JPS63107773A - Operating method of coated steel plate drying furnace - Google Patents

Abstract

PURPOSE:To maintain intrafurnace temperatures above an acid dew point for low-temperature baking and prevent shortening of the life of furnaces or equipment by keeping the temperature of a hot blast to coated steel plate at a prearranged temperature at the time of low-temperature operation, and controlling baking temperatures through variation of the air flow. CONSTITUTION:At the time of high-temperature operation, a hot blast at sufficient temperatures to cancel a deflection of baking temperature is blown by controlling the burner combustion value of air heaters 5-7. Thus coated steel plate W is baked by the hot blast ejected from air ducts 3a-3c. In the meantime, during low-temperature operation, the temperature of a hot blast from the air heaters 5-7 is maintained above the acid dew point, and for instance, if a detected baking temperature is higher than a target baking temperature, a present exhaust gas flow is decreased by a value corresponding to a baking temperature deflection by controlling an exhaust gas fan 13. Consequently an air feed amount to the air heaters 5-7 is reduced in accordance with this exhaust gas flow decrease. As a result, a total calorific value to steel plate W decreases, which in turn reduces the baking temperature.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applied to a coated steel plate production line after painting! i
The present invention relates to a method of operating a coated steel plate drying furnace for baking and drying IL plates, and particularly to an operating method that enables both high-temperature baking at 100 to 400°C and low-temperature baking at 70 to 100°C.

[Conventional technology]

Conventionally, coated steel plate drying furnaces for baking and drying coated steel plates are
Hot air from an air heater provided outside the furnace body and having a burner in its combustion chamber is guided to a blow-off duct inside the furnace, and is blown onto the steel plate from a nozzle of the duct.

When baking and drying painted steel sheets in the above-mentioned painted steel sheet drying furnace, the baking temperature is generally set at 100 to 400°C, and the furnace temperature is generally operated at 150 to 500°C. The deviation signal between the baking temperature and the detected baking temperature is cascaded to the furnace temperature controller, and the fuel flow rate to the burner is controlled so that the temperature of the hot air from the air heater becomes a temperature according to the deviation signal, thereby reducing the temperature of the hot air generated. is sprayed onto the steel plate.

[Problem that the invention seeks to solve]

By the way, recently, in order to improve the workability of painted steel sheets,
It is required to perform low temperature baking of 70 to 100°C. When performing such low-temperature baking using the conventional method described above,
The temperature of the hot air, and thus the furnace temperature, is set at 150°C or less, but in such low-temperature operation, acidic components such as SO3 in the combustion gas may be damaged by equipment such as the furnace shell, exhaust gas duct, or flow control valve. etc., these steel plates have condensation.

A problem arises in that equipment etc. are corroded and their lifespan is shortened.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for operating a coated steel sheet drying furnace that can maintain the furnace temperature above the acid dew point even during low-temperature baking and prevent the lifespan of the furnace body 1 and other equipment from decreasing.

[Means for solving problems]

The present invention provides a method for operating a coated steel plate drying oven, in which temperature control is performed to control the temperature of hot air blown onto the steel plate so that the ill plate temperature reaches a predetermined temperature during high-temperature baking, and
During low-temperature baking, the hot air temperature is maintained at a predetermined temperature, for example, above the acid dew point, and the flow rate is controlled to control the flow rate.

Here, the flow rate control of hot air during low-temperature operation in the present invention involves changing the flow rate of combustion exhaust gas discharged from the furnace to the outside according to, for example, the deviation between the detected baking temperature and the target baking temperature, and also changing the flow rate of the combustion exhaust gas discharged from the furnace to the outside. This can be achieved by changing the supply flow rate of the hot air and thereby increasing or decreasing the flow rate of hot air blown onto the steel plate.

[Effect]

In the method for operating a coated steel sheet drying furnace according to the present invention, during high-temperature operation, the temperature inside the furnace is maintained at a higher temperature than the baking temperature, as in the past, and the steel sheet is baked at a predetermined high temperature. On the other hand, during low-temperature operation, the temperature of the hot air from the air heater is maintained above the acid dew point, and the exhaust gas flow rate is reduced as the detected baking temperature is higher than the target baking temperature.
The flow rate supplied to the air heater is reduced accordingly. As a result, the flow rate of hot air to the steel plate is reduced, the furnace temperature is maintained above the acid dew point, and the baking temperature is controlled to a target low temperature. As a result, the method of the present invention enables low-temperature baking while maintaining the furnace temperature above a predetermined temperature, and while meeting the recent demands for low-temperature baking, it prevents condensation of acidic components and is suitable for use in furnace shells and exhaust gas ducts.

