JP3062719B2 - Baking furnace and baking method for heat-resistant pre-coated metal sheet - Google Patents

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 a heat-resistant precoated metal sheet using a high-frequency induction heating method, and more particularly to a baking furnace for a precoated metal sheet.

[0002]

2. Description of the Related Art In recent years, pre-painted steel sheets, so-called pre-coated steel sheets, have been widely used in various fields such as home electric appliances and the like, and pre-coated steel sheets for heat-resistant applications have begun to be used. Accordingly, high quality is required for the coating film of the steel sheet.

[0003] On the other hand, precoated steel sheets are also coated with a variety of paints of any thickness using steel sheets of various thicknesses.
Since a pre-coated steel sheet is required to be baked, it is possible to perform temperature control suitable for the material and thickness of the metal plate and paint to be baked, and to increase the baking speed and shorten the time. The development of a baking furnace capable of obtaining a coated metal plate having good surface performance is expected.

On the other hand, conventionally, for example, a coated metal plate such as a coated steel plate has been subjected to a paint baking process using a hot blast stove by a gas heating method. In recent years, a high-frequency induction heating method has been put to practical use, in which rapid heating is possible, there is no thermal inertia, and a coated metal plate with few coating defects can be obtained in a clean atmosphere.

There are two concrete methods for this, for example, a method of performing a baking treatment in an induction heating furnace using a high-frequency induction heating method disclosed in Japanese Patent Application Laid-Open No. 1-139178, and 62-99479, JP-A-62-133083, JP-A-62-133084
For example, most of the solvents are evaporated and volatilized in an induction heating furnace disclosed in Japanese Patent Application Laid-Open Publication No. H10-264, and then a baking process is performed in a hot blast furnace.

[0006]

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

There is no specially considered heat-resistant coated metal sheet baking furnace, which is manufactured within the range of the above-mentioned general coated metal sheet baking furnace. However, these conventional coated metal sheet baking furnaces have the following problems.

[0008] First, regardless of the type of heating furnace (baking furnace) used, the paint to be baked on the metal plate contains a considerable amount of a solvent. Further, the paint is used in a baking furnace of an ultraviolet curing system or an electron beam curing system. Also in this case, a paint containing a solvent is used. In a hot blast stove, since heat is transmitted from the coating film surface to the metal plate, in the process of evaporating and evaporating the solvent, it is necessary to gently heat and drive off the solvent in the paint.

Due to this, the area for performing the evaporation of the solvent consumes about half the furnace length of the entire hot air baking furnace, and the entire baking furnace is inevitably elongated. On the other hand, in the infrared heating or the high-frequency induction heating method, heating is performed from the paint itself and the metal plate side. Here, since it is necessary to flow hot air or hot air to exhaust the evaporated solvent, a solvent volatilization area similar to that of a hot-air heating furnace is required.

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 so much. In other words, if the wind speed is too high, wind ripples such as wrinkles and undulations will be generated on the painted surface, and the painted surface will be further cracked to further deteriorate the final surface finish.

Therefore, it is necessary to set the wind speed small,
In particular, in a hot blast stove, the heating rate also decreases, resulting in a longer solvent evaporation region. This tendency is more remarkable when the thickness of the paint is large. Also, if the solvent volatilization in the solvent volatilization region is not performed properly, defects such as minute cracks are likely to occur in the next fluororesin floating process, and it is necessary to set a longer heating time up to the fluororesin floating temperature. The furnace length of the part must be increased.

Further, even if the solvent volatilization is properly performed, in the case of heating to the fluorocarbon resin floating temperature, in the case of a hot air baking furnace, the maximum usable hot air temperature is about 450 ° C. Inevitably, it is not easy to maintain a constant temperature after reaching the temperature, and sometimes a problem such as poor surface performance (unsatisfactory heat resistance) due to temperature instability is caused.

