JPH07195019A - Baking furnace for heat-resistant precoated metallic sheet and baking method - Google Patents

Abstract

PURPOSE:To provide the baking furnace for a heat-resistant precoated metallic sheet and the baking method capable of imparting good surface performance at a high baking rate especially by utilizing high-frequency induction heating method. CONSTITUTION:This baking furnace for method a heat-resistant precoated metallic sheet consists of a first heating region Aa to heat a steel sheet 2 to a temp. where the solvent in an applied coating material is volatilized off, a second heating region Ca to heat the sheet 2 free from the solvent further to a temp. where the fluororesin in the coating film is remelted and floated up to the surface of the coating film and a constant temp. holding region Da wherein the sheet 2 heated in the region Ca is kept at a constant temp. to float the fluororesin up to the surface of the coating film. Consequently, good surface performance is obtained at a high baking rate, and the furnace is widely applied in various fields such as the household electric appliances required with high quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a baking furnace for precoated metal sheets, and more particularly to a baking furnace and a baking method for heat-resistant precoated metal sheets using a high frequency induction heating system.

[0002]

2. Description of the Related Art In recent years, prepainted steel sheets, so-called precoated steel sheets, have been widely used in various fields such as home electric appliances, and precoated steel sheets for heat-resistant applications have also begun to be used. Along with this, high quality is required for the coating film of this steel sheet.

On the other hand, pre-coated steel sheets also have various thicknesses after being coated with various coating materials using steel sheets having various thicknesses.
Since a precoated steel sheet baked on it is required, it is possible to perform temperature control suitable for the material and thickness of the metal plate and paint to be baked, and also to increase the baking speed in a short time. Development of a baking furnace capable of obtaining a coated metal sheet having good surface performance is expected.

On the other hand, conventionally, for example, a coated metal plate such as a coated steel plate is subjected to paint baking treatment using a hot air oven of a gas heating system. Further, recently, a high frequency induction heating method has been put into practical use, which enables rapid heating, has no thermal inertia, and can provide a coated metal plate with a clean atmosphere and few coating defects.

There are two specific methods for this, for example, a method of baking in an induction heating furnace using the high frequency induction heating method disclosed in Japanese Patent Laid-Open No. 1-139178, and further, Japanese Patent Laid-Open No. 62-99479, JP-A-62-133083, JP-A-62-133084.
Most of the solvent is vaporized and volatilized in the induction heating furnace disclosed in Japanese Patent Publication No. 1994-242242, and then baked in a hot air oven.

[0006]

As described above, as the conventional coated metal sheet baking oven, a hot air oven is used, an induction heating oven is used, and an induction heating oven is used in the first half of the heating and hot air is used in the latter half of the heating. A method of applying a furnace is known.

[0007] Further, there is nothing specially considered as a heat-resistant coated metal plate baking furnace, and it is manufactured within the production capacity range of the above-mentioned general coated metal plate baking furnace. However, these conventional coated metal plate baking furnaces have the following problems.

First of all, the paint to be baked on the metal plate is one that contains a large amount of solvent regardless of which type of heating furnace (baking furnace) is used. Also in this case, a paint containing a solvent is used. In a hot-air oven, heat is transferred from the surface of the coating film to the metal plate, so it is necessary to gently heat the solvent in the process of vaporizing the solvent to expel the solvent from the paint.

For this reason, the area for evaporating and evaporating the solvent consumes about half the length of the whole hot-air baking furnace, which inevitably lengthens the entire baking furnace. On the other hand, in the infrared heating or high frequency induction heating method, heating is performed from the paint itself and the metal plate side. Here, since hot air or warm air needs to flow to exhaust the evaporated solvent, a solvent volatilization region similar to that of the hot air heating furnace is required.

By the way, in the above-mentioned solvent volatilization region,
In order to improve the finish of the paint surface, the wind speed of hot air or warm air cannot be increased too much. That is, if the wind speed is too high, wrinkles, waviness, and other wind ripples will be produced on the coated surface, and moreover, the coating will be wrinkled, and the final surface finish will be even worse.

Therefore, it is necessary to set the wind speed low,
Especially in a hot-blast stove, the heating rate becomes low, and as a result, the solvent volatilization region becomes long. If the solvent volatilization in the solvent volatilization area is not properly performed, defects such as microscopic cracks are likely to occur in the next fluororesin floating process, and it is necessary to set the heating time to the fluororesin floating temperature long. There is no choice but to lengthen the length of the furnace part.

