CN116237363A - Process for producing aluminum foil for high-strength double-light lithium battery in four passes - Google Patents

Abstract

The invention belongs to the field of light alloy technology, and relates to a four-pass process for producing aluminum foil for high-strength dual-light lithium batteries. % is adjusted to 0.1~0.15%; the billet is distributed and rolled according to 4 passes, including 3 passes for rough rolling and 1 pass for finish rolling; taking a billet with a thickness of 0.26mm as an example, rough rolling and Arranged on the same rolling mill to roll the aluminum foil to a thickness of 0.025mm through 3 passes, and then finish rolling to the double photocell foil with a thickness of 0.012mm in 1 pass. The rolling pass distribution is: 0.26mm→0.115mm→0.055mm →0.025mm→0.012mm, slitting, corona, inspection, finished product packaging. The present invention increases the copper content in the billet, uses 95# base oil together with additive W3H, and the coincidence degree of the actual plate shape and the target plate shape reaches more than 95%. Adjust the roll process and high oil temperature, increase the volatilization and corona of the oil film on the foil surface, the surface dyne value of the finished product is > 32, the yield is increased by 10-15%, and the overall yield is over 80%.

Description

Four-pass production process of aluminum foil for high-strength dual-light lithium batteries

technical field

The invention belongs to the technical field of light alloys and relates to the production of aluminum foil, in particular to a four-pass process for producing aluminum foil for high-strength dual-light lithium batteries.

Background technique

With the rapid development of new energy electric vehicles, the demand for lithium batteries, the core component, is strong. As the anode material of lithium batteries, aluminum foil needs to have higher performance and quality requirements. The technical indicators of the battery foil are strictly required, and the customer's requirements for the thickness, strength, pattern, and cleanliness of the battery foil have reached the limit, and the production is difficult. Domestic aluminum foil for high-strength dual-light lithium batteries usually requires: thickness 15, 13, 12 μm, finished product performance tensile strength ≥ 250N/mm ² , elongation ≥ 3.0%, pattern slump ≤ 8mm, surface wetting tension ≥ 32dyn .

At present, the battery foil manufacturing technology is mostly optimized on the basis of ordinary aluminum foil rolling process, which generally includes: 1. Increase the number of rolling passes, reduce the reduction rate of passes, and achieve high tensile strength of the finished product by means of multi-pass work hardening Strength; 2. In order to improve the surface wetting tension of the battery foil, the rolling mill uses 80# and 82# base oils and special additives for battery foil, and uses high-power light box baking and corona treatment during the cutting process.

The existing problems mainly include:

(1) Difficulty in rolling high-strength lithium battery foil: When using 80# or 82# base oil in the traditional process, there are problems that the high-strength battery foil cannot be rolled or cannot be processed in one pass. For this reason, most manufacturers adopt additional rolling It is realized by reducing the number of passes and reducing the thickness of the billet. The industry generally adopts a process of 5 or 6 calendering passes, and the thickness of the billet is ≤0.24mm. In this way, the production efficiency is greatly reduced, and the production cost is also greatly increased thereupon.

(2) The flatness of the product plate is unstable, and local tightness changes are obvious: high-end battery foil customers have extremely high requirements on the form of the battery foil, and the off-line form detector needs to achieve a load of 8N/mm at a measuring distance of 2m After ² forces, the maximum collapse of the laser scanning foil surface is ≤8mm. The uneven plate shape will affect the uniformity and consistency of the carbon coating process of the battery, which is a key technical indicator of the energy density of the battery. With the development of the industry, the requirements for the accuracy of the lithium battery foil pattern are constantly increasing. When using 80# or 82# base oil, since the kinematic viscosity is only about 1.75, the wear resistance and lubrication of the rolling oil cannot fully meet the rolling needs. , resulting in uneven thermal convexity of the roll, which eventually leads to poor foil surface layout. In fact, battery foil users have a lot of quality complaints and returns about the plate type. Continuously improving the shape quality of products through process optimization and technological innovation is an important issue faced by battery foil manufacturers.

(3) Surface wetting tension: Insufficient surface wetting tension will seriously affect the quality of carbon coating on battery foil. If the wetting tension is not up to the standard, defects such as missing coating and delamination will occur during the carbon coating process. These defects will directly lead to the scrapping of the product. Therefore, the wetting tension of the foil surface must be ≥32dyn.

