JPH0677713B2 - Induction heating furnace in a continuous coating line for metal strips. - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an induction heating furnace in a so-called metal strip continuous coating line for continuously applying paint to a metal strip or printing a laminate film. It is a thing.

(Prior Art) Pre-coated steel plates, which are generally called color iron plates today, are used as a plate material in a wide range of applications such as exterior building materials, interior building materials, home appliances, steel furniture and vehicles as the most commercially available materials. Has been done.

Its main features include excellent moldability, corrosion resistance, weather resistance and nonflammability, as well as low cost.

By the way, as the applications of such pre-coated steel sheets to interior building materials, home appliances, steel furniture, and vehicles have expanded, recently, high-grade decorative steel sheets with excellent designability and bright steel sheets with high surface gloss, such as high-grade, designability and high The demand for quality is gradually increasing, and along with this, there is a demand for precoated steel sheets with a beautiful paint finish that has extremely little dust adhesion.

However, as the current paint bake-hardening furnace for pre-coated steel sheets, a hot-air circulating hot-air oven with a large heat capacity is the mainstream, and since a large amount of hot air is blown onto the strip to increase the convection efficiency, the paint is baked and hardened. However, it was not possible to completely remove the tar and dust generated during baking of the paint, and although various improvements were attempted, it was not possible to keep the inside of the furnace clean to a satisfactory degree. .

Moreover, since tars and dust generated during baking are accumulated in the furnace and ducts, periodic cleaning is necessary to ensure quality, which causes a decrease in operating rate.

In addition, for exterior building materials, the development of paints that can meet the demand for long-term guarantees, which is the demand for them, is proceeding, and for home appliances, there is a particularly strong demand for heat-resistant precoated steel sheets. In order to meet these demands, it is necessary to use a polymer resin paint as the paint, but when using such a polymer resin paint, it is necessary to perform baking at a temperature higher than the conventional paint baking temperature. Therefore, it is necessary to provide a wide processing temperature range as a baking and hardening furnace.

However, the processing temperature is up to 300 ℃ in the conventional hot-air stove.
However, the problem remains in that the performance of the polymer resin paint cannot be sufficiently exhibited because of the degree.

Recently, an induction heating furnace has attracted attention as a bake hardening furnace that is clean and capable of high-temperature processing. For example, Japanese Patent Publication No. 47-99
Japanese Patent Laid-Open Publication No. 16-45022 and Japanese Patent Laid-Open Publication No. 50-45022 propose a method for baking paint by using an induction heating coil.

(Problems to be Solved by the Invention) However, the induction heating furnace as described above has the following problems.

That is, since the induction heating coil is usually weak in heat, it usually has an internal water cooling structure, but conversely, due to the low surface temperature due to this water cooling structure, moisture and volatilization that evaporate during baking of the paint or coating of the laminate film. Solvents, resins, adhesives and the like tend to form dew condensation to form tars and dusts, and such tars and dusts adhere to the surface of the product, resulting in deterioration of quality, which leaves a problem.

The present invention advantageously solves the above problems, and in a continuous coating and coating line for metal strips, when baking and curing the coating material by using an induction heating coil, tar and dust that cause deterioration of the surface quality. It is an object of the present invention to propose an induction heating furnace that can effectively prevent the occurrence of the above and obtain a coated steel sheet with a beautiful surface.

(Means for Solving the Problems) That is, the present invention relates to an induction heating furnace (3) installed in a continuous coating and coating line for a metal strip (1), which comprises a plurality of heating zones (7) and An induction heating coil (6) comprising an exhaust zone (8) disposed between the heating zones (7), and each heating zone (7) having an appropriate gap between adjacent coil conductors in a spiral shape. ) Is installed and a masking (11) having a rectifying effect is arranged between the metal strip (1) passing through the inside of the induction heating coil (6) and the upper inner peripheral surface of the coil (6), Further, fresh hot air is supplied into the furnace from above the heating zone (7) and the exhaust zone (8), rectifies through the masking (11) from behind the induction heating coil (6), and then descends to the upper surface of the metal strip. Spray as a stream A metal strip provided with a system for blowing in fresh hot air and an exhaust system for in-furnace gas that guides the in-furnace gas to the outside of the furnace on the lower surface side of the exhaust zone (8), cleans it, and then diffuses it into the atmosphere. It is an induction heating furnace in the continuous coating and coating line.