Further, when a conventional furnace for baking a coated metal plate is used, it is difficult to apply a variety of paints to metal plates having various thicknesses at an arbitrary film thickness and then bake them. . This is because in the conventional baking furnace for painted metal plates, the time required to evaporate the solvent of the paint is very sensitive to the thickness of the paint. This is because it is not possible to perform temperature control suitable for this purpose, and it is difficult to obtain a coated metal plate having good surface performance in a short time by increasing the baking speed.

In view of the above-mentioned problems of the conventional coated metal sheet baking furnace, the present invention performs a temperature control suitable for the material and thickness of the metal sheet to be subjected to the baking process and the paint so that the baking speed can be increased. An object of the present invention 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]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the problems of the prior art. To achieve the above object, the present inventors have made various efforts to increase the printing speed. 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 baking furnace for a heat-resistant pre-coated metal plate for baking by evaporating a solvent in a coating material applied to a metal plate. A first heating region for heating and controlling to a temperature at which the solvent in the applied coating material evaporates and evaporating and evaporating the solvent while maintaining a constant temperature of the metal plate heated to the heating temperature; And a second heating region for further heating the metal plate in which the solvent has volatilized, and heating and controlling the temperature to a temperature at which the fluororesin in the coating film re-melts and floats on the coating film surface, and a metal plate heated to the heating temperature. A baking furnace for a heat-resistant pre-coated metal plate, comprising four regions of a second constant-temperature holding region in which the fluororesin floats on the coating film surface while maintaining the temperature constant.

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

(3) A method of baking a heat-resistant pre-coated metal plate using the baking furnace according to the above (1) or (2), wherein the paint is applied in a first constant temperature holding region. Is maintained at 170 ° C. to 270 ° C., and the holding time is 3 sec to 20 sec. And the holding temperature of the metal plate in the second constant temperature holding area is set to 340 ° C.
To 440 ° C., and the holding time is 3 to 60 sec. The method for baking a heat-resistant pre-coated metal plate is characterized in that it is within the range.

(4) In the method for baking a heat-resistant pre-coated metal sheet according to the above item (3), the first heating region, the first constant-temperature holding region, the second heating region, and the second constant-temperature holding region exhaust air. The gas used is 340 ° C. to 440 ° C., and the exhaust air speed is 1 m / sec. -10 m / sec. And clean air or nitrogen.

(5) In the method for baking a heat-resistant pre-coated metal sheet according to the above (3), the first heating region and the first
Gas used for exhaust in the constant temperature holding area of 170 ° C. to 27 ° C.
0 ° C., and the exhaust air velocity is 1 m / sec to 10 m / sec.
, The gas used for exhaust in the second heating area and the second constant temperature holding area is set to 340 ° C. to 440 ° C., and the exhaust air velocity is set to 1 m / sec.
c to 10 m / sec. And clean air or nitrogen.

[0021]

As described above, the baking furnace for a coated metal sheet according to the present invention is characterized by a first heating area for controlling the temperature of the metal sheet to a temperature at which the solvent in the applied coating material evaporates, A high-frequency induction heating device capable of independently controlling the heating of each metal plate for a second heating region in which the volatilized metal plate is further heated to control the heating to a temperature at which the fluororesin in the coating floats on the coating surface. A first heating zone, a first constant temperature holding zone for maintaining the temperature of the metal plate heated to a temperature at which the solvent in the coating material evaporates, and evaporating the solvent, a second heating zone, and fluorine. Hot air is blown onto the paint surface of the metal plate in the second constant temperature holding region where the temperature of the metal plate heated to the temperature at which the resin floats on the surface of the coating film is kept constant and the fluororesin floats on the surface of the coating film. Possible hot air heating It is that an on-site equipment.

First, in the coated metal sheet baking furnace of the present invention, since the metal sheet is heated by high-frequency induction heating, the coating film is heated from the inside, that is, from the metal sheet side, and the solvent inside the painted surface is removed from the metal sheet side. Can evaporate well. At the same time, blowing hot air onto the paint surface promotes evaporation of the solvent from the paint surface. Further, the solvent remaining in the paint is evaporated and evaporated in the first constant temperature holding region.

In this way, it is possible to prevent the waking phenomenon and the like in the solvent volatilization stage occurring on the paint surface and to reach the next fluororesin remelting stage in a short time.