It is possible to prevent the lifespan of equipment etc. from being shortened.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The drawing shows a block diagram of a coated steel sheet drying furnace for carrying out the operating method according to an embodiment of the present invention.In the drawing, l is the furnace main body in which the coated steel sheet W is conveyed in a catenary shape by the roll coater 2. The furnace body 1 is in the Nol zone 1a.
- No. 3 zone IC, and a pair of upper and lower hot air blowing ducts 3a to 3C are arranged in each zone 1a to 1c so that a steel plate W is sandwiched therebetween.

Each of the above-mentioned blowout ducts 3a to 3C includes a hot air circulation duct 4.
The discharge sides of ducts 3 to 4C are connected, and each duct 4a
Air heaters 5 to 7 are interposed in the middle of ~4C.

Each of the air heaters 5 to 7 has a combustion chamber 5a equipped with a burner.
, 6a, 7a, and circulation fans 5b, 6b, 7b.

Further, the discharge side of the air supply duct 8 is branched and connected between the furnace body 1 of each of the hot air circulation ducts 48 to 4C and the combustion chambers 5a to 7a, and the intake side of the cough air supply duct 8 is connected to the DI control. ;1
It is connected to an air supply fan 10 via a valve 9.

Further, the suction port of the exhaust duct 11 is connected to each zone 13 to 1c of the furnace body l, and the exhaust duct 11
An orifice type flow rate detector 12. An exhaust gas fan 13 is provided.

14 is a radiation type temperature detector that detects the baking temperature of the painted steel sheet W, and 15 is a plate temperature controller into which the detected baking temperature from the detector 14 is input, and this is a preset target baking temperature. The deviation from the baking temperature detected by the temperature detector 14 is
It outputs to the furnace temperature controller 168 #16C during high temperature operation and to the exhaust gas flow rate calculator 17 during low temperature operation.

The exhaust gas flow rate calculator 17 calculates the flow rate that can eliminate the baking temperature deviation of the hot air blown onto the painted steel plate, that is, the exhaust gas flow rate. Reference numeral 18 denotes an exhaust gas flow rate meter, which determines the deviation between the calculated exhaust gas flow rate and the detected exhaust gas flow rate from the flow rate detector 12, and outputs it to the rotation speed controller 19. The rotational speed of the exhaust gas fan 13 is controlled so that the flow rate deviation is eliminated.

Reference numeral 20 denotes a furnace pressure regulator, into which the furnace pressure and the detected exhaust gas flow rate from the flow rate detector 12 are input, and the supply air flow rate is set at a flow rate corresponding to the exhaust gas flow rate and at which the furnace pressure can be maintained at a predetermined pressure. is output, and the flow rate control valve 9 is controlled to open and close accordingly. 21 is the above style 1iftlJ? This is a rotational speed controller that increases or decreases the rotational speed of the air supply fan 10 in accordance with the air supply flow rate when the opening degree of the first valve 9 reaches a predetermined opening degree or more.

Next, a case will be described in which the method of this embodiment is implemented in the above-mentioned painted steel plate drying oven.

First, to explain high-temperature operation in which a coated steel plate W is baked at a high temperature of 100 to 400°C, the steel plate W is coated with a roll coater 2 and then conveyed in a catenary shape inside the furnace body 1. Baked by hot air from ~3C. The baking temperature of the coated steel sheet W is detected by the temperature detector 14 and input to the plate temperature controller 15, where the deviation from the target baking temperature is determined. The burner combustion amount of each air heater 5 to 7 is controlled so that the seizure temperature deviation is eliminated.

As a result, hot air having a temperature that can eliminate the baking temperature deviation is blown onto the painted steel sheet W from the blowing ducts 32 to 3c, and as a result, the painted steel sheet W is dried at the target temperature.

Next, low-temperature operation in which baking is performed at a low temperature of 100 to 70°C will be explained.

