JPS6144546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating baking method in a coating line for hot-dip galvanized steel sheets.

Cold rolled steel plates or various plated steel plates, etc.
Furthermore, surface painting may be applied to improve the appearance, electrical insulation, and corrosion resistance. In this case, the steel plate is usually subjected to pretreatment such as pickling, degreasing, and phosphate treatment, and then is coated with a paint such as polyester resin, acrylic resin, vinyl resin, etc., and then subjected to so-called baking, such as heating and drying. It is. Traditionally, a hot air drying oven was used for this baking process. However, in such a hot air oven, the surface of the paint film that is exposed to the air is at the highest temperature, so the surface layer solidifies first, and later the solvent in the middle spews out to the surface, causing the paint surface to become bumpy. arise. In addition, in hot air ovens, when there are changes in baking conditions such as changes in film thickness or line speed, the response to changes in drying conditions (hot air temperature, air volume, etc.) is slow, and baking defects may occur when baking conditions are changed. This may occur.
In addition, when the material to be painted is a hot-dip galvanized steel sheet, the plating layer contains hydrogen that comes out of the subscale layer during the pickling process of the steel sheet, and if it is heated too quickly after painting, this hydrogen gas will damage the paint film. Rapid heating cannot be applied to this type of plated steel plate, as it will break and come out to the surface, worsening the condition of the painted surface.
Productivity was poor.

The present invention eliminates such problems and provides a paint baking method that allows a smooth and beautiful painted surface to be obtained and allows the drying speed conditions to quickly respond to changes in coating conditions (film thickness, line speed, etc.). The purpose is to

Another object of the present invention is to provide a paint baking method that does not cause the painted surface to deteriorate even when rapid heating and baking are performed during the painting process of hot-dip galvanized steel sheets.

The baking method according to the present invention involves installing induction heating furnaces at positions before and after painting in a steel plate painting line,
The steel sheet is preheated in an induction heating furnace before painting to release the hydrogen gas contained in the steel sheet, and then dried in an induction heating furnace after painting.

Next, a case in which the present invention is applied to a hot-dip galvanized steel sheet will be described in more detail.

The drawing schematically shows a painting line in which the present invention is applied. A preliminary process 1 and a drying process 2 using an induction heating furnace are provided before and after a coating process 3 using a roll coater method, respectively. Further before the preheating step 1, a pickling step 4 and a plating step 5 are arranged. Hydrogen is occluded in the subscale layer in the pickling process 4 of the steel plate, and this hydrogen gas is released during the plating film growth process in the plating process 5. Hydrogen released from the subscale layer is contained in the plated steel sheet in the form of being caught up in the plated layer. If this galvanized steel sheet is painted and heated rapidly, a large amount of hydrogen gas is generated at once, which ruptures the coating and comes out on the surface, resulting in poor coating conditions. However, in the present invention, after the plating step and before entering the painting step 3, the hot-dip galvanized steel sheet is heated in a preheating step 1 using an induction heating furnace, and the hydrogen gas contained inside the steel sheet is released in the plating step. After this, paint is applied in painting process 3,
The plated steel plate after painting is heated and dried again in the drying step 2 using an induction heating furnace to complete baking.

In the present invention, since the steel plate is directly heated by electromagnetic induction, the surface of the coating film that is in contact with the steel plate becomes the highest temperature. Therefore, the solidification of the paint film progresses from the side closer to the steel plate surface rather than the paint film surface, and the solvent in the middle of the paint film does not spray out to the solidified paint film surface layer as in the past, and a good paint film surface is maintained. can get. Furthermore, since the induction heat energy can be controlled by controlling the voltage or current of the induction heating furnace, the drying conditions (steel plate temperature) can be quickly changed in accordance with the coating conditions. Even if rapid heating is performed after painting, rapid preheating is performed before the painting process to release hydrogen gas, so no defects will occur on the painted surface, and this rapid heating also has the advantage of shortening the furnace length as a whole.

[Brief explanation of the drawing]

The drawing is a diagram schematically showing a painting line for carrying out the present invention. 1... Preheating process, 2... Drying process, 3... Painting process, 4... Pickling process, 5... Plating process.

Claims (1)

[Claims] 1 Induction heating furnaces are installed before and after painting in the painting line for hot-dip galvanized steel sheets, and the induction heating furnace before painting preheats to release the hydrogen gas contained in the hot-dip galvanized steel sheets. A method for painting and baking a hot-dip galvanized steel sheet, which is characterized by drying the plated steel plate.