Even if the solvent volatilization is properly performed, in the case of heating to the fluororesin floating temperature, in the case of a hot air baking furnace, the hot air temperature that can be used is up to about 450 ° C., and if the entire heating baking furnace is long. It is unavoidable, or it is not easy to maintain a constant temperature after reaching it, and sometimes problems such as poor surface performance (heat resistance mismatch) due to temperature instability occur.

Further, in the case of using a conventional baking furnace for coated metal plates, it is difficult to coat a wide variety of paints on metal plates of various thicknesses in arbitrary thicknesses and then to bake them. . In conventional baking ovens for painted metal plates, the time required for evaporation of the paint solvent is very sensitive to the paint film thickness. This is because the temperature control suitable for the temperature cannot be performed, so that the baking speed is increased to obtain a coated metal plate having good surface performance in a short time, and the situation is unusable.

In view of the problems of the conventional coating metal plate baking furnace described above, the present invention performs temperature control suitable for the material and thickness of the metal plate and paint to be baked, and at a high baking speed. An object is to provide a baking furnace and a baking method for obtaining a heat-resistant precoated metal sheet having good surface performance in a short time.

[0015]

The present invention advantageously solves the problems of the prior art, and as a result of the inventors' ingenuity to achieve the above object, the printing speed was increased. It is possible to produce a heat-resistant pre-coated metal sheet having good surface performance in a short time,
The gist of the invention is as follows.

(1) The apparatus of the present invention is a heat-resistant pre-coated metal plate baking furnace which evaporates the solvent in the paint applied to the metal plate for baking, and the paint applied at the temperature of the metal plate. The first heating area that controls heating to a temperature at which the solvent in the film evaporates and the metal plate on which the solvent volatilizes is further heated, and heating control is performed to a temperature at which the fluororesin in the coating film remelts and floats on the coating film surface. A heat-resistant precoat comprising three heating regions, a second heating region and a constant temperature holding region for keeping the temperature of the metal plate heated to the heating region constant and floating the fluororesin on the coating film surface. It is a baking oven for metal plates.

(2) In the baking furnace for heat-resistant precoated metal sheet according to the above item (1), in each of a plurality of regions including at least a first heating region and a second heating region, with respect to each region. It is characterized in that a high-frequency induction heating device capable of independently heating and controlling each metal plate is provided.

(3) In the method of the present invention, in the method for baking a heat-resistant precoated metal sheet using the baking furnace according to the above (1) or (2), the coating material is applied on the outlet side of the first heating region. The temperature of the metal plate is set to 170 ° C. to 270 ° C., and the holding temperature of the metal plate is set to 34 in the constant temperature holding region.
0 ° C. to 440 ° C., holding time 3 sec. ~ 60se
c. The method for baking a heat-resistant precoated metal sheet is characterized in that

(4) Further, in the method for baking a heat-resistant pre-coated metal sheet according to the above item (3), the gas used for exhaust is 3 times in the first heating region, the second heating region and the constant temperature holding region.
40 ° C to 440 ° C, and exhaust air velocity is 1 m / sec to 10
m / sec. It is characterized by using clean air or nitrogen within the range.

(5) In the method for baking a heat-resistant precoated metal sheet according to the above item (3), the gas used for exhaust is 170 ° C. to 270 ° C. in the first heating region, and the exhaust air velocity is 1 m / sec to 10 m. / Sec. In the range of 340 ° C. to 440 ° C., and the exhaust air velocity is 1 m / sec to 10 m / sec. It is characterized by using clean air or nitrogen within the range.

[0021]

As described above, the feature of the baking furnace for coated metal plates according to the present invention is that the temperature of the metal plate is controlled so that the solvent in the applied paint vaporizes to the first heating region and the solvent is A high-frequency induction heating device that can independently control the heating of each metal plate in the second heating region that further controls the heating of the volatilized metal plate to a temperature at which the fluororesin in the coating floats on the coating surface. While being provided, the temperature of the first heating area, the second heating area, and the temperature of the metal plate heated to a temperature at which the fluororesin floats on the coating film surface are kept constant,
That is, a hot air heating device capable of blowing hot air to the paint surface of the metal plate is provided in the constant temperature holding region where the fluororesin is floated on the surface of the coating film.