The deviation between the detected seizure temperature and the target seizure temperature determined by the plate temperature controller 15 is output to the exhaust gas flow rate calculator 17,
On the other hand, furnace temperature! 1st section 1l6a~16c is each air heater 5~
7, the temperature of the hot air is controlled to be a constant temperature of, for example, 150° C. or higher.

Then, the exhaust gas flow rate calculator 17 calculates the hot air flow rate that can eliminate the seizure temperature deviation, that is, the exhaust gas flow rate, the exhaust gas flow rate controller 18 outputs the deviation between this exhaust gas aft and the detected exhaust gas flow rate, and the rotation speed controller 19 controls the rotational speed of the exhaust gas fan 13 so that the above exhaust gas flow rate deviation is eliminated.

At this time, the detected exhaust gas flow rate from the flow 11 detector 12 is also input to the furnace pressure regulator 20, and this furnace pressure regulator 20 outputs the air supply flow rate according to the exhaust gas flow rate, and The flow control valve 9 is controlled to open and close according to the flow rate, and when the control valve 9 reaches a predetermined opening degree or more, the rotation speed controller 21 controls the rotation speed of the air supply fan 10 according to the air supply flow rate.

As a result, the flow rate of hot air from the blow-off ducts 3a to 3G to the painted steel sheet W changes, and as a result, the shipping baking temperature is controlled to the target baking temperature.

For example, if the detected seizure temperature>target seizure temperature, the exhaust gas fan I3 is operated wtm so that the current exhaust gas flow rate is reduced by an amount corresponding to the seizure temperature deviation, and the air heaters 5 to 7 are The flow rate control valve 9 or the air supply fan 10 is controlled so that the air supply flow rate of 4 is reduced.
As a result, the amount of hot air blown onto the painted steel sheet W, that is, the total amount of heat supplied to the steel sheet W, decreases, and as a result, the baking temperature decreases and approaches the target baking temperature.

Contrary to the above, when the detected baking temperature is the target baking temperature, the exhaust gas flow rate is increased, the supply air flow rate also increases, the amount of hot air blown onto the steel plate W increases, and the baking temperature rises. I will do it.

As described above, in the method of this embodiment, during high-temperature baking, the baking temperature is controlled by controlling the temperature of hot air in the same way as in the conventional method. In addition, in low-temperature baking, the baking temperature is controlled by increasing or decreasing the exhaust gas flow rate, air supply flow rate, and hot air blowing, so even in low-temperature operation, the furnace temperature can be maintained above the acid dew point, for example, 150°C, and the No acidic condensation forms on the shell casing or in the exhaust gas ducts, and therefore no corrosion problems occur.

Further, in this embodiment, since the exhaust gas flow rate is directly controlled, there is an effect that the flammable gas generated by baking and drying the organic paint can be stably controlled to be below the explosion limit in the furnace.

In addition, in the above embodiment, the amount of hot air blowing was indirectly controlled by changing the exhaust gas flow rate.
Of course, in the present invention, the hot air flow rate may be directly detected and controlled.

〔Effect of the invention〕

As described above, according to the method of operating a painted steel plate drying oven according to the present invention, during low-temperature operation, the baking temperature is controlled by changing the flow rate while maintaining the temperature of the hot air to the coated steel plate at a predetermined temperature. Therefore, even in low>Ijz operation, the furnace temperature can be maintained above the acid dew point, which has the effect of extending the life of the furnace shell, exhaust gas duct, equipment, etc.

[Brief explanation of the drawing]

The drawing is a block diagram of a coated steel plate drying oven for carrying out a method of operating a coated steel plate drying oven according to an embodiment of the present invention. In the figure, 1 is the furnace body, and W is the painted steel plate.

Claims (1)

[Claims] (1) In the method of operating a coated steel plate drying furnace that bakes and dries a steel plate whose surface has been coated with paint, temperature control is performed to control the temperature of hot air blown onto the steel plate so that the steel plate temperature reaches a predetermined temperature during high-temperature baking; A method for operating a coated steel plate drying furnace, characterized in that during low temperature baking, flow rate control is performed to control the flow rate of the hot air while maintaining the amount of heat at a predetermined temperature so that the steel plate temperature reaches a predetermined temperature.