First, the process of clarifying the present invention will be described.

Now, the inventors have obtained the following knowledge as a result of trying to elucidate the generation state of tars and dusts.

The coating of the precoated steel sheet is generally made of solvent-based resin, water-based resin, powder resin, etc., but in the process of baking and drying these coating materials, water, solvent, resin, and further when the adhesive laminate film is dried, Volatile components in the adhesive are evaporated. The vaporized gas has a dew condensation temperature depending on its concentration. Therefore, when the temperature at the place where the vaporized gas comes into contact is lower than the dew condensation temperature, dew condensation occurs and tar or dust is generated.

In the conventional heating furnace design, only such condensation temperature was taken into consideration, but as a result of various experiments, the generation of tar and dust due to fluctuations in gas concentration and temperature fluctuations in the baking process, and pockets in the gas flow process. The situation has changed, and in particular, since the induction heating coil has a low surface temperature as described above, it has been found that vaporized gas is easily condensed to cause tar and dust.

The present invention is an induction heating furnace having a novel structure developed based on the above findings.

FIG. 1 is a schematic diagram of an entire continuous coating line incorporating an induction heating furnace according to the present invention, and FIGS. 2 and 3 show the same.
A main part of the induction heating furnace is shown in cross section.

In the figure, reference numeral 1 is a metal strip, 2 is a coating facility (including print coating), 3 is an induction heating furnace, 4 is a cooling device, and the metal strip 1 is coated while passing through such a processing line. And is wound up as a product coil 5.

The induction heating furnace 3 has a structure in which heating zones 7 having induction heating coils 6 and exhaust zones 8 are alternately arranged. Since the induction heating coil 6 has a spiral shape and an appropriate gap is provided between the adjacent coil conductors,
Fresh hot air can freely move in and out of the coil through this gap. The induction heating coil 6 is internally cooled by passing cooling water 9 through a copper tube, while the outer circumference of the induction heating coil 6 is completely protected by an insulating heat insulating seal 10.

In the present invention, a non-magnetic masking 11 having a rectifying effect is arranged between the metal strip 1 passing through the induction coil 6 and the upper inner peripheral surface of the coil 6 to prevent the fresh hot air from flowing. Guide from behind the coil 6 as shown in 12, rectify through such masking 11,
As a downflow to the strip surface (preferably perpendicular)
Spray it.

Here, as the masking, one having a large number of so-called honeycomb-shaped fine through holes having a honeycomb shape in a plan view,
Similarly, a planar shape having a large number of fine through holes such as a lattice shape and a circular shape is advantageously suitable. By passing the masking having such a structure, it is possible to effectively rectify the fresh hot air. In addition to the above-mentioned rectification effect of the fresh hot air, this masking also has a function of adhering and removing the vaporized component in the furnace gas in such fine through holes when the furnace gas rises for some reason. .

Next, the fresh hot air is the primary air from the air blower 13,
After being sufficiently cleaned by the secondary and tertiary high-performance filters 14, the temperature is raised to an appropriate temperature via the heat exchanger 15 and then fed into the heating furnace 3 from above.

Further, the hot air blown as a downward flow to the upper surface of the strip is guided to the outside of the furnace through the exhaust port 16 provided on the lower surface side of the strip in the exhaust zone 8 together with the gas generated in the furnace, and then burned by the fume incinerator 17. The components are burned and deodorized to make them harmless, and then heat is removed by the heat exchanger 15 before being released into the atmosphere.

(Operation) In the present invention, since the hot air used is completely cleaned, the plate surface is not contaminated even if such hot air is blown onto the strip surface.

Further, in the furnace, the fresh hot air is blown as a downward flow onto the strip surface, so that evaporation components such as solvent, resin, and moisture that volatilize during baking will contact the induction coil above the strip and the furnace wall to cause dew condensation. Therefore, the plate surface is not contaminated by the tar and dust caused by the vaporized components.

