JPS6258792B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a method for uniformly applying oil to the surface of a continuously running metal strip, such as tinplate and tin plate blanks, using an electrostatic oil applicator in the width direction of the plate. (Prior Art) Conventionally, an electrostatic oil applicator is used to electrostatically form a relatively thin oil film on the surface of continuously running metal strips, such as tinplate and tin plate blanks, thereby coating the metal. It is known to prevent rust of the band, improve printing suitability, and prevent scratches. As a representative example of this type of electrostatic oil applicator, the one shown in FIG. 3 is well known. That is, oil reservoir chambers 4, 4 are provided in the lower part of a casing 1, which has deflection electrodes 2, 2 inside which are vertically supported and supported by insulators 3, and the atomization chamber 4 of the oil reservoir chambers 4, 4 is provided. The oil is atomized by the atomizing nozzles 6, 6 connected to the primary air source 5 located at the atomizing chambers 4', 4', and the atomizing chambers 4', 4' are filled with suspended oil particles. During this time, large oil particles fall into the oil reservoir chambers 4, 4, and only small oil particles are suspended in the atomization chambers 4', 4'. Next, airflow from a secondary air source 7 such as a blower is sent into the atomization chambers 4', 4', mixes with oil particles suspended in the atomization chamber, carries them, and charges the charged electrodes 8, 4'. Pass through 8 parts. At this time, the surface of the oil particles is charged, and while they flow between the deflection electrodes 2, 2 and the running metal strip 11 on the secondary air, the charged oil particles are attracted by the electrostatic attraction force. This is a coating treatment method in which the coating is gradually and uniformly deflected and deposited on the metal surface. In this device, an air flow rate control device 13 is provided at an arbitrary point of the air supply system 12 that connects the secondary air source 7 and the atomization chambers 4', 4', and the control device 13 and the metal strip 11 are guided. The metal band 11 is interlocked with a rotary generator 14 provided on the roller 10 that makes it run.
The amount of air blown is changed proportionally according to the traveling speed of the vehicle, and the supply of oil particles is controlled by changing the amount of air blown according to the traveling speed. Note that 9 is a ground wire, and 15 and 16 are high voltage supply sources that supply high voltage to charging electrodes 8, 8 and deflection electrodes 2, 2, respectively. Generally, the surface of the tinplate is usually 1B/B [Base box (20 inches x 28 inches, 56 pieces) ≒
Approximately 50 to 500 mg of oil (1.25 to 12.5 mg/m ² ) is applied per 40.46 m ² of oil, and the desired amount of oil can be obtained at any time depending on the running speed of the various metal strips. Automated control will be carried out as much as possible. With the conventional electrostatic oil applicator mentioned above, the oil is not applied uniformly over the entire area, especially near both edges of the plate (from both ends).
It was found that on surfaces (within 25 mm), too much oil was applied compared to other surfaces. If too much oil is applied and the tin plate is painted as is without degreasing, the over-oiled areas are likely to splatter. This is due to poor compatibility between oil and paint, and of course the situation in which paint repelling occurs varies depending on the paint, but in general, paint repelling is more likely to occur when there is significant overapplication of oil. When such paint repellency occurs, since no paint film is naturally formed in that area, it has a large effect on not only the appearance but also corrosion resistance and other properties. For example, if paint repellency occurs on electric tinplate, stain-free steel, aluminum sheets, etc. used for cans, fish cans, etc., they can no longer be used as can materials. As a technique for solving the above-mentioned non-uniform oil application in the plate width direction, Japanese Patent Publication No. 13488/1988 and Japanese Patent Publication No. 17775/1983
According to the above-mentioned publication, the atomization chamber 4', 4' of the electrostatic oil application in the conventional device described above (FIG. 3) has a slit-shaped ejection port extending in the width direction of the metal strip. At the same time as the nozzles 6, 6 are provided, a partition plate 21 is provided in the longitudinal direction of the atomization nozzle in order to equalize and flow the conveying air flow fed into the atomization chamber, and furthermore, the partition plates 21 are provided in the longitudinal direction of the atomization nozzle. In between, valves 22 for adjusting air volume are connected to the conveying air flow supply pipes connected from the blower, respectively.