First, in the coating metal plate baking furnace of the present invention, since the metal plate is heated by high frequency induction heating, it is possible to heat the coating film from the inside, that is, from the metal plate side. It can be evaporated well from the side. At the same time, by blowing hot air onto the paint surface, evaporation of the solvent from the paint surface is promoted.

In this way, it is possible to prevent the cracking phenomenon in the solvent volatilization stage which occurs on the surface of the coating material and to reach the next fluororesin remelting stage in a short time.

Further, since the metal plate is heated again by high-frequency induction heating after evaporation of the solvent, the coating film is heated from the inside, that is, the metal plate side, and the fluororesin can be heated to the melting temperature in a short time. In addition to being possible, it is possible to obtain a coating film with good surface performance by sufficiently floating the fluororesin on the coating film surface, including the fluororesin of the paint of the steel plate and the contact portion in the subsequent constant temperature holding region. .

Therefore, the baking furnace is divided into a plurality of regions, a plurality of high-frequency induction heating devices provided in each heating region are used, and a hot air generator is also provided in an appropriate region, so that the metal plate is suitable for each region. If you control heating independently,
It is possible to perform temperature control suitable for the material and thickness of the metal plate and the paint to be baked. This hot air can be used to exhaust the solvent volatilized here, and thereby the unit cost of energy can be further reduced.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings.

FIG. 1 is a drawing showing one embodiment of a baking furnace for coated metal sheets according to the present invention. As shown in FIG. 1, the baking furnace 1 of this embodiment has three baking furnaces. Area Aa,
The induction heating coil 31a connected to the power supply device 21a is arranged in the area Aa, and the induction heating coil 33a connected to the power supply device 23a is divided into areas Ca.
And the hot air outlet 52 connected to the hot air generator 42 is arranged at the outlet of the area Aa, and the hot air outlet 54 connected to the hot air generator 44 is arranged in the area Da.

That is, in the baking furnace 1 of the present embodiment, the steel sheet 2 is induction-heated by the coil 31a in the area Aa (first heating area, preheating area), and at the same time, hot air from the hot air outlet 52 is applied to the steel sheet 2. The solvent in the paint applied by spraying is volatilized. The hot air is discharged from the system after passing through the first heating area.

Further, in the area Ca (second heating area, main heating area), the steel plate 2 is again induction-heated by the coil 33a to re-melt the fluororesin, and then the area Da (constant temperature holding area, fluororesin floating area). ), The hot air outlet 54
The steel plate 2 is kept at a constant temperature by hot air from the above, and the fluororesin in the coating film is floated. The hot air is discharged to the outside of the system after passing through the second heating area. In this way, the surface properties of the coating, such as stain resistance, can be improved.

By the way, in a conventional metal plate coating line using a normal hot air heating method, it is necessary to suppress the generation of wrinkles and cracks on the coating surface when the solvent is evaporated while heating, and it is necessary to increase the wind speed for a long time. And process it,
It takes a long time to raise the temperature to the re-melting temperature of the fluororesin in the coating film, and the furnace in the area corresponding to the volatilization area of the solvent and the heating area up to the re-melting temperature of the fluororesin in the coating film The length was long.

However, in the baking furnace of this embodiment, the high-frequency induction heating device (power supply devices 21a and 23a and induction heating coils 31a and 33a) is provided in the preheating area Aa and the main heating area C.
A metal plate (for example, steel plate 2) provided on a and subjected to a baking process
The optimal temperature rise rate can be freely set according to the material and thickness of the coating, the composition and thickness of the coating material, etc., so a coated metal plate with good surface performance in a short time with a short furnace length can be obtained. It became possible to obtain.

That is, in the baking furnace of this embodiment, the high frequency induction heating device (21a, 31) in the preheating area Aa is used.
According to a), the plate temperature of the steel plate 2 is heated to a constant preheating temperature for an optimum time to sufficiently vaporize the solvent, and the preheating area Aa
A plate with a good surface finish can be obtained and a coating film suitable for main heating can be obtained.

Here, the temperature of the steel sheet 2 on the exit side of the first heating region Aa varies depending on the resin in the paint, the solvent composition, etc., but if the temperature is lower than 170 ° C., a solvent having a medium boiling point (about 200 ° C.) or higher is sufficient. When the temperature exceeds 270 ° C., the solvent has almost completely volatilized, and it is not necessary to keep the temperature higher than this. Therefore, it is preferable to set the temperature at 170 ° C. to 270 ° C. The heating rate of the steel sheet 2 is preferably set to an optimum value in consideration of the paint film thickness, solvent composition and the like.