After the evaporation of the solvent, the metal plate is heated again by high-frequency induction heating, so that the coating is heated from the inside, that is, from the metal plate side, and the fluororesin can be heated to the melting temperature in a short time. It becomes possible, and in the subsequent constant temperature holding area, it is possible to sufficiently float the fluororesin to the coating film surface, including the fluororesin of the coating material of the steel plate and the contact portion, and to obtain a coating film having good surface performance. .

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 provided in an appropriate region. If the heating is controlled independently,
Temperature control suitable for the material and thickness of the metal plate and paint to be baked can be performed. Here, the hot air is used to exhaust the volatile solvent, whereby 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 view showing an embodiment of a baking furnace for a coated metal sheet according to the present invention. As shown in FIG. 1, the baking furnace 1 of this embodiment has four baking furnaces. Region Aa,
The induction heating coil 31a connected to the power supply device 21a is divided into Ba, Ca, and Da, and is arranged in the area Aa.
The induction heating coil 33a connected to the power supply device 23a is provided in the area Ca, the hot air outlet 52 connected to the hot air generator 42 is provided in the area Ba, and the hot air blower connected to the hot air generator 44 is provided. The outlet 54 is provided 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 the solvent in the paint applied to the steel sheet 2 evaporates. After being heated to a temperature at which the hot air blowout port 52 is heated in the area Ba (the first constant temperature holding area, the remaining solvent evaporation area).
The steel sheet 6 is kept at a constant temperature by hot air from the furnace to evaporate the remaining solvent. The hot air is discharged outside the system after passing through the first heating area.

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

By the way, in a conventional metal plate coating line using a hot air heating method, it is necessary to suppress the generation of wrinkles and wrinkles on the coating surface when evaporating and evaporating the solvent while heating. And process
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 part corresponding to the volatilization area of the solvent and the heating area to the re-melting temperature of the fluororesin in the coating film The length was long.

However, in the baking furnace of the present embodiment, the high-frequency induction heating devices (the power supply devices 21a and 23a and the induction heating coils 31a and 33a) are connected to the preheating region Aa and the main heating region C.
A metal plate (for example, steel plate 2) provided on a and subjected to a baking process
The optimum plate temperature rise rate can be set freely according to the material and thickness of the coating and the composition and film thickness of the paint. It became possible to obtain.

That is, in the baking furnace of this embodiment, the high-frequency induction heating devices (21a, 31a) in the preheating area Aa are used.
According to a), the sheet temperature of the steel sheet 2 is heated to a predetermined preheating temperature in the shortest time, and a sheet having a good surface finish is obtained in the preheating area Aa. Further, the steel plate 2 is held at a constant preheating temperature for a fixed time in the constant temperature holding region Ba.

Here, the solvent which has been volatilized at the preheating temperature is further completely discharged, and the coating film is in a good state, and a coating film state suitable for the main heating is obtained.

Here, the holding temperature of the steel sheet 2 in the first constant temperature holding area Ba varies depending on the resin in the paint, the composition of the solvent, and the like, but if the temperature is less than 170 ° C., the solvent having a medium boiling point (about 200 ° C.) or more is sufficient. If it does not volatilize, and if it exceeds 270 ° C., volatilization of the solvent is almost completely terminated, and it is not necessary to maintain the temperature at a higher temperature.

If the holding time of the steel sheet 2 is less than 3 seconds, the evaporation of the solvent is not sufficient, and if it exceeds 20 seconds, the effect hardly changes, and only the length of the constant temperature holding area Ba becomes longer. Therefore, it is preferable to set the optimum value in the range of 3 seconds to 20 seconds in consideration of the paint film thickness, the solvent composition, and the like.

Further, the exhaust air speed is 1 m / sec. If it is less than 10 m, it takes time for the solvent to evaporate from the surface of the paint film.
/ Sec. If it exceeds 1, wrinkles on the painted surface occur and a good surface finish cannot be obtained.
c. Is preferably set in the range.

