JPH04273982A - Method of drying steel strip - Google Patents

Abstract

PURPOSE:To prevent a temperature at a steel strip from being increased and to prevent dew formation on the steel strip by a method wherein a temperature of the steel strip is measured at an inlet port of a drying device during a drying process after water cleaning in a continuous processing line, the measured temperature is compared with a dew formation point of surrounding atmosphere at that time, and if the dew formation point is lower than the measured temperature, the surrounding atmosphere is directly fed into the device and in turn if the dew formation temperature is higher than the measured temperature, the air in the drying device is dehumidified and the air is circulated and used. CONSTITUTION:A temperature of a steel strip 4 is measured by a strip temperature measuring deice 11 just before a drying device 3. In turn, a dew formation point of the surrounding air is measured by a dew formation temperature measuring device 12 near a surrounding air blowing valve 8. Then, the detected steel strip temperature is compared with the dew formation temperature of the surrounding air. Then, when the dew formation temperature of the surrounding air is lower than the measured temperature, the surrounding air is taken through the surrounding air suction valve 8 and the air is blown drying device 3 by a taking fan 6 through a down duct the dew formation temperature is higher than the temperature, the air is guided from the discharging after drying into a circulation circuit A, and then a dehumidifying device 5 and a heater 7 are operated as required to perform dehumidification and heating and then the air is blown from the duct 15 into the drying device 3 and the air is circulated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying steel strips after washing in a continuous processing line.

0002

[Prior Art] Generally, in a continuous steel strip processing line, water washing is performed after pickling, degreasing, and prior to surface treatment such as plating, and then hot air is blown onto the surface of the steel strip. Drying is performed by evaporating the trace amount of moisture remaining on the surface of the steel strip. In order to save energy costs, the hot air blown onto the surface of the steel strip is recovered, recycled, and blown onto the surface of the steel strip again. Furthermore, as seen in Japanese Unexamined Patent Publication No. 19490/1983, the humidity of the exhaust air after drying the steel strip is measured, and the amount of circulating exhaust air is controlled based on this humidity. A known method is to dry the steel strip by adding fresh drying air and adjusting the temperature to produce hot air having an allowable humidity suitable for drying the steel strip.

FIG. 3 shows this conventional method. The drying chamber 3 is equipped with a blow duct 15 and a discharge duct 16, and the discharged air after drying the steel strip 4 returns from the discharge duct 16 to the blow duct 15 via a route A passing through a branch duct and is used for circulation. Ru. At this time, the valve opening degree is set based on the humidity measurement value on the outlet side of the discharge duct 16, and the circulating air volume is controlled, and outside air is added as new drying air to make up for the shortage, and the humidity is adjusted by the heater 7 as necessary. The air is blown from the blow duct 15 at the top.

0004

[Problem to be solved by the invention] The above-mentioned Japanese Patent Application Laid-Open No. 58-19
According to the method of Publication No. 490, the exhaust air after drying the steel strip has excellent effects such as making full use of its drying capacity and reducing energy costs. When the temperature of the steel strip is regulated within a low range, there is a problem in that the steel strip whose temperature has increased due to drying must be cooled.

Furthermore, if the temperature of the steel strip entering the drying chamber is lower than the dew point of the circulating air, dew will condense immediately after entering the drying chamber, and as the temperature of the steel strip increases, the condensed water droplets will evaporate, but no condensation will occur. There is also the problem that the marks become abnormally glossy and remain as defects in surface treatment. An object of the present invention is to solve these problems and provide a method for drying a steel strip without increasing the temperature of the steel strip and without forming dew condensation.

[0006]

[Means for Solving the Problems] In the present invention, the temperature of the steel strip at the inlet of the drying device is measured, and compared with the dew point temperature of the outside air at that time, if the dew point temperature of the outside air is lower, the outside air is directly supplied. The air is taken into the drying device, and when the dew point temperature of the outside air is higher than the steel strip temperature, the air inside the drying device is dehumidified and circulated to be blown onto the surface of the steel strip.

[0007]

[Function] According to the present invention, since air with a dew point temperature lower than the temperature of the steel strip immediately before the drying device is always used for drying, the steel strip is dried without an increase in the temperature of the steel strip and without condensation. can be dried.

[0008]

[Embodiment] An embodiment of the present invention will be explained with reference to FIG. The steel strip 4 washed with water in the water washing device 1 is squeezed with water by a squeezing roll 2 and then led to a drying device 3, where it is dried by blowing normal temperature air onto both sides. Room temperature air is blown into the drying device 3 from a blow duct 15, and the exhaust air that has dried the steel strip is discharged from a discharge duct 16.

Here, just before the drying device 3, a plate temperature measuring device 1 is installed.
1 is installed, and near the outside air blowing valve 8 there is also an outside air dew point temperature measuring device 12. Comparing these two measured values, if the dew point temperature of the outside air is lower than the board temperature, outside air is taken in from the outside air blowing valve 8, and the fan 6
Normal temperature air is blown from the blow duct 15. The exhaust air is discharged from the exhaust duct 16 to the outside of the system via the exhaust discharge valve 10. In this case, there is no need to operate the dehumidifier 5 and the heater 7, so the outside air passes through them.

On the other hand, when the dew point temperature of the outside air is higher than the plate temperature, the exhausted air after drying has less load and is more economical than the outside air, so the exhausted air after drying is routed from the exhaust duct 16 to the circulation circuit A.
The air is returned to the system through the fan 6 and blown through the blow duct 15. At this time, the dehumidifying device 5 and the heater 7 are operated as necessary based on the measurement results of the dew point measuring device 13 immediately before the blowing duct, and the dew point temperature of the blown air in the drying device 3 is adjusted to be equal to or lower than the plate temperature. In this figure, dotted lines represent signal systems.

[0011] In actual operation, the strip temperature may drop by 1 to 3 degrees Celsius due to vaporization of moisture on the surface of the steel strip. It is safe to use it. Figure 2 shows
This is a graph showing the relationship between the dew point temperature of the blown air, the temperature of the steel strip immediately before the drying device, and the thickness of the water film remaining on the surface of the steel strip immediately after the drying device, and the limit of the safe use of outside air is indicated by a dotted line.

0012

[Effects of the Invention] According to the present invention, the steel strip can be accurately dried without increasing the steel strip temperature and without causing dew condensation.
Energy costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a drying method according to an embodiment of the present invention.

FIG. 2 is a graph showing selection conditions for blown air according to the present invention.

FIG. 3 is a system diagram of a drying method according to the prior art.

[Explanation of symbols]

3 Drying device 4 Steel strip 6 Fan 8 Outside air blow valve 10 Exhaust release valve 11 Plate temperature measuring device 12 Outside air dew point measuring device 15 Blown duct 16 Discharge duct

Claims (1)

[Claims] Claim 1: In the drying process after water washing in a continuous steel strip processing line, the temperature of the steel strip at the inlet of the drying device is measured, and compared with the dew point temperature of the outside air at that time, it is determined that the dew point temperature of the outside air is higher. If the dew point temperature of the outside air is lower than the steel strip temperature, the outside air is taken directly into the drying device, and if the dew point temperature of the outside air is higher than the steel strip temperature, the air inside the drying device is dehumidified and circulated and blown onto the steel strip surface. How to dry steel strip.