JPH01310770A - Continuous one-side coating/baking device and method for steel strip - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to appropriate baking of a coating film and prevention of oxidation of a non-coated surface in the manufacturing process of a single-sided coated steel plate.

[Prior art] Single-sided coated steel strip is a rational material and is extremely useful as a material for, for example, automobile exterior panels, which require universal corrosion resistance on one side and individual surface treatment on the other side. It is being For single-sided coated steel strips that are used in this way, the coated side has a coating that can withstand processing, while the uncoated side on the other side is required to have properties suitable for the user's processing, such as chemical conversion treatment properties. Ru. For this reason, when baking the paint, it is necessary to strictly control the temperature and time, and chemical changes such as oxidation of the steel surface must be prevented within 1 minute on the unpainted surface.

Conventionally, one way to prevent paint burning on such single-sided coated steel strips is to
A gas hot stove was used. This is because the history of manufacturing single-sided coated steel strip is short, and the gas hot air oven used in the IT baking process for double-sided coated steel strip, which was ahead of its time, was first used.

For gas hot air stoves, the direct heating method in which high-temperature combustion gas is brought into direct contact with the painted surface is highly thermally efficient and is widely used. It has the disadvantage of contaminating the surface of the steel strip. To avoid this, when baking a single-sided coated steel plate, a latian diffuser is installed in the heating furnace (high temperature combustion gas is passed through the tube to heat the tube, and the radiant heat is used to heat the painted surface). Radiant heating was used to heat the gas (latian dew method).Thus, these gas hot air stoves
Since the baking temperature is determined by the gas temperature, the heating temperature was adjusted while measuring the gas temperature. In addition, in the Sitian 1 to Chico-Ove method, in order to prevent oxidation of the non-painted surface and exhaust volatile matter that evaporates from the paint film,
A large amount of inert gas was injected.

However, with gas hot blast stoves, it takes time to adjust the gas temperature and there are limits to temperature control, so infrared heating methods are also used, but there are differences in heating rates due to differences in the heat absorption ability of the coating film surface. , heating efficiency may be low,
In recent years, high-frequency induction heating methods have begun to be used. For example, iron and steel, vol. 72°N, 3. S44],”).

``Problem to be solved by the invention 1 With the high-frequency induction heating method, electric energy is directly introduced into the steel strip, so it is heated quickly, temperature controllability is extremely good, and there is no contamination from the heat source. Temperature measurement, which serves as a guideline for control, was unsatisfactory.In other words, the C radiation thermometer is a rapid temperature measurement method that matches the temperature controllability of high-frequency induction heating, but in the case of single-sided coated steel strips, it is difficult to measure temperature during baking. The emissivity of the coated surface changes as a result of chemical changes, and oxidation occurs on the non-coated surface, albeit to a small extent.Therefore, problems remain when the emissivity changes. This inappropriate temperature control makes it difficult to prevent contamination due to condensation of evaporated components from the paint film and oxidation of the non-painted surface, resulting in a loss of chemical conversion properties.

This invention was made to solve this problem, and it prevents contamination and oxidation of non-painted surfaces by highly accurate adjustment of the steel strip surface temperature and appropriate exhaust and atmosphere adjustment based on this. The purpose is to obtain satisfactory chemical conversion treatment properties.

Means for Solving Problem 1] The means for achieving this object are as follows: (1) In a device that coats one side of a steel strip and bakes it, the baking furnace is divided into a plurality of sorters, and A high-frequency induction heating device and a radiant temperature 3] are arranged on the non-painted surface side of the steel strip, and are also equipped with an inert gas inlet, an inert gas amount regulator, and an exhaust port. (2) A radiation thermometer is connected to a computing unit, this computing unit is connected to a command unit, and a high-frequency induction heating device receives the command via a heating current controller. and an inert gas flow rate regulator is connected to the control device, and an apparatus for continuously baking one side of a steel strip to coat one side of the steel strip. Continuous baking of a single-sided coating on a steel strip (J method, (4 ) A method for continuously baking a single-sided coating on a steel strip, in which temperature and atmosphere are adjusted based on radiation thermometer measurements and line speed.

[Function] The coating film applied to one side of the steel strip is heated in a baking furnace to complete the polymerization reaction, but the heating rate at this time needs to be adjusted depending on the thickness and width of the steel strip and the line speed. be.

For this reason, it is important to quickly and accurately measure the ever-changing temperature of the steel strip, and the radiation thermometer that is most suitable for such measurements is one that can measure the emissivity of the surface to be measured. That is the premise.

The dispersion of actual temperature measurements due to emissivity fluctuations on both sides of the steel strip was investigated, and the results shown in Figure 3 were obtained. In Figure 3, the horizontal axis is the strictly regulated temperature inside the furnace, and the vertical axis is the actual value measured by a radiation thermometer.The actual value for the painted surface is marked with an X, and the oxidized steel plate surface is marked with The surface of the steel plate that has not been oxidized is indicated by an O mark. The X mark is widely distributed in the C range, followed by the / mark in the B range, and the ○ mark in the narrowest A range.
is within the range of That is, the measured values vary the most on the painted surface, and the smallest variation occurs on the non-coated surface, which is not oxidized.In other words, to improve the accuracy of temperature measurement, it is necessary to measure the non-coated surface without oxidizing it.