The gas blown into the first constant temperature holding region is passed through the first heating region and is effectively used as a ventilation atmosphere, thereby reducing the unit cost of energy.

Next, the sheet temperature of the steel sheet 2 is heated to a constant main heating temperature in the shortest time by the high-frequency induction heating device (23a, 33a) in the main heating area Ca to re-melt the fluororesin. Further, in the second constant temperature holding region Da, the steel plate 2 is held at a constant main heating temperature for a constant time.

Here, the remelted fluororesin floats on the surface of the coating film, and a coating state suitable for the main heating is obtained. Here, the holding temperature of the steel sheet 2 in the second constant temperature holding region Da differs depending on the resin composition in the coating material, etc., but if it is less than 340 ° C., the fluororesin will be solidified, and if it exceeds 440 ° C., it is not economical. It is preferable to set the temperature to 340 ° C to 440 ° C.

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

Further, the exhaust air speed is 1 m / sec. If it is less than 10 vol.
sec. When wrinkles are exceeded, wrinkles and the like on the painted surface occur, and a good surface finish cannot be obtained.
c. Is preferably set in the range. The gas blown into the second constant-temperature holding region is effectively used as a ventilation atmosphere by passing through the second heating region, thereby reducing the unit cost of energy.

In addition, because of the induction heating, a stable temperature can be obtained in addition to a short heating time, and a stable product can be manufactured.

As described above, optimal heating control is performed in accordance with the material and thickness of the metal plate (the steel plate 2 and the like), and the type and thickness of the paint. In FIG. 1, the induction heating coils 31a and 33a are arranged so as to wind the steel plate 2, and the lines of magnetic force are generated in the strip traveling direction. Note that a pair of coils may be provided on the upper surface and the lower surface of the steel plate 2 so that the lines of magnetic force are generated in the thickness direction of the strip, and an appropriate material can be selected according to 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 furnace, but the hot air generators 42 and 44 used in this embodiment are the same as the general hot air furnace. It is only necessary to generate hot air (gas) at a lower temperature than that of the above, and a special one is not required. If the surface appearance of the coating film is particularly severe, a filter or the like may be provided at the hot air blowing port.

As a working example, an intermediate process product in which a heat-resistant resin equivalent to a dry film thickness of 15 μm was applied to a 0.6 mm-thick electro-aluminized steel plate coated with a coating type chromate solution having an adhesion amount of 50 mg / m ^2. Use, and as a baking condition,
When performing 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 performed in the conventional process.

In the present embodiment, in which the baking process is performed by a baking furnace of high-frequency induction heating and hot air heating, the temperature and the wind speed of the hot air are respectively changed. Referring to Tables 1 and 2, when the paint surface performance of the coated metal plate of this example manufactured in a baking furnace of high-frequency heating and hot-air heating is the case of only the hot-air heating of the comparative example and the case of only the high-frequency induction heating In particular, it can be seen that the primary physical properties as they are only in the painted state and the adhesion of the secondary physical properties after immersion in boiling water for 2 hours are better.

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

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

[0051]

[Table 4]

FIG. 2 is a view showing another embodiment of a furnace for baking a coated metal sheet according to the present invention. As shown in the figure, the baking furnace 1 of the present embodiment has a baking furnace of five regions A.
a, Ba, Ca, Cb, and Da, the induction heating coil 31a connected to the power supply 21a is disposed in the area Aa, and the induction heating coil 3 connected to the power supply 23a.
3a 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 and 52 connected to the hot air generator 44 are arranged in the area Ba, and hot air outlets 53 and 54 are arranged in the area Da. Here, the hot air is discharged through the region 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 feedback control, and the point that a single hot air generator is used and common hot air is used. Except for this point, the embodiment is the same as the embodiment of FIG.

As described above, the basic areas (A, B, C, and D) are further divided as necessary in consideration of the size of the board to be produced, the type of resin, the thickness of the coating film, and the overall production capacity of the equipment.
The same applies to the hot air generator. The hot air generator is 1
In the case of individual pieces, the hot air temperature is set to the required temperature in the region D where the temperature is high.