Furthermore, the volatile gases such as solvent, water, and resin generated in the furnace are quickly discharged to the outside of the furnace, so there is no explosion or fire in the furnace, and the gas in the furnace burns its combustible components. -Being deodorized and rendered harmless, and heat is recovered and then released into the atmosphere, it is also advantageous in terms of pollution prevention and heat balance.

Since the blowing speed of the fresh hot air on the surface of the metal strip is much lower than the wind speed in the conventional hot air oven, there is an advantage that the powder coating can be used.

(Example) Using the continuous coating and coating equipment equipped with the induction heating furnace according to the present invention shown in FIG. 1 above, continuous coating treatment was performed under the conditions shown in the following table.

As is clear from the table, when the induction heating furnace according to the present invention is used, the baking treatment can be performed at the optimum baking temperature of various resin coatings ranging from 180 ° C to 450 ° C, and the surface of the obtained product There was no adhesion of tar and dust, and it had a beautiful appearance.

(Effects of the Invention) The effects of the present invention are summarized as follows.

i) The supply system of fresh hot air and the exhaust system of gas in the furnace are completely separated, the gas generated during paint baking is discharged to the outside of the furnace in the shortest distance, and the product passage zone is always filled with fresh hot air. Since it is maintained at a high degree of cleanliness, it is possible to easily obtain a high-grade decorative steel sheet with a beautiful surface free from adhesion of tars and dust.

ii) The selection range of the resin is expanded by combining the induction heating coil and the fresh hot air. For example, powder-coated steel sheets could not be used in a hot-air stove because the powder would scatter, but the spraying speed of fresh hot air is sufficient to be less than the scatter wind speed of the powder, so it can be used. . In addition, resin paints that require a baking temperature of 300 ° C or higher
It could not be used in the conventional hot stove because it is dangerous,
The combination of induction heating and fresh hot air enables the coating of paints that require such high temperature baking. Furthermore, when baking resin paints that require a certain amount of oxygen in the furnace atmosphere, oxygen could not be controlled in conventional induction heating furnaces and circulating hot air stoves, so it could not be used, but gas supply was not possible. In the present invention having a system, it is possible to bake such a paint.

iii) The heating of the metal strip is performed by induction heating, and since the furnace is divided into a heating zone and an exhaust zone, the heat cycle for various resin characteristics can be instantly changed to an appropriate cycle, so good quality is achieved. The product can be stably obtained, and since the cleaning in the furnace is not necessary, the operation rate can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a continuous coating and coating line incorporating an induction heating furnace according to the present invention, and FIGS. 2 and 3 are enlarged views of the main parts of the induction heating furnace. DESCRIPTION OF SYMBOLS 1 ... Metal strip, 2 ... Coating equipment 3 ... Induction heating furnace, 4 ... Cooling device 5 ... Product coil, 6 ... Induction heating coil 7 ... Heating zone, 8 ... Exhaust zone 9 ... Cooling water, 10 ... Insulation insulation seal 11 ... Masking 12… Fresh hot air flow 13… Blower, 14… Filter 15… Heat exchanger, 16… Exhaust port 17… Fume incinerator

Claims (1)

[Claims] 1. An induction heating furnace (3) installed in a continuous coating line for a metal strip (1), wherein the induction heating furnace (3) is provided between a plurality of heating zones (7) and each of these heating zones (7). And an induction heating coil (6) provided with an appropriate gap between adjacent coil conductors in a spiral shape in each heating zone (7). A masking (11) having a rectifying effect is arranged between the metal strip (1) passing through the inside of (6) and the upper inner peripheral surface of the coil (6), and fresh hot air is heated in the heating zone (7) and A system for supplying fresh hot air that is supplied into the furnace from above the exhaust zone (8), is rectified from behind the induction heating coil (6) through the masking (11), and then is blown as a downward flow onto the upper surface of the metal strip. And the gas in the furnace Induction heating in a continuous coating and coating line for metal strips, characterized in that it is provided with an exhaust system for in-furnace gas that is introduced to the outside of the furnace on the lower surface side of the metal strip in the air zone (8) and is then cleaned and then diffused into the atmosphere Furnace.