When the steel strip is dried and cured in the curing furnace after coating, most of the organic solvents in the coating film will evaporate gradually. When the solvent volatiles in the coatings are mixed with air at the furnace temperature of 150-450
(?) C, fire and explosion may occur, which is extremely dangerous.
When the solvent volatile mixes with air, the oblique zone is the explosion zone. According to the conditions of explosion, there are two main measures to prevent fire and explosion:
(1) Controlling the content of organic solvent 20 in the atmosphere
of the curing furnace of color coated sheet to make it below 1/4, 1/6 or even 1/8 of the lower explosion limit, generally using 1/4 of the lower explosion limit (i.e. 25% IEL). Alarm concentration generally sets three alarm levels and takes different
measures to prevent explosion: when the concentration of organic solvents reaches 25% LEL, the system will alarm and automatically start the accident air supply fan; when the concentration of organic solvents reaches 35% LEL, the roller coating machine
will automatically stop coating operation; when the concentration of organic solvents reaches 50% LE. At L, the whole line should be stopped urgently. This control method is generally used in hot air circulating curing furnace and far infrared heating
curing furnace. The operation of curing furnace requires negative pressure operation.
(2) To control the oxygen content in the curing furnace of color coated sheet, the so-called inert gas method is adopted to circulate and heat the emotional exhaust
gas generated by combustion in all areas of the curing furnace, so that the oxygen content in the atmosphere of the furnace is below the explosion limit. Generally, the control level of oxygen content is also divided into three levels (3%, 4.5% and 6%).
When the explosion-proof control device works, a small amount of furnace gas is extracted (sampled) for oxygen content analysis. When the oxygen content reaches 3%, the control device will send a signal to the emotional gas switch, immediately spray human
inert gas and alarm until the oxygen content is normal. 。 When the oxygen content reaches 4.5%, when spraying inert gas, the head of the roller coating machine is opened automatically and the coating is stopped. When the oxygen content reaches 6%, the
whole line stops urgently and a large number of inert gases are injected into the furnace to wash the furnace. This control method is generally used in induction heating curing furnace, which requires positive pressure operation.
In addition, on
the basis of adopting the above explosion-proof measures. It is also required to install necessary explosion-proof and pressure relief devices on the curing furnace of color coated sheet as a safety measure when explosion occurs, so as to minimize the