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

Although the baking furnace of the present invention is mainly intended for a heat-resistant precoat, it can be sufficiently used for a general precoat. It is possible to select the optimum specification within the above described range in consideration of the material to be processed.

[0058]

As described above, according to the baking furnace and the baking method for a heat-resistant pre-coated metal sheet of the present invention, the baking furnace is provided with a first heating region and a constant temperature holding region and a second heating region and a constant temperature holding region. With the four regions, a heat-resistant pre-coated metal plate having good surface performance in a short time at a high baking speed is obtained by performing temperature control suitable for the material and thickness of the metal plate to be baked and the paint. It can be widely applied in various fields such as home electric appliances and the like where high quality is required for a coating film such as a steel plate.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view showing another embodiment of a coated metal sheet baking furnace according to the present invention.

[Description of Signs] 1 Baking furnace 2 Steel plates 21a, 23a, 23b Power supply units 31a, 33a, 33b Induction heating coils 42, 44 Hot air generators 51, 52, 53, 54 Hot air outlet Aa First heating area (preheating Area) Ba First constant temperature holding area (solvent evaporation area) Ca Second heating area (Main heating area) Cb Second heating area (Main heating area) Da Second constant temperature holding area (Fluorine resin floating area)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Ryoji Nishioka 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (56) References JP-A-3-284372 (JP, A) JP-A-63-242368 (JP, A) JP-A-5-337439 (JP, A) JP-A-61-111177 (JP, A) JP-A-63-4873 (JP, A) (58) Int.Cl. ⁷ , DB name) B05C 9/10, 9/14 B05D 3/00-3/14 B05D 7/14 F26B 23/00-23/08 F27B 9/02 F26B 15/00

Claims (5)

(57) [Claims] 1. A baking furnace for a heat-resistant pre-coated metal plate for baking by evaporating a solvent in a coating applied to a metal plate, wherein the baking furnace is provided with a solvent in the coating applied to the temperature of the metal plate. A first heating region for heating and controlling to a temperature at which the solvent evaporates, and a first constant temperature holding region for evaporating and evaporating the solvent while maintaining the temperature of the metal plate heated to the heating temperature constant.
A second heating zone in which the metal plate in which the solvent has been volatilized is further heated to control the heating to a temperature at which the fluororesin in the coating film re-melts and floats on the coating film surface, and the temperature of the metal plate heated to the heating temperature is increased. A baking furnace for a heat-resistant pre-coated metal plate, comprising four areas of a second constant temperature holding area for holding the fluororesin on the surface of the coating film while keeping the temperature constant. 2. A high-frequency induction heating apparatus capable of independently controlling the heating of 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 a heat-resistant precoated metal sheet according to claim 1, wherein: 3. The method for baking a heat-resistant pre-coated metal plate using the baking furnace according to claim 1 or 2, wherein the holding temperature of the metal plate coated with paint in the first constant temperature holding region is set to 170.
° C to 270 ° C, and the holding time is 3 to 20 sec.
And the holding temperature of the metal plate is set to 340 ° C. to 440 ° C. in the second constant temperature holding region, and the holding time is set to 3 seconds.
c to 60 sec. A method for baking a heat-resistant pre-coated metal sheet, wherein 4. A first heating region, a first constant temperature holding region,
The gas used for exhaust in the second heating area and the second constant temperature holding area is 340 ° C. to 440 ° C., and the exhaust air velocity is 1 m / s.
ec to 10 m / sec. 4. The method for baking a heat-resistant pre-coated metal sheet according to claim 3, wherein clean air or nitrogen is used. 5. The gas used for exhaust in the first heating region and the first constant temperature holding region is set to 170 ° C. to 270 ° C., and the exhaust air speed is set to 1 m / sec to 10 m / sec. And 340 ° C. gas used for exhaust in the second heating area and the second constant temperature holding area.
Up to 440 ° C, and the exhaust air velocity is 1m / sec to 10m / s
ec. 4. The method for baking a heat-resistant pre-coated metal sheet according to claim 3, wherein clean air or nitrogen is used.