Further, the exhaust air velocity is 1 m / sec. If it is less than 10, it will take time for the solvent to volatilize from the surface of the paint film, and 10
m / sec. If it exceeds the range, wrinkles on the coated surface will occur and a good surface finish will not be obtained, so 1-10 m / se
c. It is preferable to set in the range of.

Then, the high-frequency induction heating device (23a, 33a) in the main heating region Ca heats the plate temperature of the steel sheet 2 to a constant main heating temperature in the shortest time to remelt the fluororesin. Further, in the constant temperature holding region Da, the steel plate 2 is held at a constant main heating temperature for a fixed time.

The remelted fluororesin floats on the surface of the coating film, and a coating film suitable for main heating is obtained. Here, the holding temperature of the steel sheet 2 in the constant temperature holding region Da varies depending on the resin composition in the paint, etc., but if the temperature is lower than 340 ° C, the solidification of the fluororesin occurs, and if it exceeds 440 ° C, it is not economical and 340 ° C- It is preferable to set the temperature to 440 ° C.

Further, if the holding time of the steel sheet 2 is less than 3 seconds, it is not sufficient for floating the fluororesin, and if it exceeds 60 seconds, the effect is almost unchanged and only the length of the constant temperature holding area Da becomes long. Therefore, it is preferable to set in the range of 3 seconds to 60 seconds according to the required quality (for example, adhesion).

Further, the exhaust air velocity is 1 m / sec. If less than 10m /
sec. If it exceeds the range, wrinkles and the like on the coated surface will occur and a good surface finish cannot be obtained, so 1-10 m / sec.
It is preferable to set in the range of. The gas blown into the constant temperature holding region is passed through the second heating region and is effectively used as a ventilation atmosphere, thus lowering the unit cost of energy.

Further, since induction heating is used, a stable temperature can be obtained with a short heating time, and stable product manufacturing is possible.

As described above, optimum heating control is performed according to the material and thickness of the metal plate (steel plate 2 etc.) and the type and thickness of the coating material. Further, in FIG. 1, induction heating coils 31a and 33a are arranged so as to wind the steel plate 2, and magnetic force lines are generated in the strip advancing direction. A pair of coils may be provided on the upper surface and the lower surface of the steel plate 2 so that magnetic force lines are generated in the strip thickness direction, and an appropriate one can be selected depending on the material and thickness of the metal plate.

The hot air generators 42 and 44 are the same as the hot air generators used in a general hot air stove, but the hot air generators 42 and 44 used in this embodiment are the general hot air stoves. It suffices to generate hot air (gas) at a temperature lower than that of the above, and no special one is required. If the coating film surface appearance is particularly severe, a filter or the like may be installed at the hot air blowing port.

As an example of construction, an intermediate step product in which a heat resistant resin having a dry film thickness of 10 μm is applied to an electro-aluminum plated steel sheet having a thickness of 0.5 mm, which is applied with a coating type chromate solution having an adhesion amount of 45 mg / m ² is used. I used it and as baking conditions,
When performing the high frequency induction heating and hot air heating of the present embodiment,
Tables 1 and 2 show comparative examples in which only conventional hot air heating and only high frequency induction heating are used.

In this embodiment, which was baked in a baking furnace of high-frequency induction heating + hot air heating, the temperature and speed of the hot air were changed. Referring to Tables 1 and 2, the paint surface performance of the coated metal sheet of this example manufactured in a baking furnace of high frequency heating + hot air heating is the case where only the hot air heating of the comparative example and the case where only high frequency induction heating is performed. In comparison with the above, it can be seen that especially the primary physical properties as they are in the coated state and the adhesiveness of the secondary physical properties after immersion in boiling water for 2 hours are good.

In the evaluation tests listed in Tables 1 and 2, first, a sample of 50 mm × 50 mm was cut out, and this sample is shown in Table 4 for the three cases 1 to 3 shown in Table 3 (1).
The evaluation items (3) to (3) were tested.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

FIG. 2 is a view showing another embodiment of the baking furnace for coated metal plates according to the present invention. As shown in the figure, the baking furnace 1 according to the present embodiment has four areas A.
The power supply device 21a is divided into a, Ca, Cb and Da.
The induction heating coil 31a connected to the power supply device 23a is arranged in the area Aa, and the induction heating coil 33a connected to the power supply device 23a
Is arranged in the area Ca, and the induction heating coil 33b connected to the power supply device 23b is arranged in the area Cb.

