JPS61247948A - Detecting method for coating state of strip - Google Patents

Abstract

PURPOSE:To detect the baking state of a coating film accurately on-line basis by detecting the baking state of the coating film from reflection factors before and after coating. CONSTITUTION:A reflection factor measuring instrument 20 which measured the reflection factor of the surface of a strip before coating is provided at the entrance side and a reflection factor measuring instrument 24 which measures the reflection factor after the coating is provided at the exist side of a backing furnace 14; and a comparator 28 calculates the quantities of variation of values L* and b* before and after the coating from both outputs of computing elements 22 and 26. Consequently, the baking state of the coating film is detected accurately on on-line basis.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for detecting the coating condition of a strip, and in particular, the coating film on a metal strip to which a thin film coating is applied is suitable for use in detecting the condition. The present invention relates to an improved method for detecting the coating condition of strips that are dried and baked.

[Conventional technology]

Generally, a coating equipment for a strip, for example, a steel plate, is configured as shown in FIG. A predetermined coating is applied to the front and back surfaces of the strip 10 by applying the coating using an apparatus 12 and then sequentially drying and baking it in a baking oven 14. To control the baking of such coating equipment, conventionally, a plate thermometer 16 for measuring the temperature of the strip 10 is provided on the exit side of the baking furnace 14, and the baking oven exit temperature detected by the plate thermometer 16 is The baking furnace 14 was controlled using the plate temperature control circuit 18 so that the temperature remained constant. However, if the baking is only controlled by strip temperature control on the outlet side of the baking furnace 14, variations in the baking state will occur due to variations in the coating composition, variations in the line speed, and the like. In order to prevent such variations in the state of the seizure, it is essential to detect the state of the seizure.For example, in Japanese Patent Laid-Open No. 50-96638, the seizure is detected immediately after the emissivity of the steel plate surface at a specific wavelength ( A control method for a continuous coating device is disclosed in which the emissivity is determined, the quality of the paint is adjusted based on the emissivity, and fluctuations in the coating composition and coating film thickness are grasped and controlled.

[Problems to be solved by the invention]

However, the inventor of this patent publication No. 50-96638
We conducted various investigations to determine whether the state of burn-in could be detected using the method disclosed in , and it was found that it is difficult to accurately detect the state of burn-in using only one emissivity at a specific wavelength. . That is, especially in the case of thin film coatings, the substrate (
Since the emissivity of the strip 10) varies, even if the emissivity of the strip 10 immediately after the strip 10 at a specific wavelength is constant, the burning may be poor or good. Therefore, with the method disclosed in Japanese Patent Application Laid-Open No. 50-96638, the state of burn-in cannot be accurately grasped online.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned conventional problems.The baking condition of the coating film can be accurately detected online, and therefore the quality of the coating can be appropriately adjusted to ensure good quality. It is an object of the present invention to provide a method for detecting the coating state of a strip by which the coating state can be obtained.