These problems make the comprehensive yield of battery foil production low, the production cost is high, and the manufacturers of aluminum foil for lithium batteries face many difficulties. With the rapid rise of new energy vehicles, the demand for lithium battery aluminum foil has increased significantly, and it is imperative to develop and produce high-quality lithium battery aluminum foil that meets market demand.

Contents of the invention

Aiming at the problems of difficult rolling, low production efficiency and high production cost in the existing production of aluminum foil for lithium batteries, the purpose of the present invention is to disclose a four-pass process for producing aluminum foil for high-strength dual-light lithium batteries.

A four-pass process for producing aluminum foil for high-strength double-light lithium batteries, comprising the following steps:

The thickness of the billet is 0.26-0.3mm, the hardness state is H18, and the content of trace alloy element copper is adjusted from 0.05-0.1% to 0.1-0.15%;

The billet is distributed and rolled according to 4 passes, including 3 passes for rough rolling and 1 pass for finish rolling; taking a billet with a thickness of 0.26mm as an example, rough rolling and intermediate rolling are arranged in the same rolling mill through 3 passes Roll the aluminum foil to a thickness of 0.025mm for the first time, and then finish rolling to the double photocell foil with a thickness of 0.012mm in one pass. The rolling pass distribution is as follows:

0.26mm→0.115mm→0.055mm→0.025mm→0.012mm,

Slitting, corona, inspection, and finished product packaging to obtain the finished lithium battery foil.

In a preferred disclosed example of the present invention, the tensile strength of the billet in step A is ≥195/mm ² , and the performance elongation is ≥3.0%, meeting the high-strength requirements of the finished product after the billet is rolled in 4 passes.

Further, the alloy grade of the blank is 1100 alloy.

The preferred disclosed example of the present invention, in step B, the parameters of the rolls used in each pass are:

The roughness of the rough rolling work roll is selected between Ra: 0.26 ~ 0.28μm, and the convexity is selected as Cr: 0.035mm;

The roughness of the intermediate rolling work roll is selected between Ra: 0.16 ~ 0.17μm, and the convexity is selected as Cr: 0.05mm;

Roughness Ra of backup rolls used in rough and intermediate rolling: between 0.60 and 0.65 μm, crown selection Cr: 0.04 mm;

The target shape curve value of the rough rolling pass is ≤13N/mm ² , and the target shape curve value of the intermediate rolling pass is ≤11N/mm ² .

In the preferred disclosed example of the present invention, the rolling oil used in the first 3 passes in step B is 95# base oil mixed with alcohol and ester additives, wherein the alcohol content in the additives is 3-5% by mass, with C12 lauryl alcohol is the main ingredient; the ester content is 3-5%, mainly butyl stearate.

Further, the rolling oil temperature is controlled at 50-55°C during the first three rolling passes.

In the preferred disclosed example of the present invention, step B takes a single aluminum foil of 0.025 mm obtained by intermediate rolling as an example, and the roughness of the work roll used for finishing rolling is Ra: 0.12-0.13 μm, and the crown Cr: 0.06 mm;

The roughness Ra of the backup roll of the finishing mill: 0.60～0.65μm, the crown Cr0.04mm;

The target shape curve value of the finishing pass is ≤7N/mm ² .

In the preferred disclosed example of the present invention, the rolling oil used in the fourth pass finish rolling in step B is 95# base oil mixed with 5-7% ester additive W3H, wherein the ester content in additive W3H accounts for 70%, purchased from Shijiazhuang Xintai Special Oil Co., Ltd. During rolling, the rolling oil temperature is controlled at 60-65°C.

In the preferred disclosed example of the present invention, the corona described in step C belongs to the battery foil surface treatment device, and its function is to clean up a small amount of residual oil on the surface of the aluminum foil and reduce the thickness of the oil film on the foil surface, increase the surface wetting tension, and prevent the charcoal coating process from occurring Leakage, etc. Corona equipment with a power of 7-10kW and an output voltage of 25kV is used for surface corona.