Further, hot air outlets 51, 52 connected to the hot air generator 44 are arranged in the area Aa, and hot air outlets 53, 54 are arranged in the area Da. Here, the hot air is discharged through the areas Aa and / or Cb, Ca.

The main heating area C is divided into two such as Ca and Cb, the non-control area is shortened to facilitate the feedback control, and one hot air generator is used for common hot air. Except for this, it is the same as the embodiment of FIG.

In this way, the basic regions (A, C, D) are further divided as necessary in consideration of the size of the plate to be produced, the type of resin, the thickness of the coating film, the total production capacity of the equipment, and the like. The same applies to the hot air generator. When the number of hot air generators is one, the hot air temperature is set to the required temperature in the high temperature region D.

In either case of FIG. 1 or FIG.
Although not shown in the figure, it is necessary to provide an outlet for the air blown into the furnace. The position is not particularly limited here.

Although the baking furnace of the present invention is mainly intended for heat-resistant precoating, it can be sufficiently used for general precoating. Considering the material to be treated, it is possible to select the optimum specifications within the above described range.

[0055]

As described above, according to the baking furnace and the baking method for the heat-resistant precoated metal sheet of the present invention, the baking furnace is composed of the three regions of the first and second heating regions and the constant temperature holding region. This makes it possible to perform temperature control suitable for the material and thickness of the metal plate and paint to be baked, and obtain a heat-resistant pre-coated metal plate having good surface performance in a short time at a high baking speed. It can be widely applied to various fields including home electric appliances and the like, which require high quality for the coating film.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a coated metal plate baking furnace according to the present invention.

FIG. 2 is an explanatory view showing another embodiment of the coating metal plate baking furnace according to the present invention.

[Explanation of symbols]

1 Baking Furnace 2 Steel Plates 21a, 23a, 23b Power Supply Device 31a, 33a, 33b Induction Heating Coil 42,44 Hot Air Generator 51, 52, 53, 54 Hot Air Outlet Aa First Heating Area (Preheating Area) Ca Second Heating area (main heating area) Cb second heating area (main heating area) Da constant temperature holding area (fluorine resin floating area)

Claims (5)

[Claims] 1. A baking furnace for a heat-resistant pre-coated metal plate, which evaporates a solvent in a paint applied to a metal plate to perform baking, wherein the solvent in the applied paint evaporates at the temperature of the metal plate. A first heating region for controlling heating to a temperature;
A second heating region for further heating the metal plate from which the solvent has volatilized to control the heating to a temperature at which the fluororesin in the coating film remelts and floats on the coating film surface, and the temperature of the metal plate heated to the heating region. A baking furnace for a heat-resistant precoated metal sheet, which is constituted by three regions of a constant temperature holding region where the fluororesin is floated on the surface of the coating film while being kept constant. 2. A high frequency induction heating device capable of independently heating and controlling a metal plate in each of a plurality of regions including at least a first heating region and a second heating region. The baking furnace for heat-resistant precoated metal sheet according to claim 1, characterized in that. 3. The method for baking a heat-resistant precoated metal plate using the baking furnace according to claim 1, wherein the temperature of the metal plate coated with the coating material is 170 at the exit side of the first heating region.
C. to 270.degree. C., the holding temperature of the metal plate in the constant temperature holding region is 340.degree. C. to 440.degree. C., and the holding time is 3 sec. ~ 60 sec. A method for baking a heat-resistant precoated metal sheet, characterized in that 4. The gas used for exhaust in the first heating region, the second heating region and the constant temperature holding region is 340 ° C. to 440 ° C.
C., and the exhaust air velocity is 1 m / sec to 10 m / sec. The method for baking a heat-resistant precoated metal sheet according to claim 3, wherein clean air or nitrogen in the range is used. 5. In the first heating region, the gas used for exhaust is 170 ° C. to 270 ° C., and the exhaust air velocity is 1 m / sec.
10 m / sec. In the range of 340 ° C. to 440 ° C., and the exhaust air velocity is 1 m / sec to 10 m / sec. The method for baking a heat-resistant precoated metal sheet according to claim 3, wherein clean air or nitrogen in the range is used.