 15.3 Uniform distribution good 0.9 Example 5 15 14 none Extremely low 12.2 Uniform distribution good 1.3 Comparative Example 15 22 have high 116.5 uneven distribution Difference 150

[0070] The data above demonstrates that this invention has significant advantages in suppressing the oxidation of equalizing balls. By employing a segmented drying technology of "low-temperature vacuum + high-temperature hot air," this invention avoids the severe oxidation caused by the superposition of "high temperature + high humidity" in traditional processes, greatly reducing the risks associated with the oxidation of equalizing balls and ensuring product quality. Furthermore, the drying time is significantly shortened. For the same thickness of cardboard (15mm), the drying time of this invention is 14 hours, while the existing technology requires 22 hours. This shows that this invention can also effectively improve work efficiency.

[0071] It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A drying process for wet paperboard coated with an equalizing ball, characterized in that: Includes the following steps: a. Pretreatment: Cut the wet cardboard according to the perimeter and height of the equalizing ball, and clean the surface of the aluminum equalizing ball at the same time; b. After impregnating the insulating cardboard, wrap it around the surface of the equalizing ball, and then tighten it with elastic cloth to drain the water; c. Place the coated pressure-equalizing spheres in a low-temperature vacuum drying oven and dry them for 4 to 8 hours at 50–60°C and a vacuum of 2000 Pa–15000 Pa; then slowly depressurize them to restore them to normal pressure. d. Transfer the pressure equalization spheres to a high-temperature hot air drying oven and dry them at 105-110℃ for 1-6 hours. After fine finishing, the finished pressure equalization spheres are obtained.

2. The drying process for wet paperboard with equal-pressure ball coating as described in claim 1, characterized in that: In step c, the transformer condition is that the initial vacuum level is the highest, and the vacuum level is decreased sequentially.

3. The drying process for wet paperboard with equal-pressure ball coating as described in claim 1, characterized in that: In steps c and d, the drying process is indirectly monitored by weighing or a humidity sensor.

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