[Means for Solving the Problems] The present invention provides a method for detecting the coating state of a strip on which a coating is applied, continuously dried, and baked while running, as shown in FIG. Before application and after coating baking, respectively.
The above object is achieved by measuring the reflectance of the strip surface at one or more wavelengths or wavelength ranges, and detecting the burning of the coating film from the reflectance before and after coating. Further, in an embodiment of the present invention, the amount of change in the LX value and the bx value is determined from the reflectance before and after the coating, and the state of baking of the coating film is detected from this. Another embodiment of the present invention is to cancel the influence of coating film thickness when detecting the state of coating film burning from the reflectance before and after coating. [Function] The details of the present invention are as follows. As already mentioned, the inventor's investigation revealed that the reflectance after printing changes depending on the reflectance of the base (strip).For this reason, the inventor investigated The reflectance of the strip surface after baking was measured, and the relationship between baking and changes in state was investigated. As a result, it was found that the state of baking in the coating film could be detected from the reflectance before and after coating. Figure 2 shows the results when a semi-organic Cr-containing coating was applied to a non-oriented electrical steel sheet and baked in different conditions.
Printing shows how the LX value and b true value (equivalent to reflectance in two wavelength ranges), which is one of the color systems recommended by the International Commission on Illumination, change due to changes in conditions. It is. In Fig. 2, the O mark indicates the state before coating of one material A, the ■ mark indicates the state where the baking is insufficient, the O mark indicates the same state where the baking is good, and the [stock] mark indicates the state where the baking is too much. It shows. The inside of the mouth shows the state before being coated with the other material B, the figure also shows an insufficiently baked state, the cross mark similarly shows a good baked state, and the cross mark similarly shows an overly baked state. Further, the L8 value and bX value are each defined by the following equations. LX-116(Y/100)'/3-16・(1)b
East - 200 ((Y/100)'/3 - (Z/118.10) 1/3) ... (2)
Y and X in these formulas (1) and (2) are wavelengths of 380 to 78
For the reflectance at 0 nm, as shown in Figure 3,
The values are multiplied by the isochromatic numbers yλ and 2λ of the Z color system, integrated over the wavelength, and averaged. Here, the [1 value and bX value are adopted because the bX value is effective as an index that reflects the brightness of the base, especially for thin coatings such as those on electrical steel sheets, and the bX
This is because m is effective as an index that reflects a bluing color such as an oxide film. As is clear from FIG. 2, it can be seen that the state of burn-in can be detected from the change in bX value between before and after. or,
1. It can be seen that if *1 is also taken into account, the accuracy is further improved. Note that it is also possible to use parameters other than the bX value and the bx value depending on the surface quality of the steel plate and the inherent characteristics of the manufacturing line. In addition, when detecting the state of coating burn-in from the reflectance before and after coating, the coating film thickness b
By canceling out the influence on the X value and bX value, detection accuracy can be further improved. Embodiment] Hereinafter, an embodiment of coating burning control in which the strip coating state detection method according to the present invention is adopted will be described in detail with reference to the drawings. In this embodiment, as shown in FIG. 4, in a steel plate coating equipment equipped with a coating applicator 12, a baking furnace 14, a plate temperature meter 16, and a plate temperature control circuit 18 similar to the conventional example, further: The coating application device 12
A reflectance measuring device 20 measures the reflectance of the strip surface before coating is applied on the input side of the strip, and the reflectance measurement results by the reflectance measuring device 20 are processed for each wavelength to obtain the bX value and b
A calculator 22 that calculates the X value, and a reflectance measuring device 2 that measures the reflectance after the coating is baked on the exit side of the baking furnace 14.
4, an arithmetic unit 26 that processes the reflectance measurement results from the reflectance measurement B 24 for each wavelength and calculates Lx (i! and bX values), and a calculation unit 26 that calculates the Lx (i! and bX values) before coating application from the outputs of both the arithmetic units 22 and 26. For coating baking, a comparator 28 is used to calculate the subsequent bX value and the amount of change in bxm, and for coating baking, a film thickness meter 30 is used to detect the subsequent film thickness. Compare the output of the comparator 28 with the standard range that can be changed, and compare whether the amount of change before coating and after baking is within the standard range, and if it is out of the standard range, The seizure is equipped with a comparator 32 that outputs a plate temperature set value change command to the plate temperature control circuit 18 according to the state.Other points are the same as the conventional example, so explanations will be omitted. The operation of the embodiment will be described below. First, in a steady state, the plate temperature set value in the plate temperature control circuit 18 is kept constant, and the baking furnace 14 is controlled by feedback control based on the temperature measurement result of the strip 10 by the plate thermometer 16. In other words, the main loop is plate temperature control similar to the conventional one.On the other hand, the reflectance measurement results by the reflectance measuring devices 20 and 24 are processed for each wavelength by the computing units 22 and 26, and the bX value and bX
The value is calculated. Then, a comparator 28 calculates the amount of change before coating and after baking, and a comparator 32 determines whether the result is within a reference range. In addition,
The reference range can be changed based on the measurement result of the film thickness meter 30 in order to offset the influence of the film thickness on the L'[,1,X value. If the comparator 32 determines that the temperature is outside the reference range, a plate temperature set value change command is output to the plate temperature control circuit 18 depending on the seizure condition at that time. That is, for example, if it is determined that the seizing is insufficient, the plate temperature set value of the plate temperature control circuit 18 is increased to advance the seizing. Then, the seizure status is determined again at the changed plate temperature setting value. This is done until the seizure is good, but in the case of this example, the plate temperature setting value is changed by
This is only possible within a certain standard value, and an abnormality warning will be output if it deviates from this value. This means that, for example, if a problem occurs such as fluctuations in the composition of the coating liquid that deviate from the standard, the optimal baking of the coating with the standard composition will deviate greatly from the range, and the plate temperature setting will change indefinitely. This is to prevent it. In this embodiment, a film thickness gauge 30 is provided on the exit side of the baking furnace 14, and the coating film thickness detected by the film thickness gauge 30 is inputted to a comparator 32 to calculate the amount of change in the LX value and bx value. Since the reference range can be changed, Lj depending on the film thickness
The effects on the K value and bx value are canceled out, and coating state detection can be performed with high precision. Furthermore, in this embodiment, the plate temperature set value of the existing plate control circuit 18 is changed depending on the detected coating burn-in condition, so that the present invention can be applied to conventional equipment. It's easy. Incidentally, the coating and baking process depends on the state, and the objects to be controlled for quality adjustment are not limited thereto. In the above embodiments, the present invention was applied to detecting the coating state of a metal strip, such as a steel plate, but the scope of application of the present invention is not limited thereto. Effects of the Invention As explained above, according to the present invention, it is possible to accurately detect the baking state of a coating film online.A Therefore, quality adjustment is performed according to the detection result of the coating state. As a result, coating baking has excellent effects such as stabilization of the state.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the outline of the method for detecting the coating state of a strip according to the present invention, and FIG. 2 is a flowchart showing the LX value and bx value before coating application and after coating baking, for explaining the present invention in detail. FIG. 3 is a diagram showing an example of the state of change of Lxi! ! and a line diagram showing the number of isochromatic intervals of the XYZ color system used to calculate the bx value, and FIG. 4 includes a partial block diagram showing an example of the steel plate coating equipment to which the present invention is adopted. The side view, Figure 5, is
FIG. 2 is a side view, including a partial block diagram, showing an example of conventional steel plate coating equipment. DESCRIPTION OF SYMBOLS 10... Strip, 12... Coding coating device, 14... Baking furnace, 16... Plate thermometer, 18... Plate temperature side circuit, 20.24... Reflectance measuring device, 22.26... Arithmetic unit, 28.32... Comparator, 30... Film thickness meter.

Claims (3)

[Claims] (1) In a method for detecting the coating state of a strip in which a coating is applied, continuously dried and baked in a running state, the strip surface at least one wavelength or wavelength range is detected before the coating is applied and after the coating is baked, respectively. 1. A method for detecting the coating state of a strip, comprising: measuring the reflectance of the strip, and detecting the baked state of the coating film from the reflectance before and after coating. (2) The strip according to claim 1, wherein the amount of change in the L^* value and the b^* X value is determined from the reflectance before and after the coating, and the baking state of the coating film is detected from this. Coating condition detection method. (3) A method for detecting the coating state of a strip according to claim 1, characterized in that when detecting the baked-on state of the coating film from the reflectance before and after the coating, the influence of the coating film thickness is canceled out. .