A method and apparatus (FIG. 4) have been proposed for controlling the uniform distribution of airflow as a function of the speed of the sheet metal strip. It is true that if the technology described in this publication is implemented, uniform oil application over the entire board width direction can be satisfied, but it is especially accurate enough to eliminate over-oiling areas near both edges of the board (within 25 mm from both ends). The research conducted by the present inventors revealed that oil application management was not possible. (Problems to be Solved by the Invention) As described above, the present invention is capable of stably coating the amount of oil to the full extent of both ends of the plate without being affected by the threading speed, especially when directly painting electric tinplate without degreasing. The object of the present invention is to provide an electrostatic oil application method that enables uniform oil application management without causing paint repulsion. (Means for Solving the Problems) The gist of the present invention is to partially improve a conventional electrostatic oil applicator, and to improve the position near both edges of a metal strip passing through the electrostatic oil applicator. A pair of composite dummy electrodes are provided to sandwich the metal strip, and the polarity of the electrodes is maintained at the same polarity and potential as that of the metal strip to be oiled. According to this method, it is possible to prevent over-oiling on the entire surface of the metal strip to be oiled, especially on the edge of the plate (within 25 mm from both ends), and to obtain a uniform amount of oil, regardless of the threading speed. It is possible to prevent the paint from repelling, which occurs when applying non-degreased paint such as. The configuration of the present invention will be explained in detail below. According to the conventional electrostatic oil applicator shown in Fig. 3,
The edge of the oiled metal strip becomes over-oiled as described above. The cause of this over-application of oil will be discussed using a reproduction diagram. FIG. 5 is a schematic cross-sectional view of the inside of a casing of a conventional electrostatic oil applicator. Oiled metal band 1
While the oil particles 17 are passing between the deflection electrodes 2, 2, the oil particles 17 are charged to the cathode by the charging device inside the casing.
is deposited on the surface of the metal strip applied to the anode. Now, let's take a closer look at the trajectory of the oil particles until they are deposited on the surface of the metal strip. Some oil particles (a) are deposited directly on the metal strip, and (b) some are deposited on the deflection electrodes 2, 2.
It is thought that the particles are repelled by the water and deposited on the metal strip. At both edges 18 of the metal strip, edge current concentration occurs in the same manner as in electroplating due to the electrode characteristics, so overcoating of oil is inevitable regardless of the presence or absence of deflection electrodes. Therefore, as a measure to prevent excessive oil application to the edges, the present inventors have developed a shutter 20 indicated by a broken line at the secondary air outlet 19 of the known electrostatic oil applicator with secondary air conditioning shown in FIG. Experiments were conducted using a device modified to open and close the shutter 20 to limit the supply of oil particles to both edges of the metal strip, which will be described in detail in the Examples section below. However, even if the shutter opening/closing operation was added, over-application of oil on both edges 18 of the metal band could not be prevented. Therefore, as a result of further various studies, the present inventors have newly added a pair of composite dummy electrodes 23, 23, located near both edges of the metal strip 11 to be oiled, sandwiching the metal strip, as shown in FIG. 1A. 23, 23 are provided, the same polarity as that of the metal strip is applied to the composite dummy electrode, and the oil particles deposited on both edges 18 of the metal strip are deposited on these newly installed composite dummy electrodes 23. They succeeded in preventing it. With this improvement, even if oil particles are deposited on the dummy electrode 23, the over-oiling phenomenon will not be observed on both edges 18 of the solid metal strip, as demonstrated in the examples described later. Ta. As shown in FIG. The test was conducted using a pair of composite dummy electrodes placed parallel to each other with a metal strip sandwiched between them. As can be seen from the results in Figure 6, in the case of the composite dummy electrode, a uniform oil amount distribution was obtained from the center to the edges, whereas with the single dummy electrode, over-application of oil was observed at the edges. . That is, it has been found that a pair of composite dummy electrodes sandwiching a metal strip has a greater effect of preventing over-oiling than the former single dummy electrode. Table 1 shows the preferred size and arrangement of the composite dummy electrode found by the present inventors.

