KR100648616B1 - Method for forming a insulative coatiing on a non-oriented electric steel sheet - Google Patents

Abstract

A method of forming an insulation coating film on a non-oriented electric steel sheet is provided to reduce damage to coating rolls and to form thick coating film with excellent coating quality by adopting 1/2 reverse coating mode and using three-rolls type of coating device. The method comprises application of insulation coating solution to the surface of an electric steel sheet strip with thickness of 0.05 to 0.08 mils in line velocity of 250 to 350mpm. The insulation coating solution is made of organic or inorganic materials and has specific weight of 1.3 to 1.41 and viscosity of 12 to 12.9cps. The method is performed by using an apparatus which comprises: upper and lower pick-up rolls(11,21) having diameter of 300-350mm, driving velocity ratio of 15-22% and rolling reduction of 115-125kg; upper and lower transfer rolls(12,22) having diameter of 300-350mm, driving velocity ratio of 80-87% and rolling reduction of 95-105kg; and upper and lower coating rolls(13,23) having diameter of 390-420mm, driving velocity ratio of 100-110% and rolling reduction of 95-105kg.

Description

Method for forming a insulative coatiing on a non-oriented electric steel sheet}

1 is a schematic diagram of a conventional three roll type coating apparatus for coating an insulating coating on an electrical steel sheet.

Figure 2 is a schematic diagram showing a process of applying the insulating coating liquid to the electrical steel sheet while the upper and lower rolls of the coating apparatus shown in FIG.

<Description of the symbols for the main parts of the drawings>

2: stand 3: arm

4: coating liquid 11: upper pick-up roll

12: upper transfer roll 13: upper coating roll

14, 24: reservoir 21: lower pickup roll

12: lower transfer roll 23: lower coating roll

s: strip θ: strip entry angle

The present invention relates to a method for coating an insulating film of a non-oriented electrical steel sheet using a three-roll type coating apparatus, and more particularly, improved non-oriented electrical steel sheet to enable a thick film coating with excellent coating quality with little damage to the coating roll. It relates to an insulating coating method of.

In general, non-oriented electrical steel sheets used as iron cores for electric devices such as various motors, generators, and safety devices are coated with an insulating coating on their surfaces in order to minimize power loss caused by eddy currents.

1 shows a conventional three-roll type coating apparatus 1 for coating an insulating film on an electrical steel bar, as can be seen in the drawing, the three-roll type coating apparatus consists of three rolls each and is symmetrical with each other. And upper rolls 11, 12, 13: 10 and lower rolls 21, 22, 23: 20 having a conventional structure. The upper roll 10 and the lower roll 20 are installed on the stand 2 of the coating apparatus, and the lower roll 20 can be elevated by the operation of the arm 3.

As can be seen in Figure 2, the upper roll 10 is the upper pick-up roll 11 to directly pick up the coating liquid 4 stored in the reservoir 14, the coating liquid (4) picked up from the upper pick-up roll 11 The upper coating roll 13, the upper pick-up roll 11 and the upper coating roll 13 to be coated on the strip (s) for electrical steel supplied to the upper coating roll 13 from the upper pick-up roll (11) Consisting of the upper transfer roll 12 to control the amount of the coating liquid 4 is delivered to. Typically, each roll is made of a cylindrical shape, the upper pick-up roll 11 and the upper coating roll 13 is made of a rubber material, the upper transfer roll 12 is made of a steel material.

Since the lower roll 20 has a symmetrical structure with the upper roll 10, the lower roll is not necessarily explained. However, the lower coating roll 23 is eccentrically disposed with respect to the upper coating roll 13 in order to reduce the load according to the load of the upper roll 10. Usually, the eccentric distance is set to 2 to 5 mm.

On the other hand, the strip (s) is supported by the support roll 30 and drawn between the upper and lower rolls (10, 20), wherein the strip (s) at a predetermined angle with the support roll 30 at the angle introduced It is called the inlet angle θ of the strip.

With reference to Figure 2 looks at a conventional electrical steel coating film coating method using such a coating device.