Beneficial effect

The difference between the present invention and the conventional battery foil production process is that 95# base oil with a viscosity of 2.05 and new additive W3H is used after the copper content in the battery blank is increased, and the rolling oil has stronger wear resistance and lubricating performance. The high-performance battery foil produced in 4 passes, the coincidence degree between the actual plate shape and the target plate shape has reached more than 95%. Through the rolling process and high oil temperature adjustment, the volatilization of the oil film on the foil surface is increased, and combined with the fine-cut corona, the surface dyne value of the product is > 32, the yield is increased by 10-15%, and the overall yield reaches more than 80%. At the same time, the rolling process is continuous and stable, which improves production efficiency and product quality, and reduces the production cost of battery foil. It is the most potential profit growth point in the future and provides technical support for high-quality mass production of battery foil.

Detailed ways

The present technology will be described in detail below in conjunction with the embodiments, so that those skilled in the art can better understand the present technology, but the present technology is not limited to the following embodiments.

Example 1

A four-pass process for producing aluminum foil for high-strength double-light lithium batteries, comprising the following steps:

Step 1. Rough and intermediate rolling Alloy 1100H18, wool material with a thickness of 0.30×1200㎜ undergoes 2 passes of rough rolling and 1 pass of intermediate rolling to a single foil of 0.032mm. The measured tensile strength of the billet is 195N/mm ² . 3.0%;

Finished product quality requirements: thickness 15μm±3%, tensile strength ≥ 250N/mm ² , elongation ≥ 3.5%, surface dyne value ≥ 32dyn; plate shape is flat, off-line plate type A grade (roll distance 2m, tension 8N/mm ² ) Slump ≤ 5mm; the surface color is uniform and clean; the number of pinholes below 0.1mm is ≤ 10/m ² .

Rolling pass distribution: 0.30mm→0.140mm→0.066mm→0.032mm→0.015mm;

The used roll parameters of step one are as follows:

Roughness Ra of work rolls used in rough rolling 1-2 pass: 0.26～0.28μm, work roll crown Cr: 0.035mm (35‰);

The work roll roughness Ra of the 3rd intermediate rolling: 0.16～0.17μm, work roll crown Cr: 0.03mm (50‰);

Roughness Ra of back-up roll used in rough and medium rolling: 0.60～0.65μm, back-up roll crown Cr: 0.04mm (40‰);

The target shape curve value of rough rolling 1st and 2nd passes is 13N/mm ² ; the target shape curve value of intermediate rolling 3rd pass is 11N/mm ² .

The rolling oil is made of 95# base oil mixed with 3-5% ester additives and 3-5% alcohol additives and evenly mixed as lubricating oil.

During the production process, the speed of the first rough rolling pass is 800-850m/min, and the oil temperature is 50°C. The plate shape is stable, the coincidence degree between the actual plate shape and the target plate shape reaches 99%, the whole coil is produced without broken strips, and the surface quality is good; the speed of the second rough rolling pass is 1000-1100m/min, and the oil temperature is 52°C. The plate shape is stable, the coincidence degree between the actual plate shape and the target plate shape reaches 99%, the whole coil is produced without broken strips, and the surface quality is good; the speed of the third pass of the intermediate rolling is 1200-1300m/min, and the oil temperature is 54°C. The plate shape is stable, the coincidence degree between the actual plate shape and the target plate shape reaches 98%, the whole roll is produced without broken tape, and the surface quality is good;

Step 2. Rolling the obtained aluminum foil with a thickness of 0.032 mm in the fourth pass on a finishing mill to obtain a finished product of lithium battery foil with a thickness of 0.015 mm and double-sided light finish rolling;

The roughness of the finishing roll used is Ra: 0.13～0.135μm, and the convexity is Cr: 0.06mm (60‰);

Roughness Ra of back-up roll used for finishing rolling: 0.60～0.65μm, crown Cr: 0.04mm (40‰);

The target shape curve value of the finishing pass is set to 7N/mm ² ;

The rolling oil is 95# base oil with 5-7% W3H additive;

During the production process, the speed of the fourth pass of finish rolling is 1000-1200m/min, and the oil temperature is 60°C. The plate shape is stable, the matching degree between the actual plate shape and the target plate shape reaches 96%, and there is no broken belt in the whole roll production, and the surface quality is good; 260N/mm ² , elongation 4.5%, number of pinholes < 10/m ² , the finish rolling blanking inspection meets the battery foil quality requirements.

Step 3, cutting, corona, finished product packaging.