【table】

[Table] (Example) When applying electrostatic oil to electric tinplates, a dummy electrode 23 was incorporated in the conventional electrostatic oil applicator shown in Fig. 3 to carry out the method of the present invention, and some improvements were made. This was carried out using an electrostatic oil applicator (Fig. 2). In this embodiment, the conventional electrostatic oil applicator was improved as follows. (a) A dummy electrode 23 is provided between the tin steel strip 11 and the deflection electrodes 2, 2. (b) The dummy electrode 23 and the steel strip 11 were connected to the same power source and had the same polarity and potential. (c) For the purpose of finding a preferable form of the dummy electrode, different forms of dummy electrodes, a single dummy electrode and a composite dummy electrode, were provided near both edges of the steel strip. As a comparative example of the above-mentioned improved device, two devices were used, one using the conventional device shown in Fig. 3 with the dummy electrode removed, and the other using a secondary air division adjustment and shutter addition device. It was compared as an adjustment method. Furthermore, in order to see the difference in the form of the dummy electrodes, a third comparative example is shown in which single dummy electrodes are arranged near both edges of the metal strip in the same manner as the pass lines. The test materials and implementation conditions used in this example are shown in Table 2.

【table】

[Table] Figure 6 shows the results of actually measuring the amount of oil applied over the entire width of the strip by taking samples from tin steel strips threaded under the threading conditions shown in Table 2. From the center of the board to the edge of the board 50mm, in both the inventive example and the comparative example, the target amount of oil applied was maintained at 4.0mg/ ^m2 , and the oil was applied uniformly, but the oil was gradually applied to the edge of the board within 50mm of the board edge. Differences between the invention example and the comparative example appear.
In other words, in both the comparative conventional method and the atomized oil spill width adjustment method, the amount of oil applied gradually increases toward the edge of the plate.
At the edge of the plate within 15 mm, the amount of oil applied rapidly increases significantly. On the other hand, it can be seen that in the example of the present invention, a value close to the target oil application amount is maintained up to the limit of the plate edge. In addition, even when compared with the comparative example using a single method, it is clear that the example of the present invention, which was able to maintain the target oil application amount of 4.0 mg/m ² up to the edge of the plate, has an excellent effect. be. In other words, it was found that the composite method of the dummy electrode is more preferable. (Effects of the Invention) As is clear from the results of the examples, the present invention can be applied to a conventional electrostatic oil applicator by simply attaching a pair of metal strips sandwiching the metal strip near both edges of the strip to be oiled. By simply installing and modifying a new composite dummy electrode, it can prevent the paint repelling phenomenon that occurs in conventional applications such as tinplate that are directly painted without degreasing, and has a great effect on improving quality and yield. be.

[Brief explanation of the drawing]

Figure 1A is a sectional view of the main part explaining the electrostatic oil application method of the present invention, Figure 1B is a sectional view of the main part of a comparative test example, and Figure 2 is a modified conventional electrostatic oil application device. FIG. 3 is a systematic side sectional view showing an example of an electrostatic oil applicator used to carry out the method of the present invention. FIG. 4 is a systematic side sectional view of a conventional electrostatic oil applicator. A cross-sectional view of the part beyond the atomizing nozzle of the oil application device, Fig. 5 is a cross-sectional view of the main part explaining the conventional electrostatic oil application method, and Fig. 6 is a cross-sectional view of the tinplate according to an embodiment of the present invention. It is a figure which shows the measurement result of the amount of oil applied, and the same result by a comparative example. 1... Casing, 2... Deflection electrode, 3... Insulator, 4... Oil reservoir chamber, 4'... Atomization chamber, 5...
Primary air source, 6... Atomizing nozzle, 7... Secondary air source, 8... Charged electrode, 9... Earth wire, 10...
Roller, 11...Metal band, 12...Air supply system, 13...Blow rate control device, 14...Rotary generator, 15, 16...High voltage supply power source, 17...Oil particles, 18... Plate edge, 19... Secondary air outlet, 20... Shutter, 21... Partition plate, 22
...Air volume control valve, 23...Dummy electrode.

Claims (1)

[Claims] 1. In a method of applying oil to the surface of a continuously running metal band using an electrostatic oil application device, a pair of composite dummy electrodes are provided near both edges of the metal band to sandwich the metal band, and A method for uniformly applying oil to a metal strip using an electrostatic oil applicator, characterized in that the polarity of the electrode is maintained at the same polarity and the same potential as that of the metal strip to be oiled.