Table 1 below shows the process conditions for each roll corresponding to a typical line speed of 200 to 250 mpm (mpm: travel per minute of the strip). Here, the circumferential speed ratio refers to a ratio (roll speed / line speed) of the roll speed to the line speed corresponding to the traveling speed of the strip s as a percentage (%).

Process conditions Upper and lower pickup roll Upper and Lower Transfer Roll Upper and Lower Coating Roll Diameter (mm) 200-220 240 to 260 250-280 Main Speed Ratio (%) 23-27 88-92 118-122 Rolling amount (kg) 115 to 125 95-105 95-105

On the other hand, when looking at the other process conditions, commonly used insulating coating solution is an organic and inorganic coating solution, specific gravity: 1.23 ~ 1.26, viscosity: 13 ~ 14cps, temperature: 24 ~ 34 ℃ conditions, the incoming strip (s ) Temperature is 28 ~ 40 ℃, strip entry angle is 3.0 ~ 4.5 °.

Under the above process conditions, the insulating coating solution was applied to the strip using a 1/2 reverse coating method in order to obtain the best coating thickness. Here, the 1/2 reverse coating method refers to the entire amount of the coating liquid 4 supplied to the coating rolls 13 and 23 while the coating rolls 13 and 23 are in sliding contact with the advancing direction of the strips s. The rotational direction of the coating rolls 13 and 23 is determined so that the coating rolls 13 and 23 can be transferred to the coating rolls. , 23, and the pick-up rolls 11 and 21 rotate in the opposite directions to the transfer rolls 12 and 22 and transfer 1/2 of the coating liquid 4 picked up from the reservoir 24 to the transfer rolls. (12, 22) is configured to be delivered to.

According to the 1/2 reverse coating method, when the amount of the coating liquid 4 picked up from the pickup rolls 11 and 21 is 1, 1/2 is transferred to the transfer rolls 12 and 22, and the coating is performed. The rolls 13 and 23 are also supplied with 1/2. Therefore, the coating roll is applied to the strip (s) about 1/2 of the coating liquid picked up by the pickup roll (11, 21).

However, despite the insulation coating at the highest circumferential ratio condition using the 1/2 reverse coating method as described above, the maximum thickness of the film that can be obtained after the insulation coating is only about 0.04 to 0.05 mils. There was a limit in obtaining the required thickness of 0.06 to 0.08 mils. In particular, the conventional thin film coating layer of about 0.04 ~ 0.05mils was not only the peeling phenomenon of the coating layer but also the appearance of the coating layer was often poor.

In addition, in the related art, there is a problem that the replacement cycle of the roll due to roll damage is short due to a high circumferential speed ratio of the coating roll.

In addition, since the conventional line speed has been adjusted to 200 to 250mpm, an improvement in coating technology for enabling thick film coating with excellent coating quality is required even at a line speed of about 250 to 350mpm in order to improve production efficiency.

The present invention has been proposed to solve the above problems, and improved insulation coating method of the non-oriented electrical steel sheet to enable a thick film coating with excellent coating quality while less damage to the coating roll at a line speed of 250 ~ 350mpm For the purpose of providing it.

Insulation coating method of the non-oriented electrical steel sheet according to the present invention for achieving the above object, by using a three-roll type coating apparatus to coat the insulation coating liquid at a thickness of 0.06 ~ 0.08mils at a line speed of 250 ~ 350mpm , Insulating coating liquid using an organic-inorganic insulating coating liquid having a specific gravity of 1.3 to 1.41, viscosity of 12 to 12.9cps, the upper and lower pickup rolls of the coating device diameter: 300 ~ 350mm, circumferential speed ratio: 15 ~ 22%, rolling reduction: It is set to 115 to 125kg, the upper and lower transfer roll diameter: 360 ~ 410mm, circumferential speed ratio: 80 ~ 87%, rolling reduction: 95 ~ 105kg, the upper and lower coating roll diameter: 390 ~ 420mm, Speed ratio: 100 to 110%, rolling reduction: characterized in that made under the conditions set to 95 to 105kg. The three roll type coating apparatus uses the conventional apparatus described in the prior art.

The process conditions of each roll are shown in Table 2 below.