During the slitting process of the above step 2, the battery foil produced by the slitting machine has a flat plate shape, uniform waves on the plate surface, and no loose ribs or partial looseness. The standard off-line plate shape detection has a sag amount of ≤5mm, which can reach the A-level plate shape according to the industry standard, which fully meets the quality requirements of the battery foil plate shape.

During the slitting corona process, the corona power parameters of the upper and lower aluminum foil surfaces are 8kw/8KW, the slitting speed is 120m/min, and the wetting tension of the upper and lower surfaces is 34, 34dyn measured on the blanking, which meets the needs of the surface wetting tension of the battery foil.

Example 2

A four-pass process for producing aluminum foil for high-strength double-light lithium batteries, comprising the following steps:

Step 1. Rough and intermediate rolling The billet of alloy 1100H18 and thickness 0.27×1200㎜ undergoes 2 passes of rough rolling and 1 pass of intermediate rolling to a single foil of 0.026mm±3%. The measured tensile strength of the billet is 197N/mm ² , extended by 2.7%;

Finished product quality requirements: thickness 13μm±3%, tensile strength ≥ 240N/mm ² , elongation ≥ 3.0%, surface dyne value ≥ 32dyn; plate shape flat, off-line plate type A (roll distance 2m, tension 8N/mm ² ) Slump ≤ 5mm; the surface color is uniform and clean; the number of pinholes below 0.1mm is ≤ 10/m ² .

Rolling pass distribution: 0.27mm→0.128mm→0.058mm→0.026mm→0.013mm;

The used roll parameters of step one are as follows:

Roughness Ra of work rolls used in rough rolling 1-2 pass: 0.26～0.28μm, work roll crown Cr: 0.035mm (35‰);

Roughness Ra of work rolls in the third pass: 0.16～0.17μm, work roll crown Cr: 0.05mm (50‰);

Roughness Ra of back-up roll used in rough and medium rolling: 0.60～0.65μm, back-up roll crown Cr: 0.04mm (40‰);

The target shape curve value of rough rolling 1st and 2nd passes is 13N/mm ² ; the target shape curve value of intermediate rolling 3rd pass is 11N/mm ² .

The rolling oil is made of 95# base oil mixed with 4-5% ester additives and 3-5% alcohol additives and evenly mixed as lubricating oil.

During the production process, the speed of the first rough rolling pass is 800-900m/min, and the oil temperature is 50°C. The plate shape is stable, the matching degree between the actual plate shape and the target plate shape reaches 97%, there is no broken strip in the whole coil, and the surface quality is good; the speed of the second rough rolling pass is 1000-1100m/min, and the oil temperature is 50°C. The plate shape is stable, the matching degree between the actual plate shape and the target plate shape reaches 98%, the whole coil is produced without broken strips, and the surface quality is good; the speed of the third pass of the intermediate rolling is 1200-1300m/min, and the oil temperature is 53°C. The plate shape is stable, the actual plate shape and the target plate shape match up to 96%, the whole roll is produced without broken tape, and the surface quality is good;

Step 2. Rolling the obtained aluminum foil with a thickness of 0.026 mm in the fourth pass on a finishing mill to obtain a finished product of lithium battery foil with a thickness of 0.013 mm and double-sided light finish rolling;

The roughness of the finishing roll used is Ra: 0.13～0.135μm, and the convexity is Cr: 0.06mm (60‰);

Roughness Ra of back-up roll used for finishing rolling: 0.60～0.65μm, crown Cr: 0.04mm (40‰);

The target shape curve value of the finishing pass is set to 7N/mm ² ;

The rolling oil is 95# base oil with 5-7% W3H additive;

During the production process, the speed of the fourth pass of finish rolling is 1000-1100m/min, and the oil temperature is 63°C. The plate shape is stable, the actual plate shape and the target plate shape match up to 95%, the whole roll is produced without broken tape, and the surface quality is good; the measured surface wetting tension of blanking is 31, 32dyn, the measured thickness is 13.1μm, and the tensile strength is 254N/mm ² , elongation 3.5%, number of pinholes <10/m ² , and the blanking inspection of finish rolling meets the quality requirements of battery foil.

Step 3, cutting, corona, finished product packaging.