Next, in order to prevent oxidation, inert gas is generally blown into the furnace, but when we examine the relationship between the amount of inert gas blown into the furnace and the oxygen concentration in the furnace, we find that in order to lower the oxygen concentration in the furnace, a large amount of gas must be It can be seen that an amount of inert gas is required. FIG. 4 shows the above relationship, with the horizontal axis representing the amount of nitrogen gas blown and the vertical axis representing the oxygen concentration in the furnace, each scaled at equal intervals.

The two are in an exponential relationship, and it can be easily predicted that an enormous amount of inert gas will be required to lower the oxygen concentration sufficiently. Furthermore, FIG. 5 shows the results of investigating the relationship between the oxygen concentration in the furnace and the chemical conversion treatment properties. The horizontal axis in Figure 5 is the oxygen concentration in the furnace, and the vertical axis is the phosphate treatment applied to the unpainted surface of the steel strip heated from 150°C to 250°C for 4 seconds, and the treated film was visually observed. This is the evaluated chemical conversion treatment property. ○ indicates no unevenness at all, slight unevenness is observed in the mouth, Δ indicates obvious unevenness, ×
is slightly transparent. Oxygen concentration 20 Orl
Below Pm, there are no obvious unevennesses (△), and when the oxygen concentration is less than 50 ppm, there are no cases where slight unevenness (b) is observed, and the chemical conversion treatability of all steel strips is improved.

In addition to the function of preventing oxidation of the non-painted surface as described above, the inert gas also functions to replace volatile components. As the temperature of the coating film rises, volatile components within it evaporate, causing an explosion if oxygen is mixed in the furnace, or condensing again, falling onto the steel strip and contaminating the product. or To prevent these accidents, volatile components are exhausted and inert gas is blown in to adjust the atmosphere.

However, these oxidation and evaporation do not occur everywhere in the furnace, and do not occur near the entrance of the furnace where the temperature of the coating film has not yet risen, but occur after a certain amount of heating time. That is, oxidation of the unpainted surface is likely to occur when the temperature of the steel strip is 150° C. or higher, and the evaporation rate of volatile components is determined depending on the composition of the solvent distributed in the paint. Dividing the baking oven into multiple zones reduces oxidation and/or
Alternatively, it becomes possible to blow inert gas in a concentrated manner into zones where evaporation is likely to occur. Placing a high-frequency induction heating device in each zone makes it possible to adjust the baking temperature in each zone, and the radiation thermometer in each zone monitors the baking temperature in each zone, and at the same time provides feedback on monitoring results and feed forwards. enable. By providing an inert gas exhaust port, an inert gas inlet, and an inert gas amount regulator for each zone, volatile components can be quickly exhausted from each zone, and the atmosphere can be maintained by blowing in an appropriate amount of inert gas. Adjustments can be made. In this case, the inert gas may be one that is normally used industrially, and a typical example is nitrogen gas.

[Embodiment of the Invention] An embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram of a single-sided coating continuous baking device, in which 1 is a painted steel strip, 2 is a zone, a, b, and c are divided zones, 3 is a high-frequency induction heating device, 4 is a radiation thermometer, 5 is an inert gas inlet, 6 is an inert gas outlet, 7 is a heating current controller, 8
is the gas flow rate regulator, 9 is the command unit, ]0 is the calculator, ]-1
is a seal roll. This figure shows one form of control system that performs adjustment for each zone. The painted steel strip 1 travels from left to right in the figure and first enters zone a where it is heated by a high-frequency induction heating device 3. . A radiation thermometer 4 is placed on the non-painted side of the painted steel strip, and the temperature measurement results are sent to a calculator 10.
send to The calculation unit 1o contains in advance information about the line speed and type of coating according to the width and thickness of the steel strip, and the number 7a corresponding to the coating amount f-1.
The target baking temperatures for zones , b, and c have been input. The measured temperature value is compared with the target value by this calculator 10, and a
.

1], excess or deficiency of heating current in the c-sone is calculated and sent to the command unit 9, and the heating current control device 7 is activated by the current value correction command from the command unit 9 to adjust the baking temperature to 1 degree. Ru. Calculator] Another role of 0 is to calculate the measured temperature value a
, b, and c, and transmits the correction value to the command unit 9, which serves as a flow rate correction command to operate each inert gas flow rate regulator 8. The flow rate regulator 8 regulates the amount of gas in the furnace that is forcibly exhausted from the exhaust port 6, and at the same time adjusts the amount of inert gas blown in from the inlet port 5 in order to maintain the pressure balance in the furnace.

Note that each zone is partitioned by a seal IV-rule 11.

Next, the results of experiments regarding the present invention will be specifically described.