Process conditions Upper and lower pickup roll Upper and Lower Transfer Roll Upper and Lower Coating Roll Diameter (mm) 300-350 360-410 390-420 Main Speed Ratio (%) 15 to 22 80 to 87 100-110 Rolling amount (kg) 115 to 125 95-105 95-105

The strip for non-oriented electrical steel sheet which is decarburized, annealed and drawn after cold rolling is insulated coated by a 1/2 reverse coating method as in the prior art, and the temperature of the inlet strip, strip inlet angle, and the like are maintained as in the prior art.

On the other hand, the first consideration in determining the conditions of the roll corresponding to the line speed of 250 ~ 350mpm is the diameter and circumferential ratio of the upper and lower coating rolls. This is because the diameters and peripheral speed ratios of the upper and lower pick-up rolls and the upper and lower transfer rolls are determined according to the diameters and peripheral speed ratios of the upper and lower coating rolls. It is preferable to apply the rolling reduction amount of each roll similarly to the past.

First, look at the reason for maintaining the diameter of the upper and lower coating roll to 390 ~ 420mm.

When the diameter of the upper and lower coating rolls is 390 mm or less, the upper and lower coating rolls must be rotated at a high speed ratio of 110% or more to maintain the thickness of the coating liquid applied to the strip at about 0.06 to 0.08 mils. none. However, when performing the coating operation under such conditions, not only surface damage of the upper and lower coating rolls occurs early, but also the surface of the insulating coating becomes rough.

When the diameter of the upper and lower coating rolls is 420 mm or more, an excessive amount of insulating coating liquid is applied to the surface of the strip. Therefore, in this case, it is necessary to lower the peripheral speed ratio to 100% or less to make the thickness of the insulating coating solution applied to the strip surface thin. However, if the rotational speed of the coating roll is set lower than the moving speed of the strip, the surface of the coating roll is severely damaged (a phenomenon in which the surface of the coating roll is dragged without being linked with the speed of the strip, and the roll surface portion due to excessive friction between the strip and the roll contact portion Premature damage).

Next, look at the reason for limiting the peripheral speed ratio of the upper and lower coating roll to 100 ~ 110%.

When the main speed ratio of the upper and lower coating rolls is set to 100% or less, the rotational speed of the coating roll is set lower than the traveling speed of the strip for non-oriented electrical steel sheet, which is an insulation coating object, so that slip between the roll surface and the strip is generated. . In severe cases, the surface of the upper and lower coating rolls are severely damaged due to such slip, and there is a problem that the upper and lower coating rolls need to be replaced early, and the insulating coating surface is rough.

If the upper speed ratio of the upper and lower coating rolls is set to 110% or more, the amount of the insulating coating solution applied to the strip will not only be excessive, but the upper and lower coating rolls interlock with the strip due to the high speed ratio (strip running speed and coating roll). Since the rotation speed is rapidly rotated without the same phenomenon, the surface of the coating roll is prematurely damaged.

EXAMPLE

Insulating coatings include phosphate 30 consisting of magnesium phosphate (MMP) and aluminum phosphate (MAP); chromium oxide (CrO ₃ ) 3; A coating liquid having a weight ratio of 1.35 and a specific gravity of 1.35 and a viscosity of 12.5 was used. The coating liquid can be obtained from Aekyung PNC.

Insulation coating is C: 0.04 ~ 0.07wt%, Si: 2.5 ~ 4.0wt%, Mn: 0.5 ~ 0.25wt%, P: 0.03wt%, S: 0.02wt%, Al: 0.1wt%, N: 0.01wt Cold rolled strip for non-oriented electrical steel sheet (steel grade: PN23) composed of% residual Fe and other unavoidable impurities (steel grade: PN23) to a thickness of 0.5 mm, and the rolled strip was held for 2-4 minutes at a temperature of 860-1,100 ° C. After decarburization and annealing, the coating was continuously applied to the surface of the strip by a 1/2 reverse coating method using a 3-roll coating apparatus.

