JPS61146366A - Heating furnace in continuous powder electrostatic coating line - Google Patents

Abstract

PURPOSE:To obtain easily a coated film having uniform film thickness and a beautiful appearance by separating the titled heating furnace into the front and the rear part, providing an infrared or an induction heater in the first furnace as a heating means, and furnishing a hot air heater in the second furnace. CONSTITUTION:A heating furnace wherein a powder paint coated on the surface of a steel sheet is formed into a film is separated into the front first furnace 1 and the rear second furnace 4 in a continuous powder electrostatic coating line. An infrared heater 2 or an induction heater is provided as a heating means in the first furnace 1, and a hot air heater having a hot air duct 5 and a nozzle 6 is furnished as a heating means in the second furnace 4. A steel sheet 7 is heated in the infrared heating zone 2 of the first furnace 1 to melt, fluidize, and smooth a paint, and then sent into the second furnace 4 wherein the coated film is rapidly heated with hot air and cured. Consequently, a uniform and beautiful coated film can be obtained without changing the speed of the line.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a heating furnace in a continuous powder electrostatic coating line, and in particular, the present invention relates to a heating furnace for a continuous powder electrostatic coating line. The aim is to realize this advantageously without the disadvantages of lowering the performance and increasing equipment costs.

(Prior art) Conventional methods for continuously applying coating to steel plates include applying a paint containing an organic solvent to the steel plate surface, or electrostatically applying a powder coating without using an organic solvent to the steel plate surface. The common method is to electrodeposit it on the paint, then introduce it into a heating furnace of a continuous coating line, where it is baked and dried to form a film. In either case, the heating means is The so-called hot-air heating method was used, in which hot air is blown out of a nozzle to heat the device.

By the way, in the above-mentioned electrostatic coating, the electrostatically charged powder paint adheres uniformly to the steel plate due to the strength of the electric field, and melts and flows when heated.

A film is formed after smoothing and curing. Although the electric field strength at the interface between the steel plate and the powder coating is strong, the electric field strength is weak at the outer surface of the powder coating, so hot air is used as a heating method. When heating is used, the surface layer of the powder coating is scattered by the hot air blown from the nozzle before it melts, and the uniform electrodeposition layer is melted and baked while crumbling, resulting in the product having an uneven film thickness. This results in significant quality deterioration, such as uniformity and loss of appearance.

For this reason, when performing electrostatic coating using a conventional hot air heating furnace, the hot air blowing speed from the nozzle (hereinafter simply referred to as nozzle wind speed This resulted in restrictions on line speed.

(Problems to be Solved by the Invention) However, in a continuous coating line, reducing the nozzle wind speed as described above will reduce the line speed in proportion to the nozzle wind speed when using an existing heating furnace. 1i) On the other hand, in order to maintain productivity, that is, line speed, it becomes necessary to lengthen the furnace length in inverse proportion to the nozzle wind speed, etc. Problems that must be solved in any case I left a mark.

This invention advantageously solves the above problems, and enables the formation of a uniform coating film with a good surface appearance without reducing the line speed or extending the furnace length. The purpose is to propose a furnace.

(Means for Solving the Problems) That is, the present invention is a heating furnace for forming a film of powder coating applied to the surface of a steel plate in a continuous powder electrostatic coating line, and the heating furnace is divided into two parts, front and rear. Consisting of a first furnace and a second furnace,
The first furnace is a heating furnace in a continuous powder electrostatic coating line, which is equipped with an infrared heating device or an induction heating device as a heating means, and the second furnace is equipped with a hot air heating device as a heating means.

(Function) In this invention, the first furnace is responsible for melting, fluidizing, and smoothing the powder coating electrodeposited on the surface of the steel plate, and uses infrared heating or induction heating applied to electric heating to raise the temperature of the steel plate to 60°C.
By avoiding heating to around 150℃, the adhesion of the powder coating to the steel plate is increased by melting and flowing, and the condition of the coating film is maintained uniformly.On the other hand, in the second furnace, hot air heating with a high temperature rise rate is used. The steel plate is heated to a temperature of about 220 to 260°C and baked to harden the coating film. When the steel plate is introduced into the second furnace in this way, the paint on the steel plate is in a semi-hardened state after being fluidized and smoothed.
The phenomenon of scattering of the powder paint due to the nozzle wind speed does not occur, and therefore, even if the nozzle wind speed is increased in the second furnace, the surface of the coating film is not disturbed.

In addition, in this invention, by disposing a non-contact type film thickness meter between the first furnace and the second furnace, continuous and accurate measurement of the coating film thickness can be realized. The data can also be used for film thickness control by feeding back the data.