During the slitting process of the above step 2, the battery foil produced by the slitting machine has a flat plate shape, uniform waves on the plate surface, and no loose ribs or partial looseness. The standard off-line plate type detection has a sag amount of ≤5mm, which can reach the A-level plate type according to the industry standard, which fully meets the quality requirements of the battery foil plate shape.

During the slitting corona process, the corona power parameters of the upper and lower aluminum foil surfaces are 8kw/8KW, the slitting speed is 110m/min, and the wetting tension of the upper and lower surfaces of the material is measured to be 33, 34dyn, which meets the needs of the surface wetting tension of the battery foil.

Example 3

A four-pass process for producing aluminum foil for high-strength double-light lithium batteries, comprising the following steps:

Step 1. Rough and medium rolling

Alloy 1100H18, wool material with a thickness of 0.26×1200㎜ undergoes 2 passes of rough rolling and ¹ pass of medium rolling to a single sheet foil of 0.025mm±3%.

Finished product quality requirements: thickness 12μm±3%, tensile strength ≥ 240N/mm ² , elongation ≥ 3.0%, surface dyne value ≥ 32dyn; plate shape flat, off-line plate type A (roll distance 2m, tension 8N/mm ² ) Slump ≤ 8mm; the surface color is uniform and clean; the number of pinholes below 0.1mm is ≤ 10/m ² .

Rolling pass distribution: 0.24mm→0.115mm→0.055mm→0.024mm→0.012mm;

The used roll parameters of step one are as follows:

Roughness Ra of work rolls used in rough rolling 1-2 pass: 0.26～0.28μm, work roll crown Cr: 0.035mm (35‰);

Roughness Ra of work rolls in the third pass: 0.16～0.17μm, work roll crown Cr: 0.05mm (50‰);

Roughness Ra of back-up roll used for rough and medium rolling: 0.6～0.65μm, back-up roll crown Cr: 0.04mm (40‰);

The target shape curve value of rough rolling 1st and 2nd passes is 13N/mm ² ; the target shape curve value of intermediate rolling 3rd pass is 11N/mm ² .

The rolling oil is made of 95# base oil mixed with 3-5% ester additives and 3-5% alcohol additives and evenly mixed as lubricating oil.

During the production process, the speed of the first rough rolling pass is 800-850m/min, and the oil temperature is 53°C. The plate shape is stable, the actual plate shape and the target plate shape match up to 98%, the whole coil is produced without broken strips, and the surface quality is good; the speed of the second rough rolling pass is 1000-1100m/min, and the oil temperature is 53°C. The plate shape is stable, the matching degree between the actual plate shape and the target plate shape reaches 98%, the whole coil is produced without broken strips, and the surface quality is good; the third pass speed of intermediate rolling is 1200-1300m/min, and the oil temperature is 55℃. The plate shape is stable, the actual plate shape and the target plate shape match up to 96%, the whole roll is produced without broken tape, and the surface quality is good.

Step 2. Rolling the obtained aluminum foil with a thickness of 0.024 mm in the fourth pass on a finishing mill to obtain a finished product of lithium battery foil with a thickness of 0.012 mm and double-sided light finish rolling;

The roughness of the finishing roll used is Ra: 0.13～0.135μm, and the crown Cr: 0.06mm (60‰);

Roughness Ra of back-up roll used for finishing rolling: 0.60～0.65μm, crown Cr: 0.04mm (40‰);

The target shape curve value of the finishing pass is set to 7N/mm ² ; the rolling oil is 95# base oil with 5-7% W3H additive;

During the production process, the speed of the fourth pass of finish rolling is 1000-1100m/min, and the oil temperature is 63°C. The plate shape is stable, the matching degree between the actual plate shape and the target plate shape reaches 95%, the whole roll is produced without broken tape, and the surface quality is good; the measured surface wetting tension of blanking is 30, 31dyn, the measured thickness is 12..05μm, and the tensile strength The strength is 252N/mm ² , the elongation is 3.35%, the number of pinholes is less than 10/m ² , and the blanking inspection of finishing rolling meets the quality requirements of battery foil.

Step 3, cutting, corona, finished product packaging.

During the slitting process of the above step 2, the battery foil produced by the slitting machine has a flat plate shape, uniform waves on the plate surface, and no loose ribs or partial looseness. The standard off-line plate type detection has a sag amount of ≤5mm, which can reach the A-level plate type according to the industry standard, which fully meets the quality requirements of the battery foil plate shape.