The experiment was carried out at a line speed of 250 to 350mpm, and the diameter and the circumferential speed ratio of the rolls at which the coating thickness of about 0.06 to 0.08 mils was obtained while varying the diameter and the circumferential speed of the rolls were found.

Furthermore, in order to evaluate the quality of the coated insulating film, the film appearance, insulation, adhesion, corrosion resistance and weldability before stress relief annealing and film peeling phenomenon and insulation after stress relief annealing were compared. The comparison method is as follows.

That is, Stress Relief Annealing (SRA) was heat-treated at 750 ° C. for 2 hours in a dry 100% N 2 gas atmosphere. The surface appearance was comprehensively evaluated by visual observation of stains, streaks, and the like. Insulation is evaluated by the received current value (Amps) when the current is input through 0.5V, 1.0A under 300psi pressure, but 0.10 ~ 0.14Amps is good before SAR according to the usual standard, 0.14 ~ 0.90Amps is bad. In case of SAR, 0.40 Amps or less was considered good, and 0.14 Amps or more was judged to be poor.

Adhesion (mm ￠) is evaluated as the minimum arc diameter without film peeling when the specimen is bent 180 ° by bending around an annular bar having an arc of 10, 20, 30 to 100mm ￠ after annealing, but if peeling at 10mm is good, peeling at 20mm When it is usually, when peeling from 30 ~ 100mm was judged as bad. Corrosion resistance was observed by visual observation with the presence of rust on the surface of the film when left indoors for 1 year and exposed outdoors for 3 months. Weldability: appearance and blow hole appearing in the weld bead after TIG welding (welding current: 150A, electrode: pure-W (3.2 mm2), electrode gap: 0.35 mm, welding speed: 15 mm / sec) The production was evaluated by visual observation. Peeling of the film was judged by the presence or absence of adhesion of the film peeling powder which appeared when the adhesive tape (polypropylene) was stuck on the film after the stress relief annealing.

As a result of the experiment, under the same rolling reduction conditions, the diameter of the upper and lower pick-up rolls was 300 to 350 mm, the circumferential speed ratio was 15 to 22%, the diameter of the upper and lower transfer rolls was 360 to 410 mm, and the peripheral speed ratio was 80 to 87%. When the diameter of the upper and lower coating rolls was 390 to 420 mm and the peripheral speed ratio was 100 to 110%, the quality of the insulating coating layer was excellent. That is, as can be seen in Table 3 below, the appearance of the insulation coating, insulation, corrosion resistance, weldability was found to be excellent, the peeling phenomenon or insulation of the film after the stress relief annealing was found to hardly decrease.

 division Before stress relief annealing After stress relief annealing  Outer appearance  Insulation (Amps)  Adhesiveness (mm ￠) Corrosion resistance  Weldability  Film peeling phenomenon  Insulation (Amps)  inside  Outdoor  quality  Good  0.1 to 0.13  10  Good  Good  Good  none  0.2 to 0.3

According to the method of coating the insulating film of the non-oriented electrical steel sheet having the structure as described above, it is possible to reduce the damage of the coating roll even at a line speed of about 250 to 350mpm and to coat the film with excellent coating quality.

Claims (1)

In the method for applying the insulating coating liquid to the surface of the strip for non-oriented electrical steel sheet which is decarburized, annealed and drawn after cold rolling by a 1/2 reverse coating method using a 3-roll coating apparatus, Thick film coating of insulation coating liquid at 0.06 ~ 0.08mils at line speed of 250 ~ 350mpm, The insulating coating liquid is an organic-based inorganic coating liquid having a specific gravity of 1.3 to 1.41, viscosity 12 to 12.9 cps, The upper and lower pickup rolls of the coating apparatus are set to a diameter of 300 to 350 mm, a circumferential speed ratio of 15 to 22%, and a rolling reduction of 115 to 125 kg. The upper and lower transfer rolls are set to a diameter of 360 to 410 mm, a peripheral speed ratio of 80 to 87%, and a rolling reduction of 95 to 105 kg. The upper and lower coating rolls are made of a diameter of 390 to 420 mm, a circumferential speed ratio of 100 to 110%, and a rolling reduction of 95 to 105 kg.

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