(Example) Preferred embodiments of the present invention will be specifically described below while comparing them with conventional examples.

FIG. 1 schematically shows a heating furnace according to the present invention, and FIG. 2 schematically shows a conventional furnace. Since the conventional furnace has the same gist of the structure as the second furnace according to the present invention, it is indicated by the same number.

Now, in FIG. 1, the number 1 is the first furnace, and the number 2 is the heating zone, and in this example, an infrared heating method is adopted. This first
In the furnace 1, an infrared heating zone 2 is installed to increase thermal efficiency.
The infrared rays are surrounded by heat insulating material, but without impairing the efficiency of the infrared rays generating section, it is possible to maintain the permissible temperature of the infrared rays generating section itself (maximum 500℃).
), there is a space 3 above it to maintain it at a level that does not exceed
The structure is such that a relatively high temperature atmosphere can be released to the outside through the opening.

Further, 4 is a second furnace, and this second furnace 4 is of a hot air heating type and is equipped with a hot air duct 5 and a nozzle 6.

Note that 7 is a steel plate, 8 is a powder coating applied thereon, 9 is a coating film in a melted and smoothed state, 10 is a steel plate conveying device, 11 is an exhaust gas duct, and 12 is a film thickness gauge.

Now, in the conventional furnace shown in Fig. 2, when steel plates uniformly coated with powder coating by electrostatic coating are continuously inserted, hot air blown from the nozzle 6 toward the steel plate surface coats the powder coating. As mentioned above, the outer surface layer melts, flows, and hardens while scattering, resulting in a pock-like appearance on the coating surface, which significantly impairs the quality.

In this respect, this invention involves the melting and flowing of powder coatings.

Smoothing is done by infrared heating or induction heating without spraying, and hot air heating is applied after smoothing, so the coating surface is not damaged.

That is, in this invention, as shown in FIG.
The temperature of the steel plate 7 in the infrared heating zone 2 of 60 to 150
After the powder coating 8 is melted, fluidized, and smoothed by raising the temperature to about ℃, it is sent to the second furnace 4.
The temperature of the steel plate 7 is 220 to 260 by heating with hot air.
The coating film 9 is hardened by rapid heating to a temperature of Then, even if heating is performed by blowing hot air in the second furnace, the surface properties of the coating film are not impaired, and a uniform coating film profile is maintained.

Heating powder coatings with infrared rays is a thermochemical reaction, and when a paint film is irradiated with infrared rays, each paint film absorbs the infrared rays at a unique frequency (4 to 50 μm), which activates molecular vibrations. The paint film directly generates heat. Such heating allows heat to quickly penetrate into the interior of the coating film due to both the heat generation of the coating film itself and the heat transfer from the steel plate, so that the coating film melts and becomes smooth.
Up to a temperature of about 150°C, it takes about the same amount of time as high-speed hot air heating.

Therefore, during actual operation, there is no need to reduce the line speed or increase the furnace length.

In addition, in FIG. 1, a non-contact film thickness gauge 12, which can be an infrared film thickness gauge, a fluorescent X-ray film thickness gauge, etc., is placed between the first furnace 1 and the second furnace 4. As shown in the example above, by measuring the film thickness at the exit side of the first furnace 1 where the powder coating is in a semi-cured state, more accurate coating film thickness measurement can be achieved, and it is generally possible to obtain a better result. The film thickness accuracy can be improved by feeding back the measured values to the film thickness control system.

In this regard, conventionally, the film thickness was measured after the paint film was completely cured, but since the surface of the cured paint film has minute irregularities, the measurement accuracy was not very good.
Also, even with feedback υIm, there was a disadvantage of a large time lag.

For reference, FIG. 3 schematically shows the entire continuous powder electrostatic coating line.

(Effects of the Invention) Thus, according to the present invention, a coating film with a uniform thickness and beautiful appearance can be produced in a continuous powder electrostatic coating line without the disadvantages of lowering the line speed or increasing the furnace length. can be easily obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic diagram of a preferred embodiment of the present invention, and FIG.
Schematic diagram of a conventional heating furnace. FIG. 3 is a schematic diagram of a continuous powder electrostatic coating line incorporating a heating furnace according to the present invention.

Claims (1)

[Claims] 1. In a continuous powder electrostatic coating line, it is a heating furnace that aims to form a film of powder coating applied to the surface of a steel plate, and consists of a first furnace and a second furnace that are divided into two parts, the first furnace uses an infrared heating device or an induction heating device as the heating means, while the second
A heating furnace in a continuous powder electrostatic coating line, characterized in that each furnace is equipped with a hot air heating device as a heating means.