(Experiment example) Using a baking furnace divided into three parts as shown in Fig. 1, Ni-
A steel strip coated with organic composite silica 1 to 800 mg/+n2 was baked on top of the plating film of Zn alloy single-sided plated steel sheet, and contamination by volatile components and chemical conversion treatment properties of the non-painted surface were investigated. Na.

Different thicknesses of steel strips require different line speeds, resulting in different heating patterns and different locations where rapid evaporation of volatile components begins. Therefore, three different heating patterns were selected: pattern X, pattern Y, and pattern Z. In Figure 2, the vertical axis is the baking temperature, and the horizontal axis is the position in the furnace.Each pattern is input in advance to the calculator 10 in Figure 1.
Experiment No. 1 used pattern X, experiment No. 2 used pattern Y, and experiment No. 3 used pattern Z)S. v×,
v),.

Each point in (2) is the position where evaporation begins rapidly in each experiment No. 1, experiment N[L2, and experiment No. 3.

Table 1 shows the experimental conditions and results, including the conventional example conducted for comparison.

In Table 1, Experiment No. 1, since the steel strip is thin, the line speed is high and rapid evaporation occurs in zone b. Because of this, a large amount of exhaust gas is required in zone 1), and the amount of nitrogen gas blown also increases. Also, if the line speed is high, the time taken to pass through the furnace is short, so the maximum temperature must also be high, and since the temperature of the steel strip is high even in zone a, it is necessary to blow some nitrogen gas. It becomes necessary. In zone C, the rapid evaporation has already subsided, but since the steel strip temperature is high, a considerable amount of nitrogen is blown in to prevent oxidation of the unpainted surface.

In experiments No. 2, No. 3, the thickness of the steel strip was
, thicker than l, rapid evaporation does not occur until the zone is reached. In zone a, the temperature is low and nitrogen gas is not necessary. In zone b, an amount of nitrogen gas is required depending on the temperature to prevent oxidation of the non-painted surface.

Conventional example No., 1, N [L2 is the steel strip thickness or the experimental No.
, 1.

No. 3 is the same, so the line speeds are the same and the positions where rapid evaporation starts are also the same.

In the conventional example, the same amount as Experiment No. 1, which required the largest amount of nitrogen injection in the experimental example, was used, but Conventional Example No. 1
, NO, and 2 showed slight contamination by volatile components (△), and slight unevenness was observed in the chemical conversion coating. On the other hand, in the experimental examples, although there were examples in which the amount of nitrogen gas used was small, no contamination or other contamination was observed in any of the experiments. In the conventional example, it is thought that the cause was inappropriate exhaust gas and accuracy of temperature control.

[Effects of the Invention] As described in Section 2 below, this invention divides the baking furnace and adjusts the temperature in each zone by rapid and highly accurate temperature measurement.
In addition, since a large amount of exhaust inert gas is blown in a concentrated manner in the required zone, there is no contamination by volatile components, and oxidation of the non-painted surface is properly prevented. Therefore, chemical conversion treatment properties are not impaired at all. The effect of the present invention, which can provide such an excellent single-sided coated steel strip, is significant.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing one embodiment of the device of the present invention, Fig. 2 is a diagram showing the baking temperature pattern used in the embodiment of the present invention, and Fig. 3 is the relationship between the type of measurement surface and emissivity. Figure 4 is a relationship diagram between nitrogen gas injection amount and oxygen concentration in the furnace, Figure 5
The figure is a diagram showing the relationship between in-furnace oxygen concentration and chemical conversion treatment properties. ]... Painted steel strip, 2... Zone, 3... High frequency induction heating device, 4... Radiation thermometer, 5... Gas inlet, 6...
Gas outlet, 7. Heating current controller, 8. Gas flow rate regulator, 9. Command unit, 10. Arithmetic unit, 1]. Seal roll, a, b, c... Division zone.

Claims (4)

[Claims] (1) In an apparatus for painting and baking one side of a steel strip, the baking furnace is divided into multiple zones, and each zone is equipped with a high-frequency induction heating device and a radiation thermometer on the non-painted side of the steel strip, and An apparatus for continuously baking a single-sided coating film on a steel strip, characterized by being equipped with an inert gas inlet, an inert gas amount regulator, and an exhaust port. (2) A radiation thermometer is connected to a computing unit, this computing unit is connected to a command unit, a high frequency induction heating device is connected to the command unit via a heating current controller, and an inert gas flow rate regulator is connected to the command unit. 2. The apparatus for continuously baking a single-sided coating film on a steel strip according to claim 1, which is connected to said command unit. (3) In the method of painting one side of the steel strip and baking it, the baking furnace is divided into multiple zones, and the temperature is adjusted using a high-frequency induction heating device and the atmosphere is adjusted using an inert gas flow rate regulator for each zone. A method for continuously baking a single-sided coating on a steel strip. (4) The method for continuously baking a single-sided coating film on a steel strip according to claim 3, wherein the temperature adjustment and the atmosphere adjustment are carried out based on the measured value of a radiation thermometer and the line speed.