During the slitting corona process, the corona power parameters of the upper and lower aluminum foil surfaces are 8kw/8KW, the slitting speed is 100m/min, and the wetting tension of the upper and lower surfaces of the material is measured to be 32, 33dyn, which meets the needs of the surface wetting tension of the battery foil.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by the description of the present invention, or directly or indirectly used in other related technical fields, shall be the same as The theory is included in the patent protection scope of the present invention.

Claims (10)

1. A process for producing aluminum foil for high-strength double-light lithium batteries in four passes, is characterized in that, comprises the steps: A. The thickness of the billet is 0.26-0.3mm, the hardness state is H18, and the content of trace alloy element copper is adjusted from 0.05-0.1% to 0.1-0.15%; B. The billet is distributed and rolled according to 4 passes, including 3 passes for rough and intermediate rolling and 1 pass for finish rolling; taking a billet with a thickness of 0.26mm as an example, rough rolling and intermediate rolling are arranged in the same rolling mill. 3 passes of rolling to a thickness of 0.025mm aluminum foil, and then 1 pass of finish rolling to a thickness of 0.012mm of double photocell foil, the distribution of rolling passes is as follows: 0.26mm→0.115mm→0.055mm→0.025mm→0.012mm; C. Slitting, corona, inspection, and finished product packaging to obtain the finished lithium battery foil. 2. The four-pass process for producing aluminum foil for high-strength double-light lithium batteries according to claim 1, characterized in that: the tensile strength of the blank in step A is ≥195/mm ² , and the performance elongation is ≥3.0% . 3. The four-pass process for producing aluminum foil for high-strength dual-light lithium batteries according to claim 1, wherein the alloy grade of the blank in step A is 1100 alloy. 4. the process for producing aluminum foil for high-strength dual-light lithium batteries in four passes according to claim 1, is characterized in that, in step B, the parameters of the rolls used in each pass are: The roughness of the rough rolling work roll is selected between Ra: 0.26 ~ 0.28μm, and the convexity is selected as Cr: 0.035mm; The roughness of the intermediate rolling work roll is selected between Ra: 0.16 ~ 0.17μm, and the convexity is selected as Cr: 0.05mm; Roughness Ra of backup rolls used in rough and intermediate rolling: between 0.60 and 0.65 μm, crown selection Cr: 0.04 mm; The target shape curve value of the rough rolling pass is ≤13N/mm ² , and the target shape curve value of the intermediate rolling pass is ≤11N/mm ² . 5. The four-pass production process of aluminum foil for high-strength dual-light lithium batteries according to claim 1, characterized in that: the rolling oil used in the first 3 passes in step B is 95# base oil and alcohol , and ester additives, wherein the alcohol content in the additive is 3-5% by mass, mainly C12 lauryl alcohol; the ester content is 3-5%, mainly butyl stearate. 6. The four-pass process for producing aluminum foil for high-strength double-light lithium batteries according to claim 1, characterized in that in step B, the rolling oil temperature is controlled at 50-55°C during the first three rolling passes. 7. The four-pass process for producing aluminum foil for high-strength dual-light lithium batteries according to claim 1, characterized in that: Step B takes the 0.025mm single-sheet aluminum foil obtained by intermediate rolling as an example, and the finishing roll used is Roughness Ra: 0.12～0.13μm, crown Cr: 0.06mm; roughness Ra of the back-up rolls of the finishing mill: 0.60～0.65μm, crown Cr0.04mm; target shape curve value of the finishing pass ≤7N/mm ² . 8. The four-pass process for producing aluminum foil for high-strength double-light lithium batteries according to claim 1, characterized in that: the rolling oil used in the fourth pass finish rolling in step B is 95# base oil mixed with 5 ~7% ester additive W3H, of which the ester content in additive W3H accounts for 70%, was purchased from Shijiazhuang Xintai Special Oil Co., Ltd. 9. The four-pass process for producing aluminum foil for high-strength double-light lithium batteries according to claim 1, characterized in that: in step B, the rolling oil temperature is controlled at 60-65°C during the fourth rolling pass. 10. The four-pass process for producing aluminum foil for high-strength double-light lithium batteries according to claim 1, characterized in that: the corona in step C uses a corona device with a power of 7-10kW and an output voltage of 25kV Perform surface corona.